Doctor of Philosophy (PhD), Ohio University, 2010, Physics and Astronomy (Arts and Sciences)

Antifreeze proteins (AFPs) evolved in cold-adapted organisms and serve to protect them against freezing cold conditions by arresting ice crystal growth and inhibiting ice recrystallization. The freezing point depression by AFPs is defined as thermal hysteresis (TH) and AFPs are classified as hyperactive (hypAFPs) and moderate according to their TH activities. The mechanism of action of AFPs is not well understood. In particular, it is not clear what determines the concentration dependence of TH and whether the binding of AFP to ice is irreversible. Additionally, it is not known why some types of AFP are hyperactive compared to others and it was suggested that hyperactivity might be related to basal plane affinity of hypAFP to ice.The present study utilizes the techniques of microfluidic devices and fluorescence microscopy to study the interaction of AFPs with ice crystals. With novel temperature controlled microfluidic devices, we showed the accumulation and affinity of hypAFPs on the basal plane of ice. This supports the view that hypAFPs adhere to the basal plane. Additionally, for the first time in literature, small ice crystals of 30-50 µm sizes covered with adsorbed GFP tagged hypAFPs were stabilized in supercooled non-AFP solutions for hours with no observed ice growth in temperature controlled microfluidic devices. Repeated TH experiments of ice crystals incubated in AFP solutions before and after the exchange of liquids in microfluidic devices gave the same TH activity. This finding clarifies our understanding of concentration dependence of TH. Furthermore, we found that hypAFPs protect ice against melting as well as freezing, resulting in superheated ice. Ice crystals were superheated up to 0.5 °C above their equilibrium melting temperatures and remained stable in this superheated state for hours. Measurements of fast melting velocities added additional evidence to the observed superheating of ice in AFP solutions. The experimental results of the current st (open full item for complete abstract)

Committee: Ido Braslavsky Dr (Advisor) Subjects: Biophysics; Physics

Master of Science (MS), Wright State University, 2018, Physics

The influence of surface effects on a hysteresis loop for single domain, ferromagnetic nanoparticles was examined. Theoretical equations were derived to describe the magnetic behavior of the domains and a MATLAB program was used to solve them. M-H curves were calculated for the case when a magnetic field is applied in the favorable magnetization direction (easy axis). In contrast, the calculations show there were no hysteresis loops when the magnetic field was applied perpendicular to the easy axis. Our studies showed how parameters of the surface such as a associated with saturation magnetization near the surface of nanoparticles and Ks related to anisotropy had an impact on the hysteresis loop. The hysteresis loops were calculated for single-domain nanoparticles of MnBi, CoPt, and FePt. These materials have a wide range of values of radius R between the critical radius Rc10 for transition to the superparamagnetic phase and the critical radius Rc20 for transition to a multi-domain structure and also for high and low values of the volume anisotropy K0 which were used for analysis. The results showed that coercivity increased with increasing values of a, which is related to a decreasing interaction between magnetic moments, and thus saturation magnetization at the surface. They also showed that the coercivity increased with increasing values of Ks, which is related to the anisotropy. In contrast, the remanence decreased with increasing values of a and remained constant with increasing values of Ks. In addition, the coercivity and remanence increased with increasing values of the radius R of the single domain region. Furthermore, theoretical results showed that the area enclosed by each hysteresis loop have almost the same value of energy density for different values of a whereas, the area enclosed by each hysteresis loop has an increased value of energy density for increasing values of Ks.

