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Thermite Combustion: Current Trends in Modeling and Future Perspectives
No full textInternational audienceAluminum-based reactive composites, such as thermites, represent a unique class of energetic materials characterized by their high energy densities, tunability in combustion properties and safety. Prepared using techniques such as mechanical mixing, milling, and physical vapor deposition, these materials are promising for achieving energetic functions beyond the capabilities of traditional energetic materials. Applications include thermal plugging, smart initiation, pyro-fusing in civilian devices where the use of explosives is not feasible. Unfortunately, engineers and researchers face the lack of predictive combustion models to optimize the thermite materials to a given application. The reason is the insufficient knowledge and quantification of reaction and combustion mechanisms and the key variables governing them. That is why, over the past decades, several approaches and models ranging from atomic-scale modeling to macroscopic simulations using computational fluid dynamics, were developed and are reviewed in this article. These methods provided insights into key reaction pathways, ignition mechanisms, and flame propagation dynamics. Despite these advancements, substantial gaps remain, particularly in capturing multiphase flow dynamics and suboxides condensation/nucleation process during the combustion at high temperature. Boundary-resolved transient direct numerical simulation approach and particle-resolved numerical techniques will allow acquiring knowledge in gasparticle and particle-particle interaction. Recent breakthroughs in machine learning will further accelerate the design and optimization of thermites by enabling the establishment of predictive quantitative structure-property relationships in complement of heavy detailed physical models. This review highlights foundational theoretical developments for thermite materials, and emphasize the need for interdisciplinary efforts particularly between fluid dynamicists and condensed matter physicists to realize the full potential of these versatile energetic materials
Visible light activation of C–Cl and C–F bonds in persistent organic pollutants using cerium(III) triamidoamine complex
No full textInternational audienceProcedures for activating and degrading compounds containing carbon–halogen bonds are highly sought after due to the environmental persistence and potential hazards of such compounds. Such activations are challenging because of the high stability of these bonds, particularly those with C–F bonds. Here, we report on the activation of carbon–halogen bonds, including C–F bonds, by the cerium(III)-triamidoamine complex CeIIITRENTIPS (1, TRENTIPS = tris-(2-(tri-iso-propylsilylamidoethyl)amine)). Under light irradiation, 1 reaches a strongly negative excited state redox potential, and our measurements enable it to be estimated as −3.2 V relative to Cp2Fe0/+. Hence, the photo-reactivity of 1 with carbon–halogen bonds has been established with numerous examples, including Persistent Organic Pollutants (POPs) and fluorinated compounds. The photoactivation of POPs is rapid, but the photoactive nature of the cerium(IV) products precludes complete conversion. This study provides insight into the activation of POPs that may benefit the future design of photodegradation approaches for these highly problematic compounds
Quasi-classical Dynamics of Hydrogen Molecules Trapped Inside Fullerene Cages
No full textInternational audienceWe perform molecular dynamics simulations of hydrogen molecules inside fullerene cages, incorporating quantum effects via the Feynman-Hibbs effective potential method. The distance between hydrogen atoms in the molecule is kept fixed by using the constraint dynamics algorithm. We evaluate the energetic properties and the influence of quantum effects for hydrogen molecules in fullerene cages of varying size and geometry (Cn, n=24, 28, 60, 70), and within a wide range of thermodynamics conditions (i.e., from T=130 K to T=320 K). We compute the temperature dependence of quantities such as the translational and rotational kinetic energies, the total energy and the contribution of quantum effects. It is found that quantum corrections to the total energy are significant even at room temperature. We discuss the possible influence of these properties on the hydrogen storage capacity of these materials
Stacking sequence effects on compressive failure using pin-ended buckling test
No full textInternational audienceA pin-ended buckling test, inspired by the work of Wisnom (M. Wisnom, 1992), was developed to assess the influence of strain gradients on the compressive failure strain of composite laminates. Experiments were carried out on laminates manufactured with unidirectional (UD) carbon/epoxy AS4/8552 prepegs, with full-field strain measurements obtained via digital image correlation. The influence of stacking sequence on compressive failure-specifically the effects of 0°ply thickness and the adjacent ply interface-was investigated by testing a range of cross-ply and quasi-isotropic specimens. To prevent premature tensile failure, a 2024 aluminium ply was bonded to the tensile side of the 8-ply and 16-ply specimens, following the approach described in (Bianchi et al. 2025). Comparisons between the different stacking sequences were carried out by analysing the evolution of the maximum compressive strain as a function of the strain gradient. Additionally, a comparative analysis was performed between scaled specimens-32-ply, 16-ply, and 8-ply-in both cross-ply and quasi-isotropic configurations. The experimental results confirmed the nonlinear character of the strain-gradient effect on compressive failure. Furthermore, they indicated that neither the 0°ply thickness nor the adjacent ply interface exert a significant influence on the material investigated. These observations differ from earlier models that predicted such effects.</div
