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2013

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Articles 91 - 120 of 1248

Full-Text Articles in Physics

Directed Search For Continuous Gravitational Waves From The Galactic Center, J. Aasi, Daniel Bessis, Teviet Creighton, Mario C. Diaz, Soma Mukherjee, Volker Quetschke, Malik Rakhmanov, Joseph D. Romano, Robert Stone, Lappoon R. Tang, Cristina V. Torres Nov 2013

Directed Search For Continuous Gravitational Waves From The Galactic Center, J. Aasi, Daniel Bessis, Teviet Creighton, Mario C. Diaz, Soma Mukherjee, Volker Quetschke, Malik Rakhmanov, Joseph D. Romano, Robert Stone, Lappoon R. Tang, Cristina V. Torres

Physics & Astronomy Faculty Publications

We present the results of a directed search for continuous gravitational waves from unknown, isolated neutron stars in the Galactic center region, performed on two years of data from LIGO’s fifth science run from two LIGO detectors. The search uses a semicoherent approach, analyzing coherently 630 segments, each spanning 11.5 hours, and then incoherently combining the results of the single segments. It covers gravitational wave frequencies in a range from 78 to 496 Hz and a frequency-dependent range of first-order spindown values down to −7.86×10−8  Hz/s at the highest frequency. No gravitational waves were detected. The 90% confidence upper limits …

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Resonant Enhancement Of The Harmonic-Generation Spectrum Of Beryllium, Jean Marcel Ngoko Djiokap, Anthony F. Starace Nov 2013

Resonant Enhancement Of The Harmonic-Generation Spectrum Of Beryllium, Jean Marcel Ngoko Djiokap, Anthony F. Starace

Anthony F. Starace Publications

The high-order harmonic-generation (HHG) spectrum of Be is investigated in the multiphoton regime by solving the full-dimensional, two-active-electron, time-dependent Schr¨odinger equation in an intense (≈1013 W/cm2), 30-cycle laser field. As the laser frequency ωL varies from 1.7 to 1.8 eV (which is in the tunable range of a Ti:sapphire laser), the seventh harmonic becomes resonant sequentially with the transition between the ground state and two doubly excited autoionizing states, 2p4s(1P) (at ωL = 1.734 eV) and 2p5s …

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Directed Ratchet Transport In Granular Crystals, Vincent Berardi, J. Lydon, P. G. Kevrekidis, C. Daraio, R. Carretero-González Nov 2013

Directed Ratchet Transport In Granular Crystals, Vincent Berardi, J. Lydon, P. G. Kevrekidis, C. Daraio, R. Carretero-González

Psychology Faculty Articles and Research

Directed-ratchet transport (DRT) in a one-dimensional lattice of spherical beads, which serves as a prototype for granular chains, is investigated. We consider a system where the trajectory of the central bead is prescribed by a biharmonic forcing function with broken time-reversal symmetry. By comparing the mean integrated force of beads equidistant from the forcing bead, two distinct types of directed transport can be observed—spatial and temporal DRT. Based on the value of the frequency of the forcing function relative to the cutoff frequency, the system can be categorized by the presence and magnitude of each type of DRT. Furthermore, we …

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Troika Of Single Particle Tracking Programing: Snr Enhancement, Particle Identification, And Mapping, Lydia Kisley Nov 2013

Troika Of Single Particle Tracking Programing: Snr Enhancement, Particle Identification, And Mapping, Lydia Kisley

Faculty Scholarship

Single particle tracking (SPT) techniques provide a microscopic approach to probe in vivo and in vitro structure and reactions. Automatic analysis of SPT data with high efficiency and accuracy spurs the development of SPT algorithms. In this perspective, we review a range of available techniques used in SPT analysis programs. In addition, we present an example SPT program step-by-step to provide a guide so that researchers can use, modify, and/or write a SPT program for their own purposes. © 2014 the Owner Societies.

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Limits On Violations Of Lorentz Symmetry From Gravity Probe B, Quentin G. Bailey, Ryan D. Everett, James M. Overduin Nov 2013

Limits On Violations Of Lorentz Symmetry From Gravity Probe B, Quentin G. Bailey, Ryan D. Everett, James M. Overduin

Physics & Astronomy - Prescott

Generic violations of Lorentz symmetry can be described by an effective field theory framework that contains both general relativity and the Standard Model of particle physics called the Standard-Model extension (SME). We obtain new constraints on the gravitational sector of the SME using recently published final results from Gravity Probe B. These include for the first time an upper limit at the 10_3 level on the time-time component of the new tensor field responsible for inducing local Lorentz violation in the theory, and an independent limit at the 10_7 level on a combination of components of this tensor field.

