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African vultures optimization algorithm based Choquet fuzzy integral for global optimization and engineering design problems
No full textInternational audienceAddressing complex optimization problems demands innovative solutions capable of navigating the interdependencies among variables, a reality often oversimplified by traditional metaheuristics. To address this challenge, this paper presents an enhanced African Vultures Optimization Algorithm, termed ci-AVOA, that incorporates the Choquet Integral, a powerful operator adept at considering criteria significance and interconnectedness in optimization scenarios. Unlike its predecessor, the ci-AVOA treats optimization problems in their true complexity by recognizing and accounting for the relationships between variables. The performance of ci-AVOA is evaluated on ten CEC2020 benchmark functions and four engineering design problems, pitted against other renowned optimization algorithms and the original AVOA. Across low and high dimensional benchmark functions, ci-AVOA consistently outperforms its counterparts, underpinning its superiority. This superior performance is further validated using non-parametric statistical tests, solidifying ci-AVOA as an effective and robust tool for tackling complex optimization problems. In essence, this study provides a significant contribution by augmenting a well-known metaheuristic with the Choquet Integral to devise a superior algorithm, ci-AVOA. This innovation extends the problem-solving capabilities of metaheuristics, promising more accurate and robust solutions for complex, real-world optimization problems
Exploring the Limits of High- T g Epoxy Vitrimers Produced through Resin-Transfer Molding
No full textInternational audienceOver the past few years, scientists have developed new ways to overcome the recycling issues of conventional thermosets with the introduction of associative covalent adaptable networks (i.e., vitrimers) in polymer materials. Even though various end-use vitrimers have already been reported, just a few of them have targeted high performance industrial applications. Herein, we develop a promising high-performance epoxy vitrimer based on a commercially available resin widely used in aeronautics with the highest glass transition temperature (Tg) of 233 °C ever reported for a vitrimer. A complete study of its physicochemical properties and cure kinetics was conducted, enabling the construction of the first time−temperature−transformation (TTT) diagram reported in the literature. This diagram allows a full determination of the processing and curing parameters leading to the manufacturing of vitrimer samples by the resin-transfer molding (RTM) process. The reshapability and limits therefrom of this high-Tg vitrimer were evaluated by three successful thermoforming cycles without degradation
The Centralization and Sharing of Information for Improving a Resilient Approach Based on Decision-Making at a Local Home Health Care Center
No full textInternational audienceHome care centers face both an increase in demand and many variations during the execution of routes, compromising the routes initially planned; robust solutions are not effective enough, and it is necessary to move on to resilient approaches. We create a close-to-reality use case supported by interviews of staff at home health care centers, where caregivers are faced with unexpected events that compromise their initial route. We model, analyze, and compare two resilient approaches to deal with these disruptions: a distributed collaborative approach and a centralized collaborative approach, where we propose a centralization and sharing of information to improve local decision-making. The latter reduces the number of late arrivals by 11%, the total time of late arrival by 21%, and halves the number of routes exceeding the end of work time (contrary to the distributed collaborative approach due to the time wasted reaching colleagues). The use of a device, such as a smartphone application, to centralize and share information thus, allows better mutual assistance between caregivers. Moreover, we highlight several possible openings, like the coupling of simulation and optimization, to propose a more resilient approach
Modélisation des incertitudes en horizon glissant et compilation de solutions de problèmes de lot sizing pour la planification tactique d'une chaîne logistique décentralisée
