Doctoral Dissertations

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https://hdl.handle.net/10919/11041

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Teaching Robots using Interactive Imitation Learning
Jonnavittula, Ananth (Virginia Tech, 2024-06-28)
As robots transition from controlled environments, such as industrial settings, to more dynamic and unpredictable real-world applications, the need for adaptable and robust learning methods becomes paramount. In this dissertation we develop Interactive Imitation Learning (IIL) based methods that allow robots to learn from imperfect demonstrations. We achieve this by incorporating human factors such as the quality of their demonstrations and the level of effort they are willing to invest in teaching the robot. Our research is structured around three key contributions. First, we examine scenarios where robots have access to high-quality human demonstrations and abundant corrective feedback. In this setup, we introduce an algorithm called SARI (Shared Autonomy across Repeated Interactions), that leverages repeated human-robot interactions to learn from humans. Through extensive simulations and real-world experiments, we demonstrate that SARI significantly enhances the robot's ability to perform complex tasks by iteratively improving its understanding and responses based on human feedback. Second, we explore scenarios where human demonstrations are suboptimal and no additional corrective feedback is provided. This approach acknowledges the inherent imperfections in human teaching and aims to develop robots that can learn effectively under such conditions. We accomplish this by allowing the robot to adopt a risk-averse strategy that underestimates the human's abilities. This method is particularly valuable in household environments where users may not have the expertise or patience to provide perfect demonstrations. Finally, we address the challenge of learning from a single video demonstration. This is particularly relevant for enabling robots to learn tasks without extensive human involvement. We present VIEW (Visual Imitation lEarning with Waypoints), a method that focuses on extracting critical waypoints from video demonstrations. By identifying key positions and movements, VIEW allows robots to efficiently replicate tasks with minimal training data. Our experiments show that VIEW can significantly reduce both the number of trials required and the time needed for the robot to learn new tasks. The findings from this research highlight the importance of incorporating advanced learning algorithms and interactive methods to enhance the robot's ability to operate autonomously in diverse environments. By addressing the variability in human teaching and leveraging innovative learning strategies, this dissertation contributes to the development of more adaptable, efficient, and user-friendly robotic systems.
Host-pathogen interactions and conservation implications of snake fungal disease over broad geographical scales
Blanvillain, Gaelle Jh (Virginia Tech, 2024-06-27)
Emerging infectious diseases represent a threat to biodiversity, posing significant challenges to wildlife conservation globally. Infectious diseases can cause population declines, local extirpations and, in rare cases, complete species extinction. Among emerging pathogens, pathogenic fungi have been responsible for drastic declines in several high-profile vertebrate taxa, such as Batrachochytrium dendrobatidis causing chytridiomycosis in many species of amphibians worldwide. Recently, an emerging infectious disease, 'snake fungal disease' (SFD), caused by the fungal pathogen Ophidiomyces ophidiicola, is affecting the health of snake populations in North America by causing skin infections which can be fatal. Given the potential impact of this disease on snake biodiversity worldwide, compounded by the pressure of anthropogenic stressors that already jeopardize the viability of many snake populations, there is a clear need for ecological research in this understudied system. This dissertation is comprised of 4 data chapters focusing on the disease dynamics of snake fungal disease in Europe, and the factors resulting in differential infection. In chapter 2, I develop a large field-based data collection in 10 countries in Europe to investigate the presence of disease hotspots and the variation of disease prevalence across host species, and to examine the pathogen genotypes that are present on the landscape. I found isolated areas of disease hotspots, and models including an interactive effect of host species and which pathogen clade are present on the landscape were best at explaining disease prevalence. In chapter 3, I perform a virulence challenge assay using 120 corn snakes (Pantherophis guttatus) and 7 strains of O. ophidiicola (3 collected from Europe, 4 from the USA). This experiment reveals that pathogen genotypes associated with higher disease prevalence in Europe also have higher pathogen virulence, and that different strains from the USA show variation in virulence. These results also match both physiological host responses measured in the lab and landscape patterns of disease. In chapter 4, I explore two mitigation-driven snake translocation projects in Europe that were complicated due to O. ophidiicola outbreaks. One snake species, N. tessellata, appears highly susceptible to SFD, indicating that under stressful conditions, O. ophidiicola can cause mortality regardless of pathogen genotype, and that this snake species may be important in pathogen maintenance. Finally in chapter 5, I report the presence of a different fungal pathogen in Spain, Parannannizziopsis sp., never reported in wild snakes in Europe before. Broadly, my dissertation demonstrates coevolutionary relationships between hosts and pathogens and has important implications to snake conservation over large scales.
