Concentrated solar power

Concentrated solar power ( also called concentrating solar power , concentrated solar thermal , and CSP ) systems generate solar power by using mirrors or lenses to concentrate a large area of sunlight , or solar thermal energy , onto a small area . Electricity is generated when the concentrated light is converted to heat , which drives a heat engine ( usually a steam turbine ) connected to an electrical power generator or powers a thermochemical reaction ( experimental ) . Heat storage in molten salts allows some solar thermal plants to continue to generate after sunset and adds value to such systems when compared to photovoltaic panels .   CSP is being commercialized and the CSP market saw about 740 megawatt ( MW ) of generating capacity added between 2007 and the end of 2010 . More than half of this ( about 478 MW ) was installed during 2010 , bringing the global total to 1095 MW . Spain added 400 MW in 2010 , taking the global lead with a total of 632 MW , while the US ended the year with 509 MW after adding 78 MW , including two fossil -- CSP hybrid plants . The Middle East is also ramping up their plans to install CSP based projects . Shams-I has been installed in Abu Dhabi , by Masdar . The largest CSP projects in the world is Ivanpah Solar Power Facility in the United States ( which uses solar power tower technology ) and Mojave Solar Project ( which uses parabolic troughs ) .   As of January 2014 , Spain had a total capacity of 2,300 MW making this country the world leader in CSP . United States follows with 1,740 MW . Interest is also notable in North Africa and the Middle East , as well as India and China . In Italy , a handful of companies are trying to get authorization for 14 plants , totalling 392 MW , despite a strong local and political opposition . The global market has been dominated by parabolic-trough plants , which account for 90 % of CSP plants .   In most cases , CSP technologies currently can not compete on price with photovoltaics ( solar panels ) , which have experienced huge growth in recent years due to falling prices of the panels and much smaller operating costs . However , the Chile Copiapó reached cents 6.3 / kWh . In 2015 , CSP represented less than 2 % of worldwide installed capacity of solar electricity plants .   CSP is not to be confused with concentrator photovoltaics ( CPV ) . In CPV , the concentrated sunlight is converted directly to electricity via the photovoltaic effect .


Confirmation bias

Confirmation bias , also called confirmatory bias or myside bias , David Perkins , a geneticist , coined the term `` myside bias '' referring to a preference for `` my '' side of an issue . is the tendency to search for , interpret , favor , and recall information in a way that confirms one 's preexisting beliefs or hypotheses . It is a type of cognitive bias and a systematic error of inductive reasoning . People display this bias when they gather or remember information selectively , or when they interpret it in a biased way . The effect is stronger for emotionally charged issues and for deeply entrenched beliefs . People also tend to interpret ambiguous evidence as supporting their existing position . Biased search , interpretation and memory have been invoked to explain attitude polarization ( when a disagreement becomes more extreme even though the different parties are exposed to the same evidence ) , belief perseverance ( when beliefs persist after the evidence for them is shown to be false ) , the irrational primacy effect ( a greater reliance on information encountered early in a series ) and illusory correlation ( when people falsely perceive an association between two events or situations ) .   A series of experiments in the 1960s suggested that people are biased toward confirming their existing beliefs . Later work re-interpreted these results as a tendency to test ideas in a one-sided way , focusing on one possibility and ignoring alternatives . In certain situations , this tendency can bias people 's conclusions . Explanations for the observed biases include wishful thinking and the limited human capacity to process information . Another explanation is that people show confirmation bias because they are weighing up the costs of being wrong , rather than investigating in a neutral , scientific way .   Confirmation biases contribute to overconfidence in personal beliefs and can maintain or strengthen beliefs in the face of contrary evidence . Poor decisions due to these biases have been found in political and organizational contexts.Tuchman ( 1984 ) described a form of confirmation bias at work in the process of justifying policies to which a government has committed itself : `` Once a policy has been adopted and implemented , all subsequent activity becomes an effort to justify it '' ( p. 245 ) .   In the context of a discussion of the policy that drew the United States into war in Vietnam and kept the U.S. military engaged for 16 years despite countless evidences that it was a lost cause from the beginning , Tuchman argued :   Wooden-headedness , the source of self-deception is a factor that plays a remarkably large role in government . It consists in assessing a situation in terms of preconceived fixed notions while ignoring or rejecting any contrary signs . It is acting according to wish while not allowing oneself to be deflected by the facts . It is epitomized in a historian 's statement about Philip II of Spain , the surpassing wooden head of all sovereigns : `` no experience of the failure of his policy could shake his belief in essential excellence . '' ( p. 7 )  Folly , she argued , is a form of self-deception characterized by `` insistence on a rooted notion regardless of contrary evidence '' ( p. 209 )


Consciousness

Consciousness is the state or quality of awareness , or , of being aware of an external object or something within oneself . It has been defined variously in terms of sentience , awareness , subjectivity , the ability to experience or to feel , wakefulness , having a sense of selfhood or soul , the fact that there is something `` that it is like '' to `` have '' or `` be '' it , and the executive control system of the mind , or the state or quality of awareness , or , of being aware of an external object or something within oneself . In contemporary philosophy its definition is often hinted at via the logical possibility of its absence , the philosophical zombie , which is defined as a being whose behavior and function are identical to one 's own yet there is `` no-one in there '' experiencing it .   Despite the difficulty in definition , many philosophers believe that there is a broadly shared underlying intuition about what consciousness is . As Max Velmans and Susan Schneider wrote in The Blackwell Companion to Consciousness : `` Anything that we are aware of at a given moment forms part of our consciousness , making conscious experience at once the most familiar and most mysterious aspect of our lives . ''   Western philosophers , since the time of Descartes and Locke , have struggled to comprehend the nature of consciousness and identify its essential properties . Issues of concern in the philosophy of consciousness include whether the concept is fundamentally coherent ; whether consciousness can ever be explained mechanistically ; whether non-human consciousness exists and if so how can it be recognized ; how consciousness relates to language ; whether consciousness can be understood in a way that does not require a dualistic distinction between mental and physical states or properties ; and whether it may ever be possible for computing machines like computers or robots to be conscious , a topic studied in the field of artificial intelligence .   Thanks to developments in technology over the past few decades , consciousness has become a significant topic of interdisciplinary research in cognitive science , with significant contributions from fields such as psychology , neuropsychology and neuroscience . The primary focus is on understanding what it means biologically and psychologically for information to be present in consciousness -- that is , on determining the neural and psychological correlates of consciousness . The majority of experimental studies assess consciousness in humans by asking subjects for a verbal report of their experiences ( e.g. , `` tell me if you notice anything when I do this '' ) . Issues of interest include phenomena such as subliminal perception , blindsight , denial of impairment , and altered states of consciousness produced by alcohol and other drugs , or spiritual or meditative techniques .   In medicine , consciousness is assessed by observing a patient 's arousal and responsiveness , and can be seen as a continuum of states ranging from full alertness and comprehension , through disorientation , delirium , loss of meaningful communication , and finally loss of movement in response to painful stimuli . Issues of practical concern include how the presence of consciousness can be assessed in severely ill , comatose , or anesthetized people , and how to treat conditions in which consciousness is impaired or disrupted .


Conservation biology

Conservation biology is the management of nature and of Earth 's biodiversity with the aim of protecting species , their habitats , and ecosystems from excessive rates of extinction and the erosion of biotic interactions . It is an interdisciplinary subject drawing on natural and social sciences , and the practice of natural resource management .   The conservation ethic is based on the findings of conservation biology .


Conservatism in the United States

American Conservatism is a broad system of political beliefs in the United States that is characterized by respect for American traditions , support for Judeo-Christian values , economic liberalism , anti-communism , advocacy of American exceptionalism , and a defense of Western culture from threats posed by `` creeping socialism '' , moral relativism , multiculturalism and liberal internationalism . Liberty is a core value , with a particular emphasis on strengthening the free market , limiting the size and scope of government , and opposition to high taxes and government or labor union encroachment on the entrepreneur . American conservatives consider individual liberty , within the bounds of conformity to American values , as the fundamental trait of democracy , which contrasts with modern American liberals , who generally place a greater value on equality and social justice .   American conservatism originated from classical liberalism of 18th and 19th centuries , which advocates civil liberties and political freedom with representative democracy under the rule of law and emphasizes economic freedom .   Historians argue that the conservative tradition has played a major role in American politics and culture since the 1790s . However they have stressed that an organized conservative movement has played a key role in politics only since the 1950s . The recent movement is based in the Republican Party , though some Democrats were also important figures early in the movement 's history .   The history of American conservatism has been marked by tensions and competing ideologies . Fiscal conservatives and libertarians favor small government involvement in the economy , a flat tax , limited regulation , and free enterprise . Social conservatives see traditional social values as threatened by secularism ; they tend to support voluntary school prayer and oppose abortion and same sex marriage . Some also want the teaching of intelligent design or creationism allowed , as the topics are currently judicially prohibited in public schools . The 21st century has seen an increasingly fervent conservative support for Second Amendment rights of private citizens to own firearms . Neoconservatives want to expand American ideals throughout the world . Paleoconservatives advocate restrictions on immigration , non-interventionist foreign policy , and stand in opposition to multiculturalism . Nationwide most factions , except some libertarians , support a unilateral foreign policy , and a strong military . The conservative movement of the 1950s attempted to bring together these divergent strands , stressing the need for unity to prevent the spread of `` godless communism . ''   William F. Buckley Jr. , in the first issue of his magazine National Review in 1955 , explained the standards of his magazine and helped make explicit the beliefs of American conservatives :


Conservative Judaism

Conservative Judaism ( known as Masorti Judaism outside North America ) is a major Jewish denomination , which views Jewish Law , or Halakha , as both binding and subject to historical development . The Conservative rabbinate therefore employs modern historical-critical research , rather than only traditional methods and sources , and lends great weight to its constituency when determining its stance on matters of Law . The movement considers its approach as the authentic and most appropriate continuation of halakhic discourse , maintaining both fealty to received forms and flexibility in their interpretation . It also eschews strict theological definitions , lacking a consensus in matters of faith and allowing great pluralism .   While regarding itself as the heir of Rabbi Zecharias Frankel 's 19th-century Positive-Historical School in Europe , Conservative Judaism fully institutionalized as a denomination only in the United States during the mid-20th century . Its largest center today is in North America , where its main congregational arm is the United Synagogue of Conservative Judaism and the New York-based Jewish Theological Seminary of America operates as rabbinic seminary . Worldwide , affiliated communities are united within the umbrella organization Masorti Olami . Conservative Judaism is estimated to represent close to 1,100,000 people , both more than 600,000 registered congregants and many non-member identifiers .   The term `` conservative '' was meant to signify that Jews should attempt to conserve Jewish tradition , rather than reform or abandon it , and does not imply the movement 's adherents are politically conservative .


