Explanations and Proof Trees

This paper proposes a model for explanations in a set theoretical framework using the notions of closure or fixpoint. In this approach, sets of rules associated with monotonic operators allow to define proof trees. The proof trees may be considered as a declarative view of the trace of a computation. We claim they are explanations of the results of a computation. This notion of explanation is applied to constraint logic programming, and it is used for declarative error diagnosis. It is also applied to constraint programming, and used for constraint retraction

In-plane remote photoluminescence excitation of carbon nanotube by propagating surface plasmon

In this work, we demonstrate propagating surface plasmon polariton (SPP) coupled photoluminescence (PL) excitation of single-walled carbon nanotube (SWNT). SPPs were launched at a few micrometers from individually marked SWNT, and plasmon-coupled PL was recorded to determine the efficiency of this remote in-plane addressing scheme. The efficiency depends upon the following factors: (i) longitudinal and transverse distances between the SPP launching site and the location of the SWNT and (ii) orientation of the SWNT with respect to the plasmon propagation wave vector (k SPP). Our experiment explores the possible integration of carbon nanotubes as a plasmon sensor in plasmonic and nanophotonic devices

Analysis and power diversity-based cancellation of nonlinear distortions in OFDM systems

International audienceOne of the main drawbacks of orthogonal frequency division multiplexing (OFDM) systems is the high peak-to-average power ratio (PAPR) of the transmitted signals, which can cause the introduction of inter-carrier interference (ICI) due to the presence of nonlinear power amplifiers (PAs). In this paper, a theoretical analysis of ICI in nonlinear OFDM systems with polynomial PAs is made. Contrarily to other works, this analysis provides an exact description of nonlinear ICI. Moreover, three receivers for channel estimation and ICI cancellation in OFDM systems with polynomial PAs are proposed, based on the concept of power diversity that consists in re-transmitting the information symbols several times with a different transmission power each time. The transmission powers that minimize the sum of the residual mean square errors (MSEs) provided by the proposed receivers are derived in the case of a third-degree polynomial PA. An important advantage of the proposed receivers is that the optimal transmission powers do not depend on the channel nor the PA coefficients

Action palliative par le convertisseur statique en cas de défaillance d'un générateur PAC modulaire de puissance

International audienceLa montée en puissance des piles à combustible se heurte à des difficultés d'ordre mécanique et fluidique, limitant l'assemblage en série de cellules unitaires pour les piles de forte puissance. Aussi, à l'heure actuelle, est-il plus aisé de concevoir des générateurs pile à combustible associant plusieurs piles unitaires, dits " multi-stack ". L'approche multi-stack permet en outre de gérer d'éventuelles défaillances pouvant intervenir sur l'une des piles en fonctionnement. Cet article présente des actions de soulagement de la pile défaillante possibles par intervention sur les convertisseurs statiques de puissance d'interface et permettant le rétablissement de cette pile défaillante vers son état sain