The composition of the protosolar disk and the formation conditions for comets

Conditions in the protosolar nebula have left their mark in the composition of cometary volatiles, thought to be some of the most pristine material in the solar system. Cometary compositions represent the end point of processing that began in the parent molecular cloud core and continued through the collapse of that core to form the protosun and the solar nebula, and finally during the evolution of the solar nebula itself as the cometary bodies were accreting. Disentangling the effects of the various epochs on the final composition of a comet is complicated. But comets are not the only source of information about the solar nebula. Protostellar disks around young stars similar to the protosun provide a way of investigating the evolution of disks similar to the solar nebula while they are in the process of evolving to form their own solar systems. In this way we can learn about the physical and chemical conditions under which comets formed, and about the types of dynamical processing that shaped the solar system we see today. This paper summarizes some recent contributions to our understanding of both cometary volatiles and the composition, structure and evolution of protostellar disks.Comment: To appear in Space Science Reviews. The final publication is available at Springer via http://dx.doi.org/10.1007/s11214-015-0167-

Public responses to CO2 storage sites: Lessons from five European cases

Studies of the factors involved in public perceptions of CO2 storage projects reveal a level of complexity and diversity that arguably confounds a comprehensive theoretical account. To some extent, a conceptual approach that simply organises the relevant social scientific knowledge thematically, rather than seeking an integrated explanation, is as useful as any single account that fails to do justice to the contingencies involved. This paper reviews and assembles such knowledge in terms of six themes and applies these themes to five European cases of carbon capture and storage (CCS) implementation. We identify the main factors involved in community responses to CCS as relating to: the characteristics of the project; the engagement process; risk perceptions; the actions of the stakeholders; the characteristics of the community, and the socio-political context

On the origin and evolution of the material in 67P/Churyumov-Gerasimenko

International audiencePrimitive objects like comets hold important information on the material that formed our solar system. Several comets have been visited by spacecraft and many more have been observed through Earth- and space-based telescopes. Still our understanding remains limited. Molecular abundances in comets have been shown to be similar to interstellar ices and thus indicate that common processes and conditions were involved in their formation. The samples returned by the Stardust mission to comet Wild 2 showed that the bulk refractory material was processed by high temperatures in the vicinity of the early sun. The recent Rosetta mission acquired a wealth of new data on the composition of comet 67P/Churyumov-Gerasimenko (hereafter 67P/C-G) and complemented earlier observations of other comets. The isotopic, elemental, and molecular abundances of the volatile, semi-volatile, and refractory phases brought many new insights into the origin and processing of the incorporated material. The emerging picture after Rosetta is that at least part of the volatile material was formed before the solar system and that cometary nuclei agglomerated over a wide range of heliocentric distances, different from where they are found today. Deviations from bulk solar system abundances indicate that the material was not fully homogenized at the location of comet formation, despite the radial mixing implied by the Stardust results. Post-formation evolution of the material might play an important role, which further complicates the picture. This paper discusses these major findings of the Rosetta mission with respect to the origin of the material and puts them in the context of what we know from other comets and solar system objects

Characteristic features of plasma electrolytic treated layers in Na3PO4 solution

Plasma electrolytic oxidation (PEO) treatment of Ti6Al4V (Ti) using various concentrations of Na3PO4 (NAP) has been carried out. Based on the PEO process, characteristics of the treated layers, such as structure, chemical composition, phases, roughness, hardness and porosity level were investigated. Irregular micro-channel spots were found on all treated surfaces. Larger pores were more evident on the PEO treated with NAP-7.5 g/L, and are considered to be related to the high intensity of micro-arc discharges on Ti surface. XRD analyses revealed that the surfaces of treated layers are composed of Ti, TiO6 and anatase. The Profilometry test depicted that the surface roughness of PEO treated layers is significantly higher than bare Ti. The thickness and hardness of PEO-treated layers increased with increasing NAP concentration and found to be highest with sample processed with NAP-10 g/L. Among all the NAP concentration used, 5 g/L showed the least level of porosity. Reflection on the results portends that the PEO treated with 10 g/L concentrations could serve a potential candidate for clinical purposes

Digitalización del Control de Materiales del Taller de Mantenimiento : informe final

Sol·licitant de l’informe: Tractament i Selecció de Residus, S.A. (TERSA