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2,803 Matching Results
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Remotely Controlled Magneto-Phononic Devices Achieving Nonreciprocity and Anderson Localization in Ferrofluid
Motivated by previous relevant research on phononics including both active and passive phononics, the interest of faster turnability and more functions of the active phononics of further study led to this proposing research topic: magnetic field tunable active functional phononics. The first design of magnetic field tunable reciprocal--non-reciprocal transmission acoustic device was established, material was characterized, and numerical simulation has been performed. The simulation results show clear T-symmetric breaking non-reciprocity due to energy level splitting effect with Doppler effect – an acoustic Zeeman effect. Inspired by this preliminary work, further experiments were planned to demonstrate this effective Zeeman effect in phononics and effectively charged phonons in water based ferro-fluid. The objectives of this work as the next series of tasks were to illustrate acoustic Zeeman effect and acoustic Landau levels in various strength of magnetic field to investigate a design non-reciprocal sound device with magnetic field switching, which could be controlled on the amount of non-reciprocity with the strength of magnetic field. Once this new field first discovered by the proposed study tasks, more active tunable magnetic field phononics devices could be designed and exemplified in terms of both simulations and experiments. Faster and more controllable active phononic devices could …
Date:
December 2021
Creator:
Jin, Yuqi
System:
The UNT Digital Library
The Effect of Online Consumer Reviews and Brand Equity on the Consumer Decision Making Process
This research aims to investigate the (1) review effects on consumer decision making process, (2) effects of negative reviews on brand equity, and (3) consumers' likely response to a brand's request for reviews. The objective of the first essay is to investigate the nature of the relationship between skepticism and consumer decision making in an online behavior context. Its second objective is to know whether people's belief on their abilities or their hedonic principle moderates the relationship between a person's skepticism toward online reviews and their reliance on online reviews. The objective of the second essay is to explore whether negative online reviews that focus on service quality specific dimensions have a different effect on a service organization's perceived brand equity. Its second objective is to analyze the role of emotional contagion in the relationship between negative reviews related to various service quality dimensions and its effect on perceived brand equity. The main objective of the third essay is to know whether consumers are more likely to write an online review for a brand when the request comes from a higher equity brand. This essay also investigates how message trust and persuasion knowledge influence the relationship between a brand's request …
Date:
December 2021
Creator:
Ahmad, Fayez
System:
The UNT Digital Library
Corrosion Mechanism and Prevention of Wire Bonded Device in Microelectronic Manufacturing and Spectroscopic Investigation of Copper Etch Chemical Equilibria for High Density Interconnect Application
In the first part of this dissertation work, Al bond pad corrosion behavior was investigated in the presence of common industrial contaminants such as chloride (Cl-) and fluoride (F-). Al corrosion while in direct contact with Cu displayed rapid hydrogen (H2) gas evolution and dendrite propagation. In contrast, Al without bimetallic contact showed only minor surface roughening. This observed difference in the corrosion mechanism between Cl- and F- is attributed to the solubility of the corrosion products (AlCl3 vs. AlF3) formed on the Al surface. Our subsequent work explored corrosion prevention inhibition of wire-bonded devices (WBD) in the Cl- environment. Our research shows that the Al bond pad was protected against corrosion by chemically modifying the surface of the Cu wires, thereby preventing the H2 evolution. The inhibitor was observed to be highly selective, thermally stable, hydrophobic, and cost-effective, making it viable for industrial application of this coating for Al bond pad corrosion prevention. In the second part of the dissertation work, we utilized a novel approach of using ultraviolet-visible spectroscopy (UV-Vis) as a chemical-sensitive monitoring tool of the chemical environment in Cu etch bath. The UV-Vis technique illuminates the roles of H+, Cl-, Cu+, and Cu2+ to the etch …
Date:
December 2021
Creator:
Ashok Kumar, Goutham Issac
System:
The UNT Digital Library
Instrumental Development and Implementation of Portable Membrane Inlet Mass Spectrometry for Homeland Security and Environmental Applications
A rapidly growing topic of great interest is the adaptation of benchtop analytical instrumentation for use in outdoor harsh environments. Some of the areas that stand to benefit from field instrumentation development include government agencies involved with the preservation of the environment and institutions responsible for the safety of the general public. Detection systems are at the forefront of the miniaturization movement as the interest in analyte identification and quantitation appears to only be accessible through the use of analytical instrumentation. Mass spectrometry is a distinguished analytical technique known for its ability to detect the mass-to-charge (m/z) ratios of gas-phase ions of interest. Although these systems have been routinely limited to research lab-based analysis, there has been considerable development of miniaturized and portable mass spectrometry systems. Membrane Inlet Mass Spectrometry (MIMS) is becoming a common method of sample introduction that is subject to significant development. MIMS allows for minimal sample preparation, continuous sampling, and excludes complicated analyte introduction techniques. Sampling is accomplished using a semipermeable membrane that allows selective analyte passage into the vacuum of the mass spectrometer. MIMS is becoming the preeminent choice of homeland security and environmental monitoring applications with increasing opportunities for the future development of specialized …
