Raman random lasing in Ba(NO3)2 powder

Random lasing in Raman active material – barium nitrate powder – has been registered in two temporal regimes: nanosecond and picosecond. Stimulated Raman scattering (SRS) in Ba(NO3)2 for picosecond excitation has been shown to have much lower threshold and spectrum containing more components than for nanosecond excitation opposite to the case of a bulk medium. In picosecond regime SRS intensity increased with temperature decreasing and redistributed in favor of the higher order components. SRS pulse duration in picosecond regime was estimated to be in the range 16.5-22 ps. High conversion efficiency of SRS in barium nitrate powder in picosecond regime and its larger stability under laser impact than for bulk samples gives possibility to use it as an active material in Raman converters.

Active thermal cloaking and mimicking

We present an active cloaking method for the parabolic heat (and mass or light diffusion) equation that can hide both objects and sources. By active, we mean that it relies on designing monopole and dipole heat source distributions on the boundary of the region to be cloaked. The same technique can be used to make a source or an object look like a different one to an observer outside the cloaked region, from the perspective of thermal measurements. Our results assume a homogeneous isotropic bulk medium and require knowledge of the source to cloak or mimic, but are in most cases independent of the object to cloak.

FUINDAMENTALS DEVELOPMENT FOR COMPUTATION OF SCREW SCREENS FOR BULK MATERIAL SEPARATION AND EXPERIENCE OF THEIR INTRODUCTION TO PRODUCTION

The work purpose is to increase productivity in bulk material separation by means of the development of a test sample of the installation for bulk material separation into fractions. There is considered bulk material motion in a working chamber of the screw screen and the results of experimental investigations of bulk medium movement parameters are presented, depending on design and operation characteristics of screw screens, and also nomograms of dependences of a rate of bulk particle longitudinal movements upon a screw screen diameter, for different values of correction factors, weight of bulk particles, an angular velocity of the screw screen and fill factors. A design of the plant for bulk separation, test data and technical characteristics of the test plant are shown. A novelty is confirmed by six invention patents of the RF. By means of the complex method of investigations there are obtained dependences for definition of a rate of bulk particle longitudinal motion in screw screens, and also a length of working chamber of the screw screen.

COMPARISON OF THE CRUSHED MATERIAL MOVEMENT MODEL IN THE BODY OF A VERTICAL CENTRIFUGAL MILL

Introduction. Improving the performance, increasing productivity, reducing the metal consumption of grinding equipment and other mining machines is usually a very expensive process. It requires a large amount of development work, the production of prototype machines, and a large amount of experimental research. In this regard, one of the most important tasks is to simulate the movement of bulk material in operations for processing minerals in various equipment. In such modeling, the discrete element method (DEM) is widely used. The purpose of the research is to compare the models of the movement of the crushed material in the body of a vertical centrifugal mill. Research methodology The motion of the bulk medium in a vertical centrifugal mill was modeled using two models. In the first model, the cylindrical body of the centrifugal mill was assumed to be stationary, and on its surface and on the entire surface of the rotor, conditions were set for the absence of a relative speed of movement of the crushed material. In the second model, a hydrodynamic model was used to describe the motion of a granular material as a viscous incompressible liquid with a compression ratio that depends on the pres-sure. In this model, the viscosity coefficient is represented as consisting of two terms: a constant (analogous to dynamic viscosity) and an excess pressure over hydrostatic pressure. Research results It is established that both models give the same character of the movement of the material in the mill body. It is determined that the absolute velocity of the material movement near the walls and near the mill rotor is approximately the same for both models, but in the data obtained using the hydrodynamic model, as the material moves away from the walls and the rotor, it slows down more than for the model using the discrete element method. It is revealed that the absolute velocity of the material movement near the walls and at the axis of the mill rotor is approximately the same for both models, but in the data obtained using the hydrodynamic model, as it moves away from the walls and the rotor, the material slows down significantly more than for the model using the discrete element method. Based on the simulation results, it can be concluded that for a more accurate simulation of the processes occurring during the rapid movement of bulk material in the grinding equipment, it is preferable to use a model using the discrete element method. It is advisable to use the hydrodynamic model for conducting a large number of search dawns or as a predicate model that will allow you to quickly set the initial velocity values for particles in a model using the discrete element method. Conclusions 1. A hydrodynamic model of the motion of a bulk medium in a vertical centrifugal mill, represented as a viscous incompressible liquid with a compression coefficient depending on the pressure has been developed. 2. It is established that for a more correct simulation of the processes occurring during the rapid movement of bulk material in the grinding equipment, it is preferable to use a model using the discrete element method. At the same time, it is advisable to use the hydrodynamic model for conducting a large number of search calculations or as a predicate model that will allow you to quickly set the initial velocity values for particles in a model using the discrete element method.

