Masters Theses

Permanent URI for this collection

https://hdl.handle.net/10919/9291

Browse

Now showing 1 - 20 of 22999

On the application of variational mechanics in modeling the flow around a cylinder in ground effect
Zelaya Solano, Hever Jonathan (Virginia Tech, 2025-03-10)
For high Reynolds number flow over a cylinder near a flat moving surface, a potential flow model can be used to represent flow over the leading edge. However, the potential flow solution requires knowledge of the circulation around the cylinder. This circulation value can be found with an auxiliary condition using energy methods. Two choices for this variational condition exist at present. Gol'dshtik and Khanin (1978) postulated an ad-hoc variational approach that looks only at the velocity on the cylinder boundary. The other approach is guided by the novel work of Gonzalez and Taha (2022), an extension of Gauss' principle that considers the entire velocity field. The first approach was calculated by Petrov and Maklakov (2022), whereas the second approach has not yet been applied to a cylinder in ground effect. These two models are applied to modeling a cylinder in `ground effect', and the predictions of these two models are compared with a computational fluid dynamics (CFD) simulation by considering the pressure distribution and forces on the cylinder as a function of the cylinders proximity to the wall. For gap-to-radius ratios approximately between 1 and 6, it is demonstrated that gauss' principle provides an acceptable auxiliary condition that gives an accurate potential flow representation of the leading-edge flow. The model is also able to calculate the lift-coefficient given an approximation of the trailing-edge pressure distribution based on experiment.
Efficient Lateral Lane Position Sensing using Active Contour Modeling
Smith, Collin Mitchell (Virginia Tech, 2025-03-10)
As research into autonomous vehicles and Advanced Driver Assistance Systems (ADAS) has grown, research into computer vision techniques to detect objects and lane lines within images has also grown. The heavier computational load of modern techniques involving neural net- works and machine learning limits the ability to downscale to cheaper, less computationally- capable platforms when needed. The goal of the project is to develop a robust and computationally efficient method to estimate vehicle position within a lane. A clothoid lane line model based in real-world coor- dinates is projected into the image pixel-space where a novel approach to image segmentation and active contour modeling is performed. Another novel approach presented is the use of velocity as an input from a source outside the algorithm into the process to predict the initial conditions of the model in the next frame, rather than using the algorithm to produce an estimate of the velocity as an output to other systems. Validation is performed using the TuSimple dataset using both ideal and realistic scenarios to evaluate the performance of the various aspects of the algorithm against the current state-of-the-art methods.
Improved 2D Camera-Based Multi-Object Tracking for Autonomous Vehicles
Shinde, Omkar Mahesh (Virginia Tech, 2025-03-06)
Effective multi-object tracking is crucial for autonomous vehicles to navigate safely and efficiently in dynamic environments. To make autonomous vehicles more affordable one area to address is the computational limitations of the sensors, therefore, cameras are often the first choice sensor. Three challenges in implementation of multi-object tracking in autonomous vehicles are: 1) In these vehicles, sensors like cameras are not static, which can cause motion blur in the frames and make tracking inefficient. 2) Traditional methods for motion compensation, such as those used in Kalman Filter-based Multi-Object Tracking, require extensive parameter tuning to match features between consecutive frames accurately. 3) Simple intersection over union (IoU) metric is insufficient for reliable identification in such environments. This thesis proposes a novel methodology for 2D multi-object tracking in autonomous vehicles using a camera-based Tracking-by-Detection (TBD) approach, emphasizing four key innovations: (1) A real-time deblurring module to mitigate motion blur, ensuring clearer frames for accurate detection; (2) deep learning-based motion compensation module that adapts dynamically to varying motion patterns, enhancing robustness; (3) adaptive cost function for association, incorporating object appearance and temporal consistency to improve upon traditional IoU metrics; (4) The integration of the Unscented Kalman Filter to effectively address non-linearities in the tracking process, enhancing state estimation accuracy. To maintain a Simple Online and Realtime (SORT) framework, we enhance detection by fine-tuning YOLOv8 and YOLOv9 models using autonomous driving datasets like BDD100K and KITTI, which are specifically tailored for these scenarios. Additionally, we incorporate a non-linear approach using the UKF to better capture the influence of various tracking dynamics, further improving tracking performance. Our evaluations show that the proposed methodology significantly outperforms existing state-of-the-art methods while maintaining the same inference rate as the baseline SORT model. These advancements not only improve the accuracy and reliability of multi-object tracking but also reduce the computational burden associated with parameter tuning and motion compensation. Consequently, this work presents a robust and efficient tracking solution for autonomous vehicles, making it viable for real-world deployment under both computational and cost constraints.
