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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    Perspectives of Graph Diffusion: Computation, Local Partitioning, Statistical Recovery, and Applications
    (University of Waterloo, 2025-03-06) Yang, Shenghao
    Diffusion describes the process of mass moving from one region to another. In the con- text of graph, the diffusing mass spreads from nodes to nodes along the edges of the graph. Broadly speaking, this includes a number of stochastic and deterministic processes such as random walk, heat diffusion, network flow and electrical flow on graphs. Graph diffusion is a highly important primitive, and has been shown to have a variety of surprising properties both theoretically and practically. In this thesis, we present several new perspectives of graph diffusion, with an emphasis on how diffusion algorithms uncover the local clustering structure of the input data without necessarily exploring the entire graph. In the first two parts of the thesis, we introduce a new class of graph diffusion methods that are provably better at extracting the local clustering structure of a graph or a hy- pergraph. Here, diffusion is formulated as a pair of primal and dual convex optimization problems, based on the idea of spreading mass in the graph while minimizing a p-norm net- work flow cost. The primal solution of the diffusion problem provides an intuitive physical interpretation where paint (i.e. mass) spills from the source nodes, spreads over the graph, and there is a sink at each node where up to a certain amount of paint can settle. The dual solution embeds the nodes on the non-negative real line and is considered as the output of diffusion. We will show that the dual variables nicely encode the local clustering structure around a given set of seed nodes. In particular, assume the existence of a cluster C of low conductance Φ(C), the sweep cut procedure on the dual variables returns a cluster whose conductance is not too much larger than Φ(C). In the next two parts of the thesis, we introduce a weighted diffusion mechanism which allows any existing diffusion method to take into account additional node information such as node attributes and labels. The method weighs the edges of the graph based on the attributes or the labels of each node. Depending on the nature and availability of additional node information, two simple yet effective edge-weighting schemes are introduced and analyzed. Over contextual random graphs generated by a local variant of the stochastic block model with noisy node information, we will show that, if the additional information contains enough signal about the ground-truth cluster, then employing existing diffusion algorithms in the weighted graph can more accurately recover the ground-truth cluster than employing diffusion in the original graph without edge weights. In particular, statistical recovery guarantees in terms of precision and F1 score will be derived and compared. All of the results are supplemented with extensive experiments on both synthetic and real-world data to illustrate the technical results and the effectiveness of the new methods in practice. The code is open-source on GitHub.
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    Operating Systems are a Service
    (University of Waterloo, 2025-03-05) Hancock, Kenneth
    OS containers have set the standard for the deployment of applications in modern systems. OS containers are combined sandboxes/manifests of applications that isolate the running applications and its dependencies from other applications running on top of the same kernel. Containers make it easy to provide multi-tenancy and control over the application, making it ideal for use within cloud architectures such as serverless. This thesis explores and develops novel systems to address three problems faced by containers and the services that use them. First, OS containers currently lack a fast checkpoint-restore mechanism. Second, container security is still inadequate due to its underlying security mechanisms, which provide coarse-grained policies that are abused. Third, the lack of a benchmark for serverless clouds, one of the largest consumers of containers, and specifically checkpoint-restore. This thesis outlines solutions to these problems. First, ObjSnap, a storage system designed and built for two modern single-level store systems, Aurora and MemSnap, which enable checkpoint restore for container systems. ObjSnap is a transactional copy-on-write object store that can outperform other storage systems by up to 4×. Second, we introduce SlimSys, a framework that tackles security issues found within containers by binding a policy to kernel resources. Lastly, we introduce Orcbench, the first benchmark used to evaluate serverless orchestrators.
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    A Comprehensive Process for Addressing Market Power in Decentralized ADN Electricity Markets
    (University of Waterloo, 2025-03-05) AboAhmed, Yara
    Electric power systems have transformed globally, with distribution grids evolving into active distribution networks (ADNs), altering their characteristics and operations. Traditional centralized market structures have become inadequate for the complexities of the ADNs, leading to inefficiencies and challenges in reliable operation and energy pricing. ADN electricity markets offer a solution by leveraging smart grid features to integrate distributed energy resources (DERs), allowing non-utility entities, such as producers, consumers and prosumers, to participate directly, enhancing market efficiency, reducing monopoly power, and limiting utility control over prices. However, with the increasing penetration of DERs, there is a growing risk of market concentration and manipulation by entities owning large shares of DERs in ADN electricity markets. This poses a potential threat to market fairness, as some participants may exploit market power, leading to an uneven playing field, reducing the integrity and efficiency of ADN electricity markets. From this standpoint, this thesis investigates and adapts the concept of market power within ADN electricity markets, considering the unique characteristics of the market and the system. The investigation is structured around six central questions: (1) Can non-utility entities exercise market power in ADN electricity markets? (2) Is there a comprehensive framework for accurately monitoring, evaluating, and mitigating market power in decentralized ADN markets? (3) If such a framework exists, can it manage the complexity of monitoring the large number of ADN market participants? (4) If market power manipulation exists, are current investigations adequate, considering the decentralized market structure, the physical characteristics of the system, DER operational constraints, and the interplay between active and reactive power markets? (5) What types of decentralized market structures and frameworks—such as fully decentralized, community-based, or network-based peer-to-peer (P2P)—are appropriate for addressing market power in ADN electricity markets? (6) Are traditional market power mitigation methods applicable and effective in the context of ADN electricity markets considering the decentralized nature of the ADN and the dispersed DERs?. The primary objective of this thesis is to develop a fair and decentralized energy trading platform that limits monopoly power and mitigates market power abuse in ADN electricity markets. To achieve this goal, the thesis proposes an innovative comprehensive process for monitoring, evaluating, and mitigating market power, specially designed for the decentralized structure of ADNs and their market frameworks. This process considers the shifts in network configuration as well as the physical and operational characteristics of ADNs and their components. The process begins by monitoring market power of dominant market participants through introducing the zoning concept. These operational zones narrow down the number of market participants within each zone, addressing the challenge of monitoring a large number of market participants with widely distributed DERs and improving the identification and control of potential market power exercisers, thus minimizing their potential market power. These operational zones serve as decentralized interfaces between the zonal market participants and their corresponding zonal market operators, establishing a decentralized platform for energy trading. The second stage of the process focuses on evaluating market power through investigating and analyzing the strategic offering behavior of the potential market power exercisers identified in stage one. This analysis is conducted within the framework of a community-based P2P decentralized ADN electricity market, considering the physical and operational characteristics of both the system and DERs, along with the coupled active and reactive power markets. A comparative evaluation of market outcomes under competitive and strategic conditions is performed to identify strategic manipulators. In this context, the study also examines the applicability and effectiveness of conventional market power mitigation techniques used for the centralized market and assesses their impact on the strategic offering behavior of identified manipulators. While some traditional market power mitigation techniques may demonstrate efficiency, a new approach is necessary to address the unique decentralization characteristic of ADN electricity markets. A novel market power mitigation technique is proposed in the third stage of the process, targeting the root cause of market power: market concentration. This approach introduces an innovative market zoning concept, dynamically partitioning the system into "Market-Zones" to reduce market concentration while adapting to different system operational conditions, considering the uncertainties in system demand and generation, thereby aligning with the decentralized nature of ADNs and their markets. The proposed innovative zoning approach offers a robust solution for mitigating market power in decentralized ADN electricity markets. Within these Market-Zones, each player can actively engage and participate in the market and obtain the benefit without being overtaken by entities with large market shares. Consequently, the market power of the dominant players is subsided and diluted by utilizing the proposed Market-Zones, establishing a fair energy trading platform.
