(Encyclopedia) phenylketonuriaphenylketonuriafĕnˌəlkētˌən&oobreve;rˈēə [key] (PKU), inherited metabolic disorder caused by a deficiency in a specific enzyme (phenylalanine hydroxylase). The…
(Encyclopedia) cataract, in medicine, opacity of the lens of the eye, which impairs vision. In the young, cataracts are generally congenital or hereditary; later they are usually the result of…
(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…
(Encyclopedia) Vazov, IvanVazov, Ivanĭvänˈ väˈzôf [key], 1850–1921, Bulgarian poet, novelist, and playwright, the first professional man of letters in Bulgaria. His work was inspired by the political…
(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…
(Encyclopedia) tritiumtritiumtrĭtˈēəm [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…
(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…
(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.…
(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…
(Encyclopedia) Raman effectRaman effecträˈmən [key], appearance of additional lines in the spectrum of monochromatic light that has been scattered by a transparent material medium. The effect was…
