Physical Sciences and Mathematics Commons^™

Momentum Distributions For 2H (E, E' P), William P. Ford, Sabine Jeschonnek, J. W. Van Orden

Faculty Publications

Background: A primary goal of deuteron electrodisintegration is the possibility of extracting the deuteron momentum distribution. This extraction is inherently fraught with difficulty, as the momentum distribution is not an observable and the extraction relies on theoretical models dependent on other models as input.

Purpose: We present a new method for extracting the momentum distribution which takes into account a wide variety of model inputs thus providing a theoretical uncertainty due to the various model constituents. To test the extraction, pseudodata were generated, and the extracted “experimental” distribution, which has theoretical uncertainty accounted by this extraction method, can be compared …

Sulfur Vacancies In Photorefractive Sn2P2S6 Crystals, Eric M. Golden, Sergey A. Basun, A. A. Grabar, I. M. Stoika, Nancy C. Giles, D. R. Evans, Larry E. Halliburton

Faculty Publications

A photoinduced electron paramagnetic resonance (EPR) spectrum in single crystals of Sn2P2S6 (SPS) is assigned to an electron trapped at a sulfur vacancy. These vacancies are unintentionally present in undoped SPS crystals and are expected to play an important role in the photorefractive behavior of the material. Nonparamagnetic sulfur vacancies are formed during the initial growth of the crystal. Subsequent illumination below 100 K with 442 nm laser light easily converts these vacancies to EPR-active defects. The resulting S = 1/2 spectrum shows well-resolved and nearly isotropic hyperfine interactions with two P ions and two Sn ions. Partially resolved interactions …

Elastic Differential Cross Sections For Space Radiation Applications, Charles M. Werneth, Khin M. Maung, William P. Ford, John W. Norbury, Michael D. Vera

Faculty Publications

The eikonal, partial wave (PW) Lippmann-Schwinger, and three-dimensional Lippmann-Schwinger (LS3D) methods are compared for nuclear reactions that are relevant for space radiation applications. Numerical convergence of the eikonal method is readily achieved when exact formulas of the optical potential are used for light nuclei (>A≤>16), and the momentum-space representation of the optical potential is used for heavier nuclei. The PW solution method is known to be numerically unstable for systems that require a large number of partial waves, and, as a result, the LS3D method is employed. The effect of relativistic kinematics is studied with the PW and …

Nonlinear Optimal Filter Technique For Analyzing Energy Depositions In Tes Sensors Driven Into Saturation, Benjamin Shank, Jeffrey Yen, Blas Cabrera, John Mark Kreikebaum, Robert Moffatt, Peter Redl, Betty Young, Paul Brink, Matthew Cherry, Astrid Tomada

Faculty Publications

We present a detailed thermal and electrical model of superconducting transition edge sensors(TESs) connected to quasiparticle (qp) traps, such as the W TESs connected to Al qp traps used for CDMS (Cryogenic Dark Matter Search) Ge and Si detectors. We show that this improvedmodel, together with a straightforward time-domain optimal filter, can be used to analyze pulses well into the nonlinear saturation region and reconstruct absorbed energies with optimal energyresolution.

Casimir Energies In Spherically Symmetric Background Potentials Revisited, Matthew Beauregard, Michael Bordag, Klaus Kirsten

Faculty Publications

In this paper we reconsider the formulation for the computation of the Casimir energy in spherically symmetric background potentials. Compared to the previous analysis, the technicalities are much easier to handle and final answers are surprisingly simple.

Measurement Of Quasiparticle Transport In Aluminum Films Using Tungsten Transition-Edge Sensors, Jeffrey Yen, Benjamin Shank, Betty Young, Blas Cabrera, Paul Brink, Matthew Cherry, John Mark Kreikebaum, Robert Moffatt, Peter Redl, Astrid Tomada, Ted Tortorici

Faculty Publications

We report on experimental studies of phonon sensors which utilize quasiparticle diusion in thin aluminum films connected to tungsten transition-edge-sensors (TESs) operated at 35 mK. We show that basic TES physics and a simple physical model of the overlap region between the W and Al lms in our devices enables us to accurately reproduce the experimentally observed pulse shapes from x-rays absorbed in the Al films. We further estimate quasiparticle loss in Al lms using a simple diusion equation approach. These studies allow the design of phonon sensors with improved performance.

