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Oxalis corniculata (plant)
...O. cernua, known as Bermuda buttercups, with showy yellow flowers, native to southern Africa and naturalized in Florida and the Bermudas. Another yellow-flowered kind is the weedy, creeping oxalis (O. corniculata). Both O. stricta and O. corniculata are widely naturalized in the Old World. The tubers of O. tuberosa, the oca of South America, and the roots of.....
Oxalis latifolia (plant)
...O. cernua, known as Bermuda buttercups, with showy yellow flowers, native to southern Africa and naturalized in Florida and the Bermudas. Another yellow-flowered kind is the weedy, creeping oxalis (O. corniculata). Both O. stricta and O. corniculata are widely naturalized in the Old World. The tubers of O. tuberosa, the oca of South America, and the roots of.....
Oxalis montana (plant)
any plant of the genus Oxalis, numbering several hundred species, within the family Oxalidaceae. The name is chiefly used for O. montana, a stemless trifoliate (i.e., with three leaflets) herb native to North America from southern Canada southward to Tennessee and westward to Minnesota. It grows about 15 cm (6 inches) tall, has pink-tinted stems, and white or reddish......
Oxalis oregana (plant)
...sorrel (O. stricta), of the eastern United States and Canada, with yellow flowers; the violet wood sorrel (O. violacea), of the eastern United States, with rose-purple flowers; the redwood wood sorrel (O. oregana), of the coast redwood belt from California to Oregon, with pink to white flowers; and O. cernua, known as Bermuda buttercups, with showy yellow flowers,......
Oxalis pes-caprae (plant)
...United States, with rose-purple flowers; the redwood wood sorrel (O. oregana), of the coast redwood belt from California to Oregon, with pink to white flowers; and O. cernua, known as Bermuda buttercups, with showy yellow flowers, native to southern Africa and naturalized in Florida and the Bermudas. Another yellow-flowered kind is the weedy, creeping oxalis (O.......
Oxalis stricta (plant)
...ejecting the true seed. The leaflets, as in other species of the genus, fold back and droop at night. Besides the wood sorrel, about 20 other species occur in North America, among which are the yellow wood sorrel (O. stricta), of the eastern United States and Canada, with yellow flowers; the violet wood sorrel (O. violacea), of the eastern United States, with rose-purple......
Oxalis tuberosa (plant)
...ribbed fruits. A number of Oxalis species are grown as ornamentals (their foliage resembles shamrocks), and O. corniculata, with yellow flowers, is often found in greenhouses. Oxalis tuberosa (oca) is cultivated in the Andes for its edible tubers; O. pes-caprae (Bermuda buttercup) also has tubers that can be used as a vegetable, although the plant is considered......
Oxalis violacea (plant)
...Besides the wood sorrel, about 20 other species occur in North America, among which are the yellow wood sorrel (O. stricta), of the eastern United States and Canada, with yellow flowers; the violet wood sorrel (O. violacea), of the eastern United States, with rose-purple flowers; the redwood wood sorrel (O. oregana), of the coast redwood belt from California to Oregon, with...
oxaloacetate (chemical compound)
...(apart from carbon dioxide and water) one of only three possible substances: the two-carbon compound acetate, in the form of a compound called acetyl coenzyme A (Figure 1); the four-carbon compound oxaloacetate; and the five-carbon compound αあるふぁ-oxoglutarate. The first, acetate in the form of acetyl coenzyme A, constitutes by far the most common product—it is the product of two-third...
oxalonitrile (chemical compound)
Cyanogen, (CN)2, is a toxic, colourless gas that boils at −21 °C (−6 °F). It can be prepared by oxidation of hydrogen cyanide (HCN). A variety of oxidizing agents can be used, including oxygen gas, O2, chlorine gas, Cl2, and nitrogen dioxide gas, NO2. When NO2 is used, the product NO can be recycled and used again t...
oxalosuccinate (chemical compound)
Isocitrate is oxidized—i.e., hydrogen is removed—to form oxalosuccinate; the two hydrogen atoms are usually transferred to NAD+, thus forming reduced NAD+ [40]; in some microorganisms, and during the biosynthesis of glutamate in the cytoplasm of animal cells, however, the...
