Browsing by Subject "Diffusion"
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Item A piecewise linear finite element discretization of the diffusion equation(Texas A&M University, 2006-10-30) Bailey, Teresa SIn this thesis, we discuss the development, implementation and testing of a piecewise linear (PWL) continuous Galerkin finite element method applied to the threedimensional diffusion equation. This discretization is particularly interesting because it discretizes the diffusion equation on an arbitrary polyhedral mesh. We implemented our method in the KULL software package being developed at Lawrence Livermore National Laboratory. This code previously utilized Palmer's method as its diffusion solver, which is a finite volume method that can produce an asymmetric coefficient matrix. We show that the PWL method produces a symmetric positive definite coefficient matrix that can be solved more efficiently, while retaining the accuracy and robustness of Palmer's method. Furthermore, we show that in most cases Palmer's method is actually a non-Galerkin PWL finite element method. Because the PWL method is a Galerkin finite element method, it has a firm theoretical background to draw from. We have shown that the PWL method is a well-posed discrete problem with a second-order convergence rate. We have also performed a simple mode analysis on the PWL method and Palmer's method to compare the accuracy of each method for a certain class of problems. Finally, we have run a series of numerical tests to uncover more properties of both the PWL method and Palmer's method. These numerical results indicate that the PWL method, partially due to its symmetric matrix, is able to solve large-scale diffusion problems very efficiently.Item An Investigation of Bonding Mechanism in Metal Cladding by Warm Rolling(2012-02-14) Yang, WeiClad metals are extensively used for their multi-functionality and their optimal combination of quality and cost. Roll bonding is an effective and economic processing approach to making clad metals. This dissertation presents an experimental investigation of the roll cladding process as well as thermo-mechanical modeling of mechanism for roll bonding of clad metals. The objectives of this research are to investigate the bonding mechanism of dissimilar metals in a warm rolling process and to advance the knowledge of the roll cladding process. To accomplish the objectives, aluminum 1100 sheet (Al 1100) and stainless steel 304 sheet (SST 304) are bonded by warm rolling under controlled conditions. The 180 degrees peel test is used to determine the bonding property of those clad metals. The experimental results show that the rolling thickness reduction and the entry temperature are two major factors of bonding strength. Minimum thickness reduction at a particular entry temperature is required to bond Al 1100 and SST 304. Increasing of either thickness reduction or entry temperature significantly improves the bonding strength between the two metals. X-ray microanalysis is also performed to characterize the diffusion state at the bonding interface. The diffusion coefficients of aluminum and iron are estimated through experimental method. A thermo-mechanical model was developed to describe the rolling plastic deformation of component metal sheets and the diffusion evolution during a roll bonding process of dissimilar metals. The effect of various rolling conditions on the contact area ratio was quantitatively discussed. Finite element simulation of 2-D diffusion under the rolling created boundary conditions was performed. The peel strength during the diffusion evolution was predicted by the integrated roll bonding model. The modeling predictions correspond to the experimental results well. The correspondence validates the effectiveness of the thermo-mechanical roll bonding model. Based on experimental observation, this research presents a bonding mechanism for the roll cladding process of dissimilar metals. The roll bonding model can help optimize rolling parameters for varying bonding strength depending on the demands of the application. It can also provide insights into design and analysis of rolling bonding process of other groups of dissimilar metal sheets.Item Atomic-scale modeling and experimental studies for dopants and defects in Si and SiGe nano-scale CMOS devices(2010-05) Kim, Yonghyun; Banerjee, Sanjay; Kirichenko, Taras A.; Lee, Jack Chung-Yeung; Register, Leonard F.; Tutuc, Emanuel; Henkelman, GraemeContinued scaling of CMOS devices with Si and SixGe1-x down to 22 nm design node or beyond will require the formation of ever shallower and more abrupt junctions with higher doping levels in order to manage the short channel effects. With the increasing importance of surface proximity and stress effects, the lateral diffusion in gate-extension overlap region strongly influences both threshold voltage roll-off degradation and DIBL increase by requiring an optimized abruptness