Doctoral Dissertations

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Leadership Experiences of Community in State-Level Supplemental Virtual School Programs: A Qualitative Case Analysis
Warnick, Sarah Katherine (Virginia Tech, 2024-05-02)
The purpose of this study was to investigate leaders' experiences with developing a culturally inclusive community and equitable learning environment in six state-level supplemental virtual programs. Two research questions were: (1) How do leaders in state-level supplemental virtual programs describe their experiences with developing a culturally inclusive community: (a) At the program level for faculty and staff? (b) At the program and course levels for students? (2) How can instructional and course design practices address barriers to virtual learning in order to facilitate an equitable learning environment for students of diverse backgrounds? This research contributes to the field of virtual leadership by representing leaders' perspectives and practices regarding how to cultivate a sense of belonging in the online community and how to address challenges with teaching and learning in this setting. This qualitative case analysis involved leaders from six state-level supplemental virtual programs in the United States. Data were gathered using a demographic survey, semistructured one-on-one interviews, and focus groups to gain a comprehensive understanding of leadership in this setting. An online survey collected demographic data from 22 program leaders, of whom 21 from various backgrounds were purposefully selected for interviews: four executive leaders, seven directors of instruction, four curriculum leaders, two instructional designers, and four other program-area leaders. Twelve findings were identified, with six related to a culturally inclusive community and six pertaining to an equitable learning environment. The findings described how leaders built community at the program level for virtual employees and at the course level for teachers and students. Considerations for creating a shared sense of community included collaboration with colleagues, multiple staff roles, relationship building, frequent communication, teacher visibility, and some student anonymity. The findings also identified barriers to equity, including student access to online content, cultural representation, connectivity, device limitations, individual readiness, and support from a supervising adult. Leaders navigated some challenges through standards-aligned course design and instructional practices. Finally, a team-based approach to resolving technology issues and supporting individual learners' needs was found to help students access content and engage in their online courses.
Instructional Design and Technology Through the Years: A Bibliometric Analysis of Educational Technology Research and Development (ETRandD) Journal
Adeneye, Gabriel Oluwatosin (Virginia Tech, 2024-05-02)
From flickering films to microlearning in 4K, the field known as Instructional Design and Technology (IDT) today has a long history, marked by constant evolution since the 1920s. The field has been thrust into the spotlight by the COVID-19 pandemic. This bibliometric analysis examines research articles from the Educational Technology Research and Development (ETRandD) journal spanning 1957 to 2023. The study addresses the challenges posed by the influx of new IDT professionals from diverse backgrounds, as well as the opportunity presented by the occasion of the centennial celebration of the Association for Educational Communications and Technology (AECT), the key professional organization in the field. Data for this study was primarily obtained from the Web of Science, supplemented by SCOPUS and Dimensions. The analysis utilized Biblioshiny to evaluate the journal's performance and impact, identifying influential works and authors. Additionally, VOSviewer was employed to map the scientific landscape, tracing the evolution of research themes and the collaborative networks among authors, institutions, and countries. While the analysis navigates through the limitations inherent in focusing on a single journal, majorly employing a specific dataset, and adhering to an English-only corpus, it successfully illuminates the core tendencies and transformative shifts within IDT. The findings emphasize the field's enduring commitment to leveraging technological advancements within a theoretically grounded framework to enhance learning outcomes. As the field continues to evolve in response to new entrants from diverse backgrounds, emerging technologies and shifting learners' contexts, this study provides a useful reference point for future research.
