Publications

2023

• The healthy and keratoconic human cornea: structure, imaging, mechanical characterization and modeling
  
  • Giraudet Chloé
  • Allain Jean-Marc
  Revue ouverte d'ingénierie des systèmes d'information, ISTE OpenScience, 2023, 1, pp.1-55. This paper aims to give a review of our knowledge on the human cornea, its structure, and its behavior, for mechanical modeling. It presents first the general organization of the cornea, as well as its macro and microstructures. In a second time, we detail the Optical Coherence Tomography (OCT) techniques, which are used in clinics and in research to observe the cornea. Then, we present the experimental characterization of the cornea mechanical propoerties. Finally, we review the modeling approaches that have been used to describe the elastic response of the tissue.
• Acoustic and gravity waves in the ocean: a new derivation of a linear model from the compressible Euler equation
  
  • Dubois Juliette
  • Imperiale Sébastien
  • Mangeney Anne
  • Bouchut François
  • Sainte-Marie Jacques
  Journal of Fluid Mechanics, Cambridge University Press (CUP), 2023, 970, pp.A28. In this paper we construct an accurate linear model describing the propagation of both acoustic and gravity waves in water. This original model is obtained by the linearization of the compressible Euler equations, written in Lagrangian coordinates. The system is studied in the isentropic case, with a free surface, an arbitrary bathymetry, and vertical variations of the background temperature and density. We show that our model is an extension of some models from the litterature to the case of a non- barotropic fluid with a variable sound speed. Other models from the literature are recovered from our model through two asymptotic analysis, one for the incompressible regime and one for the acoustic regime. We also propose a method to write the model in Eulerian coordinates. Our model includes many physical properties, such as the existence of internal gravity waves or the variation of the sound speed with depth. (10.1017/jfm.2023.595)
  DOI : 10.1017/jfm.2023.595
• Repurposing electroencephalogram monitoring of general anaesthesia for building biomarkers of brain ageing: an exploratory study
  
  • Sabbagh David
  • Cartailler Jérôme
  • Touchard Cyril
  • Joachim Jona
  • Mebazaa Alexandre
  • Vallée Fabrice
  • Gayat Étienne
  • Gramfort Alexandre
  • Engemann Denis A
  British Journal of Anaesthesia open, Oxford: Elsevier Ltd, 2023, 7, pp.100145. Background: Electroencephalography (EEG) is increasingly used for monitoring the depth of general anaesthesia, but EEG data from general anaesthesia monitoring are rarely reused for research. Here, we explored repurposing EEG monitoring from general anaesthesia for brain-age modelling using machine learning. We hypothesised that brain age estimated from EEG during general anaesthesia is associated with perioperative risk. Methods: We reanalysed four-electrode EEGs of 323 patients under stable propofol or sevoflurane anaesthesia to study four EEG signatures (95% of EEG power <8e13 Hz) for age prediction: total power, alpha-band power (8e13 Hz), power spectrum, and spatial patterns in frequency bands. We constructed age-prediction models from EEGs of a healthy reference group (ASA 1 or 2) during propofol anaesthesia. Although all signatures were informative, state-of-the-art ageprediction performance was unlocked by parsing spatial patterns across electrodes along the entire power spectrum (mean absolute error¼8.2 yr; R 2 ¼0.65). Results: Clinical exploration in ASA 1 or 2 patients revealed that brain age was positively correlated with intraoperative burst suppression, a risk factor for general anaesthesia complications. Surprisingly, brain age was negatively correlated with burst suppression in patients with higher ASA scores, suggesting hidden confounders. Secondary analyses revealed that age-related EEG signatures were specific to propofol anaesthesia, reflected by limited model generalisation to anaesthesia maintained with sevoflurane. Conclusions: Although EEG from general anaesthesia may enable state-of-the-art age prediction, differences between anaesthetic drugs can impact the effectiveness and validity of brain-age models. To unleash the dormant potential of EEG monitoring for clinical research, larger datasets from heterogeneous populations with precisely documented drug dosage will be essential. (10.1016/j.bjao.2023.100145)
  DOI : 10.1016/j.bjao.2023.100145
• Surface microstructure of an IN718 3D coating manufactured by Laser Metal Deposition
  