Conservative Party (UK)

The Conservative Party , officially the Conservative and Unionist Party , is a centre-right political party in the United Kingdom . It is currently the governing party , having won a majority of seats in the House of Commons at the 2015 general election . The party 's leader , Theresa May , is currently serving as Prime Minister . It is the largest party in local government with 9,237 councillors . The Conservative Party is one of the two major contemporary political parties in the United Kingdom , the other being its modern rival , the Labour Party . The Conservative Party 's platform involves support for free market capitalism , free enterprise , fiscal conservatism , a strong national defence , deregulation , and restrictions on trade unions .   The Conservative Party was founded in 1834 from the Tory Party -- giving rise to the Conservatives ' colloquial name of Tories -- and was one of two dominant political parties in the nineteenth century , along with the Liberal Party . During the 1890s , it formed a coalition government with the Liberal Unionist Party , a break-away faction of the Liberal Party . In 1912 , the two parties merged to form the current Conservative and Unionist Party . In the 1920s , the Liberal vote greatly diminished and the Labour Party became the Conservatives ' main rivals . Conservative Prime Ministers led governments for 57 years of the twentieth century , including Winston Churchill ( 1940 -- 45 , 1951 -- 55 ) and Margaret Thatcher ( 1979 -- 90 ) . Thatcher 's tenure led to wide-ranging economic liberalisation . The Conservative Party 's domination of British politics throughout the twentieth century has led to them being referred to as one of the most successful political parties in the Western world .   The Conservatives are the joint-second largest British party in the European Parliament , with twenty MEPs , and sit with the European Conservatives and Reformists ( ECR ) parliamentary group . The party is a member of the Alliance of Conservatives and Reformists in Europe ( ACRE ) Europarty and the International Democrat Union ( IDU ) .   The party is the second-largest in the Scottish Parliament and the second-largest in the Welsh Assembly . The Conservatives were formerly allied to the Ulster Unionist Party ( UUP ) in Northern Ireland but there is now a separate Northern Ireland Conservative party similar to the Welsh and Scottish Conservative parties . The party is also organised in the British Overseas Territory of Gibraltar .


Conspiracy theory

A conspiracy theory is an explanation of an event or situation that invokes a conspiracy without warrant , generally one involving an illegal or harmful act carried out by government or other powerful actors . Conspiracy theories often produce hypotheses that contradict the prevailing understanding of history or simple facts . The term is a derogatory one .   According to the political scientist Michael Barkun , conspiracy theories rely on the view that the universe is governed by design , and embody three principles : nothing happens by accident , nothing is as it seems , and everything is connected . Another common feature is that conspiracy theories evolve to incorporate whatever evidence exists against them , so that they become , as Barkun writes , a closed system that is unfalsifiable , and therefore `` a matter of faith rather than proof '' .


Constanța

Constanța ( -LSB- konˈstant͡sa -RSB- ) , historically known as Tomis ( Κωνστάντζα or Κωνστάντια , Konstantia , Кюстенджа or Констанца , Köstence ) , is the oldest continuously inhabited city in Romania . It was founded around 600 BC . The city is located in the Dobruja region of Romania , on the Black Sea coast . It is the capital of Constanța County and the largest city in the region .   As of the 2011 census , Constanța has a population of 283,872 , making it the fifth most populous city in Romania . The Constanța metropolitan area includes 14 localities within 30 km of the city , and , with 425,916 inhabitants , it is the second largest metropolitan area in Romania .   The Port of Constanța has an area of 39.26 km2 and a length of about 30 km . It is the largest port on the Black Sea , and one of the largest ports in Europe .


Convection

Convection is the movement of groups of molecules within fluids such as gases and liquids , including molten rock ( rheid ) . Convection takes place through advection , diffusion or both .   Convection can not take place in most solids because neither bulk current flows nor significant diffusion of matter can take place . Diffusion of heat can take place in rigid solids , but that is called heat conduction . However , can take place in soft solids or mixtures where solid particles can move past each other .   Thermal convection can be demonstrated by placing a heat source ( e.g. a Bunsen burner ) at the side of a glass full of a liquid , and observing the changes in temperature in the glass caused by the warmer ghost fluid circulating into cooler areas .   Convective heat transfer is one of the major types of heat transfer , and convection is also a major mode of mass transfer in fluids . Convective heat and mass transfer take place both by diffusion -- the random Brownian motion of individual particles in the fluid -- and by advection , in which matter or heat is transported by the larger-scale motion of currents in the fluid . In the context of heat and mass transfer , the term `` convection '' is used to refer to the sum of advective and diffusive transfer . In common use the term `` convection '' may refer loosely to heat transfer by convection , as opposed to mass transfer by convection , or the convection process in general . Sometimes `` convection '' is even used to refer specifically to `` free heat convection '' ( natural heat convection ) as opposed to forced heat convection . However , in mechanics the correct use of the word is the general sense , and different types of convection should be qualified for clarity .   Convection can be qualified in terms of being natural , forced , gravitational , granular , or thermomagnetic . It may also be said to be due to combustion , capillary action , or Marangoni and Weissenberg effects . Heat transfer by natural convection plays a role in the structure of Earth 's atmosphere , its oceans , and its mantle . Discrete convective cells in the atmosphere can be seen as clouds , with stronger convection resulting in thunderstorms . Natural convection also plays a role in stellar physics .


Cooling tower

A cooling tower is a heat rejection device that rejects waste heat to the atmosphere through the cooling of a water stream to a lower temperature . Cooling towers may either use the evaporation of water to remove process heat and cool the working fluid to near the wet-bulb air temperature or , in the case of closed circuit dry cooling towers , rely solely on air to cool the working fluid to near the dry-bulb air temperature .   Common applications include cooling the circulating water used in oil refineries , petrochemical and other chemical plants , thermal power stations and HVAC systems for cooling buildings . The classification is based on the type of air induction into the tower : the main types of cooling towers are natural draft and induced draft cooling towers .   Cooling towers vary in size from small roof-top units to very large hyperboloid structures ( as in the adjacent image ) that can be up to 200 m tall and 100 m in diameter , or rectangular structures that can be over 40 m tall and 80 m long . The hyperboloid cooling towers are often associated with nuclear power plants , although they are also used in some coal-fired plants and to some extent in some large chemical and other industrial plants . Although these large towers are very prominent , the vast majority of cooling towers are much smaller , including many units installed on or near buildings to discharge heat from air conditioning .


Copenhagen Airport

Copenhagen Airport , Kastrup ( Københavns Lufthavn , Kastrup ) is the main international airport serving Copenhagen , Denmark , the entire Zealand , the Øresund Region , and a large part of southern Sweden ( not only Scania ) . It is the largest airport in the Nordic countries with 29 million passengers in 2016 and one of the oldest international airports in Europe . It is the third-busiest airport in Northern Europe , and by far the busiest for international travel in Scandinavia .   The airport is located on the island of Amager , just 8 km south of Copenhagen city centre , and 24 km west of Malmö city centre via the Øresund Bridge . The airport covers an area of 11.8 square kilometres . Most of the airport is situated in the municipality of Tårnby , with a small portion in the city of Dragør .   The airport is the main hub out of three used by Scandinavian Airlines and is also an operating base for Thomas Cook Airlines Scandinavia and Norwegian Air Shuttle . Copenhagen Airport handles around 60 scheduled airlines , and has a maximum operation capability of 83 operations/hour , and a total of 108 jet bridge and remote parking stands . Unlike other Scandinavian airports , most of the airport 's passengers are international . In 2015 , 6.1 % of passengers travelled to and from other Danish airports , 83.5 % to/from other European airports , and 10.4 % were intercontinental passengers . The airport is owned by Københavns Lufthavne , which also operates Roskilde Airport . The airport employs 1700 staff ( excluding shops , restaurants etc. ) .   Copenhagen Airport was originally called Kastrup Airport , since it is located in the small town of Kastrup , now a part of the Tårnby municipality . The formal name of the airport is still Copenhagen Airport , Kastrup , to distinguish it from Roskilde Airport , whose formal name is Copenhagen Airport , Roskilde .


Coral

Corals are marine invertebrates in the class Anthozoa of phylum Cnidaria . They typically live in compact colonies of many identical individual polyps . The group includes the important reef builders that inhabit tropical oceans and secrete calcium carbonate to form a hard skeleton .   A coral `` group '' is a colony of myriad genetically identical polyps . Each polyp is a sac-like animal typically only a few millimeters in diameter and a few centimeters in length . A set of tentacles surround a central mouth opening . An exoskeleton is excreted near the base . Over many generations , the colony thus creates a large skeleton that is characteristic of the species . Individual heads grow by asexual reproduction of polyps . Corals also breed sexually by spawning : polyps of the same species release gametes simultaneously over a period of one to several nights around a full moon .   Although some corals can catch small fish and plankton using stinging cells on their tentacles , most corals obtain the majority of their energy and nutrients from photosynthetic unicellular dinoflagellates in the genus Symbiodinium that live within their tissues . These are commonly known as zooxanthellae and the corals that contain them are zooxanthellate corals . Such corals require sunlight and grow in clear , shallow water , typically at depths shallower than 60 m. Corals are major contributors to the physical structure of the coral reefs that develop in tropical and subtropical waters , such as the enormous Great Barrier Reef off the coast of Queensland , Australia .   Other corals do not rely on zooxanthellae and can live in much deeper water , with the cold-water genus Lophelia surviving as deep as 3000 m . Some have been found on the Darwin Mounds , north-west of Cape Wrath , Scotland . Corals have also been found as far north as off the coast of Washington State and the Aleutian Islands .


