156 research outputs found
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
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