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2009

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Articles 61 - 90 of 907

Full-Text Articles in Physics

Reducing Microwave Loss In Superconducting Resonators Due To Trapped Vortices, Britton Plourde, C. Song, M. P. Defeo, Kang Yu Nov 2009

Reducing Microwave Loss In Superconducting Resonators Due To Trapped Vortices, Britton Plourde, C. Song, M. P. Defeo, Kang Yu

Physics - All Scholarship

Microwave resonators with high quality factors have enabled many recent breakthroughs with superconducting qubits and photon detectors, typically operated in shielded environments to reduce the ambient magnetic field. Insufficient shielding or pulsed control fields can introduce vortices, leading to reduced quality factors, although increased pinning can mitigate this effect. A narrow slot etched into the resonator surface provides a straightforward method for pinning enhancement without otherwise affecting the resonator. Resonators patterned with such a slot exhibited over an order of magnitude reduction in the excess loss due to vortices compared with identical resonators from the same film with no slot.

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Observation Of A Helical Self-Organized State In A Compact Toroidal Plasma, C. D. Cothran, Michael R. Brown, Timothy G. Gray , '01, M. J. Schaffer, G. Marklin Nov 2009

Observation Of A Helical Self-Organized State In A Compact Toroidal Plasma, C. D. Cothran, Michael R. Brown, Timothy G. Gray , '01, M. J. Schaffer, G. Marklin

Physics & Astronomy Faculty Works

A nonaxisymmetric stable magnetohydrodynamic (MHD) equilibrium within a prolate cylindrical conducting boundary has been produced experimentally. It has m=1 azimuthal symmetry, helical distortion, and flat lambda profile, all in agreement with the computed magnetically relaxed minimum magnetic energy Taylor state. Despite varied initial conditions determined by two helicity injectors on the device, this same equilibrium consistently emerges as the final state. These results therefore describe a new example of self-organization in an MHD plasma.

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G Factor Of The 2+1 State Of 172Hf, Z. Berant, E. Oster, R. J. Casperson, A. Wolf, V. Werner, A. Heinz, R. F. Casten, G. Gurdal, E. A. Mccutchan, D. S. Brenner, J. R. Terry, R. Winkler, E. Williams, J. Qian, A. Schmidt, M. K. Smith, T. Ahn, C. W. Beausang, P. H. Regan, T. J. Ross, M. Bunce, B. Darakchieva, D. A. Meyer, J. Leblanc, K. Dudziak, C. Bauer, G. Henning Nov 2009

G Factor Of The 2+1 State Of 172Hf, Z. Berant, E. Oster, R. J. Casperson, A. Wolf, V. Werner, A. Heinz, R. F. Casten, G. Gurdal, E. A. Mccutchan, D. S. Brenner, J. R. Terry, R. Winkler, E. Williams, J. Qian, A. Schmidt, M. K. Smith, T. Ahn, C. W. Beausang, P. H. Regan, T. J. Ross, M. Bunce, B. Darakchieva, D. A. Meyer, J. Leblanc, K. Dudziak, C. Bauer, G. Henning

Physics Faculty Publications

The g factor of the 2+1 state of 172Hf was measured using the perturbed angular correlation technique in a static external magnetic field. The result, g(2+1) = 0.25(5), is discussed in relation to the systematics of the previously reported g factors in the Hf isotopes and compared with the predictions of several models. An interesting outcome of the analysis presented in this paper is the agreement between the calculated g factors within the interacting boson approximation (IBA) and the results of a large-scale shell model calculation. This agreement supports the emphasis in the …

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Electroexcitation Of Nucleon Resonances From Clas Data On Single Pion Electroproduction, I. G. Aznauryan, Gerard P. Gilfoyle, Et. Al. Nov 2009

Electroexcitation Of Nucleon Resonances From Clas Data On Single Pion Electroproduction, I. G. Aznauryan, Gerard P. Gilfoyle, Et. Al.

