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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Designing for Trust: A Multi-Factor Investigation of Optometrists’ Perspectives on AI-Based Glaucoma Screening Systems
(University of Waterloo, 2025-11-07) Karim, Ali
Although glaucoma screening AI models show strong performance, their integration into clinical practice remains limited. Clinicians often face barriers rooted in technological acceptance, with trust emerging as a key determinant of adoption. Prior research has emphasized explainability, but a broader exploration of factors affecting trust is needed. This study investigates multiple factors shaping trust in AI and translates them into design requirements for next-generation glaucoma screening clinical decision support systems (CDSS). In a previous study, two real-world glaucoma patient cases, each comprising three visits at different times, were presented under both unimodal conditions (fundus images only) and multimodal conditions (fundus images, optical coherence tomography, visual fields, and medical history) through a mock interface simulating an AI-based glaucoma screening support system. During these simulated visits, nineteen licensed optometrists interacted with the system and participated in follow-up interviews, where they were asked whether they trusted the system and to explain their reasoning. The objective of this thesis is to identify the factors influencing optometrists’ trust in an AI-powered glaucoma screening tool and to propose design recommendations that can enhance trust in future iterations. The interview data were analyzed using Braun and Clarke’s thematic analysis approach. The emerging themes indicate that trust in the AI system is shaped by multiple factors: (1) alignment with clinicians’ expectations of AI’s role: flagging tool vs. consultant; (2) completeness of information; (3) communications of performance metrics: accuracy, sensitivity, confidence scores, perceived consistency and perceived quality of training data (4) clinical relevance of outputs (trends, actionable recommendations, differential diagnosis); (5) transparency in risk factor weighting, exclusions, and considered variables; (6) decision alignment between optometrists and the AI, assessed across decision inputs, identified risk factors, their relative importance, recommended actions, and the gradient of concordance in final decisions; (7) optimized the AI for cautious screening to captures all potential cases; (8) interface usability supporting timely decisions; (9) users’ self-perceived expertise, occasionally leading to overreliance; (10) onboarding and training that highlighted the system’s features and limitations; and (11) increasing familiarity over time, which helped calibrate trust. Based on these findings, 17 design principles were proposed to guide the development of the next iteration of a trust-supportive interface for glaucoma screening decision support systems.
Stream periphyton response to phosphorus loading events is constrained by antecedent conditions
(University of Waterloo, 2025-11-06) Schneider, Natalie
Phosphorus (P) loadings to streams often occur in short duration events associated with runoff from human activities. Although it has been shown that stream periphyton can uptake and assimilate event-based P, the role of antecedent P concentrations in modulating P uptake from event-based loadings and resulting effects on periphyton structure and function is not known. To assess effects of antecedent P concentration on stream periphyton response to short-term P loading events, we completed two 26-day artificial stream experiments at the Thames River Experimental Stream Sciences (TRESS) Centre in London, Canada. Experiments consisted of exposing periphyton communities in nine artificial streams to a range of 48-hour P loading event concentrations (15 to 690 μg P/L) under low (10 μg P/L) or high (50 μg P/L) antecedent P concentrations. Periphyton was sampled one day before, one day after and 10 days after P loading events to quantify periphyton structure (ash free dry mass (AFDM), chlorophyll a (chl a), P content) and function (P uptake, benthic metabolism, cellulose decomposition, biomass growth, chl a accumulation). Under low antecedent P conditions one day after the P event, P content and P uptake had a positive linear relationship with event concentration and this was similarly seen in biomass and chl a ten days after the P event. One day after the P event in high antecedent streams, P content and P uptake showed a positive linear response with P event concentration, but this additional P in periphyton did not lead to increases in biomass and chl a. Whereas, a negative linear relationship with event concentration and P uptake was seen ten days after the P event. Measures of periphyton function (benthic metabolism and cellulose decomposition) were unaffected by P event size and regardless of the antecedent condition. These findings suggest that high antecedent P concentrations caused cellular saturation of periphyton limiting the assimilation of P from event-based P loads. Therefore, streams with high antecedent P may deliver reduced water purification benefits with regards to attenuating P transport to downstream ecosystems at risk of eutrophication. Management actions to reduce antecedent P concentrations will be needed to rehabilitate ecosystem service provision in streams chronically enriched in P.
Cross-sectional Analysis of Current Care Assessment Practices in the Retirement Home Sector in Ontario
(University of Waterloo, 2025-11-06) Nasim, Anooshah
As the population of Canada ages, some older adults often have increased multimorbidity, disabilities, and frailty. As a result, they are at an increased risk of hospitalization, accelerated functional decline, and earlier institutionalization. As they face more disability and health challenges, the lack of sufficient primary, community, and home care services to support them leads many to move into retirement homes. Once there, residents continue to experience health challenges, likely as a consequence of ongoing inadequate primary care and insufficient services geared toward their needs. Yet, addressing the unmet needs of retirement home residents at the individual and population levels is made challenging by the lack of standardized information collection. While regulatory agencies stipulate that residents undergo a health assessment, there are no specific requirements as to their nature. A better understanding of their unmet needs can potentially guide better primary care planning and help identify the level of services required to deliver better resident and system outcomes. To begin, current care assessment practices and processes surrounding these assessments must first be characterized and understood before the introduction of a new standardized instrument can be contemplated.
