2,487 research outputs found
On probing the properties of QSOs through their proximity effects on the intergalactic medium
The proximity effect (PE) of QSOs is believed to be useful in constraining
the QSO lifetime. Observations on the PE so far, however, give apparently
contradictory results -- some are consistent with a long QSO lifetime (>~ a few
10^7 yr), but others appear to be only consistent with a short QSO lifetime <~
10^6 yr. In this paper, we show that this apparent contradiction may be solved
by simultaneously taking into account both the effect due to the density
enhancement in the QSO near zones and that due to the obscuration of the tori
associated with the QSOs, using a large number of Monte-Carlo generated
synthetic Lyman alpha forest spectra. We demonstrate that the QSO properties
and environment can be constrained simultaneously by the transverse PE and the
line of sight PE of bright type 1 QSOs together. The current available
measurements on the PEs of type 1 QSOs suggest that (1) the density is
significantly enhanced in the vicinity of the QSOs; (2) the QSO lifetime is
consistent with being as large as a few 10^7 yr and a substantially shorter
lifetime (e.g., <~10^6 yr) is not required; and (3) the half opening angle of
the tori associated with QSOs is ~60 deg, consistent with some other
independent estimates. Our simulations also show that the TPE of type 2 QSOs
can be significantly different from that of type 1 QSOs, which may be useful to
put further constraints on the QSO properties and the QSO environment.Comment: 14 pages, 11 figures, to appear in Ap
A Case of Dominant Dystrophic Epidermolysis Bullosa with a G2043R Mutation in the Type VII Collagen Gene
Dystrophic epidermolysis bullosa (DEB) is a subepidermal
bulla, characterized by severe itching, lichenoid
or nodular prurigo-like lesions, skin erosion,
scars, milia, and nail dystrophy, resulting from COL7A1
mutation. Herein, we report a case of dominant DEB
with a G2043R mutation in COL7A1
Increasing the Fisher Information Content in the Matter Power Spectrum by Non-linear Wavelet Weiner Filtering
We develop a purely mathematical tool to recover some of the information lost
in the non-linear collapse of large-scale structure. From a set of 141
simulations of dark matter density fields, we construct a non-linear Weiner
filter in order to separate Gaussian and non-Gaussian structure in wavelet
space. We find that the non-Gaussian power is dominant at smaller scales, as
expected from the theory of structure formation, while the Gaussian counterpart
is damped by an order of magnitude on small scales. We find that it is possible
to increase the Fisher information by a factor of three before reaching the
translinear plateau, an effect comparable to other techniques like the linear
reconstruction of the density field.Comment: 7 pages, 6 figures. Accepted for publication in The Astrophysical
Journa
Constraining Quasar and IGM Properties Through Bubble Detection in Redshifted 21-cm Maps
The infrared detection of a z>7 quasar has opened up a new window to directly
probe the IGM during the epoch of reionization. In this paper we theoretically
consider the possibility of detecting the ionized bubble around a z=8 quasar
using targeted redshifted 21-cm observations with the GMRT. The apparent shape
and size of the ionized bubble, as seen by a distant observer, depends on the
parameters \dot{N}_{phs}/C, x_HI/C and \tau_Q where \dot{N}_{phs}, \tau_Q, x_HI
and C are respectively the photon emission rate, age of the quasar, the neutral
fraction and clumping factor of the IGM.Here we have analytically estimated the
shape and size of a quasar's ionized bubble assuming an uniform IGM and
ignoring other ionizing sources besides the quasar, and used this as a template
for matched filter bubble search with the GMRT visibility data. We have assumed
that \dot{N}_{phs} is known from the infrared spectrum and C from theoretical
considerations, which gives us two free parameters x_HI and \tau_Q for bubble.
Considering 1,000 hr of observation, we find that there is a reasonably large
region of parameter space where a 3\sigma detection is possible. We also find
that it will be possible to place lower limits on x_HI and \tau_Q with this
observation. Deeper follow up observations can place upper limits on \tau_Q and
x_HI. Value of C affect the estimation of x_HI but the estimation of \tau_Q
remains unaffected.We have used a semi-numerical technique to simulate the
apparent shape and size of quasar ionized bubbles considering the presence of
other ionizing sources and inhomogeneities in the IGM. The presence of other
sources increase the size of the quasar bubble, leading to underestimation of
x_HI. Clustering of other ionizing sources around the quasar can produce severe
distortions in bubble's shape. However, this does not severely affect parameter
estimation in the bubbles that are large.Comment: 18 pages, 16 figures, 3 tables. Minor change in text. Accepted for
publication in MNRA
Oxygen environment and islet size are the primary limiting factors of isolated pancreatic islet survival
Background: Type 1 diabetes is an autoimmune disease that destroys insulin-producing beta cells in the pancreas. Pancreatic islet transplantation could be an effective treatment option for type 1 diabetes once several issues are resolved, including donor shortage, prevention of islet necrosis and loss in pre- and post-transplantation, and optimization of immunosuppression. This study seeks to determine the cause of necrotic loss of isolated islets to improve transplant efficiency.
