Identification of a time-varying mechanical system using the Akaike information criterion

Cet article démontre l'intérêt du critère d'information d'Akaike pour les méthodes d'identification contenant une étape de projection de signaux de mesure sur des bases spécifiques. On s'intéresse particulièrement au problème d'identification de paramètres mécaniques variant dans le temps. La méthode est testée expérimentalement avec succès sur un système à un degré de liberté, constitué d'une inertie et d'une poutre à longueur variable travaillant en torsion. Les variations de cette longueur rendent les paramètres du système dynamique changeant. Une approche par moindre carré combinée à une projection des signaux mesuré sur une base polynomiale permet de reconstruire aisément les fluctuations des paramètres mécaniques. Cependant le choix de l'ordre de troncature de la base de projection est toujours un problème clef dans ce genre de méthode inverse et reste bien souvent une question ouverte. On propose ici d'utiliser le critère d'information Akaike permettant ainsi une sélection robuste et automatique de cet ordre de troncature. L'étude présentée ici ainsi que l'expérimentation montrent la pertinence et l'intérêt de ce type de critère associé aux méthodes d'identification

Human neutralizing antibodies to cold linear epitopes and subdomain 1 of the SARS-CoV-2 spike glycoprotein

Emergence of SARS-CoV-2 variants diminishes the efficacy of vaccines and antiviral monoclonal antibodies. Continued development of immunotherapies and vaccine immunogens resilient to viral evolution is therefore necessary. Using coldspot-guided antibody discovery, a screening approach that focuses on portions of the virus spike glycoprotein that are both functionally relevant and averse to change, we identified human neutralizing antibodies to highly conserved viral epitopes. Antibody fp.006 binds the fusion peptide and cross-reacts against coronaviruses of the four genera, including the nine human coronaviruses, through recognition of a conserved motif that includes the S2´ site of proteolytic cleavage. Antibody hr2.016 targets the stem helix and neutralizes SARS-CoV-2 variants. Antibody sd1.040 binds to subdomain 1, synergizes with antibody rbd.042 for neutralization and, like fp.006 and hr2.016, protects mice expressing human ACE2 against infection when present as bispecific antibody. Thus, coldspot-guided antibody discovery reveals donor-derived neutralizing antibodies that are cross-reactive with Orthocoronavirinae, including SARS-CoV-2 variants

Identification expérimentale de l'équation du mouvement de milieux vibroacoustique

This works deals with a question of identification of the equation of motion based on experimental measurements. The considered structures are either one or two-dimensional plane structures. The developed methodology employs local inverse methods based on local steady-state vibration field and it is therefore independent of boundary conditions. Two different model selection techniques are used to select the most adapted equation of motion from a set of apriori candidate models. The method is applied to various experimental case studies as identification of axial force in beams and membranes, identification of plate orthotropy and identification of thick sandwich panel model.Ce travail répond à la question de l’identification de l'équation du mouvement à partir des mesures expérimentales. Les structures considérées ont soit une soit deux dimensions. La méthode présentée utilise les méthodes inverses locales qui se basent sur les mesures du champs vibratoire stationnaire. Ces méthodes sont indépendantes des conditions aux limites qui sont inconnues pour l'observateur. Deux méthodes de sélection des modèles sont utilisées pour choisir l'équation du mouvement la plus adaptée parmi un ensemble des modèles a priori. La méthode est appliquée a des nombreux cas expérimentaux. Trois problématiques sont traités: identification de la force axiale dans les poutres et membranes, identification de l'orthotropie de la plaque et identification d'un panel sandwich épais

Experimental identification of the equation of motion in vibroacoustics

Ce travail répond à la question de l’identification de l'équation du mouvement à partir des mesures expérimentales. Les structures considérées ont soit une soit deux dimensions. La méthode présentée utilise les méthodes inverses locales qui se basent sur les mesures du champs vibratoire stationnaire. Ces méthodes sont indépendantes des conditions aux limites qui sont inconnues pour l'observateur. Deux méthodes de sélection des modèles sont utilisées pour choisir l'équation du mouvement la plus adaptée parmi un ensemble des modèles a priori. La méthode est appliquée a des nombreux cas expérimentaux. Trois problématiques sont traités: identification de la force axiale dans les poutres et membranes, identification de l'orthotropie de la plaque et identification d'un panel sandwich épais.This works deals with a question of identification of the equation of motion based on experimental measurements. The considered structures are either one or two-dimensional plane structures. The developed methodology employs local inverse methods based on local steady-state vibration field and it is therefore independent of boundary conditions. Two different model selection techniques are used to select the most adapted equation of motion from a set of apriori candidate models. The method is applied to various experimental case studies as identification of axial force in beams and membranes, identification of plate orthotropy and identification of thick sandwich panel model

Identification of a time-varying mechanical system using the Akaike information criterion

International audienceThis article deals with the use of Akaike information criterion in the case of an identification problem of a time varying mechanical system. We studied a prismatic beam with a disk excited in torsion to illustrate how the proposed approach can be implemented. The boundary conditions of the beam can changein a controlled way during the experiment. Therefore, our system can be considered as a one d.o.f. system with time-varying parameters. A method based on least-square estimates is used for the identification of the parameters. The use of the Akaike information criterion allows to choose automatically the order ofpolynomial basis used during the estimation step of the derivatives of the measured angle signal. It is shown through an experimental validation that the AIC criterion is a robust and automatic tool for numerical estimation of signal derivatives

Linearized forward and inverse problems of the resonant ultrasound spectroscopy for the evaluation of thin surface layers

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Wave decomposition method for identification of structural parameters

International audienceThis paper presents a newly-developed inverse method based on decomposition of the vibration field into natural waves. It is adapted for 1D and 2D structures which are described by one equation of motion. The method permits to identify the parameters of the equation of motion. The important feature of this approach is that it does not necessitate any knowledge of the boundary conditions. It is a so-called local method. Several experimental test were performed. Two examples are presented: determination of the axial force in the straight beam and determination of flexural rigidity of the plate

Experimental identification of the bending equation of beams from the vibration shape measurements

International audienceThis paper presents an inverse method which results in experimentally determining the parameters of the equation of motion of the linear structures like beams or strings. The experimental part is based on the steady-state measurement of a vibrational shape by a scanning laser vibrometer. An inverse technique is proposed. It compares an experimentally obtained shape with an adequate general solution of the equation of motion and minimizes the error between the two by changing the parameters of the equation. This technique is experimentally verified on three beam samples: a steel beam, a glass composite sandwich beam and a QuietSteele (R) sandwich beam. (C) 2013 Elsevier Ltd. All rights reserved

Information criteria and selection of vibration models

International audienceThis paper presents a method of determining an appropriate equation of motion of two-dimensional plane structures like membranes and plates from vibration response measurements. The local steady-state vibration field is used as input for the inverse problem that approximately determines the dispersion curve of the structure. This dispersion curve is then statistically treated with Akaike information criterion (AIC), which compares the experimentally measured curve to several candidate models (equations of motion). The model with the lowest AIC value is then chosen, and the utility of other models can also be assessed. This method is applied to three experimental case studies: A red cedar wood plate for musical instruments, a thick paper subjected to unknown membrane tension, and a thick composite sandwich panel. These three cases give three different situations of a model selection

Evaluation of elastic properties of DLC layers using resonant ultrasound spectroscopy and AFM nanoindentation

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