Manifold-Aware Regularization for Self-Supervised Representation Learning
(University of Waterloo, 2025-11-04) Sepanj, Mohammad Hadi
Self-supervised learning (SSL) has emerged as a dominant paradigm for representation learning, yet much of its recent progress has been guided by empirical heuristics rather than unifying theoretical principles. This thesis advances the understanding of SSL by framing representation learning as a problem of geometry preservation on the data manifold, where the objective is to shape embedding spaces that respect intrinsic structure while remaining discriminative for downstream tasks. We develop a suite of methods—ranging from optimal transport–regularized contrastive learning (SinSim) to kernelized variance–invariance–covariance regularization (Kernel VICReg)—that systematically move beyond the Euclidean metric paradigm toward geometry-adaptive distances and statistical dependency measures, such as maximum mean discrepancy (MMD) and Hilbert–Schmidt independence criterion (HSIC). Our contributions span both theory and practice. Theoretically, we unify contrastive and non-contrastive SSL objectives under a manifold-aware regularization framework, revealing deep connections between dependency reduction, spectral geometry, and invariance principles. We also challenge the pervasive assumption that Euclidean distance is the canonical measure for alignment, showing that embedding metrics are themselves learnable design choices whose compatibility with the manifold geometry critically affects representation quality. Practically, we validate our framework across diverse domains—including natural images and structured scientific data—demonstrating improvements in downstream generalization, robustness to distribution shift, and stability under limited augmentations. By integrating geometric priors, kernel methods, and distributional alignment into SSL, this work reframes representation learning as a principled interaction between statistical dependence control and manifold geometry. The thesis concludes by identifying open theoretical questions at the intersection of Riemannian geometry, kernel theory, and self-supervised objectives, outlining a research agenda for the next generation of geometry-aware foundation models.
Towards a Novel Optical Spectroscopy Technique Using Photon Absorption Remote Sensing
(University of Waterloo, 2025-11-04) Dhillon, Jodh
Optical spectroscopy has shown great promise in the field of biomedical research. For example, works employing traditional spectroscopy approaches have demonstrated that analyzing a sample’s optical response to incoming light can effectively differentiate between healthy and diseased tissue. However, these techniques suffer from limitations due to the fact that they typically capture signals from only a single light-matter interaction type, such as absorption, scattering or fluorescence. Therefore, many traditional methods are constrained in terms of the types of samples they can feasibly analyze, as well as, potentially, the depth of their sample characterization, as they do not focus on capturing relevant information from other interaction modalities. This work employs photon absorption remote sensing (PARS) to overcome these limitations. PARS is a novel all-optical imaging technique capable of capturing radiative and non-radiative relaxation processes following electronic photon absorption. This thesis explores the initial development of the first PARS system specifically designed and optimized for optical spectroscopy applications, aimed at studying wavelength-dependent relaxation processes to characterize a wide range of liquid samples. The first step of this work was to build a non-radiative PARS spectroscopy system capable of accurately capturing the thermal and acoustic relaxation processes that arise from different ultra-violet (UV) excitation wavelengths. These signals were processed and used to construct a non-radiative PARS absorption spectrum for each sample of interest. These spectra were benchmarked against the absorption data collected from a NanoDrop spectrophotometer, which served as the ground truth in this work. This study revealed that for certain samples, such as eumelanin, which is highly absorbent to UV light and relaxes almost all absorbed energy non-radiatively, the non-radiative PARS spectroscopy system is capable of generating highly accurate absorption spectra. However, this system did not generate as close to ground truth spectra for samples that do not have as strong UV absorbing tendencies and are not as non-radiative in nature. The second step of this work was to integrate a radiative relaxation arm into the developed non-radiative PARS spectroscopy system. This pathway was configured to collect fluorescence emission spectra, which represent radiative sample relaxation, simultaneously with the collected non-radiative data. Radiative PARS absorption spectra were generated for each sample. In this way, the developed PARS system combines absorption (monitoring both relaxation pathways) and fluorescence emission spectroscopy onto a single bench-top system. The radiative PARS absorption spectra were compared to the ground truth, which revealed that molecules that are highly fluorescent in nature are more appropriately studied through the radiative relaxation arm than the non-radiative pathway. Total absorption spectra, which combine the non-radiative and radiative absorption data, were also generated, and it was determined that the absorption profiles of certain samples, such as NADH, are best studied using this approach. The final step of this work was to use the collected total absorption and fluorescence emission data from the PARS spectroscopy system to identify the composition of different mixtures of craft red and blue ink samples. Traditional linear and generalized bilinear models were employed to perform this unmixing and the results from this study indicate that the combination of the absorption and fluorescence data collected on this system allows for a more accurate identification of a mixture’s components than either data source individually. This suggests that the PARS spectroscopy system provides an increased level of detail in sample characterization compared single-modality spectroscopy systems. Ultimately, this research lays the groundwork for the development of a PARS spectroscopy system capable of being deployed in clinical settings to study samples and help inform diagnoses. This work demonstrates the feasibility of leveraging PARS for optical spectroscopy and presents a system design and framework that can be further iterated upon to enhance performance and enable a robust characterization of relevant and complex biological samples.
