Browsing by Subject "Stability"
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Item Item Analysis of Ricci flow on noncompact manifolds(2013-05) Wu, Haotian, active 2013; Knopf, Dan, 1959-In this dissertation, we present some analysis of Ricci flow on complete noncompact manifolds. The first half of the dissertation concerns the formation of Type-II singularity in Ricci flow on [mathematical equation]. For each [mathematical equation] , we construct complete solutions to Ricci flow on [mathematical equation] which encounter global singularities at a finite time T such that the singularities are forming arbitrarily slowly with the curvature blowing up arbitrarily fast at the rate [mathematical equation]. Near the origin, blow-ups of such a solution converge uniformly to the Bryant soliton. Near spatial infinity, blow-ups of such a solution converge uniformly to the shrinking cylinder soliton. As an application of this result, we prove that there exist standard solutions of Ricci flow on [mathematical equation] whose blow-ups near the origin converge uniformly to the Bryant soliton. In the second half of the dissertation, we fully analyze the structure of the Lichnerowicz Laplacian of a Bergman metric g[subscript B] on a complex hyperbolic space [mathematical equation] and establish the linear stability of the curvature-normalized Ricci flow at such a geometry in complex dimension [mathematical equation]. We then apply the maximal regularity theory for quasilinear parabolic systems to prove a dynamical stability result of Bergman metric on the complete noncompact CH[superscript m] under the curvature-normalized Ricci flow in complex dimension [mathematical equation]. We also prove a similar dynamical stability result on a smooth closed quotient manifold of [mathematical symbols]. In order to apply the maximal regularity theory, we define suitably weighted little Hölder spaces on a complete noncompact manifold and establish their interpolation properties.Item Bursting events in the stable atmospheric boundary layer(2008-05) Phillipson, Julie Ann; Basu, Sukanta; Gilliam, Xiaoning; Leary, ColleenThough recent experiments and field projects regarding the characteristics of the boundary layer have been conducted, there is still an overall lack of understanding about the mechanics of the stable boundary layer, whether it is transitionally stable, such as the nocturnal stable boundary layer in mid-latitudes, or persistently stable, such as the boundary layer in Polar Regions. ISCAT-00 is one such field project conducted in Antarctica, where an instrumented tower was used to record wind speed and temperature information, from which heat and momentum flux transfers can be discerned. Understanding of boundary layer processes is especially important for the stable layer since despite its stable nature, sporadic bursts of turbulence have been observed to occur, indicated by data collected from the ISCAT-00 campaign. These bursts, though short-lived, are responsible for most of the heat and momentum transfer that occurs within the otherwise stable layer. Since these bursts of turbulence disrupt the stable layer, they can not only pose problems for air quality forecasts, but they can also inhibit the performance of wind turbines. Transient loading from these bursting events as rotor blades pass through patches of organized, coherent turbulence can shorten the life span of a wind turbine by 5 to 10 years. However, despite the noted occurrence of turbulence bursting in the stable layer there is still very little known about its origins, causes, or basic properties. In order to explore the characteristics of turbulent bursting events in the stable layer, two methodologies are applied to analyze data obtained from the ISCAT00 campaign. The first methodology applied to discern the occurrence of turbulent bursting is one created by Nakamura & Mahrt (2005). The second methodology is a newly developed adaptive threshold methodology, which is much more robust, and removes much of the subjectivity of other turbulence bursting identification methods. The adaptive technique allows for the reduction of subjectivity in the data analysis phase, and is therefore felt to be more accurate. Also, spectral characteristics of polar turbulence are explored, and are found to have similar properties to spectra observed in mid-latitudes. This research focuses primarily on different methods, both old and newly developed that can help to further understanding about turbulence in the stable boundary layer and the corresponding heat and moisture flux properties.Item Design synthesis of multistable equilibrium systems(2004) King, Carey Wayne; Beaman, Joseph J.; Campbell, Matthew I.Mechanical systems are often desired to have features that can adapt to changing environments. Ideally these systems have a minimum number of parts and consume as little power as possible. Unfortunately many adaptable systems either have a large number of heavy parts and/or continuous actuation of smart materials to provide the adaptive capabilities. For systems where both