Perceptions of Technology/Engineering Education Influence on Integrated STEM Teaching and Learning
Greene, Clark Wayland (Virginia Tech, 2024-06-27)
The dynamics of successfully integrating science, technology/engineering and math content, practice, and delivery in K-12 education is still evolving. "A number of questions remain about the best methods by which to effectively teach engineering at the K-12 level and how they play into the integration of other STEM disciplines" (Moore, Glancy, Tank, Kersten, Smith, and Stohlmann, 2014). The International Technology and Engineering Educators Association (ITEEA) has declared that technology and engineering within STEM education as delivered by the technology education content area is defined by the Standards for Technological Literacy™ (ITEEA, 2000). Lack of applied technology/engineering pedagogical content knowledge via technology teacher collaboration may be excluding valuable contributions to more effective STEM teaching and learning. Absence of developed and identified perceptions resulting from such collaborations could be an impediment to application of valuable technology/engineering practices, beliefs, content, and structure within integrated STEM instruction. Collaboration inclusive of all STEM subject teachers is critical to effective practice and delivery of integrated STEM teaching. To achieve this, integrated STEM experiences need "to be researched and evaluated to build knowledge and understanding about the effectiveness of these experiences in promoting STEM learning and engagement within and across disciplines." (Honey et al., 2014). The purpose of this study was to examine and identify science, math, and technology education teacher perceptions of technology/engineering education influence within existing STEM collaborations. The objective was to provide useful information pertinent to further improving STEM education practice and effectiveness. A three round, mixed method, Delphi approach was employed to determine common perceptions among all STEM teachers included in this study. Consensus among study participants identified strategies specific to technology/engineering education that were perceived to positively impact STEM education. The results of this study illustrate that content, practice, and pedagogical attributes specific to technology education do exist and that those attributes are perceived to enhance student learning of STEM content and practice. Synthesized from initial qualitative responses in Round One, of the 28 presented technology/engineering strategies, 24 achieved consensus as determined by an applied two factor threshold of a 7.5 median agreement score and interquartile rating of 2.0 or less from among all participants. In a comparison of represented STEM subjects taught, there also appeared significant agreement among all groups. The level of agreement between science and the other groups was weakest, although still sizeable. Engineering design knowledge, skilled use of tools and materials to produce models and prototypes, promotion of designerly critical thinking and problem-solving skills, and both tacit and contextual knowledge of technology and engineering applications were found to be general themes specific to technology/engineering education teachers.
Effect of Interstitial Fluid Flow and Radiotherapy on Glioblastoma Invasiveness and Progression
Atay, Naciye Nur (Virginia Tech, 2024-06-27)
Glioblastoma (GBM) is the most aggressive and malignant glioma. It accounts for 48.6% of all primary, malignant gliomas with a median survival of 15 months. Infiltration into the surrounding parenchyma is a hallmark of GBM. Radiotherapy is used to address the invasion; however, recent studies have implicated that radiation contributes to increased invasiveness of glioma. Although the effect of radiation on cells has been studied extensively, its effect on the transport of fluid is not well characterized. Transport in the brain which has significant roles in physiology, GBM pathophysiology, and GBM treatment. Thus, understanding the effect of radiation on transport within the lesion and surrounding interstitium will be beneficial in characterizing the effects of radiotherapy in GBM patients. This dissertation seeks to explore the relationship between radiation, transport, and movement of glioma cells and includes the following: 1) Characterizing in vitro motility metrics of glioma stem cell lines in and relating them to in vivo invasion. 2) Studying the effect of radiation on motility, flow-mediated invasion, extracellular matrix components, and transport within the lesion and interstitium. 3) Assessing transport in clinical images and relating transport parameters to progression of GBM. 4) Developing a novel pipeline for applying vector field topology to the study of interstitial fluid flow in glioma. Surprisingly, we found that motility metrics in vitro have a negative correlation trend with in vivo invasion. Next, we found that radiation causes a transient increase in advective flow, and a more sustained decrease in diffusivity in a murine glioma model. Tenascin C was found to correlate significantly with invasion and diffusivity, indicating that it might be a link between radiation, transport, and invasion. Furthermore, interstitial fluid flow was calculated and assessed in clinical images. This showed that interstitial fluid flow velocity magnitude in the tumor correlates with overall survival in GBM patients. Lastly, vector field topology was introduced as a novel method of studying transport that provides more detailed information to identify potential drivers of transport within a flow field. Altogether, this work presents novel insight into the effects of radiation on invasion and transport in GBM. Hopefully, this work can provide a foundation to build upon in efforts of improving treatment planning and clinical outcomes for GBM patients.
