Other Physics Commons^™

Study Of Edgeless Timepix Pixel Devices, Dylan G. Hsu

Renée Crown University Honors Thesis Projects - All

Silicon micropattern devices are crucial components of detector systems designed to study decays of exotic subatomic particles containing beauty and charm quarks. Among the technologies under consideration for use in future particle physics experiments are edgeless silicon pixel detectors. In these devices a state-of-the-art fabrication process is used to create sensors with a nearly full active area, as compared to conventional sensors which have a “guard ring” which is a dead region at the sensor periphery. Prototypes used for the study described in this paper were designed and fabricated by VTT Technical Research Centre of Finland. In a test beam …

Generalized Helicity And Beltrami Fields, Roman V. Buniy, Thomas W. Kephart

Mathematics, Physics, and Computer Science Faculty Articles and Research

We propose covariant and non-abelian generalizations of the magnetic helicity and Beltrami equation. The gauge invariance, variational principle, conserved current, energy-momentum tensor and choice of boundary conditions elucidate the subject. In particular, we prove that any extremal of the Yang-Mills action functional 1/4 f(Omega) trF(mu nu) F-mu nu d(4)x subject to the local constraint epsilon(mu nu alpha beta)trF(mu nu)F(alpha beta) = 0 satisfies the covariant non-abelian Beltrami equation.

Evaluation Of Artifacts In Experimental Cine 4d Ct Acquisition Methods, Sarah Joy

Dissertations and Theses (Open Access)

Four-dimensional computed tomography (4D CT) has increased the accuracy of radiation treatment planning for patients in whom the extent of target motion is large. 4D CT has become a standard of care for radiation treatment simulation, allowing decreased motion artifacts and increased spatiotemporal localization of anatomical structures that move. However, motion artifacts may still remain. These artifacts, or artificial anatomic spatial distributions, add a systematic uncertainty to the treatment process and limit the accuracy of lung function images derived from CT. We proposed to reduce the motion artifacts in cine 4D CT by using three novel investigational 4D CT acquisition …

Forecasting Longitudinal Changes In Oropharyngeal Tumor Volume, Position, And Morphology During Image-Guided Radiation Therapy, Adam D. Yock

Dissertations and Theses (Open Access)

The purpose of this work was to generate, evaluate, and compare models that predict longitudinal changes in oropharyngeal tumor volume, position, and morphology during radiation therapy.

One volume, one position, and two morphology (size, shape, and position) feature vectors were used to describe 35 oropharyngeal gross tumor volumes (GTVs) during radiation therapy. The two morphology feature vectors comprised the coordinates of the GTV centroids and one of two shape descriptors. One shape descriptor was based on radial distances between the GTV centroid and 614 surface landmarks. The other was based on a spherical harmonic decomposition of these distances. For a …

Image-Guided Proton Therapy For Online Dose-Evaluation And Adaptive Planning, Joey P. Cheung

Dissertations and Theses (Open Access)

The main advantage for using protons in radiotherapy is their finite range in patients, allowing for potential improved sparing of normal tissues. However, this comes at a cost of increased sensitivity to range uncertainties. Density changes along the beam path will affect the proton range and the resultant dose distribution, making it difficult to estimate the impact of visible anatomic changes to the patient dose distribution. In order to better understand the effect of anatomy change on proton dose, some form of treatment-time verification is required and methods to correct for observed changes would be beneficial. Therefore, this project aims …

A Boxer's Punch, Jacob A. Ekegren

Physics

For over a year now, I have been interested in the sport of boxing. This fascination led me to explore what occurs to a human head upon impact from a boxer’s punch. It is known that a knockout occurs when blood circulation to the brain is compressed. This compression results from the sudden acceleration and deceleration of the head. Therefore, the primary focus of this experiment explores the relative effort necessary to cause significant movement to a head about a neck.

