536 research outputs found
The Optical System for the Large Size Telescope of the Cherenkov Telescope Array
The Large Size Telescope (LST) of the Cherenkov Telescope Array (CTA) is
designed to achieve a threshold energy of 20 GeV. The LST optics is composed of
one parabolic primary mirror 23 m in diameter and 28 m focal length. The
reflector dish is segmented in 198 hexagonal, 1.51 m flat to flat mirrors. The
total effective reflective area, taking into account the shadow of the
mechanical structure, is about 368 m. The mirrors have a sandwich structure
consisting of a glass sheet of 2.7 mm thickness, aluminum honeycomb of 60 mm
thickness, and another glass sheet on the rear, and have a total weight about
47 kg. The mirror surface is produced using a sputtering deposition technique
to apply a 5-layer coating, and the mirrors reach a reflectivity of 94%
at peak. The mirror facets are actively aligned during operations by an active
mirror control system, using actuators, CMOS cameras and a reference laser.
Each mirror facet carries a CMOS camera, which measures the position of the
light spot of the optical axis reference laser on the target of the telescope
camera. The two actuators and the universal joint of each mirror facet are
respectively fixed to three neighboring joints of the dish space frame, via
specially designed interface plate.Comment: In Proceedings of the 34th International Cosmic Ray Conference
(ICRC2015), The Hague, The Netherlands. All CTA contributions at
arXiv:1508.0589
Grain Size and Texture of Cu2ZnSnS4 Thin Films Synthesized by Cosputtering Binary Sulfides and Annealing: Effects of Processing Conditions and Sodium
We investigate the synthesis of kesterite Cu2ZnSnS4 (CZTS) polycrystalline
thin films using cosputtering from binary sulfide targets followed by annealing
in sulfur vapor at 500 {\deg}C to 650 {\deg}C. The films are the kesterite CZTS
phase as indicated by x-ray diffraction, Raman scattering, and optical
absorption measurements. The films exhibit (112) fiber texture and preferred
low-angle and Sigma3 grain boundary populations which have been demonstrated to
reduce recombination in Cu(In,Ga)Se2 and CdTe films. The grain growth kinetics
are investigated as functions of temperature and the addition of Na.
Significantly, lateral grain sizes above 1 um are demonstrated for samples
grown on Na-free glass,demonstrating the feasibility for CZTS growth on
substrates other than soda lime glass
Cosmic ray diffusion near the Bohm limit in the Cassiopeia A supernova remnant
Supernova remnants (SNRs) are believed to be the primary location of the
acceleration of Galactic cosmic rays, via diffusive shock (Fermi) acceleration.
Despite considerable theoretical work the precise details are still unknown, in
part because of the difficulty in directly observing nucleons that are
accelerated to TeV energies in, and affect the structure of, the SNR shocks.
However, for the last ten years, X-ray observatories ASCA, and more recently
Chandra, XMM-Newton, and Suzaku have made it possible to image the synchrotron
emission at keV energies produced by cosmic-ray electrons accelerated in the
SNR shocks. In this article, we describe a spatially-resolved spectroscopic
analysis of Chandra observations of the Galactic SNR Cassiopeia A to map the
cutoff frequencies of electrons accelerated in the forward shock. We set upper
limits on the electron diffusion coefficient and find locations where particles
appear to be accelerated nearly as fast as theoretically possible (the Bohm
limit).Comment: 18 pages, 5 figures. Accepted for publication in Nature Physics (DOI
below), final version available week of August 28, 2006 at
http://www.nature.com/nphy
The Cherenkov Telescope Array Large Size Telescope
The two arrays of the Very High Energy gamma-ray observatory Cherenkov
Telescope Array (CTA) will include four Large Size Telescopes (LSTs) each with
a 23 m diameter dish and 28 m focal distance. These telescopes will enable CTA
to achieve a low-energy threshold of 20 GeV, which is critical for important
studies in astrophysics, astroparticle physics and cosmology. This work
presents the key specifications and performance of the current LST design in
the light of the CTA scientific objectives.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
Functionalisation of PLLA nanofiber scaffolds using a possible cooperative effect between collagen type I and BMP-2: impact on growth and osteogenic differentiation of human mesenchymal stem cells
Mesenchymal stem cell differentiation of osteoblasts is triggered by a series of signaling processes including integrin and bone morphogenetic protein (BMP), which therefore act in a cooperative manner. The aim of this study was to analyze whether these processes can be remodeled in an artificial poly-(l)-lactide acid (PLLA) based nanofiber scaffold. Matrices composed of PLLA-collagen type I or BMP-2 incorporated PLLA-collagen type I were seeded with human mesenchymal stem cells (hMSC) and cultivated over a period of 22Â days, either under growth or osteoinductive conditions. During the course of culture, gene expression of alkaline phosphatase (ALP), osteocalcin (OC) and collagen I (COL-I) as well as Smad5 and focal adhesion kinase (FAK), two signal transduction molecules involved in BMP-2 or integrin signaling were analyzed. Furthermore, calcium and collagen I deposition, as well as cell densities and proliferation, were determined using fluorescence microscopy. The incorporation of BMP-2 into PLLA-collagen type I nanofibers resulted in a decrease in diameter as well as pore sizes of the scaffold. Mesenchymal stem cells showed better adherence and a reduced proliferation on BMP-containing scaffolds. This was accompanied by an increase in gene expression of ALP, OC and COL-I. Furthermore the presence of BMP-2 resulted in an upregulation of FAK, while collagen had an impact on the gene expression of Smad5. Therefore these different strategies can be combined in order to enhance the osteoblast differentiation of hMSC on PLLA based nanofiber scaffold. By doing this, different signal transduction pathways seem to be up regulated
