equation involving only sums, products, and powers in which all the constants are integers and the only solutions of interest are integers. For example, 3x + 7y = 1 or x2 − y2 = z3, where x, y, and z are integers. Named in honour of the 3rd-century ...
common silicate mineral in the pyroxene family that occurs in metamorphosed siliceous limestones and dolomites and in skarns (contact-metamorphic rocks rich in iron); it is also found in small amounts in many chondrite meteorites. Clear specimens of good green colour ...
in optics, unit of magnifying power of a lens or lens system. Because the power of a lens is proportional to unity (one) divided by the focal length (see lens), the power of a lens in diopters is numerically equal ...
three-dimensional exhibit, frequently housed in a cubicle and viewed through an aperture. It usually consists of a flat or curved back cloth on which a scenic painting or photograph is mounted. Flat or solid objects are placed in front of ...
medium- to coarse-grained intrusive igneous rock that commonly is composed of about two-thirds plagioclase feldspar and one-third dark-coloured minerals, such as hornblende or biotite. The presence of sodium-rich feldspar, oligoclase or andesine, in contrast to calcium-rich plagioclase, labradorite or bytownite, ...
the yam family of the flowering plant order Liliales, consisting of 6 genera with more than 500 species of herbaceous or woody vines and shrubs, distributed throughout tropical and warm temperate regions. Members of the family have thick, sometimes woody ...
Greek physician and pharmacologist whose work De materia medica was the foremost classical source of modern botanical terminology and the leading pharmacological text for 16 centuries.
patriarch of Alexandria and Eastern prelate whose subscription to the unorthodox beliefs of the Monophysites caused him to be deposed and excommunicated by the Council of Chalcedon in 451. He was archdeacon at Alexandria when he succeeded St. Cyril as ...
in Greek and Roman mythology, twin deities who succoured shipwrecked sailors and received sacrifices for favourable winds. They were the children of Leda and either Zeus, the king of the gods, or Tyndareus, Leda's husband. According to some versions, Castor ...
genus of over 400 species of trees and shrubs of the ebony family (Ebenaceae), either deciduous or evergreen, most of which are native to the tropics. The usually alternate leaves are entire (i.e., smooth-edged). The fruit is a large juicy ...
town, western Senegal, about 90 miles (145 km) east of Dakar. The market for a peanut- (groundnut-) growing area, Diourbel produces peanut oil as well as beverages and perfume. The town is the site of a beautiful mosque. Pop. (1985 ...
any of a group of chemical compounds that is an undesirable by-product in the manufacture of herbicides, disinfectants, and other agents. In popular terminology, dioxin has become a synonym for one specific dioxin, 2,3,7,8-tetrachlorodibenzo-p-dioxin (2,3,7,8-TCDD).
(Pali: "History of the Island"), oldest extant historical record of Sri Lanka, compiled in the 4th century. It is considered to be one of the main sources drawn upon by the author of the later and more comprehensive historical chronicle ...
synthetic drug used in the treatment of various conditions including hay fever, acute skin reactions (such as hives), contact dermatitis (such as from poison ivy), and motion sickness. Diphenhydramine counteracts the histamine reaction. Introduced into medicine in 1945 and marketed ...
in chemical warfare, poison gas widely used by Germany during World War I. Its chemical name is trichloromethyl chloroformate, and it is a colourless, moderately persistent, poisonous, organic compound, the odour of which is likened to that of newly mown ...
acute infectious disease caused by the bacillus Corynebacterium diphtheriae and characterized by a primary lesion, usually in the upper respiratory tract, and more generalized symptoms resulting from the spread of the bacterial toxin throughout the body. Diphtheria was a serious ...
in phonetics, a gliding vowel in the articulation of which there is a continuous transition from one position to another. Diphthongs are to be contrasted in this respect with so-called pure vowels-i.e., unchanging, or steady state, vowels. Though they are ...
gigantic dinosaurs found in North America as fossils from the Late Jurassic Period (159 million to 144 million years ago). Diplodocus is perhaps the most commonly displayed dinosaur. It, along with sauropods such as Apatosaurus (formerly Brontosaurus), belong to a ...
genus of graptolites, small, extinct colonial marine animals thought to be related to the primitive chordates and restricted to ancient marine environments. Forms or species of Diplograptus are useful index, or guide, fossils for the Ordovician period (which occurred from ...
the established method of influencing the decisions and behaviour of foreign governments and peoples through dialogue, negotiation, and other measures short of war or violence. Modern diplomatic practices are a product of the post-Renaissance European state system. Historically, diplomacy meant ...
in international law, the immunities enjoyed by foreign states or international organizations and their official representatives from the jurisdiction of the country in which they are present.
the study of documents. The term is derived from the Greek word diploma, meaning "doubled" or "folded." Besides the documents of legal and administrative import withwhich it is properly concerned, diplomatics also includes the study of other records such as ...
