206 research outputs found
Fermi gamma-ray `bubbles' from stochastic acceleration of electrons
Gamma-ray data from Fermi-LAT reveal a bi-lobular structure extending up to
50 degrees above and below the galactic centre, which presumably originated in
some form of energy release there less than a few million years ago. It has
been argued that the gamma-rays arise from hadronic interactions of high energy
cosmic rays which are advected out by a strong wind, or from inverse-Compton
scattering of relativistic electrons accelerated at plasma shocks present in
the bubbles. We explore the alternative possibility that the relativistic
electrons are undergoing stochastic 2nd-order Fermi acceleration by plasma wave
turbulence through the entire volume of the bubbles. The observed gamma-ray
spectral shape is then explained naturally by the resulting hard electron
spectrum and inverse Compton losses. Rather than a constant volume emissivity
as in other models, we predict a nearly constant surface brightness, and
reproduce the observed sharp edges of the bubbles.Comment: 4 pages, 4 figures; REVTeX4-1; discussion amended and one figure
added; to appear in PR
Systematic effects in the extraction of the 'WMAP haze'
The extraction of a 'haze' from the WMAP microwave skymaps is based on
subtraction of known foregrounds, viz. free-free (bremsstrahlung), thermal dust
and synchrotron, each traced by other skymaps. While the 408 MHz all-sky survey
is used for the synchrotron template, the WMAP bands are at tens of GHz where
the spatial distribution of the radiating cosmic ray electrons ought to be
quite different because of the energy-dependence of their diffusion in the
Galaxy. The systematic uncertainty this introduces in the residual skymap is
comparable to the claimed haze and can, for certain source distributions, have
a very similar spectrum and latitudinal profile and even a somewhat similar
morphology. Hence caution must be exercised in interpreting the 'haze' as a
physical signature of, e.g., dark matter annihilation in the Galactic centre.Comment: 17 pages, 12 figures; improved diffusion model; extended discussion
of spectral index maps; clarifying comments, figures and references added; to
appear in JCA
Müller Cells Stabilize Microvasculature through Hypoxic Preconditioning
BACKGROUND/AIMS: Hypoxia of the retina is a common pathogenic drive leading to vision loss as a result of tissue ischemia, increased vascular permeability and ultimately retinal neovascularisation. Here we tested the hypothesis that Müller cells stabilize the neurovascular unit, microvasculature by suppression of HIF-1α activation as a result of hypoxic preconditioning. METHODS: Tube Formation Assay and In vitro Vascular Permeability Image Assay were used to analyze angiogenesis and vascular integrity. Seahorse XF Cell Mito Stress Test was used to measure mitochondrial respiration. Gene and protein expression were examined by qRTPCR, ELISA and western blot. RESULTS: Hypoxic insult induces a significant induction of proangiogenic factors including vascular endothelial growth factor (VEGF) and angiopoietinlike 4 (ANGPTL-4) resulting in angiogenesis and increased vascular permeability of vascular endothelial cells. Hypoxic preconditioning of a human retinal Müller glia cell line significantly attenuates HIF-1α activation through the inhibition of mTOR and concomitant induction of aerobic glycolysis, stabilizing endothelial cells.
CONCLUSION: Hypoxic preconditioning of Müller cells confers a robust protection to endothelial cells, through the suppression of HIF1α activation and its downstream regulation of VEGF and ANGPTL-4
Sommerfeld Enhancement from Multiple Mediators
We study the Sommerfeld enhancement experienced by a scattering object that
couples to a tower of mediators. This can occur in, e.g., models of secluded
dark matter when the mediator scale is generated naturally by hidden-sector
confinement. Specializing to the case of a confining CFT, we show that
off-resonant values of the enhancement can be increased by ~ 20% for cases of
interest when (i) the (strongly-coupled) CFT admits a weakly-coupled dual
description and (ii) the conformal symmetry holds up to the Planck scale.
Larger enhancements are possible for lower UV scales due to an increase in the
coupling strength of the tower.Comment: 17p, 2 figures; v2 JHEP version (inconsequential typo fixed,
references added
Absolute electron and positron fluxes from PAMELA/Fermi and Dark Matter
We extract the positron and electron fluxes in the energy range 10 - 100 GeV
by combining the recent data from PAMELA and Fermi LAT. The {\it absolute
positron and electron} fluxes thus obtained are found to obey the power laws:
and respectively, which can be confirmed by the
upcoming data from PAMELA. The positron flux appears to indicate an excess at
energies E\gsim 50 GeV even if the uncertainty in the secondary positron flux
is added to the Galactic positron background. This leaves enough motivation for
considering new physics, such as annihilation or decay of dark matter, as the
origin of positron excess in the cosmic rays.Comment: Accepted by JCA
Secluded Dark Matter Coupled to a Hidden CFT
Models of secluded dark matter offer a variant on the standard WIMP picture
and can modify our expectations for hidden sector phenomenology and detection.
