The Mediterranean Sea is a sea connected to the Atlantic Ocean, surrounded by the Mediterranean Basin and almost completely enclosed by land: on the north by Western and Southern Europe and Anatolia, on the south by North Africa, and on the east by the Levant. The Sea has played a central role in the history of Western civilization. Although the Mediterranean is sometimes considered a part of the Atlantic Ocean, it is usually referred to as a separate body of water. Geological evidence indicates that around 5.9 million years ago, the Mediterranean was cut off from the Atlantic and was partly or completely desiccated over a period of some 600,000 years during the Messinian salinity crisis before being refilled by the Zanclean flood about 5.3 million years ago.

The Mediterranean Sea covers an area of about , representing 0.7% of the global ocean surface, but its connection to the Atlantic via the Strait of Gibraltar—the narrow strait that connects the Atlantic Ocean to the Mediterranean Sea and separates the Iberian Peninsula in Europe from Morocco in Africa—is only  wide. In oceanography, it is sometimes called the Eurafrican Mediterranean Sea, the European Mediterranean Sea or the African Mediterranean Sea to distinguish it from mediterranean seas elsewhere. The Mediterranean Sea encompasses a vast number of islands, some of them being of volcanic origin. The two by far largest islands are Sicily and Sardinia.

The Mediterranean Sea has an average depth of  and the deepest recorded point is  in the Calypso Deep in the Ionian Sea. It lies between latitudes 30° and 46° N and longitudes 6° W and 36° E. Its west–east length, from the Strait of Gibraltar to the Gulf of Iskenderun, on the southeastern coast of Turkey, is about . The north–south length varies greatly between different shorelines and whether only straight routes are considered. Also including longitudal changes, the shortest shipping route between the multinational Gulf of Trieste and the Libyan coastline of Gulf of Sidra is about . The water temperatures are mild in winter and warm in summer and give name to the mediterranean climate type due to the majority of precipitation falling in the cooler months. Its southern and eastern coastlines are lined with hot deserts not far inland, but the immediate coastline on all sides of the Mediterranean tends to have strong maritime moderation.

The sea was an important route for merchants and travelers of ancient times, facilitating trade and cultural exchange between peoples of the region. The history of the Mediterranean region is crucial to understanding the origins and development of many modern societies. The Roman Empire maintained nautical hegemony over the sea for centuries.

The countries surrounding the Mediterranean in clockwise order are Spain, France, Monaco, Italy, Slovenia, Croatia, Bosnia and Herzegovina, Montenegro, Albania, Greece, Turkey, Syria, Lebanon, Israel, Palestine, Egypt, Libya, Tunisia, Algeria, and Morocco; Malta and Cyprus are island countries in the sea. In addition, the disputed territory of North Cyprus, and some enclaves, notably Gibraltar and Ceuta, have coastlines on the sea. Alexandria is the largest coastal settlement. The drainage basin encompasses a large number of other countries, the Nile being the longest river ending in the Mediterranean Sea.

In spite of its great biodiversity, concentrations of chlorophyll and nutrients in the Mediterranean Sea are very low, making it one of the most oligotrophic ocean regions in the world. The Mediterranean Sea is commonly referred to as an LNLC (Low-Nutrient, Low-Chlorophyll) area. The Mediterranean Sea fits the definition of a desert in which its nutrient contents are low, making it difficult for plants and animals to develop.

There are steep gradients in nutrient concentrations, chlorophyll concentrations and primary productivity in the Mediterranean. Nutrient concentrations in the western part of the basin are about double the concentrations in the eastern basin. The Alboran Sea, close to the Strait of Gibraltar, has a daily primary productivity of about 0.25 g C (grams of carbon) m−2 day−1 whereas the eastern basin has an average daily productivity of 0.16 g C m−2 day−1. For this reason, the eastern part of the Mediterranean Sea is termed "ultraoligotrophic". The productive areas of the Mediterranean Sea are few and small. High (i.e. more than 0.5 grams of Chlorophyll a per cubic meter) productivity occurs in coastal areas, close to the river mouths which are the primary suppliers of dissolved nutrients. The Gulf of Lion has a relatively high productivity because it is an area of high vertical mixing, bringing nutrients to the surface waters that can be used by phytoplankton to produce Chlorophyll a.

Primary productivity in the Mediterranean is also marked by an intense seasonal variability. In winter, the strong winds and precipitation over the basin generate vertical mixing, bringing nutrients from the deep waters to the surface, where phytoplankton can convert it into biomass. However, in winter, light may be the limiting factor for primary productivity. Between March and April, spring offers the ideal trade-off between light intensity and nutrient concentrations in surface for a spring bloom to occur. In summer, high atmospheric temperatures lead to the warming of the surface waters. The resulting density difference virtually isolates the surface waters from the rest of the water column and nutrient exchanges are limited. As a consequence, primary productivity is very low between June and October.

Oceanographic expeditions uncovered a characteristic feature of the Mediterranean Sea biogeochemistry: most of the chlorophyll production does not occur on the surface, but in sub-surface waters between 80 and 200 meters deep. Another key characteristic of the Mediterranean is its high nitrogen-to-phosphorus ratio (N:P). Redfield demonstrated that most of the world's oceans have an average N:P ratio around 16. However, the Mediterranean Sea has an average N:P between 24 and 29, which translates a widespread phosphorus limitation.

Because of its low productivity, plankton assemblages in the Mediterranean Sea are dominated by small organisms such as picophytoplankton and bacteria.


The Middle East (, ISO 233: ) is a geopolitical region commonly encompassing Arabia (including the Arabian Peninsula and Bahrain), Asia Minor (Asian part of Turkey except Hatay Province), East Thrace (European part of Turkey), Egypt, Iran, the Levant (including Ash-Shām and Cyprus), Mesopotamia (modern-day Iraq), and the Socotra Archipelago (a part of Yemen). The term came into widespread usage as a replacement of the term Near East (as opposed to the Far East) beginning in the early 20th century. The term "Middle East" has led to some confusion over its changing definitions, and has been viewed by some to be discriminatory or too Eurocentric. The region includes the vast majority of the territories included in the closely associated definition of Western Asia (including Iran), but without the South Caucasus, and additionally includes all of Egypt (not just the Sinai Region) and all of Turkey (not just the part barring East Thrace).

Most Middle Eastern countries (13 out of 18) are part of the Arab world. The most populous countries in the region are Egypt, Iran, and Turkey, while Saudi Arabia is the largest Middle Eastern country by area. The history of the Middle East dates back to ancient times, with the geopolitical importance of the region being recognized for millennia. Several major religions have their origins in the Middle East, including Judaism, Christianity, and Islam. Arabs constitute the main socioethnic grouping in the region, followed by Turks, Persians, Kurds, Azeris, Copts, Jews, Assyrians, Iraqi Turkmen, Yazidis, and Greek Cypriots.

The Middle East generally has a hot, arid climate, especially in the Peninsula and Egyptian regions. Several major rivers providing irrigation to support agriculture in limited areas here such as the Nile Delta in Egypt, the Tigris and Euphrates watersheds of Mesopotamia, and most of what is known as the Fertile Crescent. Conversely the Levantine coast and most of Turkey have more temperate, oceanic and wetter climates. Most of the countries that border the Persian Gulf have vast reserves of petroleum, with monarchs of the Arabian Peninsula in particular benefiting economically from petroleum exports. Because of the arid climate and heavy reliance on the fossil fuel industry, the Middle East is both a heavy contributor to climate change and a region expected to be severely negatively impacted by it.

Other concepts of the region exist including the broader the Middle East and North Africa (MENA), which includes states of the Maghreb and the Sudan, or the "Greater Middle East" which additionally also includes parts of East Africa, Mauritania, Afghanistan, Pakistan, and sometimes Central Asia and the South Caucasus.

The term "Middle East" may have originated in the 1850s in the British India Office. However, it became more widely known when American naval strategist Alfred Thayer Mahan used the term in 1902 to "designate the area between Arabia and India". During this time the British and Russian Empires were vying for influence in Central Asia, a rivalry which would become known as the Great Game. Mahan realized not only the strategic importance of the region, but also of its center, the Persian Gulf. He labeled the area surrounding the Persian Gulf as the Middle East, and said that after Egypt's Suez Canal, it was the most important passage for Britain to control in order to keep the Russians from advancing towards British India. Mahan first used the term in his article "The Persian Gulf and International Relations", published in September 1902 in the National Review, a British journal.

Mahan's article was reprinted in The Times and followed in October by a 20-article series entitled "The Middle Eastern Question," written by Sir Ignatius Valentine Chirol. During this series, Sir Ignatius expanded the definition of Middle East to include "those regions of Asia which extend to the borders of India or command the approaches to India." After the series ended in 1903, The Times removed quotation marks from subsequent uses of the term.

Until World War II, it was customary to refer to areas centered around Turkey and the eastern shore of the Mediterranean as the "Near East", while the "Far East" centered on China, and the Middle East then meant the area from Mesopotamia to Burma, namely the area between the Near East and the Far East. In the late 1930s, the British established the Middle East Command, which was based in Cairo, for its military forces in the region. After that time, the term "Middle East" gained broader usage in Europe and the United States, with the Middle East Institute founded in Washington, D.C. in 1946, among other usage.

The corresponding adjective is Middle Eastern and the derived noun is Middle Easterner.

While non-Eurocentric terms such "Southwest Asia" or "Swasia" has been sparsedly used, the inclusion of an African country, Egypt, in the definition questions the usefulness of using such terms.


The Nile is a major north-flowing river in northeastern Africa. It flows into the Mediterranean Sea. The Nile is the longest river in Africa and has historically been considered the longest river in the world, though this has been contested by research suggesting that the Amazon River is slightly longer. Of the world's major rivers, the Nile is one of the smallest, as measured by annual flow in cubic metres of water. About  long, its drainage basin covers eleven countries: the Democratic Republic of the Congo, Tanzania, Burundi, Rwanda, Uganda, Kenya, Ethiopia, Eritrea, South Sudan, Republic of the Sudan, and Egypt. In particular, the Nile is the primary water source of Egypt, Sudan and South Sudan. Additionally, the Nile is an important economic river, supporting agriculture and fishing.

