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

In this thesis the hyperpolarizability of various multi-dimensional molecules is studied theoretically/computationally, with particular focus on the second-rank Kleinman-disallowed (KD) component of the hyperpolarizability. This component, which transforms as a second-rank traceless symmetric tensor, could be utilized in certain chiral-axial molecular alignment schemes to produce a bulk response. Nonpolar chiral-axial systems have been proposed in contrast to polar media, which utilize the vector component of the molecular hyperpolarizability and require parallel alignment of the molecular dipoles. Such parallel alignment of dipoles must be frozen in in order to overcome the natural tendency for dipoles to align anti-parallel. This limits the density of chromophores that can be loaded into a polar material. Nonpolar materials do not have such limits in theory. The two geometric classes of molecules that can most easily be incorporated into nonpolar chiral-uniaxial materials are propeller-shaped (C3 or D3 symmetry) and -shaped (C2v symmetry). This work describes efforts to design molecules within these classes that would be suitable for bulk NLO materials. The sum-over-states (SOS) expression is used to model the molecular hyperpolarizability, and quantum chemical calculations, along with linear absorption data (when available) provide the necessary parameters to evaluate truncated forms of the SOS expression. A host of chemical and geometric modifications will be considered in order to elucidate important structure/function relationships. Also, the SOS model will be tested in some cases when experimental measurements (via Kleinman-disallowed hyper-Rayleigh scattering) are available. While a majority of this work focuses on multi-dimensional molecules, a small section deals with the question of optimizing the hyperpolarizability of a one-dimensional system. It is suggested that the recently-proposed idea of modulated conjugation as a means for improving intrinsic mol (open full item for complete abstract)

Committee: Rolfe Petschek PhD (Advisor); Ken Singer PhD (Committee Member); Jie Shan PhD (Committee Member); Christoph Weder PhD (Committee Member) Subjects: Materials Science; Optics; Organic Chemistry; Physics

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

Nominally metallic systems can be rendered insulating by electronic interactions, disorder, or both, leading to a myriad of interesting many-body phases. In this thesis, we present electronic transport data on a variety of such insulator materials, each with their own unique emergent phenomena. We start with few-layer graphene (FLG), the multilayer counterpart to monolayer graphene, and show that electronic interactions can lead to the development of an electronic energy gap in the band structure near charge neutrality. Previously, this has been associated with spontaneous inversion symmetry breaking, but has only been observed in suspended devices of the highest quality. Here, we show that similar physics can be observed in hexagonal boron nitride-encapsulated devices, alleviating the requirement for suspension. Moreover, in very thick FLG samples, typically thick enough to be considered as three-dimensional graphite, we show the existence of fractional quantum Hall states that are extended through the bulk of the material. Next, we turn to Pt-doped TiSe2, where the interplay between a charge density wave state and a newly discovered quasi one-dimensional insulating state gives rise to ultra slow time-scale physics, along with a strong resistance anisotropy. Finally, transport data as well as angle-resolved photoemission spectroscopy data on Se-doped Ge2Sb2Te5 devices are shown. Here, a disorder-induced metal-to-insulator transition exhibits unique properties, which we attribute to the onset of strong electronic interactions.

Committee: Stuart Raby (Committee Member); Nandini Trivedi (Committee Member); Roland Kawakami (Committee Member); Marc Bockrath (Advisor) Subjects: Physics