Committee: Gregory Kozlowski Ph.D. (Advisor); Sarah Tebbens Ph.D. (Committee Member); Zafer Turgut Ph.D. (Committee Member) Subjects: Physics

Doctor of Engineering, Cleveland State University, 2008, Fenn College of Engineering

Many organisms are exposed to subzero temperatures in nature and can survive these temperatures by the effect of antifreeze proteins (AFPs), which inhibit ice crystal growth and change the morphology of ice crystals. Although the effects of these proteins, such as recrystallization inhibition, ice growth inhibition, and crystal habit changes, are known, a conclusive description of the protein-ice crystal interaction including interaction energy, surface coverage, and lifetime of adsorbate has been elusive.In this study, different antifreeze protein constructs are designed and expressed such that they can be conjugated to polymers to increase the thermal hysteresis activity especially at low concentrations. Trimers of these proteins are also constructed using a foldon domain attached to their C-terminus. New constructs of type I and type III antifreeze proteins yield significantly higher thermal hysteresis activities than the native protein. Furthermore, we determine the binding equilibrium constant for a type III fish antifreeze protein and the relationship between thermal hysteresis and surface coverage for this protein. This is possible using experimental data from a two-domain antifreeze protein and its related single domain protein. The classical Langmuir isotherm is used to describe the equilibrium exchange of the single domain type III AFP molecules at the ice crystal surface, while a modification of the Langmuir isotherm is derived to describe the adsorption of the two-domain AFP. Because the protein adsorption is governed by different isotherm relationships, there are two independent data sets allowing the determination of the two unknowns of surface coverage and binding energy. The data yield a binding equilibrium constant of 1.9 mM-1 for the type III AFP-ice interaction. The analysis results in a relationship between surface coverage and thermal hysteresis, as well as kinetic equations of the adsorption of the proteins onto the ice surface.

Committee: Nolan Holland PhD (Advisor) Subjects:

Master of Science, The Ohio State University, 1967, Graduate School

Committee: Not Provided (Other) Subjects:

Master of Science, Miami University, 2024, Mechanical and Manufacturing Engineering

A new method is proposed to mitigate ice accretions on wind turbine blades via the creation of a microstructural gradient surface geometry that facilitates spontaneous water droplet motion along the surface. The wettability gradients are formed by laser etching 35𝜇m wide, 35𝜇m deep channels into aluminum to form a surface with a gradually increasing solid area fraction. Different design permutations are then proposed and systematically evaluated on the merits of their performance. An analytical model is also derived based on a balance of hysteresis and drag forces to predict the critical airspeed necessary for droplet movement as a function of the droplet size and surface contact angle. Experimentation has shown good agreement with the model for both the baseline and fixed-pitch channel surfaces and has also demonstrated that, in certain cases, up to 70% lower critical airspeeds are needed to initiate droplet motion on these microstructured surfaces. Finally, the effects of frozen droplets on aerodynamic performance were studied via 3D-printed airfoil prototypes. This work demonstrated that at airspeeds under <15m/s and angles of attack between 0 – 20 degrees, frozen droplets on the top surface of the airfoil can be used to strengthen the lift-to-drag ratio by up to 184

Committee: Andrew Sommers (Advisor); Medhi Zanjani (Committee Member); Edgar Caraballo (Committee Member) Subjects: Alternative Energy; Energy; Engineering; Fluid Dynamics; Mechanical Engineering

Master of Science, University of Akron, 2024, Polymer Engineering

Highly branched low-density polyethylene (HB-LDPE) synthesized from solely ethylene monomer through Brookhart-type α-diimine nickel or palladium catalysts have unique microstructure, low melting temperature and thermal plastic elastomer (TPE) properties. With the increasing demand for recyclable material, synthesis of HB-LDPE has been extensively studied. However, details of its microstructure and the impact of the microstructure on solid structure as well as mechanical/thermal properties have not been fully understood. In this study, various characterizations and mechanical testing are conducted on HB-LDPE entries synthesized by original Brookhart catalyst, 8-p-tolylnaphthylimino substituted sandwich catalyst, and a multinuclear heterogeneous crosslinked catalyst. First, 13C solution-state NMR spectroscopy was employed to obtain detailed insights into their branch structure, including branch density, identity and localization. Using chemical superposition methods, detailed localization structure of the branches were revealed. Formation mechanisms of several localization structures are proposed in supplementary for existing chain walking mechanisms. Second, the solid structure of HB-LDPEs was investigated by using differential Scanning calorimetry (DSC), X-ray diffraction (XRD) and solid-state NMR spectroscopy. The formers are no longer capable of quantitative characterization due to the low crystallinity. Through solid-state 13C NMR analysis, it was found that some entries are entirely amorphous, while the others are semi-crystalline entries which range between 1 and 5 %. The molecular dynamics in the crystalline phase is characterized through 13C spin-lattice relaxation time (T1C), which ranges from 4s to 80s, implying a variable crystalline size. By examining the combination of microstructure and crystalline structure, it is revealed that only those entries with both low levels of long chain branching (LCB) below 10 b/1kC and short chain branching (SCB) below (open full item for complete abstract)

