Number 129, May 19, 1993 by Phillip F. Schewe and Ben Stein|
OPTICAL CRYSTALS are two- and three-dimensional ensembles of atoms held
together not by inter-atomic forces but by beams of laser light. Gilbert
Grynberg at the Pierre and Marie Curie University in Paris set up a standing-wave
pattern using four lasers to position cooled (to microkelvin temperatures)
cesium atoms in a cubic lattice array which persisted for about one second.
Theodor Hansche and H. Hemmerich at the University of Munich have employed
the same approach to fashion a two-dimensional lattice of cold rubidium
atoms. Presenting their data at the Quantum Electronics and Laser Science
Conference in Baltimore last week, both groups reported that the atoms
in these "dilute solids" vibrated only at particular frequencies.
(Science News, 15 May 1993.)
CLUSTERS OF FULLERENE MOLECULES seem to occur preferentially (but not
exclusively) at certain cluster sizes, such as 13, 19, 23, 35, etc. Carbon-60
and Carbon-70 buckyballs are themselves clusters held tightly together.
But clusters of buckyballs are only weakly bound by van der Waals forces.
A group of scientists at the Max Planck Institute in Stuttgart, Germany
have succeeded in ionizing the fragile clusters without breaking them apart
and cataloging their hefts in a mass spectrometer (T.P. Martin et al.,
11 May 1993 Physical Review Letters). The preferred cluster sizes were
similar (but not identical to) those for xenon and argon clusters.
REVERSIBLE COMPUTATION AND REVERSIBLE LOGIC : in the computation process,
energy is dissipated whenever information is destroyed. The lesson is:
to dissipate less energy, don't discard information. One way to do this
would be to build logic circuits that can run in reverse. That is, the
circuits (and the computers using them) would return to their original
states at the end of the computation cycle after having performed the required
calculations. This idea has been promoted by Rolf Landauer and Charles
Bennett of IBM, who spoke at the March APS Meeting in Seattle. In principle
such circuits, performing reversible operations, would dissipate less energy
than irreversible circuits (operating with no regard for the retention
or destruction of information) performing irreversible operations. Ralph
Merkle of Xerox said that the use of reversible circuitry, entailing also
the use of reversible software, was not yet a priority for computer architects
but would be early in the next century when the problems of heat dissipation
(requiring large heat sinks) and energy consumption become more pressing.
Already, Merkle said, computer systems account for 5% of all commercial
electricity use in the U.S.; this might double by the turn of the century.
(Dallas Morning News, 19 April 1993.)
PHYSICS BACHELOR DEGREES were awarded to 4965 students in the US in
1992; 38% went off to graduate school in physics/astronomy, 21% to other
graduate studies (mostly engineering), and 36% sought full time employment.
The 1991-92 Survey of Physics and Astronomy Bachelor's Degree Recipients
also showed, among other things, that the fraction of new Bachelors who
became high school teachers has doubled since the 1980's. (For more information,
contact Susanne Ellis, AIP Education and Statistics Div., 212-661-9404.)