Physics Commons^™

X-Ray Emission Produced In Charge-Exchange Collisions Between Highly Charged Ions And Argon: Role Of The Multiple Electron Capture, Sebastian Otranto, N. D. Cariatore, Ronald E. Olson

Physics Faculty Research & Creative Works

In this work we use the classical trajectory Monte Carlo method within an eight-electron scheme to theoretically study photonic spectra that follow charge-exchange processes between highly charged ions of charge states 10+, 17+, 18+, and 36+ with neutral argon. The energy range considered is 18 eV/amu to 4 keV/amu, covering typical electron beam ion traps and solar wind energies. The role played by multiple electron capture processes for the different collision systems under consideration is explicitly analyzed and its contribution separated as arising from radiative decay and autoionizing multiple capture. For the present collision systems we find that multiple electron …

Theoretical And Experimental (E, 2e) Study Of Electron-Impact Ionization Of Laser-Aligned Mg Atoms, Sadek Amami, Andrew J. Murray, Al Stauffer, Kate Nixon, Gregory Armstrong, James Colgan, Don H. Madison

Physics Faculty Research & Creative Works

We have performed calculations of the fully differential cross sections for electron-impact ionization of magnesium atoms. Three theoretical approximations, the time-dependent close coupling, the three-body distorted wave, and the distorted wave Born approximation, are compared with experiment in this article. Results will be shown for ionization of the 3s ground state of Mg for both asymmetric and symmetric coplanar geometries. Results will also be shown for ionization of the 3p state which has been excited by a linearly polarized laser which produces a charge cloud aligned perpendicular to the laser beam direction and parallel to the linear polarization. Theoretical and …

Control Power In Perfect Controlled Teleportation Via Partially Entangled Channels, Xi-Han Li, Shohini Ghose

Physics and Computer Science Faculty Publications

We analyze and evaluate perfect controlled teleportation via three-qubit entangled channels from the point of view of the controller. The key idea in controlled teleportation is that the teleportation is performed only with the participation of the controller. We calculate a quantitative measure of the controller's power and establish a lower bound on the control power required for controlled teleportation. We show that the maximally entangled Greenberger-Horne-Zeilinger state is a suitable channel for controlled teleportation of arbitrary single qubits-the controller's power meets the bound and the teleportation fidelity without the controller's permission is no better than the fidelity of a …

Enhanced Rare-Region Effects In The Contact Process With Long-Range Correlated Disorder, Ahmed K. Ibrahim, Hatem Barghathi, Thomas Vojta

Physics Faculty Research & Creative Works

We investigate the nonequilibrium phase transition in the disordered contact process in the presence of long-range spatial disorder correlations. These correlations greatly increase the probability for finding rare regions that are locally in the active phase while the bulk system is still in the inactive phase. Specifically, if the correlations decay as a power of the distance, the rare-region probability is a stretched exponential of the rare-region size rather than a simple exponential as is the case for uncorrelated disorder. As a result, the Griffiths singularities are enhanced and take a non-power-law form. The critical point itself is of infinite-randomness …

Strong-Disorder Magnetic Quantum Phase Transitions: Status And New Developments, Thomas Vojta

Physics Faculty Research & Creative Works

This article reviews the unconventional effects of random disorder on magnetic quantum phase transitions, focusing on a number of new experimental and theoretical developments during the last three years. On the theory side, we address smeared quantum phase transitions tuned by changing the chemical composition, for example in alloys of the type A_1-xB_x. We also discuss how the interplay of order parameter conservation and overdamped dynamics leads to enhanced quantum Griffiths singularities in disordered metallic ferromagnets. Finally, we discuss a semiclassical theory of transport properties in quantum Griffiths phases. Experimental examples include the ruthenates Sr_{1-x …}

Phase Transitions On Random Lattices: How Random Is Topological Disorder?, Hatem Barghathi, Thomas Vojta

