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  • Anisotropy and Non-coaxial Behaviour of Sand Along Different Strain Paths

    Resource Type:
    Thesis
    Creator:
    Selvarajah, Premnath
    Abstract:
    Anisotropic characteristics of granular soil, consolidated to various initial stress states, were evaluated under generalized strain paths using hollow cylinder torsional shear tests. Fraser River sand samples prepared by water pluviation were subjected to isotropic and anisotropic consolidation stresses and sheared under undrained con- ditions along specific strain paths characterized by constant intermediate principal strain parameter (𝑏𝜀) and various fixed principal strain directions (𝛼𝜀). A series of tests along different inclinations of the major principal strain with respect to the vertical depositional direction permitted an assessment of the interaction between principal strain directions and fabric. A decrease in strain hardening tendency is ob- served as the major principal strain aligned towards the bedding plane. Considering different levels of anisotropic consolidation stresses also allowed a detailed examina- tion of how initial static shear affects the responses. In particular, generated principal stresses and their direction, as well as the pore pressure responses, were closely exam- ined. Novel findings, that highlight range of intermediate principal stress parameter (𝑏𝜎) associated with the undrained plane strain condition, and the interaction be- tween 𝑏𝜎 and 𝑏𝜀 during shearing are presented. It was found that 𝑏𝜎 systematically decreases with shear strain in constant 𝑏𝜀 tests. The 𝑏𝜎 value in plane strain tests (𝑏𝜀=0.5) was found to be in the range of 0.2 to 0.4 depending on the loading path, and the stage of shearing. The relationship between principal stress directions and plastic-strain increment directions was assessed to identify the nature of plasticity in the material. In order to ensure confident assessment of non-coaxiality, total strain was decomposed into elas- tic and plastic strain. The existence of non-coaxiality in Fraser River sand (FRS) was observed when the sand was subjected to undrained shear at fixed principal strain di- rections that do not coincide with the fabric axis of symmetry. Non-coaxiality was not observed when the principal directions of stress/strain coincided with the fabric axis of symmetry. It was also noticed that irrespective of the initial condition, the degree of non-coaxiality reduces with increasing shear strain. The influence of initial fabric and principal strain direction on the degree of non-coaxiality was analyzed in detail. Test results show that irrespective of initial condition, the degree of non-coaxiality reduces as the principal strain direction aligns towards the bedding plane direction. The degree of non-coaxiality in FRS at the phase transformation (PT) state and the effect of intermediate principal stress on non-coaxiality were also examined. Different values of degree of non-coaxiality at PT state indicate that the phase transformation state can not be thought of as a good representation of the critical state even though the friction angle at phase transformation has been found to be similar to that at the critical state. The results revealed that the non-coaxial behaviour of soil is also influenced by the intermediate principal stress parameter (which could alternatively be represented by the Lode angle). The influence of non-coaxiality on stress-dilatancy of sand was investigated under generalized loading conditions, and it was found that the effect of non-coaxiality on stress-dilatancy characteristics of the sand was influenced by its initial fabric anisotropy. The effect of non-coaxiality in stress-dilatancy relationship has been investigated within the theoretical framework developed by Gutierrez and Ishihara (Gutierrez and Ishihara, 2000, Soils Found., 40(2):49–59) and Gutierrez and Wang (Gutierrez and Wang, 2009, Granul. Matter, 11(2):129–137) who extended the Rowe’s stress-dilatancy relation to the non-coaxial conditions. Our research study verifies this framework beyond its original context of 2D simple shear tests.
    Thesis Degree:
    Doctor of Philosophy (Ph.D.)
    Thesis Degree Discipline:
    Engineering, Civil
    Date Created:
    2023

  • Toward a "Just, Peaceful and Safe Society:" How Risk Factors and Criminogenic Needs Align with Parole Decisions

