Physics Commons^™

Pp-Waves In Modified Gravity, Ahmet Baykal

Turkish Journal of Physics

The family of metrics corresponding to the plane-fronted gravitational waves with parallel propagation, commonly referred to as the family of pp-wave metrics, is studied in the context of various modified gravitational models in a self-contained and coherent manner by using a variant of the null coframe formulation of Newman and Penrose and the exterior algebra of differential forms on pseudo-Riemannian manifolds.

Supergravity Backgrounds And Symmetry Superalgebras, Ümi̇t Ertem

Turkish Journal of Physics

We consider the bosonic sectors of supergravity theories in ten and eleven dimensions corresponding to the low energy limits of string theories and M-theory. The solutions of supergravity field equations are known as supergravity backgrounds and the number of preserved supersymmetries in those backgrounds are determined by Killing spinors. We provide some examples of supergravity backgrounds that preserve different fractions of supersymmetry. An important invariant for the characterization of supergravity backgrounds is their Killing superalgebras, which are constructed out of Killing vectors and Killing spinors of the background. After constructing Killing superalgebras of some special supergravity backgrounds, we discuss the …

Neutron Stars: Compact Objects With Relativistic Gravity, Kazim Yavuz Ekşi̇

Turkish Journal of Physics

General properties of neutron stars are briefly reviewed with an emphasis on the indispensability of general relativity in our understanding of these fascinating objects. In Newtonian gravity the pressure within a star merely plays the role of opposing self-gravity. In general relativity all sources of energy and momentum contribute to the gravity. As a result, the pressure not only opposes gravity but also enhances it. The latter role of pressure becomes more pronounced with increasing compactness, $M/R$, where $M$ and $R$ are the mass and radius of the star, and sets a critical mass beyond which collapse is inevitable. This …

Exact Solutions To The Geodesic Equations Of Linear Dilaton Black Holes, Alan Hameed Hussein Hamo, Izzet Sakalli

Turkish Journal of Physics

In this paper, we analyze the geodesics of the 4-dimensional linear dilaton black hole (LDBH) spacetime, which is an exact solution to the Einstein-Maxwell-dilaton theory. LDBHs have nonasymptotically flat geometry, and their Hawking radiation is an isothermal process. The geodesics motions of the test particles are studied via the standard Lagrangian method. After obtaining the Euler-Lagrange equations, we show that exact analytical solutions to the radial and angular geodesic equations can be obtained. In particular, it is shown that one of the possible solutions for the radial trajectories can be given in terms of the Weierstrass P-function ($\wp $-function), which …

Structure And Stability Of Primordial Stars, Aysel İbrahi̇m Karafi̇stan

Turkish Journal of Physics

For decades large-scale cosmic structures have been modeled as the gravitational amplification of small-density perturbations of the cosmological recombination epoch of the Big Bang. In astrophysics, cosmological nucleosynthesis is considered responsible for the production of the pristine gas, which should be found in the first-generation stars in the form of hydrogen and helium as the main constituents. In the later type of second-generation stars, hydrogen is converted into helium by the CN-cycle reactions, in which heavier elements are produced. These elements are believed to enrich the intergalactic medium by possible star bursts at the last stages of evolution. Stability criteria …

The Observational Status Of Simple Inflationary Models: An Update, Nobuchika Okada, Vedat Nefer Şenoğuz, Qaisar Shafi

Turkish Journal of Physics

We provide an update on five relatively well-motivated inflationary models in which the inflaton is a Standard Model singlet scalar field. These include i) the textbook quadratic and quartic potential models but with additional couplings of the inflaton to fermions and bosons, which enable reheating and also modify the naive predictions for the scalar spectral index $n_s$ and $r$, ii) models with Higgs and Coleman-Weinberg potentials, and finally iii) a quartic potential model with nonminimal coupling of the inflaton to gravity. For $n_s$ values close to 0.96, as determined by the WMAP9 and Planck experiments, most of the considered models …

Revisiting The Dyonic Majumdar-Papapetrou Black Holes, Seyedhabibollah Mazharimousavi, Mustafa Hali̇lsoy

Turkish Journal of Physics

We extend the Majumdar-Papapetrou solution of the Einstein-Maxwell equations, which are implied generally for static electric charge in nonrotating metrics, to encompass equally well magnetic charges. In the absence of Higgs and non-Abelian gauge fields, 'dyonic' is to be understood in this simpler sense. Cosmologically this may have far-reaching consequences, to the extent that existence of multimagnetic monopole black holes may become a reality in our universe. Infalling charged particle geodesics may reveal, through particular integrals, their inner secrets, which are screened from our observation.

