Virtual International Authority File
The Virtual International Authority File is an international authority file. It is a joint project of several national libraries and operated by the Online Computer Library Center. Discussion about having a common international authority started in the late 1990s. After a series of failed attempts to come up with a unique common authority file, the new idea was to link existing national authorities; this would present all the benefits of a common file without requiring a large investment of time and expense in the process. The project was initiated by the US Library of Congress, the German National Library and the OCLC on August 6, 2003; the Bibliothèque nationale de France joined the project on October 5, 2007. The project transitioned to being a service of the OCLC on April 4, 2012; the aim is to link the national authority files to a single virtual authority file. In this file, identical records from the different data sets are linked together. A VIAF record receives a standard data number, contains the primary "see" and "see also" records from the original records, refers to the original authority records.
The data are available for research and data exchange and sharing. Reciprocal updating uses the Open Archives Initiative Protocol for Metadata Harvesting protocol; the file numbers are being added to Wikipedia biographical articles and are incorporated into Wikidata. VIAF's clustering algorithm is run every month; as more data are added from participating libraries, clusters of authority records may coalesce or split, leading to some fluctuation in the VIAF identifier of certain authority records. Authority control Faceted Application of Subject Terminology Integrated Authority File International Standard Authority Data Number International Standard Name Identifier Wikipedia's authority control template for articles Official website VIAF at OCLC
Guillaume François Rouelle was a French chemist and apothecary. In 1754 he introduced the concept of a base into chemistry, as a substance which reacts with an acid to give it solid form, he is known as l'Aîné to distinguish him from his younger brother, Hilaire Rouelle, a chemist and known as the discoverer of urea. He started a public course in his laboratory in 1738 where he taught many students among whom were Denis Diderot, Antoine-Laurent de Lavoisier, Joseph Proust and Antoine-Augustin Parmentier, he was elected a foreign member of the Royal Swedish Academy of Sciences in 1749. Franckowiak, Rémi. "Rouelle, un vrai-faux anti-newtonien". Archives internationales d'histoire des sciences. 53: 240–255. Franckowiak, Rémi. "Les sels neutres de Guillaume-François Rouelle". Revue d'Histoire des Sciences. 55: 493–532. Jensen, William B.. "The origin of the term "base"". The Journal of Chemical Education. 83: 1130. Bibcode:2006JChEd..83.1130J. Doi:10.1021/ed083p1130. Lemay, Pierre. "The lectures of Guillaume Francois Rouelle".
The Journal of Chemical Education. 31: 338. Bibcode:1954JChEd..31..338L. Doi:10.1021/ed031p338. Warolin, C.. "Lavoisier". Histoire des sciences médicales. 30: 30. PMID 11624829. Warolin, C.. "Lavoisier". Revue d'histoire de la pharmacie. 42: 361–367. PMID 11624913
Mathieu is a commune in the Calvados department in the Normandy region in northwestern France. Communes of the Calvados department INSEE
Integrated Authority File
The Integrated Authority File or GND is an international authority file for the organisation of personal names, subject headings and corporate bodies from catalogues. It is used for documentation in libraries and also by archives and museums; the GND is managed by the German National Library in cooperation with various regional library networks in German-speaking Europe and other partners. The GND falls under the Creative Commons Zero licence; the GND specification provides a hierarchy of high-level entities and sub-classes, useful in library classification, an approach to unambiguous identification of single elements. It comprises an ontology intended for knowledge representation in the semantic web, available in the RDF format; the Integrated Authority File became operational in April 2012 and integrates the content of the following authority files, which have since been discontinued: Name Authority File Corporate Bodies Authority File Subject Headings Authority File Uniform Title File of the Deutsches Musikarchiv At the time of its introduction on 5 April 2012, the GND held 9,493,860 files, including 2,650,000 personalised names.
