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)

PHD, Kent State University, 2017, College of Arts and Sciences / Department of Mathematical Sciences

Using the Quadratic Covariation Differentiation (QCD) differentiation theory, we derive an infinite series non-smooth expansion of functions of solutions of Stochastic Differential Equations (SDE). We further derive the non-smooth QCD expansion explicitly in terms of the solution's transition density under additional smoothness conditions on the given SDE's drift and diffusion coefficients. We establish that, under certain smoothness conditions on the function acting on the SDE, our QCD expansion is the same as the Kloeden-Platen Stochastic Taylor Series expansion. We illustrate the applicability of these stochastic expansions with examples. We also extend our QCD expansion results from the SDE setting to the important hyperbolic Stochastic Partial Differential Equation (SPDE) setting with a non-smooth QCD representation and a non-smooth QCD expansion result for a rotated wave SPDE on the spatial lattice.

Master of Science in Engineering Mechanics, Cleveland State University, 2024, Washkewicz College of Engineering

This paper presents a computational finite element analysis (FEA) focused on the utilization of shape memory alloy (SMA) interfaces as thermal expansion compensators for ductile positive coefficient of thermal expansion (CTE) materials such as Aluminum 6061-T6. The investigation delves into the efficacy of superelastic, one-way, and two-way shape memory effects in mitigating thermal expansion-induced stresses within engineering structures utilizing beam components. The research examines critical structural factors in a fixed beam system such as thermally induced internal stresses and buckling resilience at varying thermal loads. Computational simulation software from ANSYS Mechanical was calibrated to fit previous data from the literature on commercially available NiTi-based SMA properties. Comparing noninterface and SMA-interfaced beam structures, this study demonstrates the potential of SMAs to mitigate thermally induced stresses, thereby enhancing the structural integrity and longevity of engineering structures in thermal gradient environments. Furthermore, this paper proposes potential industries where the implementation of SMA interfaces could prove advantageous over current thermal compensating practices, including aerospace, optical, and civil engineering. This paper also introduces employing two-way shape memory alloys (TWSMAs) in thermal compensation by using computational and numerical analysis to showcase that TWSMAs response can be trained to perform similarly to materials with a negative thermal coefficient. By leveraging the unique property of trained TSMAs of the bidirectional shape memory effect, the aim was to demonstrate a second stress-free thermal state at an elevated temperature to increase the structure's buckling resilience. This research underscores the practical feasibility and performance of SMA interfaces as thermal expansion compensators, setting the stage for further exploration of advanced SMA technologies.

Bachelor of Sciences, Ohio University, 2022, Biological Sciences

When a muscle is passively stretched, the sarcomeres within its fibers necessarily lengthen. Historically, the sarcomeres have been thought to lengthen uniformly as the muscle lengthens. However, preliminary unpublished work in the Hooper lab has suggested that, during the period of passive force decline following muscle stretch (see Introduction), muscles have non-uniform sarcomere lengths, and unpublished models show that decay of this non-uniformity can replicate the decline in passive force that occurs following muscle stretch. To fully investigate these preliminary observations, I used anti-myosin and phalloidin antibodies to view the thin and thick filaments of lobster (Panulirus interruptus) stomatogastric pyloric muscles fixed at different times after rapid stretches. Muscles fixed immediately after stretch contained sarcomeres lengthened to a variety of lengths and others at the unstretched length. Lobster stomatogastric sarcomeres therefore do not lengthen uniformly immediately after stretch. Sarcomeres of muscles fixed 5 seconds after stretch still showed a variety of sarcomere lengths, but with fewer unstretched sarcomeres and more areas where the sarcomeres had lengthened to a uniform length. Almost all sarcomeres of muscles fixed 10 seconds after stretch had the same length. This decrease in the sarcomere length range over time shows that, as passive force declined, the rates and amplitudes of sarcomere lengthening decreased, resulting in the sarcomeres achieving a uniform length as muscle passive force approached its steady-state value. These data suggest that the probability of any single sarcomere lengthening, and the amount it lengthens if it does so, is a function of the force acting on the sarcomere at each time following stretch. In summary, these data show that lobster pyloric muscle sarcomeres expand at non-uniform rates, and to non-uniform lengths, as a function of the passive force they experience following muscle stretch.

