Digital Commons Network^™

Decreasing Time To Market For A Medical Device: New Methods For The Product Development Process, Kelly Marie Davis

Doctoral Dissertations

"Through an example, led at a leading medical device company, this dissertation will demonstrate that by applying certain lean principals and tools to the development of a medical device, shortened development times can be obtained. The two papers presented in the dissertation will fill a gap in current literature. Literature presents lean techniques and applications used in many different industries. But, due to the uniqueness of the medical device industry, these general techniques are not ideal. New methods will be used and validated at a medical device company, Covidien. Instead of trying to implement many general lean principals to their …

Discrete Fiber-Reinforced Polyurea Systems For Infrastructure Strengthening And Blast Mitigation, Natalia L. Carey

Doctoral Dissertations

"The research presented in this dissertation focused on evaluating the effectiveness of various blast mitigation materials and coating technologies to be used for enhancing blast resistance of structural members. Mechanical properties and blast mitigation performance of different discrete fiber-reinforced polyurea (DFRP) systems were investigated through experimental and analytical work. Four technical papers discuss the research efforts conducted within this dissertation.

The first paper examined the development and characterization of different DFRP systems for infrastructure strengthening and blast retrofit. The behavior of various systems which consisted of chopped E-glass fibers discretely integrated in with the polyurea matrix was evaluated through coupon …

Development Of Third Generation Advanced High Strength Steels, Meghan C. Mcgrath

Doctoral Dissertations

"Lightweight duplex steels with combinations of either bainite, acicular ferrite, and austenite or martensite and austenite were investigated as third generation advanced high strength steels targeted for automotive applications. Large additions of manganese (>13 wt%) and carbon (

Duplex steels with different volume fractions of primary δ -ferrite were used to study the crystallography of austenite formed during the peritectic reaction. Solute profiles across the peritectic interface showed aluminum segregated near the interface which promoted bainitic ferrite formation. Thermal treatments were used to manipulate the concentration and type of oxides and the ferrite plate density was found to correlate …

Fractal Oxidation Kinetics And Risk Evaluation Of Spontaneous Combustion In Coal Mines, Yutao Zhang

Doctoral Dissertations

"The spontaneous combustion of coal occurs when air supply is sufficient for the oxidation of coal and air velocity is insufficient for the dissipation of generated heat. Spontaneous combustion, if not eradicated immediately, may lead to coal ignition and even a full-blown fire. The fire may engulf a large area and spread further if they are not immediately attended to. This will not only endanger miners and mining operations, but also result in possible mine closures and even fatalities.

Porous structure has a significant effect on coal adsorption and spontaneous combustion. In this research, fractal theory was utilized to quantitatively …

Identification And Visualization Of Electromagnetic Coupling Paths & Nonlinear Capacitors For Esd Protection, Hongyu Li

Doctoral Dissertations

"The first topic of this dissertation focuses on developing methods to identify and visualize electromagnetic coupling paths. The basis of the approach is to utilize an analogy between electromagnetic energy flow and fluid flow. This allows one to apply the theories and algorithms of fluid dynamics to electromagnetics and thereby to visualize the electromagnetic energy flow. This in turn can be utilized to identify the electromagnetic coupling path.

The second topic of this dissertation investigates the nonlinearity of capacitors and suggests improved trade-off between electrostatic discharge (ESD) protection and data bandwidth by using the antiferroelectric (AFE) capacitors as ESD protection. …

Influence Of Temperature And Microstructural Modification On Formability Of Magnesium Alloys, Arun Mohan

Doctoral Dissertations

"The ß-precipitate free AZ31, ß-precipitate rich AZ91 and a few Mg-Y-Zn alloys were studied to understand the dependence of Mg formability on microstructural condition and temperature. Friction stir processing (FSP) was used to refine the grain size and to obtain desirable distribution of precipitates in the matrix. Since Mg alloys exhibit challenges in achieving room temperature formability, superplastic deformation was utilized. This work focused on high strain rate superplasticity (HSRS, ≥10⁻² s⁻¹) which is more attractive for industrial applications as compared to the slower rates of conventional superplasticity.

