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2009

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Articles 91 - 120 of 907

Full-Text Articles in Physics

Impact Of High-Order Surface Plasmon Modes Of Metal Nanoparticles On Enhancement Of Optical Emission, Greg Sun, Jacob B. Khurgin, C. C. Yang Oct 2009

Impact Of High-Order Surface Plasmon Modes Of Metal Nanoparticles On Enhancement Of Optical Emission, Greg Sun, Jacob B. Khurgin, C. C. Yang

Physics Faculty Publications

We consider the impact of high-order surface plasmon modes supported by the metal nanoparticles on the efficiency enhancement of optical emission. Using the example of Au nanosphere embedded in the GaN dielectric, we show that for an emitter with certain original radiative efficiency, placing the emitter too close to the metal sphere does not always produce additional enhancement. Thus our model provides analytical treatment of the luminescence quenching and can be used to optimize both nanoparticle size and its separation from the emitter to yield maximum enhancement.

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Continuous Phase Amplification With A Sagnac Interferometer, David J. Starling, P. Ben Dixon, Nathan S. Williams, Andrew N. Jordan, John C. Howell Oct 2009

Continuous Phase Amplification With A Sagnac Interferometer, David J. Starling, P. Ben Dixon, Nathan S. Williams, Andrew N. Jordan, John C. Howell

Mathematics, Physics, and Computer Science Faculty Articles and Research

We describe a phase-amplification technique using a Sagnac interferometer. We monitor the relative phase between two paths of a precisely misaligned interferometer by measuring the average position of a split-Gaussian mode in the dark port. Although we monitor only the dark port, we show that the signal varies linearly with phase and that we can obtain similar sensitivity to balanced homodyne detection. We derive the source of the amplification using classical wave optics.

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Supersymmetric Lattices - A Brief Introduction, Simon Catterall Oct 2009

Supersymmetric Lattices - A Brief Introduction, Simon Catterall

Physics - All Scholarship

Recently, new theoretical ideas have allowed the construction of lattice actions which are explicitly invariant under one or more supersymmetries. These theories are local and free of doublers and in the case of Yang-Mills theories also possess exact gauge invariance. In this talk these ideas are reviewed with particular emphasis being placed on {\cal N}=4 super Yang-Mills theory.

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Reduction And Characterization Of Error In Low Current Measurements, Justin Dekany, Jr Dennison, Alec Sim Oct 2009

Reduction And Characterization Of Error In Low Current Measurements, Justin Dekany, Jr Dennison, Alec Sim

Presentations

No abstract provided.

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Intra-Annual Comparison Of Mesospheric Gravity Waves Over Halley And Rothera Stations, Antarctica, Jonathan Pugmire, Michael J. Taylor, K. Nielsen, A. Wall, J. Thompson, P. D. Pautet Oct 2009

Intra-Annual Comparison Of Mesospheric Gravity Waves Over Halley And Rothera Stations, Antarctica, Jonathan Pugmire, Michael J. Taylor, K. Nielsen, A. Wall, J. Thompson, P. D. Pautet

Graduate Student Posters

No abstract provided.

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Temperature Dependence Of Electrostatic Breakdown Of Polymeric Insulators, Charles Sim, Jr Dennison Oct 2009

Temperature Dependence Of Electrostatic Breakdown Of Polymeric Insulators, Charles Sim, Jr Dennison

Presentations

No abstract provided.

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Probes Of Nearly Conformal Behavior In Lattice Simulations Of Minimal Walking Technicolor, Simon Catterall, Joel Giedt, Francesco Sannino, Joe Schneible Oct 2009

Probes Of Nearly Conformal Behavior In Lattice Simulations Of Minimal Walking Technicolor, Simon Catterall, Joel Giedt, Francesco Sannino, Joe Schneible

Physics - All Scholarship

We present results from high precision, large volume simulations of the lattice gauge theory corresponding to minimal walking technicolor. We find evidence that the pion decay constant vanishes in the infinite volume limit and that the dependence of the chiral condensate on quark mass m_q is inconsistent with spontaneous symmetry breaking. These findings are consistent with the all-orders beta function prediction as well as the Schroedinger functional studies that indicate the existence of a nontrivial infrared fixed point.