Channel Sounding for D-Band Measurements
Frietchen, Samantha Michelle (Virginia Tech, 2025-03-06)
With the advent of new technologies introduced with each cellular generation, there is need to characterize a variety of different communications links. Areas, such as software defined radios, have been explored to fill flexibility needs for dynamic sounding. Also of heavy interest is exploring the terahertz frequency band for communication potential in 6G. However, numerous channel sounding measurements must be collected to properly support channel models for this region. The work detailed in this thesis aims to address this current research areas, with three main contributions: (1) detailing a flexible software define radio channel sounding architecture for easy, configurable channel sounding, (2) a comparison of sounding waveforms within a software defined radio framework, and (3) a detailed D-Band channel sounding framework and short-range path loss measurements. In the first contribution, a low cost radio (Ettus B210) is used as the channel sounding transmitter with a frequency retuning software to overcome the small instantaneous bandwidth of the low cost transmitter. In the second contribution, an upgraded version of the SDR channel sounder transmitter from the first contribution is used to compare different sounding waveforms. Each of the waveforms were tested within the same channel sounder architecture and the results were compared to make recommendations about which waveform to use in a variety of circumstance. In the third contribution, a new channel sounder, with sub-THz up and down conversion, was used to collect path loss measurements at D-Band. In these contributions, we target addressing two prominent areas of channel sounding research: use of low-cost radios for channel sounding and (sub-)terahetz frequency channel characterization.
Investigation of the Aerodynamic and Acoustic Performance of a Scaled eVTOL Propeller in Axial and Non-Axial Flight
Lundquist, Ryan David (Virginia Tech, 2025-03-04)
With the recent emergence of Urban Air Mobility (UAM) as a potential solution to alleviate congested urban transportation, concerns have arisen regarding adherence to noise emission regulations and general public acceptance. With the design of new and innovative air vehicles utilizing electric Vertical Takeoff and Landing (eVTOL) propulsion systems for UAM applications, significant gaps remain in the understanding of their aerodynamic and acoustic performance, particularly when interacting with disturbances such as turbulence generated by buildings. To address safety, noise, and performance challenges, effective optimization methods must be developed. However, there is a lack of sufficient experimental data to support these advancements. This study investigates the aerodynamic and acoustic performance of a scaled eVTOL propeller operating in both axial and non-axial flight. A comprehensive summary of the experimental propeller's design is provided. Thrust, torque, and sound pressure data are acquired from wind tunnel testing of the experimental propeller operating with various blade pitch angles, yaw angles, and under several inflow velocities. The experimental results are subsequently compared to a custom-developed Blade Element Momentum Theory (BEMT) utility for low-fidelity predictions. The findings aim to provide baseline data for Computational Fluid Dynamic (CFD) validation, enhancing predictive tools for advancing safe and efficient urban air transportation. Experimental results exhibit positive correlations between thrust, torque, and acoustic intensity with increasing yaw angle. The acoustic profile of the propeller at large yaw angles features an increase in broadband noise, a characteristic feature of Blade-Wake Interaction. Additionally, BEMT calculations predict thrust and torque within 10% accuracy of the measured data across most conditions. Supplementary calculations of the induced velocity fields offer preliminary insights into the distortion effects for future studies on interactions between eVTOL propellers and turbulent flows.
Using Passive Acoustic Monitoring to Estimate Bird Community Response to Land Management in Southeastern Georgia
Watson III, Daniel Hays (Virginia Tech, 2025-02-28)
Working lands, such as mine reclamation and timber production sites, may be able to provide supplementary habitat for declining disturbance-dependent birds, such as Bachman's Sparrow (Peucaea aestivalis) and Northern Bobwhite (Colinus virginianus). However, habitat use is likely contingent on specifics of land-use practices, especially those that could alter understory vegetation. My first research objective was to use autonomous recording units (ARUs) and BirdNET algorithms to compare the relative abundance of eight focal bird species across site treatments representing land management types: surface mine reclamation, timber production, young savanna, and mature savanna. All sites were established in upland pine (Pinus spp.) habitat throughout the southeastern Coastal Plain region of Georgia, USA from May-June 2024. I hypothesized that the mine reclamation site would support similar focal species, but in lower abundances than timber production and both savanna sites, and vegetation characteristics would also influence relative abundance along with site treatment. Model selection showed site treatment influenced relative abundance for all species and explained more variation in relative abundance than measured vegetation characteristics. The mine reclamation site had similar relative abundances for focal species when compared to the timber production site, suggesting these treatments provide comparable habitat. The young savanna site exhibited the highest abundances for most species, whereas the mature savanna site had lower abundances, suggesting some focal species may prefer habitat lacking overstories. Focal species responded differently to vegetation characteristics; for example, Common Nighthawk showed a positive response to grass cover, whereas Prairie Warbler responded negatively. My results provide strong evidence that site treatment influences the relative abundance of all focal species and highlight the need