Number 228, May 31, 1995 by Phillip F. Schewe and Ben Stein|
HIGHER-THAN-EXPECTED ARCTIC OCEAN TEMPERATURES were reported at this
week's meeting of the Acoustical Society of America in Washington, DC.
Applying the same acoustic technique for measuring water temperature as
the recent Heard Island experiment, a US- Russian team broadcast 50-Hz
sound waves in a 2600-km underwater path across the Arctic Ocean. Since
the speed of sound through seawater varies with temperature, measurements
of transit times can be used to calculate the water temperature. At the
ASA meeting, Peter Mikhalevsky of Science Applications International Corporation
in McLean, Virginia (703-243- 0643) reported that the sound waves took
1-2 seconds less than an estimated value based on tests conducted in the
late 1970s and early 1980s. The team concluded that the temperature of
the Arctic Ocean since that time has increased by 0.2-0.4 degrees Celsius
at ocean depths of 200-700 meters, a calculation consistent with short-range
measurements made from icebreakers last year. It's unknown whether the
increased temperatures reflect long-scale global warming or simply represent
cyclical variations over decades, but continuous monitoring of Arctic Ocean
temperature could bring better insights into the question, as would sound
data taken over many different paths in order to build up a 3-D temperature
map of the ocean.
IMAGING WITH AN ATOMIC BEAM has been accomplished by physicists at the
University of Hanover in Germany. Past efforts to use focused atoms as
an imaging source have been hampered by the velocity-spread of the beam
particles, which results in a long focal length and considerable aberration.
In the Hanover experiment, laser-cooled, polarized cesium atoms are used
to image a patterned mask with varying degrees of magnification. Those
atoms transmitted through the mask are focused by a hexapole magnet, which
tugs at the atoms' magnetic dipole moments. Further downstream, at a designated
image plane, the atoms are made to fluoresce by exposing them to laser
light. The resultant image is recorded by a video camera. The researchers
expect that if a solid substrate were positioned at the image plane then
this whole process could be used as a sort of "slide projector"
for casting images of patterns, in the form of deposited atoms, onto the
substrate. The technique may therefore be useful in sub-micron lithography.
(W.G. Kaenders et al., Nature, 18 May 1995.)
THE COSMIC INFRARED BACKGROUND , the supposed radiant heat from the first
stars in the universe, is hard to detect since so many foreground objects,
such as the Milky Way and our solar system, throw off heat of their own.
The Cosmic Background Explorer (COBE), so proficient in mapping the microwave
background, has failed so far to discern an infrared background. Discussing
their measurements at a workshop in April, COBE researchers have, however,
put new upper limits on the magnitude of an infrared background which serve
to constrain cosmological models, at least those that called for early
massive black holes or quasars. In order for COBE to say anything intelligible
about cosmological infrared, it must understand (and subtract) the foreground
infrared. This exercise has led to new insights about our galaxy (the central
bulge of stars seems more football-shaped than spherical) and the near-Earth
environment (COBE verified the existence of a circumstellar dust ring;
see Update 222). (Science, 19 May 1995.)