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Ultrafast Gain And Refractive Index Dynamics In Gainnassb Semiconductor Optical Amplifiers, Tomasz Piwonski, J. Pulka, Gillian Madden, Guillaume Huyet, John Houlihan Oct 2009

Ultrafast Gain And Refractive Index Dynamics In Gainnassb Semiconductor Optical Amplifiers, Tomasz Piwonski, J. Pulka, Gillian Madden, Guillaume Huyet, John Houlihan

Cappa Publications

The gain and refractive index dynamics of dilute nitride antimonide semiconductor optical amplifiers are studied using heterodyne pump probe spectroscopy, both in forward and reverse bias regimes. In the forward biased absorption regime, both gain and refractive index relax on the same timescale indicating that both quantities are linked to the same relaxation process, interband recombination. Above transparency, in the forward biased gain regime, the gain and phase exhibit differing timescales resulting in a dynamical alpha factor that varies strongly with time. Reversed bias measurements suggest a recombination dominated absorption recovery where the recovery timescale increases with increasing reversed bias, …

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Scaled Momentum Distributions Of Charged Particles In Dijet Photoproduction At Hera, O. Behnke, J. Behr, U. Behrens, C. Blohm, K. Borras, D. Bot, R. Ciesielski, N. Coppola, S. Fang, A. Geiser, P. Gölttlicher, J. Grebenyuk, I. Gregor, T. Haas, W. Hain, A. Hüttmann, F. Januschek, B. Kahle, I. I. Katkov, U. Klein, U. Kötz, H. Kowalski, M. Lisovyi, E. Lobodzinska, B. Löhr, R. Mankel, I. A. Melzer-Pellmann, S. Miglioranzi, A. Montanari, T. Namsoo, D. Notz, Margarita C. K. Mattingly Oct 2009

Scaled Momentum Distributions Of Charged Particles In Dijet Photoproduction At Hera, O. Behnke, J. Behr, U. Behrens, C. Blohm, K. Borras, D. Bot, R. Ciesielski, N. Coppola, S. Fang, A. Geiser, P. Gölttlicher, J. Grebenyuk, I. Gregor, T. Haas, W. Hain, A. Hüttmann, F. Januschek, B. Kahle, I. I. Katkov, U. Klein, U. Kötz, H. Kowalski, M. Lisovyi, E. Lobodzinska, B. Löhr, R. Mankel, I. A. Melzer-Pellmann, S. Miglioranzi, A. Montanari, T. Namsoo, D. Notz, Margarita C. K. Mattingly

Faculty Publications

The scaled momentum distributions of charged particles in jets have been measured for dijet photoproduction with the ZEUS detector at HERA using an integrated luminosity of 359 pb-1. The distributions are compared to predictions based on perturbative QCD carried out in the framework of the modified leading-logarithmic approximation (MLLA) and assuming local parton-hadron duality (LPHD). The universal MLLA scale, Λeff, and the LPHD parameter, κch, are extracted. © SISSA 2009.

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Photoproduction Of Π​+Π​- Meson Pairs On The Proton, M. Battaglieri, Gerard P. Gilfoyle, Et. Al. Oct 2009

Photoproduction Of Π​+Π​- Meson Pairs On The Proton, M. Battaglieri, Gerard P. Gilfoyle, Et. Al.

