Spectral and polarization effects in deterministically nonperiodic multilayers containing optically anisotropic and gyrotropic materials

Influence of material anisotropy and gyrotropy on optical properties of fractal multilayer nanostructures is theoretically investigated. Gyrotropy is found to uniformly rotate the output polarization for bi-isotropic multilayers of arbitrary geometrical structure without any changes in transmission spectra. When introduced in a polarization splitter based on a birefringent fractal multilayer, isotropic gyrotropy is found to resonantly alter output polarizations without shifting of transmission peak frequencies. The design of frequency-selective absorptionless polarizers for polarization-sensitive integrated optics is outlined

Microwave Properties of Ba(0.6)K(0.4)BiO(3) Crystals

We report on field-induced variations of the microwave surface resistance at 9.6 GHz of Ba(0.6)K(0.4)BiO(3) crystals. Energy losses have been investigated as a function of the static magnetic field in the range of temperatures 4.2 K - Tc. By analyzing the experimental results in the framework of the Coffey and Clem model we determine the temperature dependence of the first-penetration field, upper critical field and depinning frequency. The results show that the pinning energy of this bismuthate superconductor is weaker than those of cuprates.Comment: 6 pages, 8 embedded figure

Dielectric multilayer waveguides for TE and TM mode matching

We analyse theoretically for the first time to our knowledge the perfect phase matching of guided TE and TM modes with a multilayer waveguide composed of linear isotropic dielectric materials. Alongside strict investigation into dispersion relations for multilayer systems, we give an explicit qualitative explanation for the phenomenon of mode matching on the basis of the standard one-dimensional homogenization technique, and discuss the minimum number of layers and the refractive index profile for the proposed device scheme. Direct applications of the scheme include polarization-insensitive, intermodal dispersion-free planar propagation, efficient fibre-to-planar waveguide coupling and, potentially, mode filtering. As a self-sufficient result, we present compact analytical expressions for the mode dispersion in a finite, N-period, three-layer dielectric superlattice.Comment: 13 pages with figure

Non-cubic layered structure of Ba(1-x)K(x)BiO3 superconductor

Bismuthate superconductor Ba(1-x)K(x)BiO3 (x=0.27-0.49, Tc=25-32K) grown by an electrolysis technique was studied by electron diffraction and high-resolution electron microscopy. The crystalline structure thereof has been found to be non-cubic, of the layered nature, and non-centrosymmetric, with the lattice parameters a ~ ap, c ~ 2ap (ap is a simple cubic perovskite cell parameter) containing an ordered arrangement of barium and potassium. The evidence for the layered nature of the bismuthate superconductor removes the principal crystallographic contradiction between bismuthate and cuprate high-Tc superconductors.Comment: 4 pages, 3 figures, to be published in Physical Review B as a Rapid Communicatio

Full-size core epoh at laboratory research of EOR technologies

The article analyzes influence of core sample size on authenticity of data, obtained in laboratory simulation of reservoir stimulation technologies depending on reservoir type. It is found that in contrast to composite models, a full-size core reflects relationship of pore systems of complex reservoirs to the full extend. That allows making more correct conclusions about the effectiveness of technologies. In particular determination of adsorption and mechanical destruction of polymer compositions, strength of created water-proof barrier, dynamics of pressure during mixture injection etc. In order to improve authenticity of results obtained in laboratory simulation at the stage of selection of full-size core samples rock anisotropy, which is common for carbonate reservoirs and are usually connected to rocks fracture system, have to be taken into account. On the basis of ideas about improved efficiency of modeling technologies for enhanced oil recovery (EOR) for the conditions of complex carbonate reservoirs laboratory study is performed. The study used core samples with thermo reversible polymer composition МЕТКА, developed by the Institute of Petroleum Chemistry of Siberian Branch of the Russian Academy of Science. Use of a full-size core allowed evaluating the effectiveness of МЕТКА technology. The technology allowed to involve in the development low-permeability reservoirs and reservoirs that were not flooded. Study showed that results of standard-size core models are not informative to evaluate flooding efficiency. For the conditions of complex carbonate reservoirs due to low representation of standard samples the need to use core samples of maximal diameter is determined. Results obtained have practical importance in correct determination of parameters for EOR application during field development

A simple method for differential isolation of freely dispersed and particle-associated peat microorganisms

Differential isolation of physiologically and ecologically diverse microbial groups facilitates evaluation of their activities in the environment. Here we describe a new method for differential isolation of freely dispersed and particle-associated peat microorganisms. The method is based on sequential elution of peat. Two types of natural peat, young sphagnum peat and old reed-based peat that have significantly different molecular composition as revealed by solid-state 13C NMR, were used for the method development. Various combinations of elution parameters (pH values, surfactant concentration, and sonication) were tested. Protein yield, CFU counts, 16S rDNA gene sequence, and T-RFLP analyses were used as criteria for evaluating the effectiveness of the elution protocols. The optimal method consisted of sequential elutions with (i) pH 6.2, 0.1 M potassium phosphate buffer, (ii) the same buffer amended with 0.01% of Tween 80, and (iii) treatment (ii) amended with sonication for 2 min. This method allowed differential isolation of freely dispersed and particle-associated microorganisms with (i) highest yield, (ii) highest diversity within the each microbial fraction, and (iii) best discrimination between the freely dispersed and particle-associated microbial communities. The method was applied for characterization of peat microbial communities and revealed different taxonomic composition and similar spatial organization of sphagnum and reed-sage peat microorganisms