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
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Recent Submissions
Professorial intentions of engineering PhDs from historically excluded groups: The influence of graduate school experiences
Fleming, Gabriella Coloyan; Cobb, Sydni Alexa; Borrego, Maura (Wiley, 2024-07)
Background: In addition to the benefits of a diverse faculty, many institutions are under pressure from students and administrators to increase the number of faculty from historically excluded backgrounds. Despite increases in the numbers of engineering PhD earners from these groups, the percentages of Black/African American and Hispanic/Latino tenure-track faculty have not increased, and the percentage of women remains low. Purpose: The purpose of this study is to identify how experiences in graduate school encourage or deter PhD earners from historically excluded groups in pursuing an engineering academic career. Method: We conducted 20 semi-structured interviews with engineering PhD students and recent graduates, with half of participants interested and half disinterested in pursuing an academic career after graduation. Results: Three key factors emerged as strongly influential on participants' desire to pursue an academic career: their relationship with their advisor, their perception of their advisor's work–life balance, and their perception of the culture of academia. Participants extrapolated their experiences in graduate school to their imagined lives as faculty. The results illuminate the reasons why engineering PhD earners from historically underrepresented groups remain in or leave the academic career pathway after graduate school. Conclusions: The findings of this study have important implications for how graduate students' and postdoc's relationships with their advisors as well as perceptions of their advisors' work–life balances and the culture of academia affect future faculty. We make recommendations on what students, faculty, and administrators can do to create a more inclusive environment to encourage students from historically excluded groups to consider academic careers.
Synergistic organizational influences: how universities strategically prepare graduate students for industry, government, and non-profit careers
Fleming, Gabriella Coloyan; Richardson, Amy Jo; Knight, David B.; Borrego, Maura; Deters, Jessica; Grote, Dustin (Springer, 2025-11-19)
A majority of engineering postgraduate students (Master’s and PhD) enter into jobs in industry, government, and non-profit organizations. However, most postgraduate programming is geared toward careers in academia. Our study examines how universities prepare engineering postgraduate students for careers outside of academia. We draw on interview data with administrators across 11 institutions and leverage an existing framework for organizational influences to identify how institutions leverage their organizational characteristics, organizational culture, and/or management strategies to prepare engineering postgraduate students for these careers. The highest-impact efforts were those that synergistically leveraged at least two organizational influences, such as utilizing an industry advisory board to design career-relevant curricula. We conclude with recommendations for how institutions can help their students be prepared for these career sectors.
Application of Co-Design Principles for Design of Series Elastic Joints
Pressgrove, Isaac James (Virginia Tech, 2026-02-04)
Compliant joints enhance the performance of dynamic legged robots by enabling more robust, efficient, and resilient locomotion. A widely adopted approach for introducing compliance into robotic joints is the use of Series Elastic Actuators (SEAs). Designing SEAs, however, requires balancing the stiffness of the elastic element with the structure and gains of the control system, as both strongly influence actuator bandwidth, disturbance rejection, and overall efficiency. Prior work across many domains has demonstrated that co-design methodologies, those that optimize mechanical and control parameters simultaneously, can produce high-performance, robust systems.
This dissertation advances the capabilities of dynamic legged robots through the development of a comprehensive co-design strategy for SEAs. The proposed framework addresses key limitations of traditional SEA design, particularly their difficulty in balancing the trade-off between high bandwidth achievable by stiff actuators and the disturbance rejection afforded by increased compliance. By jointly optimizing the gains of a simple, easily implemented PID–feedforward controller alongside the stiffness of the elastic element, the approach presented here improves both controllable bandwidth and transient response without requiring complex control architectures. A systematic method for identifying cost functions that are broadly applicable, implementation-friendly, and reliably indicative of system performance is presented. These cost functions are then used within a co-design optimization applied to several SEA configurations, demonstrating both generality and performance improvements over conventional sequential design approaches.
In addition, this work investigates how infill density influences the flexural rigidity of fused deposition modeling (FDM) printed PLA beams. These experiments support the use of FDM-printed components as compliant elements within SEAs. Using static three-point bending tests, regression models are developed to predict part flexural rigidity as a function of print infill. These models are integrated into the co-design framework, replacing direct selection of elastic stiffness with the specification of beam geometry and infill percentage. The resulting co-designed hardware is validated on an SEA knee-joint test bench, and experimental results are compared with simulations to evaluate sim-to-real fidelity.
This work makes three key contributions: (1) the development of a broadly applicable co-design methodology for SEAs, (2) the creation of predictive regression models for the mechanical properties of FDM-printed PLA beams, and (3) the integration of these results into a unified co-design strategy enabling SEAs that leverage additively manufactured compliant elements.
