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

Azospirillum strains use phenolic compounds as intermediates for electron transfer under oxygen-limiting conditions

The effects of catechol, vanillic, caffeic (CAF), 2-hydroxyphenylacetic, 4-hydroxy- and 3,4-dihydroxybenzoic (3,4-DHBA) acids on the growth of a common rice rhizosphere inhabitant, Azospirillum lipoferum were studied. Two strains of this nonfermenting nitrogen-fixing bacterium were used: a motile strain (4B), and a nonmotile strain (4T). Under atmospheric conditions (pO 2 = 21 kPa), the growth of strain 4T was inhibited by catechol (0.1 m m ) only. None of these compounds affected the growth of strain 413. Under 5 kPa O 2 , no effect was observed on strain 413, whereas three of the six tested phenolics stimulated the growth of strain 4T; maximum effects were observed for 3,4-DHBA and CAF. As revealed by TLC and HPLC, under low oxygen, more new lipophilic compounds were formed from CAF by strain 4T, differing from CAF autooxydation products and from the products obtained under 21 kPa O 2 . It was hypothesized that strain 4T had the ability to use an oxidized derivative of CAF as a terminal electron acceptor. This hypothesis was tested in experiments under nitrogen-fixing conditions, in the absence of oxygen, and in the presence of N 2 O as a reoxidizing agent for CAF. Acetylene was used both as a substrate to measure nitrogenase activity (ARA) and to inhibit the biological transfer of electrons to N 2 O. The addition of CAF in the presence of N 2 O had the same effect on ARA rates as an addition of oxygen. It is concluded that the strain 4T of Azospirillum lipoferum is able to sustain some of its activities (e.g., N 2 fixation) using phenolics as alternative electron acceptors under low oxygen conditions.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/48113/1/248_2004_Article_BF00217426.pd

New method using growth dynamics to quantify microbial contamination of kaolinite slurries

The early and sensitive detection of microbial contamination of kaolinite slurries is needed for timely treatment to prevent spoilage. The sensitivity, reproducibility, and time required by current methods, such as the dip-slide method, do not meet this challenge. A more sensitive, reproducible, and efficient method is required. The objective of the present study was to develop and validate such a method. The new method is based on the measured growth kinetics of indigenous kaolinite-slurry microorganisms. The microorganisms from kaolinite slurries with different contamination levels were eluted and quantified as colony-forming units (CFUs). Known quantities of E. coli (ATCC 11775) were inoculated into sterilized kaolinite slurries to relate kaolinite-slurry CFUs to true microbial concentrations. The inoculated slurries were subsequently incubated, re-extracted, and microbial concentrations quantified. The ratio of the known inoculated E. coli concentration to the measured concentration was expressed as the recovery efficiency coefficient. Indigenous microbial communities were serially diluted, incubated, and the growth kinetics measured and related to CFUs. Using the new method, greater optical densities (OD) and visible microbial growth were measured for greater dilutions of kaolinite slurries with large microbial-cell concentrations. Growth conditions were optimized to maximize the correlation between contamination level, microbial growth kinetics, and OD value. A Standard Bacterial Unit (SBU) scale with five levels of microbial contamination was designed for kaolinite slurries using the experimental results. The SBU scale was validated using a blind test of 50 unknown slurry samples with various contamination levels provided by the Imerys Company. The validation tests revealed that the new method using the SBU scale was more time efficient, sensitive, and reproducible than the dip-slide method