23,235 research outputs found
Multi-particle structures in non-sequentially reorganized hard sphere deposits
We have examined extended structures, bridges and arches, in computer
generated, non-sequentially stabilized, hard sphere deposits. The bridges and
arches have well defined distributions of sizes and shapes. The distribution
functions reflect the contraints associated with hard particle packing and the
details of the restructuring process. A subpopulation of string-like bridges
has been identified. Bridges are fundamental microstructural elements in real
granular systems and their sizes and shapes dominate considerations of
structural properties and flow instabilities such as jamming.Comment: 9 pages, 7 figure
Flow rate of polygonal grains through a bottleneck: Interplay between shape and size
We report two-dimensional simulations of circular and polygonal grains
passing through an aperture at the bottom of a silo. The mass flow rate for
regular polygons is lower than for disks as observed by other authors. We show
that both the exit velocity of the grains and the packing fraction are lower
for polygons, which leads to the reduced flow rate. We point out the importance
of the criteria used to define when two objects of different shape are
considered to be of the same size. Depending on this criteria, the mass flow
rate may vary significantly for some polygons. Moreover, the particle flow rate
is non-trivially related to a combination of mass flow rate, particle shape and
particle size. For some polygons, the particle flow rate may be lower or higher
than that of the corresponding disks depending on the size comparison criteria.Comment: 9 pages, 8 figure
Exact predictions from Edwards ensemble vs. realistic simulations of tapped narrow two-dimensional granular columns
We simulate via a Discrete Element Method the tapping of a narrow column of
disk under gravity. For frictionless disks, this system has a simple analytic
expression for the density of states in the Edwards volume ensemble. We compare
the predictions of the ensemble at constant compactivity against the results
for the steady states obtained in the simulations. We show that the steady
states cannot be properly described since the microstates sampled are not in
correspondence with the predicted distributions, suggesting that the postulates
of flat measure and ergodicity are, either or both, invalid for this simple
realization of a static granular system. However, we show that certain
qualitative features of the volume fluctuations difficult to predict from
simple arguments are captured by the theory.Comment: 11 pages, 6 figure
A New Form of Path Integral for the Coherent States Representation and its Semiclassical Limit
The overcompleteness of the coherent states basis leads to a multiplicity of
representations of Feynman's path integral. These different representations,
although equivalent quantum mechanically, lead to different semiclassical
limits. Two such semiclassical formulas were derived in \cite{Bar01} for the
two corresponding path integral forms suggested by Klauder and Skagerstan in
\cite{Klau85}. Each of these formulas involve trajectories governed by a
different classical representation of the Hamiltonian operator: the P
representation in one case and the Q representation in other. In this paper we
construct a third representation of the path integral whose semiclassical limit
involves directly the Weyl representation of the Hamiltonian operator, i.e.,
the classical Hamiltonian itself.Comment: 16 pages, no figure
- …