VTechWorks
VTechWorks provides global access to Virginia Tech scholarship, including journal articles, books, theses, dissertations, conference papers, slide presentations, technical reports, working papers, administrative documents, videos, images, and more by faculty, students, and staff. Faculty can deposit items to VTechWorks from Elements, including journal articles covered by the University open access policy. Email vtechworks@vt.edu for help.
Open Access Policy
Virginia Tech's open access policy enables researchers to deposit the accepted version of scholarly articles with no embargo.
Theses and Dissertations
Virginia Tech was first in the world to require ETDs in 1997, and continues to add scans of older theses and dissertations.
Open Textbooks
More than 50 freely available and openly licensed textbooks are among our most downloaded items.
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Recent Submissions
On holomorphic conformal structures associated with lattice polarized K3 surfaces
Malmendier, Andreas; Schultz, Michael T. (American Mathematical Society, 2025-06-25)
We discuss the connection between Picard-Fuchs equations for certain families of lattice polarized K3 surfaces and the construction of integrable holomorphic conformal structures on their period domains. We then compute an explicit example of a locally conformally flat holomorphic metric associated with generic Jacobian Kummer surfaces, which allows for a novel description of the local variation of complex structure.
Observational Studies of Rare Quasar Outflows: the FeLoBALs
Walker, Andrew Isaac (Virginia Tech, 2026-01-14)
The absorption spectra of quasar outflows are studied in order to determine their kinematic and energetic properties and how they affect their host galaxy and its surroundings. If an outflow is sufficiently powerful to have an effect, a process known as active galactic nucleus (AGN) feedback, it can deplete the galaxy's gas reservoir required to produce stars, quenching its star formation rate and thus regulating the host galaxy's evolution. There is a growing body of work studying a rare type of broad absorption line (BAL) quasar that is rich in ion{Fe}{ii} absorption features, as well as ones from similar low-ionization species such as ion{Ni}{ii}, ion{Cr}{ii}, and ion{Fe}{iii}, known as FeLoBALs.
By analyzing the spectra of these objects using data from the Ultraviolet Echelle Spectrograph at the Very Large Telescope (VLT/UVES), we can determine several properties of these outflows, including the hydrogen number density $n_H$, the hydrogen column density $N_H$, and the hydrogen ionization parameter $U_H$. These values can in turn be used to calculate the distance of the outflow from its central source $R$, the mass outflow rate $dot{M}$, and the kinetic luminosity $dot{E}_k$. We have found that FeLoBALs can cover a wide parameter space of these properties.
In the first object, quasar SDSS J1130+0411, we find an FeLoBAL system with $dot{M}=4100$ solar masses per year, among the highest in the literature for any FeLoBAL to date. We additionally determine that this outflow has the capacity to contribute significantly to AGN feedback. We also find seven other outflow systems in this objects, including four outflows, two intervening systems, and a subcomponent of the main BAL. In the object SDSS J2107-0620, we find that the distance of the outflow is $R=0.21$ parsecs, closer to its central source than any other FeLoBAL to date. We also determine that its $dot{E}_k$ is several orders of magnitude too low to contribute to AGN feedback.
Investigation of Phase-Separated Polymeric Materials via X-ray Scattering Techniques
Jackson, Erin Crater (Virginia Tech, 2026-01-14)
This dissertation presents a discussion of a variety of polymeric materials and their characterization via ultra-small, small, and wide-angle X-ray scattering methods (USAXS/SAXS/WAXS). Specifically, these experimental techniques are employed to investigate the phase separated morphologies that impart unique properties to each class of materials and allow for their use in advanced applications. It is crucial that the morphologies of polymeric materials are thoroughly characterized so that robust structure-property-processing relationships can be constructed. Chapter 2 of this dissertation discusses the fundamental principles of X-ray scattering, which form the basis for more complex experiments discussed throughout this dissertation. While historical, these foundational concepts of X-ray scattering are critical to highlight, due to instruments become increasingly more accessible and user-friendly. In Chapter 3, the origins of X-ray scattering in ion-containing polymers are discussed as it pertains to their unique hydrophilic/hydrophobic phase separated morphologies. These morphologies are becoming increasingly important to understand as ion-containing polymers increase in their commercial use. Chapter 4 discusses the use of USAXS experiments to understand the droplet size distributions of a filler in a polymer matrix and reveals that the liquid droplets in these composites can uniquely change size depending on their volume fraction in the composite. Chapter 5 discusses the use of SAXS and WAXS experiments to investigate the morphology of proton exchange membranes in hydrogen fuel cells. Ultimately, the results from X-ray scattering experiments provide strong evidence that commercial polymers used to make these membranes can mix at the molecular level to form robust membranes. Chapter 6 presents the application of SAXS and WAXS experiments to probe morphologies of 3D-printed polyimide materials. Using a combination of scattering, microscopy, and computational methods, the differences between two chemical variants could be understood, and the origins of void formation were uncovered. Finally, in the Chapter 7 of this dissertation, a selection of other polymeric systems were studied via X-ray scattering methods. Since most of the work presented in this dissertation was collected on a laboratory scale instrument, these experiments display the capability of benchtop instruments to characterize a range of different materials without the need to access a beamline.