It Is Sufficient To Set The Cosmological Constant To Zero Or To A Small Number At An Initial Time, Recai̇ Erdem

Turkish Journal of Physics

I point out a simple but usually overlooked fact about the cosmological constant problem: to solve the cosmological constant problem it is sufficient to find a symmetry or mechanism that sets the cosmological constant to zero or to a tiny value at some time in the past, provided that general relativity is the relevant theory of gravity, and the energy-momentum tensor (excluding the part of the form of a cosmological constant) is conserved. The relevant symmetry or mechanism need not be applicable today. Any additional cosmological constant term induced by a phase transition in the energy-momentum tensor in this case …

Modification Of The Fundamental Properties Of Light Through Interaction With Nanostructured Materials, David W. Keene Ii

College of Graduate Studies: Theses & Dissertations

The field of photonics has been growing rapidly over the last few decades as it has endeavored to harness the potential of nanostructured materials to utilize the energy and momentum of electromagnetic radiation on the nanoscale. Using metal nanostructures provides the ability to take advantage of the sub-field of plasmonics which holds the promise of opening the world to vast increases in computational power by circumventing the limitations of conventional current that plague today’s processors. With a thorough understanding of this subject we also get one step closer to increasing the efficiency of solar technology, developing a finer scale of …

Development Of The Electron Cooling Simulation Program For Jleic, H. Zhang, J. Chen, R. Li, Y. Zhang, H. Huang, L. Luo

Mathematics & Statistics Faculty Publications

In the JLab Electron Ion Collider (JLEIC) project the traditional electron cooling technique is used to reduce the ion beam emittance at the booster ring, and to compensate the intrabeam scattering effect and maintain the ion beam emittance during collision at the collider ring. A new electron cooling process simulation program has been developed to fulfill the requirements of the JLEIC electron cooler design. The new program allows the users to calculate the electron cooling rate and simulate the cooling process with either DC or bunched electron beam to cool either coasting or bunched ion beam. It has been benchmarked …

Evaluation Of Ray-Path Integrals In Geometrical Optics, John A. Adam, Michael Pohrivchak

Mathematics & Statistics Faculty Publications

A brief summary of the physical context to this paper is provided, and the deviation angle undergone by an incident ray after k internal reflections inside a transparent unit sphere is formulated. For radially inhomogeneous spheres (in particular) this angle is related to a ray-path integral; an improper integral for which there are relatively few known exact analytical forms, even for simple refractive index profiles n(r). Thus for a linear profile the integral is a combination of incomplete elliptic integrals of the first and third kinds (though not all are as complicated as this). The ray-path integral is evaluated …

Biolabeling Through The Use Of Water-Soluble Colloidal Quantum Dots, Cody Stombaugh

Honors Projects

Nanomaterials continues to be a growing field of study due to their wide range of potential applications. Quantum dots are artificially synthesized crystalline clusters of atoms able to confine electron motion as a result of their incredibly small size. Recently, medical applications of nanomaterials have expanded greatly. Quantum dots are ideal for biolabeling due to their rather narrow photoluminescence emission peaks. By synthesizing quantum dots of a specific diameter, it is possible to predetermine the peak photoluminescence wavelength of a sample. Through ligand exchange and immunoconjugation of the quantum dots with proteins, it is possible to use the quantum dots …

Characterisation Of Strip Silicon Detectors For The Atlas Phase-Ii Upgrade With A Micro-Focused X-Ray Beam, L. Poley, A. Blue, R. Bates, I. Bloch, S. Diez, J. Fernandez-Tejero, C. Fleta, B. Gallop, B. Greenall, I.M. Gregor, K. Hara, Y. Ikegami, C. Lacasta, K. Lohwasser, D. Maneuski, S. Nagorski, I. Pape, P.W. Phillips, D. Sperlich, K. Sawhney

Articles

The planned HL-LHC (High Luminosity LHC) in 2025 is being designed to maximise the physics potential through a sizable increase in the luminosity up to 6centerdot1034 cm−2s−1. A consequence of this increased luminosity is the expected radiation damage at 3000 fb−1 after ten years of operation, requiring the tracking detectors to withstand fluences to over 1centerdot1016 1 MeV neq/cm2. In order to cope with the consequent increased readout rates, a complete re-design of the current ATLAS Inner Detector (ID) is being developed as the Inner Tracker (ITk).