Doctor of Philosophy, The Ohio State University, 2022, Chemistry

Organic-inorganic hybrid perovskites have emerged in recent years as one of the most promising materials for solution-processed electronics and optoelectronics including solar cells, light-emitting diodes, and field-effect transistors. Combining a rigid inorganic framework with soft organic materials, these hybrid perovskites provide the opportunity for investigating organic-inorganic interactions at the molecular scale. This dissertation summarizes studies of organic-inorganic hybrid halide perovskites to date, analyzes structural distortions in compounds with the n = 1 Ruddlesden-Popper structure, and describes the synthesis and characterization of new low-dimensional organic-inorganic hybrid halides. Chapter 1 discusses the variety of inorganic and hybrid halide perovskites and their applications. Perovskites with different dimensionalities have attracted scientists' interest in various fields. Though the understanding of 3-dimensional perovskite structures is in a deep stage, studies on lower-dimensional perovskites are relatively deficient. The symmetry consequences of octahedral tilting on the structures of n = 1 Ruddlesden-Popper phases are analyzed in chapter 2. Combining three different types of tilting, 47 different distorted structures are identified. A survey of the reported n = 1 Ruddlesden-Popper perovskites shows that the structures of most compounds can be explained by the group theory predictions given here. For those compounds that do not match with the symmetry predictions, other factors are considered, leading to two types of polar perovskites. Based on this analysis, rational design strategies to prepare new polar n = 1 Ruddlesden-Popper perovskites are proposed. Chapter 3 describes the synthesis and characterization of a series of silver bismuth bromide double perovskites. In these double perovskites, the B2+ cations (e.g. Pb2+, Sn2+, Cd2+) are replaced with a 1:1 mixture of Ag+ and Bi3+. In this work, our focus is primarily on compounds (open full item for complete abstract)

Committee: Patrick Woodward (Advisor); Anne Co (Committee Member); L.Robert Baker (Committee Member); Shiyu Zhang (Committee Member) Subjects: Chemistry

Doctor of Philosophy, The Ohio State University, 2022, Chemistry

Biological organisms need to respond to changes in their surrounding environments to maintain homeostasis. On a cellular level, responding generally involves activating or repressing gene expression by forming feedback circuits that sense changes of physiochemical cues or physical factors. The interactions between environmental changes and cellular responses are often “allosteric”, by which the sensed signals propagate to a remote responding element. Understanding the corresponding allosteric pathways and quantifying the relevant biological information flows are the foundation to reveal the secrets of life. Homo-oligomeric ligand-activated proteins are ubiquitous in biology. My research aims to understand the allosteric response mechanism of the model ring-shaped, homo-oligomeric TRAP (trp RNA-binding attenuation protein). TRAP serves as an orthogonal gene-regulatory switch to control Trp (tryptophan) production in Bacilli via Trp-dependent mRNA binding. This cyclic 12mer (or 11mer) protein sensor is activated by binding up to an equivalent number of Trp molecules to subsequently bind to specific sequences in the 5'UTR of the trp operon. When activated by Trp, binding of TRAP to this trp leader results in attenuated transcription and translation of enzymes responsible for Trp biosynthesis. To understand how TRAP senses and responds to Trp concentration, we first examined its homotropic binding to multiple Trp ligands, and how these Trp binding events influence heterotropic binding to RNA. As described in chapter 2, to probe the allosteric coupling between ligand binding sites, we developed the nearest-neighbor (NN) statistical thermodynamic binding model, comprising microscopic free energies for ligand binding to isolated sites ΔGN0, and for coupling between one or both adjacent sites, ΔGN1 and ΔGN2, respectively. The resulting partition function (PF) could be used to simulate the effects of these parameters on population distributions for 2N possible ligand (open full item for complete abstract)

Committee: Mark Foster (Advisor); Steffen Lindert (Committee Member); Rafael Brüschweiler (Committee Member); Vicki Wysocki (Committee Member) Subjects: Biochemistry; Biophysics; Molecular Physics

Doctor of Philosophy, The Ohio State University, 2021, Chemistry

The computational bottleneck of applying quantum chemistry methods has always been a significant obstacle to calculating the properties of condensed-phase systems. In this work we present accurate, scalable methods that push the dynamic range of ground- and excited-state quantum chemistry into the condensed-phase. First, we introduce an extension of symmetry-adapted perturbation theory that includes nonadditive (many-atom) dispersion effects that are essential in the description of large systems. Application of this approach to the study of π-π interactions has revealed that the dominant paradigm (based on low-order electrostatic multipoles) for understanding π-stacking is fundamentally flawed. We propose a reformulation of the electrostatic model of aromatic π-π interactions that is based on van der Waals forces, instead. Our work with π-stacking is exemplary of the utility that symmetry-adapted perturbation theory with many-body dispersion (SAPT+MBD) has as an interpretive tool, and our results suggest that it will be extremely useful in characterizing intermolecular interactions at the nanoscale. In the second part of this work, we introduce several efficient methods for solution-phase photochemistry. Contributions of this work include the implementation of a vibrational exciton model, a new root-homing algorithm based on level shifting, and introducing natural charge-transfer orbitals to combat spurious states in solution-phase time-dependent density functional theory (TDDFT). The vibrational exciton model is extremely scalable, and we use it to investigate the infrared spectrum of >200 surfactant molecules at the air/water interface. Our results have lead to insights into the nature of signal depletion in one-dimensional infrared spectra of self-aggregating molecules at interfaces. Our root-homing algorithm is robust to variational collapse, and shows promise in finding orbital-optimized excited states when the density of states becomes large. Lastly, our na (open full item for complete abstract)

