UWSpace

UWSpace is the University of Waterloo’s institutional repository for the free, secure, and long-term home of research produced by faculty, students, and staff.

Depositing Theses/Dissertations or Research to UWSpace

Are you a Graduate Student depositing your thesis to UWSpace? See our Thesis Deposit Help and UWSpace Thesis FAQ pages to learn more.

Are you a Faculty or Staff member depositing research to UWSpace? See our Waterloo Research Deposit Help and Self-Archiving pages to learn more.

Photo by Waterloo staff

Communities in UWSpace

Select a community to browse its collections.

Recent Submissions

  • Thumbnail Image
    Item type: Item ,
    Electro-Thermal Modeling and Evaluation of Self-Heating System for Samsung INR21700-50E Cells
    (University of Waterloo, 2026-08-21) Razmi Khanghah, Mohammadreza
    Lithium-ion batteries based on nickel-containing chemistries, including Nickel Manganese Cobalt (NMC) and Nickel Cobalt Aluminum (NCA), account for the majority of EV battery deployment outside China. At −20 °C, these batteries experience a significant increase in internal resistance, sharp capacity fade, and accelerated degradation during charging — a critical challenge for EV operation in cold climates. This thesis investigates the feasibility of internal resistance heating of Samsung INR21700-50E NCA cylindrical cells via bidirectional buck-boost pulse current excitation at −20 °C, based on the topology described in BYD (Build Your Dreams) Company Limited patent EP 4516579 A1. A two-cell bidirectional buck-boost circuit was implemented in MATLAB/Simulink using Simscape physical network blocks, with battery parameters represented as a first-order Thevenin equivalent circuit model using 5 × 5 lookup tables for R0, R1, and τ1 over SoC and temperature. The simulation was run for 2,000 s starting at −20 °C with SoC = 50%. The confirmed results show that both cells heated from −20 °C to +0.92 °C, reaching the 0 °C target at t = 1,839 s (30.6 min) at an average rate of 0.628 °C/min, consuming 9.01 % SoC and 0.954 Wh of energy to reach the target temperature. The thermal asymmetry ratio (defined as the ratio of temperature rise between the two cells) was confirmed at 1.000× throughout the entire simulation, consistent with the identical cell parameters and control inputs used in the model, validating the simultaneous self-heating principle of the BYD topology. The minimum safe inductance was determined to be L = 15 mH — a hard physical constraint imposed by the single-cell voltage window at −20 °C. The heating rate decreased progressively from 0.966 °C/min in the first 100 s to 0.340 °C/min in the final 100 s, driven primarily by the temperature-dependent reduction of R0 as the cell temperature was raised. Analytical scaling of the two-cell results to the Battery Workforce Challenge 400 V pack architecture led to derivation of the drive voltage and assembly resistance at the submodule (3s21p), module (6s21p), and half-pack (45s21p) scales, following the same first-principles voltage-window derivation validated at two-cell scale. A pack-scale feasibility verdict is not claimed, since it would require a convective heat loss model validated against pack enclosure geometry and cell-to-cell thermal coupling, neither of which is available from the two-cell result. Instead, the thermal mass equation and energy balance framework derived in this work provide a complete analytical foundation for next-stage pack-level circuit design. These results provide, to the author's knowledge, the first simulation-based feasibility assessment of the BYD bidirectional buck-boost topology applied to Samsung INR21700-50E cylindrical cells at −20 °C, and demonstrate that the self-contained internal pulse heating method is viable at single-cell scale with a practical preconditioning time of 30.6 min to reach the temperature of 0 °C.
  • Thumbnail Image
    Item type: Item ,
    Bipartite Density: From Mixing Time to Local Algorithms for Dense Subgraphs
    (University of Waterloo, 2026-08-21) Liu, Raymond Z H
    Classical spectral graph theory shows that edge conductance characterizes the optimal O(log n) mixing time of d-regular graphs when d is constant. When d grows with n, however, the optimal mixing time is O(log_d n), and this characterization no longer applies. We give a new condition based on bipartite density that provides a more refined combinatorial characterization of mixing time across different degree regimes. Using this new connection between density and mixing time, we revisit the local algorithmic approach to finding dense subgraphs and show that it can be sharpened and extended considerably. (1) We improve Andersen's bicriteria approximation algorithms for finding dense bipartite subgraphs, both in approximation ratio and in output size. Our result can be interpreted as a local version of Bilu and Linial’s converse of the expander mixing lemma. The approximation guarantee improves in the high density regime, resembling Cheeger’s inequality in the high conductance regime. (2) We provide the first tradeoff between the approximation guarantee and the output size for finding small dense bipartite subgraphs. This tradeoff interpolates between the improved bicriteria guarantee above and a true approximation algorithm with no loss in the output size. In the high density regime, the true approximation guarantee has a subpolynomial approximation ratio. (3) We extend this approach to the densest k-subgraph problem, answering a question raised by Andersen. This gives the first local approximation algorithm for the densest k-subgraph problem. Moreover, our approach identifies a new high density regime, distinct from the previous almost clique regime, where a polynomial time algorithm achieves a subpolynomial approximation ratio. This analysis also gives a new random walk proof of the converse of the expander mixing lemma. Our algorithmic results can be viewed as a realization of Bilu and Linial’s speculation that their spectral bound might be useful in designing graph partitioning algorithms.
