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Recent Submissions

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    Grounded or Guessing? An Empirical Evaluation of LLM Reasoning in Agentic Workflows for Root Cause Analysis in Cloud-based Systems
    (University of Waterloo, 2026-01-16) Riddell, Evelien
    Root cause analysis (RCA) is essential for diagnosing failures within complex software systems to ensure system reliability. The highly distributed and interdependent nature of modern cloud-based systems often complicates RCA efforts, particularly for multi-hop fault propagation, where symptoms appear far from their true causes. Recent advancements in Large Language Models (LLMs) present new opportunities to enhance automated RCA. In particular, LLM-based agents offer autonomous execution and dynamic adaptability with minimal human intervention. However, their practical value for RCA depends on the fidelity of reasoning and decision-making. Existing work relies on historical incident corpora, operates directly on high-volume telemetry beyond current LLM capacity, or embeds reasoning inside complex multi-agent pipelines---conditions that obscure whether failures arise from reasoning itself or from peripheral design choices. In this thesis, we present a focused empirical evaluation that isolates an LLM's reasoning behaviour. We design a controlled experimental framework that foregrounds the LLM by using a simplified experimental setting. We evaluate six LLMs under two agentic workflows (ReAct and Plan-and-Execute) and a non-agentic baseline on two real-world case studies (GAIA and OpenRCA). In total, we executed 48,000 simulated failure scenarios, totalling 228 days of execution time. We measure both root-cause accuracy and the quality of intermediate reasoning traces. We produce a labelled taxonomy of 16 common RCA reasoning failures and use an LLM-as-a-Judge for annotation. Our results clarify where current open-source LLMs succeed and fail in multi-hop RCA, quantify sensitivity to input data modalities, and identify reasoning failures that predict final correctness. Together, these contributions provide transparent and reproducible empirical results and a failure taxonomy to guide future work on reasoning-driven system diagnosis.
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    Enhanced Performance and Stability of Planar Heterojunction Solar Cells via Hole Transport Layer Engineering and Low-Cost Fabrication
    (University of Waterloo, 2026-01-16) Habibzadeh, Elaheh
    Global energy demand has grown extensively in recent decades, and it has continued to rely on fossil fuels that are accompanied with environmental concerns. This has intensified the research for renewable energy alternatives with solar power standing out as a leading candidate due to its abundance, scalability and rapidly declining costs. As photovoltaic (PV) technologies have evolved significantly, their widespread adoption continues to face barriers in efficiency, stability and manufacturing costs. While inorganic semiconductors such as crystalline silicon remain dominant due to their favorable band gap and long-term stability, hybrid solar cells such as organic–inorganic heterojunction solar cells have gained increasing attention for their ability to combine the tunability and ease of processing of organics with the superior charge transport and stability of inorganics. In this work, we have investigated the stabilization of planar heterojunction solar cells through the incorporation of dimethyl sulfoxide (DMSO) into PEDOT:PSS-based hole transport layers (HTLs). The acidic and hygroscopic nature of PEDOT:PSS is a well-known source of device instability, leading to accelerated degradation under ambient conditions. By employing DMSO as a cosolvent alongside ethylene glycol and methanol, this work demonstrates that optimized modification enhances electrical conductivity, reduces recombination, and markedly improves stability. Devices incorporating DMSO-treated PEDOT:PSS films retain nearly 89.4% of their initial efficiency after 72 hours of ambient storage, in contrast to the sharp decline seen in control devices without DMSO. Atomic force microscopy (AFM) and X-ray photoelectron spectroscopy (XPS) confirm improved surface morphology and a favorable redistribution of conductive domains. The findings establish DMSO modification as a practical, cost-effective strategy for producing more inherently resilient heterojunction solar cells. Following these insights, we introduce dimethyl sulfone (DMSO₂) as a solid-state additive for PEDOT:PSS films. Unlike liquid cosolvents, DMSO₂ crystallizes upon drying, inducing a unique reorganization of polymer microstructures that enhances phase separation and alignment of conductive PEDOT chains. The resulting films exhibit superior conductivity, improved charge transport, and greater stability against moisture induced degradation. Devices fabricated with DMSO₂-doped PEDOT:PSS achieve efficiencies up to 15.5% (EMD2) and an average T80 of ∼913 h of ambient storage (ED2), a substantial improvement over conventional treatment. Through a combination of external quantum efficiency (EQE), AFM, and conductivity analyses, this work highlights the ability of DMSO₂ to simultaneously enhance efficiency and extend ambient storage longevity, offering an environmentally benign and scalable pathway for advancing PEDOT:PSS-based solar technologies. We also address the challenge of electrode optimization by introducing a rapid and low-cost method of shadow mask fabrication by desktop 3D printing. While electrode geometry is critical to current collection efficiency, series resistance reduction, and overall photovoltaic performance, traditional fabrication techniques are expensive, time-consuming, and inflexible. By employing polyethylene terephthalate glycol-modified (PETG) filaments for 3D printing, this study demonstrates a streamlined approach to fabricating custom shadow masks for top electrode manufacturing in hours rather than weeks. Comparative testing of three geometries (comb-like busbar, central busbar, and crossed busbar) shows that the central busbar design achieves superior efficiency enhancement by 21.62% and improves the fill factor by reducing resistive losses and balancing optical transparency. This work illustrates how low-cost additive manufacturing can democratize device prototyping, accelerate design iterations, and lower research and production costs without compromising performance. In summary, this dissertation presents a cohesive exploration of strategies to improve efficiency, stability, and fabrication simplicity of planar heterojunction solar cells. Through targeted material modifications and innovative fabrication methods, the studies collectively highlight pathways to bridge laboratory innovation with commercial feasibility. Together, these contributions underscore the critical role of polymer modification and accessible fabrication in the evolution of next-generation solar cells, with the ultimate goal of advancing the prospects of clean, scalable, and sustainable energy technologies.
