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Improving Syngas Quality In A Downdraft Biomass Gasifier With Blended Feedstocks, Rania Almusafir

Doctoral Dissertations

"Biomass gasification is the greatest potential renewable energy source and will play an important role in the energy mix of the future. To achieve a high quality of produced synthesis gas (syngas) in the gasification system, the syngas cleaning and cooling processes pose challenges. The main objectives of the present work are advancing the knowledge of the gasification process and producing syngas in the studied pilot-scale downdraft biomass gasifier.

A Thermogravimetric analysis (TGA) has been developed and utilized to experimentally investigate the impact of biomass feedstock diversity on the performance of the gasification process of hardwood (HW), softwood (SW) pellets, …

In-Depth Characterization Of The Selective Oxidation Products Of Hafnium Carbide, Jonathan Allen Scott

Doctoral Dissertations

"Materials capable of withstanding oxidative environments at temperatures >2000°C are necessary for hypersonic applications. Hafnium carbide (HfC) shows a combination of properties that lends itself toward these applications; however, its oxidation behavior is poorly understood. At 1300°C, HfC was found to oxidize via the following mechanism: 1) Initial oxidation of both C and Hf present in the system, 2) Formation of an interconnected pore network, whose size is related to the volume of gases being generated during the oxidation process, 3) Growth of the oxide scale to become sufficiently protective, 4) Formation of an initially amorphous “HfO₂C” at …

Critical Behavior And Dynamics Of The Superfluid-Mott Glass Transition, Jack Russell Crewse

Doctoral Dissertations

This work studies the effects of disorder on the thermodynamic critical behavior and dynamical properties of the superfluid-Mott glass quantum phase transition. After a brief introduction covering relevant fundamentals, we present the dissertation in the form of four separate but related publications. In the first two publications, we calculate the thermodynamic critical exponents of the superfluid-Mott glass quantum phase transition in both two and three spatial dimensions. The undiluted transition exhibits critical exponents that violate the Harris criterion, and thus the critical behavior is expected to change upon introducing disorder. We confirm this behavior via Monte Carlo simulation of a …

Adversarial Transferability And Generalization In Robust Deep Learning, Tao Wu

Doctoral Dissertations

Despite its remarkable achievements across a multitude of benchmark tasks, deep learning (DL) models exhibit significant fragility to adversarial examples, i.e., subtle modifications applied to inputs during testing yet effective in misleading DL models. These meticulously crafted perturbations possess the remarkable property of transferability: an adversarial example that effectively fools one model often retains its effectiveness against another model, even if the two models were trained independently. This research delves into the characteristics influencing the transferability of adversarial examples from three distinct and complementary perspectives: data, model, and optimization. Firstly, from the data perspective, we propose a new method of …

Highly Dipole-Parallel Aligned Nonlinear Optical Organic Molecular Crystalline Materials: Rational Design, Experimental And Theoretical Studies Of Supramolecular Structures And Non-Covalent Interactions, Harmeet Singh Bhoday

Doctoral Dissertations

Highly dipole-parallel aligned donor-acceptor substituted organic molecules are attractive for a wide array of applications, including nonlinear optics. However, only a limited number of crystals are known to adopt polar non-centrosymmetric space groups. The concepts guiding the fabrication of these polar materials have been described. The study focused on unsymmetrical donor-acceptor substituted azines and butadiene's. An improved design over (MeO, Y)-azines led to the realization of three crystals perfectly aligned in dipole parallel orientation for (PhO, Y)-azines with Y = Cl, Br, I, and one nearly perfectly aligned crystal for Y = F (Paper I). The unique bonding properties associated …

Crystal Structure Prediction Of Metal Chalcogenides, Qi Zhang

Doctoral Dissertations

A novel crystal structure prediction (CSP) method has been developed to predict energetically favorable (stable) structures based on targeted chemical compositions. It leverages the structural characteristics of recurring motifs featured in many crystals and symmetry restrictions from space groups to effectively lower the degrees of freedom of a system when conducting CSP simulations. The proposed method is applied to predicting low-energy structures of two metal chalcogenide systems: Li₃PS₄ and Na₆Ge₂Se₆. Both systems feature rigid bodies in their structures as building blocks, making them particularly suited to the proposed method. The validity …

