Thesis (Ph. D.)--University of California, San Diego, and San Diego State University, 2004. / Vita. Includes bibliographical references (leaves 189-200).

Thesis (Ph. D.)--University of Hong Kong, 1997. / Includes bibliographical references.

Thesis (Ph. D.)--University of Hong Kong, 2000. / Includes bibliographical references.

Thesis (M. Phil.)--University of Hong Kong, 1996. / Includes bibliographical references (leaves 60-64).

Thesis (Ph. D.)--University of Texas at Austin, 2001. / Vita. Includes bibliographical references. Available also in a digital version from UMI/Dissertation Abstracts International.

Thesis (Ph. D.)--University of Texas at Austin, 2005. / Supervisor: John T. McDevitt. Vita. Includes bibliographical references.

Thesis (M. Phil.)--University of Hong Kong, 2006. / Title proper from title frame. Also available in printed format.

Thesis (Ph. D.)--University of Texas at Austin, 2006. / Vita. Includes bibliographical references.

As an electromagnetic response detection technique, non-resonant microwave absorption (NRMA) has been without doubt, one of the fundamental tools in characterizing high temperature superconductors (HTSC). The technique can explicitly give factual information on flux pinning, granularity, magnetization, and detection of iota superconducting phases among many more. The emergence of iron pnictides superconductors has brought an enormous impact on HTSC field due to their relatively high 𝑇c, high critical fields 𝐵c2, huge critical current density and low anisotropy. Accordingly, they look appealing candidates in industrial applications more especially in high magnetic field applications. As of yet, its electromagnetic response particularly the low field microwave absorption (LFMA) or the non-resonant microwave absorption (NRMA) is relatively unknown. Consequently, in this work, systematic studies have been done on SmFeAs(O,F), superconductors to determine the low field sweep microwave absorption. Furthermore, effect of varying temperature, microwave power and field modulation amplitude on NRMA line shape have been addressed and the results obtained are compared with NRMA results of cuprates superconductors. Interestingly, the NRMA line shape has been found to evolve as a function of temperature, microwave power and field modulation amplitude. A structure i.e a broad peak 1 and a narrow peak 2 have been identified. Furthermore, the line shape shows a phase reversal at moderately high microwave power. This dissertation presents the theoretical background of superconductors, experimental techniques, working principles of the equipments, results, discussions and conclusions. As pertains to the future work, recommendations have been suggested in trying other forms of sample and also different sample materials of iron based superconductors to fully understand the NRMA and ensure a progressive and continuous work in this field. Also, we will carry out extensive studies on critical current density, fluxon dynamics and irreversibility fields on iron-based superconductors by means of NRMA technique. / Physics / M. Sc. (Physics)

Doctor of Philosophy / Department of Agronomy / P. V. Vara Prasad / Drought and high temperature are major detriments to global wheat production. Wheat varies in its susceptibility to drought and high temperature stress. Three experiments were performed to address the challenges of drought and high temperature stress in wheat. The first experiment consisted of 256 genotypes of spring wheat and 301 genotypes of winter wheat, field screened for yield traits related to drought tolerance, in irrigated and dryland experiments. The experimental designs for the first experiment were both augmented incomplete block designs with one-way or row-column blocking. This experiment was performed at the Ashland Bottom Research Farm, south of Manhattan, KS, between 2011-2013. From this experiment, three conclusions were made: wheat genotypes vary widely in their responses between dryland and irrigated treatments and this variation can be used in future experiments or breeding tolerant genotypes. The number of seeds per unit of area, total biomass per unit area, and the average weight of one thousand seeds, were the best yield traits for predicting yield in both irrigated and dryland environments. Twenty genotypes were selected for future research based on their susceptibility or tolerance to drought. The second experiment was performed in the greenhouse facilities to observe the source-sink relationship of spring wheat genotype Seri 82 under drought and defoliation. The experiment was a randomized complete block design with a split-plot treatment arrangement. Post-anthesis cessation of watering and defoliation were the treatments. Both water stress and defoliation affected seed yield and total biomass. The major effect of post-anthesis water stress was a decrease in single seed weight. Defoliation affected the source-sink relationship by reducing the source strength of the leaves. This caused the stem to contribute more to overall yield. The defoliation also caused the remaining leaves to compensate for the removed leaves. The final experiment evaluated the changes in seed-filling rate and duration of three winter wheat genotypes during high temperature stress. High temperature stress reduced the duration of seed fill and increased the rate, differently in each genotype. Higher yields in the winter wheat growing regions, susceptible to post-anthesis high temperature stress, may be possible through selection of cultivars with faster seed-filling rates and/or duration of seed filling.