• Design considerations for the third generation advanced high strength steel

      Matlock, David K.; Gibbs, Paul Jacob; Van Tyne, C. J.; Speer, J. G.; Kaufman, Michael J.; Berger, John R. (Colorado School of Mines. Arthur Lakes Library, 2012)
      Advanced high strength steels containing metastable austenite are of considerable interest due to the combinations of strength and ductility that are achieved via austenite transformation to martensite during deformation. A methodology is presented to design microstructures containing systematic amounts of metastable austenite with controlled stability against transformation based on Mn enrichment of austenite during intercritical annealing of medium Mn (5 to 10 wt pct.) low carbon (0.1 and 0.15 wt pct.) steels. Five steels were selected for experimental investigation. Three cold rolled low C (0.1 wt pct. C) medium Mn-TRIP steels (5.1, 5.8, and 7.1 wt pct. Mn) steels were annealed at temperatures between 575 °C and 675 °C for 168 hr to enrich austenite in C and Mn. The predicted amount of Mn in austenite decreased from 14.7 wt pct. (575 °C) to 8.5 wt pct. (675 °C) in the 7.1Mn-0.1C steel. The heat treated microstructures consisted of ferrite, [epsilon] and [alpha]' martensite and austenite amounts between 0 and 47.5 pct. Two low C (0.14 wt. pct.) medium Mn (7.4 and 10.1 wt pct.) high Al (1.6 wt pct.) steels were annealed using a two-step method, intercritical annealing at 600 °C or 700 °C for 96 hr followed by cold rolling and supercritical annealing at 850 °C to produce martensitic microstructures with retained austenite. Uniaxial tensile testing, stress relaxation testing, and electron microscopy were used to characterize microstructural changes with deformation; in situ neutron diffraction was also performed on selected steels. The intercritically annealed 0.1C Mn-TRIP steels displayed systematic changes in tensile behavior dependent on the intercritical annealing temperature; ranging from high-ductility limited work hardening for the lowest test temperature (575 °C, 32.6 wt pct. austenite), to increasing strain hardening resulting in high strength and ductility (600 °C, 38.8 wt pct. austenite) to low ductility, high strength at the highest annealing temperatures (650 °C, 47.5 wt pct.). The stability of austenite during deformation depended on the C and Mn content of austenite, lower Mn contents corresponded to rapid transformation at yielding (650 °C) while high Mn contents resulted in limited austenite transformation (575 °C); optimum tensile properties resulted from significant austenite transformation above 10 pct. strain (600 °C). Heat treatment of the medium Mn-0.14C-1.6Al steels resulted in martensitic microstructures with alloy and processing dependent amounts of retained austenite, 8.5 wt pct. in the 7.4Mn-0.14C-1.6Al steel and 22 wt pct. in the 10.1Mn-0.14C-1.6Al steel. The 7.4Mn-0.14C-1.6Al steel showed power law hardening after austenite transformation resulting in plastic instability while the 10.1Mn-0.14C-1.6Al steel displayed apparent brittle fracture during uniform deformation. The change in tensile behavior corresponded to a change in the distribution of internal stresses between phases with austenite transformation. Austenite morphology is suggested to control the distribution of internal stresses in the microstructure.
    • Veladero high-sulfidation epithermal Au-Ag deposit, Argentina: volcanic stratigraphy, alteration, mineralization, and quartz paragenesis, The

      Monecke, Thomas; Holley, Elizabeth Ann Gleason; Bissig, Thomas; Eggert, Roderick G.; Hitzman, Murray Walter; Kelly, Nigel; Nelson, Eric P., 1951- (Colorado School of Mines. Arthur Lakes Library, 2012)
      The Veladero Au-Ag high-sulfidation epithermal deposit is located in the El Indio-Pasuca belt in Argentina. Veladero is an oxidized deposit that hosted reserves of 12.2 Moz of Au and 226.2 Moz of Ag at the end of 2008. Ore is primarily hosted in silicified breccias. The volcanic package at Veladero is a coalescing complex of domes, diatremes, and hydrothermal breccia bodies, mantled by a thick apron of volcaniclastic deposits. These units are inferred to be of Cerro de las Tortolas age (16.0 plus or minus 0.2 to 14.9 plus or minus 0.7 Ma) at Amable in the southern part of the Veladero area, and Vacas Heladas age (12.7 plus or minus 0.9 to 11.0 plus or minus 0.2 Ma) at Filo Federico in the northern part of Veladero. Emplacement of hydrothermal breccia units was accompanied or shortly followed by multiple pulses of magmatic-hydrothermal and alternating jarosite alteration from about 15.4 to 8.9 Ma. Alunite and jarosite40 Ar-39 Ar ages and U-Pb zircon ages of crosscutting dikes restrict mineralization at Amable to the period from 15.4 to 12.14 plus or minus 0.11 Ma, probably commencing closer to 12.7 Ma. At Filo Federico, Au mineralization commenced after the beginning of alunite alteration at 11.05 plus or minus 0.12 Ma. The new data suggest that the maximum age of mineralization in the belt is slightly higher than previously recognized The bulk of Veladero Ag is hosted in Ag-bearing jarosite in the jarosite-argentojarosite solid solution. Some silver occurs as less than 0.1 Mu m iodargyrite and aggregates of less than 0.1 Mu m particles with variable Ag, I, Br, Cl, Hg, Se, S, and Fe concentrations. Rare Ag-Fe sulfides were identified. Veladero Au exists as greater than 800 fineness grains of native Au. A phase of euhedral, fracture-controlled quartz with growth zone parallel iron oxide inclusions has been identified at Veladero, post-dating leaching of the host rock to vuggy quartz and pre-dating Au mineralization. The quartz is evidence that the fluids that transport the precious metals are distinct from the magmatic vapors that interact with meteoric water to produce alteration in high-sulfidation disseminated deposits, and that at least the first stage of metals are transported by a low-temperature fluid also capable of precipitating quartz
    • Anisotropic velocity analysis of P-wave reflection and borehole data