Date:
December 2021
Creator:
Anguiano Virgen, Camila
System:
The UNT Digital Library
Forging Pathways: A Multi-Case Study of Individuals with Intellectual Disability Pursuing Postsecondary Education at the Community College
This multi-case study sought to better understand how students with intellectual disability (ID) are forging pathways to higher education via the community college. Five individuals with ID who accessed higher education via the community college and their parents/guardians were interviewed. Each case provided insight into personal pathways with results given in case descriptions and individual case themes. Cross-case analysis revealed four themes positively impacting the college-going pathway for students with ID: value-driven grit, pathway knowledge, community support, and accessibility. Based on findings from this study, families appear to be the primary systems forging pathways to the community college for individuals with ID. Local education agencies and community colleges can assist these families by engaging in interagency collaboration, evaluating their systems, and aligning practices to the goal of students with ID accessing and engaging in higher education.
Date:
December 2021
Creator:
Jackson, Amanda O.
System:
The UNT Digital Library
Advanced Cathodes for High Energy Density Lithium Sulfur Battery
A systematic development of 2D alloy catalyst with synergistic performance of high lithium polysulfide (LiPS) binding energy and efficient Li+ ion/electron conduction is presented. The first section of work found that Li+ ions can flow through the percolated ion transport pathway in polycrystalline MoS2, while Na+ and K+ ions can easily flow through the percolated 1D ion channel near the grain boundaries. An unusually high ionic conductivity of extrinsic Li+, Na+, and K+ ions in 2D MoS2 film exceeding 1 S/cm was measured that is more than two orders of magnitude higher than those of conventional solid ionic materials, including 2D ionic materials. The second section of this dissertation focus on catalyzing the transformation of LiPSs to prevent the shuttle effect during the battery cycling by synthesizing 2H (semiconducting) – 1T (metallic) mixed phase 2D Mo0.5W0.5S2 alloy on CNF paper, using two step sputtering and sulfurization method. The lithium sulfur (Li-S) battery cell assembled with the 2D Mo0.5W0.5S2/CNF/S cathode shows a high specific capacity of 1228 mAh g-1 at 0.1C and much higher cyclic stability over 4 times as compared to the pristine cathodes. The high LiPSs binding energy of catalyst efficiently prevents the shuttling effect and corrosion of Li …
Date:
December 2021
Creator:
Bhoyate, Sanket
System:
The UNT Digital Library
Reliability Characterization and Performance Analysis of Solid State Drives in Data Centers
NAND flash-based solid state drives (SSDs) have been widely adopted in data centers and high performance computing (HPC) systems due to their better performance compared with hard disk drives. However, little is known about the reliability characteristics of SSDs in production systems. Existing works that study the statistical distributions of SSD failures in the field lack insights into distinct characteristics of SSDs. In this dissertation, I explore the SSD-specific SMART (Self-Monitoring, Analysis, and Reporting Technology) attributes and conduct in-depth analysis of SSD reliability in a production environment with a focus on the unique error types and health dynamics. QLC SSD delivers better performance in a cost-effective way. I study QLC SSDs in terms of their architecture and performance. In addition, I apply thermal stress tests to QLC SSDs and quantify their performance degradation processes. Various types of big data and machine learning workloads have been executed on SSDs under varying temperatures. The SSD throughput and application performance are analyzed and characterized.
Date:
December 2021
Creator:
Liang, Shuwen (Computer science and engineering researcher)
System:
The UNT Digital Library
Unraveling the Effect of Atomic Configurations and Structural Statistics on Mechanical Behavior of Multicomponent and Amorphous Alloys
Multicomponent high-entropy and amorphous alloys represent relatively new classes of structural materials with complex atomic configurations and exceptional mechanical properties. However, there are several knowledge gaps in the relationships between their atomic structure and mechanical properties. Understanding these critical relationships will enable novel alloy design and tailoring of their mechanical properties for desired engineering applications. In this dissertation, first-principles calculations and molecular dynamics simulations are applied to investigate the local atomic configurations and ordering in high-entropy and amorphous alloys. Our findings suggest that fluctuations in local atomic configurations for high- entropy alloys result in significant changes in stacking fault energy, twin energy, dislocation behavior, dislocation-twin interactions, and critical shear stress. For amorphous alloys or metallic glasses, the short-range order (SRO) and medium-range order (MRO) were found to play decisive roles in determination of their mechanical properties. Structural relaxation was found to lead to shear localization, which was attributed to free volume change and evolution of SRO and MRO to more brittle nature. In contrast, rejuvenated metallic glasses had relatively large and uniform free volume distribution giving rise to homogeneous flow and increased plasticity.
