- 行业: Printing & publishing
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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 new emerging radio technology called cognitive radio significantly increases the utilization of the current frequency bands through spectrum-sharing approaches. Electromagnetic waves (that is, radio waves) are essential to the operation of wireless transmission systems, with frequencies in the range 3 Hz–300 GHz. Traditionally, large parts of the radio frequency bands have been licensed to authorized users by government. This static spectrum allocation mechanism causes frequency bands to be insufficient at various times and locations. Practical measurements show that most of the licensed bands are either unused or partially used in different geographical areas for much of the time. In other words, spectrum bands are used sporadically. <b>Figure 1</b> shows spectrum usage in the range from 1 Hz to 6 GHz, which was measured by the Berkeley Wireless Research Center (BWRC).
Industry:Science
A new family of cationic late-transition metal α-diimine complexes that function as catalysts for polymerization of ethylene and α-olefins has recently been identified. The unprecedented tendency of these catalysts both to produce branched polymers from ethylene and to tolerate polar functionality has opened the door to a new class of polymers with unique microstructure and properties. (Such a complex is a compound of an α-diimine and a metal atom bound through the electron lone pairs on the nitrogen atoms.)
Industry:Science
A new generation of gamma-ray detectors has been developed, primarily to study the structure of atomic nuclei. Much of the knowledge about the structure of nuclei, as well as atoms and molecules, has come from studying their energy levels through the detection of electromagnetic radiation emitted when the system makes a transition from one state to another. The electromagnetic radiation from atoms and molecules has an energy around 1 electronvolt, while for nuclei it is of order 10<sup>6</sup> eV (1 MeV). Thus, for the study of nuclei it is necessary to design and build detectors aimed at an energy range which is quite different from that of the typical photomultipliers used for detecting electronvolt photons. The recent detectors incorporate new technologies and large arrays to provide high resolution and high efficiency, resulting in an improvement of about a factor of 100 in the ability to resolve rare features of nuclear structure.
Industry:Science
A new malaria vaccine recently tested in Kenya and Tanzania has halved the risk of developing the disease in children. The vaccine, known as RTS,S, was developed by GlaxoSmithKline and is designed to prevent the destructive lysis of red blood cells after the liver is infected by <i>Plasmodium falciparum</i>. This species is responsible for the highest mortality and morbidity among victims of malaria and is considered more virulent than other members of the genus. Prevention of malaria in populations living in endemic areas could lead to the control and possibly even the elimination of malaria in some regions.
Industry:Science
A New World marsupial belonging to the family Didelphidae. Didelphidae consists of one North American species, the Virginia opossum (<i>Didelphis virginiana</i>), and 65 Central and South American species, including the mouse opossums (<i>Marmosa</i>, <i>Gracilinanus</i>, <i>Marmosops</i>, <i>Micoureus</i>, <i>Thylamys</i>, and <i>Lestodelphys</i>); short-tailed opossums (<i>Monodelphis</i>); gray and black four-eyed opossums (<i>Philander</i>); brown four-eyed opossums (<i>Metachirus</i>); water opossums (<i>Chironectes</i>); woolly opossums (<i>Caluromys</i>); black-shouldered opossums (<i>Caluromysiops</i>); bushy-tailed opossums (<i>Glironia</i>); and thick-tailed opossums (<i>Lutreolina</i>).
Industry:Science
A nitrate mineral having chemical composition NaNO<sub>3</sub> (sodium nitrate). Soda niter, otherwise known as nitratite, is by far the most abundant of the nitrate minerals. It crystallizes in the rhombohedral division of the hexagonal system. It sometimes occurs as simple rhombohedral crystals but is usually massive granular. The mineral has a perfect rhombohedral cleavage, conchoidal fracture, and is rather sectile. Its hardness is 1.5 to 2 on Mohs scale, and its specific gravity is 2.266. It has a vitreous luster and is transparent. It is colorless to white, but when tinted by impurities, it is reddish brown, gray, or lemon yellow.
Industry:Science
A nonaqueous solvent system particularly useful in coordination chemistry. Fused salts are a large class of liquids which are composed largely of ions. Many simple inorganic salts melt at rather high temperatures (greater than 600°C or 1000°F), forming liquids which have high specific conductivities, 1–6 ohm<sup>−1</sup>. cm<sup>−1</sup> (<b>Table 1</b>). There are, however, a number of exceptions to this generalization; for example, the electrical conductivity of AlCl<sub>3</sub> decreases sharply upon melting due to the formation of molecular liquid (Al<sub>2</sub>Cl<sub>6</sub>).
Industry:Science
A nonconducting material that provides electric isolation of two parts at different voltages. To accomplish this, an insulator must meet two primary requirements: it must have an electrical resistivity and a dielectric strength sufficiently high for the given application. The secondary requirements relate to thermal and mechanical properties. Occasionally, tertiary requirements relating to dielectric loss and dielectric constant must also be observed. A complementary requirement is that the required properties not deteriorate in a given environment and desired lifetime.
Industry:Science
A nondestructive physical method used for chemical elemental analysis of materials in the solid or liquid state. The specimen is irradiated by photons or charged particles of sufficient energy to cause its elements to emit (fluoresce) their characteristic x-ray line spectra. The detection system allows the determination of the energies of the emitted lines and their intensities. Elements in the specimen are identified by their spectral line energies or wavelengths for qualitative analysis, and the intensities are related to their concentrations for quantitative analysis. Computers are widely used in this field, both for automated data collection and for reducing the x-ray data to weight-percent and atomic-percent chemical composition or area-related mass (of films).
Industry:Science
A nondestructive technique using electromagnetic waves to locate objects or interfaces buried beneath the Earth's surface or located within a visually opaque structure; also termed ground-probing, surface-penetrating, or subsurface radar.
Industry:Science
