<p> The light even-even nuclei have been studied using the den~ity dependent effective interaction of Sprung and Banerjeee The nuclei were studied initially, using a harmonic variational procedure, to deter mine the most appropriate parameters of t he force for the Hartree Fock study. </p> <p> This chosen force was then used in a comparative study of spherical nuclei to d e termine the inadequacies of our Hartn~e Fock approach, as opposed to the spherical basis calculations of Campi. Some deformed nuclei were then examined and our results were compared with those of K. Lassey and A. B. Volkov , and of J. Zofka and G. Ripka. </p> / Thesis / Master of Science (MSc)

Missing page viii. Page 171 was repeated with different text. / <p> The decay of 14.9 min. ⁸⁹Rb to levels in ⁸⁹Sr has been studied by use of Ge(Li) detectors, NaI(Tl) detectors and a magnetic beta ray spectrometer. Fourteen gamma rays have been studied by ɣ-ɣ and β-ɣ coincidence experiments and establish levels at 0, 1.031, 2,000, 2.277, 2.567, 2.708, 2.770, 3.225 and 3.500 MeV. The Q value is 4.486 ± .012 Mev. </p> <p> The techniques of beta and gamma ray spectroscopy using Ge(Li), NaI(Tl) and plastic beta detectors have been applied in the study of the decay of 3.2 min. ⁸⁹Kr to levels in ⁸⁹Rb. Seventy nine of the one hundred and eleven observed gamma rays have been classified in the proposed decay scheme. The Q value is 5.15 ± .03 MeV. </p> / Thesis / Doctor of Philosophy (PhD)

In this thesis we present cloud-scale ALMA observations of two local mergers, NGC 3256 and NGC 4038/9 (the "Antennae"), in CO J=2-1. Through a pixel-based analysis of NGC 3256 we measure molecular-gas properties and compare to nearby spiral galaxies from the PHANGS-ALMA survey. NGC 3256 exhibits high mass surface densities, velocity dispersions, peak brightness temperatures, virial parameters, and internal turbulent pressures. High surface densities are expected to accompany its high star-formation rate, and high brightness temperatures may indicate warmer gas, heated by the vigorous star formation. Large virial parameters and internal pressures imply the molecular gas is not bound by self-gravity, but we explore how material external to clouds could alter this. We argue the molecular gas in NGC 3256 is smoother than in nearby spiral galaxies down to 55 pc. We also perform a cloud analysis of our NGC 3256 observations, identifying 185 clouds, and find similar results to the pixel analysis. We calculate additional cloud properties including eccentricity, CO luminosity, CO-estimated mass, virial mass, size-linewidth coefficient, and free-fall time. Properties in NGC 3256 are extreme compared to clouds from PHANGS-ALMA, including slightly larger clouds and shorter free-fall times. Cloud eccentricities in NGC 3256 are similar to those in PHANGS-ALMA galaxies, possibly indicating similar average cloud dynamical states. The shape of the cloud mass function in NGC 3256 is similar to many PHANGS-ALMA galaxies. Finally, we analyse our NGC 4038/9 observations using the same pixel methods as used in NGC 3256. NGC 4038/9 also harbours extreme molecular-gas properties and potentially smoother emission compared to spiral galaxies, but not as extreme as NGC 3256. We find the most-massive spiral galaxies have central molecular-gas properties similar to the mergers. Virial parameters in NGC 4038/9 are similar to many spiral galaxies, making it quite different from NGC 3256, potentially due to their different merger stages. Comparison of the overlap region of NGC 4038/9 in CO (2-1) to CO (3-2) shows general agreement. / Thesis / Doctor of Philosophy (PhD)

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Poly(phenylene sulfide) (PPS), an engineering thermoplastic with excellent mechanical, thermal, and chemical properties, was gelled for the first time using 1,3-diphenylacetone (DPA) as the gelation solvent in a thermally induced phase separation (TIPS) process. PPS was dissolved in DPA at high temperatures to form a homogeneous solution. The solution was cooled, initiating phase separation and eventually forming a solidified PPS network around DPA-rich domains. Evacuation of DPA from the gel network creates monolithic PPS aerogels, one of few physically crosslinked polymer aerogel systems comprised of a high-performance thermoplastic. In this work, specific properties of PPS aerogels were controlled through the manipulation of various processing parameters, such as polymer concentration, post-process annealing conditions, mode of manufacturing (casting versus additive manufacturing), dissolution temperature, and drying method. The ultimate goal was to elucidate key process-morphology-property relationships in PPS aerogels, to ultimately improve aerogel performance and applicability. The phase diagram of PPS/DPA was first elucidated to determine the phase separation mechanism of the system, which guides all future processing decisions. The phase diagram indicated that the system undergoes solid-liquid phase separation, typical for solutions with relatively favorable polymer-solvent interactions. This assignment was validated by the calculation of the Flory-Huggins interaction parameter through two independent methods - Hansen solubility parameters and fitting melting point depression data. The influence of polymer composition on