Recent Submissions

  • Mathematical modeling of glucose and insulin dynamics in adolescent girls to quantify measures of insulin sensitivity

    Diniz Behn, Cecilia; Bartlette, Kai; Pankavich, Stephen; Leiderman, Karin; Klein-Seetharaman, Judith (Colorado School of Mines. Arthur Lakes Library, 2020)
    The regulation of plasma glucose is a key component of human metabolism and is largely regulated by insulin that facilitates glucose uptake by tissues. When tissues become more resistant to insulin, glucose concentrations remain elevated longer and more insulin is required to elicit the same physiologic response. Insulin resistance (IR) is a crucial element of the pathology of the metabolic syndrome, which includes increased risk of stroke, heart disease, type 2 diabetes mellitus, and nonalcoholic fatty liver disease (NAFLD). Decreased insulin sensitivity (SI) is associated with pubertal changes, is more prevalent in teenage girls, and obesity is known to further decrease SI. The Oral Minimal Model (OMM) is a differential-equations based model that describes glucose-insulin dynamics during an oral glucose tolerance test (OGTT) to quantify SI . However, the OMM framework was developed for adult data and practical identifiability issues create challenges with applying the models to diverse metabolic phenotypes. This research focuses on extending the OMM framework to describe OGTT data from a group of adolescent girls with obesity. Initial application of OMM in this cohort established OGTT protocol duration dependence of estimates of SI . To better understand which features of the data facilitate robust model parameter identification, we conducted a local sensitivity analysis of the OMM. We found that the model was least sensitive to changes in a subset of parameters and, therefore, these parameters could be difficult to estimate reliably. This finding was confirmed in an uncertainty quantification of OMM whereby we used a Markov Chain Monte Carlo approach to obtain the precision on key parameter estimates. The addition of glucose tracers in the OGTT enables estimation of the rate of appearance of exogenous glucose (Ra_exo), a key input of OMM-type models developed for separately assessing total and hepatic SI. Published methods for approximating Ra_exo had a significant impact on estimates of both total and hepatic SI. To overcome this limitation, we developed an Ra_exo model-independent method to estimate hepatic SI in this population. These methodologies may inform the analysis and adaptation of physiological models for other applications.
  • Sampling combinatorial energy landscapes by classical and quantum computation

    Kapit, Eliot; Stevanovic, Vladan; Jones, Eric B.; Toberer, Eric; Gong, Zhexuan; Wu, Bo; Graf, Peter; Jones, Wesley (Colorado School of Mines. Arthur Lakes Library, 2020)
    Combinatorial and, by extension, non-convex optimization problems are among the most difficult to solve computationally due to the inadequacy of local search methods alone to find global optima. The notion of an energy landscape provides a unified language to describe the origin of combinatorial complexity across a wide variety of fields including physics, materials science, and artificial intelligence. This thesis utilizes probabilistic techniques for efficiently sampling energy landscapes that rely on classical high-performance computers and near-term quantum computers. Such sampling techniques not only provide effective heuristics for solving combinatorial optimization problems, but also enable an explanation of physical phenomena that rely on features of the energy landscape other than the global optimum. Six use cases are considered that are of relevance to the design of future clean energy systems: i) a predictive theory of materials polymorphism based on the partitioning of the continuous energy landscape into structurally equivalent regions, ii) a theory of the structure of functional glasses based on thermally averaging structurally inequivalent regions, iii) solution of the minimum dominating set variant of the optimal phasor measurement unit placement problem on the power grid by quantum-annealing over a discrete, combinatorial solution landscape, iv) a reformulation and solution of the Markov decision process formalism underlying optimal control via quantum annealing, v) a prescription for the variational preparation of fractional quantum Hall states on a digital quantum computer that accommodates the size of the Hilbert space on quantum hardware while shifting the burden of variational minimization to classical, global optimization heuristics, and vi) the simulation of quantum cellular automata on a digital quantum computer and establishment thereby as primitives that could help design noise-resilient classically-parameterized unitary circuits such as those used in quantum machine learning. Through these domain examples, the outlook established herein is that efficient methods for exploring combinatorial energy landscapes, combined with resilience-minded near-term quantum algorithm construction and intelligent division of labor between quantum and classical resources, provide a promising path towards solving some of the most challenging problems in renewable energy science.
  • Functional resilience evaluation of road tunnels through stochastic event simulation and data analysis

    Pei, Shiling; Gutierrez, Marte S.; Khetwal, Sandeep Singh; Navidi, William Cyrus; Mooney, Michael A.; Padgett, Jamie E.; Hedayat, Ahmadreza (Colorado School of Mines. Arthur Lakes Library, 2020)
    Resilience of tunnels can have significant impact on the efficiency of the entire transportation network. The ability to assess resilience of tunnels accurately is important for tunnel owners and stakeholders when they evaluate the cost-benefit of the investment made and the monetary value of future maintenance and upgrade activities. In this thesis, a simple and direct measurement metric for tunnel functionality was proposed with the focus on the usage of road tunnels. An ideal data collection framework for tunnels was proposed to support the calculation of tunnel functionality, as well as additional data-driven analysis that can be conducted to seek correlation between tunnel design and operation parameters with its resilience. As an example, existing tunnel operational data collection practice in a large tunnel in Colorado was summarized and compared with the proposed framework. Data analysis was performed for Eisenhower Johnson Memorial Tunnel (EJMT), Colorado. Since the data for the tunnels was found to be insufficient and incomplete to perform a completely data-driven analysis, a stochastic simulation model to predict tunnel resilience over time was developed by simulation of individual disruptive events. The model was a combination of modules representing disruptive events namely, accident, vehicle fire, hazmat platooning, maintenance and operations. This model was validated to the extent that is realistic using limited data from EJMT. Further, a parametric sensitivity analysis was performed to identify the impact of tunnel parameters, associated with disruptive events, on the tunnel functionality loss and resilience. The parametric study was also expanded to conduct a preliminary correlation assessment of tunnel key parameters and their performances using 22 major road tunnels in the United States.
  • Study of excited halo states in ¹⁰Be and ¹²Be using one-neutron transfer reactions from ¹¹Be on ⁹Be at TRIUMF ISAC-II