Coral bleaching

Coral bleaching occurs when coral polyps expel algae that lives inside their tissues . Normally , coral polyps live in an endosymbiotic relationship with the algae and that relationship is crucial for the coral and hence for the health of the whole reef . Bleached corals continue to live . But as the algae provide the coral with 90 % of its energy , after expelling the algae the coral begins to starve . Above-average sea water temperatures caused by global warming have been identified as a leading cause for coral bleaching worldwide . Between 2014 and 2016 , the longest global bleaching events ever were recorded . According to the United Nations Environment Programme , these bleaching events killed coral on an unprecedented scale . In 2016 , bleaching hit 90 percent of coral on the Great Barrier Reef and killed 29 percent of the reef 's coral . In 2017 , the bleaching further expanded to areas of the park that were previously spared , such as the central one .   __ TOC __


Coral in non-tropical regions

The poleward migration of coral species refers to the phenomenon brought on by rising sea temperatures, wherein corals are colonising cooler climates in an attempt to circumvent coral bleaching, rising sea levels and ocean acidification. In the age of Anthropocene, the changing global climate has disrupted fundamental natural processes and brought about observable changes in the submarine sphere. Whilst coral reefs are bleaching in tropical areas like the Great Barrier Reef, even more striking, and perhaps more alarming; is the growth of tropical coral species in temperate regions, which has taken place over the past decade. Coral reefs are frequently compared to the "canaries in the coal mine," who were used by miners as an indicator of air quality. In much the same way, "coral reefs are sensitive to environmental changes that could damage other habitats in the future," meaning they will be the first to visually exhibit the true implications of global warming on the natural world.


Coral reef

Coral reefs are diverse underwater ecosystems held together by calcium carbonate structures secreted by corals . Coral reefs are built by colonies of tiny animals found in marine waters that contain few nutrients . Most coral reefs are built from stony corals , which in turn consist of polyps that cluster in groups . The polyps belong to a group of animals known as Cnidaria , which also includes sea anemones and jellyfish . Unlike sea anemones , corals secrete hard carbonate exoskeletons which support and protect the coral polyps . Most reefs grow best in warm , shallow , clear , sunny and agitated waters .   Often called `` rainforests of the sea '' , shallow coral reefs form some of the most diverse ecosystems on Earth . They occupy less than 0.1 % of the world 's ocean surface , about half the area of France , yet they provide a home for at least 25 % of all marine species , including fish , mollusks , worms , crustaceans , echinoderms , sponges , tunicates and other cnidarians . Paradoxically , coral reefs flourish even though they are surrounded by ocean waters that provide few nutrients . They are most commonly found at shallow depths in tropical waters , but deep water and cold water corals also exist on smaller scales in other areas .   Coral reefs deliver ecosystem services to tourism , fisheries and shoreline protection . The annual global economic value of coral reefs is estimated between US$ 29.8-375 billion . However , coral reefs are fragile ecosystems , partly because they are very sensitive to water temperature . They are under threat from climate change , oceanic acidification , blast fishing , cyanide fishing for aquarium fish , sunscreen use , overuse of reef resources , and harmful land-use practices , including urban and agricultural runoff and water pollution , which can harm reefs by encouraging excess algal growth .


Coriolis force

In physics , the Coriolis force is an inertial force that acts on objects that are in motion relative to a rotating reference frame . In a reference frame with clockwise rotation , the force acts to the left of the motion of the object . In one with anticlockwise rotation , the force acts to the right . Deflection of an object due to the Coriolis force is called the Coriolis effect . Though recognized previously by others , the mathematical expression for the Coriolis force appeared in an 1835 paper by French scientist Gaspard-Gustave de Coriolis , in connection with the theory of water wheels . Early in the 20th century , the term Coriolis force began to be used in connection with meteorology .   Newton 's laws of motion describe the motion of an object in an inertial ( non-accelerating ) frame of reference . When Newton 's laws are transformed to a rotating frame of reference , the Coriolis force and centrifugal force appear . Both forces are proportional to the mass of the object . The Coriolis force is proportional to the rotation rate and the centrifugal force is proportional to its square . The Coriolis force acts in a direction perpendicular to the rotation axis and to the velocity of the body in the rotating frame and is proportional to the object 's speed in the rotating frame ( more precisely , to the component of its velocity that is perpendicular to the axis of rotation ) . The centrifugal force acts outwards in the radial direction and is proportional to the distance of the body from the axis of the rotating frame . These additional forces are termed inertial forces , fictitious forces or pseudo forces . They allow the application of Newton 's laws to a rotating system . They are correction factors that do not exist in a non-accelerating or inertial reference frame .   In popular ( non-technical ) usage of the term `` Coriolis effect '' , the rotating reference frame implied is almost always the Earth . Because the Earth spins , Earth-bound observers need to account for the Coriolis force to correctly analyze the motion of objects . The Earth completes only one rotation per day , so for motions of everyday objects the Coriolis force is usually quite small compared to other forces ; its effects generally become noticeable only for motions occurring over large distances and long periods of time , such as large-scale movement of air in the atmosphere or water in the ocean . Such motions are constrained by the surface of the Earth , so only the horizontal component of the Coriolis force is generally important . This force causes moving objects on the surface of the Earth to be deflected to the right ( with respect to the direction of travel ) in the Northern Hemisphere and to the left in the Southern Hemisphere . The horizontal deflection effect is greater near the poles , since the effective rotation rate about a local vertical axis is largest there , and decreases to zero at the equator . Rather than flowing directly from areas of high pressure to low pressure , as they would in a non-rotating system , winds and currents tend to flow to the right of this direction north of the equator and to the left of this direction south of it . This effect is responsible for the rotation of large cyclones ( see Coriolis effects in meteorology ) .   For an intuitive explanation of the origin of the Coriolis force , consider an object moving northward in the northern hemisphere . Viewed from outer space , the object does not appear to go due north , but has an eastward motion ( it rotates around toward the right along with the surface of the Earth ) . The further north you go , the smaller the `` horizontal diameter '' of the Earth , and so the slower the eastward motion of its surface . As the object moves north , to higher latitudes , it has a tendency to maintain the eastward speed it started with ( rather than slowing down to match the reduced eastward speed of local objects on the Earth 's surface ) , so it veers east ( i.e. to the right of its initial motion ) . Though not obvious from this example , which considers northward motion , the horizontal deflection occurs equally for objects moving east or west ( or any other direction ) .


Coronal cloud

A coronal cloud is the cloud of hot plasma gas surrounding a coronal mass ejection . It is usually made up of protons and electrons . When a coronal mass ejection occurs , it is the coronal cloud that usually reaches Earth and causes damage to electrical equipment and space satellites , not the ejection or flare itself . The damage is mostly the result of the high amount of electricity moving through the atmosphere .   A coronal cloud is released when a solar flare becomes a coronal mass ejection ; the coronal cloud often contains more radioactive particles than the mass ejection itself . A coronal mass ejection occurs when a solar flare becomes so hot that it snaps and breaks in two , becoming a `` rope '' of heat and magnetism that stretches between two sunspots . The resulting coronal mass ejection can be compared to a horseshoe magnet , the sunspots being the poles and the oscillating magnetic connector the handle . Coronal mass ejections typically do not last very long , because they cool down as the coronal cloud of gas is released and begins to hurtle away from the sun .


Correlation does not imply causation

In statistics , many statistical tests calculate correlations between variables and when two variables are found to be correlated , it is tempting to assume that this shows that one variable causes the other . That `` correlation proves causation , '' is considered a questionable cause logical fallacy when two events occurring together are taken to have established a cause-and-effect relationship . This fallacy is also known as cum hoc ergo propter hoc , Latin for `` with this , therefore because of this , '' and `` false cause . '' A similar fallacy , that an event that followed another was necessarily a consequence of the first event , is the post hoc ergo propter hoc ( Latin for `` after this , therefore because of this . '' ) fallacy .   For example , in a widely studied case , numerous epidemiological studies showed that women taking combined hormone replacement therapy ( HRT ) also had a lower-than-average incidence of coronary heart disease ( CHD ) , leading doctors to propose that HRT was protective against CHD . But randomized controlled trials showed that HRT caused a small but statistically significant increase in risk of CHD . Re-analysis of the data from the epidemiological studies showed that women undertaking HRT were more likely to be from higher socio-economic groups ( ABC1 ) , with better-than-average diet and exercise regimens . The use of HRT and decreased incidence of coronary heart disease were coincident effects of a common cause ( i.e. the benefits associated with a higher socioeconomic status ) , rather than a direct cause and effect , as had been supposed .   As with any logical fallacy , identifying that the reasoning behind an argument is flawed does not imply that the resulting conclusion is false . In the instance above , if the trials had found that hormone replacement therapy does in fact have a negative incidence on the likelihood of coronary heart disease the assumption of causality would have been correct , although the logic behind the assumption would still have been flawed . Indeed , a few go further , using correlation as a basis for testing a hypothesis to try to establish a true causal relationship ; examples are the Granger causality test and convergent cross mapping .


Cosmic ray

Cosmic rays are high-energy radiation , mainly originating outside the Solar System . Upon impact with the Earth 's atmosphere , cosmic rays can produce showers of secondary particles that sometimes reach the surface . Composed primarily of high-energy protons and atomic nuclei , they are of mysterious origin . Data from the Fermi Space Telescope ( 2013 ) have been interpreted as evidence that a significant fraction of primary cosmic rays originate from the supernovae explosions of stars . Active galactic nuclei probably also produce cosmic rays .


