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Ahura Mazda Va-hur-o-'maz-doX Supreme god of ancient Iranian reli¬ gion, especially Zoroastrianism. Ahura Mazda was worshiped by Darius I and his successors as the greatest god and the protector of the just king. Zoroaster taught that Ahura Mazda created the universe and maintains the cosmic order, and that the history of the world consists of the battle between two spirits he created—the beneficent Spenta Mainyu and the destructive Angra Mainyu. The Avesta identifies Ahura Mazda himself with the beneficent spirit and represents him as bountiful, all-knowing, and the creator of everything good. In late sources (from the 3rd century), Zurvan (“Time”) is the father of the twins Ormazd (Ahura Mazda) and Ahriman (Angra Mainyu), who in orthodox Mazdaism (Zoroastrianism and Parsiism) reign alternately over the world until Ormazd’s ultimate victory.

Ai \'a-,I\ Town, eastern Canaan, ancient Palestine. In the Bible (Joshua 7-8), it was destroyed by the Israelites under Joshua. Biblical references agree in locating Ai just east of Bethel (modern Bay tin) in the West Bank, at the Early Bronze Age site now called Al-Tall. Excavations at Ai in

1933-35 uncovered a temple of the 3rd millennium bc. The biblical events at Ai are assigned to the period c. 1400-1200 bc, when evidence indicates it was not in fact occupied; early tradition may have identified the Canaan- ite town under Bethel with the nearby ruins of Al-Tall.

Aidan \'ad- 3 n\, Saint (b. Ireland—d. Aug. 31, 651, Bamburgh, Northumberland, Eng.; feast day August 31) Apostle of Northumbria and founder of Lindisfarne. He was a monk at Iona in Scotland when King Oswald of Northumbria requested that he be made bishop of the newly converted Northumbrians. He established his church, see, and monastery on the island of Lindisfarne, not far from the royal stronghold of Bam¬ burgh. From there he evangelized northern England, founding churches, monasteries, and a school. Bede praised him for his learning, charity, and simplicity of life.

aide-de-camp \,ad-di-'kamp\ Officer on the personal staff of a gen¬ eral, admiral, or other high-ranking commander who acts as a confiden¬ tial secretary. Today they are usually of junior rank, and their duties are largely social. The term also denotes a high-ranking military officer who acts as an aide to a chief of state.

AIDS in full acquired immunodeficiency syndrome Transmis¬ sible disease of the immune system caused by HIV. AIDS is the last stage of HIV infection, during which time the individual develops frequently fatal infections and cancers, including Pneumocystis carinii pneumonia, cytomegalovirus (C MV), lymphoma, and Kaposi sarcoma. The first AIDS cases were identified in 1981, HIV was isolated in 1983, and blood tests were developed by 1985. According to the UN’s 2004 report on AIDS, some 38 million people are living with HIV, approximately 5 million people become infected annually, and about 3 million people die each year from AIDS. Some 20 million people have died of the disease since 1981. Sub-Saharan Africa accounts for some 70 percent of all HIV infections. Rates of infection are lower in other parts of the world, but the epidemic is spreading rapidly in eastern Europe, India, South and Southeast Asia, Latin America, and the Caribbean.

Aiken Va-konX, Conrad (Potter) (b. Aug. 5, 1889, Savannah, Ga., U.S.—d. Aug. 17, 1973, Savannah) U.S. writer. Aiken was traumatized as a child when his father killed Aiken’s mother and then himself. Educated at Harvard University, Aiken wrote most of his fiction in the 1920s and ’30s. His works are influenced by early psychoanalytic theory. Generally more successful than his novels were his short stories, notably “Strange Moonlight” from Bring! Bring! (1925) and “Silent Snow, Secret Snow” and “Mr. Arcularis” from Among the Lost People (1934). His best poetry, including “Preludes to Definition,” is in his Collected Poems (1953).

