- 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.
Calcium (Ca<sup>2+</sup>) is a major signaling molecule that activates an array of cellular events. Accordingly, cytosolic Ca<sup>2+</sup> levels are tightly controlled at approximately 100 nM. However, elevations to approximately 300 nM initiate powerful signals that control a spectrum of cell functions, ranging from short-term contractile responses to long-term events such as transcription. Thus, maintenance of cytosolic Ca<sup>2+</sup> is a very important and elaborate process. Some of the regulatory elements that maintain these cytosolic Ca<sup>2+</sup> levels are ion channels and exchangers located on the plasma membrane of the cell. However, the endoplasmic reticulum (ER) also plays a large role in Ca<sup>2+</sup> signaling. The ER lumen stores approximately 500 μM of Ca<sup>2+</sup>, which not only provides an environment conducive for proper protein folding, but also serves as a major source of Ca<sup>2+</sup> for signaling.
Industry:Science
Classical mechanics is the study of the positions and motions of particles or extended bodies. Initially the description used the coordinates and velocities of the objects under consideration and applied Newton's laws to describe their motions. Later the Lagrangian formulation was used to relate the positions, velocities, and resulting accelerations through an action principle. In the Lagrangian method, the velocities are considered as the time derivatives of the positions, and the equations of motion are determined by varying possible paths of the system holding the end points of the variation constant. A more general method is the Hamiltonian formulation, which considers the positions and momenta of the objects in the system under consideration as independent quantities. For the Hamiltonian variation, the momenta and the positions are varied independently subject to a constraint of the relation between the velocities and the momenta.
Industry:Science
Bats are a ubiquitous group of flying mammals found on every continent except Antarctica, with highest abundance and diversity in the tropics and subtropics. Some species are very gregarious and may roost together in caves in substantial numbers. For example, the Mexican free-tailed bat may roost in maternity colonies reaching in excess of 20 million individuals in the semiarid parts of northern Mexico and the southwestern United States. These high population densities can result in bleached fur on the bats as a result of the high concentration of ammonia given off by microbial processing of bat urine and excrement (guano). Both big and smaller populations of bats produce considerable quantities of guano, which, over thousands of years, can lead to deposits many meters thick on the cave floor. Sizable guano deposits have been mined for fertilizer, with the remaining deposits now serving as valuable archives of past environmental change.
Industry:Science
Cetaceans, or whales (a group which includes the animals commonly known as dolphins and porpoises), are interesting from an evolutionary perspective because they are so different from their ancestors. The ancestors of whales were fur-covered land mammals that rarely entered the water, whereas whales today are fully aquatic and thrive in the oceans, seas, and—in some instances—great rivers of the world. The ancestors were four-footed and hoofed for running on land, whereas whales today have forelimbs modified as flippers, lack external hindlimbs, and move by pushing themselves through water using a powerfully muscled tail with a broad terminal water-foil called a fluke. The ancestors were omnivorous to herbivorous; in contrast, whales today are piscivorous (fish-eating) and planktivorous (plankton-eating). The ancestors perceived their surroundings using their eyes and noses; however, whales today “see” their surroundings with their ears.
Industry:Science
Data mining is the process of discovering valid, comprehensible, and potentially useful knowledge from large data sources with the purpose of applying this knowledge to making decisions. Although generally driven by competitive business environments, data mining is not specific to any particular industry. In fact, any organization can use data mining to extract information in the form of facts, relationships, trends, or patterns. Data mining can also be used to reveal missing pieces of data, or to discover anomalies or exceptions to assumed relationships between some different pieces of data. For this reason, data mining is sometimes referred to as knowledge discovery in databases (KDD). Data mining and KDD, however, are not synonymous. The KDD concept is generally used to describe the whole process of extracting knowledge, whereas data mining is considered a particular activity within KDD where specific algorithms are used to extract data.
Industry:Science
Any one of a number of formal ranks used for organisms in a Linnaean classification. Biological classifications are orderly arrangements of organisms in which the order specifies some relationship. Taxonomic classifications are usually hierarchical and comprise nested groups of organisms. The actual groups are termed taxa. In the hierarchy, a higher taxon may include one or more lower taxa, and as a result the relationships among taxa are expressed as a divergent hierarchy that is formally represented by tree diagrams. In Linnaean classifications, taxonomic categories are devices that provide structure to the hierarchy of taxa without the use of tree diagrams. By agreement, there is a hierarchy of categorical ranks for each major group of organisms, beginning with the categories of highest rank and ending with categories of lowest rank, and while it is not necessary to use all the available categories, they must be used in the correct order.
Industry:Science
Changes in the chemical or physical state of matter subjected to high pressure. The earliest high-pressure chemical process of commercial importance was the Haber synthesis of ammonia from hydrogen and nitrogen developed in Germany prior to World War I. The synthesis of diamonds from graphite developed in the early 1950s is a high-pressure physical process. Raising the pressure on a system may result in several kinds of change. It causes a gas or vapor to become a liquid, a liquid to become a solid, a solid to change from one molecular arrangement to another, and a gas to dissolve to a greater extent in a liquid or solid. These are physical changes. A chemical reaction under pressure may proceed in such a fashion that at equilibrium more of the product forms than at atmospheric pressure; it may also take place more rapidly under pressure; and it may proceed selectively, forming more of the desired product among multiple possible products.
Industry:Science
Cephalopoda is a class of exclusively marine, present-day mollusks that evolved during the Cambrian Period from a benthonic ancestor, probably a herbivore monoplacophoran mollusk. After 500 million years of evolution the result is a group of organisms with a variety of life-styles (there are benthonic forms, such as octopuses; nectobenthonics, such as cuttlefishes; and nectonics, such as squids), high and fast mobility (performed by a characteristic jet propulsion mechanism), a highly developed nervous system, a relatively short life-span, and a very fast growth for invertebrate standards, all supported by their carnivorous habits. Their biomass, estimated in more than 49 billion long tons (500 million metric tons) per year, together with their voracity, makes them an important component of the marine food webs. Moreover, different cephalopod species constitute an important fishery resource, representing more than 2% of world marine captures.
Industry:Science
Human females are unusual among mammals in experiencing menopause, a nonvoluntary and irreversible cessation of fertility long before the senescence of other bodily systems and the end of average lifespan. Two main hypotheses have been proposed to explain the origin of menopause. Some evolutionary biologists and anthropologists suggest that menopause is an adaptation—the result of natural selection for a postreproductive lifespan to permit increased maternal investment in rearing offspring. At some point in human evolution, females who ceased reproducing before the end of their lives gained a genetic fitness advantage from dedicating their remaining reproductive effort to enhancing the reproductive success of their existing progeny. Others hypothesize that menopause is an epiphenomenon (by-product)—either the result of a physiological trade-off favoring efficient early reproduction or merely an artifact of increased lifespan and life expectancy.
Industry:Science
Any peripheral nerve which has its central nervous system connection with the brain, as opposed to the spinal cord, and reaches the brain through a hole (foramen) in the skull. Nerve fibers are sensory if they carry information from the periphery to the brain, and motor if they carry information from the brain to the periphery. Sensory fibers are classified as somatic sensory if they come from the skin or muscle sense organs, visceral sensory if they come from the viscera, and special sensory if they come from special sense organs such as the eye and ear. Motor fibers are classified as somatic motor if they carry information to somatic striated muscles; general visceral motor if they carry information to glands, smooth muscle, or cardiac muscle; and special visceral motor if they carry information to visceral striated muscle. A cranial nerve may have only one fiber type or several; cranial nerves with several fiber types are called mixed nerves.
Industry:Science
