| Fabien Alet |
|---|
| Superfluid - Insulator transition in 2D: A cluster Monte Carlo study |
| In this talk, I will present results on the pure and disorder
Bosonic Hubbard model in 2D at zero temperature, obtained with a
new worm cluster algorithm. |
| Cécile Appert |
|---|
| Asymmetric simple exclusion process and road traffic |
| After a brief overview of recent results obtained with large
deviation functions in the ASEP model, I will focus on a
phenomenological approach which allows to study the system also in
non-stationary states. A variant of the ASEP with metastability
will then be discussed. I will conclude by mentioning how cellular
automata can be used for road traffic. |
| Jorg Baschnagel |
|---|
| Molecular dynamics simulations on the glassy behavior of polymer melts |
| We present results from molecular-dynamics simulations for a
bead-spring model of a polymer melt . We explore the correlation
between the structure and the dynamics as the melt is cooled
towards its glass transition. We show that two time regimes can be
distinguished in the supercooled state: an intermediate time
regime in which the amorphous packing between the monomers
determines the structural relaxation of the melt, and a late time
regime where the relaxation is dominated by chain-connectivity. |
| Kurt Binder |
|---|
| Monte Carlo simulations of glass transition in thin films |
| Molecular Dynamics studies of simple models (short non-entangled
polymer chains and a binary Lennard-Jones mixture) of glassing
fluids confined between various types of walls are discussed, with
an emphasis on the understanding of the nature of the glass
transition from the analysis of confinement effects. Particularly
attention is paid to the possible conclusions on a characteristic
length that grows, as the glass transition is approached.
Particulary useful is the analysis for the local relaxation
time $\tau(z)$, $z$ being the distance from the closest
confining wall. Both smooth and rough walls are considered (the
latter are constructed such that there is almost no layering
effect). In all cases it is found that the characteristic lengths
do increase with decreasing temperature, albeit rather slowly; the
relevance of these lengths for the slowing down near the glass
transition remains doubtful. |
| Eric Brunet |
|---|
| Directed polymers in random media: exact cumulants for the free energy and winding number |
| Using the replica trick and the Bethe Ansatz, we have calculated
for a finite geometry the first cumulants of the free energy and
the winding number around an obstacle of a directed polymer in a
random medium. |
| Gregor Diezemann |
|---|
| Fluctuation-disspiation relations and master equations |
| The fluctuation-dissipation relation is calculated for a class of
stochastic models obeying a master equation with continuous time.
It is shown that in general the linear response cannot be
expressed via time-derivatives of the correlation function alone,
but an additional function $\xi(t,t_w)$, which has been rarely
discussed before is required. This function depends on the two
times also relevant for the response and the correlation and
vanishes under equilibrium conditions. $\xi(t,t_w)$ can be
expressed in terms of the propagators and the transition rates of
the master equation but it is not related to any physical
observable in an obvious way. Instead, it is determined by
inhomogeneities in the temporal evolution of the distribution
function of the stochastic variable under consideration.
$\xi(t,t_w)$ is considered for some examples of stochastic models,
in particular for an extremely simple kinetic random energy
model. Even in this case $\xi(t,t_w)$ does not vanish.