  • Zurcher Theo
  • Fridrici Vincent
  • Charkaluk Eric
  Materials Characterization, Elsevier, 2023, 203, pp.113054. Laser Metal Deposition (LMD) is a well-known additive manufacturing (AM) process that offers the ability to repair metal parts, among other benefits. We have focused on IN718 parts that evolve in environments that strongly favor wear. Therefore, a good knowledge of the contact surface microstructure and its properties is necessary to better understand the tribological behavior of these parts. However, the microstructure of the top surface (which is most susceptible to wear) of IN718 coatings deposited by LMD is not particularly well documented in the literature. Most of the studies devoted to this alloy have focused on the study of the cross-sectional microstructure, and the few articles dealing with the top surface microstructure have been devoted to the Laser Powder Bed Fusion (LPBF) process. In this article, four IN718 coatings were successfully fabricated with high density using different scanning strategies. When viewing the microstructure from the top surface, the EBSD map showed a very heterogeneous microstructure with an alternation of fine and coarse grains. It also showed a weak overall texture, but a strong local texture within the fine and coarse grain region. EBSD analysis of the cross-sectional area of the coated section also revealed a microstructure variation along the build direction (BD) with the appearance of small grains between layers after some layers have been deposited. Analysis of both sides of the coated part allowed us to get a better understanding of the final microstructure. We were able to show that this heterogeneous microstructure leads to a spatial variation of the top surface hardness, the pattern of which is directly related to the scanning strategy. Finally, we found that the surface hardness of IN718 LMD samples is higher than that of conventionally produced IN718, which is a promising result in terms of repairing metal parts with good tribological properties. (10.1016/j.matchar.2023.113054)
  DOI : 10.1016/j.matchar.2023.113054
• Composite pour réacteur thermochimique
  
  • Dimanov Alexandre
  , 2023. Élaboration d'un composite nouveau à base de mousse métallique imprégnée de cristallites d'hydrates de sel (par ex. CaCl2-nH2O, n entier, entre 1 et 6), qui sert de cœur de réacteur thermochimique pour stockage d'énergie, en vue du chauffage saisonnier de bâtiments et d'eau chaude sanitaire. L'énergie excédentaire à stocker est fournie au composite sous forme thermique, afin de le déshydrater. La vapeur d'eau extraites peut être stockée (système fermé) ou évacuée dans l'atmosphère (système ouvert). La chaleur est stockée sous forme de potentiel chimique d'hydratation. Lors de l'hydratation, réaction fortement exothermique, la chaleur est utilisée pour le chauffage domestique. Les cristallites d'hydrates de sel sous forme de poudre en vrac souffrent d'un phénomène de compaction lors des cycles d’hydratation, du fait de leur déliquescence. Ceci entraîne rapidement une perte de surface spécifique de réaction et de cinétique du transfert de masse (vapeur d'eau). De plus, les hydrates de sel ne sont pas de bons conducteurs de chaleur. Le composite sert à palier à tous ces problèmes. La mousse métallique (par ex. Al, Cu, Ni...) est constituée de pores ouverts de l'ordre de 300 micromètres de diamètre. La mousse contient environ 50% en poids d'hydrates de sel, qui sont distribuées régulièrement et n'obstruent pas les entrées de pores. La mousse métallique sert simultanément pour i) assurer la tenue mécanique du composite, ii) empêcher l'agglomération des cristallites lors de leur déliquescence (liée à l'hydratation) et limiter la perte de surface spécifique de réaction, iii) assurer le transfert de masse (vapeur d'eau) et les transferts thermiques lors des cycles de déshydratation et d'hydratation. Les mesures thermochimiques cycliques réalisées en calorimètre sous conditions contrôlées (déshydratation sous azote sec et hydratation sous 55 % d'humidité relative) ont démontré la stabilité cyclique des performances thermochimiques du composite en comparaison de celles des hydrates en vrac, dont les performances se dégradent au cours des cycles. Les observations par microscopie électronique à balayage ont confirmé la stabilité de la microstructure des composites, qui maintiennent la porosité ouverte, malgré certaines redistributions locales des hydrates déliquescents. La mousse métallique joue pleinement les différents rôles sus-cités.
• Mortensen Observer for a class of variational inequalities - Lost equivalence with stochastic filtering approaches
  
