Master of Science (MS), Bowling Green State University, 2009, Communication Disorders

The purpose of this study was to describe the acoustic and aerodynamic characteristics of diatonic scale singing at different tempi in a professional female soprano. The classically trained singer sang ascending-descending ninth scales on /a/ in the F# major key at five different tempi – slow, moderately slow, moderately fast, fast, and fastest. All scales were performed with a moderate loudness level and with a pre-determined metronome marking. Tempo was controlled in order to determine whether differences existed between scales that were sung at a comfortable tempo and scales that were sung at an uncomfortable tempo. The slow (1 note = 104 beats / minute), moderately fast (2 notes = 92 beats / minute), and fastest (4 notes = 92 beats / minute) tempi were designated as comfortable because they were typically performed with integer multiple vibrato cycles per note. The moderately slow (2 notes = 72 beats / minute) and fast (4 notes = 69 beats / minute) tempi were designated as potentially uncomfortable because the note durations were not integer multiples of the singer's typical vibrato cycle period. There were a total of 5 ascending-descending scales analyzed in this study, one for each tempo. The results of the study strongly suggested trends in the acoustic and aerodynamic measures when tempo and scale direction were controlled. The following observations were noted: 1)mean fundamental frequency (F0) was higher in the descending notes than the corresponding ascending notes, 2)average F0 vibrato extent decreased as tempo increased, 3)mean note intensity was greatest at the highest notes and lowest at the lowest notes of the scale, 4)secondary intensity peaks were observed at the third (A#4) or fourth (B4) notes of both the ascending and descending portions of the scale, 5)airflow was greatest at the lowest notes of the scale and lowest at the highest notes of the scale, and 6)average airflow vibrato extent decreased as tempo increased. Distinctive trends were not (open full item for complete abstract)

Master of Arts (MA), Ohio University, 2019, Latin American Studies (International Studies)

This thesis strives to analyze the fast casual food market in order to understand if Chipotle would be successful in Brazil and what the concerns would be if the American chain decides to internationalize its operation to Brazil. This thesis has developed as a prospective case study based mainly on business and cultural analysis. The study analyzed Brazil by using the theory of market assessment, and also analyzed the fast casual, fast food, and food service industries and products by applying other business theories such as PESTEL, Porter Five Forces and VRIO. Furthermore, the study interviewed one entrepreneur in the fast casual industry in Belo Horizonte, Minas Gerais, Brazil to understand the local industry dynamics. Regarding all the information analyzed, this thesis creates a business model that consists on explaining how Chipotle would operate in the country. Brazil is an attractive market for Chipotle, there is room for rapid growth, and Chipotle could provide a positive impact for Brazilians.

Master of Science, The Ohio State University, 2016, Nuclear Engineering

The objective of this research is to conduct a comparative analysis of polyvinyltoluene (PVT) organic scintillators in order to aid Lawrence Livermore National Laboratory in the design of a PVT scintillator for fast neutron imaging. To achieve this goal, a neutron imaging apparatus has been developed to conduct neutron radiography using a neutron beam facility at The Ohio State University Research Reactor (OSURR). The neutron imaging apparatus is based on a low-cost single mirror refection configuration that consists of a neutron sensitive scintillator, a light tight box, a mirror, and a cooled charge-coupled device (CCD) camera. The light tight box was designed, machined, and built in-house specifically to fit into the space available at the neutron beam facility. The camera position is adjustable within the box in order to provide an adjustable field of view, which allows the object or region of interest to take full advantage of the CCD chip size. The spatial resolution of the scintillator was characterized by using Modulation Transfer Function (MTF) and an optical test target. The light yield was measured by the summation of pixel values in the same region of interest in each scintillator. Maximum resolution for a lithium loaded PVT (1.3% by weight) scintillator with thickness of 2.2 mm was 10.9 lp/mm for thermal neutrons. The resolution decreased by 11% with an increase of 1.1 mm in thickness. For fast neutrons with an average energy of 2 MeV, Li-loading increased the light yield of PVT by 29%. For 2.45 MeV neutrons produced by a D-D neutron generator, PVT with a Europium fluor produced 2.7 ± 0.2 times more light than a standard PVT scintillator. The combination of lithium loading with a Eu fluor in PVT produces an efficient dual-purpose fast and thermal neutron imager, as anticipated.

