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R, gas constant, universal gas constant | [in physics] the universal constant in the gas equation: pressure times volume = R times temperature; equal to 8.3143 joules per kelvin per mole | ||
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r, R | the 18th letter of the Roman alphabet | ||
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R, roentgen | a unit of radiation exposure; the dose of ionizing radiation that will produce 1 electrostatic unit of electricity in 1 cc of dry air | ||
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radius, r | the length of a line segment between the center and circumference of a circle or sphere |