- 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 method of separating the constituents of a mixture utilizing preferential solubility of one or more components in a second phase. Commonly, this added phase is a liquid, while the mixture to be separated may be either solid or liquid. As a mundane example, the preparation of tea or coffee is a process of liquid/solid extraction whereby water selectively dissolves certain components of the mixture, leaving behind the insoluble residue (as tea leaves or coffee grounds). If the starting mixture is a liquid, then the added solvent must be immiscible or only partially miscible with the original and of such a nature that the components to be separated have different relative solubilities in the two liquid phases.
Industry:Science
A method of shaping land to control erosion on slopes of rolling land used for cropping and other purposes. In early practice the land was shaped into a series of nearly level benches or steplike formations. Modern practice in terracing, however, consists of the construction of low-graded channels or levees to carry the excess rainfall from the land at nonerosive velocities. The physical principle involved is that, when water is spread in a shallow stream, its flow is retarded by the roughness of the bottom of the channel and its carrying, or erosive, power is reduced. Since direct impact of rainfall on bare land churns up the soil and the stirring effect keeps it in suspension in overland flow and rills, terracing does not prevent sheet erosion. It serves only to prevent destruction of agricultural land by gullying and must be supplemented by other erosion-control practices, such as grass rotation, cover crops, mulching, contour farming, strip cropping, and increased organic matter content.
Industry:Science
A method of supporting and transporting objects or vehicles which is based on the physical property that the force between two magnetized bodies is inversely proportional to their distance. By using this magnetic force to counterbalance the gravitational pull, a stable and contactless suspension between a magnet (magnetic body) and a fixed guideway (magnetized body) may be obtained. In magnetic levitation (maglev), also known as magnetic suspension, this basic principle is used to suspend (or levitate) vehicles weighing 40 tons or more by generating a controlled magnetic force. By removing friction, these vehicles can travel at speeds higher than wheeled trains, with considerably improved propulsion efficiency (thrust energy/input energy) and reduced noise. In maglev vehicles, chassis-mounted magnets are either suspended underneath a ferromagnetic guideway (track), or levitated above an aluminum track.
Industry:Science
A method used for determining the elemental composition of materials, based on the xrays emitted by different elements when bombarded with high-energy electrons. It is a micro method that can detect xray photons emitted by the atoms within a small volume excited by an electron beam focused to 10 nanometers diameter or less. In biology electron-probe microanalysis can be used to determine the composition of cell organelles without isolating them and therefore altering the distribution of diffusible elements Studies with electron-probe analysis have thrown light on the major problems of excitation-contraction coupling in muscle, visual transduction in retinal rods, and the functions of the endoplasmic reticulum and mitochondria in the regulation of cytoplasmic calcium.
Industry:Science
A method used in chemistry to purify substances or to isolate them from other substances, for either preparative or analytical purposes. In industrial applications the ultimate goal is the isolation of a product of given purity, whereas in analysis the primary goal is the determination of the amount or concentration of that substance in a sample. In principle it is always more convenient to carry out quantitative determinations directly on portions of the original sample. In cases where the analytical methods available are not sufficiently selective to permit this direct approach, it is necessary to employ preliminary separations to reduce the concentration of, or to remove completely, those substances which interfere in the final estimation.
Industry:Science
A microscope that utilizes polarized light to form a highly magnified image of an object. Polarizing microscopes play an important role in crystallography, petrography, microchemistry, and biology. Although all light microscopes compare poorly with electron microscopes with respect to image resolution, polarized light microscopes have the unique ability to deliver information about the submicroscopic structure of the objects being examined. They also have the advantage of being relatively nondestructive, and may be used safely with living cells. Polarized light interactions with electromagnetically anisotropic structures, down to atomic dimensions, can be measured by polarized light microscopy. The sensitivity of polarized light microscopy as well as its importance to biology have been enhanced by the use of video technology.
Industry:Science
A microscope used for making visible differences in phase or optical path in transparent or reflecting specimens. It is an important instrument for studying living cells and is used in biological and medical research.
Industry:Science
A microscope whose objective is composed of two mirrors, one convex and the other concave. The imaging properties are independent of the wavelength of light, and this freedom from chromatic aberration allows the objective to be used even for infrared and ultraviolet radiation. Although the reflecting microscope is simple in appearance, the construction tolerances are so small and so difficult to achieve that the system is used only when refracting objectives are unsuitable. The distance from the objective to the specimen can be made very large; this large working distance is useful in special applications, such as examining objects situated within metallurgical furnaces. Reflecting microscopes have been mainly used for microspectrometry in the infrared and the ultraviolet, and for ultraviolet microphotography.
Industry:Science
A microwave electronic tube in which a beam of electrons interacts continuously with a wave that travels along a circuit, the interaction extending over a distance of many wavelengths. Traveling-wave tubes can provide amplification over exceedingly wide bandwidths. Typical bandwidths are 10–100% of the center frequency, with gains of 20–60 dB. Low-noise traveling-wave tube amplifiers serve as the inputs to sensitive radars or communications receivers. High-efficiency medium-power traveling-wave tubes are the principal final amplifiers used in communication satellites, the space shuttle communications transmitter, and deep-space planetary probes and landers. High-power traveling-wave amplifiers operate as the final stages of radars, wide-band radar countermeasure systems, and scatter communication transmitters. They are capable of delivering continuous-wave power levels in the kilowatt range and pulsed power levels exceeding a megawatt.
Industry:Science
A mild, dry, extremely turbulent westerly wind on the eastern slopes of the Rocky Mountains and closely adjoining plains. The term is an Indian word which means “snow-eater,” appropriately applied because of the great effectiveness with which this wind reduces a snow cover by melting or by sublimation. The chinook is a particular instance of a type of wind known as a foehn wind. Foehn winds, initially studied in the Alps, refer to relatively warm, rather dry currents descending the lee slope of any substantial mountain barrier. The dryness is an indirect result of the condensation and precipitation of water from the air during its previous ascent of the windward slope of the mountain range. The warmth is attributable to adiabatic compression, turbulent mixing with potentially warmer air, and the previous release of latent heat of condensation in the air mass and to the turbulent mixing of the surface air with the air of greater heat content aloft.
Industry:Science
