Theses
Permanent URI for this collectionhttps://uwspace.uwaterloo.ca/handle/10012/6
The theses in UWSpace are publicly accessible unless restricted due to publication or patent pending.
This collection includes a subset of theses submitted by graduates of the University of Waterloo as a partial requirement of a degree program at the Master's or PhD level. It includes all electronically submitted theses. (Electronic submission was optional from 1996 through 2006. Electronic submission became the default submission format in October 2006.)
This collection also includes a subset of UW theses that were scanned through the Theses Canada program. (The subset includes UW PhD theses from 1998 - 2002.)
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Item type: Item , Evaluating Face Mask Efficiency on Children and Adults(University of Waterloo, 2025-12-05) El Khayri, HichamSmall infectious aerosols have been a major vector for the spread of diseases such as COVID-19 and influenza. During the recent global pandemic, masking played a key role in reducing airborne transmission, although significant variability has been noted in the ability of different mask types to limit pathogen-laden aerosol dispersion and inhalation. Moreover, there remain significant gaps in the literature regarding mask performance for children. The aim of this thesis is to characterize mask inward protection efficiency for both children and adults, and source control efficiency for children in the 0.2 μm to 1 μm particle size range. An approach based on the conservation of mass guided the experimental methodology used to estimate mask filtration characteristics. For all tested masks, the material filtration efficiency was measured to be at or near 100%, whereas fitted filtration efficiencies for both source control and personal protection were significantly lower. This disparity underscores the highly degrading effects of leakage from gaps at the mask-face interface. Inward protection efficiency of N95, KN95, and surgical masks donned regularly and using the tie and tuck method were estimated on a medium NIOSH adult head form. The tested N95 barrier provided the greatest protection, followed by the KN95 respirator, while the surgical masks offered the least protection. Use of the tie and tuck for surgical masks method yielded only a small, statistically insignificant improvement in inward protection compared to regularly worn variants. Incorporating results from broader literature, mean inward protection efficiency ranges of [67.9%,100%] and [12.5%,79.6%] were determined for the N95 and regularly worn surgical masks, respectively. Both inward protection and apparent filtration efficiencies of adult, modified adult, and child variants of the KN95, CA-N95, and surgical mask as well as the N95 respirator, were estimated on a child manikin. Results further underscore the critical importance of proper fit to mask performance. Child-sized respirators provided higher source control and personal protection compared to other barriers tested. In contrast, the adult-sized surgical mask, which exhibited a loose fit on the child manikin, demonstrated poor performance in both metrics due to the highly degrading effects of leakage. Overall, whenever both variants are available, adult-sized masks demonstrate markedly reduced fitted efficiencies on the child manikin relative to child-sized variants, attributed to larger gaps at the mask-face interface. Flow visualization of air exhaled through the tested barriers qualitatively corroborated these findings, revealing substantially reduced leakage for child-sized variants compared to adult-sized equivalents. Given the increased sensitivity of children to mask breathing resistance, pressure differentials measured across masks donned on the child head form provided relative indicators of breathability. Results demonstrated that masks with similar filtration efficiency can exhibit significant differences in breathability. For example, the child-sized CA-N95 achieved equal or greater fitted filtration efficiency while consistently maintaining lower pressure drops compared to the child KN95. In fact, KN95 respirators showed differential pressures greater than or equal to those of all other tested masks. For a given mask type, better fit was associated with higher differential pressures. However, across different mask designs, higher filtration efficiency did not necessarily compromise breathability.Item type: Item , FROM THE MOUTHS OF HUNTERS: HUNTER PERCEPTIONS IMPROVE UNDERSTANDING OF THE RELATIONSHIP BETWEEN HUNTERS AND CONSERVATION IN CANADA(University of Waterloo, 2025-12-05) Basdeo, MayaAs a group of nature-based outdoor recreationists, hunters in Canada are not well understood, particularly in the context of their role in conservation. Hunters in Canada are not typically equated with being conservation actors, however there is a dearth of current academic literature that addresses the relationship between hunting and conservation in Canada and thus hunters may not accurately be represented within conservation circles. Collaboration between different groups of conservationists could be improved, and gaining a better understanding of how hunters perceive their place in conservation may contribute to greater unity around issues of conservation concern. The research question I explored was “Do hunters in Canada perceive they contribute to conservation, and if so, in what ways?”. I used an anonymous online questionnaire to survey hunters across Canada using Qualtrics as the survey tool. The survey link was distributed through six provincial and territorial hunting-conservation organizations affiliated with the Canadian Wildlife Federation: Ontario Federation of Anglers & Hunters, Manitoba Wildlife Federation, Saskatchewan Wildlife Federation, Alberta Wildlife Federation, B.C. Wildlife Federation, and Yukon Fish & Game Association. The survey consisted of 23 questions and was conducted over a six-week period in the fall of 2023. 4022 valid responses were received from every province and territory, with the majority from Ontario. Four key themes emerged from the survey results of hunters in Canada: hunters identified more strongly as conservationists than as hunters, hunters identified numerous ways in which they participate in and support conservation, hunters are political actors, and hunters can be allies for conservation. Focusing on hunter perceptions was a necessary first step in exploring the relationship between hunters and conservation in Canada. The breadth of these results highlight opportunities for further empirical research and the need for more research to be conducted in Canada on this topic.Item type: Item , Quantum Fields in Curved Spacetimes: From Detector Entanglement to Black Hole Thermodynamics(University of Waterloo, 2025-12-05) Bhattacharya, DyumanThis thesis presents two independent investigations into quantum field theory in curved spacetime. The first concerns relativistic quantum information, with a focus on entanglement harvesting and detector-based probes of quantum fields in curved spacetimes. The second addresses semiclassical aspects of black hole thermodynamics in AdS braneworld settings, incorporating the backreaction of quantum fields to all orders of perturbation theory, and extending previous studies of quantum black holes to include both charge and spin. In Part I, we study the entanglement of quantum fields in curved spacetime, using localized particle detectors interacting with a scalar field. We analyze scenarios involving both flat and curved backgrounds, including gravitational shock waves, the BTZ black hole, and general dimensional anti–de Sitter and de Sitter spacetimes. For the case of initially entangled detectors, we find that interactions with the field can lead to either degradation or amplification of entanglement, depending on the initial state and spacetime geometry. We further derive exact expressions for density matrix elements, at the lowest perturbative order, in the form of infinite analytical series, for detectors on static worldlines in various spacetimes. The transition rate of an in-falling detector in the BTZ black hole spacetime is also derived as an infinite series. These analytic results allow for exact evaluation of quantities, namely the entanglement measures of concurrence and negativity, which are typically computed numerically. In addition, we provide a new example of the ability of detectors to distinguish topologically distinct spacetimes which are locally identical outside of horizons, focusing on the ℝP² and Swedish geons built from the BTZ spacetime. Our results show that localized measurements are sensitive not only to curvature but also to topological features of the underlying geometry. Part II is concerned with the construction and thermodynamic analysis of quantum-corrected black holes in a doubly holographic braneworld model. We obtain a charged and rotating solution localized on an AdS₃ brane embedded in an AdS₄ bulk, incorporating the full backreaction from conformal fields to all orders of perturbation theory. We compute the thermodynamic properties of these black holes, and examine their behavior in extended thermodynamic phase space where the cosmological constant is a variable. We find that the inclusion of charge or spin removes re-entrant phase transitions present in the neutral-static case, and that the critical exponents of these objects match those predicted by classical mean-field theory. The re-entrant phase transitions of the neutral-static quantum black hole has critical exponents which differ from the mean-field valuesItem type: Item , Woodland ecosystem services of the past and present in Herstmonceux and South England(University of Waterloo, 2025-12-05) Pita, KatieThis thesis quantifies ecosystem services from broad- and mixed-leaved woodlands in the