There are seven main types of GND entities: LIBRIS Virtual International Authority File Information pages about the GND from the German National Library Search via OGND Bereitstellung des ersten GND-Grundbestandes DNB, 19 April 2012 From Authority Control to Linked Authority Data Presentation given by Reinhold Heuvelmann to the ALA MARC Formats Interest Group, June 2012
Système universitaire de documentation
The système universitaire de documentation or SUDOC is a system used by the libraries of French universities and higher education establishments to identify and manage the documents in their possession. The catalog, which contains more than 10 million references, allows students and researcher to search for bibliographical and location information in over 3,400 documentation centers, it is maintained by the Bibliographic Agency for Higher Education. Official website
A chemical substance is a form of matter having constant chemical composition and characteristic properties. It cannot be separated into components by physical separation methods, i.e. without breaking chemical bonds. Chemical substances can be chemical compounds, or alloys. Chemical elements may not be included in the definition, depending on expert viewpoint. Chemical substances are called'pure' to set them apart from mixtures. A common example of a chemical substance is pure water. Other chemical substances encountered in pure form are diamond, table salt and refined sugar. However, in practice, no substance is pure, chemical purity is specified according to the intended use of the chemical. Chemical substances exist as solids, gases, or plasma, may change between these phases of matter with changes in temperature or pressure. Chemical substances may be converted to others by means of chemical reactions. Forms of energy, such as light and heat, are not matter, are thus not "substances" in this regard.
A chemical substance may well be defined as "any material with a definite chemical composition" in an introductory general chemistry textbook. According to this definition a chemical substance can either be a pure chemical element or a pure chemical compound. But, there are exceptions to this definition; the chemical substance index published by CAS includes several alloys of uncertain composition. Non-stoichiometric compounds are a special case that violates the law of constant composition, for them, it is sometimes difficult to draw the line between a mixture and a compound, as in the case of palladium hydride. Broader definitions of chemicals or chemical substances can be found, for example: "the term'chemical substance' means any organic or inorganic substance of a particular molecular identity, including – any combination of such substances occurring in whole or in part as a result of a chemical reaction or occurring in nature". In geology, substances of uniform composition are called minerals, while physical mixtures of several minerals are defined as rocks.
Many minerals, mutually dissolve into solid solutions, such that a single rock is a uniform substance despite being a mixture in stoichiometric terms. Feldspars are a common example: anorthoclase is an alkali aluminum silicate, where the alkali metal is interchangeably either sodium or potassium. In law, "chemical substances" may include both pure substances and mixtures with a defined composition or manufacturing process. For example, the EU regulation REACH defines "monoconstituent substances", "multiconstituent substances" and "substances of unknown or variable composition"; the latter two consist of multiple chemical substances. For example, charcoal is an complex polymeric mixture that can be defined by its manufacturing process. Therefore, although the exact chemical identity is unknown, identification can be made to a sufficient accuracy; the CAS index includes mixtures. Polymers always appear as mixtures of molecules of multiple molar masses, each of which could be considered a separate chemical substance.
However, the polymer may be defined by a known precursor or reaction and the molar mass distribution. For example, polyethylene is a mixture of long chains of -CH2- repeating units, is sold in several molar mass distributions, LDPE, MDPE, HDPE and UHMWPE; the concept of a "chemical substance" became established in the late eighteenth century after work by the chemist Joseph Proust on the composition of some pure chemical compounds such as basic copper carbonate. He deduced; this is now known as the law of constant composition. With the advancement of methods for chemical synthesis in the realm of organic chemistry. However, there are some controversies regarding this definition because the large number of chemical substances reported in chemistry literature need to be indexed. Isomerism caused much consternation to early researchers, since isomers have the same composition, but differ in configuration of the atoms. For example, there was much speculation for the chemical identity of benzene, until the correct structure was described by Friedrich August Kekulé.
The idea of stereoisomerism – that atoms have rigid three-dimensional structure and can thus form isomers that differ only in their three-dimensional arrangement – was another crucial step in understanding the concept of distinct chemical substances. For example, tartaric acid has three distinct isomers, a pair of diastereomers with one diastereomer forming two enantiomers. An element is a chemical substance made up of a particular kind of atom and hence cannot be broken down or transformed by a chemical reaction into a different element, though it can be transmuted into another element through a nuclear reaction; this is so, beca
Urea known as carbamide, is an organic compound with chemical formula CO2. This amide has two –NH2 groups joined by a carbonyl functional group. Urea serves an important role in the metabolism of nitrogen-containing compounds by animals and is the main nitrogen-containing substance in the urine of mammals, it is a colorless, odorless solid soluble in water, non-toxic. Dissolved in water, it is neither alkaline; the body uses it in most notably nitrogen excretion. The liver forms it by combining two ammonia molecules with a carbon dioxide molecule in the urea cycle. Urea is used in fertilizers as a source of nitrogen and is an important raw material for the chemical industry. Friedrich Wöhler's discovery in 1828 that urea can be produced from inorganic starting materials was an important conceptual milestone in chemistry, it showed for the first time that a substance known only as a byproduct of life could be synthesized in the laboratory without biological starting materials thereby contradicting the held doctrine of vitalism.