    Resource Type:
    Thesis
    Creator:
    Mularczyk, Kimberly Patrycia
    Abstract:
    Board members (BMs), as gatekeepers between continued imprisonment and freedom, decide upon the potential release of incarcerated individuals considered for parole in Canada. Although a focal concern of BMs is community protection, annual Canadian government reports do not contain information on parole populations' criminogenic needs. Literature provides little insight into what factors might relate to parole decisions. In addition, prior research has not compared the risk profiles and release decisions of those who applied for day parole (DP) or full parole (FP) exclusively to those who applied simultaneously. The current dissertation addresses these gaps in two studies using an archival sample of federally sentenced individuals (N = 3,613). The sample includes conditional release and detention decisions made by the Parole Board of Canada between 2010 and 2017 (age at decision: M = 39 years old, SD = 12.80). Study 1 showed that risk/need scores and some institutional (e.g., CSC recommendation) and parole factors (e.g., decision type) predicted conditional release. CSC recommendations predicted release probability for DP (Adjusted Odds Ratio [AOR] = 35.33), FP (AOR = 18.83), and SR (men at a detention review; AOR = 43.94). Moreover, Study 1 found that among those who reoffended on FP (10-32% at one and two-year fixed follow-up) or men who reoffended on statutory release after a detention review (44-80%; at one and two-year fixed follow-up), most revocations (72-75%) first occurred for breaches as opposed to new crimes. Study 2 showed that BMs often imposed special conditions concerning alcohol, avoiding certain persons, drugs, reporting and disclosures, and treatment. Study 2 also found that after accounting for risk/need, the number of special conditions imposed on FP did not predict revocations for any breaches or crimes on FP at one-year (AOR = 1.11) or two-year (AOR = 0.82) fixed follow-up. Future research is required to untangle the potential overlapping variance that unmeasured variables (e.g., prior conditional release successes or revocations) may share with CSC recommendations. Overall, findings support the assertion that BMs use risk/need information to inform decisions and that the number of special conditions imposed does not influence revocation rates after accounting for risk/need.
    Thesis Degree:
    Doctor of Philosophy (Ph.D.)
    Thesis Degree Discipline:
    Psychology
    Date Created:
    2023

  • Towards a critique of state secrecy: Uncovering the rhetorical practices of secret keepers and their legitimization by the discourse of law

    Resource Type:
    Thesis
    Creator:
    Lefebvre, Stephane
    Abstract:
    This thesis examines the rhetorical devices that secret keepers in Canada, the United Kingdom and the United States use to justify the non-disclosure of state secrets. It also examines the manner in which judges in these three countries write and speak about state secrets. By embracing the rhetorical devices used by secret keepers and materializing them in reported decisions, judges add legitimacy to the discourse of secret keepers and directly assist in its reproduction and distribution. Taken together, the discourse of the state and the discourse of law on state secrecy sets up the dominant interpretive frames with which any public engagement, whether supportive or critical, must engage. While the persuasive social effect and perceived legitimacy of this combined discourse may ebb and flow, it appears enduring and difficult to challenge despite the existence of counter-discourses and concessions such as the adoption of access to information legislation. This thesis seeks to understand how state secrecy discourse becomes or appears preeminent, and how it reproduces itself, as a first step in formulating a fuller critique of this discourse.
    Thesis Degree:
    Doctor of Philosophy (Ph.D.)
    Thesis Degree Discipline:
    Legal Studies
    Date Created:
    2023

  • A Web Based Architecture to Operationalize Geospatial Simulation Environments

    Resource Type:
    Thesis
    Creator:
    St-Aubin, Bruno
    Abstract:
    Simulation is inherently multi-disciplinary. It requires knowledge about the system under study, expertise in simulation theory to define models and programming skills to implement models. Geospatial simulation requires an additional layer of expertise in topology, geospatial data structures, spatial analysis, computational geometry, and other related topics. Commercial modeling and simulation software can be used to provide an environment to facilitate simulation studies for users. However, these software tend to be narrowly scoped to specific business applications and tightly couple model and simulator. As such, it is difficult to expand their usage and reuse them outside of the application domain they were intended for. The Discrete Event System Specification (DEVS) is a modular and hierarchical simulation formalism that clearly separates the model, simulator and experiments. It can be used break down the disciplinary silos within which single-use simulators are built and allow users to study real-world systems from a broad range of application domains. In this research, we present an architecture that facilitates the operationalization of DEVS based, geospatial simulation environments in multidisciplinary projects. The architecture relies on a clear definition of roles and responsibilities to leverage the different skillsets in an organization. It considers a series of business processes for modelers, subject matter experts, web developers and end users. It relies on a web-based architecture to provide simulation as a service capability and support users across the entire simulation lifecycle. It seeks to democratize DEVS simulation by making use of the strengths and skills available in larger organizations and by providing the necessary tools for collaboration. Importantly, it preserves key features of DEVS (genericity, modularity, flexibility, etc.) and encourages users to follow best practices in model documentation to foster model reusability and improve model discoverability. It relies on modeling and simulation as a service to overcome technological barriers of entry for DEVS simulation and provide a set of reusable tools to design simulation-based, web applications for end users.
    Thesis Degree:
    Doctor of Philosophy (Ph.D.)
    Thesis Degree Discipline:
    Engineering, Electrical and Computer
    Date Created:
    2023