Master of Science, The Ohio State University, 2012, Electrical and Computer Engineering

This thesis presents work on the design of 1.5V, 100mA low-dropout (LDO) regulators with fast transient responses in the IBM8HP 0.13μm BiCMOS process. A conventional LDO architecture intended for use in an RF system was implemented and measured. The design of a printed circuit board (PCB) that is capable of measuring all pertinent characteristics of the regulator is also presented. Measurements show that the conventional design achieves a recovery time of less than 100ns with output voltage variations of less than 50mV. In addition to the conventional design, a new output capacitor-free architecture is introduced that can be fully integrated onto a chip. Simulations show that the output capacitor-free design achieves a recovery time of less than 50ns with output voltage variations of less than 140mV.

Doctor of Philosophy, The Ohio State University, 2011, Physics

We live in the era of high energy demand. Sooner or later we will exhaust all of our natural resources that are currently being used to make energy most of which are non-renewable. Therefore the quest to find another source of energy is an important one and should be completed within the next few decades. Thermonuclear fusion could become the solution to our energy problem. Currently, there are two main approaches to fusion: Magnetic Confinement Fusion (MCF) and Inertial Confinement Fusion (ICF). This thesis explores the variation of the ICF concept known as the Fast Ignition (FI). The FI concept relies on fast electrons with energies above 1 MeV created from the laser-matter interaction to deposit their energy into the compressed target core and start the fusion burn. Divergence of those electrons is one of the most crucial parameters in FI. If the divergence is found to be too large, then virtually all the anticipated advantages of FI over the conventional hot spot ignition will be lost. Spatially resolved, time-integrated Kα x-ray imagers are frequently used to infer the spatial distribution, and hence the divergence, of fast electrons by looking at the Kα radiation created by those energetic electrons passing through the target. Since any electron with energy above some threshold can produce a Kα photon, the Kα emission distribution can be quite different from that of the fast electrons. This thesis describes the physics behind the formation of Kα images and settles the question of how well those images represent the spatial distributions of the hot electrons that created them. A computational study using the Particle-In-Cell code LSP is presented that shows that a Kα image is not solely determined by the initial population of forward directed hot electrons, but rather also depends upon electrons refluxing off the front, the back and the sides of the target. All these effects create significant features in the Kα time-integrated images making them hard to interp (open full item for complete abstract)

Master of Arts, The Ohio State University, 1982, Linguistics

Experimental investigations of tone 3 sandhi in Mandarin Chinese have failed to find well-defined connections between sandhi and speech rates. In this study, empirical evidence is provided that indicates that the traditional claims of tone 3 sandhi are too arbitrary. Tone 3 does not necessarily change into tone 2 by all means. Furthermore, empirical, historical and theorectical arguments are raised concerning the validity of the duration of tone 3 in sandhi situation. Spectrograms and graphs are used to study durations and fundamental frequency of tone 3 in tone sandhi at slow, normal and fast speech by three females and three males. The degree to which the values of tone 3 are influenced appears to depend on various speech speeds. In addition, it is possible that greater variance in tone 3 duration and fundamental frequency is concomitant with the variance of speech speeds. The present study may be viewed as raising some interesting questions and careful cautions in future research on tone 3 sandhi.

