Recent Submissions

  • Compositional modeling of gas injection in tight oil reservoirs

    Wu, Yu-Shu; Tian, Ye; Illangasekare, T. H.; Kee, R. J.; Winterfeld, Philip H.; Zerpa, Luis E. (Colorado School of Mines. Arthur Lakes Library, 2021)
    The commercial development of tight oil reservoirs has reshaped the landscape of the petroleum industry in North America. However, the recovery factor (RF) of tight oil with primary depletion is very low, mostly below 10%. With a large volume of remaining oil in tight oil reservoirs, the successful execution of Improved/Enhanced Oil Recovery (IOR/EOR), even with a minor improvement of 1%, would prompt a substantial production increase. Based on various field pilots, gas injection is by far the most promising IOR/EOR technology for tight oil reservoirs. This work developed an improved compositional model and its associated simulator to understand the complex multiphase and multicomponent behaviors during gas injection into tight oil reservoirs. The model accounts for the key physics in tight oil reservoirs, including nanopore confinement, multicomponent diffusion, and their coupling with geomechanics. Firstly, a hybrid algorithm combining the Successive Substitution and Newton's method was presented to improve the phase equilibrium calculation under confinement. Secondly, a modified formulation of the Maxwell-Stefan equation was presented to better quantify the multicomponent diffusion driven by the chemical potential gradient. A physics-based improvement was then proposed for the advection-diffusion model in fractured reservoirs, where fracture, matrix, and their interface are represented by three different yet interconnected continua to better capture the transient mass exchange between fracture and matrix. Thirdly, the transport is fully coupled with geomechanics during the computation of both primary and secondary variables. The numerical technique of solving the proposed model is also detailed, with special considerations to handle the numerical issues encountered during gas injection modeling. With the more general compositional model presented above, major modifications are implemented in Fortran to update the in-house simulator MSFLOW-COM for better modeling the gas injection processes in tight oil reservoirs. Fourthly, the implemented multicomponent diffusion formulation is validated with both intraphase and interphase diffusion experimental data. For the matrix-fracture mass transfer, the implemented MINC approach with three continua can better match the results of the fine grid model than the conventional double-porosity approach. The developed simulator MSFLOW-COM is validated with a commercial compositional simulator for both primary depletion and gas injection. After validation, the simulator is used to carry out two case studies. The first case study based on the Eagle Ford play investigates the impact of nanopore confinement, geomechanics, and their coupling. The simulation shows that the nanopore confinement has a minimal impact on RF for depletion and the early cycles of gas huff-n-puff (HnP), but in the long run, it reduces RF of the light components and increases RF of the heavy components. Geomechanics is an important factor in production but not always detrimental. The second case study based on the Permian Basin Wolfcamp Shale investigates the effect of multicomponent diffusion within the fractured tight oil reservoir. The simulation reveals that multicomponent diffusion has a minor impact on the performance of depletion as oil is the dominant phase. For gas injection, the simulation neglecting diffusion will underestimate the oil RF. With the diffusion included in the model, gas HnP becomes more sensitive to the soaking time than that without diffusion. Though a longer soaking time will achieve a higher RF after considering diffusion, the incremental oil is not high enough to justify a prolonged soaking time. Simulation using the double-porosity approach leads to a similar cumulative oil RF but overestimates the RF of heavy components compared with the MINC approach with three continua. To the best of the author's knowledge, the above studies cannot be done with any commercial simulators, which neglect fundamental physics, including nanopore confinement, multicomponent diffusion, and their coupling with geomechanics. The developed model and its associated simulator in this work can help researchers better understand the complex multiphase and multicomponent behaviors in tight oil production as well as be of great use for engineers to optimize gas injection parameters in field applications.
  • Nuclear forensics of uranium conversion: investigations of environmentally altered uranium compounds

