Dynamics of a bubble in oscillating viscous liquid.

This article is devoted to the investigation of gaseous bubble dynamics in oscillating viscous liquids of different density values. The study is conducted numerically using the level-set method with a non-stationary approach. The bubble is initially located near the upper wall of the container. The effects of the inclusion and host liquid viscosities on interaction of the bubble with the wall are analysed. The calculations show that in the absence of gravity, for low-viscosity fluids the bubble is attracted to the nearest wall, which is consistent with previous analytical and experimental results. With increasing viscosity, the vibrational attraction to the wall becomes weaker and is then replaced by repulsion, which can be explained by the decelerative effect of viscosity in the boundary layer near the rigid surface, where the average flow becomes less intensive. The dependencies of the repulsion force on the parameter values are obtained by using the balance method (investigation of the gravity level needed to attain the quasi-equilibrium state at a certain distance between the bubble and the wall). The calculations show that the repulsion force grows with decreasing Reynolds number (increase of the viscosity). This article is part of the theme issue 'New trends in pattern formation and nonlinear dynamics of extended systems'.

Magnetic Circular Dichroism of meso-Phenyl-Substituted Pd-Octaethylporphyrins.

Absorption and magnetic circular dichroism (MCD) spectra have been measured and theoretically simulated for a series of palladium octaethylporphyrins substituted at the meso positions with phenyl groups (n = 0-4). Analysis of the spectra included the perimeter model and time-dependent density functional theory (TDDFT) calculations. With the increasing number of phenyl substituents, the molecule is transformed from a positive hard (ΔHOMO > ΔLUMO) to a soft (ΔHOMO ≈ ΔLUMO) chromophore. This is manifested by a drastic decrease of the absorption intensity in the 0-0 region of the Q-band and by the strongly altered ratio of MCD intensities in the Q and Soret regions. Such behavior can be readily predicted using perimeter model, by analyzing frontier orbital shifts caused by various perturbations: alkyl and aryl substitution, insertion of a metal, and deviations from planarity. TDDFT calculations confirm the trends predicted by the perimeter model, but they fail in cases of less symmetrical derivatives to properly reproduce the MCD spectra in the Soret region. Our results confirm the power of the perimeter model in predicting absorption and MCD spectra of large organic molecules, porphyrins in particular. We also postulate, contrary to previous works, that the isolated porphyrin dianion is not a soft chromophore, but rather a strongly positive-hard one.

[Signs of proliferative process after laser treatment of advanced glaucoma]. / Priznaki proliferativnogo protsessa posle lazernogo lecheniia dalekozashedshei operirovannoi glaukomy.

The universally established method for effective and less-invasive reduction of the intraocular pressure (IOP) in patients with primary open-angle glaucoma (POAG) is a two-step method consisting of non-penetrating deep sclerectomy (NDSE) followed by laser goniopuncture of the Descemet's membrane (Descemet's goniopuncture; DGP). However, the hypotensive effect can diminish at different times during the follow-up due to excessive scarring in surgically formed outflow tracts (SFOT). PURPOSE: To evaluate the condition of SFOT in dynamics with Visante OCT after one-step combined laser technique consisting of modified selective laser activation of the trabecula (MSLAT) and DGP in advanced POAG patients with normalized IOP who have pronounced pigmentation of the trabecular meshwork and stage II pseudoexfoliation syndrome (PES). MATERIAL AND METHODS: OCT scans of 117 patients (117 eyes) were analyzed before laser treatments and after 1, 3, 6, 12 and 24 months. The study included 62 patients (62 eyes) comprising the main group who underwent MSLAT + DGP, and the control group consisting of 55 patients (55 eyes) who only underwent DGP. RESULTS: Visante OCT scans revealed that parameters of the filtration bleb (FB) and intrascleral cavity (ISC) in the main study group were more stable than in the control group during the whole follow-up. In the main study group there were less incorporations in the ISC and they had lower optical density, compared with the control group where there were denser incorporations in the ISC which gradually increased in count. CONCLUSION: According to Visante OCT, the growing count and the increase in density of incorporations in the ISC can be defined as adverse signs of an active proliferative process in SFOT. A one-step MSLAT with DGP help achieve both a long-lasting hypotensive effect, and decrease of active proliferative process signs in SFOT.

Nonlinear regimes of Soret-driven convection of ternary fluid with fixed vertical heat flux at the boundaries.

