26 research outputs found
Structure of the Radio Source 3C 120 at 8.4 GHz from VLBA+ Observations in 2002
Maps of the radio source 3C 120 obtained from VLBA+ observations at 8.4 GHz
at five epochs in January - September 2002 are presented. The images were
reconstructed using the maximum entropy method and the Pulkovo VLBImager
software package for VLBI mapping. Apparent superluminal motions of the
brightest jet knots have been estimated. The speeds of jet knots decreases with
distance from the core, changing from 5.40+-0.48c $ to 2.00+-0.48c over 10 mas
(where c is the speed of light) for a Hubble constant of 65 km/s/Mpc. This can
be explained by interaction of the jet with the medium through which it
propagates.Comment: 9 pages, 6 figures, 5 table
Reconstructing Images from Projections Using the Maximum-Entropy Method. Numerical Simulations of Low-Aspect Astrotomography
The reconstruction of images from a small number of projections using the
maximum-entropy method (MEM) with the Shannon entropy is considered. MEM
provides higher-quality image reconstruction for sources with extended
components than the Hogbom CLEAN method, which is also used in low-aspect
astrotomography. The quality of image reconstruction for sources with mixed
structure containing bright, compact features embedded in a comparatively weak,
extended base can be further improved using a difference-mapping method, which
requires a generalization of MEM for the reconstruction of sign-variable
functions.We draw conclusions based on the results of numerical simulations for
a number of model radio sources with various morphologies.Comment: 11 pages, 9 figure
A Solution to the Problem of Phaseless Mapping for a High-Orbit Space-Ground Radio Interferometer
We consider the problem of mapping with ultra-high angular resolution using a
space-ground radio interferometer with a space antenna in a high orbit,whose
apogee height exceeds the radius of the Earth by a factor of ten. In this case,
a multielement interferometer essentially degenerates into a two-element
interferometer. The degeneracy of the close-phase relations prevents the use of
standard methods for hybrid mapping and self-calibration for the correct
reconstruction of images. We propose a new phaseless mapping method based on
methods for the reconstruction of images in the complete absence of phase
information, using only the amplitudes of the spatial-coherence function of the
source. In connection with this problem, we propose a new method for the
reliable solution of the phase problem, based on optimizing
information-carrying nonlinear functionals, in particular, the Shannon entropy.
Results of simulations of mapping radio sources with various structures with
ultra-high angular resolution in the framework of the RADIOASTRON mission are
presented.Comment: 15 pages, 7 figure
A differential method of search for the CMBR spectral-spatial fluctuations
The CMBR spectral-spatial fluctuations (SSF) formed in early Universe during
the Dark Ages are considered. Main attention is focused on the narrow-band
spectral properties of the SSF. Based on these properties we propose to use a
differential method in order to search for these fluctuations. Description of
the method is given.Comment: Latex, 9 pages with 4 Postscript figure
Multifrequency VLBA study of the blazar S5 0716+714 during the active state in 2004 II. Large-scale jet kinematics and the comparison of the different methods of VLBI data imaging as applied to kinematic studies of AGN
We study the jet kinematics of the blazar S5 0716+714 during its active state
in 2003-2004 with multi-epoch VLBI observations. Aims. We present a kinematic
analysis of the large-scale (0-12 mas) jet of 0716+714, based on the results of
six epochs of VLBA monitoring at 5 GHz. Additionally, we compare kinematic
results obtained with two imaging methods based on different deconvolution
algorithms. The blazar 0716+714 has a diffuse large-scale jet and a very faint
bright compact core. Experiments with simulated data showed that the
conventional data reduction procedure based on the CLEAN deconvolution
algorithm does not perform well in restoring this type of structure. This might
be the reason why previous kinematic studies of this source yielded ambiguous
results. In order to obtain accurate kinematics of this source, we
independently applied two imaging techniques to the raw data: the conventional
method, based on difference mapping, which uses CLEAN deconvolution, and the
generalized maximum entropy method (GMEM) realized in the VLBImager package
developed at the Pulkovo Observatory in Russia. The results of both methods
give us a consistent kinematic scenario: the large-scale jet of 0716+714 is
diffuse and stationary. Differences between the inner (0-1 mas) and outer (1-12
mas) regions of the jet in brightness and velocity of the components could be
explained by the bending of the jet, which causes the angle between the jet
direction and the line of sight to change from ~5 deg to ~11 deg. For the
source 0716+714 both methods worked at the limit of their capability.Comment: 13 pages, 7 figures. Accepted for publication in A&A, 201
The atmospheric role in the Arctic water cycle: A review on processes, past and future changes, and their impacts