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    An Investigation Into the Effectiveness of Latent Variable Models for Domain Adaptation
    (University of Waterloo, 2025-03-04) Zeng, Xuanrui
    The proliferation of machine learning with neural networks (NNs) has revolutionized fields such as computer vision and natural language processing. However, their successes often overshadow two important weaknesses of neural networks: (i) their reliance on large amounts of training data and (ii) the assumption of independent and identically distributed (i.i.d.) data. Because of these weaknesses, the vast majority of NNs today are applicationspecific machineries tuned to one task and one data domain. This thesis investigates the effectiveness of a latent variable model for unsupervised domain adaptation, aiming to bridge the gap between two different data distributions while leveraging only labeled data samples from one, and unlabeled data samples from the other. A novel generative modeling framework is proposed to address this problem, incorporating recent advances in probabilistic modeling and variational inference techniques from the neural network literature. Empirical results of the proposed approach seem promising, and indicates adequate transfer of the labeling knowledge of the model across disparate data domains without requiring manual re-labeling or domain-specific adjustments. Moreover, the proposed approach has also shown potentials in solving the related domain translation problem. Despite these fortunes, the existing approach has shown limitation in solving more complex scenarios of unsupervised domain adaptation, speficially those involving more vibrant differences between domains.
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    A Compressive-Sensing-Capable CMOS Electrochemical Capacitance Image Sensor with Two-Dimensional Code-Division-Multiplexed Readout
    (University of Waterloo, 2025-03-04) McLachlan, Shane
    Electrochemical capacitance imaging is a technique used to observe biological analyte or processes at the surface of an electrode, immersed in an electrolyte, via small changes in capacitance. This technique has various applications in biosensing such as biomedical diagnostics, neural interfaces and DNA sensors. Complimentary metal-oxide-semiconductor (CMOS) technology is well suited for implementing electrochemical capacitance image sen- sors since high spatial resolution electrode arrays and readout circuitry can be integrated on the same chip. This thesis presents the design and simulation of a 256 × 256 pixel electrochemical capacitance image sensor fabricated in a 180-nm analog/mixed-signal CMOS process. Our image sensor features a novel two-dimensional code-division-multiplexed (2D CDM) readout architecture that directly outputs analog coefficients of the 2D Walsh transform of the image. To the best of our knowledge, we are the first to implement true 2D CDM readout in the capacitive image sensor space. For passive-pixel sensors, CDM readout yields a signal-to-noise ratio (SNR) increase over traditional time-division-multiplexed (TDM) readout through integrating orthogonal combinations of all pixels for the entire frame time. Use of the 2D Walsh transform enables compressive sensing at the time of array readout, which is achieved by exploiting the energy compaction property of the Walsh domain. Compressive sensing provides analog lossy image compression that can enable a frame rate increase or power consumption decrease. In addition, our transform domain readout architecture removes the layout requirement for pitch-matched column amplifiers, requiring only one larger column circuit for the full array. Some potential advantages introduced by this include reductions to both amplifier flicker noise and fixed-pattern noise from transistor mismatch. Our sensor uses two-transistor switched-capacitor pixels with a 3.2 × 3.2 μm² work- ing electrode and 3.88 μm grid pitch to enable charge-based capacitance measurement. On-chip 256-bit parallel Walsh code generators enable power efficient orthogonal code generation. Full-chip post-layout analog simulation with a biological capacitance image demonstrates that we can achieve a structural similarity index (SSIM) of 0.875 versus a reference image. SSIM values range from 0 to 1, where 1 indicates complete image similarity.
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    Trajectories of Psychopathology and Mental Health Service Use Among Youth with A Physical Illness
    (University of Waterloo, 2025-03-04) Dol, Megan
    Youth with chronic physical illness (CPI) are at an increased risk of developing co-occurring mental disorders (i.e., multimorbidity). About 40% of youth with CPI receive a mental disorder diagnosis. The relatively high multimorbidity prevalence suggests this is a pressing public health issue—youth with multimorbidity experience greater symptom severity and functional impairment. In addition, multimorbidity negatively impacts psychosocial outcomes, including health-related quality of life, self-esteem, and academic functioning. Although these children experience poorer outcomes and use a greater amount of mental health services, there is limited understanding of how specific trajectories of mental disorder symptoms (i.e., psychopathology) influence service use over time. By examining the course of psychopathology and its association with mental health service use (MHSU), we can identify critical intervention points aiming to improve the effectiveness of care and allocation of resources. In Canada, the financial burden of mental illness is approximately $51 billion annually, including costs arising from healthcare services, lost productivity, and poor quality of life. Compounding on these burdens, there is an acute shortage of youth-specific mental health services in Canada, where up to 70% of youth with mental health concerns do not receive the specialized services they need. Understanding MHSU in youth with CPI may help efficiently use resources, identify unmet needs, improve the timing of interventions, support families in predicting care needs, and inform policies for targeted and integrated services. This dissertation addresses critical gaps in research on youth psychopathology among you with CPI. While previous studies have explored youth MHSU, few have examined the unique trajectories of psychopathology in this population or how these trajectories affect mental health service use over time. Additionally, limited research has investigated the interplay between parent psychological distress, youth psychopathology, and healthcare use, particularly using longitudinal models. Focusing on these areas, this dissertation provides insights into the complex needs of youth with CPI. It highlights opportunities for improving integrated mental health and healthcare support for this at-risk group. To address these gaps, this dissertation examined youth psychopathology trajectories and transitions and whether psychopathology trajectories impact the association between family factors and MHSU. Specifically, the objectives were to: 1) identify distinct trajectories of psychopathology among youth with a CPI; 2) validate these trajectories by comparing with categorical classifications produced by a diagnostic interview tool; 3) examine predictors of the trajectory groups; 4) identify distinct subgroups of youth psychopathology; 5) examine transitions across these subgroups of psychopathology; 6) identify predictors of such transitions; 7) explore if youth psychopathology trajectories mediate the association between family factors and MHSU. The first study developed a trajectory model using latent class growth analysis (LCGA) to examine the optimal number of trajectories of youth psychopathology and predictors of the different trajectories. Results indicated a three-trajectory model characterized as low-stable, moderate-decreasing, and high-decreasing trajectories. Older age, higher disability, greater parent psychological distress, and higher household income were associated with less favourable trajectories. Results demonstrate that youth with CPI exhibit different courses of psychopathology, and that different individual and family characteristics are associated with trajectory group membership. The second study used latent profile analysis to identify four profiles of youth psychopathology: low psychopathology, primarily internalizing, primarily externalizing, and high psychopathology. Additionally, latent transition analysis was used to track transitions between these profiles over time. Many youths in the primarily internalizing subgroup transitioned to the low psychopathology subgroup over time. Further, youth classified in the high psychopathology subgroup from six to 24 months were more likely to have persistent psychopathology. These findings suggest that youth with CPI exhibit distinct profiles of psychopathology, with unique symptom combinations and patterns of change over time, emphasizing the potential for different mental health needs and trajectories within this population. Youth with CPI do not all experience psychopathology in the same way, and they may shift between profiles, suggesting dynamic changes in symptom patterns. The third study conducted a path analysis to determine if youth psychopathology trajectories mediate the association between family factors (parent psychological distress and family functioning) and MHSU (i.e., contact with a healthcare professional). Results demonstrated that youth psychopathology trajectories (subclinical vs. low) mediate the association between parent psychological distress and contact with a healthcare professional. These findings support using a family-centred care approach to youth healthcare to minimize the burden on families and promote well-being and positive health outcomes. This dissertation fills a critical gap in terms of knowledge of psychopathology and MHSU among youth with CPI. Taken together, these findings can be distilled into four themes: (1) call for integrated physical and mental healthcare; (2) early identification of psychopathology among youth with CPI; (3) adaptive treatment approaches to care; and (4) the need for family-centred care in youth mental health settings. Future longitudinal research should investigate transitions across psychopathology profiles over longer periods and investigate other potential mediators that facilitate or impede the use of mental health services for youth with CPI.
