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translator : ido dekkers reviewer : ariana bleau lugo so what is gravity ? i bet most of you think it 's : `` what goes up , must come down ! '' is that right ? well , sorta , but not really . technically , the law of gravity is an equation . it is : f = g x m1 x m2 / r^2 , where g is the universal gravitational constant , m1 and m2 are the masses of the two objects , and r is the distance between them squared . that was easy , right ? probably not . what does this actually mean ? well it means that - well , everything is attracted to everything else . what i mean by that is if you have two objects , any two objects , they are attracted to each other . ok. let 's try and wrap our minds around this . what happens when you drop a rock off a cliff ? it falls to the earth . right ? well , yes , but something else happens . you see , the law of gravity says that both objects , the rock and the earth , are attracted to each other . this means that the rock falls towards the earth , and the earth falls towards the rock . wait a second - you mean to tell me that if - the earth falls up to meet the rock ? yes , that 's exactly what i 'm saying . and the reason you do n't see the earth fall up to meet the rock is because the objects move towards each other proportionate to their respective masses . the earth is much much much more massive than the rock , so it moves a very very small distance , and the rock is much less massive , so it moves farther with respect to the earth . maybe a better way to understand gravity is to take two teenagers in spacesuits , and place them far out in space - away from all the planets and the stars . it turns out they will be attracted to each other . i 'm not talking about that kind of attraction . see , they have mass , and since they have mass , they will move towards each other . they are attracted to each other . maybe one more thing might help . have you ever played with two magnets ? you know , the magnets with the north and the south poles ? when you take the magnets and put them closer to each other , they move together . they are attracted to each other . and the closer they are , the stronger the attraction . think of the mass of the object like the strength of a magnet and the distance between the objects like the distance between the two magnets . now understand , i 'm not saying that gravity and magnetism are the same , they just behave in a similar way . let 's think of one other thing - astronauts . you know , astronauts , they weigh less on the moon than on the earth . why is that ? well you see , the moon is less massive than the earth . therefore it has a smaller gravitational pull on the astronaut . it 's like the moon is a weaker magnet . they are n't as attracted to each other . distance also plays a role . think back to playing with a magnet . the pull of the magnets towards each other are stronger when they are closer together . the same is true of gravity . for example , the sun is the most massive object near the earth . it dictates most of the gravitational forces in our solar system . it is very very massive . but it is relatively far away , so even though the sun is a much stronger magnet , so to speak , it is a long ways away . therefore the attraction is n't as strong . so let 's look back at that law of gravity . the equation : f = g x m1 x m2 / r ^2 . you see the force of gravity is equal to a number . that 's that universal gravitational constant g times the mass of object one , times the mass of object two . think of m1 being the mass of the sun and m2 being the mass of the earth . and then we divide by the distance between them squared . this determines the force of attraction between the sun and earth . you could just as easily plug in your mass and the earth 's mass and the distance between you and the center of the earth , and find out how much you are attracted to the earth , and the earth attracted to you . so , what 's gravity ? everything is attracted to everything else . everything . oh , one last thing , just to make you wonder . what causes gravity ? why are two objects with mass attracted to each other ? well , the answer is - we do n't know . the cause of gravity remains a mystery to scientists . we do n't really know conclusively what causes gravity . it is one of the great mysteries of science .

they are n't as attracted to each other . distance also plays a role . think back to playing with a magnet .

distance also plays a role in the force of gravity . explain how the force changes with respect to distance .

many modern musical instruments are cumbersome or have a lot of parts . some need a stand or a stool . but the cajon is a drum , a stand and a seat all in one convenient box . and this simplicity may be key to its journey across continents and cultures to become one of the most popular percussion instruments in the world today . the cajon 's story begins in west africa , whose indigenousness people had rich musical traditions centered on drumming and dancing . when many of them were captured and brought to the americas as slaves , they brought this culture with them , but without their native instruments , they had to improvise . african slaves in coastal peru did n't have the materials or the opportunity to craft one of their traditional drums such as a djembe or a djun djun . but what they did have were plenty of shipping crates . not only were these readily accessible , but their inconspicuous appearance may have helped get around laws prohibiting slaves from playing music . early peruvian cajons consisted of a simple box with five thick wooden sides . the sixth side , made of a thinner sheet of wood , would be used as the striking surface , or more commonly known as the tapa . a sound hole was also cut into the back to allow the sound to escape . as an afro-peruvian culture developed , and new forms of music and dance , such as zamacueca , festejo and landó were born , the cajon became a dedicated musical instrument in its own right . early modifications involved simply bending the planks of the box to tweak the sound , and when abolition of slavery introduced the cajon to a broader population , more improvisation and experimentation soon followed . perhaps the person most responsible for introducing the cajon to european audiences was spanish flamenco guitarist paco de lucía . when touring in peru in 1977 , he and his percussionist rubem dantas discovered the cajon and brought it back to spain , recognizing its potential for use in flamenco music . by stretching guitar strings along the inside of the tapa , the flamenco musicians were able to create a buzz-like snare sound . combined with the regular base tone , this gave the cajon a sound close to a basic drum set . the cajon quickly caught on , not only becoming standard in flamenco , but being used in genres like folk , jazz , blues and rock . today , many specialized cajons are manufactured , some with adjustable strings , some with multiple playing surfaces , and some with a snare mechansim . but the basic concept remains the same , and the story of the cajon shows that the simplest things can have the most amazing potential when you think outside and inside the box .

when many of them were captured and brought to the americas as slaves , they brought this culture with them , but without their native instruments , they had to improvise . african slaves in coastal peru did n't have the materials or the opportunity to craft one of their traditional drums such as a djembe or a djun djun . but what they did have were plenty of shipping crates .

what did the african slave 's have plenty of to use as drums ?

this is the bop . the bop is a type of social dance . dance is a language , and social dance is an expression that emerges from a community . a social dance is n't choreographed by any one person . it ca n't be traced to any one moment . each dance has steps that everyone can agree on , but it 's about the individual and their creative identity . because of that , social dances bubble up , they change , and they spread like wildfire . they are as old as our remembered history . in african-american social dances , we see over 200 years of how african and african-american traditions influenced our history . the present always contains the past . and the past shapes who we are and who we will be . ( clapping ) the juba dance was born from enslaved africans ' experience on the plantation . brought to the americas , stripped of a common spoken language , this dance was a way for enslaved africans to remember where they 're from . it may have looked something like this . slapping thighs , shuffling feet and patting hands : this was how they got around the slave owners ' ban on drumming , improvising complex rhythms just like ancestors did with drums in haiti or in the yoruba communities of west africa . it was about keeping cultural traditions alive and retaining a sense of inner freedom under captivity . it was the same subversive spirit that created this dance : the cakewalk , a dance that parodied the mannerisms of southern high society -- a way for the enslaved to throw shade at the masters . the crazy thing about this dance is that the cakewalk was performed for the masters , who never suspected they were being made fun of . now you might recognize this one . 1920s -- the charleston . the charleston was all about improvisation and musicality , making its way into lindy hop , swing dancing and even the kid n play , originally called the funky charleston . started by a tight-knit black community near charleston , south carolina , the charleston permeated dance halls where young women suddenly had the freedom to kick their heels and move their legs . now , social dance is about community and connection ; if you knew the steps , it meant you belonged to a group . but what if it becomes a worldwide craze ? enter the twist . it 's no surprise that the twist can be traced back to the 19th century , brought to america from the congo during slavery . but in the late '50s , right before the civil rights movement , the twist is popularized by chubby checker and dick clark . suddenly , everybody 's doing the twist : white teenagers , kids in latin america , making its way into songs and movies . through social dance , the boundaries between groups become blurred . the story continues in the 1980s and '90s . along with the emergence of hip-hop , african-american social dance took on even more visibility , borrowing from its long past , shaping culture and being shaped by it . today , these dances continue to evolve , grow and spread . why do we dance ? to move , to let loose , to express . why do we dance together ? to heal , to remember , to say : `` we speak a common language . we exist and we are free . ''

slapping thighs , shuffling feet and patting hands : this was how they got around the slave owners ' ban on drumming , improvising complex rhythms just like ancestors did with drums in haiti or in the yoruba communities of west africa . it was about keeping cultural traditions alive and retaining a sense of inner freedom under captivity . it was the same subversive spirit that created this dance : the cakewalk , a dance that parodied the mannerisms of southern high society -- a way for the enslaved to throw shade at the masters .

social dance allows cultural traditions to be kept alive despite what is going on in the world . why is this important ? provide an example of this from the lesson .

translator : andrea mcdonough reviewer : bedirhan cinar people often think the word `` doubt '' spelling is a little crazy because of the letter `` b '' . since it does n't spell a sound , most folks ca n't figure out what it 's doing there . but in spite of what most of us learn in school , sound is < i > never < /i > the most important aspect of spelling an english word . a word 's meaning and history need to come first . to doubt means to question , to waver , to hesitate . as a noun , it means uncertainty or confusion . the present-day english word `` doubt '' started as a latin word , `` dubitare '' . it first moved from latin into french where it lost both its `` buh '' sound and its letter `` b '' . and then it came into english in the 13th century . about 100 years later , scribes who wrote english but also knew latin , started to reinsert the `` b '' into the word 's spelling , even though no one pronounced it that way . but why would they do this ? why would anyone in their right mind reinsert a silent letter into a spelling ? well , because they knew latin , the scribes understood that the root of `` doubt '' had a `` b '' in it . over time , even as fewer literate people knew latin , the `` b '' was kept because it marked important , meaningful connections to other related words , like `` dubious '' and `` indubitalbly , '' which were subsequently borrowed into english from the same latin root , `` dubitare '' . understanding these historical connections not only helped us to spell `` doubt , '' but also to understand the meaning of these more sophisticated words . but the story does n't end there . if we look even deeper , we can see beyond the shadow of a doubt , just how revealing that `` b '' can be . there are only two base words in all of english that have the letters `` d-o-u-b '' : one is doubt , and the other is double . we can build lots of other words on each of these bases , like doubtful and doubtless , or doublet , and redouble , and doubloon . it turns out that if we look into their history , we can see that they both derive from the same latin forms . the meaning of double , two , is reflected in a deep understanding of doubt . see , when we doubt , when we hesitate , we second guess ourselves . when we have doubts about something , when we have questions or confusion , we are of two minds . historically , before english began to borrow words from french , it already had a word for doubt . that old english word was `` tweogan , '' a word whose relationship to `` two '' is clear in its spelling as well . so the next time you are in doubt about why english spelling works the way it does , take a second look . what you find just might make you do a double-take .

as a noun , it means uncertainty or confusion . the present-day english word `` doubt '' started as a latin word , `` dubitare '' . it first moved from latin into french where it lost both its `` buh '' sound and its letter `` b '' .

what is the old english word that means basically the same thing as the word doubt ?

modern computers are revolutionizing our lives , performing tasks unimaginable only decades ago . this was made possible by a long series of innovations , but there 's one foundational invention that almost everything else relies upon : the transistor . so what is that , and how does such a device enable all the amazing things computers can do ? well , at their core , all computers are just what the name implies , machines that perform mathematical operations . the earliest computers were manual counting devices , like the abacus , while later ones used mechanical parts . what made them computers was having a way to represent numbers and a system for manipulating them . electronic computers work the same way , but instead of physical arrangements , the numbers are represented by electric voltages . most such computers use a type of math called boolean logic that has only two possible values , the logical conditions true and false , denoted by binary digits one and zero . they are represented by high and low voltages . equations are implemented via logic gate circuits that produce an output of one or zero based on whether the inputs satisfy a certain logical statement . these circuits perform three fundamental logical operations , conjunction , disjunction , and negation . the way conjunction works is an `` and gate '' provides a high-voltage output only if it receives two high-voltage inputs , and the other gates work by similar principles . circuits can be combined to perform complex operations , like addition and subtraction . and computer programs consist of instructions for electronically performing these operations . this kind of system needs a reliable and accurate method for controlling electric current . early electronic computers , like the eniac , used a device called the vacuum tube . its early form , the diode , consisted of two electrodes in an evacuated glass container . applying a voltage to the cathode makes it heat up and release electrons . if the anode is at a slightly higher positive potential , the electrons are attracted to it , completing the circuit . this unidirectional current flow could be controlled by varying the voltage to the cathode , which makes it release more or less electrons . the next stage was the triode , which uses a third electrode called the grid . this is a wire screen between the cathode and anode through which electrons could pass . varying its voltage makes it either repel or attract the electrons emitted by the cathode , thus , enabling fast current-switching . the ability to amplify signals also made the triode crucial for radio and long distance communication . but despite these advancements , vacuum tubes were unreliable and bulky . with 18,000 triodes , eniac was nearly the size of a tennis court and weighed 30 tons . tubes failed every other day , and in one hour , it consumed the amount of electricity used by 15 homes in a day . the solution was the transistor . instead of electrodes , it uses a semiconductor , like silicon treated with different elements to create an electron-emitting n-type , and an electron absorbing p-type . these are arranged in three alternating layers with a terminal at each . the emitter , the base , and the collector . in this typical npn transistor , due to certain phenomena at the p-n interface , a special region called a p-n junction forms between the emitter and base . it only conducts electricity when a voltage exceeding a certain threshold is applied . otherwise , it remains switched off . in this way , small variations in the input voltage can be used to quickly switch between high and low-output currents . the advantage of the transistor lies in its efficiency and compactness . because they do n't require heating , they 're more durable and use less power . eniac 's functionality can now be surpassed by a single fingernail-sized microchip containing billions of transistors . at trillions of calculations per second , today 's computers may seem like they 're performing miracles , but underneath it all , each individual operation is still as simple as the flick of a switch .

tubes failed every other day , and in one hour , it consumed the amount of electricity used by 15 homes in a day . the solution was the transistor . instead of electrodes , it uses a semiconductor , like silicon treated with different elements to create an electron-emitting n-type , and an electron absorbing p-type .

explain the construction of a transistor and how it switches currents . how does the transistor overcome the inefficiencies of the vacuum tube ?

how does this music make you feel ? do you find it beautiful ? is it creative ? now , would you change your answers if you learned the composer was this robot ? believe it or not , people have been grappling with the question of artificial creativity , alongside the question of artifcial intelligence , for over 170 years . in 1843 , lady ada lovelace , an english mathematician considered the world 's first computer programmer , wrote that a machine could not have human-like intelligence as long as it only did what humans intentionally programmed it to do . according to lovelace , a machine must be able to create original ideas if it is to be considered intelligent . the lovelace test , formalized in 2001 , proposes a way of scrutinizing this idea . a machine can pass this test if it can produce an outcome that its designers can not explain based on their original code . the lovelace test is , by design , more of a thought experiment than an objective scientific test . but it 's a place to start . at first glance , the idea of a machine creating high quality , original music in this way might seem impossible . we could come up with an extremely complex algorithm using random number generators , chaotic functions , and fuzzy logic to generate a sequence of musical notes in a way that would be impossible to track . but although this would yield countless original melodies never heard before , only a tiny fraction of them would be worth listening to . with the computer having no way to distinguish between those which we would consider beautiful and those which we wo n't . but what if we took a step back and tried to model a natural process that allows creativity to form ? we happen to know of at least one such process that has lead to original , valuable , and even beautiful outcomes : the process of evolution . and evolutionary algorithms , or genetic algorithms that mimic biological evolution , are one promising approach to making machines generate original and valuable artistic outcomes . so how can evolution make a machine musically creative ? well , instead of organisms , we can start with an initial population of musical phrases , and a basic algorithm that mimics reproduction and random mutations by switching some parts , combining others , and replacing random notes . now that we have a new generation of phrases , we can apply selection using an operation called a fitness function . just as biological fitness is determined by external environmental pressures , our fitness function can be determined by an external melody chosen by human musicians , or music fans , to represent the ultimate beautiful melody . the algorithm can then compare between our musical phrases and that beautiful melody , and select only the phrases that are most similar to it . once the least similar sequences are weeded out , the algorithm can reapply mutation and recombination to what 's left , select the most similar , or fitted ones , again from the new generation , and repeat for many generations . the process that got us there has so much randomness and complexity built in that the result might pass the lovelace test . more importantly , thanks to the presence of human aesthetic in the process , we 'll theoretically generate melodies we would consider beautiful . but does this satisfy our intuition for what is truly creative ? is it enough to make something original and beautiful , or does creativity require intention and awareness of what is being created ? perhaps the creativity in this case is really coming from the programmers , even if they do n't understand the process . what is human creativity , anyways ? is it something more than a system of interconnected neurons developed by biological algorithmic processes and the random experiences that shape our lives ? order and chaos , machine and human . these are the dynamos at the heart of machine creativity initiatives that are currently making music , sculptures , paintings , poetry and more . the jury may still be out as to whether it 's fair to call these acts of creation creative . but if a piece of art can make you weep , or blow your mind , or send shivers down your spine , does it really matter who or what created it ?

at first glance , the idea of a machine creating high quality , original music in this way might seem impossible . we could come up with an extremely complex algorithm using random number generators , chaotic functions , and fuzzy logic to generate a sequence of musical notes in a way that would be impossible to track . but although this would yield countless original melodies never heard before , only a tiny fraction of them would be worth listening to .

name a computational approach that could lead to outcomes that would be impossible , or very difficult for humans to track .

translator : andrea mcdonough reviewer : jessica ruby big data is an elusive concept . it represents an amount of digital information , which is uncomfortable to store , transport , or analyze . big data is so voluminous that it overwhelms the technologies of the day and challenges us to create the next generation of data storage tools and techniques . so , big data is n't new . in fact , physicists at cern have been rangling with the challenge of their ever-expanding big data for decades . fifty years ago , cern 's data could be stored in a single computer . ok , so it was n't your usual computer , this was a mainframe computer that filled an entire building . to analyze the data , physicists from around the world traveled to cern to connect to the enormous machine . in the 1970 's , our ever-growing big data was distributed across different sets of computers , which mushroomed at cern . each set was joined together in dedicated , homegrown networks . but physicists collaborated without regard for the boundaries between sets , hence needed to access data on all of these . so , we bridged the independent networks together in our own cernet . in the 1980 's , islands of similar networks speaking different dialects sprung up all over europe and the states , making remote access possible but torturous . to make it easy for our physicists across the world to access the ever-expanding big data stored at cern without traveling , the networks needed to be talking with the same language . we adopted the fledgling internet working standard from the states , followed by the rest of europe , and we established the principal link at cern between europe and the states in 1989 , and the truly global internet took off ! physicists could easily then access the terabytes of big data remotely from around the world , generate results , and write papers in their home institutes . then , they wanted to share their findings with all their colleagues . to make this information sharing easy , we created the web in the early 1990 's . physicists no longer needed to know where the information was stored in order to find it and access it on the web , an idea which caught on across the world and has transformed the way we communicate in our daily lives . during the early 2000 's , the continued growth of our big data outstripped our capability to analyze it at cern , despite having buildings full of computers . we had to start distributing the petabytes of data to our collaborating partners in order to employ local computing and storage at hundreds of different institutes . in order to orchestrate these interconnected resources with their diverse technologies , we developed a computing grid , enabling the seamless sharing of computing resources around the globe . this relies on trust relationships and mutual exchange . but this grid model could not be transferred out of our community so easily , where not everyone has resources to share nor could companies be expected to have the same level of trust . instead , an alternative , more business-like approach for accessing on-demand resources has been flourishing recently , called cloud computing , which other communities are now exploiting to analyzing their big data . it might seem paradoxical for a place like cern , a lab focused on the study of the unimaginably small building blocks of matter , to be the source of something as big as big data . but the way we study the fundamental particles , as well as the forces by which they interact , involves creating them fleetingly , colliding protons in our accelerators and capturing a trace of them as they zoom off near light speed . to see those traces , our detector , with 150 million sensors , acts like a really massive 3-d camera , taking a picture of each collision event - that 's up to 14 millions times per second . that makes a lot of data . but if big data has been around for so long , why do we suddenly keep hearing about it now ? well , as the old metaphor explains , the whole is greater than the sum of its parts , and this is no longer just science that is exploiting this . the fact that we can derive more knowledge by joining related information together and spotting correlations can inform and enrich numerous aspects of everyday life , either in real time , such as traffic or financial conditions , in short-term evolutions , such as medical or meteorological , or in predictive situations , such as business , crime , or disease trends . virtually every field is turning to gathering big data , with mobile sensor networks spanning the globe , cameras on the ground and in the air , archives storing information published on the web , and loggers capturing the activities of internet citizens the world over . the challenge is on to invent new tools and techniques to mine these vast stores , to inform decision making , to improve medical diagnosis , and otherwise to answer needs and desires of tomorrow 's society in ways that are unimagined today .

to see those traces , our detector , with 150 million sensors , acts like a really massive 3-d camera , taking a picture of each collision event - that 's up to 14 millions times per second . that makes a lot of data . but if big data has been around for so long , why do we suddenly keep hearing about it now ?

what is the difference between structured and unstructured data , and where can you typically find each type ? which type makes up the largest fraction of big data today ? what extra challenges do unstructured data present to mining and analysis ?

rising temperatures and seas , massive droughts , changing landscapes . successfully adapting to climate change is growing increasingly important . for humans , this means using our technological advancement to find solutions , like smarter cities and better water management . but for some plants and animals , adapting to these global changes involves the most ancient solution of all : evolution . evolutionary adaptation usually occurs along time scales of thousands to hundreds of thousands of years . but in cases where species are under especially strong selective conditions , like those caused by rapidly changing climates , adaptive evolution can happen more quickly . in recent decades , we 've seen many plants , animals , and insects relocating themselves and undergoing changes to their body sizes , and the dates they flower or breed . but many of these are plastic , or nonheritable changes to an individual 's physical traits . and there are limits to how much an organism can change its own physiology to meet environmental requirements . that 's why scientists are seeking examples of evolutionary changes coded in species ' dna that are heritable , long-lasting , and may provide a key to their future . take the tawny owl . if you were walking through a wintry forest in northern europe 30 years ago , chances are you 'd have heard , rather than seen , this elusive bird . against the snowy backdrop , its plumage would have been near impossible to spot . today , the landscape is vastly different . since the 1980s , climate change has led to significantly less snowfall , but you 'd still struggle to spot a tawny owl because nowadays , they 're brown . the brown color variant is the genetically dominant form of plumage in this species , but historically , the recessive pale gray variant triumphed because of its selective advantage in helping these predators blend in . however , less snow cover reduces opportunities for camouflage , so lately , this gray color variant has been losing the battle against natural selection . the offspring of the brown color morphs , on the other hand , have an advantage in exposed forests , so brown tawny owls are flourishing today . several other species have undergone similar climate-change-adaptive genetic changes in recent decades . pitcher plant mosquitoes have rapidly evolved to take advantage of the warmer temperatures , entering dormancy later and later in the year . two spot ladybug populations , once comprised of equal numbers of melanic and non-melanic morphs , have now shifted almost entirely to the non-melanic color combination . scientists think that keeps them from overheating . meanwhile , pink salmon have adapted to warmer waters by spawning earlier in the season to protect their sensitive eggs . and wild thyme plants in europe are producing more repellent oils to protect themselves against the herbivores that become more common when it 's warm . these plants and animals belong to a group of about 20 identified species with evolutionary adaptations to rapid climate change , including snapping turtles , wood frogs , knotweed , and silver spotted skipper butterflies . however , scientists hope to discover more species evolving in response to climate change out of 8.7 million species on the planet . for most of our planet 's astounding and precious biodiversity , evolution wo n't be the answer . instead , many of those species will have to rely on us to help them survive a changing world or face extinction . the good news is we already have the tools . across the planet , we 're making on-the-ground decisions that will help entire ecosystems adapt . critical climate refuges are being identified and set aside , and projects are underway to help mobile species move to more suitable climates . existing parks and protected areas are also doing climate change check-ups to help their wildlife cope . fortunately , it 's still within our power to preserve much of the wondrous biodiversity of this planet , which , after all , sustains us in so many ways .

the offspring of the brown color morphs , on the other hand , have an advantage in exposed forests , so brown tawny owls are flourishing today . several other species have undergone similar climate-change-adaptive genetic changes in recent decades . pitcher plant mosquitoes have rapidly evolved to take advantage of the warmer temperatures , entering dormancy later and later in the year .

how do you think “ plastic ” , or non-heritable , changes like those listed in the lesson ( changing body sizes , breeding seasons , or flowering dates ) could help organisms adapt to climate change ? how do you think they may be limited ?

many generations have felt they 've reached the pinnacle of technological advancement , yet look back 100 years , and the technologies we take for granted today would seem like impossible magic . so will there be a point where we reach an actual limit of technological progress ? and if so , are we anywhere near that limit now ? half a century ago , russian astronomer nikolai kardashev was asking similar questions when he came up with a way to measure technological progress , even when we have no idea exactly what it might look like . anything we do in the future will require energy , so kardashev 's scale classifies potential civilizations , whether alien civilizations out there in the universe or our own , into three levels based on energy consumption . the tiny amount of energy we currently consume pales next to what we leave untapped . a type i , or planetary civilization , can access all the energy resources of its home planet . in our case , this is the 174,000 terawatts earth receives from the sun . we currently only harness about 15 terawatts of it , mostly by burning solar energy stored in fossil fuels . to approach becoming a type i civilization , we would need to capture solar energy more directly and efficiently by covering the planet with solar panels . based on the most optimistic models , we might get there within just four centuries . what would be next ? well , the earth only gets a sliver of the sun 's energy , while the rest of its 400 yottawatts is wasted in dead space . but a type ii , or stellar civilization , would make the most of its home star 's energy . instead of installing solar panels around a planet , a type ii civilization would install them directly orbiting its star , forming a theoretical structure called a dyson sphere . and the third step ? a type iii civilization would harness all the energy of its home galaxy . but we can also think of progress in the opposite way . how small can we go ? to that end , british cosmologist john barrow classified civilizations by the size of objects they control . that ranges from mechanical structures at our own scale , to the building blocks of our own biology , down to unlocking atoms themselves . we 've currently touched the atomic level , though our control remains limited . but we potentially could go much smaller in the future . to get a sense of the extent to which that 's true , the observable universe is 26 orders of magnitude larger than a human body . that means if you zoomed out by a factor of ten 26 times , you 'd be at the scale of the universe . but to reach the minimum length scale , known as the planck length , you would need to zoom in 35 times . as physicist richard feynman once said , `` there 's plenty of room at the bottom . '' instead of one or the other , it 's likely that our civilization will continue to develop along both kardashev and barrow scales . precision on a smaller scale lets us use energy more efficiently and unlocks new energy sources , like nuclear fusion , or even antimatter . and this increased energy lets us expand and build on a larger scale . a truly advanced civilization , then , would harness both stellar energy and subatomic technologies . but these predictions were n't made just for us humans . they double as a possible means of detecting intelligent life in the universe . if we find a dyson sphere around a distant star , that 's a pretty compelling sign of life . or , what if , instead of a structure that passively soaked up all the star 's energy , like a plant , an alien civilization built one that actively sucked the energy out of the star like a hummingbird . frighteningly enough , we 've observed super dense celestial bodies about the size of a planet that drain energy out of a much bigger star . it would be much too premature to conclude that this is evidence of life in the universe . there are also explanations for these observations that do n't involve alien life forms . but that does n't stop us from asking , `` what if ? ''

well , the earth only gets a sliver of the sun 's energy , while the rest of its 400 yottawatts is wasted in dead space . but a type ii , or stellar civilization , would make the most of its home star 's energy . instead of installing solar panels around a planet , a type ii civilization would install them directly orbiting its star , forming a theoretical structure called a dyson sphere .

how would you test whether stars out of which energy is actively drained would or would not be type ii ( stellar ) extraterrestrial civilizations ?

the most basic function of bodily fat is self-storage of food reserves . in prehistoric times , natural selection favored genotypes that could endure harsh conditions by stocking the most fat . with chronic malnutrition being the norm for most of human history , genetics evolved to favor fat storage . so when did body fat become problematic ? the negative impacts of being overweight were not even noted in medical literature until as late as the 18th century . then , technological advances coupled with public health measures resulted in the betterment of the quantity , quality , and variety of food . sustained abundance of good food enabled a healthier population to boom economically . output increased , and with it , leisure time and waistlines . by the mid 19th century , being excessively overweight , or obese , was recognized as a cause of ill health , and another century later , declared deadly . what is the distinction between being overweight and being obese ? a calculation called the bmi breaks it down for us . for example , if someone weighs 65 kilgorams and is 1.5 meters tall , they have a bmi of about 29 . obesity is a condition of excess body fat that occurs when a person 's bmi is above 30 , just over the overweight range of 25 to 29.9 . while bmi can be a helpful estimate of healthy weight , actual body fat percentage can only really be determined by also considering information like waist circumference and muscle mass . athletes , for instance , have a naturally higher bmi . so how does a person become obese ? at its most basic , obesity is caused by energy imbalance . if the energy input from calories is greater than the energy output from physical activity , the body stores the extra calories as fat . in most cases , this imbalance comes from a combination of circumstances and choices . adults should be getting at least 2.5 hours of exercise each week , and children a whole hour per day . but globally , one in four adults and eight out of ten adolescents are n't active enough . calorie-dense processed foods and growing portion sizes coupled with pervasive marketing lead to passive overeating . and scarce resources , and a lack of access to healthy , affordable foods creates an even greater risk in disadvantaged communities . yet , our genetic makeup also plays a part . studies on families and on separated twins have shown a clear causal hereditary relationship to weight gain . recent studies have also found a link between obesity and variations in the bacteria species that live in our digestive systems . no matter the cause , obesity is an escalating global epidemic . it substantially raises the probability of diseases , like diabetes , heart disease , stroke , high blood pressure , and cancer . it affects virtually all ages , genders , and socioeconomic groups in both developed and developing countries . with a 60 % rise in child obesity globally over just two decades , the problem is too significant to ignore . once a person is obese , the climb to recovery becomes progressively steeper . hormonal and metabolic changes reduce the body 's response to overeating . after losing weight , a formerly overweight person burns less calories doing the same exercises as a person who is naturally the same weight , making it much more difficult to shed the excess fat . and as people gain weight , damage to signaling pathways makes it increasingly difficult for the brain to measure food intake and fat storage . there is , however , some evidence that well-monitored , long-term changes in behavior can lead to improvements in obesity-related health issues . and weight loss from sustained lifestyle changes , or invasive treatments like bariatric surgery , can improve insulin resistance and decrease inflammation . what was once an advantage for survival is now working against us . as the world 's population continues to slow down and get bigger , moving and consciously eating our way towards a healthier weight is essential to our overall well-being . and with the epidemic affecting every country in the world for different socioeconomic reasons , obesity can not be seen as an isolated issue . more global measures for prevention are essential to manage the weight of the world .

athletes , for instance , have a naturally higher bmi . so how does a person become obese ? at its most basic , obesity is caused by energy imbalance .

what is one reason an obese or formerly obese person might find it more difficult to lose weight ?

vatican city : capitol of the catholic church , home to the pope , owner of impressive collections of art and history all contained within the borders of the world 's smallest country : conveniently circumnavigateable on foot in only 40 minutes . just how did the world end up with this tiny nation ? the short answer is : because mussolini and the long answer is fiendishly complicated so here 's a simplified medium version : the popes used to rule a country called the papal states that covered much of modern day italy . it was during this 1,000+ year reign that the popes constructed st. peter 's basilica the largest church in the world -- and also built a wall around the base of a hill known as vatican upon which st. peter 's stood . but the kingdom of italy next door thought rome would be an awesome capital for their country and so conquered the papal states . his nation destroyed the pope hid behind the walls of vatican and conflictingly refused to acknowledge that the kingdom of italy existed , while simultaneously complaining about being a prisoner of the kingdom of italy -- which according to him did n't exist . rather than risk religious civil war by getting rid of the pope the kingdom of italy decided to wait him out assuming he 'd eventually give up -- but religion is nothing if not obstinate -- and 1 , 2 , 3 , 4 , 5 popes and sixty years later nothing had changed . which brings us to benito mussolini the then prime minister of italy who was tired of listing to the pope complain to italian catholics about his self-imposed imprisonment so mussolini thought he could score some political points by striking a deal which looked like this : 1 ) italy gave the land of vatican to the pope . and… 2 ) italy gave the pope a bunch of apology money in return 1 ) the pope acknowledged that italy existed and and… 2 ) the pope promised to remain neutral in politics and wars . on the off chance that , you know , mussolini thought this might be a thing . the deal was signed and a new country , vatican city was born . and today the tiny nation on a hill has all the things you 'd expect of a country : its own government that makes its own laws that are enforced by its own police , who put people who break them in its own jail . it also has its own bank and prints its own stamps and issues its own license plates , though only its citizens can drive within its borders presumably because of terrible , terrible parking -- and as the true mark of any self-respecting nation : it has its own top-level domain : .va but , despite all these national trappings vatican city is not really like any other country . hold on to your fancy hat , because it 's about to get weird : to understand the vatican : there are two people and two things that you need to know about : the famous pope , the incredibly confusing holy see , the country of vatican city and along with that the almost completely unknown king of vatican city . but first the pope : who gets a throne to sit upon and from which he acts as the bishop for all the catholics in rome . actually all bishops in the catholic church get their own thrones but because the bishop of rome is also the pope his thrown is special and has it 's own special name : the holy see . every time a pope dies or retires there is a sort of game of thrones to see which of the bishops will next get to occupy the holy see . so while popes come and go the throne is eternal . as such the name the holy see not only refers to the throne but also all the rules that make the catholic church the catholic church . when mussolini crafted that aforementioned deal , technically he gave the land of vatican city to the holy see -- which , believe it or not , is a legal corporate person in international law . basically every time you hear the words the holy see think catholic church , inc of which the pope is the ceo . now back to the king . the king of vatican city has absolute , unchecked power within the country 's borders and his presence makes vatican city one of only six remanning absolute monarchies in the world , including brunei , oman , qatar , saudi arabia , and swaziland . the king 's absolute power is why vatican city ca n't join the european union because only democracies are allowed . through vatican city does , strictly speaking , have a legislative brach of government -- staffed by cardinals , appointed by the pope -- the king of vatican city can overrule their decisions and at any time for any reason . so why do you never hear about the king of vatican city ? because though king and pope are two different roles , they just happen to be occupied by the same person at the same time -- which has the funny consequence that , because the pope is elected and the king is all-powerful but they 're the same guy it makes vatican city the world 's only elected , non-hereditary absolute monarchy . it 's this dual-role that makes untangling vatican city so difficult because the pope , depending on the situation either acts as the king of the country of vatican city or the pope of the holy see . got it ? no ? ok , here 's an analogy : imagine if a powerful international company , say grey industries , had a ceo who convinced the united states to give one of its islands to the company which then made the island into a new country -- greytropolis -- with an absolute monarchy as its government and the law that the king of greytropolis is , by definition , the ceo of grey industries . it 's pretty obvious at that point that the ceo should move his corporate headquarters to the new nation -- so that the laws of the country can benefit the company and the company 's global reach can benefit the country . as for the man in the middle sometimes it 's good to the the ceo and sometimes it 's good to be the king . that is essentially vatican city . but if you 're still confused , do n't worry even other countries ca n't keep it straight . for example the united nations has the holy see the corporation as a member but not vatican city the actual country . and the holy see gives passports to vatican city citizens that other countries accept even though those passports come from a company , not a country . and speaking of vatican city citizens , they are perhaps the strangest consequence of the pope 's dual role as religious leader and monarch . while other countries mint new citizens with the ever popular process of human reproduction vatican city does not . no one in vatican city is born a citizen -- and that 's not just because , within a rounding error , there are no female vaticans . the only way to become a citizen is for the king of vatican city to appoint you as one . and the king only appoints you a citizen if you work for the pope -- who is also the king . and because the king is all-powerful your citizenship is at his whim . if you quit your job for the pope , the king -- who is also the pope -- will revoke your citizenship . these rules mean that vatican city does n't have a real permanent population to speak of : there are only about 500 full citizens -- which is fewer people that live in single skyscrapers in many countries -- and all these citizens work for the holy see as either cardinals or diplomats or the pope 's bodyguards or other catholic-related jobs . so it 's best to think of vatican city as a kind of sovereign corporate headquarters that grants temporary citizenship to its managers rather than a real city-state like singapore : which has a self-reproducing population of citizens engaged in a variety of economic activities both of which vatican city lacks . but in the end , the reason the world cares about vatican city is not because of the citizens within its walls but because of the billion members of its church outside those walls .

as for the man in the middle sometimes it 's good to the the ceo and sometimes it 's good to be the king . that is essentially vatican city . but if you 're still confused , do n't worry even other countries ca n't keep it straight .

vatican city was generously given to the catholic church from italy after the papal states were conquered .

fu manchu was one of the most notorious escape artists at the omaha zoo in the 1960s . but he was n't a performer , he was an orangutan . the keepers who locked his enclosure every night were baffled to find him outside the next day hanging out with friends in a tree , or sunning on the roof . only after installing cameras did they realize fu manchu had been picking the lock with a metal wire that he kept hidden under his cheek pouch . the keepers should n't have been surprised at fu manchu 's cunningness . along with our other great ape cousins , the gorillas , chimps , and bonobos , they belong to our hominidae family tree , which stretches back 14 million years . but it 's not just their striking red hair that makes orangutans unique among our cousins . as the only great apes from asia , orangutans have adapted to a life high in the rain forest canopies . many of the skills they learn are transmitted through the special bond they have with their mothers , the most extended in the animal kingdom next to humans . orangutan mothers usually give birth to one baby at a time , waiting up to eight years before having another . this gives the young , who begin as fully dependent infants , plenty of time to learn how to climb and distinguish the hundreds of plants and fruits that make up their diet . female orangutans even stay with their mothers into their teen years to learn child-rearing . as they grow up , orangutans also develop a complex set of cooperative social skills by interacting with their peers and siblings . much like ourselves , young orangutans involuntarily mimic the facial expressions and emotions of their playmates , with behaviors that closely parallel human smiling and laughter . once they finally venture out on their own , orangutans continue to develop their resourcefulness , putting the skills they 've learned into practice . adults build a new nest each night by carefully weaving twigs together , topping them with soft leaves , pillows , and blankets . this process requires dexterity , coordination , and an eye for design . orangutans also use a variety of tools to make their lives in the jungle easier . they turn branches into fly swatters and back scratchers , construct umbrellas when it rains , make gloves from leafy pads , and even use leaves as bandages to dress their wounds . but orangutan intelligence goes far beyond jungle survival . research in controlled environments has shown that orangutans are self-aware , being one of the few species to recognize their own reflections . they also display remarkable foresight , planning , and cognition . in one experiment , researchers taught an orangutan to use a straw to extract his favorite fruit soup from a box . that orangutan was later given the choice between the straw or a grape that could be eaten right away , and he chose the straw just in case he was given another box of soup . in another experiment , orangutans figured out how to reach peanuts at the bottom of long tubes by spitting water into them . while orangutans are able to pass cognitive tests with flying colors , there are certain problems that they need our help to solve . indonesia has the world 's highest rate of deforestation , and millions of acres of rain forest are burned annually to support the logging and palm oil industries . deforestation exposes the 30,000 orangutans remaining in the wild to poachers . they kill mothers so that baby orangutans can be sold as exotic pets . but fortunately , the story often does n't end here . orphans can be confiscated and given a second chance . at special forest schools , they recover from emotional trauma and continue to develop essential life skills . against all odds , these orphans demonstrate incredible resilience and readiness to learn . in malay , the word orangutan translates literally to `` the person of the forest , '' a reminder of our common lineage . and despite orangutans being some of the smartest animals on earth , outsmarting their extinction requires the creativity , empathy , and foresight that our species share .

female orangutans even stay with their mothers into their teen years to learn child-rearing . as they grow up , orangutans also develop a complex set of cooperative social skills by interacting with their peers and siblings . much like ourselves , young orangutans involuntarily mimic the facial expressions and emotions of their playmates , with behaviors that closely parallel human smiling and laughter . once they finally venture out on their own , orangutans continue to develop their resourcefulness , putting the skills they 've learned into practice .

why do you think an orangutan ’ s ability to mimic its playmate ’ s facial expressions is important for developing social skills ?

despite advances in medicine , cancer remains one of the most frightening diagnoses patients can receive . what makes it so difficult to cure is that it 's not one illness , but a family of over 100 diseases occurring in different types of cells . and one type of cancer has the unfortunate distinction of afflicting children more than any other type . this is leukemia , a cancer that begins in stem cells found in the bone marrow . a stem cell is a bit like an infant , undeveloped but possessing great potential . many stem cells specialize and become cells of organs , like the liver , brain and heart . but in some tissues , they can continue to divide into new stem cells throughout development , and into adulthood in order to frequently generate new cells and keep up with the body 's needs . one example is the bone marrow , where stem cells differentiate into many types of blood cells . that includes red blood cells , which carry oxygen from the lungs to all tissues , platelets , which help stop bleeding by sticking to damaged blood vessels , and white blood cells , which patrol the body , destroying potentially harmful invaders . every once in a while , something goes wrong during a stem cell 's specialization process and harmful mutations occur in the cell 's dna . cells with compromised dna are supposed to self-destruct , but some damaged cells ignore this order , replicating uncontrollably , even as they lose their original function . these are what we know as cancer cells . it is not yet clear why leukemia is the most common childhood cancer , but one contributing factor may be that leukemias are often caused by just one or two dna modifications , while most cancers require many of them , allowing leukemias to arise faster than other types of cancer . moreover , some dna alterations can occur in white blood cells during fetal development , further increasing the risk of early leukemia . but though it affects more children than any other cancer , adults constitute the majority of leukemia patients overall . once leukemia strikes , the damaged cells reproduce in the blood and the bone marrow until they take up all available space and resources . when the bone marrow can no longer produce the required amount of functional cells , the blood becomes depleted . the lack of red blood cells means that muscles do n't get enough oxygen , the reduced number of platelets is not sufficient to repair wounds , and the dearth of functional white blood cells impairs the immune system , increasing the risk of infections . to restore the normal function of the blood , leukemic cells have to be eliminated . but because leukemias are not solid tumors , they ca n't be removed surgically . instead , the cells are killed inside the body using various treatments that include chemotherapy , a combination of drugs that destroys quickly multiplying cells . unfortunately , this has the side effect of killing healthy cells , such as those found in hair follicles or intestines . and in some cases , the dosage required is so high that it kills all cells in the bone marrow , including stem cells . when this happens , the body is no longer able to create new blood cells on its own . fortunately , outside help can come in the form of stem cells from the bone marrow of a donor . once transplanted into the patient , they rapidly repopulate the bone marrow and the blood . however , bone marrow transplants are a complicated process requiring antigen compatibility between the donor and recipient to keep the transplanted cells from from attacking the patient 's own cells as foreign bodies . unlike with blood transplants , there are thousands of hla types , and even siblings and close relatives may not have compatible bone marrow . if this is the case , the search is expanded to a database containing the genetic makeup of millions of voluntary bone marrow donors . the more potential donors there are , the more patients lives can be saved through successful transplants . leukemia may be a frightening disease , but there is strength and hope in numbers .