This is the final version of the article. Available from the publisher via the DOI in this record.Atmospheric humidity, clouds, precipitation, and evapotranspiration are essential components of the Arctic climate system. During recent decades, specific humidity and precipitation have generally increased in the Arctic, but changes in evapotranspiration are poorly known. Trends in clouds vary depending on the region and season. Climate model experiments suggest that increases in precipitation are related to global warming. In turn, feedbacks associated with the increase in atmospheric moisture and decrease in sea ice and snow cover have contributed to the Arctic amplification of global warming. Climate models have captured the overall wetting trend but have limited success in reproducing regional details. For the rest of the 21st century, climate models project strong warming and increasing precipitation, but different models yield different results for changes in cloud cover. The model differences are largest in months of minimum sea ice cover. Evapotranspiration is projected to increase in winter but in summer to decrease over the oceans and increase over land. Increasing net precipitation increases river discharge to the Arctic Ocean. Over sea ice in summer, projected increase in rain and decrease in snowfall decrease the surface albedo and, hence, further amplify snow/ice surface melt. With reducing sea ice, wind forcing on the Arctic Ocean increases with impacts on ocean currents and freshwater transport out of the Arctic. Improvements in observations, process understanding, and modeling capabilities are needed to better quantify the atmospheric role in the Arctic water cycle and its changes.We thank all colleagues involved in the
Arctic Freshwater Synthesis (AFS) for
fruitful discussions. In particular, John
Walsh is acknowledged for his constructive
comments on the manuscript. AFS
has been sponsored by the World
Climate Research Programme’s Climate
and the Cryosphere project (WCRP-CliC),
the International Arctic Science
Committee (IASC), and the Arctic
Monitoring and Assessment Programme
(AMAP). The work for this paper has been
supported by the Academy of Finland
(contracts 259537 and 283101), the UK
Natural Environment Research Council
(grant NE/J019585/1), the US National
Science Foundation grant ARC-1023592
and the Program “Arctic” and the Basic
Research Program of the Presidium
Russian Academy of Sciences. NCAR is
supported by the U.S. National Science
Foundation. We gratefully acknowledge
the project coordination and meeting
support of Jenny Baeseman and
Gwenaelle Hamon at the CliC
International Project Office. No new data
were applied in the manuscript. Data
applied for Figures 2 and 3 are available
from the JRA-55 archive at http://jra.
kishou.go.jp/JRA-55/index_en.
html#usage
Genetic diversity of Escherichia coli in gut microbiota of patients with Crohn's disease discovered using metagenomic and genomic analyses
© 2018 The Author(s). Background: Crohn's disease is associated with gut dysbiosis. Independent studies have shown an increase in the abundance of certain bacterial species, particularly Escherichia coli with the adherent-invasive pathotype, in the gut. The role of these species in this disease needs to be elucidated. Methods: We performed a metagenomic study investigating the gut microbiota of patients with Crohn's disease. A metagenomic reconstruction of the consensus genome content of the species was used to assess the genetic variability. Results: The abnormal shifts in the microbial community structures in Crohn's disease were heterogeneous among the patients. The metagenomic data suggested the existence of multiple E. coli strains within individual patients. We discovered that the genetic diversity of the species was high and that only a few samples manifested similarity to the adherent-invasive varieties. The other species demonstrated genetic diversity comparable to that observed in the healthy subjects. Our results were supported by a comparison of the sequenced genomes of isolates from the same microbiota samples and a meta-analysis of published gut metagenomes. Conclusions: The genomic diversity of Crohn's disease-associated E. coli within and among the patients paves the way towards an understanding of the microbial mechanisms underlying the onset and progression of the Crohn's disease and the development of new strategies for the prevention and treatment of this disease
Genome analysis of E. coli isolated from Crohn's disease patients
© 2017 The Author(s). Background: Escherichia coli (E. coli) has been increasingly implicated in the pathogenesis of Crohn's disease (CD). The phylogeny of E. coli isolated from Crohn's disease patients (CDEC) was controversial, and while genotyping results suggested heterogeneity, the sequenced strains of E. coli from CD patients were closely related. Results: We performed the shotgun genome sequencing of 28 E. coli isolates from ten CD patients and compared genomes from these isolates with already published genomes of CD strains and other pathogenic and non-pathogenic strains. CDEC was shown to belong to A, B1, B2 and D phylogenetic groups. The plasmid and several operons from the reference CD-associated E. coli strain LF82 were demonstrated to be more often present in CDEC genomes belonging to different phylogenetic groups than in genomes of commensal strains. The operons include carbon-source induced invasion GimA island, prophage I, iron uptake operons I and II, capsular assembly pathogenetic island IV and propanediol and galactitol utilization operons. Conclusions: Our findings suggest that CDEC are phylogenetically diverse. However, some strains isolated from independent sources possess highly similar chromosome or plasmids. Though no CD-specific genes or functional domains were present in all CD-associated strains, some genes and operons are more often found in the genomes of CDEC than in commensal E. coli. They are principally linked to gut colonization and utilization of propanediol and other sugar alcohols
A922 Sequential measurement of 1 hour creatinine clearance (1-CRCL) in critically ill patients at risk of acute kidney injury (AKI)
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