Physics Faculty Publications

We present results on the electroexcitation of the low mass resonances ∆(1232)P33, N(1440)P11, N(1520)D13, and N(1535)S11 in a wide range of Q2. The results were obtained in the comprehensive analysis of data from the Continuous Electron Beam Accelerator Facility (CEBAF) large acceptance spectrometer (CLAS) detector at the Thomas Jefferson National Accelerator Facility (JLab) on differential cross sections, longitudinally polarized beam asymmetries, and longitudinal target and beam-target asymmetries for π electroproduction off the proton. The data were analyzed using two conceptually different approaches—fixed-t dispersion …

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Electron Drift Directions In Strong-Field Double Ionization Of Atoms, Stanley L. Haan, Z. S. Smith, K. N. Shomsky, P. W. Plantinga Nov 2009

Electron Drift Directions In Strong-Field Double Ionization Of Atoms, Stanley L. Haan, Z. S. Smith, K. N. Shomsky, P. W. Plantinga

University Faculty Publications and Creative Works

Longitudinal momentum spectra and electron drift directions are considered for several laser wavelengths in non-sequential double ionization of helium using three-dimensional classical ensembles. In this model, the familiar doublet for wavelength 800 nm and intensities of order 5 × 1014 W cm-2 becomes a triplet for wavelength 1314 nm, then a doublet for 2017 nm. The results are explained based on whether the post-ionization impulse from the laser results in backward drift for one or both electrons.

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Comparison Of Line-Peak And Line-Scanning Excitation In Two-Color Laser-Induced-Fluorescence Thermometry Of Oh, Stanislav Kostka, Sukesh Roy, Patrick J. Lakusta, Terrence Meyer, Michael W. Renfro, James R. Gord, Richard D. Branam Nov 2009

Comparison Of Line-Peak And Line-Scanning Excitation In Two-Color Laser-Induced-Fluorescence Thermometry Of Oh, Stanislav Kostka, Sukesh Roy, Patrick J. Lakusta, Terrence Meyer, Michael W. Renfro, James R. Gord, Richard D. Branam

Faculty Publications

Two-line laser-induced-fluorescence (LIF) thermometry is commonly employed to generate instantaneous planar maps of temperature in unsteady flames. The use of line scanning to extract the ratio of integrated intensities is less common because it precludes instantaneous measurements. Recent advances in the energy output of high-speed, ultraviolet, optical parameter oscillators have made possible the rapid scanning of molecular rovibrational transitions and, hence, the potential to extract information on gas-phase temperatures. In the current study, two-line OH LIF thermometry is performed in a well-calibrated reacting flow for the purpose of comparing the relative accuracy of various line-pair selections from the literature and …

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The Surface Relaxation And Band Structure Of Mo(112), Ning Wu, Ya. B. Losovyj, Zhaoxian Yu, Renat F. Sabirianov, Wai-Ning Mei, N. Lozova, J. A. Colón Santana, Peter Dowben Nov 2009

The Surface Relaxation And Band Structure Of Mo(112), Ning Wu, Ya. B. Losovyj, Zhaoxian Yu, Renat F. Sabirianov, Wai-Ning Mei, N. Lozova, J. A. Colón Santana, Peter Dowben

Physics Faculty Publications

The experimental and theoretical surface band structures of Mo(112) are compared. This surface band structure mapping is presented with corrections included for the lattice relaxation of the Mo(112) surface. Quantitative low energy electron diffraction (LEED) has been used to determine the details of the Mo(112) surface structure. The first layer contraction is 14.9% by LEED intensity versus voltage analysis and is in general agreement with the 17.6% contraction found from total surface energy optimization. The electronic band structure is mapped out along ¯– ¯ X and ¯–¯Y of the surface Brillouin zone (SBZ). There is strong evidence of electron–phonon coupling …

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Comparing Experts And Novices In Solving Electrical Circuit Problems With The Help Of Eye-Tracking, David Rosengrant, Colin Thomson, Taha Mzoughi Nov 2009

Comparing Experts And Novices In Solving Electrical Circuit Problems With The Help Of Eye-Tracking, David Rosengrant, Colin Thomson, Taha Mzoughi

