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Articles 1 - 24 of 24
Full-Text Articles in Physics
Displacement Of The Earth's Bow Shock And Magnetopause Due To An Impinging Interplanetary Shock Wave, William A. Olson
Displacement Of The Earth's Bow Shock And Magnetopause Due To An Impinging Interplanetary Shock Wave, William A. Olson
Theses and Dissertations
Interplanetary shock waves (ISWs) propagating through the solar wind can collide with the earth's bow shock, resulting in a series of new shocks, contact discontinuities, and rarefaction waves which interact to effectively move the bow shock and magnetopause toward the earth. A one dimensional MacCormack predictor corrector algorithm with Flux Corrected Transport (FCT) was developed to model the ISW bow shock and magnetopause interactions, and to numerically predict their propagation speeds after collision. Analytic relationships for the Mach numbers and propagation speeds of the generated shock waves and contact discontinuities were used to validate the model and to compare numerical …
Unfolding Of The Period-Two Bifurcation In A Fiber Laser Pumped With Two Modulation Tones, Scott Glasgow, T. C. Newell, A. Gavrielides, V. Kovanis, D. Sukow, T. Erneux
Unfolding Of The Period-Two Bifurcation In A Fiber Laser Pumped With Two Modulation Tones, Scott Glasgow, T. C. Newell, A. Gavrielides, V. Kovanis, D. Sukow, T. Erneux
Faculty Publications
The effect of a small second frequency component on a pump modulated neodymium fiber laser is investigated experimentally and theoretically. This term, whose frequency is exactly half the primary driver, incites an unfolding of the attractor. It breaks the period two pitchfork bifurcation and splits the period one orbit. The modification of the bifurcation diagram is studied analytically by employing a map derived from the class B laser rate equations. We determine specific conditions and scaling laws for this phenomenon. Our analytical predictions are in good agreement with recorded experimental data.
Upper Limits To The Outflow Of Ions At Mars: Implications For Atmospheric Evolution, Jane L. Fox
Upper Limits To The Outflow Of Ions At Mars: Implications For Atmospheric Evolution, Jane L. Fox
Physics Faculty Publications
Escape of ions is potentially important for the evolution of volatiles on Mars, but the mechanisms and rates of ion escape processes are not fully understood. Instruments on the Russian Phobos 2 orbiter have, however, measured fluxes of heavy ions apparently of ionospheric origin in the optical shadow of Mars. These ions are assumed to arise from escape processes induced by the interaction of the solar wind with the ionosphere. We determine here upper limits to the ion loss rates by imposing upward flux boundary conditions on models of the low and high solar activity Mars ionosphere. The maximum fluxes …
Do The Broad Emission Line Clouds See The Same Continuum That We See?, Kirk Korista, Gary J. Ferland, Jack Baldwin
Do The Broad Emission Line Clouds See The Same Continuum That We See?, Kirk Korista, Gary J. Ferland, Jack Baldwin
Physics and Astronomy Faculty Publications
Recent observations of quasars, Mrk 335 and the HST quasar composite spectrum, have indicated that many quasars have remarkably soft ionizing continua (f ∝ ~ ν-2, 13.6-100 eV). We point out that the number of photons with hν > 54.4 eV is insufficient to create the observed strengths of the He II emission lines. While the numbers of photons which energize C IV λ1549 and O VI λ1034 are sufficient, even the most efficiently emitting clouds for these two lines must each cover at least 20%-40% of the source. If the typical quasar ionizing continuum is indeed this …
System For Electron Paramagnetic Resonance Measurements At High Pressure And Low Temperature, Ke Huang, Daniel L. Decker, H. Mark Nelson, J. Dean Barnett
System For Electron Paramagnetic Resonance Measurements At High Pressure And Low Temperature, Ke Huang, Daniel L. Decker, H. Mark Nelson, J. Dean Barnett
Faculty Publications
Major improvements have been made on the sensitive high pressure electron paramagnetic resonance (EPR) system developed previously in 1978 at this laboratory. These changes allow low temperature measurements and provide a more stable signal. The high pressure EPR cell is placed inside a vacuum chamber to provide thermal isolation, so that the system may be cooled by a closed cycle refrigerator to temperatures between 45 and 60 K, depending on the energy input to the modulation coil. The combination of high pressure and low temperature greatly expands the thermodynamic range over which EPR measurements can be made. An improved and …
Locally Optimally Emitting Clouds And The Narrow Emission Lines In Seyfert Galaxies, Jason W. Ferguson, Kirk T. Korista, Jack A. Baldwin, Gary J. Ferland
Locally Optimally Emitting Clouds And The Narrow Emission Lines In Seyfert Galaxies, Jason W. Ferguson, Kirk T. Korista, Jack A. Baldwin, Gary J. Ferland
