32 research outputs found
Dynamical heterogeneities in a two dimensional driven glassy model: current fluctuations and finite size effects
In this article, we demonstrate that in a transport model of particles with
kinetic constraints, long-lived spatial structures are responsible for the
blocking dynamics and the decrease of the current at strong driving field.
Coexistence between mobile and blocked regions can be anticipated by a
first-order transition in the large deviation function for the current. By a
study of the system under confinement, we are able to study finite-size effects
and extract a typical length between mobile regions
Injected Power Fluctuations in 1D dissipative systems : role of ballistic transport
This paper is a generalization of the models considered in [J. Stat. Phys.
128,1365 (2007)]. Using an analogy with free fermions, we compute exactly the
large deviation function (ldf) of the energy injected up to time in a
one-dimensional dissipative system of classical spins, where a drift is
allowed. The dynamics are T=0 asymmetric Glauber dynamics driven out of rest by
an injection mechanism, namely a Poissonian flipping of one spin. The drift
induces anisotropy in the system, making the model more comparable to
experimental systems with dissipative structures. We discuss the physical
content of the results, specifically the influence of the rate of the Poisson
injection process and the magnitude of the drift on the properties of the ldf.
We also compare the results of this spin model to simple phenomenological
models of energy injection (Poisson or Bernoulli processes of domain wall
injection). We show that many qualitative results of the spin model can be
understood within this simplified framework.Comment: 23 pages, 8 figure
Activity statistics in a colloidal glass former: experimental evidence for a dynamical transition
In a dense colloidal suspension at a volume fraction slightly lower than that
of its glass transition, we follow the trajectories of an assembly of tracers
over a large time window. We define a local activity, which quantifies the
local tendency of the system to rearrange. We determine the statistics of the
time and space integrated activity, and we argue that it develops a low
activity tail that comes on a par with the onset of glassy behavior and
heterogeneous dynamics. These rare events may be interpreted as the reflection
of an underlying dynamic phase transition.Comment: 20 pages, 16 figure
Role of cilia activity and surrounding viscous fluid on properties of metachronal waves
Large groups of active cilia collectively beat in a fluid medium as
metachronal waves, essential for some microorganisms motility and for flow
generation in mucociliary clearance. Several models can predict the emergence
of metachronal waves, but what controls the properties of metachronal waves is
still unclear. Here, we investigate numerically a simple model for cilia in the
presence of noise on regular lattices in one- and two-dimensions. We
characterize the wave using spatial correlation and the frequency of collective
beating. Our results clearly show that the viscosity of the fluid medium does
not affect the wavelength; the activity of the cilia does. These numerical
results are supported by a dimensional analysis, which is expected to be robust
against the model for active force generation, unless surrounding fluid
influences the cilia activity. Interestingly, enhancement of cilia activity
increases the wavelength and decreases the beating frequency, keeping the wave
velocity almost unchanged. These results might have significance in
understanding paramecium locomotion and mucociliary clearance diseases.Comment: 6 pages, 5 figure
Glassy behavior of a homopolymer from molecular dynamics simulations
We study at- and out-of-equilibrium dynamics of a single homopolymer chain at
low temperature using molecular dynamics simulations. The main quantities of
interest are the average root mean square displacement of the monomers below
the theta point, and the structure factor, as a function of time. The
observation of these quantities show a close resemblance to those measured in
structural glasses and suggest that the polymer chain in its low temperature
phase is in a glassy phase, with its dynamics dominated by traps. In
equilibrium, at low temperature, we observe the trapping of the monomers and a
slowing down of the overall motion of the polymer as well as non-exponential
relaxation of the structure factor. In out-of-equilibrium, at low temperatures,
we compute the two-time quantities and observe breaking of ergodicity in a
range of waiting times, with the onset of aging.Comment: 11 pages, 4 figure
Transport on a Lattice with Dynamical Defects
Many transport processes in nature take place on substrates, often considered
as unidimensional lanes. These unidimensional substrates are typically
non-static: affected by a fluctuating environment, they can undergo
conformational changes. This is particularly true in biological cells, where
the state of the substrate is often coupled to the active motion of
macromolecular complexes, such as motor proteins on microtubules or ribosomes
on mRNAs, causing new interesting phenomena. Inspired by biological processes
such as protein synthesis by ribosomes and motor protein transport, we
introduce the concept of localized dynamical sites coupled to a driven lattice
gas dynamics. We investigate the phenomenology of transport in the presence of
dynamical defects and find a novel regime characterized by an intermittent
current and subject to severe finite-size effects. Our results demonstrate the
impact of the regulatory role of the dynamical defects in transport, not only
in biology but also in more general contexts
Driving kinetically constrained models into non-equilibrium steady states:Structural and slow transport properties
Complex fluids in shear flow and biased dynamics in crowded environments
exhibit counterintuitive features which are difficult to address both at
theoretical level and by molecular dynamic simulations. To understand some of
these features we study a schematic model of highly viscous liquid, the 2D
Kob-Andersen kinetically constrained model, driven into non-equilibrium steady
states by a uniform non-Hamiltonian force. We present a detailed numerical
analysis of the microscopic behavior of the model, including transversal and
longitudinal spatial correlations and dynamic heterogeneities. In particular,
we show that at high particle density the transition from positive to negative
resistance regimes in the current vs field relation can be explained via the
emergence of nontrivial structures that intermittently trap the particles and
slow down the dynamics. We relate such spatial structures to the current vs
field relation in the different transport regimes