590 research outputs found
Wrinkling of microcapsules in shear flow
Elastic capsules can exhibit short wavelength wrinkling in external shear
flow. We analyse this instability of the capsule shape and use the length scale
separation between the capsule radius and the wrinkling wavelength to derive
analytical results both for the threshold value of the shear rate and for the
critical wave-length of the wrinkling. These results can be used to deduce
elastic parameters from experiments.Comment: 4 pages, 2 figures, submitted to PR
Polarized positively charged hydrogen ion beams from charge exchange collisions between metastable H(2S) atoms and halogenes
Phase separation of a multiple occupancy lattice gas
A binary lattice gas model that allows for multiple occupancy of lattice
sites, inspired by recent coarse-grained descriptions of solutions of
interacting polymers, is investigated by combining the steepest descent
approximation with an exploration of the multidimensional energy landscape, and
by Gibbs ensemble Monte Carlo simulations. The one-component version of the
model, involving on site and nearest neighbour interactions, is shown to
exhibit microphase separation into two sub-lattices with different mean
occupation numbers. The symmetric two-component version of the multiple
occupancy lattice gas is shown to exhibit a demixing transition into two phases
above a critical mean occupation number.Comment: submitted to Journal of Physics
Micro-Capsules in Shear Flow
This paper deals with flow-induced shape transitions of elastic capsules. The
state of the art concerning both theory and experiments is briefly reviewed
starting with dynamically induced small deformation of initially spherical
capsules and the formation of wrinkles on polymerized membranes. Initially
non-spherical capsules show tumbling and tank-treading motion in shear flow.
Theoretical descriptions of the transition between these two types of motion
assuming a fixed shape are at variance with the full capsule dynamics obtained
numerically. To resolve the discrepancy, we expand the exact equations of
motion for small deformations and find that shape changes play a dominant role.
We classify the dynamical phase transitions and obtain numerical and analytical
results for the phase boundaries as a function of viscosity contrast, shear and
elongational flow rate. We conclude with perspectives on timedependent flow, on
shear-induced unbinding from surfaces, on the role of thermal fluctuations, and
on applying the concepts of stochastic thermodynamics to these systems.Comment: 34 pages, 15 figure
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