    Jensen, Mark; Shafer, Jenifer C.; Pastoor, Kevin J.; Navarre-Sitchler, Alexis K.; Ranville, James F.; Pylypenko, Svitlana (Colorado School of Mines. Arthur Lakes Library, 2021)
    Uranium conversion, the chemical process used to convert uranium ore concentrates (UOCs) to uranium hexafluoride (UF6), is an essential step in the nuclear fuel cycle. All uranium destined for applications requiring isotopic enrichment must be converted to UF6. Understanding the chemistry of uranium compounds coupled to the conversion process is important to both the nuclear forensics community and nuclear industry. To address a critical knowledge gap, an emerging area of research is investigating environmentally driven changes in fuel cycle relevant uranium compounds. This dissertation focuses on UOCs and uranium tetrafluoride (UF4), important compounds coupled to the uranium conversion process. The initial work focused on an emerging hardening phenomenon observed in UOCs stored for prolonged periods. Characterization of several free-flowing and hardened UOC samples revealed the hardened material had undergone hydration and oxidation evidenced by elevated moisture content and the presence of various uranium compounds, particularly metaschoepite [(UO2)4O(OH)6](H2O)5 and schoepite [(UO2)4O(OH)6](H2O)6, not found in the parent material. Drying and calcination was shown to be a means of remediating un-processable, hardened UOCs, and identified a compound of potential nuclear forensics interest, dehydrated schoepite (UO2)4O(OH)6. A controlled aging study of three UOC chemical forms found they were stable for up to 9 months in low to moderate (<40%) relative humidity (RH) but higher RH (>67%) drove changes in chemical speciation, primarily forming metaschoepite. Overall, this work determined the hardening phenomenon stems from a chemical transformation in UOCs wherein H2O, either liquid or vapor, is an essential reactant. Moving forward in the uranium conversion process, the next effort investigated UF4. A controlled aging study found UF4 was stable for up to 9 months for a wide range of environmentally relevant conditions (20 and 35 °C, and ≤75% RH). However, exposure to higher RH conditions (>90%) drove changes in chemical speciation. Specifically, UF4 hydrate formed within 30 days for UF4 aged at 20 °C and 95% RH and within 180 days for UF4 aged at 35 °C and 91% RH. Investigation of the surface composition of unaged and aged UF4 samples revealed degradation of the surface consistent with the degradation observed for the bulk UF4. This work determined UF4 may persist in the environment for several months unless exposed to very high RH conditions, driving formation of UF4 hydrates. Finally, UF4·2.5H2O, recently identified as a relevant compound for nuclear forensics, nuclear fuel cycle science, and environmental concerns, was structurally characterized using density functional theory (DFT) and neutron powder diffraction. Complete elucidation of the structure revealed an extensive hydrogen bonding network involving water-fluorine and water-water interactions. Low temperature experiments and thermal analysis showed UF4·2.5H2O is thermally stable from 10 to 358 K, undergoes dehydration at higher temperatures and is nearly dehydrated at 473 K. This work determined UF4·2.5H2O is thermally stable at environmentally relevant temperatures, indicating it may persist in the environment. Overall, this work demonstrates the importance of understanding environmentally driven changes in relevant nuclear materials. It has shown that uranium compounds, including compounds previously considered stable, may undergo changes in chemical speciation when exposed to certain environmental conditions. These chemical speciation changes can be problematic for the nuclear industry, but the resulting compounds may be useful to the nuclear forensics and nuclear nonproliferation community as indicators of UOCs and UF4 exposed to very high RH or liquid H2O during storage. Future work should consider the role of minor impurities, additional uranium compounds, and other fuel cycle relevant nuclear materials.
  • Soil burn severity and climatic analysis of post-wildfire soil hydraulic properties from across the western continental United States

    Roth, Danica; Bedwell, Caroline J.; Walton, Gabriel; Singha, Kamini; Staley, Dennis M. (Colorado School of Mines. Arthur Lakes Library, 2021)
    Rainfall infiltration into soil is a key factor in both landscape development and generation of rainfall-runoff hazards like flash flooding and debris flows in recently burned areas. However, infiltration capacity is spatially and temporally variable, which makes its prediction challenging, particularly in burned environments. The extent of fire-prone areas in the western United States is growing, and locations where historically wildfires were rare are burning more frequently, highlighting a need for additional study of post-wildfire soil hydrology and associated hazards. In this work, I have compiled and re-analyzed new and existing post-wildfire Mini Disk infiltration datasets from two dozen wildfires across the western United States. This compilation contains field saturated hydraulic conductivity (KFS) estimates from different soil burn severity classes and collection times post-burn. I quantified the impact of three common methodologies for KFS estimation on the re-processed compilation, and assessed the overall fit of burned KFS estimates to normal family statistical distributions. To test if the observed variability in post-wildfire infiltration behavior can be explained by other landscape and climatological factors, I analyzed these datasets in conjunction with soil burn severity, climatological, and environmental data from each site. My results show that cumulative infiltration (CI), cumulative linearization (CL), and differentiated linearization (DL) methods for KFS estimation produce significantly different outcomes at different spatial and temporal scales, and estimates produced using these methods should not be directly compared if precision is required. Additionally, KFS estimates from burned environments do not show strong linear correlations with climatic and other environmental variables; however, the average change in KFS estimates between burn severity classes does show an inverse linear relationship with both 15-minute duration rainfall intensity for a 2-year recurrence interval storm, and pre-wildfire soil moisture. Better understanding of how post-wildfire infiltration behavior relates to regional climatic variables and burn conditions will be valuable in post-wildfire hazard prediction and modeling under the current regime of rapidly changing wildfire behavior.
  • Design and development of a hybrid near field and far field antenna measurement system, The

    Elsherbeni, Atef Z.; Velasco, Andres; Aaen, Peter H.; Hadi, Mohammed (Colorado School of Mines. Arthur Lakes Library, 2021)
    In this thesis, a dual-purpose antenna chamber measurement system is presented. The measurement system is an anechoic chamber where the near-fields or far-fields of an antenna can be measured with the same equipment. A custom software was developed to perform either type of measurement. This antenna chamber is a much more cost-effective solution compared to conventional antenna chambers, where separate chambers are used for different types of measurements. This thesis presents the developed software and hardware for a custom-made chamber design that produces accurate results. Both mechanical and software capabilities are introduced, but emphasis is put on the development of the software capabilities throughout this thesis. Both theoretical, numerical, and experimental analysis is introduced to verify the performance of the chamber. The necessary methods to perform the near-field to far-field transformations are presented and discussed in detail. A circular patch antenna is designed, simulated and tested to verify the accuracy of the far fields measured in the chamber, and a broadband horn antenna is measured to verify the accuracy of the near field measurements. The measured results for these two types of antennas matched the expected results, verifying the accuracy of each measurement type. Lastly, an antenna array is tested using both far field and near field systems, and the results from both measurement system were compared with each other. Good agreement is obtained, but due to the physical limitations related to the equipment used in the chamber and the size of the antenna some differences in the far field patterns are observed.
  • Tilted snowplow electron acceleration with simultaneously spatially and temporally focused laser pulses

