- 行业: Printing & publishing
- Number of terms: 178089
- Number of blossaries: 0
- 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 reduces the risk of midair collision by providing advisories to the flight crew. It is known in the United States as a Traffic Alert and Collision Avoidance System (TCAS), and operates independently of the ground-based air-traffic control system to provide a safety net should normal separation standards be jeopardized.
Industry:Science
A device that screws into the combustion chamber of an internal combustion engine to provide a pair of electrodes between which an electrical discharge is passed to ignite the combustible mixture. The spark plug consists of an outer steel shell that is electrically grounded to the engine and a ceramic insulator, sealed into the shell, through which a center electrode passes (see <b>illus.</b>). The high-voltage current jumps the gap between the center electrode and the ground electrode fixed to the outer shell.
Industry:Science
A device that serves as an input source of currents and voltages from an electric power system to instruments, relays, meters, and control devices. The basic design is that of a transformer with the primary winding connected to the power system, and the secondary winding to the sensing and measuring equipment. Data from these devices are necessary for the operation, control, and protection of the power system. The primary reason for setting up the instrument-transformer interface is to provide analog information at low voltage levels, insulated from the higher system voltages. The range of use is from 480 V through the maxima of the 765–1000-kV power systems.
Industry:Science
A device that shifts the phase of a sinusoidal carrier signal, <i>c</i>(<i>t</i>), in proportion to the instantaneous amplitude of the information signal, <i>s</i>(<i>t</i>). Since the definition of frequency is the rate of change of phase, phase modulator and phase modulation are very closely related to frequency modulator and frequency modulation. (Integrate the frequency signal with respect to time in order to obtain the phase signal; differentiate the phase signal with respect to time to obtain the frequency signal.) The form of the unmodulated sinusoidal carrier signal is <i>c</i>(<i>t</i>) = <i>A</i> cos (2π<i>f</i><sub><i>c</i></sub><i>t</i>), where the amplitude and frequency of the sinusoid are <i>A</i> and <i>f</i><sub><i>c</i></sub>, respectively.
Industry:Science
A device that uses an internal resonance frequency of atoms (or molecules) to measure the passage of time. The terms atomic clock and atomic frequency standard are often used interchangeably. A frequency standard generates pulses at regular intervals. A frequency standard can be made into a clock by the addition of an electronic counter, which records the number of pulses.
Industry:Science
A device that uses the principle of amplification of electromagnetic waves by stimulated emission of radiation, and operates in the infrared, visible, or ultraviolet region. The term laser is an acronym for light amplification by stimulated emission of radiation, or a light amplifier. However, just as an electronic amplifier can be made into an oscillator by feeding appropriately phased output back into the input, so the laser light amplifier can be made into a laser oscillator, which is really a light source. Laser oscillators are so much more common than laser amplifiers that the unmodified word “laser” has come to mean the oscillator, while the modifier “amplifier” is generally used when the oscillator is not intended.
Industry:Science
A device to measure the acoustic power or intensity of a sound beam by means of the force or torque that the beam exerts on an inserted object or interface. The underlying theory involves the concept of radiation pressure, which is the time-independent part of the pressure associated with a nominally sinusoidal acoustic disturbance. Such pressure occurs, for example, when a plane sound wave is partially reflected at an interface between two materials, with the nonlinear interaction between the incident and reflected waves giving rise to a steady pressure on the interface. If a narrow beam is incident on the interface and the transmitted wave is fully absorbed by the second material, the magnitude of the radiation force <i>F</i> (area integral of radiation pressure) equals a constant times <i>W</i>/<i>c</i>, where <i>W</i> is the power of the sound beam and <i>c</i> is the sound speed. The multiplicative constant is of the order of unity and depends on the thermodynamic properties of the fluid. The force acts in the vector direction of propagation of the sound wave. When the inserted object is of small size, the force is not given by as simple an expression, but it can nevertheless be predicted from basic principles. Thus, acoustic radiometers do not require external calibration and are themselves sometimes used in the calibration of transducers.
Industry:Science
A device to measure the stagnation pressure due to isentropic deceleration of a flowing fluid. In its original form it was a glass tube bent at 90° and inserted in a stream flow, with its opening pointed upstream (<b>illustration <i>a</i></b>). Water rises in the tube a distance, <i>h</i>, above the surface, and if friction losses are negligible, the velocity of the stream, <i>V</i>, is approximately √<span style="border-top:1px solid black;">2<i>gh</i></span>, where <i>g</i> is the acceleration of gravity. However, there is a significant measurement error if the probe is misaligned at an angle α with respect to the stream (illus. <i>a</i>). For an open tube, the error is about 5% at α ≈ 10°.
Industry:Science
A device to open or close an electric power circuit either during normal power system operation or during abnormal conditions. A circuit breaker serves in the course of normal system operation to energize or deenergize loads. During abnormal conditions, when excessive current develops, a circuit breaker opens to protect equipment and surroundings from possible damage due to excess current. These currents are usually the result of short circuits created by lightning, accidents, deterioration of equipment, or sustained overloads.
Industry:Science
A device used to confine charged or neutral particles where their interaction with the wall of a container must be avoided. Electrons or protons accelerated to energies as high as 1 teraelectronvolt (10<sup>12</sup> electronvolts) are trapped in magnetic storage rings in high-energy collision studies. Other forms of magnetic bottles are designed to hold dense hot plasmas of hydrogen isotopes for nuclear fusion. At the other end of the energy spectrum, ion and atom traps can store isolated atomic systems at temperatures below 1 millikelvin. Other applications of particle traps include the storage of antimatter such as antiprotons and positrons (antielectrons) for high-energy collision studies or low-energy experiments.
Industry:Science