Committee: Toshikazu Miyoshi (Advisor); Junpeng Wang (Committee Member); James Eagan (Committee Chair) Subjects: Materials Science; Molecular Chemistry; Molecular Physics

Doctor of Philosophy, University of Toledo, 2023, Physics

Low-cost thin film absorber layer materials with high absorption coefficients (> 105 cm-1 in visible spectral range) and bandgap close to the ideal value for efficient photovoltaic conversion efficiency are leading candidates for thin film photovoltaic (PV) applications. This dissertation discusses the fabrication and optical and microstructural properties of magnetron-sputtered glancing angle deposited CdTe thin film absorber layer material and its application as an interlayer in CdS/CdTe solar cells. In addition, optoelectronic properties of non-toxic and earth-abundant absorber layer material, antimony selenide (Sb2Se3), and optimization of polycrystalline VO2 fabrication from amorphous vanadium oxide (VOx) film along with its optical properties have been discussed. Sb2Se3 is a promising candidate as an absorber layer material in PV applications. I have performed optical property characterization of thin film Sb2Se3 and identified electronic losses when used in a PV device. The indirect bandgap, direct bandgap, and Urbach energy have been determined to be 1.12 eV, 1.17 eV, and 21.1 meV, respectively using photothermal deflection spectroscopy. Optical properties of Sb2Se3 in the form of complex dielectric function (ε = ε1 + iε2) spectra in 0.75 to 4 eV spectral range is determined using spectroscopic ellipsometry. The line shape of ε is obtained using a parametric model which incorporates an Urbach tail, a band edge function, and five critical point oscillators. The optical property spectra in ε and structural parameters in terms of the thickness of solar cell layer components are used as input parameters for external quantum efficiency (EQE) simulation to investigate the electronic and optical losses in Sb2Se3-based solar cells. A carrier collection length of ~ 400 nm and a ~97 % carrier collection probability near the heterojunction in the Sb2Se3 solar cell are identified by comparing experimental and simulated EQE. Next, I describe deposition and characterizati (open full item for complete abstract)

Committee: Nikolas J. Podraza (Committee Chair); Robert W. Collins (Committee Member); Yanfa Yan (Committee Member); Song Cheng (Committee Member); Terry Bigioni (Committee Member) Subjects: Physics

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

We have elucidated details of how the microscopic structure and dynamics of filler in reinforced rubbers influence mechanical properties. Studies were performed on highly loaded, silica-filled, crosslinked styrene-butadiene rubber (SBR). Properties of the compounds studied were varied by addition of silane coupling agents, silicas of different surface area, and by addition of well-characterized, anionically-polymerized, low molecular weight, dimethylamino end-functionalized SBR additives of linear or star molecular architecture. Samples were probed with a combination of Ultra-small Angle X-ray Scattering/Small Angle Scattering (USAXS/SAXS), X-ray Photon Correlation Spectroscopy (XPCS), and mechanical measurements. Investigation of samples with or without silane coupling agents confirms that coupling agents enhance filler dispersion. This enhanced dispersion leads to slower filler dynamics when the rubber is strained and a slower change in dynamics over time. These slower dynamics and slower evolution of dynamics correlate with slower macroscopic stress relaxation. Our work also examines the temporally heterogenous dynamics that underlie the stress relaxation process. During stress relaxation, filler dynamics intermittently speed up and slow down. These results indicate that while macroscopic stress relaxation appears to be a relatively simple process, the microscopic behavior is complex. Studies on rubbers containing high surface area, milled silica under dynamic strain reveal that while rubber containing milled silica and monosulfidic coupling agent shows a large Payne effect, the breakdown of filler is suppressed. We infer that debonding and/or yielding of bridging bound layers is responsible for the Payne effect in this sample. These bridging layers provide this rubber with a high modulus and low hysteresis. Addition of end-functionalized SBRs to rubber drastically affects mechanical properties. Rubber containing conventional silica and 20 kg/mol difunctio (open full item for complete abstract)