and diffusion for better device performance. Therefore, the detailed understanding of defect-dopant interactions in the disordered and/or strained systems is essential to develop a predictive kinetic model for the evolution of dopant concentration and electrical activation profiles. Our density functional theory calculations provide the guidance for experimental designs to realize ultra-shallow junction formation required for future generations of nano-scale CMOS devices. Few systematic studies in epitaxially-grown SixGe1-x channel CMOS have been reported. The physical mechanisms of boron diffusion in strained SixGe1-x/Si heterojunction layers with different SixGe1-x layer thicknesses and Ge content (>50%) are addressed, especially with high temperature annealing. In addition, the effects of the fluorine incorporated during BF2 implant on boron diffusion are investigated to provide more insight into short channel device design. In this study, we investigate how short channel margins are affected by Ge mole fraction and SixGe1-x layer thickness in a compressively strained SixGe1-x/Si heterojunction PMOS with high temperature annealing. Series resistance characterization in S/D extension region and gate oxide interface trap characterization for Si, SixGe1-x, and Ge nMOSFETs are done. TCAD device simulation is also performed to evaluate which distributions of interface traps will significantly affect the electrical characteristics such as flatband voltage (VFB) shift and threshold voltage (Vth) shift based on capacitance-voltage (CV) and current-voltage (IV) curves. n+/p and p+/n diode structures are studied in order to decouple the electrical characteristics from the gated-diode (GD) MOSFETs. With the extraction of S/D series resistance from various channel lengths, possible reasons for performance degradation in SixGe1-x and Ge nMOSFETs, based on simulations, are proposed.Item Attributes and Barriers that Influence the Adoption and Diffusion of a Learning Management System(2014-04-03) Walker, Darrell ScottSeveral theories and technology acceptance models have been developed over the last several decades to predict user adoption. Most all of the models and theories have a foundation based from psychological and environmental factors that affect behavior intention, perception, and attitude towards accepting or rejecting a new innovation or technology. This study will examine such factors of influence towards adoption of a learning management system (LMS) at a large-scale university. The population for the study included participants from the three user groups: faculty (4,014), staff (5,997), and students (48,460). A stratified random sample from each group was determined using Cochran?s correction formula for categorical data. Sample size calculations assumed a confidence level a priori at .05 and an acceptable level of sampling error at 5% with a degree of variability of .5 and yielded sample sizes of faculty (350), staff (360), and students (381). A conceptual model was used for the study based from the Technology Acceptance and the Unified Theory of Acceptance and Use of Technology models which proved useful in determining the relationships of external factors on user perception and attitude towards adoption and diffusion. Strategies can therefore be formed and implemented to aid in the diffusion process for the LMS at the university. The study used a cross-sectional research design to observe how the different user groups were influenced by the external factors. Data collection was done over a four-week period with data analysis done afterwards using SPSS. Results revealed 92.1% of the respondents used the LMS with 91.6% agreeing that web based education (e-Learning) is an important delivery strategy used by faculty. Length of use ranged from less than one year to over six years with the level of experience ranging from a low level to a fully online level. The LMS showed widespread representation encompassing all colleges and departments of the university. Results also showed 61.6% of the respondents felt comfortable with using the LMS. Differences were identified between several of the attributes and barriers of adoption. However, one attribute and two barriers showed no statistical significant difference between the user groups. The study findings support the relationship between behavioral intention and actual behavior as presented by the Theory of Reasoned Action and Theory of Planned Behavior towards adoption of the LMS. As observed, the external factors played a role in user perception and attitude towards adopting and using the LMS, although the results showed no predictability of LMS preference based on university role or the combined factors of influence on user perception and attitude.Item Carbon dioxide absorption, desorption, and diffusion in aqueous piperazine and monoethanolamine(2009-12) Dugas, Ross Edward; Rochelle, Gary T.This work includes wetted wall column experiments