Inhibition, Synapses, and Spike-Timing: Identification and disruption of pyramidal cell-interneuron interactions in SPW-Rs.
Gilbert, Earl Thomas (Virginia Tech, 2024-06-25)
The neural circuitry responsible for memory consists of complex components with dynamic interactions. In hippocampal area CA1, interactions between excitatory pyramidal cells and inhibitory interneurons shape ensemble activity which encodes sequential experience. An extremely diverse set of inhibitory interneurons, with variation in gene expression, synaptic targeting, state-dependent activity, and connectivity, contribute substantially to circuit activity, such as theta and sharp wave-ripple oscillations. The precise roles of each interneuron group is not well understood, though characterization of their activity reveals mechanisms underlying hippocampal circuit computation. In this dissertation, I aim to identify and disrupt interactions between pyramidal cells and local interneurons to clarify their role in shaping cell assembly activity. We characterized axo-axonic cell activity in sharp wave-ripples, and compared their control of pyramidal cell activity and ripple events to parvalbumin expressing neurons. We identified pyramidal cell-interneuron interactions during ripples, suggesting they serve as lateral inhibitors between cell assemblies. We additionally developed and implemented a novel neural device to explore the role of cannabinoid disruption of hippocampal oscillations and organization of assemblies in vivo in awake animals. We demonstrate that cannabinoid receptor type 1 within CA1 is responsible for suppression of theta and SPW-Rs. We also found that cannabinoid activation within CA1 circuitry, regardless of muted input from CA3, was sufficient to disrupt sharp wave-ripples, likely through interference of pyramidal cell-interneuron interactions. The work in this dissertation provides insight suggesting that interneuron activity must be studied at the spiking timescale to characterize their control over cell assembly activity.
Dynamics and Electrostatics of Membrane Proteins using Polarizable Molecular Dynamics Simulations
Montgomery, Julia Mae (Virginia Tech, 2024-06-25)
Membrane proteins are critical to many biological processes, including molecular transport, signal transduction, and cellular interactions. Through the use of molecular dynamics (MD) simulations, we are able to model this environment at an atomistic scale. However, traditionally used nonpolarizable force fields (FF) are thought to model the unique dielectric gradient posed by the lipid environment with a limited accuracy due to the mean field approximation of charge. Advancements in polarizable FFs and computing efficiency has enabled the explicit modeling of polarization responses and charge distribution, enabling a deeper understanding of the electrostatics driving these processes. Through the use of the Drude FF, we study three specific model systems to understand where explicit polarization is important in describing membranes and membrane proteins. These studies sought to answer the questions: (1) How does explicit electronic polarization impact small molecule permeation and localization preference?, (2) What electrostatic interactions underlie membrane protein secondary structure?, and (3) How do conformational changes propagate between microswitches in G-Protein Coupled Receptors? In this work, we show small molecule dipole moments changing as a function of localization in the bilayer. Additionally, we show differences in the free energy surfaces of permeation for aromatic, polar, and negatively charged species reliant upon force field used. For secondary structure, we showed key interactions which aided to stabilize model helices in bilayers. Finally, we showed potential inductive effects of key microswitch residues underlying prototypical G-Protein coupled receptor activation. This dissertation has helped to show the importance of including explicit polarization in membrane protein systems, especially when considering interactions at the interface and modeling species with charge. This work enables a refined view of the electrostatics occurring in membranes and membrane protein systems, and in the future, can be used as a basis for methodologies in computer aided drug design efforts.
Designing Adaptive Ansätze in Quantum Simulation and Geometric Entangling Gates
Tang, Ho Lun (Virginia Tech, 2024-06-25)
Quantum Computation has attracted massive interest because of the recent technological advancement in both hardware and software suggesting the potential of quantum advantage. On the software side, hybrid classical-quantum algorithms are extensively studied as they can be implemented on the current noisy intermediate-scale quantum devices. On the hardware side, researchers are striving for faster and more noise-robustness quantum operations to achieve higher quantum processing power. The dissertation presents two topics in the above-mentioned aspects. The first one is constructing adaptive ans"atze for variational quantum eigensolver, one of the most promising hybrid algorithms. We present how to compress different required quantum resources by designing different ans"atze. The second topic is about designing fast entangling gates with a geometric approach. We show that the geometric approach can improve the existing numerical methods by locating the good initial guesses.
