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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.
The term “nebula” was originally used to refer to any fixed, extended, and usually fuzzy luminous celestial object. With increased angular resolution of telescopes, astronomers learned that nebulae can be separated into two classes: those that are stellar systems made up of individual stars, and those that are gaseous in nature and diffuse in appearance. Examples of stellar systems include galaxies (which contain billions of stars and are located outside our own Milky Way Galaxy) and star clusters such as open clusters and globular clusters (which contain thousands of stars and are within the Milky Way Galaxy). This article is restricted to the modern definition of nebulae, which are gaseous objects usually located within the Milky Way Galaxy, although with increasingly powerful telescopes gaseous nebulae can now be observed in external galaxies.
Industry:Science
The migration of electrically charged particles in solution or suspension in the presence of an applied electric field. Each particle moves toward the electrode of opposite electrical polarity. For a given set of solution conditions, the velocity with which a particle moves divided by the magnitude of the electric field is a characteristic number called the electrophoretic mobility. The electrophoretic mobility is directly proportional to the magnitude of the charge on the particle, and is inversely proportional to the size of the particle. An electrophoresis experiment may be either analytical, in which case the objective is to measure the magnitude of the electrophoretic mobility, or preparative, in which case the objective is to separate various species which differ in their electrophoretic mobilities under the experimental solution conditions.
Industry:Science
The term first applied to a particular, highly colloidal plastic clay found near Fort Benton in the Cretaceous beds of Wyoming. This clay swells to several times its original volume when placed in water and forms thixotropic gels when small amounts are added to water. Later investigations showed that this clay was formed by the alteration of volcanic ash in place; thus, the term bentonite was redefined by geologists to limit it to highly colloidal and plastic clay materials composed largely of montmorillonite clay minerals, and produced by the alteration of volcanic ash in place. Many mineralogists and geologists now use the term bentonite without reference to the physical properties of the clay. On the other hand, the term has been used commercially for any plastic, colloidal, and swelling clays without reference to a particular mode of origin.
Industry:Science
The natural range of the Atlantic salmon (<i>Salmo salar</i>) stretches from Portugal and the northern coast of New England in the United States northward to subarctic Norway, Russia, and Canada. Salmon are anadromous, whereby they breed in freshwater but migrate to sea to feed. Within their range, adult salmon spawn in cool and well-oxygenated streams. Juveniles spend 1–5 years in freshwater before transforming into silvered smolts. At this stage they migrate to sea, following ocean currents to feeding grounds in the Atlantic. Once in the sea, salmon grow rapidly, feeding on small fish and crustaceans. After 1–3 more years, the fish reach sexual maturity and migrate with great accuracy to their natal rivers, often spawning in the same tributary where they were born. As a result, salmon stocks have evolved into genetically distinct local populations.
Industry:Science
The sense of position and movement of the limbs and the sense of muscular tension. The awareness of the orientation of the body in space and the direction, extent, and rate of movement of the limbs depend in part upon information derived from sensory receptors in the joints, tendons, and muscles. Information from these receptors, called proprioceptors, is normally integrated with that arising from vestibular receptors (which signal gravitational acceleration and changes in velocity of movements of the head), as well as from visual, auditory, and tactile receptors. Sensory information from certain proprioceptors, particularly those in muscles and tendons, need not reach consciousness, but can be used by the motor system as feedback to guide postural adjustments and control of well-practiced or semiautomatic movements such as those involved in walking.
Industry:Science
The study of chemical phenomena occurring above 500 K (440°F). High temperatures represent one of the important variables available to scientists for increasing the variety of possible chemical reactions over that expected for classical ground-state atoms and molecules. One can enhance the relative population of excited rotational, vibrational, and electronic states by increasing the temperature and thus effectively create new species and new mechanisms for reaction. The potentialities of this approach are well illustrated by the three laws of high-temperature chemistry: (1) At high temperatures everything reacts with everything. (2) The higher the temperature, the faster the reaction. (3) The products may be anything. With an infinity of species available at high temperatures, the “golden age” of chemical synthesis is probably still in the future.
Industry:Science
The regulatory effect of light on plant form, involving the growth, development, and differentiation of cells, tissues, and organs. Morphogenic influences of light on plant form are quite different from the light effects that nourish the plant through photosynthesis because the former usually occur at much lower energy levels than are necessary for photosynthesis. Whereas photosynthetic processes are energy-transducing, converting light energy into chemical energy for running the machinery of the plant, light serves only as a trigger in photomorphogenesis, frequently resulting in energy expenditures that are orders of magnitude larger than the amount required to induce a given response. Photomorphogenic processes determine the nature and direction of a plant's growth and thus play a key role in its ecological adaptations to various environmental changes.
Industry:Science
The study of both experimental and theoretical consequences of mendelian heredity on the population level, in contradistinction to classical genetics which deals with the offspring of specified parents on the familial level. The genetics of populations studies the frequencies of genes, genotypes, and phenotypes, and the mating systems. It also studies the forces that may alter the genetic composition of a population in time, such as recurrent mutation, migration, and intermixture between groups, selection resulting from genotypic differential fertility, and the random changes incurred by the sampling process in reproduction from generation to generation. This type of study contributes to an understanding of the elementary step in biological evolution. The principles of population genetics may be applied to plants and to other animals as well as humans.
Industry:Science
The name given to a group of African and Asian hoofed ruminants of the order Artiodactyla. The 91 species in 31 genera are classified in five sub-families (Bovinae, Cephalophinae, Hippotraginae, Antilopinae, and Caprinae) in the family Bovidae. This group includes the bongos and kudus (<i>Tragelaphus</i>), elands (<i>Taurotragus</i>), duikers (<i>Cephalophus</i> and <i>Sylvicapra</i>), waterbucks (<i>Kobus</i>), reedbucks (<i>Redunca</i>), roan and sable antelopes (<i>Hippotragus</i>), oryx (<i>Oryx</i>), wildebeests or gnus (<i>Connochaetes</i>), impalas (<i>Aepyceros</i>), blackbucks (<i>Antilope</i>), gerenuks (<i>Litocranius</i>), gazelles (<i>Gazella</i>), and springbucks (<i>Antidorcas</i>). One genus (<i>Pseudonovibos</i>) was described only on the basis of a series of 14 horns from Cambodia and Viet Nam; the living animal has never been seen by scientists.
Industry:Science
The period in mammals during which the female ovulates and is receptive to mating. It is commonly referred to as rut or heat. From one estrus period to the next there occurs a series of changes, particularly in the ovary, uterus, and vagina, termed the estrous cycle. With reference to the ovary, the cycle can be divided into a follicular phase, during which the Graffian follicles are ripening, and a luteal phase, during which the corpora lutea develop in the ovulated follicles. During these two phases mainly estrogen and progesterone, respectively, are secreted, and these hormones control the uterine and vaginal changes. The beginning of the follicular phase is termed proestrus and the luteal phase metestrus. Following the latter, there is a period of relatively little change, termed diestrus. In species in which the latter is prolonged, it is termed anestrus.
Industry:Science