Controllable Growth Of Vertically Aligned Graphene On C-Face Sic, Yu Liu, Lianlian Chen, Donovan Hilliard, Qing-Song Huang, Fang Liu, Mao Wang, Roman Böttger, René Hübner, Alpha T. N’Diaye, Elke Arenholz Elke Arenholz, Viton Heera Viton Heera, Wolfgang Skorupa Wolfgang Skorupa, Shengqiang Zhou

Articles

We investigated how to control the growth of vertically aligned graphene on C-face SiC by varying the processing conditions. It is found that, the growth rate scales with the annealing temperature and the graphene height is proportional to the annealing time. Temperature gradient and crystalline quality of the SiC substrates influence their vaporization. The partial vapor pressure is crucial as it can interfere with further vaporization. A growth mechanism is proposed in terms of physical vapor transport. The monolayer character of vertically aligned graphene is verified by Raman and X-ray absorption spectroscopy. With the processed samples, d0 magnetism is realized …

Endovascular Aneurysm Repair Increases Aortic Arterial Stiffness When Compared To Open Repair Of Abdominal Aortic Aneurysms, Cleona Gray, Patrick J. Goodman, Stephen Badger, M. Kevin O'Malley, Martin K. O'Donohoe, Ciarán O. Mcdonnell

Articles

Objectives: The initial survival advantage seen with endovascular aneurysm repair (EVAR) over open repair does not persist in the long term. Pulse wave velocity (PWV) is a measure of arterial stiffness, and increased PWV is an independent risk factor for increased cardiovascular morbidity and mortality. This prospective comparative pilot study examined the effect of implantation of an aortic graft on PWV in patients undergoing open or endovascular aortic aneurysm repair. Patients and Methods: Thirty-four patients (15 open and 19 EVAR) were recruited. Patient demographics were similar in both the groups. Pulse wave velocity was calculated for all patients …

Multidimensional Motion Capture Using Doppler Ultrasound, Forrest Nolan Gamble

Honors Theses

Ultrasonic waves are used to measure the velocity of a target object by measuring the Doppler shift of the reflected waves. In this work, ultrasonic Doppler Sonar (UDS) was used to measure the velocity of objects, including a pendulum and a battery on a turntable. The investigation focused on developing a method to measure motion in two and three dimensions, for applications in gait analysis and sports motion capture. By using multiple ultrasonic transducers and novel data processing techniques, the UDS captured motion in two and three dimensions. In order to test the accuracy of the velocity and position measurements, …

Engineering Semiconductor Hybrids For Sensing, Godfrey Gumbs, Andrii Iurov, Danhong Huang

Publications and Research

The effect of screening of the coulomb interaction between two layers of two-dimensional electrons, such as in graphene, by a highly doped semiconducting substrate is investigated. We employ the random-phase approximation to calculate the dispersion equation of this hybrid structure in order to determine the plasmon excitation spectrum. When an electric current is passed through a layer, the low-frequency plasmons in the layer may bifurcate into separate streams due to the current-driving effect. At a critical wave vector, determined by the separation between layers and their distance from the surface, their phase velocities may be in opposite directions and a …

Investigation Of A Scalable Barrel Atmospheric Plasma Reactor For The Treatment Of Polymer Particles, Hisham Abourayana, Vladimir Milosavljevic, Peter Dobbyn, Patrick J. Cullen, Denis Dowling

