Number 145, September 28, 1993 by Phillip F. Schewe and Ben Stein
SUPERCONDUCTIVITY HAS BEEN OBSERVED ABOVE 150 K for a mercury-barium-calcium-copper
oxide material squeezed to a pressure of 150 kbar, which is about 150,000
times the pressure of the atmosphere. The previous record of 133 K was
observed in a similar mercury-bearing material earlier this year. The new
material, known as Hg-1223, was made by C.W. Paul Chu and colleagues at
the University of Houston. Why pressure should increase the superconducting
transition temperature is not completely understood, but based on previous
experiments Chu believes that making the appropriate chemical substitutions
in the material might duplicate these high temperatures at normal pressure.
(C.W. Chu et al., Nature, 23 September 1993.)
MICROLENSING EVENTS HINT AT THE EXISTENCE OF DARK MATTER. Just as the
presence of galaxies along the line of sight to a distant quasar will distort
the image of the quasar via a gravitational lensing effect (making the
quasar appear as two or more spots or as an arc), so the image of a nearby
object such as a star might be distorted by the gravitational influence
of unseen dark matter lying between us and the star. This hypothesis has
been put to the test by two survey projects which scan millions of stars
in the Large Magellanic Cloud, the nearby satellite galaxy. These stars
are close enough to be seen clearly but far enough away so that a sufficient
amount of dark matter---which may reside in the halo around the Milky Way---would
be present to distort the stars' images. At a recent meeting in Italy,
Charles Alcock of Livermore spoke on behalf of a US/Australian team. He
announced one such "microlensing" event, in which a star's apparent
brightness changed considerably over a short time, presumably by the interposing
presence of dark matter in the form of massive compact halo objects, or
MACHOs. Michel Spiro of Saclay in France also reported that his group had
observed two microlensing candidate events. Some astronomers at the meeting
believed that it was too early to attribute the star-image distortions
to dark matter. (New York Times, 21 Sept. 1993)
NANOMAGNETS EXHIBIT BISTABILITY . A Florence-Rio de Janiero-Grenoble
team of scientists have chemically prepared 12-ion clusters of manganese
and observed that at temperatures of 4 K the clusters retain their magnetization
for some time and exhibit pronounced hysteresis; that is, for a given value
of an external magnetic field, the clusters can reside in one of two magnetic
states. This feature, the scientists believe, could lead to information
storage at the molecular level if ever a way can be found to address individual
clusters. (R. Sessoli et al., Nature, 9 Sept. 1993.)
MICROSCOPIC STEAM ENGINES can deliver up to 100 times the power of comparably
sized electrostatic micromotors. Sandia physicist Jeffry Sniegowski has
built a tiny motor only 6 microns by 2 microns; sitting on a wafer, the
device consists of a micropiston moving through a silicon bore. Power comes
from a water bubble made to expand and contract by heating. Potential applications
of the motor may occur in areas where high-precision alignment or positioning
are important, such as micro-surgery or micro- manufacturing. (Science
News, 25 Sept. 1993.)
|
