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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neon bulb. A type of glow lamp made of two insulated electrodes inside a glass envelope filled with neon gas. Neon gas does not conduct electricity until the voltage across the electrodes rises to the ionization, or firing, voltage of the neon. When this voltage is reached, the neon gas ionizes and conducts. Electrons flowing through the ionized gas cause it to glow with a reddish-orange light. The gas continues to glow until the voltage across the electrodes drops to a value lower than its ionization voltage. neon-bulb oscillator (electronic circuit). A relaxation oscillator using a neon bulb to produce oscillation. The bulb is installed in parallel with a capacitor. When DC voltage is applied to the circuit through a resistor, the voltage across the bulb and capacitor rises until the ionization voltage of the bulb is reached. As soon as the neon gas ionizes, it short-circuits the capacitor, and the voltage drops to the deionization voltage, at which time conduction stops. The waveform of a neon-bulb oscillator is a sawtooth. neoprene. A type of synthetic rubber made from petroleum. Neoprene is superior to natural rubber and other synthetic rubbers because of its resistance to damage from petroleum products. neptunium. A silvery, metallic, naturally radioactive chemical element. Neptunium’s symbol is Np, its atomic number is 93, and its atomic weight is 237.0482. Neptunium is found as a trace element in uranium ores and is produced synthetically in nuclear reactions. net thrust (turbine engine specification). The thrust produced by a turbojet or turbofan engine in which the acceleration factor is the difference between the velocity of the incoming air and the velocity of the exhaust gases leaving the engine. Net thrust is actually the change in momentum of the mass of air and fuel passing through the engine. neutral axis (structures). The neutral axis of a piece of material being bent is a plane within the material along which there is no stress. The neutral axis is located approximately halfway (actually 44.5% of the thickness of the material) from the inside of the bend. The material on the outside of the bend is under a tensile stress, and that on the inside is under a compressive stress. There is no stress along the neutral axis. neutral conductor (electrical power system). A conductor in both three-wire single-phase, and Y-connected three-phase electrical systems in which the voltage is the same between it and any of the other conductors. The neutral conductor in a three-wire single-phase system is normally grounded with 110 volts between either line and the neutral conductor, and 220 volts between the two lines. In a Y-connected, three-phase system, there is normally 120 volts between any of lines and the neutral conductor and 208 volts between any two of the lines. |
