Horacio Castillo, Ohio University, Strong fluctuations in the relaxation of a 2D granular fluid

Date: Mon. April 15th, 2019, 12:45 am-1:45 am
Location: Rockefeller 221 (Les Foldy Room)
Website: https://www.ohio.edu/cas/physastro/faculty/profiles.cfm?profile=castillh

Strong fluctuations in the relaxation of a 2D granular fluid

Horacio Castillo, Department of Physics and Astronomy, Ohio University

Glass transitions are associated with a rapid increase of the
relaxation time in a system as a function of an external parameter,
usually temperature or volume fraction. In the regime near the glass
transition, materials exhibit “dynamical heterogeneity”, i.e., the
presence of correlated fluctuations in the dynamical behavior of small
regions of the system, whose origin is still poorly understood. I will
discuss the results of large-scale numerical simulations of a two
dimensional granular fluid, for different strengths of the dissipation
in the system (described by the restitution coefficient ε), including
the case of no dissipation (ε=1). I will focus on the behavior of the
system for packing fractions near structural arrest. In that regime,
the correlation length achieves values that widely exceed those
previously observed for 3D hard sphere fluids, the correlation
functions exhibit a very good scaling when the wavevector is rescaled
by the correlation length, and this scaling is remarkably independent
of ε. I will discuss two alternative descriptions of the geometry of
the correlated regions. One is based on studying the scaling of the
dynamic susceptibility, which provides a rough measure of the volume
of the correlated regions, with the correlation length. The other is
based on studying the statistics of clusters of slow and fast
particles, their volumes, and their radius of gyration. Taken
together, the results suggest that, even though the strength of the
fluctuations depends strongly on the intensity of the dissipation in
the system, the qualitative properties of the glass transition are
essentially independent of it.

Host: Philip Taylor