that measure the CO₂ equilibrium partial pressure and liquid film mass transfer coefficient (kg') in 7, 9, 11, and 13 m MEA and 2, 5, 8, and 12 m PZ solutions. A 7 m MEA/2 m PZ blend was also examined. Absorption and desorption experiments were performed at 40, 60, 80, and 100°C over a range of CO₂ loading. Diaphragm diffusion cell experiments were performed with CO₂ loaded MEA and PZ solutions to characterize diffusion behavior. All experimental results have been compared to available literature data and match well. MEA and PZ spreadsheet models were created to explain observed rate behavior using the wetted wall column rate data and available literature data. The resulting liquid film mass transfer coefficient expressions use termolecular (base catalysis) kinetics and activity-based rate expressions. The kg' expressions accurately represent rate behavior over the very wide range of experimental conditions. The models fully explain rate effects with changes in amine concentration, temperature, and CO₂ loading. These models allow for rate behavior to be predicted at any set of conditions as long as the parameters in the kg' expressions can be accurately estimated. An Aspen Plus® RateSep™ model for MEA was created to model CO₂ flux in the wetted wall column. The model accurately calculated CO₂ flux over the wide range of experimental conditions but included a systematic error with MEA concentration. The systematic error resulted from an inability to represent the activity coefficient of MEA properly. Due to this limitation, the RateSep™ model will be most accurate when finetuned to one specific amine concentration. This Aspen Plus® RateSep™ model allows for scale up to industrial conditions to examine absorber or stripper performance.Item Combustion behavior of nano-composite aluminum iron oxide(Texas Tech University, 2004-05) Plantier, KeithBum rates of nano-scale aluminum (Al) powders mixed with iron oxide (Fe2O3) were measured as a function of Fe2O3 synthesis technique and fuel/oxidizer composition. Three reactant synthesis techniques were examined; two focused on sol-gel processing of nano-scale Fe2O3 particles and the third utilized commercially available nano-scale Fe203 powder. Nano-scale aluminum particles (52.7 nm in diameter) were combined with each oxidizer in various proportions. One goal was to determine the equivalence ratio corresponding to the maximum bum rate. The bum rates of five different nanocomposites of Al/Fe203 were compared. Flame propagation was studied by igniting low density mixtures and taking data photographically with a high-speed camera. Both open and confined burning was examined. Results indicated that the bum rate was a strong function of the stoichiometry of the mixture. An Equivalence ratio of 1.4 provides an optimum bum rate regardless of oxidizer synthesis technique. The magnitude of the bum rate is also a strong function of the oxidizer synthesis technique. Oxidizers processed using the sol-gel technology originally contained impurities which retarded the bum rates. When the same oxidizers were annealed at high temperatures, the new heat-treated oxidizer showed a dramatic improvement, with bum rates on the order of 900 m/s. The results of this work ultimately optimized the sol-gel synthesis process for preparing thermites.Item Comparative Deterministic and Probabilistic Modeling in Geotechnics: Applications to Stabilization of Organic Soils, Determination of Unknown Foundations for Bridge Scour, and One-Dimensional Diffusion Processes(2013-08-08) Yousefpour, NeginThis study presents different aspects on the use of deterministic methods including Artificial Neural Networks (ANNs), and linear and nonlinear regression, as well as probabilistic methods including Bayesian inference and Monte Carlo methods to develop reliable solutions for challenging problems in geotechnics. This study addresses the theoretical and computational advantages and limitations of these methods in application to: 1) prediction of the stiffness and strength of stabilized organic soils, 2) determination of unknown foundations for bridges vulnerable to scour, and 3) uncertainty quantification for one-dimensional diffusion processes. ANNs were successfully implemented in this study to develop nonlinear models for the mechanical properties of stabilized organic soils. ANN models were able to learn from the training examples and then generalize the trend to make predictions for the stiffness and strength of stabilized organic soils. A stepwise parameter selection and a sensitivity analysis method were implemented to identify the most relevant factors for the prediction of the stiffness and strength. Also, the variations of the stiffness and strength with respect to each factor were investigated. A deterministic and a probabilistic approach were proposed to evaluate the characteristics of unknown foundations of bridges subjected to scour. The proposed methods were successfully implemented