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Additionally, an electron always tends to fall to the lowest possible energy state. It is possible for it to occupy any orbital so long as it does not violate the Pauli exclusion principle, but if lower-energy orbitals are available, this condition is unstable. The electron will eventually lose energy (by releasing a p... | Atomic orbital | Wikipedia | 494 | 1206 | https://en.wikipedia.org/wiki/Atomic%20orbital | Physical sciences | Atomic physics | null |
Although this is the general order of orbital filling according to the Madelung rule, there are exceptions, and the actual electronic energies of each element are also dependent upon additional details of the atoms (see ).
The number of electrons in an electrically neutral atom increases with the atomic number. The el... | Atomic orbital | Wikipedia | 260 | 1206 | https://en.wikipedia.org/wiki/Atomic%20orbital | Physical sciences | Atomic physics | null |
In the Bohr model, an electron has a velocity given by , where is the atomic number, is the fine-structure constant, and is the speed of light. In non-relativistic quantum mechanics, therefore, any atom with an atomic number greater than 137 would require its 1s electrons to be traveling faster than the speed of li... | Atomic orbital | Wikipedia | 449 | 1206 | https://en.wikipedia.org/wiki/Atomic%20orbital | Physical sciences | Atomic physics | null |
Bound quantum states have discrete energy levels. When applied to atomic orbitals, this means that the energy differences between states are also discrete. A transition between these states (i.e., an electron absorbing or emitting a photon) can thus happen only if the photon has an energy corresponding with the exact e... | Atomic orbital | Wikipedia | 376 | 1206 | https://en.wikipedia.org/wiki/Atomic%20orbital | Physical sciences | Atomic physics | null |
Amino acids are organic compounds that contain both amino and carboxylic acid functional groups. Although over 500 amino acids exist in nature, by far the most important are the 22 α-amino acids incorporated into proteins. Only these 22 appear in the genetic code of life.
Amino acids can be classified according to the... | Amino acid | Wikipedia | 479 | 1207 | https://en.wikipedia.org/wiki/Amino%20acid | Biology and health sciences | Biochemistry and molecular biology | null |
The unity of the chemical category was recognized by Wurtz in 1865, but he gave no particular name to it. The first use of the term "amino acid" in the English language dates from 1898, while the German term, , was used earlier. Proteins were found to yield amino acids after enzymatic digestion or acid hydrolysis. In 1... | Amino acid | Wikipedia | 432 | 1207 | https://en.wikipedia.org/wiki/Amino%20acid | Biology and health sciences | Biochemistry and molecular biology | null |
Five amino acids possess a charge at neutral pH. Often these side chains appear at the surfaces on proteins to enable their solubility in water, and side chains with opposite charges form important electrostatic contacts called salt bridges that maintain structures within a single protein or between interfacing protein... | Amino acid | Wikipedia | 342 | 1207 | https://en.wikipedia.org/wiki/Amino%20acid | Biology and health sciences | Biochemistry and molecular biology | null |
The polar, uncharged amino acids serine (Ser, S), threonine (Thr, T), asparagine (Asn, N) and glutamine (Gln, Q) readily form hydrogen bonds with water and other amino acids. They do not ionize in normal conditions, a prominent exception being the catalytic serine in serine proteases. This is an example of severe pertu... | Amino acid | Wikipedia | 304 | 1207 | https://en.wikipedia.org/wiki/Amino%20acid | Biology and health sciences | Biochemistry and molecular biology | null |
Several side chains are not described well by the charged, polar and hydrophobic categories. Glycine (Gly, G) could be considered a polar amino acid since its small size means that its solubility is largely determined by the amino and carboxylate groups. However, the lack of any side chain provides glycine with a uniqu... | Amino acid | Wikipedia | 410 | 1207 | https://en.wikipedia.org/wiki/Amino%20acid | Biology and health sciences | Biochemistry and molecular biology | null |
The common natural forms of amino acids have a zwitterionic structure, with ( in the case of proline) and functional groups attached to the same C atom, and are thus α-amino acids, and are the only ones found in proteins during translation in the ribosome.
In aqueous solution at pH close to neutrality, amino acids ex... | Amino acid | Wikipedia | 506 | 1207 | https://en.wikipedia.org/wiki/Amino%20acid | Biology and health sciences | Biochemistry and molecular biology | null |
For amino acids with charged side chains, the pKa of the side chain is involved. Thus for aspartate or glutamate with negative side chains, the terminal amino group is essentially entirely in the charged form , but this positive charge needs to be balanced by the state with just one C-terminal carboxylate group is nega... | Amino acid | Wikipedia | 252 | 1207 | https://en.wikipedia.org/wiki/Amino%20acid | Biology and health sciences | Biochemistry and molecular biology | null |
Physicochemical properties
The 20 canonical amino acids can be classified according to their properties. Important factors are charge, hydrophilicity or hydrophobicity, size, and functional groups. These properties influence protein structure and protein–protein interactions. The water-soluble proteins tend to have the... | Amino acid | Wikipedia | 506 | 1207 | https://en.wikipedia.org/wiki/Amino%20acid | Biology and health sciences | Biochemistry and molecular biology | null |
Table of standard amino acid abbreviations and properties
Although one-letter symbols are included in the table, IUPAC–IUBMB recommend that "Use of the one-letter symbols should be restricted to the comparison of long sequences".
