University of Rennes

About: University of Rennes is a education organization based out in Rennes, France. It is known for research contribution in the topics: Population & Catalysis. The organization has 18404 authors who have published 40374 publications receiving 995327 citations.

Symmetry breaking and structural changes at the neutral-to-ionic transition in tetrathiafulvalene-p-chloranil.

Abstract: The structural aspect of the temperature-induced neutral-to-ionic transition in the mixed-stack charge-transfer complex TTF-p-chloranil is directly analyzed using results obtained from neutron-scattering experiments. The symmetry breaking of the structural order parameter is determined together with the complete structural change. It is shown that the ionic phase is characterized by a dimerization along the stacking direction into weakly bond donor-acceptor dimers, which adopt a ferroelectric arrangement. Values of both dipole moment and dipolar energy in the unit cell are evaluated and commented. The evolution of the three-dimensional contacts which interconnect the chains, and in particular of the hydrogen interaction network, is discussed. Moreover, the associated intramolecular deformations are related in a satisfying way with the change of the ionicity and with the loss of centrosymmetry at the transition. Phenomena of metastability are also briefly discussed.

Progressive crustal contamination of the Bushveld Complex: evidence from Nd isotopic analyses of the cumulate rocks

Abstract: We report the first Nd isotopic data on the cumulate rocks of the Bushveld Complex, South Africa. We analysed 17 whole-rock samples covering 4700 m of stratigraphy through the Lower, Critical and Main Zones of the intrusion at Union Section, north-western Bushveld Complex. The basal ultramafic portions of the complex have markedly higher ɛNd(T) (−5.3 to −6.0) than the gabbronoritic Main Zone (ɛNd(T) −6.4 to −7.9). The rocks of the Upper Critical Zone have intermediate values. These results are in agreement with new Nd isotope data on marginal rocks and sills in the floor of the complex that are generally interpreted as representing chilled parental magmas, and with published Sr isotopic data, all of which show a larger crustal component in the upper part of the intrusion. In contrast, the concentrations of many highly incompatible trace elements are decoupled from the isotopic signatures. The basal portions of the complex have higher ratios of incompatible to compatible trace elements than the upper portions. The variations of isotopic and trace-element compositions are interpreted in terms of a change in the nature of the crustal material that contaminated Bushveld magmas. Those magmas that fed into the lower part of the complex had assimilated a relatively small amount of incompatible trace-element-rich partial melt of upper crust, whereas magmas parental to the upper part of the complex had assimilated a higher proportion of the incompatible trace-element-poor residue of partial melting.

A Markov Decision Process-based service migration procedure for follow me cloud

Abstract: The Follow-Me Cloud (FMC) concept enables service mobility across federated data centers (DCs). Following the mobility of a mobile user, the service located in a given DC is migrated each time an optimal DC is detected. The detailed criterion for optimality is defined by operator policy, but it may be typically derived from geographical proximity or load. Service migration may be an expensive operation given the incurred cost in terms of signaling messages and data transferred between DCs. Decision on service migration defines therefore a tradeoff between cost and user perceived quality. In this paper, we address this tradeoff by modeling the service migration procedure using a Markov Decision Process (MDP). The aim is to formulate a decision policy that determines whether to migrate a service or not when the concerned User Equipment (UE) is at a certain distance from the source DC. We numerically formulate the decision policies and compare the proposed approach against the baseline counterpart.