Un élément fini de poutre fissurée application à la dynamique des arbres tournants

International audienceDans ce travail on présente une méthode originale de construction d'un élément fini de poutre affectée de fissurations. La souplesse additionnelle due à la présence des fissures est identifiée à partir de calculs éléments finis tridimensionnels tenant compte des conditions de contact unilatéral entre les lèvres. Cette souplesse est répartie sur toute la longueur de l'élément dont on se propose de construire la matrice de rigidité. La démarche permet un gain considérable en temps de calcul par rapport à la représentation nodale de la section fissurée lors de l'intégration temporelle de systèmes différentiels en dynamique des structures

The Corinth Rift Laboratory, Greece (CRL): A Multidisciplinary Near Fault Observatory (NFO) on a Fast Rifting System

The western rift of Corinth (Greece) is one of the most active tectonic structures of the euro-mediterranean area. Its NS opening rate is 1.5 cm/yr ( strain rate of 10-6/yr) results into a high microseismicity level and a few destructive, M>6 earthquakes per century, activating a system of mostly north dipping normal faults. Since 2001, monitoring arrays of the European Corinth Rift Laboratory (CRL, www.crlab.eu) allowed to better track the mechanical processes at work, with short period and broad band seismometers, cGPS, borehole strainmeters, EM stations, …). The recent (300 kyr) tectonic history has been revealed by onland (uplifted fan deltas and terraces) and offshore geological studies (mapping, shallow seismic, coring), showing a fast evolution of the normal fault system. The microseismicity, dominated by swarms lasting from days to months, mostly clusters in a layer 1 to 3 km thick, between 6 and 9 km in depth, dipping towards north, on which most faults are rooting. The diffusion of the microseismicity suggests its triggering by pore pressure transients, with no or barely detected strain. Despite a large proportion of multiplets, true repeaters seem seldom, suggesting a minor contribution of creep in their triggering, although transient or steady creep is clearly detected on the shallow part of some majors faults. The microseismic layer may thus be an immature, downward growing detachment, and the dominant rifting mechanism might be a mode I, anelastic strain beneath the rift axis , for which a mechanical model is under development. Paleoseismological (trenching, paleoshorelines, turbidites), archeological and historical studies completed the catalogues of instrumental seismicity, motivating attempts of time dependent hazard assessment. The Near Fault Observatory of CRL is thus a multidisciplinary research infrastructure aiming at a better understanding and modeling of multiscale, coupled seismic/aseismic processes on fault systems.Grant for Researchers (CC) ID 188753

Volatile and nonvolatile chemical composition of some date fruits (Phoenix dactylifera L.) harvested at different stages of maturity

Physico-chemical and aroma volatile compositions of three date palm cultivars were studied throughout fruit maturation (besser, rutab and tamr stages) during 2008 harvest season. The studied parameters varied significantly through the different stages, with some variations also depending on the cultivar. Length and width of the three types of dates showed a progressive decrease during ripening. The pH level, total sugars and ash contents significantly increased up to tamr stage. Conversely, moisture, lipid and protein contents decreased. The profile of the volatile aroma compounds was evaluated using solid-phase micro-extraction. Sixty-nine compounds were detected during maturation, accounting from 98.5% to 99.6% at besser, 93.1% to 99.2% at rutab and 94.3% to 98.4% at tamr stages of the total identified volatiles. The present study sheds more light on chemical characteristics of the studied cultivars that can be used in many industrial processe

Chemical and aroma volatile compositions of date palm (Phoenix dactylifera L.) fruits at three maturation stages

The effect of maturity stage on the physicochemical composition and volatile components of date palm fruits (Phoenix dactylifera L.) was investigated at three different stages. Total sugars, pH, proteins and ash increased up to the full-ripe stage of all date types. On the contrary, weight, moisture and total lipids decreased across the same period. Pearson’s test established significant differences (p < 0.05) between the different cultivars at each stage for all the parameters. Furthermore, multivariate tests show that the composition and the variation of the chemical compositions mainly depended on the cultivar kind. Eighty volatile compounds were identified during the maturation stages, 43 of them were newly identified in Tunisian date fruits. The profiles of volatile compounds seem to be similar for Degla and Horra varieties. Results from this work revealed essential information about the richness of littoral cultivars in many nutrients and the possibility of their uses as a functional food ingredien