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Justification du système moyenne biphasée pour des gaz parfaits sans conductivité
No full textThis article concerns the mathematical justification of an averaged system of partial differential equations governing the evolution of a two-phase mixture of compressible ideal fluids, with viscosity and without conductivity, in space dimension 1 with periodic boundary conditions. The derivation is done by some homogenization procedure. The originality and the difficulty of the paper consists in the fact that both the density and temperature are allowed to oscillate (because of the absence of heat conduction), so that the limiting model is a six-equations, two-pressures, two-temperatures model. The key point is to show the strong convergence of the stress tensor in \(L^2((0,T)\times (0, 1))\). The main difficulties are to obtain uniform estimates in spite of the presence of oscillating coefficients in the energy equation. It requires to look at solutions with low regularity for the density and the temperature.Cet article concerne la justification mathématique d'un système moyenné d'équations aux dérivées partielles régissant l'évolution d'un mélange biphasique de fluides compressibles sans conductivité thermique, en dimension 1, avec des conditions aux limites périodiques. La dérivation est faite par une procédure d'homogénéisation. L'originalité et la difficulté de l'article réside dans le fait que la densité et la température sont toutes deux autorisées à osciller (à cause de l'absence de conduction thermique), de sorte que le modèle limite est un modèle à six équations, deux pressions, et deux températures. Le point clé est de montrer la convergence forte du tenseur de contrainte dans \( L^2((0, T) \times (0, 1)) \). Afin d'obtenir des estimations uniformes malgré la présence de coefficients oscillants dans l'équation de l'énergie, nous examinons des solutions de faible régularité pour la densité et la température
Load variation analysis of a class EF inverter with a RL parallel load
No full textInternational audienceIn this paper, a graphical load variation analysis of a class EF inverter loaded with a parallel RL circuit is presented, utilizing the class EF inverter design chart introduced in a previous work. Experimental results from the implementation of a 15 MHz, 25 VDC inverter are in good agreement with the predictions made using the chart. The study demonstrates that the class EF inverter with a parallel RL load can sustain Zero Voltage Switching (ZVS) over a wide load range with a fixed duty cycle. This behavior, which can be accurately predicted using the design chart, is discussed in detail.</div
Multiscale modeling of viscoelastic behavior in demineralized human trabecular bone
No full textInternational audienceA C TBone is a hierarchical composite of inorganic and organic phases, with the former governing stiffness and strength, and the latter controlling toughness and post-yield behavior. The mechanical properties of the organic phase, particularly in demineralized trabecular bone, remain poorly understood, limiting insights into fracture mechanisms and scaffold design. In this study, we investigate the time-dependent viscoelastic behavior of human demineralized trabecular bone using an integrated approach combining stress-relaxation testing, micro-finite element simulations, and Raman spectroscopy at macro-and microscales. Multiscale equilibrium and instantaneous moduli were quantified and correlated with trabecular microarchitecture and collagen spectral markers. Our results reveal how collagen integrity and microarchitecture jointly govern viscoelastic behavior, providing a mechanistic link between tissue composition and macroscopic mechanical performance. These findings not only advance fundamental understanding of the organic matrix mechanics in trabecular bone but also establish a predictive framework for designing biomimetic scaffolds that replicate the native biomechanical and biochemical microenvironment.</div
Raisonnement embarqué pour le Web des Objets
No full textThe Web of Things extends the Internet of Things with standards of the Web, such as knowledge graphs and reasoning abilities. Traditional reasoners are optimized for performance and require excessive hardware resources, especially memory, to run on the constrained objects typically used in IoT applications. In this thesis, we present optimizations of a commonly used reasoning algorithm to make its implementation possible on constrained objects, with a focus on reducing the required memory footprint for reasoning. These optimizations are (i) algorithmic, taking advantage of the characteristics of the rulesets used for reasoning, and (ii) focused on in-memory knowledge representation within the reasoner. We also present LiRoT, the implementation of a lightweight, incremental reasoner that can be embedded on constrained objects, as a result of these optimizations. We experimentally