Élaboration et caractérisation des sources solides de diffusion sur silicium par la méthode sol-gel pour la réalisation de l’émetteur d’une cellule solaire

La réalisation de l„émetteur d„une cellule solaire au silicium est une étape très importante et critique dans le procédé de fabrication des photopiles en silicium. En effet, la concentration en surface du phosphore ou du bore et la profondeur de la jonction déterminent le rendement de conversion photovoltaïque des cellules solaires au silicium. Plusieurs techniques sont utilisées pour la réalisation des émetteurs n+p et n+pp+ parmi lesquelles la diffusion en phase vapeur, l„implantation ionique et la diffusion à partir de sources solides. Ce travail sera consacré à la réalisation d„émetteurs par diffusion de sources solides que nous avons élaboré par la méthode sol gel associé au spin coating sur silicium polix monocristallins et polycristallins. Les solutions de dopage ont été préparées par la méthode  sol gel en utilisant le methyltriethoxysilane « MTEOS » ou le tétraethoxysilane « TEOS » et l„acide phosphorique H4PO3 comme précurseurs par émulsion d„acide phosphorique dans l„isopropanol pour la jonction n+, et l‟acide borique H3BO3 ou l‟aluminium pour la jonction p+. Cette expérience nous a permis d‟étudier les propriétés électriques des émetteurs n+p et n+pp+ par la méthode des quatre pointes, les résultats des mesures effectuées ont montré des valeurs de la résistance carrée R comparables aux résultats de la littérature et confirme la diffusion du phosphore et du bore à partir des sources solides de diffusion préparées par sol gel.Mots-clés : réalisation d‟émetteurs, sources dopantes solides, sol-gel, diffusion phosphore ou bore

Equation of state SAHA-S meets stellar evolution code CESAM2k

We present an example of an interpolation code of the SAHA-S equation of state that has been adapted for use in the stellar evolution code CESAM2k. The aim is to provide the necessary data and numerical procedures for its implementation in a stellar code. A technical problem is the discrepancy between the sets of thermodynamic quantities provided by the SAHA-S equation of state and those necessary in the CESAM2k computations. Moreover, the independent variables in a practical equation of state (like SAHA-S) are temperature and density, whereas for modelling calculations the variables temperature and pressure are preferable. Specifically for the CESAM2k code, some additional quantities and their derivatives must be provided. To provide the bridge between the equation of state and stellar modelling, we prepare auxiliary tables of the quantities that are demanded in CESAM2k. Then we use cubic spline interpolation to provide both smoothness and a good approximation of the necessary derivatives. Using the B-form of spline representation provides us with an efficient algorithm for three-dimensional interpolation. The table of B-spline coefficients provided can be directly used during stellar model calculations together with the module of cubic spline interpolation. This implementation of the SAHA-S equation of state in the CESAM2k stellar structure and evolution code has been tested on a solar model evolved to the present. A comparison with other equations of state is briefly discussed. The choice of a regular net of mesh points for specific primary quantities in the SAHA-S equation of state, together with accurate and consistently smooth tabulated values, provides an effective algorithm of interpolation in modelling calculations. The proposed module of interpolation procedures can be easily adopted in other evolution codes.Comment: 8 pages, 5 figure

A toolkit of mechanism and context independent widgets

Most human-computer interfaces are designed to run on a static platform (e.g. a workstation with a monitor) in a static environment (e.g. an office). However, with mobile devices becoming ubiquitous and capable of running applications similar to those found on static devices, it is no longer valid to design static interfaces. This paper describes a user-interface architecture which allows interactors to be flexible about the way they are presented. This flexibility is defined by the different input and output mechanisms used. An interactor may use different mechanisms depending upon their suitability in the current context, user preference and the resources available for presentation using that mechanism

Th Ages for Metal-Poor Stars

With a sample of 22 metal-poor stars, we demonstrate that the heavy element abundance pattern (Z > 55) is the same as the r-process contributions to the solar nebula. This bolsters the results of previous studies that there is a universal r-process production pattern. We use the abundance of thorium in five metal-poor stars, along with an estimate of the initial Th abundance based on the abundances of stable r-process elements, to measure their ages. We have four field red giants with errors of 4.2 Gyr in their ages and one M92 giant with an error of 5.6 Gyr, based on considering the sources of observational error only. We obtain an average age of 11.4 Gyr, which depends critically on the assumption of an initial production ratio of Th/Eu of 0.496. If the Universe is 15 Gyr old, then the initial Th/Eu value should be 0.590, in agreement with some theoretical models of the r-process.Comment: 26 pages, to be published in Ap

The Carina dSph galaxy: where is the edge?

