- 行业: Printing & publishing
- Number of terms: 178089
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- 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 systematic displacement toward longer wavelengths of lines in the spectra of distant galaxies, and also of the continuous part of the spectrum. First studied systematically by E. Hubble, redshift is central to observational cosmology, in which it provides the basis for the modern picture of an expanding universe. There are two fundamental properties of redshifts.
Industry:Science
A tank of water used to determine the hydrodynamic performance of waterborne bodies such as ships and submarines, as well as torpedoes and other underwater forms. In the narrow sense, towing tanks are considered to be experimental facilities used to measure the forces, such as drag, on ship models and in turn to predict the performance of the full-scale prototype. In general, towing tanks are rectangular in planform with a uniform cross section. Different section shapes are used, ranging from rectangular to semicircular. The cross-section dimension may vary from about 8 to 52 ft (2.5 to 16 m) in width, from about 4 to 33 ft (1.5 to 10 m) in depth, and from under 100 ft (30 m) to almost 6560 ft (2000 m) in length; the size of the model varies in length from 4 to 30 ft (1.5 to 9 m).
Industry:Science
A tarnish-resistant alloy of lead and tin always containing appreciably more than 63% tin. Other metals are sometimes used with or in place of the lead; among them are copper, antimony, and zinc. Pewter is commonly worked by spinning and it polishes to a characteristic luster. Because pewter work-hardens only slightly, pewter products can be finished without intermediate annealing.
Industry:Science
A technique employed in telecommunications transmission systems whereby an electromagnetic signal (the modulating signal) is encoded into one or more of the characteristics of another signal (the carrier signal) to produce a third signal (the modulated signal), whose properties are matched to the characteristics of the medium over which it is to be transmitted. The encoding preserves the original modulating signal in that it can be recovered from the modulated signal at the receiver by the process of demodulation.
The main purpose of modulation is to overcome any inherent incompatibilities between the electromagnetic properties of the modulating signal and those of the transmission medium. Of primary importance in this respect is the spectral distribution of power in the modulating signal relative to the passband of the medium. Modulation provides the means for shifting the power of the modulating signal to a part of the frequency spectrum where the medium's transmission characteristics, such as its attenuation, interference, and noise level, are favorable.
Industry:Science
A technique for braking in which mechanical energy is converted to heat or electrical energy in order to slow or stop motion. An all-mechanical dynamic brake consists of rotating vanes that circulate a viscous fluid in a manner that generates heat. This is one way that the power of the wind is harnessed for space heating. An electric dynamic brake consists of an electric dynamo in which the mechanical energy is converted to electric form, and either converted to heat in a resistor or returned to the supply lines. Typically, electric braking is accomplished with the same machine that serves as the drive motor. Electric dynamic braking is employed in electric vehicles, elevators, and other electrically driven devices that start and stop frequently.
Industry:Science
A technique for determining the properties of a material from the characteristics of light reflected from its surface. The materials studied include thin films, semiconductors, metals, and liquids.
Industry:Science
A technique for estimating the solution, <i>x</i>, of a numerical mathematical problem by means of an artificial sampling experiment. The estimate is usually given as the average value, in a sample, of some statistic whose mathematical expectation is equal to <i>x</i>. In many of the useful applications, the mathematical problem itself arises in a problem of probability in physics or other sciences, operational research, image analysis, general statistics, mathematical economics, or econometrics. The importance of the method arises primarily from the need to solve problems for which other methods are more expensive or impracticable, and from the increased importance of all numerical methods because of the development of the electronic digital computer.
Industry:Science
A technique for measuring small absorption coefficients in gaseous and condensed media, involving the sensing of optical absorption by detection of sound. It is frequently called optoacoustic spectroscopy. Although the technique dates back to 1880 when A. G. Bell used chopped sunlight as the source of radiation, it remained dormant for many years, primarily because of the lack of suitable powerful sources of tunable radiation. However, the usefulness of optoacoustic detection for spectroscopic applications was recognized early in its development, and pollution monitoring instruments (called spectrophones) dedicated for detection of specific gaseous constituents have been used intermittently since Bell's work.
Industry:Science
A technique for probing the interior of the Sun, using methods akin to terrestrial seismology. The Sun, although the nearest star by far, is a typical star, so what can be learned of its interior through helioseismology is of broad importance to the stars in general.
Industry:Science
A technique for providing a means of maintaining molecules in an inert medium at low temperature for spectroscopic study. This method is particularly well suited for preserving reactive species in a solid, inert environment. Absorption (infrared, visible, and ultraviolet), electron-spin resonance, and laser-excitation spectroscopes can be used to examine elusive molecular fragments such as free radicals that may be postulated as important controlling intermediates for chemical transformations used in industrial reactions, high-temperature molecules that are in equilibrium with solids at very high temperatures, weak molecular complexes that may be stable at low temperatures, new reactive molecular species, and molecular ions that are produced in plasma discharges or by high-energy radiation. The matrix isolation technique enables spectroscopic data to be obtained for reactive molecular fragments, many of which cannot be studied in the gas phase.
Industry:Science
