The Solar Photospheric Nitrogen Abundance: Determination with 3D and 1D Model Atmospheres

We present a new determination of the solar nitrogen abundance making use of 3D hydrodynamical modelling of the solar photosphere, which is more physically motivated than traditional static 1D models. We selected suitable atomic spectral lines, relying on equivalent width measurements already existing in the literature. For atmospheric modelling we used the co 5 bold 3D radiation hydrodynamics code. We investigated the influence of both deviations from local thermodynamic equilibrium (non-LTE effects) and photospheric inhomogeneities (granulation effects) on the resulting abundance. We also compared several atlases of solar flux and centre-disc intensity presently available. As a result of our analysis, the photospheric solar nitrogen abundance is A(N) = 7.86 +/- 0.12.Comment: 6 pages, 4 figure

Stress influence on high temperature oxide scale growth: modeling and investigation on a thermal barrier coating system.

International audienceIn thermal barrier coating (TBC) systems, an oxide layer develops at high temperature below the ceramic coating, leading at long term to the mechanical failure of the structure upon cooling. This study investigates a mechanism of stress-affected oxidation likely to induce the growth of a non-uniform oxide scale detrimental to the TBC lifetime. A continuum thermodynamics formulation is derived accounting for the influence of the stress and strain situation at the sharp metal/oxide phase boundary on the local oxidation kinetics. It specially includes the contributions of the large volumetric strain and the mass consumption associated with metal oxidation. A continuum mechanics/mass diffusion framework is used along with the developed formulation for the interface evolution to study the growth of an oxide layer coupled with local stress development. The implementation of the model has required the development of a specific simulation tool, based on a finite element method completed with an external routine for the phase boundary propagation. Results on an electron-beam physical vapor deposited (EB-PVD) TBC case are presented. The processes resulting in a non-uniform oxide scale growth are analyzed and the main influences are discussed

On the Origin of the Early Solar System Radioactivities. Problems with the AGB and Massive Star Scenarios

Recent improvements in stellar models for intermediate-mass and massive stars are recalled, together with their expectations for the synthesis of radioactive nuclei of lifetime $\tau \lesssim 25$ Myr, in order to re-examine the origins of now extinct radioactivities, which were alive in the solar nebula. The Galactic inheritance broadly explains most of them, especially if $r$-process nuclei are produced by neutron star merging according to recent models. Instead, $^{26}$Al, $^{41}$Ca, $^{135}$Cs and possibly $^{60}$Fe require nucleosynthesis events close to the solar formation. We outline the persisting difficulties to account for these nuclei by Intermediate Mass Stars (2 $\lesssim$ M/M$_\odot \lesssim 7 - 8$). Models of their final stages now predict the ubiquitous formation of a $^{13}$C reservoir as a neutron capture source; hence, even in presence of $^{26}$Al production from Deep Mixing or Hot Bottom Burning, the ratio $^{26}$Al/$^{107}$Pd remains incompatible with measured data, with a large excess in $^{107}$Pd. This is shown for two recent approaches to Deep Mixing. Even a late contamination by a Massive Star meets problems. In fact, inhomogeneous addition of Supernova debris predicts non-measured excesses on stable isotopes. Revisions invoking specific low-mass supernovae and/or the sequential contamination of the pre-solar molecular cloud might be affected by similar problems, although our conclusions here are weakened by our schematic approach to the addition of SN ejecta. The limited parameter space remaining to be explored for solving this puzzle is discussed.Comment: Accepted for publication on Ap

Modelling stress-diffusion controlled phase transformations : application to stress corrosion cracking

National audienceStress Corrosion Cracking (SCC) represents a significant cause of failure in pressurised water reactors and many efforts have been made to address this problem [1]. It involves the combined action of the environment, mechanical stresses and material properties on the damage of engineering components. Current SCC models developed to predict crack growth behaviour or SCC susceptibility criteria do not fully incorporate the complex multiphysical processes that occur during oxidation at the scale of the microstructure. The aim of the work is to formulate a multi-physics modelling framework based on continuum thermodynamics able to describe the growth of an oxide film on a polycrystalline material using the phase field method

Rebrote, rendimiento y nutrición de Leymus chinensis y Hordeum brevisubulatum en respuesta a la frecuencia e intensidad de defoliación

The effects of different defoliation intensities and frequencies were studied on regrowth and herbage mass of Leymus chinensis and Hordeum brevisubulatum in northeast China for two years. Plants were defoliated to 6, 8 or 10 cm stubble height by removing about 40% of growth down to each designated defoliation height. In the first year, L. chinensis was defoliated 22, 17 or 13 times, and in the second year was defoliated 21, 15 or 15 times to reach 6, 8 or 10 cm stubble height treatments, respectively. H. brevisubulatum was defoliated 26, 21 or 15 times in the first year, and 28, 23 or 21 times in the second year to reach the 6, 8 or 10 cm stubble, respectively. L. chinensis was more productive than H. brevisubulatum, but H. brevisubulatum showed a better forage quality than L. chinensis because H. brevisubulatum showed a higher leaf to stem ratio and crude protein concentration than L. chinensis. Both species produced the highest yield, but the lowest quality when defoliated to 10 cm stubble. There were no significant differences in water soluble carbohydrate (WSC) concentrations in below-ground culm and rhizome tissues between defoliation heights, but L. chinensis had a higher WSC concentration than H.brevisubulatum.Fil: Song, Y.. Dalian Minzu University. College of Environment and Bioresources; ChinaFil: Busso, Carlos Alberto. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Centro de Recursos Naturales Renovables de la Zona Semiárida. Universidad Nacional del Sur. Centro de Recursos Naturales Renovables de la Zona Semiárida; Argentina. Universidad Nacional del Sur. Departamento de Agronomía; ArgentinaFil: Yu, Y.. China National Environmental Monitoring Center; ChinaFil: Wang, P.. Northeast Normal University. School of Environment; ChinaFil: Wuyunna. Dalian Minzu University. College of Environment and Bioresources; ChinaFil: Zhou, D.. Chinese Academy of Sciences; República de Chin

Abundance gradients in the Milky Way for alpha elements, Iron peak elements, Barium, Lanthanum and Europium

We model the abundance gradients in the disk of the Milky Way for several chemical elements (O, Mg, Si, S, Ca, Sc, Ti, Co, V, Fe, Ni, Zn, Cu, Mn, Cr, Ba, La and Eu), and compare our results with the most recent and homogeneous observational data. We adopt a chemical evolution model able to well reproduce the main properties of the solar vicinity. We compute, for the first time, the abundance gradients for all the above mentioned elements in the galactocentric distance range 4 - 22 kpc. The comparison with the observed data on Cepheids in the galactocentric distance range 5-17 kpc gives a very good agreement for many of the studied elements. In addition, we fit very well the data for the evolution of Lanthanum in the solar vicinity for which we present results here for the first time. We explore, also for the first time, the behaviour of the abundance gradients at large galactocentric distances by comparing our results with data relative to distant open clusters and red giants and select the best chemical evolution model model on the basis of that. We find a very good fit to the observed abundance gradients, as traced by Cepheids, for most of the elements, thus confirming the validity of the inside-out scenario for the formation of the Milky Way disk as well as the adopted nucleosynthesis prescriptions.Comment: 11 pages, 9 figures, accepted for publication in A&