2022 MU Dissertations - Freely available online
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Item Sustaining Open Educational Resources (OER) initiatives in higher education: practices, successes, and challenges(University of Missouri--Columbia, 2022) Seo, Grace Zhou; Bossaller, JennyINTRODUCTION: For the past decade, many educational institutions have launched initiatives to provide services and funding for professors to adopt, adapt, and create OER for enhancing student success. The initiatives could initially encourage faculty to use OER in their courses, but the continued effort to sustain proved difficult. GOAL: The research goal is to explore how higher education institutions sustain OER initiatives by examining the experiences and perspectives of the key players: faculty, administrators, librarians, and instructional designers who work on the front line of OER initiatives as OER users, educators, and advocates. METHODS: Exploratory two-case studies with qualitative methods including interviews, focus groups, and documents. FINDINGS: The findings indicate that student success, people's ideology, and interest in OER are the driving forces behind OER initiatives. A combination of efforts was needed from grassroots and top-down to sustain the initiatives. Successful practices include a combination of institutional incentives and support, connecting key players, and implementing faculty outreach strategies. Themes are also identified for successes and challenges of sustaining initiatives. Successes include: (1) reducing costs for students; (2) helping faculty rethink courses and seek new ways of teaching; and (3) providing faculty freedom to customize for teaching as they desire. Challenges include: (1) experiencing difficulty in getting faculty on board; (2) needing a master database to increase OER discoverability; and (3) experiencing personnel turnover.Item An investigation of the single-molecule biophysics of membrane systems with atomic force microscopy(University of Missouri--Columbia, 2022) Schaefer, Katherine G.; King, Gavin M.Cell membranes define the boundary of the fundamental unit of all organisms. They maintain the biochemical gradients of the cell and are carefully regulated by various membrane proteins and factors. Understanding of these components and their mechanisms is a broad and multiphasic field of biophysical investigation, both for fundamental research and for potential therapeutic benefit. While bulk assays provide insight into overall behavior, single-molecule methods probe the underlying complexities of these systems. The atomic force microscope (AFM) is a powerful tool which can directly visualize active biomolecules on a surface in physiological buffer and temperature. It is capable of high spatial (approx 1 Ã… vertical; approx 10 Ã… lateral) and temporal resolution (approx 100 ms), and is thus poised for critical single-molecule research. This dissertation utilizes the AFM for two membrane-related studies, namely, understanding the mechanisms underlying i) P-glycoprotein (Pgp) mediated efflux which causes multi-drug resistance in cancer cells and ii) membrane remodeling induced by fungal peptide toxin candidalysin (CL). Pgp is an ABC transporter overexpressed in cancer cells that non-selectively binds and effluxes drugs from the cytosol, leading to multi-drug resistance. Crucial to inhibiting this effect and developing cancer therapies is an in-depth examination of the structure-function relationship of this protein. Pgp reconstituted into lipid bilayers is imaged using AFM in the absence and presence of multiple ligands. To identify specific conformations along the hydrolysis cycle, ATP analogs are used; for substrate-bound conditions, Pgp is imaged in the presence of chemotherapeutic drugs. We show that Pgp has a wide range of conformational flexibility, and characterize shifts in states populated by the protein. Kymographs reveal the dynamics of individual cytosolic side features with high temporal resolution. Precision particle detection and statistical analysis techniques differentiate conformational states in both images and kymographs. Novel ATP activity measurements tracking the release of inorganic phosphate product confirm that the protein remains active on a surface. Taken together, the data provide insight into a pharmaceutically relevant membrane protein in near-native conditions. Human fungal pathogen Candida albicans secretes CL as a virulence factor which forms pores in epithelial cells, triggering uncontrollable Ca2+ influx and a cascade of immune responses. AFM studies reveal a pore-assembly process by which the peptide oligomerizes into a fundamental subunit, which then polymerizes into linear arrangements. These linear features close, forming loops which are proposed to insert into the membrane and are a critical structure component of the pore. Pore development progresses in stages, from initial depressions in the membrane to pores ringed in positive punctate features, called rims. Sequential imaging gives evidence that this transition may stabilize the pore. Site-specific mutagenesis identifies a loss-of-function mutant which fails to permeabilize membranes. AFM imaging reveals that the mutant does not polymerize or form pores. A gain-of-function mutant with enhanced loop formation showed increased membrane damage over the wild-type, supporting our theory that the loops are involved in perforation. These investigations integrated several biophysical techniques in addition to single-molecule AFM and represent a collaborative effort which unveiled a novel pore-forming mechanism and a possible therapeutic target.Item Unveiling glial pathways involved in neuronal communication(University of Missouri--Columbia, 2022) Rivera, Carlos; Zhang, BingGlia have been understudied throughout time largely because of a lack of basic understanding. Early experiments showing that glia do not respond with action potentials after an electrical stimulation, like their neuronal counterparts did, greatly reduced the scope for studying glia. Now, we understand glia enough to know they respond to neurons and can influence their firing patterns. There is a lot of controversy in the details behind how glia influence neuronal activity, some groups have evidence for glio-transmission, while other groups have evidence against glio-transmission. The major discrepancies between these two hypotheses come from the use of improper controls. A stronger comprehension of basic glio-biology should reduce our ignorance and allow us to better address the questions. Neither group denies glia's ability to modulate neuronal activity, so there still exists a niche for greater genetic understanding of how glia communicate with neurons. The Drosophila model organism is an excellent model for gaining genetic insight onto basic glio-biology. The overall goal of this dissertation was to identify glial genes which