Digital Commons Network^™

Differential Cross Sections For 𝛾 + P → K⁺ + Y For Λ And Σ⁰ Hyperons, H. Bagdasaryan, M. Bektasoglu, S. L. Careccia, S. Bültmann, G. E. Dodge, N. Guler, C. E. Hyde-Wright, H. G. Juengst, A. V. Klimenko, S. E. Kuhn, S. Tkachenko, L. B. Weinstein, J. Zhang, Et Al., Clas Collaboration

Physics Faculty Publications

High-statistics cross sections for the reactions 𝛾 + p → K⁺ + Λ and 𝛾 + p → K⁺ + Σ⁰ have been measured using CLAS at Jefferson Lab for center-of-mass energies W between 1.6 and 2.53 GeV, and for -0.85 < cos θ _K^c.m. < +0.95. In the K⁺ + Λ channel we confirm a resonance-like structure near W=1.9 GeV at backward kaon angles. The position and width of this structure change with angle, indicating that more than one resonance is likely playing a role. The K⁺ + Λ channel at forward angles and all energies is well described by a t-channel scaling characteristic of Regge exchange, whereas the same scaling applied to the K⁺ + Σ⁰ channel is less successful. Several existing theoretical models are compared to the data, but none provide a good representation of the results.

Η’ Photoproduction On The Proton For Photon Energies From 1.527 To 2.227 Gev, M. Bektasoglu, S.L. Careccia, K. V. Dharmawardane, G. E. Dodge, C. E. Hyde-Wright, H. G. Juengst, A. Klein, S. E. Kuhn, A. V. Klimenko, L. M. Qin, F. Sabatié, S. Tkachenko, L. B. Weinstein, J. Yun, J. Zhang, Et Al., Clas Collaboration

Physics Faculty Publications

Differential cross sections for the reaction γp→η′p have been measured with the CLAS spectrometer and a tagged photon beam with energies from 1.527 to 2.227 GeV. The results reported here possess much greater accuracy than previous measurements. Analyses of these data suggest for the first time the coupling of the η′N channel to both the S₁₁(1535) and P₁₁(1710) resonances, known to couple strongly to the ηN channel in photoproduction on the proton, and the importance of J=3/2 resonances in the process.

Erratum: Η' Photoproduction On The Proton For Photon Energies From 1.527 To 2.227 Gev (Phys. Rev. Lett. 96, Pg 062001, 2006), H. Bagdasaryan, M. Bektasoglu, S. L. Careccia, K. V. Dharmawardane, G. E. Dodge, C. E. Hyde-Wright, A. Klein, S. E. Kuhn, L. M. Qin, F. Sabatié, L. B. Weinstein, Et Al., Clas Collaboration

Physics Faculty Publications

No abstract provided.

Assessing The Role Of Filler Atoms In Skutterudites And Synthesis And Characterization Of New Filled Skutterudites, Grant E. Fowler

USF Tampa Graduate Theses and Dissertations

For the past decade interest in skutterudites has been significant as a potentially viable material for thermoelectrics. One way to improve the effectiveness of these materials is to lower their thermal conductivity. Lattice thermal conductivity of a series of La- and Yb-filled skutterudite antimonides (with varying filling fraction) has been modeled with different phonon scattering parameters using the debye approximation. It was found that filler atoms both increase point defect scattering and resonance scattering. Subsequently, the thermal conductivity of partially-filled skutterudites AxCo4Sb12, where A = La, Eu and Yb, is analyzed using the Debye model in order to correlate the …

Laser-Controlled Local Magnetic Field With Semiconductor Quantum Rings, Yuriy V. Pershin Dr, Carlo Piermarocchi

Faculty Publications

We analyze theoretically the dynamics of N electrons localized in a narrow semiconductor quantum ring under a train of phase-locked infrared laser pulses. The pulse sequence is designed to control the total angular momentum of the electrons. The quantum ring can be put in states characterized by strong currents. The local magnetic field created by these currents can be used for a selective quantum control of single spins in semiconductor systems. The current generation in quantum rings with finite width is also studied.

Spin-Photovoltaic Effect In Quantum Wires Due To Intersubband Transitions, Arkady Fedorov, Yuriy V. Pershin Dr, Carlo Piermarocchi

Faculty Publications

We consider the current induced in a quantum wire by external electromagnetic radiation. The photocurrent is caused by the interplay of spin-orbit interaction (Rashba and Dresselhaus terms) and an external in-plane magnetic field. We calculate this current using a Wigner functions approach, taking into account radiation-induced transitions between transverse subbands. The magnitude and the direction of the current depends on the Dresselhaus and Rashba constants, strength of magnetic field, radiation frequency, and intensity. The current can be controlled by changing some of these parameters.