Thermally stable fine grains and pinning particles at HSRS temperatures were essential …

Underground Mine Fire Simulation Using Multiscale Modeling Approach, Xichen Zhang

Doctoral Dissertations

"Underground mine fires have always been a major concern. Past events show that fire poses a severe safety hazard to mine workers, and causes tremendous economic loss to the mine and surrounding communities. A good understanding of the interaction between a mine fire and the mine ventilation network is crucial for effective fire emergency planning and hazard control. Unfortunately our understanding of a fire is still limited due to the complex nature of mine fires and a lack of adequate resource for studying them.

A new multiscale modeling approach coupling conventional 1D and 3D techniques has shown to be a …

Stress Corrosion Cracking Behavior Of Friction Stir Processed Ultrafine Grained Light Metal Alloys, Gaurav Ramchandra Argade

Doctoral Dissertations

"The influence of friction stir processing (FSP), a microstructural modification tool, on the corrosion behavior of Al-Mg, Al-Mg-Sc, Mg-Al-Zn and Mg-Y-RE alloys has been studied. An attempt has been made to establish correlation between processing parameters and the subsequent microstructural evolution especially matrix grain size on the corrosion and stress corrosion properties of the alloys. A relationship between grain size and corrosion rate for Mg-Y-RE alloys was envisaged and power law type behavior was proposed. Ultrafine fine grained (UFG) microstructure showed one order magnitude lower corrosion rate.

Grain refinement achieved through different FSP parameters showed lower corrosion currents for Al-Mg …

Two Essays On The Domain Translation From Financial Options To Real Options, Hongyan Chen

Doctoral Dissertations

"Real options (ROs) extend the financial option pricing theory to the valuation of real asset investment and managerial flexibility under uncertainty. However, differences between financial and non-financial markets, and the complex real world environment of applications, build obstacles for the domain translation from financial options to ROs.

This dissertation is motivated by the challenges of domain translation and developed in two essays. The first essay studies the incentive function of ROs (named the RO incentive). The essay develops an option-game framework to model the RO incentive, examines the change of investment behavior caused by the RO incentive, and values the …

Modelling Interruptions Of Human-In-The Loop Tasks, Muhammet Servet Gulum

Doctoral Dissertations

"Interruptions are a part of our everyday experience and are increasingly becoming a part of our work. Systems are typically not designed with consideration of the effects of interrupting a user during a task sequence. Research is being done in the field of interruptions and its effects. There have been various claims about the effects of interruptions on human task performance. It has been shown that interruptions may not only increase the time to perform a task but also decrease the performance. It has also been analyzed that the effect of interruptions depends on many parameters including task complexity, point …

A Comparison Analysis Of Defensive Routines And Theories-In-Use Of Engineering And Non-Engineering Managers, Tyria Riley

Doctoral Dissertations

"Engineering managers are managers who have an understanding of both the technical and business world in organizations. Many lead teams of their peers who are purely technical individuals. However, the success of an engineering manager depends on being able to function in both worlds when necessary. There is a stigma that engineers experience challenges in areas such as communication, conflict resolution, and leadership. Due to these challenges, defensive routines are likely to exist. Defensive routines are behaviors that are common in many managers and may hinder the success of an organization. This research uses a case study approach to measure …

Analyses Of Alternative Energy Deployments, Mathew Thomas

Doctoral Dissertations

"Energy use around the world is rising drastically. Fossil fuels, including liquid fuels, natural gas, and coal, are expected to supply 80% of the world's energy need in 2035. As a result, the world's energy-related carbon dioxide emission is expected to increase from 30.2 billion metric tons in 2008 to 43.2 billion metric tons in 2035. Significant steps are necessary to reduce the dependence on fossil fuel and to reduce greenhouse gas emissions. Renewable and alternative energy technologies can assist in reducing the use of fossil fuels and can reduce greenhouse gas emissions. However, most of the renewable energy technologies …

Characterization Of Wave Transport In Non-Conservative Media With Random And Correlated Disorder, Benjamin Henry Payne

