tunicate Vtu-ni-kotV Any of some 2,000 species (chordate subphylum Tunicata, or Urochordata) of small marine invertebrates that are abundant worldwide. Tunicates are either sessile (permanently attached), free- swimming, or planktonic (floating). The name tunicate derives from a secreted protective covering (the tunic) containing cellulose. Floating spe¬ cies often form colonies that may be 13 ft (4 m) long. Some free- swimming species are too small to see. Adults filter feed on microorganisms. Sessile forms growing on ships’ hulls may be a nuisance, but some species are pharmaceutically useful. See also sea squirt.
tuning and temperament In music, the adjustment of one sound source, such as a voice or string, to produce a desired pitch in relation to a given pitch, and the modification of that tuning to lessen dissonance. Tuning assures a good sound for a given pair of tones; temperament com¬ promises the tuning to assure a good sound for any and all pairs of tones. Two vibrating strings sound best together if the ratio between their lengths can be expressed by two small whole numbers. If two strings vibrate in a ratio of 2:1, the vibrations will always coincide and so reinforce each other. But if they vibrate in a ratio of 197:100 (very close to 2:1), they will cancel each other out three times per second, creating audible “beats.” These beats are what make something sound “out of tune.” Since a tone produced by one ratio will not necessarily agree with the same tone cre¬ ated by repeatedly applying another ratio, either some intervals must be mistuned to allow for the perfect tuning of others or all intervals must be slightly mistuned. Before 1700, several systems were used based on the former compromise, including “just intonation”; since then, the compro¬ mise known as “equal temperament,” in which the ratios represented by each pair of adjacent notes are identical, has prevailed.
Tunis Vtu-nosV City (pop., 2004: 728,453), capital of Tunisia. It is situated on Tunis Lake, an inlet of the Gulf of Tunis; its port, La Goulette (Halq al-Wadl), is 6 mi (10 km) to the northeast. Founded by Libyans, it was later a small town under Carthage; it became important after the Muslim conquest in the 7th century ad. It was a religious centre during the Aghla- bid dynasty (9th century) and reached its greatest prosperity under the Hafsid dynasty (13th century). The Spanish and Ottomans controlled it during the 16th century, and it was occupied by the Germans in 1942. It was made the national capital when Tunisia gained independence from France in 1956. It produces textiles, carpets, and olive oil and has met¬ allurgical industries. Tourism is also important. The city’s historic centre was designated a UNESCO World Heritage site in 1979.
Tunisia \tii-'ne-zh9\ officially Tunisian Republic Country, North Africa. Area: 63,170 sq mi (163,610 sq km). Population (2005 est.): 10,038,000. Capitaclass="underline" Tunis. The population is of Arab and Berber (Amazigh) ancestry. Languages: Arabic (official), French. Religion: Islam (official; predominantly Sunni). Currency: Tunisian dinar. Tunisia com¬ prises a coastal region, mountains, an extensive hilly steppe, a marshy area with shallow salt lakes, and a tract of the Sahara. The Majardah is its longest (about 290 mi [460 km]) and only perennial river. Tunisia con¬ tains some of the largest phosphate and natural gas reserves in Africa, as well as substantial oil reserves. Major economic activities are services, agriculture, light industries, and the production and export of petroleum and phosphates. Tourism, focusing on Tunisia’s beaches and Roman ruins, is also important. Tunisia is a republic with one legislative house; its chief
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of state is the president, and the head of government is the prime minister. From the 12th century bc the Phoenicians had a series of trading posts on the North African coast. By the 6th century bc the Carthagin¬ ian kingdom encompassed most of present-day Tunisia. The Romans ruled from 146 bc. It was part of the Byzantine Empire until the Muslim Arab invasions in the mid-7th century ad. The area was fought over, won, and lost by many, including the ‘Abbasid dynasty, the Almohad dynasty, Spain, and the Ottoman Empire, which conquered it in 1574 and held it until the late 19th century. For a time it maintained autonomy as the French, Brit¬ ish, and Italians contended for the region. In 1881 it became a French protectorate. During World War II (1939-45) U.S. and British forces cap¬ tured it (1943), putting an end to a brief German occupation. France granted it full independence in 1956; Habib Bourguiba assumed power and remained in power until he was forced from office in 1987. His succes¬ sor, Zine al-Abidine Ben Ali, continued his authoritarian-style rule.
tunnel Horizontal or nearly horizontal underground or underwater pas¬ sageway. Tunnels are used for mining, as passageways for trains and motor vehicles, for diverting rivers around damsites, for housing under¬ ground installations such as power plants, and for conducting water. Ancient civilizations used tunnels to carry water for irrigation and drink¬ ing, and in the 22nd century bc the Babylonians built a tunnel for pedes¬ trian traffic under the Euphrates River. The Romans built aqueduct tunnels through mountains by heating the rock face with fire and rapidly cooling it with water, causing the rock to crack. The introduction of gunpowder blasting in the 17th century marked a great advance in solid-rock exca¬ vation. For softer soils, excavation is accomplished using devices such as the tunneling mole, with its rotating wheel that continuously excavates material and loads it onto a conveyor belt. Railroad transportation in the 19th-20th century led to a tremendous expansion in the number and length of tunnels. Brick and stone were used for support in early tunnels, but in modern tunneling steel is generally used until a concrete lining can be installed. A common method of lining involves spraying shotcrete onto the tunnel crown immediately after excavation.
tunneling or barrier penetration In physics, the passage of a par¬ ticle through a seemingly impassable energy barrier. Though a particle’s energy may be too low to surmount a barrier in classical physics, the par¬ ticle may still cross the barrier as a consequence of its quantum- mechanical wave properties. An important application of this phenomenon is in the operation of the scanning tunneling microscope.
Tunney, Gene orig. James Joseph Tunney (b. May 25, 1898, New York, N.Y., U.S.—d. Nov. 7, 1978, Greenwich, Conn.) U.S. boxer. Tunney boxed in the Marine Corps, earning the nickname “the Fighting
© 2006 Encyclopaedia Britannica, Inc.
Tupac Amaru ► turbot I 1949
Marine.” He defeated Jack Dempsey in 1926 to become the world heavy¬ weight champion. In a controversial rematch in Chicago in 1927, Demp¬ sey knocked Tunney to the canvas in the seventh round but failed to retire immediately to a neutral corner, thus delaying the count; the “long count” allowed Tunney to rise and win the 10-round fight. He retired the next year with a record of 65 wins in 77 bouts.
Tupac Amaru Uii-'pak-a-'mar-iA Peruvian revolutionary group. Founded in 1983, the group is best known for holding 490 people hos¬ tage in the Japanese embassy in Lima (1996) in an effort to gain the release of jailed comrades. After a standoff of several weeks, Peruvian troops stormed the embassy and killed all the guerrillas. Defections have appar¬ ently since decreased its membership. The group takes its name from the Indian revolutionary Tupac Amaru II (orig. Jose Gabriel Condorcanqui, 17427-81), who in 1780 led Peruvian Indian peasants in the last wide¬ spread rebellion against Spain before independence. The Indians identi¬ fied him with his ancestor Tupac Amaru, the last leader of the Inca, who was executed by the Spaniards in 1572.