# Alpha

Alpha (uppercase Α, lowercase α; Ancient Greek: ἄλφα, álpha, modern pronunciation álfa) is the first letter of the Greek alphabet. In the system of Greek numerals, it has a value of 1.

It was derived from the Phoenician and Hebrew letter aleph - an ox or leader.[1]

Letters that arose from alpha include the Latin A and the Cyrillic letter А.

In English, the noun "alpha" is used as a synonym for "beginning", or "first" (in a series), reflecting its Greek roots.[2]

## Uses

### Greek

In Ancient Greek, alpha was pronounced [a] and could be either phonemically long ([aː]) or short ([a]). Where there is ambiguity, long and short alpha are sometimes written with a macron and breve today: Ᾱᾱ, Ᾰᾰ.

• ὥρα = ὥρᾱ hōrā Greek pronunciation: [hɔ́ːraː] "a time"
• γλῶσσα = γλῶσσᾰ glôssa Greek pronunciation: [ɡlɔ̂ːssa] "tongue"

In Modern Greek, vowel length has been lost, and all instances of alpha simply represent IPA: [a].

In the polytonic orthography of Greek, alpha, like other vowel letters, can occur with several diacritic marks: any of three accent symbols (ά, ὰ, ᾶ), and either of two breathing marks (ἁ, ἀ), as well as combinations of these. It can also combine with the iota subscript ().

#### Greek grammar

In the AtticIonic dialect of Ancient Greek, long alpha [aː] fronted to [ɛː] (eta). In Ionic, the shift took place in all positions. In Attic, the shift did not take place after epsilon, iota, and rho (ε, ι, ρ; e, i, r). In Doric and Aeolic, long alpha is preserved in all positions.[3]

• Doric, Aeolic, Attic χώρᾱ chṓrā — Ionic χώρη chṓrē, "country"
• Doric, Aeolic φᾱ́μᾱ phā́mā — Attic, Ionic φήμη phḗmē, "report"

Privative a is the Ancient Greek prefix ἀ- or ἀν- a-, an-, added to words to negate them. It originates from the Proto-Indo-European *n̥- (syllabic nasal) and is cognate with English un-.

Copulative a is the Greek prefix ἁ- or ἀ- ha-, a-. It comes from Proto-Indo-European *sm̥.

### Math and science

The letter alpha represents various concepts in physics and chemistry, including alpha radiation, angular acceleration, alpha particles, alpha carbon and strength of electromagnetic interaction (as Fine-structure constant). Alpha also stands for thermal expansion coefficient of a compound in physical chemistry. It is also commonly used in mathematics in algebraic solutions representing quantities such as angles. Furthermore, in mathematics, the letter alpha is used to denote the area underneath a normal curve in statistics to denote significance level[4] when proving null and alternative hypotheses. In zoology, it is used to name the dominant individual in a wolf or dog pack.

The proportionality operator "" (in Unicode: U+221D) is sometimes mistaken for alpha.

The uppercase letter alpha is not generally used as a symbol because it tends to be rendered identically to the uppercase Latin A.

### International Phonetic Alphabet

In the International Phonetic Alphabet, the letter ɑ, which looks similar to the lower-case alpha, represents the open back unrounded vowel.

## History and symbolism

### Etymology

Alpha was derived from aleph, which in Phoenician means "ox".[5]

### Plutarch

Plutarch, in Moralia,[6] presents a discussion on why the letter alpha stands first in the alphabet. Ammonius asks Plutarch what he, being a Boeotian, has to say for Cadmus, the Phoenician who reputedly settled in Thebes and introduced the alphabet to Greece, placing alpha first because it is the Phoenician name for ox—which, unlike Hesiod,[7] the Phoenicians considered not the second or third, but the first of all necessities. "Nothing at all," Plutarch replied. He then added that he would rather be assisted by Lamprias, his own grandfather, than by Dionysus' grandfather, i.e. Cadmus. For Lamprias had said that the first articulate sound made is "alpha", because it is very plain and simple—the air coming off the mouth does not require any motion of the tongue—and therefore this is the first sound that children make.