adaptability and power conservation are desired characteristics, adaptability can be limited by power consumption. Multistable equilibrium (MSE) systems aim to provide a type of adaptable system that can have multiple mechanical configurations, or states, that require no power to maintain each stable configuration. Power is only needed to move among the stable states, and a level of adaptability is maintained. The stable equilibrium configurations are defined by a system potential energy being at a minimum. The design of a MSE system is based around locally shaping a potential energy curve about desired equilibrium configurations, both stable and unstable, such that the basic design goals of position, linearized natural frequency, and transition energy can be specified for the MSE system. By mapping the performance space from the design space in tandem with stochastic numerical optimization methods, the designer determines if a certain system topology can be designed as a MSE system. Qualitative and quantitative mapping procedures enable the designer to decide whether or not the desired design lies near the center or periphery of a performance space. The performance space is defined by the desired design criteria (i.e. locations of the equilibria, natural frequency at the equilibria, etc.) that the designer deems important. If the desired design lies near the periphery of the performance space, a series of optimization trials is performed. This series shows the tendency of the problem to be solved as the desired MSE system characteristics are varied within the performance space from a location where the solution is known to exist to the true desired location where the solution is not guaranteed to exist. Upon analysis of the resulting optimization trends, the designer is able to determine whether or not a feasible limit in the system performance has been reached.Item Development of efficient, stable organic-inorganic hybrid solar cells(2012-08) Jayan, Baby Reeja; Manthiram, ArumugamDeveloping a fundamental understanding of photocurrent generation processes at organic-inorganic interfaces is critical for improving hybrid solar cell efficiency and stability. This dissertation explores processes at these interfaces by combining data from photovoltaic device performance tests with characterization experiments conducted directly on the device. The dissertation initially focuses on exploring how morphologically and chemically modifying the organic-inorganic interface, between poly(3-hexylthiophene) (P3HT) as the electron donating light absorbing polymer and titanium dioxide (TiO₂) as the electron acceptor, can result in stable and efficient hybrid solar cells. Given the heterogeneity which exists within bulk heterojunction devices, stable interfacial prototypes with well-defined interfaces between bilayers of TiO₂ and P3HT were developed, which demonstrate tunable efficiencies ranging from 0.01 to 1.6 %. Stability of these devices was improved by using Cu-based hole collecting electrodes. Efficiency values were tailored by changing TiO₂ morphology and by introducing sulfide layers like antimony trisulfide (Sb₂S₃) at the P3HT-TiO₂ interface. The simple bilayer device design developed in this dissertation provides an opportunity to study the precise role played by nanostructured TiO₂ surfaces and interfacial modifiers using a host of characterization techniques directly on a working device. Examples introduced in this dissertation include X-ray photoelectron spectroscopy (XPS) depth profiling analysis of metal-P3HT and P3HT-TiO₂ interfaces and Raman analysis of bonding between interface modifiers like Sb₂S₃ and P3HT. The incompatibility of TiO₂ with P3HT was significantly reduced by using P3HT derivatives with -COOH moieties at the extremity of a polymer chain. The role of functional groups like -COOH in interfacial charge separation phenomena was studied by comparing the photovoltaic behavior of these devices with those based on pristine P3HT. Finally, for hybrid solar cells discussed in this dissertation to become commercially viable, high temperature processing steps of the inorganic TiO₂ layer must be avoided. Accordingly, this dissertation demonstrates the novel use of electromagnetic radiation in the form of microwaves to catalyze growth of anatase TiO₂ thin films at temperatures as low as 150 °C, which is significantly lower than that used in conventional techniques. This low temperature process can be adapted to a variety of substrates and can produce patterned films. Accordingly, the ability to fabricate TiO₂ thin films by the microwave process at low temperatures is anticipated to have a significant impact in processing devices based on plastics.Item Effect of Synthesis Condition and Annealing on the Sensitivity and Stability of Gas Sensors Made of Zn-Doped y-Fe2O3 Particles(2010-10-12) Kim, TaeyangIn this study, the effect of synthesis conditions and annealing process on the sensitivity and stability of gas sensors made of flame-synthesized Zn-doped ?-Fe2O3 particles was investigated. Zn-doped ?