Scalable Synthetic Trees for Transpiration-Powered Hydraulic Systems
Eyegheleme, Ndidi Lilyann (Virginia Tech, 2024-05-02)
This dissertation delves into the theory, design and fabrication, and practical uses of synthetic trees that replicate the transpiration mechanisms of natural trees. The first chapter provides an in-depth explanation of how natural trees utilize hydraulic mechanisms to draw water from the soil, through their roots, and up to their leaves, sustaining hydration through transpiration. This process is reliant on the difference in relative humidity between the leaf and the ambient to promote evaporation, and synthetic trees replicate this cycle by integrating reservoirs and conduits with wetted nanopores, mimicking the negative Laplace pressure seen in natural trees. Chapter 2 presents a detailed theoretical framework for transpiration in synthetic trees. These trees feature a vertical array of tubes connected to a nanoporous synthetic leaf. Our model considers the impact of convective gas flow on the leaf, minimizing the diffusive boundary layer and directly influencing the leaf's negative Laplace pressure. We next analyze how the rate of evaporation and tree morphology affect the required Laplace pressure for mass conservation, in an ambient environment with an appreciable diffusive boundary layer. Our model considers the changing dynamics of the menisci, including their capability to adjust their contact angle and withdraw into nanopores to self-stabilize. We then determine conditions where transpiration is limited by evaporation or constrained by the leaf's maximum Laplace pressure, across various tree geometries and ambient conditions. In Chapter 3, the focus shifts to a practical application, as the insights from the previous chapters guide the creation of a synthetic tree for water harvesting. Solar steam generation employing a porous evaporator, with a 3D design extending beyond the free surface to mitigate heat losses, is used to demonstrate how transpiration, rather than capillarity, can raise water up glass tubes, and improve liquid transport heights over conventional methods. Chapter 4 expands on the synthetic tree concept, proposing a mobile desalination water container driven by transpiration. The container features a ring-shaped fin designed to absorb solar heat, increasing water evaporation from a nanoporous synthetic leaf. This approach combines reverse osmosis and thermal evaporation, offering a promising solution for obtaining fresh water from seawater. In Chapter 5, the study explores transpiration-powered oil-water filtration using synthetic trees. Our approach showcases the potential for natural separation of oil and water in various applications, without the need for a pump and in opposition to gravity. Chapter 6 modifies the synthetic tree design to selectively absorb and retain oil from oil-water emulsions. When water evaporates from the synthetic leaf, enabled by the generated negative suction within, oil is then drawn and contained within the system through oleophilic and hydrophobic membranes. This approach offers a sustainable method for oil spill clean-up, oil extraction and purification. Chapter 7 experimentally investigates how to eliminate the capillary driving force in synthetic trees. By over-filling the synthetic leaf's top surface to remove existing concave menisci, the study hypothesizes gravity as a replacement mechanism for negative pressure, with the water in hydrostatic columns held in tension by the overlying water supported within the porous leaf. In summary, these engineered hydraulic systems offer novel approaches to water harvesting, desalination, oil-water filtration, and the cleanup of oil spills, and the study of synthetic trees opens up a realm of possibilities for sustainable water management and environmental remediation, showcasing the potential of biomimicry in solving pressing global challenges.
The Art of SRAM Security: Tactics for Remanence-based Attack and Strategies for Defense
Mahmod, Md Jubayer Al (Virginia Tech, 2024-05-02)
The importance of securing hardware, particularly in the context of the Internet of Things (IoT), cannot be overstated in light of the increasing prevalence of low-level attacks. As the IoT industry continues to expand, security has become a more holistic concern, as evidenced by the wide range of attacks that we observed, from large-scale distributed denial-of-service attacks to data theft through monitoring a device's low-level behavior, such as power consumption. Traditional software-based security measures fall short in defending against the full spectrum of attacks, particularly those involving physical tampering with system hardware. This underscores the critical importance of proactively integrating attack vectors that encompass both hardware and software domains, with a particular emphasis on considering both the analog and digital characteristics of hardware. This thesis investigates system security from a hardware perspective, specifically examining how low-level circuit behavior and architectural design choices impact SRAM's data remanence and its implications for security. This dissertation not only identifies new vulnerabilities due to SRAM data remanence but also paves the way for novel security solutions in the ongoing "security arms race". I present an attack, volt boot, that executes cold-boot style short-term data remanence in on-chip SRAM without using temperature effect. This attack exploits the fact that SRAM's power bus is externally accessible and allows data retention using a simple voltage probe. Next, I present a steganography method that hides information in the SRAM exploiting long-term data remanence. This approach leverages aging-induced degradation to imprint data in SRAM's