but in some tissues , they can continue to divide into new stem cells throughout development , and into adulthood in order to frequently generate new cells and keep up with the body 's needs . one example is the bone marrow , where stem cells differentiate into many types of blood cells . that includes red blood cells , which carry oxygen from the lungs to all tissues , platelets , which help stop bleeding by sticking to damaged blood vessels , and white blood cells , which patrol the body , destroying potentially harmful invaders . every once in a while , something goes wrong during a stem cell 's specialization process and harmful mutations occur in the cell 's dna .

where do blood cells come from ?

in this short video , we 're going to show you how we constructed and animated a pop-up book to explain earth 's tectonic plates . the supercontinent pangaea broke apart 200,000,000 years ago , but the pieces have n't stopped shifting . although with animation we can show this movement easily with drawings , we thought it 'd be more interesting to depict gigantic sliding slabs of rock using a tangible object that also moves and shifts . and the pop-up book idea was born . ( music ) to make your own pop-up book , you 'll need some basic paper tools , such as scissors , an x-acto knife , glue , double-sided scotch tape , a ruler , a bone folder or other creasing tool , and , of course , some paper . for this lesson , we first determined the visual style by making illustrations and deciding on the overall design , colors , shapes and elements we wanted on each page , or spread . you can have more detailed illustrations , but we wanted to illustrate this lesson simply by playing with shapes and colors . when you visualize your pop-up and choose a visual style , you will want to make a bunch of good old pencil sketches on paper and plan each movement for each spread . plan as much as you can : all the basic shapes and how they connect and how you want them to move , which parts you want to pop-up first . challenge yourself , and explore multiple possibilities of how your main element on the spread can pop up . for the next step , make a mock-up spread and see if your masterful paper engineering ideas translate from a sketch to the actual prototype . instead of using fancy paper , start with the cheap stuff and allow yourself to make mistakes and adjustments . this prototype lets you see how your preliminary sketches will come to life . you will want to first draw all individual parts on a single sheet , including all your main pieces , all the supporting pieces and the folds . you may be surprised that there are only two types of folds that can make your elements pop up the way you want : a step fold and a v-fold . here , you can see how we used a step fold to make each layer of the earth step out . then , cut all your individual elements and assemble using glue or double-sided scotch tape . ( music ) through trial and error , make sure that all the elements , shapes and placements are moving the way you imagined , and that they fold properly when closed and opened . ( music ) once your prototype is tested and complete , you can proceed to making the final product in color . draw or paint on your main pop-up elements as you see fit . for this lesson , we decided to just play with simple shapes in different colors to create the world of shifting continents we imagined . ( music ) when we were planning each spread , we knew we wanted some elements to move independently of the typical pop-up book using slight manipulations and animations . we had to plan well , but also use a few tricks . as always , when you 're making stop-motion , you may have to be creative and use all sorts of unusual tools and props to achieve the effect that you want . in this shot , the birds had to fly across and off the edge of the book , so we used fun-tak to move the clouds across the page . once they left the page , they had to be trimmed to get the illusion they flew off . when the pages of the book close at the end , we had to flip each page , supporting it in each position long enough to be photographed as an individual frame . we used binder clips , wedges , fun-tak , and almost every handy little thing you can think of . once all the individual frames were photographed , we put them all together and composited to make our pop-up book look like it 's moving on its own . so now , think of a special occasion where you can surprise someone with your own unique pop-up card , or an entire story that you want to tell , and start plotting the ins and outs of your pop-up book .

although with animation we can show this movement easily with drawings , we thought it 'd be more interesting to depict gigantic sliding slabs of rock using a tangible object that also moves and shifts . and the pop-up book idea was born . ( music ) to make your own pop-up book , you 'll need some basic paper tools , such as scissors , an x-acto knife , glue , double-sided scotch tape , a ruler , a bone folder or other creasing tool , and , of course , some paper .

why use a pop-up book instead of animation ?

packed inside every cell in your body is a set of genetic instructions , 3.2 billion base pairs long . deciphering these directions would be a monumental task but could offer unprecedented insight about the human body . in 1990 , a consortium of 20 international research centers embarked on the world 's largest biological collaboration to accomplish this mission . the human genome project proposed to sequence the entire human genome over 15 years with $ 3 billion of public funds . then , seven years before its scheduled completion , a private company called celera announced that they could accomplish the same goal in just three years and at a fraction of the cost . the two camps discussed a joint venture , but talks quickly fell apart as disagreements arose over legal and ethical issues of genetic property . and so the race began . though both teams used the same technology to sequence the entire human genome , it was their strategies that made all the difference . their paths diverged in the most critical of steps : the first one . in the human genome project 's approach , the genome was first divided into smaller , more manageable chunks about 150,000 base pairs long that overlapped each other a little bit on both ends . each of these fragments of dna was inserted inside a bacterial artificial chromosome where they were cloned and fingerprinted . the fingerprints showed scientists where the fragments overlapped without knowing the actual sequence . using the overlapping bits as a guide , the researchers marked each fragment 's place in the genome to create a contiguous map , a process that took about six years . the cloned fragments were sequenced in labs around the world following one of the project 's two major principles : that collaboration on our shared heritage was open to all nations . in each case , the fragments were arbitrarily broken up into small , overlapping pieces about 1,000 base pairs long . then , using a technology called the sanger method , each piece was sequenced letter by letter . this rigorous map-based approach called hierarchical shotgun sequencing minimized the risk of misassembly , a huge hazard of sequencing genomes with many repetitive portions , like the human genome . the consortium 's `` better safe than sorry '' approach contrasted starkly with celera 's strategy called whole genome shotgun sequencing . it hinged on skipping the mapping phase entirely , a faster , though foolhardy , approach according to some . the entire genome was directly chopped up into a giant heap of small , overlapping bits . once these bits were sequenced via the sanger method , celera would take the formidable risk of reconstructing the genome using just the overlaps . but perhaps their decision was n't such a gamble because guess whose freshly completed map was available online for free ? the human genome consortium , in accordance with the project 's second major principle which held that all of the project 's data would be shared publicly within 24 hours of collection . so in 1998 , scientists around the world were furiously sequencing lines of genetic code using the tried and true , yet laborious , sanger method . finally , after three exhausting years of continuous sequencing and assembling , the verdict was in . in february 2001 , both groups simultaneously published working drafts of more than 90 % of the human genome , several years ahead of the consortium 's schedule . the race ended in a tie . the human genome project 's practice of immediately sharing its data was an unusual one . it is more typical for scientists to closely guard their data until they are able to analyze it and publish their conclusions . instead , the human genome project accelerated the pace of research and created an international collaboration on an unprecedented scale . since then , robust investment in both the public and private sector has led to the identification of many disease related genes and remarkable advances in sequencing technology . today , a person 's genome can be sequenced in just a few days . however , reading the genome is only the first step . we 're a long way away from understanding what most of our genes do and how they are controlled . those are some of the challenges for the next generation of ambitious research initiatives .

in 1990 , a consortium of 20 international research centers embarked on the world 's largest biological collaboration to accomplish this mission . the human genome project proposed to sequence the entire human genome over 15 years with $ 3 billion of public funds . then , seven years before its scheduled completion , a private company called celera announced that they could accomplish the same goal in just three years and at a fraction of the cost .

what sequencing method did the human genome project and celera use to sequence fragments of dna ?

have you ever noticed something swimming in your field of vision ? it may look like a tiny worm or a transparent blob , and whenever you try to get a closer look , it disappears , only to reappear as soon as you shift your glance . but do n't go rinsing out your eyes ! what you are seeing is a common phenomenon known as a floater . the scientific name for these objects is muscae volitantes , latin for `` flying flies , '' and true to their name , they can be somewhat annoying . but they 're not actually bugs or any kind of external objects at all . rather , they exist inside your eyeball . floaters may seem to be alive , since they move and change shape , but they are not alive . floaters are tiny objects that cast shadows on the retina , the light-sensitive tissue at the back of your eye . they might be bits of tissue , red blood cells , or clumps of protein . and because they 're suspended within the vitreous humor , the gel-like liquid that fills the inside of your eye , floaters drift along with your eye movements , and seem to bounce a little when your eye stops . floaters may be only barely distinguishable most of the time . they become more visible the closer they are to the retina , just as holding your hand closer to a table with an overhead light will result in a more sharply defined shadow . and floaters are particularly noticeable when you are looking at a uniform bright surface , like a blank computer screen , snow , or a clear sky , where the consistency of the background makes them easier to distinguish . the brighter the light is , the more your pupil contracts . this has an effect similar to replacing a large diffuse light fixture with a single overhead light bulb , which also makes the shadow appear clearer . there is another visual phenomenon that looks similar to floaters but is in fact unrelated . if you 've seen tiny dots of light darting about when looking at a bright blue sky , you 've experienced what is known as the blue field entoptic phenomenon . in some ways , this is the opposite of seeing floaters . here , you are not seeing shadows but little moving windows letting light through to your retina . the windows are actually caused by white blood cells moving through the capillaries along your retina 's surface . these leukocytes can be so large that they nearly fill a capillary causing a plasma space to open up in front of them . because the space and the white blood cells are both more transparent to blue light than the red blood cells normally present in capillaries , we see a moving dot of light wherever this happens , following the paths of your capillaries and moving in time with your pulse . under ideal viewing conditions , you might even see what looks like a dark tail following the dot . this is the red blood cells that have bunched up behind the leukocyte . some science museums have an exhibit which consists of a screen of blue light , allowing you to see these blue sky sprites much more clearly than you normally would . while everybody 's eyes experience these sort of effects , the number and type vary greatly . in the case of floaters , they often go unnoticed , as our brain learns to ignore them . however , abnormally numerous or large floaters that interfere with vision may be a sign of a more serious condition , requiring immediate medical treatment . but the majority of the time entoptic phenomena , such as floaters and blue sky sprites , are just a gentle reminder that what we think we see depends just as much on our biology and minds as it does on the external world .

these leukocytes can be so large that they nearly fill a capillary causing a plasma space to open up in front of them . because the space and the white blood cells are both more transparent to blue light than the red blood cells normally present in capillaries , we see a moving dot of light wherever this happens , following the paths of your capillaries and moving in time with your pulse . under ideal viewing conditions , you might even see what looks like a dark tail following the dot .

why can you see the movement of white blood cells in your eyes ?

good evening ! what 's the matter ? are you afraid of vampires ? he he , no need to worry , i 'm not staying for dinner . ( laughter ) i 'm here to guide you through a brief history of vampires , illustrating how our image has changed from a shambling corpse to the dapper gentleman you see before you . vampires are nearly as old as you humans . stories about us , revenants , appear in cultures extending as far back as prehistoric times . but we were n't called vampires back then and most of us did not look the way we imagine vampires today . ha , far from it ! for example , the mesopotamian lamashtu was a creature with the head of a lion and the body of the donkey , and the ancient greek striges were simply described as bloodthirsty birds . others were even stranger . the philippine manananggal would sever her upper torso and sprout huge , bat-like wings to fly . the malaysian penanggalan was a flying female head with dangling entrails . ( laughter ) and the australian yara-ma-yha-who was a little red guy with a big head , a large mouth , and bloodsuckers on his hands and feet . oh , and let 's not forget the caribbean 's soucouyant , the west african obayifo , and the mexican tlahuelpuchi . ( laughter ) charming , are n't they ? though they may look vastly different , all of these beings have one common characteristic : they sustain themselves by consuming the life force of a living creature . this shared trait is what defines a vampire -- all the other attributes change with the tides . so , how do we arrive at the reanimated fellow you see before you ? our modern ideal emerges in 18th-century eastern europe . with the dramatic increase of vampire superstitions , stories of bloodsucking , shadowy creatures become nightly bedside terrors . and popular folklore , like the moroi among the romani people and the lugat in albania , provide the most common vampire traits known today , such as vampires being undead and nocturnal and shape-shifting . you see , eastern europe in the 18th century was a pretty grim place with many deaths occurring from unknown diseases and plagues . without medical explanations , people searched for supernatural causes and found what looked like evidence in the corpses of the victims . when villagers dug up bodies to discern the cause of the mysterious deaths , they would often find the cadavers looking very much alive -- longer hair and fingernails , bloated bellies , and blood at the corners of mouths . ( laughter ) clearly , these people were not really dead . heh , they were vampires ! and they had been leaving their graves to feast on the living . ( grunt ) the terrified villagers would quickly enact a ritual to kill the undead . the practices varied across the region , but usually included beheadings , burnings , and staking the body to the coffin to prevent it from getting up . ( laughter ) grizzly stuff ! but what the villagers interpreted as unholy reanimation were actually normal symptoms of death . when a body decomposes , the skin dehydrates , causing the hair and fingernails to extend . bacteria in the stomach creates gases that fill the belly , which force out blood and matter through the mouth . unfortunately , this science was not yet known , so the villagers kept digging . in fact , so many bodies were dug up that the empress of austria sent her physician around to disprove the vampire stories , and she even established a law prohibiting grave tampering . still , even after the vampire hunts had died down , the stories of legends survived in local superstition . this led to works of literature , such as polidori 's `` the vampyre , '' the gothic novel `` carmilla , '' and , most famously , bram stoker 's `` dracula . '' although stoker incorporated historical material , like elizabeth báthory 's virgin blood baths and the brutal executions of vlad dracul , it was these local myths that inspired the main elements of his story : the transylvanian setting , using garlic to defend oneself , and the staking of the heart . while these attributes are certainly familiar to us , elements he invented himself have also lasted over the years : fear of crucifixes , weakness in sunlight , and the vampire 's inability to see their reflection . by inventing new traits , stoker perfectly enacted the age-old tradition of elaborating upon and expanding the myth of vampires . as we saw , maybe you met my relatives , a huge of variety of creatures stalked the night before dracula , and many more will continue to creep through our nightmares . yet , so long as they subsist off a living being 's life force , they are part of my tribe . even sparkling vampires can be included . after all , it 's the continued storytelling and reimagining of the vampire legend that allows us to truly live forever . ( ominous laughter )

in fact , so many bodies were dug up that the empress of austria sent her physician around to disprove the vampire stories , and she even established a law prohibiting grave tampering . still , even after the vampire hunts had died down , the stories of legends survived in local superstition . this led to works of literature , such as polidori 's `` the vampyre , '' the gothic novel `` carmilla , '' and , most famously , bram stoker 's `` dracula . '' although stoker incorporated historical material , like elizabeth báthory 's virgin blood baths and the brutal executions of vlad dracul , it was these local myths that inspired the main elements of his story : the transylvanian setting , using garlic to defend oneself , and the staking of the heart .

what book about a vampire did bram stoker write ?

you 've probably heard that carbon dioxide is warming the earth , but how does it work ? is it like the glass of a greenhouse or like an insulating blanket ? well , not entirely . the answer involves a bit of quantum mechanics , but do n't worry , we 'll start with a rainbow . if you look closely at sunlight separated through a prism , you 'll see dark gaps where bands of color went missing . where did they go ? before reaching our eyes , different gases absorbed those specific parts of the spectrum . for example , oxygen gas snatched up some of the dark red light , and sodium grabbed two bands of yellow . but why do these gases absorb specific colors of light ? this is where we enter the quantum realm . every atom and molecule has a set number of possible energy levels for its electrons . to shift its electrons from the ground state to a higher level , a molecule needs to gain a certain amount of energy . no more , no less . it gets that energy from light , which comes in more energy levels than you could count . light consists of tiny particles called photons and the amount of energy in each photon corresponds to its color . red light has lower energy and longer wavelengths . purple light has higher energy and shorter wavelengths . sunlight offers all the photons of the rainbow , so a gas molecule can choose the photons that carry the exact amount of energy needed to shift the molecule to its next energy level . when this match is made , the photon disappers as the molecule gains its energy , and we get a small gap in our rainbow . if a photon carries too much or too little energy , the molecule has no choice but to let it fly past . this is why glass is transparent . the atoms in glass do not pair well with any of the energy levels in visible light , so the photons pass through . so , which photons does carbon dioxide prefer ? where is the black line in our rainbow that explains global warming ? well , it 's not there . carbon dioxide does n't absorb light directly from the sun . it absorbs light from a totally different celestial body . one that does n't appear to be emitting light at all : earth . if you 're wondering why our planet does n't seem to be glowing , it 's because the earth does n't emit visible light . it emits infared light . the light that our eyes can see , including all of the colors of the rainbow , is just a small part of the larger spectrum of electromagnetic radiation , which includes radio waves , microwaves , infrared , ultraviolet , x-rays , and gamma rays . it may seem strange to think of these things as light , but there is no fundamental difference between visible light and other electromagnetic radiation . it 's the same energy , but at a higher or lower level . in fact , it 's a bit presumptuous to define the term visible light by our own limitations . after all , infrared light is visible to snakes , and ultraviolet light is visible to birds . if our eyes were adapted to see light of 1900 megahertz , then a mobile phone would be a flashlight , and a cell phone tower would look like a huge lantern . earth emits infrared radiation because every object with a temperature above absolute zero will emit light . this is called thermal radiation . the hotter an object gets , the higher frequency the light it emits . when you heat a piece of iron , it will emit more and more frequencies of infrared light , and then , at a temperature of around 450 degrees celsius , its light will reach the visible spectrum . at first , it will look red hot . and with even more heat , it will glow white with all of the frequencies of visible light . this is how traditional light bulbs were designed to work and why they 're so wasteful . 95 % of the light they emit is invisible to our eyes . it 's wasted as heat . earth 's infrared radiation would escape to space if there were n't greenhouse gas molecules in our atmophere . just as oxygen gas prefers the dark red photons , carbon dioxide and other greenhouse gases match with infrared photons . they provide the right amount of energy to shift the gas molecules into their higher energy level . shortly after a carbon dioxide molecule absorbs an infrared photon , it will fall back to its previous energy level , and spit a photon back out in a random direction . some of that energy then returns to earth 's surface , causing warming . the more carbon dioxide in the atmosphere , the more likely that infrared photons will land back on earth and change our climate .

it gets that energy from light , which comes in more energy levels than you could count . light consists of tiny particles called photons and the amount of energy in each photon corresponds to its color . red light has lower energy and longer wavelengths .

light consists of tiny particles called ________ .

our story is about a girl named iris . iris is very sensitive . ( bird cawing ) so much that she is always in tears . she cries when she 's sad , when she 's happy , ( godzilla roars ) and even tears up when things just get to her . she has special lacrimal glands to make new tears and special tubes , called lacrimal puncta , to drain old ones away . and she cries so much that she goes through ten ounces of tears per day , thirty gallons a year ! in fact , if you look closely , you 'll see that she 's crying a little bit all the time . the basal tears that iris constantly produces form a thin coating of three layers that cover her and keep dirt and debris away . right next to iris is the mucus layer , which keeps the whole thing fastened to her . on top of it is the aqueous layer , which keeps iris hydrated , repels invasive bacteria , and protects her skin , or cornea , from damage . and , finally , there is the lipid layer , an oily outer film that keeps the surface smooth for iris to see through , and prevents the other layers from evaporating . normally , iris goes about her day without really noticing the basal tears doing their thing . that 's kind of their whole point . but one day , she meets a girl named onion . iris is immediately smitten . onion looks gorgeous in her bright purple jacket , and she smells terrific . so , iris invites onion to her house for dinner . but when she comes in and takes off her jacket , something terrible happens . you see , when onion 's jacket is removed , a chemical reaction happens , converting the sulfoxides that make her smell so great into sulfenic acid , which then becomes a nasty substance with a long name : syn-propanethial s-oxide . the gas stings iris , and suddenly , she ca n't help it , she starts weeping uncontrollably . these reflex tears are different from the basal tears that iris is used to . because they 're designed to wash away harmful substances , or particles , they 're released in much larger amounts , and their aqueous layer contains more antibodies to stop any microorganisms that may be trying to get in , as well . both iris and onion are devastated . they know they ca n't continue their relationship if iris is going to hurt and cry every time onion takes off her jacket . so , they decide to break up . as onion walks out the door , iris stops crying . and immediately starts again . only now , she 's not crying reflex tears but emotional tears . when someone is either too sad or too happy , it feels like a loss of control , which can be dangerous . so , emotional tears are sent in to stabilize the mood as quickly as possible , along with other physical reactions , such as an increased heart rate and slower breathing . but scientists still are n't sure exactly how or why the tears themselves are helpful . they may be a social mechanism to elicit sympathy or show submission . but some studies have also found that emotional tears contain higher levels of stress hormones , such as acth and enkephalin , an endorphin and natural pain killer . in this case , emotional tears are also directly calming iris down , as well as signaling her emotional state to others . sorry things did n't work out with onion , iris , but do n't worry . as long as you have all three kinds of tears working to keep you balanced and healthy , it will get better . you 'll see .

on top of it is the aqueous layer , which keeps iris hydrated , repels invasive bacteria , and protects her skin , or cornea , from damage . and , finally , there is the lipid layer , an oily outer film that keeps the surface smooth for iris to see through , and prevents the other layers from evaporating . normally , iris goes about her day without really noticing the basal tears doing their thing .

what would happen if there were no lipid layer to keep the surface of tears smooth ?

translator : andrea mcdonough reviewer : bedirhan cinar pretty much everyone loves eating pizza , but it can be a messy business . pizza is soft and bendable . so how can you stop all that cheese from falling off ? you might know some tricks : you can use two hands -- not so classy , or you can use a paper plate and allow only the tip of the pizza to peek out . there 's one other trick , though : holding the crust , you can sort of fold the slice down the middle . now the tip of the pizza is n't falling over , and you can eat it without getting tomato sauce all over yourself or accidentally biting off some of that paper plate . but why should the tip stay up just because you bent the crust ? to understand this , you need to know two things : a little bit about the math of curved shapes and a little about the physics of thin sheets . first , the math . suppose i have a flat sheet made out of rubber . it 's really thin and bendable , so it 's easy to roll into a cylinder . i do n't need to stretch the sheet at all , just bend it . this property where one shape can be transformed into another without stretching or crumpling , is called isometry . a mathematician would say that a flat sheet is isometric to a cylinder . but not all shapes are isometric . if i try to turn my flat sheet into part of a sphere , there 's no way i can do it . you can check this for yourself , by trying to fit a flat sheet of paper onto a soccer ball without stretching or crumpling the paper . it 's just not possible . so a mathematician would say that a flat sheet and a sphere are n't isometric . there 's one more familiar shape that is n't isometric to any of the shapes we 've seen so far : a potato chip . potato chip shapes are n't isometric to flat sheets . if you want to get a flat piece of rubber into the shape of a potato chip , you need to stretch it -- not just bend it , but stretch it as well . so , that 's the math . not so hard , right ? now for the physics . it can be summed up in one sentence : thin sheets are easy to bend but hard to stretch . this is really important . thin sheets are easy to bend but hard to stretch . remember when we rolled our flat sheet of rubber into a cylinder ? that was n't hard , right ? but imagine how hard you 'd have pull on the sheet to increase its area by 10 percent . it would be pretty difficult . the point is that bending a thin sheet takes a relatively small amount of force , but stretching or crumbling a thin sheet is much harder . now , finally , we get to talk about pizza . suppose you go down to the pizzeria and buy yourself a slice . you pick it up from the crust , first , without doing the fold . because of gravity , the slice bends downwards . pizza is pretty thin , after all , and we know that thin sheets are easy to bend . you ca n't get it in your mouth , cheese and tomato sauce dripping everywhere -- it 's a big mess . so you fold the crust . when you do , you force the pizza into something like a taco shape . that 's not hard to do -- after all , this shape is isometric to the original pizza , which was flat . but imagine what would happen if the pizza were to droop down while you 're bending it . now it looks like a droopy taco . and what does a droopy taco look like ? a potato chip ! but we know that potato chips are not isometric to flat pieces of rubber or flat pizzas , and that means that in order to get into the shape it 's in now , the slice of pizza had to stretch . since the pizza is thin , this takes a lot of force , compared to the amount of force it takes to bend the pizza in the first place . so , what 's the conclusion ? when you fold the pizza at the crust , you make it into a shape where a lot of force is needed to bend the tip down . often gravity is n't strong enough to provide this force . that was kind of a lot of information , so let 's do a quick backwards recap . when pizza is folded at the crust , gravity is n't strong enough to bend the tip . why ? because stretching a pizza is hard . and to bend the tip downwards , the pizza would have to stretch , because the shape the pizza would be in , the droopy taco shape , is n't isometric to the original flat pizza . why ? because of math . as the pizza example shows , we can learn a lot by looking at the mathematical properties of different shapes . and it 's especially nice when those shapes happen to be pizza slices .

but we know that potato chips are not isometric to flat pieces of rubber or flat pizzas , and that means that in order to get into the shape it 's in now , the slice of pizza had to stretch . since the pizza is thin , this takes a lot of force , compared to the amount of force it takes to bend the pizza in the first place . so , what 's the conclusion ?

which of these actions takes more force ?

so this is one of our glove-boxes . yeah , if you just look to the right of the glove-box you ’ ll see that we ’ ve got these air locks and basically what you do is you put whatever it is you want to take into the box in there and then you evacuate it and then you refill it with dry , oxygen-free nitrogen so then you can take compounds which react with air and moisture into the box safely and store them . so this is a bit like what you see pictures of a nuclear industry when you ’ ve got people handling things . ok so next up is uranium , which is my favourite actinide , it ’ s the one i handle in the lab , it ’ s also the bogeyman of the periodic table , i think . as soon as you say uranium to people , people start going “ ooh , not sure about that. ” this is the bogeyman . this is uranium turnings . you see they have a sort of dull appearance because when they are cleaned up they are really very reactive , and they react with oxygen extremely quickly , but if you acid-treat them with concentrated nitric acid you get really beautiful gleaming surfaces but it doesn ’ t hang around very long . uranium is the basis of much of nuclear power and it exists in two isotopes , that ’ s two atoms of different weight , there ’ s uranium-238 which is the most abundant one and the other , uranium-235 which is the one which , when irradiated with neutrons will split in half and release nuclear energy and a lot of work has been done , or was done in during the second world war on the separation of these isotopes of uranium and , including the construction of the biggest mass spectrometers that had ever been made . and , fortunately the separation of uranium isotopes is really very difficult which is why it is only very large and rich countries have been able to afford to make nuclear weapons . this is just oil sat on the top so just like we had to have oil to protect the potassium we also need oil to protect the uranium turnings . if you really finely divide uranium turnings they are pyrophoric which means they burst into flames in the air , just spontaneously . but it ’ s actually a really interesting element to deal with . it ’ s got a wide variety of oxidation states , and if you use it in its depleted form it ’ s actually relatively safe to handle in the laboratory . now , depleted material only contains a very small quantity of fissile uranium which is used in bombs and nuclear reactors , about 0.2 of a percent . it actually means that the problem with handling depleted uranium is not the radioactivity , although you have to make provision for this , the real problem is that it is highly poisonous and about half a gram would kill you in a very short period of time because it attacks your liver , very effectively . this is uranium tetrachloride . it ’ s solvent free , it ’ s a nice free-flowing emerald green powder and if you dissolve this up in solvents like thf , you get beautiful green solutions from it . and here ’ s another form of uranium . so this is uranyl dichloride which has got two organic molecules co-ordinated to it as well . that ’ s this beautiful yellow colour . so , once you ’ ve removed the uranium-235 you ’ re still left with a very large amount , 99-point , more than 99 % of the original mass of your uranium is uranium-238 , which you have removed most but not all of the uranium-235 and this is so-called depleted uranium which is some of the densest material you can get . and so it is used where you want something very heavy that ’ s not too large . so for example , it ’ s used in the counterweights that people put in aeroplanes and large aeroplanes to balance the plane because you can use , it takes up only a small volume of space . we have to keep it safe and secure in a safe . and we have to fill out huge amounts of paperwork , many-a-forest has been chopped down for this paperwork i ’ m sure , but it ’ s all very important because you have to be certain that when handling depleted uranium compounds that you are not going to end up poisoning anybody and you are not going to end up getting radioactive compounds all over the place . so we have log books and we have to record how much we use and when and how we dispose of it . we have detectors which we have to sweep the lab . well a lot of people usually start off with “ i imagine you glow in the dark , ” which if i could do that i ’ d have passed away a long time before that point . yeah , it ’ s the bogeyman-thing again , a lot of people are quite sort of surprised or you know sort of shocked to hear that you ’ re handling this stuff but actually it ’ s just like most other chemicals on the periodic table and once you get past the ‘ bogeyman image ’ of it , it ’ s actually a very interesting element to work with . most metal or metalloid elements do look like this . it ’ s just that the number of electrons they ’ ve got , the number of electrons they take or they get rid of , is what defines their chemistry . and is that not dangerous ? you know uranium has this reputation of being so dangerous . are you not putting us in danger by holding that there ? no , this is depleted uranium , so there is about 0.2 % of this is what you would consider fissile . the rest of it is not radioactive . so it ’ s all quite toxic , but you ’ d have your work cut out to eat this stuff because it ’ s extremely hard .

as soon as you say uranium to people , people start going “ ooh , not sure about that. ” this is the bogeyman . this is uranium turnings . you see they have a sort of dull appearance because when they are cleaned up they are really very reactive , and they react with oxygen extremely quickly , but if you acid-treat them with concentrated nitric acid you get really beautiful gleaming surfaces but it doesn ’ t hang around very long .

which nickname did steve give uranium ?

grammatical tense is how languages talk about time without explicitly naming time periods by , instead , modifying verbs to specify when action occurs . so how many different tenses are there in a language like english ? at first , the answer seems obvious : there 's past , present , and future . but thanks to something called grammatical aspect , each of those time periods actually divides further . there are four kinds of aspect . in the continuous or progressive aspect , the actions are still happening at the time of reference . the perfect aspect describes actions that are finished . the perfect progressive aspect is a combination , describing a completed part of a continuous action . and finally , there 's the simple aspect , the basic form of the past , present , and future tense where an action is not specified as continuous or discreet . that 's all a little hard to follow , so let 's see how it works in action . let 's say your friends tell you they went on a secret naval mission to collect evidence of a mysterious sea creature . the tense sets the overall frame of reference in the past , but within that , there are many options . your friends might say a creature attacked their boat , that 's the past simple , the most general aspect , which gives no further clarification . they were sleeping when it happened , a continuous process underway at that point . they might also tell you they had departed from nantucket to describe an action completed even earlier . that 's an example of the past perfect . or that they had been sailing for three weeks , something that was ongoing up until that point . in the present , they tell you that they still search for the creature today , their present simple activity . perhaps they are preparing for their next mission continuously as they speak . and they have built a special submarine for it , a completed achievement . plus , if they have been researching possible sightings of the creature , it 's something they 've been doing for a while and are still doing now making it present perfect progressive . so what does this next mission hold ? you know it still has n't happened because they will depart next week , the future simple . your friends will be searching for the elusive creature , an extended continuous undertaking . they tell you the submarine will have reached uncharted depths a month from now . that 's a confident prediction about what will be achieved by a specific point in the future , a point at which they will have been voyaging for three weeks in the future perfect progressive . the key insight to all these different tenses is that each sentence takes place in a specific moment , whether it 's past , present , or future . the point of aspects is that they tell you as of that moment the status of the action . in total , they give us twelve possibilities in english . what about other languages ? some , like french , swahili , and russian take a similar approach to english . others describe and divide time differently . some have fewer grammatical tenses , like japanese , which only distinguishes past from non-past , buli and tukang basi , which only distinguish future from non-future , and mandarin chinese with no verb tenses at all , only aspect . on the other hand , languages like yagwa split past tense into multiple degrees , like whether something happened hours , weeks , or years ago . in others , tenses are intertwined with moods that can convey urgency , necessity , or probability of events . this makes translation difficult but not impossible . speakers of most languages without certain tenses can express the same ideas with auxiliary words , like would or did , or by specifying the time they mean . are the variations from language to language just differents ways of describing the same fundamental reality ? or do their diverse structures reflect different ways of thinking about the world and even time itself ? and if so , what other ways of conceiving time may be out there ?

others describe and divide time differently . some have fewer grammatical tenses , like japanese , which only distinguishes past from non-past , buli and tukang basi , which only distinguish future from non-future , and mandarin chinese with no verb tenses at all , only aspect . on the other hand , languages like yagwa split past tense into multiple degrees , like whether something happened hours , weeks , or years ago .

share a sentence that would be difficult to translate to a language with only future/non-future distinction . what extra words might you use to make the meaning clear ?

over 100,000 metric tons of caffeine are consumed around the world every year . that 's equivalent to the weight of 14 eiffel towers . most of this caffeine is consumed in coffee and tea , but it 's also ingested in some sodas , chocolate , caffeine pills , and even beverages labeled decaf . caffeine helps us feel alert , focused , happy , and energetic , even if we have n't had enough sleep . but it can also raise our blood pressure , and make us feel anxious . it 's the world most widely used drug . so how does it keep us awake ? caffeine evolved in plants where it serves a few purposes . in high doses , as it 's found in the leaves and seeds of certain species , it 's toxic to insects . but when they consume it in lower doses , as it 's found in nectar , it can actually help them remember and revisit flowers . in the human body , caffeine acts as a stimulant for the central nervous system . it keeps us awake by blocking one of the body 's key sleep-inducing molecules , a substance called adenosine . your body needs a constant supply of energy , which it gets by breaking down a high-energy molecule called atp . in the process , it liberates adenosine , atp 's chemical backbone . neurons in your brain have receptors perfectly tailored to this molecule . when adenosine docks to these receptors , it activates a cascade of biochemical reactions that cause neurons to fire more sluggishly and slow the release of important brain-signaling molecules . in other words , you get sleepy . caffeine is what 's called an adenosine receptor antagonist . that means it derails this process of slowing your neurons down by blocking adenosine receptors . caffeine and adenosine have a similar molecular structure , close enough that caffeine can wedge into the adenosine receptors , but not close enough to activate them . to summarize , adenosine inhibits your neurons . caffeine inhibits the inhibitor , so it stimulates you . caffeine can also boost positive feelings . in some neurons , the adenosine receptors are linked to receptors for another molecule called dopamine . one of dopamine 's roles in the brain is to promote feelings of pleasure . when adenosine docks in one of these paired receptors , that can make it harder for dopamine to fit in its own spot , interrupting its mood-lifting work . but when caffeine takes adenosine 's place , it does n't have the same effect , and dopamine can slide in . there 's evidence that caffeine 's effects on adenosine and dopamine receptors can have long-term benefits , too , reducing the risk of diseases like parkinson 's , alzheimer 's , and some types of cancer . caffeine can also ramp up the body 's ability to burn fat . in fact , some sports organizations think that caffeine gives athletes an unfair advantage and have placed limits on its consumption . from 1972 until 2004 , olympic athletes had to stay below a certain blood-caffeine concentration to compete . of course , not all of caffeine 's effects are so helpful . it might make you feel better and more alert , but it can also raise your heart rate and blood pressure , cause increased urination or diarrhea , and contribute to insomnia and anxiety . plus , the foods and beverages caffeine is found in have their own impacts on your body that have to be taken into account . your brain can adapt to regular consumption of caffeine . if your adenosine receptors are perpetually clogged , your body will manufacture extra ones . that way , even with caffeine around , adenosine can still do its job of signaling the brain to power down . that 's why you may find you need to consume more and more caffeine to feel as alert . there are more and more adenosine receptors to block . it 's also why if you suddenly quit caffeine , you may experience an unpleasant withdrawal . with plenty of receptors and no competition , adenosine can work overtime , causing symptoms like headaches , tiredness , and depressed moods . but in a few days , the extra adenosine receptors will disappear , your body will readjust , and you 'll feel just as alert as ever , even without an infusion of the world 's most popular stimulant .

plus , the foods and beverages caffeine is found in have their own impacts on your body that have to be taken into account . your brain can adapt to regular consumption of caffeine . if your adenosine receptors are perpetually clogged , your body will manufacture extra ones .

which of the following isn ’ t manifested after caffeine consumption :

we 're here on a runway because for some reason brady has printed out the first 1,000,000 digits of pi on a continuous mile long piece of paper which we are going to very carefully unravel today and go for a tour of a million digits of pi . so here 's 3.14159 which - for a fun fact - that 's as far as i 've memorised and then it carries on and you 've marked every 10 digits so there 's 100,000 marker points so we wo n't get lost , we 'll always know where we are in pi . where 's the feynman point ? is that seven hundred and something ? this the feynman point , six 9s , 999999 , so that wo n't be beaten ... there is a string of seven 3s , but that takes another 710,000 digits , so we 'll be nearly three quarters of the way down the mile of pi before we find a longer string of the same digit . and the first one is in the first two metres . absolutely incredible ! brady : do you want these ? for that . hugh : bring the staple gun back . we 've just hit 123 yards so we 're long past the familiar bits of pi . so the whole 3.14159 , that is a long time ago . you 'd think anyone who has memorised pi , we 're now in unfamiliar territory , apart from one guy . what is the world record for memorising pi , so someone recited over 125 yards of pi , someone memorised all the way to here and could n't be bothered to remember the next zero . brady : not even a third . there is a run here of seven ascending digits , there it goes , 0456789 , that is the first run of seven-digits that go up . obviously we 're missing 1 , 2 and 3 , it would have been nicer with them , but nowhere in the first million digits do you get 0 to 9 in order . hugh : that 's nearly three hours . brady : i found some heavy bases for cones , i 've got them in the back ... we 're half a mile from the start , and the trolley team , are they on the horizon ? okay , pi has just got a horizon . okay , see that 4 there , it appears every now and then , square number , kind of fun , but then from here you go , wait there 's no fours ... no four , no four , in fact there 's no fours until there , look at that , 157 digits and there are no fours for that entire run . they 've just vanished . and that is the longest run we will have in the first million digits that has one digit completely missing . with a million decimal places of pi each digit should appear approximately 100,000 time each , that makes sense , but of course it 's not exactly even , some of them do n't even make it . there are not 100,000 zeroes , zero does n't make it . 1 does n't make it . 6,7,8 all do n't make it . the champion though , is 5 . there it is , that there is the 100,000th 5 . okay we 're four hours into this and we are nearly at a million digits . so they 've been coming out a rate of a quarter of a million digits and hour , which is approximately 4,167 digits a minute , and we 're almost there . so you guys have done the hard work , do you want to wind off the last of it . and a million digits is there ! there ! alright so that is , it 's one , in case you are wondering . so there you go , we have just , i mean i think a token round of applause . applause so that is absolutely fantastic , and now the very quick process of rolling it all back up again before an aeroplane lands . brady : believe it or not we printed all million digits of pi using about eight millilitres of ink . there , that 's what 8ml looks like . that 's because of hp 's clever thermal inkjet technology combined with some very clever people here at hsa systems in denmark . to see the whole story of how and why we made this film , check out the links on the screen and below in the video description . it also includes extra footage from our day out on the runway and more curious stuff about pi itself .

so you guys have done the hard work , do you want to wind off the last of it . and a million digits is there ! there !

as stated , the `` point size '' used to print the digits in this video is 8 , with each digit being 1/15th of an inch across . now imagine the team want to roll out the first million digits of pi all the way to the `` nearby '' star alpha centauri , at a distance of 4.37 light-years . but this time they can use only one million digits ( not add more digits ) , so clearly the point size will need to be scaled up . keeping all things in proportion , what will the new point size be ? how wide is each digit on this piece of paper which stretches through space ?

thousands of years in the making , what began as part of a religious festival honoring the greek god zeus in the rural greek town of olympia has today become the greatest show of sporting excellence on earth . the inception date in 776 bc became the basis for the greek 's earliest calendar , where time was marked in four-year increments called olympiads . what could it be ? why , it 's the olympic games , of course . competition fosters excellence , or so thought the ancient greeks . in addition to sporting events , contests were held for music , singing , and poetry . you can read about them all yourself in classical literary works , like homer 's `` iliad '' and virgil 's `` aeneid . '' even mythical heroes appreciate a good contest every now and then , would n't you say ? for the first thirteen games , the ancient greek olympics featured just one event , the two hundred yard dash . but over time , new exciting contests , like boxing , chariot and mule racing , and even a footrace where the competitors wore a full suit of armor enticed many hopeful champions into the olympic stadium . the combined running , jumping , wrestling , javelin throwing , and hurling the discus events known as the pentathlon inspired world-class competition , and the pankration , a no holds barred fight where only biting and eye-gouging were prohibited , ensured the toughest men were victorious . and victorious they were . nobody tops the local baker coroebus , who 776 bc became the very first olympic champion . and we 'll never forget orsippus of megara , the 720 bc olympic victor tore away his loincloth so he could race unimpeded , inaugurating the ancient greek tradition of competing in the nude . now there 's a winning streak , if ever we 've seen one . but all good things must end . in 391 ad , the christian roman emperor theodosius banned pagan practices , so the world soon bid a fond farewell to the olympic games . but just like those early pankration athletes , you ca n't keep a good one down , and 1500 years later in 1896 , the modern olympic games kicked off in athens , greece . today , the summer and winter olympics bring international world-class athletes together by the thousands , uniting fans by the billions for the world 's foremost sporting competition . citius , altius , fortius . three cheers for the olympics .

citius , altius , fortius . three cheers for the olympics .

what main differences are there between the ancient and modern olympics ?

water is virtually eveywhere , from soil moisture and ice caps , to the cells inside our own bodies . depending on factors like location , fat index , age , and sex , the average human is between 55-60 % water . at birth , human babies are even wetter . being 75 % water , they are swimmingly similar to fish . but their water composition drops to 65 % by their first birthday . so what role does water play in our bodies , and how much do we actually need to drink to stay healthy ? the h20 in our bodies works to cushion and lubricate joints , regulate temperature , and to nourish the brain and spinal cord . water is n't only in our blood . an adult 's brain and heart are almost three quarters water . that 's roughly equivalent to the amount of moisture in a banana . lungs are more similar to an apple at 83 % . and even seemingly dry human bones are 31 % water . if we are essentially made of water , and surrounded by water , why do we still need to drink so much ? well , each day we lose two to three liters through our sweat , urine , and bowel movements , and even just from breathing . while these functions are essential to our survival , we need to compensate for the fluid loss . maintaining a balanced water level is essential to avoid dehydration or over-hydration , both of which can have devastating effects on overall health . at first detection of low water levels , sensory receptors in the brain 's hypothalamus signal the release of antidiuretic hormone . when it reached the kidneys , it creates aquaporins , special channels that enable blood to absorb and retain more water , leading to concentrated , dark urine . increased dehydration can cause notable drops in energy , mood , skin moisture , and blood pressure , as well as signs of cognitive impairment . a dehydrated brain works harder to accomplish the same amount as a normal brain , and it even temporarily shrinks because of its lack of water . over-hydration , or hyponatremia , is usually caused by overconsumption of water in a short amount of time . athletes are often the victims of over-hydration because of complications in regulating water levels in extreme physical conditions . whereas the dehydrated brain amps up the production of antidiuretic hormone , the over-hydrated brain slows , or even stops , releasing it into the blood . sodium electrolytes in the body become diluted , causing cells to swell . in severe cases , the kidneys ca n't keep up with the resulting volumes of dilute urine . water intoxication then occurs , possibly causing headache , vomiting , and , in rare instances , seizures or death . but that 's a pretty extreme situation . on a normal , day-to-day basis , maintaining a well-hydrated system is easy to manage for those of us fortunate enough to have access to clean drinking water . for a long time , conventional wisdom said that we should drink eight glasses a day . that estimate has since been fine-tuned . now , the consensus is that the amount of water we need to imbibe depends largely on our weight and environment . the recommended daily intake varies from between 2.5-3.7 liters of water for men , and about 2-2.7 liters for women , a range that is pushed up or down if we are healthy , active , old , or overheating . while water is the healthiest hydrator , other beverages , even those with caffeine like coffee or tea , replenish fluids as well . and water within food makes up about a fifth of our daily h20 intake . fruits and vegetables like strawberries , cucumbers , and even broccoli are over 90 % water , and can supplement liquid intake while providing valuable nutrients and fiber . drinking well might also have various long-term benefits . studies have shown that optimal hydration can lower the chance of stroke , help manage diabetes , and potentially reduce the risk of certain types of cancer . no matter what , getting the right amount of liquid makes a world of difference in how you 'll feel , think , and function day to day .

