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The heavy alkaline earth hydrides consist of the Group II (alkaline earth metal) hydrides, namely CaH2, SrH2, and BaH2, which adopt the cotunnite-type structure at ambient pressure and temperature conditions. There has been much recent research interest in these compounds; in the past decade numerous experimental and theoretical studies exploring the hydrides in both applied and fundamental respects have been added to the literature. The present work constitutes a study of the heavy alkaline earth hydrides subjected to extreme pressure conditions (at ambient temperature). Specifically, pressure-dependent angle-dispersive powder x-ray diffraction and Raman spectroscopy experiments, as well as first-principles calculations, have been carried out to explore the structural stability, compressibility, and optical phonon spectra of the heavy alkaline earth hydrides. To complement the work on the hydrides, a companion study on BaF2---a structural analogue---is presented, as well as a description of some selected experimental techniques used to carry out the research. The powder x-ray diffraction results reveal that all of the heavy alkaline earth hydrides undergo a pressure-induced, first-order structural phase transition. The proposed Ni2ln structure for the high-pressure phase is based on both the results of first-principles calculations and an isostructural comparison with BaF2. The transition pressures and the proposed high-pressure structure are corroborated by the results of the Raman spectroscopy measurements. Where applicable, equation of state parameters from both the experimental and theoretical studios are reported, and a comparison of these respective parameters at ultra-high pressures (greater than 50 GPa) suggests that the experimentally observed bulk moduli are overestimated due to the presence of non-hydrostatic pressure conditions.

Work on film flow in liquid helium II is not new, but very little has been done in the temperature region below 1 degree. The present work describes a method of extending these measurements down to the very low temperature range. After a brief introduction laying the foundation of the problem in its proper framework in the field of low temperatures, the experiments and results obtained by other workers in film flow and associated phenomena are reviewed. Then the author proceeds to the development of experimental techniques used in attempting to seal gaseous helium at high pressures in glass capsules. Chapter II terminates with a full description of the so-called Heater Method with which helium 'bombs' were sealed at pressures ranging from 750 to 1100 psi. One of these capsules containing a capillary beaker, and partially filled with manganous ammonium sulfate, was used in determining film flow rates at temperatures ranging from approximately 2° to 0.6°K, The lower temperatures were obtained by adiabatic demagnetization techniques. Chapter III is a report of such experimentation. The results obtained are much like those of Ambler and Kurti, 1952, and support their contention that film flow rates do increase with decreasing temperatures in the region below one degree absolute. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

One of the recently developed methods for studying nuclei depends on the orientation of the spin axes of the nuclei with respect to some axis fixed in space. Since there is an association between the angular momentum properties of a nuclear system and directional effects in the absorption or emission of radiation by such a system, this nuclear ordering is characterized by anisotropic effects in the interaction of the nuclei with radiation, whether particle or electromagnetic. This thesis encompasses the preliminary work done in assembling a system consisting of cryogenic equipment and electronics to measure the anisotropy in radiation emitted from radioactive nuclei oriented in a ferromagnetic host lattice (iron) at very low temperatures (∾0.01°K) and to observe the changes in anisotropy with changes in temperature. Chapter 1 contains a condensed account of the information that can be obtained from oriented nuclei, the methods of producing oriented nuclei and the theory required for extracting information from the observed anisotropy. Chapter 2 describes the low temperature apparatus and-includes a description of the low temperature cryostat, the Dewar vessels, the specimen assembly, the superconducting solenoid, and the polarizing solenoid. Chapter 3 deals with thermometry at low temperatures, the technique used for cooling adiabatically and the preparation of the Co⁶º specimen used for thermometry. Chapter 4 explains the function of each module of electronics used in the experimental configuration. Nuclear orientation of Co⁶º is covered in Chapter 5 and includes an analysis and discussion of results. Chapter 6 outlines the improvements to be made in the design of a new low temperature system and includes a brief summary of the future program of studies in nuclear orientation at very low temperatures. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

