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  • EARTH RESOURCES AND REMOTE SENSING  (1.274)
  • ASTROPHYSICS  (1.010)
  • 2010-2014
  • 1980-1984  (1.078)
  • 1975-1979  (1.206)
  • 1925-1929
  • 1983  (1.078)
  • 1977  (1.206)
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  • 2010-2014
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  • 1
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    Gamma rays, cosmic rays, and galactic structure (1977)
    In:  CASI
    Details
    Publikationsdatum: 2006-08-09
    Beschreibung: Observations of cosmic and gamma radiation by SAS-2 satellite are summarized and analyzed to determine processes responsible for producing observed galactic radiation. In addition to the production of gamma rays in discrete galactic objects such as pulsars, there are three main mechanisms by which high-energy (greater than 100 MeV) radiation is produced by high-energy interactions involving cosmic rays in interstellar space. These processes, which produce what may be called diffuse galactic gamma-rays, are: (1) the decay of pi mesons produced by interactions of cosmic ray nucleons with interstellar gas nuclei; (2) the bremsstrahlung radiation produced by cosmic ray electrons interacting in the Coulomb fields of nuclei of interstellar gas atoms; and (3) Compton interactions between cosmic ray electrons and low-energy photons in interstellar space.
    Schlagwort(e): ASTROPHYSICS
    Materialart: The Struct. and Content of the Galaxy and Galactic Gamma Rays; p 315-346
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  • 2
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    Gamma rays and large scale galactic structure (1977)
    In:  CASI
    Details
    Publikationsdatum: 2006-08-09
    Beschreibung: Gamma ray astronomy is now beginning to provide a new look at the galactic structure and the distribution of cosmic rays, both electrons and nucleons, within the galaxy. The observations are consistent with a galactic spiral-arm model in which the cosmic rays are linearly coupled to the interstellar gas on the scale of the spiral arms. The agreement between the predictions of the model and the observations for regions of the plane where both 21-cm and 2.6-mm CO surveys exist emphasizes the need to extend these observations to include the entire plane. Future gamma-ray observations with more sensitivity and better angular resolutions, combined with these radio surveys, should shed new light on the distribution of cosmic rays, the nature of the galaxy, and the location and intensity of the spiral arms.
    Schlagwort(e): ASTROPHYSICS
    Materialart: The Struct. and Content of the Galaxy and Galactic Gamma Rays; p 301-314
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  • 3
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    Galactic distribution of pulsars (1977)
    In:  CASI
    Details
    Publikationsdatum: 2006-08-09
    Beschreibung: The density distributions of pulsars in luminosity, period, Z-distance, and galactocentric distance were derived, using a uniform sample of pulsars detected during a 408-MHz pulsar survey at Jodrell Bank. There are indications of a fine-scale structure in the spatial distributions and evidence that there is a general correlation with other galactic populations and the overall spiral structure. The electron layer in our galaxy is shown to be wider than the pulsar layer and uniform on a large scale. The number of pulsars in the galaxy has been estimated and used to derive the pulsar birthrate.
    Schlagwort(e): ASTROPHYSICS
    Materialart: NASA. Goddard Space Flight Center The Struct. and Content of the Galaxy and Galactic Gamma Rays; p 265-282
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  • 4
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    Gamma rays and supernova explosions (1977)
    In:  CASI
    Details
    Publikationsdatum: 2006-08-09
    Beschreibung: Thermal radiation associated with the explosion of supernovae is investigated. High temperature is required to produce copious gamma radiation of this sort. It appears that type 11 supernovae do not release much of their energy as gamma ray continuum radiation.
    Schlagwort(e): ASTROPHYSICS
    Materialart: NASA. Goddard Space Flight Center The Struct. and Content of the Galaxy and Galactic Gamma Rays; p 257-264
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  • 5
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    Remarks on the overall distribution of hydrogen in the galactic disk (1977)
    In:  CASI
    Details
    Publikationsdatum: 2006-08-09
    Beschreibung: The degree of saturation characterizing low altitude emission observations of H(I) and the optical depth corrections to the derived column and volume densities are discussed. The amount of fine-scale velocity and spatial structure diluted by the instrumental limitations of the presently available surveys are described. The general problem of detailed mapping of H(I) in the galaxy is explored. Comparison is made between the distribution of H(I) and that of CO and several other galactic tracers. Atomic hydrogen is unique in its distribution, instead of being typical of many Population I constituents. As defined by atomic hydrogen, the galactic disk has a diameter fully twice as large as that defined by the ionized and molecular states of hydrogen, as well as by other molecules, supernova remnants, pulsars, gamma-radiation, synchroton radiation, and the youngest stars. It is also less confined to the galactic equator than most of the other constituents. The degree of small scale structure apparent in the molecular observations is much greater than that in the H(I) observations.
    Schlagwort(e): ASTROPHYSICS
    Materialart: NASA. Goddard Space Flight Center The Struct. and Content of the Galaxy and Galactic Gamma Rays; p 163-188
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  • 6
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    Gamma ray pulsars (1977)
    In:  CASI
    Details
    Publikationsdatum: 2006-08-09
    Beschreibung: Data from the SAS-2 high-energy gamma-ray experiment reveal the existence of four pulsars emitting photons above 35 MeV. An attempt is made to explain the gamma-ray emission from these pulsars in terms of an electron-photon cascade that develops in the magnetosphere of the pulsar. Although there is very little material above the surface of the pulsar, the very intense magnetic fields (10 to the 12th power gauss) correspond to many radiation lengths which cause electrons to emit photons by magnetic bremsstrahlung and which cause these photons to pair-produce. The cascade develops until the mean photon energy drops below the pair-production threshold which is in the gamma-ray range; at this stage, the photons break out from the source.
    Schlagwort(e): ASTROPHYSICS
    Materialart: NASA. Goddard Space Flight Center The Struct. and Content of the Galaxy and Galactic Gamma Rays; p 109-118
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  • 7
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    Radiation mechanisms and magnetospheric structure of pulsars (1977)
    In:  CASI
    Details
    Publikationsdatum: 2006-08-09
    Beschreibung: Considerations made in developing a model of pulsars are explored. Observational data seems to support the argument that pulsar magnetospheres may contain large masses of plasma. The cascade process resulting from pair creation enables one to interpret the X-ray emission from the Crab and Vela pulsars as synchrotron radiation. On the other hand, the optical radiation from the Crab pulsar is best understood as coherent curvature radiation. Radio emission is interpreted as curvature radiation produced by charge bunches moving along magnetic-field lines. Certain tests of this model are proposed.
    Schlagwort(e): ASTROPHYSICS
    Materialart: NASA. Goddard Space Flight Center The Struct. and Content of the Galaxy and Galactic Gamma Rays; p 99-108
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  • 8
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    Rare earth and trace element geochemistry of metabasalts from the Point Sal ophiolite, California (1977)
    In:  Other Sources
    Details
    Publikationsdatum: 2011-08-17
    Schlagwort(e): EARTH RESOURCES AND REMOTE SENSING
    Materialart: Earth and Planetary Science Letters; 37; 2, De; Dec. 197
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  • 9
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    Primeval gas clouds and the low-energy X-ray background (1977)
    In:  Other Sources
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    Publikationsdatum: 2011-08-17
    Beschreibung: A model for the appearance of the all-sky low-energy X-ray background on a fine angular scale is presented which is based on primeval hot gas clouds associated with the formation of clusters of galaxies according to the Sunyaev-Zel'dovich (1972) model. It is noted that the background could have both granular and diffuse components if it is due to such gas clouds. The observed appearance of the granular component is predicted along with the observable characteristics of collapsing protoclusters. The effects of distant X-ray-emitting QSOs, radio galaxies, and normal galaxies on the observations are considered, and these sources are shown not to interfere with the possibility of observing the protoclusters. It is concluded that if sufficient heating occurred in an intracluster medium within some clusters of galaxies at the protocluster epoch, the ensemble properties of protoclusters could be observed with an X-ray telescope, and the time at which protoclusters formed could perhaps be estimated.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Astrophysical Journal; vol. 218
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  • 10
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    Pattern recognition of Landsat data based upon temporal trend analysis (1977)
    In:  Other Sources
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    Publikationsdatum: 2011-08-17
    Beschreibung: The Delta Classifier defined as an agricultural crop classification scheme employing a temporal trend procedure is applied to more than 100 different Landsat data sets collected during the 1974-1975 growing season throughout the major wheat-producing regions of the United States. The classification approach stresses examination of temporal trends of the Landsat mean vectors of crops in the absence of corresponding ground truth information. It is shown that the resulting classifications compare favorably to ground truth estimates for wheat proportion in those cases where ground truth is available, and that the temporal trend procedure yields estimates of the wheat proportion that are comparable to the best results from maximum likelihood classification with photointerpreter-defined training fields.