      TSvankin, I. D.; Wang, Xiaoxiang; Davis, Thomas L. (Thomas Leonard), 1947-; Miskimins, Jennifer L.; Sava, Paul C.; Tenorio, Luis (Colorado School of Mines. Arthur Lakes Library, 2012)
      Efficient application of the modern imaging technology requires development of velocity-analysis methods that take anisotropy into account. In the thesis, I present time- and depth-domain algorithms for anisotropic parameter estimation using P-wave reflection and VSP (vertical seismic profiling) data. First, I introduce a nonhyperbolic moveout inversion technique based on the velocity-independent layer-stripping (VILS) method of Dewangan and Tsvankin (2006). The layer stripping of moveout parameters in the conventional method is replaced by the more stable stripping of reflection traveltimes. Then, to estimate the interval parameters of TTI (transversely isotropic with a tilted symmetry axis) models composed of homogeneous layers separated by plane dipping interfaces, I develop 2D and 3D inversion algorithms based on combining reflection moveout with borehole information. These algorithms help build an accurate initial TTI model for migration velocity analysis. To perform parameter estimation for more complicated heterogeneous TTI media, I develop a 2D P-wave ray-based tomographic algorithm. The symmetry-direction velocity VPO and the anisotropy parameters Epsilon and Delta are iteratively updated on a rectangular grid, while the symmetry-axis tilt Nu is obtained by setting the symmetry axis orthogonal to the reflectors. To ensure stable reconstruction of parameter fields, reflection data are combined with walkaway VSP traveltimes. To improve the convergence of the inversion algorithm, I propose a three-stage model-updating procedure that gradually relaxes the constraints on the spatial variations of Epsilon and Delta. Geologic constraints are incorporated into tomography by designing appropriate regularization terms Synthetic tests for models with a "quasi-factorized" TTI syncline (i.e., Epsilon and Delta are constant inside the TTI layer) and a TTI thrust sheet are used to identify conditions for stable parameter estimation. Then the performance of the regularized joint tomography of reflection and VSP data is examined for two sections of the more complicated TTI model produced by BP that contain an anticline and a salt dome. Finally, the algorithm is applied to a 2D line from 3D OBS (ocean bottom seismic) data acquired at Volve field in the North Sea.
    • Modeling self-heating and negative bias temperature instability in FinFETs

      Carr, Lincoln D.; Graas, Carole D.; Sommer, David E. (Colorado School of Mines. Arthur Lakes Library, 2012)
    • Geochemistry of a volcanic hydrothermal system at Mount Spurr, Alaska

