Doctor of Philosophy (PhD), Ohio University, 2019, Physics and Astronomy (Arts and Sciences)

The work presented in this dissertation is concerned with properties of nuclei, their internal constituents, nucleons and quarks, of which nucleons are made, in the astrophysical settings of nucleosynthesis, core-collapse supernovae, neutron stars and their mergers. Through energetic considerations, nuclei far-off the stability line are expected to be encountered in all of the arenas mentioned above. Properties of some of these nuclei are expected to be measured in upcoming rare-isotope laboratories across the world. Focussing on the pairing properties of extremely proton- or neutron-rich nuclei, a means to set bounds on their pairing energies was devised in the published work reported here. These bounds were achieved through the introduction of a new model, the Random Spacing Model, in which single-particle energy levels randomly distributed around the Fermi surface of a nucleus were employed. This arrangement ensured that it would encompass predictions of all possible energy density functionals currently being employed. Another new feature of this model is the inclusion of pairing gap fluctuations that go beyond the commonly used mean field approach of determining pairing energies of nuclei. These features, when combined together, enabled us to reproduce the S-shaped behavior of the heat capacity measured in laboratory nuclei. In future work, nuclear level densities, which depend sensitively on pairing energies at low excitation energies, will be calculated using the Random Spacing Model with the inclusion of pairing fluctuations. For baryon densities below about two thirds the central density of heavy nuclei, a mixture of light nuclear clusters such as ${\rm \alpha}$, ${\rm d}$, ${\rm t}$, etc., are favored to be present along with nucleons (neutrons and protons), charge balancing electrons, and heavy nuclei. The concentration of each species is determined by minimizing the free energy density of the system with respect to baryon density, electron fra (open full item for complete abstract)

Committee: Madappa Prakash (Advisor); Zach Meisel (Committee Member); Steven Grimes (Committee Member) Subjects: Astrophysics; Nuclear Physics; Physics; Theoretical Physics

Master of Science in Biomedical Engineering, Cleveland State University, 2016, Washkewicz College of Engineering

Elastin-like polypeptides (ELPs) are environmentally responsive biopolymers that respond to various forms of external stimuli such as temperature, light, and pH. Several factors can influence the transitioning behavior of ELPs. These factors include the amino acid composition of the ELP, the protein concentration in solution, the salt concentration of the solution, and the polymer chain length. Elastin-like polypeptides are soluble in water below a critical solution temperature, however, above this temperature the ELPs become insoluble and phase separate. This point of temperature triggered phase separation is referred to as the transition temperature. This process is completely reversible and ELPs will redissolve once the solution temperature is decreased below the transition temperature. In this study, the phase transitioning behavior for several different concentrations of a three-armed ELP, (GVGVP)40-foldon, was investigated. After expression and purification of this ELP construct, characterization was performed starting at a highly concentrated protein solution then diluting stepwise. Transition temperature were determined using UV-Visible spectrophotometry then several calculation methods were used to analyze the transition temperature data, resulting in multiple potential phase diagrams. Finally, to further investigate the phase transitioning behavior of ELPs microscopy was used to observe the phase transitioning process for several samples of different ELP concentration.

Committee: Nolan B Holland Ph.D. (Advisor); Moo-Yeal Lee Ph.D. (Committee Member); Rolf Lustig DRE. (Committee Member) Subjects: Biomedical Engineering; Polymers