    Sarazin, Frederic; Braid, Ryan A.; Greife, Uwe; Leach, Kyle; Hackman, Greg; Shafer, Jenifer C. (Colorado School of Mines. Arthur Lakes Library, 2020)
    The structures of beryllium isotopes display a complex interplay between Shell Model and cluster configurations. From ${}^{8}\mathrm{Be}$ on, the structures of Be isotopes is expected to be built on the $\alpha-\alpha$ cluster configuration with an increasing number of valence neutrons. Interestingly, the ground state of ${}^{11}\mathrm{Be}$ and ${}^{14}\mathrm{Be}$ are also well-known halo nuclei, hence the apparent competition between cluster configurations and more traditional shell-model like structures. For ${}^{10}\mathrm{Be}$, the ground state may retain some cluster properties, but the most developed cluster states are expected to be found near 6 MeV very close to the ${}^{9}\mathrm{Be}+n$ threshold. Those states are therefore good candidates to study the competition of cluster and single particle configurations. To this end, the ${}^{11}\mathrm{Be}$(${}^{9}\mathrm{Be}$,${}^{10}\mathrm{Be}$)${}^{10}\mathrm{Be}$ transfer reaction was studied at 30.14 MeV at TRIUMF's ISAC-II facility utilizing a combination of charged particles ((PCB)$^2$) and $\gamma$-ray (TIGRESS) detectors.This Thesis seeks to answer if the resulting ${}^{10}\mathrm{Be}$ excited states are molecular-like, shell-model-like, or some exotic combination. The $\gamma$-tagged angular distributions for the 2$^+_2$, $2^-$, and $1^-$ states in ${}^{10}\mathrm{Be}$ were successfully extracted and normalized to the ${}^{11}\mathrm{Be}$(${}^{9}\mathrm{Be}$,${}^{9}\mathrm{Be}$)${}^{11}\mathrm{Be}$ elastic scattering. The transfer reaction code FRESCO was utilized to model and fit angular distributions considering the transfer of the valence $2s_{1/2}$ halo neutron in ${}^{11}\mathrm{Be}$, which couples to the unpaired $1p_{3/2}$ in the ${}^{9}\mathrm{Be}$ ground state. This transfer was $\ell = 0$ for the negative parity states, and $\ell = 1$ for the $2^+_2$. The spectroscopic factors were found to be 0.63 $\pm$ 0.33 for the 2$^-$, 0.52 $\pm$ 0.27 for the 1$^-$, and 1.4 $\pm$ 0.7 for the 2$^+_2$ states. Given the clustered nature of ${}^{9}\mathrm{Be}$(3/2$^-$, gs) and the predicted clustered nature of the 6 MeV states in ${}^{10}\mathrm{Be}$, we conclude that the $1^-$ and $2^-$ states have a ${}^{9}\mathrm{Be}$(gs) $\otimes$ s$_{1/2}$ structure. This makes these states potential hybrid states where clustered and halo structures (especially for the $2^-$, which lies closer to the one-neutron separation energy) appear to coexist. The 2$^+_2$ state may also display a molecular configuration with the s$_{1/2}$ halo neutron transferring as a $\ell=1$ neutron, likely filling a p$_{1/2}$ orbit in the final state. This work is partially supported by the US Department of Energy through Grant/Contract No. DE-FG03-93ER40789 (CSM).
  • Hydrate film growth and risk management in oil/gas pipelines using experiments, simulations, and machine learning

    Koh, Carolyn A. (Carolyn Ann); Zerpa, Luis E.; Qin, Hao; Prasad, Manika; Wu, Ning; Gardner, Tracy Quinn; Wang, Hua; Creek, Jefferson; Rao, Ishan (Colorado School of Mines. Arthur Lakes Library, 2020)
    The formation of gas hydrates in oil and gas flowlines is considered a major flow assurance (FA) issue due to hydrate blockage forming within minutes to hours. Traditionally, hydrate formation was prevented in oil and gas flowlines via the injection of Thermodynamic Hydrate Inhibitors (THIs), such as methanol or mono-ethylene glycol (MEG). THIs operate by shifting the hydrate phase equilibrium to higher pressure and lower temperature. However, this method can become uneconomic as large quantities of THIs (40 vol.%, with respect to the produced water) are often required. More recently, there has been a paradigm shift from “hydrate prevention” to “hydrate management”, in an effort to reduce operating costs. The latter method can involve allowing gas hydrates to form in the flowline, and controlling the hydrate formation and agglomeration by injecting Low Dosage Hydrate Inhibitors (LDHIs). The hydrate kinetic model CSMHyK was coupled to a transient multiphase flow simulator (OLGA) as a user-customized plug-in in this work. CSMHyK-OLGA was used to assess the level of hydrate resistance to flow in a black-oil field, in comparison with field observations. CSMHyK simulations can provide information on the hydrate volume fraction, the location of the hydrate resistance/plug, and the transportability of the fluid containing a hydrate slurry. Based on the field simulation study, it was concluded that besides water cut (WC) and gas-oil ratio (GOR), FA engineers should also take into account the hydrate cohesive force and the water-oil emulsion stability in delivering hydrate management strategies. In order to develop more advanced and cost-effective hydrate management strategies, hydrate plugging mechanisms, such as film growth and deposition at various flow conditions need to be investigated. Previous hydrate deposition studies focused predominantly on the gas-dominated systems where water can condense, be entrained, and settle on the upper part of the pipe wall. However, the deposition mechanism in the liquid phase is not well studied. A high-pressure lab-scale deposition loop, capable of handling gas-liquid flow, was used to study hydrate deposition on the pipe wall in this study. The parameters which affect hydrate film growth such as liquid holdup, liquid and gas phase velocity, water cut, and subcooling were varied. Visual ports of the high-pressure system were used to observe hydrate film growth and deposition. Based on the observed mechanism and the film growth rate, it was concluded that the hydrate film growth depends primarily on the accessibility of hydrate-forming components at the wall, and the driving force for hydrate formation. This experimental study supported the evidence that hydrate film growth in an oil-dominated system is controlled by water droplets wetting the pipe surface. In addition, after a hydrate deposit layer is established, there is a potential risk of sloughing and blockage. In the sloughing case study, it was concluded that hydrate sloughing occurs as a result of increased shear stress and warm bulk flow heating. So far there is no mathematical model that is able to describe the complex overall hydrate plugging mechanism. Standard industry predictive analytic tools like OLGA require certain a level of knowledge in fluid chemistry and multiphase flow to set up well-defined case studies. Usually, a numerical simulation study is also quite time-consuming. On the other hand, there exists a large amount of laboratory data that cannot be easily analyzed using normal statistical techniques. Machine learning, especially deep learning can serve as a universal approximator, to determine the mapping functions between operation conditions and the plugging risk and process phenomena (hydrate growth and relative pressure drop across a pipe). Machine learning models can achieve high prediction accuracy and calculation efficiency, given a sufficient number of data points and a good computer algorithm. In this thesis, we demonstrated that based on the data from the pilot-scale flowloop hydrate tests, machine learning models can predict hydrate plugging and hydrate volume fraction in the flowloop studies, as well as hydrate risks in the field pipelines.
  • Multi-scale microscopy of the Li/electrolyte interface in solid-state next-generation batteries