Doctor of Philosophy, The Ohio State University, 2016, Electrical and Computer Engineering

This thesis summarizes developments in rigorous, full-wave, numerical spectral-domain (integral plane wave eigenfunction expansion [PWE]) evaluation algorithms concerning time-harmonic electromagnetic (EM) fields radiated by generally-oriented and positioned sources within planar and tilted-planar layered media exhibiting general anisotropy, thickness, layer number, and loss characteristics. The work is motivated by the need to accurately and rapidly model EM fields radiated by subsurface geophysical exploration sensors probing layered, conductive media, where complex geophysical and man-made processes can lead to micro-laminate and micro-fractured geophysical formations exhibiting, at the lower (sub-2MHz) frequencies typically employed for deep EM wave penetration through conductive geophysical media, bulk-scale anisotropic (i.e., directional) electrical conductivity characteristics. When the planar-layered approximation (layers of piecewise-constant material variation and transversely-infinite spatial extent) is locally, near the sensor region, considered valid, numerical spectral-domain algorithms are suitable due to their strong low-frequency stability characteristic, and ability to numerically predict time-harmonic EM field propagation in media with response characterized by arbitrarily lossy and (diagonalizable) dense, anisotropic tensors. If certain practical limitations are addressed, PWE can robustly model sensors with general position and orientation that probe generally numerous, anisotropic, lossy, and thick layers. The main thesis contributions, leading to a sensor and geophysical environment-robust numerical modeling algorithm, are as follows: (1) Simple, rapid estimator of the region (within the complex plane) containing poles, branch points, and branch cuts (``critical points") (Chapter 2), (2) Sensor and material-adaptive azimuthal coordinate rotation, integration contour deformation, integration domain sub-region partition and sub-region-depend (open full item for complete abstract)

Doctor of Philosophy, University of Toledo, 2015, Chemistry

Research on control of thermal expansion of polymers has attracted significant attention, since polymers exhibit excellent mechanical and electronic properties, but suffer from high thermal expansion due to the thermal motion of their long molecular chains. Such problems can be addressed through formation of composites that contain an inorganic filler material. Filler materials reduce the thermal expansion of polymers through restriction of polymer chain motion. One particular area of interest is the introduction of negative thermal expansion (NTE) materials into polymer composites. The NTE property is expected to have an additional effect on the reduction of the coefficient of thermal expansion (CTE) of the composites. Several papers have demonstrated successful reduction of the CTE of polymer composites using cubic ZrW2O8, however, it is still unclear how much of this effect is caused by the NTE behavior, and how much is due to chain stiffening. To address whether the use of expensive NTE materials is justified, this project is designed to investigate the exact effects of NTE and chain stiffening on the reduction of thermal expansion of polymer composites. This objective was achieved through the preparation and testing of two sets of composites containing isomorphic particles with opposite thermal expansion (ZrW2O8 and ZrW2O7(OH)2¿2H2O), which possess identical chain stiffening effects. The first goal of the project was to synthesize two different particles that have identical morphology but opposite thermal expansion, with cubic ZrW2O8 as the NTE material of choice. The initial idea was to use a-Al2O3 (corundum), which has a known positive CTE value, as the second material. This phase can be obtained through heat treatment of AlOOH at about 1100 °C. The synthesis of AlOOH with controlled morphologies based on choice of synthetic conditions has been reported. Attempts on the synthesis of AlOOH were made through two different routes. Neither of them delivered par (open full item for complete abstract)