and validated by collecting data for bridges in the Bryan District. ANN models were developed and trained using the database of bridges to predict the foundation type and embedment depth. The probabilistic Bayesian approach generated probability distributions for the foundation and soil characteristics and was able to capture the uncertainty in the predictions. The parametric and numerical uncertainties in the one-dimensional diffusion process were evaluated under varying observation conditions. The inverse problem was solved using Bayesian inference formulated by both the analytical and numerical solutions of the ordinary differential equation of diffusion. The numerical uncertainty was evaluated by comparing the mean and standard deviation of the posterior realizations of the process corresponding to the analytical and numerical solutions of the forward problem. It was shown that higher correlation in the structure of the observations increased both parametric and numerical uncertainties, whereas increasing the number of data dramatically decreased the uncertainties in the diffusion process.Item Computational modeling of transport through polymer membranes and globular proteins(2012-08) Jiang, Yingying, doctor of chemical engineering; Sanchez, Isaac C., 1941-; Paul, Donald R.; Freeman, Benny D.; Truskett, Thomas M.; Elber, RonWithin a polymer thin film, free-volume elements have a wide range of size and topology. This broad range of free-volume element sizes determines the ability for a polymer to perform molecular separations. Herein, the free volume and transport properties (diffusion, permeability, and selectivity) in both rubbery and glassy polymers were simulated using fully atomistic models. Extension of the computational tool to study the void structure in proteins is also included in this thesis. Six permeable thermally rearranged (TR) polymers and their precursors were studied. Using atomistic models, cavity size (free volume) distributions determined by a combination of molecular dynamics and Monte Carlo methods were consistent with experimental observation that TR polymers are more permeable than their precursors. The cavity size distributions determined by simulation were also consistent with free volume distributions determined by positron annihilation lifetime spectroscopy. The diffusion, solubility and permeation of gases in TR polymers and their precursors were also simulated at 308 K, with results that agree qualitatively with experimental data. A new hybrid Monte Carlo/Molecular Dynamics method is developed for estimating the slow diffusion processes of light gases transporting in glassy polymers. Diffusion coefficients, as small as 10⁻⁵ to 10⁻⁹ cm²/s are estimated for penetrants in four different polymers at 298 K. In all cases, agreement between literature experimental data and values obtained from the fast hybrid molecular dynamics method ranges from good to excellent. A new technique is developed using Monte Carlo methods to characterize the cavity size distribution and surface atoms in globular proteins. New statistical metrics have been defined for the structural characterization of globular proteins. Some of these metrics include volume, surface area, asymmetry ratio, interior cavity size distribution, and the identification of percolation channels. Wild-type (WT) myoglobin (Mb) and 5 Mb mutants have been studied in this research as examples. An analysis of cavity statistics provides an efficient method to quantify local properties such as packing density and transport pathways. The average cavity sizes of WT Mb and its mutants are around 4.0-5.0 Å.Item Computations of strongly forced laminar cold-flow jet and methane-air diffusion flames(2006) Barve, Vinayak Vidyadhar; Ezekoye, Ofodike A.Previous work has shown that for sufficiently high periodic forcing amplitudes, laminar diffusion flames can burn in an effectively partially premixed mode. Experimental observations show that the luminosity and sooting properties of the forced flames are significantly modified by the presence of strong forcing. In this work, simulations are performed to study the effects of strong forcing on flow field development in strongly forced laminar isothermal jets and methane air diffusion flames. Unforced and strongly forced cold-flow jets are simulated using a higher order finite volume CFD code. The jet was forced by varying the jet exit velocity over a range of forcing amplitudes and frequencies and it was found that the jet Strouhal number (St) was the important parameter in characterizing flowfield development. Further, the forced jets showed increased entrainment and increased entrainment rates as compared to the non-forced jets. The computations are extended to laminar methane–air diffusion flames. The combustion reactions were modeled using detailed gas-phase chemistry and complex thermo-physical properties. The radiation heat transfer was modeled using the S-6 Discrete