According to Plutarch's natural order of attribution of the vowels to the planets, alpha was connected with the Moon.

### Alpha and Omega

Memorial Stained Glass window, Royal Military College of Canada features Alpha and Omega

Alpha, both as a symbol and term, is used to refer to or describe a variety of things, including the first or most significant occurrence of something. The New Testament has God declaring himself to be the "Alpha and Omega, the beginning and the end, the first and the last." (Revelation 22:13, KJV, and see also 1:8). Because of this symbolism, the characters ⍺ and ⍵ denote the left and right arguments in the APL programming language.

### Language

The term "alpha" has been used to denote position in social hierarchy, examples being "alpha males" or pack leaders.

## Computer encodings

• Greek alpha / Coptic alfa[8]
Character Α α
Unicode name GREEK CAPITAL LETTER ALPHA GREEK SMALL LETTER ALPHA COPTIC CAPITAL LETTER ALFA COPTIC SMALL LETTER ALFA
Encodings decimal hex decimal hex decimal hex decimal hex
Unicode 913 U+0391 945 U+03B1 11392 U+2C80 11393 U+2C81
UTF-8 206 145 CE 91 206 177 CE B1 226 178 128 E2 B2 80 226 178 129 E2 B2 81
Numeric character reference &#913; &#x391; &#945; &#x3B1; &#11392; &#x2C80; &#11393; &#x2C81;
Named character reference &Alpha; &alpha;
CP 437 224 E0
DOS Greek 128 80 152 98
DOS Greek-2 164 A4 214 D6
Windows 1253 193 C1 225 E1
TeX \alpha

For accented Greek characters, see Greek diacritics: Computer encoding.

• Latin / IPA alpha
Character ɑ ɒ
Unicode name LATIN SMALL LETTER ALPHA LATIN SMALL LETTER TURNED ALPHA LATIN SMALL LETTER ALPHA
WITH RETROFLEX HOOK
MODIFIER LETTER
SMALL ALPHA
MODIFIER LETTER
SMALL TURNED ALPHA
Encodings decimal hex decimal hex decimal hex decimal hex decimal hex
Unicode 593 U+0251 594 U+0252 7568 U+1D90 7493 U+1D45 7579 U+1D9B
UTF-8 201 145 C9 91 201 146 C9 92 225 182 144 E1 B6 90 225 181 133 E1 B5 85 225 182 155 E1 B6 9B
Numeric character reference &#593; &#x251; &#594; &#x252; &#7568; &#x1D90; &#7493; &#x1D45; &#7579; &#x1D9B;
• Mathematical / Technical alpha
Character 𝚨 𝛂 𝛢 𝛼
Unicode name APL FUNCTIONAL SYMBOL ALPHA APL FUNCTIONAL SYMBOL
ALPHA UNDERBAR
MATHEMATICAL BOLD
CAPITAL ALPHA
MATHEMATICAL BOLD
SMALL ALPHA
MATHEMATICAL ITALIC
CAPITAL ALPHA
MATHEMATICAL ITALIC
SMALL ALPHA
Encodings decimal hex decimal hex decimal hex decimal hex decimal hex decimal hex
Unicode 9082 U+237A 9078 U+2376 120488 U+1D6A8 120514 U+1D6C2 120546 U+1D6E2 120572 U+1D6FC
UTF-8 226 141 186 E2 8D BA 226 141 182 E2 8D B6 240 157 154 168 F0 9D 9A A8 240 157 155 130 F0 9D 9B 82 240 157 155 162 F0 9D 9B A2 240 157 155 188 F0 9D 9B BC
UTF-16 9082 237A 9078 2376 55349 57000 D835 DEA8 55349 57026 D835 DEC2 55349 57058 D835 DEE2 55349 57084 D835 DEFC
Numeric character reference &#9082; &#x237A; &#9078; &#x2376; &#120488; &#x1D6A8; &#120514; &#x1D6C2; &#120546; &#x1D6E2; &#120572; &#x1D6FC;
Character 𝜜 𝜶 𝝖 𝝰 𝞐 𝞪
Unicode name MATHEMATICAL BOLD ITALIC
CAPITAL ALPHA
MATHEMATICAL BOLD ITALIC
SMALL ALPHA
MATHEMATICAL SANS-SERIF
BOLD CAPITAL ALPHA
MATHEMATICAL SANS-SERIF
BOLD SMALL ALPHA
MATHEMATICAL SANS-SERIF
BOLD ITALIC CAPITAL ALPHA
MATHEMATICAL SANS-SERIF
BOLD ITALIC SMALL ALPHA
Encodings decimal hex decimal hex decimal hex decimal hex decimal hex decimal hex
Unicode 120604 U+1D71C 120630 U+1D736 120662 U+1D756 120688 U+1D770 120720 U+1D790 120746 U+1D7AA
UTF-8 240 157 156 156 F0 9D 9C 9C 240 157 156 182 F0 9D 9C B6 240 157 157 150 F0 9D 9D 96 240 157 157 176 F0 9D 9D B0 240 157 158 144 F0 9D 9E 90 240 157 158 170 F0 9D 9E AA
UTF-16 55349 57116 D835 DF1C 55349 57142 D835 DF36 55349 57174 D835 DF56 55349 57200 D835 DF70 55349 57232 D835 DF90 55349 57258 D835 DFAA
Numeric character reference &#120604; &#x1D71C; &#120630; &#x1D736; &#120662; &#x1D756; &#120688; &#x1D770; &#120720; &#x1D790; &#120746; &#x1D7AA;

