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Full-Text Articles in Physics
Ultra-Thin Perfect Absorber Employing A Tunable Phase Change Material, Mikhail A. Kats, Deepika Sharma, (...), M. M. Qazilbash, Et Al.
Ultra-Thin Perfect Absorber Employing A Tunable Phase Change Material, Mikhail A. Kats, Deepika Sharma, (...), M. M. Qazilbash, Et Al.
Arts & Sciences Articles
We show that perfect absorption can be achieved in a system comprising a single lossy dielectric layer of thickness much smaller than the incident wavelength on an opaque substrate by utilizing the nontrivial phase shifts at interfaces between lossy media. This design is implemented with an ultra-thin (∼λ/65) vanadium dioxide (VO2) layer on sapphire, temperature tuned in the vicinity of the VO2 insulator-to-metal phase transition, leading to 99.75% absorption at λ = 11.6 μm. The structural simplicity and large tuning range (from ∼80% to 0.25% in reflectivity) are promising for thermal emitters, modulators, and bolometers.
Universal Conductance Fluctuations In Dirac Materials In The Presence Of Long-Range Disorder, Enrico Rossi, J. H. Bardarson, M. S. Fuhrer, S. Das Sarma
Universal Conductance Fluctuations In Dirac Materials In The Presence Of Long-Range Disorder, Enrico Rossi, J. H. Bardarson, M. S. Fuhrer, S. Das Sarma
Arts & Sciences Articles
We study quantum transport in Dirac materials with a single fermionic Dirac cone (strong topological insulators and graphene in the absence of intervalley coupling) in the presence of non-Gaussian long-range disorder. We show, by directly calculating numerically the conductance fluctuations, that in the limit of very large system size and disorder strength, quantum transport becomes universal. However, a systematic deviation away from universality is obtained for realistic system parameters. By comparing our results to existing experimental data on 1/f noise, we suggest that many of the graphene samples studied to date are in a nonuniversal crossover regime of conductance fluctuations.
Insulator-To-Metal Transition And Correlated Metallic State Of V 2 O 3 Investigated By Optical Spectroscopy, M. K. Stewart, D. Brownstead, (...), M. M. Qazilbash, Et Al.
Insulator-To-Metal Transition And Correlated Metallic State Of V 2 O 3 Investigated By Optical Spectroscopy, M. K. Stewart, D. Brownstead, (...), M. M. Qazilbash, Et Al.
Arts & Sciences Articles
The optical properties of V2O3 thin films are investigated across the insulator-to-metal transition and in the metallic state. The spectral weight transfer observed across the transition, over an energy scale of 5 eV, is consistent with the Mott-Hubbard model for correlated electron systems. In the metallic phase, a strong Drude peak is observed, which exhibits a pronounced temperature dependence related to the transfer of states from the Hubbard bands to the quasiparticle peaks as the temperature is reduced. The analysis of the far-infrared spectra reveals signatures of strong electronic correlations in V2O3. Finally, a comparison to VO2 data is presented.
Coupled-Channel Theory Of Photoionization Microscopy, L. B. Zhao, I. I. Fabrikant, John B. Delos, F. Lepine, S. Cohen, C. Bordas
Coupled-Channel Theory Of Photoionization Microscopy, L. B. Zhao, I. I. Fabrikant, John B. Delos, F. Lepine, S. Cohen, C. Bordas
Arts & Sciences Articles
We develop a quantum-mechanical coupled-channel theory to simulate spatial distributions of electron current densities, produced in photoionization for nonhydrogenic atoms in the presence of a uniform external electric field. The coupled Schrodinger equations are numerically solved using the renormalized Numerov method. The expression for the outgoing wave function for photoelectrons ejected from the nonhydrogenic atomic source is derived. The theory is applied to investigations of photoionization for ground-state Li atoms. The distributions of electron current densities are computed and compared to the corresponding experimental images. Excellent agreement is obtained. It is, furthermore, found that the presence of the nonhydrogenic residual …
Electronic Correlations And Unconventional Spectral Weight Transfer In The High-Temperature Pnictide Bafe2-Xcoxas2 Superconductor Using Infrared Spectroscopy, A. A. Schafgans, S. J. Moon, (...), M. M. Qazilbash, Et Al.
Electronic Correlations And Unconventional Spectral Weight Transfer In The High-Temperature Pnictide Bafe2-Xcoxas2 Superconductor Using Infrared Spectroscopy, A. A. Schafgans, S. J. Moon, (...), M. M. Qazilbash, Et Al.
Arts & Sciences Articles
We report an infrared optical study of the pnictide high-temperature superconductor BaFe1.84Co0.16As2 and its parent compound BaFe2As2. We demonstrate that electronic correlations are moderately strong and do not change across the spin-density wave transition or with doping. By examining the energy scale and direction of spectral weight transfer, we argue that Hund's coupling J is the primary mechanism that gives rise to correlations.