In this work we extend a minimal model of secluded dark matter, comprised of a
U(1)'-charged dark matter candidate, to include a confining hidden-sector CFT.
This provides a technically natural explanation for the hierarchically small
mediator-scale, with hidden-sector confinement generating m_{gamma'}>0.
Furthermore, the thermal history of the universe can differ markedly from the
WIMP picture due to (i) new annihilation channels, (ii) a (potentially) large
number of hidden-sector degrees of freedom, and (iii) a hidden-sector phase
transition at temperatures T << M_{dm} after freeze out. The mediator allows
both the dark matter and the Standard Model to communicate with the CFT, thus
modifying the low-energy phenomenology and cosmic-ray signals from the secluded
sector.Comment: ~50p, 8 figs; v2 JHEP versio
Planck Intermediate Results. IX. Detection of the Galactic haze with Planck
Using precise full-sky observations from Planck, and applying several methods
of component separation, we identify and characterize the emission from the
Galactic "haze" at microwave wavelengths. The haze is a distinct component of
diffuse Galactic emission, roughly centered on the Galactic centre, and extends
to |b| ~35 deg in Galactic latitude and |l| ~15 deg in longitude. By combining
the Planck data with observations from the WMAP we are able to determine the
spectrum of this emission to high accuracy, unhindered by the large systematic
biases present in previous analyses. The derived spectrum is consistent with
power-law emission with a spectral index of -2.55 +/- 0.05, thus excluding
free-free emission as the source and instead favouring hard-spectrum
synchrotron radiation from an electron population with a spectrum (number
density per energy) dN/dE ~ E^-2.1. At Galactic latitudes |b|<30 deg, the
microwave haze morphology is consistent with that of the Fermi gamma-ray "haze"
or "bubbles," indicating that we have a multi-wavelength view of a distinct
component of our Galaxy. Given both the very hard spectrum and the extended
nature of the emission, it is highly unlikely that the haze electrons result
from supernova shocks in the Galactic disk. Instead, a new mechanism for
cosmic-ray acceleration in the centre of our Galaxy is implied.Comment: 15 pages, 9 figures, submitted to Astronomy and Astrophysic
The Pierre Auger Observatory III: Other Astrophysical Observations
Astrophysical observations of ultra-high-energy cosmic rays with the Pierre
Auger ObservatoryComment: Contributions to the 32nd International Cosmic Ray Conference,
Beijing, China, August 201
Serial selection for invasiveness increases expression of miR-143/miR-145 in glioblastoma cell lines
<p>Abstract</p> <p>Background</p> <p>Glioblastoma multiforme (GBM) is the most common primary central nervous system malignancy and its unique invasiveness renders it difficult to treat. This invasive phenotype, like other cellular processes, may be controlled in part by microRNAs - a class of small non-coding RNAs that act by altering the expression of targeted messenger RNAs. In this report, we demonstrate a straightforward method for creating invasive subpopulations of glioblastoma cells (IM3 cells). To understand the correlation between the expression of miRNAs and the invasion, we fully profiled 1263 miRNAs on six different cell lines and two miRNAs, miR-143 and miR-145, were selected for validation of their biological properties contributing to invasion. Further, we investigated an ensemble effect of both miR-143 and miR-145 in promoting invasion.</p> <p>Methods</p> <p>By repeated serial invasion through Matrigel<sup>®</sup>-coated membranes, we isolated highly invasive subpopulations of glioma cell lines. Phenotypic characterization of these cells included <it>in vitro </it>assays for proliferation, attachment, and invasion. Micro-RNA expression was compared using miRCURY arrays (Exiqon). In situ hybridization allowed visualization of the regional expression of miR-143 and miR-145 in tumor samples, and antisense probes were used investigate <it>in vitro </it>phenotypic changes seen with knockdown in their expression.</p> <p>Results</p> <p>The phenotype we created in these selected cells proved stable over multiple passages, and their microRNA expression profiles were measurably different. We found that two specific microRNAs expressed from the same genetic locus, miR-143 and miR-145, were over-expressed in our invasive subpopulations. Further, we also found that combinatorial treatment of these cells with both antisense-miRNAs (antimiR-143 and -145) will abrogated their invasion without decreasing cell attachment or proliferation.</p> <p>Conclusions</p> <p>To best of our knowledge, these data demonstrate for the first time that miR-143 and miR-145 regulate the invasion of glioblastoma and that miR-143 and -145 could be potential therapeutic target for anti-invasion therapies of glioblastoma patients.</p
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