arXiv subjects

R. Tsekov

Publications and source records attributed to R. Tsekov.

43 records · Page 3Linked to original sources

arXiv2012

Thermo-quantum diffusion in periodic potentials

Quantum Brownian motion in a periodic cosine potential is studied and a simple estimate of the tunneling effect is obtained in the frames of a quasi-equilibrium semiclassical approach. It is shown that the latter is applicable for heavy particles but electrons cannot be described properly since the quantum effects dominate over the thermal ones. The purely quantum electron diffusion is investigated at zero temperature and demonstrates that electrons do not obey the classical Einstein law of Brownian motion in the field of periodic potentials, since the dispersion of the wave packet increases logarithmically in time.

quant-ph↗

arXiv2012

Ermakov equations in quantum mechanics

The Ermakov equation, appearing in quantum mechanics of a harmonic oscillator, is extended via dissipative and thermal terms to take into account the effect of an environment.

quant-ph↗

arXiv2012

Adsorption component of the disjoining pressure in thin liquid films

The disjoining pressure isotherm in foam films is theoretically studied and an important contribution of adsorption is discovered. On the basis of the interfacial thermodynamics an adsorption disjoining pressure component is derived, which is repulsive and exponentially decaying by the film thickness. Expressions for its magnitude and decay length are derived in terms of well-known thermodynamic characteristics such as the partial Gibbs elasticity and adsorption length. Several adsorption isotherms are considered and the corresponding adsorption disjoining pressure components are calculated. An important coupling between the interfacial layer phases and wetting transitions is discussed as well.

cond-mat.mes-hall↗

arXiv2012

Flocculation of vesicles

The flocculation of liposomes is theoretically studied. An expression for the flocculation activation energy is derived, accounting for the electrostatic and hydrophobic interactions as well as for the correlation area of floc-spots.

cond-mat.soft↗

arXiv2011

Wetting film dynamics and stability

Although the wetting films are similar in many aspects to other thin liquid films, there are some differences in their behavior, too. In contrast to soap and emulsion films, whose surfaces are homogeneous, solid substrates of wetting films are heterogeneous as a rule, unless special measures for their homogenization are taken. Here we mean primarily heterogeneous distribution of surface energy leading to existence of hydrophobic domains on hydrophilic surfaces and vice versa. As is known, such hydrophobic domains could play the role of gas-phase nucleation centers and it is widely accepted nowadays that nano-bubbles can be formed there. The present paper reviews the effect of nano-bubbles adhered at solid surface on stability of wetting films. It is shown that the existence of nano-bubbles is crucial for the lifetime of wetting films. Another peculiarity typical for hydrophobic solid surface, the so-called slippage effect, is also investigated and its contribution to the dispersion equation of capillary waves on wetting films is accounted for.

cond-mat.mes-hall↗

arXiv2011

Where is liquid-vapor interface located in solutions?

Two-component liquid-vapor systems are modeled as two bulk phases divided by a two-dimensional surface phase and the mass and momentum balances are theoretically studied. Comparing the derived equations with some typical models of surface rheology, useful information about the interface location is obtained. It is demonstrated that the surface phase, set on the surface of tension, coincides with the equimolecular interface for insoluble surfactants, whereas it is placed on the surface of zero total mass density excess for soluble ones. The applicability of the model to surface electrostatics is also discussed by introduction of a two-dimensional Maxwell equation for the surface phase.

cond-mat.soft↗

arXiv2011

Transport coefficients in composites

The Maxwell approach from electrostatics is applied for calculation of transport coefficients in composites. The viscosity of a dilute emulsion is obtained as a function of the volume fraction of dispersed phase. The derived new formula is asymptotically correct and more general than the linear relationships usually used. The method is applied also for description of the influence of fluctuations on the transport coefficients.

cond-mat.soft↗