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  • Engineering General  (353)
  • ASTRONOMY
  • 2020-2024
  • 1995-1999  (185)
  • 1985-1989  (446)
  • 1955-1959
  • 1
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    Late-time spectra and type Ia supernova models: New clues from the Hubble Space Telescope (1995)
    In:  Other Sources
    Details
    Publication Date: 2019-07-13
    Description: Calculated late-time spectra of two classical hydrodynamical models for Type Ia supernovae (deflagration model W7 of Nomoto, Thielemann, & Yokoi, and delayed detonation model DD4 of Woosley & Weaver) are compared with observations of SN 1992A and other spectroscopically normal SNe Ia. An important new piece of information is provided by observations done with the Hubble Space Telescope (HST) which cover the ultraviolet range at the nebular phase of a SN Ia: SN 1992A in NGC 1380. For the first time a picture of SN Ia emission from the ultraviolet through the optical is obtained at these phases. Predictions of the classical model (W7 and DD4) are compared with the observed spectrum of SN 1992A and with the optical spectra of SN 1989M in NGC 4579 and SN 1990N in NGC 4639 at similar epochs. The absolute B and V magnitudes of the models are also estimated at these late phases. Taken at face value the nebular spectra of these 'classical' models are more consistent with the long extragalactic distance scale, pointing to distances to NGC 4579 around 21 +/- 3 Mpc and a slightly larger distance, 22 +/- 3 Mpc, to NGC 4639, on the back side of the Virgo Cluster. However, the calculated Fe(+3) luminosity as predicted from the models exceeds the observed limit from the HST data of SN 1992A. Other differences in the ratios of the line intensities between calculated and observed spectra, show some disagreement with the observed spectra at the nebular phases. They may not be the best choice for spectroscopically normal SNe Ia, and their use as an independent calibration of the extragalactic distance scale should be viewed with caution.
    Keywords: ASTRONOMY
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 439; 1; p. 60-73
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  • 2
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    Ultraviolet and optical observations of OB associations in M31 (1995)
    In:  Other Sources
    Details
    Publication Date: 2019-08-28
    Description: Images of the central and southern parts of the local group Sb spiral galaxy M31 were obtained by the Ultraviolet Imaging Telescope during the Astro-1 Spacelab mission. Stellar photometry is obtained for 611 stars in 59 van den Bergh associations in the near-UV A1 band (central wavelngth 2490 A), and for 130 of these stars in the far UV B1 band (central wavlength 1520 A). In addition, B-band magnitudes for 456 of the stars in approximately 30 associations, together with U- and R-band photometry for approximately 290 stars in approximately 15 associations are determined from CCD images. B-magnitudes from the catalog of Magnier et al. (1992) are given for 137 stars and R-magnitudes for 233 stars. Stellar positions are obtained from the ground based CCD images and from UIT images. Total fluxes in the UV bands are measured for 63 associations . Finding charts are presented in the NUV and FUV bands, as well as, one optical band. Tables give the images utilized in this investigation, the associations observed, with positions, total UV fluxes, extinctions estimated from color-magnitude diagrams, and stellar positions with photometry in up to five bands. UV color magnitude diagrams are presented with extinctions estimated by comparing the observed association color magnitude diagrams with colors and magnitudes of early-type stars computed from the IUE spectral atlas of Fanelli et al. (1992). Comparison with evolutionary models suggests a maximum initial mass approx. 85 solar mass. Ultraviolet extinctions within most M31 OB associations is found to follow an extinction curve similar to that of Hutchings et al. (1992). The variation in the fraction of near-UV stars also measured in the far-UV among the associations is probably caused by variations in age, extinction, and the degree of foreground contamination.
    Keywords: ASTRONOMY
    Type: Astrophysical Journal Supplement Series (ISSN 0067-0049); 98; 2; p. 595-615
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  • 3
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    Ultraviolet imaging telescope and optical emission-line observations of H II regions in M81 (1995)
    In:  Other Sources
    Details
    Publication Date: 2019-08-28
    Description: Images of the type Sab spiral galaxy M81 were obtained in far-UV and near-UV bands by the Ultraviolet Imaging Telescope (UIT) during the Astro-1 Spacelab mission of 1990 December. Magnitudes in the two UV bands are determined for 52 H II regions from the catalog of Petit, Sivan, & Karachentsev (1988). Fluxes of the H-alpha and H-beta emission lines are determined from CCD images. Extinctions for the brightest H II regions are determined from observed Balmer decrements. Fainter H II regions are assigned the average of published radio-H-alpha extinctions for several bright H II regions. The radiative transfer models of Witt, Thronson, & Capuano (1992) are shown to predict a relationship between Balmer Decrement and H-alpha extinction consistent with observed line and radio fluxes for the brightest 7 H II regions and are used to estimate the UV extinction. Ratios of Lyman continuum with ratios predicted by model spectra computed for initial mass function (IMF) slope equal to -1.0 and stellar masses ranging from 5 to 120 solar mass. Ages and masses are estimated by comparing the H-alpha and far-UV fluxes and their ratio with the models. The total of the estimated stellar masses for the 52 H II regions is 1.4 x 10(exp 5) solar mass. The star-formation rate inferred for M81 from the observed UV and H-alpha fluxes is low for a spiral galaxy at approximately 0.13 solar mass/yr, but consistent with the low star-formation rates obtained by Kennicutt (1983) and Caldwell et al. (1991) for early-type spirals.