The one-letter notation was chosen by IUPAC-IUB based on the following rules:
Initial ... | Amino acid | Wikipedia | 509 | 1207 | https://en.wikipedia.org/wiki/Amino%20acid | Biology and health sciences | Biochemistry and molecular biology | null |
In addition, many nonstandard amino acids have a specific code. For example, several peptide drugs, such as Bortezomib and MG132, are artificially synthesized and retain their protecting groups, which have specific codes. Bortezomib is Pyz–Phe–boroLeu, and MG132 is Z–Leu–Leu–Leu–al. To aid in the analysis of protein st... | Amino acid | Wikipedia | 504 | 1207 | https://en.wikipedia.org/wiki/Amino%20acid | Biology and health sciences | Biochemistry and molecular biology | null |
The 20 amino acids that are encoded directly by the codons of the universal genetic code are called standard or canonical amino acids. A modified form of methionine (N-formylmethionine) is often incorporated in place of methionine as the initial amino acid of proteins in bacteria, mitochondria and plastids (including c... | Amino acid | Wikipedia | 493 | 1207 | https://en.wikipedia.org/wiki/Amino%20acid | Biology and health sciences | Biochemistry and molecular biology | null |
Non-proteinogenic amino acids that are found in proteins are formed by post-translational modification. Such modifications can also determine the localization of the protein, e.g., the addition of long hydrophobic groups can cause a protein to bind to a phospholipid membrane. Examples:
the carboxylation of glutamate al... | Amino acid | Wikipedia | 485 | 1207 | https://en.wikipedia.org/wiki/Amino%20acid | Biology and health sciences | Biochemistry and molecular biology | null |
Semi-essential and conditionally essential amino acids, and juvenile requirements
In addition, cysteine, tyrosine, and arginine are considered semiessential amino acids, and taurine a semi-essential aminosulfonic acid in children. Some amino acids are conditionally essential for certain ages or medical conditions. Esse... | Amino acid | Wikipedia | 334 | 1207 | https://en.wikipedia.org/wiki/Amino%20acid | Biology and health sciences | Biochemistry and molecular biology | null |
Roles for nonstandard amino acids
Carnitine is used in lipid transport.
gamma-aminobutyric acid is a neurotransmitter.
5-HTP (5-hydroxytryptophan) is used for experimental treatment of depression.
L-DOPA (L-dihydroxyphenylalanine) for Parkinson's treatment,
Eflornithine inhibits ornithine decarboxylase and used in ... | Amino acid | Wikipedia | 480 | 1207 | https://en.wikipedia.org/wiki/Amino%20acid | Biology and health sciences | Biochemistry and molecular biology | null |
Amino acids have been considered as components of biodegradable polymers, which have applications as environmentally friendly packaging and in medicine in drug delivery and the construction of prosthetic implants. An interesting example of such materials is polyaspartate, a water-soluble biodegradable polymer that may ... | Amino acid | Wikipedia | 399 | 1207 | https://en.wikipedia.org/wiki/Amino%20acid | Biology and health sciences | Biochemistry and molecular biology | null |
Microorganisms and plants synthesize many uncommon amino acids. For example, some microbes make 2-aminoisobutyric acid and lanthionine, which is a sulfide-bridged derivative of alanine. Both of these amino acids are found in peptidic lantibiotics such as alamethicin. However, in plants, 1-aminocyclopropane-1-carboxylic... | Amino acid | Wikipedia | 354 | 1207 | https://en.wikipedia.org/wiki/Amino%20acid | Biology and health sciences | Biochemistry and molecular biology | null |
According to a review, amino acids, and even peptides, "turn up fairly regularly in the various experimental broths that have been allowed to be cooked from simple chemicals. This is because nucleotides are far more difficult to synthesize chemically than amino acids." For a chronological order, it suggests that there ... | Amino acid | Wikipedia | 384 | 1207 | https://en.wikipedia.org/wiki/Amino%20acid | Biology and health sciences | Biochemistry and molecular biology | null |
However, not all peptide bonds are formed in this way. In a few cases, peptides are synthesized by specific enzymes. For example, the tripeptide glutathione is an essential part of the defenses of cells against oxidative stress. This peptide is synthesized in two steps from free amino acids. In the first step, gamma-gl... | Amino acid | Wikipedia | 457 | 1207 | https://en.wikipedia.org/wiki/Amino%20acid | Biology and health sciences | Biochemistry and molecular biology | null |
The total nitrogen content of organic matter is mainly formed by the amino groups in proteins. The Total Kjeldahl Nitrogen (TKN) is a measure of nitrogen widely used in the analysis of (waste) water, soil, food, feed and organic matter in general. As the name suggests, the Kjeldahl method is applied. More sensitive met... | Amino acid | Wikipedia | 76 | 1207 | https://en.wikipedia.org/wiki/Amino%20acid | Biology and health sciences | Biochemistry and molecular biology | null |
Area is the measure of a region's size on a surface. The area of a plane region or plane area refers to the area of a shape or planar lamina, while surface area refers to the area of an open surface or the boundary of a three-dimensional object. Area can be understood as the amount of material with a given thickness th... | Area | Wikipedia | 422 | 1209 | https://en.wikipedia.org/wiki/Area | Mathematics | Geometry and topology | null |
Area plays an important role in modern mathematics. In addition to its obvious importance in geometry and calculus, area is related to the definition of determinants in linear algebra, and is a basic property of surfaces in differential geometry. In analysis, the area of a subset of the plane is defined using Lebesgue... | Area | Wikipedia | 495 | 1209 | https://en.wikipedia.org/wiki/Area | Mathematics | Geometry and topology | null |
and so, a rectangle with different sides (say length of 3 metres and width of 2 metres) would have an area in square units that can be calculated as:
3 metres × 2 metres = 6 m2. This is equivalent to 6 million square millimetres. Other useful conversions are:
1 square kilometre = 1,000,000 square metres
1 square met... | Area | Wikipedia | 476 | 1209 | https://en.wikipedia.org/wiki/Area | Mathematics | Geometry and topology | null |
Some traditional South Asian units that have fixed value:
1 Killa = 1 acre
1 Ghumaon = 1 acre
1 Kanal = 0.125 acre (1 acre = 8 kanal)
1 Decimal = 48.4 square yards
1 Chatak = 180 square feet
History
Circle area
In the 5th century BCE, Hippocrates of Chios was the first to show that the area of a disk (the regio... | Area | Wikipedia | 474 | 1209 | https://en.wikipedia.org/wiki/Area | Mathematics | Geometry and topology | null |
The development of Cartesian coordinates by René Descartes in the 17th century allowed the development of the surveyor's formula for the area of any polygon with known vertex locations by Gauss in the 19th century.
