Nucleosynthesis and mixing on the Asymptotic Giant Branch. III. Predicted and observed s-process abundances

We present the results of s-process nucleosynthesis calculations for AGB stars of different metallicities and initial masses. The computations were based on previously published stellar evolutionary models that account for the III dredge up phenomenon occurring late on the AGB. Neutron production is driven by the 13C(alpha,n)16O reaction during the interpulse periods in a tiny layer in radiative equilibrium at the top of the He- and C-rich shell. The s-enriched material is subsequently mixed with the envelope by the III dredge up, and the envelope composition is computed after each thermal pulse. We follow the changes in the photospheric abundance of the Ba-peak elements (heavy s, or `hs') and that of the Zr-peak ones (light s, or `ls'), whose logarithmic ratio [hs/ls] has often been adopted as an indicator of the s-process efficiency. The theoretical predictions are compared with published abundances of s elements for Galactic AGB giants of classes MS, S, SC, post-AGB supergiants, and for various classes of binary stars. The observations in general confirm the complex dependence of n captures on metallicity. They suggest that a moderate spread exists in the abundance of 13C that is burnt in different stars. Although additional observations are needed, a good understanding has been achieved of s-process operation in AGB. The detailed abundance distribution including the light elements (CNO) of a few s-enriched stars at different metallicity are examined.Comment: Accepted for ApJ, 59 pages, 19 figures, 5 table

La educación como industria del deseo. Un nuevo estilo comunicativo

Joan Ferrés i PratsGedisa editorial, 185 páginas, 2008ISBN 978-84-9784-288-4 El libro, redactado en un estilo coloquial y hasta si se quiere con facetas de humor motivacional y metafórico, presenta tres partes, Una invitación al viaje, Las rutas de la neurociencia y de la comunicación y por último, Las rutas de la innovación educativa. Ferres i Prats es Doctor en Ciencias de la información y como especialista en comunicación audiovisual y educación nos presenta el panorama de la educación en tiempos de conflicto donde confluyen la comunicación, las tecnologías y los procesos de interacción. En su apertura el mismo autor declara que es un libro de viajes porque en él se invita a compartir las experiencias de él mismo y a seguir una trayectoria singular. Desde su voz como educador reflexiona acerca de la importancia de la mirada como comunicador, ya que la educación toda está atravesada por ella. ¿cómo hacer de una clase un espacio seductor? ¿cómo llegar a los jóvenes de una generación que está inmersa en un nuevo mundo tecnológico-comunicacional? Su primer planteo nos lleva a redimensionar la figura del educador como mediador que no solo es capaz de resolver conflictos sino también –más aún-, de crearlos. Paradoja que implica ruptura, incertidumbre y hasta desasosiego. En la inclusión educativa del mundo de las nuevas tecnologías de la información y la comunicación, se abriría una puerta para recuperar el interés por el aprendizaje, ellas son también mediadoras. Sin embargo no solucionan per se los problemas de la comunicación, ni de la enseñanza, ni del aprendizaje; su eficacia tecnológica está en entredicho

An observational and numerical case study of a flash sea storm over the Gulf of Genoa

International audienceDuring the night between the 8 and 9 December 2006 the seawall of the Savona harbour (Liguria Region in north west of Italy) was overtopped by waves. In this work the "Savona flash sea storm" has been studied by analyzing the data recorded by meteo-marine observing stations and the data produced by high resolution meteo-marine numerical models. The data show that, due to the presence of a fast moving low pressure system, the event was characterized by a rapid transition and interaction between two different regimes of winds and related sea states. The results of the study suggest that the most damaging dynamics of the event could be correlated to a bi-modal structure of the wave spectrum. Based on this the authors suggest that a deeper study of the spectral structure of sea storms could lead to define new operational forecasting tools for the preventive evaluation of sea storms damaging potential

Telemedicine for cardiac surgery candidates

Background: Cardiac surgery is generally well or over-represented in many Western countries. Since the southern part of Switzerland relies on 300 km distance centers for cardiac surgery, we started a project of telemedicine for the distant evaluation of cardiac surgery candidates. We report our experience of the results of the diagnosis made by telemedicine and by direct scrutiny of coronary angiograms. Methods: Coronary angiography was performed at the distant hospital by an invasive cardiology team. Teletransmission of images was performed using three Integrated Service Digital Network (ISDN) lines by direct transmission of recent recording. A total of 98 cases were reviewed (87 aorto-coronary bypass candidates, seven valvular and four congenital heart disease). We further performed a prospective blinded comparison of 47 consecutive cases with severe coronary artery disease (CAD) with respect to localization and number of significant coronary lesions, obtained by direct scrutiny of the original angiograms and the evaluation obtained with the teletransmitted images. Results: In 89 cases of the 98 analyzed (91%) correct diagnosis and surgical approach could be established by distant transmission. In nine cases (9%, all aortocoronary bypass candidates) definitive diagnosis and treatment was feasible only by direct scrutiny of the original angiograms. Five critically ill patients were urgently referred to the surgical care center based on the correct distant diagnosis. The blinded comparison of distant diagnosis and direct scrutiny of angiograms in defining 1-2-3 vessel CAD was good: r=0.87, P≪0.01. Conclusion: Initial experience using non-sophisticated telemedical transmission of angiograms of cardiac surgery candidates seems to be a promising facility for distantly located center

Asymptotic Giant Branch models at very low metallicity

In this paper we present the evolution of a low mass model (initial mass M=1.5 Msun) with a very low metal content (Z=5x10^{-5}, equivalent to [Fe/H]=-2.44). We find that, at the beginning of the AGB phase, protons are ingested from the envelope in the underlying convective shell generated by the first fully developed thermal pulse. This peculiar phase is followed by a deep third dredge up episode, which carries to the surface the freshly synthesized 13C, 14N and 7Li. A standard TP-AGB evolution, then, follows. During the proton ingestion phase, a very high neutron density is attained and the s-process is efficiently activated. We therefore adopt a nuclear network of about 700 isotopes, linked by more than 1200 reactions, and we couple it with the physical evolution of the model. We discuss in detail the evolution of the surface chemical composition, starting from the proton ingestion up to the end of the TP-AGB phase.Comment: Accepted for Publication on PAS

The s-process branching at 185W

The neutron capture cross section of the unstable nucleus 185W has been derived from experimental photoactivation data of the inverse reaction 186W(gamma,n)185W. The new result of sigma = (687 +- 110) mbarn confirms the theoretically predicted neutron capture cross section of 185W of sigma = 700 mbarn at kT = 30 keV. A neutron density in the classical s-process of n_n = (3.8 +0.9 -0.8} * 1e8 cm-3 is derived from the new data for the 185W branching. In a stellar s-process model one finds a significant overproduction of the residual s-only nucleus 186Os.Comment: ApJ, in pres