cahya/simple-wikipedia huggingface dataset:
Pelycosaurs (meaning "basin lizards") were the earliest synapsids. They were not dinosaurs or reptiles. They are an informal group, meaning all synapsids except the therapsids and their descendants.

These tetrapods appeared during the Pennsylvanian and went extinct at the end of the Permian period. They were the dominant land animals for some 40 million years, and were almost wiped out by the P/Tr extinction event. A few survived until the lower Triassic to form the therapsids, a group which led to the mammals. Because the term does not include their descendants, it is not used much now.

Characteristics 
Pelycosaur fossils have been found mainly in Europe and North America, although some small, late-surviving forms are known from Russia and South Africa.

At least two pelycosaur clades independently evolved a tall sail, consisting of elongated vertebral spines: the edaphosaurids and the sphenacodontids. In life, this would have been covered by skin, and possibly functioned as a thermoregulatory device and/or a mating display. 

Unlike lepidosaurian reptiles, pelycosaurs lacked epidermal scales. Fossil evidence from some ophiacodonts shows that parts of the skin was naked, but that the belly was covered in dermal scutes. These scutes looked like the scutes present in reptile groups, but they are of a different type of structure. 

In 1940 the group was reviewed in detail and every species known at the time described (and many illustrated) in an important monograph.

Well-known pelycosaurs include the genera Dimetrodon, Sphenacodon, Edaphosaurus, and Ophiacodon.

Taxonomy 
 Order †Pelycosauria*
 Suborder †Caseasauria
 Family †Caseidae
 Family †Eothyrididae
 Suborder †Eupelycosauria
 Family †Edaphosauridae
 Family †Haplodontidae*
 Family †Lupeosauridae
 Family †Ophiacodontidae
 Family †Sphenacodontidae
 Family †Varanopseidae
 Order †Therapsida*

References 

Fossils
Therapsids, previously known as the mammal-like reptiles, are an order of synapsids. 

The clade includes the mammals, which are descended from the cynodont therapsids.

Characteristics 
The jaws of therapsids had frontal incisors for nipping, large lateral canines for puncturing and tearing, and molars for shearing and tearing, and molars for shearing and chopping food. 

Therapsid legs were positioned more vertically beneath their bodies than were the sprawling legs of Sauropsids and Pelycosaurs.

Evolution 
The therapsids were seriously affected by the P/Tr extinction event. The successful gorgonopsians died out, and the remaining groups were much reduced. 

The dicynodonts, now represented by a single family of large stocky herbivores, the Kannemeyeridae, and the medium-sized cynodonts (including both carnivorous and herbivorous forms), flourished worldwide, throughout the early to middle Triassic. They died out across much of Pangea before the end of the Upper Triassic, although they continued for some time longer in the wet equatorial band and the south.

At least three groups of eucynodonts survived. They appeared in the Upper Triassic. The extremely mammal-like family, the Tritylodonts, survived into the Lower Cretaceous. Another group, Morganucodon and similar animals, were mammaliaformes or the "stem-mammals" for the mammals.

Taxonomy 
 Class Synapsida
 ORDER THERAPSIDA *
 Suborder Biarmosuchia *
 Suborder Dinocephalia
 Suborder Anomodontia *
 Superfamily Venyukoviamorpha
 Infraorder Dicynodonta
 (unranked) Theriodontia *
 Suborder Gorgonopsia
 Suborder Therocephalia
 Suborder Cynodontia *
 (unranked) Mammaliaformes *
 Class Mammalia

References 

 Kemp T.S. 2005. The origin and evolution of mammals. Oxford University Press
 Benton M.J. 2004. Vertebrate Paleontology. 3rd ed. Blackwell, Oxford.
 Carroll R.L. 1988 Vertebrate Paleontology & Evolution. Freeman N.Y.
 Romer A.S. 1966. Vertebrate Paleontology. 3rd ed, University of Chicago Press.

Synapsids
Toccata is the title that was often given to pieces of music for solo instruments from the Renaissance onwards.  The word comes from the Italian for to touch, also meaning to play a musical instrument.  These pieces were often quite difficult, with a lot of fast notes which showed off how well the person could play.

The first toccatas were written in northern Italy by composers such as Claudio Monteverdi and Giovanni Gabrieli.  They are pieces for the keyboard (harpsichord or organ) with lots of running scales in the right hand and accompanying chords in the left hand.  

Toccatas became popular in Germany with composers such as Hans Leo Hassler who had studied in Venice with Gabrieli.  Many German Baroque organ composers wrote toccatas: Sweelinck (who was Dutch), Pachelbel, Buxtehude and Johann Sebastian Bach.  Bach wrote a Toccata and Fugue in D minor, which is one of the most famous pieces of Baroque organ music, and perhaps the most famous toccata ever written.

After the Baroque period composers did not often write toccatas.  The toccata became popular again in the late 19th century with the French organ composers such as Charles-Marie Widor whose Toccata from his Symphony No. 5 is very popular today, especially at weddings.  It has lots of quick notes in the right hand (and occasionally in the left) and a big tune in the pedals.  Another famous organ toccata is by Louis Vierne.  It is the last movement of his Symphony No. 1 (at this time French composers wrote organ works called "symphonies").

In the 20th century several composers wrote toccatas for piano including Prokofiev, Khachaturian, Ravel (part of Le Tombeau de Couperin) and Claude Debussy (part of Suite: Pour le Piano).

