MS, University of Cincinnati, 2000, Engineering : Materials Science

The residual stress profile is a major factor on the fatigue life of components that are subjected to cyclic loading.1 The residual stress profiles of two diesel engine components, a section removed from a connecting rod and a section removed from a finished crankshaft, were measured non-destructively using neutron, laboratory x-ray, and synchrotron x-ray diffraction techniques. The synchrotron source identified the near surface residual stresses, and the neutron diffraction technique used for measurements of the residual stresses from 1 mm below the surface on into the interior of the samples. The strains from the synchrotron measurements were corrected for the effect of the exponentially weighted averaging over the irradiated depth using a numerical linear inversion method. The neutron measurements did not require any corrections, as they are a measurement of strains, directly from the area of interest, and they are not weighted. After this determination of the residual stress profiles, the same locations on the components were measured using the common destructive x-ray diffraction etch layer removal technique. The measured data from this iterative etch technique were corrected for the effect of the removed material on the remaining stress field using equations put from the SAE J784a standard.2 These corrected data from this destructive technique is graphed in comparison to the residual stress profile data determined non-destructively. This data proves the etch layer removal method is as accurate as any of the other methods available due to the excellent correlation of the different techniques.

Committee: N. Jayaraman (Advisor) Subjects:

Doctor of Philosophy, The Ohio State University, 2007, Electrical Engineering

Approximate and relatively simple but closed form Uniform Geometrical Theory of Diffraction (UTD) solutions are obtained for describing the radiated, scattered and surface wave fields, respectively, excited by sources near or on a canonical geometry consisting of a thin, planar, three-dimensional (3-D) double positive/double negative (DPS/DNG) material coated metallic wedge with an arbitrary wedge angle. Thus, unlike previous works that consider primarily plane wave scattering by such DPS structures via the Wiener-Hopf (W-H) or Maliuzhinets (MZ) methods, the present development can also treat radiation and coupling problems of antennas near or on finite material coated metallic surfaces. The latter is made possible mainly through the introduction of higher order UTD slope diffraction terms added to first order UTD. It is noted that all previous solutions based on rigorous W-H and MZ formulations employ approximate boundary conditions; in contrast, the present solutions, which are developed via a heuristic spectral synthesis approach, recover the proper local plane wave Fresnel reflection and transmission coefficients and surface wave constants of the DPS/DNG material. They also include the presence of backward surface waves in DNG media. Besides being asymptotic solutions of the wave equation, the present UTD diffracted fields satisfy reciprocity to first order UTD, the radiation condition, boundary conditions on the conductor, and the Karp-Karal lemma which dictates that the first order UTD space waves vanish on a material interface.

Committee: Prabhakar Pathak (Advisor) Subjects:

Doctor of Philosophy, The Ohio State University, 2024, Chemistry

Magnetic materials are ubiquitous and are essential to everyday life and are essential for the development of new technologies. The focus of this dissertation is to investigate the magnetic properties of various solid-state materials containing 5d metals. There are mainly two characteristics that distinguish 5d metals from their 3d and 4d counterparts: higher levels of spin-orbit coupling and relatively larger d orbitals. Those differences make the magnetic properties of 5d containing materials more unpredictable and intriguing. In chapter 2, the materials studied adopted the double perovskite structure, where one of the B-sites is a 5d1 metal and the other is a diamagnetic cation. A combination of high-resolution powder diffraction techniques and solid-state NMR was utilized to explore the links between crystal structure, orbital ordering, and reported magnetism in 5d1 double perovskite systems. In Ba2ZnReO6 a cubic-tetragonal transition was observed at 23 K that breaks the degeneracy of the t2g orbitals and presumably leads to a pattern of orbital ordering that stabilizes magnetic ordering at 16 K. A similar pattern was observed for Ba2MgReO6. Prior theoretical works indicate that only the pattern of orbital order seen in the P42/mnm space group could stabilize the canted ferromagnetism of these states. Unfortunately, powder diffraction data is not sensitive enough to differentiate between the I4/mmm and P42/mnm structural models as the distortions are subtle. The near complete lack of magnetic scattering detected in NPD combined with the symmetry lowering suggests that the magnetism in these two compounds is an ordering of local quadrupolar moments rather than the much more ordinary ordering of dipolar magnetic moments. In chapter 3, the materials studied also adopted the double perovskite structure. The effect of non-stoichiometry on the cation distribution, crystal structure, and magnetic properties of a series of Cr-rich Sr2Cr1+xRe1−xO6 samples have been (open full item for complete abstract)

