cahya/wikipedia-simple-en huggingface dataset:
Water (molecule)

Water (H2O, HOH) covers 70-75% of the Earth's surface in its liquid and solid (ice) states, and is present in the atmosphere as a vapor. It is the most abundant molecule on the Earth's surface.

At room temperature, it is a nearly colorless, flavorless, and odorless liquid. Many substances dissolve in water and it is commonly seen as the universal solvent; because of this, water in nature and in use is rarely clean, and may have some properties different than those in the laboratory. But there are many compounds that are essentially, if not completely, insoluble in water. Water is the only common, pure substance found naturally in all three states of matter—for other substances, see Chemical properties.

Pure water is tasteless. It is the other chemicals in the water which may give water a flavour.

Anomalous properties of water
Generally, the volume of a liquid increases when heated, however the volume of water decreases when heated within the temperature range of 0°C to 4°C. Its volume increases only when heated above 4°C. Such behavior is one of a number of water's anomalous properties. 

This property of volume decrease allows fish and other aquatic animals to survive in a body of water when ice has frozen on the surface. In cold climates, when the temperature of a body of water reaches at 4°C, the layers of water near the top in contact with cold air continue to lose heat energy and their temperature falls below 4°C. On cooling below 4°C, these layers rise rather than sink, as water has maximum density at 4°C. Thus the layer of water with a temperature of 4°C remains at the bottom, while layers of water 3°C, 2°C, 1°C and 0°C are formed above. Because ice is poor conductor of heat, it does not allow heat energy transfer from the liquid water beneath the layers of ice, which prevents the liquid water from freezing. Hence, aquatic creatures survive in such places.

References

Other websites 
Water Structure and Behaviour A comprehensive and up-to-date NPOV resource maintained by Prof Martin Chaplin of South Bank University, UK
A spoof site on the "dangers" of dihydrogen monoxide
Stockholm International Water Institute (SIWI)
Explanation of the anomalous properties of water
Computational Chemistry Wiki
Lymphatic system

In mammals, the lymphatic system is a network of thin vessels that branch, like blood vessels, into tissues throughout the body. It is part of the immune system. It is a one-way system which carries cells and fluid back to the blood system.
 
Lymphatic vessels carry lymph, a colorless, watery fluid and white blood cells. It comes  from interstitial fluid in the tissues which is squeezed out of the blood vessels. The lymphatic system transports infection-fighting cells called lymphocytes, and is involved in the removal of foreign matter and cell debris by phagocytes. A second function is to transport fats from the small intestine to the blood. 

Lymphatic fluid gathers from the tissues and enters the valved lymphatic ducts. It is the valves which make sure the lymph flows the right way. On its way back to the blood system, the lymph passes through  glands called lymph nodes, in places like the back of the neck, the armpits and the groin. Lymph nodes swell in the region of an infected body part. This acts to keep the infection from spreading. It prevents or reduces the pathogens getting into the general blood circulation and reaching other parts of the body.

Lymph ends up back in the blood system. In mammals under normal conditions most of the lymph is returned to the blood stream through lymph-vein communications at the base of the neck. Some vertebrates have more complex lymphatic systems. Amphibians for example have multiple "lymph hearts" to control the flow of lymph.

References 

Physiology
Immunology
Chastity

Chastity is the sexual behavior of a man or woman which is right and proper according to the moral rules of a culture or religion. It has recently begun to mean sexual abstinence (not having sex at all), especially before marriage. However, it can also be used for all kinds of people (even married people) with more meaning than simply not having sex. The word chastity came from the Latin word castitatem, meaning "purity".

Related pages 
Sexual abstinence

References

Other websites 
Catechism of the Catholic Church (III.2.I)
Early Shaker Writings Relating to Sexual Abstinence

Human sexuality
Metallic bond

A metallic bond is the sharing of many detached electrons between many positive ions, where the electrons act as a "glue" giving the substance a definite structure. It is unlike covalent or ionic bonding. 
Metals have low ionization energy.  Therefore, the valence electrons can be delocalized throughout the metals. Delocalized electrons are not associated with a particular nucleus of metal, instead, they are free to move throughout the whole crystalline structure forming a "sea" of electrons.

The electrons and the positive ions in the metal have a strong attractive force between them.  Therefore, metals often have high melting or boiling points. The principle is similar to that of ionic bonds.

Metallic bonds causes many of the traits of metals, such as strength, malleability, ductility, luster, conduction of heat and electricity.

Because the electrons move freely, the metal has some electrical conductivity. It allows the energy to pass quickly through the electrons, generating an electric current. Metals conduct heat for the same reason: the free electrons can transfer the energy at a faster rate than other substances with electrons that are fixed into position. There also are few non-metals that conduct electricity: graphite (because, like metals, it has free electrons), and ionic compounds that are molten or dissolved in water, which have free moving ions.

Metal bonds have at least one valence electron which they do not share with neighboring atoms, and they do not lose electrons to form ions. Instead, the outer energy levels (atomic orbitals) of the metal atoms overlap. They are similar to covalent bonds. Not all metals exhibit metallic bonding. For example, mercury ions () form covalent metal-metal bonds.

An alloy is a solution of metals. Most alloys are shiny like pure metals are.