Having 'The Talk': Parents' Decision Making Related to Communication with Children about Sex
Murray, Michelle Marie (Virginia Tech, 2024-06-25)
Parent-child communication about sex is widely understood to be important to sexual health and wellness of adolescents and young adults. Though parents report wanting to communicate with their children comprehensively, adolescents often report this communication does not meet their needs. This study uses symbolic interactionism to explore how parents understand and make meaning of family communication about sex and how these meanings influence their decision making when it comes to family communication about sex. Eight couples participated in an observed development of plans to communicate with their children about sex and semi-structured dyadic interviews about their decision-making process. Transcriptions of the observational data and interviews were analyzed alongside the written plans developed during data collection using grounded theory methodology. Parents recognized communication with their children about sex to be an important opportunity to keep their children safe and prevent negative experiences while instilling values that will help children make healthy decisions. Rather than prescribing specific topics of conversation and times to communicate with them, parents focused on fostering strong relationships with their children and shared they would allow their kids to direct conversations. They identified clear goals for communication with their children about sex, but hoped to do things differently than their own parents by being open to questions their children bring up and addressing issues as they arise.
Exploring Antecedents to Environmentally-Consequential Consumer Choices and Behaviors
Stuebi, Richard Theodore (Virginia Tech, 2024-06-25)
This dissertation presents two essays that explore the antecedents of consumer decision-making when choices or behaviors have significant environmental consequences. The first essay involves theoretical development and experimental testing of a conceptual model describing the process by which a car-buyer evaluates the choice between an electric vehicle (EV) and a gasoline vehicle, while the second essay consists of empirical analysis of a large panel dataset of household-level 15-minute interval electricity consumption data to identify the drivers of different behavioral response patterns to electric utility requests for energy conservation on hot summer afternoons. The first essay is motivated by the observation that increased consumer adoption of battery-powered EVs is important for commercial and environmental reasons, but EV adoption is currently inhibited by both an up-front price disadvantage and the inconveniences associated with battery recharging. The research presented in the first essay leverages the Theory of Reasoned Action as well as the literature on identity signaling to develop a model on how consumers with interests in the environmental and/or technological implications of EV ownership evaluate the potential purchase of an EV versus a conventional automobile. The model generates ten pairs of hypotheses that are tested via estimation of a structural equation model using data from three online experiments. Bayesian pooling of the three sets of estimated path analysis coefficients finds considerable support for the conceptual model. These pooled results show that EV ownership signals the owner's concern about both environmental protection and technology advancement, but the effect of the environmental signal on EV purchase likelihood is positive whereas the effect of the technology signal on EV purchase likelihood is negative. Moreover, in addition to lowering EV purchase likelihood via a direct effect, the perceived inconveniences associated with EV ownership (e.g., needs for battery charging) offset the negative effect of technology signaling on EV purchase likelihood, while the corresponding interaction of inconvenience with environmental signaling value was found to be not significant. Meanwhile, a larger EV price premium had a direct negative effect on EV purchase likelihood but did not moderate the effects of either technology signaling value or environmental signaling value on EV purchase likelihood. Among other findings, specific knowledge about how EVs affect technological advancement has a direct positive influence on EV purchase likelihood. However, all downstream effects of specific knowledge about EVs effects on environmental protection are mediated by perceptions of EV effectiveness in benefitting the environment. Meanwhile, the second essay investigates consumer behavior concerning household electricity consumption. Utilities use demand response (DR) programs to induce customers to reduce electricity consumption during selected hot summer afternoons when power generation supplies may be challenged to satisfy regional demand levels. The research presented in the second essay leverages panel data on electricity consumption from households in a community where an experimental pro-social DR program was conducted to explore drivers of household responses to utility requests to voluntarily reduce electricity consumption. Analysis of the panel data shows that, on average, households with solar rooftops respond differently to utility DR notifications than non-solar households: solar households reduce electricity consumption as requested by the utility, whereas non-solar households receiving the same request actually increase electricity consumption. However, although solar households respond favorably to DR notification, they also consume significantly more electricity than non-solar households during most hours. These empirical results – greater responsiveness to DR notifications, but otherwise higher levels of electricity consumption – beg reconciliation and explanation. An experimental research study is proposed for a future examination of alternative psychological explanations for the observed differences in behavioral responses between solar and non-solar households.
