Physics Tip Sheet #52 - August 26, 2005

Contact: James Riordon
riordon@aps.org
301-209-3238
American Physical Society

Highlights in this issue: Cheaper Fuel for the Hydrogen Economy; Clear Sailing in Cells; Nanodiamond Magnets; and the Physics of Freezing Seawater

Cheaper Fuel for the Hydrogen Economy
M. K. Kostov et al.
Physical Review Letters (upcoming article)

Defects on carbon surfaces provide a cheap route to releasing Hydrogen from water, according to simulations conducted at North Carolina State University and Oak Ridge National Laboratory. The research is good news for those eagerly anticipating the Hydrogen economy, which would allows us to operate cars and other machines that exhaust only water in lieu of the hydrocarbon pollutants that produce smog, acid rain, and global warming. Heating water to a temperature of about 2000 degrees Celsius is one way to break it down and produce hydrogen gas, but the energy in the heat is wasted and results in a very expensive source of Hydrogen fuel. Defects on carbon structures, such as missing atoms in nanotubes, fibers, and Buckyballs, help break down water at only 1000 degrees, according to the simulation. Lower temperatures mean less waste heat and cheaper hydrogen, which in turn reduces the economical barriers to clean Hydrogen power production.

Natural Solutions to Cellular Traffic Jams
C. Pangarkar et al.
Physical Review Letters (upcoming article)

Endosomes, vesicles that carry nutrients and information from the perimeter of a cell to its nuclei, have evolved a more efficient means of regulated transport than modern highway systems, according to researchers from the University of California Santa Barbara. Endosomes travel through a cell via a highway-like system made of structural supports called microtubules. By marking single endosomes with florescent tags and observing their motion, researchers found that a given endosome does not travel straight to the nucleus as expected. Instead, it randomly switches between traveling toward and away from the nucleus, with no preferred direction. This method of traveling may not sound efficient, but computer simulations show that the switching symmetry distributes the endosomes evenly along the microtubules. The starburst-shaped layout of the microtubules creates a high concentration of endosomes at the nuclei. This method ensures that a nucleus gets what it needs in a well-reg! ulated fashion, even if the cell moves or there is increased traffic flow.

Nanodiamond Magnets
S. Talaptra et al.
Phys. Rev. Lett. 95, 097201 (2005) http://link.aps.org/abstract/PRL/v95/e097201  

Nanodiamonds became magnetic when bombarded with clusters of carbon or nickel atoms, in experiments conducted by researchers at Rensselaer Polytechnic Institute in Troy, New York. The tiny diamonds, which consist of carbon atoms that are not normally magnetic, are only 4 to 5 nanometers across and were deposited in thin layers on silicon substrates. The researchers fired carbon and nickel clusters into the diamonds with a type of particle accelerator called an ion implanter. Magnetic nanodiamonds are promising structures for robust, high density magnetic memory and quantum bits for quantum computers.

Freezing Seawater
L. Vrbka and P. Jungwirth
Physical Review Letters (upcoming paper)

Sea ice is less salty than seawater. This well known phenomenon of brine rejection from freezing seawater triggers ocean currents that influence global climate, but the process of brine rejection has not until now been understood at a microscopic level. Now, researchers at the Academy of Sciences of the Czech Republic have carried out simulations that allow them to follow individual water molecules and salt ions during the process of freezing seawater. They describe the mechanism of brine rejection as a fluctuation in salt density close to the ice front, followed by the growth of a new neat ice layer next to a disordered layer of brine. In addition to being relevant to climate and ocean currents, the study could have implications for desalination technology.

Journal articles are available to journalists on request.

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American Physical Society
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Email: riordon@aps.org