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wind shear

(Encyclopedia)wind shear, a sudden, drastic change in wind direction or speed over a comparatively short distance. Most winds travel horizontally, as does most wind shear, but under certain conditions, including th...

waveguide

(Encyclopedia)waveguide, device that controls the propagation of an electromagnetic wave so that the wave is forced to follow a path defined by the physical structure of the guide. Waveguides, which are useful chie...

biennial

(Encyclopedia)biennial, plant requiring two years to complete its life cycle, as distinguished from an annual or a perennial. In the first year a biennial usually produces a rosette of leaves (e.g., the cabbage) an...

blood substitute

(Encyclopedia)blood substitute, substance that mimics the function of blood. Blood substitutes typically concentrate only on reproducing the function of hemoglobin, the molecule that carries oxygen through the body...

bluebird

(Encyclopedia)bluebird, common name for a North American migratory bird of the family Turdidae (thrush family). The eastern bluebird, Sialia sialis, is among the first spring arrivals in the North. It is about 7 in...

Vazov, Ivan

(Encyclopedia)Vazov, Ivan ĭvänˈ väˈzôf [key], 1850–1921, Bulgarian poet, novelist, and playwright, the first professional man of letters in Bulgaria. His work was inspired by the political upheavals of the ...

tritium

(Encyclopedia)tritium trĭtˈēəm [key], radioactive isotope of hydrogen with mass number 3. The tritium nucleus, called a triton, contains one proton and two neutrons. It has a half-life of 12.5 years and decays ...

Schenck v. United States

(Encyclopedia)Schenck v. United States, case decided in 1919 by the U.S. Supreme Court. During World War I, Charles T. Schenck produced a pamphlet maintaining that the military draft was illegal, and was convicted ...

Simon, Herbert Alexander

(Encyclopedia)Simon, Herbert Alexander, 1916–2001, American social scientist and economist, b. Milwaukee, grad. Univ. of Chicago (B.A., 1936, Ph.D., 1943). A professor of computer science and psychology at Carneg...

phenylketonuria

(Encyclopedia)phenylketonuria fĕnˌəlkētˌəno͝orˈēə [key] (PKU), inherited metabolic disorder caused by a deficiency in a specific enzyme (phenylalanine hydroxylase). The absence of this enzyme, a recessive...