Master of Science (MS), Ohio University, 2021, Mechanical Engineering (Engineering and Technology)

Turbulated micro-channels have been gaining focus and popularity in robotics, microelectronics, aerospace, automotive, and biomedical applications due to improved heat removal capability, light weight, and compact size. In this study, an experimental setup and numerical modeling was used to investigate the effect of turbulator morphology and location as well as the mass flow rate on the heat transfer performance of micro-channels subjected to external heat flux. The micro channels were made of C12200 copper and water was used as the working fluid. With respect the location of the turbulators along the channel length, three different types of micro-channels were tested: 1) single-turbulator micro-channels (STMC) 2) double-turbulator micro-channels (DTMC), and 3) triple-turbulator micro-channels (TTMC). The results suggested that the heat transfer performance of the turbulated micro-channels increased as the distance between turbulators increased. The highest heat transfer was evident in samples with a higher spacing between turbulators. From a fluid streamline analysis, it was found that introducing turbulators resulted in enhancing the mixing of the cooler fluid in the center of the channel with the warmer fluid near the channel wall. The turbulators caused the generation of a recirculation zone downstream. Finally, the amount of heat gained by the fluid increased as working fluid Reynold's number (Re) increased. However, the rate of heat transfer was found to be smaller when the Re was greater than 1400, as the microchannels reached their thermal saturation condition.

Doctor of Philosophy, The Ohio State University, 2006, Chemical Engineering

The goal of this study is to develop novel microfabrication methods and microfluidic devices for BioMEMS applications. The emphasis is on the development of new hot embossing techniques, the design of microfluidic functions and biocompatible packaging methods for polymeric microfluidic chips. First, two unconventional hot embossing techniques were developed: laser assisted and sacrificial template based hot embossing. In laser assisted embossing, localized micro patterning can be achieved on polymer surfaces with a cycle time of less than 1 minute due to the localized heating, which is comparable with that of micro injection molding. The sacrificial template based hot embossing solved the de-molding issue involved in conventional hot embossing especially for high aspect ratio microstructures. Embossing of microstructures with aspect ratio of 6 was demonstrated successfully and the possibility of laser assisted embossing in conjunction with sacrificial template embossing was investigated. A fishbone microvalve was designed based on the concept of super-hydrophobicity such that the valve function remains after protein blocking, a required step in some enzyme-linked immuno-sorbent assays (ELISA) applications to prevent non-specific binding. Compared with another type of super-hydrophobic microvalve developed based on the micro-/nano structure formation by chemical synthesis, the fishbone valve can be easily incorporated into the microfluidic designs. Polymer compact-disk (CD) microfluidic platform integrated with different fluidic features was designed and fabricated. We have demonstrated successfully that flow sequencing can be achieved on a CD-like microfluidic platform. For packaging microfluidic platforms, a new interstitial bonding technique has been developed, which bonds the polymer-based microfluidic platforms without introducing any alien materials in to microchannels. This method can easily bond biochips with complex flow patterns, but in a relatively smaller (open full item for complete abstract)

Master of Science, The Ohio State University, 2023, Earth Sciences

If the front page of Nature, which has featured Thwaites Glacier and other retreating glaciers throughout recent years, has taught us anything, it is that the snow—the snow that supports one sixth of the world's population—is melting. Never has it been more important to quantify snow globally and regionally, on the ground and from space, macroscopically and microscopically (Sturm et al. 2017). Snow specific surface area (SSA) plays an essential role in measuring all the aspects of snow, including the remote sensing of snow, the energy budget, and avalanche mechanics (Carlsen et al., 2017; Cohen and Rind, 1991; Lemmetyinen et al., 2018; Warren, 1982). Unfortunately, the best ways of measuring SSA accurately are laboratory methods, which are both expensive and time-consuming. The IceCube, an in-situ tool for measuring SSA quickly in the field, offers a promising alternative. However, its margins of error are uncertain. This study collected large samples of rounded grains, rounding facets, faceted crystals, and small samples of other grain morphologies in order to evaluate the errors associated with measuring SSA using the IceCube and micro-computed tomography (micro-CT) in the context of a large-scale campaign. Micro-CT measurements were used as validation data; however, snow samples were stored in a cold room at -26 °C for four to five months. The effects of the long storage time on the samples is largely unknown, and this is a limitation of the study. Given the assumption that the SSA of the samples, excluding fresh snow and other fragile grain morphologies, did not change significantly, the IceCube was found to have a positive bias of ~5% with a spread of ~15% for rounded grains, rounding facets, and faceted crystals. For all grain morphologies sampled, the IceCube was found to have a positive bias of ~5% with a spread of ~16%. Errors associated with using micro-CT as a validation method for snow microstructure measurements were also evaluated. This study revealed (open full item for complete abstract)