modify neuronal activity. To accomplish this, I took advantage of the TRPA1-induced paralysis behavior and the genetic prowess of Drosophila forward genetic modifier screens to identify glial genes that modify neuronal activity. Then I conducted secondary genetic screens to identify glial subsets which utilized the candidate genes identified from the first screen. Chapter 1 lays out the general background information built on which I conducted my dissertation research. In chapter 2, I delve into specific modifiers I identified using the forward genetic screen. I find evidence that glia utilize transporters and a calcium- and SNARE-dependent mechanism to alter neuronal activity. We rationalized that despite artificial glial activation through ectopic TRPA1 expression, our data provide supporting evidence for glio-transmission. In chapter 3, I delve into the genetic complexities observed including gender differences and the broad category of genetic modifiers tested. I found strong gender differences male and female flies particularly when the modifiers were SNARE- or ion-related, and a unique biphasic temperature-dependent response in the paralysis behavior. In addition, we found evidence for gap junction modulation of the TRPA1-induced paralysis behavior. From the secondary screen, I identified the ensheathing glial subset driver NP6520-GAL4 phenocopied our results from primary screen which utilized Repo-GAL4, concluding that this subset forms tripartite synapses with a glutamate-inhibitory neuron synapse. Lastly, chapter 4 finishes up with conclusions and sets up hypotheses to be tested in the future. Overall, further glial studies are needed to fully elucidate glial interactions with neurons.Item Magnetic charge correlation and quantum disorder in honeycomb spin ice systems(University of Missouri--Columbia, 2022) Yumnam, George; Singh, Deepak K.The artificial spin ice system consists of islands comprised of nanomagnets arranged in desired lattice structures, including squares, triangles, and honeycombs. These nanomagnets can also be arranged in an aperiodic lattice structure in some cases. These systems are artificial imitation of naturally ubiquitous systems such as geometric frustration which often lead to novel magnetic phases and its phase transitions. The research in artificial spin ice systems have made it possible to explore properties that have been mostly studied in the bulk systems such as pyrochlore spin-ice crystals. Theoretically it has been predicted that magnetic honeycomb lattice manifest depth-tunable magnetic phase transition based on the temperature of the system. The vertex of the honeycomb can have four unique configurations whose arrangements over the lattice would determine the magnetic phase of the system. At high temperature, honeycomb spin ice has been predicted to exhibit paramagnetic gas state, which upon cooling exhibits a phase transition to spin-ice, charge order, and magnetic vortex spin-solid state, respectively. The state-of-the-art method for developing an artificial spin ice in the laboratory is via lithography techniques which usually renders micrometer size elements. This inhibits the study of temperature dependent phase transitions in these micrometer-size elements as it leads to a large inter-elemental energy in the order of approx 10^5 K. However, it is the aim of this thesis to explore a new technique of preparing magnetic honeycomb lattice with nanome ter size elements by utilizing diblock-copolymer of polystyrene and poly-4-vinyl-bpyridine (PS-P4VP) template and physical vapor deposition of magnetic Permalloy in oblique geometry. The resulting magnetic honeycomb elements have a length of approx 10-12 nm and 5 nm width and a variable thickness, which give rise to a very small inter-elemental energy of approx 10 K, hence making this system tunable based on the system temperature. In this thesis, we have used these nanoscale artificial magnetic honeycomb lattice to explore various novel magnetic phases and their temperature dependent properties using a combination of electrical and magnetic measurements along with neutron scattering techniques such as polarized neutron reflectivity and neutron spin echo spectroscopy. We have discovered the existence of a massively degenerate quantum disordered state in these magnetic honeycomb lattice as a result of frustrations arising from competing nearest neighbor and next neighbor exchange interactions by using polarized neutron reflectivity. By using neutron spin echo technique, we have also estimated the magnetic charge relaxation and its transport properties. Furthermore, we also discovered key underlying mechanisms of a magnetic diode in these magnetic honeycomb lattices by using neutron reflectivity, micromagnetic simulations and distorted wave born approximations (DWBA).We showed that the magnetic honeycomb lattice undergoes a fractional transformation of magnetic charge ordering which gives rise to the magnetic diode behavior via neutron reflectometry and DWBA simulations. We also highlight two complementary studies based on neutron scattering of bulk materials namely: CeAuSb2 and CoAsSe. In both the cases, we have used elastic and inelastic neutron scattering to study the magnetic structure and its order parameters. These studies are supported by first principles calculations based on the density functional theory.Item Oxidative molecular layer deposition of redox-active thin-film polymers(University of Missouri--Columbia, 2022) Wyatt, Quinton K.; Young, Matthias J.Thin film materials research for a more sustainable future is growing rapidly and new techniques for depositing these films are beginning to surface. One such technique is highlight in this body of work using gaseous precursors to grow bottom-up molecularly controlled polymers, Oxidative molecular layer deposition (oMLD). oMLD promises to enable molecular-level control of polymer structure through monomer-by-monomer growth via sequential, self-limiting, gas-phase surface reactions of monomer(s) and oxidant(s). However, only a few oMLD growth chemistry's have been demonstrated to date and limited mechanistic understanding is impairing progress in this field. Here, we establish key insights into the surface reaction mechanisms underlying oMLD growth. We identify the importance of a two-electron chemical oxidant with sufficient oxidation strength to oxidize both a surface and a gas-phase monomer to enable oMLD growth. The mechanistic insights we report will support rational molecular assembly of co-polymer structures to starkly improve the electrochemical capacity. This work is foundational to unlock molecular-level control of redox-active polymer structure and will enable the study of previously intractable questions regarding the molecular origins of polymer properties, allowing us to control and optimize polymer properties for energy storage, water desalination, and sensors.