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  • Spacecraft Design, Testing and Performance  (41)
  • Earth Resources and Remote Sensing  (29)
  • Astrophysics  (27)
  • 2015-2019  (25)
  • 2010-2014  (30)
  • 2000-2004  (42)
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  • 1
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    Vorticity Transport and Wave Emission In A Protoplanetary Disk (2002)
    In:  Other Sources
    Details
    Publication Date: 2019-07-18
    Description: Higher order numerical algorithms (4th order in time, 3rd order in space) are applied to the Euler equations and are used to examine vorticity transport and wave motion in a non-self gravitating, initially isentropic Keplerian disk. In this talk we will examine the response of the disk to an isolated vortex with a circulation about equal to the rotation rate of Jupiter. The vortex is located on the 4 AU circle and the nebula is simulated from 1 to 24 AU. We show that the vortex emits pressure-supported density and Rossby-type wave packets before it decays within a few orbits. The acoustic density waves evolve into weak (non entropy preserving) shock waves that propagate over the entire disk. The Rossby waves remain in the vicinity of the initial vortex disturbance, but are rapidly damped. Temporal frequencies and spatial wavenumbers are derived from the nonlinear simulation data and correlated with analytical dispersion relations from the linearized Euler and energy equations.
    Keywords: Astrophysics
    Type: AGU Meeting; May 28, 2002 - May 31, 2002; Washington, DC; United States
    Format: text
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  • 2
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    Ten Years of MISR Observations from Terra: Looking Back, Ahead, and in Between (2010)
    In:  Other Sources
    Details
    Publication Date: 2019-07-13
    Description: The Multi-angle Imaging SpectroRadiometer (MISR) instrument has been collecting global Earth data from NASA's Terra satellite since February 2000. With its nine along-track view angles, four visible/near-infrared spectral bands, intrinsic spatial resolution of 275 m, and stable radiometric and geometric calibration, no instrument that combines MISR's attributes has previously flown in space. The more than 10-year (and counting) MISR data record provides unprecedented opportunities for characterizing long-term trends in aerosol, cloud, and surface properties, and includes 3-D textural information conventionally thought to be accessible only to active sensors.
    Keywords: Earth Resources and Remote Sensing
    Type: IEEE Geoscience and Remote Sensing Society Conference; Jul 25, 2010 - Jul 30, 2010; Honolulu, HI; United States
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  • 3
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    Constraints and tensions in testing general relativity from Planck and CFHTLenS data including intrinsic alignment systematics (2015)
    American Physical Society (APS)
    Details
    Publication Date: 2015-07-08
    Description: Author(s): Jason N. Dossett, Mustapha Ishak, David Parkinson, and Tamara M. Davis We present constraints on testing general relativity (GR) at cosmological scales using recent data sets and assess the impact of galaxy intrinsic alignment in the CFHTLenS lensing data on those constraints. We consider data from Planck temperature anisotropies, the galaxy power spectrum from the Wig… [Phys. Rev. D 92, 023003] Published Tue Jul 07, 2015
    Keywords: Astrophysics
    Print ISSN: 0556-2821
    Electronic ISSN: 1089-4918
    Topics: Physics
    Published by American Physical Society (APS)
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    PAPER CURRENT
  • 4
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    Chandra Observations of Point Sources in Abell 2255 (2003)
    In:  CASI
    Details
    Publication Date: 2013-08-29
    Description: In our search for "hidden" AGN we present results from a Chandra observation of the nearby cluster Abell 2255. Eight cluster galaxies are associated with point-like X-ray emission, and we classify these galaxies based on their X-ray, radio, and optical properties. At least three are associated with active galactic nuclei (AGN) with no optical signatures of nuclear activity, with a further two being potential AGN. Of the potential AGN, one corresponds to a galaxy with a post-starburst optical spectrum. The remaining three X-ray detected cluster galaxies consist of two starbursts and an elliptical with luminous hot gas. Of the eight cluster galaxies five are associated with luminous (massive) galaxies and the remaining three lie in much lower luminosity systems. We note that the use of X-ray to optical flux ratios for classification of X-ray sources is often misleading, and strengthen the claim that the fraction of cluster galaxies hosting an AGN based on optical data is significantly lower than the fraction based on X-ray and radio data.
    Keywords: Astrophysics
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  • 5
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    XMM Observations of an IXO in NGC 2276 (2003)
    In:  CASI
    Details
    Publication Date: 2013-08-29
    Description: We present the results from a approx. 53 ksec XMM observation of NGC 2276. This galaxy has an unusual optical morphology with the disk of this spiral appearing to be truncated along the western edge. This XMM observation shows that the X-ray source at the western edge is a bright Intermediate X-ray Object (IXO). Its spectrum is well fit by a multi-color disk blackbody model used to fit optically thick standard accretion disks around black holes. The luminosity derived for this IXO is 1.1 x 10(exp 41) erg/s in the 0.5 - 10 keV band making it one of the most luminous discovered to date. The large source luminosity implies a large mass black hole if the source is radiating at the Eddington rate. On the other hand, the inner disk temperature determined here is too high for such a massive object given the standard accretion disk model. In addition to the IXO we find that the nuclear source in this galaxy has dimmed by at least a factor of several thousand in the eight years since the ROSAT HRI observations.