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    Cellulose Nanocrystal Coated Paraffin Wax Coating for Fog and Dew Water Harvesting
    (University of Waterloo, 2026-01-16) Yan, Riyao
    Fresh water scarcity is an urgent global issue. A sustainable and renewable method is harvesting atmospheric water, among which fog and dew water can be passively collected onto a surface. The efficiency of such collecting systems depends critically on the wetting and dynamic behavior of water droplets on the surface. Common approaches to modify surface topography and hydrophobicity often relies on lithographic, plasma, or fluoropolymer-based methods that are costly, complex, and environmentally unsustainable. In contrast, this work proposes a novel, simple, and bottom-up approach for producing surface with functional coatings through cellulose nanocrystal (CNC)–stabilized Pickering emulsions. The first part of the study focuses on understanding the stabilization and formulation behavior of CNC-based oil-in-water emulsions under varying CNC concentration, ionic strength, and oil-to-water ratios. The resulting interfacial coverage and droplet packing efficiency govern the size and assembly of the wax microparticles, allowing fine control of surface roughness and wettability. Coatings derived from these particles exhibit a wide range of wetting states—from hydrophilic to superhydrophobic—depending on CNC surface coverage and aggregation state. In the second part, these coatings are evaluated for fog and dew water collection, emphasizing the differences between liquid water deposition and humid air condensation on surface. The results show that overall water collection performance is governed by two coupled processes: the rate at which moisture is captured on the surface and the efficiency with which the accumulated water is removed. Previous studies have shown that while superhydrophobic surfaces exhibit superior droplet removal efficiency, their performance can degrade under continuous usage due to partial loss of superhydrophobicity and water film formation. On the other hand, surfaces with balanced nucleation density and drainage efficiency are more desirable, especially for condensation. This research establishes a biobased, PFAS-free, and scalable fabrication route for tailoring surface wettability using CNC-stabilized emulsions. Beyond atmospheric water harvesting, the insights gained here into interfacial assembly and condensation dynamics under realistic humid-air conditions contribute broadly to the design of sustainable coatings for humidity control and anti-fogging/anti-icing applications.