any member of the protozoan order Diplomonadida. Diplomonads are small zooflagellates that inhabit the digestive systems of various animals, including termites, rats, and humans. They typically have two nuclei, each associated with four flagella. Feeding is by digestion or absorption. ...
genus of extinct amphibians of North America and Europe known from fossils in Late Carboniferous rocks (from 320 to 286 million years ago). Diplovertebron represents a late surviving form of the anthracosaurs, a group of primitive amphibians that probably included ...
group of small primitive wingless insects (about 400 species) of the subclass Apterygota. Some entomologists consider many of their features similar to those associated with ancestral insects. Diplurans are blind, pale insects that live in soil and feed on decaying ...
Javanese leader in the 19th-century conflict known to the West as the Java War and to Indonesians as Dipo Negoro's War (1825-30). During those five years Dipo Negoro's military accomplishments severely crippled the Dutch and earned for him a prominent ...
in classical prosody, a pair of metrical feet that is taken as a single unit. Trochaic, iambic, and anapestic verse are all measured by dipodies. In them a monometer consists of one dipody (or two feet), a dimeter of four ...
theory that the Earth's magnetic field is produced or is best represented by a magnetic dipole, a body having poles of opposite sign, that is, positive and negative. In the first quantitative study made of the Earth's magnetic field, William ...
city, western Mindanao, Philippines. Dipolog is a fishing and interisland shipping port. There is also a commercial airport. Its city status dates from 1969; it had been a municipality since 1913 and, before that, had been considered an outer adjunct ...
any of four species of songbirds of the Cinclidae family (order Passeriformes) noted for insect hunting by walking underwater in rushing streams and named for their frequent body bobbing.
family of extinct marsupial mammals that existed from the Late Oligocene epoch into the Pleistocene epoch (from 30 million to roughly 10,000 years ago) in Australia. It included Diprotodon, which was the largest known marsupial (3.5 m [11 feet] long). ...
the teasel order of flowering plants, belonging to the class known as dicotyledon (q.v.; characterized by two seed leaves). It comprises 40 genera and about 1,100 species in four families and is distributed throughout the world, but is centred mainly ...
a serpent with a bite said to produce intense thirst. The snake was the subject of a story told by several Greek authors, including Sophocles. According to the legend, Zeus was grateful to those who revealed to him the identity ...
any member of the insect order Diptera, the two-winged or so-called true flies. Although many winged insects are commonly called flies, the name is strictly applicable only to members of Diptera. One of the largest insect orders, it numbers more ...
a member of the insect order Diptera, the two-winged or "true" flies. This order contains over 85,000 species divided into three suborders: the Nematocera (midges, gnats, mosquitoes, crane flies), the Brachycera (horse flies, bee flies, robber flies), and the Cyclorrhapha ...
family of South Asian and African timber trees, in the tea order (Theales), comprising 22 genera. Most of the species are lofty trees with leathery, evergreen leaves and aromatic resins. Their clustered, fragrant flowers have five twisted, leathery petals. Dipterocarpus ...
genus of very primitive lungfish, among the earliest known, found as fossils in European and North American Devonian rocks (the Devonian Period lasted from 408 to 360 million years ago). Very similar to the crossopterygians, the lobe-finned fishes that gave ...
town and district of Malakand division, North-West Frontier Province, Pakistan. The town, the district headquarters, lies just north of the Dir River, an affluent of the Panjkora, and is connected by road with Malakand, 70 mi (110 km) south. Mulla ...
(1818), major defeat dealt the Wahhabis, fanatical and puritanical Muslim reformers of Najd, central Arabia, by the forces of the Egyptian ruler Muhammad 'Ali Pasha; the Wahhabi empire was destroyed, and the Sa'udi family that created it was virtually wiped ...
English theoretical physicist who was one of the founders of quantum mechanics and quantum electrodynamics. Dirac is most famous for his 1928 relativistic quantum theory of the electron and his prediction of the existence of antiparticles. In 1933 he shared ...
town, east-central Ethiopia, located on the eastern edge of the East African Rift Valley, 30 miles (48 km) northwest of Harer. It lies at the intersection of roads from Addis Ababa, Harer, and Djibouti and has an airport. Dire Dawa, ...
British rock band whose supple, slightly blues-tinged guitar rock was popular in the late 1970s and '80s. The original members were Mark Knopfler (b. Aug. 12, 1949, Glasgow, Scot., ), David Knopfler (b. Dec. 27, 1952, Glasgow, ), John Illsley ...
(species Canis dirus), wolf that existed during the Pleistocene Epoch (1,600,000 to 10,000 years ago). It is probably the most common mammalian species to be found preserved in the La Brea Tar Pits in southern California. The dire wolf differed ...
