HAL Portal IMT Nord Europe
Not a member yet
6687 research outputs found
Sort by
Feller Property and Absorption of Diffusions for Multi-Species Metacommunities
No full textWe consider individuals of two species distributed over m patches, each with a hosting capacity , where . We assume that all the patches are linked by the dispersal of individuals. This work examines how the metacommunity evolves in these patches. The model incorporates Wright-Fisher intra-patch reproduction and a general exchange function representing dispersal. Under minimal assumptions, we demonstrate that as approaches infinity, the processes converge to a diffusion process for which we establish the Feller property. We prove that the limiting process almost surely reaches the absorbing states in finite time.</div
SIP-DDoS framework based on Federated Learning for Collaborative Anomaly Detection
No full textInternational audienceWith their inherent capacity for massive connectivity, ultra-low latency and high reliability, B5G networks provide an ideal infrastructure to support the diverse and dynamic requirements of IoT (Internet of Things) communication. Originally designed to initiate, modify and terminate multimedia sessions over IP networks, the Session Initiation Protocol (SIP), a standardized protocol developed by the 3GPP, has emerged as a promising protocol for enabling communication and coordination in IoT environments. Nonetheless, SIP encounters a multitude of Distributed Denial of Service (DDoS) threats, with INVITE flooding attacks emerging as a notable challenge. Traditional IoT-IDS (Intrusion Detection System) relies on machine learning models trained on local data of their deployment context. However, such a model may not detect some attack patterns observed in other deployment contexts. We propose a design approach based on federated learning, and in which different IDS collaborate to achieve early detection of any INVITE flooding attack faced by any of them. The results show the effectiveness of the framework in detecting and mitigating INVITE flooding attacks across a various of flow intensities under realistic SIP operational conditions. Performance evaluations under different relevant scenarios demonstrate the robustness of the proposed framework. Experiments show that federated learning (FL) enhances the analysis of SIP flooding attacks, improving accuracy from 47% to 99% through knowledge sharing. The FL model with a GRU architecture and a FedAvgM aggregation function delivers the best performance, even in varied scenarios
Advanced Composites Manufacturing and Plastics Processing, 2nd Volume
No full textEnvironmental and energy concerns and digitalization are currently having profound effects in reshaping the plastics and composites industry. Manufacturing processes and systems evolve accordingly in order to cost-effectively produce high-performance, high-quality, lightweight, and multifunctional parts with a reduced carbon footprint. All composites manufacturing and polymer processing technologies are concerned with this trend: liquid composite molding (e.g., resin transfer molding and resin infusion/vacuum infusion), automated lay-up (e.g., automated fiber placement and automated tape laying), filament winding, prepreg technology, pultrusion, autoclave, compression molding, film stacking, additive manufacturing/3D printing, injection molding, over-molding/back-molding, extrusion, blow molding, thermoforming, rotational molding, foaming, coating, preforming of textile reinforcement, joining/welding, and mold technologies (i.e., mold making and design).Following the previous Topic (Advanced Composites Manufacturing and Plastics Processing), this new Topic welcomes original research articles, state-of-the-art reviews, and short communications on the latest advances in composites manufacturing and plastics processing. Suggested contributions may address new process developments, modeling/simulation, monitoring/control, and performance or application issues, with either experimental or numerical approaches. All types of polymers (thermoplastics, thermosets, and elastomers) and fibers/fillers (glass, carbon, ceramic, mineral, and vegetal) are eligible topics of focus, whether they come from recycled, bio-based, or fossil feedstocks. Multidisciplinarity is also encouraged to cover emerging topics such as smart manufacturing, artificial intelligence applied to manufacturing, data-driven simulations, and digital twins
Critical review of the latest advances in thermal management techniques for PEM fuel cells
No full textInternational audienc
The Radial Spanning Tree is straight in all dimensions
No full textThe Radial Spanning Tree (RST) in dimension is a random geometric graph constructed on a homogeneous Poisson point process in augmented by the origin, with edges connecting each to the nearest point that lies closer to than , with respect to the Euclidean distance. By construction, it forms almost surely a tree rooted at . The RST was introduced in 2007 by Baccelli and Bordenave, who investigated straightness, a deterministic property introduced by Howard and Newman in 2001, to derive information about the asymptotic directions of infinite branches. They proved that the RST is almost surely straight in dimension , which directly implies that all infinite branches are asymptotically directed, every possibility is attained, and directions reached by multiple infinite branches form a dense subset. However, their approach relies crucially on planarity, preventing any straightforward extension to higher dimensions. In this paper, we close this gap by proving that the RST is almost surely straight in any dimension, thereby obtaining the same consequences for the behaviour of infinite branches. Our approach resolves the key barriers in the study of the RST, notably those posed by the complex dependency structure combined with the radial nature of the model, and especially beyond the planar setting. It relies on tools developed for the analysis of the Directed Spanning Forest, a closely related model, including recent progress by the author in 2025. Specifically, a key contribution of this work is the construction of a suitable renewal-type decomposition of RST paths. Leveraging this decomposition together with classical concentration inequalities, we show that RST paths cannot deviate far from straight lines and derive straightness
Porous NaTi<sub>2</sub>(PO<sub>4</sub>)<sub>3</sub>-PVDF Composite Granules as Negolyte Boosters for Sodium-Based Redox-Targeting Flow Batteries