  • Thumbnail Image
    Item type: Item ,
    Algorithms for Analytic Combinatorics: Positivity Bounds and D-finite Operators
    (University of Waterloo, 2026-08-21) Smith, John
    Analytic combinatorics is concerned with describing limiting behavior of families of combinatorial structures. While this is well-studied in the univariate case, the last two decades have seen the development of analytic combinatorics in several variables (ACSV) treating the same problem in the multivariate case. One advantage of the way ACSV is formulated is that, at least in the simplest cases, its methods are amenable to explicit computation. This thesis contributes to an ongoing effort to automate the results of ACSV by providing developments in two related areas: computing D-finite operators for diagonals of rational functions, and computing explicit error bounds for ACSV in the so-called smooth rational case. First, we provide a SageMath implementation of an algorithm of Lairez for computing periods of rational integrals. Since diagonals of rational functions are rational periods, computing operators of periods is of great importance to practitioners of algebraic and analytic combinatorics. While Lairez gave a MAGMA implementation of his algorithm, our implementation provides full-fledged documentation, robustness, and feature enhancements aimed at combinatorialists -- such as computing diagonal operators for arbitrary directions. Second, we discuss how to find explicit error bounds for asymptotics of rational diagonals, as opposed to the Big-O asymptotics typically provided by ACSV. One motivation for this is the coefficient positivity problem; having explicit bounds allows one to reduce positivity of coefficient sequences to checking asymptotic positivity and finitely many initial sequence terms. We provide fully constructive versions of ACSV arguments in the simplest case, then use these to derive an index N so that positivity of our asymptotic implies positivity of our diagonal for all larger index values, under some small additional assumptions about the form of our asymptotic. We then explore the consequences and caveats of this reduction, exhibiting some classes of functions where asymptotic positivity can be known a priori.
  • Thumbnail Image
    Item type: Item ,
    “Making sense of the holistic why:” Implementation of sustainable food in healthcare institutions in Ontario, Canada
    (University of Waterloo, 2026-08-21) Blank, Lisa
    Background Health and food systems have deleterious consequences for planetary health. Health systems are responsible for between 4% and 8% of individual countries’ greenhouse gas emissions worldwide, contributing to climate change. Yet, health system emissions not only contribute to warming temperatures but also to poor air and water quality, with cascading effects on health. An estimated 25% of global emissions are attributable to food systems through direct emissions and land clearing, while producing significant waste and pollutants, including fertilizers, pesticides, and plastic packaging. Food systems are also associated with diet-related chronic diseases, leading to increased need for health services and high health costs. Paradoxically, health and food systems not only contribute to environmental change but are also directly impacted by its effects. Environmental change is predicted to increase burdens on health services, while reducing the nutrient quality of agricultural crops. Experts have called for transformations toward more sustainable health and food systems to address the multidimensional impacts on planetary health and increase resilience to future challenges. Foodservice within healthcare institutions is a leverage point for instigating such transformations. Sustainable foodservice would contribute to improving nutrition and health, minimizing environmental impacts, strengthening cultural inclusivity, and promoting local sustainable food systems. Healthcare institutions have begun implementing sustainable food interventions. Yet, progress is small and variable, especially in Canada. The complexity of the healthcare environment creates unique considerations for changing practices. Research on practice change, sustainability, and sustainable food in healthcare indicates multiple barriers and facilitators. There are gaps in understanding the specific factors at play across individual, institutional, and community levels; different political and social contexts; and varying stages of sustainable food