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    A First-Principles Framework for Simulating Light and Snow Interactions
    (University of Waterloo, 2025-02-25) Varsa, Petri Matthew
    Interactions between light and matter give rise to an abundance of natural phenomena. Common examples include those between light and atmospheric ice crystals producing halos, and between light and liquid water droplets producing rainbows. However, interesting effects may also be observed when light impinges upon more dense materials such as snow. These may be noted as changes to the appearance of the material resulting from variations in the characteristics of the material itself. In some cases, these appearance changes may even manifest themselves as dramatic changes in colour. In this thesis, we study snow as a material and reproduce such phenomena by simulating light interactions with virtual snow samples. Accordingly, this work presents a first-principles framework for simulating light transport through snow. Data and information that describe the characteristics of snowpacks are obtained from the literature and used to devise a digital representation of them suitable for predicatively modelling light interactions with snow. The employed formulation allows for different virtual snow samples to be investigated. Simulated rays of light are cast into a virtual snow sample, and these rays are reflected and refracted until they exit from the surface of the sample, are transmitted through the sample or are absorbed. The modelling results are recorded as spectral response datasets for evaluation and analysis. These datasets are then compared with measured data and observations reported in the literature in order to assess the simulations’ fidelity. There are a number of study areas where such a framework can make a contribution. In this thesis, we discuss such contributions to two fields of research, namely, computer graphics and remote sensing. From a computer graphics perspective, the outputs of simulating light interactions with snow may be used in natural phenomena visualizations employed for educational and entertainment purposes. From a remote sensing perspective, the simulations may be used to conduct in silico experiments that help to shed light on topics that are actively being studied. Furthermore, the simulation outputs may also be used as data products in themselves, to make comparisons against remotely acquired data and support other modelling initiatives. The proposed framework presented in this thesis encapsulates a body of work that is expected to advance the state of the art of snow appearance modelling using a multi-faceted approach. The foundation of the framework is a novel radiative transfer model of light impingement on snow, whose predictive capabilities are extensively evaluated. Then, data products produced by this framework are used to address open questions in the two fields of interest, i.e., computer graphics and remote sensing. In particular, we describe a method to include the complex, visual phenomena that are predicted by the radiative transfer model introduced here into a traditional rendering pipeline. We also make use of the proposed framework to investigate open problems (e.g., the absorption of solar radiation by snow and the effect that this has on avalanche prediction) with potential interdisciplinary applications.
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    Assessment of the Proposed Policies for a Carbon Capture and Storage Regulatory Framework in Ontario
    (University of Waterloo, 2025-02-21) Kim, Duckhoon
    Since 2022, Ontario has been investigating the possibility of developing a Carbon Capture and Storage (CCS) framework as they aim to reduce carbon emissions and align with the federal government’s goals of net-zero emissions by 2050. This CCS regulatory framework should focus on hard-to-abate sectors where alternative renewable energy technologies are in their early stages, or they are difficult to be transitioned. However, within the research field of CCS in Ontario from a policy perspective, there are minimal journal articles and grey-literature documents that discuss this topic. Therefore, the purpose of this thesis is to understand and analyze Ontario’s proposal of their regulatory framework for CCS and to give recommendations to the CCS framework by comparing it against the information gathered from other jurisdictions (Alberta, Saskatchewan, the United States, Europe and Australia). Key research questions are 1. How can the knowledge gained from other regions regarding CCS help Ontario's hard-to-abate sectors to understand approvals, licensing, and liability? 2. What are some other necessary policies that Ontario would need to expand upon and potentially adopt from various jurisdictions? And 3. How did companies and governments in other jurisdictions communicate to the public about the need for this technology? The thesis first developed a literature review to compare and contrast policies from other jurisdictions by researching and synthesizing various peer-reviewed journal articles and grey literature. Then, a semi-structured interview was needed to explore any unique perspectives from interviewees with expertise in CCS, and also to understand whether the results aligned with the information from the literature review. Following the interviews, the analysis of the results were accomplished by using ‘codes’ and ‘themes’, which allows for a simplified understanding of which information is unique. As a result, there were unique findings from the interviews such as ensuring proper industries are utilizing CCS, explaining the purpose of CCS, ensuring that the regulatory framework for CCS is properly developed, and the potential for CCS to utilize a carbon market through an Emissions Trading System (ETS). In November 2024, Ontario introduced Bill 228, which contains an Act called the Geologic Carbon Storage Act, 2024. This Act contains the key core components of the regulatory framework, such as ownership, liabilities, and approvals and assessments. As a result, a description and analysis of this Act was undertaken to understand how it compares against my research findings. In conclusion, to answer the first research question, the findings resulted in requiring Ontario to vest in the pore space, implement a unitization statue, implement a transfer of liabilities once certain pre-conditions are met and a post-stewardship fund to cover liability costs. As for the second research question, the other necessary policies include expanding upon environmental assessments methods, using a systems analysis approach to understand the outcomes of developing CCS, incorporating CCS into carbon pricing schemes, and Ontario’s plans on how they should utilize their CCS. The findings for the final research question recommend that the Ontario government and companies recognize the social demographic backgrounds of Ontario; ensure that Ontario is integrating and engaging with communities closely; explaining the downsides of not developing a CCS project; and respecting a community’s decision if they do not wish to engage with the project. Bill 228 is consistent with these findings, namely the inclusion of a liability transfer; a stewardship fund to cover the liabilities for the Crown; unitization of pore spaces; risk management; monitoring, measurement and verification (MMV); emergency response; and various approvals and assessments. However, the ownership of pore spaces deviates from these findings, as Ontario vests pore ownership to the surface owners but still allows the Crown to vest in the pore space when required.
