Doctor of Philosophy, The Ohio State University, 2016, Materials Science and Engineering

Gallium ion irradiation in dual-beam FIB microscopes is well known to cause some degree of damage during the milling process. Although it has been established that cleaning passes with low energy ions can mitigate the extent of this damage, the mechanisms, extent, and type of damage caused have not been well studied due to geometrical limitations inherent to thin foils. By adapting the needle geometry used for atom probe and tomographic work, we can directly measure the extent of damage layers created during milling. Needles were made of multiple semiconductor, intermetallic, and metal systems, confirming previous estimates of damage thickness in Si and GaAs. Materials tested fell into two distinct classes, amorphous dominated and crystalline defect dominated. Amorphous dominated materials consisted of semiconductors and narrow phase field intermetallics, fitting previous radiation work. Crystalline defect dominated materials had semi-crystalline damage layers under 5 nm at all accelerating voltages, and residual defects were shown to have significant effects on lattice clarity in HAADF-STEM. Contrast between amorphous layers in HAADF-STEM was found to be minimal even under ideal conditions, and HRTEM was necessary to accurately confirm and measure damage layer thickness. The causes and extent of damage layer minimization during low keV milling steps were shown to be consistent across all materials.

Doctor of Philosophy, University of Akron, 2016, Mechanical Engineering

In this dissertation, a comprehensive study of ductile damage of metallic materials is presented, covering constitutive modeling, numerical implementation and model calibration and verification. As the first part of this dissertation, a pressure-insensitive plasticity model, expressed as a function of the second and third invariants of the stress deviator (J2 and J3), is presented. Depending on whether the power of the J3 term is odd or even, the proposed model can capture either the tension-compression strength-differential (S-D) effect or the torsion-tension strength-differential effect of the material. The plasticity model with an odd power to the J3 item has been calibrated and validated using measured experimental data of a ß-treated Zircaloy-4 with a wide range of triaxiality and Lode parameter values. Results show that this model captures the strong strength-differential (S-D) effect in the material. The plasticity model with an even power to the J3 item is able to capture the isotropic plastic behavior of a stainless steel Nitronic 40, under various stress states with good accuracy and computational efficiency. Next, the effect of the material's plasticity behavior on the ductile damage process is studied by conducting a series of unit cell analyses of a void-containing representative material volume (RMV), where the plastic response of the matrix material is governed by the J2-J3 dependent plasticity model. To simulate the ductile damage process in anisotropic materials, a new constitutive model, which combines the models proposed by Zhou et al. (2014) and Stewart and Cazacu (2011), is developed and employed to study the plasticity and ductile fracture behavior of a commercially pure titanium (CP Ti). In particular, a Gurson-type porous material model is modified by coupling two damage parameters, accounting for the void damage and the shear damage respectively, into the yield function and the flow potential. The plastic anisotropy and tension-compre (open full item for complete abstract)

Doctor of Philosophy, Case Western Reserve University, 2015, Biomedical Engineering

Cartilage tissue engineers have made great inroads on understanding the factors controlling chondrogenesis, however, the biomechanical properties of tissue engineered cartilage (TEC) are chronically inferior to that of native cartilage. The focus of this dissertation was to determine the ability of scaffold-free TEC to withstand frictional-shear stress, and if needed, to improve that ability to a physiologically relevant level. Frictional-shear testing performed at a sub-physiological normal stress of 0.55 MPa demonstrated that constructs exhibited lubrication patterns characteristic of native cartilage lubrication, but severe damage also occurred. Low absolute collagen content, and a low collagen-to-glycosaminoglycan (GAG) ratio were also found in the same constructs. Reduction in damage was attempted by increasing the collagen content of the ECM. Scaffold-free TEC treated with T4 at 25 ng/ml exhibited increased collagen concentration in a statistically significant manner, and the average collagen-to-GAG ratio was also increased although statistical significance was not achieved. Western blotting showed that type II collagen was increased, type X collagen was not detected. COL2A1, and biglycan gene expression were also found to have increased, no statistically significant difference was found for COLX gene expression. When compared to control constructs, T4 treated constructs exhibited a large and statistically significant decrease in the extent of damage incurred by frictional-shear testing. At the 2.8 MPa normal stress, total damage was reduced by 60% in the 2-month constructs. Correlation coefficients calculated between compositional properties and the amount of damage showed that at the 2.8 MPa normal stress collagen concentration and the collagen-to-GAG ratio exhibited the greatest correlation to damage (correlation coefficient of approximately -0.7 with a 95% confidence interval of approximately -0.87 to -0.38 for both). In conclu (open full item for complete abstract)

