- 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 system of chemical communication among cells. The classical vertebrate endocrine system consists of a group of discrete glands that secrete unique products (hormones) into the bloodstream. These products travel in the blood to distant sites or targets where they cause specific physiological responses. Thus endocrine glands differ from exocrine glands, in that they lack ducts and deliver their secretions in the bloodstream.
The classical definition of an endocrine system is harder to apply nowadays with the discovery of scattered cells rather than discrete glands that act as endocrine organs, of endocrine cells that affect themselves (autocrine effect) or nearby targets (paracrine effect) by diffusion through extracellular fluids rather than the bloodstream, and of neurons that secrete hormones (neurosecretion). All of these mechanisms, however, allow for chemical intercellular communication and can be considered part of the endocrine system.
Industry:Science
A system of conductors suitable for conducting electric power or signals between two or more termini. Transmission lines take many forms in practice and have application in many disciplines. For example, they traverse the countryside, carrying telephone signals and electric power. The same transmission lines, with similar functions, may be hidden above false ceilings in urban buildings. With the need to reliably and securely transmit ever larger amounts of data, the required frequency of operation has increased from the high-frequency microwave range to the still higher frequency of light. Optical fibers are installed in data-intensive buildings and form a nationwide network. Increasing demand also requires that transmission lines handle greater values of electric power.
Industry:Science
A system of convective cells, called supergranules, with diameters of about 30,000 km (20,000 mi) and lifetimes of 1 or 2 days, which cover the visible disk of the Sun, the photosphere. Smaller convection cells called granules, which are about 1500 km (900 mi) across and have lifetimes of about 10 min, are seen through a telescope in white-light images of the photosphere, but the supergranules are not visible this way.
The supergranulation is seen in Dopplergrams that measure motions in the photosphere. The gas flows horizontally from the center to the edge of each supergranule, carrying along the photospheric magnetic field that is detected by the Zeeman effect in magnetograms. The magnetism is concentrated at the edges of the supergranules, forming polygon-shaped structures called the magnetic network, which is also detected as bright calcium emission in the overlying chromosphere.
Industry:Science
A system of electric conductors, components, and apparatus for conveying electric power from a source to the point of use. In general, electric wiring for light and power must convey energy safely and reliably with low power losses, and must deliver it to the point of use in adequate quantity at rated voltage. To accomplish this, many types of electric wiring systems and components are used.
Industry:Science
A system of filaments found in the cytoplasm of cells which is responsible for cell shape, cell locomotion and elasticity, interconnection of the major cytoplasmic organelles, cell division, chromosome organization and movement, and the adhesion of a cell to a surface or to other cells.
Industry:Science
A system of geometry based upon a set of axioms different from those of the euclidean geometry based on the three-dimensional space of experience. Noneuclidean geometries, especially riemannian geometry, are useful in mathematical physics. This article will describe some of the basic concepts and axioms of noneuclidean geometries and then draw some comparisons with euclidean concepts.
Industry:Science
A system of lenses in which two or more parts are moved with respect to each other to obtain a continuously variable focal length and hence magnification, while the image is kept in the same image plane.
Industry:Science
A system of measurement units used in scientific work and for everyday applications by most countries, with the notable exception of the United States. A prime advantage of the metric system is its international acceptance as a standard of measurement, providing a common measurement language for most of the world's population.
Industry:Science
A system of small liquid droplets dispersed in a second, immiscible liquid. Emulsions are a type of colloidal dispersion. By classical definition, emulsion droplets have diameters between 1 nanometer and 1 micrometer. However, for practical purposes, the principles of colloid science can be usefully applied to emulsions whose droplets are as large as tens or even hundreds of micrometers. The droplets in an emulsion are large enough that they do not behave like the atoms and molecules of classical chemistry. For example, emulsions do not generally behave like true solutions and may have undetectable freezing-point depressions. On the other hand, the droplets are small enough that they do not behave like the macroscopic particles of classical physics. For example, emulsion droplets may rise (cream) or fall (sediment) extremely slowly in apparent violation of Stokes' law.
Industry:Science
A system of small solid particles dispersed in a liquid. Suspensions are a type of colloidal dispersion. By classical definition, suspension particles have diameters (or, if not spherical, the largest dimension) between 1 nanometer and 1 micrometer. However, for practical purposes the principles of colloid science can be usefully applied to suspensions for which the particles are smaller, down to about 0.1 nm (nanoparticle suspensions), and also to those for which the largest particle dimensions are tens or even hundreds of micrometers.
The particles in a suspension are large enough that they do not behave like the atoms and molecules of classical chemistry. For example, suspensions do not generally behave like true solutions, and may have undetectable freezing-point depressions. On the other hand, the particles are small enough that they do not behave like the macroscopic particles of classical physics. For example, sedimentation of a suspension's particles may occur extremely slowly in apparent violation of Stokes' law.
Industry:Science
