- noun a flap in the heart, blood vessels or lymphatic vessels or other organs, which opens and closes to allow liquid to pass in one direction only
- An active device consisting of a hermetically sealed envelope within which electrons are conducted between electrodes. The cathode is the source of electrons, the positive electrode to which they travel is the anode or plate, while other electrodes that may be present include control grids and screen grids. electron tubes may or may not contain a gas, and its presence and concentration affects the characteristics of said tubes. Such tubes have many applications, including their use in amplification, modulation, rectification, and oscillation. There are many examples, including CRTs, phototubes, pentodes, mercury-vapor tubes, and so on. When such a tube is evacuated to a degree that any residual gas present does not affect its electrical characteristics, it is called vacuum tube. Better known as electron tube, or tube (1).
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