Physics Faculty Publications

The exclusive reaction γp → pπ+π- was studied in the photon energy range 3.0–3.8 GeV and the momentum transfer range 0:4 < -t < 1:0 GeV2. Data were collected with the CLAS detector at the Thomas Jefferson National Accelerator Facility. In this kinematic range, the integrated luminosity was about 20 pb-1. The reaction was isolated by detecting the π+ and proton in CLAS, and reconstructing the π- via the missing-mass technique. Moments of the di-pion decay angular distributions were derived from the experimental data. Differential cross sections for the S, P, and D …

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Microboone: A New Liquid Argon Time Projection Chamber Experiment, Mitchell Soderberg Oct 2009

Microboone: A New Liquid Argon Time Projection Chamber Experiment, Mitchell Soderberg

Physics - All Scholarship

Liquid Argon Time Projection Chamber detectors are well suited to study neutrino interactions, and are an intriguing option for future massive detectors capable of measuring the parameters that characterize neutrino oscillations. These detectors combine fine-grained tracking with calorimetry, allowing for excellent imaging and particle identification ability. In this talk the details of the MicroBooNE experiment, a 175 ton LArTPC which will be exposed to Fermilab's Booster Neutrino Beamline starting in 2011, will be presented. The ability of MicroBooNE to differentiate electrons from photons gives the experiment unique capabilities in low energy neutrino interaction measurements.

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Liquid-Argon Time Projection Chambers In The U.S, Mitchell Soderberg Oct 2009

Liquid-Argon Time Projection Chambers In The U.S, Mitchell Soderberg

Physics - All Scholarship

Liquid Argon Time Projection Chamber (LAr TPC) detectors are ideally suited for studying neutrino interactions and probing the parameters that characterize neutrino oscillations. The ability to drift ionization particles over long distances in purified argon and to trigger on abundant scintillation light allows for excellent particle identification and triggering capability. Recent U.S. based work in the development of LAr TPC technology for massive kiloton size detectors will be discussed in this talk, including details of the ArgoNeuT (Argon Neutrino Test) test-beam project, which is a 175 liter LAr TPC exposed to Fermilab's NuMI neutrino beamline.

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Argoneut: A Liquid Argon Time Projection Chamber Test In The Numi Beamline, Mitchell Soderberg Oct 2009

Argoneut: A Liquid Argon Time Projection Chamber Test In The Numi Beamline, Mitchell Soderberg

Physics - All Scholarship

Liquid Argon Time Projection Chamber detectors are ideally suited for studying neutrino interactions and probing the parameters that characterize neutrino oscillations. The ability to drift ionization particles over long distances in purified argon and to trigger on abundant scintillation light allows for excellent particle identification and triggering capability. In these proceedings the details of the ArgoNeuT test-beam project will be presented after a brief introduction to the detector technique. ArgoNeuT is a 175 liter detector exposed to Fermilab's NuMI neutrino beamline. The first neutrino interactions observed in ArgoNeuT will be presented, along with discussion of the various physics analyses to …

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Radiatively Induced Lorentz And Gauge Symmetry Violation In Electrodynamics With Varying Alph A, Alejandro Ferrero, Brett David Altschul Oct 2009

Radiatively Induced Lorentz And Gauge Symmetry Violation In Electrodynamics With Varying Alph A, Alejandro Ferrero, Brett David Altschul

Faculty Publications

A time-varying fine structure constant α(t) could give rise to Lorentz- and CPT-violating changes to the vacuum polarization, which would affect photon propagation. Such changes to the effective action can violate gauge invariance, but they are otherwise permitted. However, in the minimal theory of varying α, no such terms are generated at lowest order. At second order, vacuum polarization can generate an instability—a Lorentz-violating analogue of a negative photon mass squared −m2γ∝α(˙α2α)2log(Λ2), where Λ is the cutoff for the low-energy effective theory.

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Dispersion Interactions Between Optically Anisotropic Cylinders At All Separations: Retardation Effects For Insulating And Semiconducting Single-Wall Carbon Nanotubes, Roger H. French Oct 2009

Dispersion Interactions Between Optically Anisotropic Cylinders At All Separations: Retardation Effects For Insulating And Semiconducting Single-Wall Carbon Nanotubes, Roger H. French

Faculty Scholarship

We derive the complete form of the van der Waals dispersion interaction between two infinitely long anisotropic semiconducting/insulating thin cylinders at all separations. The derivation is based on the general theory of dispersion interactions between anisotropic media as formulated in Munday et al. [Phys. Rev. A 71, 042102 (2005)]. This formulation is then used to calculate the dispersion interactions between a pair of single-walled carbon nanotubes at all separations and all angles. Nonretarded and retarded forms of the interactions are developed separately. The possibility of repulsive dispersion interactions and nonmonotonic dispersion interactions is discussed within the framework of the formulation.

