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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 community of organisms and their environment that occurs on the land masses of continents and islands. Terrestrial ecosystems are distinguished from aquatic ecosystems by the lower availability of water and the consequent importance of water as a limiting factor. Terrestrial ecosystems are characterized by greater temperature fluctuations on both a diurnal and seasonal basis than occur in aquatic ecosystems in similar climates, because water has a high specific heat, a high heat of vaporization, and a high heat of fusion compared with the atmosphere, all of which tend to ameliorate thermal fluctuations. The availability of light is greater in terrestrial ecosystems than in aquatic ecosystems because the atmosphere is more transparent than water. Gases are more available in terrestrial ecosystems than in aquatic ecosystems. Those gases include carbon dioxide that serves as a substrate for photosynthesis, oxygen that serves as a substrate in aerobic respiration, and nitrogen that serves as a substrate for nitrogen fixation. Terrestrial environments are segmented into a subterranean portion from which most water and ions are obtained, and an atmospheric portion from which gases are obtained and where the physical energy of light is transformed into the organic energy of carbon-carbon bonds through the process of photosynthesis.
Industry:Science
A compass depending for its directive force upon the attraction of the Earth's magnetism for a magnet free to turn in any horizontal direction. A compass is an instrument used for determining horizontal direction.
Industry:Science
A complete solid solution series ranging from gehlenite, Ca<sub>2</sub>Al<sub>2</sub>SiO<sub>7</sub>, to akermanite, Ca<sub>2</sub>MgSi<sub>2</sub>O<sub>7</sub>, often containing appreciable Na and Fe. Melilites are tetragonal sorosilicates and form short prismatic crystals with poor basal cleavage. The Mohs hardness is 5–6, and the density increases progressively from 2.94 for akermanite to 3.05 for gehlenite. The luster is vitreous to resinous, and the color is white, yellow, greenish, reddish, or brown. Akermanite-rich varieties occur in thermally metamorphosed siliceous limestones and dolomites, but more gehlenite-rich ones result if Al is present, as in Durango, Mexico, and Monzoni, Italy. Melilites are found instead of plagioclase in silica-deficient, feldspathoid-bearing basalts, as at Capo di Bove, Italy; in the Kaiserstuhl, Germany; in the Hawaiian Islands; and at Vesuvius, where SiO<sub>2</sub> was removed from the magma by reaction with carbonate rocks (see <b>illus.</b>). In carbonaceous chondrite meteorites, melilites ranging from pure gehlenite to 80 mole % akermanite occur with hibonite, spinel, perovskite, and pyroxenes in inclusions thought to be ancient condensates from the gas of the solar nebula.
Industry:Science
A complete, step-by-step account of how a reaction of organic compounds takes place. A fully detailed mechanism would correlate the original structure of the reactants with the final structure of the products and would account for changes in structure and energy throughout the progress of the reaction. A complete mechanism would also account for the formation of any intermediates and the rates of interconversions of all of the various species. Because it is not possible to detect directly all of these details of a reaction, evidence for a reaction mechanism is always indirect. Experiments are designed to produce results that provide logical evidence for (but can never unequivocally prove) a mechanism. For most organic reactions, there are mechanisms that are considered to be well established (that is, plausible) based on bodies of experimental evidence. Nevertheless, new data often become available that provide further insight into new details of a mechanism or that occasionally require a complete revision of an accepted mechanism.
Industry:Science
A complex endocrine organ in proximity to the kidney. Adrenal gland tissue is present in all vertebrates from cyclostomes to placental mammals. The adrenal consists of two functionally distinct tissues: steroidogenic cells of mesodermal origin and neural crest–derived catecholamine-secreting cells. While “adrenal” refers to the gland's proximity to the kidney, significant variation exists among vertebrates in its anatomic location as well as the relationship of the two endocrine tissues which make up the gland. In mammals, steroidogenic cells are separated into distinct zones that together form a cortex. This cortical tissue surrounds the catecholamine-secreting cells, constituting the medulla. In most other vertebrates, this unique anatomic cortical-medullary relationship is not present. In species of amphibians and fish, adrenal cells are found intermingling with kidney tissue, and the steroidogenic cells are often termed interrenal tissue.
Industry:Science
A complex hydrated magnesium silicate mineral named for its resemblance to cuttlefish bone, alternately named meerschaum (sea foam). The ideal composition, Mg<sub>8</sub>(H<sub>2</sub>O)<sub>4</sub>(OH)<sub>4</sub>Si<sub>12</sub>O<sub>30</sub>, is modified by some additional water of hydration, but is otherwise quite representative. The ideal density, 2.26 g/cm<sup>3</sup> (1.31 oz/in.<sup>3</sup>), is never realized in aggregates. Interlaced disoriented fibers aggregate into a massive stone so porous that it floats on water. These stones are easily carved, take a high polish with wax, and harden when warmed. They have been valued from antiquity in the eastern Mediterranean region for ornaments and make attractive smoking pipes.
Industry:Science
A complex of a transition metal combined with carbon monoxide (CO). In a metal carbonyl, the CO groups form sigma bonds to the metal through lone pairs of electrons on carbon; the metal, in turn, donates electrons to antibonding pi orbitals on CO. In so doing, the metal usually attains the electronic configuration of an inert gas (the 18-electron rule). Thus elemental chromium (Cr<sup>0</sup>), with six valence electrons, combines with six molecules of CO, each donating two electrons, to afford chromium hexacarbonyl (Cr(CO)<sub>6</sub>), in which Cr has 18 valence electrons and is isoelectronic to krypton (Kr).
Industry:Science
A complex of several related and unrelated viruses (both C-type retroviruses and herpesviruses) that are collectively responsible for a variety of benign and malignant neoplasms in chickens and, to a lesser extent, in other avian species. Although most neoplasms observed in avian species are induced by viruses, there are some that are of unknown etiology.
Industry:Science
A complex physical structure specifically designed to serve as a multipurpose platform in low Earth orbit. Functioning independently and often without a crew actively involved in onboard operations, a space station contains the structures and mechanisms to operate and maintain such support systems as command and data processing, communications and tracking, motion control, electrical power, and thermal and environmental control. Evolving together with technology and increasing in scope and complexity, the space station has a history in which each program was based upon the developments and achievements of its predecessor.
Industry:Science
A complex structure of warm gas above the visible surface, or photosphere, of the Sun and most stars. The term “chromosphere” was first applied to the red ring and large prominences seen at the edge of the eclipsed Sun with the unaided eye. Emission in the Balmer-alpha line of hydrogen at 653-nanometer wavelength accounts for the red color. The chromosphere is transparent in visible light, but is opaque and bright in the ultraviolet continuum and in strong lines of abundant elements, including hydrogen, helium (first observed during the 1868 solar eclipse), oxygen, calcium, and magnesium. Gas temperatures range from 3500 to 30,000 K (5800 to 54,000°F) and densities are between 10<sup>9</sup> and 10<sup>12</sup> particles per cubic centimeter.
Industry:Science