PPS aerogel properties was then characterized. As polymer concentration increased, aerogel density and mechanical properties increases, and porosity decreased. The particular morphology of PPS aerogels from DPA was that of a fibrillar network, where these axialitic (pre-spherulitic) fibrils are comprised of stacks of PPS crystalline lamellae, as suggested by x-ray scattering and electron microscopy. These interconnected microstructures responded more favorably to compressive load than similar globular PEEK aerogels, highlighting the importance of aerogel microstructure on its mechanical response. Upon solvent extraction, PPS aerogels were annealed in air environments to improve their mechanical behavior. Annealing did not dramatically shrink the aerogels, nor did it appear to affect the micron-scale morphology of PPS aerogels as observed by electron microscopy. The resistance to densification of PPS aerogels was mainly a product of their interconnected fibrillar morphologies, aided by subtle microstructural changes that occurred upon annealing. Exposure to a high temperature oxidative environment (160 – 240 oC) increased the degree of crystallinity of the aerogels, and also promoted chemical crosslinking within the amorphous PPS regions, both of which may have helped to prevent severe densification. With enhanced physical and chemical crosslinking, annealed PPS aerogels displayed improved compressive properties over unannealed analogues. Additionally, the thermal conductivity of both annealed and unannealed aerogel specimens was below that of air (~ 0.026 W/mK) and did not display a dependence on polymer composition nor on annealing condition. Generally, these experiments demonstrate that annealing PPS aerogels improved their mechanical performance without negatively affecting their inherent fibrillar morphology, low density, or low thermal conductivity. To fabricate aerogels with geometric flexibility and hierarchical porosity, PPS/DPA solutions were printed through material extrusion (MEX) and TIPS using a custom-built heated extruder. In this process, solid solvated gels were first re-dissolved in a heated extruder and solutions were deposited in a layer-wise fashion onto a room-temperature substrate. The large temperature gradient between nozzle and substrate rapidly initiated phase separation, solidified the deposited layers and formed a printed part. Subsequent solvent exchange and drying created printed PPS aerogels. The morphology of printed aerogels was compositionally-dependent, where the high extrusion temperature required to dissolve highly-concentrated inks (50 wt % PPS) also destroyed self-nuclei in solution, yielding printed aerogels with spherulitic microstructures. In contrast, aerogels printed from 30 wt % solutions were deposited at lower temperatures and demonstrated fibrillar microstructures, similar to those observed in 30 wt % cast aerogel analogues. Despite these microstructural differences, all printed aerogels demonstrated densities, porosities, and crystallinities similar to their cast aerogel counterparts. However, printed aerogel mechanical properties were microstructurally-dependent, and the spherulitic 50 wt % aerogels were much more brittle compared to the fibrillar cast 50 wt % analogues. This work introduces a widely-applicable framework for printing polymer aerogels using MEX and TIPS. Intrigued by the compositional morphological dependence of the printed PPS aerogels, the dissolution temperature (Tdis), and thus the self-nuclei content, of cast PPS/DPA solutions was systematically varied to understand its influence on aerogel morphology and properties. As Tdis increased, the length and diameter of axialites increased while aerogel density and porosity were relatively unaffected. Thus, the isolated influence of axialite dimensions (analogous to pore size and pore concentration) on aerogel properties could be studied independent of density. At low relative densities (below 0.3, aerogels of 10 – 30 wt %), compressive modulus and offset yield strength tended to decrease with Tdis, due to an increase in axialite length (akin to pore size) and number of axialites (akin to number of pores). At higher relative densities (above 0.3, 40 and 50 wt %), axialitic aerogels were so dense that changes in pore dimensions did not result in systematic changes in mechanical response. All spherulitic aerogels fabricated at the highest Tdis¬ demonstrated reduced mechanical properties due to poor interspherulitic connectivity. The thermal conductivity of all aerogels increased with polymer composition but demonstrated no clear trend with Tdis. A model for thermal conductivity was used to deconvolute calculated conductivity into solid, gaseous, and radiative components to help rationalize the measured conductivity data. This work demonstrates the importance of nucleation density control in TIPS aerogel fabrication, especially at low polymer concentrations. The specific method used to dry an aerogel generally has a great influence on its microstructure and density. Vacuum or ambient drying is the most industrially-attractive technique due to low cost and low energy usage; however, it is typically the most destructive process due to high capillary forces acting on the delicate aerogel microstructure. Three drying methods, vacuum drying, freeze