Thermal vibrational convection in near-critical fluids. Part 2. Weakly non-uniform heating

The governing equations and effective boundary conditions to describe thermal vibrational convection in a near-critical fluid are derived with the help of the multiple-scale method and averaging procedure. In contrast to Part 1, this paper focuses on the effects of density non-homogeneities caused not by external heating but by vibrational and gravity stratifications due to the divergent mechanical compressibility of near-critical media. It is shown that vibrations generate non-homogeneities in the average temperature, which result in the onset of thermal convection even under isothermal boundary conditions. An agreement with the results of previous numerical and asymptotical analyses and with experiments is found.<br/

Physical Parameters of Polymer Composite Materials Created on the Basis of Low and High Molecular Weight Rubbers

ABSTRACT. The theoretical foundations of the structural and mechanical behavior of filled three-dimensional cross-linked elastomers are supplemented. Numerical experiments are carried out, based on the data of numerical experiments, three dimensional cross linked, filled with dispersed particles frost-resistant elastomers based on low and high molecular weight rubbers are developed. Theoretical and experimental data are compared and their good convergence is shown. Comparison of the physical parameters of the composites created by the authors on the basis of low and high molecular weight rubbers showed that the deformation characteristics of the composite based on high molecular weight rubbers are many times superior to composites based on low molecular weight, as well as their glass transition temperature is also very different. The created composites are recommended as a structural material in relation to the engineering problem of creating wear-resistant parts and components of road and air transport operated in a wide temperature range, including the Far North and the Arctic. &nbsp

Influence of Hydrodynamic Regimes on Mixing of Waters of Confluent Rivers

At present, a significant weakening of the intensity of transverse mixing at the confluence of large rivers, which is observed in a number of cases, is widely discussed. Since the observed features of the confluence of large watercourses are not only of research interest but also of significant economic importance associated with the characteristics of water management at these water bodies, a large number of works are devoted to their study. Water resources management requires measures for the organization of water use which can be rational only under the understanding of processes occurring in water basins. To explain the phenomenon of suppression of the transverse mixing, which is interesting and important from the point of view of ecology, a wide range of hypotheses is proposed, up to the negation of turbulence in rivers. One of the possible mechanisms for explaining the suppression of transversal mixing can be the presence of transverse circulation manifesting itself as Prandtl’s secondary flows of the second kind. The characteristic velocity of these circulation flows is very small and difficult to measure directly by instruments; however, in our opinion, they can significantly complicate the transverse mixing at the confluence. The proposed hypothesis is tested in computational experiments in the framework of the three-dimensional formulation for dimensions of a real water object at the mouth of the Vishera River where it meets the Kama. Calculations demonstrate that, at sufficiently large flow rates, the two waters practically do not mix in the horizontal direction throughout the depth over long distances from the confluence. It has been found that a two-vortex flow is formed downstream the confluence, which just attenuates the mixing; the fluid motion in the vortices is such that, near the free surface, the fluid moves from the banks to the middle of the riverbed

A numerical study of the influence of channel-scale secondary circulation on mixing processes downstream of river junctions

A rapid downstream weakening of the processes that drive the intensity of transverse mixing at the confluence of large rivers has been identified in the literature and attributed to the progressive reduction in channel scale secondary circulation and shear-driven mixing with distance downstream from the junction. These processes are investigated in this paper using a three-dimensional computation of the Reynolds averaged Navier Stokes equations combined with a Reynolds stress turbulence model for the confluence of the Kama and Vishera rivers in the Russian Urals. Simulations were carried out for three different configurations: an idealized planform with a rectangular cross-section (R), the natural planform with a rectangular cross-section (P), and the natural planform with the measured bathymetry (N), each one for three different discharge ratios. Results show that in the idealized configuration (R), the initial vortices that form due to channel-scale pressure gradients decline rapidly with distance downstream. Mixing is slow and incomplete at more than 10 multiples of channel width downstream from the junction corner. However, when the natural planform and bathymetry are introduced (N), rates of mixing increase dramatically at the junction corner and are maintained with distance downstream. Comparison with the P case suggests that it is the bathymetry that drives the most rapid mixing and notably when the discharge ratio is such that a single channel-scale vortex develops aided by curvature in the post junction channel. This effect is strongest when the discharge of the tributary that has the same direction of curvature as the post junction channel is greatest. A comprehensive set of field data are required to test this conclusion. If it holds, theoretical models of mixing processes in rivers will need to take into account the effects of bathymetry upon the interaction between river discharge ratio, secondary circulation development, and mixing rates