Magnetic Correlations And Pairing In The 1/5-Depleted Square Lattice Hubbard Model, Ehsan Khatami, Rajiv R.P. Singh, Warren E. Pickett, Richard T. Scalettar

Faculty Publications

We study the single-orbital Hubbard model on the 1/5-depleted square-lattice geometry, which arises in such diverse systems as the spin-gap magnetic insulator CaV4O9 and ordered-vacancy iron selenides, presenting new issues regarding the origin of both magnetic ordering and superconductivity in these materials. We find a rich phase diagram that includes a plaquette singlet phase, a dimer singlet phase, a Néel and a block-spin antiferromagnetic phase, and stripe phases. Quantum Monte Carlo simulations show that the dominant pairing correlations at half filling change character from d wave in the plaquette phase to extended s wave upon transition to the Néel phase. …

Observation Of Heavy- And Light-Hole Split Direct Bandgap Photoluminescence From Tensile-Strained Gesn (0.03% Sn), Thomas R. Harris, Yung Kee Yeo, Mee-Yi Ryu, Richard T. Beeler, John Kouvetakis

Faculty Publications

Temperature- (T-) and laser power-dependent photoluminescence (PL) measurements have been made for the tensile-strained, undoped GeSn (0.03% Sn) film grown on Si substrate. The PL results show not only clear strain-split direct bandgap transitions to the light-hole (LH) and heavy-hole (HH) bands at energies of 0.827 and 0.851 eV at 10 K, respectively, but also clearly show both strong direct and indirect bandgap related PL emissions at almost all temperatures, which are rarely observed. This split of PL emissions can be directly observed only at low T and moderate laser power, and the two PL peaks merge into one broad …

Low-Lying Neutron Unbound States In Be-12, J. K. Smith, T. Baumann, D. Bazin, J. Brown, S. Casarotto, Paul A. De Young, N. Frank, J. Hinnefeld, M. Hoffman, M. D. Jones, Z. Kohley, B. Luther, B. Marks, N. Smith, J. Snyder, A. Spyrou, S. L. Stephenson, M. Thoennessen, N. Viscariello, S. J. Williams

Faculty Publications

The neutron decay of an unbound resonance in Be-12 has been measured at 1243 +/- 21 keV decay energy with a width of 634 +/- 60 keV. This state was populated with a one-proton removal reaction from a 71 MeV/u B-13 beam incident upon a beryllium target. The invariant mass reconstruction of the resonance was achieved by measuring the daughter fragment in coincidence with neutrons. Despite being above the 2n separation energy, the state decays predominantly by the emission of one neutron to Be-11, setting an upper limit on the branching ratio for the two-neutron decay channel to Be-10 of …

Near- And Sub-Barrier Fusion Of The Be7+ Ni58 System, E. Martinez-Quiroz, E. F. Aguilera, D. Lizcano, P Amador-Valenzuela, H. Garcia-Martinez, J. J. Kolata, A. Roberts, L. O. Lamm, G. Rogachev, V. Guimaraes, F. D. Becchetti, A. Villano, M. Ojaruega, M. Febbraro, Y. Chen, H. Jiang, Paul A. De Young, Graham F. Peaslee

Faculty Publications

Evaporation proton yields were measured for the fusion of the radioactive proton-rich nucleus Be-7 onto a Ni-58 target at six near-barrier energies. Total fusion cross sections were deduced by using calculated proton multiplicities. The resulting fusion excitation function shows a considerable enhancement with respect to calculations for a bare potential, even for energies above the Coulomb barrier. Inelastic couplings can account for the enhancement at the highest energy. Total fusion channels nearly saturate the total reaction cross section in the measured energy region. Comparison with previous results scaled appropriately for Be-7 + (Al-27, U-238) shows good agreement.

