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Atomic, Molecular and Optical Physics

2019

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Articles 91 - 110 of 110

Full-Text Articles in Physical Sciences and Mathematics

Spin- And Angle-Resolved Photoemission Studies Of The Electronic Structure Of Si(110)“16×2” Surfaces, N. K. Lewis, Y. Lassailly, L. Martinelli, I. Vobornik, J. Fujii, C. Bigi, Evan M. Brunkow, Nathan B. Clayburn, Timothy J. Gay, W. R. Flavell, E. A. Seddon Jan 2019

Spin- And Angle-Resolved Photoemission Studies Of The Electronic Structure Of Si(110)“16×2” Surfaces, N. K. Lewis, Y. Lassailly, L. Martinelli, I. Vobornik, J. Fujii, C. Bigi, Evan M. Brunkow, Nathan B. Clayburn, Timothy J. Gay, W. R. Flavell, E. A. Seddon

Timothy J. Gay Publications

The electronic structure of Si(110)“16×2” double-domain, single-domain, and 1×1 surfaces have been investigated using spin- and angle-resolved photoemission at sample temperatures of 77K and 300K. Angleresolved photoemission was conducted using horizontally and vertically polarized 60 eV and 80 eV photons. Band-dispersion maps revealed four surface states (S1 to S4) which were assigned to silicon dangling bonds on the basis of measured binding energies and photoemission intensity changes between horizontal and vertical light polarizations. Three surface states (S1, S2, and S4), observed in the Si(110)“16×2” reconstruction, were assigned to Si …

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Drift Chamber Calibration And Particle Identification In The P-349 Experiment, D. Alfs, A. Asaturyan, M. Carmignotto, M. Diermaier, W. Eyrich, B. Glowacz, D. Grzonka, Florian Hauenstein, T. Horn, K. Kilian, D. Lersch, S. Malbrunot-Ettenauer, A. Mkrtchyan, H. Mkrtchyan, P. Moskal, P. Nadel-Turonski, W. Oelert, J. Ritman, T. Sefzick, V. Tadevosyan, E. Widmann, M. Wolke, S. Zhamkochyan, M. Zieliński, A. Zink, J. Zmeskal Jan 2019

Drift Chamber Calibration And Particle Identification In The P-349 Experiment, D. Alfs, A. Asaturyan, M. Carmignotto, M. Diermaier, W. Eyrich, B. Glowacz, D. Grzonka, Florian Hauenstein, T. Horn, K. Kilian, D. Lersch, S. Malbrunot-Ettenauer, A. Mkrtchyan, H. Mkrtchyan, P. Moskal, P. Nadel-Turonski, W. Oelert, J. Ritman, T. Sefzick, V. Tadevosyan, E. Widmann, M. Wolke, S. Zhamkochyan, M. Zieliński, A. Zink, J. Zmeskal

Physics Faculty Publications

The goal of the P-349 experiment is to test whether 3.5 GeV/c antiprotons produced in high-energy proton-proton collisions are polarized in view of the preparation of a polarized antiproton beam. In this article, we present the details of the ongoing analysis focused on the drift chambers calibration and particle identification with DIRC.

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Argon Metastable And Resonant Level Densities In Ar And Ar/Cl² Discharges Used For The Processing Of Bulk Niobium, Jeremy Peshl, Roderick Mcneill, Charles I. Sukenik, Milka Nikolić, Svetozar Popović, Leposava Vŭsković Jan 2019

Argon Metastable And Resonant Level Densities In Ar And Ar/Cl² Discharges Used For The Processing Of Bulk Niobium, Jeremy Peshl, Roderick Mcneill, Charles I. Sukenik, Milka Nikolić, Svetozar Popović, Leposava Vŭsković

