Number 107, December 18, 1992 by Phillip F. Schewe and Ben Stein
OUT-OF-PLANE ATOMS PARTICIPATE IN 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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