Digital Commons Network^™

Investigation Of Urea Decomposition And Deposit Formation In Diesel Exhaust After-Treatment System, Anand Alembath

Doctoral Dissertations

“Urea-selective catalytic reduction (SCR) system has proved to be an effective solution to reduce NO_x emissions in commercial vehicle (CV) diesel engines. A significant challenge in urea injection is to comprehend its decomposition chemistry that leads to formation of undesired deposits in the exhaust system unit. Due to complex interaction of multi-phase fluid flow and transport processes, significant uncertainty is associated with the identification of interacting factors that control the deposit initiation and its growth. To meet the future ultra-low NO_x emissions and to deliver ammonia without deposit formation, there is an imminent need to develop the urea-SCR …

Thermodynamic Investigations Of Pure And Blended Cement Mixtures, Jonathan Lapeyre

Doctoral Dissertations

” This research is made up of several studies. The first study focused on understanding the reaction kinetics of Ca₃SiO₅ and metakaolin (MK) mixtures compared to Ca₃SiO₅ and silica fume (SF) mixtures. It was shown that MK was a more effective additive than SF at small replacement levels (i.e. ≥ 10% by mass) while higher replacement levels of MK became a detriment due to excess (Al(OH)₄¯) ions preventing the nucleation and growth of C-S-H. In a follow-up study where the MK particle size distribution (PSD) was modified, similar effects were observed but …

Observer-Based Event-Triggered And Set-Theoretic Neuro-Adaptive Controls For Constrained Uncertain Systems, Abdul Ghafoor

Doctoral Dissertations

"In this study, several new observer-based event-triggered and set-theoretic control schemes are presented to advance the state of the art in neuro-adaptive controls. In the first part, six new event-triggered neuro-adaptive control (ETNAC) schemes are presented for uncertain linear systems. These comprehensive designs offer flexibility to choose a design depending upon system performance requirements. Stability proofs for each scheme are presented and their performance is analyzed using benchmark examples. In the second part, the scope of the ETNAC is extended to uncertain nonlinear systems. It is applied to a case of precision formation flight of the microsatellites at the Sun-Earth/Moon …

Combustion And Emission Characteristics Of Ic Engines Fueled By Hydrogen And Hydrogen/Diesel Mixtures And Multi-Objective Optimization Of Operating Parameters, Abdulhakim Issa Jabbr

Doctoral Dissertations

“The present study considers combustion of hydrogen in IC engines. In general, the work focuses on simulating the engine performance and emissions at different operation parameters, and using optimization techniques. Task I work deals with the engine performance and emissions of a single cylinder spark-ignition (SI) engine fueled by hydrogen. The engine was simulated at different equivalence ratios, exhaust gas recirculation (EGR) and ignition timing. The results indicate that NOx emissions, engine power, and efficiency are reduced by increasing EGR level, and increased with increasing equivalence ratio and advanced ignition timing. The best operating conditions for hydrogen engines were obtained …

An Integrated Flow-Curing Model For Predicting Residual Stresses In Textile Composites, Weijia Chen

Doctoral Dissertations

Fiber-reinforced composites have been widely employed in structural applications due to their high stiffness-to-weight ratio and easily-tailored mechanical properties. However, manufacturing of these lightweight materials involves an infusion and curing process, and flow-induced defects and residual stresses can easily occur, which can compromise the mechanical performance of the composite structures. The purpose of this work is to develop an integrated flow-curing processing model to accurately predict the resin flow front and the residual stresses in the Liquid Composite Molding (LCM) process. In the infusion model, the fiber fabrics are treated as a homogeneous and porous material, and the resin flow …

Exploiting Memristors For Compressive Sensing Applications, Fengyu Qian

Doctoral Dissertations

The amount of sensory signal is increasing dramatically as we’re stepping into the era of Internet of Things (IoT). Compressive Sensing (CS), feature as Sub-Nyquist sampling rate and low complexity sensing architectures, is very promising for these kinds of applications where resources are restricted. Through applying this novel compression technology, data size of sensory signals are largely compressed such that it is very efficient within the signal processing, data transmitting and storage processes. Compared to conventional codec method, CS technique requires less hardware resources and achieve lower power consumption within sensor nodes.