Nonlinear regimes of the Soret-induced convection of a ternary mixture in a rectangular cavity with the vertical heat flux at the boundaries are studied numerically. Linear stability analysis performed earlier for a plane horizontal layer has shown that in a wide range of parameters the longwave instability is dominant. Nonlinear calculations performed in the present work for the parameter ranges where the monotonic longwave instability is dominant according to the linear stability analysis, show that at large supercriticalities the multi-vortex stationary flows could be realized. With the decrease of absolute value of the Rayleigh number Ra the series of flow structure transformations takes place. This transformation is accompanied by the decrease of a number of the vortices such that near the threshold the flow becomes two-vortex, i.e. the flow with maximum possible wavelength (minimum possible wave number) is realized. Thus, the nonlinear calculations confirm the conclusions of the linear stability analysis that the longwave instability is dominant. For the parameter ranges where according to the linear stability analysis the oscillatory longwave instability is dominant, the nonlinear calculations show that at small values of the net separation ratio the oscillatory regimes could be observed just in a narrow range of Ra close to the convection threshold and with the growth of net separation ratio the range of Ra where they can be observed is extended.

European Space Agency experiments on thermodiffusion of fluid mixtures in space.

This paper describes the European Space Agency (ESA) experiments devoted to study thermodiffusion of fluid mixtures in microgravity environment, where sedimentation and convection do not affect the mass flow induced by the Soret effect. First, the experiments performed on binary mixtures in the IVIDIL and GRADFLEX experiments are described. Then, further experiments on ternary mixtures and complex fluids performed in DCMIX and planned to be performed in the context of the NEUF-DIX project are presented. Finally, multi-component mixtures studied in the SCCO project are detailed.

Effect of Surfagon on Open Field and Elevated Plus Maze Behavior of Gonadectomized and Non-Gonadectomized Male Rats.

We studied the effect of gonadotropin-releasing hormone agonist surfagon (2 µg/kg, once, intraperitoneally) on anxious behavior of adult gonadectomized and non-gonadectomized male rats. It was shown that surfagon significantly increased anxiety of both gonadectomized and non-gonadectomized rats in the open-field test and in elevated plus maze.

Stability of a stationary plane-parallel flow of a ternary fluid between two vertical plates maintained at constant different temperatures.

The linear stability of a steady convective flow of a ternary mixture placed between differently heated vertical rigid plates is studied. The applied temperature gradient induces concentration gradients due to the Soret effect. The analysis is done for the case when separation ratios of ternary mixture, i.e., Soret coefficients, have different signs but the net separation ratio is negative. The stability maps in terms of the Grashof number and net separation ratio are obtained and discussed for monotonic and oscillatory modes of instability. The previous results for long-wave instability of a binary mixture were recovered in the limit when one of the Soret coefficients tends to zero. For finite-wavelength perturbations the previous results were extended by discovering the oscillatory instability.

Measurement of Soret coefficients in a ternary mixture of toluene-methanol-cyclohexane in convection-free environment.

We report on the measurement of Soret (ST) coefficients in the ternary system toluene (T)-methanol (M)-cyclohexane (Ch) onboard the International Space Station in the experiment selectable optical diagnostic instrument/DCMIX2 (Diffusion Coefficients Measurement in ternary mIXtures). Nine experiments were conducted in the range of mean temperatures between 298.15 K and 306.15 K in the mixture with composition 0.62 (T)-0.31 (M)-0.07 (Ch) in mass fractions. A linear dependence of the Soret coefficients on temperature was established for the ternary mixture. It has also been found that, over considered range of mean temperatures, the Soret coefficients of toluene are small and positive, while the Soret coefficients for methanol are negative and, at least, two times larger. The present work also presents a comprehensive study of possible methodologies to process raw data from the Soret experiment in ternary mixtures. All the experiments were processed by seven different schemes and two of them were identified as the most reliable. We also investigate the error propagation and explain the reasons for the discrepancy of the results obtained by different schemes.

Onset and non-linear regimes of Soret-induced convection in binary mixtures heated from above.

The paper deals with the investigation of the onset and non-linear regimes of convection of liquid binary mixtures with negative Soret effect heated from above. The linear stability of a convectionless state in a horizontal layer is studied by the numerical solution of the linearized problem on the temporal evolution of small perturbations of the unsteady base state. Non-linear regimes of convection are investigated by the numerical solution of the non-linear unsteady equations for a horizontally elongated rectangular cavity. The calculations are performed for water-ethanol and water-isopropanol liquid mixtures and for colloidal suspensions. The dependences of the instability onset time and wave number of the most dangerous perturbations on the solutal Rayleigh number (gravity level) obtained by a linear stability analysis and non-linear calculations are found to be in a very good agreement. A favorable comparison with the existing experimental and numerical data is presented.

Phase-field modelling of gravity-capillary waves on a miscible interface.

