About MacSphere

MacSphere is McMaster University's Institutional Repository (IR). The purpose of an IR is to bring together all of a University's research under one umbrella, with an aim to preserve and provide access to that research. The research and scholarly output included in MacSphere has been selected and deposited by the individual university departments and centres on campus.

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REFERRAL PATTERNS OF PRIMARY CARE PRACTICES IN ONTARIO
(2026) Rahman, Bahram; Costa, Andrew; Health Research Methodology
Background: Primary care physicians (PCPs) are critical to Ontario’s health care system, acting as the first point of contact for patients with the system. They play a critical role in facilitating referrals to specialists and laboratory services, as part of clinical decision-making to address patients’ health care needs. However, there is limited understanding of how different primary care practice models impact different aspects of referrals, such as rate of referrals to specialists, communication with specialists about their referrals, and rate of referrals to laboratory medicine services, particularly within the context of Ontario’s primary care reform. This thesis aimed to comprehensively study primary care physician referrals to specialists and laboratory services and examine the association between their practice model and referral rates to specialist services and laboratory medicine. Methods: This thesis includes three independent studies using quantitative observational research methods. Primary care physicians practicing comprehensive care were identified from health administrative databases, and their data was linked to physicians’ billing data (Ontario Health Insurance Plan), population-level patient experience survey data (Health Care Experience Survey) and other health administrative databases. Statistical analyses were conducted to examine the association between primary care physician’s practice models and referral rates to specialist and laboratory medicine services, adjusted for other physician, patient and practice-level factors. Results: The first study showed that primary care physician referrals to specialists vary by practice model and sex. Those in predominantly fee-for-service models referred fewer patients to specialists than those in Family Health Teams (FHTs), Ontario's largest team-based care model. The second study showed that while patients generally across all models reported a high level of information coordination between their primary care physician and specialist, patients rostered to predominantly fee-for-service models were more likely to report that the specialist did not receive the necessary medical information from their primary care physician. The third study found that primary care physicians in FHTs had a lower rate of referrals to laboratory services than those in other primary care practice models. Conclusion: Primary care physician practice models significantly influenced rates of referrals to specialists and laboratory medicine services. Primary care physicians in FHTs had lower referral rates for laboratory services and higher coordination of information with specialists, they had a higher referral rate to specialists and to different subspecialties. These findings emphasize the importance of considering the impact changes to primary care practice models could have on the utilization of specialist and laboratory medicine services as Ontario continues to reform the primary care system and expand team-based care models such as FHTs
Super-Earth Masses and Stellar Abundances from NIRPS Reveal Tentative Evidence for Water-Rich Formation around M Dwarfs
(2026) Weisserman, Drew
Tracing the compositional link between terrestrial super-Earths and their host stars provides clues to their dominant formation pathway. By constraining the stellar abundances of refractory elements, we can predict the core mass fractions (CMFs) of their super-Earths. The level of agreement between this prediction and the planet’s true CMF from their masses and radii can teach us about past formation processes, like mantle stripping and water-rich formation plus sequestration in the planet’s core. Here, we present the first results from the Near Infrared Planet Searcher’s (NIRPS) GTO CMF subprogram: an intensive radial velocity campaign to refine masses of transiting super-Earths and compute their host stellar abundances. We retrieve precise masses for three hot super- Earths around M dwarfs (GJ 1132 b, GJ 1252 b, and LTT 3780 b), calculating masses of 1.69 ± 0.15M⊕, 1.54 ± 0.18M⊕, and 2.34 ± 0.10M⊕ respectively. We measure the CMFs of these and five further hot super-Earths from the literature to 10-15% precision. We compare these to CMF predictions from measuring the Fe, Mg, and Si abundances of their host stars measured from the NIRPS spectra. We find that the CMFs of these planets are smaller than expected from their host stellar abundances, to a statistically significant degree. This discrepancy is suggestive of significant reservoirs of water, generally consistent with water mass fractions of ∼ 1%, sequestered inside the interiors of these planets.
STIMULUS COMPLEXITY AS A DETERMINANT OF VISUAL ATTENTION IN INFANTS
(1963-10) Adrienne Moffet
