Modal Radiation of Guided Waves by Finite-Sized Sources in a Semi-Infinite Multi-Layered Anisotropic Plate

Modal decomposition of guided waves (GW) in anisotropic multi-layered plates is helpful to interpret signals measured in GW NDE methods for testing composite materials. Simulation tools of GW NDE examinations are developed notably to provide help for interpretation. Thus, models on which they rely can provide an even greater help if they predict the various phenomena involved in terms of modal amplitudes. Most GW sources being of finite size, diffraction effects occur. Plate-like structures to be tested being of finite size, edge reflection with mode-conversion occurs too. A model is proposed to predict the field radiated in a semi-infinite multi-layered anisotropic plate which accounts for both the diffraction effect and the reflection at an edge. At first, modes in an arbitrary multi-layered anisotropic plate are computed thanks to the Semi-Analytical Finite Element (SAFE) method as implemented in CIVA software platform developed at CEA [1]. Then, a model for the calculation of the field radiated in an infinite plate by a finite-sized source was recently derived [2] making use of the modal solution computed by means of the SAFE solver. In this model, the integration over the finite size of the source is computed thanks to a change of variable of integration: the surface integral (2D) is replaced by an angular integral (1D) over angles of energy paths between the field point and the source surface. This method was shown to efficiently reproduce results obtained by means of surface integral convolution of the source with the 3D Green’s function. Special care was taken to consider the fact that, for some modes in anisotropic materials, one energy direction may be associated to more than one phase direction. Here, the same approach is extended to account for reflection on a free boundary of the plate. This is done by combining the energy path approach to the model presented in [3] for reflection at the edge of an isotropic plate. Two separate problems must be solved. The first consists in finding energy paths between the source and a field point when reflection occurs, before proceeding to angular integration. This is formally easy but details will be given to explain how to proceed efficiently. The second problem consists in computing reflection coefficients to be associated to the energy paths previously determined. For this, a system quite similar to SAFE system is formed to compute all the modes of wave-vector component parallel to the edge equal to that of the incident energy considered. This allows us to build a last system in which boundary conditions are introduced to obtain reflection coefficients. Thus, the complex mode-conversion phenomena arising at edges of anisotropic plates are fully taken into account. Interestingly, the concept of integration over energy paths extended herein to reflection is formally of the same nature as the overall pencil approach described in [4]: multiple reflections could be treated within the same theoretical framework

Stationary-Phase Method vs. Pencil Method for the Modal Radiation of Guided Waves by Finite-Sized Sources in a Semi-Infinite Isotropic Plate

Modal decomposition of guided waves (GW) in isotropic plates over Lamb and shear horizontal modes is helpful to interpret signals measured in GW NDE methods. Simulation tools of GW NDE examinations are developed notably to provide help interpretation. Thus, models on which they rely can provide an even greater help if they predict the various phenomena involved in terms of modal amplitudes. Most GW sources being of finite size, diffraction effects occur. Plate-like structures to be tested being of finite size, edge reflection with mode-conversion occurs too. Two models are proposed for the fast prediction of how the two phenomena combine. For both models, the field in a semi-infinite plate is given by the sum of the direct field and that resulting from reflections on plate edge. The expression [1] of modal 3D Green’s function is used for the direct field; in isotropic plate, this results in a modal series of cylindrical waves of amplitude decreasing as 1/√r, (r, distance of a source point to a field point). In the first model, each cylindrical wave is decomposed in the spatial Fourier domain as a spectrum of infinite plane GW. The reflection of a plane GW on the straight free edge of the plate is computed as in [2]. The inverse Fourier transform to get back to the spatial domain is calculated analytically by means of the stationary phase method, stationary phase path of a given mode with reflection being easily obtained. The total field is expressed by a convolution over the source surface of the Green’s function (direct and reflected terms) with source terms. Finally, this surface integral is calculated analytically thanks to a Fraunhofer-like approximation, shown in [3] to lead to accurate results for the direct field at a very low computational cost (analytic expressions for sources of standard geometry exerting either normal or tangential traction). In the second model, expression of the direct field is reinterpreted in terms of propagation of modal infinitesimal pencils propagating along energy paths with a spreading factor deduced from the principle of energy conservation. Evolution of the pencil of a given mode is calculated by chaining propagation matrices and boundary interaction (reflection) matrices, the latter involving the same reflection coefficients as for the first model. From this, the pencil spreading at the calculation point is obtained. Applying it to the case of a straight edge, one obtains the same final expression for the whole field as that obtained with the first modeling approach. In the first approach, assumption and approximation made are rigorously mastered but the final result is of restricted applicability (straight edge).The second modeling approach easily applies to more complex configurations, in particular, to configurations implying several reflections on possibly curved boundaries. Both models can include local calculation of reflection coefficients for different boundary conditions