## References

1. ^ Chambers concise dictionary p.30 Allied Publishers, 2004 ISBN 9798186062363 Retrieved 2017-02-06
2. ^ Alpha - Definition and More from the Free Merriam-Webster Dictionary
3. ^ Herbert Weir Smyth. Greek grammar for colleges. paragraph 30 and note.
4. ^ "Chapter 5: Analysing the Data Part II : Inferential Statistics". Research Methods and Statistics PESS202 Lecture and Commentary Notes. Archived from the original on 22 August 2011.
5. ^ alpha on the Online Etymology Dictionary
6. ^ Symposiacs, Book IX, questions II & III On-line text Archived 13 October 2008 at the Wayback Machine at Adelaide library
7. ^ Hesiod, in Works and Days (see on Perseus Project), advises the early Greek farmers, "First of all, get a house, then a woman and third, an ox for the plough."
8. ^ "Character Encodings". Retrieved 14 January 2013.
Absolute magnitude

Absolute magnitude is a measure of the luminosity of a celestial object, on a logarithmic astronomical magnitude scale. An object's absolute magnitude is defined to be equal to the apparent magnitude that the object would have if it were viewed from a distance of exactly 10 parsecs (32.6 light-years), with no extinction (or dimming) of its light due to absorption by interstellar dust particles. By hypothetically placing all objects at a standard reference distance from the observer, their luminosities can be directly compared on a magnitude scale. As with all astronomical magnitudes, the absolute magnitude can be specified for different wavelength ranges corresponding to specified filter bands or passbands; for stars a commonly quoted absolute magnitude is the absolute visual magnitude, which uses the visual (V) band of the spectrum (in the UBV photometric system). Absolute magnitudes are denoted by a capital M, with a subscript representing the filter band used for measurement, such as MV for absolute magnitude in the V band.

The more luminous an object, the smaller the numerical value of its absolute magnitude. A difference of 5 magnitudes between the absolute magnitudes of two objects corresponds to a ratio of 100 in their luminosities, and a difference of n magnitudes in absolute magnitude corresponds to a luminosity ratio of 100(n/5). For example, a star of absolute magnitude MV=3 would be 100 times more luminous than a star of absolute magnitude MV=8 as measured in the V filter band. The Sun has absolute magnitude MV=+4.83. Highly luminous objects can have negative absolute magnitudes: for example, the Milky Way galaxy has an absolute B magnitude of about −20.8.An object's absolute bolometric magnitude represents its total luminosity over all wavelengths, rather than in a single filter band, as expressed on a logarithmic magnitude scale. To convert from an absolute magnitude in a specific filter band to absolute bolometric magnitude, a bolometric correction is applied.