This thesis is concerned with investigating the extent to which the variable of complexity deter mines visual attention in infants. It was shown that infants looked longer at patterns with a larger number of rparts”, that is, a larger number of enclosed, white, rectangular spaces. This was found to be the case regardless of whether the parts were arranged regularly or irregularly, and regardless of the number of lines or the number of right angled crossings in the patterns. The same stimulus patterns were then shown to adults to be judged for complexity in order to obtain an independent psychological measure of complexity. The results showed that there was little overall agreement between infants’ looking times and adults’ ratings of complexity.
WHEAT AND sugar AGREEMENTS A COMPARATIVE STUDY
(1965-01) Leslie Kenneth
The study analyses briefly the underlying factors of price instability for basic commodities, and relate these to the price instability for wheat and sugar. It then traces the history of wheat and sugar agree ments and notes the significant changes in their development. Finally both agreements are contrasted and the significant lessons drawn
MULTIPLE-TIME-SLOT COMMUNICATION RESOURCE ALLOCATION FOR MULTIPLE ACCESS COMPUTATION OFFLOADING
(2026) Liu, Xiaomeng
The Mobile Edge Computing (MEC) framework has been proposed as a means to address the demand for extending the computational capabilities of small-scale mobile devices, especially in scenarios with tight latency requirements, or devices with limited available energy. This framework enables devices to offload computational tasks to their network access point. When multiple devices seek to offload computational tasks to their access point, the nature of the multiple access scheme plays a critical role in the system performance. The main focus of this thesis is to optimize the allocation of the available communication resources among the offloading devices, so as to minimize a weighted sum of their energy consumption. To effectively allocate the available communication resources, we adopt a multiple-time-slot (MTS) signalling architecture in which different numbers of devices transmit in each slot, according to a chosen multiple access scheme. We consider a common orthogonal multiple access scheme, namely time-division multiple access (TDMA), and various classes of non-orthogonal multiple access (NOMA), including NOMA with independent decoding(ID), NOMA with fixed-order sequential decoding (FOSD), and the “rate-region-optimal” NOMA scheme that is able to achieve any point in the capacity region. The problem is formulated as an optimization problem that involves jointly selecting the devices that will offload, along with optimizing the communication resources, namely the power and rate of each device in each time slot, and the time slot lengths. The solution strategy for this problem is to embed the resource allocation problem within a customized tree search algorithm, for the binary offloading decisions. The thesis firstly explores the case in which the devices and access point are equipped with a single antenna. We show that the communication resource allocation problems for TDMA and the “rate-region-optimal” multiple access can be formulated as reduced-dimension convex optimizations. For NOMA with ID or FOSD, we show that the resource allocation problem has a difference-of-convex structure and we develop a successive convex approximation (SCA) algorithm with feasible point pursuit. Furthermore, for the FOSD scheme we obtain a closed-form expression that provides the optimal decoding order when it is feasible, and efficient algorithms for finding a good decoding order when it is not. In the next step, we explore the case in which the devices and access point are equipped with multiple antennas. For the “rate-region-optimal” multiple access scheme, we show that the communication resource allocation problem can be formulated as a reduced-dimension convex optimization problem. For TDMA, we determine feasibility using the principles of waterfilling, and develop an iterative algorithm based on successive convex approximation (SCA) for feasible cases. For NOMA with ID or FOSD, we show that the resource allocation problem has a difference-of-convex structure and we develop an SCA algorithm with feasible point pursuit. Furthermore, for the FOSD scheme we develop an efficient algorithm for finding a good decoding order that often achieves the same performance as the “rate-region-optimal” multiple access. Our numerical results provide insight into tradeoffs between the complexity of a multiple access scheme (and its resource allocation algorithm), and its performance in computation offloading. Finally, the thesis explores the communication resource allocation problem in computation offloading from an information theoretic perspective. To gain insight into how the choice of the multiple access scheme impacts the feasibility of offloading, we determine the regions of achievable average rates. These regions highlight the role played by the particular form of time sharing enabled by our MTS signalling architecture. To gain insight into the devices’ energy consumption, we consider the region of achievable energies, the boundary of which contains the set of Pareto optimal points for the minimum energy computation offloading problem. This region intuitively illustrates the scenarios in which suboptimal multiple access schemes can achieve the same energy consumption as the “rate-region-optimal” schemes and the gap between them when that is not the case. In particular, it inspires us to prove, analytically, that when the channel gains of the devices are equal, and their energy prices are equal, the minimum possible energy consumption over all multiple access schemes can be achieved using TDMA.

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