- 行业: Printing & publishing
- Number of terms: 178089
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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 feature of the valence-bond method, which is a mathematical procedure to obtain approximate solutions to the Schrödinger equation for molecules. The term came into use because the procedure is similar to that describing how weakly coupled tuning forks, pendulums, and such resonate, that is, transfer energy back and forth to one another. The valence-bond method is based on the theorem that if two or more solutions to the Schrödinger equation are available, certain linear combinations of them will also be solutions. It has this basis in common with its rival, the molecular orbital method. The valence-bond and molecular orbital approaches are both approximations and, if carried out to their logical and exact extremes, must yield identical results; nevertheless, both are often described as theories. In the valence-bond theory, combinations of solutions represent hypothetical structures of the molecule in question. These structures are said to be resonance (or contributing) structures, and the real molecule is said to be the resonance hybrid (or just simply the hybrid) of these structures.
Industry:Science
A feature or shape at the focal plane of a camera or other optical instrument that is not present in an actual scene, or an unfocused duplicate image that is overlaid upon a desired image. Ghost images, or ghosts, are caused by reflections from the surfaces of lenses or windows. Each glass surface divides incoming light into two parts: a refracted part that passes through the surface, and a reflected part that is turned back. If the reflected light is turned back again by reflection from another glass surface or a mirror, it may travel to the focal plane to form a ghost image. Ghost images may appear as an out-of-focus blur or smudge, a sharp circle or polygon with the shape of the camera iris or other aperture, or a false image of an object within a scene.
Industry:Science
A fermented beverage produced from grain. Beer is a generic term used to describe alcoholic beverages made from cereal grains, especially barley, in the form of malt. Ale, lager, porter, and stout are different kinds of beer made by recognizably similar processes. The United States is the largest producer of beer in the world.
Industry:Science
A fertilized ovule containing an embryo which forms a new plant upon germination. Seed-bearing characterizes the higher plants—the gymnosperms (conifers and allies) and the angiosperms (flowering plants). Gymnosperm (naked) seeds arise on the surface of a structure, as on a seed scale of a pine cone. Angiosperm (covered) seeds develop within a fruit, as the peas in a pod.
Industry:Science
A fiber obtained from a plant, animal, or mineral. The commercially important natural fibers are those cellulosic fibers obtained from the seed hairs, stems, and leaves of plants; protein fibers obtained from the hair, fur, or cocoons of animals; and the crystalline mineral asbestos. Until the advent of the manufactured fibers near the beginning of the twentieth century, the chief fibers for apparel and home furnishings were linen and wool in the temperate climates and cotton in the tropical climates. However, with the invention of the cotton gin in 1798, cheap cotton products began to replace the more expensive linen and wool until by 1950 cotton accounted for about 70% of the world's fiber production. Despite the development of new fibers based on fossil fuels, cotton has managed to maintain its position as the fiber with the largest production volume, although its use has fallen.
Industry:Science
A fiber obtained from the cotton plant <i>Gossypium</i>, of the order Malvales. It has been used for more than 3000 years. It is the most widely used natural fiber, because of its versatility and comparatively low cost to produce and to manufacture into finished products. Cotton traditionally has been used alone in textile products, but blends with artificial fibers have become increasingly important.
Industry:Science
A fiber obtained from the leaves of <i>Agave fourcroydes</i>. It is produced only in Mexico, Cuba, and El Salvador. Henequen is sometimes incorrectly called sisal, which is a closely related plant grown in Brazil and Africa.
Industry:Science
A fiber obtained from the leaves of <i>Agave sisalana</i>, produced in Brazil, Haiti, and several African countries, including Tanzania, Kenya, Angola, and Mozambique.
Industry:Science
A fiber, also known as pineapple fiber, obtained from the large leaves of the pineapple plant grown in tropical countries. This natural fiber is white and especially soft and lustrous. In the Philippine Islands, it is woven into piña cloth, which is soft, durable, and resistant to moisture. Piña is also used in making coarse grass cloth and for mats, bags, and clothing.
Industry:Science
A fibrous or needlelike mineral belonging to the zeolite family of silicates. It crystallizes in the monoclinic system in pseudo-orthorhombic prismatic crystals which are often acicular (see <b>illus.</b>). Most commonly it is found in radiating fibrous aggregates. There is perfect prismatic cleavage, the hardness is 5–5½ on Mohs scale, and the specific gravity is 2.25. The mineral is white or colorless with a vitreous luster that inclines to pearly in fibrous varieties. The chemical composition is Na<sub>2</sub>(Al<sub>2</sub>Si<sub>3</sub>O<sub>10</sub>) · 2H<sub>2</sub>O, but some potassium is usually present substituting for sodium.
Industry:Science