Exploring The Mechanistic Effects Of Surface Characteristics On Uv254 And Bl405 Disinfection Efficacy, Castine Annastasia Bernardy

Doctoral Dissertations

The COVID-19 pandemic highlighted the need for more robust surface disinfection technologies. Photoinactivation efficacy for microbial pathogens and many surrogates has been well studied for water disinfection. However, there is a limited body of knowledge from research on surface disinfection applications of these technologies. The onset of the global pandemic resulted in a dramatic increase in surface disinfection devices being marketed to consumers, yet regulations for such devices have not been developed. This doctoral research studies the inactivation efficacy of two wavelengths, UV254 and BL405. The objective of this doctoral dissertation was to expand the body of knowledge required to …

Aspects Of Localizing Quantum Information In Diffeomorphism-Invariant Theories, Adam Dukehart

Doctoral Dissertations

Quantum Field Theory (QFT) is often formulated using local operators, i.e., operators defined at points on a fixed background spacetime. However, General Relativity (GR) requires that observables be fully diffeomorphism invariant. This includes invariance not only under passive diffeomorphisms, which change the coordinate system but also active diffeomorphisms, which imply background independence and a dynamical metric. Localizing such systems and observables in quantum gravity has been a long-standing problem. This dissertation makes progress on two facets of this problem. Part I shows that a typical quantum information paradox using local operators cannot be embedded in a self-consistent, low-energy prescription which …

Learning Trajectories From Human Demonstration Via Time Invariant Dynamical Systems, Paul Gesel

Doctoral Dissertations

Learning from Demonstration (LfD) is a powerful approach that enables users to program robots by simply demonstrating how to perform tasks. Rather than just mimicking the task, the robot should capture key characteristics of the task to adapt and generalize in various situations. Given that there is no explicit objective for each demonstrated task, optimal control methods cannot be directly applied. Two primary paradigms have emerged to overcome the limitation: 1) inverse learning and 2) imitation learning. In this dissertation, I formulate several time-invariant and stable dynamic system-based LfD models that leverage both inverse learning and imitation learning in the …

Potential Vorticity Dynamics Driving Variability In Mean Tidal Currents Flowing Through Bounded Estuarine Channels, Katherine Anne Kirk

Doctoral Dissertations

Tidally induced pressure gradients in sea level drive mean estuarine tidal currents that can have horizontal spatial variability across a bounded channel or inlet. Strong cross-channel gradients in along-channel mean velocity set up extremums in the background potential vorticity that can support instabilities of tidal currents flowing through narrow, bounded estuarine channels and tidal inlets. In addition, conservation of potential vorticity including frictional terms, results in intensification of along-channel tidal currents over shallow lateral shelves. In the first part of this dissertation (Chapter 2), the dispersion equation of barotropic instabilities of tidal currents is analytically solved for simple bathymetry defined …

Investigation Of Robust And Adaptive Control Methods For Systems With Uncertain Equilibrium States, Muhammad Hamad Zaheer

Doctoral Dissertations

Equilibrium states represent the natural resting point of dynamic systems in their state-space and provide vital information for the design of stabilizing feedback controllers for these systems. Stabilizing a system at an equilibrium state is desirable as it requires a zero steady-state control signal, resulting in lower energy consumption by the actuator. Mathematical models of real systems usually contain uncertainties that make it difficult to determine the exact values of these equilibrium states. Therefore, control methods requiring precise knowledge of the equilibrium state are ineffective in controlling systems when uncertainties make determining the exact value of the equilibrium state challenging …

Thoughtful Learning: An Investigation Of The Relationships Between College Students’ Achievement Appraisals And Thinking Patterns During Lecture, Shelby Lynn Smith

Doctoral Dissertations

The current set of studies examined whether two common appraisals that students make during learning (whether they have control over their learning and whether they place value into learning the material) give rise to common types of thoughts students also experience (mind wandering, personal connections, and freely-moving thought). Study One naturistically examined students’ appraisals and thoughts while learning in a real classroom. Study Two attempted to experimentally manipulate students’ appraisals and thus their thoughts in an online learning environment. Overall, results suggest that appraisals do seem to influence the thoughts students report experiencing, although results differ between online and classroom …

