840 research outputs found
Constrain intergalactic medium from the SZ effect map
In this paper, we try to detect the SZ effect in the 2MASS DWT clusters and
less bound objects in order to constrain the warm-hot intergalactic medium
distribution on large scales by cross-correlation analysis. The results of both
observed WMAP and mock SZ effect map indicate that the hot gas distributes from
inside as well as outside of the high density regions of galaxy clusters, which
is consistent with the results of both observation and hydro simulation.
Therefore, the DWT measurement of the cross-correlation would be a powerful
tool to probe the missing of baryons in the Universe.Comment: 9 pages,2 figures. Accepted for publication in Mod. Phys. Lett.
Spatial Locality of Galaxy Correlation Function in Phase Space: Samples from the 2MASS Extended Source Catalog
We analyze the statistical properties and dynamical implications of galaxy
distributions in phase space for samples selected from the 2MASS Extended
Source Catalog. The galaxy distribution is decomposed into modes which describe the number density perturbations of galaxies in phase
space cell given by scale band to and spatial
range to . In the nonlinear regime,
is highly non-Gaussian. We find, however, that the
correlations between and are always
very weak if the spatial ranges (, ) and
(, ) don't overlap. This feature is due to
the fact that the spatial locality of the initial perturbations is memorized
during hierarchical clustering. The highly spatial locality of the 2MASS galaxy
correlations is a strong evidence for the initial perturbations of the cosmic
mass field being spatially localized, and therefore, consistent with a Gaussian
initial perturbations on scales as small as about 0.1 h Mpc. Moreover,
the 2MASS galaxy spatial locality indicates that the relationship between
density perturbations of galaxies and the underlying dark matter should be
localized in phase space. That is, for a structure consisting of perturbations
on scales from to , the nonlocal range in the relation
between galaxies and dark matter should {\it not} be larger than . The stochasticity and nonlocality of the bias
relation between galaxies and dark matter fields should be no more than the
allowed range given by the uncertainty relation .Comment: 27 pages, 9 figures, accepted by Ap
Log-Poisson Hierarchical Clustering of Cosmic Neutral Hydrogen and Ly-alpha Transmitted Flux of QSO Absorption Spectrum
we study, in this paper, the non-Gaussian features of the mass density field
of neutral hydrogen fluid and the Ly-alpha transmitted flux of QSO absorption
spectrum from the point-of-view of self-similar log-Poisson hierarchy. It has
been shown recently that, in the scale range from the onset of nonlinear
evolution to dissipation, the velocity and mass density fields of cosmic baryon
fluid are extremely well described by the She-Leveque's scaling formula, which
is due to the log-Poisson hierarchical cascade. Since the mass density ratio
between ionized hydrogen to total hydrogen is not uniform in space, the mass
density field of neutral hydrogen component is not given by a similar mapping
of total baryon fluid. Nevertheless, we show, with hydrodynamic simulation
samples of the concordance CDM universe, that the mass density field
of neutral hydrogen, is also well described by the log-Poisson hierarchy. We
then investigate the field of Ly transmitted flux of QSO absorption
spectrum. Due to redshift distortion, Ly transmitted flux fluctuations
are no longer to show all features of the log-Poisson hierarchy. However, some
non-Gaussian features predicted by the log-Poisson hierarchy are not affected
by the redshift distortion. We test these predictions with the high resolution
and high S/N data of quasars Ly absorption spectra. All results given
by real data, including -hierarchy, high order moments and scale-scale
correlation, are found to be well consistent with the log-Poisson hierarchy. We
compare the log-Poisson hierarchy with the popular log-normal model of the
Ly transmitted flux. The later is found to yield too strong
non-Gaussianity at high orders, while the log-Poisson hierarchy is in agreement
with observed data.Comment: 24 pages, 9 figures, accepted by Ap
The LAMOST Survey of Background Quasars in the Vicinity of the Andromeda and Triangulum Galaxies -- II. Results from the Commissioning Observations and the Pilot Surveys
We present new quasars discovered in the vicinity of the Andromeda and
Triangulum galaxies with the LAMOST during the 2010 and 2011 observational
seasons. Quasar candidates are selected based on the available SDSS, KPNO 4 m
telescope, XSTPS optical, and WISE near infrared photometric data. We present
