1,183 research outputs found
Adaptive optics imaging of P Cygni in Halpha
We obtained Halpha diffraction limited data of the LBV star P Cyg using the
ONERA Adaptive Optics (AO) facility BOA at the OHP 1.52m telescope on October
1997. Taking P Cyg and the reference star 59 Cyg AO long exposures we find that
P Cyg clearly exhibits a large and diffuse intensity distribution compared to
the 59 Cyg's point-like source. A deconvolution of P Cyg using 59 Cyg as the
Point Spread Function was performed by means of the Richardson-Lucy algorithm.
P Cyg clearly appears as an unresolved star surrounded by a clumped envelope.
The reconstructed image of P Cyg is compared to similar spatial resolution maps
obtained from radio aperture synthesis imaging. We put independent constraints
on the physics of P Cyg which agree well with radio results. We discuss future
possibilities to constrain the wind structure of P Cyg by using
multi-resolution imaging, coronagraphy and long baseline interferometry to
trace back its evolutionary status.Comment: 10 pages, 19 Encapsulated Postscript figure
Recent Results From the EU POF-PLUS Project: Multi-Gigabit Transmission Over 1 mm Core Diameter Plastic Optical Fibers
Recent activity to achieve multi-gigabit transmission over 1 mm core diameter graded-index and step-index plastic optical fibers for distances up to 50 meters is reported in this paper. By employing a simple intensity-modulated direct-detection system with pulse amplitude or digital multi-tone modulation techniques, low-cost transceivers and easy to install large-core POFs, it is demonstrated that multi-gigabit transmission up to 10 Gbit/s over 1-mm core diameter POF infrastructure is feasible. The results presented in this paper were obtained in the EU FP7 POF-PLUS project, which focused on applications in different scenarios, such as in next-generation in-building residential networks and in datacom applications
La fièvre aphteuse
La fièvre aphteuse, l’une des maladies les plus contagieuses et qui frappe surtout les bovins, mais aussi les porcins, les ovins et les caprins, peut avoir des conséquences dévastatrices sur les agriculteurs et l’économie agricole. Par l’adoption d’une approche novatrice, cet ouvrage explore cette maladie, en apportant des faits concrets et exhaustifs. Chaque chapitre se penche sur une perspective différente, en faisant part des témoignages réfléchis d’agriculteurs et de vétérinaires, d’économistes et de journalistes, tant dans les pays en développement que dans les pays industrialisés
Dark matter profiles and annihilation in dwarf spheroidal galaxies: prospectives for present and future γ-ray observatories - I. The classical dwarf spheroidal galaxies
Due to their large dynamical mass-to-light ratios, dwarf spheroidal galaxies (dSphs) are promising targets for the indirect detection of dark matter (DM) in γ-rays. We examine their detectability by present and future γ-ray observatories. The key innovative features of our analysis are as follows: (i) we take into account the angular size of the dSphs; while nearby objects have higher γ-ray flux, their larger angular extent can make them less attractive targets for background-dominated instruments; (ii) we derive DM profiles and the astrophysical J-factor (which parametrizes the expected γ-ray flux, independently of the choice of DM particle model) for the classical dSphs directly from photometric and kinematic data. We assume very little about the DM profile, modelling this as a smooth split-power-law distribution, with and without subclumps; (iii) we use a Markov chain Monte Carlo technique to marginalize over unknown parameters and determine the sensitivity of our derived J-factors to both model and measurement uncertainties; and (iv) we use simulated DM profiles to demonstrate that our J-factor determinations recover the correct solution within our quoted uncertainties. Our key findings are as follows: (i) subclumps in the dSphs do not usefully boost the signal; (ii) the sensitivity of atmospheric Cherenkov telescopes to dSphs within ∼20 kpc with cored haloes can be up to ∼50 times worse than when estimated assuming them to be point-like. Even for the satellite-borne Fermi-Large Area Telescope (Fermi-LAT), the sensitivity is significantly degraded on the relevant angular scales for long exposures; hence, it is vital to consider the angular extent of the dSphs when selecting targets; (iii) no DM profile has been ruled out by current data, but using a prior on the inner DM cusp slope 0 ≤γprior≤ 1 provides J-factor estimates accurate to a factor of a few if an appropriate angular scale is chosen; (iv) the J-factor is best constrained at a critical integration angle αc= 2rh/d (where rh is the half-light radius and d is the distance from the dwarf) and we estimate the corresponding sensitivity of γ-ray observatories; (v) the ‘classical' dSphs can be grouped into three categories: well constrained and promising (Ursa Minor, Sculptor and Draco), well constrained but less promising (Carina, Fornax and Leo I), and poorly constrained (Sextans and Leo II); and (vi) observations of classical dSphs with the Fermi-LAT integrated over the mission lifetime are more promising than observations with the planned Cherenkov Telescope Array for DM particle mass ≲ 700 GeV. However, even the Fermi-LAT will not have sufficient integrated signal from the classical dwarfs to detect DM in the ‘vanilla' Minimal Supersymmetric Standard Model. Both the Galactic Centre and the ‘ultrafaint' dwarfs are likely to be better targets and will be considered in future wor
Benthic oxygen exchange over a heterogeneous Zostera noltei meadow in a temperate coastal ecosystem
