Role of Calcium in the Evolution of Superconductivity in a (La2?xRx)Ba2(CayCu4+y)Oz (R = Y, Er, Gd) System

It has been reported that, by adding equal amounts of CaO and CuO to non superconducting La₃Ba₃Cu₆O _z (La-336), a series of superconductors with nominal compositions La₃Ca _y Ba₃Cu_6+y O _z were prepared with maximum T^on _c 80K. Similar studies on addition of CaO and CuO in nonsuperconducting LaBaCu₂O _z (La-112) resulted into superconducting LaCaBaCu₃O _z (La-1113). To date no attempt has been made to synthesize La₂CaBa₂Cu₅O _z (La-2125) superconducting phase by addition of CaO and CuO to non superconducting La₂Ba₂Cu₄O _z (La-224) system. Also no reports are published to study the effect of replacing larger La³⁺-ions (1.01Å) by smaller rare earth ions viz Y³⁺(0.89Å), Er³⁺(0.91Å), Gd³⁺(0.91Å) on the structural and superconducting properties of (La_2–x R _x )Ba₂(Ca _y Cu_4+y )O _z (LRBCaC); 0.0 x 0.5; y=2x system. In this paper, we report the method of synthesis, structural and superconducting property characterization using X-ray diffraction, oxygen content measurements using iodometry, resistivity measurements using d.c. four probe technique and a.c. susceptibility measurements in the temperature range RT to 15K. Also a comparative study, on the evolution of superconducting phase with Ca-concentration for different rare earth substitutions for LRBCaC system in the context of hole doping mechanism, is carried out.     

Growth, optical transmission and X-ray photoemission studies of BaB2O4 single crystals

Beta barium borate (-BBO) crystals have been grown by the top seeded solution growth technique (TSSG) using Na₂O as a flux. The crystals exhibited high transparency and the absence of inclusions and found to have sodium contamination in the range 150 to 230 p.p.m. The effect of this contamination on some crystal properties of interest has been investigated. The presence of impurities causes optical absorption below 550 nm in BBO crystals of both and -phases. X-ray photo emission spectroscopy (XPS) measurements performed on these crystals show that sodium gives rise to a measurable shift in the binding energies of the constituent ions. Further, the results show that Na⁺ ions enter into the lattice substitutionally and provide charge trapping sites close to the band edge.     

ANN modeling of DNA sequences: new strategies using DNA shape code

Two new encoding strategies, namely, wedge and twist codes, which are based on the DNA helical parameters, are introduced to represent DNA sequences in artificial neural network (ANN)-based modeling of biological systems. The performance of the new coding strategies has been evaluated by conducting three case studies involving mapping (modeling) and classification applications of ANNs. The proposed coding schemes have been compared rigorously and shown to outperform the existing coding strategies especially in situations wherein limited data are available for building the ANN models.     

Antioxidant and Prooxidant Effects of Metal Dafonates on the NADPH-Dependent Lipid Peroxidation in the Murine Hepatic Microsomal System

Dafone inhibits the lipid peroxidation significantly in a concentration dependent manner. The inhibition was found to be an uncompetitive type with the inhibition constant (Ki) of 62.5muM On the other hand complexation with metal ions results in a significant reversal from antioxidant to pro-oxidant properties for the resulting complexes which are cationic and with associated halometallate anions. The nature of the potentiation in case of the ferric compound was of competitive type with activation constant (Ka) having the value 32.5muM. The neutral copper-dafonate complex, however, inhibits lipid peroxidation with increase in concentration.     

