THE SMALLEST ELECTRIC MOTOR
Date: Thursday, April 07, 2005 @ 23:55:19 UTC
Topic: Devices


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.
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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)

Source: The American Institute of Physics Bulletin of Physics News Number 726 April 7, 2005 by Phillip F. Schewe, Ben Stein





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