Investigating Access To And Attitudes Toward Programming In A Physics Camp, Gina Quan, Ayush Gupta

Faculty Publications

Computer programming has become a critical skill in much of physics research and undergraduate physics coursework. Our aim is to understand students' complex relationships (epistemological and affective associations) to coding and design, and in particular, how they experience and perceive access to programming in physics contexts. We piloted a project-based instructional module using Arduino Rovers (Arduino-integrated programmable robot-tanks) in a summer camp for high school students hosted by University of Maryland Physics Department. Throughout the program, participants worked through several open-ended design tasks before designing and completing a final project. In interviews, we asked students to reflect on their experiences …

Perturbative Unitarity Constraints On A Supersymmetric Higgs Portal, Kassahun Betre, Sonia Hedri, Devin Walker

Faculty Publications

We place perturbative unitarity constraints on both the dimensionful and dimensionless couplings in the Next-to-Minimal Supersymmetric Standard Model Higgs Sector. These constraints, plus the requirement that the singlino and/or Higgsino constitutes at least part of the observed dark matter relic abundance, generate upper bounds on the Higgs and neutralino/chargino mass spectrum. We obtain an upper bound of 12 TeV for the charginos and neutralinos and 20 TeV for the heavy Higgses outside defined fine-tuned regions. By using the NMSSM as a template, we describe a method which replaces naturalness arguments with more rigorous perturbative unitarity arguments to get a better …

Effect Of Z1/2, Eh5, And Ci1 Deep Defects On The Performance Of N-Type 4h-Sic Epitaxial Layers Schottky Detectors: Alpha Spectroscopy And Deep Level Transient Spectroscopy Studies, M. A. Mannan, S. K. Chaudhuri, K. V. Nguyen, K. C. Mandal

Faculty Publications

No abstract provided.

Linked-Cluster Expansion For The Green's Function Of The Infinite-U Hubbard Model, Ehsan Khatami, Edward Perepelitsky, Marcos Rigol, Sriram B. Shastry

Faculty Publications

We implement a highly efficient strong-coupling expansion for the Green's function of the Hubbard model. In the limit of extreme correlations, where the onsite interaction is infinite, the evaluation of diagrams simplifies dramatically enabling us to carry out the expansion to the eighth order in powers of the hopping amplitude. We compute the finite-temperature Green's function analytically in the momentum and Matsubara frequency space as a function of the electron density. Employing Padé approximations, we study the equation of state, Kelvin thermopower, momentum distribution function, quasiparticle fraction, and quasiparticle lifetime of the system at temperatures lower than, or of the …

Copper Doping Of Zno Crystals By Transmutation Of 64Zn To 65Cu: An Electron Paramagnetic Resonance And Gamma Spectroscopy Study, Matthew C. Recker, John W. Mcclory, Maurio S. Holston, Eric M. Golden, Nancy C. Giles, Larry E. Halliburton

Faculty Publications

Transmutation of ⁶⁴Zn to ⁶⁵Cu has been observed in a ZnO crystal irradiated with neutrons. The crystal was characterized with electron paramagnetic resonance (EPR) before and after the irradiation and with gamma spectroscopy after the irradiation. Major features in the gamma spectrum of the neutron-irradiated crystal included the primary 1115.5 keV gamma ray from the ⁶⁵Zn decay and the positron annihilation peak at 511 keV. Their presence confirmed the successful transmutation of ⁶⁴Zn nuclei to ⁶⁵Cu. Additional direct evidence for transmutation was obtained from the EPR of Cu²⁺ ions (where ⁶³Cu and ^{65 …}

Binding Of Solvated Peptide (Eplqlkm) With A Graphene Sheet Via Simulated Coarse-Grained Approach, Somayyeh Sheikholeslami, R. B. Pandey, Nadiya Dragneva, Wely Floriano, Oleg Rubel, Stephen A. Barr, Zhifeng Kuang, Rajiv Berry, Rajesh Naik, Barry Farmer