For Solar System bodies that shine in reflected light, a different definition of absolute magnitude (H) is used, based on a standard reference distance of one astronomical unit.

The adrenergic receptors or adrenoceptors are a class of G protein-coupled receptors that are targets of many catecholamines like norepinephrine (noradrenaline) and epinephrine (adrenaline) produced by the body, but also many medications like beta blockers, β2 agonists and α2 agonists, which are used to treat high blood pressure and asthma for example.

Many cells have these receptors, and the binding of a catecholamine to the receptor will generally stimulate the sympathetic nervous system (SNS). SNS is responsible for the fight-or-flight response, which is triggered for example by exercise or fear causing situations. This response dilates pupils, increases heart rate, mobilizes energy, and diverts blood flow from non-essential organs to skeletal muscle. These effects together tend to increase physical performance momentarily.

The alpha-1 (α1) adrenergic receptor is a G protein-coupled receptor (GPCR) associated with the Gq heterotrimeric G-protein. It consists of three highly homologous subtypes, including α1A-, α1B-, and α1D-adrenergic. Catecholamines like norepinephrine (noradrenaline) and epinephrine (adrenaline) signal through the α1-adrenergic receptor in the central and peripheral nervous systems. There is no α1C receptor. At one time, there was a subtype known as α1C, but it was found to be identical to the previously discovered α1A receptor subtype. To avoid confusion, naming was continued with the letter D.

The alpha-2 (α2) adrenergic receptor (or adrenoceptor) is a G protein-coupled receptor (GPCR) associated with the Gi heterotrimeric G-protein. It consists of three highly homologous subtypes, including α2A-, α2B-, and α2C-adrenergic. Some species other than humans express a fourth α2D-adrenergic receptor as well. Catecholamines like norepinephrine (noradrenaline) and epinephrine (adrenaline) signal through the α2-adrenergic receptor in the central and peripheral nervous systems.

Alpha Centauri

Alpha Centauri (Latinized from α Centauri, abbreviated Alpha Cen or α Cen) is the closest star system and closest planetary system to the Solar System at 4.37 light-years (1.34 pc) from the Sun. It is a triple star system, consisting of three stars: α Centauri A (officially Rigil Kentaurus), α Centauri B (officially Toliman), and α Centauri C (officially Proxima Centauri).Alpha Centauri A and B are Sun-like stars (Class G and K), and together they form the binary star Alpha Centauri AB. To the naked eye, the two main components appear to be a single star with an apparent magnitude of −0.27, forming the brightest star in the southern constellation of Centaurus and the third-brightest in the night sky, outshone only by Sirius and Canopus.

Alpha Centauri A has 1.1 times the mass and 1.519 times the luminosity of the Sun, while Alpha Centauri B is smaller and cooler, at 0.907 times the Sun's mass and 0.445 times its luminosity. The pair orbit about a common centre with an orbital period of 79.91 years. Their elliptical orbit is eccentric, so that the distance between A and B varies from 35.6 astronomical units (AU), or about the distance between Pluto and the Sun, to that between Saturn and the Sun (11.2 AU).

Alpha Centauri C, or Proxima Centauri, is a small and faint red dwarf (Class M). Though not visible to the naked eye, Proxima Centauri is the closest star to the Sun at a distance of 4.24 light-years (1.30 pc), slightly closer than Alpha Centauri AB. Currently, the distance between Proxima Centauri and Alpha Centauri AB is about 13,000 astronomical units (0.21 ly), equivalent to about 430 times the radius of Neptune's orbit. Proxima Centauri b is an Earth-sized exoplanet in the habitable zone of Proxima Centauri; it was discovered in 2016.