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    Reweighted Eigenvalues: A New Approach to Spectral Theory beyond Undirected Graphs
    (University of Waterloo, 2025-02-21) Tung, Kam Chuen
    We develop a concept called reweighted eigenvalues, to extend spectral graph theory beyond undirected graphs. Our main motivation is to derive Cheeger inequalities and spectral rounding algorithms for a general class of graph expansion problems, including vertex expansion and edge conductance in directed graphs and hypergraphs. The goal is to have a unified approach to achieve the best known results in all these settings. The first main result is an optimal Cheeger inequality for undirected vertex expansion. Our result connects (i) reweighted eigenvalues, (ii) vertex expansion, and (iii) fastest mixing time [BDX04] of graphs, similar to the way the classical theory connects (i) Laplacian eigenvalues, (ii) edge conductance, and (iii) mixing time of graphs. We also obtain close analogues of several interesting generalizations of Cheeger’s inequality [Tre09, LOT12, LRTV12, KLLOT13] using higher reweighted eigenvalues, many of which were previously unknown. The second main result is Cheeger inequalities for directed graphs. The idea of Eulerian reweighting is used to effectively reduce these directed expansion problems to the basic setting of edge conductance in undirected graphs. Our result connects (i) Eulerian reweighted eigenvalues, (ii) directed vertex expansion, and (iii) fastest mixing time of directed graphs. This provides the first combinatorial characterization of fastest mixing time of general (non-reversible) Markov chains. Another application is to use Eulerian reweighted eigenvalues to certify that a directed graph is an expander graph. Several additional results are developed to support this theory. One class of results is to show that adding $\ell_2^2$ triangle inequalities [ARV09] to reweighted eigenvalues provides simpler semidefinite programming relaxations, that achieve or improve upon the previous best approximations for a general class of expansion problems. These include edge expansion and vertex expansion in directed graphs and hypergraphs, as well as multi-way variations of some undirected expansion problems. Another class of results is to prove upper bounds on reweighted eigenvalues for special classes of graphs, including planar, bounded genus, and minor free graphs. These provide the best known spectral partitioning algorithm for finding balanced separators, improving upon previous algorithms and analyses [ST96, BLR10, KLPT11] using ordinary Laplacian eigenvalues.
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    Imagining Shared Food Futures: honouring Canada's obligations towards Anishinaabek foodways​
    (University of Waterloo, 2025-02-20) Koberinski, Jodi
    Sustainability scholars characterize climate breakdown and biodiversity loss as converging crises tied directly to settler colonial ‘resource management’ regimes. Canada gestures toward mitigating these crises by ‘including’ Indigenous knowledges in environmental impact assessments and policy. Canada prioritizes commodity market profitability over mitigating these crises by excluding Indigenous knowledges in resource management decisions when acting on that knowledge would disrupt industry-favoured practices. One such practice is glyphosate use in forest ‘management.’ Glyphosate is a broad-spectrum agricultural herbicide repurposed to ‘manage’ regrowth after clearcutting forests. Banned by Quebec in 2001, Ontario embraced this practice. In 2013, Anishinaabek Elders along the north shore of the Great Lakes formed the Traditional Ecological Knowledge Elders to campaign for a moratorium on glyphosate use, which is counter to Anishinaabek environmental governance. Proponents claim herbicide use speeds stand regeneration, yet that regeneration converts food-bearing forests to pine plantations. Ontario legislators are not seeing the forest for the trees. This dissertation contributes to radical food geographies scholarship by characterizing the cumulative impacts of forestry policies on Indigenous foodways. Foodways include economic, material, linguistic, spiritual, intergenerational, scientific, ceremonial, and social dimensions of a culture’s food governance. This study concludes that efforts to imagine shared food futures in Canada’s settler colonial context require reframing ‘renewable’ resource extraction as Indigenous foodways disruption. Applying case study and participatory action research methods, I offer three manuscripts that together characterize the limitations of settler colonial knowledge in imagining shared food futures that meet settler treaty obligations. These three studies conclude that converting Anishinaabek food-bearing forests to pine plantations undermines the conditions required for Canada to meet treaty obligations to protect Anishinaabek foodways. In the first manuscript, I adapt Vivero Pol’s multi-governance framework to Canada’s settler colonial context to analyze customary and contemporary Indigenous food initiatives through a food commons lens. This study reveals the limitations of settler colonial frameworks for imagining shared food futures. The second manuscript seeks to overcome these limitations by centring an Anishinaabek research paradigm in collaboration with Traditional Ecological Knowledge Elders of the North Shore of Lake Huron. Our case study examining the cumulative impacts of changes to forestry legislation on Anishinaabek foodways centres TEK Elders’ efforts to stop glyphosate use in forestry. Reflecting on Ontario’s Bill 197, we characterize the limitations of settler colonial knowledge systems for understanding the impacts of forest ‘management’ decisions on settler treaty obligations. To better understand the limitations raised in the first two manuscripts, I apply participatory action research methods in the third manuscript to analyze transcripts from the Canadian Society of Ecological Economics’ bi-annual conferences I co-organized between 2019 and 2021. I ask what Indigenous knowledge holders have to say about the repackaging of Indigenous concepts by sustainability researchers within colonial knowledge systems. Despite gestures towards ‘inclusion’ of Indigenous knowledge, settler colonial frameworks depoliticize Indigenous resistance and resurgence, often reinforcing colonial narratives of land cessation and dispossession. Without addressing the underlying settler colonial assumptions and structures, sustainability scholars and settler governments relying on their research risk replicating the violence inherent in food policy frameworks built on settler supremacy. Collectively, these manuscripts identify actions settler colonial scholars have the responsibility to take up, beginning with transforming settler colonial narratives.