a dehydrated brain works harder to accomplish the same amount as a normal brain , and it even temporarily shrinks because of its lack of water . over-hydration , or hyponatremia , is usually caused by overconsumption of water in a short amount of time . athletes are often the victims of over-hydration because of complications in regulating water levels in extreme physical conditions .

drinking too much water in a short amount of time is referred to as :

your brain on food if you sucked all of the moisture out of your brain and broke it down to its constituent nutritional content , what would it look like ? most of the weight of your dehydrated brain would come from fats , also known as lipids . in the remaining brain matter , you would find proteins and amino acids , traces of micronutrients , and glucose . the brain is , of course , more than just the sum of its nutritional parts , but each component does have a distinct impact on functioning , development , mood , and energy . so that post-lunch apathy , or late-night alertness you might be feeling , well , that could simply be the effects of food on your brain . of the fats in your brain , the superstars are omegas 3 and 6 . these essential fatty acids , which have been linked to preventing degenerative brain conditions , must come from our diets . so eating omega-rich foods , like nuts , seeds , and fatty fish , is crucial to the creation and maintenance of cell membranes . and while omegas are good fats for your brain , long-term consumption of other fats , like trans and saturated fats , may compromise brain health . meanwhile , proteins and amino acids , the building block nutrients of growth and development , manipulate how we feel and behave . amino acids contain the precursors to neurotransmitters , the chemical messengers that carry signals between neurons , affecting things like mood , sleep , attentiveness , and weight . they 're one of the reasons we might feel calm after eating a large plate of pasta , or more alert after a protein-rich meal . the complex combinations of compounds in food can stimulate brain cells to release mood-altering norepinephrine , dopamine , and serotonin . but getting to your brain cells is tricky , and amino acids have to compete for limited access . a diet with a range of foods helps maintain a balanced combination of brain messengers , and keeps your mood from getting skewed in one direction or the other . like the other organs in our bodies , our brains also benefit from a steady supply of micronutrients . antioxidants in fruits and vegetables strengthen the brain to fight off free radicals that destroy brain cells , enabling your brain to work well for a longer period of time . and without powerful micronutrients , like the vitamins b6 , b12 , and folic acid , our brains would be susceptible to brain disease and mental decline . trace amounts of the minerals iron , copper , zinc , and sodium are also fundamental to brain health and early cognitive development . in order for the brain to efficiently transform and synthesize these valuable nutrients , it needs fuel , and lots of it . while the human brain only makes up about 2 % of our body weight , it uses up to 20 % of our energy resources . most of this energy comes from carbohydrates that our body digests into glucose , or blood sugar . the frontal lobes are so sensitive to drops in glucose , in fact , that a change in mental function is one of the primary signals of nutrient deficiency . assuming that we are getting glucose regularly , how does the specific type of carbohydrates we eat affect our brains ? carbs come in three forms : starch , sugar , and fiber . while on most nutrition labels , they are all lumped into one total carb count , the ratio of the sugar and fiber subgroups to the whole amount affect how the body and brain respond . a high glycemic food , like white bread , causes a rapid release of glucose into the blood , and then comes the dip . blood sugar shoots down , and with it , our attention span and mood . on the other hand , oats , grains , and legumes have slower glucose release , enabling a steadier level of attentiveness . for sustained brain power , opting for a varied diet of nutrient-rich foods is critical . when it comes to what you bite , chew , and swallow , your choices have a direct and long-lasting effect on the most powerful organ in your body .

of the fats in your brain , the superstars are omegas 3 and 6 . these essential fatty acids , which have been linked to preventing degenerative brain conditions , must come from our diets . so eating omega-rich foods , like nuts , seeds , and fatty fish , is crucial to the creation and maintenance of cell membranes .

what is one thing that makes essential fatty acids so unique ?

approximately 7 million people around the world die from heart attacks every year , and cardiovascular disease , which causes heart attacks and other problems like strokes , is the world 's leading killer . so what causes a heart attack ? like all muscles , the heart needs oxygen , and during a heart attack , it ca n't get enough . fatty deposits , or plaques , develop on the walls of our coronary arteries . those are the vessels that supply oxygenated blood to the heart . these plaques grow as we age , sometimes getting chunky , hardened , or enflamed . eventually , the plaques can turn into blockages . if one of the plaques ruptures or cracks , a blood clot will form around it in minutes , and a partially closed artery can become completely blocked . blood flow is cut off to the cardiac muscle and the oxygen-starved cells start to die within several minutes . this is a myocardial infarction , or heart attack . things can rapidly deteriorate in the absence of treatment . the injured muscle may not be able to pump blood as well , and its rhythm might be thrown off . in the worst case scenario , a heart attack can cause sudden death . and how do you know that someone is having a heart attack ? the most common symptom is chest pain caused by the oxygen-deprived heart muscle . patients describe it as crushing or vice-like . it can radiate to the left arm , jaw , back , or abdomen . but it 's not always as sudden and dramatic as it is in the movies . some people experience nausea or shortness of breath . symptoms may be less prominent in women and the elderly . for them , weakness and tiredness may be the main signal . and surprisingly , in many people , especially those with diabetes , which affects the nerves that carry pain , a heart attack may be silent . if you think that someone might be having a heart attack , the most important thing is to respond quickly . if you have access to emergency medical services , call them . they 're the fastest way to get to a hospital . taking aspirin , which thins the blood , and nitroglycerin , which opens up the artery , can help keep the heart attack from getting worse . in the emergency room , doctors can diagnose a heart attack . they commonly use an electrocardiogram to measure the heart 's electrical activity and a blood test to assess heart muscle damage . the patient is then taken to a high-tech cardiac suite where tests are done to locate the blockages . cardiologists can reopen the blocked artery by inflating it with a balloon in a procedure called an angioplasty . frequently , they also insert a metal or polymer stent that will hold the artery open . more extensive blockages might require coronary artery bypass surgery . using a piece of vein or artery from another part of the body , heart surgeons can reroute blood flow around the blockage . these procedures reestablish circulation to the cardiac muscle , restoring heart function . heart attack treatment is advancing , but prevention is vital . genetics and lifestyle factors both affect your risk . and the good news is that you can change your lifestyle . exercise , a healthy diet , and weight loss all lower the risk of heart attacks , whether you 've had one before or not . doctors recommend exercising a few times a week , doing both aerobic activity and strength training . a heart-healthy diet is low in sugar and saturated fats , which are both linked to heart disease . so what should you eat ? lots of fiber from vegetables , chicken and fish instead of red meat , whole grains and nuts like walnuts and almonds all seem to be beneficial . a good diet and exercise plan can also keep your weight in a healthy range , which will lower your heart attack risk as well . and of course , medications can also help prevent heart attacks . doctors often prescribe low-dose aspirin , for example , particularly for patients who 've already had a heart attack and for those known to be at high risk . and drugs that help manage risk factors , like high blood pressure , cholesterol , and diabetes , will make heart attacks less likely , too . heart attacks may be common , but they do n't have to be inevitable . a healthy diet , avoiding tobacco use , staying fit , and enjoying plenty of sleep and lots of laughter all go a long way in making sure your body 's most important muscle keeps on beating .

like all muscles , the heart needs oxygen , and during a heart attack , it ca n't get enough . fatty deposits , or plaques , develop on the walls of our coronary arteries . those are the vessels that supply oxygenated blood to the heart .

fatty plaques that build up on the walls of the coronary arteries can eventually lead to heart attacks . what is the mechanism through which this happens ?

translator : tom carter reviewer : bedirhan cinar of all the spectacles mankind has viewed through a telescope , there are few lovelier than a spiral galaxy . majestic whirlpools of stars , they rotate in a stately and predictable dance . the fact that we see many billions of them in our telescopes tells us they are both common and stable . it is perhaps surprising that it is relatively easy to understand the inner workings of these cosmic pinwheels . by combining physical principles worked out by sir isaac newton in the late 17th century , with the observed amount of mass in a galaxy , scientists can calculate the rates at which these galaxies rotate . using these techniques , astronomers predict how fast stars at different distances from the center of the galaxy should move . stars very close to the center move slowly . that 's because there is very little mass between them and the center of the galaxy to pull them along . stars a bit further away move faster , because they are being pulled by all of the stars in between them and the center . as we get really far away , the stars are predicted to move slowly again . their great distance reduces gravity to a gentle tug , so they move leisurely in their orbits . knowing this , scientists looked at the galaxies and measured how fast stars were moving . to their surprise , they found that while the stars closer to the center of the galaxy behaved as predicted , those further away moved far too quickly . this observation was devastating to the tradtional theories of gravity and motion . if the stars were moving as fast as their measurement suggested , galaxies should have torn themselves apart . it was a crisis , and astronomers and physicists scrambled to find a mistake in their calculation . was newton 's theory of gravity wrong ? was his theory of motion wrong ? or was it possible that astronomers had incorrectly measured the galaxy 's mass ? all options were investigated , and all were ruled out . except one . today , scientists believe that the answer lies in a previously unknown kind of matter , called dark matter . this dark matter can be envisioned as a cloud which surrounds most galaxies . this matter is very unusual . it is affected by gravity , but it is invisible to visible light and all other forms of electromagnetic radiation . the name `` dark matter '' originates in this form of matter 's inability to emit or absorb light . dark matter adds to the gravity of the galaxy and explains the orbital speed of stars far from the galactic center . dark matter has not yet been directly observed , but scientists believe that it is likely to be real , mostly because the other options have been ruled out . using dozens of approaches , astronomers and physicists continue to search for direct evidence that would prove that the dark matter hypothesis is true . this question is one of the most important physics research questions of the 21st century .

except one . today , scientists believe that the answer lies in a previously unknown kind of matter , called dark matter . this dark matter can be envisioned as a cloud which surrounds most galaxies . this matter is very unusual . it is affected by gravity , but it is invisible to visible light and all other forms of electromagnetic radiation .

scientists have never observed dark matter and have inferred its existence from indirect measurements . some critics , who are typically not scientists , have claimed that the dark matter hypothesis is an example of scientists inventing a concept so as to save their theories of gravity and motion . some have even characterized dark matter as ‘ something that you can ’ t see , but it holds the universe together ’ and have drawn parallels with religious statements . do you think these claims are valid ? explain your reasoning .

it 's the first sense you use when you 're born . one out of every fifty of your genes is dedicated to it . it must be important , right ? okay , take a deep breath through your nose . it 's your sense of smell , and it 's breathtakingly powerful . as an adult , you can distinguish about 10,000 different smells . here 's how your nose does it . smell starts when you sniff molecules from the air into your nostrils . 95 % of your nasal cavity is used just to filter that air before it hits your lungs . but at the very back of your nose is a region called the olfactory epithelium , a little patch of skin that 's key to everything you smell . the olfactory epithelium has a layer of olfactory receptor cells , special neurons that sense smells , like the taste buds of your nose . when odor molecules hit the back of your nose , they get stuck in a layer of mucus covering the olfactory epithelium . as they dissolve , they bind to the olfactory receptor cells , which fire and send signals through the olfactory tract up to your brain . as a side note , you can tell a lot about how good an animal 's sense of smell is by the size of its olfactory epithelium . a dog 's olfactory epithelium is 20 times bigger than your puny human one . but there 's still a lot we do n't know about this little patch of cells , too . for example , our olfactory epithelium is pigmented , and scientists do n't really know why . but how do you actually tell the difference between smells ? it turns out that your brain has 40 million different olfactory receptor neurons , so odor a might trigger neurons 3 , 427 , and 988 , and odor b might trigger neurons 8 , 76 , and 2,496,678 . all of these different combinations let you detect a staggeringly broad array of smells . olfactory neurons are always fresh and ready for action . they 're the only neuron in the body that gets replaced regularly , every four to eight weeks . once they are triggered , the signal travels through a bundle called the olfactory tract to destinations all over your brain , making stops in the amygdala , the thalamus , and the neocortex . this is different from how sight and sound are processed . each of those signals goes first to a relay center in the middle of the cerebral hemisphere and then out to other regions of the brain . but smell , because it evolved before most of your other senses , takes a direct route to these different regions of the brain , where it can trigger your fight-or-flight response , help you recall memories , or make your mouth water . but even though we 've all got the same physiological set-up , two nostrils and millions of olfactory neurons , not everybody smells the same things . one of the most famous examples of this is the ability to smell so-called `` asparagus pee . '' for about a quarter of the population , urinating after eating asparagus means smelling a distinct odor . the other 75 % of us do n't notice . and this is n't the only case of smells differing from nose to nose . for some people , the chemical androstenone smells like vanilla ; to others , it smells like sweaty urine , which is unfortunate because androstenone is commonly found in tasty things like pork . so with the sweaty urine smellers in mind , pork producers will castrate male pigs to stop them from making androstenone . the inability to smell a scent is called anosmia , and there are about 100 known examples . people with allicin anosmia ca n't smell garlic . those with eugenol anosmia ca n't smell cloves . and some people ca n't smell anything at all . this kind of full anosmia could have several causes . some people are born without a sense of smell . others lose it after an accident or during an illness . if the olfactory epithelium gets swollen or infected , it can hamper your sense of smell , something you might have experienced when you were sick . not being able to smell anything can mess with your other senses , too . many people who ca n't smell at all also ca n't really taste the same way the rest of us do . it turns out that how something tastes is closely related to how it smells . as you chew your food , air is pushed up your nasal passage , carrying with it the smell of your food . those scents hit your olfactory epithelium and tell your brain a lot about what you 're eating . without the ability to smell , you lose the ability to taste anything more complicated than the five tastes your taste buds can detect : sweet , salty , bitter , sour , and savory . so , the next time you smell exhaust fumes , salty sea air , or roast chicken , you 'll know exactly how you 've done it and , perhaps , be a little more thankful that you can .

this kind of full anosmia could have several causes . some people are born without a sense of smell . others lose it after an accident or during an illness .

what is true about your sense of smell ?

technetium is the first element in the periodic table which is naturally radioactive , so it is the lightest radioactive element and so for a long time very little was known about it . now people are beginning to study it in suitably strong surroundings of ů to contain the radioactivity and they have discovered that the chemistry of technetium is in many ways quite similar to that of rhenium or manganese . and there are a number of medical treatments now which use the radioactivity of technetium in order to trace through the body and look at their emissions to find out about different diseases . and so the chemistry of technetium is becoming more important in the medical role , how to make a compound that you can get into the body safely and quickly so that it can be used for medical purposes .

technetium is the first element in the periodic table which is naturally radioactive , so it is the lightest radioactive element and so for a long time very little was known about it . now people are beginning to study it in suitably strong surroundings of ů to contain the radioactivity and they have discovered that the chemistry of technetium is in many ways quite similar to that of rhenium or manganese . and there are a number of medical treatments now which use the radioactivity of technetium in order to trace through the body and look at their emissions to find out about different diseases . and so the chemistry of technetium is becoming more important in the medical role , how to make a compound that you can get into the body safely and quickly so that it can be used for medical purposes .

which of these is a stable isotope of technetium ?

what 's the worst bug on the planet ? you might vote for the horsefly or perhaps the wasp , but for many people , the worst offender is by far the mosquito . the buzzing , the biting , the itching , the mosquito is one of the most commonly detested pests in the world . in alaska , swarms of mosquitos can get so thick that they actually asphyxiate caribou . and mosquito-borne diseases kill millions of people every year . the scourge that is the mosquito is n't new . mosquitoes have been around for over a hundred million years and over that time have coevolved with all sorts of species , including our own . there are actually thousands of species of mosquitos in the world , but they all share one insidious quality : they suck blood , and they 're really , really good at sucking blood . here 's how they do it . after landing , a mosquito will slather some saliva onto the victim 's skin , which works like an antiseptic , numbing the spot so we do n't notice their attack . this is what causes the itchy , red bumps , by the way . then the bug will use its serrated mandibles to carve a little hole in your skin , allowing it to probe around with its proboscis , searching for a blood vessel . when it hits one , the lucky parasite can suck two to three times its weight in blood . turns out we do n't really like that too much . in fact , humans hate mosquitos so much that we spend billions of dollars worldwide to keep them away from us -- from citronella candles to bug sprays to heavy-duty agricultural pesticides . but it 's not just that mosquitos are annoying , they 're also deadly . mosquitos can transmit everything from malaria to yellow fever to west nile virus to dengue . over a million people worldwide die every year from mosquito-borne diseases , and that 's just people . horses , dogs , cats , they can all get diseases from mosquitoes too . so , if these bugs are so dastardly , why do n't we just get rid of them ? we are humans after all , and we 're pretty good at getting rid of species . well , it 's not quite so simple . getting rid of the mosquito removes a food source for lots of organisms , like frogs and fish and birds . without them , plants would lose a pollinator . but some scientists say that mosquitos are n't actually all that important . if we got rid of them , they argue , another species would simply take their place and we 'd probably have far fewer deaths from malaria . the problem is that nobody knows what would happen if we killed off all the mosquitos . something better might take their spot or perhaps something even worse . the question is , are we willing to take that risk ? ( buzzing )

in fact , humans hate mosquitos so much that we spend billions of dollars worldwide to keep them away from us -- from citronella candles to bug sprays to heavy-duty agricultural pesticides . but it 's not just that mosquitos are annoying , they 're also deadly . mosquitos can transmit everything from malaria to yellow fever to west nile virus to dengue . over a million people worldwide die every year from mosquito-borne diseases , and that 's just people .

which of the following have mosquitos been known to spread ?

what if you could absorb another organism and take on its abilities ? imagine you swallowed a small bird and suddenly gained the ability to fly . or if you engulfed a cobra and were then able to spit poisonous venom from your teeth . throughout the history of life , specifically during the evolution of complex eukaryotic cells , things like this happened all the time . one organism absorbed another , and they united to become a new organism with the combined abilities of both . we think that around 2 billion years ago , the only living organisms on earth were prokaryotes , single-celled organisms lacking membrane-bound organelles . let 's look closely at just three of them . one was a big , simple blob-like cell with the ability to absorb things by wrapping its cell membrane around them . another was a bacterial cell that converted solar energy into sugar molecules through photosynthesis . a third used oxygen gas to break down materials like sugar and release its energy into a form useful for life activities . the blob cells would occasionally absorb the little photosynthetic bacteria . these bacteria then lived inside the blob and divided like they always had , but their existence became linked . if you stumbled upon this living arrangement , you might just think that the whole thing was one organism , that the green photosynthetic bacteria were just a part of the blob that performed one of its life functions , just like your heart is a part of you that performs the function of pumping your blood . this process of cells living together is called endosymbiosis , one organism living inside another . but the endosymbiosis did n't stop there . what would happen if the other bacteria moved in , too ? now the cells of this species started becoming highly complex . they were big and full of intricate structures that we call chloroplasts and mitochondria . these structures work together to harness sunlight , make sugar , and break down that sugar using the oxygen that right around this time started to appear in the earth 's atmosphere . organisms absorbing other organisms was one way species adapted to the changing environmental conditions of their surroundings . this little story highlights what biologists call the endosymbiotic theory , the current best explanation of how complex cells evolved . there 's a lot of evidence that supports this theory , but let 's look at three main pieces . first , the chloroplasts and mitochondria in our cells multiply the very same way as those ancient bacteria , which are still around , by the way . in fact , if you destroy these structures in a cell , no new ones will appear . the cell ca n't make them . they can only make more of themselves . second piece of evidence . chloroplasts and mitochondria both contain their own dna and ribosomes . their dna has a circular structure that is strikingly similar to the dna of the ancient bacteria , and it also contains many similar genes . the ribosomes , or protein assembly machines of chloroplasts and mitochondria , also have the same structure as ribosomes of ancient bacteria , but are different from the ribosomes hanging around the rest of eukaryotic cell . lastly , think about the membranes involved in the engulfing process . chloroplasts and mitochondria both have two membranes surrounding them , an inner and outer membrane . their inner membrane contains some particular lipids and proteins that are not present in the outer membrane . why is that significant ? because their outer membrane used to belong to the blob cell . when they were engulfed in the endosymbiosis process , they got wrapped up in that membrane and kept their own as their inner one . surely enough , those same lipids and proteins are found on the membranes of the ancient bacteria . biologists now use this theory to explain the origin of the vast variety of eukaryotic organisms . take the green algae that grow on the walls of swimming pools . a larger eukaryotic cell with spinning tail structures , or flagella , at some point absorbed algae like these to form what we now call euglena . euglena can perform photosynthesis , break down sugar using oxygen , and swim around pond water . and as the theory would predict , the chloroplasts in these euglena have three membranes since they had two before being engulfed . the absorbing process of endosymbiotic theory allowed organisms to combine powerful abilities to become better adapted to life on earth . the results were species capable of much more than when they were separate organisms , and this was an evolutionary leap that lead to the microorganisms , plants , and animals we observe on the planet today .

lastly , think about the membranes involved in the engulfing process . chloroplasts and mitochondria both have two membranes surrounding them , an inner and outer membrane . their inner membrane contains some particular lipids and proteins that are not present in the outer membrane .

describe in your own words how chloroplasts and mitochondria found within a cell have two membranes .

as you can see , i was born without fingers on my right hand . and also my right leg was several inches shorter than my left one . they broke the bones in the leg , then they screwed metal spikes into the bone . it has not only spikes , but wires that go all the way through the leg to stabilize it . i have to walk on it . i have to stretch it out so that my muscles do n't just get all atrophied . people always ask me , `` does it hurt ? '' yes , it does , but i focus on what i can do , not on what i can not do . i want to talk with you guys about overcoming obstacles . everybody has obstacles , a disability , a hurdle . we face a choice : let the obstacle overcome you or overcome the obstacle . maybe some of you have heard of jim abbott . he was a major league baseball player . he won a gold metal in the olympics . he played for the yankees , the angels . but he threw a no-hitter , and he only had one arm . when he was a kid , he came home mad one time and told his dad , `` the kids wo n't let me play baseball because i only have one hand . '' his dad replied , `` no , the kids wo n't let you play baseball because you stink at baseball . you ca n't change the fact that you only have one hand , but you can change the fact that you stink . '' so , his dad began to practice with him , and he got good . he overcame obstacles . teams would try to exploit his weak side . they would try to bunt to the side that he had a missing arm . but they never succeeded because he practiced and practiced fielding bunts to that side . there 's no dishonor in having a disability , and i wo n't let anyone diss my ability , but i do n't want anyone 's pity either . i will not use the obstacles i face as an excuse for having a pity party . i will practice harder , play harder , and push myself harder to keep getting better . last season i started on my varsity high school basketball team as a freshman , and i won rookie of the year . i was one of the top scorers on the team . one of the things that i find funny is that people judge me by appearance . they say , `` oh , look at this one-handed whitey with the limp . i do n't want him on my team ! '' but what they do n't know is that i do n't just have a disability , i have an ability . one of my favorite moments from this last season was we played a team that we had never played before . and when the game started , you could tell that they were dissing my disability . i mean , they double-teamed our tallest player . they just were playing really soft on me , and they just , you could tell they thought , `` what can this guy with one hand do ? '' so , they left me open for a three . i made that one . they left me open for another one . i made that one . then , they started to get frustrated , so they actually fouled me . i made both free throws . and they called time out . and as we were in the huddle , i could hear the other coach yelling at his players about me . they went from not covering me at all to double-teaming me . it 's all about overcoming obstacles . it 's true , i have a disability , but so do you . i also have an ability , so do you . everyone has obstacles to overcome . some are visible like mine . some are less visible . maybe your obstacle is that you come from a poor neighborhood . maybe people say you 'll never amount to anything . prove them wrong . maybe your obstacle is that you have a learning disability , and people think that you 're dumb . prove them wrong . maybe people judge you because of the color of your skin or your family background . prove them wrong . i know a lot of people who take one look at me and judge me . they say , `` oh , that kid ca n't be any good at basketball . one leg , one hand . '' if someone things you ca n't overcome the obstacles , prove them wrong .

as you can see , i was born without fingers on my right hand . and also my right leg was several inches shorter than my left one .

why did steven require surgery ?

you might have seen this symbol before , whether it 's as a temporary tattoo or at a chinese temple . it 's called the yin-yang symbol . it comes from taoism , a religion born in china and it has far more meaning than you probably realize . the yin is the dark swirl , and the yang is the light one , and each side has a dot of the opposite color , which gives a clue to the meaning of yin and yang . everything contains the seed of its opposite . darth vadar has the seed of goodness , and luke has the potential to follow his father to the dark side . like luke and his father , yin and yang are not total opposites , they are relative to each other . taoists believe that the universe is made up of energies , vibrations , and matter , which behave differently in different contexts . something can be yin or yang depending on , well , depending on lots of things . so , while wheat that 's growing is yang , when it 's being reaped , it 's yin . a wave 's crest is yang , and the trough is yin . villages on the sunny side of a valley in china have names like liuyang or shiyang , but on the shady side , for example , of the yangtze river valley , there 's jiangyin . the brake is yin to the gas pedal 's yang . an eggshell is yang , the egg inside is yin . you think you 're getting it ? yang is harder , stronger , brighter , and faster , but one can turn into the other or are two sides of the same coin . the sunbeams are yang in comparison to the shadows . the pitch is yang , the catch is yin . the yang starts an action , and the yin receives it , completes it . yin is the inside space of a cup ; it would n't be a cup without it . yang is the cup . the coffee 's heat , however , is yang , and its blackness is yin . yang goes berserk sometimes , but there 's some very powerful yins , too , if they do n't quite go berserk . yin is the darker swirl , the female , but there is a white dot in it . and yang is the lighter , the male , but it has a black dot . water flowing calmly in a river is yin , but when it goes over the waterfall , it 's very yang . toothpicks are yin compared with a telephone pole . the back of a person is more yin than the front . the top of a person is the yang end . taoism teaches that there is a power in the universe . it 's higher , deeper , and truer than any other force . they call it the tao . it means the way . like the force in star wars , the tao has two sides . unlike other religions where the higher power is all good , and perhaps has an all-evil rival , taoism teaches that we need to learn from both yin and yang . and unlike religions with gods that are personal , the higher power in taoism is not . taoists believe that living in harmony with the way , a person will not have to fight against the universe 's natural flow . so , for example , listen more , argue less . be ready to back up or undo something , and you will make even faster progress . do n't worry about being the best , be who you are . live simply . complications take you away from the tao . `` the wise person is flexible , '' taoists say . learning to use the tao is what taoism is all about , and that 's why you should know your yin from your yang .

you might have seen this symbol before , whether it 's as a temporary tattoo or at a chinese temple . it 's called the yin-yang symbol . it comes from taoism , a religion born in china and it has far more meaning than you probably realize .

think about your favorite sport . what are the yin and yang forces which , when put together , make the sport so much fun and challenging .

symmetry is everywhere in nature , and we usually associate it with beauty : a perfectly shaped leaf , or a butterfly with intricate patterns mirrored on each wing . but it turns out that asymmetry is pretty important , too , and more common than you might think , from crabs with one giant pincer claw to snail species whose shells ' always coil in the same direction . some species of beans only climb up their trellises clockwise , others , only counterclockwise , and even though the human body looks pretty symmetrical on the outside , it 's a different story on the inside . most of your vital organs are arranged asymmetrically . the heart , stomach , spleen , and pancreas lie towards the left . the gallbladder and most of your liver are on the right . even your lungs are different . the left one has two lobes , and the right one has three . the two sides of your brain look similar , but function differently . making sure this asymmetry is distributed the right way is critical . if all your internal organs are flipped , a condition called situs inversus , it 's often harmless . but incomplete reversals can be fatal , especially if the heart is involved . but where does this asymmetry come from , since a brand-new embryo looks identical on the right and left . one theory focuses on a small pit on the embryo called a node . the node is lined with tiny hairs called cilia , while tilt away from the head and whirl around rapidly , all in the same direction . this synchronized rotation pushes fluid from the right side of the embryo to the left . on the node 's left-hand rim , other cilia sense this fluid flow and activate specific genes on the embryo 's left side . these genes direct the cells to make certain proteins , and in just a few hours , the right and left sides of the embryo are chemically different . even though they still look the same , these chemical differences are eventually translated into asymmetric organs . asymmetry shows up in the heart first . it begins as a straight tube along the center of the embryo , but when the embryo is around three weeks old , the tube starts to bend into a c-shape and rotate towards the right side of the body . it grows different structures on each side , eventually turning into the familiar asymmetric heart . meanwhile , the other major organs emerge from a central tube and grow towards their ultimate positions . but some organisms , like pigs , do n't have those embryonic cilia and still have asymmetric internal organs . could all cells be intrinsically asymmetric ? probably . bacterial colonies grow lacy branches that all curl in the same direction , and human cells cultured inside a ring-shaped boundary tend to line up like the ridges on a cruller . if we zoom in even more , we see that many of cells ' basic building blocks , like nucleic acids , proteins , and sugars , are inherently asymmetric . proteins have complex asymmetric shapes , and those proteins control which way cells migrate and which way embryonic cilia twirl . these biomolecules have a property called chirality , which means that a molecule and its mirror image are n't identical . like your right and left hands , they look the same , but trying to put your right in your left glove proves they 're not . this asymmetry at the molecular level is reflected in asymmetric cells , asymmetric embryos , and finally asymmetric organisms . so while symmetry may be beautiful , asymmetry holds an allure of its own , found in its graceful whirls , its organized complexity , and its striking imperfections .

like your right and left hands , they look the same , but trying to put your right in your left glove proves they 're not . this asymmetry at the molecular level is reflected in asymmetric cells , asymmetric embryos , and finally asymmetric organisms . so while symmetry may be beautiful , asymmetry holds an allure of its own , found in its graceful whirls , its organized complexity , and its striking imperfections .

explain how the body asymmetry is established , from the molecular level to the organ level .

global oneness project a game for life i do n't know how i can really put this , but my football is really something that is very powerful in my life , that gives me the drive to be who i am now , and have the goals i have now . i think if it was n't for football… i ca n't really imagine myself without football . certain things , certain principles in my life are based on my football . i do n't know if you understand what i mean . [ ♪ native music ♪ ] [ children playing ] [ ♪ native music ♪ ] this is my place . its a very small place . its just a four room house . this is where we sit as a family , watch tv , eat supper , and chat . just family chats . i 'll show you the kitchen where we cook our dinner . this is my kitchen . its not a very big place but it is where i live . this is my bedroom ; i share it with my aunt , but unfortunately now she is asleep because she was working night shift . this is my bed . i sleep here with my kitten . oh yes , this is my kitten . it is my friend . i sleep with her almost every night . this is my aunt . she stays here . she is selling veggies and fruit and her business is definitely going very well . in one week you find that you come and buy something and then its not there , its finished . so she 's got a business that is doing well . this road that we are walking on , this is where i started playing soccer when i got to port elizabeth . we put small stones , there would be goals on each side of the road , then we 'd be playing with the guys . that was before there was grass here . there was no grass here , so we would play from that wall to this side of the road . i grew up playing here and when i see this road or when i walk here i always remember where i started playing soccer . [ ♪ native music ♪ ] most of the time i was with my other two cousin-brothers , and they would spend most of their time playing soccer and that 's how i got on to the field and played as well . [ ♪ native music ♪ ] when i was growing up i was very , very poor . when i was still in primary school , i would wash with cold water . my school shoes , the sole was broken , so when it was raining , my socks would be so wet . and in terms of food , there was absolutely nothing to eat . [ ♪ native music ♪ ] for me to be able to eat at school i would have to wait until we are writing a test . then each pupil would put on 10 cents or 20 cents . then the whole amount would go to the person who was the highest on a test , and that is how i would manage to eat , because , if we were writing a test and put on some money , it was definitely my money because i was a very good student . [ ♪ native music ♪ ] i know their are many people out there who are going through what i went through . i know they wo n't deal with it the way i dealt with it , because i was taking everyday as it was coming . [ ♪ native music ♪ ] i never thought of going out and being a prostitute or something , and i know other people who are going through that thing . always , not always , but sometimes opt for that if they are girls , and if they are boys , they go to armed robbery , bad things like that . so the main reason i always tell the story is just to let them know that poverty can not conquer you for the rest of your life . you can conquer poverty as well . [ ♪ native music ♪ ] [ dog barking ] [ ♪ native music ♪ ] there is a way that you can go . there is a solution to poverty . they always do things that are unethical because they say they are going through poverty . [ ♪ native music ♪ ] i 've never done anything to anyone when i was very poor , but here i am today . i 'm not as poor as i was before and for me , now , i do n't feel like i 'm poor , even though i do n't have everything i want . i do n't have a big house , i do n't have a car , but i still feel that i am rich because i am rich inside . [ speaking in native language ] [ laughter ] this is a very good friend of mine . i grew up playing with him on the street . he was never a very good player , but a very good goal keeper . [ laughter ] come try it : [ gaming device sounds ] [ winning tune ] [ quarters hitting the metal return ] i 've won . it 's my lucky day . there you go , that 's all the money . [ ♪ native hip-hop music ♪ ] soccer helped me to stay away from the option of being a prostitute . i have always had love for my football and discipline . if you are going to be doing all the wrong things to try and get something to eat , or money , then those things wo n't be in-line with your football . if you look at soccer , the things you do that are in line with football , they are also in line with your own life . [ ♪ native hip-hop music ♪ ] people love soccer , and the young kids out there , they are interested in soccer . if you talk about soccer , they all know what you 're talking about , because everyone knows about soccer . so its easy to reach out to the people with soccer . [ ♪ native hip-hop music ♪ ] grassroots soccer we have the kids who know how to prevent themselves from getting hiv and also to teach them life skills . [ ♪ native hip-hop music ♪ ] the older guys have gone through things in their lives , but would like to teach the kids so that they could not go through those things . the way we would do is with interactive games . so we do n't really say , `` yeah , we 're going to talk about hiv now . '' some people might just lose interest in it , but simply because its interactive , we do the actual activities where they just learn from them . and its not as if we are telling them what to do , like to abstain . [ ♪ native hip-hop music ♪ ] so why was it not easy to find the ball ? because you could n't see the ball . so remember when we play that game , what did you say ? teacher > yes my girl , say it . student > someone who has the ball is going to be hiv positive . so what does that tell you about hiv ? you ca n't see someone who has hiv . [ clapping ] since we work with kids we use the power of soccer , and we use soccer balls because kids love to play . if you just make them play , especially with our street leagues , the way we do the teaching for hiv and aids gives them time to play soccer . [ ♪ native hip-hop music ♪ ] those are tools for them to be better people , to stay away from things that could destroy their lives . [ ♪ native hip-hop music ♪ ] after we 've done the program , we also assess the change in their attitudes . [ ♪ native hip-hop music ♪ ] [ clapping ] if there 's a big difference where their attitudes were before they went through the program , i would be very happy about that . [ ♪ native music ♪ ] when you 've got something in your heart and you also want someone else to have that same feeling , i do n't know how to say it ... but it 's always important to just share things with other people . it 's just important . if you know you can do something to help the next person , just do it with all your heart . and not expect to get a reward . it really makes more sense to be able to have others help because , really , we can not live in isolation . honestly , we could be a unity here , but what about the others that are not a unity ? we are going to say , yes we are a unity , that is fine for us . they are not a unity , that 's their own problem . it should n't be like that . [ ♪ native music ♪ ] if people could unite . i 'm telling you , i do n't see anything stopping the world from being a better place . i do n't see anything stopping it . [ ♪ native music ♪ ] it does n't take much for soccer to get people together . if there 's a soccer match somewhere , as long as they know that match is somewhere , they will definitely go . it 's really easy for it to unite people . [ ♪ native music ♪ ] for me its really about passion because i love soccer . i love soccer . it just really ... even if i can be stressed out about something , at my training session or at my game , i forget about it . i do n't know what to say about soccer , but that 's the thing about it . i just do n't know what it is . [ ♪ native music ♪ ] nolusindiso `` titie '' plaatjie is 22 years old and lives in port elizabeth south africa . she studied human movement science at nelson mandela metropolitan university and dreams of becoming an engineer . titie is a well-known soccer star , and in 2001 , she was named captain of the provincial team . she has been playing soccer since the age of five . currently working for grassroots soccer as the port elizabeth project coordinator , titie is a key facilitator in raising hiv ? aids awareness among youth and people of her community . she believes that this is a fight for the world . www.globalonenessproject.org

[ ♪ native music ♪ ] for me its really about passion because i love soccer . i love soccer . it just really ...

in the united states , the sport is called soccer . in africa , europe , latin america and the rest of the world , the sport is referred to as fútbol .

translator : tom carter reviewer : bedirhan cinar ( zombie noises ) doctor 1 : so , here we are again . you know , i 've been thinking . why is this thing so angry ? doctor 2 : maybe he 's just hungry . d1 : ( laughs ) i 'm not going in there to feed it . no , this seems like something very primal . d2 : this is kind of a hard one , because we do n't really have any biological definitions for emotions like anger . sure , brain imaging studies have shown that some brain regions are more active when people are angry , but these are almost always correlational . when it 's warmer outside , people wear less clothing , but if i strip down to my birthday suit , it does n't make it sunny . d1 : ( laughs ) it 's like having someone run on a treadmill and saying `` look at how much more his arms move when he runs faster ! the arms must be where running happens . '' d2 : that 's why working with people with brain lesions is so important to neuroscience . it adds some causal evidence that a brain area might be required for a behavior . same with brain simulation studies . if stimulating a brain area causes a behavior , then that 's good evidence that the brain region is involved in that behavior . so like studies with cats in the 1950s showed that stimulating a small almond-shaped area deep in the brain called the amygdala leads to aggressive or predatory behaviors . these things look pretty aggressive to me . d1 : right . but other studies have shown that stimulating different parts of the amygdala can actually suppress predatory behaviors . so it 's kind of a complicated little brain structure . d2 : yeah . and fmri studies have found that the amygdala is active in violent criminals . d1 : whoa , whoa , whoa . careful there . just because criminals have the same active brain regions as people who are angry , does n't mean that they 're inherently aggressive . that 's like saying because i kiss with the same face hole that i use to burp , then these two things are related . it 's a false equivalence . d2 : huh ! never thought of it like that . that 's a good point . d1 : you know , the amygdala is part of the papez circuit . this system was discovered by james papez , who used the rabies virus to lesion different areas in the cat 's brain . he found that the amygdala was physically connected to another region called the hippocampus -- a little seahorse-shaped area that is needed to turn short-term memories into long-term memories . it 's thought that this connection between the amygdala and hippocampus links emotion and memory together , so that you remember really emotional stuff better than boring everyday things . d2 : yeah , like patient h.m . in the 1950s , surgeons removed both his left and right hippocampuses to treat his epilepsy . but after the surgery , he could n't remember any new information for longer than a few minutes . zombies appear to be pretty forgetful , would n't you agree ? d1 : ( laughs ) absolutely . between the amygdala-related aggression , and memory deficits from the hippocampus , papez may have actually accidentally created the first zombie cat . d2 : aw , come on now , let 's not get carried away . but now we do have some testable hypotheses . i 'd put money on its aggression and memory problems being linked to abnormalities in its amygdala and hippocampus , respectively . d1 : great ! so all we need to do now is figure out how to experimentally test this . do you think it 'll let us examine its brain to verify our hypothesis ? d2 : uh , you know , i think i might be more comfortable not knowing the answer to this one . d1 : hmm . maybe we could get a graduate student to do it for us ?

it adds some causal evidence that a brain area might be required for a behavior . same with brain simulation studies . if stimulating a brain area causes a behavior , then that 's good evidence that the brain region is involved in that behavior .

how can inferences based off of findings from individual studies ( or sets of studies ) be incorrect ? what are other examples of a neuroscience finding being misinterpreted or misrepresented ?

it 's only been the last few hundreds years or so that western civilization has been putting art in museums , at least museums resembling the public institutions we know today . before this , for most , art served other purposes . what we call fine art today was , in fact , primarily how people experienced an aesthetic dimension of religion . paintings , sculpture , textiles and illuminations were the media of their time , supplying vivid imagery to accompany the stories of the day . in this sense , western art shared a utilitarian purpose with other cultures around the world , some of whose languages incidentally have no word for art . so how do we define what we call art ? generally speaking , what we 're talking about here is work that visually communicates meaning beyond language , either through representation or the arrangement of visual elements in space . evidence of this power of iconography , or ability of images to convey meaning , can be found in abundance if we look at art from the histories of our major world religions . almost all have , at one time or another in their history , gone through some sort of aniconic phase . aniconism prohibits any visual depiction of the divine . this is done in order to avoid idolatry , or confusion between the representation of divinity and divinity itself . keeping it real , so to speak , in the relationship between the individual and the divine . however , this can be a challenge to maintain , given that the urge to visually represent and interpret the world around us is a compulsion difficult to suppress . for example , even today , where the depiction of allah or the prophet muhammad is prohibited , an abstract celebration of the divine can still be found in arabesque patterns of islamic textile design , with masterful flourishes of brushwork and arabic calligraphy , where the words of the prophet assume a dual role as both literature and visual art . likewise , in art from the early periods of christianity and buddhism , the divine presence of the christ and the buddha do not appear in human form but are represented by symbols . in each case , iconographic reference is employed as a form of reverence . anthropomorphic representation , or depiction in human form , eventually became widespread in these religions only centuries later , under the influence of the cultural traditions surrounding them . historically speaking , the public appreciation of visual art in terms other than traditional , religious or social function is a relatively new concept . today , we fetishize the fetish , so to speak . we go to museums to see art from the ages , but our experience of it there is drastically removed from the context in which it was originally intended to be seen . it might be said that the modern viewer lacks the richness of engagement that she has with contemporary art , which has been created relevant to her time and speaks her cultural language . it might also be said that the history of what we call art is a conversation that continues on , as our contemporary present passes into what will be some future generation 's classical past . it 's a conversation that reflects the ideologies , mythologies , belief systems and taboos and so much more of the world in which it was made . but this is not to say that work from another age made to serve a particular function in that time is dead or has nothing to offer the modern viewer . even though in a museum setting works of art from different places and times are presented alongside each other , isolated from their original settings , their juxtaposition has benefits . exhibits are organized by curators , or people who 've made a career out of their ability to recontextualize or remix cultural artifacts in a collective presentation . as viewers , we 're then able to consider the art in terms of a common theme that might not be apparent in a particular work until you see it alongside another , and new meanings can be derived and reflected upon . if we 're so inclined , we might even start to see every work of art as a complementary part of some undefined , unified whole of past human experience , a trail that leads right to our doorstep and continues on with us , open to anyone who wants to explore it .

