First Stars XIV. Sulfur abundances in extremely metal-poor (EMP) stars

Sulfur is important: the site of its formation is uncertain, and at very low metallicity the trend of [S/Fe] against [Fe/H] is controversial. Below [Fe/H]=-2.0, [S/Fe] remains constant or it decreases with [Fe/H], depending on the author and the multiplet used in the analysis. Moreover, although sulfur is not significantly bound in dust grains in the ISM, it seems to behave differently in DLAs and in old metal-poor stars. We aim to determine precise S abundance in a sample of extremely metal-poor stars taking into account NLTE and 3D effects. NLTE profiles of the lines of the multiplet 1 of SI have been computed using a new model atom for S. We find sulfur in EMP stars to behave like the other alpha-elements, with [S/Fe] remaining approximately constant for [Fe/H]<-3. However, [S/Mg] seems to decrease slightly as a function of [Mg/H]. The overall abundance patterns of O, Na, Mg, Al, S, and K are best matched by the SN model yields by Heger & Woosley. The [S/Zn] ratio in EMP stars is solar, as found also in DLAs. We obtain an upper limit on the abundance of sulfur, [S/Fe] < +0.5, for the ultra metal-poor star CS 22949-037. This, along with a previous reported measurement of zinc, argues against the conjecture that the light-element abundances pattern in this star, and, by analogy, the hyper metal-poor stars HE 0107-5240 and HE 1327-2326, are due to dust depletion.Comment: 10 pages, accepted for publication in A&

Typology of geometrical defects in Electron Beam Melting

Quality control in terms of material health, texture and workpiece geometry is not assured in additive manufacturing. Many literature studies address quality issues on a scale of less than one millimeter. On the other hand, few works concern geometrical defects at the level of the piece as a whole (form and dimension), on a scale therefore greater than several millimeters. From the existing bibliography and the authors’ experience, the objective of the article is to list the typologies of geometrical defects usually encountered and the configurations in which they appear.Maîtrise géométrique des pièces produites par fabrication additive métalliqu

Analyse de la variation géométrique des pièces produites en fabrication additive EBM - Cas de pièces avec volume surplombant

National audienceL'étude proposée consiste à étudier les types de défauts obtenus en fabrication additive EBM (Electron Beam Melting) pour cela, une géométrie particulière a été choisie avec un volume en surplomb. Les défauts géométriques les plus importants se sont localisés sur la face avant (perte de bord) et le dessous de la pièce (variation d'épaisseur). Afin de caractériser la forme des défauts, une Analyse en Composantes Principales (ACP) a été mise en oeuvre et permet d'identifier les modes les plus significatifs de chacun des lots de pièces produits. A partir de ces analyses, il en ressort que les défauts dépendent de la stratégie de fabrication et que les pièces placées sur la périphérie du plateau présentent des défauts de grandes amplitudes

Sulphur and zinc abundances in Galactic stars and damped Lyman-alpha systems

High resolution spectra of 34 halo population dwarf and subgiant stars have been obtained with VLT/UVES and used to derive sulphur abundances from the 8694.0, 8694.6 A and 9212.9, 9237.5 A SI lines. In addition, iron abundances have been determined from 19 FeII lines and zinc abundances from the 4722.2, 4810.5 ZnI lines. The abundances are based on a classical 1D, LTE model atmosphere analysis, but effects of 3D hydrodynamical modelling on the [S/Fe], [Zn/Fe] and [S/Zn] ratios are shown to be small. We find that most halo stars with metallicities in the range -3.2 < [Fe/H] < -0.8 have a near-constant [S/Fe] = +0.3; a least square fit to [S/Fe] vs. {Fe/H] shows a slope of only -0.04 +/- 0.01. Among halo stars with -1.2 < [Fe/H] < -0.8 the majority have [S/Fe] ~ +0.3, but two stars (previously shown to have low [alpha/Fe] ratios) have [S/Fe] ~ 0. For disk stars with [Fe/H] > -1, [S/Fe] decreases with increasing [Fe/H]. Hence, sulphur behaves like other typical alpha-capture elements, Mg, Si and Ca. Zinc, on the other hand, traces iron over three orders of magnitude in [Fe/H], although there is some evidence for a small systematic Zn overabundance ([Zn/Fe] ~ +0.1) among metal-poor disk stars and for halo stars with [Fe/H] < -2.0. Recent measurements of S and Zn in ten damped Ly-alpha systems (DLAs) with redshifts between 1.9 and 3.4 and zinc abundances in the range -2.1 < [Zn/H] < -0.15 show an offset relative to the [S/Zn] - [Zn/H] relation in Galactic stars. Possible reasons for this offset are discussed, including low and intermittent star formation rates in DLAs.Comment: Accepted for publication in A&A. 16pages; 9 figure

