Mines Repository (Colorado School of Mines)
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Magnitude and variation of lower limb joint moments and muscle excitations are symmetric during hopping
No full textAsymmetric muscle strength can influence dynamic movement in a variety of tasks and across the lifespan. While asymmetric muscle strength can occur from continuous and repeated use, most studies focus on single rep, maximal effort tasks, often with high-performing athletes. Comparing tasks of varying difficulty may help characterize muscular and movement asymmetry. Net joint moments are useful to determine mechanical requirements of dynamic tasks and are largely a result of muscle strength. Therefore, this study aimed to compare lower limb joint moments between legs for single-leg and double-leg hopping tasks in young, healthy individuals. Nine participants (4M/5F, 22.1yrs ± 3.2yrs, 1.73m ± 0.09m, 66.98kg ± 11.94kg) completed a baseline double-leg hopping task and bilateral single-leg hopping tasks. Kinetic (2000hz) and full-body kinematic (200hz) data were collected at self-selected frequency, averaging 11.11 and 8.11 cycles over 15 seconds for double-leg and single-leg tasks, respectively. Each cycle was defined from ground contact to subsequent ground contact. A 12-segment dynamic model was used to compute sagittal-plane joint moments at the hip, knee and ankle. A paired t-test revealed a significant difference between legs in bilateral peak hip joint moment during double-leg hopping (p=0.015), but there were no differences between legs at the knee or ankle, or during single-leg hopping. F-tests found no difference in peak moment variance between legs for any joint for either task. These findings indicate symmetric joint moment variation and magnitude for tasks of differing mechanical demands in young, healthy participants. Future work will evaluate a broader population
Acanthite
No full textPhotographed by Ron Wolf.Vitreous dark grey mass of acanthite, Cobalt district, Ontario, Canada
Forecasting the timeline for quantum advantage and economic viability using option pricing
No full textIncludes bibliographical references.2024 Spring.The potential for quantum computing to significantly reduce the time necessary to process and analyze data has attracted the attention of major financial institutions. These companies are continually researching ways to accelerate data processing and analysis to react faster to market changes and improve the results of their decisions. Quantum computing holds promise as a “game changer” for several different financial applications such as modeling, risk analysis, portfolio planning and automated trading. However, it is unclear if and/or when a quantum computing advantage will exist over current methods and computers. Estimates for such an advantage range anywhere from 3 to 20+ years in the future. The purpose of this project is to provide guidance on when quantum computing will be economically viable for the finance industry. To focus the research, a specific type of finance application: option pricing, was chosen for analysis. Based on this research, an economically viable quantum computer for option pricing will not be available until 2037 at the earliest, with a more likely timeframe of 2040. Further, the payoff period for investment could take another 3 to 5 years. This paper covers available data for predicted improvements in quantum computing hardware, and improvements in algorithms for option pricing, to forecast when such a computer will be available
CO₂ flooding impact on compositional changes and their effect on elastic properties in oil reservoirs
No full textIncludes bibliographical references.2024 Fall.This research aims to enhance our understanding of the CO2 interactions with the reservoir oil and brine and, consequently, improve the methods for monitoring and tracking CO2 distribution within the reservoir via P-wave velocity responses in a seismic survey. The research was motivated by the growing importance of CO2 utilization for enhanced oil recovery (EOR) and subsequent sequestration. As for the outcome, this study quantifies the effect of CO2 mixing with reservoir fluids on the elastic reservoir properties to further evaluate the hypothesis from a previous study (Oduwole 2022) that showed that not accounting for compositional changes in oil during CO2 injection would lead to an underestimation of the magnitude of the bulk modulus of the actual response.
This study uses a compositional reservoir simulator software, GEM (from Computer Modelling Group, CMG) to simulate CO2 injection and its subsequent effects on the fluid and petrophysical properties, specifically, the reservoir’s bulk modulus and acoustic velocity. This research employed two different fluid systems to compare a heavier oil composition with a lighter composition—both in miscible and immiscible conditions to determine the effect of fluid segregation during flooding. Additionally, the study compares two different approaches that implement Gassmann fluid substitution calculations to estimate bulk modulus and acoustic velocity based on the compositional reservoir simulation results: a black oil approach of Gassmann fluid substitution calculations and a compositional approach.