Committee: John Herbert (Advisor); Heather Allen (Committee Member); Sherwin Singer (Committee Member); Barbara Ryden (Committee Member) Subjects: Physical Chemistry

Doctor of Philosophy, University of Toledo, 2020, Mathematics

We study the complex symmetry of weighted composition operators Wƒ,φ on the Hilbert space Hγ of analytic functions over the open unit ball Bn with reproducing kernel function Kγw(z)=(1 - 〈 z,w 〉)-γ, where γ is any positive real number. We first characterize a new class of conjugations, which we will call weighted composition conjugations and then give necessary and sufficient conditions for a weighted composition operator Wƒ,φ to be complex symmetric with respect to a weighted composition conjugation. The results can be generalized to reproducing kernel Hilbert spaces over the unit ball in an arbitrary complex Hilbert space H. A characterization of complex symmetry of Toeplitz operators Tφ on the Bergman space A2(Bn), with respect to weighted composition conjugations is also given.

Committee: Trieu Le (Committee Chair); Zeljko Cuckovic (Committee Member); Sonmez Sahutoglu (Committee Member); Akaki Tikaradze (Committee Member); Khoi Le (Committee Member) Subjects: Mathematics

Doctor of Philosophy, University of Toledo, 2020, Exercise Science

Neuromuscular dysfunction in shoulder girdle and upper extremity muscles is commonly observed in individuals with glenohumeral labral repair as an under-appreciated consequence of joint injury. Postoperative neural impairments from muscular, spinal and supraspinal pathways are hypothesized to contribute to the persistent muscle weakness, which may negatively affect shoulder-specific function and perceived quality of life in this population. Although identifying the specific origin of impairment has been theorized to help inform targeted treatment approaches to facilitate muscular recovery, there is limited evidence regarding origin of these neural impairments in individuals with glenohumeral labral repair. In order for the assessment and interventions to be effective, understanding comprehensive profile of neuromuscular function is an important step to allow clinicians to make evidence-based clinical decision in the course of rehabilitation. The focus of manuscript 1 was to compare peripheral, spinal and supraspinal measures of neuromuscular function in the upper extremity musculature between individuals with glenohumeral labrum repair and uninjured matched controls. We found unilateral weakness in shoulder abduction strength, unilateral impairment in corticospinal excitability for the upper trapezius, and bilateral impairment in spinal-level motoneuron pool excitability for the flexor carpi radialis in individuals with glenohumeral labral repair compared to uninjured controls. The focus of manuscript 2 was to determine the relationships between objective upper extremity muscle function and patient-reported outcomes in individuals with glenohumeral labral repair. We found lesser wrist flexor strength and lower corticospinal excitability explained worse perceived regional function. Lesser activity level explained better physical health, and elder age explained better mental health. The focus of manuscript 3 was to determine whether commonly described measures of neur (open full item for complete abstract)

Committee: Grant Norte (Committee Chair); Christopher Ingersoll (Committee Member); Sadik Khuder (Committee Member); Neal Glaviano (Committee Member) Subjects: Health Sciences; Kinesiology; Neurosciences; Sports Medicine

