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Recent Submissions
Inventing a Bountiful Earth: Settler Science in the Making of New Brunswick, 1763-1859
(2024-10-28) Yeomans, Richard; Not Applicable; Doctor of Philosophy; Department of History; Not Applicable; Daniel Samson; Not Applicable; Aaron Wright; Erin Morton; Jerry Bannister
Inventing a Bountiful Earth explores the ways in which the production of natural and/or scientific knowledge shaped the development of the British settler colony of New Brunswick. It examines the ways in which both the British Imperial government and, after 1786, the House of Assembly of New Brunswick employed science, both its practical application and as an idea, in state formation. Science was an important tool used in the service of empire: through exploration; processes of drawing, surveying, or collecting; and disseminating knowledge about a particular locale via a web of scientific networks circulating across Britain’s expanding empire. Doing so gave Britain an invented dominion over vast swaths of land, including New Brunswick, and projected a form of sovereignty that reinforced the empire’s claim and access to resources across the globe that settler colonies later reproduced.
Chronic Testosterone Deficiency Promotes Maladaptive Remodeling in The Hearts of Aging Male Mice
(2024-10-28) Banga, Shubham; Yes; Doctor of Philosophy; Department of Pharmacology; Received; Dr. Céline Fiset; Yes; Dr. Ketul Chaudhary; Dr. James Fawcett; Dr. Susan Howlett
Testosterone levels decrease with age in men, while the risk for cardiovascular diseases (CVDs) increases. Low testosterone levels are associated with CVDs. Testosterone primarily exerts its effects via androgen receptors (AR), which are also present in the heart. The impact of testosterone on the aging heart is not well understood. We hypothesized that chronically low testosterone levels in aging will have deleterious effects on heart structure and function. However, first we wanted to understand whether physiological testosterone levels in male mice can impact the heart. We found that both young and aged mice with higher testosterone levels had thicker left ventricular (LV) walls and higher LV mass. Testosterone levels in young mice did not influence systolic function, and young mice with higher testosterone levels had prolonged relaxation. By contrast, aged mice with higher testosterone levels had increased ejection fraction and shorter relaxation times. Next, we investigated the effects of chronic testosterone deficiency on heart structure and function across the life course of the mice by subjecting the mice to an early life gonadectomy (GDX). Our results indicated that by 18 months of age, GDX mice had smaller left ventricles and developed signs of diastolic dysfunction. Aged GDX mice also showed QT prolongation and more arrhythmias. Studies in isolated ventricular myocytes revealed increased triggered activity and prolonged action potentials caused by an increase in late inward sodium current (INa-L) in GDX mice. Blocking NaV1.8 channels normalized electrical activity. Since some older men take anti-androgenic drugs for conditions like prostate cancer, we also wanted to understand the effects of flutamide (AR antagonist) on aged hearts. Our results showed that flutamide treatment reduced LV size and mass. Flutamide also prolonged relaxation as well as slowed repolarization. Hearts from flutamide-treated mice also had lower rates of pressure development and decay and increased mRNA expression of certain calcium reuptake genes. Therefore, testosterone levels can influence cardiac structure and function and chronically low levels of testosterone or blocking androgen receptors can cause maladaptive structural remodeling, promote diastolic dysfunction, and slow ventricular repolarization in aging, increasing the risk of developing arrhythmias and heart failure with preserved ejection fraction.
NUMERICAL INVESTIGATION OF DRILLING-INDUCED CORE DAMAGE IN HARD BRITTLE ROCKS
(2024-10-27) Amiri Ramsheh, Fatemeh; Not Applicable; Doctor of Philosophy; Department of Civil and Resource Engineering; Not Applicable; Dr. Gabriel Walton; Yes; Dr. Gordon Fenton; Dr. Dmitry Garagash; Dr. Navid Bahrani
At different design stages of underground excavations, cored samples are taken and tested to obtain geotechnical design parameters. When samples are retrieved from high-stress environments, damage in the form of micro-cracks may result in incorrect estimates of these parameters. This research investigates the impact of coring and overcoring on damage formation and the subsequent implications for geotechnical design parameters, using the well-documented case of the Underground Research Laboratory (URL) in Canada. It involves the generation of two-dimensional (2D) models: a) continuum-based heterogeneous (four mineral types) and homogeneous (one mineral) models; and b) hybrid continuum-discontinuum models consisting of triangular and Voronoi grains. The 2D models are calibrated against the laboratory properties of Lac du Bonnet (LdB) granite and subjected to an unloading (coring) stress path obtained from a 3D continuum model. The simulation results using continuum models highlight the importance of grain-scale property heterogeneity in the formation of unloading-induced damage. The simulated grain and grain boundary damage in the heterogeneous model result in a reduction in Young’s modulus and Unconfined Compressive Strength (UCS) by up to 29% and 22%, respectively. Using the hybrid method, it is demonstrated how grain-scale heterogeneities promote tensile stresses, leading to micro-crack initiation and opening, and subsequent nonlinearity in the stress-strain curve due to crack closure. In the next step, core drilling and overcoring are explicitly simulated using three-dimensional (3D) continuum and discontinuum models for various in situ stress magnitudes and borehole orientations at the URL. The tensile strength and crack initiation stress level of intact LdB granite are used to assess the potential for damage in the 3D continuum models. This, combined with the number of micro-cracks from the 3D discontinuum models, demonstrate an increase in potential for core and overcore damage with increasing depth, with fewer micro-cracks observed in samples drilled parallel to the major principal stress.
