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{at}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{at}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{at}gsi.de)

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