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    Laser Direct Writing of Copper-Graphene Heterostructures for Flexible Devices
    (University of Waterloo, 2026-09-29) Rathod, Shasvat
    Copper conductors, essential building blocks for modern electronics, degrade in performance as devices become thinner and flexible, due to oxidation, grain boundary scattering, poor substrate adhesion, and mechanical fatigue. The hybridization of graphene with metals and metal oxides such as copper-graphene (Cu-Gr) holds promise for enhancing flexible devices by overcoming these challenges. However, current fabrication techniques involve complex, multi-step mixing processes and lack a clear understanding of how graphene integrates with copper. Additionally, the effects of these fabrication methods on copper nucleation, the graphene-copper interface, and microstructure remain unclear, as do their impacts on electrical, thermal, environmental, and mechanical properties. This thesis investigates these topics through three detailed studies using laser direct writing (LDW). First, to simplify the fabrication process, a minimalist LDW technique was developed to create graphene-metal heterostructures and flexible devices by layered fabrication of laser-reduced graphene oxide (LrGO) followed by reduction of CuOx, ZnOx, and FeOx nanomaterials from metal-ion precursors. Supplied laser energy during fabrication, controlled through laser processing parameters, tuned the oxygen functional groups on the LrGO surface and determined the metal oxide composition, which enabled the process to program sensor and junction responses. The sensors showed ranged tunability in: normalized current gains from −2.7 to 3.5, response times of 0.02 and 15 s, and recovery times of 0.04 and 6 s. Additionally, LDW produced LrGO/CuOₓ PN junctions and bipolar transistors with rectification ratios up to 160 and common-emitter current gains of 35.5–38.2. Second, to overcome the weak bonding and voids characteristic of planar interfaces in layer by layer assembled composites, LDW was adapted for simultaneous fabrication of graphene and copper. By tailoring plasma plume physics through a confinement mechanism, the local energy input was controlled to toggle between keyhole and conduction irradiation modes, which respectively governed graphene formation and copper reduction. Modified LDW to initiate keyhole and conduction simultaneously produced distinct Cu-Gr nanocomposite structures, including copper-coated graphene and copper nanoparticles embedded within graphene. The resulting interconnects reached a resistivity of 9.37 × 10⁻⁸ Ω·m and breakdown current density of 1.61 × 10⁸ A·cm⁻², approaching annealed copper. Third, graphene flakes were dispersed in the copper precursor prior to laser irradiation, facilitating the in situ growth of copper on graphene. This growth pathway promotes intimate interfacial contact and uniform distribution while reducing the gaps, contamination, and agglomeration commonly associated with layered assembly of composites, or post-synthesis mixing. Graphene flakes, which substantially changed copper growth mechanisms under laser irradiation, acted as preferential nucleation sites that lowered the minimum laser energy for copper nucleation from approximately 1.5 to 0.4 J mm⁻³, producing a higher density of copper nanoparticles that sintered into a continuous network encapsulating the graphene. The resulting dense composite reached approximately 98% relative density, thermal conductivity up to 1095 W m⁻¹ K⁻¹, and sheet resistance as low as 0.15 Ω sq⁻¹. In summary, this thesis establishes LDW as a process with precise control over graphene and copper formation, progressively increasing graphene integration in Cu-Gr nanocomposites for flexible conductors, sensors, and thermally conductive films.