However, it can be related to the 'aging part' of the two-time
correlation function. This fact is of importance in the discussion
of out-of-equlibrium extensions of the FDT. |
| Yurij Holovatch |
|---|
| Where two fractals meet: the scaling of a self-avoiding walk on a percolation cluster |
| In this talk I discuss the influence of quenched disorder on the
scaling properties of long flexible polymer chains (modeled as
self-avoiding walks, SAWs). The examples include: scaling of a SAW
at presence of a weak uncorrelated or long-range correlated
disorder; scaling of a SAW on percolation cluster. |
| Ferenc Iglói |
|---|
| Asymmetric simple exclusion process with quenched disorder |
| We consider the one-dimensional partially asymmetric exclusion
process with random hopping rates, in which a fraction of
particles (or sites) have a preferential jumping direction against
the global drift. In this case the average distance traveled by a
particle, $x$, scales with the time, $t$, as $x \sim t^{1/z}$,
with a dynamical exponent $z > 1$. Using extreme value statistics
and an asymptotically exact strong disorder renormalization group
method we analytically calculate, $z_{pr}$, for particlewise (pt)
disorder, which is argued to be related to the dynamical exponent
for sitewise (st) disorder as $z_{st}=z_{pr}/2$. In the symmetric
situation with zero mean drift the particle diffusion is
ultra-slow, logarithmic in time. |
| Jaroslav Ilnytskyi |
|---|
| The relaxation processes in a bulk system of dendritic molecules |
| We consider the internal dynamics of branched macromolecules in a
melt via molecular dynamics simulation. The study is motivated by
our previous simulations of a single liquid crystalline dendrimer
in a solvent and some attempts to simulate the corresponding bulk
phases. Two models are considered - the first is of generation one
dendrimers with long tails (topologically rather similar to a
star-like polymer) and the second one of generation three
dendrimers with shorter tails. Both types of dendritic molecules
are of real-life carbosilane type and the AMBER force field is
used to describe the intramolecular interactions. We study the
intramolecular dynamics for different densities and temperatures
and observe different regimes, including reptation-like behaviour.
The simulations are compared partly with the results of Rouse-Zimm
theory. Another practical issue is to select the relevant types of
intramolecular moves which is vital for developing an effective
Monte Carlo algorithms for given systems. |
| Wolfhard Janke |
|---|
| Folding Lattice Proteins |
| We present a temperature-independent Monte Carlo method for the
determination of the density of states of lattice proteins that
combines the fast PERM (Pruned-Enriched Rosenbluth Method)
chain-growth algorithm with multicanonical reweighting strategies
for sampling the full energy space. Since the density of states
contains all energetic information of a statistical system, we can
directly calculate the mean energy, specific heat, Helmholtz free
energy, and entropy for all temperatures. We demonstrate the
efficiency of this new method in applications to lattice proteins
described by the effective hydrophobic-polar HP model. For a
selected sample of HP sequences we first discuss ground-state
properties, and then identify and characterize the transitions
between native, globule, and random coil states as temperature
increases. For short chains with up to 19 monomers our numerical
results are validated by comparison with recently obtained exact
enumeration data. |
| Des Johnston |
|---|
| A grand canonical ASEP |
| The one-dimensional Asymmetric Exclusion Process (ASEP) is a
paradigm for nonequilibrium dynamics, in particular driven
diffusive processes. It is usually considered in a canonical
ensemble in which the number of sites is fixed. We observe that
the grand-canonical normalizations for the ASEP with both random
sequential and parallel updates are remarkably simple and clearly
show the correspondence with various two dimensional path
problems. |
| Ralph Kenna |
|---|
| Scaling at higher-order phase transitions |
| Florent Krzakala |
|---|
| Out-of-equilibrium Kawasaki dynamics of Ferromagnetic models |
| The dynamics of ferromagnetic system of Ising spins evolving under
Kawasaki constraints is a classical coarsenning problem. I will
review recent results for two-time correlation and response
functions both at criticality and in the ferromagnetic phase,
stressing the difference and similarities between Kawasaki and
Glauber dynamics for response, correlation, and
fluctuation-dissipation properties. |
| Michel Pleimling |
|---|
| Out-of-equilibrium critical dynamics at surfaces |
| Nonequilibrium surface autocorrelation and autoresponse functions
are studied in semi-infinite critical systems. In the short time
regime an unusual stationary stretched exponential behaviour of
the dynamical surface autocorrelation is observed in cases where
the equilibrium surface autocorrelation function decays very fast.