No full textIn a decentralized, multi-actor supply chain, the different entities in the chain must periodically and independently plan and revise their plans using a rolling horizon planning process to coordinate. This coordination complicates information exchange and decision making, as it depends on updated data, possible disruptions, and changes in each actor's objectives. In practice, decision makers must balance the pursuit of profitability, the need to maintain stability, and the ability to respond quickly to changes in demand or other disruptions in the chain. The objective of this thesis is to propose two approaches to help actors coordinate their planning in a decentralized supply chain. The first proposal is based on the history of deterministic plans exchanged between two actors. We have tried to estimate the uncertainties on parts of a sliding horizon based on the instabilities observed in the successive plans of the history. The idea is to allow a decision maker to estimate the uncertainty of the plans received from his partners and to integrate this uncertainty in his own planning in order to improve the reactivity and flexibility of the chain. The approach uses unsupervised classification methods on plan histories, classifies rolling horizon periods and produces uncertainty models for each class. It also allowed us to study the propagation of instabilities in a supply chain based on models of actors' behavior in response to these disturbances. The second approach consists in studying the application of knowledge compilation to tactical planning, approached as a batch sizing problem. The proposal concerns the study of compilation languages that are sufficiently expressive to represent such problems. The objective is to allow a decision maker to better model his preferences and constraints, and to transmit to his partners not only a deterministic plan but also a compilation of plans close in terms of acceptability. The partners can thus make more informed and efficient planning decisions. In the framework of the ANR CAASC project, we tested and evaluated both approaches with simulated and real data, which allowed us to demonstrate their applicability and limitations in real situations. The results showed that both approaches can be useful to help actors to better coordinate their planning in a decentralized supply chain, by allowing a better modeling of uncertainties and degrees of freedom.Dans une chaîne logistique décentralisée, multi-acteurs, les différentes entités de la chaîne sont amenées à planifier et à réviser leurs plans de manière périodique et indépendante, en utilisant, pour se coordonner, un processus de planification à horizon glissant. Cette coordination complexifie l'échange d'informations et les prises de décision, car elle dépend de l'actualisation des données, des perturbations possibles et des objectifs de chacun qui peuvent évoluer. De fait, les décideurs doivent trouver un équilibre entre la recherche de la rentabilité, la nécessité de maintenir la stabilité et la capacité de répondre rapidement aux changements de la demande ou aux autres perturbations de la chaîne. L'objectif de la thèse est de proposer deux approches pour aider les acteurs dans la coordination de leur planification dans une chaîne logistique décentralisée. La première proposition est basée sur l'historique des plans déterministes échangés entre deux acteurs. Nous avons cherché à estimer les incertitudes sur des parties d'un horizon glissant à partir des instabilités constatées dans les plans successifs de l'historique. L'idée est de permettre à un décideur d'estimer l'incertitude sur les plans reçus de ses partenaires pour intégrer cette incertitude dans sa propre planification et améliorer la réactivité et la flexibilité de la chaîne. L'approche utilise des méthodes de classification non supervisée sur l'historique des plans. Elle permet de classifier les périodes d'un horizon glissant, et de produire des modèles d'incertitude par classe. Elle nous a permis aussi d'étudier la propagation des instabilités dans une chaîne logistique en fonction de modèles de comportement d'acteurs face à ces perturbations. La deuxième approche consiste à étudier l'application de la compilation de connaissances à la planification tactique, qui est abordée comme un problème de Lot Sizing. La proposition concerne l'étude de langages de compilation suffisamment expressifs pour représenter de tels problèmes. L'objectif est de permettre à un décideur de mieux modéliser ses préférences et ses contraintes pour transmettre à ses partenaires non plus un plan déterministe mais une compilation de plans proches en termes d'acceptabilité. Les partenaires pouvant ainsi prendre des décisions de planification plus éclairées et plus efficaces. Cette thèse s'inscrivant dans le projet ANR CAASC, nous avons testé et évalué les deux approches avec des données simulées et réelles, ce qui nous a permis de démontrer leur applicabilité et leurs limites dans des situations réelles. Ces résultats ont montré que les deux approches peuvent être utiles pour aider les acteurs à mieux coordonner leur planification dans une chaîne logistique décentralisée, en permettant une meilleure modélisation des incertitudes et des degrés de liberté
Évaluation des phénomènes de transport et de la cinétique chimique lors de la pyrolyse rapide de la biomasse
