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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]

We report computer simulations of the interaction of seeding particles with quantized vortices and with the normal fluid flow in thermal counterflow of superfluid $$^4$$ He. We show that if the number of particles is too large, the vortex tangle is significantly affected, posing problems in the interpretation of visualization experiments. The main effects are an increase in vortex line density and a change in polarization of the vortex tangle, caused by the action of the Stokes drag of the viscous normal fluid on the trapped particles. We argue that in the case of large particle number, typically used for the particle image velocimetry technique, the tangle properties might become significantly changed. On the contrary, the particle tracking velocimetry technique that uses smaller particle concentration should not be appreciably affected. [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]

We generalize the analysis of second sound nonlinear waves to include the case in which a turbulent tangle of superfluid vortices is present in the flow. In the limit of weakly nonlinear perturbations the analysis reduces to examining the effect of friction arising from a given vortex tangle on a propagating wave, so that the considered model describes temperature waves propagating in a background of constant quantized vorticity. The obtained analytical solution yields a simple criterion showing that a localized disturbance develops into the temperature discontinuity provided the gradient of the initial disturbance exceeds a critical value; the latter is found as a function of temperature and superfluid vortex line density. [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.