Doctor of Philosophy (Ph.D.), University of Dayton, 2024, Electro-Optics

Traditionally, spectrometers characterize the steady-state conditions of spectral signatures of materials ranging from short ultraviolet to near infrared wavelengths, mainly because linear CCD arrays are easily manufacturable for the visible wavelength region while mid and long-wave infrared linear arrays are prohibitively costly. Moreover, a big constraint on the charge coupled or CMOS detectors is the refresh rate limit. Since the detector array device serializes captured parallel data, bandwidth is strongly limited. The usual charge-discharge period of commercial products that are used inside the spectrometers is on average 8.3ms. In specific areas of research, such as dynamic or high-speed phase change materials or fast biological processes, real-time effects carry useful information and 8.3ms time range is considered as steady-state. Current state of the art spectrometers could potentially use pump-probe techniques to overcome the speed problem, although that comes at the expense of extensive exposure to pump-pulses which might not be feasible, such as in the case for irreversible processes. This dissertation proposes a new step towards real-time dynamic spectroscopy using electro-optical engineering techniques to solve speed and wavelength trade-off. In this dissertation, a new type of ultrafast spectrometer based on high-speed, low-noise electronics, fiber optics, and supercontinuum light sources is proposed to solve the bottlenecks associated with traditional spectroscopy techniques, showing a viable path toward GHz-speed spectroscopy capable of characterizing dynamic materials at the sub-nanosecond time scales.

MDES, University of Cincinnati, 2024, Design, Architecture, Art and Planning: Design

Designers play a key role in minimizing the environmental, social, and economic impacts such as damage caused by fast-fashion. Design in general helps provide value to emergent and present needs for pressing issues through human empathizing. The role of designer can benefit in shifting people to sustainable practices by redesigning systems and processes. While there is awareness of environmental issues associated with fashion, there is still a need for more detailed knowledge and tools to help change their consumption practices. This gap in sustainability awareness is often taken advantage of by the brands through greenwashing tactics in the name of sustainable alternative solutions that consumers are demanding. This necessitates an urgent need for an innovative solution that not only promotes informed decision-making but also helps consumers shift to sustainable shopping practices. This research focuses on the role of designers in tackling such pressing social issues, focusing specially on generation z as target audience. This research adopts a qualitative methodology, incorporating surveys, semi-structured interviews, photo analyses, and workshops to gather insights. The focus is on developing a mobile application (app) aimed at promoting sustainable shopping behaviors among Generation Z consumers. The final proposed mobile application lets the users scan the garment label to get information on sustainability metrics, which helps them make informed decisions. The results include information on fiber content with grading, and the app allows the users to understand the terminology and educate the consumers. The findings reveal a strong interest among the participants in using an application to improve their day-to-day shopping practices when the app offers precise and reliable sustainability metrics. This interest in such a design-driven tool shows the potential impact that an actionable solution can have on consumer behavior and their improvement in sus (open full item for complete abstract)

MA, Kent State University, 2024, College of Arts and Sciences / Department of History

This research focused on the marginalization of women in the Zimbabwean agricultural sector. It examined how patriarchy and culture have limited the participation of women in agriculture as well as their access to land. Although there has been broad and extensive scholarship on the exclusion of women in land allocation, ideas on how women maneuvered their way to attain land have been understudied. To understand the logic behind the marginalization of women in agriculture, this study examined the grassroots of the Fast Track Land Reform Program (FTLRP) of 2001 and unpack how patriarchy and culture shape the national government silence on gender inequality. Before the implementation of the program, the government made it clear that the land distribution was to benefit everyone, with certain land portions being reserved for women. The land reform program was supposedly implemented with the intention to empower all Zimbabweans and eradicate gender disparities. However, the Zimbabwean government has failed to keep its word on equal distribution of land thereby leading to the segregation of women. Due to its failure to empower women, scholars from different fields have viewed the program as rather a political stance that was strategically put in place by the ruling government to gain votes during presidential elections. The study takes a feminist approach in outlining the instances in which the program was a deception that led to further marginalization of women in terms of accessing economic resources.

Master of Science (M.S.), University of Dayton, 2024, Mechanical Engineering

This work discusses the experimental testing of a nominal six-inch diameter single airstream rotating detonation engine that utilizes a hollow core to split the airstream into two separate flow paths and causes the test article to self-balance. Hydrogen and air were selected as the fuel/oxidizer combination for this test. The hollow core is designed to mimic a venturi nozzle, enabling the collection of pressure and temperature at the throat of nozzle to determine the mass flow rate through each flow path. Two Laval nozzles with varying contraction ratios, 7.5 and 11, and three fuel rings of varying injection are experimentally examined and their impact on the operability of the self-balancing RDE is investigated. This work highlights the calculation and determination of the mass flow split between the flow paths during cold flow and hot flow conditions, the operating map across six experimental configurations, and the impact of fuel injection penetration and momentum flux on the operability of the test article.