Polynomial Controllers for Optimal Trajectory Matching with Stability Guarantees
(University of Waterloo, 2025-11-04) Kitaev, Alexander
We formulate a trajectory matching problem in which a set of reference trajectories for a plant is given, and a control law that causes the plant’s trajectories to be as close as possible to the reference trajectories is desired. These trajectories might be generated by an implicit controller such as a model predictive control (MPC) algorithm or manually chosen by a user. This thesis presents a nonconvex optimization approach for solving the trajectory matching problem that generates explicit polynomial controllers. The value of this approach is that the explicit control laws it generates are simpler to implement, and can be used for stability analysis. Additionally, the method presented in this thesis guarantees local stability of the generated controller by ensuring local contractivity towards the generated trajectories. This thesis presents several theoretical results that justify the method described here. Firstly, a proof that the local contractivity constraints used to ensure local stability can be expressed as a set of matrix inequalities is presented, which turns an infinite set of constraints into a finite one. Secondly, a theorem that describes how symmetries in the trajectory matching problem correspond to symmetries in its solution is presented and proven, which enables a reduction in the control design problem size and resulting solution. Finally, this thesis demonstrates the method it describes on two example problems motivated by real-world applications. The first of these is stabilization and disturbance recovery for a single-machine infinite-bus (SMIB) power system, and the second is a lane change manoeuvre for Dubin’s vehicle, a simple vehicle model. In each case, the reference trajectories are generated by MPC.
Influence of the Coating on the Radiative and Conductive Heat Transfer of 22MnB5 Steel in Hot Stamping
(University of Waterloo, 2025-11-03) Bhattacharya, Ardhendu
In hot stamping of Al-Si coated 22MnB5 steel, the heat transfer coefficient (HTC) during quenching is critical for determining the microstructure and mechanical properties of the formed part. Additionally, the radiative properties elucidate how the surface transforms as the steel is heated before quenching. Knowledge of the surface transformations is paramount for understanding the damage caused by the molten Al-Si coating to ceramic rollers in a production environment. This work investigates the effect of the coating on the HTC during quenching and explores the link between radiative properties and surface state changes, including the melting of the Al-Si coating and oxide layer growth. Experiments were performed using a hydraulic press fitted with cooled dies to study the impact of interfacial pressure, coating weight, and dwell time on the HTC. The HTC increased with interfacial pressure, before saturating between 6 and 10 MPa. Specimens with higher coating weights had lower HTCs, which was corroborated by a higher arithmetic roughness for specimens with higher coating weights. Furnace dwell time did not significantly affect the HTC or the roughness of the specimen. Ex situ reflectance measurements of hot stamped specimens revealed minima and maxima between 200 and 1000 nm, due to thin film interference. Wave optics analysis on the reflectance spectra suggested that the oxide layer grew with dwell time. This was confirmed using high resolution – scanning electron microscopy, wherein the measured oxide layer thicknesses were within 50 nm of the estimated oxide layer thicknesses. Additional samples were heated in a muffle furnace for between three and sixty minutes. Wave optics analysis on the reflectance spectra suggested that the oxide layer grew parabolically, as per Wagner’s law. Microscopy measurements revealed that the interdiffusion layer grew linearly simultaneously with the oxide layer. In situ specular reflectance measurements of specimens during heating were performed using a laser-driven light source. The specular reflectance peaked twice; the first peak was attributed to initial coating liquefaction, and the second peak was attributed to subsequent intermetallic reactions. In situ measurements performed on specimens coated with Thermoboost® and iron nitrate revealed a significantly lower specular reflectance peak and higher heating rates.
Understanding and Advancing Pro-Environmental Behavior in Hospitality: A Systematic Review and Multi-Method Investigation Using the Fogg Behavior Model
(University of Waterloo, 2025-11-03) Darwazeh, Durgham
Pro-environmental behavior (PEB) has recently emerged as a prominent theme in the hospitality literature, with various scholars applying social-behavioral theories to examine the determinants of environmental behaviors. Nevertheless, few studies have applied predictive models of behavioral change to offer new insights on the interaction between internal and external factors in fostering PEB in the workplace. This dissertation addresses this gap by applying and extending the Fogg Behavioral Model (FBM) to introduce new pathways toward PEB, specifically within the hospitality industry. The dissertation is composed of three studies, which are connected and contribute to the development of theoretical and practical knowledge in the field of PEB. The first study offers a systematic review of the literature, which considers the current state of research and identifies common themes. Data for the first paper were collected using three database sources: ProQuest, Scopus, and Web of Science. After screening, 104 peer-reviewed articles were included in the study for thematic analysis. This study aims to examine the progress of the current literature in exploring the concept of PEB by answering three primary questions: 1) How has the definition of PEB evolved? 2) What theories have various authors adopted? and 3) What future research recommendations have been identified in the literature? 