76 research outputs found
Intra-cellular transport of single-headed molecular motors KIF1A
Motivated by experiments on single-headed kinesin KIF1A, we develop a model
of intra-cellular transport by interacting molecular motors. It captures
explicitly not only the effects of ATP hydrolysis, but also the ratchet
mechanism which drives individual motors. Our model accounts for the
experimentally observed single molecule properties in the low density limit and
also predicts a phase diagram that shows the influence of hydrolysis and
Langmuir kinetics on the collective spatio-temporal organization of the motors.
Finally, we provide experimental evidence for the existence of domain walls in
our {\it in-vitro} experiment with fluorescently labeled KIF1A.Comment: 4 pages, REVTEX, 5 EPS figures; Accepted for Publication in Phys.
Rev. Let
Disordered driven lattice gases with boundary reservoirs and Langmuir kinetics
The asymmetric simple exclusion process with additional Langmuir kinetics,
i.e. attachment and detachment in the bulk, is a paradigmatic model for
intracellular transport. Here we study this model in the presence of randomly
distributed inhomogeneities ('defects'). Using Monte Carlo simulations, we find
a multitude of coexisting high- and low-density domains. The results are
generic for one-dimensional driven diffusive systems with short-range
interactions and can be understood in terms of a local extremal principle for
the current profile. This principle is used to determine current profiles and
phase diagrams as well as statistical properties of ensembles of defect
samples.Comment: submitted for publishin
Competition of coarsening and shredding of clusters in a driven diffusive lattice gas
We investigate a driven diffusive lattice gas model with two oppositely
moving species of particles. The model is motivated by bi-directional traffic
of ants on a pre-existing trail. A third species, corresponding to pheromones
used by the ants for communication, is not conserved and mediates interactions
between the particles. Here we study the spatio-temporal organization of the
particles. In the uni-directional variant of this model it is known to be
determined by the formation and coarsening of ``loose clusters''. For our
bi-directional model, we show that the interaction of oppositely moving
clusters is essential. In the late stages of evolution the cluster size
oscillates because of a competition between their `shredding' during encounters
with oppositely moving counterparts and subsequent "coarsening" during
collision-free evolution. We also establish a nontrivial dependence of the
spatio-temporal organization on the system size
Functional renormalization group in the broken symmetry phase: momentum dependence and two-parameter scaling of the self-energy
We include spontaneous symmetry breaking into the functional renormalization
group (RG) equations for the irreducible vertices of Ginzburg-Landau theories
by augmenting these equations by a flow equation for the order parameter, which
is determined from the requirement that at each RG step the vertex with one
external leg vanishes identically. Using this strategy, we propose a simple
truncation of the coupled RG flow equations for the vertices in the broken
symmetry phase of the Ising universality class in D dimensions. Our truncation
yields the full momentum dependence of the self-energy Sigma (k) and
interpolates between lowest order perturbation theory at large momenta k and
the critical scaling regime for small k. Close to the critical point, our
method yields the self-energy in the scaling form Sigma (k) = k_c^2 sigma^{-}
(k | xi, k / k_c), where xi is the order parameter correlation length, k_c is
the Ginzburg scale, and sigma^{-} (x, y) is a dimensionless two-parameter
scaling function for the broken symmetry phase which we explicitly calculate
within our truncation.Comment: 9 pages, 4 figures, puplished versio
Single-Bottleneck Approximation for Driven Lattice Gases with Disorder and Open Boundary Conditions
We investigate the effects of disorder on driven lattice gases with open
boundaries using the totally asymmetric simple exclusion process as a
paradigmatic example. Disorder is realized by randomly distributed defect sites
with reduced hopping rate. In contrast to equilibrium, even macroscopic
quantities in disordered non-equilibrium systems depend sensitively on the
defect sample. We study the current as function of the entry and exit rates and
the realization of disorder and find that it is, in leading order, determined
by the longest stretch of consecutive defect sites (single-bottleneck
approximation, SBA). Using results from extreme value statistics the SBA allows
to study ensembles with fixed defect density which gives accurate results, e.g.
for the expectation value of the current. Corrections to SBA come from
effective interactions of bottlenecks close to the longest one. Defects close
to the boundaries can be described by effective boundary rates and lead to
shifts of the phase transitions. Finally it is shown that the SBA also works
for more complex models. As an example we discuss a model with internal states
that has been proposed to describe transport of the kinesin KIF1A.Comment: submitted to J. Stat. Mec
An empirical test for cellular automaton models of traffic flow
Based on a detailed microscopic test scenario motivated by recent empirical
studies of single-vehicle data, several cellular automaton models for traffic
flow are compared. We find three levels of agreement with the empirical data:
1) models that do not reproduce even qualitatively the most important empirical
observations,
2) models that are on a macroscopic level in reasonable agreement with the
empirics, and 3) models that reproduce the empirical data on a microscopic
level as well.
Our results are not only relevant for applications, but also shed new light
on the relevant interactions in traffic flow.Comment: 28 pages, 36 figures, accepted for publication in PR
mer-Bis[3,5-difluoro-2-(2-pyridyl)phenyl-κ2 C 1,N]{5-(2-pyridyl-κN)-3-[3-(4-vinylbenzyloxy)phenyl]-1,2,4-triazol-1-ido}iridium(III) methanol solvate
In the title compound, [Ir(C11H6F2N)2(C22H17N4O)]·CH3OH, the coordination at iridium is essentially octahedral, but with distortions associated with the bite angles of the ligands [76.25 (9)–80.71 (12)°] and the differing trans influences of C and N ligands [Ir—N = 2.04 Å (average) trans to N but 2.14 Å trans to C]. All three bidentate ligands have coordinating ring systems that are almost coplanar [interplanar angles = 1.7 (1)–3.8 (2)°]. The vinylbenzyl group is disordered over two positions with occupations of 0.653 (4) and 0.347 (4). The methanol solvent molecule is involved in a classical O—H⋯N hydrogen bond to a triazole N atom
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