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Enfant à bord ! La place des enfants dans les trains au prisme de leurs activités en déplacement
No full textThis thesis lies at the intersection of mobility studies and children geography, and examines how children experience, inhabit, and appropriate long-distance train travel. It adopts a pluralistic theoretical framework that considers the train as both a spatio-temporal setting where various activities unfold, and as a space shaped by silent rules of interaction and its spatial layout. Children are viewed as social actors capable of acting on and with their environment. Analysing their activities and spatial practices allows to question their experience of these occasional trips and their place on board. More specifically, the study focuses on children aged approximately 6 to 11 traveling on French trains for long-term travel and accompanied by one or more relatives. The methodology is organized around three axes: observations on board trains, semi-structured interviews with families followed during a train journey, and analysis of France’s main railway operator’s (SNCF) archives and communications.The results are presented around four complementary dimensions. The first offers a diachronic reading of the SNCF's policies aimed at families, and traces the evolution of children’s consideration in its commercial offer. The second proposes an original typology of the activities carried out by children during their journey, which is then analyzed in light of the interviews to understand how these activities contribute to their experience of travel. The third considers these activities through the lens of the social and spatial constraints at work on trains, and how these constraints reconfigure family interactions on board. Finally, a fourth dimension explores how children adapt, negotiate, and circumvent these constraints, revealing their ability to actively redefine their place in this environmentCette thèse s’inscrit à l’intersection des études sur la mobilité et des travaux relevant de la géographie de l’enfance pour interroger la manière dont les enfants vivent, occupent et s’approprient leur trajet en train sur de longues durées. Elle appréhende le train comme un espace-temps où se déploient des activités, et comme un espace contraint par des règles tacites d’interactions et par son aménagement. Les enfants sont considérés comme des acteurs sociaux capables d’agir sur et de faire avec leur environnement. L’analyse de leurs activités et de leurs pratiques spatiales permet de questionner leur vécu de ces déplacements occasionnels et leur place à bord. Plus précisément, l’enquête porte sur des enfants âgés d’environ 6 à 11 ans en train grandes lignes français pour une longue durée et accompagnés par un·e ou plusieur·es de leurs proches. La méthodologie s’organise selon trois axes : des observations embarquées à bord des trains, des entretiens-semi directifs avec des familles suivies lors d’un trajet en train, l’analyse de documents d’archives et de communication de la SNCF. Les résultats sont ordonnés autour de quatre dimensions complémentaires. Le premier propose une lecture diachronique des politiques de la SNCF à destination des familles, visant à retracer l’évolution de la prise en compte des enfants dans son offre commerciale. Le deuxième propose une typologie originale des activités réalisées par les enfants pendant leur trajet qui est ensuite analysée à l’aune des entretiens réalisés avec les enfants pour comprendre comment elles participent de leur vécu du déplacement. Le troisième considère ces activités au prisme des contraintes sociales et spatiales à l’œuvre dans les trains, et la manière dont ces contraintes reconfigurent les interactions familiales à bord. Enfin, un dernier axe explore la manière dont les enfants s’arrangent, négocient et contournent ces contraintes, révélant leur capacité à redéfinir activement leur place dans cet environnemen
Trajectories of Engagement: Challenging the Materiality of Participatory Research
No full textInternational audienceParticipatory research is no longer an option; it’s an injunction. While the social consequences of this approach are often described through their effects on so-called participants, what happens to the scholars themselves, those who are moved, reshaped, or even implicated in these processes? And how do they navigate the constraints of a research model that has become both fashionable and mandatory? This book brings together more than twenty research projects from across diverse disciplines, each experimenting with participatory and collaborative forms of inquiry. Rather than prescribing what engagement should be, it investigates how it happens: the sparks that ignite it, the frictions that sustain or destabilise it, and the material and institutional conditions that make it possible or constrain it. Research projects are described through open-ended