537 research outputs found
pH-Mediated Regulation of Polymer Transport Through SiN Pores
We characterize the pH controlled polymer capture and transport thorough
silicon nitride (SiN) pores subject to protonation. A charge regulation model
able to reproduce the experimental zeta potential of SiN pores is coupled with
electrohydrodynamic polymer transport equations. The formalism can
quantitatively explain the experimentally observed non-monotonic pH dependence
of avidin conductivity in terms of the interplay between the electroosmotic and
electrophoretic drag forces on the protein. We also scrutinize the DNA
conductivity of SiN pores. We show that in the low pH regime where the
amphoteric pore is cationic, DNA-pore attraction acts as an electrostatic trap.
This provides a favorable condition for fast polymer capture and extended
translocation required for accurate polymer sequencing
Electrostatic correlations in inhomogeneous charged fluids beyond loop expansion
Electrostatic correlation effects in inhomogeneous symmetric electrolytes are
investigated within a previously developed electrostatic self-consistent (SC)
theory (R.R. Netz and H. Orland, Eur. Phys.J. E 11, 301 (2003)). To this aim,
we introduce two computational approaches that allow to solve the SC equations
beyond the loop expansion. Both approaches can handle the case of
dielectrically discontinuous boundaries where the one-loop theory is known to
fail. By comparing the theoretical results obtained from these schemes with the
results of the MC simulations that we ran for ions at neutral single dielectric
interfaces as well as with previous MC data for charged interfaces, we first
show that the weak coupling (WC) Debye-Huckel (DH) theory remains
quantitatively accurate up to the bulk ion density rhob=0.01 M, whereas the SC
theory exhibits a good quantitative accuracy up to rhob=0.2 M. Then, we derive
from the perturbative SC scheme the one-loop theory of asymmetrically
partitioned salt systems around a dielectrically homogeneous charged surface.
It is shown that correlation effects originate in these systems from a
competition between the salt screening loss at the interface driving the ions
to the bulk region, and the interfacial counterion screening excess attracting
them towards the surface. In the case of weak surface charges, the interfacial
salt screening loss is the dominant effect. As a result, correlations decrease
the MF density of both coions and counterions. With increasing surface charge,
the surface-attractive counterion screening excess starts to dominate, and
correlation effects amplify in this regime the MF density of both type of ions.
We also show that at a characteristic value of the electrostatic coupling
parameter, electrostatic correlations result in a charge inversion effect
Comment on "Nonlocal statistical field theory of dipolar particles in electrolyte solutions" by Y.A. Budkov
The article by Budkov introduces a nonlocal field-theoretic model of
solvent-explicit electrostatics. Despite giving a detailed introduction to the
early literature on the topic, the article misses out on a series of articles
that we published several years ago. Consequently, the manuscript essentially
rederives without mention several results that were derived by us for the first
time
Influence of Disorder Strength on Phase Field Models of Interfacial Growth
We study the influence of disorder strength on the interface roughening
process in a phase-field model with locally conserved dynamics. We consider two
cases where the mobility coefficient multiplying the locally conserved current
is either constant throughout the system (the two-sided model) or becomes zero
in the phase into which the interface advances (one-sided model). In the limit
of weak disorder, both models are completely equivalent and can reproduce the
physical process of a fluid diffusively invading a porous media, where
super-rough scaling of the interface fluctuations occurs. On the other hand,
increasing disorder causes the scaling properties to change to intrinsic
anomalous scaling. In the limit of strong disorder this behavior prevails for
the one-sided model, whereas for the two-sided case, nucleation of domains in
front of the invading front are observed.Comment: Accepted for publication in PR
Bit Level Correlations in Some Pseudorandom Number Generators
We present results of extensive bit level tests on some pseudorandom number
generators which are commonly used in physics applications. The generators have
first been tested with an extended version of the -tuple test. Second, we
have developed a novel {\it cluster test} where a physical analogy of the
binary numbers with the two dimensional Ising model has been utilized. We
demonstrate that the new test is rather powerful in finding periodic
correlations on bit level. Results of both test methods are presented for each
bit of the output of the generators. Some generators exhibit clear bit level
correlations but we find no evidence of discernible correlations for
generators, which have recently produced systematic errors in Monte Carlo
simulations.Comment: University of Helsinki preprint HU-TFT-93-4
Long wavelength properties of phase field crystal models with second order dynamics
The phase field crystal (PFC) approach extends the notion of phase field
models by describing the topology of the microscopic structure of a crystalline
material. One of the consequences is that local variation of the interatomic
distance creates an elastic excitation. The dynamics of these excitations poses
a challenge: pure diffusive dynamics cannot describe relaxation of elastic
stresses that happen through phonon emission. To this end, several different
models with fast dynamics have been proposed. In this article we use the
amplitude expansion of the PFC model to compare the recently proposed
hydrodynamic PFC amplitude model with two simpler models with fast dynamics. We
compare these different models analytically and numerically. The results
suggest that in order to have proper relaxation of elastic excitations, the
full hydrodynamical description of the PFC amplitudes is required.Comment: 10 pages, 7 figure
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