- 行业: Printing & publishing
- Number of terms: 178089
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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 term referring to the fact that two or more stationary states of the same quantum-mechanical system may have the same energy even though their wave functions are not the same. In this case the common energy level of the stationary states is degenerate. The statistical weight of the level is proportional to the order of degeneracy, that is, to the number of states with the same energy; this number is predicted from Schrödinger's equation. The energy levels of isolated systems (that is, systems with no external fields present) comprising an odd number of so-called fermions (for example, electrons, protons, and neutrons) always are at least twofold degenerate.
Industry:Science
A term referring to the reflecting properties of a surface. White surfaces have albedos close to 1; black surfaces have albedos close to 0.
Industry:Science
A term that became part of mathematical language during the development of analytic geometry (no equivalent word is found in the writings of Archimedes and other Greek mathematicians), and which is frequently not defined in modern works, apparently in the belief that the meaning ordinarily attached to the word is sufficiently precise. When a definition is given, it is usually to the effect that a symbol <i>x</i> is a variable if it may denote any member of a set <i>S</i> of objects. A variable is discrete or continuous according as its range (the set <i>S</i>) is discrete (for example, a subset of the natural numbers) or continuous (for example, all real numbers between two real numbers), respectively. Such a working definition usually suffices for the needs of mathematics.
Industry:Science
A term that embraces all fishes and fishlike vertebrates. In early zoological classifications fishes, like mammals, birds, reptiles, and amphibians, were ranked as a class of the vertebrates. As knowledge of fishes increased, it became apparent that, despite their common possession of gills and fins and their dependence on an aquatic environment, not all fishes were closely related. At least five groups of fishes with modern descendants were already established before the tetrapods appeared. Not only are these groups older, but some are decidedly more divergent structurally than are the four classes of tetrapods. For these reasons several classes of fishes are now recognized. The number of classes varies; one reputable but extreme classification recognizes 11 classes of fishes.
Industry:Science
A term that has two interrelated meanings: (1) the building that houses a hemispherical domed theater that displays the motions of the sky (stars, Sun, Moon, and planets) as viewed from Earth, and displays (in the modern digital planetarium) the relative position of Earth in space; and (2) the projector that generates these astronomical views. The planetarium projector can be an optomechanical device, a digital video projection system, or a combination of both, popularly called a hybrid planetarium system.
Industry:Science
A term that may refer to either a zinc mineral, Zn<sub>4</sub>Si<sub>2</sub>O<sub>7</sub>(OH)<sub>2</sub>·H<sub>2</sub>O, which is also known as hemimorphite, or to zinc oxide, ZnO, which is used in medicinal or pharmaceutical products and in cosmetics.
Industry:Science
A term that originally referred to those elements with spherically shaped nuclei that would reside on the “island of stability.” More recently, the term “superheavy elements” has been widened to include heavy nuclei whose existence is due to the nuclear shell effect. In this widened definition, therefore, elements with atomic number <i>Z</i> ≥ 104 are generally considered to be superheavy (which also coincides with the beginning of the transactinide elements).
Industry:Science
A term that refers to two processes, one atomic and the other nuclear, in both of which an electron is captured: by a charged particle (an ion) passing through matter, when an electron is captured into an atomic orbital (in the atomic case); or by a nucleus (in the nuclear case), which results in radioactive decay of the nucleus.
Industry:Science
A term that traditionally refers to the substance of which all bodies consist. In Aristotelian physics, each type (species) of material body had a distinct “essential form.” Early modern scientists, however, asserted that there is one universal type of matter. For Isaac Newton, this matter consisted of “solid, massy, hard, impenetrable, movable,” ultimate particles (“atoms”), which were discrete, localized, indivisible bodies. Modern analyses distinguish two types of mass in classical (Newtonian) matter: inertial mass, by which matter retains its state of rest or uniform rectilinear motion in the absence of external forces; and gravitational mass, by which a body exerts forces of attraction on other bodies and by which it reacts to those forces. Expressed in appropriate units, these two properties are numerically equal—a purely experimental fact, unexplained by theory. Albert Einstein made the equality of inertial and gravitational mass a fundamental principle (principle of equivalence), as one of the two postulates of the theory of general relativity. In the equation <i>E</i> = <i>mc</i><sup>2</sup> (where <i>c</i> is the velocity of light), Einstein recognized the equivalence (interconvertibility) of mass (<i>m</i>) and energy (<i>E</i>), which had been distinguished in classical theories.
Industry:Science
A term used in biology to describe substances that will disrupt a cell, with the release of some of its constituents. Unless the damage is minor, this action leads to the death of the cell. Lysins vary in the range of host species whose cells they will attack and in their requirements for accessory factors for lysis; the immune lysins are strictest in their requirements. Erythrocytes are lysed by a wide variety of chemicals, including water and hypertonic salt solutions, which displace the osmotic pressure from that of isotonicity. They are also susceptible to surface-active substances, such as saponin. Many bacteria, such as the staphylococcus and the streptococcus, elaborate one or more hemolysins that will lyse erythrocytes from certain, although not all, species of animals. These patterns may be used in the taxonomic classification of microorganisms. There are a number of other lytic substances, such as lysozyme, an enzyme in the eye aqueous humor and to some extent the bacteriophages, which attack diverse species of bacteria. These actions are not entirely nonspecific since they depend on the presence of common cell constituents or receptors which need not, however, coincide with those involved in immune lysis.
Industry:Science