However, there are several bottle-necks of existing compressive …

Fabrication, Characterization And Application Of Zinc Oxide And Zinc Magnesium Oxide Nanostructures, Abdiel Rivera

Doctoral Dissertations

Zinc oxide is a wide bandgap semiconductor with relatively large exciton energy of 60 meV, and longitudinal optical phonon energy of 72 meV. ZnO can be grown in any nanostructure (nanoribbons, nanowires, nanorods, films, core-shell, among others), under any growth condition (metal-organic chemical vapor deposition (MOCVD), molecular beam epitaxial (MBE), hydrothermal, radio-frequency sputtering, sonochemical, etc) to be implemented in a variety of applications. For instance, by adding Mg to ZnO, the energy band separation increases and shift to a lower wavelength. Using ZnMgO, in the form of vertical nanowires, can improve the resolution of solar-blind UV-detectors. Nevertheless, the sol-solubility of …

Impact Of Mixer Design On Lean Direct Injection Combustion, Xiao Ren

Doctoral Dissertations

To reduce the environmental impact of aviation, lean direct injection (LDI) combustion is being pursued to achieve very low emissions. LDI utilizes multi-point mixers to achieve low NOx emissions and satisfactory combustion stability. Since the performance of LDI directly depends on design parameters of each single LDI mixer, a series of fundamental investigations into lean-dome-relevant pilot combustor devices are conducted herein. A single LDI mixer typically uses swirlers with converging venturi and diverging flare to generate swirling flows, which facilitate mixing in the combustor dome. This dissertation aims to investigate the impact of LDI mixer design parameters, including swirler vane …

Cybersecurity Games: Mathematical Approaches For Cyber Attack And Defense Modeling, Mohammad Hadi Valizadeh

Doctoral Dissertations

Cyber-attacks targeting individuals and enterprises have become a predominant part of the computer/information age. Such attacks are becoming more sophisticated and prevalent on a day-to-day basis. The exponential growth of cyber plays and cyber players necessitate the inauguration of new methods and research for better understanding the "cyber kill chain," particularly with the rise of advanced and novel malware and the extraordinary growth in the population of Internet residents, especially connected Internet of Things (IoT) devices.

Mathematical modeling could be used to represent real-world cyber-attack situations. Such models play a beneficial role when it comes to the secure design and …

Novel Cryptographic Authentication Mechanisms For Supply Chains And Openstack, Reza Rahaeimehr

Doctoral Dissertations

In this dissertation, first, we studied the Radio-Frequency Identification (RFID) tag authentication problem in supply chains. RFID tags have been widely used as a low-cost wireless method for detecting counterfeit product injection in supply chains. We open a new direction toward solving this problem by using the Non-Volatile Memory (NVM) of recent RFID tags. We propose a method based on this direction that significantly improves the availability of the system and costs less. In our method, we introduce the notion of Software Unclonability, which is a kind of one-time MAC for authenticating random inputs. Also, we introduce three lightweight constructions …

Topological Data Analysis For Clustering And Classifying Time Series, Renjie Chen

Doctoral Dissertations

Topological Data Analysis (TDA), which refers to methods of utilizing topological

features in data (such as connected components, tunnels, voids, etc.) has gained considerable

momentum. More recently, TDA has been increasingly used for analyzing time

series. The recent researches of using TDA in time series are mainly focused on unsupervised

and supervised learning. In this thesis, a review of TDA will be provided,

following by using TDA in time series for doing unsupervised and supervised learning

for different applications.

Insurance Analytics With Tree-Based Models, Zhiyu Quan

Doctoral Dissertations

Tree-based models are supervised learning algorithms broadly described by repeated partitioning of the regions of the explanatory variables to form homogeneous groups. The partitioning is based on minimization of a loss function related to the response variable. The results form and create a tree-based structure, which helps make for better model interpretation, for predicting the response. Because of the many advantages of tree-based models, their use in disciplines like engineering, biostatistics, and ecology has been a popular alternative predictive tools for building classification and regression models. A single decision tree may not produce accurate predictions, thereby, we also examine the …

Advanced Forecasting And Optimization Techniques In Power System Planning And Operations, Xiaorong Sun

Doctoral Dissertations

Utility companies, Independent System Operators, and Transmission Operators require sophisticated techniques in short-term load forecasting, unit commitment (UC), and dynamic line rating in view of the complicated customer behavior, increasing integration of renewable energy, and characteristics of transmission lines in power systems. In this thesis, a set of novel methodologies are developed to address the challenges posed by each problem.

