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Interdépendance du réalisme visuel et comportemental pour l’acceptation des personnages virtuels en environnement immersif collaboratif.
No full textThis research explores how the appearance and intensity of facial expressions in virtual characters impact user acceptance in immersive and collaborative environments. Avatars, increasingly present in video games and virtual reality platforms, range from realistic to stylized designs. However, their success depends on factors such as the "Uncanny Valley" effect, where hyper-realistic avatars can sometimes feel unsettling to users.The study addresses two key questions: how does avatar appearance influence user perception, and how do stylization and expression intensity affect the sense of social presence? To answer these, three experiments were conducted.The first experiment evaluated the effect of facial anthropomorphism on users' sense of embodiment, attractiveness, and social presence in two collaborative virtual tasks. Three robotic avatars with varying levels of human likeness were tested. Results indicated that higher anthropomorphism enhanced attractiveness and task performance but did not affect embodiment or social presence. However, task type significantly influenced the quality of social interactions, especially when non-verbal communication played a role.The second and third experiments focused on the relationship between avatar stylization, expression intensity, and their impact on perceived eeriness, realism, and attractiveness. In the second experiment, conducted online, users viewed video sequences of avatars with three levels of stylization (stylized, semi-realistic, realistic) and four expression intensities (idle, low, moderate, exaggerated). Findings showed that perceived realism was primarily influenced by stylization level; more human-like avatars were seen as more realistic, even with exaggerated expressions. However, attractiveness decreased as expression intensity increased, and eeriness grew with higher intensity.The third experiment involved immersive interactions using three female avatars with real-time controlled expression intensities (low, standard, increased) during a guessing game. Participants reported a stronger sense of co-presence with the stylized avatar compared to the realistic one, regardless of expression intensity. No significant interaction was observed between stylization and expression intensity on the measured variables. The realistic avatar evoked a greater sense of perceived eeriness and lower trustworthiness. Nevertheless, increased expression intensity did not negatively impact social presence or avatar perception, suggesting that expressive avatars can enhance communication in virtual environments without compromising user experience.Overall, these studies highlight how immersion can affect perceptions of virtual characters. The interactivity in immersive environments appears to make users more accepting of inconsistencies between avatar stylization and expression intensity. This research provides valuable guidelines for designing avatars and autonomous agents in virtual environments.Ce travail de recherche explore la manière dont l’apparence et l’intensité des expressions faciales des personnages virtuels influencent leur acceptation par les utilisateurs dans des environnements immersifs et collaboratifs. Les avatars, que l’on retrouve de plus en plus dans les jeux vidéo et les plateformes de réalité virtuelle, varient entre un style réaliste et stylisé, mais leur intégration réussie auprès du public dépend de nombreux facteurs, comme la prise en compte du phénomène de la Vallée de l’étrange.L’étude se concentre sur deux questions : comment l’apparence des avatars affecte-t-elle la perception des utilisateurs, et comment la stylisation et l’intensité des expressions modulent-elles le sentiment de présence sociale ? Pour y répondre, trois expérimentations ont été menées.Dans un premier temps, nous avons cherché à évaluer l'impact de l'anthropomorphisme facial des avatars sur le sentiment d’incarnation, l’attractivité, et la présence sociale dans 2 tâches collaboratives en environnement virtuel. Le niveau d’anthropomorphisme facial était modulé par les caractéristiques de trois avatars robotiques. Les résultats montrent que l’anthropomorphisme influence l’attractivité et la performance, mais pas l'incarnation ni la présence sociale. Toutefois , nous avons observé que le type de tâche influence la qualité des interactions sociales, particulièrement lorsque la communication non verbale est à même de jouer un rôle positif.Les deux expérimentations suivantes ont porté sur l’étude de la relation entre la stylisation des avatars, l’intensité de leurs expressions faciales, et leur impact sur la perception, notamment l’étrangeté perçue, le réalisme et l’attractivité. D’abord dans un contexte non immersif au moyen d'une enquête en ligne reposant sur une série de vidéos (expérimentation 2), puis dans un contexte immersif, pour comprendre comment ces deux dimensions influencent les interactions en face à face, et notamment la présence sociale (expérimentation 3). Pour