Automating The Detection and Resolution of Build Conflicts in Software Merge for Java Programs
Towqir, Sheikh Shadab (Virginia Tech, 2026-01-14)
Version control systems (VCS) like Git provide an efficient environment for collaborative software development. However, a major challenge of using such systems is the conflicts that occur when developers try to merge branches. This research focuses on build conflicts--a category of higher-order software merge conflicts. The goal of our research is to develop and implement methodologies that automate the detection and resolution process of build conflicts. Our research consists of three pieces. First, we designed and implemented a graph-based pattern matching approach, BUCOND (Build Conflict Detector), to detect conflicts via static analysis. Our evaluation shows that BUCOND accurately identified build conflicts on both synthetic and real-world datasets; it demonstrated great applicability in scenarios where compiler-based tools are inapplicable. Second, we created a hybrid program transformation approach, BuCoR (Build Conflict Resolver), to opportunistically resolve conflicts. We evaluated BuCoR in real-world merging scenarios, observing its great capabilities of generating syntactically correct resolutions and mimicking human developers' resolution practices. Third, we explored a new approach of resolving conflicts using LLMs, and empirically compared the usage of different LLMs as well as diverse prompt designs. We demonstrate that, when properly guided, LLMs can provide highly accurate conflict resolutions. Our research will help developers detect conflicts more efficiently and resolve conflicts with higher effectiveness as well as rigor. Through addressing issues caused by merge conflicts, it will help improve programmer productivity and software reliability.
Microbial and Immune Signatures of Stress and Antidepressants Across Sex and Generations
Kropp, Dawson Ryan (Virginia Tech, 2026-01-14)
The gut, brain, and immune system form an integrated and dynamic network that shapes development and health outcomes across the lifespan. Increasing evidence indicates that this axis is highly sensitive to stress exposure, displays robust sex-dependent properties, and may transmit biological effects across generations. This dissertation investigated how variable stress or perinatal antidepressant exposure alters gut microbial composition, immune signaling, and behavioral phenotypes in a sex-specific and multigenerational manner. To address these questions, we utilized 16S rRNA or whole-genome shotgun metagenomic sequencing in tandem with behavioral assays and multiplex cytokine profiling in rat and mouse models of chronic stress or perinatal SSRI exposure. Across studies, we demonstrate that the gut microbiome exhibits innate sex differences that are present early in life and continue to diversify with age. Aging was associated with increased alpha diversity and marked shifts in microbial metabolic pathway representation as well as a reversal of the Firmicutes–Bacteroidota ratio. Chronic stress induced distinct microbial alterations in males and females, with males showing a greater magnitude and diversity of microbial alterations. We further observed that female offspring more closely mirrored the microbial community structure of their dams, and that perinatal citalopram treatment produced stronger and more persistent effects in female offspring than in males. These findings reveal that stress and antidepressant exposure interact with sex and developmental stage to shape gut microbial composition and immune function. Microbial alterations following stress appear context-dependent, serving either compensatory or maladaptive roles depending on biological state and environmental challenge. Collectively, this work advances our understanding of how the gut–brain–immune axis integrates life experience across sex and generations and highlights the microbiome as a dynamic mediator and potential therapeutic target in stress-related neuropsychiatric vulnerability.