The CP-PACS project

Iwasaki, Y.

doi:10.1016/s0920-5632(97)00487-8

Cited by 14 publications

(12 citation statements)

References 7 publications

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“…Here we used the latest version, GRAPE-6 (Makino 2002), which has a speed of 1 Tflops. Eight GRAPE-6 boards are combined with CP-PACS, which is a massively parallel supercomputer at the University of Tsukuba composed of 2048 processing units (PUs), with a theoretical peak speed of 614 Gflops (Iwasaki 1998). This system is called the Heterogeneous Multicomputer System (HMCS; Boku et al 2002).…”

Section: Hydrodynamics and Gravitymentioning

confidence: 99%

Formation of Dwarf Galaxies during the Cosmic Reionization

Susa¹,

Umemura²

2004

ApJ

121

122

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We reanalyze the photoevaporation problem of subgalactic objects irradiated by ultraviolet background (UVB) radiation in a reionized universe. For the purpose, we perform three-dimensional radiation smoothed particle hydrodynamics (RSPH) calculations, in which the radiative transfer is solved by a direct method and the nonequilibrium chemistry of primordial gas including H 2 molecules is also incorporated. Attention is concentrated on radiative transfer effects on the UVB for the formation of subgalactic objects with T vir P 10 4 K. We consider a reionization model with z reion % 7 and also the earlier reionization model (z reion % 17) inferred by the Wilkinson Microwave Anisotropy Probe (WMAP). We find that star formation is suppressed appreciably by UVB, but baryons at high-density peaks are self-shielded even during the reionization, forming some amount of stars eventually. In that sense, the photoevaporation for subgalactic systems is not as perfect as argued by onedimensional spherical calculations. The final stellar fraction depends on the collapse epoch and the mass of the system, almost regardless of the reionization epoch. For instance, a few tenths of the formed stars are born after the cosmic reionization in the z reion % 7 model, while more than 90% of the stars are born after the reionization in the WMAP reionization model. Thus, the effects of UVB feedback on the substructure problem with a cold dark matter (CDM) scenario should be evaluated with careful treatment of the radiative transfer. The star clusters formed at high-density peaks coalesce with each other in a dissipationless fashion in a dark matter potential, as a resultant forming a spheroidal system. As a result, these low-mass galaxies have large mass-to-light ratios, such as observed in dwarf spheroidal galaxies in the Local Group.

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Section: Hydrodynamics and Gravitymentioning

confidence: 99%

Formation of Dwarf Galaxies during the Cosmic Reionization

Susa¹,

Umemura²

2004

ApJ

121

122

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“…In the present calculations, we use 128 3 grids for space, 128 2 grids for directions and six grids for frequencies, so that the total number of operations amounts to 1.5 Tflop h (1 500 Gflop h) to obtain the ionization structure at each redshift. To perform 6D radiative transfer calculations, we employ one of highest performance supercomputers, the CP-PACS (Computational Physics by Parallel Array Computer System) at the University of Tsukuba, Japan, which is a massively parallel computer, composed of 2 048 processing units, with the theoretical peak speed of 614 Gflop (giga-flops) (Iwasaki 1998). For the present purpose, we have parallelized the radiative transfer solver by a newly developed wavefront method, which is optimized for massively parallel machines (Nakamoto 1999; see the detail in Appendix A).…”

Section: Radiative Transfermentioning

confidence: 99%

The effects of radiative transfer on the reionization of an inhomogeneous universe