Related pages
 Chemical bond
 Covalent bond
 Ionic bond
 Coordination complex
 Alloy

References 

Chemical bonding
Metals
Heat conduction

Heat conduction (or thermal conduction) is the movement of heat from one object to another one that has different temperature when they are touching each other.  For example, we can warm our hands by touching hot-water bottles. When the cold hands touch the hot-water bottle, heat flows from the hotter object (hot-water bottle) to the colder one (hand). People make things with different thermal conductivity, for example cookware to heat things or insulated containers to keep hot things hot or cold things cold.

Other ways to transfer heat are by thermal radiation and/or convection. Usually more than one of these processes happen at the same time.

Microscopic explanation 
In the atomic theory solids, liquids and gases are made of tiny particles called "atoms". The temperature of the material measures how fast the atoms are moving and the heat measures the total amount of energy due to the vibration of the atoms.

Conduction can happen when one part of a material is heated. The atoms in this part vibrate faster and are more likely to hit  their neighbors. The collisions cause those atoms also to move faster, passing the heat energy to them. In this way the energy travels through the solid. (Rather like the way energy passes along a set of tumbling dominos).

The atomic picture also helps explain why conduction is more important in solids: in solids the atoms are close together and unable to move around. In liquids and gases the particles can move past each other, so the collisions are less common.

Law of heat conduction 
The law of heat conduction, also known as Fourier's law, means that the rate, in time, of heat transfer through a material is proportional to the negative gradient in the temperature and to the area at right angles, to that gradient, through which the heat is flowing:

 

where:
Q is the amount of heat transferred, and 
t is the time taken, and 
k is the material's thermal conductivity' and 
S is the area through which the heat is flowing, and 
T is the temperature.

Thermal conductivity usually varies with temperature, but the variation can be small, over a significant range of temperatures, for some common materials.

Related pages
 Heat transfer
 Convection
 Thermal radiation

Basic physics ideas
Heat transfer
Judith Weir

Judith Weir (born 11 May 1954) is a British composer. She is well known for her theatre works, choral music, orchestral music and chamber music.

Early life 
Weir was born in Cambridge, England to Scottish parents. While she was still at school she trained with the composer John Tavener. She played the oboe in the National Youth Orchestra of Great Britain. She then studied at the University of Cambridge where her teacher was Robin Holloway.

Career 
Judith Weir’s music has harmonies which are very exciting and original. Her Christmas carol Illuminare has become very popular, but it is quite difficult and needs a good choir to pitch the notes of the dissonant chords. She often uses medieval history as inspiration for her music, as well as music from her native Scotland, e.g. piobaireachd, which is a kind of variation form using small intervals. Her music often tells stories. Her operas include A Night at the Chinese Opera, The Vanishing Bridegroom, Blond Eckbert, and Armida, an opera for television.

From 1995 to 2000, she was the Artistic Director of the Spitalfields Festival in London. She has composed works for the City of Birmingham Symphony Orchestra. She has received many honours, including the CBE in 1995.

Other websites 
 Judith Weir's homepage at Chester Music (music publishers)
 Judith Weir (b 1954) (BBC)

1954 births
Living people
20th-century English composers
21st-century British composers
People from Cambridge
Women composers
Vassal

A vassal during the feudalism of medieval Europe, was someone who had shared duties  with a lord. Usually the vassal provided soldiers to the lord. The lord used his army of soldiers from all of his vassals to protect those vassals. The lord also gave him the piece of land that he held as a fief. By analogy the term vassal is used also for similar systems in other feudal societies.

Western vassalage
The development of the vassal, in a society that was increasingly organised around the concept of "lordship"– in French the seigneur– is one sign that Antiquity ended and the Early Middle Ages began. Lordship is the basic social institution as Tacitus described them in his book Germania. The Roman West experienced them for the first time in the Migration Period.

As the system developed in the seventh century, the vassals were gangs of freemen who subjected themselves, in some degree of formality, to the authority of a leader, from whom they could expect to be fed, clothed and armed. The quality of a vassal was only in his fighting ability and the strength of his loyalty. The etymology (where the word came from) of "vassal" is from a Celtic word gwas "boy" that meant a young male slave, with a Latinised form, vassus that appeared in Salic Law (Rouche 1987 p 429), like the way  "knight" came from the from  Old English word cniht and similar words in Frisian and Dutch, all meaning "lad" .

Related pages
Gokenin, vassals of the shogunate in Japan

References
Cantor, Norman, The Civilization of the Middle Ages 1993
Ganshof, François Louis, Feudalism translated 1964
Rouche, Michel, "Private life conquers state and society," in A History of Private Life vol I, Paul Veyne, editor, Harvard University Press 1987 

History of Europe
Migration period

The migration period, or barbarian invasions or Völkerwanderung, happened in AD 300–700 in Europe, at the end of ancient history and during the Early Middle Ages.

The migrations included the Goths, Vandals, Franks, and other Germanic, Bulgar, and Slavic tribes. They may have been influenced by attacks of the Huns in the East and may also be connected to the Turkic migrations in Central Asia, overpopulation, or climate changes. The migration period also included groups of Angles, Saxons, Frisians, and some Jutes to Britain.