it 's only been the last few hundreds years or so that western civilization has been putting art in museums , at least museums resembling the public institutions we know today . before this , for most , art served other purposes .

what is a curator ?

hello , everyone . let 's begin our guided tour . welcome to the museum of museums . museums have been a part of human history for over 2000 years . but they were n't always like the ones we visit today . the history of museums is far older and much stranger than you might imagine . we 'll start over here in the greek wing . our word museum comes from the greek mouseion , temples built for the muses , the goddesses of the arts and the sciences . supplicants asked the muses to keep watch over academics and grant ingenuity to those they deemed worthy . the temples were filled with offerings of sculptures , mosaics , complex scientific apparatuses , poetic and literary inscriptions , and any other tribute that would demonstrate a mortal 's worthiness for divine inspiration . we have arrived at the mesopotamian wing . the first museum was created in 530 b.c . in what is now iraq . and the first curator was actually a princess . ennigaldi-nanna started to collect and house mesopotamian antiquities in e-gig-par , her house . when archeologists excavated the area , they discovered dozens of artifacts neatly arranged in rows , with clay labels written in three languages . she must have had interesting parties . the tradition of collecting and displaying intriguing items began to be mimicked , as you can see here in the roman empire wing . treasure houses of politicians and generals were filled with the spoils of war , and royal menageries displayed exotic animals to the public on special occasions , like gladiator tournaments . as you can see , we have a lion here and a gladiator , and , well , the janitor ought to be in this wing clearly . moving on , hurry along . the next step in the evolution of museums occurred in the renaissance , when the study of the natural world was once again encouraged after almost a millennium of western ignorance . curiosity cabinets , also referred to as wunderkammers , were collections of objects that acted as a kind of physical encyclopedia , showcasing artifacts . just step into the wardrobe here . there you go . mind the coats . and we 'll tour ole worm 's cabinet , one of the most notable wunderkammers belonged to a wealthy 17th-century naturalist , antiquarian , and physician ole worm . ole worm collected natural specimens , human skeletons , ancient runic texts , and artifacts from the new world . in other curiosity cabinets , you could find genetic anomalies , precious stones , works of art , and religious and historic relics . oh my . you might not want to touch that . these cabinets were private , again , often in residencies , curated by their owners , rulers and aristocrats , as well as merchants and early scientists . now , who hears a circus organ ? in the 1840s , an enterprising young showman named phineas t. barnum purchased some of the more famous cabinets of curiosity from europe and started barnum 's american museum in new york city . a spectacular hodgepodge of zoo , lecture hall , wax museum , theater , and freak show that was known for its eclectic residents , such as bears , elephants , acrobats , giants , siamese twins , a fiji mermaid , and a bearded lady , along with a host of modern machinery and scientific instruments . museums open to the public are a relatively new phenomenon . before barnum , the first public museums were only accessible by the upper and middle classes , and only on certain days . visitors would have to apply to visit the museum in writing prior to admision , and only small groups could visit the museum each day . the louvre famously allowed all members of the public into the museum but only three days a week . in the 19th century , the museum as we know it began to take shape . institutions like the smithsonian were started so that objects could be seen and studied , not just locked away . american museums , in particular , commissioned experiments and hired explorers to seek out and retrieve natural samples . museums became centers for scholarship and artistic and scientific discovery . this is often called the museum age . nowadays , museums are open to everybody , are centers of learning and research , and are turning into more hands-on institutions . but the question of who gets to go is still relevant as ticket prices can sometimes bar admission to those future scholars , artists and targets of divine inspiration who ca n't afford to satisfy their curiosity . thank you all for coming , and please , feel free to stop by the gift shop of gift shops on your way out .

the tradition of collecting and displaying intriguing items began to be mimicked , as you can see here in the roman empire wing . treasure houses of politicians and generals were filled with the spoils of war , and royal menageries displayed exotic animals to the public on special occasions , like gladiator tournaments . as you can see , we have a lion here and a gladiator , and , well , the janitor ought to be in this wing clearly .

who owned treasure houses ?

element 118 , ununoctium or uuo , is the last element in the periodic table , and it 's in the group which contains the noble gases , going from helium right down to radioactive radon , so it is going to be radioactive . so far , only 3 atoms , have been observed . first one atom then another two . so it 's more than ununquadium , is it more ? it 's more than ununquadium , where we had , only one atom , but it 's still not very many atoms . it 's still arguable whether it will be a gass-like radon , or it may be a solid , just like some of the other elements , perhaps a solid that 's rather volatile . so that it would evaporate easily . but nobody knows . how can you know 118 is the last element , on the periodic table ? -well formally , they could be heavier elements than 118 , but the electrons , the negatively charged particles , that surround , the positively charged nucleus , are in shells , which gradually go outwards . rather like the skins , of an onion . so that element 118 , represents the whole of a shell , being filled . so we know that there are no more electrons , that can be easily accommodated and if we make element 119 , which would be an alkali metal like sodium or cesium , then we would have to put a single electron , a lot further away , from the nucleus . and as soon as you start adding electrons , that are further away , the whole system , is expected to become very much less stable . so if we can only make 3 atoms of element 118 , something that 's going to be very much less stable , is not likely to be found in the short time . though one of the exciting things about science , is that the unexpected often happens . so , it might be that before we 've started updating , some of these videos , element 119 will be announced . and nobody will be more excited than me . www.periodicvideos.com university of nottingham captions by www.subply.com

so far , only 3 atoms , have been observed . first one atom then another two . so it 's more than ununquadium , is it more ?

when was ununoctium first made by the hot fusion method in dubna ( russia ) ?

nestled in the tissues of your neck is a small unassuming organ that wields enormous power over your body . it 's called the thyroid . like the operations manager in a company , its role is to make sure that the cells in your body are working properly . it does that by using hormones to deliver messages to every single one of them . this high-ranking organ is made up of lobules that each contains smaller cells called follicles , which store the hormones the thyroid sends out into your blood . two of the most important hormones it produces are thyroxine and triiodothyronine , or t3 and t4 . as messengers , the hormone 's job is to instruct every cell in the body when to consume oxygen and nutrients . that maintains the body 's metabolism , the series of reactions our cells perform to provide us with energy . this hormonal notification from the thyroid gets the heart pumping more efficiently , and makes our cells break down nutrients faster . when you need more energy , the thyroid helps by sending out hormones to increase metabolism . ultimately , the thyroid allows our cells to use energy , grow and reproduce . the thyroid is controlled by the pituitary gland , a hormonal gland deep in the brain that oversees the thyroid 's tasks , making sure it knows when to send out its messengers . the pituitary 's role is to sense if hormone levels in the blood are too low or too high , in which case it sends out instructions in the form of the thyroid- stimulating hormone . even in this tightly controlled system , however , management sometimes slips up . certain diseases , growths in the thryoid or chemical imbalances in the body can confuse the organ and make it deaf to the pituitary 's guiding commands . the first problem this causes is hyperthyroidism , which happens when the organ sends out too many hormones . that means the cells are overloaded with instructions to consume nutrients and oxygen . they become overactive as a result , meaning a person with hyperthyroidism experiences a higher metabolism signaled by a faster heartbeat , constant hunger , and rapid weight loss . they also feel hot , sweaty , anxious , and find it difficult to sleep . the opposite problem is hypothyroidism , which happens when the thyroid sends out too few hormones , meaning the body 's cells do n't have as many messengers to guide them . in response , cells grow listless and metabolism slows . people with hypothyroidism see symptoms in weight gain , sluggishness , sensitivity to cold , swollen joints and feeling low . luckily , there are medical treatments that can help trigger the thyroid 's activities again , and bring the body back to a steady metabolic rate . for such a little organ , the thyroid wields an awful lot of power . but a healthy thyroid manages our cells so effectively that it can keep us running smoothly without us even noticing it 's there .

when you need more energy , the thyroid helps by sending out hormones to increase metabolism . ultimately , the thyroid allows our cells to use energy , grow and reproduce . the thyroid is controlled by the pituitary gland , a hormonal gland deep in the brain that oversees the thyroid 's tasks , making sure it knows when to send out its messengers . the pituitary 's role is to sense if hormone levels in the blood are too low or too high , in which case it sends out instructions in the form of the thyroid- stimulating hormone .

why is it so important that the pituitary oversees what the thyroid does ?

a handful of species on earth share a seemingly mysterious trait : a menstrual cycle . we 're one of the select few . monkeys , apes , bats , humans , and possibly elephant shrews are the only mammals on earth that menstruate . we also do it more than any other animal , even though its a waste of nutrients and can be a physical inconvenience . so where 's the sense in this uncommon biological process ? the answer begins with pregnancy . during this process , the body 's resources are cleverly used to shape a suitable environment for a fetus , creating an internal haven for a mother to nurture her growing child . in this respect , pregnancy is awe-inspiring , but that 's only half the story . the other half reveals that pregnancy places a mother and her child at odds . as for all living creatures , the human body evolved to promote the spread of its genes . for the mother , that means she should try to provide equally for all her offspring . but a mother and her fetus do n't share exactly the same genes . the fetus inherits genes from its father , as well , and those genes can promote their own survival by extracting more than their fair share of resources from the mother . this evolutionary conflict of interests places a woman and her unborn child in a biological tug-of-war that plays out inside the womb . one factor contributing to this internal tussle is the placenta , the fetal organ that connects to the mother 's blood supply and nourishes the fetus while it grows . in most mammals , the placenta is confined behind a barrier of maternal cells . this barrier lets the mother control the supply of nutrients to the fetus . but in humans and a few other species , the placenta actually penetrates right into the mother 's circulatory system to directly access her blood stream . through its placenta , the fetus pumps the mother 's arteries with hormones that keep them open to provide a permanent flow of nutrient-rich blood . a fetus with such unrestricted access can manufacture hormones to increase the mother 's blood sugar , dilate her arteries , and inflate her blood pressure . most mammal mothers can expel or reabsorb embryos if required , but in humans , once the fetus is connected to the blood supply , severing that connection can result in hemorrhage . if the fetus develops poorly or dies , the mother 's health is endangered . as it grows , a fetus 's ongoing need for resources can cause intense fatigue , high blood pressure , and conditions like diabetes and preeclampsia . because of these risks , pregnancy is always a huge , and sometimes dangerous , investment . so it makes sense that the body should screen embryos carefully to find out which ones are worth the challenge . this is where menstruation fits in . pregnancy starts with a process called implantation , where the embryo embeds itself in the endometrium that lines the uterus . the endometrium evolved to make implantation difficult so that only the healthy embryos could survive . but in doing so , it also selected for the most vigorously invasive embryos , creating an evolutionary feedback loop . the embryo engages in a complex , exquisitely timed hormonal dialogue that transforms the endometrium to allow implantation . what happens when an embryo fails the test ? it might still manage to attach , or even get partly through the endometrium . as it slowly dies , it could leave its mother vulnerable to infection , and all the time , it may be emitting hormonal signals that disrupt her tissues . the body avoids this problem by simply removing every possible risk . each time ovulation does n't result in a healthy pregnancy , the womb gets rid of its endometrial lining , along with any unfertilized eggs , sick , dying , or dead embryos . that protective process is known as menstruation , leading to the period . this biological trait , bizarre as it may be , sets us on course for the continuation of the human race .

most mammal mothers can expel or reabsorb embryos if required , but in humans , once the fetus is connected to the blood supply , severing that connection can result in hemorrhage . if the fetus develops poorly or dies , the mother 's health is endangered . as it grows , a fetus 's ongoing need for resources can cause intense fatigue , high blood pressure , and conditions like diabetes and preeclampsia . because of these risks , pregnancy is always a huge , and sometimes dangerous , investment .

as the fetus in the human mother grows , its intense need for nutrients can cause :

hi , i ’ m john green . this is crash course world history and today we ’ re going to talk about world war ii . finally , a war with some color film ! so , here at crash course we try to make history reasonably entertaining , and fortunately , world war ii was hilarious ... said no one ever . mr. green , mr. green ! is this , like , gon na be one of the unfunny ones where you build to the big melodramatic conclusion about how i have to imagine the world more complexly ? me from the past , as long as you have that eighth rate soup-strainer , i ’ m not even going to acknowledge your existence . [ theme music ] right , so you ’ ve probably heard a lot about world war ii from movies and books , the history channel , before it decided that swamp people were history , the incessant droning of your grandparents , etc . we ’ re not gon na try to give you a detailed synopsis of the war today . instead , we ’ re going to try to give a bit of perspective on how the most destructive war in human history happened , and why it still matters globally . so one of the reasons history classes tend to be really into wars is that they ’ re easy to put on tests . they start on one day and they end on another day . and they ’ re caused by social , political , and economic conditions that can be examined in a multiple choice kind of manner . except , not really . like , when did world war ii start ? in september 1939 , when the nazis invaded poland ? i ’ d say no - it actually started when japan invaded manchuria in 1931 , or at the very latest when the japanese invaded china in 1937 , because they didn ’ t stop fighting until 1945 . then again , you could also argue 1933 , when hitler took power , or 1941 , when america started fighting . it ’ s complicated . but anyway , in china the fighting was very brutal , as exemplified by the infamous rape of nanking , which featured the slaughter of hundreds of thousands of chinese people and is still so controversial today that : 1 . it affects relations between japan & amp ; amp ; china and 2 . even though i have not described it in detail , you can rest assured that there will be angry comments about my use of the word “ slaughter. ” but the world war ii we know the most about from movies and tv is primarily the war in the european theater , the one that adolf hitler started . hitler is the rare individual who really did make history - specifically he made it worse - and if he hadn ’ t existed , it ’ s very unlikely that world war ii would ’ ve ever happened . but he did exist , and after coming to power in 1933 , with the standard revolutionary promises to return the homeland to its former glory , infused with quite a bit of paranoia and anti-semitism , germany saw rapid re-militarization and eventually , inevitably , war . in the beginning , it was characterized by a new style of combat made possible by the mechanized technology of tanks , airplanes , and especially , trucks . this was the blitzkrieg , a devastating tactic combining quick movement of troops , tanks , and massive use of air power to support infantry movements . and in the very early years of the war , it was extremely effective . the nazis were able to roll over poland , norway , denmark , the netherlands , and then all of france , all within about 9 months between the fall of 1939 and the summer of 1940 . so after knocking out most of central europe , the nazis set their sights on great britain , but they didn ’ t invade the island , choosing instead to attack it with massive air strikes . i mean , you look at this poster and think , “ man , the queen wants me to finish my term paper , so i can do it , ” but when this poster was first produced in 1939 , it was to quell terror in the face of bombardment . the battle of britain was a duel between the royal air force and the luftwaffe , and while the raf denied the nazis total control of british airspace , the nazis were still able to bomb great britain over and over again in what ’ s known as the blitz . stan , no . no jokes this time . yes , the blitz . meanwhile , europeans were also fighting each other in north africa . the desert campaigns started in 1940 and lasted through 1942 - this is where british general “ monty ” montgomery outfoxed german general irwin “ the desert fox ” rommel . it ’ s also the place where americans first fought nazis in large numbers . but most importantly , it ’ s where indiana jones discovered the ark of the covenant . okay , let ’ s go to the thought bubble . 1941 was a big year for world war ii . first , the nazis invaded russia , breaking a non-aggression pact that the two powers had signed in 1939 . this hugely escalated the war , and also made allies of the most powerful capitalist countries and the most powerful communist one , an alliance that would stand the test of time and never end ... until like three seconds after the defeat of the nazis . the nazi invasion of russia opened the war up on the so-called eastern front , although if you were russian , it was the western front , and it led to millions of deaths , mostly russian . also , 1941 saw a day that would `` live in infamy '' when the japanese bombed pearl harbor , hoping that such an audacious attack would frighten the united states into staying neutral , which was a pretty stupid gamble because : 1 . the u.s. was already giving massive aid to the allies and was hardly neutral and 2 . the united states is not exactly famed for its pacifism or political neutrality . 1941 also saw japan invading much of southeast asia , which made australia and new zealand understandably nervous . as part of the british commonwealth , they were already involved in the war , but now they could fight the japanese closer to home . and shut up about how i never talk about you australians . i just gave you 1.5 sentences . but by the time the americans and australians started fighting the japanese , it was already a world war . sometimes this meant fighting or starving or being bombed ; other times , it meant production for the war - you don ’ t think of argentina as being a world war ii powerhouse , for instance , but they were vital to the allies , supplying 40 % of british meat during world war ii . thanks , thought bubble . so , not to sound jingoistic , but the entry of the u.s. into the war really did change everything , although i doubt the nazis could ’ ve taken russia regardless . no one conquers russia in the wintertime , unless you are - wait for it - the mongols . okay , we ’ re going to skip most of the big battles of 1942 - like the battle of midway , which effectively ended japan ’ s chance of winning the war - and focus on the battle of stalingrad . the german attack on stalingrad , now known as volgograd because stalin sucks , was one of the bloodiest battles in the history of war , with more than two million dead . the germans began by dropping more than 1,000 tons of bombs on stalingrad , and then the russians responded by “ hugging ” the germans , staying as close to their front lines as possible so that german air support would kill germans and russians alike . this kind of worked , although the germans still took most of the city . but then , a soviet counterattack left the sixth army of the nazis completely cut off . and after that , due partly to hitler ’ s overreaching megalomania and partly to lots of people being scared of him , the sixth army slowly froze and starved to death before finally surrendering . and of the 91,000 axis pows from stalingrad , only about 6,000 ever returned home . stalingrad turned the war in europe and by 1944 , the american strategy of “ island hopping ” in the pacific was taking gis closer and closer to japan . rome was liberated in june by americans and canadians ; and the successful british , canadian , and american d-day invasion of normandy was the beginning of the end for the nazis . oh , it ’ s time for the open letter ? an open letter to canada . but first , let ’ s see what ’ s in the secret compartment today . oh , it ’ s canadian mittens . i wan na thank the canadian crash course fans , who sent us these mittens . canadians are just so nice , stan . like , all we ever do on this show is make fun of them , and they ’ re just like , “ it ’ s so kind of you to mention us . here ’ s some mittens ! ” dear canada , we ’ re not always nice to you here on crash course , but you are awesome . i ’ m pointing , but you can ’ t tell because i ’ m wearing mittens . 45,000 canadians died fighting for the allies in world war ii , which means that , per capita , canada lost more people than the united states . you fought with the royal air force to defend great britain from the beginning of the war and you were there on d-day , successfully invading juno beach . and , as many of you have pointed out in comments , you defeated the united states in the war of 1812 , meaning that , arguably , canada , you are the greater military power . plus , you have lumberjacks , and excellent beer , and hockey , and universal healthcare , and justin bieber . i ’ m jealous ! that 's what it is - i 'm jealous ! best wishes , john green . so , by the end of 1944 , the allies were advancing from the west and the russian red army was advancing from the east and then , the last-ditch german offensive at the battle of the bulge in the winter of 1944-1945 failed . mussolini was executed in april of 1945 . hitler committed suicide at the end of that month . and , on may 8 , 1945 the allies declared victory in europe after germany surrendered unconditionally . three months later , the united states dropped the only two nuclear weapons ever deployed in war , japan surrendered , and world war ii was over . the war had a definite cause : unbridled military expansion by germany , japan , and , to a small extent , italy . now , it ’ s easy to claim that hitler was crazy or evil , and , in fact , he was certainly both , but that doesn ’ t explain the nazis decision to invade russia , and it sure doesn ’ t explain japan ’ s decision to bomb pearl harbor . and there are many possible explanations beyond mere evil ; but the most interesting one , to me , involves food . hitler had a number of reasons for wanting to expand germany ’ s territory , but he often talked about lebensraum or living space for the german people . german agriculture was really inefficiently organized into lots of small farms , and that meant that germany needed a lot of land in order to be self-sufficient in food production . the plan was to take poland , the ukraine , and eastern russia , and then resettle that land with lots of germans , so that it could feed german people . this was called the hunger plan because the plan called for 20 million people to starve to death . many would be the poles , ukrainians , and russians who ’ d previously lived on the land . the rest would be europe ’ s jews , who would be worked to death . six million jews were killed by the nazis , many by starvation , but many through a chillingly planned effort of extermination in death camps . these death camps can be distinguished from concentration camps or labor camps in that their primary purpose was extermination of jews , roma people , communists , homosexuals , disabled people , and others that the nazis deemed unfit . some historians believe that the nazis opened the death camps because the jews weren ’ t dying as fast as the hunger plan had intended . this was a sickening plan , but it made a kind of demented sense . rather than becoming more involved in global trade , as the british had , the germans would feed themselves by taking land and killing the people who ’ d previously lived there . similarly , japan , at the beginning of the war , was suffering from an acute fear of food shortage because its agricultural sector was having trouble keeping up with population growth . and the japanese too , sought to expand their agricultural holdings by , for instance , resettling farmers in korea . so while it ’ s tempting to say that world war ii was about the allies fighting for democratic ideals against the totalitarian militaristic imperialism of the fascist axis powers , it just doesn ’ t hold up to scrutiny . for instance , a hugely important allied power , stalin ’ s soviet union , was , like , the least democratic place , ever . stan just said that was hyperbole , but it ’ s not . stalin ’ s soviet union is tied with all of the other completely undemocratic countries for last place on the democracy scale . it ’ s a big community there , at last place , but they ’ re definitely in there somewhere . and , by far , the biggest imperialists of the war were the british . they couldn ’ t have fed or clothed themselves - or resisted the nazis - without their colonies and commonwealth . so , why is world war ii so important ? well first , it proved the old roman adage homo homini lupus : man is a wolf to man . this is seen most clearly in the holocaust , but all the statistics are staggering . more than a million indian british subjects died , mainly due to famine that could have been avoided if the british had redistributed food . and their failure to do so helped convince indians that the so-called superior civilization of the british was a sham . more than a million vietnamese died , mainly due to famine . 418,000 americans . more than a million noncombatants in both germany and japan . and 20 million people in the soviet union , most of them civilians . these civilians were targeted because they helped sustain the war , mostly through industrial and agricultural production . in a total war , when a nation is at war , not just its army , there is no such thing as a non-military target . from the firebombing of dresden to tokyo to hiroshima , the line between soldier and civilian blurred . and then , of course , there is the holocaust , which horrifies us because the elements of western progress - record-keeping , industrial production , technology - were used to slaughter millions . world war ii saw modern industrial nations , which represented the best of the enlightenment and the scientific revolution , descend into once unimaginable cruelty . and what makes world war ii such a historical watershed is that in its wake , all of us - in the west or otherwise - were forced to question whether western dominance of this planet could , or should , be considered progress . thanks for watching . i ’ ll see you next week . crash course is produced and directed by stan muller . our script supervisor is meredith danko . our associate producer is danica johnson . the show is written by my high school history teacher , raoul meyer , and myself . and our graphics team is thought bubble . last week ’ s phrase of the week was “ an end to history. ” if you want to guess at this week ’ s phrase of the week or suggest future ones , you can do so in comments , where you can also ask questions about today ’ s video that will be answered by our team of historians . if you enjoy crash course , make sure you ’ re subscribed . thanks for watching , and as we say in my hometown , don ’ t forget to be awesome .

i ’ m pointing , but you can ’ t tell because i ’ m wearing mittens . 45,000 canadians died fighting for the allies in world war ii , which means that , per capita , canada lost more people than the united states . you fought with the royal air force to defend great britain from the beginning of the war and you were there on d-day , successfully invading juno beach .

true or false : canada lost more people per capita than the united states .

translator : andrea mcdonough reviewer : bedirhan cinar you look down and see a yellow pencil lying on your desk . your eyes , and then your brain , are collecting all sorts of information about the pencil : its size , color , shape , distance , and more . but , how exactly does this happen ? the ancient greeks were the first to think more or less scientifically about what light is and how vision works . some greek philosophers , including plato and pythagoras , thought that light originated in our eyes and that vision happened when little , invisible probes were sent to gather information about far-away objects . it took over a thousand years before the arab scientist , alhazen , figured out that the old , greek theory of light could n't be right . in alhazen 's picture , your eyes do n't send out invisible , intelligence-gathering probes , they simply collect the light that falls into them . alhazen 's theory accounts for a fact that the greek 's could n't easily explain : why it gets dark sometimes . the idea is that very few objects actually emit their own light . the special , light-emitting objects , like the sun or a lightbulb , are known as sources of light . most of the things we see , like that pencil on your desk , are simply reflecting light from a source rather than producing their own . so , when you look at your pencil , the light that hits your eye actually originated at the sun and has traveled millions of miles across empty space before bouncing off the pencil and into your eye , which is pretty cool when you think about it . but , what exactly is the stuff that is emitted from the sun and how do we see it ? is it a particle , like atoms , or is it a wave , like ripples on the surface of a pond ? scientists in the modern era would spend a couple of hundred years figuring out the answer to this question . isaac newton was one of the earliest . newton believed that light is made up of tiny , atom-like particles , which he called corpuscles . using this assumption , he was able to explain some properties of light . for example , refraction , which is how a beam of light appears to bend as it passes from air into water . but , in science , even geniuses sometimes get things wrong . in the 19th century , long after newton died , scientists did a series of experiments that clearly showed that light ca n't be made up of tiny , atom-like particles . for one thing , two beams of light that cross paths do n't interact with each other at all . if light were made of tiny , solid balls , then you would expect that some of the particles from beam a would crash into some of the particles from beam b . if that happened , the two particles involved in the collision would bounce off in random directions . but , that does n't happen . the beams of light pass right through each other as you can check for yourself with two laser pointers and some chalk dust . for another thing , light makes interference patterns . interference patterns are the complicated undulations that happen when two wave patterns occupy the same space . they can be seen when two objects disturb the surface of a still pond , and also when two point-like sources of light are placed near each other . only waves make interference patterns , particles do n't . and , as a bonus , understanding that light acts like a wave leads naturally to an explanation of what color is and why that pencil looks yellow . so , it 's settled then , light is a wave , right ? not so fast ! in the 20th century , scientists did experiments that appear to show light acting like a particle . for instance , when you shine light on a metal , the light transfers its energy to the atoms in the metal in discrete packets called quanta . but , we ca n't just forget about properties like interference , either . so these quanta of light are n't at all like the tiny , hard spheres newton imagined . this result , that light sometimes behaves like a particle and sometimes behaves like a wave , led to a revolutionary new physics theory called quantum mechanics . so , after all that , let 's go back to the question , `` what is light ? '' well , light is n't really like anything we 're used to dealing with in our everyday lives . sometimes it behaves like a particle and other times it behaves like a wave , but it is n't exactly like either .

and , as a bonus , understanding that light acts like a wave leads naturally to an explanation of what color is and why that pencil looks yellow . so , it 's settled then , light is a wave , right ? not so fast !

is light a particle or a wave ?

translator : jenny zurawell i am awele . daughter of alice , granddaughter of ruth , great-granddaughter of big momma alice and madir corine , great-great-granddaughter of anna and zitii benyen . it is my hope to find my best possible self in the service of others . now , my daddy , he used to tell me stories . my daddy , he would say , `` i want you to know who you are and where you come from . that will guide you as you discover who you must be . now , you listen to this story , you hear me , baby girl ? it 's not going to be in a book . your teacher is not going to tell it , but you need to understand who you are . '' that became a guiding principle in the stories that i wanted to tell . stories about legacy of who we are . i used to hear all the time that children are the future , but what does that cliché really mean and how are we preparing them ? so i looked for narratives about young people and the legacy that they bring as agents of change . the power that you have right now . today , march 2 , 1955 -- the story that i want to share with you comes from 1955 , march 2 . it 's about a courageous 16-year-old girl , claudette colvin . and it comes full circle today because a week ago today , in san francisco , my middle school students , they performed a program that i had written , `` agents of change , '' starting with the reenactment of plessy v. ferguson from 1892 to 1896 , moving to brown v. board and a student-led strike by barbara rose johns , jumping to claudette colvin and the montgomery bus boycott and ending in 1960 with the sit-in movement , the non-violent movement led by students . so i 'm going to share the story , and i would like to also share the work i do with it , as a case study . i paid my dime at the front of the bus , and then i ran to the back door with the rest of the colored kids so the driver would n't take off before we got on . also , well , whites do n't want us walking down the aisle next to them . when i got back on the bus , colored section was full , so , i sat in the middle section . i took the last row seat on the left , it was right by the window , was n't thinking about anything in particular . `` hey . '' i did n't know the girl next to me either , this older girl . so i just looked out the window . driver went more stops , more people were getting on , colored and white . pretty soon , no more seats were available . `` give me those seats , '' the driver called out . colored folks just started getting up . white folks started taking their seats , but i stayed seated . girl next to me and the other two across -- they stayed seated . i knew it was n't the restricted area . `` make light on your feet ! '' girl next to me got up immediately . she stood in the aisle , then the other two girls . but i told myself , this is n't the restricted area . the driver , he looked up , looked in the window , that mirror . he pulled over . a pregnant lady , mrs. hamilton , got on the bus . she ran to the back and got on , not knowing he was trying to have me relinquish my seat . and she sat right next to me . `` the two of you need to get up so i can drive on . '' `` sir , i paid my dime , i paid my fare . it 's my right , you know , my constitutional -- '' `` constitutional ? ha-ha , let me get the police . '' well he got off and he flagged down two motormen , and they came . and those motormen , they came onto the bus . looked at mrs. hamilton . `` now the two of you need to get up so the driver can drive on . '' `` sir , i paid my dime . i 'm pregnant . if i were to move right now , i 'd be very sick , sir . '' `` sir , i paid my dime too , you know , and it 's my right , my constitutional right . i 'm a citizen of the united states . you just read the 13th and 14th amendment , it 'll tell you so . i know the law . my teacher , she taught it at school . '' you see , my teacher , she taught the constitution , the bill of rights , the declaration of independence , patrick henry 's speech -- i even memorized it . my teacher , she would prick our minds , trying to see what we thinking about . she would say , `` who are you ? hmm ? who are you , sitting right here right now ? the person that people think they see from your outside ? who are you on the inside ? how you think ? how you feel ? what you believe ? would you be willing to stand up for what you believe in even if someone wants to hold you back because you 're different ? do you love your beautiful brown skin , children ? hmm ? are you american ? what does it mean to be an american ? huh ? homework tonight , write me an essay : `` what does it mean to be an american ? '' you need to know who you are , children ! '' my teacher , she would teach us history and current events . she said that 's how we can understand everything that 's going on and we can do something about it . `` sir , all i know is i hate jim crow . i also know if i ai n't got nothing worth living for , i ai n't got nothing worth dying for . so give me liberty or give me death ! ouch ! i do n't care ! take me to jail . '' they dragged her off the bus . next thing , claudette colvin was in a car seat , backseat of the police car , handcuffed through the windows . the following year , may 11 , 1956 , claudette colvin was the star witness in the federal court case browder v. gayle . her , an 18-year-old teenager and two others , women , mrs. browder . their case , browder v. gayle , went up to the supreme court . on the heels of brown v. board of education , the 14th amendment and her powerful testimony that day , the rest is history . now , why is it we do n't know this story ? the montgomery bus boycott -- we hear rosa parks , martin luther king , they will forever be lifted up . but the role women played in that movement , the role of claudette , as an up-stander , it teaches us important lessons that challenge us today . what does it mean to be a participant ? a responsible citizen in a democracy ? and lessons of courage and of faith ? so i find freedom movement history that includes young people so that they can explore these big ideas of identity , your chosen identity , and the imposed identity . what does membership in society mean ? who has it ? how do we make amends ? race and violence in america , as well as participatory citizenship . so these stories allow me to have conversations , to speak the unspeakable , that many are afraid to have . once in eugene , oregon , a young , blond-haired , blue-eyed boy , middle schooler , at the end of a performance in the dialogue said , `` but ms. awele , racism 's over , right ? '' and not wanting to answer for him , i said , `` turn to the person sitting next to you . see if you can come up with evidence . '' and i gave them four minutes to talk . soon , they began to tell stories , evidence of racism in their community . a girl wrote to me , a high school student in san francisco : `` i was going to skip school but then i heard we had an assembly , so i came . and after listening to the students talk and seeing your performance , i thought i should organize my friends and we should go down to a board meeting and tell them that want to have advanced classes for a through g requirements . '' so , i tell you this story today in honor of the legacy of young people that have come before , so that they will have guideposts and signs to be the change that they want to see in this world , as claudette colvin was . because she struck down the constitutionality of segregated seats in montgomery , alabama . thank you . ( applause ) thank you . ( applause )

my teacher , she taught it at school . '' you see , my teacher , she taught the constitution , the bill of rights , the declaration of independence , patrick henry 's speech -- i even memorized it . my teacher , she would prick our minds , trying to see what we thinking about .

makeba observes that the civil rights movement

imagine yourself standing on a beach , looking out over the ocean , waves crashing against the shore , blue as far as your eyes can see . let it really sink in , the sheer scope and size of it all . now , ask yourself , `` how big is it ? how big is the ocean ? '' first thing , we need to understand that there really is only one ocean , consisting of five component basins that we call the pacific , the atlantic , the indian , the arctic , and the southern . each of these five , while generally referred to as oceans in and of themselves , are really and truly a part of a single , massive body of water , one ocean , which defines the very face of planet earth . the ocean covers roughly 71 % of our planet 's surface , some 360 million square kilometers , an area in excess of the size of 36 u.s.a. 's . it 's such a vast spread , when viewed from space , the ocean is , by far , the dominant feature of our planet . speaking of space , the ocean currently holds over 1.3 billion , that 's billion with a `` b '' , cubic kilometers of water . put another way , that 's enough water to immerse the entire united states under a body of salt water over 132 kilometers tall , a height well beyond the reach of the highest clouds and extending deep into the upper atmosphere . with all that volume , the ocean represents 97 % of earth 's total water content . on top of all that , the ocean contains upwards of 99 % of the world 's biosphere , that is , the spaces and places where life exists . now let that sink in for a second . the immediate world as we know it , indeed the totality of all the living space encompassed by the continents themselves , all of that represents only 1 % of the biosphere . 1 % ! the ocean is everything else . so , the ocean is physically massive . it 's importance to life is practically unparalleled . it also happens to hold the greatest geological features of our planet . quickly , here are four of the most notable . the ocean contains the world 's largest mountain range , the mid-ocean ridge . at roughly 65,000 kilometers long , this underwater range is some 10 times longer than the longest mountain chain found purely on dry land , the andes . beneath the denmark strait exists the world 's largest waterfall . this massive cataract carries roughly 116 times more water per second over its edge than the congo river 's inga falls , the largest waterfall by volume on land . the world 's tallest mountain is actually found in the ocean , hiding in plain sight . while 4200 meters of hawaii 's mauna kea sit above sea level , its sides plummet beneath the waves for another 5800 meters . from its snow-covered top to it 's silt-covered bottom , then , this hawaiian mountain is roughly 10,000 meters in height , dwarfing tiny everest 's paltry peak by well over a kilometer . then , since we 're picking on poor everest , let 's consider the world 's deepest canyon , the challenger deep , existing 11 kilometers below the ocean 's surface , some six times deeper than the grand canyon . that 's deep enough to sink mount everest into and still have over 2.1 kilometers of water sitting atop its newly submerged peak . put another way , the depth of the challenger deep is roughly the same height that commercial airliners travel . so , pretty much however you choose to slice it , the ocean is capital b capital i , capital g , big ! it defines our planet , home to the greatest geological features , comprises the largest living space , and accordingly , is home to the greatest numbers and forms of life on earth . it is practically incomprehensible in scope . but it is not so big , so vast , so extraordinary as to be untouchable . in fact , with roughly 50 % of the world 's population living within 100 kilometers of the coastline and with most of the remainder living close enough to lakes , rivers , or swamps , all of which ultimately lead to the ocean , virtually every single person on the planet has the opportunity to influence the general health and nature of the world ocean . evidence of human influence is seen in every part of the ocean , no matter how deep , no matter how distant . the ocean defines our planet , but , in a very real sense , we define the ocean .

put another way , that 's enough water to immerse the entire united states under a body of salt water over 132 kilometers tall , a height well beyond the reach of the highest clouds and extending deep into the upper atmosphere . with all that volume , the ocean represents 97 % of earth 's total water content . on top of all that , the ocean contains upwards of 99 % of the world 's biosphere , that is , the spaces and places where life exists .

the ocean currently represents approximately ___ of earth ’ s surface and ___ of earth ’ s total water content .

to understand climate change , think of the game `` tetris . '' for eons , earth has played a version of this game with blocks of carbon . they enter the atmosphere as carbon dioxide gas from volcanoes , decaying plant matter , breathing creatures and the surface of the sea . and they leave the atmosphere when they 're used by plants during photosynthesis , absorbed back into the ocean , or stored in soil and sediment . this game of tetris is called the carbon cycle , and it 's the engine of life on earth . what 's the connection to climate ? well , when that carbon dioxide is in the air , waiting to be reabsorbed , it traps a portion of the sun 's heat , which would otherwise escape to space . that 's why carbon dioxide is called a greenhouse gas . it creates a blanket of warmth , known as the greenhouse effect , that keeps our earth from freezing like mars . the more carbon dioxide blocks hang out in the atmosphere waiting to be cleared , the warmer earth becomes . though the amount of carbon in the atmosphere has varied through ice ages and astroid impacts , over the past 8,000 years the stable climate we know took shape , allowing human civilization to thrive . but about 200 years ago , we began digging up that old carbon that had been stored in the soil . these fossil fuels , coal , oil and natural gas are made from the buried remains of plants and animals that died long before humans evolved . the energy stored inside them was able to power our factories , cars and power plants . but burning these fuels also injected new carbon blocks into earth 's tetris game . at the same time , we cleared forests for agriculture , reducing the earth 's ability to remove the blocks . and since 1750 , the amount of carbon in the atmosophere has increased by 40 % , and shows no sign of slowing . just like in tetris , the more blocks pile up , the harder it becomes to restore stability . the extra carbon dioxide in the atmosphere accelerates the greenhouse effect by trapping more heat near the surface and causing polar ice caps to melt . and the more they melt , the less sunlight they 're able to reflect , making the oceans warm even faster . sea levels rise , coastal populations are threatened with flooding , natural ecosystems are disrupted , and the weather becomes more extreme over time . climate change may effect different people and places in different ways . but , ultimately , it 's a game that we 're all stuck playing . and unlike in tetris , we wo n't get a chance to start over and try again .

that 's why carbon dioxide is called a greenhouse gas . it creates a blanket of warmth , known as the greenhouse effect , that keeps our earth from freezing like mars . the more carbon dioxide blocks hang out in the atmosphere waiting to be cleared , the warmer earth becomes .

how does the greenhouse effect influence the climate on earth ?

translator : tom carter reviewer : bedirhan cinar imagine a microscopic-sized ladder contained in the part of our brain that we 'll label our subconscious . the ladder of inference , which was first proposed by harvard professor chris argyris , is the basis of this model . every time we interact with someone , that experience enters the ladder at the bottom . that same experience zips up the ladder in the blink of an eye , exiting at the top . this process happens thousands of times a day without us knowing it . let 's focus on what happens on each rung of the ladder . on the first rung , we have the raw data and observations of our experience . this is very similar to what someone watching a video recording of our experience would see . moving up to the second rung , we filter in specific information and details from our experience . we unknowingly filter based on our preferences , tendencies , and many other aspects that we believe are important . on to the third rung . we assign meaning to the information we have filtered through . this is where we start to interpret what our information is telling us . on our fourth rung , a very crucial thing happens . we develop assumptions based on the meaning we created on the previous rung , and we start to blur the distinction between what is fact and what is story . on the fifth rung , we develop conclusions based on our assumptions . this is also where our emotional reactions are created . on the sixth rung , we adjust our beliefs about the world around us , including the person or people involved in our experience of the moment . on the seventh and final rung , we take action based on our adjusted beliefs . still with me ? great ! let 's take a real-life example and run it up the ladder to see how this all works . have you ever been cut off in a parking lot , signal light on as you steer toward your coveted spot , only to slam on your brakes at the last minute as someone pulls in front of you and steals your spot away ? imagine that experience and notice all of the data and observations landing on the first rung of your ladder . now let 's watch what we pay attention to on the second rung . who cares that it 's sunny out and the birds are chirping ? the 50 % off sign outside of your favorite store is meaningless . you filter in the sensation of your grip tightening on the wheel , you feel your blood pressure rise , you hear the squeal of your brakes , and you notice the expression on the face of the other driver as he pulls in front of you and quickly looks away . time for our third rung . ever since you were young , your parents taught you the importance of waiting in line and taking your turn . you live and die by the rule of first come , first served . and now this guy has just stolen your spot . what gives ? up to the fourth rung we go . watch closely as our assumptions take over and our story creates itself . `` that stupid jerk , did n't his parents teach him anything ? how could he not see my signal light ? he must never pay attention ! why does he think he 's more important than anyone else ? '' jumping quickly to the fifth rung , we conclude that this guy is heartless , inconsiderate , he needs to be taught a lesson and put in his place . we feel angry , frustrated , vindictive , justified . on our sixth rung , we adjust our beliefs based on the experience . `` that 's the last time i give in ! next time someone tries to cut me off , tires will be smoking on the pavement as i squeal past them into my spot . '' and finally our last rung : we take action . we back up , pull up behind his car , honk our horn , and roll down our window to scream a few choice words as well . now imagine , he walks over quickly , apologizing . his wife , who 's almost due with their first baby , called him from inside the mall to say she is in labor and needs to get to the hospital immediately . we 're momentarily shocked , apologize profusely , and wish him luck as he rushes toward the entrance . what just happened here ? what changed ? why is this so significant ? in our parking lot example , our beliefs were short-circuited by the ladder of the other individual . `` my wife is in labor , i need to get there quick , there 's a parking spot . whew ! oh , jeez , i cut someone off . i 'd better apologize quickly so they do n't think i 'm a jerk . '' but what if we were able to short-circuit our ladders ourselves ? proactively , by choice ? guess what ? we can ! let 's return to our unique human function of free will . next time you notice yourself reacting to your experience , pay focused attention to your ladder . ask yourself what beliefs are at play , where do they come from ? what data and observations did you filter in as a result of your beliefs , and why ? are your assumptions valid and supported by facts ? would a different set of assumptions create different feelings , and result in new and better conclusions and actions ? we all have our own unique ladder . be mindful of yours , and help others to see theirs .

would a different set of assumptions create different feelings , and result in new and better conclusions and actions ? we all have our own unique ladder . be mindful of yours , and help others to see theirs .

why do you suppose that the creator of this concept decided to use a ladder as his visual representation ? what else could be used in place of a ladder ?

