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The article presents results obtained based on numerical simulation of two-dimensional vortex points and inertial tracer particles in two-component counterflowing superfluid He-II. In the low temperature limit (no normal fluid, no friction) our model would reduce to Onsager’s famous vortex gas. The flow of the normal component of the He-II is assumed uniform, while the superfluid velocity field is induced by vortex points which model three-dimensional quantized vortex lines. Probability density functions of velocity and acceleration of tracer particles and superfluid velocity field are obtained. We find that tails of probability distributions follow power-laws with various exponents, except in the case of sufficiently coarse-grained superfluid velocity field, where Gaussian shape is observed. The decay of the number of vortices is also studied, yielding results in agreement with Vinen’s phenomenological model of quantum turbulence.

The milestones in the development of the urea industry in Russia are briefly outlined in commemoration of the 150th anniversary of the Bazarov reaction. It is noted that due to the unique consumer properties of urea, the demand for it and the volume of production increases from year to year. Significant volumes of production and high unit capacities of urea production reactors require the use of energy- and resource-saving technologies, the implementation of which in industry necessitates the creation of new high-performance equipment. The R&D work on such equipment was carried out in several directions. (1) Development of internal devices for high-pressure urea synthesis reactors (cross-sectional and longitudinal sectioning, feed components mixers). The developed internal devices increase the efficiency of the synthesis and the degree of conversion of raw materials into the final product, as well as reduce the recycle to the synthesis reactor. This allows not only improvement of the energy efficiency of the production (reducing steam, power, and circulating water consumption), but also creates prerequisites for increasing the productivity of the reactor. (2) Application of film-type heat and mass exchangers for melt stripping and evaporation of urea solutions. (3) Design of plate-type heat and mass exchangers. The construction of a film-type evaporation equipment of special design allows much more efficient heat and mass exchange compared to "submerged" equipment. In addition, the radically shorter residence time of the urea solution in such apparatus favors a lower amount of the biuret by-product. The use of the plate-type equipment with mass-exchange plates of special design reduces metal consumption, increases the efficiency of all processes, and reduces drop entrainment from the distillation column. [ABSTRACT FROM AUTHOR]

We apply the coarse-grained Hall-Vinen-Bekarevich-Khalatnikov (HVBK) equations to model the statistically steady-state, turbulent, cylindrically symmetric radial counterflow generated by a moderately large heat flux from the surface of a cylinder immersed in superfluid 4He. We show that a time-independent solution exists only if a spatial non-uniformity of temperature and the dependence on temperature of the thermodynamic properties are accounted for. We demonstrate the formation of a thermal boundary layer whose thickness grows with temperature of the cylinder's surface, and analyze the properties of the flow in the radial direction, including the local average vortex line density. [ABSTRACT FROM AUTHOR]

Andreev reflection of thermal quasiparticles from quantized vortices is an important technique to visualize quantum turbulence in low temperature 3He-B. We revisit a problem of Andreev reflection from the isolated, rectilinear vortex line. For quasiparticle excitations whose impact parameters, defined as distances of the closest approach to the vortex core, do not exceed some arbitrary value b, we calculate exactly the reflected fraction of the total flux of excitations incident upon the vortex in the direction orthogonal to the vortex line. We then define and calculate exactly, as a function of b, the scattering length, that is the scattering cross section per unit length of the vortex line. We also define and calculate the scattering lengths for the flux of energy carried by thermal excitations, and for the net energy flux resulting from a (small) temperature gradient, and analyze the dependence of these scattering lengths on temperature. [ABSTRACT FROM AUTHOR]

