oxygen process, basic See basic oxygen process
Oxyrhynchus \,ak-si-Tiq-k3s\ Archaeological site, Egypt, on the west¬ ern bank of the Nile River. Many ancient papyri dating from 250 bc to ad 700 were discovered there in the late 19th and early 20th centuries. The papyri, written mainly in Greek and Latin, contain both religious texts and masterpieces of Greek classical literature. Some of these texts, once considered lost, were by Pindar and Callimachus. The modem village of Al-Bahnasa is located on the site.
Oyo empire Yoruba state in present-day southwestern Nigeria that dominated the land between the Volta and Niger rivers in 1650-1750. Two waves of immigrants probably entered the area c. ad 700-1000, and the second wave formed a state at Oyo. This state became preeminent among Yoruba states because of its good trading position, natural resources, and industrious inhabitants. Though at first less powerful than its neighbours, by the end of the 16th century its ruler, Orompoto, had used trade-derived wealth to maintain a trained army. In the 18th century Oyo subjugated the Dahomey kingdom and had begun trading with European merchants at Dahomey’s ports. Oyo’s wealth increased, but Abiodun (r. c. 1770- 90) neglected the army and the pos¬ sibilities for territorial expansion, thus weakening central authority for his successor. Soon after 1800 Oyo was captured by Fuiani Muslims from Hausaland. See also Hausa.
oyster Any bivalve of two families,
Ostreidae (true oysters) or Avicul- idae (pearl oysters), found in temper¬ ate and warm coastal waters worldwide. Both valves (halves) have a rough, often dirty-gray outer
surface and a smooth white inner lining (nacre). The lower valve, which affixes to a surface, is nearly flat. The smaller upper valve is convex and has rougher edges. The oyster filters its food, minute organic particles, from the water. Cultivated as food, oysters are regarded as a delicacy. Pearls are the accumulation of nacre around a piece of foreign matter.
oyster plant See salsify
oystercatcher Any of about seven species (genus Haematopus, fam¬ ily Haematopodidae) of stout-bodied shorebirds inhabiting temperate and tropical seacoasts and inland waters in Europe, Asia, Africa, the Western Hemisphere, and Australia. Oystercatchers are 16-20 in. (40-50 cm) long, with thick pinkish legs; long pointed wings; and a long, flattened, wedge- shaped, orange-red bill. Their plumage varies from black-and-white, including a bold white wing patch, to entirely black. They attack mol- lusks as the tide ebbs, when the shells are exposed and still partially open.
Oz, Amos orig. Amos Klausner (b. May 4, 1939, Jerusalem, Israel) Israeli novelist, short-story writer, and essayist. A second-generation Israeli, Oz lived primarily on a kibbutz from the 1950s to the 1980s. He served in the Israeli Army (1957-60, 1967, and 1973) but later became a leading advocate of peace. His symbolic works—including Where the Jackals Howl, and Other Stories (1965); My Michael (1968), perhaps his best-known novel; and Black Box (1987)—reflect the conflicts in Israeli life.
Ozal \o-'zal\, Turgut (b. Oct. 13, 1927, Malatya, Tur.—d. April 17, 1993, Ankara) Prime minister (1983-89) and president (1989-93) of Tur¬ key. After studying electrical engineering, he oversaw Turkey’s electrifi¬ cation program in the 1950s and ’60s. After working as a World Bank economist for most of the 1970s, he was elected prime minister as head of his own Motherland Party in 1983 and was reelected in 1987. In 1989 he persuaded the parliament to make him president, a traditionally non¬ political position, and used the office to claim for Turkey an important role in the Persian Gulf War (1990-91).
Ozark Mountains or Ozark Plateau Heavily forested highlands, south-central U.S. Extending southwest from St. Louis to the Arkansas River, they occupy an area of about 50,000 sq mi (130,000 sq km) in Mis¬ souri, Arkansas, Illinois, and Kansas. Many of the highest peaks exceed 2,000 ft (600 m). Tourism is one of the region’s chief industries. Lake of the Ozarks provides power and recreational facilities. The name Ozark probably derives from the French trading post, Aux Arc, established in the area in the 1700s.