Doctor of Philosophy, University of Akron, 2013, Chemistry

Semiflexible polymers of sufficient stiffness exhibit liquid crystalline order at low temperature and high polymer concentration. Blends of liquid crystalline and flexible polymers have interesting physical properties and important applications in organic electronics. We investigate melts and blends of flexible and semiflexible polymers with the aid of Monte Carlo simulations of an extension of Shaffer's bond-fluctuation model. To control chain stiffness we include a bending term in the Hamiltonian and investigate two models for semiflexibility that differ in the range of penalized bond angles. A study of structural, dynamic and thermodynamic properties of the first model shows that it describes melts of semiflexible chains that do not undergo a transition to a liquid crystalline state. Simulations of the second model reveal orientational order without positional order at high density and low temperature. The transition from the isotropic high-temperature phase to the nematic low-temperature phase, the IN transition, is accompanied by discontinuous changes in structural and thermodynamic properties. This agrees with mean-field theories and experimental observation that show that the IN transition is a discontinuous transition. To characterize our system fully, we determine the phase diagram and find that the IN transition temperature increases with increasing filling fraction, which agrees qualitatively with predictions by Onsager and Flory. Since pair distribution functions give insight into structure and morphology of polymers, we construct same-chain and different-chain distributions that we further differentiate by flexible and rod-like chain conformations. A study of same-chain pair distributions shows that the rod-like chains in our model align with a face diagonal in the nematic phase. Results for different-chain pair distribution functions show that a melt phase separates into a dense ordered region and a low-density disordered region when undergoing t (open full item for complete abstract)

Committee: Jutta Luettmer-Strathmann Dr. (Advisor); David Perry Dr. (Committee Member); Alper Buldum Dr. (Committee Member); David Modarelli Dr. (Committee Member); Kevin Cavicchi Dr. (Committee Member) Subjects: Chemistry; Physics; Polymers

Master of Science, Miami University, 2005, Physics

The mineral zirconium silicate, ZrSiO4, or zircon is of interest due to its low coefficient of thermal expansion. Metamict zircon heated above 800 °C undergoes a structural displacive phase transition. These properties are favorable for applications in the foundry industry as form liners, wave guide materials, and actinide-bearing structures for nuclear waste containment. Perturbed angular correlation (PAC) techniques are used to study the short range order of any phase transition at a Zr-site. PAC measurements of the electric field gradient (EFG) were obtained for two samples from room temperature to 1100 °C. Samples for the PAC experiments were prepared from commercial materials obtained from Aldrich and Alfa Aesar. The primary EFG parameters for both samples were consistent with previously published data. The quadrupole interaction frequency decreased linearly with increasing temperature and the asymmetry values were near zero. Uncharacteristic observations in the anisotropy may be resultant of an after effect condition. Evidence of a displacive phase transition in the temperature range of 800 °C could not be confirmed.

Committee: Herbert Jaeger (Advisor) Subjects:

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

The Wigner crystal (WC) phase represents one of the earliest proposed strongly correlated states of electrons. In this phase, when the density of a two-dimensional electron system is sufficiently low, the system becomes unstable (at low temperatures) and undergoes a phase transition into a solid phase with spontaneously broken translational symmetry. This occurs because, at such low densities, the Coulomb interaction, which localizes electrons, dominates the kinetic energy. Motivated by recent experimental progress on realizing and controlling low density two-dimensional electron systems, this thesis considers various fundamental properties of the WC phase and modifications and extensions of the traditional WC phase. In the first project, we consider the fate of the WC state in a two-dimensional system of massive Dirac electrons as the effective fine structure constant $\alpha$ is increased. In a Dirac system, larger $\alpha$ naively corresponds to stronger electron-electron interactions, but it also implies a stronger interband dielectric response that effectively renormalizes the electron charge. We calculate the critical density and critical temperature associated with the quantum and thermal melting of the WC state using two independent approaches. We show that at $\alpha \gg 1$, the WC state is best understood in terms of logarithmically-interacting electrons and that both the critical density and the melting temperature approach a universal, $\alpha$-independent value. We discuss our results in the context of recent experiments in twisted bilayer graphene near the magic angle. In the second project we focus on WC state formed in Bernal bilayer graphene (BBG) under the application of a perpendicular displacement field. Here, the applied perpendicular electric field flattens the bottom of the conduction band, thereby facilitating the formation of strongly correlated states. Initially, we consider a model of BBG without trigonal warping and theoretically de (open full item for complete abstract)

Committee: Brian Skinner (Advisor); Ulrich Heinz (Committee Member); Jay Gupta (Committee Member); Ilya Gruzberg (Committee Member) Subjects: Physics

