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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 barrier or structure across a stream, river, or waterway for the purpose of confining and controlling the flow of water. Dams vary in size from small earth embankments for farm use to high, massive concrete structures for water supply, hydropower, irrigation, navigation, recreation, sedimentation control, and flood control. As such, dams are cornerstones in the water resources development of river basins. Dams are now built to serve several purposes and are therefore known as multipurpose (<b>Fig. 1</b>). The construction of a large dam requires the relocation of existing highways, railroads, and utilities from the river valley to elevations above the reservoir. The two principal types of dams are embankment and concrete. Appurtenant structures of dams include spillways, outlet works, and control facilities; they may also include structures related to hydropower and other project purposes.
Industry:Science
A base to which to refer physical events. A physical event occurs at a point in space and at an instant of time. Each reference frame must have an observer to record events, as well as a coordinate system for the purpose of assigning locations to each event. The latter is usually a three-dimensional space coordinate system and a set of standardized clocks to give the local time of each event. For a discussion of the geometrical properties of space-time coordinate systems
Industry:Science
A basic carbonate of copper with the chemical formula Cu<sub>3</sub>(OH)<sub>2</sub>(CO<sub>3</sub>)<sub>2</sub>. Azurite is normally associated with copper ores and often occurs with malachite. Azurite is monoclinic. It may be massive or may occur in tabular, prismatic, or equant crystals (see <b>illus.</b>). Invariably blue, azurite was originally used extensively as a pigment. Hardness is 3.5–4 (Mohs scale) and specific gravity is 3.8. It can be synthesized by gentle heating of cupric nitrate or sulfate solutions with calcium carbonate in a closed tube. Notable localities for azurite are at Tsumeb, Southwest Africa, and Bisbee, Arizona.
Industry:Science
A basic linkage mechanism used in machinery and mechanical equipment. The term has been applied to three types of linkages: plane, spherical, and skew.
Industry:Science
A basic mathematical relation used in population genetics. It gives the proportion of the various genotypes in a randomly mating population in terms of the frequencies of the genes. The formula is useful for genetic analysis of populations, such as human populations or plants and animals in nature where experimental matings are not possible. It was discovered independently in 1908 by G. H. Hardy, a British mathematician, and W. Weinberg, a German physician who made a number of important contributions to the methodology of human genetics.
Industry:Science
A basic property of elementary particles of matter. One does not define charge but takes it as a basic experimental quantity and defines other quantities in terms of it. The early Greek philosophers were aware that rubbing amber with fur produced properties in each that were not possessed before the rubbing. For example, the amber attracted the fur after rubbing, but not before. These new properties were later said to be due to “charge.” The amber was assigned a negative charge and the fur was assigned a positive charge.
Industry:Science
A basketball or an American football looks the same (ignoring its lettering) if one reflects its right and left sides. We say they are reflection symmetric. In the case of a pear whose right end is large and whose left end is small, reflecting the pear puts the large end on the left and small end on the right. Such a pear is reflection asymmetric.
Industry:Science
A battery in which both electrodes and the electrolyte are solids. Solid electrolytes are a class of materials also known as superionic conductors and fast ion conductors, and their study belongs to an area of science known as solid-state ionics. As a group, these materials are very good conductors of ions but are essentially insulating toward electrons, properties that are prerequisites for any electrolyte. The high ionic conductivity minimizes the internal resistance of the battery, thus permitting high power densities, while the high electronic resistance minimizes its self-discharge rate, thus enhancing its shelf life. Examples of such materials include Ag<sub>4</sub>RbI<sub>5</sub> for Ag<sup>+</sup> conduction, LiI/Al<sub>2</sub>O<sub>3</sub> mixtures for Li<sup>+</sup> conduction, and the clay and β-alumina group of compounds (NaAl<sub>11</sub>O<sub>17</sub>) for Na<sup>+</sup> and other mono- and divalent ions. At room temperature the ionic conductivity of a single crystal of sodium β-alumina is 0.035 S/cm, comparable to the conductivity of a 0.1 <i>M</i> HCl solution. This conductivity, however, is reduced in a battery by a factor of 2–5, because of the use of powdered or ceramic material rather than single crystals. Of much interest are glassy and polymeric materials that can be readily made in thin-film form, thus enhancing the rate capability of the overall system.
Industry:Science
A battery that converts the energy of particles emitted from atomic nuclei into electric energy. Two basic types have been developed: (1) a high-voltage type, in which a beta-emitting isotope is separated from a collecting electrode by a vacuum or a solid dielectric, provides thousands of volts but the current is measured in picoamperes; (2) a low-voltage type gives about 1 V with current in microamperes.
Industry:Science
A beam assembled from steel plates which are welded or bolted to one another, used to support the horizontal surface of a bridge. Plate girders generally have I-shaped cross sections (<b>Fig. 1</b>). Cross sections with two or more webs that form a U- or box-shape can also be considered plate girders, but are generally classified separately as box girders. Plate girders are commonly used in bridge structures where large transverse loads and spans are encountered. On average, the height (measured from the top of the top flange to the bottom of the bottom flange) of plate girders is one-tenth to one-twelfth the length of the span, which can vary based on the loading and architectural requirements. The dimensions of plate girders are tailored to specific applications by adjusting the width and thickness of the web and flange plates along the length of the beam. By contrast, hot-rolled beams produced at steel mills are formed to specific dimensions according to a standardized list of structural shapes, and have limitations on their size. Plate girders can be produced with much greater depths than hot-rolled beams. The depth is generally considered to be the distance between the centroids of the flanges which defines the effective moment arm in bending. When different-grade steels are used for the flanges and webs, a plate girder is classified as a hybrid plate girder.
Industry:Science
