- 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.
An effect on spectral lines obtained when the light source is placed in a very strong magnetic field, first explained by F. Paschen and E. Back in 1921. In such a field the anomalous Zeeman effect, which is obtained with weaker fields, changes over to what is, in a first approximation, the normal Zeeman effect. The term “very strong field” is a relative one, since the field strength required depends on the particular lines being investigated. It must be strong enough to produce a magnetic splitting that is large compared to the separation of the components of the spin-orbit multiplet.
Industry:Science
An effect whereby a conductor carrying an electric current perpendicular to an applied magnetic field develops a voltage gradient which is transverse to both the current and the magnetic field. It was discovered by E. H. Hall in 1879. Important information about the nature of the conduction process in semiconductors and metals may be obtained through analysis of this effect.
Industry:Science
An effect, due to discontinuities in size or orientation of magnetic domains as a body of ferromagnetic material is magnetized, whereby the magnetization proceeds in a series of minute jumps.
Industry:Science
An efficient way to propagate energy from one medium to another is with sound. Acoustic transducers provide a means for redirecting energy over long distances. This energy redirection results in instrumentation that provides information for many everyday needs. The operating frequency ranges (and corresponding wavelength sizes) of the various applications provided by acoustic transducers serve to dictate the preferred transduction means. To couple transformations of energy from electrical to mechanical and then to acoustical (and vice versa), it is necessary to use active materials capable of transferring energy from one type to another. A common excitation mechanism is based on piezoelectric ceramics. Acoustic transmitters (projectors) operate by applying an electric field to the active materials within the transducer device to produce mechanical movement within the device such that an acoustic pressure (sound) is output from the transducer. The converse is also true; that is, a sound impinging upon an acoustic receiver (a microphone for in-air detection or a hydrophone for underwater use) mechanically excites the active material in the transducer so that an electrical signal is generated and may be analyzed in terms of a local sound field. The active materials that convert electrical signals to mechanical vibrations and then to sound are the focus of most transducer research, which centers on developing such materials to achieve specific performance gains. Thus, the design of many transducers begins with the tailoring of the active material component with regard to its intended applications. Among the active materials are piezoceramics, piezocomposites, electrostrictive relaxors, magnetostrictive alloys, and single crystals.
Industry:Science
An effort organized by society to protect, promote, and restore the people's health. It is the combination of sciences, skills, and beliefs that is directed to the maintenance and improvement of health through collective or social actions. The programs, services, and institutions of public health emphasize the prevention of disease and the health needs of the population as a whole. Additional goals include the reduction of the amount of disease, premature death, disability, and discomfort in the population.
Industry:Science
An electric circuit in which the principal circuit elements have their terminals joined in sequence so that a common current flows through all the elements.
Industry:Science
An electric current induced within the body of a conductor when that conductor either moves through a nonuniform magnetic field or is in a region where there is a change in magnetic flux. It is sometimes called Foucault current. Although eddy currents can be induced in any electrical conductor, the effect is most pronounced in solid metallic conductors. Eddy currents are utilized in induction heating and to damp out oscillations in various devices.
Industry:Science
An electric or magnetic field, or a combination thereof, which acts upon an electron beam in a manner analogous to that in which an optical lens acts upon a light beam. Electron lenses find application for the formation of sharply focused electron beams, as in cathode-ray tubes, and for the formation of electron images, as in infrared converter tubes, various types of television camera tubes, and electron microscopes.
Industry:Science
An electric rotating machine energized by direct current and used to convert electric energy to mechanical energy. It is characterized by its relative ease of speed control and, in the case of the series-connected motor, by an ability to produce large torque under load without taking excessive current. Output of this motor is given in horsepower, the unit of mechanical power. Normal full-load values of voltage, current, and speed are generally given.
Industry:Science
An electrical apparatus which produces very short high-voltage or high-current surges. Such devices can be classified into two types: impulse voltage generators and impulse current generators. High impulse voltages are used to test the strength of electric power equipment against lightning and switching surges. Also, steep-front impulse voltages are sometimes used in nuclear physics experiments. High impulse currents are needed not only for tests on equipment such as lightning arresters and fuses but also for many other technical applications such as lasers, thermonuclear fusion, and plasma devices.
Industry:Science
