129 research outputs found
Weakly nonlinear rheology of transiently crosslinked biopolymer gels
Recent experimental investigations have revealed a non-Maxwellian absorption
pattern in the rheological spectra of actin gels, which was interpreted in
terms of transient bonds. Here we examine the consequences of reversible
crosslinking on the apparent linear spectra of biopolymer solutions
theoretically. For a schematic model consisting of a reversibly crosslinked
power-law fluid we obtain a simple analytical prediction for the position of
the absorption peak, which is backed up by a numerical evaluation of the
inelastic glassy wormlike chain model. This establishes bond breaking as a
nonlinear non-equilibrium effect that can already be significant for very small
driving amplitudes. Our results may be useful for inferring binding affinities
and reaction rates of biochemical crosslinkers from rheological measurements of
{\it in-vitro} reconstituted cytoskeletal gels
Brownian Molecules Formed by Delayed Harmonic Interactions
A time-delayed response of individual living organisms to information
exchanged within flocks or swarms leads to the emergence of complex collective
behaviors. A recent experimental setup by (Khadka et al 2018 Nat. Commun. 9
3864), employing synthetic microswimmers, allows to emulate and study such
behavior in a controlled way, in the lab. Motivated by these experiments, we
study a system of N Brownian particles interacting via a retarded harmonic
interaction. For , we characterize its collective behavior
analytically, by solving the pertinent stochastic delay-differential equations,
and for by Brownian dynamics simulations. The particles form
molecule-like non-equilibrium structures which become unstable with increasing
number of particles, delay time, and interaction strength. We evaluate the
entropy and information fluxes maintaining these structures and, to
quantitatively characterize their stability, develop an approximate
time-dependent transition-state theory to characterize transitions between
different isomers of the molecules. For completeness, we include a
comprehensive discussion of the analytical solution procedure for systems of
linear stochastic delay differential equations in finite dimension, and new
results for covariance and time-correlation matrices.Comment: 36 pages, 26 figures, current version: further improvements and one
correctio
Tension dynamics in semiflexible polymers. II. Scaling solutions and applications
In part I O. Hallatschek , preceding paper, Phys. Rev. E 75, 031905 (2007)] of this contribution, a systematic coarse-grained description of the dynamics of a weakly bending semiflexible polymer was developed. Here, we discuss analytical solutions of the established deterministic partial integro-differential equation for the spatiotemporal relaxation of the backbone tension. For prototypal experimental situations, such as the sudden application or release of a strong external pulling force, it is demonstrated that the tensile dynamics reflects the self-affine conformational fluctuation spectrum in a variety of intermediate asymptotic power laws. Detailed and explicit analytical predictions for the tension propagation and relaxation and corresponding results for common observables, such as the end-to-end distance, are obtained
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