Creationism

Creationism is the religious belief that the universe and life originated `` from specific acts of divine creation , '' as opposed to the scientific conclusion that they came about through natural processes . The first use of the term `` creationist '' to describe a proponent of creationism is found in an 1856 letter of Charles Darwin describing those who objected on religious grounds to the emerging science of evolution .   Creationists base their beliefs on a fundamentalist reading of religious texts , including the creation myths found in Genesis and the Quran . For young Earth creationists , these beliefs are based on a literalist interpretation of the Genesis creation narrative and rejection of the scientific theory of evolution . Literalist creationists believe that evolution can not adequately account for the history , diversity , and complexity of life on Earth . Pseudoscientific branches of creationism include creation science , flood geology , and intelligent design , as well as subsets of pseudoarchaeology , pseudohistory , and pseudolinguistics .


Creation–evolution controversy

The creation -- evolution controversy ( also termed the creation vs. evolution debate or the origins debate ) involves an ongoing , recurring cultural , political , and theological dispute about the origins of the Earth , of humanity , and of other life . Within the Christian world creationism was once widely believed to be true , but since the mid-19th century evolution by natural selection has been established as an empirical scientific fact . Efforts to sustain the traditional view are widely regarded in the scientific community as pseudoscience . While the controversy has a long history , today it has retreated to be mainly over what constitutes good science education , with the politics of creationism primarily focusing on the teaching of creation and evolution in public education . Among majority-Christian countries , the debate is most prominent in the United States , and to a lesser extent in Europe and elsewhere , and is often portrayed as part of a culture war . Parallel controversies also exist in some other religious communities , such as the more fundamentalist branches of Judaism and Islam .   Christian fundamentalists dispute the evidence of common descent of humans and other animals as demonstrated in modern paleontology , genetics , histology and cladistics and those other sub-disciplines which are based upon the conclusions of modern evolutionary biology , geology , cosmology , and other related fields . They argue for the Abrahamic accounts of creation , framing them as reputable science ( `` creation science '' ) .   The Catholic Church now recognizes the existence of evolution ( see Catholic Church and evolution ) . Pope Francis has stated : `` God is not a divine being or a magician , but the Creator who brought everything to life ... Evolution in nature is not inconsistent with the notion of creation , because evolution requires the creation of beings that evolve . '' The rules of genetic evolutionary inheritance were first discovered by a Catholic priest , the Augustinian monk Gregor Mendel , who is known today as the founder of modern genetics .   According to a 2014 Gallup survey , `` More than four in 10 Americans continue to believe that God created humans in their present form 10,000 years ago , a view that has changed little over the past three decades . Half of Americans believe humans evolved , with the majority of these saying God guided the evolutionary process . However , the percentage who say God was not involved is rising . ''   The debate is sometimes portrayed as being between science and religion , and the United States National Academy of Sciences states :


Creep (deformation)

In materials science , creep ( sometimes called cold flow ) is the tendency of a solid material to move slowly or deform permanently under the influence of mechanical stresses . It can occur as a result of long-term exposure to high levels of stress that are still below the yield strength of the material . Creep is more severe in materials that are subjected to heat for long periods , and generally increases as they near their melting point .   The rate of deformation is a function of the material properties , exposure time , exposure temperature and the applied structural load . Depending on the magnitude of the applied stress and its duration , the deformation may become so large that a component can no longer perform its function -- for example creep of a turbine blade will cause the blade to contact the casing , resulting in the failure of the blade . Creep is usually of concern to engineers and metallurgists when evaluating components that operate under high stresses or high temperatures . Creep is a deformation mechanism that may or may not constitute a failure mode . For example , moderate creep in concrete is sometimes welcomed because it relieves tensile stresses that might otherwise lead to cracking .   Unlike brittle fracture , creep deformation does not occur suddenly upon the application of stress . Instead , strain accumulates as a result of long-term stress . Therefore , creep is a `` time-dependent '' deformation .


Cretaceous

The Cretaceous ( -LSB- pronkrᵻˈteɪʃəs -RSB- , ) is a geologic period and system that spans 79 million years from the end of the Jurassic Period million years ago ( Mya ) to the beginning of the Paleogene Period Mya . It is the last period of the Mesozoic Era . The Cretaceous Period is usually abbreviated K , for its German translation Kreide ( chalk ) .   The Cretaceous was a period with a relatively warm climate , resulting in high eustatic sea levels that created numerous shallow inland seas . These oceans and seas were populated with now-extinct marine reptiles , ammonites and rudists , while dinosaurs continued to dominate on land . During this time , new groups of mammals and birds , as well as flowering plants , appeared . The Cretaceous ended with a large mass extinction , the Cretaceous -- Paleogene extinction event , in which many groups , including non-avian dinosaurs , pterosaurs and large marine reptiles died out . The end of the Cretaceous is defined by the abrupt Cretaceous -- Paleogene boundary ( K -- Pg boundary ) , a geologic signature associated with the mass extinction which lies between the Mesozoic and Cenozoic eras .


Cretaceous–Paleogene extinction event

The Cretaceous -- Paleogene ( K -- Pg ) extinction event , also known as the Cretaceous -- Tertiary ( K -- T ) extinction , was a mass extinction of some three-quarters of the plant and animal species on Earth that occurred over a geologically short period of time approximately 65 million years ago . With the exception of some ectothermic species like the leatherback sea turtle and crocodiles , no tetrapods weighing more than 25 kg survived . It marked the end of the Cretaceous period and with it , the entire Mesozoic Era , opening the Cenozoic Era that continues today .   In the geologic record , the K -- Pg event is marked by a thin layer of sediment called the K -- Pg boundary , which can be found throughout the world in marine and terrestrial rocks . The boundary clay shows high levels of the metal iridium , which is rare in the Earth 's crust but abundant in asteroids .   As originally proposed in 1980 by a team of scientists led by Luis Alvarez , it is now generally thought that the K -- Pg extinction was caused by a massive comet or asteroid impact , estimated to be 10 km wide , 66 million years ago and its catastrophic effects on the global environment , including a lingering impact winter that made it impossible for plants and plankton to carry out photosynthesis . The impact hypothesis , also known as the Alvarez hypothesis , was bolstered by the discovery of the 180 km Chicxulub crater in the Gulf of Mexico in the early 1990s , which provided conclusive evidence that the K -- Pg boundary clay represented debris from an asteroid impact . The fact that the extinctions occurred at the same time as the impact provides strong situational evidence that the K -- Pg extinction was caused by the asteroid . It was possibly accelerated by the creation of the Deccan Traps . However , some scientists maintain the extinction was caused or exacerbated by other factors , such as volcanic eruptions , climate change , or sea level change , separately or together .   A wide range of species perished in the K -- Pg extinction . The best-known victims are the non-avian dinosaurs . However , the extinction also destroyed a plethora of other terrestrial organisms , including certain mammals , pterosaurs , birds , lizards , insects , and plants . In the oceans , the K -- Pg extinction killed off plesiosaurs and the giant marine lizards ( Mosasauridae ) and devastated fish , sharks , mollusks ( especially ammonites , which became extinct ) and many species of plankton . It is estimated that 75 % or more of all species on Earth vanished . Yet the devastation caused by the extinction also provided evolutionary opportunities . In the wake of the extinction , many groups underwent remarkable adaptive radiations -- a sudden and prolific divergence into new forms and species within the disrupted and emptied ecological niches resulting from the event . Mammals in particular diversified in the Paleogene , producing new forms such as horses , whales , bats , and primates . Birds , fish and perhaps lizards also radiated .


Criticism of NASCAR

The National Association for Stock Car Auto Racing ( NASCAR ) is the sanctioning body for the Monster Energy NASCAR Cup Series , the Xfinity Series and the Camping World Truck Series . NASCAR also oversees a number of regional racing series , including the Whelen Modified Tour , and the Whelen All-American Series . In its role , NASCAR sanctions over 1,500 races at over 100 tracks in 39 states , Canada , Mexico , and Europe .   Similar to other professional leagues and sanctioning bodies , NASCAR has been the target of criticism on various topics , from various sources . Some critics note the significant differences between today 's NASCAR vehicles and true `` stock cars '' . As NASCAR has made moves to improve its national appeal , it has begun racing at new tracks , and ceased racing at some traditional ones , a sore spot for the traditional fan base .   Others frequently cite the dominance of the France family in NASCAR 's business structure , policies , and decision making . Recently , the increased number of Cup drivers competing consistently in the Xfinity Series races has been hotly debated . Most recently , NASCAR has been challenged on the types and frequency of caution flags , with some critics suggesting the outcome of races is being manipulated , and that the intention is not safety , as NASCAR claims , but closer racing .   Another general area of criticism , not only of NASCAR but other motorsports as well , includes questions about fuel consumption , emissions and pollution , and the use of lead additives in the gasoline .


Criticism of the IPCC Fourth Assessment Report

The IPCC Fourth Assessment Report ( AR4 ) is a report on climate change created with the help of a large number of contributors , both scientists and governmental representatives . There has been considerable political controversy over a small number of errors found in the report , and there have been calls for review of the process used to formulate the report . The overwhelming majority view of scientists with expertise in climate change is that errors , when found , are corrected , and the issues as identified do not undermine the conclusions of the report that the climate system is warming in response to increased levels of greenhouse gases , largely due to human activities .


