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.
Communities in VTechWorks
Select a community to browse its collections.
Recent Submissions
Computational Approaches to Answering Evolutionary Biology Questions
Sarkar, Chandra (Virginia Tech, 2026-10-15)
Advances in computational biology have expanded the scale at which evolutionary questions can be addressed, allowing patterns of molecular evolution, genome evolution, and host-symbiont diversification to be examined using large comparative datasets. Additionally, the repurposing of publicly available datasets provides opportunities to address new questions beyond those for which the data were originally generated, thus avoiding contributing to already exploding amounts of data in the current data-driven world. In this dissertation, I reuse and integrate existing next-generation sequencing datasets through computational pipelines to investigate contradictions to an already established molecular evolution paradigm, survey the occurrence of possible symbiotic bacteria and elucidate host-symbiont co-evolution. My first chapter provides insight into the current state of bioinformatics and challenges in evolutionary biology and provides an overview of the aims of my dissertation. My second chapter examines how cellular environment and spatial organization of proteins influences protein evolutionary rates. Highly expressed proteins evolve slowly, a pattern known as the expression level evolutionary rate anticorrelation (E-R anticorrelation). Using transmembrane proteins, I found that this anticorrelation is stronger in intracellular domains of the proteins as compared to their extracellular counterparts. These results support the hypothesis that protein evolution is constrained to selection against misfolding and deleterious molecular interactions. My third chapter provides a literature review of lice-Wolbachia endosymbiosis, an understudied ectoparasitic-endosymbiont system, that provides the background for my work in the following chapters. My fourth chapter uses publicly available whole-genome sequencing data from avian chewing lice to investigate their associations with the known arthropod-associated Alphaproteobacteria, Wolbachia. Screening and genome reconstruction from a large dataset of 1025 avian chewing lice shotgun sequences show a substantial association between the two organisms. I also report on the classification of these associated Wolbachia into supergroups and their substantial variation of genomic characteristics including genome size, GC content, and coding sequence counts among other metrics. My fifth and last chapter delves into understanding the possible coevolution events of lice and their associated Wolbachia. I use phylogenomics and comparative genomic analyses to understand their shared evolutionary history and indicate possible candidates for mutualism using computational validation. Together, these studies illustrate how existing biological datasets can be reanalyzed through computational pipelines to address new evolutionary questions and aims. Across molecular, genomic, and host-symbiont scales, this dissertation examines how we can understand layers of biological processes using computational prowess.
Using Nacre-Inspired Architecture to Improve the Mechanical Performance of Binder Jetted Parts
Espinosa Borja, Juan Fernando (Virginia Tech, 2026-10-15)
Residual porosity remains a barrier for industrial adoption of additively manufactured metallic parts fabricated through Binder Jetting (BJT), due to its detriment in the mechanical performance. However, local control of the pore structure poses an opportunity to turn an apparent process defect into a design feature for creating architected composites. Nacre is a natural composite that achieves high toughness by directing crack propagation through a softer, more compliant phase, effectively preventing failure in the brittle ceramic material. This research investigates whether a nacre-inspired architecture can be introduced into BJT metal composites to improve toughness relative to conventional, homogeneous parts.
Two strategies within a BJT and infiltration workflow were used to control porosity at different length scales: selective binder deposition governs mesoscale porosity by dictating where powder is bound or left loose during printing, while pre-sintering provides control of the microscale porosity by controlling neck formation and pore evolution within each region. This work leverages both controls together to architect distinct infiltration pathways within a single part, producing a Nacre-inspired brick-and-mortar pattern of bronze-lean "Brick" (unbound) and bronze-rich "Mortar" (bound) regions in SS316L and bronze composites.
The progression of densification of bound and unbound SS316L powder throughout the sintering process was found to differ, with unbound powder showing an advanced densification because of its greater powder packing density. A pre-sintering temperature of 1250℃ produced the greatest contrast in pore structure while providing a viable, complete infiltration path. Nacre composites were fabricated at this temperature, achieving up to a 9% bronze-content difference between the designed Brick and Mortar sections. Conventionally printed and infiltrated composites outperformed the Nacre composites, with Modulus of Toughness recording values of 0.024 J/mm3 and 0.016 J/mm3, respectively, with stiffness showing no distinction. These results are attributed to large fabrication defects and high residual porosity in the final parts (6.6 – 8.5%), rather than to the tailored architecture itself.
This thesis demonstrates a novel method for producing complex architected composites with spatial composition contrast in a BJT and infiltration process, by combining selective binder deposition and a pre-sintering step. Additionally, it develops an image-analysis method applicable to other porosity-based patterns for quantifying such contrast from optical microscopy.
Predicting Heat Accumulation and Layer Geometry Variation in Continuous DED-Arc of Thin-Walled Aluminum Structures
Rosenhein, Drew David (Virginia Tech, 2026-10-15)
Compared to other metal additive manufacturing (AM) processes, wire-arc directed energy deposition-arc (DED-Arc) offers high deposition rates. However, its throughput is limited by heat accumulation within the part during the build; continuous printing without balanced heat dissipation can lead to part slumping and distortion. Existing thermal mitigation approaches, including interlayer dwell time, active cooling, and in-process parameter control, impose costs in productivity, system complexity, and/or limited applicability to large and complex parts. Continuous deposition without arc interruption eliminates dwell time and arc start and stop defects but produces a severe heat accumulation condition. Under fixed process parameters, the thermal balance determining this accumulation is strongly influenced by the part's geometry.