Oxamycin (drug)
...bacillus. All these drugs are absorbed from the gastrointestinal tract and penetrate tissues and cells. An isoniazid-induced hepatitis can occur, particularly in patients 35 years of age or older. Cycloserine, an antibiotic produced by Streptomyces orchidaceus, is also used in the treatment of tuberculosis. A structural analog of the amino acid D-alanine, it......
Oxandra lanceolata (plant)
tough, heavy, elastic, straight-grained wood obtained from several different trees of the custard-apple family (Annonaceae). True lancewood, Oxandra lanceolata, of the West Indies and Guianas, furnishes most of the lancewood of commerce in the form of spars about 13 feet (4 m) in length and 5 inches (13 cm) in diameter at the small end. Lancewood was formerly used by carriage builders......
oxazepam (drug)
...at high doses. They also require a much smaller dosage than do barbiturates to achieve their effects. The benzodiazepines include chlordiazepoxide (Librium), diazepam (Valium), alprazolam (Xanax), oxazepam (Serax), and triazolam (Halcion). They are, however, intended only for short- or medium-term use, since the body does develop a tolerance to them and withdrawal symptoms (anxiety,......
oxazolidinone (drug)
The oxazolidinones are a novel class of synthetic agents that inhibit protein synthesis by microbes. Linezolid is highly active in vivo against infections caused by many common gram-positive pathogens, including Enterococcus bacteria that are resistant to vancomycin (described in the section Other antibiotics). It is available orally or intravenously. One major......
oxbird (bird)
one of the most common and sociable birds of the sandpiper group. The dunlin is a member of the family Scolopacidae (order Charadriiformes). It is about 20 cm (8 inches) long and has a bill curved downward at the tip. In breeding season, its plumage is brightly coloured, with its belly black and its back reddish (or dun-coloured, hence the n...
oxbird (common name of several birds)
any of certain small sandpipers, especially the dunlin. In Africa the buffalo weaver and the oxpecker are called oxbirds....
oxbird (bird)
either of the two African birds constituting the subfamily Bubalornithinae of the family Ploceidae. The more widespread species is the black buffalo weaver, or oxbird (Bubalornis albirostris); it is black, with white in the wings. The white-headed buffalo weaver (Dinemellia dinemelli), confined to eastern Africa, is brown and white, with red rump and vent. Both are stout-bodied,......
oxblood (pottery glaze)
a glossy, rich, bloodred glaze often slashed with streaks of purple or turquoise used to decorate pottery, particularly porcelain. The effect is produced by a method of firing that incorporates copper, a method first discovered by the Chinese of the Ming dynasty, probably during the reign of Wanli (1573...
oxbow lake (geology)
small lake located in an abandoned meander loop of a river channel. It is generally formed as a river cuts through a meander neck to shorten its course, causes the old channel to be rapidly blocked off, and then migrates away from the lake. If only one loop is cut off, the lake formed will be crescent shaped, whereas if more than one loop is cut off, the lake will be serpentine...
Oxcart, The (work by Marqués)
His best-known play, La Carreta (1956; “The Wagon”; Eng. trans. The Oxcart), concerns a rural Puerto Rican family who immigrate to New York City in search of their fortune but fail and subsequently return to Puerto Rico, where they find it hard to adapt. In 1959 he published three plays together in the collection Teatro.....
Oxenstierna af Södermöre, Axel, Greve (chancellor of Sweden)
chancellor of Sweden (1612–54), successively under King Gustav II Adolf and Queen Christina. He was noted for his administrative reforms and for his diplomacy and military command during the Thirty Years’ War. He was created a count in 1645....
