539 research outputs found
Sagittarius dwarf spheroidal galaxy observed by H.E.S.S
Dwarf spheroidal galaxies are characterized by a large measured mass-to-light
ratio and are not expected to be the site of high-luminosity non-thermal
high-energy gamma-ray emissions. Therefore they are among the most promising
candidates for indirect searches of dark matter particle annihilation signals
in gamma rays. The Sagittarius dwarf spheroidal galaxy has been regularly
observed by the High Energy Stereoscopic System (H.E.S.S.) of Cherenkov
telescopes for more than 90 hours, searching for TeV gamma-ray emission from
annihilation of dark matter particles. In absence of a significant signal, new
constraints on the annihilation crosssection of the dark matter particles
applicable for Majorana Weakly Interacting Massive Particles (WIMPs) are
derived.Comment: In Proceedings of the 33rd International Cosmic Ray Conference
(ICRC2013), Rio de Janeiro (Brazil
A stacking method to study the gamma-ray emission of source samples based on the co-adding of Fermi LAT count maps
We present a stacking method that makes use of co-added maps of gamma-ray
counts produced from data taken with the Fermi Large Area Telescope. Sources
with low integrated gamma-ray fluxes that are not detected individually may
become detectable when their corresponding count maps are added. The combined
data set is analyzed with a maximum likelihood method taking into account the
contribution from point-like and diffuse background sources. For both simulated
and real data, detection significance and integrated gamma-ray flux are
investigated for different numbers of stacked sources using the public Fermi
Science Tools for analysis and data preparation. The co-adding is done such
that potential source signals add constructively, in contrast to the signals
from background sources, which allows the stacked data to be described with
simply structured models. We show, for different scenarios, that the stacking
method can be used to increase the cumulative significance of a sample of
sources and to characterize the corresponding gamma-ray emission. The method
can, for instance, help to search for gamma-ray emission from galaxy clusters.Comment: accepted for publication in Astronomy & Astrophysics, 10 pages, 12
figure
Cholesterol, a cell size-dependent signal that regulates glucose metabolism and gene expression in adipocytes.
Enlarged fat cells exhibit modified metabolic capacities, which could be involved in the metabolic complications of obesity at the whole body level. We show here that sterol regulatory element-binding protein 2 (SREBP-2) and its target genes are induced in the adipose tissue of several models of rodent obesity, suggesting cholesterol imbalance in enlarged adipocytes. Within a particular fat pad, larger adipocytes have reduced membrane cholesterol concentrations compared with smaller fat cells, demonstrating that altered cholesterol distribution is characteristic of adipocyte hypertrophy per se. We show that treatment with methyl-beta-cyclodextrin, which mimics the membrane cholesterol reduction of hypertrophied adipocytes, induces insulin resistance. We also produced cholesterol depletion by mevastatin treatment, which activates SREBP-2 and its target genes. The analysis of 40 adipocyte genes showed that the response to cholesterol depletion implicated genes involved in cholesterol traffic (caveolin 2, scavenger receptor BI, and ATP binding cassette 1 genes) but also adipocyte-derived secretion products (tumor necrosis factor alpha, angiotensinogen, and interleukin-6) and proteins involved in energy metabolism (fatty acid synthase, GLUT 4, and UCP3). These data demonstrate that altering cholesterol balance profoundly modifies adipocyte metabolism in a way resembling that seen in hypertrophied fat cells from obese rodents or humans. This is the first evidence that intracellular cholesterol might serve as a link between fat cell size and adipocyte metabolic activity
