4,115 research outputs found
Nature Versus Nurture: Luminous Blue Variable Nebulae in and near Massive Stellar Clusters at the Galactic Center
Three Luminous Blue Variables (LBVs) are located in and near the Quintuplet
Cluster at the Galactic Center: the Pistol star, G0.120-0.048, and qF362. We
present imaging at 19, 25, 31, and 37 {\mu}m of the region containing these
three LBVs, obtained with SOFIA using FORCAST. We argue that the Pistol and
G0.120-0.048 are identical ``twins" that exhibit contrasting nebulae due to the
external influence of their different environments. Our images reveal the
asymmetric, compressed shell of hot dust surrounding the Pistol Star and
provide the first detection of the thermal emission from the symmetric, hot
dust envelope surrounding G0.120-0.048. Dust and gas composing the Pistol
nebula are primarily heated and ionized by the nearby Quintuplet Cluster stars.
The northern region of the Pistol nebula is decelerated due to the interaction
with the high-velocity (2000 km/s) winds from adjacent Wolf-Rayet Carbon (WC)
stars. With the DustEM code we determine that the Pistol nebula is composed of
a distribution of very small, transiently-heated grains (10-~35 {\AA}) and that
it exhibits a gradient of decreasing grain size from the south to the north due
to differential sputtering by the winds from the WC stars. Dust in the
G0.120-0.048 nebula is primarily heated by the central star; however, the
nebular gas is ionized externally by the Arches Cluster. Unlike the Pistol
nebula, the G0.120-0.048 nebula is freely expanding into the surrounding
medium. Given independent dust and gas mass estimates we find that the Pistol
and G0.120-0.048 nebulae exhibit similar gas-to-dust mass ratios of ~310 and
~290, respectively. Both nebulae share identical size scales (~ 0.7 pc) which
suggests that they have similar dynamical timescales of ~10^5 yrs, assuming a
shell expansion velocity of v_exp 60 km/s.Comment: 18 pages, 7 figures, accepted to Ap
Old supernova dust factory revealed at the Galactic center
Dust formation in supernova ejecta is currently the leading candidate to
explain the large quantities of dust observed in the distant, early Universe.
However, it is unclear whether the ejecta-formed dust can survive the hot
interior of the supernova remnant (SNR). We present infrared observations of
~0.02 of warm (~100 K) dust seen near the center of the ~10,000
yr-old Sgr A East SNR at the Galactic center. Our findings signify the
detection of dust within an older SNR that is expanding into a relatively dense
surrounding medium ( ~ 100 ) and has survived the
passage of the reverse shock. The results suggest that supernovae may indeed be
the dominant dust production mechanism in the dense environment of early
Universe galaxies.Comment: 25 pages, 5 figures. Includes supplementary materials. Published
Online March 19 2015 on Science Expres
Systematic study of the jet fragmentation function for inclusive jet-production in p+p collisions at sqrt{s}=200 GeV in STAR
Jet fragmentation functions measured in e^+e^- and p+\bar{p} experiments are
well-described on an inclusive hadron level by QCD-based calculations.
Fragmentation is expected to be modified by the presence of a strongly
interacting medium, but full theoretical description of this modification must
still be developed. It has recently been suggested that particle-identified
fragmentation functions may provide additional insight into the processes
underlying jet quenching. To assess the applicability of QCD-based
fragmentation calculations to RHIC data, and to provide a baseline with which
to compare fragmentation function measurements in heavy ion collisions, we
present the first measurements of charged hadron and particle-identified
fragmentation functions of jets reconstructed via a midpoint-cone algorithm
from p+p collisions at 200 GeV in STAR. We study the dependence on jet
cone-size and jet-energy, and compare the results to PYTHIA simulations based
on the Modified Leading Log Approximation (MLLA).Comment: 6 pages, 5 figures, proceedings of Hard Probes 2008 conferenc
Genome-Based Targeted Sequencing as a Reproducible Microbial Community Profiling Assay.
