Masters Theses

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  • The Emergence of Lyme Disease in Appalachia (2000-2019)
    Otieno, Geoffrey Omondi (Virginia Tech, 2024-03-15)
    Emerging infectious diseases continue to threaten human health and healthcare resources across the world, and with the sustained emergence of some like Lyme disease, this trend is only expected to get worse. Even though some research has examined the spread of Lyme disease in different parts of the United States, focusing on its origin, spread, surveillance, and reporting, there has been minimal research on the recent spread of Lyme disease into and within Central and Southern Appalachia. This is an important gap, considering that this region is at the edge of the disease's expanding incidence and range. Considering this factor and the consequences that this disease may have on the residents of Appalachia who already face an array of underlying problems like chronic conditions, decreased access to health care, and exposure through outdoor work like resource extraction, addressing this gap will be important in understanding the current and future spatial range and impacts of the continued emergence of Lyme disease in Appalachia. This study thus sought to examine the extent of the emergence of Lyme disease in Appalachia between 2000 and 2019 using spatial scan statistic. This type of analysis uses spatiotemporal information to quantify disease emergence and diffusion using retrospective case and location data within a GIS environment; hence it helped quantify the spatial distribution and diffusion of Lyme disease into and within Appalachia and identify additional areas that can be targeted with public health prevention measures. We found five statistically significant clusters of Lyme disease across the contiguous US, indicating that the disease expanded spatially over the study period. Lyme disease has more than tripled across the US, with the number of counties with RR>1 increasing from 130 in 2000 to 453 by 2019. Lyme disease also increased more than eightfold in Appalachia, with spread southwards into and within Appalachia. The number of Appalachian counties with RR>1 increased from 16 in 2000 to 127 in 2019. These findings are important in understanding the current and future spatial range and the impacts of the continued emergence of Lyme disease in Appalachia. With this understanding, we can minimize the misdiagnosis of Lyme disease and inform public health action to reduce public vulnerability.
  • Tire Performance Estimation Under Combined Slip and Empirical Parametrization of the Tire Rut on Dry Sand
    Ravichandran, Nikhil (Virginia Tech, 2024-03-15)
    Applications like military, agriculture, and extra-planetary explorations require the successful navigation of vehicles across different types of terrain like soil, mud, and snow. As the properties of the terrain heavily influence the interaction with the tire, it is necessary to characterize the terrain from a tire performance and vehicle mobility perspective. Failure to properly understand the tire-terrain interaction can lead to undesirable conditions like loss of vehicle mobility due to excessive sinkage. As a result, it is essential to understand the tire terrain interaction between an off-road tire and a sandy terrain. This study was done to assess the performance of tires in both pure slip (only traction and braking) and combined slip conditions (steering and acceleration). A single-wheel indoor test rig was used to conduct tests under different conditions and a force transducer was used to capture the forces and moments generated in the tire hub. In addition to this, the tire footprint was captured with the help of a light-based 3-D scanner. Key parameters were defined in the 3D scan, and these parameters were correlated to the input test conditions. Additionally, a grid of force sensors was made, and measurements of the normal force acting at a depth below the undisturbed terrain were taken. Inferences were made about the linear speed of the wheel and the length of the pressure bulb under the tire.
  • Exploiting Update Leakage in Searchable Symmetric Encryption
    Haltiwanger, Jacob Sayid (Virginia Tech, 2024-03-15)
    Dynamic Searchable Symmetric Encryption (DSSE) provides efficient techniques for securely searching and updating an encrypted database. However, efficient DSSE schemes leak some sensitive information to the server. Recent works have implemented forward and backward privacy as security properties to reduce the amount of information leaked during update operations. Many attacks have shown that leakage from search operations can be abused to compromise the privacy of client queries. However, the attack literature has not rigorously investigated techniques to abuse update leakage. In this work, we investigate update leakage under DSSE schemes with forward and backward privacy from the perspective of a passive adversary. We propose two attacks based on a maximum likelihood estimation approach, the UFID Attack and the UF Attack, which target forward-private DSSE schemes with no backward privacy and Level 2 backward privacy, respectively. These are the first attacks to show that it is possible to leverage the frequency and contents of updates to recover client queries. We propose a variant of each attack which allows the update leakage to be combined with search pattern leakage to achieve higher accuracy. We evaluate our attacks against a real-world dataset and show that using update leakage can improve the accuracy of attacks against DSSE schemes, especially those without backward privacy.