l'expérimentation 2, nous avons modélisé des personnages masculin et féminin, chacun avec 3 niveaux de stylisation (stylisé, semi-réaliste, réaliste) et 4 intensités d'expressivité (statique, faible, modérée, exagérée).Les résultats montrent que le réalisme perçu est surtout influencé par le niveau de stylisation : les avatars avec l’apparence se rapprochant le plus d’un humain étaient jugés plus réalistes, même avec des expressions exagérées. L'attractivité, quant à elle, diminuait avec l'intensité des expressions faciales. Enfin, à mesure que l’intensité des expressions faciales augmentait, le sentiment d’étrangeté s’intensifiait. Pour l'expérimentation 3, nous avons utilisé les mêmes trois avatars féminins, dont nous avons modulé en temps réel l’intensité des expressions faciales (faible, standard et augmentée). Les participants ont ressenti un plus grand sentiment de co-présence avec l’avatar stylisé qu'avec l’avatar réaliste, indépendamment du niveau d’intensité. Nous n'avons pas observé d'interaction entre la stylisation et l'intensité des expressions faciales sur les variables considérées. L’avatar réaliste a suscité un sentiment d’étrangeté perçue supérieur, et un niveau de fiabilité plus faible. Enfin, l’augmentation de l’intensité des expressions n'a pas eu d'impact négatif sur la présence sociale ou la perception des avatars, suggérant que des avatars plus expressifs peuvent améliorer la communication dans les environnements virtuels sans nuire à l’expérience des utilisateurs.Les trois études rapportées dans cette thèse mettent en lumière que l’immersion peut profondément influencer la manière dont les personnages virtuels sont perçus. L’interactivité propre aux environnements immersifs semble rendre les utilisateurs plus enclins à accepter les incohérences entre la stylisation et l’intensité des expressions faciales. Ainsi, nos travaux offrent des lignes directrices pour la conception d'avatars et d'agents autonomes
A comparison of anticipatory processes between gait and step initiation: The role of the final state
No full textInternational audienceBACKGROUND: Whole-body movement initiation with change of base of support is a common paradigm used to assess balance-movement coordination. During clinical evaluation, two transitions are commonly used: gait or step initiation. During their respective anticipatory periods, two mechanisms regulate the whole-body centre of mass acceleration: a shift in the centre of pressure (CoP); and modulation of internal wholebody angular momentum (HM). These transitions have different final states, and we do not know whether the two mechanisms are used similarly during the anticipatory period.RESEARCH QUESTION: Is the final state already taken into account during the anticipatory period of a whole-body movement initiation?METHODS: We compared the time evolution of the CoP and HM in the sagittal plane during the anticipatory period of both gait and step initiation in 13 young, healthy participants.RESULTS: During gait initiation, we observed a larger backward CoP shift (31-56% and 75-100% of the anticipatory period), a larger forward-directed HM (45-68%), and a lower backward-directed HM (84-100%) compared to step initiation.SIGNIFICANCE: Our results show that mechanical instability is larger during gait initiation, while HM modulation is larger during step initiation. These findings suggest that the final state of a transition is taken into account during the anticipatory period. Based on our results, we suggest future research should use gait and step initiation to evaluate the generation of mechanical instability, and the use of free segments, respectively, in populations with balance deficits
Digital Twins, Extended Reality, and Artificial Intelligence in Manufacturing Reconfiguration: A Systematic Literature Review
No full textInternational audienceThis review draws on a systematic literature review and bibliometric analysis to examine how Digital Twins (DTs), Extended Reality (XR), and Artificial Intelligence (AI) support the reconfiguration of Cyber-Physical Systems (CPSs) in modern manufacturing. The review aims to provide an updated overview of these technologies' roles in CPS reconfiguration, summarize best practices, and suggest future research directions. In a two-phase process, we first analyzed related work to assess the current state of assisted manufacturing reconfiguration and identify gaps in existing reviews. Based on these insights, an adapted PRISMA methodology was applied to screen 165 articles from the Scopus and Web of Science databases, focusing on those published between 2019 and 2025 addressing DT, XR, and AI integration in Reconfigurable Manufacturing Systems (RMSs). After applying the exclusion criteria, 38 articles were selected for final analysis. The findings highlight the individual and combined impact of DTs, XR, and AI on reconfiguration processes. DTs notably reduce reconfiguration time and improve system availability, AI enhances decision-making, and XR improves human-machine interactions. Despite these advancements, a research gap exists regarding the combined application of these technologies, indicating potential areas for future exploration. The reviewed studies recognized limitations, especially due to diverse study designs and methodologies that may introduce risks of bias, yet the review offers insight into the current DT, XR, and AI landscape in RMS and suggests areas for future research