    Durfee, Charles G.; Wilhelm, Alex Matthew; Adams, Daniel E.; Squier, Jeff A.; Pankavich, Stephen (Colorado School of Mines. Arthur Lakes Library, 2021)
    Advances in high power laser technology have enabled a new generation of laser driven particle accelerator technologies. These accelerators offer unique benefits such as larger acceleration gradients or higher repetition rates over conventional radio frequency acceleration methods. In this thesis I demonstrate both analytically and numerically a novel laser driven ponderomotive acceleration scheme for accelerating electrons in free space. The technique exploits the pulse front tilt (PFT) of simultaneously spatially and temporally focused (SSTF) laser pulses to reduce the pulse’s interaction speed with the electrons to below the vacuum speed of light. The reduction in the pulse front velocity allows electrons to be captured and accelerated sideways, like snow on a snowplow, by the ponderomotive force of the intense laser pulse. The analytic scaling laws of tilted snowplow ponderomotive acceleration are derived, and single particle simulations are performed to verify the basic scheme. In addition, a model of SSTF pulse propagation is implemented in the particle-in-cell (PIC) code OSIRIS 4.0 and used to study collective dynamics of the acceleration scheme. To study the dynamic evolution of the SSTF pulse, a novel version of the dispersion scan pulse characterization technique is demonstrated which can measure the temporal profile of the SSTF pulse at any longitudinal position in the focus and characterizes the angular chirp. This method is combined with a novel, improved phase retrieval algorithm for dispersion scan which uniquely determines the correct sign of the retrieved field through the application of Newton’s method. Additional work demonstrates a nonlinear optical process where photon spin can be converted to photon orbital angular momentum through second harmonic generation in underdense plasmas. This helps illuminate the fundamental nature of the angular momentum of light and its interaction with ordinary matter.
  • Effect of PWHT and filler metal on stress relaxation cracking susceptibility in 347H stainless steel welds for elevated temperature service

    Yu, Zhenzhen; Pickle, Timothy J.; Vidal, Judith; Findley, Kip Owen; Liu, Stephen (Colorado School of Mines. Arthur Lakes Library, 2021)
    347H stainless steel (SS) welds, used in commercial concentrating solar power (CSP) thermal energy storage at temperatures of 565 °C, are reported to be susceptible to stress-relaxation cracking (SRC) within months or years of service. Without prior stress relief via post weld heat treatment (PWHT), stress relaxation cracking may occur. The welded heat-affected zone (HAZ) and fusion zone (FZ) of 347H SS, particularly in thick sections greater than a half-inch, may be susceptible to reheat cracking during PWHT. The goal of this project is to determine the effect of PWHT and alternative alloys/filler consumables on reheat cracking in 347H SS welds to avoid SRC during service. Welding experiments on 347H SS substrates, using GTAW and SMAW, were completed to duplicate the susceptible microstructure for crack susceptibility testing using E347 and E16.8.2 weld consumables. Finite element modeling (FEM) was performed to reveal residual stress profiles. Reheat crack tests, using a Gleeble© 3500, were performed as a function of temperature, stress/strain, and microstructure. Four different sets of microstructures and materials were investigated: 1) simulated HAZ on 347H SS substrate material, 2) simulated HAZ on a modified 316L substrate material, 3) transverse cross-welded samples of E347-347H SS, and 4) transverse cross-welded samples of E16.8.2-347H SS. Finally, elevated temperature tensile tests at 600°C using the Gleeble© 3500 were used to determine the effect of PWHT on mechanical properties for all four sets of materials. The reheat crack tests indicate more rapid failure in higher pre-strains/stresses and higher test temperatures. The E347 FZ was demonstrated to be the most susceptible to cracking. The 347H HAZ samples exhibited a higher critical stress to failure threshold than E347 FZ and is deemed to be less susceptible to reheat cracking. Plastic strain (1%) in the E16.8.2 FZ was needed to cause cracking. Furthermore, failure occurred preferentially in the 347H HAZ instead of the E16.8.2 FZ. No cracking was detected in the modified 316L SS samples up to 16% strain. Careful PWHT design is needed to prevent cracking in 347H welds, and E16.8.2 consumable demonstrates to be the best SRC mitigation technique in FZ among the filler tested.
  • Advancing cyanobacterial production of sustainable chemical feedstocks

    Boyle, Nanette R.; Newman, Darrian M.; Ramey, C. Josh; Krebs, Melissa D. (Colorado School of Mines. Arthur Lakes Library, 2021)
    The temperature on earth is rising. Studies show that the average surface temperature is already 1°C higher than in pre-industrial times. This rise in temperature is directly linked to anthropogenic carbon emissions and will only continue to rise if immediate action is not taken. Work to improve sustainability in our society has already begun, with vast improvements in solar, wind, geothermal, and other forms of sustainable energy production being made every day. Fossil fuel dependency is pumping carbon dioxide into our atmosphere at unsustainable rates, and cyanobacteria present a feasible means to combat emissions and close the carbon loop for a more sustainable future. Cyanobacteria are prokaryotic, photosynthetic microorganisms with the capability to produce a wide range of chemicals, from biofuels to plastics to sugar to rubber, all while utilizing minimal resources. Only sunlight, trace minerals, unarable land, and sub-optimal water such as ocean water are needed for growth and production of valuable specialty and commodity chemicals. With a higher photosynthetic eciency and genetic tractability than plants and no competition for arable land or fresh water, cyanobacteria have the potential to be pivotal in the ght against climate change. In this thesis, I characterize the central metabolism of a biofuel producing strain of cyanobacteria to gain a better understanding of how to manipulate cyanobacterial metabolism for increased production of not only biofuels but a range of valuable products. I probe pathways of primary and secondary metabolism using metabolic engineering techniques in an eort to glean useful information and help demystify the complex metabolic network of these complex organisms. Additionally I improve and validate existing tools needed to accelerate the design-build-test-learn cycle and establish cyanobacteria as a commercially viable sustainable producer of valuable products.
  • Breaking the barrier of drilling automation: measuring the distance drilled at the bottom of the well using an imaging while drilling tool

