Biomedical subjects

Patrick Oswald

Publications and source records attributed to Patrick Oswald.

4 recordsLinked to original sources

PubMed2005

Backflow-induced asymmetric collapse of disclination lines in liquid crystals.

We present experiments where opposed pairs of planar parallel disclination lines of topological strength s=+/-1 move due to their mutual attraction. Our measurements show that their motion is clearly asymmetric, with +1 defects moving up to twice as fast as -1 ones. This is a clear indication of backflow, given the intrinsic isotropic elasticity of our system. A phenomenological model is able to account for the experimental observations by renormalizing the orientational diffusivity estimated from the velocity of each defect.

Cholesterol↗

PubMed2005

Chirality-biased point defects dynamics on a disclination line in a nematic liquid crystal.

Chiral additives in the nematic liquid crystal can alter the dynamics of point defects moving on a disclination line. They exert a constant force on defects, leading to the bimodal distribution of distances between them at long times. The evolution of the system of defects in the presence of chiral additives provides a very direct proof of the existence of repulsive forces between the defects at large distances. We find that addition of a sufficient amount of chiral compound removes all point defects from the system. The process is studied in the system of 8CB (4-n-octyl-4'-cyanobiphenyl) doped with the chiral compound S811 (from Merck Co.) and in the computer simulations.

Journal Article↗

PubMed2002

Annihilation of point defects on a line.

We discuss the evolution of the distribution function of distances between point defects of opposite signs distributed on a line of finite length interacting via a potential attractive at short distances and repulsive at large distances. The standard deviation of the distribution grows quickly at short times, attains maximum, and decreases logarithmicaly at longer times. The distance between the defects increases monotonically and at equilibrium is about two times larger than the distance at which the repulsive force attains maximum. The distance dependent viscosity does not change qualitatively these conclusions, but only increases the time scale of evolution by one order of magnitude.

Journal Article↗

PubMed2001

When boundaries dominate: dislocation dynamics in smectic films.

We discuss the influence of dissipation at a system boundary (film-meniscus interface) on the dynamics of dislocation loops inside a smectic film. This dissipation induces a strong coupling between dislocations-effectively independent of their separation-leading to their nontrivial dynamics. Because of these dynamics, the effective "dynamical" radius of nucleation can be 10 times larger than the usual static critical radius.

Journal Article↗