Doctor of Philosophy, Case Western Reserve University, 2020, EMC - Aerospace Engineering

For more than two decades researchers have sought to develop a micro aerial vehicle (MAV) capable of discrete remote surveillance and reconnaissance in hazardous environments where no other alternative means of observation exist. While some success has been found in multi-rotor designs such as quadcopters, these vehicles are limited in their flight duration, flight range, robustness, stealth, safety, and agility. Biology offers a source of inspiration in insect flight. Flapping-wing micro aerial vehicles (FWMAVs) have the potential to address the current shortcomings of MAVs. This dissertation approaches the development of FWMAVs by attempting to mimic two major flight components of a particular insect, the hawk moth Manduca sexta (L.). Novel methods are established to design, fabricate and assess the performance of artificial M. sexta forewings and a flapping-wing mechanism inspired by the M. sexta thorax. Results from forewing experiments indicate successful emulation of mass and forewing geometry, including camber. Flexural stiffness values are an order of magnitude greater than desired and suggest that membrane and venation structure material must change. However, lift production analysis reveals that the artificial forewings are capable of generating comparable amounts of force to naturally occurring M. sexta forewings. Kinematic simulations demonstrate advantages to using a Scotch yoke mechanism as opposed to a more traditional crank-slider mechanism to convert continuous rotary motion into oscillatory flapping-wing motion. A multibody dynamic simulation of a Scotch yoke mechanism and passively rotating forewings is developed as a tool to investigate areas of improvement for increased mechanism efficiency such as the addition of energy storing and releasing components and potential changes in mechanism geometry. Empirical performance data on various configurations of a flapping-wing system comprised of a Scotch yoke mechanism and artificial M. sexta forewings (open full item for complete abstract)

Master of Science (MS), Wright State University, 2019, Biological Sciences

Two closely related Caenorhabditis species, C. briggsae and C. nigoni are cross fertile and produce viable adult progeny. From C. nigoni mothers, F1 adult females are viable and fertile, F1 males are viable but sterile. In crosses that utilize C. nigoni males and C. briggsae hermaphrodites produce viable adult F1 females but F1 males arrest during embryogenesis. A mutation in the Cbr-him-8 gene is a recessive maternal-effect suppressor of male-specific lethality. Hybrid crosses with cbr-him-8 mutant mothers produce viable adult male progeny. The HIM-8 protein in C. elegans is required for the pairing of X-chromosomes during meiosis. This function is likely conserved in C. briggsae. Unpaired chromosomes are transcriptionally silenced in a wide variety of taxa. Based on this information it's been proposed that the meiotic silencing of unpaired chromosomes (MSUC) is suppressing an X-linked hybrid lethal gene responsible for male specific lethality. Multiple co-suppression assays identified two genes as candidate hybrid lethal genes, CBG30927 and CBG00239. These genes were knocked out with RNAi and CRISPR to evaluate if either of these genes were a hybrid lethal gene. sgRNA/Cas9 complexes and dsRNA of the candidate hybrid lethal genes was injected into C. briggsae hermaphrodites. Injections using CRISPR were able to disrupt expression of control targets but not the candidate hybrid lethal genes. Both RNAi and CRISPR injected nematodes were mated with C. nigoni males and the resulting progeny were scored for viable F1 males. From injections of dsRNA containing copies of CBG30927 or Cbr-hig-1, male progeny were derived. Cbr-hig-1 has a syntenic ortholog in C. nigoni that is not present in any other Caenorhabditis species. Several regions were identified in the C. briggsae and C. nigoni transcripts including an exon 5 extension that is responsible for a change in the predicted structure of the proteins that could be responsible for the dysgenic interactions.

