• 3D multicomponent seismic characterization of a clastic reservoir in the Middle Magdalena Valley Basin, Colombia

      Davis, Thomas L. (Thomas Leonard), 1947-; Velásquez-Espejo, Antonio Jose; Lynn, Walter; Sonnenberg, Stephen A.; McKay, Scott (Colorado School of Mines. Arthur Lakes Library, 2012)
      The main goal of this research is to characterize the combined structural-stratigraphic trap of the Tenerife Field in the Middle Magdalena Valley Basin (MMVB), Colombia. For the rst time in Colombia the structural and quantitative interpretation of modern three-dimensional multicomponent (3D-3C) seismic imaging enables a geometric description, a kinematic interpretation of the structural styles, and the facies distribution of the reservoir. A seismic petrophysics work- ow to better achieve the seismic well-tie. Edited and check-shot calibrated P-wave sonic logs were obtained and coecients of the Gardner and Castagna equations were calibrated to match the density and shear-wave velocity depth trends for the basin. Seismic modeling was performed to evaluate the PP and PS seismic response of the reservoir interval (Mugrosa Formation). The structural interpretation methodology involves a 3D fault-correlation and horizon picking for both PP- and PS-PSTM data volumes. Geometric attributes such as coherence and curvature were used to enhance the structural discontinuities. The main unconformity of the Middle Eocene (MEU) was interpreted, and an attributeassisted interpretation of the reservoir was conducted in detail. While P-wave data provided most of the structural interpretation, converted-wave data provide a better understanding of the faults. Traditionally, compressive thrust-propagation folds and tectonic inversion have been considered as the main mechanisms controlling the deformation in the MMVB. However, the new interpretation shown in this work provides a dierent structural concept that involves two major structural styles: 1. Under the MEU the Late Cretaceous and Early Paleocene deformation, dominated by east-verging thrust and partially inverted Mesozoic normal faults, is preserved. Associated folds exhibit a iii north-south strike, and their structural development is controlled by a long-lived structural element that dominates the area (the Infantas Paleo-high). 2. Northeast striking younger normal faults indicate younger local extension, that aects the entire Cenozoic sequence. Normal faults are, in fact, the structural heterogeneities that most aect the geometry of the reservoir compartments in Tenerife Field. This normal faulting oriented oblique to the maximum horizontal stress, together with the associated folding, can arise from a left-lateral shear deformation that creates a local trans-tensional regime. Hence, the structure of Tenerife Field at the top of the Oligocene sandstones, can be described as a two-way closure anticline within a negative ower structure. In addition, Upper Eocene - Early Oligocene syn-tectonic deposits are also documented in this work, dating the last episode of deformation associated with the Infantas Paleohigh uplift. The value of multicomponent data goes beyond the structural interpretation since it provides an independent seismic measure of shear-wave velocities for obtaining VP/VS ratios from interpretation and for performing elastic inversion. From the interpretation of both PP and PS data, the interval VP/VS ratio was computed for the entire Mugrosa Formation. Forward modeling of PS wave response showed that computing VP/VS ratio from picking thin intervals may lead to erroneous values since it is not possible to interpret the same seismic events in both PP and PS data. Nonetheless, analysis of the full-waveform (dipole) sonic log together with Gamma Ray measured in the reservoir interval, showed that there is a close correlation between lithology and VP/VS ratio. VP/VS 1:85 is an eective upper bound to characterize sandstones from ne grained rocks. Further, a model-based elastic inversion of acoustic impedance and VP/VS ratio performed using the PP volume and the sonic logs available, allowed to nd stratigraphic features in the Mugrosa and Esmeraldas formations. The attribute extraction from the inverted P-wave amplitude for both acoustic impedance and VP/VS ratio allowed the characterization of stratigraphic features, in particular some channel geometries that are interpreted as part of a meandering uvial system (point bars and crevasse splays). The lithological and petrophysical correlation of additional attributes from the elastic inversion and AVO is not reliable since there is no independent density, porosity, resistivity, permeability, etc., measurements to guarantee accurate and stable results; nonetheless VP/VS analysis using multicomponent seismic in the MMVB shows signicant promise. Therefore, the acquisition of critical log data with new well drilling as well as an additional multi-attribute analysis based on AVO and a joint PP-PS inversion are strongly recommended.
    • 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.
    • Application of simulated annealing inversion to automated model calibration for residential building energy simulation