104 peer-reviewed articles were analyzed using thematic analysis. The results indicate that PEB definitions have been advanced to distinguish between voluntary and involuntary behaviors for employees and acknowledge the psychological effect of hotel guests on their engagement in environmental practices; traditional theories such as the theory of planned behavior and the social-oriented theories remain dominant; and most studies recommend future research to integrate constructional and psychological factors to expand on current research models. Overall, the review can be a useful tool for future studies to identify a more descriptive definition and theoretical lens. Additionally, the review calls for the use of diverse frameworks to deepen our understanding of how PEB unfolds within hospitality settings. To respond to this call, the second study adopts the FBM as a new behavioral framework to explain how employees’ motivation and ability, along with hotels’ environmental management practices (EMP), interact to influence workplace PEB. The third study extends the FBM by positioning organizational trust (OT) as a contextual-psychological factor that is influenced by behavioral change elements to enhance employees’ engagement in PEB. Thus, it offers a novel perspective on the development of PEB within organizational contexts. Data for the second and third studies were collected through Qualtrics from 337 hotel employees in the United States and Canada. Structural equation modeling—path analysis was used to test the proposed hypotheses in studies 2 and 3. The results indicate that extrinsic and intrinsic motivations, ability, EMP, and OT are key factors for fostering PEB. Firstly, environmental motivation influences PEB directly and through employees’ perceived ability and hotels’ EMP. Secondly, ability mediates the relationship between motivation and hotels’ EMP. Thirdly, EMP mediates the relationship between ability and PEB and has a positive and direct impact on PEB. Last but not least, OT is a full and partial mediator that facilitates the relationship between both ability and hotels’ EMP and PEB. Based on the outcomes, this dissertation sheds light on the important role of motivation as a powerful element in the behavioral change process, driving employees to develop a positive perception of their ability, which subsequently enhances their responsiveness to hotels’ EMP and thereby increases engagement in PEB. Nonetheless, the relationship between motivation and OT turns out to be complex and may require another factor, such as organizational support, to bridge the two constructs. However, OT plays a primary role in workplace behavior, bridging employees’ ability and hotels’ EMP (behavioral triggers) with PEB. Therefore, this dissertation contributes to the advancement of theories by utilizing the Fogg Behavioral Model as an integrative and action-oriented model that defines the interrelationship between behavioral elements in a simple, straightforward context; it reconceptualizes the role of hotels’ EMP as a catalyst that transforms employees’ motivation and ability into PEB; and it extends the FBM by positioning OT as a key component in the behavioral change process that translates employees’ confidence and hotels’ structural environmental management practices into PEB.
Effects of Phospholipase A/Acyltransferase-1 (Plaat1) gene deletion on brain molecular and biochemical measures and memory
(University of Waterloo, 2025-10-30) Cocco, Alex
Phospholipase A1/2 and Acyltransferase-1 (PLAAT1) is a small lipid metabolizing enzyme that possesses transacylase activity and is expressed highly in the rodent heart and brain. Recently, our lab has found that in vitro, PLAAT1 is capable of acylating monolysocardiolipin with an acyl chain donated from phosphatidylcholine acyl donors to produce cardiolipin. Cardiolipin is a glycerophospholipid that is essentially exclusive to the mitochondria and is vital for trans-membrane protein stability, inner mitochondrial membrane structure, apoptosis, and more. The de novo synthesis and acyl chain alterations (‘remodeling’) of cardiolipin are important for the health and proper functioning of cells. Previous work in our lab has demonstrated that mice deficient in Plaat1 (Plaat1-/-) had significant deficiencies in cardiac cardiolipin content, suggesting an in vivo role of PLAAT1 in cardiolipin metabolism. However, Plaat1-/- mice are poorly characterized, especially with regards to the brain, and study of this tissue, and phenotypic changes related to brain function, could help to delineate the role that PLAAT1 may serve there. Thus, the purpose of this thesis project was to explore the effects of Plaat1-deficiency on mouse brain cardiolipin metabolism and related functions. Lipid analyses of cardiolipin, monolysocardiolipin and phosphatidylcholine revealed small, sex-specific alterations in composition but not content, while analyses of gene expression for relevant biosynthetic and remodeling enzymes exhibited significant transcriptional downregulation in female but not male Plaat1-/- brains. Immunoblotting for mitochondrial protein markers suggested changes to mitochondrial shape in female Plaat1-/- brains, while both male and female Plaat1-/- brains experienced perturbations in subunit content for complexes of the electron transport chain. Lastly, mouse anxiety and short-term memory behaviour was tested, revealing that female Plaat1-/- mice are relatively anxiolytic (relaxed), while neither male nor female Plaat1-/- mice had altered short-term memory. Taken altogether, the data collected in this project suggests that PLAAT1 acts in a tissue- and sex-specific manner for reasons that were unable to explored within the scope of this thesis project. The present thesis project demonstrates both a cellular and physiological role of PLAAT1 in the female brain, and provides a foundation from which further work on PLAAT1 can be explored. These results have implications for the interaction of sex and cardiolipin metabolism in the function of brain mitochondria and resultant behavioural outcomes.
