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    Multi‑source analyses of average treatment effects with failure time outcomes
    (Springer Nature, 2025-07-04) Wen, Lan; Steingrimsson, Jon; Robertson, Sarah; Dahabreh, Issa
    Analyses of multi-source data, such as data from multi-center randomized trials, individual participant data meta-analyses, or pooled analyses of observational studies, combine information to estimate an overall average treatment effect. However, if average treatment effects vary across data sources, commonly used approaches for multi-source analyses may not have a clear causal interpretation with respect to a target population of interest. In this paper, we provide identification and estimation of average treatment effects in a target population underlying one of the data sources {in a point treatment setting} for failure time outcomes potentially subject to right-censoring. We do not assume the absence of effect heterogeneity and hence our results are valid, under certain assumptions, when average treatment effects vary across data sources. We derive the efficient influence functions for source-specific average treatment effects using multi-source data under two different sets of assumptions, and propose a novel doubly robust estimator for our estimand. We evaluate the finite-sample performance of our estimator in simulation studies, and apply our methods to data from the HALT-C multi-center trials.
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    Doubly Robust Estimation of Monotonic Survival Curves for Time-Varying Treatments in Observational Studies
    (De Gruyter Brill, 2026-09-18) Wen, Lan
    Doubly robust estimators of the longitudinal g-computation formula enhance robustness against model misspecification, offering an improvement over the standard inverse probability weighted estimators. However, existing doubly robust estimators for discrete-time survival outcomes do not necessarily guarantee that the estimated survival curves remain monotonic. In this manuscript, we propose a novel estimator of the g-computation formula specifically designed for discrete-time survival outcomes, ensuring that the resulting estimated survival curves are monotonic in the presence of treatment-confounder feedback and simultaneously guaranteeing double robustness at all time points. We establish theoretical properties of this estimator and compare its performance with existing estimators that do not impose monotonicity constraints. Through simulation studies, we compare our proposed approach with existing methodologies in terms of bias, efficiency, and robustness under various model misspecifications, and demonstrate its application using an illustrative real-world dataset.
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    Individual Qubit Manipulation Using Dual Acousto-Optic Deflectors in a Trapped Ion Quantum Processor
    (University of Waterloo, 2026-09-30) Patil, Sakshee
    Quantum processors offer computational advantages over classical computers by lever- aging quantum phenomena such as superposition and entanglement to efficiently solve certain classes of problems. Trapped-ion systems represent one of the leading platforms for quantum information processing, owing to their long coherence times, high-fidelity state preparation and measurement, high-fidelity quantum gates, and native all-to-all qubit con- nectivity. However, scaling these processors introduces significant challenges, including the need for increasingly complex control systems and improved stabilization against en- vironmental noise. In particular, scalable trapped-ion architectures require the ability to individually address and precisely control selected subsets of qubits while maintaining high-fidelity operations. Here I present my contributions toward the development and characterization of an individual ion addressing system for a scalable trapped-Ytterbium ion quantum processor. A common method of implementing coherent gates in 171Yb+ is via laser beams that are tuned in frequency far away from any atomic transition, relying on a stimulated Raman transition instead. Additionally, the light momentum is capable of coupling to the motional degrees of freedom of the ion, creating the ‘bus of entanglement’. By investigating the im- pact of experimental imperfections on single-qubit gate fidelities, I establish the tolerances that such an optical individual addressing system must satisfy to achieve high-fidelity gate operation. Based on these requirements, I develop an acousto-optic deflector (AOD)-based optical architecture that provides fast, programmable spatial control of addressing laser beams. The design is validated through optical simulations before being experimentally implemented and characterized in comparison to the requirements established for main- taing high-fidelity gates. Based on our trap parameters, I verify that the AOD optical relay is capable of providing an array of beams spaced apart by∼4 µm, though we have the controls required to match the beams to a non-uniformly spaced chain of ions. The global beam drift of this array of beams is intrinsically less than the proposed beam waist at the ion location, owing to the mechanical engineering practices employed in the optics design. Though the optical cross-talk at an intermediate image plane is greater than design re- quirements, there is room for improvement via custom-optics solutions or active aberration compensation. Finally, I model the decoherence of the qubit state due to heating up of ions along the chain, as these axial vibrational frequencies are lower and often hard to cool to their ground states – a necessity for high-fidelity quantum operations. In this thesis, I propose an optical solution that enables the real-time coupling of the laser momentum to the axial motional modes via a commerically available galvonometer mirror. Overall, the optical scheme presented in this thesis should be able to individually ad- dress a linear chain of around 50 ions, spaced by approximately 4 µm. This is greater than the anticipated number of useable qubits in this processor, where the limiting factors are likely dominated by diminishing fidelity in coherent operations due to spectral crowding of the vibrational modes as the system size scales up.
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    Unsplittable Multicommodity Flows
    (University of Waterloo, 2026-09-30) Aleman Espinosa, David
    An instance (G,u,H,d) of multicommodity flow is given by an undirected graph G=( V, E(G) ) with edge capacities u: E(G)→ℝ, and a collection of source-sink pairs (s_i,t_i) in V with associated nonnegative demands d(s_i, t_i). It will be convenient to think of the source-sink pairs as forming the edges of a demand graph H=( V, E(H) ). The problem is to determine the existence of a flow x that routes all the demands and that does not violate the edge capacity constraints, i.e., x(e) ≤ u(e) for all e ∈ E(G). An instance is feasible if such a flow exists. In the standard multicommodity flow setting, the demand between a source-sink pair may be split across multiple paths. In this thesis we focus mainly on two classes of instances for which feasibility has a nice characterization, the cut-condition: for every cut, the total demand crossing the cut is at most the total capacity of the edges crossing it. Okamura and Seymour showed that the cut-condition is sufficient for routing demands in outerplanar graphs. Seymour showed that the same result holds when G+H is planar. We study the unsplittable version of the problem and prove that, if the cut-condition is satisfied for either of these two classes, then each demand can be routed along a single path while exceeding the capacity of any edge by at most an additive amount of 2Dmax, where Dmax denotes the maximum demand value. We also show that both of these results are almost tight.
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    New Nomadism in the Mongolian Gobi
    (University of Waterloo, 2026-09-30) Battur, Khuslen
    Nomadism refers to a spatial practice in which people move cyclically or periodically from one place to another to sustain their livelihoods. In Mongolia, this way of life has been central to cultural identity, social organization, and resilience for centuries. Historically, Mongolian cities were temporary encampments that moved in response to seasonal conditions, resource availability, and political needs. Even today, Mongolian traditional pastoral herders make up one of the world’s largest last remaining nomadic cultures. An estimated one-third of Mongolia’s population continues to practice pastoral nomadism, relying on animal husbandry and the stewardship of ancestral lands that have been passed down for millennia. However, after decades of political, economic, and environmental transformation, Mongolia’s nomadic way of life is increasingly challenged by the pressures of urbanization, climate change, land privatization, and resource extraction. In the Great Gobi region of Mongolia, this shift is much evident, where prolonged drought, desertification, and land degradation have accelerated rural displacement and forced many families to abandon their herding livelihoods. This thesis examines how architecture can respond to the changing conditions of Mongolian pastoralism and proposes a new form of nomadism that strengthens the resilience, autonomy, and continuity of herder communities. The intervention focuses on Gobi herders, exploring how a network of infrastructure and mobile, temporary spaces can support seasonal movement, provide essential services, and reinforce social and ecological stability of nomadic living.