southern United Kingdom. Synthesizing concepts and approaches from historical ecology, environmental history, community ecology, dendrological allometry, and punctuated equilibrium theory, this thesis illuminates the multifaceted ways in which woodlands provide ecosystem services that are valued by people in the UK, both socially and ecologically. A complex relationship between people and woodlands emerges through time, which can be understood directly via management decisions, but also more abstractly through the sentiments that people attach to trees. Both of these approaches carry normative implications about the value of particular woodland ecosystem services. While the values that guided past decisions in woodland management are not always explicit, archival maps and remotely sensed data can reveal the nature of land use changes that manifest over long periods of time, i.e., 150 years. Within a case study context in Herstmonceux, East Sussex, archival data demonstrated a progression towards a modern day multifunctional wooded landscape. Within this modern context, historical woodland management regimes like coppicing drive specific ecosystem services like biodiversity and carbon storage to change measurably on a near-annual basis. This indicates that historic management regimes have important implications for ecosystem service provision not just over the course of generations, but also on fairly short time frames, e.g., 15 years. Land managers of coppice woodlands must therefore be cognizant of how everyday land management decisions can impact the ecosystem services, and therefore values (both intrinsic and instrumental) derived from them. Importantly, land management decisions and regimes also change abruptly in response to exogenous factors. When extreme damage was caused to trees and woodlands as a result of the October 1987 Great Storm, there occurred a traceable punctuation reflected in both the public sentiment and the priorities of woodland managers regarding trees. Changes in woodland ecosystem services can thus be slow-moving or sudden. Ultimately, it is this complex, always-changing relationship between humans and the environment that shape not only the actual provision of ecosystem services, but also perceptions of that provision, and, furthermore, how ecosystem services themselves are valued. The ecosystem services perspective, therefore, may be applied to and represent both intrinsic and instrumental values, rather than solely instrumental values, which has been a longstanding critique of the framework. However, researchers aiming to employ the ecosystem services framework in this manner must be intentional and explicit in their doing so, in order to shift the guiding paradigms in conservation away from “nature for people,” and towards a “people are nature” perspective.Item type: Item , Making Political Party Leaders: The Practice of Political Leadership in Canadian Party Leadership Races(University of Waterloo, 2025-12-04) Columb, Conor DonnieParty leaders are central to the Canadian party system because they represent their political parties at the national level, hold significant power within them over policy and messaging, and they often go on to form government following elections. Although scholars have studied leadership selection methods, party organization, and political campaigning, less attention has been paid to how aspiring party leaders develop political leadership in their respective campaigns. This gap invites the following questions: (1) how is political leadership constructed and communicated by aspiring leaders in Canadian political party leadership races; and (2) what campaign strategies do they most commonly use to present themselves as viable party leaders to party members? This study examined 16 candidates across three federal leadership races: the Liberal Party (2013); the New Democratic Party (NDP) (2017); and the Conservative Party of Canada (CPC) (2022). Through a qualitative content analysis of the campaign materials of each candidate in these races, such as media coverage, debate performances, and websites, this study identified the ways that candidates construct and communicate political leadership through their campaigns to persuade party members to vote for them as the party leader. Overall, this study further contextualized how leadership is marketed and performed in party politics.Item type: Item , A Study on the Impacts of Wide-Bandgap Devices on Turn-to-Turn Insulation Performance in Hairpin Winding for Electric Vehicle Traction Motors(University of Waterloo, 2025-12-03) Kholgh Khiz, AliElectric Vehicles (EVs) are one of the important levers of transportation electrification. However, charging time and limited mileage per charge remain significant barriers to widespread EV adoption. Continuous advancements in EV technology aim to mitigate these challenges. Three major improvements addressing these issues include increasing the operating voltage level, replacing random-wound motors with hairpin winding, and utilizing wide-bandgap (WBG)-based power converters to drive the motors. These advancements, however, raise concerns regarding motor reliability, particularly in the winding insulation system. Therefore, it is crucial to study and characterize the effects of higher voltage levels and WBG device-based drives on hairpin winding insulation. Turn-to-turn insulation is the most vulnerable point in motor stators. Power electronic converters employ pulse-width modulation (PWM) techniques to generate AC output waveforms, producing pulses with fast (short) rise times, overshoot, high frequency, and variable duty cycles. These PWM-driven systems subject insulation to greater electrical stress than conventional AC-fed machines. The adoption of WBG device-based drives exacerbates this stress due to their inherently fast switching characteristics and high-frequency components. Increased electrical stress may lead to partial discharge (PD) activity, which accelerates insulation degradation. Consequently, evaluating turn-to-turn insulation under WBG device-based drive operation and PD exposure is critical. This study develops a high-voltage SiC-MOSFET pulse generator to investigate the impact of WBG device-based drives on turn-to-turn insulation. A comprehensive analysis is conducted by examining the effects of pulse rise time, overshoot, frequency, and duty cycle. Three rise times (40 ns, 500 ns, and 800 ns) are considered to assess the influence of fast-switching transients inherent to WBG devices. Overshoot effects are examined using 10% and 20% overshoot pulses, while frequency effects are evaluated at 5 kHz and 10 kHz. Additionally, the impact of duty cycle is studied at 20% and 50%. Since traction motors operate under elevated thermal conditions, this study also evaluates the effect of increased temperature on insulation degradation to more accurately replicate in-service stress conditions. To assess turn-to-turn insulation performance, back-to-back test samples replicating hairpin winding structures are developed using actual flat wires employed in EV motors. Two wire types, corona-resistant and non-corona-resistant, are evaluated and compared. Experimental tests are designed based on Design of Experiment (DOE) principles, with samples subjected to 24-hour aging under high-voltage pulses generated by the SiC-MOSFET pulse generator in the presence of PD activity. Insulation performance is assessed before and after aging by measuring partial discharge inception voltage (PDIV) and conducting dielectric frequency response (DFR) analysis. Wire surface temperature is continuously monitored during the aging process, and PD activity is confirmed through the detection of PD electromagnetic wave emissions using a UHF antenna. Furthermore, optical microscopy, atomic force microscopy (AFM), scanning electron microscopy (SEM) images, and EDX analysis are utilized to examine wire coating integrity before and after aging. Results indicate that corona-resistant wires exhibit superior performance under PD conditions compared to non-corona-resistant wires. Additionally, frequency is identified as the dominant factor influencing PDIV drop, whereas overshoot has the most significant effect on the increase in dissipation factor after aging. Microscopy, AFM, SEM, and EDX analysis reveal clear evidence of PD-induced wire coating damage. The combined impact of thermal and electrical stress is examined, with findings compared to room-temperature test results. This research provides critical insights into the reliability of turn-to-turn insulation in hairpin-wound EV motors under WBG device-based drive operation, offering valuable guidance for motor reliability improvement in next-generation EV powertrains.Item type: Item , Performance Analysis and Optimization of Hybrid Edge-Cloud Architectures for Real-Time Robotics Applications(University of Waterloo, 2025-12-03) Salehpoor, MahdisThis thesis explores the optimization of distributed robotic perception systems for real-time applications such as autonomous navigation, smart surveillance, and multi-agent coordi- nation. These systems require fast processing of high-frequency sensor data under tight latency and reliability constraints. Edge computing offers low-latency inference and privacy, while cloud computing pro- vides centralized scalability and resource efficiency, but suffers from transmission delays and network dependency. Critically, the bandwidth required to transmit raw video streams and LiDAR pointcloud messages to the cloud is often infeasible, necessitating edge-side preprocessing. To address these challenges, this work proposes and evaluates a hybrid edge–cloud architecture in which each sensor node that is equipped with its own LiDAR and camera performs background removal and motion detection locally at the edge, while the remaining perception tasks are offloaded