Physics and Astronomy Electronic Theses and Dissertations (UMKC)
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The items in this collection are the theses and dissertations written by students of the Department of Physics and Astronomy. Some items may be viewed only by members of the University of Missouri System and/or University of Missouri-Kansas City. Click on one of the browse buttons above for a complete listing of the works.
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Item Ultra wideband pulse propagation in dispersive biological tissue : a computational, statistical and experimental study(2025) Drake, Doug Robert; Hassan, Ahmed M.; Caruso, Anthony N.The performance of implantable devices in biological media requires consistent coupling between the antenna and the surrounding environment. Electromagnetic losses in biological tissues can degrade antenna performance. This performance loss compounds within biological material due to reflections and dispersions caused by the high variations in dielectric properties from host to host. Variation could be caused by multiple molecular-level interactions that are expressed at the macro level through variations in the complex relative dielectric permittivities of biological tissues. Different concentrations of conducting ions or water content in the tissue could lead to large variations in conductivity and permittivity across tissues. To quantify the effects of these variations in dielectric tissue properties, multiple simulations are performed in which the dielectric properties of tissues are varied ±25% to approximate these molecular changes on the macro scale. These results are compiled into a meta-model using Polynomial Chaos Expansion and Kriging methods to create a computationally efficient statistical model for examining the varying behavior. After examining this behavior, an implantable electric-field probe is calibrated to quantify how changes in the dielectric properties of biological tissue affect the propagation of ultra-wideband electromagnetic pulses. By shielding a monopole antenna with a dielectric sheath, the antenna can exhibit more consistent capacitive coupling to the environment, improving measurements of local electric-field effects in different media. The methods developed herein for calibrating this probe can be applied to implantable antennas to achieve more consistent performance across diverse environmental conditions.Item Investigating the evolution of red and blue quasars(2025) Cionitti, Rachel; McIntosh, Daniel H.We investigate the host galaxy and central supermassive black hole (SMBH) accretion properties of a sample of 218 red and blue broadline quasars (AGN with Lₓ > 10⁴⁴ erg/s) to test the predictions of the major merger-driven evolutionary model. Using rich multiwavelength data, we analyze differences in bolometric luminosity, specific star formation rate (sSFR), black hole mass, and their mutual relationships across the two populations. We find no statistically significant differences between red and blue quasars in any of these key parameters. Both populations exhibit similar distributions in accretion power, lie predominantly on the star-forming main sequence, and deviate similarly from the local Mʙʜ-M⁎ relation, suggesting concurrent rather than sequential growth of black holes and stellar mass. These findings challenge the view that red quasars represent a younger, dust-obscured, and more active phase of quasar evolution. Instead, the similarities between red and blue quasars suggest they are likely drawn from the same population, with no clear evidence of a transition in star formation or accretion behavior. Our results are consistent with emerging models of "backward growth,'' where black hole growth precedes that of the stellar component. Further observations, especially in the radio and submillimeter regimes, will be crucial to understanding feedback mechanisms and the broader evolutionary context of luminous quasars.Item Shocks & fronts in the merging x-ray bright cluster Abell 2219(2025) Huber, Joe (Graduate student in physics); Rulis, Paul Michael, 1976-We present a deep 470 ks Chandra observation of Abell 2219, a very hot and X-ray luminous cluster experiencing a major merger event. Abell 2219, at a redshift of z = 0.225, is only the second galaxy cluster merger where both the forward and reverse shock fronts are identified with X-ray temperature and density measurements (Russell et al., 2012, the other is Abell 2146) and one of only a handful with any shock fronts unambiguously detected as both temperature and density discontinuities. The reason for this rarity is the requirement of a near plane-of-sky merger, to mitigate the effects of projection, and also the inherently low X-ray surface brightness of shocked regions in the outskirts of clusters. Nonetheless, these sharp discontinuities, along with cluster cold fronts, have the potential to illuminate the micro-scale transport processes occurring in the hot intracluster medium. Abell 2219 is also one of the hottest and most X-ray luminous galaxy clusters known, with a system temperature of 12 keV, and unusually, a hot yet dense core, suggesting evidence for ongoing shock activity at the core. It hosts a bright radio halo and three strong radio galaxies. Previous Chandra observations have revealed this system is in the early throes of a violent merger. In this work we present the development of data reduction and analysis pipelines to process our high spatial-resolution, deeper X-ray data, allowing us to confirm the presence of of both shocks and cold fronts within the cluster merger.Item Electronic band structure variations in photothermal catalytic materials(2025) Vanderslice, Jennifer Kylie; Rulis, Paul Michael, 1976-Novel photothermal catalytic devices based on layered semiconductors have great promise as efficient overall water splitting devices for hydrogen production, which can help make H2 into an economically viable alternative to fossil fuels. The effectiveness of the proposed device is sensitively influenced by both the electronic structure of the materials and their interfaces. Yet, the electronic band structure of many of these materials under thermal expansion is under explored. In this study we calculate the electronic structures of a select group of sulfide semiconductors and their lattice thermal expansions, focusing on key parameters such as their band gaps, valence band edges, and conduction band edges. The materials (CoS₂, CoAsS, FeS₂) were selected for their simple structures, lower electron numbers and increasing band gaps compared to each other. By calculating band structures along a universal high-symmetry path in k-space, we can compare how temperature induced asymmetric lattice changes impact the electronic properties of the different materials and the overall stability of the proposed photothermal catalytic device. These insights help identify what materials can function reliably at higher temperatures without compromising charge separation or light absorption, two important factors in water splitting performance. This approach provides valuable insights into optimizing materials for efficient photothermal catalytic devices and guides future designs for water splitting applications.Item Quenching mechanisms in recently quenched elliptical galaxies: insights from neutral hydrogen studies and environmental analysis(2025) Deo, Deepak Kumar; Rulis, Paul Michael, 1976-; Schlein, CandaceRecently Quenched Elliptical galaxies (RQEs) represent a critical phase in the transition from star-forming to quiescent galaxies. However, the mechanisms driving their quenching remain elusive. We conduct a multi-wavelength analysis of 695 RQEs, along with their precursors (preRQEs) and descendants (postRQEs), focusing on their neutral hydrogen (HI) content and star formation properties. Contrary to conventional quenching models emphasizing gas depletion, RQEs retain substantial HI reservoirs (fgas ≥ 17%), suggesting that quenching is not primarily driven by gas exhaustion. We identify a critical halo mass threshold at log(Mhalo) = 12.1 M⊙, delineating different evolutionary pathways for RQEs. This threshold aligns with the transition from cold-mode to hot-mode gas accretion in theoretical models. RQEs in lower-mass halos (log Mhalo < 12.1M⊙) likely experience rapid quenching, possibly initiated by major mergers, followed by brief AGN activity and sustained LINER emission. We propose two evolutionary pathways: (a) rapid quenching via major mergers followed by AGN/LINER activity and passive evolution, and (b) rapid quenching followed by rejuvenation through minor mergers before evolving into more massive, long-term quenched ellipticals. These results challenge the conventional understanding of galaxy quenching, especially in low-density environments where RQEs typically reside. Our findings suggest that while RQEs may follow a rapid quenching pathway, their evolution is influenced by interactions between gas accretion modes, feedback mechanisms, and environmental factors. Future observations with advanced radio interferometers like SKA will be crucial for elucidating the quenching mechanisms in RQEs and their role in galaxy evolution.