Number 156, December 17, 1993 by Phillip F. Schewe and Ben Stein
SUPERCONDUCTIVITY AT 250 K (-10 F) has been reported by a group of scientists
at the Ecole Superieure de Physique et de Chemie in Paris. Michel Lagues
and his colleagues synthesized a BiSrCaCuO compound with a unit cell comprising
eight adjacent CuO planes. This development seems to bear out the general
idea that high temperature superconductivity happens mostly in copper-oxygen
planes and that the more such contiguous planes the better. The French
researchers used beam epitaxy to lay down the atomic layers one by one,
a cumbersome process that would be difficult to implement on an industrial
scale. Reports of superconductivity in complex materials at these temperatures
have been made before, only to be withdrawn, so some scientists such as
Venky Venkatesan (301-405-7320) of the University of Maryland are skeptical.
However, in contrast to these earlier materials, Lagues' sample remained
superconducting for weeks. (Science, 17 Dec.)
DATA FROM TWO GREENLAND ICE PROJECTS DIFFER for the sections of ice
deposited during the Eemian period, the last "interglacial" (warm)
period prior to the current one. Representatives from the US-funded Greenland
Ice Sheet Project 2 (GISP2) and the European- funded Greenland Ice-core
Project (GRIP) discussed their results at the Fall Meeting of the American
Geophysical Union in San Francisco. According to Willi Dansgaard of the
University of Copenhagen, the GRIP ice core shows that temperatures during
the Eemian fluctuated wildly, typically by 5-7 degrees Celsius over a matter
of decades. This implies that the current interglacial period (the Holocene),
is either unusually stable or is subject to the same fluctuations in climate.
However, Ken Taylor of the University of Nevada reported that the GISP2
ice core does not exhibit these same fluctuations for the Eemian period.
Both teams are trying to work out the discrepancy, which may have been
caused by distortions in the ice. The data for the top 90% (2700 m) of
the cores agree excellently, which the researchers believe will lead to
a climate model of unprecedented accuracy stretching back to 100,000 years
with "significantly better than bi-annual resolution," according
to Paul Mayewski of the University of New Hampshire.
SUPER-INTENSE LASER FIELDS MAKE ATOMS RESISTANT TO IONIZATION, according
to computer simulations performed by J.H. Eberly of Rochester, K.C. Kulander
of Lawrence Livermore, and others. Contrary to the expectation that as
the incident light becomes more intense it would eject electrons from atoms
more easily, very intense fields (2 to 5 times stronger than the static
electric fields which bind electrons to the atom) actually cause the electrons
to become locked in an orbit that follows the oscillations of light's electric
field. Ironically, the atom becomes stabilized since the electron's orbit
remains fixed relative to the atom. In hydrogen, for example, the electron
ground state, represented in a density distribution as a single peak centered
around the nucleus, would be distorted by the intense fields into a pair
of peaks, each at some distance from the nucleus and each other. Eberly
and Kulander believe that an experimental demonstration of this phenomenon
is likely in the near future; lasers at sufficiently high intensities exist,
but light with higher frequencies from these lasers are still needed. (Science,
19 November 1993.)
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