    Keywords: ASTRONOMY
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 438; 1; p. 181-187
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  • 4
    Electronic Resource
    Electronic Resource
    Letters to the editor (1989)
    New York, NY [u.a.] : Wiley-Blackwell
    International Journal for Numerical and Analytical Methods in Geomechanics 13 (1989), S. 101-107 
    Details
    ISSN: 0363-9061
    Keywords: Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Architecture, Civil Engineering, Surveying , Geosciences
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/nag.1610130109
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  • 5
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    Measurements of the millimeter-wave spectrum of interstellar dust emission (1995)
    In:  Other Sources
    Details
    Publication Date: 2019-08-28
    Description: We report measurements of the differential brightness of interstellar dust emission near the Galactic plane and at high Galactic latitudes. The data were obtained as part of a program to measure anisotropy in the cosmic microwave background (CMB). The measurements were made with a 0.5 deg beam size and a 1.3 deg sinusoidal chop, in broad bands (Delta nu/nu approximately 0.3) centered near frequencies of 6, 9, and 12 cm(exp -1). A measurement made toward the Galactic plane, at longitude 1 = 23.7 deg, is compared with the contrast observed in the 100 micrometers IRAS data. Assuming the dust emission has a brightness I(sub nu) proportional to nu(sup n)B(sub nu)(T(sub d)), where B(sub nu) is the Planck function, a best fit yields n = 1.6 +/- 0.4, T(sub d) = 24 +/- 5 K. In a region near the star mu Pegasi (mu PEG l = 91 deg, b = -31 deg), the comparison of our data with the 100 micrometers IRAS data yields n = 1.4 +/- 0.4, and T(sub d) = 18 +/- 3 K. In a second region near the star gamma Ursa Minoris (GUM l = 108 deg, b = 41 deg), an upper limit is placed on contrast in dust emission. This upper limit is consistent with spectrum measured at mu PEG and the IRAS 100 micrometer emission contrast at GUM, which is approximately 8 times lower than mu PEG.
    Keywords: ASTRONOMY
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 444; 1; p. 226-230
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  • 6
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    Analysis of Gaspra lightcurves using Galileo shape and photometric models (1995)
    In:  Other Sources
    Details
    Publication Date: 2019-08-28
    Description: Galileo-based models for the shape of 951 Gaspra and the global-average photometric behavior of its surface have been used to model a representative subset of the asteroid's telescopic lightcurves. Fitting the synthetic lightcurves to the observed timing of lightcurve extrema, and knowing the orientation of Gaspra's axes at the time of the Galileo flyby, leads to a sidereal rotation period for the asteroid of 7.042024 +/- 0.000020 hr, a slight change from the period reported by Magnusson et al. (1992). Initially, the shapes, amplitudes, and absolute photometry of the synthetic and observed lightcurves agree with each other to within 0.05-0.1 mag. Small modifications to the Gaspra shape model on sides of the asteroid poorly imaged by Galileo (changes of 700 m or less in the southern hemisphere at longitudes 90 deg-270 deg W) reduce the typical discrepancies to approximately 0.05 mag in lightcurve shape and less than 0.03 mag in absolute photometry. The result demonstrates that Earth-based lightcurves can be used to refine the shape of a spacecraft-imaged irregular object in areas that are poorly constrained by the spacecraft observations. The consistency and phase-angle dependence of the Galileo-based model for Gaspra photometry, supports the accuracy of the absolute calibration of the Galileo SSI camera, and confirms the Earth-based determination of the V-filter geometric albedo of the asteroid (0.22 +/- 0.03; Tholen et al., submitted for publication). Remaining discrepancies between the synthetic and observed lightcurves show no indication of systematic latitudinal variations in albedo and also cannot be explained entirely by isolated albedo spots. These discrepancies are most likely caused by (1) small, remaining, hard-to-constrain errors in the Gaspra shape model and/or (2) moderate variations in macroscopic roughness across the asteroid's surface, in particular making longitudes 130 deg to 300 deg W moderately rougher than the opposite hemisphere.