for future studies to parse out the exact mechanisms underlying these differences. Additionally, this study highlights the potential for working lands to provide habitat for disturbance-dependent birds and the effectiveness of using ARUs to assess the effects of land management on bird relative abundances. My second research objective assessed optimal survey frequency when using Royle-Nichols (RN) models to estimate abundance or relative abundance from ARU data. Passive acoustic monitoring with ARUs can enable efficient monitoring of avian populations. RN models may be well suited for estimating abundance or relative abundance from ARU detection/non-detection data; as repeated surveys can easily be conducted with ARUs. Yet, optimal survey effort using these methods remains unexplored. Using ARU data from four site treatments in southeastern Georgia, I assessed how survey frequency and mean cumulative detection probability influenced estimates for Blue Grosbeak (Passerina caerulea) and Bachman's Sparrow from May–June 2024. A baseline dataset of 50 daily surveys was subsampled into reduced frequencies: 25 surveys every 2nd day, 17 every 3rd day, 13 every 4th day, 8 every 7th day, and 5 every 10th day. RN models were fitted to each subsample. Abundance estimates decreased with subsampling, showing survey frequency arbitrarily influences estimates and RN models should be viewed as relative, not absolute, abundance estimates. However, the specific order of relative abundance across site treatments remained consistent for both species during subsampling, indicating RN models can still reliably infer effects across sites. Mean cumulative detection probability decreased with subsampling yet remained >70% for both species. Subsampling reduced precision in relative abundance estimates for both species; particularly for Bachman's Sparrow, emphasizing species-specific sensitivity to survey effort. However, subsampling every 2nd day or every 3rd day resulted in moderate losses of precision (≤ 34%) for both species, suggesting reduced survey frequency may be a viable strategy for efficient data collection depending on species detectability and study goals. Together, these findings from my research objectives highlight the potential of working lands to support disturbance-dependent bird conservation and demonstrate how passive acoustic monitoring with ARUs can be an effective tool for the conservation and management of bird populations.
Functions of Mediodorsal Thalamic Astrocytes in Cue-Based Learning
Marschalko, Kathleen Rose (Virginia Tech, 2025-02-25)
To successfully navigate daily life, organisms must be able to identify stimuli that are predictive of beneficial outcomes. A key thalamic nucleus involved in this process is the mediodorsal thalamus (MD), which bidirectionally communicates with the prefrontal cortex, facilitating cognitive and decision-making functions. Despite the MD's involvement in higher-order relays, the precise mechanisms underlying its astrocytic activity, its contribution to synaptic plasticity, and the subsequent effects on cognitive processing remain poorly understood. Emerging data highlights the pivotal role of astrocytes in regulating synaptic transmission, with astrocytic calcium activity being linked to gliotransmitter release. Abnormalities in astrocytic calcium activity have been found to impair learning and memory, thus insights into their mechanism during cognitive processes in the MD could reveal novel targets for investigating cognitive disorders. In this study, we investigated astrocytic activity during a cue-based learning task, uncovering notable differences in the timing of astrocytic calcium release between early and late stages of the task. To investigate plasticity-related changes between early and late stages, the density of astrocytes, glutamatergic nerve terminals, and astrocyte glutamate transporter proteins will be examined. We found that MD astrocytic calcium activity responds to the initial cue and the reward, suggesting that this activity mediates the temporal dynamics of synaptic plasticity, influencing how thalamic circuits adjust to both cues and outcomes during learning.
Impact of Interdependent Physical and Social characteristics on Housing Recovery Following Tropical Cyclones
Haque, Anmol (Virginia Tech, 2021-09-03)
The aim of this study is to explore the interdependent impact of existing social (median household income) and physical (percent damage) characteristics on housing risk of a coastal community as the percent chance of vacancy followed by tropical cyclones. We developed a housing risk assessment framework for an idealized hypothetical study area consistent with existing physical and social characteristics of Hampton Roads, Virginia, USA. The housing risk assessment framework was simulated for a time period of 10 years and the distinct trends in housing recovery were observed for variations in the physical and social variables. The unique feature of the framework is its ability to demonstrate housing recovery risk for single and consecutive multi-hazards (combined storm surge and wind hazard) with a consideration of both existing physical and social characteristics of a coastal community. The applicability of the framework further lies in user-defined scenarios like events of gentrification (lower income households being replaced by medium income households) and modified recovery rates. To distinguish between the trends we grouped the percent damage and median household income in high, low and medium classes. It was found that the highest damage and lowest income groups recovered the slowest with an expected residual chance of housing vacancy even after 10 years. Some major findings of the study included - multi-hazards caused an amplification in housing risk compared to single hazard and gentrification was found to reduce effects of multi-hazard and hence faster recovery than without gentrification. This framework therefore has promising implications in disaster resilience and risk management policies and planning for coastal multi-hazards as it can predict impacts of extreme scenarios along with contributions towards the need for immediate intervention post disaster.