Alpha Kappa Alpha

Alpha Kappa Alpha (ΑΚΑ) is a Greek-lettered sorority, the first established by African-American college women. Membership is for college-educated women. The organization was founded on five basic tenets:

To cultivate and encourage high scholastic and ethical standards, to promote unity and friendship among college women, to study and help alleviate problems concerning girls and women in order to improve their social stature, to maintain a progressive interest in college life, and to be of 'Service to All Mankind'.

The sorority was founded on January 15, 1908, at the historically black Howard University in Washington, D.C., by a group of sixteen students led by Ethel Hedgeman Lyle. Forming a sorority broke barriers for African-American women in areas where they had little power or authority due to a lack of opportunities for minorities and women in the early 20th century. Alpha Kappa Alpha was incorporated on January 29, 1913.

Consisting of college-educated women of many diverse backgrounds from around the world, the sorority serves through a membership of more than 300,000 women in 1024 chapters in the United States and several other countries. Women may join through undergraduate chapters at a college or university or they may also join through a graduate chapter after acquiring an undergraduate or advanced college degree.After the organization's establishment, Alpha Kappa Alpha has helped to improve social and economic conditions through community service programs. Members have improved education through independent initiatives, contributed to community-building by creating programs and associations, such as the Mississippi Health Clinic, and influenced federal legislation by Congressional lobbying through the National Non-Partisan Lobby on Civil and Democratic Rights. The sorority works with communities through service initiatives and progressive programs relating to education, family, health, and business.

Alpha Kappa Alpha is part of the National Pan-Hellenic Council (NPHC). The current International President is Dr. Glenda Glover and the sorority's document and pictorial archives are located at Moorland-Spingarn Research Center.

Alpha Phi Alpha

Alpha Phi Alpha Fraternity, Inc. (ΑΦΑ) is the first African-American, intercollegiate Greek-lettered fraternity. It was initially a literary and social studies club organized in the 1905–1906 school year at Cornell University but later evolved into a fraternity with a founding date of December 4, 1906, at Cornell. It employs an icon from Ancient Egypt, the Great Sphinx of Giza, as its symbol. Its aims are "Manly Deeds, Scholarship, and Love For All Mankind," and its motto is "First of All, Servants of All, We Shall Transcend All." Its archives are preserved at the Moorland-Spingarn Research Center.

Chapters were chartered at Howard University and Virginia Union University in 1907. The fraternity has over 290,000 members and has been open to men of all races since 1945. Currently, there are more than 730 active chapters in the Americas, Africa, Europe, the Caribbean, and Asia. It is the largest predominately African-American fraternity and one of the ten largest collegiate fraternities in the nation.Alpha Phi Alpha is a social organization with a service organization mission and provided leadership and service during the Great Depression, World Wars, and Civil Rights Movement. The fraternity addresses social issues such as apartheid, AIDS, urban housing, and other economic, cultural, and political issues of interest to people of color. National programs and initiatives of the fraternity include A Voteless People Is a Hopeless People, My Brother's Keeper, Go To High School, Go To College, Project Alpha, and the World Policy Council. It also conducts philanthropic programming initiatives with the March of Dimes, Head Start, the Boy Scouts of America, and Big Brothers Big Sisters of America.

Members of this fraternity include many historical civil rights leaders such as Martin Luther King Jr., NAACP founder W. E. B. Du Bois, John Mack (civic leader) and Dick Gregory. Other world renowned-members include political activist Cornel West, musicians Duke Ellington and Lionel Richie, NBA legend Walt Frazier, Jamaican Prime Minister Norman Manley, Olympic gold medalist Jesse Owens, Justice Thurgood Marshall, Investor and founder of Vista Equity Partners Robert F. Smith, United Nations Ambassador Andrew Young, Academy Award-winning director Barry Jenkins, six time MTV Video Music Awards - winning director/choreographer Frank Gatson Jr., hero of the Nashville Waffle House shooting, James Shaw Jr., and ESPN sportscasters Stuart Scott, Stan Verrett and Jay Harris.

Alpha Phi Alpha was directly responsible for the conception, funding, and construction of the Martin Luther King Jr. Memorial next to the National Mall in Washington D.C.

