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Physics and Astronomy Faculty Publications

2013

Articles 31 - 42 of 42

Full-Text Articles in Physical Sciences and Mathematics

Classification And Analysis Of Emission-Line Galaxies Using Mean Field Independent Component Analysis, James T. Allen, Paul C. Hewett, Chris T. Richardson, Gary J. Ferland, Jack A. Baldwin Apr 2013

Classification And Analysis Of Emission-Line Galaxies Using Mean Field Independent Component Analysis, James T. Allen, Paul C. Hewett, Chris T. Richardson, Gary J. Ferland, Jack A. Baldwin

Physics and Astronomy Faculty Publications

We present an analysis of the optical spectra of narrow emission-line galaxies, based on mean field independent component analysis (MFICA), a blind source separation technique. Samples of galaxies were drawn from the Sloan Digital Sky Survey (SDSS) and used to generate compact sets of ‘continuum’ and ‘emission-line’ component spectra. These components can be linearly combined to reconstruct the observed spectra of a wider sample of galaxies. Only 10 components – five continuum and five emission line – are required to produce accurate reconstructions of essentially all narrow emission-line galaxies to a very high degree of accuracy; the median absolute deviations …

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Strongly Localized Magnetization Modes In Permalloy Antidot Lattices, J. Sklenar, V. S. Bhat, Lance E. De Long, O. Heinonen, J. B. Ketterson Apr 2013

Strongly Localized Magnetization Modes In Permalloy Antidot Lattices, J. Sklenar, V. S. Bhat, Lance E. De Long, O. Heinonen, J. B. Ketterson

Physics and Astronomy Faculty Publications

Antidot lattices (ADLs) patterned into soft magnetic thin films exhibit rich ferromagnetic resonance (FMR) spectra corresponding to many different magnetization modes. One of the predicted modes is highly localized at the edges of the antidots; this mode is difficult to detect experimentally. Here we present FMR data for a permalloy thin film patterned into a square array of square antidots. Comparison of these data with micromagnetic simulations permits identification of several edge modes. Our simulations also reveal the effect of the antidot shape on the mode dispersion.

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Suppression Of Dielectronic Recombination Due To Finite Density Effects, D. Nikolić, T. W. Gorczyca, K. T. Korista, Gary J. Ferland, N. R. Badnell Apr 2013

Suppression Of Dielectronic Recombination Due To Finite Density Effects, D. Nikolić, T. W. Gorczyca, K. T. Korista, Gary J. Ferland, N. R. Badnell

Physics and Astronomy Faculty Publications

We have developed a general model for determining density-dependent effective dielectronic recombination (DR) rate coefficients in order to explore finite-density effects on the ionization balance of plasmas. Our model consists of multiplying by a suppression factor those highly-accurate total zero-density DR rate coefficients which have been produced from state-of-the-art theoretical calculations and which have been benchmarked by experiment. The suppression factor is based upon earlier detailed collision-radiative calculations which were made for a wide range of ions at various densities and temperatures, but used a simplified treatment of DR. A general suppression formula is then developed as a function of …

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Erratum: 'Improved He I Emissivities In The Case B Approximation', R. L. Porter, Gary J. Ferland, P. J. Storey, M. J. Detisch Apr 2013

Erratum: 'Improved He I Emissivities In The Case B Approximation', R. L. Porter, Gary J. Ferland, P. J. Storey, M. J. Detisch

Physics and Astronomy Faculty Publications

No abstract provided.