Faculty Publications

Binding of a solvated peptide A1 (¹E ²P ³L ⁴Q ⁵L ⁶K ⁷M) with a graphene sheet is studied by a coarse-grained computer simulation involving input from three independent simulated interaction potentials in hierarchy. A number of local and global physical quantities such as energy, mobility, and binding profiles and radius of gyration of peptides are examined as a function of temperature (T). Quantitative differences (e.g., the extent of binding within a temperature range) and qualitative similarities are observed in results from three simulated potentials. Differences in variations of both local and …

Absence Of Long-Wavelength Cerenkov Radiation With Isotropic Lorentz And Cpt Violation, Brett David Altschul

Faculty Publications

Modified theories of electrodynamics that include violations of Lorentz symmetry often allow for the possibility of vacuum Cerenkov radiation. This phenomenon has previously been studied in a number of Lorentz-violating theories, but none of the methods that have previously been developed are sufficient to study a theory with a timelike Chern-Simons term k_AF, because such a term may generate exponentially growing solutions to the field equations. Searching for vacuum Cerenkov radiation in a theory with a purely timelike Chern-Simons term using only elementary methods, we find that, despite the presence of the runaway modes, a charge in uniform …

Implications Of The Landauer Limit For Quantum Logic, F. Matthew Mihelic

Faculty Publications

The design of any system of quantum logic must take into account the implications of the Landauer limit for logical bits. Useful computation implies a deterministic outcome, and so any system of quantum computation must produce a final deterministic outcome, which in a quantum computer requires a quantum decision that produces a deterministic qubit. All information is physical, and any bit of information can be considered to exist in a physicality represented as a decision between the two wells of a double well potential in which the energy barrier between the two wells must be greater than kT·ln2. Any proposed …

The Real-Time Instructor Observing Tool For Future Teachers, Cassandra Paul

Faculty Publications

Current educational research shows that students achieve higher learning gains in science classrooms when interactive techniques are used. As a result, we are seeing more high schools and institutions of higher education adopt interactive courses. Unfortunately, it's difficult for future teachers to envision interactive science courses because their experience as students has been dominated by traditional lecture. New educators need to know what interactive science classrooms look like, so that they can model this experience in their own classrooms. The Real-time Instructor Observing Tool (RIOT), a computer application that allows an observer to quickly categorize classroom interactions, can help with …

Three-Point Current Correlation Functions As Probes Of Effective Conformal Theories, Kassahun Betre

Faculty Publications

See abstract in PDF.

Lorentz Violation In Fermion-Antifermion Decays Of Spinless Particles, Brett David Altschul

Faculty Publications

If Lorentz and CPT violation exist, they could affect the decays of scalar and pseudoscalar particles. For a decay into a fermion and an antifermion (not necessarily of the same mass), both the total decay rate and the outgoing particle distribution may be modified, through interference between the conventional decay mechanism and a separate Lorentz-violating mechanism. The modifications are sensitive to forms of Lorentz violation that are otherwise rather difficult to study, since at tree level they do not affect particle propagation, but only interaction vertices. Using existing experimental data on charged pion decay, it is possible to constrain three …

Triplet Ground State Of The Neutral Oxygen-Vacancy Donor In Rutile Tio2, A. T. Brant, Eric M. Golden, Nancy C. Giles, Shan Yang, M. A. R. Sarker, S. Watauchi, M. Nagao, I. Tanaka, D. A. Tryk, A. Manivannan, Larry E. Halliburton

Faculty Publications

Electron paramagnetic resonance (EPR) is used to investigate the triplet (S = 1) ground state of the neutral oxygen vacancy in bulk rutile TiO₂ crystals. This shallow donor consists of an oxygen vacancy with two nearest-neighbor, exchange-coupled ³⁺ ions located along the [001] direction and equidistant from the vacancy. The spins of the two trapped electrons, one at each ³⁺ ion, align parallel to give the S = 1 state. These neutral oxygen vacancies are formed near 25 K in as-grown oxidized TiO₂ crystals by illuminating with sub-band-gap 442 nm laser light. The angular dependence of the EPR …

Neutral Nitrogen Acceptors In Zno: The 67Zn Hyperfine Interactions, Eric M. Golden, S. M. Evans, Larry E. Halliburton, Nancy C. Giles