evaluate the impact of the various optimizations, and show that they significantly reduce the memory footprint of the reasoner, with minimal impact on computation time. We also compare LiRoT to several state of the art reasoners, and show that it is better suited for handling datasets with sizes typical of IoT applications. Finally, we evaluate the use of LiRoT on platforms such as ESP32 and Arduino Due, and show that it is possible to perform reasoning tasks on such constrained platforms. This thesis was funded by the CoSWoT project (ANR-19-CE23-0012).Le Web des Objets étend l'Internet des Objets avec des standards du Web, tels que des graphes de connaissances et des capacités de raisonnement. Les raisonneurs traditionnels sont optimisés pour la performance et nécessitent trop de ressources matérielles, notamment de mémoire, pour être exécutés sur les objets contraints typiquement utilisés dans les applications IoT. Dans cette thèse, nous proposons des optimisations d'un algorithme de raisonnement couramment utilisé pour rendre son implémentation possible sur des objets contraints, en nous concentrant sur la réduction de l'empreinte mémoire du raisonnement. Ces optimisations sont (i) algorithmiques, tirant profit des caractéristiques des jeux de règles utilisés pour le raisonnement, et (ii) axées sur la représentation des connaissances en mémoire au sein du raisonneur. Nous proposons également LiRoT, l'implémentation d'un raisonneur léger et incrémental pouvant être embarqué sur des objets contraints, résultat de ces optimisations. Nous évaluons expérimentalement l'impact des diverses optimisations, et nous montrons qu'elles permettent de réduire significativement l'empreinte mémoire du raisonnement, tout en ayant un impact minimal sur le temps de calcul. Nous comparons également LiRoT à plusieurs raisonneurs de référence, et nous montrons qu'il est plus adapté pour traiter des jeux de données d'une taille typique des applications IoT. Enfin, nous évaluons l'usage de LiRoT sur des plateformes telles qu'ESP32 et Arduino Due et montrons qu'il est possible de faire du raisonnement sur des plateformes aussi contraintes. Cette thèse a été financée par le projet CoSWoT (ANR-19-CE23-0012)
Structural mutations set an equilibrium non-coding genome fraction
No full textInternational audienceNon-coding genome size evolution is poorly understood. While some fraction of non-coding DNA has arguably a regulatory function, a large part does not seem to have a detectable impact on any phenotypic trait. The abundance of non-functional DNA in genomes, observed across the Tree of Life, challenges a purely adaptationist explanation. Several non-adaptive theories have been proposed to explain its presence and identify its determinants, emphasizing either the mutational processes or the mutational hazard entailed by non-coding and non-functional DNA. However, those theories have not yet been integrated into a single framework, and the exact nature of the mutational hazard is not yet fully understood. In this work, we propose a simple mathematical model of genome size evolution. The model shows how the non-coding fraction of the genome is shaped by two factors: unavoidable biases in the neutrality of the different mutation types (adding base pairs is more likely to be neutral than removing some), and the robustness selection imposed by the mere existence of structural mutations (larger genomes are more prone to double-strand breaks that can initiate structural mutations, imposing a second-order selection on robustness). Together, these two factors ensure the existence of an equilibrium non-coding fraction. We show that this equilibrium depends solely on mutation biases and the product of population size and mutation rate
Scenario for the formation of fretting obtained TTS in TA6V from detailed microstructural analysis
No full textInternational audienceFretting is defined as surface degradation caused by small oscillatory movements. Fretting in the gross slip regime produces high local stresses at the surface. This results in wear and subsurface plastic deformation, which can create a nanosized-grained structure known as a Tribologically Transformed Structure (TTS). If the condition of TTS formation in the fretted interface is well documented in the literature, the metallurgical transformation leading to this structure is not well known. This article aims to study this phenomenon thanks to an innovative in-depth texture analysis of the TTS which is carried out using a TEM crystal plane indexing technique. Several TTS from different steps in the TTS formation are studied. Special care is taken in determining their texture, and chemical analysis is carried out. Considering the temperatures involved and the successive structures analyzed, a new model of continuous dynamic recrystallization via the apparition of shear bands is proposed to explain the heterogeneity of TTS and its microstructural characteristics
