process

process

[pros-es; especially Brit. proh-ses]
process, in law: see procedure.
or thought

Action of using one's mind to produce thoughts, or covert symbolic responses to stimuli. Theories of thought and thought processes have concentrated largely on directed thinking, including problem solving. At the beginning of the 20th century, researchers focused on studying mental associations. Theorists of Gestalt psychology in the 1920s and '30s believed the elements of thought to be in the nature of patterns elicited from experience. Today these elements are often regarded as bits of information undergoing processing. Seealso cognitive psychology, information processing.

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In probability theory, a family of random variables indexed to some other set and having the property that for each finite subset of the index set, the collection of random variables indexed to it has a joint probability distribution. It is one of the most widely studied subjects in probability. Examples include Markov processes (in which the present value of the variable depends only upon the immediate past and not upon the whole sequence of past events), such as stock-market fluctuations, and time series (in which temperature or rainfall measurements, for example, are taken at the same time each day over several days).

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20th-century school of philosophy that emphasizes the elements of becoming, change, and novelty in experienced reality and opposes the traditional Western philosophical stress on being, permanence, and uniformity. Reality, including both the natural world and the human sphere, is essentially historical in this view, emerging from (and bearing) a past and advancing into a novel future. Hence, it cannot be grasped by old static spatial concepts that ignore the temporal and novel aspects of the universe given in human experience. The foremost contributors to process philosophy have been Henri Bergson and Alfred North Whitehead.

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or Mexican process

Method of isolating silver from its ore, apparently dating from pre-Columbian times. The ore was crushed and ground by mule power in arrastras, reducing it to a fine mud. This was then spread over a courtyard or patio, sprinkled with mercury, salt, and copper sulfate, and mixed by driving mules over it. Chemical reactions caused the silver to dissolve in the mercury. When the amalgamation was complete, the material was agitated with water in large tubs and the mud run off. The amalgam at the bottom was collected and heated to drive off the mercury. Used for much of the world's silver production for 350 years, the process was replaced by the cyanide process early in the 20th century.

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or Siemens-Martin process

Steelmaking technique that for most of the 20th century accounted for most steel made in the world. William Siemens made steel from pig iron in a reverberatory furnace of his design in 1867. The same year the French manufacturer Pierre-Émile Martin (1824–1915) used the idea to produce steel by melting wrought iron with steel scrap. Siemens used the waste heat given off by the furnace: he directed the fumes from the furnace through a brick checkerwork, heating it to a high temperature, and then used the same path to introduce air into the furnace; the preheated air significantly increased the flame temperature. The open-hearth process furnace (which replaced the Bessemer process) has itself been replaced in most industrialized countries by the basic oxygen process and the electric furnace. Seealso reverberatory furnace.

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Chemical method for producing wood pulp using caustic soda and sodium sulfide as the liquor in which the pulpwood is cooked to loosen the fibres. The process (from German kraft, “strong”) produces particularly strong and durable paper; another advantage is its capability of digesting pine chips; resins dissolve in the alkaline liquor and are recovered as tall oil, a valuable by-product. Recovery of sodium compounds is important in the economy of the process. In modern kraft mills, operations are completely contained; waste streams are recycled and reused, eliminating water pollution.

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In printing, a technique of breaking up an image into a series of dots to permit reproduction of the full tone range of a photograph or artwork. It is traditionally done by placing a glass screen printed with a tight grid of lines over the plate being exposed. The grid breaks up the image into hundreds of tiny dots, each of which is read by the camera as either black or white—or, in the case of colour art, as either a single printing colour or white. The resulting image, called a halftone, is then rephotographed for printing. Screens are made with a varying number of lines per inch, depending on the application; for newspapers the range is about 80–120, whereas glossy magazines usually require 133–175 lines per inch.

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Legal proceedings carried out fairly and in accord with established rules and principles. Due process standards are sometimes referred to as either substantive or procedural. Substantive due process refers to a requirement that laws and regulations be related to a legitimate government interest (e.g., crime prevention) and not contain provisions that result in the unfair or arbitrary treatment of an individual. The 5th Amendment to the Constitution of the United States states that “no person shallelipsisbe deprived of life, liberty, or property, without due process of law.” This right was extended to the states by the 14th Amendment (1868). Fundamental to procedural due process are adequate notice before the government can deprive one of life, liberty, or property, and the opportunity to be heard and defend one's rights. The boundaries of due process are not fixed and are the subject of endless judicial interpretation and decision making. Seealso rights of the accused; double jeopardy.

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or MacArthur-Forrest process

Method of extracting silver and gold from their ores by dissolving them in a dilute solution of sodium cyanide or potassium cyanide. The process—invented in 1887 by the Scottish chemists John S. MacArthur, Robert W. Forrest, and William Forrest—includes contacting the finely ground ore with the cyanide solution, separating unwanted solids from the clear solution, and recovering the precious metals from the solution by precipitation with zinc dust.

