- 行业: Printing & publishing
- Number of terms: 178089
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- Company Profile:
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 device that converts variations in one energy form into corresponding variations in another, usually electrical form. Measurement transducers or input transducers may exploit a wide range of physical, chemical, or biological effects to achieve transduction, and their design principles usually revolve around high sensitivity and minimum disturbance to the measurand, that is, the quantity to be measured. Output transducers or actuators are designed to achieve some end effect, for example, opening of a valve or deflection of a control surface on an aircraft. Actuators, therefore, normally operate at high power levels. The term sensor is often used instead of transducer, but strictly a sensor does not involve energy transformation; the term should be reserved for devices such as a thermistor, which is not energy-changing but simply changes its intrinsic electrical resistance in response to changes in temperature.
Industry:Science
A device that detects or measures electromagnetic radiation by generating a current or a voltage, or both, upon absorption of radiant energy. Specially designed photovoltaic cells are used for power generation, as in solar batteries or solar cells, and for sensitive detection of electromagnetic radiation in radiometry, optical communications, spectroscopy, and other applications. An important advantage of the photovoltaic cell in these particular applications is that no separate bias supply is needed—the device generates a signal (voltage or current) simply by the absorption of radiation.
Industry:Science
A device that determines the critical angle of attack for a given aircraft, at which point the lift stops increasing and the aircraft will no longer sustain itself in steady-state condition (level flight or climb/descent). The indicator usually operates from vane sensors, airflow pressure sensors, tabs on the leading edge of the wings, and computing devices which include accelerometers, airspeed detectors, and vertical gyros. The indicator may be a pointer over a dial, lights, or an audible signal. In some cases, the computer may actuate a control-column shaker to alert the pilot.
Industry:Science
A device that eliminates the need for mechanical clearance in the valve train of internal combustion engines. Clearance is normally required to prevent the valve's being held open and destroyed as the valve train undergoes thermal expansion. However, clearance requires frequent adjustment and is responsible for much operating noise. The hydraulic lifter is a telescoping compression strut in the linkage between cam and valve, consisting of a piston and cylinder (see <b>illus.</b>). When no opening load exists, a weak spring moves the piston, extending the strut and eliminating any clearance. This action sucks oil into the cylinder past a check valve. The trapped oil transmits the valve-opening forces with little deflection. A slight leakage of oil during lift shortens the strut, assuring valve closure. The leakage oil is replaced as the spring again extends the strut at no load.
Industry:Science
A device that extracts the analog information from a received pulse or from a set of pulses.
Industry:Science
A device that facilitates and greatly simplifies the measurement of very high frequencies, particularly in the optical range from 10<sup>14</sup> to 10<sup>15</sup> Hz. Extremely stable and reproducible optical frequencies <i>f</i><sub>opt</sub> in this range are produced by trapped-atom and trapped-ion atomic clocks. Frequency-comb technology is based on the train of short-duration pulses of optical radiation emitted at a stable and measurable repetition rate <i>f<sub>R</sub></i> of 100 MHz to 1 GHz by a femtosecond laser. Such a pulse train can be equivalently represented as a continuously produced “comb” of frequencies. The “teeth” of the comb are discrete phase-related frequencies spaced by <i>f<sub>R</sub></i> from one another, and the frequency of the <i>m</i>th tooth is <i>mf<sub>R</sub></i>, where <i>m</i> is an integer (see <b>illustration</b>). The frequencies produced typically span a rather narrow wavelength range of 30 nm to around 800 nm, but this span can be increased to a factor of 2 by passing the pulsed light through an optical fiber made from a highly nonlinear material, enabling a comb frequency to be matched to many different optical frequency standards.
Industry:Science
A device that integrates the functions of the central processing unit (CPU) of a computer onto one semiconductor chip or integrated circuit (IC). In essence, the microprocessor contains the core elements of a computer system, its computation and control engine. Only a power supply, memory, peripheral interface ICs, and peripherals (typically input/output and storage devices) need be added to build a complete computer system.
Industry:Science
A device that is designed to offer protection against voltage surges on the power line that supplies electrical energy to the sensitive components in electronic devices and systems. The device offers a limited type of protection to computers, television sets, high-fidelity equipment, and similar types of electronic systems.
Industry:Science
A device that is interposed between two systems to prevent one of them from having undesired effects on the other, while transmitting desired signals between the systems by optical means. Optical isolators are used for both electrical systems and optical systems such as lasers.
Industry:Science
A device that is used to define a fixed direction in space or to determine the change in angle or the angular rate of its carrying vehicle with respect to a reference frame. Gyroscopes (also called gyros) respond to vehicle angular rates, that is, rates of change of angles between vehicle axes and reference axes, from which these angles can be computed. Gyros are used for guidance, navigation, and stabilization, for example, to measure the angular deviation of a guided missile from its desired flight trajectory; to determine the heading of a vessel for steering; to determine the heading of an automobile as it turns through city streets; to indicate the heading and orientation of aircraft during and after a series of maneuvers; and to stabilize and point radar dishes and satellites.
Industry:Science