Numerical and Data Analysis of a Portable Free Fall Penetremeter
Moore, Jonathan Joseph (Virginia Tech, 2025-02-24)
Coastal environments are among the most economically and environmentally significant regions on Earth. However, rising sea levels and increasingly frequent storms driven by climate change pose growing risks to these critical zones. Understanding and predicting the evolution of coastal environments requires advanced models and high-resolution geotechnical data to characterize the mechanical behavior of coastal soils. Portable free-fall penetrometers (PFFPs) are widely used for this purpose, offering a rapid and efficient means of collecting in situ soil data. Despite their utility, the interpretation of PFFP data remains uncertain due to the empirical nature of existing methods used to infer soil properties from impact acceleration measurements. This research aims to improve the reliability of PFFP-based soil characterization by advancing both numerical modeling and data processing techniques. To this end, a two-pronged approach was taken. First, efforts were made to refine and streamline numerical modeling techniques to work towards the creation of a digital twin of BlueDrop PFFP impacting into the soil. This included identifying the current limitations of the MPM framework to simulate PFFP impact and addressing some of these limitations. In particular, this thesis focuses on the mitigation of volumetric locking by means of the implementation of the B-Bar algorithm in quadrilateral elements and the availability of strain-rate advanced consecutive models by testing the accuracy and efficiency of different stress integration algorithms. In addition, a Python library was also developed to streamline the testing of soil constitutive models using the IncrementalDriver software. Second, the processing of BlueDrop field data was centralized, standardized, and automated through the development of a Python library integrated with an SQLite database. This ensures consistency and accessibility of PFFP datasets for broader scientific and engineering applications. By advancing data processing methodologies and improving numerical modeling capabilities, this research contributes to a more rigorous framework for interpreting PFFP measurements and understanding soil behavior during impact. These developments support broader efforts to enhance geotechnical modeling of coastal systems, ultimately aiding in the prediction and management of environmental changes affecting these vulnerable regions.
Performance in Multipath & High-Mobility Leveraging Terrestrial and Satellite Networks
Ghafoori, Amirreza (Virginia Tech, 2024-12-17)
High-mobility scenarios, such as those experienced by autonomous vehicles or users in transit, demand reliable and high-performance network communication. This thesis presents a comprehensive measurement study comparing the performance of terrestrial 5G networks (ATT, Verizon, T-Mobile) and the Starlink satellite network in high-mobility scenarios. The study evaluates key performance metrics, including throughput and latency, across six globally distributed server locations: Virginia, California, Paris, Singapore, Tokyo, and Sydney. Measurements were conducted using a carefully designed testbed while driving a total of 860 km across urban, suburban, and rural terrains. The results reveal that 5G networks, particularly Verizon, excel in urban regions with higher peak throughput and lower latency, while Starlink demonstrates consistent performance in rural and remote areas. The impact of vehicle speed on network performance was also analyzed, highlighting Starlink’s resilience to high speeds compared to terrestrial networks. Heatmaps and statistical analyses underscore the complementary strengths of these networks, suggesting their integration via multipath protocols (e.g., MPTCP, MPQUIC) could enhance reliability and performance in critical applications such as autonomous vehicles, video conferencing, and AR/VR. This work provides valuable insights into the behavior of 5G and satellite networks in real-world high-mobility scenarios and lays a foundation for designing robust and efficient communication systems.
Toward Transformer-based Large Energy Models for Smart Energy Management
Gu, Yueyan (Virginia Tech, 2024-11-01)
Buildings contribute significantly to global energy demand and emissions, highlighting the need for precise energy forecasting for effective management. Existing research tends to focus on specific target problems, such as individual buildings or small groups of buildings, leading to current challenges in data-driven energy forecasting, including dependence on data quality and quantity, limited generalizability, and computational inefficiency. To address these challenges, Generalized Energy Models (GEMs) for energy forecasting can potentially be developed using large-scale datasets. Transformer architectures, known for their scalability, ability to capture long-term dependencies, and efficiency in parallel processing of large datasets, are considered good candidates for GEMs. In this study, we tested the hypothesis that GEMs can be efficiently developed to outperform in-situ models trained on individual buildings. To this end, we investigated and compared three candidate multi-variate Transformer architectures, utilizing both zero-shot and fine-tuning strategies, with data from 1,014 buildings. The results, evaluated across three prediction horizons (24, 72, and 168 hours), confirm that GEMs significantly outperform Transformer-based in-situ (i.e., building-specific) models. Fine-tuned GEMs showed performance improvements of up to 28% and reduced training time by 55%. Besides Transformer-based in-situ models, GEMs outperformed several state-of-the-art non-Transformer deep learning baseline models in efficiency and efficiency. We further explored the answer to a number of questions including the required data size for effective fine-tuning, as well as the impact of input sub-sequence length and pre-training dataset size on GEM performance. The findings show a significant performance boost by using larger pre-training datasets, highlighting the potential for larger GEMs using web-scale global data to move toward Large Energy Models (LEM).