Related pages
Fugue
Prelude

Musical forms
The P-38 Lightning is a World War II fighter aircraft made by Lockheed. It was mainly used by the United States Air Force. It first flew in 1939. It was different from other fighters because it had two engines instead of one, and was twice the size of other fighters. The plane fought in the Pacific and in Europe. It could carry 4 50-caliber machine guns and a 20mm cannon. With a top speed of over 400 miles per hour the P-38 was one of the fastest fighters of its time. The P-38 is also accounted for capturing 90% of all aerial footage over Europe. By 1944, it was replaced by the faster P-51 Mustang in Europe. The P-38 was the only American fighter being built at the beginning and the end of the war. The Germans called it the "fork tailed devil."

References

United States Army aircraft
P-38
World War II American aircraft
The Messerschmitt Bf 109 was a fighter aircraft usually called the Me 109. It was a German World War II aircraft.

Made by Messerschmitt, it first flew in 1935, and was used by the Luftwaffe during the Spanish Civil War and throughout World War II.  It was one of the first modern fighters of the time. It had an all-metal construction, a closed cockpit, and retractable landing gear. It was powered by a liquid-cooled, inverted-V12 aero engine.

There were many variations designed for special purposes. Overall, the Me 109 was the most produced fighter aircraft in history, with a total of 33,984 airframes produced from 1936 up to April 1945.

The design of the plane caused some problems on the ground, and with take-off and landing. At least 10% of all Bf 109s were lost in takeoff and landing accidents, 1,500 of which occurred between 1939 and 1941. A new fixed tailwheel helped correct the problem.

Bf 109 was used by Luftwaffe together with FW 190. The Messerschmitt had two machine guns and one cannon while FW 190 had two machine guns and four cannons. Bf 109 was much lighter than FW 190, by 1500 kg. Despite that Bf 109 was almost as fast as FW 190 (Fw 190 A-8 was only 16kph faster than Bf 109 G-6) and climbed at 17 m/s, 2 m/s faster than FW 190.

Related pages
P-51 Mustang
Fw 190
Hawker Hurricane
Supermarine Spitfire

References 

World War II German aircraft
The Me 262 was a German fighter aircraft flown during late World War II. It was the first jet to be used in war. It began test flights in 1942, but was not used in combat by the German air force, the Luftwaffe, until 1944. Very few were built because Germany's enemies were bombing factories. It saw little action because the war was nearly over. The jet engines of the new machine often caused problems, that's why a lot of machines had deathly accidents.

Related pages
 Jet aircraft

References

World War II German aircraft
Osmosis (/ɒzˈmoʊ.sɪs/) is the spontaneous net movement of solvent molecules through a selectively permeable membrane into a region of higher solute concentration, in the direction that tends to equalize the solute concentrations on the two sides. It may also be describe how any solvent moves across a selectively permeable membrane (permeable to the solvent, but not the solute) separating two solutions of different concentrations. Osmosis can be made to do work. Osmotic pressure is defined as the external pressure required to be applied so that there is no net movement of solvent across the membrane. Osmotic pressure is a colligative property, meaning that the osmotic pressure depends on the molar concentration of the solute but not on its identity.

Osmosis is a vital process in biological systems, as biological membranes are semipermeable. In general, these membranes are impermeable to large and polar molecules, such as ions, proteins, and polysaccharides, while being permeable to non-polar or hydrophobic molecules like lipids as well as to small molecules like oxygen, carbon dioxide, nitrogen, and nitric oxide. Permeability depends on solubility, charge, or chemistry, as well as solute size. Water molecules travel through the plasma membrane, tonoplast membrane (vacuole) or protoplast by diffusing across the phospholipid bilayer via aquaporins (small transmembrane proteins similar to those responsible for facilitated diffusion and ion channels). Osmosis provides the primary means by which water is transported into and out of cells. The turgor pressure of a cell is largely maintained by osmosis across the cell membrane between the cell interior and its relatively hypotonic environment.

Hypotonic, isotonic, and hypertonic 

Solutions may have more or less solute per unit of solvent. The one with less is called Hypotonic. When the two solutions have equal concentration, they are isotonic. The one with more is Hypertonic. When the hypotonic solution is outside the cell,and hypertonic solution inside, the cell becomes swollen and distorted.

Cell membranes 
The plasma membrane of a cell is semi-permeable, which means it allowed the entry of certain molecules in or out, it lets small molecules pass through, but blocks larger molecules,. The membrane also has ports or gateways which get certain macromolecules through. This is active transport, which uses energy and is selective. It is outermost covering of the animal cell. It is made up of proteins and lipids. Example:- Exchange of gases like oxygen and carbon dioxide.

Related pages 
 Reverse osmosis

References 

Cell biology
Thermodynamics
The MiG-17 Fresco is a fighter aircraft made by Mikoyan, a Russian company. It first flew in 1950, and was supposed to replace the MiG-15 in the Korean War, but it did not arrive fast enough. It was used by the North Vietnamese in the Vietnam War. It carried 3 guns on it, and later versions carried missiles. Today, it is used as a trainer in other air forces.

Related pages
F-8 Crusader
F-4 Phantom II
MiG-21

Soviet military aircraft
Military of China
Vietnamese military aircraft
Polish military aircraft
Vietnam War aircraft
Mikoyan is a Russian company that designs fighter airplanes. The company was first formed in December 1939 as a design office called Mikoyan-Gurevich or MiG, this was because its designers were Artem Mikoyan and Mikhail Gurevich. Mikoyan will join other Russian airplane companies in a new company called United Aircraft Corporation.