    Pylypenko, Svitlana; Al-Jassim, Mowafak; Seitzman, Natalie; Clarke, Amy; DeCaluwe, Steven C.; Gennett, Thomas; Nelson Weker, Johanna (Colorado School of Mines. Arthur Lakes Library, 2020)
    The transition to renewable energy sources is dependent on the availability of sufficient storage. To meet these urgent demands, scientists are racing to find new battery chemistries and architectures One of the promising next-generation technologies is all-solid lithium (Li) batteries, which utilizes ion-conducting solids such as β-Li3PS4 (LPS) ceramic in place of conventional organic liquid electrolytes. This enables use of a Li metal anode which increases theoretical capacity, improves battery safety by replacing flammable liquid electrolytes, and in some cases widens the stable voltage window over traditional Li-ion electrolytes. However, Li anodes in solid-state systems experience undesired Li migration which can result in short-circuit and premature battery death. The core focus of my research is to use imaging techniques to detail the fundamental electrochemical processes governing the Li migration in ceramic solid electrolytes, using LPS as a model system. To achieve comprehensive understanding, it is necessary to characterize the Li/electrolyte interface at all relevant scales, which is only possible by using a collection of different techniques. In my work I used scanning electron microscopy (SEM) paired with Li sensitive energy dispersive spectroscopy (EDS) as well as two X-ray imaging techniques: synchrotron computed tomography (CT) and transmission X-ray microscopy (TXM). This presentation will first highlight the results of operando synchrotron CT studies, collecting 3D X-ray images of the Li/LPS interface while the battery is cycling, supported with complementary SEM studies with Li-sensitive EDS. The development of this operando synchrotron CT technique to control and manipulate variables that are relevant in realistic solid-state batteries will be described along with major results that show interaction between the Li metal and pre-existing defects in the LPS electrolyte and reveal that multiple mechanisms of Li migration may be dominant depending on cell operating conditions. Next, methodologies that advance TXM, a nano-scale X-ray imaging technique, toward the operando capabilities necessary for detailed investigation of mechanisms at nanoscale will be covered, including detailed discussion of challenges associated with sample preparation and fabrication of the cells with appropriate dimensions, TXM experiments, and data analysis. The outcome of this work is a multi-scale morphological characterization, ranging from the nano-scale to micro-scale to the whole device, contributing to mechanistic understandings of fundamental science related to battery degradation and development of novel capabilities that could be applied to wider range of systems.
  • Wideband antennas with polarization diversity for wireless applications

    Nayeri, Payam; Desai, Ami; Brennecka, Geoffrey; Haupt, Randy L.; Mohagheghi, Salman (Colorado School of Mines. Arthur Lakes Library, 2020)
    The rapid growth of our wireless system infrastructure has created an environment that numerous devices communicate in close proximity, sometimes even in co-located positions. In addition, data rates in communication systems have increased significantly over the last decade, and all projections indicate that this will continue to increase. To address these network demands, many challenges exist. From a hardware perspective, antennas and RF frontends that can support high data-rates and close proximity operation are the primary challenges.This research focuses on developing new methodologies for design, analysis, and synthesis of novel antennas with broad bandwidth and polarization diversity features, while taking advantage of the state-of-the-art in manufacturing technology. In the course of this research, three novel antenna configurations were proposed that can achieve wide bandwidth and at the same time provide dual-linear or dual-circular polarization features. Namely, printed crossed-dipoles with integrated balun mechanisms, aperture couple microstrip patch antennas with dual wide-offset feed mechanisms, and multi-layer and multi-ring heterogenous dielectric resonator antennas with very wide bandwidths have been introduced. The first two antenna configurations are enabled by printed circuit board technology, while the third configuration takes advantage of the most recent advances in additive manufacturing, i.e. multi-material techniques that enable creation of heterogenous dielectric solids. The versatile and compact nature of the proposed antennas, as well as their simple form factors, make them a strong candidate for wideband hand-held communication systems. Moreover, the proposed design methodologies are applicable to a broad range of different types of antennas and microwave devices.
  • Separation of trivalent actinides and lanthanides with sulfur donor ligands and extractants

