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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.
Genetic, paleontological, and archeological data indicate that modern humans evolved in Africa and then spread to other parts of the world. Genetic data, primarily from mitochondrial deoxyribonucleic acid (mtDNA) and Y chromosomes, firmly place the exodus from Africa between 65,000 and 50,000 years before present (BP). Archeology adds crucial evidence that humans reached northern Australia by 55,000–50,000 BP. The earliest human fossils from Australia come from Lake Mungo in the southeast and date to 45,000 BP. Y chromosomes and mtDNA indicate an early rapid movement from Africa to Australia, probably along the coastline of the Indian Ocean. Genetic, archeological, and fossil evidence shows that modern humans occupied the rest of Eurasia between 50,000 and 30,000 BP. In Africa, fossils indicate that modern humans evolved gradually from archaic ancestors often described as <i>Homo heidelbergensis, Homo helmei</i>, or more generally “archaic <i>Homo sapiens</i>.” This process began by 400,000 BP and resulted in the emergence of anatomically modern people in Africa by 195,000–150,000 BP.
Industry:Science
Analytical techniques that involve the addition to a sample of an isotopically labeled compound. Soon after the discovery of the stable heavy isotopes of hydrogen, carbon, nitrogen, and oxygen, their value in analytical chemistry was recognized. Stable isotopes were particularly useful in the analysis of complex mixtures of organic compounds where the isolation of the desired compound with satisfactory purity was difficult and effected only with low or uncertain yields.
The addition of a known concentration of an isotopically labeled compound to a sample immediately produces isotope dilution if the particular compound is present in the sample. After thorough mixing of the isotopically labeled compound with the sample, any technique that determines the extent of the isotopic dilution suffices to establish the original concentration of the compound in the mixture. Isotope dilution techniques exploit the difficulty in the separation of isotopes, with the isotopically labeled “spike” following the analytically targeted compound through a variety of separation procedures prior to isotopic analysis.
Industry:Science
Concise, graphical symbolism whereby the engineer communicates to others the functional relationship of the parts in a component and, in turn, of the components in a system. The symbols do not attempt to describe in complete detail the characteristics or physical form of the elements, but they do suggest the functional form which the ensemble of elements will take in satisfying the functional requirements of the component. They are different from a block diagram in that schematics describe more specifically the physical process by which the functional specifications of a block diagram are satisfied. Rather than expressing a mathematical relationship between, for example, an input and an output variable as in a block diagram, a schematic illustrates the physical principles and techniques by which the mathematical requirements of the element are realized. For instance, the schematic indicates whether electrical, hydraulic, mechanical, or pneumatic techniques are employed, and suitable symbols indicate the appropriate elements, such as batteries, resistors, valves, gearing, vacuum tubes, and motors.
Industry:Science
In 1995 the Advanced Photon Source at Argonne National Laboratory near Chicago, Illinois, ended a 5-year construction program and began providing insertion-device and bending-magnet radiation in the hard x-ray spectral region for research on the structure and composition of matter. Users of the Advanced Photon Source include scientists from universities, industry, and federal laboratories. They apply advanced synchrotron x-ray technology to experiments in materials science; biological science; chemical science; agricultural science; environmental science; geoscience; atomic, molecular, and optical physics; and the development of novel synchrotron x-ray instrumentation. The Advanced Photon Source belongs to the class of third-generation synchrotron light sources, which also includes the Advanced Light Source in California, the European Synchrotron Radiation Facility in France, and the 8-GeV Super Photon Ring in Japan. All of these facilities afford new opportunities for research by extending those characteristics that make synchrotron-based x-ray beams highly useful to a broad spectrum of disciplines.
Industry:Science
Atomic nuclei consist of neutrons and protons bound by the strong force. Guided by the quantum-mechanical nature of the nuclear many-body system—driven, for example, by the Pauli exclusion principle and the concept of isospin—the attraction between a neutron and a proton is stronger than the attraction between two protons or between two neutrons. As a consequence, most stable, light nuclei are composed of equal numbers of protons and neutrons. Starting at about calcium (20 protons), the Coulomb repulsion between the positively charged protons reduces the binding of the nuclear system so that the most stable isotopes of an element have more neutrons than protons. Of the 3000 nuclei that have been produced in laboratories, only about 300 are stable. The other nuclei are short-lived and prone to decay until a stable nucleus is reached. The study of these so-called exotic nuclei that often exist only for fractions of a second has proven crucial for the understanding of the nuclear force and continues to provide important input for nuclear astrophysics in the quest to explain the isotopic composition of the universe.
