244 research outputs found
Blocked All-Pairs Shortest Paths Algorithm on Intel Xeon Phi KNL Processor: A Case Study
Manycores are consolidating in HPC community as a way of improving
performance while keeping power efficiency. Knights Landing is the recently
released second generation of Intel Xeon Phi architecture. While optimizing
applications on CPUs, GPUs and first Xeon Phi's has been largely studied in the
last years, the new features in Knights Landing processors require the revision
of programming and optimization techniques for these devices. In this work, we
selected the Floyd-Warshall algorithm as a representative case study of graph
and memory-bound applications. Starting from the default serial version, we
show how data, thread and compiler level optimizations help the parallel
implementation to reach 338 GFLOPS.Comment: Computer Science - CACIC 2017. Springer Communications in Computer
and Information Science, vol 79
The unbounded dead-end depth propertie is not a group invariant
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Hydrogen Dynamics in Superprotonic CsHSO4
We present a detailed study of proton dynamics in the hydrogen-bonded
superprotonic conductor CsHSO4 from first-principles molecular dynamics
simulations, isolating the subtle interplay between the dynamics of the O--H
chemical bonds, the O...H hydrogen bonds, and the SO4 tetrahedra in promoting
proton diffusion. We find that the Grotthus mechanism of proton transport is
primarily responsible for the dynamics of the chemical bonds, whereas the
reorganization of the hydrogen-bond network is dominated by rapid angular hops
in concert with small reorientations of the SO4 tetrahedra. Frequent proton
jumping across the O--H...O complex is countered by a high rate of jump
reversal, which we show is connected to the dynamics of the SO4 tetrahedra,
resulting in a diminished CsHSO4/CsDSO4 isotope effect. We also find evidence
of multiple timescales for SO4 reorientation events, leading to distinct
diffusion mechanisms along the different crystal lattice directions. Finally,
we employ graph-theoretic techniques to characterize the topology of the
hydrogen-bond network and demonstrate a clear relationship between certain
connectivity configurations and the likelihood for diffusive jump events.Comment: 12 pages, 10 figure
Common Representation of Information Flows for Dynamic Coalitions
We propose a formal foundation for reasoning about access control policies
within a Dynamic Coalition, defining an abstraction over existing access
control models and providing mechanisms for translation of those models into
information-flow domain. The abstracted information-flow domain model, called a
Common Representation, can then be used for defining a way to control the
evolution of Dynamic Coalitions with respect to information flow
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