184 research outputs found
Accretion Disk Spectra of the Ultra-luminous X-ray Sources in Nearby Spiral Galaxies and Galactic Superluminal Jet Sources
Ultra-luminous Compact X-ray Sources (ULXs) in nearby spiral galaxies and
Galactic superluminal jet sources share the common spectral characteristic that
they have unusually high disk temperatures which cannot be explained in the
framework of the standard optically thick accretion disk in the Schwarzschild
metric. On the other hand, the standard accretion disk around the Kerr black
hole might explain the observed high disk temperature, as the inner radius of
the Kerr disk gets smaller and the disk temperature can be consequently higher.
However, we point out that the observable Kerr disk spectra becomes
significantly harder than Schwarzschild disk spectra only when the disk is
highly inclined. This is because the emission from the innermost part of the
accretion disk is Doppler-boosted for an edge-on Kerr disk, while hardly seen
for a face-on disk. The Galactic superluminal jet sources are known to be
highly inclined systems, thus their energy spectra may be explained with the
standard Kerr disk with known black hole masses. For ULXs, on the other hand,
the standard Kerr disk model seems implausible, since it is highly unlikely
that their accretion disks are preferentially inclined, and, if edge-on Kerr
disk model is applied, the black hole mass becomes unreasonably large (> 300
M_solar). Instead, the slim disk (advection dominated optically thick disk)
model is likely to explain the observed super-Eddington luminosities, hard
energy spectra, and spectral variations of ULXs. We suggest that ULXs are
accreting black holes with a few tens of solar mass, which is not unexpected
from the standard stellar evolution scenario, and that their X-ray emission is
from the slim disk shining at super-Eddington luminosities.Comment: ApJ, accepte
Non-Gaussianity of the density distribution in accelerating universes
According to recent observations, the existence of the dark energy has been
considered. Even though we have obtained the constraint of the equation of the
state for dark energy () as by combining WMAP
data with other astronomical data, in order to pin down , it is necessary to
use other independent observational tools. For this purpose, we consider the
dependence of the non-Gaussianity of the density distribution generated by
nonlinear dynamics. To extract the non-Gaussianity, we follow a semi-analytic
approach based on Lagrangian linear perturbation theory, which provides an
accurate value for the quasi-nonlinear region. From our results, the difference
of the non-Gaussianity between and is about 4% while that
between and is about . For the highly non-linear
region, we estimate the difference by combining this perturbative approach with
N-body simulation executed for our previous paper. From this, we can expect the
difference to be more enhanced in the low- region, which suggests that the
non-Gaussianity of the density distribution potentially plays an important role
for extracting the information of dark energy.Comment: 15 pages, 4 figures, accepted for publication in JCAP; v2: smoothing
scale has been change
Transients from initial conditions based on Lagrangian perturbation theory in N-body simulations
We explore the initial conditions for cosmological N-body simulations
suitable for calculating the skewness and kurtosis of the density field. In
general, the initial conditions based on the perturbation theory (PT) provide
incorrect second-order and higher-order growth. These errors implied by the use
of the perturbation theory to set up the initial conditions in N-body
simulations are called transients. Unless these transients are completely
suppressed compared with the dominant growing mode, we can not reproduce the
correct evolution of cumulants with orders higher than two, even though there
is no problem with the numerical scheme. We investigate the impact of
transients on the observable statistical quantities by performing -body
simulations with initial conditions based on Lagrangian perturbation theory
(LPT). We show that the effects of transients on the kurtosis from the initial
conditions, based on second-order Lagrangian perturbation theory (2LPT) have
almost disappeared by , as long as the initial conditions are set at . This means that for practical purposes, the initial conditions based on
2LPT are accurate enough for numerical calculations of skewness and kurtosis.Comment: 21 pages, 5 figures; accepted for publication in JCA
Advances in small lasers
M.T.H was supported by an Australian Research council Future Fellowship research grant for this work. M.C.G. is grateful to the Scottish Funding Council (via SUPA) for financial support.Small lasers have dimensions or modes sizes close to or smaller than the wavelength of emitted light. In recent years there has been significant progress towards reducing the size and improving the characteristics of these devices. This work has been led primarily by the innovative use of new materials and cavity designs. This Review summarizes some of the latest developments, particularly in metallic and plasmonic lasers, improvements in small dielectric lasers, and the emerging area of small bio-compatible or bio-derived lasers. We examine the different approaches employed to reduce size and how they result in significant differences in the final device, particularly between metal- and dielectric-cavity lasers. We also present potential applications for the various forms of small lasers, and indicate where further developments are required.PostprintPeer reviewe