Oxenstierna, Bengt Gabrielsson, Greve (Swedish statesman)
Swedish statesman who, as the principal foreign policy adviser of King Charles XI, established a virtually neutral foreign policy for Sweden, breaking the existing alliance with France and forming ties with the Netherlands, England, and the ...
Oxenstierna, Johan Gabriel (Swedish diplomat and author)
...the controversy was carried on by Carl Gustaf af Leopold, who imposed pseudo-Classical standards on the Swedish Academy (founded 1786) and applied them in his own rhetorical odes and tragedies. Johan Gabriel Oxenstierna did his most original work while a diplomat in Vienna; his Skördarne (1796; “Harvests”) reveals pre-Romantic feeling for the beauty of nature.....
Oxenstierna, Jöns Bengtsson (Swedish archbishop)
...that a new joint king would be elected when both were dead. Charles refused to accept this compromise, and war broke out between the two countries. In 1457 the noble opposition, led by Archbishop Jöns Bengtsson Oxenstierna, rebelled against Charles, who fled to Danzig. Oxenstierna and Erik Axelsson Tott, a Danish noble, became the regents, and Christian was hailed as king of Sweden.......
oxepine (chemical compound)
...ring heterocycles, although these compounds are usually stable and some of them have found practical application. Of the seven-membered ring compounds, one-heteroatom heterocycles—azepines, oxepines, and thiepines—and their derivatives are the most comprehensively studied....
oxetane (chemical compound)
Azetidine, oxetane, and thietane—four-membered rings containing, respectively, one nitrogen, oxygen, or sulfur atom—are prepared by nucleophilic displacement reactions similar to those used to prepare the corresponding three-membered rings....
oxeye (fish)
...breaks water and gulps air. It regularly grows to 1.8 metres (6 feet) and 45.4 kg (100 pounds) or larger and is a favourite game fish. The largest recorded catches weighed more than 136 kg. The Pacific tarpon, M. cyprinoides, is similar....
oxeye (common name for several birds)
in Britain, any of certain small sandpipers (especially the dunlin) and the great tit (titmouse). See also tit....
oxeye (bird)
one of the most common and sociable birds of the sandpiper group. The dunlin is a member of the family Scolopacidae (order Charadriiformes). It is about 20 cm (8 inches) long and has a bill curved downward at the tip. In breeding season, its plumage is brightly coloured, with its belly black and its back reddish (or dun-coloured, hence the n...
oxeye daisy (plant)
garden perennial plant (Chrysanthemum leucanthemum) in the family Asteraceae. The compound flower has 15–30 white ray flowers surrounding a bright yellow disk flower, about 1–2 inches (2.5–5 cm) across. It grows about 2 feet (60 cm) h...
Oxfam International (international organization)
privately funded international organization that provides relief and development aid to impoverished or disaster-stricken communities worldwide. The original Oxfam was founded at Oxford, Eng., in 1942 to raise funds for the feeding of hungry children in war-torn Greece. It is now a federation of 12 organizations (Australia, ...
Oxford (Mississippi, United States)
city, seat (1837) of Lafayette county, northern Mississippi, U.S. It is situated about 75 miles (120 km) southeast of Memphis, Tennessee. Originating as a trading post, it was incorporated in 1837 and named for the English centre of learning, reflecting the townspeople’s early desire for a universit...
Oxford (England, United Kingdom)
city (district), administrative and historic county of Oxfordshire, England, best known for the University of Oxford, which is located within it....
Oxford (county, Maine, United States)
county, western Maine, U.S. It consists of a mountainous region bordered to the west by New Hampshire and to the north by Quebec, Canada. The Appalachian National Scenic Trail crosses the Maine–New Hampshire border along the Mahoosuc Range and traverses the northern part of the county via Old Speck, Baldpate, and Goose Eye mountains. The Andros...
Oxford (sheep)
The Oxford, a breed popular in England and in the Great Lakes region of the U.S., was produced in the mid-19th century in Oxfordshire, England, by crossing Hampshires and Cotswolds....