Using the approach of direct numerical simulations we investigate the gravity-capillary waves induced on a horizontal interface between two slowly miscible liquids. It is assumed that the liquids are just brought into contact, and thus the interface is slowly smeared by the action of interfacial diffusion. It is also assumed that the initial shape of the interface is distorted by harmonic perturbations, which results in the development of the gravity-capillary surface waves. The evolution of the binary mixture is modelled on the basis of the phase-field method. Our results show that in the limiting case of negligible diffusion the classical dispersion relations for immiscible interfaces can be reproduced. Although, for the waves with shorter wavelengths such an agreement is more difficult to obtain. The interfacial diffusion brings an additional dissipation to the fluid system, strongly damping the development of the shorter waves. We also show that the mixing (or the transition of a binary system to the state of thermodynamic equilibrium) is intensified by the presence of the surface waves, and this effect is more important when the liquids are slowly miscible, i.e. when the interfacial diffusion is weak.

Onset of Soret-induced convection in a horizontal layer of ternary fluid with fixed vertical heat flux at the boundaries.

The paper deals with the investigation of the onset and weakly nonlinear regimes of the Soret-driven convection of ternary liquid mixture in a horizontal layer with rigid impermeable boundaries subjected to the prescribed constant vertical heat flux. It is found that there are monotonous and oscillatory longwave instability modes. The boundary of the monotonous longwave instability in the parameter plane Rayleigh number Ra - net separation ratio [Formula: see text] at fixed separation ratio of one of solutes consists of two branches of hyperbolic type. One of the branches is located at [Formula: see text], the other one at [Formula: see text]. The oscillatory longwave instability exists at [Formula: see text] only for the heating from below and at [Formula: see text] there exist two oscillatory longwave instability modes: one at [Formula: see text] and the other at [Formula: see text]. Corrections to the Rayleigh number obtained in the higher order of the expansion show that the longwave perturbations can be most dangerous at any values of [Formula: see text]. The numerical solution of the linear stability problem for small perturbations with finite wave numbers confirms this conclusion. The weakly nonlinear analysis shows that all steady solutions are unstable to the modes of larger wavelength and stable to the modes of smaller wavelength, i.e. the solution with maximal possible wavelength is realized.

Onset and nonlinear regimes of ternary mixture convection in a square cavity.

We present the results of numerical simulations of onset and nonlinear regimes of a ternary mixture convection in a square cavity subjected to the gravity field and vertical gradients of temperature and concentration. The stability problem for the non-convective state of the mixture is solved using a software package for the investigation of the stability of flows. Nonlinear regimes of convection are studied numerically by the finite difference method. The dependences of critical parameters on the net separation ratio are obtained for the cases of heating from above and below. Numerical data on the temporal evolution of the integral characteristics of flow and heat and mass transfer and of the fields of stream function, temperature and concentration are obtained for different values of the Rayleigh number and net separation ratio.

Benchmark values for the Soret, thermodiffusion and molecular diffusion coefficients of the ternary mixture tetralin+isobutylbenzene+n-dodecane with 0.8-0.1-0.1 mass fraction.

With the aim of providing reliable benchmark values, we have measured the Soret, thermodiffusion and molecular diffusion coefficients for the ternary mixture formed by 1,2,3,4-tetrahydronaphthalene, isobutylbenzene and n-dodecane for a mass fraction of 0.8-0.1-0.1 and at a temperature of 25°C. The experimental techniques used by the six participating laboratories are Optical Digital Interferometry, Taylor Dispersion technique, Open Ended Capillary, Optical Beam Deflection, Thermogravitational technique and Sliding Symmetric Tubes technique in ground conditions and Selectable Optical Diagnostic Instrument (SODI) in microgravity conditions. The measurements obtained in the SODI installation have been analyzed independently by four laboratories. Benchmark values are proposed for the thermodiffusion and Soret coefficients and for the eigenvalues of the diffusion matrix in ground conditions, and for Soret coefficients in microgravity conditions.

Soret separation in a binary liquid mixture near its critical temperature.

The values of transport coefficients near a critical point are typically enhanced compared to the values in the classical region far away from a critical point. We report on the impact of the asymptotic behavior of the mass diffusion near the critical region on the Soret separation of the components in a model binary mixture. Concentration patterns are numerically investigated in the case of a spatially varying temperature. The Soret separation in ordinary mixture leads to the establishing of a linear concentration distribution in a steady state. The presence of the critical point redistributes the concentration field, it creates a thin layer with sharp concentration change at the critical region which can be seen as a horizontal plateau on vertical profiles. Large concentration gradients are established across this layer. The analysis showed that the kinetic of the separation significantly depends on whether the critical temperature is inside or outside of the applied temperature region, which is T(cold) ≤ T ≤ T(hot). Critical separation road is suggested for the case when T(cr) is located inside this region, T(cold) ≤ T(cr) ≤ T(hot).

