29 research outputs found
NuSTAR Hard X-ray Survey of the Galactic Center Region I: Hard X-ray Morphology and Spectroscopy of the Diffuse Emission
We present the first sub-arcminute images of the Galactic Center above 10
keV, obtained with NuSTAR. NuSTAR resolves the hard X-ray source IGR
J17456-2901 into non-thermal X-ray filaments, molecular clouds, point sources
and a previously unknown central component of hard X-ray emission (CHXE).
NuSTAR detects four non-thermal X-ray filaments, extending the detection of
their power-law spectra with - up to ~50 keV. A
morphological and spectral study of the filaments suggests that their origin
may be heterogeneous, where previous studies suggested a common origin in young
pulsar wind nebulae (PWNe). NuSTAR detects non-thermal X-ray continuum emission
spatially correlated with the 6.4 keV Fe K fluorescence line emission
associated with two Sgr A molecular clouds: MC1 and the Bridge. Broad-band
X-ray spectral analysis with a Monte-Carlo based X-ray reflection model
self-consistently determined their intrinsic column density (
cm), primary X-ray spectra (power-laws with ) and set a
lower limit of the X-ray luminosity of Sgr A* flare illuminating the Sgr A
clouds to erg s. Above ~20 keV, hard
X-ray emission in the central 10 pc region around Sgr A* consists of the
candidate PWN G359.95-0.04 and the CHXE, possibly resulting from an unresolved
population of massive CVs with white dwarf masses . Spectral energy distribution analysis suggests that G359.95-0.04 is
likely the hard X-ray counterpart of the ultra-high gamma-ray source HESS
J1745-290, strongly favoring a leptonic origin of the GC TeV emission.Comment: 27 pages. Accepted for publication in the Astrophysical Journa
Mycobacterium tuberculosis Responds to Chloride and pH as Synergistic Cues to the Immune Status of its Host Cell
PubMed ID: 23592993This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited
Probing the charging mechanisms of carbon nanomaterial polyelectrolytes
Chemical charging of single-walled carbon nanotubes (SWCNTs) and graphenes to generate soluble salts shows great promise as a processing route for electronic applications, but raises fundamental questions. The reduction potentials of highly-charged nanocarbon polyelectrolyte ions were investigated by considering their chemical reactivity towards metal salts/complexes in forming metal nanoparticles. The redox activity, degree of functionalisation and charge utilisation were quantified via the relative metal nanoparticle content, established using thermogravimetric analysis (TGA), inductively coupled plasma atomic emission spectroscopy (ICP-AES) and X-ray photoelectron spectroscopy (XPS). The fundamental relationship between the intrinsic nanocarbon electronic density of states and Coulombic effects during charging is highlighted as an important area for future research
Occludin Phosphorylation and Ubiquitination Regulate Tight Junction Trafficking and Vascular Endothelial Growth Factor-induced Permeability*
Vascular endothelial growth factor (VEGF) alters tight junctions (TJs) and promotes vascular permeability in many retinal and brain diseases. However, the molecular mechanisms of barrier regulation are poorly understood. Here we demonstrate that occludin phosphorylation and ubiquitination regulate VEGF-induced TJ protein trafficking and concomitant vascular permeability. VEGF treatment induced TJ fragmentation and occludin trafficking from the cell border to early and late endosomes, concomitant with increased occludin phosphorylation on Ser-490 and ubiquitination. Furthermore, both co-immunoprecipitation and immunocytochemistry demonstrated that VEGF treatment increased the interaction between occludin and modulators of intracellular trafficking that contain the ubiquitin interacting motif, including Epsin-1, epidermal growth factor receptor pathway substrate 15 (Eps15), and hepatocyte growth factor-regulated tyrosine kinase substrate (Hrs). Inhibiting occludin phosphorylation by mutating Ser-490 to Ala suppressed VEGF-induced ubiquitination, inhibited trafficking of TJ proteins, and prevented the increase in endothelial permeability. In addition, an occludin-ubiquitin chimera disrupted TJs and increased permeability without VEGF. These data demonstrate a novel mechanism of VEGF-induced occludin phosphorylation and ubiquitination that contributes to TJ trafficking and subsequent vascular permeability
The genetic basis and experimental evolution of inbreeding depression in Caenorhabditis elegans
Determining the genetic basis of inbreeding depression is important for understanding the role of selection in the evolution of mixed breeding systems. Here, we investigate how androdioecy (a breeding system characterized by partial selfing and outcrossing) and dioecy (characterized by obligatory outcrossing) influence the experimental evolution of inbreeding depression in Caenorhabditis elegans. We derived inbred lines from ancestral and evolved populations and found that the dioecious lineages underwent more extinction than androdioecious lineages. For both breeding systems, however, there was selection during inbreeding because the diversity patterns of 337 single-nucleotide polymorphisms (SNPs) among surviving inbred lines deviated from neutral expectations. In parallel, we also followed the evolution of embryo to adult viability, which revealed similar starting levels of inbreeding depression in both breeding systems, but also outbreeding depression. Under androdioecy, diversity at a neutral subset of 134 SNPs correlated well with the viability trajectories, showing that the population genetic structure imposed by partial selfing affected the opportunity for different forms of selection. Our findings suggest that the interplay between the disruptions of coevolved sets of loci by outcrossing, the efficient purging of deleterious recessive alleles with selfing and overdominant selection with outcrossing can help explain mixed breeding systems