1. Short-term load forecasting at the distribution level is difficult in view of the complicated load features, the large number of distribution-level nodes, and possible switching operations. A hierarchical forecasting approach is established to capture load characteristics at different levels. …

Sense Of Belonging And Racial Diversity At The U.S. Service Academies, Leah Pound

Doctoral Dissertations

On college campuses, access does not equal inclusion as students of color have to navigate through a predominately White space as they struggle to feel like they belong (Jack, 2019). This dissertation focuses on racial experiences and belonging within a total institution (Goffman, 1961): the U.S. service academies, colleges that are part university and part military. Across three separate papers, I explore the institutional factors that impact the disparity between Black and White students’ belonging. In Chapter 1, I apply Allport’s contact theory (1954) alongside the concept of relative deprivation (Stouffer, 1949) to systematically compare the experiences of Black and …

Application Of Machine Learning To Enhance The Diagnostic Utility Of Interictal High Frequency Oscillations In Drug-Resistant Epilepsy, Stefan Sumsky

Doctoral Dissertations

There is a need for novel biomarkers to aid in the clinical treatment of epilepsy and improve the understanding of seizure generation and the seizure onset zone (SOZ). High frequency oscillations (HFO) are a promising biomarker with the potential to fill this role, but early efforts to apply them have fallen short of clinical quality tools and validity and application of their association with seizure have not been fully explored. This study will advance the understanding and application of HFO to the clinical setting in three ways. First, the relevance of HFO to SOZ and their utility for SOZ localization …

African American Female Law Enforcement Officers' Lived Experiences And Mentoring: A Thematic Narrative, Harold Wilson

Doctoral Dissertations

Black female officers are an underrepresented sub-group of the law-enforcement profession. The bulk of research on women’s policing has focused on the growth of women in law enforcement, barriers, sexual harassment, gender differences, why women are deterred from law enforcement, physical limitations, and instruments used during the recruitment process, and the stress endured after entry into the profession. When looking at Black female officers’ lived experience and perceptions around mentoring; research is lacking. Eight Black female officers from the San Francisco Bay Area participated in this study. Findings revealed that all of the women have faced a recurring sense of …

Community Leader-Scholars With Refugee Experiences: Collective Hope, Healing, And Multi-Generational Resistance, Jane Pak

Doctoral Dissertations

Through a Critical Refugee Studies (CRS) lens that inherently challenges power, encourages multi-disciplinary approaches, and centers refugee epistemologies, this study centers ways of knowing and being among a group of ten Community Leader-Scholars (CoLS) with refugee experiences. This dissertation posits that CoLS offer critical perspectives that introduce new logics that disrupt traditional spaces and power dynamics. I frame CoLS as undergraduate or graduate students (or recent alumni) with refugee experiences who have self-identified and illustrated a commitment to community well-being in one or more of their transnational communities. This study employed qualitative research methods that included 10 interviews and four …

Perceptions Of Physics Teachers In Singapore About Curriculum Sequencing, Lay Lean Fong

Doctoral Dissertations

Curricular sequencing is central to instruction design and enactment. If carefully planned for, the order of topics to be taught would determine how the fundamentals of the discipline can be presented and introduced to learners, in a sequence that eases them into more complex ways of reasoning and thinking about the domain. These sequences or learning progressions often reflect the experts’ conceptual schemas of the discipline and are conceived as strategic models for instruction (Duschl et al., 2011).

