Physics tip sheet #22 - July 17, 2002

July 17, 2002

1) Extending the second law of thermodynamics to microscales
G. M. Wang, E. M. Sevick, E. Mittag, D. J. Searles, D. J. Evans
Physical Review Letters (Print issue: July 29, 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. Azaïs, L. Duclaux, A.-M. Faugère, F. Béguin
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
-end-


American Physical Society

Related Dark Matter Articles from Brightsurf:

Dark matter from the depths of the universe
Cataclysmic astrophysical events such as black hole mergers could release energy in unexpected forms.

Seeing dark matter in a new light
A small team of astronomers have found a new way to 'see' the elusive dark matter haloes that surround galaxies, with a new technique 10 times more precise than the previous-best method.

Holding up a mirror to a dark matter discrepancy
The universe's funhouse mirrors are revealing a difference between how dark matter behaves in theory and how it appears to act in reality.

Zooming in on dark matter
Cosmologists have zoomed in on the smallest clumps of dark matter in a virtual universe - which could help us to find the real thing in space.

Looking for dark matter with the universe's coldest material
A study in PRL reports on how researchers at ICFO have built a spinor BEC comagnetometer, an instrument for studying the axion, a hypothetical particle that may explain the mystery of dark matter.

Looking for dark matter
Dark matter is thought to exist as 'clumps' of tiny particles that pass through the earth, temporarily perturbing some fundamental constants.

New technique looks for dark matter traces in dark places
A new study by scientists at Lawrence Berkeley National Laboratory, UC Berkeley, and the University of Michigan -- published today in the journal Science - concludes that a possible dark matter-related explanation for a mysterious light signature in space is largely ruled out.

Researchers look for dark matter close to home
Eighty-five percent of the universe is composed of dark matter, but we don't know what, exactly, it is.

Galaxy formation simulated without dark matter
For the first time, researchers from the universities of Bonn and Strasbourg have simulated the formation of galaxies in a universe without dark matter.

Taking the temperature of dark matter
Warm, cold, just right? Physicists at UC Davis are using gravitational lensing to take the temperature of dark matter, the mysterious substance that makes up about a quarter of our universe.

Read More: Dark Matter News and Dark Matter Current Events
Brightsurf.com is a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for sites to earn advertising fees by advertising and linking to Amazon.com.