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A Sub-Kpc-Scale Binary Active Galactic Nucleus With Double Narrow-Line Regions, Jong-Hak Woo, Hojin Cho, Bernd Husemann, S. Komossa, Daeseong Park, Vardha N. Bennert Nov 2013

A Sub-Kpc-Scale Binary Active Galactic Nucleus With Double Narrow-Line Regions, Jong-Hak Woo, Hojin Cho, Bernd Husemann, S. Komossa, Daeseong Park, Vardha N. Bennert

Physics

We present the kinematic properties of a type-2 Quasi stellar object (QSO), SDSS J132323.33−015941.9 at z ∼ 0.35, based on the analysis of Very Large Telescope integral field spectroscopy and Hubble Space Telescope (HST) imaging, which suggest that the target is a binary active galactic nucleus (AGN) with double narrow-line regions. The QSO features double-peaked emission lines ([O iii] and Hβ) which can be decomposed into two kinematic components. The flux-weighted centroids of the blue and red components are separated by ∼0.2 arcsec (0.8 kpc in projection) and coincide with the location of the two stellar cores detected …

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Molecular Fluorescence In The Vicinity Of A Charged Metallic Nanoparticle, H. Y. Chung, P. T. Leung, D. P. Tsai Nov 2013

Molecular Fluorescence In The Vicinity Of A Charged Metallic Nanoparticle, H. Y. Chung, P. T. Leung, D. P. Tsai

Physics Faculty Publications and Presentations

The modified fluorescence properties of a molecule in the vicinity of a metallic nanoparticle are further studied accounting for the possible existence of extraneous charges on the particle surface. This is achieved via a generalization of the previous theory of Bohren and Hunt for light scattering from a charged sphere, with the results applied to the calculation of the various decay rates and fluorescence yield of the admolecule. Numerical results show that while charge effects will in general blue-shift all the plasmonic resonances of the metal particle, both the quantum yield and the fluorescence yield can be increased at emission …

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The Stochastic Background: Scaling Laws And Time To Detection For Pulsar Timing Arrays, X. Siemens, Justin A. Ellis, Fredrick A. Jenet, Joseph D. Romano Nov 2013

The Stochastic Background: Scaling Laws And Time To Detection For Pulsar Timing Arrays, X. Siemens, Justin A. Ellis, Fredrick A. Jenet, Joseph D. Romano

Physics & Astronomy Faculty Publications

We derive scaling laws for the signal-to-noise ratio of the optimal cross-correlation statistic, and show that the large power-law increase of the signal-to-noise ratio as a function of the observation time T that is usually assumed holds only at early times. After enough time has elapsed, pulsar timing arrays enter a new regime where the signal to noise only scales as . In addition, in this regime the quality of the pulsar timing data and the cadence become relatively unimportant. This occurs because the lowest frequencies of the pulsar timing residuals become gravitational-wave dominated. Pulsar timing arrays enter this regime …

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Searching For Millisecond Pulsars: Surveys, Techniques And Prospects, Kevin Stovall, Duncan R. Lorimer, R. S. Lynch Nov 2013

Searching For Millisecond Pulsars: Surveys, Techniques And Prospects, Kevin Stovall, Duncan R. Lorimer, R. S. Lynch

Physics & Astronomy Faculty Publications

Searches for millisecond pulsars (which we here loosely define as those with periods < 20 ms) in the galactic field have undergone a renaissance in the past five years. New or recently refurbished radio telescopes utilizing cooled receivers and state-of-the art digital data acquisition systems are carrying out surveys of the entire sky at a variety of radio frequencies. Targeted searches for millisecond pulsars in point sources identified by the Fermi Gamma-ray Space Telescope have proved phenomenally successful, with over 50 discoveries in the past five years. The current sample of millisecond pulsars now numbers almost 200 and, for the first time in 25 years, now outnumbers their counterparts in galactic globular clusters. While many of these searches are motivated to find pulsars which form part of pulsar timing arrays, a wide variety of interesting systems are now being found. Following a brief overview of the millisecond pulsar phenomenon, we describe these searches and present some of …

