Science & Mathematics

A propos d'une maladie fongique des daphnies. Contribution à l'étude de la lutte des phagocytes contre les agents pathogènes.

Aims. The formation of high-mass stars is still debated. For this reason, several projects such as Herschel-HOBYS are focussed on the study of the earliest phases of massive star formation. As a result, massive star-forming complexes such as NGC 6334 and NGC 6357 have been observed in the far-infrared to study their massive dense cores where massive stars are expected to form. However, to better characterise the environments of these cores we need to understand the previous massive star formation history. To better characterise the environment of these massive dense cores we study the previous high-mass star formation and how these stars act on their environments. Methods. This study is based on the spectral classification of the OB stars identified towards NGC 6334 and NGC 6357 with spectra taken with the AAOmega spectrograph on the Anglo-Australian Telescope (AAT). From the subsequent spectral classification of 109 stars across these regions we were able to evaluate the following: distance, age, mass, global star-forming efficiency (SFE), and star formation rate (SFR) of the regions. The physical conditions of the ionised gas for both complexes was also derived. Results. We confirm that NGC 6334 and NGC 6357 belong to the Saggitarius-Carina arm which, in this direction, extends from 1 kpc to 2.2 kpc. From the location of the stars in Hertzprung-Russell diagram we show that stars older than ∼10 Myr are broadly spread across these complexes, while younger stars are mainly located in the H ii regions and stellar clusters. Our data also suggests that some of the young stars can be considered runaway stars. We evaluate a SFE of 0.019 +0.008 −0.007 and 0.021 +0.004 −0.003 and a SFR of 1.1 × 10 3 ± 300 M Myr −1 and 1.7 × 10 3 ± 400 M Myr −1 for NGC 6334 and NGC 6357, respectively. We note that 29 OB stars have X-ray counterparts, most of them belonging to NGC 6357. This suggests that molecular clouds in NGC 6357 are more impacted by X-ray flux and stellar winds than in NGC 6334. Finally, from the analysis of nebular lines (Hα, [NII], and [SII]) from spectra from several regions of ionised gas, we confirm that the filaments in NGC 6357 are shock heated.

Cette thèse s’effectue au sein de l’université de Bordeaux. Ce projet concerne la construction en bois et en particulier la compréhension des phénomènes à l’origine des fissures dans les structures bois. L’un des objectifs étant de concevoir des méthodes efficaces de renforcement local pour les éléments de structure. Pour cela, l’étude se décompose en plusieurs étapes, la compréhension des phénomènes mis en jeu dans la création des fissures sur des bois de construction. Ce travail s’orientera sur la modélisation de fissure en mode mixte, la recherche de solution de renforcement avec compréhension fine de l’impact de types de renforts sur la propagation de la fissure. Cette étude sera accompagnée d’une campagne d’essais, afin de vérifier l’efficacité des renforcements choisis et d’identifier l’impact de l’effet d’échelle sur les modèle de prédiction. Des essais de grandes dimensions seront donc réalisés pour mieux appréhender les effets de groupes et les effets d’échelle sur du matériau d’emploi. On vise ensuite à définir des outils prédictifs de la résistance des systèmes renforcés et de moyens de contrôles pour les Plan d’Assurance Qualité.

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