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, 2020, Psychology

The current research program seeks to explain a phenomenal visual experience. Namely, appearances of the shapes of three-dimensional (3D) rigid objects remain to be rigid when we walk around and view them from different angles and distances. This is a hard problem to solve given the ambiguities arising from the optical projection and constantly changing retinal images as we navigate. Two hypotheses were proposed. Hypothesis 1 explains this phenomenon by arguing that the visual system can reconstruct the 3D shape veridically. Alternatively, Hypothesis 2 argues that even though the reconstructed 3D shape is distorted with viewpoint, the resulting nonrigidity in the 3D shape percepts is not detected by the visual system under ordinary circumstances. Eight psychophysical experiments were conducted to test the two hypotheses by investigating the perception of 3D metric shape of well-structured polyhedral objects from binocular stereopsis. In Experiment 1 to 7, participants adjusted the 3D shape of an adjustable object to match the perceived 3D shape of a reference object under a variety of conditions. In Experiment 8, participants discriminated a nonrigid polyhedral object from a rigid one in an immersive virtual reality environment. Results of the eight experiments reported in this thesis reject Hypothesis 1 and support Hypothesis 2. Thus, the phenomenal rigid appearance of rigidly moving objects does not arise from the veridical perception of 3D shape. Rather, the 3D metric shape percepts vary systematically with viewing distance (Experiment 1, 4, 7), object size (Experiment 2), in-plane orientation (Experiment 3), different types of optical projection (Experiment 4, 5, 6), and scene context (Experiment 7). And testing with more symmetric objects or in a more naturalist scene context cannot make the perception more accurate (Experiment 7). However, a comparison between participants' performance in Experiment~8 with their performance in Experiment 1, 4, or 7 suggests th (open full item for complete abstract)

Committee: Alexander Petrov (Advisor); James Todd (Committee Member); Julie Golomb (Committee Member); Declan Smithies (Committee Member) Subjects: Psychology

Master of Sciences, Case Western Reserve University, 2020, Physics

In this thesis we explore mechanical analogs of electronic topological insulators. We develop continuum models for the mechanical instability and spontaneous symmetry breaking for monolayer antimonene and bilayer graphene. We find that walls form between domains corresponding to different symmetry breaking minima. These domain walls are solitons in our model. Perturbations about the symmetry breaking equilibria propagate as waves with a gapped dispersion in the bulk but there is a gapless mode with linear dispersion that propagates along the domain wall in a manner reminiscent of the electronic edge modes of a topological insulator. We establish that monolayer antimonene is a mechanical topological insulator by demonstrating a mapping between our continuum model and an underlying Dirac equation of the symmetry class BDI which is known to be a topological insulator in one dimension and a weak topological insulator in two dimensions. Following a similar argument we expect that bilayer graphene as well is a weak topological insulator in two dimensions. We surmise that the effects studied here (namely low scale symmetry breaking, strain solitons and gapless edge modes) are not limited to antimonene and bilayer graphene but are common features of two dimensional materials.

Committee: Harsh Mathur (Advisor) Subjects: Condensed Matter Physics; Physics

Doctor of Philosophy, The Ohio State University, 2019, Physics

Magnetic skyrmions have attracted substantial interest due to their potential for use in spintronics devices and next-generation information storage, and due to the novel phenomena that result from the topological winding of skyrmions. In this dissertation we theoretically study the properties of magnetic skyrmions in chiral magnets. We focus on two key parameters that must be optimized to achieve maximum device performance: skyrmion size, and skyrmion stability. Skyrmions are stabilized in materials where inversion symmetry is broken. We show that the skyrmion crystal phase is more stable in systems with broken mirror inversion symmetry compared with systems where only bulk inversion symmetry is broken. To understand this effect we study a system where both mirror and bulk inversion symmetry are broken. We show that broken bulk inversion symmetry tends to stabilize a conical phase, and this phase becomes progressively less stable when broken mirror inversion symmetry is introduced. The phase diagram reveals a large region of skyrmion crystal stability, as well as a stable elliptic cone phase, and a square skyrmion crystal phase. In addition to crystal structures with broken inversion symmetry, the presence of an interface in magnetic films introduces a source of broken mirror symmetry. We show that this added source of symmetry breaking enhances the stability of the skyrmion crystal phase. Films surfaces and interfaces also stabilize a novel phase of matter called a chiral bobber crystal. This phase can be uniquely identified by the presence of a two-dimensional lattice of singular points in the magnetization field called Bloch points. We present experimental evidence for the observation of a chiral bobber crystal using magnetization data. Skyrmions can also be found outside the skyrmion crystal phase as metastable, particle-like excitations with a finite lifetime. We show that the lifetime and size of skyrmions have a strong interdependence. Putting limits o (open full item for complete abstract)

