HAL Université de Toulouse, et Toulouse INP
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The magnetic and spin-down properties of slowly rotating fully convective M dwarfs
No full textInternational audienceThe evolution of the magnetism, winds and rotation of low-mass stars are all linked. One of the most common ways to probe the magnetic properties of low-mass stars is with the Zeeman-Doppler imaging (ZDI) technique. The magnetic properties of partially convective stars has been relatively well explored with the ZDI technique, but the same is not true of fully convective stars. In this work, we analyse a sample of stars that have been mapped with ZDI. Notably, this sample contains a number of slowly rotating fully convective M dwarfs whose magnetic fields were recently reconstructed with ZDI. We find that the dipolar, quadrupolar and octupolar field strengths of the slowly rotating fully convective stars do not follow the same Rossby number scaling in the unsaturated regime as partially convective stars. Based on these field strengths, we demonstrate that previous estimates of spin-down torques for slowly rotating fully convective stars could have been underestimated by an order of magnitude or more. Additionally, we also find that fully convective and partially convective stars fall into distinct sequences when comparing their poloidal and toroidal magnetic energies
Dispersion analysis in a 3D lattice elastic waveguide for the design of an absolute filter
No full textInternational audienceThis study presents a method for analyzing and designing elastic waveguides using 3D printed periodic truss structures to control the propagation of elastic waves. We propose an algorithm, based on the application of Bloch boundary conditions on a beam spectral model, to perform fast and efficient extraction of the full wave dispersion. Thanks to symmetry arguments, we introduce an identification method allowing for a better understanding of the dispersion. We then apply this method to a case study and demonstrate how it can be used to identify and design a structure exhibiting broadband absolute forbidden gaps
The Price of Opportunity Fairness in Matroid Allocation Problems
No full textWe consider matroid allocation problems under opportunity fairness constraints: resources need to be allocated to a set of agents under matroid constraints (which includes classical problems such as bipartite matching). Agents are divided into C groups according to a sensitive attribute, and an allocation is opportunity-fair if each group receives the same share proportional to the maximum feasible allocation it could achieve in isolation. We study the Price of Fairness (PoF), i.e., the ratio between maximum size allocations and maximum size opportunity-fair allocations. We first provide a characterization of the PoF leveraging the underlying polymatroid structure of the allocation problem. Based on this characterization, we prove bounds on the PoF in various settings from fully adversarial (wort-case) to fully random. Notably, one of our main results considers an arbitrary matroid structure with agents randomly divided into groups. In this setting, we prove a PoF bound as a function of the size of the largest group. Our result implies that, as long as there is no dominant group (i.e., the largest group is not too large), opportunity fairness constraints do not induce any loss of social welfare (defined as the allocation size). Overall, our results give insights into which aspects of the problem's structure affect the trade-off between opportunity fairness and social welfare
Effective Data Generation and Feature Selection in Learning for Planning
No full textInternational audiencePrevious studies have shown that leveraging data beyond optimal training plans improves the learning of search guidance for planning. Specifically, state ranking information can be extracted from states on optimal plan traces and their siblings. In this paper, we generalise this approach by extracting additional rankings from the A⋆ search tree for generating optimal training plans. As in the previous approach, we incur no additional search effort and negligible computational overhead for data extraction. However, extracting more data in this way may introduce many redundant features and states which slows down training. We formalise the problem of sound, redundant feature pruning and show that it is NP-complete to solve. Furthermore, we introduce several algorithms and approximations for redundant feature pruning. Experiments show that rankings learned by extracting more data from search trees for generating optimal training plans improve planner coverage. However, pairing with unsound pruning methods often results in diminishing performance, while our sound feature pruning methods provide consistent improvements across tested domains