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Steelmaking method in which pure oxygen is blown through a long, movable lance into a bath of molten blast-furnace iron and scrap, in a steel furnace with a refractory lining called a converter. The oxygen initiates a series of heat-releasing reactions, including the oxidation of such impurities as silicon, carbon, phosphorus, and manganese; carbon dioxide is released, and the oxidation products of the other impurities form molten slag that floats on the molten steel. The advantages of using pure oxygen instead of air in refining iron into steel were recognized as early as the 1850s (see Bessemer process), but the process could not be commercialized until the late 1940s, when cheap, high-purity oxygen became available. Within 40 years it had replaced the open-hearth process and was producing more than half of all steel worldwide. Commercial advantages include high production rates, less labour, and steel with a low nitrogen content.

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Modification of the Bessemer process for converting pig iron into steel. The original Bessemer converter was not effective in removing the phosphorus from iron made from the high-phosphorus ores common in Britain and Europe. The invention of the basic process in England by Sidney G. Thomas (1850–1885) and Percy Gilchrist overcame this problem; the Thomas-Gilchrist converter was lined with a basic material such as burned limestone rather than an acid siliceous material. The introduction of the basic Bessemer process in 1879 made it possible for the first time for such high-phosphorus ore to be used for making steel.

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or ammonia-soda process

Modern method of manufacturing sodium carbonate (soda ash), devised and commercialized in Belgium by Ernest Solvay (1838–1922). Common salt (sodium chloride) is treated with ammonia and then carbon dioxide, under carefully controlled conditions, to form sodium bicarbonate and ammonium chloride. When heated, the bicarbonate yields sodium carbonate, the desired product; the ammonium chloride is treated with lime to produce ammonia (for reuse) and calcium chloride. The process proved of great commercial value, since large quantities of soda ash are used in making glass, detergents, and cleansers. Seealso caustic soda.

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The r-process is a nucleosynthesis process occurring in core-collapse supernovae (see also supernova nucleosynthesis) responsible for the creation of approximately half of the neutron-rich atomic nuclei that are heavier than iron. The process entails a succession of rapid neutron captures on iron seed nuclei, hence the name r-process. The other predominant mechanism for the production of heavy elements is the s-process, which is nucleosynthesis by means of slow neutron captures, primarily occurring in AGB stars, and together these two processes account for a majority of galactic chemical evolution of elements heavier than iron.

History

The r-process was seen to be needed from the relative abundances of isotopes of heavy elements and from a newly published table of abundances by Hans Suess and Harold Urey in 1956. Among other things, this data showed abundance peaks for Germanium, Xenon, and Platinum. According to quantum mechanics and the nuclear shell model, radioactive nuclei that decay into isotopes of these elements have closed neutron shells near the neutron drip line. This implies that some abundant nuclei must be created by rapid neutron capture, and it was only a matter of determining what other nuclei could be accounted for by such a process. A table apportioning the heavy isotopes between s-process and r-process was published in a famous review paper in 1957, which proposed the theory of stellar nucleosynthesis and set the frame-work for contemporary nuclear astrophysics.

Nuclear physics

Immediately after a core-collapse supernova, there is an extremely high neutron flux (on the order of 1022 neutrons per cm² per second) and temperature, so that neutron captures occur much faster than beta-minus decays far from stability, meaning that the r-process "runs up" along the neutron drip line. The only two hold-ups inhibiting this process of climbing the neutron drip line are a notable decreases in the neutron-capture cross section at nuclei with closed neutron shells, and the degree of nuclear stability in the heavy-isotope region, which terminates the r-process when such nuclei become readily unstable to spontaneous fission (currently believed to be in the neutron-rich region near A = 270 (number of nucleons) in the chart of nuclides). After the neutron flux decreases, these highly unstable radioactive nuclei quickly decay to form stable, neutron-rich nuclei. So, while the s-process creates an abundance of stable nuclei with closed neutron shells, the r-process creates an abundance of nuclei about 10 Atomic mass units below the s-process peaks, as the r-process nuclei decay back towards stability on a constant A line in the chart of nuclides.

Astrophysical sites

The most widely believed candidate site for the r-process are core-collapse supernovae (spectral Type Ib, Ic and II), which provide the necessary physical conditions for the R-process. However, the abundance of r-process nuclei requires that either only a small fraction of supernovae eject r-process nuclei to the interstellar medium, or that each supernova ejects only a very small amount of r-process material. A recently proposed alternative solution is that neutron star mergers (a binary star system of two neutron stars that collide) may also play a role in the production of r-process nuclei, but this has yet to be observationally confirmed.

References

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