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

Liquid-vapor phase change is a key to modeling countless multiphase flows, notably in the storage of cryogenic propellants during long-term space missions. Although recent studies have progressed our understanding of the physics of phase change, reliable models to compute the interphase mass transfer remain elusive, and popular phase change models rely heavily on tuning coefficients to model the phase change mass transfer. Large inconsistencies in the phase change calculations occur due to the unpredictable nature of these tuning coefficients. In this work, several pieces of the kinetic phase change mechanism are used from other studies to build a new computational routine capable of modeling kinetic phase change without the need for tuning parameters. A common problem with implementing kinetic phase change models is the need for values of the accommodation coefficient. This problem is solved by using a transition state theory-based model to compute the accommodation coefficient as a function of the liquid and vapor densities. Vapor temperature is found to play a critical role in the accurate prediction of phase change rates. Errors as large as one order of magnitude are seen for deviations as small as 0.1% in the values of the vapor temperature. Accurate modeling of phase change rates requires vapor temperature within the Knudsen layer to be used as inputs to the kinetic models. Due to the inability of macro-scale computational fluid dynamics (CFD) models to capture temperature gradients in the Knudsen layer, a new parameter, γ, is introduced to approximate the Knudsen layer vapor temperature. This new computational routine is implemented within Ansys Fluent™ with the help of User-Defined Functions (UDFs). CFD simulations are used to recreate phase change experiments from recent studies involving Hydrogen and Methane. Data from the CFD simulations are used to correlate γ to the evaporation rate. A function to calculate γ using the area-averaged phase change molar f (open full item for complete abstract)

Committee: Kishan Bellur Ph.D. (Committee Chair); Prashant Khare Ph.D. (Committee Member); Shaaban Abdallah Ph.D. (Committee Member) Subjects: Fluid Dynamics

Master of Science, The Ohio State University, 2024, Chemistry

Layered transition metal chalcogenides have great potential for a variety of applications in electronics, energy harvesting, catalysis, and membrane technologies, owing to their distinctive textural and photoelectronic properties. Intercalation of organic molecules into the interlayer spaces of these compounds can result in profound changes in the physical and chemical properties and lead to the emergence of unique phenomena. In this study, we report on the intercalation of ammonium and organic amines into interlayer spaces of layered chalcogenides of the form K2Ni3S4 via ion-exchange reactions. This unique family of layered transition metal chalcogenides is comprised of anionic layered, honeycomb networks of perpendicularly oriented MS4 square planes, separated by alkali ions. The growth of thin crystallites of K2Ni3S4 was carried out using potassium sulfide flux. After exploring a variety of substitution reaction schemes, we find that ammonium cations and cationic organic amines can be readily exchanged with the alkali cations in aqueous solution using a combination of X-ray diffraction, X-ray fluorescence, infrared spectroscopy, thermogravimetric analysis, transmission electron microscopy, and scanning electron microscopy with energy dispersive spectroscopy. Overall, this work establishes an intriguing new family of hybrid organic-inorganic layered materials.

Committee: Joshua Goldberger (Advisor); Yiying Wu (Committee Member); Patrick Woodward (Committee Member) Subjects: Chemical Engineering; Chemistry; Inorganic Chemistry; Materials Science; Nanoscience

Doctor of Philosophy, The Ohio State University, 2023, Physics

Random quantum circuits play an important role in the study of non-equilibrium properties of quantum many-body systems, such as entanglement and thermalization. In this thesis, we study the spreading of quantum information in two important examples of random circuits: a quantum circuit with charge and dipole conservation laws, and the random tree tensor network, which corresponds to the all-to-all circuit. We find that the dynamics of these two systems can fall into different phases depending on the spreading of quantum information in the system/Hilbert space. We first study the time evolution of a one-dimensional fracton system with charge and dipole moment conservation using a random unitary circuit description. Previous work has shown that when the random unitary operators act on four or more sites, an arbitrary initial state eventually thermalizes via a universal subdiffusive dynamics. In contrast, a system evolving under three-site gates fails to thermalize due to strong ``fragmentation'' of the Hilbert space. Here we show that three-site gate dynamics causes a given initial state to evolve toward a highly nonthermal state on a time scale consistent with Brownian diffusion. Strikingly, the dynamics produces an effective attraction between isolated fractons or between a single fracton and the boundaries of the system, as in the Casimir effect of quantum electrodynamics. We show how this attraction can be understood by exact mapping to a simple classical statistical mechanics problem, which we solve exactly for the case of an initial state with either one or two fractons. What's more, we further find that in the limit of maximal single charge goes to infinity, the fragmentation of Hilbert space of different filling can be solved by mapping to a mathematical tournament problem. Using this mapping we can show that the system exhibits a transition from a non-thermalized to a thermalized phase by tuning the filling number, as observed in a previous work. Our tech (open full item for complete abstract)