Committee: Mark Foster (Advisor); Roderic Quirk (Other); Jutta Luettmer-Strathmann (Committee Member); Mesfin Tsige (Committee Member); Junpeng Wang (Committee Member); Li Jia (Committee Chair) Subjects: Materials Science

Doctor of Philosophy (PhD), Ohio University, 2022, Chemistry and Biochemistry (Arts and Sciences)

Antibiotic resistance is a global threat beside the ongoing pandemic by SARS-CoV-2. The number of deaths due to antibiotic-resistant infections is increasing at an alarming rate. The COVID-19 pandemic has already claimed millions of deaths worldwide. Fighting against antibiotic-resistant superbugs and the SARS-CoV-2 has become a challenge. A significant amount of research is going on to develop the vaccine and small molecule antiviral and antibacterial therapeutics targeting proteins. Fortunately, novel non-coding regulatory RNA targets have been identified for developing new antibacterial and antiviral drugs such as bacterial T-box riboswitch, RNA thermometers, and viral stem-loop II motif. T-box riboswitch can control the transcription or translation of amino acid-related genes in bacteria by forming unique interactions between tRNA and mRNA. RNA thermometers (RNATs) are temperature-responsive riboswitches that control the translation based on temperature sensing thus controlling the interaction with the mRNA and 16S rRNA. In Shigella dysenteriae, three RNATs, i.e., ompA, shuT, and shuA, have been discovered. ompA RNAT controls the translation of outer membrane protein A. shuT, and shuA RNAT controls the translation of two proteins that are crucial to the bacterial heme utilization system. The Stem-loop II motif (S2M) is a highly conserved RNA element found in most coronaviruses, astroviruses, and picornaviruses that plays a potential role in viral replication and invasion. The RNA structure plays a significant role in its regulatory function for all of these potential therapeutic targets. Consequently, it is essential to examine the factors that affect the RNA structure and RNA-RNA interaction. Despite having limited building blocks, RNA has diverse functions in the cells. Base protonation and protonated base pairs often occur in RNA when interacting with other biomolecules, thus could play a critical role in vital biological processes. Diff (open full item for complete abstract)

Committee: Jennifer Hines (Advisor) Subjects: Biochemistry; Biology; Genetics

Master of Science in Electrical Engineering, Cleveland State University, 2020, Washkewicz College of Engineering

This thesis provides a summary on renewable energy sources integration into the grid, using an inverter, along with a comprehensive literature research on variety of available control methods. A new generalized method for grid side inverter control under unbalanced operating conditions is also proposed. The presented control method provides complete harmonic elimination in line currents and DC link voltage with adjustable power factor. The method is general, and can be used for all levels of imbalance in grid voltages and line impedances. The control algorithm proposed in this work has been implemented by using MATLAB Simulink and dSPACE RT1104 control system. Simulation and experimental results presented in this thesis are in excellent agreement.