Ozarks, Lake of the Lake, south-central Missouri, U.S. One of the largest man-made lakes in the U.S., it is located in the scenic Ozark Moun¬ tains. It is about 125 mi (200 km) long, with an area of 93 sq mi (242 sq km). It is formed by the Bagnell Dam in the Osage River. The area of Lake of the Ozarks State Park has recreational fishing and water sport facilities and is a popular resort destination. Nearby are several limestone caverns.
Ozawa \o-'za-w3\, Seiji (b. Sept. 1, 1935, Hoten, Manchukuo) Manchurian-born Japanese-U.S. conductor. After initial conducting expe¬ rience in Japan and study at Tanglewood in the U.S., he went to Europe to study with Herbert von Karajan. He became assistant to Leonard Bern¬ stein at the New York Philharmonic (1961-65), then held posts in Chi¬ cago (1964-68), Toronto (1965-69), and San Francisco (1970-76) before becoming music director of the Boston Symphony Orchestra in 1973 (retired 2002). Noted for his energetic style and his sweeping perfor¬ mances of 19th-century Western symphonic works, he also had a distin¬ guished opera-conducting career in Europe.
Ozick \'o-zik\, Cynthia (b. April 17, 1928, New York, N.Y., U.S.) U.S. novelist and short-story writer. She graduated from New York University and received an M.A. from Ohio State University. She wrote often on Jewish themes, and much of her work presents a struggle with the notion that artistic creation can be a hubristic attempt to rival the Creator. Among these works are Trust (1966), Leviathan (1982), The Messiah of Stock¬ holm (1987), The Shawl (1990), and The Puttermesser Papers (1997). Her essays have been collected in Art & Ardor (1983), Metaphor & Memory (1989), and Fame & Folly (1996).
Ozma, Project Attempt in 1960 to detect radio signals generated by hypothetical intelligent beings from planets of other stars. Frank D. Drake (bom 1930), director of the search, named the project for the princess of L. Frank Baum’s imaginary Oz. The search used a special receiver attached to a radio telescope at the U.S. National Radio Astronomy Observatory
© 2006 Encyclopaedia Britannica, Inc.
ozone ► Ozu I 1429
at Green Bank, W.V. Some 150 hours of occasional observation over four months detected no recognizable signals. See also Drake equation, SETI.
ozone Pale blue gas (0 3 ) that is irritating, explosive, and toxic. Like ordinary oxygen gas (0 2 ), it contains oxygen atoms, but the bonding of three atoms per molecule gives it distinctive properties. It is formed in electrical discharges and accounts for the distinctive odour of the air after thunderstorms or near electrical equipment. Usually manufactured on the spot by passing an electric discharge through oxygen or air, it is used in water purification, deodorization, bleaching, and various chemical reac¬ tions that require a strong oxidizing agent (see oxidation-reduction). Small amounts that occur naturally in the stratospheric ozone layer absorb ultra¬ violet (UV) radiation that otherwise could severely damage living organ¬ isms. Near Earth’s surface, ozone contributes to air pollution, ozone produced by auto emissions in the presence of sunlight being a deleteri¬ ous component of smog, and also accelerates the deterioration of rubber.
ozone layer or ozonosphere Region in the upper atmosphere, about 6-30 mi (10-50 km) high, with significant concentrations of ozone, formed by the effect of solar ultraviolet (UV) radiation on oxygen and also present in trace quantities elsewhere in earth’s atmosphere. Ozone strongly absorbs solar UV radiation, causing atmospheric temperature to climb to about 30°F (0°C) at the top of the layer, and preventing much of this radiation from reaching earth’s surface, where it would injure many
living things. Chlorofluorocarbons, or CFCs, and some other air pollut¬ ants that diffuse into the ozone layer destroy ozone. In the mid-1980s, scientists discovered that a “hole”—an area where the ozone is up to 50% thinner than normal—develops periodically in the ozone layer above Ant¬ arctica. This severe regional depletion, explained as a natural seasonal depletion, appears to have been exacerbated by the effects of CFCs, and may have led to an increase in skin cancer caused by UV exposure. Restrictions on the manufacture and use of CFCs and other ozone- destroying pollutants were imposed in 1978.