No full textThe fast pyrolysis process primarily converts biomass particles into bio-oil. This liquid, which is more or less viscous and composed of hundreds of organic compounds, can be utilized as liquid biofuel or a source of organic products for the chemical industry. Kinetic modeling, particularly determining intrinsic kinetic parameters, presents a significant challenge in establishing optimal operating conditions and maximizing desired product yields. This study aims to generate experimental datasets that describe the reactivity of biomass in a kinetically controlled regime. For this purpose, a micropyrolyzer coupled directly to a mass spectrometer (Py-MS) was used, enabling online detection and identification of low molecular weight compounds released during pyrolysis. A detailed description of heat transfers within the micropyrolyzer was performed. The numerical simulations provided information that was not accessible experimentally, such as the thermal history of the sample and the heat flux at its surface, allowing for the evaluation of heat transfer limitations. The micropyrolyzer enables rapid heating rates and aims to create isothermal conditions. However, the finite element model used to simulate heating in the Py-MS instrument and the analysis of dimensionless numbers demonstrated that under typical Py-MS analysis conditions, assuming isothermal conditions for a significant period of time is not possible. Therefore, it is essential to incorporate the thermal history of the samples when performing kinetic studies. Additionally, it has been proven that, unlike external heat transfer to the sample, temperature gradients within the biomass sample can be minimized by carefully controlling its size and arrangement in the cup. Furthermore, transport phenomena involving molecular diffusion and advection within the system were quantified by measuring residence time distribution. Calibration strategies were developed to account for the effects of "thermal lag" and "delay in product detection" by the MS, thus obtaining reliable Py-MS data for samples pyrolyzed under kinetically controlled conditions. These corrected experimental data were processed using a non-linear and non-discriminating isoconversional method to interpret and model biomass devolatilization. The obtained isoconversional dependencies of Eα for biomass and its main components (holocellulose and lignins) exhibited significant variations with conversion, confirming the multi-stage nature of the fast pyrolysis process. Based on this study, reactivity- based models such as the constant activation energy model (CAEM), variable activation energy model (VAEM), and distributed activation energy model (DAEM) were developed to simulate the biomass fast devolatilization. The results were then compared to pure empirical primary kinetics determined using a screen heater. The configuration of this reactor and the vacuum conditions allowed for the control of primary pyrolysis and the quantification of vapors, gases, intermediate products, and solid residues as a function of reaction time, providing a comprehensive picture of the fast primary pyrolysis of biomass and a description of the formation of key primary products such as levoglucosan and cellobiosan.La pyrolyse rapide transforme principalement la biomasse solide en bio-huile, un liquide visqueux composé de centaines de composés organiques. Cette bio-huile peut être valorisée comme biocarburant liquide ou utilisée comme source de produits organiques pour l'industrie chimique. La modélisation cinétique, en particulier la détermination des paramètres "intrinsèques", joue un rôle essentiel pour optimiser les rendements et la composition des produits de pyrolyse. Ce travail vise à obtenir des ensembles de données expérimentales décrivant la réactivité de la biomasse dans un régime contrôlé par la cinétique chimique. Pour cela, des ensembles de données expérimentales ont été collectés à l'aide d'un micropyrolyseur couplé à un spectromètre de masse (Py-MS), permettant ainsi la détection en ligne des composés volatils libérés lors de la pyrolyse. Les simulations numériques ont été réalisées pour étudier les transferts thermiques au sein du micropyrolyseur, fournissant des informations inaccessibles expérimentalement, telles que le profil thermique de l'échantillon et le flux de chaleur à sa surface, et évaluant l'existence de limitations du transfert de chaleur. Bien que le micropyrolyseur permette d'atteindre des vitesses de chauffe élevées et vise à établir des conditions isothermes, le modèle à éléments finis et l'analyse des nombres sans dimension ont démontré que dans des conditions typiques d'analyses Py-MS, il n'est pas possible de supposer une condition isotherme pendant un temps significatif. Il est donc nécessaire de prendre en compte l'histoire thermique des échantillons lors des études cinétiques. Contrôler la taille et la disposition de