PhD, University of Cincinnati, 2024, Arts and Sciences: Chemistry

Real-time monitoring of neurotransmitters is of great importance because of the roles these neurochemicals play in vital bodily functions. Fast-scan cyclic voltammetry (FSCV) at carbon-fiber microelectrodes (CFMEs) has advanced our understanding of neurotransmitter dynamics as a prominent electroanalytical technique. Innate biocompatibility, functionalization, etc. make carbon an attractive electrode substrate; unfortunately, decades of research have rarely branched away from dopamine due to poor CFME morphology tunability and reliance on adsorption interactions. Here, we developed tunable carbon-based microelectrode surfaces through geometry manipulation and surface chemical doping for enhanced neurochemical interfacial interactions. Chapter 1 provides a critical perspective on the future of carbon-based neurochemical detection with a summary of novel FSCV electrode materials used to date; we identified three challenges FSCV detection faces and routes to address these challenges through novel carbon electrodes. Challenge one involves unobserved events caused by diminished temporal resolution. Chapters 2-5 addressed this issue by introducing porous structures to CFMEs or surface roughness to graphene oxide microelectrodes (GFMEs) for improved electrochemical reversibility. Chapter 2 uses nanoporous carbon nanofibers electrodeposited onto CFME frameworks. These microelectrodes improve dopamine sensitivity and electron transfer kinetics, but low pore dimensions fail to trap dopamine generating negligible changes in temporal resolution. Chapter 3 uses biomass syntheses of macroporous carbon demonstrating the first instance of the use of biomass-derived porous carbons for implantable electrode applications. Macroporous framework-modified CFMEs provide increased surface defects and pores large enough to momentarily trap dopamine for improved electrochemical reversibility, sensitivity, and frequency independence. Chapter 4 uses copolymer wetspinning to synthesize u (open full item for complete abstract)

Doctor of Philosophy, The Ohio State University, 2023, Nuclear Engineering

Neutron radiography and computed tomography (CT) offer unique opportunities in the field of non-destructive evaluation (NDE) for both reactor-based and accelerator-based neutron sources. The most widely implemented and advanced state-of-the-art techniques in radiography and CT use X-ray sources. However, in scenarios where X-ray penetration or contrast among materials are limited, advanced thermal and fast neutron methods can offer additional insights. X-ray attenuation is generally minimal for materials with a low atomic number (Z) and increases as the atomic number grows. This characteristic can sometimes result in inadequate contrast for low-Z materials or excessive attenuation for high-Z materials. Thermal neutron radiography – using neutrons near the thermal equivalent energy of 0.025 eV – takes advantage of the variable thermal neutron capture cross sections as a function of Z to provide high contrast, especially for certain elements such as Li and B. Attenuation values for thermal neutrons do not tend to follow a specific trend which enables contrast to be high for specific combinations of elements or isotopes. However, these lower energy neutrons have difficulty penetrating thicker objects, and certain elements can become activated due to nuclear transformations. Fast neutron radiography (using ~MeV neutrons) exhibits a more consistent attenuation across varying Z values, potentially benefiting both low-Z and high-Z materials. The primary advantage of fast neutron radiography and CT lies in the ability of MeV neutrons to penetrate high-Z materials like lead and tungsten better than MeV X-rays. The main challenge is ensuring adequate contrast between materials and achieving high detection efficiency, since these high energy neutrons are so penetrating. Generally, the most probable interactions of elements with fast neutrons are elastic scattering interactions which tends to reduce activation of target materials compared to thermal neutron techniques. This can (open full item for complete abstract)

