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  • ASTROPHYSICS  (10)
  • OPTICS  (5)
  • Engineering  (4)
  • 2000-2004
  • 1990-1994  (19)
  • 1940-1944
  • 2003
  • 1993  (19)
Collection
Keywords
Publisher
Years
  • 2000-2004
  • 1990-1994  (19)
  • 1940-1944
Year
  • 1
    Electronic Resource
    Electronic Resource
    Numerical simulation of ultrasonic transmission through curved interface (1993)
    Chichester [u.a.] : Wiley-Blackwell
    International Journal for Numerical Methods in Engineering 36 (1993), S. 2369-2393 
    Details
    ISSN: 0029-5981
    Keywords: Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: The direct boundary integral equation formalism is used to model reflected and transmitted wave fields due to a bounded ultrasonic beam incident upon an arbitrarily curved interface separating a fluid and a solid media. The numerical procedure involves application of point collocation with quadratic isoparametric approximation that reduce the integral equations to a discrete set of linear algebraic equations. Numerical results are provided for plane, concave and convex interfaces for incident beam profiles which are Gaussian or approximately rectangular. The case of surface wave excitation on a plane interface is considered and features of their numerical solution are discussed. Constraints on the various parameters of the numerical model and their effects on the accuracy of the solution are investigated in detail.
    Additional Material: 24 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/nme.1620361405
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    Paper (German National Licenses)
    Fulltext
  • 2
    Electronic Resource
    Electronic Resource
    Evaluation of field singularities by an iterative boundary-element method (1993)
    Chichester : Wiley-Blackwell
    Communications in Numerical Methods in Engineering 9 (1993), S. 337-343 
    Details
    ISSN: 1069-8299
    Keywords: Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: A numerical method is presented for the evaluation of field singularities of the type (1/r1-λ) using iterative solutions of standard boundary-element analyses in a region surrounding the origin of singularity. Results for λ are presented for both two and three-dimensional problems, and representative asymptotic fields for these examples are discussed.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/cnm.1640090407
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    Paper (German National Licenses)
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  • 3
    Electronic Resource
    Electronic Resource
    Coincident collocation of displacement and tangent derivative boundary integral equations in elasticity (1993)
    Chichester [u.a.] : Wiley-Blackwell
    International Journal for Numerical Methods in Engineering 36 (1993), S. 2837-2849 
    Details
    ISSN: 0029-5981
    Keywords: Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: The regular boundary integral equations of elastostatics are combined with regularized versions of the tangent derivative equations and collocated at the same points to formulate the elasticity problem in terms of displacements, tractions and the tangential displacement gradients. Hermitian cubic polynomials are used for functional interpolation on certain elements to formulate the boundary element method in terms of displacements, tractions and their tangent derivatives. Commensurate accuracy of nodal values of these functions and the tangent derivatives is obtained and makes possible the accurate and immediate recovery of all stress components. An example problem demonstrates the accuracy and atility of the approach.
    Additional Material: 11 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/nme.1620361611
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    Paper (German National Licenses)
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  • 4
    Electronic Resource
    Electronic Resource
    Is the steady viscous incompressible two-dimensional flow over a backward-facing step at Re = 800 stable? (1993)
    Chichester : Wiley-Blackwell
    International Journal for Numerical Methods in Fluids 17 (1993), S. 501-541 
    Details
    ISSN: 0271-2091
    Keywords: Backward-facing step ; Flow stability ; Incompressible flow ; 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: A detailed case study is made of one particular solution of the 2D incompressible Navier-Stokes equations. Careful mesh refinement studies were made using four different methods (and computer codes): (1) a high-order finite-element method solving the unsteady equations by time-marching; (2) a high-order finite-element method solving both the steady equations and the associated linear-stability problem; (3) a second-order finite difference method solving the unsteady equations in streamfunction form by time-marching; and (4) a spectral-element method solving the unsteady equations by time-marching. The unanimous conclusion is that the correct solution for flow over the backward-facing step at Re = 800 is steady - and it is stable, to both small and large perturbations.
    Additional Material: 21 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/fld.1650170605
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    Paper (German National Licenses)
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  • 5
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    ROSAT PSPC spectra of six Seyfert 1 galaxies (1993)
    In:  Other Sources
    Details
    Publication Date: 2011-08-24
    Description: We present six ROSAT Position-Sensitive Proportional Counter (PSPC) observations of Seyfert 1 galaxies chosen to have low Galactic line-of-sight absorption (N(sub H) approx. = 10(exp 20)/sq cm). As expected, it is found that all of these sources possess significantly steeper spectra below approximately 1 keV, than that observed at higher X-ray energies. In addition we find evidence for soft X-ray spectral features, which are best parameterized as line emission at approximately 0.63 keV in NGC7469 and approximately 0.75 keV in ESO198-G24. We examine these results in the light of the accuracy of the PSPC spectral calibration. We suggest that Seyfert galaxies are a class of object whose spectra are similar to the diffuse X-ray background in the soft X-ray band. We suggest these data provide the first direct evidence that the sources which dominate the background differ as a function of energy.
    Keywords: ASTROPHYSICS
    Type: Advances in Space Research (ISSN 0273-1177); 13; 12; p. (12)387-(12)390
    Format: text
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  • 6
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    The broad-band X-ray spectral variability of Mrk 841 (1993)
    In:  Other Sources
    Details
    Publication Date: 2011-08-24
    Description: A detailed spectral analysis of five X-ray observations of Mrk 841 with the EXOSAT, Ginga, and ROSAT satellites is reported. Variability is apparent in both the soft (0.1-1.0 keV) and medium (1-20 keV) energy bands. Above, 1 keV, the spectra are adequately modeled by a power law with a strong emission line of equivalent width 450 eV. The large equivalent width of the emission line indicates a strongly enhanced reflection component of the source compared with other Seyferts observed with Ginga. The implications of the results of the analysis for physical models of the emission regions in this and other X-ray bright Seyferts are briefly examined.