Committee: Brian Skinner (Advisor); Jeanie Lau (Committee Member); Samir Mathur (Committee Member); Mohit Randeria (Committee Member) Subjects: Physics

PHD, Kent State University, 2022, College of Arts and Sciences / Department of Physics

Strongly correlated electron systems are at the borderline of competing phases and can be tuned through different ground states by slight modifications. Therefore, they are good examples to study a quantum phase transition (QPT), to reveal how a quan tum critical point (QCP) at zero temperature is responsible for the unconventional properties observed at finite temperatures. QPTs are zero-temperature phase tran sitions, they are more complex and less understood than common phase transitions at finite temperatures. Examples are lacking, especially in the case where disorder is involved. Recent theories predict the possibility of an exotic quantum critical point in itinerant magnets with induced disorder that is accompanied by a quantum Grif- fiths phase. To explore such unconventional properties in close neighborhood to a magnetic phase, we aim to reveal the relevant quantum critical fluctuations with neutron scattering. We select systems with different magnetic order and choose as tuning parameter chemical substitution to study the effect of disorder. Such exper imental study aims to find key elements of a QCP with disorder. The two systems are the ferromagnetic (FM) alloy, Ni-V, tuned by the V-concentration into a para magnetic phase, and the non-magnetic Kondo semimetal, Ce(Cu,Ni)Sn, tuned by Cu concentration into an antiferromagnetic state. We apply different neutron scat- tering techniques and simple models to get essential characteristics of the magnetic correlations and fluctuations close to the QCP. Ni-V is a simple FM-alloy with a random atomic distribution that undergoes a quantum phase transition from a ferromagnetic to a paramagnetic state with sufficient substitution of Ni by V. First indication of a quantum Griffiths phase came from magnetization and μSR data, but the scale of the magnetic clusters remained elusive. Optimized small angle neutron scattering (SANS) data on different polycrystalline Ni- V samples close to the QCP (open full item for complete abstract)

Committee: Almut Schroeder (Advisor); Carmen Almasan (Committee Member); Gokarna Sharma (Committee Member); Maxim Dzero (Committee Member); Sanjaya Abeysirigunawardena (Committee Member) Subjects: Condensed Matter Physics

PHD, Kent State University, 2022, College of Arts and Sciences / Department of Physics

The heavy fermions (HF) are strongly correlated electron systems consisting of intermetallic compounds of lanthanides and actinides ions with f -electrons unfilled shells. These systems are very rich in physics and the interplay between competing interactions results in various interesting physical phenomena such as heavy fermion behavior, unconventional superconductivity, non-Fermi-liquid behavior, coexistence of superconductivity and magnetism, and quantum criticality. The origin of such phenomena comes from the interaction of itinerant conduction states with the partially filled 4f - or 5f -electron states of rare earth elements. The study of such important physical phenomena can be possible by tuning the system using nonthermal control parameters, such as chemical composition, magnetic field, and applied pressure. So, studying the chemical pressure effect on heavy fermion systems with or without magnetic field is an intriguing idea to construct various phase diagrams and study their phase transitions. We performed heat capacity (HC), magnetoresistance (MR), and resistivity measurements on the Ce-based 115 and U-based 122 heavy fermion materials at low temperatures. We studied the nature of the quantum critical point, second-order phase transition, and the possible interplay between superconductivity and magnetism. First, we were motivated by the possibility of observing the coexistence of magnetism and unconventional superconductivity in the heavy fermion Ce1−xSmxCoIn5 alloys. We performed specific heat, MR, and resistivity measurements in different magnetic fields. We investigated how the samarium substitution on the cerium site affects the magnetic-field-tuned quantum criticality of stoichiometric CeCoIn5. We have observed Fermi-liquid to non-Fermi-liquid crossovers in the temperature dependence of the electronic specific heat and resistivity at higher external magnetic fields. We obtained the magnetic-field-induced quantum critical point (open full item for complete abstract)