translator : tom carter reviewer : bedirhan cinar as you can imagine , 400 years ago , navigating the open ocean was difficult . the winds and currents pushed and pulled ships off course , and so sailors based their directions on the port they left , attempting to maintain an accurate record of the ship 's direction and the distance sailed . this process was known as dead reckoning , because being just half a degree off could result in sailing right past the island that lay several miles just over the horizon . this was an easy mistake to make . thankfully , three inventions made modern navigation possible : sextants , clocks and the mathematics necessary to perform the required calculations quickly and easily . all are important . without the right tools , many sailors would be reluctant to sail too far from the sight of land . john bird , an instrument maker in london , made the first device that could measure the angle between the sun and the horizon during the day , called a sextant . knowing this angle was important , because it could be compared to the angle back in england at the exact same time . comparing these two angles was necessary to determine the longitude of the ship . clocks came next . in 1761 , john harrison , an english clockmaker and carpenter , built a clock that could keep accurate time at sea . the timepiece that could maintain accurate time while on a pitching , yawing deck in harsh conditions was necessary in order to know the time back in england . there was one catch though : since such a timepiece was handmade , it was very expensive . so an alternate method using lunar measurements and intense calculations was often used to cut costs . the calculations to determine a ship 's location for each measurement could take hours . but sextants and clocks were n't useful unless sailors could use these tools to determine their position . fortunately , in the 1600s , an amateur mathematician had invented the missing piece . john napier toiled for more than 20 years in his castle in scotland to develop logarithms , a calculation device . napier 's ideas on logarithms involved the form of one over e and the constant 10 to the seventh power . algebra in the early 1600s was not fully developed , and napier 's logarithm of one did not equal zero . this made the calculations much less convenient than logarithms with a base of 10 . henry briggs , a famous mathematician at gresham college in london , read napier 's work in 1614 , and the following year made the long journey to edinburgh to meet napier . briggs showed up unannounced at napier 's castle door and suggested that john switch the base and form of his logarithms into something much simpler . they both agreed that a base of 10 with the log of one equal to zero would greatly simplify everyday calculations . today we remember these as briggs common logarithms . until the development of electric calculating machines in the 20th century , any calculations involving multiplication , division , powers , and extraction of roots with large and small numbers were done using logarithms . the history of logarithms is n't just a lesson in math . there were many players responsible for successful navigation . instrument makers , astronomers , mathematicians , and of course sailors . creativity is n't only about going deep into one 's field of work , it 's about cross-pollination between disciplines too .

the calculations to determine a ship 's location for each measurement could take hours . but sextants and clocks were n't useful unless sailors could use these tools to determine their position . fortunately , in the 1600s , an amateur mathematician had invented the missing piece .

obviously , we no longer use sextants and clocks to navigate the sea . name three inventions that have carried us past the use of logarithms .

so this sample , it ’ s a very , very interesting sample ; it ’ s arsenic . so this is quality arsenic . so arsenic used to much more common in the community than it is nowadays . it was used as a pigment in the nineteenth century for green wallpaper contained copper arsenite , because there weren ’ t any other good green pigments to make the wallpaper . and when the rooms were damp , victorians didn ’ t like opening the windows in their rooms , then mould would grow on the wall . and because arsenic is poisonous to most life forms the mould would convert the arsenic into a volatile compound , trimethylarsine , and the trimethylarsine went into the air and several people were killed by the arsenic coming from their wall paper . now arsenic as we know is very toxic and there have been a number of very high profile and very famous cases of people that have poisoned perhaps their partners or their business partners using arsenic . okay , so i ’ m going to very carefully take this vial out . he says very carefully then knocks it really hard . arsenic was also used quite widely by people to dispose of husbands , wives , lovers . though now it is much less common . it is used in the electronics industry for getting electronic properties for making transistors . and also it is still sometimes used for medication for feeding to livestock . it is only quite recently that the use of arsenic has been banned as an additive to chicken feed in the united states . so here you see the arsenic powder okay . now this is a metallic very dark metal , but i ’ m not going to open this because like i said it ’ s very , very toxic . it ’ s a very dark metallic sample , you can see a very fine powder in the bottom of this vial . now i ’ m going to put this back in before i get any on my skin because it ’ s a very toxic material and i don ’ t want to expose myself .

so this sample , it ’ s a very , very interesting sample ; it ’ s arsenic . so this is quality arsenic . so arsenic used to much more common in the community than it is nowadays . it was used as a pigment in the nineteenth century for green wallpaper contained copper arsenite , because there weren ’ t any other good green pigments to make the wallpaper .

what is the most common allotrope of arsenic you can find in nature at room temperature and atmospheric pressure ?

i 'm mckenna pope . i 'm 14 years old . and when i was 13 , i convinced one of the largest toy companies , toy makers in the world , hasbro , to change the way that they marketed one of their best-selling products . so , allow me to tell you about it . so , i have a brother , gavin . when this whole shebang happened , he was four . he loved to cook . he was always getting ingredients out of the fridge and mixing them into these , needless to say , uneatable concoctions or making invisible macaroni and cheese . he wanted to be a chef really badly . and , so what better gift for someone , for a kid who wanted to be a chef , than an easy bake oven , right ? i mean , we all had those when we were little . and he wanted one so badly . but then , he started to realize something . in the commercials and on the boxes for the easy bake oven , hasbro marketed them specifically to girls . and the way that they did this was they would only feature girls on the boxes or in the commercials , and there would be flowery prints all over the ovens , and it would be in bright pink and purple . very gender-specific colors to females , right ? so , it kind of was sending a message that only girls are supposed to cook . boys are n't . and this discouraged my brother a lot . he thought that he was n't supposed to want to be a chef . because that was something girls did . girls cooked , boys did n't . or so , the message that hasbro was sending . and this got me thinking , `` god , i wish there was a way i could change this , that i could have my voice heard by hasbro , so i could ask them and tell them what they were doing wrong and ask them to change it . '' and that got me thinking about a website that i had learned about a few months prior called change.org . change.org is an online petition-sharing platform , where you can create a petition and share it across all these social media networks , through facebook , through twitter , through youtube , through reddit , through tumblr , through whatever you can think of . and so , i created a petition , along with a youtube video that i added to the petition , basically asking hasbro to change the way that they marketed it , in featuring boys in the commercials and on the boxes , and most of all creating them in less gender-specific colors . so , this petititon started to take off , like humongously fast , you have no idea . i was getting interviewed by all these national news outlets and press outlets , and it was amazing . in three weeks , maybe three and a half , i had 46,000 signatures on this petition . ( applause ) thank you . so , needless to say , it was crazy . eventually , hasbro themselves invited me to their headquarters so they could go and unveil their new easy bake oven product to me , in black , silver and blue . it was literally one of the best moments of my life . it was like `` willy wonka and the chocolate factory . '' that thing was amazing . what i did n't realize at the time , however , was that i had become an activist . i could change something that , even as a kid , or maybe even especially as a kid , my voice mattered . and your voice matters , too ! i want to let you know that it 's not going to be easy , and it was n't easy for me because i faced a lot of obstacles . people online , and sometimes even in real life , were disrespectful to me and my family and talked about how the whole thing was a waste of time , and it really discouraged me . and actually , i have some examples because what 's better revenge than displaying their idiocy ? so , let 's see . from username liquidsword29 , interesting usernames we have here , `` disgusting liberal moms making their son 's gay . '' liquidsword29 , really ? really ? okay , how about from whiteboy77ags , `` people always need something to 'female dog ' about . '' from jeffrey gutierrez , `` omg shut up ! you just want money and attention . '' so , it was comments like these that really discouraged me from wanting to make change in the future because i thought , `` people do n't care . people think it 's a waste of time . and people are going to be disrespectful to me and my family . '' it hurt me . and it made me think , `` what 's the point in making change in the future ? '' but then i started to realize something . haters gon na hate . come on , say it with me ! one , two , three , haters gon na hate ! so let your haters hate , you know what ! and make your change because i know you can . i look out into this crowd , and i see 400 people who came out because they wanted to know how they could make a change . and i know that you can , and all of you watching at home can , too , because you have so much that you can do and that you believe in . and you can trade it across all the social media , through facebook , through twitter , through youtube , through reddit , through tumblr , through whatever else you can think of . and you can make that change . you can take what you believe in and turn it into a cause and change it . and that spark that you 've been hearing about all day today you can use that spark that you have within you and turn it into a fire . thank you . ( applause )

but then , he started to realize something . in the commercials and on the boxes for the easy bake oven , hasbro marketed them specifically to girls . and the way that they did this was they would only feature girls on the boxes or in the commercials , and there would be flowery prints all over the ovens , and it would be in bright pink and purple .

as of december 2012 , what percentage of easy bake oven commercials were targeted towards both genders :

okay weíre going to be looking today at copper . this is something looking back at the old video , itís a short video and there isnít any experimentation in it so i thought weíd do something a bit practical . copper is an element which people are very familiar with because itís such a characteristic coloured metal , sort of reddish colour , though it gets darker when oxide forms . but itís quite a soft metal and you can cut it quite easily if you have a cutter like this which has steel blades , it will just dig into the metal and it should just cut off . when you cut the metal you get this very nice , shiny , fresh surface coloured just like copper . this is a ball of copper , copper metal . as you might imagine itís a ball of metal so therefore it is quite dense and heavy . i mean itís not as dense as , i think steve told me this morning , that if we had a ball this size of plutonium he told me it would weigh about a kilo and a half so he thought . so itís not quite as heavy as that but still itís pretty heavy and dense . so this is a very , very nice sample of very fine copper wire . so the copper wire here is , what width is this ? this isö phew ! point zero , iím not even going toöthatís just too small , so itís point one of a millimetre . so inside the beaker weíve got a solution called sodium potassium tartrate , so no copper in there at the moment . weíre going to introduce that through this . this is a solution of copper sulphate . copper is very popular for architectural use because if you put it on the roofs of buildings it then reacts , particularly with carbon dioxide in the air , to give a very nice green colour . first of all though we need to heat this to about 50∞c , and to the sodium potassium tartrate we need to add some very weak , hydrogen peroxide so this is only 3 % hydrogen peroxide , so in it goes . we need to make sure they mix together which is why thereís a stirring bar at the bottom there stirring away . okay so thatís stirring nicely , so as i said sodium potassium tartrate and hydrogen peroxide and we need to add only one mill so thatís 1cm3 of the copper sulphate . the copper wire here is very , very high grade , this is grade one copper wire and itís point one of a millimetre in diameter and you can see the wonderful copperas lustre coming off the side there . what do you mean by grade one copper ? so this is very high purity , this is like 99.99 % copper , used for electronics fabrications and high quality research samples . itís also used for electrical wiring , in fact itís used so much that in a country like the uk each person has about 175 kilos of copper associated with each person , in the piping , the wiring and so on . the problem is that in many other countries , for example in china , people have very much less copper associated with them , there isnít so much electrical wiring in rural parts of china . and if everybody in china had the same amount of copper associated with them as those in england or america or canada there wouldnít be enough copper in all the known deposits around the world . copper is actually necessary for life , plants and animals use copper . but actually you can have a disease called wilsonís disease which basically your body canít metabolise copper properly , itís actually an inherited disease . ready ? whatís going on there is itís producing a lot of gas so itís reacting to form a complex . and itís going from the potassium tartrate complex there to well , its producing carbon dioxide and oxygen , mainly oxygen gas is being produced which is why youíre seeing the fizzing . and itís become copper oxide , cuprous oxide actually . copper is found as a metal lying around in various places in the world . i believe the name came from the island of cyprus in the middle of the mediterranean , but copper has always been know even in pre-historic times people found small amounts of copper . but as we use more and more copper people have had to dig deeper and deeper mines . the mine in chile where those very brave miners were entombed for more than two months and then rescued was a copper mine . and to get the metal that we need weíre going to have to go deeper and deeper and deeper into the earth . so what weíve got in there now is cuprous oxide itís copper 1 oxide . and itís actually gone from what was a kind of clear see-through , all right itís got a colour on it , but see-through solution to something thatís very cloudy . so what weíve got there is a precipitate of copper oxide . copper is very good because it has very high thermal and electrical conductivity . what that means is that heat flows through it very well and also electricity . if you make wires for electrical transmission out of copper , when the electricity goes through them you get very much less heating than say if you made the wires out of iron , and all this heating is of course lost energy . youíd do even better if you made the wires out of silver , but silver is too expensive . ok . so letís see if we can change this reaction back . so at the moment it started out as being about 50∞c and itís shot up to about 63∞c , i imagine it was even hotter than that when it originally changed colour . so weíll see if we can take it back , iíll put that back in . i actually bought this from the british geological survey which is just down the road from here , i think it is in keyworth i think . and i just saw this and it was a christmas present from my husband and i picked it out . i just think itís really cool actually . what did your husband think of getting that as a christmas present ? he knows what iím like ! so he buys these things for me he knows iím a bit of a magpie , i like to collect shiny things , and pretty things , thatís my copper . so the colour is gradually changing , itís gone from orange and now kind of a murky yellow . you can see itís kind of green now . and again a gradual change , it wasnít a sudden spontaneous straight back to being blue and see-through , you know clear . now weíve got back to that clear solution . and again you can see on the stirrer bar all the bubbles of the oxygen , little bit of c02 forming on that . most organisms , you and me , use iron in our blood to transport oxygen , thatís what makes our blood red . but in some sorts of crustaceans , crabs and lobsters , theyíre different they use copper . they use a compound called hemocyanin , itís a blue compound of copper . cyanine is some classical word for blue . so they really have blue blood . and these hemocyanin use two atoms of copper in each molecule to transport the oxygen around the body of the crab or lobster . but itís not nearly as good as haemoglobin , so if you start running after a crab or lobster it quickly gets tired compared to running after a rabbit or something like that , which can keep going faster than you can .

when you cut the metal you get this very nice , shiny , fresh surface coloured just like copper . this is a ball of copper , copper metal . as you might imagine itís a ball of metal so therefore it is quite dense and heavy .

what is the color of copper sulfate and many copper compounds ?

translator : andrea mcdonough reviewer : bedirhan cinar great weather we 're having ! awesome job ! you 're a tremendous athlete ! compliments , right ? well , maybe . depending on the attitude and tone of voice behind these lines , they very well may be compliments . they may also be , though , pointed and attacking lines . this slight change of attitude behind the lines reveals what we call verbal irony . so when someone says , `` great weather we 're having , '' it is quite possible that the person really means that if the sun is shining , the birds are singing , and the wind is calm . but if the weather is horrible , the clouds are looming , and the wind is a raging tempest , and someone says , `` great weather we 're having , '' he probably does n't actually mean that . he probably means that the weather is horrible , but he has said the opposite . this is verbal irony when the speaker says the opposite of what he means . i know what you 're thinking . is n't this sarcasm , is n't the speaker being sarcastic ? yes . when a speaker says the opposite of what he means , that is verbal irony . when a speaker then goes the step farther to mean the opposite of what he says and seeks to be a little pointed and mean , like he 's making fun of something , then you have sarcasm . take the second example : `` awesome job ! '' someone accomplishing his life-long dream : awesome ! someone winning a sports championship : awesome ! someone rear-ends another car : not awesome . so when the passenger says , `` awesome job ! '' they probably mean the opposite with a hint of poking fun . that is verbal irony and that is sarcastic . `` you 're a talented athlete , '' said to an olympian : authentic , no verbal irony present . said to the klutzy kid tripping into english class and spilling his books and pencil case all over the room , now that is just harsh and verbally ironic because what you said is not what you meant . that is verbal irony . you have said the opposite of what you mean . additionally , since you have the intention of mocking this poor person , you have not only been verbally ironic , but sarcastic as well . beware , though . while all sarcasm fits the definition of verbal irony , not all verbal irony is sarcastic . verbal irony is where what is meant is the opposite of what is said , while sarcasm adds that little punch of attitude . there are times , though , where another layer of meaning can be present without that sarcastic tone . alright , now go out there and find those examples of verbal irony and sarcasm . good luck ! no , seriously , i mean it , good luck . no , no , really , i truly want to wish you luck on this difficult task . ok , ok , sincerely good luck . you can do it ! no verbal irony here .

said to the klutzy kid tripping into english class and spilling his books and pencil case all over the room , now that is just harsh and verbally ironic because what you said is not what you meant . that is verbal irony . you have said the opposite of what you mean .

verbal irony and compliments are basically the same thing .

translator : tom carter reviewer : bedirhan cinar dialogue gives a story color , makes it exciting and moves it forward . romeo : o , wilt thou leave me so unsatisfied ? juliet : what satisfaction canst thou have tonight ? romeo : the exchange of thy love 's faithful vows for mine . without dialogue : ( cricket sounds ) so what goes into writing effective dialogue ? well , there are social skills : making friends , solving conflicts , being pleasant and polite . we wo n't be using any of those today . instead , we 'll be working on -- let 's call them `` anti-social skills . '' if you 're a writer , you may already have a few of these . the first is eavesdropping . if you 're riding a bus and hear an interesting conversation , you could write it all down . of course , when you write fiction , you 're not describing real people , you 're making up characters . but sometimes the words you overhear can give you ideas . `` i did not , '' says one person . `` i saw you , '' the other replies . who might be saying those words ? maybe it 's two kids in a class , and the boy thinks the girl pushed him . maybe it 's a couple , but one of them is a vampire , and the woman vampire saw the man flirting with a zombie . or maybe not . maybe the characters are a teenager and his mother , and they 're supposed to be vegetarians , but the mother saw him eating a burger . so let 's say you 've decided on some characters . this is anti-social skill number two : start pretending they 're real . what are they like ? where are they from ? what music do they listen to ? spend some time with them . if you 're on a bus , think about what they might be doing if they were there too . would they talk on the phone , listen to music , draw pictures , sleep ? what we say depends on who we are . an older person might speak differently than a younger person . someone from the south might speak differently than someone from the north . once you know your characters , you can figure out how they talk . at this stage , it 's helpful to use anti-social skill number three : muttering to yourself . when you speak your character 's words , you can hear whether they sound natural , and fix them if necessary . remember , most people are usually pretty informal when they speak . they use simple language and contractions . so , `` do not attempt to lie to me '' sounds more natural as `` do n't try to lie to me . '' also keep it short . people tend to speak in short bursts , not lengthy speeches . and let the dialogue do the work . ask yourself : do i really need that adverb ? for instance , `` 'your money or your life , ' she said threateningly . '' here , `` threateningly '' is redundant , so you can get rid of it . but if the words and the actions do n't match , an adverb can be helpful . `` 'your money or your life , ' she said lovingly . '' so , to recap : first , eavesdrop . next , pretend imaginary people are real . finally , mutter to yourself , and write it all down . you already have everything you need . this is fictional dialogue , or `` how to hear voices in your head . ''

romeo : the exchange of thy love 's faithful vows for mine . without dialogue : ( cricket sounds ) so what goes into writing effective dialogue ? well , there are social skills : making friends , solving conflicts , being pleasant and polite .

why might an author add dialogue to a story ?

they say that if walls could talk , each building would have a story to tell , but few would tell so many fascinating stories in so many different voices as the hagia sophia , or holy wisdom . perched at the crossroads of continents and cultures , it has seen massive changes from the name of the city where it stands , to its own structure and purpose . and today , the elements from each era stand ready to tell their tales to any visitor who will listen . even before you arrive at the hagia sophia , the ancient fortifications hint at the strategic importance of the surrounding city , founded as byzantium by greek colonists in 657 bce . and successfully renamed as augusta antonia , new rome and constantinople as it was conquered , reconquered , destroyed and rebuilt by various greek , persian and roman rulers over the following centuries . and it was within these walls that the first megale ekklesia , or great church , was built in the fourth century . though it was soon burned to the ground in riots , it established the location for the region 's main religious structure for centuries to come . near the entrance , the marble stones with reliefs are the last reminders of the second church . built in 415 ce , it was destroyed during the nika riots of 532 when angry crowds at a chariot race nearly overthrew the emperor , justinian the first . having barely managed to retain power , he resolved to rebuild the church on a grander scale , and five years later , the edifice you see before you was completed . as you step inside , the stones of the foundation and walls murmur tales from their homelands of egypt and syria , while columns taken from the temple of artemis recall a more ancient past . runic inscriptions carved by the vikings of the emperor 's elite guard carry the lore of distant northern lands . but your attention is caught by the grand dome , representing the heavens . reaching over 50 meters high and over 30 meters in diameter and ringed by windows around its base , the golden dome appears suspended from heaven , light reflecting through its interior . beneath its grandiose symbolism , the sturdy reinforcing corinthian columns , brought from lebanon after the original dome was partially destroyed by an earthquake in 558 ce , quietly remind you of its fragility and the engineering skills such a marvel requires . if a picture is worth a thousand words , the mosaics from the next several centuries have the most to say not only about their biblical themes , but also the byzantine emperors who commissioned them , often depicted along with christ . but beneath their loud and clear voices , one hears the haunting echoes of the damaged and missing mosaics and icons , desecrated and looted during the latin occupation in the fourth crusade . within the floor , the tomb inscription of enrico dandolo , the venetian ruler who commanded the campaign , is a stark reminder of those 57 years that hagia sophia spent as a roman catholic church before returning to its orthodox roots upon the byzantine reconquest . but it would not remain a church for long . weakened by the crusades , constantinople fell to the ottomans in 1453 and would be known as istanbul thereafter . after allowing his soldiers three days of pillage , sultan mehmed the second entered the building . though heavily damaged , its grandeur was not lost on the young sultan who immediately rededicated it to allah , proclaiming that it would be the new imperial mosque . the four minarets built over the next century are the most obvious sign of this era , serving as architectural supports in addition to their religious purpose . but there are many others . ornate candle holders relate suleiman 's conquest of hungary , while giant caligraphy discs hung from the ceiling remind visitors for the first four caliphs who followed muhammad . though the building you see today still looks like a mosque , it is now a museum , a decision made in 1935 by kemal ataturk , the modernizing first president of turkey following the ottoman empire 's collapse . it was this secularization that allowed for removal of the carpets hiding the marble floor decorations and the plaster covering the christian mosaics . ongoing restoration work has allowed the multiplicity of voices in hagia sophia 's long history to be heard again after centuries of silence . but conflict remains . hidden mosaics cry out from beneath islamic calligraphy , valuable pieces of history that can not be uncovered without destroying others . meanwhile , calls sound from both muslim and christian communities to return the building to its former religious purposes . the story of the divine wisdom may be far from over , but one can only hope that the many voices residing there will be able to tell their part for years to come .

ornate candle holders relate suleiman 's conquest of hungary , while giant caligraphy discs hung from the ceiling remind visitors for the first four caliphs who followed muhammad . though the building you see today still looks like a mosque , it is now a museum , a decision made in 1935 by kemal ataturk , the modernizing first president of turkey following the ottoman empire 's collapse . it was this secularization that allowed for removal of the carpets hiding the marble floor decorations and the plaster covering the christian mosaics .

mustafa kemal became the modernizing president of turkey and he ________ .

if you 've got a cold , mucus is hard to miss . but what is it , and what does it do besides making you miserable ? your body produces more than a liter of mucus every day , and all the wet surfaces of your body that are not covered by skin , like your eyes , nose , mouth , lungs , and stomach get a liberal coating . that 's why they 're known as mucus membranes . mucus plays lots of roles in your body . it keeps delicate tissues from drying out and cracking , which would expose them to infection . it lubricates your eyes so you can blink . it protects your stomach lining from acid . it neutralizes threats by removing or trapping substances that could make you sick . and finally , it houses and keeps your body 's trillions of bacterial inhabitants , your microbiota , under control . mucus contains lots of different compounds , including proteins , fats , and salts . but a key component of mucus versatility is a set of proteins called mucins . mucins are the primary large molecules in mucus and are essential for giving mucus its slippery feel . they belong to a class of proteins called glycoproteins which are built out of both amino acids and sugars . in mucin , long chains of sugars are attached to specific amino acids in the protein backbone . the hydrophilic sugar chains help mucin dissolve in your body 's watery fluids . mucus , which is up to 90 % water , stays hydrated thanks to these sugar chains . some of these mucins can interact with other mucin molecules to create a complex network that establishes a barrier against pathogens and other invaders . that 's why mucus is the body 's first line of defense against foreign objects , like bacteria and dust . it 's continuously produced to clear them from the respiratory tract , like a slimy conveyor belt . this keeps bacteria from getting a solid purchase on delicate lung tissue , or making it to the blood stream , where they could cause a major infection . many of those harmful bacteria also cause diseases when they cluster into slimy growths called biofilms . but mucus contains mucins , antimicrobial peptides , antibodies , and even bacteria-hungry viruses called bacteriophages that all work together to prevent biofilms from forming . if microbes do become harmful and you get sick , the body ramps up mucus production to try to quickly flush out the offenders , and the immune system floods your mucus with extra white blood cells . in fact , the greenish mucus often associated with infections gets its color from an enzyme produced by those white blood cells . this multi-pronged approach to bacterial management is one of the main reasons why we 're not sick all the time . even though mucus protects against the infectious bacteria , the vast majority of your body 's bacterial tenants are not harmful , and many are actually beneficial . that 's particularly true when they live in mucus , where they can perform important functions , like synthesizing vitamins , suppressing harmful inflammation , and controlling the growth of more harmful species . so even though you probably associate mucus with being ill , it 's really helping you stay healthy . sure , it might seem gross , but can you think of any other substance that can lubricate , keep your body clean , fight infection , and domesticate a teeming bacterial population ? nope , just mucus .

it neutralizes threats by removing or trapping substances that could make you sick . and finally , it houses and keeps your body 's trillions of bacterial inhabitants , your microbiota , under control . mucus contains lots of different compounds , including proteins , fats , and salts .

which of the following does your microbiota not do ?

it 's the first sense you use when you 're born . one out of every fifty of your genes is dedicated to it . it must be important , right ? okay , take a deep breath through your nose . it 's your sense of smell , and it 's breathtakingly powerful . as an adult , you can distinguish about 10,000 different smells . here 's how your nose does it . smell starts when you sniff molecules from the air into your nostrils . 95 % of your nasal cavity is used just to filter that air before it hits your lungs . but at the very back of your nose is a region called the olfactory epithelium , a little patch of skin that 's key to everything you smell . the olfactory epithelium has a layer of olfactory receptor cells , special neurons that sense smells , like the taste buds of your nose . when odor molecules hit the back of your nose , they get stuck in a layer of mucus covering the olfactory epithelium . as they dissolve , they bind to the olfactory receptor cells , which fire and send signals through the olfactory tract up to your brain . as a side note , you can tell a lot about how good an animal 's sense of smell is by the size of its olfactory epithelium . a dog 's olfactory epithelium is 20 times bigger than your puny human one . but there 's still a lot we do n't know about this little patch of cells , too . for example , our olfactory epithelium is pigmented , and scientists do n't really know why . but how do you actually tell the difference between smells ? it turns out that your brain has 40 million different olfactory receptor neurons , so odor a might trigger neurons 3 , 427 , and 988 , and odor b might trigger neurons 8 , 76 , and 2,496,678 . all of these different combinations let you detect a staggeringly broad array of smells . olfactory neurons are always fresh and ready for action . they 're the only neuron in the body that gets replaced regularly , every four to eight weeks . once they are triggered , the signal travels through a bundle called the olfactory tract to destinations all over your brain , making stops in the amygdala , the thalamus , and the neocortex . this is different from how sight and sound are processed . each of those signals goes first to a relay center in the middle of the cerebral hemisphere and then out to other regions of the brain . but smell , because it evolved before most of your other senses , takes a direct route to these different regions of the brain , where it can trigger your fight-or-flight response , help you recall memories , or make your mouth water . but even though we 've all got the same physiological set-up , two nostrils and millions of olfactory neurons , not everybody smells the same things . one of the most famous examples of this is the ability to smell so-called `` asparagus pee . '' for about a quarter of the population , urinating after eating asparagus means smelling a distinct odor . the other 75 % of us do n't notice . and this is n't the only case of smells differing from nose to nose . for some people , the chemical androstenone smells like vanilla ; to others , it smells like sweaty urine , which is unfortunate because androstenone is commonly found in tasty things like pork . so with the sweaty urine smellers in mind , pork producers will castrate male pigs to stop them from making androstenone . the inability to smell a scent is called anosmia , and there are about 100 known examples . people with allicin anosmia ca n't smell garlic . those with eugenol anosmia ca n't smell cloves . and some people ca n't smell anything at all . this kind of full anosmia could have several causes . some people are born without a sense of smell . others lose it after an accident or during an illness . if the olfactory epithelium gets swollen or infected , it can hamper your sense of smell , something you might have experienced when you were sick . not being able to smell anything can mess with your other senses , too . many people who ca n't smell at all also ca n't really taste the same way the rest of us do . it turns out that how something tastes is closely related to how it smells . as you chew your food , air is pushed up your nasal passage , carrying with it the smell of your food . those scents hit your olfactory epithelium and tell your brain a lot about what you 're eating . without the ability to smell , you lose the ability to taste anything more complicated than the five tastes your taste buds can detect : sweet , salty , bitter , sour , and savory . so , the next time you smell exhaust fumes , salty sea air , or roast chicken , you 'll know exactly how you 've done it and , perhaps , be a little more thankful that you can .

all of these different combinations let you detect a staggeringly broad array of smells . olfactory neurons are always fresh and ready for action . they 're the only neuron in the body that gets replaced regularly , every four to eight weeks .

olfactory neurons are the only neurons that are replaced on a regular basis .

`` some are born great , some achieve greatness , and others have greatness thrust upon them '' , quoth william shakespeare . or did he ? some people question whether shakespeare really wrote the works that bear his name , or whether he even existed at all . they speculate that shakespeare was a pseudonym for another writer , or a group of writers . proposed candidates for the real shakespeare include other famous playwrights , politicians and even some prominent women . could it be true that the greatest writer in the english language was as fictional as his plays ? most shakespeare scholars dismiss these theories based on historical and biographical evidence . but there is another way to test whether shakespeare 's famous lines were actually written by someone else . linguistics , the study of language , can tell us a great deal about the way we speak and write by examining syntax , grammar , semantics and vocabulary . and in the late 1800s , a polish philosopher named wincenty lutosławski formalized a method known as stylometry , applying this knowledge to investigate questions of literary authorship . so how does stylometry work ? the idea is that each writer 's style has certain characteristics that remain fairly uniform among individual works . examples of characteristics include average sentence length , the arrangement of words , and even the number of occurrences of a particular word . let 's look at use of the word thee and visualize it as a dimension , or axis . each of shakespeare 's works can be placed on that axis , like a data point , based on the number of occurrences of that word . in statistics , the tightness of these points gives us what is known as the variance , an expected range for our data . but , this is only a single characteristic in a very high-dimensional space . with a clustering tool called principal component analysis , we can reduce the multidimensional space into simple principal components that collectively measure the variance in shakespeare 's works . we can then test the works of our candidates against those principal components . for example , if enough works of francis bacon fall within the shakespearean variance , that would be pretty strong evidence that francis bacon and shakespeare are actually the same person . what did the results show ? well , the stylometrists who carried this out have concluded that shakespeare is none other than shakespeare . the bard is the bard . the pretender 's works just do n't match up with shakespeare 's signature style . however , our intrepid statisticians did find some compelling evidence of collaborations . for instance , one recent study concluded that shakespeare worked with playwright christopher marlowe on `` henry vi , '' parts one and two . shakespeare 's identity is only one of the many problems stylometry can resolve . it can help us determine when a work was written , whether an ancient text is a forgery , whether a student has committed plagiarism , or if that email you just received is of a high priority or spam . and does the timeless poetry of shakespeare 's lines just boil down to numbers and statistics ? not quite . stylometric analysis may reveal what makes shakespeare 's works structurally distinct , but it can not capture the beauty of the sentiments and emotions they express , or why they affect us the way they do . at least , not yet .

could it be true that the greatest writer in the english language was as fictional as his plays ? most shakespeare scholars dismiss these theories based on historical and biographical evidence . but there is another way to test whether shakespeare 's famous lines were actually written by someone else .

research and describe the shakespeare identity debate . how have scholars framed their arguments over the decades ? what tools did they use to analyze evidence surrounding the identity of shakespeare ?

let 's say you 're on a game show . you 've already earned $ 1000 in the first round when you land on the bonus space . now , you have a choice . you can either take a $ 500 bonus guaranteed or you can flip a coin . if it 's heads , you win $ 1000 bonus . if it 's tails , you get no bonus at all . in the second round , you 've earned $ 2000 when you land on the penalty space . now you have another choice . you can either take a $ 500 loss , or try your luck at the coin flip . if it 's heads , you lose nothing , but if it 's tails , you lose $ 1000 instead . if you 're like most people , you probably chose to take the guaranteed bonus in the first round and flip the coin in the second round . but if you think about it , this makes no sense . the odds and outcomes in both rounds are exactly the same . so why does the second round seem much scarier ? the answer lies in a phenomenon known as loss aversion . under rational economic theory , our decisions should follow a simple mathematical equation that weighs the level of risk against the amount at stake . but studies have found that for many people , the negative psychological impact we feel from losing something is about twice as strong as the positive impact of gaining the same thing . loss aversion is one cognitive bias that arises from heuristics , problem-solving approaches based on previous experience and intuition rather than careful analysis . and these mental shortcuts can lead to irrational decisions , not like falling in love or bungee jumping off a cliff , but logical fallacies that can easily be proven wrong . situations involving probability are notoriously bad for applying heuristics . for instance , say you were to roll a die with four green faces and two red faces twenty times . you can choose one of the following sequences of rolls , and if it shows up , you 'll win $ 25 . which would you pick ? in one study , 65 % of the participants who were all college students chose sequence b even though a is shorter and contained within b , in other words , more likely . this is what 's called a conjunction fallacy . here , we expect to see more green rolls , so our brains can trick us into picking the less likely option . heuristics are also terrible at dealing with numbers in general . in one example , students were split into two groups . the first group was asked whether mahatma gandhi died before or after age 9 , while the second was asked whether he died before or after age 140 . both numbers were obviously way off , but when the students were then asked to guess the actual age at which he died , the first group 's answers averaged to 50 while the second group 's averaged to 67 . even though the clearly wrong information in the initial questions should have been irrelevant , it still affected the students ' estimates . this is an example of the anchoring effect , and it 's often used in marketing and negotiations to raise the prices that people are willing to pay . so , if heuristics lead to all these wrong decisions , why do we even have them ? well , because they can be quite effective . for most of human history , survival depended on making quick decisions with limited information . when there 's no time to logically analyze all the possibilities , heuristics can sometimes save our lives . but today 's environment requires far more complex decision-making , and these decisions are more biased by unconscious factors than we think , affecting everything from health and education to finance and criminal justice . we ca n't just shut off our brain 's heuristics , but we can learn to be aware of them . when you come to a situation involving numbers , probability , or multiple details , pause for a second and consider that the intuitive answer might not be the right one after all .

this is an example of the anchoring effect , and it 's often used in marketing and negotiations to raise the prices that people are willing to pay . so , if heuristics lead to all these wrong decisions , why do we even have them ? well , because they can be quite effective .

do heuristics always lead to a wrong choice ?

food does n't last . in days , sometimes hours , bread goes moldy , apple slices turn brown , and bacteria multiply in mayonnaise . but you can find all of these foods out on the shelf at the grocery store , hopefully unspoiled , thanks to preservatives . but what exactly are preservatives ? how do they help keep food edible and are they safe ? there are two major factors that cause food to go bad : microbes and oxidation . microbes like bacteria and fungi invade food and feed off its nutrients . some of these can cause diseases , like listeria and botulism . others just turn edibles into a smelly , slimy , moldy mess . meanwhile , oxidation is a chemical change in the food 's molecules caused by enzymes or free radicals which turn fats rancid and brown produce , like apples and potatoes . preservatives can prevent both types of deterioration . before the invention of artificial refrigeration , fungi and bacteria could run rampant in food . so we found ways to create an inhospitable environment for microbes . for example , making the food more acidic unravels enzymes that microbes need to survive . and some types of bacteria can actually help . for thousands of years , people preserved food using bacteria that produce lactic acid . the acid turns perishable vegetables and milk into longer lasting foods , like sauerkraut in europe , kimchi in korea , and yogurt in the middle east . these cultured foods also populate your digestive track with beneficial microbes . many synthetic preservatives are also acids . benzoic acid in salad dressing , sorbic acid in cheese , and propionic acid in baked goods . are they safe ? some studies suggest that benzoates , related to benzoic acid , contribute to hyperactive behavior . but the results are n't conclusive . otherwise , these acids seem to be perfectly safe . another antimicrobial strategy is to add a lot of sugar , like in jam , or salt , like in salted meats . sugar and salt hold on to water that microbes need to grow and actually suck moisture out of any cells that may be hanging around , thus destroying them . of course , too much sugar and salt can increase your risk of heart disease , diabetes , and high blood pressure , so these preservatives are best in moderation . antimicrobial nitrates and nitrites , often found in cured meats , ward off the bacteria that cause botulism , but they may cause other health problems . some studies linking cured meats to cancer have suggested that these preservatives may be the culprit . meanwhile , antioxidant preservatives prevent the chemical changes that can give food an off-flavor or color . smoke has been used to preserve food for millennia because some of the aromatic compounds in wood smoke are antioxidants . combining smoking with salting was an effective way of preserving meat before refrigeration . for antioxidant activity without a smoky flavor , there are compounds like bht and tocopherol , better known as vitamin e. like the compounds in smoke , these sop up free radicals and stave off rancid flavors that can develop in foods like oils , cheese , and cereal . other antioxidants like citric acid and ascorbic acid help cut produce keep its color by thwarting the enzyme that causes browning . some compounds like sulfites can multitask . they 're both antimicrobials and antioxidants . sulfites may cause allergy symptoms in some people , but most antioxidant preservatives are generally recognized as safe . so should you be worried about preservatives ? well , they 're usually near the end of the ingredients list because they 're used in very small amounts determined by the fda to be safe . nevertheless , some consumers and companies are trying to find alternatives . packaging tricks , like reducing the oxygen around the food can help , but without some kind of chemical assistance , there are very few foods that can stay shelf stable for long .

how do they help keep food edible and are they safe ? there are two major factors that cause food to go bad : microbes and oxidation . microbes like bacteria and fungi invade food and feed off its nutrients . some of these can cause diseases , like listeria and botulism .

which of these compounds wards off microbes by lowering a food ’ s ph ?

a boy named prince tamino runs through a dark wood pursued by a dragon . just as it rears up to devour him , three mysterious ladies appear and slay the dragon with their fierce battle cry . so begins wolfgang amadeus mozart 's `` die zauberflöte , '' or `` the magic flute . '' this fantasy singspiel , a type of folk opera with music and dialogue , premiered in 1791 in vienna . though it may seem like a childish fairytale , this intricate opera is full of subversive symbolism , and it 's now regarded as one of the most influential operas in history . tamino 's run in with the dragon is only the start of his journey . the three women summon their leader , the queen of the night . she , in turn , sends tamino on a quest to rescue her daughter pamina from the evil sorcerer , sarastro . and to help him on his journey , she gives him the titular magic flute . tamino eventually finds pamina at sarastro 's temple , but behind enemy lines , tamino and pamina learn that they 're on the wrong side . the queen of night actually wants to plunge the world into darkness . everything tamino thought he knew was wrong , filling him with doubt and confusion . so , a new quest begins for tamino and pamina . they must pass three trials of wisdom , and only then can the day vanquish the night . helped by the flute 's magic power , the two youths overcome these trials and the queen 's attempts to sabotage them . they 're finally initiated into the temple having restored balance to the kingdom . many elements in this peculiar fairytale were inspired by mozart 's involvement in freemasonry , a network of fraternal organizations throughout europe . much of their history , symbolism , and ritual came from the middle ages . but the freemasons of mozart 's time were also influenced by 18th century european ideals - rationalism , humanism , and skepticism towards traditional authorities , like monarchy and the church . the symbols of freemasonry and these ideals of the enlightenment are found throughout the opera . if this sounds like a conspiracy theory , that 's because it sort of was at the time , but it 's now taken quite seriously and has been the subject of considerable scholarly publication . for example , some mozart scholars believe the queen of the night symbolizes maria theresa , the empress of the holy roman empire who opposed freemasonry and banned it in austria . while there continues to be debate as to the specific meaning , interpretation , and location of these masonic references , scholars agree that they 're there and are fully intentional . one of these symbols is the number three , which represented balance and order to freemasons . now the number three is , of course , easy to find in any work of storytelling , but it 's particularly prominent in `` the magic flute '' : three trials , three ladies , three spirits , and three doors , much of the music is written in e-flat major , which has three flats in its key signature , and historically , masonic rituals began with three knocks . the opera references them by opening with three majestic chords complete with dramatic pauses . those chords , which reoccur throughout the opera , serve another purpose . they capture the dramatic arc of the opera in miniature . the first chord , e-flat major , is in its most natural root position , simple and unadorned . it echoes the child-like prince tamino , who , in his naiveté , accepts everything the queen and her ladies say without question . the second chord is c minor , a sour sonority that mirrors tamino 's sadness and doubt in the middle of the opera . that 's when his world and notions of good and evil get turned on their heads . and good and evil are just two of the opera 's extreme opposites . it features some of the highest and lowest notes in opera , day and night , simple hummable melodies and complicated forward-looking music . the opera 's central theme concerns balancing these extremes to achieve perfect harmony . to reflect this , the final chord in the opening restores musical order . it returns to the triumphant e-flat major , the same chord it started with but inverted , meaning mozart moved the bottom note to the top . although it retains its original harmony , the chord sounds higher , pointing towards enlightenment . that 's similar to tamino , who in passing his trials restores balance to the kingdom while growing stronger , wiser , and more complete .

just as it rears up to devour him , three mysterious ladies appear and slay the dragon with their fierce battle cry . so begins wolfgang amadeus mozart 's `` die zauberflöte , '' or `` the magic flute . '' this fantasy singspiel , a type of folk opera with music and dialogue , premiered in 1791 in vienna .

what are some of the occurrences of the number 3 in the `` magic flute '' ? why was this significant and most likely deliberate on mozart ’ s part ?

so , you 're thinking of moving to mars . have you picked out a spot for your new home ? no ? well , i 'm here to help . first things first , here are some of the things you 'll need to bring to the red planet : a high tolerance for cold , loneliness , and radiation ; a lifetime supply of breathable air and food ; a multibillion dollar spaceship ; a desire to just get away from it all ; and water . you 're definitely going to need water . so what sort of real estate are you looking for ? how about a mansion in the maze-like noctis labyrinthus ? a hideaway in the happy face crater ? a fortress on the face mesa ? an oceanview ? uh , bad news on the last one . you 're about 4 billion years late . we 're pretty sure that mars used to have oceans , lakes , rivers , the whole package . but over time , almost all of it froze beneath the surface , or evaporated off into space . there 's probably still some trapped beneath the seasonally expanding and contracting carbon dioxide ice caps , though . so what might mars look like today if it had surface water ? that , of course , depends on how much we 're talking about , but maybe something like this . the relatively flat northern hemisphere is below the average elevation , so it would become one giant ocean , while the crater-ridden southern hemisphere would stay mostly high and dry . that difference between hemispheres is a bit bizarre , and we do n't know why it 's like that . the southern half is probably much older , judging by features like the number of craters , and the evidence of increased volcanic activity in the north . okay , so who knows ? maybe one day mars will have oceans again , but for now , what we 've got is essentially one giant dusty desert . in fact , it 's similar enough to deserts on earth , that we 've been able to learn a great deal about mars on our home planet . for instance , martian sand dunes form and behave similarly to our sand dunes , though the martian versions often grow twice as large thanks to a gravitational pull that 's about a third as strong as ours . and mars has some features you wo n't see on earth , like tars , which are crestless sand dunes up to fifteen meters tall , whose formations we have yet to understand . you 're probably wondering , `` what do you get when you combine a planet-wide desert with an atmosphere that , like ours , is subject to wind-generating pressure differentials , dust storms ? '' these will be your main weather hazards on the red planet . they play a large part in making the planet red by distributing rusted iron particles across the surface and into the air . thanks to the low gravity and lack of moisture , these dust storms can last for months and cover the planet . so , you might want to build your home as high as possible . well , look no further . this is olympus mons , the largest volcano in the solar system . even if mars had a breathable atmosphere , you 'd find the views from the 25 kilometer summit breathtaking . or are volcanos not your thing ? then how about valles marineris , the largest canyon in the solar system ? it 's so wide that from one side , the opposite rim would be below the curve of the horizon . still , you 'll catch some spectacular blue sunsets in the normally red sky , which gets its color from the dust absorbing most of the blue light , and the way sunlight is scattered by the atmosphere . have you got spirit , curiosity , or are you just looking for opportunity ? then stop stalling and make the move to mars today . mars : redder than ever .