In silico and In vitro Discovery of Plant-Based Pro-Inflammatory Cytokine Inhibitors
(University of Waterloo, 2025-10-28) Huynh, Cassandra
Purpose: Dry eye disease (DED) is a prevalent condition range between 44.2% to 62.9% of the population, with female sex and aging being the greatest risk factors. The pathogenesis of DED is based on the dysregulation of tear film homeostasis, resulting in a vicious circle of desiccating stress, inflammation, and tissue damage. Mild DED is managed with artificial tears and warm compresses, whereas moderate-to-severe DED require additional anti-inflammatory therapies to break the vicious circle. Anti-inflammatory drugs such as corticosteroids are effective treatments but are associated with adverse side effects including increased risk of cataracts and glaucoma. Discovering novel anti-inflammatory therapeutics with minimal adverse side effects would greatly benefit DED patients who depend on anti-inflammatory treatment to mitigate symptoms. Flavonoids are a class of chemicals found in all vegetation; some are known for their anti-inflammatory effects. The numerous members of the flavonoid class could be leveraged to discover novel inhibitors against inflammatory DED targets. The purpose of this thesis was to discover a novel flavonoid that could act as an anti-inflammatory agent to treat DED. Methods: This thesis employed a hybrid approach using network analysis, computational modelling, and in vitro validation. Network analysis was employed to select DED-associated protein targets and candidate flavonoids. “Dry Eye Syndrome” proteins were extracted from the STRING-DISEASE database and were cross-referenced with drug databanks using the functional enrichment analysis tool, ToppFun, for flavonoids. A network analysis tool, Cytoscape (v 3.9.1.), was utilized to visualize and rank DED-associated proteins and flavonoids by number of edge interactions. Two proteins were selected for their distinct roles in the immune response, and two flavonoids were selected for their association with multiple pro-inflammatory DED-associated proteins. Molecular docking and molecular dynamic (MD) simulations modelled and simulated the protein-ligand complex of both protein targets with each flavonoid molecule. Four protein-ligand complexes were assessed for stability and specific residue-ligand interactions. The inhibitory effects of both flavonoids were assessed in vitro with ELISAs against both protein targets. The biocompatibility of the most effective flavonoid inhibitor was assessed with human corneal epithelial cells (HCEC) using an Alamar Blue metabolic activity assay; viability was assessed by evaluating the proportion of live, apoptotic, and dead cells. Results: The network analysis generated a protein-protein interaction network of 64 DED-associated proteins and a drug-protein network of 108 flavonoids. Tumour necrosis factor (TNF) 𝛂 interactions and interleukin (IL) 17A (14 interactions) were amongst the 5 highly ranked proteins and selected for their roles in the innate and adaptive immune response, respectively. Luteolin (19 interactions) and rutin (17 interactions) were the highest ranked flavonoids associated with DED-associated proteins. Molecular docking and MD simulations predicted that both flavonoids could bind directly to the receptor binding sites of both cytokines. However, ELISAs showed that neither luteolin nor rutin could inhibit TNF-𝛂 and TNF receptor interaction (all p≥0.07). On the other hand, both luteolin (IC50 = 16.54 mM) and rutin (IC50 = 8.73 mM) had inhibitory effects against IL-17A and IL-17A receptor interaction (all p<0.01). Metabolic activity and viability of HCEC remained high (all ≥ 85.95%) below 3.0 mM rutin; no significant difference in metabolic activity and viability were detected in all concentrations of rutin compared to the control (all p>0.06). Conclusion: This thesis identified rutin as a novel flavonoid inhibitor of IL-17A. These findings suggest that rutin may play a role in anti-inflammatory therapeutics for DED.
Preserving and Generalizing χ-boundedness
(University of Waterloo, 2025-10-27) Chaniotis, Aristotelis
The notion of χ-boundedness, introduced by Gyárfás in the mid-1980s, captures when, for every induced subgraph of a graph, large chromatic number can occur only due to the presence of a sufficiently large complete subgraph. The study of χ-boundedness is a central topic in graph theory. Understanding which hereditary classes of graphs are χ-bounded is of particular importance for advancing our understanding of how restrictions on the induced subgraphs of a graph affect both its global structure and key parameters such as the clique number and the independence number. Which classes of graphs are χ-bounded? A method that has been used to prove that a class C of graphs is χ-bounded proceeds as follows: we prove that C can be obtained by applying operations that preserve χ-boundedness to already χ-bounded classes. This approach gives rise to the following question: which operations preserve χ-boundedness? Given k graphs G₁,…,Gₖ, their intersection is the graph (∩{i∈[k]}V(Gᵢ), ∩{i∈[k]}E(Gᵢ)). Given k graph classes G₁,…,Gₖ, we call the class {G : ∀i∈[k], ∃Gᵢ∈Gᵢ such that G = G₁ ∩ ⋯ ∩ Gₖ} the graph-intersection of G₁,…,Gₖ. In the mid-1980s, in his seminal paper “Problems from the world surrounding perfect graphs”, Gyárfás observed that, due to early results of Asplund and Grünbaum, and Burling, graph-intersection does not preserve χ-boundedness in general, and he raised some questions regarding the interplay between graph-intersection and χ-boundedness. This topic has not received much attention since then. In this thesis, we formalize and explore the connection between the operation of graph-intersection and χ-boundedness. Let r ≥ 2 be an integer. We denote by Kᵣ the complete graph on r vertices. The Kᵣ-free chromatic number of a graph G, denoted by χᵣ(G), is the minimum size of a partition of V(G) into sets each of which induces a Kᵣ-free graph. Generalizing χ-boundedness, we say that a class C of graphs is χᵣ-bounded if there exists a function f:ℕ→ℕ such that for every G∈C and every induced subgraph G′ of G, we have χᵣ(G′) ≤ f(ω(G′)), where ω(G′) denotes the clique number of G′. We study the induced subgraphs of graphs with large Kᵣ-free chromatic number. Finally, we introduce the fractional Kᵣ-free chromatic number, and for every r ≥ 2 we construct K_{r+1}-free intersection graphs of straight-line segments in the plane with arbitrarily large fractional Kᵣ-free chromatic number.
