- 行业: Printing & publishing
- Number of terms: 178089
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- 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 toxic effect in a living organism caused by a species of oxygen. Oxygen has two aspects, one benign and the other malignant. Those organisms that avail themselves of the enormous metabolic advantages provided by dioxygen (O<sub>2</sub>) must defend themselves against its toxicity. The complete reduction of one molecule of O<sub>2</sub> to two of water (H<sub>2</sub>O) requires four electrons; therefore, intermediates must be encountered during the reduction of O<sub>2</sub> by the univalent pathway. The intermediates of O<sub>2</sub> reduction, in the order of their production are the superoxide radical O<sub>2</sub><sup>−</sup>), hydrogen peroxide (H<sub>2</sub>O<sub>2</sub>), and the hydroxyl radical (HO·).
Industry:Science
A tracking system that provides a ground control approach (GCA) air-traffic controller with a precise display of an aircraft's position relative to a runway final-approach course. To ensure absolute safety, precise information is displayed on a plan position indicator (PPI). This display provides the controller with aircraft position information for control of heading and rate of descent.
To accomplish this and maintain the required precision for a final-approach aid, the display shows the aircraft position in relation to range, azimuth, and elevation. The information presented on the precision approach radar display allows an air-traffic controller to direct a pilot down along a runway approach course to a precision landing. Precision radar approaches are accomplished in most weather conditions and do not require any on-board avionics equipment, such as an instrument landing system (ILS).
Industry:Science
A transient change in certain electrical properties of the skin, associated with the sweat gland activity and elicited by any stimulus that evokes an arousal or orienting response. Originally termed the psychogalvanic reflex, this phenomenon became known as the galvanic skin response. Electrodermal response (EDR) has replaced galvanic skin response as the collective term.
Industry:Science
A transient electromagnetic signal produced by a nuclear explosion in or above the Earth's atmosphere. Though not considered dangerous to people, the electromagnetic pulse (EMP) is a potential threat to many electronic systems.
Industry:Science
A transient form of gaseous conduction. This type of discharge is difficult to define, and no universally accepted definition exists. It can perhaps best be thought of as the transition between two more or less stable forms of gaseous conduction. For example, the transitional breakdown which occurs in the transition from a glow to an arc discharge may be thought of as a spark.
Industry:Science
A transistor in which emitter and collector barriers are formed by <i>pn</i> junctions between semiconductor regions of opposite conductivity type. These junctions are separated by a distance considerably less than a minority-carrier diffusion length, so that minority carriers injected at the emitter junction will not recombine before reaching the collector barrier and therefore be effective in modulating the collector-barrier impedance. Junction transistors are widely used both as discrete devices and in integrated circuits. The discrete devices are found in the high-power and high-frequency applications. Junction transistors range in power rating from a few milliwatts to about 300 W, in characteristic frequency from 0.5 to 2000 MHz, and in gain from 10 to 50 dB. Silicon is the most widely used semiconductor material, although germanium is still used for some applications. Junction transistors are applicable to any electronic amplification, detection, or switching problem not requiring operation above 200°C (392°F), 700 V, or 2000 MHz. Not all these limits can be achieved in one device, however. Junction transistors are classified by the number and order of their regions of different conductivity type, by the method of fabricating and structure, and sometimes by the principle of operation. Most modern transistors are fabricated by the silicon self-masked planar double-diffusion technique. The alloy technique and the grown-junction technique are primarily of historical importance. For a general description and definition of terms used here and a description of the mechanism of operation
Industry:Science
A transit of Venus, when Venus crosses the face of the Sun as seen from Earth, is one of the most unusual events in astronomy. Until 2004, only five transits had been seen in history: in 1639, 1771, 1779, 1874, and 1882. Nobody alive had seen one. But on June 8, 2004, a transit of Venus was widely visible and was seen by millions.
Industry:Science
A transmissible, invariably fatal disease of adult sheep and goats characterized by degeneration of the central nervous system. It is one of the transmissible spongiform encephalopathies, a disease family which includes bovine spongiform encephalopathy (BSE) in cattle (commonly known as mad cow disease), chronic wasting disease in deer, and Kuru and variant Creutzfeldt-Jakob disease in humans. Scrapie was first discovered in European sheep in the early eighteenth century and is now present in many sheep populations worldwide, excluding Australia and New Zealand.
Industry:Science
A transmission line (as nearly dissipationless as possible) or an electric network approximation of it which, if terminated in its characteristic impedance, will reproduce at its output a waveform applied to its input terminals with little distortion but at a time delayed by an amount dependent upon the electrical length of the line.
Industry:Science
A transmission network used to selectively modify the components of a signal according to their frequencies. In most cases a filter is used to enhance signals of desired frequencies while suppressing signals of undesired frequencies. An ideal filter would pass only desired frequencies while completely suppressing all unwanted frequencies, without any dispersion in time of the frequencies. Unfortunately, ideal filters are impossible to achieve.
Industry:Science