Committee: Patrick Woodward (Advisor); Yiying Wu (Committee Member); Casey Wade (Committee Member) Subjects: Chemistry

Doctor of Philosophy, The Ohio State University, 2017, Electrical and Computer Engineering

It is of importance to understand the physics as electromagnetic (EM) waves propagate through stratified media, are scattered back from buried irregularities, and are received by an antenna in the near field. To generate better images, we need to incorporate the physics of the phenomena into the imaging algorithm, such as multiple reflections, refractions resulting from the existence of interfaces, and diffractions from embedded targets. A forward model is developed based on the spectral Green's function associated with layered media weighted by the antenna gain pattern, satisfying the near-field condition and incorporating all refraction effects. Thereby, the weak scattering from deeper layers and wide angles will be compensated in a model-based imaging algorithm with the consideration of the refraction coefficients and gain pattern, respectively. To form real-time continuous images of targets embedded in a layered structure, a near-field uniform diffraction tomographic (UDT) imaging algorithm is developed. Conventional diffraction tomography (DT) improperly applies the stationary phase method for stratified environments to evaluate the innermost spectral integral. In DT the large argument is assumed to be the depth, which is not appropriate for near-field imaging. This results in amplitude discontinuities occurring at the interfaces between adjacent layers. The correct dimensionless large argument is the product of the free space wavenumber and the depth, as used in high-frequency asymptotic solutions. UDT therefore yields uniformly continuous images across the interfaces. And like DT, UDT retains the fast Fourier transform (FFT) relation in the algorithm for generating images very efficiently. Both 2D and 3D cases are investigated to verify the efficacy of the proposed UDT algorithm. To overcome the singularity problem caused by nulls in the antenna gain pattern in DT and UDT, a fast back-projection (FBP) imaging algorithm is propose to provide balanced monosta (open full item for complete abstract)

Committee: Robert Burkholder Dr. (Committee Member); Fernando Teixeira Dr. (Committee Member); Graeme Smith Dr. (Committee Member) Subjects: Electrical Engineering; Electromagnetics

Doctor of Philosophy, University of Akron, 2015, Polymer Science

Although single crystal X-ray diffraction remains the most important technique for analyzing periodically ordered structures at atomic resolution, single crystal X-ray diffraction of organic macromolecules is challenged by difficulty in growing single crystals of desired size and quality. Electron crystallography of organic macromolecules, on the other hand, is limited by image resolution due to radiation damage and highly dependent on high-resolution instrumentation. Novel alkylated benzothiophene derivatives synthesized previously can be readily fabricated into semiconductor devices for various applications (photodetectors, explosive sensors, field-effect transistors, light-emitting diodes, etc.) via solution process. The object of this research is to identify phase transitions of organic macromolecules of this kind via differential scanning calorimetry and temperature-resolved wide angle X-ray diffraction, and to determine their lattice parameters and space groups by reconstruction of their reciprocal space via transmission electron microscopy / selected area electron diffraction followed by refinement with X-ray diffraction, supplemented by polarized light microscopy. Computer simulation was performed to rationalize the molecular packing schemes, so as to understand the origin of their electronic performance from crystallographic perspective.

Committee: Stephen Z. D. Cheng Dr. (Advisor); Yu Zhu Dr. (Committee Chair); Toshikazu Miyoshi Dr. (Committee Member); Tianbo Liu Dr. (Committee Member); Xiong Gong Dr. (Committee Member) Subjects: Chemistry; Condensed Matter Physics; Materials Science; Organic Chemistry; Physical Chemistry; Physics; Polymers; Solid State Physics

Doctor of Philosophy, The Ohio State University, 2015, Welding Engineering

Very High Power Ultrasonic Additive Manufacturing (VHP-UAM) was used to fabricate 10 layers and up to 80 layers samples from aluminum alloy 3003-H18 foil (Al3003-H18) of 150 µm thickness with varying vibration amplitude and normal force. This research was aimed at studying the change in hardness, microstructure, and texture in Al3003-H18 foil both in as-processed conditions and in heat-treated (343°C-2hr) condition compared to original foil, and to utilize neutron diffraction method to characterize the bulk texture analysis of the bulk VHP-UAM samples. Results from Vicker microhardness measurement, optical microscopy, scanning electron microscopy, electron backscattered diffraction (EBSD), and neutron diffraction were used to describe the changes in hardness, microstructure, and texture. The difference in microstructure and texture evolution in VHP-UAM samples processed at different process parameters can be related to the energy input during VHP-UAM and the post-processing heat-treatment.