The Logarithmic Sobolev Constant of The Lamplighter

We give estimates on the logarithmic Sobolev constant of some finite lamplighter graphs in terms of the spectral gap of the underlying base. Also, we give examples of application

A new comprehensive set of elemental abundances in DLAs III. Star formation histories

We obtained comprehensive sets of elemental abundances for eleven damped Ly-alpha systems (DLAs) at z_DLA=1.7-2.5. In Paper I of this series, we showed for three DLA galaxies that we can derive their star formation histories and ages from a detailed comparison of their intrinsic abundance patterns with chemical evolution models. We determine in this paper the star formation properties of six additional DLA galaxies. The derived results confirm that no single star formation history explains the diverse sets of abundance patterns in DLAs. We demonstrate that the various star formation histories reproducing the DLA abundance patterns are typical of local irregular, dwarf starburst and quiescent spiral galaxies. Independent of the star formation history, the DLAs have a common characteristic of being weak star forming galaxies; models with high star formation efficiencies are ruled out. All the derived DLA star formation rates per unit area are moderate or low, with values between -3.2 < log SFR < -1.1 M_sol yr^{-1} kpc^{-2}. The DLA abundance patterns require a large spread in ages ranging from 20 Myr up to 3 Gyr. The oldest DLA in our sample is observed at z_DLA=1.864 with an age estimated to more than 3 Gyr; it nicely indicates that galaxies were already forming at z_f>10. But, most of the DLAs show ages much younger than that of the Universe at the epoch of observation. Young galaxies thus seem to populate the high redshift Universe at z>2, suggesting relatively low redshifts of formation (z~3) for most high-redshift galaxies. The DLA star formation properties are compared with those of other high-redshift galaxies identified in deep imaging surveys with the aim of obtaining a global picture of high-redshift objects.Comment: 19 pages, 11 figures, Accepted for publication in A&

Study of mechanical effects of lumbar disc arthroplasty on facet joints at the index level/adjacent levels by using a validated finite element analysis

Introduction: Lumbar disc arthroplasty is a surgical procedure designed to treat degenerative disc disease by replacing the affected disc with a mobile prosthesis. Several types of implants fall under the term total disc replacement, such as balland-socket, mobile core or elastic prostheses. Some studies have shown that facet arthritis can develop after arthroplasty, without much precision on the mechanical impact of the different implant technologies on the facet joints. This study aims to create validated patient-specific finite element models of the intact and post-arthroplasty lumbar spine in order to compare the mechanical response of ball-and-socket and elastic prostheses. Methods: Intact models were developed from CT-scans of human lumbar spine specimens (L4-S1), and arthroplasty models were obtained by replacing the L4-L5 disc with total disc replacement implants. Pure moments were applied to reproduce physiological loadings of flexion/extension, lateral bending and axial rotation. Results: Models with ball-and-socket prosthesis showed increased values in both range of motion and pressure at the index level and lower values at the adjacent level. The mechanical behaviour of the elastic prosthesis and intact models were comparable. The dissipated friction energy in the facet joints followed a similar trend. Conclusion: Although both implants responded to the total disc replacement designation, the mechanical effects in terms of range of motion and facet joint loads varied significantly not only between prostheses but also between specimens. This confirms the interest that patient-specific surgical planning using finite element analysis could have in helping surgeons to choose the appropriate implant for each patient

Study of mechanical effects of lumbar disc arthroplasty on facet joints at the index level/adjacent levels by using a validated finite element analysis