The Nile has two major tributaries – the White Nile and the Blue Nile. The White Nile is traditionally considered to be the headwaters stream. However, the Blue Nile is the source of most of the water of the Nile downstream, containing 80% of the water and silt. The White Nile is longer and rises in the Great Lakes region. It begins at Lake Victoria and flows through Uganda and South Sudan. The Blue Nile begins at Lake Tana in Ethiopia and flows into Sudan from the southeast. The two rivers meet at the Sudanese capital of Khartoum.

The northern section of the river flows north almost entirely through the Nubian Desert to Cairo and its large delta, and the river flows into the Mediterranean Sea at Alexandria. Egyptian civilization and Sudanese kingdoms have depended on the river and its annual flooding since ancient times. Most of the population and cities of Egypt lie along those parts of the Nile valley north of Aswan Dam. Nearly all the cultural and historical sites of Ancient Egypt developed and are found along river banks. The Nile is, with the Rhône and Po, one of the three Mediterranean rivers with the largest water discharge.

The standard English names "White Nile" and "Blue Nile" refer to the river's source, derived from Arabic names formerly applied to only the Sudanese stretches that meet at Khartoum.

In the ancient Egyptian language, the Nile is called Ḥ'pī (Hapy) or Iteru, meaning "river". In Coptic, the word ⲫⲓⲁⲣⲟ, pronounced piaro (Sahidic) or phiaro (Bohairic), means "the river" (lit. p(h).iar-o "the.canal-great"), and comes from the same ancient name. In Nobiin the river is called Áman Dawū, meaning "the great water". In Luganda the river is called Kiira or Kiyira. In Runyoro it is called Kihiira. In Egyptian Arabic, the Nile is called en-Nīl, while in Standard Arabic it is called an-Nīl. In Biblical Hebrew, it is , Ha-Ye'or or , Ha-Shiḥor.

The English name Nile and the Arabic names en-Nîl and an-Nîl both derive from the Latin  and the Ancient Greek . Beyond that, however, the etymology is disputed. Homer called the river , Aiguptos, but in subsequent periods, Greek authors referred to its lower course as Neilos; this term became generalised for the entire river system. Thus, the name may derive from Ancient Egyptian expression nꜣ rꜣw-ḥꜣw(t) (lit. 'the mouths of the front parts'), which referred specifically to the branches of the Nile transversing the Delta, and would have been pronounced ni-lo-he in the area around Memphis in the 8th century BCE. Hesiod at his Theogony refers to Nilus (Νεῖλος) as one of the Potamoi (river gods), son of Oceanus and Tethys.

Another derivation of Nile might be related to the term Nil (; ), which refers to Indigofera tinctoria, one of the original sources of indigo dye. Another may be Nymphaea caerulea, known as "The Sacred Blue Lily of the Nile", which was found scattered over Tutankhamun's corpse when it was excavated in 1922. Another possible etymology derives from the Semitic term Nahal, meaning "river". Old Libyan has the term lilu, meaning water (in modern Berber ilel ⵉⵍⴻⵍ means sea).


In celestial mechanics, an orbit is the curved trajectory of an object such as the trajectory of a planet around a star, or of a natural satellite around a planet, or of an artificial satellite around an object or position in space such as a planet, moon, asteroid, or Lagrange point. Normally, orbit refers to a regularly repeating trajectory, although it may also refer to a non-repeating trajectory. To a close approximation, planets and satellites follow elliptic orbits, with the center of mass being orbited at a focal point of the ellipse, as described by Kepler's laws of planetary motion.

For most situations, orbital motion is adequately approximated by Newtonian mechanics, which explains gravity as a force obeying an inverse-square law. However, Albert Einstein's general theory of relativity, which accounts for gravity as due to curvature of spacetime, with orbits following geodesics, provides a more accurate calculation and understanding of the exact mechanics of orbital motion.

Historically, the apparent motions of the planets were described by European and Arabic philosophers using the idea of celestial spheres. This model posited the existence of perfect moving spheres or rings to which the stars and planets were attached. It assumed the heavens were fixed apart from the motion of the spheres and was developed without any understanding of gravity. After the planets' motions were more accurately measured, theoretical mechanisms such as deferent and epicycles were added. Although the model was capable of reasonably accurately predicting the planets' positions in the sky, more and more epicycles were required as the measurements became more accurate, hence the model became increasingly unwieldy. Originally geocentric, it was modified by Copernicus to place the Sun at the centre to help simplify the model. The model was further challenged during the 16th century, as comets were observed traversing the spheres.

The basis for the modern understanding of orbits was first formulated by Johannes Kepler whose results are summarised in his three laws of planetary motion. First, he found that the orbits of the planets in our Solar System are elliptical, not circular (or epicyclic), as had previously been believed, and that the Sun is not located at the center of the orbits, but rather at one focus. Second, he found that the orbital speed of each planet is not constant, as had previously been thought, but rather that the speed depends on the planet's distance from the Sun. Third, Kepler found a universal relationship between the orbital properties of all the planets orbiting the Sun. For the planets, the cubes of their distances from the Sun are proportional to the squares of their orbital periods. Jupiter and Venus, for example, are respectively about 5.2 and 0.723 AU distant from the Sun, their orbital periods respectively about 11.86 and 0.615 years. The proportionality is seen by the fact that the ratio for Jupiter, 5.23/11.862, is practically equal to that for Venus, 0.7233/0.6152, in accord with the relationship. Idealised orbits meeting these rules are known as Kepler orbits.

Isaac Newton demonstrated that Kepler's laws were derivable from his theory of gravitation and that, in general, the orbits of bodies subject to gravity were conic sections (this assumes that the force of gravity propagates instantaneously). Newton showed that, for a pair of bodies, the orbits' sizes are in inverse proportion to their masses, and that those bodies orbit their common center of mass. Where one body is much more massive than the other (as is the case of an artificial satellite orbiting a planet), it is a convenient approximation to take the center of mass as coinciding with the center of the more massive body.

Advances in Newtonian mechanics were then used to explore variations from the simple assumptions behind Kepler orbits, such as the perturbations due to other bodies, or the impact of spheroidal rather than spherical bodies. Joseph-Louis Lagrange developed a new approach to Newtonian mechanics emphasizing energy more than force, and made progress on the three-body problem, discovering the Lagrangian points. In a dramatic vindication of classical mechanics, in 1846 Urbain Le Verrier was able to predict the position of Neptune based on unexplained perturbations in the orbit of Uranus.

Albert Einstein in his 1916 paper The Foundation of the General Theory of Relativity explained that gravity was due to curvature of space-time and removed Newton's assumption that changes propagate instantaneously. This led astronomers to recognize that Newtonian mechanics did not provide the highest accuracy in understanding orbits. In relativity theory, orbits follow geodesic trajectories which are usually approximated very well by the Newtonian predictions (except where there are very strong gravity fields and very high speeds) but the differences are measurable. Essentially all the experimental evidence that can distinguish between the theories agrees with relativity theory to within experimental measurement accuracy. The original vindication of general relativity is that it was able to account for the remaining unexplained amount in precession of Mercury's perihelion first noted by Le Verrier. However, Newton's solution is still used for most short term purposes since it is significantly easier to use and sufficiently accurate.


An orchestra (; ) is a large instrumental ensemble typical of classical music, which combines instruments from different families, including
 bowed string instruments such as the violin, viola, cello, and double bass
 woodwinds such as the flute, oboe, clarinet, saxophone, and bassoon
 brass instruments such as the horn, trumpet, trombone, cornet, and tuba
 percussion instruments such as the timpani, snare drum, bass drum, cymbals, triangle, tambourine, and mallet percussion instruments
each grouped in sections.

Other instruments such as the piano, harpsichord, and celesta may sometimes appear in a fifth keyboard section or may stand alone as soloist instruments, as may the concert harp and, for performances of some modern compositions, electronic instruments and guitars.

A full-size Western orchestra may sometimes be called a  or philharmonic orchestra (from Greek phil-, "loving", and "harmony"). The actual number of musicians employed in a given performance may vary from seventy to over one hundred musicians, depending on the work being played and the size of the venue. A  (sometimes concert orchestra) is a smaller ensemble of not more than about fifty musicians. Orchestras that specialize in the Baroque music of, for example, Johann Sebastian Bach and George Frideric Handel, or Classical repertoire, such as that of Haydn and Mozart, tend to be smaller than orchestras performing a Romantic music repertoire, such as the symphonies of Johannes Brahms. The typical orchestra grew in size throughout the 18th and 19th centuries, reaching a peak with the large orchestras (of as many as 120 players) called for in the works of Richard Wagner, and later, Gustav Mahler.

Orchestras are usually led by a conductor who directs the performance with movements of the hands and arms, often made easier for the musicians to see by use of a conductor's baton. The conductor unifies the orchestra, sets the tempo and shapes the sound of the ensemble. The conductor also prepares the orchestra by leading rehearsals before the public concert, in which the conductor provides instructions to the musicians on their interpretation of the music being performed.

The leader of the first violin section – commonly called the concertmaster – also plays an important role in leading the musicians. In the Baroque music era (1600–1750), orchestras were often led by the concertmaster, or by a chord-playing musician performing the basso continuo parts on a harpsichord or pipe organ, a tradition that some 20th century and 21st century early music ensembles continue. Orchestras play a wide range of repertoire, including symphonies, opera and ballet overtures, concertos for solo instruments, and as pit ensembles for operas, ballets, and some types of musical theatre (e.g., Gilbert and Sullivan operettas).

