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Index (V)
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Moment of truth
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The Voyager I spacecraft is the most distant man-made object in the universe. It was launched in 1977 and as in 2002, it was more than 8 billions miles from the Earth. |
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vacuum Phys.
A space in which there is a low pressure of gas matter. The pressure is much less than the standard atmospheric pressure. However, a perfect vacuum that contains no matter only
exists theoretically and is unattainable in laboratory as all materials that enclose such a space have a finite vapor pressure.
The quality of a vacuum depends on how closely it approaches a perfect vacuum. Lower pressure means less number of residue gas left in the enclosure. In a low or medium vacuum condition, the pressure is about
10-2 Pa, whereas a high vacuum condition has a pressure of down to 10-7 Pa. Below this limit is called the ultra high vacuum (UHV). The outer space that do not have an enclosure has
a much lower pressure than that is attainable in a laboratory. With an average number of only a few hydrogen atom per cubic centimeter, the pressure in outer space is only about 10-15 Pa.
vacuum distillation Chem.
Distillation process carry out under reduced pressure (lower than that of atomspheric pressure). This lowers the boiling point of the liquid distillate which otherwise would have
decomposed at a higher boiling point if it is to distill under normal atomspheric condition.
vasodilator Med.
An agent that causes expansion (dilation) of blood vessels thereby increasing blood flow and dropping of blood pressure. Example of such agent
is glyceryl trinitrate for use to relieve the pain of angina attack.
VA - VC
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