Processes In Dense Media Research Articles

Ab initio multiscale simulation of high-order harmonic generation in solids

High-harmonic generation by a highly non-linear interaction of infrared laser fields with matter allows for the generation of attosecond pulses in the XUV spectral regime. This process, well established for atoms, has been recently extended to the condensed phase. Remarkably well pronounced harmonics up to order ~30 have been observed for dielectrics. We present the first ab-initio multi-scale simulation of solid-state high-harmonic generation. We find that mesoscopic effects of the extended system, in particular the realistic sampling of the entire Brillouin zone, the pulse propagation in the dense medium, and the inhomogeneous illumination of the crystal have a strong effect on the formation of clean harmonic spectra. Our results provide a novel explanation for the formation of clean harmonics and have implications for a wide range of non-linear optical processes in dense media.

The Application and Development of Microbubble Column Flotation Technology in China

Since the early 1980s, great progress has been made in microbubble column flotation technology. As one of the important mineral processing methods, the application and development of this technology in China are summarized in this paper from four respects. Firstly, a patented cyclone- static microbubble separation method was proposed to overcome the notable problems mentioned in the previous flotation columns. Secondly, microbuble column flotation was introduced to separate the high ash as well hard-to-separate coal slime generated from dense medium processes. The characteristics of the microbubble column, and the flotation process for fine coal and the high ash coal separation was analyzed. Thirdly, the application of microbubble column flotation in China was detailed introduced, especially the characteristics of series microbubble column flotation equipment, and efficient column type coal slime separation crafts were discussed. The application of microbubble column flotation particularly in low ash content coal preparation, and discarded coal slime processing technology were presented. Finally, microbubble column flotation has been extended to non-coal mineral processing, such as magnetite concentrate upgrading (concentration iron and removing silicon), sulfide copper mine separation, white tungsten flotation, etc., the related research was briefly introduced in this paper as well.

The Influence of Near-Dense Material on the Separation Efficiency of Dense-Medium Processes

Near-dense (also termed near-gravity) material is material that has a relative density that is close to that of the separating liquid or dense medium used to separate coal and the impurities contained in raw coal. Near-dense material makes the separation more difficult because it settles very slowly in the dense-medium due to the fact that its density is close to that of the medium. This increases the probability that material that should have reported to floats wrongly reports to sinks and vice versa, hence increasing the amount of misplaced material. Data is presented that show how the amount of misplaced material increases with an increase of near-dense material in the feed coal. The data furthermore illustrates the influence of near-dense material on the separation efficiency of dense-medium washers. A new definition for near-dense material is proposed.

In-Plant Evaluation of Dense Medium Process Performances

The separation density and process efficiency values achieved by dense medium processes are a function of the particle size fractions being treated, hydrodynamics of the separator, and medium rheology. An in-plant evaluation of the dense medium processes being used in an operating preparation plant was conducted in an effort to develop relationships between the actual separation density and the medium density and to quantify the separation efficiency values. The results were found to correlate well with current fundamental and operating principles governing the processes, which are reviewed and discussed.

Nonexponential temperature dependence of the rate of threshold inelastic processes in dense media

The influence of the density of the medium on the temperature dependence of the rate constants of inelastic processes is investigated. It is shown that besides the effects like lowering of the ionization potential, which accelerate excitation and ionization processes in a nonideal plasma, there is a stronger mechanism for such acceleration, which is associated with the high frequency of collisions between particles and leads to destruction of the one-to-one relation between the energy and momentum of the particles in a dense medium. It is manifested by the presence of power-law tails in the equilibrium momentum distribution of the particles, which leads to a nonexponential temperature dependence of the rates of inelastic reactions in dense gases and nonideal plasmas. A kinetic equation for the generalized energy and momentum distribution function of electrons in an external electric field, which permits investigation of the effect under consideration under nonequilibrium conditions, is presented.

The Effect of Dense Medium Viscosity on Separation Efficiency

This paper reviews the literature on the influence of viscosity on separation in dense medium processes, for both baths and cyclones, in the context of the well-known fundamentals of particle motion in fluids. It is concluded that viscosity does play a role in determining both the separation density and the extent of separation inefficiency (Ep). because most DMS processes probably operate in the intermediate particle flow regime. A high viscosity increases particle misplacement in baths and cyclones. It increases or decreases the separation density of bath separators (depending on whether the bath is top or bottom fed. Respectively) and decreases the separation density in cyclones due to a reduction in the medium differential. The effects of viscosity are strongly size dependent. In practice, viscosity is not seen as a major problem in most coal preparation applications, as long as it is properly managed.

The Design and Operation of Heavy Medium Recovery Circuits for Improved Medium Recovery

Abstract In dense medium processes for the beneficiation of minerals the consumption of medium (generally ferrosilicon) represents a major component of the operating cost. This provides a strong incentive for improvement in heavy medium recovery circuit design and operation. A major thrust in heavy medium plant design over the past decade has therefore been towards circuits which reduce medium losses. In this paper recent trends in plant design are examined in relation to the factors influencing circuit performance and medium losses. Operational details which have a significant effect on losses are discussed and illustrated by means of plant and pilot plant test data, with particular emphasis on the performance of wet drum magnetic separators. While the emphasis is on reducing the consumption of the high-cost ferrosilicon medium used in minerals beneficiation, most of the principles described in this paper are equally relevant to the design and operation of magnetite recovery circuits for coal preparation...

Molecular dynamics with stochastic boundary conditions

We present and illustrate a simple approach for carrying out molecular dynamics simulations subject to stochastic boundary conditions. Methods of this type are expected to be useful in the study of chemical reactions and other localized processes in dense media.

Erratum: Local Equilibrium Approach to Transport Processes in Dense Media

Erratum: Local Equilibrium Approach to Transport Processes in Dense Media

Local Equilibrium Approach to Transport Processes in Dense Media

The viscosity and thermal conductivity of a dense medium is studied. A model is constructed in which the singlet distribution function remains in local equilibrium whereas the doublet distribution function deviates from its local equilibrium value. It is this deviation of the pair function which accounts for the potential contributions to the transport of momentum and energy in the dense fluid. An integral equation is deduced for that part of the correlation function relevant to these transport coefficients and an approximate solution is sketched. Finally this approximation is briefly discussed in connection with some other approaches to transport processes in liquids. Numerical results for the evaluation of the approximate expression for the viscosity coefficient will be published in due course.