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- Distribution and Characterization of Herbicide-Resistant Italian ryegrass and Palmer amaranth in VirginiaViric, Milos (Virginia Tech, 2026-03-11)Weed infestation is the major reason for economic losses in agriculture. Italian ryegrass and Palmer amaranth are some of the most troublesome weed species in Virginia. These species are strong competitors with crops for growth resources which eventually leads to significant yield losses in absence of adequate control. One of the challenges for the control of these species is development of herbicide-resistant populations. There is a limited knowledge about the distribution of resistant populations of Italian ryegrass and Palmer amaranth in Virginia. Palmer amaranth resistance to glyphosate was confirmed in 2011 and Italian ryegrass resistance to diclofop was confirmed in 1993. These are the only two confirmed cases of herbicide resistance in Virginia but based on control failure reports, resistance to these species is suspected to be more widespread in Virginia. To investigate the distribution and levels of resistance in populations from Virginia there is a necessity for more updated surveys. A total of 32 populations of Italian ryegrass were collected. Plants were grown in the greenhouse to test for sensitivity to herbicides commonly used for burndown or in-crop control of Italian ryegrass: pinoxaden, diclofop, glyphosate, mesosulfuron, pyroxsulam, and pyroxasulfone. At 21 days after the herbicide treatments, visible injury ratings were recorded on a scale 0 to 100%, where 0 indicates no control and 100 represents complete plant necrosis. Populations exhibiting ≤49% control were suspected to be resistant. Based on this criteria, 10, 27, 0, 14, 0, and 7 populations were found to be resistant to pinoxaden, diclofop, glyphosate, mesosulfuron, pyroxasulfone, and pyroxsulam, respectively. Following the initial screening, dose-response assays with pinoxaden, diclofop, mesosulfuron and pyroxsulam were conducted. Resistance indices (R/S ratios), calculated based on GR50 (herbicide dose that reduced biomass by 50%) values for resistant and susceptible populations, were 20 for pinoxaden, 87 for mesosulfuron, and 161 for pyroxsulam. The R/S value for diclofop could not be determined because even the highest tested dose could not achieve 50% growth reduction in the resistant population. Cross and multiple resistance was observed in this study and 6% of populations were found resistant to pinoxaden, diclofop-methyl, mesosulfuron, and pyroxsulam. A total of 68 Palmer amaranth populations were collected from corn, soybean and cotton fields across Virginia. Palmer amaranth seedlings grown in the greenhouse were treated with: trifloxysulfuron, 2,4-D, fomesafen, atrazine, mesotrione, glyphosate, glufosinate and dicamba. Visible control ratings were recorded on a 0 to 100% scale, where populations with up to 49% injury were considered resistant. Upon testing the populations, resistance was found in 46, 1, 3, 7, 3, 50, 0 and 0 populations to trifloxysulfuron, 2,4-D, fomesafen, atrazine, mesotrione, glyphosate, glufosinate and dicamba, respectively. Dose-response assay for glyphosate revealed that GR50 value for resistant population was 1,238 g ae ha-1, however R/S value could not be calculated as susceptible population was not available. The R/S values for trifloxysulfuron, fomesafen and atrazine were 47, 14 and 18, respectively. Approximately 69% of the populations showed multiple resistance to two or more herbicide sites of action. Overall, findings from these statewide surveys provide critical insights into the current herbicide resistance status for both Italian ryegrass and Palmer amaranth in Virginia. This information will help growers better understand the effectiveness of commonly used herbicides and make more informed management decisions.