Physics and Astronomy Faculty Publications
The narrow emission line spectra of active galactic nuclei are not accurately described by simple photoionization models of single clouds. Recent Hubble Space Telescope images of Seyfert 2 galaxies show that these objects are rich with ionization cones, knots, filaments, and strands of ionized gas. Here we extend to the narrow-line region the ``locally optimally emitting cloud'' (LOC) model, in which the observed spectra are predominantly determined by powerful selection effects. We present a large grid of photoionization models covering a wide range of physical conditions and show the optimal conditions for producing many of the strongest emission lines. We …
Inclination Effects In Spiral Galaxy Gravitational Lensing, Ariyeh Maller, Ricardo Flores, Joel Primack
Inclination Effects In Spiral Galaxy Gravitational Lensing, Ariyeh Maller, Ricardo Flores, Joel Primack
Physics Faculty Works
Spheroidal components of spiral galaxies have been considered to be the only dynamically important component in gravitational lensing studies to date. Here we point out that including the disk component can have a significant effect, which depends on the disk inclination, on a variety of lensing properties that are relevant to present studies and future surveys. As an example, we look at the multiple image system B1600+434, which was recently identified as being lensed by a spiral galaxy. We find that by including the disk component, one can understand the fairly large image separation as being caused by the inclination …
Hydrocarbon Ions In The Ionosphere Of Titan, Jane L. Fox, Roger V. Yelle
Hydrocarbon Ions In The Ionosphere Of Titan, Jane L. Fox, Roger V. Yelle
Physics Faculty Publications
We have constructed a new model of the ionosphere of Titan that includes 67 species and 626 reactions. Although N2+ is the major ion produced over most of the ionosphere, the ionization flows to ions whose parent neutrals have lower ionization potentials and to ions formed from species with large proton affinities. In contrast to other models, which have predicted that HCNH+ should be the major ion, our calculations suggest that the major ions at and below the ion peak are hydrocarbon ions, and H, C, and N-containing ions. Our predicted peak electron density for a solar …
Charge Transfer Between Neutral Atoms And Highly Ionized Species: Implications For Iso Observations, Gary J. Ferland, K. T. Korista, D. A. Verner, A. Dalgarno
Charge Transfer Between Neutral Atoms And Highly Ionized Species: Implications For Iso Observations, Gary J. Ferland, K. T. Korista, D. A. Verner, A. Dalgarno
Physics and Astronomy Faculty Publications
We estimate rate coefficients for charge transfer between neutral hydrogen and helium and moderately to highly ionized heavy elements. Although charge transfer does not have much influence on hot collisionally ionized plasmas, its effects on photoionized plasmas can be profound. We present several photoionization models that illustrate the significant effect of charge transfer on the far-infrared lines detected by ISO.
Physical Conditions Of The Coronal Line Region In Seyfert Galaxies, Jason W. Ferguson, Kirk Korista, Gary J. Ferland
Physical Conditions Of The Coronal Line Region In Seyfert Galaxies, Jason W. Ferguson, Kirk Korista, Gary J. Ferland
Physics and Astronomy Faculty Publications
The launch of the Infrared Space Observatory and new atomic data have opened a window for the study of high-ionization gas in active galactic nuclei (AGNs). We present the results of a large number of photoionization simulations of the "coronal line" region in AGNs, employing new atomic data from the Opacity and Iron Projects. Our grid of line emission spans 8 orders of magnitude in gas density and 14 orders of magnitude in ionizing flux in an effort to identify the optimal conditions in which these lines form. We show that coronal lines form at distances from just outside the …
Accurate Hydrogen Spectral Simulations With A Compact Model Atom, Jason W. Ferguson, Gary J. Ferland
Accurate Hydrogen Spectral Simulations With A Compact Model Atom, Jason W. Ferguson, Gary J. Ferland
Physics and Astronomy Faculty Publications
Many large-scale numerical simulations of astrophysical plasmas must also reproduce the hydrogen ionization and the resulting emission spectrum, in some cases quite accurately. We describe a compact model hydrogen atom that can be readily incorporated into such simulations. It reproduces the recombination efficiency and line spectrum predicted by much larger calculations for a very broad range of densities and temperatures. Uncertainties in hydrogen collision data are the largest source of differences between our compact atom and predictions of more extensive calculations and underscore the need for accurate atomic data.
