Numerical modelling of current transfer in nonlinear anisotropic conductive media

Current transfer behaviour in anisotropic superconducting bodies is the central topic of this thesis and focuses on the effect that the nonlinearity of the electric field dependence upon the local current density value and anisotropy have on the nature of current transport. The main motivation for this work was the desire for a better understanding of the conceptually difficult behaviour of current transport in superconducting bodies and examines current transfer quantitatively for a number of important problems on the macroscopic and microscopic scale. This behaviour is examined both experimentally and using computer models. The successful development of a powerful, robust and adaptable numerical model for analysing the complex current transfer behaviour has been the primary aim of this work. The range of parameters appropriate to macroscopic models of the Bi-2212 CRT system has been experimentally examined using a specifically constructed apparatus for the measurement of current transport characteristics. A study of the self-field properties of the Bi-2212 CRT material using a new experimental technique and mathematical analysis is presented and has allowed the importance of the self-field effect in the numerical model to be assessed. An essential requirement for the practical application of high current superconducting devices is the development of low resistance current contacts. The research presented examines this macroscopic current transfer problem and aims to explain experimentally observed current transfer characteristics at high applied currents. Existing models cannot explain these characteristics. Current transfer on the microscopic scale is also examined. Models of current transfer have been developed from descriptions of specific microstructures that are thought to characterise the microstructure of Bi-2223 and Bi-2212 silver-sheathed tapes. This thesis specifically presents modelling of current transfer between c-axis, low-angle c-axis and edge-on c-axis tilt oriented grain interfaces; the principal current transfer paths between individual current elements of the microstructural models of current flow in polycrystalline HTSs

A first-principles study and some applied researches of high-temperature superconductors and other low-dimensional functional materials

This thesis comprises two parts: The first is a fundamental theoretical study of hightemperature superconductors (HTS), addressing the energy balances involved in the superconducting pairing (research started under supervision of Prof. A.J. Leggett, in stays at the University of Illinois at Urbana-Champaign, USA). The study presents an extension, to the case of HTS, of equations originally derived for simple superconductors by G.V. Chester that link the energy saved by the superconductivity with the structural properties of the materials. The second part addresses applied aspects of various micro and nanostructured functional materials, including both HTS (optimization of superconducting devices, as bolometric radiation sensors, hybrid piezoelectric-superconducting films, and other) and electrostatic nanostructured microporous (ENM) media for nanofluid filtration

APS Science 2007.

This report provides research highlights from the Advanced Photon Source (APS). Although these highlights represent less than 10% of the published work from the APS in 2007, they give a flavor of the diversity and impact of user research at the facility. In the strategic planning the aim is to foster the growth of existing user communities and foresee new areas of research. This coming year finds the APS engaged in putting together, along with the users, a blueprint for the next five years, and making the case for a set of prioritized investments in beamlines, the accelerator, and infrastructure, each of which will be transformational in terms of scientific impact. As this is written plans are being formulated for an important user workshop on October 20-21, 2008, to prioritize strategic plans. The fruit from past investments can be seen in this report. Examples include the creation of a dedicated beamline for x-ray photon correlation spectroscopy at Sector 8, the evolution of dedicated high-energy x-ray scattering beamlines at sectors 1 and 11, a dedicated imaging beamline at Sector 32, and new beamlines for inelastic scattering and powder diffraction. A single-pulse facility has been built in collaboration with Sector 14 (BioCARS) and Phil Anfinrud at the National Institutes of Health, which will offer exceptionally high flux for single-pulse diffraction. The nanoprobe at Sector 26, built and operated jointly by the Argonne Center for Nanoscale Materials and the X-ray Operations and Research (XOR) section of the APS X-ray Science Division, has come on line to define the state of the art in nanoscience