Faculty Articles

In order to help introductory physics students understand and learn to solve problems with circuits, we must first understand how they differ from experts. This preliminary study focuses on problem-solving dealing with electrical circuits. We investigate difficulties novices have with circuits and compare their work with those of experts. We incorporate the use of an eye-tracker to investigate any possible differences or similarities on how experts and novices solve electrical circuit problems. Our results show similarities in gaze patterns among all subjects on the components of the circuit. We further found that experts would look back at the circuit while …

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Damping And Decoherence Of A Nanomechanical Resonator Due To A Few Two-Level Systems, Laura G. Remus, Miles P. Blencowe, Yukihiro Tanaka Nov 2009

Damping And Decoherence Of A Nanomechanical Resonator Due To A Few Two-Level Systems, Laura G. Remus, Miles P. Blencowe, Yukihiro Tanaka

Dartmouth Scholarship

We consider a quantum model of a nanomechanical flexing beam resonator interacting with a bath comprising a few damped tunneling two-level systems. In contrast with a resonator interacting bilinearly with an ohmic free oscillator bath (modeling clamping loss, for example), the mechanical resonator damping is amplitude dependent, while the decoherence of quantum superpositions of mechanical position states depends only weakly on their spatial separation.

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Radiation Force Of Scalar And Electromagnetic Twisted Gaussian Schell-Model Beams, Chengliang Zhao, Yangjian Cai, Olga Korotkova Nov 2009

Radiation Force Of Scalar And Electromagnetic Twisted Gaussian Schell-Model Beams, Chengliang Zhao, Yangjian Cai, Olga Korotkova

Physics Articles and Papers

Radiation force of a focused scalar twisted Gaussian Schell-model (TGSM) beam on a Rayleigh dielectric sphere is investigated. It is found that the twist phase affects the radiation force and by raising the absolute value of the twist factor it is possible to increase both transverse and longitudinal trapping ranges at the real focus where the maximum on-axis intensity is located. Numerical calculations of radiation forces induced by a focused electromagnetic TGSM beam on a Rayleigh dielectric sphere are carried out. It is found that radiation force is closely related to the twist phase, degree of polarization and correlation factors …

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Simulations Of The Dipole-Dipole Interaction Between Two Spatially Separated Groups Of Rydberg Atoms, Thomas J. Carroll, Christopher Daniel, Leah Hoover, Timothy Sidie, Michael Noel Nov 2009

Simulations Of The Dipole-Dipole Interaction Between Two Spatially Separated Groups Of Rydberg Atoms, Thomas J. Carroll, Christopher Daniel, Leah Hoover, Timothy Sidie, Michael Noel

Physics Faculty Research and Scholarship

The dipole-dipole interaction among ultracold Rydberg atoms is simulated. We examine a general interaction scheme in which two atoms excited to the x and x(') states are converted to y and y(') states via a Förster resonance. The atoms are arranged in two spatially separated groups, each consisting of only one species of atom. We monitor the state mixing by recording the fraction of atoms excited to the y(') state as the distance between the two groups is varied. With zero detuning a many-body effect that relies on always resonant interactions causes the state mixing to have a finite range. …

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Galaxy Zoo Green Peas: Discovery Of A Class Of Compact Extremely Star-Forming Galaxies, Carolin Cardamone, Kevin Schawinski, Marc Sarzi, Steven P. Bamford, Vardha N. Bennert, C. M. Urry, Chris Lintott, William C. Keel, John Parejko, Robert C. Nichol, Daniel Thomas, Dan Andreescu, Phil Murray, M. Jordan Raddick, Anže Slosar, Alex Szalay, Jan Vandenberg Nov 2009

Galaxy Zoo Green Peas: Discovery Of A Class Of Compact Extremely Star-Forming Galaxies, Carolin Cardamone, Kevin Schawinski, Marc Sarzi, Steven P. Bamford, Vardha N. Bennert, C. M. Urry, Chris Lintott, William C. Keel, John Parejko, Robert C. Nichol, Daniel Thomas, Dan Andreescu, Phil Murray, M. Jordan Raddick, Anže Slosar, Alex Szalay, Jan Vandenberg