More than 90% of world industrial production of urea is destined for use as a nitrogen-release fertilizer. Urea has the highest nitrogen content of all solid nitrogenous fertilizers in common use. Therefore, it has the lowest transportation costs per unit of nitrogen nutrient. Many soil bacteria possess the enzyme urease, which catalyzes conversion of urea to ammonia or ammonium ion and bicarbonate ion, thus urea fertilizers transform to the ammonium form in soils. Among the soil bacteria known to carry urease, some ammonia-oxidizing bacteria, such as species of Nitrosomonas, can assimilate the carbon dioxide the reaction releases to make biomass via the Calvin cycle, harvest energy by oxidizing ammonia to nitrite, a process termed nitrification. Nitrite-oxidizing bacteria Nitrobacter, oxidize nitrite to nitrate, mobile in soils because of its negative charge and is a major cause of water pollution from agriculture. Ammonium and nitrate are absorbed by plants, are the dominant sources of nitrogen for plant growth.
Urea is used in many multi-component solid fertilizer formulations. Urea is soluble in water and is therefore very suitable for use in fertilizer solutions, e.g. in'foliar feed' fertilizers. For fertilizer use, granules are preferred over prills because of their narrower particle size distribution, an advantage for mechanical application; the most common impurity of synthetic urea is biuret. Urea is spread at rates of between 40 and 300 kg/ha but rates vary. Smaller applications incur lower losses due to leaching. During summer, urea is spread just before or during rain to minimize losses from volatilization; because of the high nitrogen concentration in urea, it is important to achieve an spread. The application equipment must be calibrated and properly used. Drilling must not occur on contact with or close to seed, due to the risk of germination damage. Urea dissolves in water for application through irrigation systems. In grain and cotton crops, urea is applied at the time of the last cultivation before planting.
In high rainfall areas and on sandy soils and where good in-season rainfall is expected, urea can be side- or top-dressed during the growing season. Top-dressing is popular on pasture and forage crops. In cultivating sugarcane, urea is side-dressed after planting, applied to each ratoon crop. In irrigated crops, urea can be applied dry to the soil, or dissolved and applied through the irrigation water. Urea dissolves in its own weight in water, but becomes difficult to dissolve as the concentration increases. Dissolving urea in water is endothermic—the solution temperature falls when urea dissolves; as a practical guide, when preparing urea solutions for fertigation, dissolve no more than 3 g urea per 1 L water. In foliar sprays, urea concentrations of between 0.5% and 2.0% are used in horticultural crops. Low-biuret grades of urea are indicated. Urea absorbs moisture from the atmosphere and therefore is stored either in closed or sealed bags on pallets or, if stored in bulk, under cover with a tarpaulin.
As with most solid fertilizers, storage in a cool, well-ventilated area is recommended. Overdose or placing urea near seed is harmful. Urea is a raw material for the manufacture of two main classes of materials: urea-formaldehyde resins and urea-melamine-formaldehyde used in marine plywood. Urea can be used to make urea nitrate, a high explosive, used industrially and as part of some improvised explosive devices, it is a stabilizer in nitrocellulose explosives. Urea is used in SNCR and SCR reactions to reduce the NOx pollutants in exhaust gases from combustion from Diesel, dual fuel, lean-burn natural gas engines; the BlueTec system, for example, injects a water-based urea solution into the exhaust system. The ammonia produced by the hydrolysis of the urea reacts with the nitrogen oxide emissions and is converted into nitrogen and water within the catalytic converter. Trucks and cars using these catalytic converters need to carry a supply of diesel exhaust fluid, a solution of urea in water. Urea in concentrations up to 10 M is a powerful protein denaturant as it disrupts the noncovalent bonds in the proteins.
This property can be exploited to increase the solubility of some proteins. A mixture of urea and choline chloride is used as