  • Demography of a declining Dunlin (Calidris alpina arcticola): influences on adult survival and mate fidelity of an Arctic-breeding migratory shorebird
    Hermanns, Lindsay F. (Virginia Tech, 2024-03-15)
    Understanding what restricts vital rates is crucial in conservation efforts. For migratory birds, vital rates can be impacted by conditions experienced throughout the year. Migratory shorebird populations are rapidly declining, including populations of Dunlin (Calidris alpina arcticola), an Arctic-breeding shorebird. Prior adult survival estimates (0.41– 0.60) appeared insufficient to maintain a stationary population, however, it was unclear if estimates were reflective of bias or a real survival signal. Additionally, C. a. arcticola mate fidelity has yet to be determined, and because demographic rates can be linked to breeding ecology, understanding factors affecting both adult survival and mate fidelity might illuminate specific constraints on demographic rates for this species. I used a Barker (1997) model to estimate true survival (unbiased relative to fidelity) rates of adult C. a. arcticola using 19 years (2003 – 2021) of mark-recapture data and environmental data, collected from a breeding area, Utqiaġvik, Alaska, U.S.A. Breeding site data were supplemented with resighting observations and habitat data from non-breeding sites in eastern Asia (Japan, China, Taiwan). I examined breeding site environmental (temperature, snow melt date, precipitation) and ecological (predator abundance and predator-prey cycles, food resources, shorebird nesting density) in conjunction non-breeding site habitat (area of intertidal extent) effects on survival estimates. True survival averaged 0.62 (95% C.I. 0.50 – 0.72), and marginally declined six percent throughout the study period. Survival was positively related to intertidal extent on non-breeding grounds and heavy precipitation events on the breeding grounds; with precipitation influence on survival likely being driven by outliers in the data. I propose intertidal habitat (which declined 22% across 19 years) is likely a core driver of low survival rates. These results enforce that low adult survival rates are suppressing C. a. arcticola populations, as while other demographic rates (reproductive output, breeding propensity) are comparable with North American Arctic-breeding C. alpina subspecies, both adult survival rates and estimated population growth remain relatively lower. I emphasize that conservation efforts should be focused at areas currently losing intertidal habitat within the East Asian-Australasian Flyway to mitigate future C. a. arcticola declines. Using C. a. arcticola breeding site data, I tested four hypotheses to understand divorce in C. a. arcticola: the better option hypothesis, in which divorce improves reproductive success by obtaining a higher quality mate; the habitat mediated hypothesis, when divorce might occur if an opportunity exists to nest at a higher quality site than the prior breeding season; musical chairs, in which divorce is related to site-specific settlement choices upon arrival to the breeding grounds; and bet-hedging, in which divorce is more likely when mates arrive to the breeding grounds asynchronously, and an individual will pair with a new mate to avoid the cost of waiting for a previous mate to return to it. I used a logistic regression model to investigate effects on C. a. arcticola divorce with environmental and ecological factors that might influence divorce. Of the females nesting in consecutive years, 20% of those females divorced; and in the cases of males nesting in consecutive years, 55% of those males divorced. Both sexes were more likely to divorce when there was greater availability of experienced mates on the breeding grounds, significantly in males (β = 0.81, 95% CI = -0.65 – 2.28), compared to females (β = 1.27, 95% CI = 0.28 − 2.25). The results indicate males divorce behavior supports the better-option hypothesis, in which males divorced to "upgrade" to a mate with more breeding experience than their prior mate. However, male divorce behaviors also supported the bet-hedging hypothesis, as evidenced by similar nest initiation dates between divorced and reuniting males, which indicated males may divorce to avoid reproductive costs associated with waiting for a later-returning mate. Female divorce behavior was linked to either the habitat-mediated hypothesis, in which individuals attempt to acquire better habitat than their prior breeding site, or the better-option hypothesis, both evidenced by divorced females improving their reproductive success from the prior year. Divorced females exhibited higher egg success rates compared to divorced males, indicating females are likely the sex breaking the pair. Together, the results present novel information concerning C. a. arcticola. The first chapter presents direct connections between intertidal habitat loss and lower adult survival, and enforce calls for restoration of Asian intertidal areas along flyways to aid the conservation of migratory shorebirds. The second chapter provides the first estimates of C. a. arcticola mate fidelity and insight towards better understanding migratory shorebird breeding ecology.  
  • Comparison of Cation-Anion Oxidizer Pairings in Electrically Controllable Solid Propellants
    Sellards, Emily Rose (Virginia Tech, 2024-02-13)
    Electrically controllable solid propellants are an area of interest as a viable solution to the lack of throttle-ability in solid propellant rocket motors. Existing studies have focused on propellants compositions using hydroxyl-ammonium nitrate, ammonium nitrate, or lithium perchlorate as oxidizers. Additionally, the thermochemical and electrochemical reaction mechanisms have not yet been fully defined. The research in this thesis explores the nitrate and perchlorate oxidizer families to compare their cation-anion relationships. Using these oxidizers, pseudo electrically controllable solid propellant compositions were created with the addition of multi-wall carbon nanotubes to enhance ohmic heating capabilities. These additives were selected based on theory that with a non-complexing polymer, an oxidizer melt layer is required for ions to dissociate and electrically controlled ignition to occur. Using an applied voltage, ignition delay and current draw experiments were performed to expand on prior findings that ignition delay follows oxidizer melt temperature while mobility is associated with the size of the ionic radii. Additionally, neat oxidizer pellets were electrically decomposed to determine their linear regression rate. These results help to characterize the mechanism of reaction. This advances the knowledge of oxidizers in electrically controllable applications.