We present results of numerical study of motion of micron-size, neutrally buoyant, solid particles in liquid helium at temperatures small enough that the normal fluid is negligible and turbulence manifests itself as a tangle of superfluid line vortices. Based on dynamically self-consistent model of interaction between a solid particle and the quantized vortex, we analyze first an influence of temperature on particle trapping on the vortex core. We find that the particle can be trapped only in the case where the particle experiences the damping force, such as the viscous drag force exerted by the normal fluid. However, at temperature below 0.7 K, when the normal fluid is practically absent, the moving particle still experiences the damping force caused by the ballistic scattering of quasiparticles (phonons and rotons) off the particle surface. Using, together with our calculation of close interaction between the particle and the quantized vortex, available experimental data and theoretical results for this force, we show that trapping of micron-size, neutrally buoyant particles on quantized vortices becomes impossible at temperatures below 0.5 K. At such temperatures, the particle motion in the vortex tangle can be studied based on the simpler, “one-way coupling” model ignoring the backreaction of the particle on the motion and evolution of quantized vortices. Based on such a model, we present results of numerical calculation of particle trajectories in the vortex tangle and show that, due to instability of trajectories and the mismatch of initial velocities of particles and the fluid, the motion of inertial particles does not reveal the motion of turbulent superfluid. We show that particle trajectories between vortex cores are ballistic. Interaction of particles with moving vortices leads to increase of the average particle velocity until it saturates at the value much larger than the fluid rms velocity. These results prevent the use of small tracer particles to study vortex tangles at low temperatures, but open to investigation a new and remarkably simple model of Lagrangian turbulence. We present the probability density function of the turbulent velocity and show that the particle velocity spectrum obeys a simple scaling law. [ABSTRACT FROM AUTHOR]

β-Crystallins are major protein constituents of the mammalian lens, where their stability and association into higher order complexes are critical for lens clarity and refraction. They undergo modification as the lens ages, including cleavage of their terminal extensions. The energetics of βA3- and βB2-crystallin association was studied using site-directed mutagenesis and analytical ultracentrifugation. Recombinant (r) murine wild type βA3.- and βB2-crystallins were modified by removal of either the N-terminal extension of βA3 (rβA3Ntr) or βB2 (rβB2Ntr), or both the N- and C-terminal extensions of βB2 (rβB2NCtr). The proteins were expressed in Sf9 insect cells or Escherichia coli and purified by gel-filtration and ion-exchange chromatography. All β-crystallins studied demonstrated fast reversible monomer-dimer equilibria over the temperature range studied (5-35 °C) with a tendency to form tighter dimers at higher temperatures. The N-terminal deletion of rβA3 (rβA3Ntr) significantly increases the enthalpy (+ 10.9 kcal/mol) and entropy (+40.7 cal/deg mol) of binding relative to unmodified protein. Removal of both N- and C-terminal extensions of rβB2 also increases these parameters but to a lesser degree. Deletion of the βB2-crystallin N-terminal extension alone (rβB2Ntr) gave almost no change relative to rβB2. The resultant net negative changes in the binding energy suggest that βA3- and βB2-crystallin association is entropically driven. The thermodynamic consequences of the loss of βA3-crystallin terminal extensions by in vivo proteolytic processing could increase their tendency to associate and so promote the formation of higher order associates in the aging and cataractous lens. [ABSTRACT FROM AUTHOR]

A steady flow of a very dilute suspension of solid particles in the turbulent flow near the wall is considered. The particle phase is described by the system of mean field mass, momentum, and turbulent Reynolds stress conservation equations incorporating the closure approximation for the third-order correlation of particle fluctuating velocity; this closure approximation, as well as the mean field equations, were derived earlier from the PDF (probability density function) kinetic equation governing the particle transport in the turbulent flow. In the turbulent flow near the wall, particles can be characterized as “high inertia” or “low inertia” by small or large values, respectively, of a single nondimensional parameter: the normalized particle relaxation time combining the wall friction velocity and physical parameters of the fluid and particle phase. Making use of the technique of matching asymptotic expansions, the distributions are found of the normal and shear turbulent stress, volume fraction, and mean velocity in the particle phase of the suspension of high inertia particles. © 2002 American Institute of Physics. [ABSTRACT FROM AUTHOR]

An abstract of the article "The Large-Scale Campaign for Diagnosis and Treatment of Onychomycosis: First Experience," by Y. V. Sergeev, O. I. Buchinsky, and A. Y. Sergeeev is presented.

Quantum turbulence, easily generated in superfluid helium, consists of a disordered tangle of thin, discrete vortex lines of quantised circulation which move in a fluid without viscosity. In this report we show that, in very intense quantum turbulence, the vortex tangle contains small coherent vortical structures (bundles of quantised vortices) which arise from the fundamental Biot-Savart interaction between vortices, and which are similar to the intermittent, coherent structures (“worms”) observed in ordinary viscous turbulence. Our result highlights the similarity between quantum turbulence and ordinary turbulence, and sheds new light into the origin of the “worms” in ordinary turbulence. [ABSTRACT FROM AUTHOR]

An abstract of the article "Clinical Pattern, Predisposing Factors and Quality of Life in Onychomycosis: Results of the Epidemiologic Survey," by E. V. Mokina and colleagues is presented.