Physics Faculty Research & Creative Works

We study the effects of topological (connectivity) disorder on phase transitions. We identify a broad class of random lattices whose disorder fluctuations decay much faster with increasing length scale than those of generic random systems, yielding a wandering exponent of ω = (d−1)/(2d) in d dimensions. The stability of clean critical points is thus governed by the criterion (d+1)ν > 2 rather than the usual Harris criterion dν > 2, making topological disorder less relevant than generic randomness. The Imry-Ma criterion is also modified, allowing first-order transitions to survive in all dimensions d > 1. These results explain a host of puzzling violations …

Effect Of The Center-Of-Mass Approximation On The Scaling Of Electron-Capture Fully Differential Cross Sections, A. L. Harris, Don H. Madison

Physics Faculty Research & Creative Works

We present results for p+He single electron capture and transfer with target excitation using the first Born approximation. The effect of approximating the center of mass of the helium atom and outgoing hydrogen atom at the respective nuclei is explored. Semianalytical results are compared for the calculations with and without the approximation, and it is shown that one must properly account for the center of mass of the atoms. It is also shown that this approximation is the result of the apparent v⁴ scaling that was previously observed with the four-body transfer with target excitation model.

A Women In Mathematics, Computer Science, And Physics Course, Jim Crumley, Kristen Nairn, Lynn Ziegler, Pamela L. Bacon, Yu Zhang

MapCores Faculty Publications

Increasing women's participation is a concern in disciplines beyond
physics. As part of our Mathematics, Physics, Computer Science
Research Scholars (MapCores) program, we teach a women in science
class covering these three areas. Our course is a special version of
our college's first year seminar, which is a course designed to
prepare our students to read, write, and speak at a college-level. We
structure our FYS to promote academic confidence and interest in our
disciplines for the women in MapCores. It covers not only contributions
that women have made and barriers that women face in these
disciplines, but also research …

Evidence For Magnetic Clusters In Ni₁₋ₓvₓ Close To The Quantum Critical Concentration, R. Wang, S. Ubaid-Kassis, A. Schroeder, P. J. Baker, F. L. Pratt, S. J. Blundell, T. Lancaster, I. Franke, J. S. Möller, Thomas Vojta

Physics Faculty Research & Creative Works

The d-metal alloy Ni_1-xV_x undergoes a quantum phase transition from a ferromagnetic ground state to a paramagnetic ground state as the vanadium concentration x is increased. We present magnetization, ac-susceptibility and muon-spin relaxation data at several vanadium concentrations near the critical concentration x_c ~ 11.6 % at which the onset of ferromagnetic order is suppressed to zero temperature. Below x_c, the muon data reveal a broad magnetic field distribution indicative of a long-range ordered ferromagnetic state with spatial disorder. We show evidence of magnetic clusters in the ferromagnetic phase and close to the phase …

Theoretical And Experimental Investigation Of (E, 2e) Ionization Of Argon 3p In Asymmetric Kinematics At Intermediate Energy, Sadek Amami, Melike Ulu, Zehra Nur Ozer, Murat Yavuz, Suay Kazgoz, Mevlut Dogan, Oleg Zatsarinny, Klaus Bartschat, Don H. Madison

Physics Faculty Research & Creative Works

The field of electron-impact ionization of atoms, or (e, 2e), has provided significant detailed information about the physics of collisions. For ionization of hydrogen and helium, essentially exact numerical methods have been developed which can correctly predict what will happen. For larger atoms, we do not have theories of comparable accuracy. Considerable attention has been given to ionization of inert gases and, of the inert gases, argon seems to be the most difficult target for theory. There have been several studies comparing experiment and perturbative theoretical approaches over the last few decades, and generally qualitative but not quantitative agreement is …

Rare Regions And Griffiths Singularities At A Clean Critical Point: The Five-Dimensional Disordered Contact Process, Thomas Vojta, John Igo, José A. Hoyos