Faculty Publications

Electron paramagnetic resonance (EPR) is used to characterize the ⁶⁷Zn hyperfine interactions associated with neutral nitrogen acceptors in zinc oxide. Data are obtained from an n-type bulk crystal grown by the seeded chemical vapor transport method. Singly ionized nitrogen acceptors (N⁻) initially present in the crystal are converted to their paramagnetic neutral charge state (N⁰) during exposure at low temperature to 442 or 633 nm laser light. The EPR signals from these N⁰ acceptors are best observed near 5 K. Nitrogen substitutes for oxygen ions and has four nearest-neighbor cations. The zinc ion …

Grading By Response Category: A Simple Method For Providing Students With Meaningful Feedback On Exams In Large Courses, Cassandra Paul, Wendell Potter, Brenda Weiss

Faculty Publications

As instructors, we want our students to develop a deep understanding of course material, and feedback is essential in their sense-making process. Providing effective individualized feedback to students in large courses is especially difficult. While researcherssuggest,1 and many instructors of large courses are,2,3incorporating interactive techniques that allow peer feedback, studies have shown that it's important for students to also have direct feedback from the instructor.4 Since the requirement for individualized feedback is difficult to meet during class time in large courses, providing effective feedback on exams and quizzes takes on added importance. Some instructors choose to …

Sixteen Years Of Collaborative Learning Through Active Sense-Making In Physics (Clasp) At Uc Davis, Wendell Potter, David Webb, Cassandra Paul, Emily West, Mark Bowen, Brenda Weiss, Lawrence Coleman, Charles De Leone

Faculty Publications

This paper describes our large reformed introductory physics course at UC Davis, which bioscience students have been taking since 1996. The central feature of this course is a focus on sense-making by the students during the five hours per week discussion/labs in which the students take part in activities emphasizing peer-peer discussions, argumentation, and presentations of ideas. The course differs in many fundamental ways from traditionally taught introductory physics courses. After discussing the unique features of CLASP and its implementation at UC Davis, various student outcome measures are presented showing increased performance by students who took the CLASP course compared …

Measurement Of D^*\Pm Production In Deep Inelastic Scattering At Hera, Margarita C. K. Mattingly, Zeus Collaboration

Faculty Publications

The production of D^∗± mesons in deep inelastic ep scattering has been measured for exchanged photon virtualities 5 < Q²<1000GeV², using an integrated luminosity of 363 pb⁻¹ with the ZEUS detector at HERA. Differential cross sectionshave been measured and compared to next-to-leading-order QC D calculations. The cross-sections are used to extract the charm contribution to the protonstructure functions, expressed in terms of the reduced charm cro ss section, σ^c̄c_red. Theoretical calculations based on fits to inclusive HERA data are compared to the results.

Shooting Fish In A Barrel: A Demonstration Of The Refraction Of Light, Walter Trikosko

Faculty Publications

This is not a treatise on optics or the index of refraction. It is merely a demonstration that will surprise and engage many of your students. We have all put a pencil in a beaker of water and observed how it appears to bend.1 Not so much fun or engaging, is it? Why not illustrate this optical effect by taking your students spearfishing? Simulated spearfishing, to avoid the financial and legal ramifications. I intercepted a quiver of 30-in long aluminum shaft arrows that were on their way to the dumpster because, if for no other reason, my office could …

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 …

Fluctuation-Dissipation Theorem In Isolated Quantum Systems Out Of Equilibrium, Ehsan Khatami, Guido Pupillo, Mark Srednicki, Marcos Rigol

Faculty Publications

We study the validity of the fluctuation-dissipation theorem for an isolated quantum system of harmonically trapped dipolar molecules taken out of equilibrium by means of a quench, a sudden change in the Hamiltonian parameters. We find that the integrability of the system plays a crucial role in the validity of the fluctuation-dissipation theorem. Namely, the system thermalizes according to the eigenstate thermalization hypothesis and the theorem holds if the system is nonintegrable after the quench. However, it fails if the system is integrable, unless the initial state is an eigenstate of a nonintegrable Hamiltonian, in which case the system still …

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 …