Committee: Carmen Almasan (Advisor); Maxim Dzero (Committee Member); Almut Schroeder (Committee Member); Gokarna P. Sharma (Committee Member); Songping Huang (Committee Member) Subjects: Physics

PHD, Kent State University, 2022, College of Arts and Sciences / Department of Physics

The study of quantum phase transitions is a promising route for understanding the origin of unusual properties in strongly correlated electron systems. Recent theories predict a new quantum critical point (QCP) with exotic properties such as an observable quantum Griffiths phase in disordered itinerant systems. Previous studies on disordered ferromagnetic (FM) system Ni(1−x)V(x) showed only “signs” of magnetic clusters close to the critical concentration xc where FM is destroyed. This dissertation provides direct evidence of magnetic correlations at various length scales and fluctuations at different time scales close to the QCP using Ni-V and Ni-Cr samples. Polarized small-angle neutron scattering (SANS) measurements reveal short-range magnetic correlations in Ni-V samples close to QCP. This polarization study also supports long-range magnetic correlations within macroscopic domains. The structure characterization of Ni-Cr confirms a high-quality chemical structure with random atomic distribution after optimizing the annealing protocol. Muon spin rotation (µSR) measurements successfully show the advantage of Ni-Cr. The response is not dominated by any strong nuclear moment like Ni-V. The µSR asymmetry of Ni(1−x)Cr(x) close to xc reveals magnetic order at low temperatures with coexisting dynamic clusters. Both SANS and µSR measurements support that the long-range FM order and short-range fluctuations are present in FM alloys Ni-V and Ni-Cr close to QCP.

Committee: Almut Schroeder (Advisor); Maxim Dzero (Committee Member); Carmen Almasan (Committee Member); Songping Huang (Committee Member); Hanbin Mao (Committee Member) Subjects: Physics

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

Since the 1970s, elastin-like polypeptides (ELPs) have been extensively characterized for their reversible phase transition in solutions. ELPs are soluble in aqueous solution at temperatures below their transition temperature (Tt) and undergo phase transition when the temperature is raised above Tt, at which ELPs are insoluble. While applications of surface-grafted ELPs continue to rise, there is limited knowledge of whether the phase transition behavior of surface-grafted ELPs follows that of the free ELPs. The motivation of this research study is to understand the surface phenomena of ELPs to support the development of ELP-based electrodes. The thesis pioneers the study of molecular arrangement of surface-grafted ELPs on confined spaces of metal electrodes. The discovery of grafting conditions presented in this thesis provides a path to consistent fabrication of ELP-based electrodes. The demonstrated applications of surface-grafted ELPs provide insight into their physical properties and phase transition behavior.

Committee: Julie Renner (Advisor); Michael Hore (Committee Member); Chung-Chiun Liu (Committee Member); Donald Feke (Committee Member) Subjects: Biophysics; Chemical Engineering; Higher Education

