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.     

To what extent can methyl derivatives be regarded as stabilized tautomers of xanthine?

Taking xanthine (Xan) as an example, validity of an approach to experimental investigations of nucleotide bases' tautomeric equilibrium, based on the use of methyl derivatives corresponding to their prototropic tautomers, was studied by (1)H NMR in dimethylsulfoxide (DMSO) and by quantum chemical calculations at the B3LYP/6-311++G(d,p) level of theory. From (1)H NMR spectra of m(7)Xan, m(9)Xan, Xan and m(3)Xan conclusion was made that the N7H tautomeric forms of the last two compounds dominate in solution, which was supported by quantum chemical data. Calculated relative energies of the N9H tautomers of Xan and m(3)Xan (8.74 and 9.57 kcal/mol, accordingly) are rather close to the m(9)Xan one (9.11 kcal/mol). Nonspecific influence of DMSO modelled by the COSMO algorithm therewith reduces these values by approximately 2-3 kcal/mol. The data obtained imply that methyl derivatives are rather good models of high-energy tautomers of nucleotide bases, if their relative energies are not less than a few kcal/mol.     

Ab initio comprehensive conformational analysis of 2'-deoxyuridine, the biologically significant DNA minor nucleoside, and reconstruction of its low-temperature matrix infrared spectrum

A comprehensive conformational analysis of isolated 2'-deoxyuridine (dU), a minor DNA nucleoside, has been performed by means of ab initio calculations at the MP2/6-311++G (d,p)//DFT B3LYP/6-31G (d,p) level of theory. At 298.15 and 420 K, all 94 allowed conformers of dU are within 8.96 and 7.91 kcal/mol Gibbs energy ranges, respectively. Syn orientation for the base and South (S) conformers for the sugar dominate at 298.15 K: syn/anti=62.3%:37.7% and S/N=77.2%:22.8%. At 420 K in the majority of conformers, the base is anti oriented and the population of North (N) sugars increases: syn/anti=39.3%:60.7% and S/N=63.0%:37.0%. Values of all conformational parameters and correlations between them, as well as their correlations with valence bonds, and also correlations between valence bonds and angles were estimated. In general, 14 types of intramolecular H-bonds were detected (1-3 H-bonds per conformer, the total number 175), namely, C1'H...O2 (16 H-bonds), C2'H1...O5' (9), C2'H2...O2 (21), C3'H...O2 (21), C5'H1...O2 (14), C5'H2...O2 (11), C6H...O4' (37), C6H...O5' (22), C3'H...HC6 (4), O5'H...HC6 (2), O3'H...O5' (5), O5'H...O4' (1), O5'H...O3' (4), and O5'H...O2 (8). Geometric, vibrational, structural-topological, and energetic features of the OH...O intramolecular H-bonds in dU conformers were determined. The close similarity between energetic and geometric characteristics of dU and thymidine DNA-like conformers in anti and relevant syn conformations and their transition states of the anti-->syn interconversion implies that mismatch DNA glycosylase discriminates between the two nucleosides, mainly because of the difference in the shapes of their bases. Convolution of calculated IR spectra of all the dU conformers within the limits 3400-3700 cm(-1) appears to be consistent with its low-temperature matrix IR spectrum (Ivanov et al. Spectrochim. Acta, Part A 2003, 59, 1959), wavenumber discrepancy not exceeding 1%. It was concluded that, for a reliable reproduction of the experimental spectrum, the whole set of conformers should be taken into consideration. The suggested method makes reconstruction of the isolated nucleoside IR spectrum at a physiological interval of temperature reasonably possible.     

Enhancement of second harmonic generation efficiency: Growth and characterization of magnesium(II)-doped tetrakis(thiourea)nickel(II) chloride crystals

The influence of magnesium doping on the properties of tetrakis(thiourea)nickel(II) chloride crystals has been described. The reduction in the intensity observed in powder X-ray diffraction of doped specimen and slight shifts in vibrational frequencies confirm the lattice stress as a result of doping. Surface morphological changes due to doping of the alkaline earth metal are observed by scanning electron microscopy. The incorporation of Mg(II) into the crystal lattice was confirmed by energy dispersive X-ray spectroscopy. Lattice parameters are determined by single crystal XRD analysis. The thermogravimetric and differential thermal analysis studies reveal the purity of the materials and no decomposition is observed up to the melting point. The crystal is further characterized by Kurtz powder technique and dielectric studies.