    Schlagwort(e): EARTH RESOURCES AND REMOTE SENSING
    Materialart: Remote Sensing of Environment; 6; 4, 19; 1977
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  • 11
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    2.8 and 6 cm wavelength observations of NGC 7822 (1977)
    In:  Other Sources
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    Publikationsdatum: 2011-08-17
    Schlagwort(e): ASTROPHYSICS
    Materialart: Astronomy and Astrophysics; 61; 2, Oc; Oct. 197
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  • 12
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    V 701 Scorpii and its place among early contact binaries (1977)
    In:  Other Sources
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    Publikationsdatum: 2011-08-17
    Schlagwort(e): ASTROPHYSICS
    Materialart: Astronomy and Astrophysics; 61; 1, Oc; Oct. 197
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  • 13
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    Structure of radio sources with remarkably flat spectra - PKS 0735+178 (1977)
    In:  Other Sources
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    Publikationsdatum: 2011-08-17
    Beschreibung: Three incoherent synchrotron models are used to account for the very flat radio spectrum of the BL Lac object PKS 0735+178. The first interpretation is that the spectrum results from optically-thin synchrotron emission from relativistic electrons with a particular energy distribution. The second posits a single nonuniform, self-absorbed source generated by a wind flowing from a central object. The third suggests that sources with flat spectra are caused by the presence of multiple (three or more) discrete uniform components, and that the magnetic field and relativistic electron distribution for each source is correlated with the size of the individual components. It is proposed that the last model is the most tenable explanation of the phenomenon, and multi-frequency VLBI observations are suggested for the evaluation of the detailed structure of compact radio sources.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Astronomical Journal; 82; Oct. 197
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  • 14
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    Search for microarcsecond structure in low-frequency variable radio sources (1977)
    In:  Other Sources
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    Publikationsdatum: 2011-08-17
    Beschreibung: A search for interstellar scintillation (ISS) of low-frequency variable radio sources is reported. Observations of 28 confirmed or suspected low-frequency variables, 21 nonvariable sources, and two pulsars were made at 408 MHz. As expected, the pulsars showed ISS, but scintillation was not detected in any other source. A typical upper limit to the rms modulation due to ISS is 150 mJy, giving lower limits to the apparent angular diameter of about 10 to the -6th arcsec. The possibilities that a true point source is broadened to an apparent angular diameter greater than or roughly equal to 10 to the -6th arcsec by scattering local to the source or in a general intergalactic medium are discussed.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Astronomical Journal; 82; Oct. 197
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  • 15
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    Extragalactic sources with strong millimeter-wave emission (1977)
    In:  Other Sources
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    Publikationsdatum: 2011-08-17
    Beschreibung: Observations at 90 GHz of a sample of 38 sources chosen to have flat or rising spectra between 0.318 and 5 GHz are reported. Roughly 25% of the sources were found to have flat or rising spectra between 5 and 90 GHz. The optical magnitude of each of the sources from the E print of the Palomar Sky Survey has also been estimated. Evidence is found for a correlation between the 90-GHz flux density and the optical magnitude, suggesting a relationship between the emission processes at these frequencies. Little evidence is found for a correlation between the low- and high-frequency spectral indices of the sources. This suggests that the sources tend to be opaque at centimeter wavelengths and optically thin at millimeter wavelengths. The properties of two of the more interesting sources are also discussed. Evidence is presented that strong millimeter activity may be generally associated with the BL Lac phenomenon.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Astronomical Journal; 82; Oct. 197
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  • 16
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    X-ray spectra of young supernova remnants (1983)
    In:  Other Sources
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    Publikationsdatum: 2011-08-18
    Beschreibung: Einstein solid-state-spectrometer (SSS) spectra are presented for the Crab Nebula, Cas A, SN 1006, the Tycho SNR, and the Kepler SNR. The history of X-ray observations of SNRs is reviewed; the SSS instrument is briefly characterized; a reduction technique which accounts for all background sources in the 0.5-4.5-keV band is applied; and the physical models of SNRs constructed to reproduce the refined spectra are discussed. The limitations of the modeling methods and the need for further observations, especially of localized regions, are indicated.
    Schlagwort(e): ASTROPHYSICS
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  • 17
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    Magnetic topology and the heating of extended chromospheres (1983)
    In:  Other Sources
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    Publikationsdatum: 2011-08-18
    Beschreibung: New data indicate that red giants are surrounded by geometrically thick chromospheres of several stellar radii extent. Such chromospheres occur among stars which apparently lack coronae. Maintenance of this extended warm region may require non-compressional wave heating of a magnetic character, and this may provide a crucial clue to the mechanism of rapid mass loss from red giant stars.
    Schlagwort(e): ASTROPHYSICS
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  • 18
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    A sampling procedure to guide the collection of narrow-band, high-resolution spatially and spectrally representative reflectance data (1983)
    In:  Other Sources
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    Publikationsdatum: 2011-08-18
    Beschreibung: A multistage sampling procedure using image processing, geographical information systems, and analytical photogrammetry is presented which can be used to guide the collection of representative, high-resolution spectra and discrete reflectance targets for future satellite sensors. The procedure is general and can be adapted to characterize areas as small as minor watersheds and as large as multistate regions. Beginning with a user-determined study area, successive reductions in size and spectral variation are performed using image analysis techniques on data from the Multispectral Scanner, orbital and simulated Thematic Mapper, low altitude photography synchronized with the simulator, and associated digital data. An integrated image-based geographical information system supports processing requirements.
    Schlagwort(e): EARTH RESOURCES AND REMOTE SENSING
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  • 19
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    Radiometric calibration of Seasat SAR imagery (1983)
    In:  Other Sources
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    Publikationsdatum: 2011-08-18
    Beschreibung: A goal of future synthetic aperture radar (SAR) system design is to yield the radiometrically accurate imagery necessary for use in classification problems. To accomplish this, a reliable calibration technique must be developed. Many such techniques have been proposed (e.g., Stiles and Holtzman, 1982); however, until now, none have been tested on spaceborne SAR digital data. In this paper, a method of significantly increasing the reproducibility of several independent Seasat SAR data sets of a test site using an automated correction procedure is described.
    Schlagwort(e): EARTH RESOURCES AND REMOTE SENSING
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  • 20
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    A note on the oxygen gradient in NGC 628 (1983)
    In:  Other Sources
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    Publikationsdatum: 2011-08-18
    Beschreibung: The Kitt Peak 2.1-m telescope and Intensified Image Dissector Scanner have been used to gather spectrophotometric data in the 3600-5200 A spectral region for five H II regions in the spiral galaxy NGC 628. The Pagel et al (1979) technique was then applied to determine the relative number abundances of O to H in each of the H II regions. An examination of the abundance values obtained as a function of the radial coordinate yields an O gradient of -0.05 + or - 0.03 dex/kpc.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Astronomical Society of the Pacific, Publications (ISSN 0004-6280); 95; 986-988
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  • 21
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    Testing for a cosmological influence on local physics using atomic and gravitational clocks (1983)
    In:  Other Sources
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    Publikationsdatum: 2011-08-18
    Beschreibung: The existence of a possible influence of the large-scale structure of the universe on local physics is discussed. A particular realization of such an influence is discussed in terms of the behavior in time of atomic and gravitational clocks. Two natural categories of metric theories embodying a cosmic infuence exist. The first category has geodesic equations of motion in atomic units, while the second category has geodesic equations of motion in gravitational units. Equations of motion for test bodies are derived for both categories of theories in the appropriate parametrized post-Newtonian limit and are applied to the Solar System. Ranging data to the Viking lander on Mars are of sufficient precision to reveal (1) if such a cosmological influence exists at the level of Hubble's constant, and (2) which category of theories is appropriate for a descripton of the phenomenon.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Physical Review D - Particles and Fields, 3rd Series (ISSN 0556-2821); 28; 1822-182
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  • 22
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    Observations of NGC 7027 from 5.2 to 7.5 microns - The detection of Ni II and additional dust features (1983)
    In:  Other Sources
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    Publikationsdatum: 2011-08-18
    Beschreibung: NGC 7027 was observed with a multichannel grating spectrometer from 5.2 to 7.5 microns at a spectral resolving power of 120-200. Two new dust emission features are resolved at 5.62 and 6.95 microns, and for the first time the Ni II fine-structure line at 6.64 microns is detected. It is shown that a single molecular dust constituent might account for six of the nine observed dust features between 2 and 14 microns. The strength of the Ni II line indicates either that Ni is not depleted in the neutral gas, or that the line is formed at high density.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Astrophysical Journal, Part 1 (ISSN 0004-637X); 274; 666-670
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  • 23
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    A new calibration of the extragalactic distance scale using Cepheids and RR Lyrae stars (1983)
    In:  Other Sources
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    Publikationsdatum: 2011-08-18
    Beschreibung: Visual absolute magnitudes of classical Cepheids, metal-poor RR Lyrae stars and short-period type II Cepheids have been determined with very high precision by combining a large number of old and new astrophysical data. Five independent methods (four observational and one theoretical) have been successfully used: (1) secular and statistical parallaxes; (2) moving-group parallaxes; (3) cluster main-sequence fitting; (4) the Baade-Wesselink method and its modifications; and (5) light-curve and velocity-curve fitting (the theoretical method). With these five adopted methods, the zero point of the galactic and extragalactic distance scale can be set on a relatively firm and self-consistent basis. Classical Cepheids and RR Lyrae stars now provide essentially identical distances to nearby galaxies: the distance modulus to the Large Magellanic Cloud is 18.5 and to the Small Magellanic Cloud is 18.8, both with an uncertainty of 0.1. The distance to the center of our Galaxy is 8.6 plus or minus 0.5 kiloparsecs. The major uncertainty in these values lies in the correction for interstellar extinction.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Astrophysical Journal, Part 1 (ISSN 0004-637X); 274; 20-30
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  • 24
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    On the line profile coefficient for stimulated emission (1983)
    In:  Other Sources
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    Publikationsdatum: 2011-08-18
    Beschreibung: It is pointed out that the line profile coefficients for spontaneous and stimulated emission are identical in low-intensity radiation fields. In more intense radiation fields, however, the stimulated emission profiles in the radiative transfer equation and in the rate equations for the atomic level populations may differ from each other, owing to their different physical nature. A seeming discrepancy between the stimulated emission profiles of the usual semi-classical aproach and a recent quantum mechanical approach by Cooper et al. (1982), which should also be valid for intense 'broadband' fields, is discussed and shown to have negligible consequences for low-intensity radiation fields.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Astronomy and Astrophysics (ISSN 0004-6361); 127; 1, Oc; 224-226
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  • 25
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    Observational tests of baryon symmetric cosmology (1983)
    In:  Other Sources
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    Publikationsdatum: 2011-08-18
    Beschreibung: Observational evidence for Baryon symmetric (matter/antimatter) cosmology and future observational tests are reviewed. The most significant consequences of Baryon symmetric cosmology lie in the prediction of an observable cosmic background of gamma radiation from the decay of Pi(O)-mesons produced in nucleon-antinucleon annihilations. Equations for the prediction of the gamma ray background spectrum for the case of high redshifts are presented. The theoretical and observational plots of the background spectrum are shown to be in good agreement. Measurements of cosmic ray antiprotons and the use of high energy neutrino astronomy to look for antimatter elsewhere in the universe are also addressed. Previously announced in STAR as N83-10996
    Schlagwort(e): ASTROPHYSICS
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  • 26
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    Remote sensing technology transfer at the NASA Technology Application Center, University of New Mexico (1983)
    In:  Other Sources
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    Publikationsdatum: 2011-08-18
    Schlagwort(e): EARTH RESOURCES AND REMOTE SENSING
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  • 27
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    Segmentation of remotely sensed data using parallel region growing (1983)
    In:  Other Sources
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    Publikationsdatum: 2011-08-18
    Beschreibung: The improved spatial resolution of the new earth resources satellites will increase the need for effective utilization of spatial information in machine processing of remotely sensed data. One promising technique is scene segmentation by region growing. Region growing can use spatial information in two ways: only spatially adjacent regions merge together, and merging criteria can be based on region-wide spatial features. A simple region growing approach is described in which the similarity criterion is based on region mean and variance (a simple spatial feature). An effective way to implement region growing for remote sensing is as an iterative parallel process on a large parallel processor. A straightforward parallel pixel-based implementation of the algorithm is explored and its efficiency is compared with sequential pixel-based, sequential region-based, and parallel region-based implementations. Experimental results from on aircraft scanner data set are presented, as is a discussioon of proposed improvements to the segmentation algorithm.
