Identification of the Coronal Sources of the Fast Solar Wind

The present spectroscopic study of the ultraviolet coronal emission in a polar hole, detected on April 6-9, 1996 with the Ultraviolet Coronagraph Spectrometer aboard the SOHO spacecraft, identifies the inter-plume lanes and background coronal hole regions as the channels where the fast solar wind is preferentially accelerated. In inter-plume lanes, at heliocentric distance 1.7 \rsun, the corona expands at a rate between 105 km/s and 150 km/s, that is, much faster than in plumes where the outflow velocity is between 0 km/s and 65 km/s. The wind velocity is inferred from the Doppler dimming of the O VI $\lambda\lambda$ 1032, 1037 \AA lines, within a range of values, whose lower and upper limit corresponds to anisotropic and isotropic velocity distribution of the oxygen coronal ions, respectively.Comment: 14 pages, 4 figures, 3 tables, Accepted by ApJ Letter

Il monitoraggio delle aree archeologiche per l'ottimizzazione del progetto delle coperture

The aim to keep the original architectures and decoration in their excavation site, that has been emerging in the last years, requires to protect them by temporary or definitive shelters. Soprintendenza per i Beni Archeologici of Cagliari and Oristano promoted and started monitoring four shelters already existing on the archaeological areas of these provinces, with the aim to check the effectiveness in the local environment, and to plan their improvement or/and new structures. Politecnico di Milano collaborated at the research by monitoring the environment and remains conditions, especially underneath the shelters, modelling the effects of the existing shelters and planning new solutions. In San Cromazio (Villaspeciosa), monitoring the new definitive shelter allowed the researchers to discover the critical points and to find out their improvement. In Su Monte (Sorradile), monitoring allowed the researchers to define the expected performances of the new shelter. In San Saturnino (Cagliari) monitoring and numerical analysis was applied to 2D and 3D models for improving the ventilation of the volume underneath the new shelter. In Nora (Pula) the results of monitoring and the innovative approach of design served to check the performances of the present temporary shelters. Nora approach shows how to overcome the limits of current protective systems, combining the requirements for preservation with new issues as feasibility of technical textiles, low maintenance and easy deconstruction to allow the reuse and adaptability of shelters in different locations and seasons. The ultimate goal was to renovate the design process by covering archaeological sites in a more environmentally conscious way and without the least destruction of the site

On wind-wave interaction phenomena at low Reynolds numbers

After decades of research efforts, wind-wave interaction mechanisms have been recognized as extremely elusive. The reason is the complex nature of the problem, which combines complex coupling mechanisms between turbulent wind and water waves with the presence of multiple governing parameters, such as the friction Reynolds number of the wind, the water depth and the wind fetch. As shown unequivocally here, the use of suitable flow settings allows us to reduce the complex problem of wind-wave interaction to its essential features, mainly as a function of the sole friction Reynolds number of the wind. The resulting numerical solution allows us to study the interactions between water and air layers with their own fluid properties, and to unveil very interesting features, such as an oblique wave pattern travelling upstream and a wave-induced Stokes sublayer. The latter is responsible for a drag reduction mechanism in the turbulent wind. Despite the simulated flow conditions being far from the intense events occurring at the ocean-atmosphere interface, the basic flow phenomena unveiled here may explain some experimental evidence in wind-wave problems. Among other things, the wave-induced Stokes sublayer may shed light on the large scatter of the drag coefficient data in field measurements where swell waves of arbitrary directions are often present. Hence the present results and the developed approach pave the way for the understanding and modelling of the surface fluxes at the ocean-atmosphere interface, which are of overwhelming importance for climate science

On the role of alternatives in the acquisition of simple and complex disjunctions in French and Japanese

International audienc

Metal micro drilling combining high power femtosecond laser and trepanning head

Trepanning heads are well known to be efficient in high aspect drilling and to provide a precise control of the hole geometry. Secondly, femtosecond lasers enable to minimize the heat effects and the recast layer on sidewalls but are typically used on thin sheet. The combination of both present a high potential for industrial applications such as injector or cooling holes where the bore sidewall topology has a major influence on the dynamics of the gas flow. In this paper we present results using this combination. The effect of pulse energy, repetition rate and revolution speed of the head on both geometry and roughness are discussed. The quality of the sidewall is checked by roughness measurement and by metallographic analysis (SEM; chemical etching, micro hardness)

LESSON LEARNED ON MONITORING CULTURAL HERITAGE AT RISK UNDER CLIMATE CHANGES: STRATEGY, TECHNIQUES AND RESULTS

Rising damp is a recurrent cause of damage, and the climatic changes are going towards the increase of humidity (quantity and spreading distribution) in the historic masonry: at 40/50° latitudes, at continental/Mediterranean climatic conditions, the alternance of dry seasons and almost monsoon seasons dramatically affects the distribution of rising damp in porous materials, as well as the water content. Monitoring the presence and distribution of the water is useful to support the choice of the most appropriate intervention, reducing the risk to apply not effective and expensive products and preventing an oversize intervention.The evaluation of the increase of rising damp is a critical issue for preventing the damages, because the presence of the water can sharply, naturally decrease in the dry seasons, as well as rapidly increases one month or more after the beginning of heavy and constant rain.The study cases will show the interaction between climate changes and the inadequacy of the present plant for collecting and drain rain in archaeological areas and historic buildings and as well as the nearby infrastructures that should prevent stagnant rain close to the bottom of the masonry.</p

Comparing extrapolations of the coronal magnetic field structure at 2.5 solar radii with multi-viewpoint coronagraphic observations

The magnetic field shapes the structure of the solar corona but we still know little about the interrelationships between the coronal magnetic field configurations and the resulting quasi-stationary structures observed in coronagraphic images (as streamers, plumes, coronal holes). One way to obtain information on the large-scale structure of the coronal magnetic field is to extrapolate it from photospheric data and compare the results with coronagraphic images. Our aim is to verify if this comparison can be a fast method to check systematically the reliability of the many methods available to reconstruct the coronal magnetic field. Coronal fields are usually extrapolated from photospheric measurements typically in a region close to the central meridian on the solar disk and then compared with coronagraphic images at the limbs, acquired at least 7 days before or after to account for solar rotation, implicitly assuming that no significant changes occurred in the corona during that period. In this work, we combine images from three coronagraphs (SOHO/LASCO-C2 and the two STEREO/SECCHI-COR1) observing the Sun from different viewing angles to build Carrington maps covering the entire corona to reduce the effect of temporal evolution to ~ 5 days. We then compare the position of the observed streamers in these Carrington maps with that of the neutral lines obtained from four different magnetic field extrapolations, to evaluate the performances of the latter in the solar corona. Our results show that the location of coronal streamers can provide important indications to discriminate between different magnetic field extrapolations.Comment: Accepted by A&A the 20th of May, 201

Influence of Neutron Enrichment on Disintegration Modes of Compound Nuclei

Cross sections, kinetic energy and angular distributions of fragments with charge 6$\le$Z$\le$28 emitted in 78,82Kr+40C at 5.5 MeV/A reactions were measured at the GANIL facility using the INDRA apparatus. This experiment aims to investigate the influence of the neutron enrichment on the decay mechanism of excited nuclei. Data are discussed in comparison with predictions of transition state and Hauser-Feshbach models.Comment: 8 pages, 1 figure, paper presented at the First Workshop on "State of the Art in Nuclear Cluster Physics" 13-16 May, 2008, at Strasbourg, France (SOTANCP2008) and accepted for publication at International Journal of Modern Physics E (Special Issue), Proceedings of SOTANCP2008 (to be published