-Fe2O3 particles were synthesized by flame spray pyrolysis using either H2/Air or H2/O2 coflow diffusion flames. The particles were then annealed at 325~350?C in a tube furnace under air atmosphere. Both as-synthesized and annealed particles were used as gas sensing materials to construct gas sensors. Transmission electron microscopy (TEM), X-ray diffraction (XRD), Brunauer-Emmett-Teller surface area measurement (BET), Williamson and Hall (WH) method were employed to characterize the particles. Gas sensors were fabricated by applying the as-synthesized and annealed particles on interdigitated electrodes. The response of the gas sensor to acetone vapor, H2 in dry synthetic air was measured before and after three days of aging. High-temperature flame (H2/O2) generated nanometer-sized particles; lower temperature flame (H2/Air) generated micrometer-sized particles. Fe2O3 particles doped with 15% Zn showed the highest sensitivity. The sensors made from as-synthesized particles showed a gas sensing sensitivity that was 20 times higher than the literature value. The sensors made of microparticles lost their sensing ability after three days of aging, but sensors made of nanoparticles did not show significant change after aging. Sensors made of annealed particles (either micro or nano) did not have significant gas sensing ability, but annealing process improved the stability of gas sensors. Analysis using the WH method showed that the microstrains decreased significantly in both H2/O2 and H2/Air flame particles after annealing. The results showed that sensors made of nanoparticles have higher gas sensing signal, and more resistant toward aging than sensors made of microparticles. In addition, annealing process affected on the stability favorably due to reduction of structural defects.Item Effects of Economic Structure on Regional Economic Performance(2014-06-04) Hong, Sa HeumSince the most recent recession, many local governments, which excessively paid attention to economic growth, have undergone tremendous difficulties caused by severe fluctuations. It shows that economic stability also has to be considered as another critical factor that constitutes regional economic performance. Thus, in this dissertation, I evaluate regional economic performance in terms of both growth and stability. In most previous studies, economic structure was found to be a factor that can affect both growth and stability at the same time. However, in terms of measuring economic structure, diversity and specialization have been commonly treated as the exact opposite, increasing in one means decreasing in the other. Some researchers recognized the existence of multiple specializations in an economy but this concept has never been operationalized and empirically tested. Therefore, I extend the body of previous research by formulating an indicator to empirically measure multiple specializations in regional economies and examine the effect of multiple specializations on both growth and stability in one framework. Moreover, the economic structural effects can be estimated differently depending on the macro-economic situations. However, previous studies rarely considered the effects of macro-economic situations when investigating the effect of economic structure. Thus, to overcome this limitation, I apply panel analysis for the same statistical models in the above using the panel data which were constructed with four different time periods based on different macro-economic situations. The empirical analysis in this study finds that multiple specializations might positively affect economic growth while diversity can hinder growth. Otherwise, this study finds that increasing the levels of both diversity and multiple specializations can help regions to promote economic stability. It suggests that a region with a multiply specialized economic structure is more likely to experience both growth and stability at the same time. Additionally, the results of panel analyses inform that the effects of economic structure on growth vary across different macroeconomic situations while these structural effects on stability are consistently estimated, regardless of macroeconomic situations. This suggests that the economic development strategy using economic structure may indicate the different effectiveness by their objectives (i.e., growth or stability) or the macro-economic situations (i.e., boom or bust).Item Energy storage sizing for low-inertia microgrids, and lessons learned from a potential microgrid(2016-05) Toliyat, Amir; Baldick, Ross; Kwasinski, Alexis; Arapostathis, Aristotle; Hallock, Gary; Uriarte, FabianThe coordinated control of multiple distributed generators in a microgrid and the preservation of adequate system inertia in real-time operations are some of the principal technical challenges for stable microgrid operation. One issue in particular pertains to grid-tied inverters, which, as mandated by present standards, are only permitted to operate at unity power factor, thereby requiring the microgrid’s synchronous generators to operate at a low power factor. This behavior