Testing Evolutionary Models of Dwarf Irregular Galaxies through Gas and Stellar Metallicity Determinations in HII Galaxies

Dwarf irregular galaxies are usually low-metallicity objects, and show ongoing or very recent star formation, giving rise to their irregular appearance. Especially HII galaxies, a sub-category of dwarf irregulars showing unusually high star formation activity, are believed to be among the least evolved galaxies in existence today. Therefore, they are very interesting objects for studies of early galaxy evolution and of metallicity enrichment mechanisms. Several groups have developed theoretical evolutionary models of galaxies of this type, describing different possible formation and evolutionary scenarii, and varying factors such as gas infall and outflow, as well as the star formation history, and making predictions about their chemical evolution. One way to evaluate these models is by determining the metallicities of the different components of these galaxies, their gas and stars. We examine a sample of HII galaxies from the Sloan Digital Sky Survey, which possibly contains the largest homogeneous sample of HII galaxy spectra to date. Using very restrictive selection criteria, which guarantee a sample of high quality spectra and avoid "contamination” by spectra of objects of other nature, we defined a sample of ∼ 700 HII galaxies spectra. Through emission line strength calibrations and a detailed stellar population synthesis, we determined the metallicities of both the gas and the stellar content of these galaxies. For HII galaxies up to stellar masses of 5 × 109 M ⊙, we find enrichment mechanisms not to vary with galactic mass, being the same for low- and high-mass galaxies on average. They do seem to present a greater variety at the high-mass end, though, indicating a more complex assembly history. Our results favour galaxy evolutionary models featuring constantly infalling low-metallicity clouds that retain part of the galactic winds. Above 5 × 109 M ⊙ stellar mass, the retention of high metallicity gas by the galaxies' gravitational potential dominates. I would like to thank the Fundação de Amparo à Pesquisa do Estado do São Paulo (FAPESP) for financial suppor

Orniérage des chaussées : identification des paramètres élasto-plastiques d'un enrobé bitumineux à partir d'un essai structurel

Le béton bitumineux est un matériau hétérogène composé d'un squelette granulaire formant l'ossature rigide et d'un liant bitumineux assurant la cohésion de l'ensemble. L'orniérage est un des principaux modes de dégradation des chaussées bitumineuses. Il se traduit par l'apparition de déformations permanentes longitudinales sous le passage répété des véhicules. Prédire, par le calcul, ce type de dégradations nécessite la connaissance fine du comportement de ce matériau élasto-viscoplastique. Le critère de Drucker-Prager semble adapté pour modéliser la part élasto-plastique des déformations. L'enjeu est donc d'en identifier les paramètres à partir d'essais structurels simples. L'expression des déformations plastiques volumiques et déviatoriques cumulées est obtenue par dérivation d'un champ de déplacement mesuré régularisé. L'amplitude de l'angle de frottement interne est alors directement identifiable. La méthode de mesure de champ de déplacements par corrélation d'images est utilisée

Myocardial function at the early phase of traumatic brain injury: a prospective controlled study

The concept of brain-heart interaction has been described in several brain injuries. Traumatic brain injury (TBI) may also lead to cardiac dysfunction but evidences are mainly based upon experimental and clinical retrospective studies. Methods We conducted a prospective case-control study in a level I trauma center. Twenty consecutive adult patients with severe TBI were matched according to age and gender with 20 control patients. The control group included adult patients undergoing a general anesthesia for a peripheral trauma surgery. Conventional and Speckle Tracking Echocardiography (STE) was performed within the first 24 post- traumatic hours in the TBI group and PRE/PER-operative in the control group. The primary endpoint was the left ventricle ejection fraction (LVEF) measured by the Simpson’s method. Secondary endpoints included the diastolic function and the STE analysis. Results We found similar LVEF between the TBI group and the PER-operative control group (61 % [56–76]) vs. 62 % [52–70]). LV morphological parameters and the systolic function were also similar between the two groups. Regarding the diastolic function, the isovolumic relaxation time was significantly higher in the TBI cohort (125 s [84–178] versus 107 s [83–141], p = 0.04), suggesting a subclinical diastolic dysfunction. Using STE parameters, we observed a trend toward higher strains in the TBI group but only the apical circumferential strain and the basal rotation reached statistical significance. STE-derived parameters of the diastolic function tended to be lower in TBI patients. Discussion No systematic myocardial depression was found in a cohort of severe TBI patients. Conclusions STE revealed a correct adaptation of the left systolic function, while the diastolic function slightl