  • Chaintron Louis-Pierre
  • González Álvaro Mateos
  • Mertz Laurent
  • Moireau Philippe
  ESAIM: Proceedings and Surveys, EDP Sciences, 2023, 73, pp.130-157. We address the problem of deterministic sequential estimation for a nonsmooth dynamics governed by a variational inequality. An example of such dynamics is the Skorokhod problem with a reflective boundary condition. For smooth dynamics, Mortensen introduced in 1968 a nonlinear estimator based on likelihood maximisation. Then, starting with Hijab in 1980, several authors established a connection between Mortensen's approach and the vanishing noise limit of the robust form of the so-called Zakai equation. In this paper, we investigate to what extent these methods can be developed for dynamics governed by a variational inequality.On the one hand, we address this problem by relaxing the inequality constraint by penalization: this yields an approximate Mortensen estimator relying on an approximating smooth dynamics. We verify that the equivalence between the deterministic and stochastic approaches holds through a vanishing noise limit.On the other hand, inspired by the smooth dynamics approach, we study the vanishing viscosity limit of the Hamilton-Jacobi equation satisfied by the Hopf-Cole transform of the solution of the robust Zakai equation. In contrast to the case of smooth dynamics, the zero-noise limit of the robust form of the Zakai equation cannot be understood in our case from the Bellman equation on the value function arising in Mortensen's procedure. This unveils a violation of equivalence for dynamics governed by a variational inequality between the Mortensen approach and the low noise stochastic approach for nonsmooth dynamics. (10.1051/proc/202373130)
  DOI : 10.1051/proc/202373130
• Salt Creep: Transition Between the Low and High Stress Domains
  
  • Bérest Pierre
  • Gharbi Hakim
  • Blanco-Martín Laura
  • Brouard Benoît
  • Brückner Dieter
  • Devries Kerry
  • Hévin Grégoire
  • Hofer Gerd
  • Spiers Christopher
  • Urai Janos
  Rock Mechanics and Rock Engineering, Springer Verlag, 2023. (10.1007/s00603-023-03485-y)
  DOI : 10.1007/s00603-023-03485-y
• Additive Manufacturing of Metal Alloys 2
  
  • Peyre Patrice
  • Charkaluk Éric
  , 2023. (10.1002/9781394229055)
  DOI : 10.1002/9781394229055
• Predicting fretting-fatigue endurance of rotating bending shrink-fitted assemblies using a sequential RUIZ-SWT approach: The effect of entrapped debris layer
  
  • Dieu B.
  • Fouvry Siegfried
  • Doquet V.
  • Bridier F.
  Tribology International, Elsevier, 2023, 186, pp.108593. Fretting-fatigue damage often appears in shaft shrink-fitted assemblies submitted to rotating bending. This paper focuses on the influence of the sleeve edge geometry on such damage. Rotating bending tests have been performed and broken and unbroken specimens have been expertized confirming fretting-fatigue phenomena. A 3D finite element method model was developed to evaluate the sliding and opening lengths. A sequential tribological - fatigue stress analysis strategy allowed the prediction of the maximum crack location ( Ruiz criterion) then the estimation of the fatigue endurance of the assembly using the SWT criterion. The last step of this σSWT(XΓmax) approach considers the presence of a debris layer within the contact to improve the consistency of the service life prediction. (10.1016/j.triboint.2023.108593)
  DOI : 10.1016/j.triboint.2023.108593
• Controlling phase ratio in directed energy deposition of duplex stainless steels and effect on stresses
  
  • Weisz-Patrault Daniel
  , 2023. Optimal material properties of duplex stainless steels generally require near 50-50 ferrite-austenite microstructures. The development of additive manufacturing of duplex steels is hindered by difficulty in controlling cooling conditions to ensure a balanced phase ratio. In addition, non-uniform phase distribution is usually observed. Thus, sufficiently fast partscale process simulations are interesting to optimize process parameters to better predict and control the temperature history during fabrication and therefore solid-state phase transitions. Furthermore, stresses should also be taken into account in the optimization of the phase field in order to avoid cracking, buckling or excessive distortions. Numerical results obtained from a fast modeling of directed energy deposition including thermal analysis, diffusion of alloying element to account for phase transitions, and stress computation are analyzed. On this basis, we investigate the effect on stresses of an optimized fabrication strategy designed to target uniform and balanced ferrite-austenite ratio with respect to a reference printing strategy.
• Microrheology and structural quantification of blood clots as a diagnosis of hypercoagulability
  