accordingly introduces ramifications by limiting the generator’s active power output, which would compromise frequency and voltage stability margins. Consideration is also given to the effect of line impedances, since interconnecting microgrid lines can be described by a variety of X/R ratios that affect the control and flow of active and reactive power. Moreover, the absence of a stiff grid presents control challenges for grid-tied inverters due to the inverters’ tendency to regulate the voltage at the point of common coupling. These same inverters also jeopardize microgrid stability due to their low equivalent inertia as traditional forms of generation (i.e., spinning sources) become displaced by inertia-less inverters. Because of this low microgrid inertia, fluctuations in the output power of renewable energy sources or changes in local load levels may lead to power quality or frequency/voltage stability concerns. Therefore, energy storage sizing is investigated in this dissertation, as it is closely related to the stability analysis of microgrids. Furthermore, an existing residential community (in Austin, TX) described by a moderate penetration of photovoltaic sources and electric vehicle charging is considered, and the implications of said community being retrofitted to a microgrid are examined.Item Exact solution of a stable inviscid vortical flow inside a two-dimensional rectangular chamber with inlet and outlet(2008-08) Gurung, Dil K.; Bhattacharya, Sukalyan; James, Darryl; Parameswaran, SivaIn this thesis, we analyze vortical circulation inside a rectangular enclosure where flow enters via an opening and exits to the ambient atmosphere through another slot situated at the opposite side of the inlet. The characteristic Reynolds number is considered to be high so that viscous effects are neglected. We present a semi-analytical procedure to determine the velocity field in such system for arbitrary chamber geometry specified by the aspect ratio of the enclosure as well as by the dimensions and positions of the inlet and outlet. In this problem, one has to satisfy both inlet and exit conditions to find a unique flow solution. The inlet condition can easily be implemented from the velocity profile at the entry plane. The flow at the outlet is, however, difficult to account for. The most accurate exit condition is the continuity constraint between the velocities inside and outside the chamber. Such continuity is difficult to ensure because it requires additional computation of a semi-infinite flow-domain representing the ambient. Hence, generally, in numerical schemes either an arbitrary exit condition is assumed or the outside domain is truncated by a finite hypothetical boundary. In contrast, in the present study, the true exit-condition is enforced by expressing the fields as an expansion of proper basis solutions with unknown amplitudes which are evaluated from a system of linear equations consistent with the outlet geometry. As a result, we are able to accurately calculate velocity fields for different geometries and boundary conditions. The stability of the obtained solution can be ensured by constraining the system parameters. Consequently, our results can be useful in analysis of steady cross-circulations in rectangular chambers where Reynold’s number is typically high.Item Feedback system design: the pole placement problem(Texas Tech University, 1982-12) Iyer, AshokNot availableItem A fragmentation model for sprays and L² stability estimates for shockes solutions of scalar conservation laws using the relative entropy method(2010-05) Leger, Nicholas Matthew; Vasseur, Alexis F.; Arbogast, Todd J.; Gamba, Irene M.; Vishik, Mikhail M.; Raman, VenkatramananWe present a mathematical study of two conservative systems in fluid mechanics. First, we study a fragmentation model for sprays. The model takes into account the break-up of spray droplets due to drag forces. In particular, we establish the existence of global weak solutions to a system of incompressible Navier-Stokes equations coupled with a Boltzmann-like kinetic equation. We assume the particles initially have bounded radii and bounded velocities relative to the gas, and we show that those bounds remain as the system evolves. One interesting feature of the model is the apparent accumulation of particles with arbitrarily small radii. As a result, there can be no nontrivial hydrodynamical equilibrium for this system. Next, with an interest in understanding hydrodynamical limits in discontinuous regimes, we study a classical model for shock waves. Specifically, we consider scalar nonviscous conservation laws with strictly convex flux in one spatial dimension, and we investigate the behavior of bounded L² perturbations of shock wave solutions to the Riemann problem using the relative entropy method. We show that up to a time-dependent translation of the shock, the L² norm of a perturbed solution relative to the shock wave is bounded above by the L² norm of the initial perturbation. Finally, we include some preliminary relative entropy estimates which are suitable