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Recent Submissions

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    On the origins of prompt features in time-resolved laser-induced incandescence measurements of metal and carbonaceous nanoparticles
    (University of Waterloo, 2025-12-22) Robinson-Enebeli, Stephen
    Synthetic nanoparticles have become highly beneficial in many applications, including, for example, catalytic conversion, enhancing the functionality of electronic devices, targeted drug delivery in medicine, and purifying water through the removal of bacteria and heavy metals. Nanoparticles are often synthesized through gas-phase synthesis, where the nanoparticles are formed in a bath gas, resulting in a nanoparticle aerosol. Such aerosols are also unintentionally emitted through processes such as welding or combustion. The benefits and negative impacts of nanoaerosols significantly depend on their properties, such as particle size and concentration. Laser and optical-based characterization techniques can provide such information in an in situ and time-resolved manner. Time-resolved laser-induced incandescence (TiRe-LII) is a widely used laser-based diagnostic for soot characterization and is increasingly being applied to non-carbonaceous nanoparticles. The technique involves heating nanoparticles in an aerosol to incandescent temperatures with a laser and recording their radiative emissions with a photodetector, as they cool to the temperature of the bath gas. Nanoparticle properties such as size and concentration are obtained from temporally- and spectrally-resolved measurements through inference techniques that involve regressing a TiRe-LII instrument model to the data. Accurate and reliable inference of the nanoaerosol properties relies on the robustness of the instrument model. Unfortunately, previously developed models do not fully describe experimental observations, and the reported discrepancies need to be reconciled to improve fundamental understanding, modeling capabilities, and ultimately measurements. These discrepancies include effects previously termed excessive absorption and anomalous cooling. The effect of excessive absorption is observed when the measured particle temperatures exceed the values predicted by the related model, and the anomalous cooling was related to the effect that occurred when the measured particle cooling rate, immediately following the peak-temperature phase, is faster than what is predicted based on the model. This thesis work addresses these reported data–model discrepancies, providing insight into laser–nanoparticle interactions in the context of TiRe-LII and the impact of certain experimental conditions. In particular, it is shown that for metal nanoparticle aggregates, radiative properties are enhanced compared to isolated metal nanoparticles, and laser energy absorption becomes spatially nonuniform within aggregates. Under laser heating, the primary nanoparticle may melt; subsequently, the aggregates may partially sinter or coalesce, which further alters their radiative properties as a function of time, phenomena that do not occur in the case of soot. Furthermore, the existence of nanoparticles of different sizes within the aerosol and spatial energy variations across the irradiating laser sheet influence the data in ways that are not accounted for in current TiRe-LII instrument models. The investigations combined theoretical modeling and experimental work. The modeling utilized several light absorption models to explore the light–matter interactions between nanoaerosols and the electromagnetic field of the laser. The experimental component employed calibrated, time- and spectrally-resolved detection techniques to observe the radiative emissions from irradiated particles within the aerosol. The findings of this thesis contribute to a deeper understanding of laser–nanoparticle interactions and open new avenues for further research in this area.
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    Advanced venous flow dynamics and return mechanisms during physiological stress and aging
    (University of Waterloo, 2025-12-22) Cohen, Jeremy
    Human veins are dynamic vessels responsible for managing return of blood to the heart. Unlike arteries, veins are structurally limited, creating exceptional hemodynamic susceptibility to hydrostatic forces and pressure generating forces. The precise extent of venous flow regulating mechanisms to these forces have implication for disease pathogenesis yet have been historically limited by technological tools. Thus, the purpose of this thesis is addressing the responses to hydrostatic volume stress, muscle pump activation and healthy aging through the piezoelectric lens of vector flow imaging ultrasound through a series of projects. First, progressive hydrostatic volume stress is applied to the internal jugular vein to address regional flow complexity and volume expansion behaviour. The internal jugular vein presented step-wise volume expansion in a trapezoidal shape and increasing flow complexity, increasing the risk for flow stasis and thrombus formation. Second, hydrostatic volume stress is used to compare artery-adjacent and non-adjacent veins to probe the existence of an arterial pump. During relevant hydrostatic driving forces, artery-adjacent veins demonstrated a preservation of venous flow, suggestive of a newly described mechanism of venous and an elegant conservation of mechanical energy within the cardiovascular system. Third, a comparison of younger and older adults leveraged differences in venous compliance to investigate flow complexity features during muscle pump activation during hydrostatic volume stress. Older adults were found to utilize their lower compliance to maintain venous ejection efficiency, whereas younger adults experienced great turbulence and vorticity flow features for the same venous outflow. Finally, venous valves were explicitly investigated during progressive hydrostatic volume stress and muscle pump activation to describe flow complexity features. Healthy valves generated efficient forward jets with downstream disturbed, low-shear zones, and volume stress amplified regional differences, underscoring the role of valve geometry in venous hemodynamics. Together, these studies establish new mechanistic links between venous structure, hydrostatic and muscle pump forces, and aging, advancing understanding of venous flow regulation and its implications for thrombotic risk and cardiovascular health.
