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  • ASTROPHYSICS  (20)
  • Engineering General  (2)
  • 2020-2022
  • 1990-1994  (11)
  • 1975-1979  (11)
  • 1
    Electronic Resource
    Electronic Resource
    Chichester [u.a.] : Wiley-Blackwell
    International Journal for Numerical Methods in Engineering 12 (1978), S. 1383-1397 
    ISSN: 0029-5981
    Keywords: Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: The boundary-integral equation medthod is particularly well suited for solution of stress concentration and elastic fracture mechanics problems. The method was not previously applicable to anisotropic three dimensional problems because no efficient technique existed for calculation of the required point load solution for an infinite body. A technique has been developed to evaluate numerically the anisotropic point load soultions, and used to generate data bases for various materials. An intrpolation technique is used to evaluate the point load solutions efficiently within a higher order boundary-intgral equation code. The effectiveness of the technique is verified by solution of problems involving both uniaxial stress states and stress concentrations.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Chichester [u.a.] : Wiley-Blackwell
    International Journal for Numerical Methods in Engineering 29 (1990), S. 1737-1757 
    ISSN: 0029-5981
    Keywords: Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: In practical applications, it is often necessary to determine the natural frequencies and mode shapes of a solid, in addition to the static response under a variety of loading conditions. This paper discusses the calculation of natural frequencies and mode shapes of three-dimensional solids using the boundary element method. The method developed is based on the use of particular integrals of the elastic equilibrium equations, and employs only real arithmetic. It represents an extension to three dimensions of work previously carried out for two-dimensional problems in References 1 and 15. The method has been incorporated, for multiregion analysis, in the BEST3D (Boundary Element Solution Technology - Three Dimensional) computer program.Much of the work described in this paper was carried out under the support of National Aeronautics and Space Administration Contract NAS3-23697, ‘3D Inelastic Analysis Methods for Hot Section Components’. The program managers at the NASA-Lewis Research Center are Dr C. C. Chamis and Mr Dale Hopkins. The program manager at Pratt & Whitney is Dr E. S. Todd Results of the boundary element calculations are compared with analytical, finite element and experimental results.
    Additional Material: 14 Ill.
    Type of Medium: Electronic Resource
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  • 3
    Publication Date: 2011-08-24
    Description: We calculate the spectral hardness ratios for several intense gamma-ray bursts (GRBs) which have sufficient statistics in four energy channels. We study the evolution of these hardness ratios during the events using color-color diagrams (CCDs) and we attempt a preliminary classification of GRBs based on their CCD evolution.
    Keywords: ASTROPHYSICS
    Type: Astronomy and Astrophysics Supplement Series (ISSN 0365-0138); 97; 1; p. 55-57.
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  • 4
    Publication Date: 2011-08-24
    Description: A tentative detection of the J = 1 - 0 emission line of (C-13)O has been obtained with SEST from a 24.4 hour integration. The velocity resolution used was 0.23 km/s and the FWHP beamwidth was 45 arcsec. If the (C-13)O line data are conservatively interpreted as an upper limit, the (C-12)O/(C-13)O ratio is not less than 60. Our result supports the previous determination of a large value of the isotope ratio in this cloud, made using radio emission lines with a 1.6-arcmin beam, and extends the ratio based on emission lines to a smaller region. When interpreted as a lower limit, our data is consistent with the ratio obtained from UV absorption line data for (C-12)O and (C-13)O.
    Keywords: ASTROPHYSICS
    Type: Astronomy and Astrophysics (ISSN 0004-6361); 262; 1; p. 248-250.
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  • 5
    Publication Date: 2011-08-24
    Description: The first available 44 gamma-ray bursts (GRBs) detected by the Burst and Transient Source Experiment on board the Compton Gamma-Ray Observatory have been inspected for echo signals following shortly after the main signal. No significant echoes have been found. Echoes would have been expected were the GRBs distant enough and the universe populated with a sufficient density of compact objects composing the dark matter. Constraints on dark matter abundance and GRB redshifts from the present data are presented and discussed. Based on these preliminary results, a universe filled to critical density of compact objects between 10 exp 6.5 and 10 exp 8.1 solar masses are now marginally excluded, or the most likely cosmological distance paradigm for GRBs is not correct. We expect future constraints to be able either to test currently popular cosmological dark matter paradigms or to indicate that GRBs do not lie at cosmological distances.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 414; 1; p. 36-40.
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  • 6
    Publication Date: 2011-08-24
    Description: The integrated number-peak-flux relation measured by the Burst and Transient Source Experiment (BATSE) on board the Compton Gamma Ray Observatory is compared with several standard cosmological distributions for gamma-ray bursts (GRBs). Friedmann-Robertson-Walker models were used along with the assumption that the bursts are standard candles and have no number or luminosity evolution. For a given Omega spectral shape, we used a free parameter, essentially the comoving number density of bursts, to generate a best fit between the cosmology and the measured relation. Our results are shown for a subsample of the first 260 GRBs recorded by BATSE. We find acceptable fits between simple cosmological models and the brightness distribution data, as determined by the Kolmogorov-Smirnov one-distribution statistical test. One cannot distinguish a single best cosmological model from the goodness of the fits. The best fit implies that BATSE GRBs are complete out to a redshift of about unity. However, significantly higher and lower redshifts, by as much as a factor of 2, are possible for other marginally acceptable fits.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 2 - Letters (ISSN 0004-637X); 411; 2; p. L55-L58.
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  • 7
    Publication Date: 2011-08-24
    Description: We present an analysis of density, temperature, and excitation conditions in a one half square degree region around BN/KL in Orion A using new C(O-l8) J = 1 yields 0 and J = 2 yields 1 data. This paper extends a previous study of Orion A, based on a multitransition analysis of (C-13)O, to the optically thinner C(O-18) species that traces better the dense inner regions of giant molecular clouds. From the C(O-18) maps we identify several condensations and are able to derive their size, linewidth, average density, mass, and virial mass.
    Keywords: ASTROPHYSICS
    Type: Astronomy and Astrophysics (ISSN 0004-6361); 270; 1-2; p. 468-476.
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  • 8
    Publication Date: 2011-08-19
    Description: Evidence is found for periodic density structure in the highly fragmented interior of the Orion A molecular cloud from analysis of a large scale map of C(O-18) J = 1 - 0 emission. The spatial wavelength is about 1 parsec, and extends at least over 2 degrees along the main filament of Orion A and is also observed in other filamentary structures in Orion. This periodicity in the clumps is a result of externally triggered and magnetically mediated cloud collapse and fragmentation.
    Keywords: ASTROPHYSICS
    Type: Astronomy and Astrophysics (ISSN 0004-6361); 247; 1, Ju
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  • 9
    Publication Date: 2011-08-17
    Keywords: ASTROPHYSICS
    Type: Astronomy and Astrophysics; 61; 1, Oc; Oct. 197
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  • 10
    Publication Date: 2011-08-17
    Description: Balloon observations registering scatter angles in a liquid scintillator have revealed gamma-ray bursts having energies as low as 10 to the -7th ergs per square cm. The burst distribution is graphed according to energy and frequency. The hypothesis that the bursts are galactic in origin is in good agreement with their small recorded energies and their predicted distribution on the graph.
    Keywords: ASTROPHYSICS
    Type: Nature; 271; Feb. 16
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