    Shafer, Jenifer C.; Bessen, Nathan Patrick; Jensen, Mark; Trewyn, Brian; Vyas, Shubham; Osborne, Andrew (Colorado School of Mines. Arthur Lakes Library, 2020)
    The separation of trivalent actinides and lanthanides in the processing of used nuclear fuel is challenging due to the similar sizes, charges, and redox properties of the two classes of metals. Typical separations procedures rely on ligands or extractants that can coordinate the metals with polarizable soft donor atoms such as nitrogen or sulfur. These soft donor atoms display a preference for coordinating the actinides which can be utilized to provide selectivity in this separation. Among the different ligands and extractants used for this separation, the sulfur containing dithiophosphinic acids have shown some of the highest reported selectivities, with separation factors of up to 100,000 for the separation of americium and europium. However, the extraction mechanism for the dithiophosphinic acids are not fully defined, especially for the transcurium actinides. The most commonly studied dithiophosphinic acid, bis(2,4,4-trimethylpentyl)dithiophosphinic acid (HC301), is known to extract metals as several different complexes dependent upon both the extracted metal and the conditions used. A more complete understanding this behavior will promote the optimization of HC301-based separation procedures and possibly the development of extractants with even greater selectivity. Additionally, HC301 is susceptible to degradation by radiolysis, oxidation, and hydrolysis which both reduces the amount of HC301 in the system and forms new species that can impact the separation. In this work, the current knowledge in the use of sulfur donating extractants, including the dithiophosphinic acids and HC301, for the separation of lanthanides and actinides is summarized and two new developments in the use of HC301 are reported. The first development is a novel method to quickly determine concentrations of HC301 by a colorimetric permanganometric titration to enable more effective monitoring of a potential separation process. The second project is a characterization of the extraction of the transplutonium actinides, Am-Es, by HC301 to determine how extensively these metals are extracted and what complexes are extracted. Additionally, the use of more degradation resistant and water-soluble sulfur donating ligands as an alternative to dithiophosphinic acids is examined. Overall, both HC301 and the aqueous sulfur donating ligands display selectivity for all the actinides tested. This selectivity seems to be greatly influenced by the formation of different complexes between the lanthanide and actinide series. The actinides tend to form complexes where the metal is more completely coordinated by sulfur and the metal-sulfur bonds are shorter whereas the lanthanides tend to have less coordination by sulfur and longer metal-sulfur bonds.
  • Effects of austenite conditioning on microstructural development and interphase precipitation in titanium-molybdenum microalloyed steels, The

    Speer, J. G.; De Moor, Emmanuel; Felker, Caleb A.; Findley, Kip Owen; Field, Robert; Eberhart, Mark E. (Colorado School of Mines. Arthur Lakes Library, 2020)
    A challenge exists in the automotive industry to develop new, hot-rolled, microalloyed steels offering a balance of high tensile strength and superior stretch-flange formability. The steel industry has responded by developing ferritic steels strengthened with extensive nanometer-scale precipitation. The single-phase ferritic matrix eliminates hard constituents and imparts superior stretch-flange formability, while high strengths are derived from nanometer-scale precipitates. In this context, interphase precipitation has regained substantial academic and industrial interest. Interphase precipitates repeatedly nucleate at the austenite (γ)/ferrite (α) interface during γ → α decomposition resulting in densely packed sheets of precipitates. The precipitation strengthening due to interphase precipitation in some recent steel designs has been estimated to be over 300 MPa, which is two or three times higher than the precipitation strengthening obtained in more conventional microalloyed steels. This study investigated the influence of austenite strain accumulation on γ → α kinetics, microstructural development, and interphase precipitation within polygonal ferrite using a low carbon, titanium-molybdenum microalloyed steel. Deformation dilatometry was performed to study γ → α kinetics after different levels of austenite strain accumulation and associated microalloy precipitation. Austenite conditioning was performed above and below the non recrystallization temperature (Tnr). Greater austenite strain accumulation resulted in accelerated γ → α kinetics. Microalloy precipitation within polygonal ferrite was investigated with transmission electron microscopy (TEM) using specimens constructed from regions exhibiting incoherent γ (martensite)/α interfaces with focused ion beam (FIB) techniques. Interphase precipitation was observed after both austenite conditioning simulations, where relatively slower γ → α kinetics resulted in a finer interphase precipitation sheet spacing compared to faster γ → α kinetics. Multipass hot torsion testing was performed to study the influence of extensive differences in austenite strain accumulation on microstructural development and associated microalloy precipitation. Again, austenite conditioning was performed above and below the Tnr. The amount of imposed true strain was between approximately 2.76 and 4.97, where three radial positions were investigated. A metallographic technique was used to quantify austenite strain accumulation. Austenite conditioning above the Tnr resulted in negligible austenite strain accumulation, while austenite conditioning below the Tnr accumulated roughly 0.85 true strain. Extensive austenite strain accumulation resulted in enhanced austenite recrystallization and substantial refinement in prior austenite grain size. Isothermal holding was performed after austenite conditioning to simulate coiling. Extensive austenite strain accumulation was required to achieve fine, homogeneous microstructures of polygonal ferrite desired for the application of this steel, avoiding small amounts of hard, secondary phase constituents. Microalloy precipitation was investigated with TEM, where specimens were constructed from polygonal ferrite grains that exhibited a near <100>α grain normal using FIB techniques so that two of the three possible Baker-Nutting orientation relationship variants could be imaged within a given specimen. Interphase precipitation was inferred after transformation following austenite conditioning above the Tnr (based on variant selection) and directly observed after transformation following austenite conditioning below the Tnr. Greater austenite strain accumulation resulted in a less regular interphase precipitation morphology (i.e. incomplete sheets, localized variations in sheet spacing, and relatively few sheets). Tested hole-expansion samples of industrially produced material were examined to relate microstructure and precipitation behavior with hole expansion performance. The samples exhibited a variation in hole-expansion performance despite being taken from the same respective hot-rolled coil. Fractography, uniaxial tensile testing, and multiple microstructural analysis techniques were used to investigate the samples. Differences in microalloy precipitation were likely not responsible for the variation in measured hole-expansion performance, while small differences in hard, secondary phase constituents and non-metallic inclusions may have contributed to the reported variation.
  • Linking morphology to electronic properties in small-molecular organic semiconductors