    Keywords: ASTRONOMY
    Type: Icarus (ISSN 0019-1035); 114; 2; p. 387-402
    Format: text
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  • 7
    Electronic Resource
    Electronic Resource
    Analysis of laminated bimodulus composite thin shells of revolution using a doubly curved quadrilateral finite element (1985)
    Chichester [u.a.] : Wiley-Blackwell
    International Journal for Numerical Methods in Engineering 21 (1985), S. 285-299 
    Details
    ISSN: 0029-5981
    Keywords: Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: This paper presents a finite element analysis of laminated bimodulus composite thin shells of revolution using a 48 d.o.f. doubly curved quadrilateral finite element. All the three displacements of the shell element reference surface are expressed as products of one-dimensional first-order Hermite interpolation polynomials. The constitutive relationship for a bimodulus composite is assumed to depend on the fibre-direction strain experienced by each orthotropic layer. Consequently the true state of strain and the corresponding constitutive relationship in a bimodulus composite structure are to be determined iteratively. The true state of stress/strain is obtained by specifying a maximum error in the locations of the two neutral surfaces (one along each of the orthogonal reference axes) in the shell. The use of the quadrilateral shell finite element is validated by solving the problem of (i) a freely supported single layer (0°) bimodulus composite square plate and (ii) a freely supported single layer (0°) cylindrical panel, which are subjected to sinusoidal transverse loading and for which analytical solutions are available. Next, the problems of a single layer (90°) pinched cylindrical shell and a single layer (0°) open crown hemispherical shell are solved to show the ability of the present program.
    Additional Material: 14 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/nme.1620210207
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  • 8
    Electronic Resource
    Electronic Resource
    A numerical study of various algorithms related to the preconditioned conjugate gradient method (1985)
    Chichester [u.a.] : Wiley-Blackwell
    International Journal for Numerical Methods in Engineering 21 (1985), S. 1315-1338 
    Details
    ISSN: 0029-5981
    Keywords: Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: We present the results of a numerical study of the preconditioned conjugate gradient algorithm, the minimal residual algorithm, the biconjugate gradient algorithm and the bi-minimal residual algorithm using both simple test matrices and more realistic test matrices derived from physical problems. The application of the methods to unsymmetric matrices is considered. We emphasize the importance of a good preconditioning, look at various methods including ICGG(n) and incomplete block factorization, and make some practical recommendations. Some of the folk-lore surrounding the semi-iterative methods is dispelled.
    Additional Material: 9 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/nme.1620210711
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  • 9
    Electronic Resource
    Electronic Resource
    TRUNC for shells - an element possibly to the taste of Bruce Irons (1986)
    Chichester [u.a.] : Wiley-Blackwell
    International Journal for Numerical Methods in Engineering 22 (1986), S. 93-115 
    Details
    ISSN: 0029-5981
    Keywords: Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: In his delightful and original textbook,18 Bruce Irons introduces the chapter of plate bending with the remark ‘History of disasters, but the pioneering days are past’. This is certainly true. On the other hand, we learn in the same context from Irons: ‘We believe that the world has not yet exhausted the older formulations.’ In this paper we present a review of theoretical aspects of the plate-bending triangle TRUNC (Reference 4), together with extensive tests in linear statics, dynamics, buckling and nonlinear large deformations both for plates and shells. The unconventional TRUNC model is based on the patch test, which was originated by Irons.1 In spite of its limited theoretical foundation, the performance of this element on a fairly broad field of applications appears at least from the practical point of view very satisfactory.
    Additional Material: 23 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/nme.1620220108
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  • 10
    Electronic Resource
    Electronic Resource
    Numerical studies of buoyancy-driven turbulent flow in a rectangular cavity (1987)
    Chichester [u.a.] : Wiley-Blackwell
    International Journal for Numerical Methods in Engineering 24 (1987), S. 89-99 
    Details
    ISSN: 0029-5981
    Keywords: Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: In this paper some numerical predictions are presented for the buoyancy-driven turbulent flow and heat transfer in a large cavity using both a prescribed eddy viscosity model and a k-∊ model. The results from these models are in good agreement, although the calculations with the prescribed eddy viscosity model are considerably cheaper. The results also show the correct qualitative behaviour, but there are some differences between the predictions and the available experimental data. Possible reasons for these are discussed.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/nme.1620240107
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