Ordinates Method. A 2 equation soot chemistry model for soot nucleation, surface growth and oxidation was used. First an unforced flickering methane–air diffusion flame was modeled and then the flame was forced by varying the amplitude and frequency of the fuel velocity in the nozzle. Cases where the peak velocity in the fuel stream reached 6 times the mean velocity are examined. The internal nozzle flow was also simulated since the near-nozzle region was of particular interest due to the strong mixing processes occurring there and the subsequent effect on the flame properties. Lifted forced flames were also examined, and it was found that the partial premixing in the near nozzle region and modified gas phase chemistry in the forced flames can explain the reduction in soot production for the strongly forced flames.Item Detection of metal vapor atoms in bubbles at room temperature(2006) Molloy, John Leo; Holcombe, James A.One of the largest obstacles in miniaturizing traditional atomic spectroscopic sources is the need for a thermal/electrical source for free atom production. A single article in the literature has demonstrated atomic absorption detection of Ag, Cu, and Pd in aqueous solution at room temperature for atoms in the gas phase, which may ultimately permit miniaturization. Unfortunately, several laboratories have found that reproducing the phenomenon has been difficult. Without a sound fundamental explanation of the processes leading to the signal, one must conclude that it can be done, but some unsuspected and unknown design/methodological nuances are responsible for only a single reported success. Gas phase atoms could exist at room temperature “in solution” if the atoms were trapped in very small bubbles. A simpler system containing Hg vapor within a single 500 µL bubble was first studied using atomic absorption measurements. The use of experimental data and computer simulations revealed that metal transport out of bubbles suffers from slow diffusion through solution and limited solubility of the elemental species. Absorption signals for Hg vapor decayed over thousands of seconds, with slower decay rates associated with solutions higher in metal concentration and reducing power. Submicron sized bubbles were created in a flow-through cell during mixing of a 20% ethanol solution containing a reducing agent with Pd in 2% HCl. A repeatable atomic absorption signal was produced using this method. Replacement of ethanol with 1-propanol and use of a surfactant enhanced the signal through generation of more bubbles with lower internal pressures present. Limits of detection of ca. 100 ppb in Pd were achieved, although it is estimated that about 0.4% of the Pd initially added is contained within the bubbles as gaseous atoms. Further discussion includes exploration of the fundamental processes present in a procedure that delivers a repeatable signal.Item Diffusion of the Texas Cooperative Extension's horse theft awareness and prevention initiative(Texas A&M University, 2006-04-12) Swaim, Pattrick Lee, Jr.The primary purpose of this study was to identify the Horse Theft Awareness and Prevention Initiative (HTAPI) participants and the theft prevention practices used in Texas. The secondary purpose was to evaluate the educational effectiveness of the HTAPI on the first three of Kirkpatrick??s levels, namely learner satisfaction, knowledge acquired, and change in behavior. The third purpose was to examine relationships between the rate of adoption of HTAPI recommended practices and the following demographic variables: gender, age, equine discipline, number of horses owned, and size of investment in the equine business. Survey instruments were used to gather data. Due to sampling constraints, the Solomon four step research design method was modified by removing one group following Seger??s (1998). The sample groups consisted of a pre/only test group, pre/post test group, post/only test group minus the control pre/post test group. The pre/only sample group data was collected in Denton and Montgomery Counties and yielded 56 usable instruments. Using Dillman??s (2000) procedures, data from participants of the HTAPI programs were collected using two mailed survey instruments. One hundred ninety two participants of the 2004 Mare Foal, Basic Horse Management 101, and the Performance Horse workshops were mailed a post/only instrument; 96 were returned for a 49% response rate. Thirty two pre-test instruments were administered in Hopkins and Polk County and thirty days later these participants were mailed a post/only instrument. A response rate of 66% and 63% in the respective sample groups. The sample population can be described as mainly women (68.3%) 43 years of age who owned 7.3 horses each. The average investment in horses totaled $31,658. The most frequently owned breed was the Quarter Horse (f=133), and the most frequently listed discipline was for breeding purposes (f=121). There were no relationships