    Zerpa, Luis E.; Sampaio, Jorge; Mansour, Ahmed Khaled Abdelmaksoud; Prasad, Manika; Shragge, Jeffrey; Eustes, Alfred William (Colorado School of Mines. Arthur Lakes Library, 2021)
    Drilling technology has advanced rapidly over the past few decades. The petroleum industry is motivated to automate directional drilling operations, making them safer, more cost- effective, and efficient. The main input parameters fed to directional drilling tools (e.g., rotary steerable systems) are inclination, azimuth, and distance. Inclination and azimuth are measured downhole; however, the distance drilled is computed using a pipe tally system installed on the surface. Having continuous downhole measurements of distance, inclination, and azimuth allow the directional drilling tool to determine the drilling bit's location. Moreover, if most calculations were made downhole, then the bit could follow a preprogrammed trajectory and drill autonomously. Many researchers have proposed different methods for measuring the distance drilled in the bottomhole as a solution for directional drilling automation. However, the suggested approaches have experienced challenges during field applications. For this reason, this dissertation focuses on solving one of the main limiting factors, i.e., real-time downhole measurements of the distance drilled.This work proposes a method that senses the distance drilled at the bottom of the well based on automated image analysis. The dissertation involves the development of a tool prototype with multiple identical imaging sensors spaced at known distances. The sensors acquire images of the formation at synchronized times, with the imaging sensors capturing an image of the same formation location at different times. Based on this concept, an algorithm was developed to identify the "fingerprints" of the images captured and register similar images according to those fingerprints. Under wellbore conditions, each fingerprint reveals unique marks left by the bit, natural geological features of the rocks drilled, and the topology of the borehole wall, all of which contribute to the image registration process. Therefore, when two images captured by two sensors match, the timestamps of each image and the distance between the sensors can be used to calculate the average rate of penetration in that time interval. Subsequently, integrating the rate of penetration results in an estimate of the interval distance drilled. Adding all intervals drilled is then equivalent to the total distance of the well, and combining this information with azimuth and inclination can provide an estimate of the depth drilled. This dissertation aims to demonstrate that an image-matching process is an attractive candidate for downhole measurements that compute the distance drilled. In this work, an image-matching algorithm is developed with the sole intention of estimating the distance drilled. Tests were designed to analyze the effect of different variables on the accuracy of the distance calculation. Experiments were devised to investigate how sampling criteria, the distance between the sensors, velocity, matches missed, and noise affect the method's efficacy. The method was tested in homogeneous and heterogeneous scenarios (i.e., images with distinct and repetitive features) to ensure that the algorithm can match images when exposed to analog scenarios that model wellbore conditions. The results show that the image-matching algorithm can accurately match images even when wellbore features are considerably repetitive. Additionally, having an optimized velocity-dependent combination of sampling criterion and distance between the sensors can minimize errors, especially those associated with missed matches, and therefore, increase the accuracy of the distance calculation. The main contribution of this Ph.D. dissertation is that it demonstrates that having identical sensors capture images showing topological features can be a robust method to measure the distance traveled. Additionally, this work provides initial research on how to optimize controllable variables to minimize errors. The results suggest that the proposed method has the potential to automate directional drilling and continuously determine the well path when combined with inclination and azimuth information.
  • Video rate spatial frequency modulation imaging

    Squier, Jeff A.; Kingsolver, Ian Mars; Durfee, Charles G.; Adams, Daniel E. (Colorado School of Mines. Arthur Lakes Library, 2021)
    This thesis discusses the first Spatial Frequency Modulation Imaging (SPIFI) system capable of collecting data at video rate speeds. In the brief history of SPIFI, systems have been limited in imaging dynamic samples due to line imaging rates in the range of 20 to 30 hertz. The creation of a Video Rate SPIFI (V-SPIFI) system, utilizing a stationary reflective rectangular modulation plane and an air-bearing polygonal scan mirror, allows for dynamic sample imaging with concurrent data availability. The resulting V-SPIFI system is capable of capturing line images over 240 times faster than previous SPIFI systems. By implementing a prototype electronic optical control subsystem, the V-SPIFI system is also capable of automatically scanning a sample and rendering 25 first and second harmonic order images in approximately five seconds. To provide context, a brief history of modern microscopy techniques and limitations is included. Next, using the theory of SPIFI imaging, the modeling and construction of the six interconnected optical and electronic subsystems required for the V-SPIFI system are detailed. Resulting first and second order harmonic images are presented, including pixel size and estimated first order image resolution. A visual verification of image accuracy is also provided. Finally, concepts for future V-SPIFI systems are discussed, as well as possible applications of the V-SPIFI system.
  • Laser-produced spark test bed for plasma diagnostics