  • Westbrook Nathalie
  • Moreau Julien
  • Allain Jean-Marc
  • Ceripa Adrien
  • James Chloé
  • Wolff-Trombini Laura
  • Galinat Hubert
  , 2023. Clotting is the process by which the flow of blood is stopped after an injury. This process may occur pathologically, in both arteries and veins. In the venous system, the severe forms are called Venous Thromboembolic Events which include Deep Vein Thrombosis and Pulmonary Embolism. Today, 50% of recurrent Venous Thromboembolic Events remain unexplained. Hypercoagulability is likely due to a modification of the conditions of polymerization of the fibrin, the main clot component. Using passive microrheology, we measured the mechanical properties of clots and correlated them under the same conditions with structural information obtained with confocal microscopy. We tested our approach with known alterations: an excess of fibrin monomer and of coagulation Factor VIII. We observed simultaneously a rigidification and densification of the fibrin network, showing the potential of microrheology for hypercoagulability diagnosis.
• Characterisation of 3D strain heterogeneity at the microstructure scale during Low Cycle Fatigue of an AlSi7Cu3Mg alloy at 250°C
  
  • Limodin Nathalie
  • Dahdah Nora
  • Wang Long
  • El Bartali Ahmed
  • Witz Jean-François
  • Buffiere Jean-Yves
  • Charkaluk Eric
  International Journal of Fatigue, Elsevier, 2023, 172, pp.107476. 3D tomographic images of a cast AlSi7Cu3Mg alloy were obtained using synchrotron X-ray tomography during in-situ Low Cycle Fatigue tests at 250°C. While image analysis highlights the role of eutectic Si particles close to pores in damage mechanisms, high resolution digital volume correlation reveals the relationship between strain heterogeneity at the microstructural scale and hard particles failure or cracks. Monitoring strains evolution with cycles within hard particles, i.e. eutectic Si and Fe or Cu intermetallics, allows measuring their local failure strains and drawing a hierarchy of the deformation to failure. Then, a local Manson-Coffin curve per hard phase is proposed. (10.1016/j.ijfatigue.2022.107476)
  DOI : 10.1016/j.ijfatigue.2022.107476
• A phase-field model for ferroelectrics with general kinetics, Part I: Model formulation
  
  • Guin Laurent
  • Kochmann Dennis M
  Journal of the Mechanics and Physics of Solids, Elsevier, 2023, 176, pp.105301. When subjected to electro-mechanical loading, ferroelectrics see their polarization evolve through the nucleation and evolution of domains. Existing mesoscale phase-field models for ferroelectrics are typically based on a gradient-descent law for the evolution of the order parameter. While this implicitly assumes that domain walls evolve with linear kinetics, experiments instead indicate that domain wall kinetics is nonlinear. This, in turn, is an important feature for the modeling of rate-dependent effects in polarization switching. We propose a new multiplephase-field model for ferroelectrics, which permits domain wall motion with nonlinear kinetics, with applications in other solid-solid phase transformation problems. By means of analytical traveling wave solutions, we characterize the interfacial properties (energy and width) and the interface kinetics of straight domain walls, as furnished by the general kinetics model, and compare them to those of the classical Allen-Cahn model. We show that the proposed model propagates domain walls with arbitrarily chosen nonlinear kinetic relations, which can be tuned to differ for the different types of domain walls in accordance with experimental evidence. (10.1016/j.jmps.2023.105301)
  DOI : 10.1016/j.jmps.2023.105301
• CLEO®/Europe-EQEC 2023, One Page Summary Template Ultrafast Nano Generation of Acoustic Waves in Water: Thermophone Versus Mechanophone
  
  • Diego Michele
  • Gandolfi Marco
  • Giordano Stefano
  • Casto Alessandro
  • Belussi Francesco Maria
  • Crut Aurélien
  • Vialla Fabien
  • Roddaro Stefano
  • Fasano Matteo
  • Vallée Fabrice
  • Maioli Paolo
  • Fatti Natalia Del
  • Banfi Francesco
  , 2023, pp.1-1. Nanoscale photothermoacoustics generation in liquids, by reason of its implications in nanoimaging and therapeutic, is a booming topic at the forefront of nanoscale heat transfer, optics and biosciences [1]. Within this frame, liquid-immersed nanotransducers play a major role as efficient photoacoustic generators because of their biocompatibility together with tunable optical absorption properties. Research efforts focused on enhancing photoacoustic conversion acting on the nano transducers' materials, geometry and size. Despite these efforts and the applicative interest, the effects of the Kapitza resistance and the laser pulse duration on the acoustic wave generation mechanism [2-4] are yet to be fully uncovered and lack of a thorough understanding. (10.1109/CLEO/EUROPE-EQEC57999.2023.10231581)
  DOI : 10.1109/CLEO/EUROPE-EQEC57999.2023.10231581
• Newly designed metal foam-salt hydrate composite for thermochemical heat storage
  
