- ItemOpen AccessKarst Hydrogeology in the Spray Mountains of Kananaskis, Alberta, Canada(2023-09-20) Lilley, Sara; Hayashi, Masaki; Mayer, Bernhard; Lauer, RachelAlpine karst aquifers serve as vital sources of groundwater and play an important role in supporting local ecosystems. This study investigated the hydrogeology of the Watridge Karst Spring in the southern Canadian Rocky Mountains, an example of a snowmelt-dominated alpine karst aquifer with rapid, long-distance flow. An annual water budget suggested a catchment area of around 20 km2 and dye tracer tests revealed groundwater velocities of up to 0.14 m s−1. The aquifer has a hierarchical conduit structure with underflow-overflow dynamics, and year-round discharge is sustained by fracture flow. This dual flow network allows the aquifer to behave similarly to a surface stream over long distances, but also as a large groundwater reservoir. An innovative approach was introduced to estimate groundwater response times to snowmelt in alpine karst springs using diurnal discharge and electrical conductivity fluctuations, expanding upon previous methods using spectral analysis and cross-correlation. A continuous record of response times was obtained throughout the entire snowmelt seasons of 2020 and 2021. These showed that dilution response time steadily increased alongside decreasing hydraulic head, while celerity remained constant. Geologically analogous karst catchments in the Rocky Mountains hold the potential for storing mountain water, which warrants further studies of groundwater flow in these systems. Climate change may impact the hydrological functioning of alpine karst springs, highlighting the importance of understanding these systems for sustainable water resource management.
- ItemOpen AccessPlasticity of Reproductive Traits in Response to Pollen-Limited Fruit Initiation in an Annual Plant(2023-09-26) Mount, Nathaniel James Hamnett; Harder, Lawrence; Rogers, Sean; Reid, Mary; Samuel, MarcusPollination is a highly uncertain and variable process, and insufficient pollination commonly limits seed production and siring success by flowering plants. Due to this unpredictability, plants, particularly those with annual or otherwise semelparous life-histories, could benefit from phenotypic plasticity in their reproductive growth and function that enhances the overall likelihood of pollination and provides some compensation for pollen limitation. To test this hypothesis, three hand-pollination experiments were conducted using a rapid-cycling variety of Brassica rapa to determine whether limited pollination stimulated plastic responses that could increase seed production relative to the fecundity that would be realized in the absence of plasticity. Plants on which a limited fraction of flowers had been pollinated exhibited many differences from well-pollinated plants. Compared to well-pollinated plants, pollination of 25% of a plant’s flowers reduced fruit production, indicating pollen limitation. In contrast, fruit number did not vary with pollination if at least 50% of flowers were pollinated, indicating resource limitation. In response to pollen limitation, poorly pollinated plants produced more flowers than well-pollinated plants, which should increase their overall pollination success. Neither pollen number per flower on terminal racemes nor its siring ability varied with pollination success. However, plants with few developing fruits produced more ovules in distal flowers of their axillary racemes and more seeds per distal fruit on all racemes compared to plants with many developing fruits. Pollen-limited plants with relatively few seeds overall produced larger seeds, which should enhance seed germination and seedling establishment. Overall, pollen-limited plants also opened fewer flowers per day, extending their total flowering period and exposure to pollinators. Nevertheless, pollen-limited plants opened more flowers per day during late flowering, which increased the number of flowers displayed simultaneously and should enhance pollinator attraction. These results indicate that, rather than being helpless against pollen limitation, plasticity of reproductive characteristics allows annual plants to compensate, at least partially, for low per-flower pollination probability.
- ItemOpen AccessRealization of an electromechancial nano-string device(2023-09) Tabesh, Armin; Barzanjeh, Shabir; Barclay, Paul; Oblak, DanielElectromechanics is the field of studying the interaction between microwave resonators and mechanical oscillators. It has been an interesting topic in the recent decade due to its numerous potential applications in science and technology, including ground-state cooling of macroscopic objects, quantum sensing, quantum memory, and quantum transduction. This thesis presents a comprehensive analysis of a project focused on simulating, designing, and modeling electromechanical devices with the ultimate objective of achieving their successful implementation. Through the thesis, after an overview of the theoretical model of electromechanics, I will introduce our design for the device and explain how we simulated it to optimize its characteristics. Next, I will discuss the nanofabrication process we have developed for the device, along with the fundamental aspects of the characterization method and setup. Subsequently, I will present the theoretical model I have developed based on electromechanics. This model has significant potential to open up new avenues for future research, building upon the foundation laid by the current project.