Efficacy and Safety of Ezetimibe Added to Atorvastatin Versus Atorvastatin Uptitration or Switching to Rosuvastatin in Patients With Primary Hypercholesterolemia
Hypercholesterolemic patients (n = 1,547) at high atherosclerotic cardiovascular disease risk with low-density lipoprotein cholesterol (LDL-C) levels 65100 and 64160 mg/dl while treated with atorvastatin 10 mg/day entered a multicenter, randomized, double-blind, active-controlled, clinical trial using two 6-week study periods. Period I compared the efficacy/safety of (1) adding ezetimibe 10 mg (ezetimibe) to stable atorvastatin 10 mg, (2) doubling atorvastatin to 20 mg, or (3) switching to rosuvastatin 10 mg. Subjects in the latter 2 groups who persisted with elevated LDL-C levels ( 65100 and 64160 mg/dl) after period I, entered period II; subjects on atorvastatin 20 mg had ezetimibe added to their atorvastatin 20 mg, or uptitrated their atorvastatin to 40 mg; subjects on rosuvastatin 10 mg switched to atorvastatin 20 mg plus ezetimibe or uptitrated their rosuvastatin to 20 mg. Some subjects on atorvastatin 10 mg plus ezetimibe continued the same treatment into period II. At the end of period I, ezetimibe plus atorvastatin 10 mg reduced LDL-C significantly more than atorvastatin 20 mg or rosuvastatin 10 mg (22.2% vs 9.5% or 13.0%, respectively, p <0.001). At the end of period II, ezetimibe plus atorvastatin 20 mg reduced LDL-C significantly more than atorvastatin 40 mg (17.4% vs 6.9%, p <0.001); switching from rosuvastatin 10 mg to ezetimibe plus atorvastatin 20 mg reduced LDL-C significantly more than uptitrating to rosuvastatin 20 mg (17.1% vs 7.5%, p <0.001). Relative to comparative treatments, ezetimibe added to atorvastatin 10 mg (period I) or atorvastatin 20 mg (period II) produced significantly greater percent attainment of LDL-C targets <100 or <70 mg/dl, and significantly greater percent reductions in total cholesterol, non-high-density lipoprotein cholesterol, most lipid and lipoprotein ratios, and apolipoprotein B (except ezetimibe plus atorvastatin 20 vs atorvastatin 40 mg). Reports of adverse experiences were generally similar among groups. In conclusion, treatment of hypercholesterolemic subjects at high cardiovascular risk with ezetimibe added to atorvastatin 10 or 20 mg produced significantly greater improvements in key lipid parameters and significantly greater attainment of LDL-C treatment targets than doubling atorvastatin or switching to (or doubling) rosuvastatin at the compared doses
Progress in Monte Carlo design and optimization of the Cherenkov Telescope Array
The Cherenkov Telescope Array (CTA) will be an instrument covering a wide
energy range in very-high-energy (VHE) gamma rays. CTA will include several
types of telescopes, in order to optimize the performance over the whole energy
range. Both large-scale Monte Carlo (MC) simulations of CTA super-sets
(including many different possible CTA layouts as sub-sets) and smaller-scale
simulations dedicated to individual aspects were carried out and are on-going.
