- 行业: Printing & publishing
- Number of terms: 178089
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- 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.
Landscapes change dramatically with climate on short time scales (for example, during the Dust Bowl of the 1930s) and long time scales (for example, swamps existed on Antarctica 50 million years ago). But we know relatively little about how landscapes change during climatic transitions and, particularly, what processes control ecosystem dynamics during these transitions. Recent geochemical studies have begun to shed light on this process. These studies have focused on how soil development and landscape evolution control the availability of essential plant nutrients. They also reveal how landscapes and ecosystem nutrient supplies respond to climate change on rapid time scales.
Industry:Science
Liquid rocket propellants often require the largest component volume aboard a rocket vehicle. They must be contained by very bulky and heavy tanks that keep the liquids at the right pressure and temperature until they are used in a rocket engine. An increase in the propellant density, or mass per volume, can reduce the mass of the tanks, structure, and other parts of the rocket that depend upon the propellant volume. The use of higher-density propellants is therefore an excellent way to improve the performance of rocket vehicles. Reducing the mass of the rocket will lead in turn to a reduction in the weight of fuel needed to move the rocket, so there is a powerful cascade effect.
Industry:Science
Infrared radiations occupy the span between the visible spectrum and radio waves, and encompass wavelengths 780–400,000 nanometers, neither boundary being precisely delimited. All bodies above absolute zero in temperature are potential sources of infrared radiations; therefore, all organisms are continually exposed to them. About 60% of the Sun's rays are infrared. Water absorbs infrared radiations strongly, except for the band of transparency between 780 and 1400 nm. Since protoplasm contains much water, it absorbs infrared radiations readily. A large animal absorbs infrared radiations at its surface, only the span from 780 to 1400 nm penetrating as far as the blood vessels.
Industry:Science
Much can be learned from studying the concentrations of the ubiquitous long-lived radioactive isotopes. W. Libby and coworkers first demonstrated in 1949 that trace analysis of carbon-14 (<sup>14</sup>C; half-life = 5730 years, isotopic abundance ~1 × 10<sup>−12</sup>) can be used for archeological dating. Since then, two well-established methods, low-level counting and accelerator mass spectrometry, have been used to analyze many different trace isotopes and to extract valuable information encoded in the production, transport, and decay processes of these isotopes. The impact of ultrasensitive trace-isotope analysis has reached a wide range of scientific and technological fields.
Industry:Science
Small frequency shifts or broadening from the frequency of the incident radiation in the light scattered from a liquid, gas, or solid. The term quasielastic arises from the fact that the frequency changes are usually so small that, without instrumentation specifically designed for their detection, they would not be observed and the scattering process would appear to occur with no frequency changes at all, that is, elastically. The technique is used by chemists, biologists, and physicists to study the dynamics of molecules in fluids, mainly liquids and liquid solutions. It is often identified by a variety of other names, the most common of which is dynamic light scattering (DLS).
Industry:Science
Marine fungi are not a taxonomically or physiologically defined group of organisms; rather, they are an ecologically defined group. According to a commonly accepted definition, they are divided into <i>obligate marine fungi</i>, which grow and sporulate exclusively in the marine or estuarine environment, and <i>facultative marine fungi</i>, which may grow in marine as well as freshwater or terrestrial habitats. Consequently, they range from residents, that is, those that complete their life cycles exclusively in marine habitats and thus are never found outside of the marine environment, to transients, that is, those that occur in the sea accidentally by being washed or blown into it.
Industry:Science
Measurement of the hotness of a body relative to a standard scale. The fundamental scale of temperature is the thermodynamic scale, which can be derived from any equation expressing the second law of thermodynamics. Efforts to approximate the thermodynamic scale as closely as possible depend on relating measurements of temperature-dependent physical properties of systems to thermodynamic relations expressed by statistical thermodynamic equations, thus in general linking temperature to the average kinetic energy of the measured system. Temperature-measuring devices, thermometers, are systems with properties that change with temperature in a simple, predictable, reproducible manner.
Industry:Science
Phosphorus is indispensable to life on Earth, as it is involved in the passage of genetic information, energy transfer, and the construction of plant cells. Despite this, the amount of phosphorus available for biological uptake is relatively small, so productivity in many terrestrial and aquatic ecosystems is often limited by phosphorus availability. As a result, human interference in the phosphorus cycle can have severe environmental consequences. For example, phosphorus pollution of water bodies by sewage effluents and drainage from agricultural land can contribute to the growth of toxic blue-green algae, fish deaths, and a drastic reduction in the quality of affected water bodies.
Industry:Science
Predation occurs when one animal (the predator) eats another living animal (the prey) to utilize the energy and nutrients from the body of the prey for growth, maintenance, or reproduction. In the special case in which both predator and prey are from the same species, predation is called cannibalism. Sometimes the prey is actually consumed by the predator's offspring. This is particularly prevalent in the insect world; for example, a wasp may paralyze and lay eggs on a butterfly caterpillar, leaving its offspring to consume the prey. Insect predators that follow this type of lifestyle are called parasitoids, since the offspring grow parasitically on the prey provided by their mother.
Industry:Science
One of the four primary tissues of the body, which constitutes the epidermis and the lining of respiratory, digestive, and genitourinary passages. The major characteristic of epithelium is that the cells are close together, separated by a very small amount of intercellular substance. The epithelium (endothelium) lining the inner cavities of the heart, blood vessels, and lymphatics differs from that of all the other groups because under abnormal conditions it may be transformed into a different type of cell characteristic of connective tissue, the fibroblast. Epithelium may be derived from any of the three primary germ layers of the very early embryo—ectoderm, endoderm, or mesoderm.
Industry:Science