Oxford (Ohio, United States)
The Oxford, a breed popular in England and in the Great Lakes region of the U.S., was produced in the mid-19th century in Oxfordshire, England, by crossing Hampshires and Cotswolds.......
Oxford Clay Vale (region, England, United Kingdom)
...strata of the Jurassic Period. The Berkshire Downs and Chiltern Hills are developed on Cretaceous chalk. The intervening clay vale stretches from northeast to southwest. It is divided into the Oxford Clay Vale and the White Horse Vale by an outcrop of Corallian limestone, giving rise to the Oxford Heights....
Oxford College (college, Oxford, Georgia, United States)
...strata of the Jurassic Period. The Berkshire Downs and Chiltern Hills are developed on Cretaceous chalk. The intervening clay vale stretches from northeast to southwest. It is divided into the Oxford Clay Vale and the White Horse Vale by an outcrop of Corallian limestone, giving rise to the Oxford Heights.......
Oxford Committee for Famine Relief (international organization)
privately funded international organization that provides relief and development aid to impoverished or disaster-stricken communities worldwide. The original Oxfam was founded at Oxford, Eng., in 1942 to raise funds for the feeding of hungry children in war-torn Greece. It is now a federation of 12 organizations (Australia, ...
Oxford, Edward de Vere, 17th Earl of (English poet and dramatist)
English lyric poet and patron of an acting company, Oxford’s Men, who became, in the 20th century, the strongest candidate proposed (next to William Shakespeare himself) for the authorship of Shakespeare’s plays....
Oxford English Dictionary, The (English dictionary)
definitive historical dictionary of the English language, originally consisting of 12 volumes and a 1-volume supplement. The dictionary is a corrected and updated revision of A New English Dictionary on Historical Principles (NED), which was published in 10 volumes from February 1, 1884, to April 19...
“Oxford Gazette” (British newspaper)
Steele’s most important appointment in the early part of Queen Anne’s reign was that of gazetteer—writer of The London Gazette, the official government journal. Although this reinforced his connection with the Whig leaders, it gave little scope for his artistic talents, and, on April 12, 1709, he secured his place in literary history by launching the thrice-weekly essay...
Oxford Group (religious movement)
a modern, nondenominational revivalistic movement founded by American churchman Frank N.D. Buchman (1878–1961). It sought to deepen the spiritual life of individuals and encouraged participants to continue as members of their own churches. Primarily a Protestant movement, it was criticized by some Roman Catholic authorities and praised by others....
Oxford, John de Vere, 13th Earl of (English soldier)
English soldier and royal official, a Lancastrian leader in the Wars of the Roses. He helped to restore the deposed King Henry VI (1470) and later (1485) to secure the English throne for the last surviving male claimant from the house of Lancaster, Henry Tudor, Earl of Richmond, afterwar...
Oxford Junior Encyclopaedia
Unlike World Book, Compton’s, and the Britannica Junior Encyclopædia, the Oxford Junior Encyclopaedia (intended for children of age 11 upward) was systematically arranged. Each of the 12 text volumes is devoted to a broad subject field: humankind, natural history, the universe, communications, great lives, farming and fisheries, ind...
Oxford movement (religion)
19th-century movement centred at the University of Oxford that sought a renewal of “catholic,” or Roman Catholic, thought and practice within the Church of England in opposition to the Protestant tendencies of the church. The argument was that the Anglican church was by history and identity a truly “catholic” chur...
Oxford Parliament (British history)
...again an unyielding Parliament met at Oxford (1681). By now the king had shown his determination and had frightened the local elites into believing that there was danger of another civil war. The Oxford Parliament was dissolved in a week, the “Whig” (Scottish Gaelic: “Horse Thief”) councillors, as they were now called, were dismissed from their places, and the king.....
Oxford philosophy
method of philosophical investigation concerned with how verbal expressions are used in a particular, nontechnical, everyday language. The basic source for this school of thought is the later writings of the Viennese-born philosopher Ludwig Wittgenstein, followed by the contributions of John Langshaw Austin, ...