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

The pivot of this dissertation is the numerical analysis of turbulence-driven secondary motions in rectangular ducts, fully and partially filled with water. Flow through horizontal ducts are characterized by a unique flow pattern known as secondary flow of the second kind or ‘Nikuradse' flow who first discovered them in 1926, while working under Prandtl. The secondary flows are 1-2% of the axial flow and are in addition, and perpendicular, to the axial flow. Despite their weak strength, the secondary motions significantly influence stress distribution and scalar transport such as heat transfer. The mean secondary flow consists of four pairs of counter-rotating vortices, anti-symmetric about the diagonal bisector and each pair is flanked by a shear layer on the intersecting side walls. Turbulence-driven secondary flow in straight ducts appears only above a critical Reynolds number. These are absent in the laminar regime. From this perspective, the aim of the present study is to investigate the appearance and evolution of turbulence-driven secondary motions in a square cross-section duct near the transition, and explore their asymptotic behavior for high Reynolds number, Re. We perform a numerical experiment which involves calculating the flow in a square duct over100=Re=50,000. At a critical Reynolds number Rec = 704, the flow becomes turbulent, with the pressure drop, dp/dx, discontinuously increasing and a weak cross-flow discontinuously developing. The cross-flow may be quantified by the circulation in each octant of the duct. For Re > 2500, the bulk Nikuradse vortex contributes ~ 9/5 and the wall vorticity ~ -4/5 to the circulation. A sub-class of turbulent duct flow is turbulent flow through open ducts or partially-filled ducts. Flow through an open or partially-filled duct is characterized by the presence of an air-water interface interacting with a solid wall, forming a mixed-boundary corner. A novel feature of the mixed-boundary corner i (open full item for complete abstract)

Committee: Urmila Ghia Ph.D. (Committee Chair); Leonid Turkevich (Committee Member); Milind Jog Ph.D. (Committee Member); Shaaban Abdallah Ph.D. (Committee Member) Subjects: Mechanical Engineering

Doctor of Philosophy, University of Toledo, 2021, Physics

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

Committee: Sanjay Khare Dr. (Committee Chair); Jacques Amar Dr. (Committee Member); Richard Irving Dr. (Committee Member); Aniruddha Ray Dr. (Committee Member); Anju Gupta Dr. (Committee Member) Subjects: Physics

Doctor of Philosophy, The Ohio State University, 2021, Mechanical Engineering

With the advantages of high bandwidth and abilities to see through opaque materials, millimeter wave (mmW) band (30 to 300 GHz) has been intensively explored in recent years. Although there are increasing demands for reconfigurable mmW systems for their potential applications in defense, switching, imaging, and sensing, overcoming the limitations such as high losses and large power consumption in mmW systems is still a challenge. Phase change materials (PCM) like vanadium dioxide (VO2), which have novel and tunable physical properties such as electrical resistivity and optical transmittance, are appealing choices for mmW reconfiguration to provide faster operation speed and lower loss microsystems. One aspect of VO2 thin film that is not fully exploited is the metal-insulator transition (MIT) region, where the electrical resistivity changes about four orders of magnitude with external stimuli. In this work, we present a highly sensitive antenna-coupled VO2 microbolometer for mmW imaging. The proposed microbolometer takes advantage of the large thermal coefficient of resistance (TCR) of VO2 at the non-linear region. The thermal resistance of the device is significantly improved by micro-electro-mechanical systems (MEMS) techniques to suspend the device above the substrate, compared with non-suspended microbolometers. The finite element method is employed to analyze the electrothermal and electromagnetic performance of the device. The frequency range of operation is 65 to 85 GHz, and the realized gain at broadside is > 1.0 dB. Simulation results indicate a high responsivity of 1.72x10^3 V/W and a low noise equivalent power (NEP) of 33 pW/√Hz. Targeting for broader applications, it is highly desired to deposit VO2 thin films on silicon (Si) substrate. Here, we employ the annealed alumina (Al2O3) buffer layers to obtain high-contrast VO2 thin films. The fabrication details for the Al2O3 buffer layers using atomic layer deposition (ALD) and VO2 thin films using DC sput (open full item for complete abstract)

Committee: Nima Ghalichechian (Advisor); Hanna Cho (Committee Member); Renee Zhao (Committee Member) Subjects: Electrical Engineering; Materials Science; Mechanical Engineering; Nanotechnology

Doctor of Philosophy, Case Western Reserve University, 2021, EMC - Aerospace Engineering

