636 research outputs found
N-body simulation for self-gravitating collisional systems with a new SIMD instruction set extension to the x86 architecture, Advanced Vector eXtensions
We present a high-performance N-body code for self-gravitating collisional
systems accelerated with the aid of a new SIMD instruction set extension of the
x86 architecture: Advanced Vector eXtensions (AVX), an enhanced version of the
Streaming SIMD Extensions (SSE). With one processor core of Intel Core i7-2600
processor (8 MB cache and 3.40 GHz) based on Sandy Bridge micro-architecture,
we implemented a fourth-order Hermite scheme with individual timestep scheme
(Makino and Aarseth, 1992), and achieved the performance of 20 giga floating
point number operations per second (GFLOPS) for double-precision accuracy,
which is two times and five times higher than that of the previously developed
code implemented with the SSE instructions (Nitadori et al., 2006b), and that
of a code implemented without any explicit use of SIMD instructions with the
same processor core, respectively. We have parallelized the code by using
so-called NINJA scheme (Nitadori et al., 2006a), and achieved 90 GFLOPS for a
system containing more than N = 8192 particles with 8 MPI processes on four
cores. We expect to achieve about 10 tera FLOPS (TFLOPS) for a self-gravitating
collisional system with N 105 on massively parallel systems with at most 800
cores with Sandy Bridge micro-architecture. This performance will be comparable
to that of Graphic Processing Unit (GPU) cluster systems, such as the one with
about 200 Tesla C1070 GPUs (Spurzem et al., 2010). This paper offers an
alternative to collisional N-body simulations with GRAPEs and GPUs.Comment: 14 pages, 9 figures, 3 tables, accepted for publication in New
Astronomy. The code is publicly available at
http://code.google.com/p/phantom-grape
Phenomenology of NMSSM in TeV scale mirage mediation
We study the next-to-minimal supersymmetric standard model (NMSSM) with the
TeV scale mirage mediation, which is known as a solution for the little
hierarchy problem in supersymmetry. Our previous study showed that 125 GeV
Higgs boson is realized with O(10) % fine-tuning for 1.5 TeV gluino (1 TeV
stop) mass. The term could be as large as 500 GeV without sacrificing the
fine-tuning thanks to a cancellation mechanism. The singlet-doublet mixing is
suppressed by . In this paper, we further extend this analysis. We
argue that approximate scale symmetries play a role behind the suppression of
the singlet-doublet mixing. They reduce the mixing matrix to a simple form that
is useful to understand the results of the numerical analysis. We perform a
comprehensive analysis of the fine-tuning including the singlet sector by
introducing a simple formula for the fine-tuning measure. This shows that the
singlet mass of the least fine-tuning is favored by the LEP anomaly for
moderate . We also discuss prospects for the precision measurements
of the Higgs couplings at LHC and ILC and direct/indirect dark matter searches
in the model.Comment: 47 pages, 46 figures, version accepted by JHE
Duplicability of self-interacting human genes
BACKGROUND There is increasing interest in the evolution of protein-protein interactions because this should ultimately be informative of the patterns of evolution of new protein functions within the cell. One model proposes that the evolution of new protein-protein interactions and protein complexes proceeds through the duplication of self-interacting genes. This model is supported by data from yeast. We examined the relationship between gene duplication and self-interaction in the human genome. RESULTS We investigated the patterns of self-interaction and duplication among 34808 interactions encoded by 8881 human genes, and show that self-interacting proteins are encoded by genes with higher duplicability than genes whose proteins lack this type of interaction. We show that this result is robust against the system used to define duplicate genes. Finally we compared the presence of self-interactions amongst proteins whose genes have duplicated either through whole-genome duplication (WGD) or small-scale duplication (SSD), and show that the former tend to have more interactions in general. After controlling for age differences between the two sets of duplicates this result can be explained by the time since the gene duplication. CONCLUSIONS Genes encoding self-interacting proteins tend to have higher duplicability than proteins lacking self-interactions. Moreover these duplicate genes have more often arisen through whole-genome rather than small-scale duplication. Finally, self-interacting WGD genes tend to have more interaction partners in general in the PIN, which can be explained by their overall greater age. This work adds to our growing knowledge of the importance of contextual factors in gene duplicability.At the time of publication the author Pérez-Bercoff was affiliated with Smurfit Institute of Genetics, University of Dublin, Trinity College, Dublin
Identifying the Impact of the Built Environment on Wildfire Property Damage in California
Wildfires are a natural hazard that present an increasing risk to communities in fire-prone areas. This study examines the impacts of the municipal-level built environment upon fire damages in California, a particularly fire-vulnerable state. This study uses a multivariate linear regression model to isolate the effects of the human built environment upon reported monetary wildfire damages. Reported monetary losses from wildfires for the years 2007 to 2010 are examined against relevant built environment variables, while statistically controlling for biophysical and socio-economic variables.