to the cloud. This design reduces bandwidth usage and enables real‑time responsiveness under constrained conditions. While edge modules cannot perform full object classification, they provide fast ”reflex-like” responses that enable event filtering, alert triggering, and resource prioritization, reserving the more computationally intensive object recognition for cloud processing. LiDAR processing was parallelized using Intel TBB and spatial chunking, achieving up to 2× speedups across 1–32 cores. For camera-based perception, Frame Differencing, GMM, and Dense Optical Flow were tested. Frame Differencing proved most effective for edge deployment, achieving 100% message reliability and 80.9% bandwidth savings with a 20.8 ms average processing time. Scalability tests showed that a 64-core system can support up to 75 nodes at 10 Hz or 50 nodes at 20 Hz with no message loss while meeting real-time constraints. Communication protocol testing revealed latencies ranging from 0.24 ms (ROS) to 2,589 ms (ZeroMQ over WiFi), setting architectural limits for cloud offloading. Finally, cost analysis showed that a 64-core cloud instance could replace 50 edge devices ($44,950 upfront), offering cost- effective scalability in suitable deployments. This work delivers: (1) empirical benchmarks that reveal how LiDAR and camera perception scale under parallel processing, (2) motion‑based filtering techniques that sig- nificantly reduce bandwidth without sacrificing accuracy, (3) real‑world measurements of communication protocol latency under 5G and Wi‑Fi, and (4) practical deployment guide- lines for hybrid edge–cloud robotic systems.Item type: Item , Towards Multi-Language Visualization Coding Agents(University of Waterloo, 2025-12-03) Ni, YuanshengLarge language models (LLMs) have made remarkable progress in general-purpose code generation, but they continue to struggle with visualization coding, generating executable code that produces accurate and semantically consistent plots. Visualization coding requires alignment across language, data, and rendered outputs, where execution success is non-binary and semantic correctness cannot be ensured by syntax alone. Existing instruction-tuning datasets rarely include runtime validation or feedback-based supervision, leading to fragile and unreliable plot generation. This thesis advances the development of \textit{visualization coding agents} that can generate, execute, and iteratively refine visualization code grounded in execution feedback. We first present VisCode-200K, a large-scale instruction-tuning dataset for Python-based visualization and self-correction. It contains over 200K examples from two sources: (1) validated plotting code from open-source repositories, paired with natural language instructions and rendered plots; and (2) 45K multi-turn correction dialogues from Code-Feedback, enabling models to revise faulty code using runtime feedback. We fine-tune Qwen2.5-Coder-Instruct on VisCode-200K to create VisCoder, and evaluate it on PandasPlotBench. VisCoder significantly outperforms strong open-source baselines and approaches the performance of proprietary models like GPT-4o-mini. A self-debug evaluation protocol further demonstrates the benefits of feedback-driven learning for executable and visually accurate code generation. Building on this foundation, we extend the approach to a multi-language setting. We introduce three complementary resources for advancing visualization coding agents: VisCode-Multi-679K, a large-scale supervised dataset comprising 679K validated executable visualization samples and multi-turn correction dialogues, covering 12 programming languages; VisPlotBench, a benchmark for systematic evaluation featuring executable tasks, rendered outputs, and protocols for both initial generation and multi-round self-debug; and VisCoder2, a family of multi-language visualization models trained on VisCode-Multi-679K. Experiments show that VisCoder2 significantly outperforms strong open-source baselines and approaches the performance of proprietary models like GPT-4.1, reaching 82.4% overall execution pass rate at the 32B scale, particularly in symbolic or compiler-dependent languages such as LaTeX, LilyPond, and Asymptote. Together, VisCoder and VisCoder2 form a coherent research trajectory towards reliable, generalizable visualization coding agents. By integrating executable supervision, semantic grounding, and feedback-based refinement across languages, this thesis establishes methodological and resource foundations for future systems capable of robust, self-correcting visualization code generation in real-world analytical workflows.Item type: Item , Resource Rhetoric in Three Canadian Novels, 1919-1945(University of Waterloo, 2025-12-02) Uher, ValerieIn this dissertation, I propose the term resource rhetoric to describe the cultural logic that renders extractivism an interminable part of Canadian identity. As Canada solidified its settler-colonial expansion in the nineteenth and early twentieth century, there was an attendant formalization of infrastructures promoting the extractivist ambitions of the state. Within those infrastructures a resource discourse—of natural resources and human resource management—was born. In Resource Rhetoric in Three Canadian Novels, 1919-1945, I examine three novels that articulate a cultural dimension to Canada’s broad attempt to adapt workers to a confluence of precarious working conditions in the first half of the twentieth century. I analyze the downplaying of class formation in these novels and link it to their use of resource rhetoric—tropes and figures that assert the primacy of the extractivist state over and against the primacy of the working-class collective. My thesis develops by first establishing the 1919-1945 period as one marked by an unease about whether workers could truly become the “human resources” Canada’s extractivist economy needed. I explore how this uncertainty is manifested in Douglas Durkin’s 1923 novel The Magpie, an economic novel set during the 1919 Winnipeg General Strike. I then demonstrate that during the interwar period, a worker’s success in embodying the ideal Canadian “human resource” identity was measured against a racial hierarchy emerging from eugenic ideology. In my analysis of Irene Baird’s 1938 novel Waste Heritage, I consider how the “rank and sort” logic of eugenics is used to calibrate moral rectitude in the novel’s portrayal of labour strife among Canada’s Depression-era unemployed. In the second part of my thesis, I consider how human resource discourse expanded to include social reproductive labour in the period just prior to the establishment of Canada’s welfare state. I argue that Gabrielle Roy’s 1945 novel The Tin Flute makes the home a terrain for potential class struggle against the exploitation of women’s work, while at the same time positioning this work as vital for the Canadian state to function. The rhetorical framing of workers in these novels consistently emphasizes their lack of agency and cooperation; foregrounds their interchangeability, and stresses workers’ inability to overcome their circumstances because of these factors. They articulate a deep-seated clash between the imperative that workers act as assets to Canada’s resource state, and the imperative that they might improve their lives through class formation and solidarity. While these novels are generally aligned with the resource discourse of the era, they demonstrate one fundamental failure of extractivist ideologies and resource logic: a person can never truly be a “dematerialized asset,” or a “universal Canadian worker subject.” My main claim in this thesis is that these novels show that to be a human resource is an unattainable goal.Item type: Item , Isotopic Study of Bromine: Determining Bromine Isotope Fractionation During Evaporation and Diagenesis(University of Waterloo, 2025-12-02) Ryuh, Yon-GyungStable isotopes of bromine (δ⁸¹Br) and chlorine (δ³⁷Cl) provide new opportunities to trace geochemical processes in various natural systems. While chlorine isotopes have long been applied in diverse hydrologic and geochemical fields, bromine isotopes have only recently drawn attention. Recent analytical advances have revealed unexpectedly large δ⁸¹Br variations in formation waters and evaporite deposits, yet the controls on the δ⁸¹Br variability remain incompletely understood. Resolving the fractionation mechanisms and the relationship between bromine and chlorine isotopes is essential. Understanding δ⁸¹Br-δ³⁷Cl systematics can support interpretations of evaporite basin evolution, and groundwater sources and mixing, and identification of diagenetic overprints in the subsurface. This thesis integrates three complementary approaches, including a global synthesis of published δ⁸¹Br-δ³⁷Cl datasets, controlled seawater evaporation experiments, and analyses of paleo-evaporite sequences. The integrated work provides insights into when and how stable bromine isotopes fractionate, and when and why its isotopic behavior decouples from that of stable chlorine isotopes. The synthesis of published datasets harmonizes unconnected studies to enable a comparison of the isotopic behaviors of bromine and chlorine across hydrologic and lithologic settings. The laboratory experiments isolate mineral-specific isotopic behavior and incorporation of bromine during sequential mineral precipitation under well-constrained conditions relevant to natural evaporative concentration of seawater. The analyses of paleo-evaporite sequences reveal how depositional signatures can be subsequently modified by post-depositional processes, and how such processes alter the isotopic and geochemical signature of bromine from chlorine. The global comparison of δ⁸¹Br and δ³⁷Cl values in groundwater and surface waters reveals a consistent pattern: δ⁸¹Br often diverges from δ³⁷Cl, with broader