[ Back to EurekAlert! ] Public release date: 26-Sep-2008
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Contact: James Riordon
riordon@aps.org
301-919-2173
American Physical Society

Tsunami invisibility cloak, dark energy v. the void, sorting nanotubes with light, and more

News from the American Physical Society

IMAGE: Laboratory experiments show that obstacles arranged in fluids in certain patterns can effectively make objects they surround invisible to waves. If it works as well in in scaled-up versions, it...

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Tsunami Invisibility Cloak
M. Farhat, S. Enoch, S. Guenneau and A.B. Movchan
Physical Review Letters (forthcoming)

Rather than building stronger ocean-based structures to withstand tsunamis, it might be easier to simply make the structures disappear. A collaboration of physicists from the Centre National de la Recherche Scientifique (CNRS) and Aix-Marseille Universite in France and the University of Liverpool in England have conducted laboratory experiments showing that it's possible to make type of dike that acts as an invisibility cloak that hides off-shore platforms from water waves. The principle is analogous to the optical invisibility cloaks that are currently a hot area of physics research.

Tsunami invisibility cloaks wouldn't make structures disappear from sight, but they could manipulate ocean waves in ways that makes off-shore platforms, and possibly even coastlines and small islands, effectively invisible to tsunamis. If the scheme works as well in the real world as the lab-scale experiments suggest, a tsunami should be able to pass right by with little or no effect on anything hidden behind the cloak. - JR


Dark Energy v. The Void: What if Copernicus was Wrong?
Timothy Clifton, Pedro G. Ferreira, and Kate Land
Physical Review Letters (forthcoming)

Dark energy is at the heart of one of the greatest mysteries of modern physics, but it may be nothing more than an illusion, according physicists at Oxford University. The problem facing astrophysicists is that they have to explain why the universe appears to be expanding at an ever increasing rate. The most popular explanation is that some sort of force is pushing the accelerating the universe's expansion. That force is generally attributed to a mysterious dark energy.

Although dark energy may seem a bit contrived to some, the Oxford theorists are proposing an even more outrageous alternative. They point out that it's possible that we simply live in a very special place in the universe - specifically, we're in a huge void where the density of matter is particularly low. The suggestion flies in the face of the Copernican Principle, which is one of the most useful and widely held tenants in physics.

Copernicus was among the first scientists to argue that we're not in a special place in the universe, and that any theory that suggests that we're special is most likely wrong. The principle led directly to the replacement of the Earth-centered concept of the solar system with the more elegant sun-centered model.

Dark energy may seem like a stretch, but it's consistent with the venerable Copernican Principle. The proposal that we live in a special place in the universe, on the other hand, is likely to shock many scientists. The maverick physicists at Oxford conclude their paper by pointing out that forthcoming tests of the Copernican principle should help us sort out the mystery in the next few years. -JR


Meta-Screens: Squeezing Light into Sub-Wavelength Spots
Loic Markley, Alex M.H. Wong, Yan Wong, and George V. Eleftheriades
Physical Review Letters
http://link.aps.org/abstract/PRL/v101/e113901

In a new study, physicists at the University of Toronto have invented a simple structure called a meta-screen, designed to focus light into tiny spots smaller than the wavelength of the photons in use. These sub-wavelength spots overcome the diffraction limit, thus allowing even the smallest details of an object to be visualized.

Researchers developed a meta-screen composed of slots cut into a metallic screen, each narrowly spaced (less than half a wavelength apart) and of a precise length. They found that screen was able to effectively increase the range of sub-wavelength spots, enabling greater image resolution.

The meta-screen is the first sub-wavelength focusing technique capable of being scaled to any arbitrary wavelength, thereby offering unprecedented levels of resolution and flexibility for imaging and sensing apparatuses involving electromagnetic waves, such as radio waves for medical diagnostics or light for optical microscopy. -NR


Tweezers Trap Nanotubes by Color
T. Rodgers, S. Shoji, Z. Sekkat and S. Satoshi Kawata
Physical Review Letters
http://link.aps.org/abstract/PRL/v101/e127402

Singled-walled carbon nanotubes are graphene sheets wrapped into tubes, and are typically made up of various sizes and with different amounts of twist (also known as chiralities). Each type of nanotube has its own electronic and optical properties. Physicists at Osaka University in Japan used colored light to selectively manipulate different types of carbon nanotubes. They found that some of nanotubes displayed a tendency to cluster at the focal area of a focused laser beam.

Nanotubes are known for their strong color-dependant interactions with light. By using an optical tweezer, a device that traps microscopic or nanoscopic objects in laser beams, researchers were able to selectively pull only specific colors of nanotube into focus.

Their results are the first experimental evidence demonstrating that colored light drives the clustering of nanotubes in a laser tweezer. Moreover, this color dependence can be exploited to select one type of nanotube over another. The study is a significant step towards developing optical methods for sorting and purification of nanotubes, a process that remains a major challenge for the application of nanotubes to engineering. -NR

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