for a study of shock wave solutions to n x n systems of conservation laws having a convex entropy.Item High-order finite element methods for seismic wave propagation(2009-05) De Basabe Delgado, Jonás de Dios, 1975-; Sen, Mrinal K.; Wheeler, Mary F. (Mary Fanett)Purely numerical methods based on the Finite Element Method (FEM) are becoming increasingly popular in seismic modeling for the propagation of acoustic and elastic waves in geophysical models. These methods o er a better control on the accuracy and more geometrical exibility than the Finite Di erence methods that have been traditionally used for the generation of synthetic seismograms. However, the success of these methods has outpaced their analytic validation. The accuracy of the FEMs used for seismic wave propagation is unknown in most cases and therefore the simulation parameters in numerical experiments are determined by empirical rules. I focus on two methods that are particularly suited for seismic modeling: the Spectral Element Method (SEM) and the Interior-Penalty Discontinuous Galerkin Method (IP-DGM). The goals of this research are to investigate the grid dispersion and stability of SEM and IP-DGM, to implement these methods and to apply them to subsurface models to obtain synthetic seismograms. In order to analyze the grid dispersion and stability, I use the von Neumann method (plane wave analysis) to obtain a generalized eigenvalue problem. I show that the eigenvalues are related to the grid dispersion and that, with certain assumptions, the size of the eigenvalue problem can be reduced from the total number of degrees of freedom to one proportional to the number of degrees of freedom inside one element. The grid dispersion results indicate that SEM of degree greater than 4 is isotropic and has a very low dispersion. Similar dispersion properties are observed for the symmetric formulation of IP-DGM of degree greater than 4 using nodal basis functions. The low dispersion of these methods allows for a sampling ratio of 4 nodes per wavelength to be used. On the other hand, the stability analysis shows that, in the elastic case, the size of the time step required in IP-DGM is approximately 6 times smaller than that of SEM. The results from the analysis are con rmed by numerical experiments performed using an implementation of these methods. The methods are tested using two benchmarks: Lamb's problems and the SEG/EAGE salt dome model.Item How perceptions impact real estate decisions : an analysis of residential demand in Austin, Texas(2015-12) Fulmer, Kristen Alyse; Atkinson, Simon, Ph. D.; Wegmann, JacobThis thesis examines how social media trends create perceptions, which influence real estate decision-making within the Millennial generation, ultimately affecting their long-term investment and longevity in the city of Austin, Texas. To investigate the residential real estate market in Austin, specifically within the Millennial generation, I discuss decision factors with the residents and developers, known as stakeholders. By completing a mixed-methods analysis, I determine how Internet-based tendencies affect perceptions and economic realities of specific neighborhoods or the city, thereby affecting the residential real estate market as a whole. Approaching this research as a post-positivist, I hypothesize that the Millennial cohort is currently creating short-term demand for residential development with no long-term intentions of staying in the city. By discovering this future instability of sectors within the Millennial generation, especially in newcomers to the city, I question Austin’s plans, which seem to lack amenities to provide for this cohort’s residential longevity.Item Hydraulic performance and stability of geosynthetic landfill cover systems with constrained drainage at the outlet(2011-08) Yates, Trevor Butler; Zornberg, Jorge G.; Gilbert, Robert B. (Robert Bruce), 1965-; El Mohtar, ChadiSliding failures of landfill cover systems are common, and the slip surface is often at the interface between a geosynthetic drainage layer and an underlying textured geomembrane. In an effort to understand the sliding failures, the objectives of this research project are to summarize current regulation and practice in landfill cover design, use experimental methods to characterize the behavior of geosynthetic landfill materials in cover systems approaching failure, and develop models to evaluate the hydraulic performance and stability of landfill cover systems. Inclined plane tests were conducted to explore the behavior of a geosynthetic drainage material/textured geomembrane interface. The interface had effective normal stress dependent strain softening behavior, with more strain softening measured at higher effective normal stresses. A numerical model for confined flow in a drainage layer with a constrained outlet was developed. The model was used to evaluate how water fills and empties from a geosynthetic drainage layer for a variety of inflow conditions and constraints to flow at the outlet. The model was used to demonstrate that a drainage layer