On the compact HII galaxy UM 408 as seen by GMOS-IFU: Physical conditions

We present Integral Field Unit GMOS-IFU data of the compact HII galaxy UM408, obtained at Gemini South telescope, in order to derive the spatial distribution of emission lines and line ratios, kinematics, plasma parameters, and oxygen abundances as well the integrated properties over an area of 3"x4".4(~750x1100 pc) located in the central part of the galaxy. The starburst in this area is resolved into two giant regions of ~375 and 250pc diameter, respectively. The ages of these two regions, estimated using Hb equivalent widths, suggest that they are coeval events of ~5Myr with stellar masses of ~10^4M_o. We have also used [OIII]/Hb and [SII]/Ha ratio maps to explore the excitation mechanisms in this galaxy. The Ha emission line was used to measure the radial velocity and velocity dispersion. We derived an integrated oxygen abundance of 12+log(O/H)=7.87 summing over all spaxels in our field of view. An average value of 12+log(O/H)=7.77 and a difference of D(O/H)=0.47 between the minimum and maximum values (7.58+-0.06-8.05+-0.04) were found, considering all data points where the oxygen abundance was measured. The spatial distribution of oxygen abundance does not show any significant gradient across the galaxy. On the other hand, the bulk of data points are lying in a region of +-2sigma dispersion (with sigma=0.1 dex) around the average value, confirming that this compact HII galaxy as other previously studied dwarf irregular galaxies is chemically homogeneous. Therefore, the new metals processed and injected by the current star formation episode are possibly not observed and reside in the hot gas phase, whereas the metals from previous events are well mixed and homogeneously distributed through the whole extent of the galaxy.Comment: 30 pages, 10 figures. AJ accepte

Formation & evolution of the Galactic bulge: constraints from stellar abundances

We compute the chemical evolution of the Galactic bulge in the context of an inside-out model for the formation of the Milky Way. The model contains updated stellar yields from massive stars. The main purpose of the paper is to compare the predictions of this model with new observations of chemical abundance ratios and metallicity distributions in order to put constraints on the formation and evolution of the bulge. We computed the evolution of several alpha-elements and Fe and performed several tests by varying different parameters such as star formation efficiency, slope of the initial mass function and infall timescale. We also tested the effect of adopting a primary nitrogen contribution from massive stars. The [alpha/Fe] abundance ratios in the Bulge are predicted to be supersolar for a very large range in [Fe/H], each element having a different slope. These predictions are in very good agreement with most recent accurate abundance determinations. We also find a good fit of the most recent Bulge stellar metallicity distributions. We conclude that the Bulge formed on a very short timescale (even though timescales much shorter than about 0.1 Gyr are excluded) with a quite high star formation efficiency of about 20 Gyr$^{-1}$ and with an initial mass function more skewed toward high masses (i.e. x <= 0.95) than the solar neighbourhood and rest of the disk. The results obtained here are more robust than previous ones since they are based on very accurate abundance measurements.Comment: 26 pages, 9 figures, accepted for publication in A&

Orniérage des chaussées : identification des paramètres élasto-plastiques d'un enrobé bitumineux à partir d'un essai structurel

Colloque avec actes et comité de lecture. Internationale.International audienceLe béton bitumineux est un matériau hétérogène composé d'un squelette granulaire formant l'ossature rigide et d'un liant bitumineux assurant la cohésion de l'ensemble. L'orniérage est un des principaux modes de dégradation des chaussées bitumineuses. Il se traduit par l'apparition de déformations permanentes longitudinales sous le passage répété des véhicules. Prédire, par le calcul, ce type de dégradations nécessite la connaissance fine du comportement de ce matériau élasto-viscoplastique. Le critère de Drucker-Prager semble adapté pour modéliser la part élasto-plastique des déformations. L'enjeu est donc d'en identifier les paramètres à partir d'essais structurels simples. L'expression des déformations plastiques volumiques et déviatoriques cumulées est obtenue par dérivation d'un champ de déplacement mesuré régularisé. L'amplitude de l'angle de frottement interne est alors directement identifiable. La méthode de mesure de champ de déplacements par corrélation d'images est utilisée

Myocardial function at the early phase of traumatic brain injury: a prospective controlled study

International audienceBackground: The concept of brain-heart interaction has been described in several brain injuries. Traumatic brain injury (TBI) may also lead to cardiac dysfunction but evidences are mainly based upon experimental and clinical retrospective studies.Methods: We conducted a prospective case-control study in a level I trauma center. Twenty consecutive adult patients with severe TBI were matched according to age and gender with 20 control patients. The control group included adult patients undergoing a general anesthesia for a peripheral trauma surgery. Conventional and Speckle Tracking Echocardiography (STE) was performed within the first 24 post-traumatic hours in the TBI group and PRE/PER-operative in the control group. The primary endpoint was the left ventricle ejection fraction (LVEF) measured by the Simpson's method. Secondary endpoints included the diastolic function and the STE analysis.Results: We found similar LVEF between the TBI group and the PER-operative control group (61 % [56–76]) vs. 62 % [52–70]). LV morphological parameters and the systolic function were also similar between the two groups. Regarding the diastolic function, the isovolumic relaxation time was significantly higher in the TBI cohort (125 s [84–178] versus 107 s [83–141], p = 0.04), suggesting a subclinical diastolic dysfunction. Using STE parameters, we observed a trend toward higher strains in the TBI group but only the apical circumferential strain and the basal rotation reached statistical significance. STE-derived parameters of the diastolic function tended to be lower in TBI patients.Discussion: No systematic myocardial depression was found in a cohort of severe TBI patients.Conclusions: STE revealed a correct adaptation of the left systolic function, while the diastolic function slightly impaired

Proteomic Studies of Saliva: A Proposal for a Standardized Handling of Clinical Samples

International audienc