Amateur orchestras include those made up of students from an elementary school or a high school, youth orchestras, and community orchestras; the latter two typically being made up of amateur musicians from a particular city or region.

The term orchestra derives from the Greek ὀρχήστρα (orchestra), the name for the area in front of a stage in ancient Greek theatre reserved for the Greek chorus.

The typical symphony orchestra consists of four groups of related musical instruments called the woodwinds, brass, percussion, and strings. Other instruments such as the piano and celesta may sometimes be grouped into a fifth section such as a keyboard section or may stand alone, as may the concert harp and electric and electronic instruments. The orchestra, depending on the size, contains almost all of the standard instruments in each group.

In the history of the orchestra, its instrumentation has been expanded over time, often agreed to have been standardized by the classical period and Ludwig van Beethoven's influence on the classical model. In the 20th and 21st century, new repertory demands expanded the instrumentation of the orchestra, resulting in a flexible use of the classical-model instruments and newly developed electric and electronic instruments in various combinations.

The terms symphony orchestra and philharmonic orchestra may be used to distinguish different ensembles from the same locality, such as the London Symphony Orchestra and the London Philharmonic Orchestra. A symphony or philharmonic orchestra will usually have over eighty musicians on its roster, in some cases over a hundred, but the actual number of musicians employed in a particular performance may vary according to the work being played and the size of the venue.

A chamber orchestra is usually a smaller ensemble; a major chamber orchestra might employ as many as fifty musicians, but some are much smaller. Concert orchestra is an alternative term, as in the BBC Concert Orchestra and the RTÉ Concert Orchestra.


Physical chemistry is the study of macroscopic and microscopic phenomena in chemical systems in terms of the principles, practices, and concepts of physics such as motion, energy, force, time, thermodynamics, quantum chemistry, statistical mechanics, analytical dynamics and chemical equilibria.

Physical chemistry, in contrast to chemical physics, is predominantly (but not always) a supra-molecular science, as the majority of the principles on which it was founded relate to the bulk rather than the molecular or atomic structure alone (for example, chemical equilibrium and colloids).

Some of the relationships that physical chemistry strives to resolve include the effects of:
 Intermolecular forces that act upon the physical properties of materials (plasticity, tensile strength, surface tension in liquids).
 Reaction kinetics on the rate of a reaction.
 The identity of ions and the electrical conductivity of materials.
 Surface science and electrochemistry of cell membranes.
 Interaction of one body with another in terms of quantities of heat and work called thermodynamics.
 Transfer of heat between a chemical system and its surroundings during change of phase or chemical reaction taking place called thermochemistry
 Study of colligative properties of number of species present in solution.
 Number of phases, number of components and degree of freedom (or variance) can be correlated with one another with help of phase rule.
 Reactions of electrochemical cells.
 Behaviour of microscopic systems using quantum mechanics and macroscopic systems using statistical thermodynamics.

Some journals that deal with physical chemistry include Zeitschrift für Physikalische Chemie (1887); Journal of Physical Chemistry A (from 1896 as Journal of Physical Chemistry, renamed in 1997); Physical Chemistry Chemical Physics (from 1999, formerly Faraday Transactions with a history dating back to 1905); Macromolecular Chemistry and Physics (1947); Annual Review of Physical Chemistry (1950); Molecular Physics (1957); Journal of Physical Organic Chemistry (1988); Journal of Physical Chemistry B (1997); ChemPhysChem (2000); Journal of Physical Chemistry C (2007); and Journal of Physical Chemistry Letters (from 2010, combined letters previously published in the separate journals)

Historical journals that covered both chemistry and physics include Annales de chimie et de physique (started in 1789, published under the name given here from 1815 to 1914).


Paul (previously called Saul of Tarsus;  AD), commonly known as Paul the Apostle and Saint Paul, was a Christian apostle who spread the teachings of Jesus in the first-century world. Generally regarded as one of the most important figures of the Apostolic Age, he founded several Christian communities in Asia Minor and Europe from the mid-40s to the mid-50s AD.

According to the New Testament book Acts of the Apostles, Paul was a Pharisee. He participated in the persecution of early disciples of Jesus, possibly Hellenised diaspora Jews converted to Christianity, in the area of Jerusalem, prior to his conversion. Some time after having approved of the execution of Stephen, Paul was traveling on the road to Damascus so that he might find any Christians there and bring them "bound to Jerusalem" (ESV). At midday, a light brighter than the sun shone around both him and those with him, causing all to fall to the ground, with the risen Christ verbally addressing Paul regarding his persecution. Having been made blind, along with being commanded to enter the city, his sight was restored three days later by Ananias of Damascus. After these events, Paul was baptized, beginning immediately to proclaim that Jesus of Nazareth was the Jewish messiah and the Son of God. Approximately half of the content in the book of Acts details the life and works of Paul.

Fourteen of the 27 books in the New Testament have traditionally been attributed to Paul. Seven of the Pauline epistles are undisputed by scholars as being authentic, with varying degrees of argument about the remainder. Pauline authorship of the Epistle to the Hebrews is not asserted in the Epistle itself and was already doubted in the 2nd and 3rd centuries. It was almost unquestioningly accepted from the 5th to the 16th centuries that Paul was the author of Hebrews, but that view is now almost universally rejected by scholars. The other six are believed by some scholars to have come from followers writing in his name, using material from Paul's surviving letters and letters written by him that no longer survive. Other scholars argue that the idea of a pseudonymous author for the disputed epistles raises many problems.

Today, Paul's epistles continue to be vital roots of the theology, worship and pastoral life in the Latin and Protestant traditions of the West, as well as the Eastern Catholic and Orthodox traditions of the East. Paul's influence on Christian thought and practice has been characterized as being as "profound as it is pervasive", among that of many other apostles and missionaries involved in the spread of the Christian faith.

Paul's Jewish name was "Saul" (), perhaps after the biblical King Saul, the first king of Israel and like Paul a member of the Tribe of Benjamin; the Latin name Paul, meaning small, was not a result of his conversion as it is commonly believed but a second name for use in communicating with a Greco-Roman audience.

According to the Acts of the Apostles, he was a Roman citizen. As such, he bore the Latin name "Paul" – in Latin  and in biblical Greek  (). It was typical for the Jews of that time to have two names: one Hebrew, the other Latin or Greek.

Jesus called him "Saul, Saul" in "the Hebrew tongue" in the Acts of the Apostles, when he had the vision which led to his conversion on the road to Damascus. Later, in a vision to Ananias of Damascus, "the Lord" referred to him as "Saul, of Tarsus". When Ananias came to restore his sight, he called him "Brother Saul".

In Acts 13:9, Saul is called "Paul" for the first time on the island of Cyprus – much later than the time of his conversion. The author of Luke–Acts indicates that the names were interchangeable: "Saul, who also is called Paul." He refers to him as Paul through the remainder of Acts. This was apparently Paul's preference since he is called Paul in all other Bible books where he is mentioned, including those that he authored. Adopting his Roman name was typical of Paul's missionary style. His method was to put people at their ease and to approach them with his message in a language and style to which they could relate, as in 1 Corinthians 9.


Quantum mechanics is a fundamental theory in physics that provides a description of the physical properties of nature at the scale of atoms and subatomic particles. It is the foundation of all quantum physics including quantum chemistry, quantum field theory, quantum technology, and quantum information science.

Classical physics, the collection of theories that existed before the advent of quantum mechanics, describes many aspects of nature at an ordinary (macroscopic) scale, but is not sufficient for describing them at small (atomic and subatomic) scales. Most theories in classical physics can be derived from quantum mechanics as an approximation valid at large (macroscopic) scale.

Quantum mechanics differs from classical physics in that energy, momentum, angular momentum, and other quantities of a bound system are restricted to discrete values (quantization); objects have characteristics of both particles and waves (wave–particle duality); and there are limits to how accurately the value of a physical quantity can be predicted prior to its measurement, given a complete set of initial conditions (the uncertainty principle).

Quantum mechanics arose gradually from theories to explain observations which could not be reconciled with classical physics, such as Max Planck's solution in 1900 to the black-body radiation problem, and the correspondence between energy and frequency in Albert Einstein's 1905 paper which explained the photoelectric effect. These early attempts to understand microscopic phenomena, now known as the "old quantum theory", led to the full development of quantum mechanics in the mid-1920s by Niels Bohr, Erwin Schrödinger, Werner Heisenberg, Max Born, Paul Dirac and others. The modern theory is formulated in various specially developed mathematical formalisms. In one of them, a mathematical entity called the wave function provides information, in the form of probability amplitudes, about what measurements of a particle's energy, momentum, and other physical properties may yield.

Quantum mechanics has had enormous success in explaining many of the features of our universe, with regards to small-scale and discrete quantities and interactions which cannot be explained by classical methods. Quantum mechanics is often the only theory that can reveal the individual behaviors of the subatomic particles that make up all forms of matter (electrons, protons, neutrons, photons, and others). Solid-state physics and materials science are dependent upon quantum mechanics.

In many aspects modern technology operates at a scale where quantum effects are significant. Important applications of quantum theory include quantum chemistry, quantum optics, quantum computing, superconducting magnets, light-emitting diodes, the optical amplifier and the laser, the transistor and semiconductors such as the microprocessor, medical and research imaging such as magnetic resonance imaging and electron microscopy. Explanations for many biological and physical phenomena are rooted in the nature of the chemical bond, most notably the macro-molecule DNA.


Roald Engelbregt Gravning Amundsen (, ; ; 16 July 1872 – ) was a Norwegian explorer of polar regions. He was a key figure of the period known as the Heroic Age of Antarctic Exploration.

Born in Borge, Østfold, Norway, Amundsen began his career as a polar explorer as first mate on Adrien de Gerlache's Belgian Antarctic Expedition of 1897–1899. From 1903 to 1906, he led the first expedition to successfully traverse the Northwest Passage on the sloop Gjøa. In 1909, Amundsen began planning for a South Pole expedition. He left Norway in June 1910 on the ship Fram and reached Antarctica in January 1911. His party established a camp at the Bay of Whales and a series of supply depots on the Barrier (now known as the Ross Ice Shelf) before setting out for the pole in October. The party of five, led by Amundsen, became the first to successfully reach the South Pole on 14 December 1911.