detected between gender or age and theft prevention practices or innovativeness. Positive relationships were found between the breeds of horses owned and the type of permanent identification of horses and the theft prevention practices used. Additionally, positive relationships were detected between breeding and riding discipline of horses, the types of permanent identification, the theft prevention practices used, and owner innovativeness.Item Diffusion, closure temperatures, and accessory mineral petrogeneses in a high-temperature aureole: refining the integration of P-T and t(2003) McFarlane, Christopher R. M.; Connelly, James N.; Carlson, William D.Static heating during intrusion of the 1322 Ma Makhavinekh Lake Pluton (MLP) caused replacement of garnet in the adjacent country rocks (Tasiuyak Gneiss) by coronal assemblages of orthopyroxene + cordierite. Thermometry based on Al solubility in orthopyroxene, applied to relict garnet and neighboring orthopyroxene, preserves a temperature gradient from 700°C to 900°C at distances between 5750 and 20 m from the intrusion, reaffirming the robustness of this thermometry technique. Intracrystalline and intergranular Al zoning in M2 orthopyroxene are interpreted with the aid of numerical models for conductive heat flow in the aureole. The results document the ability of Al-in-orthopyroxene thermometry to preserve a detailed record of thermal histories in contactmetamorphic granulites. Zircon in the Tasiuyak Gneiss formed at ~1850 Ma near the peak of the Torngat Orogeny (M1 metamorphism). These M1 zircons were reheated during contact heating at 1322 Ma (M2 metamorphism). U-Pb dating of M1 zircon, using thermal ionization mass spectrometry (TIMS) and in situ sensitive high resolution ion microprobe (SHRIMP) geochronology, tested whether temperatures in the aureole exceeded the closure temperature for Pb diffusion in zircon. TIMS analyses failed to resolve appreciable resetting towards 1322 Ma even in samples that reached ~900 ºC. In contrast, high spatial resolution SHRIMP data revealed that cores of M1 zircon in samples that reached temperatures >800 ºC are significantly younger than rims. This reversal of core and rim ages implies that Pb was preferentially lost from cores. This observation is hypothesized to be the result of Pb migration during high-temperature recovery of lattice strain induced by higher impurity concentrations (REE, P) in cores. While M1 zircon suffered intracrystalline Pb diffusion during contact heating, it did not react with the surrounding major mineral assemblage. In contrast, low-Y monazite inclusions in M1 garnet were consumed as they were exposed to the M2 coronas. New growth of high-Y monazite records both the age and temperature of metamorphism in the aureole. Dissolution and new growth of monazite occurred under anhydrous conditions, highlighting the potential use of monazite as a high-temperature thermochronometer in granulites and ultra-hightemperature rocks.Item Drivers of environmentally-friendly technology adoption : electric vehicle and residential solar PV adoption in California(2016-05) Nath, Vivek; Rai, Varun; Zarnikau, JayThe use of electric vehicles (EVs) and residential solar photovoltaic (PV) panels is expected to play a role in stabilizing greenhouse gas concentrations in the atmosphere within an acceptable range, to mitigate detrimental climate change impacts. This thesis uses two uniquely rich datasets from the EV and residential solar PV market in California to study the demographic, motivational, social and informational influences on technology adoption decision-making. Rogers’ diffusion of innovations theory and the theory of planned behavior (TPB) are extensively used to contextualize the findings. Several findings aligned with Rogers’ generalizations regarding communication channels and characteristics of earlier adopters, and the increasing role of interpersonal communication channels signaled a shift to the early majority. Strong support was also found for the theory of planned behavior through the identification of the role of personal norms, subjective norms, attitude, and perceived behavioral control on intention and, ultimately, behavior. Information channels used by the EV cohort suggest a possible departure from TPB through the role of habitual behavior and attitudinal formation.Item The effect of restrictive diffusion on hydrate growth(2016-05) Andris, Ryan Gerald; Daigle, Hugh; Mohanty, KishoreMethane hydrate is formed naturally in a number of geologic settings around the world. The most predominant methane hydrate reservoirs are found in shallow oceanic basins at low temperatures and high pressures. A widely observed phenomenon in these oceanic sequences is extensive fine-grained sediments containing little to no hydrate interbedded with highly saturated sand bodies (20-60%). At Walker Ridge Block 313 in the Gulf of Mexico, one particular coarse-grained bed (approximately 3m-thick) is