you 're about 4 billion years late . we 're pretty sure that mars used to have oceans , lakes , rivers , the whole package . but over time , almost all of it froze beneath the surface , or evaporated off into space .

which part of mars has lower elevation and once had oceans ?

we read fiction for many reasons . to be entertained , to find out who done it , to travel to strange , new planets , to be scared , to laugh , to cry , to think , to feel , to be so absorbed that for a while we forget where we are . so , how about writing fiction ? how do you suck your readers into your stories ? with an exciting plot ? maybe . fascinating characters ? probably . beautiful language ? perhaps . `` billie 's legs are noodles . the ends of her hair are poison needles . her tongue is a bristly sponge , and her eyes are bags of bleach . '' did that description almost make you feel as queasy as billie ? we grasp that billie 's legs are n't actually noodles . to billie , they feel as limp as cooked noodles . it 's an implied comparison , a metaphor . so , why not simply write it like this ? `` billie feels nauseated and weak . '' chances are the second description was n't as vivid to you as the first . the point of fiction is to cast a spell , a momentary illusion that you are living in the world of the story . fiction engages the senses , helps us create vivid mental simulacra of the experiences the characters are having . stage and screen engage some of our senses directly . we see and hear the interactions of the characters and the setting . but with prose fiction , all you have is static symbols on a contrasting background . if you describe the story in matter of fact , non-tactile language , the spell risks being a weak one . your reader may not get much beyond interpreting the squiggles . she will understand what billie feels like , but she wo n't feel what billie feels . she 'll be reading , not immersed in the world of the story , discovering the truths of billie 's life at the same time that billie herself does . fiction plays with our senses : taste , smell , touch , hearing , sight , and the sense of motion . it also plays with our ability to abstract and make complex associations . look at the following sentence . `` the world was ghost-quiet , except for the crack of sails and the burbling of water against hull . '' the words , `` quiet , '' `` crack , '' and `` burbling , '' engage the sense of hearing . notice that buckell does n't use the generic word sound . each word he chooses evokes a particular quality of sound . then , like an artist laying on washes of color to give the sense of texture to a painting , he adds anoter layer , motion , `` the crack of sails , '' and touch , `` the burbling of water against hull . '' finally , he gives us an abstract connection by linking the word quiet with the word ghost . not `` quiet as a ghost , '' which would put a distancing layer of simile between the reader and the experience . instead , buckell creates the metaphor `` ghost-quiet '' for an implied , rather than overt , comparison . writers are always told to avoid cliches because there 's very little engagement for the reader in an overused image , such as `` red as a rose . '' but give them , `` love ... began on a beach . it began that day when jacob saw anette in her stewed-cherry dress , '' and their brains engage in the absorbing task of figuring out what a stewed-cherry dress is like . suddenly , they 're on a beach about to fall in love . they 're experiencing the story at both a visceral and a conceptual level , meeting the writer halfway in the imaginative play of creating a dynamic world of the senses . so when you write , use well-chosen words to engage sound , sight , taste , touch , smell , and movement . then create unexpected connotations among your story elements , and set your readers ' brushfire imaginations alight .

probably . beautiful language ? perhaps .

if non-tactile language is used in fiction :

what rights do people have , and where do they come from ? who gets to make decisions for others and on what authority ? and how can we organize society to meet people 's needs ? these questions challenged an entire nation during the upheaval of the french revolution . by the end of the 18th century , europe had undergone a profound intellectual and cultural shift known as the enlightenment . philosophers and artists promoted reason and human freedom over tradition and religion . the rise of a middle class and printed materials encouraged political awareness , and the american revolution had turned a former english colony into an independent republic . yet france , one of the largest and richest countries in europe was still governed by an ancient regime of three rigid social classes called estates . the monarch king louis xvi based his authority on divine right and granted special privileges to the first and second estates , the catholic clergy , and the nobles . the third estate , middle class merchants and craftsmen , as well as over 20 million peasants , had far less power and they were the only ones who paid taxes , not just to the king , but to the other estates as well . in bad harvest years , taxation could leave peasants with almost nothing while the king and nobles lived lavishly on their extracted wealth . but as france sank into debt due to its support of the american revolution and its long-running war with england , change was needed . king louis appointed finance minister jacques necker , who pushed for tax reforms and won public support by openly publishing the government 's finances . but the king 's advisors strongly opposed these initiatives . desperate for a solution , the king called a meeting of the estates-general , an assembly of representatives from the three estates , for the first time in 175 years . although the third estate represented 98 % of the french population , its vote was equal to each of the other estates . and unsurprisingly , both of the upper classes favored keeping their privileges . realizing they could n't get fair representation , the third estate broke off , declared themselves the national assembly , and pledged to draft a new constitution with or without the other estates . king louis ordered the first and second estates to meet with the national assembly , but he also dismissed necker , his popular finance minister . in response , thousands of outraged parisians joined with sympathetic soldiers to storm the bastille prison , a symbol of royal power and a large storehouse of weapons . the revolution had begun . as rebellion spread throughout the country , the feudal system was abolished . the assembly 's declaration of the rights of man and citizen proclaimed a radical idea for the time -- that individual rights and freedoms were fundamental to human nature and government existed only to protect them . their privileges gone , many nobles fled abroad , begging foreign rulers to invade france and restore order . and while louis remained as the figurehead of the constitutional monarchy , he feared for his future . in 1791 , he tried to flee the country but was caught . the attempted escape shattered people 's faith in the king . the royal family was arrested and the king charged with treason . after a trial , the once-revered king was publicly beheaded , signaling the end of one thousand years of monarchy and finalizing the september 21st declaration of the first french republic , governed by the motto `` liberté , égalité , fraternité . '' nine months later , queen marie antoinette , a foreigner long-mocked as `` madame déficit '' for her extravagant reputation , was executed as well . but the revolution would not end there . some leaders , not content with just changing the government , sought to completely transform french society -- its religion , its street names , even its calendar . as multiple factions formed , the extremist jacobins lead by maximilien robespierre launched a reign of terror to suppress the slightest dissent , executing over 20,000 people before the jacobin 's own downfall . meanwhile , france found itself at war with neighboring monarchs seeking to strangle the revolution before it spread . amidst the chaos , a general named napoleon bonaparte took charge , becoming emperor as he claimed to defend the revolution 's democratic values . all in all , the revolution saw three constitutions and five governments within ten years , followed by decades alternating between monarchy and revolt before the next republic formed in 1871 . and while we celebrate the french revolution 's ideals , we still struggle with many of the same basic questions raised over two centuries ago .

but the revolution would not end there . some leaders , not content with just changing the government , sought to completely transform french society -- its religion , its street names , even its calendar . as multiple factions formed , the extremist jacobins lead by maximilien robespierre launched a reign of terror to suppress the slightest dissent , executing over 20,000 people before the jacobin 's own downfall .

changes to the calendar , street names , and religion were examples of :

translator : andrea mcdonough reviewer : jessica ruby what 's an algorithm ? in computer science , an algorithm is a set of instructions for solving some problem , step-by-step . typically , algorithms are executed by computers , but we humans have algorithms as well . for instance , how would you go about counting the number of people in a room ? well , if you 're like me , you probably point at each person , one at a time , and count up from 0 : 1 , 2 , 3 , 4 and so forth . well , that 's an algorithm . in fact , let 's try to express it a bit more formally in pseudocode , english-like syntax that resembles a programming language . let n equal 0 . for each person in room , set n = n + 1 . how to interpret this pseudocode ? well , line 1 declares , so to speak , a variable called n and initializes its value to zero . this just means that at the beginning of our algorithm , the thing with which we 're counting has a value of zero . after all , before we start counting , we have n't counted anything yet . calling this variable n is just a convention . i could have called it almost anything . now , line 2 demarks the start of loop , a sequence of steps that will repeat some number of times . so , in our example , the step we 're taking is counting people in the room . beneath line 2 is line 3 , which describes exactly how we 'll go about counting . the indentation implies that it 's line 3 that will repeat . so , what the pseudocode is saying is that after starting at zero , for each person in the room , we 'll increase n by 1 . now , is this algorithm correct ? well , let 's bang on it a bit . does it work if there are 2 people in the room ? let 's see . in line 1 , we initialize n to zero . for each of these two people , we then increment n by 1 . so , in the first trip through the loop , we update n from zero to 1 , on the second trip through that same loop , we update n from 1 to 2 . and so , by this algorithm 's end , n is 2 , which indeed matches the number of people in the room . so far , so good . how about a corner case , though ? suppose that there are zero people in the room , besides me , who 's doing the counting . in line 1 , we again initialize n to zero . this time , though , line 3 does n't execute at all since there is n't a person in the room , and so , n remains zero , which indeed matches the number of people in the room . pretty simple , right ? but counting people one a time is pretty inefficient , too , no ? surely , we can do better ! why not count two people at a time ? instead of counting 1 , 2 , 3 , 4 , 5 , 6 , 7 , 8 , and so forth , why not count 2 , 4 , 6 , 8 , and so on ? it even sounds faster , and it surely is . let 's express this optimization in pseudocode . let n equal zero . for each pair of people in room , set n = n + 2 . pretty simple change , right ? rather than count people one at a time , we instead count them two at a time . this algorithm 's thus twice as fast as the last . but is it correct ? let 's see . does it work if there are 2 people in the room ? in line 1 , we initialize n to zero . for that one pair of people , we then increment n by 2 . and so , by this algorithm 's end , n is 2 , which indeed matches the number of people in the room . suppose next that there are zero people in the room . in line 1 , we initialize n to zero . as before , line 3 does n't execute at all since there are n't any pairs of people in the room , and so , n remains zero , which indeed matches the number of people in the room . but what if there are 3 people in the room ? how does this algorithm fair ? let 's see . in line 1 , we initialize n to zero . for a pair of those people , we then increment n by 2 , but then what ? there is n't another full pair of people in the room , so line 2 no longer applies . and so , by this algorithm 's end , n is still 2 , which is n't correct . indeed this algorithm is said to be buggy because it has a mistake . let 's redress with some new pseudocode . let n equal zero . for each pair of people in room , set n = n + 2 . if 1 person remains unpaired , set n = n + 1 . to solve this particular problem , we 've introduced in line 4 a condition , otherwise known as a branch , that only executes if there is one person we could not pair with another . so now , whether there 's 1 or 3 or any odd number of people in the room , this algorithm will now count them . can we do even better ? well , we could count in 3 's or 4 's or even 5 's and 10 's , but beyond that it 's going to get a little bit difficult to point . at the end of the day , whether executed by computers or humans , algorithms are just a set of instructions with which to solve problems . these were just three . what problem would you solve with an algorithm ?

for a pair of those people , we then increment n by 2 , but then what ? there is n't another full pair of people in the room , so line 2 no longer applies . and so , by this algorithm 's end , n is still 2 , which is n't correct .

if there are 50 people in the room which line of our final algorithm never executes ?

translator : andrea mcdonough reviewer : bedirhan cinar i do n't know about you , but i 'm trying to get this beach body , that p90x , brad pitt , bradley cooper , tyrese , trey songz , matthew mcconaughey beach body ! i 'm trying to sweat in front of everybody . word . and get that shorty with them angelina jolie lips to lick my torso , get me looking like a wet chocolate . look at my biceps . they 're kind of puny . they 're kind of chunky . but i 've been working on them . we can be models . i could take off my shirt mad sexy . i could stare at a camera intensely for 37 seconds straight and not blink . i could bathe in baby oil . i could run on the beach in slow motion . i could cat walk down a runway in zebra panties . i ca n't do that . having a slow metabolism ruins everything . all my friends will be in tank tops , and i 'll be in a hoodie . i 'm good at zipping up my insecurities , thinking i could sweat them out . i 'm trying to get this beach body ! i 'm too skinny . i guzzle junk food like my mouth 's a garbage chute , but my intestines are allergic to trans fat . i want to be a flexing horse leg , galloping beach sand into a red carpet , customized for me to strut the shore side like a centaur on a conveyor belt . i 'm trying to get this beach body , but there is salvation in snack closets , on licked plates of seconds , at the bottom of a pint of ice cream . i use haagen dazs as a morphine cylinder because she said my arms were n't strong enough to carry her . i think i 'm weak . i think i 'm fat . i think i 'm ugly . the beach is no place for a whale like me , for a mini van with its tank on e. i want to be baywatch bareable , broken , bottle-cut , have you seen my muscles and my scars ? you smell that ? that 's macho moisture . my hour-long work out routine consists of 5 minutes of push-ups on my bedroom floor , a denial mirror repelling my lanky limbs ; 5 minutes of keeping my chin high over the bar of self doubt ; 10 minutes placing 100 pounds of failure on my chest so it becomes the elephant in the room ; 10 minutes jogging with ghosts chuckling at my chunky thighs , and i 'll smile , knowing i 'll soon be able to fit in my old butt pants ; 30 minutes thinking sweat is a masculinity cloak . and i 'm weary from trying to work out my irrational fears , drown them in a puddle of perspiration , shove the imperfections i should be proud of under water : my gap-tooth smile , my frizzy hair , my funny shaped head , the extra weight that kept me grounded , the missing pounds that make me a kite flailing free through the wind , not bound by muscle . so , yes , i 'm trying to get this beach body , that channing tatum , david beckham , ll cool j beach body ! but we 're tired and exhausted from trying to be something we 're not .

i use haagen dazs as a morphine cylinder because she said my arms were n't strong enough to carry her . i think i 'm weak . i think i 'm fat .

do most people struggle with insecurity ? what do you think is the best way to conquer low self esteem ?

[ ♪ ] a lone explorer on a mission to reveal the grandeur of saturn , its rings and moons [ ♪ ] after 20 years in space nasa 's cassini spacecraft is running out of fuel . and so , to protect moons of saturn that could have conditions suitable for life , a spectacular end has been planned for this long-lived traveler from earth . cassini 's grand finale 5 - 4 - 3 - 2 - 1 [ rockets roar ] and liftoff of the cassini spacecraft on a billion-mile trek to saturn . we have cleared the tower . [ mission audio ] [ ♪ ] in 2004 , following a 7-year journey through the solar system , cassini arrived at saturn . [ mission audio ] june 30 , 2004 saturn orbit insertion the spacecraft carried a passenger , the european huygens probe -- the first human-made object to land on a world in the distant outer solar system . january 14 , 2005 huygens probe landing on titan for over a decade , cassini has shared the wonders of saturn and its family of icy moons , taking us to astounding worlds where methane rivers run to a methane sea . where jets of ice and gas are blasting material into space from a liquid water ocean that might harbor the ingredients for life . [ mission audio ] and saturn -- a giant world ruled by raging storms and delicate harmonies of gravity . [ ♪ ] now , cassini has one last , daring assignment . april 26 , 2017 the grand finale begins . [ ♪ ] cassini 's grand finale is a brand new adventure . [ ♪ ] twenty-two dives through the space between saturn and its rings . [ ♪ ] as it repeatedly braves this unexplored region , cassini seeks new insights about the origins of the rings , and the nature of the planet 's interior -- closer to saturn than ever before . [ ♪ ] on the final orbit , cassini will plunge into saturn fighting to keep its antenna pointed at earth as it transmits its farewell . [ ♪ ] in the skies of saturn , the journey ends , [ ♪ ] as cassini becomes part of the planet itself . [ ♪ ] september 15 , 2017 end of mission . [ ♪ ] nasa jet propulsion laboratory california institute of technology

and so , to protect moons of saturn that could have conditions suitable for life , a spectacular end has been planned for this long-lived traveler from earth . cassini 's grand finale 5 - 4 - 3 - 2 - 1 [ rockets roar ] and liftoff of the cassini spacecraft on a billion-mile trek to saturn . we have cleared the tower .

what passenger did cassini have on board ? why was it significant ?

light is the fastest thing we know . it 's so fast that we measure enormous distances by how long it takes for light to travel them . in one year , light travels about 6,000,000,000,000 miles , a distance we call one light year . to give you an idea of just how far this is , the moon , which took the apollo astronauts four days to reach , is only one light-second from earth . meanwhile , the nearest star beyond our own sun is proxima centauri , 4.24 light years away . our milky way is on the order of 100,000 light years across . the nearest galaxy to our own , andromeda , is about 2.5 million light years away space is mind-blowingly vast . but wait , how do we know how far away stars and galaxies are ? after all , when we look at the sky , we have a flat , two-dimensional view . if you point you finger to one star , you ca n't tell how far the star is , so how do astrophysicists figure that out ? for objects that are very close by , we can use a concept called trigonometric parallax . the idea is pretty simple . let 's do an experiment . stick out your thumb and close your left eye . now , open your left eye and close your right eye . it will look like your thumb has moved , while more distant background objects have remained in place . the same concept applies when we look at the stars , but distant stars are much , much farther away than the length of your arm , and the earth is n't very large , so even if you had different telescopes across the equator , you 'd not see much of a shift in position . instead , we look at the change in the star 's apparent location over six months , the halfway point of the earth 's yearlong orbit around the sun . when we measure the relative positions of the stars in summer , and then again in winter , it 's like looking with your other eye . nearby stars seem to have moved against the background of the more distant stars and galaxies . but this method only works for objects no more than a few thousand light years away . beyond our own galaxy , the distances are so great that the parallax is too small to detect with even our most sensitive instruments . so at this point we have to rely on a different method using indicators we call standard candles . standard candles are objects whose intrinsic brightness , or luminosity , we know really well . for example , if you know how bright your light bulb is , and you ask your friend to hold the light bulb and walk away from you , you know that the amount of light you receive from your friend will decrease by the distance squared . so by comparing the amount of light you receive to the intrinsic brightness of the light bulb , you can then tell how far away your friend is . in astronomy , our light bulb turns out to be a special type of star called a cepheid variable . these stars are internally unstable , like a constantly inflating and deflating balloon . and because the expansion and contraction causes their brightness to vary , we can calculate their luminosity by measuring the period of this cycle , with more luminous stars changing more slowly . by comparing the light we observe from these stars to the intrinsic brightness we 've calculated this way , we can tell how far away they are . unfortunately , this is still not the end of the story . we can only observe individual stars up to about 40,000,000 light years away , after which they become too blurry to resolve . but luckily we have another type of standard candle : the famous type 1a supernova . supernovae , giant stellar explosions are one of the ways that stars die . these explosions are so bright , that they outshine the galaxies where they occur . so even when we ca n't see individual stars in a galaxy , we can still see supernovae when they happen . and type 1a supernovae turn out to be usable as standard candles because intrinsically bright ones fade slower than fainter ones . through our understanding of this relationship between brightness and decline rate , we can use these supernovae to probe distances up to several billions of light years away . but why is it important to see such distant objects anyway ? well , remember how fast light travels . for example , the light emitted by the sun will take eight minutes to reach us , which means that the light we see now is a picture of the sun eight minutes ago . when you look at the big dipper , you 're seeing what it looked like 80 years ago . and those smudgy galaxies ? they 're millions of light years away . it has taken millions of years for that light to reach us . so the universe itself is in some sense an inbuilt time machine . the further we can look back , the younger the universe we are probing . astrophysicists try to read the history of the universe , and understand how and where we come from . the universe is constantly sending us information in the form of light . all that remains if for us to decode it .

we can only observe individual stars up to about 40,000,000 light years away , after which they become too blurry to resolve . but luckily we have another type of standard candle : the famous type 1a supernova . supernovae , giant stellar explosions are one of the ways that stars die . these explosions are so bright , that they outshine the galaxies where they occur .

besides type ia supernovae , which are usually due to less massive stars , there are other types of supernovae such as type ii supernovae that are due to more massive stars . why are n't the other types of supernovae used as standard candles ? do a search on the internet and discuss the most recent recorded supernovae in both the milky way galaxy and the andromeda galaxy . what type of supernovae are they ?

berkelium which , i assume was named after the place of its discovery , which was berkeley and they made 3 billionths of a gram of it , which was just enough to record some spectroscopic data on it and prove that they had actually made it .

berkelium which , i assume was named after the place of its discovery , which was berkeley and they made 3 billionths of a gram of it , which was just enough to record some spectroscopic data on it and prove that they had actually made it .

who were the three people who synthesized berkelium in december 1949 for the first time ?

light , bright , and cheerful . it 's some of the most familiar of all early 18th century music . it 's been featured in uncounted films and television commercials , but what is it and why does it sound that way ? this is the opening of `` spring '' from `` the four seasons , '' by italian composer antonio vivaldi . `` the four seasons '' are famous in part because they are a delight to the ear . however , even more notable is the fact that they have stories to tell . at the time of their publication in amsterdam in 1725 , they were accompanied by poems describing exactly what feature of that season vivaldi intended to capture in musical terms . in providing specific plot content for instrumental music , vivaldi was generations ahead of his time . if one were to read the poems simultaneously to hearing the music , one would find the poetic scenes synchronizing nicely with the musical imagery . we are told that the birds welcome spring with happy song , and here they are doing exactly that . soon , however , a thunderstorm breaks out . not only is there musical thunder and lightning , there are also more birds , wet , frightened , and unhappy . in `` summer , '' the turtle dove sings her name `` tortorella '' in italian , before a hail storm flattens the fields . `` autumn '' brings eager hunters dashing out in pursuit of their prey . the `` winter '' concerto begins with teeth chattering in the cold before one takes refuge by a crackling fire . then it 's back out into the storm where there 'll be slips and falls on the ice . in these first weeks of winter , the old year is coming to a close , and so does vivaldi 's musical exploration of the seasons . not until the early 19th century would such expressive instrumental program music , as it was known , become popular . by then , larger , more varied ensembles were the rule with woodwinds , brass , and percussion to help tell the tale . but vivaldi pulled it off with just one violin , strings , and a harpsichord . unlike his contemporary bach , vivaldi was n't much interested in complicated fugues . he preferred to offer readily accessible entertainment to his listeners with melodies that pop back up later in a piece to remind us of where we 've been . so the first movement of the `` spring '' concerto begins with a theme for spring and ends with it , too , slightly varied from when it was last heard . it was an inspired way to attract listeners , and vivaldi , considered one of the most electrifying violinists of the early 18th century , understood the value of attracting audiences . such concerts might feature himself as the star violinist . others presented the young musicians of the pietà , a venetian girls ' school where vivaldi was director of music . most of the students were orphans . music training was intended not only as social skills suitable for young ladies but also as potential careers for those who might fail to make good marriages . even in the composer 's own time , vivaldi 's music served as diversion for all , not just for the wealthy aristocrats . 300 years later , it 's an approach that still works , and vivaldi 's music still sounds like trotting horses on the move .

music training was intended not only as social skills suitable for young ladies but also as potential careers for those who might fail to make good marriages . even in the composer 's own time , vivaldi 's music served as diversion for all , not just for the wealthy aristocrats . 300 years later , it 's an approach that still works , and vivaldi 's music still sounds like trotting horses on the move .

vivaldi was composing at a time in history when there had been major improvements to the ways in which string instruments were made , allowing them to sound stronger and be capable of playing even more difficult music . in part for this reason , he chose to focus nearly all of his compositions on strings instruments , such as violins and cellos . in what other ways have technological developments brought new ideas into the music business , even in recent years ?

many elements of traditional japanese culture , such as cuisine and martial arts , are well-known throughout the world . kabuki , a form of classical theater performance , may not be as well understood in the west but has evolved over 400 years to still maintain influence and popularity to this day . the word kabuki is derived from the japanese verb kabuku , meaning out of the ordinary or bizarre . its history began in early 17th century kyoto , where a shrine maiden named izumo no okuni would use the city 's dry kamo riverbed as a stage to perform unusual dances for passerby , who found her daring parodies of buddhist prayers both entertaining and mesmerizing . soon other troops began performing in the same style , and kabuki made history as japan 's first dramatic performance form catering to the common people . by relying on makeup , or keshou , and facial expressions instead of masks and focusing on historical events and everyday life rather than folk tales , kabuki set itself apart from the upper-class dance theater form known as noh and provided a unique commentary on society during the edo period . at first , the dance was practiced only by females and commonly referred to as onna-kabuki . it soon evolved to an ensemble performance and became a regular attraction at tea houses , drawing audiences from all social classes . at this point , onna-kabuki was often risque as geishas performed not only to show off their singing and dancing abilities but also to advertise their bodies to potential clients . a ban by the conservative tokugawa shogunate in 1629 led to the emergence of wakashu-kabuki with young boys as actors . but when this was also banned for similar reasons , there was a transition to yaro-kabuki , performed by men , necessitating elaborate costumes and makeup for those playing female roles , or onnagata . attempts by the government to control kabuki did n't end with bans on the gender or age of performers . the tokugawa military group , or bakufu , was fueled by confucian ideals and often enacted sanctions on costume fabrics , stage weaponry , and the subject matter of the plot . at the same time , kabuki became closely associated with and influenced by bunraku , an elaborate form of puppet theater . due to these influences , the once spontaneous , one-act dance evolved into a structured , five-act play often based on the tenets of confucian philosophy . before 1868 , when the tokugawa shogunate fell and emperor meiji was restored to power , japan had practiced isolation from other countries , or sakoku . and thus , the development of kabuki had mostly been shaped by domestic influences . but even before this period , european artists , such as claude monet , had become interested in and inspired by japanese art , such as woodblock prints , as well as live performance . after 1868 , others such as vincent van gogh and composer claude debussy began to incorporate kabuki influences in their work , while kabuki itself underwent much change and experimentation to adapt to the new modern era . like other traditional art forms , kabuki suffered in popularity in the wake of world war ii . but innovation by artists such as director tetsuji takechi led to a resurgence shortly after . indeed , kabuki was even considered a popular form of entertainment amongst american troops stationed in japan despite initial u.s. censorship of japanese traditions . today , kabuki still lives on as an integral part of japan 's rich cultural heritage , extending its influence beyond the stage to television , film , and anime . the art form pioneered by okuni continues to delight audiences with the actors ' elaborate makeup , extravagant and delicately embroidered costumes , and the unmistakable melodrama of the stories told on stage .

attempts by the government to control kabuki did n't end with bans on the gender or age of performers . the tokugawa military group , or bakufu , was fueled by confucian ideals and often enacted sanctions on costume fabrics , stage weaponry , and the subject matter of the plot . at the same time , kabuki became closely associated with and influenced by bunraku , an elaborate form of puppet theater .

name three sanctions the bakufu placed against kabuki theatres during the tokugawa era .

if you know an older left-handed person , chances are they had to learn to write or eat with their right hand . and in many parts of the world , it 's still common practice to force children to use their `` proper '' hand . even the word for right also means correct or good , not just in english , but many other languages , too . but if being left-handed is so wrong , then why does it happen in the first place ? today , about 1/10 of the world 's population are left-handed . archeological evidence shows that it 's been that way for as long as 500,000 years , with about 10 % of human remains showing the associated differences in arm length and bone density , and some ancient tools and artifacts showing evidence of left-hand use . and despite what many may think , handedness is not a choice . it can be predicted even before birth based on the fetus ' position in the womb . so , if handedness is inborn , does that mean it 's genetic ? well , yes and no . identical twins , who have the same genes , can have different dominant hands . in fact , this happens as often as it does with any other sibling pair . but the chances of being right or left-handed are determined by the handedness of your parents in surprisingly consistent ratios . if your father was left-handed but your mother was right-handed , you have a 17 % chance of being born left-handed , while two righties will have a left-handed child only 10 % of the time . handedness seems to be determined by a roll of the dice , but the odds are set by your genes . all of this implies there 's a reason that evolution has produced this small proportion of lefties , and maintained it over the course of millennia . and while there have been several theories attempting to explain why handedness exists in the first place , or why most people are right-handed , a recent mathematical model suggests that the actual ratio reflects a balance between competitive and cooperative pressures on human evolution . the benefits of being left-handed are clearest in activities involving an opponent , like combat or competitive sports . for example , about 50 % of top hitters in baseball have been left-handed . why ? think of it as a surprise advantage . because lefties are a minority to begin with , both right-handed and left-handed competitors will spend most of their time encountering and practicing against righties . so when the two face each other , the left-hander will be better prepared against this right-handed opponent , while the righty will be thrown off . this fighting hypothesis , where an imbalance in the population results in an advantage for left-handed fighters or athletes , is an example of negative frequency-dependent selection . but according to the principles of evolution , groups that have a relative advantage tend to grow until that advantage disappears . if people were only fighting and competing throughout human evolution , natural selection would lead to more lefties being the ones that made it until there were so many of them , that it was no longer a rare asset . so in a purely competitive world , 50 % of the population would be left-handed . but human evolution has been shaped by cooperation , as well as competition . and cooperative pressure pushes handedness distribution in the opposite direction . in golf , where performance does n't depend on the opponent , only 4 % of top players are left-handed , an example of the wider phenomenon of tool sharing . just as young potential golfers can more easily find a set of right-handed clubs , many of the important instruments that have shaped society were designed for the right-handed majority . because lefties are worse at using these tools , and suffer from higher accident rates , they would be less successful in a purely cooperative world , eventually disappearing from the population . so by correctly predicting the distribution of left-handed people in the general population , as well as matching data from various sports , the model indicates that the persistence of lefties as a small but stable minority reflects an equilibrium that comes from competitive and cooperative effects playing out simultaneously over time . and the most intriguing thing is what the numbers can tell us about various populations . from the skewed distribution of pawedness in cooperative animals , to the slightly larger percentage of lefties in competitive hunter-gatherer societies , we may even find that the answers to some puzzles of early human evolution are already in our hands .

but the chances of being right or left-handed are determined by the handedness of your parents in surprisingly consistent ratios . if your father was left-handed but your mother was right-handed , you have a 17 % chance of being born left-handed , while two righties will have a left-handed child only 10 % of the time . handedness seems to be determined by a roll of the dice , but the odds are set by your genes .

which pairing of parent handedness gives the best chance of their offspring being left-handed ?

how do nerves work ? are nerves simply the wires in the body that conduct electricity , like the wires in the walls of your home or in your computer ? this is an analogy often made , but the reality is that nerves have a much more complex job in the body . they are not just the wires , but the cells that are the sensors , detectors of the external and internal world , the transducers that convert information to electrical impulses , the wires that transmit these impulses , the transistors that gate the information and turn up or down the volume- and finally , the activators that take that information and cause it to have an effect on other organs . consider this . your mother gently strokes your forearm and you react with pleasure . or a spider crawls on your forearm and you startle and slap it off . or you brush your forearm against a hot rack while removing a cake from the oven and you immediately recoil . light touch produced pleasure , fear , or pain . how can one kind of cell have so many functions ? nerves are in fact bundles of cells called neurons and each of these neurons is highly specialized to carry nerve impulses , their form of electricity , in response to only one kind of stimulus , and in only one direction . the nerve impulse starts with a receptor , a specialized part of each nerve , where the electrical impulse begins . one nerve 's receptor might be a thermal receptor , designed only to respond to a rapid increase in temperature . another receptor type is attached to the hairs of the forearm , detecting movement of those hairs , such as when a spider crawls on your skin . yet another kind of neuron is low-threshold mechanoreceptor , activated by light touch . each of these neurons then carry their specific information : pain , warning , pleasure . and that information is projected to specific areas of the brain and that is the electrical impulse . the inside of a nerve is a fluid that is very rich in the ion potassium . it is 20 times higher than in the fluid outside the nerve while that outside fluid has 10 times more sodium than the inside of a nerve . this imbalance between sodium outside and potassium inside the cell results in the inside of the nerve having a negative electrical charge relative to the outside of the nerve , about equal to -70 or -80 millivolts . this is called the nerve 's resting potential . but in response to that stimulus the nerve is designed to detect , pores in the cell wall near the receptor of the cell open . these pores are specialized protein channels that are designed to let sodium rush into the nerve . the sodium ions rush down their concentration gradient , and when they do , the inside of the nerve becomes more positively charged- about +40 millivolts . while this happens , initially in the nerve right around the receptor , if the change in the nerve 's electrical charge is great enough , if it reaches what is called threshold , the nearby sodium ion channels open , and then the ones nearby those , and so on , and so forth , so that the positivity spreads along the nerve 's membrane to the nerve 's cell body and then along the nerve 's long , thread-like extension , the axon . meanwhile , potassium ion channels open , potassium rushes out of the nerve , and the membrane voltage returns to normal . actually , overshooting it a bit . and during this overshoot , the nerve is resistant to further depolarization-it is refractory , which prevents the nerve electrical impulse from traveling backwards . then , ion pumps pump the sodium back back out of the nerve , and the potassium back into the nerve , restoring the nerve to its normal resting state . the end of the nerve , the end of the axon , communicates with the nerve 's target . this target will be other nerves in a specialized area of the spinal cord , to be processed and then transmitted up to the brain . or the nerve 's target may be another organ , such as a muscle . when the electrical impulse reaches the end of the nerve , small vesicles , or packets , containing chemical neurotransmitters , are released by the nerve and rapidly interact with the nerve 's target . this process is called synaptic transmission , because the connection between the nerve and the next object in the chain is called a synapse . and it is here , in this synapse , that the neuron 's electrical information can be modulated , amplified , blocked altogether or translated to another informational process .

how do nerves work ? are nerves simply the wires in the body that conduct electricity , like the wires in the walls of your home or in your computer ?

describe what you think it would be like to live without nerves . why do you think this would be a good thing ? why would it be bad ?

it 's the first sense you use when you 're born . one out of every fifty of your genes is dedicated to it . it must be important , right ? okay , take a deep breath through your nose . it 's your sense of smell , and it 's breathtakingly powerful . as an adult , you can distinguish about 10,000 different smells . here 's how your nose does it . smell starts when you sniff molecules from the air into your nostrils . 95 % of your nasal cavity is used just to filter that air before it hits your lungs . but at the very back of your nose is a region called the olfactory epithelium , a little patch of skin that 's key to everything you smell . the olfactory epithelium has a layer of olfactory receptor cells , special neurons that sense smells , like the taste buds of your nose . when odor molecules hit the back of your nose , they get stuck in a layer of mucus covering the olfactory epithelium . as they dissolve , they bind to the olfactory receptor cells , which fire and send signals through the olfactory tract up to your brain . as a side note , you can tell a lot about how good an animal 's sense of smell is by the size of its olfactory epithelium . a dog 's olfactory epithelium is 20 times bigger than your puny human one . but there 's still a lot we do n't know about this little patch of cells , too . for example , our olfactory epithelium is pigmented , and scientists do n't really know why . but how do you actually tell the difference between smells ? it turns out that your brain has 40 million different olfactory receptor neurons , so odor a might trigger neurons 3 , 427 , and 988 , and odor b might trigger neurons 8 , 76 , and 2,496,678 . all of these different combinations let you detect a staggeringly broad array of smells . olfactory neurons are always fresh and ready for action . they 're the only neuron in the body that gets replaced regularly , every four to eight weeks . once they are triggered , the signal travels through a bundle called the olfactory tract to destinations all over your brain , making stops in the amygdala , the thalamus , and the neocortex . this is different from how sight and sound are processed . each of those signals goes first to a relay center in the middle of the cerebral hemisphere and then out to other regions of the brain . but smell , because it evolved before most of your other senses , takes a direct route to these different regions of the brain , where it can trigger your fight-or-flight response , help you recall memories , or make your mouth water . but even though we 've all got the same physiological set-up , two nostrils and millions of olfactory neurons , not everybody smells the same things . one of the most famous examples of this is the ability to smell so-called `` asparagus pee . '' for about a quarter of the population , urinating after eating asparagus means smelling a distinct odor . the other 75 % of us do n't notice . and this is n't the only case of smells differing from nose to nose . for some people , the chemical androstenone smells like vanilla ; to others , it smells like sweaty urine , which is unfortunate because androstenone is commonly found in tasty things like pork . so with the sweaty urine smellers in mind , pork producers will castrate male pigs to stop them from making androstenone . the inability to smell a scent is called anosmia , and there are about 100 known examples . people with allicin anosmia ca n't smell garlic . those with eugenol anosmia ca n't smell cloves . and some people ca n't smell anything at all . this kind of full anosmia could have several causes . some people are born without a sense of smell . others lose it after an accident or during an illness . if the olfactory epithelium gets swollen or infected , it can hamper your sense of smell , something you might have experienced when you were sick . not being able to smell anything can mess with your other senses , too . many people who ca n't smell at all also ca n't really taste the same way the rest of us do . it turns out that how something tastes is closely related to how it smells . as you chew your food , air is pushed up your nasal passage , carrying with it the smell of your food . those scents hit your olfactory epithelium and tell your brain a lot about what you 're eating . without the ability to smell , you lose the ability to taste anything more complicated than the five tastes your taste buds can detect : sweet , salty , bitter , sour , and savory . so , the next time you smell exhaust fumes , salty sea air , or roast chicken , you 'll know exactly how you 've done it and , perhaps , be a little more thankful that you can .

this kind of full anosmia could have several causes . some people are born without a sense of smell . others lose it after an accident or during an illness .

would you rather lose your sense of smell or your sense of hearing ? why ?

welcome to the i grad fafsa tutorial this step-by-step instruction will walk you through an answer any questions , feel free to complete the fafsa alongside this video and press pause or rewind if you need it instant replay before you begin filling out the fafsa you may want to make sure you 're equipped with the following ... your driver 's license number , your social security number , a list to the schools you plan on applying to , or have already applied to , your tax return for the prior-year and your parents if you 're considered a dependent student here is how to determine whether you are dependent or independent student . to be considered an independent student you must meet at least one of the following criteria : be 24 years of age or older when you file a fafsa , be an orphan or a ward of court , be a us military veteran be a graduate or professional student , be married , have legal dependence of your own , have a financial aid administrator who is documented your independence because of unusual circumstances . even if you do n't live with your parents , they do n't claim you on their taxes or support you financially , you may still be considered a dependent student . if you are filling out the fafsa for the first time , you and one of your parents , if you 're a dependent will be asked at the end of the online form to apply for pin before signing electronically . make sure the pin and security question you choose are ones that you will remember , also , make sure that you have a printer nearby so that you can print up all the important documentation you 'll need this information every year you attend school the website for the fafsa is www.fafsa.ed.gov please note that filling out the fafsa is free and does not cost any money if you are being asked to pay for the form you are on the wrong site champ . okay let 's get started ... once you 're on the site you want to click the start here button , whether you 're filling out the fafsa for the first time or you 've done this before you 'll be asked 4 very important questions . your first and last name , your social security number , and your date of birth . just make sure to use your full legal name , as written on your social security card . click next and continue on to the next page . award years run from july 1st to june 30th , not january 1st to december 31st , so just make sure to pick the correct award year for your attendance , for example ... if you filling out the fafsa in february you 're not going to attend school until september , just make sure to select the correct award year that september falls within . you 'll then be asked to choose a password . this is different than your pin , but you should keep track of it just the same , once you 've filled out both entries for your password , go ahead and click next to continue . use the links on this page to answer any questions about the fafsa before getting started , otherwise just go ahead to the next section . as you can see the top portion of this form is already filled out for you , fill out all the information below that correctly , and then you have the option to enter in your driver 's license information , once you finished just click next . now , ... to confirm your eligibility just choose the option that best describes your citizenship status . if you 're neither a citizen nor an eligible non-citizen contact the financial aid department at the school to which you 're applying , they 'll assist you with determining your eligibility . the next question will ask you about your high school completion status for the upcoming award year , be sure to choose the best answer for your situation and degree or certificate if you 're unsure you can contact the financial aid department if you qualify , work-study programs at your school can be a great way for you to pay off your tuition costs but that sounds like a good option for you and your school offers it , click yes on the drop down option , if you 're unsure do a little research and if work-study just is n't for you choose the not interested option and continue on . make sure to choose the correct option for whether or not you have a bachelor 's degree , double check it too , because it could really cause trouble should you choose incorrectly . when the fafsa asked about your parents educational status these questions are designed to determine if you or a first-generation college student or not finish with this page in just click next . on the next page you 'll be asked the name city and state of the high school you attend okay ... in this section just enter all the schools that you 're applying to or which you 've been accepted . to choose schools for what you 're applying , click on the school 's state and city . at the bottom type in the school name or click on search for a list of all schools in the area choose your school from the box and add it to the selected school portion of the form . to choose more than one school , click add another school and just start the process over . make sure to apply to any school you may want to attend once you 're done double check to make sure they 're all correct . you will have the option of choosing whether you want to live on campus , off-campus , or with a parent . make your choice and click the next button . there are two types of students in the world ; dependent and independent . you 'll need to answer the following questions in order to determine your status , with each question there will be an explanation just to the right of the dependency section if you are under the age of 24 , but answered yes to one or more of these questions then you 're declared as an independent . if you answered yes to one or more the questions you may also be required to show documented proof . that 's why it 's important that you answer all the questions correctly and honestly . if you 're confused by a question or not sure if the situations applicable to you , you 'll want to contact your financial aid department at the schools to which you 've applied . if you choose emancipated minor-in foster care both parents are deceased a dependent or ward of the court or homeless , make sure you have the right documentation to follow up with these claims . if you answered no to all these questions but believe you have special circumstances that might declare you an independent contact the financial aid department and they 'll request the proper documentation from you in order to request the dependency change . however , supplying documentation does n't guarantee your dependency change request will be approved . if you 're dependent make sure you have your and your parents tax returns from the previous year . before we get started on entering in all that information it 's important to know that there is an irs data retrieval tool . that allows fafsa on the web applicants to a request and retrieve their tax information data right from the irs . in order to use the irs data retrieval tool applicants must ; have a valid social security number , have filed a federal tax return to the previous year , and have an unchanged marital status since december 31st of the previous year if you 've just filed your taxes you may not be able to use the tool . do n't worry though , if you have the proper documentation you can enter it manually on the fafsa form . if you 're eligible to use the irs data retrieval tool you 'll be led to the following pages , please note that if you 're dependent student your parents information will be required first , and then you 'll be redirected back to the beginning to enter your own information . first , choose from the drop down tab already filed if you answered no to the questions below you 'll be asked for your pin , then click the irs button to proceed . then you leave the fafsa website be led to the irs website click ok to continue . once on the irs website enter all of your information correctly , all information must match your tax return , once you 're done , click submit . if the irs is able to retrieve your information will then be asked if you like your information transferred to the fafsa , check the box and click transfer now then you 'll sign and submit your fafsa if you 're ineligible to use the irs data retrieval tool will need to enter everything in the old fashion way , ... so get to typing ! now this is the part where those tax returns will come in handy , if you just filed your tax return or have n't done so yet you may estimate the information from the prior year 's tax return , once you 've filed you can return to the fafsa and make corrections . you can also use the irs data retrieval tool to make those updates corrections if you have any questions or are n't sure what to enter you can always refer to the side of the page in the help and hints box . this will give you instructions to each question and assist you in filling everything out correctly and completely . continue filling out all your information and click next to continue . congratulations ! ... you have completed the fafsa on your way to be receiving financial aid to help pay for school the next page gives you when efc number efc stands for estimated family contribution , you later receive an award letter from the school or schools to which you applied . the award letter will tell you how much money you will be awarded ! thanks for watching our little igrad fafsa tutorial we wish you the best of luck this school season .