Towards Canonical and Minimal Solutions in a Constraint-based Plan-Space Planner
No full textInternational audienceTemporal planning is the problem of selecting and scheduling a set of actions in order to achieve a distant objective from an initial state. Constraint Programming (CP) has historically played an important role in many automated temporal planners based on the Plan-Space Planning (PSP) algorithm. In a nutshell, PSP would drive the search for a plan by selecting which actions to add and how to resolve conflicts, with an embedded CP engine in charge of ensuring the coherence of the plan.In this paper, we consider an existing encoding of temporal planning into constraint programming that adheres to a plan-space approach, but encodes the decision of the PSP algorithm as decision variables of the CSP, thus letting the CP engine entirely drive the search for a solution plan. Analyzing the encoding, we show that the induced search space contains many symmetries that would be absent from the original PSP algorithm. Another caveat of the encoding is that it allows for non-minimal solutions, i.e., solutions in which some actions may be removed without invalidating it.We propose to extend the encoding with additional symmetry breaking constraints to enforce canonicity of the considered plans. The encoding is further improved with additional constraints to limit the presence of non-minimal plans. We show the extended encoding to very substantially improve the performance of the original version and to be competitive with state-of-the-art state-space temporal planners on the considered benchmarks
Preparation and Characterization of Single-Step Sodium Nitrate-Calcium Chloride Crosslinked Polyvinyl Alcohol-Alginate Sheets for Quorum Quenching Application in Membrane Bioreactors
No full textInternational audienceQuorum Quenching (QQ) is a proven anti-biofouling strategy in Membrane Bioreactors (MBRs). This study presents a novel approach for preparing and characterizing Poly (vinyl alcohol) (PVA) and Alginate (ALG) sheets for biofouling mitigation in MBRs. A significant challenge is posed in achieving QQ sheet preparation without using boric acid (H3BO3), a toxic crosslinker, and in a single-step crosslinking process. In this context, novel PVA-ALG sheets were prepared using sodium nitrate (NaNO3) and calcium chloride (CaCl2) in a single crosslinking step. Another new type of porous sheets was also prepared using a primary crosslinking solution composed of H3BO3, NaNO3, and CaCl2. The structural, mechanical, and textural properties of newly prepared sheets were compared to those of sheets crosslinked using the conventional primary crosslinking solution containing H3BO3 and CaCl2. Additionally, degradation of the QS signal molecule C8-HSL was investigated using all types of sheets entrapped with the QQ bacteria Rhodococcus sp. BH4. Differences in the composition of the crosslinking solutions among the various sheet types led to variations in their structural properties, characterized by increased crosslinking density and macro-void formation. Mesopores dominate in all PVA-ALG sheets, while their specific surface areas range from 45 m2/g to 77 m2/g, and tensile strength between 0.1 MPa and 0.3 MPa. New sheets crosslinked with NaNO3 and CaCl2 display the highest tensile strength and specific surface area. Furthermore, QQ sheets crosslinked with NaNO3 and CaCl2 demonstrated a superior C8-HSL degradation capacity compared to those prepared using the conventional crosslinking method involving boric acid
Instituer des dispositifs environnementaux. Le cas de l'invention des "guichets uniques haie" par des agents administratifs
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Rôle de la terminaison de surface dans le mécanisme de stockage de charge du carbure métallique 2D
No full textThe main objective of the thesis was to synthesize and conduct an in-depth study of novel 2D metal carbide material called as MXenes, for energy storage applications. In the thesis, most widely studied Ti3C2 MXenes were synthesized through two different techniques: etching of a MAX (Ti3AlC2) precursor in hydrogen fluoride to prepare F-terminated Ti3AlC2 MXene (HF-MXene) and molten salt-based synthesis (MS-MXene) to modify their surface terminations. The thesis started with tuning the MXene surface terminations and analyzing their electrochemical performance in aqueous electrolyte. Hydrophilic properties were found to be dependent on the surface terminations, where highest expansion in the d-spacing along with improved wettability was observed for -O terminated MXene followed by N,O - MXene. Electrochemical performance of N,O-Ti3C2 was observed to produce a mirror like Cyclic Voltammetry signature with a pair of redox peak. The redox