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    On Spoken Confidence: Characteristics of Explicit Metacognition in Reasoning
    (University of Waterloo, 2025-02-20) Stewart, Kaiden
    In this thesis, I assess how explicit, subjective evaluations of confidence influence monitoring and control (i.e., metacognitive) processes in reasoning. Metacognitive processes play a crucial role in modern dual-process theories of reasoning and decision-making, the consequences of which have been implicated in numerous significant real-world decisional outcomes. It is tacitly assumed that monitoring one’s reasoning for the purpose of optimal deployment of controlled, deliberative processing functions similarly to monitoring one’s reasoning for the purpose of providing a judgment of confidence, despite evidence from other domains indicating otherwise. This thesis takes a critical step toward evaluating metacognitive theories of reasoning and their broader application by assessing the degree to which standard approaches represent realistic accounts of metacognitive processes. To aid in interpretation of the work directly testing this possibility, I first present six experiments addressing foundational issues with respect to the operation of metacognition in reasoning. Chapter 2 provides evidence for a causal relationship between confidence judgments and controlled behavior (specifically deliberation), a reality often assumed in the absence of direct evidence. I demonstrate across four experiments that processing manipulations affect confidence and influence control behavior, consistent with a causal relationship, but also that it is possible to target control behaviour without mirroring effects on confidence. Chapter 3 develops a simple predictive model of confidence that identifies heretofore unidentified, item-based predictors of confidence. This simple model allows a unique approach to testing the central question in Chapter 4. Chapter 4 investigates whether the relationship between confidence and controlled behavior partly depends on the requirement to make explicit confidence judgments. Using a paradigm adapted from research involving nonhuman primates, I compare implicit and explicit confidence conditions. Results reveal small differences in controlled behavior and substantial differences in monitoring. In the present thesis, I provide evidence of plausibly systematic influences of common measurement approaches on reasoning. To this effect, it is likely that the reasoning processes in which individuals engage in day-to-day life are reliably different than those commonly assessed in the lab. This has practical, but also theoretical implications which I discuss.
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    Wideband Signal Generation at Millimeter-Wave and Sub-THz Frequencies
    (University of Waterloo, 2025-02-20) Su, Zi Jun
    The rise of sixth-generation (6G) wireless technology has created a need for wideband signal generation at high radio frequencies (RF). However, current digital-to-analog converters (DACs) face limitations, offering either wide bandwidth with low resolution or high resolution with limited bandwidth. This thesis proposes two methods that utilize multiple DACs to generate multiple narrowband sub-bands of a wideband signal, that are combined to produce the desired wideband signal. These methods employ distinct digital processing approaches tailored to specific applications, such as instrumentation or real-time Orthogonal Frequency Division Multiplexing (OFDM) signal generation. To address non-idealities in frequency-stitching-based transmitters, a frequency-domain calibration technique using multi-tone signals is introduced. Experiments at X-band (9.6 GHz) and D-band (129.6 GHz) validate these methods, demonstrating up to 8 GHz bandwidth and achieving an error vector magnitude (EVM) as low as 0.3\% for a 7.2 GHz 256-QAM OFDM signal. A comparative study of three signal generation approaches—direct Arbitrary Waveform Generator (AWG) generation, baseband in-phase and quadrature (IQ) generation with up-conversion, and frequency stitching—shows EVMs of 1.5\%, 0.8\%, and 1\%, respectively, for an 8 GHz OFDM signal. A novel architecture using phase-coherent IQ-DACs and mixers for each sub-band is also presented. Calibration using non-uniformly interleaved tones corrects IQ imbalances and distortions, enabling the generation of a 256-QAM OFDM signal with 12 GHz bandwidth at D-band (149 GHz) and achieving a peak data rate of 96 Gbps. Calibration improves EVM and normalized mean square error (NMSE) from 82.6\% and 23.8\% to below 2\% and 1\%, respectively. Additionally, D-band amplifier linearization with a 4 GHz modulation bandwidth improves adjacent channel power ratio (ACPR) from -27.8/-26 dBc to -42.8/-43.1 dBc and EVM from 8.5\% to 1.2\%. Finally, two architectures for sub-band combination are compared. One generates a wideband signal at intermediate frequency (IF) and up-converts it, while the other up-converts narrowband IF signals and combines them. The second approach demonstrates superior ACPR at high IF power levels, enhancing ACPR by up to 8 dB when generating a 1.2 GHz modulated signal at 142.5 GHz. These results highlight the efficacy of the proposed methods for generating and linearizing high-quality wideband signals, supporting advanced applications in millimeter wave and sub-THz frequency bands for 6G technologies.
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    A Study of the Opportunities and Challenges of Using Edge Computing to Accelerate Cloud Applications
    (University of Waterloo, 2025-02-18) Qadi, Hala
    I explore the viability of using edge clusters to host latency-sensitive applications and to run services that can improve end-to-end communication performance across both wide area networks (WANs) and 5G environments. The study examines the viability of using edge clusters in three scenarios: accelerating TCP communications through TCP splitting in 5G deployments, hosting an entire application-level service or the latency-sensitive part of an application on an edge cluster, and deploying a TCP splitting service on edge clusters to support WAN communication. I explore these scenarios while varying packet drop rates, communication stacks, congestion control protocols, and TCP buffer sizes. My findings bring new insights about these deployment scenarios. I show that edge computing, especially through TCP splitting, can significantly improve end-to-end communication performance over the classical communication stack. TCP splitting over the 5G communication stack does not bring any benefit and can reduce throughput. This is because of the unique characteristics of the 5G communication stack. Furthermore, over the classical communication stack, TCP splitting brings higher benefit for flows larger than 64 KB. These findings provide valuable insights into how edge clusters can accelerate TCP communication in different network environments and identify high-impact research ideas for future work.
