Maxwell demon in Granular gas: a new kind of bifurcation? The hypercritical bifurcation

This paper starts with the investigation of the behaviour of a set of two subsystems which are able to exchange some internal quantity according to a given flux function. It is found that this sytem exhibit a bifurcation when the flux passes through a maximum and that its kind (super-critical/sub-critical) depends on the dissymmetry of the flux function near the maximum. It is also found a new kind of bifurcation when the flux function is symmetric: we call it hypercritical bifurcation because it generates much stronger fluctuations than the super-critical one. The effect of a white noise is then investigated. We show that an experimental set-up, leading to the Maxwell demon in granular gas, displays all these kinds of bifurcation, just by changing the parameters of excitation. It means that this system is much less simple as it was thought.Comment: 19 pages, 10 figure

Granular Media under Vibration in Zero Gravity: Transition from Rattling to Granular Gas

We report on different experimental behaviours of granular dissipative matter excited by vibration as studied during the 43rd ESA campaign of Airbus A300-0g from CNES. The effect of g-jitter is quantified through the generation of a rattle effect. The French-European team's electromagnetic set-up is used, with 20Hz cam recording and high speed camera for a short duration (1s) during each parabola.Comment: Poudres et Grains 201

Effect of aging on the reinforcement efficiency of carbon nanotubes in epoxy matrix

The reinforcement efficiency of carbon nanotubes (CNTs) in epoxy matrix was investigated in the elastic regime. Cyclic uniaxial tensile tests were performed at constant strain amplitude and increasing maximum strain. Post-curing of the epoxy and its composite at a temperature close to the glass transition temperature allowed us to explore the effect of aging on the reinforcement efficiency of CNT. It is found that the reinforcement efficiency is compatible with a mean field mixture rule of stress reinforcement by random inclusions. It also diminishes when the maximum strain increased and this effect is amplified by aging. The decrease of elastic modulus with increasing cyclic maximum strain is quite similar to the one observed for filled elastomers with increasing strain amplitude, a phenomenon often referred as the Payne effect

Avalanche statistics of sand heaps

Large scale computer simulations are presented to investigate the avalanche statistics of sand piles using molecular dynamics. We could show that different methods of measurement lead to contradicting conclusions, presumably due to avalanches not reaching the end of the experimental table.Comment: 6 pages, 4 figure

Phase transition in inelastic disks

This letter investigates the molecular dynamics of inelastic disks without external forcing. By introducing a new observation frame with a rescaled time, we observe the virtual steady states converted from asymptotic energy dissipation processes. System behavior in the thermodynamic limit is carefully investigated. It is found that a phase transition with symmetry breaking occurs when the magnitude of dissipation is greater than a critical value.Comment: 9 pages, 6 figure

Placement of metallic biliary endoprostheses in complex hilar tumours

AbstractPurposeTo assess the technical success, clinical success and complications after 1 month of percutaneous biliary drainage with the placement of several metallic endoprostheses in complex hilar liver tumours.Materials and methodsThis is a retrospective study, on a homogenous target population of 68 consecutive patients, who underwent multiple percutaneous biliary drainage for complex hilar tumour (Bismuth type II, III and IV) between August 1998 and August 2010. Patients benefiting from previous endoscopic drainage were excluded from the study. The clinical data, biological data, imaging and interventional radiology procedures were studied.ResultsThe rate of success of the technique was 98.5% and the clinical rate of success was 84% after 1 week and 93% after 1 month. The rate of minor and major complications was 25 and 13% respectively.ConclusionMultiple percutaneous biliary drainage in complex hilar tumour is a safe and effective first intention procedure

Logarithmic Relaxations in a Random Field Lattice Gas Subject to Gravity

A simple lattice gas model with random fields and gravity is introduced to describe a system of grains moving in a disordered environment. Off equilibrium relaxations of bulk density and its two time correlation functions are numerically found to show logarithmic time dependences and "aging" effects. Similitudes with dry granular media are stressed. The connections with off equilibrium dynamics in others kinds of "frustrated" lattice models in presence of a directional driving force (gravity) are discussed to single out the appearance of universal features in the relaxation process.Comment: 15 pages, latex, 7 figures include

Granular Elasticity without the Coulomb Condition

An self-contained elastic theory is derived which accounts both for mechanical yield and shear-induced volume dilatancy. Its two essential ingredients are thermodynamic instability and the dependence of the elastic moduli on compression.Comment: 4pages, 2 figure