Physics Faculty Publications

A comparative analysis of two popular spectroscopy techniques is conducted in a coaxial cylindrical capacitively coupled discharge designed for the plasma processing of superconducting radio frequency (SRF) cavities. The density of the metastable and resonant levels in Ar is measured in both Ar and Ar/Cl2 discharges to properly characterize the unique discharge system and aid in the development of a cavity etching routine. The first method, deemed the “branching fraction method,” utilizes the sensitivity of photon reabsorption of radiative decay to measure the lower state (metastable and resonant) densities by taking ratios of spectral lines with a common upper …

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Molecular Symmetry-Mixed Dichroism In Double Photoionization Of H2, Jean Marcel Ngoko Djiokap, Alexei V. Meremianin, N. L. Manakov, L. B. Madsen, S. X. Hu, Anthony F. Starace Jan 2019

Molecular Symmetry-Mixed Dichroism In Double Photoionization Of H2, Jean Marcel Ngoko Djiokap, Alexei V. Meremianin, N. L. Manakov, L. B. Madsen, S. X. Hu, Anthony F. Starace

Anthony F. Starace Publications

Dichroism in double photoionization of H2 molecules by elliptically polarized extreme ultraviolet pulses is formulated analytically as a sum of atomiclike dichroism (AD) and molecular symmetry-mixed dichroism (MSMD) terms. The MSMD originates from an interplay of 1Σ+u and 1Π+u continuum molecular ionization amplitudes. For detection geometries in which the AD vanishes, numerical results for the sixfold differential probabilities for opposite pulse helicities show that the MSMD is significant in the electron momentum and angular distributions and is controllable by the ellipticity.

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Variations Of Heavy Ion Abundances Relative To Proton Abundances In Large Solar Energetic (E > 10 Mev) Particle Events, J. F. Round, Robert D. Loper, Omar A. Nava, Stephen W. Kahler Jan 2019

Variations Of Heavy Ion Abundances Relative To Proton Abundances In Large Solar Energetic (E > 10 Mev) Particle Events, J. F. Round, Robert D. Loper, Omar A. Nava, Stephen W. Kahler

Faculty Publications

The elemental composition of heavy ions (with atomic number Z > 2) (hi-Z) in large gradual E > 10 MeV nuc-1 SEP events has been extensively studied in the 2-15 MeV nuc-1 range to determine the acceleration processes and transport properties of SEPs. These studies invariably are based on abundances relative to those of a single element such as C or O and often neglect H and He, the elements of primary interest for space weather. The total radiation of an SEP event is determined not only by the H and He properties but also by those of hi-Z ions …

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Searching For Clean Observables In $B -> D* /Tau- \Bar{\Nu}_{\Tau}$ Decays, Michael D. Williams Jr. Jan 2019

Searching For Clean Observables In $B -> D* /Tau- \Bar{\Nu}_{\Tau}$ Decays, Michael D. Williams Jr.

Theses and Dissertations

In this thesis, the clean angular observables in the $\bar{B} \to D^{*+} \ell^- \bar{\nu}_{\ell}$ angular distribution is studied. Similar angular observables are widely studied in $B \to K^* \mu^+ \mu^-$ decays. We believed that these angular observables may have different sensitivities to different new physics structures.

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A Hydrogen-Bond Stabilized Mechanism Of Oxygen Evolution In Photosystem Ii: A Proposed Computational Experiment, Christopher King Jan 2019

A Hydrogen-Bond Stabilized Mechanism Of Oxygen Evolution In Photosystem Ii: A Proposed Computational Experiment, Christopher King

Undergraduate Theses, Professional Papers, and Capstone Artifacts

The ability of plants to take in water and release oxygen into the atmosphere is crucial to the survival of life on Earth. During photosynthesis, water is oxidized to O2 (dioxygen) at the Oxygen Evolving Complex (OEC) of Photosystem II. Structurally, the OEC resembles a box with an open lid, consisting of metal atoms (four manganese and one calcium) bridged by oxygen atoms. The mechanism of action of this complex, however, is not well understood. Various mechanisms have been proposed in recent years to explain how the OEC oxidizes water to dioxygen, but all of these mechanisms contain gaps …