The varied findings from current research on learning progressions underscore the complexity of teaching and learning, and imply that even ‘well-crafted’, standards-based, …

Towards Embedded System Hardware Security Design And Analysis, Yanping Gong

Doctoral Dissertations

Security in embedded system design, which has long been a critical problem for ensuring the confidentiality, data integrity and system reliability for embedded system designers and users, is now facing a new dimension of threat from the attacks on hardware. As the IC design reaches sub-micron regime, increased sensitivity of device under environmental condition has made some new types of attacks possible, while the analysis and detection for design vulnerabilities against these attacks are harder on the much more complicated designs nowadays. In the meanwhile, more efficient and diverse attack methodologies are developed by attackers as the technology advances. On …

Improved Understanding Of Trends, Variations, And Causes Of Atmospheric Aerosols Using Ground Measurements, Satellite Observations, And Atmospheric Chemistry Modeling, Xueke Li

Doctoral Dissertations

A good understanding of trends, variations, and causes of atmospheric aerosols is vital to quantifying the role of air quality in climate change and health concerns and for informing relevant regulatory policies. This thesis presents four projects that exploit a range of observational data and modeling tools to characterize and interpret aerosol dynamics and its potential determinates.

An econometric model is implemented to identify aerosol variations, predictions, and the driving forces using six sites spreading across North America and East Asia during 2003–2015. Regional differences caused by impacts of climatology and land cover types are observed. Statistical validation of time …

Evaluating Climate Change Impacts On Drinking Water Reservoirs And Wastewater System Resilience In Connecticut, U.S.A., Cristina Mullin

Doctoral Dissertations

Societies depend on the proper functioning and resilience of critical infrastructure systems including those for drinking water and wastewater, but these systems are vulnerable to natural and anthropogenic stressors. For example, wastewater systems are especially susceptible to extreme weather events while drinking water systems are vulnerable to diminished source water quality — both of which can disrupt proper functioning. Climate change and human development, economic problems, and pollution further challenge water system resilience. Despite the criticality of these systems and known vulnerabilities, little scholarship exists that aims to interrogate their resilience. This dissertation attempts to narrow this gap in the …

Preparation And Characterization Of Collagen-Hydroxyapatite-Based Composites For Biomedical Applications, Le Yu

Doctoral Dissertations

Collagen, the most abundant protein, and hydroxyapatite, the main component in natural bone, are usually used as a biomimetic composite in many biomedical applications due to their excellent biocompatibility, great biodegradability, and flexible structural and compositional alterability. In this dissertation, a systematic study was conducted to design, develop and characterize collagen-hydroxyapatite-based (Col-HA-based) composite materials and explore their wide biomedical applications.

First, the biomeralization mechanism of collagen was investigated. The degree of intrafibrillar mineralization of Col-HA fibrils was enhanced by the employment of carboxyl-rich brushlike polymers, which is believed to be capable of replicating the sequestration functions of non-collagenous proteins (NCPs) …

Characterization And Optimization Of Carbon Based Electrocatalysts And Supports For Fuel Cell Applications, Abhinav Poozhikunnath

Doctoral Dissertations

The use of expensive platinum-based catalysts has been a major obstacle for the widespread use of low temperature fuel cells. As a result, there is significant commercial and scientific interest in replacing platinum-based electrocatalysts with cost-effective alternatives of comparable performance. This thesis explores the process-structure-property relationship of platinum group metal-free (PGM-free), metal-nitrogen-doped carbon (M-N-C) electrocatalysts for oxygen reduction synthesized by a flame spray pyrolysis process called Reactive Spray Deposition Technology (RSDT). Metal-Nitrogen-Carbon (M-N-C) type Platinum Group Metal-free (PGM-free) electrocatalyst, synthesized directly from liquid solution precursors by the partial combustion of organic material in the RSDT flame. Central to this work …

Phase-Field Modeling Of Selective Laser Melting And Freezing Dynamics In Thermal Manufacturing Processes, Jiqin Li

Doctoral Dissertations

Laser-based additive manufacturing (AM) has been rapidly growing in applied and scientific research areas due to its advantages for manufacturing geometrically complicated parts and functional materials. However, the surface quality and geometric accuracy are great concerns of AM-produced parts because of the formation of surface defects such as voids, notches, or even cracks caused by incomplete melting of powders, lapping, or gas entrapment during melting and solidification processes. From theoretical view points, temperature prediction and multi-phase dynamics at the powder level are of the greatest challenges, yet necessary for better understanding of relevant laser-material interactions as well as for the …

