Interlayer pairing in high temperature superconductors: effect of nonmagnetic impurities

The influence of impurity scattering is studied theoretically in a two-layer model for the high-T _c superconductor Y₁Ba₂Cu₃O_7– with intra- and inter-layer pairing. Two types of impurities are considered: (I) impurities which conserve the reflection symmetry of the two layers and (II) impurities which break it. Impurities of type (I) have no influence on the critical temperature. Type (II) impurities have strong influence onT _c as well as onH _c2 if there is a pairing interaction between carriers of different layers. The treatment of type (II) impurities is generalized to a periodic layer model appropriate for La_2–x Ba _x CuO₄. Available experiments on impurities in Y₁Ba₂Cu₃O_7– and La_2–x Ba _x CuO₄ are interpreted with our theory.     

Restoration of universality for the rod-to-coil transition scaling in the infinite-dimensionality limit: Exact results for directed walks

We derive scaling forms for the thermodynamic and correlation quantities for the turn-weighted fully and partially directed self-avoiding walks on the hypercubic lattices ind2. In the grand canonical (fixed fugacity per step) ensemble, the conformational rod-to-coil transition sets up in the regimew¯N=O(1), wherew is the weight of each 90° turn and¯N is the (fugacity-dependent) average number of steps. Contrary to the conventional critical phenomena wisdom, the scaling functions for the two different walk models, directed and partially directed, become universal only in the limitd.     

Conditioning of industrial waste in cement matrix

Results are presented of a series of experimental tests performed to determine the influence of matrix characteristics on the leaching mechanism of copper aluminium oxychloride immobilized into cement matrices. The objective of this research was to investigate the leaching mechanism of copper as a constituent of copper aluminium oxychloride (CAOX).     

Unified quantum logic

Unified quantum logic based on unified operations of implication is formulated as an axiomatic calculus. Soundness and completeness are demonstrated using standard algebraic techniques. An embedding of quantum logic into a new modal system is carried out and discussed.On leave of absence from Department of Mathematics, University of Zagreb, Pot. Pret. 165, YU-41001 Zagreb, Yugoslavia.     

1,3,6,9,12,14,17,20-octaethynyltetrabenz[a,b,f,j,k,o]-4,5,10,11,15,16,21,22- octadehydro[18]annulene: a carbon-rich hydrocarbon

Dodecaynes 1a-d have been prepared via a convergent strategy that employs Sonogashira couplings as the carbon-carbon bond-forming tool. Due to the steric bulk of the DMTS groups, 1c adopts a nonplanar conformation, the dynamics of which have been probed by VT-NMR. The cobalt-catalyzed isomerization of 1a,b produced the new conjugated phenylenes 2a,b and 3a,b, respectively. [structure: see text]     

Determination of total chromium in fresh water by atomic absorption spectrometry following flotation preconcentration

A flotation method is proposed for the quantitative preconcentration and determination of total chromium by electrothermal atomic absorption spectrometry in fresh water samples, without previous reduction or oxidation of the chromium ion state. Hydrated iron(III) oxide and iron(III) tetramethylenedithiocarbamate were used as precipitating collectors. The detection limit of the method is 0.01 g/L.     

Transition metal complexes with Girard reagent-based ligands

The ligand, salicylaldehyde Girard-T hydrazonium chloride, [H₂SalGT]Cl (1), and two complexes [Cu(HSalGT)X₂]·H₂O (X = Br(2); Cl(3)) were synthesized and their crystal structures were determined by single-crystal X-ray analysis. In the two isostructural complexes, the Cu(II) is located in a square-pyramidal environment, with the chelating ligand and one halogen atom in the basal plane and the second halogen in the apical position. The most apparent structural difference between the 1 and its complexes 2 and 3 is the orientation of the N(CH₃)₃ group: in 1, it is practically coplanar to the rest of the molecule, while in 2 and 3 it is oriented to the side of the axially bonded halogen, which can be explained by the C–H…X intramolecular interactions. The compounds were characterized by elemental analysis, molar conductivity, magnetic susceptibility and electronic absorption spectra.     

Sorption of chromium(VI) and chromium(III) on aluminium hydroxide

Factors that influence the sorption of Cr(VI) and Cr(III) on aluminium hydroxide were investigated. The sorption of chromates decreases as the pH of the suspension increases. The mechanism of CrO ₄ ^2– sorption was interpreted in terms of reactions between chromates and –OH and/or H₂O groups at the hydroxide/liquid interface. It has been shown that chromates are more tightly sorbed on aluminium hydroxide compared to other anions, e.g. chlorides. On the other hand, specifically absorbed anions, such as molybdates, compete strongly with chromates for the sorption sites. The sorption of chromium(III) increases with the pH of the suspension. Also, the sorption of chromium(III) is suppressed in the presence of citrate ions. The best conditions for the fixation of Cr(VI) and Cr(III) by aluminium hydroxide are presented.     

Detection of processed genetically modified food using CIM monolithic columns for DNA isolation

The availability of sufficient quantities of DNA of adequate quality is crucial in polymerase chain reaction (PCR)-based methods for genetically modified food detection. In this work, the suitability of anion-exchange CIM (Convective Interaction Media; BIA Separations, Ljubljana, Slovenia) monolithic columns for isolation of DNA from food was studied. Maize and its derivates corn meal and thermally pretreated corn meal were chosen as model food. Two commercially available CIM disk columns were tested: DEAE (diethylaminoethyl) and QA (quaternary amine). Preliminary separations were performed with standard solution of salmon DNA at different pH values and different NaCl concentrations in mobile phase. DEAE groups and pH 8 were chosen for further isolations of DNA from a complex matrix-food extract. The quality and quantity of isolated DNA were tested on agarose gel electrophoresis, with UV-scanning spectrophotometry, and by amplification with real-time PCR. DNA isolated in this way was of suitable quality for further PCR analyses. The described method is also applicable for DNA isolation from processed foods with decreased DNA content. Furthermore, it is more effective and less time-consuming in comparison with the existing proposed methods for isolation of DNA from plant-derived foods.