Self-injection length in La0.7Ca0.3MnO3-YBa2Cu3O7-δ ferromagnet-superconductor multilayer thin films

We have carried out extensive studies on the self-injection problem in barrierless heterojunctions between La_0.7Ca_0.3MnO₃ (LCMO) and YBa₂Cu₃O_7-δ (YBCO) thin films. The heterojunctions were formed in situ by sequentially growing LCMO and YBCO films on 〈100〉 LaAlO₃ (LAO) substrate using a pulsed laser deposition (PLD) system. YBCO micro-bridges with 64 μm width were patterned both on the LAO (control) and LCMO side of the substrate. Critical current, I _c, was measured at 77 K on both the control side as well as the LCMO side for different YBCO film thickness. It was observed that while the control side showed a J _c of ∼ 2 × 10⁶ A/cm², the LCMO side showed about half the value for the same thickness (1800 ?). The difference in J _c indicates that a certain thickness of YBCO has become ‘effectively’ normal due to self-injection. From the measurement of J _c at two different thicknesses (1800 ? and 1500 ?) of YBCO films both on the LAO as well as the LCMO side, the value of self-injection length (at 77 K) was estimated to be ∼ 900 ?. To the authors’ best knowledge, this is the first time that self-injection length has been quantified. A control experiment carried out with LaNiO₃ deposited by PLD on YBCO did not show any evidence of self-injection.     

Study of magnetoresistance and conductance of bicrystal grain boundary in La0.67Ba0.33MnO3 thin film

La_0.67Ba_0.33MnO₃ (LBMO) thin film is deposited on a 36.7°C SrTiO₃ bicrystal substrate using laser ablation technique. A microbridge is created across bicrystal grain boundary and its characteristics are compared with a microbridge on the LBMO film having no grain boundary. Presence of grain boundary exhibits substantial magnetoresistance ratio (MRR) in the low field and low temperature region. Bicrystal grain boundary contribution in MRR disappears at temperature T>175 K. At low temperature, I-V characteristic of the microbridge across bicrystal grain boundary is nonlinear. Analysis of temperature dependence of dynamic conductance-voltage characteristics of the bicrystal grain boundary indicates that at low temperatures (T<175 K) carrier transport across the grain boundary in LBMO film is dominated by inelastic tunneling via pairs of manganese atoms and tunneling through disordered oxides. At higher temperatures (T>175 K), magnetic scattering process is dominating. Decrease of bicrystal grain boundary contribution in magnetoresistance with the increase in temperature is due to enhanced spin-flip scattering process.     

Molar extinction coefficients of some carbohydrates in aqueous solutions

Molar extinction coefficients of some carbohydrates viz. l-arabinose (C₅H₁₀O₅), d-glucose (C₆H₁₂O₆), d-mannose (C₆H₁₂O₆), d-galactose (C₆H₁₂O₆), d(-) fructose (C₆H₁₂O₆) and maltose (C₁₂H₂₄O₁₂) in aqueous solutions have been determined at 81, 356, 511, 662, 1173 and 1332 keV by gamma ray transmission method in a narrow beam good geometry set-up. These coefficients have been found to depend upon the photon energy following a 4-parameter polynomial. These extinction coefficients for different sugars having the same molecular formula have same values varying within experimental uncertainty. Within concentration ranges studied, Beer-Lambert law is obeyed very well.     

Synthesis of two new p-tert-butylcalix[4]arene β-ketoimin derivatives for extraction of dichromate anion

In this study the selective derivatization of p-tert-butylcalix[4]arene was carried out and two new p-tert-butylcalix[4]arene β-ketoimin, 5,11,17,23-tetra-tert-butyl-25,27-bis-3-methyl-[(β-ketoimine)-ethoxy]-26,28-dihydroxycalix[4]arene (4), and 5,11,17,23-tetra-tert-butyl-25,27-bis-3-chloro-[(β-ketoimine)-ethoxy]-26,28-dihydroxycalix[4]arene (5) have been synthesized. In the synthesis, the lower rim of p-tert-butylcalix[4]arene was modified in order to acquire binding site for the recognition of dichromate anion. It was observed that these ionophores 4 and 5 showed high affinity towards dichromate anion. The protonated Schiff-base forms of the receptors were effective for transferring the HCr₂O₇ ^? anion from aqueous phase to a dichloromethane phase.     

Synthesis of new water-soluble phosphonate calixazacrowns and their use as drug solubilizing agents

This study presents the selective chloromethylation of calix[4](aza)crown ethers 2a–c, using chloromethyl n-octyl ether and SnCl₄ in chloroform at room temperature in good yield for the first time. Chloromethylated products 2a–c are used as key intermediates to synthesize new water-soluble p-phosphonato calix[4](aza)crown ethers 5a–c. Liquid–liquid phase extraction and phase solubility studies with poor water soluble drug molecules such as nifedipine, niclosamide and furosemide are performed to evaluate their binding properties. Among the studied drugs, furosemide was the most effectively dissolved drug by p-phosphonato calix[4](aza)crown ethers 5a–c in water.     

Square-like Functions Generated by a Composite Wavelet Transform

The classical square functions play important role in Harmonic Analysis and have a very direct connection with L ₂-estimates and Littlewood-Paley theory. In this paper we introduce a new variant of square-like functions generated by some composite wavelet transform. We establish Calderón-type reproducing formula and then prove L ₂-boundedness of newly defined square-like functions.