History 
In 1939 Russia was part of the Soviet Union and was communist. In the Soviet communist system there were two types of airplane companies, companies that designed aircraft known as design offices or OKB, and companies that made airplanes called zavods. Artom Mikoyan and Mikhail Gurevich had been designers in another design office helping a designer called Nikolai Polikarpov. One airplane design that Artem Mikoyan and Mikhail Gurevich worked on at Polikarpov was called the I-200. When Nikolai Polikarpov lost the trust of the Soviet leader Stalin, Artem Mikoyan and Mikhail Gurevich were given the I-200 design to finish. This airplane was given a new name and was called the Mikoyan-Gurevich MiG-1. As it was being made, ways to make the MiG-1 into a better airplane were found and airplanes with these changes became known as the MiG-3 and later the MiG-7. However even with changes the MiG fighter airplanes were not as good as the fighter airplanes designed by the design offices of Lavochkin or Yakovlev.

After World War II Mikoyan-Gurevich designed jet aircraft. In the Soviet system the airplane designs of the design offices would compete to see which was the best.  When the best design had been found the design would be built by the airplane manufacturing company.  Even though Mikoyan-Gurevich airplanes in World War II had not been as good as airplanes by Lavochkin or Yakovlev. Mikoyan-Gurevich jet aircraft won more of the competitions to be sent to the zavods and in the time of the Cold War Mikoyan-Gurevich, together with another design office called Sukhoi, became one of the two most important design offices of fighter planes in the Soviet Union.

In the Soviet system decisions were made to protect the government from its own soldiers. In many countries there is only one airforce, the Soviet Union had five airforces. Two of these airforces were the main users of Soviet fighter airplanes. One airforce was called PVO Strany, this airforce was used to defend the cities and land of the Soviet Union. One airforce was called Frontal Aviation, this airforce was used to defend the Soviet Union's ground soldiers against enemy fighter airplanes, and to attack enemy ground forces. Mikoyan-Gurevich became the main designer of aircraft for Frontal Aviation.

Aircraft made 

Mikoyan has designed the following airplanes:

 Mikoyan MiG-1
 Mikoyan MiG-3 (also called MiG-7)
 MiG DIS
 MiG-9 Fargo
 MiG-15 Fagot
 MiG-17 Fresco
 MiG-19 Farmer
 MiG-21 Fishbed
 MiG-23 Flogger
 MiG-25 Foxbat
 MiG-27 Flogger
 MiG-29 Fulcrum
 MiG-31 Foxhound

Companies of Russia
Aircraft companies
1939 establishments
1930s establishments in Europe
Transport in Russia
Juno could mean:

 Juno (mythology), a major Roman goddess
 June, the month named after Juno
 3 Juno, one of the largest main belt asteroids

Music 
 Juno (band), an American indie rock band
 Juno (musical), a Broadway musical with score by Marc Blitzstein based on Sean O'Casey's play Juno and the Paycock
 Juno Reactor, a trance music project of Ben Watkins
 Juno Mak, a Cantopop artist
 Juno Award, a Canadian music award
 Roland Juno-60, Roland Juno-106 or Roland Juno-D (1983?-Present), synthesizers by Roland
 "Juno", a song by Funeral for a Friend, from their debut EP Between Order & Model. Later re-recorded for debut LP Casually Dressed and Deep in Conversation and released as a single under the name Juneau
 Juno Records, an online music store

Vehicles 
 Juno (spacecraft), a planned NASA mission to Jupiter
 HMS Juno, the name of seven vessels of Royal Navy
 Jupiter-C (rocket), also known as Juno or Juno I
 Jupiter (missile) also known as Juno II
 Juno (1864 – 1884), one of the eight South Devon Railway Dido class steam locomotives
 Juno, a Great Western Railway Banking Class 0-6-0ST steam locomotive.
 Juno, a Spanish ship sank in 1802. After its 1997 discovery in Assateague coast (Virginia) the Spanish government claimed ownership of the wreck.

Other uses 
 Juno (movie) a 2007 comedy-drama movie directed by Jason Reitman
 Juno (Dune), a Titan in the fictional Dune universe
 Juno Beach, one of five beaches used as landing zones in the Battle of Normandy in World War II
 3 Juno, the third asteroid to be discovered
 Juno clump, a probable asteroid family near 3 Juno
 Juno Online Services, an internet service provider in the United States
 Project Juno, a British commercial venture that sent Helen Sharman to space
 Juno, protagonist of the video game Jet Force Gemini
 MegaMan Juno, a villain in the video game Mega Man Legends
 Juno Skinner, a villain in the 1994 film True Lies
 Juno Lighting, a company that specializes in commercial and residential lighting
 Juno creator of Star Cross'd Destiny
 Juno the game by Mountain King Studios
 Juno, a powerful Denial of Service attack program, written in the C Programming Language
 Juno, a German cigarette brand produced by Reemtsma
 Juno Temple, an English actress
Neptune (Latin: Neptūnus) is the god of water and the sea in ancient Roman religion and mythology. His Greek equivalent is the god Poseidon. The Roman conception of Neptune was mainly influenced by the Etruscan god Nethuns. Neptune was associated with fresh water as well as the sea, while Oceanus was the god of the world-ocean. Like his Greek equivalent, Neptune was also worshipped by the Romans as the god of horses, and, under the name Neptune Equester, he was a patron god of horse-racing.

The planet Neptune is named after this Roman god.

