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Maxantalet träffar du kan exportera från sökgränssnittet är 250. Vid större uttag använd dig av utsökningar.
  • 251. Tak, Ng
    et al.
    Johnsson, Lennart
    KTH, Skolan för datavetenskap och kommunikation (CSC), Centra, Parallelldatorcentrum, PDC.
    Generation of Layouts from Circuit Schematics; A Graph Theoretic Approach21984Konferansepaper (Fagfellevurdert)
    Abstract [en]

    A graph model is proposed to capture the topological properties of metal-oxide semiconductor (MOS) transistors and interconnections among transistors. A set of algorithms is devised for the enumeration of layout topologies of a circuit from its graph model. Layout topologies are presented in stick diagrams. The algorithms select a set of embedded layout topologies with the “fewest” number of jumpers for layout generation and compaction. Layouts for circuits with up to 36 transistors have been generated successfully. The layouts corresponding to the topologies generated and selected by the algorithms are, in most cases, smaller than compact hand layouts. The worst case computational complexity is O(n 2), where n is the number of transistors in the circuit.

  • 252. Vapirev, A.
    et al.
    Deca, J.
    Lapenta, G.
    Markidis, Stefano
    KTH, Skolan för datavetenskap och kommunikation (CSC), Centra, Parallelldatorcentrum, PDC.
    Hur, I.
    Cambier, J. -L
    Initial results on computational performance of Intel many integrated core, sandy bridge, and graphical processing unit architectures: implementation of a 1D c++/OpenMP electrostatic particle-in-cell code2015Inngår i: Concurrency and Computation, ISSN 1532-0626, E-ISSN 1532-0634, Vol. 27, nr 3, s. 581-593Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We present initial comparison performance results for Intel many integrated core (MIC), Sandy Bridge (SB), and graphical processing unit (GPU). A 1D explicit electrostatic particle-in-cell code is used to simulate a two-stream instability in plasma. We compare the computation times for various number of cores/threads and compiler options. The parallelization is implemented via OpenMP with a maximum thread number of 128. Parallelization and vectorization on the GPU is achieved with modifying the code syntax for compatibility with CUDA. We assess the speedup due to various auto-vectorization and optimization level compiler options. Our results show that the MIC is several times slower than SB for a single thread, and it becomes faster than SB when the number of cores increases with vectorization switched on. The compute times for the GPU are consistently about six to seven times faster than the ones for MIC. Compared with SB, the GPU is about two times faster for a single thread and about an order of magnitude faster for 128 threads. The net speedup, however, for MIC and GPU are almost the same. An initial attempt to offload parts of the code to the MIC coprocessor shows that there is an optimal number of threads where the speedup reaches a maximum.

  • 253. Vapirev, A. E.
    et al.
    Lapenta, G.
    Divin, A.
    Markidis, Stefano
    KTH, Skolan för datavetenskap och kommunikation (CSC), High Performance Computing and Visualization (HPCViz). KTH, Skolan för datavetenskap och kommunikation (CSC), Centra, Parallelldatorcentrum, PDC.
    Henri, P.
    Goldman, M.
    Newman, D.
    Formation of a transient front structure near reconnection point in 3-D PIC simulations2013Inngår i: Journal of Geophysical Research, ISSN 0148-0227, E-ISSN 2156-2202, Vol. 118, nr 4, s. 1435-1449Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Massively parallel numerical simulations of magnetic reconnection are presented in this study. Electromagnetic full-particle implicit code iPIC3D is used to study the dynamics and 3-D evolution of reconnection outflows. Such features as Hall magnetic field, inflow and outflow, and diffusion region formation are very similar to 2-D particle-in-cell (PIC) simulations. In addition, it is well known that instabilities develop in the current flow direction or oblique directions. These modes could provide for anomalous resistivity and diffusive drag and can serve as additional proxies for magnetic reconnection. In our work, the unstable evolution of reconnection transient front structures is studied. Reconnection configuration in the absence of guide field is considered, and it is initialized with a localized perturbation aligned in the cross-tail direction. Our study suggests that the instabilities lead to the development of finger-like density structures on ion-electron hybrid scales. These structures are characterized by a rapid increase of the magnetic field, normal to the current sheet (Bz). A small decrease in the magnetic field component parallel to the reconnection X line and the component perpendicular to the current sheet is observed in the region ahead of the front. The instabilities form due to fact that the density gradient inside the front region is opposite to the direction of the acceleration Lorentz force. Such density structures may possibly further develop into larger-scale earthward flux transfer events during magnetotail reconnection. In addition, oscillations mainly in the magnetic and electric fields and the electron density are observed shortly before the arrival of the main front structure which is consistent with recent THEMIS observations. Key PointsThree dimensional particle-in-cell simulation of reconnection in the magnetotailEvolution of dipolarization front at reconnection and associated plasma flowDevelopment of instabilities in the plasma population

