- 行业: Printing & publishing
- Number of terms: 178089
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McGraw Hill Financial, Inc. is an American publicly traded corporation headquartered in Rockefeller Center in New York City. Its primary areas of business are financial, publishing, and business services.
A measure of the strength of a source of electrical energy. The term is often shortened to emf. It is not, of course, a force in the usual mechanical sense (and for this reason has sometimes been called electromotance), but it is a conveniently descriptive term for the agency which drives current through an electric circuit. In the simple case of a direct current <i>I</i> (measured in amperes) flowing through a resistor <i>R</i> (in ohms), Ohm's law states that there will be a voltage drop (or potential difference) of <i>V</i> = <i>IR</i> (in volts) across the resistor. To cause this current to flow requires a source with emf (also measured in volts) <i>E</i> = <i>V</i>. More generally, Kirchhoff's voltage law states that the sum of the source emf's taken around any closed path in an electric circuit is equal to the sum of the voltage drops. This is equivalent to the statement that the total emf in a closed circuit is equal to the line integral of the electric field strength around the circuit.
Industry:Science
A mechanical fastening device for connecting the ends of two shafts together. There are three major coupling types: rigid, flexible, and fluid.
Industry:Science
A mechanical linkage whose purpose is to produce, by means of a contoured cam surface, a prescribed motion of the output link of the linkage, called the follower. Cam and follower are a higher pair.
Industry:Science
A mechanical means for feeding coal into, and for burning coal in, a furnace. There are three basic types of stokers. Chain or traveling-grate stokers have a moving grate on which the coal burns; they carry the coal from a hopper into the furnace and move the ash out. Spreader stokers mechanically or pneumatically distribute the coal from a hopper at the furnace front wall and move it onto the grate which usually moves continuously to dispose of the ash after the coal is burned. Underfeed stokers are arranged to force fresh coal from the hopper to the bottom of the burning coal bed, usually by means of a screw conveyor. The ash is forced off the edges of the retort peripherally to the ashpit or is removed by hand.
Industry:Science
A mechanical method of separating a mixture of solid particles into fractions by size. The mixture to be separated, called the feed, is passed over a screen surface containing openings of definite size. Particles smaller than the openings fall through the screen and are collected as undersize. Particles larger than the openings slide off the screen and are caught as oversize. A single screen separates the feed into only two fractions. Two or more screens may be operated in series to give additional fractions. Screening occasionally is done wet, but most commonly it is done dry.
Industry:Science
A mechanical method of separating immiscible liquids or solids from liquids by the application of centrifugal force. This force can be very great, and separations which proceed slowly by gravity can be speeded up enormously in centrifugal equipment.
Industry:Science
A mechanical or electrical pump for drawing fuel from a storage tank and forcing it to an engine or furnace. The type of pump chosen for a given fuel depends to a great extent on the volatility of the liquid to be pumped. In a gasoline engine the fuel is highly volatile at ambient temperature. Therefore, the fuel line is completely sealed from the tank to the carburetor or fuel-injection system to prevent escape of fuel and to enable the pump to purge the line of vapor in the event of vapor lock—a condition in which the fuel vaporizes owing to abnormally high ambient temperature.
Industry:Science
A mechanical or electromechanical instrument that measures acceleration. The two general types of accelerometers measure either the components of translational acceleration or angular acceleration.
Industry:Science
A mechanical wave of large amplitude, propagating at supersonic velocity, across which pressure or stress, density, particle velocity, temperature, and related properties change in a nearly discontinuous manner. Unlike acoustic waves, shock waves are characterized by an amplitude-dependent wave velocity. Shock waves arise from sharp and violent disturbances generated from a lightning stroke, bomb blast, or other form of intense explosion, and from steady supersonic flow over bodies. This article discusses shock waves in gases and in condensed materials.
Industry:Science
A mechanism by which single cells of the animal kingdom, such as smaller protozoa, engulf and carry particles into the cytoplasm. It differs from endocytosis primarily in the size of the particle rather than in the mechanism; as particles approach the dimensions and solubility of macromolecules, cells take them up by the process of endocytosis.
Industry:Science