    Schlagwort(e): EARTH RESOURCES AND REMOTE SENSING
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  • 28
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    Interacting binary stars - Freaks or rosetta stones (1983)
    In:  Other Sources
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    Publikationsdatum: 2011-08-18
    Beschreibung: Attention is given to semidetached binaries of the Algol type and to related interacting systems, such as Beta Lyrae and the W Serpentis stars. A brief description is given of observational problems. The basic properties of the Algol variables are satisfactorily explained by means of evolutionary models that assume considerable mass transfer between the components. It is pointed out that ultraviolet spectra obtained with the IUE satellite corroborate the view that the present subgiant secondary component was initially the more massive star and that it has been stripped of a large fraction of its mass so that the deep layers affected by CNO processing are now denuded. It is believed that the present-day 'classical' Algols must have undergone a phase of rapid mass transfer in the past and that Beta Lyrae and the W Serpentis stars are probably closer to that stage than ordinary Algols. Around the accreting star a complex structure is formed, and an induced stellar wind may blow a large part of the transferred matter out of the system.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Royal Astronomical Society of Canada, Journal (ISSN 0035-872X); 77; 283-304
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  • 29
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    The SIR-A radar of the American Space Shuttle - Technical characteristics and overview of French experiments (1983)
    In:  Other Sources
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    Publikationsdatum: 2011-08-18
    Beschreibung: The scientific instruments comprising the OSTA-1 package flown on the second Shuttle mission (November 12-14, 1981) are listed, and the Shuttle Imaging Radar (SIR-A) experiments are examined in detail: SIR-A operated for 8 h and obtained images covering more than 10 million sq km at 40-m resolution. The images were recorded on photographic film and processed in holographic form at JPL, and data for Southern Europe and parts of Africa were distributed to French scientists by the Groupement pour le Developpement de la Teledetection Aerospatiale. The main areas of research were environmental studies and geology, and the SIR-A images were used in combination with aerial photography, thematic maps, and Landsat images. The technical specifications of the SIR-B radar planned for STS-17 in 1984 are compared with those of SIR-A and Seasat SAR in tables.
    Schlagwort(e): EARTH RESOURCES AND REMOTE SENSING
    Materialart: Societe Francaise de Photogrammetrie et de Teledetection, Bulletin (ISSN 0244-6014); 91, 1; 5-9
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  • 30
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    Remote sensing for exploration - An overview (1983)
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    Publikationsdatum: 2011-08-18
    Beschreibung: The use of remote sensing in resource exploration is reviewed, with emphasis placed on new developments in high spectral resolution remote-sensing techniques for mineralogic and vegetation mapping. Topics discussed include aerial photography and satellite remote sensing, concepts and principles of spectral data collection, spectral properties of rocks and minerals, spectral properties of vegetation, and botanical aspects of geochemical stress. The discussion also covers applications of Landsat multispectral scanner data to lithologic and geobotanic studies and the future development of data acquisition and data interpretation techniques.
    Schlagwort(e): EARTH RESOURCES AND REMOTE SENSING
    Materialart: Economic Geology and Society of Economic Geologists, Bulletin (ISSN 0361-0128); 78; 573-590
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  • 31
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    Monte Carlo simulation of the effect of soil moisture variation on the microwave emission from soils (1983)
    In:  Other Sources
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    Publikationsdatum: 2011-08-18
    Beschreibung: In this paper, results of a Monte Carlo simulation of the effect of noise on the relationship between the microwave emissivity of soil and its moisture content are presented. It is found that whenever the magnitude of the noise for the independent variable, in this case the soil moisture, is increased, both the slope of the regression and the correlation coefficient decrease. In particular, when the noise has magnitude equivalent to a coefficient of variation of 0.25, the slope and correlation coefficient are in good agreement with those obtained from the data of a 21-cm airborne microwave radiometer which was flown over a test site in hand county, South Dakota. The comparison was made using a linear relationship to determine the estimated emissivity from the ground measurements of soil moisture. The linear relationship was derived from a radiative transfer model calculation of the microwave emissivities using realistic soil-moisture profiles. The effect of surface roughness was included in the relationship, and the variability of the surface roughness was also simulated by a Monte Carlo technique.
    Schlagwort(e): EARTH RESOURCES AND REMOTE SENSING
    Materialart: IEEE Transactions on Geoscience and Remote Sensing (ISSN 0196-2892); GE-21; 473-479
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  • 32
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    What causes the buoyancy reversal in compressible convection? (1983)
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    Publikationsdatum: 2011-08-18
    Beschreibung: The problem posed by the existence of a negative buoyancy work region at the top of cellular type convection in a deeply stratified superadiabatic layer (Massaguer and Zahn, 1980) is addressed. It is approached by studying two-dimensional cellular compressible convection with different physical parameters. The results suggest that a large viscosity, together with density stratification, is responsible for the buoyancy reversal. The numerical results obtained are analyzed. It is pointed out, however, that in an astrophysical situation a fluid involved in convection will generally have very small viscosity. It is therefore thought unlikely that buoyancy reversal occurs in this way.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Astrophysics and Space Science (ISSN 0004-640X); 95; 2, Se; 453-457
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  • 33
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    On a vibronic origin for the diffuse band spectrum (1983)
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    Publikationsdatum: 2011-08-18
    Beschreibung: Duley (1982) has proposed that many of the diffuse interstellar bands in the wavelength interval 542-677 nm arise from vibronic transitions of Cr (3+) ions in MgO grains. No explanation has been offered for the fact that as many as 85 of the possible 108 transitions of this system have not been observed in the interstellar medium. Moreover, the relative intensities of the diffuse bands which are observed appear to be inconsistent with their assignment. It is therefore concluded that this model is not consistent with the observations.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Astrophysics and Space Science (ISSN 0004-640X); 95; 1, Se
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  • 34
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    A note on the composition and structure of interstellar grains (1983)
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    Publikationsdatum: 2011-08-18
    Beschreibung: The plausibility of relatively pure diatomic oxide crystals forming in the expanding atmospheres of cool stars is commented on, and the likelihood of SiO grains condensing is discussed on the basis of laboratory nucleation experiments. Results of annealing experiments are used to consider the further evolution of silicon oxide and silicate grains. The evidence shows that SiO solids form only when SiO condenses directly onto surfaces, and that the probability of pure crystalline SiO grains forming is rather small.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Astrophysics and Space Science (ISSN 0004-640X); 95; 1, Se
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  • 35
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    Planetary nebulae and stellar evolution (1983)
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    Publikationsdatum: 2011-08-18
    Beschreibung: Newly defined characteristics of planetary nebulae (PN) derived from analysis of a photometric survey of 57 PN are reported. The data were combined with measurements of 27 other PN made since 1918 and were found to indicate core masses ranging from 0.55-1.0 solar mass. N/O elemental abundance ratios observed were correlated with the planetary nuclei masses, and were in direct proportion. IUE data on PN that overlapped a large part of the survey indicated that the PN in the galactic disk are more massive than PN in the halo. It is suggested that PN evolve into white dwarfs, a hypothesis supported by astrometric solutions for three nearby visual binaries featuring white dwarfs with well-determined masses. It is noted, however, that PN with masses exceeding one solar mass have been sighted in the Magellanic Clouds.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Nature (ISSN 0028-0836); 305; 670
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  • 36
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    Development of the JSC Thematic Mapper quick-look preprocessing capability (1983)
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    Publikationsdatum: 2011-08-18
    Beschreibung: The development of a preprocessing unit for Landsat Thematic Mapper (TM) data for the Earth Observations Data Laboratory at Johnson Space Center is reported. The background of the project is sketched, including the greatly increased data-handling requirements compared to MSS, the influence of the JPL VICAR system on the system design, and the completeness of the GSFC SCROUNGE (LASLIB) TM data tapes. The design approach and realization are discussed, and the performance and transportability of the preprocessor programs (totaling about 2000 lines of source code in FORTRAN and IBM Assembly languages) are indicated. The system is able to read the TM image tapes, extract areas of interest to particular studies, and register the extracted imagery to suitable references. Ancillary programs include image enhancement, rotation, filtering and pixel-size modification.
    Schlagwort(e): EARTH RESOURCES AND REMOTE SENSING
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  • 37
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    NASA technology transfer in the southwest states - Arizona, Colorado, Nevada and Utah (1983)
    In:  Other Sources
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    Publikationsdatum: 2011-08-18
    Beschreibung: Features of the NASA Regional Application Program for providing state and local land management agencies an opportunity to assess the usefulness of emerging remote sensing technology are described. The Program guidelines necessitated configuring software for local facilities, assuring that the aggncy involved furnished manpower, and applying the technology to local needs. The study focused on the southwestern U.S., particularly for purposes of water management, federal/state ownership/policy, energy development, environmental impact issues, timber and range inventory, fire control, and urban expansion. Demonstration projects were conducted in various topics, according to the state surveyed, with the success of the projects determined by the willingness of the agencies to continue with the technology, which happened in several cases.