  • Liu Yutong
  • Dimanov Alexandre
  • Dalmazzone Didier
  • Hallais Simon
  , 2023. Thermochemical heat storage system based on the sorption mechanism between water vapor and hygroscopic salts is a promising technology. However, hygroscopic salts have drawbacks such as swelling and agglomeration during hydration/dehydration cycles, which leads to decreasing specific reaction surface and heat and mass transfer problems, resulting in poor cyclic performance and stability. In this context, we propose a composite of open-cell metal foam and calcium chloride for sorption thermal energy storage. An open-cell metal foam host matrix improves the heat and mass transfer kinetics thanks to the porous structure and the high thermal conductivity. Additionally, it offers elevated mechanical strength ensuring the mechanical resistance of the composite. The composite showed significant improvement in cyclic performance compared to that of bulk salt powder. Composites exhibited a stable heat release during cycles, which improved to 5-6 times that of bulk salt powder by the 12th cycle, whereas the bulk salt degraded by 78.5%. In situ environmental scanning electron microscope observations during hydration/dehydration cycles demonstrated that swelling and deliquescence induced redistribution of salt hydrates within the metal foam while preserving essential open pores for heat and mass transfer, along with the specific reaction surface, which explains the amelioration of the composite thermochemical performance.
• Dimensionnement fiabiliste sous chargements complexes : de la spécification à la validation
  
  • Baroux Emilien
  , 2023. Durant l’usage normal (service) d’un véhicule personnel, les pièces de suspension et de la caisse subissent les efforts induits par la route sur les essieux de roue. Ces chargements sont susceptibles d'endommager les soudures et bords de tôles laminées par fatigue polycyclique.La résistance de ces pièces est assurée par la définition d’exigences sur leur fiabilité. Leur dimensionnement suit une approche probabiliste : leur risque de défaillance avant une durée de vie objective est soumis à un maximum admissible, spécifié au niveau du système et propagé à travers tous ses composants.Tout au long du développement d’un modèle de véhicule, les prototypes de nouvelles pièces sont soumis à des procédures de validation numériques ou physiques. Les chargements soumis en entrée de ces tests représentent une mission spécifique et artificielle. Celle-ci consiste en une agrégation représentative des situations les plus endommageantes auxquelles le véhicule peut faire face.L’Interférence Contrainte-Résistance (SSI) est le procédé théorique majeur capable de maîtriser le risque de défaillance des pièces de la suspension et de la caisse d’un véhicule. Une variable aléatoire univariée, la Contrainte, évalue le potentiel d’endommagement qu’une mission du système peut induire sur une ou plusieurs de ses zones sensibles. Cette variable est opposée à la Résistance, qui prend en charge la variabilité du procédé de fabrication.En théorie, la méthode SSI permet de définir des niveaux (objectifs) de référence pour la conception et la validation de la fiabilité du système. En revanche, son implémentation est actuellement réalisée séparément pour chaque jeu de zones sensibles simultanément endommagées lors de cas de chargement particuliers.En pratique, une définition préliminaire et générale des conditions et niveaux de chargement pour les tests de validation est donnée par une référence historique. Cette référence peut prendre la forme d’un contrat d’éléments d’une piste d’essai, rencontrés par le véhicule à tester avec trajectoire et vitesse maîtrisées. L’adéquation du contrat piste est vérifiée a posteriori par l’application d’une méthode SSI sur les mesures d’un nouveau marché.L’objectif de cette thèse est d’améliorer le processus de détermination de chargements de validation adéquats pour la fiabilité de futurs projets de modèles de véhicules. La fatigue induite isolément sur différents jeux de zones sensibles doit être caractérisée par plusieurs variables de comptage distinctes. Nous adaptons donc l’ensemble de la méthode de caractérisation de la Contrainte à l’usage de vecteurs de variables d’intérêt. Cette décomposition complète et minutieuse de la méthode et de ses hypothèses sous-jacentes la transforme en une « boîte blanche » qui révèle pléthore de nouvelles pistes de recherche pour aller plus loin dans la caractérisation des chargements de service du véhicule.Notre stratégie est de révéler de nouvelles variables de sévérité associées aux différences de comportement conducteur et de contenu des trajets. Ces variables expliquent et quantifient la variabilité du potentiel de fatigue induit sur toutes les zones d’intérêt du véhicule. Elles sont déterminées au cours d’une analyse statistique multivariée sur les pseudo-endommagements induits par un échantillon de chargements en clientèle. Une distribution des conducteurs sur ces variables de sévérité est réalisée à partir d’une restriction motivée de la population des missions du véhicule. Cette distribution multivariée est ensuite traduite en chacune des distributions nécessaires à l’implémentation locale d’une méthode SSI. De nouvelles références de conception peuvent être proposées directement à partir de l’interprétation de la distribution de sévérité.Enfin, nous formalisons une méthode de détermination de contrats de chargement équivalents qui reproduisent les cas de chargements et pseudo-endommagements de ces références de conception.
• Effect of Spatial and Temporal Resolution on the Accuracy of Motion Tracking Using 2D and 3D Cine Cardiac Magnetic Resonance Imaging Data
  
