Physics tip sheet #22 -- July 17, 2002

Physicists have experimentally demonstrated how microscopic systems can run in the opposite direction to that which the second law of thermodynamics requires for large systems. The experiment confirms the predictions of the fluctuation theorem, which states how often and for how long a small object can extract energy from a surrounding bath instead of the usual process of dissipating heat into the bath. This has implications for the construction of nanodevices, which might unexpectedly run backwards or fail to work if these fluctuations are not taken into account. The effect was noticeable for particles six micrometers in size over timescales as long as two seconds.

Physics News Update: http://www.aip.org/enews/physnews/2002/split/598-1.html
Journal article: http://link.aps.org/abstract/PRL/v89/e050601
Further background and analysis available on request

2) Historical experiment repeated with high-tech equipment
I. T. Lee, S. Fan, V. Halyo, E. R. Lee, P. C. Kim, M. L. Perl, H. Rogers
Physical Review D (Print issue: July 1, 2002)

All high school students learn how Millikan determined the elementary charge of an electron in an experiment that balanced the weight of an oil drop against the force from an electric field on the charged drop. The results showed that electric charge only comes in multiples of some fixed quantity, the charge of the electron. This experiment performs the largest ever search for fractionally charged particles using silicone oil in a modern version of Millikan's experiment. No fractionally charged particles were found in the experiment, indicating that any such particles must occur less often than 1 in 10^22 particles if at all.

Journal article: http://link.aps.org/abstract/PRD/v66/e012002

3) Transforming diamond
H. He, T. Sekine, T. Kobayashi
Applied Physics Letters (Print issue: July 22, 2002)

Diamond is one structural form of carbon and it comes in two different structures, hexagonal and cubic. The cubic structure is the hardest known material whereas graphite, another form of carbon, is quite soft. These three different forms of carbon can all be transformed into each other since the experiment reported in this paper. Previously, there had been no direct way to convert cubic diamond into hexagonal diamond. The authors sent a shock wave through the cubic diamond, which caused the crystal structure to rearrange into the hexagonal form. They note that temperatures too high or low can cause the cubic diamond to turn directly into graphite.

Journal article: http://link.aip.org/link/?apl/81/610

4) Making better lithium batteries
P. Aza�s, L. Duclaux, A.-M. Faug�re, F. B�guin
Applied Physics Letters (Print issue: July 22, 2002)

Commercial lithium batteries are made with graphite electrodes but would have better electrical properties if the graphite were mixed with some lithium. However, most preparation techniques for combining the lithium with graphite actually lead to worse electrical properties and preclude the use of such a mixture in commercial products. A new technique that involves ball-milling lithium with graphite in an argon atmosphere has shown that much better electrical characteristics are possible than those currently used.

Journal article: http://link.aip.org/link/?apl/81/775

5) Using Internet "pings" to simulate earthquakes
S. Abe, N. Suzuki
arXiv preprint server

The times taken for messages to bounce around the Internet (pings) are like seismic vibrations - sudden drastic changes in timescales correspond to earthquakes. The mathematical correspondence is perfect and the authors develop the equivalent of the Richter scale for earthquakes in this paper. The authors comment that this behavior means we can learn about earthquake behavior by doing experiments on the Internet.

Preprint: http://www.arxiv.org/abs/cond-mat/0207302

6) Galaxies help weigh neutrinos
O. Elgaroy, et al.
Physical Review Letters (Print issue: August 5, 2002)

Using data from an ongoing galactic survey, researchers have constrained the mass of neutrinos to no more than a billionth of the mass of a hydrogen atom. The result means that the ubiquitous particles could account for at most one-eighth of the invisible dark matter suffusing the universe.

Physical Review Focus: http://focus.aps.org/v10/st2.html
Journal article: Available on request

7) Background: Dark Matter and Dark Energy (two papers)
M. Turner; M. Loidl
arXiv preprint server

Stars account for only about 0.5% of the content of the Universe; the bulk of the Universe is optically dark. The dark side of the Universe is comprised of at least 0.1% light neutrinos; 3.5% baryons; 29% cold dark matter; and 66% dark energy. The first paper examines some critical questions about dark matter and energy such as: What form do the dark baryons take? What is (are) the constituent(s) of the cold dark matter? What is the nature of the mysterious dark energy that is causing the Universe to speed up. The second paper describes experimental efforts to characterize dark matter and the current state of the most important experiments.

Preprint (Turner): http://www.arxiv.org/abs/astro-ph/0207297
Preprint (Loidl): http://www.arxiv.org/abs/astro-ph/0207308