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Exchange Bias Training Effect In Magnetically Coupled Bilayers, Srinivas Polisetty Oct 2009

Exchange Bias Training Effect In Magnetically Coupled Bilayers, Srinivas Polisetty

Department of Physics and Astronomy: Dissertations, Theses, and Student Research

Interfaces in magnetically coupled bilayer heterostructures play a vital role in novel spintronics devices. Particularly, control of the interface spin structure enables the development of progressively down-scalable magnetic read-heads which are of major importance for non volatile magnetic recording media. Exchange bias and its accompanying training effect are fundamental magnetic coupling phenomena taking place at the interfaces of antiferromagnetic/ferromagnetic and hard/soft ferromagnetic bilayers. Here, in my thesis I present the experimental results of exchange bias training in the prototypical antiferromagnetic/ferromagnetic exchange bias system CoO/Co and the corresponding coupling and aging phenomena in the all ferromagnetic hard/soft bilayer CoPtCrB/CoCr. The latter …

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Project: F.U.N.B.O.E. (Follow-Up Nucleate Boiling On-Flight Experiment), Getaway Special Team 2009 Oct 2009

Project: F.U.N.B.O.E. (Follow-Up Nucleate Boiling On-Flight Experiment), Getaway Special Team 2009

Education and Outreach

No abstract provided.

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Observation Of Giant Positive Magnetoresistance In A Cooper Pair Insulator., H Q. Nguyen, Shawna M. Hollen, M D. Stewart Jr, J Shainline, Aijun Yin, J M. Xu, J M. Valles Oct 2009

Observation Of Giant Positive Magnetoresistance In A Cooper Pair Insulator., H Q. Nguyen, Shawna M. Hollen, M D. Stewart Jr, J Shainline, Aijun Yin, J M. Xu, J M. Valles

Physics & Astronomy

Ultrathin amorphous Bi films, patterned with a nanohoneycomb array of holes, can exhibit an insulating phase with transport dominated by the incoherent motion of Cooper pairs (CP) of electrons between localized states. Here, we show that the magnetoresistance (MR) of this Cooper pair insulator (CPI) phase is positive and grows exponentially with decreasing temperature T, for T well below the pair formation temperature. It peaks at a field estimated to be sufficient to break the pairs and then decreases monotonically into a regime in which the film resistance assumes the T dependence appropriate for weakly localized single electron transport. We …

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The Lambert W Function And Quantum Statistics, Sree Ram Valluri, M. Gil, D. J. Jeffrey, Shantanu Basu Oct 2009

The Lambert W Function And Quantum Statistics, Sree Ram Valluri, M. Gil, D. J. Jeffrey, Shantanu Basu

Physics and Astronomy Publications

We present some applications of the Lambert W function (W function) to the formalism of quantum statistics (QS). We consider the problem of finding extrema in terms of energy for a general QS distribution, which involves the solution of a transcendental equation in terms of the W function. We then present some applications of this formula including Bose–Einstein systems in d dimensions, Maxwell–Boltzmann systems, and black body radiation. We also show that for the appropriate parameter values, this formula reduces to an analytic expression in connection with Wien’s displacement law that was found in a previous study. In addition, we …

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Optimizing The Signal-To-Noise Ratio Of A Beam-Deflection Measurement With Interferometric Weak Values, David J. Starling, P. Ben Dixon, Andrew N. Jordan, John C. Howell Oct 2009

Optimizing The Signal-To-Noise Ratio Of A Beam-Deflection Measurement With Interferometric Weak Values, David J. Starling, P. Ben Dixon, Andrew N. Jordan, John C. Howell