Exploring Nitrogen Cycling in Lagos Lagoon, Nigeria: First Steps Towards an Integrated Monitoring Program
(2024-08-18) Orji, Chukwuka; Not Applicable; Master of Science; Department of Earth and Environmental Sciences; Not Applicable; Dr. Suzanne Budge; Not Applicable; Dr. Carolyn Buchwald; Dr. Shannon Sterling; Dr. Douglas Wallace; Dr. Owen Sherwood
Lagos lagoon, a critical coastal ecosystem in West Africa, faces escalating pollution threats from dense human habitation, yet lacks a coordinated water quality monitoring program. This study aimed to provide an integrated baseline of nutrient levels using stable isotope analyses of carbon (δ¹³C) and nitrogen (δ¹⁵N) in sediments, biota, and water. In Chapter 2, δ¹³C values were lower in freshwater-influenced zones and higher in marine-influenced areas, reflecting differences in carbon sources. δ¹⁵N showed predictable trophic enrichment, with minor seasonal effects. Baseline δ¹⁵N values were within the natural range of seawater and soil nitrate, complicating attribution of anthropogenic impacts. Chapter 3 compared nutrient analysis between Canadian and Nigerian labs, revealing discrepancies potentially due to procedural differences. These findings offer a baseline for future monitoring and highlight the need for standardized methods and international collaboration to improve nutrient measurement accuracy and reliability in Lagos lagoon.
ASSESSING THE COMPLETION TIME OF ON-SCENE RESCUE MISSIONS IN THE MARITIME AREAS OF THE CANADIAN ARCTIC USING MARINE OR AIR
(2024-10-28) Rezaei, Parsa; Not Applicable; Master of Applied Science; Department of Industrial Engineering; Not Applicable; n/a; Not Applicable; Dr. Robert Brown; Dr. Colleen Dewis; Dr. Ronald Pelot; Dr. Floris Goerlandt
Increasing shipping in the Canadian Arctic enabled by climate change and economic
growth heighten the need for efficient search and rescue (SAR) operations. Understanding
rescue response times, including the maximum expected time of rescue (METR), is crucial.
Current research lacks detailed metrics on rescue duration, which this study aims to address
by modeling on-scene rescue mission durations based on various influencing factors.
The research employs discrete event simulation (DES) and a Monte Carlo (MC) approach
to estimate the duration of maritime rescue missions in the Canadian Arctic. It combines
expert models to evaluate the weather factors and parameter uncertainties, using scenarios
based on expert insights and literature. The DES model is tested across different Canadian
Arctic locations.
The research indicates that on-scene rescue missions in the Canadian Arctic are notably
prolonged during winter compared to summer, with additional time required if icebreaking
is needed in the vicinity of the incident. Key factors influencing rescue duration include
wave conditions, visibility, air temperature, and wind speed. Adverse sea conditions and
darkness extend on-scene rescue times. The study primarily considers rescues from
lifeboats or life rafts and suggests future research should explore a broader range of rescue
scenarios and vessel types.
EXPERIMENTAL AND THEORETICAL STUDY OF SUSTAINABLE SANDWICH STRUCTURES WITH RECYCLED PET CORE
(2024-10-18) Kassab, Raghad; Not Applicable; Doctor of Philosophy; Department of Civil and Resource Engineering; Not Applicable; Dr. Douglas Tomlinson; Not Applicable; Dr. Kyle Tousignant; Tamunoiyala Koko; Dr. Pedram Sadeghian
This thesis investigates the use of recycled polyethylene terephthalate (R-PET) in the cores of sandwich structures to assess their suitability for integration as part of structural components. It commences with an experimental examination and comparative analysis of beams comprised of two configurations of R-PET cores: R-PET foam and R-PET honeycomb. Building on previous
studies, which focused solely on a limited number of sandwich beams with PET fibre-reinforced polymer (FRP) facings and R-PET foam cores; this research expands the scope by systematically varying core thickness, density, and facing thickness across these configurations. To enhance the sustainability of the sandwich beams, the effect of utilizing bio-resin in the FRP composite facings
was studied, examining how changes in polymer type impact the flexural strength of the beams. Additionally, this study incorporates finite element simulation alongside experimental testing of the sandwich beams to deepen the understanding of the structural properties and potential applications of these materials. The research progresses from beam bending testing and analysis, providing insights into the anticipated flexural performance of large-scale sandwich panels, to creating condensed guidelines for designing structural floors, roofs, and walls using these panels. The final phase involves testing full-scale sandwich panels, with each panel measuring 8 feet (2438 mm) in length, 4 feet (1219 mm) in width, and a core thickness of 6 inches (152 mm), under cyclic transverse loading, reflecting real-world dimensions and conditions. The experimental results are validated through modelling, leading to the creation of a detailed design table. This table provides essential guidance for designers, specifying the maximum allowable spans for the panels under typical dead and live loads, considering both strength and deflection criteria. Through these methods, the research offers insights and practical guidelines for the integration of R-PET core sandwich panels in structural applications.