- 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.
A key stage in the evolutionary history of life on Earth is the transition between fish with fins and animals with limbs and digits (such animals are known as tetrapods). This event is thought to have happened between about 370 and 360 million years ago, in the Devonian Period. In 1999, a team of paleontologists mounted their first expedition to Ellesmere Island in the Canadian territory of Nunavut in the Arctic Circle, with the hope of finding fossils that represent this transition. Although this locality had never before been visited by vertebrate paleontologists, the team's visit was an informed guess or prediction that the geological age and type of sediments there were just right for potentially finding relevant material. The sediments were formed in meandering streams and river estuaries in the early part of the Late Devonian about 370 million years ago. Over a series of four expeditions, the collective hunch paid off. After three seasons, the team found a rich seam of vertebrate-bearing rocks that yielded an array of many different kinds of fishes, including some lower jaws and a snout of a previously unknown form but which looked tantalizingly like a transitional form. In the fourth season, they discovered almost complete skeletons and many isolated parts of this creature, which indeed proved to be a spectacular and important new addition to the story of the origin of tetrapods. They called it <i>Tiktaalik roseae</i>: <i>Tiktaalik</i> is the local Inuktitut name for a large freshwater fish seen in the shallows, and <i>roseae</i> honors the benefactor who provided much of the expeditionary funds.
Industry:Science
A label used to indicate the physical and chemical characteristics of a star, as indicated by study of the star's spectrum. Stars possess a remarkable variety of spectra, some simple, others extraordinarily complex. To understand the natures of the stars, it was first necessary to bring order to the subject and to classify the spectra.
Industry:Science
A laboratory or facility for investigation and handling of radioactive chemicals which provides a safe environment for the worker and the public. It's features can vary depending on the type of radioactive emissions to be handled, the quantity, the half-life, and the physical form (solid, liquid, gas, or powder). Special measures to minimize spread of contaminated material and to dispose of radioactive waste are required. Working surfaces should be smooth and easily washable to permit effective decontamination if necessary. Good ventilation and detectors for monitoring radiation and contamination on surfaces or people are also typical features. Space for clothing change, lockers, and showers are commonly provided.
Industry:Science
A laboratory technique for studying the behavior of minerals under high-pressure conditions.
Industry:Science
A lake whose water is permanently stratified and therefore does not circulate completely throughout the basin at any time during the year. Normally lakes in the Temperate Zone mix completely during the spring and autumn when water temperatures are approximately the same from top to bottom. In meromictic (<i>mero</i>, partial; <i>mixis</i>, circulation) lakes, there are no periods of overturn or complete mixing because seasonal changes in the thermal gradient either are small or are overridden by the stability of a chemical gradient, or the deeper waters are physically inaccessible to the mixing energy of the wind. Commonly in meromictic lakes, the vertical stratification in density is stabilized by a chemical gradient.
Industry:Science
A laminated, microbial structure in carbonate rocks (limestone and dolomite). Stromatolites are the oldest macroscopic evidence of life on Earth, at least 2.5 billion years old, and they are still forming in the seas. During the 1.5 billion years of Earth history before marine invertebrates appeared, stromatolites were the most obvious evidence of life, and they occur sporadically throughout the remainder of the geologic record. In Missouri and Africa, stromatolite reefs have major accumulations of lead, zinc, or copper; and in Montana, New Mexico, and Oman, stromatolites occur within oil and gas reservoirs. For geologists, the shapes of stromatolites are useful indications of their environmental conditions, and variations in form and microstructure of the laminations may be age-diagnostic in those most ancient sedimentary rocks that lack invertebrate fossils.
Industry:Science
A lamp that creates radiant energy when its metallic filament is heated by an electric current. The filament is designed to produce radiant energy in the visible portion of the electromagnetic spectrum (light). The filament is of a special material that is supported in an envelope (bulb) that has been evacuated or filled with an inert gas such as argon, nitrogen, or krypton. In addition to light, the heated filament emits infrared and ultraviolet energy. When either of these radiations is accentuated, the lamp may be used as a source of that energy but with a reduction in luminous efficacy. The luminous efficacy (formerly called light-source efficiency) is the ratio of the units of light produced (lumens) to the power (watts) required, and is expressed in units of lumens per watt (lm/W).
Industry:Science
A lamp that produces light largely by conversion of ultraviolet energy from a low-pressure mercury arc to visible light. Phosphors, chemicals that absorb radiant energy of a given wavelength and reradiate at longer wavelengths, produce most of the light provided by fluorescent lamps.
Industry:Science
A landscape is considered connected when it has few impediments that restrict the ability of animals to move about, particularly between core areas of habitat. Although natural features such as steep canyons can also restrict animal movement, scientists are increasingly concerned about the rapid expansion of human-related features and activities such as highways, roads, agricultural fields, and urban areas that impede movement between patches of habitat. Habitat fragmentation is commonly cited as one of the leading causes of the loss of biodiversity because it leads to smaller, more isolated populations that have less genetic diversity and are more likely to become extinct.
Industry:Science
A landslide is the failure and movement of a mass of rock, sediment, soil, or artificial fill under the influence of gravity. Landslides range in volume from tens of cubic meters to tens of cubic kilometers, and they move at rates ranging from millimeters per year to more than 100 meters per second. Landslides are primarily associated with mountainous terrain but also occur in areas of low relief, for example, in roadway and building excavations, mine-waste piles, and river bluffs.
Industry:Science
