時間：2011-03-11 23:13來源：藍(lán)天飛行翻譯 作者：admin 點擊：次
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implode. To burst inwardly. Electron tubes, such as the cathode-ray tubes used in television sets and computer displays, have the air evacuated from them so the pressure of the air outside the tube is much greater than the pressure inside the tube. If the glass envelope of the tube cracks, outside air will rush violently onto the tube and the tube will implode. improper fraction (mathematics). A common fraction in which the numerator, the number above the line, is greater than the denominator, the number below the line. impulse coupling (magneto component). A spring-loaded coupling between a magneto and an aircraft reciprocating engine that causes the magneto to produce a hot and late spark for starting the engine. The rotating magnet in a magneto must be turned at a fast rate to produce a hot spark, but when the engine is being started, the magneto turns slowly. Arms inside the impulse coupling contact stop pins in the magneto housing and hold the magnet while the crankshaft turns. A heavy, flat spring winds up as the crankshaft continues to turn, with the magnet held stationary. When the crankshaft turns about thirty degrees past the point at which ignition normally occurs, a cam forces the arms off the stop pins, and the spring spins the magnet at a fast rate. When the magnet spins, it produces a hot spark. And since the spark occurs late, the piston is moving downward, preventing the engine kicking back. As soon as the engine is running normally, counterweights on the arms sling outward and hold the arms in, away from the stop pins. This keeps the impulse coupling disengaged so it has no effect on the ignition timing for normal engine operation. impulse-reaction turbine (gas turbine engine component). A type of turbine in which hot, high-velocity gases produce an aerodynamic force as well as an impulse force as they move the turbine blades in the direction needed to spin the turbine wheel. impulse turbine (gas turbine engine component). A form of turbine that is rotated by air striking bucket-shaped turbine blades. An impulse turbine changes the direction of the air flowing through it. The energy that causes this change in direction spins the turbine. An impulse turbine does not produce a pressure drop across the blade as the reaction turbine does. impurity (semiconductor material). A chemical element added to silicon or germanium to give it specific electrical characteristics. Arsenic, phosphorus, and antimony are pentavalent elements, elements having five electrons in their valence shell. When these elements are used as impurities, they form N-type material because there are more electrons than are needed to form covalent bonds within the material. Atoms of N-type material are called donor atoms. Aluminum, boron, gallium, and indium are elements having only three electrons in their valence shell, and when used as impurities with silicon or germanium, produce P-type materials. P-type materials have fewer electrons than are needed to form covalent bonds, and they accept electrons from other materials. Atoms of P-type materials are called acceptor atoms. |
