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  • Other Sources  (24)
  • Astronomy  (17)
  • FLUID MECHANICS AND HEAT TRANSFER  (4)
  • Numerical Analysis  (3)
  • 2005-2009  (20)
  • 1970-1974  (4)
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  • Other Sources  (24)
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  • 1
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    Gauge Conditions for Moving Black Holes Without Excision (2006)
    In:  CASI
    Details
    Publication Date: 2018-06-06
    Description: Recent demonstrations of unexcised, puncture black holes traversing freely across computational grids represent a significant advance in numerical relativity. Stable an$ accurate simulations of multiple orbits, and their radiated waves, result. This capability is critically undergirded by a careful choice of gauge. Here we present analytic considerations which suggest certain gauge choices, and numerically demonstrate their efficacy in evolving a single moving puncture.
    Keywords: Astronomy
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  • 2
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    Mergers of Non-spinning Black-hole Binaries: Gravitational Radiation Characteristics (2008)
    In:  CASI
    Details
    Publication Date: 2018-06-06
    Description: We present a detailed descriptive analysis of the gravitational radiation from black-hole binary mergers of non-spinning black holes, based on numerical simulations of systems varying from equal-mass to a 6:1 mass ratio. Our primary goal is to present relatively complete information about the waveforms, including all the leading multipolar components, to interested researchers. In our analysis, we pursue the simplest physical description of the dominant features in the radiation, providing an interpretation of the waveforms in terms of an implicit rotating source. This interpretation applies uniformly to the full wavetrain, from inspiral through ringdown. We emphasize strong relationships among the l = m modes that persist through the full wavetrain. Exploring the structure of the waveforms in more detail, we conduct detailed analytic fitting of the late-time frequency evolution, identifying a key quantitative feature shared by the l = m modes among all mass-ratios. We identify relationships, with a simple interpretation in terms of the implicit rotating source, among the evolution of frequency and amplitude, which hold for the late-time radiation. These detailed relationships provide sufficient information about the late-time radiation to yield a predictive model for the late-time waveforms, an alternative to the common practice of modeling by a sum of quasinormal mode overtones. We demonstrate an application of this in a new effective-one-body-based analytic waveform model.
    Keywords: Astronomy
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  • 3
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    The High Energy Telescope for STEREO (2008)
    In:  CASI
    Details
    Publication Date: 2018-08-10
    Description: The IMPACT investigation for the STEREO Mission includes a complement of Solar Energetic Particle instruments on each of the two STEREO spacecraft. Of these instruments, the High Energy Telescopes (HETs) provide the highest energy measurements. This paper describes the HETs in detail, including the scientific objectives, the sensors, the overall mechanical and electrical design, and the on-board software. The HETs are designed to measure the abundances and energy spectra of electrons, protons, He, and heavier nuclei up to Fe in interplanetary space. For protons and He that stop in the HET, the kinetic energy range corresponds to approx. 13 to 40 MeV/n. Protons that do not stop in the telescope (referred to as penetrating protons) are measured up to approx. 100 MeV/n, as are penetrating He. For stopping He, the individual isotopes He-3 and He-4 can be distinguished. Stopping electrons are measured in the energy range approx. 0.7 - 6 MeV.
    Keywords: Astronomy
    Type: To appear in Space Science Reviews
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  • 4
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    COMOC: Three dimensional boundary region variant, theoretical manual and user's guide (1974)
    In:  CASI
    Details
    Publication Date: 2019-06-27
    Description: The theoretical and mechanical structure of the computer program is presented along with guidance on adaptation of the code to solution of a particular problem. Sample solutions are discussed for several problems, especially with respect to solution accuracy and speed as a function of parameters under control of the user. Construction of input data decks for sample problems is discussed.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: NASA-CR-132450 , D9192-950002
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  • 5
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    COMOC: Three dimensional boundary region variant, programmer's manual (1974)
    In:  CASI
    Details
    Publication Date: 2019-06-27
    Description: The three-dimensional boundary region variant of the COMOC computer program system solves the partial differential equation system governing certain three-dimensional flows of a viscous, heat conducting, multiple-species, compressible fluid including combustion. The solution is established in physical variables, using a finite element algorithm for the boundary value portion of the problem description in combination with an explicit marching technique for the initial value character. The computational lattice may be arbitrarily nonregular, and boundary condition constraints are readily applied. The theoretical foundation of the algorithm, a detailed description on the construction and operation of the program, and instructions on utilization of the many features of the code are presented.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: NASA-CR-132449 , D9192-954001
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  • 6
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    Finite element solution theory for three-dimensional boundary flows (1974)
    In:  Other Sources
    Details
    Publication Date: 2019-06-27