Committee: Avraham Benatar (Advisor); Sudarsanam Suresh Babu (Advisor); John Lippold (Committee Member); Wei Zhang (Committee Member) Subjects: Materials Science; Metallurgy

Doctor of Philosophy, The Ohio State University, 2009, Chemistry

This work describes the synthesis and characterization of a number of new AA'BB'O6 perovskites which possess the unusual combination of rock salt ordering of B/B' and layered ordering of A/A'. These compounds have been structurally characterized by powder X-ray and neutron diffraction as well as transmission electron microscopy. Several of these compounds are found to adopt polar P21 space group symmetry as a result of the cation ordering in combination with a–a–c+ octahedral tilting. A number of other compounds are shown to have a compositional modulation of the A-site cations that is accompanied by a twinning of the octahedral tilt system. Using UV-Vis spectroscopy the band gaps of these compounds have been determined. This analysis shows that NaLnMgWO6 compounds are insulators while NaLnMnWO6 compounds are semiconductors. The dielectric constants are found to be in the range of approximately 20-35. The magnetic properties of the NaLnMnWO6 and NaLnMgWO6 compounds have been measured. All NaLnMnWO6 compounds are found to order antiferromagnetically at temperatures ranging from 6-15 K. The NaLnMgWO6 compounds do not show any indications of magnetic order. The magnetic structures of NaLaMnWO6, NaNdMnWO6, and NaTbMnWO6 have been determined from neutron powder diffraction. NaLaMnWO6 is found to order into a simple commensurate structure. NaNdMnWO6 orders incommensurately due to interactions between the two magnetic ions. NaTbMnWO6 is found to pass through two magnetic phase transitions. Just below its Neel temperature it has an incommensurate modulation of its structure which disappears as it is further cooled.

Committee: Patrick Woodward PhD (Advisor); Yiying Wu PhD (Committee Member); Malcolm Chisholm PhD (Committee Member) Subjects: Chemistry

Doctor of Philosophy, The Ohio State University, 2003, Chemistry

The perovskite structure with 1:1 M-site cation ordering (or double perovskite; A 2 MM'X 6 ) is a well known and extensively studied structure type in solid state chemistry. The ideal double perovskite has cubic symmetry, but many are distorted from the ideal structure. Structural distortions seen in perovskites are caused by electronic factors (i.e., Jahn-Teller ions), M-cation displacement from the center of the MX 6 octahedra (i.e., cations with a stereoactive lone pair of electrons), and most commonly, octahedral tilting. Tilting of the octahedra within the perovskite structure leads to lowering of its symmetry. A major factor that influences the degree of octahedral tilting in a given compound is the nature of the cuboctahedral A-cation. Perovskites with Ba 2+ as the A-site cation typically exhibit cubic symmetry and those with Ca 2+ have orthorhombic or monoclinic symmetry. Changes (or lack thereof) in space group symmetry for A = Ba 2+ and Ca 2+ are often easily seen in the X-ray powder diffraction data (XRPD) of their respective compounds. Yet, compounds with A = Sr 2+ are prone to subtle octahedral tilting distortions that are not readily seen in XRPD, so many are mistakenly assigned to the incorrect space group. In this study, nine double perovskites with A = Sr 2+ (M 3+ = Al, Sc, Cr, Mn, Fe, Co, Ga, Y; M 5+ = Nb, Ta, Sb), were examined using Rietveld refinements of XRPD and neutron powder diffraction data (NPD) in order to appropriately discern their respective crystallographic symmetry. The approach taken for determining appropriate possible space groups, the reliability of peak splitting seen in the XRPD data for determining space group symmetry, the extent of M-site cation ordering, and the degree of octahedral tilting seen in this family of compounds will be discussed. The principles used to determine the appropriate space group symmetry for the nine compounds examined by NPD was applied to the XRPD data of sixteen additional double perovskites. The p (open full item for complete abstract)

Committee: Patrick Woodward (Advisor) Subjects: Chemistry, Inorganic

Master of Science, The Ohio State University, 1966, Graduate School

Committee: Not Provided (Other) Subjects:

PHD, Kent State University, 2024, College of Arts and Sciences / Materials Science Graduate Program