Phys 3003 Course Proposal 12/01/2005, Curriculum Committee

Curriculum Committee Reports

No abstract provided.

Klein Paradox With Spin-Resolved Electrons And Positrons, P Krekora, Q Su, Rainer Grobe

Faculty publications – Physics

Using numerical solutions to relativistic quantum field theory with space-time resolution, we illustrate how an incoming electron wave packet with a definite spin scatters off a supercritical potential step. We show that the production rate is reduced of only those electrons that have the same spin as the incoming electron is reduced. This spin-resolved result further clarifies the importance of the Pauli-exclusion principle for the Klein paradox.

Low Magnetic Prandtl Number Dynamos With Helical Forcing, Pablo D. Mininni, David C. Montgomery

Dartmouth Scholarship

We present direct numerical simulations of dynamo action in a forced Roberts flow. The behavior of the dynamo is followed as the mechanical Reynolds number is increased, starting from the laminar case until a turbulent regime is reached. The critical magnetic Reynolds for dynamo action is found, and in the turbulent flow it is observed to be nearly independent on the magnetic Prandtl number in the range from ∼0.3 to ∼0.1. Also the dependence of this threshold with the amount of mechanical helicity in the flow is studied. For the different regimes found, the configuration of the magnetic and velocity …

Photovoltaic Effect In Bent Quantum Wires In The Ballistic Transport Regime, Yuriy V. Pershin Dr, Carlo Piermarocchi

Faculty Publications

A scheme for the generation of a photocurrent in bent quantum wires is proposed. We calculate the current using a generalized Landauer-Büttiker approach that takes into account the electromagnetic radiation. For circularly polarized light, it is demonstrated that the curvature in the bent wire induces an asymmetry in the scattering coefficients for left and right moving electrons. This asymmetry results in a current at zero bias voltage. The effect is due to the geometry of the wire which transforms the photon angular momentum into translational motion for the electrons. Possible experimental realizations of this scheme are discussed.

Limits Of Quintessence, R. R. Caldwell, Eric V. Linder

Dartmouth Scholarship

We present evidence that the simplest particle-physics scalar-field models of dynamical dark energy can be separated into distinct behaviors based on the acceleration or deceleration of the field as it evolves down its potential towards a zero minimum. We show that these models occupy narrow regions in the phase plane of w and w′, the dark energy equation of state and its time derivative in units of the Hubble time. Restricting an energy scale of the dark energy microphysics limits how closely a scalar field can resemble a cosmological constant. These results, indicating a desired measurement resolution of order σ(w′)≈(1+w), …

Persistent And Radiation-Induced Currents In Distorted Quantum Rings, Yuriy V. Pershin Dr, Carlo Piermarocchi

Faculty Publications

Persistent and radiation-induced currents in distorted narrow quantum rings are theoretically investigated. We show that ring distorsions can be described using a geometrical potential term. We analyze the effect of this term on the current induced by a magnetic flux (persistent current) and by a polarized coherent electromagnetic field (radiation-induced current). The strongest effects in persistent currents are observed for distorted rings with a small number of electrons. The distortion smoothes the current oscillations as a function of the magnetic flux and changes the temperature dependence of the current amplitude. For radiation-induced currents, the distortion induces an ac component in …

Electron-Impact Ionization Of Hydrogen And Lithiumlike Systems, M A. Uddin, Abul Kalam Fazlul Haque, A K. Basak, Khondkar R. Karim, B C. Saha

Faculty publications – Physics

The electron impact single ionization cross sections on a number of targets with atomic number Z=1-92 in the H and Li isoelectronic sequences are calculated using a modified version of the recently propounded relativisitic improved binary-encounter dipole (MRIBED) model [M. A. Uddin , Phys. Rev. A 70, 032706 (2004); 71, 032715 (2005)]. The modified RQIBED (MRIBED) model along with a Z-dependent factor in it is found remarkably successful in the applications to H- and Li-like systems and also valid for the ionization of a filled s orbit including the He-like targets.

Investigation Of Laser Beam Induced Current Techniques For Heterojunction Photodiode Characterization, Weifu Fang, David A. Redfern, Kazufumi Ito, G. Bahir, Charles A. Musca, John M. Dell, Lorenzo Faraone

Mathematics and Statistics Faculty Publications

A reduced model is developed that has significant advantages over the full drift-diffusion model for the simulation of laser beam-induced current (LBIC) signals in the presence of heterojunctions. The model determines the contribution to the LBIC signal that would occur from photogeneration at any position within the semiconductor, and is particularly useful for heterostructures where judicious choice of illumination wavelength can result in photogeneration at different depths within the device structure. The reduced model is used to examine the basic features of LBIC as applied to two types of planar P-n HgCdTe heterojunction photodiode structures. In particular, the question of …