    Keywords: ASTROPHYSICS
    Type: Royal Astronomical Society, Monthly Notices (ISSN 0035-8711); 260; 1; p. 111-120.
    Format: text
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  • 7
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    ROSAT Position Sensitive Proportional Counter spectra of six Seyfert 1 galaxies (1993)
    In:  Other Sources
    Details
    Publication Date: 2011-08-24
    Description: We present the results from ROSAT Position Sensitive Proportional Counter observations of six Seyfert 1 galaxies in the soft (0.1-2.0 keV) X-ray band. The sources (Mrk 335, ESO 198-G24, ESO 141-G55, Mrk 509, NGC 7469, and MCG-2-58-22) were chosen to have low absorbing column densities along the line of sight. As expected, it is found that all the sources possess significantly steeper spectra below about 1 keV than observed at higher X-ray energies. Assuming a simple absorbed power-law spectral model, the mean (photon) spectral index for the sample is Gamma = 2.38 +/- 0.25, compared to the canonical 1.7 typically observed in the 2-10 keV band. Furthermore, we find strong evidence for soft X-ray spectral features in half the sources. In NGC 7469 and ESO 198-G24, we find that the addition of a narrow emission line or an absorption edge to the underlying continuum is a significant improvement to the parameterization of the spectra. Mrk 335 also shows evidence for spectral complexity, but from these data it is not possible to unambiguously distinguish between an absorption edge and a steepening of the spectrum at low energies. We examine these results in the light of the accuracy of the PSPC spectral calibration.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 412; 1; p. 72-81.
    Format: text
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  • 8
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    Classificational parameters for acapulcoites and lodranites: The cases of FRO 90011, EET 84302 and ALH A81187/84190 (1993)
    In:  CASI
    Details
    Publication Date: 2013-08-31
    Description: Acapulcoites and lodranites probably sample a common parent body, which has experienced a range of partial melting. We present classificational parameters which allow acapulcoites-lodranites to be distinguished from other groups of meteorites, as well as from each other. Petrography can complement oxygen isotopic compositions in separating these meteorites from other groups of stony-irons and primitive achondrites, while petrographic properties alone distinguish acapulcoites from lodranites. Acapulcoites differ from lodranites in having smaller grain sizes, abundant Fe, Ni-FeS as micron-sized veins and plagioclase which escaped melting. We have applied these criteria to three new members of the group. FRO 90011 is a typical lodranite; EET 84302 is intermediate in many properties between acapulcoites and lodranites; and ALH A81187/84190 are paired meteorites and are first low-FeO acapulcoites. These meteorites provide a wider spectrum of samples from the acapulcoite-lodranite parent body and suggests that this body may have had a complex structure.
    Keywords: ASTROPHYSICS
    Type: Lunar and Planetary Inst., Twenty-Fourth Lunar and Planetary Science Conference. Part 2: G-M; p 945-946
    Format: application/pdf
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  • 9
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    I-Xe structure of ILAFEGH 009 and shallowater: Evidence for early formation and rapid cooling of impact-derived enstatite meteorites (1993)
    In:  CASI
    Details
    Publication Date: 2013-08-31
    Description: Enstatite meteorites have proven to be ideal samples for past studies of the I-Xe system. This work focuses on two enstatite meteorites that were formed by impact processes. Ilafegh 009 is a clast-free impact melt rock from the EL chondrite parent body. The Shallowater aubrite likely formed when a fully molten planetesimal collided with a solid planetesimal, mixing fragments of the solid planetesimal into the enstatite mantle of the molten planetesimal. A complex three-stage cooling history resulted from this mixing and later break-up and reassembly of the parent body. The present study indicates that the I-Xe structure of these two meteorites resulted from in situ decay of live I-129 and that both experienced xenon closure of the iodine host phase at approximately the same time. I-Xe cooling rates are consistent with the cooling rates derived from mineralogic and petrologic studies of these objects. The similarities in ages suggest that the region of the nebula in which enstatite parent bodies formed must have experienced an intense early bombardment.
    Keywords: ASTROPHYSICS
    Type: Lunar and Planetary Inst., Twenty-Fourth Lunar and Planetary Science Conference. Part 2: G-M; p 777-778
    Format: application/pdf
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  • 10
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    Ultraviolet Imaging Spectrometer (1993)
    In:  CASI
    Details
    Publication Date: 2014-09-04
    Description: Wide-field imaging systems equipped with objective prisms or gratings have had a long history of utility in groundbased observations of meteors and comets. Deployment of similar instruments from low Earth orbit would allow the first UV observations of meteors. This instrument can be used for comets and Lyman alpha coronae of Earth-orbit-crossing asteroids. A CaF2 prism imaging spectrograph designed for stellar observations was used aboard Skylab to observe Comet Kohoutek (1973f), but its 1300-A cut-off precluded Lyman alpha images and it was not used for observation of meteors. Because the observation of the UV spectrum of a meteor has never been attempted, researchers are denied the opportunity to obtain composition information from spectra at those wavelengths. We propose construction of a flight instrument functioning in the 1100-3200 A spectral range that is suitable for a dedicated satellite ('Quick Star') or as a space-station-attached payload. It can also be an autonomous package in the space shuttle cargo bay.
    Keywords: OPTICS
    Type: Lunar and Planetary Inst., Workshop on Advanced Technologies for Planetary Instruments, Part 1; p 27
    Format: application/pdf
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