Universal features of the off-equilibrium fragmentation with the Gaussian dissipation

We investigate universal features of the off-equilibrium sequential and conservative fragmentation processes with the dissipative effects which are simulated by the Gaussian random inactivation process. The relation between the fragment multiplicity scaling law and the fragment size distribution is studied and a dependence of scaling exponents on the parameters of fragmentation and inactivation rate functions is established.Comment: 10 pages, 2 figure

Phase Transitions in Non-extensive Spin Systems

The spherical spin model with infinite-range ferromagnetic interactions is investigated analytically in the framework of non-extensive thermostatics generalizing the Boltzmann-Gibbs statistical mechanics. We show that for repulsive correlations, a new weak-ferromagnetic phase develops. There is a tricritical point separating para, weak-ferro and ferro regimes. The transition from paramagnetic to weak-ferromagnetic phase is an unusual first order phase transition in which a discontinuity of the averaged order parameter appears, even for finite number of spins. This result puts in a new way the question of the stability of critical phenomena with respect to the long-ranged correlations.Comment: 4 pages, 3 figures, in the final form as in the journa

Scanning the critical fluctuations -- application to the phenomenology of the two-dimensional XY-model --

We show how applying field conjugated to the order parameter, may act as a very precise probe to explore the probability distribution function of the order parameter. Using this `magnetic-field scanning' on large-scale numerical simulations of the critical 2D XY-model, we are able to discard the conjectured double-exponential form of the large-magnetization asymptote.Comment: 4 pages, 4 figure

The duality between a non-Hermitian two-state quantum system and a massless charged particle

International audienceWe show that the equations for the dynamics of a non-Hermitian two-state quantum system are the same as the equations of motion for a massless charged particle in an electromagnetic field. Using simple analytical arguments to prove this unexpected duality between two very different domains in Physics, we further exemplify it through a case-study of polarization of light propagating in a dichroic medium with magneto-optic activity

Scaling behaviors of colloidal aggregates under pressure

We present a theoretical model for the compaction of a colloidal sediment under uniaxial mechanical pressure in the continuous three-dimensional space. The initial system is formed with aggregated particles dispersed in a fluid, and softly sedimented in a vessel. When a uniform pressure is applied, it evolves irreversibly through successive creation and destruction of bonds between the particles. The rules governing the bonds depend on both geometrical constraints and current stresses. Numerical simulations of such systems exhibit three different scenarios, corresponding, respectively, to the fragile, elastic, and plastic behaviors. In the elastic regime, where most bonds are permanent, the pressure scales as a power law of the volume fraction of particles, with a numerical exponent equal to 4.4. In the plastic regime, where many bonds are broken and many others created, the pressure also scales with volume fraction, but the exponent is much lower, equal to 1.7. These scaling behaviors agree remarkably well with recent experiments realized on the compaction of systems with aggregated silica particles in the oedometer cell. They also can be explained with simple theoretical arguments using a plausible morphology of the resistant paths acting throughout the system. Finally, at very large applied pressures, all these regimes converge to the random close packing of spheres

How a colloidal paste flows – scaling behaviors in dispersions of aggregated particles under mechanical stress –

We have developed a novel computational scheme that allows direct numerical simulation of the mechanical behavior of sticky granular matter under stress. We present here the general method, with particular emphasis on the particle features at the nanometric scale. It is demonstrated that, although sticky granular material is quite complex and is a good example of a challenging computational problem (it is a dynamical problem, with irreversibility, self-organization and dissipation), its main features may be reproduced on the basis of rather simple numerical model, and a small number of physical parameters. This allows precise analysis of the possible deformation processes in soft materials submitted to mechanical stress. This results in direct relationship between the macroscopic rheology of these pastes and local interactions between the particles