References 

 Poseidon -- Greek version of Neptune

 

Roman gods and goddesses
Fortuna (Latin and Spanish: "fortune") can mean:

 Fortuna, the Roman goddess of luck (from the Greek Tyche)

Geographical
 19 Fortuna, an asteroid
 Fortuna, California, a town on the north coast of California
 Fortuna, North Dakota, a town in the northwest of North Dakota, near the Canadian border.
 Fortuna (SEPTA station)
 Fortuna, Murcia, a town in the province of Murcia in Spain

People
 Fortuna (Brazilian singer), a female singer and composer from Brazil of Jewish origin
 Wojciech Fortuna, a former ski jumper and Olympic gold medallist

Sports
 Fortuna Düsseldorf
 Fortuna Köln
 Fortuna Sittard

Other
 Fortuna (philosophy), Philosophy of the Fellowship of Fortuna Movement
 Fortuna (PRNG), a cryptographically secure pseudo-random number generator design by Niels Ferguson and Bruce Schneier
 Fortuna, a fictional planet from the Star Fox series of video games
 Fortuna (cigarette), a cigarette brand owned by Altadis
 "O Fortuna", widely recognizable opening movement of Carl Orff's Carmina Burana
 Fortuna Saga, an original sprite-based webcomic set in the world of Final Fantasy VI.
 A name for bagatelle, a game developed from billiard
For the folk music band, see Sol Invictus (band).

Sol Invictus ("the Unconquered Sun") or, more fully, Deus Sol Invictus ("the Unconquered Sun God") was a religious title applied to at least three distinct deities during the later Roman Empire: El Gabal, Mithras, and Sol.

The earlier cult of Sol Indiges ("the native sun" or "the invoked sun") was agrarian. The title Deus Sol Invictus was formed similar to the imperial titulature pius felix invictus ("dutiful, fortunate, unconquered").

The Romans held a festival on December 25 called Dies Natalis Solis Invicti, "the birthday of the unconquered sun." The use of the title Sol Invictus allowed several solar deities to be worshipped together, including Elah-Gabal, a Syrian sun god; Sol, the patron god of Emperor Aurelian (AD 270-274); and Mithras, a soldiers' god of Persian origin. Emperor Elagabalus (218-222) introduced the festival, and it reached the height of its popularity under Aurelian, who promoted it as an empire-wide holiday that was a possible inspiration of Christmas.

Notes

Further reading
Halsberghe, L. 1972. The Cult of Sol Invictus (Leiden)

Other websites 
Encyclopedia Britannica Online: Sol
Probus and Sol, includes images of coins 
Roman-Emperors: Aurelian
Gibbon's Decline and Fall: Triumph of Aurelian
Gibbon's references for Aurelian's Temple of Sol Invictus 
 Clement A. Miles, Christmas in Ritual and Tradition, Christian and Pagan (1912): December 25 and the Natalis Invicti
Catholic Encyclopedia (1908): Christmas
Ancient sources

Roman gods and goddesses
An optical printer is a device. It can be used to copy rolls of movies. It is made of one or more movie projectors, which are linked to a movie camera. It allows filmmakers to re-photograph one or more strips of movie. The optical printer is used for making special effects for motion pictures or for copying and restoring old movie material.

Common optical effects include fade outs and fade ins, dissolves, slow motion, fast motion, and matte work. More complicated work needs dozens of elements, all combined into a single scene. Ideally, the audience in a theater should not be able to notice any optical printers work, but this is not always the case. For economical reasons, especially in the 1950s, and later in TV series produced on movie, printer work was limited to only the actual parts of a scene needing the effect, so there is a clear change in the image quality when the transition occurs.

The first, simple optical printers were constructed in the early 1920s. Linwood G. Dunn expanded the concept in the 1930s. The development continued well into the 1980s, when the printers were controlled with minicomputers.

Sice the late 1980s, digital compositing began to replace optical effects. Since the mid nineties the conversion to digital effects has been almost total. Optical printing today is used most widely by artists working exclusively with movie. As a technique, it proves particularly useful for making copies of hand painted or physically manipulated movie.

Printers
Charter Trustees are the English district councillors for an area that used to be a city.

They are allowed by the Charter Trustees Act 1985, so that some of the privileges and dignities of former city can be carried on.

References
Charter Trustees Acts 1985 c45
In Roman mythology, Quirinus was an early god of the Roman state. In Augustan Rome, Quirinus was also a name of Janus, as Janus Quirinus.

History

Quirinus was originally most likely a Sabine god. The Sabines had a settlement near the site of what was to become Rome, and erected an altar to Quirinus on the Collis Quirinalis, the Quirinal Hill, one of the Seven Hills of Rome.  When the Romans settled there, they absorbed the cult of Quirinus into their early belief system — previous to direct Greek influence — and he was said to be the deified Romulus.  

In later times, however, Quirinus became far less important, losing his place to (Juno and Minerva and Mars' place).

Notes

Roman gods and goddesses
The name kreisfreie Stadt (plural: kreisfreie Städte) is used for German towns that have their own government. This town government is independent of the government of the next-higher level of authority, the Landkreis. Today, most of the cities that have this statute, are big cities, with 100.000 people living there, or more. The concept grew historically. That means that there are big cities, with more than 100.000 people that do not have the statute. There are also some cities who have only taken a part of the responsibilities of a Landkreis (or Kreis). The smallest city with the statute is Zweibrücken. About 35.000 people live there. The biggest of these cities is Munich, with about 1.3 million people. Hamburg and Berlin are bigger. They are city states, though. The city state of Bremen (state) is made of two kreisfreie Städte, the city of Bremen, and the city of Bremerhaven, about 60 km to the north. About half a million people live in Bremen (1.5 million in the agglomeration), about 117.000 people live in Bremerhaven.