Methodology: The oxygen tension inside isolated human islets of different sizes was simulated under varying oxygen environments using a computational in silico model. In vitro human islet viability was also assessed after culturing in different oxygen conditions. Correlation between simulation data and experimentally measured islet viability was examined. Using these in vitro viability data of human islets, the effect of islet diameter and oxygen tension of the culture environment on islet viability was also analyzed using a logistic regression model.
Principal findings: Computational simulation clearly revealed the oxygen gradient inside the islet structure. We found that oxygen tension in the islet core was greatly lower (hypoxic) than that on the islet surface due to the oxygen consumption by the cells. The hypoxic core was expanded in the larger islets or in lower oxygen cultures. These findings were consistent with results from in vitro islet viability assays that measured central necrosis in the islet core, indicating that hypoxia is one of the major causes of central necrosis. The logistic regression analysis revealed a negative effect of large islet and low oxygen culture on islet survival.
Conclusions/Significance: Hypoxic core conditions, induced by the oxygen gradient inside islets, contribute to the development of central necrosis of human isolated islets. Supplying sufficient oxygen during culture could be an effective and reasonable method to maintain isolated islets viable
Testing nonstandard cosmological models with SNLS3 supernova data and other cosmological probes
We investigate the implications for some nonstandard cosmological models
using data from the first three years of the Supernova Legacy Survey (SNLS3),
assuming a spatially flat universe. A comparison between the constraints from
the SNLS3 and those from other SN Ia samples, such as the ESSENCE, Union2,
SDSS-II and Constitution samples, is given and the effects of different
light-curve fitters are considered. We find that SN Ia with SALT2 or SALT or
SIFTO can give consistent results and the tensions between different data sets
and different light-curve fitters are obvious for fewer-free-parameters models.
At the same time, we also study the constraints from the SNLS3 along with data
from the cosmic microwave background and the baryonic acoustic oscillations
(CMB/BAO), and the latest Hubble parameter versus redshift (H(z)). Using model
selection criteria such as /dof, GoF, AIC and BIC, we find that, among
all the cosmological models considered here (CDM, constant ,
varying , DGP, modified polytropic Cardassian, and the generalized Chaplygin
gas), the flat DGP is favored by the SNLS3 alone. However, when additional
CMB/BAO or H(z) constraints are included, this is no longer the case, and the
flat CDM becomes preferred.Comment: 24 pages, 12 figures and 4 tables, version to be published in Ap
Intestinal carriage of methicillin-resistant Staphylococcus aureus in nasal MRSA carriers hospitalized in the neonatal intensive care unit
BACKGROUND: The current data regarding the correlation between the methicillin-resistant Staphylococcus aureus (MRSA) clones carried in the nasal cavity and digestive tract are inadequate. METHODS: MRSA strains were isolated from both the feces and nasal swabs of 21 nasal-MRSA carriers ranging from 10 to 104Â days of age treated at the neonatal intensive care units of two hospitals. The molecular epidemiological characteristics of the isolates were determined: multilocus sequence types, spa-types, staphylococcal cassette chromosome mec (SCCmec) types, carriage of four exotoxin genes, and genes contained in commercially available kit. RESULTS: The feces of all nasal carriers contained MRSA at levels ranging from 4.0 Ă— 10(2) to 2.8 Ă— 10(8) colony forming units/g feces. The MRSA clones isolated from the feces and the nasal swabs of each patient were the same. Four MRSA clones, clonal complex (CC) 8-SCCmec IVl, CC8-SCCmec IVb, CC1-SCCmec IVa and CC5-SCCmec IIa were identified from 21 patients. All CC8-SCCmec IVl strains and one of three CC5-SCCmec IIa strains carried the toxic shock syndrome toxin gene. CONCLUSIONS: The feces of tested MRSA carriers contained the same MRSA clones as the nasal isolates in considerable amounts, suggesting that more careful attention should be paid for the handling of excrement in the case of newborn babies or infants than that of adults
Mechanisms of necroptosis in T cells
In caspase 8-deficient mouse T cells, necroptosis occurs via a Ripk3- and Ripk1-dependent pathway independent of autophagy and programmed necrosis
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