Text 379, 68 rader
Skriven 2005-04-07 16:07:05 av Herman Trivilino (1:106/2000.7)
Ärende: PNU 726
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PHYSICS NEWS UPDATE
The American Institute of Physics Bulletin of Physics News
Number 726 April 7, 2005
by Phillip F. Schewe, Ben Stein
        
THE SMALLEST ELECTRIC MOTOR in the world, devised by physicists at UC Berkeley,
is based on the shuttling of atoms between two metal droplets---one large and
one small---residing on the back of a carbon nanotube. An electric current
transmitted through the nanotube causes atoms to move from the big to the small
droplet. In effect, potential energy is being stored in the smaller droplet in
the form of surface tension. Eventually the smaller drop grows so much that the
two droplets touch.  Then the accumulated energy is suddenly discharged as the
larger droplet reabsorbs its atoms through the newly created hydrodynamic
channel. This device constitutes a "relaxation oscillator" with an adjustable
operating frequency. If the oscillator is attached to a mechanical linkage, it
acts as a motor and can be used to move a MEMS device in inchworm fashion
(movie:
physics.berkeley.edu/research/zettl/projects/Relax_pics.html). The peak pulsed
power is 20 microwatts. Considering that the device is less than 200 nm on a
side, the power density works out to about 100 million times that of the 225 hp
V6 engine in a Toyota Camry. Chris Regan (bcregan@berkeley.edu), a member of
Alex Zettl's group at Berkeley, reported these and related results at the
recent APS meeting in Los Angeles and in the 21 March 2005 issue of Applied
Physics Letters.
                
A SINGLE-PROTEIN WET BIOTRANSISTOR has been devised by physicists at the
INFM-S3 Center in Modena, Italy.  Metalloproteins help to shuttle electrons
among molecules, a necessary task for powering such life-critical functions as
respiration, photosynthesis, and enzyme reactions.  To do this the protein
bristles with side chains where binding can be achieved.  Why not harness all
this functionality normally used for keeping an organism alive for performing
digital information processing?  Paolo Facci (p.facci@unimo.it,
39-059-205-5654) and his colleagues use a particular bacterial protein called
azurin in a strategic position between two gold electrodes, which act as the
source and drain of a transistor.  A third electrode, acting as the gate,
enables the centrally located azurin to allow the passage of an electrical
current (see figure at www.aip.org/png).  The whole process takes place in a
wet environment, the first time a single-protein bio-transistor has been
operated in this way.  Facci believes that with the addition of bio-inorganic
electrodes, his bio-transistor could be implemented in various wet situations,
such as serving in brain-machine interfaces or for sensing cellular events.
(Alessandrini et al., Applied Physics Letters, 4 April, 2005 )
                                                                
USING THE LHC TO STUDY HIGH ENERGY DENSITY PHYSICS? The Large Hadron Collider
(LHC) will be the most powerful particle accelerator around when, according to
the plans, it will start operating in the year 2007.  Each of its two 7-TeV
proton beams will consist of 2808 bunches and each bunch will contain about 100
billion protons, for a total energy of 362 megajoules, enough to melt 500 kg of
copper.  What if one of these full-power beams were to accidentally strike a
solid surface, such as a beam pipe or a magnet? To study this possibility,
scientists have now simulated the material damage the beam would cause.  (In
the case of an actual emergency, the beam is extracted and led to a special
beam dump.)  The computer study showed, first of all, that the proton beam
could penetrate as much as 30 m of solid copper, the equivalent of two of LHC's
giant superconducting magnets. It is also indicated that the beam penetrating
through a solid material would not merely bore a hole but would create a potent
plasma with a high density (10 percent of solid density) and low temperature
(about 10 eV). Such plasmas are known as strongly coupled plasmas.  One way of
studying such plasmas would therefore be to deliberately send the LHC beam into
a solid target to directly induce states of high-energy-density (HED) in
matter, without using shock compression. This is a novel technique and could be
potentially a very eff
icient method to study this venerable subject. (Tahir et al., Physical Review
Letters, upcoming article; contact Naeem Tahir of the GSI Laboratory in
Darmstadt, n.tahir@gsi.de)

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