Wisps or streaks of water or ice particles falling out of a cloud but evaporating before reaching the earth’s surface as precipitation. Virga is frequently seen trailing from altocumulus and altostratus clouds, but also is discernible below the bases of high-level cumuliform clouds from which precipitation is falling into a dry subcloud layer. It typically exhibits a hooked form in which the streaks descend nearly vertically just under the precipitation source but appear to be almost horizontal at their lower extremities. Such curvature of virga can be produced simply by effects of strong vertical windshear, but ordinarily it results from the fact that droplet or crystal evaporation decreases the particle terminal fall velocity near the ends of the streaks. Also called FALL STREAKS, PRECIPITATION TRAILS.
The lowest temperature at which a liquid gives off sufficient vapor to form a flammable mixture with air near the surface of the liquid. The flashpoint temperature is determined by laboratory testing in a prescribed apparatus.
Establishes the danger point when transferring, pumping, and firing procedures are concerned.
1. In petroleum refining, removal of final traces of impurities, as for a lubricant, by clay adsorption or mild hydrogen treating. Smoothing and brightening a surface such as a metal or a rock through the use of abrasive materials.
A method of displaying the character of a particular trajectory without examining its complete time development, in which the trajectory is sampled periodically, and the rate of change of a quantity under study is plotted against the value of that quantity at the beginning of each period. Also known as surface of section.
A semiconductor rectifier that uses the barrier formed between a specially prepared semiconductor surface and a metal point to produce the rectifying action.
1.A flat plate against which something rests or is pressed. 2. The rubber-covered roller of a typewriter against which paper is pressed when struck by the typebars. 2. A flat surface for exchanging heat in a boiler or heat exchanger which may have extended heat transfer surfaces.
A surface blasting method used when no rock drill is necessary or one is not available; consists of placing a charge of gelignite, primed with safety fuse and detonator, in close contact with the rock or boulder and covering it completely with stiff damp clay.
A method of ion implantation in which the workpiece is placed in a plasma containing the appropriate ion species and is repetitively pulse-biased to a high negative potential so that positive plasma ions are accelerated to the surface and implant in the bulk material. Abbreviated PSII.