    Durfee, Charles G.; Hinnegan, Sarah; Flammer, P. David; Adams, Daniel E. (Colorado School of Mines. Arthur Lakes Library, 2021)
    A laser-produced spark test bed for plasma diagnostics has been developed to investigate the complex processes involved in the development of a plasma spark. By using a pair of laser pulses to ionize the test gas, a plasma is produced that has a well-defined start time and repeatable characteristics. These diagnostics include time-resolved spectra in ultraviolet and visible, spectral line broadening, and continuum evolution. These measurements can be used to analyze plasma and electron temperatures and the evolution of the plasma species. Analysis of laser-produced sparks supports a collaborative investigation between the Colorado School of Mines and Los Alamos National Lab into how much energy from electrostatic discharges is delivered to a victim load. We use the fourth harmonic (λ = 266 nm) from a high-power Q-switched laser to pre-ionize the gas at the lens focus. This low-density plasma is heated by a high-energy second pulse at the fundamental (λ = 1064 nm) to produce a denser plasma through collisional ionization. The spark is produced in a vacuum chamber where the composition and pressure of the gas is controlled to simplify identification of plasma species as well as to compare the spectral measurements between different gases. High-speed imaging and precise camera triggering are used to produce time-resolved experimental imaging and spectroscopy measurements. The initial results from the direct spark imaging and spectral imaging demonstrate our ability to analyze plasma species evolution, broadband evolution, and spectral line broadening of sparks in various gas compositions and at controllable pressures through the lifetime of the sparks using the laser-produced spark test bed.
  • Exploring the impact of heterogeneity on weathering in fractured rocks

    Navarre-Sitchler, Alexis K.; Andrews, Elizabeth M.; Gorman, Brian P.; Singha, Kamini; Maxwell, Reed M. (Colorado School of Mines. Arthur Lakes Library, 2021)
    Fractured rock is ubiquitous throughout the Earth's surface and near-surface environments. Fractures act as preferential flow pathways through an otherwise relatively impermeable medium, delivering reactive fluids and transporting solute through the subsurface. The ubiquity of fractures in the natural environment and the important role they play in rapid delivery of fluid to the subsurface makes flow, transport, and reaction in fractures an important field of study. This study uses numerical simulations to better understand how heterogeneity associated with fractures impacts mineral dissolution rates. In addition, the rate of mineral dissolution impacts the extent of reaction front propagation, which has important implications for anthropogenic use of fractured rocks as repositories for geologic storage of CO2 or nuclear waste. In 2 and 3 dimensional models, the rate of mineral dissolution is impacted more by the fluid flow rate than the structure of the subsurface fracture pattern, additionally, the reaction over geologic timescales becomes transport-limited. The findings from the numerical studies are then applied to a field site with unique subsurface structures across a north and south-facing hillslope in the Gordon Gulch catchment of the Boulder Creek Critical Zone Observatory. The presence of groundwater wells across the catchment allows us to determine that water draining the fractured bedrock is saturated with respect to the major minerals and therefore reaction is transport-limited at the field scale. This study shows that mineral dissolution in heterogeneous domains leads to depletion of minerals in fast flowpaths over relatively short geologic timescales, but reaction over long geologic timescales occurs in protected regions, or matrix, that are transport-limited.
  • Recrystallization of Cu(In,Ga)Se₂ thin films by metal halide vapor treatments

    Rockett, Angus A.; Palmiotti, Elizabeth C.; Packard, Corinne E.; Wolden, Colin Andrew; Gorman, Brian P. (Colorado School of Mines. Arthur Lakes Library, 2021)
    CuIn_(1-x)Ga_xSe_2 (CIGS) thin film photovoltaic module performance and manufacturing have shown significant successes; however, cost has limited a large-scale commercial presence. Significant reductions in absorber deposition time and temperature are necessary to minimize expenses to compete as a single junction technology. Due to a tunable band gap, an alternative future for CIGS is using a wide band gap alloy, CuGaSe_2 (CGS) as a top cell in a tandem structure with silicon. However, wide gap CIGS materials produce devices which are typically of poor quality due to kinetically-limited growth which results in secondary phases, small grains, and inhomogeneities. In this thesis these problems are addressed through novel metal halide vapor treatments to recrystallize CIGS thin films. In this work, metal halide compounds used for treatment are selected such that the cation is already a species in the (Cu,Ag)(In,Ga)Se_2 alloy system and the anion is a halide. Metal halide vapor treatments to CIGS films deposited at 350°C result in large grain growth and improved crystallinity. Composition variation occurs depending on the metal halide used, though, gallium depletion is common for all. It is also demonstrated that the metal halide treatments catalyze and accelerate the crystallization kinetics for CIGS using in-situ high-temperature x-ray diffraction (HT-XRD). An evaluation of metal halide thermodynamic properties is presented and compared to experimental results. Based on bond dissociation energies, CuBr, CuI, AgBr, and AgI are recommended as metal halide source materials with a preference to AgBr and AgI due to the known benefits of Ag alloying. It is proposed that growth occurs by vapor phase transport induced by a halide transport agent. The halide anion forms volatile compounds with metal cations on the surface of one grain, which etch and re-deposit onto the surface of a neighboring grain. This causes the observed grain growth and defect passivation. For such volatile compounds with very high vapor pressures, such as the Ga-halide compounds, re-deposition to a neighboring grain surface is too slow and results in the preferential etching of such metallic species. The beneficial treatments are applied to CGS films to replace a long, high-temperature deposition procedure necessary to fabricate uniform films. Instead, the deposition is interrupted and AgBr evaporated during growth, reducing deposition time by ~50%. This results in large grains, phase homogeneity, and device efficiency improvements due to open-circuit voltage and fill factor.
  • Modeling the reduction thermodynamics of simple and Ruddlesden-Popper cerium-doped perovskites for solar thermochemical hydrogen production

