From: revu@ellis.uchicago.edu (Sendhil Revuluri)
Subject: Physics News Update #107 (12/18)
Summary: Latest Physics News Update
Keywords: physics news interesting banana
Reply-To: revu@midway.uchicago.edu
Organization: University of Chicago
Date: Sat, 19 Dec 1992 01:52:09 GMT

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Happy holidays to all those readers of sci.physics out there.

Sendhil Revuluri (s-revuluri@uchicago.edu)
University of Chicago

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PHYSICS NEWS UPDATE
A digest of physics news items prepared by Phillip F. Schewe, AIP
Public Information
Number 107   December 18, 1992

OUT-OF-PLANE ATOMS PARTICIPATE IN THE
SUPERCONDUCTIVITY in yttrium-barium-copper-oxide-based
materials.  Researchers previously thought that if the vibrational
(phonon) modes of atoms played any part in the mechanism
responsible for high-temperature superconductivity, they would
occur exclusively in the two-dimensional copper-oxide planes in
these layered materials.  Janice Nickel and Donald Morris of
Morris Research, Inc. (510-704-1012) and Joel Ager of LBL have
demonstrated the influence of out-of-plane atoms by studying the
"isotope shift," the shift in the critical temperature which takes
place when the common elements in the superconductor are
replaced by their less-common isotopes.  The researchers found a
0.10-0.14 K increase in the critical temperature when they replaced
the naturally abundant oxygen-16 with oxygen-18 in the copper-
oxide plane sites (but not elsewhere), in contrast to the 0.20 K-0.23
K overall decrease that occurs when the oxygen-18 isotope
replaces the oxygen-16 at all sites.  (Physical Review Letters, 14
Dec.)

THE LARGE SCALE STREAMING OF GALAXIES presents
some problems for cosmologists.  In the 1970s and 80s scientists
came to realize that the motion of galaxies could not all be
attributed to the expansion of the universe.  For example, a net
flow of nearby galaxies has been attributed to the gravitational pull
of a large concentration of matter---the Great Attractor---150
million light years away in the constellation Hydra.  A new study
of 120 galaxy clusters by Tod Lauer of Kitt Peak and Marc
Postman of the Space Telescope Science Institute looks at this
streaming on a larger scale.  They find that in order to ensure that
the brightest galaxies in these clusters all have the same intrinsic
brightness (as independent studies suggest) then the velocity of our
own galaxy relative to the cosmic microwave background (CMB)
would be different from the velocity deduced using the east-west
asymmetry (dipole moment) in the CMB measured by COBE. 
Lauer and Postman offer two tentative explanations of this velocity
discrepancy: first, that the expansion of the universe is actually
asymmetric and the dipole part of the measured CMB cannot be
subtracted to "correct" for the motion of the Milky Way toward
other galaxies; or, second, that the universe is symmetrical after all
but that mass concentrations even larger (100,000 galactic masses)
than the Great Attractor must loom at distances of 300 million
light years.  (Science News, 12 Dec.)

RADAR IMAGES OF ASTEROIDS keep improving.  In
monitoring the approach of the asteroid 4179 Toutatis this month,
Steven Ostro of JPL hopes to see features as small as 160 m on
the 5-km-wide object.  Using the Goldstone telescope to transmit
(3.5-cm waves) and the VLA radio telescope to receive reflected
waves, he expects to make a movie of Toutatis's approach to
within 10 lunar distances of Earth.  Other recent feats of radar
astronomy include the observation of what looks like water ice at
Mercury's poles and measurements of Saturn's moon Titan (the
echo signal was only 10**-22 watts), suggesting that the moon's
rotation period is not precisely the same as its orbital period, as
had been thought.  (New Scientist, 5 Dec.)

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