Positron annihilation measurements across the superconducting transition in Y1Ba2Cu3O7−x

Positron lifetime and Doppler broadened annihilation radiation lineshape measurements have been carried out in Y₁Ba₂Cu₃O_7−x as a function of temperature in the range of 300 K to 58 K. The positron lifetime and the peak parameter of the annihilation radiation lineshape are observed to decrease on lowering the temperature without showing any discontinuous change across the superconducting transition temperature of 90 K as determined by susceptibility measurements. The variation of positron annihilation parameters with temperature in the superconducting state is significantly larger than that in the normal state. This is qualitatively explained in terms of the dimerization of oxygen ions in the superconducting state of Y₁Ba₂Cu₃O_7−x .     

The anti-inflammatory activity of metal complexes and salts of amine carboxyboranes

The metal complexes and salts of amine carboxyboranes were shown to be potent anti-inflammatory agents in rodents at 8 mg kg^?1. They were effective in blocking induced edema, pleurisy and endotoxic shock while blocking both local and central pain processes. The ability of the agents to function as anti-inflammatory agents is multi-fold. First, lysosomal enzymes of specific cells, e.g. macrophages, were inhibited with IC₅₀ values in the range of 10^?6 M . Collagenase I and II activities were inhibited with IC₅₀ values approximately equal to 10^?4 M . The anti-inflammatory activity of these agents at the molecular levels appears to be due to inhibition of the release of TNFα and Il-1 from macrophages which indirectly control chemotaxic migration of white blood cells as indicated by the suppression of PMN and macrophage invasion into sponges implanted subcutaneously (SC) in mice. Furthermore, in these invading cells, the agents' blockage of TNFα and Il-1 or Il-2 release down-regulates prostaglandin and leukotriene enzymatic synthetic rates and, consequently, their release, resulting in a reduction of the inflammation process.     

Energy levels of the nucleus248Bk

The ambiguities and contradictions in presently available experimental information on the energy levels of the doubly odd deformed nucleus²⁴⁸Bk are sought to be cleared through calculation of the band head energies of the two-particle states based on evaluation of the residualn-p interaction energy for a zero range interaction. The applicability of the Gallagher-Moszkowski rule for the relative ordering of the spin triplet and singlet states is critically examined. It is concluded that the 8^? state from the {7/2⁺[633]p; 9/2^?[734]n configuration is the long lived isomer and forms the ground state of this nucleus. The 1^? state of the same configuration is the short lived isomer and an excited state in accordance with the GM rule and so is the 6⁺ state of the {3/2^?[521]p; 9/2^?[734]n configuration. The expected location of 20 two particle states comprising 10 GM pairs is calculated and compared with the available experimental information.     

Substituent directive effects in 1,2-benzodiazepine synthesis via electrocyclic aromatic substitution by the diazo-group: a rearrangement of 9- to 7-substituted 3H-1,2-benzodiazepines

The directive effect of aryl-substituents on the site of ring closure in the electrocyclisation of 1-aryl-3-diazoalkenes has been investigated. At 80°C the product ratio is determined by kinetic control but for some substituents the kinetically favoured 9-substituted 3$\text{H}$-1,2-benzodiazepines undergo a new rearrangement to their more stable 7-substituted isomers.     

On the linear two-point boundary-value problem

In this note, a noniterative scheme for solving two-point boundary-value problems for single and multi-input, linear constant systems is developed. The scheme requires the solution of 2n differential equations.     

Aggregation and precipitation stages in NaCl:Pb2+ studied by UV absorption

UV absorption measurements during isochronal annealing of homogenised and as-grown single crystals show two distinct stages in NaCl:Pb²⁺ where number density of free impurities reduce. With the help of our earlier light scattering results the low temperature stage has been attributed to aggregation of impurity-vacancy dipoles whereas the stage appearing at the higher temperature is assigned to the precipitation process.     

Phonons and fractons in sol-gel alumina: Raman study

We report Raman scattering from the boehmite,γ-, δ- andα-phases of the alumina gel. Samples are characterized by transmission and scanning electron microscopy, X-ray diffraction and density measurements. The main Raman line in the boehmite phase is red-shifted as well as asymmetrically broadened with respect to that in the crystalline boehmite, signifying the nanocrystalline nature of the gel. Raman signatures are absent in theγ- andδ-phases due to the disorder in cation vacancies. We also show that low frequency Raman scattering from the boehmite phase resembles that from a fractal network, characterized in terms of fraction dimension . Taking Hausdorff dimension D of the boehmite gel to be 2.5 (or 3.0), the value of is 1.33±0.02 (or 1.44±0.02), which is close to the theoretically predicted value of 4/3.