Numerical investigation of meniscus deformation and flow in an isothermal liquid bridge subject to high-frequency vibrations under zero gravity conditions

International audienceThis paper deals with meniscus deformation and flow in an isothermal liquid bridge maintained between two circular rods, when one rod is subject to axial monochromatic vibrations. It concerns a fundamental aspect of the problem of crystal growth from melt by the floating-zone technique which is often considered in weightlessness conditions. In the absence of vibrations the bridge is cylindrical; but due to vibration the mean shape of the meniscus is no more cylindrical and the meniscus oscillates around this mean shape. Two models are developed. First, we take into account the pulsating deformations of the meniscus (free surface), but we assume that the mean shape of meniscus remains cylindrical (i.e., we neglect the influence of vibration on this mean shape). For this simple case, a solution of the problem for the pulsating meniscus deformations and the pulsating velocity field is found in explicit form. For the mean flow, the problem is solved numerically by a finite-difference method. The calculations demonstrate the contribution of two basic mechanisms of mean flow generation due to vibrations, related to the generation of mean vorticity in the viscous boundary layer near the rigid boundaries and surface-wave propagation at a free surface. The intensity of the mean flow induced by surface waves is found to be sharply increasing when the vibration frequency approaches the resonance values that are determined from the explicit form of the solution of pulsation problem. In the second model, we take into account both pulsating and mean deformations of the meniscus. The governing equations for the potential of pulsating velocity and mean velocity, and for the pressure, are solved by using a finite-difference method and a boundary-fitted curvilinear coordinate system fitting the free surface

Numerical approximation of the fractional Laplacian via hp-finite elements, with an application to image denoising

The fractional Laplacian operator (−∆)s on a bounded domain Ω can be realized as a Dirichlet-to-Neumann map for a degenerate elliptic equation posed in the semi-infinite cylinder Ω × (0,∞). In fact, the Neumann trace on Ω involves a Muckenhoupt weight that, according to the fractional exponent s, either vanishes (s 1/2). On the other hand, the normal trace of the solution has the reverse behavior, thus making the Neumann trace analytically well-defined. Nevertheless, the solution develops an increasingly sharp boundary layer in the vicinity of Ω as s decreases. In this work, we extend the technology of automatic hp-adaptivity, originally developed for standard elliptic equations, to the energy setting of a Sobolev space with a Muckenhoupt weight, in order to accommodate for the problem of interest. The numerical evidence confirms that the method maintain exponential convergence. Finally, we discuss image denoising via the fractional Laplacian. In the image processing community, the standard way to apply the fractional Laplacian to a corrupted image is as a filter in Fourier space. This construction is inherently affected by the Gibbs phenomenon, which prevents the direct application to “spliced” images. Since our numerical approximation relies instead on the extension problem, it allows for processing different portions of a noisy image independently and combine them, without complications induced by the Gibbs phenomenon

Prevention of HIV and Associated Infections among Adolescents and Young People at High Risk of Infection : Methodology Guide

