- 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.
Measurements of electrical impedance at frequencies ranging from a few tens of kilohertz to about 1 gigahertz. This broad radio-frequency (rf) range encompasses frequencies from the extralow-frequency band, through the long-, medium-, and short-wave ranges, and then through the very high frequency (VHF) and the ultrahigh-frequency (UHF) bands. In the electrical context, impedance is defined as the ratio of voltage to current (or electrical field strength to magnetic field strength), and it is measured in units of ohms (Ω).
Industry:Science
Semiconductors are an important class of materials with unique and attractive properties. By controlling the amount and type of impurities in a semiconductor, its electric conductivity can be varied by more than seven orders of magnitude. Because of their peculiar properties, some semiconductors can detect and generate light efficiently. These properties make semiconductors the basic materials for microelectronics and optoelectronics, which provide the technological foundations for the computer and communications industries.
Industry:Science
Solidified droplets of extraterrestrial materials that melted either during high-velocity entry into the atmosphere or during hypervelocity impact of large meteoroids onto the Earth's surface. Cosmic spherules are rounded particles that are millimeter to microscopic in size and that can be identified by unique physical properties. Although great quantities of the spheres exist on the Earth, they are ordinarily found only in special environments where they have concentrated and are least diluted by terrestrial particulates.
Industry:Science
Instruments that register the presence of gamma (γ) radiation. Such detectors convert some or all of the energy of gamma radiation into an electrical signal. Most instruments are capable of detecting individual gamma-ray photons (or quanta), each of which produces a short (0.1–5-microsecond) current pulse at the detector output. The output pulses may be made visible on an oscilloscope, made audible through a speaker (such as the familiar Geiger counter), or be electronically processed further, depending on the application.
Industry:Science
Mechanical, electromechanical, or hydromechanical devices which enable a person to perform manual operations while separated from the site of the work. Remote manipulators are designed for situations where direct contact would be dangerous to the human (working with radioactive material), where direct human contact is ill-advised or impossible (certain medical procedures), and where human force-producing capabilities are absent (the disabled) or need to be amplified to complete some task (industrial assembly or construction).
Industry:Science
In the most general use of this term, a sediment that consists of a mixture of calcium carbonate (CaCO<sub>3</sub>) and any other constituents in varying proportions. Marls usually are fine-grained, so that most marls consist of CaCO<sub>3</sub> mixed with silt and clay. The dominant carbonate mineral in most marls is calcite (CaCO<sub>3</sub>), but other carbonate minerals such as aragonite (another form of CaCO<sub>3</sub>), dolomite (Ca, Mg (CO<sub>3</sub>)<sub>2</sub>), and siderite (FeCO<sub>3</sub>) may be present also.
Industry:Science
On December 26, 2004, a 1300-km (800-mi) length of sea-floor boundary between two tectonic plates ruptured in the Sumatra-Andaman earthquake. This earthquake was one of the five largest earthquakes of the past 100 years and the largest since 1964. Sea-floor deflection from this massive earthquake created one of the largest and most far-reaching tsunamis observed by humans. Estimated deaths along the coastlines of Indian Ocean nations approached 300,000, marking this as one of the most lethal natural disasters in human history.
Industry:Science
Planets that orbit stars other than the Sun. Since 1995, the number of such planets known has increased from zero to more than 100. Prior to the discovery of extrasolar planets, theoretical studies suggested that most planetary systems would look like the solar system, with small rocky planets orbiting near the star and the larger gas giants further out, all in nested concentric quasicircular orbits. These theories have been disproven, and in their place a much richer understanding of planet formation and evolution has emerged.
Industry:Science
Powering, maneuvering, and seakeeping constitute the three central areas of ship hydrodynamics. Although this article focuses on these areas in connection with displacement ships, that is, vessels supported entirely (or almost entirely) by hydrostatic forces, basic concepts of powering, maneuvering, and seakeeping are also critical to an understanding of high-speed craft, such as planing boats, hydrofoil craft, and air-cushion vehicles, even if the physical phenomena governing dynamically supported craft are somewhat different.
Industry:Science
Infectious diseases are any of those pathological conditions spread among all biological species. Infectious diseases, although varied in their effects, are always associated with viruses, bacteria, fungi, protozoa, multicellular parasites and aberrant proteins known as prions. A complex series of steps, mediated by factors contributed by both the infectious agent and the host, is required for microorganisms or prions to establish an infection or disease. Worldwide, infectious diseases are the third leading cause of human death.
Industry:Science