No full textInternational audienceRedox-Targeting Flow Batteries (RTFBs) are promising alternatives to classical vanadium-based batteries for large-scale and stationary energy storage. Typically, RTFBs are marked by higher energy densities thanks to the addition of solid boosters within aqueous systems, taking care to limit the use of critical raw materials. This work subsequently investigates the case of sodium titanium phosphate (NTP, NaTi2(PO4)3, 132.8 mAh/g) as a potential booster material for the negolyte side of aqueous RTFBs. Pure NTP and carbon-coated NTP (C-NTP) particles were synthesized and characterized by various techniques (X-ray, TEM, TGA, Raman). So-obtained NTP and C-NTP particles were found to be suitable for creating innovative porous composite boosters formed as centimeter-sized granules by dry processing. Porous composite granules with an open porosity of 65% and 50 wt % of immobilized NTP or C-NTP were successfully produced by an extrusion–dissolution process using a regular PVDF binder and PEO as a porogen agent. Subsequently, intensive electrochemical tests were performed using an innovative dual-mediator reaction system (Fe-Tiron and 2,7-AQDS). High NTP reactivity, with booster utilization rates of up to 84% of its theoretical capacity, can be achieved under flow conditions, with an increase in volumetric capacity by a factor of 1.5, from 4 Ah L–1 to 6 Ah L–1. The mediator concentration (10 – 100 mM) and the mediator/booster ratio (0.5 – 1) play key roles in NTP reactivity. The fundamental work also highlights the benefit of C-NTP, allowing higher reactivity at low mediator concentrations. The study consequently validates the potential of NTP as an interesting booster material in future RTFB applications, with its scalable extrusion–dissolution technique to create innovative porous booster granules
Decomposition of O3 onto natural Gobi dust: From uptake to surface reactivity
No full textInternational audienceBeyond synthetic metal oxides, this work investigates natural mineral dust as a material of interest for O3 uptake and decomposition. Ozone and Gobi dust interactions are addressed combining gas phase and adsorbed phase approach. It allows for determining: (i) the drivers of O3 decomposition process on Gobi and (ii) surface reactions and mechanism. First, the steady catalytic decomposition of ozone onto Gobi is explored on a large O3 concentration range: 20 ppb − 10 ppm, with steady uptake coefficients ranging from 2.6 x 10-9 to 6.2 x 10-8. If moisture (20 % RH) does not impact initial uptake of O3 it is evidenced to hinder the steady state behavior. Cyclic surface regeneration evidences that: (i) wet air flushing restores initial uptake properties, and (ii) mild thermal treatment (150 °C) restores the complete uptake process. Along O3 decomposition, adsorbed phase monitoring using DRIFT allows for identification and dynamic monitoring of specific IR bands on Gobi surface. Oxide and peroxide surface species are created. To meet environmental conditions, the role of water on surface groups created by O3 uptake is addressed through water molecule uptake experiments. Finally, a five-step mechanism is proposed to describe uptake and surface reactivity of O3 on Gobi dust. This work provides a comprehensive evaluation of the surface properties and reactivity of Gobi dust towards O3, valuable for atmospheric, geocatalytic and plasma-catalytic processes
VOC emissions from in-use asphalt pavements: Environmental drivers, atmospheric impacts, and mitigation strategies
No full textInternational audienceVolatile organic compounds (VOCs) emitted from asphalt pavements are increasingly recognized as contributors to urban air pollution and associated health risks. While emissions during production and paving have been widely studied, continuous releases during the service life of pavements remain poorly quantified, despite asphalt covering over 90 % of global road surfaces and up to 20 % of urban areas. These in-use emissions are influenced by binder type, mixture design, and environmental drivers such as temperature, solar radiation, humidity, and material aging. Recent chamber studies show that hydrocarbons and oxygenated VOCs dominate at service temperatures (20–70 °C), contributing to ozone and secondary organic aerosol (SOA) formation with yields of 10–20 % of the reacted VOC mass. Mitigation strategies such as warm mix asphalt, recycling, and bio-based binders reduce production-phase emissions, yet their effectiveness in limiting service-phase releases remains uncertain. This review consolidates current knowledge on VOC emissions from in-use asphalt pavements and highlights major gaps, including the absence of standardized quantification methods and emission factors suitable for inventories within life-cycle assessment frameworks. Addressing these gaps is essential in order to comprehensively evaluate the current contribution of asphalt pavements to urban air quality and to guide sustainable infrastructure strategies that mitigate the effects of climate change
Experimental validation of an approach to reduce uncertainties in the in-situ estimation of straw bales' thermal conductivity
No full textInternational audienceThe energy consumption of a structure is largely determined by the thermo-physical properties of its envelope. The thermal conductivity of the materials composing the envelopes is among the most important properties to be determined. However, this value has not been precisely defined in-situ for the straw material. Despite the fact that several studies have been conducted to quantify this value, yet disparate findings have been reported. For a more in-depth understanding of the thermal behavior of building components, experimental measurements are essential. Therefore, a protracted experimental campaign was carried out on a newly built structure in northern France under real weather and occupation conditions. Temperature, relative humidity and flux sensors were implanted through the wall and wheat straw bale thickness to understand hygrothermal behavior transfers and heat flow profiles changes along the whole monitored period. The instrumentation and data processing were compliant with the heat flow meter extended average method, a modified version of the ISO 9869-1 standardized approach. The experiment’s results are satisfactory; when comparing the measured values using the extended average method with the theoretically calculated value, a good agreement was obtained, with a deviation of 4.66 %. The extended average method has proven to be an accurate and reliable in-situ measuring approach for determining the effective thermal conductivity of wheat straw bales at various temperatures and moisture levels