Hypolipidemic and hypoglycemic effect of peptide Lys-Glu-Trp-NH(2) in rats with associated metabolic disorders.

The effect of peptide Lys-Glu-Trp-NH2 in doses of 0.2, 20, and 2000 µg/kg on lipid and carbohydrate metabolism was studied in Wistar rats with experimental hyperlipidemia and diabetes mellitus. This tripeptide in a dose of 2000 µg/kg produced a hypolipidemic effect on atherogenic lipoproteins, decreased the intensity of LPO, improved the state of the antioxidant system, and normalized the content of HDL. Treatment with this tripeptide had a hypolipidemic effect and reduced the severity of specifi c morphofunctional changes in the pancreatic and hepatic tissue.

Kelvin-Helmholtz and Holmboe instabilities of a diffusive interface between miscible phases.

The stability of a shear flow imposed along a diffusive interface that separates two miscible liquids (a heavier liquid lies underneath) is studied using direct numerical simulations. The phase-field approach is employed for description of a thermo- and hydrodynamic evolution of a heterogeneous binary mixture. The approach takes into account the dynamic interfacial stresses at a miscible interface and uses the extended Fick's law for setting the diffusion transport (the diffusion flux is proportional to the gradient of chemical potential). The shear flow is unstable to two kinds of instabilities: (1) the Kelvin-Helmholtz instability, with an immovable vortex formed in the middle of an interface (in the vertical direction) and (2) the Holmboe instability, with traveling waves along the interfacial boundary. The development of the Holmboe instability results in a stronger enhancement of molecular mixing between the mixture components. Earlier, the boundaries of these instabilities were determined using the linear stability analysis and employing the concept of a "frozen interface." In the current work, through the solution of full equations, we obtain the stability boundaries for several sets of governing parameters, showing a greater variety of the possible shapes of the stability diagrams. The Kelvin-Helmholtz instability always occurs at lower gravity effects (lower density contrasts), while the Holmboe instability occurs when gravity is stronger. We show that for some parameters these two instabilities are separated by a zone where the shear flow is stable, and this zone disappears for the other sets of parameters.

Phase-field modeling of an immiscible liquid-liquid displacement in a capillary.

We develop a numerical model for a two-phase flow of a pair of immiscible liquids within a capillary tube. We assume that a capillary is initially saturated with one liquid and the other liquid is injected via one of the capillary's ends. The governing equations are solved in the velocity-pressure formulation, so the pressure levels are imposed at the capillary inlet and outlet ends. We model the structure of the flow and the shape of the interface. We are able to reproduce the flow for a wide range of capillary numbers, when the meniscus preserves its shape moving together with the flow, and when the meniscus constantly stretches resembling the transport of a passive impurity. We demonstrate that the phase-field approach is capable of reproducing all features of the liquid-liquid displacement, including the motion of a contact line, the dynamic changes of the capillary pressure, and the dynamic changes of the apparent contact angle.

Phase diagram of a binary mixture in a closed cavity.

Normally, the phase diagram is reported as a property of the binary mixture. We show that the phase diagram (that is, the zones of thermodynamic stability of the states of the binary mixture) is also affected by the size of the container. We investigate the thermodynamic stability of the binary mixture in a closed cavity, and identify the zone in parameters where the binary mixture is heterogeneous in equilibrium (the zone of spinodal decomposition), the zone where the mixture is always homogeneous in equilibrium, and the zone where the transition between these two states is possible (the metastable nucleation zone). In addition, we investigate the properties of the smallest single droplet that may be in equilibrium in the closed cavity (for the given average concentration, all smaller droplets would always dissolve). We show that the size of such droplets depends on the cavity's size, as ∼L^{1/2}.

Band instability in near-critical fluids subjected to vibration under weightlessness.

Periodical patterns (bands) developing at the interface of two immiscible fluids under vibration parallel to interface are observed under zero-gravity conditions. Fluids are slightly below their liquid-vapor critical point where they behave in a scaled, universal manner. In addition, liquid and vapor densities are close and surface tension is very low. Linear stability analyses and direct numerical simulation show that this instability, although comparable to the frozen wave instability observed in a gravity field, is nonetheless noticeably different when gravity becomes zero. In particular, the neutral curve minimum corresponds to the long-wave perturbations with k=0 and zero dimensionless vibrational parameter, corresponding to no instability threshold. The pattern wavelength thus corresponds to the wavelength of the perturbations with maximal growth rate. This wavelength differs substantially from the neutral perturbations wavelength at the same vibrational parameter value. The role of viscosity is highlighted in the pattern formation, with a critical wavelength dependence on vibration parameters that strongly depends on viscosity. These results compare well with experimental observations performed in the liquid-vapor phases near the critical point of CO_{2} (in weightlessness) and H_{2} (under magnetic levitation).