Committee: Ana Stankovic PhD (Committee Chair); Lili Dong PhD (Committee Member); Chansu Yu PhD (Committee Member) Subjects: Electrical Engineering

Doctor of Philosophy, University of Akron, 2019, Mechanical Engineering

Mechanical connection of parts through jointed connections are prolific throughout modern engineering applications; however, precision analysis and design of these systems remains difficult. Experimental findings have revealed a myriad of nonlinear properties of these systems such as nonlinear damping, hysteresis, etc., and these complex effects lead to extreme difficulties in the characterization and modeling of these common structural elements. To exacerbate matters, high-fidelity numerical analysis of these systems is often impractical due to disparate length and time-scales between microslip in the joint and macro-scale effects of interest. In this dissertation, original research on the analysis of damping of jointed structures is presented. This includes theoretical work in advancement of reduced-order modal models as well as practical development of Abaqus subroutines to implement cutting-edge damping models into finite element models. This work culminates in the study of a practical problem of interest to Sandia National Labs involving a jointed structure under blast loading, and important conclusions are draw about the nature of jointed structures under complex loads.

Committee: Donald Quinn (Advisor); Graham Kelly (Committee Member); Xiaosheng Gao (Committee Member); Ernian Pan (Committee Member); Kevin Kreider (Committee Member) Subjects: Aerospace Engineering; Applied Mathematics; Mathematics; Mechanical Engineering; Mechanics

Master of Science, University of Akron, 2017, Geology-Environmental Geology

Scrap tires are shredded and kept in monofills as one way of disposing or storing them for further processes such as recycling. Although monofills are safer than other means of disposing tires, long-term storage in fills and stockpiles, where the shredded tires are in a compressed state, has led to incidences of tire fires. In order to safely and more efficiently manage shredded tire monofills, it is imperative to understand the heat generation process in such settings. This study is an experimental investigation performed with the overall aim of determining the directional variations of the bulk thermal conductivity of shredded tires. To approximate the situation at monofills, an experimental apparatus was designed and constructed using an open-end steel drum with a diameter of 0.28 m (11 in) and 0.85 m (33.5 in) height. Heat was generated by compression of interstitial air/voids, and temperature distribution was measured when heat was in transit across the bulk volume of shredded tires. Experiments were conducted on three shred sizes: 12.5 mm (0.5 in), 25 mm (1 in), and 150 mm (6 in) to determine thermal conductivity variations as a function of size, density and compressibility. The three shred sizes correspond to three experimental set-ups. A fourth configuration was composed of 150 mm (6 in) shred sizes with a 75 mm (3 in) covering of mine spoils to determine the contribution of mine spoils to the temperature difference, heat flux, thermal conductivity and compressibility of interstitial air of bulk shredded tires. The compression/strain of the large size tire shreds was found to be higher than that of small size tire shreds. The reloading experiment also shows that shredded tires compress less during the second round of loading (i.e., showing a low level of hysteresis), although both the first time loading and the reloading curves depict a similar non-linear stress-strain behavior. One of the ramifications of the results is the finding that the t (open full item for complete abstract)

Committee: Ira D. Sasowsky Dr. (Advisor); David N. Steer Dr. (Committee Member); John M. Senko (Committee Member) Subjects: Environmental Engineering; Environmental Geology

Doctor of Philosophy, The Ohio State University, 1957, Graduate School

Committee: Not Provided (Other) Subjects: Engineering

MS, University of Cincinnati, 2017, Engineering and Applied Science: Computer Engineering