estimated to have methane hydrate occupying as much as 60% of the available pore space surrounded by hydrate-free clay. Here, I develop a numerical model that simulates methane hydrate growth in shallow oceanic basins in order to test whether diffusive transport of methane is a viable transport mechanism for forming highly saturated sand layers. I conclude that methane diffusion is likely responsible for the key identifying features of hydrate formation in interbedded sands and shales (i.e. greater hydrate saturations at the sand boundaries surrounded by hydrate-free zones in the fine-grained matrix). In addition, I show that the key parameters affecting the hydrate saturation profile include the amount of available methane for hydrate growth, thickness of the sand layer, and the radius of the fine grained pore space. I also discuss the shortcomings of the developed model and what complexities need to be added to more accurately reproduce hydrate growth throughout intricate hydrogeologic systems.Item Exploiting high precision single particle diffusion measurements to probe cellular functions in vitro and in vivo(2014-05) Keidel, Andrea; Florin, Ernst-Ludwig; Shubeita, George T; Gordon, Vernita D; Fink, Manfred; Stachowiak, Jeanne CDiffusion plays an important role for many processes at the microscopic level in cells. In this dissertation we present two model systems in which we monitor diffusion with high precision single particle tracking to gain insight into cellular functions. First we present an in vitro membrane fusion assay, in which fusion intermediates are described by the thermal motion of a membrane coated tracer particle. In the second part the diffusive motion of endogenous lipid droplets in the model organism Schizosaccharomyces pombe is utilized to probe the cytoplasmic behavior in response to glucose starvation.Item Faculty perceptions about attributes and barriers impacting the adoption and diffusion of Web-Based Educational Technologies (WBETs) at the University of Cape Coast and the University of Ghana, Legon(Texas A&M University, 2006-10-30) Yakah, Jemima AbenaThe purpose of this study was to determine faculty perceptions about factors impacting the adoption and diffusion of Web-Based Educational Technologies (WBETs) at the University of Cape Coast and the University of Ghana, Legon. This study, based on Rogers?????? theory of adoption and diffusion, is a modified replication of a study by Li (2004), in the context of Ghana. Data were collected with a modified instrument created by Li (2004), from 61 teaching faculty out of a target accessible population of 200. The instrument comprised of four sections: The first, was used to collect data about faculty stage in the innovation development process. The second was used to collect data describing five attributes (relative advantage, compatibility, complexity, trialability, and observability) impacting the adoption and diffusion of WBETs. The third was used to collect data about ten barriers (concerns about time, concerns about incentives, program credibility, financial concerns, planning issues, conflict with traditional education, fear of technology, technical expertise, administrative support, and infrastructure) impacting the adoption and diffusion of WBETs. The fourth section was used to collect data on personal characteristics of the faculty. Descriptive, correlational and regression analyses were used to examine relationships between faculty personal characteristics, stage in the innovation-decision process, and perceptions of attributes and barriers impacting the adoption and diffusion of WBETs. From the descriptive results, respondents perceived ??????relative advantage?????? and ??????observability?????? as the two most important attributes that impact the adoption and diffusion of WBETs. Infrastructure, financial concerns, and technical expertise were perceived as posing moderate to strong barriers to the adoption and diffusion of WBETs. Only compatibility (attribute) and technical expertise (barrier) had statistically significant correlations with faculty stage in the innovation decision process. The attributes and barriers altogether explained only 10.6% and 17.3% respectively of faculty stage in the innovation-decision process. Of the eight personal characteristics examined, only ??????experience with WBETs?????? had a statistically significant correlation with faculty stage in the innovation-decision process. Recommendations to administrators and policy makers include allocating investments and resources that promote attributes and eliminate barriers, and conduct further research into factors that affect the adoption and diffusion of WBETs.Item Gene expression evolution after duplication(2015-12) Thompson, Ammon Michael; Zakon, H. H.; Hillis, David; Bull, James J; Gross, Jeff; Phelps, Steven MGene duplication is a mutational process that seeds genomes with new geneticmaterial. Ion channels comprise a large