Number 330 (Story #2), July 17, 1997 by Phillip F. Schewe and Ben Stein|
A PRESSURE STANDARD FROM QUANTUM-MECHANICAL SOUNDS may be possible, Berkeley researchers reported at last month's Acoustical Society of America meeting. Applying pressure to a superfluid--an ultra cold liquid with zero resistance to flow--can cause it to move through a tiny hole and emit sounds at a characteristic frequency. The sound is created when the superfluid sheds energy in the form of "quantum vortices" whose size and other properties depend on precisely known quantum mechanical constants. The Berkeley physicists, who recently used helium-4 superfluids to measure the Earth's rotation rate (Update 318), said their setup can potentially determine pressure from the sound frequency if they can minimize temperature fluctuations which create additional unwanted vortices. (ScienceNOW, June 18, 1997).