drying, and supercritical CO2 drying, were used to evacuate PPS gels fabricated at three PPS concentrations (10, 15, and 20 wt %). Almost all aerogel specimens displayed excellent resilience against shrinkage as a function of the drying method, besides the 10 wt % vacuum dried sample which shrunk almost 40%. While the micron-scale aerogel morphology captured by electron microscopy appeared to be unaffected by the drying method, other properties such as aerogel surface area, mesoporous volume, and mechanical properties were effectively functions of the degree of aerogel shrinkage. Aerogel thermal conductivity was low for all samples, and in particular, vacuum dried aerogels demonstrated slightly lower conductivities than other ambiently-dried aerogel systems such as silica and carbon. In general, vacuum drying appears to be industrially viable for PPS aerogels at concentrations above 10 wt %. / Doctor of Philosophy / Polymer aerogels are nanoporous solid networks of low density. These materials are used in applications such as thermal insulation, absorbance/filtration, drug delivery, biomedical scaffolds, solid state batteries, and others. One method of creating polymeric aerogels is through thermally induced phase separation (TIPS), where a polymer is first dissolved in a high boiling point solvent at a high temperature. Next, the solution is cooled, inducing phase separation and gelation. Extraction of the gelation solvent transforms the solvated gel into an aerogel. To create polymeric aerogels with good properties and wide-ranging applicability, one should use a high-performance polymer. In this work, aerogels are for the first time made from poly(phenylene sulfide) (PPS), an engineering thermoplastic with good mechanical properties, thermal stability, and chemical resistance. PPS aerogels are fabricated using TIPS over a wide compositional range, and their microstructures, physical properties, thermal properties, and compressive properties are fully characterized. To further enhance aerogel performance, the fabrication process can be optimized to precisely control the aerogel morphology and thus the resulting properties. The influence of processing variables such as the polymer concentration, the post-fabrication aerogel annealing conditions, the method of manufacturing (traditional casting versus additive manufacturing), the dissolution temperature (temperature at which the polymer dissolves in solution prior to gelation), and the drying method on the aerogel behavior is investigated. Generally, results suggest that understanding critical process-morphology-property relationships allows for precise control over the nature of PPS aerogels.

Axionartige Teilchen sind pseudoscalare Teilchen welche in Theorien jenseits des Standardmodells vorhergesagt werden. Falls ein axionartiges Teilchen innerhalb eines kosmischen magnetischen Felds gebildet wird, wird dieses nicht durch das Hintergrundlicht absorbiert. Daher kann es kosmische Distanzen überbrücken bevor es wieder in ein Photon zurück oszilliert. Dieser Effekt erhöht die Reichweite der Gammastrahlung im Universum. Im Rahmen dieser Dissertation werden Daten des Fermi Large Area Telescopes, aufgenommen über eine Zeitraum von sechs Jahren, systematisch analysiert. Hierbei wird nach axionartigen Teilchen mit Hilfe von Transparenzeffekten des Universums gesucht. In diesem Zusammenhang werden verschiedene Modelle des extragalaktischen Hintergrundlichts mit und ohne Berücksichtigung axionartiger Teilchen verglichen. Hierfür werden Likelihood-Funktionen für das höchst energetische Photon verschiedener entfernter Quelle kombiniert. Diese sind aktive galaktische Kerne mit einer Rotverschiebung z ≥0.1 des Second Catalog of Hard Fermi-LAT Sources. Unter den Annahmen einer intergalaktischen magnetischen Feldstärke von B = 1 nG und einer Kohärenzlänge von s = 1 Mpc wurde keine Veränderungen der Transparenz durch axionähnliche Teilchen nachgewiesen. Für eine Masse eines axionartigen Teilchens mit m≅ 3.0 neV wird eine Photonen-Axion Kopplungskonstante über 10(^11) GeV(^−1) ausgeschlossen. / Axion-like particles, pseudo-scalar particles that arise in theories beyond the Standard Model, mix with photons in the presence of magnetic fields. If an axion-like particle is produced within a cosmic magnetic field, it evades extragalactic background light absorption and thus it can survive cosmological distances until oscillating back into a photon. This leads to an increased transparency of the Universe to gamma rays. In the scope of this thesis, we search for transparency effects compatible with the existence of axion-like particles with six years of data from the Fermi Large Area Telescope. We derive and combine the likelihoods of the highest-energy photon events from a sample of hard distant sources, in order to compare models that include axion-like particles and models with only extragalactic background light. The sources are active galactic nuclei from the Second Catalog of Hard Fermi sources at redshift z≥0.1. For values of the intergalactic magnetic field strength B = 1 nG and coherence length s = 1 Mpc, we find no evidence for a modified transparency induced by axion-like particles and therefore we set upper limits. We exclude photon-axion coupling constants above 10(^11) GeV(^−1) for axion masses m≅ 3.0 neV.