Master of Science (MS), Wright State University, 2018, Biological Sciences

In the cross of C. nigoni males to C. briggsae hermaphrodites, all F1 males arrest during embryogenesis. However in the reciprocal cross there are some viable F1 male progeny. This unidirectional male-specific lethality in the F1 hybrids has been attributed to a hybrid lethal gene in a 500 Kb region of the X chromosome of C. briggsae. Cbr-him-8 is a recessive maternal suppressor of the male-specific lethal phenotype, due to the requirement of the him-8 protein for proper X chromosome pairing. Without proper pairing of any one of the chromosomes in the Caenorhabditis genome, genes present on the unpaired chromosome will be silenced due to a process known as meiotic silencing of unpaired chromosomes (MSUC). It has been proposed that MSUC-based silencing of the X-linked hybrid lethal gene is the mechanism by which the male-specific lethality is suppressed. Based on this model, a co-suppression assay was used to identify the hybrid lethal gene. Transgenic strains of C. briggsae were constructed via microinjection of bacterial artificial chromosomes (BACs) of small portions of the X chromosome in which the hybrid lethal gene resides. The BACs were mixed with pCFJ909, a plasmid containing a functional cbr-unc-119 gene, this mixture was then microinjected directly into the gonad of cbr-unc-119 mutant hermaphrodites. A proportion of the resulting progeny incorporated the injected DNA into their nucleus and formed heritable extra-chromosomal arrays. These offspring were then selected based on the rescue of the unc-119 phenotype. Transgenic hermaphrodites were then mated to C. nigoni males and scored for viable F1 male progeny. Two BAC rescued the male specific hybrid lethal phenotype. Multiple other BACs failed to rescue the lethality phenotype. Focusing on a single BAC clone, using gene groupings and pCFJ909 the number of possible genes have been narrowed to two candidate hybrid lethal genes within the BAC 08G05. As well as 5 candidate hybrid lethal genes in the non-adjacen (open full item for complete abstract)

PhD, University of Cincinnati, 2015, Engineering and Applied Science: Mechanical Engineering

This dissertation presents the fabrication and testing of a new design of an electro-osmotic flow (EOF) driven micro-pump. Considering thermal management applications, three different types of micro-pumps were tested using multiple liquids. The micro-pumps were fabricated from a combination of materials, which included: silicon-polydimethylsiloxane (Si-PDMS), Glass-PDMS, or PDMS-PDMS. The flow rates of the micro-pumps were experimentally and numerically assessed. Different combinations of materials and liquids resulted in variable values of zeta-potential. The ranges of zeta-potential for Si-PDMS, Glass-PDMS, and PDMS-PDMS were –42.5 to –50.7 mV, –76.0 to –88.2 mV, and –76.0 to –103.0 mV, respectively. The flow rates of the micro-pumps were proportional to their zeta-potential values. In particular, flow rate values were found to be linearly proportional to the applied voltages below 500 V. A maximum flow rate of 75.9 µL/min was achieved for the Glass-PDMS micro-pump at 1 kV. At higher voltages non-linearity and reduction in flow rate occurred due to Joule heating and the axial electro-osmotic current leakage through the silicon substrate. The fabricated micro-pumps could deliver flow rates, which were orders of magnitude higher compared to the previously reported values for similar size micro-pumps. It is expected that such an increase in flow rate, particularly in the case of the Si-PDMS micro-pump, would lead to enhanced heat transfer for micro-chip cooling applications as well as for applications involving micro-total analysis systems. The Si-PDMS micro-pump was modified to be used as a micro-scale heat exchanger for the thermal management of hot spots generated by microchips. Various cooling liquids including, deionized water, distilled water, borax buffer, and Al2O3 nano-particle solution, were tested and compared based on their flow rates and the increase in the temperature of the cooling liquid. A constant heat flux heater wa (open full item for complete abstract)

