1,204 research outputs found
How the asymmetry of internal potential influences the shape of I-V characteristic of nanochannels
Ion transport in biological and synthetic nanochannels is characterized by
such phenomena as ion current fluctuations, rectification, and pumping.
Recently, it has been shown that the nanofabricated synthetic pores could be
considered as analogous to biological channels with respect to their transport
characteristics \cite{Apel, Siwy}. The ion current rectification is analyzed.
Ion transport through cylindrical nanopores is described by the Smoluchowski
equation. The model is considering the symmetric nanopore with asymmetric
charge distribution. In this model, the current rectification in asymmetrically
charged nanochannels shows a diode-like shape of characteristic. It is
shown that this feature may be induced by the coupling between the degree of
asymmetry and the depth of internal electric potential well. The role of
concentration gradient is discussed
The Effect of the Third Dimension on Rough Surfaces Formed by Sedimenting Particles in Quasi-Two-Dimensions
The roughness exponent of surfaces obtained by dispersing silica spheres into
a quasi-two-dimensional cell is examined. The cell consists of two glass plates
separated by a gap, which is comparable in size to the diameter of the beads.
Previous work has shown that the quasi-one-dimensional surfaces formed have two
distinct roughness exponents in two well-defined length scales, which have a
crossover length about 1cm. We have studied the effect of changing the gap
between the plates to a limit of about twice the diameter of the beads.Comment: 4 pages, 4 figures, submitted to IJMP
Scale Free Cluster Distributions from Conserving Merging-Fragmentation Processes
We propose a dynamical scheme for the combined processes of fragmentation and
merging as a model system for cluster dynamics in nature and society displaying
scale invariant properties. The clusters merge and fragment with rates
proportional to their sizes, conserving the total mass. The total number of
clusters grows continuously but the full time-dependent distribution can be
rescaled over at least 15 decades onto a universal curve which we derive
analytically. This curve includes a scale free solution with a scaling exponent
of -3/2 for the cluster sizes.Comment: 4 pages, 3 figure
Substrate concentration dependence of the diffusion-controlled steady-state rate constant
The Smoluchowski approach to diffusion-controlled reactions is generalized to
interacting substrate particles by including the osmotic pressure and
hydrodynamic interactions of the nonideal particles in the Smoluchoswki
equation within a local-density approximation. By solving the strictly
linearized equation for the time-independent case with absorbing boundary
conditions, we present an analytic expression for the diffusion-limited
steady-state rate constant for small substrate concentrations in terms of an
effective second virial coefficient B_2*. Comparisons to Brownian dynamics
simulations excluding HI show excellent agreement up to bulk number densities
of B_2* rho_0 < 0.4 for hard sphere and repulsive Yukawa-like interactions
between the substrates. Our study provides an alternative way to determine the
second virial coefficient of interacting macromolecules experimentally by
measuring their steady-state rate constant in diffusion-controlled reactions at
low densities.Comment: 7 pages, 3 figure
Selection of the scaling solution in a cluster coalescence model
The scaling properties of the cluster size distribution of a system of
diffusing clusters is studied in terms of a simple kinetic mean field model. It
is shown that a one parameter family of mathematically valid scaling solutions
exists. Despite this, the kinetics reaches a unique scaling solution
independent of initial conditions. This selected scaling solution is marginally
physical; i.e., it is the borderline solution between the unphysical and
physical branches of the family of solutions.Comment: 4 pages, 5 figure
Kinetics of viral self-assembly: the role of ss RNA antenna
A big class of viruses self-assemble from a large number of identical capsid
proteins with long flexible N-terminal tails and ss RNA. We study the role of
the strong Coulomb interaction of positive N-terminal tails with ss RNA in the
kinetics of the in vitro virus self-assembly. Capsid proteins stick to
unassembled chain of ss RNA (which we call "antenna") and slide on it towards
the assembly site. We show that at excess of capsid proteins such
one-dimensional diffusion accelerates self-assembly more than ten times. On the
other hand at excess of ss RNA, antenna slows self-assembly down. Several
experiments are proposed to verify the role of ss RNA antenna.Comment: 4 pages, 3 figures, several experiments are proposed, a new idea of
experiment is adde
Shear-induced reaction-limited aggregation kinetics of Brownian particles at arbitrary concentrations
The aggregation of interacting Brownian particles in sheared concentrated
suspensions is an important issue in colloid and soft matter science per se.
Also, it serves as a model to understand biochemical reactions occurring in
vivo where both crowding and shear play an important role. We present an
effective medium approach within the Smoluchowski equation with shear which
allows one to calculate the encounter kinetics through a potential barrier
under shear at arbitrary colloid concentrations. Experiments on a model
colloidal system in simple shear flow support the validity of the model in the
range considered. By generalizing Kramers' rate theory to the presence of
collective hydrodynamics, our model explains the significant increase in the
shear-induced reaction-limited aggregation kinetics upon increasing the colloid
concentration
Liquid friction on charged surfaces: from hydrodynamic slippage to electrokinetics
Hydrodynamic behavior at the vicinity of a confining wall is closely related
to the friction properties of the liquid/solid interface. Here we consider,
using Molecular Dynamics simulations, the electric contribution to friction for
charged surfaces, and the induced modification of the hydrodynamic boundary
condition at the confining boundary. The consequences of liquid slippage for
electrokinetic phenomena, through the coupling between hydrodynamics and
electrostatics within the electric double layer, are explored. Strong
amplification of electro-osmotic effects is revealed, and the non-trivial
effect of surface charge is discussed. This work allows to reconsider existing
experimental data, concerning Zeta potentials of hydrophobic surfaces and
suggest the possibility to generate ``giant'' electro-osmotic and
electrophoretic effects, with direct applications in microfluidics
Direct Numerical Simulations of Electrophoresis of Charged Colloids
We propose a numerical method to simulate electrohydrodynamic phenomena in
charged colloidal dispersions. This method enables us to compute the time
evolutions of colloidal particles, ions, and host fluids simultaneously by
solving Newton, advection-diffusion, and Navier--Stokes equations so that the
electrohydrodynamic couplings can be fully taken into account. The
electrophoretic mobilities of charged spherical particles are calculated in
several situations. The comparisons with approximation theories show
quantitative agreements for dilute dispersions without any empirical
parameters, however, our simulation predicts notable deviations in the case of
dense dispersions.Comment: 4pages, 3figures, to appear in Phys. Rev. Let
- …