Physics

We investigate a class of rapidly growing emission line galaxies, known as ‘Green Peas’, first noted by volunteers in the Galaxy Zoo project because of their peculiar bright green colour and small size, unresolved in Sloan Digital Sky Survey imaging. Their appearance is due to very strong optical emission lines, namely [O iii]λ5007 Å, with an unusually large equivalent width of up to ∼1000 Å. We discuss a well-defined sample of 251 colour-selected objects, most of which are strongly star forming, although there are some active galactic nuclei interlopers including eight newly discovered narrow-line Seyfert 1 galaxies. The star-forming Peas …

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The Lick Agn Monitoring Project: Broad-Line Region Radii And Black Hole Masses From Reverberation Mapping Of HSs, Misty C. Bentz, Jonelle L. Walsh, Aaron J. Barth, Nairn Baliber, Vardha N. Bennert, Gabriela Canalizo, Alexei V. Filippenko, Mohan Ganeshalingam, Elinor L. Gates, Jenny E. Greene, Marton G. Hidas, Kyle D. Hiner, Nicholas Lee, Weidong Li, Matthew A. Malkan, Takeo Minezaki, Yu Sakata, Frank J.D. Serduke, Jeffrey M. Silverman, Thea N. Steele, Daniel Stern, Rachel A. Street, Carol E. Thornton, Tommaso Treu, Xiaofeng Wang, Jong-Hak Woo, Yuzuru Yoshii Nov 2009

The Lick Agn Monitoring Project: Broad-Line Region Radii And Black Hole Masses From Reverberation Mapping Of HSs, Misty C. Bentz, Jonelle L. Walsh, Aaron J. Barth, Nairn Baliber, Vardha N. Bennert, Gabriela Canalizo, Alexei V. Filippenko, Mohan Ganeshalingam, Elinor L. Gates, Jenny E. Greene, Marton G. Hidas, Kyle D. Hiner, Nicholas Lee, Weidong Li, Matthew A. Malkan, Takeo Minezaki, Yu Sakata, Frank J.D. Serduke, Jeffrey M. Silverman, Thea N. Steele, Daniel Stern, Rachel A. Street, Carol E. Thornton, Tommaso Treu, Xiaofeng Wang, Jong-Hak Woo, Yuzuru Yoshii

Physics

We have recently completed a 64-night spectroscopic monitoring campaign at the Lick Observatory 3-m Shane telescope with the aim of measuring the masses of the black holes in 12 nearby (z < 0.05) Seyfert 1 galaxies with expected masses in the range ~106-107 M ☉ and also the well-studied nearby active galactic nucleus (AGN) NGC 5548. Nine of the objects in the sample (including NGC 5548) showed optical variability of sufficient strength during the monitoring campaign to allow for a time lag to be measured between the continuum fluctuations and the response to these fluctuations in the broad Hβ emission. We present here the light curves for all …

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Linker-Free Modification Of Tio2 Nanorods With Pbse Nanocrystals, Krishna P. Acharya, Taiwo R. Alabi, Nicholas Schmall, Nishshanka N. Hewa-Kasakarage, Maria Kirsanova, Alexander Nemchinov, Elena Khon, Mikhail Zamkov Nov 2009

Linker-Free Modification Of Tio2 Nanorods With Pbse Nanocrystals, Krishna P. Acharya, Taiwo R. Alabi, Nicholas Schmall, Nishshanka N. Hewa-Kasakarage, Maria Kirsanova, Alexander Nemchinov, Elena Khon, Mikhail Zamkov

Physics and Astronomy Faculty Publications

We report on a colloidal synthesis of Pbse/TiO2 heterostructures, comprising small-diameter PbSe nanocrystals epitaxially grown onto the surface of TiO2 nanorods. The deposition of lead selenide onto prefabricated TiO2 nanocrystals proceeds via formation of a thin PbSe shell that subsequently breaks into sub-2-nm islands. Additional precursor injections are then used to increase the size of PbSe nanocrystals up to 5 nm. In the case of small-size PbSe, a 2.1-ns transfer of photoinduced carriers into TiO2 domain was evidenced through quenching of the PbSe band gap emission. Overall, the present synthesis demonstrates a colloidal approach to all-inorganic modification of TiO2 surfaces …