RESEARCH OF VIBROREOLOGICAL MODELS OF LAYER OF BULK ENVIRONMENT

Vibration mechanics and vibroreology play an important role in the new section of applied vibration theory formed in recent years - the theory of vibration processes and devices. This theory studies the patterns of excitation and vibration in different mechanical systems; it also includes the theory of machines in which vibration is used to achieve useful goals. Based on the considered models, it was possible to describe the chaotic motion of the bulk medium layer over the vibrating plane. Such movements, well known for liquids, have indeed been observed in the case of a bulk medium, which serves as another confirmation of the possibility of modeling slow motions of a bulk medium during vibration in the form of viscous fluid motions (of course, with the above caveats and additions). When studying the described simplest models, motion (including we are interested in slow motion) can be found by directly using the solution of the problem of vibrotransportation of the body (particles). The value of this approach is determined, however, by the possibility of its application for an approximate solution in more complex cases. In the study of slow motions of bodies interacting with both the forces of dry friction and collisions, these interactions can be modeled by the forces of viscous friction, taking into account the driving vibration force. This leads to the following vibroreological approach to modeling the behavior of the bulk medium in vibrating trays and vessels. Of all the considered models, the most promising is the model of the behavior of the bulk medium under the influence of vibration in the form of a viscous medium.The described models can be used when considering a practically important task of vibration penetration into a free medium.

Analysis of physical properties of granular materials on their numerical models (2D case)

The paper describes a method for determining the density and specific surface of the package of rock particles represented by discs with the size corresponding to the size of the rock fragments of real dump massifs (2D case). The packing method of the particles corresponds to the schemes of dumping used in open-pit mining - areal and peripheral ones. The influence of boundaries, in which the dump is located, on the physical characteristics of this massif - density and porosity - is revealed. It was revealed that the way of formation of the bulk of particles affects its density, especially at the boundaries of the massif. The massif of particles formed in accordance with the area technology of dumping has a denser composition and is less affected by the effect of its boundaries than the massif formed in accordance with the peripheral technology of dumping. The applied method of determining the physical characteristics of the bulk medium differs from the statistical methods (e.g., Monte Carlo) and is well-proven for static media, such as dumps and filtering massifs in open-pit mining.

CONTROLLED VIBRATING MILL FOR GRINDING BULK MEDIUM

One of the advanced types of grinding equipment are vibrating mills, which provide high specific productivity at relatively low energy consumption, adjustable tone of grinding products. Vibration impact on the product significantly increases the shock-absorbing effect with the possibility of wide and separate variation of shock and abrasion factors. Significant speed of mechanical and heat and mass transfer processes, a high degree of homogeneity of the obtained products, the possibility of efficient fine grinding and dispersion of the product at relatively low energy consumption lead to the widespread use of vibratory grinding. The constructive scheme of the mill is developed, in which the flat vertical vibrating field provides lifting of a part of loading and by means of the transport-reloading device carries out its continuous adjustable movement from one grinding chamber to another, thereby circulating-spatial movement of the environment in which there is a grinding process. shock interaction of grinding bodies and material that is crushed. The priority direction of development of science and technologies at the modern level is the development, creation and implementation of new generation mechatronic systems. One of the most important rules for the construction of vibrating mills is the need to maximize the degree of their automation in order to increase productivity, improve the quality of grinding and reduce the cost of the process. Also in the article the structural model of the controlled vibromill with spatial-circulating loading movement which at change of weight of a working body in the course of separation and unloading of the crushed material from a grinding chamber constantly adapt to a resonant mode of work at the set technologically optimum parameters (productivity) and the minimum power consumption.

Impact of off-shell dynamics on the transport properties and the dynamical evolution of charm quarks at RHIC and LHC temperatures

We evaluate drag and diffusion transport coefficients comparing a quasi-particle approximation with on-shell constituents of the QGP medium and a dynamical quasi-particles model with off-shell bulk medium at finite temperature T. We study the effects of the width $$\gamma $$ γ of the particles of the bulk medium on the charm quark transport properties exploring the range where $$\gamma < M_{q,g}$$ γ < M q , g . We find that off-shell effects are in general quite moderate and can induce a reduction of the drag coefficient at low momenta that disappear already at moderate momenta, $$p \gtrsim $$ p ≳ 2–3 GeV. We also observe a moderate reduction of the breaking of the fluctuation–dissipation theorem (FDT) at finite momenta. Moreover, we have performed a first study of the dynamical evolution of HQ elastic energy loss in a bulk medium at fixed temperature extending the Boltzmann (BM) collision integral to include off-shell dynamics. A comparison among the Langevin dynamics, the BM collisional integral with on-shell and the BM extension to off-shell dynamics shows that the evolution of charm energy when off-shell effects are included remain quite similar to the case of the on-shell BM collision integral.

Modeling the transfer of radiant energy to a bulk medium in electric furnaces with the upper position of the radiating elements

A new design of suspended radiating elements, which was developed for heating systems of electric furnaces with moving hearth platforms and modular-trigger furnaces, is considered. The transfer of radiant energy on the surface of the firing modules and on the flow of expanded vermiculite is simulated. Analytical dependences are obtained for calculating the temperatures of radiating elements, a refractory base and a heat-insulating cover, as well as grains of the material itself. The possibility of a significant increase in the performance of modular-launch furnaces due to the fact that in the areas of pouring out of the firing modules the crowding of vermiculite will not lead to burnout of the radiating elements, as was observed in tape nichrome systems, is shown.