Grains In Ionized Nebulae. Ii. Heavy-Element Depletion, J. B. Kingdon, Gary J. Ferland
Grains In Ionized Nebulae. Ii. Heavy-Element Depletion, J. B. Kingdon, Gary J. Ferland
Physics and Astronomy Faculty Publications
The presence of grains in gaseous nebulae can have significant effects on the thermal balance and radiative line transfer in these objects. The depletion of condensable elements onto grains provides evidence that dust exists in the ionized regions of nebulae. In this paper, we consider the elements Sc, Ti, V, and Cr, all of which are strongly depleted in the general interstellar medium. We construct simple three-level atoms for several ions of these elements, and incorporate them into our photoionization code CLOUDY. For both a model planetary nebula and a model H II region, we find that several lines of …
An Atlas Of Computed Equivalent Widths Of Quasar Broad Emission Lines, Kirk Korista, Jack Baldwin, Gary J. Ferland, Dima Verner
An Atlas Of Computed Equivalent Widths Of Quasar Broad Emission Lines, Kirk Korista, Jack Baldwin, Gary J. Ferland, Dima Verner
Physics and Astronomy Faculty Publications
We present graphically the results of several thousand photoionization calculations of broad emission-line clouds in quasars, spanning 7 orders of magnitude in hydrogen ionizing flux and particle density. The equivalent widths of 42 quasar emission lines are presented as contours in the particle density-ionizing flux plane for a typical incident continuum shape, solar chemical abundances, and cloud column density of N(H) = 1023 cm-2. Results are similarly given for a small subset of emission lines for two other column densities (1022 and 1024 cm-2), five other incident continuum shapes, and a gas …
On Protostellar Disks In Herbig Ae/Be Stars, Anatoly Miroshnichenko, Željko Ivezić, Moshe Elitzur
On Protostellar Disks In Herbig Ae/Be Stars, Anatoly Miroshnichenko, Željko Ivezić, Moshe Elitzur
Physics and Astronomy Faculty Publications
The spectral shape of IR emission from Herbig Ae/Be stars has been invoked as evidence for accretion disks around high-mass protostars. Instead, we present here models based on spherical envelopes with an r-1.5 dust density profile that successfully explain the observed spectral shapes. The spectral energy distributions of eight primary candidates for protostellar disks are fitted in detail for all wavelengths available, from visual to far-IR. The only envelope property adjusted in individual sources is the overall visual optical depth, and it ranges from 0.3 to 3. In each case, our models properly reproduce the data for IR excess, …
[Fe Iv] In The Orion Nebula, R. H. Rubin, R. J. Dufour, Gary J. Ferland, P. G. Martin, C. R. O'Dell, J. A. Baldwin, J. J. Hester, D. K. Walter, Z. Wen
[Fe Iv] In The Orion Nebula, R. H. Rubin, R. J. Dufour, Gary J. Ferland, P. G. Martin, C. R. O'Dell, J. A. Baldwin, J. J. Hester, D. K. Walter, Z. Wen
Physics and Astronomy Faculty Publications
Using the Goddard High-Resolution Spectrograph on the Hubble Space Telescope, we measured the flux of [Fe IV] (3d5 4P5/2 --> 3d5 6S5/2) λvac = 2836.56 Å in the Orion Nebula, the first detection of an [Fe IV] line in an H II region. A useful upper limit is set on the sum of fluxes of [Fe IV] (3d5 4D5/2, 3/2 --> 3d5 6S5/2) λvac = 2568.4, 2568.2 Å. By comparing these observations with predicted fluxes from simply ``retrofitting'' our two previous photoionization models, …
Three-Dimensional Direct Simulation Monte Carlo Method For Slider Air Bearings, Alejandro Garcia, W. Huang, D. B. Bogy
Three-Dimensional Direct Simulation Monte Carlo Method For Slider Air Bearings, Alejandro Garcia, W. Huang, D. B. Bogy
Alejandro Garcia
The direct simulation Monte Carlo (DSMC) method is used to solve the three-dimensional nano-scale gas film lubrication problem between a gas bearing slider and a rotating disk, and this solution is compared to the numerical solution of the compressible Reynolds equations with the slip flow correction based on the linearized Boltzmann equation as presented by Fukui and Kaneko [molecular gas film lubrication (MGL) method] [ASME J. Tribol. 110, 253 (1988)]. In the DSMC method, hundreds of thousands of simulated particles are used and their three velocity components and three spatial coordinates are calculated and recorded by using a hard-sphere collision …
Anomalous Flow Profile Due To The Curvature Effect On Slip Length, Alejandro Garcia, K. Tibbs, F. Baras
Anomalous Flow Profile Due To The Curvature Effect On Slip Length, Alejandro Garcia, K. Tibbs, F. Baras
Alejandro Garcia
No abstract provided.
Anomalous Flow Profile Due To The Curvature Effect On Slip Length, Alejandro Garcia, K. Tibbs, F. Baras
Anomalous Flow Profile Due To The Curvature Effect On Slip Length, Alejandro Garcia, K. Tibbs, F. Baras
Faculty Publications
No abstract provided.