Engineering Studies Of An Experimental Open Ocean Seaweed Farm Design, Zachary Moscicki

Doctoral Dissertations

An experimental seaweed cultivation system was designed for offshore and exposed locations. Novel features were incorporated to address major barriers to the expansion of seaweed, including limited nearshore and sheltered marine locations and risk of marine animal entanglement. A novel modular mooring geometry was developed to improve stability, reliability, and spatial efficiency to achieve an economical and robust structure viable in high wave energy environments. Stiff composite (e.g. fiberglass) rods were used to replace components typically made of rope, including mooring lines and seaweed growth substrate (cultivation lines), as a means to mitigate risk of marine animal entanglement.

This dissertation …

Modeling And Analysis Of The Selective Lightning Strike Phenomenon At Locations In A Chemical Manufacturing Plant, Terver Maor

Doctoral Dissertations

This research was motivated by the overly simplified claims, from a previous study, that attempted to explain the cause of the reportedly repeated lightning strikes at certain locations in the chemical manufacturing plant. The findings, without any model, claimed that the electronic monitoring and control devices’ fire damage occurred, due to the raised electrical ground potential during lightning strikes. It proceeded that the raised electrical ground potential caused a power flow reversal, which exceeded the ratings of the affected electronic control modules, damaging them. This claim is inconsistent with published research work in the failure mechanisms of industrial control systems, …

Atomistic-Informed And Machine Learning-Assisted Crystal Plasticity Modeling For Materials Interface, Ibrahim Altarabsheh

Doctoral Dissertations

This dissertation presents a comprehensive study that addresses two critical challenges in the field of computational materials science and engineering from nano- to mesoscale. First, to overcome the well-acknowledged length scale limitation associated with atomistic simulations, a novel two-step approach is introduced for a probabilistic prediction of stress-strain curves in terms of material volume. The method combines Molecular Dynamics (MD) simulations and a multioutput Gaussian process (MOGP) with Bayesian analysis to model stress-strain behavior and predict stress and strain values. The model effectively captures the intricate three-stage curve shape exhibited in stress-strain plots, discerning key points such as yielding, hardening, …

Hypergroups From Fusion Subcategories And Their Integral Forms, Alice A. Hempel

Doctoral Dissertations

Fusion categories are generalizations of finite groups and are found in areas of mathematics that involve algebraic structures. They are also found in other fields, such as theoretical physics (quasiparticles) and computer science (quantum computing). Their ubiquitousness in these areas make them useful subjects to study.

As a generalization of finite groups, fusion category theory contains many analogs to the objects and constructions found in group theory. But an analog to an essential object of study in group theory, that of the quotient group, is relatively unexplored. In this work, we introduce quotients of braided fusion categories as certain hypergroups …

Acoustic Waveform Optimization For Three-Dimensional Object Geometries, Justin Ng

Doctoral Dissertations

In recent years, deep learning (DL) has become an increasingly important tool for many different types of classification, identification, and related problems including inverse radar and sonar applications. This thesis studies the degree to which radar and sonar systems may be optimized for DL algorithms in a theoretical setting. Most of the current existing literature found on using DL involve solving a full inverse scattering problem (ISP), that is to determine the properties and/or geometry of the scatter from nearly complete measurements of the scattered field. Methods suitable for use in two-dimensional space have been proposed and demonstrated with varying …

Affecting Martensitic Transformation And Residual Stress Development Through Stress Superposition And Incremental Forming, Elizabeth Marie Mamros

Doctoral Dissertations

Stress superposition is defined as the incorporation of additional stresses into an existing manufacturing process during a single operation. In this thesis, experiments, simulations, and modeling of stress superposition in sheet metal deformation were investigated. Stress superposition can be used in manufacturing to reduce forming forces, increase material formability, and tailor the final part properties of products according to their intended applications, creating so-called functionally graded materials. Austenitic stainless steels (SS) were the focus due to their susceptibility to strain-induced phase transformation from austenite to martensite based on the stress state applied. In the first chapter, a novel cruciform specimen …