Migrations would continue well into the Middle Ages, beyond 1000 AD, with successive waves of Slavs, Alans, Avars, Bulgars, Hungarians, Pechenegs, Cumans, and Tatars that changed the ethnic makeup of Eastern Europe. Western European historians, however, tend to stress the migrations that were most relevant to Western Europe.

Related pages
 Human migration

References

Other websites 
 J.B. Bury (1923). History of the Later Roman Empire

Periods and ages in history
San Francisco Bay

San Francisco Bay is a shallow, productive estuary through which water draining about forty percent of California, flowing in the Sacramento and San Joaquin rivers from the Sierra Nevada mountains and Central Valley, enters the Pacific Ocean. Technically, both rivers flow into Suisun Bay, which help flows through the Carquinez Strait to meet with the Napa River at the entrance to San Pablo Bay, which connects at its south end to San Francisco Bay, although the entire group of interconnected bays are often referred to as "the San Francisco Bay."

San Francisco Bay lies in the US state of California and is surrounded by a region known as the San Francisco Bay Area, that is near the big cities of San Francisco, Oakland, and San Jose.

The Bay covers somewhere between 400  and 1,600  square miles (1,040 to 4,160 square kilometres), depending on which sub-bays (such as San Pablo Bay), estuaries, wetlands, and so on are included in the measurement.

Photography

References 
 1999 Grolier Multimedia Encyclopedia.
 1988 Encyclopædia Britannica.

Other websites 
 San Francisco Bay: Portrait of an Estuary, David Sanger and John Hart, University of California Press
 Barging In - A Short History of Liveaboards on the Bay 
 Army Corps of Engineers Bay Model: Working scale model of the Bay 
 BoatingSF.com: Photos of SF Bay and its boats, plus online cruising guide
 SF Estuary Institute: San Francisco Bay Historical View Maps

San Francisco Bay Area
Bodies of water of California
Bays of the United States
Alameda County, California
Santa Clara County, California
Contra Costa County, California
Solano County, California
San Mateo County, California
Marin County, California
Ahmed Yassin

Ahmed Yassin (January 1, 1937 – March 22, 2004) was a spiritual leader of the militant Palestinian group Hamas. Yassin's birth date is in dispute. He claimed he was born 1/1/1938, however, his passport indicated 1/1/1937. To some he was a hero, to some he was a notorious member of a terrorist organization. He was also a symbolic figure for Palestinians to fight against Israel. 

Yassin was born in al-Jura, British Mandate of Palestine. He helped create Hamas and became its spiritual leader in 1987. To other members of Hamas he was a hero but he was blamed by the Israeli government for planning suicide bombings and other attacks against Israel. He claimed that was the only way of fighting occupation. He was confined to a wheelchair because he was paralyzed since age 12, he was also nearly blind and could barely hear. He was very powerful and influential. He was assassinated in an airstrike in Gaza City by the Israeli Army after he left a mosque in Gaza in the early morning hours.

Other websites 
 Israel Bombing of Refugee Camp 
 Yassin killed, Ahmed Yassin biography 
 Yassin's letter and kids named after him

1937 births
2004 deaths
Deaths by airstrike
Assassinated people
Muslim terrorists
Palestinian Muslims
Palestinian nationalists
Palestinian terrorists
Field strength

In physics, the field strength of a field is the magnitude (size) of its (vector) value. This means that the force exerted by the field on a given object is proportional to the field strength.

In differential geometry, the field strength is another name for the curvature form.  For the electromagnetic field, the curvature form is an antisymmetric matrix whose elements are the electric field and magnetic field: the electromagnetic tensor.

In radio engineering, field strength is the strength of radio waves in a particular location. 

Physics
Field (physics)

In physics, a field means that a physical quantity is assigned to every point in space (or, more generally, spacetime). A field is seen as extending throughout a large region of space so that it influences everything. The strength of a field usually varies over a region. Michael Faraday became the first to coin the term "field", in 1849.

For some fields, there is a number for each point in space. They are called scalar fields. For more complicated fields, there are more than one number for each point in space. They are called vector fields or tensor fields. For example, one can model a gravitational field by a vector field where a vector indicates the acceleration a mass would experience at each point in space. Other examples are temperature fields or air pressure fields, which are often illustrated on weather reports by isotherms and isobars by joining up the points of equal temperature or pressure respectively.

Types of fields

Classical fields 
Newtonian gravitation: describes the gravitational force as a mutual interaction between two masses.
Electromagnetism:  electric and magnetic fields are not only fields of force which dictate the motion of particles, but also have an independent physical reality because they carry energy.
Gravitation in general relativity: this is Einstein's theory of gravity. 
Waves as fields

Quantum fields 
It is now believed that quantum mechanics should underlie all physical phenomena.

Field theory 
A field theory is a physical theory that describes how one or more physical fields interact with matter.

Related pages 
 Elasticity
 Fluid dynamics
 General relativity
 Maxwell's equations
 Particle physics

References 

 Landau, Lev D. and Lifshitz, Evgeny M. 1971. Classical theory of fields. 3rd ed, London: Pergamon.  Vol. 2 of the Course of Theoretical Physics.

Basic physics ideas
Gradient

In vector calculus, the gradient of a multivariate function measures how steep a curve is. On a graph of the function, it is the slope of the tangent of that curve. More generally, it is a vector that points in the direction in which the function grows the fastest. Its coordinates are partial derivatives of that function. The gradient of a function f is often written as  or .