A series of simulations which utilize a Non-equilibrium Green's function (NEGF) formalism is suggested which can provide indirect evidence of the fine and non-local electrostatic tuning of the onset of spin polarization in two closely spaced quantum point contacts (QPCs) that experience a phenomenon known as lateral spin-orbit coupling (LSOC). Each of the QPCs that create the device also has its own pair of side gates (SGs) which are in-plane with the device channel. Numerical simulations of the conductance of the two closely spaced QPCs or four-gate QPC are carried out for different biasing conditions applied to two leftmost and rightmost SGs. Conductance plots are then calculated as a function of the variable, Vsweep, which is the common sweep voltage applied to the QPC. When Vsweep is only applied to two of the four side gates, the plots show several conductance anomalies, i.e., below G0 = 2e2/h, characterized by intrinsic bistability, i.e., hysteresis loops due to a difference in the conductance curves for forward and reverse common voltage sweep simulations. The appearance of hysteresis loops is attributed to the co-existence of multistable spin textures in the narrow channel of the four-gate QPC. The shape, location, and number of hysteresis loops are very sensitive to the biasing conditions on the four SGs. The shape and size of the conductance anomalies and hysteresis loops are shown to change when the biasing conditions on the leftmost and rightmost SGs are swapped, a rectifying behavior providing an additional indirect evidence for the onset of spontaneous spin polarization in nanoscale devices made of QPCs. The results of the simulations reveal that the occurrence and fine tuning of conductance anomalies in QPC structures are highly sensitive to the non-local action of closely spaced SGs. It is therefore imperative to take into account this proximity effect in the design of all electrical spin valves making use of middle gates to fine tune the spin preces (open full item for complete abstract)

Committee: Marc Cahay Ph.D. (Committee Chair); Rashmi Jha Ph.D. (Committee Member); Punit Boolchand Ph.D. (Committee Member) Subjects: Nanotechnology

Master of Science, The Ohio State University, 2017, Electrical and Computer Engineering

GaN is a promising material for energy efficient high power switching applications due to its wide bandgap, and high critical field. However, for such applications normally off devices with high positive threshold voltage and low off-state current is desirable. In this thesis, first, we investigated the effects of different scattering mechanisms on the low field mobility of GaN MOSFET. We found that, unlike AlGaN/GaN HEMTs, where mobility is limited by phonon scattering, mobility in GaN MOSFET is limited by interface ionized impurity scattering and surface roughness scattering. Next, we investigate the effect of different process steps, namely, O2 plasma treatment, post dielectric anneal(PDA), and post metal anneal(PMA), on the threshold voltage, hysteresis, and mobility of Al2O3/GaN MOSFETs. Our study reveals that (a) lower hysteresis can be achieved by high temperature PDA in the presence of O2 plasma and PMA treatment, (b) large positive threshold voltage can be achieved with high temperature PDA and PMA treatment in absence of O2 plasma, and (c) high mobility can be achieved with only high temperature PMA treatment without O2 plasma and PDA treatment. Using our optimized process condition we achieved GaN MOSFET with 1.5 V threshold, 0.1 V hysteresis, 225 cm2V-1s-1 mobility, 67 mV/dec subthreshold swing, and 1010 on-off ratio. We also investigated the potential of AlON as a gate dielectric in GaN MOSFET. It is found that AlON can increase the threshold voltage in both HEMTs and MOSFET structures, most probably due to behavior of nitrogen atoms as acceptor like states. We demonstrate a 5 V, and 1.5 V shift in HEMT, and MOSFET structure using AlON as gate dielectric.

Committee: Rajan Siddharth Dr. (Advisor); Steven Ringel Dr. (Committee Member) Subjects: Electrical Engineering

Doctor of Philosophy, University of Toledo, 2016, Physics

Photovoltaic (PV) devices are becoming more important due to a number of economic and environmental factors. PV research relies on the ability to quickly fabricate and characterize these devices. While there are a number of deposition methods that are available in a laboratory setting, they are not necessarily able to be scaled to provide high throughput in a commercial setting. A close-space sublimation (CSS) system was developed to provide a means of depositing thin films in a very controlled and scalable manner. Its viability was explored by using it to deposit the absorber layer in Zn3P2 and CdTe solar cell devices. Excellent control over morphology and growth conditions and a high level of repeatability was demonstrated in the study of textured Zn3P2 thin films. However, some limitations imposed by the structure of Zn3P2-based PV devices showed that CSS may not be the best approach for depositing Zn3P2 thin films. Despite the inability to make Zn3P2 solar cell devices, high efficiency CdTe solar cells were fabricated using CSS. With the introduction of Perovskite-based solar cell devices, the viability of data collected from conventional J-V measurements was questioned due to the J-V hysteresis that Perovskite devices exhibited. New methods of solar cell characterization were developed in order to accurately and quickly assess the performance of hysteretic PV devices. Both J-V measurements and steady-state efficiency measurements are prone to errors due to hysteresis and maximum power point drift. To resolve both of these issues, a maximum power point tracking (MPPT) system was developed with two algorithms: a simple algorithm and a predictive algorithm. The predictive algorithm showed increased resistance to the effects of hysteresis because of its ability to predict the steady-state current after a bias step with a double exponential decay model fit. Some publications have attempted to quantify the degree of J-V hysteresis present in fabricated Perovski (open full item for complete abstract)