We summarize results of the prior round of large-scale simulations, show where
the design has now evolved beyond the conservative assumptions of the prior
round and present first results from the on-going new round of MC simulations.Comment: 4 pages, 5 figures. In Proceedings of the 33rd International Cosmic
Ray Conference (ICRC2013), Rio de Janeiro (Brazil). All CTA contributions at
arXiv:1307.223
treatment effect of alirocumab according to age group smoking status and hypertension pooled analysis from 10 randomized odyssey studies
Background Age, smoking, hypercholesterolemia, and hypertension are major risk factors for atherosclerotic cardiovascular disease. Objective We examined whether the effects of alirocumab on low-density lipoprotein cholesterol (LDL-C) differed according to age, hypertension, or smoking status. Methods Data were pooled from 10 Phase 3 ODYSSEY randomized trials (24–104 weeks' duration) in 4983 people with heterozygous familial hypercholesterolemia (FH) or non–familial hypercholesterolemia (3188 on alirocumab, 1795 on control [620 on ezetimibe and 1175 on placebo]). Most participants received concomitant maximum tolerated statin therapy. In 8 trials, the alirocumab dose was increased from 75 mg every 2 weeks (Q2W) to 150 mg Q2W at Week 12 if predefined risk-based LDL-C goals were not achieved at Week 8 (≥70 mg/dL in very high cardiovascular risk; ≥100 mg/dL in moderate or high cardiovascular risk). Two trials compared alirocumab 150 mg Q2W vs placebo. The efficacy and safety of alirocumab were assessed post hoc in subgroups stratified by age ( Results Alirocumab reduced LDL-C by 23.7% (75/150 mg vs ezetimibe + statin) to 65.4% (150 mg vs placebo + statin) from baseline to Week 24 vs control. Subgroup analyses confirmed no significant interactions in response to alirocumab between age group, hypertension, or smoking status. Overall rates of treatment-emergent adverse events were similar between alirocumab and control groups. Conclusions In this pooled analysis from 10 trials, alirocumab led to substantial LDL-C reductions vs control in every age group and regardless of hypertension or smoking status. Alirocumab was well tolerated in all subgroups
H.E.S.S. observations of gamma-ray bursts in 2003-2007
Very-high-energy (VHE; >~100 GeV) gamma-rays are expected from gamma-ray
bursts (GRBs) in some scenarios. Exploring this photon energy regime is
necessary for understanding the energetics and properties of GRBs. GRBs have
been one of the prime targets for the H.E.S.S. experiment, which makes use of
four Imaging Atmospheric Cherenkov Telescopes (IACTs) to detect VHE gamma-rays.
Dedicated observations of 32 GRB positions were made in the years 2003-2007 and
a search for VHE gamma-ray counterparts of these GRBs was made. Depending on
the visibility and observing conditions, the observations mostly start minutes
to hours after the burst and typically last two hours. Results from
observations of 22 GRB positions are presented and evidence of a VHE signal was
found neither in observations of any individual GRBs, nor from stacking data
from subsets of GRBs with higher expected VHE flux according to a
model-independent ranking scheme. Upper limits for the VHE gamma-ray flux from
the GRB positions were derived. For those GRBs with measured redshifts,
differential upper limits at the energy threshold after correcting for
absorption due to extra-galactic background light are also presented.Comment: 9 pages, 4 tables, 3 figure
Discovery of VHE gamma-rays from the high-frequency-peaked BL Lac object RGB J0152+017
Aims: The BL Lac object RGB J0152+017 (z=0.080) was predicted to be a very
high-energy (VHE; > 100 GeV) gamma-ray source, due to its high X-ray and radio
fluxes. Our aim is to understand the radiative processes by investigating the
observed emission and its production mechanism using the High Energy
Stereoscopic System (H.E.S.S.) experiment. Methods: We report recent
observations of the BL Lac source RGB J0152+017 made in late October and
November 2007 with the H.E.S.S. array consisting of four imaging atmospheric
Cherenkov telescopes. Contemporaneous observations were made in X-rays by the
Swift and RXTE satellites, in the optical band with the ATOM telescope, and in
the radio band with the Nancay Radio Telescope. Results: A signal of 173
gamma-ray photons corresponding to a statistical significance of 6.6 sigma was
found in the data. The energy spectrum of the source can be described by a
powerlaw with a spectral index of 2.95+/-0.36stat+/-0.20syst. The integral flux
above 300 GeV corresponds to ~2% of the flux of the Crab nebula. The source
spectral energy distribution (SED) can be described using a two-component
non-thermal synchrotron self-Compton (SSC) leptonic model, except in the
optical band, which is dominated by a thermal host galaxy component. The
parameters that are found are very close to those found in similar SSC studies
in TeV blazars. Conclusions: RGB J0152+017 is discovered as a source of VHE
gamma-rays by H.E.S.S. The location of its synchrotron peak, as derived from
the SED in Swift data, allows clearly classification it as a
high-frequency-peaked BL Lac (HBL).Comment: Accepted for publication in A&A Letters (5 pages, 4 figures
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