Stimuli-responsive functional soft materials have been the focus of attention and been widely applied in advanced devices. Chiral nematic liquid crystals (also called cholesteric liquid crystals, CLCs), which possess intrinsic self-organized helical superstructures, are good candidates to create diffraction gratings (DGs) for optical devices, due to the characteristics of adjustable pitch under external stimuli like light, temperature, electric field, and so forth. Here, we develop two novel photoresponsive CLCs, which are enabled by adding two novel axially chiral molecular switches into the nematic LC host, respectively. Those chiral molecular switches exhibit superior compatibility, high helical twisting power (HTP), and a big HTP change under photoisomerization. Accordingly, electro- and photo-driven orthogonal switching of CLC diffraction gratings, and visible light, temperature, and electric field-driven in-plane rotation of CLC diffraction gratings are demonstrated, which exhibit great potential application in beam steering, spectrum scanning, and beyond. Like CLCs, twist-bend nematic liquid crystals (NTB LCs) also possess an intrinsic heliconical structure although the constituent molecules are achiral, but the molecular director is tilted with a cone angle around the conic helical axis and the heliconical pitch is very small. We study the structure and optical properties of NTB LCs when the chiral dopant is introduced. We show that adding chiral dopant does not induce a twisting of the heliconical axis, but increases the cone angle. Then, based on this fundamental study, we develop a novel thermally switchable smart window enabled by phase transition from NTB phase to chiral nematic phase. Such smart window is energy-saving and exhibits great potential in applications for buildings, vehicles, and beyond. Moreover, we develop a novel switching mechanism between planar and focal conic states in bistable reflective display. The CLC is switched from the foca (open full item for complete abstract)

Committee: Deng-Ke Yang (Advisor); Quan Li (Advisor); Barry Dunietz (Committee Member); Xiaoyu Zheng (Committee Member); Philip J. Bos (Committee Member) Subjects: Chemistry; Materials Science; Physical Chemistry; Physics

Master of Science, The Ohio State University, 1960, Graduate School

Committee: Not Provided (Other) Subjects:

MS, University of Cincinnati, 2024, Engineering and Applied Science: Mechanical Engineering

Acoustic pressure measurement (beamforming) is an emerging structural health monitoring (SHM) technique that can localize defects based on the sound field generated or transmitted through these defects. It can detect damage initiated with small physical irregularities like cracks, holes and worn out material thickness which ultimately lead to deformation and breakdown. Compared to other SHM techniques, acoustic beamforming has the advantages of being a non-contact method, having improved signal quality and precise directional sensitivity for localizing sound sources. State of the art acoustic measurement setups are limited to sealed hollow structures where an acoustic source is placed inside and a microphone array outside the structure captures the acoustic signal leaking through defects and gaps. This work extends the use of acoustic beamforming using the delay and sum algorithm to open structures and studies (numerically and experimentally) the ability of acoustic beamforming to detect defects in plates actively excited by sound in an open environment. Our numerical results, using the finite element method, show that sound diffraction around the plate is the main limiting factor for detecting defects in this configuration. To address the problem of diffraction, two solutions are proposed. An insulation material is used as a barrier around the plate to reduce diffraction around the plate and the directivity of the exciting sound source is improved by introducing a frustum-shaped enclosure to focus sound onto the plate. Subsequently, the beamformer is able to accurately identify the location of the defect, down to a defect size of 5 mm numerically and 7 mm experimentally. The minimum detectable defect size is identified as a function of diffraction pressure and a metric is developed for the detectability of a given defect size based on pressure measurements. Our results show that acoustic beamforming is a viable solution for detecting defects in open structures and (open full item for complete abstract)

Committee: Ahmed Allam Ph.D. (Committee Chair); Jay Kim Ph.D. (Committee Member); Yongfeng Xu Ph.D. (Committee Member) Subjects: Acoustics

Doctor of Philosophy, The Ohio State University, 2024, Electrical and Computer Engineering