From King Solomon To Ian Smith: Rhodesian Alternate Histories Of Zimbabwe, Edward Guimont

Doctoral Dissertations

In the eleventh century CE, the Shona people of Central Africa built the city of Great Zimbabwe, an administrative center and royal home. Connected to the Indian Ocean gold trade, it would become the largest pre-colonial city in sub-Saharan Africa. However, it entered into decline and was ultimately abandoned by the sixteenth century – when the first Portuguese expeditions came in contact with the region. The fact that this city entered into decline just as Europeans encountered it set it up to become the center of a number of fantastical legends about its origins, typically linking it with the Biblical …

Differences In Creativity Across Domains Between Students With Dyslexia And Those Without, Maria Avitia

Doctoral Dissertations

When a student has a learning disability in reading and or dyslexia, interventions focus on remediating the weakness. Positive psychology is a field of psychology that looks to help people, based on harnessing a person's strengths, to create better outcomes. Strengths-based or asset-based interventions have been used with people with developmental disabilities to learn new skills. This study hoped to help identify strengths for people with dyslexia in two areas that have been hypothesized to be strengths for them: creativity and visual-spatial ability. Creativity has typically been assessed with domain-general measures rather than actual measures of creativity. Similarly, visual-spatial ability …

Interpreting The Information Embedded In Observed And Modeled Air Quality Time Series And Using Regional Air Quality Models For Regulatory Policies, Huiying Luo

Doctoral Dissertations

Regional-scale air quality models are being used to perform research, forecasting, regulatory assessments and planning. Thus, it is important to critically assess the models’ capability in reproducing the spatio-temporal features seen in observations. The main scope of this work is to develop new methods for assessment and evaluation of EPA’s Community Multiscale Air Quality Modeling System (CMAQ) in the context of building confidence when regional-scale air quality models like CMAQ are used for policy support. The research is divided into three parts. In the first part, features embedded in two decades of ozone and PM_2.5 observations and coupled WRF-CMAQ …

E-Hailing Pricing And Strategies For Transportation System Performance Improvement, Qixing Wang

Doctoral Dissertations

App-based e-hailing ride services, which connect both drivers and riders through their GPS-enabled mobile devices, have rapidly developed into a viable transportation alternative for many travelers. This technology has changed the set of choices for travelers and has shifted travel patterns, most significantly away from traditional taxi services. These applications provide convenience and flexibility to both drivers and passengers, however, they have also caused several issues. For example, they have pulled ridership off public transportation, damaged the taxi industry, and created new congestion etc. during their expansion. In this research, we analyze available information to arrive at a solution to …

Deciphering The Gene Expression Control In Epigenetic, Post-Transcriptional And Translational Regulation, Jianan Lin

Doctoral Dissertations

Regulation of gene expression, through which cells increase or decrease the gene products, is an essential part of development, which not only determines the cellular differentiation but also responds to the environmental changes. A wide range of gene regulation mechanisms are involved in two major processes, from Deoxyribonucleic acid (DNA) to Ribonucleic acid (RNA), and from RNA to protein, also known as transcription and translation, respectively. Though the regulation of gene expression is not fully understood, this complex process has been characterized to several major steps, which includes epigenetic regulation, transcriptional regulation, post-transcriptional regulation and translational regulation. The present study …

The Economics Of Climate Change Adaptation And Water Resources: An Application To Dams, Yuan Niu

Doctoral Dissertations

Dam construction has increased rapidly since the 1950’s, especially in developing countries. Climate change is likely to impact the demand for new dams as well as future water and sediment inflow in rivers, thereby influencing the utility, management, and lifetime of dams. Proper construction of dams and sediment management can also help reduce the cost and mitigate the risks dams might be facing as a result of changing climate patterns, which will allow communities to utilize water resources more efficiently and sustainably.

This dissertation develops a series of dynamic optimization models to determine how the size of different type of …