Master of Science, The Ohio State University, 2014, Atmospheric Sciences

The Great Basin National Park (GBNP) embedded sensor network (ESN) consisting of Lascar micro-loggers was established in 2006 to characterize near surface temperature and humidity. With respect to micro-logger networks, based on available literature, GBNP's ESN contains the densest deployment of micro-loggers (currently 15) above 3000 m in North America for a limited local area. Primary purposes were to assess local climate conditions, evaluate how climate may be changing and support other research projects with meteorological data. In this work, surface temperature lapse rates and surface specific humidity lapse rates were calculated and analyzed on three different time scales (annual, seasonal and monthly) using linear regression. Furthermore, the ESN was subdivided into different geographic subsets which encompass different elevation ranges and landcover types. Results indicated a calculated study-wide (2006 - 2012) mean annual temperature lapse rate, -6.0°C km-1, compared favorably to the common environmental lapse rate (ELR) value of -6.5°C km-1. However, surface temperature lapse rates varied considerably for different geographic subsets and time scales. Mean monthly temperature lapse rates for the entire study area varied from -3.8°C km-1 in January to -7.3°C km-1 in June. Additional variability was introduced when elevation zones were considered. For locations below 3000 m (all QC data), the mean monthly temperature lapse rate ranged from -3.6°C km-1 in January to -9.1°C km-1 in August. Perhaps more significant, in May and summer (JJA) surface lapse rates below 3000 m became quite steep. Here, surface lapse rates exceeded -9.0°C km-1 and approached the dry adiabatic lapse rate. Above 3000 m, surface mean monthly temperature lapse rates were more compressed ranging from -4.5°C km-1 in May to -7.3°C km-1 in September. Throughout summer, mean monthly temperature lapse rate differences between high elevations (> 3000 m) and low elevations (< 300 (open full item for complete abstract)

Master of Science in Engineering (MSEgr), Wright State University, 2014, Mechanical Engineering

Flapping wing micro air vehicles (FWMAV) have very unique flight mechanics in two-wing orientation. Many challenges arise with two wing configuration: lift production, design construction, and control systems. Control surfaces used in fixed wings can be used but at low Reynolds numbers they become less effective. In order to truly mimic insects with two wings, control mechanisms must be developed. Since MAVs are designed to navigate through confined spaces they need to have many degrees of freedom in motion. One way is to use a continuous variable transmission (CVT) mechanism, by integrating its infinite gear ratios to change the flapping frequency of each wing independently it will be able to generate a roll maneuver. In previous work, two motor designs were used; by using a CVT design an additional motor weight can be neglected. The work completed was the development of a cone CVT design for MAV use that could produce variable frequency in each wing. Testing and analysis of the prototype model shows the design as possible control method in MAVs.

Doctor of Philosophy (PhD), Wright State University, 2011, Engineering PhD

Recently, the use of micro-Doppler (µD) radar signatures for classification has become an area of focus, in particular for the case of dynamic targets where many components are interacting over time. To fully exploit the signature information, individual scattering centers may be extracted and associated over the full target observation. Due to the complexity of the target signature, the automated analysis is very difficult. However, the availability of ultra-fine resolution or micro-range (µR) resolution along with target scattering knowledge, can aid this process immensely. Here, we describe a feature extraction algorithm which utilizes both µD and µR data. We apply this algorithm to measured data to gain knowledge of dismount-radar phenomenology. Specifically, we associate µD/µR features to physical human components resulting in an intuitive and physically-relevant model. Additionally, we statistically characterize the radar cross-section (RCS) behavior of the individual body features.