Alpha compositing

In computer graphics, alpha compositing is the process of combining an image with a background to create the appearance of partial or full transparency. It is often useful to render image elements in separate passes, and then combine the resulting multiple 2D images into a single, final image called the composite. For example, compositing is used extensively when combining computer-rendered image elements with live footage.

In order to combine these image elements correctly, it is necessary to keep an associated matte for each element. This matte contains the coverage information—the shape of the geometry being drawn—making it possible to distinguish between parts of the image where the geometry was actually drawn and other parts of the image that are empty.

Alpha helix

The alpha helix (α-helix) is a common motif in the secondary structure of proteins and is a right hand-helix conformation in which every backbone N−H group donates a hydrogen bond to the backbone C=O group of the amino acid located three or four residues earlier along the protein sequence.

The alpha helix is also called a classic Pauling–Corey–Branson α-helix. The name 3.613-helix is also used for this type of helix, denoting the average number of residues per helical turn, with 13 atoms being involved in the ring formed by the hydrogen bond.

Among types of local structure in proteins, the α-helix is the most regular and the most predictable from sequence, as well as the most prevalent.

Alpha particle

Alpha particles, also called alpha ray or alpha radiation, consist of two protons and two neutrons bound together into a particle identical to a helium-4 nucleus. They are generally produced in the process of alpha decay, but may also be produced in other ways. Alpha particles are named after the first letter in the Greek alphabet, α. The symbol for the alpha particle is α or α2+. Because they are identical to helium nuclei, they are also sometimes written as He2+ or 42He2+ indicating a helium ion with a +2 charge (missing its two electrons). If the ion gains electrons from its environment, the alpha particle becomes a normal (electrically neutral) helium atom 42He.

Alpha particles, like helium nuclei, have a net spin of zero. Due to the mechanism of their production in standard alpha radioactive decay, alpha particles generally have a kinetic energy of about 5 MeV, and a velocity in the vicinity of 5% the speed of light. (See discussion below for the limits of these figures in alpha decay.) They are a highly ionizing form of particle radiation, and (when resulting from radioactive alpha decay) have low penetration depth. They can be stopped by a few centimeters of air, or by the skin.

However, so-called long range alpha particles from ternary fission are three times as energetic, and penetrate three times as far. As noted, the helium nuclei that form 10–12% of cosmic rays are also usually of much higher energy than those produced by nuclear decay processes, and are thus capable of being highly penetrating and able to traverse the human body and also many meters of dense solid shielding, depending on their energy. To a lesser extent, this is also true of very high-energy helium nuclei produced by particle accelerators.

When alpha particle emitting isotopes are ingested, they are far more dangerous than their half-life or decay rate would suggest, due to the high relative biological effectiveness of alpha radiation to cause biological damage. Alpha radiation is an average of about 20 times more dangerous, and in experiments with inhaled alpha emitters, up to 1000 times more dangerous than an equivalent activity of beta emitting or gamma emitting radioisotopes.

Amino acid

Amino acids are organic compounds containing amine (-NH2) and carboxyl (-COOH) functional groups, along with a side chain (R group) specific to each amino acid. The key elements of an amino acid are carbon (C), hydrogen (H), oxygen (O), and nitrogen (N), although other elements are found in the side chains of certain amino acids. About 500 naturally occurring amino acids are known (though only 20 appear in the genetic code) and can be classified in many ways. They can be classified according to the core structural functional groups' locations as alpha- (α-), beta- (β-), gamma- (γ-) or delta- (δ-) amino acids; other categories relate to polarity, pH level, and side chain group type (aliphatic, acyclic, aromatic, containing hydroxyl or sulfur, etc.). In the form of proteins, amino acid residues form the second-largest component (water is the largest) of human muscles and other tissues. Beyond their role as residues in proteins, amino acids participate in a number of processes such as neurotransmitter transport and biosynthesis.