509 new quasars discovered in a stripe of ~135 sq. deg from M31 to M33 along
the Giant Stellar Stream in the 2011 pilot survey datasets, and also 17 new
quasars discovered in an area of ~100 sq. deg that covers the central region
and the southeastern halo of M31 in the 2010 commissioning datasets. These 526
new quasars have i magnitudes ranging from 15.5 to 20.0, redshifts from 0.1 to
3.2. They represent a significant increase of the number of identified quasars
in the vicinity of M31 and M33. There are now 26, 62 and 139 known quasars in
this region of the sky with i magnitudes brighter than 17.0, 17.5 and 18.0
respectively, of which 5, 20 and 75 are newly-discovered. These bright quasars
provide an invaluable collection with which to probe the kinematics and
chemistry of the ISM/IGM in the Local Group of galaxies. A total of 93 quasars
are now known with locations within 2.5 deg of M31, of which 73 are newly
discovered. Tens of quasars are now known to be located behind the Giant
Stellar Stream, and hundreds behind the extended halo and its associated
substructures of M31. The much enlarged sample of known quasars in the vicinity
of M31 and M33 can potentially be utilized to construct a perfect astrometric
reference frame to measure the minute PMs of M31 and M33, along with the PMs of
substructures associated with the Local Group of galaxies. Those PMs are some
of the most fundamental properties of the Local Group.Comment: 26 pages, 6 figures, AJ accepte
FACT, the Bur Kinase Pathway, and the Histone Co-Repressor HirC Have Overlapping Nucleosome-Related Roles in Yeast Transcription Elongation
Gene transcription is constrained by the nucleosomal nature of chromosomal DNA. This nucleosomal barrier is modulated by FACT, a conserved histone-binding heterodimer. FACT mediates transcription-linked nucleosome disassembly and also nucleosome reassembly in the wake of the RNA polymerase II transcription complex, and in this way maintains the repression of ‘cryptic’ promoters found within some genes. Here we focus on a novel mutant version of the yeast FACT subunit Spt16 that supplies essential Spt16 activities but impairs transcription-linked nucleosome reassembly in dominant fashion. This Spt16 mutant protein also has genetic effects that are recessive, which we used to show that certain Spt16 activities collaborate with histone acetylation and the activities of a Bur-kinase/Spt4–Spt5/Paf1C pathway that facilitate transcription elongation. These collaborating activities were opposed by the actions of Rpd3S, a histone deacetylase that restores a repressive chromatin environment in a transcription-linked manner. Spt16 activity paralleling that of HirC, a co-repressor of histone gene expression, was also found to be opposed by Rpd3S. Our findings suggest that Spt16, the Bur/Spt4–Spt5/Paf1C pathway, and normal histone abundance and/or stoichiometry, in mutually cooperative fashion, facilitate nucleosome disassembly during transcription elongation. The recessive nature of these effects of the mutant Spt16 protein on transcription-linked nucleosome disassembly, contrasted to its dominant negative effect on transcription-linked nucleosome reassembly, indicate that mutant FACT harbouring the mutant Spt16 protein competes poorly with normal FACT at the stage of transcription-linked nucleosome disassembly, but effectively with normal FACT for transcription-linked nucleosome reassembly. This functional difference is consistent with the idea that FACT association with the transcription elongation complex depends on nucleosome disassembly, and that the same FACT molecule that associates with an elongation complex through nucleosome disassembly is retained for reassembly of the same nucleosome
Understanding Novel Superconductors with Ab Initio Calculations
This chapter gives an overview of the progress in the field of computational
superconductivity.
Following the MgB2 discovery (2001), there has been an impressive
acceleration in the development of methods based on Density Functional Theory
to compute the critical temperature and other physical properties of actual
superconductors from first-principles. State-of-the-art ab-initio methods have
reached predictive accuracy for conventional (phonon-mediated) superconductors,
and substantial progress is being made also for unconventional superconductors.
The aim of this chapter is to give an overview of the existing computational
methods for superconductivity, and present selected examples of material
discoveries that exemplify the main advancements.Comment: 38 pages, 10 figures, Contribution to Springer Handbook of Materials
Modellin
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