  • 254. Weidel, Philipp
    et al.
    Djurfeldt, Mikael
    KTH, Skolan för datavetenskap och kommunikation (CSC), Centra, Parallelldatorcentrum, PDC.
    Duarte, Renato C.
    Morrison, Abigail
    Closed Loop Interactions between Spiking Neural Network and Robotic Simulators Based on MUSIC and ROS2016Inngår i: Frontiers in Neuroinformatics, ISSN 1662-5196, E-ISSN 1662-5196, Vol. 10, artikkel-id 31Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    In order to properly assess the function and computational properties of simulated neural systems, it is necessary to account for the nature of the stimuli that drive the system. However, providing stimuli that are rich and yet both reproducible and amenable to experimental manipulations is technically challenging, and even more so if a closed-loop scenario is required. In this work, we present a novel approach to solve this problem, connecting robotics and neural network simulators. We implement a middleware solution that bridges the Robotic Operating System (ROS) to the Multi-Simulator Coordinator (MUSIC). This enables any robotic and neural simulators that implement the corresponding interfaces to be efficiently coupled, allowing real-time performance for a wide range of configurations. This work extends the toolset available for researchers in both neurorobotics and computational neuroscience, and creates the opportunity to perform closed-loop experiments of arbitrary complexity to address questions in multiple areas, including embodiment, agency, and reinforcement learning.

  • 255. Zdenek, Johan
    et al.
    Mathur, Kapil K
    Johnsson, Lennart
    KTH, Skolan för datavetenskap och kommunikation (CSC), Centra, Parallelldatorcentrum, PDC.
    Thomas, J.R
    Mesh Decomposition and Communication Procedures for Finite Element Applications on the Connection Machine CM–5 System1994Inngår i: High–Performance Computing and Networking, Springer-Verlag New York, 1994, 2, s. 233-240Kapittel i bok, del av antologi (Fagfellevurdert)
    Abstract [en]

    The objective of this paper is to analyze the impact of data mapping strategies on the performance of finite element applications. First, we describe a parallel mesh decomposition algorithm based on recursive spectral bisection used to partition the mesh into element blocks. A simple heuristic algorithm then renumbers the mesh nodes. Large three-dimensional meshes demonstrate the efficiency of those mapping strategies and assess the performance of a finite element program for fluid dynamics.

  • 256. Zdenek, Johan
    et al.
    Thomas, J.R
    Mathur, Kapil K
    Johnsson, Lennart
    KTH, Skolan för datavetenskap och kommunikation (CSC), Centra, Parallelldatorcentrum, PDC.
    Data Parallel Finite Element Techniques for Computational Fluid Dynamics on the Connection Machine Systems1993Inngår i: Parallel Computational Fluid Dynamics , North Holland , 1993, s. 215-229Kapittel i bok, del av antologi (Fagfellevurdert)
    Abstract [en]

    A finite element method for computational fluid dynamics has been implemented on the Connection Machine systems CM-2 and CM-200. An implicit iterative solution strategy, based on the preconditioned matrix-free GMRES algorithm, is employed. Parallel data structures built on both nodal and elemental sets are used to achieve maximum parallelization. Communication primitives provided through the Connection Machine Scientific Software Library substantially improved the overall performance of the program. Computations of three-dimensional compressible flows using unstructured meshes having close to one million elements, such as a complete airplane, demonstrate that the Connection Machine systems are suitable for these applications. Performance comparisons are also carried out with the vector computers Cray Y-MP and Convex C-1. ii Contents Abstract . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ii 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 2. T...

  • 257.
    Zhang, Ziyang
    et al.
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Mikroelektronik och tillämpad fysik, MAP.
    Andersson, Ulf
    KTH, Skolan för datavetenskap och kommunikation (CSC), Centra, Parallelldatorcentrum, PDC. KTH, Skolan för datavetenskap och kommunikation (CSC).
    Qiu, Min
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Mikroelektronik och tillämpad fysik, MAP.
    Subwavelength-diameter Silica Wire and Photonic Crystal Waveguide Slow Light Coupling2007Inngår i: Active and Passive Electronic Components, ISSN 0882-7516, E-ISSN 1563-5031, Vol. 2007, s. 78602-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Counter-directional coupling between subwavelength-diameter silica wire and single-line-defect two-dimensional photonic crystal slab waveguide is studied numerically using parallel three-dimensional finite-different time-domain method. By modifying silica wire properties or engineering photonic crystal waveguide dispersion band, the coupling central wavelength can be moved to the slow light region and the coupling efficiency improves simultaneously. One design gives 82 peak power transmission from silica wire to photonic crystal waveguide over an interacting distance of 50 lattice constants. The group velocity is estimated as 1/35 of light speed in vacuum.