first , choose from the drop down tab already filed if you answered no to the questions below you 'll be asked for your pin , then click the irs button to proceed . then you leave the fafsa website be led to the irs website click ok to continue . once on the irs website enter all of your information correctly , all information must match your tax return , once you 're done , click submit .

what is the website for the fafsa ?

translator : jessica ruby reviewer : caroline cristal let 's say that it would take you ten minutes to solve this puzzle . how long would it take if you received constant electric shocks to your hands ? longer , right ? because the pain would distract you from the task . well , maybe not ; it depends on how you handle pain . some people are distracted by pain . it takes them longer to complete a task , and they do it less well . other people use tasks to distract themselves from pain , and those people actually do the task faster and better when they 're in pain than when they 're not . some people can just send their mind wandering to distract themselves from pain . how can different people be subjected to the exact same painful stimulus and yet experience the pain so differently ? and why does this matter ? first of all , what is pain ? pain is an unpleasant sensory and emotional experience , associated with actual or potential tissue damage . pain is something we experience , so it 's best measured by what you say it is . pain has an intensity ; you can describe it on a scale from zero , no pain , to ten , the most pain imaginable . but pain also has a character , like sharp , dull , burning , or aching . what exactly creates these perceptions of pain ? well , when you get hurt , special tissue damage-sensing nerve cells , called nociceptors , fire and send signals to the spinal cord and then up to the brain . processing work gets done by cells called neurons and glia . this is your grey matter . and brain superhighways carry information as electrical impulses from one area to another . this is your white matter . the superhighway that carries pain information from the spinal cord to the brain is our sensing pathway that ends in the cortex , a part of the brain that decides what to do with the pain signal . another system of interconnected brain cells called the salience network decides what to pay attention to . since pain can have serious consequences , the pain signal immediately activates the salience network . now , you 're paying attention . the brain also responds to the pain and has to cope with these pain signals . so , motor pathways are activated to take your hand off a hot stove , for example . but modulation networks are also activated that deliver endorphins and enkephalins , chemicals released when you 're in pain or during extreme exercise , creating the runner 's high . these chemical systems help regulate and reduce pain . all these networks and pathways work together to create your pain experience , to prevent further tissue damage , and help you to cope with pain . this system is similar for everyone , but the sensitivity and efficacy of these brain circuits determines how much you feel and cope with pain . this is why some people have greater pain than others and why some develop chronic pain that does not respond to treatment , while others respond well . variability in pain sensitivities is not so different than all kinds of variability in responses to other stimuli . like how some people love roller coasters , but other people suffer from terrible motion sickness . why does it matter that there is variability in our pain brain circuits ? well , there are many treatments for pain , targeting different systems . for mild pain , non-prescription medications can act on cells where the pain signals start . other stronger pain medicines and anesthetics work by reducing the activity in pain-sensing circuits or boosting our coping system , or endorphins . some people can cope with pain using methods that involve distraction , relaxation , meditation , yoga , or strategies that can be taught , like cognitive behavioral therapy . for some people who suffer from severe chronic pain , that is pain that does n't go away months after their injury should have healed , none of the regular treatments work . traditionally , medical science has been about testing treatments on large groups to determine what would help a majority of patients . but this has usually left out some who did n't benefit from the treatment or experienced side effects . now , new treatments that directly stimulate or block certain pain-sensing attention or modulation networks are being developed , along with ways to tailor them to individual patients , using tools like magnetic resonance imaging to map brain pathways . figuring out how your brain responds to pain is the key to finding the best treatment for you . that 's true personalized medicine .

pain is something we experience , so it 's best measured by what you say it is . pain has an intensity ; you can describe it on a scale from zero , no pain , to ten , the most pain imaginable . but pain also has a character , like sharp , dull , burning , or aching .

pain is defined as ________ .

some of the issues that are important if you want to have people in space for long periods of time . one is that people will tend to lose bone and muscle mass . we know this . if you have to put a cast on your leg , and you take the cast off after a few weeks , you 'll see that your muscles have shrunk in size . and if you measured the bone strength , you 'd also see that might have gone down a little bit , too . and so , it 's very interesting that our body has that ability to adapt to the loads that are put on it , so that bones and muscles are n't static , they 're always changing . while we think of bone as being a solid thing that does n't change very much , it changes too . and it turns out that in weightlessness , you lose bone . and then you also cause the muscles that work against gravity , what are called the postural muscles , they 'll start to shrink and lose strength . there are other things in the cardiovascular system , the heart and blood vessels . and if you think about it , standing up in gravity means you have to work against gravity in order to keep blood pumping to your head . so , if you could n't keep blood pumping in the head , you 'd pass out every time you stood up because when you 're lying down , you do n't have to push against gravity . but when you stand up , you got to work against gravity to keep blood flowing to your head . and your heart and blood vessels have a really nicely worked-out system to make that happen every time . but that system can also change in weightlessness . and then the other area that changes is the system that has to do with balance . again , maintaining your balance is something that you 're doing against gravity , right ? if you did n't have gravity present , you would n't have to worry about falling . but you obviously do have to worry about falling , and we have a very highly developed sense of balance to keep us upright and to prevent us from falling . and when you see what skaters do , you realize just how exquisite a system it is . but when you go into weightlessness , your balance system changes . you do n't really notice it while you are in weightlessness , but when you come back , you do notice it , that your balance has changed and you have a little bit of trouble maintaining your balance . and what it shows is that while you 're in space , your brain is trying to allow you to function in weightlessness . and so , it re-adapts you to be weightless , which you do n't notice until you come back and find out that you 're now back on earth with a balance system that 's been adapted to space . you know , all life developed here on earth with gravity being present , so life evolved under the influence of gravity , and then we grow up with gravity being present , so we learn how to walk and catch a ball and ice skate or whatever , all with gravity being present . and what if you were to grow up without gravity ? what about the systems that depend on gravity , like your muscles or your balance system or the heart and blood vessels ? would they develop normally , or would they be different in some way ? one reason why you might think that it would go down a different pathway is from an experiment that was done some time ago by two neuroscientists called hubel and wiesel . and what they did is they had a kitten , and they put a patch over the eye of the kitten . and then the kitten grew up to be a cat , and they removed the patch . and so , the question is , can the cat see out of that eye ? now , there 's nothing wrong with the eye , right ? but it just has n't seen anything , there has n't been any light coming in . and the answer is that the cat ca n't see out of that eye because what happens is that the brain goes down a different pathway when it develops and the connections that would ordinarily develop to that eye do n't develop . and that ca n't be undone , that 's a permanent change . so , the brain of that cat is fundamentally different from the brain of a cat that grew up seeing out of that eye . that cat grew up with a different brain , in essence . so , then you wonder , well , what about gravity ? what if you do n't have the forces that gravity produces ? is your balance organ going to develop in the same way , or will it be different ? if somebody grew up in space , could they come back to earth and function , or would they really be a different person ?

and the answer is that the cat ca n't see out of that eye because what happens is that the brain goes down a different pathway when it develops and the connections that would ordinarily develop to that eye do n't develop . and that ca n't be undone , that 's a permanent change . so , the brain of that cat is fundamentally different from the brain of a cat that grew up seeing out of that eye .

bones and muscle are n't always static . they change .

tattoos have often been presented in popular media as either marks of the dangerous and deviant or trendy youth fads . but while tattoo styles come and go , and their meaning has differed greatly across cultures , the practice is as old as civilization itself . decorative skin markings have been discovered in human remains all over the world , with the oldest found on a peruvian mummy dating back to 6,000 bce . but have you ever wondered how tattooing really works ? you may know that we shed our skin , losing about 30-40,000 skin cells per hour . that 's about 1,000,000 per day . so , how come the tattoo does n't gradually flake off along with them ? the simple answer is that tattooing involves getting pigment deeper into the skin than the outermost layer that gets shed . throughout history , different cultures have used various methods to accomplish this . but the first modern tattooing machine was modeled after thomas edison 's engraving machine and ran on electricity . tattooing machines used today insert tiny needles , loaded with dye , into the skin at a frequency of 50 to 3,000 times per minute . the needles punch through the epidermis , allowing ink to seep deep into the dermis , which is composed of collagen fibers , nerves , glands , blood vessels and more . every time a needle penetrates , it causes a wound that alerts the body to begin the inflammatory process , calling immune system cells to the wound site to begin repairing the skin . and it is this very process that makes tattoos permanent . first , specialized cells called macrophages eat the invading material in an attempt to clean up the inflammatory mess . as these cells travel through the lymphatic system , some of them are carried back with a belly full of dye into the lymph nodes while others remain in the dermis . with no way to dispose of the pigment , the dyes inside them remain visible through the skin . some of the ink particles are also suspended in the gel-like matrix of the dermis , while others are engulfed by dermal cells called fibroblasts . initially , ink is deposited into the epidermis as well , but as the skin heals , the damaged epidermal cells are shed and replaced by new , dye-free cells with the topmost layer peeling off like a heeling sunburn . blistering or crusting is not typically seen with professional tattoos and complete epidermal regeneration requires 2-4 weeks , during which excess sun exposure and swimming should be avoided to prevent fading . dermal cells , however , remain in place until they die . when they do , they are taken up , ink and all , by younger cells nearby , so the ink stays where it is . but with time , tattoos do fade naturally as the body reacts to the alien pigment particles , slowly breaking them down to be carried off by the immune system 's macrophages . ultraviolet radiation can also contribute to this pigment breakdown , though it can be mitigated by the use of sunblock . but since the dermal cells are relatively stable , much of the ink will remain deep in the skin for a person 's whole life . but if tattoos are embedded in your skin for life , is there any way to erase them ? technically , yes . today , a laser is used to penetrate the epidermis and blast apart underlying pigment colors of various wavelengths , black being the easiest to target . the laser beam breaks the ink globules into smaller particles that can then be cleared away by the macrophages . but some color inks are harder to remove than others , and there could be complications . for this reason , removing a tattoo is still more difficult than getting one , but not impossible . so a single tattoo may not truly last forever , but tattoos have been around longer than any existing culture . and their continuing popularity means that the art of tattooing is here to stay .

and it is this very process that makes tattoos permanent . first , specialized cells called macrophages eat the invading material in an attempt to clean up the inflammatory mess . as these cells travel through the lymphatic system , some of them are carried back with a belly full of dye into the lymph nodes while others remain in the dermis . with no way to dispose of the pigment , the dyes inside them remain visible through the skin .

macrophages are immune cells that are also part of the lymphatic system . describe the components of lymphatic system and why it ’ s important for immunity .

have you ever noticed something swimming in your field of vision ? it may look like a tiny worm or a transparent blob , and whenever you try to get a closer look , it disappears , only to reappear as soon as you shift your glance . but do n't go rinsing out your eyes ! what you are seeing is a common phenomenon known as a floater . the scientific name for these objects is muscae volitantes , latin for `` flying flies , '' and true to their name , they can be somewhat annoying . but they 're not actually bugs or any kind of external objects at all . rather , they exist inside your eyeball . floaters may seem to be alive , since they move and change shape , but they are not alive . floaters are tiny objects that cast shadows on the retina , the light-sensitive tissue at the back of your eye . they might be bits of tissue , red blood cells , or clumps of protein . and because they 're suspended within the vitreous humor , the gel-like liquid that fills the inside of your eye , floaters drift along with your eye movements , and seem to bounce a little when your eye stops . floaters may be only barely distinguishable most of the time . they become more visible the closer they are to the retina , just as holding your hand closer to a table with an overhead light will result in a more sharply defined shadow . and floaters are particularly noticeable when you are looking at a uniform bright surface , like a blank computer screen , snow , or a clear sky , where the consistency of the background makes them easier to distinguish . the brighter the light is , the more your pupil contracts . this has an effect similar to replacing a large diffuse light fixture with a single overhead light bulb , which also makes the shadow appear clearer . there is another visual phenomenon that looks similar to floaters but is in fact unrelated . if you 've seen tiny dots of light darting about when looking at a bright blue sky , you 've experienced what is known as the blue field entoptic phenomenon . in some ways , this is the opposite of seeing floaters . here , you are not seeing shadows but little moving windows letting light through to your retina . the windows are actually caused by white blood cells moving through the capillaries along your retina 's surface . these leukocytes can be so large that they nearly fill a capillary causing a plasma space to open up in front of them . because the space and the white blood cells are both more transparent to blue light than the red blood cells normally present in capillaries , we see a moving dot of light wherever this happens , following the paths of your capillaries and moving in time with your pulse . under ideal viewing conditions , you might even see what looks like a dark tail following the dot . this is the red blood cells that have bunched up behind the leukocyte . some science museums have an exhibit which consists of a screen of blue light , allowing you to see these blue sky sprites much more clearly than you normally would . while everybody 's eyes experience these sort of effects , the number and type vary greatly . in the case of floaters , they often go unnoticed , as our brain learns to ignore them . however , abnormally numerous or large floaters that interfere with vision may be a sign of a more serious condition , requiring immediate medical treatment . but the majority of the time entoptic phenomena , such as floaters and blue sky sprites , are just a gentle reminder that what we think we see depends just as much on our biology and minds as it does on the external world .

if you 've seen tiny dots of light darting about when looking at a bright blue sky , you 've experienced what is known as the blue field entoptic phenomenon . in some ways , this is the opposite of seeing floaters . here , you are not seeing shadows but little moving windows letting light through to your retina .

seeing floaters is normal . but if you suddenly see many more small floaters , there might be a serious problem . what might be happening ?

it was a night like any other night , except here i was climbing the platonic peaks like romeo on a second date . ( ugh ) i was there for the dame . she had eyes like imaginary numbers and curves that went on forever . said she wanted to go home . said i could help . said the pay was good . did n't say anything about climbing a ... voice : `` who 's there ? '' manny brot : `` manny brot , private eye . '' voice : `` what are you doing here ? '' `` a pretty number sent me to find a stolen dingus . '' voice : `` well , to enter the cave , you must answer my riddles three . '' what was it with riddles , and why do they always come in threes ? `` is it an egg ? '' `` no . why would it be an egg ? '' `` it 's usually an egg . '' `` what can i hold in my hand , but has zero area ? '' `` is it a dodo egg ? '' `` it 's not an egg ! '' i took out the rock that had nearly brained me before and gave it a hard ponder . the size of the rising bump on my conk said to me that this thing had area , and a lot of it . but what if i carved out a triangle from this side here ? as any mook could see , this triangle had a quarter of the area of the full triangle . i did the same thing again with each of the smaller triangles . again , a quarter of the remaining area -- gone . and i just kept going . after an infinite number of cuts , i was satisfied that my triangle had zero area . a bounded shape with zero area . now , it 's not often that i surprise myself , but my own two mitts had created something crazy , and new . `` very good . ( ahem ) now , show me a shape with finite area , but an infinitely long perimeter . '' `` let me get this straight . if i want to make a snip in the border of this shape , smooth it out , and lay it on the ground ... `` `` it would go on for ... `` `` wait 'til i 'm through , and then you can talk . it would go on forever . '' `` are you through ? '' `` yeah . '' `` so show me that shape then . '' mmm ... i had n't been this stuck since the rubik 's cube fiasco of '58 . all the shapes i knew had perimeters . circles : 2πr . triangles : sum of their sides . what 's this ? an angle . an angle from heaven . what if i were to pinch each side , like so . a third of the way through , just so . and do it again , and again , and again . after each pinch , the perimeter got a third longer because where there had been three line segments , now there were four . as for the area , every pinch made more triangles , that 's true . but those triangles were getting smaller and smaller . you could say that the area was converging , approaching a fixed number , while the perimeter was just getting bigger and bigger , uncontrollably ballooning like an overindulgent birthday clown . after infinity pinches , flimflam , there it was : finite area , but infinite perimeter . now that is a piece of work . `` oh , you 're good . ( ahem ) riddle three : show me a picture that if i magnify it under my microscope , i 'll keep seeing the original picture , no matter how much i zoom in . '' `` you 're a strange little man . '' `` thank you . '' i was out of ideas , so i looked at my muse , my complex dora . voice : `` who 's the dame ? '' and then it hit me . `` she 's a heart breaker , my fractal femme fatale . will she do ? '' `` yes , she 'll do just fine . '' ( lightning ) it was dark , and at first i thought the cave was empty , but then i noticed : the box . the dame had played me like a triangle . she had told me she wanted to go home . ( lightning ) what she really wanted was to bring her home here . the fractals spread everywhere . most of them the same no matter how deep you looked at them , like dora 's mugshot . some had infinitely long perimeters , others were objects with no area or volume , all of them created through infinite repetition . so , you wanted to know what fractals are ? well , kid , they 're the stuff that dreams are made of . ( music )

( lightning ) what she really wanted was to bring her home here . the fractals spread everywhere . most of them the same no matter how deep you looked at them , like dora 's mugshot .

which of these is a characteristic of fractals ?

think about all the things that need to happen for a human settlement to thrive : obtaining food , building shelter , raising children and more . there needs to be a way to divide resources , organize major efforts and distribute labor efficiently . now imagine having to do this without any sort of planning or higher level communication . welcome to the ant colony . ants have some of the most complex social organization in the animal kingdom , living in structured colonies containing different types of members who perform specific roles . but although this may sound similar to some human societies , this organization does n't arise from any higher level decisions , but is part of a biologically programmed cycle . in many species , all the winged males and winged virgin queens from all the nearby colonies in the population each leave from their different nests and meet at a central place to mate , using pheromones to guide each other to a breeding ground . after mating , the males die off , while females try to establish a new colony . the few that are successful settle down in a suitable spot , lose their wings , and begin laying eggs , selectively fertilizing some using stored sperm they 've saved up from mating . fertilized eggs grow into female workers who care for the queen and her eggs . they will then defend the colony and forage for food , while unfertilized eggs grow into males whose only job is to wait until they are ready to leave the nest and reproduce , beginning the cycle again . so how do worker ants decide what to do and when ? well , they do n't really . although they have no methods of intentional communication , individual ants do interact with one another through touch , sound and chemical signals . these stimuli accomplish many things from serving as an alarm to other ants if one is killed , to signaling when a queen is nearing the end of her reproductive life . but one of the most impressive collective capabilities of an ant colony is to thoroughly and efficiently explore large areas without any predetermined plan . most species of ants have little or no sense of sight and can only smell things in their vicinity . combined with their lack of high level coordination , this would seem to make them terrible explorers , but there is an amazingly simple way that ants maximize their searching efficiency ; by changing their movement patterns based on individual interactions . when two ants meet , they sense each other by touching antennae . if there are many ants in a small area this will happen more often causing them to respond by moving in more convoluted , random paths in order to search more thoroughly . but in a larger area , with less ants , where such meetings happen less often , they can walk in straight lines to cover more ground . while exploring their environment in this way , an ant may come across any number of things , from threats or enemies , to alternate nesting sites . and some species have another capability known as recruitment . when one of these ants happens to find food , it will return with it , marking its path with a chemical scent . other ants will then follow this pheromone trail , renewing it each time they manage to find food and return . once the food in that spot is depleted , the ants stop marking their return . the scent dissipates and ants are no longer attracted to that path . these seemingly crude methods of search and retrieval are , in fact , so useful that they are applied in computer models to obtain optimal solutions from decentralized elements , working randomly and exchanging simple information . this has many theoretical and practical applications , from solving the famous traveling salesman problem , to scheduling computing tasks and optimizing internet searches , to enabling groups of robots to search a minefield or a burning building collectively , without any central control . but you can observe these fascinatingly simple , yet effective , processes directly through some simple experiments , by allowing ants to enter empty spaces of various sizes and paying attention to their behavior . ants may not be able to vote , hold meetings or even make any plans , but we humans may still be able to learn something from the way that such simple creatures are able to function so effectively in such complex ways .

when two ants meet , they sense each other by touching antennae . if there are many ants in a small area this will happen more often causing them to respond by moving in more convoluted , random paths in order to search more thoroughly . but in a larger area , with less ants , where such meetings happen less often , they can walk in straight lines to cover more ground . while exploring their environment in this way , an ant may come across any number of things , from threats or enemies , to alternate nesting sites .

when is it best to search thoroughly , and when is it best to cover more area ?

is it a flying comma , or a quotation mark chopped in half ? either way , you may already be well-versed in how to use the apostrophe , but here 's a quick refresher on its usage . the apostrophe can be used in three ways : to mark possession , to mark contraction , to mark the plural of single letters . most of the time , if you see an apostrophe hovering helpfully near a word , it 's trying to mark possession or contraction . first , let 's look at how the apostrophe marks possession . as you can see , the placement of this punctuation mark can really change the meaning of a sentence . `` those robots in the sand are my sister 's . '' `` those robots in the sand are my sisters . ' '' `` those robots in the sand are my sisters . '' when showing possession , the apostrophe belongs next to the noun that owns or possesses something . the noun can be singular or plural . proper nouns work , too . so if lucy needs to get her robots under control before they cause mayhem , those dangerous creatures would be `` lucy 's robots . '' but what if lucy was lucas ? would we write `` lucas ' robots '' or `` lucas 's robots '' ? and what if lucas gave his robots to the robinsons family ? would it be `` the robinsons ' robots , '' or `` the robinsons 's robots '' ? the truth is , even grammar nerds disagree on the right thing to do . the use of 's after a proper noun ending in s is a style issue , not a hard and fast grammar rule . it 's a conundrum without a simple answer . professional writers solve this problem by learning what 's considered correct for a publication , and doing that . the important thing is to pick one style and stick with it throughout a piece of writing . one more wrinkle . certain pronouns already have possession built in and do n't need an apostrophe . remembering that will help you avoid one of the trickiest snags in english grammar : its vs. it 's . `` it 's '' only take an apostrophe when it 's a contraction for `` it is '' or `` it has . '' if you can replace `` it 's '' with one of those two phrases , use the apostrophe . if you 're showing possession , leave it out . otherwise , contractions are pretty straightforward . the apostrophe stands in for missing letters , and lets common phrases squash into a single word . in rare cases , you can have a double contraction , though those generally are n't accepted in writing , with the exception of dialogue . so it 's possessive , it 's often followed by s 's , and it 's sometimes tricky when it comes to its usage . it 's the apostrophe .

would it be `` the robinsons ' robots , '' or `` the robinsons 's robots '' ? the truth is , even grammar nerds disagree on the right thing to do . the use of 's after a proper noun ending in s is a style issue , not a hard and fast grammar rule .

why do even grammar nerds disagree on whether to use an apostrophe-s after a proper noun ending in `` s '' ?

it begins with a bit of discomfort and soon becomes a pressing sensation that 's impossible to ignore . finally , it 's all you can think about , and out of sheer desperation , you go on a hunt for a bathroom until `` ahh . '' humans should urinate at least four to six times a day , but occasionally , the pressures of modern life forces us to clench and hold it in . how bad is this habit , and how long can our bodies withstand it ? the answers lie in the workings of the bladder , an oval pouch that sits inside the pelvis . surrounding this structure are several other organs that together make up the whole urinary system . two kidneys , two ureters , two urethral sphincters , and a urethra . constantly trickling down from the kidneys is the yellowish liquid known as urine . the kidneys make urine from a mix of water and the body 's waste products , funneling the unwanted fluid into two muscular tubes called ureters . these carry it downward into the hollow organ known as the bladder . this organ 's muscular wall is made of tissue called detrusor muscle which relaxes as the bladder fills allowing it to inflate like a balloon . as the bladder gets full , the detrusor contracts . the internal urethral sphincter automatically and involuntarily opens , and the urine is released . whooshing downwards , the fluid enters the urethra and stops short at the external urethral sphincter . this works like a tap . when you want to delay urinating , you keep the sphincter closed . when you want to release it , you can voluntarily open the flood gates . but how do you sense your bladder 's fullness so you know when to pee ? inside the layers of detrusor muscles are millions of stretch receptors that get triggered as the bladder fills . they send signals along your nerves to the sacral region in your spinal cord . a reflex signal travels back to your bladder , making the detrusor muscle contract slightly and increasing the bladder 's pressure so you 're aware that it 's filling up . simultaneously , the internal urethral sphincter opens . this is called the micturition reflex . the brain can counter it if it 's not a good time to urinate by sending another signal to contract the external urethral sphincter . with about 150 to 200 milliliters of urine inside of it , the bladder 's muscular wall is stretched enough for you to sense that there 's urine within . at about 400 to 500 milliliters , the pressure becomes uncomfortable . the bladder can go on stretching , but only to a point . above 1,000 milliliters , it may burst . most people would lose bladder control before this happens , but in very rare cases , such as when as a person ca n't sense the need to urinate , the pouch can rupture painfully requiring surgery to fix . but under normal circumstances , your decision to urinate stops the brain 's signal to the external urethral sphincter , causing it to relax and the bladder to empty . the external urethral sphincter is one of the muscles of the pelvic floor , and it provides support to the urethra and bladder neck . it 's lucky we have these pelvic floor muscles because placing pressure on the system by coughing , sneezing , laughing , or jumping could cause bladder leakage . instead , the pelvic floor muscles keep the region sealed until you 're ready to go . but holding it in for too long , forcing out your urine too fast , or urinating without proper physical support may over time weaken or overwork that muscular sling . that can lead to an overactive pelvic floor , bladder pain , urgency , or urinary incontinence . so in the interest of long-term health , it 's not a great habit to hold your pee . but in the short term , at least , your body and brain have got you covered , so you can conveniently choose your moment of sweet release .

but holding it in for too long , forcing out your urine too fast , or urinating without proper physical support may over time weaken or overwork that muscular sling . that can lead to an overactive pelvic floor , bladder pain , urgency , or urinary incontinence . so in the interest of long-term health , it 's not a great habit to hold your pee .

what do you think would happen to the muscles of the pelvic floor if a human only went to empty their bladder once or twice per day ?

if you think of culture as an iceberg , only a small fraction of it is visible . food , flags , and festivals , which are often talked about in schools , are the visible parts that we rightly celebrate . however , only when we look deeper , under the water , are we able to focus on the common values that connect us . in what seems to be an increasingly troubled world , where social and political systems are being stretched , conflict within and between countries is at times heightened , while human rights are being ignored , this desire for peace grows ever stronger . sometimes we see this common value emerging above the surface and becoming visible . for example , it is part of everyday language used when people greet one another and welcome the new day . in many parts of the arab world and parts of south asia , such as bangladesh for example , the greeting of `` as-salamu alaykum '' can be translated to `` peace be with you . '' the same is true as you walk through markets or into schools each morning in india , or nepal , or bhutan , where greetings of `` namaste , '' which has not only a strong message of peace - `` the spirit in me greets the spirit in you '' - but also its physical gesture , the palms brought together slowly at the heart , to honor a special place in each of us . in myanmar , greetings of `` mingalarbar '' are met by bowing monks as they internalize a message where others add blessing to enhance the auspiciousness of the moment , or by giggling children as they scurry off to school . after many hours of hiking through the mountains of lesotho , surrounded by the tranquility and rugged terrain , you are likely to meet a herdboy who has slept the night in a vacant rondoval and bellows out greetings of `` lumela '' or `` khotso '' , which means `` peace be with you . '' if you took a moment to research further the meanings behind `` shalom , '' or the korean greeting , you would find that they too have deeply-seated connections to peace . however , they have become quick comments made to welcome , greet , and say hello , and in this overuse , have likely lost the focus that was originally intended when put into practice hundreds or thousands of years ago . in highlighting this simple evidence of ingrained behavior , we can create the necessary shift in thinking needed to incorporate flexibility and open-mindedness in us all when looking at the globalization of the world .

for example , it is part of everyday language used when people greet one another and welcome the new day . in many parts of the arab world and parts of south asia , such as bangladesh for example , the greeting of `` as-salamu alaykum '' can be translated to `` peace be with you . '' the same is true as you walk through markets or into schools each morning in india , or nepal , or bhutan , where greetings of `` namaste , '' which has not only a strong message of peace - `` the spirit in me greets the spirit in you '' - but also its physical gesture , the palms brought together slowly at the heart , to honor a special place in each of us .

in the video , there are many images that conjure thoughts of peace . name some of those images , and explain why they make you think of peace . what are some images not seen in the video that make you think of peace .

each time you take a step , 200 muscles work in unison to lift your foot , propel it forward , and set it down . it 's just one of the many thousands of tasks performed by the muscular system . this network of over 650 muscles covers the body and is the reason we can blink , smile , run , jump , and stand upright . it 's even responsible for the heart 's dependable thump . first , what exactly is the muscular system ? it 's made up of three main muscle types : skeletal muscle , which attaches via tendons to our bones , cardiac muscle , which is only found in the heart , and smooth muscle , which lines the blood vessels and certain organs , like the intestine and uterus . all three types are made up of muscle cells , also known as fibers , bundled tightly together . these bundles receive signals from the nervous system that contract the fibers , which in turn generates force and motion . this produces almost all the movements we make . some of the only parts of the body whose motions are n't governed by the muscular system are sperm cells , the hair-like cilia in our airways , and certain white blood cells . muscle contraction can be split into three main types . the first two , shortening muscle fibers and lengthening them , generate opposing forces . so the biceps will shorten while the triceps will lengthen or relax , pulling up the arm and making it bend at the elbow . this allows us to , say , pick up a book , or if the muscle relationship is reversed , put it down . this complementary partnership exists throughout the muscular system . the third type of contraction creates a stabilizing force . in these cases , the muscle fibers do n't change in length , but instead keep the muscles rigid . this allows us to grip a mug of coffee or lean against a wall . it also maintains our posture by holding us upright . skeletal muscles form the bulk of the muscular system , make up about 30-40 % of the body 's weight , and generate most of its motion . some muscles are familiar to us , like the pectorals and the biceps . others may be less so , like the buccinator , a muscle that attaches your cheek to your teeth , or the body 's tiniest skeletal muscle , a one-millimeter-long tissue fragment called the stapedius that 's nestled deep inside the ear . wherever they occur , skeletal muscles are connected to the somatic nervous system , which gives us almost complete control over their movements . this muscle group also contains two types of muscle fibers to refine our motions even further , slow-twitch and fast-twitch . fast-twitch fibers react instantly when triggered but quickly use up their energy and tire out . slow-twitch fibers , on the other hand , are endurance cells . they react and use energy slowly so they can work for longer periods . a sprinter will accumulate more fast-twitch muscles in her legs through continuous practice , enabling her to quickly , if briefly , pick up the pace , whereas back muscles contain more slow-twitch muscles to maintain your posture all day . unlike the skeletal muscles , the body 's cardiac and smooth muscles are managed by the autonomic nervous system beyond our direct control . that makes your heart thump roughly 3 billion times over the course of your life , which supplies the body with blood and oxygen . autonomic control also contracts and relaxes smooth muscle in a rhythmic cycle . that pumps blood through the smooth internal walls of blood vessels , enables the intestine to constrict and push food through the digestive system , and allows the uterus to contract when a person is giving birth . as muscles work , they also use energy and produce an important byproduct , heat . in fact , muscle provides about 85 % of your warmth , which the heart and blood vessels then spread evenly across the body via the blood . without that , we could n't maintain the temperature necessary for our survival . the muscular system may be largely invisible to us , but it leaves its mark on almost everything we do , whether it 's the blink of an eye or a race to the finish line .

this complementary partnership exists throughout the muscular system . the third type of contraction creates a stabilizing force . in these cases , the muscle fibers do n't change in length , but instead keep the muscles rigid .

one type of muscle contraction results in a stabilizing force . this :

how many people here would like to live to be at least 80 years old ? yeah . i think we all have this hopeful expectation of living into old age . let 's project out into the future , to your future `` you 's , '' and let 's imagine that we 're all 85 . now , everyone look at two people . one of you probably has alzheimer 's disease . ( laughter ) alright , alright . and maybe you 're thinking , `` well , it wo n't be me . '' then , ok. you are a caregiver . so -- ( laughter ) so in some way , this terrifying disease is likely to affect us all . part of the fear around alzheimer 's stems from the sense that there 's nothing we can do about it . despite decades of research , we still have no disease-modifying treatment and no cure . so if we 're lucky enough to live long enough , alzheimer 's appears to be our brain 's destiny . but maybe it does n't have to be . what if i told you we could change these statistics , literally change our brain 's destiny , without relying on a cure or advancements in medicine ? let 's begin by looking at what we currently understand about the neuroscience of alzheimer 's . here 's a picture of two neurons connecting . the point of connection , this space circled in red , is called the synapse . the synapse is where neurotransmitters are released . this is where signals are transmitted , where communication happens . this is where we think , feel , see , hear , desire ... and remember . and the synapse is where alzheimer 's happens . let 's zoom in on the synapse and look at a cartoon representation of what 's going on . during the business of communicating information , in addition to releasing neurotransmitters like glutamate into the synapse , neurons also release a small peptide called amyloid beta . normally , amyloid beta is cleared away metabolized by microglia , the janitor cells of our brains . while the molecular causes of alzheimer 's are still debated , most neuroscientists believe that the disease begins when amyloid beta begins to accumulate . too much is released , or not enough is cleared away , and the synapse begins to pile up with amyloid beta . and when this happens , it binds to itself , forming sticky aggregates called amyloid plaques . how many people here are 40 years old or older ? you 're afraid to admit it now . this initial step into the disease , this presence of amyloid plaques accumulating , can already be found in your brains . the only way we could be sure of this would be through a pet scan , because at this point , you are blissfully unaware . you 're not showing any impairments in memory , language , or cognition ... yet . we think it takes at least 15 to 20 years of amyloid plaque accumulation before it reaches a tipping point , then triggering a molecular cascade that causes the clinical symptoms of the disease . prior to the tipping point , your lapses in memory might include things like , `` why did i come in this room ? '' or `` oh ... what 's his name ? '' or `` where did i put my keys ? '' now , before you all start freaking out again , because i know half of you did at least one of those in the last 24 hours -- these are all normal kinds of forgetting . in fact , i would argue that these examples might not even involve your memory , because you did n't pay attention to where you put your keys in the first place . after the tipping point , the glitches in memory , language and cognition are different . instead of eventually finding your keys in your coat pocket or on the table by the door , you find them in the refrigerator , or you find them and you think , `` what are these for ? '' so what happens when amyloid plaques accumulate to this tipping point ? our microglia janitor cells become hyper-activated , releasing chemicals that cause inflammation and cellular damage . we think they might actually start clearing away the synapses themselves . a crucial neural transport protein called `` tau '' becomes hyperphosphorylated and twists itself into something called `` tangles , '' which choke off the neurons from the inside . by mid-stage alzheimer 's , we have massive inflammation and tangles and all-out war at the synapse and cell death . so if you were a scientist trying to cure this disease , at what point would you ideally want to intervene ? many scientists are betting big on the simplest solution : keep amyloid plaques from reaching that tipping point , which means that drug discovery is largely focused on developing a compound that will prevent , eliminate , or reduce amyloid plaque accumulation . so the cure for alzheimer 's will likely be a preventative medicine . we 're going to have to take this pill before we reach that tipping point , before the cascade is triggered , before we start leaving our keys in the refrigerator . we think this is why , to date , these kinds of drugs have failed in clinical trials -- not because the science was n't sound , but because the people in these trials were already symptomatic . it was too late . think of amyloid plaques as a lit match . at the tipping point , the match sets fire to the forest . once the forest is ablaze , it does n't do any good to blow out the match . you have to blow out the match before the forest catches fire . even before scientists sort this out , this information is actually really good news for us , because it turns out that the way we live can influence the accumulation of amyloid plaques . and so there are things we can do to keep us from reaching that tipping point . let 's picture your risk of alzheimer 's as a see-saw scale . we 're going to pile risk factors on one arm , and when that arm hits the floor , you are symptomatic and diagnosed with alzheimer 's . let 's imagine you 're 50 years old . you 're not a spring chicken anymore , so you 've accumulated some amyloid plaques with age . your scale is tipped a little bit . now let 's look at your dna . we 've all inherited our genes from our moms and our dads . some of these genes will increase our risk and some will decrease it . if you 're like alice in `` still alice , '' you 've inherited a rare genetic mutation that cranks out amyloid beta , and this alone will tip your scale arm to the ground . but for most of us , the genes we inherit will only tip the arm a bit . for example , apoe4 is a gene variant that increases amyloid , but you can inherit a copy of apoe4 from mom and dad and still never get alzheimer 's , which means that for most of us , our dna alone does not determine whether we get alzheimer 's . so what does ? we ca n't do anything about getting older or the genes we 've inherited . so far , we have n't changed our brain 's destiny . what about sleep ? in slow-wave deep sleep , our glial cells rinse cerebral spinal fluid throughout our brains , clearing away metabolic waste that accumulated in our synapses while we were awake . deep sleep is like a power cleanse for the brain . but what happens if you shortchange yourself on sleep ? many scientists believe that poor sleep hygiene might actually be a predictor of alzheimer 's . a single night of sleep deprivation leads to an increase in amyloid beta . and amyloid accumulation has been shown to disrupt sleep , which in turn causes more amyloid to accumulate . and so now we have this positive feedback loop that 's going to accelerate the tipping of that scale . what else ? cardiovascular health . high blood pressure , diabetes , obesity , smoking , high cholesterol , have all been shown to increase our risk of developing alzheimer 's . some autopsy studies have shown that as many as 80 percent of people with alzheimer 's also had cardiovascular disease . aerobic exercise has been shown in many studies to decrease amyloid beta in animal models of the disease . so a heart-healthy mediterranean lifestyle and diet can help to counter the tipping of this scale . so there are many things we can do to prevent or delay the onset of alzheimer 's . but let 's say you have n't done any of them . let 's say you 're 65 ; there 's alzheimer 's in your family , so you 've likely inherited a gene or two that tips your scale arm a bit ; you 've been burning the candle at both ends for years ; you love bacon ; and you do n't run unless someone 's chasing you . ( laughter ) let 's imagine that your amyloid plaques have reached that tipping point . your scale arm has crashed to the floor . you 've tripped the cascade , setting fire to the forest , causing inflammation , tangles , and cell death . you should be symptomatic for alzheimer 's . you should be having trouble finding words and keys and remembering what i said at the beginning of this talk . but you might not be . there 's one more thing you can do to protect yourself from experiencing the symptoms of alzheimer 's , even if you have the full-blown disease pathology ablaze in your brain . it has to do with neural plasticity and cognitive reserve . remember , the experience of having alzheimer 's is ultimately a result of losing synapses . the average brain has over a hundred trillion synapses , which is fantastic ; we 've got a lot to work with . and this is n't a static number . we gain and lose synapses all the time , through a process called neural plasticity . every time we learn something new , we are creating and strengthening new neural connections , new synapses . in the nun study , 678 nuns , all over the age of 75 when the study began , were followed for more than two decades . they were regularly given physical checkups and cognitive tests , and when they died , their brains were all donated for autopsy . in some of these brains , scientists discovered something surprising . despite the presence of plaques and tangles and brain shrinkage -- what appeared to be unquestionable alzheimer 's -- the nuns who had belonged to these brains showed no signs of having the disease while they were alive . how can this be ? we think it 's because these nuns had a high level of cognitive reserve , which is a way of saying that they had more functional synapses . people who have more years of formal education , who have a high degree of literacy , who engage regularly in mentally stimulating activities , all have more cognitive reserve . they have an abundance and a redundancy in neural connections . so even if they have a disease like alzheimer 's compromising some of their synapses , they 've got many extra backup connections , and this buffers them from noticing that anything is amiss . let 's imagine a simplified example . let 's say you only know one thing about a subject . let 's say it 's about me . you know that lisa genova wrote `` still alice , '' and that 's the only thing you know about me . you have that single neural connection , that one synapse . now imagine you have alzheimer 's . you have plaques and tangles and inflammation and microglia devouring that synapse . now when someone asks you , `` hey , who wrote 'still alice ? ' '' you ca n't remember , because that synapse is either failing or gone . you 've forgotten me forever . but what if you had learned more about me ? let 's say you learned four things about me . now imagine you have alzheimer 's , and three of those synapses are damaged or destroyed . you still have a way to detour the wreckage . you can still remember my name . so we can be resilient to the presence of alzheimer 's pathology through the recruitment of yet-undamaged pathways . and we create these pathways , this cognitive reserve , by learning new things . ideally , we want these new things to be as rich in meaning as possible , recruiting sight and sound and associations and emotion . so this really does n't mean doing crossword puzzles . you do n't want to simply retrieve information you 've already learned , because this is like traveling down old , familiar streets , cruising neighborhoods you already know . you want to pave new neural roads . building an alzheimer's-resistant brain means learning to speak italian , meeting new friends , reading a book , or listening to a great ted talk . and if , despite all of this , you are someday diagnosed with alzheimer 's , there are three lessons i 've learned from my grandmother and the dozens of people i 've come to know living with this disease . diagnosis does n't mean you 're dying tomorrow . keep living . you wo n't lose your emotional memory . you 'll still be able to understand love and joy . you might not remember what i said five minutes ago , but you 'll remember how i made you feel . and you are more than what you can remember . thank you . ( applause )

building an alzheimer's-resistant brain means learning to speak italian , meeting new friends , reading a book , or listening to a great ted talk . and if , despite all of this , you are someday diagnosed with alzheimer 's , there are three lessons i 've learned from my grandmother and the dozens of people i 've come to know living with this disease . diagnosis does n't mean you 're dying tomorrow .

what are the three lessons that genova has learned from her grandmother and other alzheimer ’ s patients ?