Antagonistic factors control the unproductive splicing of SC35 terminal intron

Alternative splicing is regulated in part by variations in the relative concentrations of a variety of factors, including serine/arginine-rich (SR) proteins. The SR protein SC35 self-regulates its expression by stimulating unproductive splicing events in the 3′ untranslated region of its own pre-mRNA. Using various minigene constructs containing the terminal retained intron and flanking exons, we identified in the highly conserved last exon a number of exonic splicing enhancer elements responding specifically to SC35, and showed an inverse correlation between affinity of SC35 and enhancer strength. The enhancer region, which is included in a long stem loop, also contains repressor elements, and is recognized by other RNA-binding proteins, notably hnRNP H protein and TAR DNA binding protein (TDP-43). Finally, in vitro and in cellulo experiments indicated that hnRNP H and TDP-43 antagonize the binding of SC35 to the terminal exon and specifically repress the use of SC35 terminal 3′ splice site. Our study provides new information about the molecular mechanisms of SC35-mediated splicing activation. It also highlights the existence of a complex network of self- and cross-regulatory mechanisms between splicing regulators, which controls their homeostasis and offers many ways of modulating their concentration in response to the cellular environment

Structural and functional analysis of the Rous Sarcoma virus negative regulator of splicing and demonstration of its activation by the 9G8 SR protein

Retroviruses require both spliced and unspliced RNAs for replication. Accumulation of Rous Sarcoma virus (RSV) unspliced RNA depends upon the negative regulator of splicing (NRS). Its 5′-part is considered as an ESE binding SR proteins. Its 3′-part contains a decoy 5′-splice site (ss), which inhibits splicing at the bona fide 5′-ss. Only the 3D structure of a small NRS fragment had been experimentally studied. Here, by chemical and enzymatic probing, we determine the 2D structure of the entire RSV NRS. Structural analysis of other avian NRSs and comparison with all sequenced avian NRSs is in favour of a phylogenetic conservation of the NRS 2D structure. By combination of approaches: (i) in vitro and in cellulo splicing assays, (ii) footprinting assays and (iii) purification and analysis of reconstituted RNP complex, we define a small NRS element retaining splicing inhibitory property. We also demonstrate the capability of the SR protein 9G8 to increase NRS activity in vitro and in cellulo. Altogether these data bring new insights on how NRS fine tune splicing activity

Repetitive non-typhoidal Salmonella exposure is an environmental risk factor for colon cancer and tumor growth

During infection, Salmonella hijacks essential host signaling pathways. These molecular manipulations disrupt cellular integrity and may induce oncogenic transformation. Systemic S. Typhi infections are linked to gallbladder cancer, whereas severe non-typhoidal Salmonella (NTS) infections are associated with colon cancer (CC). These diagnosed infections, however, represent only a small fraction of all NTS infections as many infections are mild and go unnoticed. To assess the overall impact of NTS infections, we performed a retrospective serological study on NTS exposure in patients with CC. The magnitude of exposure to NTS, as measured by serum antibody titer, is significantly positively associated with CC. Repetitively infecting mice with low NTS exposure showed similar accelerated tumor growth to that observed after high NTS exposure. At the cellular level, NTS preferably infects (pre-)transformed cells, and each infection round exponentially increases the rate of transformed cells. Thus, repetitive exposure to NTS associates with CC risk and accelerates tumor growth

Du côté des pères divorcés : quelle situation aujourd'hui ? Étude de la place et du rôle du père dans la famille et examen des conséquences du divorce, pour lui, à l'égard des enfants

Master [120] en droit, Université catholique de Louvain, 201

Rayonnement des ondes ultrasonores guidées dans une structure mince et finie, métallique ou composite, en vue de son contrôle non-destructif