      Wendlandt, Richard F.; Garchar, Laura; Simmons, S. F. (Stuart Frank); Monecke, Thomas (Colorado School of Mines. Arthur Lakes Library, 2012)
      Mount Spurr is an ice and snow-covered andesitic volcano located at the northern extent of the Aleutian arc in south central Alaska. Previous workers have identified a prospective geothermal resource on the volcano's south side. This research aims to characterize more fully the hydrothermal system and builds on published geological mapping, geophysical surveys, soil sampling, exploration drilling, and water sampling. Aqueous and mineralogical geochemical investigations at a field area on the south flank of Mt. Spurr focus on the possible extent of the hydrothermal system, its temperature at depth, the origin of waters, and location fluid pathways in the system. Three spatially distinct water compositions have been identified: 1) moderate temperature (around 50 degrees C), acidic, bicarbonate-poor, d18O and dD-enriched waters from Crater Lake; 2) low temperature (14-40 degrees C), neutral, bicarbonate and Mg-rich, slightly d18O and dD-enriched peripheral waters from Crater Canyon, Kid Canyon, and South Spurr; and 3) cold (less than 9 degrees C), neutral, sulfate-rich, dilute/meteoric waters from Chaka Ridge and South Spurr. Geochemical modeling and stable hydrogen, oxygen, and carbon isotopes have confirmed that water chemistry cannot be explained solely by meteoric water-andesite interaction, or by mixing of Crater Lake and meteorically derived waters. Contributions to chemistry must come at least in part from a magmatic system. No alteration minerals were observed at the surface near springs, but kaolinite likely lies along the flow path of waters in the subsurface. Spring and seep waters are derived primarily from shallowly circulating meteoric water that has variously interacted with rock, incorporated condensed steam, in some cases mixed with andesitic water, and been diluted by rain and snowmelt overall. Montmorillonite-rich conglomerates and sandstones of the West Foreland Formation were encountered in exploration core holes located in the eastern field area. Post-depositional changes including the formation of montmorillonite from tuff, the presence of replacement-style calcite, as well as compaction and faulting processes are observed in hand samples and thin sections of 26-11 core. Stable carbon and oxygen isotopes of calcite samples are similar to published calcite isotopes from Cook Inlet sedimentary rocks. If all the calcite examined in this research formed from a fluid of the same isotopic composition, a 15 per mil fractionation happened over around 30 degrees C. The calcite samples are interpreted to be of meteoric-dominated origin and to have formed at low temperature diagenetic conditions. The sedimentary rocks of the West Foreland Formation have low visual porosity, and no evidence of recent hydrothermal alteration has been observed. Surface discharges do not seem to represent rapidly upwelling, deep, hydrothermal fluid. It appears that meteoric water doesn't circulate to depth and that deep water doesn't make it to the surface, except locally. The transport of hydrothermal fluids to the surface seems to be controlled by faults. However, not all mapped faults are conduits for deep fluid flow. The montmorillonite of the West Foreland Formation could be acting as a barrier to deep circulation of meteoric water, and could prevent upwelling of deeply sourced hydrothermal fluids. Montmorillonite could also be the source of resistivity anomalies in the field area. Exploration drilling has not penetrated the entire thickness of the West Foreland Formation, and what lies below is unknown. If a fractured granite basement that contains hydrothermal fluids exists beneath the West Foreland Formation, it could be a viable geothermal reservoir. Precise mapping of fault structures that act as conduits to fluid flow and deeper drilling, especially near Crater Canyon, will enhance the understanding of a possible geothermal resource at Mt. Spurr.
    • Reserve recovery and production evaluation of tight gas fluvial systems

      Miskimins, Jennifer L.; Ramirez, Kelly Madelein; Hoffman, B. Todd; Carr, Mary; Curtis, John B. (Colorado School of Mines. Arthur Lakes Library, 2012)
      Hydrocarbon resources such as tight sands have become one of the most sought after types of unconventional plays, given the extensive amounts of gas they contain. In order to access these reserves, the industry is focused on improving hydraulic fracturing techniques with the purpose of increasing gas recovery. However, proper reservoir management practices, in conjunction with improved completion processes, are also key factors for maximizing these gas reserves. Additionally, reservoir understanding becomes even more relevant when dealing with reservoirs deposited under complex fluvial environments. This study integrates the accurate stratigraphy and detailed reservoir characterization of a 160-acre 3D fluvial geologic outcrop model with detailed hydraulic fracturing modeling to better understand the effects that fluvial depositional environments have on hydraulic fracture growth. Subsequently, the hydraulic fracturing growth parameters are implemented in a robust 3D reservoir simulation model, representing the heterogeneous geologic environment. Finally, reservoir simulation is used to determine the dynamic flow conditions associated with the fluvial geologic model with the ultimate goal of determining optimum reserve recovery practices such as well spacing and placement, hydraulic fracture design components, etc. The methodology applied in this study, which starts with the 3D outcrop mapping and characterization, followed by the development of a geostatistical model, hydraulic fracturing modeling, and reservoir simulation are presented. Additionally, the results of a series of cases representing different well counts, locations, spacing, and perforated intervals within the fluvial reservoir model are shown. Seven different cases, in two geologic models, consisting of various well locations and spacings, are described. First, three cases in a lower geologic model with well locations selected in the most prospective areas of the reservoir. Then, the production of a full field model, which includes the lower model plus an extended geologic interpretation of the outcrop, was evaluated using 40-acre, 20-acre, and 10-acre spacings. Finally, the implementation of a horizontal well was assessed in the full field model. Results show that the continuity of sandstone bodies in the near wellbore vicinity, whether part of the completion interval or not, is critical to the ultimate reserve recovery and the hydraulic fracture growth pattern is greatly dependent on this sandstone continuity. Additionally, amalgamation of the sandstone bodies, which also affects the hydraulic fracture growth patterns, has a strong effect on gas recoveries. The benefits of infill drilling, in the stratigraphically lower model and in the combined stratigraphically lower and upper intervals, or full field model, comparing the 20-acre and 10-acre scenarios, were mainly obvious in reserve acceleration versus reserve addition. Conversely, in the full field model, the 20-acre spacing scenario achieved drainage of more sandstone bodies than the 40-acre spacing, resulting in an increase of reserves. Finally, for the reservoir evaluated in this study, the horizontal well results are not encouraging when compared to the vertical wells evaluated in the rest of the scenarios.
    • Control of self-propagating high-temperature synthesis derived aluminum-titanium carbide metal matrix composites

