Volume 6 Issue 7, July 2010

The critical point of a fluid is defined as the point beyond which it ceases to exhibit distinct liquid- or gas-like states. A crossover between liquid-like and gas-like behaviour observed by inelastic X-ray scattering suggests subtle effects involving nanoscale fluctuations in the one-phase region above the critical point.

The Turing mechanism provides a paradigm for the spontaneous generation of patterns in reaction–diffusion systems. A framework that describes Turing-pattern formation in the context of complex networks should provide a new basis for studying the phenomenon.

The orientation of the magnetic field wrapped around a galaxy cluster has been measured for the first time, through a previously unexplored combination of traditional astronomy and computer simulations.

Confinement of helium in a micrometre-size box rounds the sharp transition and depresses the specific-heat maximum. But coupling an array of boxes through a thin, non-superfluid film is now shown to raise that maximum, while the boxes also enhance superfluidity in the film.

Experiments aimed at finding Einstein's elusive gravitational waves have reached their designed sensitivity. Yet we are still waiting for the first detection. What can we learn from this?

The optical spectrum of a single quantum dot is strongly affected by coherent tunnelling to a nearby sea of electrons.

The process of diffusion isn't usually expected to be able to generate useful work. But when a neutrally buoyant wedge object is placed in a fluid with a vertical density gradient, the diffusion-driven flow of material can indeed generate a measureable horizontal propulsion.

Luttinger-liquid theory describes interacting electrons in one dimension, so long as their energies are linear as a function of momentum. When the energies become nonlinear, particles and holes behave differently, with particles able to relax when injected into a quantum wire.

The observation of positive noise cross-correlations in a hybrid system consisting of a superconductor sandwiched between two normal metals provides evidence that in such a device Cooper pairs can be split into pairs of spatially separated, entangled electrons.

Some effects that have long been observed in superconductors are difficult to see in superfluid helium-4, despite the similar physics governing these systems, owing to the small correlation length in helium-4. Proximity effects have now been observed in that system, using an array of micrometre-size boxes linked by a thin helium film.

By conventional definition, a supercritical fluid is one that doesn’t exhibit distinct liquid- or gas-like states. This may need to be revised in light of measurements that show a sharp change in the speed of sound in supercritical argon when it crosses a well-defined line on its pressure versus temperature phase diagram.

Interatomic Coulombic decay is a recently discovered ionization process by which energy absorbed from incident radiation by one atom is rapidly transferred to another. A study of this process in helium now shows that it can operate over remarkably long distances of more than 45 atomic radii.

It has now been demonstrated that a dye-filled optical microresonator can trap photons such that their number doesn’t decrease even when the trap is cooled. The idea could lead to a Bose–Einstein condensate of light.

Few would expect the process of diffusion to generate useful work. But when a buoyant wedge-shaped object is placed in a fluid with a vertically stratified density gradient, the upward flow driven by diffusion can be translated into a measurable horizontal propulsion.

Large clusters of galaxies are cosmologically significant, and their thermal history is determined by magnetic fields. Simulations show that the magnetic-field lines in the Virgo cluster, rather surprisingly, are oriented radially. This would explain the observed ridged structure. Moreover, the model may explain why some clusters have not cooled as expected.

Similar to atoms in cold gases, exciton–polaritons in semiconductor microcavities can undergo Bose–Einstein condensation, but under non-equilibrium conditions. Now, quantized vortices and persistent currents — hallmarks of superfluid behaviour — have been observed in such condensates.

Despite all of the fundamental research carried out on them, artificial atoms continue to be a source of surprise. The intersection between the electrons in a quantum dot and a nearby sea of electrons can create unusual many-body states. A spectroscopic study now makes these states observable.

Networks have been widely explored in the context of classical statistical mechanics. But when quantum effects are added, qualitatively different behaviours emerge, even for the simplest cases.

Differences in diffusion constants of activator and inhibitor species can destabilize biological and chemical processes, leading to the spontaneous emergence of periodic spatial patterns. A general framework now provides the tools for studying such so-called Turing patterns in systems organized in complex networks.