Related pages 

 Laplace operator

References 

Mathematics
Calculus
Archer

An archer is someone who practices archery (shooting with bows and arrows). 

Archer can also mean:

Fictional characters
 Sean Archer, character portrayed by John Travolta/Nicolas Cage in the movie Face/Off
 Danny Archer, character portrayed by Leonardo DiCaprio in the movie Blood Diamond

Other
 Jeffrey Archer, Baron Archer of Weston-super-Mare, British author, former politician
 Archer River, one of the best-known rivers in Cape York Peninsula, Australia
 Archer (horse) - an Australian racehorse that won the first two Melbourne Cups
Archery

Archery is the practice of using a bow to shoot arrows. Archery has historically been used in hunting and combat and has become a precision sport. A person practicing archery is called an archer, and one who enjoys or is an expert at archery is sometimes called an toxophilite.

History

The earliest evidence of archery dates back more than 9,000 years. The bow probably was used in hunting first and later adopted as a tool of warfare. It was one of the earliest forms of artillery. 

Classical civilizations, notably the Persians, Macedonians, Nubians, Greeks, Parthians, Indians, Japanese, Chinese, and Koreans, had large numbers of archers in their armies. Archers in chariots were especially important in armies of ancient Egypt. Arrows were very destructive against massed formations, and the use of archers helped win battles. The army of the Mongol Empire was mostly archers on horseback.

Other websites 

 Archery Interchange UK The UK's largest online archery community.
 The Great Northwood Bowmen  Medieval Longbow Archery and re-enactment Society, re-enacting the 15th century, based in London. 
 Bowhunting Basics
 Archery Information
 Archery Pictures

       
 
War
Summer Olympic sports
Signal transduction

A signal transduction in biology is a  cellular mechanism. It converts a stimulus into a response in the cell. There are two stages in this process:
A signalling molecule attaches to a receptor protein on the cell membrane.
A second messenger transmits the signal into the cell, and a change takes place in the cell.
So, signal transduction starts with a signal to a cell receptor, and ends with a change in cell function. In either step, the signal can be amplified. Thus, one signalling molecule can cause many responses.

Receptors are in the cell membrane, with part of the receptor outside and part inside the cell.  The  chemical signal binds to the outer portion of the receptor, changing its shape. This causes another signal inside the cell.  Some chemical messengers, such as testosterone, can pass through the cell membrane, and bind directly to receptors in the cytoplasm or nucleus.

Sometimes there is a cascade of signals within the cell. With each step of the cascade, the signal can be amplified, so a small signal can result in a large response. Eventually, the signal creates a change in the cell, either in the expression of the DNA in the nucleus or in the activity of enzymes in the cytoplasm.

Most often, ordered sequences of biochemical reactions inside the cell are involved. These are carried out by enzymes and linked through second messengers. So a "second messenger pathway" is produced. These things usually happen quickly, sometimes very quickly. They may last from milliseconds (in the case of ion flux) to days for gene expression.

The number of proteins and other molecules that take part increases during the process. So a 'signal cascade' develops and a relatively small stimulus may cause a large response.

In bacteria and other single-cell organisms, the transduction processes a cell has limits the number of ways it can respond to its environment. In multicellular organisms, lots of different signal transduction processes are used to coordinate the behavior of individual cells. By this means the function of the organism as a whole is organized. The more complex the organism, the more complex the repertoire of signal transduction processes the organism must possess.

Thus, sensing of both the external and internal environment at the cellular level, relies on signal transduction. Many disease processes such as diabetes, heart disease, autoimmunity and cancer arise from defects in signal transduction pathways. This highlights the critical importance of signal transduction to biology and medicine.

These systems of communication between cells are extremely ancient, and are found in all metazoa.

Related pages 
Transduction (physiology)
Ligand
Cytokine

References

Other websites 

 [http://stke.sciencemag.org/ Science'''s STKE - Signal transduction knowledge environment], from Science'', published by AAAS.
 Cosma Shalizi's Signal transduction notebook

Cell biology
Molecular biology
Flux

Flux is a term in physics and mathematics. It is broadly defined as "How much stuff goes through a thing" (or into an area). The word "flux" is similar to "flow".

For instance, imagine a butterfly net. The amount of air passing through the net is the flux.

Movement of substances 
In the study of transport phenomena (heat transfer, mass transfer and fluid dynamics), flux is defined as flow per unit area, where flow is the movement of some quantity per time. Flux, in this definition, is a vector.
 
There are many fluxes used in the study of transport phenomena. Each type of flux has its own distinct unit of measurement along with distinct physical constants. Six of the most common forms of flux from the transport literature are defined as:
Momentum flux, the rate of transfer of momentum across a unit area (N·s·m−2·s−1). (Newtonian fluid, viscous flow)
Heat flux, the rate of heat flow across a unit area (J·m−2·s−1). (Fourier's Law) (This definition of heat flux fits Maxwell's original definition.)
Chemical flux, the rate of movement of molecules across a unit area (mol·m−2·s−1). (Fick's law of diffusion)
Volumetric flux, the rate of volume flow across a unit area (m3·m−2·s−1). (Darcy's law)
Mass flux, the rate of mass flow across a unit area (kg·m−2·s−1). (Either an alternate form of Fick's law that includes the molecular mass, or an alternate form of Darcy's law that includes the density).
Radiative flux, the amount of energy moving in the form of photons at a certain distance from the source per steradian per second (J·m−2·s−1). Used in astronomy to study and classify stars.  Also acts as a generalization of heat flux, which is equal to the radiative flux when restricted to the infrared spectrum.
Magnetic flux, the density of a magnetic field.