Cross-correlation

In signal processing , cross-correlation is a measure of similarity of two series as a function of the displacement of one relative to the other . This is also known as a sliding dot product or sliding inner-product . It is commonly used for searching a long signal for a shorter , known feature . It has applications in pattern recognition , single particle analysis , electron tomography , averaging , cryptanalysis , and neurophysiology .   For continuous functions f and g , the cross-correlation is defined as :     where denotes the complex conjugate of , and is the displacement , also known as lag , although a positive value of actually means that leads .   Similarly , for discrete functions , the cross-correlation is defined as :   The cross-correlation is similar in nature to the convolution of two functions .   In an autocorrelation , which is the cross-correlation of a signal with itself , there will always be a peak at a lag of zero , and its size will be the signal energy .   In probability and statistics , the term cross-correlations is used for referring to the correlations between the entries of two random vectors X and Y , while the correlations of a random vector X are considered to be the correlations between the entries of X itself , those forming the correlation matrix ( matrix of correlations ) of X . If each of X and Y is a scalar random variable which is realized repeatedly in temporal sequence ( a time series ) , then the correlations of the various temporal instances of X are known as autocorrelations of X , and the cross-correlations of X with Y across time are temporal cross-correlations .   Furthermore , in probability and statistics the definition of correlation always includes a standardising factor in such a way that correlations have values between − 1 and +1 .   If and are two independent random variables with probability density functions f and g , respectively , then the probability density of the difference is formally given by the cross-correlation ( in the signal-processing sense ) ; however this terminology is not used in probability and statistics . In contrast , the convolution ( equivalent to the cross-correlation of f ( t ) and g ( − t ) ) gives the probability density function of the sum .


Cross-validation (statistics)

Cross-validation , sometimes called rotation estimation , is a model validation technique for assessing how the results of a statistical analysis will generalize to an independent data set . It is mainly used in settings where the goal is prediction , and one wants to estimate how accurately a predictive model will perform in practice . In a prediction problem , a model is usually given a dataset of known data on which training is run ( training dataset ) , and a dataset of unknown data ( or first seen data ) against which the model is tested ( testing dataset ) . The goal of cross validation is to define a dataset to `` test '' the model in the training phase ( i.e. , the validation dataset ) , in order to limit problems like overfitting , give an insight on how the model will generalize to an independent dataset ( i.e. , an unknown dataset , for instance from a real problem ) , etc. .   One round of cross-validation involves partitioning a sample of data into complementary subsets , performing the analysis on one subset ( called the training set ) , and validating the analysis on the other subset ( called the validation set or testing set ) . To reduce variability , multiple rounds of cross-validation are performed using different partitions , and the validation results are averaged over the rounds .   One of the main reasons for using cross-validation instead of using the conventional validation ( e.g. partitioning the data set into two sets of 70 % for training and 30 % for test ) is that there is not enough data available to partition it into separate training and test sets without losing significant modelling or testing capability . In these cases , a fair way to properly estimate model prediction performance is to use cross-validation as a powerful general technique .   In summary , cross-validation combines ( averages ) measures of fit ( prediction error ) to derive a more accurate estimate of model prediction performance .


Crown-of-thorns starfish

The crown-of-thorns starfish , Acanthaster planci , is a large , multiple-armed starfish that usually preys upon hard , or stony , coral polyps ( Scleractinia ) . The crown-of-thorns starfish receives its name from venomous thorn-like spines that cover its upper surface , resembling the biblical crown of thorns . It is one of the largest starfish in the world .   A. planci has a very wide Indo-Pacific distribution . It is perhaps most common in Australia , but can occur at tropical and subtropical latitudes from the Red Sea and the east African coast across the Indian Ocean , and across the Pacific Ocean to the west coast of Central America . It occurs where coral reefs or hard coral communities occur in this region .


Cryosphere

The cryosphere ( from the Greek κρύος kryos , `` cold '' , `` frost '' or `` ice '' and σφαῖρα sphaira , `` globe , ball '' ) is those portions of Earth 's surface where water is in solid form , including sea ice , lake ice , river ice , snow cover , glaciers , ice caps , ice sheets , and frozen ground ( which includes permafrost ) . Thus , there is a wide overlap with the hydrosphere . The cryosphere is an integral part of the global climate system with important linkages and feedbacks generated through its influence on surface energy and moisture fluxes , clouds , precipitation , hydrology , atmospheric and oceanic circulation . Through these feedback processes , the cryosphere plays a significant role in the global climate and in climate model response to global changes . The term deglaciation describes the retreat of cryospheric features . Cryology is the study of cryospheres .


Cyanobacteria

Cyanobacteria -LSB- saɪˌænoʊbækˈtɪəriə -RSB- , also known as Cyanophyta , is a phylum of bacteria that obtain their energy through photosynthesis , and are the only photosynthetic prokaryotes able to produce oxygen . The name `` cyanobacteria '' comes from the color of the bacteria ( κυανός ( kyanós ) = blue ) . Cyanobacteria used to be incorrectly called blue-green algae , but being prokaryotes , the term `` algae '' in modern usage refers to eukaryotes .   Like other prokaryotes , cyanobacteria have no membrane-sheathed organelles . Photosynthesis is performed in distinctive folds in the outer membrane of the cell ( unlike green plants which use chloroplasts for this purpose ) . Biologists commonly agree that chloroplasts found in eukaryotes have their ancestry in cyanobacteria , via a process called endosymbiosis .   By producing oxygen as a byproduct of photosynthesis , cyanobacteria are thought to have converted the early oxygen-poor , reducing atmosphere , into an oxidizing one , causing the `` rusting of the Earth '' and the Great Oxygenation Event , that dramatically changed the composition of life forms and led to the near-extinction of anaerobic organisms .   Cyanobacteria are thought to eventually have evolved into plastids found in eukaryotic plants , which later differentiated into specialized organelles like the etioplast , leucoplast and the chloroplast .


Cyclone

In meteorology , a cyclone is a large scale air mass that rotates around a strong center of low atmospheric pressure . Cyclones are characterized by inward spiraling winds that rotate about a zone of low pressure . The largest low-pressure systems are polar vortices and extratropical cyclones of the largest scale ( the synoptic scale ) . Warm-core cyclones such as tropical cyclones and subtropical cyclones also lie within the synoptic scale .  Mesocyclones , tornadoes and dust devils lie within the smaller mesoscale . Upper level cyclones can exist without the presence of a surface low , and can pinch off from the base of the Tropical Upper Tropospheric Trough during the summer months in the Northern Hemisphere . Cyclones have also been seen on extraterrestrial planets , such as Mars and Neptune .  Cyclogenesis describes the process of cyclone formation and intensification . Extratropical cyclones begin as waves in large regions of enhanced mid-latitude temperature contrasts called baroclinic zones . These zones contract and form weather fronts as the cyclonic circulation closes and intensifies . Later in their life cycle , extratropical cyclones occlude as cold air masses undercut the warmer air and become cold core systems . A cyclone 's track is guided over the course of its 2 to 6 day life cycle by the steering flow of the subtropical jet stream .   Weather fronts mark the boundary between two masses of air of different temperature , humidity , and densities , and are associated with the most prominent meteorological phenomena . Strong cold fronts typically feature narrow bands of thunderstorms and severe weather , and may on occasion be preceded by squall lines or dry lines . Such fronts form west of the circulation center and generally move from west to east ; warm fronts form east of the cyclone center and are usually preceded by stratiform precipitation and fog . Warm fronts move poleward ahead of the cyclone path . Occluded fronts form late in the cyclone life cycle near the center of the cyclone and often wrap around the storm center .   Tropical cyclogenesis describes the process of development of tropical cyclones . Tropical cyclones form due to latent heat driven by significant thunderstorm activity , and are warm core . Cyclones can transition between extratropical , subtropical , and tropical phases . Mesocyclones form as warm core cyclones over land , and can lead to tornado formation . Waterspouts can also form from mesocyclones , but more often develop from environments of high instability and low vertical wind shear . In the Atlantic and the northeastern Pacific oceans , a tropical cyclone is generally referred to as a hurricane ( from the name of the ancient Central American deity of wind , Huracan ) , in the Indian and south Pacific oceans it is called a cyclone , and in the northwestern Pacific it is called a typhoon .


Córdoba, Argentina

Córdoba ( -LSB- ˈkorðoβa -RSB- ) is a city in the geographical center of Argentina , in the foothills of the Sierras Chicas on the Suquía River , about 700 km northwest of the Autonomous City of Buenos Aires . It is the capital of Córdoba Province and the second most populous city in Argentina after Buenos Aires , with about 1,330,023 inhabitants according to the 2010 census . It was founded on 6 July 1573 by Jerónimo Luis de Cabrera , who named it after Córdoba , Spain . It was one of the first Spanish colonial capitals of the region that is now Argentina ( the oldest city is Santiago del Estero , founded in 1553 ) . The National University of Córdoba is the oldest university of the country and the second to be inaugurated in Latin America . It was founded in 1613 by the Jesuit Order . Because of this , Córdoba earned the nickname La Docta ( roughly translated , `` the learned one '' ) .   Córdoba has many historical monuments preserved from Spanish colonial rule , especially buildings of the Roman Catholic Church . The most recognizable is perhaps the Jesuit Block ( Spanish : Manzana Jesuítica ) , declared in 2000 as a World Heritage Site by UNESCO which consists of a group of buildings dating from the 17th century , including the Colegio Nacional de Monserrat and the colonial university campus . The campus belongs today to the historical museum of the National University of Córdoba , which has been the second-largest university in the country since the early 20th century ( after the University of Buenos Aires ) , in terms of the number of students , faculty , and academic programs . Córdoba is also known for its historical movements , such as Cordobazo and La Reforma del '18 ( known as University Revolution in English ) .