Different models are developed to provide generic tools for simulating nondestructive methods relying on elastic guided waves applied to metallic or composite plates. Various inspection methods of these structures exist or are under study. Most of them make use of ultrasonic sources of finite size; all are sensitive to reflection phenomena resulting from the finite size of the monitored objects. The developed models deal with transducer diffraction effects and edge reflection. As the interpretation of signals measured in guided wave inspection often uses the concept of modes, the models themselves are explicitly modal. The case of isotropic plates (metal) and anisotropic (multilayer composites) are considered; a general approach under the stationary phase approximation allows us to consider all the cases of interest. For the first, the validity of a Fraunhofer-like approximation leads to a very efficient computation of the direct and reflected fields radiated by a source. For the second, special attention is paid to the treatment of caustics. The stationary phase approximation being difficult to generalize, a model (so-called “pencil model”) of more geometrical nature is proposed with a high degree of genericity. It chains terms of isotropic or anisotropic propagation and terms of interaction with a boundary. The equivalence of the stationary phase approximation and the pencil model is demonstrated in the case of the radiation and reflection in an isotropic plate, for which an experimental validation is proceeded.Différents modèles sont développés de façon à constituer des outils génériques pour la simulation de méthodes de contrôle non-destructif par ondes élastiques guidées de plaques métalliques ou composites. Diverses méthodes de contrôle de ces structures existent ou sont à l’étude. La plupart font appel à des sources ultrasonores de taille finie ; toutes sont confrontées aux phénomènes de réflexion résultant de la taille finie des objets contrôlés. Les modèles développés traitent des phénomènes de diffraction associés aux sources et de réflexion sur un bord de plaques. Comme l’interprétation des signaux mesurés lors de contrôle par ondes guidées fait souvent appel à la notion de modes guidés, les modèles sont eux-mêmes modaux. Les cas de plaques isotropes (métalliques) et anisotropes (composites multicouches) sont considérés ; une approche générale suivant l’approximation de la phase stationnaire permet de traiter tous les cas d’intérêt. Pour les premiers, la validité d’une approximation de type Fraunhofer permet de traiter très efficacement les champs directs et réfléchis rayonnés par une source. Pour les derniers, une attention particulière est portée sur le traitement des caustiques. La méthode de la phase stationnaire étant difficile à généraliser, un modèle de pinceau, de nature plus géométrique, est proposé présentant un haut degré de généricité. Il met en cascade des termes de propagation en milieu isotrope ou anisotrope et d’interaction avec une frontière. L’équivalence de la méthode de la phase stationnaire au modèle de pinceau est démontrée pour le rayonnement et la réflexion dans une plaque isotrope, cas faisant l’objet d’une validation expérimentale

Guided wave radiation in a finite-sized metallic or composite plate-like structure for its non-destructive testing

Différents modèles sont développés de façon à constituer des outils génériques pour la simulation de méthodes de contrôle non-destructif par ondes élastiques guidées de plaques métalliques ou composites. Diverses méthodes de contrôle de ces structures existent ou sont à l’étude. La plupart font appel à des sources ultrasonores de taille finie ; toutes sont confrontées aux phénomènes de réflexion résultant de la taille finie des objets contrôlés. Les modèles développés traitent des phénomènes de diffraction associés aux sources et de réflexion sur un bord de plaques. Comme l’interprétation des signaux mesurés lors de contrôle par ondes guidées fait souvent appel à la notion de modes guidés, les modèles sont eux-mêmes modaux. Les cas de plaques isotropes (métalliques) et anisotropes (composites multicouches) sont considérés ; une approche générale suivant l’approximation de la phase stationnaire permet de traiter tous les cas d’intérêt. Pour les premiers, la validité d’une approximation de type Fraunhofer permet de traiter très efficacement les champs directs et réfléchis rayonnés par une source. Pour les derniers, une attention particulière est portée sur le traitement des caustiques. La méthode de la phase stationnaire étant difficile à généraliser, un modèle de pinceau, de nature plus géométrique, est proposé présentant un haut degré de généricité. Il met en cascade des termes de propagation en milieu isotrope ou anisotrope et d’interaction avec une frontière. L’équivalence de la méthode de la phase stationnaire au modèle de pinceau est démontrée pour le rayonnement et la réflexion dans une plaque isotrope, cas faisant l’objet d’une validation expérimentale.Different models are developed to provide generic tools for simulating nondestructive methods relying on elastic guided waves applied to metallic or composite plates. Various inspection methods of these structures exist or are under study. Most of them make use of ultrasonic sources of finite size; all are sensitive to reflection phenomena resulting from the finite size of the monitored objects. The developed models deal with transducer diffraction effects and edge reflection. As the interpretation of signals measured in guided wave inspection often uses the concept of modes, the models themselves are explicitly modal. The case of isotropic plates (metal) and anisotropic (multilayer composites) are considered; a general approach under the stationary phase approximation allows us to consider all the cases of interest. For the first, the validity of a Fraunhofer-like approximation leads to a very efficient computation of the direct and reflected fields radiated by a source. For the second, special attention is paid to the treatment of caustics. The stationary phase approximation being difficult to generalize, a model (so-called “pencil model”) of more geometrical nature is proposed with a high degree of genericity. It chains terms of isotropic or anisotropic propagation and terms of interaction with a boundary. The equivalence of the stationary phase approximation and the pencil model is demonstrated in the case of the radiation and reflection in an isotropic plate, for which an experimental validation is proceeded

Modal Radiation of Guided Waves by Finite-Sized Sources in a Semi-Infinite Multi-Layered Anisotropic Plate