  • Constrained Geometric Optimization Problems

    Resource Type:
    Thesis
    Creator:
    D'Angelo, Anthony Mark
    Abstract:
    In this thesis we consider constrained geometric optimization problems. The first is a constrained version of the k-Steiner tree problem restricting the Steiner points to lie on a restricted set of curves. We solve the 1-Steiner tree problem in the Euclidean plane in optimal asymptotic time and space bounds when the Steiner point is constrained to lie on an input line. We then show how existing results can be used to generalize the result. The second problem is the smallest k-enclosing disc problem for a point set S contained in a simple polygon. In this problem we work with geodesic discs, meaning we use the geodesic distance function (i.e., the length of the shortest path). We present both a 2-approximation algorithm and an algorithm that finds the optimal radius for the smallest k-enclosing geodesic disc of a set of points inside a simple polygon. The last problem we consider is the smallest k-enclosing geodesic disc problem for a set of points in a simple polygon when the computed disc must be centred on an input chord of the polygon.
    Thesis Degree:
    Doctor of Philosophy (Ph.D.)
    Thesis Degree Discipline:
    Computer Science
    Date Created:
    2023

  • MAWT: Multi-Attention-Weight Transformers

    Resource Type:
    Thesis
    Creator:
    Askin, Enver Deniz
    Abstract:
    Transformers are machine learning models designed to learn and predict sequential and structured data, which are crucial to tasks such as neural machine translation and semantic parsing. They have become state-of-the-art engines for both of these tasks and much research in natural language processing is devoted to increasing their performance by introducing modifications to their architectures. In light of this trend, this thesis introduces a new Transformer architecture called MAWT: Multi-Attention-Weight Transformers in an attempt to increase the accuracy and variety of the acceptable predictions of a Transformer. It attempts to achieve this by training multiple weights per each Transformer attention head, which then are used to test the accuracy of the engine. This creates a new architecture under which the system produces a candidate set of outputs (instead of a singly output), along with a method for selecting from the candidate set. My proposal rests on the assumption -- motivated by statistical considerations -- that having a candidate set increases the probability of finding an exact match within the set. Upon testing, I observed that my system outperforms the regular transformer on 5/6 benchmark neural machine translation and semantic parsing datasets, where engine performance is measured by exact match accuracy. Exact match accuracy demands syntactic identity between the output and the target. In order to investigate how well my new architecture generalizes to measures of semantic equivalence that don't also demand syntactic identity, I also recorded the BLEU scores on these datasets. The BLEU score is a measure of performance based on n-grams rather than exact symbolic match (i.e., how many contiguous sequence of n-many strings from the predicted output match the desired output). The results I report on the BLEU scores are more mixed, raising important questions that I highlight about the role of syntax in measures of semantic equivalence.
    Thesis Degree:
    Doctor of Philosophy (Ph.D.)
    Thesis Degree Discipline:
    Cognitive Science
    Date Created:
    2023

  • Petrogenesis of Mafic-Ultramafic Intrusions in the Southern Goiás Magmatic Arc, Central Brazil