Robust Behavior Cloning For Multi-Step Sequential Task Learning By Robots, Mostafa Abdallah Mohamed Hussein

Doctoral Dissertations

This research is about learning high-level policies of multi-step sequential (MSS) tasks – such as activities of daily living – from demonstrations in a sample efficient manner. This research does not assume access to a simulator or an expert to provide more demonstrations. Learning a task policy in such a setting using state-of-the-art end-to-end approaches is sample inefficient due to a reliance on deep learning frameworks, which are known to require a large amount of data. Besides that, most imitation learning frameworks in robotics assume that a domain expert’s demonstration always contains a correct way of doing the task. Despite …

An Analysis Of Fine-Scale Structure Within Ion Upwelling Processes, Niharika Godbole

Doctoral Dissertations

This dissertation showcases the projects that I have been involved with since I joined the Magnetosphere-Ionosphere Research Laboratory (MIRL) at the University of New Hampshire (UNH) in August 2017, under the guidance of my research advisor, Marc Lessard. Chapters 1, 2, and 3 of this dissertation are intended to provide the science background necessary to discuss the research projects presented in Chapters 4, 5, and 6 respectively.

The system that this dissertation addresses is complex and interconnected. In the most general sense, the Sun interacts with the Earth through the highly conductive, magnetized plasma that it emits, which directly shapes …

Symmetry, Bifurcations And Transition To Turbulence, Pratik Prashant Aghor

Doctoral Dissertations

This thesis focuses on two wall-bounded shear flows, namely, plane Poiseuille flow, where a fluid is pushed between two infinite parallel plates and radially heated Taylor-Couette flow, where a fluid is sheared between two independently rotating cylinders maintained at different temperatures. An overarching theme of this thesis is understanding and exploiting the interplay between symmetries and dynamics.

Chapter 1 presents an overview of the field of transition to turbulence and introduces the dynamical systems viewpoint of turbulence. In particular, we discuss subcritical transition to turbulence, where flows are observed to be turbulent below critical thresholds predicted by linear stability analysis. …

Nonlinear System Identification And Motion Control System Design For Uncrewed Underwater Vehicles, Oguzhan Oruc

Doctoral Dissertations

Modeling and control of marine robotics have become a conspicuous research topic in the controlengineering community in the last decade. Remotely operated underwater vehicles (ROVs) are deployed and used in commercial, military, and scientific areas for many different purposes such as inspection and maintenance of submerged infrastructure, underwater surveillance/maritime, security, and ocean floor mapping most of which cannot be achieved effectively by human operators. However, to be able to operate these vehicles, an effective controller must be obtained, and an accurate dynamic mathematical model of the vehicle from which to design the controller is necessary. Although conventional modeling approaches are …

Threads, Buckets, And Impact: A Framework For Tool Accelerated Machine Learning Courses, Jonathan Adam Niemirowski

Doctoral Dissertations

Artificial intelligence and machine learning (ML) have exploded in use, accessibility, and awareness in the past few years, particularly with the release of ChatGPT in late 2022. Advances in end-user ML tools are accelerating the development of ML applications, lowering the technical barrier of entry for users outside of the computer science (CS) community. Access to ML education within STEM is mostly limited to upper-level computer science courses that have deep pre-requisite requirements or to introductory workshops that yield limited ML skills. Despite the critical need for ML education, there is a lack of guidance in instructional design for applied …

The Effectiveness Of Interventions To Increase Antiretroviral Therapy (Art) Adherence Among Latinx Men Who Have Sex With Men (Msm) With Human Immunodeficiency Virus (Hiv) In The United States: A Systematic Review, Everardo Leon

Doctoral Dissertations

The human immunodeficiency virus (HIV) continues to affect Latinx men who have sex with men (MSM). Interventions have been developed to improve antiretroviral therapy (ART) adherence, but little is known about the number of available interventions and their effectiveness to assist Latinx MSM. The current systematic review investigated the effects of interventions aimed at improving ART adherence for the treatment of adult Latinx MSM with HIV in the United States. The systematic review followed the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines to communicate the results. The inclusion criteria comprised Latinx MSM with HIV, any type of …

