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transducer

(Encyclopedia)transducer, device that accepts an input of energy in one form and produces an output of energy in some other form, with a known, fixed relationship between the input and output. One widely used class...

optical character recognition

(Encyclopedia)optical character recognition (OCR), method for the machine-reading of typeset, typed, and, in some cases, hand-printed letters, numbers, and symbols using optical sensing and a computer. The light re...

Orbiting Astronomical Observatory

(Encyclopedia)Orbiting Astronomical Observatory (OAO), series of four orbiting observatories (see observatory, orbiting) launched between 1966 and 1972 by the National Aeronautics and Space Administration (NASA) to...

ceilometer

(Encyclopedia)ceilometer sēlŏmˈĭtər [key], in aviation and meteorology, automatic instrument used to record ceiling, i.e., the altitude of the lowest cloud layer covering more than half of the sky. The ceilome...

thallium

(Encyclopedia)thallium thălˈēəm [key], metallic chemical element; symbol Tl; at. no. 81; interval in which at. wt. ranges 204.382–204.385; m.p. 303.5℃; b.p. about 1,457℃; sp. gr. 11.85 at 20℃; valence +...

placebo

(Encyclopedia)placebo pləsēˈbō [key], inert substance given instead of a potent drug. Placebo medications are sometimes prescribed when a drug is not really needed or when one would not be appropriate because t...

quantum theory

(Encyclopedia)quantum theory, modern physical theory concerned with the emission and absorption of energy by matter and with the motion of material particles; the quantum theory and the theory of relativity togethe...

Josephson, Brian David

(Encyclopedia)Josephson, Brian David, 1940–, British physicist, Ph.D. Cambridge, 1964. After several postdoctoral appointments, he joined the faculty at Cambridge in 1974. Josephson was co-recipient, with Leo Esa...

selenium

(Encyclopedia)selenium səlēˈnēəm [key], nonmetallic chemical element; symbol Se; at. no. 34; at. wt. 78.96; m.p. 217℃; b.p. about 685℃; sp. gr. 4.81 at 20℃; valence −2, +4, or +6. Selenium is directly ...

Sims, Christopher Albert

(Encyclopedia)Sims, Christopher Albert, 1942–, American economist, b. Washington, D.C., Ph.D. Harvard (1968). Sims has taught at Harvard (1967–70), the Univ. of Minnesota (1970–90), Yale (1990–99), and Prin...