330 research outputs found
Motion of an Adhesive Gel in a Swelling Gradient: a Mechanism for Cell Locomotion
Motivated by the motion of nematode sperm cells, we present a model for the
motion of an adhesive gel on a solid substrate. The gel polymerizes at the
leading edge and depolymerizes at the rear. The motion results from a
competition between a self-generated swelling gradient and the adhesion on the
substrate. The resulting stress provokes the rupture of the adhesion points and
allows for the motion. The model predicts an unusual force-velocity relation
which depends in significant ways on the point of application of the force.Comment: 4 pages, 1 figur
Universal Critical Behavior of Noisy Coupled Oscillators
We study the universal thermodynamic properties of systems consisting of many
coupled oscillators operating in the vicinity of a homogeneous oscillating
instability. In the thermodynamic limit, the Hopf bifurcation is a dynamic
critical point far from equilibrium described by a statistical field theory. We
perform a perturbative renormalization group study, and show that at the
critical point a generic relation between correlation and response functions
appears. At the same time the fluctuation-dissipation relation is strongly
violated.Comment: 10 pages, 1 figur
Motor regulation results in distal forces that bend partially disintegrated Chlamydomonas axonemes into circular arcs
The bending of cilia and flagella is driven by forces generated by dynein
motor proteins. These forces slide adjacent microtubule doublets within the
axoneme, the motile cytoskeletal structure. To create regular, oscilla- tory
beating patterns, the activities of the axonemal dyneins must be coordinated
both spatially and temporally. It is thought that coordination is mediated by
stresses or strains, which build up within the moving axoneme, and somehow
regulate dynein activity. While experimenting with axonemes subjected to mild
proteolysis, we observed pairs of doublets associate with each other and form
bends with almost constant curvature. By model- ing the statics of a pair of
filaments, we show that the activity of the motors concentrates at the distal
tips of the doublets. Furthermore, we show that this distribution of motor
activity accords with models in which curvature, or curvature-induced normal
forces, regulates the activity of the motors. These observations, together with
our theoretical analysis, provide evidence that dynein activity can be
regulated by curvature or normal forces, which may, therefore, play a role in
coordinating the beating of cilia and flagella
Synchronization in the presence of distributed delays
We study systems of identical coupled oscillators introducing a distribution
of delay times in the coupling. For arbitrary network topologies, we show that
the frequency and stability of the fully synchronized states depend only on the
mean of the delay distribution. However, synchronization dynamics is sensitive
to the shape of the distribution. In the presence of coupling delays, the
synchronization rate can be maximal for a specific value of the coupling
strength.Comment: 6 pages, 3 figure
Synchronization Dynamics in the Presence of Coupling Delays and Phase Shifts
In systems of coupled oscillators, the effects of complex signaling can be captured by time delays and phase shifts. Here, we show how time delays and phase shifts lead to different oscillator dynamics and how synchronization rates can be regulated by substituting time delays by phase shifts at a constant collective frequency. For spatially extended systems with time delays, we show that the fastest synchronization can occur for intermediate wavelengths, giving rise to novel synchronization scenarios.This work was supported by spanish Ministry of Economy and Competitiveness (MINECO) through Grant PHYSDEV (No. FIS2012-32349) and from CSIC
through the Junta para la Ampliación de Estudios program
(JAEDOC014, 2010 call) cofunded by the European Social FundPublicad
Nonlinear Relaxation Dynamics in Elastic Networks and Design Principles of Molecular Machines
Analyzing nonlinear conformational relaxation dynamics in elastic networks
corresponding to two classical motor proteins, we find that they respond by
well-defined internal mechanical motions to various initial deformations and
that these motions are robust against external perturbations. We show that this
behavior is not characteristic for random elastic networks. However, special
network architectures with such properties can be designed by evolutionary
optimization methods. Using them, an example of an artificial elastic network,
operating as a cyclic machine powered by ligand binding, is constructed.Comment: 12 pages, 9 figure
Mechanical control of the directional stepping dynamics of the kinesin motor
Among the multiple steps constituting the kinesin's mechanochemical cycle,
one of the most interesting events is observed when kinesins move an 8-nm step
from one microtubule (MT)-binding site to another. The stepping motion that
occurs within a relatively short time scale (~100 microsec) is, however, beyond
the resolution of current experiments, therefore a basic understanding to the
real-time dynamics within the 8-nm step is still lacking. For instance, the
rate of power stroke (or conformational change), that leads to the
undocked-to-docked transition of neck-linker, is not known, and the existence
of a substep during the 8-nm step still remains a controversial issue in the
kinesin community. By using explicit structures of the kinesin dimer and the MT
consisting of 13 protofilaments (PFs), we study the stepping dynamics with
varying rates of power stroke (kp). We estimate that 1/kp <~ 20 microsec to
avoid a substep in an averaged time trace. For a slow power stroke with 1/kp>20
microsec, the averaged time trace shows a substep that implies the existence of
a transient intermediate, which is reminiscent of a recent single molecule
experiment at high resolution. We identify the intermediate as a conformation
in which the tethered head is trapped in the sideway binding site of the
neighboring PF. We also find a partial unfolding (cracking) of the binding
motifs occurring at the transition state ensemble along the pathways prior to
binding between the kinesin and MT.Comment: 26 pages, 10 figure
Extended Standard Map with Spatio-Temporal Asymmetry
We analyze the transport properties of a set of symmetry-breaking extensions
%, both spatial and temporal, of the Chirikov--Taylor Map. The spatial and
temporal asymmetries result in the loss of periodicity in momentum direction in
the phase space dynamics, enabling the asymmetric diffusion which is the origin
of the unidirectional motion. The simplicity of the model makes the calculation
of the global dynamical properties of the system feasible both in phase space
and in controlling-parameter space. We present the results of numerical
experiments which show the intricate dependence of the asymmetric diffusion to
the controlling parameters.Comment: 6 pages latex 2e with 12 epsf fig
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