Turbulence, Climate And Supercomputers, Georgios Matheou

The Transdisciplinary STEAM+ Journal

Turbulence is often referred to as the last mystery of classical physics. Although turbulence is ubiquitous and prominent in our daily lives – from the mixing of milk in a cup of coffee to the perpetual motion of the atmosphere and the resulting weather variation – our understanding of this complex phenomenon is comparatively very limited (e.g., Davidson et al., 2011).

Impact Testing Of Youth-Level Helmets Versus College-Level Helmets, Nicole Hermann

Industrial Technology and Packaging

With so many studies being conducted on professional football players regarding concussions and other related brain injuries, it’s amazing that such an important demographic has been missed. While NFL players are just as subjected to serious injuries as anyone else or even more so, it is important to remember that these players are outfitted, in most cases, with top-of-the-line equipment -- especially their helmets. If the focus is shifted to a younger demographic, youth football players in middle school and high school, the equipment is far less advanced and in a vast majority of cases, has been previously used by …

Using Acrylamide Based Photopolymers For Fabrication Of Holographic Optical Elements In Solar Energy Applications, Hoda Akbari, Izabela Naydenova, Suzanne Martin

Articles

A holographic device is under development that aims to improve light collection in solar cells. The aim is to explore the potential of using photopolymer Holographic Optical Elements (HOE) to collect light from a moving source, such as the sun, and re-direct it for concentration by a holographic lens.. A working range of 45 degrees is targeted for such a device to be useful in solar applications without tracking. A photopolymer HOE is capable of efficiently re-directing light, but the angular selectivity of a single grating is usually of the order of one degree at the thicknesses required for high …

Gauge/ Gravity Correspondence, Bulk Locality And Quantum Black Holes, Debajyoti Sarkar

Dissertations, Theses, and Capstone Projects

The aim of this dissertation is threefold. We begin by the study of two parallel ideal cosmic strings in the presence of non-minimal scalar fields and spin- 1 gauge fields. We show that the contributions of the non-minimal term on the interaction energy between the strings are similar to that of the gauge field for a particular value of non-minimal coupling parameter. In this context we clarify some of the issues that arise when comparing the renormalization of black hole entropy and entanglement entropy using the replica trick.

In the second part of the dissertation we study the process of …

Mems Approaches In Infrared Imaging, George Papavieros

Theses

The design and performance simulation of a novel Microelectromechanical System (MEMS) based infrared detector, that utilizes coefficient of thermal expansion, is discussed. The detector design uses a variety of thermal expansion coefficient materials, including alloys which are connected to ambient through a thermal conducting bridge. The thermal flux, due to the incident IR photons, is determined by the Extended Blackbody Calculator (BBC). These materials are physically interfaced with different types of piezoelectric resonators, constructed using the MEMS process. The expansion due to heating, applies stress to the piezoelectric resonator material. This thermally induced stress forces the resonator to alter its …

Boosted Top Production: Factorization And Resummation For Single-Particle Inclusive Distributions, Andrea Ferroglia, Simone Marzani, Ben D. Pecjak, Li Lin Yang

Publications and Research

We study single-particle inclusive (1PI) distributions in top-quark pair production at hadron colliders, working in the highly boosted regime where the top-quarkpTis much larger than its mass. In particular, we derive a novel factorization formula validin the small-mass and soft limits of the differential partonic cross section. This providesa framework for the simultaneous resummation of soft gluon corrections and small-mass logarithms, and also an efficient means of obtaining higher-order corrections to the differential cross section in this limit. The result involves five distinct one-scale functions, three of which arise through the subfactorization of soft real radiation in the small-mass limit. …

Low Mach Number Fluctuating Hydrodynamics Of Diffusively Mixing Fluids, Aleksandar Donev, Andy J. Nonaka, Yifei Sun, Thomas Fai, Alejandro Garcia, John B. Bell

Faculty Publications

We formulate low Mach number fluctuating hydrodynamic equations appropriate for modeling diffusive mixing in isothermal mixtures of fluids with different density and transport coefficients. These equations eliminate the fast isentropic fluctuations in pressure associated with the propagation of sound waves by replacing the equation of state with a local thermodynamic constraint. We demonstrate that the low Mach number model preserves the spatio-temporal spectrum of the slower diffusive fluctuations. We develop a strictly conservative finite-volume spatial discretization of the low Mach number fluctuating equations in both two and three dimensions. We construct several explicit Runge-Kutta temporal integrators that strictly maintain the …

