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  • Other Sources  (12)
  • NASA Technical Reports  (12)
  • Communications and Radar  (5)
  • Computer Systems  (5)
  • ELECTRONIC COMPONENTS AND CIRCUITS  (2)
  • 1995-1999  (12)
  • 1950-1954
  • 1
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    NAS Parallel Benchmark Results 11-96 (1997)
    In:  CASI
    Details
    Publication Date: 2019-07-10
    Description: The NAS Parallel Benchmarks have been developed at NASA Ames Research Center to study the performance of parallel supercomputers. The eight benchmark problems are specified in a "pencil and paper" fashion. In other words, the complete details of the problem to be solved are given in a technical document, and except for a few restrictions, benchmarkers are free to select the language constructs and implementation techniques best suited for a particular system. These results represent the best results that have been reported to us by the vendors for the specific 3 systems listed. In this report, we present new NPB (Version 1.0) performance results for the following systems: DEC Alpha Server 8400 5/440, Fujitsu VPP Series (VX, VPP300, and VPP700), HP/Convex Exemplar SPP2000, IBM RS/6000 SP P2SC node (120 MHz), NEC SX-4/32, SGI/CRAY T3E, SGI Origin200, and SGI Origin2000. We also report High Performance Fortran (HPF) based NPB results for IBM SP2 Wide Nodes, HP/Convex Exemplar SPP2000, and SGI/CRAY T3D. These results have been submitted by Applied Parallel Research (APR) and Portland Group Inc. (PGI). We also present sustained performance per dollar for Class B LU, SP and BT benchmarks.
    Keywords: Computer Systems
    Type: NAS-96-18
    Format: text
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    NASA TECHNICAL REPORTS
  • 2
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    Technique for Extension of Small Antenna Array Mutual-Coupling Data to Larger Antenna Arrays (1996)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: A technique is presented whereby the mutual interaction between a small number of elements in a planar array can be interpolated and extrapolated to accurately predict the combined interactions in a much larger array of many elements. An approximate series expression is developed, based upon knowledge of the analytical characteristic behavior of the mutual admittance between small aperture antenna elements in a conducting ground plane. This expression is utilized to analytically extend known values for a few spacings and orientations to other element configurations, thus eliminating the need to numerically integrate a large number of highly oscillating and slowly converging functions. This paper shows that the technique can predict very accurately the mutual coupling between elements in a very large planar array with a knowledge of the self-admittance of an isolated element and the coupling between only two-elements arranged in eight different pair combinations. These eight pair combinations do not necessarily have to correspond to pairs in the large array, although all of the individual elements must be identical.
    Keywords: Communications and Radar
    Type: NASA-TP-3603 , L-17553 , NAS 1.60:3603
    Format: application/pdf
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  • 3
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    Closed-Form Evaluation of Mutual Coupling in a Planar Array of Circular Apertures (1996)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: The integral expression for the mutual admittance between circular apertures in a planar array is evaluated in closed form. Very good accuracy is realized when compared with values that were obtained by numerical integration. Utilization of this closed-form expression, for all element pairs that are separated by more than one element spacing, yields extremely accurate results and significantly reduces the computation time that is required to analyze the performance of a large electronically scanning antenna array.
    Keywords: Communications and Radar
    Type: NASA-TP-3552 , L-17493 , NAS 1.60:3552
    Format: application/pdf
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  • 4
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    Design of a Foldable Low-loss Microstrip Array Antenna (1999)
    In:  Other Sources
    Details
    Publication Date: 2018-06-05
    Description: The design and analysis of a series-fed, foldable microstrip array antenna for radiometer applications is presented. The array antenna is composed of two equal sub arrays. Each sub array consists of a series of patches connected together through segments of microstrip lines. The sub arrays are fed 180 degree out of phase to ensure a symmetric radiation pattern. The design approach, is accomplished using the IE3D code that utilizes the method of moments. All experimental and simulated data are presented and discussed.