    Schlagwort(e): EARTH RESOURCES AND REMOTE SENSING
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  • 38
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    Two new possible planetary nebulae (1983)
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    Publikationsdatum: 2011-08-18
    Beschreibung: Two new possible planetary nebulae have been identified using the Parker, Gull, and Kirshner (1979) emission-line survey of the galactic plane. Both objects exhibit very strong forbidden O III lambda 5007 line emission, a symmetrical morphology, and a faint blue central star.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Astronomical Society of the Pacific, Publications (ISSN 0004-6280); 95; 614-618
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  • 39
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    Ultraviolet observations of M1-2 (= VV 8) (1983)
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    Publikationsdatum: 2011-08-18
    Beschreibung: First IUE spectrograms of the peculiar emission-line object M1-2 (= VV 8) are presented. In the wavelength region 1150-3200 A this object is characterized by emission lines superposed on a moderately strong continuum. Some ultraviolet and optical properties of M1-2 are discussed in the context of symbiotic stars and protoplanetary and planetary nebulae. An E(B-V) extinction of 0.37 mag is obtained from the ratio of the He II flux at 1640 and 4686 A and is compared with values derived from other parameters. The ultraviolet observations suggest that M1-2 is a young, high-density planetary nebula of excitation class 5 or 6 with characteristics similar to IC 4997.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Astrophysical Journal, Part 1 (ISSN 0004-637X); 275; 628-635
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  • 40
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    The origin of the Gum nebula (1983)
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    Publikationsdatum: 2011-08-18
    Beschreibung: Obsrvations and theoretical investigations of the Gum nebula (GN) since about 1971 are reviewed. Direct observations of the GN, the Vela X supernova remnant (SNR), the Vela pulsar, and other stars in or near the GN are discussed with those of related phenomena such as the radio loops and known SNRs; the emphasis is on studies of the interstellar absorption lines, the evidence for hot gas in the GN, and the extended diffuse emission. The four basic models proposed for the GN are considered: a fossil Stromgren sphere, an old SNR, an H II region, or a superbubble. The GN physical parameters predicted by each model are listed in a table and compared. A minimum explanation which attributes the 36 x 36-deg filamentary structure and the 125-pc radius structure to the action of the stellar winds from Zeta Pup and Gamma-2 Vel (and perhaps the effect of a Vel X supernova explosion 20,000 years ago) is found most appropriate, at least until the questions of the net expansion rate of the GN (about 20 km/sec or about zero?) and the existence of the diffuse emission beyond the filamentary structure are resolved by observations.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Comments on Modern Physics, Part C - Comments on Astrophysics (ISSN 0146-2970); 10; 1-14
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  • 41
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    Electron velocity distributions near interplantary shocks (1983)
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    Publikationsdatum: 2011-08-18
    Beschreibung: Previous work on electron heating mechanisms operating at the supercritical earth's bow shock is extended to the generally lower Mach number interplanetary shocks. This is done by studying electron velocity distributions observed both upstream and downstream of interplanetary shocks observed by ISEE 3 between August 1978 and December 1979. It is found that perpendicular heating accompanied by little or no parallel heating occurs at the weaker shocks but that parallel heating is dominant for the stronger shocks. When perpendicular heating is dominant, downstream velocity distributions are for the most part Gaussian at low energies (core) and Lorentzian at high energies (halo). When parallel heating is dominant, however, these distributions are flat-topped at low energies, having power law extensions to higher energies. At the weaker shocks, the observations are consistent with electron heating resulting from conservation of the magnetic moment, whereas at the stronger shocks the heating is quite similar to that observed at the earth's bow shock.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Journal of Geophysical Research (ISSN 0148-0227); 88; 9949-995
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  • 42
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    Sharp shortward-shifted features in the spectra of O subdwarfs (1983)
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    Publikationsdatum: 2011-08-18
    Beschreibung: Preliminary inspection of archival high-dispersion ultraviolet spectra obtained by the International Ultraviolet Explorer reveal sharp shortward-shifted features in the spectra of O subdwarfs. In three examples presented here, BD + 75.325 deg, HD 128220 B, and BD + 28.4211 deg, stable, multiple, discrete shortward-shifted components of the N V, C IV, and Si IV resonance doublets are seen. The available data suggest that some of these features are persistent, being relatively stable in velocity and intensity over at least 9 months. It is tentatively suggested that the mechanism, or mechanisms, producing these discrete features operates universally in hot stars, from luminous O and B stars down through the O subdwarfs to include the hot white dwarfs. If true, this has important ramifications for current knowledge of mass loss in hot stars.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Astrophysical Journal, Part 2 - Letters to the Editor (ISSN 0004-637X); 274; L87-L91
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  • 43
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    Images in the rocket ultraviolet - The starburst in the nucleus of M83 (1983)
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    Publikationsdatum: 2011-08-18
    Beschreibung: Ultraviolet images of the SAB(s)c I-II galaxy M83 (NGC 5236) obtained with a rocketborne telescope in broad bandpasses centered at 1540 A and 2360 A show a bright resolved nuclear source which accounts for approximately 20 percent of the flux of the galaxy in both bandpasses. Low-resolution International Ultraviolet Explorer spectra of this source reveal an energy distribution similar to that of the starburst nucleus of NGC 7714. Strong blueshifted absorption lines can be interpreted as evidence for a nuclear wind powered by supernovae. Observations from UV, X-ray, optical, and far-infrared bandpasses are consistent with a starburst approximately one-sixth as strong as that in M82. A scaling of the M82 models of Rieke et al. (1980) predicts that the nucleus of M83 contains 10 to the 6th - 3 x 10 to the 7th solar masses in young stars and has a supernova rate of approximately 0.01 per yr.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Astrophysical Journal, Part 2 - Letters to the Editor (ISSN 0004-637X); 274; L53-L56
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  • 44
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    X-ray observations of LMC X-3 with the monitor proportional counter aboard the HEAO 2 Einstein observatory - A comparison with Cygnus X-1 (1983)
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    Publikationsdatum: 2011-08-18
    Beschreibung: A comparison is presented of the black hole candidates LMC X-3 and Cygnus X-1 based on Einstein observations of LMC X-3 with the monitor proportional counter. A spectral analysis shows LMC X-3 to be more like the typical bright galactic X-ray source than Cygnus X-1. A search for periodic pulsations over a period range from 0.2 ms to over 1000 s set upper limits at the 90 percent confidence level of the order of 10 percent. An analysis of the aperiodic variability of LMC X-3 shows none of the shot noise behavior characteristic of Cygnus X-1. The absence of distinctive X-ray properties common to both sources suggests that the identification of black hole candidates on the basis of X-ray properties similar to Cygnus X-1 (or LMC X-3) is not reliable.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Astrophysical Journal, Part 2 - Letters to the Editor (ISSN 0004-637X); 274; L65-L69
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  • 45
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    Stellar evolution in N-body simulations of disk galaxies. I (1983)
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    Publikationsdatum: 2011-08-18
    Beschreibung: The Kalnajs (1972, 1976) Omega models of global mass and velocity distributions are employed in the present two-dimensional N-body simulation, which allows for a spectrum of particle masses, stellar explosions, explosion remnant interactions with an interstellar medium, and the creation of new stars from the gas. Two sequences of runs using the Omega values of 0.8 and 0.9 examine the separate and combined effects of particle mass distribution, the gravitational influence of an interstellar gas distribution on the N-body particles, and stellar evolution, allowing for stellar explosions and star formation from the gas. It is found that both Omega values' nonequilibrium results dramatically change when evolution is allowed to occur. These results call for more realistic coupled N-body and evolution simulations in order to improve the understanding of disk galaxy evolution.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Astrophysical Journal, Part 1 (ISSN 0004-637X); 274; 595-610
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  • 46
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    The (an)isotropy of the X-ray sky (1983)
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    Publikationsdatum: 2011-08-18
    Beschreibung: An assessment is made of the extent to which the study of the isotropy of the X-ray sky has contributed to the present understanding of the structure of the universe at moderate redshifts. It is, of course, the anisotropic character of the sky flux that is valuable in this context. Although it is not currently possible to undertake measurements with the precision and small solid angles that are typically achieved in the microwave range, the comparatively crude limits from the X-ray fluctuations place limits on the largest scale structure of the universe. After indicating the nature of measurements made, with the HEAO 1 A-2 experiment, of the X-ray sky and its anisotropies, it is shown how these place limits on the origin of the X-ray sky and on any large scale structure of the universe.
    Schlagwort(e): ASTROPHYSICS
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  • 47
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    Comments concerning magnetic fields as a possible cause of rapid, irregular variability of early-type stars (1983)
    In:  Other Sources
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    Publikationsdatum: 2011-08-19
    Beschreibung: It is noted that it is helpful to divide the atmosphere of an early-type star into two parts: a photosphere and a mantle. The photosphere can be modeled satisfactorily by normal model-atmosphere procedures. When modeling the mantle, one must take account of the deposition of nonradiative heat and momentum and one should recognize that the mantles of hot stars do not appear to be uniform or spherically symmetric. Five areas of discrepancy between classical theory and observation are noted and a possible way of modeling the mantles of early-type stars is outlined. The model consists of arcades of magnetic loops which form helmet-type structures in the equatorial band of the star, and of coronal-hole-type structures emmanating from weak unipolar regions which are chiefly distributed at polar latitudes.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Hvar Observatory, Bulletin (ISSN 0351-2651); 7; 1, 19
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  • 48
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    Observational knowledge about the physical properties of O stars (1983)
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    Publikationsdatum: 2011-08-19
    Beschreibung: Information about the effective temperatures, radii, and masses of O-type stars is presented. It is argued that rapid variations in the amount of light from O stars and the spectral distribution are a result chiefly of changes which occur in the envelope of the star. The stability of the photospheric layers of O stars against convection is reviewed and it is noted that late O stars and early B stars have a convection zone in the deeper parts of the photosphere. This convection zone is due to the second ionization of helium. Evidence is reviewed that most of the line-profile changes seen for O stars are generated by changes in the physical state of the mantle of the star, that is of the outer atmosphere where the deposition of non-radiative energy and momentum controls the physical state of the atmosphere. The physical state of the mantle may change in response to changes in the upper envelope of a star with a different time constant than the photosphere does.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Hvar Observatory, Bulletin (ISSN 0351-2651); 7; 1, 19; 1-15; Di
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  • 49
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    Geodetic measurements on the ocean (1977)
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    Publikationsdatum: 2011-08-17
    Beschreibung: This paper covers the topic of marine geodesy, its goals, and applications. Specifically discussed are position determination and establishment of geodetic control on the ocean bottom, ocean surface, and subsurface, and the determination of the geoid, a vertical reference surface. The various techniques used in position determination (including satellite, airborne, radio, inertial and acoustic techniques) are assessed in terms of accuracy, coverage, and contribution to the solution of specific problems associated with position and control. The results of several marine geodetic control experiments are presented. Classical techniques for the determination of the geoid are discussed and assessed, as are new techniques such as satellite altimetry. The outlook for marine geodetic measurements in the ocean is outlined in terms of what is being planned or considered for the next decade, and several recommendations are made.
