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  • Engineering General  (686)
  • Life and Medical Sciences  (629)
  • Cell & Developmental Biology  (458)
  • Life Sciences  (315)
  • ASTROPHYSICS
  • 1995-1999  (1,633)
  • 1990-1994
  • 1985-1989
  • 1996  (1,633)
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  • 1995-1999  (1,633)
  • 1990-1994
  • 1985-1989
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  • 1
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    Research activities in nuclear astrophysics and related areas (1996)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: NASA/GRO grant NAG 5-2081, at the University of Chicago, has provided support for a broad program of theoretical research in nuclear astrophysics and related areas, with regard to gamma-ray and hard X-ray emission from classical nova explosions. This research emphasized the possible detection of 22Na gamma-ray line emission from nearby novae involving ONeMg white dwarfs, the detailed examination of 26Al production in novae, and the possible detection of the predicted early gamma ray emission from novae that arises from the decay of the short lived, positron emitting isotopes of CNO elements. Studies of nova related problems have consumed an increasing fraction of the Principal Investigator's research efforts over the past decade. Current research addresses problems associated with the standard model for the outbursts of the classical novae: the occurrence of thermonuclear runaways (TNR) in the accreted hydrogen rich envelopes on white dwarfs in close binary systems (see, e.g., the reviews by Truran 1982; and Shara 1989). Research in progress and planned for the next three years has three main objectives: (1) to gain an improved understanding of the early evolution of the light curves of, particularly, the fastest novae; (2) to gain an improved understanding of the relative importance of the various possible mechanisms of envelope hydrogen depletion (e.g. winds, common envelope driven mass loss, and nuclear burning) to the long term evolution of novae in outburst; and (3) to seek to provide a somewhat more definitive statement of the role of classical novae in nucleosynthesis. Our proposed 2-D studies of convection during the early phases of the TNR and our systematic attempt to incorporate an improved treatment of radiation hydrodynamics into the hydrodynamic code utilized in our calculations, are particularly relevant to the first of these objectives. Further 2-D studies of the effects of common envelope evolution are intended to provide more realistic constraints on the mass depletion mechanisms. Finally, detailed calculations of the thermonuclear history of the matter ejected in novae will be carried out for representative nova configurations involving both carbon-oxygen (CO) and oxygen-neon-magnesium (ONeMg) white dwarfs.
    Keywords: ASTROPHYSICS
    Type: NASA-CR-200193 , NAS 1.26:200193 , NIPS-96-08389
    Format: application/pdf
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    NASA TECHNICAL REPORTS
  • 2
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    Observations and analysis activities of the International Ultraviolet Explorer satellite telescope (1996)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: The funds from this grant were used to support observations and analysis with the International Ultraviolet Explorer (IUE) satellite telescope. The main area of scientific research concerned the variability analyses of ultraviolet spectra of Active Galactic Nuclei, primarily quasars, Seyfert galaxies, and BL Lacertae objects. The Colorado group included, at various times, the P.I. (J.M. Shull), Research Associate Dr. Rick Edelson, and graduate students Jon Saken, Elise Sachs, and Steve Penton. A portion of the work was also performed by CU undergraduate student Cheong-ming Fu. A major product of the effort was a database of all IUE spectra of active galactic nuclei. This database is being analyzed to obtain spectral indices, line fluxes, and continuum fluxes for over 500 AGN. As a by-product of this project, we implemented a new, improved technique of spectral extraction of IUE spectra, which has been used in several AGN-WATCH campaigns (on the Seyfert galaxy NGC 4151 and on the BL Lac object PKS 2155-304).
    Keywords: ASTROPHYSICS
    Type: NASA-CR-200196 , NAS 1.26:200196 , NIPS-96-08385
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    NASA TECHNICAL REPORTS
  • 3
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    Progress report for the Monte-Carlo gamma-ray spectrum simulation program BSIMUL (1996)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: The progress made during 1995 on the Monte-Carlo gamma-ray spectrum simulation program BSIMUL is discussed. Several features have been added, including the ability to model shields that are tapered cylinders. Several simulations were made on the Near Earth Asteroid Rendezvous detector.
    Keywords: ASTROPHYSICS
    Type: NASA-CR-200089 , NAS 1.26:200089 , NIPS-96-07659
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    NASA TECHNICAL REPORTS
  • 4
    Electronic Resource
    Electronic Resource
    An efficient Riemann solver for open channel flows (1996)
    Chichester : Wiley-Blackwell
    Communications in Numerical Methods in Engineering 12 (1996), S. 13-20 
    Details
    ISSN: 1069-8299
    Keywords: open channel flows ; Riemann solver ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: An efficient numerical method is developed for the one-dimensional open channel flow equations. The scheme is a modification of one presented recently, but with an improvement in the efficiency made through the use of the arithmetic mean as an average of flow variables across the interface between adjacent states. Numerical results are shown for two problems, and an indication of the efficiency gained is given.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
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    Paper (German National Licenses)
  • 5
    Electronic Resource
    Electronic Resource
    An explicit sparse unsymmetric finite element solver (1996)
    Chichester : Wiley-Blackwell
    Communications in Numerical Methods in Engineering 12 (1996), S. 21-29 
    Details
    ISSN: 1069-8299
    Keywords: finite element systems ; elliptic partial differential equations ; approximate LU factorization ; explicit matrix inversion ; preconditioning ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: A new class of explicit generalized approximate inverse finite element matrix algorithmic methods, based on the concept of LU-sparse factorization procedures, without inverting the decomposition factors, has recently been introduced. The large sparse unsymmetric coefficient matrix of irregular structure is factorized approximately and, in conjunction with approximate inverse matrix techniques, yields explicit preconditioned methods for the finite element (FE) and finite difference (FD) method. The numerical implementation of these algorithms is presented and Fortran subroutines for the efficient solution of the sparse unsymmetric linear systems are given.