Doctor of Philosophy, University of Toledo, 2006, Physics

The main effort of the present dissertation is to establish a framework for construction of the numerical solution of the system of partial differential equations for the coefficients in the N-term expansion of the solution of the Boltzmann equation in Legendre polynomials, also known as the PN approximation of the Boltzmann equation. The key feature of the discussed solution is the presence of multiple waves moving in opposite directions in both velocity and spatial domains, which requires transformation of the expansion coefficients to characteristic variables and a directional treatment (up/down winding) of their velocity and spatial derivatives. After the presence of oppositely directed waves in the general solution is recognized, the boundary conditions at the origin of velocity space are formulated in terms of the arriving and reflected waves, and the meaning of the characteristic variables is determined, then the construction proceeds employing the standard technique of operator splitting. Special effort is made to insure numerically exact particle conservation in treatment of the advection and scattering processes. The constructed numerical routine has been successfully coupled with a solver for the Poisson equation in a self-consistent model of plasma discharge in argon for a two parallel-plate bare electrode geometry. The results of this numerical experiment were presented at the workshop on "Nonlocal, Collisionless Electron Transport in Plasmas" held at Plasma Physics Laboratory of Princeton University on August 2-4, 2005.

Doctor of Philosophy, The Ohio State University, 1999, Business Administration

As firms have responded to the increasing pressure to compete on a global basis, the process of incremental expansion has received considerable attention. The incremental approach to international expansion contends that firms build up their operations gradually to reduce uncertainty that stems from their operating in unfamiliar foreign countries. It has intuitive appeal, but empirical tests of the model have yielded mixed results. This dissertation sets out to better understand the process of international expansion by addressing two important questions: (1) Does the level of foreign market uncertainty firms face affect the extent to which they follow the incremental expansion process? And (2) why do firms that face similar foreign market uncertainty vary in their extent of incremental expansion?This study's data set consists of sixty-one Korean firms and covers the forty-three year period from 1954 to 1996. Unlike previous studies, which assumed a relationship between foreign market uncertainty and incremental expansion, this study provides empirical confirmation of the long-standing assumption that foreign market uncertainty increases the extent to which firms undertake incremental international expansion. By taking a contingency approach toward international expansion, this study also finds that firm, industry and host country characteristics moderate the relationship between foreign market uncertainty and incremental expansion. Specifically, when cultural distance is used as a measure of foreign market uncertainty, the results of this dissertation indicate that the effect of foreign market uncertainty on incremental expansion is weaker for firms that 1) have higher levels of organizational slack, 2) are operating in industries in which invested resources are more recoverable, or 3) are operating in foreign countries that offer greater labor-cost advantages. For the second and the third conditions, these results also hold true when firm inexperience is used as a (open full item for complete abstract)

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

Traditional conceptual-level aerodynamic analysis is limited to empirical and/or inviscid models due to considerations of computational cost and complexity. There is a distinct desire to incorporate higher-fidelity analysis into the conceptual-design process as early as possible. This work seeks to enable the use of high-fidelity data by developing and applying multi-fidelity surrogate models that can efficiently predict the underlying response of a system with high accuracy. To that end, a novel form of the multi-fidelity polynomial chaos expansion (PCE) method is introduced, extending the surrogate modeling technique to accept three distinct fidelities of input. The PCE implementation is evaluated for a series of analytical test functions, showing excellent accuracy in creating multi-fidelity surrogate models. Aerodynamic analysis of a generic hypersonic vehicle (GHV) is performed using three codes of increasing fidelity: CBAERO (panel code), Cart3D (Euler), and FUN3D (RANS). The multi-fidelity PCE technique is used to model the aerodynamic responses of the GHV over a broad, five-dimensional input domain defined by Mach number, dynamic pressure, angle of attack, and left and right control surface settings. Mono-, bi-, and tri-fidelity PCE surrogates are generated and evaluated against a high-fidelity “truth” database to assess the global error of the surrogates focusing on the prediction of lift, drag, and pitching moment coefficients. Both monofidelity and multi-fidelity surrogates show excellent predictive capabilities. Multi-fidelity PCE models show significant promise, generating aerodynamic databases anchored to RANS fidelity at a fraction of the cost of direct evaluation.

