656 research outputs found
Simulating the universe on an intercontinental grid of supercomputers
Understanding the universe is hampered by the elusiveness of its most common
constituent, cold dark matter. Almost impossible to observe, dark matter can be
studied effectively by means of simulation and there is probably no other
research field where simulation has led to so much progress in the last decade.
Cosmological N-body simulations are an essential tool for evolving density
perturbations in the nonlinear regime. Simulating the formation of large-scale
structures in the universe, however, is still a challenge due to the enormous
dynamic range in spatial and temporal coordinates, and due to the enormous
computer resources required. The dynamic range is generally dealt with by the
hybridization of numerical techniques. We deal with the computational
requirements by connecting two supercomputers via an optical network and make
them operate as a single machine. This is challenging, if only for the fact
that the supercomputers of our choice are separated by half the planet, as one
is located in Amsterdam and the other is in Tokyo. The co-scheduling of the two
computers and the 'gridification' of the code enables us to achieve a 90%
efficiency for this distributed intercontinental supercomputer.Comment: Accepted for publication in IEEE Compute
MPWide: a light-weight library for efficient message passing over wide area networks
We present MPWide, a light weight communication library which allows
efficient message passing over a distributed network. MPWide has been designed
to connect application running on distributed (super)computing resources, and
to maximize the communication performance on wide area networks for those
without administrative privileges. It can be used to provide message-passing
between application, move files, and make very fast connections in
client-server environments. MPWide has already been applied to enable
distributed cosmological simulations across up to four supercomputers on two
continents, and to couple two different bloodflow simulations to form a
multiscale simulation.Comment: accepted by the Journal Of Open Research Software, 13 pages, 4
figures, 1 tabl
Super computers in astrophysics and High Performance simulations of self-gravitating systems
The modern study of the dynamics of stellar systems requires the use of
high-performance computers. Indeed, an accurate modelization of the structure
and evolution of self-gravitating systems like planetary systems, open
clusters, globular clusters and galaxies imply the evaluation of body-body
interaction over the whole size of the structure, a task that is
computationally very expensive, in particular when it is performed over long
intervals of time. In this report we give a concise overview of the main
problems of stellar systems simulations and present some exciting results we
obtained about the interaction of globular clusters with the parent galaxy.Comment: Invited talk at the SAIt 2003 national meeting (Trieste, Italy, 14 -
17 aprile 2003) to be published in the Proceedings; 6 pages+3 ps figure
Stability of Multiplanetary Systems in Star Clusters
Most stars form in star clusters and stellar associated. To understand the
roles of star cluster environments in shaping the dynamical evolution of
planetary systems, we carry out direct -body simulations of four planetary
systems models in three different star cluster environments with respectively
N=2k, 8k and 32k stars. In each cluster, an ensemble of initially identical
planetary systems are assigned to solar-type stars with and
evolved for 50~Myr. We found that following the depletion of protoplanetary
disks, external perturbations and planet-planet interactions are two driving
mechanisms responsible for the destabilization of planetary systems. The planet
survival rate varies from in the N=2k cluster to in the
N=32k cluster, which suggests that most planetary systems can indeed survive in
low-mass clusters, except in the central regions. We also find that planet
ejections through stellar encounters are cumulative processes, as only of encounters are strong enough to excite the eccentricity by . Short-period planets can be perturbed through orbit crossings with
long-period planets. When taking into account planet-planet interactions, the
planet ejection rate nearly doubles, and therefore multiplicity contributes to
the vulnerability of planetary systems. In each ensemble, of
planetary orbits become retrograde due to random directions of stellar
encounters. Our results predict that young low-mass star clusters are promising
sites for next-generation planet surveys, yet low planet detection rates are
expected in dense globular clusters such as 47 Tuc. Nevertheless, planets in
denser stellar environments are likely to have shorter orbital periods, which
enhances their detectability.Comment: 19 pages, 13 figures, 4 tables, accepted for publication in MNRA
Working Papers: Astronomy and Astrophysics Panel Reports
The papers of the panels appointed by the Astronomy and Astrophysics survey Committee are compiled. These papers were advisory to the survey committee and represent the opinions of the members of each panel in the context of their individual charges. The following subject areas are covered: radio astronomy, infrared astronomy, optical/IR from ground, UV-optical from space, interferometry, high energy from space, particle astrophysics, theory and laboratory astrophysics, solar astronomy, planetary astronomy, computing and data processing, policy opportunities, benefits to the nation from astronomy and astrophysics, status of the profession, and science opportunities
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