Global ETD Search
Search theses and dissertations gathered from participating repositories worldwide. Every result links back to the library that holds it. No account is needed.
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Showing 1 to 20 of 21 for “"critical currents"”.
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Critical currents in granular high temperature superconductors
… of an investigation into the behaviour of the critical current density (Jc) of several different high temperature superconductors (HTSCs) as a function of temperature and applied magnetic field. The focus of this research has been to investigate the discrepancies which generally exist between …
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Electrical characterization of high temperature superconductors as a function of temperature
The critical currents of silver sheathed multifilamentary Bi 2Sr 2Ca2 Cu3010 (BSCCO- 2223/Ag) tapes at temperatures ranging from 77 K to 110 K were measured using a typical four-terminal technique for two different BSCCO-2223/Ag tapes manufactured by Vacuumschmelze (VAC). The critical currents for …
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Effect of disorder on the vortex dynamics in superconducting Josephson junction arrays and clusters
… that features due to disorder in the junction critical currents, dominate the properties. We have developed a simple model in real space to understand the static vortex configurations and the motion of the vortices.
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Critical current anisotropy in high temperature superconductors
… their successful technological development. The critical current density (Jc) in HTS is directly dependent on the structure and pinning of the Flux Line Lattice (FLL) in these materials. This thesis presents an investigation of the Jc anisotropy in HTS. The use of thin films grown on off c-axis …
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Electrical characterization of thick film superconductors
… than 50 mils. On either substrate material, critical currents of the films consistently decreased with thinner, narrower lines and environmental exposure. The maximum critical current on 2 magnesia substrates was 635 A/cm² for an unaged 77μm thick by 200 mil wide line, and the minimum was 345 …
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YBa2Cu3O7-x thin films prepared by Chemical Solution Deposition
… of high Tc-superconductors require large critical currents and high-applied magnetic fields. Effective ways to increase the critical current density at high magnetic fields in YBCO are the introduction of nanoparticles and chemical substitution of yttrium by other rare earth elements. …
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Switching Current Distributions of Superconducting Nanowires: Evidence of Quantum Phase Slip Events
… measurements of the distribution of switching currents---the high-bias currents at which superconductivity gives way to resistive behavior---whose width exhibits a rather counter-intuitive, monotonic increase with decreasing temperature. A stochastic model of phase slip kinetics which relates …
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The Properties of Grain Boundaries in YBa2Cu3O7-d
… the cuprates and also limit the superconducting critical currents attainable in practical, polycrystalline materials. An improved understanding of these defects is therefore important for applications. The status of the current understanding of cuprate grain boundaries is summarised and …
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Microscopic physics of transition edge sensors
… allowing predictions of resistance surfaces, critical currents and the small signal electrothermal parameters. To test my model, I calculate I(V) curves for device designs used by different research groups and compare them to experimental measurements. Using my model, I design a TES wafer for …
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Characterization of Josephson Devices for Use in Quantum Computation
… 10 x 10 um^2 Nb/AlOx/Nb qubit junctions, with critical currents of roughly 30 uA. The state of a device was initialized by cooling below 50 mK in a dilution refrigerator. In order for quantum mechanical superpositions to be long-lived, it is necessary to isolate the junction from noisy bias …
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Numerical modelling of current transfer in nonlinear anisotropic conductive media
… 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 …
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Superior pinning properties in nano-engineered YBa2Cu3O7-δ
… novel pinning addition capable to increase the critical current and to reduce the YBa2Cu3O7-δ critical currents angular dependencies anisotropy. The Ba2YNbO6 + Gd3TaO7 + YBa2Cu3O7-δ is found to produce a new complex pinning landscape extremely effective. At high fields the synergetic combination …
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An investigation into a flux-pumped high-temperature superconducting MRI system
… could operate at higher temperatures with higher critical currents and fields. In the last two to three decades, the production of HTS tapes has increased significantly making them easily accessible for researchers at a reasonable cost. HTS is slowly making its way into high-field magnet …
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On convection and stability of some welding and solidification processes
… equations both become unstable at different critical currents dependent on the sign and magnitude of d^/dT. An investigation of the eigenvectors indicates the onset of instability near to the point source. For the upper modes instability occurs only when m = 1 and in a very small region of …
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Magnetic fields near microstructured surfaces : application to atom chips
… magnetic field fluctuations generated by thermal currents in the chip elements may induce spin flips of atoms and result in loss, heating and decoherence. In this thesis, we extend previous work on spin flip rates induced by magnetic noise and consider the more complex geometries that are …
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Josephson Junctions Fabricated by Focussed Ion Beam
… of the relatively large spread in individual critical currents. Strategies for minimizing junction parameter spread and producing large-scale arrays are discussed. The opportunities offered by the FIB for the creation of novel device structures has not been overlooked. By milling a circular …
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The Electronic Properties of Thin Film YBa2Cu3O7 Low Angle Grain Boundaries
Critical currents in the latest biaxially textured ‘coated conductors’ are now limited by 2D networks of low angle grain boundaries (LAGBs) with misorientation θm = 1 - 10°. In order to understand and optimise current transfer in these materials it is essential to elucidate the electromagnetic …
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A study of oxide superconductors by electron energy loss spectroscopy in STEM.
… the properties of the sample. Studies on critical currents in bulk materials and single cystals have shown that the currents in the bulk materials are a factor of 10 less than for the single crystals. This discrepancy can be associated with a change in oxygen stoichiometry at the boundary …
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