Date:
December 2021
Creator:
Yang, Yu Chia
System:
The UNT Digital Library
The Examination of Black and Latino/a/x Students' and Responsive STEM Teachers' Perceptions of Teacher Cultural Consciousness and Culturally Responsive Instructional Practices
School cultures, curriculum, and instruction are too often created through a monocultural lens, which excludes Black and Latino/a/x students both socially and academically, and perpetuates the false notion that these students are inherently less capable of achieving academic success when compared to their White counterparts. This is visible across all content areas, but especially in secondary science, technology, engineering, and mathematics (STEM) classes, which means that our Black and Latino/a/x students are continually denied preparation for the critical, high demand careers in the STEM field. Just as critical, with the dominance of White teachers in the classroom, out Black and Latino/a/x students often do not have access to teachers who share their lived experiences or who understand the nuances of their home cultures. However, teachers and school instructional leaders can change course by focusing their efforts to develop a rich cultural consciousness, and by focusing on the utilization of culturally responsive pedagogy (CRP) and related instructional strategies with great intentionality in the classroom. This mixed method, single site, exploratory case study was conducted to examine Black and Latino/a/x students' perceptions of their culturally responsive STEM teachers' cultural consciousness, and culturally responsive STEM teachers' perceptions of culturally responsive practices and their …
Date:
December 2021
Creator:
Norris, Margaret Louise
System:
The UNT Digital Library
Homoleptic and Heteroleptic Platinum(II) Complexes for Organic Light Emitting Diodes and Humidity Sensors: Synthesis, Characterization, and Applications
This dissertation focuses on the design, synthesis, characterization of platinum (II) pyridylazolate complexes and develop high performance organic light emitting diodes (OLEDs) and design and execute high-sensitivity humidity sensors based on the luminescent metal-organic complexes of platinum. A majority of existing platinum compounds do not dissolve in organic solvents, making it difficult to analyze the photophysical characteristics of complexes in solution, a key part of understanding chemical photophysical properties. Furthermore, due to the poor quantum yield, it is inefficient for use in devices such as OLEDs. Chapter 2 reports the synthesis and characterization of a novel heteroleptic platinum(II) pyridylazolate complex with high solubility and quantum yield. The photochemistry of the complex is studied, including efficiency, emission profiles, and lifetimes at different temperatures. Chapter 3 reports the power efficiency (lm/W), current efficiency (cd/A), external quantum efficiency (EQE), luminance and operating voltage (V) of OLED devices made with the heteroleptic platinum(II) pyridylazolate complex. The relation between thickness of hole transport layer and electron transport layer on performance of devices has been studied through building a variety of devices. Chapter 4 includes application of a homoleptic platinum(II) pyridylazolate complex in humidity sensor. In many environments, the relationship between moisture content and emissive wavelength …
Date:
December 2023
Creator:
Farvid, Seyedmajid
System:
The UNT Digital Library
Promoting Women? Causes and Effects of Gender-Informed Transitional Justice
Quantitative research investigating the causes and subsequent impact of transitional justice practices has further developed thanks to the production of cross-national data on justice practices, namely by the Justice Data Project and the Transitional Justice Research Collaborative. Current work, however, does not consider the role of justice from a feminist perspective. For example, with respect to causes, we know little about whether and how justice processes are gender inclusive, and what the factors lead to gendered inclusion within justice practices. There is also a need for further inquiry to explain how gendered conflict violence, e.g., sexual violence directed at women, influences justice adoption, and if so, whether these justice processes are more likely to be inclusive of women and gendered issues. Regarding justice impact (its post-hoc effects), there is much to know about the implications gendered justice pose for post-violence societies. Moving away from essentialist notions that position men as protectors and women as inherently peaceful and mere victims of abuse, feminist scholars advocate for research to showcase women's agency as security providers in peacebuilding and peacemaking. I introduce a framework to explain how women and gendered issues become integrated into justice practices and evaluate implications that result from these …
