14 research outputs found
Effective temperature and jamming transition in dense, gently sheared granular assemblies
We present extensive computational results for the effective temperature,
defined by the fluctuation-dissipation relation between the mean square
displacement and the average displacement of grains, under the action of a
weak, external perturbation, of a sheared, bi-disperse granular packing of
compressible spheres. We study the dependence of this parameter on the shear
rate and volume fractions, the type of particle and the observable in the
fluctuation-dissipation relation. We find the same temperature for different
tracer particles in the system. The temperature becomes independent on the
shear rate for slow enough shear suggesting that it is the effective
temperature of the jammed packing. However, we also show that the agreement of
the effective temperature for different observables is only approximate, for
very long times, suggesting that this defintion may not capture the full
thermodynamics of the system. On the other hand, we find good agreement between
the dynamical effective temperature and a compactivity calculated assuming that
all jammed states are equiprobable. Therefore, this definition of temperature
may capture an instance of the ergodic hypothesis for granular materials as
proposed by theoretical formalisms for jamming. Finally, our simulations
indicate that the average shear stress and apparent shear viscosity follow the
usual relation with the shear rate for complex fluids. Our results show that
the application of shear induces jamming in packings whose particles interact
by tangential forces.Comment: Preprint form, 23 pages, 18 figure
From crystal to amorphopus: a novel route towards unjamming in soft disk packings
It is presented a numerical study on the unjamming packing fraction of bi-
and polydisperse disk packings, which are generated through compression of a
monodisperse crystal. In bidisperse systems, a fraction f_+ = 40% up to 80% of
the total number of particles have their radii increased by \Delta R, while the
rest has their radii decreased by the same amount. Polydisperse packings are
prepared by changing all particle radii according to a uniform distribution in
the range [-\Delta R,\Delta R]. The results indicate that the critical packing
fraction is never larger than the value for the initial monodisperse crystal,
\phi = \pi/12, and that the lowest value achieved is approximately the one for
random close packing. These results are seen as a consequence of the interplay
between the increase in small-small particle contacts and the local crystalline
order provided by the large-large particle contacts.Comment: two columns, 14 pages, 12 figures, accepted for publication in Eur.
Phys. J.
Nonextensive perfect hydrodynamics - a model of dissipative relativistic hydrodynamics?
We demonstrate that nonextensive perfect relativistic hydrodynamics
(-hydrodynamics) can serve as a model of the usual relativistic dissipative
hydrodynamics (-hydrodynamics) facilitating therefore considerably its
applications. As illustration we show how using -hydrodynamics one gets the
-dependent expressions for the dissipative entropy current and the
corresponding ratios of the bulk and shear viscosities to entropy density,
and .Comment: Invited talk presented at SigmaPhi2008 conference, Kolymbari, Crete,
14-18 July 2008, revised version to be published in Cent. Eur. J. Phys.
(2009