Following a failed attempt in 1918 to reach the North Pole by traversing the Northeast Passage on the ship Maud, Amundsen began planning for an aerial expedition instead. On 12 May 1926, Amundsen and 15 other men in the airship Norge became the first explorers verified to have reached the North Pole. Amundsen disappeared in June 1928 while flying on a rescue mission for the airship  in the Arctic. The search for his remains, which have not been found, was called off in September of that year.

Amundsen was born into a family of Norwegian shipowners and captains in Borge, between the towns Fredrikstad and Sarpsborg. His parents were Jens Amundsen and Hanna Sahlqvist. Roald was the fourth son in the family. His mother wanted him to avoid the family maritime trade and encouraged him to become a doctor, a promise that Amundsen kept until his mother died when he was aged 21. He promptly quit university for a life at sea.

When he was fifteen years old, Amundsen was enthralled by reading Sir John Franklin's narratives of his overland Arctic expeditions. Amundsen wrote "I read them with a fervid fascination which has shaped the whole course of my life".


A star is an astronomical object comprising a luminous spheroid of plasma held together by its gravity. The nearest star to Earth is the Sun. Many other stars are visible to the naked eye at night, but their immense distances from Earth make them appear as fixed points of light. The most prominent stars have been categorised into constellations and asterisms, and many of the brightest stars have proper names. Astronomers have assembled star catalogues that identify the known stars and provide standardized stellar designations. The observable universe contains an estimated  to  stars. Only about 4,000 of these stars are visible to the naked eye, all within the Milky Way galaxy.

A star's life begins with the gravitational collapse of a gaseous nebula of material composed primarily of hydrogen, along with helium and trace amounts of heavier elements. Its total mass is the main factor determining its evolution and eventual fate. A star shines for most of its active life due to the thermonuclear fusion of hydrogen into helium in its core. This process releases energy that traverses the star's interior and radiates into outer space. At the end of a star's lifetime, its core becomes a stellar remnant: a white dwarf, a neutron star, or—if it is sufficiently massive—a black hole.

Stellar nucleosynthesis in stars or their remnants creates almost all naturally occurring chemical elements heavier than lithium. Stellar mass loss or supernova explosions return chemically enriched material to the interstellar medium. These elements are then recycled into new stars. Astronomers can determine stellar properties—including mass, age, metallicity (chemical composition), variability, distance, and motion through space—by carrying out observations of a star's apparent brightness, spectrum, and changes in its position in the sky over time.

Stars can form orbital systems with other astronomical objects, as in the case of planetary systems and star systems with two or more stars. When two such stars have a relatively close orbit, their gravitational interaction can significantly impact their evolution. Stars can form part of a much larger gravitationally bound structure, such as a star cluster or a galaxy.

The concept of a constellation was known to exist during the Babylonian period. Ancient sky watchers imagined that prominent arrangements of stars formed patterns, and they associated these with particular aspects of nature or their myths. Twelve of these formations lay along the band of the ecliptic and these became the basis of astrology. Many of the more prominent individual stars were given names, particularly with Arabic or Latin designations.

As well as certain constellations and the Sun itself, individual stars have their own myths. To the Ancient Greeks, some "stars", known as planets (Greek πλανήτης (planētēs), meaning "wanderer"), represented various important deities, from which the names of the planets Mercury, Venus, Mars, Jupiter and Saturn were taken. (Uranus and Neptune were Greek and Roman gods, but neither planet was known in Antiquity because of their low brightness. Their names were assigned by later astronomers.)

Circa 1600, the names of the constellations were used to name the stars in the corresponding regions of the sky. The German astronomer Johann Bayer created a series of star maps and applied Greek letters as designations to the stars in each constellation. Later a numbering system based on the star's right ascension was invented and added to John Flamsteed's star catalogue in his book "Historia coelestis Britannica" (the 1712 edition), whereby this numbering system came to be called Flamsteed designation or Flamsteed numbering.

The internationally recognized authority for naming celestial bodies is the International Astronomical Union (IAU). The International Astronomical Union maintains the Working Group on Star Names (WGSN) which catalogs and standardizes proper names for stars. A number of private companies sell names of stars which are not recognized by the IAU, professional astronomers, or the amateur astronomy community. The British Library calls this an unregulated commercial enterprise, and the New York City Department of Consumer and Worker Protection issued a violation against one such star-naming company for engaging in a deceptive trade practice.


Sugar is the generic name for sweet-tasting, soluble carbohydrates, many of which are used in food. Simple sugars, also called monosaccharides, include glucose, fructose, and galactose. Compound sugars, also called disaccharides or double sugars, are molecules made of two bonded monosaccharides; common examples are sucrose (glucose + fructose), lactose (glucose + galactose), and maltose (two molecules of glucose). White sugar is a refined form of sucrose. In the body, compound sugars are hydrolysed into simple sugars.

Longer chains of monosaccharides (>2) are not regarded as sugars, and are called oligosaccharides or polysaccharides. Starch is a glucose polymer found in plants, and is the most abundant source of energy in human food. Some other chemical substances, such as glycerol and sugar alcohols, may have a sweet taste, but are not classified as sugar.

Sugars are found in the tissues of most plants. Honey and fruit are abundant natural sources of simple sugars. Sucrose is especially concentrated in sugarcane and sugar beet, making them ideal for efficient commercial extraction to make refined sugar. In 2016, the combined world production of those two crops was about two billion tonnes. Maltose may be produced by malting grain. Lactose is the only sugar that cannot be extracted from plants. It can only be found in milk, including human breast milk, and in some dairy products. A cheap source of sugar is corn syrup, industrially produced by converting corn starch into sugars, such as maltose, fructose and glucose.

Sucrose is used in prepared foods (e.g. cookies and cakes), is sometimes added to commercially available processed food and beverages, and may be used by people as a sweetener for foods (e.g. toast and cereal) and beverages (e.g. coffee and tea). The average person consumes about  of sugar each year, with North and South Americans consuming up to  and Africans consuming under .

As sugar consumption grew in the latter part of the 20th century, researchers began to examine whether a diet high in sugar, especially refined sugar, was damaging to human health. Excessive consumption of sugar has been implicated in the onset of obesity, diabetes, cardiovascular disease, and tooth decay. Numerous studies have tried to clarify those implications, but with varying results, mainly because of the difficulty of finding populations for use as controls that consume little or no sugar. In 2015, the World Health Organization recommended that adults and children reduce their intake of free sugars to less than 10%, and encouraged a reduction to below 5%, of their total energy intake.

The etymology reflects the spread of the commodity. From Sanskrit (śarkarā), meaning "ground or candied sugar", came Persian shakar, then to 12th century French sucre and the English sugar.

The English word jaggery, a coarse brown sugar made from date palm sap or sugarcane juice, has a similar etymological origin: Portuguese jágara from the Malayalam cakkarā, which is from the Sanskrit śarkarā.


A state is a centralized political organization that imposes and enforces rules over a population within a territory. There is no undisputed definition of a state. One widely used definition  comes from the German sociologist Max Weber: a "state" is a polity that maintains a monopoly on the legitimate use of violence, although other definitions are not uncommon. A state does not preclude the existence of a society, such as stateless societies like the Haudenosaunee Confederacy that "do not have either purely or even primarily political institutions or roles". The level of governance of a state, government being considered to form the fundamental apparatus of contemporary states, is used to determine whether it has failed.

In a federal union, the term "state" is sometimes used to refer to the federated polities that make up the federation. (Other terms that are used in such federal systems may include “province”, “region” or other terms.)

Most of the human population has existed within a state system for millennia; however, for most of prehistory people lived in stateless societies. The earliest forms of states arose about 5,500 years ago  as governments gained state capacity in conjunction with rapid growth of cities, invention of writing and codification of new forms of religion. Over time, a variety of forms of states developed, which used many different justifications for their existence (such as divine right, the theory of the social contract, etc.). Today, the modern nation state is the predominant form of state to which people are subject.

There is no academic consensus on the definition of the state. The term "state" refers to a set of different, but interrelated and often overlapping, theories about a certain range of political phenomena. According to Walter Scheidel, mainstream definitions of the state have the following in common: "centralized institutions that impose rules, and back them up by force, over a territorially circumscribed population; a distinction between the rulers and the ruled; and an element of autonomy, stability, and differentiation. These distinguish the state from less stable forms of organization, such as the exercise of chiefly power."

The most commonly used definition is by Max Weber who describes the state as a compulsory political organization with a centralized government that maintains a monopoly of the legitimate use of force within a certain territory. Weber writes that the state "is a human community that (successfully) claims the monopoly of the legitimate use of physical force within a given territory."

Charles Tilly defines states as "coercion-wielding organisations that are distinct from households and kinship groups and exercise clear priority in some respects over all other organizations within substantial territories." Tilly includes city-states, theocracies and empires in his definition along with nation-states, but excludes tribes, lineages, firms and churches. According to Tilly, states began appearing around 990, but became particularly prominent after 1490. Tilly defines a state's "essential minimal activities" as:

 War making – "eliminating or neutralizing their own rivals"
 State making – "eliminating or neutralizing their rivals inside their own territory"
 Protection – "eliminating or neutralizing the enemies of their clients"
 Extraction – "acquiring the means of carrying out the first three activities"
 Adjudication – "authoritative settlement of disputes among members of the population"
 Distribution – "intervention in the allocation of goods among the members of the population"
 Production – "control of the creation and transformation of goods and services produced by the population"

Modern academic definitions of the state frequently include the criteria that a state has to be recognized as such by the international community.

