- 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.
An alternating-current (ac) synchronous generator driven by a steam turbine for 50- or 60-Hz electrical generating systems operation.
Industry:Science
An alternating-current motor in which the currents in the secondary winding (usually the rotor) are created solely by induction. These currents result from voltages induced in the secondary by the magnetic field of the primary winding (usually the stator). An induction motor operates slightly below synchronous speed and is sometimes called an asynchronous (meaning not synchronous) motor.
Industry:Science
An alternative to the sequential, or von Neumann–based, model of computing, offering an inherently parallel metaphor. The dataflow concept is characterized by an orientation toward producing and consuming data values rather than updating storage cells. Such systems are made up of dataflow machines which execute programs expressed as a partial ordering of operations. This partial ordering, called a dataflow graph, is created by high-level language compilers. Dataflow systems are capable of exploiting all of the parallelism inherent in an algorithm. The economies of scale of very large-scale integration can be exploited quite naturally by using the dataflow approach.
Industry:Science
An amazing feature of many dinosaurs was their size, and the group included some of the largest terrestrial animals to inhabit Earth. But how did the largest dinosaurs get so big? Did they grow slowly, like living reptiles, reaching adulthood over periods perhaps exceeding a century? Or did they grow very rapidly, like living birds and mammals, attaining adult size in just a few decades? How did birds, now known to be direct descendants of carnivorous dinosaurs, acquire their exceptionally fast growth rates? Was it through their dinosaurian ancestry?
Industry:Science
An ambiguous term used in connection with both gaseous-discharge devices and photoelectric cells or tubes. In gaseous-conduction tubes it refers to the region of operation known as the Townsend discharge. The name is derived from the fact that photons produced in the gas do not play an important part in the production of ionization. The initial ionization arises from independent effects such as cosmic rays, radioactivity, or thermionic emission. When applied to photoelectric devices, the term applies to background current. This is current which may be present as the result of thermionic emission or other effects when there is no light incident on the photosensitive cathode.
Industry:Science
An amorphous form of carbon produced commercially by thermal or oxidative decomposition of hydrocarbons, It is used principally in rubber goods, pigments, and printer's ink.
Industry:Science
An amphibole (a double-chain silicate mineral) with the idealized chemical formula Mg<sub>7</sub>Si<sub>8</sub>O<sub>22</sub>(OH)<sub>2</sub> that crystallizes with monoclinic symmetry. Naturally occurring samples generally are solid solutions between Mg<sub>7</sub>Si<sub>8</sub>O<sub>22</sub>(OH)<sub>2</sub> and the corresponding iron (Fe)-end member with the general formula (Mg,Fe)<sub>7</sub>Si<sub>8</sub>O<sub>22</sub>(OH)<sub>2</sub>. The name cummingtonite (derived from the location Cummington, Massachusetts) is applied to all solid solutions with Mg/(Mg + Fe<sup>2+</sup>) ≥ 0.5, whereas those with Mg/(Mg + Fe<sup>2+</sup>) <0.5 are termed grunerite. Up to a total of 1.0 (Ca + Na) atom per formula unit may also be present in cummingtonite.
Industry:Science
An amphiphilic (also called amphipathic) compound that adsorbs at interfaces to form oriented monolayers and shows surface activity. An amphiphilic compound is a molecule that has a hydrophilic (polar) head and a hydrophobic (nonpolar) tail. Common synonyms for the term “surfactant” include amphiphile, surface-active agent, and tenside. If a surfactant is placed into contact with both a polar medium, such as water, and a nonpolar medium, such as an oil, one part of its molecule has an affinity for the polar medium and one part that has an affinity for the nonpolar medium. An example is an organic molecule such as sodium dodecyl sulfate (SDS), which can be thought of as having a hydrocarbon (dodecyl) tail and a highly polar (sulfate) head group. If the molecule is placed into a system containing water and oil, the sulfate head group will have an affinity for the water, while the dodecyl tail will have an affinity for the oil. The energetically most favorable orientation for such molecules is at the interface between the polar and nonpolar media, so that each part of the molecule can reside in an environment for which it has the greatest affinity. In the case of SDS in a mixture of oil and water, the SDS molecules will preferentially adsorb at the water/oil interface, with the polar sulfate group oriented into the water and the dodecyl tail group oriented into the oil. Three consequences of the amphiphilic nature of surfactants are their ability (1) to adsorb and form layers at interfaces, (2) to reduce the interfacial tension between fluids, and (3) to associate to form clusters, called micelles.
Industry:Science
An amplifying circuit in a radio-frequency (RF) receiver that processes and enhances a downconverted or modulated signal. Signal frequency spectrum downconversion is achieved by multiplying the radio-frequency signal by a local oscillator signal in a circuit known as a mixer. This multiplication produces two signals whose frequency content lies about the sum and difference frequencies of the center frequency of the original signal and the oscillator frequency. A variable local oscillator is used in the receiver to hold the difference-signal center frequency constant as the receiver is tuned. The constant frequency of the downconverted signal is called the intermediate frequency (IF), and it is this signal that is processed by the intermediate-frequency amplifier.
Industry:Science
An analysis of relationships within a dc circuit. Any combination of direct-current (dc) voltage or current sources, such as generators and batteries, in conjunction with transmission lines, resistors, inductors, capacitors, and power converters such as motors is termed a dc circuit. Historically the dc circuit was the first to be studied and analyzed mathematically.
Industry:Science
