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Différences de processus anticipatoires entre l'initiation de la marche et du pas
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Numerical Analysis of a New Corona Ionic Wind Blower Used for Solar Panel Cleaning
No full textInternational audienceThe potential of solar energy as a sustainable power source remains hindered by various efficiency limitations. One of the major challenges is the accumulation of dust on photovoltaic (PV) panels, leading to the decrease of the efficiency and the need for regular cleaning. To address this issue, this work aims to explore the use of ionic wind, generated by corona discharge, as an innovative method for dust removal from PV panels. In line with this objective, this paper presents a numerical analysis of electro-hydrodynamic (EHD) air blowers with wire-to-rectangle configurations to harness the potential of ionic wind for cleaning PV panels. The study utilizes 2D models that have undergone experimental validation. The results highlight a parametric analysis, shedding light on how different geometrical parameters influence the performance of the ionic wind air blower and its energetic efficiency
Convertisseur DC/DC pour réseau MVDC avec services systèmes
No full textInternational audienceL'accroissement de l'intégration des énergies renouvelables et des charges électriques en courant continu dans le réseau électrique impose une évolution de son architecture, notamment au niveau des réseaux moyenne tension en courant continu. Des convertisseurs d'électronique de puissance devront être insérés dans ceux-ci permettant de tenir les tensions, équilibrer les contraintes et assurer des services systèmes (par exemple inertie virtuelle, creux de tension, grid forming,…). De part, les contraintes techniques et de disponibilité, leur architecture sera modulaire avec des briques de base isolées. Cet article présente un convertisseur DC/DC basé sur une cascade de structures de type Triple Active-Bridge (TAB) avec une association en série en entrée et en série en sortie (ISOS) intégrant des systèmes de stockage d'énergie pour une interconnexion de deux réseaux MVDC. Les limites de fonctionnement des topologies sont également identifiées. Des stratégies de pilotage et de contrôle sont proposées pour assurer les transferts de puissance et les équilibrages de contraintes
Postural Control in Children with Autism Spectrum Disorders: What are the Most Striking Specificities and How Can They be Quantified?
No full textInternational audienceAutistic children (AT) are known to exhibit distinct postural control patterns compared to neurotypical (NT) children. However, identifying and interpreting these differences can be complex due to the wide range of variables used to analyse Centre of Pressure (CoP) trajectories. This study aims to elucidate the specific characteristics of postural control in AT children by identifying the most discriminative CoP variables that distinguish them from NT children. The study evaluated 24 AT and 24 NT children while they stood on a force plate for 30 s under three conditions: eyes open (EO), eyes closed (EC), and the feet on a foam pad with eyes open (EOF). A total of 75 variables—including frequential, linear, and non-linear variables—were extracted from the CoP trajectory. These variables, expressed as the rate of change between the EC and EOF conditions relative to the EO condition, were compared between the AT and NT groups. A best-subsets approach was used to identify the most discriminative variables, and Pearson correlations were calculated to assess their relationship with age and Social Responsiveness Scale (SRS) scores. Of the 75 variables analysed, 15 showed significant differences between the AT and NT groups. The best-subsets analysis and the correlations revealed that variables such as the rate of change between the EOF and EO conditions, and the root mean square of the trembling component of the CoP trajectory, were particularly discriminative. Autistic children demonstrated a more rigid and regular CoP trajectory, particularly in the EO condition, compared to NT children. These findings suggest that AT children have greater difficulty integrating multisensory information and an increased reliance on supraspinal processes for postural control
Investigation of the Mechanical Characteristics and Tribological Performance of a Chrome Molybdenum Steel After Ball Burnishing
No full textInternational audienceThe objective of this work is to study the mechanical behavior of Chrome-Molybdenum steel subjected to a mechanical surface treatment, specifically burnishing by varying the number of passes and the applied pressure, in order to evaluate the mechanical properties such as micro-hardness (Hv), Young's modulus (E), and the induced compressive residual stresses. Friction tests were also conducted to determine the coefficient of friction and assess the wear resistance of the surface. Structural analysis and estimation of micro-strains were performed by X-ray diffraction, through Rietveld refinement. Measurements of micro-hardness and Young's modulus were carried out through indentation tests, and the worn surface after friction was evaluated using a 3D profilometer. The results show an increase in micro-strains for the surface treated with maximum parameters (P=20 kgf,i=4), as well as an improvement in surface hardness, reaching a maximum value of 254.57Hv, representing a 17.5% increase compared to the untreated surface and Young's modulus follow the same trend as superficial hardness. Additionally, a reduction in the coefficient friction, ranging from 16% to 30% compared to the undeformed surface, was recorded. A correlation between the wear rate and micro-strains was also identified, indicating that the predominant wear mechanism is adhesive wear