Committee: Mohit Randeria Professor (Advisor); Nandini Trivedi Professor (Committee Member); Samir Mathur Professor (Committee Member); Fengyuan Yang Professor (Committee Member) Subjects: Condensed Matter Physics

Doctor of Philosophy, The Ohio State University, 2019, Physics

In crystalline materials, the symmetry of the crystal lattice imposes strict conditions on the observable properties of the material. These symmetry restricted conditions can be, in turn, probed by light via the electromagnetic interaction. Studying the electromagnetic excitations in solids can reveal many fundamental properties of these systems. A quick introduction and guide to symmetry in solids will be given, with an emphasis on how it can be used to interpret spectroscopic measurements. The measurement techniques used will also be described. Time domain Terahertz spectroscopy (TDTS) is the main technique used in this dissertation. Important experimental considerations pertaining to the construction of the THz spectrometer will be given. In the multiferroic Sr_2 FeSi_2O_7, we found multiple excitations in the few meV energy scale (THz), in the material's paramagnetic phase. Measurements with varying temperature and magnetic field revealed that these excitations are both electric and magnetic dipole active. By considering the ground state of the Fe 2+ magnetic ion in Sr 2 FeSi 2 O 7 , we concluded that our observation is coming from the spin-orbital coupled states of the ion. This realization demonstrated that spin-orbit coupling plays a crucial role in these exotic materials. Interestingly, these spin-orbital THz excitations persist into the magnetically ordered phase. The single-ion picture of the paramagnetic phase needs to be expanded theoretically to explain our observations. CaFe_2O_4 orders antiferromagnetically below ~ 200 K. Two co-existing magnetic structures (A and B phase) have been measured previously by neutron diffraction. The anti-phase boundaries between these two phases have been proposed to be the cause of the quantized magnetic excitations (magnons) measured by an inelastic neutron scattering study. We measured two antiferromagnetic resonances (magnons) with TDTS. Our observation can be explained by the orthorhombic crystal anisotropy of CaF (open full item for complete abstract)

Committee: Rolando Valdes Aguilar (Advisor); P. Chris Hammel (Committee Member); Nandini Trivedi (Committee Member); Douglass Schumacher (Committee Member) Subjects: Physics

PhD, University of Cincinnati, 2018, Arts and Sciences: Physics

In this thesis work, we present a systematic classification of four dimensional rank-1 N=2 superconformal field theories (SCFTs). The analysis is based on extracting the low energy properties of N=2 SCFTs through the study of the structure of their Coulomb branch geometries. The original work of Seiberg and Witten provided the key to interpret features of $\cN=2$ theories in terms of geometrical objects. Generalizing from that seminal work, we show how a systematic description of rank-1 N=2 SCFTs is possible. An important property to consider is that a scale invariant Coulomb Branch geometry does not fully characterize a theory; we have to introduce a set of deformations, that still preserve the N=2 supersymmetry structure, together with consistency conditions for them, to distinguish theories sharing the same scale invariant behavior. The main outcome of our study is to provide a classification of the flavor algebras for the theories corresponding to the geometries we study. We carry this out in two ways. The first, called the algebraic approach, directly extends the work of Seiberg and Witten (and subsequent research). The second, topological approach, is a field theoretic extension of work originated in the string theory literature. In either case, the preexisting research provided only a partial answer to our problem, essentially describing only the subset of all the possible geometries that we call the ``maximal deformations''. Our construction is to be contrasted and in fact complements the conformal bootstrap framework, which instead of studying the low energy properties of these theories relies on the constraints of the full conformal symmetry of the microscopic theory.