CD40L Deficiency Attenuates Diet-Induced Adipose Tissue Inflammation by Impairing Immune Cell Accumulation and Production of Pathogenic IgG-Antibodies
BACKGROUND: Adipose tissue inflammation fuels the metabolic syndrome. We recently reported that CD40L--an established marker and mediator of cardiovascular disease--induces inflammatory cytokine production in adipose cells in vitro. Here, we tested the hypothesis that CD40L deficiency modulates adipose tissue inflammation in vivo. METHODOLOGY/PRINCIPAL FINDINGS: WT or CD40L(-/-) mice consumed a high fat diet (HFD) for 20 weeks. Inflammatory cell recruitment was impaired in mice lacking CD40L as shown by a decrease of adipose tissue macrophages, B-cells, and an increase in protective T-regulatory cells. Mechanistically, CD40L-deficient mice expressed significantly lower levels of the pro-inflammatory chemokine MCP-1 both, locally in adipose tissue and systemically in plasma. Moreover, levels of pro-inflammatory IgG-antibodies against oxidized lipids were reduced in CD40L(-/-) mice. Also, circulating low-density lipoproteins and insulin levels were lower in CD40L(-/-) mice. However, CD40L(-/-) mice consuming HFD were not protected from the onset of diet-induced obesity (DIO), insulin resistance, and hepatic steatosis, suggesting that CD40L selectively limits the inflammatory features of diet-induced obesity rather than its metabolic phenotype. Interestingly, CD40L(-/-) mice consuming a low fat diet (LFD) showed both, a favorable inflammatory and metabolic phenotype characterized by diminished weight gain, improved insulin tolerance, and attenuated plasma adipokine levels. CONCLUSION: We present the novel finding that CD40L deficiency limits adipose tissue inflammation in vivo. These findings identify CD40L as a potential mediator at the interface of cardiovascular and metabolic disease
Binding Properties and Stability of the Ras-Association Domain of Rap1-GTP Interacting Adapter Molecule (RIAM)
The Rap1-GTP interacting adapter protein (RIAM) is an important protein in Rap1-mediated integrin activation. By binding to both Rap1 GTPase and talin, RIAM recruits talin to the cell membrane, thus facilitating talin-dependent integrin activation. In this article, we studied the role of the RIAM Ras-association (RA) and pleckstrin-homology (PH) domains in the interaction with Rap1. We found that the RA domain was sufficient for GTP-dependent interaction with Rap1B, and the addition of the PH domain did not change the binding affinity. We also detected GTP-independent interaction of Rap1B with the N-terminus of RIAM. In addition, we found that the PH domain stabilized the RA domain both in vitro and in cells
Gamma-Ray Emission Concurrent with the Nova in the Symbiotic Binary V407 Cygni
Novae are thermonuclear explosions on a white dwarf surface fueled by mass
accreted from a companion star. Current physical models posit that shocked
expanding gas from the nova shell can produce X-ray emission but emission at
higher energies has not been widely expected. Here, we report the Fermi Large
Area Telescope detection of variable gamma-ray (0.1-10 GeV) emission from the
recently-detected optical nova of the symbiotic star V407 Cygni. We propose
that the material of the nova shell interacts with the dense ambient medium of
the red giant primary, and that particles can be accelerated effectively to
produce pi0 decay gamma-rays from proton-proton interactions. Emission
involving inverse Compton scattering of the red giant radiation is also
considered and is not ruled out.Comment: 38 pages, includes Supplementary Online Material; corresponding
authors: C.C. Cheung, A.B. Hill, P. Jean, S. Razzaque, K.S. Woo
A change in the optical polarization associated with a gamma-ray flare in the blazar 3C 279
It is widely accepted that strong and variable radiation detected over all
accessible energy bands in a number of active galaxies arises from a
relativistic, Doppler-boosted jet pointing close to our line of sight. The size
of the emitting zone and the location of this region relative to the central
supermassive black hole are, however, poorly known, with estimates ranging from
light-hours to a light-year or more. Here we report the coincidence of a
gamma-ray flare with a dramatic change of optical polarization angle. This
provides evidence for co-spatiality of optical and gamma-ray emission regions
and indicates a highly ordered jet magnetic field. The results also require a
non-axisymmetric structure of the emission zone, implying a curved trajectory
for the emitting material within the jet, with the dissipation region located
at a considerable distance from the black hole, at about 10^5 gravitational
radii.Comment: Published in Nature issued on 18 February 2010. Corresponding
authors: Masaaki Hayashida and Greg Madejsk
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