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How Much Can Guided Modes Enhance Absorption In Thin Solar Cells?, Peter N. Saeta, Vivian E. Ferry, Domenico Pacifici, Jeremy N. Munday, Harry A. Atwater Nov 2009

How Much Can Guided Modes Enhance Absorption In Thin Solar Cells?, Peter N. Saeta, Vivian E. Ferry, Domenico Pacifici, Jeremy N. Munday, Harry A. Atwater

All HMC Faculty Publications and Research

Absorption enhancement in thin metal-backed solar cells caused by dipole scatterers embedded in the absorbing layer is studied using a semi-analytical approach. The method accounts for changes in the radiation rate produced by layers above and below the dipole, and treats incoherently the subsequent scattering of light in guided modes from other dipoles. We find large absorption enhancements for strongly coupled dipoles, exceeding the ergodic limit in some configurations involving lossless dipoles. An antireflection-coated 100-nm layer of a-Si:H on Ag absorbs up to 87% of incident above-gap light. Thin layers of both strong and weak absorbers show similar strongly enhanced …

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Search For Gravitational-Wave Bursts In The First Year Of The Fifth Ligo Science Run, Benjamin P. Abbott, Marco Cavaglia, For Full List Of Authors, See Publisher's Website. Nov 2009

Search For Gravitational-Wave Bursts In The First Year Of The Fifth Ligo Science Run, Benjamin P. Abbott, Marco Cavaglia, For Full List Of Authors, See Publisher's Website.

Physics Faculty Research & Creative Works

We present the results obtained from an all-sky search for gravitational-wave (GW) bursts in the 64-2000 Hz frequency range in data collected by the LIGO detectors during the first year (November 2005-November 2006) of their fifth science run. The total analyzed live time was 268.6 days. Multiple hierarchical data analysis methods were invoked in this search. The overall sensitivity expressed in terms of the root-sum-square (rss) strain amplitude hrss for gravitational-wave bursts with various morphologies was in the range of 6 x 10-22 Hz -1/2 to a few x 10-21Hz-1/2. No GW signals were …

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Correlated Two-Photon Emission By Transitions Of Dirac-Volkov States In Intense Laser Fields: Qed Predictions, Erik Lotstedt, Ulrich D. Jentschura Nov 2009

Correlated Two-Photon Emission By Transitions Of Dirac-Volkov States In Intense Laser Fields: Qed Predictions, Erik Lotstedt, Ulrich D. Jentschura

Physics Faculty Research & Creative Works

In an intense laser field, an electron may decay by emitting a pair of photons. The two photons emitted during the process, which can be interpreted as a laser-dressed double Compton scattering, remain entangled in a quantifiable way: namely, the so-called concurrence of the photon polarizations gives a gauge-invariant measure of the correlation of the hard gamma rays. We calculate the differential rate and concurrence for a backscattering setup of the electron and photon beam, employing Volkov states and propagators for the electron lines, thus accounting nonperturbatively for the electron-laser interaction. The nonperturbative results are shown to differ significantly compared …

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Nuclear Form Factor, Validity Of The Equivalent Photon Approximation And Coulomb Corrections To Muon Pair Production In Photon-Nucleus And Nucleus-Nucleus Collisions, Ulrich D. Jentschura, V. G. Serbo Nov 2009

Nuclear Form Factor, Validity Of The Equivalent Photon Approximation And Coulomb Corrections To Muon Pair Production In Photon-Nucleus And Nucleus-Nucleus Collisions, Ulrich D. Jentschura, V. G. Serbo

Physics Faculty Research & Creative Works

We study in detail the influence of the nuclear form factor both on the Born cross section and on the Coulomb corrections to the photo-production of muon pairs off heavy nuclei (γ Z→μ + μ - Z) and in heavy-ion collisions (ZZ→ZZ μ + μ -). Our findings indicate a number of issues which have not been sufficiently described as yet in the literature: (i) the use of a realistic form factor, based on the Fermi charge distribution for the nucleus, is absolutely indispensable for reliable theoretical predictions; (ii) we checked quantitatively that the equivalent photon approximation has a very …