    Schlagwort(e): EARTH RESOURCES AND REMOTE SENSING
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  • 50
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    Supernovae, grains and the formation of the solar system (1977)
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    Publikationsdatum: 2011-08-17
    Beschreibung: An investigation is conducted concerning the possibility that observed Mg-26 anomalies in meteorites may be related to a nucleosynthetic event which preceded the formation of the solar system by at most a few million years. The Al-26, which decayed to form the observed excess Mg-26, could have been produced in either explosive carbon burning or in a high temperature carbon burning shell source immediately preceding the explosion. The results of supernova grain condensation calculations are presented and related to the hypothesis that a 'last event' supernova was indeed related to the formation of the solar system and thus might have created the observed isotopic anomalies in magnesium, oxygen, neon, and xenon.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Nature; 269; Sept. 8
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  • 51
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    Simultaneous crystallization of feldspar intergrowths from the melt (1977)
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    Publikationsdatum: 2011-08-17
    Schlagwort(e): EARTH RESOURCES AND REMOTE SENSING
    Materialart: American Mineralogist; 62; 1977
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  • 52
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    The composition of comets (1977)
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    Publikationsdatum: 2011-08-17
    Beschreibung: Questions concerning the origin of comets are considered. It is pointed out that the molecular composition of a dense interstellar cloud appears to have exactly the composition needed to produce the observed features of the visible cometary spectrum, which consists mainly of emission bands of unstable free radicals. A working model of cometary structure is discussed together with the classical observations which have led to it. The discussed model was originally described by Whipple (1951). It is emphasized that the model can serve only as a rough guide in efforts to interpret the evolution of cometary behavior. A survey is provided of new techniques which have only recently been applied to cometary observations, taking into account the spectrum of a comet, radio observations, and ultraviolet observations.
    Schlagwort(e): ASTROPHYSICS
    Materialart: American Scientist; 65; May-June
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  • 53
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    Nonradial pulsational instability of massive stars (1977)
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    Publikationsdatum: 2011-08-17
    Beschreibung: Pulsational eigenfrequencies and stability coefficients of the lowest modes of nonradial quadrupole (l = 2) oscillation have been obtained for chemically homogeneous stellar models constructed with Carson's (1976) radiative opacities. Instability is found to develop as a result of the same operation of the kappa-mechanism in the CNO ionization zone and at nearly the same stellar masses as was the case for the radial (l = 0) modes studied previously. A survey of the l = 5 modes indicates that the instability gradually declines with increasing degree of the spherical harmonics.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Astrophysical Journal; vol. 214
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  • 54
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    Remote sensing techniques applied to multispectral recognition of the Aranjuez pilot zone (1977)
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    Publikationsdatum: 2011-08-17
    Beschreibung: A rectangular (7 x 14 km) area 40 km S of Madrid was remote-sensed with a three-stage recognition process. Ground truth was established in the first phase, airborne sensing with a multispectral scanner and photographic cameras were used in the second phase, and Landsat satellite data were obtained in the third phase. Agronomic and hydrological photointerpretation problems are discussed. Color, black/white, and labeled areas are displayed for crop recognition in the land-use survey; turbidity, concentrations of pollutants and natural chemicals, and densitometry of the water are considered in the evaluation of water resources.
    Schlagwort(e): EARTH RESOURCES AND REMOTE SENSING
    Materialart: IAA/Ingenieria Aeronautica y Astronautica; 29; Mar. 197
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  • 55
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    Galactic distribution of X-ray burst sources (1977)
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    Publikationsdatum: 2011-08-17
    Beschreibung: Data on X-ray bursts recorded by the OSO-8 and SAS-3 satellites and criteria (rise time, duration, recurrence) for X-ray bursts are examined in a study of possible correlation between the galactic longitude distribution of X-ray burst sources and globular clusters. Correlations are weak, with only two X-ray bursts sources (NGC6624 and the rapid burster) coinciding with globular clusters, another seven possibly coinciding, most not correlated. Ad hoc explanations (globular clusters obscured by dust clouds, bursts associated with remnants of disrupted globular clusters evolved into supermassive black holes) are considered briefly.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Nature; 267; May 5
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    The continuous UV flux of Alpha Lyrae - Non-LTE results (1977)
    In:  Other Sources
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    Publikationsdatum: 2011-08-17
    Beschreibung: Non-LTE calculations for the ultraviolet C I and Si I continuous opacity show that LTE results overestimate the importance of these sources of opacity and underestimate the emergent flux in Alpha Lyr. The largest errors occur between 1100 and 1160 A, where the predicted flux in non-LTE is as much as 50 times larger than in LTE, in reasonable accord with Copernicus observations. The discrepancy between LTE models and observations has been interpreted to result from the existence of a chromosphere. Until a self-consistent non-LTE model atmosphere becomes available, such an interpretation is premature.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Astrophysical Journal; vol. 214
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  • 57
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    Submillisecond measurements of the low state of Cygnus X-1 (1977)
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    Publikationsdatum: 2011-08-17
    Beschreibung: Cygnus X-1 was observed on two occasions separated by a year by the same Goddard X-ray rocket payload. High-resolution temporal and spectral data reveal that Cyg X-1 was essentially unchanged in these two observations a year apart; the bursts of millisecond duration observed in the earlier flight were observed in the second as well. Analysis of these bursts has failed to reveal any internal temporal structure, either luminous or spectral. The shot-noise character of temporal fluctuations on time scales of at least 1 s can be explained by the presence of exponential pulses with a time constant of a fraction of a second and a rate near 8 per sec. The possible connection of these pulses with the bursts is examined.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Astrophysical Journal; vol. 213
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    On the rapid variability of central stars of planetary nebulae (1977)
    In:  Other Sources
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    Publikationsdatum: 2011-08-17
    Beschreibung: Envelope models for central stars of planetary nebulae have been constructed with Carson's (1976) radiative opacities. A stability analysis of these envelopes indicates that for a sufficiently high luminosity, the fundamental mode of radial pulsation is excited by the kappa mechanism operating in the CNO ionization zone. At somewhat higher luminosities the lowest overtones also become unstable. This may possibly explain the rapid variability that is observed in some central stars, if the time scale of the variations is minutes to hours.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Astrophysical Journal; vol. 213
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  • 59
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    Accretion torques in X-ray pulsars (1977)
    In:  Other Sources
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    Publikationsdatum: 2011-08-17
    Beschreibung: An analysis of the accretion process in an X-ray pulsar, whereby angular momentum is transferred to the star and its rotation period is changed, is presented, and an expression for the fractional rate of change of the pulse period in terms of X-ray luminosity and other star parameters is derived. It is shown that observed characteristic spin-up time scales for seven X-ray pulsars strongly support the view that in every source (1) the pulse period reflects the rotation period of a compact object, (2) the accretion is mediated by a disk surrounding the compact object and rotating in the same sense, and (3) the compact object is a neutron star rather than a white dwarf.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Nature; 266; Apr. 21
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  • 60
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    Observations of the unidentified 3.3 micron emission feature in nebulae (1977)
    In:  Other Sources
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    Publikationsdatum: 2011-08-17
    Beschreibung: Spectrophotometric observations from 2.1 to 4.1 microns of a variety of objects exhibiting the 3.3-micron emission feature (first detected in NGC 7027) are reported. The characteristics of the feature, the various environments in which it is found, and possible emission mechanisms are discussed in light of all the available observations of the feature to date. A resonance feature in solids is the most probable emission mechanism; however, no satisfactory identification has yet been made on the basis of infrared spectroscopy of terrestrial materials.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Astrophysical Journal; vol. 213
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  • 61
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    Spectrum of the Kleinmann-Low nebula from 29 to 125 micrometers (1977)
    In:  Other Sources
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    Publikationsdatum: 2011-08-17
    Beschreibung: The infrared spectrum of the Kleinmann-Low nebula in M42 has been measured from 80 to 350 kaysers (approximately 29 to 125 microns) with a Michelson interferometer aboard the NASA Kuiper Airborne Observatory. The frequency spectrum peaks at about 185 kaysers. A simple model of the emission implies that the temperature is in the range 70-95 K and that the optical depth is at least 0.2 at the peak frequency. A possible absorption is seen at about 176 kaysers. Thermal emission by dust at a temperature of 71 K, with the absorption cross section proportional to frequency, provides a good fit to the data. Other thermal-emission models can also fit the spectrum. The data are compared with previous broad-band measurements. Upper limits are placed on expected line emission from the surrounding H II region at the position of the nebula.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Astrophysical Journal; vol. 212
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  • 62
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    The supernova trigger for formation of the solar system (1977)
    In:  Other Sources
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    Publikationsdatum: 2011-08-17
    Beschreibung: It is suggested that the explosion of a Type II supernova triggered the collapse of a nearby interstellar cloud and led to the formation of the solar system. Estimates of the abundances resulting from nuclear processing of the supernova ejecta are presented. It appears promising that nucleosynthesis in this single supernova event can account for most isotopic anomalies and traces of extinct radioactivities in solar-system material.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Icarus; 30; Mar. 197
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  • 63
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    Binary X-ray pulsars (1977)
    In:  Other Sources
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    Publikationsdatum: 2011-08-17
    Beschreibung: Recent progress in the study of the pulse profiles of the nine known binary X-ray pulsars is discussed. The sources considered include SMC X-1, Her X-1, Cen X-3, A0535+26, GX1+4, 3U 0900-40, A1118-61, GX301-2, and 3U 0352+30. Sample X-ray profiles for these sources are provided, and general features exhibited by the profiles are identified. It is noted that the apparent existence of a gap in the period distribution of X-ray pulsars, in the range from about 5 to 100 sec, seems to be genuine within obvious statistical limitations and is probably not an observational effect. Two explanations for the production of X-ray pulsations are examined: one requiring a temporal modulation of mass accretion onto the surface of a neutron star and another requiring the funnelling of matter along magnetic field lines to the neutron star's surface.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Nature; 266; Mar. 10
