[MURG] [>Htech] Physics News Update 688 (fwd from alito@organicrobot.com)

Sun Jun 13 14:55:12 EST 2004

----- Forwarded message from Alejandro Dubrovsky <alito at organicrobot.com> -----

From: Alejandro Dubrovsky <alito at organicrobot.com>
Date: Sun, 13 Jun 2004 16:18:23 +1000
To: transhumantech <transhumantech at yahoogroups.com>
Subject: [>Htech] Physics News Update 688
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PHYSICS NEWS UPDATE
The American Institute of Physics Bulletin of Physics News
Number 688 June 11, 2004  by Phillip F. Schewe, Ben Stein

A NEW CHEMOTAXIS ASSAY reveals nerve cells' surprising sensitivity.
A new method for studying the guidance (change in direction) of
neurons amid a sea of protein molecules shows how sensitive this
process is to the surrounding protein gradient.  Chemotaxis is the
process by which living cells sniff out their local environment and
act accordingly, which usually means moving or growing toward higher
concentrations of beneficial molecules.  In the case of neurons
removed from their natural setting and put down on a bed of collagen
gel in a dish, growth will follow the increasing gradient of
proteins in their vicinity, such as the nerve growth factor (NGF)
protein.  Neuronal growth, the way in which the long axon bodies of
a nerve cells wire themselves into a network, is of great interest
since this aids in knowing how brains form.  Now a team of
scientists at Georgetown University has developed a new method for
measuring the gradient of local proteins (which have been
fluorescently tagged) and the axon's response.  In this case the
neural cells come originally from a rat's brain.  The Georgetown
team of neuroscientists and physicists find that axon growth is
sensitive to gradients so small (0.1%) that they correspond to about
one additional molecule across the spatial extent of the axon's
"growth cone," the sensing device at the tip of the growing axon.
This is a remarkable feat considering that, at any one instant,
there are large statistical fluctuations in the 1000 or so NGF
molecules in the vicinity of the growth cone.  The researchers
suggest that axons may thus be "nature's most-sensitive gradient
detectors."  (Rosoff et al., Nature Neuroscicence, June 2004;
contact Jeffrey Urbach, urbach at physics.georgetown.edu, 202-687-6594;
or Geoffrey Goodhill, geoff at georgetown.edu)

PERFORMING BOOLEAN SURGERY TO UNLOCK BIOSONAR'S SECRETS.  Over the
last approximately 60 million years of evolutionary history, bats
have developed highly optimized biosonar systems in which they
broadcast ultrasound at various frequencies and then detect the
echoes to sense their surroundings.  At last month's meeting of the
Acoustical Society of America in New York, researchers (Rolf
Mueller, University of Southern Denmark, +45-6550-3655,
rolfm at mip.sdu.dk) presented the first high-resolution,
three-dimensional maps to depict spatial regions in which the ears
are sensitive to low- mid-, and high-frequency ultrasound. These
biologically based ultrasound-sensitivity maps vary considerably
over the studied sample of bat species and are likely to vary even
more over the approximately 1000 species which exist in total.  They
may help inspire much better designs for artificial antennas of any
type, from the acoustic ones in ship sonar systems and medical
devices to the electromagnetic antennas in cell phones. In their
approach the researchers perform CT scans of bat ears to obtain
highly detailed images and 3D shapes which are then rendered on a
computer. Next they model the interaction between each ear shape and
ultrasound waves from the bat's surroundings.  The researchers can
understand how the anatomical features of an ear shape bring about
the spatial sensitivity patterns by performing painless "Boolean
surgery," in which they can modify an ear's shape on a computer
(often by removing some features and--as part of their future
plans--mixing features from different species) and see how the
modifications change the ear's detection of ultrasound.  (Paper
4aAB6 at meeting; lay-language paper at
http://www.acoustics.org/press/147th/Mueller.html)

MICROWAVE TISSUE WELDING.  A conventional microwave oven uses an
antenna to squirt microwaves into a reflective box where they
preferentially excite and heat anything rich in water molecules.  A
new experiment performed in the group of Michael Golosovsky and Dan
Davidov  at the Racah Institute of Physics, the Hebrew University of
Jerusalem reduces the antenna size and dispenses with the resonant
box and, by getting really close to the sample of soft matter, can
heat a tiny spot, one half by one quarter of a millimeter in size,
up to temperatures of 120 C (or 250 F).  One possible application
would be "tissue welding," the process of binding together edges of
cut tissue using "biological solder" such as albumin.  Infrared
lasers can do such welding, but Golosovsky (golos at vms.huji.ac.il,
972-2658-6551) says that the microwave approach uses much lower
power, can do the job faster, can deposit radiation at deeper levels
in the wound, and bandages are transparent to the microwaves.  Also
collateral tissue damage would be better controlled.  (Copty et al.,
Applied Physics Letters, 14 June 2004)

***********
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
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Physics News Update appears approximately once a week.

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