Substrat architecturé pour une gestion thermique efficace dans les modules électroniques de puissance

National audienceLes modules électroniques de puissance sont des composants essentiels pour le développement de nombreuses fonctions dans les véhicules électriques et hybrides. Ces modules sont des assemblages de composants électroniques en silicium (transistor et diode) sur un substrat généralement en cuivre. Le substrat assure le maintien mécanique et le transfert de la chaleur pour obtenir une température de fonctionnement convenable (<175°C) du silicium. En fonctionnement, une partie de la puissance est dissipée sous forme d'un flux de chaleur à cause de la résistance interne des semi-conducteurs. Ce flux diffuse de la face inferieure des composants électroniques vers le substrat et engendre l'échauffement de l'assemblage. Du fait que cet assemblage comprend divers matériaux, les dilatations thermiques différentes génèrent des contraintes de cisaillement dans la zone de liaison (brasure) en provoquant l'endommagement des modules électroniques. Pour résoudre ce problème, le substrat doit avoir un compromis entre des caractéristiques électriques et thermiques proches de celles du substrat actuel (Cu) et un coefficient de dilatation linéique proche de celui du semi-conducteur (Si). Une des solutions alternatives consiste à développer un matériau composite architecturé. Nous proposons d'atténuer les effets mécaniques de la dilatation différentielle à l'aide d'un substrat architecturé. Le substrat proposé est un matériau composite métallique dont les paramètres de forme ont été optimisés par simulation numérique et validés expérimentalement afin d'accroître au mieux la conductivité du substrat et d'en réduire la dilatation macroscopique. De plus, nous avons validé la mise en oeuvre du substrat proposé par des procédés conventionnels de colaminage, de pliage et de découpe

Length-weight relationships for 13 fish species from the Gulf of Gabes (Southern Tunisia, Central Mediterranean)

Length-weight relationships (LWR) were estimated for 13 fish species which are of economic relevance in the commercial fisheries of the Gulf of Gabes (southern Tunisia). A total of 2403 fish specimens were sampled with several fishing gears from October 2008 to September 2009. The sample size ranged from 65 individuals for Coryphaena hippurus to 346 for Euthynnus alletteratus. The b values in the LWR, W = aLb ranged from 2.807 to 3.284, with a mean of 3.015 ± 0.102 and intercepts between 0.0011 and 0.0432 with a mean of 0.0139. The condition factor (c.f.) values significantly (p &lt; 0.05) ranged from 0.64 to 1.55.Key words: Gulf of Gabes, length-weight, fish species, condition factor

Fit between humanitarian professionals and project requirements: hybrid group decision procedure to reduce uncertainty in decision-making

Choosing the right professional that has to meet indeterminate requirements is a critical aspect in humanitarian development and implementation projects. This paper proposes a hybrid evaluation methodology for some non-governmental organizations enabling them to select the most competent expert who can properly and adequately develop and implement humanitarian projects. This methodology accommodates various stakeholders’ perspectives in satisfying the unique requirements of humanitarian projects that are capable of handling a range of uncertain issues from both stakeholders and project requirements. The criteria weights are calculated using a two-step multi-criteria decision-making method: (1) Fuzzy Analytical Hierarchy Process for the evaluation of the decision maker weights coupled with (2) Technique for Order Preference by Similarity to Ideal Solution (TOPSIS) to rank the alternatives which provide the ability to take into account both quantitative and qualitative evaluations. Sensitivity analysis have been developed and discussed by means of a real case of expert selection problem for a non-profit organisation. The results show that the approach allows a decrease in the uncertainty associated with decision-making, which proves that the approach provides robust solutions in terms of sensitivity analysis

Architectured bimetallic laminates by roll bonding : bonding mechanisms and applications

International audienceManufacturing of bimetallic laminates (<2 mm) with an internal architecture by roll bonding allows to obtain a compromise of conflicting properties. Two applications are considered: copper-steel-copper sheets for high power electronic component substrates and lightweight aluminium-steel-aluminium laminates for structural, electromagnetic applications in power generation and for electromagnetic compatibility. They have in common an architecture, with three-dimensional percolating networks of two metals produced with a sufficient precision. The bonding mechanisms are investigated through microstructural and thermomechanical characterisation of the assemblies produced. Roll bonding fills the voids in a central component by plastic deformation and creates the bonds by cold welding. It may be followed or preceded by surface and heat treatments with the objective to improve the cold welding and to relieve the internal stress state. Architectural rules to optimise the properties of the two-phase laminates in view of the applications may be guided by finite element models combining physical and thermomechanical aspects

Prévalence des différents schémas occlusaux en diduction mandibulaire et leur corrélation avec la présence d’interférences

