2,487 research outputs found
Investigation of -dependent dynamical heterogeneity in a colloidal gel by x-ray photon correlation spectroscopy
We use time-resolved X-Photon Correlation Spectroscopy to investigate the
slow dynamics of colloidal gels made of moderately attractive carbon black
particles. We show that the slow dynamics is temporally heterogeneous and
quantify its fluctuations by measuring the variance of the instantaneous
intensity correlation function. The amplitude of dynamical fluctuations has a
non-monotonic dependence on scattering vector , in stark contrast with
recent experiments on strongly attractive colloidal gels [Duri and Cipelletti,
\textit{Europhys. Lett.} \textbf{76}, 972 (2006)]. We propose a simple scaling
argument for the -dependence of fluctuations in glassy systems that
rationalizes these findings.Comment: Final version published in PR
The Electric Double Layer Structure Around Charged Spherical Interfaces
We derive a formally simple approximate analytical solution to the
Poisson-Boltzmann equation for the spherical system via a geometric mapping.
Its regime of applicability in the parameter space of the spherical radius and
the surface potential is determined, and its superiority over the linearized
solution is demonstrated.Comment: 7 pages, 5 figure
Research Notes : United States : Evaluation of soybean germplasm for stress tolerance and biological efficiency : To evaluate soybean germplasm and cultivars for stress tolerance toward - Soil Acidity
Field experiments conducted on a silt loam soil with six culti-vars under four pH ranges (5.9-6.7, 5.7-6.5, 5.3-6.0 and 5.0-5.6) in-dicated significant tolerance of \u27Bedford\u27 and \u27Forrest\u27 under acid soil pH ranges. The two cultivars were superior to \u27Bragg\u27, \u27Braxton\u27, \u27Co-237\u27, and \u27Tracy M\u27 in 1981 and 1982 trials. However, lowering of pH to 4.6-5.4, 4.5-5.4, 4.1-5.1, and 3.8-4.5 resulted in nullified seed formation in all the cultivars
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
Nonlinear effects in charge stabilized colloidal suspensions
Molecular Dynamics simulations are used to study the effective interactions
in charged stabilized colloidal suspensions. For not too high macroion charges
and sufficiently large screening, the concept of the potential of mean force is
known to work well. In the present work, we focus on highly charged macroions
in the limit of low salt concentrations. Within this regime, nonlinear
corrections to the celebrated DLVO theory [B. Derjaguin and L. Landau, Acta
Physicochem. USSR {\bf 14}, 633 (1941); E.J.W. Verwey and J.T.G. Overbeck, {\em
Theory of the Stability of Lyotropic Colloids} (Elsevier, Amsterdam, 1948)]
have to be considered. For non--bulklike systems, such as isolated pairs or
triples of macroions, we show, that nonlinear effects can become relevant,
which cannot be described by the charge renormalization concept [S. Alexander
et al., J. Chem. Phys. {\bf 80}, 5776 (1984)]. For an isolated pair of
macroions, we find an almost perfect qualitative agreement between our
simulation data and the primitive model. However, on a quantitative level,
neither Debye-H\"uckel theory nor the charge renormalization concept can be
confirmed in detail. This seems mainly to be related to the fact, that for
small ion concentrations, microionic layers can strongly overlap, whereas,
simultaneously, excluded volume effects are less important. In the case of
isolated triples, where we compare between coaxial and triangular geometries,
we find attractive corrections to pairwise additivity in the limit of small
macroion separations and salt concentrations. These triplet interactions arise
if all three microionic layers around the macroions exhibit a significant
overlap. In contrast to the case of two isolated colloids, the charge
distribution around a macroion in a triple is found to be anisotropic.Comment: 10 pages, 9 figure
Entropic phase separation of linked beads
We study theoretically a model system of a transient network of microemulsion
droplets connected by telechelic polymers and explain recent experimental
findings. Despite the absence of any specific interactions between either the
droplets or polymer chains, we predict that as the number of polymers per drop
is increased, the system undergoes a first order phase separation into a dense,
highly connected phase, in equilibrium with dilute droplets, decorated by
polymer loops. The phase transition is purely entropic and is driven by the
interplay between the translational entropy of the drops and the
configurational entropy of the polymer connections between them. Because it is
dominated by entropic effects, the phase separation mechanism of the system is
extremely robust and does not depend on the particlular physical realization of
the network. The discussed model applies as well to other polymer linked
particle aggregates, such as nano-particles connected with short DNA linkers
A Systems Approach to Developing an Affordable Space Ground Transportation Architecture using a Commonality Approach
This paper presents a structured approach for achieving a compatible Ground System (GS) and Flight System (FS) architecture that is affordable, productive and sustainable. This paper is an extension of the paper titled "Approach to an Affordable and Productive Space Transportation System" by McCleskey et al. This paper integrates systems engineering concepts and operationally efficient propulsion system concepts into a structured framework for achieving GS and FS compatibility in the mid-term and long-term time frames. It also presents a functional and quantitative relationship for assessing system compatibility called the Architecture Complexity Index (ACI). This paper: (1) focuses on systems engineering fundamentals as it applies to improving GS and FS compatibility; (2) establishes mid-term and long-term spaceport goals; (3) presents an overview of transitioning a spaceport to an airport model; (4) establishes a framework for defining a ground system architecture; (5) presents the ACI concept; (6) demonstrates the approach by presenting a comparison of different GS architectures; and (7) presents a discussion on the benefits of using this approach with a focus on commonality
Brownian Entanglement
We show that for two classical brownian particles there exists an analog of
continuous-variable quantum entanglement: The common probability distribution
of the two coordinates and the corresponding coarse-grained velocities cannot
be prepared via mixing of any factorized distributions referring to the two
particles in separate. This is possible for particles which interacted in the
past, but do not interact in the present. Three factors are crucial for the
effect: 1) separation of time-scales of coordinate and momentum which motivates
the definition of coarse-grained velocities; 2) the resulting uncertainty
relations between the coordinate of the brownian particle and the change of its
coarse-grained velocity; 3) the fact that the coarse-grained velocity, though
pertaining to a single brownian particle, is defined on a common context of two
particles. The brownian entanglement is a consequence of a coarse-grained
description and disappears for a finer resolution of the brownian motion. We
discuss possibilities of its experimental realizations in examples of
macroscopic brownian motion.Comment: 18 pages, no figure
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
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