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Picture Tube: An ordinary TV picture tube, however, is a bulky vacuum tube and requires relatively high power for its operation. Researchers are attempting to replace the TV tube with a thin, flat display panel requiring no vacuum. This panel, the "solid-state picture tube," operates on a principle known as electroluminescence, a phenomenon in which certain materials, such as zinc sulfide and semiconductor p-n junctions, emit light when an appropriate voltage is applied across the material.Every electronic instrument, however, whether a TV receiver or a complex computer, must have an input and an output device that "connects" with the outside world. In the TV receiver, for example, the input is the antenna and the output is the picture tube. For the computer, the input device may be a typewriter or a magnetic tape, while the output may be sheets of paper printed by a typewriter, or a TV-like picture on a cathode ray tube.
The largest single project in the system was the $180 million Trans-Bay Tube that extends 3.6 mi (5.8 km) under San Francisco Bay. When underground approaches are included, the total length of the tube will be about 6 mi (10 km). The tube will follow the contours of the bay floor, changing direction six times vertically and twice horizontally to avoid a rock outcropping. By following the bay floor, the entire structure will lie in a bed of mud; in the event of an earthquake, the tube would be cushioned by the mud, which is expected to absorb the shock. To permit the tube to be displaced several inches in all directions during the motions of an earthquake, the tube will be connected to its terminals by means of Flexible joints. |
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