Master of Science, The Ohio State University, 2010, Physics

The GMR effect has revolutionized the information technology industry. GMR read-out heads, MRAM and magnetic field sensors have become standard technologies of today's society, while magnetic random access memory (MRAM) is one of several applications of this effect which are in earlier stages. The presumption is that these materials are radiation hard with respect to both photons and particles, potentially indicating utility for nuclear energy and space based applications. However, few detailed studies of magnetism in GMR devices have been performed in radioactive environments. This work explores the effects of gamma ray and neutron irradiation on GMR spin valves. The sample structure used in this experiment is Py/Cu/Py/FeMn/Ge. To study the effects of radiation three probes of magnetization, VSM, MR, and MOKE, are correlated pre and post radiation. We present characterization of the devices for multiple device geometries and doses up to 50Mrad for gamma rays and a minimum fast flux of (En>0.5MeV) of 6.3E12 nv for neutrons, both of which are well above the failure threshold for radiation-hard semiconducting devices. We found that these devices were hard to both gamma and neutron irradiation, but that there were environmental factors that caused accelerated aging of our samples during the gamma irradiation experiment. We show follow-up studies based on these results, and future experiments that are currently in their early stages.

Doctor of Philosophy, University of Akron, 2024, Mechanical Engineering

Gigantic off-the-road (OTR) tires used in mining industries are usually damaged and both their damage resistance and damage mechanisms of fiber-reinforced rubbers have not been well understood. In order to optimize OTR tire fillers and mechanical properties, the damage resistance needs to be studied under consideration of size independence and size dependence. In this research, rubbers reinforced with different fiber stiffness and varied fiber amount fabrics were fabricated by vulcanization. The mechanical properties including performance of tensile, scratch, impact, fracture, and debonding were studied under size-independent condition. Natural rubber (NR) having a lower stiffness was better than styrene-butadiene rubber (SBR) in tensile and fracture performance. Increasing fiber stiffness and fiber amount improved tensile, scratch, and impact resistance. Reinforcing Kevlar fabric reduced the matrix crack occurrence in the impact test and the damage level in the scratch test. Carbon fiber-reinforced rubber had the most serious damage level in the scratch and impact test. The fracture toughness decreases with increasing fiber volume ratio and fiber stiffness. The delamination resistance rises as fiber ductility reduces. In the studies of fracture performance, we studied both the thickness effect and the length-width effect. Increasing the SBR thickness to fourfold (3 mm, 6 mm, 9 mm, and 12 mm) exhibited decreased fracture toughness and the varied stress state from plane stress to plane strain in compact tension (CT) tests. For delamination resistance, a higher matrix thickness caused more energy dissipation to increase the adhesion strength. In the study of the length-width effect, specimens tested using single-edge-notched tension (SENT) had increased the same proportion length and width, and unvaried thickness (3mm) to evaluate the size effect under plane-stress condition. The fracture toughness of the unreinforced rubbers was independent of re (open full item for complete abstract)

Doctor of Philosophy, The Ohio State University, 2022, Civil Engineering

There are three main research conducted in this paper, including using deep learning methods with vision-based technologies on Structural Damage Detection (SDD), Structural Health Monitoring (SHM) and progressive collapse study. During the learning and improvement process, many goals of automation in SDD and SHM have been achieved, although there will be a large room for further improvement and development on these studies. In progressive collapse study, remote sensing technologies and data fusion are applied on a field experiment of a real building at the Central Campus of the Ohio State University. The major contributions of this paper are shown as follows: A few comprehensive experimental studies for automated SDD in extreme events using deep learning methods for processing 2D images. In the first study, a 152-layer Residual Network (ResNet) is utilized to identify multiple classes in eight SDD tasks, which include identification of scene levels, damage levels, material types, etc. The proposed ResNet achieved high accuracy for each task while the positions of the damage are not identifiable. In the second study, the existing ResNet and a segmentation network (U-Net) are combined into a new pipeline, cascaded networks, for categorizing and locating structural damage. The results show that the accuracy of damage detection is significantly improved compared to only using a segmentation network. In the third and fourth studies, end-to-end networks are developed and tested as a new solution to directly detect cracks and spalling in the image collections of recent large earthquakes. One of the proposed networks can achieve an accuracy above $67.6\%$ for all tested images at various scales and resolutions, and shows its robustness for these human-free detection tasks. Studies are conducted with a pipeline to automatically track and measure displacements and vibrations of structures or structural components in laboratory and field experiments. This novel framework (open full item for complete abstract)