peaks were associated with an activation process at the first cycle, related to the reversible intercalation of protons along with water molecules confirmed through in-situ XRD and EQCM. The dependence of surface termination in tuning the interlayer water was then found to enhance the electrochemical performance in aqueous electrolyte. Afterward surface termination characterization through ss-NMR revealed presence of higher amount of hydroxyl terminations for HF-MXene, owing to the wet chemical etching method, whereas increased presence of water and oxidation for MS-MXene. These variation in surface terminations were found to play a pivotal role in the SEI formation studied from ssNMR post SEI. Reduction in hydroxyl and water signals were observed for both MXene, with an entrapment of ethylene carbonate solvent only observed for HF-MXene suggesting lithium insertion with solvation shell. LiF fluoride was observed to be dominant SEI component owing to the higher presence of -F termination observed prior to SEI for HF-MXene, while the higher presence of O terminations led to a thick Li2CO3 rich SEI for MS-MXene. In the last part of the work direct visualization, using iDPC-STEM, of the desolvated lithium intercalation for MS-MXene owing to the thick SEI and lithium entering with the solvent in HF MXene was observed. Further in-plane resistance study also revealed the differences in the SEI formation on both the MXenes. Importance of surface termination of MXene in charge storage in aqueous and non-aqueous electrolyte were studied.L'objectif principal de la thèse était de synthétiser et d'effectuer une étude approfondie de nouveaux matériaux carbures métalliques 2D appelés MXènes, pour des applications de stockage d'énergie. Dans cette thèse, les MXènes Ti3C2 les plus largement étudiés ont été synthétisés à l'aide de deux techniques différentes: l'attaque chimique d'un précurseur MAX (Ti3AlC2) par du fluorure d'hydrogène pour préparer des MXènes Ti3AlC2 à terminaisons F (HF-MXène), et la synthèse à base de sels fondus (MS-MXène) pour modifier leurs terminaisons de surface. La thèse a commencé par la mise au point des terminaisons de surface du MXène et l'analyse de leur performance électrochimique dans un électrolyte aqueux. Les propriétés hydrophiles se sont avérées dépendantes des terminaisons de surface, où l'expansion la plus importante de l'espacement inter-feuillet, ainsi que l'amélioration de la mouillabilité ont été observées pour le MXène à terminaison -O suivi par le N,O-MXène. Les performances électrochimiques du N,O-Ti3C2 ont été observées pour produire une signature de voltampérométrie cyclique capacitive avec une paire de pics d'oxydoréduction réversibles. Les pics d'oxydoréduction ont été associés à un processus d'activation lors du premier cycle, lié à l'intercalation réversible de protons avec des molécules d'eau, confirmée par XRD et EQCM in situ. La dépendance de la terminaison de surface dans l'insertion de l'eau inter-feuillet a ensuite été trouvée pour améliorer la performance électrochimique dans l'électrolyte aqueux. Ensuite, la caractérisation des terminaisons de surface par ss-NMR a révélé la présence d'une plus grande quantité de terminaisons hydroxyle pour le HF-MXene, en raison de la méthode d'attaque chimique par voie humide, tandis que la présence accrue d'eau et d'oxydation pour le MS-MXene. Ces variations dans les terminaisons de surface se sont avérées jouer un rôle essentiel dans la formation du SEI, étudiée à partir de la RMN ss après le SEI. Une réduction des signaux d'hydroxyle et d'eau a été observée pour les deux MXene, avec un piégeage du solvant de carbonate d'éthylène uniquement observé pour le HF-MXene, ce qui suggère une insertion de lithium avec une sphère de solvatation. On a observé que le fluorure LiF était le composant SEI dominant en raison de la présence plus importante de terminaisons -F observées avant la formation de la SEI pour le HF-MXene, tandis que la présence plus importante de terminaisons O a conduit à une SEI épaise et riche en Li2CO3 pour le MS-MXene. Dans la dernière partie du travail, nous avons réalisé une visualisation directe, à l'aide de l'iDPC-STEM, de l'intercalation du lithium désolvaté dans le MS-MXène en raison de l'épaisseur de la SEI et de l'entrée du lithium avec le solvant dans le HF MXène. Une étude plus poussée de la variation de résistance dans le plan de l'électrode a également révélé des différences dans la formation de la SEI pour les deux MXènes. L'importance de la terminaison de surface du MXène dans le stockage de la charge dans un électrolyte aqueux et non aqueux a été étudiée
Nouveaux restes de vertébrés aquatiques et ichnologiques dans le Carbonifère Supérieur de Decazeville (Aveyron, France) : implications sur les paléofaunes des bassins varisques français.