With rapidly increasing demands for high-speed and data-intensive wireless communications, mm-wave technology has become a promising way to provide unparalleled data rates, ultra-reliable low latency, and a massive increase in device connectivity. However, there are some fundamental challenges in the deployment of mm-wave networks. Considering the same communication distance, the mm-wave suffers from a higher free-space path loss due to its shortened wavelength. The path loss becomes an issue especially when the device is working in rural areas where a longer coverage distance is required. Also, a shorter wavelength can result in extra attenuation brought by random obstacles, for example, the raindrops whose diameter is comparable to the wavelength. For the mm-wave antenna systems with a fixed narrow beam, even light mechanical motions can cause misalignment between the transmitter and receiver leading to intermittent communication. To address these challenges, mm-wave antennas are designed to be highly directional, concentrating energy in narrow beams to combat the high path loss. Besides, beam-steerable antennas, which can dynamically adjust the radiation direction, have been developed to maintain reliable communication links. While the conventional phased array designs have a planar aperture with beam-forming capability, their usage in the mm-wave band is limited by its cost, potentially low efficiency, and high power consumption due to numerous active RF components. The reflector antennas, which have been widely adopted thanks to their decent gain level and high efficiency, face the challenges of a complex reflecting aperture and a large volume due to the separated feeding source. Similar limitations have been observed in other designs using metasurfaces or lenses as well. Therefore, there is an innovation gap for a simple low-cost, low-volume, high-efficiency, high gain, and beam-steerable antenna design for the next-generation mm-wave applications. A low-prof (open full item for complete abstract)

Committee: Chi-Chih Chen (Advisor); Scott Scheer (Committee Member); Fernando Teixeira (Committee Member); Kubilay Sertel (Committee Member) Subjects: Electrical Engineering; Electromagnetics

Master of Science, University of Toledo, 2024, Chemistry

Thermal expansion is a physical property that may contribute to materials' malfunctioning in applications ranging from various electronics to construction and other engineering fields. As heat is applied to or inherently generated by materials, they tend to expand, thereby causing stress, strain, cracks, and structural distortion at the interfaces between dissimilar materials. These structural misalignments, resulting from thermal expansion, adversely affect the properties of a material, which in turn leads to a change in a material's performance. This change in performance may disrupt the original purpose for which the material was made. These challenges make complementary materials that can reduce or eliminate the thermal expansion of other materials when incorporated into a composite attractive. Negative thermal expansion (NTE) materials are materials that contract upon heating. These materials can serve as fillers in composites to complement positive expansion materials and reduce overall thermal expansion in composite materials. Such composites can find applications in high precision optical mirrors, in the aerospace industry, in dental fillings, and ultimately, in various electronics. However, a thorough investigation of these promising materials is needed to understand some of the problems currently preventing full implementation. Among these challenges, avoiding temperature and pressure induced phase transitions that form positive expansion polymorphs has been an important factor. These phase transitions destroy the NTE property of the materials. Hence, stabilizing the NTE phase in a wider temperature and pressure range will enhance the materials' potential applications. This research focuses on the scandium tungstate (Sc2W3O12) family of NTE materials, represented as A2M3O12 (A = trivalent cation, M = tungsten, molybdenum). This family was chosen because of the wide range of cations that can be incorporated into the structure due to the chemical flexibil (open full item for complete abstract)

Committee: Cora Lind-Kovacs (Committee Chair); Michal Marszewski (Committee Member); Jon Kirchhoff (Committee Member) Subjects: Chemistry; Materials Science

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

There is a continuous thrust for cleaner and more sustainable alternatives for energy conversion with the increasing global energy demand. Among them, photovoltaics, specifically thin film solar cells are highly promising and are one of the fastest growing clean energy technologies in the United States. This research presents the synthesis and characterization of a set of novel multinary copper chalcogenide semiconductor nanocrystals (NCs), CuZn2ASxSe4-x consisting primarily of earth-abundant elements for applications in photovoltaic devices. A modified hot-injection method was used to synthesize these semiconductor NCs containing both S and Se chalcogens. The novelty of the new semiconductor NCs lies in the incorporation of multiple cations as well as two different chalcogen anions within the crystal lattice, which is an achievement from the materials synthesis aspect. The composition-controlled optical and photoluminescence properties of the CuZn2ASxSe4-x NCs were investigated via multi-modal material characterization including x-ray diffraction (XRD), ultraviolet-visible (UV-vis) spectroscopy, and photoluminescence spectroscopy (PL). The crystal structure, as determined from the XRD primarily consisted of the metastable wurtzite (P63mc) phase. The NCs exhibited direct band gap in the visible range that could be tuned both by varying the group III cation within the composition as well as the ratio of S/Se, based on the Tauc plot obtained from the UV-vis characterization. This work lays the groundwork for future investigations into the practical applications of copper chalcogenide NCs in solar energy conversion.