Doctor of Philosophy, Case Western Reserve University, 2024, Biology

The calvaria is composed of interlocking plates of bone with sutures that encase the brain. Calvarial development is an error-prone process potentially leading to persistent gaps between bones or premature suture fusion (craniosynostosis, CS), impacting the brain and sensory organs. The mechanism of directional growth of the calvarial bones and impact on suture patency remains unknown. Here, we identify that graded expression of fibronectin (Fn1) in the mouse embryonic cranial mesenchyme (CM) precedes the apical expansion of calvarial osteoblasts. In humans, syndromic forms of CS exhibit dysregulated fibronectin expression. We find Fn1 expression altered in several mouse CS models as well, including Apert, Crouzon and Twist1+/- mouse embryos, accompanied by abnormal apical expansion of the frontal bone primordia. We hypothesize that fibronectin expression in CM is required for both the apical expansion of calvaria and maintenance of suture patency. Conditional deletion of Fn1 in CM causes diminished apical frontal bone expansion by altering cell shape and actin enrichment without perturbing other cell behaviors. To address how osteoprogenitors use FN1, we conditionally ablate Wasl/N-Wasp in cranial neural crest cells to disrupt F-actin nucleation in lamellipodial protrusions. Dramatic reduction in apical expansion occurs in Wasl mutants, phenocopying Fn1 mutants without a significant change in proliferation, survival, or osteogenesis. Additionally, we find that CM-restricted Fn1 deletion leads to premature fusion of coronal sutures at 81% penetrance. The Fn1 mutants show decreased levels of suture mesenchyme markers, Six2 and Erg, in coronal suture space. The coronal suture mesenchyme has diminished proliferation index and ectopic expression of osteogenic cell markers suggesting premature differentiation. These data support a model of FN1 as a directional substrate for calvarial osteoblast migration that may be a common mechanism underlying many cranial disorders of (open full item for complete abstract)

Master of Science, Miami University, 2024, Biology

Lyme disease, caused by the bacterium Borrelia burgdorferi , is transmitted to humans through ticks, and it has become an increasing problem in the Midwest. In recent years, cases have been expanding from a hotspot in Wisconsin to Michigan's Lower Peninsula (LP) along the coastline of Lake Michigan. The expansion of cases coincides with increasing populations of deer tick, Ixodes scapularis , and of the white-footed mouse, Peromyscus leucopus , which serves as the primary reservoir host for the bacterium. A study from 2010 testing the infection prevalence in both deer ticks and white-footed mice found no infections in either species in most of the northern LP. For this study, mice were trapped along a transect from the edge of the known range of infected mice northeastwards toward the tip of the LP. Infected mice and ticks were found more than 100km beyond the previous limit but were not found along the eastern part of the transect. The proportion of P. leucopus carrying ticks was correlated with higher infection prevalence in both ticks and mice.

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

This dissertation focuses on the coordinated operation and expansion planning of power and freshwater systems in regions experiencing freshwater shortages. Our work is motivated by the important challenges posed by the increasing installation of desalination plants, which rely almost exclusively on electricity to produce freshwater, and link power and freshwater systems. We propose models and solution techniques to address these challenges, namely, comprehending the coordinated operation of power and freshwater systems, investigating such coordination in the case of high renewable penetration, and studying the expansion planning and operation of fully renewable power and freshwater systems. Each of these challenges is comprehensively analyzed in separate chapters of this dissertation. The first challenge pertains to coordinating the operation of power and freshwater systems. We propose a model that integrates the dispatch of the freshwater system with the network-constrained scheduling of the thermal units of the power system, where the freshwater electric loads are incorporated into the supply-balance constraints of the power system. This model is mixed-integer nonlinear due to the nonlinear constraints describing the operation of the freshwater system. To achieve tractability, we employ a piecewise linearization technique to approximate nonlinear single-variable constraints and a triangular linearization to approximate nonlinear two-variable constraints. We conclude that a coordinated operation of the power and freshwater systems yields lower operation costs for both systems as compared to an uncoordinated operation. The second challenge pertains to the integration of weather-dependent renewable units and its impact on the coordinated operation of power and freshwater systems. We propose a model that integrates the dispatch of the freshwater system with the network-constrained scheduling of the thermal units of the power system, and includes a (open full item for complete abstract)

