July 31, 2009

LE12150

Ghost Images Reveal Quantum Properties

Ghost imaging occurs when a image is obtained using light that never
passes through the object in question. Such systems measure the
correlation between two optical beams and there has been an ongoing
debate as to whether they can be explained by classical as opposed to
quantum physics. We make a new kind of ghost imaging system
incorporating a hologram which is also placed remotely from the object.
The "non-local" hologram gives edge enhancement of our images and in
doing so reveals a violation of a Bell inequality. Such violations are
a hallmark of quantum physics and hence our system shows that some ghost
imaging is indeed quantum imaging...

...and here is the image!

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LF12649BR

There is order in the carbon cage

Endohedral fullerenes are scientifically intriguing and technologically relevant nano-objects where one or several atoms are enclosed in a cage of carbon atoms. In our work, we show that such endohedral atoms are ordered when a single layer of a particular multi-atom endohedral fullerene (Dy3N@C80) is adsorbed on a crystalline metal surface. By combining two experimental techniques - scanning tunneling microscopy and X-ray photoelectron diffraction - we are able to analyze both the ordering of the encaging carbon atoms as well as the ordering of the endohedral dysprosium and nitrogen atoms. With the large variety of currently available multi-atom endohedral fullerenes, the adsorption of such endohedral fullerenes on single crystal surfaces, as shown in our work, provides a means to create ordered arrays of endohedral, decoupled clusters in two dimensions. Apart from its scientific value, there is an inherent beauty associated with the photoelectron diffraction experiments: Analogous to the shadow produced by a lampshade where a light bulb is sitting inside, the scattering at encaging carbon atoms of the photoelectrons from the endohedral nitrogen atoms produces an inverted shadow of the cage - due to the so-called forward-focusing effect - hence producing a forward-projected picture of a fullerene as viewed from inside.

LC12636ER

Swimming in Sand

One of the properties of granular materials that makes them unique and leads to striking and unexpected behaviors is their ability to act either as a solid,
supporting a load like sand on a beach, or as a fluid, flowing freely as in avalanches. Nowhere is this behavior more remarkable than in the behavior of lizards known as Sand Swimmers. These creatures, being cold blooded, cannot survive on the surface of their desert habitats during the day, and have evolved the ability to submerge up to 10 cm beneath the sand to lower temperature regions, and even to travel within the sand bed. In this paper we present the first computational study of "sand swimming", using a simple model that has been recently proposed. It was found that optimal conditions that idealized swimmers must use to critically fluidize a sand bed so that it is rigid enough to support a load when needed, but fluid enough to permit motion with minimal resistance. In other words, the sand swimmers locally probe the fundamental time-scale in a granular packing.

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LE12132

Stirring, not mixing: binary black holes action on electromagnetic fields.

Electromagnetic fields threading a spinning black hole have long
been key in models attempting to explain powerful emissions in
fascinating astrophysical systems such as active galactic nuclei, gamma
ray bursts, quasars, etc. This work studies the effects produced by a binary
black hole system on an encompassing electromagnetic field.
In particular, it highlights the possibility that the merger of the black holes
may amplify the electromagnetic field strength. In addition, a time varying
oscillation of the electromagnetic field induced by the shrinking orbit and
merger which may lead to observable emissions that cab be captured
by current and future power telescopes. These systems will also
emit copiously in gravitational waves as the black hole collide.
Consequently, merging black holes interacting with electromagnetic fields
would provide an unprecedented opportunity for studying such systems via
both electromagnetic and gravitational waves. Such studies will advance our
understanding of these systems, and gravity within general relativity and
beyond.