A movable barrier across an opening in a large barrier, a fence, or a wall.

1. A circuit having an output and a multiplicity of inputs and so designed that the output is energized only when a certain combination of pulses is present at the inputs.

2. A circuit in which one signal, generally a square wave, serves to switch another signal on and off.

3. One of the electrodes in a field-effect transistor.

4. An output element of a cryotron.

5. To control the passage of a pulse or signal.

6. In radar, an electric waveform which is applied to the control point of a circuit to alter the mode of operation of the circuit at the time when the waveform is applied. Also known as gating waveform.

1. A device, such as a valve or door, for controlling the passage of materials through a pipe, channel, or other passageway.

2. A device for positioning the film in a camera, printer, or projector.

The area or component in which the film is held at a fixed relationship to a lens.

The opening in a casting mold through which molten metal enters the cavity. Also known as in- gate.

The position on the extension of the axis of a runway in use above which an aircraft heading toward that runway is required to pass at a time assigned by proper control authority.

A movable barrier of shielding material used for closing a hole in a nuclear reactor.

A metal part in the rear of the cylinder of old-pattern revolvers that was turned out to expose the cylinder for loading.