Nakamoto

Umemura

Susa

2001

Monthly Notices of the Royal Astronomical Society

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Assuming simple dynamics for the growth of density fluctuations, we implement six‐dimensional (6D) radiative transfer calculations to elucidate the effects of photon propagation during the reionization of an inhomogeneous universe. The ionizing sources are postulated to be AGN‐like in this paper. The present simulations reveal that radiative transfer effects are still prominent considerably after the percolation epoch, in which patchy ionized regions connect with each other. In other words, owing to the collective opacity, the Universe does not become perfectly transparent against ionizing radiation even though strongly self‐shielded regions disappear. It turns out that the inhomogeneity of the medium enhances the opacity effects and delays the end of reionization. Owing to such radiative transfer effects, the reionization in an inhomogeneous universe proceeds fairly slowly, in contrast to the prompt reionization in a homogeneous universe, and as a result the surface of reionization is not so sharply edged, but highly uneven. As a signature of the uneven surface of reionization, the cosmic IR background (CIB) radiation, which is produced by Lyα photons resulting from radiative recombination, could exhibit strong anisotropies, reflecting the amplitude of density fluctuations at the reionization era. The predicted CIB intensity lies on a level of possible detection by forthcoming IR space telescope facilities.

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“…This is an endeavor demanding considerable computing resources, which we hope to meet with the use of the CP-PACS parallel computer with a peak speed of 614 GFLOPS developed at the University of Tsukuba [19,20]. We explore, as a first step toward a realistic simulation of QCD, the case of dynamical up and down quarks, which are assumed degenerate, treating the strange quark in the quenched approximation.…”

Section: Introductionmentioning

confidence: 99%

Erratum: Light hadron spectroscopy with two flavors of dynamical quarks on the lattice [Phys. Rev. D65, 054505 (2002)]

Khan¹,

Aoki²,

Boyd³

et al. 2003

Phys. Rev. D

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We present results of a numerical calculation of lattice QCD with two degenerate flavors of dynamical quarks, identified with up and down quarks, and with a strange quark treated in the quenched approximation. The lattice action and simulation parameters are chosen with a view to carrying out an extrapolation to the continuum limit as well as chiral extrapolations in dynamical up and down quark masses. Gauge configurations are generated with a renormalization-group improved gauge action and a mean field improved clover quark action at three values of β = 6/g 2 , corresponding to lattice spacings of a ≈ 0.22, 0.16 and 0.11 fm, and four sea quark masses corresponding to mPS/mV ≈ 0.8, 0.75, 0.7 and 0.6. The sizes of lattice are chosen to be 12 3 × 24, 16 3 × 32 and 243 × 48 so that the physical spatial size is kept constant at La ≈ 2.5 fm. Hadron masses, light quark masses and meson decay constants are measured at five valence quark masses corresponding to mPS/mV ≈ 0.8, 0.75, 0.7, 0.6 and 0.5. We also carry out complementary quenched simulations with the same improved actions. The quenched spectrum from this analysis agrees well in the continuum limit with the one of our earlier work using the standard action, quantitatively confirming the systematic deviation of the quenched spectrum from experiment. We find the twoflavor full QCD meson masses in the continuum limit to be much closer to experimental meson masses than those from quenched QCD. When using the K meson mass to fix the strange quark mass, the difference between quenched QCD and experiment of 2.6 −0.031 in two-flavor full QCD, approaching the experimental value J ≈ 0.48. We take these results as manifestations of sea quark effects in two-flavor full QCD. For baryon masses full QCD values for strange baryons such as Ξ and Ω are in agreement with experiment, while they differ increasingly with decreasing strange quark content, resulting in a nucleon mass higher than experiment by 10% and a ∆ mass by 13%. The pattern suggests finite size effects as a possible origin for this deviation. For light quark masses in the continuum limit we obtain m −11 MeV (φ-input), which are reduced by about 25% compared to the values in quenched QCD. We also present results for decay constants where large scaling violations obstruct a continuum extrapolation. Need for a non-perturbative estimate of renormalization factors is discussed.

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The CP-PACS project

Cited by 14 publications

References 7 publications

Formation of Dwarf Galaxies during the Cosmic Reionization

Formation of Dwarf Galaxies during the Cosmic Reionization

The effects of radiative transfer on the reionization of an inhomogeneous universe

Erratum: Light hadron spectroscopy with two flavors of dynamical quarks on the lattice [Phys. Rev. D65, 054505 (2002)]

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