Text 404, 67 rader
Skriven 2005-04-17 22:50:30 av Herman Trivilino (1:106/2000.7)
Ärende: PNU 725
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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 las
er 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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 * Origin: Big Bang (1:106/2000.7)