Ulm, Battle of (Sept. 25-Oct. 20, 1805) Major victory by France over Austria at Ulm, Bavaria. In August 1805 Austria joined the Anglo-Russian alliance against Napoleon and on September 11 sent 72,000 troops under Baron Karl Mack (1752-1828) into Bavaria, an ally of France. Napoleon, hoping to crush the Austrians before Russian troops could join them, sent his Grand Army of 210,000 French troops across the Rhine River, march¬ ing 18 mi (29 km) a day to reach the Danube River on September 25. After several battles, he encircled the Austrians and forced them into the city of Ulm, where they faced French artillery attacks. Seeing little chance that his troops could hold out until Russian reinforcements arrived, Baron Mack surrendered on October 20 with about 50,000 men.
Ulmanis Vul-ma-nisV, Karlis (b. Sept. 4, 1877, Berze, Latvia, Russian Empire—d. 1942) Latvian independence leader and premier of Latvia (1918, 1919-21, 1925-26,1931-32,1934-40). An agronomist, he worked to improve farming in Latvia while becoming active in the Latvian inde¬ pendence movement. In 1905 he was forced into exile to the U.S., where he taught agriculture at the University of Nebraska until 1913. Returning to Latvia, he founded the Latvian Farmers’ Union (1917) to press for independence from Russia. In 1918 he became premier of the newly inde¬ pendent republic. In his various terms of office he worked to resist inter¬ nal dissension—instituting authoritarian rule in 1934—and military threats from Russia. Soviet occupation forced his resignation in 1940, and he was arrested and deported to Russia, where he died.
Ulster Historical province, northern Ireland. It now forms Northern Ire¬ land and Ulster province of Ireland. The ancient province was home to the Roman Catholic O’Neills (earls of Tyrone), who rebelled against English rule c. 1600. After they fled, most of the land was confiscated by British King James I and settled with Protestant Scots, Welsh, and English. It was further colonized after Cromwellian settlement in the mid-17th century. In the early 20th century its opposition to Irish Home Rule led to the formation of Northern Ireland.
Ulster cycle or Ulaid Vu-l3th y , 'u-log y \ cycle In early Irish literature, a group of legends and tales dealing with the heroic age of the Ulaid, a people of northeast Ireland from whom the modern name Ulster derives. The stories, set in the 1st century bc, were recorded from oral tradition between the 8th and 11th century and are preserved in the 12th-century manuscripts The Book of the Dun Cow and The Book of Leinster and later compilations. Reflecting the customs of a free pre-Christian aristocracy, they combine mythological and legendary elements. Among the stories are “Bricriu’s Feast,” containing a beheading game that appeared in medi¬ eval narratives, and “The Tragic Death of the Sons of Usnech,” drama¬ tized in the 20th century by William Butler Yeats and John Millington Synge.
ultra Member of the extreme right (ultraroyalist) wing of the royalist movement in the French Bourbon Restoration (1815-30). The ultras included large landowners, clericalists, and the former emigre nobility. Opposed to the French Revolution’s secular and egalitarian principles, they called for restrictions on the press and greater power for the Catholic church. They controlled the Chamber of Deputies and the cabinet for most of the 1820s, especially during the reign of their leader Charles X. Their policies proved unpopular, and they lost power after 1827; with the July Revolution (1830), the faction ceased to exist.
Ultra Allied intelligence project that, in tapping the very highest-level communications among the armed forces of Germany and Japan, contrib-
© 2006 Encyclopaedia Britannica, Inc.
ultrasonics ► Unamuno I 1961
uted to the Allied victory in World War II. In the early 1930s Polish cryp¬ tographers first broke the code of Germany’s cipher machine Enigma. In 1939 they turned their information over to the Allies, and Britain estab¬ lished the Ultra project at Bletchley Park to intercept and decipher Enigma messages. The Japanese also had a modified version of the Enigma, known as “Purple” by the Americans, who were able to duplicate it well before Pearl Harbor. The intercept of signals helped Allied forces win the Battle of Britain and the battles of the Coral Sea and Midway and led to the destruction of a large part of the German forces following the Allied landing in Normandy.
ultrasonics Vibrational or stress waves in elastic media that have a fre¬ quency above 20 kilohertz, the highest frequency of sound waves that can be detected by the human ear. They can be generated or detected by piezoelectric transducers (see piezoelectricity). High-power ultrasonics pro¬ duce distortion in a medium; applications include ultrasonic welding, drilling, irradiation of fluid suspensions (as in wine clarification), clean¬ ing of surfaces (such as jewelry), and disruption of biological structures. Low-power ultrasonic waves do not cause distortions; uses include sonar, structure testing, and medical imaging and diagnosis. Some animals, including bats, employ ultrasonic echolocation for navigation.
ultrasound or ultrasonography Use of ultrasonic waves to pro¬ duce images of body structures. The waves travel through tissues and are reflected back where density differs (e.g., the border between a hollow organ’s wall and its inside). The reflected echoes are received by an elec¬ tronic apparatus that measures their intensity level and the position of the tissue reflecting them. The results can be displayed as still images or as a moving picture of the inside of the body. Unlike X-rays or other ionizing radiation, ultrasound carries minimal, if any, risk. Most often used during pregnancy to examine the fetus, ultrasound imaging is also used on internal organs and on the eye, breast, and major blood vessels. It can often show whether a growth is benign or malignant. See also diagnostic imaging.
ultraviolet astronomy Study of astronomical objects and phenom¬ ena by observing the ultraviolet radiation (UV radiation) they emit. It has yielded much information about chemical abundances and processes in interstellar matter, the Sun, and other stellar objects, such as hot young stars and white dwarf stars. Ultraviolet astronomy became feasible once rockets could carry instruments above Earth’s atmosphere, which absorbs most electromagnetic radiation of UV wavelengths. Since the early 1960s, a number of unmanned space observatories carrying UV telescopes, including the Hubble Space Telescope, have collected UV data on objects such as comets, quasars, NEBUiAe, and distant star clusters. The Extreme Ultraviolet Explorer, launched in 1992, was the first orbiting observatory to map the sky in the shortest UV wavelengths, at the boundary with the X-ray region of the electromagnetic spectrum.
ultraviolet radiation Portion of the electromagnetic spectrum extend¬ ing from the violet end of visible light to the X-ray region. Ultraviolet (UV) radiation lies between wavelengths of about 400 nanometres and 10 nanometres, corresponding to frequencies of 7.5 x 10 14 Hz to 3 x 10 16 Hz. Most UV rays from the Sun are absorbed by the Earth’s ozone layer. UV has low penetrating power, so its effects on humans are limited to the skin. These effects include stimulation of production of vitamin D, sun¬ burn, suntan, aging signs, and carcinogenic changes. UV radiation is also used to treat jaundice in newborns, to sterilize equipment, and to produce artificial light.
Ulysses See Odysseus
( Umar ibn al-Khattab Vu-mar- 1 ib-nul-kat- , tab\ (b. c. ad 586, Mecca, Arabian Peninsula—d. Nov. 3, 644, Medina) Second Muslim caliph (634- 644). He initially opposed the Prophet Muhammad but became a Muslim c. 615. His daughter Hafsah married Muhammad in 625. He was nomi¬ nated by Abu Bakr as his successor. As caliph he spread Islam to Egypt, Syria, and Persia. His innovations affected taxation, social welfare, and the empire’s entire financial and administrative fabric, and he was noted for his justice, social ideals, and candour.