Doctoral Dissertations

"Passive quasi-one-dimensional random media exhibit one of the three regimes of transport - ballistic, diffusive, or Anderson localization - depending on system size. The ballistic and diffusion approximations assumes particle transport, whereas Anderson Localization occurs when wave self-interference effects are dominant. When the system contains absorption or gain, then how the regimes can be characterized becomes unclear. By investigating theoretically and numerically the ratio of transmission to energy in a random medium in one dimension, we show this parameter can be used to characterize localization in random media with gain. Non-conservative media implies a second dimension for the transport parameter …

Updated Eor Screening Criteria And Modeling The Impacts Of Water Salinity Changes On Oil Recovery, Ahmad Aladasani

Doctoral Dissertations

"Developing technologies for enhanced oil recovery (EOR) from existing oil fields would supply the world's energy needs for several decades. The application of EOR in many major oil-producing countries remains in its conceptual stage. Thermal and gas EOR methods achieve high incremental rates; however, their application range has not broadened significantly as they have matured, while the rate at which new, promising EOR methods such as Low-salinity water flooding (LSWF) are being implemented is alarming. Despite, the potential of LSWF its development and application has been hindered by the lack of consensus concerning its recovery mechanism(s). Every oil reservoir has …

Evolutionary Computing Driven Search Based Software Testing And Correction, Joshua Lee Wilkerson

Doctoral Dissertations

"For a given program, testing, locating the errors identified, and correcting those errors is a critical, yet expensive process. The field of Search Based Software Engineering (SBSE) addresses these phases by formulating them as search problems. This dissertation addresses these challenging problems through the use of two complimentary evolutionary computing based systems. The first one is the Fitness Guided Fault Localization (FGFL) system, which novelly uses a specification based fitness function to perform fault localization. The second is the Coevolutionary Automated Software Correction (CASC) system, which employs a variety of evolutionary computing techniques to perform testing, correction, and verification of …

Periodic Q-Difference Equations, Rotchana Chieochan

Doctoral Dissertations

"The concept of periodic functions defined on the real numbers or on the integers is a classical topic and has been studied intensively, yielding numerous applications in every kind of science. It is of importance that the real numbers and the integers are closed with respect to addition. However, for a number q > 1, the so-called q-time scale, i.e., the set of nonnegative integer powers of q, is not closed with respect to addition, and therefore it was not possible to define periodic functions on the q-time scale in an obvious way. In this thesis, this important open problem has …

The Pricing Of Multiple Exercisable American-Style Real Options, Yu Meng

Doctoral Dissertations

"Real options embedded in a project provide management with the flexibility to alter initial investment decisions, thus making them a practical tool for project planning and budgeting. Additional values are contributed to the underlying project due to the flexibilities that are provided by real options. This dissertation presents two models for pricing multiple exercisable American real options, one that employs the binomial tree method and the other one that employs the finite difference method. Different examples of multiple exercisable real options are discussed to demonstrate the two pricing models. Interactions between options and reality constraints are also considered. These two …

Surface Expressions Of Discontinuities, And The Estimation Of Their 3-D Orientations Using Combined Lidar And Optical Imaging, James Nii Aboh Otoo

Doctoral Dissertations

"The importance of the collection and analysis of data on discontinuities cannot be overemphasized. Problems which include sampling difficulties, risks, limited access to rock faces and exposures, and the delay in data collection has led to a high need for data collection tools and analysis techniques that can overcome these problems.

Discontinuities manifest themselves as either traces or as facets. Traces are linear features that intersect with both the discontinuity and the rock cut. Facets are the actual discontinuity surfaces that are exposed in the rock cut. Facets can be natural or induced. Identifying a facet as either natural or …

Characterization Of Soil Variability For Reliability-Based Design, Sitenikechukwu Onyejekwe