But not every big city with more than 100.000 inhabitants is a kreisfreie Stadt. Some of them, for example Recklinghausen or Göttingen (both more 120.000 inhabitants) are part of a Landkreis.

There are very few cities, who only took part of the paperwork from the Landkreis. Some of these are called Große selbständige Stadt (Translates to Big sovereign city). They only seem to exist in Lower Saxony. They are:
Celle, Cuxhaven, Goslar, Hameln, Hildesheim, Lingen, and Lüneburg. Things like hunting permits cannot be delegated to the cities. Other things, like what to do with the trash have sometimes been delegated.

Similar concepts to that of the kreisfreie Stadt are Unitary authorities in the United Kingdom, or that of independent city in the United States.

Political systems
Politics of Germany
The Egypt–Israel Peace Treaty was a peace treaty between Egypt and Israel. It was signed by both countries in 1979, at the end of the Camp David Accords. It was the first treaty with Israel from a Middle-Eastern Arabic nation. After signing it, Egypt was removed from the Arab League.

The Egypt–Israel treaty was signed by Egyptian president Anwar Sadat and Israeli prime minister Menachem Begin, and witnessed by United States president Jimmy Carter.

References

1979
20th century in Egypt
1970s in Israel
1970s treaties
Downtown (called a city centre in British English) is a word used in North America which refers to the main part of a city. It is usually the central business district where most commercial and office areas are; many of them being in skyscrapers. Tourism also concentrates there.

Cities
IEEE 802.11 is a series of protocols for wireless networking. Often these are called Wireless LAN, WLAN, or Wi-Fi. Such a protocol allows computers that have the needed radio parts to communicate with each other, without a cable. There are many types of Wi-Fi standards, known as 802.11 a, b, g, n, and recently ac & ad. These specifications are different in terms of speed and how far away you can use them.

Later standards 
The first Wi-Fi standard was made in 1997.  It is called IEEE 802.11.  It allows communication with 1-2 MBit per second.  Today it is outdated, and rare.  Later standards add a letter to the name.  They are labelled IEEE  802.11a to IEEE 802.11g.  There are plans for ones labeled h, i, j, n, p and s.  They are all compatible with each other.

Newer standards have a Bit rate of 54 MBit/s.  About 40-50% of this is usable in real-life situations.  As of 2007, the standards most widely used are IEEE 802.11g, and IEEE 802.11b.

Frequency bands
Data communication is either done in the 2.4 GHz band or in the 5 GHz band. The 2.4 GHz band is a general use band. Microwave ovens and Bluetooth are among the things that emit radio waves in this band. The 2.4 GHz band has the problem that there are only very few channels that can be used at the same time, without the signals interfering. There are three usable channels there. When more than three networks operate in the same place, signals still get to the user correctly, but interference slows them. 

The 5 GHz band can solve some of these problems, but it introduces others. That band has 19 usable channels. Overall the band is less used. However there are more regulations. Most devices need to be able to choose their channel to minimize interference. Some channels require that those participating can do Transmitter Power Control. This means they adapt the strength of the signal to what is actually needed. This helps reduce the amount of interference between different networks.

Computer protocols
Computer networking
In computing, Wireless LAN (WLAN) or Wireless local area network is a term to refer to a Local Area Network that does not need cables to connect the different devices. Instead, radio waves and  IEEE 802.11 are used to communicate.

Benefits of Wireless LANs 
 People can access the network from where they want; they are no longer limited by the length of the cable
 Some places and vehicles have a Wireless LAN hotspot. This lets people access the internet even outside their normal work environment, for example in a restaurant or train.
 Setting up a wireless LAN can be done with one box called wireless access point or wireless router. This box can handle many connections at the same time. Wired networks require cables to be laid. This can be difficult for certain places.
 Access points can serve a varying number of computers.

Disadvantages of Wireless LANs 
 Wireless LANs use radio waves to communicate. Special care needs to be taken to encrypt information.  
 The signal is noisier than on wires, and more bandwidth needs to be spent on error correction. 
 A typical IEEE 802.11 access point has A range of meters from where devices can connect. To extend the range more access points are needed. 
 There are many reliability problems, especially those connected to interference from other devices.
 Wireless LANs are much slower than wired ones; this may not matter for most users though, because the bottleneck in a home network is usually the speed of the ADSL line or other Internet connection.

Technologies used 
Today, most  technologies used for WLANs use Orthogonal Frequency Division Multiplexing. This means that several frequencies are used at the same time. Signals that are close to each other, but that belong to different channels do not disturb each other, as they use different coding schemes. Depending on the material used, it is possible to cover between 30 metres and 100 metres indoors; outdoors, the range is about 100-300m, if there are no obstacles.

Computer networking
Bluetooth is a protocol for wireless communication over short distances. It was developed in the 1990s, to reduce the number of cables.  Devices such as mobile phones, laptops, PCs, printers, digital cameras and video game consoles can connect to each other, and exchange information. This is done using radio waves. It can be done securely. Bluetooth is usually only used for relatively short distances, like a few metres. Some signals can be up to 100 metres.

There are different standards. Data rates vary. Currently, they are at 1-3 MBit per second. Typical Bluetooth applications are to connect a headset to a mobile phone, or to connect a computer mouse, keyboard or printer.

Bluetooth devices use the ISM Band around 2.4 GHz. This can be used worldwide, without the need to pay license fees, but many other devices, like DECT telephones (wireless phones), smart tags with RFID, baby phones use it too. Bluetooth uses the same bands as some WLANs, but the modulation technique is different. Bluetooth uses Frequency-hopping spread spectrum.