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    Advanced Separator Modifications for Lithium-Sulfur Batteries: Multifunctional Organic Frameworks and Nanostructured Composites to Mitigate the Polysulfide Shuttle Effect
    (University of Waterloo, 2025-02-18) Fazaeli, Razieh
    This thesis explores innovative approaches to addressing critical challenges in lithium-sulfur (Li-S) battery technology through the development of modified separator materials. The escalating concerns surrounding climate change, pollution, and fossil fuel depletion are propelling a global transition toward renewable energy sources like wind, solar, and hydropower. Alongside this shift is an increasing demand for efficient, high-capacity, and cost-effective energy storage systems that support these sustainable energy technologies, especially for applications in electric vehicles. Various rechargeable battery technologies, such as lithium-ion, sodium-ion, potassium-ion, magnesium-ion, zinc-ion, and aluminum-ion batteries, have garnered significant research attention due to their high efficiency, reversibility, light weight, and environmental friendliness. Although lithium-ion batteries have achieved widespread success in portable electronics and electric vehicles, they have limitations when it comes to the growing demand for energy density, long cycle life, and affordability. Consequently, next-generation batteries—particularly those based on sulfur chemistry—are being developed to meet these requirements. This thesis specifically investigates how functional materials for separator modification can address the main issues of polysulfide shuttle and conductivity in Li-S batteries, aiming to make these batteries more feasible for next-generation energy storage applications. The first study in this thesis focuses on designing a series of melamine-based porous organic frameworks (POFs) as efficient polysulfide reservoirs to modify glass fiber (GF) separators in Li-S batteries (LSBs). Despite the promising energy density of Li-S systems, the polysulfide shuttle effect—where lithium polysulfides (LiPSs) dissolve and migrate between electrodes—remains a significant barrier to achieving stable cycling and high capacity retention. To tackle this challenge, we synthesized a series of POF materials (POF-C4, POF-C8, and POF-C12) by reacting melamine with dibromoalkanes of varying chain lengths (C4, C8, and C12). The resulting POFs displayed distinct nanoscale pore sizes and solubility properties, which are critical for effective LiPS trapping and utilization. These POFs were then combined with conductive Super P (SP) and polyvinylpyrrolidone (PVP) binder to create a composite layer (POF-Cn/SP/PVP) that was coated onto GF membranes, forming modified separators that enhance the electrochemical performance of Li-S batteries. The batteries incorporating these modified separators were evaluated through various electrochemical tests, and the POF-C8/SP/PVP-modified separator, in particular, demonstrated outstanding performance. It delivered an initial specific capacity of 1392 mAh g⁻¹ at 0.1C and retained 90% capacity over 300 cycles at 0.5C. This enhanced performance can be attributed to the optimal pore structure of POF-C8 and its high nitrogen content, which work in tandem to capture soluble LiPSs and limit their migration toward the lithium anode. Furthermore, the good solubility of POF-C8 ensures uniform dispersion and strong interactions with LiPSs, enabling efficient redox reactions. This study highlights the potential of functional polymer-based separator modifications to mitigate polysulfide migration, improving the stability and longevity of Li-S batteries. The second study investigates the use of Congo Red (CR), a redox-active organic compound, in conjunction with cetyltrimethylammonium bromide (CTAB), a cationic surfactant, to modify GF separators for improved LSB performance. CR has a unique capability of engaging in redox reactions, which aids in suppressing the polysulfide shuttle by capturing LiPSs at the separator interface. The CR-CTAB/SP/PVP-modified GF separators demonstrated enhanced ion transport properties and higher sulfur utilization, addressing core issues that commonly degrade Li-S battery performance. Electrochemical performance tests revealed that LSBs with these CR-CTAB-modified separators achieved an initial specific capacity of 1161.9 mAh g⁻¹ and maintained 994.1 mAh g⁻¹ after 300 cycles at 0.5C, showing significant improvement over the baseline unmodified GF separators. The CR molecules in the separator modification layer serve as efficient adsorbents for polysulfides, while the CTAB molecules aid in stabilizing the structure and enhancing ion transport across the separator. This work emphasizes the importance of incorporating redox-active molecules into separator designs, showing that such molecules can effectively reduce the shuttle effect, enhance performance, and create more durable energy storage systems. The third study delves into the incorporation of a nanocomposite composed of CR and tin dioxide (SnO₂) nanoparticles for further improvement of polysulfide-trapping capability and redox kinetics in GF separators. The CR-SnO₂/SP/PVP-modified separators were synthesized by combining CR, SnO₂ nanoparticles, conductive SP, and PVP binder. This approach resulted in a composite layer with enhanced surface interactions and improved electron transport pathways. Structural characterization using techniques such as scanning electron microscopy (SEM), X-ray diffraction (XRD), and transmission electron microscopy (TEM) confirmed the uniform dispersion of CR and SnO₂, indicating strong cooperative interactions between these components. Electrochemical tests demonstrated that LSBs incorporating the CR-SnO₂-modified separators exhibited exceptional performance, with an initial specific capacity of 1377 mAh g⁻¹ at 0.1C and capacity retention of 91% over 300 cycles at 0.5C. The CR-SnO₂ composite material provides dual benefits: CR molecules effectively capture LiPSs, while SnO₂ nanoparticles act as catalysts, promoting redox reactions and enhancing ion transport. This synergy between CR and SnO₂ in the separator layer contributes to stable cycling performance and mitigates capacity loss due to polysulfide migration, making this composite a promising solution for improving Li-S battery stability. The forth study address the shuttle effect challenge by employing cysteine and layered double hydroxides (LDHs) as 2D materials to create an innovative 2D heterostructure (Cys/FeNi-LDH). This heterostructure serves as a robust support for immobilizing V2O5 nanoparticles (NPs). Incorporating V2O5/Cys/FeNi-LDH (VCFN) into a GF separator ensured stable electron and ion pathways, significantly enhancing long-term cycling capabilities. The use of L-cysteine, a cost-effective and readily available amino acid, played a crucial role in enhancing the Li-S battery performance. The remarkable enhancement in electrochemical performance is attributed to the synergistic effects of VCFN nanoparticles, cysteine, and SP. A Li-S battery featuring the VCFN GF separator demonstrated an impressive initial capacity of 1036.8 mAh g⁻¹ and, after 300 cycles at 0.5C, retained a capacity of 920.1 mAh g⁻¹. This thesis demonstrates that modifying the separator is a highly effective strategy for addressing the primary challenges in Li-S batteries, particularly the polysulfide shuttle effect. By tailoring the physical and chemical properties of the separator layer, significant improvements in capacity retention, cycling stability, and rate performance have been achieved. Each of the materials that used for modification of GF separators demonstrates the potential to enhance battery performance through unique mechanisms. The melamine-based POF-C8-modified separator leverages a nanoscale porous framework to trap polysulfides and improve LiPS utilization. Meanwhile, the CR-CTAB and CR-SnO₂ composites add a redox-active element to the separator, aiding in polysulfide trapping and catalyzing redox reactions at the interface. A novel composite of V₂O₅ nanoparticles on Cys/FeNiLDH sheets (VCFN) was synthesized and used to modify GF separators, enhancing the electrochemical stability of LSBs. This research contributes to the field of LSBs by providing insights into the design of multifunctional separators that simultaneously address multiple performance issues, including polysulfide retention, ion transport, and redox catalysis.
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    Model Predictive Control for Systems with Partially Unknown Dynamics Under Signal Temporal Logic Specifications
    (University of Waterloo, 2025-02-18) Dai, Zhao Feng
    Autonomous systems are seeing increased deployment in real-world applications such as self-driving vehicles, package delivery drones, and warehouse robots. In these applications, such systems are often required to perform complex tasks that involve multiple, possibly inter-dependent steps that must be completed in a specific order or at specific times. One way of mathematically representing such tasks is using temporal logics. Specifically, Signal Temporal Logic (STL), which evaluates real-valued, continuous-time signals, has been used to formally specify behavioral requirements for autonomous systems. This thesis proposes a design for a Model Predictive Controller (MPC) for systems to satisfy STL specifications when the system dynamics are partially unknown, and only a nominal model and past runtime data are available. The proposed approach uses Gaussian Process (GP) regression to learn a stochastic, data-driven model of the unknown dynamics, and manages uncertainty in the STL specification resulting from the stochastic model using Probabilistic Signal Temporal Logic (PrSTL). The learned model and PrSTL specification are then used to formulate a chance-constrained MPC. For systems with high control rates, a modification is discussed for improving the solution speed of the control optimization. In simulation case studies, the proposed controller increases the frequency of satisfying the STL specification compared to controllers that use only the nominal dynamics model. An initial design is also proposed that extends the controller to distributed multi-agent systems, which must make individual decisions to complete a cooperative task.