    O'Hayre, Ryan P.; Sanders, Michael; Bergeson-Keller, Anyka M.; Jackson, Gregory; Stevanovic, Vladan (2021)
    In this work, the compositional families Sr1-xCexMnO3−δ (SCMX, X = 100x,x= 0.10, 0.20, & 0.30) and CexSr2-xMnO4−δ (CSMX, X=100x, x= 0.10, 0.20, & 0.30) are studied to determine the effects of perovskite structure and cerium content on the thermal reduction thermodynamics and the resulting impact on solar thermochemical hydrogen-production (STCH). Relying on thermogravimetric results from oxygen nonstoichiometry experiments, fits for various thermodynamic quantities, including defect-reaction specific enthalpy and entropy, ∆H◦ and ∆S◦, as well as theδ-dependent standard partial molar enthalpy and entropy of oxygen, ∆ ̄h◦O and ∆ ̄s◦O, are produced as a function of composition within these two perovskite families using a thermodynamic model developed herein. The results of this thermodynamic study in the context of structure and cerium dopant level are discussed, and several improvements to the model are proposed and explored. Experimental hydrogen production results show that the SCM family produces slightly larger amounts of hydrogen per mole of oxide compared to the CSM family under similar reduction and oxidation temperature conditions, however a direct correlation between structure, cerium content and water-splitting capacity could not be discerned. Lastly, compositions of Ca1-xCexMnO3−δ(CCMX, X = 100x, x= 0, 0.10 & 0.20) are explored for the composition’s predicted ability to reduce on both the A- and B-sites of the simple perovskite oxide material, however low melting temperatures prevent further study of this compositional family for STCH purposes.
  • Analog and digital adiabatic quantum annealing with oscillating transverse fields

    Kapit, Eliot; Tang, Zhijie; Han, Qi; Eley, Serena; Gong, Zhexuan (Colorado School of Mines. Arthur Lakes Library, 2021)
    This thesis investigates both analog Quantum Annealing and digital Quantum Annealing with oscillating transverse field in solving hard optimization problems. In the first part, we consider a range of unconventional modifications to Quantum Annealing (QA), applied to an artificial trial problem with continuously tunable difficulty. In this problem, inspired by “transverse field chaos” in larger systems, classical and quantum methods are steered toward a false local minimum. To go from this local minimum to the global minimum, all N spins must flip, making this problem exponentially difficult to solve. We numerically study this problem by using a variety of new methods from the literature: inhomogeneous driving, adding transverse couplers, and other types of coherent oscillations in the transverse field terms (collectively known as RFQA). We show that all these methods improve the scaling of the time to solution (relative to the standard uniform sweep evolution) in at least some regimes. Comparison of these methods could help identify promising paths towards a demonstrable quantum speedup over classical algorithms in solving some realistic problems with near-term quantum annealing hardware. In the second part of the thesis, we explore a digitized version of RFQA inspired by the performance of RFQA in analog quantum computing. The digitization of Quantum Annealing is a combination of analog Quantum Annealing(QA) and Quantum Approximate Optimization Algorithm (QAOA). Digitized-QA can be applied to full-scale, fault-tolerant quantum algorithms. We apply the digitized version of RFQA and QA to various trial problems using classical numerical simulation and show that digitized-RFQA is a potentially promising tool in solving hard optimization problems and can be a new tool to complement QAOA and traditional digitized-QA. In the third part of the thesis, for the preparation of an experiment, we investigate the 1D TFIM(transverse field ising model) and show that RFQA-D is able to accelerating the N-spin tunneling, the acceleration suggests that RFQA has the potential of mitigating the cost of minor embedding overhead.
  • Thermal and thermal electric measurements in superconductor-ferromagnetic heterostructures

    Singh, Meenakshi; Blagg, Kirsten Elizabeth; Toberer, Eric; Gong, Zhexuan; Lu, Tzu-Ming; Brennecka, Geoffrey (Colorado School of Mines. Arthur Lakes Library, 2021)
    Electrical and spin transport measurements at cryogenic temperatures have powered new arenas of research and applications. However, exploration into thermal effects at cryogenic temperatures has only just begun. Recent thermal transport measurements at low temperatures have led to interesting novel physics in the fields of quantized heat flows, quantum thermodynamics, thermal Josephson effects, quantum heat engines, and thermoelectric materials. In particular, superconductor-ferromagnetic (S-F) systems have recently been proposed as effective thermoelectric devices. While conventional superconductors are known to be poor thermoelectric materials, the combined effects of spin splitting and spin filtering provided by an external magnetic field and magnetic material are predicted to create an asymmetry in the superconducting density of states and generate thermoelectric effects. These S-F systems have been predicted to have a thermoelectric figure of merit (zT) of 1.8, far exceeding any other thermoelectric materials at cryogenic temperatures. If these predictions hold true, S-F thermoelectrics could have applications in nanoscale cooling and as radiation or single photon detectors. In this thesis, we have directly measured the Seebeck voltage in S-F structures down to 8 mK and developed the hardware and techniques necessary to make such a measurement at cryogenic temperatures. First, we review the background and theoretical underpinnings which inform and motivate the study of S-F systems as thermoelectric materials. Second, we report our development of methods for the electrodeposition of superconductor and ferromagnetic nanowires, including the first fabrication of niobium nanowires via electrodeposition. Third, as methods of thermal measurements at cryogenic temperatures are not well established, we have developed an experimental platform for low dimensional temperature measurements. Our experimental advances in this area include the development of an on-chip cryogenic thermometer that is sensitive down to 8 mK and can be placed on the chip with 100s of nm precision in a lithography free process. We also have quantified local, on-chip heating using AC and DC power as a function of distance, power, frequency, and sample configurations. Finally, we directly measure the Seebeck coefficient of Al, Ni, and an Al-Ni junction below 1 K.
  • DC-RST: a highly parallel, divide-and-conquer algorithm for creating random spanning trees on a clique