We present an incremental Lagrangian framework based on meshfree methods, the Hot Optimal Transportation Meshfree (HOTM) method, for a robust and efficient solution of the dynamic response of materials in extreme multi-physics problems, possibly involving strongly coupled thermomechanical conditions, extremely large deformation, phase transition, and multi-phase mixing. The HOTM method combines the Optimal Transportation Meshfree (OTM) method and the variational thermomechanical constitutive updates. The variational structure of a dynamic system with general internal dissipative mechanisms is discretized in time by applying the Optimal Transportation theory, while the material points sampling approach and Local Maximum Entropy approximation are introduced for spatial discretization. Meanwhile, a phase-aware constitutive model is proposed to describe the material behavior with general dissipation mechanisms, which involves elasticity, plasticity, viscosity, and phase transition. The fully discretized mechanical balance equations and thermal balance equations are solved using an operator splitting algorithm to predict the deformation, temperature, and internal state variables of the material. The convergence of the computational framework is studied in a three-dimensional transient heat conduction problem, while the accuracy of the HOTM method is validated in the example of upsetting a metallic billet. The scope and robustness of the HOTM method are demonstrated in the application of hot pressing manufacturing processes of resin-based friction composites and an emerging additive manufacturing process called laser cladding technology.

Committee: Bo Li (Committee Chair); Ya-Ting Tseng Liao (Committee Member); Chirag Kharangate (Committee Member); Xiong Yu (Committee Member) Subjects: Aerospace Engineering; Mechanical Engineering; Mechanics

PHD, Kent State University, 2020, College of Arts and Sciences / Chemical Physics

Light interacts with liquid crystals. It is one of the most useful tools that can reveal the director field of liquid crystals, which can be either uniform or spatially varied. On the other hand, liquid crystals can also be used to control the photon current which is light. In this dissertation, the complementary relation between light and liquid crystals is explored. Understanding the behavior of nematics in inhomogeneous external fields is of fundamental interest. The director field of a nematic sample in radially varying magnetic field was studied experimentally by interferometry and theoretically by modeling and numerics. Experimental studies involved recording far-field interference patterns using coherent polarized light. The magnetic field was described analytically, and the director configuration and the interference pattern in the far field were modeled numerically. A comparison of the experimentally determined and the numerically calculated far-field patterns was made. The optical, dielectric and thermal properties of cholesterics were studied, including their bandgap structure. These experimental results were useful for developing an optical device: an optical transistor and realizing distributed feedback lasing, which were both demonstrated in this work. Light carries momentum and energy. The energy can be harvested to do mechanical work directly and indirectly. There are many advantages of converting the light energy directly to mechanical work. Two photomechanical systems were studied in this work; liquid crystal elastomer and molecular crystals. Based on the way nematics modify light, a tunable waveplate using nematics was constructed which can be adjusted by controlling the director field. This waveplate is one of the key components in the optical transistor. Another goal of this work is to use one light beam to control liquid crystals in order to control an other beam of light. The optical transistor has two components; (open full item for complete abstract)

Committee: Peter Palffy-Muhoray (Advisor); Hiroshi Yokoyama (Committee Member); Deng-Ke Yang (Committee Member); Xiaoyu Zheng (Committee Member); Michael Tubergen (Committee Member) Subjects: Condensed Matter Physics

Doctor of Philosophy, The Ohio State University, 2019, Chemical Engineering

n-Alkanes play important roles in our everyday lives, and they are basic constituents of many complex lipid molecules. The importance of saturated aliphatic hydrocarbons is not limited to terrestrial applications, as interplanetary studies have shown that they are both major and minor components of the giant planet atmospheres and Saturn's moon -Titan. Thus, in these situations, short chain alkanes can play a role similar to that of water on earth. Nucleation is a phenomenon that initiates many phase transitions, and supersonic nozzles are characterized by a large temperature gradient that results in high supersaturations and nucleation rates. Therefore, the goal of this work is to study the phase transitions of lower n-alkanes in a supersonic nozzle. First, we investigate and expand the vapor to liquid nucleation and condensation database for lower n-alkanes – pentane, hexane, and heptane - over a broad range of temperatures and partial pressures. Secondly, we apply the first and second nucleation theorems to determine the properties of the critical clusters of these chain molecules and advance our understanding of the nucleation physics. Thirdly, we study the freezing behavior of n-pentane, n-hexane, and n-heptane droplets and advance our understanding of the surface-templating effect in these short chain n-alkanes. The experimental vapor to liquid nucleation rates, at temperatures between 109 K and 168 K, for n-pentane, n-hexane and n-heptane were obtained by combining data from pressure trace measurements and small angle x-ray scattering experiments. For all n-alkanes, the nucleation rates increase with increase in supersaturation and decrease in temperature. Using two nozzles, the critical cluster sizes of n-heptane ranged from ~ 8 to ~12 and increased with temperature. Overall, the molecular contents of the critical clusters determined from experiments are higher than predictions from classical nucleation theory. Motivated by (open full item for complete abstract)