Radiographic Image Quality Enhancement By The Use Of Copper Filters, Timothy T. Sakogawa, Bernice Mills

STAR Program Research Presentations

In x-radiography, filters are often used in order to improve the overall image quality. Filters achieve this by making the x-ray beam have less energy spread, resulting in a cleaner image. Step wedges of different materials were used to compare radiographic density with and without a copper filter to identify the effect of the copper filter at different energies and exposure times. The step wedges used were CRS 1018 (cold rolled steel), Stainless Steel 304L, Al 1100, Al 6061 T6, titanium, copper, PTFE (polytetrafluoroethylene or Teflon), brass, carbon, magnesium, phenolic, tungsten, and tantalum. Out of the 14 step wedges tested, …

Investigation Of The Structure Of The Few Body Kaonic Nuclei Using The Method Of Hyperspherical Functions In Momentum Space, Roman Ya. Kezerashvili, Shalva M. Tsiklauri

Publications and Research

The kaonic clusters KNN and KNNN are studied within the method of hyperspherical functions in the momentum representation. Binding energies and widths of three- and four-body nuclear quasibound states are calculated by employing realistic NN potentials and the energy dependent chiral KN interaction, as well as a phenomenological KN potential. The comparison of the results of calculations obtained in the framework of the variational method, Faddeev, Faddeev-Yakubovsky equations, and method of hyperspherical functions in configuration space are discussed.

Normal Modes Of A Small Gamelan Gong, Robert Perrin, Daniel Elford, Luke Chambers, Gerry M. Swallowe, Thomas R. Moore, Sinin Hamdan, Benjamin J. Halkon

Faculty Publications

Studies have been made of the normal modes of a 20.7 cm diameter steel gamelan gong. A finite-element model has been constructed and its predictions for normal modes compared with experimental results obtained using electronic speckle pattern interferometry. Agreement was reasonable in view of the lack of precision in the manufacture of the instrument. The results agree with expectations for an axially symmetric system subject to small symmetry breaking. The extent to which the results obey Chladni's law is discussed. Comparison with vibrational and acoustical spectra enabled the identification of the small number of modes responsible for the sound output …

Comparison Of The Sharpness Of Tungsten Field Emission Tips From Traditional Electrical Characterization To Tip Geometries Imaged By Scanning Electron Microscopy, Emma C. Reeves

Departmental Honors Projects

Using field emission data obtained from 11 etched Tungsten successful field emission tips of radius about 20 to 100 nanometers, FN type linear models were compared. The emission tip radii were determined using an iteration method derived from the modified FN linear equation. In addition, Scanning Electron Microscopy images of 5 successful emitters were obtained. These images were fit to a circular model to estimate the actual radius and compared to empirically predicted radius values. A hyperbolic model was further fit to the images and the circle of similar apex curvature was derived. A method for calculating the electric field …

Chirally Sensitive Electron-Induced Molecular Breakup And The Vester-Ulbricht Hypothesis, J. M. Dreiling, Timothy J. Gay

Timothy J. Gay Publications

We have studied dissociative electron attachment in sub-eV collisions between longitudinally polarized electrons and chiral bromocamphor molecules. For a given target enantiomer, the dissociative Br anion production depends on the helicity of the incident electrons, with an asymmetry that depends on the electron energy and is of order 3 × 10⁻⁴. The existence of chiral sensitivity in a well-defined molecular breakup reaction demonstrates the viability of the Vester-Ulbrict hypothesis, namely, that the longitudinal polarization of cosmic beta radiation was responsible for the origins of biological homochirality.

