Number 144, September 20, 1993 by Phillip F. Schewe and Ben Stein
COMPETING ATTRACTORS make some physical systems more chaotic than others.
For all chaotic systems the inability to forecast longterm behavior is
tied to an exquisite sensitivity to errors in specifying the systems' initial
conditions. Still, the state of a chaotic classical system can often be
predicted at least qualitatively because its movements are generally confined
to an attractor, a zone in the abstract multidimensional phase space used
to describe the system. John Sommerer of Johns Hopkins and Edward Ott of
the University of Maryland have contrived a system---a particle moving
in a plane under the influence of frictional and other forces---whose attractor
is riddled with holes leading to other, competing, attractors; this pathological
behavior precludes even qualitative predictions of future behavior. (Nature,
9 Sept. 1993.)
THE HIGH-ENERGY X-RAY BACKGROUND , the diffuse x-ray glow spread across
the sky, comes mostly from active galactic nuclei (AGN). Julian Krolick
of Johns Hopkins and Andrzej Zdziarski and Piotr Zycki of the Copernicus
Astronomical Center in Warsaw have reinterpreted data from the Japanese
satellite Ginga, the U.S. Gamma Ray Observatory, and the Russian satellite
GRANAT and conclude (in the 10 Sep. Astrophysical Journal Letters) that
earlier analyses were wrong and that the bulk of background x radiation
at energies of tens of keV do come from the cores of powerful galaxies.
The lower-energy portion of the x-ray background had already been attributed
to AGN's. (Science News, 18 Sept. 1993.)
ORGANIC SUPERLATTICE STRUCTURE has been observed directly for the first
time in a material grown with molecular beam deposition techniques. The
structures, made by scientists at Hitachi in Japan, consist of many nm-thick
alternating layers of copper phthalocyanine and another organic semiconductor
called NTCDA. Electron microscope pictures of the material reveal the thinness
and uniformity of the layers. The strain that arises at the boundary between
layers owing to the lattice mismatch of the two compounds may be less for
organic than for inorganic materials, making it possible for greatly different
species to sit well together. Scientists expect that versatile organic
compounds can be combined in different multi-quantum-well structures to
produce unique opto-electronic properties. (Y. Imanishi et al., 27 Sept.
1993 Physical Review Letters.)
THE LASER FEEDBACK MICROSCOPE (LFM) achieves vertical resolutions of
10 nm, much better than for standard scanning electron microscopes (SEM).
The LFM horizontal resolution, about 200 nm, is not as good as for the
SEM; on the other hand, LFM can look at living cells without damaging them,
unlike SEM, which operates in a vacuum. In general, microscopes illuminating
targets with light usually have a resolution no finer than the light's
wavelength, a fact which has ruled out optical microscopy for much biological
work. The LFM overcomes this problem by forming computer-processed images
from the interference of laser light going to, and reflecting from, the
target via a pinhole baffle. The LFM was developed by Berkeley biophysicist
Alan Bearden. (Science, 3 Sept. 1993.)
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