    Zimmerman, Jeramy D.; Jaskot, Matthew B.; Sellinger, Alan; Collins, Reuben T.; Toberer, Eric; Diercks, David R. (Colorado School of Mines. Arthur Lakes Library, 2020)
    In organic electronics, morphology inevitably affects important device properties. The understanding of these relationships and ultimately control of morphology in small-molecular organic materials is necessary for their further development. Understanding the influence of morphology on device properties is critical not only to improving device efficiency, but also to extending usable device lifetimes by careful design to reduce material degradation. Difficulty in imaging these organic materials due to their sensitivity to damage from ion, electron and X-Ray irradiation, as well as their lack of elemental contrast between molecular species has so far limited the study of their morphology. Atom probe tomography (APT) is used as a tool to provide chemically-sensitive three-dimensional tomographs of organic materials which can be used to study morphological phenomena in these systems. In this work, several results are presented which demonstrate the importance of morphology on device properties in organic semiconductor materials. First, the presence of a chemical product confined to the donor-acceptor interface in tetracene/C60 organic photovoltaics (OPVs) is identified using APT and Fourier-transform infrared spectroscopy (FTIR), and it is shown to increase device open-circuit voltage with increasing concentration. Next, APT and high-angle annular dark-field scanning electron microscopy (HAADF-STEM) are used to characterize organic light-emitting diode (OLED) emissive layer (EML) films, showing that the emissive dopant aggregates in codeposited host/dopant films, influencing several important device properties, specifically the hole mobility and rates of triplet-polaron quenching (TPQ) and triplet-triplet annihilation (TTA). Two strategies are then used to kinetically limit aggregation of the dopant and as a consequence, change electronic properties: reduction of the substrate temperature during film growth, and the addition of a wide-gap co-host molecule.
  • Numerical investigation of the perforation friction loss, coefficient of discharge and erosional processes during limited entry hydraulic fracturing treatments

    Miskimins, Jennifer L.; Almulhim, Abdulraof Othman; Fleckenstein, William W.; Yin, Xiaolong; Sonnenberg, Stephen A.; Bogin, Gregory E. (Colorado School of Mines. Arthur Lakes Library, 2020)
    Hydraulic fracturing is behind the successful and feasible exploitation of unconventional hydrocarbon resources around the world. Pioneered by North American operators, the multi-stage massive treatments have enabled producing shale resources very efficiently and at a competitive cost. Recently, limited entry perforating has been found to be useful to increase the stage length and reduce the total stage count with no compromise on productivity. Limited entry hydraulic fracturing treatments rely on the concept of limiting the number of perforations, creating a high perforation frictional loss, and elevating the pressure inside the wellbore. The elevated pressure helps to overcome the closure stress variations along the stage and divert the fracturing fluid more evenly among the clusters. The slurry flow at such a high flow rate through limited perforations is very abrasive, causing a rapid and significant change to the perforation shape and size. This dissertation addresses two critical aspects of the limited entry hydraulic fracturing treatments; the high perforation frictional loss and the dynamic perforation erosion process. Utilizing Computational Fluid Dynamics (CFD), this work modeled the flow through perforations and developed a quantitative understanding of the kinetic energy correction factor used in the perforation friction equation, the coefficient of discharge (Cd). The Cd sensitivity to the perforation design parameters was investigated using an experimentally calibrated model. Using the discrete phase model (DPM), the proppant distribution among the clusters for actual field completion designs was modeled, and the steady-state erosion distribution and rate were predicted. The erosion rate sensitivity analysis was carried out on a field-scale completion design case and showed reasonable agreement to the erosion field data analysis. The results identified a Cd value of 0.72 for a 0.35 in. sharp-edge drilled perforation. Real jet perforations of the same size display higher Cd values, ranging from 0.75 to 0.83 due to the semi-round perforation entry and inlet burr effect. The erosion process increases the perforation discharge efficiency, and the Cd value increases significantly, reaching the 0.9 range as estimated by the transient erosion model. The model indicated that the smaller the perforation size, the longer the tunnel, the higher the viscosity and proppant concentration, and the smaller the proppant size, the lower the Cd. The two-phase DPM modeling results revealed the importance of the particle inertia and gravity force on the proppant transport and distribution. CFD is a useful tool in capturing the impact of those two major forces, predicting the proppant and erosion distribution for various completion designs. The DPM modeling indicated that the perforation erosion process is governed by the mass of particles flowing out and their impact velocity. Supported by field data, the erosion rate is highly sensitive to the flow rate; a 20% rise in the flow rate showed more than 60% increase in the erosion rate. The gravity force also has an impact on the erosion rate; bottom perforations suffer from 20% more erosion than top perforations.
  • Characterizing the excavation process associated with removal of shotcrete reinforced underground structural liners using waterjet technology

    Miller, Hugh B.; Bourgeois, Josef P.; Steele, John P. H.; Asbury, Brian; Kaunda, Rennie; Rostami, Jamal (Colorado School of Mines. Arthur Lakes Library, 2020)
    The primary objective of this research is to characterize the operating parameters and fragmentation mechanisms associated with the hydroexcavation of reinforced shotcrete and concrete liners used in underground mines and tunnels. Through empiric testing, this research also seeks to validate the hypothesis that waterjet removal of these support systems will result in greater selectivity and less unintended damage than conventional removal methods. The intent is to develop a viable technology that will reduce the collateral damage caused to surrounding liners during excavation, improve the adhesion between shotcrete and the substrate for longer lasting ground support, and improve overall safety for workers in underground environments.Waterjet excavation has the potential to eliminate many of the technical and operating challenges associated with conventional shotcrete removal and repair. Evidence derived through empiric laboratory testing indicates that waterjets are capable of selectively removing damaged areas of support liners without structurally compromising the substrate and adjacent intact sections of the liner. This research illustrates the contrast between the excavation process associated with both conventional mechanical impact hammers and waterjet excavation methods during empiric testing. An analysis on the fracture mechanisms and operating parameters of each method was completed. Within this analysis, instrumented shotcrete panels were physically tested to quantify vibration during excavation, and examined through visual and analytic processes to determine substrate damage and delamination. After testing was completed, this data strongly indicated that waterjet cutting causes less collateral damage to the surrounding intact liner and substrate when compared to that of conventional impact hammers. This research is intended to provide a scientific basis for additional applied research in the rapid excavation and repair of shotcrete support systems.
  • Application of machine learning to gas flaring

