29 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
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
Finite-size effects and intermittency in a simple aging system
We study the intermittent dynamics and the fluctuations of the dynamic
correlation function of a simple aging system. Given its size and its
coherence length , the system can be divided into independent
subsystems, where , and is the dimension of space.
Each of them is considered as an aging subsystem which evolves according to
an activated dynamics between energy levels.
We compute analytically the distribution of trapping times for the global
system, which can take power-law, stretched-exponential or exponential forms
according to the values of and the regime of times considered. An effective
number of subsystems at age , , can be defined, which
decreases as increases, as well as an effective coherence length,
, where characterizes the trapping
times distribution of a single subsystem. We also compute the probability
distribution functions of the time intervals between large decorrelations,
which exhibit different power-law behaviours as increases (or
decreases), and which should be accessible experimentally.
Finally, we calculate the probability distribution function of the two-time
correlator.
We show that in a phenomenological approach, where is replaced by the
effective number of subsystems , the same qualitative behaviour
as in experiments and simulations of several glassy systems can be obtained.Comment: 15 pages, 6 figures, published versio