      Collis, Jon M.; Robertson, Joseph J.; Bialecki, Bernard; Hering, Amanda S. (Colorado School of Mines. Arthur Lakes Library, 2012)
      Building energy simulation programs are often used in the residential sector to model home thermal performance and estimate energy savings for changes to building parameters (retrofit measures). Accurate model predictions are not guaranteed since uncertainty in model inputs leads to uncertainty in model output. Analysts may calibrate model inputs to reduce disagreement between simulation-predicted and measured energy uses, however no widely-accepted guidelines exist for systematic and cost-effective residential building model calibration. This study uses a building energy optimization program developed by the National Renewable Energy Laboratory called BEopt(TM)/DOE-2.2 to evaluate three automated residential calibration techniques in the context of monthly, daily, and hourly synthetic utility data for a 1960's era existing home. The home's model inputs are assigned probability distributions representing uncertainty ranges, random selections are made from the uncertainty ranges to define "explicit" input values, and synthetic utility data are generated using the explicit input values. The calibration techniques search for the explicit input values, starting with an uncalibrated model consisting of nominal input values (best-guess values estimated by home audit), using an automated simulated annealing parameter inversion algorithm. Each of the techniques employs this simulated annealing algorithm for recovering calibrated model input values (i.e., approximations of explicit input values) by minimizing residuals between the simulation-predicted energy uses and synthetic utility data. The three calibration techniques evaluated in this study are: a direct simulated annealing approach, a regression metamodeling approach, and an approach based on ASHRAE 1051-RP. Various retrofit measures are applied to the calibrated models and the methods are evaluated based on the accuracy of predicted savings, computational cost, repeatability, automation, and ease of implementation. Results show more computationally expensive techniques generally produced more accurate energy savings predictions than less expensive techniques, although the accuracy improvements were modest and may not have warranted the additional expense. Calibrations may benefit from additional informational content in utility billing data since calibrations to higher frequency data generally provided more accurate energy savings predictions.
    • 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)
    • Beam characterization at the neutron radiography reactor

      King, Jeffrey C.; Morgan, Sarah; Greife, Uwe; Ahrens, Cory; Pope, Chad L. (Colorado School of Mines. Arthur Lakes Library, 2012)
      The quality of a neutron imaging beam directly impacts the quality of radiographic images produced using that beam. Fully characterizing a neutron beam, including determination of the beam's effective length-to-diameter ratio, neutron flux profile, energy spectrum, image quality, and beam divergence, is vital for producing quality radiographic images. This thesis characterized the east neutron imaging beamline at the Idaho National Laboratory Neutron Radiography Reactor (NRAD). The experiments which measured the beam's effective length-to-diameter ratio and image quality are based on American Society for Testing and Materials (ASTM) standards. An analysis of the image produced by a calibrated phantom measured the beam divergence. The energy spectrum measurements consist of a series of foil irradiations using a selection of activation foils, compared to the results produced by a Monte Carlo n-Particle (MCNP) model of the beamline. Improvement of the existing NRAD MCNP beamline model includes validation of the model's energy spectrum and the development of enhanced image simulation methods. The image simulation methods predict the radiographic image of an object based on the foil reaction rate data obtained by placing a model of the object in front of the image plane in an MCNP beamline model.
    • Bioplastic blends incorporating polyamide-11

      Dorgan, John R.; Ruehle, David A. (Colorado School of Mines. Arthur Lakes Library, 2012)
    • Building a better wind forecast: a stochastic forecast system using a fully-coupled hydrologic-atmospheric model

      Maxwell, Reed M.; Williams, John; Cohen, Ronald R. H.; Delle Monache, Luca; Hering, Amanda S.; Lundquist, Julie K. (Colorado School of Mines. Arthur Lakes Library, 2012)
      Wind power is rapidly gaining prominence as a major source of renewable energy. Harnessing this promising energy source is challenging because of the intermittent nature of wind and its propensity to change speed and direction over short time scales. Accurate forecasting tools are critical to support the integration of wind energy into power grids and to maximize its impact on renewable energy portfolios. A numerical weather prediction tool is limited by model errors arising from simplifications in the way it represents the physics of the natural system. Land surface - atmosphere feedbacks are strongly dependent on both atmospheric processes and hydrologic processes at and below the land surface. It has been shown in the literature that improving the physical representation of these feedbacks leads to better forecast results for precipitation distribution and wind speeds. Key to this physical representation is soil moisture distribution. By using PF.WRF, a fully-coupled hydrologic and atmospheric model incorporating the ParFlow hydrologic model in the the Weather Research and Forecasting atmospheric code, it is possible to dynamically simulate water movements in the subsurface generating more realistic soil moisture fields to interact directly with atmospheric processes. This work traces uncertainty propagation from subsurface hydraulic conductivity through soil moisture and latent heat flux and into the atmosphere to analyze its impact on wind speed, the extent of that impact in the presence of prevailing winds, and the length scales over which that impact is important. A data assimilation system using an implementation of the ensemble Kalman filter is developed and verified to reduce uncertainty in simulated wind speed by informing the forecast system with observed soil moisture values, demonstrating that even in a small model domain wind speed is sensitive to variation in soil moisture distribution.
    • Buried penny-shaped cracks