Electromagnetism 

In the field of electromagnetism, flux is usually the integral of a vector quantity over a finite surface. The result of this integration is a scalar quantity. The magnetic flux is thus the integral of the magnetic vector field over a surface, and the electric flux is defined similarly. Using this definition, the flux of the Poynting vector over a specified surface is the rate at which electromagnetic energy flows through that surface. Confusingly, the Poynting vector is sometimes called the power flux,  which is an example of the first usage of flux, above. It has units of watts per square metre (W/m2).

Related pages 
Fluid dynamics

References

Further reading

Physical quantity
Mathematics
Neuroscience

Neuroscience (or neurobiology) is the scientific study of the nervous system. It is the branch of biology which investigates every aspect of the brain and nervous system.

The nervous system is made of billions of neurons connected together and to other systems in the body.  The central nervous system includes the brain, spinal cord and retina. It is connected to the rest of the body via the peripheral nervous system.

Research themes 
Neuroscience research focusses on a set of themes and questions.  
 Behavior/cognition/language
 Biological rhythms
 Brain imaging or neuroimaging
 Cell biology
 Cell imaging & Electrophysiology
 Learning/memory
 Signal transduction
 Neurobiology of the neuron
 Sensation and perception
 Sleep
 Autonomic nervous system and homeostasis
 Arousal, attention and emotion
 Genetics of the nervous system
Developmental biology of the nervous system 
Diseases of the nervous system

Related pages 

 Biology
 Cognitive neuropsychology
 Ethology
 Neurology
 Neuropsychology
 Psychiatry

References

Textbooks 

Squire, L. et al. (2003). Fundamental Neuroscience, 2nd edition. Academic Press; 
Byrne and Roberts (2004). From Molecules to Networks. Academic Press; 
Sanes, Reh, Harris (2005). Development of the Nervous System, 2nd edition. Academic Press; 
Siegel et al. (2005). Basic Neurochemistry, 7th edition. Academic Press; 
Rieke, F. et al. (1999). Spikes: Exploring the Neural Code. The MIT Press; Reprint edition

Online textbooks 
Neuroscience 2nd ed. Dale Purves et al. Published by Sinauer Associates, Inc., 2001.
Basic Neurochemistry: Molecular, Cellular, and Medical Aspects 6th ed. by George J. Siegel et al. Published by Lippincott, Williams & Wilkins, 1999.

Popular works
 
 Damasio, A. R. (1994). Descartes' Error: Emotion, Reason, and the Human Brain. New York, Avon Books.  (Hardcover)  (Paperback)
 Gardner, H. (1976). The Shattered Mind: The Person After Brain Damage. New York, Vintage Books, 1976 
 Luria, A. R. (1997). The Man with a Shattered World: The History of a Brain Wound. Cambridge, Massachusetts, Harvard University Press.  (Hardcover)  (Paperback)
 Sacks, O. The Man Who Mistook His Wife for a Hat. Summit Books  (Hardcover)  (Paperback)
 Sacks, O. (1990). Awakenings. New York, Vintage Books. (See also Oliver Sacks)  (Hardcover)  (Paperback)
 Sternberg, E. (2007) Are You a Machine? The Brain, the Mind and What it Means to be Human. Amherst, NY: Prometheus Books.

Other websites 
 High-Resolution Cytoarchitectural Primate Brain Atlases 
 Society for Neuroscience
 Neural Plasticity-Open Access Journal (Hindawi Publishing)
 Neuroscience. 2nd ed. by Purves et al. (online textbook)
 Neuroscience for Kids
Conversation analysis

Conversation analysis (commonly abbreviated as CA) is the study of talk in social interaction. CA tries to describe the structure and patterns of interaction, whether this is institutional (in the school, doctor's surgery, courts or elsewhere) or casual conversation. 

The term “conversation” to label this disciplinary movement is misleading if read in a colloquial sense, as many have.

Other websites 

 An Introduction to Conversation Analysis  (by  Discourse and Rhetoric Group,  Loughborough University)
 Online bibliography of pre-1990 CA literature
 Online bibliography of post-1989 CA literature 
 Online clearinghouse for the CA community

Science
Human communication
Mark-Anthony Turnage

Mark-Anthony Turnage (born Grays, Essex, 10 June 1960) is an English composer.  He is one of the most original composers in his country today.  

Turnage studied at the Royal College of Music and won all the major prizes.  He became famous when he wrote an opera called Greek.  It is typical of his musical style: quite lyrical but also very dramatic and aggressive.  His music is often inspired by jazz.  Other works include Kai, Rockaby, Blood on the Floor, Dispelling the Fears, Drowned Out and Three Screaming Popes.  He has written music for the English National Opera, City of Birmingham Symphony Orchestra and the Chicago Symphony Orchestra.