The superfluid phase of helium-4, known as He~II, is predominantly used to cool low-temperature devices. It transfers heat by a unique thermally driven counterflow of its two constituents, a classical normal fluid and an inviscid superfluid devoid of entropy. It also has potential use for economical reproduction and study of high Reynolds number turbulent flow due to the extremely small kinematic viscosity and classical characteristics exhibited by mechanically driven flow. A number of diagnostic techniques have been applied in attempts to better understand the complex behavior of this fluid, but one of the most useful, flow visualization, remains challenging because of complex interactions between foreign tracer particles and the normal fluid, superfluid, and a tangle of quantized vortices that represents turbulence in the superfluid. An apparatus has been developed that enables application of flow visualization using particle tracking velocimetry (PTV) in conjunction with second sound attenuation, a mature technique for measuring quantized vortex line density, to both thermal counterflow and mechanically-driven towed-grid turbulence in He~II. A thermal counterflow data set covering a wide heat flux range and a number of different fluid temperatures has been analyzed using a new separation scheme for differentiating particles presumably entrained by the normal fluid ("G2") from those trapped on quantized vortices ("G1"). The results show that for lower heat flux, G2 particles move at the normal fluid velocity vn, but for higher heat flux all particles move at roughly vn/2 ("G3"). Probability density functions (PDFs) for G1 particle velocity vp are Gaussian curves with tails proportional to |vp|⁻³, which arise from observation of particles trapped on reconnecting vortices. A probable link between G1 velocity fluctuations and fluctuations of the local vortex line velocity has been established and used to provide the first experimental estimation of c₂, a parameter related to energy dissipation in He~II. Good agreement between the length of observed G2 tracks and a simple model for the mean free path of a particle traveling through the vortex tangle suggests that flow visualization may be an alternative to second sound attenuation for measurement of vortex line density in steady-state counterflow. Preliminary PTV and second sound data in decaying He~II towed-grid turbulence shows agreement with theoretical predictions, and enables reliable estimation of an effective kinematic viscosity and calculation of longitudinal and transverse structure functions, from which information about the energy spectrum evolution and intermittency enhancement can be obtained. / A Dissertation submitted to the Department of Mechanical Engineering in partial fulfillment of the requirements for the degree of Doctor of Philosophy. / Fall Semester 2018. / August 21, 2018. / Includes bibliographical references. / Wei Guo, Professor Directing Dissertation; Jorge Piekarewicz, University Representative; William Oates, Committee Member; Kunihiko Taira, Committee Member.

A wide variety of scientifically interesting missions could be enabled by orbital flight altitudes of 150 – 250 km. For the present work, this range of altitudes is defined as extremely Low Earth Orbit (eLEO). The use of low-cost nanosatellites (mass < 10 kg) has reduced the cost barrier to orbital flight over the last decade and the present study investigates the feasibility of using primarily commercial, off-the-shelf (COTS) hardware to build a nanosat specifically to allow extended mission times in eLEO. CubeSats flying in the lower thermosphere have the potential to enable close monitoring of the Earth’s surface for scientific, commercial, and defense-related missions. The results of this research show that the proper selection of primary and attitude control thrusters combined with precise control techniques result in significant extension of the orbital life of a CubeSat in eLEO, thus allowing detailed explorations of the atmosphere. In this study, the orbit maintenance controller is designed to maintain a mission-averaged, mean altitude of 244 km. An estimate is made of the primary disturbance torque due to aerodynamic drag using a high-fidelity calculation of the rarefied gas drag based on a Direct Simulation, Monte-Carlo simulation. The primary propulsion system consists of a pair of electrospray thrusters providing a combined thrust of 0.12 mN at 1 W. Results of a trade study to select the best attitude control option indicate pulsed plasma thrusters operating at 1 W are preferable to reaction wheels or mangetorquers at the selected altitude. An extended Kalman filter is used for orbital position and spacecraft attitude estimations. The attitude determination system consists of sun sensors, magnetometers, gyroscopes serving as attitude sensors. The mission consists of two phases. In Phase I, a 4U CubeSat is deployed from a 414 km orbit and uses the primary propulsion system to deorbit to an initial altitude within the targeted range of 244 +/- 10 km. Phase I lasts 12.73 days with the propulsion system consuming 5.6 g of propellant to deliver a ∆V of 28.12 m/s. In Phase II the mission is maintained until the remaining 25.2 g of propellant is consumed. Phase II lasts for 30.27 days, corresponding to a ∆V of 57.22 m/s with a mean altitude of 244 km. The mean altitude for an individual orbit over the entire mission was found to vary from a maximum of 252 km to a minimum of 236 km. Using this approach, a primary mission life of 30.27 days could be achieved, compared with 3.1 days without primary propulsion.