Doctoral Dissertations

"A very carefully planned Missouri-wide field exploration and laboratory investigation program, with a focus on fine-grained soils, was executed with the aim of characterizing the variability of geotechnical parameters statistically with a view to increasing the use of reliability-based design (RBD) among geotechnical engineers. Geotechnical parameters were characterized in terms of both their first and second statistical moments and their coefficient of variation (COV). Their probability distributions and their scale of fluctuation, θ, were also determined. Correlations between difficult-to-obtain parameters and more easily-obtained parameters were developed and the degree of fit of study data to published empirical correlations was investigated. …

Free-Radical Maleation Of Poly(Butylene Adipate-Co-Terephthalate) In Supercritical Carbon Dioxide And Its Effect On The Percolation And Deformation Mechanism Of Layered Silicate Nanocomposites, Alexandria Niemoeller

Doctoral Dissertations

The utilization of compostable polymers such as poly(butylene adipate-co-terephthalate) (PBAT) in single-use packaging applications can mitigate the water, solvents, and energy required for processing plastic waste. PBAT exhibits exceptional elongational properties, but its moderate water vapor permeability and low tensile modulus limit the applications in which PBAT can be employed. In this work, PBAT nanocomposites were produced at various loadings of organically-modified montmorillonite. The secondary structure of nanoparticles formed within the PBAT matrix was evident in the terminal region of the linear viscoelastic response under oscillatory shear, and a percolation threshold was determined to occur at 3.88% clay by weight. …

Thermal Properties Of Spinel Based Solid Solutions, Kelley R. Wilkerson

Doctoral Dissertations

"Solid solution formation in spinel based systems proved to be a viable approach to decreasing thermal conductivity. Samples with systematically varied additions of MgGa₂O₄ to MgAl₂O₄ were prepared and thermal diffusivity was measured using the laser ash technique. Additionally, heat capacity was measured using differential scanning calorimetry and modeled for the MgAl₂O₄-MgGa₂O₄ system. At 200⁰C thermal conductivity decreased 24% with a 5 mol% addition of MgGa₂O₄ to the system. The solid solution continued to decrease the thermal conductivity by 13% up to 1000⁰C with 5 mol% addition. The decrease in thermal conductivity ultimately resulted in a decrease in heat flux …

Nitrification Performance Of Activated Sludge Under Low Dissolved Oxygen Conditions, Guoqiang Liu

Doctoral Dissertations

"The combined effects of solids retention time (SRT) and dissolved oxygen (DO) concentration on nitrification, nitrifying bacterial communities, and aeration needs in the activated sludge process were studied. Nitrification was almost completed in the 10, 20, and 40-day SRT reactors with a minimum DO of 0.37, 0.25, and 0.16 mg/L, respectively. Under long-term low DO conditions, the endogenous decay of nitrifiers was slowed down and then nitirfier biomass concentration increased, thereby reducing the adverse effect of low DO on nitrification. Under long-term low DO conditions, the oxygen affinity of nitrite-oxidizing bacteria (NOB) increased significantly and as a result, NOB became …

Search-Based System Architecture Development Using A Holistic Modeling Approach, Renzhong Wang

Doctoral Dissertations

"This dissertation presents an innovative approach to system architecting where search algorithms are used to explore design trade space for good architecture alternatives. Such an approach is achieved by integrating certain model construction, alternative generation, simulation, and assessment processes into a coherent and automated framework. This framework is facilitated by a holistic modeling approach that combines the capabilities of Object Process Methodology (OPM), Colored Petri Net (CPN), and feature model. The resultant holistic model can not only capture the structural, behavioral, and dynamic aspects of a system, allowing simulation and strong analysis methods to be applied, it can also specify …

The Effect Of Supercritical Water On Crude Glycerin Solution, Jared Bouquet

Doctoral Dissertations

"Crude glycerin solution, a principal byproduct of the conventional biodiesel process, was reacted in supercritical water using a specially designed Haynesʼ Alloy 282 reactor system for the production of hydrogen rich syngas. The effects of temperature, pressure, water-to-carbon molar ratio, reactor residence time, and glycerin-to-methanol weight ratio on the extent of carbon gasification and gas composition were explored. Based on the results, the extent and selectivity of reactions that concurrently occur when methanol and glycerin are in the presence of supercritical water were analyzed. A decomposition reaction pathway for glycerin conversion to syngas was hypothesized, and then utilizing the results …

