- 行业: Printing & publishing
- Number of terms: 178089
- Number of blossaries: 0
- 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 directional antenna consisting of the combination of a reflector comprising two conducting planes forming a dihedral angle and a driven radiator or dipole which usually is in the bisecting plane. It is widely used both singly and in arrays, gives good gain in comparison with cost, and covers a relatively wide band of frequency. Corner reflector antennas are used in very high-frequency (VHF) and ultrahigh-frequency (UHF) communications systems, telemetry systems, and electronic intelligence gathering systems.
Industry:Science
A directional change in an ecological community. Populations of animals and plants are in a dynamic state. Through the continual turnover of individuals, a population may expand or decline depending on the success of its members in survival and reproduction. As a consequence, the species composition of communities typically does not remain static with time. Apart from the regular fluctuations in species abundance related to seasonal changes, a community may develop progressively with time through a recognizable sequence known as the sere. Pioneer populations are replaced by successive colonists along a more or less predictable path toward a relatively stable community. This process of succession results from interactions between different species, and between species and their environment, which govern the sequence and the rate with which species replace each other. The rate at which succession proceeds depends on the time scale of species' life histories as well as on the effects species may have on each other and on the environment which supports them.
Industry:Science
A direct-reading instrument for indicating the density, specific gravity, or some similar characteristic of liquids. Almost all hydrometers are made of a high-grade glass tubing. The main body is the float section in the bottom of which ballast, such as small shot, is secured. A small-diameter tube, the stem, extends from the upper end of the float section. Inside the stem is the scale, printed on heavy-grade paper, and well-secured within the stem so its position will not change. When the hydrometer is placed in a liquid, the stem extends vertically above the surface for a portion of its length.
Industry:Science
A direct-reading instrument formerly widely used to measure the <i>Q</i> of an electrical component or passive network of components at radio frequencies. The instrument measures the voltage applied to a component or circuit together with the voltage across a key component and calculates the <i>Q</i> of the circuit from their ratio. An impedance-measuring instrument (bridge or analyzer) is more likely to be employed now.
Industry:Science
A discipline concerned both with the structure of antibody (immunoglobulin) molecules and with their ability to bind an apparently limitless number of diverse chemical structures (antigens); with the structure, organization, and rearrangement of the genes coding for the immunoglobulin molecules; and with the structure and function of molecules on the surface of animal cells, such as the transplantation (histocompatability) antigens, which recognize antibodies and the thymus-derived lymphocytes mediating the cellular immune response. A development of immunochemistry that is of medical, scientific, and commercial importance uses the binding specificity of immunoglobulins to measure complex (but sometimes simple) chemical structures such as alkaloids, hormones, proteins, peptides, complex carbohydrates, and lipids. The tests used for such measurements employ the binding of radioactive antigens (the radioimmunoassay) or the ligation of an antigen bound to an enzyme (the enzyme-linked immunoassay). These assay methods are highly sensitive and specific.
Industry:Science
A discipline concerned with genetically determined resemblances and differences among human beings. The idea that certain physical and mental characteristics, normal or abnormal, can “run in families” goes back to ancient times, though the mechanism by which heredity operates remained mostly unknown until the twentieth century. Formerly, genetics was thought to be concerned only with the familial transmission of rare and insignificant characteristics, but its fundamental biological role is now apparent. Genes, the units of heredity, have two unique properties: they are self-replicating, and they carry in their biochemical structure the codes for protein synthesis. Consequently, genes play the double role of transmitting genetic information from generation to generation and of governing all the activities of living cells.
Industry:Science
A discipline concerned with solving the engineering problems of providing food and fiber for the people of the world. These problems include designing improved tools to work the soil and harvest the crops, as well as developing water supplies for agriculture and systems for irrigating and draining the land where necessary. Agricultural engineers design buildings in which to house animals or store grains. They also work on myriad problems of processing, packaging, transporting, and distributing the food and fiber products.
Industry:Science
A discipline in which biotechnology and electronics are joined in at least three areas of research and development: biosensors, molecular electronics, and neuronal interfaces. Some workers in the field include so-called biochips and biocomputers in this area of carbon-based information technology. They suggest that biological molecules might be incorporated into self-structuring bioinformatic systems which display novel information processing and pattern recognition capabilities, but these applications—although technically possible—are speculative.
Industry:Science
A discipline involving the description and interpretation of layered sediments and rocks, and especially their correlation and dating. Correlation is a procedure for determining the relative age of one deposit with respect to another. The term “dating” refers to any technique employed to obtain a numerical age, for example, by making use of the decay of radioactive isotopes found in some minerals in sedimentary rocks or, more commonly, in associated igneous rocks. To a large extent, layered rocks are ones that accumulated through sedimentary processes beneath the sea, within lakes, or by the action of rivers, the wind, or glaciers; but in places such deposits contain significant amounts of volcanic material emplaced as lava flows or as ash ejected from volcanoes during explosive eruptions.
Industry:Science
A discipline involving the study of the atmosphere and its phenomena. Meteorology and climatology are rooted in different parent disciplines, the former in physics and the latter in physical geography. They have, in effect, become interwoven to form a single discipline known as the atmospheric sciences, which is devoted to the understanding and prediction of the evolution of planetary atmospheres and the broad range of phenomena that occur within them. The atmospheric sciences comprise a number of interrelated subdisciplines.
Industry:Science