Non-Gaussianity of the density distribution in accelerating universes II:N-body simulations
We explore the possibility of putting constraints on dark energy models with
statistical property of large scale structure in the non-linear region. In
particular, we investigate the dependence of non-Gaussianity of the
smoothed density distribution generated by the nonlinear dynamics. In order to
follow the non-linear evolution of the density fluctuations, we apply N-body
simulations based on scheme. We show that the relative difference
between non-Gaussianity of model and that of model is (skewness) and (kurtosis) for Mpc. We also calculate the
correspondent quantities for Mpc, (skewness) and
(kurtosis), and the difference turn out to be greater, even though
non-linearity in this scale is so strong that the complex physical processes
about galaxy formation affect the galaxy distribution. From this, we can expect
that the difference can be tested by all sky galaxy surveys with the help of
mock catalogs created by selection functions, which suggests that
non-Gaussianity of the density distribution potentially plays an important role
for extracting information on dark energy.Comment: 21 pages, 14 figure
Myosin Light-Chain Kinase Is Necessary for Membrane Homeostasis in Cochlear Inner Hair Cells
The structural homeostasis of the cochlear hair cell membrane is critical for all aspects of sensory transduction, but the regulation of its maintenance is not well understood. In this report, we analyzed the cochlear hair cells of mice with specific deletion of myosin light chain kinase (MLCK) in inner hair cells. MLCK-deficient mice showed impaired hearing, with a 5- to 14-dB rise in the auditory brainstem response (ABR) thresholds to clicks and tones of different frequencies and a significant decrease in the amplitude of the ABR waves. The mutant inner hair cells produced several ball-like structures around the hair bundles in vivo, indicating impaired membrane stability. Inner hair cells isolated from the knockout mice consistently displayed less resistance to hypoosmotic solution and less membrane F-actin. Myosin light-chain phosphorylation was also reduced in the mutated inner hair cells. Our results suggest that MLCK is necessary for maintaining the membrane stability of inner hair cells
Global Expression Profiling in Atopic Eczema Reveals Reciprocal Expression of Inflammatory and Lipid Genes
Atopic eczema (AE) is a common chronic inflammatory skin disorder. In order to dissect the genetic background several linkage and genetic association studies have been performed. Yet very little is known about specific genes involved in this complex skin disease, and the underlying molecular mechanisms are not fully understood.We used human DNA microarrays to identify a molecular picture of the programmed responses of the human genome to AE. The transcriptional program was analyzed in skin biopsy samples from lesional and patch-tested skin from AE patients sensitized to Malassezia sympodialis (M. sympodialis), and corresponding biopsies from healthy individuals. The most notable feature of the global gene-expression pattern observed in AE skin was a reciprocal expression of induced inflammatory genes and repressed lipid metabolism genes. The overall transcriptional response in M. sympodialis patch-tested AE skin was similar to the gene-expression signature identified in lesional AE skin. In the constellation of genes differentially expressed in AE skin compared to healthy control skin, we have identified several potential susceptibility genes that may play a critical role in the pathological condition of AE. Many of these genes, including genes with a role in immune responses, lipid homeostasis, and epidermal differentiation, are localized on chromosomal regions previously linked to AE.Through genome-wide expression profiling, we were able to discover a distinct reciprocal expression pattern of induced inflammatory genes and repressed lipid metabolism genes in skin from AE patients. We found a significant enrichment of differentially expressed genes in AE with cytobands associated to the disease, and furthermore new chromosomal regions were found that could potentially guide future region-specific linkage mapping in AE. The full data set is available at http://microarray-pubs.stanford.edu/eczema
ILC3 function as a double-edged sword in inflammatory bowel diseases
Inflammatory bowel diseases (IBD), composed mainly of Crohn’s disease (CD) and ulcerative colitis (UC), are strongly implicated in the development of intestinal inflammation lesions. Its exact etiology and pathogenesis are still undetermined. Recently accumulating evidence supports that group 3 innate lymphoid cells (ILC3) are responsible for gastrointestinal mucosal homeostasis through moderate generation of IL-22, IL-17, and GM-CSF in the physiological state. ILC3 contribute to the progression and aggravation of IBD while both IL-22 and IL-17, along with IFN-γ, are overexpressed by the dysregulation of NCR− ILC3 or NCR+ ILC3 function and the bias of NCR+ ILC3 towards ILC1 as well as regulatory ILC dysfunction in the pathological state. Herein, we feature the group 3 innate lymphoid cells’ development, biological function, maintenance of gut homeostasis, mediation of IBD occurrence, and potential application to IBD therapy
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