Data-Driven Decision-Making Under Uncertainty: An Empirical Study of U.S. Wildfire Management
(University of Waterloo, 2025-10-24) Garros, Gong
Wildfire management in the United States faces prediction accuracy, cost efficiency, and fiscal sustainability issues. This dissertation integrates three interrelated research topics to develop integrated decision models applicable to each stage of wildfire management. The first study evaluates the role of social media analytics (SMA) and Web 3.0 technologies towards improving wildfire prediction, real-time tracking, and response decisions. The study reviewed current social media analytics tools for crisis response, showing how they support crisis tracking, response timing, and crisis communication. The same functionality can presumably be applied to wildfire management. The second study introduces a temporal gravity model that links population- and location-weighted social media activity to wildfire response costs per acre. The model captures behavioral visibility prior to operational deployment and demonstrates stronger informational value than tweet volume alone. The third study investigates how federal budget changes relate to the accuracy of state preparedness decisions. Higher funding is associated with improved accuracy in the short term, but this association weakens in later budget cycles. The analysis treats federal budgets as exogenous inputs and uses panel methods with robustness checks to evaluate decision dynamics under fixed fiscal constraints. Across all three essays, the dissertation highlights the importance of integrating behavioral data and fiscal signals to better inform wildfire planning. It provides empirical evidence that public attention, budget expectations, and institutional coordination jointly influence the quality of response decisions. These findings suggest that effective wildfire management requires models that account for informational uncertainty, fragmented authority, and the timing structure of operational and fiscal systems. Keywords: Wildfire Management, Decision Science, Behavioral Operations Management, Crisis Informatics, Public Finance, Panel Data Analysis, Gravity Model, Time Series Analysis.
Cybersickness: Linking Postural Control to User Discomfort in a Virtual Roller Coaster
(University of Waterloo, 2025-10-23) Gulifeire, Alimu
Cybersickness (CS) remains a major obstacle to the widespread use of Virtual Reality (VR), with leading explanations emphasizing sensory conflict, sensory reweighting, and postural instability. Prior research has shown that individuals who flexibly reweight visual, vestibular, and body cues report lower CS, particularly in interactive VR tasks where users can move freely. Whether this relationship generalizes to more passive, visually intense VR experiences is less clear. This thesis examined sensory cue reweighting and postural control as predictors of CS during an immersive roller coaster simulation. Nineteen younger adults completed the Oriented Character Recognition Task (OCHART) before and after VR exposure to estimate perceptual upright and quantify cue weightings. During VR exposure, postural movement was recorded using markerless motion capture, and participants reported symptoms using the Fast Motion Sickness (FMS) scale after each trial. Contrary to findings from interactive VR contexts, sensory reweighting was not significantly associated with CS in this passive roller coaster environment. In contrast, measures of postural control, particularly total path length, were robust predictors of sickness severity, with greater displacement linked to higher FMS scores. These findings suggest that in visually dominant VR tasks with limited bodily engagement, postural instability provides a more reliable marker of CS than sensory reweighting. This work clarifies that the predictive value of sensory reweighting is context dependent, emerging more clearly in interactive than passive VR tasks. It further points toward movement-based strategies for mitigating discomfort in VR experiences where movement is restricted but visual conflict is high.
Evaluating a priori and data-driven weighting of the Healthy Eating Food Index-2019 for assessing diet quality and gastrointestinal and aerodigestive cancer risk in Canadian adults
(University of Waterloo, 2025-10-23) Singh, Navreet
Background: Diet is a modifiable exposure implicated in gastrointestinal and aerodigestive cancers. Because foods are consucmed in combination, diet quality indices are used to summarize overall dietary patterns. The Healthy Eating Food Index-2019 (HEFI-2019) measures adherence to Canada’s Food Guide 2019, and its component scores are nearly equally weighted, reflecting the importance of all foods in a healthful dietary pattern. Its discriminatory capacity for measuring diet-disease associations, and the influence of the weighting schema of the index, remains uncertain. Objective: To assess whether associations between diet quality and gastrointestinal and aerodigestive cancer risk differ among adults in Canada based on the a priori Healthy Eating Food Index-2019 (HEFI-2019) versus a novel modified version with components reweighted using a data-driven approach. Methods: A prospective cohort analysis was conducted using the Canadian Community Health Survey 2004 Nutrition (CCHS 2004) linked with the Canadian Cancer Registry (CCR) through 2016. After exclusions, 10,530 adults were included, representing approximately 23.5 million Canadians. Diet was assessed using interviewer-administered 24-hour recalls. HEFI-2019 total scores were computed using standard weights and using data-driven weights derived from ridge-penalized Cox models in 10 iterations of 80/20 training–test splits with cross-validated penalty selection. Weighted Cox proportional hazards models, adjusted for age, sex, education, income, marital status, smoking status, body mass index, and alcohol consumption, estimated associations with incident gastrointestinal and aerodigestive cancers (ICD-9 140–149, 150–159, 160–161). Discrimination was assessed with Harrell’s C-index. Results: The data-driven approach altered component weights substantially (e.g., protein foods increased from 5 to 16.4; vegetables and fruits decreased from 20 to 3.73). No associations with cancer risk were observed for either the a priori (adjusted HR per unit increase 1.01; 95% CI: 0.99, 1.04) or reweighted HEFI-2019 scores (adjusted HR: 1.00; 95% CI: 0.98, 1.02). Model discrimination was similar (Harrell’s C-index: 0.81 [95% CI: 0.77, 0.85] for a priori; 0.87 [95% CI: 0.80, 0.93] for reweighted). Discussion: Neither the a priori nor reweighted HEFI-2019 was associated with gastrointestinal and aerodigestive cancer risk. Data-driven reweighting did not meaningfully improve associations or discriminatory capacity. These findings suggest challenges in using diet quality indices for complex diet-disease relationships and highlight the need for further research on index construction and application in cancer epidemiology.