Optimal Control Protocols for Quantum Memory Network Applications
Takou, Evangelia (Virginia Tech, 2024-06-25)
Quantum networks play an indispensable role in quantum information tasks such as secure communications, enhanced quantum sensing, and distributed computing. In recent years several platforms are being developed for such tasks, witnessing breakthrough technological advancement in terms of fabrication techniques, precise control methods, and information transfer. Among the most mature and promising platforms are color centers in solids. These systems provide an optically active electronic spin and long-lived nuclear spins for information storage. The first part of this dissertation is concerned with error mechanisms in the control of electronic and nuclear spins. First, I will focus on control protocols for improved electron-spin rotations tailored to specific color centers in diamond. I will then discuss how to manipulate the entanglement between the electron and the always-coupled nuclear spin register. I will describe a general formalism to quantify and control the generation of en- tanglement in an arbitrarily large nuclear spin register. This formalism incorporates exactly the dynamics with unwanted nuclei, and quantifies the performance of entangling gates in the presence of unwanted residual entanglement links. Using experimental parameters from a well-characterized multinuclear spin register, I will show that preparation of multipartite entanglement in a single-shot is possible, which drastically reduces the total gate time of conventional protocols. Then, I will present a new formalism for describing all-way entanglement and show how to design gates that prepare GHZM states. I will show how to incorporate errors such as unwanted correlations, electronic dephasing errors or pulse control errors. The second part of this thesis focuses on the preparation of all-photonic graph states from a few quantum emitters. I will introduce heuristic algorithms that exploit graph theory concepts in order to reduce the entangling gate counts, and also discuss the role of locally equivalent graphs in the optimization of the generation circuits.
DQ-Frame Small-Signal Stability Analysis of AC Systems with Single-Phase and Three-Phase Converters
Lin, Qing (Virginia Tech, 2024-06-21)
The widespread integration of power converters in applications such as microgrids and data centers has introduced significant stability challenges. This dissertation presents a novel approach to modeling and comprehensive stability analysis for both single-phase and three-phase converters, addressing vital gaps in the existing literature. The first part of the dissertation (Chapters 2 to 4) focuses on single-phase power supply units, proposing an impedance model and a loop gain model based on dq-frame analysis. These models have been validated through extensive experimental testing, demonstrating their effectiveness in stability analysis across a range of system configurations, including single-phase, three-phase three-wire, and three-phase four-wire systems. The second part (Chapters 5 and 6) examines three-phase converters used for integrating renewable energy into microgrids. It introduces a grid-forming control, followed by a detailed investigation into its impedance modeling and stability assessment. This part specifically tackles the challenges posed by the appearance of right-half-plane poles in stability analysis, proposing a new stability margin index to address these issues. The efficacy of these research findings is further substantiated by the development and implementation of a Power-Hardware-in-the-Loop testbed, providing practical validation. Overall, this dissertation has enhanced the modeling, understanding, and management of stability issues in power electronics systems, offering valuable insights and methodologies that are likely to influence future research and development in the field.
Three Essays in Experimental Economics
Bradley, Austin Edward (Virginia Tech, 2024-06-21)
The experiments presented and analyzed in this dissertation concern two well-established phenomena in behavioral economics: that human decision makers hold biased beliefs about probability and that free-form communication between economic agents promotes cooperation far in excess of what standard theory predicts. First, Chapter 2 studies subjective probability, focusing on the well-established existence of both the Hot Hand and Gambler's Fallacies — the false expectation of positive and negative autocorrelation, respectively. Both biases are prevalent throughout a wide variety of real-world contexts; what causes a person to favor one over the other? We conduct an experiment in which we observe fully informed subjects switching between the Hot Hand and Gambler's Fallacies when predicting future outcomes of mathematically identical sequences. Subjects exhibit the Gambler's Fallacy when predicting single outcomes but favor the Hot Hand when asked explicitly to estimate probabilities. Connecting our results to existing theory suggests that very subtle changes in framing lead decision makers to employ substantially different approaches to form predictions. The remainder of this dissertation studies cheap talk communication between human subjects playing incentivised trust games. In Chapter 3, we study free-form communication using a dataset of over 1000 messages sent between participants in a laboratory Trust game. We employ Natural Language Processing to systematically generate meaningful partitions of the messages space which we can then examine with established regression approaches. Our investigation reveals features correlated with trust that have not previously been considered. Most notably, highly detailed, specific promises establish trust more effectively than other messages which signal the same intended action. Additionally, we observe that the most and least trusted messages in our dataset differ starkly in their quality. Highly trusted messages are longer, more detailed, and contain fewer grammatical errors whereas the least trusted messages tend to be brief and prone to errors. In Chapter 4, we examine whether the difference is message quality affects trust by acting as a signal of effort. We report the results of an experiment designed to test whether promises which require higher levels of effort result in greater trust from their recipients. We find that more costly promises lead recipients to trust more frequently. However, there is no corresponding, significant difference in the trustworthiness of their senders. Further, when asked their beliefs explicitly, recipients do not believe that higher cost promises are more likely to be trustworthy. This presents a potential challenge to our understanding of trust between economic decision makers. If effort increases trust without altering receivers' beliefs, receivers must be concerned with factors other than their own payoff maximization. We conclude by presenting a follow-up experiment where varying effort cost cannot convey the sender's intentions, however, the results are inconclusive.