As for numerical modeling and solution, several issues need careful attention. The first one is the fact that CO2 dissolves in brine substantially, and the second item is the grid-orientation effect on the position and distribution of the fluid-displacing front. For instance, in this thesis, a nine-point finite difference approach was implemented instead of a five-point finite difference in the solution of the flow equations. The latter distorts the injection fluid front due to the higher mobility of the displacing phase in comparison with reservoir fluids. In addition, accounting for CO2 solubility in brine delays the displacing front and reduces the concentration of CO2 dissolved in hydrocarbon phases.
The findings of this study show that in a three-phase system, the velocity change is predominately influenced by the supercritical CO2 phase. However, the supercritical CO2 phase’s density and bulk modulus are significantly influenced by the components from the oil phase. Heavier oils result in the CO2 absorbing more heavy components, whereas lighter oils lead to the supercritical CO2 absorbing more lighter components. Therefore, the supercritical CO2 phase density varies from the injection site to the production as it mobilizes different components from the oil phase.
The changes in saturated bulk modulus, acoustic P-wave velocity, and acoustic impedance are initially significantly different when the Gassmann black oil approach is compared to the compositional approach. These differences are more pronounced for miscible conditions than for immiscible conditions. This is a result of the supercritical CO2 mixing within the oil phase at the displacement front, which the black oil Gassmann approach is incapable of capturing. This leads to an underestimation of the location of the front that is behind the actual front in years for the miscible model and months for the immiscible. Additionally, due to the increasing purity of the injected CO2 as time elapses, the models start aligning with each other despite the changes in the oil density and bulk modulus
Understanding deformation and cyclic behavior of shape memory ceramics: a quantitative phase-field study
No full textIncludes bibliographical references.2024 Spring.Zirconia-based shape memory ceramics (SMCs) are a class of intelligent materials that can be utilized in industries such as aerospace and biomedical engineering for their remarkable superelasticity (SE) and shape memory effect (SME). These ceramics are brittle and unable to fully accommodate the large shape change due to martensitic phase transformation (MPT) and this leads to their low fracture toughness and short cyclic life.
In this Ph.D. research, we aimed to develop a reliable computational framework to study the complex interactions between phase transformation, microstructural features, fracture, and plasticity in order to design SMCs with a higher fatigue life. For this purpose, first, we proposed a modified phase-field (PF) fracture model to study cracking in brittle materials at microscopic domains. Unlike traditional models, this modified model incorporates the influence of both fracture strength and cleavage plane effects simultaneously. As a result, it accurately reproduces the mechanical response and crack propagation path and reveals that intergranular fracture is the dominant type of cracking in ceramics.
Additionally, to investigate the interaction between cracking and MPT in SE SMCs, an advanced PF-based model was developed. Unlike previous PF-MPT models, this model successfully predicts the correct elastic response in the stress-strain curve. This improvement is attributed to the proposed modified chemical free energy formulation. This is the first PF model used for simulating cracking in SE regime and accurately predicts reverse MPT behind the crack tip, a phenomenon attributed to SE regime. In addition, the model captures the effects of grain orientation and predicts a final stress drop in the stress-strain curve.
Furthermore, to explore the influence of different microstructural features on the cyclic life of SMCs prior to fatigue crack initiation, the modified chemical free energy model was integrated with a viscoplasticity model. The plastic strain accumulation (PSA) was used as a cyclic life indicator, and we aimed to lower PSA by microstructure tailoring. Simulations revealed that by controlling grain orientations, lowering the GB density, or locating pores at GBs, the PSA decreases significantly.
Finally, a new predictive numerical framework was developed incorporating the PF fracture, PF-MPT, and crystal viscoplasticity to study crystal-orientation dependent SE and SME behaviors of 3D micropillars. Through validation against experimental data, the proposed framework demonstrated the ability to accurately predict the intricate interplay between MPT, cracking, and plasticity. Our investigation revealed a broad spectrum of crystal orientations in which these ceramics undergo a complete MPT cycle without experiencing fracturing or slipping. However, we also identified certain orientations where either fracturing or slipping emerges as the dominant mechanism, with little to no observable MPT.
The findings of this Ph.D. research provided valuable insights into the crystal-orientation dependent mechanical properties of SMCs and strategies for enhancing their cyclic life, thus possibly enabling their practical applications
Rhodochrosite
No full textPhotographed by Ron Wolf.Botryoidal clusters of pale pink rhodochrosite on aggregate of small dark brown crystals, near Kuruman, Northern Cape Province, South Africa
Elbaite
No full textPhotographed by Ron Wolf.Purple and green glassy elbaite (tourmaline), Ohio City district, Gunnison County, Colorado
Malachite with azurite
No full textPhotographed by Ron Wolf.Botryoidal malachite with small malachite crystals
