Time series of high resolution photospheric spectra in a quiet region of the Sun. II. Analysis of the variation of physical quantities of granular structures

From the inversion of a time series of high resolution slit spectrograms obtained from the quiet sun, the spatial and temporal distribution of the thermodynamical quantities and the vertical flow velocity is derived as a function of logarithmic optical depth and geometrical height. Spatial coherence and phase shift analyzes between temperature and vertical velocity depict the height variation of these physical quantities for structures of different size. An average granular cell model is presented, showing the granule-intergranular lane stratification of temperature, vertical velocity, gas pressure and density as a function of logarithmic optical depth and geometrical height. Studies of a specific small and a specific large granular cell complement these results. A strong decay of the temperature fluctuations with increasing height together with a less efficient penetration of smaller cells is revealed. The T -T coherence at all granular scales is broken already at log tau =-1 or z~170 km. At the layers beyond, an inversion of the temperature contrast is revealed. Vertical velocities are in phase throughout the photosphere and penetrate into the highest layers under study.Comment: 13 pages, 12 figures, 1 table; Astronomy & Astrophysics, Volume 441, Issue 3, pp.1157-1169, 200

Usages d'une plate-forme de travail collaboratif par les professeurs des écoles stagiaires à l'IUFM de la Réunion

National audienceWe present a synthesis of the research carried out for four years on theuses of a platform of groupware by the primary school teacher trainees. To carry out this research, we used the higher level shared folders which allow an analysis of the traces in agreement with the Activity theory.Nous présentons une synthèse des recherches effectuées depuis quatre ans sur les usages d’une plate-forme de travail collaboratif par les professeurs des écoles stagiaires. Pour effectuer ces recherches, nous avons utilisé les dossiers partagés de plus haut niveau qui permettent une analyse des traces en accord avec la Théorie de l’activité

Usages d'une plate-forme de travail collaboratif par les professeurs des écoles stagiaires à l'IUFM de la Réunion

National audienceWe present a synthesis of the research carried out for four years on theuses of a platform of groupware by the primary school teacher trainees. To carry out this research, we used the higher level shared folders which allow an analysis of the traces in agreement with the Activity theory.Nous présentons une synthèse des recherches effectuées depuis quatre ans sur les usages d’une plate-forme de travail collaboratif par les professeurs des écoles stagiaires. Pour effectuer ces recherches, nous avons utilisé les dossiers partagés de plus haut niveau qui permettent une analyse des traces en accord avec la Théorie de l’activité

Influence of Water on Alkali-Silica Reaction: Experimental Study and Numerical Simulations

International audienceAlkali-Silica Reaction (ASR) is a concrete pathology due to chemical reactions involving reactive silica from reactive aggregates and the inner solution of concrete. Main effects are swelling, cracking and the reduction in the mechanical properties of affected concretes. Water is very important for ASR, the more available water the more expansion and degradation. This article presents new laws for the modelling of the influence of water upon ASR. They are based on experimental results and then used to simulate results taken out of scientific literature

Observational survey of the puzzling star HD 179821: Photometric variations and period analysis

From new photometric observations (UBVRI), we present the characteristic features of the light variations of the evolved star HD 179821 (= SAO 124414 = IRAS 19114+0002). Our data, collected through 1999 and 2000, have been combined together with previous photometric measurements available in the literature. Thus, a long term V-light curve (gathering more than 10 years of observations for HD 179821) has been composed. We have analysed it with the Fourier transform method. Two main frequencies are present in the resulting power spectrum, reflecting a dominant bimodal pulsator behavior. A long term phenomenon is also found, but it is not possible to decide whether it is periodic. The Fourier analysis has also been applied on two other filters (U and B) and confirms the detected frequencies. On the basis of our period analysis, we discuss the nature of HD 179821: low-mass post-AGB star or high-mass star