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Tuning Electronic Structure Via Exipatial Strain In Sr2Iro4 Thin Films, J. Nichols, Jsaminka Terzic, Emily Geraldine Bittle, Oleksandr B. Korneta, Lance E. De Long, Joseph Brill, Gang Cao, Sung S. Ambrose Seo Apr 2013

Tuning Electronic Structure Via Exipatial Strain In Sr2Iro4 Thin Films, J. Nichols, Jsaminka Terzic, Emily Geraldine Bittle, Oleksandr B. Korneta, Lance E. De Long, Joseph Brill, Gang Cao, Sung S. Ambrose Seo

Physics and Astronomy Faculty Publications

We have synthesized epitaxial Sr2IrO4 thin-films on various substrates and studied their electronic structure as a function of lattice-strain. Under tensile (compressive) strain, increased (decreased) Ir-O-Ir bond-angle is expected to result in increased (decreased) electronic bandwidth. However, we have observed that the two optical absorption peaks near 0.5 eV and 1.0 eV are shifted to higher (lower) energies under tensile (compressive) strain, indicating that the electronic-correlation energy is also affected by in-plane lattice-strain. The effective tuning of electronic structure under lattice-modification provides an important insight into the physics driven by the coexisting strong spin-orbit coupling and electronic …

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Expanded Iron Uta Spectra—Probing The Thermal Stability Limits In Agn Clouds, Gary J. Ferland, R. Kisielius, F. P. Keenan, P. A. M. Van Hoof, V. Jonauskas, Matt L. Lykins, R. L. Porter, R. J. R. Williams Apr 2013

Expanded Iron Uta Spectra—Probing The Thermal Stability Limits In Agn Clouds, Gary J. Ferland, R. Kisielius, F. P. Keenan, P. A. M. Van Hoof, V. Jonauskas, Matt L. Lykins, R. L. Porter, R. J. R. Williams

Physics and Astronomy Faculty Publications

The Fe unresolved transition arrays (UTAs) produce prominent features in the ~15-17 Å wavelength range in the spectra of active galactic nuclei (AGNs). Here, we present new calculations of the energies and oscillator strengths of inner-shell lines from Fe XIV, Fe XV, and Fe XVI. These are crucial ions since they are dominant at inflection points in the gas thermal stability curve, and UTA excitation followed by autoionization is an important ionization mechanism for these species. We incorporate these, and data reported in previous papers, into the plasma simulation code Cloudy. This updated physics is subsequently employed to reconsider the …

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The Nature Of The H2-Emitting Gas In The Crab Nebula, C. T. Richardson, J. A. Baldwin, Gary J. Ferland, E. D. Loh, C. A. Kuehn, A. C. Fabian, Philippe Salomé Apr 2013

The Nature Of The H2-Emitting Gas In The Crab Nebula, C. T. Richardson, J. A. Baldwin, Gary J. Ferland, E. D. Loh, C. A. Kuehn, A. C. Fabian, Philippe Salomé

Physics and Astronomy Faculty Publications

Understanding how molecules and dust might have formed within a rapidly expanding young supernova remnant is important because of the obvious application to vigorous supernova activity at very high redshift. In previous papers, we have mapped the Crab nebula (the Crab) in a rotovibrational H2emission line, and then measured the molecular excitation temperature for a few of the brighter H2-emitting knots that we have found to be scattered throughout the Crab's filaments. We found that H2 emission is often quite strong, correlates with optical low-ionization emission lines and has a surprisingly high excitation temperature. Here, …

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Radiative Cooling In Collisionally Ionized And Photoionized Plasmas, Matt Lykins, Gary J. Ferland, Ryan L. Porter, Peter A. M. Van Hoof, R. J. R. Williams, Orly Gnat Mar 2013

Radiative Cooling In Collisionally Ionized And Photoionized Plasmas, Matt Lykins, Gary J. Ferland, Ryan L. Porter, Peter A. M. Van Hoof, R. J. R. Williams, Orly Gnat

Physics and Astronomy Faculty Publications

We discuss recent improvements in the calculation of the radiative cooling in both collisionally ionized and photoionized plasmas. We are extending the spectral simulation code CLOUDY so that as much as possible of the underlying atomic data are taken from external data bases, some created by others and some developed by the CLOUDY team. This paper focuses on recent changes in the treatment of many stages of ionization of iron, and discusses its extensions to other elements. The H- and He-like ions are treated in the isoelectronic approach described previously. Fe II is a special case treated with a large …

