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    Characterizing the effects of diel temperature fluctuations on thermal and hypoxia tolerance in adult zebrafish
    (University of Waterloo, 2026-04-10) Clow, Tanner
    Aquatic ecosystems naturally experience temperature fluctuations, which are often accompanied by shifts in dissolved oxygen. However, climate change has exacerbated the prevalence and magnitude of these fluctuations, often leaving organisms exposed to sub-optimal conditions. Due to their inherent relationship, these abiotic factors are thought to share common signalling pathways (cross-talk) and protective mechanisms (cross-tolerance) that confer cross-protection. Much of what we understand about the effect of temperature on fish originates from static exposures, despite physiological performance differing in fluctuating environments. Therefore, in this study, I aimed to determine whether diel temperature fluctuations influence thermal and hypoxia tolerance, while simultaneously characterizing the underpinning molecular and biochemical adjustments. Three experimental series were conducted, during which adult zebrafish were acclimated to either static control conditions (27ºC) or a thermal flux (23-33ºC) for approximately two weeks. Following the acclimation, I quantified whole-animal tolerance (critical thermal maximum and time to loss of equilibrium), heat-shock response genes (heat-shock proteins; hsp70 and hsp90αα), hypoxia response genes (hypoxia-inducible factor 1 alpha: hif-1αb; insulin-like growth factor binding protein: igfbp1), microRNAs (let-7d-5p, miR-301c-5p, miR-29a, miR-22b-3p), heat-shock proteins (Hsp70 and Hsp90α), and enzymatic activity (lactate dehydrogenase: LDH; citrate synthase: CS; pyruvate kinase: PK) in the brain and liver tissue. Together, the data suggest that fish acclimated to diel thermal variability exhibit distinct molecular and biochemical responses that may be involved in the observed increase in thermal and hypoxia tolerance
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    Optimizing Weld Geometry for High-Speed Wire-Fed Laser Welding of Thin-Gauge Press-Hardened Steel
    (University of Waterloo, 2026-04-10) Embleton, Andrew
    As the automotive industry continues to prioritize fuel efficiency and performance, the demand for stronger, lighter materials, such as press-hardened steel (PHS) increases in vehicle design. This research examines the impact of high-speed wire-fed laser welding parameters on the final weld bead geometry for thin-gauge Al-Si coated PHS sheets used as tailor welded blanks. The primary objective is to determine the optimal laser welding parameters that consistently produce defect-free welds, with reinforcement and undercut values not exceeding 10% of the material thickness, while achieving the highest possible travel speeds. A comparative analysis is conducted on key welding parameters including laser spot diameter size, laser power, wire feed speed, travel speed, and sheet gap size to establish best practices for laser welding in thin-gauge press-hardened steels. To identify the individual contribution of each laser welding parameter on the final weld geometry, a variety of welding conditions are tested such that the individual influence of each specific welding parameter is isolated and compared against macroscopic weld cross-sectional measurements, primarily focusing on the degree of excess reinforcement and undercut. It is shown for welding 1 mm thick Al-Si coated PHS blanks that utilizing a laser spot diameter size of 0.6 mm, a laser power of 4500 W, a wire feed speed of 2.75 m/min, a travel speed of 8 m/min and a sheet gap size of 0.04 mm consistently produced welds with geometry not varying by more than 10% of the base materials thickness for undercut and excess reinforcement. These findings provide a better understanding of laser welding parameters required for welding Usibor®1500 at higher welding speeds.
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    Rigorous Security Proofs for Practical Quantum Key Distribution
    (University of Waterloo, 2026-04-08) Tupkary, Devashish Jayant
    This thesis is concerned with the rigorous security analysis of practical Quantum Key Distribution (QKD) protocols, using a variety of modern proof techniques. Throughout, the emphasis is on mathematical rigor across a wide range of security proof frameworks. We begin by presenting a security proof for variable-length QKD protocols against IID collective attacks, which represents the first such result for generic QKD protocols. We then show that this analysis can be lifted to hold against coherent attacks by an adversary, using the postselection technique. In doing so, we extend the application of the postselection technique to practical QKD protocols, and resolve a long-standing flaw in the method, thereby placing its application to QKD on a rigorous mathematical footing. We next study security proofs based on entropic uncertainty relations. These proofs proceed by bounding the so-called ``phase error rate", using the observed statistics available in the actual protocol. All known methods of bounding the phase error rate require strong assumptions on hardware: namely, that all detectors have exactly equal probability of detection. This renders these security analysis inapplicable to practical QKD scenarios. We show that such phase error rates can be bounded even when detectors are imperfect and only approximately characterized. This resolves a long-standing well-known open problem of nearly two decades, and renders this proof technique applicable to realistic scenarios. We then study security proofs using the recently obtained marginal-constrained entropy accumulation theorem, and obtain a highly rigorous and general result for the security analysis for practical QKD protocols. Most importantly, the proof is constructed in a transparent and self-contained manner, and is designed to be a key ingredient in certification efforts for QKD. Moreover, it can be easily modified to apply to other protocols of interest, and to device imperfections and side-channels. We also revisit the assumptions on authentication traditionally made in QKD security analyses, which assume that all classical messages are delivered faithfully and on time, without any aborts. We show that these assumptions are generally unrealistic, and that adopting realistic authentication assumptions necessitates a modification of both the standard QKD security definition and the corresponding security analysis. However, under mild and easily satisfied protocol design conditions, security under realistic authentication can be reduced to the usual idealized setting. As a result, existing QKD security proofs can be lifted to the realistic authentication setting with only a minor protocol modification. A distinctive feature of this thesis is its unified presentation of multiple major QKD security proof frameworks using consistent protocol descriptions and notation. This first-of-its-kind treatment enables direct comparison and contrast between different approaches, a perspective that is often obscured when these techniques are developed in isolation. Consequently, this work is intended not only as a collection of new technical results, but also as a pedagogical reference for understanding rigorous security analysis in quantum key distribution.