Evolution of Preconsolidation Pressure of Normally Consolidated Clays Over Full Temperature Range
Gevorgyan, Suzanna (Virginia Tech, 2025-02-19)
While it has been established that temperature can change the preconsolidation pressure of clays, the current understanding is limited to specific ranges of temperatures, with temperatures above freezing being studied entirely independently of temperatures below freezing. However, as temperature is a continuous domain and clays may be subjected to both above- and below- freezing temperatures over the course of an engineering application, a unified view is necessary. The first goal of this thesis is to develop a single model which can be used to predict the preconsolidation pressure of a normally consolidated clay at any temperature over a wide range which includes both frozen and elevated temperatures. To do so, consolidation tests were run at various temperatures between -7 °C and 50 °C, and the yield stress at each consolidation temperature was determined. As previous studies have established that the temperature response of clays is dependent upon their mechanical stress history, the specimens were consolidated initially at a reference temperature until they reached the normally consolidated state. Subsequently, the temperature of the specimens was changed and the volume changes during the temperature change stage were recorded. Once the specimens stabilized at the new temperature, they were consolidated once again and the preconsolidation pressure determined at the new consolidation temperature. The volumetric strains and changes in preconsolidation pressure for each temperature used in this study align generally with the previous data published for each temperature domain. Heating led to a decrease in the volume of the specimens, cooling to minimal strain, and freezing to an increase in the specimen volume. Changing the consolidation temperature by either heating, cooling, or freezing the specimen led to various degrees of increase in the preconsolidation pressure. A mathematical model was developed to fit the observed preconsolidation pressures at each consolidation temperature. This model can be used to predict the yield stress of NC kaolinite at any temperature within the tested range, and captures the smaller magnitude increases in yield stress which occur upon heating and cooling as well as the large increases which occur upon freezing the clay. With the effects of unidirectional thermal paths having been treated in the previous portion, a second investigation was also undertaken to assess how much of the temperature history of the soil might influence the behavior at its final consolidation temperature. In particular, the impacts of previous freezing on the preconsolidation pressure at elevated temperatures were investigated. The same clay material was first consolidated to the NC state and then frozen to -15 °C. Subsequently, the material was thawed or heated to various final temperatures and consolidated further to determine the preconsolidation pressure. The results of these tests indicate that the preconsolidation pressure was independent of the consolidation temperature for previously-frozen soil. While increasing contractive axial strains were recorded with increasing temperature, there was no accompanying increase in the preconsolidation pressure. These results indicate the thermal history of the clay can alter its behavior at the current temperature, overriding the effects of the most recent thermal path.
Vector Based Control for Power Electronics Dominated AC Power Grid
Ashraf, Haris Bin (Virginia Tech, 2025-02-14)
The global trend towards electrifying the grid has positioned power electronics at the forefront of modern power systems. To control power electronics in grid-connected applications, Grid Forming (GFM) control has become a focal point of research. GFM control utilizes control laws derived from steady-state relationships in the phasor domain. Although these control methods have historically performed well in traditional power systems dominated by electrical machines, they exhibit unexpected control issues in power electronics-dominant power systems. The root of these unexpected behaviors lies in the foundational assumptions of these control methods (Droop control and Virtual Synchronous Machine) i.e. frequency is considered to be a steady state quantity which is constant within the fundamental line cycle. This thesis critically examines these assumptions and elucidates their potential inapplicability in power electronics-dominated power systems. This thesis also introduces vectors as an alternative representation of voltages and currents. Unlike phasors, vectors are instantaneous and time-varying representation of electrical quantities at any point in time, defined by three time-varying values: Magnitude, Polar angle, and Azimuthal angle, using the spherical coordinate system. An initial attempt to demonstrate the capability of using these vectors to control the active and reactive power in inverters connected to the grid has also been presented in this thesis. The proposed vector-based control is able to track the commanded power setpoints within a fraction of the fundamental AC voltage cycle.
