Number 301, December 31, 1996 by Phillip F. Schewe and Ben Stein
OXYGEN DATING THE MILKY WAY . A new technique uses stardust to formulate
an age for our galaxy. By looking at the isotopic composition of meteorites,
scientists can tell whether certain grains came from outside the solar
system. Such specks of matter would also necessarily predate the solar
system and would have originated in other stars, either as part of the
stellar wind gusting away from red giant stars or as the debris of ancient
supernovas (Science, 15 November). Larry Nittler, now of the Carnegie Institution
of Washington (202- 686-4370, x4421), has sorted 87,000 oxide grains according
to two composition ratios: O-16/O-17 and O-16/O-18. From this huge sample
he has isolated 87 grains that seem to be "presolar" in nature.
Employing these bits of stardust to represent extrasolar material, and
using theories about how the heavier elements are cooked in successive
cycles of supernovas, Nittler can estimate an age for the Milky Way galaxy---14.4
(with a statistical uncertainty of 1.3) billion years. (L.R. Nittler and
R. Cowsik, upcoming article in Physical Review Letters.)
TURBULENCE MAY BE MORE OF A PROBLEM FOR ITER than was previously thought.
New computer studies of magnetically contained plasmas show that instabilities
which do not plague smaller tokamaks might represent a threat to long-term
confinement of plasmas in machines on the larger scale of the proposed
$10-billion International Thermonuclear Experimental Reactor (ITER). Speaking
at the APS plasma physics meeting in November, University of Texas physicists
William Dorland and Michael Kotschenreuther said that as a result of the
heat lost through the plasma instability, the power output of ITER would
fall far short of its design goal. (Science, 6 December.)
TINY SILICON BEAMS VIBRATE AT A FREQUENCY OF 70 MHZ. Scientists at Caltech
have used a combination of photo- lithography and etching techniques to
create minuscule free- standing silicon bridges only 7.7 microns long.
By sending a current through a gold coating atop the beam and by applying
a magnetic field at right angles to the current, the beam can be excited
to vibrate at a resonant frequency (A.N. Cleland and M.L. Roukes, Applied
Physics Letters, 28 October). Suspended structures of this size---the researchers
expect to make even smaller beams with resonant frequencies of a GHz or
more--- might be useful in particle or phonon detectors. (Nature, 12 December.)
SPACE WEATHER , like the more familiar lower-atmosphere weather, is a
vast agglomeration of fronts and storms that changes by the minute. Filled
with radiation and particles arriving from the sun and influenced by a
potent terrestrial magnetic field, the near-earth space environment is
increasingly important because of the numerous communications and positioning
satellites parked there. Components on these craft, as well as astronauts
and even passengers in high-flying aircraft, are also potentially endangered
when storms on the sun send flurries of particles toward our planet. The
National Space Weather Program, an inter-agency system of weather-forecasting
instruments and data processing centers, will in coming years provide up-to-the-minute
assessments of near-earth conditions. (Session at the American Geophysical
Union meeting in San Francisco earlier this month.)
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