Articles

This study reports on the performance of a scalable barrel atmospheric plasma system for the treatment of polymer particles. A novel feature of the barrel system design is the use of a biased electrode, which also acts as the roller for the glass barrel. The plasma is generated using either helium or helium / oxygen gas mixtures. The reactor was used to activate 20 g batches of silicone, polypropylene (PP), acrylonitrile butadiene styrene (ABS) and polyethylene terephthalate (PET) particles, each with diameters in the range 3 to 5 mm. The effect of plasma treatment time and gas flow rate on …

Holography In The Secondary Physics Curriculum, Stephen P. Hogan

Masters Theses

This paper presents a unit plan for effective implementation of a holography learning activity in the secondary science physics classroom. The study of holography has traditionally been limited to collegiate optics courses due to financial and physical constraints. Recent developments in the technology of holographic film has eliminated these two limiting factors. Recent secondary educators who have introduced holography with their secondary science classes have completed the activities, without much discussion or explanation regarding the scientific principles that allow the phenomenon to occur. In this paper we develop a foundational unit plan that finishes with holography as the pinnacle activity, …

Lifetime And Efficiency Improvement Of Organic Luminescent Solar Concentrators For Photovoltaic Applications, Yamna El Mouedden

Theses: Doctorates and Masters

In order to achieve the goal of zero net-energy consumption in residential and commercial buildings, substantial research has been devoted to developing methods for energy harvesting from window glass that is capable of passing visible light through the windows of buildings while converting the unwanted invisible solar radiation into electricity. Research has focussed on two particular aspects, namely (i) the integration of thin-film technology for solar radiation transmission control and (ii) light guiding structures for solar radiation routing towards the edges of the glass window.

Recently, photovoltaic (PV) solar cells have been investigated and promoted as products for converting solar …

Sensing Using Specialty Optical Fibers, Amy Van Newkirk

Electronic Theses and Dissertations

Fiber optic based sensing is a growing field with many applications in civil and aerospace engineering, oil and gas industries, and particularly in harsh environments where electronics are not able to function. Optical fibers can be easily integrated into structures, are immune to electromagnetic interference, can be interrogated from remote distances, and can be multiplexed for distributed measurements. Because of these properties, specialty fiber designs and devices are being explored for sensing temperature, strain, pressure, curvature, refractive index, and more. Here we show a detailed analysis of a multicore fiber (MCF) for sensing, including its design and optimization in simulation, …

Size, Shape, Composition And Chemical State Effects In Nanocatalysis, Mahdi Ahmadi

Electronic Theses and Dissertations

The field of nanocatalysis has gained significant attention in the last decades due to the numerous industrial applications of nanosized catalysts. Size, shape, structure, and composition of the nanoparticles (NPs) are the parameters that can affect the reactivity, selectivity and stability of nanocatalysts. Therefore, understanding how these parameters affect the catalytic properties of these systems is required in order to engineer them with a given desired performance. It is also important to gain insight into the structural evolution of the NP catalysts under different reaction conditions to design catalysts with long durability under reaction condition. In this dissertation a synergistic …

Investigating The Predictive Power Of Student Characteristics On Success In Studio-Mode, Algebra-Based Introductory Physics Courses, Jarrad Pond

Electronic Theses and Dissertations

As part of a project to explore the differential success of similar implementations of the studio-mode of physics instruction, the objective of this work is to investigate the characteristics of students enrolled in algebra-based, studio-mode introductory physics courses at various universities in order to evaluate what effects these characteristics have on different measures of student success, such as gains in conceptual knowledge, shifts to more favorable attitudes toward physics, and final course grades. In my analysis, I explore the strategic self-regulatory, motivational, and demographic characteristics of students in algebra-based, studio-mode physics courses at three universities: the University of Central Florida …

Electrical Parasitic Bandwidth Limitations Of Oxide-Free Lithographic Vertical-Cavity Surface-Emitting Lasers, Xu Yang

Electronic Theses and Dissertations

Nowadays, Vertical-Cavity Surface-Emitting Lasers (VCSELs) are the most popular optical sources in short-reach data communications. In the commercial oxide VCSEL technology, an oxide aperture is created inside resonant cavity in realizing good mode and current confinement, however, high electrical resistance comes along with forming the oxide aperture and the electrical parasitic bandwidth becomes the main limitation in modulation speed. In this report, electrical bandwidths of oxide-free lithographic VCSELs have been studied along with their general lasing properties. Due to the new ways of fabricating the aperture, record low resistances have been achieved in oxide-free lithographic VCSELs with various sizes, while …