    Miskimins, Jennifer L.; Lu, Rong; Bandyopadhyay, Soutir; Eustes, Alfred William; Fan, Yilin; Crompton, James Scott (Colorado School of Mines. Arthur Lakes Library, 2020)
    Currently in the petroleum industry, operators often flare the produced gas instead of commodifying it. The flaring magnitudes are large in some states, which constitute problems with energy waste and CO\textsubscript{2} emissions. In North Dakota, operators are required to estimate and report the volume flared. The questions are, how good is the quality of this reporting, and what insights can be drawn from it? Apart from the company-reported statistics, which are available from the North Dakota Industrial Commission (NDIC), flared volumes can be estimated via satellite remote sensing, serving as an unbiased benchmark. Since interpretation of the Landsat 8 imagery is hindered by artifacts due to glow, the estimated volumes based on the Visible Infrared Imaging Radiometer Suite (VIIRS) are used. Reverse geocoding is performed for comparing and contrasting the NDIC and VIIRS data at different levels, such as county and oilfield. With all the data gathered and preprocessed, Bayesian learning implemented by Markov chain Monte Carlo methods is performed to address three problems: county level model development, flaring time series analytics, and distribution estimation. First, there is heterogeneity among the different counties, in the associations between the NDIC and VIIRS volumes. In light of such, models are developed for each county by exploiting hierarchical models. Second, the flaring time series, albeit noisy, contains information regarding trends and patterns, which provide some insights into operator approaches. Gaussian processes are found to be effective in many different pattern recognition scenarios. Third, distributional insights are obtained through unsupervised learning. The negative binomial and Gaussian mixture models are found to effectively describe the oilfield flare count and flared volume distributions, respectively. Finally, a nearest-neighbor-based approach for operator level monitoring and analytics is introduced.
  • Porphyry and skarn deposits of the Chillagoe mining district, northeast Queensland, Australia, The

    Goldfarb, R. J.; Illig, Peter Edward; Leach, David; Bohrson, Wendy A.; Holley, Elizabeth A. (Colorado School of Mines. Arthur Lakes Library, 2020)
    The Chillagoe mining district is located in northeast Queensland and hasintermittently produced zinc, lead, silver, copper and gold from porphyry, skarn and carbonate replacement deposits since 1888. To understand the timing and controls on ore deposit formation, I remapped 121km2 of the district, re-logged 40km of core to create eight new cross sections for the four deposits, dated 21 rocks with U-Pb, Re-Os and 40Ar/39Ar geochronology, analysed the whole rock geochemistry of 89 rocks, acquired electron microprobe analyses of skarn and igneous minerals, and analyzed C-O isotope of calcite. The deposits of the district are the Red Dome Au-Cu skarn deposits, the Mungana Zn- Pb-Ag-Cu skarn and Au-Cu porphyry deposits, the King Vol Zn-Pb-Ag-Cu deposit and the Redcap Zn-Pb-Ag-Cu-Au prospect. The gold + copper deposits are associated with rhyolite porphyry intrusions that have exsolved magmatic fluids within Silurian to Devonian shallow marine sedimentary rocks of the Chillagoe Formation. The lead-zinc-silver-copper skarn and carbonate replacement deposits are present along steeply dipping sedimentary contacts between carbonate rocks and other sedimentary units and along thrust faults. The magmatism associated with these deposits occurred between 335 and 290 Ma and took place in four stages. The earliest potential magmatism occurred at 335 Ma with the formation of the Mungana base metal deposit. The ca 335 Ma molybdenite at Mungana does not overlap with any known intrusions of the district. Between 322 to 315 Ma, magmatism at Red Dome and Mungana formed Au-Cu porphyry deposits and associated skarns. The dacite and rhyolite composition Redcap volcanic rocks erupted contemporaneously with porphyry formation at Mungana. Sometime after the formation of the 317 Ma gold porphyry deposit at Mungana, the base metal deposit was deformed and migrated along the contact of the porphyry gold resource. Contraction followed shortly afterwards as evidenced by ca 312 Ma thrusting of the Chillagoe formation, Red Dome and Mungana over the Redcap volcanic rocks. Magmatism followed thrusting at Redcap as 310 Ma skarn formed along the thrust contact between the volcanic rocks and the overlying Chillagoe formation carbonate rocks. The 310 Ma Redcap base metal skarns were sourced from an undiscovered intrusion to the southeast or south at depth. The Red Hill granite pluton and a granite intrusion below Mungana formed at the same time as the Redcap skarns, however they are not directly related. Magmatic quiescence followed as much of what is now Queensland entered a period of extension and basin development. The final episode of magmatism of the Chillagoe district occurred at ca 290 with the intrusion of the Belgravia and Ruddygore granodiorite plutons, and the formation of the King Vol Zn-Pb-Ag-Cu skarn and carbonate replacement deposit. While the majority of the base metal deposits and prospects of the district are distal and thin (<10m) tabular Zn-Pb-Ag + Cu skarns hosted along near vertical sedimentary contacts, the largest deposit of the district (Red Dome) was hosted by a hydrothermal breccia at the top of the causative intrusion. Coexisting vapor rich and hypersaline fluid inclusions and rounded clasts of the causative porphyry within the skarn suggest fluid exsolution occurred from the top of the intrusion. These processes controlled the formation of the 150m wide breccia which hosted the largest resource of the district. The magmatic sources for the distal base metal deposits remain undiscovered at depth and may be the distal fringes of mineralized Cu-Au porphyry systems.
  • Submarine canyons, channels, levees, and lobes: an investigation of the linkages between depositional processes, stratigraphy, and sedimentology

    Jobe, Zane R.; Pettinga, Luke A.; Wood, Lesli J.; Plink-Björklund, Piret; Dugan, Brandon (Colorado School of Mines. Arthur Lakes Library, 2020)
    Continental margin depositional systems are of great importance to science and society in that their deposits are an important record of earth history and host valuable natural resources. Submarine fans form the largest sedimentary accumulations within continental margins and are comprised of the deposits from several distinct depositional environments, including canyons, channels, levees, and lobes. Understating how sedimentary processes affect the stratigraphy and sedimentary properties of these deposits is critical to properly interpret them for use in deciphering global events of the past and explore for the natural resources they contain. This thesis contributes to that understanding through quantitative analysis and modeling of sediment transport and accumulations related to submarine fans through: 1) documenting and interpreting the geomorphic relationships between longitudinal profiles of canyon-channel systems and surrounding continental margins in tectonically active and passive settings; 2) demonstrating how turbidity current properties and channel kinematics affect the depositional properties of levees; and 3) documenting scaling relationships between related channel and lobe-shaped deposits. Each of these contributions can be applied to improve the interpretation and prediction of sedimentary properties of modern and ancient continental margins.
  • X-ray photoelectron spectroscopy investigation of surfaces and interfaces in fuel cell applications