Physics Faculty Research & Creative Works

We investigate the nonequilibrium phase transition of the disordered contact process in five space dimensions by means of optimal fluctuation theory and Monte Carlo simulations. We find that the critical behavior is of mean-field type, i.e., identical to that of the clean five-dimensional contact process. It is accompanied by off-critical power-law Griffiths singularities whose dynamical exponent z' saturates at a finite value as the transition is approached. These findings resolve the apparent contradiction between the Harris criterion, which implies that weak disorder is renormalization-group irrelevant, and the rare-region classification, which predicts unconventional behavior. We confirm and illustrate our theory by …

Fully Differential Cross Sections For Electron-Impact Excitation-Ionization Of Aligned D₂, Esam Ali, A. L. Harris, J. Lower, E. Weigold, Chuang-Gang Ning, Don H. Madison

Physics Faculty Research & Creative Works

We examine fully differential cross sections for 176 eV electron-impact dissociative excitation-ionization of orientated D2 for transitions to final ion states 2sσ_g, 2pσ_u, and 2pπ_u. In previous work [Phys. Rev. A 88, 062705 (2013)PLRAAN1050-294710.1103/PhysRevA.88.062705], we calculated these cross sections using the molecular four-body distorted wave (M4DW) method with the ground-state D2 wave function being approximated by a product of two Dyson 1s-type orbitals. The theoretical results were compared with experimental measurements for five different orientations of the target molecule (four in the scattering plane and one perpendicular to the scattering plane). For the unresolved …

Theoretical Triple-Differential Cross Sections Of A Methane Molecule By A Proper-Average Method, Hari Chaluvadi, C. G. Ning, Don H. Madison

Physics Faculty Research & Creative Works

For the last few years, our group has calculated cross sections for electron-impact ionization of molecules using the molecular three-body distorted-wave approximation coupled with the orientation-averaged molecular orbital (OAMO) approximation. This approximation was very successful for calculating ionization cross sections for hydrogen molecules and to a lesser extent nitrogen molecules. Recently we used the approximation to calculate single ionization cross sections for the 1t₂ state of methane (CH₄) and we found major discrepancies with the experimental data. Here we investigate the validity of the OAMO approximation by calculating cross sections that have been properly averaged over all …

Mapcores 2013-2014 Assessment Report, Kristen Nairn, Pamela L. Bacon, Jim Crumley, Yu Zhang

MapCores Faculty Publications

This is a report showing the assessment results for the MapCores (MAthematics, Physics, COmputer science REsearch Scholars) program at the College of Saint Benedict. Started in 2009, MapCores is a cohort-based program designed to increase women's interest and achievement in mathematics, physics, computer science and engineering. The report was submitted for the National Science Foundation grant number 0965705.

Volume 06, Kristen Gains, Amanda Willis, Holly Backer, Monika Gutierrez, Cara O'Neal, Sara Nelson, Sasha Silberman, Jessica Beardsley, Jamie Gardner, Edward Peeples, Matthew Sakach, Tess Lione, Emily Wilkins, Kelsey Holt, Jessica Page, Jamie Clift, Charles Vancampen, Gilbert Hall, Jenny Nehrt, Kasey Dye, Amanda Tharp, Jamie Leeuwrik, Ashley Mcgee, Emily Poulin, Michael Kropf, Nick Pastore, Austin Polasky, Morgan Glasco, Laura L. Kahler, Melinda L. Edwards, Brandon C. Smith, Mariah Asbell, Cabell Edmunds, Amelia D. Perry, Alyssa Hayes, Irina Boothe, Perry Bason, James Early

Incite: The Journal of Undergraduate Scholarship

Introduction from Dean Dr. Charles Ross

Caught Between Folklore and the Cold War: The Americanization of Russian Children's Literature by Kristen Gains

Graphic Design by Amanda Willis

Graphic Design by Holly Backer

Prejudices in Swiss German Accents by Monika Gutierrez

Photography by Cara O'Neal

Photography by Sara Nelson

Edmund Tyrone's Long Journey through Night by Sasha Silberman

Photography by Jessica Beardsley

Photography by Jamie Gardner and Edward Peeples

The Republican Razor: The Guillotine as a Symbol of Equality by Jamie Clift

Graphic Design by Matthew Sakach

Genocide: The Lasting Effects of Gender Stratification in Rwanda By Tess Lione and Emily …