Committee: Philip Argyres Ph.D. (Committee Chair); Carlos Bolech Ph.D. (Committee Member); Alexandre Sousa Ph.D. (Committee Member); L.C.R. Wijewardhana Ph.D. (Committee Member) Subjects: Physics

Doctor of Philosophy, The Ohio State University, 2018, Physics

In this dissertation, we focus on topological phases protected or enforced by crystalline symmetries. The topological phase can appear in the ground state of fermion and interacting boson or in the excitation bands of the free boson such as phonon and magnon. Those topics are covered in three parts. In the second chapter, we study the Glide Symmetry Protected Topological (GSPT) phases of interacting bosons and fermions in three spatial dimensions with certain on-site symmetries. They are crystalline Symmetry Protected Topological (SPT) phases, which are distinguished from a trivial product state only in the presence of non-symmorphic glide symmetry. We classify these GSPT phases with various on-site symmetries such as $U(1)$ and time reversal, and show that they can all be understood by stacking and coupling two-dimensional short-range-entangled phases in a glide-invariant way. Using such a coupled layer construction we study the anomalous surface topological orders of these GSPT phases, which gap out the two-dimensional surface states without breaking any symmetries. While this framework can be applied to any non-symmorphic SPT phase, we demonstrate it in many examples of GSPT phases including the non-symmorphic topological insulator with "hourglass fermion" surface states. In the third chapter, we discuss the non-symmorphic crystalline symmetry enforced Quantum Spin Hall effect (QSHE). In the generic classification frame of SPT phases, the classification is $\mbz_2$ for the ground state of fermion in 2D with charge conservation and time-reversal (TR) symmetry. The ground state can be in either trivial state or QSHE state, which depends on the specific model. However, we prove that the gapped ground state must be QSHE other than trivial as long as given non-symmorphic symmetry present. We also propose a crystal structure as one realization, and make an effort on material searching based on the space group. This work can supply a new principle of QSHE mater (open full item for complete abstract)

Committee: Yuan-Ming Lu (Advisor); Tin-Lon Ho (Committee Member); Eric Braaten (Committee Member); Jay Gupta (Committee Member) Subjects: Physics; Theoretical Physics

BA, Oberlin College, 2017, Physics and Astronomy

The relationship between degeneracy and symmetry in quantum mechanics is explored using two dimensional infinite potential wells with boundaries |x|^n + |y|^n = an for n = 2, whose limiting cases are circular (n = 2) and square (n ¿ 8) well. Analytic solutions for the circular and square cases are derived from separation of variables. Boundary element method (BEM) is a numerical method that solves PDEs using boundary conditions. The BEM is used to solve potential well problems. The method is first tested by comparing numerical solutions with analytic solutions for the circular and square wells. For the ground state of the circular well, the error as a function of the number of discretization points N decreased like 1/N^2. As the potential well changed shape from circle to square, energy eigenvalues and degeneracies are tracked. Energy levels split (when degeneracies are lifted), merge, and cross.

Committee: Daniel F. Styer (Advisor) Subjects: Physics; Quantum Physics

PhD, University of Cincinnati, 2017, Arts and Sciences: Psychology

The mathematical theory of symmetry provides a framework to understand higher order structures of behavioral organization across various contexts; the same principle that explains the organization of quadruped gaits can also be applied to behavioral coordination in interpersonal contexts. The current studies examined how symmetries of perceptual coupling and social information influenced interpersonal coordination during a three-person drumming task. In Study 1, triads of participants performed a drumming task without explicit instructions to coordinate; each participant drummed to given metronome beats for 10 seconds and maintained his or her rhythm for the rest of the trial. Half of the 24 triads drummed at 60 bpm, and the other drummed at 45 bpm. Each triad performed the task under five auditory coupling conditions: the all-, rotation-, partial-, clamped-, and no-coupling conditions. During the task, participants could hear but not see each other's drumming. The results showed that when coupling was present, the spontaneous coordination mode that emerged tended to be inphase. Regardless of drumming frequency, coordination in the all- and clamped-coupling conditions was more stable than in the partial-coupling conditions, indicating the effect of asymmetric coupling functions. In addition, period shifts were observed in the 45-bpm all-, rotation-, and clamped-coupling conditions. In Study 2, the minimal group paradigm was used to manipulate the symmetry of social identity among a triad. Fifteen triads were assigned to the heterogeneous condition, where two participants were in the minimal ingroup—the red group—and one in the minimal outgroup—the blue group. The other 14 triads were in the homogeneous condition (i.e., the control group) with all of them assigned to the red group. Beside the minimal group manipulation, there was no constraint on either visual or auditory information in Study 2. The participants first performed the drumming task without explicit inst (open full item for complete abstract)

