PHYSICS NEWS UPDATE A digest of physics news items prepared by Phillip F. Schewe, AIP Publ

PHYSICS NEWS UPDATE
A digest of physics news items prepared by Phillip F. Schewe, AIP
Public Information
Number 170  March 28, 1994

CONTROLLING CHAOS through the use of small perturbations has been possible
in a number of systems, such as erratically vibrating metal strips, certain
electrical circuits, and mixing in chemical reactions.  At the APS Meeting
last week in Pittsburgh, Rajarshi Roy of Georgia Tech reported that by using
a subtle feedback mechanism he has been able to synchronize two separate
chaotic lasers, a development which might be applicable to schemes for
encrypting data.  Understanding and controlling fibrillating heart tissue
may also be possible with chaos-control methods.  Mark Spano of the Naval
Surface Warfare Center in Whiteoak, Maryland (also speaking at the meeting)
has determined that human atrial fibrillation, the massively irregular
beating of the atrial chambers of the heart, is chaotic in nature.  He also
has preliminary evidence that the more life-threatening ventricular
fibrillation (erratic behavior in the ventricle chambers) is also chaotic.
In studies with rabbit heart tissue, he has been able to control arrhythmia
through the application of electrical stimuli.  He reported similar work
done with rat brain tissue in an effort to control (apparently chaotic)
electrical patterns characteristic of epileptic behavior.

BUILDING WHOLE INSTRUMENTS ON A CHIP with integrated-circuit technology is a
major goal in the field of microelectromechanical systems (MEMS).  At a
session devoted to this subject at the APS meeting, Susanne Arney of AT&T
Bell Labs described, for example, efforts to make tiny tunneling probe
microscopes with the same lithographic, etching, undercutting (etc.) steps
used in micro-circuit fabrication.  Jason Yao of Rockwell described
micro-resonators consisting of micron-sized arms of silicon which, once
excited by voltage pulses, oscillate consistently at MHz frequencies.  The
purity of the tone of this "tuning fork" is such that the resonator might
serve (particularly if encased in a tiny evacuated shell) as an internal
clock for computers.  At higher frequencies (100 MHz) the resonator could
serve as a generator of radio waves.

HIGH-SPEED STM can reveal the incessant motion of atoms across a silicon
surface.  Not yet as fast as a movie and looking more like a jerky
time-lapse study of commuters on the go, picture sequences recorded by
scanning tunneling microscopes at a rate of several frames per second for
area views, or up to 1000 per second for single rows of atoms, show how
atoms touch down and lift off of terraced surfaces under the influence of
thermal agitation.  At the meeting, Ellen Williams of the University of
Maryland referred to these images as "a stunning visualization of the ideas
of statistical mechanics."

SOFT GAMMA RAY REPEATERS (SGR's) are celestial sources of gamma bursts. Only
three are known to exist in our galaxy.  Unlike the larger sample of gamma
bursts---more than a thousand discovered in recent years by the Gamma Ray
Observatory---bursts from SGR's are repeated and are at lower ("softer")
gamma energies.  The first SGR was discovered 15 years ago.  Its apparent
association with a supernova remnant was doubted by some, but now a
counterpart of the second SGR, an object called SGR1806, has been observed
at x-ray (with the ASCA spacecraft) and radio (with the VLA telescope)
wavelengths.  The gamma-ray and x-ray observations were made while the
object was in the act of emitting bursts.  The astronomers involved believe
that SGR's are indeed neutron stars.  (Nature, 10 Mar.)