scatter and distinct behaviors across settings. The data show that δ⁸¹Br values often cannot be predicted from δ³⁷Cl values alone, highlighting that the two halogens respond to overlapping but non-identical processes differently. Multiple regression approaches and the comparisons among them indicate additional fractionation pathways, beyond simple mass-dependent behavior, differentially affect bromine and chlorine. Relatively high δ⁸¹Br values often cluster under specific geologic or hydrologic contexts, including organic complexation/decomposition, atmospheric interaction, elevated temperature-pressure regimes, and cryogenic processes. The comprehensive review provides a structured map of where bromine and chlorine behave similarly, where they diverge, and what that implies for interpreting natural datasets. Controlled seawater evaporation experiments demonstrate that bromine isotopes fractionate during sequential mineral precipitation, and crucially, that detectable shifts are observed before halite saturation. To better understand the underlying mechanisms, a laboratory evaporation series using synthetic seawater was conducted with continuous monitoring and stepwise sampling of brines, precipitates, and gas traps. Precipitates were characterized mineralogically, and both precipitates and coexisting brines were analyzed for δ⁸¹Br and δ³⁷Cl values to evaluate isotope fractionation during evaporation and mineral formation. Carbonates, gypsum, and halite have distinct δ⁸¹Br signatures consistent with differing pathways of Br incorporation, while δ³⁷Cl values are consistently higher in minerals than in coexisting brines. Capture of bromine in the gas phase sampled during the experiment confirms volatilization as an additional fractionation pathway for bromine isotopes. These experimental results explain why δ⁸¹Br values can vary widely, and differently from δ³⁷Cl, during progressive evaporation, mineral formation, and volatilization. Analyses of paleo-evaporite sequences show that primary depositional signals can be systematically reshaped by post-depositional modification. To evaluate depositional and post-depositional signals, basin-wide stratigraphic sampling for Br, Cl, δ⁸¹Br and δ³⁷Cl analysis across evaporite horizons and locations in the Salina Formation in the Michigan Basin was combined with lithological characterization. Br/Cl ratios were examined with petrographic indicators of diagenetic overprints, and basin-evolution context from previous studies was integrated. Paired measurements of δ⁸¹Br and δ³⁷Cl were then linked to these signatures. Consistent with the compiled groundwater and surface water datasets, evaporite δ⁸¹Br and δ³⁷Cl values often show weak correlation, reflecting multiple fractionation pathways rather than a single control acting on both isotopes simultaneously. Diagenetic processes often produce path-dependent shifts: either δ³⁷Cl or δ⁸¹Br values can increase, decrease, or remain unchanged depending on the processes involved (e.g., dissolution-reprecipitation, fluid-salt interaction, thermal regimes, organic interaction). The δ⁸¹Br–δ³⁷Cl dataset provides clear basin-evolution interpretations in complex evaporite records. The combined results establish that bromine isotopes are particularly sensitive to specific geochemical processes and that their variability cannot be explained by chlorine isotope systematics alone. This research contributes three main advances: (1) it provides a systematic review and defines the variability of bromine isotopes associated with diverse hydrogeologic settings; (2) it demonstrates experimentally that bromine isotopes fractionate significantly during evaporation and mineral precipitation, including prior to halite saturation; and (3) it shows that natural evaporite systems preserve complex isotopic signatures that integrate depositional and post-depositional processes, and that these signals are better understandable when both halogens are considered. Overall, this thesis develops a conceptual framework for bromine isotope geochemistry and demonstrates the value of Br-Cl dual isotope systematics to disentangle overlapping depositional and diagenetic processes, with implications for groundwater studies and evaporite basin evolution.Item type: Item , Manila's Other City: Toward a Counter-Relocation Approach(University of Waterloo, 2025-12-01) Reyes, Mary AngelineThis thesis explores the spatial and economic dynamics of informality in Barangay 105, Tondo, Manila, one of the most densely populated informal settlements in Metro Manila. Located along the industrial edge of the city, the barangay is shaped by rural displacement, state-led resettlement efforts, and infrastructural neglect. At the heart of the site are 25 warehouse structures, originally constructed as temporary relocation housing. Over time, these buildings have been incrementally transformed by residents into permanent live-work spaces, generating a distinct informal morphology that mirrors broader patterns of adaptation across Manila’s socioeconomic landscape. Informality, in this context, is not peripheral but central to the city’s functioning. Approximately 20–35% of Metro Manila’s population resides in informal settlements, many of which operate as self-sufficient ecosystems in the absence of state support. In Barangay 105, waste picking and small-scale recycling form the core of the local economy. Each day, informal workers collect, sort, and resell large volumes of waste, integrating themselves into larger material flows that connect domestic labor to regional and global waste economies. Despite their critical contributions, these workers remain structurally excluded from planning, labor protections, and service provision. To analyze these dynamics, the research draws on large-scale cartography, detailed studies of urban vernaculars, comparative case studies, and the documentation of daily routines. Government housing responses have historically relied on mass relocation, often displacing communities to distant peripheries. Programs such as those led by the National Housing Authority (NHA), the Community Mortgage Program (CMP), and the Zonal Improvement Program (ZIP) have repeatedly failed to address the needs of informal residents, instead severing their access to livelihoods and social networks. This thesis critiques these relocation paradigms and proposes a counter-relocation approach: one that strengthens communities in place rather than removing them. The design focuses on reimagining 15 of the existing warehouse structures as a distributed network of community depots: multi-use infrastructures that embed housing and economic production into the urban fabric. The project centers incremental, solidaristic, and community-led spatial strategies that reflect and strengthen the informal socioeconomic landscape of Tondo.Item type: Item , An Investigation of Overt Visual Attention and Gaze Behaviour in Social Human-Robot Interaction and Human-Computer Interaction Contexts(University of Waterloo, 2025-12-01) Shaghaghi, SahandIn human-human and human-robot interaction gaze has a consequential role as a type of non-verbal communication behaviour, affecting the social interaction depending on gaze behaviour's characteristics. As such, gaze behaviour has been a topic of major research throughout the past number of years since a better understanding of gaze behaviour could lead to design of robot behaviour for social interactions. In the context of the human-human interaction (HHI) and human-robot interaction (HRI) studies, gaze behaviour has been seldom investigated while taking into consideration all social interaction elements including interaction partners' personalities and social roles in addition to the social context. There are a number of studies which investigate conversational roles and personality matching in relation to gaze behaviour in the context of HRI in separate studies. However, works which investigate gaze behaviour in tandem with these social interaction elements are needed since such a study will contextualize gaze behaviour in relation to variations in these social elements (e.g. gaze behaviour characteristics based on introverted and extroverted personalities) while taking into consideration the compounded effects of these social elements in combination. What this thesis accomplishes is incorporation of all these social elements in tandem with gaze, all under the umbrella of one body of research. Utilization of this integrative approach was inspired by recent HRI literature, encouraging the investigation of verbal and non-verbal social interaction elements together with social interaction elements. This thesis investigates gaze behaviour in the context of HRI while taking into account social role and designed personalities in robotic platforms. As the social context, this thesis explores dyadic human-robot interactions involving objects of discourse from a gaze-centric point of view while considering the robot's gaze-centric perspective and the participant's gaze-centric perspective. Four major studies are conducted in the context of this thesis to fulfill this exploration. Tools for recording overt visual behaviour are vital in conducting human-computer interaction (HCI) research. However, specific tools enabling the recording of these metrics in online settings, facilitating video viewing were not available, therefore Study 1 created the FocalVid platform. This platform collects cursor location attentional data for the participants in online settings such as Amazon Mechanical Turk. The cursor metrics gathered through this platform were then compared to eye tracking data and our rendition of another relevant platform (BubbleView). It was determined that human gaze and cursor movements are distinct but have similarities in relation to velocities and dwell timing. This platform allowed for large-scale data