- ItemOpen AccessA Modified Framework to Describe Stress-Strain Behavior and Volumetric Response of Hydrate-Bearing Sand(2023-09-19) Goharzay, Maral; Priest, Jeffrey; Wan, Richard; Karchewski, Brandon; Sudak, Les JozefGas hydrate-bearing sands (GHBS) contain a large volume of methane in the form of hydrate, which makes them an attractive source of energy. Hydrates exert a strong influence on the mechanical properties of sands, where increasing hydrate saturation (Sh) of the pore space leads to an increase in peak strength, post-peak strain softening, and dilation. Methane recovery from hydrates requires dissociation of the hydrate, which involves coupled and complex processes involving methane gas generation, increases in fluid pressure and reduction in effective stresses, along with changes in the mechanical behavior of GHBS, all of which may present potential geo-hazards and engineering challenges. Field-scale hydrate production tests have been carried out to evaluate the potential for methane recovery, however, these have sometimes ended abruptly due to technical failures. For this reason, numerical models are required to evaluate the long-term feasibility of hydrate production and reduce the risk of failure. Thus, the development of an appropriate constitutive geomechanical model is necessary in order to conduct realistic numerical analyses to assess the long-term response of the GHBS reservoir during hydrate production. Early attempts at modeling the geomechanical behavior of hydrate-bearing soils modified the Mohr-Coulomb (MC) model by incorporating a relationship between cohesion (𝑐) and hydrate Sh of the pore space. As the MC model did not capture the overall stress-strain, including volumetric, response of hydrate-bearing sands, recent models have considered Rowe's stress-dilatancy theory. In this model, the increase in strength is related to dilation of hydrate-bearing sand and assumes the impact of hydrate in the pore space to be kinematic in nature (function of soil friction) and ignores any 𝑐 component of the hydrate. Although modifications to Rowe’s theory have included a 𝑐 component, both soil friction (kinematic) and 𝑐 are considered to be constants, although recent laboratory studies suggest that 𝑐 is mobilized and subsequently lost during shearing. In this study, a stress-dilatancy model is developed to better describe stress-strain response of GHBS, including 𝑐 effects. The model includes extensions to the well-known equations for Rowe’s theory to incorporate functions that consider the unique hydrate characteristics, as well as soil density and 𝜎3. The developed model better represents the geomechanical stress dilatancy behavior applicable to GHBS that can easily be implemented in standard elastoplastic models for use in numerical simulations to assess the impact of hydrate, and its dissociation, on the long-term response of a GHBS reservoir.
- ItemOpen AccessDesign Optimization of Truss Structures Using Artificial Neural Networks(2023-09-22) Nourian, Navid; El-Badry, Mamdouh; Dann, Markus; Billah, Muntasir; Xue, DeyiOne of the primary objectives of structural design optimization is to achieve a design possessing the lowest possible weight, while it can safely withstand the effects of external loads. In the case of a truss of a specific topology, the role of an optimization algorithm is to determine the configuration and number of the truss elements as well as their cross-sectional areas. In this study, a novel model is proposed, by which the main optimization problem is decomposed into two more manageable problems: a size optimization within a shape optimization problem. A Deep Neural Network (DNN) is trained to approximate the optimal cross-sectional areas of the elements of a truss with a given shape and support positions. Furthermore, truss structures are characterized by pin joints connected by truss members, a concept that can be analogized to vertices and edges in a mathematical graph. Leveraging this analogy, a Graph Neural Network (GNN) is utilized to exploit the advantages of representing trusses as graphs. Specifically, a graph neural network-based surrogate model integrated with Particle Swarm Optimization (PSO) algorithm is developed to approximate nodal displacements of trusses during the design optimization process. Several truss examples are used to investigate the validity and effectiveness of the proposed optimization techniques in comparison with conventional FEM-based models.