l'échantillon dans le creuset permet de minimiser les gradients de température à l'intérieur des particules. De plus, les phénomènes de transport par diffusion moléculaire et advection ont été quantifiés en mesurant la distribution du temps de séjour. Des stratégies de calibration ont été développées pour tenir compte des effets du "retard thermique" et du "retard dans la détection des produits", garantissant ainsi la collecte de données fiables à partir du Py- MS pour les échantillons pyrolysés "dans un régime contrôlé par la cinétique chimique". Ces données corrigées ont été analysées à l'aide d'une méthode isoconversionnelle non linéaire et non discriminante pour interpréter et modéliser la dévolatilisation de la biomasse. Les tendances isoconversionnelles des énergies d’activation, Eα, pour la biomasse et ses composants (holocellulose et lignines) ont montré des variations considérables avec la conversion, confirmant la nature multi-étape du processus de pyrolyse rapide. À partir de cette étude préliminaire, des modèles basés sur la réactivité tels que le modèle d'énergie d'activation constante (CAEM), le modèle d'énergie d'activation variable (VAEM) et le modèle d'énergie d'activation distribuée (DAEM) ont été développés pour simuler la dévolatilisation rapide de la biomasse. Ces modèles ont été comparés aux cinétiques primaires empiriques déterminées à l'aide d'un réacteur constitué de tamis chauffés. L’utilisation de ce réacteur sous vide a permis de contrôler la pyrolyse primaire et de quantifier des produits de réaction d’intérêt tels que le levoglucosane et le cellobiosane au cours du temps
Synthesis, Characterization, and Adsorption Properties of Nitrogen-Doped Nanoporous Biochar: Efficient Removal of Reactive Orange 16 Dye and Colorful Effluents
No full textInternational audienceIn this work, nitrogen-doped porous biochars were synthesized from spruce bark waste using a facile single-step synthesis process, with H3PO4 as the chemical activator. The effect of nitrogen doping on the carbon material’s physicochemical properties and adsorption ability to adsorb the Reactive Orange 16 dye and treat synthetic effluents containing dyes were evaluated. N doping did not cause an important impact on the specific surface area values, but it did cause an increase in the microporosity (from 19% to 54% of micropores). The effect of the pH showed that the RO-16 reached its highest removal level in acidic conditions. The kinetic and equilibrium data were best fitted by the Elovich and Redlich–Peterson models, respectively. The adsorption capacities of the non-doped and doped carbon materials were 100.6 and 173.9 mg g−1, respectively. Since the biochars are highly porous, pore filling was the main adsorption mechanism, but other mechanisms such as electrostatic, hydrogen bond, Lewis acid-base, and π-π between mechanisms were also involved in the removal of RO-16 using SB-N-Biochar. The adsorbent biochar materials were used to treat synthetic wastewater containing dyes and other compounds and removal efficiencies of up to 66% were obtained. The regeneration tests have demonstrated that the nitrogen-doped biochar could be recycled and reused easily, maintaining very good adsorption performance even after five cycles. This work has demonstrated that N-doped biochar is easy to prepare and can be employed as an efficient adsorbent for dye removal, helping to open up new solutions for developing sustainable and effective adsorption processes to tackle water contamination
Polymer Supercritical CO2 Foaming under Peculiar Conditions: Laser and Ultrasound Implementation
No full textInternational audienceThe two-step batch foaming process of solid-state assisted by supercritical CO2 is a versatile technique for the foaming of polymers. In this work, it was assisted by an out-of-autoclave technology: either using lasers or ultrasound (US). Laser-aided foaming was only tested in the preliminary experiments; most of the work involved US. Foaming was carried out on bulk thick samples (PMMA). The effect of ultrasound on the cellular morphology was a function of the foaming temperature. Thanks to US, cell size was slightly decreased, cell density was increased, and interestingly, thermal conductivity was shown to decrease. The effect on the porosity was more remarkable at high temperatures. Both techniques provided micro porosity. This first investigation of these two potential methods for the assistance of supercritical CO2 batch foaming opens the door to new investigations. The different properties of the ultrasound method and its effects will be studied in an upcoming publication
On the tribological behavior of cobalt-based nanocomposite coatings containing ZnO@Graphene oxide core-shell nanoparticles