Liberal thought provides another possible teleology of the state. According to John Locke, the goal of the state or commonwealth is "the preservation of property" (Second Treatise on Government), with 'property' in Locke's work referring not only to personal possessions but also to one's life and liberty. On this account, the state provides the basis for social cohesion and productivity, creating incentives for wealth-creation by providing guarantees of protection for one's life, liberty and personal property. Provision of public goods is considered by some such as Adam Smith as a central function of the state, since these goods would otherwise be underprovided. Tilly has challenged narratives of the state as being the result of a societal contract or provision of services in a free market – he characterizes the state more akin as a protection racket in the vein of organized crime.

While economic and political philosophers have contested the monopolistic tendency of states, Robert Nozick argues that the use of force naturally tends towards monopoly.

Another commonly accepted definition of the state is the one given at the Montevideo Convention on Rights and Duties of States in 1933. It provides that "[t]he state as a person of international law should possess the following qualifications: (a) a permanent population; (b) a defined territory; (c) government; and (d) capacity to enter into relations with the other states." And that "[t]he federal state shall constitute a sole person in the eyes of international law."

Confounding the definition problem is that "state" and "government" are often used as synonyms in common conversation and even some academic discourse. According to this definition schema, the states are nonphysical persons of international law, governments are organizations of people. The relationship between a government and its state is one of representation and authorized agency.


Tea or cha is an aromatic beverage prepared by pouring hot or boiling water over cured or fresh leaves of Camellia sinensis, an evergreen shrub native to East Asia which probably originated in the borderlands of southwestern China and northern Myanmar. Tea is also rarely made from the leaves of Camellia taliensis. After plain water, tea is the most widely consumed drink in the world. There are many different types of tea; some have a cooling, slightly bitter, and astringent flavour, while others have vastly different profiles that include sweet, nutty, floral, or grassy notes. Tea has a stimulating effect in humans primarily due to its caffeine content.

An early credible record of tea drinking dates to the third century AD, in a medical text written by Chinese physician Hua Tuo. It was popularised as a recreational drink during the Chinese Tang dynasty, and tea drinking subsequently spread to other East Asian countries. Portuguese priests and merchants introduced it to Europe during the 16th century. During the 17th century, drinking tea became fashionable among the English, who started to plant tea on a large scale in British India.

The term herbal tea refers to drinks not made from Camellia sinensis. They are the infusions of fruit, leaves, or other plant parts, such as steeps of rosehip, chamomile, or rooibos. These may be called tisanes or herbal infusions to prevent confusion with tea made from the tea plant.

The etymology of the various words for tea reflects the history of transmission of tea drinking culture and trade from China to countries around the world. Nearly all of the words for tea worldwide fall into three broad groups: te, cha and chai, present in English as tea, cha or char, and chai.  The earliest of the three to enter English is cha, which came in the 1590s via the Portuguese, who traded in Macao and picked up the Cantonese pronunciation of the word. The more common tea form arrived in the 17th century via the Dutch, who acquired it either indirectly from the Malay teh, or directly from the tê pronunciation in Min Chinese. The third form chai (meaning "spiced tea") originated from a northern Chinese pronunciation of cha, which travelled overland to Central Asia and Persia where it picked up a Persian ending yi.


A tool is an object that can extend an individual's ability to modify features of the surrounding environment. Although many animals use simple tools, only human beings, whose use of stone tools dates back hundreds of millennia, have been observed using tools to make other tools.

Early human tools, made of such materials as stone, bone, and wood, were used for preparation of food, hunting, manufacture of weapons, and working of materials to produce clothing and useful artifacts. The development of metalworking made additional types of tools possible. Harnessing energy sources, such as animal power, wind, or steam, allowed increasingly complex tools to produce an even larger range of items, with the Industrial Revolution marking an inflection point in the use of tools. The introduction of widespread automation in the 19th and 20th centuries allowed tools to operate with minimal human supervision, further increasing the productivity of human labor.

While a common-sense understanding of the meaning of tool is widespread, several formal definitions have been proposed.

In 1981, Benjamin Beck published a widely used definition of tool use. This has been modified to:Other, briefer definitions have been proposed:


A fertilizer (American English) or fertiliser (British English; see spelling differences) is any material of natural or synthetic origin that is applied to soil or to plant tissues to supply plant nutrients. Fertilizers may be distinct from liming materials or other non-nutrient soil amendments. Many sources of fertilizer exist, both natural and industrially produced. For most modern agricultural practices, fertilization focuses on three main macro nutrients: nitrogen (N), phosphorus (P), and potassium (K) with occasional addition of supplements like rock dust for micronutrients. Farmers apply these fertilizers in a variety of ways: through dry or pelletized or liquid application processes, using large agricultural equipment or hand-tool methods.

Historically fertilization came from natural or organic sources: compost, animal manure, human manure, harvested minerals, crop rotations and byproducts of human-nature industries (i.e. fish processing waste, or bloodmeal from animal slaughter). However, starting in the 19th century, after innovations in plant nutrition, an agricultural industry developed around synthetically created fertilizers. This transition was important in transforming the global food system, allowing for larger-scale industrial agriculture with large crop yields.

Nitrogen-fixing chemical processes such as the Haber process at the beginning of the 20th century, amplified by production capacity created during World War II led to a boom in using nitrogen fertilizers. In the latter half of the 20th century, increased the use of nitrogen fertilizers (800% increase between 1961 and 2019) have been a crucial component of the increased productivity of conventional food systems (more than 30% per capita) as part of the so-called "Green Revolution". The use of artificial and industrially-applied fertilizers has led to a number of environmental impacts, creating water pollution and Eutrophication caused by nutritional runoff, carbon and other emissions from fertilizer production and mining, and contamination and pollution of soil. Various types of sustainable agriculture practices can be implemented to reduce the environmental impact of fertilizer uses alongside other environmental impacts of agriculture.

Fertilizers are classified in several ways.  They are classified according to whether they provide a single nutrient (e.g., K, P, or N), in which case they are classified as "straight fertilizers."  "multinutrient fertilizers" (or "complex fertilizers") provide two or more nutrients, for example N and P.  Fertilizers are also sometimes classified as inorganic (the topic of most of this article) versus organic.  Inorganic fertilizers exclude carbon-containing materials except ureas.  Organic fertilizers are usually (recycled) plant- or animal-derived matter.  Inorganic are sometimes called synthetic fertilizers since various chemical treatments are required for their manufacture.


The Himalayas, or Himalaya (; ; ), is a mountain range in Asia, separating the plains of the Indian subcontinent from the Tibetan Plateau. The range has some of the planet's highest peaks, including the very highest, Mount Everest. Over 100 peaks exceeding  in elevation lie in the Himalayas. By contrast, the highest peak outside Asia (Aconcagua, in the Andes) is  tall.

The Himalayas abut or cross five countries: Bhutan, India, Nepal, China, and Pakistan. The sovereignty of the range in the Kashmir region is disputed among India, Pakistan, and China. The Himalayan range is bordered on the northwest by the Karakoram and Hindu Kush ranges, on the north by the Tibetan Plateau, and on the south by the Indo-Gangetic Plain. Some of the world's major rivers, the Indus, the Ganges, and the Tsangpo–Brahmaputra, rise in the vicinity of the Himalayas, and their combined drainage basin is home to some 600 million people; 53 million people live in the Himalayas. The Himalayas have profoundly shaped the cultures of South Asia and Tibet. Many Himalayan peaks are sacred in Hinduism and Buddhism; the summits of several—Kangchenjunga (from the Indian side), Gangkhar Puensum, Machapuchare, Nanda Devi and Kailas in the Tibetan Transhimalaya—are off-limits to climbers.

Lifted by the subduction of the Indian tectonic plate under the Eurasian Plate, the Himalayan mountain range runs west-northwest to east-southeast in an arc  long. Its western anchor, Nanga Parbat, lies just south of the northernmost bend of the Indus river. Its eastern anchor, Namcha Barwa, lies immediately west of the great bend of the Yarlung Tsangpo River. The range varies in width from  in the west to  in the east.

The Himalayas are home to a diversity of medicinal resources. Plants from the forests have been used for millennia to treat conditions ranging from simple coughs to snake bites. Different parts of the plants – root, flower, stem, leaves, and bark – are used as remedies for different ailments. For example, a bark extract from an Abies pindrow tree is used to treat coughs and bronchitis. Leaf and stem paste from an Andrachne cordifolia is used for wounds and as an antidote for snake bites. The bark of a Callicarpa arborea is used for skin ailments. Nearly a fifth of the gymnosperms, angiosperms and pteridophytes in the Himalayas are found to have medicinal properties, and more are likely to be discovered.

Most of the population in some Asian and African countries depends on medicinal plants rather than prescriptions and such. Since so many people use medicinal plants as their only source of healing in the Himalayas, the plants are an important source of income. This contributes to economic and modern industrial development both inside and outside the region. The only problem is that locals are rapidly clearing the forests on the Himalayas for wood, often illegally.


Obesity is a medical condition, sometimes considered a disease, in which abnormal or excess body fat has accumulated to such an extent that it may have a negative effect on health. People are classified as obese when their body mass index (BMI)—a measurement obtained by dividing a person's weight by the square of the person's height (despite known allometric inaccuracies)—is over ; the range  is defined as overweight. Some East Asian countries use lower values to calculate obesity.

Obesity is a major cause of disability and is correlated with various diseases and conditions, particularly cardiovascular diseases, type 2 diabetes, obstructive sleep apnea, certain types of cancer, and osteoarthritis. High BMI is a marker of risk for, but not a direct cause of, diseases caused by diet and physical activity. A reciprocal link has been found between obesity and depression, with obesity increasing the risk of clinical depression, and also depression leading to a higher chance of developing obesity.

