Bioleaching of low grade uranium ore containing pyrite using A. ferrooxidans and A. thiooxidans

A process of uranium extraction from ore containing 3.1 % pyrite by bacterial leaching was investigated in shaken flasks during 90 days. The highest uranium recovery amounting to 85.1 % was obtained using binary mixture of Acidithiobacillus ferrooxidans and Acidithiobacillus thiooxidans that was exceeding results obtained by traditional acid leaching technique up to 27 %. High uranium recovery was founded to be due to the high degree of pyrite dissolution that can be readily achieved by bacterial leaching (up to 98.0 %).     

Simulation of light generation in cholesteric liquid crystals using kinetic equations: Time-independent solution

We report on the results of calculating the conditions for light generation in cholesteric liquid crystals doped with fluorescent dyes using kinetic equations. Specific features of spectral properties of the chiral cholesteric medium as a photonic structure and spatially distributed type of the feedback in the active medium are taken into account. The expression is derived for the threshold pump radiation intensity as a function of the dye concentration and sample thickness. The importance of taking into account the distributed loss level in the active medium for calculating the optimal parameters of the medium and for matching the calculated values with the results of experiments is demonstrated.     

Low-temperature ignition of methane-air mixtures under the action of nonequilibrium plasma

A plasma-chemical kinetic mechanism of the low-temperature (600 < T < 1000 K) oxidation/combustion of methane under conditions of nonequilibrium plasma over a wide pressure range (P = 0.1?100 atm) is developed and verified. The mechanism is comprised of three types of elementary processes: chemical reaction of neutral atoms and molecules, primary plasma-chemical processes involving electrons, and secondary plasma-chemical processes involving atomic and molecular ions and excited species. Application of the developed mechanism to describing the plasma-assisted oxidation of methane shows that this mechanism can describe the experimental results qualitatively and quantitatively.     

Angular dependences of transmission spectra of chiral liquid crystals

Transmission spectra of chiral nematic liquid crystals (CNLCs) and chiral smectic С* liquid crystals (CSLCs) are studied in a wide range of angles of light propagation with respect to the direction of the helical structure axis. To this end, both a planar LC cell and a cell consisting of two substrates in the form of rectangular prisms (30° × 60° × 90°) were used, which allowed measurements of the transmission spectra at the light propagation at angles up to 65° with respect to the helical axis direction. The transmission spectra are numerically simulated; the results are in good agreement with the experimental spectra. A technique for determining the tilt angle of molecules in smectic layers is proposed based on the comparative analysis of experimental and calculated transmission spectra of CSLC.     

Contactless measurement of the conductivity of two-dimensional electrons in the regime of microwave-induced giant magnetoresistance oscillations

Magnetic-field dependences of the conductivity of a two-dimensional electron system obtained by contact and contactless measurements in the regime of microwave-induced giant magnetoresistance oscillations have been comparatively analyzed. The contactless technique for studying the conductivity of two-dimensional electrons is based on measuring the attenuation of the RF signal propagating along a coplanar waveguide manufactured using lithography on the sample surface. It has been found that Shubnikov-de Haas oscillations of conductivity are observed in both techniques, whereas the microwave-induced giant magnetoresistance oscillations appear only in the contact measurements. This contradiction indicates that the contact and/or boundary regions of the two-dimensional system with a strong potential gradient play an important role for the observation of the induced magnetoresistance oscillations.     

Computer program for calculating electronic excited states in the valence approximation of the unrestricted Hartree-Fock method

State University, Khar'kov. Translated from Zhurnal Strukturnoi Khimii, Vol. 31, No. 1, pp. 160–161, January–February, 1990.     

The appearance and development of turbulence in a flow past a sphere: Problems and the existing approaches to their solution

The results of the direct numerical integration of the Navier-Stokes equations and integration of the pair functions theory equations are evaluated against experimental data for the problem of a flow past a hard sphere at rest in an unstable regime. Calculations based on the Navier-Stokes equations satisfactorily reproduced three stable medium states observed for a flow past a sphere. In agreement with experiment, each of these three states begins to develop after stability loss in its own direction different from those characteristic of the other states. Calculations were, however, incapable of reproducing any of the three directions of turbulence development recorded experimentally. Most likely, the reason for this is the Navier-Stokes equations themselves. The possibility is discussed that the assumption made in the derivation of the Boltzmann equation, namely, the molecular chaos hypothesis (Stosszahlansatz), may be responsible for the failure of classic hydrodynamics. This assumption is a closure to the Boltzmann equation that allows hydrodynamics to be constructed on the lower three hydrodynamic values. The inaccuracy mentioned introduced no substantial error into stable flow calculations. The error, however, increased rapidly after stability loss. We suggest the use of hydrodynamic equations based on pair functions theory as an alternative to the Navier-Stokes equations for unstable modes. These equations are derived without invoking any additional assumptions such as the Stosszahlansatz hypothesis. As distinct from classic hydrodynamics equations, pair functions theory equations predict the direction of turbulence development close to that observed experimentally.     

Amplification of the Fluorescence Propagating in the Waveguide Regime in a Planar Layer of NLC

Crystallography Reports - The amplification of spontaneous fluorescence in a planar layer of nematic liquid crystal doped with DCM dye in the mode of waveguide light propagation has been studied....     

Lasing in micro-grating liquid crystal systems

A waveguide lasing effect has been observed and investigated in a dye-doped layer of a nematic liquid crystal (NLC) between two quartz plates. One of the plates has an electrode micro-grating, which allows (i) creating the feedback, (ii) guiding a part of the lasing emission into the quartz substrate and (iii) modulating the NLC refractive index by an electric field. At 0 V, a single Transverse Magnetic mode (TM)-polarised mode lasing has been observed. The emission goes out from the edge of the quartz plate in a narrow angular sector (±1.5°) at an angle of about 67.0° with respect to the NLC layer normal. At voltage applied, a number of additional lasing modes propagating at the same angle, but located at different wavelengths, appear. The experimental results are interpreted on account of numerical simulations based on the finite difference time domain method.