Areas determined using calculus
The development of integral calculus in the late 17th century provided ... | Area | Wikipedia | 512 | 1209 | https://en.wikipedia.org/wiki/Area | Mathematics | Geometry and topology | null |
Area of curved shapes
Circles
The formula for the area of a circle (more properly called the area enclosed by a circle or the area of a disk) is based on a similar method. Given a circle of radius , it is possible to partition the circle into sectors, as shown in the figure to the right. Each sector is approximatel... | Area | Wikipedia | 488 | 1209 | https://en.wikipedia.org/wiki/Area | Mathematics | Geometry and topology | null |
A triangle: (where B is any side, and h is the distance from the line on which B lies to the other vertex of the triangle). This formula can be used if the height h is known. If the lengths of the three sides are known then Heron's formula can be used: where a, b, c are the sides of the triangle, and is half of its ... | Area | Wikipedia | 485 | 1209 | https://en.wikipedia.org/wiki/Area | Mathematics | Geometry and topology | null |
where f(x) is the quadratic upper bound and g(x) is the quadratic lower bound.
By the area integral formulas above and Vieta's formula, we can obtain that
The above remains valid if one of the bounding functions is linear instead of quadratic.
Surface area of 3-dimensional figures
Cone: , where r is the radius of t... | Area | Wikipedia | 499 | 1209 | https://en.wikipedia.org/wiki/Area | Mathematics | Geometry and topology | null |
For a circle, the ratio of the area to the circumference (the term for the perimeter of a circle) equals half the radius r. This can be seen from the area formula πr2 and the circumference formula 2πr.
The area of a regular polygon is half its perimeter times the apothem (where the apothem is the distance from the cen... | Area | Wikipedia | 509 | 1209 | https://en.wikipedia.org/wiki/Area | Mathematics | Geometry and topology | null |
The triangle of largest area of all those inscribed in a given circle is equilateral; and the triangle of smallest area of all those circumscribed around a given circle is equilateral.
The ratio of the area of the incircle to the area of an equilateral triangle, , is larger than that of any non-equilateral triangle.
... | Area | Wikipedia | 108 | 1209 | https://en.wikipedia.org/wiki/Area | Mathematics | Geometry and topology | null |
The astronomical unit (symbol: au or AU) is a unit of length defined to be exactly equal to . Historically, the astronomical unit was conceived as the average Earth-Sun distance (the average of Earth's aphelion and perihelion), before its modern redefinition in 2012.
The astronomical unit is used primarily for measuri... | Astronomical unit | Wikipedia | 350 | 1210 | https://en.wikipedia.org/wiki/Astronomical%20unit | Physical sciences | Length and distance | null |
Earth's orbit around the Sun is an ellipse. The semi-major axis of this elliptic orbit is defined to be half of the straight line segment that joins the perihelion and aphelion. The centre of the Sun lies on this straight line segment, but not at its midpoint. Because ellipses are well-understood shapes, measuring the ... | Astronomical unit | Wikipedia | 334 | 1210 | https://en.wikipedia.org/wiki/Astronomical%20unit | Physical sciences | Length and distance | null |
In 1976, to establish a more precise measure for the astronomical unit, the IAU formally adopted a new definition. Although directly based on the then-best available observational measurements, the definition was recast in terms of the then-best mathematical derivations from celestial mechanics and planetary ephemeride... | Astronomical unit | Wikipedia | 422 | 1210 | https://en.wikipedia.org/wiki/Astronomical%20unit | Physical sciences | Length and distance | null |
In 1983, the CIPM modified the International System of Units (SI) to make the metre defined as the distance travelled in a vacuum by light in 1 / . This replaced the previous definition, valid between 1960 and 1983, which was that the metre equalled a certain number of wavelengths of a certain emission line of krypton-... | Astronomical unit | Wikipedia | 448 | 1210 | https://en.wikipedia.org/wiki/Astronomical%20unit | Physical sciences | Length and distance | null |
Usage and significance
With the definitions used before 2012, the astronomical unit was dependent on the heliocentric gravitational constant, that is the product of the gravitational constant, G, and the solar mass, . Neither G nor can be measured to high accuracy separately, but the value of their product is known v... | Astronomical unit | Wikipedia | 442 | 1210 | https://en.wikipedia.org/wiki/Astronomical%20unit | Physical sciences | Length and distance | null |
The astronomical unit is typically used for stellar system scale distances, such as the size of a protostellar disk or the heliocentric distance of an asteroid, whereas other units are used for other distances in astronomy. The astronomical unit is too small to be convenient for interstellar distances, where the parsec... | Astronomical unit | Wikipedia | 401 | 1210 | https://en.wikipedia.org/wiki/Astronomical%20unit | Physical sciences | Length and distance | null |
According to Eusebius in the Praeparatio evangelica (Book XV, Chapter 53), Eratosthenes found the distance to the Sun to be "σταδιων μυριαδας τετρακοσιας και οκτωκισμυριας" (literally "of stadia myriads 400 and ") but with the additional note that in the Greek text the grammatical agreement is between myriads (not stad... | Astronomical unit | Wikipedia | 508 | 1210 | https://en.wikipedia.org/wiki/Astronomical%20unit | Physical sciences | Length and distance | null |