Committee: Yanfa Yan PhD (Advisor); Jon Bjorkman PhD (Committee Member); Bo Gao PhD (Committee Member); Dean Giolando PhD (Committee Member); Cora Lind-Kovacs PhD (Committee Member); Nikolas Podraza PhD (Committee Member) Subjects: Solid State Physics

Master of Science (MS), Ohio University, 2016, Mechanical and Systems Engineering (Engineering and Technology)

With the increase in the importance of vehicular transportation, the study of contact patch parameters including the contact patch forces and the tire-road friction has become essential from the perspective of improving vehicle safety as well as vehicle performance. The current work aims at analyzing the effect of the nonlinear elastic and nonlinear viscoelastic nature of tire tread rubber by modifying two commonly used rubber friction models (Gim's analytical model and Heinrich-Kluppel (HK) friction model) in order to implement the nonlinear elasticity and the nonlinear viscoelasticity of rubber. Gim's analytical model is modified by changing the linear elastic constitutive equation used in the original model to a nonlinear elastic equation based on the strain energy density of rubber. Results are obtained for a test simulation using this modified model and an experimental method is proposed to validate the modified model's force predictions. The HK friction model computes the hysteretic sliding friction coefficient of rubber based on the viscoelastic modulus. It however, does not consider the (experimentally proven) dependence of viscoelastic modulus of rubber on the applied strain amplitude and temperature. The current work thus aims at implementing this dependence and modifying the classical HK friction model. A test simulation run for a rubber block sliding on a rough surface using the modified HK friction model yielded friction results that are sensitive to the input strain amplitude and temperature.

Committee: Alireza Sarvestani PhD (Advisor); John Cotton PhD (Committee Member); Munir Nazzal PhD (Committee Member); Ardalan Vahidi PhD (Committee Member) Subjects: Automotive Materials; Materials Science; Mechanical Engineering

Doctor of Philosophy, The Ohio State University, 2016, Aero/Astro Engineering

Takeoffs in crosswind conditions are a common occurrence in flight operations around the world, and flow separation from the inlet of a jet engine at this condition can lead to fan stall, surge, or aeromechanical excitation. The ability to predict flow separation and reattachment is critical to the design of a performance-optimized inlet and to reduce the risk of crosswind performance shortfalls during engine certification. This dissertation shows the derivation of an aerodynamic loading coefficient referred to as the Reattachment Parameter (RP). Analysis of wind tunnel test data for five different inlet designs at five different crosswind speeds show that inlet reattachment occurs when a single, critical value of RP is reached. A process for predicting flow reattachment is developed that relies solely on static pressure distributions from inviscid CFD and the RP coefficient. Validation of predictions from this process were accomplished with wind tunnel testing of two new ultra-high bypass ratio (UHBR) inlets and full-scale testing of a new conventional-length inlet on a modern turbofan engine. The average error in the reattachment predictions of the two UHBR inlets was 1.4% of peak flow and 4.3% of peak flow for the full-scale engine test. Reattachment predictions with the RP process were consistently found to be more accurate than those from RANS CFD. A second key advantage of the RP process is that, by leveraging inviscid CFD, a reattachment prediction can be made with about 1/100,000th the computational cost of a RANS prediction, which provides a tremendous advantage during inlet design work. Results from the RP process suggested that spinner size and shape may affect the crosswind performance of an inlet, so the effect of replacing a standard wind tunnel spinner with one that is larger and more representative of flight hardware was examined. Analysis with the RP process predicted reattachment with the larger spinner would occur 10.6% of peak flow earlier than t (open full item for complete abstract)

