- 行业: Printing & publishing
- Number of terms: 178089
- Number of blossaries: 0
- Company Profile:
McGraw Hill Financial, Inc. is an American publicly traded corporation headquartered in Rockefeller Center in New York City. Its primary areas of business are financial, publishing, and business services.
A popular name applied to several groups of extinct jawless vertebrates (fishes). Most of them were covered with an external skeleton or armor of bone, from which is derived their name, meaning “shell-skinned” (see <b>illus</b>.). They are known from the Ordovician, Silurian, and Devonian periods, and thus include the earliest known vertebrates.
Industry:Science
A popular term for an automatic radio direction finder used for navigation purposes on ships and aircraft. It is not strictly a compass, because it indicates direction with respect to the radio station to which it is tuned, rather than to the north magnetic pole. The modern radio compass uses a nondirectional antenna in combination with a bidirectional loop antenna to provide a unidirectional bearing indication. The navigator thus knows at all times whether the craft is traveling toward or away from the radio station used as a reference. The antennas are used with a special radio receiver that provides a visual indication of direction on a meter or cathode-ray indicator.
Industry:Science
A porous silica deposit formed around hot springs. It is white to light gray and sometimes friable. Geyserite is a variety of siliceous sinter formed around geysers. The siliceous sinters are deposited as the hot subterranean waters cool after issuing at the surface and become supersaturated with silica that was picked up at depth. The sinters are frequently deposited on algae that live in the pools around the hot springs.
Industry:Science
A porous solid product containing 85–98% carbon produced by heating carbonaceous materials such as cellulose, wood, peat, and coals of bituminous or lower rank at 930–1110°F (500–600°C) in the absence of air. Chars or charcoals are rendered more porous and more efficient for sorption by heating in air, carbon dioxide, or steam at 1650°F (900°C) for a brief period. The surface area of activated char produced by this technique is about 800,000 ft<sup>2</sup>/oz (1000 m<sup>2</sup>/g). Chars from cellulose or wood are soft and friable. They are used chiefly for decolorizing solutions of sugar and other foodstuffs and for removing objectionable tastes and odors from water. Chars from nutshells and coal are dense, hard carbons. They are used in gas masks and in chemical manufacturing for many mixture separations. Another use is for the tertiary treatment of wastewater. Residual organic matter is adsorbed effectively to improve the water quality.
Industry:Science
A portable instrument that measures time. The direct forerunner of the watch was the pendulum clock, invented by Christian Huygens in 1656.
Industry:Science
A portion of the autonomic system. It consists of two neuron chains, but differs from the sympathetic nervous system in that the first neuron has a long axon and synapses with the second neuron near or in the organ innervated. In general, its action is in opposition to that of the sympathetic nervous system, which is the other part of the autonomic system. It cannot be said that one system, the sympathetic, always has an excitatory role and the other, the parasympathetic, an inhibitory role; the situation depends on the organ in question. However, it may be said that the sympathetic system, by altering the level at which various organs function, enables the body to rise to emergency demands encountered in flight, combat, pursuit, and pain. The parasympathetic system seems in control during such pleasant periods as digestion and rest. The alkaloid pilocarpine excites parasympathetic activity, the atropine inhibits it.
Industry:Science
A positively charged particle that is the nucleus of the lightest chemical element, hydrogen. The hydrogen atom consists of a proton as the nucleus, to which a single negatively charged electron is bound by an attractive electrical force (since opposite charges attract). The proton is about 1836 times heavier than the electron, so that the proton constitutes almost the entire mass of the hydrogen atom. Most of the interior of the atom is empty space, since the sizes of the proton and the electron are very small compared to the size of the atom.
Industry:Science
A possible ground state of a metal in which the conduction-electron charge density is sinusoidally modulated in space. The periodicity of this extra modulation is unrelated to the lattice periodicity. Instead, it is determined by the dimension of the conduction-electron Fermi surface in momentum space.
Industry:Science
A potassium nitrate mineral with chemical composition KNO<sub>3</sub>. Niter crystallizes in the orthorhombic system, generally in thin crusts and delicate acicular crystals; it also occurs in massive, granular, or earthy forms. It has good cleavage in three directions; fracture is subconchoidal to uneven; it is brittle; hardness is 2 on Mohs scale; specific gravity is 2.109. The luster is vitreous, and the color and streak are colorless to white.
Industry:Science
A potentially fatal infection caused by parasites of the genus <i>Trypanosoma</i>.
Industry:Science
