Biomedical subjects

Roumen Tsekov

Publications and source records attributed to Roumen Tsekov.

3 recordsLinked to original sources

PubMed2005

A qualitative theory of wimples in wetting films.

It has long been known that hydrodynamic pressures in a thin draining liquid film can cause inversion of the curvature of a drop surface as it approaches another surface, creating a so-called dimple. However, it was recently found that a different shape, dubbed a wimple, can be formed if a fluid drop, which is already in the field of repulsive surface forces, is abruptly pushed toward the wall. The drop shape might include a central region in which the film remains thin, surrounded by a ring of greater film thickness bounded at the outer edge by a barrier rim. Here we present a qualitative theory of the wimple formation. It is shown that this is mainly driven by the film hydrodynamics, and a qualitative criterion for the wimple/dimple transition is derived.

Journal Article↗

PubMed2005

Resonant diffusion on modulated surfaces.

Some theoretical methods for description of the diffusion on modulated surfaces are reviewed. A general formula for calculation of the diffusion coefficient of a particle moving in the field of a periodic potential is developed, which takes into account both the potential barrier effect and the dependence of the friction coefficient on the potential. The application of the theory to the diffusion of dimers on solid surfaces reveals a non-monotonous dependence of the diffusion coefficient on the ratio between the dimer and solid spatial parameters. This resonant dependence sometimes can be suppressed by the rotations and vibrations on the dimer. In the present theory the latter are described via an adiabatic approach.

Biophysics↗

PubMed2000

Size Dependence of Protein-Induced Flocculation of Phosphatidylcholine Liposomes.

The adsorption of lysozyme and cytochrome C on phosphatidylcholine liposomes essentially changes the physical properties of the phospholipid membranes and under certain circumstances greatly affects the stability of the colloid dispersion by inducing bridging liposome flocculation. This study was designed to examine experimentally the influence of liposome size on two kinetic parameters of the flocculation, its rate constant and activation energy. As the liposome radius increased in the range 50-500 nm, the activation energy tended to decrease, resulting in an increased flocculation rate, except for the flocculation of 400-nm liposomes, which was greatly impeded. The pronounced influence of the liposome size on the flocculation rate constant was evident, since a well-defined minimum in the kinetic rate of flocculation of 400-nm liposomes was detected experimentally. The obtained nonlinear radius dependencies of the flocculation rates and activation energies are interpreted in terms of the bridging mechanism of the protein-induced liposome flocculation and the supplementary concept of the stability of thin liquid films formed between approaching protein-adsorbed liposomes. Copyright 2000 Academic Press.

Journal Article↗