Optimizing reaction and transport fluxes in temperature-gradient-driven chemical reaction-diffusion systems
No full textInternational audienceTemperature gradients represent energy sources that can be harvested to generate steady reaction or transport fluxes. Technological developments could lead to the transfer of free energy from heat sources and sinks to chemical systems for the purpose of extraction, thermal batteries, or nonequilibrium synthesis.We present a theoretical study of 1D chemical systems subjected to temperature gradients, for sustaining nonequilibrium chemical fluxes. A complete theoretical framework describes the behavior of the system induced by various temperature profiles. An exact mathematical derivation was established for a simple two-compartment model and was generalized to arbitrary reaction-diffusion systems based on numerical models. An experimental system was eventually scaled and tuned to optimize either nonequilibrium chemical transport or reaction.The relevant parameters for this description were identified; they focused on the system symmetry for chemical reaction and transport. Nonequilibrium thermodynamic approaches lead to a description analogous to electric circuits. Temperature gradients lead to the onset of a steady chemical force, which maintains steady reaction-diffusion fluxes moderated by chemical resistance. The system activity was then assessed using the entropy production rate as a measure of its dissipated power.The chemical characteristics of the system can be tuned for general optimization of the nonequilibrium state or for the specific optimization of either transport or reaction processes. The shape of the temperature gradient can be tailored to precisely control the spatial localization of active processes, targeting either precise spatial localization or propagation over large areas. The resulting temperature-driven chemical system can in turn be used to drive secondary processes into either nonequilibrium reaction fluxes or concentration gradients
Finite element modelling of the oxidation gradients of epoxy-diamine matrices below and above their glass transition temperature
No full textInternational audienceThis article outlines a numerical calculation code developed under finite elements to simulate as accurately as possible the thermal aging of epoxy-diamine (EPO-DA) matrices below and above their glass transition temperature (Tg. The code is based on a kinetic model that couples, in a single balance equation, the diffusion of oxygen (O2) and its consumption by the chemical reaction with the epoxy network. The reliability of the oxidation rate expression was carefully checked for six EPO-DA matrices over wide ranges of temperature and O2 partial pressure in previous publications. The code gives access to the oxidation gradients within the sample thickness whose validity is successfully checked through a literature compilation (completed by our own recent results) of more than 40 thicknesses of oxidized layer (TOL), measured with different physico-chemical techniques on various EPO-DA matrices thermally aged in air below and above their Tg. In the glassy state, where the coefficient of O2 diffusion (DO2) obeys a well-established Arrhenius’ law depending on the chemical structure of the diamine hardener (either aliphatic or aromatic), the estimates of TOL are in nice agreement with the experimental data. In the rubbery state, in contrast, the calculations largely underestimate the experimental data for the stiffest EPO-DA matrices if a sharp increase in DO2 is not also considered when passing above Tg.. This positive jump in DO2 places all EPO-DA matrices at the same level of molecular mobility in the rubbery state, thus completely erasing the stiffening effect of aromatic rings observed in the glassy stat
Experimental Study of Axial Fan Performances Operating In Constrained Environment: Application of Axial and Combined Axial-Radial Blockage
No full textInternational audienceThis paper aimed to develop an experimental procedure for axial fans characterisation operating in constrained fields. The influence of an obstacle located downstream of a fan is studied experimentally on standardised test bench of the suction box type under different specific angular speeds. The axial fan of forward sweep category operates in free field referred as baseline configuration and in fields constrained by two blocking configurations axial and combined axial-radial. The blockages are produced by a flat plate, perpendicular to the axis of rotation of the fan for axial blockage case and two other plates placed radially for combined axial-radial blockage case, modelling, for example, the obstruction of a car internal combustion engine block. The four sets of global performances (pressure rise, flow rate, mechanical power and static efficiency) evolving with the different obstacles are compared to highlight their similarities. Variations in pressure rise as a function of flow rate were observed as the obstacle was changed depending upon the operating regime of the fan weather is working on axial or radial pattern discharge. The characteristic curves seem to evolve with substantial gain compared to the free field case especially when the blockage matched the flow configuration in the fans' wake
