LL12418AR

Novel evidence of matter interference

This is a nanometer-sized version of an experiment imagined by the colorful physicist Richard Feynman half a century ago. Single electrons within a very narrow energy band follow two different paths simultaneously and interfere with themselves. As a result, their distribution would oscillate with the detection angle. The present approach, which will certainly induce a new generation of experiments with matter particles and light, has never been tried or even imagined before. Its novelty is that it seeks and finds oscillations on the energy width that, in principle, were not expected to occur.

LN12132

A new mechanism for atmospheric teleconnections in the laboratory?

‘Teleconnections’ occur in the climate system when variations in the weather at two remotely separated regions follow each other and are noticeably correlated. Conventional wisdom in meteorology explains this phenomenon through waves propagating from one location to another, but is this the only way to make the connection? In a new set of laboratory experiments, using analogs of the mid-latitude atmospheric circulation on Earth, we have demonstrated an alternative mechanism that may represent a new pathway for coupled chaotic behavior in the Earth's climate system. Our experiment consists of two liquid-filled, rotating cylindrical annular tanks, both mounted on the same rotating table. Each tank consists of two thermally conducting cylinders, one inside the other, between which a carefully controlled temperature contrast is applied, recreating the temperature contrast between the warm tropics and the cold polar regions on a rotating Earth-like planet. The combination of differential heating with rapid rotation captures the essential physics of the large-scale atmospheric circulation in mid-latitudes that leads to the formation of cyclone “storms” and anticyclones. When the two tanks are coupled, by allowing variations in the heat transfer in one tank affect the boundary conditions of the other, changes in the amplitude of the “storms” in both systems are found to synchronize, even when the flows are chaotic. Only a tiny perturbation to the boundary conditions is needed to produce detectable synchronization, suggesting that this may be an important mechanism affecting the predictability of the real atmosphere.

EK10620

Common Contagion Patterns for Traders, YouTube users, school kids and insurgents

Despite the flood of published works, network science ‑‑ and in
particular, the study of contagion phenomena on networks ‑‑ has an
Achilles heel. Until now, the transmission of information, viruses or
rumors on a network has always been assumed to be fast enough that the
network could be considered to be quasi‑static, or at most slowly
varying. By contrast, we show that a wide range of important real‑
world phenomena (from YouTube downloads to the transmission of
destabilizing rumors in markets) lie in the network 'twilight zone'
where the network can evolve on the same timescale as the contagion
process. Our accompanying dynamical network model describes social
group dynamics which are quantitatively consistent with empirical
observations from financial markets through to modern insurgent
groups. Despite the visual differences in their activity profiles
(i.e. level of infection vs time), these social and biological systems
can all be explained using this common group‑dynamical contagion
model, simply by varying the relative timescales for groups forming
and breaking as compared to the transmission process. One implication
of our work is that the problems of understanding (i) how flu
pandemics spread around schools, (ii) how destabilizing rumors spread
around financial markets, (iii) how the unexpected popularity of
YouTube downloads (e.g. Susan Boyle) spreads among Internet users, and
(iv) how secret messages should spread among insurgents in Afghanistan
and Iraq, are all the 'same' problem. In particular, their diverse
contagion profiles can all be described using the same dynamical model.

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LN12331

Reprogrammable Control of Spin Wave Flow

A meta-material consisting of magnetic nanowires has been realized where the propagation of wave-like spin excitations is allowed or stopped depending on the magnetic state. This device forms a novel kind of artificial crystal where the dynamic response in the microwave frequency regime is reprogrammable.

Nanotechnology allows one to generate artificial materials with unforeseen physical properties, i.e., meta-materials. Using periodic arrangements of dielectric nanostructures, so-called artificial crystals have been shown to exist for electro-magnetic waves in the optical frequency regime. Such photonic crystals have led to unprecedented control of light propagation on microchips and improved performance of optical devices. We have now shown that magnetic materials periodically patterned on the nanoscale form a novel kind of artificial crystal for collective spin excitations which can be reprogrammed. Due to the non-volatility of magnetic states the fabricated one-dimensional magnonic crystal has provided an enhanced level of control of GHz excitations propagating in magnetic solids. Such spin wave excitations have a wavelength on the nanoscale which is several orders of magnitude shorter than corresponding electromagnetic waves. Nanodevices are thus possible which are operating at microwave frequencies and offer multi-functionality in magnonic applications.