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  • 64
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    Spectrographic observations of comet West /1975 n/ (1977)
    In:  Other Sources
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    Publikationsdatum: 2011-08-17
    Beschreibung: The spectrum of comet West (1975 n) was recorded on March 7 and 11, 1976, in the wavelength interval from 5700 to 8200 A at an intermediate resolution. One hundred twenty-two emission lines are reported, with 78 lines having identifications with spectral features of NH2, H2O(+), C2, O I forbidden emission, and Na I.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Astronomical Society of the Pacific; vol. 89
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  • 65
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    Hydrostatic equilibrium of gas, extent of cosmic ray confinement, and radio emission in the Galaxy (1977)
    In:  Other Sources
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    Publikationsdatum: 2011-08-17
    Beschreibung: A detailed study of the hydrostatic equilibrium of the gas-field system perpendicular to the galactic plane in the neighborhood of the sun, assuming that the magnetic field is parallel to the plane, has been carried out. It is found that the distribution of pressure due to cosmic rays and the magnetic field is different from that due to the gas. The observed radio spectrum in the direction of the galactic pole can be understood if one includes in the hydrostatic equilibrium the distribution of gas in the halo. The results of this analysis show that in the galactic plane, the cosmic-ray density is approximately 2 to 3 eV/cu cm with a magnetic-field strength of about 5 to 6 microgauss. It is inferred that cosmic rays are confined to a more extended volume in the Galaxy (with an equivalent thickness of at least 2 kpc in the solar neighborhood) than the gas disk, and the magnetic-field strength slowly decreases to a value of 1 microgauss only beyond about 5 kpc from the plane. Further, there is no evidence for a quasi-spherical radio halo, although the radio emission extends beyond the gas disk with scale height of at least 1 kpc. A lower limit of about 6 million years for the confinement of cosmic rays in the Galaxy has been set.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Astrophysical Journal; vol. 212
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  • 66
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    The black tide model of QSOs (1977)
    In:  Other Sources
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    Publikationsdatum: 2011-08-17
    Beschreibung: The paper develops certain aspects of a model wherein a QSO is a massive black hole located in a dense galactic nucleus, with its growth and luminosity fueled by tidal disruption of passing stars. Cross sections for tidal disruptions are calculated, taking into account the thermal energy of stars, relativistic effects, and partial disruption removing only the outer layers of a star. Accretion rates are computed for a realistic distribution of stellar masses and evolutionary phases, the effect of the black hole on the cluster distribution is examined, and the red-giant disruption rate is evaluated for hole mass of at least 300 million solar masses, the cutoff of disruption of main-sequence stars. The results show that this black-tide model can explain QSO luminosities of at least 1 trillion suns if the black hole remains almost maximally Kerr as it grows above 100 million solar masses and if 'loss-cone' depletion of the number of stars in disruptive orbits is unimportant.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Astrophysical Journal; vol. 212
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    Isotopic abundance of CO in interstellar clouds (1977)
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    Publikationsdatum: 2011-08-17
    Beschreibung: The fractional abundances of the isotopic species of carbon monoxide in interstellar clouds are calculated on a basis of gas-phase ion-molecule reactions. The (C-13)O/(C-12)O ratio varies significantly with extinction of the ultraviolet radiation field, and in the outer regions of dark dense clouds (C-13)O may be enhanced by a factor of 10. The observational interpretation of the CO to H2 or interstellar-reddening relation and the isotopic abundances of carbon are complicated by these effects.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Astrophysical Journal; vol. 212
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    The hard X-ray pulse profile of the transient source A0535+26 (1977)
    In:  Other Sources
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    Publikationsdatum: 2011-08-17
    Beschreibung: Measurements of the 104 sec pulse profile of A0535+26 at energies near 50 keV are reported. The data were obtained with a balloon-borne detector system which was launched on May 22, 1975 with the objective to observe transient or periodic emissions from X-ray or gamma-ray sources. The presence of the source was detected by a superposed epoch analysis. The pulse profile of A0535+26 in two energy channels is presented in a graph.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Astrophysical Journal; vol. 212
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    All-Sky Monitor observations of the decay of A0620-00 /Nova Monocerotis 1975/ (1977)
    In:  Other Sources
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    Publikationsdatum: 2011-08-17
    Beschreibung: The All-Sky X-ray Monitor on board Ariel-5 has observed the 3-6 keV decline of the bright transient X-ray source A0620-00 on a virtually continuous basis during the period 1975 September-1976 March. The source behavior on time scales greater than about 100 minutes is characterized by smooth, exponential decays interrupted by substantial increases in October and February. The latter increase was an order-of-magnitude rise above the extrapolated exponential falloff, and was followed by a final rapid decline below a level of about 0.05 per sq cm per sec by late March. Upper limits of 2.5% and 10% were found for any periodicities in the range 0.2-10 days during the early and later decay phases, respectively. A probable correlation between the optical and 3-6 keV emission from A0620-00 has been noted, effectively ruling out models involving traditional optical novae in favor of Roche-lobe overflow in a binary system. The existing data on the transient X-ray sources are consistent with two distinct luminosity-lifetime classes of these objects.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Astrophysical Journal; vol. 212
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  • 70
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    Orbital changes of the gaseous ring around Be stars (1977)
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    Publikationsdatum: 2011-08-17
    Beschreibung: In order to understand the seemingly erratic V/R variations and radial velocity curves of emission edges and central absorption of some Be stars, we have advanced, for the changes of structure of the gaseous ring around these stars, a theory that is based on the interaction between the existing ring and the newly ejected matter from the star. It shows that the structural change of the ring is completely controlled by the angular-momentum input factor and the dissipation factor. In light of this understanding, we have gone on to interpret the observed results of Beta-1 Mon and Pi Aqr.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Astrophysical Journal; vol. 212
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    The measurements of latitude, time, and height variations at a single laser tracking station (1977)
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    Publikationsdatum: 2011-08-17
    Beschreibung: Recent analysis of laser data for determining variation of latitude have been based on apparent variations in the orbital inclination of the satellite derived from short orbital arcs of 6-8 hours. An alternative method, based on the daily adjustment of the station position to a much longer arc of 2 or 3 weeks has recently been developed and tested. In the new method a long orbital arc is derived from many days of data and is subsequently used as a reference orbit for the adjustment of the position of the station (only) on each day of the long arc for which tracking data are available. This new technique appears to give slightly better results when it is applied to a test period in August 1970, with the added advantage that earth rotation measurements can be derived from the same data at the same time. The results for the test period indicate a precision of 74 cm in variation of latitude and 0.81 ms in monitoring the earth's rotation with 6 hours of data.
    Schlagwort(e): EARTH RESOURCES AND REMOTE SENSING
    Materialart: Journal of Geophysical Research; 82; Feb. 10
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  • 72
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    Recurrent X-ray outbursts from Aquila X-1 (1977)
    In:  Other Sources
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    Publikationsdatum: 2011-08-17
    Beschreibung: Ariel V All-Sky Monitor observations of Aql X-1 are reported and compared with previous observations that indicate the existence of 'low' and 'high' intensity states. All the data considered are shown to be consistent with flaring episodes having a mean flare interval of 435 days with an rms scatter of about 10%. It is suggested that the observations are most easily interpreted in terms of an 'X-ray dwarf nova' binary of the type proposed for the transient X-ray source A0620-00. Constraints on more detailed features of the source model are discussed.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Nature; 265; Feb. 17
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    On the relationship of interstellar N2H/+/, HCO/+/, HCN, and CN (1977)
    In:  Other Sources
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    Publikationsdatum: 2011-08-17
    Beschreibung: A survey of 73 sources has been made in the emission lines of N2H(+) and HCO(+), including detailed maps of four sources (Ori A, OMC-2, DR 21 OH, and NGC 6334). These data are combined with equally extensive data for HCN and CN to make a detailed study of the spatial relationship of these four species. Actual abundance ratios are shown to vary, often sharply, over small scale lengths (of the order of 1 arcmin) within the mapped sources. Excitation temperatures also vary. All four species appear to be subthermally excited. The abundance ratios and their spatial variations are interpreted in terms of ion-molecular formation and destruction processes. It is concluded that the relative abundances of CO may be considerably lower in some regions than previously believed. No evidence is found for variations in the C/O ratio over small scale lengths in Ori A. The degree of ionization of the Ori A molecular cloud may be significantly different from that of other molecular clouds.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Astrophysical Journal; vol. 211
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  • 74
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    A simple physical model for X-ray burst sources (1977)
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    Publikationsdatum: 2011-08-17
    Beschreibung: In connection with information considered by Illarianov and Sunyaev (1975) and van den Heuvel (1975), a simple physical model for an X-ray burst source in the galactic disk is proposed. The model includes an unevolved OB star with a relatively weak stellar wind and a compact object in a close binary system. For some reason, the stellar wind from the OB star is unable to accrete steadily on to the compact object. When the stellar wind is sufficiently weak, the compact object accretes irregularly, leading to X-ray bursts.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Nature; 265; Jan. 20
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    Remote sensing investigations of wetland biomass and productivity for global biosystems research (1983)
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    Publikationsdatum: 2011-08-18
    Beschreibung: Monitoring biomass of wetlands ecosystems can provide information on net primary production and on the chemical and physical status of wetland soils relative to anaerobic microbial transformation of key elements. Multispectral remote sensing techniques successfully estimated macrophytic biomass in wetlands systems. Regression models developed from ground spectral data for predicting Spartina alterniflora biomass over an entire growing season include seasonal variations in biomass density and illumination intensity. An independent set of biomass and spectral data were collected and the standing crop biomass and net primary productivity were estimated. The improved spatial, radiometric and spectral resolution of th LANDSAT-4 Thematic Mapper over the LANDSAT MSS can greatly enhance multispectral techniques for estimating wetlands biomass over large areas. These techniques can provide the biomass data necessary for global ecology studies.
