- 行业: Printing & publishing
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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.
An even-toed ungulate, <i>Ovibos moschatus</i>, which is a member of the family Bovidae in the mammalian order Artiodactyla. This single species is the northernmost representative of the family, ranging through the tundra areas and snowfields of Canada and Alaska, as well as Greenland.
Industry:Science
An evolutionary phenomenon that involves changes in the rate and timing of development. As animals and plants grow from their earliest embryonic stages to the adult, they undergo changes in shape and size. This life history of an individual organism is known as its ontogeny. The amount of growth that an organism experiences during its ontogeny can be more or less than its ancestor. This can apply to the organism as a whole or to specific parts.
Industry:Science
An evolving star of luminosity class IV. Such a star is brighter than the main-sequence dwarfs and fainter than the true giants in its spectral class, lying between the two on the Hertzsprung-Russell diagram. The classic subgiants fall in a small region from class F to K (with effective temperatures ranging from 7000 to 4000 K or 12,000 to 7000°F). In class G they lie at absolute visual magnitude +3 with luminosities about five times the solar luminosity. Classic subgiants have masses similar to or a bit greater than that of the Sun and violate the mass-luminosity relation as too bright for their masses. The concept is extended to the hot part of the Hertzsprung-Russell diagram from class F to O, in which the distinctions between subgiants and neighboring dwarfs and giants are much smaller, only a magnitude or less. The apparently brightest star usually considered a subgiant is Procyon, though it is more a transition between dwarf and subgiant.
Industry:Science
An excavation made to extract water, oil, gas, brine, or other fluid substance from the earth. Wells are the source of about one quarter of the water supplies in the United States, all gas and oil, and most of the industrial brines and sulfur. Water wells are recorded in the earliest historic documents and probably originated during periods of drought when ancient humans attempted to reach water by digging a shallow excavation at the site of springs that had ceased to flow or in the dry channels of rivers. Later they learned to dig deeper for water where it did not issue at the land surface. The first wells were dug by hand, and some large deep ones were provided with elaborate ramps which enabled those drawing water to walk or even drive a donkey down to the water level. In the Near East for thousands of years wells (khanats) have been constructed by tunneling nearly horizontally into the outwash gravel to tap ground water which flows down the tunnel to its entrance. Horizontal wells are also used in Hawaii to skim fresh ground water from underlying salt ground water.
Industry:Science
An excited electronic state in a large molecule, or a semiconducting or insulating solid composed of a negatively charged electron and a positively charged hole bound together by their electrical attraction. Its creation through internal charge separation is most frequently caused by the absorption of light, and its demise is occasioned by the emission of light. The exciton is thus an important portal for the study of the properties of an insulator by optical means and for applications such as optoelectronics. Its external neutrality enables it to move through the system as an energy carrier, an important agent in energy transfer processes of special importance in biological functions such as photosynthesis. When the excited electron and hole are restricted to a plane, a wire, or a microscopic box in an artificially fabricated structure known, respectively, as a quantum well, quantum wire, or quantum dot, a new dimension is added to the ability to explore fundamental nonlinear and nonequilibrium physics and coherent quantum optics as well as quantum control of microscopic objects.
Industry:Science
An exothermic reaction front or wave in a gaseous medium. Consider a uniform body of gas in which an exothermic chemical reaction (that liberates heat) is initiated by raising the temperature to a sufficiently high level; the reaction is started by a localized release of heat, as by a sufficiently energetic spark, and then spreads from the point of initiation. If the reaction is relatively slow, the whole gas will be involved before the initial region has finished reacting. If, however, the reaction is relatively fast, the reaction zone will develop as a thin front or wave propagating into the unreacted gas, leaving fully reacted gas behind. If the front, in addition, shows luminosity (emission of light), the flame may be considered a classical example. However, perceptible emission of visible radiation is not essential to the definition, and some flames are indeed vanishingly faint under ordinary viewing conditions.
Industry:Science
An exotic atom, mu or (μ<sup>+</sup><i>e</i><sup>-</sup>), formed when a positively charged muon (μ<sup>+</sup>) and an electron are bound by their mutual electrical attraction. It is a light, unstable isotope of hydrogen, with a muon replacing the proton. Muonium has a mass 0.11 times that of a hydrogen atom due to the lighter mass of the muon, and a mean lifetime of 2.2 microseconds, determined by the spontaneous decay of the muon (μ<sup>+</sup> → <i>e</i><sup>+</sup>ν<sub><i>e</i></sub><span style="text-decoration:overline">ν</span><sub>μ</sub>).
Industry:Science
An expanding nebula, or cloud, of gas thrown off by a dying star just before the star settles down to its ultimate endpoint as a white dwarf. Planetary nebulae are among the brightest and best-studied nebular objects in the sky, even though they are generally a few thousand light-years from Earth. The many shapes of planetary nebulae reflect poorly understood processes that occur inside most stars late in their lives. The Sun is likely to eject a planetary nebula in about 5 billion years. Many of the most prominent planetary nebulae seen today formed and emerged from their dusty cocoons within just the past 1000–2000 years.
Industry:Science
An expansion technique useful for solving complicated quantum-mechanical problems in terms of solutions for simple problems. Perturbation theory in quantum mechanics provides an approximation scheme whereby the physical properties of a system, modeled mathematically by a quantum-mechanical description, can be estimated to a required degree of accuracy. Such a scheme is useful because very few problems occurring in quantum mechanics can be solved analytically. Consequently an approximation technique must be employed in order to give an approximate analytic solution or to provide suitable algorithms for a numerical solution. Even for problems which admit an exact analytic solution, the exact solution may be of such mathematical complexity that its physical interpretation is not apparent. For these situations, perturbation techniques are also desirable. Here the discussion of the application of perturbation techniques to quantum mechanics will be limited to the domain of nonrelativistic quantum theory. Applications of a similar but mathematically more intricate nature have also been made in quantum electrodynamics and quantum field theory.
Industry:Science
An expendable device that enables aircraft to detect underwater objects, such as submarines, acoustically. Acoustics is the preferred energy form for use in salt water, because it tends to be the least attenuated by the medium.
Industry:Science