Phonon Density Of States And Anharmonicity Of Uo₂, Judy W. Pang, Aleksandr V. Chernatynskiy, Bennett C. Larson, William J. Buyers, Douglas L. Abernathy, Kenneth J. Mcclellan, Simon R. Phillpot

Physics Faculty Research & Creative Works

Phonon density of states (PDOS) measurements have been performed on polycrystalline UO₂ at 295 and 1200 K using time-of-flight inelastic neutron scattering to investigate the impact of anharmonicity on the vibrational spectra and to benchmark ab initio PDOS simulations performed on this strongly correlated Mott insulator. Time-of-flight PDOS measurements include anharmonic linewidth broadening, inherently, and the factor of ~7 enhancement of the oxygen spectrum relative to the uranium component by the increased neutron sensitivity to the oxygen-dominated optical phonon modes. The first-principles simulations of quasiharmonic PDOS spectra were neutron weighted and anharmonicity was introduced in an approximate way by …

Criticality And Quenched Disorder: Harris Criterion Versus Rare Regions, Thomas Vojta, José A. Hoyos

Physics Faculty Research & Creative Works

We employ scaling arguments and optimal fluctuation theory to establish a general relation between quantum Griffiths singularities and the Harris criterion for quantum phase transitions in disordered systems. If a clean critical point violates the Harris criterion, it is destabilized by weak disorder. At the same time, the Griffiths dynamical exponent z' diverges upon approaching the transition, suggesting unconventional critical behavior. In contrast, if the Harris criterion is fulfilled, power-law Griffiths singularities can coexist with clean critical behavior, but z' saturates at a finite value. We present applications of our theory to a variety of systems including quantum spin chains, …

Role Of Electron Saddle Swaps In The Photon Spectra Following Li³⁺ Charge-Exchange Collisions With H*(N = 2), Na(3s), Na*(3p), And Li(2s) Targets, Sebastian Otranto, R. Hoekstra, Ronald E. Olson

Physics Faculty Research & Creative Works

The role of electron saddle swaps in collisions of bare Li with metastable hydrogen and alkali-metal atoms is investigated by means of the classical trajectory Monte Carlo method. In particular, we show that oscillations as a function of collision energy in the photon spectra resulting from charge exchange are directly related to the number of potential-saddle crossings that a receding electron can achieve during a given reaction. The range of impact energies spanned is 0.01-50 keV/amu, an area of interest for diagnostic purposes in tokamak nuclear fusion power reactors.

Enhanced Capillary Rise Of Wetting Liquids In Reduced Gravitational Shielding Under Microgravity Conditions, George D. Zouganelis, Ioannis Gkigkitzis, Ioannis Haranas

Physics and Computer Science Faculty Publications

We study the capillary rise of wetting in liquids by slightly modifying Ponomarenko’s result, a recently derived and observed t^1/3 law, without omitting the corresponding gravity term and therefore we find h_new (t)≅0.9085h_Pon (t) instead, which corresponds to a 9% difference. Furthermore, in order to examine the effect of corrected gravity, we extend the result on the surface of a planetary body by correcting the gravitational acceleration for its oblateness coefficient and rotation. We find that experiments that take place on the equator result in highest capillary heights, than those at mid latitudes and the poles. …

Cms Use Of A Data Federation, Kenneth A. Bloom, C.

Kenneth Bloom Publications

CMS is in the process of deploying an Xrootd based infrastructure to facilitate a global data federation. The services of the federation are available to export data from half the physical capacity and the majority of sites are configured to read data over the federation as a back-up. CMS began with a relatively modest set of use-cases for recovery of failed local file opens, debugging and visualization. CMS is finding that the data federation can be used to support small scale analysis and load balancing. Looking forward we see potential in using the federation to provide more flexibility in the …

Strong-Randomness Infinite-Coupling Phase In A Random Quantum Spin Chain, Fawaz Hrahsheh, José A. Hoyos, Rajesh Narayanan, Thomas Vojta