Obesity has individual, socioeconomic, and environmental causes. Some of the known causes are diet, physical activity, automation, urbanization, genetic susceptibility, medications, mental disorders, economic policies, endocrine disorders, and exposure to endocrine-disrupting chemicals.
Epidemiologic studies of overweight and obesity in children and adults covering 195 countries have shown that the prevalence of obesity has steadily increased in most countries, doubling in 73 countries between the years 1980 and 2015. As of 2015, the United States and China had the largest numbers of obese adults, and China and India had the largest numbers of obese children. By 2018, 42% of Americans were obese.

While a majority of obese individuals at any given time are attempting to lose weight and are often successful, research shows that maintaining that weight loss over the long term proves to be rare. The reasons for weight cycling are not fully understood but may include decreased energy expenditure combined with an increased biological urge to eat during and after caloric restriction. More studies are needed to determine if weight cycling and yo-yo dieting contribute to inflammation and disease risk in obese individuals.

Although there is no effective, well-defined, evidence-based intervention for preventing obesity, obesity prevention will require a complex approach, including interventions at community, family, and individual levels. Changes to diet and exercising are the main treatments recommended by health professionals. Diet quality can be improved by reducing the consumption of energy-dense foods, such as those high in fat or sugars, and by increasing the intake of dietary fiber. However, large-scale analyses have found an inverse relationship between energy density and energy cost of foods in developed nations. Medications can be used, along with a suitable diet, to reduce appetite or decrease fat absorption. If diet, exercise, and medication are not effective, a gastric balloon or surgery may be performed to reduce stomach volume or length of the intestines, leading to feeling full earlier, or a reduced ability to absorb nutrients from food.

Obesity is a leading preventable cause of death worldwide, with increasing rates in adults and children. In 2015, 600 million adults (12%) and 100 million children were obese in 195 countries. Obesity is more common in women than in men. Public health officials view it as one of the most serious public health problems of the 21st century. Today, obesity is stigmatized in most of the world. Conversely, some cultures, past and present, have a favorable view of obesity, seeing it as a symbol of wealth and fertility. Nevertheless, in 2013, several medical societies, including the American Medical Association and the American Heart Association, classified obesity as a disease.

The main treatment for obesity consists of weight loss via lifestyle interventions, including prescribed diets and physical exercise. Although it is unclear what diets might support long-term weight loss, and although the effectiveness of low-calorie diets is debated, lifestyle changes that reduce calorie consumption or increase physical exercise over the long term also tend to produce some sustained weight loss, despite slow weight regain over time. Although 87% of participants in the National Weight Control Registry were able to maintain 10% body weight loss for 10 years, the most appropriate dietary approach for long term weight loss maintenance is still unknown. In the US, intensive behavioral interventions combining both dietary changes and exercise are recommended. Intermittent fasting has no additional benefit of weight loss compared to continuous energy restriction. Adherence is a more important factor in weight loss success than whatever kind of diet an individual undertakes.

Several hypo-caloric diets are effective. In the short-term low carbohydrate diets appear better than low fat diets for weight loss. In the long term, however, all types of low-carbohydrate and low-fat diets appear equally beneficial. A 2014 review found that the heart disease and diabetes risks associated with different diets appear to be similar. Promotion of the Mediterranean diets among the obese may lower the risk of heart disease. Decreased intake of sweet drinks is also related to weight-loss. Success rates of long-term weight loss maintenance with lifestyle changes are low, ranging from 2–20%. Dietary and lifestyle changes are effective in limiting excessive weight gain in pregnancy and improve outcomes for both the mother and the child. Intensive behavioral counseling is recommended in those who are both obese and have other risk factors for heart disease.


An electric motor is an electrical machine that converts electrical energy into mechanical energy. Most electric motors operate through the interaction between the motor's magnetic field and electric current in a wire winding to generate force in the form of torque applied on the motor's shaft. An electric generator is mechanically identical to an electric motor, but operates with a reversed flow of power, converting mechanical energy into electrical energy.

Electric motors can be powered by direct current (DC) sources, such as from batteries, or rectifiers, or by alternating current (AC) sources, such as a power grid, inverters or electrical generators.

Electric motors may be classified by considerations such as power source type, construction, application and type of motion output. They can be powered by AC or DC, be brushed or brushless, single-phase, two-phase, or three-phase, axial or radial flux, and may be air-cooled or liquid-cooled.

Standardized motors provide convenient mechanical power for industrial use. The largest are used for ship propulsion, pipeline compression and pumped-storage applications with output exceeding 100 megawatts.

Applications include industrial fans, blowers and pumps, machine tools, household appliances, power tools, vehicles, and disk drives. Small motors may be found in electric watches. In certain applications, such as in regenerative braking with traction motors, electric motors can be used in reverse as generators to recover energy that might otherwise be lost as heat and friction.

Electric motors produce linear or rotary force (torque) intended to propel some external mechanism, such as a fan or an elevator. An electric motor is generally designed for continuous rotation, or for linear movement over a significant distance compared to its size. Magnetic solenoids are also transducers that convert electrical power to mechanical motion, but can produce motion over only a limited distance.

Electric motors operate on one of three physical principles: magnetism, electrostatics and piezoelectricity.

In magnetic motors, magnetic fields are formed in both the rotor and the stator. The product between these two fields gives rise to a force, and thus a torque on the motor shaft. One, or both, of these fields must change with the rotation of the rotor. This is done by switching the poles on and off at the right time, or varying the strength of the pole.

The main types are DC motors and AC motors, with the latter replacing the former.

AC electric motors are either asynchronous or synchronous.

Once started, a synchronous motor requires synchrony with the moving magnetic field's speed for all normal torque conditions.

In synchronous machines, the magnetic field must be provided by means other than induction, such as from separately excited windings or permanent magnets.

A fractional-horsepower motor either has a rating below about 1 horsepower (0.746 kW), or is manufactured with a standard-frame size smaller than a standard 1 HP motor. Many household and industrial motors are in the fractional-horsepower class.

Notes:

 Rotation is independent of the frequency of the AC voltage.
 Rotation is equal to synchronous speed (motor-stator-field speed).
 In SCIM, fixed-speed operation rotation is equal to synchronous speed, less slip speed.
 In non-slip energy-recovery systems, WRIM is usually used for motor-starting but can be used to vary load speed.
 Variable-speed operation.
 Whereas induction- and synchronous-motor drives are typically with either six-step or sinusoidal-waveform output, BLDC-motor drives are usually with trapezoidal-current waveform; the behavior of both sinusoidal and trapezoidal PM machines is, however, identical in terms of their fundamental aspects.
 In variable-speed operation, WRIM is used in slip-energy recovery and double-fed induction-machine applications.
 A cage winding is a shorted-circuited squirrel-cage rotor, a wound winding is connected externally through slip rings.
 Mostly single-phase with some three-phase.

Abbreviations:

 BLAC – Brushless AC
 BLDC – Brushless DC
 BLDM – Brushless DC motor
 EC – Electronic commutator
 PM – Permanent magnet
 IPMSM – Interior permanent-magnet synchronous motor
 PMSM – Permanent magnet synchronous motor
 SPMSM – Surface permanent magnet synchronous motor
 SCIM – Squirrel-cage induction motor
 SRM – Switched reluctance motor
 SyRM – Synchronous reluctance motor
 VFD – Variable-frequency drive
 WRIM – Wound-rotor induction motor
 WRSM – Wound-rotor synchronous motor
 LRA – Locked-rotor amps: The current you can expect under starting conditions when you apply full voltage. It occurs instantly during start-up.
 RLA – Rated-load amps: The maximum current a motor should draw under any operating conditions. Often mistakenly called running-load amps, which leads people to believe, incorrectly, that the motor should always pull these amps.
 FLA – Full-load amps: Changed in 1976 to "RLA – rated-load amps".


Health, according to the World Health Organization, is "a state of complete physical, mental and social well-being and not merely the absence of disease and infirmity". A variety of definitions have been used for different purposes over time. Health can be promoted by encouraging healthful activities, such as regular physical exercise and adequate sleep, and by reducing or avoiding unhealthful activities or situations, such as smoking or excessive stress. Some factors affecting health are due to individual choices, such as whether to engage in a high-risk behavior, while others are due to structural causes, such as whether the society is arranged in a way that makes it easier or harder for people to get necessary healthcare services. Still, other factors are beyond both individual and group choices, such as genetic disorders.

The meaning of health has evolved over time. In keeping with the biomedical perspective, early definitions of health focused on the theme of the body's ability to function; health was seen as a state of normal function that could be disrupted from time to time by disease. An example of such a definition of health is: "a state characterized by anatomic, physiologic, and psychological integrity; ability to perform personally valued family, work, and community roles; ability to deal with physical, biological, psychological, and social stress". Then, in 1948, in a radical departure from previous definitions, the World Health Organization (WHO) proposed a definition that aimed higher, linking health to well-being, in terms of "physical, mental, and social well-being, and not merely the absence of disease and infirmity". Although this definition was welcomed by some as being innovative, it was also criticized for being vague and excessively broad and was not construed as measurable. For a long time, it was set aside as an impractical ideal, with most discussions of health returning to the practicality of the biomedical model.

Just as there was a shift from viewing disease as a state to thinking of it as a process, the same shift happened in definitions of health. Again, the WHO played a leading role when it fostered the development of the health promotion movement in the 1980s. This brought in a new conception of health, not as a state, but in dynamic terms of resiliency, in other words, as "a resource for living". In 1984, WHO revised the definition of health defined it as "the extent to which an individual or group is able to realize aspirations and satisfy needs and to change or cope with the environment. Health is a resource for everyday life, not the objective of living; it is a positive concept, emphasizing social and personal resources, as well as physical capacities." Thus, health referred to the ability to maintain homeostasis and recover from adverse events. Mental, intellectual, emotional and social health referred to a person's ability to handle stress, to acquire skills, to maintain relationships, all of which form resources for resiliency and independent living. This opens up many possibilities for health to be taught, strengthened and learned.

