HIGH-Tc superconductivity in perovskite oxides of the Y─Ba─Cu─O system

Abstract

Several biphasic compositions of the type Y_3?xBa_3+xCu₆O₁₄ show an onset of superconductivity in the 90-115K range, attaining zero resistance in the 70-85K range. The phase responsible for superconductivity in these compositions is a perovskite oxide of composition YBa₂Cu₃ O₇. This oxide annealed in oxygen shows the onset of superconductivity at 120K and zero resistance at 87K. YBa₂,Cu₃O₇ shows the highest Meissner effect of all oxide superconductors. The superconducting behaviour of the two perovskite oxides, Y_0.95Ba_1.95,Cu₃O₇ and Y_1.05Ba_1.95Cu₃O₇ show interesting features; a marked decrease in resistivity is observed from room temperature itself in the former oxide with zero resistance at 89K. Electron microscopy and infrared spectra of these oxides are briefly discussed.     

Intelligence Testing and its Implications for Disability Evaluation in Individuals with Mental Retardation

Disability evaluation in mental retardation, which is done through assessment of intelligence, has certain inherent problems. The situation gets more complex if the person has additional disabilities, which is very likely in mental retardation. As an initiative, this study aims to study problems faced in intelligence testing in persons with mental retardation. The study included 88 randomly selected files of the individuals with mental retardation registered at the National Institute for the Mentally Handicapped (NIMH) Regional Centre, Kolkata during 2007-08. Each file was reviewed for information on diagnosis mental retardation, associated conditions and the intelligence testing reports. The results indicated that specific factors including both the characteristics of mental retardation and the nature of the tests available were interfering with intelligence testing. The problems are discussed in the context of current constructs related to mental retardation, diagnostic systems and legislation.     

Resource orchestration and dynamic managerial capabilities: focusing on sales managers as effective resource orchestrators

Resource-based theory (RBT) posits that firms gain competitive advantage through bundles of valuable and rare resources and sustain that advantage over time when such resources are difficult to imitate or nonsubstitutable by competitors. Recent applications of RBT emphasize the role of managers in mobilizing and leveraging organizational resources and capabilities for achieving business objectives. The purpose of this research is to advance the sales literature by applying learning from two specific perspectives based on RBT that focus explicitly on managerial actions pertaining to resources and capabilities: resource orchestration and dynamic managerial capabilities. These perspectives provide insights into the role of sales managers as orchestrators of sales and nonsales resources for achieving sales, organizational, and customer outcomes. Consistent with the stated purpose, this research provides (1) a review of research on resources and capabilities in the sales literature, (2) an overview of resource orchestration and related research, (3) an overview of dynamic managerial capabilities and related research, (4) a research agenda and propositions based on research orchestration and dynamic managerial capabilities for further investigation on the role of sales managers as effective resource orchestrators in sales organizations.     

Pressure dependence of the electrical resistivity of natural cassiterite SnO2 and of undoped and Co-doped nanocrystalline SnO2

The pressure dependence of the electrical resistivity of three different samples of cassiterite, namely natural cassiterite SnO₂, synthetic nanocrystalline SnO₂ (with crystallite size 46?nm) and nanocrystalline Co-doped SnO₂ (with crystallite size 32?nm), has been measured up to 7?GPa at room temperature. The resistivity of natural cassiterite SnO₂ decreases from 2.5?×?10⁴?Ωm at normal pressure and temperature to 1.7?×?10⁴?Ωm at 7.0?GPa. The nanocrystalline SnO₂ has a high resistivity 6.0?×?10⁵?Ωm at normal pressure and temperature and decreases with pressure reaching a value of 2.98?×?10⁵?Ωm at 7?GPa. The activation energy of the electrical conduction of the studied samples were found to be 0.32?eV for the natural SnO₂, 0.40?eV for the nanocrystalline SnO₂ sample and 0.28?eV for the nanocrystalline Co-doped SnO₂. Measurements of the pressure dependence of the electrical resistivity of the Co-doped SnO₂ showed a decrease from 3.60?×?10⁵ to 5.4?×?10⁴?Ωm at 7.0?GPa. We did not observe any pressure-induced phase transition in SnO₂ up to 7?GPa. This study of the high-pressure phase stability of cassiterite corroborates the experimental findings of SnO₂ nanoinclusions in diamonds.