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    The Philosophy of Reconstructions of Quantum Theory: Axiomatization, Reformulation, and Explanation
    (University of Waterloo, 2025-02-18) Oddan, Jessica
    The quantum reconstruction programme is a novel research program in theoretical physics aimed at deriving the key features of quantum mechanics from fundamental physical postulates. Unlike standard interpretations of quantum theory, which take the Hilbert space formalism at face value, quantum reconstructions seek to derive this formalism from axiomatic principles. Reconstructions represent a new shift in foundations of physics away from interpreting quantum theory and towards understanding its foundational origins. The reconstruction programme has been a major focus of research in physics, beginning with Hardy (2001)’s “Quantum Theory from Five Reasonable Axioms.” However, the quantum reconstruction programme has been met with very little interest in philosophy. The goal of this project is to situate the quantum reconstruction programme in a broader philosophical context, investigating themes such as scientific methodology, explanation, the applicability of mathematics to physical theories, and theory exploration and development in the philosophy of science. I argue that reconstructions demonstrate a contemporary application of axiomatization with significant points of continuity to historical axiomatizations. I also argue that we should best understand reconstructions as provisional, practical representations of quantum theory that are conducive to theory exploration and development. Further, I contend that reconstructions function as alternative formulations of quantum theory, which is methodologically advantageous. I discuss Bokulich (2019)’s “Losing the Forest for the Ψ: Beyond the Wavefunction Hegemony” which argues that the existence of alternative formulations of quantum theory undermines our ability to literally interpret a single formulation. I argue that Bokulich (2019)’s conclusions further support the reconstructionist’s rejection of the standard interpretative project. I also argue that reconstructionists have gone beyond Bokulich (2019)’s insistence on the consideration of alternative formulations to develop a methodology that systematically constructs alternative formulations of quantum theory. Additionally, I argue that reconstructions of quantum theory are genuinely explanatory as they answer Wheeler (1971)’s “Why the quantum?” question. I contend that reconstructions are explanatory in the same spirit as Bokulich (2016)’s account of explanation in “Fiction As a Vehicle for Truth: Moving Beyond the Ontic Conception” which focuses on patterns of counterfactual dependence that correctly capture underlying dynamics. However, in order to accommodate the reconstruction case, I expand Bokulich’s account to consider theories and models as well as representations that are neither fictional nor literal interpretations. Thus, I offer an account of explanation in the reconstruction programme that is noncausal and non–interventionist, utilizing w–questions a la Woodward (2003). I conclude that reconstructions of quantum theory give us genuine insight into the structure of quantum theory via the generalized physical principles which carry physical content.
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    The Power of Experimental Approaches to Social Choice
    (University of Waterloo, 2025-02-14) Armstrong, Ben
    With increasing connectivity between humans and the rise of autonomous agents, group decision-making scenarios are becoming ever more commonplace. Simultaneously, the requirements placed upon decision-making procedures grow increasingly nuanced as social choices are made in more niche settings. To support these demands, a deeper understanding of the behaviour of social choice procedures is needed. The standard theoretical approach to analyze social choice procedures is limited in the type of question it can answer. Theoretical analyses can be rigid: It may speak to the incompatibility of different properties without also providing a deeper understanding of the properties themselves, or might stop at proving the worst-case outcome of a voting rule without communicating the rule's typical behaviour. In this dissertation, we address these limitations by demonstrating that experimental analysis of social choice domains can provide an understanding of social choice which is both complementary and additional to theoretical findings. In particular, experimental approaches can form a middle ground between theory and practice: more practical than theoretical approaches in a setting more controlled than real-world application. We apply this approach to a new form of delegative voting and to a task of learning existing and novel voting rules. In each area we find results of a type and scale which are infeasible to traditional analysis. We first examine an abstract model of delegative voting -- agents use liquid democracy to transitively delegate their vote -- in a setting where the voters collectively agree on a correct outcome. Through extensive simulations we show the dynamic effects on group accuracy from varying a wide range of parameters that collectively encompass many types of human behaviour. We identify two features of this paradigm which result in improvements to group accuracy and highlight a possible explanation for their effectiveness. Subsequently, we apply this liquid democracy framework to the process of training an ensemble of classifiers. We show that the experimental findings from our simulations are largely maintained on a task involving real-world data and result in further improvements when considering a novel metric of the training cost of ensembles. Additionally, we demonstrate the creation of a robust framework for axiomatic comparison of arbitrary voting rules. Rather than proving whether individual rules satisfy particular axioms, we establish a framework for showing experimentally the degree to which rules general satisfy sets of axioms. This enables a new type of question -- degrees of axiom satisfaction -- and provides a clear example of how to compare a wide range of single and multi-winner voting rules. Using this framework, we develop a procedure for training a model to act as a novel voting rule. This results in a trained model which realizes a far lower axiomatic violation rate than most existing rules and demonstrates the possibility for new rules which provide superior axiomatic properties.
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    A Multi-Phase Analysis of Gas Dynamics and Perturbations in the Galaxy Cluster Cores
    (University of Waterloo, 2025-02-14) Li, Muzi
    This thesis provides a detailed analysis of gas kinematics and their interactions across various phases within galaxy cluster cores. It examines the processes that generate gas perturbations and the factors that contribute to the thermal stability of the intracluster medium (ICM). A focus is placed on exploring the origins of multi-phase gas and the mechanisms—particularly AGN feedback—that either couple or decouple their motions. Radio-mechanical AGN feedback is identified as one of the most promising heating mechanisms that prevent the cooling of gas. However, the debate on the details of the heating transport processes has remained open. The atmospheres of 5 cool-core clusters, Abell 2029, Abell 2107, Abell 2151, RBS0533 and RBS0540, have short central cooling times but little evidence of cold gas, and jet-inflated bubbles. The amplitudes of gas density fluctuations were measured using a new statistical analysis of X-ray surface brightness fluctuations within the cool cores of these ‘spoil’ clusters in Chapter 2. The derived velocities of gas motions, typically around 100 - 200 km/s, are comparable to those in atmospheres around central galaxies experiencing energetic feedback, such as in the Perseus Cluster, and align well with the turbulent velocities expected in the ICM. Regardless of the mechanisms driving these perturbations, turbulent heating appears sufficient to counteract radiative losses in four of the five spoiler cluster cores. We thus suggest that other mechanisms, such as gas sloshing, may be responsible for generating turbulence, offering a plausible solution to suppress cooling in these structureless atmospheres. Multiphase filaments, key byproducts of AGN feedback, are frequently observed near central galaxies, with their morphologies and kinematics closely linked to bubbles. In Chapter 3, we analyzed the velocity structure functions (VSFs) of warm ionized gas and cold molecular gas, identified through [OII] emission and CO emissions observed by the Keck Cosmic Web Imager (KCWI) and the Atacama Large Millimeter/submillimeter Array (ALMA), respectively, in four clusters: Abell 1835, PKS 0745-191, Abell 262, and RXJ0820.9+0752. Excluding Abell 262, where gas forms a circumnuclear disk, the remaining clusters exhibit VSFs steeper than the Kolmogorov slope. The VSFs of CO and [OII] in RXJ0820 and Abell 262 show close alignment, whereas in PKS 0745 and Abell 1835, were differentiated across most scales, likely due to the churning caused by the radio-AGN. The large-scale consistency in Abell 1835 and RXJ0820, together with scale-dependent velocity amplitudes of the hot atmospheres obtained from Chandra X-ray data, may support the idea of cold gas condensation from the hot atmospheres. X-ray observations have previously been constrained by low energy resolution, which has impeded direct measurements of velocity fields in galaxy clusters. However, the recent release of initial data from the X-ray Imaging and Spectroscopy Mission (XRISM) provides a non-dispersive energy resolution of about 5 eV, facilitating the measurement of line broadening and shifts. In Chapter 4 of this thesis, I detail my contributions to calibrating the optical blocking filters for XRISM using synchrotron beamlines at the Canadian Light Source (CLS) and Advanced Light Source (ALS) prior to its launch, and I discuss the model-based estimation of the parameters of the calibrated filters. This capability for direct measurement of plasma velocities is expected to greatly improve our understanding of the ICM dynamics with high accuracy.
