23,040 research outputs found
GPU Accelerated Particle Visualization with Splotch
Splotch is a rendering algorithm for exploration and visual discovery in
particle-based datasets coming from astronomical observations or numerical
simulations. The strengths of the approach are production of high quality
imagery and support for very large-scale datasets through an effective mix of
the OpenMP and MPI parallel programming paradigms. This article reports our
experiences in re-designing Splotch for exploiting emerging HPC architectures
nowadays increasingly populated with GPUs. A performance model is introduced
for data transfers, computations and memory access, to guide our re-factoring
of Splotch. A number of parallelization issues are discussed, in particular
relating to race conditions and workload balancing, towards achieving optimal
performances. Our implementation was accomplished by using the CUDA programming
paradigm. Our strategy is founded on novel schemes achieving optimized data
organisation and classification of particles. We deploy a reference simulation
to present performance results on acceleration gains and scalability. We
finally outline our vision for future work developments including possibilities
for further optimisations and exploitation of emerging technologies.Comment: 25 pages, 9 figures. Astronomy and Computing (2014
Hadron structure after 25 years of QCD
We briefly review the status of our understanding of hadron structure based
on QCD. This includes the role of symmetries, especially chiral symmetry, and
the insights provided by lattice QCD. The main focus is on baryon structure and
especially the nucleon, but this cannot be treated realistically without
reference to spectroscopy. Our aim is to highlight recent insights and
promising directions for future work.Comment: Invited talk presented at the 16th Int. Conf. on Few Body Problems
(Taipei, March 6-10, 2000); 13 pages, 3 figure
APECS - The Atacama Pathfinder Experiment Control System
APECS is the distributed control system of the new Atacama Pathfinder
EXperiment (APEX) telescope located on the Llano de Chajnantor at an altitude
of 5107 m in the Atacama desert in northern Chile. APECS is based on Atacama
Large Millimeter Array (ALMA) software and employs a modern, object-oriented
design using the Common Object Request Broker Architecture (CORBA) as the
middleware. New generic device interfaces simplify adding instruments to the
control system. The Python based observer command scripting language allows
using many existing software libraries and facilitates creating more complex
observing modes. A new self-descriptive raw data format (Multi-Beam FITS or
MBFITS) has been defined to store the multi-beam, multi-frequency data. APECS
provides an online pipeline for initial calibration, observer feedback and a
quick-look display. APECS is being used for regular science observations in
local and remote mode since August 2005.Comment: 4 pages, A&A, accepte
hadroproduction with massive bottom quarks with PowHel
The associated production of top-antitop-bottom-antibottom quarks is a
relevant irreducible background for Higgs boson analyses in the
top-antitop-Higgs production channel, with Higgs decaying into a
bottom-antibottom quark pair. We implement this process in the PowHel event
generator, considering the bottom quarks as massive in all steps of the
computation which involves hard-scattering matrix-elements in the 4-flavour
number scheme combined with 4-flavour Parton Distribution Functions.
Predictions with NLO QCD + Parton Shower accuracy, as obtained by PowHel +
PYTHIA, are compared to those which resulted from a previous PowHel
implementation with hard-scattering matrix-elements in the 5-flavour number
scheme, considering as a baseline the example of a realistic analysis of
top-antitop hadroproduction with additional -jet activity, performed by the
CMS collaboration at the Large Hadron Collider.Comment: 9 pages, 6 figure
Recent Pythia 8 developments: Hard diffraction, Colour reconnection and collisions
An overview of recent developments in \pythia~8 is given. First the new hard
diffraction model, which is implemented as a part of the multiparton
interactions (MPI) framework, is discussed. Then the new colour reconnection
model, which includes beyond leading colour effects that can become important
when MPI are present, is briefly reviewed. As a last topic an introduction is
given to our implementation of photon-photon collisions. In particular photon
PDFs, required modifications for the initial state radiation algorithm and beam
remnant handling with photon beams is discussed.Comment: Contribution to proceedings of 7th International Workshop on Multiple
Partonic Interactions at the LHC, 23 - 27 November 2015, Miramare, Trieste,
Ital
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