HolyLand U.S.A. and Other Stories
Culmone, Jason Steven (Virginia Tech, 2026-02-04)
HolyLand U.S.A. and Other Stories is a collection of voice-driven, satirical short stories, many speculative in mode, whose settings—a religious theme park, a Japanese game show, a far-future conglomo-corp supercity—are sites of spectacle and performance against which its characters, whether from misperceptions or a self-destructive impulse, fail despite—and often because of—their best efforts to succeed. These settings are, more so than the other, supporting characters, the primary source of conflict advancing the story. Often the stories include invented technologies, both to build out an unconventional world and to serve as the means through which a society's value system is interrogated. In my short story "Psychomanteus"—in which a private investigator who solves the unfinished business of the dystopian city's ghost population must, in order to save the spirit of his late husband, sacrifice his better principles and harvest ghosts who are in the process of passing on—embedded temple implants that run on the power of ectoplasm facilitate much of the story's themes of grief and being stuck in the past. In "Phronk Breaks His Cycle," elaborate staging contraptions called Cycle-o-Ramas™ enable employees working in a far-future emporium to perform an infinitude of hypothetical gig favors to appeal to their viewing customers.
UAV-Enabled Wireless Communications: Deployment, Optimization, and Analysis
SabzehAli Touranposhti, Javad (Virginia Tech, 2026-02-04)
Unmanned aerial vehicles (UAVs), known as drones, are a promising solution, as aerial base stations (BSs) or relays, in wireless communications systems. Due to their high likelihood of line-of-sight (LoS) links and ease of deployment, they play a crucial role in providing faster and better wireless network access and service where extra network resources are needed short term, like sports events, or to those emerging services that require high-capacity communications. Moreover, they can help extend wireless coverage to locations deprived of end-to-end wireless communications services in remote/rural areas due to natural disasters or being distant from the conventional terrestrial BSs. However, utilizing this new technology comes with its own novel challenges. In this dissertation, we focus on unprecedented challenges in UAV communications and networks, considering some unique features of UAV networks, such as their optimal placement and wireless backhaul links.
First, we focus on provisioning wireless coverage to those emerging services, like extended reality, demanding high-capacity communications. High frequencies, i.e., millimeter-wave (mmWave) and, terahertz frequency bands offer the substantial bandwidth required for such services. These high-frequency communications, however, depend critically on maintaining LoS connections to user terminals. In practical scenarios, users distributed in three-dimensional space often experience severely limited visibility due to environmental obstructions like buildings and foliage. We study the problem of finding an optimal 3D placement and antenna orientation for mmWave-equipped UAVs to minimize the number of required UAVs while maximizing the signal-to-noise ratios (SNRs) to all users. Our approach formulates this as an integer linear programming (ILP) optimization problem, establishes its computational intractability (NP-hardness), and develops a computationally efficient geometric algorithm that consistently achieves near-complete LoS coverage across diverse simulation scenarios.
Our second research thrust targets wireless connectivity in remote rural environments—such as agricultural Internet of Things (IoT) deployments—where conventional terrestrial infrastructure is limited or absent. A fundamental challenge in such UAV-assisted networks is determining the minimal UAV deployment that simultaneously achieves two objectives: complete ground user coverage and reliable wireless backhaul connectivity linking all UAVs to terrestrial BSs. We formulate this joint optimization—termed the Backhaul-and-coverage-aware Drone Deployment (BoaRD) problem—as an ILP problem and prove its NP-hardness. Our solution approach employs a graph-theoretic algorithm that efficiently solves the problem with provable performance bounds. Comparative analysis using ILP solvers demonstrates that our algorithm achieves near-optimal performance for smaller problem instances. For large-scale scenarios with extensive coverage areas and numerous users, comprehensive simulations show our algorithm substantially outperforms baseline algorithms while guaranteeing complete user coverage and end-to-end connectivity.
Finally, building upon these deployment optimization contributions, our third research thrust develops a comprehensive analytical framework for multi-hop UAV-assisted cellular networks. While the previous work provides deterministic algorithms for specific deployments, understanding system-wide performance requires statistical modeling of networks with random spatial distributions. We develop a comprehensive stochastic geometry framework for analyzing multi-hop UAV-assisted cellular networks that addresses fundamental gaps in existing analytical approaches. Traditional stochastic geometry techniques for terrestrial networks are insufficient for characterizing the complex 3D spatial relationships, interference patterns, and unique propagation characteristics inherent in multi-hop UAV deployments. We extend existing mathematical frameworks to accommodate the distinctive features of aerial networks, including realistic 3D spatial distributions of UAVs across multiple operational altitudes, probabilistic air-to-ground channel models that distinguish between LoS and NLoS conditions, and the intricate interference correlations that arise in multi-hop communication paths. Our framework derives novel mathematical constructs and probability distributions that enable precise characterization of multi-hop network behavior under random spatial deployments in the 3D space. We provide comprehensive closed-form expressions for coverage probability analysis covering both amplify-and-forward (AF) and decode-and-forward (DF) relaying protocols, accounting for the hybrid communication scheme where UEs can connect either directly to serving BSs or through the multi-hop UAV network based on received signal quality. Additionally, we introduce optimal relay selection strategies that maximize end-to-end SINR by jointly considering all link qualities in the formed multi-UAV network and accounting for the complex interdependencies between sequential links in the presence of interference. Through extensive theoretical analysis and simulation validation, our results demonstrate that well-designed multi-hop UAV networks can significantly enhance coverage probability and network reliability compared to single-hop architectures, particularly in challenging environments where direct links between UAVs and terrestrial BSs are weak or unavailable due to distance or environmental obstructions.