Oxford Propositions (English history)
...would be to compromise. Both of these groups were loose coalitions, and neither of them dominated parliamentary politics. Until his death in 1643, Pym steered a course between them, supporting the Oxford Propositions (1643) for peace as well as creating the administrative machinery to raise and finance armies. The excise, modeled on impositions, and the monthly assessments, modeled on ship......
Oxford Provident Building Association of Philadelphia, The (American financial institution)
The Oxford Provident Building Association of Philadelphia, which began operating in 1831 with 40 members, was the first savings and loan association in the United States. By 1890 they had spread to all states and territories....
Oxford, Provisions of (English history)
(1258), in English history, a plan of reform accepted by Henry III, in return for the promise of financial aid from his barons. It can be regarded as England’s first written constitution....
Oxford Psalter
...50 years (c. 1120) of the Conquest, Eadwine’s Psalterium triplex, which contained the Latin version accompanied by Anglo-Norman and Anglo-Saxon renderings, appeared. The contemporary Oxford Psalter achieved such influence that it became the basis of all subsequent Anglo-Norman versions. By 1361 a prose translation of most of Scripture in this dialect had been executed....
Oxford, Robert de Vere, 9th earl of (English statesman)
favourite of King Richard II of England (ruled 1377–99) during that monarch’s minority. He led the group of courtiers who unsuccessfully supported Richard’s efforts in 1385–87 to wrest control of the government from powerful nobles....
Oxford, Robert Harley, 1st Earl of, Earl Mortimer, Baron Harley of Wigmore (English statesman)
British statesman who headed the Tory ministry from 1710 to 1714. Although by birth and education he was a Whig and a Dissenter, he gradually over the years changed his politics, becoming the leader of the Tory and Anglican party....
Oxford University (university, Oxford, England, United Kingdom)
English autonomous institution of higher learning at Oxford, Oxfordshire, England, one of the world’s great universities. It lies along the Upper River Thames (called by Oxonians the Isis), 50 miles (80 km) north-northwest of London....
Oxford, University of (university, Oxford, England, United Kingdom)
English autonomous institution of higher learning at Oxford, Oxfordshire, England, one of the world’s great universities. It lies along the Upper River Thames (called by Oxonians the Isis), 50 miles (80 km) north-northwest of London....
Oxford University Press (British publishing company)
...result of direct subsidies, coupled with their assured, if limited, market, enables many to reach high standards of production and commercial viability. Some of the older establishments, such as the Oxford University Press, are, of course, large, profitable organizations with worldwide connections and a long list of more general publications....
Oxfordian Stage (geology)
lowest of the three divisions of the Upper Jurassic Series, representing all rocks formed worldwide during the Oxfordian Age, which occurred between 161.2 million and 155.6 million years ago during the Jurassic Period. (Some researchers have proposed a longer span for this stage that extends into more rece...
Oxfordshire (county, England, United Kingdom)
administrative and historic county of south-central England, bounded on the north by Warwickshire and Northamptonshire, on the west by Gloucestershire, on the south by Berkshire, and on the east by Buckinghamshire. Wiltshire lies to the southwest of the administrative county, which covers a larger area than the historic coun...
Oxherding Tale (work by Johnson)
...to today’s African American struggle began with Ishmael Reed’s exuberant Flight to Canada (1976) and extended into the metafiction of philosophical novelist Charles R. Johnson. In Oxherding Tale (1982), Johnson sends his biracial fugitive slave protagonist on a quest for emancipation that he can attain only by extricating himself, in Johnson’s own ...
oxidant injury (pathology)
Ozone and peroxyacetyl nitrate injury (also called oxidant injury) are more prevalent in and near cities with heavy traffic problems. Exhaust gases from internal combustion engines contain large amounts of hydrocarbons (substances that principally contain carbon and hydrogen molecules—gasoline, for example). Smaller amounts of unconsumed hydrocarbons are formed by combustion of fossil......