Design and Testing of a Bubble Generator for Molten Salt Surrogate Fluid
Breeden, Courts Holland (Virginia Tech, 2025-02-13)
This study explores the design, testing, and modeling of a bubble injector intended for use in studying bubble dynamics in molten salt reactors using a room temperature surrogate fluid by matching the Reynolds number, Eötvös number, and Morton number defined by the properties of the helium bubbles in the pump bowl of the Molten Salt Reactor Experiment (MSRE). The injector, constructed from polydimethylsiloxane (PDMS) and acrylic, was tested to generate bubbles within a precise size range suitable for simulating conditions in molten salt reactors. Experimental data showed that the equivalent bubble diameter is directly proportional to gas flow rate and inversely proportional to liquid flow rate, with clear trends emerging when data were subdivided into constant flow rate plots. The study applied and adapted the bubble size control model proposed by Lu et al. (2014), revealing limitations in existing models under modified conditions such as an elongated two-phase channel. A novel model was developed to better predict bubble size, incorporating dependencies on both flow rate ratios and the capillary number of the microchannels. The injector's design facilitates convenient modifications in channel geometry to achieve target bubble sizes, and future improvements in pressure monitoring and imaging are recommended. This work contributes to the advancement of microfluidic bubble injection technology.
Reproductive Injustice: Abortion Restrictions and Maternal Mortality Rates
Ayala, Calinda Carolina (Virginia Tech, 2025-02-13)
This research establishes a statistically significant connection between maternal mortality rates and abortion restrictions from a reproductive injustice perspective, integrating the theory of necropolitics. Using a time-series cross-sectional analysis of all 50 U.S. states from 2009 to 2019, this study highlights the impact of restrictive abortion policies during a period of intensified legislative activity, including pre-abortion counseling requirements, TRAP laws, and trigger laws. Data from the Guttmacher Institute's hostility scale and the Institute for Health Metrics and Evaluation's maternal mortality statistics reveal that states with higher hostility toward abortion experienced increased maternal mortality. Notably, a 1% increase in state hostility is associated with a 0.45% rise in overall maternal mortality rates (p < 0.001). The analysis further demonstrates that each marginalized racial and ethnic group examined face heightened risks from higher abortion hostility, with maternal mortality rising among Hispanic women by 0.40% (p < 0.001); among non-Hispanic American Indian and Alaskan Native women increasing by 0.29% (p < 0.05); among non-Hispanic Asian, Native Hawaiian or Other Pacfic Islander women by 0.53% (p < 0.001); and non-Hispanic Black women by 0.39% (p < 0.001) per 1% increase in state hostility. However, the largest increase was found among non-Hispanic White women (p < 0.001). This study contributes to reproductive justice scholarship by incorporating a feminist and sociological perspective on the relationship between abortion restrictions and maternal mortality, particularly as moderated by race and ethnicity. The findings call for urgent policy interventions to dismantle systemic inequities in healthcare access, ensuring the protection of reproductive rights and the reduction of maternal mortality across all communities.
Urban Brownfield Integration – Site Planning and Design Implementation of the Baltimore Community Center
Scherer, Hope Anne (Virginia Tech, 2025-02-13)
Many of the mid-west and eastern cities in the United States were first formed through industrial manufacturing which relied on waterways – rivers, canals, and lakes – to ship the necessary raw materials. As industry and manufacturing declined throughout the 19th century, many cities were left with large, waterfront sites, often contaminated with chemicals and empty industrial buildings. These waterfront sites – designated "Urban Brownfields" – became important potential centerpieces to the revitalization of the cities where manufacturing facilities were slowly being replaced by buildings that would better serve the modern community for tourism, office space, and land use uses ranging from parks to centers for cultural arts. The basic premise of this thesis project is to investigate what can be done to reclaim the often-vast parcels of land that are considered Urban Brownfields – land that once held active industry, but now is left abandoned. The Allied Chemical plant site in Baltimore is a prototypical site that exemplifies many of the issues shared by these types of sites. The project is a vehicle to explore design in terms of structures and their relationship to "domesticated nature." The project development process also considers urban planning and components of growth for urban areas, as well as the importance of density. Design elements incorporate industrial imagery and considerations relative to human scale and experience – from macro to micro. Out of these goals stemmed a project that became the Baltimore Community Waterfront Park and Recreation Center.