MS, University of Cincinnati, 2021, Engineering and Applied Science: Mechanical Engineering

Vibration-based damage detection methods have been extensively used in structural health monitoring as these are response-based techniques and can be applied to experimental/operational data. The conventional methods of obtaining full-field vibration measurements are limited due to the location and number of sensors. Advancements in imaging technology have enabled the use of the digital image correlation (DIC) technique to measure the full-field deformation of a vibrating structure. In this study, the DIC technique was used to obtain vibration measurements from an impact test of a cantilever beam for damage identification. The application of curvature mode shapes (CMSs) developed from the mode shapes (MSs) of the beam is studied to detect and locate the damage. The CMSs of the undamaged state of the beam are determined only from the damaged state of the beam, without prior information about the associated undamaged beam, provided the beam is geometrically smooth. It is shown that the polynomial fit of the appropriate order of measured MS is equivalent to the associated MS of the undamaged beam. The objective of this study was to investigate the use of DIC technique and CMSs to locate and detect damage in the form of a machined area with reduced thickness in a cantilever beam. The modal parameter estimation (MPE) was done using X-Modal software, based on the unified matrix polynomial approach (UMPA), to obtain mode shapes and natural frequencies from the vibration measurements. It is shown that the proposed method can successfully detect and locate damage in the beam, for the data obtained from a single-input impact test. The work focuses on understanding how the parameters used in the DIC technique and MPE influence the damage detection. The influences of parameters such as subset size and step size used in the DIC technique are studied. The influences of parameters such as type of MPE algorithm, frequency band selection and model order during MPE are studied. (open full item for complete abstract)

Master of Science, The Ohio State University, 2021, Mechanical Engineering

Teeth of a gear undergo cyclic forces as they rotate in and out of the gear mesh contact zone. The resultant contact and bending stresses produce fatigue damage, which can lead to failure through contact surface degradation and tooth breakage through the root fillet. The fatigue process is not instantaneous, and damage accumulates at different rates throughout the fatigue life. Many proposed diagnostic techniques to detect the onset of gear failure rely on changes in mechanical properties due to crack growth. Moreover, theoretical studies to predict fatigue crack growth rate rely on only a few experimental measurements for their validation with little extension to gears. The focus of this study is to develop an optics-based system for measuring surface crack length coupled with an acoustic emission system for measuring the release of elastic stress waves generated in the tooth root of a fatiguing spur gear, which may be related to early life fatigue damage. A gear single-tooth bending machine, a high-speed camera, and an acoustic emission sensor are utilized in unison to demonstrate the methodology. A digital image correlation technique is used to compute crack length during each load cycle to obtain cyclic crack growth rate, and acoustic emission signals are examined for signature behaviors.

MS, University of Cincinnati, 2019, Arts and Sciences: Biological Sciences

Hyperthermophilic Archaea have adapted to unusual and extreme habitats and the mechanisms they employ to maintain their genomic integrity have been elusive for quite some time now. The hyperthermophilic archaeon Sulfolobus acidocaldarius, despite its extreme optimal growth conditions of about 80° C and pH 3, is capable of preserving its genomic integrity. Hence, it will be used as the model organism to understand the DNA damage coping mechanisms representing hyperthermophilic Archaea. The three specific goals of this thesis are as follows: 1) Investigate genes implicated to deal with oxidative stress, 2) Identify AP endonuclease genes and investigate their biological roles and, 3) Examine the association of accessory polymerases with DNA repair and damage-tolerance pathways. The approach involved the construction of mutant strain(s) of the genes implicated to be involved in DNA repair or damage-tolerance and, investigation of its effects using a combination of in vitro and in vivo assays. Reactive oxygen species predominantly lead to the oxidation of deoxyguanosine in DNA to 8-oxo-7,8-dihydro-2'-deoxyguanine (8-oxoG). If left unrepaired this often leaves a genetic mark in the form of G:C to T:A transversion mutation. The deletion of a putative OxoG glycosylase and Dbh TLS polymerase individually led to a significant increase in the mutagenic signature left behind by 8-oxoG. However, the deletion of both the genes led to a five-fold increase in the mutation rate and a 47-fold increase in the G:C to T:A mutagenic signature. To analyze the bypass of 8-oxoG specifically, all four strains were transformed with a synthetic oligo carrying an 8-oxoG lesion within it, and in each resulting transformant, the base inserted opposite the lesion was identified. The results showed that the double mutant exclusively inserts a dAMP across the 8-oxoG lesion whereas the wild type strain inserts dCMP. Apurinic/apyrimidinic sites are one of the most common DNA lesions which can either a (open full item for complete abstract)