oxidase (enzyme)
...chemical changes in organic substances. Enzyme action in milk systems is extremely important for its effect on the flavour and body of different milk products. Lipases (fat-splitting enzymes), oxidases, proteases (protein-splitting enzymes), and amylases (starch-splitting enzymes) are among the more important enzymes that occur naturally in milk. These classes of enzymes are also produced......
oxidation (chemical reaction)
Alcohols may be oxidized to give ketones, aldehydes, and carboxylic acids. These functional groups are useful for further reactions; for example, ketones and aldehydes can be used in subsequent Grignard reactions, and carboxylic acids can be used for esterification. Oxidation of organic compounds generally increases the number of bonds from carbon to oxygen (or another electronegative element,......
oxidation, doctor process of (chemistry)
Sweetening processes oxidize mercaptans into more innocuous disulfides, which remain in the product fuels. Catalysts assist in the oxidation. The doctor process employs sodium plumbite, a solution of lead oxide in caustic soda, as a catalyst. At one time this inexpensive process was widely practiced, but the necessity of adding elemental sulfur to make the reactions proceed caused an increase......
oxidation number (chemistry)
the total number of electrons that an atom either gains or loses in order to form a chemical bond with another atom....
oxidation pond (sanitation engineering)
Oxidation ponds, also called lagoons or stabilization ponds, are large, shallow ponds designed to treat wastewater through the interaction of sunlight, bacteria, and algae. Algae grow using energy from the sun and carbon dioxide and inorganic compounds released by bacteria in water. During the process of photosynthesis, the algae release oxygen needed by aerobic bacteria. Mechanical aerators......
oxidation potential (chemistry)
...sequence. Atmospheric conditions are characterized by low temperatures and pressures, and under such conditions stability fields of minerals can often conveniently be expressed in terms of Eh (oxidation potential) and pH (the negative logarithm of the hydrogen ion concentration [H+]; a pH of 0–7 indicates acidity, a pH of 7–14 indicates basicity, and neutral......
oxidation state (chemistry)
the total number of electrons that an atom either gains or loses in order to form a chemical bond with another atom....
oxidation-reduction couple (chemistry)
...litre is maintained at 25° C (77° F) in equilibrium with hydrogen in its reduced form (hydrogen gas, H2) at a pressure of one atmosphere. The reversible oxidation–reduction half reaction is expressed by the equation 2H+ + 2e- ⇌ H2, in which e- represents an electron....
oxidation-reduction reaction (chemical reaction)
any chemical reaction in which the oxidation number of a participating chemical species changes. The term covers a large and diverse body of processes. Many oxidation-reduction reactions are as common and familiar as fire, the rusting and dissolution of metals, the browning of fruit, a...
oxidation-reduction titration (chemical process)
In oxidation-reduction (redox) titrations the indicator action is analogous to the other types of visual colour titrations. In the immediate vicinity of the end point, the indicator undergoes oxidation or reduction, depending upon whether the titrant is an oxidizing agent or a reducing agent. The oxidized and reduced forms of the indicator have distinctly different colours....
oxidative addition (chemistry)
The converse of reductive elimination is oxidative addition....
oxidative fluorination (chemical reaction)
...electrons from other substances and confers on them a positive charge. Its fluorinating ability means that it transfers an F− ion to other substances. Hence, in a formal sense, oxidative fluorination is the net result of extraction of two electrons and addition of F−; this can be considered to be equivalent to the transfer of F+.) KrF2.....
oxidative phosphorylation (chemical reaction)
In oxidative phosphorylation the oxidation of catabolic intermediates by molecular oxygen occurs via a highly ordered series of substances that act as hydrogen and electron carriers. They constitute the electron transfer system, or respiratory chain. In most animals, plants, and fungi, the electron transfer system is fixed in the membranes of mitochondria; in bacteria (which have no......