      Martin, P. A.; Floyd, Christopher L.; Collis, Jon M.; Ahrens, Cory (Colorado School of Mines. Arthur Lakes Library, 2012)
      Penny-shaped cracks are commonly used mathematical models, generally used in the field of fracture mechanics. One specific application is the modeling of micro-structures, within elastic materials. From a purely mathematical perspective, a penny-shaped crack can be described as a flat, disk-shaped crack. In this work, we consider the buried penny-shaped crack problem, consisting of a single crack, buried below the surface of a half-space. Specifically, the flat surface of the crack is taken to be parallel to the boundary, and the radius of the crack is held constant. The primary point of interest in this problem is the depth dependence of the stress intensity factor, which characterizes the fracture conditions near the tip of the crack. Determining the stress intensity factor for this problem is reduced to solving a pair of dual integral equations, specifically looking at these equations evaluated at the upper bound of integration. These equations were amenable to numerical solution, where the distance between the crack and the boundary was allowed to become small. The values of these equations, at the upper bound of integration, both tend toward 0. Based on the numerical results, the stress intensity factors for this problem were dependent on the depth at which the penny-shaped crack is buried.
    • Characterization of organosilane-modified silicon/silicon dioxide systems for biological and nanotechnology applications

      Cowley, Scott W.; Shircliff, Rebecca; Branz, Howard M.; Posewitz, Matthew C.; Spear, John R.; Martins, Gerard P.; Boyes, Stephen G. (Colorado School of Mines. Arthur Lakes Library, 2012)
      Silane functionalization of Si/SiO2 systems is a versatile technique that can be used in DNA microarray and nanotechnology applications. Control of the composition, chemistry and structure of the underlying silane film is crucial for optimization of the final devices. In this dissertation, aminosilanes and alkysilanes are investigated for applications in DNA microarrays and nanoparticle modification. Innovative methods are used to quantify the composition of these silane films, including X-ray photoelectron spectroscopy. In addition, low-temperature-plasma grown Si nanoparticles are modified for the first time using self-limited silanization techniques. Mixed silane monolayers provide a method for controlling DNA attachment via dilution of amine density. DNA hybridization results suggest these films are restrictive, thus reducing DNA hybridization efficiencies. To investigate the effect of the silane film structure on DNA hybridization, three distinct aminosilane films were generated: 1) a self-limited monolayer, 2) a 1-2 layer film and 3) a thick, multilayer film. DNA radiometric assays show restriction of DNA hybridization by the self-limited monolayer and high DNA hybridization efficiencies on the 1-2 layer film, demonstrating the important role the silane film structure plays in DNA microarray efficacy. This silane chemistry is extended to Si nanoparticles to improve their suitability for nanotechnology applications. Specifically, Si nanoparticles are modified with a monolayer-thick alkylsilane film, making them stable for over two months in air, and producing a colloidal suspension of the particles. The size, stability and colloidal suspension of these Si nanoparticles distinguish them as useful components for nanotechnology applications, such as light-emitting diodes, biological sensors and markers, and photovoltaics.
    • Comparison of Raman LIDAR signal estimation and smoothing methods and correlation between the Pierre Auger side scattering method for determining aerosol content in the troposphere, A

      Wakin, Michael B.; Coco, Michael B.; Wiencke, Lawrence; Vincent, Tyrone; Moore, Kevin L., 1960- (Colorado School of Mines. Arthur Lakes Library, 2012)
      Raman backscatter LIDAR is the standard method in atmospheric physics for measuring atmospheric aerosol optical depth profiles. Cosmic ray observatories, including HiRes and Pierre Auger, measure the aerosol optical depth using an elastic side scattering technique. A first ever comparison between the two methods was carried out in southeastern Colorado at the Pierre Auger R\&D site. Between September 2010 and June 2011, over 300 hours of data was collected by the side scattering and Raman LIDAR system in parallel and over 900 hours of data was collected by the LIDAR alone. LIDAR backscattering signals become increasingly dominated by noise as height increases due to an ever decreasing photon return. Smoothing of the signals is required to obtain a usable aerosol optical depth profile. Free-degree density estimation and a customized kernel density estimation smoothing technique were applied to the Raman LIDAR data. It was found that both the free-degree density estimation and the kernel density estimation smoothing techniques work well for LIDAR signals. A strong linear correlation coefficient above 0.9 was calculated between the two techniques. These smoothing techniques were compared with the Savitzky-Golay smoothing technique currently used by a Raman LIDAR group in L'Aquila, Italy. Although the correlations between the density estimation techniques and Savitzky-Golay technique were still strong (above 0.8), there is a systematic difference in the aerosol optical depths observed of around 0.02. Since the two density smoothing techniques smooth the LIDAR signals well, this shift might be explained by differences in the two analyses. A similar systematic offset is seen when comparing the density smoothing methods to the side scattering data.
    • 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.
    • Computational study on the thermal conductivity degradation of annealed and irradiated U-Mo/Al alloy dispersion fuels, A

