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  • 1
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    Evidence for a 17d periodicity from Cyg X-3 (1976)
    In:  CASI
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    Publikationsdatum: 2006-04-18
    Beschreibung: Data which indicate a periodicity of 17d from Cyg X-3 are reviewed. The data are taken from the Ariel 5 satellite All-Sky Monitor and the Sky Survey Experiment.
    Schlagwort(e): ASTROPHYSICS
    Materialart: X-ray Binaries; p 245-253
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  • 2
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    Two-step method for evolving nonlinear acoustic systems to a steady state (1992)
    In:  Other Sources
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    Publikationsdatum: 2011-08-24
    Schlagwort(e): ACOUSTICS
    Materialart: AIAA Journal (ISSN 0001-1452); 30; 7, Ju; 1724-173
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  • 3
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    Numerical computation of steady-state acoustic disturbances in flow (1992)
    In:  Other Sources
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    Publikationsdatum: 2011-08-24
    Beschreibung: Two time domain methods for computing two dimensional steady-state acoustic disturbances propagating through internal subsonic viscous flow fields in the presence of variable area are investigated. The first method solves the Navier-Stokes equations for the combined steady and acoustic field together and subtracts the steady flow to obtain the acoustic field. The second method solves a system of perturbation equations to obtain the acoustic disturbances, making use of a separate steady flow computation as input to the system. In each case the periodic steady-state acoustic fluctuations are obtained numerically on a supercomputer using a second order unsplit explicit MacCormack predictor-corrector method. Results show that the first method is not very effective for computing acoustic disturbances of even moderate amplitude. It appears that more accurate steady flow algorithms are required for this method to succeed. On the other hand, linear and nonlinear acoustic disturbances extracted from the perturbation approach are shown to exhibit expected behavior for the problems considered. It is also found that inflow boundary conditions for an equivalent uniform duct can be successfully applied to a nonuniform duct to obtain steady-state acoustic disturbances.
    Schlagwort(e): ACOUSTICS
    Materialart: In: DGLR(AIAA Aeroacoustics Conference, 14th, Aachen, Germany, May 11-14, 1992, Proceedings. Vol. 1 (A93-19126 05-71); p. 428-437.
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  • 4
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    Multiple, narrow lines in the spectrum of an astrophysical maser in a velocity gradient (1988)
    In:  Other Sources
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    Publikationsdatum: 2011-08-19
    Beschreibung: The emergent radiation spectrum is obtained for an astrophysical maser in the presence of a velocity gradient without making the 'large velocity gradient' (or 'Sobolev') approximation on which previous calculations have been based. Even in the presence of a velocity gradient, the spectral lines of saturated masers are found to remain narrow. More surprisingly, however, the spectrum breaks up into multiple narrow lines. Hence, individual features in the observed spectra of astrophysical masers need not always be interpreted as separate clumps of gas. Specifically, this result may be related to the occurrence of multiple lines from the same location in the H2O masers in star-forming regions and to be the occurrence of numerous, narrow features recently detected in the spectra of circumstellar OH masers.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Astrophysical Journal, Part 2 - Letters (ISSN 0004-637X); 335; L19-L22
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  • 5
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    Evidence for a 17-d periodicity from Cyg X-3 (1976)
    In:  Other Sources
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    Publikationsdatum: 2011-08-16
    Beschreibung: Data are presented from the Ariel-V All-Sky Monitor which indicate a 17-day periodicity of the X-ray spectra from Cyg X-3 (3U2030+40). The data are consistent with data from the Ariel V Sky Survey Experiment. Assuming that the high intensity state of Cyg X-3 is well fitted by a structureless black body (Serlemitsos et al., 1975), and that the 17-day maxima correspond to increased electron scattering in the source, it is suggested that the 17-day effect is analogous to the 35-day variation in Her X-1. The possible explanation of this phenomenon as a result of the 17-day orbital period of the binary system containing Cyg X-3 is severely constrained by the stability of the well-known 4.8-hour variation.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Nature; 260; Apr. 15
    Format: text
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  • 6
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    Mechanisms for the circular polarization of astrophysical OH masers in star-forming regions and the inferred magnetic fields (1987)
    In:  CASI
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    Publikationsdatum: 2013-08-31
    Beschreibung: Results of further calculations to explore the cause for the circular polarization of astrophysical OH masers in regions of star formation are presented. Calculations are given for both the nonlinear, Zeeman overlap mechanishm, and the Cook mechanism. The previous result that magnetic field strengths of a few milligauss or greater are required, still survives.