MS, Kent State University, 2023, College of Arts and Sciences / Department of Biological Sciences

Eastern redcedar (Juniperus virginiana L. var. virginiana) is a native species currently invading open areas and grasslands outside of its original range in the United States. I studied the eastern redcedar's (ERC) invasion patterns in the Lakeside Daisy State Nature Preserve (LDSNP), a short grass prairie located on the Marblehead Peninsula in Ohio, examining the changes in the genetic diversity and structure of the encroaching population. I investigated the relative importance of long-distance dispersal vs. diffusion in the invasion of this short grass prairie by ERC. I used eight microsatellite marker loci and a database of single nucleotide polymorphisms to infer gene flow from external sources vs. within-population recruitment. I found that the older trees in this preserve were less than fifty-years-old, indicating that the population was established between 1970 and 1980. When I grouped trees into five age categories of 10-year increments, we found that the allelic diversity, as indicated by the average number of alleles per locus, increased as the age of the trees decreased. Principal Coordinate Analysis showed two distinct groups of trees in the LDSNP that I investigated further using soil type. Analysis of the population structure of the ERC trees using ADMIXTURE revealed three ancestral clusters in the ERC populations. All ancestral clusters are present in all age groups, suggesting that there is continual input of genetic information from the ancestral clusters. Overall, my findings indicate that ERC encroachment of the LDSNP results from multiple and reiterated gene flow events from the edge of the range through animal-mediated seed dispersal at short and intermediate distances.

Bachelor of Science (BS), Ohio University, 2023, Economics

Many policymakers support universal healthcare to improve the health of the population. Some economists, however, are concerned that universal healthcare policy may negatively impact the general health of the population due to ex-ante moral hazard whereby a higher level of risk is incurred by the insured. In this paper, I analyze ex-ante moral hazard using the Medicaid expansion with the risky behavior of driving under the influence (DUI) on accidents involving drinking, accidents involving drugs, accidents in which the driver is not wearing a seatbelt, and DUI arrests by state. Unique to this study, I compile the data on risky driving behavior from the Federal Bureau of Investigation (FBI) and the National Highway Traffic Safety Administration (NHTSA). Then, I use a difference-in-differences model to identify the effect of the Medicaid expansion on the number of DUI arrests at the state level. I find that there is a no effect at the state level of the Medicaid expansion on passenger vehicle accidents involving drinking, drug impairments, driver not wearing a seatbelt, or DUI arrests. Therefore, I fail to provide evidence of ex-ante moral hazard in this context. This means there is no evidence that any of the mentioned risky driving behaviors increase at the state level as a result of expanding Medicaid.

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

A 32.5% water-urea mixture, commercially known as AdBlue®, is stored onboard diesel vehicles as a liquid within storage tanks and is used for exhaust aftertreatment. In cold weather conditions, the mixture may freeze and expand over the span of several hours or days, resulting in the damage of the enclosing tank. However, computational modelling of the solidification/melting process in tanks of such “large” size and over such “long” durations is a challenging task, partly due to the simultaneous presence of all three phases (solid, liquid and gas). Furthermore, as natural convection plays an important role during the freezing process, it cannot be ignored. Capturing the dynamics of natural convection requires the use of extremely small time-step sizes, in relation to the overall freezing time scales, which significantly affects the computational speed of these simulations. This fact is demonstrated in the preliminary assessment phase of this study, where the in-built models of the commercial CFD solver ANSYS FluentTM are utilized to study the freezing process in a simple, small, partially filled 2D tank. Results show that though the models are able to provide great physical details of the solidification process, they result in impractically long simulation run times (~year). This led to the main objective of this work: the development, validation, and demonstration of an efficient 3D computational model that can be used to model the solidification process in large, partially-filled tanks containing either water or Adblue®. The first part of this work developed a new “reduced” model that accounts for the heat transfer due to natural convection during solidification/melting but, ignores the movement of the gas-(solid/liquid) interface due to expansion of ice. This new reduced natural convection model bypasses solving for flow and reduces the energy equation to a pure conduction equation by modeling convective heat fluxes using an equivalent conductive heat flux via (open full item for complete abstract)