In a closed contour geometry, the layer contour length of the profile determines the toolpath length, setting the time available for heat to dissipate between depositions of successive layers, while also determining wall surface area. Longer layer contours have been observed to reduce heat accumulation in previous research, but the relationship has not been directly investigated as a design variable in DED-Arc, nor has it been established whether interlayer temperature reaches a plateau at sufficient contour length and/or part height. The aim of this thesis is to establish a design-stage workflow that relates continuous build geometry to its in-process thermal condition and deposited wall geometry, thus allowing layer-wise prediction of part geometry before fabrication.
To close this research gap, three thin-walled ER5556 aluminum cylinders of 50, 100, and 200 mm diameter were deposited continuously under identical process parameters and instrumented with embedded thermocouples along the build height. Contour length variation produced a 212.1 °C spread in interlayer temperature across builds and dictated whether steady-state interlayer temperatures could be reached. Calibrated thermal simulation indicated that the interlayer temperature of 200mm diameter cylinder reached a plateau during processing and declined as convective loss exceeded layer-wise heat input. However, the 50mm diameter contour part's interlayer temperature climbed to 401 °C by layer 50 with no sign of stabilizing. This thermal variation increased effective wall width by 99.4% along the part height, whereas porosity and microhardness remained consistent for this alloy. The calibrated simulation was applied to a test geometry and, combined with the measured temperature-geometry correlations, predicted effective wall width and layer height to 3.28% and 2.26% mean absolute percentage error, respectively, across 10 layers sampled from a 50-layer build.
The study was also extended to oscillating weave deposition for producing thicker wall widths. Interlayer temperatures in the weave builds were up to 60.4 °C lower than single-track at matched contour length, despite depositing 2.8 times the path length per layer. This longer layer time increased heat dissipation, more than offsetting the higher heat input.
Through The Keyhole: A Nature Retreat
Perry, Mason Thomas (Virginia Tech, 2026-10-15)
Looking Through the Keyhole: A Nature Retreat explores how architecture can encourage meaningful social connection while providing opportunities for privacy, reflection, and reconnection with nature. The project responds to the growing separation between people, community, and nature by proposing a retreat organized around spatial transitions rather than isolated buildings.
The design consists of three primary architectural moments: the threshold gate, firepit, and elevated cabins. The threshold transitions from everyday life to the retreat, the firepit creates a communal center, and the elevated cabins offer increasingly private spaces.
A recurring keyhole motif symbolizes transitions between public and private, exterior and interior, and movement and reflection. These elements create a progression from crossing, gathering, to ascending, demonstrating how spatial sequence, material expression, and nature connection shape social interaction, solitude, and restoration.
Under New Management: Restructuring an Established Service for Long Term Sustainability
Fletcher, Lauren; Kraus, Hilary; Haygood, Laura; Sawyer, Kelsey (Virginia Tech, 2026-06-15)
Since 2019, at our mid-size R1 university, the library's unit that serves health and biomedicine has offered a Systematic Review Service. Our service population is broadly defined; we serve a cross-section of clinicians, academic faculty, researchers, and scholars at all levels in medicine, public health, psychology and psychiatry, and related disciplines. Requests submitted to the service have been high since its inception, but it is staffed by a team of only four librarians whose jobs comprise a great deal more than this one responsibility.
After five years, we realized our informal approach, combined with ever-increasing demand, was unsustainable. Because the service had grown organically, and due to inevitable turnover in departmental staffing, workflows were decidedly ad hoc. There was limited coordination in how and when requests were received, responded to, and claimed. Each librarian approached their projects differently, including in how they documented the substance of their work and the time commitment required. Team members also possessed varying levels of expertise in some aspects of evidence synthesis methodology. And frankly, more researchers wanted librarians to take on author-level labor than we could possibly accommodate.
In the summer of 2025, we decided a significant overhaul of the Systematic Review Service was essential. Our primary goals included creating clearer and more sustainable policies, formalizing and streamlining our internal processes, and playing to the strengths of members of our team. Ultimately, the most effective part of this process, which now seems inevitable, was assigning a team lead to manage the service.
The role of the team lead is a demanding one. It was important they had deep methodological expertise with the evidence synthesis process, as well as institutional knowledge of the department and the existing service. To make the position feasible, we kept our eye on the original goals, restructuring the service in a way that supported, rather than overwhelmed, the librarian who took on the role.
This presentation will discuss the changes we made to serve that purpose: creating a structured process for requesting support with a single entry point, defining workflows for all requests; and integrating new tools (JotForm and Airtable) with Google Drive. The team lead became responsible for implementing these strategies, including setting up and managing selected tools, establishing the new workflows, coordinating the request queue to ensure timely service, and providing an intake consultation to researchers when requests were received. We will discuss the successes and challenges of our management model, and how we plan to review its effectiveness and long-term sustainability.