xG-SS: Towards a Hardware and Simulation Experimentation Platform for Spectrum Sharing with 5G NR-U
Sathish, Aditya (Virginia Tech, 2025-02-13)
The advent of 6th Generation (6G) wireless systems and the increasing demand for spectrum to accommodate a growing number of users and diverse services have necessitated novel ap- proaches to spectrum sharing. Among these approaches, distributed spectrum sharing offers the most flexibility by allowing real-time spectrum use based on user demand and network con- straints. However, this approach presents significant challenges due to the probabilistic nature of system dynamics and the autonomous behavior of each incumbent, which require advanced strategies to predict and manage spectrum usage effectively. Listen-Before-Talk (LBT) is the most widely adopted method for distributed spectrum sharing in unlicensed bands. While LBT has been extensively studied in the context of Wireless Fidelity (Wi-Fi), providing key insights into its performance under various conditions, its application in synchronized, slot-scheduled sys- tems like New Radio (NR) Unlicensed (NR-U) remains underexplored. This gap exists primarily due to the lack of hardware testbeds and system-level simulation platforms that are essential for evaluating the effectiveness of LBT in NR-U and for developing improved methods for operating in shared spectrums with deterministic worst-case delays. This thesis addresses the existing gap by proposing a reference architecture for spectrum sharing based on 5th Generation (5G) NR-U to facilitate further research and experimentation in distributed spectrum sharing. The approach taken in this thesis is threefold: (i) the establishment of a system architecture for an end-to-end 5G NR-U system based on existing work in hardware and simulation models; (ii) the realization of this system model on the Network Simulator 3 (ns-3) discrete-event simulator by leveraging developments from the 5G Long-Term Evolution (LTE) Enhanced Packet Core (EPC) Network Simulator (LENA) (5G-LENA) system architecture; and (iii) the conceptual design for implement- ing the Physical (PHY) layer of a 5G NR-U system using Software-Defined Radios (SDRs) and the OpenAirInterface (OAI) 5G software platform. A key novelty of this reference architecture is the proposed mitigation of LBT latency in split architectures with SDRs and General-Purpose Processors (GPPs). The LBT block is designed for implementation within the Field Program- ming Gate Array (FPGA) of Universal Software Radio Peripheral (USRP) SDRs, thereby enabling heterogeneous coexistence experimentation with Common Off-the-Shelf (COTS) Wi-Fi Access Points (APs). The thesis presents a simulation-based experiment that optimizes traffic manage- ment to improve the ability to serve delay-critical traffic in NR-U systems operating under ho- mogeneous coexistence conditions. The thesis then outlines a reference design for exploring heterogeneous coexistence between Wi-Fi and NR-U in the sub-7 GHz spectrum. This concep- tual framework leverages a proposed hardware experimentation platform with SDRs. The in- frastructure supporting these simulations and proposed hardware experiments is envisioned as virtualized resources over the Commonwealth Cyber Initiative (CCI) xG Testbed, with potential extensions for advanced spectrum sharing use cases across indoor and outdoor testbed sites. The thesis outlines potential enhancements to this testbed, specifically toward spectrum sharing with scheduled-access systems.
Assessing the Potential of Granular Activated Carbon Filters to Limit Pathogen Growth in Drinking Water Plumbing Through Probiotic Versus Prebiotic Mechanisms
Deck, Madeline Emma (Virginia Tech, 2025-02-06)
Legionella pneumophila (Lp) and nontuberculous mycobacteria (NTM) are opportunistic pathogens that can be transmitted via drinking water, when tiny droplets containing the bacteria are aerosolized and inhaled during activities such as showering. The resulting respiratory illnesses, Legionnaires' Disease and NTM lung disease, are among the leading sources of drinking water associated disease in the United States and other parts of the world. Lp and NTM are both difficult to control, because they establish as part of natural biofilms that form within the interiors of pipes and fixtures that deliver drinking water to the point of use. These pathogens are especially problematic within premise (i.e., building) plumbing, where intermittent use throughout the day leads to long periods of stagnation, increased water age, warmer temperatures, and depleted disinfectant residuals that exacerbate bacterial growth. The recent advent of high throughput DNA sequencing has led to the discovery that drinking water microbiomes are diverse, complex, and largely comprised of non-pathogenic microbes. This has further led researchers to hypothesize that the microbial ecology of this diverse microbiome could be harnessed as a natural means to control Lp and NTM, i.e., a "probiotic" approach, but such an approach has not yet been demonstrated. The objective of this study was to assess this hypothesis by utilizing biologically active granular activated carbon (GAC) filters, which are already a widely used drinking water treatment both at the municipal and household scale, as a means to naturally shape the microbial ecology of downstream premise plumbing and inhibit Lp and NTM proliferation. GAC has an extremely high surface area that aids removal of organic carbon via adsorption but also provides an ideal habitat for establishment of biofilms, which removes organic carbon from the water via biodegradation. Convectively-mixed pipe reactors (CMPRs) were used for replicable simulation of premise plumbing distal taps. The CMPRs consisted of four-foot-long closed polyvinyl chloride (PVC) pipe segments with the sealed bottom portion resting in a ~48 °C water bath and with the top portion plugged and exposed to the cooler, ambient atmosphere (25 °C in this study), inducing convective mixing and resulting in an internal water temperature of 37 °C. PVC was chosen because it is common in premise plumbing and generally leaches the least organic