Doctor of Philosophy, Case Western Reserve University, 2022, Biomedical Engineering

Patients with inadequate stent expansion are at high risk for adverse outcomes, including stent thrombosis as well as in-stent restenosis. Both are well-described complication usually causing acute coronary syndromes and, in the worst-case scenario, sudden cardiac death. Once a stent is deployed in atherosclerotic tissue that is highly resistant to dilation, it is often tricky to fully expand the implanted stent, even using a noncompliant balloon. Careful evaluation of these risks prior to the intervention will aid treatment planning, including potential application of a plaque modification strategy. Moderate to severe calcification in the treated vessel restrict full deployment of a stent. Intravascular optical coherence tomography (IVOCT) is a useful tool to identify calcification lesion severity, reference vessel size, lesion length, and extent of calcification for PCI planning. In addition, IVOCT imaging provides detailed evaluation of stent deployment including areas, stent expansion index, floating stent struts and stent dissection. In this dissertation, we developed a machine learning method to predict stent deployment with the intervention of creating software that one can use to identify lesions needing a plaque modification strategy. However, we confronted a challenge in that IVOCT single pullback generated more than 500 images in less than 2.5 second scan. The need for specialized training, uncertain interpretation, and image overload required automated analysis of IVOCT images. Therefore, we built on previous studies and used deep learning to perform semantic segmentation of the lumen and calcification within IVOCT images. We evaluated our segmentation model on manually annotated IVOCT volumes with calcifications, lipidous, or mixed lesions. We obtained sensitivities of 0.85 ± 0.04, 0.99 ± 0.01, and 0.97 ± 0.01 for calcified, lumen, and other tissue classes, respectively. Segmented lumen and calcifications labels were then used to develop the stent u (open full item for complete abstract)

PHD, Kent State University, 2021, College of Arts and Sciences / Department of Geography

Cancer epidemiology has a long history of applying geographic thinking to address long-standing place-based disparities. This dissertation adds new knowledge to geospatial approaches to social determinants of cancer outcomes. It establishes a framework consisting of three dimensions in evaluating, identifying, and prioritizing spatially heterogeneous risk factors of cancer outcomes. The first dimension is protection. Using a space-time statistic, the first study evaluated whether a non-spatial healthcare policy, Medicaid expansion, has offered protection targeting spatially vulnerable populations against adverse cancer outcomes such as breast cancer late-stage diagnosis. The second dimension is phenotype. Using a classification and regression tree, the study disentangled how risk factors of late-stage breast cancer diagnosis were conceptualized and capsulized as phenotypes that labeled groups of homogenous geographic areas. It provides a novel angle to uncover cancer disparities and to provide insights for cancer surveillance, prevention, and control. The third dimension is priority. Using a geographic random forest along with several validation methods, the study emphasized the importance of the competing effect among risk factors of cancer mortality that are specific to geographic areas. The findings from this study can be used directly for priority settings in addressing the most urgent issues associated with cancer mortality. This dissertation demonstrated that geographic methodologies and frameworks are useful and are imperative to cancer epidemiology.