But : Évaluer la fréquence des schémas occlusaux lors de la diduction mandibulaire pour un échantillon de la population tunisienne, étudier la fréquence des interférences du côté non travaillant et chercher une éventuelle corrélation entre ces interférences et le type du schéma occlusal. Matériel et méthodes : Cette étude a été réalisée sur 220 personnes âgées de 15 à 64 ans. Les contacts d’occlusion travaillants et non travaillants ont été enregistrés dans une position bout à bout des canines. Les schémas occlusaux ont été classés en protection canine, protection de groupe, occlusion balancée et la non participation canine. La présence d’interférences occlusales lors des excursions mandibulaires ont été enregistrées. Le test statistique SPSS a été utilisé avec une signification de P = 0,5. Résultats : Le schéma occlusal le plus répondu était la protection de groupe (45.9 %) suivi par la protection canine (24.09 %) ; l’occlusion balancée était présente pour 11.36 % des cas et la non participation canine présentait le pourcentage de 18.63 %. Les interférences du côté non travaillant étaient présentes pour 13.21 % des sujets ayant une fonction de groupe, 14.85 % avec une protection canine, 100 % présentant l’occlusion balancée et 56.1 % avec une canine qui ne participe pas en diduction mandibulaire. Conclusion : Le schéma occlusal le plus fréquent était la fonction de groupe. Les interférences présentaient le pourcentage le moins important en cas de protection canine et de protection de groupe

Deep Learning-Based Image Denoising Approach for the Identification of Structured Light Modes in Dusty Weather

Structured light is gaining importance in free-space communication. Classifying spatially-structured light modes is challenging in a dusty environment because of the distortion on the propagating beams. This article addresses this challenge by proposing a deep learning convolutional autoencoder algorithm for modes denoising followed by a neural network for modes classification. The input to the classifier was set to be either the denoised image or the latent code of the convolutional autoencoder. This code is a low-dimensional representation of the inputted images. The proposed machine learning (ML) models were trained and tested using laboratory-generated mode data sets from the Laguerre and Hermite Gaussian mode bases. The results show that the two proposed approaches achieve an average classification accuracy exceeding 98&#x0025;, and both are better than the classification accuracy reported recently (83&#x2013;91&#x0025;) in the literature

Biochemical adaptation of phytoplankton to salinity and nutrient gradients in a coastal solar saltern, Tunisia

International audienceThe distribution of protein and carbohydrate concentrations of the particulate matter (size fraction: 0.45–160 mm) was studied, from 22 January 2003 to 02 December 2003, in three ponds of increasing salinity in the Sfax solar saltern (Tunisia). The coupling of N/P: DIN (DIN ¼ NO2 þ NO3 þ NH4þ) to DIP (DIP¼ PO4 3 ) with P/C: protein/carbohydrates ratios along salinity gradient allowed the discrimination of three types of ecosystems. Pond A1 (mean salinity: 45.0 5.4) having marine characteristics showed enhanced P/C ratios during a diatom bloom. N/P and P/C ratios were closely coupled throughout the sampling period, suggesting that the nutritional status is important in determining the seasonal change in the phytoplankton community in pond A1. In pond A16 (mean salinity: 78.7 8.8), despite the high nitrate load, P/C ratios were overall lower than in pond A1. This may be explained by the fact that dinoflagellates, which were the most abundant phytoplankton in pond A16 might be strict heterotrophs and/or mixotrophs, and so they may have not contributed strongly to anabolic processes. Also, N/P and P/C ratios were uncoupled, suggesting that cells in pond A16 were stressed due to the increased salinity caused by water evaporation, and so cells synthesized reserve products such as carbohydrates. In pond M2 (mean salinity: 189.0 13.8), P/C levels were higher than those recorded in either pond A1 or A16. N/P and P/C were more coupled than in pond A16. Species in the hypersaline pond seemed paradoxally less stressed than in pond A16, suggesting that salt-tolerant extremophile species overcome hypersaline constraints and react metabolically by synthesizing carbohydrates and proteins

Distribution of ciliates in relation to environmental factors along the coastline of the Gulf of Gabes, Tunisia

International audienceWe studied the seasonal distribution of the ciliate community coupled with environmental factors along the coast at three stations sampled (from March 2006 to February 2007) in the Gulf of Gabes (Tunisia, Eastern Mediterranean Sea). A total of 56 species belonging to 11 orders, were identified. Harbor of Gabes station was more diversified (45 species) than both Tabia (26 species) and Karboub (31 species) stations. The ciliate assemblage was numerically dominated by Spirotrichea in Tabia (82% of the total abundance), in the Harbor of Gabes (86% of the total abundance), whereas, in Karboub, Spirotrichea represented only 40% of the total abundance. The unexpected lower quantitative importance of Spirotrichea in Karboub station was apparently the result of the high salt concentration found in water samples throughout the study, probably originating from the saline area surrounding Karboub station, known as Sabkha. The distribution of species in the nearshore of the Gulf of Gabes seemed most likely influenced by the combined effects of temperature, salinity and hydrographic conditions