980 research outputs found
Probing Rotation of Core-collapse Supernova with Concurrent Analysis of Gravitational Waves and Neutrinos
The next time a core-collapse supernova (SN) explodes in our galaxy, vari-
ous detectors will be ready and waiting to detect its emissions of
gravitational waves (GWs) and neutrinos. Current numerical simulations have
successfully introduced multi-dimensional effects to produce exploding SN
models, but thus far the explosion mechanism is not well understood. In this
paper, we focus on an investigation of progenitor core rotation via comparison
of the start time of GW emission and that of the neutronization burst. The GW
and neutrino de- tectors are assumed to be, respectively, the KAGRA detector
and a co-located gadolinium-loaded water Cherenkov detector, either EGADS or
GADZOOKS!. Our detection simulation studies show that for a nearby supernova
(0.2 kpc) we can confirm the lack of core rotation close to 100% of the time,
and the presence of core rotation about 90% of the time. Using this approach
there is also po- tential to confirm rotation for considerably more distant
Milky Way supernova explosions.Comment: 31pages, 15figures, submit to Ap
Markov Chain Monte Carlo Method without Detailed Balance
We present a specific algorithm that generally satisfies the balance
condition without imposing the detailed balance in the Markov chain Monte
Carlo. In our algorithm, the average rejection rate is minimized, and even
reduced to zero in many relevant cases. The absence of the detailed balance
also introduces a net stochastic flow in a configuration space, which further
boosts up the convergence. We demonstrate that the autocorrelation time of the
Potts model becomes more than 6 times shorter than that by the conventional
Metropolis algorithm. Based on the same concept, a bounce-free worm algorithm
for generic quantum spin models is formulated as well.Comment: 5 pages, 5 figure
Space laser interferometers can determine the thermal history of the early Universe
It is shown that space-based gravitational wave detectors such as DECIGO
and/or Big Bang Observer (BBO) will provide us with invaluable information on
the cosmic thermal history after inflation and they will be able to determine
the reheat temperature provided that it lies in the range preferred by
the cosmological gravitino problem, GeV. Therefore it is
strongly desired that they will be put into practice as soon as possible.Comment: 5 page
Stochastic backgrounds of gravitational waves from extragalactic sources
Astrophysical sources emit gravitational waves in a large variety of
processes occurred since the beginning of star and galaxy formation. These
waves permeate our high redshift Universe, and form a background which is the
result of the superposition of different components, each associated to a
specific astrophysical process. Each component has different spectral
properties and features that it is important to investigate in view of a
possible, future detection. In this contribution, we will review recent
theoretical predictions for backgrounds produced by extragalactic sources and
discuss their detectability with current and future gravitational wave
observatories.Comment: 10 pages, 9 figures, proceedings of the GWDAW 10 Conference,
submitted to Class. & Quantum Gra
Shapes of Gas, Gravitational Potential and Dark Matter in Lambda-CDM Clusters
We present analysis of the three-dimensional shape of intracluster gas in
clusters formed in cosmological simulations of the Lambda-CDM cosmology and
compare it to the shape of dark matter distribution and the shape of the
overall isopotential surfaces. We find that in simulations with radiative
cooling, star formation and stellar feedback (CSF), intracluster gas outside
the cluster core is more spherical compared to non-radiative (NR) simulations,
while in the core the gas in the CSF runs is more triaxial and has a distinctly
oblate shape. The latter reflects the ongoing cooling of gas, which settles
into a thick oblate ellipsoid as it loses thermal energy. The shape of the gas
in the inner regions of clusters can therefore be a useful diagnostic of gas
cooling. We find that gas traces the shape of the underlying potential rather
well outside the core, as expected in hydrostatic equilibrium. At smaller
radii, however, the gas and potential shapes differ significantly. In the CSF
runs, the difference reflects the fact that gas is partly rotationally
supported. Interestingly, we find that in NR simulations the difference between
gas and potential shape at small radii is due to random gas motions, which make
the gas distribution more spherical than the equipotential surfaces. Finally,
we use mock Chandra X-ray maps to show that the differences in shapes observed
in three-dimensional distribution of gas are discernible in the ellipticity of
X-ray isophotes. Contrasting the ellipticities measured in simulated clusters
against observations can therefore constrain the amount of cooling of the
intracluster medium and the presence of random gas motions in cluster cores.Comment: 11 pages, 8 figures, 3 tables, updated to match the version accepted