Simulation Of Charged Particle Trajectories In The Neutron Decay Correlation Experiment Abba, D. Desai, G. Greene, R. Mahurin, D. Bowman, John R. Calarco

Physics & Astronomy

The proposed neutron decay correlation experiment, abBA, will directly detect the direction of emission of decay protons and electrons as well as providing spectroscopic information for both particles. In order to provide this information, the abBA experiment incorporates spatially varying electric and magnetic fields. We report on detailed simulations of the decay particle trajectories in order to assess the impact of various systematic effects on the experimental observables. These include among others; adiabaticity of particle orbits, tracking of orbits, reversal of low energy protons due to inhomogeneous electric field, and accuracy of proton time of flight measurements. Several simulation methods …

Economics: The Next Physical Science?, J. Doyne Farmer, Martin Shubik, Eric Smith

Cowles Foundation Discussion Papers

We review an emerging body of work by physicists addressing questions of economic organization and function. We suggest that, beyond simply employing models familiar from physics to economic observables, remarkable regularities in economic data may suggest parts of social order that can usefully be incorporated into, and in turn can broaden, the conceptual structure of physics.

Physicist's Reformed Critique Of Nonreductive Physicalism And Emergence, Arnold E. Sikkema

Pro Rege

Two figures are included. Dr. Sikkema has obtained permission from the first author of the paper from which Fig. 2 is adapted, as well as from the publisher.

Deep-Uv Light Emitting Diodes: An Experimental Investigation Of Characterization And Optimization Techniques, Eric M. Fraser

Pomona Senior Theses

Light emitting diodes (LEDs) and laser diodes (LDs) have many advantages over conventional light sources. Current commercial LEDs span the spectrum from IR to near- UV. There are a variety of applications for devices that extend into the deep-UV, including biological agent detection and optical storage. The nitride material system is a set of semiconducting compounds that have wavelengths that span a broad range, from yellow to deep-UV. AlGaN has a direct bandgap that extends into the deep-UV range; we will try to grow device-quality material, deposited epitaxially using metalorganic chemical vapor deposition on sapphire substrates.

Temperature-Dependent Asymmetry Of The Nonlocal Spin-Injection Resistance: Evidence For Spin Nonconserving Interface Scattering, Samir Garzon, Igor Žutić, Richard A. Webb

Faculty Publications

We report nonlocal spin injection and detection experiments on mesoscopic Co-Al₂O₃-Cu spin valves. We have observed a temperature-dependent asymmetry in the nonlocal resistance between parallel and antiparallel configurations of the magnetic injector and detector. This strongly supports the existence of a nonequilibrium resistance that depends on the relative orientation of the detector magnetization and the nonequilibrium magnetization in the normal metal providing evidence for increasing interface spin scattering with temperature.

Microscopic Theory Of The Low Frequency Raman Modes In Germanium Nanocrystals, Shang-Fen Ren, Peter Y. Yu

Faculty publications – Physics

We have studied the Raman intensities of low-frequency phonon modes in germanium (Ge) nanocrystals (NC) with varying sizes by using a microscopic valence force field model. The results are compared with the predictions of the continuum model of Lamb using a projection method. We found that the l=0 spheroidal Lamb modes are Raman active in the parallel polarization scattering geometry, while the l=2 spheroidal Lamb modes are active in the crossed polarization geometry. This result agrees with the group theory prediction that the torsional Lamb modes are not Raman active, but is in disagreement with the identification of torsional Lamb …

Deep-Uv Light Emitting Diodes: An Experimental Investigation Of Characterization And Optimization Techniques, Eric M. Fraser

Pomona Senior Theses

Light emitting diodes (LEDs) and laser diodes (LDs) have many advantages over conventional light sources. Current commercial LEDs span the spectrum from IR to near- UV. There are a variety of applications for devices that extend into the deep-UV, including biological agent detection and optical storage. The nitride material system is a set of semiconducting compounds that have wavelengths that span a broad range, from yellow to deep-UV. AlGaN has a direct bandgap that extends into the deep-UV range; we will try to grow device-quality material, deposited epitaxially using metalorganic chemical vapor deposition on sapphire substrates.