Comparing Bluetooth to Wireless LAN 

There are many situations today where either Bluetooth or Wireless LANs can be used. Examples include setting up networks, printing or transferring files and data from a PDA to a computer. Both are versions of unlicensed wireless technology. WLANs can span bigger distances and offer higher throughput. Bluetooth does not require expensive hardware. It also needs less power to operate.

Both use the same radio frequency range, but their modulation techniques are different. Both have been developed to replace cabling. Bluetooth wanted to get rid of the peripheral equipment cables, WLANs wanted to get rid of the cables needed to set up a LAN.

Bluetooth devices 

Bluetooth exists in many products, such as telephones, the Wii or PlayStation 3. It has recently been built into some electronic watches, modems and headsets. The technology is useful when transferring information between two or more devices that are near each other in low-bandwidth situations. Bluetooth is commonly used to transfer sound data with telephones (i.e. with a Bluetooth headset) or byte data with hand-held computers (transferring files).

Bluetooth uses protocols that make it easy to discover devices that are nearby, and to set up a connection between these devices. Bluetooth devices can advertise all the services they offer. Using services becomes easier; a lot of the setup related to security, networking or permissions is automatic.

Wireless LAN 
WLANs are more like traditional LANs. More configuration is needed to set up the network, and to make resources accessible by other devices in the network. WLAN devices also consume more power than Bluetooth ones. 
Sometimes WLANs are called wireless Ethernet. WLAN needs more resources to be set up, but it also offers faster transfer speeds. The security is also better than that offered by Bluetooth.

References

Computer protocols
Computer networking
The hominids are members of the biological family Hominidae (the great apes). This family includes humans, chimpanzees, gorillas and orangutans. "Great ape" is a common name rather than a taxonomic label, and people use it in different ways. Sometimes people mean to include humans in the category of “great apes,” and sometimes they mean non-human apes. Homo sapiens is definitely a hominid, as judged by all modern reference works.

Hominids range in weight from 48 kg to 270 kg. Males are larger than females. Hominids are primates with no tails, strong bodies, and well-developed forearms. Their thumbs (and big toes, except in humans) oppose the fingers, and form a grip. All digits have flattened nails.

At present, the family Hominidae includes four genera and five species. However, if fossil hominids were included, all of the Australopithecines and the genus Homo would be members of the Hominidae family. Today, nonhuman great apes live only in the rainforests of equatorial Africa, Sumatra and Borneo.

The first hominid fossils are from the Miocene period. Archaeologists found these in Asia and Europe. Also in Asia, they found fossils of a huge version of the orangutan called Gigantopithecus, which is now extinct. Fossils also show that Neanderthals were in Europe and western Asia for at least half a million years before modern humans appeared.

Classification
Scholars do not agree on exactly how to classify the family Hominidae.

Past versions
In the past, the family Hominidae have been classified this way:
Family Hominidae: Great apes
 Subfamily Ponginae
 Genus Pongo  orangutans
 Subfamily Homininae
 Genus Gorilla – gorillas
 Genus Pan – chimpanzees
 Australopithecus† and other extinct relatives
 Genus Homo – humans

Modern version
A more recent classification shows humans and the Australopithecines as distinct from the rainforest apes. Two major reference works have supported this approach.

Superfamily Hominoidea
Family Hylobatidae
Genus Hylobates
Family Hominidae
Subfamily Ponginae
Genus Pongo
Subfamily Gorillinae
Genus Gorilla
Subfamily Homininae
Tribe Panini
Genus Pan
Tribe Hominini
Subtribe Australopithecina/Hominina
Genus Ardipithecus
Genus Australopithecus
Genus Kenyanthropus
Genus Sahelanthropus
Genus Orrorin
Genus Paranthropus
Genus Homo

Related pages
 Human timeline
 Human evolution

References

Hominids
The Acropolis of Athens is  the most famous acropolis. It is a large hill in the center of Athens, on which the Parthenon and other Greek buildings were built. It is often known as The Acropolis.

Buildings and structures in Athens
Ancient Athens
Toki Pona (in Toki Pona it means good language or simple language) is a constructed (made-up) language. Sonja Lang (in past time Sonja Elen Kisa), a Canadian translator and linguist, made the language. It is based on simple ideas that are known to all cultures. It is not created to be an international auxiliary language (a language for communication between people speaking different languages). It is meant to test ideas about minimalism and pidgins. It is influenced by Taoist ideas. It has only 120 root words, although there is over 50,000 different possible combinations. Toki Pona relies very heavily on expressing ideas by using root words together. For example, jan pona means friend in Toki Pona (literally it means: good person). 

Normally Toki Pona uses the Latin alphabet, but many Toki Pona speakers create other systems of writing for this language. There are some attempts to create a writing system based on pictograms, but they have not been very successful.

Example of text 
Lord's Prayer (translated by Pije/Jopi):

mama pi mi mute o, sina lon sewi kon.
nimi sina li sewi.
ma sina o kama.
jan o pali e wile sina lon sewi kon en lon ma.
o pana e moku pi tenpo suno ni tawa mi mute.
o weka e pali ike mi. sama la mi weka e pali ike pi jan ante.
o lawa ala e mi tawa ike.
o lawa e mi tan ike.
tenpo ali la sina jo e ma e wawa e pona.
Amen.

References

Other websites
Toki Pona official website
Toki pona lessons

Constructed languages
The Canadian Hurricane Centre (CHC) is a Canadian agency that is responsible for monitoring and tracking tropical cyclones that come near or affects Canadian territory. The agency warns people about on-coming tropical cyclones and makes hurricane advisories when needed. Its headquarters are in Dartmouth, Nova Scotia.