Industry:Science
Developments in integrated circuits and storage devices used in computers have proceeded at an exponential rate: at present it takes 2–3 years for each successive halving of the component size. Information storage has followed a similar trend in miniaturization of the size of the bits of magnetized material used in hard disks. However, these technologies have fundamental limits, below which the devices no longer function in a predictable manner. For instance, the oxide layers used in complementary metal oxide semiconductor (CMOS) devices are becoming so thin that they conduct electricity in a quantum-mechanical manner by electron tunneling. In 1998 it was estimated that microelectronics and magnetic storage technologies would reach their ultimate limits within 10–30 years. Projections for very large scale integration (VLSI) predict that a single chip will accommodate 90 million transistors with a feature size of 70 nanometers and a clock speed of 900 MHz by the year 2010. Currently, many critical dimensions in semiconductor devices are in the 100-nm range, with some insulating layers being tens of nanometers thick.
Industry:Science
Biological materials have exceptional mechanical properties in comparison to synthetic or engineered materials. Wood has a strength (the ability to carry a load) per unit weight that is comparable to that of the strongest steels. Seashell, bone, antler, and keratin have a toughness (the ability to resist fracture) more than 10 times greater than engineering ceramics. And mature bamboo stalks or culms have slenderness ratios (the ratio of length to diameter) that are remarkable even by standards of modern engineering. Natural materials are optimized to fulfill the complex biological and mechanical requirements posed by the way plants and animals function. Frequently, these requirements are mechanical in nature. For example, tree trunks and branches as well as animal legs and wings support or propel the organism. In doing so, their structural materials (wood and bone) are highly stressed. Beyond this, living natural materials are unique in that they can self-repair and adapt to changes during their lifetime (bone) or during the cycle of a year (wood), modifying their properties according to the requirements placed on them.
Industry:Science
Apoptosis is a form of programmed cell death in which cells play an active role in their own death, ensuring that they die in a controlled and regulated manner with little disruption to the surrounding cells. Apoptosis allows unwanted cells (for example, damaged or virus-infected cells) to be efficiently removed from the body. It plays important roles in a variety of biological processes, including embryo development, the immune system, and cancer prevention.
Cells undergo apoptosis in response to a wide variety of stimuli, both internal and external. Internal signals include DNA damage, cytoplasmic stress, and nutrient deprivation. By contrast, external signals can induce apoptosis by interacting with a class of cell surface receptors known as death receptors. The death receptors bind a variety of ligands known collectively as the death-inducing ligands, which can exist either as soluble, secreted proteins or as membrane-bound proteins on the surface of cells such as T lymphocytes. The binding of these ligands to the death receptors allows the apoptotic signal to be transmitted to the cell, triggering the onset of apoptosis.
Industry:Science
In 1990, the first indication for the existence of nucleic acid sequence guided gene silencing came from scientists who were introducing additional copies of a gene responsible for the darkening of flower color into the <i>Petunia</i> genome. In addition to creating darker flowers, the insertion of multiple copies of the gene created white flowers or flowers with patches of white mixed with patches of color (variegated). The white and variegated plants had recognized the newly introduced transgenes as foreign and marked them as well as the endogenous homologous gene for silencing—a process that became known as cosuppression.
Subsequent experiments showed that ribonucleic acid (RNA) transcribed from the transgenes was the silencing trigger. Andrew Fire and colleagues discovered in 1998 that injection of double-stranded RNA (dsRNA) into the nematode worm <i>Caenorhabditis elegans</i> caused sequence-specific degradation of cytoplasmic messenger RNAs (mRNAs) containing the same sequence as the dsRNA trigger. This phenomenon was termed RNA interference (RNAi), and was soon related to the cosuppression events described earlier in plants.
Industry:Science
Combinations of gold and other metals. Gold is not oxidized in air, and for thousands of years was the only metal available that remained bright indefinitely. This, coupled with its pleasing yellow color, made it cherished for personal adornment and other decorative uses and valuable as a medium of exchange. The high specific gravity of gold (19.3) also gave some insurance against dilution with cheaper metals of lower density. Pure gold is soft. The addition of copper hardens the gold, and ultimately gold-copper alloys became standard for coinage. Gold coins in the United States contained 10% copper, the balance gold. Prior to 1934 the value of coinage had been based on the price of gold. In that year coinage of gold ceased in the United States, and gold was priced at a market value. The United States Mint sold gold to licensed users for industrial and ornamental uses from 1934 to March 17, 1968. From this date to January 1, 1975, some banks and one broker were licensed to sell gold, but only to licensed users for industrial and artistic purposes. Since 1975, there have been no restrictions on the buying and selling of gold.
Industry:Science