Since the late 1970s, the federal Healthy People Program has been a visible component of the United States’ approach to improving population health. In each decade, a new version of Healthy People is issued, featuring updated goals and identifying topic areas and quantifiable objectives for health improvement during the succeeding ten years, with assessment at that point of progress or lack thereof. Progress has been limited to many objectives, leading to concerns about the effectiveness of Healthy People in shaping outcomes in the context of a decentralized and uncoordinated US health system. Healthy People 2020 gives more prominence to health promotion and preventive approaches and adds a substantive focus on the importance of addressing social determinants of health. A new expanded digital interface facilitates use and dissemination rather than bulky printed books as produced in the past. The impact of these changes to Healthy People will be determined in the coming years.

Systematic activities to prevent or cure health problems and promote good health in humans are undertaken by health care providers. Applications with regard to animal health are covered by the veterinary sciences. The term "healthy" is also widely used in the context of many types of non-living organizations and their impacts for the benefit of humans, such as in the sense of healthy communities, healthy cities or healthy environments. In addition to health care interventions and a person's surroundings, a number of other factors are known to influence the health status of individuals. These are referred to as the "determinants of health", which include the individual's background, lifestyle, economic status, social conditions and spirituality; Studies have shown that high levels of stress can affect human health.

In the first decade of the 21st century, the conceptualization of health as an ability opened the door for self-assessments to become the main indicators to judge the performance of efforts aimed at improving human health. It also created the opportunity for every person to feel healthy, even in the presence of multiple chronic diseases or a terminal condition, and for the re-examination of determinants of health (away from the traditional approach that focuses on the reduction of the prevalence of diseases).


The World Health Organization describes mental health as "a state of well-being in which the individual realizes his or her own abilities, can cope with the normal stresses of life, can work productively and fruitfully, and is able to make a contribution to his or her community". Mental health is not just the absence of mental illness.

Mental illness is described as 'the spectrum of cognitive, emotional, and behavioral conditions that interfere with social and emotional well-being and the lives and productivity of people. Having a mental illness can seriously impair, temporarily or permanently, the mental functioning of a person. Other terms include: 'mental health problem', 'illness', 'disorder', 'dysfunction'.

Approximately twenty percent of all adults in the US are considered diagnosable with a mental illness. Mental illnesses are the leading cause of disability in the US and Canada. Examples of these illnesses include schizophrenia, ADHD, major depressive disorder, bipolar disorder, anxiety disorder, post-traumatic stress disorder and autism.

 Many factors contribute to mental health problems, including:
 Biological factors, such as genes or brain chemistry
 Life experiences, such as trauma or abuse
 Family history of mental health problems


The common cold, also known simply as a cold, is a viral infectious disease of the upper respiratory tract that primarily affects the respiratory mucosa of the nose, throat, sinuses, and larynx. Signs and symptoms may appear less than two days after exposure to the virus. These may include coughing, sore throat, runny nose, sneezing, headache, and fever. People usually recover in seven to ten days, but some symptoms may last up to three weeks. Occasionally, those with other health problems may develop pneumonia.

Well over 200 virus strains are implicated in causing the common cold, with rhinoviruses, coronaviruses, adenoviruses and enteroviruses being the most common. They spread through the air during close contact with infected people or indirectly through contact with objects in the environment, followed by transfer to the mouth or nose. Risk factors include going to child care facilities, not sleeping well, and psychological stress. The symptoms are mostly due to the body's immune response to the infection rather than to tissue destruction by the viruses themselves. The symptoms of influenza are similar to those of a cold, although usually more severe and less likely to include a runny nose.

There is no vaccine for the common cold. The primary methods of prevention are hand washing; not touching the eyes, nose or mouth with unwashed hands; and staying away from sick people. Some evidence supports the use of face masks. There is also no cure, but the symptoms can be treated. Zinc may reduce the duration and severity of symptoms if started shortly after the onset of symptoms. Nonsteroidal anti-inflammatory drugs (NSAIDs) such as ibuprofen may help with pain. Antibiotics, however, should not be used, as all colds are caused by viruses, and there is no good evidence that cough medicines are effective.

The common cold is the most frequent infectious disease in humans. Under normal circumstances, the average adult gets two to three colds a year, while the average child may get six to eight. Infections occur more commonly during the winter. These infections have existed throughout human history.

The common cold is the most common human disease and affects people all over the globe. Adults typically have two to three infections annually, and children may have six to ten colds a year (and up to twelve colds a year for school children). Rates of symptomatic infections increase in the elderly due to declining immunity.

Native Americans and Inuit are more likely to be infected with colds and develop complications such as otitis media than Caucasians. This may be explained as much by issues such as poverty and overcrowding as by ethnicity.


Domestication is a sustained multi-generational relationship in  which humans assume a significant degree of control over the reproduction and care of another group of organisms to secure a more predictable supply of resources from that group. A broader biological definition is that it is a coevolutionary process that arises from a mutualism, in which one species (the domesticator) constructs an environment where it actively manages both the survival and reproduction of another species (the domesticate) in order to provide the former with resources and/or services. The domestication of plants and animals by humans was a major cultural innovation ranked in importance with the conquest of fire, the manufacturing of tools, and the development of verbal language.

Charles Darwin recognized the small number of traits that made domestic species different from their wild ancestors. He was also the first to recognize the difference between conscious selective breeding (i.e. artificial selection) in which humans directly select for desirable traits, and unconscious selection where traits evolve as a by-product of natural selection or from selection on other traits. There is a genetic difference between domestic and wild populations. There is also such a difference between the domestication traits that researchers believe to have been essential at the early stages of domestication, and the improvement traits that have appeared since the split between wild and domestic populations. Domestication traits are generally fixed within all domesticates, and were selected during the initial episode of domestication of that animal or plant, whereas improvement traits are present only in a proportion of domesticates, though they may be fixed in individual breeds or regional populations.

The dog was the first domesticated species, and was established across Eurasia before the end of the Late Pleistocene era, well before cultivation and before the domestication of other animals. The archaeological and genetic data suggest that long-term bidirectional gene flow between wild and domestic stocks – including donkeys,  horses, New and Old World camelids, goats, sheep, and pigs – was common. Given its importance to humans and its value as a model of evolutionary and demographic change, domestication has attracted scientists from archaeology, paleontology, anthropology, botany, zoology, genetics, and the environmental sciences.
Among birds, the major domestic species today is the chicken, important for meat and eggs, though economically valuable poultry include the turkey, guineafowl and numerous other species. Birds are also widely kept as cagebirds, from songbirds to parrots. The longest established invertebrate domesticates are the honey bee and the silkworm. Land snails are raised for food, while species from several phyla are kept for research, and others are bred for biological control.

The domestication of plants began at least 12,000 years ago with cereals in the Middle East, and the bottle gourd in Asia. Agriculture developed in at least 11 different centres around the world, domesticating different crops and animals.

The earliest human attempts at plant domestication occurred in the Middle East. There is early evidence for conscious cultivation and trait selection of plants by pre-Neolithic groups in Syria: grains of rye with domestic traits dated 13,000 years ago have been recovered from Abu Hureyra in Syria, but this appears to be a localised phenomenon resulting from cultivation of stands of wild rye, rather than a definitive step towards domestication.

The bottle gourd (Lagenaria siceraria) plant, used as a container before the advent of ceramic technology, appears to have been domesticated 10,000 years ago. The domesticated bottle gourd reached the Americas from Asia by 8,000 years ago, most likely due to the migration of peoples from Asia to America.

Cereal crops were first domesticated around 11,000 years ago in the Fertile Crescent in the Middle East. The first domesticated crops were generally annuals with large seeds or fruits. These included pulses such as peas and grains such as wheat. The Middle East was especially suited to these species; the dry-summer climate was conducive to the evolution of large-seeded annual plants, and the variety of elevations led to a great variety of species. As domestication took place humans began to move from a hunter-gatherer society to a settled agricultural society. This change would eventually lead, some 4000 to 5000 years later, to the first city states and eventually the rise of civilization itself.

Continued domestication was gradual, a process of intermittent trial and error, and often resulted in diverging traits and characteristics. Over time perennials and small trees including the apple and the olive were domesticated. Some plants, such as the macadamia nut and the pecan, were not domesticated until recently.

In other parts of the world very different species were domesticated. In the Americas squash, maize, beans, and perhaps manioc (also known as cassava) formed the core of the diet. In East Asia millet, rice, and soy were the most important crops. Some areas of the world such as Southern Africa, Australia, California and southern South America never saw local species domesticated.


The Scramble for Africa, also called the Partition of Africa, or Conquest of Africa,  was the invasion, annexation, division, and colonization of most of Africa by seven Western European powers during a short period known as New Imperialism (between 1881 and 1914). The 10 percent of Africa that was under formal European control in 1870 increased to almost 90 percent by 1914, with only Liberia and Abyssinia remaining independent.

The Berlin Conference of 1884, which regulated European colonization and trade in Africa, is usually accepted as the beginning. In the last quarter of the 19th century, there were considerable political rivalries within the empires of the European continent, leading to the African continent being partitioned without wars between European nations. The later years of the 19th century saw a transition from "informal imperialism" – military influence and economic dominance – to direct rule.

By 1841, businessmen from Europe had established small trading posts along the coasts of Africa, but they seldom moved inland, preferring to stay near the sea. They primarily traded with locals. Large parts of the continent were essentially uninhabitable for Europeans because of their high mortality rates from tropical diseases such as malaria. In the middle of the 19th century, European explorers mapped much of East Africa and Central Africa.

As late as the 1870s, Europeans controlled approximately 10% of the African continent, with all their territories located near the coasts. The most important holdings were Angola and Mozambique, held by Portugal; the Cape Colony, held by Great Britain; and Algeria, held by France. By 1914, only Ethiopia and Liberia remained independent of European control, with the latter having strong connections to the United States.