analog domain, ultimately resulting in hidden and plausibly deniable information storage in the hardware. Finally, I show how an adversary weaponizes SRAM data remanence to develop an attack on a hardware-backed security isolation mechanism. The following provides a brief overview of the three major contributions of this thesis: 1. Volt boot is an attack that demonstrates the vulnerability of on-chip SRAM due to the physical separation common in modern SoCs' power distribution networks. By probing external power pins (to the cache) of an SoC while simultaneously shutting down the main system power, Volt boot creates data retention across power cycles. On-chip SRAM can be a safe memory when the threat model considers traditional off-chip cold-boot-style attacks. This research demonstrates an alternative method for preserving information in on-chip SRAM through power cycles, expanding our understanding of data retention capabilities. Volt boot leverages asymmetrical power states (e.g., on vs. off) to force SRAM state retention across power cycles, eliminating the need for traditional cold boot attack enablers, such as low-temperature or intrinsic data retention time. 2. Invisible Bits is a hardware steganography technique that hides secret messages in the analog domain of SRAM embedded within a computing device. Exploiting accelerated transistor aging, Invisible Bits stores hidden data along with system data in an on-chip cache and provides a plausible deniability guarantee from statistical analysis. Aging changes the transistor's behavior which I exploit to store data permanently (ie long-term data remanence) in an SRAM. Invisible Bits presents unique opportunities for safeguarding electronic devices when subjected to inspections by authorities. 3. UntrustZone utilizes long-term data remanence to exfiltrate secrets from on-chip SRAM. An attacker application must be able to read retained states in the SRAM upon power cycles, but this needs changing the security privilege. Hardware security schemes, such as ARM TrustZone, erase a memory block before changing its security attributes and releasing it to other applications, making short-term data remanence attacks ineffective. That is, attacks such as Volt boot fail when hardware-backed isolation such as TEE is enforced. UntrustZone unveils a new threat to all forms of on-chip SRAM even when backed by hardware isolation: long-term data remanence. I show how an attacker systematically accelerates data imprinting on SRAM's analog domain to effectively burn in on-chip secrets and bypass TrustZone isolation.
Mechanisms of Intercellular Communication During Breast Cancer Progression Through Metastasis
Wheeler, Christina Eileen (Virginia Tech, 2024-04-30)
Breast cancer is the second leading cause of cancer-related death in women worldwide. Despite more frequent and efficient screening measures, subtype-specific treatments, and overall improved patient outcomes, metastasis remains difficult to treat and accounts for 90% of breast cancer patient deaths. While the role of intercellular communication in metastasis, either among cancer cells, or between cancer cells and the tumor microenvironment is well established, additional research on specific molecular and cellular mechanisms underlying these interactions is necessary to develop novel therapeutic strategies. One mechanism that facilitates metastasis is epithelial-mesenchymal transition (EMT), which can be induced in cancer cells following the secretion of growth factors by tumor-associated macrophages (TAMs). During EMT, epithelial cells lose their cell-cell junctions, resulting in an alteration of intercellular communication. One of the junctions lost during EMT is gap junctions composed of connexin43 (Cx43), however, this is paired with an increase in expression of cytoplasmic Cx43 which binds microtubules. To elucidate the role of cytoplasmic Cx43 during EMT and breast cancer metastasis, we utilize a Cx43 mutant that has reduced binding with microtubules. We demonstrate disruption of the interaction between Cx43 and microtubules decreases mesenchymal marker expression and cell migration in vitro during EMT, and reduces breast cancer metastasis to the lungs in vivo, identifying a novel non-junctional tumorigenic role for Cx43 in metastasis and a potential therapeutic target in the treatment of breast cancer.
Boundary Resilience: A New Approach to Analyzing Behavior in Complex Systems
Wilhelm, Julia Claire Wolf (Virginia Tech, 2024-04-30)
Systems engineering has many subdisciplines which would be useful to study in terms of complex system behavior. However, it is the interactions between a complex system and its operating environment which drive the motivation for this analysis. Specifically, this work introduces a new approach to assessing these interactions called "boundary resilience." While classical resilience theory measures a system's internal reaction to adverse event, boundary resilience evaluates the impacts such an event may have on the surrounding environment. As the scope of this analysis is quite large, it was deemed appropriate to conduct a case study to determine the fundamental tenants of boundary resilience. SpaceX's satellite Internet mega-constellation (StarLink) was chosen due to its large potential to impact the space environment as well as its size and complexity. This study produced two boundary resilience measures, one for local boundary resilience of a single component and one for the global boundary behavior of the entire system. The local metric measures the likelihood of an adverse event occurring at that boundary location as well as its potential to impact the surrounding environment. The global boundary resilience metric reflects a nonlinear relationship among the system components.