    Keywords: Astrophysics
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  • 6
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    Hyperspectral sensor systems data sources for enhanced analysis (2003)
    In:  Other Sources
    Details
    Publication Date: 2018-06-08
    Keywords: Earth Resources and Remote Sensing
    Type: International Geoscience and Remote Sensing Symposium (IGARSS); Toulouse; France
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  • 7
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    Tracking the moving photocenters of active galaxies: binary black holes, accretion disks, and relativistic jets (2003)
    In:  Other Sources
    Details
    Publication Date: 2018-06-11
    Description: SIM Science Team Meeting #10 December 16-18, 2003 Pasadena, California, USA.
    Keywords: Astrophysics
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  • 8
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    Chandra Observations of Point Sources in A2255 (2003)
    In:  Other Sources
    Details
    Publication Date: 2018-06-06
    Description: In our search for "hidden" active galactic nuclei (AGNs), we present results from a Chandra observation of the nearby cluster A2255. Eight cluster galaxies are associated with pointlike X-ray emission, and we classify these galaxies based on their X-ray, radio, and optical properties. At least three are associated with AGNs with no optical signatures of nuclear activity, with a further two being potential AGNs. Of the potential AGNs, one corresponds to a galaxy with a post-starburst optical spectrum. The remaining three X-ray-detected cluster galaxies consist of two starbursts and an elliptical with luminous hot gas. Of the eight cluster galaxies, five are associated with luminous (massive) galaxies, and the remaining three lie in much lower luminosity systems. We note that the use of X-ray-to-optical flux ratios for classification of X-ray sources is often misleading and strengthens the claim that the fraction of cluster galaxies hosting an AGN based on optical data is significantly lower than the fraction based on X-ray and radio data.
    Keywords: Astrophysics
    Type: Astrophysical Journal; Volume 597; 202-209
    Format: text
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  • 9
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    Representation of the Geosynchronous Plasma Environment for Spacecraft Charging Calculations (2004)
    In:  CASI
    Details
    Publication Date: 2018-06-12
    Description: Historically, our ability to predict and postdict surface charging has suffered from both a lack of reliable secondary emission and backscattered electron yields and poor characterization of the plasma environment. One difficulty lies in the common practice of fitting the plasma data to a Maxwellian or Double Maxwellian distribution function, which may not represent the data well for charging purposes. For 13 years Los Alamos National Laboratory (LANL) has been accumulating measurements of electron and proton spectra from Magnetospheric Plasma Analyzer (MPA) instruments aboard a series of geosynchronous satellites. These data provide both a plasma characterization and the potential of the instrument ground. We use electron and ion flux spectra measured by the LANL MPA to examine how the use of different spectral representations of the charged particle environment in computations of spacecraft potentials during magnetospheric substorms affects the accuracy of the results. We calculate the spacecraft potential using both the measured fluxes and several different fits to these fluxes. These flux measurements and fits have been corrected for the difference between the measured and calculated potential. The potentials computed using the measured fluxes, the best available material properties of graphite carbon, and a secondary electron escape fraction of 81%, are within a factor of three of the measured potential for nearly all the data. Using a Kappa fit to the electron distribution function and a Maxwellian fit to the ion distribution function gives agreement similar to the calculations using the actual data. Alternative spectral representations, including Maxwellian and double Maxwellian for both species, lead to less satisfactory agreement between predicted and measured potentials.
    Keywords: Spacecraft Design, Testing and Performance
    Type: 8th Spacecraft Charging Technology Conference; NASA/CP-2004-213091
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  • 10
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    NASCAP-2K: An Overview (2004)
    In:  CASI
    Details
    Publication Date: 2018-06-12
    Description: Nascap-2k is the modern replacement for the older 3-D charging codes NASCAP/GEO, NASCAP/LEO, POLAR, and DynaPAC. Built on the DynaPAC kernel and incorporating surface charging, environment and space potential models from the older codes, Nascap-2k performs charging calculations for a wide variety of space environments under control of a unified graphical interface. In this paper we illustrate the use of Nascap-2k for spacecraft charging calculations. We touch on some of the unique physical and mathematical models on which the code is based. Examples/demos include the use of Object Toolkit, charging calculations in geosynchronous substorm, solar wind, low earth orbit, and auroral environments, and display and analysis of surface potentials, space potentials and particle trajectories.
    Keywords: Spacecraft Design, Testing and Performance
    Type: 8th Spacecraft Charging Technology Conference; NASA/CP-2004-213091
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