- 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 for suddenly producing an explosive neutron chain reaction in a fissile material such as uranium-235 (<sup>235</sup>U) or plutonium-239 (<sup>239</sup>Pu). In a wider sense, any explosive device that derives its energy from nuclear reactions, including not only the foregoing fission weapon but also a fusion weapon, which gets its energy largely from fusion reactions of heavy hydrogen isotopes, and a fission-fusion weapon, which derives its energy from both fission and fusion. Because an atomic bomb derives its energy from nuclear reactions, it is properly called a nuclear explosive or nuclear weapon.
Industry:Science
A device for the conversion of acoustical or mechanical energy into electrical energy, and vice versa, which utilizes a quasipermanently charged or polarized dielectric material (electret). Examples are certain microphones, headphones, hydrophones, and ultrasonic devices. Depending on the electret material and the usage, either the external electric field of real-charge electrets or the piezoelectric activity of dipolar electrets is used. In the simplest implementation, a transducer based on real-charge electrets consists of a metal backplate (first electrode) covered by a mechanically tensioned diaphragm. The diaphragm is a film electret carrying a metal coating (second electrode) on the side facing away from the backplate. Provisions are made to maintain a shallow air gap between electret and backplate. The air gap is occupied by an electrostatic field originating from the electret charges. Upon acoustical or mechanical deflection of the diaphragm, such a device generates an electrical output signal between its two electrodes; similarly, application of an electrical signal results in diaphragm deflections. Such electret devices are therefore self-biased electrostatic or condenser transducers. They thus exhibit all the advantages of this transducer class, such as wide dynamic range and flat response over a frequency range of several decades, without requiring the external bias necessary in conventional transducers of this kind. On the other hand, a transducer based on the piezoelectric activity of a dipolar electret may consist of just the electret film covered by two electrodes. Compression or bending of the film causes again an electrical output signal between the electrodes, while the application of a voltage to the electrodes results in mechanical action.
Industry:Science
A device for the detection or demodulation of a frequency-modulated (FM) wave. Frequency-modulation detectors operate in several ways. In one class of detector, known as a discriminator, the frequency modulation is first converted to amplitude modulation, which is then detected by an amplitude-modulation detector. Another type of FM detector employs a phased-locked oscillator to recover the modulation. A still different type converts the frequency modulation to pulse-rate modulation, which can be converted to the desired signal by use of an integrating circuit. Examples of these types will be discussed here.
Industry:Science
A device for tightening a rod or wire rope. Its parts are a sleeve with a screwed connection at one end and a swivel at the other or, more commonly, a sleeve with screwed connections of opposite hands (left and right) at each end so that by turning the sleeve, the connected parts will be drawn together, taking up slack and producing necessary tension (see <b>illus.</b>). Types of ends available are hook, eye, and clevis. The turnbuckle can be connected at any convenient place in the rod or rope, and several may be used in series if required.
Industry:Science
A device for transferring heat efficiently between two locations by using the evaporation and condensation of a fluid contained therein. Originally developed for refrigeration and spacecraft thermionic generator applications, heat pipes (and their close relative, the thermosiphon) have become routine components in systems ranging from missiles to domestic tuner-amplifiers and furnaces. They have many applications in areas where reliable performance and low cost are of prime importance—for example, in electronics and heat exchangers.
Industry:Science
A device in which a vapor is brought into direct contact with a cooling liquid and condensed by giving up its latent heat to the liquid. In almost all cases the cooling liquid is water, and the condensing vapor is steam. Contact condensers are classified as jet, barometric, and ejector condensers (see <b>illus.</b>). In all three types the steam and cooling water are mixed in a condensing chamber and withdrawn together. Noncondensable gases are removed separately from the jet condenser, entrained in the cooling water of the ejector condenser, and removed either separately or entrained in the barometric condenser. The jet condenser requires a pump to remove the mixture of condensate and cooling water and a vacuum breaker to avoid accidental flooding. The barometric condenser is self-draining. The ejector condenser converts the energy of high-velocity injection water to pressure in order to discharge the water, condensate, and noncondensables at atmospheric pressure.
Industry:Science
A device in which an uncontrolled, self-sustaining, thermonuclear fusion reaction is carried out in heavy hydrogen (deuterium or tritium) to produce an explosion. In a fusion reaction, the collision of two energy-rich nuclei results in a mutual rearrangement of their protons and neutrons to produce two or more reaction products, together with a release of energy of amount <i>E</i> given by A. Einstein's formula <i>E</i>=<i>mc</i><sup>2</sup>, where <i>m</i> is the mass difference between the original and produced nuclei, and <i>c</i> is the velocity of light.
Industry:Science
A device in which detection of radiation takes place in or near the depletion region of a reverse-biased semiconductor junction. The electrical output pulse is linearly proportional to the energy deposited in the junction depletion layer by the incident ionizing radiation.
Industry:Science
A device in which electrons can travel through a sealed chamber containing at least two electrodes and gas at a very low pressure. The gas pressure usually ranges from about 10<sup>−6</sup> to 10<sup>−9</sup> atm (10<sup>−1</sup> to 10<sup>−4</sup> pascal). At the low extreme of this pressure range, electron tubes are sometimes referred to as vacuum tubes, and at the high extreme as gas tubes.
Industry:Science
A device in which the temperature difference between the ends of a pair of dissimilar metal wires is deduced from a measurement of the difference in the thermoelectric potentials developed along the wires. The presence of a temperature gradient in a metal or alloy leads to an electric potential gradient being set up along the temperature gradient. This thermoelectric potential gradient is proportional to the temperature gradient and varies from metal to metal. It is the fact that the thermoelectric emf is different in different metals and alloys for the same temperature gradient that allows the effect to be used for the measurement of temperature.
Industry:Science