Honors-for-All: The Effect of Detracking on Teachers' Beliefs and Pedagogy
Langstein, Hanna Beth Preizler (Virginia Tech, 2024-04-30)
Tracking, having separate advanced, standard, and/or remedial classes intended to homogeneously group students by perceived or actual ability, is a frequent practice used in U.S. schools, particularly at the secondary level. To promote educational equity, close achievement gaps, and counteract the de facto racial separation between advanced and standard-level courses, some districts and individual schools in Virginia are moving to detrack their offerings and stop offering separate advanced and standard-level courses. This qualitative case study explored how a middle school's newly adopted detracking policy with an honors-for-all approach impacted teachers' beliefs and pedagogy. Data were collected from documents and interviews with six school and district personnel and analyzed using inductive coding techniques until a mutually exclusive scheme of categories had been generated. The study concluded with the discussion, implications, recommendations, and conclusion of the results. The findings identified four categories that answered the research questions: opinions on honors-for-all, defining what "honors" means, instructional shifts in an honors-for-all classrooms, and challenges in practices. Overall, the study found that: (a) teachers' beliefs on tracking and honors-level classes did not change after implementation of detracking and there was a general divide in opinions between the teachers and non-teaching faculty, (b) there were varying definitions of what "honors" means among the district, school, and staff, (c) teachers' instruction shifted to adopt new pedagogical tools and strategies to meet the diverse learning needs in a mixed-ability honors classroom, and (d) teaching in an honors-for-all classroom was challenging, especially in differentiating for students' needs, the impact of the COVID-19 pandemic, and the accelerated standards in honors mathematics courses. Implications of the study included: (a) the necessity of having teacher buy-in when implementing a new programming initiative, (b) the benefits of vertical articulation with feeder elementary schools to prepare students for the rigor of middle school honors courses, (c) the need for common language and clear definitions across the district and school, and (d) the importance of providing professional development and support personnel to assist teachers in adopting new pedagogical practices in an honors-for-all setting.
Guidelines for Informed Instructional Strategy Selection in Online Higher Education: A Design and Development Research
Alghamdi, Bushra Abdulkarim (Virginia Tech, 2024-04-25)
The demand for online education has significantly increased in recent years, prompting many educational institutions to consider its continued adoption in many ways. However, some faculty members have encountered challenges in teaching online due to a lack of adequate training and guidance on effective online teaching practices. This study aims to provide evidence-based guidance for higher education instructors in selecting effective instructional strategies in online learning environments. It employs design and development research methodology to create instructional strategy selection guidelines for online courses in higher education. The guidelines, rooted in pedagogical approaches, are designed to assist faculty in selecting appropriate instructional strategies for online learning. They comprehensively outline the various instructional strategies and the factors influencing the decision-making process for selecting instructional strategies in online learning environments. The study makes contributions to research and content development by providing strategy selection guidelines for quality online education.
Indian Wives of Incarcerated Men Tell Their Stories: An Intersectional Narrative Analysis of Disenfranchisement and Resilience
Gupta, Shivangi (Virginia Tech, 2024-04-25)
When a family member is incarcerated, the task of emotionally and financially supporting the remaining family members and the incarcerated loved one often falls upon women, who are likely to be under-resourced and overwhelmed. Women whose husbands are incarcerated in India are likely to possess multiple marginalized identities, increasing their vulnerability to intersecting forms of oppression. Empirical research is lacking on wives of incarcerated men in India, contributing to their invisibility in policy-making and programmatic interventions. Guided by intersectional feminism and symbolic interactionism, the purpose of this study was to document the stories of women who had experienced spousal incarceration in the Indian context. In-depth, semi-structured interviews were conducted with 14 wives of prison inmates who resided in or around the National Capital Territory of Delhi, all of whom either held a lower caste identity or a Muslim religious identity. Transcribed interviews were analyzed following the steps of narrative analysis. Results illustrate the diversity of storied experiences of wives of incarcerated husbands in India. First, by grouping narratives that conveyed the same overall storyline into the same cluster, I identified three story clusters: Ambivalent but Hanging On, Unconditionally Devoted, and Independent and Disillusioned. Second, by attending to how women's day-to-day lives are shaped by intersecting systems of privilege and oppression, particularly those tied to gender and class, I identified three overarching themes that spanned women's narratives: (a) a complicated relationship with patriarchy, (b) the weight of socioeconomic disenfranchisement, and (c) when resilience is not a choice. The results of this study emphasize the need to distinguish between feminist agency and welfare agency, to recognize women's experiences of ambiguous loss and disenfranchised grief, and to critique the systemic injustices that forced women to be resilient. Documenting their stories is instrumental in bringing attention to the needs, challenges, and triumphs of this underserved and overlooked population.