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Dusty Structure Around Type-I Active Galactic Nuclei: Clumpy Torus Narrow-Line Region And Near-Nucleus Hot Dust, Rivay Mor, Hagai Netzer, Moshe Elitzur Nov 2009

Dusty Structure Around Type-I Active Galactic Nuclei: Clumpy Torus Narrow-Line Region And Near-Nucleus Hot Dust, Rivay Mor, Hagai Netzer, Moshe Elitzur

Physics and Astronomy Faculty Publications

We fitted Spitzer/IRS ~ 2-35 μm spectra of 26 luminous quasi-stellar objects in an attempt to define the main emission components. Our model has three major components: a clumpy torus, dusty narrow-line region (NLR) clouds, and a blackbody-like dust. The models utilize the clumpy torus of Nenkova et al. and are the first to allow its consistent check in type-I active galactic nuclei (AGNs). Single torus models and combined torus-NLR models fail to fit the spectra of most sources, but three-component models adequately fit the spectra of all sources. We present torus inclination, cloud distribution, covering factor, and …

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Analysis Of Angular Dependence Of Strong-Field Tunneling Ionization For Co₂, Song-Feng Zhao, Cheng Jin, Anh-Thu Le, T. F. Jiang, C. D. Lin Nov 2009

Analysis Of Angular Dependence Of Strong-Field Tunneling Ionization For Co₂, Song-Feng Zhao, Cheng Jin, Anh-Thu Le, T. F. Jiang, C. D. Lin

Physics Faculty Research & Creative Works

We analyzed the discrepancy of the angular dependence of strong-field ionization for CO₂ among the different theoretical calculations and experiments. Using a more accurate ground-state wave function of CO₂ in the asymptotic region, we showed that the accuracy in the earlier tunneling ionization theory of Tong et al. [Phys. Rev. A 66, 033402 (2002)] is much improved. We also concluded that the angular dependence deduced from the experiment of Pavicic [Phys. Rev. Lett. 98, 243001 (2007)] appears to be too narrowly distributed.

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Search For High Frequency Gravitational-Wave Bursts In The First Calendar Year Of Ligo's Fifth Science Run, Benjamin P. Abbott, Marco Cavaglia, For Full List Of Authors, See Publisher's Website. Nov 2009

Search For High Frequency Gravitational-Wave Bursts In The First Calendar Year Of Ligo's Fifth Science Run, Benjamin P. Abbott, Marco Cavaglia, For Full List Of Authors, See Publisher's Website.

Physics Faculty Research & Creative Works

We present an all-sky search for gravitational waves in the frequency range 1 to 6 kHz during the first calendar year of LIGO's fifth science run. This is the first untriggered LIGO burst analysis to be conducted above 3 kHz. We discuss the unique properties of interferometric data in this regime. 161.3 days of triple-coincident data were analyzed. No gravitational events above threshold were observed and a frequentist upper limit of 5.4 year-1 on the rate of strong gravitational-wave bursts was placed at a 90% confidence level. Implications for specific theoretical models of gravitational-wave emission are also discussed.

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Finite Temperature Effects In Magnetic Materials: Model And Ab Initio Studies, Aleksander L. Wysocki Nov 2009

Finite Temperature Effects In Magnetic Materials: Model And Ab Initio Studies, Aleksander L. Wysocki

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

The understanding of finite temperature behavior of magnetic materials is of vital importance for spintronic applications. In this dissertation different theoretical techniques for studying magnetic thermodynamics of various materials are discussed. Cr2O3 is an antiferromagnetic insulator that was proposed to be a key component of new spintronic devices. The magnetic properties of Cr2O3 were studied using the LDA+U method. Magnetism was found to be very well described by the Heisenberg model. Subsequently, magnetic thermodynamics was explored using quantum pair cluster approximation. Overall, very good agreement with experiment was found for the ground state and …