    Schlagwort(e): ASTROPHYSICS
    Materialart: NASA, Washington Star Formation in Galaxies; p 87-90
    Format: application/pdf
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  • 7
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    Powering the superwind in NGC 253 (1993)
    In:  CASI
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    Publikationsdatum: 2013-08-31
    Beschreibung: NGC 253 is a prototypical moderate nuclear starburst galaxy. It is a barred SBc spiral galaxy at a distance of approximately 3 Mpc and can be studied on scales down to 15 pc in the optical and near IR. It is a bright IRAS source with a flux of 1000 Jy at 60 microns and a FIR luminosity of 3 x 10(exp 10) solar luminosity. It has a strong Br(gamma) emission line, a signature of ongoing massive star formation and deep CO absorption bands, which are indicative of the dominance of red supergiants in the near IR. It contains a population of compact radio sources, similar to those seen in M82. Optical spectra show that the nucleus is heavily reddened, with a Balmer decrement of approximately 30. NGC 253 possesses a 'superwind,' seen both in x-ray emission and in optical line emission. Nuclear ejection was first suggested to explain the kinematics of the nuclear region. We have obtained J, H, and K images of the entire galaxy at 1.3 arcsec/pixel (18 pc/pixel) using the superconducting quantum interference device (SQUID) on the KPNO 1.3 m. We have constructed a mosaic of 180 s exposures which traces the galaxy over much of its optical extent. The data were shifted, rotated, magnified, and calibrated following normal practice.
    Schlagwort(e): ASTROPHYSICS
    Materialart: NASA. Ames Research Center, The Evolution of Galaxies and Their Environment; p 383-385
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  • 8
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    An X-ray, optical and radio study of PKS 0745-191 - A massive cooling flow (1985)
    In:  Other Sources
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    Publikationsdatum: 2011-08-19
    Beschreibung: The X-ray source 3A 0745-191 is identified with intracluster gas surrounding the giant galaxy containing the radio source, PKS 0745-191, which lies at z = 0.1. The gas is cooling at the unprecedented rate of 1000 solar mass/yr. Optical line-emitting gas extends more than 10 kpc from the centre of the galaxy and corroborates the high mass-flow rate. The optical spectrum is similar to that of distant 3CR radio galaxies reported by others. It is concluded that formation of a giant galaxy was observed.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Royal Astronomical Society, Monthly Notices (ISSN 0035-8711); 216; 923-932
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  • 9
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    An acoustic evaluation of circumferentially segmented duct liners (1984)
    In:  Other Sources
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    Publikationsdatum: 2011-08-18
    Schlagwort(e): ACOUSTICS
    Materialart: AIAA Journal (ISSN 0001-1452); 22; 1229-123
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  • 10
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    Evaluation of several non-reflecting computational boundary conditions for duct acoustics (1994)
    In:  CASI
    Details
    Publikationsdatum: 2019-06-28
    Beschreibung: Several non-reflecting computational boundary conditions that meet certain criteria and have potential applications to duct acoustics are evaluated for their effectiveness. The same interior solution scheme, grid, and order of approximation are used to evaluate each condition. Sparse matrix solution techniques are applied to solve the matrix equation resulting from the discretization. Modal series solutions for the sound attenuation in an infinite duct are used to evaluate the accuracy of each non-reflecting boundary conditions. The evaluations are performed for sound propagation in a softwall duct, for several sources, sound frequencies, and duct lengths. It is shown that a recently developed nonlocal boundary condition leads to sound attenuation predictions considerably more accurate for short ducts. This leads to a substantial reduction in the number of grid points when compared to other non-reflecting conditions.
    Schlagwort(e): ACOUSTICS
    Materialart: NASA-TM-109118 , NAS 1.15:109118
    Format: application/pdf
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