Development and Evaluation of a Decision Support Tool to Incorporate Redundancy in the Development of Instructional Materials
Cox II, Larry Alenda (Virginia Tech, 2024-04-25)
Novice Instructional Designers (IDs) often struggle to perform at the same level as experts. Specialized knowledge and experience are needed to discover the challenges and device appropriate solutions. Scaffold, guides, and heuristics can help novice when needing to perform tasks that require specialized knowledge. One common instructional design task requiring specialized knowledge is the development of instructional materials. Instructional message design (IMD) is a problem solving process to improve the quality of instructional materials through the application of research based principles. As this process is often not covered in novice IDs training, they will encounter more issues while attempting to address the challenges that come with creating instructional materials. Using a developmental study, a decision support tool was created to assist novice IDs with applying IMD, specifically the redundancy principle due to its ability to improve the communication within the materials. This study describes the operationalization of the principle, the design and development of the tool, expert review and revisions made based on their feedback, and the implications from the development of such a tool.
The Quantized Velocity Finite Element Method
Cook, Charles (Virginia Tech, 2024-04-23)
The Euler and Navier-Stokes-Fourier equations will be directly expressed as distribution evolution equations, where a new and proper continuum prescription will be derived. These equations of motion will be numerically solved with the development of a new and unique finite element formulation. Out of this framework, the 7D phasetime element has been born. To provide optimal stability, a new quantization procedure is established based on the principles of quantum theory. The entirety of this framework has been coined the "quantized velocity finite element method" (QVFEM). The work performed herein lays the foundational development of what is hoped to become a new paradigm shift in computational fluid dynamics.
Exploring the drivers and consequences of emerging infectious disease of wildlife
Grimaudo, Alexander Thomas (Virginia Tech, 2024-04-22)
Emerging infectious diseases of wildlife have threatened host populations of diverse taxa in recent history, which is largely attributable to anthropogenic global change. In three data chapters, this dissertation examines the drivers of individual- to population-level variation in how host populations respond to novel and emerging pathogens. Each chapter explores these processes in bat populations of North America, predominantly the Northeast and Midwest regions of the United States, impacted by the emerging fungal pathogen that causes white-nose syndrome, Pseudogymnoascus destructans. In Chapter 2, I disentangle the effects of adaptive host traits and environmental influences in driving host population stabilization of the little brown bat (Myotis lucifugus), finding that host-pathogen coexistence in this system is the product of their complex interaction. In Chapter 3, I characterize the range-wide variation in white-nose syndrome impacts on a federally endangered and poorly studied species, the Indiana bat (Myotis sodalis), as well as environmental and demographic determinants of its declines over epidemic time. In Chapter 4, I explore the role of individual variation in roosting microclimate selection of little brown bats in driving their infection severity, yielding important insights into the pathophysiology and environmental dependence of white-nose syndrome. Ultimately, this dissertation characterizes complex drivers of variation in host responses to emerging and invading pathogens, yielding insights essential to the successful mitigation of their impacts.
A Multilevel Analysis to Examine Interdisciplinary Research Experience Among Doctoral Graduates and Its Effect on Career Outcomes
Lawrence, Kacy (Virginia Tech, 2024-04-23)
This study was designed to explore the impact of interdisciplinary research on the likelihood of a doctoral student obtaining a faculty job upon degree completion. Additionally, this study examined the important individual and institutional components of socialization that contribute to differences in career outcomes. A socialization framework likely substantiates the extent to which doctoral training environments are consequential to careers. Results were obtained from a sample of 28,928 doctoral students who participated in the 2021 Survey of Earned Doctorates. Hierarchical Generalized Linear Modeling was used because it measures the effects of both student characteristics and institutional factors. The findings from this analysis suggest student demographics are an important predictor, but the significance of those characteristics' changes when doctoral field of study is considered. Additionally, there are institutional characteristics that impact the likelihood of obtaining a faculty job related to the proportion of various student backgrounds, faculty backgrounds, and broad field of study, and the prestige of the institution. The independent variable of interest, interdisciplinary dissertation, was not statistically significant at the student level, but the proportion of doctoral students completing an interdisciplinary dissertation at the institution level was statistically significant and negatively associated with obtaining a faculty position adjusting for other institutional factors. These findings show the importance of applying hierarchical models to research questions related to career outcomes for doctoral students. Without a hierarchical model, this important differential finding across levels would have been hidden.
