HAL Portal IMT Nord Europe
Not a member yet
6687 research outputs found
Sort by
A SOA framework for resilient IoT integration into production systems: application to e-coating ultrafiltration monitoring
No full textHow impactful is die swell in material extrusion-based additive manufacturing of thermoplastic polymers?
No full textInternational audienceDie swell is a well-known phenomenon occurring when a polymer melt is subjected to a constriction flow, resulting in an expansion of the melt as it exits an extrusion die. This flow-induced effect is ubiquitous in the field of extrusion-based polymer processing, including material extrusion-based additive manufacturing such as fused filament fabrication (FFF). However, its implications in FFF remain poorly understood, notably because the melt strand deposition flow occurs quite close to the printing nozzle exit, where the die swell does not happen freely (as for a simple extrusion flow) but in a confined layered flow. To better describe the relevance of this phenomenon in the context of FFF processes, we propose an examination of die swell in both free extrusion and confined flow conditions, where we underline the influences of the polymer molecular weight and processing conditions in the case of isotactic polypropylenes. A combination of rheological measurements, numerical flow analysis, and optical characterizations highlights significant swelling ratios at the exit of the printing nozzle in a typical range of FFF printing conditions. These results are counterbalanced by how little effects such die swells have on the final dimensions of the printed strands (the opposite is often hypothesized in the literature), as evidenced by cross-sectional analysis and transient lengths measurements. This study points to a different influence of die swell in confined FFF flow conditions, more related to the impact on interlayer adhesion and polymer chain orientation rather than the expected change in print dimensions
A Comparative Survey of Authentication Schemes Suitable for the Audit of V2X Communications
No full textInternational audienceThe rise of connected vehicles has transformed transportation by enhancing mobility, safety, and driving comfort. However, ensuring secure and trustworthy communications in vehicular networks remains a challenge due to the risks of malicious activities, privacy breaches, and unauthorized access. This paper aims to address these challenges by evaluating and comparing existing authentication schemes used in vehicular communications. Specifically, the article focuses on analyzing their efficiency, security, and applicability for audit systems in Vehicle-to-Everything (V2X) communications. The main objectives of this study are to provide a clear taxonomy of authentication strategies, evaluate their ability to preserve anonymity and integrity while ensuring accountability, and identify protocols suitable for robust audit mechanisms. Through qualitative and quantitative analysis, this paper highlights the strengths and limitations of current solutions, emphasizing aspects like scalability, privacy preservation, and infrastructure dependency. Findings indicate that combining Public Key Infrastructure (PKI)-based methods with Blockchain technology can yield secure and transparent communication solutions. Nevertheless, significant hurdles remain in scenarios lacking infrastructure support. The key contribution of this work consists in identifying authentication protocols that successfully balance security, efficiency, and privacy–while still enabling effective audits–thereby laying the groundwork for designing reliable, trust-oriented audit systems in tomorrow’s vehicular networks, including outside the infrastructure coverage
Une hybridation repensée : définition, modèle, méthode
No full textInternational audienceThis article is about hybridization. It provides a definition, model and method for the design of learning units – in training contexts that combine presence and distance. Based on these contributions, we want to develop a plugin for the MOODLE Learning Management System. The objective is to help teachers face the complexity of the role of designer (pedo-digital learning program), which they are now being forced to assume. Teachers are needed to help our training system meet the educational, economic and societal challenges that arise. Once the context and issues are introduced, we examine briefly two main research questions, three state of the art, a design model and method proposal and the studies that validate them. We then approach the plugin perspective through a UML formalization of the structure of a training, on which is based the method (HYRIS) that is subsequently implemented. Finally, we conclude on the perspective of sub-models that remain to be developed – as part of a complete automation of the design process – and studies that will be necessary.Cet article s'intéresse à l'hybridation. Il propose une définition, un modèle et une méthode pour la conception d'unités d'apprentissagesdans des contextes de formation qui mêlent présence et distance. À partir de ces contributions, nous souhaitons développer un plugin pour le Learning Management System MOODLE. L'objectif est d'aider les enseignants face à la complexité du rôle de concepteur (de dispositifs pédago-numériques), qu'ils sont désormais amenés à endosser. Il s'agit que les enseignants contribuent à ce que notre système de formation puisse faire face aux défis pédagogiques, économiques et sociétaux qui s'imposent. Une fois introduit le contexte et les enjeux, nous examinons successivement, deux questions de recherche principales, trois états de l'art, une proposition de modèle et de méthode de conception et les études qui les valident. Nous abordons ensuite la perspective du plugin à travers une formalisation UML de la structure d'une formation, sur laquelle se base la méthode (HYRIS) qui est ensuite mise en oeuvre. Enfin, nous concluons sur la perspective de sous-modèles qu'il reste à développerdans le cadre d'une automatisation complète du processus de conception -et des études qu'il sera nécessaire de mener
Multi-time Positive Matrix Factorization approach for enhanced source apportionment of organic aerosols from aerosol mass spectrometry and molecular speciation in two urban environments (Lyon and Bordeaux, France)
No full textInternational audienc
Unveiling the Amorphous Phase Contribution to Shear Piezoelectric Properties of Polylactide