Graph-Based Product Form
No full textProduct-form stationary distributions in Markov chains have been a foundational advance and driving force in our understanding of stochastic systems. In this paper, we introduce a new product-form relationship that we call "graph-based product form". As our first main contribution, we prove that two states of the Markov chain are in graph-based product form if and only if the following two equivalent conditions are satisfied: (i) a cut-based condition, reminiscent of classical results on product-form queueing systems, and (ii) a novel characterization that we call joint-ancestor freeness. The latter characterization allows us in particular to introduce a graph-traversal algorithm that checks product-form relationships for all pairs of states, with time complexity , if the Markov chain has a finite transition graph . We then generalize graph-based product form to encompass more complex relationships, which we call "higher-level product form", and we again show these can be identified via a graph-traversal algorithm when the Markov chain has a finite state space. Lastly, we identify several examples from queueing theory that satisfy this product-form relationship
Bogomolov-Gieseker inequality for log terminal Kähler threefolds (with an appendix by Frédéric Campana, Andreas Höring and Thomas Peternell)
No full textInternational audienceIn this article we prove the orbifold version of the Bogomolov-Gieseker inequality for stable \Q-sheaves on log terminal Kähler threefolds
Méthodologie innovante pour la caractérisation dynamique, reproductible et sans parasite de composants p-GaN HEMTs ; mise en évidence d'effets exclusivement dynamiques
No full textNational audienceDes p-GaN HEMTs à grille schottky sont étudiés en fonctionnement dynamique, sans parasites, grâce à un environnement de test 50 Ohms spécialement conçu. Des phénomènes dynamiques exclusifs sont mis en évidence, notamment une phase de transition des énergies de commutation ; et une montée drastique du Ron, allant jusqu'à cinquante fois sa valeur nominale en présence de surtensions transitoires de grille. Ce phénomène est structurel, causé par la grille schottky. Contrairement au comportement observé en mesures quasi-statiques, les résultats sont reproductibles sans préconditionnement
Planification des tâches d'une flotte de robots mobiles autonomes pour la logistique interne de systèmes de production
No full textInternational audienc
Directional light scattering in Mie-resonant Si particles with ultra-thin Au shells
No full textInternational audienceMetamaterial research has sought to create nanostructures with strong directional optical scattering to control light propagation at the nanoscale. Core–shell architectures comprised of both resonant cores and resonant shells are suggested as candidate particles in which the spectral overlap of the electric and magnetic dipoles is controlled to create strong directional scattering. In this study, Au-decorated Si core–shell (Si@Au) particles are presented, studying the role of the architecture (particulate, discontinuous shells vs continuous) and dimensions of the shell. The core–shell particles are synthesized by first creating Si particles, through the thermal disproportionation of hydrogen silsesquioxane (HSQ), which are then decorated with ≈4 nm diameter Au nanoparticles. The resonant behavior of the core–shell particles is characterized using electron energy-loss spectroscopy mapping and optical single-particle scatter spectroscopy. These observations are supported by T-matrix simulations and Mie-theory calculations of the scattering spectra, which show that, compared to Si, Si@Au particles demonstrate a dampened magnetic dipole resonance for smaller Si core diameters (100–130 nm) and an enhanced magnetic dipole resonance for larger Si core sizes (150–200 nm). The study indicates that the previously reported hybridized modes do not exist in particulate Au shells around a Si core and can only exist in continuous plasmonic shells. Thus, it is shown here how important it is to be as precise as possible regarding the nanomaterial architecture used in simulations. No configuration of Si@Au core–shell particles with a particulate shell could be found that strongly enhanced directional scattering, and a continuous shell may do so only modestly. However, the simulations show that the synthesis of thin, continuous Ag shells might represent an alternative route towards achieving good directional scattering properties
Quantum trajectory of the one-atom maser
No full textInternational audienceThe evolution of a quantum system undergoing repeated indirect measurements naturally leads to a Markov chain on the set of states which is called a quantum trajectory. In this paper we consider a specific model of such a quantum trajectory associated to the one-atom maser model. It describes the evolution of one mode of the quantized electromagnetic field in a cavity interacting with two-level atoms. When the system is non-resonant we prove that this Markov chain admits a unique invariant probability measure. We moreover prove convergence in the Wasserstein metric towards this invariant measure. These results rely on a purification theorem: almost surely the state of the system approaches the set of pure states. Compared to similar results in the literature, the system considered here is infinite dimensional. While existence of an invariant measure is a consequence of the compactness of the set of states in finite dimension, in infinite dimension existence of an invariant measure is not free. Furthermore usual purification criteria in finite dimension have no straightforward equivalent in infinite dimensions