collection for HCI and HRI studies, which is not possible in the context of in-person studies. Personality and social role are major elements of social interactions; however, perception of designed introverted/extroverted personalities for the humanoid iCub robot were not previously examined and additionally these two elements have not been explored simultaneously in the previous literature involving the iCub robot. In the second study, I explore the participants' perception of a robot in interactions between a robot and a human actor utilizing recorded online scenarios. In this study, the robot takes on different social roles while embodying different personalities. The robot is either a teacher, a student or a collaborator while either introverted or extroverted. To conduct this study, the Amazon Mechanical Turk platform and HRI video recordings were used. I discovered the presence of perceiver effects in participants’ assessment of the robot’s Ten-Item Personality Inventory (TIPI) dimensions perception vs. self TIPI dimensions, where participants' self-assessment of their personality correlated to their assessment of robot’s personality. TIPI questionnaire is a measure used to assess personality dimensions. It was also determined that the designed robot personality was perceived accordingly by the participants. These findings indicated that even though participants’ self-assessment of their personality dimensions affects their perception of the robot, they could still perceive the robot’s designed personality as intended. Observation and analysis of people’s overt visual attention dynamics in HRI could allow for better understanding of these interactions however, such overt attention while considering social interaction elements have not been previously explored in detail. The third study investigated participants' overt visual attention in the context of dyadic social settings using the FocalVid platform. In this study, I was also interested in the efficacy of the use of the FocalVid platform to collect attention metrics relating to such social settings. This study, taking advantage of the HRI scenarios designed in Study 2 and using the FocalVid platform, recorded the cursor attentional data for participants while the robot was enabled with different social roles and personalities. It was determined that the robot’s social role and personality significantly affected the participants’ overt visual attention. It was also determined that the presence of the FocalVid platform did not adversely affect the perception of the robot. Gaze studies in Human Robot Interaction should investigate both the human partner’s gaze behaviour’s effect on the social interaction, in addition to the robot’s gaze behaviour’s effect on the social interaction. A limited number of studies have explored the effects of gaze-architecture-enabled robots' behaviour on social interaction. In the fourth study, after the design of gaze-based interaction architectures based on Social Gaze Space taxonomy in dyadic interactions involving objects of discourse, the effects of using these gaze interaction architectures for robot gaze control were evaluated utilizing eye tracking data and Human Robot Interaction questionnaires. Through this study, it was determined that the SGS-IA architecture led to higher visual engagement by the participants towards the robot’s face and eye region compared to the TutorSpotter architecture, which was used for comparison purposes. One of the main contributions of this thesis is the design and evaluation of these gaze-based interaction architectures for anthropomorphic humanoid robots involved in human-robot interactions. All four of these studies were geared towards gathering a better understanding of gaze behaviour in HRI and HCI. Studies 1 and 2 had a preparatory role to this end. Study 1 allowed us to design the FocalVid platform and to investigate the attention metrics gathered through this platform against gaze metrics in this Human Computer Interaction platform. Study 2 allowed us to design the Human Robot Interaction scenarios needed for Studies 3 and 4. Study 3 investigated gaze behaviour of the human interaction partner involved in Human Robot Interaction using the FocalVid platform, and in Study 4 we designed and evaluated a gaze interaction architecture for the iCub robot through an in-person Human Robot Interaction study. These studies allowed for better understanding of the role of gaze behaviour in social HRI settings. These studies also enabled us to design gaze-specific interaction architectures for the iCub robot.Item type: Item , Rooted Elsewhere: Understanding the impact of immigration on health and wellbeing from the perspective of Black immigrant women in Ontario(University of Waterloo, 2025-11-28) Ike, Nnenna Arianzu UmaIntroduction Canada has long relied on immigration to shape its demographic landscape, social fabric, and economic development. Historically, immigration policies have favoured white European settlers, but changes to the Canadian Immigration Act opened pathways for more diverse populations, including Black immigrants from the Caribbeans and various African countries. However, Black immigrants, particularly women, continue to face systemic inequities in healthcare, employment, housing, and other areas of life. Black immigrant women often carry the compounded weight of racialized and gendered expectations as they navigate caregiving responsibilities, financial pressures, and resettlement barriers in their new socio-cultural context in Canada. When combined, these social determinant of health can negatively impact their health and resilience as they resettle in Canada. Canadian immigrants are rigorously vetted for the positive educational, health and economic impact they can make to the economy however, their health start to decline after their arrival to the country. Though studies abound establishing patterns linking unmet needs, structural and institutional inequity to immigrant health, for Black immigrant women, health is further shaped by intersecting forces such as race, gender, and migration. While quantitative studies have captured broad patterns in immigrant health, they often fail to capture the lived experiences behind those numbers. This study offers critical insight into the social and emotional complexities of resettlement, health-seeking behaviours, and identity negotiation of immigrants and their impact on physical and mental health. It contributes to a growing body of qualitative scholarship that centres the voices of Black immigrant women in Canada, by offering a deeper understanding of how immigration and resettlement experiences shape their health and well-being. Research Aim This thesis explores the multifaceted immigration and resettlement experiences of Black immigrant women in Ontario, Canada, with a focus on the implications for their physical and mental health. To capture the depth and complexity of the participants’ experiences, this thesis is separated into three papers, each drawing from the same research question but having their own distinct aim. Paper one examines the resettlement challenges specifically encountered by Black immigrant women as they settle and integrate into the Canadian society. It highlights how meeting Canadian immigration eligibility criteria does not ensure effective integration into the Canadian society. It showcases specific resettlement challenges and the resultant impact on their health and wellbeing. Paper two captures the employment experiences of Black immigrant women in the Ontario labour market and produces a three-stage employment narrative common to all participants. Also, paper two highlights the physical and mental health impact associated with the three different stages, along with the different coping strategies deployed by the women. Paper three explores how Black immigrant women make sense of their immigration and resettlement experiences and how the meanings they ascribe to their experiences impact on their health and wellbeing. These meanings significantly influence their choices and behaviors and profoundly impacts their self-identity and engagement with the Canadian society. Methods This thesis employs a qualitative approach to immigrant health research. Purposive sampling recruited a total of twenty-two Black immigrant women living in Ontario, aged 18-54 years. The women participated in virtual and in-person semi-structured interviews that lasted between 45 minutes to two hours. Three analytical approaches were used. First, thematic analysis was utilized in paper one to systematically code and interpret the broader resettlement challenges encountered by participants, such as the persistent devaluation of foreign credentials, experiences of racialized housing discrimination and negative dietary acculturation. Paper two drew on Reissman and Polkinghorne’s narrative analysis approaches to construct a framework that mapped participants’ employment stories across three distinct phases: the initial entry to the labour market, the early employment period, and the longer-term navigation of workplace environment. Paper three used Interpretative Phenomenological Analysis (IPA) to delve into how participants made meaning of their immigration and resettlement experiences within their cultural and socio-political contexts. Findings Findings from the thematic analysis of paper one illuminate how structural and systemic barriers were internalized by the participants, and contribute to their heightened stress, feelings of marginalization, and prolonged sense of frustration which are closely tied to both physical and mental health outcomes. The themes in paper one are: 1.) Hopes and aspiration for a better life, 2.) Facing reality, and 3.) Intentionality. Also, paper one shows that the combination of resilience level and the ability to leverage social capital