- 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.
The principle that, when a system of masses is subject only to forces that masses of the system exert on one another, the total vector momentum of the system is constant. Since vector momentum is conserved, in problems involving more than one dimension the component of momentum in any direction will remain constant. The principle of conservation of momentum holds generally and is applicable in all fields of physics. In particular, momentum is conserved even if the particles of a system exert forces on one another or if the total mechanical energy is not conserved.
Industry:Science
The subdiscipline of genetics concerned with genetic variation and inheritance in forest trees. The study of forest genetics is important because of the unique biological nature of forest trees (large, long-lived plants covering 30% of the Earth's land surface) and because of the social and economic importance of forests, Knowledge of forst genetics is important. Forest genetics is the basis for conservation, maintenance, and management of healthy forest ecosystems; and development of programs which breed high-yielding varieties of commercially important tree species.
Industry:Science
The system in an internal combustion engine that initiates the chemical reaction between fuel and air in the cylinder charge by producing a spark. An ignition system for a multicylinder internal combustion engine has three basic functions: (1) to provide a sufficiently energetic spark to initiate the burning of the fuel-air mixture within each cylinder; (2) to control spark timing for optimum efficiency so that cylinder pressure reaches its maximum value shortly after the piston reaches the top of its compression stroke; and (3) to select the correct cylinder fired.
Industry:Science
The term “materials science and engineering” emerged in the 1960s to represent how the engineering application of materials was increasingly based on scientific principles, rather than the empiricism typically used prior to World War II. Materials science focuses on understanding how the properties (or characteristics) of materials are based on their atomic- and microscopic-scale structure. The term microstructure refers to this microscopic-scale structure. Materials science grew out of the fields of physical chemistry, polymer chemistry, and condensed-matter physics.
Industry:Science
The term adopted by E. Schulze in 1891 to designate the plant cell components which are made soluble by dilute alkali or which go into solution quite readily in hot dilute mineral acids with the formation of simple sugars. Hemicelluloses constitute about one-fourth of perennial plants and about one-third of annual plants. The term is usually applied to those polysaccharides in the cell wall of land plants which are extractable by dilute alkaline solutions. The term has also been used to include all the polysaccharide components of the cell wall other than cellulose.
Industry:Science
The light-harvesting pigment chlorophyll is found in great abundance wherever conditions are conducive for photosynthetic organisms to live. Although chlorophyll facilitates very efficient absorption of visible light (wavelengths between 400 and 700 nanometers) by these organisms, no organism can utilize all of the absorbed energy for photosynthesis under full sunlight. In addition plants are often exposed to environmental stress (for example, temperature extremes in winter and summer, limiting water or nutrients, and high salinity) that reduces photosynthesis further.
Industry:Science
The only extant order of the chondrichthyan subclass Holocephali, and the closest living relatives of the Elasmobranchii (sharks and rays). The chimaeriformes (ratfishes) are a distinctive group of marine fishes that mostly inhabit the deeper parts of the world's oceans, especially in the Atlantic and Pacific. Some species move to coastal waters during the winter months, and a few species may be restricted to these environments. Modern ratfishes are divided into three families, distinguished by the shape of the snout: Chimaeridae, Rhinochimaeridae, and Callorhinchidae.
Industry:Science
The number of times which sound pressure, electrical intensity, or other quantities specifying a wave vary from their equilibrium value through a complete cycle in unit time. The most common unit of frequency is the hertz; 1 Hz is equal to 1 cycle per second. In one cycle there is a positive variation from equilibrium, a return to equilibrium, then a negative variation, and return to equilibrium. This relationship is often described in terms of the sine wave, and the frequency referred to is that of an equivalent sine-wave variation in the parameter under discussion.
Industry:Science
The process of having a machine or machines accomplish tasks hitherto performed wholly or partly by humans. As used here, a machine refers to any inanimate electromechanical device such as a robot or computer. As a technology, automation can be applied to almost any human endeavor, from manufacturing to clerical and administrative tasks. An example of automation is the heating and air-conditioning system in the modern household. After initial programming by the occupant, these systems keep the house at a constant desired temperature regardless of the conditions outside.
Industry:Science
The study of communication and control within and between humans, machines, organizations, and society. This is a modern definition of the term cybernetics, which was first utilized by N. Wiener in 1948 to designate a broad subject area he defined as “control and communication in the animal and the machine.” A distinguishing feature of this broad field is the use of feedback information to adapt or steer the entity toward a goal. When this feedback signal is such as to cause changes in the structure or parameters of the system itself, it appears to be self-organizing.
Industry:Science