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    Physically-Based Simulation and Visualization of Optical Phenomena Elicited by Negative Refraction
    (University of Waterloo, 2026-04-08) Steinfield, Scott
    Metamaterials characterized by a negative refractive index are being the object of intense research across a broad range of fields, from mathematics and physics to photonics and engineering. Nonetheless, the development of materials exhibiting this property in the visible spectral domain remains challenging. This situation, along with their potential transformative role in new technological advances, has motivated the scientific community to instrumentally employ computer graphics software to visually explore their interactions with light. In this work, we contribute to the initiatives in this area by describing a white-box methodology aimed at the physically-based simulation and visualization of optical phenomena elicited by these materials. We demonstrate its suitability to applications, both within and outside computer graphics, through the rendering of images depicting these phenomena under different optical scenarios, including those not examined in the literature to date.
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    Application of Latent Class Analysis to Examine the Association Between Allostatic Load and Profiles of Perceived Stress and Lack of Support Among Firefighters in the Waterloo Region
    (University of Waterloo, 2026-04-08) Adejumo, Seun
    Background and Objectives Firefighters are often exposed to significant occupational hazards due to the demanding nature of their work. They are repeatedly exposed to trauma, physical strain, and emotional pressure because they are daily faced with fire rescue calls that involves live and properties. Such exposures make firefighters vulnerable to events that cause both physical and psychological stress. The cumulative effect of occupational stress among firefighters over the course of their career leads to wear and tear of their body system, and this has negative impact on their health outcomes. Additionally, their perception of stress may influence how they process and respond to everyday demands, which in turn could change their psychological resilience, quality of sleep, emotional regulation, and overall well-being. The effects of perceived stress may be further compounded when social support, which is meant to be a resiliency factor is lacking. With these points in mind, this thesis proposed a new paradigm of using validated instruments from the domains of psychosocial stress (PSS-10, SOOS-14) and social support (MS-PSS, SSS-FF) to develop a multidimensional profile, which we called Perceived Stress and (lack of) Support. In particular, this thesis used Latent Class Analysis as a means of modeling Perceived Stress and (lack of) Social Support Profiles (PSSP) via the aforementioned variables. This new concept of PSSP was motivated and applied to data gathered from firefighters in the City Waterloo. With these data, we examined the association between our proposed PSSP, and physiological stress captured by an Allostatic Load Profiles (ALP; developed for the same participants by Elliot 2024). This approach provided an understanding of how perceived stress and lack of social support can co-exist and their association with physiological wear and tear in this high-risk population. Methods This study used male-only data from the firefighter’s study in Waterloo. Latent class analysis (LCA) was applied to identify PSSP based on validated psychosocial indicators. Then, the ALP that was previously developed from physiological biomarkers in the same male-only data was used as the outcome variable in logistic regression models to examine its association with PSSP as the predictor variable. Furthermore, these models sequentially adjusted for relevant occupational and behavioural confounders which included length of service, sleep disturbance, alcohol use, exercise, and smoking. Finally, sensitivity analyses were conducted to assess the stability of the aforementioned objectives when using the pooled study sample, which included both male and female firefighters. Results For the male-only sample, approximately 50% of firefighters were classified into the elevated-ALP, while 70.1% were classified into the high-PSSP. The pooled sample had about 25.4% of firefighters with elevated ALP and 65.1% high PSSP class. Logistic regression results for the male-only sample indicated a positive association between elevated-PSSP and high-ALP; however, this association was not statistically significant in unadjusted (OR = 1.25, 95% CI: 0.38 – 4.51) and adjusted models (OR range 1.01 – 1.10). Adjusted models controlled for length of service, sleep disturbance, alcohol use, exercise, and smoking. Sensitivity analyses yielded similar results with narrow confidence intervals (CI), but still not statistically significant. Conclusion This study expands understanding of occupational stress in firefighters by showing that perceived stress and lack of social support co-occur as a distinct psychosocial profile. The association between the ‘high perceived stress and lack of social support’ profile and ‘elevated allostatic load’ profile was consistently positive, regardless of adjustment for confounders. Future research should build on these findings by using longitudinal designs and larger samples to inform occupational health interventions that simultaneously reduce stress and strengthen support systems within this unique sample.