  • 258.
    Zhang, Ziyang
    et al.
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Mikroelektronik och tillämpad fysik, MAP.
    Dainese, Matteo
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Mikroelektronik och tillämpad fysik, MAP.
    Wosinski, Lech
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Mikroelektronik och tillämpad fysik, MAP.
    Xiao, Sanshui
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Mikroelektronik och tillämpad fysik, MAP.
    Qiu, Min
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Mikroelektronik och tillämpad fysik, MAP.
    Swillo, Marcin
    PhoXtal Communications AB.
    Andersson, Ulf
    KTH, Skolan för datavetenskap och kommunikation (CSC), Centra, Parallelldatorcentrum, PDC. KTH, Skolan för datavetenskap och kommunikation (CSC).
    Optical filter based on two-dimensional photonic crystal surface-mode cavity in amorphous silicon-on-silica structure2007Inngår i: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 90, nr 4, s. 041108-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    An optical filter based on side coupling between silicon wire waveguide and two-dimensional photonic crystal surface-mode cavity is presented. The design is optimized numerically by parallel three-dimensional finite-different time-domain simulations. The device is then fabricated on amorphous silicon-on-silica structure. The drop wavelength is observed around 1580 nm. The extinction ratio of the filter is larger than 10 dB and the intrinsic quality factor of the surface-mode cavity is approximately 2000.

  • 259.
    Zhang, Ziyang
    et al.
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Mikroelektronik och tillämpad fysik, MAP.
    Qiu, Min
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Mikroelektronik och tillämpad fysik, MAP.
    Andersson, Ulf
    KTH, Skolan för datavetenskap och kommunikation (CSC), Centra, Parallelldatorcentrum, PDC. KTH, Skolan för datavetenskap och kommunikation (CSC).
    Tong, Limin
    Department of Optical Engineering, Zhejiang University.
    Subwavelength-diameter Silica Wire for Light In-coupling to Silicon-based Waveguide2007Inngår i: Chinese optics letters, ISSN 1671-7694, Vol. 5, nr 10, s. 577-579Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Coupling between subwavelength-diameter silica wires and silicon-based waveguides is studied using the parallel three-dimensional (3D) finite-different time-domain method. Conventional butt-coupling to a silica-substrated silicon wire waveguide gives above 40% transmission at the wavelength range from 1300 to 1750 nm with good robustness against axial misalignments. Slow light can be generated by counter-directional coupling between a silica wire and a two-dimensional (2D) silicon photonic crystal slab waveguide. Through dispersion-band engineering, 82% transmission is achieved over a coupling distance of 50 lattice constants. The group velocity is estimated as 1/35 of the light speed in vacuum.

  • 260. Zhao, Feng
    et al.
    Johnsson, Lennart
    KTH, Skolan för datavetenskap och kommunikation (CSC), Centra, Parallelldatorcentrum, PDC.
    The Parallel Multipole Method on the Connection Machine1991Inngår i: SIAM Journal on Scientific and Statistical Computing, Vol. 12, nr 6, s. 1420-1437Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    This paper reports on a fast implementation of the three-dimensional nonadaptive Parallel Multipole Method (PMM) on the Connection Machine system model CM-2. The data interactions within the decomposition tree are modeled by a hierarchy of three-dimensional grids forming a pyramid in which parent nodes have degree eight- The base of the pyramid is embedded in the Connection Machine as a three-dimensional grid. The standard grid embedding feature is used. For 10 or more particles per processor the communication time is insignificant. The evaluation of the potential field for a system with 128k particles takes 5 seconds, and a system of a million particles about 3 minutes. The maximum number of particles that can be represented in 2G bytes of primary storage is approximately 50 million. The execution rate of this implementation of the PMM is at about 1.7 Gflops/sec for a particle-processor-ratio of 10 or greater. A further speed improvement is possible by an improved use of the memory hierarchy associated with each floating-point unit in the system.

3456 251 - 260 of 260
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