Doctor of Philosophy (Ph.D.), Bowling Green State University, 2019, Photochemical Sciences

The first chapter of this dissertation is devoted to the investigation of the pimerization and photo-induced electron-transfer processes in the series of bis(pyridinium) alkane salts and covalently linked monoquat. The DFT analysis of bis(pyridinium) alkane systems allowed us to compare the energies of the different conformations of dications and radical cations of these salts formed upon single electron reduction which is important for the determination of the conformations that favor the formation of the dimer radical cation. The results of these calculations made an important contribution to the studies of pimerization in bis(pyridinium)alkane salts. Reduction of monomeric and covalently linked monoquat (1-methyl-4-(4-pyridyl)pyridinium) was assessed experimentally by means of Cyclic Voltammetry and transient absorption spectroscopy. A number of interesting observations were made to provide a basis for the improved design of novel photochemical DNA damaging agents that contain electron-poor pyridinium or monoquat `arms' able to undergo pimerization process. The second part of the dissertation covers the spontaneous aerobic catalyst-free transition from 1,1,2,2-tetrakis(N-methylpyridin-4-ium)ethane iodide to the corresponding epoxide (major product) and alkene (minor product). This reaction represents a rare transition from a substituted alkane to the epoxide. The mechanism of the reaction was proposed based on the intermediates and products characterization and further supported by the kinetic modeling. It was demonstrated that the oxidation proceeds through the formation of the air sensitive monomethine cyanine dye dimer. This reaction intermediate was involved in the production of the Reactive Oxygen Species (ROS) that are known to induce DNA damage. In light of this observation, the DNA toxicity of 1,1,2,2-tetrakis(N-methylpyridin-4-ium)ethane under aerobic aqueous conditions was examined. The results of this study are presented in the last chapter of th (open full item for complete abstract)

Doctor of Philosophy, University of Akron, 2018, Mechanical Engineering

This dissertation aims to develop valid numerical approaches to investigate the micromechanics of ductile fracture process and predict the ductile material failure under various loading conditions. As the first portion of this work, a layered unit cell micromechanics model is proposed. This model consists of three void containing material units stacked in the direction normal to the localization plane. Localization takes place in the middle material unit while the two outer units undergo elastic recovery after failure occurs. Thus, a failure criterion is established as the material is considered failure when the macroscopic effective strain of the outer material units reaches the maximum value. Comparisons of the present model with several previous models suggest that the present model is not only easy to implement in finite element analysis but also more suitable to robustly determine the failure strain. A series of unit cell analyses are conducted for various macroscopic stress triaxialities and Lode parameters to investigate the dependency of failure strain on stress state. The analysis results also reveal the effect of the stress state on the deformed void shape within and near the localization band. Additionally, analyses are conducted to demonstrate the effect of the voids existing outside the localization band. Next, the unit cell model is utilized to investigate the effect of hydrogen on ductile fracture demonstrated by its influence on the process of void growth and coalescence. The evolution of local stress and deformation states results in hydrogen redistribution in the material, which in turn changes the material's flow property due to the hydrogen enhanced localized plasticity effect. The result shows that hydrogen reduces the ductility of the material by accelerating void growth and coalescence, and the effect of hydrogen on ductile fracture is strongly influenced by the stress state experienced by the material, as characterized by the stress tr (open full item for complete abstract)