      Kaufman, Michael J.; Garrett, William; Moore, J. J. (John Jeremy), 1944-; Gorman, Brian P.; Vidal, Edgar E.; Ayers, Reed A.; Ranville, James F. (Colorado School of Mines. Arthur Lakes Library, 2012)
      Self-propagating High-temperature Synthesis (SHS) is a combustion process that can be used to form Metal Matrix Composite (MMC) reinforcing phases in situ. Generally, the kinetic processes in these reactions are poorly understood but are affected by reactant particle size, reactant green density, reactant stoichiometry, reaction preheat temperature, and reaction product cooling rate. These reaction parameters also affect the microstructure of the reaction products because of changes in the rate of heat evolution, reaction rate, surface area available for heterogeneous nucleation, reaction temperature, and the stable phases during and after the reaction. Post-reaction processes affecting the microstructure and properties of the SHS products include densification, melt alloying (SHS reaction products are used as a master alloy), and die casting techniques. Matrix alloy additions should be controlled to prevent unwanted reactions between the matrix and the reinforcement. In the present study, Ti + C + X [right arrow] TiC + X (X = Al or TiC) is the SHS reaction system studied, with varying amounts of Al (10-50wt%) or TiC (0-20wt%) added to the reactants as a thermal diluent. Addition of these diluents decreases the reaction temperatures and decreases the TiC reinforcing particle size and interaction during particle growth. A method of direct thermal analysis of the self-heating behavior of diluted SHS reactions is developed and compared to existing methods used to measure the apparent activation energy of single step SHS reactions. The activation energies are used to determine a probable reaction path for Ti + C + Al [right arrow] TiC + Al. SHS reaction products of various diluent concentrations are analyzed for TiC particle size and shape. SHS reaction products containing 55v% TiC - 45v% Al are dispersed as a master alloy in aluminum melts; reaction products containing higher concentrations of TiC particles are difficult to disperse. To show compatibility with the TiC reinforcing particles, MMCs with aluminum alloy matrices of pure aluminum, Al-4.5Mg, and Al-4.5Mg-4.5Cu-1Mn-0.25Cr are coupled with TiC particle concentrations of 0, 10, and 20v%. MMC compositions were Thixocast at VForge in Lakewood, CO and squeeze cast at CWRU in Cleveland, OH. A pure aluminum matrix MMC with 55v% TiC was densified after the SHS reaction and thixocast, though the other MMCs with pure aluminum matrices were not thixocast because they lack a semisolid matrix condition required for thixocasting. The cast MMCs are tested for tensile, hardness, wear, and ballistic properties with properties apparently dominated by agglomerated TiC particles.
    • Control of balance of plant components for solid oxide fuel cell systems with sensitivity to carbon formation

      Vincent, Tyrone; Kupilik, Matthew J.; Sullivan, Neal P.; Mehta, Dinesh P.; Moore, Kevin L., 1960-; Braun, Robert J. (Colorado School of Mines. Arthur Lakes Library, 2012)
      Solid oxide fuel cell systems have the potential to provide efficient, low greenhouse gas emitting power without the availability problems of both wind and solar energy. SOFC systems operate at high temperatures (600 C) in order to reduce ionic transport losses through a ceramic electrolyte. The benefits of the ceramic electrolyte include not requiring platinum based catalysts and a robustness to fuel composition. However such high temperatures create engineering challenges in construction, operation, and durability of the system as a whole. Both fuel and air must be pre-heated prior to entering the fuel cell stack. In order to ensure that carbon does not build up and degrade the system some form of fuel preprocessing is required. To move air and fuel through the system, blowers and valves must be used. Additionally during system start up, a method for pre-heating the fuel cell to within an operating range is required. All these components are tightly coupled to the time response and overall performance of the system. They also all have constraints and operating ranges, for example the fuel reformer must remain within a set temperature range or risk damage. Thus model predictive control is a natural choice to ensure that the maximum load following and overall system efficiency can be maintained without damaging components. This thesis analyzes system wide control of a solid oxide fuel cell system comprised of a tubular stack bundle, fuel reformer, air pre-heat exchanger, tailgas burner, and air blowers. Control oriented, dynamic component models have been created, allowing for estimation of temperatures and gas compositions throughout the system. The effects on system response of each component is analyzed, providing insight into realizeable response to load changes and sensitivity to noisy input parameters such as varying fuel stocks.
    • Mechanical properties of the Bakken Formation