Committee: Rachel Kallen Ph.D. (Committee Chair); Michael Richardson Ph.D. (Committee Member); Michael Riley Ph.D. (Committee Member) Subjects: Psychology

Doctor of Philosophy, The Ohio State University, 1987, Graduate School

Committee: Not Provided (Other) Subjects: Physics

Doctor of Philosophy, The Ohio State University, 1985, Graduate School

Committee: Not Provided (Other) Subjects: Physics

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

The use of soft and hard magnetic materials in the construction of electric machines has become a common practice. However, demand for machines with higher power density and efficiency sets new challenges; new machines require non-conventional geometries, materials with higher energy densities, higher operating temperatures and reliable mechanisms of control. The Permanent Magnet Synchronous Machine (PMSM) is one of the key enabling technologies that have been subject of investigation in the past few decades because it can outperform other types of electric machines in a broad range of applications. In the manufacturing of high power density PMSMs, even small manufacturing variations can impact heavily on their performance. The tolerances and imperfections lead to physical machine asymmetries, and this work deals with the modeling and analysis of these asymmetries. It is noteworthy that asymmetries can also be introduced in the machine intentionally to enhance the functionality in certain cases. By means of electromagnetic field theory, analytic models have been developed in this study; Also, numerical analysis on the basis of Finite Element Method (FEM) have been extensively used throughout this work with the aim to validate the results and further investigate the non-linear nature of materials. Prototypes of Surface-Mounted Permanent Magnet (SPM) machines, Interior Permanent Magnet (IPM) machines and Synchronous Reluctance Machines assisted Permanent Magnets (PMaSynRM) were built and tested to verify the validity of the proposed models under loaded and unloaded conditions. The results provided by the analytic models were considerably more time-efficient without compromising accuracy when compared to those of FE-based models, even when the geometries do not match perfectly owing to the limitations of solving the model in polar coordinates. %Discrepancies were found only when the machine goes beyond the linear region due to the assumption of infinite permeabilit (open full item for complete abstract)

Committee: Longya Xu (Advisor); Vadim Utkin (Committee Member); Mahesh Illindala (Committee Member) Subjects: Electrical Engineering

Doctor of Philosophy (PhD), Ohio University, 2015, Physics and Astronomy (Arts and Sciences)

In this dissertation we study transport properties of graphene within the low energy Dirac approximation. We utilize partial wave scattering methods and relate the scattering matrix elements to physical observables such as the elastic time, transport time, and skewness of scattering. We suggest that experimentally measurable quantities, such as the transport to elastic time ratio, indicate the presence of perturbations that lead to the reduction of symmetries of graphene, as well as spin-orbit interactions. This result relies on the fact that perturbations that leave graphene symmetries untouched, such as potential scatterers, display a constant ratio of transport to elastic times at low energies, making this ratio robust to random scatterer size and strength disorder. We also show that this ratio is not robust to either symmetry breaking perturbations or spin-orbit interactions, as these interactions lead to the ratio deviating from its ideal value. Even though both kinds of perturbations, symmetry breaking and spin-orbit interactions, lead to changes in the ratio, we show that the qualitatively different dependence on energy for each of these perturbations allows the experimental identification and quantification of both effects simultaneously. We have also shown, in relation to the spin Hall effect detection in graphene, that even though the local enhancement of spin-orbit interactions leads to the appearance of a spin Hall effect signal robust to potential and size disorder, the breaking of effective time reversal symmetry through local perturbations leads to the appearance of a valley Hall effect through skew scattering. This valley skew processes contribute to the non-local resistance that helps quantify the Hall effect. Similarly, we show that multiple potential scatterers with space dependence that breaks parity in graphene, also lead to the appearance of a valley Hall effect due to the separation of electrons from different valleys in space through skew (open full item for complete abstract)

Committee: Ulloa Sergio E. PhD (Advisor) Subjects: Condensed Matter Physics; Physics; Solid State Physics