    Schlagwort(e): EARTH RESOURCES AND REMOTE SENSING
    Materialart: NASA. Goddard Space Flight Center LANDSAT-4 Sci. Characterization; 4 p
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    An evaluation of LANDSAT-4 thematic mapper data for their geometric and radiometric accuracies and their relevance to geologic mapping (1983)
    In:  Other Sources
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    Publikationsdatum: 2011-08-18
    Beschreibung: Thematic mapper scenes for Washington, D.C. and Macon, Georgia were examined to determine their radiometry and geometric accuracy. Specific band ratios were used to determine their effectiveness in defining vegetation and rock mineralogy. the TM 3/4 band ratio was used to define vegetation and the 5/2 band ratio was used to define limonitic rocks. The 5/7 band ratio was evaluated to test the effectiveness of the 1.6 and 2.2 mm bands in detecting clay and carbonate bearing rocks. Preliminary results show that clay minerals containing absorption bands at 2.2 mm, which are centered in the TM band 7, can be readily detected when the band ratio images are suitably contrast stretched. Bright rocks, such as marbles, which contain absorption bands in the 2.33 mm region, near the wavelength of TM band 7, are only evident upon harsher contrast stretching of the 5/7 band ratio. Geobotanical studies of Washington, D.C. show that monospecific forest canopies can be differentiated.
    Schlagwort(e): EARTH RESOURCES AND REMOTE SENSING
    Materialart: NASA. Goddard Space Flight Center LANDSAT-4 Sci. Characterization; 5 p
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    Thematic mapper intraband radiometric performance (1983)
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    Publikationsdatum: 2011-08-18
    Beschreibung: There are small differences between the average DN for the 16 detectors in each band, typically 0.8 DN; the standard deviations also differ typically by 0.4 DN. Differences of mode in a band are as large as 6 DN. Some DN levels appear to be strongly favored over adjacent levels. Differences between forward and reverse scans are approximately 0.1 DN in the mean, and 0 to 0.6 DN in the standard deviation. Geometrically resampled images (P data), in which the fixed correspondence between lines and single detectors is lost, are statistically similiar to the ensemble of detectors in each band in A data. The magnitude of inter-detector variation is readily seen by making an image of the first derivative in the vertical (line) direction of a flat field and stretching progressively wider ranges to gray; most detectors differ from their neighbors by 1 to 2 DN. The film output from the GSFC filmwriter used for TM images was found to have scale errors in both sample and line directions corresponding to four pixels in a TM image, and skew corresponding to three pixels.
    Schlagwort(e): EARTH RESOURCES AND REMOTE SENSING
    Materialart: NASA. Goddard Space Flight Center LANDSAT-4 Sci. Characterization; 2 p
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    In-progress absolute radiometric inflight calibration of the LANDSAT-4 sensors (1983)
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    Publikationsdatum: 2011-08-18
    Beschreibung: An approach is described for providing periodic inflight absolute radiometric calibrations of the LANDSAT-4 sensors by reference to selected, instrumented ground areas. Results of some early ground measurements and computer simulations are presented. Selection of a suitable ground reference site, accurate measurement of the spectral reflectance of the selected area, determination of atmospheric characteristics during the morning of the sensor overpass, reduction of the measured data and their use in an appropriate atmospheric radiative transfer program, and comparison of the radiance level data with the digital counts of for the images of the selected areas are discussed. Preliminary measurements of gypsum are being made as an aid in defining the characteristics of field equipment to be constructed and calibrated for use over the White Sands Missile Range.
    Schlagwort(e): EARTH RESOURCES AND REMOTE SENSING
    Materialart: NASA. Goddard Space Flight Center LANDSAT-4 Sci. Characterization; 3 p
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    Spectral characterization of the LANDSAT-4 thematic mapper sensors (1983)
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    Publikationsdatum: 2011-08-18
    Beschreibung: Data collected on the spectral characteristics of the LANDSAT-4 and LANDSAT-4 backup thematic mapper instruments, the protoflight (PF) and flight (F) models, respectively are analyzed and summarized. Tests were conducted on the instruments and their components to determine compliance with two sets of spectral specifications: Band-by-band spectral coverage and channel-by-channel within-band spectral matching.
    Schlagwort(e): EARTH RESOURCES AND REMOTE SENSING
    Materialart: LANDSAT-4 Sci. Characterization; 2 p
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    Thermal band characterization of LANDSAT-4 thematic mapper (1983)
    In:  Other Sources
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    Publikationsdatum: 2011-08-18
    Beschreibung: The TM band 6 shutter background and the 34.7 C internal black body signal were measured over 50 day dates. Variability of the shutter background temperature was from 7 C to 11 C. For ten specific images, the digital counts of the calibration data were measured. The average pulse value of the black body peak decreased from 174 to 149 counts while the shutter background counts varied as a function of shutter temperature from 77 to 85. Relative internal gains between the four channels were calculated and compared to prelaunch values. They showed gains over 9 months of up to 5%. Frequency histograms of number of pixels vs. digital counts from a night scene were used to determine gain relative to the mean and to discern a systematic along-scan pattern in a difference between forward and reverse scan counts of up to 0.5. A corrected digital image was obtained. A temperature estimate for and area of Lake Erie of 18.5 C to 19.9 C was obtained. Local temperature records showed 21 C.
    Schlagwort(e): EARTH RESOURCES AND REMOTE SENSING
    Materialart: LANDSAT-4 Sci. Characterization; 3 p
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    Impact of LANDSAT MSS sensor differences on change detection analysis (1983)
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    Publikationsdatum: 2011-08-18
    Beschreibung: Differences in overall sensor response, due to both factors within the sensor system, and external factors such as atmospheric effects, must be dealt with before change detection techniques using image differencing can be successfully implemented. The approach used to be coregister data to a base, followed by between image scatterogram generation and evaluation, and image differencing. Data from LANDSAT 2 and 3 were registered to LANDSAT 4 data. The area was limited to a small protion of the scene near the City of Santa Cruz because this was the only area cloud and haze free on all the images. Visual examination of each image, as well as the between image scatterograms, provide information on radiometric characteristics of each sensor. The image differencing, after normalizing for radiometric differences, provides a visual depiction of geometric distortions.
    Schlagwort(e): EARTH RESOURCES AND REMOTE SENSING
    Materialart: NASA. Goddard Space Flight Center LANDSAT-4 Sci. Characterization; 2 p
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    Investigation of radiometric properties of LANDSAT-4 MSS (1983)
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    Publikationsdatum: 2011-08-18
    Beschreibung: Two full frames of radiometrically corrected (Type A) LANDSAT-4 MSS data were analyzed digitally and visually for evidence of residual calibration differences between detectors, quantization effects, and other sensor-related artifacts. Both standard statistical and Fourier analysis techniques were employed. Opportunities for coincident coverage by LANDSATS 3 and 4 were identified in the contiguous 48 states. Paired acquisitions for two scenes were obtained and analyzed to establish relationships between signal values from common areas imaged by the two MSS Systems. Initial findings on detector-to-detector differences, coherent noise, and LANDSAT 4 to LANDSAT 3 calibration are summarized. Results show that LANDSAT 4 MSS produces data of generally good quality with dynamic ranges and target responses similar to those of previous sensors.
    Schlagwort(e): EARTH RESOURCES AND REMOTE SENSING
    Materialart: NASA. Goddard Space Flight Center LANDSAT-4 Sci. Characterization; 3 p
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    TM report (1983)
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    Publikationsdatum: 2011-08-18
    Beschreibung: Key spectral, radiometric, and geometric characteristics of the TM sensor are examined. Spectrally, band 5 is slightly wider than specified and its upper edge at 50% of miximum of 1784 nm includes some unintended overlap with water absorption bands. Thermal band 6 is half the expected width. Radiometrically, the TM has extreme linearity and stability in comparison with previous MSS photomultiplier systems. Forward and reverse scans on TM show some unexplained radiometric differences of up to four digital levels. Primary focal plane bands show a monotomic decrease in gain of about 5% in the five months since launch. The relative internal gains of bands 5 and 7 varied with a period of about 60 days and an amplitude of about 6%. Radiometric calibration must be applied before histogram equalization algorithms to preserve radiometric accuracy. Geometrically, channel 4 in band 2 has a smaller modulation transfer function than desired. There is apparent misregistration of .75 pixels along scan and 0.2 pixels across scan.
    Schlagwort(e): EARTH RESOURCES AND REMOTE SENSING
    Materialart: LANDSAT-4 Sci. Characterization; 2 p
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  • 84
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    LANDSAT-4 evaluation program and scientific characterization activities (1983)
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    Publikationsdatum: 2011-08-18
    Beschreibung: The characterization objectives of the LANDSAT 4 Science Office at GSFC are to: (1) determine the accuracy and precision of sensor and spacecraft performance, image data quality, and derived information; (2) recommend LANDSAT 4 system improvements; and (3) communicate results to the research community. In-house activities are directed toward full access and utilization of the prelaunch and in-orbit engineering test data on the sensor and spacecraft. Principle scientists in remote sensing are involved as part of a major scientific characterization effort, and workshops were held for these investigative teams. A symposium is scheduled prior to turnover of the TM to NOAA.
    Schlagwort(e): EARTH RESOURCES AND REMOTE SENSING
    Materialart: LANDSAT-4 Sci. Characterization; 2 p
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  • 85
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    LANDSAT-4 hightlights (1983)
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    Publikationsdatum: 2011-08-18
    Beschreibung: The LANDSAT 4 thematic mapper sensor possesses approximately twice the spectral resolution, three times the spatial resolution, and four times the spectral sensitivity of the MSS sensor on earlier LANDSAT satellites. Spectral bands on the TM, particularly those at wavelengths of 1.6 and 2.2 micrometers are useful for: (1) distinguishing crops such as rice and soybeans; (2) surveying areas that are cultivated in strip crop fashion; (3) determining clay variations and abundances and rock classifications; and (4) differentiating nutrients and sediments found in coastal waters. The sensor can identify surface features 30 meters on a side, which roughly corresponds to a standard city block. Highway construction, land excavation, urban growth, and the health and extent of vegetation can be detected.
    Schlagwort(e): EARTH RESOURCES AND REMOTE SENSING
    Materialart: LANDSAT-4 Sci. Characterization; 3 p
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  • 86
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    Interplanetary current sheets at 1 AU (1977)
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    Publikationsdatum: 2011-08-17
    Beschreibung: The structure and nature of 'discontinuities' in the interplanetary magnetic field at 1 AU in the period from March 18 to April 9, 1971, is determined by using high-resolution magnetic-field measurements from Explorer 43. The discontinuities that were selected for this analysis occurred under a variety of interplanetary conditions at an average rate of 0.5/hour. Both tangential and rotational discontinuities were identified. Tangential discontinuities were observed every day, even among Alfvenic fluctuations. In particular, on one day during which Alfvenic fluctuations were intense and persistent in a high-speed stream, tangential discontinuities (TD's) were seen throughout the day at an average rate of 0.5/hour; rotational discontinuities (RD's) were also observed during this day at a higher than usual rate, the ratio of TD's to RD's being approximately one. The structure of most of the current sheets was simple and ordered; i.e., the magnetic field usually changed smoothly and monotonically from one side of the current sheet to the other. The thickness distributions of the TD's and RD's with very smooth current sheets were similar. The average thickness of the RD's was 1200 km (13 proton Larmor radii), and the average thickness of the TD's was 1300 km (12 proton Larmor radii).
