Text 209, 58 rader
Skriven 2004-10-15 08:13:00 av Herman Trivilino (1:106/2000.7)
Ärende: PNU 704
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PHYSICS NEWS UPDATE
The American Institute of Physics Bulletin of Physics News
Number 704 October 13, 2004
by Phillip F. Schewe, Ben Stein

A REALISTIC LASER-OPERATED MOLECULAR LOCOMOTIVE has been proposed by a Texas
A&M researcher (Zhisong Wang, nargate@jewel.tamu.edu). For those designing
materials at the smallest workable scales, a major dream is to build
nano-locomotives that would move through a molecular-scale track to perform
various tasks, such as transporting building blocks for nanomachines.  Earlier
proposals have outlined some innovative designs for these nanoengines (for
example, see http://www.aip.org/pnu/2000/split/pnu490-1.htm).  While
nano-locomotives are still in the blueprint stage, a new model brings the idea
closer to reality by incorporating the latest working knowledge of
nanomaterials as well as the probabilistic, jiggly nature of the molecular
world.  In Wang's design, a nano-locomotive would have a main body consisting
of cars each made up of a linear polymer chain.  Either end of the train would
have a chemically tailored "head" group that could bind to or break from a
track, which could be a cylinder-shaped microtubule found in biology.  Either
end of the locomotive could attach via covalent bonds to special molecular
groups on the track.  Laser pulses would move the train: one light pulse would
break the bond from one of the train's ends and another laser pulse would cause
each car of the train to change its molecular configuration, and expand its
size to reach the next part of the track.  Thermal fluctuations of the motor
itself and the environment play a vital role, for example as the train's head
seeks the next binding site on the track.  Wang has proposed a multistep
"optomechanical work cycle" that precisely outlines the laser steps needed to
move the train, and even reverse its direction.  The locomotive would work not
only as a motor, but a powerful molecular engine that could generate a pulling
force 10 times greater than of the natural biomotor kinesin.  Such forces, of
about 100 piconewton, could allow the nano-locomotive to break molecular bonds
and help in constructing nanomaterials while delivering ca
rgo. (Wang, Physical Review E, 15 September 2004; also see
http://focus.aps.org/story/v13/st27).

FINDING A VEIN, necessary for administering intravenous solutions, can often be
difficult.  A new device, called a Vein Contrast Enhancer (VCE), uses sensitive
infrared sensing to find the vein beneath the skin and then also projects the
rather spooky vein image back onto the patient's wrist.  This makes it appear
as if the veins were lying right on top, making it easy for a nurse to make an
injection. How does it work?  An array of light emitting diodes shines infrared
light at the subject, and one depends on the fact that red blood cells scatter
light differently from surrounding fatty tissue.  The scattered light passes
through some filters and then is captured by a CCD TV camera, processed by
computer, and rendered as a sort of movie at a rate of 30 frames per second.
These images can be projected onto the subject through a careful aligning
process to register the surface projection with subcutaneous anatomy (see
figure at www.aip.org/png).  Herbert Zeman and his colleagues at the University
of Tennessee Health Science Center in Memphis have done extensive clinical
trials with VCE devices and are now doing trials with the projection
capability. The general spatial resolution of the process is about 0.1 mm. 
Veins as deep as 8 mm have been imaged.  This work is being presented at this
week's Frontiers in Optics meeting in Rochester, co-sponsored by the Optical
Society of America (OSA) and the American Physical Society (APS).
(http://www.osa.org/meetings/annual/. See also http://www.conenhill.com/)

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 * Origin: Big Bang (1:106/2000.7)