PhD, University of Cincinnati, 2001, Engineering : Electrical Engineering

A novel approach for three-dimensional (3-D) display systems implemented with a micromirror array was proposed, designed, realized and tested. The major advantages of this approach include: (1) micromirrors are reflective and hence achromatic (panchromatic), (2) a wide variety of displays can be used as image sources, and (3) time-multiplexing can be introduced on top of space-multiplexing to optimize the viewing-zone arrangements. Real-time auto-stereoscopy and motion parallax were the goals for these single-user 3-D display systems. First, auto-stereoscopy allows an observer see left and right images without any special eyewear or head-tracking devices. Second, different pairs of stereoscopic images can be seen according to the viewer's head position under horizontal displacement, denoted by series of viewing zones, so horizontal motion parallax is provided. These 3-D display systems use two spatial light modulators (SLM). The first one acts as the image source, which is relayed onto the second SLM, a micromirror array. Micromirrors redirect the light into appropriate viewing zones. We used backlit transparencies and a color CRT as the first SLM, which exemplifies the wide acceptance of image sources. Three simplifications in the optical design were made to lower the actuation requirements of the micromirrors. First, a collecting lens was introduced so that the micromirrors needed uniform actuation in one dimension (horizontal). Second, an interleaved actuation profile of the micromirrors was introduced to dedicate odd columns of micromirrors for the right eye views and even columns for the left ones. Finally, a double-opening pupil was used to further lower the actuation requirements of the micromirrors. A two-view (left and right) 3-D autostereoscopic display system was first constructed. Left and right eye views in the forms of both still and motion 3-D scenes were displayed and viewers were able to fuse the stereo information. A multi-view (2 left and 2 right) (open full item for complete abstract)

Doctor of Philosophy, The Ohio State University, 2010, Chemical Engineering

Micro and Nano-fluidic devices represent an emerging new area of medical therapeutics and diagnostics. Micro and Nano-scale systems have unique properties that lead to increasing the control, accuracy, efficiency, and speed, while reducing waste and operator error of various medical tests and drug delivery techniques. In order to fully realize the potential of this exciting field the flow behavior of relevant systems must be studied and understood so that new devices can be properly designed. Confocal microscopy is a well developed technique in the area of medical imaging due to its thin focus planes, increased resolution, and 3D imaging capabilities. However, until recently it has not been a viable technique for imaging dynamic systems where fast image capturing is required. This is due to the point scanning nature of the traditional confocal system in which single pixel intensities are measured with a scanning photon multiplying tube. New high-speed confocal systems have been developed utilizing arrays of pinholes on spinning disks that enable the use of a camera for faster full frame detection. A high-speed spinning disk confocal microscope system has been developed at Ohio State to use for studying dynamic processes and flow behavior within micro and nano-scale devices. The high-speed confocal system was used to generate 3D particle tracking velocity profiles for fluid flow in a micro-channel. Gas-liquid bubble formation was studied in micro-channels and compared with simulations. It was determined that the dimensionless Capillary number, along with gas to liquid flow rate ratio and mixer geometry, could be used to accurately predict bubble size and frequency within a micro-channel mixer. The flow of biological polymers in a micro-contraction was studied to gain insight into the fundamental molecular behavior of long chain polymer systems, as well as study the flow behavior of long chain DNA solutions that may be present in useful micro-fluidic devices where c (open full item for complete abstract)

Master of Arts (MA), Ohio University, 2006, International Studies - International Development Studies

This research analyzes the impact of micro-finance on the lives of women in Temeke District, Dar-es-Salaam, Tanzania. Despite the growing number of micro-finance programs in Tanzania, limited analysis of the impact of micro-finance on women has been conducted. Women in Tanzania lack economic opportunities such as credit due to deep rooted traditional cultural barriers and existing social norms among others. A sample size of 71 respondents made up of 61 women borrowers from FINCA Tanzania and 10 staff members from FINCA Temeke branch office were used in the study. The results revealed that the majority of the women have experienced positive changes on their lives through micro-financial opportunities offered by FINCA Tanzania. Some women respondents encountered a wide ranging risks associated with taking a loan, including business, institution lending methodology and family constraints.

Master of Science in Engineering, Youngstown State University, 2013, Department of Mechanical, Industrial and Manufacturing Engineering