Hybrid Integrated Photonic Platforms And Devices, Jeffrey Chiles

Electronic Theses and Dissertations

Integrated photonics has the potential to revolutionize optical systems by achieving drastic reductions in their size, weight and power. Remote spectroscopy, free-space communications and high-speed telecommunications are critical applications that would benefit directly from these advancements. However, many such applications require extremely wide spectral bandwidths, leading to significant challenges in their integration. The choice of integrated platform influences the optical transparency and functionality which can be ultimately achieved. In this work, several new platforms and technologies have been developed to meet these needs. First, the silicon-on-lithium-niobate (SiLN) platform is discussed, on which the first compact, integrated electro-optic modulator in the …

Monolithically Integrated Inp-Based Unidirectional Circulators Utilizing Non-Hermiticity And Nonlinearity, Parinaz Aleahmad

Electronic Theses and Dissertations

The need to integrate critical optical components on a single chip has been an ongoing quest in both optoelectronics and optical communication systems. Among the possible devices, elements supporting non-reciprocal transmission are of great interest for applications where signal routing and isolation is required. In this respect, breaking reciprocity is typically accomplished via Faraday rotation through appropriate magneto-optical arrangements. Unfortunately, standard light emitting optoelectronic materials like for example III-V semiconductors, lack magneto-optical properties and hence cannot be directly used in this capacity. To address these issues, a number of different tactics have been attempted in the last few years. These …

Internal Degrees Of Freedom And Spin Transitions In Single Molecule Magnets, James Atkinson

Electronic Theses and Dissertations

This thesis covers a range of work detailing the transitions between spin eigenstates in molecular magnet systems. Broadly speaking, these transitions can be divided into two kinds: Those that involve a the tunneling of spin through a potential barrier to a resonant state on the other side, a phenomenon known as quantum tunneling of magnetization, and those that occur through the absorption or emission of a photon. In this latter case, the energy of the photon must match the difference between two eigenstates with a difference in angular momentum of ?. We will detail research performed on single molecule magnets, …

Optical Parity Time Metasurface Structures, Ahmed El Halawany

Electronic Theses and Dissertations

In the last few years, optics has witnessed the emergence of two fields namely metasurfaces and parity-time (PT) symmetry. Optical metasurfaces are engineered structures that provide unique responses to electromagnetic waves, absent in natural materials. Optical metasurfaces are known for their reduced dimensionality i.e. subwavelength and consequently lower losses are anticipated. The other paradigm is the PT symmetric materials, also known as photonic synthetic matter. PT symmetry has emerged from quantum mechanics when a new class of non-Hermitian Hamiltonian quantum systems was highlighted to have real eigenvalues, hence eradicating Hermiticity of the Hamiltonian as an essential condition to the existence …

Coupling Of Laser Beams For Filament Propagation, Daniel Kepler

Electronic Theses and Dissertations

Laser filamentation is a nonlinear process involving high-energy, ultrashort pulses that create narrow, non-diffracting structures over many times the Raleigh length. While many of the characteristics of filaments can vary greatly depending on the physical parameters used to create them, they share several defining features: a high intensity core, a lower intensity cladding of photons that serves as an energy reservoir to the core, and spectral broadening into a supercontinuum. While there have been many studies on the creation and control of multiple filaments from one laser pulse and a few studies on the interaction of two single filaments, many …

Dynamical Formation Of Protoplanetesimals, Akbar Whizin

Electronic Theses and Dissertations

The seeds of planetesimals that formed in the gaseous protoplanetary disk (PPD) have many barriers to overcome in their growth from millimeter to meter-sized and larger bodies. Centimeter-sized aggregates are weakly bound and self-gravity is almost non-existent so surface forces play a critical role in holding small loosely-bound rubble-piles together. Their orbital motions and effects form disk processes impart relative velocities leading to collisions so understanding the macroscopic disk environment is also necessary. To this end we analyze the dynamics of particles in Saturn's F ring as an analogue to understanding the orbital evolution of proto-planetesimals embedded in a PPD. …