  • Škardová Kateřina
  • Hussain Tarique
  • Genet Martin
  • Chabiniok Radomír
  , 2023, LNCS-13958, pp.235-244. In this paper, we investigate the effect of spatial and temporal resolution of cardiac MRI cine images on the extracted left ventricle motion. A previously developed and validated finite-element-based image registration method was used for the motion extraction. The study is performed on three subjects, for which the standard 2D cine stack (SA) in short axis orientation and 3D cine MRI series were acquired. The set of acquired image series was augmented by artificially constructed SA-like cine series created from the 3D cine images. Image series with several combinations of spatial and temporal resolution were evaluated for each subject. The study showed a strong correlation between the slice thickness and the accuracy of extracted displacement in the longitudinal direction. The effect of a lower temporal resolution was shown to be less significant. This could prove useful to update current guidelines for cardiac MRI acquisitions. (10.1007/978-3-031-35302-4_24)
  DOI : 10.1007/978-3-031-35302-4_24
• Neural networks for large deformation plasticity. Towards real-time interactive simulations
  
  • Lesueur Louis
  • Thorin Anders
  • Weisz-Patrault Daniel
  , 2023. In the last years, neural networks have been used to learn physical simulations in a wide range of contexts. The present work tackles the training of neural networks for large deformation plasticity. There are two sources of nonlinearity: geometric (large deformation) and material (plasticity). Traditional numerical methods for plastic simulations (such as the Finite Element method) are computationally expensive. NNs architectures have been proposed in plasticity in some simple cases, in the small deformations framework. The main contributions are i) the application of NN for plasticity in large deformations, ii) a review and comparison of the existing methods, iii) the use of a Temporal Convolutional Network that trains faster than the existing methods, iv) an open source benchmark to the scientific community. Altogether, these contributions enable real-time simulation of plastic behaviors.
• Damping optimization of viscoelastic thin structures, application and analysis
  
  • Joubert Antoni
  • Allaire Grégoire
  • Amstutz Samuel
  • Diani Julie
  Structural and Multidisciplinary Optimization, Springer Verlag, 2023, 66 (7), pp.149. In this work damping properties of bending viscoelastic thin structures are enhanced by topology optimization. Homogeneous linear viscoelastic plates are optimized and compared when modeled by either the Kirchhoff-Love or Reissner-Mindlin plate theories as well as by the bulk 3D viscoelastic constitutive equations. Mechanical equations are numerically solved by the finite element method and designs are represented by the level-set approach. High performance computing techniques allow to solve the transient viscoelastic problem for very thin 3D meshes, enabling a wider range of applications. The considered isotropic material is characterized by a generalized Maxwell model accounting for the viscoelasticity of both Young modulus and Poisson's ratio. Numerical results show considerable design differences according to the chosen mechanical model, and highlights a counterintuitive section shrinking phenomenon discussed at length. The final numerical example extends the problem to an actual shoe sole application, performing its damping optimization in an industrial context. (10.1007/s00158-023-03602-z)
  DOI : 10.1007/s00158-023-03602-z
• Trending Ability of End-Tidal Capnography Monitoring During Mechanical Ventilation to Track Changes in Arterial Partial Pressure of Carbon Dioxide in Critically Ill Patients With Acute Brain Injury: A Monocenter Retrospective Study
  
