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  • ASTRONOMY  (13)
  • Engineering  (6)
  • 2020-2021
  • 1990-1994  (14)
  • 1985-1989  (5)
  • 1950-1954
  • 1
    Electronic Resource
    Electronic Resource
    Analysis of some fully-discrete algorithms for the one-dimensional heat equation (1985)
    Chichester [u.a.] : Wiley-Blackwell
    International Journal for Numerical Methods in Engineering 21 (1985), S. 163-168 
    Details
    ISSN: 0029-5981
    Keywords: Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: A fully discrete stability and accuracy analysis of some algorithms for the one-dimensional heat equation is presented. Results illustrate that 2-pass explicit schemes which simultaneously employ lumped and coupled capacity matrices are capable of improved performance over the standard 1-pass explicit scheme.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/nme.1620210113
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    Paper (German National Licenses)
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  • 2
    Electronic Resource
    Electronic Resource
    Letter to the editor (1989)
    Chichester [u.a.] : Wiley-Blackwell
    International Journal for Numerical Methods in Engineering 28 (1989), S. 1485-1485 
    Details
    ISSN: 0029-5981
    Keywords: Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/nme.1620280621
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    Paper (German National Licenses)
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  • 3
    Electronic Resource
    Electronic Resource
    Studies of domain-based formulations for computing exterior problems of acoustics (1994)
    Chichester [u.a.] : Wiley-Blackwell
    International Journal for Numerical Methods in Engineering 37 (1994), S. 2935-2950 
    Details
    ISSN: 0029-5981
    Keywords: Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: The propagation and decay of acoustic waves in exterior domains in an essential ingredient in the study of fluid-structure interaction. A strategy must be devised to compute solutions over domains which are unbounded. Exact impedance conditions at an artificial external boundary are specified by the DtN method, yielding an equivalent problem that is suitable for domain-based computation. The DtN boundary condition is non-reflective, giving rise to exact (and thereby unique) solutions. The truncated DtN operator, which is employed in practice, fails to inhibit the reflection of higher modes, so that non-unique solutions may occur at their harmonics. Simple expressions determine a sufficient number of terms in the truncated operator for unique solutions at any given wave number. There are three characteristic length scales in the computational problem: the radius of the artificial boundary, the geometry of the body (represented by the internal boundary) and the mesh size. Numerical studies examine the dependence of the conditioning of finite element coefficient matrices on the number of terms in the truncated DtN operator vs. the wave number non-dimensionalized by each of the length scales. Analytic results regarding the number of terms sufficient for unique solutions are confirmed. As long as this criterion is respected, no upper limit on the allowable wave number is detected. A local approximation of the boundary conditions restores uniqueness for all wave numbers.
    Additional Material: 9 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/nme.1620371706
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  • 4
    Electronic Resource
    Electronic Resource
    Tensile stresses around boreholes due to transient fluid flow (1993)
    New York, NY [u.a.] : Wiley-Blackwell
    International Journal for Numerical and Analytical Methods in Geomechanics 17 (1993), S. 659-667 
    Details
    ISSN: 0363-9061
    Keywords: Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Architecture, Civil Engineering, Surveying , Geosciences
    Notes: We present solutions for the effective stress induced by gas flow through a porous solid into a borehole resulting from sudden pressure reduction. Tensile effective stress that exceeds the strength of the solid will lead to borehole failure. This has applications to the intentional creation of cavities, relevant to the efficient recovery of coalbed methane, and the avoidance of borehole stability problems in conventional gas production.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/nag.1610170905
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  • 5
    Electronic Resource
    Electronic Resource
    Recent progress in the development and understanding of SUPG methods with special reference to the compressible Euler and Navier-Stokes equationsBased on an invited lecture.Supported by NASA Langley Research Center under Grant NASA-NAG-1-361 and the IBM Almaden Research Center under Grant No. 604912. (1987)
    Chichester : Wiley-Blackwell
    International Journal for Numerical Methods in Fluids 7 (1987), S. 1261-1275 
    Details
    ISSN: 0271-2091
    Keywords: Advection-diffusion equation ; Advective-diffusive systems ; Artificial-diffusion ; Compressible flows ; Discontinuous Galerkin method ; Entropy Error analysis ; Euler equations ; Finite elements ; Galerkin method ; Hyperbolic systems ; Incompressible flow ; Navier-Stokes equations ; Petrov-Galerkin method ; Space-time formulation ; Upwind methods ; Weighted residual methods ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: SUPG methods were originally developed for the scalar advection-diffusion equation and the incompressible Navier-Stokes equations. In the last few years successful extensions have been made to symmetric advective-diffusive systems and, in particular, the compressible Euler and Navier-Stokes equations. New procedures have been introduced to improve resolution of discontinuities and thin layers. In this paper a brief overview is presented of recent progress in the development and understanding of SUPG methods.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/fld.1650071108
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  • 6
    Electronic Resource
    Electronic Resource
    Convergence of transverse shear stresses in the finite element analysis of platesThis research was sponsored by the U.S. Office of Naval Research under Contract N00014-84-K-0600 (Scientific Officer: Dr. Alan Kushner). (1988)
    New York, NY [u.a.] : Wiley-Blackwell
    Communications in Applied Numerical Methods 4 (1988), S. 185-187 
    Details
    ISSN: 0748-8025
    Keywords: Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: If bending moments converge at a sufficiently fast rate, it is proved that transverse shear stress resultants calculated from the moment equilibrium equation also converge. The result holds independent of the plate theory or type of element employed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/cnm.1630040208
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  • 7
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    Wide-angle astrometry with the Mark III stellar interferometer (1990)
    In:  Other Sources
    Details
    Publication Date: 2011-08-19
    Description: Astrometric measurements made with the Mark III stellar interferometer on five nights in August-September 1988 yielded average formal 1-sigma errors for 12 FK5 stars of 6 mas in declination and 10 mas in right ascension. This improvement in precision over previously reported measurements with this instrument made in 1986 is attributable to several factors: a second 12 m baseline; oriented E-S, was added to the instrument to improve the determination of right ascension; two-color analysis was included in the data-reduction process, along with a new central-fringe identification algorithm using three spectral channels, in order to reduce atmospheric errors; thermal control was greatly improved; and changes were made to observational procedures and hardware to monitor variations in the delay offset due to residual thermal drifts. Approximately half of the new positions are within 50 mas of their FK5 positions. However, an extended series of measurements are needed to ascertain the accuracy that can be achieved by interferometry.
