- 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 hydrodynamic facility used for research, test, and evaluation, comprising a well-guided and controlled stream of water in which items for test are placed. The water tunnel is in many ways similar in appearance, arrangement, and operation to a subsonic wind tunnel. It is related to and complementary to the towing tank, in which the test item, usually a scale model of a ship or ship component, is towed through stationary water and evaluated through observation and measurement. In a water tunnel the test item is held stationary while the water is circulated around it. Many water tunnels are capable of operation with variable internal pressure to simulate the phenomenon of cavitation.
Industry:Science
A hydrogenlike system that consists of a strongly interacting particle (hadron) bound in the Coulomb field and in orbit around any ordinary nucleus. The kinds of hadronic atoms that have been made and the years in which they were first identified include pionic (1952), kaonic (1966), Σ<sup>−</sup> hyperonic (1968), and antiprotonic (1970). They were made by stopping beams of negatively charged hadrons in suitable targets of various elements, for example, potassium, zinc, or lead. The lifetime of these atoms is of the order of 10<sup>−12</sup> s, but this is long enough to identify them and study their characteristics by means of their x-ray spectra. They are available for study only in the beams of particle accelerators. Pionic atoms can be made by synchrocyclotrons and linear accelerators in the 500-MeV range. The others can be generated only at accelerators where the energies are greater than about 6 GeV.
Industry:Science
A hydrostatic sphere of gas in the process of becoming a star. A protostar forms by the gravitational collapse of a dense core within a giant cloud of dust and molecular gas (mostly H<sub>2</sub>). As the core collapses from the inside out, it surrounds a central protostar with a cocoon of accreting dust and gas that hides it from view at optical wavelengths. Observations at longer wavelengths penetrate this material and reveal that the protostar is radiating due to the impact of infalling gas and dust. Most of the envelope material accretes first onto a circumstellar disk, from which it is then conveyed to the protostellar surface. As the envelope dissipates around a low-mass star such as the Sun, the protostar becomes visible as a pre-main-sequence T Tauri star that continues for a time to add to its mass from the accretion disk. It becomes a full-fledged star when the core temperature reaches the level required for nuclear fusion of hydrogen (temperature <i>T</i> ~ 10<sup>7</sup> K). For stars at least 10 times more massive than the Sun, nuclear burning begins before infalling material is dissipated, and the resulting high-intensity radiation quickly clears away the remaining envelope.
Industry:Science
A hydrous calcium potassium silicate containing fluorine. The composition is variable but approximates to KFCa<sub>4</sub>(Si<sub>2</sub>O<sub>5</sub>)<sub>4</sub>· 8H<sub>2</sub>O. It resembles the zeolites, with which it is sometimes classified, but differs from most zeolites in having no aluminum. It exfoliates (swells) when heated, losing water, and is named from this characteristic; the water can be reabsorbed. The mineral decomposes in hydrochloric acid, with separation of silica. It is essentially white, with a vitreous luster, but may show shades of green, yellow, or red. The symmetry is tetragonal and the crystal structure contains sheets of linked SiO<sub>4</sub> groups, and this accounts for the perfect basal cleavage of the mineral (see <b>illus.</b>). It occurs as a secondary mineral in cavities in basic igneous rocks, commonly in association with zeolites. The specific gravity of apophyllite is about 2.3–2.4, the hardness is 4.5–5 on Mohs scale, the mean refractive index is about 1.535, and the birefringence is 0.002.
Industry:Science
A hydrous iron aluminum silicate mineral with an ideal formula of Fe<sub>2</sub><sup>2+</sup>Al<sub>4</sub>O<sub>2</sub>(SiO<sub>4</sub>)<sub>2</sub>(OH)<sub>4</sub>. Chloritoid occurs as platy, black or dark green crystals, rarely more than a few millimeters in size. Its density ranges from 3.46 to 3.80 g/cm<sup>3</sup>, and its hardness on the Mohs scale is 6.5.
Industry:Science
A hypothetical elementary particle that might make up most of the matter in the universe, and that is also predicted to exist in supersymmetry theory. Most matter is detected only through its gravitational effects; this “dark matter” has not been observed to emit, absorb, or reflect light of any wavelength. The total amount of dark matter appears to be approximately ten times as great as all the ordinary matter in the universe, and about one hundred times as great as all the visible matter. The nature of the dark matter is not yet known, although many experiments are under way to try to discover it directly or indirectly.
Industry:Science
A hypothetical massive scalar elementary particle, the avatar (embodiment) of electroweak symmetry breaking in the Glashow–Weinberg–Salam theory. Interactions with the Higgs boson endow the quarks, leptons, and weak gauge bosons with mass. Although experiments provide indirect evidence for the influence of the Higgs boson, no direct observation has yet been made (as of 2006).
Industry:Science
A hypothetical thermodynamic cycle originated by Sadi Carnot and used as a standard of comparison for actual cycles. The Carnot cycle shows that, even under ideal conditions, a heat engine cannot convert all the heat energy supplied to it into mechanical energy; some of the heat energy must be rejected. In a Carnot cycle, an engine accepts heat energy from a high-temperature source, or hot body, converts part of the received energy into mechanical (or electrical) work, and rejects the remainder to a low-temperature sink, or cold body. The greater the temperature difference between the source and sink, the greater the efficiency of the heat engine.
Industry:Science
A hypothetical wind based upon the assumption that a perfect balance exists between the horizontal components of the Coriolis force and the horizontal pressure gradient force per unit mass, with the implication that viscous forces and accelerations are negligible. Application of the geostrophic wind facilitates an approximation of the wind field from the pressure data over vast regions in which few wind observations are available.
Industry:Science
A key source of genetic variation is exchange of genetic material among individuals. Genetic exchange among closely related individuals is common in nature, and occurs in prokaryotes via conjugation and other processes, and in eukaryotes during sexual reproduction. When these same processes occur among individuals that are more distantly related and would not typically exchange genetic material, they are referred to as hybridization. But occasionally genetic material is exchanged among organisms that are very distantly related. This phenomenon, termed horizontal (or lateral) gene transfer, occurs relatively rarely, and was long presumed not to be important in evolution. However, as increasing amounts of information from deoxyribonucleic acid (DNA) sequences have become available, it has become clear that horizontal gene transfer is a significant part of evolution in nature.
Industry:Science