Three-Dimensional Direct Simulation Monte Carlo Method For Slider Air Bearings, Alejandro Garcia, W. Huang, D. B. Bogy
Three-Dimensional Direct Simulation Monte Carlo Method For Slider Air Bearings, Alejandro Garcia, W. Huang, D. B. Bogy
Faculty Publications
The direct simulation Monte Carlo (DSMC) method is used to solve the three-dimensional nano-scale gas film lubrication problem between a gas bearing slider and a rotating disk, and this solution is compared to the numerical solution of the compressible Reynolds equations with the slip flow correction based on the linearized Boltzmann equation as presented by Fukui and Kaneko [molecular gas film lubrication (MGL) method] [ASME J. Tribol. 110, 253 (1988)]. In the DSMC method, hundreds of thousands of simulated particles are used and their three velocity components and three spatial coordinates are calculated and recorded by using a hard-sphere collision …
Constraints On The Production Of Ultra–High-Energy Cosmic Rays By Isolated Neutron Stars, Aparna Venkatesan, M Coleman Miller, Angela V. Olinto
Constraints On The Production Of Ultra–High-Energy Cosmic Rays By Isolated Neutron Stars, Aparna Venkatesan, M Coleman Miller, Angela V. Olinto
Physics and Astronomy
The energetics, spectrum, and composition of cosmic rays with energies below ~1015 eV are fairly well explained by models involving supernova shocks. In contrast, no widely accepted theory exists for the origin of ultra-high-energy cosmic rays (UHECRs), which have energies above 1015 eV. Instead of proposing a specific model, here we place strong constraints on any model of UHECRs involving isolated neutron stars (no companions). We consider the total power requirements and show that the only viable power source associated with isolated neutron stars is rotation. Mechanisms based on accretion from the interstellar medium fall short of the …
Astrophysical Bounds On Global Strings, Shane L. Larson, William A. Hiscock
Astrophysical Bounds On Global Strings, Shane L. Larson, William A. Hiscock
All Physics Faculty Publications
Global topological defects produce nonzero stress energy throughout spacetime, and as a result can have observable gravitational influence on surrounding matter. Gravitational effects of global strings are used to place bounds on their cosmic abundance. The minimum separation between global strings is estimated by considering the defects' contribution to the cosmological energy density. More rigorous constraints on the abundance of global strings are constructed by examining the tidal forces such defects will have on observable astrophysical systems. The small number of observed tidally disrupted systems indicates there can be very few of these objects in the observable Universe.
Semiclassical Effects In Black Hole Interiors, William A. Hiscock, Shane L. Larson, Paul R. Anderson
Semiclassical Effects In Black Hole Interiors, William A. Hiscock, Shane L. Larson, Paul R. Anderson
All Physics Faculty Publications
First-order semiclassical perturbations to the Schwarzschild black hole geometry are studied within the black hole interior. The source of the perturbations is taken to be the vacuum stress-energy of quantized scalar, spinor, and vector fields, evaluated using analytic approximations developed by Page and others (for massless fields) and the DeWitt-Schwinger approximation (for massive fields). Viewing the interior as an anisotropic collapsing cosmology, we find that minimally or conformally coupled scalar fields, and spinor fields, decrease the anisotropy as the singularity is approached, while vector fields increase the anisotropy. In addition, we find that for massless fields of all spins, the …
Large-Amplitude Solitary Waves In Finite Temperature Dusty Plasma, R. Roychoudhury, S. Mukherjee
Large-Amplitude Solitary Waves In Finite Temperature Dusty Plasma, R. Roychoudhury, S. Mukherjee
Physics and Astronomy Faculty Publications and Presentations
Large-amplitude solitary waves in dusty plasma are investigated, taking into account the dusty particle temperature. It is shown that finite dusty temperature restricts the region for the existence of solitary waves.
Damped Diocotron Quasi-Modes Of Non-Neutral Plasmas And Inviscid Fluids, S. Neil Rasband, Ross L. Spencer
Damped Diocotron Quasi-Modes Of Non-Neutral Plasmas And Inviscid Fluids, S. Neil Rasband, Ross L. Spencer
Faculty Publications
Computations of damped diocotron oscillations (quasi-modes) are described for non-neutral plasmas and inviscid fluids. The numerical method implements a suggestion made by Briggs, Daugherty, and Levy some 25 years ago [Phys. Fluids 13, 421 (1970)] to push the branch line that forms the continuum into the complex w-plane by solving the mode equation in the complex r-plane. For the special case of power-law density profiles the calculation finds the same quasi-mode frequencies found recently by Corngold [Phys. Plasmas 2, 620 (1995)]. It is found that the feature of the continuum eigenfunctions which indicates the presence of a nearby quasi-mode is …