135 research outputs found
Structural relaxation in orthoterphenyl: a schematic mode coupling theory model analysis
Depolarized light scattering spectra of orthoterphenyl showing the emergence
of the structural relaxation below the oscillatory microscopic excitations are
described by solutions of a schematic mode--coupling--theory model
Driven lattice gas of dimers coupled to a bulk reservoir
We investigate the non-equilibrium steady state of a one-dimensional (1D)
lattice gas of dimers. The dynamics is described by a totally asymmetric
exclusion process (TASEP) supplemented by attachment and detachment processes,
mimicking chemical equilibrium of the 1D driven transport with the bulk
reservoir. The steady-state phase diagram, current and density profiles are
calculated using both a refined mean-field theory and extensive stochastic
simulations. As a consequence of the on-off kinetics, a new phase coexistence
region arises intervening between low and high density phases such that the
discontinuous transition line of the TASEP splits into two continuous ones. The
results of the mean-field theory and simulations are found to coincide. We show
that the physical picture obtained in the corresponding lattice gas model with
monomers is robust, in the sense that the phase diagram changes quantitatively,
but the topology remains unaltered. The mechanism for phase separation is
identified as generic for a wide class of driven 1D lattice gases.Comment: 15 pages, 10 figures, 1tabl
Light-Scattering by Longitudinal phonons in Supercooled Molecular Liquids II: Microscopic Derivation of the Phenomenological Equations
The constitutive equations for the orientational dynamics of a liquid formed
of linear molecules are derived microscopically. The resulting generalised
Langevin equations coincide with the phenomenological approach of Dreyfus et
al. Formally exact expressions are given for the phenomenological coefficients
and various constraints are shown to be consequences of this microscopic
approach.Comment: 18 page
Structure and structure relaxation
A discrete--dynamics model, which is specified solely in terms of the
system's equilibrium structure, is defined for the density correlators of a
simple fluid. This model yields results for the evolution of glassy dynamics
which are identical with the ones obtained from the mode-coupling theory for
ideal liquid--glass transitions. The decay of density fluctuations outside the
transient regime is shown to be given by a superposition of Debye processes.
The concept of structural relaxation is given a precise meaning. It is proven
that the long-time part of the mode-coupling-theory solutions is structural
relaxation, while the transient motion merely determines an overall time scale
for the glassy dynamics
A mode-coupling theory for the glassy dynamics of a diatomic probe molecule immersed in a simple liquid
Generalizing the mode-coupling theory for ideal liquid-glass transitions,
equations of motion are derived for the correlation functions describing the
glassy dynamics of a diatomic probe molecule immersed in a simple glass-forming
system. The molecule is described in the interaction-site representation and
the equations are solved for a dumbbell molecule consisting of two fused hard
spheres in a hard-sphere system. The results for the molecule's arrested
position in the glass state and the reorientational correlators for
angular-momentum index and near the glass transition are
compared with those obtained previously within a theory based on a
tensor-density description of the molecule in order to demonstrate that the two
approaches yield equivalent results. For strongly hindered reorientational
motion, the dipole-relaxation spectra for the -process can be mapped on
the dielectric-loss spectra of glycerol if a rescaling is performed according
to a suggestion by Dixon et al. [Phys. Rev. Lett. {\bf 65}, 1108 (1990)]. It is
demonstrated that the glassy dynamics is independent of the molecule's inertia
parameters.Comment: 19 pages, 10 figures, Phys. Rev. E, in prin
Long-Wavelength Anomalies in the Asymptotic Behavior of Mode-Coupling Theory
We discuss the dynamic behavior of a tagged particle close to a classical
localization transition in the framework of the mode-coupling theory of the
glass transition. Asymptotic results are derived for the order parameter as
well as the dynamic correlation functions and the mean-squared displacement
close to the transition. The influence of an infrared cutoff is discussed.Comment: 15 pages, 8 figures, to appear in J Phys Condens Matte
Reorientational relaxation of a linear probe molecule in a simple glassy liquid
Within the mode-coupling theory (MCT) for the evolution of structural
relaxation in glass-forming liquids, correlation functions and susceptibility
spectra are calculated characterizing the rotational dynamics of a top-down
symmetric dumbbell molecule, consisting of two fused hard spheres immersed in a
hard-sphere system. It is found that for sufficiently large dumbbell
elongations, the dynamics of the probe molecule follows the same universal
glass-transition scenario as known from the MCT results of simple liquids. The
-relaxation process of the angular-index-j=1 response is stronger,
slower and less stretched than the one for j=2, in qualitative agreement with
results found by dielectric-loss and depolarized-light-scattering spectroscopy
for some supercooled liquids. For sufficiently small elongations, the
reorientational relaxation occurs via large-angle flips, and the standard
scenario for the glass-transition dynamics is modified for odd-j responses due
to precursor phenomena of a nearby type-A MCT transition. In this case, a major
part of the relaxation outside the transient regime is described qualitatively
by the -relaxation scaling laws, while the -relaxation scaling
law is strongly disturbed.Comment: 40 pages. 10 figures as GIF-files, to be published in Phys. Rev.
Universal and non-universal features of glassy relaxation in propylene carbonate
It is demonstrated that the susceptibility spectra of supercooled propylene
carbonate as measured by depolarized-light-scattering, dielectric-loss, and
incoherent quasi-elastic neutron-scattering spectroscopy within the GHz window
are simultaneously described by the solutions of a two-component schematic
model of the mode-coupling theory (MCT) for the evolution of glassy dynamics.
It is shown that the universal beta-relaxation-scaling laws, dealing with the
asymptotic behavior of the MCT solutions, describe the qualitative features of
the calculated spectra. But the non-universal corrections to the scaling laws
render it impossible to achieve a complete quantitative description using only
the leading-order-asymptotic results.Comment: 37 pages, 16 figures, to be published in Phys. Rev.
Traffic jams induced by rare switching events in two-lane transport
We investigate a model for driven exclusion processes where internal states are assigned to the particles. The latter account for diverse situations, ranging from spin states in spintronics to parallel lanes in intracellular or vehicular traffic. Introducing a coupling between the internal states by allowing particles to switch from one to another induces an intriguing polarization phenomenon. In a mesoscopic scaling, a rich stationary regime for the density profiles is discovered, with localized domain walls in the density profile of one of the internal states being feasible. We derive the shape of the density profiles as well as resulting phase diagrams analytically by a mean-field approximation and a continuum limit. Continuous as well as discontinuous lines of phase transition emerge, their intersections induce multi-critical behaviour
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