35,503 research outputs found
Grid Search in Stellar Parameters: a software for spectrum analysis of single stars and binary systems
The currently operating space missions, as well as those that will be
launched in the near future, (will) deliver high-quality data for millions of
stellar objects. Since the majority of stellar astrophysical applications still
(at least partly) rely on spectroscopic data, an efficient tool for the
analysis of medium- to high-resolution spectroscopy is needed. We aim at
developing an efficient software package for the analysis of medium- to
high-resolution spectroscopy of single stars and those in binary systems. The
major requirements are that the code has a high performance, represents the
state-of-the-art analysis tool, and provides accurate determinations of
atmospheric parameters and chemical compositions for different types of stars.
We use the method of atmosphere models and spectrum synthesis, which is one of
the most commonly used approaches for the analysis of stellar spectra. Our Grid
Search in Stellar Parameters (GSSP) code makes use of the OpenMPI
implementation, which makes it possible to run in parallel mode. The method is
first tested on the simulated data and is then applied to the spectra of real
stellar objects. The majority of test runs on the simulated data were
successful in the sense that we could recover the initially assumed sets of
atmospheric parameters. We experimentally find the limits in signal-to-noise
ratios of the input spectra, below which the final set of parameters gets
significantly affected by the noise. Application of the GSSP package to the
spectra of three Kepler stars, KIC11285625, KIC6352430, and KIC4931738, was
also largely successful. We found an overall agreement of the final sets of the
fundamental parameters with the original studies. For KIC6352430, we found that
dependence of the light dilution factor on wavelength cannot be ignored, as it
has significant impact on the determination of the atmospheric parameters of
this binary system.Comment: 19 pages, 6 figures, 4 tables, 2 appendices one of which includes
detailed description of input and output files. Accepted for publication in
Astronomy & Astrophysi
Optimizing Splicing Junction Detection in Next Generation Sequencing Data on a Virtual-GRID Infrastructure
The new protocol for sequencing the messenger RNA in a cell, named RNA-seq produce millions of short sequence fragments. Next Generation Sequencing technology allows more accurate analysis but increase needs in term of computational resources. This paper describes the optimization of a RNA-seq analysis pipeline devoted to splicing variants detection, aimed at reducing computation time and providing a multi-user/multisample environment. This work brings two main contributions. First, we optimized a well-known algorithm called TopHat by parallelizing some sequential mapping steps. Second, we designed and implemented a hybrid virtual GRID infrastructure allowing to efficiently execute multiple instances of TopHat running on different samples or on behalf of different users, thus optimizing the overall execution time and enabling a flexible multi-user environmen
Preparing HPC Applications for the Exascale Era: A Decoupling Strategy
Production-quality parallel applications are often a mixture of diverse
operations, such as computation- and communication-intensive, regular and
irregular, tightly coupled and loosely linked operations. In conventional
construction of parallel applications, each process performs all the
operations, which might result inefficient and seriously limit scalability,
especially at large scale. We propose a decoupling strategy to improve the
scalability of applications running on large-scale systems.
Our strategy separates application operations onto groups of processes and
enables a dataflow processing paradigm among the groups. This mechanism is
effective in reducing the impact of load imbalance and increases the parallel
efficiency by pipelining multiple operations. We provide a proof-of-concept
implementation using MPI, the de-facto programming system on current
supercomputers. We demonstrate the effectiveness of this strategy by decoupling
the reduce, particle communication, halo exchange and I/O operations in a set
of scientific and data-analytics applications. A performance evaluation on
8,192 processes of a Cray XC40 supercomputer shows that the proposed approach
can achieve up to 4x performance improvement.Comment: The 46th International Conference on Parallel Processing (ICPP-2017
A posteriori inclusion of PDFs in NLO QCD final-state calculations
Any NLO calculation of a QCD final-state observable involves Monte Carlo
integration over a large number of events. For DIS and hadron colliders this
must usually be repeated for each new PDF set, making it impractical to
consider many `error' PDF sets, or carry out PDF fits. Here we discuss ``a
posteriori'' inclusion of PDFs, whereby the Monte Carlo run calculates a grid
(in x and Q) of cross section weights that can subsequently be combined with an
arbitrary PDF. The procedure is numerically equivalent to using an interpolated
form of the PDF. The main novelty relative to prior work is the use of
higher-order interpolation, which substantially improves the tradeoff between
accuracy and memory use. An accuracy of about 0.01% has been reached for the
single inclusive cross-section in the central rapidity region |y|<0.5 for jet
transverse momenta from 100 to 5000 GeV. This method should facilitate the
consistent inclusion of final-state data from HERA, Tevatron and LHC in PDF
fits, thus helping to increase the sensitivity of LHC to deviations from
standard Model predictions.Comment: contribution to the CERN DESY workshop on "HERA and LHC
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