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    “We Still Have the Land, Right?”: Catholic Agricultural Sites as Hubs for Social and Ecological Teaching in Canada
    (University of Waterloo, 2026-09-29) Szoller, Ben
    This ethnographic research examines the influence of Roman Catholic ecological agro-activism, that is, ecological activism that involves growing food, in Canadian society. For over a century, Catholic social teaching has informed the Roman Catholic Church’s response to various social issues and injustices, especially those brought about by the industrial revolution. More recently, this body of work has incorporated concern for ecological issues such as climate change, over-consumption, and industrial agriculture, and was popularized through the work of Pope Francis and his landmark encyclical, Laudato ‘Si, or Care for Our Common Home. At the same time, local and regional Catholic communities have developed their own unique blend of Catholic social and ecological programming to meet the needs of local parishes, clergy, institutions, and lay people. These top-down and bottom-up activities can appear at times seamlessly connected, disjointed, or even in conflict. As a result, questions remain about the degree to which these principles actually influence the attitudes and behaviours of Catholics. To assess the impact of Catholic ecological agro-activism in public discourse in Canada, this project examines three levels of Catholic activity: regional programming, individual beliefs and practices, and official Church doctrine. I conducted ethnographic research at three Catholic sites to examine how they articulate the Church’s social and ecological teaching through various agricultural programs and advocacy efforts. Methods included participant observation and extensive interviews with regional Catholic leaders, as well as interviews with non-Catholic participants and leaders from other Catholic organizations. I develop my analysis according to four primary themes—places, people, participation, and politics. Key findings include a strong correlation between religious vocations and the formation of ecological “narratives,” the proliferation of partnerships with non-Catholic stakeholders, and the surprising role the COVID-19 pandemic played in bringing greater visibility for the congregations and their skills-training programs. In the end, I argue that these sites act as “hubs” that help develop and deploy a unique blend of Catholic social and ecological teaching to the public through various agricultural projects (organic growing workshops, community gardens, etc.) and advocacy efforts. These hubs promote pro-environmental narratives and influence public discourse through organizational partnerships, various political activities, and the day-to-day interactions of Catholic parishioners and leaders. Such findings help to highlight both the challenges faced by Catholic congregations today and the creativity with which they navigate the Church’s complex structure. Moreover, describing the rural congregations at the heart of these activities helps not only to better understand the unique experiences of rural Catholics, but also the religious landscape in Canada more broadly.
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    How Well Do Large Language Models Detect Bugs in Code Changes?
    (University of Waterloo, 2026-09-29) Yakubu, Ayinde
    This thesis evaluates how well general-purpose open-weight large language models detect bugs in software code changes. The evaluation uses historical development data from the Apache Kafka project obtained through the ApacheJIT dataset. From approximately 12,000 commit records, the dataset was filtered to obtain 524 one-to-one bug-inducing commit (BIC) and bug-fixing commit (BFC) relationships and 530 non-bug-inducing commits. An automated framework was developed to retrieve commit patches, submit code changes for LLM-based review, and record predictions and review comments. Three open-weight LLMs—gpt-oss-120b, gemma-4-31B-it, and Qwen3.6-35B-A3B—were evaluated under a common zero-shot prompting strategy across three repeated experimental runs. Performance was measured using precision, accuracy, recall, F1-score, balanced accuracy, Matthews correlation coefficient, and processing coverage. In addition, an LLM-as-a-Judge procedure assessed whether generated defect reports were semantically consistent with evidence from corresponding bug-fixing commits and Apache Kafka JIRA issue records. The results show that the evaluated LLMs have limited reliability as autonomous defect detectors. Although the models identified subsets of historically labelled bug-inducing changes, substantial numbers of false positives and false negatives were observed. The first gpt-oss-120b run achieved the highest reported recall of 0.5163, while the highest individual-run accuracy was 0.4872. However, comparison with a trivial always-NOBUG baseline showed that model accuracies did not exceed the corresponding baseline accuracies on successfully processed records. Across the reported runs, balanced accuracy remained below 0.5 and Matthews correlation coefficient (MCC) remained negative, indicating weak overall discrimination between BIC and non-BIC benchmark examples. The results further demonstrate that conventional classification metrics alone provide an incomplete characterisation of LLM bug-detection reliability, because useful review requires semantic correctness, actionable explanations, and sufficient project context. Classification metrics alone do not establish explanation quality. The assigned judges rated 16–23% of first-run true-positive explanations as matching the historically documented defect. The findings suggest that assistant-style use is a more appropriate direction for further evaluation than autonomous defect detection. The thesis contributes a real-world evaluation framework, a comparative empirical assessment of three open-weight LLMs, and an evidence-based methodology for assessing generated explanations against historical defect evidence. The results also highlight repository context, semantic grounding, and hallucination reduction as important directions for improving future LLM-based bug detection systems.
