Dynamical clustering in driven granular gas

in Europhysics Letters [=EPL] (2012), 99

Driven granular gases present rich dynamical behaviors. Due to inelastic collisions, particles may form dense and slow regions. These clusters emerge naturally during a cooling phenomenon but another ... [more ▼]

Driven granular gases present rich dynamical behaviors. Due to inelastic collisions, particles may form dense and slow regions. These clusters emerge naturally during a cooling phenomenon but another dynamical clustering is observed when the system is continuously excited. In this paper, the physical processes that trigger the transition from a granular gas to a dynamical cluster are evidenced through numerical simulations. At the granular scale, the transition is evidenced by the observation of caging effects. At the scale of the system, the transition is emphasized by density fluctuations. Physical arguments, based on relaxation times, provide an analytical prediction for the edge between dynamical regimes. [less ▲]

Nuclear forward and inelastic spectroscopy on 125Te and Sb2 125Te3 2

in Europhysics Letters [=EPL] (2010)

We report on the observation of nuclear forward and nuclear inelastic scattering of synchrotron radiation by Te-125 and the application of both spectroscopic methods to tellurium compounds by using a high ... [more ▼]

We report on the observation of nuclear forward and nuclear inelastic scattering of synchrotron radiation by Te-125 and the application of both spectroscopic methods to tellurium compounds by using a high-resolution backscattering sapphire monochromator in combination with fast detection electronics. The lifetime of the nuclear resonance and the energy of the transition were determined to be 2.131(12) ns and 35493.12(30) eV, respectively. As applications, the nuclear inelastic spectrum in Sb2Te3 and the nuclear forward scattering by Te metal were measured. These measurements open the field of nuclear resonance spectroscopy on tellurium compounds such as thermoelectric and superconducting materials. [less ▲]

Energetic approach for the characterization of taps in granular compaction

in Europhysics Letters [=EPL] (2008), 84(4),

We report numerical investigations for the compaction dynamics of dense granular assemblies. The studies are based on the non-smooth contact dynamics model. Our work suggests that the dimensionless ... [more ▼]

We report numerical investigations for the compaction dynamics of dense granular assemblies. The studies are based on the non-smooth contact dynamics model. Our work suggests that the dimensionless acceleration parameter Gamma, used by a large majortiy of authors, is not appropriate for rescaling the data. We prove that the dimensionless energy Xi, injected in the granular system at lift-off, is more appropriate and leads to robust interpretations of the compaction dynamics. Indeed, the injected energy allows to pass energy barriers that separate local equilibrium states. Using the Eyring picture of relaxation dynamic, we show that the consideration of Xi leads to a new law for compaction. [less ▲]

Aging of an antibubble

in Europhysics Letters [=EPL] (2005), 69(6), 966-970

Antibubbles are unusual fluid objects consisting of a thin spherical air shell surrounding a liquid globule. Here we study and analyze the aging of these inverted bubbles. The lifetime is found to be ... [more ▼]

Antibubbles are unusual fluid objects consisting of a thin spherical air shell surrounding a liquid globule. Here we study and analyze the aging of these inverted bubbles. The lifetime is found to be distributed along an exponential law. Moreover, the breakdown of the air film is observed to be the analogue of dewetting by spinodal decomposition. We interpret the long lifetime of the antibubbles as resulting from the slow drainage of the air until the film reaches a critical thickness. Then, van der Waals forces act, leading to the collapse of the film. [less ▲]

Block-to-granular-like transition in dense bubble flows

in Europhysics Letters [=EPL] (2004), 65(3), 316-322

We have experimentally investigated 2-dimensional dense bubble flows underneath inclined planes. Velocity profiles and velocity fluctuations have been measured. A broad second-order phase transition ... [more ▼]

We have experimentally investigated 2-dimensional dense bubble flows underneath inclined planes. Velocity profiles and velocity fluctuations have been measured. A broad second-order phase transition between two dynamical regimes is observed as a function of the tilt angle theta. For low theta values, a block motion is observed. For high theta values, the velocity pro. le becomes curved and a shear velocity gradient appears in the flow. [less ▲]

Nondispersive two-electron wave packets in the collinear driven helium atom

in Europhysics Letters [=EPL] (1999), 46(1), 24-30

Nondispersive two-electron wave packets are found in the Floquet spectrum of the driven, one-dimensional helium atom. In classical phase space, they are anchored to the principal nonlinear resonance ... [more ▼]

Nondispersive two-electron wave packets are found in the Floquet spectrum of the driven, one-dimensional helium atom. In classical phase space, they are anchored to the principal nonlinear resonance between the collinear frozen planet orbit and the driving field linearly polarized along the orbit. These novel, highly correlated eigenstates of the driven three-body Coulomb problem, exhibit lifetimes of the order of 10(3)...10(7) periods of the driving field, with strong fluctuations reminiscent of chaos-assisted tunneling. [less ▲]

Coulomb interaction and ferroelectric instability of BaTiO3

in Europhysics Letters [=EPL] (1996), 33(9), 713-718

Using first-principles calculations, the phonon frequencies at the Gamma-point and the dielectric tensor are determined and analysed for the cubic and rhombohedral phases of BaTiO3. The dipole-dipole ... [more ▼]

Using first-principles calculations, the phonon frequencies at the Gamma-point and the dielectric tensor are determined and analysed for the cubic and rhombohedral phases of BaTiO3. The dipole-dipole interaction is then separated a la Cochran from the remaining short-range forces, in order to investigate their respective influence on lattice dynamics. This analysis highlights the delicate balance of forces leading to an unstable phonon in the cubic phase and demonstrates its extreme sensitivity to effective charge changes. Within our decomposition, the stabilization of the unstable mode in the rhombohedral phase or under isotropic pressure has a different origin. [less ▲]

Magnetic Eden model

in Europhysics Letters [=EPL] (1993), 24(8), 629-634

We introduce the <<Magnetic Eden Model(s)>>. It consists in the usual Eden growth model(s), but allowing for the elements of the growth to have an extra degree of freedom (a <<spin>>). The growth is ... [more ▼]

We introduce the <<Magnetic Eden Model(s)>>. It consists in the usual Eden growth model(s), but allowing for the elements of the growth to have an extra degree of freedom (a <<spin>>). The growth is controlled by a condition depending on the <<magnetic state>> of the perimeter (through some <<spin coupling>>) and an external parameter, the <<magnetic field>>. Even though these words seem to refer to some <<energetic condition>> the growth model is of purely kinetic origin. This is demonstrated by exactly solving the 1-dimensional growth model for a semi-open chain, and, e.g. finding the correlation functions. In two-dimensions, simulations of clusters lead us to show that the perimeter growth exponent is coupling dependent. We show the morphologies of growth clusters on a <<phase diagram>> and indicate the <<physical origin>> and transition(s) between compact and lacunar clusters. [less ▲]