Enhancing Security and Privacy in Head-Mounted Augmented Reality Systems Using Eye Gaze
Corbett, Matthew (Virginia Tech, 2024-04-22)
Augmented Reality (AR) devices are set apart from other mobile devices by the immersive experience they offer. Specifically, head-mounted AR devices can accurately sense and understand their environment through an increasingly powerful array of sensors such as cameras, depth sensors, eye gaze trackers, microphones, and inertial sensors. The ability of these devices to collect this information presents both challenges and opportunities to improve existing security and privacy techniques in this domain. Specifically, eye gaze tracking is a ready-made capability to analyze user intent, emotions, and vulnerability, and as an input mechanism. However, modern AR devices lack systems to address their unique security and privacy issues. Problems such as lacking local pairing mechanisms usable while immersed in AR environments, bystander privacy protections, and the increased vulnerability to shoulder surfing while wearing AR devices all lack viable solutions. In this dissertation, I explore how readily available eye gaze sensor data can be used to improve existing methods for assuring information security and protecting the privacy of those near the device. My research has presented three new systems, BystandAR, ShouldAR, and GazePair that each leverage user eye gaze to improve security and privacy expectations in or with Augmented Reality. As these devices grow in power and number, such solutions are necessary to prevent perception failures that hindered earlier devices. The work in this dissertation is presented in the hope that these solutions can improve and expedite the adoption of these powerful and useful devices.
NF-kB Inducing Kinase (NIK) Influences Eosinophil Development, Survival, and Plasticity
Trusiano, Briana Lynn (Virginia Tech, 2024-04-22)
Hypereosinophilic (HES) syndrome is an umbrella term encompassing several disease subsets that affects humans and veterinary species, ultimately resulting in >1,500 eosinophils/uL circulating in the blood documented over six-months. This eventually culminates in end-organ infiltration and increased patient morbidity and mortality. In mice where the gene Map3k14 encoding NF -kB inducing kinase (NIK) is knocked out, a HES-like syndrome develops that is dependent on Th2 cells and cytokines. NIK is the upstream regulator of the noncanonical NF-kB pathway and is involved in lymphoid organ development, B cell lymphopoiesis, and myelopoiesis. In addition to regulating the noncanonical NF-kB pathway, NIK is also involved in regulation of kB dimers of the canonical NF-kB pathway and can function independent of NF-kB signaling by regulating lipid and glucose metabolism, mitochondrial, and RIP1 binding to influence cell survival and death. Despite previous studies performed in the Nik-/- model, the mechanisms underlying eosinophil development, plasticity, and fitness in conjunction with the bone marrow and splenic microenvironments have not been fully elucidated. In the present work, we reviewed current data exploring the influence of the noncanonical NF-kB pathway and NIK specifically on the development of acute myeloid leukemias (AMLs) and Myelodysplastic Syndrome (MDS) with a focus on how these mechanisms might induce subvariants of HES. We next examined the effect of NIK loss on eosinophilopoiesis within hematopoietic tissues in vivo and in various cell culture environments in vitro via cytology, histology, flow cytometry, FACS, positive cell selection, MTT assay, BrDU assay, and protein microarray analysis. Overall, our findings suggest that NIK influences eosinophil maturation, proliferation, metabolism, survival, and potentially plasticity in vivo and in vitro under different environmental conditions and Th2 cytokine influence. NIK loss was also associated with altered free and bound TNFR1 levels on day 13 in vitro. TNFR1 acts upstream of RIP1 and suggests that these differences may be due to NF-kB independent functions of NIK. Overall, these results provide further insight into the potential mechanisms underlying eosinophilopoiesis in the Nik-/- murine model. This information may prove useful in discovering new treatment options underlying subvariants of HES in both human and veterinary patients.