    Keywords: Communications and Radar
    Type: IEEE Antennas and Propagation Society International Symposium 1999 Digest, Volume Four; 2732-2735; IEEE-Catalog-99CH37010-Vol-4
    Format: text
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  • 5
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    Analysis of Stub Loaded Microstrip Patch Antennas (1997)
    In:  CASI
    Details
    Publication Date: 2018-06-02
    Description: A microstrip patch antenna fed by a coaxial probe and reactively loaded by a open circuited microstrip line has been used previously to produce circular polarization and also as a building block for a series fed microstrip patch array. Rectangular and circular patch antennas loaded with a microstrip stub were previously analyzed using the generalized Thevenin theorem. In the Thevenin theorem approach, the mutual coupling between the patch current and the surface current on the stub was not taken into account. Also, the Thevenin theorem approach neglects continuity of current at the patch-stub junction. The approach in this present paper includes the coupling between the patch and stub currents as well as continuity at the patch-stub junction. The input impedance for a stub loaded microstrip patch is calculated by the general planar dielectric dyadic Green's function approach in the spectral domain, as was initiated much earlier and has been extensively expanded upon and utilized successfully throughout the literature for microstrip antenna configurations. Using the spectral domain dyadic Green s function derived earlier with the electric field integral equation (EFIE), the problem is formulated by using entire domain basis functions to represent the surface current densities on the patch, the loading stub and the attachment mode at the junction. Galerkin's procedure is used to reduce the EFIE to a matrix equation, which is then solved to obtain the amplitudes of the surface currents. These surface currents are then used for calculating the input impedance of stub loaded rectangular and circular microstrip patches. Numerical results are compared with measured results and with previous results calculated by the Thevenin's theorem approach.
    Keywords: Communications and Radar
    Format: application/pdf
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  • 6
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    Design of a low-loss series-fed microstrip array antenna (1998)
    In:  Other Sources
    Details
    Publication Date: 2018-06-05
    Description: The design and analysis of a series-fed, low-loss, inverted microstrip array antenna, operating at 1.413 GHz is presented. The array antenna is composed of two sub arrays. Each sub array consists of an equal number of microstrip patches all connected together through a series microstrip line. The first element of each sub array is coaxially fed but 180 degree out of phase. This approach ensures a symmetric radiation pattern. The design approach, is accomplished using the IE3D code that utilizes the method of moments. All experimental and simulated data are presented and discussed.
    Keywords: Communications and Radar
    Type: IEEE Antennas and Propagation Society International Symposium 1998 Digest. Antennas: Gateways to the Global Network, Volume 2; 1146-1149; IEEE-Catalog-98CH36194-Vol-2
    Format: text
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  • 7
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    Automated Generation of Message-Passing Programs: An Evaluation of CAPTools using NAS Benchmarks (1998)
    In:  Other Sources
    Details
    Publication Date: 2019-07-18
    Description: Scientists at NASA Ames Research Center have been developing computational aeroscience applications on highly parallel architectures over the past ten years. During the same time period, a steady transition of hardware and system software also occurred, forcing us to expand great efforts into migrating and receding our applications. As applications and machine architectures continue to become increasingly complex, the cost and time required for this process will become prohibitive. Various attempts to exploit software tools to assist and automate the parallelization process have not produced favorable results. In this paper, we evaluate an interactive parallelization tool, CAPTools, for parallelizing serial versions of the NAB Parallel Benchmarks. Finally, we compare the performance of the resulting CAPTools generated code to the hand-coded benchmarks on the Origin 2000 and IBM SP2. Based on these results, a discussion on the feasibility of automated parallelization of aerospace applications is presented along with suggestions for future work.