gene family that arose through gene duplicationsthat has played a substantial role in the evolution of novel traits across all of the domainsof life. For my dissertation, I investigated the evolutionary dynamics that allow geneduplicates to evolve novel functions. To do so, I focused on measuring and modeling theexpression evolution of voltage-gated sodium ion channel duplicates implicated in theconvergent evolution of electric organs in two families of electric fish.In chapter 1, I measured the expression stoichiometry of two sodium channelduplicates in electric fish species as well as non-electric relatives. I found that before amajor shift in expression from skeletal muscle and neofunctionalization in the musclederivedelectric organ, one of the duplicate genes was first down-regulated in theancestors of both electric lineages. In chapter 2, I introduce a new model of the dynamicsof duplicate genes co-evolving under dosage balance selection for their sharedexpression. I used the model to estimate the strength of selection on the duplicate genesfound in the electric fish lineages and to show that dosage balance selection impedes theevolution of novel function early after gene duplication but can later facilitate novelfunction evolution once a particular expression threshold is reached. In chapter 3 Iinvestigate the role a duplicate sodium channel played in the evolution of a novel electricorgan derived from motor neurons in a lineage of fish. In this lineage I show that aviskeletal-muscle-specific sodium channel duplicated and one of the duplicates gainedexpression in the spinal cord. In this tissue this channel exhibits sequence evolutionarypatterns consistent with it evolving to contribute to the unique electrophysiologicalattributes of the electric organ. This is the first observation of such a radical shift inexpression for a muscle-specific gene.Item Group-Contribution Methods in Estimating Liquid-Liquid Distribution Coefficients(Texas Tech University, 1981-05) Liu, Che KeungNot Available.Item Hybrid Sn/Diffusion and Sn/P3 Neutronics Calculations(2013-03-14) Manolov, SergiyIn this thesis we investigate coupling and preconditioning techniques for 19D hybrid neutronics calculations. Each problem is represented by two spatial regions with Sn in one region and either Diffusion (P1) or P3 in the other region. For each of these two cases we define one coupling scheme and two different preconditioned systems. These systems are solved with both fixed9point iteration and the GMRES Krylov method. The solution techniques are compared in terms of iteration count and computational cost. Preconditioning with a global diffusion operator is found to be very effective for the most difficult problems.Item Local structure and dynamics of complex fluids(2013-12) Carmer, James Lee; Truskett, Thomas Michael, 1973-There is a well-known connection between the structure and dynamics that is present in molecular and colloidal systems. Using this connection as a guide we are able to design interparticle potentials that optimizes the diffusivity of a single particle. While structure-dynamic correlations provide the insight that diffusion could be enhanced, the effect of this enhancement on the dynamics of neighboring particles is more difficult to quantify. A novel method for calculating position-dependent dynamics is introduced that can be easily implemented into existing simulation protocols. The computational requirements are very low compared to existing methods and this technique can also be applied to a wide variety of systems, including experiments where particle trajectories can be determined. Using this method, the position-dependent diffusivity of solvent particles in the vicinity of a tracer particle can be measured. This information allows for determination of the microscopic changes that take place as a result of the optimization discussed above. To study the effect of a non-continuum solvent, we design a system that eliminates inhomogeneous structuring near an interface. Hydrodynamic theory can predict the position-dependent diffusivity of a sphere in continuum solvent. Comparing these systems not only highlights the difference in position-dependent dynamics for continuum and non-continuum solvents, but is a starting point to study what happens to dynamics when structure is reintroduced. This allows us to answer many other questions about the relationships between structure and dynamics. While these connections have been studied extensively for average properties, they have not been explored for their position-dependent counterparts. For bulk fluids, the insertion probability and two-body excess entropy has proven useful for predicting average dynamic properties. We develop expressions for the position-dependent versions of both of these quantities. We show that when using the appropriate reference state the position-dependent diffusivity can be qualitatively related to the insertion probability.