368,727 research outputs found

    Microscopic Calculation of in-Medium Proton-Proton Cross Sections

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    We derive in-medium PROTON-PROTON cross sections in a microscopic model based upon the Bonn nucleon-nucleon potential and the Dirac-Brueckner approach for nuclear matter. We demonstrate the difference between proton-proton and neutron-proton cross sections and point out the need to distinguish carefully between the two cases. We also find substantial differences between our in-medium cross sections and phenomenological parametrizations that are commonly used in heavy-ion reactions.Comment: 9 pages of RevTex and 4 figures (postscript in separate uuencoded file), UI-NTH-930

    Darwinian Data Structure Selection

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    Data structure selection and tuning is laborious but can vastly improve an application's performance and memory footprint. Some data structures share a common interface and enjoy multiple implementations. We call them Darwinian Data Structures (DDS), since we can subject their implementations to survival of the fittest. We introduce ARTEMIS a multi-objective, cloud-based search-based optimisation framework that automatically finds optimal, tuned DDS modulo a test suite, then changes an application to use that DDS. ARTEMIS achieves substantial performance improvements for \emph{every} project in 55 Java projects from DaCapo benchmark, 88 popular projects and 3030 uniformly sampled projects from GitHub. For execution time, CPU usage, and memory consumption, ARTEMIS finds at least one solution that improves \emph{all} measures for 86%86\% (37/4337/43) of the projects. The median improvement across the best solutions is 4.8%4.8\%, 10.1%10.1\%, 5.1%5.1\% for runtime, memory and CPU usage. These aggregate results understate ARTEMIS's potential impact. Some of the benchmarks it improves are libraries or utility functions. Two examples are gson, a ubiquitous Java serialization framework, and xalan, Apache's XML transformation tool. ARTEMIS improves gson by 16.516.5\%, 1%1\% and 2.2%2.2\% for memory, runtime, and CPU; ARTEMIS improves xalan's memory consumption by 23.523.5\%. \emph{Every} client of these projects will benefit from these performance improvements.Comment: 11 page
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