      Batzle, Michael L.; Havens, Jesse; Sarg, J. F. (J. Frederick); Andrews-Hanna, Jeffrey C.; Ross, Jeffrey G. (Colorado School of Mines. Arthur Lakes Library, 2012)
      The Bakken Formation is located in the Williston Basin in North Dakota, Montana, and up into southern Saskatchewan, Canada. The Bakken Formation lies unconformably over the Upper Devonian Three Forks Formation and is conformably overlain by the Lodgepole Formation. Production in the Bakken depends on horizontal wells with multistage fracture stimulations. The effective minimum horizontal stress is a primary controller of fracture growth. Knowledge of the elastic properties and Biot's poroelastic coefficients is required to accurately determine the effective minimum horizontal stress. In this study I have measured dry rock velocities for four geologic facies from the middle Bakken interval and one from the Lodgepole Formation. Mineralogy data was also obtained for many samples including the rocks measured in the laboratory. This data along with available literature measurements in the Bakken Shales allows for estimation of dry rock elastic constants and Biot's coefficients in-situ. The dry rock stiffness tensor was determined by treating the dipole shear log as a dry rock measurement. Empirical equations were then derived from laboratory data and applied to the shear waves to predict the remaining components of the stiffness tensor. Fluid substitution was performed with Gassmann's equation to acquire the saturated stiffness tensor. Biot's coefficients were calculated using the dry rock stiffness tensor and an estimate of the mineral bulk modulus by assuming a Voigt-Reuss-Hill effective medium for the pure grain moduli. Biot's coefficients describe the ability of the pore pressure to counteract the outward stresses on the rock and will be between zero and one. The values for all formations were well below one and ranged from 0.15-0.75 over the unit of interest. The saturated stiffness tensor and Biot's coefficients were input into the effective minimum horizontal stress equation assuming uniaxial strain. The stress profile showed no major contrast over the area of interest. A slight decrease in horizontal stress was observed in the common reservoir facies of the middle Bakken, but the remaining units all had similar horizontal stress. Mini-Frac tests were performed in the Upper Bakken Shale and the Scallion member of the Lodgepole Formation. The tests provide estimates of reservoir pressure, total minimum horizontal stress, tensile strength, and total maximum horizontal stress. The interpreted stress from the Mini-Frac tests matched well with the modeled results, and showed low stress contrast between the Upper Bakken Shale and Scallion member. A total minimum horizontal stress profile was provided by Schlumberger for the same well along with transversely isotropic elastic properties. The stress profile was only able to predict the Mini-Frac test in the Upper Bakken Shale, and a calculation of Thomsen anisotropy parameters (Thomsen, 1986) showed the delta parameter in the Bakken Shales ranged from 0.5-1.2. These delta values are much higher than any existing anisotropy measurements in the Bakken Shales (Vernik and Nur, 1992). The likely cause for the high values was an attempt by Schlumberger to match the Mini-Frac tests by adjusting the anisotropy and disregarding the possibility of Biot's coefficients less than unity. This lead to a massive stress contrast in the Bakken Shales that would ultimately be interpreted as a strong fracture barrier. The in-situ pressure testing and modeled results show low stress contrast throughout the unit of interest. The analysis by Schlumberger predicted a contrasting stress profile, but the input parameters were unrealistic and the profile did not match in-situ pressure testing. This demonstrates the importance of estimating accurate Biot's coefficients and realistic anisotropy parameters. A poor interpretation will impact completion strategies and potentially damage resource recovery.
    • Debris-flow hazard assessment and monitoring within the 2010 Medano fire burn area, Great Sand Dunes National Park and Preserve, Colorado

      Santi, Paul M. (Paul Michael), 1964-; Friedman, Evan Quelle (Colorado School of Mines. Arthur Lakes Library, 2012)
    • Whole-body angular momentum during walking on stairs using passive and powered lower-limb prostheses

      Silverman, Anne K.; Pickle, Nathaniel T.; Bach, Joel M.; Steele, John P. H. (Colorado School of Mines. Arthur Lakes Library, 2012)
      Stair walking is a biomechanically challenging task, particularly for impaired populations such as individuals with unilateral transtibial amputation (TTA). In addition, TTA have an increased fall risk relative to able-bodied individuals (AB). The regulation of whole-body angular momentum (H) is important for maintaining balance and avoiding a fall. This study therefore evaluated H during stair ascent and descent in TTA using passive and powered prostheses compared to AB. The range of H was generally reduced in TTA and AB during descent relative to ascent, which may be a mechanism to reduce fall risk during descent. TTA using both types of prostheses had an increased range of sagittal H during prosthetic limb stance compared to AB during ascent, but no differences in H were observed between prostheses. Thus, TTA have altered H relative to AB during stair ascent, and H is not significantly affected by the use of a powered prosthesis.
    • Scaled mapping approach for treating sloping interfaces in range-dependent parabolic equation solutions, A

