Black opal from Australia; in the collec¬ tion of the Department of Earth Sci¬ ences, Washington University, St. Louis, Mo.
JOHN H. GERARD
© 2006 Encyclopaedia Britannica, Inc.
operating system ► opium poppy I 1411
recitative began to be clearly distinguished from aria, an achievement that would prove decisive for opera’s future success. In France, Jean-Baptiste Lully produced a prototype for courtly opera that influenced French opera through the mid-18th century. Jean-Philippe Rameau, George Frideric Han¬ del, and Christoph Willibald Gluck were the most significant opera com¬ posers of the first two-thirds of the 18th century; their works were surpassed by the brilliant operas of Wolfgang Amadeus Mozart. In the early 19th century, Gioacchino Rossini and Gaetano Donizetti dominated Italian opera. In the later 19th century the greatest works were those of Giuseppe Verdi and Richard Wagner; the latter, with his bold innovations, became the most influential operatic figure since Monteverdi. Richard Strauss and Giacomo Puccini wrote the most popular late 19th- and early 20th-century operas. Though the death of Puccini in 1924 is often cited as the end of grand opera, new and often experimental works—by com¬ posers such as Alban Berg, Benjamin Britten, Gian Carlo Menotti, John Adams, and Philip Glass —continued to be produced to critical acclaim. Opera entered the 21st century as a vibrant and global art form. See also BALLAD OPERA; OPERETTA.
operating system (OS) Software that controls the operation of a computer, directs the input and output of data, keeps track of files, and controls the processing of computer programs. Its roles include managing the functioning of the computer hardware, running the applications pro¬ grams, serving as an interface between the computer and the user, and allocating computer resources to various functions. When several jobs reside in the computer simultaneously and share resources (multitasking), the OS allocates fixed amounts of CPU time and memory in turn or allows one job to read data while another writes to a printer and still another performs computations. Through a process called time-sharing, a large computer can handle interaction with hundreds of users simultaneously, giving each the perception of being the sole user. Modern computer oper¬ ating systems are becoming increasingly machine-independent, capable of running on any hardware platform; a widely used platform-independent operating system in use today on mainframe computers is UNIX. Most per¬ sonal computers run on Microsoft’s Windows operating system, which grew out of and eventually replaced MS-DOS. See also Linux.
operationalism In the philosophy of science, the attempt to define all scientific concepts in terms of specifically described operations of mea¬ surement and observation. The length of a rod, for example, may be defined as the number of times a certain stick can be laid end to end alongside it. Propositions that are not amenable to verification through measurement and observation are rejected as meaningless (see also logi¬ cal positivism). Operationalists rejected the idea of nature as a thing-in-itself existing behind the appearances observed in experimentation. Operation¬ alism is closely associated with the work of the U.S. physicist Percy W. Bridgman (1882-1961).
operations management See production management
operations research Application of scientific methods to manage¬ ment and administration of military, government, commercial, and indus¬ trial systems. It began during World War II in Britain when teams of scientists worked with the Royal Air Force to improve radar detection of enemy aircraft, leading to coordinated efforts to improve the entire sys¬ tem of early warning, defense, and supply. It is characterized by a sys¬ tems orientation, or systems engineering, in which interdisciplinary research teams adapt scientific methods to large-scale problems that must be modeled, since laboratory testing is impossible. Examples include resource allocation and replacement, inventory control, and scheduling of large-scale construction projects.
operator, differential See differential operator
operetta Musical drama similar to opera, usually with a romantically sentimental plot, employing songs, dances, and orchestral interludes inter¬ spersed with spoken dialogue. The modern tradition begins with Jacques Offenbach, who wrote some 90 operettas and inspired a Viennese tradi¬ tion that began with the works of Franz von Suppe and Johann Strauss. In Britain most of the 14 comic operettas (1871-96) of W.S. Gilbert and Arthur Sullivan have been enduringly popular. In the U.S. the works of such European immigrant composers as Victor Herbert and Rudolf Friml were widely popular in the early 20th century. See also musical.
operon Va-p3r-,an\ Genetic regulatory system of single-celled organ¬ isms (prokaryotes) and their viruses, in which genes coding for function¬ ally related proteins are clustered along the DNA, enabling their
expression to be coordinated in response to the cell’s needs. By provid¬ ing a means to produce proteins only when and where they are required, the operon allows the cell to conserve energy. A typical operon consists of a group of structural genes that code for enzymes involved in a meta¬ bolic pathway, such as the biosynthesis of an amino acid. A single unit of messenger RNA is transcribed from the operon and is then translated into separate proteins. Operons are controlled by various regulatory ele¬ ments that respond to environmental cues. The operon system was first proposed by Francois Jacob and Jacques Monod in the early 1960s.
Opet Vo- ,pet\ Ancient Egyptian festival of the New Year. In the celebra¬ tion of Opet, statues of Amon and Mut and their son Khons were carried down the Nile on barges in a ritual journey from their shrines at Karnak to the temple of Luxor. There the statues remained about 24 days, a fes¬ tival time for Luxor. The images were returned to Karnak by the same route in a second public appearance that closed the festival.
Ophite Va-.fit, 'o-.fnA Member of any of several Gnostic sects that flour¬ ished in the Roman empire in the 2nd century ad and for several centu¬ ries thereafter. The sects shared a dualistic theology, opposing a beneficent and entirely spiritual Supreme Being to a chaotic and evil material world. To the Ophites, the human dilemma resulted from the mixture of these conflicting spiritual and material elements in human nature. Only gnosis, the esoteric knowledge of good and evil, could redeem one from the bonds of matter. See also dualism, Gnosticism.
ophthalmology \ l af-th9l-'ma-b-je\ Medical specialty dealing with the eyes, dating to 1805. Frans C. Donders’s 1864 advances in optics allowed eyeglasses to be fitted to vision problems. The ophthalmoscope made it possible to look inside the eye and relate eye defects to internal condi¬ tions. More recent advances include eye exams, early treatment of con¬ genital defects, and eye banks to store corneas for transplants. Ophthalmologists test visual function and examine the eye for faulty development, disease, injury, degeneration, aging, or refractive errors. They prescribe treatment for eye disease and lenses for refraction and perform surgery when needed. See also optometry, visual-field defect.
Ophuls Vo-ftelsX, Max orig. Max Oppenheimer (b. May 6, 1902, Saarbriicken, Ger.—d. March 26, 1957, Hamburg, W.Ger.) German film director. An actor, stage director, and producer in Germany and Austria (1921-30), he gained renown as a film director with Liebelei (1933). He left Nazi Germany and directed popular but undistinguished films in France, Russia, Italy, and The Netherlands until 1940, when he moved to the U.S. In Hollywood he directed The Exile (1947), Letter from an Unknown Woman (1948), and The Reckless Moment (1949). He returned to France to make The Roundabout (1950), House of Pleasure (1952), and The Sins of Lola Montes (1955), considered his masterpiece. His son, Marcel (b. 1927), worked in France principally as a maker of documen¬ tary films, most notably The Sorrow and the Pity (1971), which examines French conduct under German occupation.