- 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.
Pluto has been an intriguing object ever since its discovery in 1930, lying in relative darkness nearly 31 astronomical units (at present) from the Sun. It is difficult to study because of its great distance from the Earth and the Sun; however, observational efforts since the 1970s have revealed it to be an interesting place. In 1978 Pluto was discovered to have a satellite, Charon, about half its diameter, which orbits Pluto with a period of 6.37 days—the same as Pluto's rotation period. Spectral measurements reveal Pluto to have surface ices of methane (CH<sub>4</sub>), carbon monoxide (CO), and nitrogen (N<sub>2</sub>), and the gaseous phase of these molecules forms a tenuous atmosphere that stretches at least 100 km (60 mi) above the planet's surface.
Industry:Science
Sciences that involve attempts to understand the nature, origin, evolution, and behavior of the Earth or of its parts and to comprehend its place in the universe, especially in the solar system. Understanding has advanced primarily through improved appreciation of the complex, usually cyclical interactions that take place among distinct parts of the Earth such as the lithosphere, atmosphere, hydrosphere, and biosphere. Geophysics is the study of the physics of the Earth, emphasizing its physical structure and dynamics. Geochemistry is the study of the chemistry of the Earth, dealing with its composition and chemical change. Geology is the study of the solid Earth and of the processes that have formed and modified it throughout its 4.5-billion-year history.
Industry:Science
In solid-state materials, the term superlattice usually means a synthetically prepared set of lattice planes, of variable thickness and composition, lying parallel to those of the host (substrate). (Such a structure is also known as an artificially layered structure or artificial crystal.) Similarly, in the case of extended molecular adlayers (adsorbed layers), interactions between the terminal atoms of the adsorbed molecule and the solid surface, acting in concert with strong intramolecular interactions, can lead to formation of a self-assembled monolayer. The monolayer structure is, in a sense, a superlattice with only one artificial lattice plane extending from the substrate, with a composition and thickness that can be controlled by choice of adsorbate.
Industry:Science
Reduction in the useful properties of materials because of chemical changes resulting from the absorption of light. The chemical changes can include bond scission (especially of the molecular backbone), color formation, cross-linking, and chemical rearrangements. All organic materials can photodegrade, but the process has greatest practical relevance for polymers where scission of the polymer backbone is particularly important. Photodegradations of polymers in the absence of oxygen (photolysis) or using wavelengths shorter (more energetic) than those at the Earth's surface (<280 nanometers) have been studied extensively, but only the more practical situation of polymers exposed to terrestrial sunlight (or its equivalent) in air is discussed in this article.
Industry:Science
One of the main events in the evolution of animals was the transition from soft-bodied organisms to those that possessed mineralized hard parts for protection and support. This major evolutionary hallmark supported the rapid diversification of animals and their occupation of a diverse range of novel ecological niches at the dawn of the Phanerozoic, between 560 and 530 million years ago (mya). The understanding of the evolution of genes and gene regulatory networks that enable and control the construction of mineralized body parts (biominerals) is therefore vital to the understanding of how animals, including humans, evolved and will also provide clues for the fabrication of biomimetic materials (that is, artificial materials designed to mimic natural forms).
Industry:Science
In the ocean ecosystem, competition for food and living space is often very intense, and some of the adaptations of marine organisms for carving out a spot to live on, or in, the sea floor are remarkable. One very special adaptation is bioerosion, or the biological process of excavating holes in rocks or shells. A wide spectrum of organisms, ranging from bacteria to sponges to barnacles, are able to bioerode quite effectively. Some animals, such as parrot fish, sea urchins, and chitons (polyplacophoran mollusks), bioerode by scraping the surface of rocks or shells in order to eat encrusting algae. Others, such as certain groups of sponges, worms, and bivalves (pelecypods), bioerode by creating holes (borings) in hard substrates, which they occupy permanently.
Industry:Science
It is interesting to imagine what would happen to a bar magnet if it were broken up into smaller and smaller pieces. Eventually one would end up with very small bar magnets, yet their properties could be vastly different from those of large-scale permanent magnets. Even if a macroscopic object made of a ferromagnetic material such as iron or cobalt may have no magnetic polarization, its nanometer-scale counterparts can be made into perfect bar magnets. The size and shape of these nanometer-scale magnets (nanomagnets) determine their strength, polarization direction, and the ways in which this polarization can be changed by external magnetic fields. The applications of such nanoscale magnets range from mass data storage to cancer treatment and medical imaging.
Industry:Science
Lithium batteries have become commercially important power sources because they can supply significantly more energy for a given volume or weight of cell in comparison with conventional cells, such as alkaline zinc or nickel-cadmium. The reason is that lithium is the lightest metal and has one of the highest electrode potentials. One kilogram of lithium can supply 3860 ampere-hours of electricity in comparison with 820 Ah for zinc or 260 Ah for lead. However, because lithium is such an active metal, it reacts with water. Therefore, lithium battery electrolytes must be based on nonaqueous solvents or polymers, manufacture must be carried out in specially constructed dry rooms, and safety precautions are necessary both for use and for disposal of lithium cells.
Industry:Science
Resistance to sliding, a property of the interface between two solid bodies in contact. Many everyday activities like walking or gripping objects are carried out through friction, and most people have experienced the problems that arise when there is too little friction and conditions are slippery. However, friction is a serious nuisance in devices that move continuously, like electric motors or railroad trains, since it constitutes a dissipation of energy, and a considerable proportion of all the energy generated by humans is wasted in this way. Most of this energy loss appears as heat, while a small proportion induces loss of material from the sliding surfaces, and this eventually leads to further waste, namely, to the wearing out of the whole mechanism.
Industry:Science
Significant advances in the development of cermet materials for applications in the cutting-tool industry have been made. During the 1960s, several companies began to market cermet inserts with improved toughness with the addition of tungsten carbide (WC) and tantalum carbide (TaC). The additional elements produced a more stable cutting tool; however, the mechanical structure provided levels of toughness well below those of traditional cemented carbide materials. Applications of cermet materials was restricted to light finishing cuts with light feed rates. Such a restriction adds an expense to the manufacturing process and limits that expense to a single operation in the process. The expense would, in most cases, outweigh the value of the cermet cutting tool.
Industry:Science