- Family and Friend Support, Strain, and Loneliness Among Dementia Caregivers in Rural AppalachiaStanfill-Carrillo, Brenda Liana (Virginia Tech, 2026-02-04)Background: Loneliness, defined as a perceived deficit in the quantity or quality of social relationships, is associated with a range of adverse physical and mental health outcomes. Understanding contributors to loneliness among caregivers of people living with dementia (PLwD) is therefore an important public health concern. Family caregivers, particularly spouses or adult children, report higher levels of loneliness compared to non-caregivers and some other caregiver groups. This vulnerability may stem from time constraints on social activities, misunderstandings within existing relationships regarding care management, and losses in shared experiences as dementia progresses. Across the life course, family and friends serve as important sources of social support and relational connection, both of which may be associated with lower loneliness. Research Questions and hypotheses: Guided by Perlman and Peplau’s definition of loneliness and the Stress Process Model, this thesis examined whether perceived support and strain from caregivers’ family and friends are associated with loneliness among spousal and adult child caregivers of PLwD living in rural Appalachia, above and beyond caregiving demands. Caregiver relationships with the PLwD (wife, husband, daughter, son) were examined categorically to account for differences in relational roles and expectations. It was hypothesized that (1) caregiver relationship type would be associated with loneliness, with wives reporting the highest levels, and (2) greater family strain would be associated with higher loneliness, whereas greater family and friend support would be associated with lower loneliness. Methodology: Data were drawn from the Families in Appalachia Caring for Elders with Alzheimer’s Disease (FACES) study (N = 141). A three-step hierarchical multiple linear regression analysis was conducted to examine associations between caregiver relationship type, perceived family and friend support, perceived family and friend strain, and loneliness, controlling for unsupervised time and assistance with personal activities of daily living. Results: Wives reported higher levels of loneliness than husbands, daughters, and sons. After accounting for caregiving demands and relationship type, higher perceived family strain was associated with higher loneliness, whereas greater perceived friend support was associated with lower loneliness. Family support and friend strain were not significantly associated with loneliness in the final model. Implications: Findings suggest that perceived relationship quality, rather than the mere presence or number of social ties, is central to understanding loneliness among caregivers of PLwD in rural Appalachia. While friend support was associated with lower loneliness, addressing familial strain in caregiver interventions and psychosocial programming may be particularly relevant for efforts aimed at reducing caregiver loneliness.
- A Qualitative Exploration of School-Based Intervention Needs Among Rural Appalachian YouthWinograd, Dayna Gael (Virginia Tech, 2025-12-05)Disordered eating is prevalent in the United States, with over 20% of children and adolescents reporting some form of disordered eating. Eating disorders are associated with detrimental physical effects and co-occurring mental health difficulties. One population that appears to be at high risk for developing disordered eating symptoms is rural youth. Unfortunately, rural youth often do not receive treatment for their disordered eating symptoms due to myriad care barriers, including geographical restrictions and financial constraints. School-based interventions offer promise to address such barriers and increase access to treatment among this vulnerable group. This study represents a first step at identifying rural youth needs and formatting preferences for a school-based intervention. Participants were 11 rural adolescents (Mage = 15.09) from Appalachia. Participants reported their demographic characteristics in surveys and completed a semi-structured interview assessing their needs and formatting preferences for a school-based intervention for disordered eating. Data were analyzed using inductive thematic analysis; the following themes emerged. Rural youth reported that an intervention should promote healthy and balanced eating, teach social media literacy, and discuss external factors and overlapping mental health difficulties, and de-emphasize the value of weight and shape. Rural youth also suggested that the intervention design take into consideration logistical and cultural factors of rural communities. These data suggest that rural youth’s treatment preferences align with existing school-based interventions for disordered eating. However, modifications may be needed to address logistical and cultural factors that may impact acceptability and feasibility of school-based eating disorder interventions in rural communities