After Greek astronomy was transmitted to the medieval Islamic world, astronomers made some changes to Ptolemy's cosmological model, but did not greatly change his estimate of the Earth–Sun distance. For example, in his introduction to Ptolemaic astronomy, al-Farghānī gave a mean solar distance of Earth radii, whereas ... | Astronomical unit | Wikipedia | 451 | 1210 | https://en.wikipedia.org/wiki/Astronomical%20unit | Physical sciences | Length and distance | null |
Christiaan Huygens believed that the distance was even greater: by comparing the apparent sizes of Venus and Mars, he estimated a value of about Earth radii, equivalent to a solar parallax of . Although Huygens' estimate is remarkably close to modern values, it is often discounted by historians of astronomy because of... | Astronomical unit | Wikipedia | 474 | 1210 | https://en.wikipedia.org/wiki/Astronomical%20unit | Physical sciences | Length and distance | null |
Another method involved determining the constant of aberration. Simon Newcomb gave great weight to this method when deriving his widely accepted value of for the solar parallax (close to the modern value of ), although Newcomb also used data from the transits of Venus. Newcomb also collaborated with A. A. Michelson to... | Astronomical unit | Wikipedia | 503 | 1210 | https://en.wikipedia.org/wiki/Astronomical%20unit | Physical sciences | Length and distance | null |
The measurements of the secular variations of the astronomical unit are not confirmed by other authors and are quite controversial.
Furthermore, since 2010, the astronomical unit has not been estimated by the planetary ephemerides.
Examples
The following table contains some distances given in astronomical units. It i... | Astronomical unit | Wikipedia | 92 | 1210 | https://en.wikipedia.org/wiki/Astronomical%20unit | Physical sciences | Length and distance | null |
Ada is a structured, statically typed, imperative, and object-oriented high-level programming language, inspired by Pascal and other languages. It has built-in language support for design by contract (DbC), extremely strong typing, explicit concurrency, tasks, synchronous message passing, protected objects, and non-det... | Ada (programming language) | Wikipedia | 507 | 1242 | https://en.wikipedia.org/wiki/Ada%20%28programming%20language%29 | Technology | "Historical" languages | null |
Ada is designed for developing very large software systems. Ada packages can be compiled separately. Ada package specifications (the package interface) can also be compiled separately without the implementation to check for consistency. This makes it possible to detect problems early during the design phase, before imp... | Ada (programming language) | Wikipedia | 512 | 1242 | https://en.wikipedia.org/wiki/Ada%20%28programming%20language%29 | Technology | "Historical" languages | null |
Though the semantics of the language allow automatic garbage collection of inaccessible objects, most implementations do not support it by default, as it would cause unpredictable behaviour in real-time systems. Ada does support a limited form of region-based memory management; also, creative use of storage pools can ... | Ada (programming language) | Wikipedia | 407 | 1242 | https://en.wikipedia.org/wiki/Ada%20%28programming%20language%29 | Technology | "Historical" languages | null |
History
In the 1970s the US Department of Defense (DoD) became concerned by the number of different programming languages being used for its embedded computer system projects, many of which were obsolete or hardware-dependent, and none of which supported safe modular programming. In 1975, a working group, the High Ord... | Ada (programming language) | Wikipedia | 344 | 1242 | https://en.wikipedia.org/wiki/Ada%20%28programming%20language%29 | Technology | "Historical" languages | null |
Requests for proposals for a new programming language were issued and four contractors were hired to develop their proposals under the names of Red (Intermetrics led by Benjamin Brosgol), Green (Honeywell, led by Jean Ichbiah), Blue (SofTech, led by John Goodenough) and Yellow (SRI International, led by Jay Spitzen). I... | Ada (programming language) | Wikipedia | 400 | 1242 | https://en.wikipedia.org/wiki/Ada%20%28programming%20language%29 | Technology | "Historical" languages | null |
The first validated Ada implementation was the NYU Ada/Ed translator, certified on April 11, 1983. NYU Ada/Ed is implemented in the high-level set language SETL. Several commercial companies began offering Ada compilers and associated development tools, including Alsys, TeleSoft, DDC-I, Advanced Computer Techniques, Ta... | Ada (programming language) | Wikipedia | 299 | 1242 | https://en.wikipedia.org/wiki/Ada%20%28programming%20language%29 | Technology | "Historical" languages | null |
Because of Ada's safety-critical support features, it is now used not only for military applications, but also in commercial projects where a software bug can have severe consequences, e.g., avionics and air traffic control, commercial rockets such as the Ariane 4 and 5, satellites and other space systems, railway tran... | Ada (programming language) | Wikipedia | 450 | 1242 | https://en.wikipedia.org/wiki/Ada%20%28programming%20language%29 | Technology | "Historical" languages | null |
