- 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.
Convection plumes, anchored in the lower mantle of the Earth, were proposed by W. J. Morgan in 1970 to explain the existence of oceanic islands such as Hawaii, their relative fixity with respect to one another over geological time, and the “tracks” of volcanoes left by the lithospheric plate sliding over such a “hotspot.” The basalts found on oceanic islands differ in their isotopic composition from basalts found at midocean ridges, which lent geochemical support to the notion that these islands tap into a different reservoir for basaltic material, presumably the lower mantle, the silicate shell of the Earth below about 660 km (410 mi) depth where the upper-mantle minerals olivine, garnet, and pyroxene break down to very high pressure phases of perovskite and magnesiowuestite. But while the geochemical observations give some strong arguments in favor of the plume hypothesis, only seismology can pinpoint the source location of such plumes. Until recently, direct seismic evidence was missing. This allowed a small but vocal minority to oppose the plume hypothesis, advocating instead shallow lithospheric processes to be responsible for the observed phenomena.
Industry:Science
As defined by P. H. A. Sneath and R. R. Sokal, the grouping by numerical methods of taxonomic units based on their character states. According to G. G. Simpson, taxonomy is the theoretical study of classification, including its bases, principles, procedures, and rules. The application of numerical methods to taxonomy, dating back to the rise of biometrics in the late nineteenth century, has received a great deal of attention with the development of the computer and computer technology. Numerical taxonomy provides methods that are objective, explicit, and repeatable, and is based on the ideas first put forward by M. Adanson in 1963. These ideas, or principles, are that the ideal taxonomy is composed of information-rich taxa (“taxon,” plural “taxa,” is the abbreviation for taxonomic group of any nature or rank as suggested by H. Lam) based on as many features as possible, that a priori every character is of equal weight, that overall similarity between any two entities is a function of the similarity of the many characters on which the comparison is based, and that taxa are constructed on the basis of diverse character correlations in the groups studied.
Industry:Science
Genomic imprinting refers to a phenomenon whereby one of the two alleles at a gene locus is preferentially expressed depending upon the parent of origin. Imprinting manifests at the level of the genome, the individual chromosome/chromosomal region and the gene. For many years it has been recognized in the mouse, and more recently has been identified in humans. The mechanisms of imprinted gene expression are not fully understood, but deoxyribonucleic acid (DNA) methylation and asynchronous replication of the parental alleles (allele-specific replication) are common characteristics of imprinted genes. DNA methylation and allele-specific DNA replication are involved in both the somatic cell expression and inheritance of the imprint. Abnormalities related to genomic imprinting have been observed in several human disorders, marked by alterations in prenatal and/or postnatal growth. The best-characterized disorders that result from abnormal genomic imprinting include triploidy, complete hydatidiform moles (a condition in which the placenta degenerates and the fetus is reabsorbed), ovarian teratomas, and the Beckwith-Wiedemann, Angelman, and Prader-Willi syndromes.
Industry:Science
C<i>aenorhabditis elegans</i> is a small nematode worm. In the wild it lives in the soil and eats bacteria. Sydney Brenner chose <i>C. elegans</i> in the early 1960s as a “model organism” for biological research, particularly the genetic control of development and the nervous system. He was interested in a simple animal that was easy to grow, easy to observe, and easy to work with genetically. <i>Caenorhabditis elegans</i> grows quickly in the laboratory (it takes 3 days to proceed from a newly fertilized egg to a reproducing adult). This worm is transparent at all stages of development, so it has been possible to observe <i>C. elegans</i> from egg to adult in exquisite detail. One fascinating outcome of this study has been the realization that development in <i>C. elegans</i> is strongly determined; that is, each adult has very nearly the same number of cells, and in development these cells arise at the same time and in identical patterns. The complete cell lineage of <i>C. elegans</i>, from single-celled fertilized egg to 959-celled adult female, is known. Male adults have an additional set of muscle and nerve cells used in mating, making 1031 cells in all.
Industry:Science
Ethanol is commonly referred to as bioethanol when it is manufactured from agricultural sources, for example, corn or wood. The production of bioethanol from biomass is a proven industrial process for producing fuel from a renewable source. It can be directly mixed with gasoline (petrol) and used in today's automotive vehicles, or used as a fuel for the generation of electricity. Currently, there are two types of blends of ethanol and gasoline on the market: E10, which is 10% ethanol and 90% gasoline, and E85, which is 85% ethanol and 15% gasoline (E85). In the United States, many states currently mandate E10. It is generally accepted that bioethanol gives a 70% carbon dioxide reduction (compared to unblended gasoline), which means 7% in an E10 blend or 50% in an E85 blend. Increased bioethanol usage could reduce U.S. greenhouse gas emissions to 1.7 billion tons/year (22% of the 2002 emissions). Recent investigations have established that polysaccharides in biomass can be hydrolyzed enzymatically into glucose sugar that can be fermented to bioethanol. Fungi, including yeast, are a key source for some of the industrially important enzymes used in this process.
