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Developing Complete Paths Pedestrian Networks in Openstreetmap and Neptune for Link-By-Link Impedance Application
No full textPedestrian navigation often lacks ADA considerations, resulting in routes that minimize travel time for most pedestrians, but overlook accessibility needs for individuals with disabilities. Most routing applications do not consider physical and environmental factors that affect mobility aid and wheelchair users, such as sidewalk width, surface quality, availability of curb ramps, and provision of safe crossings, which are essential for equitable mobility. This gap in current routing approaches presents challenges for creating accessible, reliable pathways within urban networks.
To improve routing for the disability community, the FHWA ITS4US program (FHWA, 2024) initiated a series of projects designed to develop new decision support tools. The ITS4US project in Georgia (Wakhisi, et al., 2021), is implementing a routing tool known as the Georgia Mobility and Accessibility Planner (G-MAP) designed to find the lowest impedance origin-to-destination pedestrian routes for members of the disability community, across a variety of mobility modes (e.g., manual wheelchair, mobility scooter, etc.). As part of the larger ITS4US project, the research reported in this thesis, develops systematic methods within OpenStreetMap (OSM) to developed pedestrian path link-and-node structures for use with impedance-based routing tools that incorporate facility design and condition features critical for accessibility. Using Gwinnett County, Georgia, as a case study, this research applies customized editing protocols and a structured workflow to integrate attributes such as curb ramps, smooth surfaces, and well-maintained crossings. SidewalkSim, a routing simulation tool, is used to implement and verify the impedance-based routing functionality on OSM’s enhanced pedestrian network. The structured methodology not only supports scalable ADA-compliant navigation but also offers cities a replicable framework for creating more inclusive urban environments. By enabling OSM’s open-source platform to capture essential ADA routing data, this approach lays the groundwork for an adaptable, community-driven resource that can be used widely to improve pedestrian accessibility and enhance the quality of urban life.M.S.Civil Engineering/City and Regional Plannin
Advanced simulation and design of gas-cooled solid tungsten divertor systems
No full textA critical challenge for magnetic fusion energy is the design of the divertor, which must withstand extreme
heat fluxes from the burning plasma while extracting this heat for power generation. As building and testing
prototypes is very expensive, physics-based numerical modeling offers a cost-effective pathway to evaluate
and optimize divertor designs.
This thesis presents a novel validated computational framework to model and predict the performance and
safety of a modular, helium-cooled, solid tungsten (W) T-tube divertor concept. The methodology integrates
thermal-transport computational fluid dynamics (CFD) simulations with thermal-structural finite-element
methods (FEM) models. These models uniquely incorporate temperature- and time-dependent properties
for state-of-the-art W alloys, explicitly including the effects of kinetic recrystallization on material integrity.
This framework establishes the T-tube’s operational limits under various realistic future fusion reactor
conditions, benchmarking achievable survivability and performance metrics for helium-cooled W divertors.
The resulting methodology provides an essential tool for satisfying plasma-physics constraints while
optimizing plant efficiency, enabling the robust assessment and optimization of divertor designs for longpulse fusion reactorsPh.D.Mechanical Engineerin
Virtual Reality as a Tool for Assessing Augmented Reality in First Responder Contexts
No full textThis dissertation investigates the use of Virtual Reality (VR) as a testing environment for future Augmented Reality (AR) technologies, particularly heads-up displays (HUDs), intended for First Responders. Given that AR hardware remains limited in real-world applications, VR offers a practical stand-in for testing critical features like field of view, resolution, and situational awareness. However, the validity of VR as a proxy for real-world AR interactions has not been thoroughly established, especially in high-stress, mission-critical situations where performance is vital.
To address this gap, I leveraged immersive simulations through the ARTEMIS platform, which allows for controlled, repeatable testing scenarios for First Responders. I specifically focused on investigating whether the inclusion of intentionally stressful scenarios could better differentiate between designs. I incorporated a combination of qualitative methods and sensor-based techniques to study user responses to VR simulations and their real-world equivalents. The research explored the stress-inducing conditions that first responders face during tasks like traffic stops, evaluating how HUDs impact their performance and decision-making under these conditions.
One critical aspect of this work involved the consideration of immersion from the perspectives of simulations research as well as from the “storytelling” perspective of serious games research. Anoter critical aspect of this work involved analyzing different types of data generated by VR environments, which I categorized as Simple Discrete Data (SDD), Combined Discrete Data (CDD), and Continuous Signal Data (CSD).