Committee: Soubantika Palchoudhury (Committee Chair); Guru Subramanyam (Committee Member); Robert Wilkens (Committee Member); Robert Wilkens (Committee Member); Guru Subramanyam (Committee Member); Kevin Myers (Advisor); Soubantika Palchoudhury (Committee Chair) Subjects: Aerospace Materials; Alternative Energy; Analytical Chemistry; Biochemistry; Chemical Engineering; Chemistry; Energy; Engineering; Environmental Science; Industrial Engineering; Information Science; Inorganic Chemistry; Materials Science; Nanoscience; Nanotechnology; Nuclear Chemistry; Nuclear Engineering

Doctor of Philosophy, The Ohio State University, 2024, Materials Science and Engineering

Simulations of materials are a cost-efcient way to study materials that aid in experimental planning and material design. For example, stress and plasticity analysis is readily performed by numerically-based simulations, like fnite element or spectral based methods, and are typically faster than performing the experiment itself. However, slow computation times of more complex simulations limit their use in the design space. Deep learning (DL) networks have been shown to be orders of magnitude faster than numerically-based simulations but are lacking in numerical accuracy by comparison. Furthermore, large datasets are required to train a DL network and collecting a sufcient amount is a difcult task in materials science. Incorporating physical laws of the material system within the DL model has been shown to create a more physically accurate network, but can be difcult to implement. In this thesis, DL networks are physically informed through the data, network architecture, or loss function to create a model that accurately refects the underlying physics of the material system. First, a network is proposed to study the feasibility of 3D grain reconstruction from mid-feld high energy difraction refections. Each refection corresponds to its own subnetwork, tailoring the weights to a specifc refection. In a diferent network, a U-Net is used to simulate the micromechanical evolution of a 3D polycrystal at small strain increments and predict the full-feld orientation and elastic strain. The network is physically informed about the Von Mises stress relationship from the predicted elastic strain tensors. The training requirements of networks having physics-informed characteristics are studied in more depth using stress feld prediction as a case study. A Pix2Pix model is used to translate a two-phase composite having high elastic contrast to the corresponding stress fields. Several diferent physics-based regularization methods are implemented to enforce stress equilibrium in t (open full item for complete abstract)

Committee: Stephen Niezgoda (Advisor); Dennis Dimiduk (Committee Member); Reeju Pokharel (Committee Member); Aeriel Leonard (Committee Member); Michael Groeber (Committee Member) Subjects: Materials Science

Master of Science (MS), Bowling Green State University, 2023, Physics

Thin film metal oxide semiconductors have always been the materials of interest for various device applications due to their wide bandgap and interesting electrical properties. The role of defects in controlling these properties of the materials has also been widely known through extensive research. In order to use these materials for advanced device applications, it is necessary to characterize defects and understand their effect on the electrical properties. The main objective of this thesis is to study three different thin film metal oxide semiconductor samples of Gallium Indium Oxide named as depositions 55, 68 and 70 deposited by using the MOCVD technique. The samples were characterized to examine their electrical properties, and defects were studied to explain the origin of the electrical conductivity and resistivity shown by each of these samples. The samples were measured using Hall effect measurements for electrical characterization, and X-ray Diffraction (XRD) was used for structural characterization. Positron Annihilation Spectroscopy (PAS) technique was applied to study the vacancy type defects in these depositions. Hall effect results indicate that deposition 55 is the most conductive with high electron mobility and low value of sheet resistance, and it is found that this sample exhibits n-type conductivity. The electrical characterization data suggests that deposition 68 is the most resistive among the three depositions with high value of sheet resistance. Deposition 70 was found to exhibit n-type conductivity but showed higher value of sheet resistance as compared to deposition 55. Among the various techniques used for PAS, we applied Doppler Broadening Spectroscopy (DBS) for defects characterization of the depositions. DBS results show the presence of vacancy type defects in all of the three samples and indicate the crucial role of defects in the electrical properties exhibited by the thin films. The defects measurements were analyzed, and it (open full item for complete abstract)

Committee: Farida Selim Ph.D (Committee Chair); Marco Nardone Ph.D (Committee Member); Alexey Zayak Ph.D (Committee Member) Subjects: Physics