trajectories, negotiated in the heat of genuine encounters between institutions, publics, and material infrastructures. Born from an international meeting held at the University of Paris Nanterre in September 2023, this collective work extends a shared effort to think through the trajectories of engagement that characterise today’s research landscape. Combining conceptual reflection with diagrammatic elicitation methodologies, it maps how researchers and non-academic actors move, connect, and transform one another throughout the research process. At once analytical and experimental, this volume invites readers to question the forms, ethics, and politics of participation. Rather than approaching engagement as a fixed model or moral ideal, it proposes reframing it as a dynamic, situated practice
Intelligent Aggregation of Single-Sensor Classifiers for Enhanced Structural Health Monitoring Networks
No full textInternational audienceStructural health monitoring (SHM) systems for large-scale infrastructures often rely on dense sensor networks, which are prone to faults, generate high-volume data, and require computationally efficient algorithms to ensure low-latency inference for real-time monitoring. To enhance overall network accuracy and robustness, aggregating the predictions of individual sensors provides a way to leverage complementary information across the network while mitigating sensor-level errors. In this study, we investigate intelligent aggregation strategies for singlesensor classifiers in SHM networks. We leverage acceleration time series data from the RT345 bridge dataset, collected from a real instrumented structure, to detect and classify structural damages. Individual sensor classifiers produce probabilistic predictions, which are then combined using different aggregation strategies. Soft averaging serves as a baseline, while stacking ensembles employs linear meta-classifiers (Logistic Regression) for interpretable per-sensor weighting and nonlinear metaclassifiers (Random Forest) to capture complex conditional dependencies across sensors, albeit at the cost of interpretability and stability. Experimental results demonstrate that meta-learning strategies significantly improve classification accuracy and robustness. We further evaluate prediction time, scalability, and model size, highlighting trade-offs between linear and nonlinear aggregation for real-time SHM applications. Finally, we extend the study by exploring alternative acceleration time series representations, showing that system efficiency can be improved without compromising damage detection performance
Estimation of stress and elasticity of the abdominal wall from in-vivo breathing data
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Nonnegative Cross-Curvature in Infinite Dimensions: Synthetic Definition and Spaces of Measures
No full textInternational audienceNonnegative cross-curvature (NNCC) is a geometric property of a cost function defined on a product space originating in optimal transportation and the Ma–Trudinger–Wang theory. Motivated by applications in optimization, gradient flows and mechanism design, we propose a variational formulation of nonnegative cross-curvature on c-convex domains applicable to infinite dimensions and nonsmooth settings. The resulting class of NNCC spaces is closed under Gromov–Hausdorff convergence and for this class, we extend many properties of classical nonnegative cross-curvature: stability under generalized Riemannian submersions, characterization in terms of the convexity of certain sets of c-concave functions, and in the metric case, it is a subclass of positively curved spaces in the sense of Alexandrov. One of our main results is that Wasserstein spaces of probability measures inherit the NNCC property from their base space. Additional examples of NNCC costs include the Bures–Wasserstein and Fisher–Rao squared distances, the Hellinger–Kantorovich squared distance (in some cases), the relative entropy on probability measures, and the 2-Gromov–Wasserstein squared distance on metric measure spaces
Survey of concrete blocks submitted to artificial sea water tide during one year by electrical resistivity tomography
No full textInternational audienceElectrical resistivity methods are very sensitive to the evolution of water and chloride contents of concrete. The multi-electrode device, used in this study, is applied on the concrete surface to measure the apparent resistivities. After data inversion, we get ‘true’ resistivity profiles function of depth. In this study, we present the survey methodology based on this electrical resistivity tomography method. It was implemented to monitor the penetration of salt water in concrete blocks placed in a tidal basin. Three concrete formulations are studied: the first named C100-0 mixed with ordinary Portland cement CEM I, the second, named C70-30, containing 30% of replacement blast furnace slag and the third named C50-50, containing 50% of replacement slag. The artificial tidal cycles reproduce natural tides and the salt water contains 35 g/L of sodium chloride like seawater. The blocks were inspected at short intervals at the start of exposure and then at more spaced monthly intervals. The method for inversion of apparent resistivities is briefly summarized. The results corresponding to the three concretes are presented for one year, firstly as apparent resistivity values and then as ‘true’ resistivity profiles with respect to depth. The influence of slag is discussed: it induces a higher resistivity but the results do not show a mitigation of the penetration kinetics of the salted water in the actual studied conditions