for publication in the Astrophysical Journa
Constraining Cluster Physics with the Shape of X-ray Clusters: Comparison of Local X-ray Clusters versus LCDM Clusters
Simulations of cluster formation have demonstrated that condensation of
baryons into central galaxies during cluster formation can drive the shape of
the gas distribution in galaxy clusters significantly rounder, even at radii as
large as half of the virial radius. However, such simulations generally predict
stellar fractions within cluster virial radii that are ~2 to 3 times larger
than the stellar masses deduced from observations. In this work we compare
ellipticity profiles of clusters simulated with and without baryonic cooling to
the cluster ellipticity profiles derived from Chandra and ROSAT observations in
an effort to constrain the fraction of gas that cools and condenses into the
central galaxies within clusters. We find that the observed ellipticity
profiles are fairly constant with radius, with an average ellipticity of 0.18
+/- 0.05. The observed ellipticity profiles are in good agreement with the
predictions of non-radiative simulations. On the other hand, the ellipticity
profiles of the clusters in simulations that include radiative cooling, star
formation, and supernova feedback (but no AGN feedback) deviate significantly
from the observed ellipticity profiles at all radii. The simulations with
cooling overpredict (underpredict) ellipticity in the inner (outer) regions of
galaxy clusters. By comparing the simulations with and without cooling, we show
that the cooling of gas via cooling flows in the central regions of simulated
clusters causes the gas distribution to be more oblate in the central regions,
but makes the outer gas distribution more spherical. We find that late-time gas
cooling and star formation are responsible for the significantly oblate gas
distributions in cluster cores, but the gas shapes outside of cluster cores are
set primarily by baryon dissipation at high redshift z > 2.Comment: 10 pages, 6 figures, matching the published version in ApJ. Corrected
missing reference in the arxiv versio
Flat-Band Ferromagnetism in Organic Polymers Designed by a Computer Simulation
By coupling a first-principles, spin-density functional calculation with an
exact diagonalization study of the Hubbard model, we have searched over various
functional groups for the best case for the flat-band ferromagnetism proposed
by R. Arita et al. [Phys. Rev. Lett. {\bf 88}, 127202 (2002)] in organic
polymers of five-membered rings. The original proposal (poly-aminotriazole) has
turned out to be the best case among the materials examined, where the reason
why this is so is identified here. We have also found that the ferromagnetism,
originally proposed for the half-filled flat band, is stable even when the band
filling is varied away from the half-filling. All these make the ferromagnetism
proposed here more experimentally inviting.Comment: 11 pages, 13figure
Search extension transforms Wiki into a relational system: A case for flavonoid metabolite database
<p>Abstract</p> <p>Background</p> <p>In computer science, database systems are based on the relational model founded by Edgar Codd in 1970. On the other hand, in the area of biology the word 'database' often refers to loosely formatted, very large text files. Although such bio-databases may describe conflicts or ambiguities (e.g. a protein pair do and do not interact, or unknown parameters) in a positive sense, the flexibility of the data format sacrifices a systematic query mechanism equivalent to the widely used SQL.</p> <p>Results</p> <p>To overcome this disadvantage, we propose embeddable string-search commands on a Wiki-based system and designed a half-formatted database. As proof of principle, a database of flavonoid with 6902 molecular structures from over 1687 plant species was implemented on MediaWiki, the background system of Wikipedia. Registered users can describe any information in an arbitrary format. Structured part is subject to text-string searches to realize relational operations. The system was written in PHP language as the extension of MediaWiki. All modifications are open-source and publicly available.</p> <p>Conclusion</p> <p>This scheme benefits from both the free-formatted Wiki style and the concise and structured relational-database style. MediaWiki supports multi-user environments for document management, and the cost for database maintenance is alleviated.</p
Gate-induced band ferromagnetism in an organic polymer
We propose that a chain of five-membered rings (polyaminotriazole) should be
ferromagnetic with an appropriate doping that is envisaged to be feasible with
an FET structure. The ferromagnetism is confirmed by a spin density functional
calculation, which also shows that ferromagnetism survives the Peierls
instability. We explain the magnetism in terms of Mielke and Tasaki's flat-band
ferromagnetism with the Hubbard model. This opens a new possibility of band
ferromagnetism in purely organic polymers.Comment: 4 pages, 7 figure
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