Not only due to its versatility and inexpensive availability, lab-on-a-chip integrates multitasks for a complete µTAS. Due to easy portability in micro-devices, microfluidics has potential to revolutionize in many applications that include food, pharmaceutical, biomedical and chemical industries, etc. Mixing is inevitable for the analysis of trace chemicals, drugs, bio-molecules, fluidic controls in microfluidics, etc. Such miniaturized microfluidics had already proven better over bulky instrumentations, because of time and transportation required in handling. In this work, both active and passive were computationally studied. Passive mixing is considered with the mass fraction at different velocities of various mixer models when the fluids are in contact with each other. A two dimensional comparative analysis was performed to see the degree of mixing on two standard geometries including T and Y for general purposes. Along with standard geometries including T & Y, combinatory models with more than two inlet ports were also investigated using ANSYS Fluent, finite volume software. The engulfment flow was the major reason responsible for the mixing process. The engulfment flow was one of the major reasons responsible for the mixing process. Diffusion is a dominant phenomenon in passive mixing at the junction where various inlets meet and convective process becomes prevalent. Identification of geometrical correlation with the flow field variables and mixing parameters are crucial for better mixing design. The active mixing would be mathematically modeled with additional body force in the momentum equation. Thus, active mixers are externally activated for better mixing possibilities than the time consuming and possible complex geometries in passive mixing. Concentration variances over time at the outlet were simultaneously compared in all models for mixing. Also average concentration was tracked over time so as to confirm uniformity in mixing. Active circular mixers w (open full item for complete abstract)

Master of Science, The Ohio State University, 2013, Mechanical Engineering

This experimental study focuses on the impact of operating conditions including entraining speed, sliding ratio, and load on micro-pitting performance of two typical bearing steels. Case hardened roller specimens made of alloy 9310 and through-hardened roller specimens made of alloy 485-2 are procured. Test matrices are defined according to the Latin Hypercube Space Filling Design of Experiment approach and executed to evaluate the micro-pitting performance of both materials by manipulating the speed, sliding ratio, load, and material. A two-disk test set-up is used for this purpose with each test documented by initial, interim, and final roughness, wear, and micro-pitting measurements. Before each test, a run-in process is implemented for the purpose of surface roughness break-in. By counting the distributed micro-pitted areas on the surface, a Micro-pitting Severity Index (MSI), defined as the ratio of the total micro-pitted area to the entire inspection area, is quantified for every test condition. Results indicate that the 9310 specimens showed significantly better resistance to micro-pitting compared to the 485-2 specimens, with nearly ten times lower MSI values. The data collected in this study establishes a database for micro-pitting failure of these two steel alloys that is required for validation of point contact lubrication models with circumferentially oriented surface roughnesses.

Master of Sciences, Case Western Reserve University, 2025, Materials Science and Engineering

Silicon nitride fluidic devices show promise in the application of high-heat-flux cooling for high-powered electronics. Such devices can be manufactured from layered ceramic tapes if the material and process are sufficiently developed. This work approaches the manufacture of such devices through three investigations. Firstly, the organic composition of two selected silicon nitride tapes was developed and refined, and an automated segmentation method was used to compare the particle size distribution (approximately 0.1 μm-10 μm) of tapes as a function of location. Secondly, various processes were refined in the manufacture of fluidic devices from alumina tapes, namely the identification of an appropriate lamination procedure, a prediction of shrinkage during sintering, and the development of flattening techniques to reduce curvature in the devices. Lastly, the mechanical behavior of green PVB-based tapes has been characterized as a function of tape stack thickness, strain rate, and surface, through the use of microindentation.

Doctor of Philosophy, The Ohio State University, 2024, Biomedical Engineering

Glioblastoma (GBM) is the most common malignant brain tumor, and even with standard treatment, median patient survival is only about 15 months. This poor prognosis is likely due to the extreme heterogeneity of GBM tumors and a unique tumor microenvironment (TME) that drives tumor cell invasion, adaptive drug resistance, and recurrence after treatment. Additionally, the blood-brain barrier (BBB) prevents most therapeutics from reaching the tumor. The failure of many promising drug candidates may indicate that current preclinical models do not accurately replicate tumor biology and human BBB function. Recent advances in bioengineering technologies have enabled the development of complex human cell based in vitro models that can be used to study disease mechanisms and test therapeutics. The goal of this dissertation was to utilize these tissue engineering and biofabrication tools to develop in vitro models that can be used to advance our knowledge of certain aspects of the GBM tumor microenvironment. First, a novel hydrogel was developed that supports physiological astrocyte phenotype. We used this hydrogel to study astrocyte activation in response to GBM cell secreted factors to better understand how astrocytes contribute to neuroinflammation in GBM. Second, we developed a 3D microfluidic blood brain barrier model using a brain mimetic ECM hydrogel, and third, we applied this 3D BBB model and demonstrated that it can be used to investigate how different populations of GBM tumor cells influence BBB permeability. These new bioengineered model systems will allow us to further investigate disease mechanisms and allow for the testing of novel drugs to treat GBM in the future.