Modeling the Lifecycle of Knowledge Artefacts in Qualitative Research Methodologies
No full textInternational audienceThis paper proposes a knowledge artefact lifecycle model tailored for qualitative research projects. Knowledge artefacts are deep analysis artefacts that give semantic to various types of content, such as surveys, interviews, codebooks, and field diaries. The proposal emerges from an empirical study of an e-social science research project that applies Grounded Theory as its theoretical framework. In this context, we propose a model to delineate the lifecycle of artefacts within a qualitative research process workflow. Our research contributes to developing a first approach on the problem of modeling the very diverse content produced through qualitative research processes. We argue that modeling the lifecycle of knowledge artefacts within a qualitative research process could shed light on the reliability and transparency of the process itself
Reconstruction of tensile and shear elastic moduli in anisotropic nearly incompressible media using Rayleigh wave phase and group velocities
No full textInternational audienceSignificance: Dynamic optical coherence elastography can excite and detect propagating mechanical waves in soft tissue without physical contact and in near real time. However, most soft tissue is anisotropic, characterized by at least three independent elastic moduli. As a result, reconstructing these moduli from mechanical wave fields requires a complex procedure.Aim: We consider a nearly incompressible transverse isotropic (NITI) material, which has been shown to locally define the symmetry of many soft tissues such as muscle, tendon, skin, cornea, heart, and brain. Reconstruction of elastic moduli in the NITI medium using Rayleigh waves is addressed here. A method to accurately compute the angular dependence of Rayleigh wave phase velocity for the most common geometries (point-like and line sources) of mechanical wave excitation is described.Approach: When a line source is used to launch plane mechanical waves over the medium surface, the phase velocity of Rayleigh waves in the direction of propagation is directly accessible. For a point-like source, propagation of the energy flux is tracked (i.e., its group velocity), which cannot be directly used for moduli inversion. In this case, angular spectrum decomposition is used to access the phase velocity. Both numerical simulations in OnScale and experiments in a stretched PVA phantom were performed.Results: We show that both methods (line source wave excitation and angular decomposition from a point-like source) produce similar results and accurately estimate the angular anisotropy of the Rayleigh wave phase velocity. We also explicitly show that a commonly used group velocity approach leads to inadequate moduli inversion and should not be used for reconstruction.Conclusions: We suggest that the line source is best when a surface area must be scanned, whereas the point-like source with the proposed phase velocity reconstruction is best for single-point moduli estimation or when tissue motion is a concern
Analysis of a polarization model with exchange at the boundary
No full textHere we analyze a drift-diffusion model on the half-line. The drift is linked to exchanges at 0. This corresponds to the modeling of filament generation following protein exchanges between the membrane and the cytoplasm of a cell. This model has a critical mass and the asymptotic behaviors can be divided into three categories. In subcritical mass regime, diffusive behavior dominates and convergence in self-similar variables can be obtain with parabolic scaling. In supercritical mass regime, drift compensates for diffusion and convergence towards equilibrium distributions occurs. In the critical case, convergence towards 0 for the drift occurs over a long period of time, the behavior exhibits a distinct relevant scaling. We quantify the convergences in the relevant variables in the three regimes
Numerical Simulation of the Mitral Valve Repair: A Pilot Model
No full textInternational audienceMitral regurgitation is the second most common valve disease in Europe. This pathology is characterized by a leak in the mitral valve leading to retrograde blood flow from the left ventricle to the left atrium during systole. The annuloplasty is a surgical operation that aims to reduce the valve’s diameter and to stabilize the repair, preventing recurrence of mitral regurgitation by mean of a prosthetic ring. This prosthetic ring is attached to the native mitral annulus with sewing nitinol threads or anchors. The dehiscence of the anchors after a substantial number of cardiac cycles is conditioned by mechanical and hemodynamical solicitations applied on the system, the healing process at anchors’ locations and the tissue and prothesis’ properties. We aim to develop a digital twin of the mitral valve and its environment. The objective is to obtain a prosthetic ring according to patients’ physiology and pathology