    Mehta, Dinesh P.; Henke, Lucas R.; Belviranli, Mehmet E.; Painter-Wakefield, Christopher (Colorado School of Mines. Arthur Lakes Library, 2021)
    We describe DC-RST, a highly parallel, divide and conquer algorithm for generating a random spanning tree of a complete graph on $n$ vertices such that each edge in the graph is chosen with equal probability. DC-RST parallelizes Wilson's sequential random-walk algorithm which has an expected complexity of $\Theta(n)$ on a complete graph. On a system with 48 cores, on some instances, DC-RST was up to 4X faster when first creating random partitions and up to 20X faster without this sub-step. Although the spanning trees generated by DC-RST are random, unlike those generated by Wilson's algorithm, they are not \textit{uniform} random spanning trees. The proposed application of DC-RST is network analytics, where we seek to determine whether two distance metrics on a graph with $n$ entities are statistically correlated. DC-RST utilizes parallelization to speed up \textsc{DimeCost}, a sequential linear-time algorithm based on uniform random spanning trees. Although DC-RST does not create \textit{uniform} random spanning trees, our preliminary statistical testing comparing it with \textsc{DimeCost}, indicates that results obtained by DC-RST are reliable.
  • Equilibrium and kinetic characterization of the ALSEP process: probing organic phase metal complex speciation & defining the role of buffer in the strip step

    Jensen, Mark; Picayo, Gabriela A.; Shafer, Jenifer C.; Williams, S. Kim R.; Anderson, Corby G. (Colorado School of Mines. Arthur Lakes Library, 2021)
    Implementation of advanced nuclear fuel cycles is critical to a sustainable future for nuclear energy production. Closed nuclear fuel cycles proposing to transmute long-lived minor actinide elements, such as americium, into shorter-lived nuclides using advanced reactors hinge on the separation of americium from the lanthanides. Though many separation schemes have been proposed, the physicochemical properties of the trivalent actinides and lanthanides pose a challenge to refining their efficiency for industrial application. The ALSEP (Actinide-Lanthanide SEParation) process is a relatively new separations protocol whereby the An3+ and Ln3+ cations are (1) co-extracted from 3-4 M nitric acid into a mixture of the extractants HEH[EHP] (2-ethylhexyl phosphonic acid mono-2-ethylhexyl ester) and TEHDGA (N,N,N’,N’-tetra(2-ethylhexyl)diglycolamide) in n-dodecane, (2) scrubbed of excess nitric acid with a buffered aqueous solution, and (3) selectively stripped of americium by a buffered aqueous phase containing polyaminopolycarboxylate ligand, commonly DTPA (diethylenetriaminepentaacetic acid) or HEDTA (N-(2-hydroxyethyl)ethylenediamine-N,N’,N’-triacetic acid). Though ALSEP has demonstrated many advantages over its predecessors, the fundamental chemistry of the strip step remains a critical bottleneck to the process’ implementation. The body of work available for understanding equilibrium complexation and the kinetic barriers in ALSEP is limited. Accurate interpretation of kinetic data begins with defining the speciation of the metals, ligands, and extractants in each phase and step. The equilibrium characterization work presented here is the first to provide a definitive stoichiometry for the metal extracting complex in ALSEP. In addition, changes in complexation were probed in both buffered and un-buffered systems, over a broad range of process relevant acidities. A speciation model of the metal-extractant complexes that describes the speciation transitions from start to finish are also defined for the first time. Finally, the kinetics of the strip step was investigated using buffered and self-buffered EDTA (ethylenediaminetetraacetic acid) solutions. Rate laws were attained, and reactions contributing to the rate-limiting mechanism were suggested. Additionally, EDTA was replaced with the self-buffering picolinic acid-substituted derivative EDTA-Mpic (N-2-methylpicolinate-ethylenediamine-N,N’,N’-triacetic acid), to access the stripping kinetics under lower pH conditions. The evidence so far suggests that picolinate functionalization improves mass transfer rates through the solubility of the picolinic acid substituted arm and provides effective self-buffering for similar kinetic benefits to that seen in the standard ALSEP system.
  • Quantum error mitigation and autonomous correction using dissipative engineering and coupling techniques

    Kapit, Eliot; Rodríguez Pérez, David; Strong, Scott A.; Singh, Meenakshi; Gong, Zhexuan (Colorado School of Mines. Arthur Lakes Library, 2021)
    Realizations of quantum computing devices have progressed significantly, with each choice of architecture possessing advantages and disadvantages. Superconducting qubits are able to perform very fast gates, and benefit from standard manufacturing, but they suffer from very short coherence times compared to other architectures like trapped ions or spin qubits. This presents one of the greatest challenges towards achieving fault-tolerant quantum computing with superconducting architectures---improving coherence times. To that end, considerable research has been devoted to engineering qubits with longer lifetimes. Likewise, several error correction protocols have been introduced to provide a route towards fault-tolerance using noisy qubits, where a logical qubit is encoded in a collective state of many physical qubits, using stabilizer operations to detect and correct single qubit errors, thereby prolonging the logical state lifetime. However, the quantum resources required for the thousands of logical qubits needed for a factorization algorithm can be on the order of tens of millions of physical qubits for realistic error rates using surface codes. This would also require an immense amount of resources for the classical post-processing and decoding, a challenge for which there has not been a well established solution. The work in this thesis focuses on the implementation of logical qubits with autonomous error correction using dissipative engineering, in which high-coherence qubit devices are stabilized by coupling to lossy ancilla. The systems studied here have the advantage that a logical manifold can be encoded with a much smaller number of physical qubits compared to more traditional digital error correction codes, thus are called small logical qubits. This thesis presents results on improving autonomous error correction using numerically optimized pulse shaping for time parameterized coupling strength in different small logical qubits. It also presents results on a proposed scheme for error mitigation for the implementation of two-qubit gates---a dominant source of error in NISQ algorithms. Lastly, this thesis presents ongoing work with the simulation of dissipative engineering for variational quantum algorithms to improve algorithm performance.
  • Assessing the environmental, economic, and social sustainability of guar and guayule cultivated in the southwest United States