Other websites 

1960 births
Living people

20th-century English composers
21st-century English composers
Guava

Guavas are plants in the genus Psidium of the family Myrtaceae. There are about 100 species of tropical shrubs and small trees in the genus.

They are native to Mexico, the Caribbean, Central America and the northern part of South America. Now they are found in all the tropical, and in some subtropical, regions because they are edible fruits.

Guava are also a kind of berry fruit on those plants. There are many kinds of guavas. The most common guava is the apple guava (Psidium guajava): it is so common that the word 'guava' usually refers to this species. Red guavas are called maroonguava. In 100 g of guava are 200 mg of vitamin C, which means that guavas have five times more vitamin C than oranges.

Myrtaceae
Tropical fruit
Resting potential

The resting potential of a cell is the membrane potential that would be maintained if there were no action potentials, synaptic potentials, or other active changes in the membrane potential. In most cells the resting potential has a negative value, which by convention means that there is excess negative charge inside compared to outside. The resting potential is mostly determined by the concentrations of the ions in the fluids on both sides of the cell membrane and the ion transport proteins that are in the cell membrane. How the concentrations of ions and the membrane transport proteins influence the value of the resting potential is outlined below.

Other websites 
Neuroscience - online textbook by Purves, et al.
 Basic Neurochemistry Molecular, Cellular, and Medical Aspects by Siegel, et al.
 Bertil Hille Ion channels of excitable membranes, 3rd ed., Sinauer Associates, Sunderland, MA (2001). 
 Generation of resting membrane potential Wright, S.H., Advances in Physiology Education, 28(1-4): 139-142, 2004,

Biochemistry
Robert A. Heinlein

Robert Anson Heinlein (July 7, 1907 – May 8, 1988) was an American writer. He mostly wrote science fiction books. He won the Hugo Award four times. Probably his best-known novels are Starship Troopers (1959, Hugo Award, was made into a film), and Stranger in a Strange Land (1961, Hugo Award). Two other Hugo awards were for Double Star (1956) and The Moon is a Harsh Mistress (1966). Together with Isaac Asimov and Arthur C. Clarke he is seen as one of the Big Three of Science Fiction.

References 

1907 births
1988 deaths
Hugo Award winning writers
Writers from Missouri
Libertarians
List of video game genres

There are many computer and video game genres. Here is a list of some of the common ones.
 Role-playing game (RPG)
 Massively-Multiplayer Online Role-Playing Game (MMORPG)
 Arcade
 Adventure
 First-person shooter
 Platformer
 Simulation
 Real-time strategy
 Survival
 Survival horror
 Battle Royale
 Sandbox
Fable

A fable is a type of story which shows something in life or has a meaning to a word. A fable teaches a lesson or suggests a moral from it. A fable starts in the middle of the story, that means, jumps into the main event without detailed introduction of characters. The characters of a fable may be animals, plants and legendary creatures. When animals are used in fables, they think and talk like people, even though they act like animals. For example, in a fable a clay pot might say that it is frightened of being broken.

The stories told by fables are usually very simple. To understand a fable, the reader or listener does not need to know all about the characters, only one important thing. For this reason animals are often used in fables in a way that is easily understood because it is always the same. They keep the same characteristics from story to story.
 A lion is noble
 A rooster is boastful
 A peacock is proud
 A fox is cunning
 A wolf is fierce
 A horse is brave
 A donkey is hard-working

The most famous fables are those attributed to Aesop (6th century B.C.). Many fables are so well-known that their morals have become English sayings.

For example:
 If a person says "sour grapes!" then they are referring to "The Fox and the Grapes". This fable is about a fox who saw a beautiful bunch of grapes hanging on a vine. He wanted to eat them but they were high up. He tried and tried to jump high enough to pull them down. When he was too tired to jump anymore, he went away saying "I'll bet those grapes were sour!"

So, if a person sees a beautiful thing that they want, but cannot have, sometimes they say "I don't want it, anyway! I'll bet it is really no good!" This way of thinking is called "sour grapes".

"Crying wolf" is another well-known English saying. This comes from "The Boy Who Cried Wolf". This fable is about a boy who was sent to mind the sheep. The boy got lonely while minding the sheep, so he shouted "Wolf! Wolf!"  The people came running. The next day, he did it again and they were very angry. On the third day the boy saw a wolf. He cried "Wolf! Wolf!" but no one came and the wolf ate him.

So if a person always makes a great fuss to get attention, or if a person says something bad has happened when it has not, then it is called "crying wolf" and people will stop bothering to pay attention, even when things go really wrong.

Related pages
 Children's literature
 Jean de La Fontaine
 Myth
 Fairy tale

Other websites

 Animal Symbolism List of frequently described animals and their characteristics
 The Dragon-Tyrant
 Fables - Collection and guide to fables for children 
 Imaginexus  A collection of interconnected stories that anyone can edit
 Beast Fable Society  An academic society focused on fables and related genres

Fairy tales
Drainage

Drainage is the natural or artificial removal of surface and sub-surface water from a given area.  Many agricultural soils need drainage to improve production or to manage water supplies.