Numerical Simulations Of Fracture Propagation And Sealing: Implications For Wellbore Strengthening, Saeed Salehi

Doctoral Dissertations

"To mitigate the small tolerance between pore pressure and fracture gradients an engineering practice referred to as "wellbore strengthening" is conducted to increase the fracture gradient. The method relies on propping and/or sealing the fractures with specially designed materials. Different competing theories exist for physical wellbore strengthening mechanisms which can be categorized into two groups. The first group explains that strengthening happens as a result of increasing wellbore hoop stress when fractures are sealed while the second group emphasis is on fracture tip isolation with suitable materials and enhancing fracture propagation pressure. The numerical models and lab experiments …

Real-Time Supply Chain Predictive Metrics, William Scott Hunter

Doctoral Dissertations

"Supply chains drive the production world. Virtually all products use a supply chain to produce them and they can determine the success of companies using them. The ability to manage supply chains is currently a mix of relationship management and science, combining personal and company relationships with data analysis.

The increased dependency on supply chains has increased the need to develop and use predictive real-time metrics to manage supply chain risk, measure suppliers and drive performance. Current metrics used are reactive and stagnant in nature. Real-time metrics will allow supply chain professionals to better manage risk. Current management techniques include …

Modeling And Synthesis Of Pvdf-Based Dielectrics For Energy Storage Applications, Xuhui Lu

Doctoral Dissertations

"The purpose of this research was to develop dielectric films for high energy density capacitor applications. Also desired was to develop a deeper understanding of dielectric breakdown and electric energy storage related phenomena through simulation, theoretical analysis, and experimental investigation.

An analytical model incorporating Weibull dielectric strength statistics was developed to establish quantitative relationships between material properties and device performance of self-healing capacitors. The model is useful for designing high voltage capacitors and developing dielectric materials where the effects of electric field-dependent permittivity need to be considered.

In the experimental work, solution-cast poly(vinylidene difluoride) (PVDF) homopolymer PVDF films with high …

Perceptions Of Bilingualism And Home Language Maintenance And Loss: A Study Of Latino Parents At A San Francisco Bay Area Elementary Charter School, Emily Mccormick Enstice

Doctoral Dissertations

There is limited research that investigates parent perceptions with respect to their early elementary school children's home language use. To fill the gap in research, this study explores the relationship between first generation Latino parent perspectives of bilingualism, home language maintenance and loss, and the intersection of culture and identity in an elementary school community. It also investigates how parents create an additive bilingual environment in the home.

This participatory action research (PAR) study involved group dialogue sessions and individual interviews in order to engage co-researchers and participants. PAR provided this study with the structure and tools to change and …

The Separate And Collective Effects Of Personalization, Personification, And Gender On Learning With Multimedia Chemistry Instructional Materials, Shannon James Halkyard

Doctoral Dissertations

Chemistry is a difficult subject to learn and teach for students in general. Additionally, female students are under-represented in chemistry and the physical sciences. Within chemistry, atomic and electronic structure is a key concept and several recommendations in the literature describe how this topic can be taught better.

These recommendations can be employed in multimedia instructional materials designed following principles understood through the Cognitive Theory of Multimedia Learning. Additionally, these materials can expand the known use of principles like personalization (addressing the learner as "you") and test prospective design principles like personification (referring to abstract objects like atoms as "she" …

Sealing The Cracks Of The Educational Pipeline: Counterstories That Reveal Cultural Resiliency And Collective Responsibility In Latinas’ K-16 Success, Angela Shaw

Doctoral Dissertations

The purpose of this qualitative research is to discover and describe the successes and institutional barriers along the educational pipeline for Latinas who are the first in their families to have successfully completed their undergraduate degrees. This research explores the unique elements of gender such as gender role socialization and stereotyping under the context of student retention and successful completion of a baccalaureate degree. This research includes nine counterstories of Latinas who were the first in their families to have successfully completed their undergraduate degrees. The results of this study find that throughout childhood, many participants' parents taught their children …