1,890 research outputs found
Theory of nonlinear rheology and yielding of dense colloidal suspensions
A first principles approach to the nonlinear flow of dense suspensions is
presented which captures shear thinning of colloidal fluids and dynamical
yielding of colloidal glasses. The advection of density fluctuations plays a
central role, suppressing the caging of particles and speeding up structural
relaxation. A mode coupling approach is developed to explore these effects.Comment: 4 pages, 2 figures; slightly corrected version; Phys. Rev. Lett., to
be published (2002
Influence of polydispersity on the critical parameters of an effective potential model for asymmetric hard sphere mixtures
We report a Monte Carlo simulation study of the properties of highly
asymmetric binary hard sphere mixtures. This system is treated within an
effective fluid approximation in which the large particles interact through a
depletion potential (R. Roth {\em et al}, Phys. Rev. E{\bf 62} 5360 (2000))
designed to capture the effects of a virtual sea of small particles. We
generalize this depletion potential to include the effects of explicit size
dispersity in the large particles and consider the case in which the particle
diameters are distributed according to a Schulz form having degree of
polydispersity 14%. The resulting alteration (with respect to the monodisperse
limit) of the metastable fluid-fluid critical point parameters is determined
for two values of the ratio of the diameters of the small and large particles:
and . We find that inclusion of
polydispersity moves the critical point to lower reservoir volume fractions of
the small particles and high volume fractions of the large ones. The estimated
critical point parameters are found to be in good agreement with those
predicted by a generalized corresponding states argument which provides a link
to the known critical adhesion parameter of the adhesive hard sphere model.
Finite-size scaling estimates of the cluster percolation line in the one phase
fluid region indicate that inclusion of polydispersity moves the critical point
deeper into the percolating regime. This suggests that phase separation is more
likely to be preempted by dynamical arrest in polydisperse systems.Comment: 11 pages, 10 figure
Non--Newtonian viscosity of interacting Brownian particles: comparison of theory and data
A recent first-principles approach to the non-linear rheology of dense
colloidal suspensions is evaluated and compared to simulation results of
sheared systems close to their glass transitions. The predicted scenario of a
universal transition of the structural dynamics between yielding of glasses and
non-Newtonian (shear-thinning) fluid flow appears well obeyed, and calculations
within simplified models rationalize the data over variations in shear rate and
viscosity of up to 3 decades.Comment: 6 pages, 2 figures; J. Phys. Condens. Matter to be published (Jan.
2003
Effective Interactions and Volume Energies in Charge-Stabilized Colloidal Suspensions
Charge-stabilized colloidal suspensions can be conveniently described by
formally reducing the macroion-microion mixture to an equivalent one-component
system of pseudo-particles. Within this scheme, the utility of a linear
response approximation for deriving effective interparticle interactions has
been demonstrated [M. J. Grimson and M. Silbert, Mol. Phys. 74, 397 (1991)].
Here the response approach is extended to suspensions of finite-sized macroions
and used to derive explicit expressions for (1) an effective electrostatic pair
interaction between pseudo-macroions and (2) an associated volume energy that
contributes to the total free energy. The derivation recovers precisely the
form of the DLVO screened-Coulomb effective pair interaction for spherical
macroions and makes manifest the important influence of the volume energy on
thermodynamic properties of deionized suspensions. Excluded volume corrections
are implicitly incorporated through a natural modification of the inverse
screening length. By including nonlinear response of counterions to macroions,
the theory may be generalized to systematically investigate effective many-body
interactions.Comment: 13 pages (J. Phys.: Condensed Matter, in press
Like-charge attraction through hydrodynamic interaction
We demonstrate that the attractive interaction measured between like-charged
colloidal spheres near a wall can be accounted for by a nonequilibrium
hydrodynamic effect. We present both analytical results and Brownian dynamics
simulations which quantitatively capture the one-wall experiments of Larsen and
Grier (Nature 385, p. 230, 1997).Comment: 10 pages, 4 figure
Environmental Effects on Corrosion Properties of Alloy 22
During the regulatory life of the Yucca Mountain High Level Nuclear Waste (HLNW) repository the primary engineered barrier that is to prevent release of radioactive material into the environment is proposed to be a Corrosion-Resistant Material (CRM) outer shell covering the Waste Package (WP) container. The current selection for the CRM is Alloy 22 (UNS N06022), a Ni-Cr-Mo-W-Fe alloy. Alloy 22 forms a defective chromic oxide passive film which results in excellent corrosion resistance; the presence of molybdenum in Alloy 22 offers corrosion resistance in reducing environments as well as oxidizing environments
Integration through transients for Brownian particles under steady shear
Starting from the microscopic Smoluchowski equation for interacting Brownian
particles under stationary shearing, exact expressions for shear-dependent
steady-state averages, correlation and structure functions, and
susceptibilities are obtained, which take the form of generalized Green-Kubo
relations. They require integration of transient dynamics. Equations of motion
with memory effects for transient density fluctuation functions are derived
from the same microscopic starting point. We argue that the derived formal
expressions provide useful starting points for approximations in order to
describe the stationary non-equilibrium state of steadily sheared dense
colloidal dispersions.Comment: 17 pages, Submitted to J. Phys.: Condens. Matter; revised version
with minor correction
Colloidal electrophoresis: Scaling analysis, Green-Kubo relation, and numerical results
We consider electrophoresis of a single charged colloidal particle in a
finite box with periodic boundary conditions, where added counterions and salt
ions ensure charge neutrality. A systematic rescaling of the electrokinetic
equations allows us to identify a minimum set of suitable dimensionless
parameters, which, within this theoretical framework, determine the reduced
electrophoretic mobility. It turns out that the salt-free case can, on the Mean
Field level, be described in terms of just three parameters. A fourth
parameter, which had previously been identified on the basis of straightforward
dimensional analysis, can only be important beyond Mean Field. More complicated
behavior is expected to arise when further ionic species are added. However,
for a certain parameter regime, we can demonstrate that the salt-free case can
be mapped onto a corresponding system containing additional salt. The
Green-Kubo formula for the electrophoretic mobility is derived, and its
usefulness demonstrated by simulation data. Finally, we report on
finite-element solutions of the electrokinetic equations, using the commercial
software package COMSOL.Comment: To appear in Journal of Physics: Condensed Matter - special issue on
occasion of the CODEF 2008 conferenc
Sequential quasi-Monte Carlo: Introduction for Non-Experts, Dimension Reduction, Application to Partly Observed Diffusion Processes
SMC (Sequential Monte Carlo) is a class of Monte Carlo algorithms for
filtering and related sequential problems. Gerber and Chopin (2015) introduced
SQMC (Sequential quasi-Monte Carlo), a QMC version of SMC. This paper has two
objectives: (a) to introduce Sequential Monte Carlo to the QMC community, whose
members are usually less familiar with state-space models and particle
filtering; (b) to extend SQMC to the filtering of continuous-time state-space
models, where the latent process is a diffusion. A recurring point in the paper
will be the notion of dimension reduction, that is how to implement SQMC in
such a way that it provides good performance despite the high dimension of the
problem.Comment: To be published in the proceedings of MCMQMC 201
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