時間：2011-03-11 23:13來源：藍(lán)天飛行翻譯 作者：admin 點(diǎn)擊：次
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halo (atmospheric phenomenon). A prismatically colored or whitish circle or arc of a circle, with the sun or moon at its center. Coloration of a halo changes from red inside to blue outside, which is opposite to the coloration of a corona. See corona. A halo is fixed in size and has an angular diameter of 22° (common) or 46° (rare). Halos are characteristic of clouds composed of ice crystals and are useful in telling the difference between cirriform (ice) clouds and lower clouds, which are composed of liquid water. halo (cathode-ray oscilloscope). A bright ring around the spot produced by a beam of electrons striking the fluorescent coating in a cathode-ray tube. The halo is caused by light reflecting from the back side of the phosphorescent screen. halogen. Any of the five chemical elements in Group VII of the periodic table of chemical elements. Fluorine, chlorine, bromine, iodine, and astatine are the halogens. halogenated hydrocarbon. A hydrocarbon compound in which one or more of the hydrogen atoms have been replaced with an atom of one of the halogen elements, such as fluorine, chlorine, or bromine. Halon 1211. A halogenated hydrocarbon fire-extinguishing agent that is used in many of the HRD (high-rate discharge) fire-extinguishing systems for powerplant protection. The technical name for Halon 1211 is bromochlorodifluoromethane. Halon 1301. A halogenated hydrocarbon fire-extinguishing agent that is one of the best for extinguishing cabin and powerplant fires. It is highly effective and is the least toxic of the extinguishing agents available. The technical name for Halon 1301 is bromotrifluoromethane. hammer. A hand-held tool used for pounding. A hammer has a heavy, hard steel head mounted across the end of its handle. There are a number of types of hammer heads. Claw hammers have claws on one side of the head for removing nails. Ball peen hammers have a ball on one side of the head for forming heads on rivets. Cross peen and straight peen hammers have a wedge on one side of their head for shaping sheet metal. hammer welding. A form of forge welding in which the edges of two pieces of metal are heated red-hot and then pounded together with a hammer. handbook. A manual that describes an operation or a system of operations. A handbook normally contains specific rather than general information, and is usually prepared in a format that allows it to be kept at the point it is to be used. For example, a handbook on the operation of a piece of machinery should be kept with the machinery, rather than in a library or office. hand-cranked inertia starter (reciprocating engine starter). A starter for a large aircraft reciprocating engine that uses a hand crank to store energy in a spinning flywheel. The crank drives the flywheel through a high-ratio gear system to spin it at a high speed and store a great deal of kinetic energy. When the flywheel is spinning, the hand crank is removed and the flywheel is coupled, through a slip clutch, to the engine crankshaft. There is enough energy in the spinning flywheel to turn the engine fast enough for it to start. |
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