Date:
December 2023
Creator:
Roark, Polly DeAnne
System:
The UNT Digital Library
The Local Organization of Refugee Service Provision: A Qualitative Comparison of Two Resettlement Cities in Texas
This comparative case study examines the organizational variations in refugee services in Dallas and Amarillo, Texas. Engaging sociological theories of organizations, migration, and the state, this study conceptualizes immigrant-serving organizations as brokers that operate within fields of similar entities that channel resources and services to refugees. Drawing on 60 in-depth interviews and over two hundred hours of participant observation, this study finds two distinct models of resource brokerage. In Dallas, immigrant-serving organizations operated as networked resource brokers, characterized by high levels of collaboration, robust local political support, and community engagement through consistent volunteer labor. These characteristics facilitated the sharing of resources and knowledge, resulting in the establishment of more professionalized services for immigrants and refugees. In contrast, immigrant-serving organizations in Amarillo operated as atomized resource brokers, characterized by fragmented collaborations, inter-organizational competition, limited volunteer labor, and varying levels of political support from local representatives. This atomized brokerage model hindered the efficient allocation of resources and support, leading to fragmented and less comprehensive services for refugees. In conclusion, this study provides valuable insights into the variations within the organizational fields of ISOs in Texas. The comparative analysis of Dallas and Amarillo offers a nuanced understanding of the impact of local context …
Date:
December 2023
Creator:
Fessenden, Deborah June
System:
The UNT Digital Library
A New Class of Stochastic Volatility Models for Pricing Options Based on Observables as Volatility Proxies
One basic assumption of the celebrated Black-Scholes-Merton PDE model for pricing derivatives is that the volatility is a constant. However, the implied volatility plot based on real data is not constant, but curved exhibiting patterns of volatility skews or smiles. Since the volatility is not observable, various stochastic volatility models have been proposed to overcome the problem of non-constant volatility. Although these methods are fairly successful in modeling volatilities, they still rely on the implied volatility approach for model implementation. To avoid such circular reasoning, we propose a new class of stochastic volatility models based on directly observable volatility proxies and derive the corresponding option pricing formulas. In addition, we propose a new GARCH (1,1) model, and show that this discrete-time stochastic volatility process converges weakly to Heston's continuous-time stochastic volatility model. Some Monte Carlo simulations and real data analysis are also conducted to demonstrate the performance of our methods.
Date:
December 2021
Creator:
Zhou, Jie
System:
The UNT Digital Library
Optimal Pair-Trading Decision Rules for a Class of Non-Linear Boundary Crossings by Ornstein-Uhlenbeck Processes
The most useful feature used in finance of the Ornstein-Uhlenbeck (OU) stochastic process is its mean-reverting property: the OU process tends to drift towards its long- term mean (its equilibrium state) over time. This important feature makes the OU process arguably the most popular statistical model for developing best pair-trading strategies. However, optimal strategies depend crucially on the first passage time (FPT) of the OU process to a suitably chosen boundary and its probability density is not analytically available in general. Even for crossing a simple constant boundary, the FPT of the OU process would lead to crossing a square root boundary by a Brownian motion process whose FPT density involves the complicated parabolic cylinder function. To overcome the limitations of the existing methods, we propose a novel class of non-linear boundaries for obtaining optimal decision thresholds. We prove the existence and uniqueness of the maximizer of our decision rules. We also derive simple formulas for some FPT moments without analytical expressions of its density functions. We conduct some Monte Carlo simulations and analyze several pairs of stocks including Coca-Cola and Pepsi, Target and Walmart, Chevron and Exxon Mobil. The results demonstrate that our method outperforms the existing procedures.