This dissertation describes the propagation of near atmospheric nitrogen gas that rushes into a liquid helium cooled vacuum tube after the tube suddenly loses vacuum. The loss-of-vacuum scenario resembles accidental venting of atmospheric air to the beam-line of a superconducting radio frequency particle accelerator and is investigated to understand how in the presence of condensation, the in-flowing air will propagate in such geometry. In a series of controlled experiments, room temperature nitrogen gas (a substitute for air) at a variety of mass flow rates was vented to a high vacuum tube immersed in a bath of liquid helium. Pressure probes and thermometers installed on the tube along its length measured respectively the tube pressure and tube wall temperature rise due to gas flooding and condensation. At high mass in-flow rates a gas front propagated down the vacuum tube but with a continuously decreasing speed. Regression analysis of the measured front arrival times indicates that the speed decreases nearly exponentially with the travel length. At low enough mass in-flow rates, no front propagated in the vacuum tube. Instead, the in-flowing gas steadily condensed over a short section of the tube near its entrance and the front appeared to `freeze-out'. An analytical expression is derived for gas front propagation speed in a vacuum tube in the presence of condensation. The analytical model qualitatively explains the front deceleration and flow freeze-out. The model is then simplified and supplemented with condensation heat/mass transfer data to again find the front to decelerate exponentially while going away from the tube entrance. Within the experimental and procedural uncertainty, the exponential decay length-scales obtained from the front arrival time regression and from the simplified model agree. / A Dissertation submitted to the Department of Mechanical Engineering in partial fulfillment of the requirements for the degree of Doctor of Philosophy. / Spring Semester 2016. / February 23, 2016. / accelerator, accident, condensation, shock, superconducting, vacuum / Includes bibliographical references. / Steven W. Van Sciver, Professor Directing Dissertation; David A. Kopriva, University Representative; Eric E. Hellstrom, Committee Member; Wei Guo, Committee Member; Kunihiko Taira, Committee Member.

This paper investigates the voltage and phase dynamics of a low inertia inverter based Microgrid in islanded operation. In such case, the network is less robust to disturbances due to the lack of associated inertia within an inverter. In islanded operation, the assumption of a stiff grid is no longer valid due to the voltage and phase adjustment based on conventional droop control have a resulting effect on the power flows throughout the network where voltage and frequency stability of the network may be compromised. Other approaches neglect the network dynamics when there are power imbalances in the system and how each node is affected and if the resulting increase in demand can be met with the available power generation. This paper uses the fact that the phase dynamics of coupled inverters that employ droop control closely resemble the phase dynamics proposed by the Kuramoto model. Using this model allows the network stability to be analyzed under the true nonlinear operation. It Is observed through the strong coupling impedance of the secondary distribution transmission lines and the implementation of proportional droop control will provide an appropriate means for rural and suburban neighborhoods to operate independently, given the proportional droop gain is tuned appropriately.

Bibliography: pages 333-338. / This thesis presents a critical evaluation of the current responses being made by the new Government of National Unity towards solving the low cost housing and community development crisis. This crisis is largely confined to the black low-income residential areas and is manifest in a shortage of adequate formal accommodation, municipal infrastructure and public facilities. Moreover, these areas are also characterised by poverty, poor living conditions, environmental degradation and the socio-economic deprivation of the households living within them. The Reconstruction and Development Programme and the National Housing Policy have recently been introduced by the new Government in response to this problem. The purpose of this study is to examine the degree to which these policies represent an effective long-term solution to this crisis and whether they are an appropriate means through which low-income households can obtain the type of housing-they both need and can realistically afford. Emphasis is placed upon a critical evaluation of the National Housing Policy and the Cape Metropolitan Region is used as a study area. A household survey was carried out in the black low-income residential areas of this region in an effort to determine the actual housing and development needs, perceptions, socio economic characteristics and locational preferences of these communities. The results of the survey are presented along with an analysis of the origins, nature and magnitude of the housing crisis in the Cape Metropolitan Area.

Indiana University-Purdue University Indianapolis (IUPUI) / In this exploratory, qualitative study, the author examined the lived experiences of low-income type 2 diabetics around managing their diabetes. Semi-structured, individual interviews were conducted with volunteer participants from a Midwest student outreach clinic (N=14; 8 men, 6 women). Interviews were first analyzed using LUUUUTT model from the Coordinated Management of Meaning (CMM) theory for gaps between stories lived and stories told. Findings suggest that the lived experience of the majority of the participants had low social support and heightened stress around managing their diabetes. Using the Communication Complex framework, the patterns of interactions around these two tensions were analyzed to make suggestions for change.