86 research outputs found
Taylor Dispersion with Adsorption and Desorption
We use a stochastic approach to show how Taylor dispersion is affected by
kinetic processes of adsorption and desorption onto surfaces. A general theory
is developed, from which we derive explicitly the dispersion coefficients of
canonical examples like Poiseuille flows in planar and cylindrical geometries,
both in constant and sinusoidal velocity fields. These results open the way for
the measurement of adsorption and desorption rate constants using stationary
flows and molecular sorting using the stochastic resonance of the adsorption
and desorption processes with the oscillatory velocity field.Comment: 6 pages, 4 figure
Nonequilibrium fluctuations and enhanced diffusion of a driven particle in a dense environment
We study the diffusion of a tracer particle driven out-of-equilibrium by an
external force and traveling in a dense environment of arbitrary density. The
system evolves on a discrete lattice and its stochastic dynamics is described
by a master equation. Relying on a decoupling approximation that goes beyond
the naive mean-field treatment of the problem, we calculate the fluctuations of
the position of the tracer around its mean value on a lattice of arbitrary
dimension, and with different boundary conditions. We reveal intrinsically
nonequilibrium effects, such as enhanced diffusivity of the tracer induced both
by the crowding interactions and the external driving. We finally consider the
high-density and low-density limits of the model and show that our
approximation scheme becomes exact in these limits
Contact Kinetics in Fractal Macromolecules
We consider the kinetics of first contact between two monomers of the same
macromolecule. Relying on a fractal description of the macromolecule, we
develop an analytical method to compute the Mean First Contact Time (MFCT) for
various molecular sizes. In our theoretical description, the non-Markovian
feature of monomer motion, arising from the interactions with the other
monomers, is captured by accounting for the non-equilibrium conformations of
the macromolecule at the very instant of first contact. This analysis reveals a
simple scaling relation for the MFCT between two monomers, which involves only
their equilibrium distance and the spectral dimension of the macromolecule,
independently of its microscopic details. Our theoretical predictions are in
excellent agreement with numerical stochastic simulations
Reply to Comment on "Inverse Square L\'evy Walks are not Optimal Search Strategies for d \geq 2 "
We refute here the concernes raised in the Comment of our letter. This reply
states clearly the validity range of our results and shows that the optimality
of inverse-square Levy walks at the basis of the Levy flight foraging
hypothesis is generically unfounded. We also give the precise set of conditions
for which inverse-levy square Levy walks turn to be optimal, conditions which
are unlikely to be verified biologically
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