Perceptions of the Initial Steps a Planning Principal Takes to Open a New Plus One Elementary School
Dubiel, Karen Lee (Virginia Tech, 2024-06-21)
The purpose of this study was to identify the initial steps that a planning principal takes to open a new plus one elementary school. Too often, the focus is on the completion of the bricks and mortar of the facility instead of what takes place in the building once construction is complete (Lane, 2008). "Effective planning for the opening of a new school produces an environment in which teachers can teach and students can learn effectively and efficiently" (Lane, 2008, p. 2). Thus, the opening of a new plus one school requires a well-planned, detailed, organized approach for occupying the facility as the success or failure of the school opening process weighs heavily on the ability of the planning principal (Lane, 2008). New plus one schools are continuing to be built regularly within the United States to address student enrollment increases in existing schools with limited capacity, yet there is no set of instructions to guide a planning principal. With new school construction still needed to address increasing student enrollment in local school districts, the perceptions of the initial steps planning principals take to open a new plus one elementary school are valuable. This study involved interviewing four planning principals in the Mid-Atlantic region of the United States. Interview questions sought the actions that planning principals take to start a new plus one elementary school. All four planning principals indicated that they had no playbook or guide, were self-directed and initiated support when needed, and exercised a high level of autonomy with decision making, specifically with staffing, developing a school vision, and determining the school mascot and school colors. Implications for practitioners were identified including the need for a guide or handbook, a structure of support, and training or professional development. The outcome of the study provided opportunities for future planning principals to identify the key responsibilities, experiences, and guidance recommended for opening new plus one elementary schools.
Magnetohydrodynamic Simulations of Fast Instability Development in Pulsed-Power--Driven Explosions and Implosions of Electrical Conductors
Carrier, Matthew James (Virginia Tech, 2024-06-21)
Recent concepts for controlled magneto-inertial fusion (MIF), such as magnetized liner inertial fusion (MagLIF), have suffered from magnetohydrodynamic (MHD) instabilities that lead to degradations in fusion yield. High levels of azimuthally-correlated MHD instability structures have been observed on cylindrical liner experiments without a pre-imposed axial magnetic field (Bz=0) elsewhere in the literature and are believed to be seeded from surface machining roughness. This dissertation uses highly resolved (0.5 μm and less resolution) 1D and 2D resistive magnetohydrodynamics (MHD) arbitrary-Lagrangian-Eulerian (ALE) simulations of electrical wire explosions (EWEs) and liner implosions to show that micrometer-scale surface roughness seeds the electrothermal instability (ETI), which induces early melting in pockets across the conductor and leads to millimeter-scale instability growth. The relationship between the ETI and the MRTI in liner implosions is also described in this dissertation, which shows that the traditional growth rates associated with these modes are coupled together and are not linearly independent. This dissertation also describes the preliminary implementation of a Koopman neural network architecture for learning the nonlinear dynamics of a high energy density (HED) exploding or imploding electrical conductor.
Automated Detection and Analysis of Low Latitude Nightside Equatorial Plasma Bubbles
Adkins, Vincent James (Virginia Tech, 2024-06-21)
Equatorial plasma bubbles (EPBs) are large structures consisting of depleted plasma that generally form on the nightside of Earth's ionosphere along magnetic field lines in the upper thermosphere/ionosphere. While referred to as `bubbles', EPBs tend to be longer along magnetic latitudes and narrower along magnetic longitudes which are on the order of thousands and hundreds of kilometers, respectively. EPBs are a well documented occurrence with observations spanning many decades. As such, much is known about their general behavior, seasonal variation of occurrences, increasing/decreasing occurrences with increasing/decreasing solar activity, and their ability to interact and interfere with radio waves such as GPS. This dissertation expands on this understanding by focusing on the detection and tracking of EPBs in the upper thermosphere/ionosphere along equatorial to low latitudes. To do this, far ultraviolet (FUV) emission observations of the recombination of O$^+$ with electrons via the Global-Scale Observations of the Limb and Disk (GOLD) mission are analyzed. GOLD provides consistent data from geostationary orbit with the eastern region of the Americas, Atlantic, and western Africa. The optical data can be used to pick out gradients in brightness along the 135.6 nm wavelength which correlate with the location of EPBs in the nightside ionosphere. The dissertation provides a novel method to look at and analyze 2-dimensional data with inconsistent time-steps for EPB detection and tracking. During development, preprocessing of large scale (multiple years) data proved to be the largest time sync. To that end, this dissertation tests the possibility of using convolution neural networks for detection of EPBs with the end goal of reducing the amount of preprocessing necessary. Further, data from the Ionospheric Connection Explorer's (ICON's) ion velocity meter (IVM) are compared to EPBs detected via GOLD to understand how the ambient plasma around the EPBs behave. Along with the ambient plasma, zonal and meridional thermospheric winds observed by ICON's Michelson Interferometer for Global High-resolution Thermospheric Imaging (MIGHTI) instrument are analyzed in conjunction with the same EPBs to understand how winds coincident with EPBs behave. An analysis of winds before EPBs form is also done to observe the potential for both zonal and meridional winds' ability to suppress and amplify EPB formation.
