What makes a boundary less accessible

For the growth and transport processes driven by Laplacian fields, the accessibility of an interface for Brownian motion is characterized by the harmonic measure. Its multifractal properties help one to understand how the irregular geometry of biological membranes, metallic electrodes, porous catalysts, or growing aggregates is "seen" by diffusing particles. To clarify this point, we performed an extensive numerical study of the harmonic measure on two families of self-similar triangular Koch curves of variable Hausdorff dimension which may represent branched pore networks or fjordlike rough interfaces. Although these structures are apparently different, the multifractal properties of the harmonic measure in two cases are found to be very close for curves of small Hausdorff dimensions and to differ for higher irregularity. This provides new insight into optimization problems in chemical engineering.     

Study of Relaxation in Micellar Solution by the Numerical Experiment

A numerical simulation of the relaxation process of surfactant micellar solution to a new equilibrium state is performed using model analytical representations for the main characteristics of micellar aggregates. Relaxation stages of molecular aggregate size distribution in the typical regions of aggregation number variations predicted by the analytical theory in two-flux approximation are revealed. Good agreement between the predicted values of the relaxation times of micellar solution and those obtained in numerical simulation is disclosed within the domain of applicability of two-flux approximation. Numerical algorithm proposed in this work makes it possible to study the relaxation process of micellar solution even in the case when two-flux approximation becomes inapplicable. The realization of numerical algorithm can be considered as a kind of experiment for studying the relaxation process of a model micellar solution.     

Effect of Pr-Ca substitution on the transport and magnetic behavior of LaMnO3 perovskite

The effect of simultaneous substitution of a fluctuating cation and a divalent cation in LaMnO₃ perovskite modifies the properties of the material to exhibit large valence colossal magnetoresistance (CMR) effect. A good example of these properties is (La_1−2x Pr _x Ca _x )MnO₃ (LPCMO) type CMR material. In this communication it is reported that, with the increase in x (for x=0.1, 0.15, 0.2), the T _c varies between 100 and 120 K with improvisation in metal-insulator transition. Interestingly, resistance increases with x from few hundred ohms to few kilo ohms with corresponding decrease in the unit cell volume. The results of the studies using X-ray diffraction (XRD), electrical resistivity, magnetoresistance and ac susceptibility measurements on LPCMO samples for understanding the structural, transport and magnetic properties are discussed in detail.     

Kinetics of Active Surface-Mediated Diffusion in Spherically Symmetric Domains

We present an exact calculation of the mean first-passage time to a target on the surface of a 2D or 3D spherical domain, for a molecule alternating phases of surface diffusion on the domain boundary and phases of bulk diffusion. We generalize the results of Bénichou et al. in (J. Stat. Phys. 142:657, 2011) and consider a biased diffusion in a general annulus with an arbitrary number of regularly spaced targets on a partially reflecting surface. The presented approach is based on an integral equation which can be solved analytically. Numerically validated approximation schemes, which provide more tractable expressions of the mean first-passage time are also proposed. In the framework of this minimal model of surface-mediated reactions, we show analytically that the mean reaction time can be minimized as a function of the desorption rate from the surface.     

An experimental investigation and modelling of the solubility, density and surface tension of 1,1,1,3,3-pentafluoropropane (R-245fa)/synthetic polyolester compressor oil solutions

This paper reports experimental data for the solubility, density and capillary constant for solutions of refrigerant 1,1,1,3,3-pentafluoropropane (R-245fa) with polyolester compressor oil Planetelf ACD 100FY over a wide range of temperatures and concentrations. The experimental data were obtained in the temperature range from 333 to 425 K and at pressures up to 33 bar using static methods. Based on information for the capillary constant, the surface tension of the solutions R-245fa/Planetelf ACD 100FY is determined. The enthalpy of liquid phase of the R-245fa/Planetelf ACD 100FY solutions is calculated. The analysis of the behaviour of the excess thermodynamic functions is carried out. Information about the changing concentration of refrigerant in the liquid phase of the refrigerant/oil solutions (ROS) and in the surface layer of the liquid phase of the ROS at increasing temperature is presented.     

Mean First-Passage Time of Surface-Mediated Diffusion in Spherical Domains

We present an exact calculation of the mean first-passage time to a target on the surface of a 2D or 3D spherical domain, for a molecule alternating phases of surface diffusion on the domain boundary and phases of bulk diffusion. The presented approach is based on an integral equation which can be solved analytically. Numerically validated approximation schemes, which provide more tractable expressions of the mean first-passage time are also proposed. In the framework of this minimal model of surface-mediated reactions, we show analytically that the mean reaction time can be minimized as a function of the desorption rate from the surface.     

Parametric equations of the theory of formation of spherical micelles

Using the notion of aggregation work, we construct a system of differential equations for the aggregation number of micelles which is a function of the parameters of micellization (parametric equations). There are explicit solutions for two important models of spherical micelles. Based on these solutions, we obtain an analytical expression for the equilibrium concentration of surfactant monomers and consequently for the whole spectrum of equilibrium concentrations of molecular aggregates in this framework. Accuracy of these expressions is discussed, and they are applied to an example of micelles formed by sodium dodecyl sulfate.