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Thermal Analysis And Design Of Conduction Links For A Superconducting Radio Frequency Resonator, Aaron Mckeown Jan 2019

Thermal Analysis And Design Of Conduction Links For A Superconducting Radio Frequency Resonator, Aaron Mckeown

Graduate Research Theses & Dissertations

The SRF conduction link project at Fermi National Accelerator Laboratory aims to develop an SRF particle accelerator design that is more applicable for industrial use. Collaboration between NIU college of engineering and NIU department of physics provided the bulk of design and analysis for this project. Currently, cooling systems, used in SRF particle accelerators, pump liquid helium across the SRF cavity to provide convection based cooling. The goal of this project is to incorporate a conduction based cooling system. In a conduction based cooling system, heat will flow from the SRF cavity into a cryocooler through a conduction link. In …

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New Perspectives On The Schrödinger-Pauli Theory Of Electrons: Part I, Viraht Sahni Jan 2019

New Perspectives On The Schrödinger-Pauli Theory Of Electrons: Part I, Viraht Sahni

Publications and Research

Schrödinger-Pauli (SP) theory is a description of electrons in the presence of a static electromagnetic field in which the interaction of the magnetic field with both the orbital and spin moments is explicitly considered. The theory is described from the new perspective of the individual electron via its equation of motion or ‘Quantal Newtonian’ first law. The law is in terms of ‘classical’ fields whose sources are quantum mechanical expectation values of Hermitian operators taken with respect to the system wave function. The law states that each electron experiences an external and an internal field, the sum of which vanish. …

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Expansion Of An Ultracold Neutral Plasma, Yin Li Jan 2019

Expansion Of An Ultracold Neutral Plasma, Yin Li

Honors Theses

Ultracold neutral plasmas (UNP) exhibit interesting behavior and are more feasible to control than hot plasmas. Physicists would like to lower the temperature of a UNP to achieve a higher Coulomb coupling parameter, Γ for both electrons and ions. However, the three body recombination (TBR) between ions and electrons produces Rydberg atoms and heats up the plasma electrons, thereby ionizing them to Γe < 0.2. Adding Rydberg atoms to the plasma will reduce the temperature of a UNP in certain situations. In this honors project, we tried to achieve a Γe value greater than 0.5 by embedding Rydberg atoms multiple times in the plasma. We did extensive numerical simulations, but we were unable to replicate previous results from another group which obtained Γe = 0.5 in the first 1 µ s of plasma evolution. However, we were able to use the simulation results to test various different experiment scenarios. For experiments, we created a UNP of Rubidium atoms in the magneto-optical trap by laser cooling and photoionization. We figured out a nice way to zero the electric field within the field meshes by looking at the plasma expansion very late in its evolution through the micro-channel plate. We set the voltage and delay on the field mesh bias to find expansion velocity of the plasma for time t > 50 µs, and we used different methods to deduce the expansion velocity from the ion time of flight signals. However, we found that there was no relation of Γe at 1 µ s and the expansion velocity …

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Measurement Of The Beam Spin Asymmetry Of →Ep → E'P'Η In The Deep-Inelastic Regime With Clas, B. Zhao, A. Kim, K. Joo, I . Bedlinskiy, W. Kim, V. Kubarovsky, M. Ungaro, G. Gavalian, A. Klein, S. E. Kuhn, Clas Collaboration Jan 2019

Measurement Of The Beam Spin Asymmetry Of →Ep → E'P'Η In The Deep-Inelastic Regime With Clas, B. Zhao, A. Kim, K. Joo, I . Bedlinskiy, W. Kim, V. Kubarovsky, M. Ungaro, G. Gavalian, A. Klein, S. E. Kuhn, Clas Collaboration

