- 行业: Printing & publishing
- Number of terms: 178089
- Number of blossaries: 0
- 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.
Physical barriers designed to provide protection from the effects of ionizing radiation; also, the technology of providing such protection. Major sources of radiation are nuclear reactors and associated facilities, medical and industrial x-ray and radioisotope facilities, charged-particle accelerators, and cosmic rays. Types of radiation are directly ionizing (charged particles) and indirectly ionizing (neutrons, gamma rays, and x-rays). In most instances, protection of human life is the goal of radiation shielding. In other instances, protection may be required for structural materials which would otherwise be exposed to high-intensity radiation, or for radiation-sensitive materials such as photographic film and certain electronic components.
Industry:Science
Most oil is produced from giant oil fields found before the 1970s and is collectively termed conventional oil. This oil will continue to dominate supply until well past peak production. Some nonconventional oil is already in production and will be increasingly important after peak. At that time a discontinuity will mark the onset of a decline in the supply of this fuel that has powered the world economy for most of the twentieth century. To obtain an accurate estimate of the oil reserves, it is necessary to determine how much oil has been found and when it was found. The amount discovered at any reference date comprises how much had been produced to that date (cumulative production) and how much remains to be produced from known fields (reserves).
Industry:Science
Rocks that are formed from melted rock, usually by cooling. The melted rock is called magma when it is below the surface, and lava when it flows out onto the surface. When the magma or lava cools or moves into areas of lower pressure, crystals or glass or both form. Thus, igneous rocks are composed of crystals, glass, or combinations of these materials. Magmas sometimes erupt explosively, creating ash that is composed of broken crystals, glass, and rock materials called pyroclastic material. Rocks formed at or very near the surface, including pyroclastic rocks, are called volcanic rocks, whereas those formed from magma at depth are called plutonic rocks. In the past, some rocks that formed below the surface but near it were called hypabyssal rocks.
Industry:Science
Recent developments include the use of ceramic tools in high-speed machining of superalloys. An important application is machining of nickel-based superalloys, such as Inconel 718 and Incoloy 901. Nickel-based superalloys are widely used for components with high strength at elevated temperatures, which is a typical requirement for the aircraft industry as well as for gas and steam turbines. However, these superalloys are extremely difficult to cut. The main reasons for the poor machinability of the nickel-based superalloys are their high shear strength and rate of work hardening. The poor thermal diffusivity of these alloys also results in heat concentration in the vicinity of the cutting tip, limiting tool life because of the rapid increase in wear.
Industry:Science
Sexually transmitted genital ulcerative diseases are a worldwide health problem and have been strongly associated with an increased risk of human immunodeficiency virus (HIV) transmission. Chancroid, caused by the gram-negative pathogen <i>Haemophilus ducreyi</i>, is the leading cause of genital ulcer disease in developing countries of Asia and Africa. In Europe and North America, <i>H. ducreyi</i> infections account for a smaller proportion of reported genital ulcers. However, recent studies in the United States suggest that many more cases of chancroid occur than are reported. <i>Haemophilus ducreyi</i> has been the focus of recent research aimed at understanding the mechanisms of pathogenesis of chancroid and its association with HIV transmission.
Industry:Science
Natural fission reactors (NFR) are high-grade uranium deposits in which self-sustained fission chain reactions took place approximately 2 billion years ago. Found only in southeast Gabon, Africa, they are unique physical phenomena in the Earth's crust and the only place where some minerals are composed of elements with nonprimordial isotopic abundance. Despite great efforts, evidence for large-scale nuclear reactions has not been found anywhere else. Natural fission reactors have recently been studied as “natural analogs” for the disposal of high-level radioactive waste in the lithosphere, because they provide the exceptional opportunity to study geochemical behavior of natural fission products that do not normally occur in any significant quantities.
Industry:Science
Objects or devices which insert into the ear canal or cover the outer ear and which have a variety of applications. They may protect the ears from exposure to caustic materials, extremely cold temperatures, or excessive noise; serve as a barrier against solid particles collecting on the surface of the outer ear (auricle); prevent accidental injuries from flying objects in industrial activities, from contact during physical activities, or from excessive heat or fire; prevent moisture or solid particles from entering the ear canal; reduce noise to acceptable levels so signals are heard better through earphones; and protect the outer ear from direct sun rays. The purpose for wearing ear protectors determines the characteristics of the device to be used.
Industry:Science
Plant hormones are naturally occurring organic molecules that regulate multiple aspects of plant growth and development at concentrations much lower than nutrients and other metabolites. At least five classes of plant hormones, including auxins, cytokinins, gibberellins (GAs), ethylene, and abscisic acid (ABA), have been characterized and studied in detail for many decades with respect to their occurrence and biosynthesis in plants, their molecular mechanisms of action, and the resulting alterations in cellular structure and function that lead to defined physiological responses to each hormone. In the past decade, a sixth class of plant hormones, brassino-steroids (BRs), has been added to the list of essential regulators of plant growth and development.
Industry:Science
Positive psychology as a “movement” began in 1998 when Martin Seligman proposed, during his term as president of the American Psychological Association, that psychology be just as concerned with what is right with people as it is with what is wrong. Approximately 20–30% of people in the United States suffer from a mental disorder at one time or another, and that slice of the population has received much attention in the psychology literature for many decades. Positive psychology sprang from a desire to rebalance psychology as a field so that, in addition to understanding the etiology and optimal treatment strategies for mental disorders, it would be possible to understand and better the lives of the other 70–80% of people who are not severely distressed.
Industry:Science
Prokaryotic cells are usually microscopic, but some recently discovered prokaryotes are visible to the naked eye. A taxonomic kingdom comprising microorganisms that lack a true nucleus or any other membrane-bound organelle. Instead of a nucleus, prokaryotic cells contain a nucleoid, which is a DNA-dense region of the cell where DNA replication and transcription occur. The chromosome of these cells is circular and, in contrast to eukaryotic cells, continuously codes for cellular proteins and other molecules. Some cells also contain a plasmid, which is a smaller separate piece of circular DNA. The ribosomes of prokaryotes are found floating loose in the cytoplasm, whereas in eukaryotic cells the ribosomes are found in or on the rough endoplasmic reticulum.
Industry:Science