    Resource Type:
    Thesis
    Creator:
    Augustin, Claudia Tharis
    Abstract:
    The Americano do Brasil and Mangabal Complexes belong to a cluster of Neoproterozoic mafic-ultramafic intrusions in the southern Goiás Magmatic Arc in Brazil that lies within the Brasília Belt, a complex, long-lived Neoproterozoic Orogen that formed during the amalgamation of the São Francisco/Congo, Amazonian, and Paranapanema Cratons in western Gondwana. Although deformed and partially recrystallized by a regional metamorphic overprint, the rocks of both complexes still preserve igneous textures. The rocks in both complexes show cumulate textures that range from adcumulate to orthocumulate. Petrography, geochemistry, geochronology, and petrological modeling were carried out to constrain the petrogenesis of the complexes. Modeling indicates that the parental magma for the Americano do Brasil Complex had an OIB-like Fe-rich picrite composition, while the parental magma of the Mangabal Complex could have been a tholeiitic basalt. Considering the temporal and spatial correlations, decompression melting of upwelling asthenosphere triggered by rollback subduction and/or influence of a mantle plume are plausible mechanisms to explain the petrogenesis of these mafic-ultramafic intrusions in the vicinities of the eastern Arenópolis arc and westernmost Anápolis-Itauçu belt. The complexes have experienced a protracted metamorphic evolution with peaks indicating amphibolite facies. The rock from both complexes shows late-stage alteration associated with metasomatism by CO2-Ca-S-rich fluids.
    Thesis Degree:
    Doctor of Philosophy (Ph.D.)
    Thesis Degree Discipline:
    Earth Sciences
    Date Created:
    2022

  • A Theoretical Analysis of the COVID-19 Pandemic using a Public Database

    Resource Type:
    Thesis
    Creator:
    Paul, Subhendu
    Abstract:
    This thesis investigates several issues (incubation and recovery periods, effect of lockdown, digital prognosis, prediction of new cases) of the pandemic COVID-19 based on mathematical models, computational methods and a publicly available database. Traditional compartment-based models have various partitions such as lockdown, susceptible, infected, confirmed cases, recovered, deaths, etc., with the inclusion of several model parameters. The first model is based on a set of coupled delay differential equations with fourteen delays to estimate the incubation period. The estimated mean incubation period we obtain is 6.74 days (95% Confidence Interval (CI): 6.35 to 7.13), and the 90th percentile is 11.64 days (95% CI: 11.22 to 12.17), which is a good agreement with statistical supported studies. The second model is a large-scale extension of the first model, including several hundred groups for recovered individuals and the death toll. This proposed model generates a new refined database of recovery as well as the death toll, the key source for studying recovery and decease periods. The estimated mean recovery period we obtain is 22.14 days (95% CI: 22.00 to 22.27), and the 90th percentile is 28.91 days (95% CI: 28.71 to 29.13), which is in agreement with statistical-supported studies. The third model is an extended SIRS model that includes lockdown as a model compartment. In addition, an electronic application has been developed that allows for a rapid digital prognosis of COVID-19 patients using the information, extracted from the publicly available database of Canadian patients. This tool aims to assist health specialists in their decision regarding COVID-19 patients, based on symptoms and age. Finally, a hybrid approach, a combination of neural networks, inverse problem and Taylor series expansion, based on a second order nonlinear differential equation for the total cases has been derived to forecast COVID-19 cases. The test results show that the proposed prediction model can forecast a range of 55 days.
    Thesis Degree:
    Doctor of Philosophy (Ph.D.)
    Thesis Degree Discipline:
    Applied Mathematics
    Date Created:
    2022

  • Design, Manufacturing, and Characterization of a Novel Ceramic Matrix Composite

