Number 259, February 21, 1996 by Phillip F. Schewe and Ben Stein
NEW STUDIES CONFIRM THAT CFCs CAUSE OZONE DEPLETION . Because of the
"political sensitivity of the ozone- depletion issue," a team
of NASA (Langley) and UC Irvine scientists undertook satellite measurements
of stratospheric hydrogen chloride and hydrogen fluoride. Their four-year
study, the Halogen Occultation Experiment (HALOE), shows that chlorofluorocarbon
emissions, and not natural emissions arising, say, from oceans and biomass
burning (sources which can now be accounted for), are chiefly to blame
for the recent global buildup of stratospheric chlorine and the consequential
depletion of ozone. International agreements limiting CFC emissions have
already begun to lessen the growth of chlorine in the stratosphere. (James
Russell et al., Nature, 8 February 1996.)
DARK MATTER, LIKE LUMINOUS MATTER, IS HIERARCHICAL. That is, it congregates
at the galactic level and at the level of galaxy clusters. This view is
based on new observations made with the orbiting Japanese x-ray telescope
ASCA, which recorded x-ray emissions from gas in the Fornax galaxy cluster
(Y. Ikebe et al., Nature, 1 February 1996). The density of dark matter
at any location is deduced from the density of the hot (up to 10**8 K)
gas, which is probably held in equilibrium by the gravitational influence
of the unseen dark matter thereabouts. The ASCA scientists suggest that
one explanation of their measurements is the presence of two different
kinds of dark matter. This is in keeping with some hybrid cosmological
models which propose that cold dark matter (e.g., axions) influences affairs
at the galactic level and hot dark matter (e.g., massive neutrinos) at
the cluster level. (Science News, 10 Feb. 1996.)
ONE OF THE GREAT MYSTERIES OF WATER , its tendency to shrink when warmed,
has been successfully modeled for the first time. As cold water is heated,
it reaches a minimum volume--and therefore a maximum density--at around
4 degrees Celsius. No theoretical model has been able to explain this "density
anomaly." This shortcoming compromises the accuracy of molecular-scale
models of proteins and other systems involving water. Now, researchers
at Texas Tech University (G. Wilse Robinson, 806- 742-3099) have proposed
an explanation for the density anomaly by looking beyond neighboring molecules
in the liquid and focusing on more distant "second neighbors."
In all ten known forms of ice, an H20 molecule is surrounded by its closest
neighbors in the same way. However, in low-density ice, second-neighbor
molecules are relatively distant from the central molecule, while in some
of the higher-pressure, dense forms of ice, oxygens belonging to second-
neighbor molecules bend around to form a closer approach to the central
molecule. The researchers propose that in the liquid these "bent"
second neighbors would have somewhat less stability than those in the low-density
arrangement and therefore the denser bent neighbors would form only at
warmer temperatures. Using a simple model in which an oxygen atom and its
second neighbors arrange themselves on a one-dimensional array, the Texas
Tech researchers obtained density curves with a temperature and pressure
behavior similar to that of water. (C.H. Cho et al., Physical Review Letters,
5 March 1996.)
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