that effectively conveys water out of a cover system with a free flowing drainage outlet quickly fills with water when the outlet has a modest constraint to flow. An iterative, numerical model was developed to calculate stability solutions for landfill cover slopes that satisfy force equilibrium and strain compatibility while accounting for effective normal stress dependent strain softening and various pore water pressure conditions. Stability solutions reveal that depending on the water pressure in the drainage layer, the geosynthetic drainage material may experience tension at many points along the slope. It is crucial for the stability of the landfill cover system to maintain free-flowing conditions at the drainage layer outlet. A modest constraint to flow at the outlet has a significant adverse effect on the ability of the landfill cover drainage layer to convey water out of the system, which can lead to instability. The drainage layer outlet should be designed to ensure free flow of water out of the drainage layer.Item Identifying mutations that enhance the evolutionary stability of fluorescent protein expression from a plasmid in Escherichia coli(2014-05) Rodríguez Mendoz, Álvaro Eugenio; Barrick, Jeffrey E.; Harshey, RasikaSynthetic biologists and metabolic engineers seek to design and create organisms with novel functions. A major difficulty with many designed genetic devices is that they lack evolutionary robustness. In this study, our aim was to identify mutations that could enhance the evolutionary stability of green fluorescent protein (GFP) expression from a plasmid in Escherichia coli. To achieve this goal, we created a mutagenized strain library and performed an evolution experiment. To enrich potential mutants with improved GFP stability, we periodically sorted for cells that remained highly fluorescent as this population was propagated for several hundred generations and less-robust strains accumulated inactivating mutations. Further testing of clones isolated from the final evolved population showed that GFP expression was more stable in these strains and suggested mutations in the chromosome were responsible. Re-sequencing the genomes of four of these strains found that, among other genetic differences from the ancestor, all had a mutation in either PolA or PolB. These two types of DNA polymerase mutations may enhance GFP stability by causing a lower point mutation rate in the E. coli host.Item Importance of stability of pharmaceutical formulations(2016-12) Hengsawas, Soraya; Williams, Robert O., 1956-; Cui, Zhengrong; Frei, Christopher R; Zhang, Feng; McGinity, James WStability is an essential quality attribute for pharmaceutical formulations. Evaluation of drug stability can prevent toxicity and increase safety, efficacy and quality of the final drug product. In this work, various factors affecting stability of both small molecule and biopharmaceutical compounds were investigated. In the first study, we initially hypothesized that albendazole, a poorly water soluble drug, could be prepared by melt extrusion to enhance its dissolution and bioavailability. However, it was found that albendazole was severely degraded by heat and shear during extrusion. When combined with methanesulfonic acid and Kollidon VA 64, amorphous albendazole solid dispersion was successfully prepared by an alternative process, spray drying, to enhance dissolution and shelf-stability. In the second study, the stability of a caveolin-1 scaffolding domain (CSP7), which is a newly developed peptide for the treatment of idiopathic pulmonary fibrosis, was investigated in order to achieve an optimal formulation for in vivo clinical studies. This study showed the physical instability of the peptide, which was aggregation induced by moisture, and the crystallization of bulking agent on its stabilizing effect. It was found that the moisture-induced aggregates were reversible and could be prevented by pH adjustment and incorporation of lactose in the composition. Lactose, a reducing sugar, stabilized the peptide possibly as a result of chemical interactions with CSP7 (e.g., formation of a Schiff base with the N-terminal amino group of CSP7). Based on these results, lactose stabilized CSP7 against moisture-induced aggregation in the solid state to a greater degree than mannitol. Additionally, stability of the CSP7-bulking agent formulations was not affected by nebulization using vibrating mesh nebulizers. Lastly, the effect of nebulization using vibrating mesh nebulizers on stability of tissue-type plasminogen activator (tPA) and single-chain urokinase plasminogen activator (scuPA), being studied for the treatment of inhalational smoke-induced acute lung injury (ISALI), was evaluated. For scuPA, the effect of lyophilization on its stability was also studied. The results showed that scuPA was stable after lyophilization (scuPA) and that both proteins were stable following reconstitution and nebulization. There were only slightly differences between the active and passive vibrating mesh nebulizers. In conclusion, from our work, the physical