Early history
The earliest archaeological record of an advanced system of drainage comes from the  Indus Valley Civilization from around 3100 BC in what is now Pakistan and North India. The ancient Indus systems of sewerage and drainage that were developed and used in cities throughout the civilization were far more advanced than any found in contemporary urban sites in the Middle East and even more efficient than those in some areas of modern Pakistan and India today. All houses in the major cities of Harappa and Mohenjo-daro had access to water and drainage facilities. Waste water was directed to covered drains, which lined the major streets.

Reasons for artificial drainage 

Wetland soils may need drainage to be used for agriculture. In the northern USA and Europe, glaciation created numerous small lakes which gradually filled with humus to make marshes. Some of these were drained using open ditches and trenches.

The largest project of this type in the world has been in process for centuries in the Netherlands. The area between Amsterdam, Haarlem and Leiden was, in prehistoric times swampland and small lakes. Turf cutting (Peat mining), subsidence and shoreline erosion gradually caused the formation of one large lake, the Haarlemmermeer, or lake of Haarlem. The invention of wind powered pumping engines in the 15th century permitted drainage of some of the marginal land, but the final drainage of the lake had to await the design of large, steam powered pumps and agreements between regional authorities. The elimination of the lake occurred between 1849 and 1852, creating thousands of km2 of new land.

Other websites 

WebCom Systems, software created for designing soakaways and filter trenches.
NDS , drainage calculator.
Ancient drains, a series of images of the earliest drainage systems in the ancient Indus city of Mohenjo daro
Stormwater DesignInformation on stormwater design 
Draining for Profit, and Draining for Health by George E. Waring, 1867, from Project Gutenberg
 Drainage photos 

Agriculture
Engineering
Polder

Empoldering is a method of reclaiming land from the sea, and a way to control floods.  Empoldering involves the use of a polder, a piece of land in a low-lying area that has been reclaimed from a body of water by building dikes and drainage canals.

Although empoldering is usually carried out in low-lying coastal areas, it can also be dome in inland areas such as lakes and rivers.  It is common in countries like the Netherlands, where much of the country is below sea level and subject to flooding.  About one-fifth of the land in the Netherlands has been reclaimed from the sea.  Their largest and most successful project is the Zuider Zee project.

Polders have two distinct features.  Firstly, they are enclosed by dikes to keep the water out.  The dikes also serve to protect the polder from erosion.  Secondly, polders are continually maintained by systems of drainage canals and pumps which prevent them from becoming waterlogged and hence, suitable for cultivation.

Process 

Stage 1: Dike constructed around the area to be reclaimed to keep water from coming in.

Stage 2: The area is drained using pumps and drainage canals.

Stage 3: "Reeds" (a type of salt tolerant plant) are sown by aircraft to help the soil form.

Stage 4: After 3 years, reeds are burnt and the ash is used as fertilizers for the soil.

Stage 5: After a period of up to 15 years, the polder is ready for growing crops, building houses and constructing roads.

Limits of land reclamation 

1. Cost of reclaiming from deeper waters 

2. Availability of sand 

3. Dispute over territorial boundaries

Physical geography
Doctor of Philosophy

The Doctor of Philosophy, (PhD, Ph.D., DPhil or D.Phil.) is a degree a person gets from a university by finishing a doctorate program. In many areas of study, the PhD/DPhil is the highest degree that a person can earn (this is called the "terminal degree"). There are PhD/DPhil degrees for many different fields, such as PhDs/DPhils in literature, philosophy, history, science, mathematics, and engineering. Some PhD/DPhil degrees have existed for hundreds of years, such as the PhD/DPhil in Canon Law. Other PhD/DPhil degrees were developed in the 1970s and 1980s, such as the PhD/DPhil in Computer Science.

Requirements for degree
To be admitted to a PhD/DPhil program, a person usually has to have completed their Bachelor's degree or master's degree that is related to the PhD/DPhil degree. For example, a person applying to be admitted to a PhD/DPhil degree in Theater would normally have to have a master's degree such as a Master of Arts (MA) degree in Theater, English Literature, or a related area.

Elements of a PhD/DPhil degree
The PhD/DPhil degree usually takes between three and six years of full-time study to complete. They may or may not require a master's degree beforehand. Many PhD/DPhil degrees begin with a period of graduate courses. After the PhD/DPhil student has taken these courses, they take examinations to test what the student knows about their area of study. After the student passes the exams, they begin to do original research. The product is a long research report called a dissertation (or a "thesis"). Some PhD/DPhil degrees also require students to pass exams in languages (such as French, German, or other languages). Many PhD/DPhil students teach undergraduate students or assist professors with research during their PhD/DPhil studies.

As a requirement for university teaching 
Requirements for university teaching vary in different subjects and in different countries. A PhD/DPhil is necessary or usual to become a university professor in many fields, especially in science. However, many famous professors have not had higher degrees, though that is less common today. In some fields, there is no PhD/DPhil, and so another degree is required to become a university professor. For example, the highest degree in Fine Arts fields such as printmaking or graphic design is the Master of Fine Arts (MFA) degree. A person with an MFA degree can become a university professor in some Fine Arts fields.

Other websites 
 The Mathematics PhD in the United Kingdom: Notes on its History Contains information/links of more general relevance than mathematics.