- Likelihood-Free Bayesian Inference with Efficient Uncertainty QuantificationNouri, Arash (Virginia Tech, 2026-02-09)Uncertainty quantification (UQ) in inverse problems is essential for reliable parameter estimation in scientific and engineering applications. This thesis presents a study on two frameworks that separately quantifies two fundamental types of uncertainty: aleatoric uncertainty, arising from inherent measurement noise and non-identifiability in the inverse mapping, and epistemic uncertainty, stemming from limited training data and model inadequacy. For aleatoric uncertainty quantification, a conditional Wasserstein Generative Adversarial Network with Full Gradient Penalty (cWGAN-GP) is employed to approximate the posterior distribution over parameters given observations. The trained generator enables efficient posterior sampling through a single forward pass, providing credible intervals and capturing potential multimodality in the solution space. A physics-informed extension, SGML-cWGAN, incorporates domain knowledge through physics-based loss terms to improve estimation accuracy. For epistemic uncertainty quantification, Prediction with Neural Network Corrections (PNC) is utilized, leveraging Neural Tangent Kernel theory to provide theoretically grounded uncertainty estimates. Bootstrap and stacking resampling methods generate multiple model instances, with prediction variance across instances serving as the epistemic uncertainty measure. The framework is evaluated on two benchmark problems: the FitzHugh-Nagumo (FHN) dynamical system and the Pacejka tire model. Results demonstrate that PNC achieves excellent performance on clean and structured noisy datasets, while cWGAN scales efficiently to large datasets containing up to 864,000 samples. The physics informed SGML-cWGAN achieves up to 33% improvement in mean squared error over the baseline cWGAN on the Pacejka dataset. However, a fundamental trade-off emerges: PNC faces computational constraints limiting applicability to datasets smaller than approximately 7,000 samples, while cWGAN requires a minimum of 8,000 samples for reliable performance. This incompatibility highlights the need for scalable epistemic uncertainty methods that complement data-hungry generative models. The findings demonstrate the viability of neural network-based approaches for uncertainty quantification in inverse problems, while identifying key limitations and directions for future research, including alternative simulation-based inference methods and improved posterior evaluation metrics
- Communication in a Fractional World: MIMO MC-OTFS Precoder PredictionAllen, Evan James (Virginia Tech, 2025-04-23)As 6G technologies advance, international bodies and regulatory agencies are intensifying efforts to extend seamless connectivity especially for high-mobility scenarios such as Mobile Ad-Hoc Networks (MANETs) types such as Vehicular Ad-Hoc Networks (VANETs) and Flying Ad-Hoc Networks (FANETs). For these environments to be considered for long term adoption and use they must support Multiple-Input-Multiple- (MIMO) technology, rapidly fluctuating channel conditions in these environments place a heavy burden on traditional time-frequency CSI feedback schemes required for MIMO precoding. This motivates a shift toward delay-Doppler representations like those employed by Orthogonal Time-Frequency Space(OTFS) modulation, which offers greater stability under mobility. We derive an expression for the variation over time in the OTFS I/O relationship. We then use this to create a physics informed complex exponential basis expansion model prediction framework that maximizes the usefulness of outdated Channel State Information (CSI) in the presence of integer and fractional delay-Doppler channels and facilitates high mobility MIMO communication.
- Arabinoxylan: Derivative Synthesis, Film Formation and DegradationMensah, Enock Dugbatey (Virginia Tech, 2025-08-06)Polysaccharides are sustainable resources that can be processed into biofuel and biomaterials. However, a good understanding of their degradation kinetics and moisture content, which are critical factors in processing, is lacking and this merits investigation. In this work, the moisture content and chelator-mediated Fenton (CMF) degradation rate of regenerated arabinoxylan (RAX) films were studied and compared with regenerated cellulose (RC) films using a quartz crystal microbalance with dissipation monitoring (QCM-D) and atomic force microscopy (AFM). Results from the study revealed that RAX films had more water than RC films of comparable thickness. RAX films were more susceptible to CMF treatment than RC films and their degradation was maximum at pH 5 and 35 ℃. The regenerated arabinoxylan films described here would allow for in situ studies of biomacromolecule and small molecule interactions with hemicellulose films.
- How Well Do Multimodal Large Language Models Score on Visual Personnel AssessmentsLiu, Siyi (Virginia Tech, 2025-12-18)Multimodal Large Language Models (MLLMs) pose new threats to the validity of visual personnel assessments in high stakes selection contexts, as their emergent visual perception and understanding capabilities may facilitate applicant cheating. The study investigated the performance of three popular MLLMs on one visual cognitive ability test bundle and one visual forced-choice personality test, across three prompt approaches and three temperature settings. It was found that MLLMs only achieved median-level scores (the 50th percentile) on the visual cognitive ability test, not as competitive as high-performing human test takers. However, they exhibited top-tier performance (over the 98th percentile) on Conscientiousness on the visual personality test, while exhibiting high scores on Agreeableness and Emotional Stability by nudging temperatures or prompts. Given MLLMs’ potential to enable applicant cheating in unproctored pre-employment assessments, the study urged test vendors and employers to implement anti-cheating measures and offered related recommendations.