An abstract of the article "Causative Agents of Onychomycosis in Russia: Prevalence of Fungal Species and Quality of Mycologic Diagnosis," by N. E. Zharikova and colleagues is presented.

An abstract of the article "Epidemiology of Onychomycosis in Modern Russia: Incidence Is Growing," by V. M. Bunin and colleagues is presented.

An abstract of the article "Severity of Onychomycosis Measured With Scio Revealed in Onychoindex Project," by V. I. Lysenko and colleagues is presented.

We address a question which, after a decade-long discussion, still remains open: what is the nature of the ultraquantum regime of decay of quantum turbulence? The model developed in this work reproduces both the ultraquantum and the quasiclassical decay regimes and explains their hydrodynamical natures. In the case where turbulence is generated by forcing at some intermediate length scale, e.g. by the beam of vortex rings in the experiment of Walmsley and Golov |Phys. Rev. Lett. 100, 245301 (2008).], we explain the mechanisms of generation of both ultraquantum and quasiclassical regimes. We also find that the anisotropy of the beam is important for generating the large-scale motion associated with the quasiclassical regime [ABSTRACT FROM AUTHOR]

We present a combined numerical and experimental study of Andreev scattering from quantum turbulence in superfluid ³He-B at ultralow temperatures. We simulate the evolution of moderately dense, three-dimensional, quasiclassical vortex tangles and the Andreev reflection of thermal quasiparticle excitations by these tangles. This numerical simulation enables us to generate the two-dimensional map of local Andreev reflections for excitations incident on one of the faces of a cubic computational domain, and to calculate the total coefficient of Andreev reflection as a function of the vortex line density. Our numerical simulation is then compared with the experimental measurements probing quantum turbulence generated by a vibrating grid. We also address the question of whether the quasiclassical and ultraquantum regimes of quantum turbulence can be distinguished by their respective total Andreev reflectivities. We discuss the screening mechanisms which may strongly affect the total Andreev reflectivity of dense vortex tangles. Finally, we present combined numerical-experimental results for fluctuations of the Andreev reflection from a quasiclassical turbulent tangle and demonstrate that the spectral properties of the Andreev reflection reveal the nature and properties of quantum turbulence. [ABSTRACT FROM AUTHOR]

Superfluid 3He-B in the zero-temperature limit offers a unique means of studying quantum turbulence by the Andreev reflection of quasiparticle excitations by the vortex flow fields. We validate the experimental visualization of turbulence in 3He-B by showing the relation between the vortex-line density and the Andreev reflectance of the vortex tangle in the first simulations of the Andreev reflectance by a realistic 3D vortex tangle, and comparing the results with the first experimental measurements able to probe quantum turbulence on length scales smaller than the intervortex separation. [ABSTRACT FROM AUTHOR]

In most experiments with superfluid helium, turbulence is generated thermally (by applying a heat flux, as in thermal counterflow) or mechanically (by stirring the liquid). By modeling the superfluid vortex lines as reconnecting space curves with fixed circulation, and the driving normal fluid as a uniform flow (for thermal counterflow) and a synthetic turbulent flow (for mechanically driven turbulence), we determine the difference between thermally and mechanically driven quantum turbulence. We find that in mechanically driven turbulence, the energy is concentrated at the large scales, the spectrum obeys Kolmogorov scaling, vortex lines have large curvature, and the presence of coherent vortex structures induces vortex reconnections at small angles. On the contrary, in thermally driven turbulence, the energy is concentrated at the mesoscales, the curvature is smaller, the vorticity field is featureless, and reconnections occur at larger angles. Our results suggest a method to experimentally detect the presence of superfluid vortex bundles. [ABSTRACT FROM AUTHOR]

We studied numerically the Andreev scattering cross-sections of three-dimensional isolated quantized vortex rings in superfluid 3He-B at ultralow temperatures. We calculated the dependence of the cross-section on the ring's size and on the angle between the beam of incident thermal quasiparticle excitations and the direction of the ring's motion. We also introduced, and investigated numerically, the cross-section averaged over all possible orientations of the vortex ring; such a cross-section may be particularly relevant for the analysis of experimental data. We also analyzed the rôle of screening effects for Andreev reflection of quasiparticles by systems of vortex rings. Using the results obtained for isolated rings we found that the screening factor for a system of unlinked rings depends strongly on the average radius of the vortex ring, and that the screening effects increase with decreasing the rings' size. [ABSTRACT FROM AUTHOR]