      Collis, Jon M.; Moran, Daniel; Martin, P. A.; Ganesh, Mahadevan (Colorado School of Mines. Arthur Lakes Library, 2012)
      An area of research in ocean acoustics is on solution techniques for environments with sloping seafloors. In these range-dependent environments the oceanic waveguide varies in the direction of propagation and exact analytic solutions do not exist. In order to enforce continuity conditions at the seaoor, the environment is approximated as a series of range-independent regions. An alternative to this approach, the mapping solution [M. D. Collins et al., JASA 107] applies a change of variables that results in a vertical translation of the environment and makes it easier to enforce ocean bottom interface conditions. An alternate mapping approach that uses a characteristic depth length scale is considered here. In contrast to the earlier mapping solution, the new approach uses a change of variables in which the depth variable is scaled relative to the depth of the bottom interface. The earlier approach distorted the surface, whereas the new mapping does not, which is a potential improvement. Along with the simplification of bottom interface conditions in both approaches, extra terms arising from the mapping are neglected. The new approach is implemented in a parabolic equation solution and is benchmarked against an existing solution. The accuracy of this new approach is established initially for problems involving fluid sediments.
    • Compressive system identification (CSI): theory and applications of exploiting sparsity in the analysis of high-dimensional dynamical systems

      Vincent, Tyrone; Wakin, Michael B.; Molazem Sanandaji, Borhan; Poolla, Kameshwar; Moore, Kevin L., 1960-; Mehta, Dinesh P.; Tenorio, Luis (Colorado School of Mines. Arthur Lakes Library, 2012)
      The information content of many phenomena of practical interest is often much less than what is suggested by their actual size. As an inspiring example, one active research area in biology is to understand the relations between the genes. While the number of genes in a so-called gene network can be large, the number of contributing genes to each given gene in the network is usually small compared to the size of the network. In other words, the behavior of each gene can be expressed as a sparse combination of other genes. The purpose of this thesis is to develop new theory and algorithms for exploiting this type of simplicity in the analysis of high-dimensional dynamical systems with a particular focus on system identification and estimation. In particular, we consider systems with a high-dimensional but sparse impulse response, large-scale interconnected dynamical systems when the associated graph has a sparse flow, linear time-varying systems with few piecewise-constant parameter changes, and systems with a high-dimensional but sparse initial state. We categorize all of these problems under the common theme of Compressive System Identification (CSI) in which one aims at identifying some facts (e.g., the impulse response of the system, the underlying topology of the interconnected graph, or the initial state of the system) about the system under study from the smallest possible number of observations. Our work is inspired by the field of Compressive Sensing (CS) which is a recent paradigm in signal processing for sparse signal recovery. The CS recovery problem states that a sparse signal can be recovered from a small number of random linear measurements. Compared to the standard CS setup, however, we deal with structured sparse signals (e.g., block-sparse signals) and structured measurement matrices (e.g., Toeplitz matrices) where the structure is implied by the system under study.
    • Associating biophysical and thermodynamic changes induced by xenon to the general anesthetic effect

      Sum, Amadeu K.; Booker, Ryan D. (Colorado School of Mines. Arthur Lakes Library, 2012)
    • Stratigraphy and source rock analyses of the Heath Formation in Fergus, Garfield, Golden Valley, Musselshell, Petroleum, and Rosebud counties, central Montana

