Number and location of zero-group-velocity modes

The frequency-wavenumber spectra of laminated media often exhibit anomalous modes with descending branches whose group velocity is negative, and these terminate at a minimum point at which the group velocity transitions from negative to positive. These minima are associated with resonant conditions in the medium, which have been clearly observed in experiments and in the nondestructive testing of laminated plates. Starting from first principles, this paper provides a theoretical analysis on the number and location of such zero-group-velocity (ZGV) modes for horizontally layered media bounded by any arbitrary combination of external boundaries. It is found that these ZGV points are few in number and show up mostly in low-order modes which are characterized by a negative second derivative at the cutoff frequencies, a condition that can readily be tested. It is also shown that the effective number of ZGVs is small even when the ratio of the dilatational and shear wave velocity is a rational number and there exist coincidences in cutoff frequencies, a condition that at first would suggest that the number of ZGVs is infinite. Finally, it is shown that the number of ZGVs decreases with the Poisson’s ratio

Age-related vulnerability of pattern separation in C57BL/6J mice

International audienceAging is associated with impaired performance in behavioral pattern separation (PS) tasks based on similarities in object features and in object location. These deficits have been attributed to functional alterations in the dentate gyrus (DG)-CA3 region. Animal studies suggested a role of adult-born DG neurons in PS performance. The present study investigated the effect of aging in C57BL/6J mice performing PS tasks based on either object features or object location. At the age of 18 months or more, performance was severely impaired in both tasks. Spatial PS performance declined gradually over adult lifespan from 3 to 21 months. Subchronic treatment with the cognitive enhancer D-serine fully rescued spatial PS performance in 18-month-old mice and induced a modest increase in the number of 4-week-old adult-born cells in the DG. Performance of mice in these PS tasks shows an age-dependence which appears to translate well to that found in humans. This model should help in deciphering physiological changes underlying PS deficits and in identifying future therapeutic targets

Why Is Case Management Effective? A Realist Evaluation of Case Management for Frail, Community-Dwelling Older People: Lessons Learned from Belgium

Despite many attempts to evaluate the effectiveness of case management for frail older people, systematic reviews including experimental designs show inconsistent results. Starting from the view that case management is a complex intervention occurring in multilayered realities, we conducted a realist evaluation of case management in Belgium, where this type of intervention is new. Realist approaches are particularly well suited to evaluate complex interventions as they seek to investigate iteratively the literature and empirical data to uncover mid-range theories underpinning the intervention under study. As such, realist evaluations are works in progress which provide tools to describe how, why and for whom an intervention is supposed to work. In this paper, we describe two mid-range theories that can explain why case management can help frail older people to remain at home, through the lens of capacity and social support

Le soutien à domicile des personnes âgées dépendantes en Belgique : approche socio-économique

Ageing in our familiar environment is a widely shared desire in the population. To fulfil the increasing future needs of support, current policies tend to foster non-residential strategies. However, resources used to support disabled elderly persons at home has been little studied. This thesis proposes to describe and analyse the utilisation of services and the informal care provided by relatives and to estimate the associated costs. The objective is to determine to what extent the support currently provided is adequate for the needs of dependent older persons and for the expectations of informal carers. To answer these questions, nine different types of situations at home have been defined by crossing three disability profiles and three levels of informal carer presence.(SP - Sciences de la santé publique) -- UCL, 201

Etude théorique et expérimentale des résonances mécaniques locales de modes guidés par des structures complexes.

This PhD thesis is about Zero Group Velocity Lamb modes. For these peculiar modes, the group velocity vanishes and the phase velocity remains finite, giving rise to narrow local resonances whose properties are very interesting. Attractive prospects in non destructive evaluation can be found because the frequency of those modes depends on the thickness and the mechanical properties of the plate. The behavior of the modes has primarily been explained. The experimental study have been lead using a non-contact optical set up including a pulsed laser source and an interferometric probe for the generation and the detection of those modes. The resonances have been used to determine the thickness and elastic constants of plates and of an anisotropic pipe. Then, the lateral resolution of the thickness measurement has been studied. The influence of the plate edge has been explored : an abrupt transition between the first ZGV resonance and the edge resonance has been observed at the distance of one thickness to the edge. The effect of the deposit of a thin layer on the ZGV resonances has then been numerically studied, which permitted to measure the thickness of a few hundreds nanometers thin gold layers deposited on a millimetric substrate. Finally, the function of the losses has been examined for two different cases, the intrinsic attenuation and the radiation of a fluid in contact with one face.Cette thèse traite des modes de Lamb à vitesse de groupe nulle. Ces modes singuliers, pour lesquels la vitesse de groupe est nulle et la vitesse de phase finie, donnent lieu à des résonances locales étroites aux propriétés très intéressantes. Leur fréquence dépend de l'épaisseur et des propriétés mécaniques de la plaque, ouvrant ainsi des perspectives intéressantes en contrôle non destructif (CND). Les propriétés de ces modes ont d'abord été rappelées. L'étude expérimentale a été menée en utilisant un dispositif optique sans contact comprenant un laser source impulsionnel et une sonde interférométrique, pour la génération et la détection de ces modes. Les résonances ont été utilisées pour déterminer l'épaisseur et les constantes élastiques de plaques et d'un tube anisotrope. Ensuite, la résolution latérale de la mesure d'épaisseur a été étudiée. L'influence du bord de la plaque a été explorée : une transition abrupte entre la première résonance ZGV et la résonance de bord a été observée à la distance d'une épaisseur du bord. L'effet sur les résonances ZGV du dépôt d'une couche mince a alors été étudié numériquement, permettant ainsi la mesure de l'épaisseur de couches d'or de quelques centaines de nanomètres déposées sur un substrat millimétrique. Pour finir, le rôle des pertes a été examiné dans deux cas distincts, l'atténuation intrinsèque et le rayonnement dans un fluide en contact sur une face

Maintien à domicile: initiatives soutenues par l'INAMI

Pour soutenir le maintien à domicile des personnes âgées fragiles et renforcer les dispositifs existants, l’INAMI a lancé en 2009 un appel à projets visant à maintenir les personnes le plus longtemps possible au domicile, à un coût inférieur à celui d’une admission en maison de repos, pour l’INAMI . Comme le montre cet article, la première évaluation de ces projets est quelque peu mitigée, la recherche continue puisqu’un deuxième appel à projets a été lancé en août 2013 pour des projets démarrant en septembre 2014. A suivre…/

Mascara. A son Altesse Royale Monseigneur le duc d'Orléans, par le Bon de Cès-Caupenne,...

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