- 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.
The electromagnetic radiation and particles (electrons, protons, alpha particles, and rarer heavy atomic nuclei) emitted by the Sun. The electromagnetic radiation covers a wavelength range from x-rays to radio waves, that is, from about 0.01 nanometer to 30 km. The annual mean irradiance at Earth, integrated over the whole spectrum, amounts to 1365 W · m<sup>−2</sup>, and 99% of its energy is carried by radiation with wavelengths between 278 and 4600 nm, with the maximum at 472 nm. The division into two energetically equal parts is at a wavelength of 731 nm. Although the total solar irradiance is often called the solar constant, it varies with time, for example, with the solar activity cycle with a period of about 11 years. These variations have been monitored since 1978 by radiometers on space platforms and amount to about 0.1%, with the radiation higher during the maximum of solar activity. There are also shorter-term variations such as decreases due to the passage of dark sunspots or increases due to faculae.
Industry:Science
The generation of a temperature-dependent electromotive force (emf) at the junction of two dissimilar metals. This phenomenon provides the physical basis for the thermocouple. In 1821, T. J. Seebeck discovered that near a closed circuit composed of two linear conductors of two different metals a magnetic needle would be deflected if, and only if, the two junctions were at different temperatures, and that if the temperatures of the two junctions were reversed the direction of deflection would also be reversed. He investigated 35 different metals and arranged them in a series such that at a hot junction, current flows from a metal earlier in the series to a later one.
Industry:Science
The ability of biological and chemical systems to distinguish between molecules and regulate behavior accordingly. How molecules fit together is fundamental in disciplines such as biochemistry, medicinal chemistry, materials science, and separation science. A good deal of effort has been expended in trying to evaluate the underlying intermolecular forces. The weak forces that act over short distances (hydrogen bonds, van der Waals interactions, and aryl stacking) provide most of the selectivity observed in biological chemistry and permit molecular recognition. The recognition event initiates behavior such as replication in nucleic acids, immune response in antibodies, signal transduction in receptors, and regulation in enzymes. Most studies of recognition in organic chemistry have been inspired by these biological phenomena. It has been the task of bioorganic chemistry to develop systems capable of such complex behavior with molecules that are comprehensible and manageable in size, that is, with model systems.
Industry:Science
The alignment of three celestial objects within a solar system. Syzygy is most often used to refer to the alignment of the Sun, Earth, and Moon at the time of new or full moon. Although syzygy is strongly associated with these two lunar phases in many minds, it must be emphasized that the alignment of any three celestial objects within the solar system (or within any other system of objects in orbit about a star) constitutes syzygy. Alignments need not be perfect in order for syzygy to occur: because the orbital planes for any three bodies in the solar system rarely coincide, the geometric centers of three objects that are in syzygy almost never lie along the same line.
Industry:Science
The gravitational weight of a body is the force with which the Earth attracts the body. By extension, the term is also used for the attraction of the Sun or a planet on a nearby body. This force is proportional to the body's mass and depends on the location. Because the distance from the surface to the center of the Earth decreases at higher latitudes, and because the centrifugal force of the Earth's rotation is greatest at the Equator, the observed weight of a body is smallest at the Equator and largest at the poles. The difference is sizable, about 1 part in 300. At a given location, the weight of a body is highest at the surface of the Earth; it diminishes with altitude and with the depth below the surface. For example, the weight of a body diminishes by about 0.1% if it is raised 2 mi (3 km) above the Earth's surface or taken 4 mi (6 km) below the surface. Weight also depends to a smaller but measurable degree on the density of the Earth's crust below the body. Weight is measured by several procedures.
Industry:Science
Systems that locate suitably equipped users by means of measurements made by electronic sensors. Typical measurements include distance or bearing from a vehicle to a known point, or direct determination of the present position of the vehicle in a particular coordinate system. From the knowledge of present position, the course and distance to a destination at a known location can be calculated. Most systems are based on the use of electromagnetic (radio) or acoustic waves or inertial sensing. The systems described here are typically used by aircraft, ships, and land and space vehicles. In addition, the use of satellites for land navigation by individuals has become common.
Industry:Science
The application of physical anthropology theory and techniques to answering questions for the law. Most human remains are soon discovered and thus available for analysis. Medical evidence and biological techniques used on the living can be applied to these intact remains, as can extensive internal examinations and histological preparations. However, burned, decomposed, mutilated, or fragmented bodies contain less soft tissue evidence and are therefore more difficult for the medical examiner or forensic pathologist to analyze. In these cases, the information provided by the skeleton becomes more important, and may yield the only information available about the identity of the individual and the circumstances surrounding death. Age, sex, ancestry, stature, muscularity, handedness, habits, occupational activities, disease, and injuries can be ascertained from elements of the skeleton, and in such cases the services of a forensic anthropologist may be a valuable adjunct to the work of the forensic pathologist or coroner.
Industry:Science
The emission of electrons into vacuum by a heated electronic conductor. In its broadest meaning, thermionic emission includes the emission of ions, but since this process is quite different from that normally understood by the term, it will not be discussed here. Thermionic emitters are used as cathodes in electron tubes and hence are of great technical and scientific importance. Although in principle all conductors are thermionic emitters, only a few materials satisfy the requirements set by practical applications. Of the metals, tungsten is an important practical thermionic emitter; in most electron tubes, however, the oxide-coated cathode is used to great advantage.
Industry:Science
The <i>Mars Global Surveyor</i> (<i>MGS</i>) was launched in November 1996 and attained Mars orbit in September 1997. In late 2003 it was still in operation, its mission having been extended twice since the nominal end date of January 31, 2001. <i>Mars Global Surveyor</i> was the first successful mission of the National Aeronautics and Space Administration (NASA) to be launched to Mars since <i>Viking</i> in 1976. The only other spacecraft to reach Mars in the intervening decades were the Soviet <i>Phobos 2</i> in 1989, which lasted only two months in Mars orbit before losing contact with Earth, and NASA's <i>Mars Pathfinder</i>, a lander-rover combination that was launched a month after <i>Mars Global Surveyor</i> but reached Mars 2 months ahead of it, and transmitted data from the planet's surface for 85 days. <i>Mars Global Surveyor</i> was conceived as a low-cost replacement for the <i>Mars Observer</i> spacecraft that was lost in 1993, and carries four of the original six <i>Mars Observer</i> science instruments.
Industry:Science
The influence of the spatial configuration of reacting substances upon the rate, nature, and extent of reaction. The sizes and shapes of atoms and molecules, the electrical charge distribution, and the geometry of bond angles influence the courses of chemical reactions. The steric course of organochemical reactions is greatly dependent on the mode of bond cleavage and formation, the environment of the reaction site, and the nature of the reaction conditions (reagents, reaction time, and temperature). The effect of steric factors is best understood in ionic reactions in solution. The nucleophilic substitution reaction at a saturated carbon atom can serve as an illustration.
Industry:Science