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Science Goals And Overview Of The Radiation Belt Storm Probes (Rbsp) Energetic Particle, Composition, And Thermal Plasma (Ect) Suite On Nasa’S Van Allen Probes Mission, Harlan E. Spence, G. D. Reeves, D. N. Baker, J. B. Blake, M. Bolton, S. Bourdarie, A. A. Chan, S. G. Claudepierre, J. H. Clemmons, J. P. Cravens, S. R. Elkington, J. F. Fennell Nov 2013

Science Goals And Overview Of The Radiation Belt Storm Probes (Rbsp) Energetic Particle, Composition, And Thermal Plasma (Ect) Suite On Nasa’S Van Allen Probes Mission, Harlan E. Spence, G. D. Reeves, D. N. Baker, J. B. Blake, M. Bolton, S. Bourdarie, A. A. Chan, S. G. Claudepierre, J. H. Clemmons, J. P. Cravens, S. R. Elkington, J. F. Fennell

Physics & Astronomy

The Radiation Belt Storm Probes (RBSP)-Energetic Particle, Composition, and Thermal Plasma (ECT) suite contains an innovative complement of particle instruments to ensure the highest quality measurements ever made in the inner magnetosphere and radiation belts. The coordinated RBSP-ECT particle measurements, analyzed in combination with fields and waves observations and state-of-the-art theory and modeling, are necessary for understanding the acceleration, global distribution, and variability of radiation belt electrons and ions, key science objectives of NASA’s Living With a Star program and the Van Allen Probes mission. The RBSP-ECT suite consists of three highly-coordinated instruments: the Magnetic Electron Ion Spectrometer (MagEIS), the …

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The Magnetic Electron Ion Spectrometer (Mageis) Instruments Aboard The Radiation Belt Storm Probes (Rbsp) Spacecraft, J. B. Blake, P. A. Carranza, S. G. Claudepierre, J. H. Clemmons, W. R. Crain, Y. Dotan, J. F. Fennell, F. H. Fuentes, R. M. Galvan, J. S. George, M. G. Henderson, M. Lalic Nov 2013

The Magnetic Electron Ion Spectrometer (Mageis) Instruments Aboard The Radiation Belt Storm Probes (Rbsp) Spacecraft, J. B. Blake, P. A. Carranza, S. G. Claudepierre, J. H. Clemmons, W. R. Crain, Y. Dotan, J. F. Fennell, F. H. Fuentes, R. M. Galvan, J. S. George, M. G. Henderson, M. Lalic

Physics & Astronomy

This paper describes the Magnetic Electron Ion Spectrometer (MagEIS) instruments aboard the RBSP spacecraft from an instrumentation and engineering point of view. There are four magnetic spectrometers aboard each of the two spacecraft, one low-energy unit (20–240 keV), two medium-energy units (80–1200 keV), and a high-energy unit (800–4800 keV). The high unit also contains a proton telescope (55 keV–20 MeV). The magnetic spectrometers focus electrons within a selected energy pass band upon a focal plane of several silicon detectors where pulse-height analysis is used to determine if the energy of the incident electron is appropriate for the electron momentum selected …

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Helium, Oxygen, Proton, And Electron (Hope) Mass Spectrometer For The Radiation Belt Storm Probes Mission, H. O. Funsten, R. M. Skoug, A. A. Guthrie, E. A. Macdonald, J. R. Baldonado, R. W. Harper, K. C. Henderson, K. H. Kihara, J. E. Lake, B. A. Larsen, A. D. Puckett, V. J. Vigil, Harlan E. Spence Nov 2013

Helium, Oxygen, Proton, And Electron (Hope) Mass Spectrometer For The Radiation Belt Storm Probes Mission, H. O. Funsten, R. M. Skoug, A. A. Guthrie, E. A. Macdonald, J. R. Baldonado, R. W. Harper, K. C. Henderson, K. H. Kihara, J. E. Lake, B. A. Larsen, A. D. Puckett, V. J. Vigil, Harlan E. Spence