      Sonnenberg, Stephen A.; McClave, Graham A.; Curtis, John B.; Emme, James J. (Colorado School of Mines. Arthur Lakes Library, 2012)
      The Mississippian Heath Formation is recognized as the key source rock for the Heath-Tyler-Amsden (!) petroleum system in the Big Snowy Trough of central Montana which has produced an estimated 137 million bbl of oil to date from conventional traps. Due to the limited amount of conventional production to date within this petroleum system over the region's 90 year history of development, and estimates that 60% of total generated oil still remains in place within the source rock, the Heath is well suited for being assessed as a resource play. This research project is designed around addressing this possibility. Specifically it seeks to gain a thorough understanding of the Heath's potential as a resource play, and does this by meeting two primary objectives: 1) conducting a petroleum system analysis of regional stratigraphy in the Big Snowy Trough of central Montana with an emphasis toward identifying the Mississippian Heath Formation's contribution to this system, and 2) performing a source rock assessment of the Heath Formation. The results drawn from meeting these objectives lead to establishing the view of the Heath as its own stand-alone petroleum system that can potentially serve as a resource play target. The stratigraphic analysis yielded the following observations. Thickness of the Heath varies regionally from 150-450 ft, and its present depth ranges from outcropping at the surface to occurring at 6,000 ft total vertical depth, while averaging around 3,000-6,000 ft within the central region of the trough. It is composed of various marine lithologies including mostly black micritic shale interbedded with thin fossiliferous limestone and dolomite stringers, and minor gypsum/anhydrite occurrences. The most organic-rich zone of the Heath, the Cox Ranch shale unit, ranges from 5-25 ft in thickness, and is composed of finely-laminated micritic black shale. Adjacent to this organic zone is the informally defined Heath B carbonate unit (from this study) which is composed of interbedded limestone, dolomite and shale. The carbonate beds within this interval are thin (2-5 ft thick), but generally are more developed and more prevalent in the southern region of the study area. Less organic-rich shale intervals occur abundantly in the Upper and Lower Heath units that are informally defined in this study. The source rock analysis provided the following results. Programmed pyrolysis, TOC, and vitrinite reflectance data for the Heath shales indicate very good source rock character. Within the Cox Ranch section, TOC wt. % ranges from 0.5-26% and averages 9% with S2 peak values averaging 20 mg HC/g rock. Kerogen type analyses point mainly to Type I/Type II kerogen, while Tmax suggests marginal maturity to oil window maturity with values ranging from 420 to 449 deg C. Maps of the thermal maturity parameters indicate a salient zone of oil maturity in the south-central region of the study area. Burial history and thermal maturity models from southern wells indicate oil expulsion from the Heath with the critical moment occurring in the Early Tertiary. The results of the stratigraphic and source rock analyses of the Heath combined clearly indicate the presence of the necessary lithologic elements needed for comprising a stand-alone petroleum system. They also exhibit the presence of system processes that signal a once active petroleum system which has subsequently been uplifted and is no longer active. Thus, the Heath's overall character suggests that it should be considered a viable candidate as a resource play target, especially when taking into consideration the result of the oil-generation-based volumetrics analysis conducted in this study. Estimates of the Heath's production potential could be 1.37 billion bbls of recoverable oil through unconventional development. In addition, thermal maturity results and reservoir facies trends indicate a highly prospective zone for this type of play in the south-central region within the study area. Based on an overall assessment, this study establishes the Heath Formation as a prospective target for resource play development. Given these results, the time has come for industry to test the Heath's viability as an oil producer.
    • Multi-nucleon transfer reaction studies of 6HE on 12C at 30 MeV using the SHARC and TIGRESS arrays

      Sarazin, Frederic; Smalley, Duane D.; Blackmon, Jeff; Greife, Uwe; Wiencke, Lawrence; King, Jeffrey C. (Colorado School of Mines. Arthur Lakes Library, 2012)
      Two multi-nucleon transfer reactions were studied using 6He on 12C with the Silicon Highly-segmented Array for Reactions and Coulex (SHARC), a compact charged particle silicon array, and the TRIUMF-ISAC Gamma-Ray Escape Suppressed Spectrometer (TIGRESS), a high-efficiency gamma-ray detector, at the TRIUMF ISAC-II facility. First, the reaction mechanisms of the (6He, 4He) two-neutron transfer were studied to determine the dominant mechanism; one-step simultaneous transfer or two-step sequential transfer. Second, the multi-nucleon transfer (6He, 8Be) reaction was observed and its reaction mechanism could proceed two ways, by a two-proton transfer or an alpha transfer. The two-neutron and multi-nucleon transfer reactions were analyzed and angular distributions extracted. These angular distributions were then compared to the microscopic models investigating the effects of the simultaneous vs. sequential transfer mechanisms. Detailed simulations in GEANT4 were performed of the SHARC array to characterize detector performance. This thesis will discuss the experimental challenges, the data analysis, GEANT4 reaction simulations and interpretation of the data within the reaction models.
    • Theoretic and empirical issues related to border carbon adjustments

      Balistreri, Edward J. (Edward Jay); Yonezawa, Hidemichi; Kaffine, Daniel; Eggert, Roderick G.; Walls, Michael; Delborne, Jason (Colorado School of Mines. Arthur Lakes Library, 2012)
      Faced with the failure in coordinating a global policy to limit carbon emissions, one of the key issues in climate policy is carbon leakage, where emissions reductions in regulated regions stimulate emissions in unregulated regions. Many studies discuss border carbon adjustments to mitigate leakage and propose a rate of adjustments based on the carbon price (a Pigouvian rate). But, the question arises, is such a prescription optimal? This thesis analyzes optimal border carbon adjustments, specifically showing that the conventional Pigouvian rates are suboptimal. In Chapter 2, a general-equilibrium simulation model shows that the optimal trade policy is to set a net import tariff less than the Pigouvian rate. In Chapter 3, an analytical model demonstrates that the optimal import tariff consists of both the marginal social damage of the externality and the ability of the home country to influence foreign prices and thus foreign production. Furthermore, the model proves that the optimal rate is less than the Pigouvian rate because of the foreign consumer response. Chapter 4 shows that the findings in the previous chapters hold in an empirical context. Specifically, a general-equilibrium simulation model calibrated to the GTAP 7.1 global dataset demonstrates that the optimal border adjustments are smaller than the Pigouvian rates by 20% to 50% depending on export policy. This thesis contributes to the ongoing discussion of border carbon adjustments by showing the suboptimality of Pigouvian rates in both the theoretical and empirical contexts. Admittedly, using Pigouvian rates to set border adjustments provides a simple rule. The tradeoff between the efficiency improvement that I explore, and the cost increase related to implementing and maintaining the optimal rates (compared to the Pigouvian rates) should be considered.
    • Dynamic consensus networks: spectral properties, consensus, and control