and chemical stability of small- and macromolecules was affected by formulation composition, processing and post-processing factors.Item Improving the Educational Outcomes for Minorities: A Study of the Interactive Effects of Personnel Stability and Representative Bureacracy(2013-08-06) Morton, Tabitha Susan MarieThe goal of this dissertation is to determine how to create more equal public policy outcomes within the realm of public education. It is a well known fact that despite the passage of legal decisions such as Brown (1954) and federal policies like No Child Left Behind (2001), Latino and African American students still perform at lower rates than Anglo students. This poor academic performance results in lower graduation rates, lower college attendance, and a lower socioeconomic status than Anglos. This dissertation therefore sought to determine if two common bureaucratic theories, representative bureaucracy and personnel stability, could be used in combination with one another in order to improve the educational policy outcomes for African American and Latino students. Using data from Texas school districts from 1994-2010 and a cross-sectional longitudinal research design, I find that while each theory on its own improved the outcomes for these groups, the two did not have a significant combined effect on every indicator. Instead I find evidence of a substitution effect which allows one strategy to be used in place of the other in order to improve the academic performance of minority students. This creates a unique situation as this analysis suggests that there are other bureaucratic factors working to prevent an interactive effect from occurring on a consistent basis. Thus the next steps are to apply the same theories to other public organizations in order to determine if my findings are unique to public education and to determine if other public administration theories can be used to improve the outcomes for African American and Latino students.Item Influence of Biomechanical Constraints on Endpoint Control, Interlimb Coordination and Learning(2010-07-14) Rodriguez, Tiffany M.A number of movements produced in everyday life require not only coordination of joints within a limb, but also coordination between one or more limbs. The aim of this dissertation was to examine the influence of biomechanical constraints on intralimb coordination, interlimb coordination, and learning. Experiment 1 sought to determine if principles of the Leading Joint Hypothesis, when applied to a multijoint bimanual coordination task, could provide insight into the contribution of intralimb dynamics to interlimb coordination. Participants repetitively traced ellipse templates in an asymmetrical coordination pattern (i.e. both limbs moving counter-clockwise). Kinematic data of the upper limbs were recorded with a VICON camera system. Ellipse templates were oriented either tilted right or tilted left; yielding a total of four left arm-right arm leading joint combinations. The findings indicated that stability of interlimb coordination patterns were found to be influenced by whether arm movements were produced with similar or different leading joints. Bimanual asymmetric ellipse-tracing produced with similar leading joints were more stable than patterns produced with different leading joints. For example, asymmetric coordination patterns produced with similar leading joints exhibited less transient behavior than coordination patterns produced with different leading joints (p < .01). Experiment 2 expanded on these findings by employing a similar task and incorporating a learning component to assess how intralimb dynamics are tuned with practice of a novel coordination pattern. Participants were randomly assigned to one of three groups. One group practiced tracing a pair of ellipse templates that were oriented in such a way that required similar leading joints while the other two groups practiced tracing ellipse templates that required different leading joints. Early in practice, the group learning the coordination pattern with similar leading joints exhibited greater interlimb stability than the two groups learning with different leading joints. However, following two days of practice, performance of the groups learning with different leading joints improved to match that of the group learning with similar leading joints. The findings suggest that initial biomechanical constraints can be overcome with practice, resulting in similar performance regardless of whether being produced with similar or different leading joints.Item Modeling, Design and Optimization of IC Power Delivery with On-Chip Regulation(2014-12-11) Lai, SumingAs IC technology continues to follow the Moore?s Law, IC designers have been constantly challenged with power delivery issues. While useful power must be reliably delivered to the on-die functional circuits to fulfill the desired functionality and performance, additional power overheads arise due to the loss associated with voltage conversion and parasitic resistance in the metal wires. Hence, one of the key IC power