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    Effects of Stabilizing Binder on the Formability, Microstructure, and Mechanical Performance of Wet Compression Molded Unidirectional Non-Crimp Fabric Composites
    (University of Waterloo, 2026-01-16) Miranda Portela, Renan
    Wet Compression Molding (WCM) with highly reactive resins is a manufacturing process capable of high-volume production that has recently gained interest in the automotive industry as an alternative to traditional methods for producing structural components. These components are subject to high loads and may experience impact loads during service; therefore, to achieve the desired mechanical properties and performance requirements, the structural components may require several layers and a significant amount of resin. For typical WCM processes utilizing molds with deep cavities, resin management can be challenging as the fabric stack may drape prematurely due to the mass of the resin; however, the use of binder-stabilized fabric can overcome this problem by enhancing the fabric bending stiffness. While the influence of stabilizing binder on the permeability of various fabrics and the flow characteristics of different resins has been previously studied, its impact on void formation and mechanical performance is less understood. This study focuses on the effects of stabilizing binders on the intra-ply draping mechanisms of wet, unidirectional, non-crimp fabric (UD-NCF), as well as on the microstructure and mechanical performance of the UD-NCF composite fabricated via WCM, which comprises PX35-UD300 carbon fiber fabric and EPIKOTE resin 06150 snap cure epoxy resin, through physical experiments. The objectives of this study are to investigate the influence of the stabilizing binder on the formability of infiltrated carbon-fiber UD-NCF (including membrane behaviour, bending, and compaction), to examine its effects on the microstructure and mechanical performance of UD-NCF composites manufactured via WCM, and to assess the impact of the stabilizing binder on the energy-absorption performance. For Objective 1, the UD-NCF carbon fiber was characterized through a series of physical experiments, including membrane, bending, and compaction tests. An infiltrated bias-extension test setup was used to analyze the membrane mechanism, a rheometer bending test setup was employed to examine the bending mechanism, and a punch-to-plate setup was utilized to study the compaction mechanism. The fabric infiltration was found to influence the membrane and bending behaviors by reducing the friction between the carbon fiber and the stitching yarns, which consequently decreased the membrane stiffness and the bending stiffness up to 30%. However, impregnation was found to have no significant impact on the compaction response due to the low friction of the carbon fibers. In contrast to fabric impregnation, the pre-activation of the stabilizing binder was found to affect all three draping mechanisms by increasing fiber/fiber and fiber/yarn friction, thereby increasing membrane stiffness by up to 100% and bending stiffness by up to 50%. For Objective 2, flat UD-NCF composite panels were fabricated by WCM to examine how the stabilizing binder and its state, as well as the vacuum application to the mold and its duration, influence the formation of voids and mechanical properties. It was observed that the use of binder-stabilized fabrics decreased the void content of WCM parts by up to 70%, likely due to reduced relative layer movement and lower air entrapment. The void size decreases further when a vacuum is applied to the mold for more than 20 seconds, which partially removes air inside the mold. This reduction in void size leads to an increase in interlaminar shear strength. Additionally, applying a vacuum enhances preform compaction, resulting in more consistent panel thickness and a higher fiber volume fraction (FVF). For Objective 3, UD-NCF composite hat channels were fabricated by WCM to examine the influence of the stabilizing binder and vacuum application on energy absorption during axial crush experiments. The use of binder-stabilized fabric and vacuum increased energy absorption; however, this increase was not statistically significant, possibly due to the high FVF of the components. The WCM hat channels achieved energy absorption levels comparable to those of similar hat channels comprising the same constituents and ply stacking sequence and fabricated by high-pressure resin transfer molding (HP-RTM) in a previous study. The WCM hat channels also showed a similar brittle fracture failure mode to the HP-RTM hat channels. The main results of this investigation include a new dataset on the viscous draping mechanisms of the binder-stabilized UD-NCF. Additionally, mechanical tests provided strong evidence of the influence of the stabilizing binder on the mechanical performance of the UD-NCF composites. These results indicate the feasibility of using the WCM process as an alternative to HP-RTM in the manufacturing of structural components.
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    Hybridizable discontinuous Galerkin methods for coupled flow and transport systems
    (University of Waterloo, 2026-01-16) Yackoboski, Elizabeth
    In this thesis, we propose and analyze hybridizable discontinuous Galerkin methods for coupled flow and transport systems. Such systems may be used to model real-world scenarios in which a fluid contaminant travels through another medium. Common applications include environmental engineering problems and biochemical transport. This thesis focuses on the Stokes/Darcy-transport and Navier--Stokes/Darcy-transport systems. We consider a two-way coupling between each flow and transport problem: the solution to the flow problem is directly involved in the transport problem, and the solution to the transport problem appears in the flow problem through a parameter function. In each of our considered systems, the flow problem is stationary while the transport problem is time-dependent. The resulting coupled flow and transport systems are quasi-stationary in the sense that the evolution of solutions to the flow problems over time is driven by the transport problem. Our numerical schemes use a time-lagging method in which the flow and transport problems are decoupled and solved sequentially using hybridizable discontinuous Galerkin methods. This decoupling allows us to establish separate conditions on the discrete flow problem and on the discrete transport problem such that solutions to the combined scheme converge at optimal rates. Moreover, we show how existing results on related discrete flow problems and on the discrete transport problem may be exploited for efficient analysis of the coupled systems. We present this approach in a general setting, and illustrate its use through the specific examples of the Stokes/Darcy-transport and Navier--Stokes/Darcy-transport systems. For all schemes, we establish the existence of unique numerical solutions over a considered time interval. We prove optimal rates of convergence in space and time, and provide numerical examples to support the theory.