carbon among the different types of plastic pipe. Four different influent water conditions were implemented in the experimental design: 1) Untreated, dechlorinated municipal tap water with high organic carbon and low biomass; 2) GAC-treated tap water with low organic carbon and elevated, viable biomass; 3) GAC-treated + 0.22-m pore size membrane-filtered tap water to remove both nutrients and biomass; 4) GAC-treated tap water pasteurized at 70 °C with low nutrients and elevated, killed biomass. The 0.22-m pore size membrane filter simulated the use of a building scale particle filter, while pasteurization simulated water passing through a hot water heater at an elevated temperature recommended for pathogen thermal disinfection. To understand the influence of these experimental conditions on older pipes containing mature biofilms versus new pipes that leach more organics and are being freshly colonized, a set of older pipes colonized with mature ~4-year-old biofilms were compared to newly purchased pipes. Each set of pipes was tested in triplicate for the four different experimental conditions with the full volume replaced three times a week for eight months, simulating infrequently used taps containing warm, continuously mixing water thought to create conditions at a very high risk for opportunistic pathogen growth. In the aged CMPR bulk water effluents, droplet-digital-polymerase-chain-reaction measurements showed a one-log reduction of Lp and NTM when receiving GAC-treated or GAC-treated + particle-filtered influent water versus receiving dechlorinated municipal tap water or GAC-treated + pasteurized water. These findings suggest that decreased biodegradable dissolved organic carbon achieved by GAC filtration acted to suppress Lp and NTM growth, while the additional step of biomass removal by particle filtration provided a more modest benefit. In the CMPRs consisting of new pipes, concentrations of Lp and NTMs in the effluent bulk water were similar among the experimental conditions, except that the CMPRs receiving the GAC-treated + particle-filtered influent water experienced a two-log reduction in NTMs. These results demonstrate that the colonization and proliferation of NTM within premise plumbing can be significantly controlled by limiting nutrients and biomass in the influent water. This work demonstrates the potential of harnessing GAC-treatment as a means to Control Lp and NTM in premise plumbing via nutrient removal. In scenarios where chemical disinfectants have been depleted, off-the-shelf GAC-treatment used as point-of-entry treatment to large buildings with recirculating plumbing could provide benefits that have previously been unrecognized. Alternatively, pasteurization in very hot water heaters could provide a short-term disinfection benefit, but eventually the nutrients embodied in the dead biomass undermine the positive influence of the nutrient removal provided by the GAC-treatment. Improved mechanistic understanding of probiotic strategies to opportunistic pathogen control would be needed to overcome inherent limitations to the approaches examined herein, if more effective control is desired in the absence of thermal or chemical disinfection.
A Choreography of Water, Light, and Space Interplay
Pourkhodagholi, Negar (Virginia Tech, 2025-02-06)
This thesis explores the interplay of water, light, and space in a choreography of architectural sequences. Through the design of a spa, it explores how these elements can evoke sensory and emotional responses, shaping human perception and interaction within spatial environments. The project unfolds as a choreography where water in its various states and qualities interacts with light and architectural space, creating an immersive sensory journey. This choreography carefully modulates centrifugal (outward-directed) and centripetal (inward-directed) experiences, crafting a dynamic interplay between the individual and the surrounding space.
Improving Precision in Forest Inventory through Small Area Estimation for Loblolly Pine Plantations in Coastal Georgia
Subedi, Bipana (Virginia Tech, 2025-01-31)
The use of small area estimation (SAE) in forest inventory has shown promise for improving the precision of estimates needed for informed decision-making when sample data are sparse. We evaluated the potential of unit-level SAE for increasing the precision of stand-level estimates of basal area, volume, and above-ground biomass estimates in loblolly pine plantations in coastal Georgia. Following the unit-level approach, field plots sampled in plantations owned by Rayonier Inc. were georeferenced to aerial lidar data using high-quality GPS field coordinates. Results focused on A) gains in precision for stand-level basal area, volume, and above-ground biomass estimates achieved by combining data from field plots with lidar-derived canopy height models in a SAE framework, B) impacts of small sample sizes on the precision of estimated stand level attributes, and C) the effects of nonrandom field plot placement in stands of interest when using unit-level SAE. Findings indicate that higher precision is achievable with greater variance stability than what is possible from very small samples of field data alone. This was true for all three attributes of interest. With careful attention to checking assumptions of the unit-level SAE approach, the use of non-random sampling does not appear to impair SAE's ability to deliver unbiased estimates for forest plantation stands. Simulating the entire population's basal area to test for the effects of non-random plot placement showed that SAE is robust to the type of sampling technique used. However, results can be affected when sampling is intentionally biased. This work can be useful to landowners and forest managers working with southern loblolly pine plantations. By leveraging simulation techniques to generate non-random sampling data from the available random sampling data, this study attempted to bridge the gap between the available empirical data and the desired sampling framework, ultimately widening the applicability of SAE in forest inventory settings.

Browse

Recent Submissions