5,602 research outputs found
Marginal scaling scenario and analytic results for a glassy compaction model
A diffusion-deposition model for glassy dynamics in compacting granular
systems is treated by time scaling and by a method that provides the exact
asymptotic (long time) behavior. The results include Vogel-Fulcher dependence
of rates on density, inverse logarithmic time decay of densities, exponential
distribution of decay times and broadening of noise spectrum. These are all in
broad agreement with experiments. The main characteristics result from a
marginal rescaling in time of the control parameter (density); this is argued
to be generic for glassy systems.Comment: 4 pages, 4 figure
Cluster growth in far-from-equilibrium particle models with diffusion, detachment, reattachment and deposition
Monolayer cluster growth in far-from-equilibrium systems is investigated by
applying simulation and analytic techniques to minimal hard core particle
(exclusion) models. The first model (I), for post-deposition coarsening
dynamics, contains mechanisms of diffusion, attachment, and slow activated
detachment (at rate epsilon<<1) of particles on a line. Simulation shows three
successive regimes of cluster growth: fast attachment of isolated particles;
detachment allowing further (epsilon t)^(1/3) coarsening of average cluster
size; and t^(-1/2) approach to a saturation size going like epsilon^(-1/2).
Model II generalizes the first one in having an additional mechanism of
particle deposition into cluster gaps, suppressed for the smallest gaps. This
model exhibits early rapid filling, leading to slowing deposition due to the
increasing scarcity of deposition sites, and then continued power law (epsilon
t)^(1/2) cluster size coarsening through the redistribution allowed by slow
detachment. The basic (epsilon t)^(1/3) domain growth laws and epsilon^(-1/2)
saturation in model I are explained by a simple scaling picture. A second,
fuller approach is presented which employs a mapping of cluster configurations
to a column picture and an approximate factorization of the cluster
configuration probability within the resulting master equation. This allows
quantitative results for the saturation of model I in excellent agreement with
the simulation results. For model II, it provides a one-variable scaling
function solution for the coarsening probability distribution, and in
particular quantitative agreement with the cluster length scaling and its
amplitude.Comment: Accepted in Phys. Rev. E; 9 pages with figure
Real-space renormalisation group approach to driven diffusive systems
We introduce a real-space renormalisation group procedure for driven
diffusive systems which predicts both steady state and dynamic properties. We
apply the method to the boundary driven asymmetric simple exclusion process and
recover exact results for the steady state phase diagram, as well as the
crossovers in the relaxation dynamics for each phase.Comment: 10 pages, 5 figure
Disordered asymmetric simple exclusion process: mean-field treatment
We provide two complementary approaches to the treatment of disorder in a
fundamental nonequilibrium model, the asymmetric simple exclusion process.
Firstly, a mean-field steady state mapping is generalized to the disordered
case, where it provides a mapping of probability distributions and demonstrates
how disorder results in a new flat regime in the steady state current--density
plot for periodic boundary conditions. This effect was earlier observed by
Tripathy and Barma but we provide treatment for more general distributions of
disorder, including both numerical results and analytic expressions for the
width of the flat section. We then apply an argument based on
moving shock fronts to show how this leads to an increase in the high current
region of the phase diagram for open boundary conditions. Secondly, we show how
equivalent results can be obtained easily by taking the continuum limit of the
problem and then using a disordered version of the well-known Cole--Hopf
mapping to linearize the equation. Within this approach we show that adding
disorder induces a localization transformation (verified by numerical scaling),
and maps to an inverse localization length, helping to give a new
physical interpretation to the problem.Comment: 13 pages, 16 figures. Submitted to Phys. Rev.
Non-universal disordered Glauber dynamics
We consider the one-dimensional Glauber dynamics with coupling disorder in
terms of bilinear fermion Hamiltonians. Dynamic exponents embodied in the
spectrum gap of these latter are evaluated numerically by averaging over both
binary and Gaussian disorder realizations. In the first case, these exponents
are found to follow the non-universal values of those of plain dimerized
chains. In the second situation their values are still non-universal and
sub-diffusive below a critical variance above which, however, the relaxation
time is suggested to grow as a stretched exponential of the equilibrium
correlation length.Comment: 11 pages, 5 figures, brief addition
Fluctuation-dissipation relation and the Edwards entropy for a glassy granular compaction model
We analytically study a one dimensional compaction model in the glassy
regime. Both correlation and response functions are calculated exactly in the
evolving dense and low tapping strength limit, where the density relaxes in a
fashion. The response and correlation functions turn out to be
connected through a non-equilibrium generalisation of the
fluctuation-dissipation theorem. The initial response in the average density to
an increase in the tapping strength is shown to be negative, while on longer
timescales it is shown to be positive. On short time scales the
fluctuation-dissipation theorem governs the relation between correlation and
response, and we show that such a relationship also exists for the slow degrees
of freedom, albeit with a different temperature. The model is further studied
within the statistical theory proposed by Edwards and co-workers, and the
Edwards entropy is calculated in the large system limit. The fluctuations
described by this approach turn out to match the fluctuations as calculated
through the dynamical consideration. We believe this to be the first time these
ideas have been analytically confirmed in a non-mean-field model.Comment: 4 pages, 3 figure
Limit order market analysis and modelling: on an universal cause for over-diffusive prices
We briefly review data analysis of the Island order book, part of NASDAQ,
which suggests a framework to which all limit order markets should comply.
Using a simple exclusion particle model, we argue that short-time price
over-diffusion in limit order markets is due to the non-equilibrium of order
placement, cancellation and execution rates, which is an inherent feature of
real limit order markets.Comment: 6 pages, 3 figures. Contribution to the proceedings of Econophysics
Bali Conference 200
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