- 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 process in which a molecule moving with high velocity strikes a solid and the electrons that bond the molecule are torn off rapidly in violent collisions with the electrons of the solid; as a result, the molecule is suddenly transformed into a cluster of charged atomic constituents that then separate under the influence of their mutual Coulomb repulsion. The initial velocity of the molecule is typically greater than 3 × 10<sup>6</sup> ft/s (10<sup>6</sup> m/s), and it takes on the order of 10<sup>-17</sup> s for electrons to be torn off the molecule. Typically, it takes about 10<sup>-15</sup> s for the initial Coulomb potential energy of the cluster to be converted into kinetic energy as the charged fragments recede from one another.
Industry:Science
A process in which a nitro group (–NO<sub>2</sub>) becomes chemically attached to a carbon, oxygen, or nitrogen atom in an organic compound. A hydrogen or halogen atom is often replaced by the nitro group. Three general reactions summarize nitration chemistry:
Industry:Science
A process in which an electron and a positron are simultaneously created in the vicinity of a nucleus or subatomic particle. Electron-positron pair production is an example of the materialization of energy predicted by special relativity and is accurately described by quantum electrodynamics. Pair production usually refers to external pair production, in which the positron (positively charged antielectron) and electron are created from a high-energy gamma ray as it passes through matter. Electron-positron pairs are also produced from internal pair conversions in nuclei, decays of unstable subatomic particles, and collisions between charged particles.
Industry:Science
A process in which atomic and molecular species residing on the surface of a solid leave the surface and enter the surrounding gas or vacuum. In stimulated desorption studies, species residing on a surface are made to desorb by incident electrons or photons. Measurements of these species provide insight into the ways that radiation affects matter, and are useful analytical probes of surface physics and chemistry. In thermal desorption studies, adsorbed surface species are caused to desorb as the sample is heated under controlled conditions. These measurements can provide information on surface-bond energies, the species present on the surface and their coverage, the order of the desorption process, and the number of bonding states or sites.
Industry:Science
A process in which atoms or molecules move from a bulk phase (that is, solid, liquid, or gas) onto a solid or liquid surface. An example is purification by adsorption where impurities are filtered from liquids or gases by their adsorption onto the surface of a high-surface-area solid such as activated charcoal. Other examples include the segregation of surfactant molecules to the surface of a liquid, the bonding of reactant molecules to the solid surface of a heterogeneous catalyst, and the migration of ions to the surface of a charged electrode.
Industry:Science
A process in which the heat for producing the weld is generated by the resistance to the flow of current through the parts to be joined. The application of external force is required; however, no fluxes, filler metals, or external heat sources are necessary. Most metals and their alloys can be successfully joined by resistance welding processes.
Industry:Science
A process in which the rate of an organic reaction in a heterogeneous two-phase system is enhanced by the addition of a compound that transfers one of the reactants across the interface between the two phases.
Industry:Science
A process in which two or more crystals, or parts of crystals, assume orientations such that one may be brought to coincidence with the other by reflection across a plane or by rotation about an axis. Crystal twins represent a particularly symmetric kind of grain boundary; however, the energy of the twin boundary is much lower than that of the general grain boundary because some of the atoms in the twin interface are in the correct positions relative to each other.
Industry:Science
A process of extractive distillation in which a salt that is soluble in the liquid phase of the system being separated is used in place of the normal liquid additive introduced to the extractive distillation column in order to effect the separation.
Industry:Science
A process of navigation by which a destination is approached by keeping some navigation parameter constant. In its early uses, the most commonly chosen parameter was the relative bearing from the vehicle to destination as determined from a signal emitted at or near the destination point. The vehicle then steers to travel in the direction of its destination. The signal can be of many forms, ranging from a visual image to a radio wave or even an odor. This simple form of homing requires minimal on-board equipment, but the path taken by the vehicle over the Earth's surface is influenced by vehicle drift due to winds, currents, or other causes.
Industry:Science