  • Coëffic Adrien
  • Joachim Jona
  • Manquat Elsa
  • Felliot Élodie
  • Vallée Fabrice
  • Mebazaa Alexandre
  • Gayat Étienne
  • Chousterman Benjamin Glenn
  • Barthélémy Romain
  Anesthesia & Analgesia, Lippincott, Williams & Wilkins, 2023, 138 (3), pp.607-615. BACKGROUND: Changes in arterial partial pressure of carbon dioxide (Pa co 2 ) may alter cerebral perfusion in critically ill patients with acute brain injury. Consequently, international guidelines recommend normocapnia in mechanically ventilated patients with acute brain injury. The measurement of end-tidal capnography (Et co 2 ) allows its approximation. Our objective was to report the agreement between trends in Et co 2 and Pa co 2 during mechanical ventilation in patients with acute brain injury. METHODS: Retrospective monocenter study was conducted for 2 years. Critically ill patients with acute brain injury who required mechanical ventilation with continuous Et co 2 monitoring and with 2 or more arterial gas were included. The agreement was evaluated according to the Bland and Altman analysis for repeated measurements with calculation of bias, and upper and lower limits of agreement. The directional concordance rate of changes between Et co 2 and Pa co 2 was evaluated with a 4-quadrant plot. A polar plot analysis was performed using the Critchley methods. RESULTS: We analyzed the data of 255 patients with a total of 3923 paired ΔEt co 2 and ΔPa co 2 (9 values per patient in median). Mean bias by Bland and Altman analysis was −8.1 (95 CI, −7.9 to −8.3) mm Hg. The directional concordance rate between Et co 2 and Pa co 2 was 55.8%. The mean radial bias by polar plot analysis was −4.4° (95% CI, −5.5 to −3.3) with radial limit of agreement (LOA) of ±62.8° with radial LOA 95% CI of ±1.9°. CONCLUSIONS: Our results question the performance of trending ability of Et co 2 to track changes in Pa co 2 in a population of critically ill patients with acute brain injury. Changes in Et co 2 largely failed to follow changes in Pa co 2 in both direction (ie, low concordance rate) and magnitude (ie, large radial LOA). These results need to be confirmed in prospective studies to minimize the risk of bias. (10.1213/ANE.0000000000006553)
  DOI : 10.1213/ANE.0000000000006553
• Solveur numérique générique pour la modélisation de l'influence des contraintes mécaniques sur la propagation des ondes guidées pour les applications SHM
  
  • Dalmora Andre
  • Imperiale Alexandre
  • Imperiale Sébastien
  • Moireau Philippe
  , 2023, 28, pp.28536 (4 p.). Dans les applications industrielles de pointe, l'évaluation de l'intégrité des structures est un aspect important des exigences de sécurité. Cependant, l'application des méthodes classiques d'évaluation non destructive (END) peut être coûteuse et entraîne généralement des interruptions d'activité. Pour surmonter ces inconvénients, le Structural Health Monitoring (SHM) propose d'utiliser des capteurs et des unités de traitement du signal in situ. Les ondes ultrasonores guidées constituent l'un des moyens de mettre en œuvre les systèmes SHM. Elles peuvent être utilisées pour évaluer les caractéristiques internes du matériau, telles que ses propriétés et ses défauts. Les performances d'une solution SHM sont affectées par les conditions opérationnelles et en particulier les contraintes mécaniques et il est donc important de prédire l'influence pour l'interprétation des signaux ou la démonstration de performance et la conception des systèmes. Un exemple typique est celui des charges opérationnelles induisant de grandes déformations et par conséquent des contraintes internes qui entraînent des changements dans la propagation des ondes. Dans ce contexte, il est important que les efforts de modélisation de la propagation des ondes prennent en compte ces phénomènes. L'objectif de notre travail est de proposer un modèle, et les méthodes numériques correspondantes, pour la propagation élastique des ondes dans un milieu précontraint. Comme les structures considérées sont généralement minces, nous utilisons une formulation de coque pour la mécanique non linéaire pour résoudre le problème statique, représentant les effets du chargement de la structure. Le déplacement calculé est ensuite transmis à la méthode des éléments finis spectraux (SFEM) pour résoudre le problème élastodynamique linéarisé dans le domaine temporel, représentant la propagation des ondes. Au-delà de la modélisation directe nous visons à utiliser ces outils dans les boucles d'inversion pour la reconstruction de la contrainte mécanique à partir de mesures ultrasonores avec capteurs traditionnels. Le modèle s'applique de la même façon à des configurations SHM ou à des configurations d'END et il a pour vocation d'enrichir la plateforme CIVA. (10.58286/28536)
  DOI : 10.58286/28536
• Flow recovery from distal pressure in linearized hemodynamics: an optimal control approach
  