In biochemistry, amino acids having both the amine and the carboxylic acid groups attached to the first (alpha-) carbon atom have particular importance. They are known as 2-, alpha-, or α-amino acids (generic formula H2NCHRCOOH in most cases, where R is an organic substituent known as a "side chain"); often the term "amino acid" is used to refer specifically to these. They include the 22 proteinogenic ("protein-building") amino acids, which combine into peptide chains ("polypeptides") to form the building-blocks of a vast array of proteins. These are all L-stereoisomers ("left-handed" isomers), although a few D-amino acids ("right-handed") occur in bacterial envelopes, as a neuromodulator (D-serine), and in some antibiotics.Twenty of the proteinogenic amino acids are encoded directly by triplet codons in the genetic code and are known as "standard" amino acids. The other two ("non-standard" or "non-canonical") are selenocysteine (present in many prokaryotes as well as most eukaryotes, but not coded directly by DNA), and pyrrolysine (found only in some archea and one bacterium). Pyrrolysine and selenocysteine are encoded via variant codons; for example, selenocysteine is encoded by stop codon and SECIS element. N-formylmethionine (which is often the initial amino acid of proteins in bacteria, mitochondria, and chloroplasts) is generally considered as a form of methionine rather than as a separate proteinogenic amino acid. Codon–tRNA combinations not found in nature can also be used to "expand" the genetic code and form novel proteins known as alloproteins incorporating non-proteinogenic amino acids.Many important proteinogenic and non-proteinogenic amino acids have biological functions. For example, in the human brain, glutamate (standard glutamic acid) and gamma-amino-butyric acid ("GABA", non-standard gamma-amino acid) are, respectively, the main excitatory and inhibitory neurotransmitters. Hydroxyproline, a major component of the connective tissue collagen, is synthesised from proline. Glycine is a biosynthetic precursor to porphyrins used in red blood cells. Carnitine is used in lipid transport.

Nine proteinogenic amino acids are called "essential" for humans because they cannot be produced from other compounds by the human body and so must be taken in as food. Others may be conditionally essential for certain ages or medical conditions. Essential amino acids may also differ between species.Because of their biological significance, amino acids are important in nutrition and are commonly used in nutritional supplements, fertilizers, feed, and food technology. Industrial uses include the production of drugs, biodegradable plastics, and chiral catalysts.

Bessel function

Bessel functions, first defined by the mathematician Daniel Bernoulli and then generalized by Friedrich Bessel, are the canonical solutions y(x) of Bessel's differential equation

${\displaystyle x^{2}{\frac {d^{2}y}{dx^{2}}}+x{\frac {dy}{dx}}+\left(x^{2}-\alpha ^{2}\right)y=0}$

for an arbitrary complex number α, the order of the Bessel function. Although α and α produce the same differential equation for real α, it is conventional to define different Bessel functions for these two values in such a way that the Bessel functions are mostly smooth functions of α.

The most important cases are when α is an integer or half-integer. Bessel functions for integer α are also known as cylinder functions or the cylindrical harmonics because they appear in the solution to Laplace's equation in cylindrical coordinates. Spherical Bessel functions with half-integer α are obtained when the Helmholtz equation is solved in spherical coordinates.

Global city

A global city, also called world city or sometimes alpha city or world center, is a city which is a primary node in the global economic network. The concept comes from geography and urban studies, and the idea that globalization is created, facilitated, and enacted in strategic geographic locales according to a hierarchy of importance to the operation of the global system of finance and trade.

The most complex node is the "global city", with links binding it to other cities having a direct and tangible effect on global socio-economic affairs. The term "global city", rather than "megacity", was popularized by sociologist Saskia Sassen in her 1991 work, The Global City: New York, London, Tokyo. "World city", meaning a city heavily involved in global trade, appeared in the May 1886 description of Liverpool, by The Illustrated London News. Patrick Geddes later used the term "world city" in 1915. More recently, the term has focused on a city's financial power and high technology infrastructure, with other factors becoming less relevant.