Physics Faculty Publications

The beam spin asymmetry of the exclusive pseudoscalar channel →ep→e′p′η was measured for the first time in the deep-inelastic regime (W > 2 GeV/c2 and Q2 > 1 GeV2 /c2) using a longitudinally polarized 5.78 GeV electron beam at Jefferson Lab with the CEBAF Large Acceptance Spectrometer. The data were accumulated in 144 four-dimensional bins of Q2, xB, −t and ϕ over a wide kinematic range, where ϕ is the azimuthal angle between the lepton and hadron scattering planes, The measured azimuthal dependence with large amplitudes of the sin ϕ moments is …

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Energy Transfer Between Eu2+ And Mn2+ For Na(Sr,Ba)Po4 And Ba2mg(Bo3)2, Kevin Bertschinger Jan 2019

Energy Transfer Between Eu2+ And Mn2+ For Na(Sr,Ba)Po4 And Ba2mg(Bo3)2, Kevin Bertschinger

Dissertations, Master's Theses and Master's Reports

There is no debate of the affect that solid-state lighting has had on the world we live in. Throughout the centuries, lighting has continued to improve from kerosene lanterns to white light emitting diodes. Even though lighting today is sufficient there is still much room to improve color rendering index and efficiency. An active area of research to improve today's lighting technology is by doping inorganic phosphors with luminescent ion centers. There have been numerous reports of inorganic phosphors showing a variety of emission color and luminescence. In this thesis we discuss two new inorganic phosphors codoped with Eu2+ …

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Physics And Applications Of Exceptional Points, Qi Zhong Jan 2019

Physics And Applications Of Exceptional Points, Qi Zhong

Dissertations, Master's Theses and Master's Reports

Exceptional points (EPs) are singularities that arise in non-Hermitian physics. Crossing EPs is believed to be related with phase transitions between parity-time-(PT-)symmetric phase and broken PT phase. Owing to their peculiar topology, EPs can remotely induce observable effects when encircled by closed trajectories in the parameter space. In this dissertation, first of all, we investigate the extreme dynamics of non-Hermitian systems near higher order EPs constructed using the bosonic algebra method. The strong power oscillations for certain initial conditions can occur as a result of the peculiar eigenspace geometry and its dimensionality collapse near these singularities. And in the PT …

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Equilibrium Structures And Thermal Fluctuations In Interacting Monolayers, Emmanuel Rivera Jan 2019

Equilibrium Structures And Thermal Fluctuations In Interacting Monolayers, Emmanuel Rivera

Williams Honors College, Honors Research Projects

Coherency strains appear in interacting atomic monolayers due to differing bond lengths, which can arise from different materials or geometries. Examples include extended monolayers interacting with a substrate and the interacting walls of a multi-walled carbon nanotube. These strains can induce various equilibrium configurations, which we will analyze by means of a phenomenological model that incorporates forces from bond stretching and bending within each layer and the weak van der Waals interactions connecting the separate layers. We vary the strengths of each interaction to explore their effects on equilibrium structures, and the specific case of a two-walled carbon nanotube is …

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Imaging Technologies And Strategies For Detection Of Extant Extraterrestrial Microorganisms, Jay Nadeau, Manuel Bedrossian, Chris Lindensmith Jan 2019

Imaging Technologies And Strategies For Detection Of Extant Extraterrestrial Microorganisms, Jay Nadeau, Manuel Bedrossian, Chris Lindensmith

Physics Faculty Publications and Presentations

There is no reductionist definition of life, so the way organisms look, behave, and move is the most definitive way to identify extraterrestrial life. Life elsewhere in the Solar System is likely to be microbial, but no microscope capable of imaging prokaryotic life has ever flown on a lander mission to a habitable planet. Nonetheless, high-resolution microscopes have been developed that are appropriate for planetary exploration. Traditional light microscopy, interferometric microscopy, light-field microscopy, scanning probe microscopy, and electron microscopy are all possible techniques for the detection of extant micro-organisms on Mars and the moons of Jupiter and Saturn. This article …

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Photoemission Electron Microscopy To Characterize Slow Light In A Photonic Crystal Line Defect, Theodore Stedmark, Rolf Könenkamp Jan 2019

Photoemission Electron Microscopy To Characterize Slow Light In A Photonic Crystal Line Defect, Theodore Stedmark, Rolf Könenkamp