The fully-specified regression model indicates that wildfire property damage is driven primarily by the built environment. Socioeconomic and biophysical variables contribute comparatively little explanatory power to the model. Findings from this study will be of particular interest to fire management officials, land developers, and urban planners interested in creating a more fire-resilient future for cities within California
Grain boundary diffusion of W in lower mantle phase with implications for isotopic heterogeneity in oceanic island basalts by core-mantle interactions
Tungsten isotopes provide important constraints on the ocean-island basalt (OIB) source regions. Recent analyses of μ182W in modern basalts with high 3He/4He originating from the core-mantle boundary region reveal two distinct features: positive μ182W in Phanerozoic flood basalts indicating the presence of primordial reservoir, and negative μ182W in modern OIBs. One possibility to produce large variations in μ182W is interaction between the mantle and outer core. Here, we report grain boundary diffusion of W in lower mantle phases. High pressure experimental results show that grain boundary diffusion of W is fast and strongly temperature dependent. Over Earth's history, diffusive transport of W from the core to the lowermost mantle may have led to significant modification of the W isotopic composition of the lower mantle at length scales exceeding one kilometer. Such grain boundary diffusion can lead to large variations in μ182W in modern basalts as a function of the distance of their source regions from the core mantle boundary. Modern oceanic island basalts from Hawaii, Samoa and Iceland exhibit negative μ182W and likely originated from the modified isotope region just above the core-mantle boundary, whereas those with positive μ182W could be derived from the thick Large Low Shear Velocity Provinces (LLSVPs) far from the core-mantle boundary (CMB). When highly-oxidized slabs accumulate at the CMB oxidizing the outer core at the interface, a large W flux with negative μ182W can be added to the silicate mantle. As a result, the source region of the OIB would be effectively modified to a negative μ182W
Shock-induced star cluster formation in colliding galaxies
We studied the formation process of star clusters using high-resolution
N-body/smoothed particle hydrodynamcs simulations of colliding galaxies. The
total number of particles is 1.2x10^8 for our high resolution run. The
gravitational softening is 5 pc and we allow gas to cool down to \sim 10 K.
During the first encounter of the collision, a giant filament consists of cold
and dense gas found between the progenitors by shock compression. A vigorous
starburst took place in the filament, resulting in the formation of star
clusters. The mass of these star clusters ranges from 10^{5-8} Msun. These star
clusters formed hierarchically: at first small star clusters formed, and then
they merged via gravity, resulting in larger star clusters.Comment: 4 pages, 3 figures, Proceedings of IAU Symposium 270, Computational
Star Formatio
Toward first-principle simulations of galaxy formation: I. How should we choose star formation criteria in high-resolution simulations of disk galaxies?
We performed 3-dimensional N-body/SPH simulations to study how mass
resolution and other model parameters such as the star formation efficiency
parameter, C* and the threshold density, nth affect structures of the galactic
gaseous/stellar disk in a static galactic potential. We employ 10^6 - 10^7
particles to resolve a cold and dense (T 100 cm^{-3}) phase. We
found that structures of the ISM and the distribution of young stars are
sensitive to the assumed nth. High-nth models with nth = 100 cm^{-3} yield
clumpy multi-phase features in the ISM. Young stars are distributed in a thin
disk of which half-mass scale height is 10 - 30 pc. In low-nth models with nth
= 0.1 cm^{-3}, the stellar disk is found to be several times thicker, and the
gas disk appears smoother than the high-nth models. A high-resolution
simulation with high-nth is necessary to reproduce the complex structure of the
gas disk. The global properties of the model galaxies in low-nth models, such
as star formation histories, are similar to those in the high-nth models when
we tune the value of C* so that they reproduce the observed relation between
surface gas density and surface star formation rate density. We however
emphasize that high-nth models automatically reproduce the relation, regardless
of the values of C*. The ISM structure, phase distribution, and distributions
of young star forming region are quite similar between two runs with values of
C* which differ by a factor of 15. We also found that the timescale of the flow
from n_H ~1 cm^{-3} to n_H > 100 cm^{-3} is about 5 times as long as the local
dynamical time and is independent of the value of C*. The use of a high-nth
criterion for star formation in high-resolution simulations makes numerical
models fairy insensitive to the modelling of star formation. (Abridged)Comment: 15 pages, 14 figures, accepted for publication in PASJ. Abridged
abstract. For high resolution figures, see
http://www.cfca.nao.ac.jp/~saitoh/Papers/2008/Saitoh+2008a.pd
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