- 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.
A sound source that is based on the regular interruption of a stream of fluid (usually air) by a perforated rotating disk or cylinder. The components of a siren are a source of air, a rotor containing a number of ports which interrupt the airflow at the desired frequency, and ports in a stator through which the air escapes. The air is supplied by a compressor, and a motor drives the rotor. The frequency of the sound wave produced by the siren is the product of the speed of rotation and the number of ports in the rotor. The shape of the rotor and stator ports determines the wave shape at the entrance of the stator port. The stator ports feed into a horn in order to improve radiation.
Siren performance parameters are sound power output, acoustic pressure, and efficiency, that is, the ratio of acoustic power output to compressor power.
Industry:Science
A sound wave which has been reflected or otherwise returned with sufficient magnitude and time delay to be perceived in some manner as a sound wave distinct from that directly transmitted. Multiple echo describes a succession of separately indistinguishable echoes arising from a single source. When the reflected waves occur in rapid succession, the phenomenon is often termed a flutter echo.
Industry:Science
A sound-reproducing system in which sound is recorded or transmitted by using two microphones mounted at the ears of a dummy human head. To preserve the binaural effect, the sound must be monitored by a listener wearing a set of earphones identically spaced. In an ideal binaural transmission system, both the amplitude and phase of the sound waves incident on the dummy's ears are duplicated at the listener's ears.
Industry:Science
A source of data pertaining to features of various objects, usually astronomical, that depend on time. The ephemeris can be a printed or computer-readable table such as on a compact disk, or it can be a set of numerical data accessible by computer programs. Most ephemerides pertain to positions of celestial objects as seen from any place in the solar system. The term may also apply to other parameters, such as those describing the state of rotation or orientation of a body in space.
Industry:Science
A source of electric power (voltage and current) to operate electronic circuits. Active electronic circuits contain such devices as transistors or vacuum tubes and require external power to amplify, filter, modify, or create electrical signals. The most common source of energy for electronic circuits is obtained by converting the electrical energy available in the conventional alternating-current (ac) electric power mains to an appropriate voltage or current. These converters, or electronic power supplies, can be implemented with a wide variety of circuits. Other power sources include batteries, mechanically driven generators, photovoltaic (solar) cells, and fuel cells.
Industry:Science
A source of high-quality alternating power to sensitive electrical equipment. An ideal uninterruptible power supply (UPS) provides a critical load with power when the main supply suffers from an over- or undervoltage condition causing interruption of the supply. It thus ensures power without break for the critical load. The UPS should be reliable and highly efficient, requiring low maintenance, low cost, and light weight.
Uninterruptible power supplies were originally designed to furnish reliable and high-quality continuous power to large computer systems. They are now applied to a wide variety of critical equipment, such as medical facilities, life-support systems, financial transaction data storage and computer systems, telecommunications, industrial processing, and on-line management systems. UPS ratings range from a few hundred volt-ampere (VA) up to several thousand kilovolt-ampere (kVA). Three types of UPS systems are available: static, rotary, and hybrid static/rotary.
Industry:Science
A source of radiant energy excited by a supply of electricity which creates a current of ionized gas between electrodes in an enclosure that contains the arc while permitting transmission of the radiant energy. Gaseous-discharge lamps or vapor lamps are given various names relating to the element responsible for the majority of the radiation (mercury, sodium metal-halide, xenon), to the physical attribute of the lamp (short-arc, high-pressure), or, in the case of fluorescent lamps, to the way a phosphor on the bulb wall fluoresces as a result of the lamp's low-pressure mercury-vapor excitation.
Industry:Science
A southerly or southeasterly wind current from the Sahara or from the deserts of Saudia Arabia which occurs in advance of cyclones moving eastward through the Mediterranean Sea. The sirocco is most pronounced in the spring, when the deserts are hot and the Mediterranean cyclones are vigorous. It is observed along the southern and eastern coasts of the Mediterranean Sea from Morocco to Syria as a hot, dry wind capable of carrying sand and dust great distances from the desert source. The sirocco is cooled and moistened in crossing the Mediterranean and produces an oppressive, muggy atmosphere when it extends to the southern coast of Europe. Rain that falls in this air is often discolored by the dust or sand which is precipitated along with the waterdrops. Under sunny conditions, the sirocco can produce temperatures in excess of 100°F (38°C) in southern Europe. Various other names are used to denote the sirocco in specific localities, such as khamsin in Egypt.
Industry:Science
A spacecraft that is in orbit about a planet (usually the Earth) or a moon. Spacecraft are devices intended for observation, research, or communication in space. Even those spacecraft which are on the way to probe the outer reaches of the solar system usually complete at least a partial revolution around Earth before being accelerated into an interplanetary trajectory. Devices such as sounding rockets follow ballistic (approximately parabolic) paths after fuel exhaustion, but they are not satellites because they do not achieve velocities great enough to avoid falling back to Earth before completing even one revolution.
Industry:Science
A spacecraft which is precisely measuring the cosmic microwave background (CMB) radiation. The <i>Wilkinson Microwave Anisotropy Probe</i> (<i>WMAP</i>) is a space mission of the National Aeronautics and Space Administration (NASA) that has put fundamental theories of the nature of the universe to a precise test. Since August 2001, <i>WMAP</i> has continually surveyed the full sky, mapping out tiny differences in the temperature of the cosmic microwave background radiation, which is the radiant heat from the big bang.
A fossil remnant of the hot big bang, the cosmic microwave background permeates the universe and is seen today with an average temperature of only 2.725 kelvins. Tiny variations about this average temperature were first discovered by NASA's <i>Cosmic Background Explorer</i> (<i>COBE</i>) mission. <i>WMAP</i> followed up on the <i>COBE</i> results by characterizing the detailed statistical nature of the temperature variations of the cosmic microwave background (called anisotropy), revealing a wealth of detail about the global properties of the universe.
Industry:Science