Doctor of Philosophy, The Ohio State University, 2024, Welding Engineering

This research focuses on the non-destructive characterization of microstructures in Grade 91 (9Cr-1Mo-V) and Grade 92 (Fe-9Cr-2W-0.5Mo) steel welds. These alloys are creep strength-enhanced ferritic (CSEF) steels commonly used in fossil-fuel-fired and nuclear power plants. The weld integrity of these two steels is crucial for power plants' safe and reliable operations. Two welding processes, cold metal transfer (CMT) and flux-cored arc welding (FCAW), were investigated for the Grade 91 steel weld test samples. For the Grade 92 weld samples, three different heat inputs (low, medium, and high) of gas tungsten arc welding (GTAW) were utilized to replicate traditional field welding processes. The non-destructive evaluation (NDE) method used for this research was immersion ultrasonic testing (UT). Using a newly patented micro-resolution ultrasonic imaging methodology specifically designed to operate in the through-transmission configuration. A 20 MHz focused probe with an ultrasonic beam focal diameter between 250-300 μm was used as the transmitter. As the receiver, a laser vibrometer with a 6-10 μm beam diameter was used to produce highly resolved ultrasonic images with longitudinal and mode-converted shear waves. Based on the micro-resolution ultrasonic C-scan images obtained during this investigation, three microstructural regions, such as weld metal (WM), heat-affected zone (HAZ), and base metal (BM), were clearly identifiable. Various levels of ultrasonic amplitudes distributed over the three regions were correlated with electron beam backscattered diffraction (EBSD) images using grain size, grain boundaries, and dislocation densities. The results showed that areas with relatively higher ultrasonic amplitude levels were associated with smaller grains and higher dislocation densities, while areas with lower amplitude levels were associated with larger grains and lower dislocation densities. In addition, ultrasonic velocity data obtained across the three differ (open full item for complete abstract)

Master of Science in Engineering, Youngstown State University, 2024, Department of Electrical and Computer Engineering

As part of this project, a complex terahertz (THz) antenna was fabricated using two-photon polymerization (2PP), a highly precise additive manufacturing method. The design and rigorous simulation testing were conducted using Ansys HFSS, with a focus on achieving minimal losses. Special emphasis was placed on impedance matching, confirmed by the S11 parameter showing minimal power reflection over a large part of the THz band. The antenna was fabricated using OrmoComp, a hybrid polymer. A significant portion of the thesis is dedicated to fine-tuning the intricate fabrication steps necessary for producing complex designs, demonstrating the capability to also fabricate simpler structures. The most significant outcomes of this work on the highly directional THz antenna are the optimized process parameters such as slicing direction, way of printing, power and speed settings of laser for 2PP and finally development time of post processing, which enabled the production of the complex structure. The fidelity of the final fabricated design was verified using electron and light microscopy.

Master of Science, The Ohio State University, 2024, Food, Agricultural and Biological Engineering

This thesis discusses the use of fly ash particles coated by sulfurized vegetable oil created by our colleagues at the University of Illinois Urbana-Champaign to greatly increase the hydrophobicity of the material as partial replacement of carbon black in Hevea natural rubber composites. Composites created with surface modified fly ash retained their tensile strengths and crosslink densities up to 20 wt% replacement of carbon black, while composites created with unmodified fly ash only retained their physical properties up to 10 wt% replacement of carbon black. The partial replacement of petroleum-based carbon black in rubber-based products with fly ash would increase the sustainability of the rubber industry while simultaneously reducing the overall cost by using a waste-derived filler. The thesis will also discuss a micro-compounding procedure that was adopted from a saturated polyisobutylene-based thermoplastic elastomer to effectively compound, cure, and test natural rubber compounds with a polymer mass less than 10 grams. Based on tensile tests and crosslink density measurement using solvent swelling, this micro-compounding method was found to be comparable to conventional macro-compounding for use in laboratory settings when testing commercial Hevea and semicommercial guayule control polymers. Comparative tests of greenhouse guayule rubbers were also carried out.