Physics & Astronomy

The HOPE mass spectrometer of the Radiation Belt Storm Probes (RBSP) mission (renamed the Van Allen Probes) is designed to measure the in situ plasma ion and electron fluxes over 4π sr at each RBSP spacecraft within the terrestrial radiation belts. The scientific goal is to understand the underlying physical processes that govern the radiation belt structure and dynamics. Spectral measurements for both ions and electrons are acquired over 1 eV to 50 keV in 36 log-spaced steps at an energy resolution ΔE FWHM/E≈15 %. The dominant ion species (H+, He+, and O+) of the magnetosphere are identified using foil-based …

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A Bioinformatics Method For Identifying Rna Structures Within Human Cells, Stephen Donald Huff Nov 2013

A Bioinformatics Method For Identifying Rna Structures Within Human Cells, Stephen Donald Huff

Physics Seminars

Single-stranded, negative-sense RNA (ssRNA-) serves many varied roles within the eukaryotic cell. Currently known examples include snRNA (short nuclear), snoRNA (short nucleolar), tRNA (transfer), siRNA (silencing), miRNA (micro), and others [1,2]. Unknown examples are currently being studied, also, including the long, non-coding ssRNA- found in the nuclear paraspeckle, a component of unknown function located within the eukaryotic nucleus and comprised of ssRNA- sequences transcribed from so-called ‘junk’ DNA [3,4]. While a growing list of confirmed physiological functions have been attributed to ssRNA-, additional roles likely exist and have yet to be discovered. Further, since ssRNA- is known to bind to …

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Molecular Mechanisms Of Disease-Causing Missense Mutations, Shannon Stefl, Hafumi Nishi, Marharyta Petukh, Anna R. Panchenko, Emil Alexov Nov 2013

Molecular Mechanisms Of Disease-Causing Missense Mutations, Shannon Stefl, Hafumi Nishi, Marharyta Petukh, Anna R. Panchenko, Emil Alexov

Publications

Genetic variations resulting in a change of amino acid sequence can have a dramatic effect on stability, hydrogen bond network, conformational dynamics, activity and many other physiologically important properties of proteins. The substitutions of only one residue in a protein sequence, so-called missense mutations, can be related to many pathological conditions, and may influence susceptibility to disease and drug treatment. The plausible effects of missense mutations range from affecting the macromolecular stability to perturbing macromolecular interactions and cellular localization. Here we review the individual cases and genome-wide studies which illustrate the association between missense mutations and diseases. In addition we …

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Defects And Dark Current In Organic Photovoltaics And Impacts On Device Physics, Xin Jiang Nov 2013

Defects And Dark Current In Organic Photovoltaics And Impacts On Device Physics, Xin Jiang

Electronic Theses and Dissertations

In this dissertation, we discussed the shape, energy level and density of defects in Organic Photovoltaic (OPV) devices by both theoretical and experimental methods. The energy band structure and intrinsic junctions of general standard and inverted OPV devices are investigated in detail. Transportation of separated holes and electrons in both structures are well analyzed. In chapter II, we developed a Monte-Carlo model to simulate charge transport process in organic materials. Marcus theory is applied to calculate the carrier transfer rate to build up hopping process in ideal lattices. Results of this model showed several properties of carriers regarding mobility, reorganization …

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Carrier-Envelope-Phase-Induced Asymmetries In Double Ionization Of Helium By An Intense Few-Cycle Xuv Pulse, Jean Marcel Ngoko Djiokap, N. L. Manakov, A. V. Meremianin, Anthony F. Starace Nov 2013

Carrier-Envelope-Phase-Induced Asymmetries In Double Ionization Of Helium By An Intense Few-Cycle Xuv Pulse, Jean Marcel Ngoko Djiokap, N. L. Manakov, A. V. Meremianin, Anthony F. Starace

Anthony F. Starace Publications

The carrier-envelope-phase (CEP) dependence of electron angular distributions in double ionization of He by an arbitrarily polarized, few-cycle, intense XUV pulse is formulated using perturbation theory (PT) in the pulse amplitude. Owing to the broad pulse bandwidth, interference of first- and second-order PT amplitudes produces asymmetric angular distributions sensitive to the CEP. The PT parametrization is shown to be valid by comparing with results of solutions of the full-dimensional, two-electron time-dependent Schrödinger equation for the case of linear polarization.