Date:
December 2021
Creator:
Tamakloe, Emmanuel Edem Kwaku
System:
The UNT Digital Library
Behavioral and Neural Correlates of Speech Perception Outcomes in Adults with Cochlear Implants
Postlingually deafened cochlear implant (CI) adults have large variability in speech perception abilities. While CIs are one of the most successful neural prosthetic devices, they are not able to adequately provide fine structure cues which results in a degraded signal for the listener to interpret. While behavioral measures remain the gold standard for determining speech perception abilities, an objective measure is needed for patients who are unable to provide reliable behavioral responses. Behavioral, cognitive, and neural measures were collected in this study to identify potential neural biomarkers that correlate with speech perception performance. Behavioral experiments evaluated participants' abilities to identify, discriminate, and recognize words as well as sentences in quiet and in noise. Cognitive measures were assessed to determine the roles of attention, impulse control, memory, and cognitive flexibility on speech recognition. Auditory event-related potentials (ERP) were obtained with a double oddball paradigm to produce the mismatch negativity (MMN) response, which has been shown to have associations with phonetic categorical perception at the group level. The results indicated that executive function is highly predictive of speech performance and that the MMN is associated with categorical perception at the individual level. These findings are clinically relevant to determining appropriate follow-up care …
Date:
December 2021
Creator:
Manning, Jacy
System:
The UNT Digital Library
Online Testing of Context-Aware Android Applications
This dissertation presents novel approaches to test context aware applications that suffer from a cost prohibitive number of context and GUI events and event combinations. The contributions of this work to test context aware applications under test include: (1) a real-world context events dataset from 82 Android users over a 30-day period, (2) applications of Markov models, Closed Sequential Pattern Mining (CloSPAN), Deep Neural Networks- Long Short Term Memory (LSTM) and Gated Recurrent Units (GRU), and Conditional Random Fields (CRF) applied to predict context patterns, (3) data driven test case generation techniques that insert events at the beginning of each test case in a round-robin manner, iterate through multiple context events at the beginning of each test case in a round-robin manner, and interleave real-world context event sequences and GUI events, and (4) systematically interleaving context with a combinatorial-based approach. The results of our empirical studies indicate (1) CRF outperforms other models thereby predicting context events with F1 score of about 60% for our dataset, (2) the ISFreqOne that iterates over context events at the beginning of each test case in a round-robin manner as well as interleaves real-world context event sequences and GUI events at an interval one achieves …
Date:
December 2021
Creator:
Piparia, Shraddha
System:
The UNT Digital Library
Integrating Multiple Deep Learning Models to Classify Disaster Scene Videos
Recently, disaster scene description and indexing challenges attract the attention of researchers. In this dissertation, we solve a disaster-related multi-labeling task using a newly developed Low Altitude Disaster Imagery dataset. In the first task, we realize video content by selecting a set of summary key frames to represent the video sequence. Through inter-frame differences, the key frames are generated. The key frame extraction of disaster-related video clips is a powerful tool that can efficiently convert video data into image-level data, reduce the requirements for the extraction environment and improve the applicable environment. In the second, we propose a novel application of using deep learning methods on low altitude disaster video feature recognition. Supervised learning-based deep-learning approaches are effective in disaster-related features recognition via foreground object detection and background classification. Performed dataset validation, our model generalized well and improved performance by optimizing the YOLOv3 model and combining it with Resnet50. The comprehensive models showed more efficient and effective than those in prior published works. In the third task, we optimize the whole scene labeling classification by pruning the lightweight model MobileNetV3, which shows superior generalizability and can disaster features recognition from a disaster-related dataset be accomplished efficiently to assist disaster recovery.
Date:
December 2021
Creator:
Li, Yuan
System:
The UNT Digital Library
Body Doubles: Materiality and Gender Non-Binarism in Victorian Supernatural Fiction
This dissertation is a study of supernatural doubles in Victorian literature. It argues that these doubles expand our understanding of gender variance in the Victorian period. The texts in this dissertation privilege gender non-binarism through their depictions of materiality, gender embodiment, and temporality.
Date:
December 2021
Creator:
Schneider, Katherine
System:
The UNT Digital Library
The Impact of Computational Methods on Transition Metal-containing Species
Quantum chemistry methodologies can be used to address a wide variety of chemical problems. Key to the success of quantum chemistry methodologies, however, is the selection of suitable methodologies for specific problems of interest, which often requires significant assessment. To gauge a number of methodologies, the utility of density functionals (BLYP, B97D, TPSS, M06L, PBE0, B3LYP, M06, and TPSSh) in predicting reaction energetics was examined for model studies of C-O bond activation of methoxyethane and methanol. These species provide excellent representative examples of lignin degradation via C-O bond cleavage. PBE0, which performed better than other considered DFT functionals, was used to investigate late 3d (Fe, Co, and Ni), 4d (Ru, Rh, and Pd), and 5d (Re, Os, and Ir) transition metal atom mediated Cβ -O bond activation of the β–O–4 linkage of lignin. Additionally, the impact of the choice of DFT functionals, basis sets, implicit solvation models, and layered quantum chemical methods (i.e., ONIOM, Our Own N-layered Integrated molecular Orbital and molecular Mechanics) was investigated for the prediction of pKa for a set of Ni-group metal hydrides (M = Ni, Pd, and Pt) in acetonitrile. These investigations have provided insight about the utility of a number of theoretical methods in …
Date:
December 2015
Creator:
Wang, Jiaqi (Physical chemistry researcher)
System:
The UNT Digital Library