17,778 research outputs found
Diffusiophoresis in non-adsorbing polymer solutions: the Asakura-Oosawa model and stratification in drying films
A colloidal particle placed in an inhomogeneous solution of smaller
non-adsorbing polymers will move towards regions of lower polymer
concentration, in order to reduce the free energy of the interface between the
surface of the particle and the solution. This phenomenon is known as
diffusiophoresis. Treating the polymer as penetrable hard spheres, as in the
Asakura-Oosawa model, a simple analytic expression for the diffusiophoretic
drift velocity can be obtained. In the context of drying films we show that
diffusiophoresis by this mechanism can lead to stratification under easily
accessible experimental conditions. By stratification we mean spontaneous
formation of a layer of polymer on top of a layer of the colloid. Transposed to
the case of binary colloidal mixtures, this offers an explanation for the
stratification observed recently in these systems [A. Fortini et al, Phys. Rev.
Lett. 116, 118301 (2016)]. Our results emphasise the importance of treating
solvent dynamics explicitly in these problems, and caution against the neglect
of hydrodynamic interactions or the use of implicit solvent models in which the
absence of solvent backflow results in an unbalanced osmotic force which gives
rise to large but unphysical effects.Comment: 11 pages, 6 figure
Assembly for recovering a capsule Patent
Assembly for opening flight capsule stabilizing and decelerating flaps with reference to capsule recover
Space capsule ejection assembly Patent
Describing assembly for opening stabilizing and decelerating flaps of flight capsules used in space researc
On the electrical double layer contribution to the interfacial tension of protein crystals
We study the electrical double layer at the interface between a protein
crystal and a salt solution or a dilute solution of protein, and estimate the
double layer's contribution to the interfacial tension of this interface. This
contribution is negative and decreases in magnitude with increasing salt
concentration. We also consider briefly the interaction between a pair of
protein surfaces.Comment: 6 pages, 3 figures, revtex
Distribution of the second virial coefficients of globular proteins
George and Wilson [Acta. Cryst. D 50, 361 (1994)] looked at the distribution
of values of the second virial coefficient of globular proteins, under the
conditions at which they crystallise. They found the values to lie within a
fairly narrow range. We have defined a simple model of a generic globular
protein. We then generate a set of proteins by picking values for the
parameters of the model from a probability distribution. At fixed solubility,
this set of proteins is found to have values of the second virial coefficient
that fall within a fairly narrow range. The shape of the probability
distribution of the second virial coefficient is Gaussian because the second
virial coefficient is a sum of contributions from different patches on the
protein surface.Comment: 5 pages, including 3 figure
Multi-Thread Hydrodynamic Modeling of a Solar Flare
Past hydrodynamic simulations have been able to reproduce the high
temperatures and densities characteristic of solar flares. These simulations,
however, have not been able to account for the slow decay of the observed flare
emission or the absence of blueshifts in high spectral resolution line
profiles. Recent work has suggested that modeling a flare as an sequence of
independently heated threads instead of as a single loop may resolve the
discrepancies between the simulations and observations. In this paper we
present a method for computing multi-thread, time-dependent hydrodynamic
simulations of solar flares and apply it to observations of the Masuda flare of
1992 January 13. We show that it is possible to reproduce the temporal
evolution of high temperature thermal flare plasma observed with the
instruments on the \textit{GOES} and \textit{Yohkoh} satellites. The results
from these simulations suggest that the heating time-scale for a individual
thread is on the order of 200 s. Significantly shorter heating time scales (20
s) lead to very high temperatures and are inconsistent with the emission
observed by \textit{Yohkoh}.Comment: Submitted to Ap
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