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Harmonic Generation Spectroscopy With A Two-Colour Laser Field Having Orthogonal Linear Polarizations, T. S. Sarantseva, M. V. Frolov, N. L. Manakov, M. Yu. Ivanov, Anthony F. Starace Nov 2013

Harmonic Generation Spectroscopy With A Two-Colour Laser Field Having Orthogonal Linear Polarizations, T. S. Sarantseva, M. V. Frolov, N. L. Manakov, M. Yu. Ivanov, Anthony F. Starace

Anthony F. Starace Publications

The interpretation of many high-order harmonic generation (HHG) experiments is based on the assumption that the HHG yield of an atom can be factorized into (i) a laser-dependent ‘electron wave packet’ with rather simple properties, including a nearly universal shape, and (ii) an atomic photorecombination cross section. We show that this factorization is restricted to linearly polarized laser fields and fails in two-colour laser fields with orthogonal polarizations. At the same time, we show how two-colour HHG spectroscopy using orthogonally polarized intense fundamental and relatively weak second harmonic fields makes a complete experiment possible that enables the retrieval of the …

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Preferential Scattering By Interfacial Charged Defects For Enhanced Thermoelectric Performance In Few-Layered N-Type Bi2te3, Pooja Puneet, Ramakrishna Podila, Mehmet Karakaya, Song Zhu, Jian He, Terry M. Tritt, Mildred S. Dresselhaus, Apparao Rao Nov 2013

Preferential Scattering By Interfacial Charged Defects For Enhanced Thermoelectric Performance In Few-Layered N-Type Bi2te3, Pooja Puneet, Ramakrishna Podila, Mehmet Karakaya, Song Zhu, Jian He, Terry M. Tritt, Mildred S. Dresselhaus, Apparao Rao

Publications

Over the past two decades several nano-structuring methods have helped improve the figure of merit (ZT) in the state-of-the art bulk thermoelectric materials. While these methods could enhance the thermoelectric performance of p-type Bi2Te3, it was frustrating to researchers that they proved ineffective for n-type Bi2Te3 due to the inevitable deterioration of its thermoelectric properties in the basal plane. Here, we describe a novel chemical-exfoliation spark-plasma-sintering (CE-SPS) nano-structuring process, which transforms the microstructure of n-type Bi2Te3 in an extraordinary manner without compromising its basal plane …

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Solution Scattering And Fret Studies Of Nucleosomes Reveal Dna: Unwrapping Effects Of H3 And H4 Tail Removal, Kurt Andresen, Isabel Jimenez-Useche, Steven C. Howell, Chongli Yuan, Xiangyun Qiu Nov 2013

Solution Scattering And Fret Studies Of Nucleosomes Reveal Dna: Unwrapping Effects Of H3 And H4 Tail Removal, Kurt Andresen, Isabel Jimenez-Useche, Steven C. Howell, Chongli Yuan, Xiangyun Qiu

Physics and Astronomy Faculty Publications

Using a combination of small-angle X-ray scattering (SAXS) and fluorescence resonance energy transfer (FRET) measurements we have determined the role of the H3 and H4 histone tails, independently, in stabilizing the nucleosome DNA terminal ends from unwrapping from the nucleosome core. We have performed solution scattering experiments on recombinant wild-type, H3 and H4 tail-removed mutants and fit all scattering data with predictions from PDB models and compared these experiments to complementary DNA-end FRET experiments. Based on these combined SAXS and FRET studies, we find that while all nucleosomes exhibited DNA unwrapping, the extent of this unwrapping is increased for nucleosomes …

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Moving Difference (Mdiff) Non-Adiabatic Rapid Sweep (Nars) Epr Of Copper(Ii), James S. Hyde, Brian Bennett, Aaron W. Kittell, Jason M. Kowalski, Jason Walter Sidabras Nov 2013

Moving Difference (Mdiff) Non-Adiabatic Rapid Sweep (Nars) Epr Of Copper(Ii), James S. Hyde, Brian Bennett, Aaron W. Kittell, Jason M. Kowalski, Jason Walter Sidabras

Physics Faculty Research and Publications

Non-adiabatic rapid sweep (NARS) EPR spectroscopy has been introduced for application to nitroxide-labeled biological samples (Kittell et al., 2011). Displays are pure absorption, and are built up by acquiring data in spectral segments that are concatenated. In this paper we extend the method to frozen solutions of copper-imidazole, a square planar copper complex with four in-plane nitrogen ligands. Pure absorption spectra are created from concatenation of 170 5-gauss segments spanning 850 G at 1.9 GHz. These spectra, however, are not directly useful since nitrogen superhyperfine couplings are barely visible. Application of the moving difference (MDIFF) algorithm to the digitized NARS …

