Physics News Update
The American Institute of Physics Bulletin of Physics News
Number 315, April 3, 1997 by Phillip F. Schewe and Ben Stein
THE WORLD'S SMALLEST FOCUSED BEAM OF LIGHT is a 50-nm-diameter x-ray
beam created at the Brookhaven National Synchrotron Light Source in New
York. At the APS March Meeting Janos Kirz and Chris Jacobsen at SUNY-Stony
Brook reported that they and their colleagues had for the first time produced
images showing the distribution of DNA and protein in sperm from bulls
and other mammals. Using a 5-micron-diameter x-ray beam at the Brookhaven
synchrotron, Slade Cargill at Columbia reported the first real-time measurements
of the stresses that occur when electric current traveling through an aluminum
wire displaces atoms in the wire; this "electromigration" effect
is expected to be a problem in the ever- shrinking aluminum-based wires
of future-generation computer chips. (Associated graphics can be seen at
Physics News Graphics.)
FRACTAL MAGNETORESISTANCE. Canadian and Australian physicists have performed
an experiment in which electrons enter a two-dimensional square enclosure
(made from GaAs) through one tiny opening and leave by another. Voltage
applied to an overlying electrode controls the electron flow. An additional
electrode serves to squeeze off a circular region in the middle of the
square, transforming the enclosure into a "Sinai billiard," named
for Ya. G. Sinai who pioneered this research area in 1963. A plot of resistance
through the device as a function of the applied magnetic field exhibits,
for the first time in a billiards-type experiment, a fractal shape; that
is, the resistance plot looks the same at several different magnifications
(R.P.Taylor et al., Physical
Review Letters, 10 March). The source of the geometry-induced fractal
resistance is not known. This peculiar billiard table should provide an
excellent laboratory for studying quantum chaos. (Nature,
13 March.)
A GALAXY HAS BEEN OPTICALLY SIGHTED at the same apparent location as
a gamma ray burst object. In February the new orbiting telescope BeppoSAX
spotted one of the mysterious gamma bursts that have baffled astronomers;
do the bursts originate in our own galaxy or much further away? But quick
follow-up measurements by optical telescopes located a galaxy at what seems
to be the same position. BeppoSAX expects to find one burst a month, so
future searches at optical wavelengths may settle the issue of whether
some bursts are extragalactic. ( Science
News, 22 March 1997.) TENTH ANNIVERSARY OF THE WOODSTOCK OF PHYSICS.
High-temperature superconductivity (HTSC) became famous at a late-night
session at the March 1987 APS meeting. Paul Grant of the Electric Power
Research Institute reviews the matter a decade along.First, HTSC wire is
manufactured now in km lengths and should be ready to carry industrial
electric power on a test basis within two years, Grant believes. Thin films
of HTSC materials are used in SQUID detectors and communications devices.
No HTSC theory has yet emerged victorious, and HTSC supercurrents may be
both s-wave and d- wave in nature. Government spending on research is currently
$150 million per year in the U.S. and $200 million in Japan. The highest
confirmed transition temperature seen so far, 164 K, occurs in a Hg-based
material under pressure. (Nature, 13
March 1997.)
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