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  • Other Sources  (9)
  • Computer Systems  (5)
  • Communications and Radar  (4)
  • Chemistry
  • 2005-2009
  • 1995-1999  (9)
  • 1960-1964
  • 1925-1929
  • 1999  (6)
  • 1997  (3)
  • 1995
  • 1
    Publication Date: 2018-06-08
    Description: The Optical Communications Demonstrator (OCD) is a laboratory based lasercom terminal that was developed to validate several key technologies such as precision beam pointing, high bandwidth beacon tracking and beacon acquisition.
    Keywords: Communications and Radar
    Type: International Society for Optical Engineering (SPIE) - Laser Communications Technologies; United States
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  • 2
    Publication Date: 2018-06-08
    Description: This paper presents an overview of the preliminary design of both the flight and ground systems of the Optical Communication Demonstration and High-Rate Link Facility which will demonstrate optical communication from the International Space Station to ground after its deployment in October 2002.
    Keywords: Communications and Radar
    Type: International Society for Optical Engineering (SPIE), Free-Space Optical Communication; San Jose, CA; United States
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  • 3
    Publication Date: 2018-06-08
    Keywords: Communications and Radar
    Type: Diode Laser Technology Review; FL; United States
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  • 4
    Publication Date: 2018-06-08
    Description: Introduction to free space optical communications.
    Keywords: Communications and Radar
    Type: DESCANSO Symposium; Pasadena, CA; United States
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  • 5
    Publication Date: 2019-07-13
    Description: Classical mesh partitioning algorithms were designed for rather static situations, and their straightforward application in a dynamical framework may lead to unsatisfactory results, e.g., excessive data migration among processors. Furthermore, special attention should be paid to their amenability to parallelization. In this paper, a novel parallel method for the dynamic partitioning of adaptive unstructured meshes is described. It is based on a linear representation of the mesh using self-avoiding walks.
    Keywords: Computer Systems
    Type: IPPS''99; Apr 12, 1999 - Apr 16, 1999; San Juan; Puerto Rico
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  • 6
    Publication Date: 2019-07-10
    Description: Understanding the interplay between machines and problems is key to obtaining high performance on parallel machines. This paper investigates the interplay between programming paradigms and communication capabilities of parallel machines. In particular, we explicate the communication capabilities of the IBM SP-2 distributed-memory multiprocessor and the SGI PowerCHALLENGEarray symmetric multiprocessor. Two benchmark problems of bitonic sorting and Fast Fourier Transform are selected for experiments. Communication-efficient algorithms are developed to exploit the overlapping capabilities of the machines. Programs are written in Message-Passing Interface for portability and identical codes are used for both machines. Various data sizes and message sizes are used to test the machines' communication capabilities. Experimental results indicate that the communication performance of the multiprocessors are consistent with the size of messages. The SP-2 is sensitive to message size but yields a much higher communication overlapping because of the communication co-processor. The PowerCHALLENGEarray is not highly sensitive to message size and yields a low communication overlapping. Bitonic sorting yields lower performance compared to FFT due to a smaller computation-to-communication ratio.
    Keywords: Computer Systems
    Type: NAS-96-005
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  • 7
    Publication Date: 2019-07-13
    Description: Mesh adaption is a powerful tool for efficient unstructured- grid computations but causes load imbalance among processors on a parallel machine. We present a novel method to dynamically balance the processor workloads with a global view. This paper presents, for the first time, the implementation and integration of all major components within our dynamic load balancing strategy for adaptive grid calculations. Mesh adaption, repartitioning, processor assignment, and remapping are critical components of the framework that must be accomplished rapidly and efficiently so as not to cause a significant overhead to the numerical simulation. Previous results indicated that mesh repartitioning and data remapping are potential bottlenecks for performing large-scale scientific calculations. We resolve these issues and demonstrate that our framework remains viable on a large number of processors.
    Keywords: Computer Systems
    Type: NASA-CR-204487 , NAS 1.26:204487 , RIACS-TR-97-03 , Parallel Algorithms and Architectures; Jun 22, 1997 - Jun 25, 1997; Newport, RI; United States
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  • 8
    Publication Date: 2019-07-13
    Description: The success of parallel computing in solving real-life computationally-intensive problems relies on their efficient mapping and execution on large-scale multiprocessor architectures. Many important applications are both unstructured and dynamic in nature, making their efficient parallel implementation a daunting task. This paper presents the parallelization of a dynamic unstructured mesh adaptation algorithm using three popular programming paradigms on three leading supercomputers. We examine an MPI message-passing implementation on the Cray T3E and the SGI Origin2OOO, a shared-memory implementation using cache coherent nonuniform memory access (CC-NUMA) of the Origin2OOO, and a multi-threaded version on the newly-released Tera Multi-threaded Architecture (MTA). We compare several critical factors of this parallel code development, including runtime, scalability, programmability, and memory overhead. Our overall results demonstrate that multi-threaded systems offer tremendous potential for quickly and efficiently solving some of the most challenging real-life problems on parallel computers.
    Keywords: Computer Systems
    Type: Supercomputing; Nov 13, 1999 - Nov 19, 1999; Portland, OR; United States
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  • 9
    Publication Date: 2019-07-13
    Description: Partitioning unstructured graphs is central to the parallel solution of computational science and engineering problems. Spectral partitioners, such recursive spectral bisection (RSB), have proven effecfive in generating high-quality partitions of realistically-sized meshes. The major problem which hindered their wide-spread use was their long execution times. This paper presents a new inertial spectral partitioner, called HARP. The main objective of the proposed approach is to quickly partition the meshes at runtime in a manner that works efficiently for real applications in the context of distributed-memory machines. The underlying principle of HARP is to find the eigenvectors of the unpartitioned vertices and then project them onto the eigerivectors of the original mesh. Results for various meshes ranging in size from 1000 to 100,000 vertices indicate that HARP can indeed partition meshes rapidly at runtime. Experimental results show that our largest mesh can be partitioned sequentially in only a few seconds on an SP2 which is several times faster than other spectral partitioners while maintaining the solution quality of the proven RSB method. A parallel WI version of HARP has also been implemented on IBM SP2 and Cray T3E. Parallel HARP, running on 64 processors SP2 and T3E, can partition a mesh containing more than 100,000 vertices into 64 subgrids in about half a second. These results indicate that graph partitioning can now be truly embedded in dynamically-changing real-world applications.
    Keywords: Computer Systems
    Type: NASA-CR-204489 , NAS 1.26:204489 , RIACS-TR-97-01 , Parallel Algorithms and Architectures; Jun 22, 1997 - Jun 25, 1997; Newport, RI; United States
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