D. B. Cooper

D. B. Cooper is a media epithet popularly used to refer to an unidentified man who hijacked a Boeing 727 aircraft in the airspace between Portland , Oregon , and Seattle , Washington , on November 24 , 1971 . He extorted $ 200,000 in ransom and parachuted to an uncertain fate . Despite an extensive manhunt and protracted FBI investigation , the perpetrator has never been located or identified . The case remains the only unsolved air piracy in commercial aviation history .   While available evidence and a preponderance of expert opinion suggested from the beginning that Cooper probably did not survive his high-risk jump , the FBI nevertheless maintained an active investigation for 45 years following the hijacking . Despite a case file that grew to over 60 volumes over that time period , no definitive conclusions have been reached regarding Cooper 's true identity or whereabouts . The suspect purchased his airline ticket using the alias Dan Cooper , but because of a news media miscommunication he became known in popular lore as `` D. B. Cooper '' .   Numerous theories of widely varying plausibility have been proposed over the years by investigators , reporters , and amateur enthusiasts . The discovery of a small cache of ransom bills along the banks of the Columbia River in February 1980 triggered renewed interest , but ultimately only deepened the mystery , and the great majority of the ransom remains unrecovered .   The FBI officially suspended active investigation of the case in July 2016 , but continues to request that any physical evidence that might emerge related to the parachutes or the ransom money be submitted for analysis .


Daniel Bryan

Bryan Lloyd Danielson ( born May 22 , 1981 ) is an American retired professional wrestler currently signed to WWE under the ring name Daniel Bryan , where he is the on-screen general manager of SmackDown .   In WWE , Bryan held the WWE ChampionshipDanielson 's first two reigns were as WWE Champion . His final reign was as WWE World Heavyweight Champion . three times and WWE 's World Heavyweight Championship once , in addition to being a one-time United States Champion , a one-time Intercontinental Champion , and a one time WWE Tag Team Champion as part of Team Hell No ( with Kane ) . He was also the 2011 SmackDown Money in the Bank winner and the 2013 Superstar of the Year Slammy Award winner . He is the 26th Triple Crown Champion and the 6th Grand Slam Champion in WWE history and headlined several major pay-per-view events , including SummerSlam in 2013 and WrestleMania XXX .   Danielson was previously signed to the WWE , then known as the WWF , for an 18-month period from 2000 -- 2001 . Prior to joining WWE for his second stint in 2009 , Danielson wrestled for various companies internationally using both his real name and the ring name ( and later nickname ) `` American Dragon '' . He wrestled for Ring of Honor ( ROH ) from 2002 to 2009 , being recognized as a `` Founding Father '' of the promotion , where he was a one-time ROH World Champion , as well the final Pure Wrestling Champion ( unifying the Pure title with the World title ) . He was the first winner of ROH 's annual Survival of the Fittest tournament in 2004 . Danielson also wrestled extensively in Japan , winning the GHC Junior Heavyweight Championship in Pro Wrestling Noah and the IWGP Junior Heavyweight Tag Team Championship ( with Curry Man ) in New Japan Pro-Wrestling ( NJPW ) . Between WWE , ROH , and Japanese promotions , he held eleven total championships . Danielson also won numerous titles on the independent circuit , including two PWG World Championships , the FIP Heavyweight Championship , and the wXw World Heavyweight Championship .   In 2016 , at age 34 , Danielson retired from professional wrestling due to medical issues ( including seizures ) arising from multiple concussions and a brain lesion . Later that year in July , he was named the General Manager of SmackDown following the return of the WWE brand extension .


Data mining

Data mining is the computing process of discovering patterns in large data sets involving methods at the intersection of artificial intelligence , machine learning , statistics , and database systems . It is an interdisciplinary subfield of computer science . The overall goal of the data mining process is to extract information from a data set and transform it into an understandable structure for further use . Aside from the raw analysis step , it involves database and data management aspects , data pre-processing , model and inference considerations , interestingness metrics , complexity considerations , post-processing of discovered structures , visualization , and online updating . Data mining is the analysis step of the `` knowledge discovery in databases '' process , or KDD .   The term is a misnomer , because the goal is the extraction of patterns and knowledge from large amounts of data , not the extraction ( mining ) of data itself .  It also is a buzzword and is frequently applied to any form of large-scale data or information processing ( collection , extraction , warehousing , analysis , and statistics ) as well as any application of computer decision support system , including artificial intelligence , machine learning , and business intelligence . The book Data mining : Practical machine learning tools and techniques with Java ( which covers mostly machine learning material ) was originally to be named just Practical machine learning , and the term data mining was only added for marketing reasons . Often the more general terms ( large scale ) data analysis and analytics -- or , when referring to actual methods , artificial intelligence and machine learning -- are more appropriate .   The actual data mining task is the automatic or semi-automatic analysis of large quantities of data to extract previously unknown , interesting patterns such as groups of data records ( cluster analysis ) , unusual records ( anomaly detection ) , and dependencies ( association rule mining , sequential pattern mining ) . This usually involves using database techniques such as spatial indices . These patterns can then be seen as a kind of summary of the input data , and may be used in further analysis or , for example , in machine learning and predictive analytics . For example , the data mining step might identify multiple groups in the data , which can then be used to obtain more accurate prediction results by a decision support system . Neither the data collection , data preparation , nor result interpretation and reporting is part of the data mining step , but do belong to the overall KDD process as additional steps .   The related terms data dredging , data fishing , and data snooping refer to the use of data mining methods to sample parts of a larger population data set that are ( or may be ) too small for reliable statistical inferences to be made about the validity of any patterns discovered . These methods can , however , be used in creating new hypotheses to test against the larger data populations .


Data visualization

Data visualization or data visualisation is viewed by many disciplines as a modern equivalent of visual communication . It involves the creation and study of the visual representation of data , meaning `` information that has been abstracted in some schematic form , including attributes or variables for the units of information '' .   A primary goal of data visualization is to communicate information clearly and efficiently via statistical graphics , plots and information graphics . Numerical data may be encoded using dots , lines , or bars , to visually communicate a quantitative message . Effective visualization helps users analyze and reason about data and evidence . It makes complex data more accessible , understandable and usable . Users may have particular analytical tasks , such as making comparisons or understanding causality , and the design principle of the graphic ( i.e. , showing comparisons or showing causality ) follows the task . Tables are generally used where users will look up a specific measurement , while charts of various types are used to show patterns or relationships in the data for one or more variables .   Data visualization is both an art and a science . It is viewed as a branch of descriptive statistics by some , but also as a grounded theory development tool by others . Increased amounts of data created by Internet activity and an expanding number of sensors in the environment are referred to as `` big data '' or Internet of things . Processing , analyzing and communicating this data present ethical and analytical challenges for data visualization . The field of data science and practitioners called data scientists help address this challenge .


Daylight saving time

Daylight saving time ( abbreviated DST ) , also sometimes erroneously referred to as daylight savings time , is the practice of advancing clocks during summer months so that evening daylight lasts longer , while sacrificing normal sunrise times . Typically , regions that use daylight saving time adjust clocks forward one hour close to the start of spring and adjust them backward in the autumn to standard time .   American inventor and politician Benjamin Franklin proposed a form of daylight time in 1784 . He wrote an essay `` An Economical Project for Diminishing the Cost of Light '' to the editor of The Journal of Paris , suggesting , somewhat jokingly , that Parisians could economize candle usage by getting people out of bed earlier in the morning , making use of the natural morning light instead . New Zealander George Hudson proposed the idea of daylight saving in 1895 . The German Empire and Austria-Hungary organized the first nationwide implementation , starting on April 30 , 1916 . Many countries have used it at various times since then , particularly since the energy crisis of the 1970s .   The practice has both advocates and critics . Some early proponents of DST aimed to reduce evening use of incandescent lighting -- once a primary use of electricity -- today 's heating and cooling usage patterns differ greatly , and research about how DST affects energy use is limited and contradictory .   DST clock shifts sometimes complicate timekeeping and can disrupt travel , billing , record keeping , medical devices , heavy equipment , and sleep patterns . Computer software often adjusts clocks automatically , but policy changes by various jurisdictions of DST dates and timings may be confusing .


Daylight saving time in the United States is the practice of setting the clock forward by one hour during the warmer part of the year , so that evenings have more daylight and mornings have less . Most areas of the United States observe daylight saving time ( DST ) , the exceptions being Arizona ( except for the Navajo , who do observe daylight saving time on tribal lands ) , Hawaii , and the overseas territories of American Samoa , Guam , the Northern Mariana Islands , Puerto Rico , and the United States Virgin Islands . In general , daylight time is not observed in lower-latitude regions , as summer days are not much longer than winter ones as in higher latitudes , so the advantage of the change is smaller .   Daylight saving time starts on the second Sunday in March and ends on the first Sunday in November , with the time changes taking place at 2:00 a.m. local time . With a mnemonic word play referring to seasons , clocks `` spring forward and fall back '' -- that is , in springtime the clocks are moved forward from 2:00 a.m. to 3:00 a.m. , and in fall they are moved back from 2:00 a.m. to 1:00 a.m. Daylight saving time lasts for a total of 34 weeks ( 238 days ) every year , about 65 % of the entire year ( including leap years ) .   The following table lists recent past and near future starting and ending dates of daylight saving time in the United States :


Dead zone (ecology)

Dead zones are hypoxic ( low-oxygen ) areas in the world 's oceans and large lakes , caused by `` excessive nutrient pollution from human activities coupled with other factors that deplete the oxygen required to support most marine life in bottom and near-bottom water . ( NOAA ) . '' In the 1970s oceanographers began noting increased instances of dead zones . These occur near inhabited coastlines , where aquatic life is most concentrated . ( The vast middle portions of the oceans , which naturally have little life , are not considered `` dead zones '' . )   In March 2004 , when the recently established UN Environment Programme published its first Global Environment Outlook Year Book ( GEO Year Book 2003 ) , it reported 146 dead zones in the world 's oceans where marine life could not be supported due to depleted oxygen levels . Some of these were as small as a square kilometre ( 0.4 mi ² ) , but the largest dead zone covered 70,000 square kilometres ( 27,000 mi ² ) . A 2008 study counted 405 dead zones worldwide .