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The Lick Agn Monitoring Project: Photometric Light Curves And Optical Variability Characteristics, Jonelle L. Walsh, Takeo Minezaki, Misty C. Bentz, Aaron J. Barth, Nairn Baliber, Weidong Li, Daniel Stern, Vardha Nicola Bennert, Timothy M. Brown, Gabriela Canalizo, Alexei V. Filippenko, Elinor L. Gates, Jenny E. Greene, Matthew A. Malkan, Yu Sakata, Rachel A. Street, Tommaso Treu, Jong-Hak Woo, Yuzuru Yoshii Nov 2009

The Lick Agn Monitoring Project: Photometric Light Curves And Optical Variability Characteristics, Jonelle L. Walsh, Takeo Minezaki, Misty C. Bentz, Aaron J. Barth, Nairn Baliber, Weidong Li, Daniel Stern, Vardha Nicola Bennert, Timothy M. Brown, Gabriela Canalizo, Alexei V. Filippenko, Elinor L. Gates, Jenny E. Greene, Matthew A. Malkan, Yu Sakata, Rachel A. Street, Tommaso Treu, Jong-Hak Woo, Yuzuru Yoshii

Physics

The Lick AGN Monitoring Project targeted 13 nearby Seyfert 1 galaxies with the intent of measuring the masses of their central black holes using reverberation mapping. The sample includes 12 galaxies selected to have black holes with masses roughly in the range 106-107 M ☉, as well as the well-studied active galactic nucleus (AGN) NGC 5548. In conjunction with a spectroscopic monitoring campaign, we obtained broadband B and V images on most nights from 2008 February through 2008 May. The imaging observations were carried out by four telescopes: the 0.76 m Katzman Automatic Imaging Telescope, the …

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Assessing The Merits Of The Ctbt, David W. Hafemeister Nov 2009

Assessing The Merits Of The Ctbt, David W. Hafemeister

Physics

The Treaty on the Non-Proliferation of Nuclear Weapons and the nonproliferation regime have been weakened; perhaps no other issue demonstrates this as dramatically as the status of the Comprehensive Nuclear-Test-Ban Treaty (CTBT), the ratification of which the U.S. Senate rejected in October 1999. Despite the U.S. rejection, the test ban has strong international support—the most recent vote to promote the CTBT in the UN General Assembly passed overwhelmingly, with 175 votes to 1 (the United States) and three abstentions. The Obama administration favors U.S. ratification of the CTBT, but this is no guarantee that Washington will ratify the test ban. …

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Fragmentation Properties Of Three-Membered Ring Heterocyclic Molecules By Partial Ion Yield Spectroscopy: C2h4o And C2h4s, Wayne C. Stolte, I. Dumitriu, S-W Yu, Gunnar Ohrwall, Maria Novella Piancastelli, Dennis W. Lindle Nov 2009

Fragmentation Properties Of Three-Membered Ring Heterocyclic Molecules By Partial Ion Yield Spectroscopy: C2h4o And C2h4s, Wayne C. Stolte, I. Dumitriu, S-W Yu, Gunnar Ohrwall, Maria Novella Piancastelli, Dennis W. Lindle

Chemistry and Biochemistry Faculty Research

We investigated the photofragmentation properties of two three-membered ring heterocyclic molecules, C2H4O and C2H4S, by total and partial ion yield spectroscopy. Positive and negative ions have been collected as a function of photon energy around the C 1s and O 1s ionization thresholds in C2H4O, and around the S 2p and C 1s thresholds in C2H4S. We underline similarities and differences between these two analogous systems. We present a new assignment of the spectral features around the C K-edge and the sulfur L2 …

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Coupled Ray-Tracing And Fokker-Planck Ebw Modeling For Spherical Tokamaks, Jakub Urban, Joan Decker, Y. Peysson, Josef Preinhaelter, Gary Taylor, Linda L. Vahala, George Vahala Nov 2009

Coupled Ray-Tracing And Fokker-Planck Ebw Modeling For Spherical Tokamaks, Jakub Urban, Joan Decker, Y. Peysson, Josef Preinhaelter, Gary Taylor, Linda L. Vahala, George Vahala

Electrical & Computer Engineering Faculty Publications

The AMR (Antenna—Mode-conversion—Ray-tracing) code [1, 2] has been recently coupled with the LUKE [3] Fokker-Planck code. This modeling suite is capable of complex simulations of electron Bernstein wave (EBW) emission, heating and current drive. We employ these codes to study EBW heating and current drive performance under spherical tokamak (ST) configurations—typical NSTX discharges are employed. EBW parameters, such as frequency, antenna position and direction, are varied and optimized for particular configurations and objectives. In this way, we show the versatility of EBWs.

