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navigation satellite

(Encyclopedia)navigation satellite, artificial satellite designed expressly to aid the navigation of sea and air traffic. Early navigation satellites, from the Transit series launched in 1960 to the U.S. navy's Nav...

city

(Encyclopedia)city, densely populated urban center, larger than a village or a town, whose inhabitants are engaged primarily in commerce and industry. In the United States a city is legally an incorporated municipa...

blood groups

(Encyclopedia)blood groups, differentiation of blood by type, classified according to immunological (antigenic) properties, which are determined by specific substances on the surface of red blood cells. Blood group...

antiviral drug

(Encyclopedia)antiviral drug, any of several drugs used to treat viral infections. The drugs act by interfering with a virus's ability to enter a host cell and replicate itself with the host cell's DNA. Some drugs ...

electors

(Encyclopedia)electors, in the history of the Holy Roman Empire, the princes who had the right to elect the German kings or, more exactly, the kings of the Romans (Holy Roman emperors). Until the reign (1493–1519...

barcode

(Encyclopedia)CE5 Barcode barcode, computer coding system that uses a printed pattern of lines and bars to identify such things as products, mail and packages, and customer accounts; the term also is used for s...

tornado

(Encyclopedia)tornado, dark, funnel-shaped cloud containing violently rotating air that develops below a heavy cumulonimbus cloud mass and extends toward the earth. The funnel twists about, rises and falls, and whe...

ultraviolet radiation

(Encyclopedia)ultraviolet radiation, invisible electromagnetic radiation between visible violet light and X rays; it ranges in wavelength from about 400 to 4 nanometers and in frequency from about 1015 to 1017 hert...

genetics

(Encyclopedia)genetics, scientific study of the mechanism of heredity. While Gregor Mendel first presented his findings on the statistical laws governing the transmission of certain traits from generation to genera...

harmonic motion

(Encyclopedia)CE5 Harmonic motion is exhibited by a weight vibrating on the end of a spring. In A, the displacement of the object from its equilibrium position and the acceleration of the object are at a maximum...