Modal decomposition of guided waves (GW) in anisotropic multi-layered plates is helpful to interpret signals measured in GW NDE methods for testing composite materials. Simulation tools of GW NDE examinations are developed notably to provide help for interpretation. Thus, models on which they rely can provide an even greater help if they predict the various phenomena involved in terms of modal amplitudes. Most GW sources being of finite size, diffraction effects occur. Plate-like structures to be tested being of finite size, edge reflection with mode-conversion occurs too. A model is proposed to predict the field radiated in a semi-infinite multi-layered anisotropic plate which accounts for both the diffraction effect and the reflection at an edge. At first, modes in an arbitrary multi-layered anisotropic plate are computed thanks to the Semi-Analytical Finite Element (SAFE) method as implemented in CIVA software platform developed at CEA [1]. Then, a model for the calculation of the field radiated in an infinite plate by a finite-sized source was recently derived [2] making use of the modal solution computed by means of the SAFE solver. In this model, the integration over the finite size of the source is computed thanks to a change of variable of integration: the surface integral (2D) is replaced by an angular integral (1D) over angles of energy paths between the field point and the source surface. This method was shown to efficiently reproduce results obtained by means of surface integral convolution of the source with the 3D Green’s function. Special care was taken to consider the fact that, for some modes in anisotropic materials, one energy direction may be associated to more than one phase direction. Here, the same approach is extended to account for reflection on a free boundary of the plate. This is done by combining the energy path approach to the model presented in [3] for reflection at the edge of an isotropic plate. Two separate problems must be solved. The first consists in finding energy paths between the source and a field point when reflection occurs, before proceeding to angular integration. This is formally easy but details will be given to explain how to proceed efficiently. The second problem consists in computing reflection coefficients to be associated to the energy paths previously determined. For this, a system quite similar to SAFE system is formed to compute all the modes of wave-vector component parallel to the edge equal to that of the incident energy considered. This allows us to build a last system in which boundary conditions are introduced to obtain reflection coefficients. Thus, the complex mode-conversion phenomena arising at edges of anisotropic plates are fully taken into account. Interestingly, the concept of integration over energy paths extended herein to reflection is formally of the same nature as the overall pencil approach described in [4]: multiple reflections could be treated within the same theoretical framework.</p

Stationary-Phase Method vs. Pencil Method for the Modal Radiation of Guided Waves by Finite-Sized Sources in a Semi-Infinite Isotropic Plate

Modal decomposition of guided waves (GW) in isotropic plates over Lamb and shear horizontal modes is helpful to interpret signals measured in GW NDE methods. Simulation tools of GW NDE examinations are developed notably to provide help interpretation. Thus, models on which they rely can provide an even greater help if they predict the various phenomena involved in terms of modal amplitudes. Most GW sources being of finite size, diffraction effects occur. Plate-like structures to be tested being of finite size, edge reflection with mode-conversion occurs too. Two models are proposed for the fast prediction of how the two phenomena combine. For both models, the field in a semi-infinite plate is given by the sum of the direct field and that resulting from reflections on plate edge. The expression [1] of modal 3D Green’s function is used for the direct field; in isotropic plate, this results in a modal series of cylindrical waves of amplitude decreasing as 1/√r, (r, distance of a source point to a field point). In the first model, each cylindrical wave is decomposed in the spatial Fourier domain as a spectrum of infinite plane GW. The reflection of a plane GW on the straight free edge of the plate is computed as in [2]. The inverse Fourier transform to get back to the spatial domain is calculated analytically by means of the stationary phase method, stationary phase path of a given mode with reflection being easily obtained. The total field is expressed by a convolution over the source surface of the Green’s function (direct and reflected terms) with source terms. Finally, this surface integral is calculated analytically thanks to a Fraunhofer-like approximation, shown in [3] to lead to accurate results for the direct field at a very low computational cost (analytic expressions for sources of standard geometry exerting either normal or tangential traction). In the second model, expression of the direct field is reinterpreted in terms of propagation of modal infinitesimal pencils propagating along energy paths with a spreading factor deduced from the principle of energy conservation. Evolution of the pencil of a given mode is calculated by chaining propagation matrices and boundary interaction (reflection) matrices, the latter involving the same reflection coefficients as for the first model. From this, the pencil spreading at the calculation point is obtained. Applying it to the case of a straight edge, one obtains the same final expression for the whole field as that obtained with the first modeling approach. In the first approach, assumption and approximation made are rigorously mastered but the final result is of restricted applicability (straight edge).The second modeling approach easily applies to more complex configurations, in particular, to configurations implying several reflections on possibly curved boundaries. Both models can include local calculation of reflection coefficients for different boundary conditions.</p