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On stochastic operators, fitness landscapes, and optimization heuristics performances
No full textInternational audienceStochastic operators are the backbone of many optimization algorithms. Besides the existing theoretical analysis that studies the asymptotic runtime of such algorithms, characterizing their performance using fitness landscape analysis is far away. The fitness landscape approach proceeds by considering multiple characteristics to understand and explain an optimization algorithm’s performance or the difficulty of an optimization problem, and hence would provide a richer explanation. This paper analyzes the fitness landscapes of stochastic operators by focusing on the number of local optima and their relation to the optimization performance. The search spaces of two combinatorial problems are studied: the NK-landscape and the Quadratic Assignment Problem, using binary string-based and permutation-based stochastic operators. The classical bit-flip search operator is considered for binary strings, and a generalization of the deterministic exchange operator for permutation representations is devised. We study small instances, ranging from randomly generated to real-like instances, and large instances from the NK-landscape. For large instances, we propose using an adaptive walk process to estimate the number of locally optimal solutions. Given that stochastic operators are usually used within population and single-solution-based evolutionary optimization algorithms, we contrast the performance of the (μ+λ)-EA, and an Iterated Local Search, versus the landscape properties of large size instances of the NK-landscapes. Our analysis shows that characterizing the fitness landscapes induced by stochastic search operators can effectively explain the optimization performances of the algorithms we considered
Qual digitalização para a agricultura familiar ?
No full textSource Agritrop Cirad (https://agritrop.cirad.fr/615901/) * Autres projets (id;sigle;titre): ;;(FRA) Projet Fracture Numérique// ;ACOTAF;(FRA) Renforcer le conseil agricole pour accompagner les transitions agroécologiques de l’agriculture familiale en Afrique subsaharienne// ;Compairs;(FRA) Certification par les pairs pour une qualité éco-solidaire : co-construction d’un commun intellectuel// ;DigiCLA;(BEN) Le digital pour lutter contre la Chenille Légionnaire d'Automne//International audienceA digitalização do sector agrícola na África Ocidental gera muitas promessas para os stakeholders das cadeias de valor agrícolas e tecnológicas. Estas promessas baseiam-se na apropriação voluntária e massiva, por parte dos produtores agrícolas, de ferramentas telefónicas ligadas à rede internet. A utilização do celular e das suas aplicações poderia favorecer a criação de uma rede autónoma de produtores, estruturar melhor as cadeias de valor e aumentar o valor económico do setor. Os produtores agrícolas são atualmente alvo de um número crescente de fornecedores de "serviços digitais", desenvolvidos sob a forma de aplicativos por startups da Tech e AgriTech. No entanto, o sucesso dos aplicativos desenvolvidos para benefício dos produtores agrícolas é mitigado. Que tipo de lição podemos tirar deste sucesso limitado e que ações deveriam ser tomadas para colocar a tecnologia digital plenamente ao serviço dos produtores e facilitar uma transição para práticas social, económica e ambientalmente sustentáveis
Offline and Online Use of Interval and Set-Based Approaches for Control and State Estimation : A Selection of Methodological Approaches and Their Application
No full textInternational audienceControl and state estimation procedures need to be robust against imprecisely known parameters, uncertainty in initial conditions, and external disturbances. Interval methods and other set-based techniques form the basis for the implementation of powerful approaches that can be used to identify parameters of dynamic system models in the presence of the aforementioned types of uncertainty. Moreover, they are applicable to a verified feasibility and stability analysis of controllers and state estimators. In addition to these approaches which are typically used offline for analysis of system models designed with classical floating point procedures, interval and set-based methods have also been developed in recent years, which allow to directly solve the associated design tasks and to implement reliable techniques that are applicable online, i.e., during system operation. The latter approaches include set-based model predictive control, online parameter adaptation techniques for nonlinear variable-structure and backstepping controllers, interval observers, and fault diagnosis techniques. This paper provides an overview of the methodological background and reviews numerous practical applications for which interval and other set-valued approaches have been employed successfully