Breath-By-Breath Analysis Of Cardiorespiratory Interaction For Quantifying Developmental Maturity In Premature Infants, Matthew T. Clark, Craig G. Rusin, John L. Hudson, Hoshik Lee, John B. Delos, Et Al.
Breath-By-Breath Analysis Of Cardiorespiratory Interaction For Quantifying Developmental Maturity In Premature Infants, Matthew T. Clark, Craig G. Rusin, John L. Hudson, Hoshik Lee, John B. Delos, Et Al.
Arts & Sciences Articles
Breath-by-breath analysis of cardiorespiratory interaction for quantifying developmental maturity in premature infants. J Appl Physiol 112: 859-867, 2012. First published December 15, 2011; doi:10.1152/japplphysiol.01152.2011.-In healthy neonates, connections between the heart and lungs through brain stem chemosensory pathways and the autonomic nervous system result in cardiorespiratory synchronization. This interdependence between cardiac and respiratory dynamics can be difficult to measure because of intermittent signal quality in intensive care settings and variability of heart and breathing rates. We employed a phase-based measure suggested by Sch fer and coworkers (Sch fer C, Rosenblum MG, Kurths J, Abel HH. Nature 392: 239-240, 1998) to obtain …
Chaotic Escape From An Open Vase-Shaped Cavity. I. Numerical And Experimental Results, Jaison Allen Novick, Matthew L. Keeler, Joshua Geifer
Chaotic Escape From An Open Vase-Shaped Cavity. I. Numerical And Experimental Results, Jaison Allen Novick, Matthew L. Keeler, Joshua Geifer
Arts & Sciences Articles
No abstract provided.
Dark Matter In The Heavens And At Colliders: Models And Constraints, Reinard Primulando
Dark Matter In The Heavens And At Colliders: Models And Constraints, Reinard Primulando
Dissertations, Theses, and Masters Projects
In this dissertation, we investigate various aspects of dark matter detection and model building. Motivated by the cosmic ray positron excess observed by PAMELA, we construct models of decaying dark matter to explain the excess. Specifically we present an explicit, TeV-scale model of decaying dark matter in which the approximate stability of the dark matter candidate is a consequence of a global symmetry that is broken only by instanton-induced operators generated by a non-Abelian dark gauge group. Alternatively, the decaying operator can arise as a Planck suppressed correction in a model with an Abelian discrete symmetry and vector-like states at …
Chaotic Escape From An Open Vase-Shaped Cavity. I. Numerical And Experimental Results, Jaison Novick, Matthew L. Keeler, Joshua Giefer, John B. Delos
Chaotic Escape From An Open Vase-Shaped Cavity. I. Numerical And Experimental Results, Jaison Novick, Matthew L. Keeler, Joshua Giefer, John B. Delos
Arts & Sciences Articles
We present part I in a two-part study of an open chaotic cavity shaped as a vase. The vase possesses an unstable periodic orbit in its neck. Trajectories passing through this orbit escape without return. For our analysis, we consider a family of trajectories launched from a point on the vase boundary. We imagine a vertical array of detectors past the unstable periodic orbit and, for each escaping trajectory, record the propagation time and the vertical detector position. We find that the escape time exhibits a complicated recursive structure. This recursive structure is explored in part I of our study. …
Parity-Violating Asymmetry In The Nucleon To Delta Transition: A Study Of Inelastic Electron Scattering In The G0 Experiment, Carissa Lee Capuano
Parity-Violating Asymmetry In The Nucleon To Delta Transition: A Study Of Inelastic Electron Scattering In The G0 Experiment, Carissa Lee Capuano
Dissertations, Theses, and Masters Projects
The parity-violating asymmetry arising from inelastic electron scattering at backward angle (∼ 95??) near the Delta resonance has been measured for both hydrogen and deuterium targets as part of the G 0 experiment. For Q2 = 0.34 (GeV/c) 2 and W = 1.18 GeV, the asymmetries were found to be AHinel=-33.4+/-5 .3stat+/-5 .1sysppm, ADinel=-43.6+/-1 4.6stat+/- 6.2sysppm. .;From the hydrogen asymmetry, the axial transition form factor, GAND , can be extracted. GAND is related to probability of the quark spin-flip that occurs as the proton transitions to the Delta. From the measured asymmetry, the form factor is found to be GAND=-0.046+/- …
Surface Impedance Of Superconducting Radio Frequency (Srf) Materials, Binping Xiao
Surface Impedance Of Superconducting Radio Frequency (Srf) Materials, Binping Xiao
Dissertations, Theses, and Masters Projects
Superconducting radio frequency (SRF) technology is widely adopted in particle accelerators. There remain many open questions, however, in developing a systematic understanding of the fundamental behavior of SRF materials, including niobium treated in different ways and various other bulk/thin film materials that are fabricated with different methods under assorted conditions. A facility that can measure the SRF properties of small samples in a range of 2∼40 K temperature is needed in order to fully answer these questions. The Jefferson Lab surface impedance characterization (SIC) system has been designed to attempt to meet this requirement. It consists of a sapphire-loaded cylindrical …