determine participants’ ability to effectively integrate into the Canadian society. Participants’ employment narratives in paper two expose the emotional strain and disrupted career trajectory experienced by the participants as they tried to continue their professional path after arriving in Canada. Paper two highlights how participants experience structural and social exclusion at the workplace and the resulting negative impact on their physical and mental health. Most importantly, paper two develops a three-stage narrative model of early employment of newcomer Black immigrant women in Ontario. This model links the devaluation of credential and professional experience and racialized gatekeeping of employment to health outcomes in Black immigrant women. Further, this narrative model highlights not only the challenges encountered during the different stages of the employment journey but also how these experiences can contribute to the onset and progression of imposter syndrome (IS). The Interpretive phenomenological Analysis (IPA) method used in paper three foregrounds the embodied and affective dimensions of resettlement by showing how the participants’ identities, aspirations, and understandings of their health evolved in response to both visible and invisible pressures from their immigration. Paper three shows how participants sense of immigration was different before and after their arrival in Canada. Further, it shows that how they internalised and made sense of their experiences determined the decisions and actions they take which in turn impacted on their health and wellbeing. By privileging participants sense-making, paper three reveals the Black immigrant woman’s nuanced portrait of resilience and negotiation of self identity in their destination country. Conclusion Paper one highlights the feelings of disadvantage and stress expressed by all the participants as a result of their resettlement experiences of dietary acculturation, housing and healthcare discrimination. It showcases the results of the intersectionality of the participants identities and how social capital influences the extent to which participants are were able to navigate their resettlement challenges. Paper two portrays how people internalise the devaluation of their educational and professional qualifications because of systemic barriers and sexism and racism in Canadian workplaces. Further, Paper two identifies how participants experience of the imposter syndrome has far-reaching effect on their physical and mental health. Also, it shows that somatic symptoms can be easily developed as a result of workplace stress, and if they are misdiagnosed or overlooked, can lead to more serious and chronic health conditions. Paper three shows that beyond physical relocation, immigration is a deeply emotional and psychological journey shaped by the intersecting forces of gender, race and identity. Participants’ experience of racial trauma and systemic exclusion resulted in a sense of resignation to conserve their emotional energy. However, they demonstrate resilience through positive reframing and biographical reinvention to reconstruct their self identity in order to live and thrive in Canada as an immigrant. Overall, the contributions of this thesis include: 1. A methodological contribution showing productive complementarity between Interpretative Phenomenological Analysis Narrative Inquiry, and Thematic Analysis for capturing both idiographic depth and substantive patterns across the dataset. 2. A theoretical refinement by demonstrating how the Intersectionality lens, backed by the Critical Race Theory, and Migration and Integration theories can be used to capture and categorize data for analytic navigation and story telling. 3. An empirical contribution by way of a three-stage narrative employment model for newcomer Black immigrant women in Ontario that links credential devaluation and racialized gatekeeping to health impacts. Ultimately, this thesis affirms that immigration and resettlement, for Black immigrant women, is not just about relocating and fitting in a new country but is about renegotiating their entire self-identity in environments with limited socio-cultural and professional support. When these are not appropriately addressed, will impact negatively on their health and wellbeing in their destination country.Item type: Item , Safety and Security of Reinforcement Learning for Autonomous Driving(University of Waterloo, 2025-11-27) Lohrasbi, SaeedehIn the context of autonomous driving, reinforcement learning (RL) presents a powerful paradigm: agents capable of learning to drive efficiently in unseen situations through experience. However, this promise is shadowed by a fundamental concern—how can we entrust decision-making to agents that rely on trial-and-error learning in safety-critical environments where errors may carry severe consequences? This thesis advances a step toward resolving this dilemma by integrating three foundational pillars: adversarial robustness, simulation realism, and model-based safety. We begin with a comprehensive survey of adversarial attacks and corresponding defences within the domains of deep learning (DL) and deep reinforcement learning (DRL) for autonomous vehicles. This survey reveals the porous boundary between safety and security—both natural disturbances and adversarial perturbations can destabilize learned policies. Motivated by this insight, we introduce the Optimism Induction Attack (OIA), a novel adversarial technique that manipulates an RL agent’s perception of safety, causing it to act with unwarranted confidence in hazardous situations. Evaluated in the context of an Adaptive Cruise Control (ACC) task, the OIA significantly impairs policy performance, exposing critical vulnerabilities in state-of-the-art RL algorithms. To counter the demonstrated threats, we present a systematic defence architecture. We develop REVEAL, a high-fidelity simulation framework designed to support the training and evaluation of safe RL agents under realistic vehicle dynamics, traffic scenarios, and adversarial conditions. By narrowing the gap between abstract simulation and real-world complexity, REVEAL facilitates rigorous and nuanced testing, which is essential for safety-critical applications. To enhance learning efficiency within this environment, we employ a transfer learning (TL) strategy: policies initially trained in simplified simulators (e.g., SUMO) are adapted and fine-tuned in REVEAL, leading to faster convergence and improved safety performance during both training and deployment. Central to our approach is the development of a Multi-Output Control Barrier Function (MO-CBF), which simultaneously supervises throttle and brake commands to enforce safety constraints in real time. Rather than relying on hard overrides, the MO-CBF operates cooperatively with the learning agent—gently adjusting unsafe actions and introducing corresponding penalties during training. This enables the agent not only to learn safe behaviour but also to internalize safety principles and anticipate potentially unsafe scenarios. Our empirical evaluation demonstrates the effectiveness of the proposed framework across a spectrum of disturbances, adversarial inputs, and realistic high-risk maneuvers. The results consistently show improved safety and robustness, highlighting the framework’s capacity to transform RL agents from vulnerable learners into trustworthy autonomous systems. In summary, this thesis presents a comprehensive methodology for safe and secure RL in autonomous driving. By grounding agent training in high-fidelity simulation, leveraging adversarial awareness, and embedding real-time model-based safety mechanisms, we provide a cohesive and scalable pathway toward deploying RL in the real world with confidence.Item type: Item , How Architectural Style, Height, and Complexity Influence Perceived Oppressiveness in Urban Spaces(University of Waterloo, 2025-11-27) Lapietra Garcia, ThomasThe design of urban environments strongly influences psychological experience, yet research on how building form influences affective responses remains limited. This study used immersive virtual reality to examine the combined effects of architectural style (modern vs. contemporary), building height (low-, mid-, and high-rise), and façade complexity (low, medium, high) on affective perceptions of urban streetscapes. Forty-nine participants explored 18 virtual environments and rated each on oppressiveness, openness, restoration, arousal, and environmental liking. Results showed that greater building height consistently increased perceived oppressiveness and arousal while reducing openness, stress restoration, and liking. Greater façade complexity increased preference, openness, and restoration, and buffered the oppressive effects of high-rises, particularly in modern-style settings. Participants also expressed a clear preference for low- and mid-rise settings over high-rises. These findings reiterate and expand on the restorative and aesthetic benefits of architectural complexity and the value of human-scale design in supporting psychological well-being in urban dwellings.Item type: Item , Quantifying Endplate Deflection in Response to Cyclic Load Exposures Using a Porcine Cervical Spine Model(University of Waterloo, 2025-11-27) Watson, MichaelThe vertebral endplate is a thin layer of cartilage and bone that separates the intervertebral disc from adjacent vertebral bodies and facilitates the transmission of compressive force through the spine. Despite this essential function, it remains the weakest component of the vertebra-disc unit and is highly susceptible to mechanical failure. Endplate failure typically arises from localized tensile strains that manifest as deflection, defined as the out-of-plane displacement of the surface under load. While prior work has demonstrated