- 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 naturally occurring, high-molecular-weight (ranging 200,000 and up), organic plant product of unknown detailed structure. The term is loosely used, often interchangably with the term gum. Chemically, mucilage is closely allied to gums and pectins but differs in certain physical properties. Although gums swell in water to form sticky, colloidal dispersions and pectins gelatinize in water, mucilages form slippery, aqueous colloidal dispersions which are optically active and can be hydrolyzed and fermented. Mucilages are not pathological products but are formed in normal plant growth within the plant by mucilage-secreting hairs, sacs, and canals, but they are not found on the surface as exudates as a result of bacterial or fungal action after mechanical injury, as are gums. Mucilages occur in nearly all classes of plants in various parts of the plant, usually in relatively small percentages, and are not infrequently associated with other substances, such as tannins. The most common sources are the root, bark, and seed, but they are also found in the flower, leaf, and cell wall. Any biological functions within the plant are unknown, but they may be considered to aid in water storage, decrease diffusion in aquatic plants, aid in seed dispersal and germination, and act as a membrane thickener and food reserve. Mucilages are commonly identified by physical properties, most recently by infrared spectroscopy.
Industry:Science
A navigation instrument used for measuring angles, primarily altitudes of celestial bodies. Originally, the sextant had an arc of 60°, or one-sixth of a circle, from which the instrument derived its name. Because of the double-reflecting principle used, such an instrument could measure angles as large as 120°.
Industry:Science
A navigation system from which hyperbolic lines of position are determined by measuring the difference in times of arrival of pulses from widely spaced, synchronized transmitting stations. Since radio waves travel at the speed of light, a line of position represents a constant range difference from two transmitters. Loran is used by commercial and military ships and aircraft. The name is derived from “long-range navigation.”
Industry:Science
A navigation system in which one or more signals are emitted from a facility (or colocated facilities) to produce simultaneous indication of bearing and distance. Since a bearing is a radial line of position and a distance is a circular line of position, the rho-theta system always ensures a position fix produced by the intersection of two lines of position which are at right angles to each other. This produces a minimum geometric dilution of position (GDOP), a figure of merit for all radio navigation systems, and is one of the chief advantages of a rho-theta system. Another major advantage is that it is a single-site system and can thus be installed on a ship or an island. This has also made it attractive politically, enabling small countries to have their own navigation systems.
Industry:Science
A nearby neutron star that emits pulsed x-rays and gamma rays, steady optical radiation, and possibly radio and optical pulsations. Since the 1970s, it has been studied at a level of detail very unusual for a neutron star. As a result, not only are its nature and distance well known, but also a good understanding has been reached of the physical processes responsible for its multiwavelength emission.
Industry:Science
A nearly continuous cycle whereby iron from organic and inorganic sources is converted to form iron-porphyrin compounds, which can be utilized by the body. One such compound, termed a heme, is hemoglobin; more than 60% of the iron in the body is used in hemoglobin metabolism. Iron is also essential for other heme compounds, such as myoglobin and cytochromes, and for a wide variety of nonheme enzymes, including many in the citric acid cycle.
Industry:Science
A nearly level, generally dry surface in the lowest part of a desert basin with internal drainage (see <b>illustration</b>). When its surface is covered by a shallow sheet of water, it is a playa lake. Playas and playa lakes are also called dry lakes, alkali flats, mud flats, saline lakes, salt pans, inland sabkhas, ephemeral lakes, salinas, and sinks. The original meaning in Spanish of shore or beach has been lost. An example is Death Valley in California.
Industry:Science
A necessary but not sufficient condition for the achievement of a net release of energy from nuclear fusion reactions in a fusion reactor. As originally formulated by J. D. Lawson, this condition simply stated that a minimum requirement for net energy release is that the fusion fuel charge must combust for at least enough time for the recovered fusion energy release to equal the sum of energy invested in heating that charge to fusion temperatures, plus other energy losses occurring during combustion.
Industry:Science
A neoplastic disease of primarily woody plants, although the disease can be reproduced in species representing more than 90 plant families. The disease results from infection of wounds by the free-living soil bacterium <i>Agrobacterium</i> <i>tumefaciens</i> which is commonly associated with the roots of plants.
Industry:Science
A nerve cell: the functional unit of the nervous system. Structurally, the neuron is made up of a cell body or soma and one or more long processes: a single axon and dendrites (see <b>illus.</b>). The cell body contains the nucleus and usual cytoplasmic organelles with an exceptionally large amount of rough endoplasmic reticulum, called Nissl substance in the neuron. The longest cell process is the axon, which is capable of transmitting propagated nerve impulses. There may be none, one, or many dendrites composing part of a neuron. If there is no dendrite, it is a unipolar neuron; with one dendrite, it is a bipolar neuron; if there is more than one dendrite, it is a multipolar neuron. The dendrites are shorter and more branched than the axon. Dorsal-root spinal ganglia and most cranial nerve ganglia have unusual pseudounipolar neurons. Here a single process leaves the soma and then bifurcates, sending a long peripheral process to skin, muscle, or viscera and sending a central process into the spinal cord or brain. Both processes can conduct nerve impulses. These pseudounipolar neurons are always sensory. In most neurons only the axon propagates nerve impulses; the dendrites and somas are also irritable but do not propagate nerve impulses.
Industry:Science