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    From For To With: Towards an Allographic Approach in Architecture
    (University of Waterloo, 2025-02-13) Fournier, Marc-
    Although transformations to buildings are inevitable, architecture often aims to achieve idealized, finalized artifacts that refute the passage of time. This professional bias towards temporality – or the problem of permanence – creates and perpetuates non-reciprocal relationships between architects, users, and the built environment that often results in the exploitation and alienation of the people the discipline attempts to serve. By examining architecture's failure to account for diverse temporalities, this research sheds light on the ways in which architects overlook their potential to cultivate meaningful social interactions with the built environment. The architect’s role, therefore, needs to be redefined as a translator of collective desires and needs, as a designer of structures that promote agency and empower individuals to engage with their environments. This paradigm shift implies an inquiry into the architect’s conventional design apparatus and the expansion of its scope to include tools that embrace temporality and contingency as key variables. The thesis proposes a shift in focus from the production of artifacts to the design of architectural scores inspired by allographic arts. Allographic thinking shifts the emphasis from end product to process; forcing a renegotiation of author-designer / performer-user relationships, focusing on affordances and obstacles, favoring user agency, and embracing contingency. The context of the Habitations Jeanne-Mance, a post-war social housing in Montréal, acts as a case study for an exploration of the disciplinary problems of permanence, alienation, and non-reciprocity, as well as the testing ground for a speculative design intervention that integrates allographic thinking into architecture to create a system that promotes user participation, indeterminacy, and reciprocal relationships between residents and their built environment.
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    Learning-Based Safety-Critical Control Under Uncertainty with Applications to Mobile Robots
    (University of Waterloo, 2025-02-13) Aali, Mohammad
    Control theory is one of the key ingredients of the remarkable rise in robotics. Due to technological advancements, the use of automated robots, which was once primarily limited to industrial and manufacturing settings, has now expanded to impact many different parts of everyday life. Various control strategies have been developed to satisfy a wide range of performance criteria arising from recent applications. These strategies have different characteristics depending on the problem they solve. But, they all have to guarantee stability before satisfying any performance-driven criteria. However, as robotic technologies become increasingly integrated into everyday life, they introduce safety concerns. For autonomous systems to be trusted by the public, they must guarantee safety. In recent years, the concept of set invariance has been incorporated into modern control strategies to enable systematic safety guarantees. In this thesis, we aim to develop safety-critical control methods that can guarantee safety while satisfying performance-driven requirements. In the proposed strategies, we considered formal safety guarantees, robustness to uncertainty, and computational efficiency to be the highest design priorities. Each of them introduces new challenges which are addressed with theoretical contributions. We selected motion control in mobile robots as a use case for proposed controllers which is an active area of research integrating safety, stability, and performance in various scenarios. In particular, we focused on multi-body mobile robots, an area with limited research on safe operation. We provide a comprehensive survey of the recent methods that formalize safety for the dynamical systems via set invariance. A discussion on the strengths and limitations of each method demonstrates the capabilities of control barrier functions (CBFs) as a systematic tool for safety assurance in motion control. A safety filter module is also introduced as a tool to enforce safety. CBF constraints can be enforced as hard constraints in quadratic programming (QP) optimization, which rectifies the nominal control law based on the set of safe inputs. We propose a multiple CBF scheme that enforces several safety constraints with high relative degrees. Using the multi-input multi-output (MIMO) feedback linearization technique, we derive conditions that ensure all control inputs contribute effectively to safety. This control structure is essential for challenging robotic applications requiring multiple safety criteria to be met simultaneously. To demonstrate the capabilities of our approach, we address reactive obstacle avoidance for a class of multi-body mobile robots, specifically tractor-trailer systems. The lack of fast response due to poor maneuverability makes reactive obstacle avoidance difficult for these systems. We develop a control structure based on a multiple CBFs scheme for a multi-steering tractor-trailer system to ensure a collision-free maneuver for both the tractor and trailer in the presence of several obstacles. Model predictive control serves as the nominal tracking controller, and we validate the proposed strategy in several challenging scenarios. Although the CBF method has demonstrated a great potential for ensuring safety, it is a model-based method and its effectiveness is closely tied to an accurate system model. In practice, model uncertainty compromises safety guarantees and may lead to conservative safety constraints, or conversely, allow the system to operate in unsafe regions. To address this, we explore developing safety-critical controllers that account for model uncertainty. Achieving this requires combining the theoretical guarantees of model-based methods with the adaptability of data-driven techniques. For this study, we selected Gaussian processes (GPs) which bring together required capabilities. It provides bounds on the posterior distribution, enabling theoretical analysis, and producing reliable approximations even with a low amount of training data, which is common in data-driven control. The proposed strategy mitigates the adverse effects of uncertainty on high-order CBFs (HOCBFs). A particular structure of the covariance function is designed that enables us to convert the chance constraints of HOCBFs into a second-order cone constraint, which results in a convex constrained optimization as a safety filter. A discussion on the feasibility of the resulting optimization is presented which provides the necessary and sufficient conditions for feasibility. In addition, we consider an alternative approach that uses matrix variate GP (MVGP) to approximate unknown system dynamics. A comparative analysis is presented which highlights the differences and similarities of both methods. The proposed strategy is validated on adaptive cruise control and active suspension systems, common applications in mobile robots. This study next explores the safety of switching systems, focusing on cases where system stability is assured through control Lyapunov functions (CLFs) and CBFs are applied for safety. We show that the effect of uncertainty on the safety and stability constraint forms piecewise residuals for each switching surface. We introduce a batch multi-output Gaussian process (MOGP) framework to approximate these piecewise residuals, thereby mitigating the adverse effects of uncertainty. We show that by leveraging a specific covariance function, the chance constrained safety filter can be converted to a convex optimization, that is solvable in real-time. We analyze the feasibility of the resulting optimization and provide the necessary and sufficient conditions for feasibility. The effectiveness of the proposed strategy is validated through a simulation of a switching adaptive cruise control system.