Methodology Guide on Prevention of HIV and Associated Infections among Adolescents and Young People at High Risk of Infection was prepared as part of project “Building capacity in prevention of HIV and associated infections among youth at high risk in the Northern Dimension area” (cf. www.ndphs.org/?database,view,project,1467) co-funded by the European Union. The project was implemented from September 1, 2013 to August 31, 2015 by the project consortium led by Secretariat of the Northern Dimension Partnership in Public Health and Social Well-being (NDPHS) and including also Regional NGO “Stellit”, National Institute for Health and Welfare, Kaliningrad Regional Non-governmental Youth Organisation “Young Leaders Army” (YLA), Social AIDS Committee and Baltic HIV Association. The Methodology Guide contains overview of theories applicable for addressing the priorities of HIV and associated infections prevention among adolescents and young people at high risk of infection, theories which might be used to evaluate the effectiveness of prevention programs. It provides the results of assessment of needs of children and young people at high risk of infection in prevention programs, overview of prevention programs implemented in Russia, Latvia, Poland, Finland and Germany which might be recommended to be spread to other countries of the NDPHS and examples of tool which might be used in prevention work. The Methodology Guide might be useful for authorities, representatives of governmental organizations, NGOs, international organizations, public health specialists and other experts involved into HIV and associated infections prevention among children and young people. The Methodology Guide is available for downloading at: http://urn.fi/URN:NBN:fi-fe2015102715069. Other methodological materials produced within the project can be downloaded at: https://www.thl.fi/en/web/thlfi-en/about-us/organisation/departments-and-units/administration-and-development/planning/international-affairs-unit/projects

Solubilization of Proteins in 2DE: An Outline

Protein solubilization for two-dimensional electrophoresis (2DE) has to break molecular interactions to separate the biological contents of the material of interest into isolated and intact polypeptides. This must be carried out in conditions compatible with the first dimension of 2DE, namely isoelectric focusing. In addition, the extraction process must enable easy removal of any nonprotein component interfering with the isoelectric focusing. The constraints brought in this process by the peculiar features of isoelectric focusing are discussed, as well as their consequences in terms of possible solutions and limits for the solubilization process

STUDY OF THE EFFICIENCY AND SAFETY OF MYCOPHENOLATE MOFETIL THERAPY IN PATIENTSWITH SYSTEMIC SCLERODERMA

Interstitial lung disease (ILD) is one of the major causes of death in systemic scleroderma (SSD). Treatment of these patients remains difficult and controversial. Mycophenolate mofetil (MPM) has been in vitro shown to inhibit overproduction of type I collagen and hence may be effective against SSD. Objective: to study the efficiency and safety of MPM therapy in patients with SSD and clinically relevant ILD in an open-label prospective study. Subjects and methods. Ten patients with SSD (7 and 3 with its diffuse and limited forms, respectively) and ILD were given MPM in combination with glucocorticoids (mean daily dose was 10+4 mg). The mean MPM therapy duration was 11.4+1.3 months. The Rodnan total skin thickness score, flexion index, forced vital capacity (FVC), diffusing capacity of the lung for carbon monoxide (DLCO), and European Scleroderma Study Group (EScSG) activity index were estimated and a 6-minute walk test (6MWT) was carried out before and after MPM therapy. Results. After therapy, the whole group showed a significant reduction in skin scores from 12.9+9.8 to 5.6+3.2 (p=0.036) and EScSG from 3.9+1.4 to 2.25+1.03 (p=0.015) and an increase in exercise tolerance from 446+155 to 535+78 m (p=0.03) as evidenced by 6MWT. The degree of flexion contractures decreased from 15+21 to 3.7+11.3 mm (p>0.05). FVC (77.8+18.7% versus 73.8+11.3%) and DLCO (45+14.4% versus 42+16.4%) were significantly unchanged. A 10% or more clinically significant fall was noted in FVC and DLCO in 3 and 1 patients, respectively. In the remaining patients, the lung functional test results remained stable. MPM tolerability was satisfactory. All the patients completed their course of treatment. Conclusion. Stabilization of lung function with higher exercise tolerance and significantly reduced skin density allow therapy with MPM in combination with low-dose glucocorticoids to be regarded as an effective and well-tolerated treatment in patients with ILD in the presence of SS