Fruit chemical traits shape bat nutritional ecology: from basic science to applications
Gelambi Desiato, Mariana (Virginia Tech, 2024-04-22)
Ripe fleshy fruits contain an enormous diversity of metabolites that influence ecological interactions with mutualistic and antagonistic species. This dissertation investigates the impact of fruit secondary metabolites on the foraging behavior and digestive physiology of bats (Chapters 2-4) while applying insights from basic chemical ecology to inform forest regeneration strategies (Chapter 5). The studies were conducted in northeastern Costa Rica at La Selva Biological Station. Chapter Two examines the variability and associations between nutrients and secondary metabolites within ripe Piper sancti-felicis fruits, showing that intraindividual variation of chemical traits can surpass interindividual variation and associations between chemical traits are scale-dependent, varying in strength and direction. Chapter Three explores how bats balance nutrient acquisition with defensive metabolite avoidance and the impact of metabolite consumption on bat nutrient absorption. It reveals that nutrient composition is the primary driver of bat foraging behavior and that defensive metabolites can interfere with protein absorption. Chapter Four further uses untargeted metabolomics to explore the influence of secondary metabolites on nutrient absorption, demonstrating that four commercial secondary metabolites induce dose-dependent changes in bat fecal metabolome, altering essential nutrient absorption. Chapter Five translates principles of chemical ecology into practical use by demonstrating the effectiveness of synthetic volatiles in attracting fruit bats and increasing seed rain. Taken together, this dissertation shows the impact of defensive metabolites on a key seed disperser while demonstrating the potential application of chemical ecology to address forest regeneration challenges.
Developing a Prototypical Biophilic Localized Natural Airflow Simulator (BLNAS) for a Modular Workstation
Rabab'ah, Ikhlas Oqlah (Virginia Tech, 2024-04-22)
Reduced-order Adaptive Output Predictor for a Class of Uncertain Dynamical Systems: Application to EEG-Based Control of Working Memory
Ansari, Roghaiyeh (Virginia Tech, 2024-04-18)
This dissertation aims to develop a formal foundation to design an adaptive output feedback predictor for a class of unknown systems where parameters and order are unknown or high-dimensional. We present a reduced-order adaptive output-predictor scheme based on modal reduction and Lyapunov's method. Moreover, the credibility of the proposed reduced-order adaptive output-predictor scheme is validated by mathematical proof, and numerical and experimental studies, such as single pendulum, double pendulum, six-link pendulum, rope as a high-dimensional rope, and EEG data. Then the dissertation goal is to experimentally validate the proposed reduced-order model parameterization technique for tracking uncertain linear time-invariant (LTI) single-input, single-output (SISO) systems. The proposed theory focuses on parameterizing a high-dimensional, uncertain model and introduces a reduced-order adaptive output predictor capable of forecasting the system's output. This predictor utilizes auto-regressive filtered vectors, incorporating the input and output history. The adaptive output predictor is a simplified and known model, making it suitable for controlling high-dimensional, uncertain SISO systems without access to full-state measurements. Specifically, this work establishes the foundation for parameterizing uncertain models, creating a virtual structure that emulates the actual system, and offering a more manageable model for control when the objective is solely to regulate the system's output. The primary focus of this research is to assess the effectiveness and output-tracking capabilities of the proposed approach. These capabilities are extensively examined across diverse platforms and hardware configurations, relying solely on input and output data from the models without incorporating any additional information on the system dynamics. In the first experiment, the predictor's ability to track the angle of a single pendulum, including additional dynamics, is evaluated using only input-output data. The second experiment targets tracking the endpoint of a rope connected to a single pendulum, where the rope emulates a high-dimensional model. A vision system is designed and employed to acquire the rope endpoint position data. Before the rope experiment, a set of experiments is conducted on single pendulum hardware to ensure the accuracy of the vision system's data collection. Comparative analysis between data from object tracking via vision and data acquired through an encoder demonstrates negligible error. Finally, the input and the endpoint output data from the rope experiment are fed into the predictor to assess its capability to track the rope endpoint position without utilizing specific knowledge of the experimental hardware. Achieving negligible error in tracking implies that the predictor provides a simple and accurate representation of the rope dynamics. Consequently, designing a controller for this known model is equivalent to designing a controller for the actual rope system dynamics. The predictor, by closely emulating the behavior of the rope, becomes a reliable surrogate model for control design, simplifying the task of controller design for the complex and uncertain high-dimensional system. Finally, this study introduces a novel approach to enhance controller design for complex brain dynamics by employing a reduced-order adaptive output predictor proposed in [1], fine-tuned with chirp binaural beats. The proposed technique is promising for developing closed-loop controllers in non-invasive brain stimulation therapies, such as binaural beats stimulation, to improve working memory. The study focuses on parameterizing uncertain models and creates a predictor that utilizes auto-regressive filtered vectors to forecast mean phase lock values generated by binaural beats stimulation. The simplified and known model of the predictor proves effective in tracking brain responses, as demonstrated in experiments evaluating its ability to track mean phase locking values. The results indicate negligible tracking error, suggesting the predictor's reliability in representing brain dynamics and simplifying the task of controller design for the complex and uncertain high-dimensional system.