Doctor of Philosophy, University of Toledo, 2017, Medicinal Chemistry

Constituents of the endogenous exposome include reactive oxygen species, which cause oxidative damage to nucleic acids, proteins, and lipids. It has been shown that such damage to RNA plays a role in the initiation of neurodegenerative diseases, such as Alzheimer's. To investigate this phenomenon at the molecular level, the synthesis of a modified uridine was improved upon and subjected to photolytic activation, generating a C5'-uridinyl radical mimicking the hydrogen atom abstraction normally observed under conditions of oxidative stress. This was accomplished using a tert-butyl ketone at the C5' position, which undergoes Norrish Type I cleavage. Studies were performed under anaerobic conditions in the presence or absence of reductant at varying pH to emulate the diversity of the cellular environment, and it was found that the base release product uracil was predominant. Aerobic conditions were also utilized, which led to the formation of a C5' aldehyde. The C5'-uridinyl radical precursor was further derivatized for its incorporation into oligoribonucleotides. Development of a new automated RNA synthesis method in the 5' to 3' direction using 5' H-phosphonates was initiated. This included the synthesis of the building blocks required for the method development.

Doctor of Philosophy, University of Akron, 2013, Mechanical Engineering

This thesis sought to investigate and develop valid numerical approaches to predict ductile fracture under different stress state and loading conditions. As the first portion of this work, the plastic flow and fracture behaviors of three aluminum alloys (5083-H116, 6082-T6 and 5183 weld metal) under the effects of strain rate and temperature were studied through a series of experiments and finite element analyses. The fracture behavior under the influential factor of stress triaxiality was also studied. The applicability of the Johnson-Cook plasticity and fracture models were investigated with mixed results. For all three materials, the dependency of the failure strain on triaxiality is adequately described.The stress state effect on plasticity and ductile fracture behaviors was further explored for aluminum alloy 5083-H116 through tests on plane strain specimens and torsion specimens, focusing on the third deviatoric stress invariant (lode angle). A stress state dependent plasticity model, J2-J3 model, together with the Xue-Wierzbicki fracture criterion which defined the damage parameter as a function of the stress triaxiality and the Lode angle, was implemented and calibrated with the test data. The calibrated model was utilized to study the residual stress effect on ductile fracture resistance, using compact tension specimens with residual stress fields generated from a local out-of-plane compression approach. Fracture tests with positive and negative residual stresses were conducted on the C(T) specimens. Both experimental and finite element results showed significant effect of residual stress on ductile fracture resistance.In an attempt to predict ductile fracture under shear-dominated conditions, this study combined the damage mechanics concept with the Gurson-Tvergaard-Needleman porous plasticity model that accounts for void nucleation, growth and coalescence. The GTN model was extended by coupling two damage parameters, representing volumetric damage and she (open full item for complete abstract)

Doctor of Philosophy, The Ohio State University, 2009, Mechanical Engineering

In this dissertation, finite element models are used to investigate catastrophic failure of thermal barrier coatings (TBCs) due to delaminations along susceptible interfaces of thermally grown oxide (TGO) with the ceramic top coat and the inter-metallic bond coat. The materials and geometries in the studies are chosen to be representative of TBC materials in real applications. The characteristics of the failure modes along the TGO and bond coat interface (e.g. buckling instability and strain energy driven delamination propagation) are investigated using thermo-elastic finite element models. The solution of a linear elastic eigen-value problem determines the onset of the buckling instability with a pre-existing delamination between bond coat and the TGO. The virtual crack extension method is employed to study strain energy release rate driven interfacial delamination at wavy interfaces. The materials and geometries in the study are chosen to be representative of TBC materials in real applications. Extensive sensitivity analyses are conducted to identify the critical design parameters affecting the onset of buckling and extension of interfacial delamination, as well as to develop parametric relations that enhance the understanding of these mechanisms. Finally, a numerical exercise demonstrates that the buckling instability is the leading failure mechanism at flat interfaces or at the locations of minimum cross-section in a wavy interface. However, in the vicinity of waviness, crack extension becomes a dominant mode of failure. The top coat crack initiation and propagation is investigated using a thermo-elastic finite element model with bond coat creep. Cracks are assumed to initiate when the maximum principal stress exceeds rupture stress of the top coat. A sensitivity analysis estimates the contribution of geometric and material parameters and forms a basis to develop parametric relation to estimate maximum principal stress. Subsequently, crack propagation simulati (open full item for complete abstract)