From residual mesogens to responsive materials : recycled liquid crystals from end-of-life screens in photocurable acrylate networks
No full textInternational audiencePhotocurable composites were developed using isobornyl acrylate and recycled liquid crystal components, cured under ultraviolet light with a reactive crosslinker and photoinitiator. Physical characterization included infrared spectroscopy, differential scanning calorimetry, dynamic mechanical analysis, and rheology. Spectroscopy confirmed over 90% conversion of carbon–carbon double bonds. Calorimetry revealed suppression of mesophase transitions, indicating effective encapsulation. Mechanical analysis showed a glass transition temperaturedecrease from approximately 90°C to 65°C and a marked reduction in stiffness.Rheological measurements indicated enhanced flow due to lower viscosity. Theseresults demonstrate a plasticizing effect and compatibility of the recycled liquidcrystals, enabling tunable functional properties for optical applications.Des composites photodurcissables ont été développés à partir d'acrylate d'isobornyle et de composants à cristaux liquides recyclés, durcis sous lumière ultraviolette à l'aide d'un agent de réticulation réactif et d'un photo-initiateur. La caractérisation physique comprenait la spectroscopie infrarouge, la calorimétrie différentielle à balayage, l'analyse mécanique dynamique et la rhéologie. La spectroscopie a confirmé une conversion de plus de 90 % des doubles liaisons carbone-carbone. La calorimétrie a révélé une suppression des transitions mésophases, indiquant une encapsulation efficace. L'analyse mécanique a montré une diminution de la température de transition vitreuse d'environ 90 °C à 65 °C et une réduction marquée de la rigidité. Les mesures rhéologiques ont indiqué une amélioration de l'écoulement due à une viscosité plus faible. Ces résultats démontrent un effet plastifiant et la compatibilité des cristaux liquides recyclés, permettant des propriétés fonctionnelles ajustables pour des applications optiques
Self-assembly synthesis of Cu-modified urchin flower-like graphitic carbon nitride for efficient nitrophenol reduction
No full textInternational audienceA novel copper-modified graphitic carbon nitride catalyst (CuNC) with a hierarchical, urchin-like flower morphology was developed for the catalytic reduction of 4-nitrophenol (4-NP). Synthesized via a facile hydrothermal method, the CuNC catalyst with 32 wt% copper loading exhibited exceptional activity, achieving complete conversion of 4-NP to 4-aminophenol (4-AP) within 14 s at a concentration of 0.11 mM in both river water and tap water. This performance surpasses that of conventional catalysts, highlighting the significant impact of the unique urchin-like flower morphology on catalytic efficiency. The enhanced activity is attributed to the synergistic effects of high copper dispersion, nitrogen doping, and efficient mass transfer facilitated by the hierarchical structure. This study demonstrates the potential of CuNC as an eco-friendly and cost-effective catalyst for the reduction of nitroaromatic compounds in real water samples, paving the way for its integration into sustainable catalytic systems for environmental remediation
Les glissements sous-marins du Cône de l'Amazone: caractérisation de leurs processus de mise en place
No full textInternational audienceLes glissements sous-marins sont un « objet » sédimentaire communs à toutes lesmarges continentales. Ils résultent du déplacement gravitaire de blocs cohérents le long desurfaces de rupture. De par leur volume, ils modifient quasi-instantanément la morphologie etla physiographie des marges. Leur compréhension est essentielle pour évaluer les risquestsunamogènes, notamment dans un contexte de changement climatique et d’anthropisationcroissante des littoraux qui affectent l’hydrodynamisme, la vitesse de sédimentation et lastabilité des pentes, et augmentent ainsi potentiellement la fréquence de ces phénomènes. Cetravail vise à comprendre les mécanismes de mise en place des dépôts de transport en masse(Mass-Transport Deposits – MTD) observés sur le haut de pente du Cône sous-marin del’Amazone, en analysant leurs compositions et leurs organisations internes, en déterminantl’origine des sédiments mobilisés et en datant les épisodes de dépôt pour établir leur possiblelien avec les variations climato-eustatiques. Ce travail s’inscrit dans le cadre du projet ANRMEGA. Il repose sur l’analyse de trois carottes et de données acoustiques haute résolution(profils Chirp) obtenues durant la campagne AMARYLLIS-AMAGAS (2023).Les analyses microgranulométriques, XRF, des cortèges argileux et des foraminifèresbenthiques indiquent que les sédiments remobilisés des MTD et les argiles hémipélagiques enplace sont très similaires en termes de composition lithologique, de contenumicropaléontologique et de géochimie. Les datations 14C et les analyses biostratigraphiquesont permis d’identifier