Durabilité des matériaux cimentaires bas carbone soumis à des phénomènes de dégradation simples et couplés
No full textThe durability of cementitious materials in harsh environments is an important consideration for sustainable construction, especially as the cement industry shifts to low-carbon alternatives. This thesis investigates the resistance of various low-carbon binders, ranging from blended cements to geopolymers, up to key degradation mechanisms such as those due to external sulfate attack, chloride bonding capacity, coupled sulfate-chloride interactions, and other durability issues. A comprehensive experimental program, conducted at the paste scale, was developed to investigate the chemical and microstructural evolution of these materials, linking their composition and curing practices to long-term performance. The first phase of the study assessed the sulfate resistance of blended cementitious materials that included supplementary cementitious materials like blast furnace slag, fly ash, and metakaolin. The study revealed that some of these supplementary cementitious materials significantly improve sulfate resistance by reducing available calcium hydroxide and refining pore structure. Based on these findings, four optimized mixes were chosen for further investigation: a reference CEM I, one binary, one ternary, and one quaternary blend. The second phase of the study investigated the combined effects of sulfate and chloride ions, a common degradation process in marine and harsh environments. Findings revealed a complex interaction: chloride delayed ettringite formation, whereas sulfate destabilized Friedel's salt, allowing chloride ingress. These findings highlighted the need to account for multi-factorial degradation processes when conducting durability assessments. The third phase of the study investigated the role of curing duration in cementitious materials' resistance to coupled sulfate-chloride attack. Extended curing improved chloride binding and overall hydration, but it also exacerbated the production of sulfate-induced expensive products, emphasizing curing's dual role in long-term durability. This study challenged the widely held belief that longer curing times always improve performance, emphasizing the importance of optimizing curing protocols based on environmental exposure conditions. The final phase of the study focused on geopolymers as an alternative low-carbon binder, comparing their durability to standardized low-carbon cement (CEM III). This study examined ambient-cured geopolymers without heat or nanomaterials to determine their viability in practical construction applications. Results confirmed their superiority in carbonation, sulfate, and acid resistance due to their calcium-free composition, but their limitations in chloride binding capacity and freeze-thaw resistance.Overall, this thesis provides a comprehensive framework for understanding the durability of some low-carbon cementitious materials in harsh environments. The findings underscore the importance of mix design, curing strategies, and exposure-specific assessments in optimizing the material performance. Furthermore, the study emphasizes the need to move from cement paste-scale studies to mortar and concrete applications to ensure real-world structural applicability. The findings contribute to the development of more sustainable and durable infrastructure, as well as advance scientific understanding of degradation mechanisms in novel cementitious systemsLa durabilité des matériaux cimentaires dans des environnements agressifs est une considération essentielle pour la construction durable, en particulier à mesure que l'industrie du ciment évolue vers des alternatives à faible empreinte carbone. Cette thèse explore la résistance de divers liants à faible teneur en carbone, allant des ciments composés aux géopolymères, face aux principaux mécanismes de dégradation tels que l'attaque sulfatique externe, la fixation des chlorures, les interactions couplées sulfate-chlorure, ainsi que d'autres problématiques de durabilité. Un programme expérimental mené à l’échelle de la pâte a été mis en place pour étudier l'évolution chimique et microstructurale de ces matériaux, en