Number 28, April 4, 1991 by Phillip F. Schewe and Ben Stein|
SCREW DISLOCATIONS IN SUPERCONDUCTING FILMS have shown up in scanning tunneling microscope images made by J. Georg Bednorz's group at IBM-Zurich. The spiral structures, which form when the Y-B-Cu-O films are grown epitaxially, may be one reason why the pinning of magnetic flux lines (and hence the critical current density) is better in thin-film high-temperature superconductors than in bulk versions (Nature, Mar. 28, 1991). Ian Raistrick and a group of scientists at Los Alamos have also observed the spiral grains; they found that the grains were rectangular in shape if grown on magnesium oxide and more circular if grown on strontium titanate. (Science, Mar. 29, 1991). Both groups previously reported their results on March 18 at the APS March Meeting in Cincinnati.
SOLAR SEISMOLOGY studies seem to discount theories that call for the existence of weakly interacting massive particles (WIMPS) at the Sun's core. Much as geologists study the Earth's interior by following the reflection of earthquake shocks, astronomers can use the observed oscillations of the Sun's surface to infer temperature and density for points in the interior. Yvonne Elsworth and Rachel Howe of Birmingham University in Great Britain assert that their measurements of waves on the Sun's surface agree better with the standard models of the Sun than with those that invoke WIMPS: "This did not appear to be the case a few years ago; it is the models which have changed while the observations have remained substantially the same but with improved accuracy." They believe therefore that the so-called solar neutrino problem--the discrepancy between the expected number of solar neutrinos and the number actually seen--has more to do with neutrino physics than with solar physics. (Physics World, March 1991.)
INVESTIGATING CP VIOLATION is the chief aim of new competing B-factory proposals from Cornell and Stanford. CP violation was first observed in neutral kaon-decay experiments in 1964; the effect essentially consists of a slight discrepancy (0.2%) in the rates at which a kaon turns into an anti-kaon and vice versa. Such a tiny difference is of great interest, however, since it might account for the present preponderance of matter over antimatter in the visible universe. Some scientists suspect that CP violation can best be pursued by studying the behavior of B and anti-B mesons, which are much more massive than kaons; hence the proposals for building dedicated B-meson facilities. SLAC submitted its proposal to the U.S. Dept. of Energy on 18 Feb., while Cornell submitted its proposal to the NSF on 21 Feb. The proposals, in the $100-200 million range, call for finished machines by 1997. (Science, 22 Mar. 1991.)
A STREAMER OF GAS AT THE GALACTIC CENTER , connecting a ring of material surrounding the galactic nucleus at a distance of 2 parsecs with molecular clouds lying at a distance of 10-20 parsecs, has been recorded by a Harvard-MIT-Boston-Naval Observatory team of astronomers using the Very Large Array radio telescope. They believe that the material in the outer clouds may be impelled by nearby supernovas toward the inner ring which, in turn, fuels activity (perhaps a black hole) at the galactic center. (Nature, 28 Mar. 1991.)