- 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.
A change in the chemical, physical, biological, and radiological quality of water that is injurious to its existing, intended, or potential uses. (for example, boating, waterskiing, swimming, the consumption of fish, and the health of aquatic organisms and ecosystems). The term “water pollution” generally refers to human-induced (anthropogenic) changes to water quality. Thus, the discharge of toxic chemicals from a pipe or the release of livestock waste into a nearby water body is considered pollution. Conversely, nutrients that originate from animals in the wild (for example, a herd of elk) or toxins that originate from natural processes (for example, red tides) are not considered pollution.
Industry:Science
A changing magnetic field always produces an electric field, and conversely, a changing electric field always produces a magnetic field. This interaction of electric and magnetic forces gives rise to a condition in space known as an electromagnetic field. The characteristics of an electromagnetic field are expressed mathematically by Maxwell's equations.
Industry:Science
A characteristic of an organism that makes it fit for its environment or for its particular way of life. For example, the Arctic fox (<i>Alopex lagopus</i>) is well adapted for living in a very cold climate. Appropriately, it has much thicker fur than similar-sized mammals from warmer places; measurement of heat flow through fur samples demonstrates that the Arctic fox and other arctic mammals have much better heat insulation than tropical species. Consequently, Arctic foxes do not have to raise their metabolic rates as much as tropical mammals do at low temperatures. This is demonstrated by the coati (<i>Nasua narica</i>), which lives in Panama and has a body mass similar to Arctic foxes and about the same metabolic rate at comfortable temperatures. When both animals are cooled, however, the coati's metabolic rate starts to rise steeply as soon as the temperature falls below 68°F (20°C), while that of the Arctic fox begins to rise only below −22°F (−30°C). The insulation is so effective that Arctic foxes can maintain their normal deep-body temperatures of 100°F (38°C) even when the temperature of the environment falls to −112°F (−80°C). Thus, thick fur is obviously an adaptation to life in a cold environment.
Industry:Science
A characteristic property of the state of a thermodynamic system, introduced in the first law of thermodynamics. For a static, closed system (no bulk motion, no transfer of matter across its boundaries), the change Δ<i>U</i> in internal energy for a process is equal to the heat <i>Q</i> absorbed by the system from its surroundings minus the work <i>W</i> done by the system on its surroundings. Only a change in internal energy can be measured, not its value for any single state. For a given process, the change in internal energy is fixed by the initial and final states and is independent of the path by which the change in state is accomplished.
Industry:Science
A chemical compound that contains the peroxy (–O–O–) group. The simplest member of the series is hydrogen peroxide (HOOH), and the higher members of the series result from substituting a group for one or both of the hydrogen atoms in HOOH. Peroxidic compounds occur in nature, and they have commercial applications
Industry:Science
A chemical compound, CH<sub>3</sub>COCH<sub>3</sub>; the first member of the homologous series of aliphatic ketones. It is a colorless liquid with an ethereal odor. Its physical properties include boiling point 56.2°C (133°F), melting point −94.8°C (−138.6°F), and specific gravity 0.791. Acetone is an extremely important, low-cost raw material that is used for production of other chemicals.
Industry:Science
A chemical discipline that uses mathematical and statistical methods to design or select optimal measurement procedures and experiments and to provide maximum chemical information by analyzing chemical data. Chemometrics is actually a collection of procedures, mathematics, and statistics that can help chemists perform well-designed experiments and proceed rapidly from data, to information, to knowledge of chemical systems and processes.
Industry:Science
A chemical element, Ac, atomic number 89, and atomic weight 227.0. Actinium was discovered by A. Debierne in 1899. Milligram quantities of the element are available by irradiation of radium in a nuclear reactor. Actinium-227 is a beta-emitting element whose half-life is 22 years. Six other radioisotopes with half-lives ranging from 10 days to less than 1 minute have been identified.
Industry:Science
A chemical element, Ar, atomic number 18, and atomic weight 39.948. Argon is the third member of group 0 in the periodic table. The gaseous elements in this group are called the noble, inert, or rare gases, although argon is not actually rare. The Earth's atmosphere is the only natural argon source; however, traces of this gas are found in minerals and meteorites. Argon constitutes 0.934% by volume of the Earth's atmosphere. Of this argon, 99.6% is the argon-40 isotope; the remainder is argon-36 and argon-38. There is good evidence that all the argon-40 in the air was produced by the radioactive decay of the radioisotope potassium-40.
Industry:Science
A chemical element, At, atomic number 85. Astatine is the heaviest of the halogen groups, filling the place immediately below iodine in group 17 of the periodic table. Astatine is a highly unstable element existing only in short-lived radioactive forms. About 25 isotopes have been prepared by nuclear reactions of artificial transmutation. The longest-lived of these is <sup>210</sup>At, which decays with a half-life of only 8.3 h. It is unlikely that a stable or long-lived form will be found in nature or prepared artificially. The most important isotope, used for tracer studies, is <sup>211</sup>At. Astatine exists in nature in uranium minerals, but only in the form of trace amounts of short-lived isotopes, continuously replenished by the slow decay of uranium, The total amount of astatine in the Earth's crust is less than 1 oz (28 g).
Industry:Science