Doctor of Philosophy in Biomedical Sciences (Ph.D.), University of Toledo, 2009, College of Medicine

The Mismatch repair (MMR) system maintains genomic stability byrepairing DNA mismatches and insertion-deletion loops (IDLs) resulting from replication and recombination errors. Defective MMR can lead to hereditary non-polyposis colorectal cancer (HNPCC) and sporadic forms of cancer. In human cells, mismatches are recognized and bound by a heterodimer, hMSH2-hMSH6 (hMutSα). A second heterodimer, hMLH1-hPMS2 (hMutLα) interacts with hMutSα and is thought to act as a mediator for downstream repair proteins. An additional role for MMR pathway is to trigger cell cycle arrest and apoptosis upon recognition and binding of MutSα to specific DNA lesions such as O6 methyldeoxyguanine (O6-meG). Limited information is available regarding the cellular regulation of these proteins. Within this report, we demonstrate that hMSH6, but not hMSH2, undergoes phosphorylation within cells. Phosphorylation of hMSH6 is enhanced by addition of TPA, a PKC activator. Alternatively, UCN-01, a PKC and Chk1/Chk2 kinase inhibitor, decreases hMSH6 phosphorylation and mismatchbinding activity of hMutSα to both G:T and O6 -meG:T-containing DNA. We show that phosphorylated hMSH6 is higher in concentration in the presence of a G:T mismatch, as compared to an O6 -meG:T lesion. However, the total quantity of hMutSα bound to O6 -meG:T–containing DNA is higher than that bound to G:T-containing DNA. We also demonstrate that MMR proficient cells treated with a low concentration of N-methyl-N'-nitro-N-nitrosoguanidine (MNNG) undergo cell cycle arrest after one complete cell cycle. When these cells are co-treated with UCN-01 the G2/M arrest is abrogated and the cells rapidly die. This abrogation of arrest is not due to Chk1 kinase inhibition but rather through Cdc2 activation by increased Tyr15 dephosphorylation. Taken together, we hypothesize that both phosphorylation and total concentration of hMutSα are involved in the signaling of either DNA mismatch repair or damage recognition activities. We also hypothe (open full item for complete abstract)

Doctor of Philosophy (Ph.D.), University of Dayton, 2011, Mechanical Engineering

As the use of composite materials in aerospace structures continues to increase, the need to properly characterize these materials, especially in terms of damage tolerance, takes on additional importance. The world wide failure exercises (WWFE) are an example of the international interest in this issue. But though there has been a great deal of progress in understanding the initiation of damage and modeling damage propagation along known interfaces, methods that can capture the effects of interactions among various failure modes accurately remain elusive. A method of modeling coupled matrix cracks and delamination in laminated composite materials based on the finite element method has been developed and experimentally validated. Damage initiation is determined using the LARC03 failure criterion. Delamination along ply interfaces is modeled using cohesive zones. Matrix cracks are incorporated into the discretization of the problem domain through a robust Mesh-Independent Cracking (MIC) technique. The matrix cracking technique, termed the Regularized Extended Finite Element Method (Rx-FEM), uses regularized forms of the Heaviside and Dirac Delta generalized functions to transform the crack surface into a volumetric crack zone. The Regularized Extended Finite Element method is compared to benchmark cases. The sensitivity of the solution to mesh size and parameters within the cohesive zone model is studied. Finally, the full method with delamination is employed to study a set of experimental tests performed on open-hole quasi-isotropic laminates. The trends of hole-size and ply thickness are well predicted for the laminates. Rx-FEM is also able to simulate the pattern of damage, as demonstrated by comparisons to x-ray images. From the results of this series of analyses it can be concluded that failures occur when delamination originating at the hole links up with delamination originating at the edge along the path of matrix cracks.