Master of Science (M.S.), University of Dayton, 2023, Aerospace Engineering

In recent years there has been a rapid expansion of UAVs being used for agricultural spraying. UAVs have many advantages, and their use has the potential to greatly benefit the agricultural industry through reduction in cost, labor, and potentially, off target contamination. There are currently conflicting claims within the literature regarding various factors involved in spraying with UAVs and the potential for drift from sprays emitted in their wake. This inhibits implementation of rules and regulations and can misinform operators of the best practices to ensure minimal drift of chemicals being applied. This is in part due to limitations in the robustness of testing practices being implemented, whether in field or laboratory settings. To explore this problem several experimental methods were employed to examine the effect propeller wake, nozzle location, and number of propellers have on agricultural spray droplet distributions. Experiments were conducted using standard agricultural nozzles sprayed at varying transverse and downwind distances from one of two APC 17x7 propellers at different RPMs. Traditional droplet size testing was performed by traversing the nozzle and propeller across a laser diffraction instrument to determine droplet size distributions. Results indicated a shift to larger droplet sizes with the introduction of propeller wake. However, flow visualization, volume collection, and shadowgraph images coupled with an extinction based statistical algorithm reveal a plume widening effect and significant oscillations induced by the propeller wake leading to a loss in total volume and significant reduction in probability of droplets existing downwind of the propeller due to finer droplets being carried away by the wake before reaching the measurement 4 plane of the laser diffraction instrument. The results clearly show that placing a nozzle directly beneath the propeller hub for both 1 and 2 propellers is the worst (open full item for complete abstract)

Committee: Sidaard Gunasekaran (Committee Chair); Timothy Anderson (Committee Member); Kyle Butz (Committee Member); C. Taber Wanstall (Committee Member) Subjects: Aerospace Engineering; Agriculture

PHD, Kent State University, 2023, College of Arts and Sciences / Materials Science Graduate Program

Waveguide liquid crystal display (WLCD) is a newly developed transparent display technology. Since polarizers and color filters are not necessary for the WLCD, high transparency is easily reached. A light-emitting diode (LED) is installed on the edge of the display and the produced light is coupled into the display. When no voltage is applied, the liquid crystal is uniformly aligned and is transparent. The incident light propagates through the display in waveguide mode due to the total internal reflection at the interface between the substrate and air, and no light comes out of the viewing side of the display. The display appears transparent. When a voltage is applied, the liquid crystal is switched to a micrometer-sized polydomain state and becomes scattering. The incident light is scattered out of the waveguide mode and comes out of the viewing side of the display. We developed a few methods to improve the performance of the waveguide display. First, by using patterned photo-polymerization or patterned ITO electrode, the scattering efficiency of the liquid crystal in the voltage-on state is significantly enhanced. Second, the spatial uniformity of the light intensity of the display is significantly improved by the light waveguide plate. Third, we achieved 8 inch full color transparent light waveguide LCD prototype that utilizes field sequential color (FSC) scheme to display full color images. Fourth, we developed a light waveguide LCD based on the flexoelectric effect using dimer, which exhibits high contrast ratio. Lastly, based on the flexoelectric effect we developed a reconfigurable liquid crystal diffraction grating whose diffraction angle and efficiency can be controlled by the applied voltage. The light waveguide liquid crystal transparent display has the merits of high contrast ratio, suitable driving voltage, and a sub-milli second ultrafast response time. It does not use polarizers and color filter as in conventional LCDs. It also has an ultrahigh tra (open full item for complete abstract)

Committee: Dengke Yang (Advisor); Philip J. Bos (Committee Member); Songping Huang (Committee Member); Sam Sprunt (Committee Member); Hiroshi Yokoyama (Committee Member) Subjects: Materials Science; Optics; Physics

Master of Engineering, Case Western Reserve University, 2023, Materials Science and Engineering

Understanding phase transitions and their behaviors are critical in nuclear fuel applications. The transmission electron microscopy (TEM) diffraction field is used to further the understanding of plutonium-zirconium alloys in metallic fuels. Indexing patterns to gain an understanding is time intensive for researchers. Convolutional neural networks (CNN) have exhibited exceptional performance in classification tasks in other fields. Applying them to selected area electron diffraction (SAED) patterns has yielded better than random results. A CNN is capable of classifying between three phase groups, at 650 patterns per second, with a total accuracy up to 83.74%. CNNs can also classify between two phase groups at 82.31% accuracy while being able to discern a difference between patterns of identical symmetry but distinct structure.

Committee: Jennifer Carter (Advisor); Sunniva Collins (Committee Member); Laura Bruckman (Committee Member) Subjects: Computer Science; Materials Science