Multi-Outcome Trajectories in Traumatic Brain Injury
(University of Waterloo, 2025-10-23) Shein, Vladyslav
Traumatic Brain Injury (TBI) presents a global health challenge, affecting millions of individuals annually, resulting in diverse outcome trajectories that complicate patient management. The heterogeneity in TBI outcomes, influenced by varied clinical presentations and injury responses, requires advanced analytical approaches. The analysis of trajectories using single metrics, such as the Glasgow Outcome Scale Extended Global (GOSE), falls short of capturing the multi-faceted nature of TBI progression, often overlooking the complexity of individual patient experiences. This thesis reports on two studies. First, a systematic scoping review was conducted to synthesize the current research on trajectory analysis in TBI, followed by a modeling study. This work identifies 6 distinct multi-outcome trajectories in TBI patients by employing Latent Class Mixed Models (LCMM) and clustering approaches. Utilizing longitudinal data from the Transforming Research and Clinical Knowledge in Traumatic Brain Injury study (TRACK-TBI), a prospective multicenter observational cohort study conducted at 18 level 1 trauma centers across the United States, which includes 17 selected outcome measures collected at four time points post-injury, provides a comprehensive understanding of the heterogeneous progression of TBI. By addressing the limitations of single outcome analyses, this research contributes to a better understanding of TBI progression that can lead to the optimization of TBI management and treatment. The future integration of these trajectories will facilitate the development of personalized treatment strategies, ultimately improving patients’ recovery.
Learning-Based Stability Certification and System Identification of Nonlinear Dynamical Systems
(University of Waterloo, 2025-10-23) Zhou, Ruikun
In recent decades, by taking advantage of the abundance of sensory measurements, learning-based methods have been prevalent and shown their effectiveness in tackling challenging or intractable problems for classical approaches in systems and control. For instance, many systems with complex nonlinearities, high-dimensional state spaces, or unknown dynamics cannot be effectively handled by classical mathematical tools, and computing stability certifications for such systems is often intractable. This thesis aims to construct systematic approaches to perform system identification tasks and learning-based Lyapunov functions for nonlinear dynamical systems, with some extensions to optimal control. The first aspect of this thesis is to develop an efficient method based on a special feedforward neural network structure, an extreme learning machine, to compute stability certificates for nonlinear systems by solving linear PDEs when the dynamics are accessible. Differing from the typical neural network-based approaches that require training on high-performance computing platforms, one only needs to solve a convex optimization problem. On top of that, the proposed method can also be used to efficiently solve the notable HJB equation via policy iteration to obtain optimal control policies for nonlinear systems. The second aspect of this research is to tackle these issues for nonlinear systems with (partially) unknown dynamics. We first show that with two feedforward neural networks, the unknown system and a Lyapunov-based stability certificate can be learned simultaneously. With the help of satisfiability modulo theories (SMT) solvers, the resulting Lyapunov function can be formally verified to provide stability certificates for the unknown nonlinear system. Alternatively, in the past two decades, the Koopman operator and its generator have demonstrated advantages in identifying discrete-time systems and continuous-time systems, respectively, requiring significantly less data while achieving better performance than most existing classical methods. For unknown continuous-time dynamical systems, we propose a novel resolvent operator-based learning framework to learn the Koopman generator, which is a linear operator that describes the infinitesimal evolution of the Koopman operator. The learned generator, thereafter, can be used to identify the vector field of the nonlinear systems. Moreover, with the learned high-accuracy Koopman generator, we can also construct a Lyapunov-based stability certificate for the unknown nonlinear system in the same function space. By formulating the linear PDEs as a linear least squares problem, Lyapunov functions can be computed efficiently. The learned Lyapunov functions can be formally verified using an SMT solver and provide less conservative estimates of the region of attraction, compared to existing methods. Taken together, these contributions provide a coherent pathway that begins with model-based stability certification computation and continues to fully data-driven system identification and thereafter computing Lyapunov-based stability certificates.
Polymorphic Type Qualifiers
(University of Waterloo, 2025-10-21) Edward, Lee
Type qualifiers offer a simple yet effective mechanism for extending existing type systems to deal with additional constraints or safety requirements. For example, the const qualifier is a popular mechanism for annotating existing types to signify that the value in question is read-only in addition. A variable of type const int is both an integer and also cannot be written to. While type qualifiers themselves are well-studied, polymorphism over type qualifiers remains an area less well examined. This has led to a number of ill-desired outcomes. For one, many practical systems implementing type qualifiers in their type systems simply ignore their interaction with generic types. Other systems implement polymorphism with seemingly unique and ad-hoc rules for dealing with qualifiers. In this thesis, we show that this does not need to be the case. We start by examining three well-known qualifier systems: systems for tracking immutability, function colour, and captured variables, and show that despite their differences that they share surprising common structure. We then give a design recipe, inspired by that structure, using the mathematical structure of free lattices for modelling polymorphism over type qualifiers, to give a framework for polymorphic type qualifiers. We then show that our design recipe precisely captures this structure by recasting those three existing systems in our framework for qualifier polymorphism by free lattices. Finally, we extend type qualifiers from ranging over lattices to type qualifiers ranging over Boolean algebras, which we then use to extend an existing effect system with effect exclusion to support subeffecting as well via subqualification and subtyping.
