This thesis presents a detailed study of the composition dependence of the thermal and transient mobility of electrons in binary rare gas mixtures. The time independent electron real mobility in binary inert gas mixtures is calculated versus mole fraction for different electric field strengths. The deviations from the linear variation of the reciprocal of the mobility of the mixture with mole fraction, that is from Blanc's law, is determined and explained in detail. Very large deviations from the linear behavior were calculated for several binary mixtures at specific electric strengths, in particular for He-Xe mixtures. An interesting effect was observed whereby the electron mobility in He-Xe mixtures, for particular compositions and electron field strength could be greater than in pure He or less than in pure Xe. The time dependent electron real mobility and the corresponding relaxation time, in particular for He-Ar and He-Ne mixtures are reported for a wide range of concentrations, field strengths (d.c. electric field), and frequencies (microwave electric field). For a He-Ar mixture, the time dependent electron mobility is strongly influenced by the Ramsauer-Townsend minimum and leads to the occurrence of an overshoot and a negative mobility in the transient mobility. For He-Ne, a mixture without the Ramsauer-Townsend minimum, the transient mobility increases monotonically towards the thermal value. The energy thermal relaxation times 1/Pτ for He-Ne, and Ne-Xe mixtures are calculated so as to find out the validity of the linear relationship between the 1/Pτ of the mixture and mole fraction. A Quadrature Discretization Method of solution of the time dependent Boltzmann-Fokker-Planck equation for electrons in binary inert gas mixture is employed in the study of the time dependent electron real mobility. The solution of the Fokker-Planck equation is based on the expansion of the solution in the eigenfunctions of the Fokker-Planck operator. / Science, Faculty of / Chemistry, Department of / Graduate

Emission of positive muons (μ⁺) of low kinetic energy, with yield peaked at 5 to 20 electron volts and slowly decreasing to higher energy, has been observed by moderating a muon beam (p~28MeV/c, Δp/p~4%) with solid argon, krypton and xenon moderators. Emission at these energies is consistent with the muons escaping the target material still carrying part of their initial kinetic energy. The underlying cause of this enhancement of low energy positive muons is not determined. Variation of charge-exchange, elastic or inelastic collision cross sections with energy, resulting in an increased charged fraction or greater mean free path for muons at these energies, are possible causes. / Science, Faculty of / Physics and Astronomy, Department of / Title page of the thesis missing. / Graduate

Clusters of atoms have remarkable optical properties that were exploited since the antiquity. It was only during the late 20th century though that their production was better controlled and opened the door to a better understanding of matter. Lasers are the tool of choice to study these nanoscopic objects so scientists have been blowing clusters with high intensities and short duration laser pulses to gain insights on the dynamics at the nanoscale. Clusters of atoms are an excellent first step in the study of bio-molecules imaging. New advancements in laser technology in the shape of Free Electron Lasers (FEL) made shorter and shorter wavelengths accessible from the infrared (IR) to the vacuum and extreme ultra-violet (VUV and XUV) to even X-rays. Experiments in these short wavelengths regimes revealed surprisingly high energy absorption that are yet to be fully explained. This thesis tries to increase the global knowledge of clusters of rare-gas atoms interacting with short duration and high intensity lasers in the VUV and XUV regime. Theoretical and numerical tools were developed and a novel model of energy transfer based on excited states will be presented. The first part describes the current knowledge of laser-cluster interaction in the short wavelength regime followed by the description of the new model. In the second part of the thesis the different tools and implementations used throughout this work are presented. Third, a series of journal articles (of which four are published and one to be submitted) are included where our models and tools were successfully used to explain experimental results.

