2,209 research outputs found
Spatially heterogenous dynamics in dense, driven granular flows
Interest in the dynamical arrest leading to a fluid --> solid transition in
thermal and athermal systems has led to questions about the nature of these
transitions. These jamming transitions may be dependent on the influence of
extended structures on the dynamics of the system. Here we show results from a
simple driven, dissipative, non-equilibrium system which exhibits dynamical
heterogeneities similar to those observed in a supercooled liquid which is a
system in thermal equilibrium. Observations of the time required
for a particular particle to move a distance reveal the existence of
large-scale correlated dynamical regions with characteristic timescales chosen
from a broad distribution. The mean squared displacement of ensembles of
particles with varying characteristic reveals an intriguing
spatially heterogenous mobility. This suggests that a unified framework for
jamming will have to be based on the connection between the nature of these
heterogeneities and the effective dynamics.Comment: 6 pages, 5 figures, submitted to Europhys. Let
Entropy-vanishing transition and glassy dynamics in frustrated spins
In an effort to understand the glass transition, the dynamics of a
non-randomly frustrated spin model has been analyzed. The phenomenology of the
spin model is similar to that of a supercooled liquid undergoing the glass
transition. The slow dynamics can be associated with the presence of extended
string-like structures which demarcate regions of fast spin flips. An
entropy-vanishing transition, with the string density as the order parameter,
is related to the observed glass transition in the spin model.Comment: 4 pages,5 figures, accepted in PRL January 200
Shear induced rigidity in athermal materials: a unified statistical framework
Recent studies of athermal systems such as dry grains and dense, non-Brownian
suspensions have shown that shear can lead to solidification through the
process of shear jamming in grains and discontinuous shear thickening in
suspensions. The similarities observed between these two distinct phenomena
suggest that the physical processes leading to shear-induced rigidity in
athermal materials are universal. We present a non-equilibrium statistical
mechanics model, which exhibits the phenomenology of these shear-driven
transitions: shear jamming and discontinuous shear thickening in different
regions of the predicted phase diagram. Our analysis identifies the crucial
physical processes underlying shear-driven rigidity transitions, and clarifies
the distinct roles played by shearing forces and the density of grains.Comment: Comments welcom
A hybrid shifting bottleneck-tabu search heuristic for the job shop total weighted tardiness problem
In this paper, we study the job shop scheduling problem with the objective of minimizing the total weighted tardiness. We propose a hybrid shifting bottleneck - tabu search (SB-TS) algorithm by replacing the reoptimization step in the shifting bottleneck (SB) algorithm by a tabu search (TS). In terms of the shifting bottleneck heuristic, the proposed tabu search optimizes the total weighted tardiness for partial schedules in which some machines are currently assumed to have infinite capacity. In the context of tabu search, the shifting bottleneck heuristic features a long-term memory which helps to diversify the local search. We exploit this synergy to develop a state-of-the-art algorithm for the job shop total weighted tardiness problem (JS-TWT). The computational
effectiveness of the algorithm is demonstrated on standard benchmark instances from the literature
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