    Landis, Amy E.; Mealing, VeeAnder S.; McCray, John E.; Munakata Marr, Junko; Smith, Jessica, 1980- (Colorado School of Mines. Arthur Lakes Library, 2021)
    Since the mid 20th century, energy consumption has been the main driver of human-induced climate change, rapidly warming the planet’s atmosphere, oceans, and land. These trends have led to growing efforts to develop more sustainable feedstocks to meet increasing energy demands. Guar (Cyamopsis tetragonoloba) and guayule (Parthenium argentatum) are potential feedstocks for renewable fuels; these crops have highly valuable co-products that can enhance their economic viability. Guar and guayule are draught tolerant crops that can be cultivated in the Southwest US. Guar bagasse can be utilized to produce bioenergy, and its co-products include guar gum, a highly valuable chemical used in the food industry as an emulsifier and in the hydraulic fracturing industry as a friction reducer. Guayule bagasse can also be utilized to produce bioenergy, and its valuable co-products include natural rubber and resin, the latter of which can be used to make adhesives, coatings, antifungal agents, and fuels. To ensure holistic sustainability of these emerging agricultural feedstocks, an array of sustainability tools must be utilized in tandem. This thesis quantifies the three pillars of sustainability - environmental, economic, and social – for guar and guayule and assesses their potential to be integrated into the southwestern bio-economy. Life cycle analysis (LCA) was used to quantify the environmental impacts of guar and guayule, highlighting that irrigation is the main driver of agricultural impacts and thus provides the biggest opportunity for improved agricultural sustainability. Techno-economic analysis (TEA) quantifies the economic impact of guayule rubber production showing irrigation as the main agricultural contributor of economic impacts, while the largest processing contributor is capital/loans. This research is unique in its LCA and TEA approach, where data was collected from field trials and interviews of farmers and researchers were utilized to determine data quality and likelihood. This process produces more robust LCA and TEA results that are more representative of commercial farming practices. Existing social assessment tools were reviewed to determine the most appropriate approach for evaluating social sustainability. Ultimately, social sustainability was assessed by conducting focus groups of guar and guayule farmers and experts to identify social challenges and opportunities. This research aids in providing a clear path for the holistic sustainable development of a bio-economy in the Southwest US for guar and guayule.
  • Nanomaterial-loaded contact lenses for treating anterior segment ophthalmic diseases

    Chauhan, Anuj; Liu, Zhen; Knauss, Daniel M.; Samaniuk, Joseph R.; Krebs, Melissa D.; Kompella, Uday B. (Colorado School of Mines. Arthur Lakes Library, 2021)
    Most eye diseases are treated by eye drops which are not efficient due to low bioavailability. Contact lenses are ideally suited to treat anterior segment diseases because of their proximity to cornea. Prior research has demonstrated that contact lenses are useful for increasing bioavailability and providing sustained drug release. Here we investigate gold nanoparticle-loaded contact lenses (GoldinLenses), which can be potentially useful for treating multiple ophthalmic diseases. Ocular cystinosis is a metabolic disease, which is characterized by an accumulation of cystine crystals in the cornea. Since cystine can bind to gold particles, when a GoldinLens is worn, cystine molecules in the tear film are expected to transport into the GoldinLens and attached to the surface of gold nanoparticles due to the high affinity of cystine molecules to the gold. Therefore, the concentration of cystine molecules in the tear film decreases, which result in the transport of cystine molecules from the cornea to the tear film, followed by a clearance (dissolution) of the cystine crystals in the cornea. Result shows that a maximum cystine uptake in vitro reaches 47 µg/lens within 5 hours, which may be therapeutic, but the permeability of cornea which may reduce the maximum amount that can be transport if the lens is worn for a few hours each day. We also explore the feasibility of utilizing GoldinLenses for laser protection (532 nm) due to the existence of gold nanoparticles. Gold nanoparticles absorb the radiation, which provide a superior laser protection efficacy, compared with the commercial laser safety glasses (around 50\%). Besides, the absorbed radiation by the gold nanoparticles results in a heat generation due to the electron clouds oscillation under the laser radiation, which can be utilized for meibomian gland dysfunction (MGD) dry eye treatment. MGD dry eye can be treated by warm compression treatment because warming the glands is expected to increase the lipid secretion. Therefore, GoldinLens will serve as an inner heating source to warm up the glands, which will be beneficial for increasing the lipid secretion from the glands. Since GoldinLenses may not be able to effectively treat cystinosis, we also explore designing contact lenses for sustained drug delivery. Prior research has shown that vitamin E aggregates in the contact lens behave as diffusion barriers to increase the diffusion pathway, which results in a more sustained drug delivery. Prior research was based on soaking lenses in vitamin E dissolved in ethanol which is effective but the process has challenges due to significant lens swelling. In our study, we increase the water content in the vitamin E loading solution up to 25\% (wt\%) to reduce the extent of swelling. Addition of water however reduces the solubility of vitamin E, but there is a concurrent increase in partition coefficient of vitamin E, which still allows loading of significant amount. This process does not affect the morphology of vitamin E barriers in the lens. Therefore, as for the contact lenses with similar vitamin E loading, the hydrophilic drug release profiles are similar, regardless the water content in the loading solution.

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