in the early days of organic chemistry , chemists understood that molecules were made of atoms connected through chemical bonds . however , the three-dimensional shapes of molecules were utterly unclear , since they could n't be observed directly . molecules were represented using simple connectivity graphs like the one you see here . it was clear to savvy chemists of the mid-19th century that these flat representations could n't explain many of their observations . but chemical theory had n't provided a satisfactory explanation for the three-dimensional structures of molecules . in 1874 , the chemist va n't hoff published a remarkable hypothesis : the four bonds of a saturated carbon atom point to the corners of a tetrahedron . it would take over 25 years for the quantum revolution to theoretically validate his hypothesis . but va n't hoff supported his theory using optical rotation . va n't hoff noticed that only compounds containing a central carbon bound to four different atoms or groups rotated plane-polarized light . clearly there 's something unique about this class of compounds . take a look at the two molecules you see here . each one is characterized by a central , tetrahedral carbon atom bound to four different atoms : bromine , chlorine , fluorine , and hydrogen . we might be tempted to conclude that the two molecules are the same , if we just concern ourselves with what they 're made of . however , let 's see if we can overlay the two molecules perfectly to really prove that they 're the same . we have free license to rotate and translate both of the molecules as we wish . remarkably though , no matter how we move the molecules , we find that perfect superposition is impossible to achieve . now take a look at your hands . notice that your two hands have all the same parts : a thumb , fingers , a palm , etc . like our two molecules under study , both of your hands are made of the same stuff . furthermore , the distances between stuff in both of your hands are the same . the index finger is next to the middle finger , which is next to the ring finger , etc . the same is true of our hypothetical molecules . all of their internal distances are the same . despite the similarities between them , your hands , and our molecules , are certainly not the same . try superimposing your hands on one another . just like our molecules from before , you 'll find that it ca n't be done perfectly . now , point your palms toward one another . wiggle both of your index fingers . notice that your left hand looks as if it 's looking in a mirror at your right . in other words , your hands are mirror images . the same can be said of our molecules . we can turn them so that one looks at the other as in a mirror . your hands - and our molecules - possess a spatial property in common called chirality , or handedness . chirality means exactly what we 've just described : a chiral object is not the same as its mirror image . chiral objects are very special in both chemistry and everyday life . screws , for example , are also chiral . that 's why we need the terms right-handed and left-handed screws . and believe it or not , certain types of light can behave like chiral screws . packed into every linear , plane-polarized beam of light are right-handed and left-handed parts that rotate together to produce plane polarization . chiral molecules , placed in a beam of such light , interact differently with the two chiral components . as a result , one component of the light gets temporarily slowed down relative to the other . the effect on the light beam is a rotation of its plane from the original one , otherwise known as optical rotation . va n't hoff and later chemists realized that the chiral nature of tetrahedral carbons can explain this fascinating phenomenon . chirality is responsible for all kinds of other fascinating effects in chemistry , and everyday life . humans tend to love symmetry and so if you look around you , you 'll find that chiral objects made by humans are rare . but chiral molecules are absolutely everywhere . phenomena as separate as optical rotation , screwing together furniture , and clapping your hands all involve this intriguing spatial property .

packed into every linear , plane-polarized beam of light are right-handed and left-handed parts that rotate together to produce plane polarization . chiral molecules , placed in a beam of such light , interact differently with the two chiral components . as a result , one component of the light gets temporarily slowed down relative to the other .

van ’ t hoff postulated that chiral compounds contained at least one atom with what geometry ?

tattoos have often been presented in popular media as either marks of the dangerous and deviant or trendy youth fads . but while tattoo styles come and go , and their meaning has differed greatly across cultures , the practice is as old as civilization itself . decorative skin markings have been discovered in human remains all over the world , with the oldest found on a peruvian mummy dating back to 6,000 bce . but have you ever wondered how tattooing really works ? you may know that we shed our skin , losing about 30-40,000 skin cells per hour . that 's about 1,000,000 per day . so , how come the tattoo does n't gradually flake off along with them ? the simple answer is that tattooing involves getting pigment deeper into the skin than the outermost layer that gets shed . throughout history , different cultures have used various methods to accomplish this . but the first modern tattooing machine was modeled after thomas edison 's engraving machine and ran on electricity . tattooing machines used today insert tiny needles , loaded with dye , into the skin at a frequency of 50 to 3,000 times per minute . the needles punch through the epidermis , allowing ink to seep deep into the dermis , which is composed of collagen fibers , nerves , glands , blood vessels and more . every time a needle penetrates , it causes a wound that alerts the body to begin the inflammatory process , calling immune system cells to the wound site to begin repairing the skin . and it is this very process that makes tattoos permanent . first , specialized cells called macrophages eat the invading material in an attempt to clean up the inflammatory mess . as these cells travel through the lymphatic system , some of them are carried back with a belly full of dye into the lymph nodes while others remain in the dermis . with no way to dispose of the pigment , the dyes inside them remain visible through the skin . some of the ink particles are also suspended in the gel-like matrix of the dermis , while others are engulfed by dermal cells called fibroblasts . initially , ink is deposited into the epidermis as well , but as the skin heals , the damaged epidermal cells are shed and replaced by new , dye-free cells with the topmost layer peeling off like a heeling sunburn . blistering or crusting is not typically seen with professional tattoos and complete epidermal regeneration requires 2-4 weeks , during which excess sun exposure and swimming should be avoided to prevent fading . dermal cells , however , remain in place until they die . when they do , they are taken up , ink and all , by younger cells nearby , so the ink stays where it is . but with time , tattoos do fade naturally as the body reacts to the alien pigment particles , slowly breaking them down to be carried off by the immune system 's macrophages . ultraviolet radiation can also contribute to this pigment breakdown , though it can be mitigated by the use of sunblock . but since the dermal cells are relatively stable , much of the ink will remain deep in the skin for a person 's whole life . but if tattoos are embedded in your skin for life , is there any way to erase them ? technically , yes . today , a laser is used to penetrate the epidermis and blast apart underlying pigment colors of various wavelengths , black being the easiest to target . the laser beam breaks the ink globules into smaller particles that can then be cleared away by the macrophages . but some color inks are harder to remove than others , and there could be complications . for this reason , removing a tattoo is still more difficult than getting one , but not impossible . so a single tattoo may not truly last forever , but tattoos have been around longer than any existing culture . and their continuing popularity means that the art of tattooing is here to stay .

dermal cells , however , remain in place until they die . when they do , they are taken up , ink and all , by younger cells nearby , so the ink stays where it is . but with time , tattoos do fade naturally as the body reacts to the alien pigment particles , slowly breaking them down to be carried off by the immune system 's macrophages .

tattooing can be permanent if the ink particles get trapped in which layer ?

the dead coming back to life sounds scary . but for scientists , it can be a wonderful opportunity . of course , we 're not talking about zombies . rather , this particular opportunity came in the unlikely form of large , slow-moving fish called the coelacanth . this oddity dates back 360 million years , and was believed to have died out during the same mass extinction event that wiped out the dinosaurs 65 million years ago . to biologists and paleontologists , this creature was a very old and fascinating but entirely extinct fish , forever fossilized . that is , until 1938 when marjorie courtenay-latimer , a curator at a south african museum , came across a prehistoric looking , gleaming blue fish hauled up at the nearby docks . she had a hunch that this strange , 1.5 meter long specimen was important but could n't preserve it in time to be studied and had it taxidermied . when she finally was able to reach j.l.b . smith , a local fish expert , he was able to confirm , at first site , that the creature was indeed a coelacanth . but it was another 14 years before a live specimen was found in the comoros islands , allowing scientists to closely study a creature that had barely evolved in 300 million years . a living fossil . decades later , a second species was found near indonesia . the survival of creatures thought extinct for so long proved to be one of the biggest discoveries of the century . but the fact that the coelacanth came back from the dead is n't all that makes this fish so astounding . even more intriguing is the fact that genetically and morphologically , the coelacanth has more in common with four-limbed vertebrates than almost any other fish , and its smaller genome is ideal for study . this makes the coelacanth a powerful link between aquatic and land vertebrates , a living record of their transition from water to land millions of years ago . the secret to this transition is in the fins . while the majority of ocean fish fall into the category of ray-finned fishes , coelacanths are part of a much smaller , evolutionarily distinct group with thicker fins known as lobe-finned fish . six of the coelacanth 's fins contain bones organized much like our limbs , with one bone connecting the fin to the body , another two connecting the bone to the tip of the fin , and several small , finger-like bones at the tip . not only are those fins structured in pairs to move in a synchronized way , the coelacanth even shares the same genetic sequence that promotes limb development in land vertebrates . so although the coelacanth itself is n't a land-walker , its fins do resemble those of its close relatives who first hauled their bodies onto land with the help of these sturdy , flexible appendages , acting as an evolutionary bridge to the land lovers that followed . so that 's how this prehistoric fish helps explain the evolutionary movement of vertebrates from water to land . over millions of years , that transition led to the spread of all four-limbed animals , called tetrapods , like amphibians , birds , and even the mammals that are our ancestors . there 's even another powerful clue in that unlike most fish , coelacanths do n't lay eggs , instead giving birth to live , young pups , just like mammals . and this prehistoric fish will continue to provide us with fascinating information about the migration of vertebrates out of the ocean over 300 million years ago . a journey that ultimately drove our own evolution , survival and existence . today the coelacanth remains the symbol of the wondrous mysteries that remain to be uncovered by science . with so much left to learn about this fish , the ocean depths and evolution itself , who knows what other well-kept secrets our future discoveries may bring to life !

a living fossil . decades later , a second species was found near indonesia . the survival of creatures thought extinct for so long proved to be one of the biggest discoveries of the century .

where was a second species of coelacanth found decades after marjorie courtenay-latimer ?

i 'm mckenna pope . i 'm 14 years old . and when i was 13 , i convinced one of the largest toy companies , toy makers in the world , hasbro , to change the way that they marketed one of their best-selling products . so , allow me to tell you about it . so , i have a brother , gavin . when this whole shebang happened , he was four . he loved to cook . he was always getting ingredients out of the fridge and mixing them into these , needless to say , uneatable concoctions or making invisible macaroni and cheese . he wanted to be a chef really badly . and , so what better gift for someone , for a kid who wanted to be a chef , than an easy bake oven , right ? i mean , we all had those when we were little . and he wanted one so badly . but then , he started to realize something . in the commercials and on the boxes for the easy bake oven , hasbro marketed them specifically to girls . and the way that they did this was they would only feature girls on the boxes or in the commercials , and there would be flowery prints all over the ovens , and it would be in bright pink and purple . very gender-specific colors to females , right ? so , it kind of was sending a message that only girls are supposed to cook . boys are n't . and this discouraged my brother a lot . he thought that he was n't supposed to want to be a chef . because that was something girls did . girls cooked , boys did n't . or so , the message that hasbro was sending . and this got me thinking , `` god , i wish there was a way i could change this , that i could have my voice heard by hasbro , so i could ask them and tell them what they were doing wrong and ask them to change it . '' and that got me thinking about a website that i had learned about a few months prior called change.org . change.org is an online petition-sharing platform , where you can create a petition and share it across all these social media networks , through facebook , through twitter , through youtube , through reddit , through tumblr , through whatever you can think of . and so , i created a petition , along with a youtube video that i added to the petition , basically asking hasbro to change the way that they marketed it , in featuring boys in the commercials and on the boxes , and most of all creating them in less gender-specific colors . so , this petititon started to take off , like humongously fast , you have no idea . i was getting interviewed by all these national news outlets and press outlets , and it was amazing . in three weeks , maybe three and a half , i had 46,000 signatures on this petition . ( applause ) thank you . so , needless to say , it was crazy . eventually , hasbro themselves invited me to their headquarters so they could go and unveil their new easy bake oven product to me , in black , silver and blue . it was literally one of the best moments of my life . it was like `` willy wonka and the chocolate factory . '' that thing was amazing . what i did n't realize at the time , however , was that i had become an activist . i could change something that , even as a kid , or maybe even especially as a kid , my voice mattered . and your voice matters , too ! i want to let you know that it 's not going to be easy , and it was n't easy for me because i faced a lot of obstacles . people online , and sometimes even in real life , were disrespectful to me and my family and talked about how the whole thing was a waste of time , and it really discouraged me . and actually , i have some examples because what 's better revenge than displaying their idiocy ? so , let 's see . from username liquidsword29 , interesting usernames we have here , `` disgusting liberal moms making their son 's gay . '' liquidsword29 , really ? really ? okay , how about from whiteboy77ags , `` people always need something to 'female dog ' about . '' from jeffrey gutierrez , `` omg shut up ! you just want money and attention . '' so , it was comments like these that really discouraged me from wanting to make change in the future because i thought , `` people do n't care . people think it 's a waste of time . and people are going to be disrespectful to me and my family . '' it hurt me . and it made me think , `` what 's the point in making change in the future ? '' but then i started to realize something . haters gon na hate . come on , say it with me ! one , two , three , haters gon na hate ! so let your haters hate , you know what ! and make your change because i know you can . i look out into this crowd , and i see 400 people who came out because they wanted to know how they could make a change . and i know that you can , and all of you watching at home can , too , because you have so much that you can do and that you believe in . and you can trade it across all the social media , through facebook , through twitter , through youtube , through reddit , through tumblr , through whatever else you can think of . and you can make that change . you can take what you believe in and turn it into a cause and change it . and that spark that you 've been hearing about all day today you can use that spark that you have within you and turn it into a fire . thank you . ( applause )

i 'm mckenna pope . i 'm 14 years old .

what percentage of chefs are male ?

what you 're looking at is n't some weird x-ray . it 's actually a baby yellow tang surgeonfish at two months old . and you thought your childhood was awkward . but here is the same fish as an adult , a beautiful inhabitant of the indian and pacific oceans ' coral reefs and one of the most popular captive fish for salt water aquariums . of the 27,000 known fish species , over a quarter live on coral reefs that make up less than 1 % of the earth 's surface . but prior to settling down in this diverse tropical environment , baby coral reef fish face the difficult process of growing up on their own , undergoing drastic changes , and the journey of a lifetime before they find that reef to call home . the life cycle for most of these fish begins when their parents spew sperm and eggs into the water column . this can happen daily , seasonally , or yearly depending on the species , generally following lunar or seasonal tidal patterns . left to their fate , the fertilized eggs drift with the currents , and millions of baby larvae hatch into the world . when they first emerge , the larvae are tiny and vulnerable . some do n't even have gills yet and must absorb oxygen directly from the water through their tissue-thin skin . they may float in the water column anywhere from minutes to months , sometimes drifting thousands of miles across vast oceans , far from the reefs where they were born . along the way , they must successfully avoid predators , obtain food , and ride the right currents to find their way to a suitable adult habitat , which might as well be a needle in vast haystack of ocean . so , how did they accomplish this feat ? until recently , marine biologists thought of larval fish as largely passive drifters , dispersed by ocean currents to distant locales . but in the last 20 years , new research has suggested that larvae may not be as helpless as they seem , and are capable of taking their fate in their own fins to maximize their chances of survival . the larvae of many species are unexpectedly strong swimmers , and can move vertically in the water column to place themselves in different water masses and preferentially ride certain currents . these fish may be choosing the best routes to their eventual homes . when searching for these homes , evidence suggests that larvae navigate via a complex suite of sensory systems , detecting both sound and smell . odor , in particular , allows larvae to distinguish between different environments , even adjacent reefs , helping guide them toward their preferred adult habitats . many will head for far-flung locales miles away from their birth place . but some will use smell and other sensory cues to navigate back to the reefs where they were born , even if they remain in the larval stage for months . so , what happens when larvae do find a suitable coral reef ? do they risk it all in one jump from the water column , hoping to land in exactly the right spot to settle down and metamorphose into adults ? not exactly . instead , larvae appear to have more of a bungee system . larvae will drop down in the water column to check out a reef below . if conditions are n't right , they can jump back up into higher water masses and ride on , chancing that the next reef they find will be a better fit . but this is the point where our knowledge ends . we do n't know the geographic movements of individual larva for most species . nor do we know which exact environmental cues and behaviors they use to navigate to the reefs they will call home . but we do know that these tiny trekkers are more than the fragile and helpless creatures science once believed them to be . the secret lives of baby fish remain largely mysterious to us , unknown adventures waiting to be told .

and you thought your childhood was awkward . but here is the same fish as an adult , a beautiful inhabitant of the indian and pacific oceans ' coral reefs and one of the most popular captive fish for salt water aquariums . of the 27,000 known fish species , over a quarter live on coral reefs that make up less than 1 % of the earth 's surface .

over 90 % of the coral reef fish kept in saltwater aquariums and sold at pet stores in the us and europe are collected from the wild . why might these fish be wild-caught rather than farmed in captivity ?

for as far back as we can trace our existence , humans have been fascinated with death and resurrection . nearly every religion in the world has some interpretation of them , and from our earliest myths to the latest cinematic blockbusters , the dead keep coming back . but is resurrection really possible ? and what is the actual difference between a living creature and a dead body , anyway ? to understand what death is , we need to understand what life is . one ancient theory was an idea called vitalism , which claimed that living things were unique because they were filled with a special substance , or energy , that was the essence of life . whether it was called qi , lifeblood , or humors , the belief in such an essence was common throughout the world , and still persists in the stories of creatures who can somehow drain life from others , or some form of magical sources that can replenish it . vitalism began to fade in the western world following the scientific revolution in the 17th century . rené descartes advanced the notion that the human body was essentially no different from any other machine , brought to life by a divinely created soul located in the brain 's pineal gland . and in 1907 , dr. duncan mcdougall even claimed that the soul had mass , weighing patients immediately before and after death in an attempt to prove it . though his experiments were discredited , much like the rest of vitalism , traces of his theory still come up in popular culture . but where do all these discredited theories leave us ? what we now know is that life is not contained in some magical substance or spark , but within the ongoing biological processes themselves . and to understand these processes , we need to zoom down to the level of our individual cells . inside each of these cells , chemical reactions are constantly occurring , powered by the glucose and oxygen that our bodies convert into the energy-carrying molecule known as atp . cells use this energy for everything from repair to growth to reproduction . not only does it take a lot of energy to make the necessary molecules , but it takes even more to get them where they need to be . the universal phenomenon of entropy means that molecules will tend towards diffusing randomly , moving from areas of high concentration to low concentration , or even breaking apart into smaller molecules and atoms . so cells must constantly keep entropy in check by using energy to maintain their molecules in the very complicated formations necessary for biological functions to occur . the breaking down of these arrangements when the entire cell succumbs to entropy is what eventually results in death . this is the reason organisms ca n't be simply sparked back to life once they 've already died . we can pump air into someone 's lungs , but it wo n't do much good if the many other processes involved in the respiratory cycle are no longer functioning . similarly , the electric shock from a defibrillator does n't jump-start an inanimate heart , but resynchronizes the muscle cells in an abnormally beating heart so they regain their normal rhythm . this can prevent a person from dying , but it wo n't raise a dead body , or a monster sewn together from dead bodies . so it would seem that all our various medical miracles can delay or prevent death but not reverse it . but that 's not as simple as it sounds because constant advancements in technology and medicine have resulted in diagnoses such as coma , describing potentially reversible conditions , under which people would have previously been considered dead . in the future , the point of no return may be pushed even further . some animals are known to extend their lifespans or survive extreme conditions by slowing down their biological processes to the point where they are virtually paused . and research into cryonics hopes to achieve the same by freezing dying people and reviving them later when newer technology is able to help them . see , if the cells are frozen , there 's very little molecular movement , and diffusion practically stops . even if all of a person 's cellular processes had already broken down , this could still conceivably be reversed by a swarm of nanobots , moving all the molecules back to their proper positions , and injecting all of the cells with atp at the same time , presumably causing the body to simply pick up where it left off . so if we think of life not as some magical spark , but a state of incredibly complex , self-perpetuating organization , death is just the process of increasing entropy that destroys this fragile balance . and the point at which someone is completely dead turns out not to be a fixed constant , but simply a matter of how much of this entropy we 're currently capable of reversing .

similarly , the electric shock from a defibrillator does n't jump-start an inanimate heart , but resynchronizes the muscle cells in an abnormally beating heart so they regain their normal rhythm . this can prevent a person from dying , but it wo n't raise a dead body , or a monster sewn together from dead bodies . so it would seem that all our various medical miracles can delay or prevent death but not reverse it .

suppose you had a dead person ’ s dna and a living fertilized egg . would it be possible to return that person to life through cloning ?

a solar eclipse happens when the moon ’ s shadow falls somewhere on the surface of earth and a lunar eclipse is the opposite -- when the earth ’ s shadow falls on the moon the two sections of the shadow , the dark umbra and the partially shaded penumbra , their placement determines which type of eclipse we can see from earth . but not all eclipses are made equal . the most spectacular , the one for your bucket list is a total eclipse of the sun . a total solar eclipse begins as a partial eclipse . you ’ ll notice trees projecting the crescent sun , and shadows becoming sharper than normal . the landscape darkens to a bluish-grey and you ’ ll start to feel the temperature drop . from the west , the moon ’ s shadow rushes toward you like a silent storm . look up and you ’ ll see the last sliver of the sun sparkling like a diamond ring , before it ’ s broken into a string of beads by the moon ’ s rough terrain . now you can see the pearly glow of the sun ’ s corona and the pink and red light from the hydrogen gas of the chromosphere . together these make up the sun ’ s outer atmosphere , and a total solar eclipse is the only occasion you have to lay eyes on it . this is totality and if you get a chance to see it , you should . the moon orbits earth every 29.5 days , but we don ’ t get eclipses every month . that ’ s because the moon ’ s orbit is not in line with earth ’ s orbit . it ’ s tilted about 5 degrees . that doesn ’ t seem like much but keep in mind that the scale of the model we ’ re showing to you is way off . if the earth and moon are this size , the distance between them should be around 10 ft. at this distance , 5 degrees is enough to keep the moon ’ s shadow off of earth and the earth ’ s shadow off the moon most months . so why do we ever get eclipses ? because there are two points where the moon ’ s orbit crosses the sun ’ s plane , called nodes . and as the earth moves along its annual orbit , those points line up with the sun about twice a year . as the moon passes between the sun and earth at that time , we get a solar eclipse . when it ’ s behind earth at that time , we get a lunar eclipse . there are a ton of orbital quirks that make predicting eclipses really complicated , but in general we ’ ll have a few solar and lunar eclipses of some sort and a few lunar eclipses of some sort every year . but you ’ re more likely to see a total lunar eclipse in your lifetime than a total solar one . the totality of a lunar eclipse can last well over an hour and it ’ s viewable for anyone on the night side of earth . the moon often turns red during a total lunar eclipse because our planet ’ s atmosphere scatters the shorter bluer wavelengths of light , while the longer , redder wavelengths pass through . or to put it another way , a total lunar eclipse projects all of the world ’ s sunsets and sunrises onto the moon . total solar eclipses seem much more rare because totality lasts just a few minutes , and although earth gets a total solar eclipse every 18 months on average , each one is only viewable by less than half a percent of earth ’ s surface . eclipse chasers travel all over the world to put themselves in the path of the shadow . in a total solar eclipse , the moon precisely covers the sun from the vantage point of some place on earth . this is possible because by coincidence , the sun and the moon appear to be about the same size in our sky . while the sun is 400 times bigger than the moon , it ’ s also about 400 times farther away . but this alignment isn ’ t constant . the moon has an elliptical orbit . its size varies about 12 % throughout a month . when it ’ s closer to us , we can get total solar eclipses , but less than 30 % of solar eclipses are total . more often , we get partial eclipses , where the alignment is a bit off , or annular eclipses , where the moon is too far away to fully block the sun , leaving a ring of sunlight around the moon . in the far future , earth will only get annular and partial solar eclipses because our moon is moving further away . we know that because buzz aldrin and neil armstrong left mirrors on the moon in 1969 . astronomers bounce lasers off those mirrors to measure the moon ’ s distance . and that ’ s how they found out that the moon is moving away from earth by more than 3 cm per year . so in a billion years or so , whatever creatures live here will witness earth ’ s very last total solar eclipse . “ we can see on the radio one screen , a fantastic total solar eclipse taken from the pictures above the clouds. ” “ this is just fantastic. ” a lot of early civilizations feared eclipses . they were often seen as an attack on the sun or moon by the forces of darkness . but now that we understand our place in space , eclipses are an occasion for awe , and for gratitude . all over the galaxy rocks are casting shadows on other rocks . but only here , as far as we know , is there someone to notice them .

the most spectacular , the one for your bucket list is a total eclipse of the sun . a total solar eclipse begins as a partial eclipse . you ’ ll notice trees projecting the crescent sun , and shadows becoming sharper than normal .

what coincidence makes it so that the moon is able to perfectly cover the sun during a total solar eclipse ?

what is proof ? and why is it so important in mathematics ? proofs provide a solid foundation for mathematicians logicians , statisticians , economists , architects , engineers , and many others to build and test their theories on . and they 're just plain awesome ! let me start at the beginning . i 'll introduce you to a fellow named euclid . as in , `` here 's looking at you , clid . '' he lived in greece about 2,300 years ago , and he 's considered by many to be the father of geometry . so if you 've been wondering where to send your geometry fan mail , euclid of alexandria is the guy to thank for proofs . euclid is not really known for inventing or discovering a lot of mathematics but he revolutionized the way in which it is written , presented , and thought about . euclid set out to formalize mathematics by establishing the rules of the game . these rules of the game are called axioms . once you have the rules , euclid says you have to use them to prove what you think is true . if you ca n't , then your theorem or idea might be false . and if your theorem is false , then any theorems that come after it and use it might be false too . like how one misplaced beam can bring down the whole house . so that 's all that proofs are : using well-established rules to prove beyond a doubt that some theorem is true . then you use those theorems like blocks to build mathematics . let 's check out an example . say i want to prove that these two triangles are the same size and shape . in other words , they are congruent . well , one way to do that is to write a proof that shows that all three sides of one triangle are congruent to all three sides of the other triangle . so how do we prove it ? first , i 'll write down what we know . we know that point m is the midpoint of ab . we also know that sides ac and bc are already congruent . now let 's see . what does the midpoint tell us ? luckily , i know the definition of midpoint . it is basically the point in the middle . what this means is that am and bm are the same length , since m is the exact middle of ab . in other words , the bottom side of each of our triangles are congruent . i 'll put that as step two . great ! so far i have two pairs of sides that are congruent . the last one is easy . the third side of the left triangle is cm , and the third side of the right triangle is - well , also cm . they share the same side . of course it 's congruent to itself ! this is called the reflexive property . everything is congruent to itself . i 'll put this as step three . ta dah ! you 've just proven that all three sides of the left triangle are congruent to all three sides of the right triangle . plus , the two triangles are congruent because of the side-side-side congruence theorem for triangles . when finished with a proof , i like to do what euclid did . he marked the end of a proof with the letters qed . it 's latin for `` quod erat demonstrandum , '' which translates literally to `` what was to be proven . '' but i just think of it as `` look what i just did ! '' i can hear what you 're thinking : why should i study proofs ? one reason is that they could allow you to win any argument . abraham lincoln , one of our nation 's greatest leaders of all time used to keep a copy of euclid 's elements on his bedside table to keep his mind in shape . another reason is you can make a million dollars . you heard me . one million dollars . that 's the price that the clay mathematics institute in massachusetts is willing to pay anyone who proves one of the many unproven theories that it calls `` the millenium problems . '' a couple of these have been solved in the 90s and 2000s . but beyond money and arguments , proofs are everywhere . they underly architecture , art , computer programming , and internet security . if no one understood or could generate a proof , we could not advance these essential parts of our world . finally , we all know that the proof is in the pudding . and pudding is delicious . qed .

so if you 've been wondering where to send your geometry fan mail , euclid of alexandria is the guy to thank for proofs . euclid is not really known for inventing or discovering a lot of mathematics but he revolutionized the way in which it is written , presented , and thought about . euclid set out to formalize mathematics by establishing the rules of the game . these rules of the game are called axioms .

what effects do you think euclid had on mathematics ? in what ways did it progress because of his contributions ?

if you live on the east coast of the united states , you 've spent the last 17 years of your life walking , eating and sleeping above a dormant army of insects . these are the cicadas . every 17 years , billions of them emerge from the ground to do three things : molt , mate and die . there are 15 different broods of cicadas out there , grouped by when they 'll emerge from the ground . some of these broods are on a 13-year cycle , others are on a 17-year clock . either way , the cicadas live underground for most of their lives , feeding on the juices of plant roots . when it 's time to emerge , the adults begin to burrow their way out of the ground and up to the surface , where they 'll live for just a few weeks . during these weeks , though , everybody will know the cicadas have arrived . there will be billions of them . and they 're loud . male cicadas band together to call for female mates , and their collective chorus can reach up to 100 decibels -- as loud as a chain saw . in fact , if you happen to be using a chain saw or a lawn mower , male cicadas will flock to you , thinking that you 're one of them . now , like most things in nature , the cicadas do n't arrive without a posse . there are all sort of awesome and gross predators and parasites that come along with the buzzing bugs . take the fungus massospora for example . this little white fungus buries itself in the cicada 's abdomen and eats the bug alive , leaving behind its spores . when those spores rupture , they burst out of the still-alive cicada , turning the bug into a flying saltshaker of death , raining spores down upon its unsuspecting cicada neighbors . but while we know pretty precisely when the cicadas will arrive and fade away , we 're still not totally certain of why . there are certain advantages to having your entire species emerge at once , of course . the sheer number of cicadas coming out of the ground is so overwhelming to predators , it is essentially guaranteed that a few bugs will survive and reproduce . and since cicadas emerge every 13 or 17 years , longer than the lifespan of many of their predators , the animals that eat them do n't learn to depend on their availability . but why 13 and 17 years , instead of 16 or 18 or 12 ? well , that part no one really knows . it 's possible the number just happened by chance , or , perhaps , cicadas really love prime numbers . eventually , the cicadas will mate and slowly die off , their call fading into the distance . the eggs they lay will begin the cycle again , their cicada babies burrowing into the earth , feeding on plant juice , and waiting for their turn to darken the skies and fill the air with their songs . in 17 years , they 'll be ready . will you ?

if you live on the east coast of the united states , you 've spent the last 17 years of your life walking , eating and sleeping above a dormant army of insects . these are the cicadas . every 17 years , billions of them emerge from the ground to do three things : molt , mate and die . there are 15 different broods of cicadas out there , grouped by when they 'll emerge from the ground . some of these broods are on a 13-year cycle , others are on a 17-year clock .

how often do cicadas emerge from the ground ?

watch the center of this disk . you are getting sleepy . no , just kidding . i 'm not going to hypnotize you . but are you starting to see colors in the rings ? if so , your eyes are playing tricks on you . the disk was only ever black and white . you see , your eyes do n't always capture the world as a video camera would . in fact , there are quite a few differences , owing to the anatomy of your eye and the processing that takes place in your brain and its outgrowth , the retina . let 's start with some similarities . both have lenses to focus light and sensors to capture it , but even those things behave differently . the lens in a camera moves to stay focused on an object hurtling towards it , while the one in your eye responds by changing shape . most camera lenses are also achromatic , meaning they focus both red and blue light to the same point . your eye is different . when red light from an object is in focus , the blue light is out of focus . so why do n't things look partially out of focus all the time ? to answer that question , we first need to look at how your eye and the camera capture light : photoreceptors . the light-sensitive surface in a camera only has one kind of photoreceptor that is evenly distributed throughout the focusing surface . an array of red , green and blue filters on top of these photoreceptors causes them to respond selectively to long , medium and short wavelength light . your eye 's retinas , on the other hand , have several types of photoreceptors , usually three for normal light conditions , and only one type for lowlight , which is why we 're color blind in the dark . in normal light , unlike the camera , we have no need for a color filter because our photoreceptors already respond selectively to different wavelengths of light . also in contrast to a camera , your photoreceptors are unevenly distributed , with no receptors for dim light in the very center . this is why faint stars seem to disappear when you look directly at them . the center also has very few receptors that can detect blue light , which is why you do n't notice the blurred blue image from earlier . however , you still perceive blue there because your brain fills it in from context . also , the edges of our retinas have relatively few receptors for any wavelength light . so our visual acuity and ability to see color falls off rapidly from the center of our vision . there is also an area in our eyes called the blind spot where there are no photoreceptors of any kind . we do n't notice a lack of vision there because once again , our brain fills in the gaps . in a very real sense , we see with our brains , not our eyes . and because our brains , including the retinas , are so involved in the process , we are susceptible to visual illusions . here 's another illusion caused by the eye itself . does the center of this image look like it 's jittering around ? that 's because your eye actually jiggles most of the time . if it did n't , your vision would eventually shut down because the nerves on the retina stop responding to a stationary image of constant intensity . and unlike a camera , you briefly stop seeing whenever you make a larger movement with your eyes . that 's why you ca n't see your own eyes shift as you look from one to the other in a mirror . video cameras can capture details our eyes miss , magnify distant objects and accurately record what they see . but our eyes are remarkably efficient adaptations , the result of hundreds of millions of years of coevolution with our brains . and so what if we do n't always see the world exactly as it is . there 's a certain joy to be found watching stationary leaves waving on an illusive breeze , and maybe even an evolutionary advantage . but that 's a lesson for another day .

most camera lenses are also achromatic , meaning they focus both red and blue light to the same point . your eye is different . when red light from an object is in focus , the blue light is out of focus .

what improvements might you like to make to the human eye ?

translator : andrea mcdonough reviewer : bedirhan cinar so we live in what i think of as a csi age where we take for granted that scientists are going to work together with the police , help them solve crimes , map fingerprints , analyze poisons , but in fact , this is really a very new idea . we only actually started training scientists and forensics in this country in the 1930s . so as a writer interested in chemistry , what i wondered was , `` what was it like before scientists knew how to tease a poison out of a corpse , before you could actually catch a killer that way ? '' and it wo n't surprise you to learn that the answer is pretty dangerous . and in fact , in 1918 , new york city issued a report admitting that smart poisoners could operate with impunity in the city . this is a 1918 crime scene photo from brooklyn , and at this time , the coroner system was so corrupt that you could literally buy your cause of death . often coroners did n't even show up at crime scenes . and if you go back and you look at the death certificates of the time , i found one that read , `` could be an auto accident or possibly diabetes . '' and another , which involved a man who shot himself in the head , said , `` ruptured aneurysm '' . so you find , not surprisingly , the police saying , `` we 're going to look a lot smarter if we stay away from the science side of the story . '' but , in 1918 new york city appointed the first trained medical examiner it ever had . that 's the gentleman sitting down there . and he hired the first forensic toxicologist ever attached to an american city . and together , these two men , charles norris , the medical examiner , and alexander gettler , the chemist sitting next to him , rewrote the rules of crime detection in this country . and that was n't easy because poisons were everywhere . if we take this one , arsenic trioxide , arsenic trioxide 's probably the most famous homicidal poison in history and it was in every home . anyone could go to the grocery store or the pharmacy and buy it . it was in every kitchen because , believe it or not , it was used to color food . it was in medicines and it was in cosmetics in ways that prevented people from really understanding how dangerous these poisons were or how they worked . now , scientists had in the 19th century begun developing tests to look for poisons in corpses . but as this cartoon shows you of the first test for arsenic , these were very primitive tests , so , that our heroes really have to figure this out as they go in the 1920s . gettler , for instance , was the first person in the world to know how to tell if someone was drunk at time of death . he figured that out right about 1930 and he said later it took him 6,000 brains from the morgue to get to the point that he could get to that answer . and to give you a sense of what this is like , i 'm going to ask you for a moment to become 1920s forensic detectives . this is a case based on one solved by alexander gettler in 1923 , and as you can probably tell , it 's a case that begins in a tenement building . this particular one was on the lower east side of manhattan . and these buildings were very crowded with families who had very little money . and the rooms were very poor . this is actually an abandoned room at the tenement house museum that is in lower manhattan today . these rooms often had no electricity , they had no hot water , and people who lived this way depended on gas to fuel everything from their stove to their electric lights . and this gas was called illuminating gas , and it was both a toxic and explosive mixture of carbon monoxide and hydrogen . so you , the forensic scientist , are called to a crime scene in a tenement house . this is actually a police photo from the time in question , but the story that i 'm going to tell you is a little more complicated than this . nevertheless , you 're going to go into this building , you 're going to walk down this hall , you 're going to go through the door , and you 're going to find yourself in a very shabby apartment . the floors are splintered , the walls are peeling , there 's only gas lighting , and in this case , you go into the back bedroom . there 's clearly been a gas leak , there 's a broken fitting on the wall . the police are opening the windows , and in the bed there 's the body of young woman who 's clearly been dead for some time because she 's cold and she 's stiff and she 's pale . and you turn to the police and you say , `` no , this is not an illuminating gas death because ... . '' because if you 're killed by carbon monoxide , there is such a powerful chemical reaction in your blood as the oxygen is muscled out of the blood stream that the blood cells are turned a bright , cherry red . and this red is so strong that it flushes the skin of the corpse a cherry pink . in fact , people who see bodies after someone has died of a carbon monoxide death , they 'll often talk about how healthy they look . so your poor , pale corpse could not have been killed by this gas . you take the body back to the morgue , you run more blood tests , and you find another gas at extremely high levels , carbon dioxide . and what does that tell you ? if you think about the way we breath , we inhale oxygen , we exhale carbon dioxide , but what if you ca n't exhale ? what if that gas ca n't get out ? it backs up into your lungs , and the number one clue of a suffocation or a strangulation is elevated levels of carbon dioxide in the blood . and in fact , what they found when they took a closer look at the body were the bruise marks left by her husband 's fingers as he had held her down and suffocated her . and it turned out that he had taken out an insurance policy on her life , suffocated her , broken the gas fitting to try to stage an accident scene , and it turned out that it was chemistry that sent him to prison . there are so many good poison and murder stories from this time period that i would love to tell you . it 's one of my favorite subjects obviously . but i want to leave you with this thought . two things . one is that case that i just described to you is one of my favorites because it 's the beginning of a series of investigations that persuade the new york police that they do need to work with scientists and it lays the foundation for , in fact , our csi-era age , and , because it 's such a good story of two very determined people , in this case two city scientists , who were able to change the world around them . thank you .

and it wo n't surprise you to learn that the answer is pretty dangerous . and in fact , in 1918 , new york city issued a report admitting that smart poisoners could operate with impunity in the city . this is a 1918 crime scene photo from brooklyn , and at this time , the coroner system was so corrupt that you could literally buy your cause of death .

in 1918 , new york city issued a report saying that smart poisoners could operate with ______ in the city .

in many ways , our memories make us who we are , helping us remember our past , learn and retain skills , and plan for the future . and for the computers that often act as extensions of ourselves , memory plays much the same role , whether it 's a two-hour movie , a two-word text file , or the instructions for opening either , everything in a computer 's memory takes the form of basic units called bits , or binary digits . each of these is stored in a memory cell that can switch between two states for two possible values , 0 and 1 . files and programs consist of millions of these bits , all processed in the central processing unit , or cpu , that acts as the computer 's brain . and as the number of bits needing to be processed grows exponentially , computer designers face a constant struggle between size , cost , and speed . like us , computers have short-term memory for immediate tasks , and long-term memory for more permanent storage . when you run a program , your operating system allocates area within the short-term memory for performing those instructions . for example , when you press a key in a word processor , the cpu will access one of these locations to retrieve bits of data . it could also modify them , or create new ones . the time this takes is known as the memory 's latency . and because program instructions must be processed quickly and continuously , all locations within the short-term memory can be accessed in any order , hence the name random access memory . the most common type of ram is dynamic ram , or dram . there , each memory cell consists of a tiny transistor and a capacitor that store electrical charges , a 0 when there 's no charge , or a 1 when charged . such memory is called dynamic because it only holds charges briefly before they leak away , requiring periodic recharging to retain data . but even its low latency of 100 nanoseconds is too long for modern cpus , so there 's also a small , high-speed internal memory cache made from static ram . that 's usually made up of six interlocked transistors which do n't need refreshing . sram is the fastest memory in a computer system , but also the most expensive , and takes up three times more space than dram . but ram and cache can only hold data as long as they 're powered . for data to remain once the device is turned off , it must be transferred into a long-term storage device , which comes in three major types . in magnetic storage , which is the cheapest , data is stored as a magnetic pattern on a spinning disc coated with magnetic film . but because the disc must rotate to where the data is located in order to be read , the latency for such drives is 100,000 times slower than that of dram . on the other hand , optical-based storage like dvd and blu-ray also uses spinning discs , but with a reflective coating . bits are encoded as light and dark spots using a dye that can be read by a laser . while optical storage media are cheap and removable , they have even slower latencies than magnetic storage and lower capacity as well . finally , the newest and fastest types of long-term storage are solid-state drives , like flash sticks . these have no moving parts , instead using floating gate transistors that store bits by trapping or removing electrical charges within their specially designed internal structures . so how reliable are these billions of bits ? we tend to think of computer memory as stable and permanent , but it actually degrades fairly quickly . the heat generated from a device and its environment will eventually demagnetize hard drives , degrade the dye in optical media , and cause charge leakage in floating gates . solid-state drives also have an additional weakness . repeatedly writing to floating gate transistors corrodes them , eventually rendering them useless . with data on most current storage media having less than a ten-year life expectancy , scientists are working to exploit the physical properties of materials down to the quantum level in the hopes of making memory devices faster , smaller , and more durable . for now , immortality remains out of reach , for humans and computers alike .

so how reliable are these billions of bits ? we tend to think of computer memory as stable and permanent , but it actually degrades fairly quickly . the heat generated from a device and its environment will eventually demagnetize hard drives , degrade the dye in optical media , and cause charge leakage in floating gates .

why does a computer need to use several types of memory ?

one of the most striking properties about life is that it has color . to understand the phenomenon of color , it helps to think about light as a wave . but , before we get to that , let 's talk a little bit about waves in general . imagine you 're sitting on a boat on the ocean watching a cork bob up and down in the water . the first thing you notice about the motion is that it repeats itself . the cork traces the same path over and over again ... up and down , up and down . this repetitive or periodic motion is characteristic of waves . then you notice something else ... using a stopwatch , you measure the time it takes for the piece of cork to go over its highest position down to its lowest and then back up again . suppose this takes two seconds . to use the physics jargon , you 've measured the period of the waves that cork is bobbing on . that is , how long it takes a wave to go through its full range of motion once . the same information can be expressed in a different way by calculating the wave 's frequency . frequency , as the name suggest , tells you how frequent the waves are . that is , how many of them go by in one second . if you know how many seconds one full wave takes , then it 's easy to work out how many waves go by in one second . in this case , since each wave takes 2 seconds , the frequency is 0.5 waves per second . so enough about bobbing corks ... what about light and color ? if light is a wave , then it must have a frequency . right ? well ... yes , it does . and it turns out that we already have a name for the frequency of the light that our eyes detect . it 's called color . that 's right . color is nothing more than a measure of how quickly the light waves are waving . if our eyes were quick enough , we might be able to observe this periodic motion directly , like we can with the cork and the ocean . but the frequency of the light we see is so high , it waves up and down about 400 million million times a second , that we ca n't possibly see it as a wave . but we can tell , by looking at its color , what its frequency is . the lowest frequency light that we can see is red and the highest frequency is purple . in between all the other frequencies form a continous band of color , called the visible spectrum . so , what if you had a yellow pencil sitting on your desk ? well , the sun emits all colors of light , so light of all colors is hitting your pencil . the pencil looks yellow because it reflects yellow light more than it reflects the other colors . what happens to the blue , purple and red light ? they get absorbed and the energy they are carrying is turned into heat . it is similar with objects of other colors . blue things reflect blue light , red things reflect red light and so on . white objects reflect all colors of light , while black things do exactly the opposite and absorb at all frequencies . this - by the way - is why it 's uncomfortable to wear your favorite metallica t-shirt on a sunny day .

well , the sun emits all colors of light , so light of all colors is hitting your pencil . the pencil looks yellow because it reflects yellow light more than it reflects the other colors . what happens to the blue , purple and red light ?

why does a yellow pencil look yellow ?