- 行业: Printing & publishing
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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.
Definitions of aging differ between biologists and behavioral scientists. The biologists regard aging as reflecting the sum of multiple and typical biological decrements occurring after sexual maturation; the behavioral scientists view it as reflecting regular and expected changes occurring in genetically representative organisms advancing through the life cycle under normal environmental conditions. It is difficult to define normal aging, since many changes observed in older adults and previously perceived as concomitants of normal aging are now recognized as effects of disease in later life. The behavioral science view allows for incremental as well as decremental changes with aging. Senescence is not always equated with aging; it is viewed as the increasing vulnerability or decreasing capacity of an organism to maintain homeostasis as it progresses through its life span. Gerontology refers to the study of aging. Geriatrics refers to the clinical science that is concerned with health and illness in the elderly.
Industry:Science
Electronic instruments that mimic the human senses, known as electronic noses and tongues, recently have been developed and used to evaluate the quality of coffee, to assess the odor emanating from packaging materials, and to diagnose diseases such as urinary tract infections. These devices use a common feature—a set (array) of sensors, ranging from a few to 32 or more components. The sensors are nondiscriminating gas detectors of various types, including polymer-based films, electrochemical probes, and thin films. Some use changes in electrical resistance as the signal produced in the sensing process, others produce a color change, while others operate by changing their resonating frequency. In general, these devices do not recognize a specific substance; instead, they detect a signature, a “fingerprint” of an odor, or a quality of what is being measured. The availability of pattern-recognition techniques for effective signal analysis has enabled the development of complex sensor arrays for artificial olfaction.
Industry:Science
Coalbed methane production occurs within an economically important and unique petroleum system. A petroleum system typically consists of a sedimentary basin that contains a hydrocarbon source rock and all of the oil and gas related to the source rock. The classical petroleum system consists of a hydrocarbon-generative shale source rock that, with burial and resultant heating, expulses oil and gas that are free to migrate to porous reservoir rock such as sandstone or limestone. A coalbed methane system is different in that the coal itself is both source and reservoir. The coal is a hydrocarbon source rock that evolved during burial heating into a substance similar in structure to activated carbon (an organic-based material that is chemically treated or heat-treated to markedly increase micropores, with a corresponding increase in the internal surface area and gas sorption capacity). The coal both produces methane gas and has the storage capacity to hold the gas in place. Migration outside the coalbed is unnecessary.
Industry:Science
Earth is an extraordinarily hot planet. The center of Earth, which on average is 6371 km (3982 mi) below the surface, is as hot as the surface of the Sun—around 6273 K (6000°C; 10,800°F). The source of this heat is the radioactive decay of long-lived isotopes of potassium (<sup>40</sup>K), thorium (<sup>232</sup>Th), and uranium (<sup>238</sup>U); without the heat generated from these decaying isotopes, Earth would have cooled since its formation to a cold solid mass. That Earth's surface is livable with such high temperatures in its interior is due mainly to the low thermal conductivity of most crustal rocks. In some places, however, very high temperatures are present right at Earth's surface. Volcanic eruptions can bring molten lava to the surface, while in other locations geysers, fumaroles, and hot springs are strong reminders of Earth's internal heat. Such heat, produced from Earth's natural processes whether at the surface or at depth, is the source of the sustainable energy supply known as geothermal energy.
Industry:Science
Gamma-ray imaging attempts to capture the distribution of radioactive decays within a body or from a distant source by detecting the emitted gamma rays. Unlike conventional x-ray or magnetic resonance imaging, gamma-ray imaging in humans and animals requires the introduction of a radioactive source into the body through injection, inhalation, or oral administration. The principal advantage of gamma-ray imaging over more conventional methods is that specially designed radiotracers can follow physiological pathways in the body. A number of chemicals are absorbed by specific organs. For example, the thyroid gland takes up iodine and the brain consumes glucose. With this knowledge, radiopharmacists are able to attach various radiotracers to biologically active substances such as iodine or glucose. In more conventional imaging such as transmission x-ray imaging, the anatomy of the patient is revealed, whereas gamma-ray imaging reveals the functional dynamics of processes in the body through so-called functional imaging.