CHC usually works together with its United States counterpart, the National Hurricane Center in Miami, to coordinate the tracks and positions of all storms that show a possible threat to Canada.

While Atlantic hurricanes are normally uncommon in Canada, they do approach or strike from time to time. Among recent events are Hurricane Bob, which struck New Brunswick, in 1991, Hurricane Luis which struck Newfoundland in September 1995, Hurricane Hortense which struck Nova Scotia in September 1996, Hurricane Michael which struck Newfoundland in October 2000, and Hurricane Juan, which struck Nova Scotia in September 2003.

Other websites
CHC website
Official Canadian Weather Warnings 
Hurricane Bulletins for your wireless device 

Canada
Vulcans are a humanoid species in the fictional Star Trek universe who hail from the planet Vulcan, and are noted for their attempt to live by reason and logic with no interference from emotion. They were the first 
extraterrestrial species encountered by Humans, and later became one of the founding members of the United Federation of Planets. Vulcans are featured in all six Star Trek series, four of which featured a Vulcan as a main character.

Related pages
 Vulcan, Alberta - a town in Canada that has incorporated Star Trek themes due to its name.
 Stoicism

Bibliography
 Star Trek: The Magazine v3#10 (February 2003 - "Romulan Propulsion Historical Overview" by Rick Sternbach & Tim Earls)
 Spock's World Diane Duane Pg. 359 Pocket Books, a division of Simon & Schuster Inc.  1230 Avenue of the Americas, NY, 10020 Paperback Edition 1989.

Fictional races
Star Trek
The W. M. Keck Observatory is a pair of two large, ground-based telescopes located at Mauna Kea, Hawaii. Sitting four km (more than two miles) above sea level, the paired telescopes are used to examine light from distant stars in great detail. The primary mirrors of each of the two telescopes are 10 meters (33 feet) across, making them slightly smaller than the Gran Telescopio Canarias primary mirrors.

However, all of the light collected by the Keck Observatory primary mirrors (75.76m2) is sent to the secondary mirror and the instruments, compared to GTC's primary mirror, which has an effective light-collection area of 73.4m2, or 25.4 square feet less than each of the Keck Observatory primary mirrors. Because of this fundamental difference in design, Keck Observatory's telescopes arguably remain the largest steerable, optical/infrared telescopes on Earth.

Related pages
 La Silla Observatory
 Very Large Telescope

Other websites 
 W.M. Keck Observatory (official site)
 The Mauna Kea Observatory (official site)

Observatories in the United States
Buildings and structures in Hawaii
A metamorphic rock is a type of rock which has been changed by extreme heat and pressure. Its name is from 'morph' (meaning form), and 'meta' (meaning change).

The original rock gets heated (temperatures greater than 150 to 200 °C) and pressured (1500 bars). This causes profound physical and/or chemical change. The original rock may be sedimentary rock, igneous rock or another older metamorphic rock.

There is always more pressure and higher temperature under the Earth's surface. In the root of a mountain chain or a volcano these forces will be enough to change shape of the strata and the minerals it is made of. Sedimentary rock which has been near such forces often looks as if a giant had twisted it and heated it over a fire. Examples of metamorphic rock:
 Marble is a metamorphic rock formed from limestone.
 Slate is a metamorphic mudstone or shale.
 Quartzite is a metamorphic sandstone.

The recrystallisation of minerals after heating generally causes the destruction of any fossils the rocks might have contained. These rocks are formed when igneous or sedimentary rocks are subjected to extreme heat and pressure as result they undergo a complete change in their form and characteristics. Such form rocks are called metamorphic rocks.

Types of metamorphism

Regional metamorphism

Regional metamorphism, or dynamic metamorphism, occurs in great masses of rock. Rocks can be metamorphosed just by being at great depths below the Earth's surface. There they get high temperatures and the great weight of the rock layers above.

Much of the lower continental crust is metamorphic, except for recent igneous intrusions. Horizontal tectonic movements such as the collision of continents create orogenic belts. High temperature, pressures and deformation occurs along these belts. If the metamorphosed rocks are later uplifted and exposed by erosion, they are seen as long belts or other large areas at the surface.

Contact metamorphism

Contact metamorphism occurs when magma is injected into the surrounding solid rock (country rock). The changes that occur are greatest where the magma comes into contact with the rock. The temperatures were highest there and decreased with distance from it.

Metamorphic minerals 
Metamorphic minerals are those that form only at the high temperatures and pressures of metamorphism. These minerals, known as index minerals, include sillimanite, kyanite, staurolite, andalusite, and some garnet.

Other minerals, such as olivines, pyroxenes, amphiboles, micas, feldspars, and quartz may be found in metamorphic rocks. They are not necessarily the result of the process of metamorphism. These minerals formed during the crystallization of igneous rocks. They are stable at high temperatures and pressures and may remain chemically unchanged during the metamorphic process.

Related pages 
 List of rocks
 Igneous rock
 Sedimentary rock
 List of minerals

References

Other websites 

 Metamorphic textures - Middle East Technical University 
 Metamorphism - U. of Alabama 
 Types of metamorphism - Tulane U.
 Contact metamorphism example 

Rocks
An intrusion is magma (melted rock) which cools and becomes solid under the Earth's surface.  It occurs when there are lines of weakness such as faults, joints, or bedding planes in the crust. Then magma enters these lines of weakness.  By contrast, an extrusion is magma which cools into rock above the surface of the crust. Both intrusive and extrusive rocks are classed as igneous rocks.