This behaviour, which is due to a novel mechanism called cluster
dissolution, also takes place in the critical semi-infinite
three-dimensional Ising model. Ageing processes showing up in the
dynamical scaling regime are also discussed. Integrated surface
response functions are confronted with predictions coming from the
theory of local scale invariance. The asymptotic value of the
nonequilibrium surface fluctuation-dissipation ratio is shown to
depend on the value of the surface scaling dimension. |
| Vladislav Popkov |
|---|
| Why spontaneous symmetry breaking disappear in a bridge system with PDE-friendly boundaries |
| We consider a driven diffusive system with two types of particles,
A and B, coupled at the ends to reservoirs with fixed particle
densities. To define stochastic dynamics that correspond to
boundary reservoirs we introduce projection measures. The
stationary state is shown to be approached dynamically through
infinite reflection of shocks from the boundaries. We argue that
spontaneous symmetry breaking observed in similar systems is due
to placing effective impurities at the boundaries and therefore
does not occur in our system. |
| Attila Rakos |
|---|
| Bethe Ansatz and Random Matrices |
| Recently for many growth models of the KLS universality class the
distribution of the height was calculated and it was shown that
for late times this relates to the Tracy-Widom distribution of the
largest eigenvalues of some Gaussian random matrix ensembles. In
the present work we study how this result relates to the Bethe
Ansatz solution of a class of asymmetric exclusion processes. |
| Gunter Schütz |
|---|
| Phase coexistence in nonequilibrium reaction-diffusion systems: Exact results |
| We study the flow of fluctuations in driven diffusive systems with
two conserved densities. This yields a criterion for the
microscopic stability of shocks. We also investigate the
hydrodynamic limit on the Euler scale and obtain two coupled
nonlinear PDE's for the evolution of the local density. For the
selection of the physical solution of this system of conservation
laws we introduce a viscosity matrix. Simulation of a specific
lattice model suggests that, unlike in one-component systems, the
choice of the infinitesimal viscosity term is not irrelevant in
finite systems. This raises the unexpected question how the
physical viscosity term has to be determined. For a special class
of systems we propose a prescription that reproduces Monte-Carlo
data reasonably well. |
| H. Singer |
|---|
| Analysis of scale-invariant properties in experimentally grown
morphologies of diffusion limited growth in 3 dimensions |
| We investigate in our in situ experiments three-dimensional xenon
crystals during free growth into pure supercooled melt.
Supercooling is the only control parameter of the system and
determines the morphology of the crystal. Dendritic, seaweed and
doublon morphologies have been observed. Characteristic parameters
of dendrites and doublons were deduced from experimental data and
compared with theoretical predictions and simulations of 2D and 3D
phase field models. We present a morphology diagram based on our
simulations and our experimental results. Fractal dimensions
(contour and area) have been determined by correlation method and
an optimized box-counting algorithm. We present a technique to
detect integral hidden length scales in experimental structures
and find these length scales to depend on morphology. We present a
method of reconstructing the three-dimensional shape of an
experimentally grown xenon dendrite based on a hybrid approach of
sophisticated image processing and measured parameters of
dendrites. The reconstruction is quantitative and reveals more
details as conventional techniques. A quantitative investigation
of the dendrite surface and volume shows in both cases a power law
dependence on distance from the tip and temporal evolution.
Three-dimensional doublons are studied experimentally and are
reconstructed. A hyperbolic dependence of the width of the growth
channel on supercooling is found. The temporal evolution of
doublons and the relaxtion to dendritic growth is analyzed and
quantitatively reconstructed. |
| Simon Trebst |
|---|
| Overcoming entropic barriers in disordered spin systems |
| We present an adaptive algorithm which overcomes the slowdown of
flat-histogram sampling by optimizing the statistical-mechanical
ensemble in a generalized broad-histogram Monte Carlo simulation
to maximize the system's rate of round trips in total energy. We
discuss applications to classical spin lattice systems. |
| Frédéric van Wijland |
|---|
| Current-carrying ground-state of a quantum system: the Ising chain in a transverse field |
| The nonequilibrium properties of the ground-state of the quantum
Ising chain in a transverse field are considered: correlation
functions and distribution of global observables exhibit features
quite distinct from their equilibrium counterparts |