Physics Faculty Publications and Presentations

Using femtosecond nonlinear photoemission electron microscopy (PEEM) we provide a detailed characterization of slow light in a small-size asymmetric photonic crystal structure. We show that PEEM is capable of providing a unique description of the light propagation in such structures by direct imaging of the guided mode. This noninvasive characterization technique allows modal properties such as effective index, phase velocities, and group velocities to be determined. Combining experimental results with finite element method simulation calculations, we study slow light phenomena in a photonic crystal defect mode, and we produce a comprehensive picture of the mechanisms behind it. Our results illustrate …

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Quantized Circulation In Racetrack Atomtronic Circuits At Non-Zero Temperature, Benjamin R. Eller Jan 2019

Quantized Circulation In Racetrack Atomtronic Circuits At Non-Zero Temperature, Benjamin R. Eller

Electronic Theses and Dissertations

We extend previous theoretical investigations of the creation of quantized circulation states by stirring Bose-Einstein condensates (BEC) confined in ``racetrack" potentials. The previous study, {\em Producing Smooth Flow in Atom Circuits by Stirring}, used the Gross-Pitaevskii equation (GPE), which is valid at $T=0$ K. Here we use a non-zero temperature model based on the Zaremba, Nikuni, Griffin (ZNG) theory to simulate stirring racetrack BECs. The two main goals of this thesis are 1) to understand the effects of temperature on the production of circulation and 2) to understand the mechanism by which the circulation is excited. We find that it …

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Electronic And Geometric Structure Of Alnom And Alnom +, Albert R. Armstrong Jan 2019

Electronic And Geometric Structure Of Alnom And Alnom +, Albert R. Armstrong

Theses and Dissertations

Generally, the electronic stability of aluminum clusters is associated with either closed electronic shells of delocalized electrons, or aluminum in the +3 state. To explore alternative routes for electronic stability in aluminum oxide clusters, theoretical methods were used to examine the geometric and electronic structure of AlnOm (2≤n≤7; 1≤m≤10) clusters. Two types of electronically stable clusters with large HOMO-LUMO gaps were identified the first being Al2nO3m clusters with a +3 oxidation state on the aluminum, and the second being planar clusters such as Al4O4, Al5O3, Al …

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Optimizing Gas Mixture Composition For The Rtpc Detector For Bonus 12 At Jefferson Lab., Joshua H. Lehman Jan 2019

Optimizing Gas Mixture Composition For The Rtpc Detector For Bonus 12 At Jefferson Lab., Joshua H. Lehman

Theses and Dissertations

The main objective of this thesis is to perform a study of and optimize the most direct and practical gas mixture composition inside the Radial Time Projection Chamber for the Barely-Offshell Nucleon Structure (BONuS 12) detector for use in the CLAS 12 detector in Experimental Hall B at Thomas Jefferson National Accelerator Facility (JLab). The optimization of these conditions will enhance the performance and resolution of the detector. The original BONuS 6 experiment utilized a gas composition of 80 % He and 20% Dimethyl Ether (DME). With the extensive 12 GeV energy upgrade constructed at JLab and the new BONuS …

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Electronic Structure Of Cathode Materials In Lithium Ion Batteries, John M. Swanlund Jan 2019

Electronic Structure Of Cathode Materials In Lithium Ion Batteries, John M. Swanlund

Theses and Dissertations

Lithium ion batteries are ubiquitous in modern life, from powering hand-held electronic devices to electric vehicles. And with the necessary drive toward renewable energy sources like solar and wind, electricity storage for the grid promises to drive up the demand for higher performing, less expensive, safer, and more environmentally friendly secondary batteries. Recent research has theorized that replacing halogens in batteries’ electrolytes with non-halogens can yield desirable performance characteristics while eliminating the most dangerous and problematic chemicals. This thesis explores the possibility that a similar approach can be taken with the cathodes of lithium ion batteries. The active material in …

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