Ada 95, the joint ISO/IEC/ANSI standard ISO/IEC 8652:1995 was published in February 1995, making it the first ISO standard object-oriented programming language. To help with the standard revision and future acceptance, the US Air Force funded the development of the GNAT Compiler. Presently, the GNAT Compiler is part of... | Ada (programming language) | Wikipedia | 490 | 1242 | https://en.wikipedia.org/wiki/Ada%20%28programming%20language%29 | Technology | "Historical" languages | null |
"Hello, world!" in Ada
A common example of a language's syntax is the Hello world program:
(hello.adb)
with Ada.Text_IO;
procedure Hello is
begin
Ada.Text_IO.Put_Line ("Hello, world!");
end Hello;
This program can be compiled by using the freely available open source compiler GNAT, by executing
gnatmake hello.adb
... | Ada (programming language) | Wikipedia | 485 | 1242 | https://en.wikipedia.org/wiki/Ada%20%28programming%20language%29 | Technology | "Historical" languages | null |
Work_Load: constant array(Working_Day) of Working_Hours -- implicit type declaration
:= (Friday => 6, Monday => 4, others => 10); -- lookup table for working hours with initialization
Types can have modifiers such as limited, abstract, private etc. Private types do not show their inner structure; objects... | Ada (programming language) | Wikipedia | 495 | 1242 | https://en.wikipedia.org/wiki/Ada%20%28programming%20language%29 | Technology | "Historical" languages | null |
Functions differ from procedures in that they must return a value. Function calls cannot be used "as a statement", and their result must be assigned to a variable. However, since Ada 2012, functions are not required to be pure and may mutate their suitably declared parameters or the global state.
Example:
Package spec... | Ada (programming language) | Wikipedia | 440 | 1242 | https://en.wikipedia.org/wiki/Ada%20%28programming%20language%29 | Technology | "Historical" languages | null |
Alpha decay or α-decay is a type of radioactive decay in which an atomic nucleus emits an alpha particle (helium nucleus) and thereby transforms or "decays" into a different atomic nucleus, with a mass number that is reduced by four and an atomic number that is reduced by two. An alpha particle is identical to the nucl... | Alpha decay | Wikipedia | 486 | 1267 | https://en.wikipedia.org/wiki/Alpha%20decay | Physical sciences | Nuclear physics | Physics |
Approximately 99% of the helium produced on Earth is the result of the alpha decay of underground deposits of minerals containing uranium or thorium. The helium is brought to the surface as a by-product of natural gas production.
History
Alpha particles were first described in the investigations of radioactivity by... | Alpha decay | Wikipedia | 479 | 1267 | https://en.wikipedia.org/wiki/Alpha%20decay | Physical sciences | Nuclear physics | Physics |
where is the initial mass of the nucleus, is the mass of the nucleus after particle emission, and is the mass of the emitted (alpha-)particle, one finds that in certain cases it is positive and so alpha particle emission is possible, whereas other decay modes would require energy to be added. For example, performing... | Alpha decay | Wikipedia | 406 | 1267 | https://en.wikipedia.org/wiki/Alpha%20decay | Physical sciences | Nuclear physics | Physics |
Quantum tunneling
Quantum mechanics, however, allows the alpha particle to escape via quantum tunneling. The quantum tunneling theory of alpha decay, independently developed by George Gamow and by Ronald Wilfred Gurney and Edward Condon in 1928, was hailed as a very striking confirmation of quantum theory. Essentially... | Alpha decay | Wikipedia | 367 | 1267 | https://en.wikipedia.org/wiki/Alpha%20decay | Physical sciences | Nuclear physics | Physics |
The isotopes in beta-decay stable isobars that are also stable with regards to double beta decay with mass number A = 5, A = 8, 143 ≤ A ≤ 155, 160 ≤ A ≤ 162, and A ≥ 165 are theorized to undergo alpha decay. All other mass numbers (isobars) have exactly one theoretically stable nuclide. Those with mass 5 decay to heliu... | Alpha decay | Wikipedia | 389 | 1267 | https://en.wikipedia.org/wiki/Alpha%20decay | Physical sciences | Nuclear physics | Physics |
Toxicity
Highly charged and heavy, alpha particles lose their several MeV of energy within a small volume of material, along with a very short mean free path. This increases the chance of double-strand breaks to the DNA in cases of internal contamination, when ingested, inhaled, injected or introduced through the skin... | Alpha decay | Wikipedia | 394 | 1267 | https://en.wikipedia.org/wiki/Alpha%20decay | Physical sciences | Nuclear physics | Physics |
The largest natural contributor to public radiation dose is radon, a naturally occurring, radioactive gas found in soil and rock. If the gas is inhaled, some of the radon particles may attach to the inner lining of the lung. These particles continue to decay, emitting alpha particles, which can damage cells in the lung... | Alpha decay | Wikipedia | 214 | 1267 | https://en.wikipedia.org/wiki/Alpha%20decay | Physical sciences | Nuclear physics | Physics |
The analytical engine was a proposed digital mechanical general-purpose computer designed by English mathematician and computer pioneer Charles Babbage. It was first described in 1837 as the successor to Babbage's Difference Engine, which was a design for a simpler mechanical calculator.