    Keywords: Computer Systems
    Type: ACM International Conference on Supercomputing; Jul 13, 1998 - Jul 17, 1998; Melbourne; Australia
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  • 8
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    The Automated Instrumentation and Monitoring System (AIMS): Design and Architecture (1997)
    In:  Other Sources
    Details
    Publication Date: 2019-07-18
    Description: Whether a researcher is designing the 'next parallel programming paradigm', another 'scalable multiprocessor' or investigating resource allocation algorithms for multiprocessors, a facility that enables parallel program execution to be captured and displayed is invaluable. Careful analysis of such information can help computer and software architects to capture, and therefore, exploit behavioral variations among/within various parallel programs to take advantage of specific hardware characteristics. A software tool-set that facilitates performance evaluation of parallel applications on multiprocessors has been put together at NASA Ames Research Center under the sponsorship of NASA's High Performance Computing and Communications Program over the past five years. The Automated Instrumentation and Monitoring Systematic has three major software components: a source code instrumentor which automatically inserts active event recorders into program source code before compilation; a run-time performance monitoring library which collects performance data; and a visualization tool-set which reconstructs program execution based on the data collected. Besides being used as a prototype for developing new techniques for instrumenting, monitoring and presenting parallel program execution, AIMS is also being incorporated into the run-time environments of various hardware testbeds to evaluate their impact on user productivity. Currently, the execution of FORTRAN and C programs on the Intel Paragon and PALM workstations can be automatically instrumented and monitored. Performance data thus collected can be displayed graphically on various workstations. The process of performance tuning with AIMS will be illustrated using various NAB Parallel Benchmarks. This report includes a description of the internal architecture of AIMS and a listing of the source code.
    Keywords: Computer Systems
    Type: NAS-97-001
    Format: text
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  • 9
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    Electronic Compensation For Distortion Of Antenna Reflector (1995)
    In:  Other Sources
    Details
    Publication Date: 2019-07-13
    Description: Proposed method of obtaining approximately desired radiation or reception pattern from antenna that includes reflector based on concept of superposition of electromagnetic fields generated by multiple feedhorns or feed antenna elements arrayed at various positions near reflector and excited at electronically adjustable magnitudes and phases. In intended application, reflector nominally paraboloidal, feed elements N feedhorns in hexagonal array, and method used to compensate for deviations of real reflector surface from nominal paraboloidal shape. Method and concept also applicable to electronic beam steering and electronic antenna compensation in other situations.
    Keywords: ELECTRONIC COMPONENTS AND CIRCUITS
    Type: LAR-14461 , NASA Tech Briefs (ISSN 0145-319X); 19; 1; P. 32
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  • 10
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    Methodologies and Tools for Tuning Parallel Programs: 80% Art, 20% Science, and 10% Luck (1996)
    In:  Other Sources
    Details
    Publication Date: 2019-07-18
    Description: The need for computing power has forced a migration from serial computation on a single processor to parallel processing on multiprocessors. However, without effective means to monitor (and analyze) program execution, tuning the performance of parallel programs becomes exponentially difficult as program complexity and machine size increase. In the past few years, the ubiquitous introduction of performance tuning tools from various supercomputer vendors (Intel's ParAide, TMC's PRISM, CRI's Apprentice, and Convex's CXtrace) seems to indicate the maturity of performance instrumentation/monitor/tuning technologies and vendors'/customers' recognition of their importance. However, a few important questions remain: What kind of performance bottlenecks can these tools detect (or correct)? How time consuming is the performance tuning process? What are some important technical issues that remain to be tackled in this area? This workshop reviews the fundamental concepts involved in analyzing and improving the performance of parallel and heterogeneous message-passing programs. Several alternative strategies will be contrasted, and for each we will describe how currently available tuning tools (e.g. AIMS, ParAide, PRISM, Apprentice, CXtrace, ATExpert, Pablo, IPS-2) can be used to facilitate the process. We will characterize the effectiveness of the tools and methodologies based on actual user experiences at NASA Ames Research Center. Finally, we will discuss their limitations and outline recent approaches taken by vendors and the research community to address them.
    Keywords: Computer Systems
    Type: European Parallel Tools Meeting; Oct 23, 1996 - Oct 25, 1996; Chatillon; France
    Format: text
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