Doctor of Philosophy, Case Western Reserve University, 2008, Chemistry

The purpose of this thesis research is to better understand the role of oxidative damage in age related macular degeneration (AMD), the most common cause of legal blindness in the elderly population. In angiogenesis studies, carboxyethylpyrrole (CEP) adducts, derived from free radical oxidation of docosahexaenoyl lipids, were found to stimulate neovascularization in chick chorioallantoic membrane and rat corneal micropocket assays. Monoclonal anti-CEP antibody was found to neutralize CEP stimulated neovascularization, however, anti- vascular endothelial growth factor antibody only partially neutralized vessel growth. Primary retinal pigment epithelial (RPE) cells and the human ARPE19 treated in vitro with CEP-dipeptide did not stimulate vascular endothelial growth factor secretion, suggesting CEP adducts follow a vascular endothelial growth factor independent pathway. Overall, these results suggest that CEP may play a role in choroidal neovascularization, and anti-CEP therapeutic modalities might be of value in limiting choroidal neovascularization in AMD. In retinal light damage studies, CEP, argpyrimidine, and nitrotyrosine immunoreactivities in rodent retina were found to be significantly greater after 4 h green light exposure compared with control animals maintained in the dark. These findings justify further consideration of protein modifications as mediators in the light-induced biochemical sequelae leading to photoreceptor cell death. Similar results were obtained with 6 h blue light exposure. CEP adducts and autoantibodies were lowered after pretreatment with drugs prior to blue light exposure. Because CEP adducts and autoantibodies are also elevated in human AMD plasma, experimental drugs that lowered retinal light damage may eventually become useful as therapeutics for dry AMD. In studies directed at characterizing RPE lipofuscin, lipofuscin granules were purified with proteinase K or with SDS. Purified and crude lipofuscin were found to be equally phototo (open full item for complete abstract)

Doctor of Philosophy, University of Akron, 2012, Civil Engineering

Structural health monitoring (SHM) has gained more attentions recently since nearly 140,000 of a total 600,000 highway bridges in the US are nearing 50 years of age and are approaching the end of their design life. Most in-service highway bridge structures are suspected to be undergoing deterioration processes induced by the physical and harsh environmental changes. Therefore, timely maintenance with a robust SHM system having capability of early detection of impending damage is required to prevent catastrophic events for the public safety with reduced expenses. Vibrational modal properties may not be sufficient for detecting early damage in local regions of complex civil infrastructure. Moreover, most of current damage detection methods require reference data which are not always available. There have also been pressing needs for real-time monitoring to prevent sudden catastrophic disasters. This dissertation addresses current challenges and needs identified in existing vibration-based damage detection methods, focusing on wavelet-based reference-free real-time damage identification and subsequent finite element model updating for quantifying damage severity. First, a damage detection method based on a wavelet entropy analysis has been embedded in wireless smart sensor nodes (Imote2) and tested with three-story shear building and a laboratory truss bridge structure. To realize the reference-free damage detection, a continuous relative wavelet entropy (CRWE)-based damage detectionmethod is also proposed and demonstrated with a laboratory truss bridge structure. Although the reference-free CRWE method can detect damage locations without reference data,computational times put limitations in its applications to a real-time SHM system. To make real-time monitoring feasible in SHM systems, a statistical referencefree real-time damage detection method has been developed based on the wavelet packet transformation and log likelihood ratios. Second, finite element model (open full item for complete abstract)

Master of Science, University of Akron, 2006, Civil Engineering

The main objective of this study is to show the specific capabilities of the Scanning Laser Vibrometer (SLV) for global damage detection using a recent defect energy parameter technique proposed by Saleeb and coworkers. The experimental technique used for extraction of signature is the first and most important part in any damage detection technique. Signatures considered here are full-field SLV measurements for modal shapes and associated frequencies of plated structures. The damage feature extraction capability was studied extensively by analyzing various simulation and experimental results. The practical significance in structural health monitoring is that the detection at early stages of small-size defects is always desirable. The amount of changes in the structure's response due to these small defects was determined to show the needed level of accuracy in the experimental methods. The signal – noise ratio of experiment shows the capability of the same experiment to be used for damage detection purpose. Various experiments were performed to verify a significant signal – noise ratio for a successful detection. Very high number of scanning points, for optical experimental measurement, for any civil structure can be impractical and uneconomical. So, a pragmatic direction for the development of new experimental measurement tools was studied where different number of scanning points and different types of statically loaded simulations were performed to verify the specific capabilities of the defect energy parameter technique. It was further observed that powerful graphic user interface should also be an integral part in any present in the damage detection scheme for successful and more accurate detection. Furthermore, some potential use of SLV techniques in detection are provided, both for dynamic and static applications.

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)