Academia
Academic degrees
Marsh

In geography, a marsh is a type of wetland. It has grasses, rushes, reeds, typhas, sedges, and other herbaceous plants (possibly with low-growing woody plants) in a context of shallow water.  A marsh is different from a swamp, which has a greater proportion of open water surface, which is generally deeper than a marsh. In the US, the term 'swamp' is used for wetland dominated by trees rather than grasses and low herbs.

The water of a marsh can be fresh, brackish or saline. Coastal marshes may be associated with estuaries and along waterways between coastal barrier islands and the inner coast.  Estuarine marshes often are based on soils consisting of sandy bottoms or bay muds.

Marshes are critically important wildlife habitat, often serving as breeding grounds for a wide variety of animal life.

Related pages
Fen
Swamp
Ecoregion

Other websites 
 Marshes of the Lowcountry (South Carolina) -- Beaufort County Library

Wetlands
Ulan-Ude

Ulan-Ude (Russian:Ула́н-Удэ́; Buryat: Улаан-Үдэ), formerly Verkhneudinsk (), the capital city of the Buryat Republic, Russia. The city is located about 100 km south-east of Lake Baikal. It sits at the foot of the Khamar-Daban and Khrebet Ulan-Burgasy mountain ranges, next to the confluence of the Selenga River and its tributary, the Uda. The city is divided into two parts by the Uda. Population 359,391 (2002 Census); 352,530 (1989 Census). It is the third largest city in East Siberia.  It is served by Ulan-Ude Airport (Mukhino) as well as the smaller Ulan-Ude Vostochny Airport.

Ulan-Ude was founded in 1666 by the Russian Cossacks. Due to its geographical position, the city grew rapidly and became a large trade centre which connected Russia with China and Mongolia. There are old merchants' mansions richly decorated with wood and stone carving in the historical center of Ulan-Ude, along the river banks. They represent beautiful examples of Russian classicism.  There is also a large and highly unusual head of Lenin in the central square.

Gallery

Sources

Other websites

Siberia
Pelagic zone

The pelagic zone is the open sea or ocean that is not near the coast. The name comes from the Greek πέλαγος (pélagos), which might be translated as "open sea".

To make this clear, seas around continents have continental crust beneath them. They are shallow. Seas away from continents can be very deep, and do not have continental shelves beneath them.

Sub-zones 
The pelagic (or open ocean) zone is divided into a number of sub-zones:

 Epipelagic (surface to 200m): the illuminated surface zone where there is enough light for photosynthesis. Because of this, plankton, and the food chain which feeds on it, are in this zone. The top predators are fish such as tuna and many sharks.
 Mesopelagic (from 200m to 1000m): the twilight zone.  Although some light penetrates this deep, it is insufficient for photosynthesis. The name comes from Greek μέσον, middle. 
 Bathyal zone (from 1000m to 4000m): by this depth the ocean is almost entirely dark (with only the occasional bioluminescent organism). There are no living plants, and most animals survive by consuming the snow of detritus falling from the zones above, or (like the marine hatchetfish) by preying upon others. Giant squid live at this depth, and here they are hunted by deep-diving sperm whales. From Greek βαθύς (bathys), deep.
 Abyssal zone (from 4000m to the ocean floor): no light penetrates to this depth, and some creatures are blind and colourless. Bioluminescence also occurs in this zone. 
 Hadal zone (the deep water in ocean trenches) – the name comes from Hades, the classical Greek underworld. This zone is less well known. Very few species live in the open areas, but many organisms live in hydrothermal vents.

The last three zones are similar in character, and some marine biologists count them as a single zone or consider the latter two to be the one zone. Some define the hadopelagic as waters below 6000 meters, whether in a trench or not.

Other features of the deep ocean 
Seamounts
Ocean ridges

Other websites 
 The Deep Sea pages at Oceanlink 

Biological oceanography
Ecology
Biomes
Vitamin A

Vitamin A is a vitamin, a group of organic chemicals including retinal and several carotenoids. The human body does not make these chemicals, and must take them from food. Egg yolks and liver are both rich in vitamin A. Many parts of the body need vitamin A. For example, vitamin A helps sight and is good for the immune system. It is also important for a growing embryo.

β-carotene, a provitamin found in foods like carrots can be converted to vitamin A. The efficiency of the conversion depends on genetics and fat consumption.

Too little vitamin A is dangerous to health. People who do not get enough of the vitamin may lose the ability to see in poor light and suffer from a weakened immune system. They may also have problems with memory, because vitamin A is important for the brain. People with malnutrition often have too little vitamin A. This is common in poor countries.

Hypervitaminosis A 
Too much vitamin A is also dangerous to one's health. It is a condition known as hypervitaminosis. Vitamin A is not soluble in water, and the human body can not get rid of the excess vitamin A easily by urination.  Too much vitamin A can make someone very sick.  People may get too much vitamin A from taking too many vitamin pills or from eating too much A-rich food like liver.

What applies to humans applies to all mammals at least. Some large predators, such as the big cats, seem not to eat their preys' livers. On the other hand, polar bears apparently do so, and they store vitamin A in their liver cells. However, they have long, sometimes very long, periods between kills. In contrast, African big cats kill about every three or four days, and they do seem to avoid eating the preys' livers.

References 

Fat-soluble vitamins