Spin Density Waves In Periodically Strained Graphene Nanoribbons, Nabil M. Al-Aqtash, Renat F. Sabirianov

Nebraska Center for Materials and Nanoscience: Faculty Publications

Zigzag graphene nanoribbons (ZGNRs) are antiferromagnetic in the ground state with zero net magnetization due to the compensation of contributions from opposite edges. Uniform deformations (both shear and axial) do not produce magnetization due to symmetry restrictions. However, we report the results of first-principles calculations that predict the induction of spin density waves (SDWs) in ZGNRs under non-uniform periodic strain. Using the density functional theory (DFT) method, we show that a sinusoidal magnetization variation along the axis of the ribbon occurs under a sinusoidal transversal shear strain. SDWs appear due to the presence of a strain gradient that induced asymmetry …

Momentum And Spin In Entropic Quantum Dynamics, Shahid Nawaz

Legacy Theses & Dissertations (2009 - 2024)

We study quantum theory as an example of entropic inference. Our goal is to remove conceptual difficulties that arise in quantum mechanics. Since probability is a common feature of quantum theory and of any inference problem, we briefly introduce probability theory and the entropic methods to update probabilities when new information becomes available. Nelson's stochastic mechanics and Caticha's derivation of quantum theory are discussed in the subsequent chapters. Our first goal is to understand momentum and angular momentum within an entropic dynamics framework and to derive the corresponding uncertainty relations. In this framework momentum is an epistemic concept -- it …

Observation Of A Quantum Cheshire Cat In A Matter-Wave Interferometer Experiment, Tobias Denkmayr, Hermann Geppert, Stephan Sponar, Hartmut Lemmel, Alexandre Matzkin, Jeff Tollaksen, Yuji Hasegawa

Mathematics, Physics, and Computer Science Faculty Articles and Research

From its very beginning, quantum theory has been revealing extraordinary and counter-intuitive phenomena, such as wave-particle duality, Schrodinger cats and quantum non-locality. Another paradoxical phenomenon found within the framework of quantum mechanics is the 'quantum Cheshire Cat': if a quantum system is subject to a certain pre- and postselection, it can behave as if a particle and its property are spatially separated. It has been suggested to employ weak measurements in order to explore the Cheshire Cat's nature. Here we report an experiment in which we send neutrons through a perfect silicon crystal interferometer and perform weak measurements to probe …

Finite Density Qed At Strong Magnetic Field, Paul Lee Springsteen

Open Access Theses & Dissertations

In this Thesis we study the effect of a dense medium on the quantum properties of a relativistic electron-positron plasma under a magnetic field. From the calculation of the photon polarization operator depending on temperature, chemical potential, and the magnetic field; we study how the electric susceptibility of the strongly magnetized plasma is charged with temperature and density. In the same manner we study the dependence of the Debye mass with density. Then we investigated the phenomenon of magnetic catalysis of chiral symmetry breaking for a dense medium. We found that there exist a critical value of the chemical potential …

Quantum Non-Locality Vs. Quasi-Local Measurement In The Conditions Of The Aharonov-Bohm Effect, Armen Gulian

Mathematics, Physics, and Computer Science Faculty Articles and Research

Theoretical explanation of the Meissner effect involves proportionality between current density and vector potential, which has many deep consequences. As noticed by de Gennes, superconductors in a magnetic field "find an equilibrium state where the sum of kinetic and magnetic energies is minimum" and this state "corresponds to the expulsion of the magnetic field". This statement still leaves an open question: from which source is the superconducting current acquiring its kinetic energy? A naïve answer, perhaps, is from the energy of the magnetic field. However, one can consider situations (Aharonov-Bohm effect), where the classical magnetic field is locally absent in …

Quantum Harmonic Oscillator With Superoscillating Initial Datum, Roman V. Buniy, Fabrizio Colombo, Irene Sabadini, Daniele C. Struppa

Mathematics, Physics, and Computer Science Faculty Articles and Research

In this paper, we study the evolution of superoscillating initial data for the quantum driven harmonic oscillator. Our main result shows that superoscillations are amplified by the harmonic potential and that the analytic solution develops a singularity in finite time. We also show that for a large class of solutions of the Schrodinger equation, superoscillating behavior at any given time implies superoscillating behavior at any other time.