Supersymmetric Leptophilic Models Of Electroweak Symmetry Breaking, Gardner Rush Marshall
Supersymmetric Leptophilic Models Of Electroweak Symmetry Breaking, Gardner Rush Marshall
Dissertations, Theses, and Masters Projects
Over the years, the Standard Model has proved itself to be an extremely durable theory. In spite of its success, very few empirical clues have emerged about the nature of the electroweak symmetry breaking that lies at its heart. With results from the LHC around the corner, this will hopefully change soon. In this dissertation we examine several possibilities for electroweak symmetry breaking and discuss various extensions to the Standard Model to resolve known problems. We begin by providing a brief overview of electroweak symmetry breaking, two Higgs doublet models, and supersymmetry. We then present a supersymmetric model that allows …
Measurement Of Single And Double Spin Asymmetries In P(E, E' Pi(+/-,0))X Semi-Inclusive Deep-Inelastic Scattering, Sucheta Shrikant Jawalkar
Measurement Of Single And Double Spin Asymmetries In P(E, E' Pi(+/-,0))X Semi-Inclusive Deep-Inelastic Scattering, Sucheta Shrikant Jawalkar
Dissertations, Theses, and Masters Projects
Measurements in the late 1980s at CERN revealed that quark spins account for a small fraction of the proton's spin. This so-called spin crisis spurred a number of new experiments to identify the proton's silent spin contributors, namely, the spin of the gluons, which hold the quarks together, and the orbital angular momentum of both quarks and gluons. One such experiment was eg1-dvcs at the Thomas Jefferson National Accelerator Facility in Newport News, Va., which ran in 2009 and collected approximately 19 billion electron triggers for hydrogen. I will present new measurements of the single and double-spin asymmetries ALU, AUL …
The First Direct Measurement Of The Weak Charge Of The Proton, John Poague Leckey Iv
The First Direct Measurement Of The Weak Charge Of The Proton, John Poague Leckey Iv
Dissertations, Theses, and Masters Projects
Qweak is an experiment currently running at the Thomas Jefferson National Accelerator Facility that uses parity-violating elastic electron-proton scattering to measure the weak charge of the proton QPweak . Longitudinally polarized electrons are scattered off a liquid hydrogen target and pass through a toroidal-field magnetic spectrometer. This experiment is a sensitive test for physics beyond the Standard Model, as QPweak is well predicted in the Standard Model. This dissertation describes the first direct measurement of QPweak . The precision that will be generated by the final 4% measurement will allow the probing of certain classes of new physics up to …
Chaotic Escape From An Open Vase-Shaped Cavity. Ii. Topological Theory, Jaison Allen Novick, John B. Delos
Chaotic Escape From An Open Vase-Shaped Cavity. Ii. Topological Theory, Jaison Allen Novick, John B. Delos
Arts & Sciences Articles
We present part II of a study of chaotic escape from an open two-dimensional vase-shaped cavity. A surface of section reveals that the chaotic dynamics is controlled by a homoclinic tangle, the union of stable and unstable manifolds attached to a hyperbolic fixed point. Furthermore, the surface of section rectifies escape-time graphs into sequences of escape segments; each sequence is called an epistrophe. Some of the escape segments (and therefore some of the epistrophes) are forced by the topology of the dynamics of the homoclinic tangle. These topologically forced structures can be predicted using the method called homotopic lobe dynamics …
Studies Of Polarized And Unpolarized Helium -3 In The Presence Of Alkali Vapor, Kelly Anita Kluttz
Studies Of Polarized And Unpolarized Helium -3 In The Presence Of Alkali Vapor, Kelly Anita Kluttz
Dissertations, Theses, and Masters Projects
At the Thomas Jefferson National Accelerator Facility, glass target cells containing a high density of highly polarized 3He nuclei are used in electron scattering experiments studying the substructure of the neutron. In addition to 3He, these cells contain a small amount of rubidium (Rb), potassium (K), and nitrogen (N2), which facilitate the polarization process. The work presented here represents studies of the interactions between the alkali vapor and 3He nuclei when both are polarized and unpolarized.;Our investigations into the mechanisms responsible for the relaxation of the 3He polarization have measured unusually large polarization losses. In addition, most cells studied exhibited …