oxide (chemical compound)
any of a large and important class of chemical compounds in which oxygen is combined with another element. With the exception of the lighter inert gases (helium [He], neon [Ne], argon...
oxide glass (material science)
Electronic conduction of charge is important in only two families of glasses: oxide glasses containing large amounts of transition-metal ions and chalcogenides. In metallic solids there are a large number of weakly bound electrons that can move about freely through the crystal structure, but in insulating solids the electrons are confined to specific energy levels known as valence and......
oxide mineral
any naturally occurring inorganic compound with a structure based on close-packed oxygen atoms in which smaller, positively charged metal or other ions occur in interstices. Oxides are distinguished from other oxygen-bearing compounds such as the silicates, borates, and carbonates, which have a readily definable group conta...
oxidizing agent (chemical compound)
The metabolic activities of organisms produce highly reactive chemicals, including strong oxidizing agents. The internal structure of the cell, however, minimizes the harmful effects of such agents. The critical reactions take place within enclosed structures such as ribosomes, membranes, or mitochondria, and counteractive enzymes such as peroxidases are present in abundance. It is nevertheless......
oxidizing flame (chemistry)
When a premixed flame burns in open air with an excess of fuel, there appears in addition to the flame zone a zone of diffusion flame; this is accounted for by the diffusion of atmospheric oxygen, as, for example, in the Bunsen flame produced by a burner to which the air intake can be regulated, thereby altering the flow from an intensely hot one—in which most of the fuel gases are......
oxido-reductase (enzyme)
any member of a class of enzymes, commonly known as dehydrogenases or oxidases, that catalyze the removal of hydrogen atoms and electrons from the compounds on which they act. Substances called coenzymes, associated with the oxidoreductase enzymes and necessary for their activity, accept the hydrogen and electrons, which—in metabolic systems of animals—eventually are transferred to ...
oxidoreductase (enzyme)
any member of a class of enzymes, commonly known as dehydrogenases or oxidases, that catalyze the removal of hydrogen atoms and electrons from the compounds on which they act. Substances called coenzymes, associated with the oxidoreductase enzymes and necessary for their activity, accept the hydrogen and electrons, which—in metabolic systems of animals—eventually are transferred to ...
oxime (chemical compound)
any of a class of nitrogen-containing organic compounds usually prepared from hydroxylamine and an aldehyde, a ketone, or a quinone. Oximes have the structure X\Y/C= N−OH, in which X and Y are hydrogen atoms or organic groups derived by removal of a hydrogen atom from an organic compound. Bec...
oxirane (chemical compound)
The three-membered ring heterocycles containing single atoms of nitrogen, oxygen, and sulfur—aziridine, oxirane (or ethylene oxide), and thiirane, respectively—and their derivatives can all be prepared by nucleophilic reactions, of the type shown. Thus, aziridine is formed by heating βべーた-aminoethyl hydrogen sulfate with a base (in this case Y is......
Oxisol (pedology)
one of the 12 soil orders in the U.S. Soil Taxonomy. Oxisols form principally in humid tropical zones under rainforest, scrub and thorn forest, or savanna vegetation on flat to gently sloping uplands. They are typically found on old landscapes that have been subject to ...
Oxlahuntiku (Mayan deities)
...above the earth, which itself rested on the back of a huge crocodile or reptilian monster floating on the ocean. Under the earth were nine underworlds, also arranged in layers. Thirteen gods, the Oxlahuntiku, presided over the heavens; nine gods, the Bolontiku, ruled the subterranean worlds. These concepts are closely akin to those of the Postclassic Aztec, but archaeological evidence, such......
Oxley, John Joseph William Molesworth (British explorer)
surveyor-general and explorer who played an important part in the exploration of eastern Australia and also helped open up Van Diemen’s Land (later Tasmania)....
Oxmantown, Lord (Irish astronomer)
Irish astronomer and builder of the largest reflecting telescope, the “Leviathan,” of the 19th century....