The analytical engine incorpor... | Analytical engine | Wikipedia | 415 | 1271 | https://en.wikipedia.org/wiki/Analytical%20engine | Technology | Early computers | null |
There was to be a store (that is, a memory) capable of holding 1,000 numbers of 40 decimal digits each (ca. 16.6 kB). An arithmetic unit (the "mill") would be able to perform all four arithmetic operations, plus comparisons and optionally square roots. Initially (1838) it was conceived as a difference engine curved bac... | Analytical engine | Wikipedia | 456 | 1271 | https://en.wikipedia.org/wiki/Analytical%20engine | Technology | Early computers | null |
In 1878, a committee of the British Association for the Advancement of Science described the analytical engine as "a marvel of mechanical ingenuity", but recommended against constructing it. The committee acknowledged the usefulness and value of the machine, but could not estimate the cost of building it, and were unsu... | Analytical engine | Wikipedia | 398 | 1271 | https://en.wikipedia.org/wiki/Analytical%20engine | Technology | Early computers | null |
In October 2010, John Graham-Cumming started a "Plan 28" campaign to raise funds by "public subscription" to enable serious historical and academic study of Babbage's plans, with a view to then build and test a fully working virtual design which will then in turn enable construction of the physical analytical engine. A... | Analytical engine | Wikipedia | 441 | 1271 | https://en.wikipedia.org/wiki/Analytical%20engine | Technology | Early computers | null |
The Engine's Card Reader is not constrained to simply process the cards in a chain one after another from start to finish. It can, in addition, directed by the very cards it reads and advised by whether the Mill's run-up lever is activated, either advance the card chain forward, skipping the intervening cards, or backw... | Analytical engine | Wikipedia | 506 | 1271 | https://en.wikipedia.org/wiki/Analytical%20engine | Technology | Early computers | null |
Vannevar Bush's paper Instrumental Analysis (1936) included several references to Babbage's work. In the same year he started the Rapid Arithmetical Machine project to investigate the problems of constructing an electronic digital computer.
Despite this groundwork, Babbage's work fell into historical obscurity, and th... | Analytical engine | Wikipedia | 413 | 1271 | https://en.wikipedia.org/wiki/Analytical%20engine | Technology | Early computers | null |
In popular culture
The cyberpunk novelists William Gibson and Bruce Sterling co-authored a steampunk novel of alternative history titled The Difference Engine in which Babbage's difference and analytical engines became available to Victorian society. The novel explores the consequences and implications of the early i... | Analytical engine | Wikipedia | 343 | 1271 | https://en.wikipedia.org/wiki/Analytical%20engine | Technology | Early computers | null |
Abalone ( or ; via Spanish , from Rumsen aulón) is a common name for any small to very large marine gastropod mollusc in the family Haliotidae, which once contained six genera but now contains only one genus, Haliotis. Other common names are ear shells, sea ears, and, now rarely, muttonfish or muttonshells in parts of... | Abalone | Wikipedia | 439 | 1300 | https://en.wikipedia.org/wiki/Abalone | Biology and health sciences | Gastropods | Animals |
A mantle cleft in the shell impresses a groove in the shell, in which are the row of holes characteristic of the genus. These holes are respiratory apertures for venting water from the gills and for releasing sperm and eggs into the water column. They make up what is known as the selenizone, which forms as the shell gr... | Abalone | Wikipedia | 448 | 1300 | https://en.wikipedia.org/wiki/Abalone | Biology and health sciences | Gastropods | Animals |
The haliotid family has a worldwide distribution, along the coastal waters of every continent, except the Pacific coast of South America, the Atlantic coast of North America, the Arctic, and Antarctica. The majority of abalone species are found in cold waters, such as off the coasts of New Zealand, South Africa, Austra... | Abalone | Wikipedia | 407 | 1300 | https://en.wikipedia.org/wiki/Abalone | Biology and health sciences | Gastropods | Animals |
Farming of abalone began in the late 1950s and early 1960s in Japan and China. Since the mid-1990s, there have been many increasingly successful endeavors to commercially farm abalone for the purpose of consumption. Overfishing and poaching have reduced wild populations to such an extent that farmed abalone now supplie... | Abalone | Wikipedia | 356 | 1300 | https://en.wikipedia.org/wiki/Abalone | Biology and health sciences | Gastropods | Animals |
As abalone became more popular and less common, the prices adjusted accordingly. In the 1920s, a restaurant-served portion of abalone, about 4 ounces, would cost (in inflation adjusted dollars) about US$7; by 2004, the price had risen to US$75. In the United States, prior to this time, abalone was predominantly eaten, ... | Abalone | Wikipedia | 512 | 1300 | https://en.wikipedia.org/wiki/Abalone | Biology and health sciences | Gastropods | Animals |
Victoria has had an active abalone fishery since the late 1950s. The state is sectioned into three fishing zones, Eastern, Central and Western, with each fisher required a zone-allocated licence. Harvesting is performed by divers using surface-supplied air "hookah" systems operating from runabout-style, outboard-powere... | Abalone | Wikipedia | 399 | 1300 | https://en.wikipedia.org/wiki/Abalone | Biology and health sciences | Gastropods | Animals |
As of 2017, abalone season is May to October, excluding July. Transportation of abalone may only legally occur while the abalone is still attached in the shell. Sale of sport-obtained abalone is illegal, including the shell. Only red abalone may be taken, as black, white, pink, flat, green, and pinto abalone are protec... | Abalone | Wikipedia | 462 | 1300 | https://en.wikipedia.org/wiki/Abalone | Biology and health sciences | Gastropods | Animals |
Like all New Zealand shellfish, recreational harvesting of pāua does not require a permit provided catch limits, size restrictions, and seasonal and local restrictions set by the Ministry for Primary Industries (MPI) are followed. The legal recreational daily limit is 10 per diver, with a minimum shell length of for H... | Abalone | Wikipedia | 359 | 1300 | https://en.wikipedia.org/wiki/Abalone | Biology and health sciences | Gastropods | Animals |
For the last few years, however, no permits have been issued for collecting abalone, but commercial harvesting still continues as does illegal collection by syndicates.