    Pylypenko, Svitlana; Dzara, Michael J.; Ricote, Sandrine; Trewyn, Brian; Gennett, Thomas (Colorado School of Mines. Arthur Lakes Library, 2020)
    Advanced characterization methods play a central role in materials development, from initial exploratory synthesis to the testing and validation stage. A particularly powerful technique widely employed to identify synthesis-property-processing-performance correlations is X-ray photoelectron spectroscopy (XPS). XPS yields surface sensitive, element-specific information which can be analyzed to reveal differences in composition, oxidation state, and chemical interactions within a sample set. While typical XPS measurements are conducted under ultra-high vacuum (UHV), its applicability can be expanded towards in situ measurements through specialized XPS instruments that operate under near-ambient pressure (nAP-XPS). The core focus of my thesis is the application of both UHV and nAP-XPS to characterize the surfaces and interfaces within the cathode of polymer electrolyte membrane (PEM) fuel cell systems, where the electrocatalytic oxygen reduction reaction (ORR) occurs. Materials investigated in this work include both state-of-the art Pt/C and Pt-group metal free (PGM-free) ORR catalysts using earth abundant elements. Contributions within my thesis fall under three generalized research arcs: i) investigation of surface properties of PGM-free catalysts using UHV XPS, ii) analysis of gas-solid interfaces relevant to the ORR in PGM-free catalysts by nAP-XPS, and iii) studies of the catalyst-ionomer interface in Pt/C cathodes, with both UHV and nAP-XPS. This thesis features an overview of UHV and nAP-XPS techniques, highlighting both the direction of the field and possible applications. Next, results of the UHV XPS studies of PGM-free catalysts are discussed, which yielded the identification of surface properties linking variations in synthetic parameters with trends in ORR activity. The gas-solid interface studies first focused on methodology development towards adsorption studies, which was then applied towards identification of O2-adsorption sites in a set of PGM-free catalysts with various ORR activities. Finally, efforts towards characterizing the catalyst-ionomer interface will be discussed. This includes tracking the stability of the Nafion ionomer species during XPS measurement, proposes protocols that enable reliable XPS studies, and presents initial findings, including evidence of re-orientation of Nafion within an electrode in response to humidification. Methodologies developed herein enable further studies of both the gas-solid interface and the catalyst-ionomer interfaces in PEM electrodes with various state of the art and novel catalyst, support, and ionomer chemistries as part of the over-arching efforts towards wide-spread commercialization of PEM devices.
  • Universal observable chemical bond analysis: gradient bundle decomposition of the electron charge density

    Eberhart, Mark E.; Wilson, Timothy R.; Ciobanu, Cristian V.; Vyas, Shubham; Mehta, Dinesh P. (Colorado School of Mines. Arthur Lakes Library, 2020)
    Our curiosity-driven desire to "see" chemical bonds dates back at least one-hundred years, perhaps to antiquity.Sweeping improvements in the accuracy of measured and predicted electron charge densities, alongside our largely bondcentric understanding of molecules and materials, heighten this desire with means and significance. Energetic analysis of arbitrary regions of charge density is problematic, however, because electronic kinetic energy is ambiguous over such regions. If the flux of the charge density gradient is zero across the boundary of a region, then the ambiguity vanishes and such a region is found to possess a well-defined kinetic energy. Such regions are called gradient bundles. Here we present gradient bundle decomposition, a method for the infinitesimal partitioning of a three-dimensional charge density that results in a two-dimensional projected space in which kinetic—and thus total—energy is everywhere well-defined; a space called the condensed charge density (P). Bond "silhouettes" in P can be reverse-projected to reveal precise three-dimensional bonding regions we call bond bundles, and P enables direct inspection of the energy distribution within a bond. We show that delocalized metallic bonds and organic covalent bonds alike can be objectively analyzed, the formation of bonds observed, and that the crystallographic structure of simple metals can be rationalized in terms of bond bundle structure.We demonstrate that gradient bundle decomposition also reveals the charge density's intrinsic ridge structure indicative of regions of energetic—hence chemical—significance. Bond bundle analysis also effortlessly resolves many concerns regarding the chemical significance of bond critical points and bond paths in The Quantum Theory of Atoms in Molecules. Our method also reproduces the expected results of organic chemistry, enabling the recontextualization of existing bond models from a charge density perspective. Gradient bundles had been successfully demonstrated previously as a proof of concept in systems with linear symmetry. The complexity of a generalized gradient bundle decomposition—to systems of any symmetry—necessitated a programmatic approach. Here we also outline the resulting novel algorithms.
  • Protonic ceramics for electrochemical hydrogen compression

    DeCaluwe, Steven C.; Kee, Benjamin Lyons; Ricote, Sandrine; Porter, Jason M.; O'Hayre, Ryan P. (Colorado School of Mines. Arthur Lakes Library, 2020)
    The topic of this thesis is designing and characterizing protonic ceramics for the electrochemical hydrogen compression. Protonic-ceramic reactors are attractive for compressed hydrogen production from natural gas because they can effectively integrate steam reforming, hydrogen separation, and electrochemical compression. The current technology requires many unit processes, which introduces significant inefficiency. This thesis first explores protonic-ceramic electrochemical hydrogen compression on tubular cells. Compression to 10 bar was demonstrated, but progress was limited by material availability and scale-up opportunities. A method was developed to fabricate protonic-ceramic cells. The easily-produced samples were characterized and modeled. Discs were made for planar stack development to investigate sealing and reactor design strategies. Scaling up protonic-ceramic electrochemical hydrogen compression is an ongoing challenge. Experiments with tubular cells have compressed H2 up to 10 bar. Tubes are ideal for heavy compression due to strong hoop stress resistance, which is applied from the pressure difference during compression. Unfortunately, tubular geometries do not lend themselves well to stacking, due to poor electrode connections and footprint size. The scarcity and poor compatibility of tubular cells create an opening for new methods to make protonic-ceramic cells. The polymer clay method is a novel processing technique for moldable ceramics in the green state, that fire completely dense. Herein, fabrication of protonic-ceramic membranes is demonstrated in a variety of shapes. Conductivity relaxation measurements between moist and dry reducing conditions on polymer clay coupons were collected and fit to an ambipolar diffusion model. Results demonstrate that polymer clay samples are competitive to samples made by other methods. The final topic of this thesis is how to incorporate efficient cells in robust and durable stacks for electrochemical H2 compression. Planar stack configurations have been heavily explored with other electrochemical devices, including fuel cells. Planar geometries are more conducive to stacking and have tightly integrated electrode connections. Sealing strategies between the bipolar plate and the membrane electrode assembly were explored to determine best practices. Our results demonstrate hydrogen pumping on single cells. While hermetic seals for planar cell stacking remain an ongoing area of study, this study identifies potential solutions.
  • Surface interactions and locked cycle flotation of novel collectors on bastnäsite ore