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Directed Search For Continuous Gravitational Waves From The Galactic Center, J. Aasi, Marco Cavaglia, For Full List Of Authors, See Publisher's Website. Nov 2013

Directed Search For Continuous Gravitational Waves From The Galactic Center, J. Aasi, Marco Cavaglia, For Full List Of Authors, See Publisher's Website.

Physics Faculty Research & Creative Works

We present the results of a directed search for continuous gravitational waves from unknown, isolated neutron stars in the Galactic center region, performed on two years of data from LIGO's fifth science run from two LIGO detectors. The search uses a semicoherent approach, analyzing coherently 630 segments, each spanning 11.5 hours, and then incoherently combining the results of the single segments. It covers gravitational wave frequencies in a range from 78 to 496 Hz and a frequency-dependent range of first-order spindown values down to -7.86 x 10-8 Hz/s at the highest frequency. No gravitational waves were detected. The 90% …

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Plasmonic Scaling Of Superconducting Metamaterials, Cihan Kurter, John A. Abrahams, Gennady Shvets, Steven Mark Anlage Nov 2013

Plasmonic Scaling Of Superconducting Metamaterials, Cihan Kurter, John A. Abrahams, Gennady Shvets, Steven Mark Anlage

Physics Faculty Research & Creative Works

Superconducting metamaterials are utilized to study the approach to the plasmonic limit simply by tuning temperature to modify the superfluid density, and thus the superfluid plasma frequency. We examine the persistence of artificial magnetism in a metamaterial made with superconductors in the plasmonic limit, and compare to the electromagnetic behavior of normal metals as a function of frequency as the plasma frequency is approached from below. Spiral-shaped Nb thin film meta-atoms of scaled dimensions are employed to explore the plasmonic behavior in these superconducting metamaterials, and the scaling condition allows extraction of the temperature dependent superfluid density, which is found …

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Investigating Fault Structure Using Electrical Resistivity Tomography, Sara Michelle Monahan Nov 2013

Investigating Fault Structure Using Electrical Resistivity Tomography, Sara Michelle Monahan

Physics

The resolving power of two-dimensional Direct Current (DC) Electrical Resistivity Tomography (ERT) is investigated in the context of shallow faults. Subsurface electrical resistivity data was collected perpendicular to a secondary fault scarp of the Los Osos Fault Zone with a Syscal KID Switch 24 resistivity meter and processed with Prosys II and Res2DInv software to produce two-dimensional cross sections of resistivity values via a smoothness-constrained least-squares optimization method. Comparison of ERT inversion results to a trench wall map of the same fault scarp suggest the location and dip direction of faults is resolvable, while detailed fault structure, such as dip …

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Top Quark Working Group Report, Nikolaos Kidonakis, Et. Al. Nov 2013

Top Quark Working Group Report, Nikolaos Kidonakis, Et. Al.

Faculty Articles

The top quark was discovered in 1995 [1, 2] and it is still the heaviest elementary particle known today. Thanks to its large mass, and the related strength of its coupling to the Higgs boson, the top quark may be a key player in understanding the details of electroweak symmetry breaking. Studies of the top quark properties at the Tevatron and Run I of the LHC have given us a detailed understanding of many properties of this particle, including its mass, production and decay mechanisms, electric charge and more. With the exception of the large forward-backward asymmetry in tt¯ production …

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Establishing Normative Data For The Visual Skills Of Gaelic Footballers, Valerie Kennelly Nov 2013

Establishing Normative Data For The Visual Skills Of Gaelic Footballers, Valerie Kennelly

Masters

Although sports vision procedures have been implemented in many sports worldwide, no rigorous scientific investigation of the visual skills trends of Gaelic Athletic Association (GAA) participants has been carried out in Ireland to date. The aim of this study was to identify the visual skills required to play Gaelic football and to establish normative data for those skills which can be used to classify, superior, above average, average, below average and inferior visual performance. Hardware visual skills including high and low contrast vision, stereo acuity, colour vision, and contrast sensitivity and software skills including eye hand co-ordination, dynamic fixation and …