Committee: Barbara Wyslouzil (Advisor); Isamu Kusaka (Committee Member); Nicholas Brunelli (Committee Member) Subjects: Chemical Engineering

PHD, Kent State University, 2019, College of Arts and Sciences / Department of Physics

Heavy ion collisions allow us to study the formation and characteristics of Quark-Gluon Plasma (QGP), a state of matter now known to exist at very high temperature and/or very high energy density. QGP also existed around a millionth of a second after the Big Bang, and it may persist today at the center of compact stars. A brief time (a few fm/c) after the QGP phase is achieved in a heavy ion collision, the hadronization process starts to take place. This leads to the production of particles such as protons, pions, etc., which can be observed by particle detectors. What symmetry or asymmetry went into the motion of particles during the collision process? There are other interesting, yet unanswered questions, such as what is the order of the phase transition between the QGP and hadronic phases? Such questions intrigue many high-energy nuclear physics researchers. The Relativistic Heavy Ion Collider (RHIC) located at Brookhaven National Laboratory began operation in the year 2000 in a mission to produce controlled heavy ion collisions and QGP. The STAR (Solenoidal Tracker at RHIC) collaboration operates one of four experiments at RHIC, and STAR is at present the only remaining experiment taking data. The Beam Energy Scan (BES) program at RHIC explores collisions over the widest possible range of beam energies, and allows us to study the properties of the Quantum Chromodynamics (QCD) phase diagram in the regions where a first-order phase transition and a critical point may exist. Phase-I of this program (BES-I) collected data during 2011-2014 and interesting results have been observed. For example, there is a minimum in an azimuthal anisotropy parameter called directed flow (v1) for protons and other baryons at collision energies of √sNN = 10-20 GeV, and it qualitatively resembles the predicted signature of a softening of the equation of state associated with the first-order phase transition. To better identify this softest point, we need to make measurements of d (open full item for complete abstract)

Committee: Declan Keane (Advisor); Spyridon Margetis (Committee Member); Michael Strickland (Committee Member); Diane Stroup (Committee Member); Arvind Bansal (Committee Chair) Subjects: Nuclear Physics; Physics

PHD, Kent State University, 2019, College of Arts and Sciences / Department of Physics

The study of quantum phase transitions (QPT) is a promising route to comprehend the origin of unconventional properties in strongly correlated electron systems. Recent theories predict a new quantum critical point (QCP) in disordered itinerant system with exotic properties such as observable quantum Griffiths phase (QGP). The binary alloy Ni-V presents such QGP and looks like the best example to study a ferromagnetic QPT with controlled disorder. In this work, we investigate further Ni-V with advanced local methods using neutron scattering and μSR techniques. Initial doubts on sample quality and sample-dependent impact on different magnetic phases and disordered scenarios can be resolved. A structural characterization indicates that the investigated Ni-V samples show a high-quality chemical structure with expected random atomic distribution. We provide direct evidence of the "disorder" with μSR methods. We clarify essential details of the Ni-V phase diagram such as the nature and the boundaries of ferromagnetic and cluster glass phases. These new data reinforce the location of the QCP and the limits of the QGP in Ni-V. The main results are consistent with theories predicting an infinite randomness quantum critical point associated with a QGP.

Committee: Almut Schroeder PhD (Committee Chair); Carmen C. Almasan PhD (Committee Member); Maxim Dzero PhD (Committee Member); Songping Huang PhD (Committee Member); Michael Tubergen PhD (Committee Member) Subjects: Condensed Matter Physics; Experiments; Physics