No full textIssu de : 24th International Conference on Wear of Materials, 16-20 avril 2023, Banff, Alberta, CanadaInternational audienceA hybrid nanocrystalline cobalt-based coating was prepared by cathode plasma electrolytic deposition (CPED). Zinc oxide and graphene oxide (GO) nanoparticles were mixed to form a core-shell structure through electrostatic self-assembly by using (3-aminopropyl)triethoxysilane (APTES) modifier. ZnO@GO nanoparticles were used as additives to improve wear and friction properties of deposited coatings. The concentration effect of core-shell ZnO@GO addition (0.1, 0.2 and 0.3 %wt) on the friction, wear, coating thickness and mechanical properties was investigated. The composition and microstructure of deposited coatings were studied by scanning electron microscope (SEM), X-ray diffraction (XRD), Raman spectroscopy and energy dispersive spectroscopy (EDS). Reciprocating sliding wear tests using a ball-on-plate configuration were carried out on a PLINT TE67 tribometer. AISI 52100 steel was used as ball and the coating deposited onto a AISI 304 stainless steel substrate was used as plate. Coatings were dense, nanocrystalline and uniform with a FCC metastable cobalt structure. Core-shell concentration above to 0.2 %wt resulted in a decrease of grain size and an increase of hardness and wear resistances. Nanoparticles act as nucleation sites for grain formation, decreasing grain sizes. Samples using 0.3% ZnO@GO displayed the lowest wear and friction coefficients. ZnO@GO nanoparticles enables the formation of a protective layer consisting of oxide and exfoliated GO on the top of worn surfaces
Influence of iron dilution on plastic deformation mechanisms in cobalt-based alloys: Consequence of phase transformations on tribological behavior
No full textIssu de : 24th International Conference on Wear of Materials, 16-20 avril 2023, Banff, Alberta, CanadaInternational audienceThe chemical composition and microstructure of metallic parts are parameters that affect plastic deformation accommodation mechanisms under friction stresses. The content of alloying elements impacts the stacking fault energy and the plastic deformation, and thus affects the tribological behavior. Depending on this content and the levels of mechanical stresses, plastic deformation of some alloys obtained under non-equilibrium conditions can occur. It is caused by different mechanisms, such as perfect slip and/or partial dislocation slip, as well as by phase transformation. The purpose of this study is to determine the influence of the plastic deformation accommodation mechanisms on tribological behavior by studying the effect of the iron content in cobalt-based alloys. For manufacturing purposes, cobalt-based coatings are produced on steel substrate using a additive manufacturing process (SLM). With this process, the microstructures of the cobalt-based coatings are essentially metastable FCC phase at room temperature with different contents of diluted iron. Tribological tests were carried out with a ball-to-disc contact. Iron contents were estimated by EDS-SEM. Analytical techniques such as XRD and EBSD were used to identify the microstructural changes observed in TTS due to tribological loading. The friction coefficient is linked to the evolution of the plastic deformation mechanisms activated to accommodate the contact. In particular, in addition to work-hardening phenomena, phase transformations are possible, namely a metastable FCC phase gives an HCP phase and a metastable FCC phase gives an α′-BCC phase under tribological loading. Both types of transformations can occur, individually or simultaneously, depending on the iron content in the coating
restoptr: an R package for ecological restoration planning
No full textInternational audienceEcological restoration is essential to curb the decline of biodiversity and ecosystems worldwide. Since the resources available for restoration are limited, restoration efforts must be cost-effective to achieve conservation outcomes. Although decision support tools are available to aid in the design of protected areas, little progress has been made to provide such tools for restoration efforts. Here, we introduce the restoptr R package, a decision support tool designed to identify priority areas for ecological restoration. It uses constraint programming – an artificial intelligence technique – to identify optimal plans given ecological and socio-economic constraints. Critically, it can identify strategic locations to enhance connectivity and reduce fragmentation across a broader landscape using complex landscape metrics. We illustrate its usage with a case study in New Caledonia. By applying this tool, we identified priority areas for restoration that could reverse forest fragmentation induced by mining activities in a specific area. We also found that relatively small investments could deliver large returns to restore connectivity. The restoptr R package is a free and open-source decision support tool available on the Comprehensive R Archive Network (https://cran.r-project.org/package=restoptr