Meteorite cloudy zone formation as a quantitative indicator of paleomagnetic field intensities and cooling rates on planetesimals

Metallic microstructures in slowly-cooled iron-rich meteorites reflect the thermal and magnetic histories of their parent planetesimals. Of particular interest is the cloudy zone, a nanoscale intergrowth of Ni-rich islands within a Ni-poor matrix that forms below 350{\deg}C by spinodal decomposition. The sizes of the islands have long been recognized as reflecting the low-temperature cooling rates of meteorite parent bodies. However, a model capable of providing quantitative cooling rate estimates from island sizes has been lacking. Moreover, these islands are also capable of preserving a record of the ambient magnetic field as they grew, but some of the key physical parameters required for recovering reliable paleointensity estimates from magnetic measurements of these islands have been poorly constrained. To address both of these issues, we present a numerical model of the structural and compositional evolution of the cloudy zone as a function of cooling rate and local composition. Our model produces island sizes that are consistent with present-day measured sizes. This model enables a substantial improvement in the calibration of paleointensity estimates and associated uncertainties. In particular, we can now accurately quantify the statistical uncertainty associated with the finite number of islands and the uncertainty on their size at the time of the record. We use this new understanding to revisit paleointensities from previous pioneering paleomagnetic studies of cloudy zones. We show that these could have been overestimated but nevertheless still require substantial magnetic fields to have been present on their parent bodies. Our model also allows us to estimate absolute cooling rates for meteorites that cooled slower than 10000{\deg}C My-1. We demonstrate how these cooling rate estimates can uniquely constrain the low-temperature thermal history of meteorite parent bodies.Comment: Manuscript resubmitted after revision

La gestion sociétalement responsable est-elle en cours d’intégration dans les Scop ?

International audienc

Les Scop et l’intégration des dimensions de la performance : étude du cas MATELOC

Cette recherche a pour objet d’approfondir le concept de performance globale, dans le contexte des SCOP, afin de mettre en évidence le caractère spécifique ou non de la notion de performance pour une structure coopérative. Dans cette optique, il s’agira d’observer et d’identifier les pratiques et outils de gestion - spécifiques ou non - dédiés à ce type particulier d’entreprises du champ de l’Economie Sociale et Solidaire, par l’intermédiaire de la méthode des cas. En l’occurrence, la société coopérative MATELOC, prestataire de service pour les entreprises du Bâtiment, des Travaux Publics et de l\u27Industrie - domaine d’activité statistiquement prépondérant pour les SCOP - servira de socle à notre étude. Au travers de ce cas exemplaire, nous montrons que la performance globale n’est pas totalement intégrée puisque les dimensions économique et sociale sont pilotées ensemble, mais la dimension environnementale vient ponctuellement en complément

Les comportements en matière de RSE des sociétés coopératives : homogénéité discursive et hétérogénéité des pratiques

CSR behaviors of cooperative companies: a discursive homogeneity and heterogeneity of practicesThis research aims to improve knowledge on CSR and the CSR behaviors, specifically in cooperative enterprises (Scop, in French). By studying five Scop, the research shows a relative discourse homogeneity in terms of CSR but heterogeneous practices. Thus, the results lead us to identify the main characteristics of CSR behaviors for a Scop and suggest the importance of management support al along the process and the membership in the cooperatives enterprises network as positives factors that aim the CSR commitment

Competitiveness indices: interpretation and limits

Some competitiveness indices and the rankings of countries according to these indices are widely publicized. We discuss here how they should be interpreted and their empirical robustness, focusing on the indices published by the World Economic Forum (WEF). These indices suffer from several weaknesses. First, their theoretical basis is approximate. Second, they rest on many a priori assumptions regarding growth and competitiveness factors, which may be not empirically founded. Lastly, measurement of these factors is based on questionable indicators. Such weaknesses may lead to fragile indices and rankings. This is confirmed by an empirical analysis of the building of the main index (GCI) published by the WEF. We thus attempt to reproduce WEF's construction, on a more rigorous statistical basis. Starting from the same elementary indicators as the WEF's 2001 GCI index, we aggregate them with weights chosen to maximize the correlation between the aggregate index and GDP per capita growth for the retained countries, which is the supposed aim of the GCI index. The rankings we obtain differ, sometimes considerably, from WEF's rankings, although all the considered indices are similarly correlated with GDP per capita growth. The new indices do not however pretend to replace WEF's ones. They have obviously the same limits in terms of robustness, notably a weak capacity to account precisely for between countries growth discrepancies.