An Empirical Study of Privacy Leakage Vulnerability in Third-Party Android Logs Libraries
(University of Waterloo, 2025-10-21) ZHAO, YIXI
Mobile logging libraries are essential tools for debugging and monitoring Android applications, yet their privacy implications remain largely unexplored. This paper presents the first large-scale empirical study of privacy risks in Android logging practices, analyzing 48,702 applications from Google Play to identify sensitive data leakage through third-party logging frameworks. Our findings reveal that while logging library adoption is limited (3.4% of applications), nearly half (49.3%) of logging-enabled applications exhibit privacy leaks, creating significant security vulnerabilities. Three dominant libraries—Timber (35.2%), SLF4J (35.1%), and Firebase (29.4%)—account for 99.7% of all verified privacy leakage instances. We identify distinct logging patterns across frameworks, with SLF4J showing balanced log level distribution, Timber concentrating heavily on DEBUG levels (78.5%), and Firebase dominated by Analytics Events (98.0%). Our analysis reveals that privacy violations predominantly stem from indirect data flows (62.5%) requiring intermediate processing steps, with most leaks occurring through moderate-complexity paths of 2-4 statements. User-info sources dominate privacy leaks (69.7%), while user-input sources represent a substantial portion (30.3%), highlighting GUI components as significant risk vectors. Longitudinal analysis of application updates demonstrates that privacy leaks tend to improve over time, indicating growing developer awareness of privacy concerns, though persistent vulnerabilities underscore the need for systematic privacy protection measures. Our study contributes the largest dataset of third-party logging-based privacy violations to date, a reproducible analysis pipeline for future research, and actionable insights for developers and library maintainers. These findings emphasize the critical need for practitioners to recognize both user information and user input as significant privacy threats when implementing third-party logging frameworks in Android applications.
Healthy living by design : Exploring the blue zones as a framework for a multi-generational housing typology
(University of Waterloo, 2025-10-20) Ali, Syed Bahroz
This thesis begins by examining the pervasive urban sprawl in Toronto, analyzing the profound health impacts associated with suburban living—challenges such as social isolation, poor walkability, and a general decline in well-being. While the city has responded to housing pressures with mid-rise densification, many existing problems persist and are often intensified: smaller living spaces and inadequate community infrastructure continue to undermine both physical and mental health. In response, the research turns to the Blue Zones—regions where people consistently enjoy longer, healthier lives, largely free from the chronic health issues prevalent in suburban and urban environments. By closely investigating the architectural and spatial qualities of these communities, the thesis explores the fundamental role of design and space in fostering well-being. The study identifies key overlaps between the principles found in Blue Zones and the recommendations outlined in age-friendly and World Health Organization guidelines. These shared values inform strategies aimed at addressing the underlying health concerns of both suburban and densified urban contexts. Central to this approach is a re imagining of housing: specifically, promoting multi generational homes and neighborhood designs that support aging in place, encourage social cohesion, and create opportunities for intergenerational connection.This thesis advances alternative models of housing and community development—drawing on co-housing and co-living precedents from Canada and the Nordic countries—that respond more effectively to Toronto’s climate and cultural context. Instead of pursuing density as an end in itself, the proposed designs emphasize creating environments where people of all ages can flourish, maintain strong social connections, and lead healthier, more fulfilling lives.
Structured Wavefunctions for Precision Quantum Metrology
(University of Waterloo, 2025-10-20) Kapahi, Connor
In this thesis, several projects from biomedical optics measurements of the retina to precision gravimetric designs with neutron interferometers are presented, united by the common theme of applied quantum information techniques to develop next-generation precision metrological instruments. In particular, we introduce theoretical tools for analyzing neutron optical experiments and highlight parallels between neutron and light optics. These tools are applied to a new neutron prism design, demonstrating significantly higher transmission than traditional designs. Designs for devices applying these techniques, including a neutron Fresnel prism, spectrum analyzer, and spin collimator, are discussed. Potential advantages in neutron flux and spectrum resolution are quantified for these designs. The isometry between neutron spin and the polarization of light is exploited to validate the neutron spin collimator experimentally. Applications of structured states of light and experiments applying spin-orbit states to create patterns in the human visual system are described. Results demonstrate an increase in the perceived extent of these patterns, from 3° for Haidinger's Brush to 10° for a spin-orbit state. Work demonstrating a new method of generating a lattice of spin-orbit states in light is applied to neutron optics. Throughout the preceding experiments, methods of modeling neutron optics experiments with light and a semi-classical path-integral approximation have been developed. These methods are then applied to design an experiment that measures the gravitational constant using a neutron interferometer. A three-phase grating moiré interferometer (3-PGMI) design is first tested with infrared light. The deflection caused by a wafer sample is measured with the 3-PGMI and found to match direct measurements. The path-integral model is then applied to determine the uncertainty in the gravitational constant that can be achieved with a near-term measurement with a neutron 3-PGMI. An experiment to measure the gravitational constant is described, with an uncertainty budget, resulting in a measurement to 150 ppm. Potential corrections to previous experiments measuring the gravitational constant, due to lunar gravitational forces are quantified. Future applications of the tools and techniques described in this thesis are then discussed.

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