Debbie Stabenow

Deborah Ann Greer Stabenow -LSB- ˈstæbəˌnaʊ -RSB- ( born April 29 , 1950 ) is the senior United States Senator from Michigan and a member of the Democratic Party . Before her election to the U.S. Senate , she was a member of the United States House of Representatives , representing Michigan 's 8th congressional district from 1997 to 2001 . She previously served as a member of the Ingham County Board of Commissioners , Michigan House of Representatives , and Michigan Senate .   Stabenow served as Chairwoman of the Senate Agriculture Committee from 2011 to 2015 . She was re-elected to the Senate for a third term in November 2012 . She became the state 's senior senator upon the retirement of Carl Levin on January 3 , 2015 . She served as Vice Chair of the Senate Democratic Policy Committee from 2011 to 2017 and became its Chair in 2017 .


Deccan Traps

The Deccan Traps are a large igneous province located on the Deccan Plateau of west-central India ( 17 ° -- 24 ° N , 73 ° -- 74 ° E ) and one of the largest volcanic features on Earth . They consist of multiple layers of solidified flood basalt that together are more than 2000 m thick , cover an area of 500000 km2 , and have a volume of 1000000 km3 . Originally , the Deccan Traps may have covered 1500000 km2 , with a correspondingly larger original volume .


December

December is the twelfth and final month of the year in the Julian and Gregorian Calendars . It is the seventh and last month to have the length of 31 days .   December got its name from the Latin word decem ( meaning ten ) because it was originally the tenth month of the year in the Roman calendar , which began in March . The winter days following December were not included as part of any month . Later , the months of January and February were created out of the monthless period and added to the beginning of the calendar , but December retained its name .   In Ancient Rome , one of the four Agonalia , this day in honor of Sol Indiges was held on December 11 , as was Septimontium . Dies Natalis was held on of the temple of Tellus on December 13 , Consualia was held on December 15 , Saturnalia was held December 17 -- 23 , Opiconsivia held on December 19 , Divalia on December 21 , Larentalia on December 23 , and the Dies Natalis of Sol Invictus was held on December 25 . These dates do not correspond to the modern Gregorian calendar .   The Anglo-Saxons referred to December/January as Ġēolamonaþ ( modern English : `` Yule month '' ) . The French Republican Calendar contained December within the months of Frimaire and Nivôse .


Deep hypothermic circulatory arrest

Deep hypothermic circulatory arrest ( DHCA ) is a surgical technique that involves cooling the body to temperatures below 20 ° C ( 68 ° F ) , and stopping blood circulation and brain function for up to one hour . It is used when blood circulation to the brain must be stopped because of delicate surgery within the brain , or because of surgery on large blood vessels that lead to or from the brain . DHCA is a form of carefully managed clinical death in which heartbeat and all brain activity cease .   At normal body temperature of 37 ° C only several minutes of stopped blood circulation causes changes within the brain leading to permanent damage after circulation is restored . Reducing body temperature extends the time interval that such stoppage can be survived . At a brain temperature of 14 ° C , blood circulation can be safely stopped for 30 to 40 minutes . There is an increased incidence of brain injury at times longer than 40 minutes , but sometimes circulatory arrest for up to 60 minutes is used if life-saving surgery requires it . Infants tolerate longer periods of DHCA than adults .   Applications of DHCA include repairs of the aortic arch , repairs to head and neck great vessels , repair of large cerebral aneurysms , repair of cerebral arteriovenous malformations , pulmonary thromboendarterectomy , and resection of tumors that have invaded the vena cava .


Deep sea fish

Deep-sea fish are fish that live in the darkness below the sunlit surface waters , that is below the epipelagic or photic zone of the sea . The lanternfish is , by far , the most common deep-sea fish . Other deep sea fishes include the flashlight fish , cookiecutter shark , bristlemouths , anglerfish , viperfish , and some species of eelpout .   Only about 2 % of known marine species inhabit the pelagic environment . This means that they live in the water column as opposed to the benthic organisms that live in or on the sea floor . Deep-sea organisms generally inhabit bathypelagic ( 1000 -- 4000m deep ) and abyssopelagic ( 4000 -- 6000m deep ) zones . However , characteristics of deep-sea organisms , such as bioluminescence can be seen in the mesopelagic ( 200 -- 1000m deep ) zone as well . The mesopelagic zone is the disphotic zone , meaning light there is minimal but still measurable . The oxygen minimum layer exists somewhere between a depth of 700m and 1000m deep depending on the place in the ocean . This area is also where nutrients are most abundant . The bathypelagic and abyssopelagic zones are aphotic , meaning that no light penetrates this area of the ocean . These zones make up about 75 % of the inhabitable ocean space .   The epipelagic zone ( 0 -- 200m ) is the area where light penetrates the water and photosynthesis occurs . This is also known as the photic zone . Because this typically extends only a few hundred meters below the water , the deep sea , about 90 % of the ocean volume , is in darkness . The deep sea is also an extremely hostile environment , with temperatures that rarely exceed 3 ° C ( 37.4 ° F ) and fall as low as − 1.8 ° C ( 28.76 ° F ) ( with the exception of hydrothermal vent ecosystems that can exceed 350 ° C , or 662 ° F ) , low oxygen levels , and pressures between 20 and 1,000 atmospheres ( between 2 and 100 megapascals ) .


Deforestation

Deforestation , clearance or clearing is the removal of a forest or stand of trees where the land is thereafter converted to a non-forest use . Examples of deforestation include conversion of forestland to farms , ranches , or urban use . The most concentrated deforestation occurs in tropical rainforests . About 30 % of Earth 's land surface is covered by forests .   Deforestation occurs for multiple reasons : trees are cut down to be used for building or sold as fuel , ( sometimes in the form of charcoal or timber ) , while cleared land is used as pasture for livestock and plantation . The removal of trees without sufficient reforestation has resulted in damage to habitat , biodiversity loss and aridity . It has adverse impacts on biosequestration of atmospheric carbon dioxide . Deforestation has also been used in war to deprive the enemy of vital resources and cover for its forces . Modern examples of this were the use of Agent Orange by the British military in Malaya during the Malayan Emergency and the United States military in Vietnam during the Vietnam War . As of 2005 , net deforestation rates have ceased to increase in countries with a per capita GDP of at least US$ 4,600 . Deforested regions typically incur significant adverse soil erosion and frequently degrade into wasteland .   Disregard of ascribed value , lax forest management and deficient environmental laws are some of the factors that allow deforestation to occur on a large scale . In many countries , deforestation , both naturally occurring and human-induced , is an ongoing issue . Deforestation causes extinction , changes to climatic conditions , desertification , and displacement of populations as observed by current conditions and in the past through the fossil record . More than half of all plant and land animal species in the world live in tropical forests .   Between 2000 and 2012 , 2.3 e6sqkm of forests around the world were cut down . As a result of deforestation , only 6.2 e6km2 remain of the original 16 e6km2 of forest that formerly covered the Earth .


Deforestation and climate change

Deforestation is one of the main contributors to climate change . It is the second largest anthropogenic source of carbon dioxide to the atmosphere , after fossil fuel combustion . Deforestation and forest degradation contribute to atmospheric greenhouse gas emissions through combustion of forest biomass and decomposition of remaining plant material and soil carbon . It used to account for more than 20 % of carbon dioxide emissions , but it 's currently somewhere around the 10 % mark . By 2008 , deforestation was 12 % of total , or 15 % if peatlands are included . These proportions are likely to have fallen since given the continued rise of fossil fuel use .   Averaged over all land and ocean surfaces , temperatures warmed roughly 1.53 ° F ( 0.85 ° C ) between 1880 and 2012 , according to the Intergovernmental Panel on Climate Change . In the Northern Hemisphere , 1983 to 2012 were the warmest 30-year period of the last 1400 years .


Deforestation in Indonesia

Deforestation in Indonesia involves the long-term loss of forests and foliage across much of the country ; it has had massive environmental and social impacts . Indonesia is home to some of the most biologically diverse forests in the world and ranks third in number of species behind Brazil and the Democratic Republic of Congo .   As late as 1900 , Indonesia was still a densely forested country : forests represented 84 percent of the total land area . Deforestation intensified in the 1970s and has accelerated further since then . The estimated forest cover of 170 million hectares around 1900 decreased to less than 100 million hectares by the end of the 20th century . In 2008 , it was estimated that tropical rainforests in Indonesia would be logged out in a decade . Of the total logging in Indonesia , up to 80 % is reported to be performed illegally .   Large areas of forest in Indonesia have been cleared by large multinational pulp companies , such as Asia Pulp and Paper , and replaced by plantations . Forests are often burned by farmers and plantation owners . Another major source of deforestation is the logging industry , driven by demand from China and Japan . Agricultural development and transmigration programs moved large populations into rainforest areas , further increasing deforestation rates .   Logging and the burning of forests to clear land for cultivation has made Indonesia the world 's third largest emitter of greenhouse gases , behind China and the United States . Forest fires often destroy high capacity carbon sinks , including old-growth rainforest and peatlands . In May 2011 , Indonesia declared a moratorium on new logging contracts to help combat this . This appeared to be ineffective in the short-term , as the rate of deforestation continued to increase . By 2012 Indonesia had surpassed the rate of deforestation in Brazil , and become the fastest forest clearing nation in the world .


Deglaciation

Deglaciation describes the transition from full glacial conditions during ice ages , to warm interglacials , characterized by global warming and sea level rise due to change in continental ice volume ( IPCC AR5 ) . Thus , it refers to the retreat of a glacier , an ice sheet or frozen surface layer , and the resulting exposure of the Earth 's surface . The decline of the cryosphere due to ablation can occur on any scale from global to localized to a particular glacier . After the Last Glacial Maximum ( ca. 21k years ago ) , the last deglaciation begun , which lasted until the early Holocene .   The previous deglaciation took place between approximately 22ka until 11.5 ka . This occurred when there was an annual mean atmospheric temperature on the earth that increased by roughly 5 ° C , which was also accompanied by regional high-latitude warming that exceeded 10 ° C . This was also followed by noteworthy deep-sea and tropical-se warming , between about 1-2 ° C ( deep-sea ) and 2-4 ° C ( tropical sea ) . Not only did this warming occur , but the global hydrological budget also experienced noticeable changes and regional precipitation patters changed . As a result of all of this , the worlds main ice sheets , including the ones located in Eurasia , North America and parts of the Antarctic Ice Sheets melted . As a consequence , sea levels rose roughly 120 metres ) . These processes did not occur steadily , and they also did not occur at the same time .