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
Optimisation topologique sous incertitudes géométriques aléatoires et épistémiques
No full textAdditive manufacturing is an innovative manufacturing process enabling the production of parts with complex geometries. However, due to the effects of uncertainties, this process lacks repeatability. Consequently, the produced parts inherently exhibit geometric imperfections. The aim of this thesis is to integrate process-related information into the design workflow. To achieve this, a topology optimisation approach was developed. Topology optimisation assists designers by providing complex and performance-optimised geometries. The formulation has been modified to mitigate the effects of both aleatory and epistemic uncertainties. To address the impact of geometric imperfections in topology optimisation, several innovations were introduced.First, dedicated taxonomies for robust topology optimisation under geometric imperfections, uncertainty characterisation, and robust optimisation problems are developed.Moreover, a comprehensive methodological framework was conceived and applied.Subsequently, a model characterising geometric deviations as a function of local geometric features is compared against deterministic cases and a reference model from the literature.Finally, a method specifically designed to reduce the effects of epistemic uncertainties in robust topology optimisation is developed. This method allows the designer to adopt an optimistic or pessimistic approach depending on the accuracy of the models and the project context.The proposed work has proven effective in mitigating the impact of geometric imperfections during the design process for robustness.La fabrication additive est un procédé de fabrication innovant permettant de fabriquer des pièces aux formes complexes. Toutefois, à cause des effets des incertitudes, ce procédé de fabrication manque de répétabilité. Les pièces produites affichent emph{ipso facto} des imperfections géométriques. Le but de cette thèse est d'intégrer les informations venues du procédé dans le processus de conception. C'est pourquoi une approche basée sur l'optimisation topologique a été développée. L'optimisation topologique permet de guider le concepteur en fournissant des topologies aux formes complexes et optimisées vis-à-vis de critères de performance. La formulation est modifiée pour atténuer les effets des incertitudes aléatoires et épistémiques. Pour atténuer les effets des imperfections géométriques avec l'optimisation topologique, plusieurs nouveautés sont développées.Tout d’abord, des taxonomies dédiées à l'optimisation topologique robuste sous des imperfections géométriques, à la caractérisation des incertitudes et des problèmes d'optimisation robuste sont développés.De plus, un cadre méthodologique est développé et est appliqué.Puis, un modèle caractérisant les écarts géométriques en fonction des motifs géométriques est utilisé et est analysé aux cas déterministes et à un modèle de la littérature.Enfin, une méthode permettant d'atténuer les effets des incertitudes épistémiques est spécialement développée pour l'optimisation topologique robuste, permettant au concepteur de choisir entre une conception optimiste ou pessimiste en fonction de l'exactitude des modèles et du contexte du projet.Les travaux se sont révélés efficaces dans l'atténuation des effets des imperfections géométriques lors du processus de conception pour la robustesse
Geometrical comparison between instrumented and non-instrumented mouthguards for rugby: A pilot study
No full textInternational audienceRugby is a sport with a high injury rate. Much has been done to make the sport safer, particularly in terms of limiting and identifying concussions. Recently, instrumented mouthguards have been developed and used to measure events that may lead to concussion. However, these instrumented mouthguards may not have an appropriate geometry regarding shock absorption and comfort. In addition, there is no specific international standard for instrumented mouthguards. This study proposed a geometric analysis of both instrumented and non-instrumented mouthguards. Ten instrumented mouthguards were analysed and compared with three non-instrumented mouthguards. They were inspected visually, with a 3D envelope scan and with a CT scan. The results showed that the mouthguards did not comply with recommendations such as indentation with the lower teeth which may increase injury or fracture risk
Numerical Simulation of the Viscoplastic Behavior of Rock Salt : Bridging Grain Boundary Cracking and Bulk Deformation
No full textInternational audienceNumerical Simulation of the Viscoplastic Behavior of Rock Salt : Bridging Grain Boundary Cracking and Bulk Deformatio