时间：2011-03-11 23:18来源：蓝天飞行翻译 作者：航空 点击：次
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yield point (material strength). A measure of the amount of stress needed to permanently deform a material. When a piece of material is stressed to a value within its elastic limit, it will deform, but will return to its original size and shape when the stress is removed. When the material is stressed to its yield point, it will not return to its original size and shape when the stress is removed; it will be permanently deformed. yield strength. The amount of stress needed to permanently deform a material. yoke (airplane control). The control column in an airplane on which the control wheel is mounted. Back-and-forth movement of the yoke moves the elevators, and rotation of the control wheel moves the ailerons. Young’s modulus. The ratio of the amount of tensile stress applied to a material to the amount of resulting strain parallel to the stress. ytterbium. A soft, bright, silvery, rare-earth, metallic chemical element. Ytterbium’s symbol is Yb, its atomic number is 70, and its atomic weight is 173.04. Ytterbium is used as an X-ray source and in the study of superconductivity. yttrium. A silvery, rare-earth, metallic chemical element. Yttrium’s symbol is Y, its atomic number is 39, and its atomic weight is 88.905. Yttrium is used in nuclear technology and as an alloy for other metals. Z Zahn cup (viscosity measuring instrument). A specially designed viscosimeter, or cup for measuring the viscosity of a liquid. The Zahn cup is filled with the liquid whose viscosity is to be measured. A specially calibrated hole in the bottom of the cup is opened, and the time needed for the liquid to flow from the cup is measured. The number of seconds between the start of the flow and the time at which the first break in the flow occurs relates to the viscosity of the liquid. Z-axis. The vertical, or yaw, axis of an aircraft. The X-axis is the longitudinal, or roll axis, and the Y-axis is the lateral, or pitch axis. See vertical axis. zener diode (electronic component). A special type of semiconductor device that allows electrons to flow through it in one direction, but normally opposes flow in the opposite direction. If the voltage across the zener diode, in the direction that does not allow flow, is increased to a specific value, the zener diode will break down, and electrons will flow through it. The voltage at which a zener diode breaks down is called the zener voltage. Zener diodes are also called avalanche diodes. zenith. The point in the orbit of a satellite or any body rotating around another body, at which the orbiting body is the greatest distance from the object around which it is rotating. The zenith of an orbit is opposite the nadir of the orbit. |