Une approche diagrammatique des fonctions de corrélation dans les superfluides
No full text16 pages, 2 figuresRenaud Parentani has given a vast contribution to the development of gravitational analogue models as tools to explore various important aspects of general relativity and of quantum field theory in curved space-time. In these systems, two-point correlation functions are of the utmost importance for the characterization of processes taking place close to the acoustic horizon. In the present paper, dedicated to him, we present a study of path integral methods that allow to determine two-point correlation functions by a perturbative expansion, in a way that -- beyond its generality -- is especially suited to analyze these processes. Our results apply to non-relativistic superfluids, realizable in terrestrial experiments, as well as to relativistic superfluids, relevant for compact stellar objects.Renaud Parentani a largement contribué au développement des modèles analogues gravitationnels, utilisés comme outils pour explorer divers et importants aspects de la relativité générale et de la théorie quantique des champs en espace-temps courbe. Dans ces systèmes, les fonctions de corrélation à deux points revêtent une importance capitale pour la caractérisation des processus se produisant à proximité de l'horizon acoustique. Dans le présent article, dédié à sa mémoire, nous présentons une étude des méthodes de l'intégrale de chemin permettant de déterminer les fonctions de corrélation à deux points par un développement perturbatif, d'une manière qui -au-delà de sa généralité -est particulièrement approprié pour étudier ces processus. Nos résultats s'appliquent tant aux superfluides non relativistes, réalisables dans des expériences en laboratoire, qu'aux superfluides relativistes, pertinents pour les objets stellaires compacts
Analytical Model of the Evolution of Surface Topography During Sliding Wear
No full textInternational audienceDuring the wear process of surfaces in sliding friction, there is a running-in period during which the topography of surfaces changes with time before reaching the steady wear regime. In the steady wear regime, the statistical parameters used to describe the topography of the surfaces remain almost constant. Some experimental studies have shown that starting friction tests with different surface finish levels leads to the same final topography of surfaces in the regime of steady wear. This article proposes an analytical model to describe the evolution of the topography of surfaces during sliding wear. First of all, the Greenwood and Williamson approach is used to describe the contact between nominally flat rough surfaces. The asperities in contact may undergo plastic deformation or adhesion with the opposing surface. Using a plasticity criterion and an adhesion criterion, it is possible to obtain a differential equation for the evolution of the standard deviation of the asperities of the surfaces. This equation has an analytical solution that is in good agreement with experimental results from the literature. It is shown that the final surface topography is the result of the competition between abrasive wear and adhesive wear. The model is then used to describe different wear processes from polishing to galling
Influence of the SrVO3 thin film thickness integrated on glass thanks to [CaNbO]- nanosheets
No full textInternational audienceNanosheets (NS) provide an innovative method for growing perovskite thin films on diverse substrates like glass and silicon, serving as germination seeds and offering a cost-effective alternative to expensive monocrystalline substrates. According to the NS transfer process onto the substrate, more than 85–90% of the substrate is covered. However, a small fraction of the perovskite film grows directly on the substrate. This raises several questions: Is the perovskite film grown on glass conductive? How does the NS network influence electrical properties at macroscopic and submicron scales?To address these questions, we investigated the impact of thickness on the transport properties of transparent conductive SrVO3 vanadate deposited on glass coated with [Ca2Nb3O10]- nanosheets (CNO NS). Macroscopic measurements revealed significant degradation of transport properties at thicknesses below 15 nm. In-plane local electrical properties were examined using Scanning Spreading Resistance Microscopy. Our findings indicate that local transport remains nearly constant when SrVO3 is grown on NS, while a strong thickness dependence is observed when SrVO3 is directly deposited on glass. These results contribute to a better understanding of the growth process, the integration of functional oxides on NS and open new perspectives for tuning the properties of vanadate films as transparent electrodes