- Episodic Detail Production and Semantic Coherence in Down Syndrome and Fragile X Syndrome: Longitudinal Findings from Expressive Language SamplingVan Vorce, Hailey (Virginia Tech, 2025-12-09)Autobiographical memory requires the integration of episodic and semantic information and is closely tied to expressive language abilities. This study examined episodic detail production and narrative coherence in children and adolescents with Down syndrome (DS) and Fragile X syndrome (FXS) using conversational samples from the Expressive Language Sampling (ELS) Conversation task (Abbeduto et al., 2020, 2023). Participants (N = 50) contributed one matched autobiographical topic at two visits approximately 18 months apart. Episodic and semantic details were coded using the Autobiographical Interview (AI) framework (Levine et al., 2002), and narrative coherence was assessed using Semantic Distance (SemDis), a computational measure of conceptual relatedness (Beaty & Johnson, 2021). Multilevel models evaluated whether diagnostic group, expressive language, narrative length, and time predicted autobiographical memory performance. Across aims, children showed substantial variability in narrative output, with greater within-group than between-group differences. Diagnostic group did not significantly predict episodic detail production, and episodic content showed minimal change across time. Word count was the only significant predictor, indicating that children who produced more language provided more episodic content. No demographic or language variables uniquely predicted episodic detail production once narrative length was controlled. Semantic coherence was also stable across visits and did not differ by diagnostic group or narrative length. The only significant effect was a diagnostic group × CELF-FS interaction: higher expressive syntax predicted more coherent narratives among children with DS, whereas children with FXS showed a slight decrease in coherence as expressive syntax increased. Overall, findings indicate that expressive output, rather than diagnostic status, is the primary driver of autobiographical narrative performance in DS and FXS.
- Towards Accurate and Reliable Industrial Intrusion Detection Systems Using Shadow ReplicasNwodo, Kenechukwu Anthony (Virginia Tech, 2023-05-10)Supervisory Control and Data Acquisition (SCADA) systems manage the operations of a plethora of safety-critical industrial control systems. Due to their sensitive nature, SCADA systems have been the target of adversaries employing a wide range of attacks. This thesis proposes an approach to protect SCADA systems against attacks that evade detection because of the lack of a comprehensive view of both application and network-layer responses. Specifically, we leverage multiple open-source Network Intrusion Detection Systems (NIDSs) paired with a SCADA shadow replica to provide both network and application threat detection. The shadow replica is augmented with a Finite State Machine (FSM) to compute the anticipated states of both the SCADA system and connected devices. Isolated from the operational network, it is protected from direct front-end attacks. When the SCADA system becomes compromised, even without an IDS alert, the replica can expose the attack and offer an operational failover. We implement a prototype of our system and evaluate it against locally executed attacks on commercial out-of-the-box devices and public IoT datasets. Results indicate that incorporating the shadow replica alongside NIDSs can enhance detection coverage in our evaluations.
- Associations Between Resting State Functional Connectivity and Trajectories of General Psychopathology in Emerging AdolescentsDevine, Jenna Jones (Virginia Tech, 2025-12-16)Background: The general psychopathology “p-factor” captures shared variance across psychiatric symptoms and is associated with alterations in resting state functional connectivity (RSFC). Specifically, aberrant connectivity within and between networks responsible for higher-order cognition and attention has been concurrently related to higher levels of p-factor scores in youth. It remains unclear whether and how RSFC prospectively relates to future psychopathology during early adolescence, a developmental period during which many forms of disorders onset and worsen. Methods: Data from 9,344 preadolescents from the Adolescent Brain Cognitive Development (ABCD) study were analyzed to examine the relationship between baseline RSFC and trajectories of general psychopathology in early adolescence. I used longitudinal multilevel modeling to determine whether altered connectivity of the default mode (DMN), frontoparietal (FPN), salience (SN), ventral and dorsal attention (VAN and DAN), and cingulo-opercular (CON) networks were associated with between-person differences and within-person rates of change of p-factor scores over three years. Results: Findings indicate that reduced connectivity within-DMN and DAN, and reduced connectivity between DMN-DAN, DMN-CON, and VAN-CON were associated with higher levels of p-factors scores at baseline, and at the one-year, two-year, and three-year follow-ups. VAN-DAN and SN-CON hyperconnectivity and DMN-VAN hypoconnectivity were prospectively associated with steeper within-person quadratic rates of change in p-factor scores over time. Conclusions: Results suggest that altered connectivity between networks responsible for self-referential processing, filtering salient information, attention processing, and cognitive control may be a vulnerability for increased transdiagnostic psychopathology, exacerbated by significant developmental changes associated with emerging adolescence.
