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  • Other Sources  (14)
  • COMPUTERS  (4)
  • FLUID MECHANICS AND HEAT TRANSFER  (4)
  • ASTROPHYSICS  (3)
  • Numerical Analysis  (3)
  • 2005-2009  (3)
  • 1970-1974  (11)
Collection
  • Other Sources  (14)
Source
Keywords
Years
Year
  • 1
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    The interaction of interstellar gas with stellar density wave packets (1974)
    In:  Other Sources
    Details
    Publication Date: 2011-08-16
    Description: We have numerically studied the interaction between interstellar gas and a gravitational perturbation produced by a fluctuation in the stellar mass distribution. For a simple equation of state, shock waves develop even if the gravitational perturbation is aperiodic and transient. In a medium which can change thermal phase, shocks do not form and the gas makes a transition directly to the cold, dense phase. The cold material has an anomalous velocity imparted to it by the gravitational perturbation and it becomes an accretion front moving through the hot gas and capturing it. The accretion fronts trigger thermal phase change on a large scale and can reproduce the extent of observed cold clouds. Furthermore their high mass is favorable to gravitational instability and subsequent star formation.
    Keywords: ASTROPHYSICS
    Type: Astronomy and Astrophysics; 36; 2, No; Nov. 197
    Format: text
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  • 2
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    Fine-scale structure of a cold hydrogen layer (1974)
    In:  Other Sources
    Details
    Publication Date: 2011-08-16
    Description: Neutral-hydrogen absorption-line interferometer observations are reported for five continuum radio sources situated behind an extensive layer of cold interstellar H I gas. In contrast to low-spatial-resolution emission-line observations reported earlier which show the large-scale uniformity of the layer, the high-spatial-resolution absorption-line observations reveal variations in the velocity and density within the layer. The new results together with the old indicate the apparent coexistence of a large-scale mechanism for triggering the formation of cold hydrogen and an instability mechanism leading to small-scale irregularities.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal; 194; Dec. 1
    Format: text
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  • 3
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    An experimental test of the homogeneity of the interstellar medium (1974)
    In:  Other Sources
    Details
    Publication Date: 2011-08-16
    Description: Observations of nonthermal continuum radio emission at 750 MHz and hydrogen-line emission at 1420 MHz have been compared in order to test the extent to which cosmic-ray electrons, magnetic fields, and hydrogen gas coexist in the interstellar medium. If the interstellar medium is homogeneous in the sense that its constituents are mixed together and can interact, then regions of line and continuum emission should be spatially correlated. The measurements indicate that at most 28% of continuum emission in the Galaxy comes from such a homogeneous medium. The remaining nonthermal emission agrees in magnitude with the residual emission found by Berkhuijsen after subtraction of the polarized component of nonthermal emission. In addition, the data discussed here show that the major filamentary structures found in the two forms of emission rarely coincide spatially. Consequently, both the average and the exceptional structure in the medium indicate that the synchrotron-radiating magnetoplasma and the neutral hydrogen gas are not closely interacting in the present state of the medium.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal; 194; Dec. 1
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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
    Format: application/pdf
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  • 5
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    Arbitrary grammars generating context-free languages (1972)
    In:  CASI
    Details
    Publication Date: 2019-06-27
    Description: If G is a grammar such that in each noncontext-free rule of G, the right side contains a string of terminals longer than any terminal string appearing between two nonterminals in the left side; then the language generated by G is context-free. Six previous results follow as simple corollaries of this theorem.
    Keywords: COMPUTERS
    Type: NASA-CR-127764 , REPT-11-72
    Format: application/pdf
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  • 6
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    A spacecraft computer repairable via command. (1971)
    In:  Other Sources
    Details
    Publication Date: 2019-06-27
    Description: The MULTIPAC is a central data system developed for deep-space probes with the distinctive feature that it may be repaired during flight via command and telemetry links by reprogramming around the failed unit. The computer organization uses pools of identical modules which the program organizes into one or more computers called processors. The interaction of these modules is dynamically controlled by the program rather than hardware. In the event of a failure, new programs are entered which reorganize the central data system with a somewhat reduced total processing capability aboard the spacecraft. Emphasis is placed on the evolution of the system architecture and the final overall system design rather than the specific logic design.
    Keywords: COMPUTERS
    Type: IEEE Transactions on Aerospace and Electronic Systems; AES-7; Sept
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  • 7
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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
    Format: application/pdf
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  • 8
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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
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  • 9
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    Non-context-free grammars generating context-free languages (1974)
    In:  Other Sources
    Details
    Publication Date: 2019-06-27
    Description: If G is a grammar such that in each non-context-free rule of G, the right side contains a string of terminals longer than any terminal string appearing between two nonterminals in the left side, then the language generated by G is context free. Six previous results follow as corollaries of this theorem.
    Keywords: COMPUTERS
    Type: Information and Control; 24
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  • 10
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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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