An Investigation into the Psychological Capital of Second-Career Teachers and Factors Influencing Their Scores
Flanagan, Amanda Grace (Virginia Tech, 2024-04-12)
The purpose of this qualitative study was to examine the Psychological Capital (PsyCap) of second-career teachers (SCTs) and their perceptions of what affects their PsyCap in the workplace by surveying and interviewing second-career teachers in public school districts in central eastern and northern Virginia. The research questions were: What is the PsyCap of a second-career teacher? What are the factors that second-career teachers perceive to contribute to their PsyCap? Participants were located in rural and suburban school districts in central eastern and northern Virginia. Data collection consisted of demographic surveys, the Psychological Capital Questionnaire survey (PCQ-24), and semi-structured interviews. Eighteen second-career teachers were purposefully selected from 34 who completed the demographic survey data and PsyCap-24 to participate in semi-structured interviews using the interview questions protocol. Common themes from the interviews were determined using deductive and inductive coding. Major findings were that second-career teachers exhibited a high average workplace positive PsyCapof 4.8; mentorship and strong peer support significantly influence second-career teachers' positive PsyCap; and a teacher's relationships with colleagues and their team's impact second-career teachers' positive PsyCap. Additional findings also showed that positive relationships with administration and prior-life experiences in other fields contributed to an increase in positive PsyCap. Whereas extra duties assigned to second-career teachers negatively impact their overall PsyCap. These results underscored the significance of nurturing positive PsyCap among second-career teachers, adding to the broader research on educators' PsyCap and its impact on teacher retention and job satisfaction in education.
Studies on Molten Salt Fuels: Properties, Purification, and Materials Degradation
Park, Jaewoo (Virginia Tech, 2024-04-12)
The molten salt reactor (MSR) is one of the advanced nuclear reactors expected to be alternatives to the conventional water-cooled nuclear reactor systems. Despite many advantages of MSRs, properties of molten salts have not been sufficiently measured in previous studies. In addition, the corrosion of structural alloys by molten salt is the biggest challenge for the operation of MSRs. This study focuses on measurements of thermophysical and thermodynamic properties of fluoride salt fuels, salt purification, and the degradation of structural materials in static and flowing molten-salt fuels. For the measurements of properties, phase transition, specific heat capacity, vapor pressure, contact angle on nuclear-grade graphite, and density were measured. The methodologies for the property measurements used in this study were validated by measuring the properties of metals or salts that have been well studied. For the flow-induced corrosion tests, the salt flow with different velocities was simulated by rotating the stainless steel 316H (SS316H) specimens in molten NaF-KF-UF4 (FUNaK) contained in glassy carbon crucibles at 1073 K. Salt samples were intermittently collected to monitor concentration changes of corrosion products in the salt, and surfaces and cross-sections of post-test SS316H specimens were analyzed to study their corrosion behaviors. Different batches of FUNaK were synthesized using different methods of purification, such as thermal purification, U-metal purification, and hydrofluorination with electrochemical purification (chemical purification) to study impacts of salt purification on the corrosion of SS316H. The corrosion test of SS316H by thermally purified FUNaK showed that the Fe concentration increased at the beginning and then decreased while the Cr concentration continued increasing while the rate decreased. In addition, (Cr, Fe)7C3 layers, Cr-metal particles, and dendritic structures concentrated with Cr and Fe were observed on the glassy carbon crucible after the 2 m/s test. The U-metal purification and hydrofluorination with electrochemical purification reduced concentrations of oxygen and hydrogen in FUNaK and mitigated the corrosion of SS316H significantly. The infiltration of the fluoride fuel salts into graphite and the fluorination of graphite by the salts at different pressures and temperatures were also studied. The salt infiltration into graphite at pressures above its threshold pressure was observed, and the formation of carbon fluorides on the surface of post-test graphite specimens was identified.

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