- 行业: Printing & publishing
- Number of terms: 178089
- Number of blossaries: 0
- Company Profile:
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 substance that will cause a clumping of particles such as bacteria or erythrocytes. Of major importance are the specific or immune agglutinins, which are antibodies that will agglutinate bacteria containing the corresponding antigens on their surfaces. Agglutinin activity is frequently displayed by purified antibody preparations that also precipitate or give other serological reactions. Agglutinins are readily determined, and their presence is of diagnostic value to indicate present or past host contact with the microbial agent sufficient to result in antibody formation.
Industry:Science
A substance that, when present at a lower concentration than that of the oxidizable substrate, significantly inhibits or delays oxidative processes, while being itself oxidized. In primary antioxidants, such as polyphenols, this antioxidative activity is implemented by the donation of an electron or hydrogen atom to a radical derivative, and in secondary antioxidants by the removal of an oxidative catalyst and the consequent prevention of the initiation of oxidation.
Industry:Science
A substance used to enhance the cleansing action of water. A detergent is an emulsifier, which penetrates and breaks up the oily film that binds dirt particles, and a wetting agent, which helps them to float off. Emulsifier molecules have an oillike nonpolar portion which is drawn into the oil, and a polar group that is water-soluble; by bridging the oil-water interface, they break the oil into dispersible droplets (emulsion). As a surfactant, a detergent decreases the surface tension of water to help it penetrate soil.
Industry:Science
A substance used to withdraw moisture from other materials. Although the removal of large quantities of water is done by evaporation, aided by moving air currents and by elevated temperature, the last traces of moisture are often held very tightly and do not evaporate readily. Furthermore, evaporation ceases when the moisture content of the material is reduced to that of the drying-air current. For final drying, a desiccant is used. This is a substance with a high affinity for water, that is, it is hygroscopic. It may retain water through capillarity or adsorption or by reacting chemically.
A substance, such as calcium chloride, which retains enough water to become wet and dissolve is said to be deliquescent. The drying agent is placed directly into the gas or liquid to be dried; solid materials are placed in a desiccator, a closed vessel in which moisture escapes by vapor pressure and diffuses to the desiccant through the dry desiccator atmosphere. A desiccant loses potency as it takes on water; often it can be renewed by heating. Desiccants which form hydrates can be selected to maintain certain levels of low humidity in a closed vessel.
Industry:Science
A substance which by chemical action and at low dosage can kill or injure living organisms. Broadly defined, poisons include chemicals toxic for any living form: microbes, plants, or animals. For example, antibiotics such as penicillin, although nontoxic for mammals, are poisons for bacteria. In common usage the word is limited to substances toxic for humans and mammals, particularly where toxicity is a substance's major property of medical interest. Because of their diversity in origin, chemistry, and toxic action, poisons defy any simple classification. Almost all chemicals with recognized physiological effects are toxic at sufficient dosage. The same compound may be considered a drug or a poison, depending on dosage, effect, or intended use.
Industry:Science
A substance which is capable of stopping or retarding a chemical reaction. To be technically useful, such compounds must be effective in low concentrations, usually under 1%. The type of reaction which is most easily inhibited is the free-radical chain reaction. The study of inhibitor action is often used as a diagnostic test for free-radical chain character of a reaction. Vinyl polymerization and autoxidation are two important examples of the class. Another reaction type for which inhibitors have been found is corrosion, particularly in aqueous systems. The economic importance of corrosion inhibition can scarcely be overestimated. An understanding of inhibitor action depends on an understanding of the processes to be interrupted.
Industry:Science
A subsurface zone that yields economically important amounts of water to wells. The term is synonymous with water-bearing formation. An aquifer may be porous rock, unconsolidated gravel, fractured rock, or cavernous limestone. Economically important amounts of water may vary from less than a gallon per minute for cattle water in the desert to thousands of gallons per minute for industrial, irrigation, or municipal use.
Industry:Science
A subtropical semienclosed sea bordering the western North Atlantic Ocean. It connects to the Caribbean Sea on the south through the Yucatán Channel and with the Atlantic on the east through the Straits of Florida. To the north, it is bounded by North America, to the west and south by Mexico and Central America, and on the east and southeast by Florida and Cuba respectively. The Gulf of Mexico Basin lies wholly within the boundaries of the North American tectonic plate.
Industry:Science
A succession of generation after generation of acts of division (called fission) of certain heavy nuclei. The fission process releases about 200 MeV (3.2 × 10<sup>-4</sup> erg = 3.2 × 10<sup>-11</sup> joule) in the form of energetic particles including two or three neutrons. Some of the neutrons from one generation are captured by fissile species (<sup>233</sup>U, <sup>235</sup>U, <sup>239</sup>Pu) to cause the fissions of the next generations. The process is employed in nuclear reactors and nuclear explosive devices.
Industry:Science
A succession of towers of steel, timber, or reinforced concrete supporting the horizontal beams of a roadway, bridge, or other structure. Little distinction can be made between a trestle and a viaduct, and the terms are used interchangeably by many engineers. A viaduct is defined as a long bridge consisting of a series of short concrete or masonry spans supported on piers or towers, and is used to carry a road or railroad over a valley, gorge, another roadway, or across an arm of the sea. A viaduct may also be constructed of steel girders and towers. It is even more difficult to draw a distinction between a viaduct and a bridge than it is between a viaduct and a trestle.
Industry:Science