les périodes de déclenchement des MTD. Les images RX révèlent desstructures de déformation dominées par des plissements de tailles variées, associés à ducisaillement, des rafts microfracturés, voire à des écoulements gravitaires de type débrite.Les MTD prendraient leur source vers 200 m de profondeur d’eau, avec des distancesde déplacement variées, de quelques centaines de mètres à plusieurs dizaines de kilomètres, etparfois des mises en place polyphasées. Leur déclenchement serait lié aux variations climato-eustatiques du Dernier Maximum Glaciaire et de la déglaciation. Il serait causé soit par unesurcharge sédimentaire liée à la forte augmentation des taux de sédimentation soit par ladissociation des hydrates de gaz causée par les variations de température des eaux de fondaffectant le haut de pent
Valorisation de biogaz pour la production d’hydrogène ou du gaz de synthèse : produits à forte valeur ajoutée et énergétique
No full textIn a global context marked by climate change and the need to reduce greenhouse gas emissions, the valorization of landfill biogas represents a promising pathway toward a sustainable energy transition. This project, carried out in collaboration with the landfill site Opale Environnement, aligns with this approach by investigating dry reforming of methane (DRM) as a catalytic process for converting biogas into synthesis gas. Initially, DRM was investigated using a synthetic CH4/CO2 mixture, leading to the identification of an optimized catalytic formulation based on Co-Ni-Mg-Al, exhibiting both high activity and thermal stability. This formulation was then shaped and evaluated at a semi-pilot scale to validate its catalytic performance under conditions close to industrial application. The raw biogas produced by methanation was subsequently sampled and analyzed, with major components (CH4 and CO2) and trace compounds (sulfur, nitrogen containing species, aromatics, terpenes, and hydrocarbons) being identified and quantified. The catalyst’s efficiency was then tested using both real biogas and a synthetic mixture doped with selected impurities, in order to assess the impact of complex contaminants on catalytic activity and material durability.Dans un contexte mondial marqué par le changement climatique et la nécessité de réduire les émissions de gaz à effet de serre, la valorisation du biogaz issu des centres d’enfouissement constitue une voie prometteuse pour une transition énergétique durable. Ce projet, mené en collaboration avec le centre d’enfouissement Opale Environnement, s’inscrit dans cette dynamique en explorant le reformage à sec du méthane (DRM) comme procédé catalytique de conversion du biogaz en gaz de synthèse. Dans un premier temps, le DRM a été étudié à partir d’un mélange synthétique CH4/CO2, conduisant à l’identification d’une formulation catalytique optimisée à base de Co-Ni-Mg-Al, combinant activité élevée et stabilité thermique. Cette formulation a ensuite été mise en forme et évaluée à l’échelle semi-pilote, afin de valider ses performances catalytiques dans des conditions proches de l’application industrielle. Le biogaz brut issu de méthanisation a ensuite été prélevé, analysé, et ses composants majoritaires (CH4 et CO2) ainsi que minoritaires (soufrés, azotés, aromatiques, terpènes, hydrocarbures) ont été identifiés et quantifiés. L’efficacité du catalyseur a été testée avec du biogaz réel ainsi qu’en présence d’impuretés ajoutées à un mélange synthétique stœchiométrique, afin d’évaluer leur impact sur l’activité catalytique et la durabilité du matériau
Innovative Design and Investigation on Resistive and Capacitive Network Based NGD Topology
No full textInternational audienceThis paper investigates the circuit theory of elementary passive topology exhibiting reconfigurable positive/negative delay (RPND) effect. This novel evaluated framework enables identification of the first-order L-topology constituted by RC-network operating under RPND effect. The investigated passive L-cell can operate in both negative and positive group delay (NGD or PGD) mode depending on the RC-network parameter. After establishing the NGD existence condition, the design equations versus the RPND effect including the target parameter values are formulated. To validate the theory, an RC-circuit representing a RPND Proof-of-Concept (PoC) was designed, implemented and tested especially in the time-domain by verifying the time-advance signature corresponding to the NGD operation mode. By tuning a PoC resistor, experimentation of pulse and arbitrary waveform signals confirm the feasibility to observe RPND reconfigurability. In the NGD mode, it is observed that outputs in time-advance of their own inputs about -3 ms. The RPND circuit is particularly useful for adjusting delay effect and signal synchronization in the communication system
La naissance d'un sentiment patrimonial en Égypte aux XIXe-XXe siècles
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