    Keywords: ASTRONOMY
    Type: Astronomical Journal (ISSN 0004-6256); 100; 1701-171
    Format: text
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    NASA TECHNICAL REPORTS
  • 8
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    The project EGRET (Energetic Gamma-Ray Experiment Telescope) on NASA's Gamma-Ray Observatory (GRO) (1988)
    In:  Other Sources
    Details
    Publication Date: 2011-08-19
    Description: The design, predicted performance, and scientific objectives of the 20-30,000-MeV gamma-ray telescope EGRET for the NASA GRO spacecraft (scheduled for Space Shuttle launch to a 450-km 28.5-deg orbit in 1990) are reviewed. The other GRO instruments are briefly characterized, including the burst and transient-source experiment, the oriented scintillation spectrometer, and the imaging Compton telescope. EGRET comprises an anticoincidence system, a spark chamber, a triggering telescope, an NaI total-absorption spectrometer, a gas supply capable of refilling the chamber four times, and support electronics. EGRET will operate with energy resolution about 15 percent, effective area about 2000 sq cm, sensitivity about 5 x 10 to the -8th/sq cm sec, angular resolution 0.1-0.4 deg, and FOV about 40 deg FWHM. Observations of Galactic point sources, Galactic and extragalactic diffuse emission, gamma-ray bursts, and solar flares are planned.
    Keywords: ASTRONOMY
    Type: Space Science Reviews (ISSN 0038-6308); 49; 1-2,
    Format: text
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    NASA TECHNICAL REPORTS
  • 9
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    ROSAT HRI observations of Magellanic Cloud supernova remnants (1994)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: Analysis of deep ROSAT high resolution imager (HRI) observations of two oxygen-rich supernova remnants (SNR's) in the Magellanic Clouds is described. For N132D, I exploit the limited spectral information provided by the HRI to investigate arcsecond scale spectral variations. I find that there is a region of harder X-ray emission near the southern limb and regions of softer emission near the center and northwestern limb. The remnant is believed to be interacting with a molecular cloud and the harder emission to the south is explained as a result of increased absorption along the line-of-sight there. I argue that the softer emission comes from X-ray emitting material with an enhanced abundance of oxygen. For the second SNR, E0102.2 72.2, the spatial structure is investigated in detail using two-dimensional image fitting techniques. Evidence is found for a ring-like and a spherically symmetric shell-like component both of which were modeled as homogeneous regions. In addition, a significant fraction of the observed flux (approximately 11 percent) must come from a resolved clumped component. A comparison with optical and radio imagery is made to provide a physical basis for the components identified in the X-ray analysis. The mass of X-ray emitting gas in the remnant is estimated and a value of approximately 75 M(solar mass) was determined. The dominant uncertainty on this quantity is the extent of unresolved clumping in the X-ray gas. Such clumping would tend to reduce the mass estimate by f(exp 1/2), where f is the mean volume filling factor of the gas.
    Keywords: ASTRONOMY
    Type: NASA-CR-199740 , NAS 1.26:199740 , NIPS-95-06221
    Format: application/pdf
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    NASA TECHNICAL REPORTS
  • 10
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    Spectral determinations for discrete sources with EGRET (1990)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: The ability of the EGRET (Energetic Gamma-Ray Experimental Telescope) to determine the spectral parameters of point sources in 14-day exposures, as planned for the initial survey phase of the GRO (Gamma Ray Observatory) mission, is explored by numerical simulation. Results are given for both galactic and extragalactic objects as a function of source strength and for representative levels of diffuse background emission.
    Keywords: ASTRONOMY
    Type: NASA, Goddard Space Flight Center, The Energetic Gamma-Ray Experiment Telescope (EGRET) Science Symposium; p 201-213
    Format: application/pdf
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    NASA TECHNICAL REPORTS
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