My findings suggest that VR can indeed replicate key aspects of AR system performance, particularly when stress-inducing elements are included. Notably, more invasive HUD designs led to higher mental load, effort, and frustration, supporting the hypothesis that stress influences the perception of new technologies. My approach also extended the concept of simulation fidelity to include storytelling immersion that can leverage the substitution of symbolic elements in virtual environments. This work refines testing pipelines by identifying which factors, such as sensory inputs or stress, impact user performance and cognitive load in mission-critical situations, while also saving costs on early prototyping.Ph.D.Computer Scienc
Spatial And Temporal Variation in Primary Productivity in The Western Tropical North Atlantic: Experimental and Stable Isotope Approaches
No full textPhytoplankton photosynthesis, which converts inorganic carbon into organic matter, is the foundational process fueling marine ecosystems. This primary productivity supports the growth and metabolic needs of higher trophic levels. It plays a critical role in regulating the global carbon cycle by facilitating carbon dioxide removal from the atmosphere over longer time scales. Studying these dynamic biological processes is essential to understanding and predicting the impacts of environmental change on marine ecosystems. We can unravel the complexities of this vital process by employing experimental and natural abundance measurements that capture both instantaneous and time-integrated processes.
My research focused on the Western Tropical North Atlantic (WTNA), a region significantly influenced by the Amazon River Plume (ARP). The ARP creates a distinctive environment where freshwater from the Amazon River mixes with oceanic waters, leading to unique nutrient dynamics, light conditions, and phytoplankton distributions. This study explored the spatial variations (using a novel habitat delineation approach) and temporal changes (using field data from three distinct seasons) in primary production and biomass within this region. I utilized a combination of direct observational data, experimental rate measurements, satellite data, modeling, and the natural abundance of carbon stable isotope analysis, complemented with advanced statistical analysis.
Using 13C tracer techniques, we measured phytoplankton growth and carbon fixation rates across different habitats and seasons within the ARP region. The results uncovered significant seasonal and regional variations in productivity, with peak carbon fixation rates occurring in the plume core during high discharge periods. Large phytoplankton cells dominated production in the nutrient-rich, mesohaline plume-core areas, showing lateral contrasts among habitats across different seasons, while smaller cells prevailed in nutrient-poor offshore waters. The photosynthetic efficiency of phytoplankton varied substantially across the ARP, with the highest light-saturated growth and production rates in the plume core and lower rates offshore.
In addition to measuring instantaneous carbon fixation rates (on the scale of one day), we utilized carbon stable isotope analysis of suspended particles, capturing a time scale of approximately one week, to trace organic carbon sources within the ARP. This approach allows us to evaluate the extent of phytoplankton influence on the ecosystem across a broad range of temporal scales. These data revealed a strong terrestrial influence near the river mouth, characterized by more negative δ13C values and higher C:N ratios. As the plume extended offshore, the influence of marine processes became more pronounced, as reflected by higher δ13C values and lower C:N ratios.
This integrative approach reveals key environmental drivers of productivity, highlights the role of phytoplankton photophysiology in carbon cycling, and underscores the importance of terrestrial inputs and marine production on coastal and oceanic biogeochemistry. It also provides critical insights for improving ecological models, which are essential for predicting climate change impacts, particularly in river-influenced regions like the Amazon Plume.Ph.D.Biolog
Designing Adaptive Responsible AI through Participatory Value Alignment
No full textThis dissertation begins by asking: How do different stakeholders define 'responsible behavior' in professional practice, and what does it mean for an AI agent to embody that (or not)? I approach this question from a stakeholder-centric perspective that views responsible behavior as situated and shaped by diverse professional values that may exist in tension.
Using academic advising as a research site, I explore how value articulation processes and artifacts support stakeholders in surfacing and reasoning about diverse values around responsible AI behavior. Drawing from literature in HCI, values in design, and STS, and through empirical work, I investigate: (1) what dimensions characterize the affordances and constraints that value articulation processes and artifacts create for stakeholder engagement with values; (2) how stakeholders engage in collaborative meaning-making and reasoning around responsible behavior through collaborative value elicitation activities; and (3) how explicit configuration of conversational agents supports stakeholders in exploring and reflecting on the operationalization of responsible behavior and what resists it in their professional practice.