Degrees of freedom (physics and chemistry)

In physics , a degree of freedom is an independent physical parameter in the formal description of the state of a physical system . The set of all dimensions of a system is known as a phase space , and degrees of freedom are sometimes referred to as its dimensions .


Democratic Party (United States)

The Democratic Party is one of the two major contemporary political parties in the United States , along with the Republican Party . Tracing its heritage back to Thomas Jefferson and James Madison 's Democratic-Republican Party , the modern-day Democratic Party was founded around 1828 by Andrew Jackson , making it the world 's oldest active party .   The Democrats ' dominant worldview was once social conservativism and economic liberalism , while , especially in the rural South , populism was its leading characteristic . In 1912 , Theodore Roosevelt ran as a third-party candidate in the Progressive ( `` Bull Moose '' ) Party , leading to a switch of political platforms between the Democratic and Republican Party and Woodrow Wilson being elected as the first fiscally progressive Democrat . Since Franklin D. Roosevelt and his New Deal coalition in the 1930s , the Democratic Party has also promoted a social-liberal platform , supporting social justice .   Today , the House Democratic caucus is composed mostly of progressives and centrists , with a smaller minority of conservative Democrats . The party 's philosophy of modern liberalism advocates social and economic equality , along with the welfare state . It seeks to provide government intervention and regulation in the economy . These interventions , such as the introduction of social programs , support for labor unions , affordable college tuitions , moves toward universal health care and equal opportunity , consumer protection , and environmental protection form the core of the party 's economic policy . The party has united with smaller liberal regional parties throughout the country , such as the Farmer -- Labor Party in Minnesota and the Nonpartisan League in North Dakota .   Well into the 20th century , the party had conservative pro-business and southern conservative-populist anti-business wings . The New Deal Coalition of 1932 -- 1964 attracted strong support from voters of recent European extraction -- many of whom were Catholics based in the cities . After Franklin D. Roosevelt 's New Deal of the 1930s , the pro-business wing withered outside the South . After the racial turmoil of the 1960s , most southern whites and many northern Catholics moved into the Republican Party at the presidential level . The once-powerful labor union element became smaller and less supportive after the 1970s . White Evangelicals and Southerners became heavily Republican at the state and local level in the 1990s . Racial and ethnic minorities in the U.S. such as ( but not limited to ) Jewish Americans , Hispanic Americans , Arabic Americans , and African Americans , tend to support the Democratic Party in proportions higher than their overall representation in American society . Overall , the Democratic Party has retained a membership lead over its major rival the Republican Party ( GOP ) .   15 Democrats have served as president under 16 administrations : the first was seventh president Andrew Jackson , who served from 1829 to 1837 ; Grover Cleveland served two nonconsecutive terms from 1885 to 1889 and 1893 to 1897 , and is thus counted twice ( as the 22nd and 24th president ) . The most recent was the 44th president Barack Obama , who held the office from 2009 to 2017 .   In the 115th Congress , following the 2016 elections , Democrats are the opposition party , holding a minority of seats in both the House of Representatives and the Senate . The party also holds a minority of governorships ( 16/50 ) , and state legislatures ( full control of 12/50 , split control of six others ) , though they do control the mayoralty of cities such as New York City , Los Angeles , Chicago , Houston , and Washington , D.C.


Dengue fever

Dengue fever is a mosquito-borne tropical disease caused by the dengue virus . Symptoms typically begin three to fourteen days after infection . This may include a high fever , headache , vomiting , muscle and joint pains , and a characteristic skin rash . Recovery generally takes two to seven days . In a small proportion of cases , the disease develops into the life-threatening dengue hemorrhagic fever , resulting in bleeding , low levels of blood platelets and blood plasma leakage , or into dengue shock syndrome , where dangerously low blood pressure occurs .   Dengue is spread by several species of mosquito of the Aedes type , principally A. aegypti . The virus has five different types ; infection with one type usually gives lifelong immunity to that type , but only short-term immunity to the others . Subsequent infection with a different type increases the risk of severe complications . A number of tests are available to confirm the diagnosis including detecting antibodies to the virus or its RNA .   A novel vaccine for dengue fever has been approved and is commercially available in a number of countries . Other methods of prevention are by reducing mosquito habitat and limiting exposure to bites . This may be done by getting rid of or covering standing water and wearing clothing that covers much of the body . Treatment of acute dengue is supportive and includes giving fluid either by mouth or intravenously for mild or moderate disease . For more severe cases blood transfusion may be required . About half a million people require admission to hospital a year . Nonsteroidal anti-inflammatory drugs ( NSAIDs ) such as ibuprofen should not be used .   Dengue has become a global problem since the Second World War and is common in more than 110 countries . Each year between 50 and 528 million people are infected and approximately 10,000 to 20,000 die . The earliest descriptions of an outbreak date from 1779 . Its viral cause and spread were understood by the early 20th century . Apart from eliminating the mosquitoes , work is ongoing for medication targeted directly at the virus . It is classified as a neglected tropical disease .


Density

The density , or more precisely , the volumetric mass density , of a substance is its mass per unit volume . The symbol most often used for density is ρ ( the lower case Greek letter rho ) , although the Latin letter D can also be used . Mathematically , density is defined as mass divided by volume :   where ρ is the density , m is the mass , and V is the volume . In some cases ( for instance , in the United States oil and gas industry ) , density is loosely defined as its weight per unit volume , although this is scientifically inaccurate -- this quantity is more specifically called specific weight .   For a pure substance the density has the same numerical value as its mass concentration .  Different materials usually have different densities , and density may be relevant to buoyancy , purity and packaging . Osmium and iridium are the densest known elements at standard conditions for temperature and pressure but certain chemical compounds may be denser .   To simplify comparisons of density across different systems of units , it is sometimes replaced by the dimensionless quantity `` relative density '' or `` specific gravity '' , i.e. the ratio of the density of the material to that of a standard material , usually water . Thus a relative density less than one means that the substance floats in water .   The density of a material varies with temperature and pressure . This variation is typically small for solids and liquids but much greater for gases . Increasing the pressure on an object decreases the volume of the object and thus increases its density . Increasing the temperature of a substance ( with a few exceptions ) decreases its density by increasing its volume . In most materials , heating the bottom of a fluid results in convection of the heat from the bottom to the top , due to the decrease in the density of the heated fluid . This causes it to rise relative to more dense unheated material .   The reciprocal of the density of a substance is occasionally called its specific volume , a term sometimes used in thermodynamics . Density is an intensive property in that increasing the amount of a substance does not increase its density ; rather it increases its mass .


Desert

A desert is a barren area of land where little precipitation occurs and consequently living conditions are hostile for plant and animal life . The lack of vegetation exposes the unprotected surface of the ground to the processes of denudation . About one third of the land surface of the world is arid or semi-arid . This includes much of the polar regions where little precipitation occurs and which are sometimes called polar deserts or `` cold deserts '' . Deserts can be classified by the amount of precipitation that falls , by the temperature that prevails , by the causes of desertification or by their geographical location .   Deserts are formed by weathering processes as large variations in temperature between day and night put strains on the rocks which consequently break in pieces . Although rain seldom occurs in deserts , there are occasional downpours that can result in flash floods . Rain falling on hot rocks can cause them to shatter and the resulting fragments and rubble strewn over the desert floor is further eroded by the wind . This picks up particles of sand and dust and wafts them aloft in sand or dust storms . Wind-blown sand grains striking any solid object in their path can abrade the surface . Rocks are smoothed down , and the wind sorts sand into uniform deposits . The grains end up as level sheets of sand or are piled high in billowing sand dunes . Other deserts are flat , stony plains where all the fine material has been blown away and the surface consists of a mosaic of smooth stones . These areas are known as desert pavements and little further erosion takes place . Other desert features include rock outcrops , exposed bedrock and clays once deposited by flowing water . Temporary lakes may form and salt pans may be left when waters evaporate . There may be underground sources of water in the form of springs and seepages from aquifers . Where these are found , oases can occur .   Plants and animals living in the desert need special adaptations to survive in the harsh environment . Plants tend to be tough and wiry with small or no leaves , water-resistant cuticles and often spines to deter herbivory . Some annual plants germinate , bloom and die in the course of a few weeks after rainfall while other long-lived plants survive for years and have deep root systems able to tap underground moisture . Animals need to keep cool and find enough food and water to survive . Many are nocturnal and stay in the shade or underground during the heat of the day . They tend to be efficient at conserving water , extracting most of their needs from their food and concentrating their urine . Some animals remain in a state of dormancy for long periods , ready to become active again when the rare rains fall . They then reproduce rapidly while conditions are favorable before returning to dormancy .   People have struggled to live in deserts and the surrounding semi-arid lands for millennia . Nomads have moved their flocks and herds to wherever grazing is available and oases have provided opportunities for a more settled way of life . The cultivation of semi-arid regions encourages erosion of soil and is one of the causes of increased desertification . Desert farming is possible with the aid of irrigation and the Imperial Valley in California provides an example of how previously barren land can be made productive by the import of water from an outside source . Many trade routes have been forged across deserts , especially across the Sahara Desert , and traditionally were used by caravans of camels carrying salt , gold , ivory and other goods . Large numbers of slaves were also taken northwards across the Sahara . Some mineral extraction also takes place in deserts and the uninterrupted sunlight gives potential for the capture of large quantities of solar energy .