      Kee, R. J.; Hofman, Gerard L.; Drera, Saleem S. (Colorado School of Mines. Arthur Lakes Library, 2012)
    • Continuum generation in ultra high numerical aperture fiber with application to multiphoton microscopy

      Squier, Jeff A.; Sayler, Nicholas Austin; Durfee, Charles G.; Ohno, Timothy R. (Colorado School of Mines. Arthur Lakes Library, 2012)
      Nonlinear microscopy benefits from broadband laser sources, enabling efficient excitation of an array of fluorophores, for example. This work demonstrates broadening of a narrow band input pulse (6 nm to 40 nm) centered at 1040 nm with excellent shot-to-shot stability. In a preliminary demonstration, multiphoton imaging with pulses from the fiber is performed. In particular second harmonic imaging of corn starch is performed.
    • 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.
    • 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.
    • Culture, transboundary river negotiations, and the problem of implementation of agreement

      Amery, Hussein A., 1958-; Ibrahim, Hamed D. (Colorado School of Mines. Arthur Lakes Library, 2012)
    • 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)
    • Defects and alloying in semiconductors: computational studies of clusters and surfaces

      Ciobanu, Cristian V.; Agarwal, Sumit; Maddox, Willie Burton; Mehta, Dinesh P.; Richards, Ryan; Reimanis, Ivar E. (Ivar Edmund); Kappes, Branden Bernard (Colorado School of Mines. Arthur Lakes Library, 2012)
      This thesis addresses two main systems that are important in the lore of energy efficient nanomaterials, titanium dioxide and group IV alloy nanoclusters. Titanium dioxide, widely used in heterogeneous catalysis, photocatalysis, solar cells, or gas sensors, has become the prototype material for studying the reactivity of metal-oxide surfaces. Defects such as oxygen vacancies are always present on rutile surfaces and, depending on their coverage and spatial distribution, can strongly influence the reactivity of the surface. The interactions between vacancies determine their spatial distribution on the surface. Highly reactive vacancy clusters or pairs have not been expected to form because of vacancy repulsions, but recent experiments do show the possibility of spontaneously formed oxygen vacancy pairs. In this thesis, The interaction between oxygen vacancies is studied, as well as their electronic properties and scanning tunneling microscopy signature. The second thrust of the thesis concerns group IV nanomaterials, which are important semiconductors for photovoltaic applications due to their relative abundance and nontoxicity. Alloy nanoclusters, specifically germanium-tin (GeSn) nanoclusters show great promise for achieving higher photoconversion efficiencies since the band gap can be tuned by adjusting the Ge/Sn ratio. To accurately model alloy nanoclusters one must first verify that the physical properties of the constituent nanoclusters are described correctly. As these nanoclusters are composed of thousands to hundreds of thousands of atoms, we employ molecular dynamics (MD) simulations which are capable of calculating properties for large systems in reasonable timeframes. In MD simulations, atomic interactions are described using empirical potentials. The well-known Tersoff potential has proven to describe well the properties of group IV elements up to Ge. As Sn is also a group IV element, we have extended this potential to include parameters for Sn by developing an algorithm that determines the parameters that best fit known experimental data. To supplement the study of the mechanical and thermal behavior of Ge and Sn nanoclusters, A rotationally invariant local order parameter capable of determining at what temperature nanoclusters undergo crystallization has also been developed. This local order parameter also has the ability to distinguish between different Bravais lattices.
    • 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.
    • Design optimization techniques for improved power factor and energy efficiency for industrial processes

      Sen, Pankaj K.; Rabosky, Darren R.; Ammerman, Ravel F.; Rebennack, Steffen (Colorado School of Mines. Arthur Lakes Library, 2012)
      Poor power quality such as reduced power factor and high levels of harmonic distortion create a number of problems for electrical utilities, and large industrial consumers are typically charged accordingly. Reduced power factor is such a common problem based on typical loads that techniques are frequently applied to improve power factor when it is below certain levels. Traditional methods for improving power factor typically include adding power factor correction capacitors to supply the reactive volt-ampere reactive (VARs) near the location that inductive loads are absorbing VARs. In addition to inductive loads creating reduced lagging power factor, power electronic devices often reduce power factor similarly. Power electronic devices have become so commonly used that sophisticated techniques have been developed to improve power factor and reduce current total harmonic distortion for such devices. A common technique utilized for processes that must provide a large range of possible voltages is to include additional transformer taps coupled with the power electronic devices. In addition to traditional methods for improving power factor, by careful consideration during the design phase of processes and load cycles that have a repetitive nature, power factor can be improved even further. Such a technique uses a computer algorithm approach to determine the ideal compromise of the relevant design parameters for improved energy efficiency and power factor.