Committee: Jen-Ping Chen (Advisor); Jeffrey Bons (Committee Member); Michael Dunn (Committee Member); Richard Freuler (Committee Member) Subjects: Aerospace Engineering

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

The objective of this research was to investigate the mechanical behavior of Divinycell PVC H100 foam under combined cyclic compression-shear loading, and to develop material constitutive models to predict response of the foam under these conditions. Structural polymeric foams are used for the core of sandwich structures in aerospace, marine, transportation, and other industries. They are valued for enabling high specific stiffness and strength as well as energy absorption and impact resistance of sandwich structures. This research addresses energy absorption of the foam due to plastic collapse, damage and hysteresis. Experiments were done to obtain out-of-plane mechanical properties of Divinycell PVC H100 foam under cyclic compression-shear loading. Stress-strain curves for the Divinycell PVC H100 foam under various combinations of compression-shear deformation and deformation rates were obtained. Rate-dependent behavior was observed before and after foam yielding. Yielding and damage in the foam occurred simultaneously. Foam yielding was associated with permanent change in cell micro-structure either by buckling cell walls when the foam is under compression or by bending and stretching cell walls when they were under shear. The Tsai-Wu failure criterion was shown to be a good predictor of yielding and damage initiation. The foam produced hysteresis either due to viscoelasticity and/or viscoplasticity if it was allowed to undergo reverse yielding during unloading and reloading. A phenomenological model was developed to describe the behavior of PVC H100 foam. This model consisted of a standard linear material model for viscoelastic response before yielding/damage initiation. After yielding/damage initiation, combined plastic flow and damage was modeled by modifying the viscoelastic properties of the standard linear model with damage properties and adding a viscoplastic element in series with it in order to control the plastic flow stress. Tsai-W (open full item for complete abstract)

Committee: Michelle Hoo Fatt (Advisor); Gregory Morscher (Committee Member); Kwek-Tze Tan (Committee Member); Anil Patnaik (Committee Member); Kevin Kreider (Committee Member) Subjects: Mechanical Engineering

Doctor of Philosophy (PhD), Ohio University, 2016, Mathematics (Arts and Sciences)

Chagas disease is a major health problem in rural South and Central America where an estimated 8 to 11 million people are infected. It is a vector-borne disease caused by the parasite Trypanosoma cruzi, which is transmitted to humans mainly through the bite of insect vectors from several species of so-called “kissing bugs” or triatomines. One of the control measures to reduce the spread of the disease is insecticide spraying of housing units to prevent (re)infestation by the triatomines. However, (re)infestation of housing units by triatomines has been shown to occur as early as four to six months after insecticide-based control interventions. In this thesis, (re)infestation models that shed light on the effectiveness of the insecticide spraying are constructed and analyzed. In Chapter 2 we introduce ODE-based mathematical models of the effect of insecticide spraying on triatomine (re)infestation. Conditions for existence and uniqueness of infestation-free and endemic equilibria are established for these models, with or without assuming migration of triatomines from sylvatic areas. Additionally, conditions for local as well as global stability of the equilibria are derived. In Chapter 3 we describe a hysteresis-like effect when two different spraying rates lead to two different numbers of infested units at equilibrium. We prove that it occurs under fairly general conditions and under a variety of different modeling assumptions. These results have potentially important implications for designing cost-effective spraying strategies. A mathematical model of intermittent spraying at fixed time intervals is introduced in Chapter 4. The model is based on a mixture of differential and difference equations. Conditions for the existence and uniqueness of a fixed point are established for this model. Numerical results indicate richer possibilities for the dynamics than in the ODE-based models of Chapter 2. In particular, periodic points of period 2 were discovered. (open full item for complete abstract)

Committee: Winfried Just (Advisor) Subjects: Mathematics