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On this day in 1947, President Harry S. Truman delivered the first televised presidential address from the White House — to a limited audience. Television was still in its infancy: There were only about 44,000 TV sets in U.S. homes, concentrated in a few cities, compared with some 40 million radios. (Five days earlier saw the first telecast of a World Series game, pitting the New York Yankees against the Brooklyn Dodgers.)
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A transistor is a semiconductor device used to amplify and switch electronic signals and power. It is composed of a semiconductor material with at least three terminals for connection to an external circuit. A voltage or current applied to one pair of the transistor's terminals changes the current flowing through another pair of terminals.
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In 1954, in response to the Communist threat of the times, President Eisenhower encouraged Congress to add the words "under God," creating the 31-word pledge we say today. Bellamy's daughter objected to this alteration. Today it reads: "I pledge allegiance to the flag of the United States of America, and to the republic for which it stands, one nation under God, indivisible, with liberty and justice for all."
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Two polio vaccines are used throughout the world to combat poliomyelitis (or polio). The first was developed by Jonas Salk and first tested in 1952. Announced to the world by Salk on April 12, 1955, it consists of an injected dose of inactivated (dead) poliovirus. An oral vaccine was developed by Albert Sabin using attenuated poliovirus.
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The Shippingport Atomic Power Station, "the world’s first full-scale atomic electric power plant devoted exclusively to peacetime uses. It was located near the present-day Beaver Valley Nuclear Generating Station on the Ohio River in Beaver County, Pennsylvania. The reactor went online December 2, 1957, and was in operation until October, 1982.
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The National Aeronautics and Space Administration (NASA) is the agency of the United States government that is responsible for the nation's civilian space program and for aeronautics and aerospace research. Since February 2006, NASA's mission statement has been to "pioneer the future in space exploration, scientific discovery and aeronautics research."