    Description: A finite element algorithm is derived for the numerical solution of a three-dimensional flow field described by a system of initial-valued, elliptic boundary value partial differential equations. The familiar three-dimensional boundary layer equations belong to this description when diffusional processes in only one coordinate direction are important. The finite element algorithm transforms the original description into large order systems of ordinary differential equations written for the dependent variables discretized at node points of an arbitrarily irregular computational lattice. The generalized elliptic boundary conditions is piecewise valid for each dependent variable on boundaries that need not explicitly coincide with coordinate surfaces. Solutions for sample problems in laminar and turbulent boundary flows illustrate favorable solution accuracy, convergence, and versatility.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: Computer Methods in Applied Mechanics and Engineering; 4; Nov. 197
    Format: text
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  • 7
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    Observing Merging Massive Black Hole Binaries with LISA (2009)
    In:  Other Sources
    Details
    Publication Date: 2019-07-19
    Description: The Laser Interferometer Space Antenna (LISA) is expected to detect gravitational radiation from the inspiral and merger of massive black hole binaries at high redshifts with large signal-to-noise ratios (SNRs). These high-SNR observations will make it possible to extract physical parameters such as hole masses and spins, luminosity distance, and sky position from the observed waveforms. LISA'S effectiveness as a tool for astrophysics will be influenced by the precision with which these parameters can be measured. In addition, the practicality of coordinated observations with other instruments will be affected by the temporal evolution of parameter errors such as sky position. We present estimates of parameter errors for the special case of non-spinning black holes. Our focus is on the contribution of the late inspiral and merger portions of the waveform, a regime which typically dominates the SNR but has not been extensively studied due to the historic lack of a precise description of the waveform. Advances in numerical relativity have recently made such studies possible. Initial results suggest that the portion of the waveform beyond the Schwarzchild inner-most stable circular orbit can reduce parameter uncertainties by up to a factor of two.
    Keywords: Astronomy
    Type: 2009 Meeting of the American Physical Society; May 02, 2009 - May 05, 2009; Colorado; United States
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  • 8
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    Nonlinear initial-boundary value solutions by the finite element method (1974)
    In:  Other Sources
    Details
    Publication Date: 2019-07-13
    Description: The finite-element method is used to establish a numerical solution algorithm for the Navier-Stokes equations for two-dimensional flows of a viscous compressible fluid. Numerical experiments confirm the advection property for the finite-element equivalent of the nonlinear convection term for both unidirectional and recirculating flowfields. For linear functionals, the algorithm demonstrates good accuracy using coarse discretizations and h squared convergence with discretization refinement.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: Computational methods in nonlinear mechanics; International Conference; Sep 23, 1974 - Sep 25, 1974; Austin, TX
    Format: text
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  • 9
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    MESSENGER Observations of Mercury's Bow Shock and Magnetopause (2008)
    In:  Other Sources
    Details
    Publication Date: 2019-07-19
    Description: MESSENGER'S 14 January 2008 encounter with Mercury will provide the first new observations of the solar wind interaction with this planet since the Mariner 10 flybys that took place over 30 years ago. The closest approach distance for this first MESSENGER flyby is targeted for an altitude of 200 km as compared with the 707 km and 327 km attained by Mariner 10 on 29 March 1974 and 16 March 1975, respectively. The locations of the bow shock and magnetopause boundaries observed by MESSENGER will be examined and compared against those found in the earlier Mariner 10 measurements and the predictions of theoretical models and numerical simulations. The structure of the magnetopause will be investigated for the presence of flux transfer events or other evidence of magnetic reconnection as will the more general implications of these new MESSENGER bow shock and magnetopause observations for the global solar wind interaction with Mercury.
    Keywords: Astronomy
    Type: European Geophysical Union Conference; Apr 10, 2008 - Apr 19, 2008; Vienna; Austria
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  • 10
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    Binary Black Hole Mergers and Recoil Kicks (2006)
    In:  Other Sources
    Details
    Publication Date: 2019-07-19
    Description: Recent developments in numerical relativity have made it possible to follow reliably the coalescence of two black holes from near the innermost stable circular orbit to final ringdown. This opens up a wide variety of exciting astrophysical applications of these simulations. Chief among these is the net kick received when two unequal mass or spinning black holes merge. The magnitude of this kick has bearing on the production and growth of supermassive black holes during the epoch of structure formation, and on the retention of black holes in stellar clusters. Here we report the first accurate numerical calculation of this kick, for two nonspinning black holes in a 1.5:1 mass ratio, which is expected based on analytic considerations to give a significant fraction of the maximum possible recoil. We have performed multiple runs with different initial separations, orbital angular momenta, resolutions, extraction radii, and gauges. The full range of our kick speeds is 86-116 kilometers per second, and the most reliable runs give kicks between 86 and 97 kilometers per second. This is intermediate between the estimates from two recent post-Newtonian analyses and suggests that at redshifts z greater than 10, halos with masses less than 10(exp 9) M(sub SUN) will have difficulty retaining coalesced black holes after major mergers.
    Keywords: Astronomy
    Type: High Energy Astrophysics Division (HEAD) Meeting; Oct 04, 2006 - Oct 07, 2006; San Francisco, CA; United States
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