    Resource Type:
    Thesis
    Creator:
    Robertson, Taylor
    Abstract:
    A novel ceramic matrix composite (CMC) system consisting of a commercially available SiC fibre, variations of electrophoretically deposited (EPD) fibre-matrix interphases, and a liquid metal melt infiltrated matrix was designed and characterised. A factorial design of experiments approach was undertaken to evaluate the deposition variables which would result in a functioning fibre-matrix interphase. A 25-2 partial factorial design matrix was selected with factors: electric potential, deposition time, surfactant, binder, and solids loading. The design matrix was replicated for four different EPD fibre-matrix interphase coating combinations: Al2O3/SiC, BN/PSZ, ZrC/ZTA, and SiC/Si3N4/SiC. Microcomposites were evaluated for tensile properties using a standard displacement controlled tensile test program. Microcomposites were tested at room temperature immediately following fabrication and following exposure to a standard atmosphere at 1000 °C for 1 h. Samples with ZrC/ZTA and SiC/Si3N4/SiC coatings demonstrated the best tensile properties in room temperature tests while samples with BN/PSZ and SiC/Si3N4/SiC coatings demonstrated the best retention of tensile properties following high temperature exposure. Subsequent SEM analysis revealed that coatings with smaller particle diameters as the inner layer of the fibre-matrix interphase coating produced more uniform coatings and the less fibre degradation due to oxidation following high temperature exposure. Additional microcomposites were fabricated for high temperature tensile testing; however, these samples were unable to bear recordable loads, an SEM examination revealed significant degradation of the matrix phase beneath the high temperature adhesive. Optical microscopy was used to evaluate coating thicknesses of coated fibre bundles prior to heat treatments. Measured coating thickness indicated that generally higher deposition times resulted in thicker coatings; however, coatings produced using 25 V electric potential were thicker than coatings produced using 12.5 V and 50 V electric potentials. This is likely due to a greater deposition efficiency factor at 25 V. FEA analysis was used to evaluate the electrical properties of an idealized version of the stationary EPD cell. This analysis showed a significant variation in the electric field along the fibre axis as well as a significant variation in electrical field between fibres in the centre of the fibre bundle and on the outer edge of the fibre bundle.
    Thesis Degree:
    Doctor of Philosophy (Ph.D.)
    Thesis Degree Discipline:
    Engineering, Mechanical
    Date Created:
    2022

  • Effects of Anaerobic and Aerobic Digestion at Mesophilic and Thermophilic Temperatures on the Quantity of Carbapenem Resistance Genes in Wastewater Sludge

    Resource Type:
    Thesis
    Creator:
    Poorasgari, Eskandar
    Abstract:
    Antibiotic resistance genes (ARGs) encode resistance against antibiotic drugs in bacteria. Carbapenem antibiotics are one of the last lines of defence against bacterial infections and carbapenem resistance genes (CRGs) accumulate in sludge during wastewater treatment. Anaerobic and aerobic digestions are commonly used for sludge treatment. Due to the public health relevance of the land application of digested sludge, this research aimed to investigate the effects of the digestion on the abundance and removal of CRGs. To reach the aim, sludge samples were obtained from mesophilic and thermophilic digesters, sludge DNA was isolated and purified, and target genes were quantified. The target genes included CRGs (blaGES, blaOXA-48 and blaIMP-27), 16S rRNA and Int1. Sharp declines of up to 96.9% in DNA extraction yields were observed during biological digestion. As well, the purity of the DNA isolates declined up to 79.5% in 10 days. These observations indicate that the change in DNA extraction yield was at least partly due to the change in DNA extraction efficiency. Therefore, the absolute quantity of the target genes of each sludge sample was defined as copy number of the gene per unit mass of DNA. The absolute quantity declined during the process, and it was analyzed by kinetic models. The absolute value of the first-order kinetic rate constants followed the order blaOXA-48 > blaGES > Int 1 > 16S rRNA during batch anaerobic digestion. Because gene quantification is time-consuming, costly and sensitive to contamination, multiple regression models were proposed to estimate the abundance of target genes from sludge parameters that are routinely measured for monitoring and design of biological sludge digesters. The multiple regression models were constructed in linear (LM) and non-linear (NLM) fashions. Adjusted R2 ranged 0.352-0.988 and 0.916-0.996 for the LM and NLM models, respectively. Overall, the NLM models predicted the abundance more accurately than the LM models. This research proposed the first NLM models to simulate the abundance of target genes during aerobic digestion of sludge. The NLM models may be useful tools for researchers and practitioners of biological sludge digestion to estimate the removal rate of target genes under different conditions.
    Thesis Degree:
    Doctor of Philosophy (Ph.D.)
    Thesis Degree Discipline:
    Engineering, Environmental
    Date Created:
    2023