Psy. D., Antioch University, 2023, Antioch Santa Barbara: Clinical Psychology

Existing frameworks of psychopathology have received criticism from evolutionary researchers. It is argued that mental health research lacks theoretical unity and that there is no comprehensive understanding of psychiatric disorders. Evolutionary researchers have posited that a paradigm of psychopathology informed by evolution could accomplish this aim. Drawing from evolutionary biology, life history theory provides such a framework. Life history theory is a subfield of evolutionary biology that examines how organisms allocate limited environmental resources over their lifespan in order to maximize their fitness. The strategies that organisms adopt in response to their environment are referred to as life history strategies. These strategies are graphed on a spectrum between two poles, fast and slow. The fast and slow life history classifications form the basis of the fast-slow-defense activation model of psychopathology which describes causal pathways for mental disorder. Within this framework, sex is a moderating factor between life history strategy and psychopathology. At present, there is little empirical research evaluating the fast-slow-defense activation model. The current research seeks to provide an analysis of the fast-slow-defense activation framework by exploring the relationship between life history strategy, sex, and defense activation disorders particularly, depression. It is expected that there will be a causal relationship between life history strategy and depression. Specifically, a fast life history strategy will predict for increased symptoms of depression. In addition to this, it is expected that women with fast life histories experience greater symptoms of depression. This dissertation is available in open access at AURA, https://aura.antioch.edu/ and OhioLINK ETD Center, https://etd.ohiolink.edu.

MS, University of Cincinnati, 2023, Arts and Sciences: Chemistry

Neuroinflammation, oxidative stress, and glutamatergic excitotoxicity are prevalent in several neurological disorders including stroke, substance abuse, and neurodegenerative diseases. Chemical compounds and biomolecules which can ameliorate those conditions are gaining interest for new treatments. Despite many advances in understanding brain anatomy and physiology, the underlying neuropathological mechanisms behind ischemic stroke are still poorly understood. The purine nucleosides adenosine and guanosine have been shown to exhibit neuroprotective behavior in both in vivo and ex vivo models of ischemia. However, real-time detection of guanosine sub-second signaling dynamics in the brain is not understood. Various techniques have been developed for the detection of guanosine in vivo and in in vitro. We have used fast-scan cyclic voltammetry (FSCV), a novel electrochemical technique for real-time detection of the neurochemical release in sub-second timescales at carbon-fiber microelectrodes (CFME). Previously our lab has observed a significant increase in the concentration of guanosine during ischemia with the help of FSCV, showing a neuroprotective effect in ischemia. Despite prior studies, it is still unknown how guanosine released during ischemia is impacted as the function of ischemic severity. Here, we have developed an ex vivo oxygen-glucose deprivation model to investigate the guanosine signaling changes as a function of ischemic severity. Characterization of three different ischemic conditions was studied: normoxia, mild ischemia, and severe ischemia with the help of an optically dissolved oxygen sensor. triphenyl tetrazolium chloride assay and immunohistochemical staining were used to validate these ischemic conditions. Overall, we have successfully developed and maintained three different ex vivo experimental ischemic condition.

PhD, University of Cincinnati, 2023, Arts and Sciences: Chemistry

The importance of the gut-brain axis has become increasingly apparent, insights into the neurotransmission along this axis could provide crucial information into roles along the gut-brain-immune axis. Physiologic culture methods of ex vivo tissue slice models are imperative to assess physiological function ex vivo. Microfluidics has been adapted to improve the physiological environment of current culture methods. In this thesis I have detailed microfluidic improvements to analytical detection methods, single organ slice culture devices and multi-organ communication devices. The first chapter details the importance of the gut-brain axis and the communication pathways along this connection. Detection methods for this multi-organ communication are also detailed in the first chapter. Wrapping up this chapter the need to expand our ex vivo culture platforms currently in the field is discussed. In the second chapter, I detail a microfluidic electrochemical flow cell to improve the current experimental procedure. The T-channel device design followed by a long microfluidic channel facilitate full mixing of solutions before the electrode surface. Flow rates can be varied to allow for a full concentration curve to be performed from a single stock analyte solution. This device reduces human error drastically in the experiment and decreases time and cost due to the microfluidic nature of the device. Chapter three describes a culture platform for ex vivo intestinal slices that recreates the physiological oxygen gradient that occurs in the intestine. Flow rates of oxygenated and deoxygenated media can be varied to allow for strategic delivery to different sized slices. The delivery of this gradient was proven to remain steady over the course of an hour. This device also provides an open culture platform for easy coupling with external detection methods such as fast scan cyclic voltammetry and microscopy techniques. Chapter four details a multi-organ (open full item for complete abstract)