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Validity Of The Spin-Susceptibility “Glue” Approximation For Pairing In The Two-Dimensional Hubbard Model, Ehsan Khatami, A. Macridin, M. Jarrell Nov 2009

Validity Of The Spin-Susceptibility “Glue” Approximation For Pairing In The Two-Dimensional Hubbard Model, Ehsan Khatami, A. Macridin, M. Jarrell

Faculty Publications

We examine the validity of the weak-coupling spin-susceptibility “glue” approximation (SSGA) in a two-dimensional Hubbard model for cuprates. For comparison, we employ the well-established dynamical cluster approximation (DCA) with a quantum Monte Carlo algorithm as a cluster solver. We compare the leading eigenvalues and corresponding eigenfunctions of the DCA and SSGA pairing matrices. For realistic model parameters, we find that the SSGA fails to capture the leading pairing symmetries seen in the DCA. Furthermore, when the SSGA is improved through the addition of a term with d-wave symmetry, the strength of this additional term is found to be larger than …

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Exact Algorithm For Sampling The 2d Ising Spin Glass, Alan Middleton, Creighton K. Thomas Oct 2009

Exact Algorithm For Sampling The 2d Ising Spin Glass, Alan Middleton, Creighton K. Thomas

Physics - All Scholarship

A sampling algorithm is presented that generates spin glass configurations of the 2D Edwards-Anderson Ising spin glass at finite temperature, with probabilities proportional to their Boltzmann weights. Such an algorithm overcomes the slow dynamics of direct simulation and can be used to study long-range correlation functions and coarse-grained dynamics. The algorithm uses a correspondence between spin configurations on a regular lattice and dimer (edge) coverings of a related graph: Wilson's algorithm [D. B. Wilson, Proc. 8th Symp. Discrete Algorithms 258, (1997)] for sampling dimer coverings on a planar lattice is adapted to generate samplings for the dimer problem corresponding to …

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Differential Cross Sections For The Reactions Γp→Pη And Γp→Pη', M. Williams, Gerard P. Gilfoyle, Et. Al. Oct 2009

Differential Cross Sections For The Reactions Γp→Pη And Γp→Pη', M. Williams, Gerard P. Gilfoyle, Et. Al.

Physics Faculty Publications

High-statistics differential cross sections for the reactions γp → pη and γp → pη' have been measured using the CEBAF large acceptance spectrometer (CLAS) at Jefferson Lab for center-of-mass energies from near threshold up to 2.84 GeV. The η' results are the most precise to date and provide the largest energy and angular coverage. The η measurements extend the energy range of the world’s large-angle results by approximately 300 MeV. These new data, in particular the η' measurements, are likely to help constrain the analyses being performed to search for new baryon resonance states.

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Ion Observations From Geosynchronous Orbit As A Proxy For Ion Cyclotron Wave Growth During Storm Times, L. W. Blum, E. A. Macdonald, S. P. Gary, M. F. Thomsen, Harlan E. Spence Oct 2009

Ion Observations From Geosynchronous Orbit As A Proxy For Ion Cyclotron Wave Growth During Storm Times, L. W. Blum, E. A. Macdonald, S. P. Gary, M. F. Thomsen, Harlan E. Spence

Physics & Astronomy

[1] There is still much to be understood about the processes contributing to relativistic electron enhancements and losses in the radiation belts. Wave particle interactions with both whistler and electromagnetic ion cyclotron (EMIC) waves may precipitate or accelerate these electrons. This study examines the relation between EMIC waves and resulting relativistic electron flux levels after geomagnetic storms. A proxy for enhanced EMIC waves is developed using Los Alamos National Laboratory Magnetospheric Plasma Analyzer plasma data from geosynchronous orbit in conjunction with linear theory. In a statistical study using superposed epoch analysis, it is found that for storms resulting in net …

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