Seagrass meadows support intense but highly variable benthic metabolic rates that still need to be better evaluated to determine an accurate trophic status. The present study assessed how seagrasses and associated benthic macrofauna control spatiotemporal changes in benthic oxygen exchanges within a temperate bay. Based on seasonal sampling over a complete year cycle, the diffusive oxygen uptake (DOU), community respiration (CR) and gross primary production (GPP) were measured in a Zostera noltei meadow within Arcachon Bay, taking into account its spatial heterogeneity. Oxygen fluxes were assessed in sediment cores, within which benthic macrofauna and seagrass abundances and biomasses were quantified. The presence of Z. noltei did not significantly affect the DOU. Seasonal changes in CR and GPP correlated strongly with temperature in the presence of Z. noltei. The characteristics of benthic macrofauna associated with Z. noltei only weakly affected seasonal changes in CR. High spatial changes in both GPP and CR were mainly driven by the aboveground biomass of Z. noltei. When extrapolated to the whole intertidal area of the bay, in spite of limitations, our results suggest (1) overall higher contributions to CR and GPP from the seagrass meadow than from bare sediments, even though alternative primary producers in bare sediments (likely microphytobenthos) contributed significantly during winter; (2) an annual decrease in CR and GPP of 35 and 41%, respectively, resulting from the decline in Z. noltei of 25% between 2005 and 2007; and (3) a strong seasonality in the magnitude of this decrease, which was high during autumn and low during winter.
Super-resolution in map-making based on a physical instrument model and regularized inversion. Application to SPIRE/Herschel
We investigate super-resolution methods for image reconstruction from data
provided by a family of scanning instruments like the Herschel observatory. To
do this, we constructed a model of the instrument that faithfully reflects the
physical reality, accurately taking the acquisition process into account to
explain the data in a reliable manner. The inversion, ie the image
reconstruction process, is based on a linear approach resulting from a
quadratic regularized criterion and numerical optimization tools. The
application concerns the reconstruction of maps for the SPIRE instrument of the
Herschel observatory. The numerical evaluation uses simulated and real data to
compare the standard tool (coaddition) and the proposed method. The inversion
approach is capable to restore spatial frequencies over a bandwidth four times
that possible with coaddition and thus to correctly show details invisible on
standard maps. The approach is also applied to real data with significant
improvement in spatial resolution.Comment: Astronomy & Astrophysic
Multidisciplinary Design and Optimization of Regional Jet Retrofitting Activity
A retrofit analysis on a 90 passengers regional jet aircraft is performed through a multidisciplinary collaborative aircraft design and optimization highlighting the impact on costs and performance. Two different activities are accounted for selecting the best aircraft retrofit solution: a re-engining operation that allows to substitute a conventional power-plant platform with advanced geared turbofan and an on-board-systems architecture modernization, considering different levels of electrification. Besides the variables that are directly dependent from these activities, also scenario variables are considered during the optimization such as the fuel price, the fleet size and the years of utilization of the upgraded systems. The optimization is led by impacts of the retrofitting process on emissions, capital costs and saving costs, computed at industrial level. Overall aircraft design competences (aerodynamics, masses, performance, noise, and emissions) have been computed increasing the level of fidelity and reliability. The whole process is implemented in the framework of the AGILE 4.0 research project in a collaborative remote multidisciplinary approach. Results show that the engine retrofitting can be a profitable solution for both manufacturers and airliners. Conversely, the on-board-system electrification seems to be not convenient in a retrofitting process due to the high capital costs. Depending on the operative scenario, involved stakeholders can properly orient their decision on a retrofitting strategy
Design of the strut braced wing aircraft in the agile collaborative MDO framework
The paper describes the deployment of the AGILE Development Framework to investigate the Strut Braced Wing aircraft configuration. The design process consists of a multilevel multidisciplinary architecture, progressing from the initial conceptual synthesis to the physics based analysis. All the main disciplinary domains, including on board system design and cost assessment, are accounted for in the assembled workflow. Due to the specific characteristics of the Strut Braced Wing configuration, the aeroelastic analysis is the main focus of the study and it is addressed at both high and low fidelity levels. The integration of the engine-wing system is also included in the design process. All the design competences, which are hosted at the different partners, communicate via CPACS (Common Parametric Aircraft Configuration Schema) data schema. All the results generated, including the multidisciplinary design process itself, will be published and made available as part of the AGILE Overall Aircraft Design database
Visualizing mineralization processes and fossil anatomy using synchronous synchrotron X-ray fluorescence and X-ray diffraction mapping
International audienc
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