delivery design challenges is to develop voltage conversion/regulation circuits and the corresponding design strategies to provide a guaranteed level of power integrity while achieving high power efficiency and low area overhead. On-chip voltage regulation, a significant ongoing design trend, offers appealing active supply noise suppression close to the loads and is well positioned to address many power delivery challenges. However, to realize the full potential of on-chip voltage regulation requires systemic optimization of and tradeoffs among settling time, steady-state error, power supply noise, power efficiency, stability and area overhead, which are the key focuses of this dissertation. First, we develop new low-dropout voltage regulators (LDOs) that are well optimized for low power applications. To this end, dropout voltage, bias current and speed are important competing design objectives. This dissertation presents new flipped voltage follower (FVF) based topologies of on-chip voltage regulators that handle ultra-fast load transients in nanoseconds while achieving significant improvement on bias current consumption. An active frequency compensation is embedded to achieve high area efficiency by employing a smaller amount of compensation capacitors, the major silicon area contributor. Furthermore, in one of the proposed topologies an auxiliary digital feedback loop is employed in order to lower quiescent power consumption further. Second, coping with supply noise is becoming increasingly more difficult as design complexity grows, which leads to increased spatial and temporal load heterogeneity, and hence larger voltage variations in a given power domain. Addressing this challenge through a distributed methodology wherein multiple voltage regulators are placed across the same voltage domain is particularly promising. This distributive nature allows for even faster suppression of multiple hot spots by the nearby regulators within the power domain and can significantly boost power integrity. Nevertheless, reasoning about the stability of such distributively regulated power networks becomes rather complicated as a result of complex interactions between multiple active regulators and the large passive subnetwork. Coping with this stability challenge requires new theory and stability-ensuring design practice, as targeted by this dissertation. For the first time, we adopt and develop a hybrid stability framework for large power delivery networks with distributed voltage regulation. This framework is local in the sense that both the checking and assurance of network stability can be dealt with on the basis of each individual voltage regulator, leading to feasible design of large power delivery networks that would be computationally impossible otherwise. Accordingly, we propose a new hybrid stability margin concept, examine its tradeoffs with power efficiency, supply noise and silicon area, and demonstrate the resulted key design implications pertaining to new stability-ensuring LDO circuit design techniques and circuit topologies. Finally, we develop an automated hybrid stability design flow that is computationally efficient and provides a practical guarantee of network stability.Item Nonlinear control with two complementary Lyapunov function(2016-12) Zelenak, Andrew J.; Landsberger, Sheldon; Pryor, Mitchell; Deshpande, Ashish; Fernandez, Benito; Kautz, DougIf a Lyapunov function is known, a dynamic system can be stabilized. However, computing or selecting a Lyapunov function is often challenging. This dissertation presents a new approach which eliminates this challenge: a simple control Lyapunov function [CLF] is assumed then the algorithm seeks to reduce the value of the Lyapunov function. If the control effort would have no effect at any iteration, the CLF is switched in an attempt to regain control. There is some flexibility in choosing these two complementary CLF’s but they must satisfy a few characteristics. The method is proven to asymptotically stabilize a wide range of nonlinear systems and was tested on an even broader variety in simulation. It was also tested on an industrial robot to provide compliant behavior. The simulated and hardware demonstrations provide a broad perspective on the algorithm’s usefulness and limitations. In comparison to the ubiquitous PID controller, the algorithm’s advantages include enhanced performance, ease of tuning, and extensions to higher-order and/or coupled systems. Those claimed advantages are validated by a test with four engineering students, which validates the controller as a viable option for nonlinear control (even at the undergraduate level). The algorithm’s drawbacks include the necessity of a dynamic model and, when linearization is required, the reliance on a small simulation time step; however, for the motivating application –interactive industrial robotic systems – both requirements were already met. Finally, the developed software was released to the public as part of the Robot Operating System (ROS) and the details of that release are included in this report.