Doctor of Philosophy, University of Akron, 2023, Polymer Science

Water scarcity has had a severe impact on the ecosystem and global warming is resulting in extreme weather conditions. The increasing world's population and societal modernization have made water scarcity a global challenge. Conventional water treatment is out of reach for poor countries. Therefore, there is a need to find new technology that fulfills the need for fresh water, and atmospheric water harvesting is one of them. Among the different approaches in atmospheric water harvesting, sorption-based vapor harvesting is useful, and it can be applied in any type of environment, transcending country boundaries. Using sorbent materials to separate and concentrate ambient humidity is a promising option for atmospheric water harvesting in the face of impending worldwide freshwater scarcity. The method of cycled sorption and forced release can facilitate efficient condensation, but performance strongly depends on device-scale issues of heat and mass transfer. We examine the potential of using microwave radiation to liberate sorbed vapor in proof-of-concept experiments with porous materials, such as electrospun nanofibers and hygroscopic salt-infused cellulose fiber-based porous materials, as simple sorbents in the first part of the thesis. We quantify performance (the ability to separate water from air) as a function of tunable system parameters and ambient humidity. Our results demonstrate promising aspects: rapid desorption and regeneration, due to water-tuned dielectric heating and directing flow through fibrous sorbents, respectively; substantial efficiency of moisture separation toward very low ( 25%)relative humidity; and robust repeatability over many cycles. Finally, in the second part of the thesis, the selection criteria for sorbent materials are explored. Candidates are chosen on the basis of their amenable chemistry and structure and are evaluated by the magnitude and reversibility of their vapor uptake. The equilibrium water uptak (open full item for complete abstract)

Doctor of Philosophy, Case Western Reserve University, 2023, Biomedical Engineering

Magnetic Resonance Imaging is a clinical imaging modality that has excellent soft tissue contrast, enabling it to answer clinical questions on a range of pathologies that other imaging methods cannot. However, conventional MR techniques typically have slow acquisitions that prevent applications in imaging physiological motion. In addition, other imaging modalities such as CT produce quantitative, reproducible pixel values, whereas MRI generally produces qualitative images. To address these issues, many new MR techniques have been developed but require additional optimization or development to be adopted clinically. Three main projects involving the translation of emerging techniques in MR to clinical application will be described in this thesis. In the first project, a fast imaging technique known as through-time radial GRAPPA is optimized to reduce total acquisition time and reconstruction overhead to enable free-breathing un-gated cardiac CINE. The second project discusses a new quantitative imaging technique in the heart, known as Cardiac Magnetic Resonance Fingerprinting (cMRF), which requires a lengthy dictionary simulation step to be performed with each reconstruction. cMRF dictionary simulation is implemented and optimized on a reconstruction platform known as Gadgetron to enable clinically integration of cMRF. In the final project, in-bore MR-guided prostate biopsy is an interventional technique that requires long T2-weighted imaging. A simulation approach taken to find a faster T2-weighted imaging sequence among Cartesian and spiral TSE sequence variants.

Master of Science, Miami University, 2022, Physics

For this thesis, the focus is on both the continuation of the process towards the synthesis of a 87Rb Bose-Einstein condensate (BEC) and studying the resulting quantum fidelity for a non-interacting BEC that is transported using shortcuts-to-adiabaticity (STA) by counter-diabatic driving. These are relevant to each other since the end goal, after the BEC is synthesized, is to transport the BEC quickly. This will be done using STA to maintain the BEC's coherence and keep the system in its ground state while moving it quicker than would be possible using traditional methods without heating it up, such as moving it 30 µm in tens of milliseconds. Eventually, other elements such as sodium, lithium, or potassium may be substituted, so their behavior could be observed. Some of these elements, especially certain alkali metals, can be tuned using Feshbach resonance to minimize the interactions between individual atoms. The simulations explore these scenarios, what the lack of internal interactions mean for the transport time, and the importance of the auxiliary potential for this STA protocol.