- Evaluating the role of flow and specific conductivity on stream metabolism across a mining-induced salinity gradient in the Appalachian CoalfieldMeehan, Caleigh Elizabeth (Virginia Tech, 2026-03-02)Freshwater salinization is a notable concern for headwater streams in Appalachia with the history of resource extraction in the region. Mountaintop removal/valley fill mining techniques in Appalachia result in the burial of headwater streams and mobilization of ions, specifically SO42-, Ca, and Mg into waters, raising specific conductivity (SpC). Organismal responses to salinization have been well documented in freshwater ecosystems, but there are few measurements assessing how salinity effects on organisms influence whole-ecosystem processes, specifically stream metabolism. Understanding how gross primary production (GPP) and ecosystem respiration (ER) respond to salinity, stream flow, and their association is needed to characterize the consequences of salinization on stream processes. To assess the role of salinization and discharge on metabolism, we recorded high-frequency SpC, discharge, and dissolved oxygen data in three headwater streams in the Appalachian (U.S.) coalfields, where mining has resulted in widespread headwater stream salinization. Sites included a reference stream (REF) with SpC ranging from 0.2 - 57.69 μS/cm, a mid-salinity site (MID; 2.03- 594.7 μS/cm), and a high-salinity site (HI; 84.6-1920 μS/cm) with similar flow regimes, helping to characterize these covarying and potentially interacting drivers of metabolism. Across all sites, SpC decreased with increased discharge and with significant breakpoints. This study did not find a clear relationship between SpC and ecosystem metabolism. All streams, regardless of SpC levels, were heterotrophic (|ER|>GPP). Our high salinity site had the highest GPP and ER, suggesting salt may subsidize ecosystem metabolism, though differences in canopy cover complicate this. While we saw no consistent effect of SpC on metabolism, deviation in patterns at mining-impacted sites from expected discharge-metabolism patterns at our reference sites suggests some impact of salinity. This study reinforces the need for research across diverse ecosystems and salinization sources to characterize the role of freshwater salinization on ecosystem metabolism, as mediated by discharge.
- Subband Stitching for D-Band MeasurementsBroome, Paul Wallace IV (Virginia Tech, 2026-02-24)
- An investigation of the anion chemistry of DiazepamReitter, Barbara E. (Virginia Polytechnic Institute and State University, 1979)
- Stability of a shallow planar truss model under multiple loadsValenta, Steven J. (Virginia Polytechnic Institute and State University, 1979)
- An evaluation of the action of polyelectrolyte coagulants as precursors to chloroform productionLittlefield, Elizabeth M. (Virginia Polytechnic Institute and State University, 1979)
- The acceleration of a journal-bearing rotor through the critical speedReiff, Dave Eric (Virginia Polytechnic Institute and State University, 1979)
- Estimating region-wide damages caused by the southern pine beetleReed, David Doss (Virginia Polytechnic Institute and State University, 1979)
- The effects of minimum wages on employment patterns: a case study of the Washington metropolitan areaLoizou, Mary Jane (Virginia Polytechnic Institute and State University, 1979)
- Composition and quality of red clover (Trifolium pratense L.) with seasons and growth stageMas, Carlos Jaime (Virginia Polytechnic Institute and State University, 1979)
- The use of biotic value allocation in the assessment of heated dischargesLeslie, Michele (Virginia Polytechnic Institute and State University, 1979)