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    Studies on the Characterization and Measurement Optimization of Superconducting Microwave Resonators
    (University of Waterloo, 2025-12-22) Chen, Mengyang
    This work presents a study aimed at improving the accuracy and efficiency of low-temperature loss-tangent measurements in superconducting resonators. Measurements were performed on aluminum and niobium devices, where a plateau in the internal quality factor at the single-photon level was observed, consistent with prior reports. By truncating the acquired resonance data, it was shown that the loss tangent experienced no systematic shift even when only four points spanned the resonance linewidth; the resulting increase in uncertainty was attributed to reduced effective averaging. Based on this result, an optimized data acquisition scheme was developed, reducing measurement time by a factor of four while maintaining approximately 1% accuracy. Further improvements were achieved through the use of a lower-noise HEMT amplifier, which reduced measurement noise and decreased acquisition time to 60% of the original. Additional circuit modifications showed that improved infrared shielding reduced total resonator loss, while the nonlinear behavior at high RF power was attributed to intrinsic device nonlinearity rather than external circuitry. Finally, crossover temperature measurements showed agreement with BCS theory at high temperatures, although its accuracy could be limited by not fully saturated TLS-loss, indicating the need for improved device designs.
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    Revisiting the ‘Lensing is Low’ Problem With UNIONS
    (University of Waterloo, 2025-12-22) Campbell, Martine
    In this thesis, we present new measurements of the galaxy–galaxy lensing (GGL) signal around Baryon Oscillation Spectroscopic Survey (BOSS) CMASS galaxies using background sources from the Ultraviolet Near-Infrared Optical Northern Survey (UNIONS). With an overlap of approximately 2650 square degrees between CMASS lenses and background source galaxies—the largest to date—we obtain precise large-scale GGL measurements. With these new measurements, we revisit the so-called ‘lensing is low’ problem, wherein galaxy–halo connection models calibrated on clustering data over-predict the GGL signal by 20–40% under cosmic microwave background (CMB)-based cosmologies. We model the galaxy–halo connection using a halo occupation distribution (HOD), and perform joint fits to both GGL and clustering signals across a wide range of scales, as well as a clustering-only fit. Similar to previous work, we find a lensing–is–low effect in the CMASS sample, although our GGL and clustering predictions are less inconsistent with each other. The best joint fits are achieved by lowering the amplitude of the matter power spectrum relative to Planck 2018, driven by the precision of our large-scale GGL measurements. Once a lower matter power spectrum amplitude is adopted, feedback is the only HOD extension that further improves the joint fit. Our feedback model redistributes matter within a halo, modifying the halo–matter cross–power spectrum. Overall, we find that two models describe our observables equally well: one where HOD and cosmological parameters are free, and one where HOD, cosmological, and feedback parameters are free. Importantly, we emphasize the role of large scales in driving the lensing–is–low effect, shifting the narrative away from a purely small-scale issue.
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    Influence of Cellulose Nanocrystals and Surfactants on Catastrophic Phase Inversion and Stability of Emulsions
    (University of Waterloo, 2025-12-22) Kim, Hyungseak
    This thesis presents the first quantitative comparison of catastrophic phase inversion in emulsions stabilized by nanocrystalline cellulose (NCC) versus surfactants. NCC extends stability limits, raising the critical aqueous fraction from 0.253 to 0.545. Conversely, surfactants show non-monotonic behavior, delaying inversion at low concentrations and accelerating inversion at high concentrations. These findings demonstrate the effectiveness of NCC in high-internal-phase systems, validating its potential as a robust, bio-based stabilizer for industrial applications.