Physics Faculty Research & Creative Works

We study the ground-state phase diagram of the Ashkin-Teller random quantum spin chain by means of a generalization of the strong-disorder renormalization group. In addition to the conventional paramagnetic and ferromagnetic (Baxter) phases, we find a partially ordered phase characterized by strong randomness and infinite coupling between the colors. This unusual phase acts, at the same time, as a Griffiths phase for two distinct quantum phase transitions, both of which are of infinite-randomness type. We also investigate the quantum multicritical point that separates the two-phase and three-phase regions, and we discuss generalizations of our results to higher dimensions and other …

Gpu Accelerated Long-Term Simulations Of Beam-Beam Effects In Colliders, B. Terzić, V. Morozov, Y. Roblin, F. Lin, H. Zhang, M. Aturban, D. Ranjan, M. Zubair

Computer Science Faculty Publications

We present an update on the development of the new code for long-term simulation of beam-beam effects in particle colliders. The underlying physical model relies on a matrix-based arbitrary-order particle tracking (including a symplectic option) for beam transport and the generalized Bassetti-Erskine approximation for beam-beam interaction. The computations are accelerated through a parallel implementation on a hybrid GPU/CPU platform. With the new code, previously computationally prohibitive long-term simulations become tractable. The new code will be used to model the proposed Medium-energy Electron-Ion Collider (MEIC) at Jefferson Lab.

Dynamical (E,2e) Studies Of Tetrahydropyran And 1,4-Dioxane, J. D. Builth-Williams, G. Da Silva, L. Chiari, D. B. Jones, Hari Chaluvadi, Don H. Madison, M. J. Brunger

Physics Faculty Research & Creative Works

We present experimental and theoretical results for the electron-impact ionization of the highest occupied molecular orbitals of tetrahydropyran and 1,4-dioxane. Using an (e,2e) technique in asymmetric coplanar kinematics, angular distributions of the slow ejected electron, with an energy of 20 eV, are measured when incident electrons at 250 eV ionize the target and scatter through an angle of either -10° or -15°. The data are compared with calculations performed at the molecular 3-body distorted wave level. Fair agreement between the theoretical model and the experimental measurements was observed. The similar structures for these targets provide key insights for assessing the …

Contact Process On Generalized Fibonacci Chains: Infinite-Modulation Criticality And Double-Log Periodic Oscillations, Hatem Barghathi, David Nozadze, Thomas Vojta

Physics Faculty Research & Creative Works

We study the nonequilibrium phase transition of the contact process with aperiodic transition rates using a real-space renormalization group as well as Monte Carlo simulations. The transition rates are modulated according to the generalized Fibonacci sequences defined by the inflation rules A → AB^k and B → A. For k=1 and 2, the aperiodic fluctuations are irrelevant, and the nonequilibrium transition is in the clean directed percolation universality class. For k ≥ 3, the aperiodic fluctuations are relevant. We develop a complete theory of the resulting unconventional "infinite-modulation" critical point, which is characterized by activated dynamical scaling. Moreover, observables …

An Experimental Study On The Heat Enhancement And The Bio-Heat Transfer Using Gold Macro Road And Ultrasound: A Potential Alternative To Kill Cancer Cells, C. Austerlitz, Ioannis Gkigkitzis, Ioannis Haranas, Diana Campos

Physics and Computer Science Faculty Publications

We have previously proposed a method of treating solid tumors with a combination of gold macro-rods irradiated with ultrasound. Macro particle sized rods offer a greater circumferential treatment area over nanoparticle options. Experimental studies were conducted to investigate the heat enhancement and the bio-heat transfer to breast chicken using gold macro rod and ultrasound. An ultrasound, other than a focused ultrasound, may produce heat enough to cook a chicken breast up to about 1 cm diameter if a single gold rod is placed on the superficial tissue. Simulations and experimental results will provide the means to evaluate the treatment, to …

Simultaneous Optimization Of The Cavity Heat Load And Trip Rates In Linacs Using A Genetic Algorithm, Balša Terzić, Alicia S. Hofler, Cody J. Reeves, Sabbir A. Khan, Geoffrey A. Krafft, Jay Benesch, Arne Freyberger, Desh Ranjan

