Entity

Time filter

Source Type

Torrejón de Ardoz, Spain

Duchene G.,CNRS Grenoble Institute for Particle Astrophysics and Cosmology Laboratory | Bouvier J.,CNRS Grenoble Institute for Particle Astrophysics and Cosmology Laboratory | Moraux E.,CNRS Grenoble Institute for Particle Astrophysics and Cosmology Laboratory | Bouy H.,Instituto Nacional Of Tecnica Aerospacial | And 2 more authors.
Astronomy and Astrophysics | Year: 2013

Aims. We present the first high-angular resolution survey for multiple systems among very low-mass stars and brown dwarfs in the Hyades open cluster. Methods. Using the Keck II adaptive optics system, we observed a complete sample of 16 objects with estimated masses 2;0.1 M·. Results. We have identified three close binaries with projected separation 2;0"I, or 2;5 AU. A number of wide, mostly faint candidate companions are also detected in our images, most of which are revealed as unrelated background sources based on astrometric and/or photometric considerations. The derived multiplicity frequency, 19+13 -6% over the 2-350 AU range, and the rarity of systems wider than 10 AU are both consistent with observations of field very low-mass objects. In the limited 3-50 AU separation range, the companion frequency is essentially constant from brown dwarfs to solar-type stars in the Hyades cluster, which is also in line with our current knowledge for field stars. Combining the binaries discovered in this surveys with those already known in the Pleiades cluster reveals that very low-mass binaries in open clusters, as well as in star-forming regions, are skewed toward lower mass ratios (0.6 2; q 2; 0.8) than are their field counterparts, a result that cannot be accounted for by selection effects. Although the possibility of severe systematic errors in model-based mass estimates for very low-mass stars cannot be completely excluded, it is unlikely to explain this difference. Conclusions. We speculate that this trend indicates that surveys among very low-mass field stars may have missed a substantial population of intermediate mass ratio systems, implying that these systems are more common and more diverse than previously thought. © 2013 ESO. Source


Stelzer S.,University of Leoben | Brunner A.J.,Empa - Swiss Federal Laboratories for Materials Science and Technology | Arguelles A.,University of Oviedo | Murphy N.,University College Dublin | And 3 more authors.
Engineering Fracture Mechanics | Year: 2014

Two round robins on mode I fatigue delamination propagation organized by Technical Committee 4 of the European Structural Integrity Society compared three unidirectional carbon fiber reinforced composites, one with thermoplastic (poly-ether-ether-ketone) and two with thermoset (epoxy) matrix tested at five laboratories. Different approaches for data evaluation and their effect on the in- and inter-laboratory scatter are discussed and compared. Calculated delamination rates da/dN and applied GImax from displacement controlled tests are sensitive to small scatter in the load signal, and, therefore, a new route to evaluate the crack growth rate from pairs of load and displacement data is presented. © 2013 Elsevier Ltd. Source


Ponsin J.,Instituto Nacional Of Tecnica Aerospacial | Meheut M.,ONERA
ECCOMAS 2012 - European Congress on Computational Methods in Applied Sciences and Engineering, e-Book Full Papers | Year: 2012

Within the EU-funded research program DeSiReH (Design, Simulation and flight Reynolds number testing for advanced High-lift solutions) one activity is being devoted to investigating grid adaptation techniques aimed at improving the accuracy of CFD predictions within optimization processes. This paper describes the application of two grid adaptation approaches suitable to be used within design optimization. The first grid adaptation approach is based on the far-field drag breakdown method. Two adaptation indicators that target regions of spurious drag creation are proposed and applied to a 3D high lift test case (KH3Y tunnel model). The results obtained indicate that an improvement of the drag prediction can be achieved with this method with a moderate increase of nodes relative to the initial grid. The second adaptive approach is based on the application of adjoint methods for a posteriori output functional error estimation and grid adaptation. The results obtained with the A310 section in landing configuration show that similar levels of accuracy with respect to a sequence of uniform adaptations can be achieved with 5-10 times fewer grid points. Source


Sawamura P.,University of Maryland Baltimore County | Vernier J.P.,NASA | Barnes J.E.,National Oceanic and Atmospheric Administration | Berkoff T.A.,Joint Center for Earth Systems Technology | And 16 more authors.
Environmental Research Letters | Year: 2012

Nabro volcano (13.37°N, 41.70°E) in Eritrea erupted on 13 June 2011 generating a layer of sulfate aerosols that persisted in the stratosphere for months. For the first time we report on ground-based lidar observations of the same event from every continent in the Northern Hemisphere, taking advantage of the synergy between global lidar networks such as EARLINET, MPLNET and NDACC with independent lidar groups and satellite CALIPSO to track the evolution of the stratospheric aerosol layer in various parts of the globe. The globally averaged aerosol optical depth (AOD) due to the stratospheric volcanic aerosol layers was of the order of 0.018±0.009 at 532nm, ranging from 0.003 to 0.04. Compared to the total column AOD from the available collocated AERONET stations, the stratospheric contribution varied from 2% to 23% at 532nm. © 2012 IOP Publishing Ltd. Source


Vargas J.,CSIC - National Center for Biotechnology | Restrepo R.,Instituto Nacional Of Tecnica Aerospacial | Sorzano C.O.S.,CSIC - National Center for Biotechnology | Du Y.-Z.,University of Sichuan | Carazo J.M.,CSIC - National Center for Biotechnology
Applied Optics | Year: 2012

We present a Shack-Hartmann (SH) centroid detection algorithm capable to measure in presence of strong noise, background illumination and spot modulating signals, which are typical limiting factors of traditional centroid detection algorithms. The proposed method is based on performing a normalization of the SH pattern using the spiral phase transform method and Fourier filtering. The spot centroids are then obtained using global thresholding and weighted average methods. We have tested the algorithm with simulations and experimental data obtaining satisfactory results. A complete MATLAB package that can reproduce all the results can be downloaded from [http://goo.gl/o2JhD]. © 2012 Optical Society of America. Source

Discover hidden collaborations