inferior endplates of intervertebral joints exhibiting greater deflection and higher incidence of failure than their superior counterpart, current techniques for quantifying endplate deflection face notable limitations. Early studies using metallic markers or displacement transducers required drilling channels into the vertebral body, potentially exaggerating deformation by weakening subchondral bone support. Imaging-based approaches, particularly micro-CT, offer high spatial resolution but are limited to static or stepwise loading due to temporal constraints. These static conditions do not capture the cyclic loading patterns experienced by the spine during daily activity, where repeated deformation can cause fatigue-induced microdamage and eventual failure. Additionally, static loading promotes excess fluid loss from the nucleus pulposus, altering endplate deflections in ways that do not reflect physiological motion. Consequently, existing measurement techniques may misrepresent true endplate behavior and are unable to evaluate changes in deflection as a function of cyclic load exposure. This study addresses these limitations by developing a unique method to assess endplate deflection during cyclic loading without requiring prolonged stepwise protocols or causing damage to the vertebral bone. By comparing superior and inferior endplates across different load magnitudes and cyclic durations, this work aims to clarify the mechanisms underlying endplate vulnerability and further validate the porcine cervical spine as an experimental model for human lumbar spine deflection. Eighteen porcine cervical spine functional units (C3C4, C4C5, and C5C6; n = 6 per level) were dissected to yield 36 individual vertebrae. High-resolution laser profilometry was then used to capture the topography of the caudal endplates of C3, C4, and C5 and the cranial endplates of C4, C5, and C6. Custom indenters, designed as negative molds of the nucleus-occupying endplate region, were created from the resulting surface scans and fabricated via 3D printing. Specimens were then oriented such that the tested endplate was in a neutral position and subjected to a normalized haversine waveform, ranging from 0.3 kN to 30% of the predicted ultimate compressive strength using a servohydraulic materials testing system. The cycle-dependent changes in endplate deflection were measured at 0, 1000, 3000, and 5000 total cycles. At each time point, endplate deflection measurements were captured via the indenter’s displacement while specimens were exposed to a brief static force of 0.3 kN, 1 kN, and 3 kN, totaling 12 measurements per vertebra. Three separate linear mixed effects models were used to evaluate the impact of loading magnitude, loading cycles, endplate level and the proportion of the nucleus occupying endplate area on superior and inferior endplate deflection within each joint. A fourth linear mixed effects model was used to evaluate the impact of loading magnitude, loading cycles, and joint level on the magnitude of the differences between superior and inferior endplate deflection. Utilizing this novel methodology, this study was the first to quantify endplate deflection under cyclic loading conditions, observing greater deflection of the inferior endplate across all spinal levels, except at baseline (0.3 kN, 0 cycles). This method also enabled comparison of deflection rates between endplates, with the C4C5 and C5C6 inferior endplates showing a significantly greater rate of deflection during the first 1000 cycles. Among joints, C4C5 exhibited the largest difference in superior and inferior endplate deflection compared to C3C4 and C5C6. Endplate deflection was not influenced by the proportion of the nucleus occupying endplate area at any spinal level. Lastly, as the first study to examine endplate deflection in porcine cervical vertebrae, the observation of greater inferior endplate deflection being consistent with human cadaveric studies further supports the validity of this model. Overall, this study demonstrates the utility of a novel methodology for measuring and comparing superior and inferior endplate deflection under cyclic loading.Item type: Item , Zero-Knowledge Proof-Enabled SAT Co-processor for Blockchain Systems(University of Waterloo, 2025-11-26) Yusiuk, VladyslavThis thesis explores the possibility of building classical SAT solvers in Circom Domain Specific Language to create zero-knowledge proofs (ZKPs) usable in blockchain contexts. I implemented DPLL and Chaff as arithmetic circuits within Circom and analyze them based on constraint count, proving delay, and zk-SNARK verification layers. With this evaluation, the aim is to determine the feasibility of solvers integration into off-chain computation systems and rollup-centric architectures on Ethereum. The findings indicate that incorporating SAT solvers within zero-knowledge circuits is achievable though some degradation in efficiency occurs based on algorithm used and input representation. This research provides a thorough assessment of known SAT methods across an unconventional boundary, linking symbolic logic with blockchain technologies reliant on zk-SNARKs.Item type: Item , Development of High Strength Aluminum Alloys for Directed Energy Deposition Additive Manufacturing(University of Waterloo, 2025-11-26) Waqar, TahaAmong additive manufacturing (AM) techniques, directed energy deposition (DED) is of particular interest for structural Al alloys, as it combines the faster cooling rates with the flexibility to repair or build large-scale geometries. The localized thermal cycling inherent to the DED process influences solidification behavior, grain refinement and precipitate evolution for high strength age-hardenable Al alloys such as Al 7075, which in turn governs the mechanical performance. These capabilities position DED as a promising pathway for expanding use of high strength heat-treatable aluminum alloys in aerospace and automotive applications where a good strength to weight ratio is crucial. However, Al 7075 tends to crack during solidification and possesses a limited service temperature range. The research conducted explores the tailoring of an existing Al 7075 composition and delves into the development of novel Al alloy compositions for DED-AM processes. In the initial phase of the research, laser-directed energy deposition of Al 7075 wire feedstock enhanced with TiC nanoparticles to promote grain refinement was investigated. It was found that the combination of high laser power (3400 W) along with low travel speed (400 mm/min) and low wire feed speed (400 mm/min) resulted in the reduction of lack of fusion defects and reducing cracks within the multilayer prints. However, substantial evaporation during printing led to a reduced amount of Mg and Zn bearing phases in the as-printed samples. It was shown that the direct aged sample heated for 5 hours was of comparable hardness to the T6 (solution heat treated and then artificially aged) sample (115 HV0.5), which highlights the presence of solute trapping in the as-printed material. To compare the behavior of the same Al 7075 + TiC wire feedstock under arc-based solidification conditions, the research continued to investigate the microstructural evolution and mechanical response of Al 7075 reinforced with TiC nanoparticles processed via arc-based DED, with a particular focus on aging behavior. Grain refinement was primarily attributed to heterogeneous nucleation and grain boundary pinning by TiC clusters. Moreover, TiC inoculants influenced solute redistribution, driving segregation of Mg and Cr, which in turn altered the precipitation behavior during aging. Heat-treated samples revealed the co-formation of MgZn₂ strengthening precipitates and the E-phase (Al18Mg3Cr2), with the latter contributing to the heterogeneous distribution of precipitates. These findings highlight both the benefits and challenges of TiC inoculation in tailoring microstructure and age-hardening response in arc-DED processed Al 7075 alloys. The second phase of the research presents the design and evaluation of a novel Al-Ce-Mg alloy tailored for wire arc-DED. The objective was to overcome the limitations of conventional high-strength aluminum alloys, which suffer from solidification cracking, volatile element loss, and poor thermal stability at elevated temperatures. Alloy selection was guided by CALPHAD simulations, leading to the identification of a near-eutectic Al-10Ce-9Mg composition. Thin-wall structures were fabricated, and porosity was quantified using micro-computed tomography, supported by high-speed imaging that revealed oxide-film entrapment as the dominant cause of porosity. The solidified microstructure consisted of α-Al, eutectic, and primary Al₁₁Ce₃ phases, as well as β-AlMg phase, which contributed to both strength and thermal stability. Compression testing demonstrated high room-temperature strength but brittle failure. At elevated temperatures, however, the alloy retained superior strength compared to conventional precipitation-strengthened Al 7075 alloy, even after extended thermal exposure. This observation was attributed to the stability of Al-Ce intermetallics. Incorporation of Sc into Al-Ce-Mg alloys can provide a dual strengthening and thermal stabilizing effect. Therefore, in the final phase of the conducted research, an Al-8Ce-8Mg-0.2Sc alloy was developed. Laser surface remelting was employed to replicate AM-like conditions, producing a refined bimodal grain structure and fragmenting coarse Al₁₁Ce₃ networks into discontinuous, blocky morphologies. Compared to the as-cast state, the remelted alloy exhibited increased hardness (114.5 HV1 vs 133 HV1), aided by refined grains and secondary phases such as Al11Ce3 and Mg2Si. Direct aging produced an irregular hardening response, with peak hardness achieved at 375 °C for 1 h due to the precipitation of coherent