Current sequencing-based methods for profiling microbial communities rely on marker gene (e.g., 16S rRNA) or metagenome shotgun sequencing (mWGS) analysis. We present an approach based on a single-primer extension reaction using a highly multiplexed oligonucleotide probe pool. This approach, termed MA-GenTA (microbial abundances from genome tagged analysis), enables quantitative, straightforward, cost-effective microbiome profiling that combines desirable features of both 16S rRNA and mWGS strategies. The use of multiple probes per target genome and rigorous probe design criteria enabled robust determination of relative abundance. To test the utility of the MA-GenTA assay, probes were designed for 830 genome sequences representing bacteria present in mouse stool specimens. Comparison of the MA-GenTA data with mWGS data demonstrated excellent correlation down to 0.01% relative abundance and a similar number of organisms detected per sample. Despite the incompleteness of the reference database, nonmetric multidimensional scaling (NMDS) clustering based on the Bray-Curtis dissimilarity metric of sample groups was consistent between MA-GenTA, mWGS, and 16S rRNA data sets. MA-GenTA represents a potentially useful new method for microbiome community profiling based on reference genomes
Genome-Based Targeted Sequencing as a Reproducible Microbial Community Profiling Assay.
Current sequencing-based methods for profiling microbial communities rely on marker gene (e.g., 16S rRNA) or metagenome shotgun sequencing (mWGS) analysis. We present an approach based on a single-primer extension reaction using a highly multiplexed oligonucleotide probe pool. This approach, termed MA-GenTA (microbial abundances from genome tagged analysis), enables quantitative, straightforward, cost-effective microbiome profiling that combines desirable features of both 16S rRNA and mWGS strategies. The use of multiple probes per target genome and rigorous probe design criteria enabled robust determination of relative abundance. To test the utility of the MA-GenTA assay, probes were designed for 830 genome sequences representing bacteria present in mouse stool specimens. Comparison of the MA-GenTA data with mWGS data demonstrated excellent correlation down to 0.01% relative abundance and a similar number of organisms detected per sample. Despite the incompleteness of the reference database, nonmetric multidimensional scaling (NMDS) clustering based on the Bray-Curtis dissimilarity metric of sample groups was consistent between MA-GenTA, mWGS, and 16S rRNA data sets. MA-GenTA represents a potentially useful new method for microbiome community profiling based on reference genomes
A gene regulatory network armature for T lymphocyte specification
Choice of a T lymphoid fate by hematopoietic progenitor cells depends on sustained Notch–Delta signaling combined with tightly regulated activities of multiple transcription factors. To dissect the regulatory network connections that mediate this process, we have used high-resolution analysis of regulatory gene expression trajectories from the beginning to the end of specification, tests of the short-term Notch dependence of these gene expression changes, and analyses of the effects of overexpression of two essential transcription factors, namely PU.1 and GATA-3. Quantitative expression measurements of >50 transcription factor and marker genes have been used to derive the principal components of regulatory change through which T cell precursors progress from primitive multipotency to T lineage commitment. Our analyses reveal separate contributions of Notch signaling, GATA-3 activity, and down-regulation of PU.1. Using BioTapestry (www.BioTapestry.org), the results have been assembled into a draft gene regulatory network for the specification of T cell precursors and the choice of T as opposed to myeloid/dendritic or mast-cell fates. This network also accommodates effects of E proteins and mutual repression circuits of Gfi1 against Egr-2 and of TCF-1 against PU.1 as proposed elsewhere, but requires additional functions that remain unidentified. Distinctive features of this network structure include the intense dose dependence of GATA-3 effects, the gene-specific modulation of PU.1 activity based on Notch activity, the lack of direct opposition between PU.1 and GATA-3, and the need for a distinct, late-acting repressive function or functions to extinguish stem and progenitor-derived regulatory gene expression
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