by VACUUM:
Def: A vacuum is a space with no or very little gas pressure. It is the pressure less than atmospheric pressure; it has the state of negative pressure. Vacuum is created through use of a vacuum pump or aspirator pump, to facilitate specific biological preparations, such as inclusions or disinfection of material for in vitro culture, etc.
A vacuum is a volume of space that is substansively empty of matter, so that gaseous pressure is much less than standard atmospheric pressure. The root of the word vacuum is the Latin adjective vacuus which means "empty," but space can never be perfectly empty. A perfect vacuum, known as "free space", with a gaseous pressure of absolute zero is a philosophical concept with no physical reality, not least because no volume of space is perfectly empty in this way. Physicists often use the term "vacuum" slightly differently. They discuss ideal test results that would occur in a perfect vacuum, which they simply call "vacuum" in this context, and use the term partial vacuum to refer to the imperfect vacua realized in practice.
The quality of a vacuum is measured by how closely it approaches a perfect vacuum. The residual gas pressure is the primary indicator of quality, and it is most commonly measured in units of torr, even in metric contexts. Lower pressures indicate higher quality, although other variables must also be taken into account. Quantum mechanics sets limits on the best possible quality of vacuum. Outer space is a natural high quality vacuum, mostly of much higher quality than what can be created artificially with current technology. Low quality artificial vacuums have been used for suction for millennia.
Vacuum has been a common topic of philosophical debate since Ancient Greek times, but it was not studied empirically until the 17th century. Experimental techniques were developed following Evangelista Torricelli's theories of atmospheric pressure. Vacuum became a valuable industrial tool in the 20th century with the introduction of the light bulb and vacuum tube, and a wide array of vacuum technology has since become available. The recent development of human spaceflight has raised interest in the impact of vacuum on human health, and life forms in general.
Vacuum is useful in a variety of processes and devices. Its first common use was in Incandescent light bulbs to protect the tungsten filament from chemical degradation. Its chemical inertness is also useful for electron beam welding, for chemical vapor deposition and dry etching in semiconductor fabrication and optical coating fabrication, for cold welding, and for ultra-clean inert storage. The reduction of convection improves the thermal insulation of thermos bottles and double-paned windows.
Deep vacuum promotes out gassing which is used in freeze drying, adhesive preparation, distillation, metallurgy, and process purging. The electrical properties of vacuum make electron microscopes and vacuum tubes possible, including cathode ray tubes. The removal of air friction is useful for flywheel energy storage and ultracentrifuges.