Magnesium has the lowest density of any structural metal making it a strong candidate for weight savings in the aerospace and automotive industries. However, strong crystallographic textures combine with anisotropic deformation modes to severely limit formability in wrought magnesium alloys. Recently improved formability has been achieved by the addition of small concentrations of solute rare earth elements which reduce the intensity of recrystallisation textures. Developing a mechanistic understanding of this effect is critical in leading alloy design towards a new class of highly formable wrought magnesium alloys. In this study the static recrystallisation mechanism of rolled magnesium rare earth alloys, which causes the texture weakening, is examined with a particular emphasis on the contrasting texture weakening effects in binary and tertiary magnesium rare earth alloys. In binary magnesium-rare earth alloys the `rare-earth' texture is simply a weakened deformation texture, while recrystallisation of magnesium-zinc-rare earth alloys produces unique `rare-earth' texture components. In the binary alloys weakened recrystallisation textures are attributed to the generation of `off-basal' orientations within regions of high strain localisation during deformation. These orientations recrystallise and subsequently dominate the recrystallised texture. Texture weakening by this mechanism is also thought to be observed in non-rare earth magnesium alloys where dynamic recrystallisation is suppressed by cold rolling. The unique rare-earth texture components in magnesium-zinc-rare earth alloys are found to be determined by the orientation of shear bands in the material. Similarly to texture weakening in the binary alloys, nuclei for these orientations are thought to develop during deformation as a result of strain incompatibilities within shear bands. The mechanism forming these orientations remains unclear, however it is postulated that a complex change in recovery behaviour within shear bands, as a result of rare earth and zinc additions, may be the cause. Retarded dynamic recrystallisation is suggested to be of critical importance in the texture weakening mechanisms of all magnesium alloys, both rare earth and non-rare earth. In rare earth alloys dynamic recrystallisation is suppressed by the segregation of rare earth atoms to grain boundaries. A combination of high resolution TEM and EDX shows rare earth atoms form clusters approximately 2nm in diameter on grain boundaries which are expected to retard dynamic recrystallisation through a solute drag mechanism.

Ph.D. (Physics) / Please refer to full text to view abstract

Introduction: The scarcity of rigorous evidence regarding rare disease therapies contributes to uncertainty for stakeholders who make decisions about the use, prescription, or funding of such therapies. My dissertation objective was to integrate stakeholder perspectives and evidence related to how rare disease therapies are evaluated to better understand drivers of uncertainty in decision making and develop an evaluation framework for future evidence generation, synthesis, and decision support. Methods: To better understand the perceived challenges in generating robust treatment effectiveness evidence, and describe various methods for mitigating these challenges, I used a meta-narrative literature review. I also conducted focus group interviews with key rare disease stakeholders (patients/caregivers, physicians, and policy advisors) to elicit different perspectives on how evidence is generated, evaluated, and synthesized in the context of health care decision making, both at a personal and population level. Finally, I integrated the focus group findings with a targeted literature review to identify characteristics of rare diseases and their candidate therapies that may warrant special consideration in health technology assessment (HTA) and health care decision making. Findings: My dissertation data revealed three fundamental challenges in generating robust treatment effectiveness evidence for rare diseases: limitations in recruiting a sufficient sample; inability to account for clinical heterogeneity; and reliance on outcomes with unclear clinical relevance. Several methodological solutions have been proposed to overcome these challenges. In addition, study participants described different perspectives on how they choose to participate in and use research in their roles as health care users, care providers, and policy advisors. Notably, conventional wisdom that patients/caregivers participate in clinical research studies because of therapeutic misconception was not supported. Finally, focus group and literature review findings identified information that potentially warrants special consideration in future HTA specific to rare diseases, including characteristics of the disease, understanding of causal hypotheses relevant to the therapy, and complexities of cost-effectiveness given the high price of many rare disease therapies. Discussion: Together, the findings from this dissertation support an evaluation framework with eight key principles that aim to mitigate important aspects of uncertainty from various stakeholder perspectives and promote evidence-informed decision making about rare disease therapies.

No scale provided. Researched by Dr. Nat E. Hyder and Midred Kozsuch. Cartography and illustration by Alan Park in 1980. Overmountain Press. Indicates mills, forges, and places of interest. / https://dc.etsu.edu/rare-maps/1120/thumbnail.jpg

Scale 1 inch = 1.9 Statute Miles. Indicates churches, schoolhouses, mills, and homes. Includes an enlarged map of the town of Stuart. Drawn in 1976 for the Patrick County - Stuart Chamber of Commerce by Eugene M. Scheel of Waterford, Va. / https://dc.etsu.edu/rare-maps/1121/thumbnail.jpg

Hand drawn map by Susan Patrick of the Woman's Civic Club (no. 435 out of 500), with a handwritten date of 1976. Includes drawings of Sinking Creek Baptish Church, covered bridge, Roan Mountain, Seeger Memorial Chapel, Fort Watauga, the Monument, and the Mansion. No scale provided. / https://dc.etsu.edu/rare-maps/1124/thumbnail.jpg

No scale provided. Drawn by Louis T. Ketron in 1971. Map of Hawkins County (Tenn.) marking historically significant spots from 1771 to 1971. A legend in the front upper left corner (continues on back) lists over 400 events important to the history of Hawkins County, including the founding of Rogersville, a Civil War battle in Rogersville, the organization of the first Circuit Court, and the establishment of post offices. / https://dc.etsu.edu/rare-maps/1127/thumbnail.jpg