Al₃Sc nanoprecipitates. Long-term thermal exposure at 200 °C for up to 1000 hours showed negligible hardness loss and minimal coarsening of Ce-bearing intermetallics. Strengthening contributions were dominated by Al₃Sc precipitation, supported by solid-solution, grain refinement, dislocation hardening, and stable Al₁₁Ce₃ dispersoids.Item type: Item , Heterogeneous Decomposition of Convolutional Neural Networks Using Tucker Decomposition(University of Waterloo, 2025-11-26) Mokadem, FrankConvolutional Neural Network (CNN) remain the architecture of choice for computer vision tasks on compute-constrained platforms such as edge and personal devices, delivering both close to state-of-the-art performance metrics and linear inference complexity with respect to input resolution and number of channels. However, the deployment of larger and more complex CNN architectures is limited by the restrained memory offered by such platforms. This brings about a need to compress pretrained CNN into smaller models in number of parameters while controlling for degradation in performance. This thesis tackles CNN compression using low rank approximation of convolution layers using Tucker Decomposition (TD). We introduce a new heuristics-based Neural Architectural Search procedure to select low rank configurations for the convolution tensors, which we call Heterogeneous Tucker Decomposition (HTD). Standard low rank approximation using TD factorizes and approximates convolution layers using uniform ranks for all convolution tensors, then applies a few fine–tuning epochs to recover degradation in performance. An approach we show to be suboptimal against a heterogeneous selection of ranks for each convolution layer, followed by same number of fine-tuning epochs. Our primary contribution is the development and evaluation of TD, which applies layers-pecific compression rate (low rank divided by full rank) inferred from a Neural Architectural Search (NAS) process. Furthermore, we introduce a sampling heuristic to efficiently explore the search space of layer-specific compression rates, thus preserving performance while significantly reducing search time. We present a mathematical formulation for the HTD optimization problem and an NAS algorithm to find admissible solutions. We test our approach on multiple varieties of CNN architectures: AlexNet, VGG16, and ResNet18, adapted for the MNIST classification task. Our findings confirm that HTD performs better than TD on all models tested. For the same compression rate, HTD enables to recover a higher precision after fine-tuning, with gains ranging from 1.2% to 5.8%. For equivalent accuracy targets, HTD delivers 15-30% higher compression rates than TD. This thesis advances Neural Architectural Search by highlighting the efficacy of heterogeneous tensor decomposition approaches. It provides a robust framework for their implementation and evaluation, with significant implications for deploying convolutional deep learning models in resource-limited settings. Future work will explore incorporating low-rank constraints as a regularization objective during training, potentially enabling end-to-end compression-aware optimization.Item type: Item , Proactive Characterization of Wildfire Impacts on Drinking Water Treatability(University of Waterloo, 2025-11-26) Bahramian, SoosanForested catchments are important sources of drinking water globally. They are increasingly threatened by disturbances, prominently climate shocks, including large wildfires. Wildfires alter watershed hydrology and biogeochemistry, leading to reduced infiltration, increased overland flow, and enhanced delivery of sediments, burned vegetation, and pyrogenic material into aquatic systems. Such inputs can alter drinking water source quality and challenge treatability. Ash is the residual material from wildland fuel combustion, composed of mineral particles and organic matter that can leach into water. While inorganic dissolved compounds from ash can impact water quality by, for example, increasing ionic strength and alkalinity, water-extractable organic matter (WEOM) from wildfire ash contributes to increased post-fire dissolved organic carbon (DOC) concentrations. During drinking water treatment, higher DOC concentrations increase chemical demand (e.g., coagulant, disinfectant), enhance the formation of potentially harmful disinfection by-products (DBPs), cause taste and odor issues, and promote bacterial regrowth in distribution systems. These impacts may also necessitate new infrastructure to manage changes in source water quality, ultimately increasing overall treatment costs. Although they cannot reflect all watershed processes, bench-scale evaluations provide valuable insights into wildfire impacts on drinking water treatability by isolating treatment-relevant mechanisms at controlled laboratory conditions. However, different approaches used to prepare wildfire ash-impacted waters (WAIWs) limit the inferences that can be drawn from them. Here, key factors (e.g., mixing duration and condition, ash-to-water ratio, and source water quality) that can impact organic matter leaching from wildfire ash to water were investigated. WEOM concentration increased within the first 24 hours of mixing before plateauing or declining as mixing progressed, regardless of ash type and background water source. Continuous mixing yielded higher WEOM concentrations than stagnant conditions, indicating that particle-particle interactions and surface exposure enhanced leaching. WEOM yield also decreased as ash-to-water ratios increased. Despite anecdotal suggestions, a relationship between wildfire ash color and WEOM concentration was not observed (Chapter 2). Wildfire ash collection methods may also impact inferences drawn from bench-scale drinking water treatability assessments. Unburned vegetation, rocks, or other debris may have physico-chemical properties different from those of ash deposits; thus, increasing uncertainty in treatability assessments. Dry ash homogenization methods (i.e., manual separation, sieving, and pulverization) were investigated because they may mitigate these impacts. Sieving was shown to be the most practical and reliable method for ensuring ash homogeneity. Pulverization enhanced organic matter release from large particles by increasing surface area, but it also generated aerosolized ash, complicating sample handling. In addition, pulverization altered WEOM character, potentially by increasing the availability of smaller organic matter compounds previously encapsulated within ash particles or by mechanically fragmenting larger organic molecules into smaller compounds (Chapter 3). Subsequent investigations examined the role of settleable ash solids (SAS), a previously overlooked fraction of wildfire ash. SAS substantially increased water alkalinity and make pH control for coagulation extremely difficult. Although pH adjustment enhances DOC removal from WAIW, SAS increased acid demand substantially. The removal of SAS reduced both alkalinity and acid demand; however, as ionic strength was concurrently reduced, floc formation and turbidity reduction for a given coagulant dose decreased somewhat. A limited complementary analysis was conducted to evaluate whether atmospheric ash deposition could also act as a significant driver of source water quality and treatability change. While the impact of atmospheric deposition of ash on water alkalinity depends on the surface area of water body, only exceptionally high atmospheric ash loading could meaningfully alter source water alkalinity in reservoirs that hold large volume of water (Chapter 4). Wildfire ash alters multiple aspects of water quality concurrently, including turbidity, DOC concentration and character, and alkalinity, so its overall implications for water treatment cannot be adequately assessed by examining individual mechanisms in isolation. Coagulation experiments with WAIWs demonstrated these interacting impacts. At low coagulant (i.e., alum) doses, turbidity was effectively reduced, yet DOC removal remained limited, despite pH adjustment to coagulant-specific optima. Enhanced coagulation combined with higher alum doses improved DOC removal but introduced trade-offs, as turbidity reduction declined somewhat because of reduced ionic strength associated with decreased alkalinity. The results indicated, while wildfire ash can severely deteriorate water quality by increasing turbidity, alkalinity, DOC concentration, and aromaticity, which may increase coagulant demand or necessitate more advanced treatment methods, the underlying coagulation mechanisms for WAIW remain consistent with those in natural waters. Thus, wildfire ash does not present fundamentally new challenges to coagulation; rather, the magnitude of water quality changes following wildfire can pose risk to treatment performance and operational resilience (Chapter 5). Collectively, this research demonstrates that while bench-scale studies cannot fully replicate the complexity of post-fire watershed processes and wildfire impacts on water quality, they remain essential for isolating and investigating the specific effects of wildfire ash on drinking water treatment processes. Accordingly, it is practical to adopt methods that maximize the extraction of organic matter from wildfire ash and represent worst-case treatment scenarios. These methodological insights help ensure the comparability of bench-scale investigations. This work also shows that wildfire impacts coagulation primarily by complicating pH control and deteriorating drinking water source quality, increasing the need for more intensive treatment processes. Overall, this research establishes a robust methodological foundation for reliably assessing wildfire ash impacts on water quality and for informing the development of strategies to mitigate wildfire impacts on drinking water treatability.