Technological advances facilitated European expansion overseas. Industrialization brought about rapid advancements in transportation and communication, especially in the forms of steamships, railways and telegraphs. Medical advances also played an important role, especially medicines for tropical diseases, which helped control their adverse effects. The development of quinine, an effective treatment for malaria, made vast expanses of the tropics more accessible for Europeans.


The Cold War is a term commonly used to refer to a period of geopolitical tension between the United States and the Soviet Union and their respective allies, the Western Bloc and the Eastern Bloc. Historians do not fully agree on its starting and ending points, but the period is generally considered to span from the announcement of the Truman Doctrine on 12 March 1947 to the dissolution of the Soviet Union on 26 December 1991. The term cold war is used because there was no large-scale fighting directly between the two superpowers, but they each supported major regional conflicts known as proxy wars. The conflict was based around the ideological and geopolitical struggle for global influence by these two superpowers, following their temporary alliance and victory against Nazi Germany and Imperial Japan in 1945. Aside from the nuclear arsenal development and conventional military deployment, the struggle for dominance was expressed via indirect means such as psychological warfare, propaganda campaigns, espionage, far-reaching embargoes, rivalry at sports events, and technological competitions such as the Space Race.

The Western Bloc was led by the United States as well as a number of other First World nations that were generally liberal democratic but tied to a network of authoritarian states, most of which were their former colonies. The Eastern Bloc was led by the Soviet Union and its Communist Party, which had an influence across the Second World and was also tied to a network of authoritarian states. The US government supported anti-communist and right-wing governments and uprisings across the world, while the Soviet government funded left-wing parties and revolutions around the world. As nearly all the colonial states achieved independence in the period from 1945 to 1960, they became Third World battlefields in the Cold War.

The first phase of the Cold War began shortly after the end of World War II in 1945. The United States and its allies created the NATO military alliance in 1949 in the apprehension of a Soviet attack and termed their global policy against Soviet influence containment. The Soviet Union formed the Warsaw Pact in 1955 in response to NATO. Major crises of this phase included the 1948–1949 Berlin Blockade, the 1945–1949 Chinese Communist Revolution, the 1950–1953 Korean War, the 1956 Hungarian Revolution, the 1956 Suez Crisis, the 1961 Berlin Crisis, the 1962 Cuban Missile Crisis, and the 1964–1975 Vietnam War. The US and the USSR competed for influence in Latin America, the Middle East, and the decolonizing states of Africa, Asia, and Oceania.

Following the Cuban Missile Crisis, a new phase began that saw the Sino-Soviet split between China and the Soviet Union complicate relations within the Communist sphere leading to a series of border confrontations, while France, a Western Bloc state, began to demand greater autonomy of action. The USSR invaded Czechoslovakia to suppress the 1968 Prague Spring, while the US experienced internal turmoil from the civil rights movement and opposition to the Vietnam War. In the 1960s–1970s, an international peace movement took root among citizens around the world. Movements against nuclear weapons testing and for nuclear disarmament took place, with large anti-war protests. By the 1970s, both sides had started making allowances for peace and security, ushering in a period of détente that saw the Strategic Arms Limitation Talks and the US opening relations with the People's Republic of China as a strategic counterweight to the USSR. A number of self-proclaimed Marxist–Leninist governments were formed in the second half of the 1970s in the Third World, including Angola, Mozambique, Ethiopia, Cambodia, Afghanistan, and Nicaragua.

Détente collapsed at the end of the decade with the beginning of the Soviet–Afghan War in 1979. The early 1980s was another period of elevated tension. The United States increased diplomatic, military, and economic pressures on the Soviet Union, at a time when it was already suffering from economic stagnation. In the mid-1980s, the new Soviet leader Mikhail Gorbachev introduced the liberalizing reforms of glasnost ("openness", c. 1985) and perestroika ("reorganization", 1987) and ended Soviet involvement in Afghanistan in 1989. Pressures for national sovereignty grew stronger in Eastern Europe, and Gorbachev refused to militarily support their governments any longer.

In 1989, the fall of the Iron Curtain after the Pan-European Picnic and a peaceful wave of revolutions (with the exception of Romania and Afghanistan) overthrew almost all communist governments of the Eastern Bloc. The Communist Party of the Soviet Union itself lost control in the country and was banned following an abortive coup attempt in August 1991. This in turn led to the formal dissolution of the USSR in December 1991, the declaration of independence of its constituent republics and the collapse of communist governments across much of Africa and Asia. The United States was left as the world's sole superpower.

The Cold War and its events have left a significant legacy. It is often referred to in popular culture, especially with themes of espionage and the threat of nuclear warfare. For subsequent history, see international relations since 1989.

As soon as the term "Cold War" was popularized to refer to post-war tensions between the United States and the Soviet Union, interpreting the course and origins of the conflict has been a source of heated controversy among historians, political scientists, and journalists. In particular, historians have sharply disagreed as to who was responsible for the breakdown of Soviet–US relations after the Second World War; and whether the conflict between the two superpowers was inevitable, or could have been avoided. Historians have also disagreed on what exactly the Cold War was, what the sources of the conflict were, and how to disentangle patterns of action and reaction between the two sides.

Although explanations of the origins of the conflict in academic discussions are complex and diverse, several general schools of thought on the subject can be identified. Historians commonly speak of three different approaches to the study of the Cold War: "orthodox" accounts, "revisionism", and "post-revisionism".

"Orthodox" accounts place responsibility for the Cold War on the Soviet Union and its expansion further into Europe. "Revisionist" writers place more responsibility for the breakdown of post-war peace on the United States, citing a range of US efforts to isolate and confront the Soviet Union well before the end of World War II. "Post-revisionists" see the events of the Cold War as more nuanced, and attempt to be more balanced in determining what occurred during the Cold War. Much of the historiography on the Cold War weaves together two or even all three of these broad categories.


Muḥammad ibn Mūsā al-Khwārizmī (; ), or al-Khwarizmi was a Persian polymath from Khwarazm, who produced vastly influential works in mathematics, astronomy, and geography. Around 820 CE, he was appointed as the astronomer and head of the library of the House of Wisdom in Baghdad.

Al-Khwarizmi's popularizing treatise on algebra (The Compendious Book on Calculation by Completion and Balancing, c. 813–833 CE) presented the first systematic solution of linear and quadratic equations. One of his principal achievements in algebra was his demonstration of how to solve quadratic equations by completing the square, for which he provided geometric justifications. Because he was the first to treat algebra as an independent discipline and introduced the methods of "reduction" and "balancing" (the transposition of subtracted terms to the other side of an equation, that is, the cancellation of like terms on opposite sides of the equation), he has been described as the father or founder of algebra. The term algebra itself comes from the title of his book (the word al-jabr meaning "completion" or "rejoining"). His name gave rise to the terms algorism and algorithm, as well as Spanish, Italian and Portuguese terms algoritmo, and Spanish guarismo and Portuguese algarismo meaning "digit".

In the 12th century, Latin translations of his textbook on arithmetic (Algorithmo de Numero Indorum) which codified the various Indian numerals, introduced the decimal positional number system to the Western world. The Compendious Book on Calculation by Completion and Balancing, translated into Latin by Robert of Chester in 1145, was used until the sixteenth century as the principal mathematical text-book of European universities.

In addition to his best-known works, he revised Ptolemy's Geography, listing the longitudes and latitudes of various cities and localities. He further produced a set of astronomical tables and wrote about calendaric works, as well as the astrolabe and the sundial. He also made important contributions to trigonometry, producing accurate sine and cosine tables, and the first table of tangents.

Al-Khwarizmi (crater) — A crater on the far side of the moon →  NASA Portal: Apollo 11, Photography Index.
13498 Al Chwarizmi — Main-belt Asteroid, Discovered 1986 Aug 6 by E. W. Elst and V. G. Ivanova at Smolyan.
11156 Al-Khwarismi — Main-belt Asteroid, Discovered 1997 Dec 31 by P. G. Comba at Prescott.


Gastroenteritis, also known as infectious diarrhea and gastro, is inflammation of the gastrointestinal tract including the stomach and intestine. Symptoms may include diarrhea, vomiting, and abdominal pain. Fever, lack of energy, and dehydration may also occur. This typically lasts less than two weeks. It is not related to influenza, even though in the U.S. it is sometimes called the "stomach flu".

Gastroenteritis is usually caused by viruses; however, gut bacteria, parasites, and fungi can also cause gastroenteritis. In children, rotavirus is the most common cause of severe disease. In adults, norovirus and Campylobacter are common causes. Eating improperly prepared food, drinking contaminated water or close contact with a person who is infected can spread the disease. Treatment is generally the same with or without a definitive diagnosis, so testing to confirm is usually not needed.

For young children in impoverished countries, prevention includes hand washing with soap, drinking clean water, breastfeeding babies instead of using formula, and proper disposal of human waste. The rotavirus vaccine is recommended as a prevention for children. Treatment involves getting enough fluids. For mild or moderate cases, this can typically be achieved by drinking oral rehydration solution (a combination of water, salts and sugar). In those who are breastfed, continued breastfeeding is recommended. For more severe cases, intravenous fluids may be needed. Fluids may also be given by a nasogastric tube. Zinc supplementation is recommended in children. Antibiotics are generally not needed. However, antibiotics are recommended for young children with a fever and bloody diarrhea.

In 2015, there were two billion cases of gastroenteritis, resulting in 1.3 million deaths globally. Children and those in the developing world are affected the most. In 2011, there were about 1.7 billion cases, resulting in about 700,000 deaths of children under the age of five. In the developing world, children less than two years of age frequently get six or more infections a year. It is less common in adults, partly due to the development of immunity.

Gastroenteritis is defined as vomiting or diarrhea due to inflammation of the small or large bowel, often due to infection. The changes in the small bowel are typically noninflammatory, while the ones in the large bowel are inflammatory. The number of pathogens required to cause an infection varies from as few as one (for Cryptosporidium) to as many as 108 (for Vibrio cholerae).