Mathematics, Physics, and Computer Science Faculty Articles and Research

The amplification obtained using weak values is quantified through a detailed investigation of the signal-to-noise ratio for an optical beam-deflection measurement. We show that for a given deflection, input power and beam radius, the use of interferometric weak values allows one to obtain the optimum signal-to-noise ratio using a coherent beam. This method has the advantage of reduced technical noise and allows for the use of detectors with a low saturation intensity. We report on an experiment which improves the signal-to-noise ratio for a beam-deflection measurement by a factor of 54 when compared to a measurement using the same beam …

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Photodisintegration Of 4He Into P + T, R. Nasseripour, Gerard P. Gilfoyle, Et. Al. Oct 2009

Photodisintegration Of 4He Into P + T, R. Nasseripour, Gerard P. Gilfoyle, Et. Al.

Physics Faculty Publications

The two-body photodisintegration of 4He into a proton and a triton has been studied using the CEBAF Large-Acceptance Spectrometer (CLAS) at the Thomas Jefferson National Accelerator Facility. Real photons produced with the Hall-B bremsstrahlung-tagging system in the energy range from 0.35 to 1.55 GeV were incident on a liquid 4He target. This is the first measurement of the photodisintegration of 4He above 0.4 GeV. The differential cross sections for the γ 4He → pt reaction were measured as a function of photon-beam energy and proton-scattering angle and are compared with the latest model calculations by J.M. …

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Josephson Scanning Tunneling Microscopy: A Local And Direct Probe Of The Superconducting Order Parameter, Richard P. Barber Jr., Hikari Kimura, Shuhei Ono, Yoichi Ando, Robert C. Dynes Oct 2009

Josephson Scanning Tunneling Microscopy: A Local And Direct Probe Of The Superconducting Order Parameter, Richard P. Barber Jr., Hikari Kimura, Shuhei Ono, Yoichi Ando, Robert C. Dynes

Physics

Direct measurements of the superconducting superfluid on the surface of vacuum-cleaved Bi2Sr2CaCu2O8+ BSCCO samples are reported. These measurements are accomplished via Josephson tunneling into the sample using a scanning tunneling microscope STM equipped with a superconducting tip. The spatial resolution of the STM of lateral distances less than the superconducting coherence length allows it to reveal local inhomogeneities in the pair wave function of the BSCCO. Instrument performance is demonstrated first with Josephson measurements of Pb films followed by the layered superconductor NbSe2. The relevant measurement parameter, the Josephson ICRN product, is discussed within the context of both BCS superconductors …

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Development And Comparison Of Methods For Measuring Directional Sound Arrivals In Rooms, Brian Trevor Thornock Oct 2009

Development And Comparison Of Methods For Measuring Directional Sound Arrivals In Rooms, Brian Trevor Thornock

Theses and Dissertations

In room acoustics, the directional information of sound arrivals at a listening location can be used to diagnose the origins of problematic reflections so offending surfaces or other features can be properly treated. It can also be used for other purposes, including the study of psychoacoustic indicators. Many methods have been developed in the past to derive directional information, but despite their benefits, each has had significant drawbacks that have necessitated further research into their properties and development of an improved method. This thesis presents a review of past methods, their benefits and shortcomings. It discusses many theoretical and practical …

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Electronic Transport Properties Of A Tilted Graphene P-N Junction, Tony Low, Joerg Appenzeller Oct 2009

Electronic Transport Properties Of A Tilted Graphene P-N Junction, Tony Low, Joerg Appenzeller

Birck and NCN Publications

Spatial manipulation of current flow in graphene could be achieved through the use of a tilted p-n junction. We show through numerical simulation that a pseudo-Hall effect (i.e., nonequilibrium charge and current density accumulating along one of the sides of a graphene ribbon) can be observed under these conditions. The tilt angle and the p-n transition length are two key parameters in tuning the strength of this effect. This phenomenon can be explained using classical trajectory via ray analysis, and is therefore relatively robust against disorder. Lastly, we propose and simulate a three terminal device that allows direct experimental access …

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Third Grade Lesson Plan: Where Does Heat Come From?, Getaway Special Team 2009 Oct 2009

Third Grade Lesson Plan: Where Does Heat Come From?, Getaway Special Team 2009

Education and Outreach

No abstract provided.

