Effective temperature and jamming transition in dense, gently
sheared granular assemblies |
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Authors: | F Q Potiguar H A Makse |
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Institution: | (1) Levich Institute and Physics Department, City College of New York, New York, NY 10031, USA;(2) Departamento de Física, Universidade Federal do Ceará, Campus do Pici, 60455-760 Fortaleza, CE, Brazil |
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Abstract: | 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. |
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Keywords: | 45 70 -n Granular systems 45 70 Vn Granular models of complex systems traffic flow |
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