      Moore, Kevin L., 1960-; Lashhab, Fadel; Vincent, Tyrone; Johnson, Kathryn E.; Vincent, Tyrone; Griffiths, D. V.; Mehta, Dinesh P.; Newman, Alexandra M. (Colorado School of Mines. Arthur Lakes Library, 2012)
      The idea of consensus in networking has received great attention due to its wide array of applications in fields such as robotics, transportation, sensor networking, communication networking, biology, and physics. The focus of this dissertation is to study a generalization of consensus problems whereby the weights of network edges are no longer static gains, but instead are dynamic systems, leading to the notion of dynamic consensus networks. We transform each concept of static graph theory into dynamic terms, out of which a generalized dynamic graph theory naturally emerges. Three different types of dynamic consensus networks are addressed based on node dynamics and network topology. We investigate stability and consensus for each type of dynamic consensus network and develop conditions under which dynamic networks achieve consensus. For the first type, we use conditions of connectedness, positivity, and diagonal dominance to show consensus. For the second type, we use the condition of strictly-positive realness of edges. For the third type, which is composed of more general dynamics, we use graphical verification based on the relationship of the eigenvalues of the dynamic Laplacian matrix with the Nyquist plots of individual node dynamics. In order to investigate consensus using Nyquist's graphical-stability test, we develop a method to estimate the bounds of the eigenvalues of the dynamic Laplacian matrix by introducing the idea of a Dynamic Grounded Laplacian sub-matrix as a means of reducing the order of complexity of computation that would be necessary in the case of the full dynamic Laplacian matrix. The dissertation finally considers controllability and controller design for dynamic consensus networks. The ideas developed for dynamic graph theory, in conjunction with the behavioral approach, lead to the development of a controllability analysis methodology for dynamic consensus networks. We finally establish a generalized methodology for designing a controller for a dynamic consensus network in the presence of external disturbances, focusing especially on using decentralized controllers that achieve consensus in the absence of disturbances and attenuation of disturbances to a prescribed H[infinity] performance level.
    • Laboratory hydraulic fracture characterization using acoustic emission

      Gutierrez, Marte S.; Hampton, Jesse Clay; Mooney, Michael A.; Tutuncu, Azra (Colorado School of Mines. Arthur Lakes Library, 2012)
      For many years acoustic emission (AE) testing has aided in the understanding of fracture initiation and propagation in materials ranging from high strength steel to polymers to composite and geologic materials. Acoustic emissions are the phenomenon in which a material or structure emits elastic waves caused by the sudden occurrence of fractures or frictional sliding along discontinuous surfaces and grain boundaries. Throughout this project AE monitoring has been employed during laboratory hydraulic fracturing tests for the purpose of Enhanced Geothermal Systems (EGS) reservoir creation, as well as sample and material characterization. EGS consists of inducing fracture networks in deep Earth hot, dry impermeable rock in order to extract heat energy for production. Sample material testing and characterization played a major role throughout AE monitoring and analysis, which enhanced the capabilities and understanding of fracture growth prior to laboratory hydraulic fracturing tests. Multiple large, 30 cm cubical, analog rock and granite blocks have been monitored throughout laboratory hydraulic fracturing and geothermal reservoir simulation. Unconfined and true-triaxially confined and heated boundary conditions have been utilized. AE monitoring of laboratory hydraulic fracturing experiments showed multiple phenomena including winged fracture growth from a borehole, cross-field well communication, fracture reorientation, borehole casing failure and much more. AE data analysis consisted of event source location determination, AE fracture surface identification and validation, source mechanism determination, geothermal production well location optimization, and determining the overall effectiveness of the induced fracture network. Field scale AE data obtained from the National Institute of Advanced Industrial Science and Technology, Japan, and Central Research Institute of Electric Power Industry, Japan, for two EGS fields have been compared to laboratory data in order to determine the applicability of the laboratory testing performed.
    • Diffusion of innovation in the mining industry: agent-based modeling and simulation, The

      Nakagawa, Masami; Fujiono, Hendro (Colorado School of Mines. Arthur Lakes Library, 2012)