Oxnard (California, United States)
city, Ventura county, southwestern California, U.S. It lies near the Pacific coast, between Los Angeles and Santa Barbara. Originally inhabited by Chumash Indians, the city was founded in 1898 near the site of the Spanish colonial Mission San Buenaventura (1782). The city developed around a sugar-beet factory financed by H...
oxo acid (chemical compound)
...exhibits the oxidation states of −1 (F− ion) and +1 (hypofluorous acid). The principal oxidation states of chlorine, bromine, and iodine are −1, +1, +3, +5, and +7. The oxyacids are compounds in which halogen atoms are joined to oxygen atoms. The oxyacids are all powerful oxidizing agents, which can be reduced to the corresponding hydrogen halides—the......
oxo halide (chemical compound)
...in bonding is for them to become partially occupied in accommodating lone-pair electrons from another atom, which is already attached by a single bond, thereby strengthening the bond. The phosphorus oxyhalides, of general formula POX3, appear to be examples of this; their phosphorus–oxygen bonds are observed to be shorter and stronger than expected for ordinary single bonds....
oxodecenoic acid (entomology)
Primer pheromones are especially important in the maintenance of colony structure in social insects. Queen honeybees secrete “queen substance” from their mandibular glands. When an unfertilized queen leaves the colony, queen substance acts as an olfactory attractant for males. The same compound within the colony modifies the behaviour of workers, preventing them from rearing more......
oxonium salt (chemical compound)
...between peroxides (R−OO−R), disulfides (R−SS−R), and diselenides (R−SeSe−R), and between oxonium (R3O+), sulfonium (R3S+), and selenonium salts (R3Se+), where R represents a general carbon group—e.g., the methyl......
oxosulfonium salt (chemical compound)
...typically written R2SO), sulfones (R2S(=O)2, typically written R2SO2), sulfonic acids (RSO3H), and oxosulfonium salts (R3S+=O). Analogs of the above sulfur compounds also exist for selenium. These higher-valence compounds of sulfur (or selenium) are stabilized......
oxosulfonium ylide (chemical compound)
...each losing a proton to give zwitterions of a special type, with the negative charge on the carbon adjacent to the positively charged sulfonium sulfur. These compounds are called sulfonium and oxosulfonium ylides, respectively—or, more broadly, sulfur ylides, by analogy with phosphorus ylides employed in the Wittig reaction. The structures of sulfonium ylides and oxosulfonium ylides......
oxpecker (bird)
either of the two species of the African genus Buphagus, of the family Sturnidae (order Passeriformes). Both species—the yellow-billed (B. africanus) and the red-billed (B. erythrorhynchus)—are brown birds 20 cm (8 inches) long, with wide bills, stiff tails, and sharp claws. They cling to cattle and big-game animals to remove ticks, flies, and maggots from their ...
Oxuna (Spain)
town, Sevilla provincia (province), in the comunidad autónoma (autonomous community) of Andalusia, southern Spain. Osuna lies at the foot of a hill at the edge of an extensive plain, east-southeast of Sevilla city. Of Iberian origin, the town became the Ro...
Oxus River (river, Asia)
one of the longest rivers of Central Asia. The Amu Darya was traditionally known to the Western world from Greek and Roman times as the Oxus and was called the Jayḥūn by the Arabs. It allegedly derives its present name from the city of Āmul, which is said to have occupied the site of modern Ch...
Oxus treasure (Persian metalwork)
...interest. Of greater artistic importance are the many surviving examples of Achaemenian metalsmiths’ work, which continued to draw extensively on the native tradition of Iranian design. The Oxus Treasure includes outstanding and characteristic examples of Achaemenian metalwork....
Oxus Valley (valley, Asia)
...Banawali is an important major settlement, surrounded by massive brick defenses. One of the most surprising discoveries, far outside the central area of the Indus civilization, is Shortughai in the Amu Darya (Oxus River) valley, in northern Afghanistan. There the remains of a small Harappan colony, presumably sited so as to provide control of the lapis lazuli export trade originating in......