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Determining The Gasb/Gaas-(2 × 8) Reconstruction, Jessica E. Bickel, Normand A. Modine, Joanna Mirecki Millunchick Oct 2009

Determining The Gasb/Gaas-(2 × 8) Reconstruction, Jessica E. Bickel, Normand A. Modine, Joanna Mirecki Millunchick

Physics Faculty Publications

Highly strained thin layers of GaSb/GaAs possess a (2 × 4) reconstruction at low Sb overpressures, and a (2 × 8) reconstruction at high Sb overpressures. While the atomic details of the Sb/GaAs-(2 × 4) are well known, the details of the (2 × 8) are not understood. In this paper, we use density functional theory to analyze possible (2 × 8) structures. Comparing scanning tunneling microscope images from both simulation and experiment and examining the relative energies of possible (2 × 8) structures, we show the α(2 × 8) and β(2 × 8) are the thermodynamically stable surface reconstructions …

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Fifth Grade Lesson Plan: Solid, Liquid, And Gas, Getaway Special Team 2009 Oct 2009

Fifth Grade Lesson Plan: Solid, Liquid, And Gas, Getaway Special Team 2009

Education and Outreach

No abstract provided.

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Sixth Grade Lesson Plan: Heat Moves, Getaway Special Team 2009 Oct 2009

Sixth Grade Lesson Plan: Heat Moves, Getaway Special Team 2009

Education and Outreach

No abstract provided.

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Nanoscale Domain Patterns In Ultrathin Polymer Ferroelectric Films, Pankaj Sharma, Timothy J. Reece, Daniel W. Wu, Vladimir M. Fridkin, Stephen Ducharme, Alexei Gruverman Oct 2009

Nanoscale Domain Patterns In Ultrathin Polymer Ferroelectric Films, Pankaj Sharma, Timothy J. Reece, Daniel W. Wu, Vladimir M. Fridkin, Stephen Ducharme, Alexei Gruverman

Stephen Ducharme Publications

High-resolution studies of domain configurations in Langmuir–Blodgett films of ferroelectric polymer poly(vinylidene fluoride-trifluoroethylene), P(VDF-TrFE), have been carried out by means of piezoresponse force microscopy (PFM). Changes in film thickness and morphology cause significant variations in polarization patterns. In continuous films and nanomesas with relatively low thickness/grain aspect ratio (<1/10), the relationship between the average domain size and thickness follows the Kittel law. Nanomesas with high aspect ratio (>1/5) exhibit significant deviations from this law, suggesting additional surface-energy-related mechanisms affecting the domain patterns. Polarization reversal within a single crystallite has been demonstrated and local switching parameters (coercive voltage and remnant piezoresponse) have been measured by monitoring the local hysteresis loops. Reliable control of polarization at the sub-grain level demonstrates …

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General Theoretical Description Of N-Body Recombination, Nirav P. Mehta, Seth T. Rittenhouse, J P. D’Incao, J Von Stecher, Chris H. Greene Oct 2009

General Theoretical Description Of N-Body Recombination, Nirav P. Mehta, Seth T. Rittenhouse, J P. D’Incao, J Von Stecher, Chris H. Greene

Physics and Astronomy Faculty Research

Formulas for the cross section and event rate constant describing recombination of N particles are derived in terms of general S-matrix elements. Our result immediately yields the generalized Wigner threshold scaling for the recombination of N bosons. A semianalytical formula encapsulates the overall scaling with energy and scattering length, as well as resonant modifications by the presence of N-body states near the threshold collision energy in the entrance channel. We then apply our model to the case of four-boson recombination into an Efimov trimer and a free atom.

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