(Mis)communicating postsecondary opportunities through diploma policies: A content analysis of Louisiana public high school websites
Adams, Venice Marie (Virginia Tech, 2024-06-21)
This study explored high school communication (i.e., policy translation) of Louisiana statutes pertaining to postsecondary opportunities aligned with the CTE graduation pathway and the implementation of curriculum tracks through high school track-shifting policies. Two research questions guided this study: 1) To what extent do diploma policies listed on high school websites in the Louisiana Acadiana region describe the actual postsecondary opportunities available to students in a CTE program? and 2) What information do high school websites reveal about curriculum track-shifting policies? To answer these questions, I conducted a manifest content analysis (Kleinheksel et al., 2020) of websites for 29 traditional public high schools operated by school districts in Louisiana's Acadiana region. My analysis was guided by a conceptual framework that included horizontal differentiation, track shifting, and misinformation (Rosenbaum, 1978; Sørensen, 1970). Two major themes emerged in the findings: Inconsistent and Incomplete Information about Postsecondary Options for CTE Diploma Pathway Students and Limited Flexibility (Semi-Closed) Curriculum System. These themes and their respective subthemes revealed that high school websites contained inconsistent and incomplete information about graduation pathways that constrains students' postsecondary options. Findings from this study offer implications for practice, policy and policy translation, and future research regarding high school diploma policies, curriculum tracks, track-shifting policies, and curriculum enrollment decisions. This study also offers recommendations for officials at the state level and school leaders at the local level.
Perceptions of Middle School Counselors on Adolescent Anxiety Coping Skills Post-Pandemic in One Suburban School Division
Tait, Kristin Marie (Virginia Tech, 2024-06-21)
Students and educators around the world faced many challenges when returning to the physical school building and environment after the disruption to our educational systems throughout the height of the COVID-19 pandemic. Educational leaders across the U.S. have expressed concerns over the substantially higher levels of anxiety and chronic absenteeism among adolescents. This study examined middle school adolescents' abilities to use coping skills for managing anxiety in the school environment post-pandemic. Qualitative data were collected from eight middle school counselors through one-on-one semi-structured interviews. Findings indicated an increase in the number of students presenting with symptoms of anxiety and the severity of symptoms. Middle school counselors noted an increase in school refusal and self-harm and indicated that the majority of their direct service time is spent with individual students. In order to better support students with managing anxiety, middle school counselors expressed the need for explicit coping skills instruction and additional mental health staffing in the school buildings.