PhD, University of Cincinnati, 2021, Engineering and Applied Science: Aerospace Engineering

The overarching objective of this research is to investigate novel aircraft engine exhaust nozzle concepts in search of acoustically quieter designs that offer benefits in multiple areas of operations. They include transonic to supersonic regime operations in both civil and military aviation sectors. Exhaust systems are a crucial component of aerial vehicles that tremendously impact their aero-propulsive as well as acoustic and stealth characteristics. Thus, in this endeavor to investigate a nozzle design that has the potential to meet current generations' highly demanding performance requirements, this research focuses on a type of rectangular nozzle called Single Expansion Ramp Nozzle (SERN), with moderate to high aspect ratio configurations. The overarching objective of this research is to investigate novel aircraft engine exhaust nozzle concepts in search of acoustically quieter designs that offer benefits in multiple areas of operations. They include transonic to supersonic regime operations in both civil and military aviation sectors. Exhaust systems are a crucial component of aerial vehicles that tremendously impact their aero-propulsive as well as acoustic and stealth characteristics. Thus, in this endeavor to investigate a nozzle design that has the potential to meet current generations' highly demanding performance requirements, this research focuses on a type of rectangular nozzle called Single Expansion Ramp Nozzle (SERN), with moderate to high aspect ratio configurations.

Master of Science (M.S.), University of Dayton, 2021, Electro-Optics

The durability of thin film optical interference filters, integrated in systems ranging from imaging sensors to energy-efficient IR-blocking windows, is affected by its stress. The purpose of this work is to explore the thermal stress in thin films, the result of a contrast in the coefficient of thermal expansion (CTE) between the substrate and the film. While much research is focused on thin film intrinsic stress, thermal stress should also be considered for systems designed for high temperature variability and for systems where the film and substrate material properties vary greatly. This work characterizes the coefficient of thermal expansion and the Young's Modulus of SiO2 and Ta2O5 films, common low and high-index optical materials, along with composite SiO2-Ta2O5 thin films grown by reactive co-sputtering. A model for the variation of the CTE as a function of film composition is proposed, showing general agreement with the measured data. Characterization of the thermal stress in the film-substrate system is measured using a custom-built instrument, and the Young's Modulus is verified using nano-indentation. A method for evaluating the instrument noise, and its effect on the precision of the calculated CTE and Modulus values is characterized for this instrument. A model is proposed to enhance future designs-of-experiment using this instrument.

Doctor of Philosophy, University of Toledo, 2021, Physics

This dissertation is a systematic computational investigation of transition metal nitrides in M4N structure and in two alloy systems of Ti1-xScxN and Ti1-xYxN (0 ≤ x ≤ 1). Transition metal nitrides constitute a class of materials which have been broadly applied in the industry of hard coatings and cuttings. Our objective is to expand the currently existing database of these materials by exploring their structural, mechanical, magnetic, electronic, and thermodynamic properties, stability and hardness using the state-of-the-art first principles computational approach. Chapters 4 and 6 contain the main results and are summarized as follows. 1. We performed first-principles calculations with density functional theory on 28 metal rich cubic binary M4N structures. We provided a high through-put database of mechanical, electronic, magnetic, and structural properties for these compounds. We observed three compounds with Vickers hardness around or above 20 GPa, such as Re4N, Tc4N, and Mn4N (Chapter 4). We also identified 25 M4N compounds as mechanically stable while the remaining 3 (V4N, Nb4N, and Pt4N) as unstable. 2. We showed the relationship between the hardness and stability of these compounds and the density of states. We also calculated the magnetic properties of five magnetic compounds and exhibited that the consideration of electronic spin-polarization is very important in accurately calculating ground state energy and hence mechanical properties of these transition metal nitrides. 3. We also studied the phase stability, mechanical and electronic properties of two ceramic quasi-binary systems, Ti1-xScxN and Ti1-xYxN using density functional theory, cluster expansions and Monte Carlo simulations. We predicted strong exothermic mixing of TiN and ScN due to cationic similarity with the formation of 4 novel intermetallic compounds TiScN2, TiSc8N9, TiSc9N10, and Ti3Sc2N5 in the Ti1-xScxN system having hardness as high as 27.3 GPa. The phase diagram of Ti1-xScxN sys (open full item for complete abstract)