    Schlagwort(e): ASTROPHYSICS
    Materialart: Journal of Geophysical Research; 82; Aug. 1
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  • 87
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    Mass loss, long-period variables, and the formation of circumnebular shells (1977)
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    Publikationsdatum: 2011-08-17
    Beschreibung: We have found that the rate of mass loss M increases with an increase in the period of pulsation for Mira-type variables. This result suggests that the rate of mass loss is accelerated with time until a maximum value is reached before the ejection of the outer envelope. The matter from the continuous mass loss during the evolution of the star produces supersonic shock waves that sweep up the interstellar gas upon encountering the interstellar medium, so that a shell is formed. This phenomenon may account for the observations of extended regions of emission that surround planetary nebulae.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Astrophysical Journal; vol. 216
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  • 88
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    Evidence for mass loss in the mid-ultraviolet spectra of Be stars (1977)
    In:  Other Sources
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    Publikationsdatum: 2011-08-17
    Beschreibung: The spectral region about the Mg II doublet lines near 2800 A of Be and shell stars has been observed. The star Gamma Cas shows narrow components to each resonance doublet line shifted 215 km/s toward shorter wavelengths. The resonance and subordinate lines of Zeta Tau are shifted toward shorter wavelengths by 75 km/s, and the subordinate lines are greatly strengthened. The star Kappa Dra, which is much later in spectral type, shows a comparatively normal doublet spectrum.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Astrophysical Journal; vol. 216
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  • 89
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    Scale-covariant theory of gravitation and astrophysical applications (1977)
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    Publikationsdatum: 2011-08-17
    Beschreibung: Generalized Einstein equations invariant under scale transformations are presented, and several astrophysical tests studied. It is assumed that the dynamics of atoms or clocks used as measuring apparatus is given a priori. Connection with gauge fields and broken symmetries is made through the cosmological constant.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Physical Review Letters; 39; Aug. 22
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  • 90
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    Antarctic topography from balloons (1977)
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    Publikationsdatum: 2011-08-17
    Beschreibung: A description is presented of an investigation involving the collection of Antarctic ice sheet surface topography data by means of balloons, floating at an altitude of about 12.5 km, which traversed the Antarctic during its 1975 summer. These balloons were part of 411 constant density balloons launched in the Southern Hemisphere during the Tropical Wind, Energy conversion and Reference Level Experiment. The three sensors carried by each balloon included a radio altimeter, a pressure sensor, and an ambient temperature sensor. Data transmitted by a balloon are received by a measuring system on board the Nimbus-6 satellite. A synoptic map is presented of the 150 mbar pressure surface at 1200 GMT, December 11, 1975.
    Schlagwort(e): EARTH RESOURCES AND REMOTE SENSING
    Materialart: Nature; 268; Aug. 11
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  • 91
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    What is a cometary nucleus (1977)
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    Publikationsdatum: 2011-08-17
    Beschreibung: The meaning of the term 'cometary nucleus' is discussed, taking into account observations of comets with different characteristics. It is pointed out that for some comets, there may be no nucleus to be seen at any time, while in others as the comet brightens or undergoes changes, a nucleus may develop to be seen for a time or even intermittently, while occasionally more than one nucleus may be seen to be present. On the basis of a study of observational reports it emerges that no more than about 30 per cent of comets exhibit anything resembling a starlike nucleus.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Royal Astronomical Society; vol. 18
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  • 92
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    Statistical equilibrium in cometary C2. I (1977)
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    Publikationsdatum: 2011-08-17
    Beschreibung: Swan-band emission from the C2 molecule provides important information for a study of the physical processes occurring in comets. It is, therefore, a disturbing factor that many quantitative Swan-band observations are in clear contradiction of predictions of resonance fluorescence excitation of the Swan bands. A description is presented of an investigation involving an application of resonance fluorescence theory to C2. The investigation takes into account all important electronic transitions which determine the population distribution of the lowest energy states. It is found that the previous discrepancy for the brighter band sequences disappears.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Astrophysical Journal; vol. 216
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  • 93
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    Evolution of helium stars (1977)
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    Publikationsdatum: 2011-08-17
    Beschreibung: The evolution of helium stars in the mass range from 4 to 15 solar masses has been followed from the initial helium main sequence to the end of carbon burning in the core, with the use of Carson's (1976) radiative opacities. As compared with earlier work based on smaller opacities, the main-sequence band in the H-R diagram is now both wider and cooler than before. If neutrino losses are neglected in the stellar models, the phase of carbon burning in the core occurs in the red-supergiant region; otherwise, it occurs, as it does in the earlier models with or without neutrino emission, close to the helium main sequence. Observational data for Wolf-Rayet stars and R Coronae Borealis variables are found to lend some support to the present models.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Astrophysical Journal; vol. 216
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  • 94
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    Optical, infrared and radio studies of compact H II regions. II - The H alpha knot S88B (1977)
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    Publikationsdatum: 2011-08-17
    Schlagwort(e): ASTROPHYSICS
    Materialart: Astronomy and Astrophysics; 59; 2, Ju; July 197
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  • 95
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    Rare accessory uraninite in a Sierran granite (1977)
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    Publikationsdatum: 2011-08-17
    Beschreibung: One grain of uraninite was found in a single thin-section of Sierran granite. Electron and ion microprobe analysis were used to determine the composition. Since the U-Pb age calculated for the uraninite does not differ greatly from the K-Ar age of the unit in which it occurs, it is suggested that the mineral is primary and not reworked from a preexisting rock. No uraninite has been detected in heavy mineral concentrates from other rocks of the local area.
    Schlagwort(e): EARTH RESOURCES AND REMOTE SENSING
    Materialart: American Mineralogist; 62; 1977
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  • 96
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    Lyman-alpha observations of Comet West /1975n/ (1977)
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    Publikationsdatum: 2011-08-17
    Beschreibung: The rate of hydrogen production of Comet West is studied through rocket observation of solar Lyman-alpha radiation resonantly scattered by the escaping hydrogen atoms. Two sets of Lyman-alpha exposure sequences are used to obtain computer-smoothed brightness contour (isophote) maps covering a density range of 100:1. A simple radial outflow model is applied to the contour maps to determine the rate of hydrogen production (3.2 by 10 to the 30th power atoms/sec.) Discrepancies between the observed shape of the outer isophotes and predicted models may be explained by optical depth effects, or by the presence of small pieces of the comet's nucleus distributed along the orbit. Hydrogen, carbon, and oxygen production for Comet West and Comet Kohoutek are compared; differences may be accounted for by variations in the composition or evolution of the two comets.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Icarus; 31; Aug. 197
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  • 97
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    Interstellar clouds and molecular hydrogen (1977)
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    Publikationsdatum: 2011-08-17
    Beschreibung: Data obtained from the Copernicus Orbiting Astronomical Observatory, launched in 1972 and still obtaining information, are used in a discussion of the interstellar medium. The Copernicus instruments have facilitated direct estimates for the density and temperature of individual interstellar clouds, and improved the ability to determine where along the line of sight a cloud lies with respect to background stars. The physical characteristics of hydrogen molecules are considered, with attention to the formation and destruction of interstellar hydrogen. The differences between 'thin' clouds, in which molecular hydrogen is optically thin, and 'thick' clouds are examined. Several features of the interstellar medium are described.
    Schlagwort(e): ASTROPHYSICS
    Materialart: American Scientist; 65; July-Aug
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  • 98
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    Positions of X-ray sources near the galactic center measured by the Ariel-5 RMC experiment (1977)
    In:  Other Sources
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    Publikationsdatum: 2011-08-17
    Schlagwort(e): ASTROPHYSICS
    Materialart: Astrophysical Journal; vol. 215
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  • 99
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    Spectroscopic studies of very old hot stars. III - Atmospheric properties of seven planetary nuclei (1977)
    In:  Other Sources
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    Publikationsdatum: 2011-08-17
    Beschreibung: The atmospheric properties of seven planetary nuclei which have O or Of-type spectra were determined by use of the Zanstra method and by analysis of the visual line spectra. One finding is that the O-type spectral sequence may extend to effective temperatures of 90,000 kelvins or more, if the results of the Zanstra method are to be believed. However, there are some indications of internal inconsistency in the Zanstra method and some outstanding discrepancies between the effective temperatures indicated by the Zanstra method and those indicated from analysis of the visual line spectra. Two ways to resolve these discrepancies are to postulate an excess of extreme-UV stellar flux or to postulate a hot binary companion for some central stars. In either case the validity of the Harmon-Seaton evolutionary sequence for central stars becomes questionable.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Astrophysical Journal; vol. 215
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    The relationship between the galactic matter distribution, cosmic-ray dynamics, and gamma-ray production (1977)
    In:  Other Sources
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    Publikationsdatum: 2011-08-17
    Beschreibung: The concept that cosmic-ray density is related to the matter to which cosmic rays are dynamically coupled through magnetic fields on the scale of galactic arm segments is considered with specific reference to gamma-ray astronomy. A model of the galactic-matter and cosmic-ray distributions is developed on the basis of 21-cm radio surveys and recent observations of the 2.6-mm CO emission line by assuming that cosmic rays are galactic in origin, their column density is proportional to the total interstellar-gas column density, their scale height is considerably larger than that of the matter, and the Galaxy is a spiral with an arm/interarm density ratio of about 3 to 1. It is found that there is a good correlation between the observed gamma-ray intensity and that predicted on the basis of essentially complete coupling of cosmic rays to the best estimate of atomic and molecular hydrogen in the Galaxy. Individual maxima observed in gamma-radiation from the central region of the Galaxy are shown to be well correlated with those predicted to result from certain spiral-arm tangents if all the matter is assumed to be modulated in a particular spiral-arm segment pattern.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Astrophysical Journal; vol. 215
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