Doctor of Philosophy, The Ohio State University, 2022, Electrical and Computer Engineering

Gallium nitride (GaN) represents a wide bandgap semiconductor material that has been widely utilized in optoelectronic and electronic devices. As silicon (Si) based power devices are quickly approaching their fundamental material limits, GaN exhibits great potential for next generation power electronic devices due to its wide bandgap (3.4 eV), high breakdown field (3.3 MV/cm), and high electron mobility (1500 cm2/(V∙s)). With the availability of free-standing GaN substrates, GaN vertical power devices with superior performances have been demonstrated. One of the key challenges to further advance the GaN vertical power devices lies in the development of high quality, thick GaN epitaxy with low background doping and high mobility. This dissertation focuses on the development of high-quality GaN metal-organic chemical vapor deposition (MOCVD) growths and vertical GaN PN diodes for high performance power electronic applications. The sources and incorporation mechanisms of typical compensations in GaN MOCVD are investigated. The pre-growth wafer cleaning process and growth susceptor are identified as two major sources of iron (Fe) impurity incorporation. The (EC-0.6) eV defect peak is confirmed to be associated with Fe impurity. Fe impurity can be suppressed with proper wafer cleaning and full coverage of susceptor pocket. An optimized MOCVD GaN growth condition with a typical growth rate (GR) of 2 µm/hr is established as the baseline with low controllable doping (Nd-Na) at 4×1015 cm-3. Background carbon (C) impurity typically increases monotonically with GR. The high background C impurity in MOCVD GaN is related to the low pyrolysis efficiency of NH3. Laser-assisted MOCVD (LA-MOCVD) growth technique is proposed to address this issue using a 9.219 µm wavelength carbon dioxide (CO2) laser. The LA-MOCVD shows higher effective V/III ratios via efficient NH3 decomposition. The background [C] in LA-MOCVD GaN films decreases monotonically as the laser power increases. A lo (open full item for complete abstract)

Master of Science, The Ohio State University, 2022, Mechanical Engineering

The Department of Energy has prioritized extreme fast charging (XFC) for customer adoption of Electric Vehicles (EVs). Range anxiety is a major public concern when purchasing an EV, so comparable refueling time to conventional vehicles is highly sought after. There are multiple barriers to achieving XFC at all levels: infrastructure, vehicle systems, and battery cell. A major concern is on a cell degradation phenomenon known as lithium plating, a side reaction that is favored at high C-rates and low temperatures. Lithium plating can significantly reduce the cell capacity and can also pose serious safety concerns due to potential internal shorting and thermal runaway. For these reasons, accurate prediction of the physical mechanisms related to plating is extremely important and can be used to mitigate effects and prevent occurrence of plating during charging. This work is focused on developing physics-based modeling techniques and integrating them with experimental testing to predict the cell behavior associated with lithium plating. Fast charge testing was performed at various charging C-rates using different charging methods (CC vs. CC-CV). Reference Performance Tests (RPTs) were conducted between each fast charge cycle to track cell performance after lithium plating. The collected data was used to calibrate a pre-existing lithium plating model within a DFN electrochemical model. After calibration, specific issues with prediction in voltage degradation and capacity loss were addressed. Using differential capacity analysis of the RPTs, different aging effects onset by lithium plating were identified, showing both a loss of cyclable lithium (LCL) and a loss of anode active material (LAM). Optimization of electrochemical model parameters to RPT data confirms this and provides ideal changes in capacity related parameters after each fast charge cycle. A new model was then developed to attribute the LAM to dendrite growth behavior, which relies on results from phase-f (open full item for complete abstract)