    Anderson, Corby G.; Keller, Philip; Eggert, Roderick G.; O'Kelley, Brock; Taylor, Patrick R. (Colorado School of Mines. Arthur Lakes Library, 2020)
    Flotation of a bastnäsite containing ore with novel collectors was investigated using locked cycle froth flotation. Previous research into the flotation of bastnäsite ore simply considered single stage flotation and while this is a good place to start the testing of novel collectors, it is not representative of the conditions employed in a full-scale flotation plant. This study investigates both salicylhydroxamic acid (collector 2) and n,2-hydrocyclohexanecarboxamide (collector 5) in locked cycle flotation and contact angle studies and includes a comparative economic assessment comparing the two novel collectors listed above to the fatty acid flotation previously used at Mountain Pass in California. Locked cycle flotation allows for the simulation of continuous flotation processes using bench scale flotation equipment. This allows the collectors to be tested in conditions that more closely match the conditions that would be found in flotation plants in industry. Locked cycle flotation with collector 2 returned rare earth oxide grades between 58.5% and 66.9% and recovery between 42.8% and 74.7% while rejecting 78% of the calcite. Locked cycle flotation with collector 5 returned rare earth oxide grades between 13.2% and 13.8% with recoveries between 26.6% and 41.3% while rejecting 9% of the calcite. The rejection of calcite is an important consideration because it affects the downstream reagent consumption in the leaching step of the rare earth element processing. Locked cycle flotation showed a large disparity in performance between collector 2 and collector 5. This disparity was investigated using contact angle studies. Performing contact angle test work allows for comparisons to be made regarding the applied hydrophobicity of a collector to the surface of a mineral.
  • Improving plastic scintillators for detection of neutrons and gamma rays

    Sellinger, Alan; Lim, Allison; Cash, Kevin J.; Domaille, Dylan; Greife, Uwe (Colorado School of Mines. Arthur Lakes Library, 2020)
    Detection of special nuclear materials (SNMs) at borders and ports of entry is critical to ensuring peaceful use of fissile materials. Plastic scintillators are viable option for first line of detection for these materials due to their low cost and scalability. Based on common polymers such as poly(vinyl toluene) (PVT) or polystyrene, plastic scintillators can distinguish between neutron and gamma radiation via a technique called pulse shape discrimination (PSD). PSD capable plastic scintillators allow for more accurate detection of SNMs and would theoretically reduce the number of “nuisance alarms,” triggered by naturally occurring radioactive materials. Unfortunately, the high concentration (> 20 weight%) of fluorescent molecules required for PSD leads to unfavorable plasticizing effects like softening, low glass transition temperature, and dopant precipitation and leaching. Additionally, the best quality scintillators are achieved through a tedious oxygen-free, 5-7 day thermal polymerization. This dissertation describes the enhancement of the material properties and PSD capabilities of plastic scintillators using chemistry, polymer, and material science techniques. Initially the aim was to manipulate and improve the material properties through established polymer science strategies. Cross-linking the traditional PVT matrix with an aromatic dimethacrylate increased the hardness and reduced dopant aggregation without sacrificing radiation detection capabilities in PSD capable plastic scintillators. Building off the methacrylate motif, novel dopants with polymerizable methacrylate groups were synthesized. By co-polymerizing the dopant with the vinyl toluene matrix, dopant aggregation and leaching were eliminated and hardness and glass transition temperature increased without losing PSD capabilities. In order to broaden the application of PSD capable plastic scintillators, polysiloxanes were explored as an alternative to the traditional PVT matrix. The elastomeric polysiloxane scintillators required only 5 weight% or less of dopants to achieve neutron and gamma ray discrimination comparable to commercial PVT scintillators. Additionally, the polysiloxane scintillator could be fabricated in 3 hours in air, compared to the traditional 5-7 day process in oxygen free environments typically required for PVT scintillators. Both switching the polymer matrix and altering the traditional PVT matrix demonstrated that common polymer science techniques could be applied to plastic scintillators to balance material and radiation detection properties. The discovery of the dimethacrylate cross-linker also afforded the opportunity to explore alternative fabrication techniques. Unlike vinyl toluene or styrene, methacrylate groups can be easily photopolymerized. The second portion of this thesis applied established photopolymerization formulations to plastic scintillators in order to fabricate PSD capable plastics in 1 day via photoinitiation, compared to the traditional 5-7 day process. Plastic scintillators fabricated via photopolymerization had comparable radiation detection capabilities and material properties to traditional thermally polymerized analogues. The final part of the dissertation forays into the potential for gamma ray spectroscopy plastic scintillators. Incorporating high Z elements into plastic scintillators can result in the photoelectric effect, providing spectroscopic information on the gamma ray source and improving detection of SNMs. Three classes of bismuth dopants, triaryl, trialkoxy, and nanoparticles were explored as potential high Z dopants for plastic scintillators. Functionalized bismuth oxide nanoparticles were the most promising high Z dopants due to their combination of scalability and dispersibility in PVT matrices. To conclude, this dissertation highlights how an interdisciplinary approach to plastic scintillators can lead to a balance between material properties and radiation detection capabilities. Chemistry, materials, and polymer science techniques such as dopant synthesis, cross-linking, photopolymerization, and co-polymerization originally developed for other applications can be applied to PSD capable plastic scintillators to increase hardness, decrease dopant aggregation, and decrease fabrication time.

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