Recent cosmological N-body simulations suggest that current empirical estimates of tidal radii in dSphs might be underestimated by at least one order of magnitude. To constrain the plausibility of this theoretical framework, we undertook a multiband (U,B,V,I) survey of the Carina dSph. Deep B,V data of several fields located at radial distances from the Carina center ranging from 0.5 to 4.5 degrees show a sizable sample of faint blue objects with the same magnitudes and colors of old, Turn-Off stars detected across the center. We found that the (U-V,B-I) color-color plane is a robust diagnostic to split stars from background galaxies. Unfortunately, current U,I-band data are too shallow to firmly constrain the real extent of Carina.Comment: To be published on the proceedings of the XLIX meeting of the Italian Astronomical Society. Requires mem.cl

On the fine structure of the Cepheid metallicity gradient in the Galactic thin disk

We present homogeneous and accurate iron abundances for 42 Galactic Cepheids based on high-spectral resolution (R~38,000) high signal-to-noise ratio (SNR>100) optical spectra collected with UVES at VLT (128 spectra). The above abundances were complemented with high-quality iron abundances provided either by our group (86) or available in the literature. We paid attention in deriving a common metallicity scale and ended up with a sample of 450 Cepheids. We also estimated for the entire sample accurate individual distances by using homogeneous near-infrared photometry and the reddening free Period-Wesenheit relations. The new metallicity gradient is linear over a broad range of Galactocentric distances (Rg~5-19 kpc) and agrees quite well with similar estimates available in the literature (-0.060+/-0.002 dex/kpc). We also uncover evidence which suggests that the residuals of the metallicity gradient are tightly correlated with candidate Cepheid Groups (CGs). The candidate CGs have been identified as spatial overdensities of Cepheids located across the thin disk. They account for a significant fraction of the residual fluctuations, and in turn for the large intrinsic dispersion of the metallicity gradient. We performed a detailed comparison with metallicity gradients based on different tracers: OB stars and open clusters. We found very similar metallicity gradients for ages younger than 3 Gyrs, while for older ages we found a shallower slope and an increase in the intrinsic spread. The above findings rely on homogeneous age, metallicity and distance scales. Finally we found, by using a large sample of Galactic and Magellanic Cepheids for which are available accurate iron abundances, that the dependence of the luminosity amplitude on metallicity is vanishing.Comment: Accepted in A&A, 11 figures, 7 table

Return to sport and re-tears after anterior cruciate ligament reconstruction in children and adolescents

BACKGROUND: The primary objective of this study was to determine the time to and level of return to sports after anterior cruciate ligament (ACL) reconstruction in children and adolescents. The secondary objectives were to evaluate the risk of early ACL re-tear after return to sports and the risk of ACL tear in the contralateral knee. HYPOTHESIS: The time to return to sports in young patients is considerably longer than in adults. METHODS: A prospective multicentre study was conducted at 12 centres specialised in knee ligament surgery, in children and adolescents younger than 18 years, between 1 January 2015 and 31 October 2015. The patients were divided into a paediatric group with open physes and a skeletally mature group with closed physes. We recorded the time to return to sport, the type of sport resumed, and the occurrence of early re-tears on the same side. A poor outcome was defined as a re-tear or an objective IKDC score of C or D. A contralateral ACL tear was not considered a poor outcome. RESULTS: Of 278 included patients, 100 had open physes and 178 closed physes. In the open physes group, return to running occurred after 10.4±4.7 months, return to pivoting/contact sport training after 13.1±3.9 months, and return to pivoting/contact sport competitions after 13.8±3.8 months. Of the 100 patients, 80% returned to the same sport and 63.5% to pivoting/contact sport competitions. Re-tears occurred in 9% of patients, after 11.8±4.1 months, and contralateral tears in 6% of patients, after 17.2±4.4 months. In all, 19.4% of patients had a poor outcome, including 10.4% with an IKDC score of C or D and 9% with re-tears. In the group with closed physes, return to running occurred after 8.8±5.1 months, return to pivoting/contact sport training after 11.7±4.7 months, and return to pivoting/contact sport competitions after 12.3±4.2 months. Of the 178 patients, 76.9% returned to the same sport and 55.6% to pivoting/contact sport competitions. The re-tear rate was only 2.8% and the contralateral tear rate 5%. In all, 14.7% of patients had poor outcome, including 11.9% with an IKDC score of C or D and 2.8% with re-tears. No risk factors for re-tears were identified; the quadruple-bundle semitendinosus technique showed a non-significant association with re-tears. CONCLUSION: In young children, the return to sport time after ACL reconstruction is considerably longer than 1 year and the return to competitions occurs later and is more difficult. The results of this study indicate that reservations are in order when informing the family about return to sports prospects after ACL reconstruction. The return to pivoting/contact sport competitions should not be allowed until 14 months after surgery in young skeletally immature patients, and the risk of re-injury is high within the first 2 years. LEVEL OF EVIDENCE: IV, retrospective study