Policy-Based Optimization for Drag Reduction via Spanwise Wall Oscillations
No full textThis study introduces a novel computational framework that synergistically integrates Policy-Based Optimization (PBO) and implicit Large Eddy Simulations (LES) to optimise oscillating spanwise wall motions for drag reduction in turbulent channel flows. Drag reduction remains a critical challenge in fluid dynamics, particularly in the context of improving energy efficiency in various engineering systems. Previous investigations aiming to determine optimal Spanwise Wall Oscillation (SWO) parameters have predominantly relied on computationally expensive methods, such as parametric grid search using Direct Numerical Simulations (DNS). Consequently, these studies have been limited in their exploration of the parameter space due to the associated high computational costs. The primary contribution of the present study lies in presenting a significant advancement through a more efficient and cost-effective exploration of the SWO parameter space, without compromising the precision of the simulations.By leveraging machine learning techniques, specifically PBO, the proposed framework enables rapid convergence to optimal control strategies while minimising the number of simulations required. This approach marks a departure from the conventional a priori parameter selection based on grid search methods. Beyond this, the study also demonstrates the effectiveness of PBO for parametric optimization in turbulent flow control applications and corroborates the previously identified optimal drag reduction parameters while providing deeper insights into their precise optimal ranges and sensitivities. The optimization process is conducted in two stages: initially focusing solely on maximising drag reduction, followed by the incorporation of control costs to optimise the net energy balance of the system. The optimal oscillation parameters obtained for drag reduction closely align with those reported in the literature, with the optimal period T+opti falling within the range [110, 125] and the optimal amplitude W +opti being the highest within the investigated range. Regarding net energy balance, the present study offers additional precision compared to previous works, identifying the optimum at T +opti ∈ [125, 155] and W +opti ∈ [3.5, 5]. These results reveal that higher amplitudes fail to offset control costs, while the optimal period slightly increases when accounting for the required energy, consistent with the expected decrease in operational costs. The proposed PBO-LES framework establishes a new paradigm for leveraging machine learning to identify optimal control strate-gies for real-world applications, demonstrating its potential to revolutionise the design of efficient flow control techniques and contribute to the development ofsustainable, energy-efficient technologies across various industrial sectors.</p
Tribo-electrostatic separation of plastic flakes originating from packaging waste
No full textInternational audienceFree-fall tribo-electrostatic separators are commonly used in the recycling industry for sorting granular waste plastics but are much less effective in the case of flake-like materials of irregular shapes. This work was aimed at demonstrating that by modifying the design of a commercial rotating-cylinder-type tribocharger it is possible to expand the usage of such a separator to processing flakes originating from the shredding of packaging waste. The study was conducted on a mixture of flakes consisting of roughly 60 % PEHD (Polyethylene) and 40 % PP (Polypropylene), with an average size ranging from 8 mm to 10 mm. The plastic flakes were first introduced into the modified tribocharger, then transferred to a vibratory-plate conveyor that fed them as a mono-layer curtain at the upper end of an industrial free-fall electrostatic separator, equipped with two vertical plate electrodes (width: 150 cm; length: 200 cm), energized from two high-potential generators of opposing polarities (+60 kV, −100 kV). Under the action of the electric field, the respectively negatively- and positively-charged PEHD et PP flakes were sorted into distinct compartments. The modified design of the commercial tribocharger enabled the increase of the number and the frequency of the flake/wall and flake/flake collisions that ensure the electric charging. To investigate the impact of residence time, the experiment involved repeated passages of the material through the tribocharger. The effect of the high potential applied to the electrodes on the separation efficiency was also studied, and the results demonstrate the possibility to attain purity levels exceeding 98 %. Finally, the experiments conducted at three different humidity levels of the ambient air demonstrate that this factor has a detrimental effect on the outcome of the tribo-electrostatic separation