Understanding Filipino Wellness: Investigating The Effects Of Colonial Mentality And Enculturation, Juliene Grace P. Fresnedi

Doctoral Dissertations

Filipino Americans are the third largest Asian American group within the United States and report significantly worse mental health when compared to other population groups. As a result of colonization by both Spain and the United States, Filipino culture has been perceived as a unique blend of cultural influences. Despite there being over 4.1 million Filipinos residing in the US there is a significant lack of research that directly investigates the well-being of this population and to what extent factors such as colonial mentality, enculturation, and generational status have an impact. The present study seeks to address this gap in …

Alleviating Mathematics Anxiety For Middle School Students Using A Combined Intervention Approach Versus Only Using The Cognitive Intervention Approach For Increasing Mathematical Achievement: A Comparative Study, Patricia Anna Garcia

Doctoral Dissertations

Current research has found evidence of effective interventions for mathematics anxiety, both motivational and cognitive interventions can affect learning through instructional design and increased student engagement. Thus, this study investigated whether a combined (cognitive and motivation) intervention approach was more effective than only using a cognitive intervention approach for alleviating mathematics anxiety in middle-school students in order to develop a positive mathematical self-concept. The design used in this study was a comparison pretest-posttest study using the modified Abbreviated Math Anxiety Scale (mAMAS) to measure the participants’ level of mathematics anxiety and the STAR Mathematics diagnostic assessment to measure gradual mathematics …

A Case Study Of A School-Supported Extracurricular Activity's Influence On Stem Identity And Interest For Females, Letta Meyer

Doctoral Dissertations

Even though there has been a narrowing of the gender gap in STEM, there is still a pronounced gap in the physical sciences, engineering, and computer science. Females who persist in these fields have a strong STEM identity, including developing specific STEM interests. Females can develop STEM identity through long-term, active involvement in extracurricular STEM programs. Extracurricular STEM programs significantly impact the persistence of females in the STEM pipeline. This case study examined the effect of Science Olympiad, an extracurricular STEM program, on current high school students and alumnae’s perceptions of their STEM identity and personal specific STEM interest. Potential …

Research On Rubik's Snake And Quasi-Surfaces, Yu Chen

Doctoral Dissertations

In this dissertation, we have two topics in applied math. For the first one, we studied the Rubik’s snake by mathematical methods.

The Rubik’s snake is a toy invented by Professor Erno Rubik in 1981. It consists of right isosceles triangular prisms. Since the shape of a snake depends only on how we twist it, we can get a unique sequence from every snake. Those sequences record the way we twist snakes. In this dissertation, we will study the relations between some structures of the snake and the sequences.

For a snake with a specific structure, we will find out …

Wigner's Theorem For Semi-Finite Von Neumann Algebras, Devin Daley Gent

Doctoral Dissertations

Wigner’s theorem, an important result in quantum mechanics, shows that a transitionprobability preserving bijection on the set of rank-one projections on a Hilbert space H extends to a Jordan ∗-isomorphism ρ on the algebra of all bounded linear operators on H. In this work we consider generalizations of Wigner’s theorem within the context of von Neumann algebras. Let M and N be two semi-finite von Neumann algebras with faithful normal semi-finite tracial weights τM and τN, respectively. Suppose that M has no direct summand of type I2 and is either diffuse or atomic such that every minimal projection in M …

Highly Dispersed Metal Sites On Semiconductor Surface For Small Molecule Activation, Ehab Shaaban

Doctoral Dissertations

Heterogeneous catalysts have been extensively used in various chemical transformations that have important ecological and economical relevance. The rational design of such catalysts, however, is still not effectively implemented due to the ambiguity that encircles their structure-activity correlations. The origin of synergetic effects which make the binary system (metal/metal oxide) distinct from the individual components continues to elude researchers. In this work, binding and structural properties that emerge from metal/metal oxide interaction were investigated using in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) and X-ray absorption spectroscopy (XAS). Different catalytic structures, including highly dispersed Cu sites on TiO2, were …