Physics Faculty Publications

In this paper, a genetic algorithm-based optimization is used to simultaneously minimize two competing objectives guiding the operation of the Jefferson Lab's Continuous Electron Beam Accelerator Facility linacs: cavity heat load and radio frequency cavity trip rates. The results represent a significant improvement to the standard linac energy management tool and thereby could lead to a more efficient Continuous Electron Beam Accelerator Facility configuration. This study also serves as a proof of principle of how a genetic algorithm can be used for optimizing other linac-based machines.

Kapitza Resistance Of Si/Sio₂ Interface, Bowen Deng, Aleksandr V. Chernatynskiy, Marat Khafizov, David H. Hurley, Simon R. Phillpot

Physics Faculty Research & Creative Works

A phonon wave packet dynamics method is used to characterize the Kapitza resistance of a Si/SiO₂ interface in a Si/SiO₂/Si heterostructure. By varying the thickness of SiO₂ layer sandwiched between two Si layers, we determine the Kapitza resistance for the Si/SiO ₂ interface from both wave packet dynamics and a direct, non-equilibrium molecular dynamics approach. The good agreement between the two methods indicates that they have each captured the anharmonic phonon scatterings at the interface. Moreover, detailed analysis provides insights as to how individual phonon mode scatters at the interface and their contribution to the Kapitza …

Lattice-Boltzmann Simulations Of The Thermally Driven 2d Square Cavity At High Rayleigh Numbers, Dario Contrino, Pierre Lallemand, Pietro Asinari, Li-Shi Luo

Mathematics & Statistics Faculty Publications

The thermal lattice Boltzmann equation (TLBE) with multiple-relaxation-times (MRT) collision model is used to simulate the steady thermal convective flows in the two-dimensional square cavity with differentially heated vertical walls at high Rayleigh numbers. The MRT-TLBE consists of two sets of distribution functions, i.e., a D2Q9 model for the mass-momentum equations and a D2Q5 model for the temperature equation. The dimensionless flow parameters are the following: the Prandtl number Pr = 0.71 and the Rayleigh number Ra = 10⁶, 10⁷, and 10⁸. The D2Q9 + D2Q5 MRT-TLBE is shown to be second-order accurate and …

Phonon Thermal Transport Through Tilt Grain Boundaries In Strontium Titanate, Zexi Zheng, Xiang Chen, Bowen Deng, Aleksandr V. Chernatynskiy, Shengfeng Yang, Jinjun Xiong, Youping Chen

Physics Faculty Research & Creative Works

In this work, we perform nonequilibrium molecular dynamics simulations to study phonon scattering at two tilt grain boundaries (GBs) in SrTiO₃. Mode-wise energy transmission coefficients are obtained based on phonon wave-packet dynamics simulations. The Kapitza conductance is then quantified using a lattice dynamics approach. The obtained results of the Kapitza conductance of both GBs compare well with those obtained by the direct method, except for the temperature dependence. Contrary to common belief, the results of this work show that the optical modes in SrTiO₃ contribute significantly to phonon thermal transport, accounting for over 50% of the Kapitza …

Triply Differential (E,2e) Studies Of Phenol, Silva G. Da, R. F. Neves, L. Chiari, D. B. Jones, E. Ali, Don H. Madison, C. G. Ning, K. L. Nixon, M. C. Lopes, M. J. Brunger

Physics Faculty Research & Creative Works

We have measured (e,2e) triple differential cross sections (TDCS) for the electron-impact ionisation of phenol with coplanar asymmetrical kinematics for an incident electron energy of 250 eV. Experimental measurements of the angular distribution of the slow outgoing electrons at 20 eV are obtained when the incident electron scatters through angles of -5°, -10°, and -15°, respectively. The TDCS data are compared with calculations performed within the molecular 3-body distorted wave model. In this case, a mixed level of agreement, that was dependent on the kinematical condition being probed, was observed between the theoretical and experimental results in the binary peak …