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Mar 2009
  • CINES received a 150 TFlops machine
  • GENCI has acquired for the French University Supercomputing Center a 12288 core SGI Altix. It is ranked 14th in the World and first in France.
  • Site Web du CINES
  • IDRIS received a 140 Tflops BlueGene/P machine.
  • The CNRS supercomputing centre has acquired a new BlueGene machine with 40480 processors and 20 To of RAM memory.
  • See the press release.
  • Mare Nostrum simulation down to z=1.55
  • We carried out our fourth run of MareNostrum down to z=1.55 while producing 150 Million "stars". More info is given here
  • Horizon 4Pi 4096^3 down to z=0
  • We have carried a full sky 2Gpc/h 4096^3 Dark Matter simulation down to z=0. More details can be found here
  • Horizon 4Pi run 2048^3 completed
  • We have completed a full sky cone run of DM with RAMSES on platine CEA with 2048^3 particles. See a slice here
  • Mare Nostrum @ z=1.9
  • We carried out our third run of MareNostrum down to z=1.9 while producing 120 Million "stars"
  • Mare Nostrum simulation down to z=2.4
  • We carried our second run on the Mare Nostrum supercomputing center down to z=2.4, thanks to 4-fold improvement in overall performance.
  • 1024^3 500 h-1Mpc simulation completed
  • RAMSES run of the HORIZON initial condition was carried down to z=0 using 1024^3 dark matter particles in a (500 Mpc/h)^3 box with up to 16 levels of refinement (corresponding to local effective resolution of 65536).
  • Horizon 1024^3 100 Mpc/h simulation completed.
  • A RAMSES run of the HORIZON initial condition was carried down to z=0 using 1024^3 dark matter particles in a (100 Mpc/h)^3 box with up to 16 levels of refinement (corresponding to local effective resolution of 65536).
  • A 43 Tflops supercomputer at CEA
  • CCRT, the supercomputing centre of CEA, has just received a new BULL supercomputer with 6800 processors and 13.6 Tb of RAM memory. This facility is dedicated to academic and industrial research.
  • Lire le communiqué
  • Fourth Horizon Workshop 2006b
  • The 4th workshop takes place from December, the 11th to December, the 12th at Paris Observatory. Registration form available here.
  • MareNostrum simulation has started at BSC
  • After 1 week of operations, we have reached redshift 4. The simulation will proceed further more during the next quarters. We have started to post-process these initial data.
  • Horizon Grid
  • The Horizon grid is now in operation. It links the 6 quadri opteron of Meudon, Paris, Lyon, Saclay, IAP and Marseille and is open to all members of the collaboration. Voir ce lien
  • Third Horizon Workshop 2006a
  • Horizon Workshop 2006a 10, 11 and 12 april 2006 in Lyon. It will be dedicated to progress reports. Registration form
  • Horizon is part of the DEISA "Extreme Computing Initiative"
  • Horizon will launch one extreme application for galaxy formation using the DEISA infrastructure at Mare Nostrum
  • DEISA web site
  • Second Horizon Workshop
  • Horizon Workshop 2005 took place at Paris Observatory the 14th and 15th november. It was dedicated to internal discussions and management issues.
  • November 2005: Horizon méso-machine is fully operational at HPC1
  • October 2005: Horizon was awarded a 500 k€ grant by ANR, the French Science Foundation.
  • Horizon response to «ANR Blanche» Call for Proposals has been succesfull in the «UNIVERS» program.
  • ANR web site
  • July 2005: HP France was selected to host the Horizon "meso-computer"
  • HP company has succesfully answered the "call for proposals" issued by the Hrizon Project for a medium-size dedicated super-computer. The computer will be hosted at HPC1, the HP high performance computing center near Paris.
  • February 2005: INSU and CEA agree to fund the Horizon "meso-machine".
  • Horizon has submitted to INSU a proposal for funding a medium-size computer dedicated to the project. The proposal was accepted as a joint CEA and INSU operation.
  • September 2004: Kick-off meeting in Paris
  • During 3 days (13, 14 and 15 of september), 30 scientists have met at Observatoire de Paris to set up the basic organisation and objectives of the Horizon Project.
  • KO Meeting
  • June 2004: Project report at SF2A in Paris
  • April 2004: Horizon received official support from ASSNA.
  • The french initiative «Action Spécifique pour les Simulations Numériques en Astrophysique» have given to the Horizon project its "label" for outstanding and structuring computational project.
  • April 2004: The french Astroparticule program provides financial support for the Horizon "mini-grid"
  • The Programme Astro-Particule, a joint IN2P3 and INSU initiative, has agreed to finance 6 quad AMD64 servers dedicated to the Horizon Project.
  • January 2004: Review by PNC and PNG
  • Both PNG and PNC scientific comitees are officially supporting the Horizon Project initiative.
  • June 2003: Presentation of the project to SF2A
  • Theoretical Virtual Observatory workshop (IAP April 5-6, 2006)
  • A workshop dedicated to the Theoretical Virtual Observatory will take place at IAP on April 5-6th.