Aiken, Howard H(athaway) (b. March 9, 1900, Hoboken, N.J., U.S.—d. March 14, 1973, St. Louis, Mo.) U.S. mathematician and inven¬ tor. He received his Ph.D. from Harvard University. With three other engineers, he began work in 1939 on an automatic calculating machine that could perform any selected sequence of five arithmetical operations (addition, subtraction, multiplication, division, and reference to previous results) without human intervention. The first such machine, the Harvard Mark I (1944), was 51 ft (15 m) long and 8 ft (2.4 m) high, and weighed 35 tons (31,500 kg).

aikido X.I-ki-'do, I-'ke-doX Japanese art of self-defense. It employs locks and holds and utilizes the principle of nonresistance to cause an oppo¬ nent’s own momentum to work against him or her. Aikido emphasizes the importance of achieving complete mental calm and control of one’s own body to master an opponent’s attack. There are no offensive moves. It traces its origins to Japanese martial (samurai) traditions dating to the 14th century, and it was developed as a modem form in the early 20th century by Ueshiba Morihei. See martial art.

a i la nth us Xa-'lan-thosX Any of the flowering plants that make up the genus Ailanthus, in the quassia family (Simaroubaceae), native to eastern and southern Asia and northern Australia and naturalized in subtropical and temperate regions elsewhere. Ailanthus leaves alternate along the stem and are composed of multiple leaflets arranged along an axis. The most familiar species is the tree of heaven.

Ailey X'a-leX, Alvin, Jr, (b. Jan. 5, 1931, Rogers, Texas, U.S.—d. Dec. 1, 1989, New York, N.Y.) U.S. dancer and choreographer. In 1942 he moved to Los Angeles, where he studied dance and choreography (1949- 54). He then moved to New York, where he performed in various theat¬ rical productions. In 1958 he founded the Alvin Ailey American Dance Theater, composed primarily of blacks. The numerous works he choreo-

© 2006 Encyclopaedia Britannica, Inc.

32 I Ailly ► oir warfare

graphed for the company included its signature Revelations (1960), set to black spirituals. From the 1960s to the 1980s, the company toured worldwide, and Ailey became one of the best-known U.S. choreographers.

Aintab See Gaziantep

air brake Either of two kinds of braking systems. The first, used by trains, trucks, and buses, operates by a piston driven by compressed air from reservoirs connected to brake cylinders (see piston and cylinder). When air pressure in the brake pipe is reduced, air is automatically admit¬ ted into the brake cylinder. The first practical air brake for railroads was invented in the 1860s by George Westinghouse. The second type, used by aircraft and race cars, consists of a flap or surface that can be mechani¬ cally projected into the airstream to increase the resistance of the vehicle to air and lower its speed.

air-conditioning Control of temperature, humidity, purity, and motion of air in an enclosed space, independent of outside conditions. In a self- contained air-conditioning unit, air is heated in a boiler unit or cooled by being blown across a refrigerant-filled coil and then distributed to a con¬ trolled indoor environment. Central air-conditioning in a large building generally consists of a main plant located on the roof or mechanical floor and intermittently spaced air-handling units, or fans that deliver air through ducts to zones within the building. The air then returns to the central air-conditioning machinery through spaces called plenums to be recooled (or reheated) and recirculated. Alternate systems of cooling use chilled water, with water cooled by a refrigerant at a central location and circulated by pumps to units with fans that circulate air locally.

air-cushion vehicle or hovercraft Vehicle supported above the surface of land or water by an air cushion, produced by downwardly directed fans, enclosed within a flexible skirt beneath the hull. The con¬ cept was first proposed by John Thornycroft in the 1870s, but a working model was not produced until 1955, when Christopher Cockerell solved the problem of keeping the air cushion from escaping from under the vehicle, and formed Hovercraft Ltd. to manufacture prototypes. Problems with skirt design and engine maintenance have restricted the vehicle’s commercial application; today hovercraft are used mainly as ferries.