- 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 mildly infectious, chronic, granulomatous disease principally affecting skin and subcutaneous tissues of the genital and rectal areas. Although rare in the United States, the disease is very common in New Guinea, the Caribbean, and other tropical and subtropical areas.
Industry:Science
A mill for grinding or pulverizing, in which a flat siliceous rock, generally of cellular quartz, rotates against a stationary stone of the same material. The Buhrstone mill is one of the oldest types of mill and, with either horizontal or vertical stones, has long been used to grind grains and hard materials. Grooves in the stones facilitate the movement of the material. Fineness of the product is controlled by the pressure between the stones and by the grinding speed. A finely ground product is achieved by slowly rotating the stone at a high pressure against the materials and its mate (see <b>illus.</b>). The capacity, or output, of a Buhrstone mill is low and its power requirements are high. The stones require frequent maintenance, even when grinding only slightly abrasive materials.
Industry:Science
A mine that either passively listens to a target's sound noises, or periodically interrogates its environment by actively emitting acoustic pulses that may return echoes if prospective targets come within range. A mine is an underwater weapon consisting of a shell case which contains high explosives. Mines can be planted by airplanes, surface ships, or submarines. Submarines are used for deployment when secrecy is important. There are three types of mines: drifting, moored, and bottom. Drifting mines float freely at the sea surface. Moored mines are positively buoyant and are held at a given depth by a cable anchored to the bottom. Bottom mines rest on the sea floor. A mine can be activated by various means, such as by actually contacting a target, by sensing a target's magnetic field, by listening to the acoustic noises that emanate from a target, by sensing the excess pressure field that may be induced on the mine's sensor by a target passing above it, by the reception of acoustic echoes that a target may return to the mine's sonar after it has sent out its interrogating pings, or by a combination of several of these.
Industry:Science
A mineral (FeCO<sub>3</sub>) with the same space group and hexagonal crystal system as calcite (CaCO<sub>3</sub>). Siderite has a gray, tan, brown, dark brown, or red color, has rhombohedral cleavages, and occasionally may show rhombohedral crystal terminations. It may display curved crystal faces like dolomite (CaMg(CO<sub>3</sub>)<sub>2</sub>), but more commonly is found as massive, compact, or earthy masses.
Industry:Science
A mineral belonging to the zeolite family of silicates and crystallizing in the monoclinic system. It usually occurs in crystals with prominent side pinacoid, often having a diamond shape. There is perfect side pinacoid cleavage on which the luster is pearly; elsewhere the luster is vitreous. The crystals often have undulating faces, and are made up of subindividuals in nearly parallel position (see <b>illus</b>.). In polarized light they show optical anomalies of a sectoral nature. The hardness is 3½ to 4 on Mohs scale; specific gravity is 2.18–2.20. The mineral is usually white or colorless but may be yellow or red.
Industry:Science
A mineral belonging to the zeolite family of silicates. It commonly occurs in well-crystallized groupings of crystals with external rhombohedral symmetry (point group <span style="text-decoration:overline">3</span>2/<i>m</i>) with nearly cubic angles. This well-developed external form suggests an internal structure compatible with space group <i>R</i> <span style="text-decoration:overline">3</span><i>m</i>; however, one structure refinement suggests lower symmetry (triclinic) with space group <i>P</i> <span style="text-decoration:overline">1</span>. In addition to recognizing the distinct rhombohedral habit of chabazite crystals, the following physical properties are significant: hardness (on the Mohs hardness scale) in the range 4–5; light colors ranging from white to yellow, pink, and red; vitreous luster; and transparent to translucent in transmitted light. It is distinguished from calcite by a poorer rhombohedral cleavage and lack of effervescent reaction with dilute hydrochloric acid (HCl).
Industry:Science
A mineral belonging to the zeolite family of silicates. It crystallizes in the monoclinic system in crystals that are tabular parallel to the side pinacoid. Most characteristic are sheaflike aggregates of thin tabular crystals. There is perfect cleavage parallel to the side pinacoid, and here the mineral has a pearly luster; elsewhere the luster is vitreous. The color is usually white but may be brown, red, or yellow. Hardness is 3½–4 on Mohs scale; specific gravity is 2.1–2.2. Stilbite is a calcium-sodium aluminum silicate, Ca(Al<sub>2</sub>Si<sub>7</sub>O<sub>18</sub>) · 7H<sub>2</sub>O, but usually contains some sodium replacing calcium.
Industry:Science
A mineral best known for its use as a gemstone. Crystals are usually colorless but may be red, yellow, green, blue, or brown. The wine-yellow variety is the one usually cut and most highly prized as a gem. Corundum of similar color sometimes goes under the name of Oriental topaz. Citrine, a yellow variety of quartz, is the most common substitute and may be sold as quartz topaz.
Industry:Science
A mineral composed entirely of carbon; the hardest substance known. Diamond is a polymorph of carbon; lonsdaleite, another polymorph, is sometimes referred to as hexagonal diamond. Diamond is found on all continents except Antarctica, which has not yet been explored for it. It occurs in nature as single crystals of gem or industrial quality, and as polycrystalline masses referred to as boart, framesite, or carbonado. It has also been found as minute black grains in some meteorites. Diamond can be synthesized in the laboratory and is produced commercially in large amounts for industrial uses.
Industry:Science
A mineral composed of calcium carbonate (CaCO<sub>3</sub>); one of the most common and widespread minerals in the Earth's crust. Calcite may be found in a great variety of sedimentary, metamorphic, and igneous rocks. It is also an important rock-forming mineral and is the sole major constituent in limestones, marbles, and many carbonatites. Calcite in such rocks is the main source of the world's quicklime and hydrated, or slaked, lime. It is also widely used as a metallurgical flux to scavenge siliceous impurities by forming a slag in smelting furnaces. It provides the essential calcium oxide component in common glasses and cement. Limestones and marbles of lower purity may find uses as dimension stone, soil conditioners, industrial acid neutralizers, and aggregate in concrete and road building. Calcite in transparent well-formed crystals is used in certain optical instruments.
Industry:Science