This research contributes: (1) the Values Articulation framework, providing dimensions for characterizing how processes and artifacts shape value articulation; (2) Values Mapping artifacts and process template for collaborative value articulation around responsible AI behavior; (3) a configurable conversational agent as a technology probe for exploring value operationalization; and (4) empirical documentation of relationships between activity characteristics and value articulation. These contributions have implications for researchers designing value elicitation activities and organizations developing AI systems
Process Engineering for High-Energy Density and High-Power Lithium Metal Batteries
No full textLithium (Li) metal batteries (LMBs) offer much higher energy density than conventional Li-ion batteries, but their practical application faces challenges such as electrolyte leakage and the formation of Li dendrites, which pose safety risks like thermal runaway. Solid-state electrolytes (SSEs) present a promising solution by preventing leakage and inhibiting dendrite growth, making them safer and more reliable for electric vehicles and large-scale energy storage systems. Additionally, 3D-structured current collectors (CCs) improve Li plating and stripping by increasing surface area and reducing local current density, helping to prevent dendrite formation. While these technologies are highly promising, there is a growing need for thin, lightweight designs that deliver high energy density, stable cycling performance, and scalability for commercialization. As part of my PhD research at the George W. Woodruff School of Mechanical Engineering at the Georgia Institute of Technology, I have developed scalable processing techniques for fabricating LMB components with enhanced energy density and stability. These include thin, flexible composite solid electrolytes (CSEs) made using the non-solvent-induced phase separation (NIPS) method, which improves safety and suppresses dendrite growth. My research also includes in-situ polymerizable CSEs that offer high mechanical stability against dendrites and electrode volume changes, achieving excellent cycling performance in all-solid-state LMBs (ASSLMBs). Furthermore, I designed lightweight, 9 µm-thick 3D porous composite CCs to prevent Li dendrite growth and enhance energy density. These innovations bring us closer to the commercialization of safer, more efficient LMBs.Ph.D.Mechanical Engineerin
Influence Of Water Vapor on the Adsorption of Exhaled Breath-Borne VOC Biomarkers for COVID-19
No full textThe detection of volatile organic compounds (VOCs) from exhaled human breath is fast becoming an acceptable technique for easy and rapid testing for several illnesses. There is great potential for the development of COVID-19 breath tests as an easier alternative to the current invasive PCR testing methods. This dissertation discusses the investigation of material design for the selective capture of four VOCs that have been identified as biomarkers for COVID-19 under humid conditions using carbons, zeolites, and especially metal-organic framework (MOF) adsorbents.Ph.D.Chemical and Biomolecular Engineerin
Learning and Transfer of Hypogravity Adaptation Across Motor and Cognitive Systems
No full textThe motor and cognitive systems are easy to think of as inhabiting different domains, but they overlap in many of their functions. Generally, motor learning has important cognitive components, and cognition makes use of motor areas of the nervous system. However, the specifics of the overlap between the motor and cognitive systems remain elusive. The goal of this set of experiments was to determine if different motor and cognitive systems share a single representation of gravity, or if gravity is accommodated separately by each system. Gravity was chosen due to its ubiquitous influence on motor action and cognitive predictions of movement. I hypothesized that gravity is represented in the nervous system in a generalizable way, such that adaptation in one gravity-dependent motor task will affect other, gravity-dependent motor actions, or even cognitive actions. To test this, three experiments were conducted, aimed at 1) characterizing the adaptation to simulated hypogravity jumping, 2) determining if gravity adaptation in jumping transfers to gravity-dependent arm movement, and 3) if the same gravity adaptation transfers to a gravity-dependent cognitive task. In support of my hypothesis, after participants successfully adapted to simulated hypogravity jumping, this adaptation then affected gravity-dependent arm movements as well as the cognitive task. The results support a shared representation of gravity between motor and cognitive systems that is adaptable and relies on accurate predictions of gravity-related sensory feedback, contributing to our understanding of transfer of learning and how abstract phenomena (like gravity) are managed by the neuromuscular system.Ph.D.Applied Physiolog
Engineering genetic circuits and biological memory for advanced biological security
No full textSynthetic biology brings abilities to precise, modular, and complex control of cellular function, providing circuitry components into genetic network and bringing intelligence into biology. This approach allows researchers to improve on the ever-increasing demand for complex but reliable genetic programming. In this thesis, we explore the development of recombinase-based genetic circuits for memory and bio-cryptography, addressing the growing demand for complex and reliable genetic programming. These circuits play a crucial role in history-dependent programs that record and respond to transient environments in living cells.
First, we introduce a novel design strategy called interception by repurposing the transcription factors to regulate recombination events by physically blocking the attachment sites, providing an innovative approach to genetic regulation. Furthermore, an intelligent chassis cell with controllable recombinase memory arrays is developed. This technology allows for precise control over recombinase activities through the induction of transcription factors processing various inputs, enabling the creation of new unit operations. This breakthrough leads to the construction of tools for memory writing, erasing, rewriting, memory expansion through CRISPR, and enhanced cell-cell communication between probiotic and gut microbe.
The thesis leverages recombinase-based memory to establish a platform for applying cybersecurity principles within biological systems. This platform enables the development of sequential passcodes based on diverse combinations of chemical input signals, redefining biological security practices and offering a paradigm shift in how we secure valuable intellectual properties in the area of biotechnology and genetic engineering. Overall, this research contributes to the advancement of engineered genetic circuits and their applications, offering innovative solutions for reliable and controllable genetic programming and enhanced biological security.Ph.D.Chemical and Biomolecular Engineerin