ISO 3166-1 alpha-2

ISO 3166-1 alpha-2 codes are two-letter country codes defined in ISO 3166-1, part of the ISO 3166 standard published by the International Organization for Standardization (ISO), to represent countries, dependent territories, and special areas of geographical interest. They are the most widely used of the country codes published by ISO (the others being alpha-3 and numeric), and are used most prominently for the Internet's country code top-level domains (with a few exceptions). They are also used as country identifiers extending the postal code when appropriate within the international postal system for paper mail, and has replaced the previous one consisting one-letter codes. They were first included as part of the ISO 3166 standard in its first edition in 1974.

ISO 3166-1 alpha-3

ISO 3166-1 alpha-3 codes are three-letter country codes defined in ISO 3166-1, part of the ISO 3166 standard published by the International Organization for Standardization (ISO), to represent countries, dependent territories, and special areas of geographical interest. They allow a better visual association between the codes and the country names than the two-letter alpha-2 codes (the third set of codes is numeric and hence offers no visual association). They were first included as part of the ISO 3166 standard in its first edition in 1974.

Software release life cycle

A software release life cycle is the sum of the stages of development and maturity for a piece of computer software: ranging from its initial development to its eventual release, and including updated versions of the released version to help improve software or fix software bugs still present in the software.

Taxonomy (biology)

In biology, taxonomy (from Ancient Greek τάξις (taxis), meaning 'arrangement', and -νομία (-nomia), meaning 'method') is the science of defining and naming groups of biological organisms on the basis of shared characteristics. Organisms are grouped together into taxa (singular: taxon) and these groups are given a taxonomic rank; groups of a given rank can be aggregated to form a super-group of higher rank, thus creating a taxonomic hierarchy. The principal ranks in modern use are domain, kingdom, phylum (division is sometimes used in botany in place of phylum), class, order, family, genus, and species. The Swedish botanist Carl Linnaeus is regarded as the father of taxonomy, as he developed a system known as Linnaean taxonomy for categorizing organisms and binomial nomenclature for naming organisms.

With the advent of such fields of study as phylogenetics, cladistics, and systematics, the Linnaean system has progressed to a system of modern biological classification based on the evolutionary relationships between organisms, both living and extinct.

Tumor necrosis factor alpha

Tumor necrosis factor (TNF, tumor necrosis factor alpha, TNFα, cachexin, or cachectin) is a cell signaling protein (cytokine) involved in systemic inflammation and is one of the cytokines that make up the acute phase reaction. It is produced chiefly by activated macrophages, although it can be produced by many other cell types such as CD4+ lymphocytes, NK cells, neutrophils, mast cells, eosinophils, and neurons.The primary role of TNF is in the regulation of immune cells. TNF, being an endogenous pyrogen, is able to induce fever, apoptotic cell death, cachexia, inflammation and to inhibit tumorigenesis and viral replication and respond to sepsis via IL1 & IL6 producing cells. Dysregulation of TNF production has been implicated in a variety of human diseases including Alzheimer's disease, cancer, major depression, psoriasis and inflammatory bowel disease (IBD). Though controversial, studies of depression and IBD are currently being linked to TNF levels. Recombinant TNF is used as an immunostimulant under the INN tasonermin. TNF can be produced ectopically in the setting of malignancy and parallels parathyroid hormone both in causing secondary hypercalcemia and in the cancers with which excessive production is associated.

XFL (2020)

The XFL is a planned professional American football league owned by Vince McMahon's Alpha Entertainment, and is headquartered in Stamford, Connecticut. It is a successor to the previous XFL, which was controlled by the World Wrestling Federation (WWF, now WWE) and NBC, and ran for a single season in 2001. The league will follow a similar structure as the original XFL did in 2001, with eight teams, centrally owned and operated by the league and spread across the United States in markets currently or recently represented by a National Football League (NFL) franchise, competing in a ten-game season and a two-week postseason in the winter and spring months.

In announcing the reformed XFL, McMahon stated that while it would share its name and trademark with the previous incarnation, it will not rely on professional wrestling-inspired features and entertainment elements as its predecessor did, instead aiming to create a league with fewer off-field controversies and faster, simpler play compared to the NFL.

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