No full textInternational audiencePolylactide (PLA) represents an interesting biobased alternative to ferroelectric fluoropolymers with shear piezoelectric coefficients d14 of up to 10 pC/N solely activated by uniaxial orientation. A significant contribution of the oriented amorphous phase is suspected, and this work consequently proposes a detailed analysis of the piezoelectric activity for a fully amorphous polylactide grade (aPLA). Oriented aPLA films were produced by machine-direction orientation (MDO), and the amorphous phase orientation (Fam) was precisely measured along with piezoelectric responses. The absence of mesophase/cavitation phenomena is confirmed, and Fam increases with the draw ratio, in agreement with deformation theories of rubber networks. Oriented aPLA films display d14 values up to 2 pC/N with perfect linear coupling to Fam. The significant contribution of the oriented amorphous phase is validated, and for the first time, the intrinsic piezoelectricity of the amorphous phase was extrapolated to 7.2 pC/N. Additional experiments at various draw rates indicate that relaxation modes of aPLA are only active below 0.3 s−1. Relaxation phenomena are consequently inactive in MDO conditions at an elevated draw rate. The effect of the optical purity was finally discussed. The intrinsic piezoelectricity of the amorphous phase can be considered constant for PLA grades with low D-content. This study helps in refining the current models for future detailed analyses on oriented semicrystalline PLA films
Overview of French efforts for the innovative characterisation of aerosols and cloud interactions with the future Atmosphere Observing System
No full textInternational audienceAerosols and clouds play a major role in the Earth Climate systems, while the quantification and clear understanding of their variabilities, interactions and feedbacks remain a great challenge. In particular, aerosols strongly impact the energy budget by direct modification of solar and infrared radiation, alteration of cloud properties and their formation processes as well as the thermodynamic properties of the atmosphere. Aerosols are also the most harmful air pollutant, being responsible of several millions of premature deaths worldwide each year. Even though diverse observation and modelling approaches of aerosols exist, numerous unknowns remain concerning the chemical and physical mechanisms that affect them, their vertical redistribution in the atmosphere, the quantification of their environmental impacts and their interactions with clouds and convective processes. In order to tackle these major environmental issues at global scale, a new spaceborne Atmosphere Observing System (AOS) has been conceived as an international cooperation between NASA from USA, CNES from France, JAXA from Japan, CSA from Canada and ASI from Italy. This mission is built as a constellation of several satellites following two orbits, a polar orbit with global coverage in the continuity of the A-Train constellation and an inclined designed to document the diurnal variation of convection in the Tropics and mid-latitudes. They satellites will carry new generation active and passive instruments for sounding aerosols, clouds, convection, and precipitation, including an advanced multiwavelength lidar in tandem with a multi-angular polarimeter, whose launching period is planned for 2030.In the current presentation, we will provide an overview of French efforts for the innovative characterization of aerosols and its interactions with clouds for preparing the scientific exploitation of AOS. They gather relevant contributions from 8 French scientific laboratories: LISA, LOA, LATMOS, CNRM, LAERO, LACy, CERI EE and LSCE and a French industrial partner: GRASP-SAS. These efforts are threefold: (i) the development of innovative French aerosol satellite products based on AOS observations, (ii) suborbital measurements for feeding both the aerosol products and conceiving a synergetic exploitation with AOS and (iii) synergism with chemistry-transport models. The AOS aerosol observations will provide a new quantification of the vertical profile of aerosol concentration simultaneously for different particle types and chemical species. This information will be derived from lidar only and the synergism of lidar and polarimeter measurements using a so-called GRASP retrieval approach. Additional products aim the quantification of cloud condensation nuclei for studying aerosols/cloud interactions. The suborbital contribution will characterize aerosol optical, microphysical, and chemical properties from airborne, ground-based from several French sites and laboratory instrumentation. While documenting aerosols properties for different aerosol types and species, they provide a scientific framework for studying complex interactions such as the impact of aerosols on convective activity in specific regions. This is the case of the BACCOPA French field campaign aiming the studying of the impact of biomass burning aerosols emitted from Central Africa on convective activity. Finally, synergetic approaches with chemistry transport-models aim the development of data assimilation methods of AOS measurements and the use of these last ones for evaluating their numerical simulations
Région de débits atteignable en NOMA avec amplificateur non linéaire
No full textNational audienceDans ce papier, nous donnons une expression du débit pour la technique d'accès multiple non orthogonale (NOMA) dans le sens descendant, prenant en compte une non-linéarité induite par un amplificateur de puissance au niveau de l'émetteur. Nous comparons ensuite ces résultats à ceux obtenus pour un modèle linéaire et comparons également à une technique d'accès multiple orthogonale
Déploiement de réseaux de capteurs sans fil : architecture, objectifs et méthodologies
No full textInternational audienceWireless Sensor Networks (WSNs) have become a critical technology in the Internet of Things (IoT) era, enabling the seamless integration of sensing, communication, and computational capabilities. WSNs have emerged as a transformative technology with applications ranging from environmental monitoring to industrial automation. As WSNs become more prevalent in various applications, the deployment phase takes center stage in defining their efficiency, effectiveness, and scalability. This paper provides a comprehensive overview of the multifaceted landscape of WSN deployment strategies. Digging deeper into sensor nodes, deployment types, goals, sensing patterns, and deployment methodologies, it comprehensively explores the multifaceted domain of WSN deployment and provides a map for optimizing the deployment across a spectrum of applications
The central heat trace on large compact classical groups
No full textWe establish the large- asymptotic expansion of the (central) trace of the heat kernel on any compact classical group , which extends a previous result known only for \cite{LM2}. It admits two new interpretations of the trace: in terms of ramified coverings of the torus, and Gromov-Witten invariants on elliptic curves. These connections allow us to explore several aspects of the gauge/string duality in two dimensions: a Yang-Mills/Hurwitz duality, and Yang-Mills/Gromov-Witten duality