Industry:Science
Despite the availability of an advanced system of geostationary satellites covering the United States, the detection of severe or violent thunderstorms has been dependent mainly on radar and storm spotters, when available. In Europe and Africa, radar and spotter networks are less developed or nonexistent. The question arises, to what extent can satellites be used for detecting severe weather phenomena? Research into this question started with the first satellite observations more than 40 years ago in the United States. This paper reviews the principal findings from this research, with some current applications of the satellite data. The emphasis will be on inferring the intensity or severity of existing thunderstorms, which includes the occurrence of damaging winds, hail, and tornadoes. The estimation of rainfall from satellite imagery and the use of the data in numerical weather prediction are important topics, but beyond the scope of this paper. However, storm initiation and intensification will be covered briefly.
Industry:Science
Any protozoon moving by means of protoplasmic flow. In their entirety, the ameboid protozoa include naked amebas, those enclosed within a shell or test, as well as more highly developed representatives such as the heliozoians, radiolarians, and foraminiferans. Ameboid movement is accomplished by pseudopods—cellular extensions which channel the flow of protoplasm. Pseudopods take varied forms and help distinguish among the different groups. A lobe-shaped extension or lobopod is perhaps the simplest type of pseudopod. The shapelessness and plasticity of these locomotory organelles impart an asymmetric, continually changing aspect to the organism. Other, more developed, representatives have pseudopodial extensions containing fibrous supporting elements (axopods) or forming an extensive network of anastomosing channels (reticulopods). Though involved in locomotion, these organelles are also functional in phagocytosis—the trapping and ingesting of food organisms (usually bacteria, algae, or other protozoa) or detritus.
Industry:Science
Electrical devices whose principle of operation is based upon the use and properties of ferrites, which are magnetic oxides. Ferrite devices are divided into two categories, depending on whether the ferrite is magnetically soft (low coercivity) or hard (high coercivity). Soft ferrites are used primarily as transformers, inductors, and recording heads, and in microwave devices. Since the electrical resistivity of soft ferrites is typically 10<sup>6</sup>–10<sup>11</sup> times that of metals, ferrite components have much lower eddy current losses and hence are used at frequencies generally above about 10 kHz. Hard ferrites are used in permanent-magnet motors, loudspeakers, and holding devices, and as storage media in magnetic recording devices. In this article, discussion of hard ferrites will be restricted to recording only. One type of soft ferrite, referred to as square-loop ferrites, was once deployed in huge quantities as cores for digital computer memories but has now been replaced by semiconductor integrated circuits.
Industry:Science
Cancer is the second leading cause of death in the United States. About 1,200,000 new cases will be diagnosed and over 550,000 Americans are expected to die of cancer in 2001. Despite developments in surgery, chemotherapy, and radiation therapy of cancer, new strategies for treatment are sorely needed. Advances in knowledge of the molecular basis for cancer have led to the understanding that cancer is a multistep process involving a variety of gene alterations. These genetic lesions accumulate until malignant cells are created and proliferate to form a malignant neoplasm, or tumor. To take advantage of these new understandings, gene therapy has emerged as a new treatment strategy. It involves introducing genes to either reverse or counteract the molecular defects or alterations associated with cancer cells. The potential advantage of gene therapy is that it can be directed to tumor cells with greater specificity than conventional chemotherapy. Thus it is less likely to affect normal cells or to cause undesired systemic effects.
Industry:Science
Genetically determined markers on the surface of cellular blood elements (red and white blood cells, platelets). They have medical, legal, and anthropologic importance. In medicine, the matching of ABO and Rh groups of recipients and donors before blood transfusion is of paramount importance; other blood groups also can be implicated in incompatibility. Markers on white cells (histocompatibility antigens) are shared by a number of body tissue cells; these markers are important to the survival of transplanted organs and bone marrow. In law, the recognition of identity between bloodstains found at the scene of a crime and those on clothing of a suspect has resulted in many convictions, and blood typing has served to resolve paternity disputes. From an anthropologic standpoint, some blood groups are unique to specific populations and can be a reflection of tribal origin or migration patterns. Blood groups are also valuable markers in gene linkage analysis, and their study has contributed enormously to the mapping of the human genome.
Industry:Science