In 2007, because of widespread poaching of abalone, the South African government listed abalone as an endangered species according to the CITES section... | Abalone | Wikipedia | 492 | 1300 | https://en.wikipedia.org/wiki/Abalone | Biology and health sciences | Gastropods | Animals |
Indigenous use
Abalone has been an important staple in a number of Indigenous cultures around the world, specifically in Africa and on the Northwest American coast. The meat is a traditional food, and the shell is used to make ornaments; historically, the shells were also used as currency in some communities.
Threat ... | Abalone | Wikipedia | 283 | 1300 | https://en.wikipedia.org/wiki/Abalone | Biology and health sciences | Gastropods | Animals |
Aromatic compounds or arenes are organic compounds "with a chemistry typified by benzene" and "cyclically conjugated."
The word "aromatic" originates from the past grouping of molecules based on odor, before their general chemical properties were understood. The current definition of aromatic compounds does not have an... | Aromatic compound | Wikipedia | 403 | 1313 | https://en.wikipedia.org/wiki/Aromatic%20compound | Physical sciences | Hydrocarbons | null |
Benzene, C6H6, is the least complex aromatic hydrocarbon, and it was the first one defined as such. Its bonding nature was first recognized independently by Joseph Loschmidt and August Kekulé in the 19th century. Each carbon atom in the hexagonal cycle has four electrons to share. One electron forms a sigma bond with t... | Aromatic compound | Wikipedia | 325 | 1313 | https://en.wikipedia.org/wiki/Aromatic%20compound | Physical sciences | Hydrocarbons | null |
Benzene derivatives have from one to six substituents attached to the central benzene core. Examples of benzene compounds with just one substituent are phenol, which carries a hydroxyl group, and toluene with a methyl group. When there is more than one substituent present on the ring, their spatial relationship becomes... | Aromatic compound | Wikipedia | 469 | 1313 | https://en.wikipedia.org/wiki/Aromatic%20compound | Physical sciences | Hydrocarbons | null |
Monocyclic arenes
Of annulenes larger than benzene, [12]annulene and [14]annulene are weakly aromatic compounds and [18]annulene, Cyclooctadecanonaene, is aromatic, though strain within the structure causes a slight deviation from the precisely planar structure necessary for aromatic categorization. Another example of... | Aromatic compound | Wikipedia | 449 | 1313 | https://en.wikipedia.org/wiki/Aromatic%20compound | Physical sciences | Hydrocarbons | null |
Substitution
In aromatic substitution, one substituent on the arene ring, usually hydrogen, is replaced by another reagent. The two main types are electrophilic aromatic substitution, when the active reagent is an electrophile, and nucleophilic aromatic substitution, when the reagent is a nucleophile. In radical-nucle... | Aromatic compound | Wikipedia | 348 | 1313 | https://en.wikipedia.org/wiki/Aromatic%20compound | Physical sciences | Hydrocarbons | null |
In modern physics, antimatter is defined as matter composed of the antiparticles (or "partners") of the corresponding particles in "ordinary" matter, and can be thought of as matter with reversed charge, parity, and time, known as CPT reversal. Antimatter occurs in natural processes like cosmic ray collisions and some ... | Antimatter | Wikipedia | 472 | 1317 | https://en.wikipedia.org/wiki/Antimatter | Physical sciences | Antimatter | null |
There is strong evidence that the observable universe is composed almost entirely of ordinary matter, as opposed to an equal mixture of matter and antimatter. This asymmetry of matter and antimatter in the visible universe is one of the great unsolved problems in physics. The process by which this inequality between ma... | Antimatter | Wikipedia | 467 | 1317 | https://en.wikipedia.org/wiki/Antimatter | Physical sciences | Antimatter | null |
The modern theory of antimatter began in 1928, with a paper by Paul Dirac. Dirac realised that his relativistic version of the Schrödinger wave equation for electrons predicted the possibility of antielectrons. Although Dirac had laid the groundwork for the existence of these “antielectrons” he initially failed to pick... | Antimatter | Wikipedia | 445 | 1317 | https://en.wikipedia.org/wiki/Antimatter | Physical sciences | Antimatter | null |
Properties
There is no difference in the gravitational behavior of matter and antimatter. In other words, antimatter falls down when dropped, not up. This was confirmed with the thin, very cold gas of thousands of antihydrogen atoms that were confined in a vertical shaft surrounded by superconducting electromagnetic co... | Antimatter | Wikipedia | 350 | 1317 | https://en.wikipedia.org/wiki/Antimatter | Physical sciences | Antimatter | null |
Antiparticles are created everywhere in the universe where high-energy particle collisions take place. High-energy cosmic rays striking Earth's atmosphere (or any other matter in the Solar System) produce minute quantities of antiparticles in the resulting particle jets, which are immediately annihilated by contact wit... | Antimatter | Wikipedia | 467 | 1317 | https://en.wikipedia.org/wiki/Antimatter | Physical sciences | Antimatter | null |
Antimatter quantum interferometry has been first demonstrated in 2018 in the Positron Laboratory (L-NESS) of Rafael Ferragut in Como (Italy), by a group led by Marco Giammarchi.