  • Surrogate Analysis and Calibration of Safety-Related Driver Behavior Modeling in Microscopic Traffic Simulation and Driving Simulator for Aggressive Driving
    Hong, Dawei (Virginia Tech, 2024-03-12)
    The increasingly urbanized world needs a solution to solve one of the most difficult problems – traffic congestion and safety. Researchers, consultants, and local officials are all attempting to solve these problems with different methods. However, it is apparent that understanding the driving behaviors on the roadway network and implementing roadway configurations accordingly is one of the great solutions. Therefore, the modeling of driving behavior would be the focus of this two-part thesis. Chapter two of this thesis will elaborate on the modeling of various driving behavior types in the microsimulation software by providing an easier-to-calibrate alternative for the driver behavior model in the microsimulation. The calibration method would leverage VISSIM, its highly customizable External driver model (EDM) API, JMP Pro's experiment design and sensitivity analysis, and SSAM's trajectory analysis. Then a set of driver model parameters are produced through sensitivity analysis, which is effective in producing a set of traffic conflicts that matches a preset target. Chapter three of this thesis focuses on simulating aggressive driving behaviors in a microsimulation and driving simulator co-simulation environment. Two co-simulation platforms are demonstrated, and the data collection are done in the VISSIM-Unity platform to collect microscopic driving data and trajectory data from the aggressive driver. Data analysis are performed on both datasets and determine the aggressive driver's safety impact.
  • A Role for Inositol Pyrophosphates in Arabidopsis Defense Against Herbivorous Insects
    Vanwinkle, Ashlynn Brook (Virginia Tech, 2024-03-12)
    Inositol pyrophosphates (PP-InsPs) are a family of molecules recently discovered to be implicated in a number of plant pathways such as auxin regulation, phosphate (Pi) sensing, and jasmonate-(JA)-regulated plant defense. Transgenic plants that overexpress inositol tetrakisphosphate 1-kinase (ITPK1) and the kinase domain of the dual domain diphosphoinositol pentakisphosphate kinase 2 (VIP2KD) have been previously studied to display uniquely elevated PP-InsPs. Here it is reported that the JA defense pathway is constitutively upregulated in VIP2KD OX plants, resulting in a lower rate of herbivory on the transgenic plants. ITPK1 OX, although also having elevated PP-InsPs, was fed upon by insect larvae comparably to Wild-Type Arabidopsis (WT). The data implicate VIP2, InsP8, and possibly the PP-InsP biosynthesis as a whole.
  • Trends in education as revealed in popular periodical literature published from 1949-53, inclusive
    Andrews, Mildred Bollinger (Virginia Polytechnic Institute, 1957)
  • A study of English usage on the part of twelfth-year pupils in a Virginia high school
    Jordan, Isabel Reynolds (Virginia Polytechnic Institute, 1955)
  • A study of college students' attitudes toward democratic living and principles
    Stone, Laura Reese (Virginia Polytechnic Institute, 1954)
  • Adhesively bonded systems subjected to substitute ocean water
    Aartun, Lars (Virginia Polytechnic Institute and State University, 1995)
  • Laboratory performance of geogrid and geotextile reinforced flexible pavements
    Smith, Timothy E. (Virginia Polytechnic Institute and State University, 1994)
  • Wildlife management on Virginia Conservation Reserve Program land: the farmer's view
    Miller, Edwin Joseph (Virginia Polytechnic Institute and State University, 1989)
  • The effects of hydrogen on the fracture behavior of welded carbon steel plate
    Watson, Thomas (Virginia Polytechnic Institute and State University, 1983)
  • Sequential sampling and analysis of precipitation in the Shenandoah Valley
    Walker, Allen R. (Allen Randall) (Virginia Polytechnic Institute and State University, 1983)
  • The effects of industry in Smyth County
    Broyles Thomas Clark (Virginia Polytechnic Institute, 1954)
  • The effect of mercury exposure and season on the physiological status of field collected rock bass
    Bidwell, Joseph R. (Virginia Polytechnic Institute and State University, 1988)
  • Dam type: maternal effects upon dam reproductive performance, calf mortality to weaning and preweaning growth parameters
    Kirsch, Gretchen L. (Gretchen Lise) (Virginia Polytechnic Institute and State University, 1983)