implementation, as well as the interactions between different actors and foodservice options within the institutional food environment. Objectives This thesis aimed to 1) explore the barriers and facilitators to sustainable food interventions in the foodservice of an exemplar healthcare institution in Ontario, Canada, and 2) compare barriers and facilitators to two additional institutions at different stages of sustainable food implementation. Methodology The design of this thesis was informed by a critical research paradigm guided by my philosophical assumptions, which value planetary health as the well-being of the whole system, acknowledging that the worth of non-humans is not relative to humans. The thesis was informed by systems science, implementation science, and social science, which contributed to developing a theoretical framework merging the Consolidated Framework for Implementation Research with Institutional Theory, guiding data collection, analysis, and interpretation. I set out to conduct a collective case study of three healthcare institutions in Ontario, Canada, each in different stages of sustainable food implementation: an exemplar institution with multiple sustainable food interventions, a comparative institution with some evidence toward sustainable food, and a second comparative institution with less evidence toward sustainable food. I conducted ten semi-structured interviews with eight participants predominantly working in foodservice. Interviews were complemented by review of 47 documents, including strategic plans and sustainability reports, pertaining to the three institutions. Data were analyzed by institution and across institutions using a systems-based approach and a six-stage framework analysis method. Results Six conceptual themes, including efficiency meets sustainability, making sense of sustainable food, making sense through change management, development from the bottom-up, “the patient voice is at the center of what we do,” and a disconnected food environment, were generated. Themes were mapped to the theoretical framework, highlighting that implementation of sustainable food interventions cuts across all domains of the Consolidated Framework for Implementation Research, and is influenced by multiple pillars of Institutional Theory. The strongest barriers originated from the regulative pillar of Institutional Theory, and the strongest facilitators stemmed from the cultural-cognitive pillar of Institutional Theory. However, barriers and facilitators interacted with one another in complex ways. External partnerships and staff and visitor food options were identified as promising for expanding implementation and potentially weakening negative feedback channels maintaining efficient systems, particularly patient preferences that conflicted with sustainable menus. Accreditation standards incorporating sustainable food indicators were deemed a promising policy direction by participants, with the potential to weaken negative feedback channels by combining normative, cultural-cognitive, and regulative pillars of Institutional Theory to promote change. Conclusions Though there was some alignment with barriers and facilitators identified in prior research, the application of a systems lens in this research identified how barriers and facilitators interacted and seemed to combine into negative and positive feedback channels in a dynamic process, either constraining or reinforcing change toward sustainable food interventions. The findings provide insights into the institutions and individuals slowly shifting norms that dictate everyday practice in healthcare foodservice necessary to move toward sustainable health and food systems that address the negative consequences of such systems for planetary health.
  • Thumbnail Image
    Item type: Item ,
    ASH: Agents that self-hone via Embodied Learning
    (University of Waterloo, 2026-08-21) Schneider, Benjamin
    Long-horizon embodied tasks remain a fundamental challenge in AI, as current methods rely on hand-engineered rewards or action-labeled demonstrations, neither of which scales. We introduce ASH, an agentic system that learns an embodied policy from unlabeled, noisy internet video, without reward shaping or expert annotation. ASH follows a self improvement loop; when it gets stuck, ASH learns an Inverse Dynamics Model (IDM) from its own trajectories, and uses its IDM to extract supervision from relevant internet video. ASH uses unsupervised learning to identify key moments from large-scale internet video and retains them as long-term memory — allowing it to tackle long-horizon problems. We evaluate ASH on two complementary environments demanding multi-hour planning: Pokémon Emerald, a turn-based RPG, and The Legend of Zelda: The Minish Cap, a real time action-adventure game. In both games, behavioral cloning, retrieval-augmented and zero-shot foundation-model baselines plateau, while ASH sustains progression across our 8-hour evaluation. ASH reaches an average of 11.2/12 milestones in Pokémon Emerald and 9.9/12 in Legend of Zelda, while the strongest baseline gets stuck in both environments at an average of 6.5/12 and 6.0/12 milestones, respectively. We demonstrate that self-improving agents are a scalable recipe for long-horizon embodied learning.