Science > Physics > PHYSICS NEWS UPDATE -- Number 725 April 1, 2005 by Phillip F. Schewe,Ben Stein
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PHYSICS NEWS UPDATE -- Number 725 April 1, 2005 by Phillip F. Schewe,Ben Stein |
PHYSICS NEWS UPDATE
The American Institute of Physics Bulletin of Physics News
Number 725 April 1, 2005 by Phillip F. Schewe, Ben Stein
ZEPTOGRAM MASS DETECTION---WEIGHING MOLECULES. Michael Roukes and
his Caltech colleagues produce some of the finest nanoscopic
electromechanical systems (NEMS) devices in the world. His latest
achievement is performing mass measurements with nearly zeptogram
(zg) sensitivity, that is, with an uncertainty of only a few times
10^-21 grams. At this level you can start to weigh molecules one at
a time. In experiments, the presence of xenon accretions of only
about 30 atoms (7 zg, or about 4 kilodaltons, or the same as for a
small protein) have been detected in real time. Minuscule masses
are measured through their effect on an oscillating doubly clamped
silicon carbide beam, which serves as the frequency-determining
element in a tuned circuit. So, in practice, the beam would be set
to vibrating at a rate of more than 100 MHz and then would be
exposed to a faint puff of biomolecules. Each molecule would strike
the beam, where its presence (and its mass) would show up as a
changed resonant frequency. After a short sampling time, the
molecule would be removed and another brought in. Through this kind
of miniaturization and automation, the NEMS approach to mass
spectroscopy could change the way bioengineering approaches its
task, especially in the search for cancer and its causes. The
Roukes (roukes@caltech.edu, 626-395-2916) group reported its
findings at last week's meeting of the American Physical Society
(APS) in Los Angeles.
LASER SCATTERING OF MITOCHONDRIA, the "power plants" of cells, can
immediately identify early-stage liver cancer cells and potentially
monitor stem cells as they undergo various stages of development.
At the APS March Meeting, Paul Gourley of Sandia
(plgourl@sandia.gov) reported the latest uses of the "biocavity
laser," an aluminum-gallium-arsenide based design that continuously
pumps in single human cells into a chamber for analysis. The
laser's beams are altered in their passage through the cells. The
800-nanometer light in the experiments is not absorbed by most of
the cell, except by its hundreds of mitochondria, which are
responsible for scattering 90-95 percent of the light. By analyzing
the scattering patterns, the researchers determined the distribution
of mitochondria in the cell, and could instantly determine whether
the cell was healthy (in which case the mitochondria cluster
cooperatively around the cell nucleus) or cancerous (in which case
they are apathetically sprawled across the cell). The process is
highly accurate, works much more quickly than traditional
techniques, and does not require the usual pre-treatment of cells
with chemical reagents or fluorescent molecules. Co-author Bob
Naviaux of UC-San Diego added the biocavity laser technique also has
the potential to rapidly identify the in-between states of stem
cells as they transform into their final identities. (Also see
Sandia News release at http://www.sandia.gov/news-center)
NO SPLASH ON THE MOON. Sidney Nagel's lab at the University of
Chicago has explored the behavior of liquid drops---how and when
they fall from a faucet---granular materials, crumpling, and other
everyday-but-difficult-to-explain phenomena. At the APS meeting,
Nagel's graduate student, Lei Xu, revealed a surprising discovery
concerning one of the commonest physical effects: the splash a
liquid drop makes when it strikes a flat surface. Under ordinary
atmospheric conditions a liquid drop will flatten out on impact,
splay sideways, and also raise a tiara-like crown of splash
droplets. Remove some of the ambient atmosphere, and surprisingly
the splash becomes less. At about one-fifth atmosphere the splash
disappears altogether, leaving the outward going splat but no
upwards splash (see movie at kauzmann.uchicago.edu ). Apparently it
is the presence of the air molecules that give the impacting liquid
something to push off of; remove the surrounding atmosphere, and the
splash stops
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PHYSICS NEWS UPDATE is a digest of physics news items arising
from physics meetings, physics journals, newspapers and
magazines, and other news sources. It is provided free of charge
as a way of broadly disseminating information about physics and
physicists. For that reason, you are free to post it, if you like,
where others can read it, providing only that you credit AIP.
Physics News Update appears approximately once a week.
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