The Spin State Of A Molecular Adsorbate Driven By The Ferroelectric Substrate Polarization†, Xin Zhang, Tatiana Palamarciuc, Jean-François Létard, Patrick Rosa, Eduardo Vega Lozada, Fernand Torres, Luis G. Rosa, Bernard Doudin, Peter A. Dowben

Peter Dowben Publications

The spin state of [Fe(H₂B(pz)₂)₂(bipy)] thin films is mediated by changes in the electric field at the interface of organic ferroelectric polyvinylidene fluoride with trifluoroethylene (PVDF–TrFE). Signatures of the molecular crossover transition are evident in changes in the unoccupied states and the related shift from diamagnetic to paramagnetic characteristics. This may point the way to the molecular magneto-electric effect on devices.

Positive Exchange Bias In Epitaxial Permalloy/Mgo Integrated With Si (100), S. S. Rao, J. T. Prater, Fan Wu, S. Nori, D. Kumar, Lanping Yue, Sy_Hwang Liou, Jagdish Narayan

Sy-Hwang Liou Publications

In magnetic random access memory (MRAM) devices, soft magnetic thin film elements such as permalloy (Py) are used as unit cells of information. The epitaxial integration of these elements with the technologically important substrate Si (100) and a thorough understanding of their magnetic properties are critical for CMOS-based magnetic devices. We report on the epitaxial growth of Ni_82.5Fe_17.5 (permalloy, Py) on Si (100) using a TiN/MgO buffer layer. Initial stages of growth are characterized by the formation of discrete islands that gradually merge into a continuous film as deposition times are extended. Interestingly, we find that the …

Three‐Dimensional Brain Mri For Dbs Patients Within Ultra‐Low Radiofrequency Power Limits, Subhendra N. Sarkar, Efstathios Papavassiliou, David Hackney, David Alsop, Ananth Madhuranthakam, Ludy Shih, Reed Busse, Susan Laruche, Rafeeque Bhadelia

Publications and Research

Background: For patients with deep brain stimulators (DBS), local absorbed radiofrequency (RF) power is unknown and is much higher than what the system estimates. We developed a comprehensive, highquality brain magnetic resonance imaging (MRI) protocol for DBS patients utilizing three-dimensional (3D) magnetic resonance sequences at very low RF power. Methods: Six patients with DBS were imaged (10 sessions) using a transmit/receive head coil at 1.5 Tesla with modified 3D sequences within ultra-low specific absorption rate (SAR) limits (0.1 W/kg) using T2, fast fluid-attenuated inversion recovery (FLAIR) and T1- weighted image contrast. Tissue signal and tissue contrast from the low-SAR images …

An Investigation Of Nurbs-Based Deformable Image Registration, Travis J. Jacobson

Theses and Dissertations

Deformable image registration (DIR) is an essential tool in medical image processing. It provides a means to combine image datasets, allowing for intra-subject, inter-subject, multi-modality, and multi-instance analysis, as well as motion detection and compensation. One of the most popular DIR algorithms models the displacement vector field (DVF) as B-splines, a sum of piecewise polynomials with coefficients that enable local shape control. B-splines have many advantageous properties in the context of DIR, but they often struggle to adequately model steep local gradients and discontinuities. This dissertation addresses that limitation by proposing the replacement of conventional B-splines with a generalized formulation …

“Spaghetti” Design For Gravitational Wave Superconducting Antenna, Armen Gulian, J Foreman, Vahan Nikoghosyan, Shmuel Nussinov, Louis Sica, Jeff Tollaksen

Mathematics, Physics, and Computer Science Faculty Articles and Research

A new concept for detectors of gravitational wave radiation is discussed. Estimates suggest that strain sensitivity essentially better than that of the existing devices can be achieved in the wide frequency range. Such sensitivity could be obtained with devices about one meter long. Suggested device consists of multi-billion bimetallic superconducting wires ("spaghettis") and requires cryogenic operational temperatures (~0.3K in the case considered).