Introduction: Lumbar disc arthroplasty is a surgical procedure designed to treat degenerative disc disease by replacing the affected disc with a mobile prosthesis. Several types of implants fall under the term total disc replacement, such as ball-and-socket, mobile core or elastic prostheses. Some studies have shown that facet arthritis can develop after arthroplasty, without much precision on the mechanical impact of the different implant technologies on the facet joints. This study aims to create validated patient-specific finite element models of the intact and post-arthroplasty lumbar spine in order to compare the mechanical response of ball-and-socket and elastic prostheses.Methods: Intact models were developed from CT-scans of human lumbar spine specimens (L4-S1), and arthroplasty models were obtained by replacing the L4-L5 disc with total disc replacement implants. Pure moments were applied to reproduce physiological loadings of flexion/extension, lateral bending and axial rotation.Results: Models with ball-and-socket prosthesis showed increased values in both range of motion and pressure at the index level and lower values at the adjacent level. The mechanical behaviour of the elastic prosthesis and intact models were comparable. The dissipated friction energy in the facet joints followed a similar trend.Conclusion: Although both implants responded to the total disc replacement designation, the mechanical effects in terms of range of motion and facet joint loads varied significantly not only between prostheses but also between specimens. This confirms the interest that patient-specific surgical planning using finite element analysis could have in helping surgeons to choose the appropriate implant for each patient

Dust depletion, chemical uniformity and environment of CaII H&K quasar absorbers

CaII 3934,3969 absorbers, which are likely to be a subset of damped Lyman alpha systems, are the most dusty quasar absorbers known, with an order of magnitude more extinction in E(B-V) than other absorption systems. There is also evidence that CaII absorbers trace galaxies with more ongoing star-formation than the average quasar absorber. Despite this, relatively little is known in detail about these unusual absorption systems. Here we present the first high resolution spectroscopic study of 19 CaII quasar absorbers, in the range 0.6=0.2A. Their general depletion patterns are similar to measurements in the warm halo phase of the Milky Way and Magellanic Clouds ISM. Dust depletions and alpha-enrichments profiles of sub-samples of 7 and 3 absorbers, respectively, are measured using a combination of Voigt profile fitting and apparent optical depth techniques. Deviations in [Cr/Zn]~0.3+-0.1dex and in [Si/Fe]>~0.8+-0.1dex are detected across the profile of one absorber, which we attribute to differential dust depletion. The remaining absorbers have <0.3dex (3sigma limit) variation in [Cr/Zn], much like the general DLA population, though the dustiest CaII absorbers remain relatively unprobed in our sample. A limit on electron densities in CaII absorbers, n_e<0.1cm^-3, is derived using the ratio of neutral and singly ionised species, assuming a MW-like radiation field. These electron densities may imply hydrogen densities sufficient for the presence of molecular hydrogen in the absorbers. The CaII absorber sample comprises a wide range of velocity widths, v_90=50-470km/s, and velocity structures, thus a range of physical models for their origin, from simple discs to galactic outflows and mergers, would be required to explain the observations.Comment: Minor revision after publication proofs to ensure arXiv version of paper matches MNRAS published versio

A new comprehensive set of elemental abundances in DLAs - II. Data analysis and chemical variation studies

We present new elemental abundance studies of seven damped Lyman-alpha systems (DLAs). Together with the four DLAs analyzed in Dessauges-Zavadsky et al. (2004), we have a sample of eleven DLA galaxies with uniquely comprehensive and homogeneous abundance measurements. These observations allow one to study the abundance patterns of 22 elements and the chemical variations in the interstellar medium of galaxies outside the Local Group. Comparing the gas-phase abundance ratios of these high redshift galaxies, we found that they show low RMS dispersions, reaching only up 2-3 times the statistical errors for the majority of elements. This uniformity is remarkable given that the quasar sightlines cross gaseous regions with HI column densities spanning over one order of magnitude and metallicities ranging from 1/55 to 1/5 solar. The gas-phase abundance patterns of interstellar medium clouds within the DLA galaxies detected along the velocity profiles show, on the other hand, a high dispersion in several abundance ratios, indicating that chemical variations seem to be more confined to individual clouds within the DLA galaxies than to integrated profiles. The analysis of the cloud-to-cloud chemical variations within seven individual DLAs reveals that five of them show statistically significant variations, higher than 0.2 dex at more than 3 sigma. The sources of these variations are both the differential dust depletion and/or ionization effects; however, no evidence for variations due to different star formation histories could be highlighted. These observations place large constraints on the mixing timescales of protogalaxies and on scenarios of galaxy formation within the CDM hierarchical theory. Finally, we provide an astrophysical determination of the oscillator strength of the NiII 1317 transition.Comment: 45 pages, 33 figures (high-resolution figures available on request from the authors or in the A&A journal). Accepted for publication in A&