Dissipative Gases

The clusters shown in the figure appear naturally after some time when an initially homogeneous dissipative gas cools by itself or when the sytem is driven, i.e. energy is injected into the system at a low rate. With Stefan Luding we studied in detail the growth of the clusters and the evolution of the granular temperature as published in Chaos, Vol.9, 673-681 (1999). In this case also the velocity distribution is not Maxwellian anymore. With Matthias Müller we used Event-driven Molecular Dynamics and DSMC to obtain these distributions as published in the proceedings of a workshop in Jülich in 1996.

With Rafaele Cafiero and Stefan Luding we found that deviations from the Maxwell distribution also exist when the system is apparently still homogeneous and that the dependence of these deviation from the driving can be calculated (Phys. Rev. Lett. Vol.84, p.6014-6017 (2000)). Interesting is in particular the case of driving through particle rotation (submitted to Phys. Rev. E) . More details can be found in the paper published in Physica A, Vol.295, p.93-100 (2001). Very interesting is also that when energy is injected with Maxwellian distribution into the rotational degrees of freedom then the resulting translational velocities have again a non-Maxwellian distribution as documented in our paper published in Europhys. Lett. Vol.60, p.854-860 (2002). A review on these issues will be published as proceedings of a CECAM workshop or in the paper published in Rev. Mexicana de Fisica, Vol.49, Suppl.3, p.29-32 (2003). Finally, with Olaf Herbst and Annette Zippelius we also studied the case when the dissipative gas has Coulomb friction as presented in a preprint . You can also download a talk that I gave in several occasions on the subject.

It is in fact not easy to justify the definition of a granular temperature because of this strong deviation from equilibrium thermodynamics. In a paper published in J. Physique II Vol.3, p.427-433 (1993).