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Top Quark Production, Nikolaos Kidonakis Nov 2013

Top Quark Production, Nikolaos Kidonakis

Faculty Articles

I discuss top quark production in hadronic collisions. I present the soft-gluon resummation formalism and its derivation from factorization and renormalization-group evolution, and two-loop calculations of soft anomalous dimensions in the eikonal approximation. I discuss the contributions of next-to-next-to-leading order (NNLO) soft-gluon corrections to the total cross sections and top-quark transverse momentum and rapidity distributions for top-antitop pair production, and for single-top production in the t and s channels and in association with a W boson or a charged Higgs boson.

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Probing The Circulation Of Ring-Shaped Bose-Einstein Condensates, Noel Murray, Michael Krygier, Mark Edwards, K. C. Wright, Gretchen K. Campbell, Charles W. Clark Nov 2013

Probing The Circulation Of Ring-Shaped Bose-Einstein Condensates, Noel Murray, Michael Krygier, Mark Edwards, K. C. Wright, Gretchen K. Campbell, Charles W. Clark

Physics & Astronomy: Faculty Publications

This paper reports the results of a theoretical and experimental study of how the initial circulation of ring-shaped Bose-Einstein condensates (BECs) can be probed by time-of-flight (TOF) images. We have studied the dynamics of a BEC after release from a toroidal trap potential by solving the three-dimensional Gross-Pitaevskii (GP) equation. The trap and condensate characteristics matched those of a recent experiment. The circulation, experimentally imparted to the condensate by stirring, was simulated by imprinting a linear azimuthal phase on the initial condensate wave function. The simulated TOF images were in good agreement with the experimental data. We find that upon …

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Characterization Of Planar Wave Guides By Angle-Dependent Excitation Of Guided Modes, Edward D. Lunde Nov 2013

Characterization Of Planar Wave Guides By Angle-Dependent Excitation Of Guided Modes, Edward D. Lunde

Physics

In this project a high resolution rotation stage was used to measure the angle of coupling of light into planar waveguide modes. Control of the stage and acquisition of light intensity data was done using the commercially available programming environment, MATLAB. Reliable, repeatable excitation of modes was done using prism coupling. We also investigated coupling using a surface grating on the waveguide.

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Interface States In Cofe2O4 Spin-Filter Tunnel Junctions, Pavel V. Lukashev, John D. Burton, Alexander Smogunov, Julian P. Velev, Evgeny Y. Tsymbal Oct 2013

Interface States In Cofe2O4 Spin-Filter Tunnel Junctions, Pavel V. Lukashev, John D. Burton, Alexander Smogunov, Julian P. Velev, Evgeny Y. Tsymbal

Evgeny Tsymbal Publications

Spin-filter tunneling is a promising way to generate highly spin-polarized current, a key component for spintronics applications. In this paper we explore the tunneling conductance across the spin-filter material CoFe2O4 interfaced with Au electrodes, a geometry which provides nearly perfect lattice matching at the CoFe2O4/Au(001) interface. Using density functional theory calculations we demonstrate that interface states play a decisive role in controlling the transport spin polarization in this tunnel junction. For a realistic CoFe2O4 barrier thickness, we predict a tunneling spin polarization of about −60%. We show that this value …

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Polarization-Controlled Ohmic To Schottky Transition At A Metal/Ferroelectric Interface, Xiaohui Liu, Yong Wang, John D. Burton, Evgeny Y. Tsymbal Oct 2013

Polarization-Controlled Ohmic To Schottky Transition At A Metal/Ferroelectric Interface, Xiaohui Liu, Yong Wang, John D. Burton, Evgeny Y. Tsymbal

Evgeny Tsymbal Publications

Ferroelectric polar displacements have recently been observed in conducting electron-doped BaTiO3 (n-BTO). The coexistence of a ferroelectric phase and conductivity opens the door to new functionalities that may provide a unique route for novel device applications. Using first-principles methods and electrostatic modeling, we explore the effect that the switchable polarization of n-BTO has on the electronic properties of the SrRuO3/n-BTO (001) interface. Ferroelectric polarization controls the accumulation or depletion of electron charge at the interface, and the associated bending of the n-BTO conduction band determines the transport regime across the interface. The …

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