Number 726, April 7, 2005
by Phil Schewe and Ben Stein
The Smallest Electric Motor
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
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. (Alessandriniet al., Applied Physics Letters, 28 March, 2005; lab site at www.s3.infm.it
)
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 efficient 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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