Cardiac Relaxation Dynamics Investigated By Doppler Tissue Imaging (Dti), Gerard J. King

Doctoral

Following an initial pilot study to explore the usefulness of Doppler tissue imaging (DTI) for the assessment of regional systolic dysfunction in the ischaemic heart, new techniques for the diagnosis of diastolic dysfunction have been developed

In the refinement of the techniques further evidence to support the existence of the early diastolic mechanism was obtained prior to assessing its clinical utility. For this the relationship between peak early diastolic mitral ring tissue velocity (EA) as a surrogate for recoil, and the acceleration of early transmitral flow (ventricular filling) was investigated in patients with diastolic dysfunction and in normal subjects. This …

Cloud Detection And Trace Gas Retrieval From The Next Generation Satellite Remote Sensing Instruments, North Fredrick Larsen

Physics

The objective of this thesis is to develop a cloud detection algorithm suitable for the National Polar Orbiting Environmental Satellite System (NPOESS) Visible Infrared Imaging Radiometer Suite (VIIRS) and methods for atmospheric trace gas retrieval for future satellite remote sensing instruments. The development of this VIIRS cloud mask required a flowdown process of different sensor models in which a variety of sensor effects were simulated and evaluated. This included cloud simulations and cloud test development to investigate possible sensor effects, and a comprehensive flowdown analysis of the algorithm was conducted. In addition, a technique for total column water vapor retrieval …

Long-Lived Spin Coherence States In Semiconductor Heterostructures, Yuriy V. Pershin Dr

Faculty Publications

We study evolution of electron spin coherence having nonhomogeneous direction of spin polarization vector in semiconductor heterostructures. It is found that the electron spin relaxation time due to the D’yakonov- Perel’ relaxation mechanism essentially depends on the initial spin polarization distribution. This effect has its origin in the coherent spin precession of electrons diffusing in the same direction. We predict a long spin relaxation time of a novel structure: a spin coherence standing wave and discuss its experimental realization.

Physics Alumni Newsletter Spring 2005, Terry Goforth

Physics Alumni Newsletter

Physics Alumni Newsletter

The Physics Alumni Newsletter is produced by the SWOSU Physics Department.

Our Engineering Physics students are recruited in fields such as electronics, aerospace, mechanical engineering, petroleum engineering and software engineering. Graduates also have careers in meteorology, architecture, education and more.

Computation Of Electron-Impact K-Shell Ionization Cross Sections Of Atoms, M A. Uddin, Abul Kalam Fazlul Haque, M Masum Billah, A K. Basak, Khondkar R. Karim, B C. Saha

Faculty publications – Physics

The total cross sections of electron impact single K-shell ionization of atomic targets, with a wide range of atomic numbers from Z=6-50, are evaluated in the energy range up to about 10 MeV employing the recently proposed modified version of the improved binary-encounter dipole (RQIBED) model [Uddin , Phys. Rev. A 70, 032706 (2004)], which incorporates the ionic and relativistic effects. The experimental cross sections for all targets are reproduced satisfactorily even in the relativistic energies using fixed generic values of the two parameters in the RQIBED model. The relativistic effect is found to be significant in all targets except …

The Equation, Winter 2005, College Of Science And Mathematics, Wright State University

College of Science and Mathematics Newsletters

This 14 page newsletter discusses various happenings within the College of Science and Mathematics. It begins with a letter from the dean, and continues on with news, events, alumni news, and other community news.

Against Realist Instruction: Superficial Success Masking Catastrophic Failure And An Alternative, Dewey I. Dykstra

Physics Faculty Publications and Presentations

Purpose: Often radical constructivists are confronted with arguments why radical constructivism is wrong. The present work presents a radical constructivist alternative to such arguments: a comparison of the results of two instructional practices, the standard, realistbased instruction and a radical constructivist-based instruction, both in physics courses. Design: Evidence from many studies of student conceptions in standard instruction (Duit 2004) is taken into account. In addition, diagnostic data, pre and post instruction, were collected from over 1,000 students in multiple institutions across the U. S. over a period of about 15 years via an established diagnostic of conceptual understanding of motion …

Interstellar Helium Pickup Ion Flux Variations Observed With Soho/Celias, Lukas A. Saul

Doctoral Dissertations

Interstellar pickup ions are formed when neutral atoms freely enter the heliosphere and are subsequently ionized. Once these particles are charged they become a component of the interplanetary plasma and are transported outward with the solar wind (SW). Measurements of these particles give information about the local interstellar gas in which our sun resides. However, fluxes of pickup ions in the solar wind are observed to vary substantially in both magnitude and energy spectrum.

Hypothesized is that the main causes of these variations are transport phenomenon in the solar wind, determined by the solar wind and the interplanetary magnetic field. …

High-Energy Effective Action From Scattering Of Qcd Shock Waves, Ian Balitsky

Physics Faculty Publications

At high energies, the relevant degrees of freedom are Wilson lines—infinite gauge links ordered along straight lines collinear to the velocities of colliding particles. The effective action for these Wilson lines is determined by the scattering of QCD shock waves. I develop the symmetric expansion of the effective action in powers of strength of one of the shock waves and calculate the leading term of the series. The corresponding first-order effective action, symmetric with respect to projectile and target, includes both up and down fan diagrams and pomeron loops.