  • Imperiale Sébastien
  • Manganotti Jessica
  • Moireau Philippe
  Inverse Problems, IOP Publishing, 2023, 39 (7), pp.075004. The goal of this work is to derive a reliable stable and accurate inverse problem strategy for reconstructing cardiac output blood flow entering the ascending aorta from pressure measurements at a distal site of the arterial tree, assumed here to be the descending aorta. We assume that a reduced one-dimensional model of the aorta can be linearized around its steady state, resulting in a wave system with absorbing boundary condition at the outlet. Using this model, we attempt to reconstruct the inlet flow from a pressure measurement at the distal outlet. First, we investigate the observability of the problem and prove that the inversion of the input-output operator for the flow and pressure in the space of time-periodic solutions is ill-posed of degree one. We then develop a variational approach where we minimize the discrepancy between measurements and a simulated state and penalize the error with respect to a periodic state. It is shown that the penalty strategy is convergent and provides an efficient solution for the minimization. Numerical results illustrate the robustness of our approach to noise and the potential of our method to reconstruct inlet flow from real pressure recordings during anesthesia. (10.1088/1361-6420/acd274)
  DOI : 10.1088/1361-6420/acd274
• Essai d'une nouvelle analyse de la mortalité causée par la petite vérole, et des avantages de l'inoculation pour la prévenir
  
  • Bernoulli Daniel
  • Chapelle Dominique
  , 2023. Note du transcripteur: Cette transcription se veut parfaitement fidèle à l'original du mémoire (accessible sur le site Gallica de la BNF), ma motivation étant avant tout de rendre celui-ci plus facile d'accès et de lecture, et rendre ainsi hommage à cette oeuvre pionnière, et relativement méconnue parmi toutes les contributions de Daniel Bernoulli. Je me suis donc contenté d'appliquer des modifications mineures liées à l'orthographe moderne, sans changer la ponctuation (qui, quoiqu'un peu datée, ne suscite pas de difficulté de lecture), la grammaire étant par ailleurs parfaitement conforme aux règles encore en usage. Il va de soi que tous les retours sont les bienvenus sur cette transcription, qui pourra faire l'objet de révisions futures en fonction de ceux-ci.
• Estimating the effect of operational loading condition from ultrasonic guided wave measurements using an iterated Unscented Kalman Filter
  
  • Dalmora Andre
  • Imperiale Alexandre
  • Imperiale Sébastien
  • Moireau Philippe
  , 2023. In leading-edge industrial applications, assessing structural integrity is an important aspect of safety requirements. Structural Health Monitoring (SHM) proposes to use sensors and signal processing units in situ. One of the most attractive SHM techniques relies on ultrasonic guided waves. Operational conditions can change wave propagation and therefore affect the interpretation of recorded signals. Modeling and simulation can be helpful tools for the design or the reliability assessment of SHM solutions. In , we have proposed a wave propagation model to take into account effects of operational conditions such as internal stresses caused by mechanical loading. In this work, we develop a strategy for estimating these load-induced (large) deformations from ultrasonic measurements. In the context of least-squares optimization, we minimize the difference between measurements and the observed direct model. Among the available methods there exist variational methods, such as Full Waveform Inversion , and sequential approaches, such as Kalman Filtering. As the linearized aspect of the direct model leads to an unwieldy tangent dynamics, tangent-free methods are preferable. After reducing the dimension of the parametric space by decomposing the deformation on selected eigenmodes of a static problem, we apply iteratively the Reduced-Order Unscented Kalman Filter as estimation method. We will show how this method can be understood as a gradient free alternative to an iterated Gauss-Newton based minimisation of the least squares functional, or incremental 4D-variational method. Moreover it allows to launch multiple direct solvers in parallel leading to an efficient exploration of the parametric space and sensitivity analysis w.r.t. extended sets of eigenmodes. We illustrate the proposed inversion strategy by applying it to realistic cases.
• Rapport d’évaluation de l’unité FEMTO-ST – Franche-Comté Électronique, Mécanique, Thermique et Optiques - Sciences et Technologies
  
  • Tournié Eric
  • Allain Jean-Marc
  • Arnoux Mathieu
  • Bardou Nathalie
  • Basrour Skandar
  • Bassat Jean-Marc.
  • Bergaud Christian
  • Brun Xavier
  • Destouches Nathalie
  • Fatu Aurelian
  • Folio David
  • Grall Antoine
  • Guidoni Luca
  • Guitton Alexandre
  • Joubert Pierre-Yves
  • Landragin Arnaud
  • Racoceanu Daniel
  • Restoin Christine
  • Salaün Gwen
  • Serra Roger
  • Trichet Didier
  , 2023, pp.1-51.