Selective flocculation of iron oxide-kaolin mixtures using a modified polyacrylamide flocculant

High molecular weight polyacrylamides were synthesized and successfully modified to contain up to 8·3% hydroxamate functional groups. The selective flocculation tests carried out on 1:1 iron oxide/kaolin mixtures using parent polyacrylamide, polyacrylic acid and the modified polyacrylamide, confirm the possibility of enhancing selectivity through introduction of iron chelating functional groups in commercially available polymers. Starting with a feed grade of 35% iron, 92% recovery with acceptable grade of 60% iron has been achieved using the modified polyacrylamide. NCL communication No. 4415     

Crystallographic and electrical study of the chromium substituted ferrous zinc copper ferrites

The structural and electrical properties of the oxidic spinel Zn_0·5Cu_0·5Fe _x Cr_2−x O₄ (x=0·8, 0·9, 1·0, 1·1) have been investigated through X-ray diffraction, electrical resistivity, and thermoelectric measurements. X-ray diffraction data showed formation of single spinel phase with cubic structure. D.C. resistivity measurements from room temperature to 850 K was carried out and activation energy for all the compositions evaluated. Thermoelectric measurements showedp-type semiconducting nature in all the samples.     

Synthesis of Sr0.5Ba0.5Nb2O6 by Coprecipitation Method—Dielectric and Microstructural Characteristics

Sr_0.5Ba_0.5Nb₂O₆ (SBN50) has been synthesized by coprecipitation method using Sr(NO₃)₂, Ba(NO₃)₂ and Nb-oxalate as precursors and ammonium hydroxide as precipitant. Calcination at 1150C resulted in pure SBN50 phase (XRD) and nano powder with size varying between 100–250 nm (TEM). The average grain size (SEM) in the sintered pellets ranged from 2.5 to 5 m as the sintering temperature varied from 1250 to 1350C. The maximum sintered density was observed to be 93% of _th. The plot of dielectric constant vs. temperature clearly showed a shift of dielectric maxima (_max) with frequency, indicating the relaxor nature of SBN50. The room temperature dielectric constant (_RT > 2300) observed for all these samples is higher compared to the earlier reported values (_RT 1500). The T_c (for 1 KHz) varied from 47–60C depending on the sintering conditions. The hystersis loops were recorded at various temperatures. The maximum saturation polarization for the unpoled pellets was found to be 2.3 C/cm² when sintered at 1350C. The improvement in dielectric and ferroelectric behavior is attributed to the enhanced homogeneity attained by the coprecipitation synthesis route used in the present study. Correlations between microstructure (sintering conditions) and dielectric behavior is explored.     

Sidelobe cancellation technique for achieving high rejection in SAW filters

A new technique called sidelobe cancellation technique (SCT) to achieve high stopband rejection in SAW filters is described, for varying requirements of shape factor and sidelobe levels, by using an eigenfunction approach. Cosine series functions with improved sidelobe levels are employed. Each design is characterized by the order of the cosine series and the number of functions used to obtain a particular shape factor and rejection. Limited trimming of shape factor also can be achieved in each design. The filters described here are compared with the Kaiser window filter and are found to be efficient. Measured response of a prototype SAW filter using the approach given in this paper is plotted, and it is in good agreement with the simulated response     

Mesoscopic assembly of magnetic Pd-Ni nanocrystals into ordered arrays by using alkane thiols

Two-dimensional arrays of core-shell Pd561 Nin (n = 38, 280, 561, 800, 1500, 3000, 4500) nanocrystals have been prepared by using alkanethiols. The arrays of Pd561 Nin nanocrystals are particularly well ordered; those with high Ni coverage show a tendency to form multilayers or crystallites. Two-dimensional arrays also have been obtained of Pd561 Ni3000 nanocrystals further covered by a Pd layer with a Pd561 Ni3000 Pd1500 composition.     

Preparation of cross-linked sodium alginate microparticles using glutaraldehyde in methanol

Polymeric sodium alginate microparticles were prepared by precipitating sodium alginate in methanol, followed by cross-linking with glutaraldehyde. The extent of cross-linking was controlled by the time of exposure to glutaraldehyde. The topology of microparticles was characterized by scanning electron microscopy (SEM), which indicated smooth surfaces. The equilibrium swelling experiments were carried out in water to observe the effect of cross-linking and drug loading for better utility of microparticles. It was found that swelling decreased, but drug loading increased, with an increase in cross-linking of the matrix.