    The goal is to bring together experts of the Virtual Observatory and theoreticians who would like to make results of their simulations (e.g. databases or catalogs) or numerical codes available to the worldwild astronomical community.

  • Program and speakers

Initial Conditions

by Combes Françoise (Tuesday 13 June 2006)

Download Horizon Initial Conditions and Related Softwares (expert only)

CMB temperature fluctuations as seen by WMAP after one year of operation

The initial cosmological conditions are built by linearly integrating an almost scale-invariant fluctuations spectrum produced by the assumed early inflation. These density fluctuations are integrated in the linear regime until the non-linear evolution has to be treated by numerical simulations.

The linear integration is performed using the COSMICS package, including LINGER (linear equations in general relativity) and GRAFIC (Gaussian RAndom Field Initial Conditions). This package has been created by E. Bertschinger (see the web site and the related paper).

The program uses a set of parameters to define the model of universe used (flat curvature, densities of baryonic and dark matter and dark energy content), selects the power spectrum shape, and its normalisation, and outputs the density and velocity field on a regular lattice, with periodic boundary conditions.

The density perturbations are given by a displacement field at each position of the cartesian lattice, and a velocity field, obeying the Zeldovich approximation (displacement and velocities are coherent to produce the density perturbations).

The method uses the key equation which develops the density perturbation field as the convolution of a white noise function with a transfer function, which represents the power spectrum P(k). The largest and smallest scale that can be treated is limited by the size of the cartesian grid, and the smallest cell used (the resolution).

The challenge of the Horizon project is to study galaxy formation at the smallest scale, taking into account the cosmological context, widely using multi-scale resolution. It is now possible with GRAFIC2 to generate Gaussian random fields, with adaptive mesh refinement (Bertschinger 2001). The advantage of this package is to provide codes able to relate the large scale density perturbations to the refined small scales ones. Indeed, it is not only dividing the smallest cells in the refined zone by a certain refinement factor r, but also ensures that the phase of the coarse grid fluctuations are the same as those in the fine grid, for the same wave-number. The convolution with multi-scale resolution enforces a constraint on the white noise functions that made them coherent at the relevant scales, and not completely independent. This ensures that the small-scale structures that will develop in the high resolution simulations through gravitational collapse will know in which large-scale structure they form, at low resolution.

Before recombination, the ionized baryons are tightly coupled to the photons and participate closely to the acoustic oscillations, which are visible as the characterictics peaks in the anisotropy power spectrum of the CMB (Cosmic Microwave Background) . These peaks occur at low and intermediate scale, and then are damped at small scale. Although the baryonic fraction (4-5% in Omega_b) is low, these perturbations remain imprinted in the density power spectrum, and could be an interesting signature, that can be observed in large-scale structures. The cosmological initial conditions will therefore also include the baryon wiggles and damping, according to the precise treatment by Eisenstein and Hu (1998). The baryons affect the transfer function of dark matter through the acoustic oscillations, and suppression of power below the sound horizon.