The process of forming intrusive rocks may take millions of years. As the rock slowly cools into a solid, the different parts of the magma crystallize into minerals. The crystals are usually larger than in extrusive rocks. Many mountain ranges, such as the Sierra Nevada in California, are formed mostly by intrusive rock. Often they are huge granite (or related rock) formations.

Intrusions vary widely, from mountain range sized batholiths to thin vein-like fracture fillings. When exposed by erosion, these cores called batholiths may occupy huge areas of Earth's surface. Large bodies of magma that solidify underground before they reach the surface of the crust are called plutons.

Intrusive structures may go between bedding planes of earlier 'country' rock. A sill is an intrusion which makes a table along bedding planes. A dyke is an intrusion which moves up, crossing older strata.

Related pages 
Volcanic plug

Geology
Igneous rocks
Radiation pressure is the pressure exerted upon any surface exposed to electromagnetic radiation. If absorbed, the pressure is the energy flux density divided by the speed of light. If the radiation is totally reflected, the radiation pressure is doubled.  This happens because the waves that make up electromagnetic radiation carry momentum with them and pass that momentum on when they reach a surface.

A Crookes radiometer appears to demonstrate the pressure of light, but instead it demonstrate the energy that light brings to a surface.  The black side of each paddle absorbs most of the light's energy an causes the air near that surface to have a higher pressure.  So, while a Crookes radiometer turns because of pressure, it is air pressure caused by the heat energy that light brings to the device.

Solar radiation at Earth
The solar radiation at Earth's distance from the Sun has an energy flux density of 1370 W/m2, and more than half of this energy reaches surface.  A calculation shows that this value of the flux would cause on an absorbing surface to experience 4.6 µPa of radiation pressure.  A convenient way to compare the Sun's energy flux and radiation pressure is to imagine the pressure and energy deposited on one square meter:

Power =  (or about 1.4 kilowatts.) 
Force = 

To understand how small a micro-newton is, convert calculate how much mass you need on Earth to get that force using :
Mass =  (or about ½ milligram.)

The difference between the energy flux and the pressure is like the difference between the heat coming through a large window and the weight of a very small mosquito.

References

Further reading
 Demir, Dilek,"A table-top demonstration of radiation pressure",2011, Diplomathesis, E-Theses univie (http://othes.univie.ac.at/16381/)

electromagnetism
Ca-Al-rich inclusions (CAIs) are centimeter-sized light-coloured calcium and aluminium rich inclusions found in carbonaceous chondrites. CAIs contains high-temperature minerals and are among the first solids which solidified from the cooling protoplanetary disk. CAIs were formed at much higher temperatures than the associated chondrules, and may have survived many high-temperature events, whereas most chondrules are the product of a single transient melting event.

The isotopic anomalies of CAIs give valuable clues about the solar system's formation, suggesting that the solar nebula collapsed shortly after a nearby supernova. Radiometric dating shows that the CAIs formed about 2 million years before the chondrules formed.

References
 Gilmour J. 2002. The Solar System's first clocks Science 297, 1658-1659. 
 Amelin Y. et al. 2002. Lead isotopic ages of chondrules and calcium-aluminum-rich inclusions Science, 297, 1678-1683.
 Krot A.N. 2002.  Dating the earliest solids in our Solar System. Planetary science research discoveries. http://www.psrd.hawaii.edu/Sept02/isotopicAges.html
 Shukolyukov A. & Lugmair G.W. 2002. Chronology of asteroid accretion and differentiation 687-695, in Bottke W.F. et al. (eds) Asteroids III. University of Arizona Press. 

Meteorites
Eucrites are achondritic stony meteorites that originate from the surface of the asteroid 4 Vesta, and as such are part of the HED meteorite group. They are the most common achondrite group with well over 100 distinct finds at present.

Eucrites consist of basaltic rock from the crust of 4 Vesta. They are mostly made up of Ca-poor pyroxene, pigeonite, and Ca-rich plagioclase (anorthite).

Eucrites are named from a Greek word meaning "easily distinguished".

Other websites 
 HED Group - Meteorites from Vesta

Meteorites

it:Meteorite HED#Eucriti
Comet 81P/Wild, also known as Wild 2, is a comet named after Swiss astronomer Paul Wild (pronounced Vilt), who discovered it in 1978.

It is believed that for most of its 4.5 billion-year lifetime, Wild 2 had a more distant and circular orbit. In 1974, it passed within only about one million kilometers of the planet Jupiter, whose strong gravitational pull altered the comet's orbit and brought it into the inner solar system. Its orbital period changed from 40 years to about 6 years, and its perihelion is now about 1.59 AU (astronomical unit).

Gallery

Other websites 
 NASA Team Analyzes Stardust Particle Capture January 18, 2006
 NASA/JPL homepage for Stardust project
 Stardust@Home Volunteer Particle Analysis Project
 IAU Ephemerides page for 81P
 Catalogue of all 72 raw images of Wild 2 

Comets
An ion thruster is a kind of spacecraft engine. It works by using static electricity or magnetism to push ions (electrically charged atoms) out the back of the spacecraft. It takes a very long time to speed up, but its fuel lasts much longer than a rocket engine. It has to be carried into outer space by a regular rocket, because the ions don't push hard enough for it to escape the Earth's gravity, but after it gets to outer space it can travel a very long way. An ion thruster needs electricity to run, so the spacecraft has to also carry solar panels or a nuclear reactor.

In 2011 the NASA space probe called Dawn used an ion thruster to get to the asteroid Vesta. In 2015 the thruster brought it to the dwarf planet Ceres.

Rockets