Industry:Science
Geoarcheology entails the use of geologic concepts, methods, and knowledge for solving archeological problems. Geology and archeology are historical sciences based largely on the study of a complex stratigraphy that contains mineral, fossil, and cultural remains in a spatial and implicitly chronological context, and that is used to reconstruct the succession of events that produced the sedimentary record. Of all the natural sciences now incorporated into archeology, geology has the longest association with it. A union of the young science of geology with the even younger discipline of archeology occurred in the midnineteenth century, growing out of the same intellectual ferment that gave birth to evolutionary biology and much of modern geology. The importance of geology in the solution of archeological problems is now well understood by archeologists. Colin Renfrew, a leading British archeologist, wrote in 1976 that “since archaeology, or a least prehistoric archaeology, recovers almost all of its basic data by excavation, every archaeological problem starts as a problem in geoarchaeology.” The term “archeological geology” is essentially synonymous with geoarcheology.
Industry:Science
Extracting gold from ores, refining it, and preparing it for use. Total world resources of gold are estimated at about 83,000 tons (75,000 metric tons). South Africa has about half of these resources, and Brazil, Russia, and the United States have about 12% each. The United States produces about 330 tons (300 metric tons) per year. In the United States, gold is used for jewelry and arts (70%), industry and electronics (23%), and dentistry (7%). There are only a few dozen placer mines in the United States, nearly all in Alaska. In such mines, gold is processed with the modern equivalent of gold panning—sluicing, tabling, and jigging. In addition, by-product gold from copper mining is only about 10% (historically, this source used to be much larger). There are several hundred lode mines in the United States, where the ore is mined from solid rock. This gold is often difficult to recover because it is associated with sulfide or carbonaceous minerals. As technology has improved, possibilities for processing the more difficult-to-treat (refractory) ores have expanded. A particular ore is more or less refractory depending on its combination of chemical compounds and minerals.
Industry:Science
An organizational technique in which a number of processor units are employed in a single computer system to increase the performance of the system in its application environment above the performance of a single processor. In order to cooperate on a single application or class of applications, the processors share a common resource. Usually this resource is primary memory, and the multiprocessor is called a primary memory multiprocessor. A system in which each processor has a private (local) main memory and shares secondary (global) memory with the others is a secondary memory multiprocessor, sometimes called a multicomputer system because of the looser coupling between processors. The more common multiprocessor systems incorporate only processors of the same type and performance and thus are called homogeneous multiprocessors; however, heterogeneous multiprocessors are also employed. A special case is the attached processor, in which a second processor module is attached to a first processor in a closely coupled fashion so that the first can perform input/output and operating system functions, enabling the attached processor to concentrate on the application workload.
Industry:Science
Commonly, the processes by which living organisms take up oxygen and eliminate carbon dioxide in order to provide energy. A more formal, comprehensive definition is the various processes associated with the biochemical transformation of the energy available in the organic substrates derived from foodstuffs to energy usable for synthetic and transport processes, external work, and, eventually, heat. This transformation, generally identified as metabolism, most commonly requires the presence of oxygen and involves the complete oxidation of organic substrates to carbon dioxide and water (aerobic respiration). If the oxidation is incomplete, resulting in organic compounds as end products, oxygen is typically not involved, and the process is then identified as anaerobic respiration. The oxygen required in aerobic respiration is ultimately derived from the atmosphere or from oxygen dissolved in water. The process of the exchange and transport of oxygen from an animal's environment to the intracellular sites involved in metabolism, and the reverse transport and exchange of the end product carbon dioxide, is often called respiration, although it is only a part of the overall process.
Industry:Science
Glands located in the mouth that secrete fluids that moisten and lubricate the mouth and food and may initiate digestive activity; some perform other specialized functions. Fishes and aquatic amphibians have only solitary mucus (slime) secreting cells, distributed in the epithelium of the mouth cavity. Multicellular glands first appeared in land animals to keep the mouth moist and make food easier to swallow. These glands occur in definite regions and bear distinctive names. Some glands of terrestrial amphibians have a lubricative secretion; others serve to make the tongue sticky for use in catching insects. Some frogs secrete a watery serous fluid that contains ptyalin, a digestive enzyme. The oral glands of reptiles are much the same, but are more distinctly grouped. In poisonous snakes and the single poisonous lizard, the Gila monster, certain oral glands of the serous type are modified to produce venom. Also many of the lizards have glands that are mixed in character, containing both mucous and serous cells. Oral glands are poorly developed in crocodilians and sea turtles. Birds bolt their food, yet grain-eaters have numerous glands, some of which secrete ptyalin.
Industry:Science
