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In the present paper, a technique called Excitelet is presented for the imaging of damages in thin-walled structures using the correlation of the measured signals with dispersed versions of the excitation signal. Piezoceramic (PZT) actuators are used to generate burst Lamb waves which interact with defects in metallic structures and the measurement is taken using sparse and compact array configurations of PZT sensors. The sparse sensing configuration consists of individual circular PZT elements distributed over the plate while the compact array configuration consists of a linear arrangement of sensors micro-machined on a single piece of bulk PZT wafer. This approach is presented as an extension of the classical imaging techniques and takes advantage of the chirplet-based matching pursuit algorithm. The approach is investigated experimentally on a 1.54 mm thick aluminum plate and comparison with existing Embedded Ultrasonic Structural Radar (EUSR) algorithm is performed for A0 and S0 modes for two frequency ranges of interest (centered at 150 kHz and 550 kHz). Damages are simulated using stacked magnets at different locations on the plate. Significant improvement of imaging quality is demonstrated with respect to existing imaging techniques based on group velocity and Time-of-Flight (ToF), for both sparse and compact PZT array configurations. Multimodal imaging strategies are presented to improve the imaging results. Moreover, it is shown that the proposed imaging technique provide accurate results in the case of dispersive propagation, while existing imaging techniques are no longer applicable.

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Bien que le phénomène de l’aide aux proches ait toujours fait partie de la réalité de la société canadienne, il prend aujourd’hui des proportions plus importantes que jamais. Le vieillissement de la population et la mutation des soins du milieu institutionnel vers le milieu de vie naturel contribuent à l’accroissement du nombre de proches aidants et des responsabilités qu’ils assument. Sous les pressions du milieu, les gouvernements ont amorcé une réflexion sur la reconnaissance du rôle des aidants et le soutien à leur apporter. Cette réflexion a mené à l’adoption de quelques mesures d’aide financière, dont la prestation de compassion mise en place par le gouvernement fédéral en janvier 2004. Quoique nettement insuffisantes, les mesures actuelles visant à soutenir financièrement les aidants et à protéger leurs emplois constituent un début d’action prometteur dans le champ de l’aide aux proches.

During the afternoon of April 21, 1996, a massive landslide occurred in Champlain Sea sediments along the Machiche River, 5 km south of St-Boniface-de-Shawinigan, Quebec. The slide occurred in a wooded area following a period of intense rainfall. The landslide is thought to be a multiple retrogressive type with a volume estimated to be about 8 X 106 m3. It is one of the largest landslides (31 ha) to have occurred in the St-Lawrence Lowlands in this century. The debris blocked the valley of the Machiche River and caused a lake to form upstream. This landslide has shown the vulnerability of hydroelectric facilities and roads to major landslides in Champlain Sea sediments.