Natural production
Positrons are produced naturally in β+ decays of naturally occurring radioactive isotopes (for example, potassium-40) and... | Antimatter | Wikipedia | 369 | 1317 | https://en.wikipedia.org/wiki/Antimatter | Physical sciences | Antimatter | null |
Satellite experiments have found evidence of positrons and a few antiprotons in primary cosmic rays, amounting to less than 1% of the particles in primary cosmic rays. This antimatter cannot all have been created in the Big Bang, but is instead attributed to have been produced by cyclic processes at high energies. For ... | Antimatter | Wikipedia | 503 | 1317 | https://en.wikipedia.org/wiki/Antimatter | Physical sciences | Antimatter | null |
There is an ongoing search for larger antimatter nuclei, such as antihelium nuclei (that is, anti-alpha particles), in cosmic rays. The detection of natural antihelium could imply the existence of large antimatter structures such as an antistar. A prototype of the AMS-02 designated AMS-01, was flown into space aboard t... | Antimatter | Wikipedia | 448 | 1317 | https://en.wikipedia.org/wiki/Antimatter | Physical sciences | Antimatter | null |
The existence of the antiproton was experimentally confirmed in 1955 by University of California, Berkeley physicists Emilio Segrè and Owen Chamberlain, for which they were awarded the 1959 Nobel Prize in Physics. An antiproton consists of two up antiquarks and one down antiquark (). The properties of the antiproton th... | Antimatter | Wikipedia | 421 | 1317 | https://en.wikipedia.org/wiki/Antimatter | Physical sciences | Antimatter | null |
In 1999, CERN activated the Antiproton Decelerator, a device capable of decelerating antiprotons from to – still too "hot" to produce study-effective antihydrogen, but a huge leap forward. In late 2002 the ATHENA project announced that they had created the world's first "cold" antihydrogen. The ATRAP project released... | Antimatter | Wikipedia | 495 | 1317 | https://en.wikipedia.org/wiki/Antimatter | Physical sciences | Antimatter | null |
Most of the sought-after high-precision tests of the properties of antihydrogen could only be performed if the antihydrogen were trapped, that is, held in place for a relatively long time. While antihydrogen atoms are electrically neutral, the spins of their component particles produce a magnetic moment. These magnetic... | Antimatter | Wikipedia | 509 | 1317 | https://en.wikipedia.org/wiki/Antimatter | Physical sciences | Antimatter | null |
Antihelium
Antihelium-3 nuclei () were first observed in the 1970s in proton–nucleus collision experiments at the Institute for High Energy Physics by Y. Prockoshkin's group (Protvino near Moscow, USSR) and later created in nucleus–nucleus collision experiments. Nucleus–nucleus collisions produce antinuclei through the... | Antimatter | Wikipedia | 407 | 1317 | https://en.wikipedia.org/wiki/Antimatter | Physical sciences | Antimatter | null |
Cost
Scientists claim that antimatter is the costliest material to make. In 2006, Gerald Smith estimated $250 million could produce 10 milligrams of positrons (equivalent to $25 billion per gram); in 1999, NASA gave a figure of $62.5 trillion per gram of antihydrogen. This is because production is difficult (only very ... | Antimatter | Wikipedia | 431 | 1317 | https://en.wikipedia.org/wiki/Antimatter | Physical sciences | Antimatter | null |
If matter–antimatter collisions resulted only in photon emission, the entire rest mass of the particles would be converted to kinetic energy. The energy per unit mass () is about 10 orders of magnitude greater than chemical energies, and about 3 orders of magnitude greater than the nuclear potential energy that can be ... | Antimatter | Wikipedia | 428 | 1317 | https://en.wikipedia.org/wiki/Antimatter | Physical sciences | Antimatter | null |
Antimatter has been considered as a trigger mechanism for nuclear weapons. A major obstacle is the difficulty of producing antimatter in large enough quantities, and there is no evidence that it will ever be feasible. Nonetheless, the U.S. Air Force funded studies of the physics of antimatter in the Cold War, and began... | Antimatter | Wikipedia | 86 | 1317 | https://en.wikipedia.org/wiki/Antimatter | Physical sciences | Antimatter | null |
In particle physics, every type of particle of "ordinary" matter (as opposed to antimatter) is associated with an antiparticle with the same mass but with opposite physical charges (such as electric charge). For example, the antiparticle of the electron is the positron (also known as an antielectron). While the electro... | Antiparticle | Wikipedia | 433 | 1327 | https://en.wikipedia.org/wiki/Antiparticle | Physical sciences | Antimatter | null |
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