Public Release: 

Physics tip sheet #18 - June 19, 2002

American Physical Society

1) How to find life on extra-solar planets (2 papers)
L. Arnold, et al./N. J. Woolf, et al.
arXiv preprint server (To appear in Astronomy & Astrophysics/Astrophysical Journal)

With the discovery of Sun-like solar systems, many researchers are interested in ways of detecting life on planets in those systems. One technique would be to look for the characteristic spectrum of light given off by vegetation. Two groups have determined what this light would look like by observing Earthshine - the light given off by the Earth. They observe that light by seeing it faintly reflected from the surface of the moon. Another application of Earthshine studies is as a monitor for global ozone and other climate data.

Preprint (Arnold): http://www.arxiv.org/abs/astro-ph/0206314
Preprint (Woolf): http://www.arxiv.org/abs/astro-ph/0203465

2) Liquid light
H. Michinel, J. Campo-Táboas, R. García-Fernández, J. R. Salgueiro, M. L. Quiroga-Teixeiro
Physical Review E (Print issue: June 2002)

A laser beam can be regarded as a gas of photons. Some researchers use this analogy to propose a technique for making a liquid state of light. They plan to direct a laser beam into a special type of crystal that has the effect of making photons interact with other photons. The light then acts if it were a liquid droplet with properties such as surface tension.

Journal article: http://link.aps.org/abstract/PRE/v65/e066604

3) Sharks detecting electrical signals
B. R. Brown, J. C. Hutchison, M. E. Hughes, D. R. Kellogg, R. W. Murray
Physical Review E (Print issue: June 2002)

Sharks use electrosensors to enhance prey detection, to orient themselves in external magnetic fields and to detect mates. However, the process of the electrical sensing is poorly understood. Some areas of a shark's body, such as the "cheeks" contain a high density of gel-filled bulbs that connect to gel-filled canals 3-20 centimeters in length. Although the gel was identified as early as 1678, its use has been unknown. This research looks at the electrical properties of the gel and concludes that it is has the right characteristics to play a vital role in electrical sensing.

Journal article: http://link.aps.org/abstract/PRE/v65/e061903

4) Nano-flashlight
C. Favre, V. Boutou, S. C. Hill, W. Zimmer, M. Krenz, H. Lambrecht, J. Yu, R. K. Chang, L. Woeste, J.-P. Wolf
To appear in Physical Review Letters

Researchers have created a nano-scale flashlight by directing a laser beam into a microscopic water droplet. The laser causes plasma to form inside the droplet from which white-light is emitted in one direction. The droplet acts as a lens that focuses the incoming laser energy. The energy heats the water so much that it forms a plasma around 5000-7000 degrees. This temperature, similar to the sun's surface, causes light to be emitted in the visible spectrum.

Journal article: Available to journalists on request

5) Nanodevices feel forces from "empty" space
O. Kenneth, I. Klich, A. Mann, M, Revzen
To appear in Physical Review Letters

Paradoxically, empty space exerts a force on objects. These forces are significant on the scale of nanotechnological devices and must be taken into account when designing those future technologies. This "Casimir effect" was first predicted in 1948 and has been experimentally confirmed. The force between objects is attractive in most cases but is a big problem for nanodevices, which could effectively weld solid from the effect. However, new calculations show that the Casimir effect still holds surprises and that some common techniques for predicting the effects of these vacuum forces not only get the size of the force wrong but also the direction - sometimes it is repulsive. Furthermore, the direction is temperature dependent.

Journal article: Available to journalists on request

6) Relativity affects structure of metals
H. Häkkinen, M. Moseler, U. Landman
To appear in Physical Review Letters

Knowing how small clusters of atoms join together is vital in the drive to create nanoscale devices. Surprisingly, the structures that appear depend heavily on Einstein's special theory of relativity, usually most applicable to extremely fast-moving objects. This paper analyzes the structures of gold, silver and copper, all of interest in nanotechnology. Among the surprising results is that for up to 13 atoms gold likes to cluster in flat planes rather than three-dimensional structures. Although this seems few atoms, some nanodevice proposals operate on this scale. If relativity is not taken into account, calculations predict that gold will cluster in 3D structures even for small numbers of atoms.

Journal article: Available to journalists on request

7) Close-up of colliding magnetic fields
F. S. Mozer, S. D. Bale, T. D. Phan
Physical Review Letters (Print issue: July 1, 2002)

At the region where magnetic fields from the Sun and Earth meet, field lines buckle, break, and snap together again, powering dramatic events like auroras in the process. Theorists have begun to understand this mysterious region, known as the magnetopause, but have yet to observe it up close. Now, a group reports the results of the closest encounter yet between a space probe and the central magnetopause. The data mostly confirm existing theory, but also hint at new phenomena. Researchers expect the observations will herald a new phase in their understanding of astrophysical magnetic fields.

Physical Review Focus: http://focus.aps.org/v9/st30.html
Journal article: http://link.aps.org/abstract/PRL/v89/e015002

8) Now in print (previously mentioned preprints now published)
TS#3.1: The origins of friction: Budakian, Putterman (PRB, June 15)
From: http://www.aps.org/media/tips/tips030602.html
Journal article: http://link.aps.org/abstract/PRB/v65/e235429

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