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    Combinatorics of the Symmetric Group
    (University of Waterloo, 2026-09-29) Singh, Kartik
    This thesis studies two distinct manifestations of symmetric-group combinatorics in algebra and geometry. In the first, the symmetric group appears as the Weyl group governing decompositions of flag varieties and Grassmannians. In the second, its representation theory motivates the Robinson--Schensted--Knuth correspondence and its connections with crystals, symmetric functions, and positivity. The first part concerns the Deodhar decomposition of the Grassmannian. Deodhar components refine Richardson and positroid-type decompositions and are indexed combinatorially by Go-diagrams. Each component is isomorphic to $\mathbb{F}^a\times (\mathbb{F}^*)^b$ for some non-negative integers $a$ and $b$. Even though the topology of components is simple, the decomposition is not a stratification, and its closure relations are poorly understood. We introduce the \emph{restricted path parametrization}, an alternative parametrization of Deodhar components constructed directly from the pipe dreams associated with Go-diagrams. This parametrization admits a product factorization that makes changes to the filling of a Go-diagram transparent. We use it to describe Grassmannian duality, to organize the terms appearing in Pl\"ucker coordinates through restricted diagrams, and to establish a family of closure relations between Deodhar components. In particular, we prove a codimension-one closure relation arising from a crossing--uncrossing pair of pipes with consecutive labels. The second part studies the Robinson--Schensted--Knuth correspondence and its variants from a crystal-theoretic perspective. Crystal structures make representation-theoretic decompositions combinatorially visible and help distinguish insertion algorithms through their compatibility with crystal operators and natural gradings. We focus on the $t=0$ specialization of the Macdonald polynomials: the $q$-Whittaker functions, whose Schur positivity is encoded by the charge statistic and, equivalently, by the energy function on tensor products of Kirillov--Reshetikhin crystals. These crystals are modelled using multiline queues, which admit a combinatorial correspondence analogous to dual RSK. We show that this correspondence is compatible with the decomposition of multiline queues underlying the nonsymmetric and quasisymmetric refinements of the $q$-Whittaker functions. As a consequence, the $t=0$ ASEP polynomials expand positively in Demazure atoms, giving a nonsymmetric refinement of the Schur positivity of the $q$-Whittaker functions.
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    Passive Microwave Remote Sensing of Terrestrial Snow — Preparing for the Copernicus Imaging Microwave Radiometer
    (University of Waterloo, 2026-09-28) Zschenderlein, Lina
    Seasonal terrestrial snow is a crucial freshwater resource and a fundamental indicator of climate change. Spaceborne passive microwave radiometry is capable of monitoring both snow cover extent (SCE) and snow water equivalent (SWE) on a global scale, by exploiting the distinctive frequency-dependent characteristics of the microwave emission of snow. The main limitation of passive microwave approaches is the coarse spatial resolution which, amongst other reasons, causes systematic underestimation and large uncertainties of both SCE and SWE. The upcoming Copernicus Imaging Microwave Radiometer (CIMR), with its higher spatial resolution and full 360° scan promises substantial improvements—provided current methodologies and the influence of instrument geometry and topography are well understood. In preparation for CIMR, this thesis advances passive microwave snow methodologies through three studies, focused on dry snow detection and its implications for SWE retrieval on hemispheric, continental and regional scales. The first study presents the first comprehensive long-term, hemispheric evaluation of six dry snow detection algorithms for CIMR-like frequencies of SMMR, SSM/I and SSMIS, which are validated against in situ snow depth measurements and IMS snow maps. All algorithms underestimate SCE, but cumulative snow masks counteract this bias during the accumulation season. Implementing the best algorithms within the GlobSnow framework improves SWE statistics, most notably for shallow autumn snow. This highlights the impact that the algorithm choice for dry snow detection has on the quality of SWE retrieval and therefore on long-term climate data records. The second study is the first to investigate WindSat’s near-instantaneous dual-look brightness temperatures for snow mapping over Eurasia. The scan azimuth angle systematically affects detection: south-looking observations (capturing deeper, drier snow on north-facing slopes) consistently detect more snow. Spatially superimposing both looks increases mapped SCE while maintaining high agreement with reference data. Dual-look snow mapping further highlights the need for water-spillover corrections and renews the interest in relief effects. The third study then quantifies, for the first time, how topography affects brightness temperatures of snow-covered land. WindSat’s fore-aft brightness temperatures generally have a high correlation over Eurasia; however, the correlation drops over mountains and during peak winter. This drop, as demonstrated for the Greater Alpine Region in Europe, is due to subpixel rather than coarse-pixel topography and can be expressed through sensor-independent and sensor-dependent characteristics. This motivates topographic corrections on fine spatial scales as well as regionally varying incidence angles within snow retrievals. Overall, this thesis demonstrates that algorithm choice, viewing geometry, and subpixel topography each measurably affect passive microwave snow estimates. These effects and related uncertainties will persist for CIMR, despite the higher spatial resolution, making the findings directly transferable to CIMR snow product development and to global snow monitoring for enhanced climate adaptation and water resource management.