Etude comparative entre deux modèles de prédiction du dommage avec des résultats expérimentaux pour les matériaux composites soumises aux chargements spectraux

Les résultats d'essais statiques et dynamiques effectuées sur un ensemble de stratifiés composites ont été exploitées afin de déterminer deux modèles de fatigue, l'un basé sur la loi de Miner et l'autre basé sur la dégradation de la rigidité globale. Divers simulation ont été effectuées et comparées à des résultats expérimentaux menées par M. Aboussaleh et R. Boukhili [2]. Nous avons conclu que le modèle phénoménologique est en bon accord avec ces essais expérimentaux que le modèle linéaire

Resonant states in GaAs/Ga1-xAlxAs Multi-Quantum-Wells

The effect of buffer layers on resonant states in a Multi-Quantum-Well (MQW) sandwiched between two substrates is investigated here theoretically. These resonances appear as well-defined peaks in the density of states (DOS). The local and total densities of states are obtained from an analytical determination of the Green functions. Due to the substrate/buffer layer/ MQW /substrate interaction, different kinds of resonant states are found and their properties are investigated. We show in particular that an incident electron in the left-hand side substrate is transmitted in the right hand side substrate of the structure with large time delays in the phase time. The peaks in the phase time associated with the transmission coefficient are found to be similar to those corresponding to the DOS. The intensity of these peaks associated with extended states in MQW’s and Tamm like states lying at the MQW/buffer layer interface, strongly depends on the width of the buffer layer.The effect of buffer layers on resonant states in a Multi-Quantum-Well (MQW) sandwiched between two substrates is investigated here theoretically. These resonances appear as well-defined peaks in the density of states (DOS). The local and total densities of states are obtained from an analytical determination of the Green functions. Due to the substrate/buffer layer/ MQW /substrate interaction, different kinds of resonant states are found and their properties are investigated. We show in particular that an incident electron in the left-hand side substrate is transmitted in the right hand side substrate of the structure with large time delays in the phase time. The peaks in the phase time associated with the transmission coefficient are found to be similar to those corresponding to the DOS. The intensity of these peaks associated with extended states in MQW’s and Tamm like states lying at the MQW/buffer layer interface, strongly depends on the width of the buffer layer

Surface and interface shear horizontal acoustic waves in piezoelectric superlattices

7 pages, 7 figures, 1 table.-- PACS: 68.35.Gy; 68.35.Ja; 63.22.+m; 73.20.DxThe propagation of acoustic waves of shear horizontal polarization in infinite and semi-infinite superlattices made of two piezoelectric media is studied within a Green's function method. Localized modes induced by a free surface of the superlattice or a superlattice/substrate interface are investigated theoretically. These modes appear as well-defined peaks of the total density of states inside the minigaps of the superlattice. The spatial localization of the different modes is studied by means of the local density of states. The surface of the superlattice and the superlattice/substrate interface are considered to be either metallized or nonmetallized. We show the possibility of the existence of interface modes, which are without analogue in the case of the interface between two homogeneous media (the so-called Maerfeld–Tournois modes). We also generalize to piezoelectric superlattices a rule about the existence and number of surface states, namely when one considers two semi-infinite superlattices together obtained by the cleavage of an infinite superlattice, one always has as many localized surface modes as minigaps, for any value of the wave vector k (parallel to the interfaces). Specific applications of these results are given for CdS–ZnO superlattices with a free surface or in contact with a BeO substrate.The work of A.B., E.E., D.B., and A.N. has been supported by the Program-in-Aid for Scientific Research (PARS). The work of V.R.V. has been supported by the Dirección General de Enseñanza Superior (Spain) through Grant No. PB96-0916. E.E., A.N. and V.R.V. thank the CNCPRST (Morocco) and CSIC (Spain) for a cooperation project.Peer reviewe

Endothelial CFTR dysfunction and its involvement in the pathogenesis of pulmonary arterial hypertension

International audienceNo abstract availabl

Comparative meta-analysis of cystic fibrosis cell models suggests partial endothelial-to-mesenchymal transition

International audienceThe mesenchymal conversion of epithelial cells (EMT) has been suggested as a potential contributor in cystic fibrosis (CF) disease progression. Endothelial cells (EndCs), the cells lining blood vessels, express functional CFTR and CFTR impairment promotes endothelial activation and dysfunction. However, if the mesenchymal switch also exists in CF EndCs remains uncharacterized. To understand whether the endothelial-to-mesenchymal transition (EndMT) could occur in CF, we have conducted a transcriptomic meta-analysis of primary CFTR-impaired and patient-derived EndCs, and further compared our results to data from CF epithelial cells (EpCs) where EMT has been demonstrated. As compared to EpCs, we show that CFTR-impaired EndCs display a limited signature of EndMT, and that expression of the mesenchymal inducer Twist1 remained unchanged. Nonetheless, the use of CFTR modulators reduced the expression of mesenchymal markers from CF patient-derived EndCs, suggesting an additional therapeutic added-value next to the known effect on CFTR ion transport

Absolute acoustic band gap in coupled multilayer structures

We show theoretically that by combining two or more finite superlattices, it is possible to realize an omnidirectional acoustic mirror that prevents propagation of acoustic waves over a wide range of frequencies. An appropriate choice of the elastic parameters in the superlattices enables us to propose a structure in which any incident wave launched from any type of substrate (or vacuum) falls inside a minigap of the coupled SLs and therefore undergoes a total reflection

Stoneley-type waves in anisotropic periodic superlattices

The paper investigates the existence of interfacial (Stoneley-type) acoustic waves localised at the internal boundary between two semi-infinite superlattices which are adjoined with each other to form one-dimensional phononic bicrystal. Each superlattice is a periodic sequence of perfectly bonded homogeneous and/or functionally graded layers of general anisotropy. Given any asymmetric arrangement of unit cells (periods) of superlattices, it is found that the maximum number of interfacial waves, which can emerge at a fixed tangential wavenumber for the frequency varying within a stopband, is three for the lowest stopband and six for any upper stopband. Moreover, we show that this number of three or six waves in the lowest or upper stopband, is actually the maximum for the number of waves occurring per stopband in a given bicrystal plus their number in the “complementary” bicrystal, which is obtained by swapping upper and lower superlattices of the initial one (so that both bicrystals have the same band structure). An example is provided demonstrating attainability of this upper bound, i.e. the existence of six interfacial waves in a stopband. The results obtained under no assumptions regarding the material anisotropy are also specified to the case of monoclinic symmetry leading to acoustic mode decoupling