No full textInternational audienceThe Decazeville Basin (Aveyron, France) is an Upper Carboniferous intra-Variscan basin of the southern part of the French Massif Central. Its geology and paleontological content (fauna and flora) have been the subject of regular studies before and during its coal mining activities, but unfortunately not since they ceased: no fossil from the Decazeville Basin has been described over the past 50 years. Recent fieldwork at the La Découverte locality led to the rediscovery of a vertebrate-rich deposit in the Bourran Formation, of which we describe new material here. This material consists of numerous specimens including new skeletal remains of the xenacanthiform Orthacanthus sp. and the acrolepid cf. Progyrolepis, two taxa never before reported in the Decazeville Basin. We also describe here the first coprolites from the Decazeville Basin, likely produced by Orthacanthus. The nature and taphonomy of these finds highlight the hypothesis that the depositional environment of the La Découverte locality was an anoxic freshwater lake, acting as the discharge zone of a powerful river. These discoveries confirm the similarity of the Decazeville fauna to the other intra-Variscan basins of the French Massif Central, although a few endemic forms such as the aeduellid Decazella vetteri (Heyler, 1964) are reported. The new ichthyofauna list provided here constitutes a solid basis for future comparisons with other Upper Carboniferous basins.Le bassin de Decazeville (Aveyron, France) est un bassin intra-varisque du Carbonifère supérieur de la partie méridionale du Massif central. Sa géologie et son contenu paléontologique (faune et flore) ont fait l’objet d’études régulières avant et pendant l’exploitation minière du charbon, mais malheureusement pas après son arrêt : aucun fossile du bassin de Decazeville n’a été décrit au cours de ces 50 dernières années. Cependant, des fouilles récentes à la localité de La Découverte ont permis de redécouvrir un gisement riche en vertébrés dans la Formation de Bourran, et de décrire ici du nouveau matériel. Ce matériel consiste en de nombreux spécimens, dont de nouveaux restes squelettiques du xénacanthiforme Orthacanthus sp. et de l’acrolépidé cf. Progyrolepis, deux taxons jamais rapportés dans le bassin de Decazeville jusqu’à présent. De plus, nous décrivons ici les premiers coprolites du bassin de Decazeville, probablement produits par Orthacanthus. La nature et la taphonomie de ces découvertes appuient l’hypothèse selon laquelle l’environnement de dépôt du site de La Découverte était un lac d’eau douce anoxique, faisant office de zone de déversement d’un cours d’eau puissant. Ces découvertes confirment la similitude de cette paléofaune avec celles des autres bassins intravarisques du Massif Central, même si quelques formes endémiques comme l’aeduellidé Decazella vetteri (Heyler, 1964) y sont présentes. La nouvelle liste ichtyofaunique fournie ici constitue une base solide de comparaisons futures avec d’autres bassins du Carbonifère Supérieu
Giant enhancement of phonon–electron coupling in graphene under femtosecond laser heating at room temperature
No full textInternational audienceIn recent years, phonon–electron carrier dragging has emerged as an innovative approach for modulating energy transfer in low-dimensional systems. In this letter, we explore the fundamental mechanisms of electron–phonon coupling and the role of thermal lag behavior in ultrafast heat transport. We present a theoretical investigation of non-equilibrium (n-eq) thermal dynamics in graphene under femtosecond laser excitation, emphasizing the role of phonon-branch-resolved electron–phonon coupling. This framework provides new insight into ultrafast energy transfer processes at femtosecond timescales and illustrates key deviations from the predictions of the classical two-temperature model, particularly in spatially localized heat transport. Our results show that a 190 fs laser pulse induces a strong n-eq state, followed by momentum redistribution among the excited carriers. This is then followed by effective cooling of the carrier distribution on a 450 fs timescale through phonon emission