    Additional Material: 1 Tab.
    Type of Medium: Electronic Resource
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    Paper (German National Licenses)
  • 6
    Electronic Resource
    Electronic Resource
    Conference diary (1996)
    Chichester : Wiley-Blackwell
    Communications in Numerical Methods in Engineering 12 (1996), S. 147-148 
    Details
    ISSN: 1069-8299
    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/cnm.1640120202
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    Fulltext
  • 7
    Electronic Resource
    Electronic Resource
    Annoucement (1996)
    Chichester : Wiley-Blackwell
    Communications in Numerical Methods in Engineering 12 (1996), S. 149-150 
    Details
    ISSN: 1069-8299
    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/cnm.1640120203
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  • 8
    Electronic Resource
    Electronic Resource
    An asymptotic formula for correcting finite element predicted natural frequencies of membrane vibration problems (1996)
    Chichester : Wiley-Blackwell
    Communications in Numerical Methods in Engineering 12 (1996), S. 63-73 
    Details
    ISSN: 1069-8299
    Keywords: asymptotic solution ; natural frequencies ; membrane vibrations ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: In the paper an asymptotic formula has been developed to correct the discretization error for the finite element predicted natural frequencies of membrane transverse vibration problems. The general idea behind deriving this asymptotic formula is that, when the finite element size approaches zero, a discretized finite element system approaches a continuous system and the predicted natural frequencies of the system from the finite element analysis therefore approach the exact solutions of the system. Without losing generality, several different finite element mesh patterns have been considered and the same asymptotic formula for correcting the finite element predicted natural frequency has been obtained for all the different mesh patterns because of the uniqueness of the exact solution to the natural frequency of a real structure. The usefulness, effectiveness and efficiency of the present asymptotic formula have been assessed by a simple but critical problem, for which the exact solution is available for comparison. In order to investigate the applicability of the asymptotic formula to practical engineering problems, two challenging membrane vibration problems of irregular shapes, an L-shape and a tapered shape with a circular hole in the centre, have also been analysed. The related numerical results have demonstrated that the asymptotic formula provides a very useful post-processing error corrector for the finite element predicted natural frequencies of membrane transverse vibration problems, even though the problem domains are of irregular shape. The greatest advantage in using the present asymptotic formula is that it yields a solution of higher accuracy, by simply using the formula to correct the rough solution obtained from a much coarser finite element mesh with fewer degrees of freedom, without any further finite element calculation.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
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  • 9
    Electronic Resource
    Electronic Resource
    Vibration of continuous beams using modified beam vibration functions (1996)
    Chichester : Wiley-Blackwell
    Communications in Numerical Methods in Engineering 12 (1996), S. 107-114 
    Details
    ISSN: 1069-8299
    Keywords: beam ; vibration ; trial functions ; Ritz method ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: Free vibration of beams with intermediate point supports is studied by the classical Ritz method within the context of Euler beam theory. For the Ritz method, the displacement of a beam is approximated by a set of admissible trial functions which must satisfy the kinematic conditions at the ends and intermediate supports of the beam. To this end, a polynomial is superimposed on the conventional single-span beam vibration functions to form continuous-span or modified beam vibration functions. These modified beam functions are taken as the admissible trial functions for subsequent formulation. Stiffness and mass matrices are formulated using the conventional procedure and the resulting linear eigen-equation can be solved easily. A number of numerical examples are given to demonstrate the accuracy and efficiency of the present method.
    Additional Material: 3 Tab.
    Type of Medium: Electronic Resource
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  • 10
    Electronic Resource
    Electronic Resource
    A symbolic computation procedure for the generation of Gauss quadrature rules with a user-defined weight function (1996)
    Chichester : Wiley-Blackwell
    Communications in Numerical Methods in Engineering 12 (1996), S. 141-145 
    Details
    ISSN: 1069-8299
    Keywords: numerical integration ; Gauss quadrature rules ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: The advance of powerful software for symbolic and numerical computations such as Mathematica sheds a new light on a paper by Golub and Welsch from 1969. Based on this paper the author describes a Mathematica procedure for determining the weights and abscissae of a Gauss quadrature rule with a user-defined weight function. After a brief description of the algorithm and its implementation examples demonstrate the usefulness of the procedure. The procedure is extremely useful if one has to compute many integrals with the same, possibly weakly singular, weight function. This might happen, for example, in the boundary element method.
    Additional Material: 1 Tab.
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