s-Process Nucleosynthesis in Carbon Stars

We present the first detailed and homogeneous analysis of the s-element content in Galactic carbon stars of N-type. Abundances of Sr,Y, Zr (low-mass s-elements, or ls) and of Ba, La, Nd, Sm and Ce (high-mass s-elements, hs) are derived using the spectral synthesis technique from high-resolution spectra. The N-stars analyzed are of nearly solar metallicity and show moderate s-element enhancements, similar to those found in S stars, but smaller than those found in the only previous similar study (Utsumi 1985), and also smaller than those found in supergiant post-AGB stars. This is in agreement with the present understanding of the envelope s-element enrichment in giant stars, which is increasing along the spectral sequence M-->MS-->S-->SC-->C during the AGB phase. We compare the observational data with recent $s$-process nucleosynthesis models for different metallicities and stellar masses. Good agreement is obtained between low mass AGB star models (M < 3 M_o) and s-elements observations. In low mass AGB stars, the 13C(alpha, n)16O reaction is the main source of neutrons for the s-process; a moderate spread, however, must exist in the abundance of 13C that is burnt in different stars. By combining information deriving from the detection of Tc, the infrared colours and the theoretical relations between stellar mass, metallicity and the final C/O ratio, we conclude that most (or maybe all) of the N-stars studied in this work are intrinsic, thermally-pulsing AGB stars; their abundances are the consequence of the operation of third dredge-up and are not to be ascribed to mass transfer in binary systems.Comment: 31 pages, 10 figures, 6 tables. Accepted in Ap

The Kr85 s-process Branching and the Mass of Carbon Stars

We present new spectroscopic observations for a sample of C(N)-type red giants. These objects belong to the class of Asymptotic Giant Branch stars, experiencing thermal instabilities in the He-burning shell (thermal pulses). Mixing episodes called third dredge-up enrich the photosphere with newly synthesized C12 in the He-rich zone, and this is the source of the high observed ratio between carbon and oxygen (C/O > 1 by number). Our spectroscopic abundance estimates confirm that, in agreement with the general understanding of the late evolutionary stages of low and intermediate mass stars, carbon enrichment is accompanied by the appearance of s-process elements in the photosphere. We discuss the details of the observations and of the derived abundances, focusing in particular on rubidium, a neutron-density sensitive element, and on the s-elements Sr, Y and Zr belonging to the first s-peak. The critical reaction branching at Kr85, which determines the relative enrichment of the studied species, is discussed. Subsequently, we compare our data with recent models for s-processing in Thermally Pulsing Asymptotic Giant Branch stars, at metallicities relevant for our sample. A remarkable agreement between model predictions and observations is found. Thanks to the different neutron density prevailing in low and intermediate mass stars, comparison with the models allows us to conclude that most C(N) stars are of low mass (M < 3Mo). We also analyze the C12/C13 ratios measured, showing that most of them cannot be explained by canonical stellar models. We discuss how this fact would require the operation of an ad hoc additional mixing, currently called Cool Bottom Process, operating only in low mass stars during the first ascent of the red giant branch and, perhaps, also during the asymptotic giant branch.Comment: 54 pages + 6 figures + 6 tables. ApJ accepte