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Studies Of Ngc 6720 With Calibrated Hst/Wfc3 Emission-Line Filter Images. Ii. Physical Conditions, C. R. O'Dell, Gary J. Ferland, W. J. Henney, M. Peimbert Feb 2013

Studies Of Ngc 6720 With Calibrated Hst/Wfc3 Emission-Line Filter Images. Ii. Physical Conditions, C. R. O'Dell, Gary J. Ferland, W. J. Henney, M. Peimbert

Physics and Astronomy Faculty Publications

We have performed a detailed analysis of the electron temperature and density in the Ring Nebula using the calibrated Hubble Space Telescope WFC3 images described in the preceding paper. The electron temperature (Te) determined from [NII] and [O III] rises slightly and monotonically toward the central star. The observed equivalent width (EW) in the central region indicates that Te rises as high as 13,000 K. In contrast, the low EWs in the outer regions are largely due to scattered diffuse Galactic radiation by dust. The images allowed determination of unprecedented small-scale variations in Te. …

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Studies Of Ngc 6720 With Calibrated Hst/Wfc3 Emission-Line Filter Images. I. Structure And Evolution, C. R. O'Dell, Gary J. Ferland, W. J. Henney, M. Peimbert Feb 2013

Studies Of Ngc 6720 With Calibrated Hst/Wfc3 Emission-Line Filter Images. I. Structure And Evolution, C. R. O'Dell, Gary J. Ferland, W. J. Henney, M. Peimbert

Physics and Astronomy Faculty Publications

We have performed a detailed analysis of the Ring Nebula (NGC 6720) using Hubble Space Telescope WFC3 images and derived a new three-dimensional model. Existing high spectral resolution spectra played an important supplementary role in our modeling. It is shown that the Main Ring of the nebula is an ionization-bounded irregular non-symmetric disk with a central cavity and perpendicular extended lobes pointed almost toward the observer. The faint outer halos are determined to be fossil radiation, i.e., radiation from gas ionized in an earlier stage of the nebula when it was not ionization bounded. The narrowband WFC3 filters that isolate …

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Equilibrating Temperaturelike Variables In Jammed Granular Subsystems, James G. Puckett, Karen E. Daniels Jan 2013

Equilibrating Temperaturelike Variables In Jammed Granular Subsystems, James G. Puckett, Karen E. Daniels

Physics and Astronomy Faculty Publications

Although jammed granular systems are athermal, several thermodynamiclike descriptions have been proposed which make quantitative predictions about the distribution of volume and stress within a system and provide a corresponding temperaturelike variable. We perform experiments with an apparatus designed to generate a large number of independent, jammed, two-dimensional configurations. Each configuration consists of a single layer of photoelastic disks supported by a gentle layer of air. New configurations are generated by cyclically dilating, mixing, and then recompacting the system through a series of boundary displacements. Within each configuration, a bath of particles surrounds a smaller subsystem of particles with a …

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Calculated Vibrational Properties Of Ubisemiquinones, Hari P. Lamichhane, Gary Hastings Jan 2013

Calculated Vibrational Properties Of Ubisemiquinones, Hari P. Lamichhane, Gary Hastings

Physics and Astronomy Faculty Publications

Density functional theory has been used to calculate harmonic normal mode vibrational frequencies for unlabeled and isotopelabeled ubisemiquinones in both the gas phase and in several solvents. It is shown that four methoxy group conformations are likely to be present in solution at room temperature. Boltzmann weighted infrared and Raman spectra for the four conformers were calculated, and composite spectra that are the sum of the Boltzmann weighted spectra were produced. These composite spectra were compared to experimental FTIR and resonance Raman spectra, and it is shown that the calculated band frequencies, relative band intensities, and 13C and 18 …

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