Multifunctional Polymer Fiber Probes for Biomedical Application
Kim, Jongwoon (Virginia Tech, 2024-06-17)
Biomedical devices play a crucial role in the healthcare system, enabling more effective treatments, less invasive procedures, and more precise diagnoses. Due to these compelling reasons, development of new biomedical devices and biomaterials have always been in high demand. Exploring and refining fabrication methods are essential to the development of new biomedical devices. Some of the common fabrication methods include microfabrication methods (photolithography and soft lithography), 3D printing (additive manufacturing), laser machining, thermal drawing, and electrospinning. The choice of fabrication methods heavily depends on the materials, geometry, and functionalities of biomedical devices. Currently, the thermal drawing process has proven to be an excellent scalable fabrication platform for neural interface, tissue engineering, tumor/cancer treatment, soft robotics, and smart textiles. This Ph.D. dissertation summarizes my research on the fabrication and validation of thermally drawn multifunctional polymer fiber probes for modern biomedical applications, primarily in the fields of neural interfaces and tumor treatments. Understanding the neural basis of behavior requires monitoring and manipulating combinations of physiological elements and their interactions in behaving animals. Utilizing the thermal drawing process, we developed T-DOpE (Tapered Drug delivery, Optical stimulation, and Electrophysiology) probes and Tetro-DOpE (Tetrode-like Drug delivery, Optical stimulation, and Electrophysiology) probes that can simultaneously record and manipulate neural activity in behaving rodents. Taking advantage of the triple-functionality, we monitored local field potential (LFP) while manipulating cannabinoid receptors (CB1R; microfluidic agonist delivery) and CA1 neuronal activity using optogenetics. Focal infusion of CB1R agonist downregulated theta and sharp wave-ripple oscillations (SPW-Rs). Furthermore, we found that CB1R activation reduces sharp wave-ripples by impairing the innate SPW-R-generating ability of the CA1 circuit. Microscale electroporation devices are mostly restricted to in vitro experiments (i.e., microchannel and microcapillary). We developed a flexible microscale electroporation fiber probe through a thermal drawing process and femtosecond laser micromachining techniques. The novel fiber microprobes enable microscale electroporation and arbitrarily select the cell groups of interest to electroporate. Successful reversible and irreversible microscale electroporation was observed in a 3D collagen scaffold (seeded with U251 human glioma cells) using fluorescent staining. Leveraging the scalable thermal drawing process, we envision a wide distribution of multifunctional polymer fiber probes in research facilities and hospitals. Along with the fiber probes presented in this dissertation, additional insight and future perspective on thermally drawn biomedical devices are discussed.
Production Pressure in Complex Socio-Technical Systems: Analysis, Measurement, and Prediction
Hashemian, Seyed Mohammad (Virginia Tech, 2024-06-17)
This dissertation brings together the areas of safety science and operations management through a mixed-methods approach to investigate the complex relationships between two, often conflicting, organizational goals - efficiency and safety, in sociotechnical systems (STSs). This research mainly focuses on production pressure (PrP) which is considered as one of the main negative outcomes of overprioritizing the efficiency aspect of STSs. This work seeks to introduce novel methodologies for assessing PrP in real time for the purpose of mitigating its risks and unwanted consequences, particularly in safety critical environments such as traffic control centers (TCCs). Essay 1 concentrates on the theoretical underpinnings of PrP by systematically reviewing the existing literature to clarify and unify the concept under the context of safety science. It identifies key factors contributing to PrP, its negative effects on safety performance in various industries, and potential mitigation strategies. By doing so, this essay contributes to the field through laying the groundwork for more effective management strategies to improve workplace safety. Essay 2 addresses a significant gap identified in Essay 1 by developing a methodology based on Data Envelopment Analysis (DEA) for the ongoing measurement and monitoring of PrP. This innovative approach introduces a quantitative mechanism that juxtaposes efficiency and safety related outcomes of hourly performance in safety critical environments. This proposed method allows for a detailed analysis of performance dynamics within STSs. The practical application of this model is demonstrated through its implementation in the infrastructure management system of INFRABEL, the Belgian National Railroad Company. Essay 3 advances the conversation by tackling the predictive limitations of the DEA model established in Essay 2. It integrates Machine Learning (ML) techniques with DEA to develop an innovative method for forecasting near-future PrP levels for proactive management of safety risks. The major contribution of Essay 3 is the novel interface between ML and DEA that can improve decision-making capabilities of managers in safety-critical STSs through real-time monitoring and predictive analytics. Together, these studies contribute to the theoretical discussions around PrP and present practical solutions to longstanding challenges in safety science and operational management.
Utilization-adaptive Memory Architectures
Panwar, Gagandeep (Virginia Tech, 2024-06-14)
DRAM contributes significantly to a server system's cost and global warming potential. To make matters worse, DRAM density scaling has not kept up with the scaling in logic and storage technologies. An effective way to reduce DRAM's monetary and environmental cost is to increase its effective utilization and extract the best possible performance in all utilization scenarios. To this end, this dissertation proposes Utilization-adaptive Memory Architectures that enhance the memory controller with the ability to adapt to current memory utilization and implement techniques to boost system performance. These techniques fall under two categories: (i) The techniques under Utilization-adaptive Hardware Memory Replication target the scenario where memory is underutilized and aim to boost performance versus a conventional system without replication, and (ii) The techniques under Utilization-adaptive Hardware Memory Compression target the scenario where memory utilization is high and aim to significantly increase memory capacity while closing the performance gap versus a conventional system that has sufficient memory and does not require compression.

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