établissant des liens entre leur composition, leurs conditions de cure et leur performance à long terme. La première phase a évalué la résistance aux sulfates des matériaux cimentaires intégrant des ajouts tels que le laitier de haut-fourneau, les cendres volantes et le métakaolin. Les résultats ont montré que ces ajouts améliorent la résistance aux sulfates en réduisant la quantité d'hydroxyde de calcium disponible et en raffinant la microstructure. Quatre formulations ont alors été sélectionnées pour une analyse approfondie : un ciment CEM I, un liant binaire, un ternaire et un quaternaire. La deuxième phase a permis d’étudier les effets couplés des ions sulfate et chlorure, un processus courant dans les milieux marins et agressifs. Les résultats ont révélé une interaction complexe : les chlorures retardent l’ettringite, tandis que les sulfates déstabilisent le sel de Friedel, facilitant la pénétration des chlorures. Ces observations soulignent la nécessité de prendre en compte les processus de dégradation multifactoriels. La troisième phase a examiné l’influence de la durée de cure sur la résistance des matériaux à l’attaque couplée sulfate-chlorure. Une cure prolongée a amélioré la fixation des chlorures et l’hydratation, mais aussi accentué la formation de produits induits par les sulfates, mettant en évidence le rôle ambivalent de la cure. Cette étude remet en question l’idée selon laquelle une cure prolongée améliore systématiquement les performances, et insiste sur l’optimisation des protocoles selon les conditions environnementales. La dernière phase s’est concentrée sur les géopolymères comme alternative aux liants cimentaires à faible empreinte carbone, en comparant leur durabilité à celle d’un ciment à faible teneur en clinker (CEM III). Contrairement à d’autres travaux basés sur la cure thermique ou l'ajout de nanomatériaux, cette recherche s’est focalisée sur des géopolymères curés à température ambiante. Les résultats ont confirmé leur excellente résistance aux attaques sulfatiques, acides et à la carbonatation grâce à leur matrice aluminosilicatée sans calcium, mais ont révélé des limites concernant la fixation des chlorures et le cycle gel-dégel. Dans l’ensemble, cette thèse propose un cadre détaillé pour comprendre la durabilité des matériaux cimentaires à faible teneur en carbone dans des milieux agressifs. Les résultats mettent en évidence l'importance du choix des formulations, des stratégies de cure et des méthodes d’évaluation adaptées aux conditions d’exposition. Cette étude souligne aussi la nécessité de passer de l’échelle de la pâte à celle du mortier et du béton, pour assurer la validité des résultats en conditions réelles. Les conclusions contribuent au développement d'infrastructures plus durables, tout en approfondissant la compréhension des mécanismes de dégradation des nouveaux systèmes cimentaire
Données 3D MLS et gestion des risques en talus : caractérisation des surplombs
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Highlighting the Dynamic Effect on Dissipator by Friction Installed in Flexible Barriers
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Visions of Tomorrow: Emotional drivers of climate change mitigation and adaptation intentions
No full textInternational audienceThis research explores the effects of exposure to utopian vs. dystopian vs. neutral visions of the future (with regards to environmental sustainability or unsustainability) on individuals' intentions to mitigate and to adapt to climate change, through emotional arousal. In two pre-registered experimental studies, participants were randomly assigned to read about a utopian, dystopian, or neutral vision of future society. In Study 1 (N = 303), behavioural intentions, emotional responses to the scenario (fear, anger, sadness, hope and happiness), the ability to imagine a positive future, and beliefs about sustainable futures were assessed. Results indicated no direct effects of the visions on behavioural intentions, future imagination, or beliefs. However, exposure to a utopian (vs. neutral) and a dystopian (vs. neutral) vision indirectly affect both mitigation and adaptation intentions through feelings of hope (increased and decreased, respectively). Study 2 (N = 401) partially replicated the findings of Study 1. As expected, exposure to a utopian and a dystopian vision indirectly affect mitigation intentions through feelings of hope (increased and decreased, respectively). Adaptation intentions, however, were predicted by happiness rather than hope. These findings highlight the role of positive emotions in promoting pro-environmental intentions and suggest that positive emotions can drive climate actions. While negative emotions like fear, sadness and anger were correlated with intentions, they did not predict behaviours in path analysis. This research underscores the potential of using emotionally engaging future visions to foster sustainable behaviours