Publications

2024

• Development and analysis of efficient multi-scale numerical methods, with applications to plasma discharge simulations relying on multi-fluid models
  
  • Reboul Louis
  , 2024. Our main focus is the design and analysis of multi-scale numerical schemes for the simulation of multi-fluid models applied to low-temperature low-pressure plasmas. Our typical configuration of interest includes the onset of instabilities and sheaths, i.e. micrometric charged boundary layers that form at the plasma chamber walls. Our prototypical plasma model is the isothermal Euler-Poisson system of equations, but we also consider simpler models, the hyperbolic heat equations and the isothermal Euler-friction Equations, for the development and analysis of numerical methods. In a first axis, we develop and analyze a uniformly asymptotic-preserving second-order time-space coupling implicit-explicit method for the hyperbolic heat equations (linear case). We provide theoretical results on flux limiters for asymptotic-preserving methods, and a new well-balanced strategy. In a second axis, we propose several methods for the Euler-Poisson system of equations, to improve the accuracy of simulations of configurations featuring sheaths. In a third axis, we use these methods to conduct a parametric study of a 2D (rectangular) isothermal non-magnetized plasma discharge with sheaths, at various collisional regimes and aspect-ratios. We compare our result to PIC simulations and reference solutions. We show that simulating a fluid model with a tailored numerical method substantially reduces the time of simulation and improves the accuracy of the obtained solution. A discussion on the extensions of the multi-scale methods for the full non-isothermal Euler equations and to highly-magnetized cases is provided in the perspectives of our work.
• Distributed Quantum Advantage for Local Problems
  
  • Balliu Alkida
  • Brandt Sebastian
  • Coiteux-Roy Xavier
  • d'Amore Francesco
  • Equi Massimo
  • Le Gall François
  • Lievonen Henrik
  • Modanese Augusto
  • Olivetti Dennis
  • Renou Marc-Olivier
  • Suomela Jukka
  • Tendick Lucas
  • Veeren Isadora
  , 2024. We present the first local problem that shows a super-constant separation between the classical randomized LOCAL model of distributed computing and its quantum counterpart. By prior work, such a separation was known only for an artificial graph problem with an inherently global definition [Le Gall et al. 2019]. We present a problem that we call iterated GHZ, which is defined using only local constraints. Formally, it is a family of locally checkable labeling problems [Naor and Stockmeyer 1995]; in particular, solutions can be verified with a constant-round distributed algorithm. We show that in graphs of maximum degree $\Delta$, any classical (deterministic or randomized) LOCAL model algorithm will require $\Omega(\Delta)$ rounds to solve the iterated GHZ problem, while the problem can be solved in $1$ round in quantum-LOCAL. We use the round elimination technique to prove that the iterated GHZ problem requires $\Omega(\Delta)$ rounds for classical algorithms. This is the first work that shows that round elimination is indeed able to separate the two models, and this also demonstrates that round elimination cannot be used to prove lower bounds for quantum-LOCAL. To apply round elimination, we introduce a new technique that allows us to discover appropriate problem relaxations in a mechanical way; it turns out that this new technique extends beyond the scope of the iterated GHZ problem and can be used to e.g. reproduce prior results on maximal matchings [FOCS 2019, PODC 2020] in a systematic manner.
• Role of melting and solidification in the spreading of an impacting water drop
  
  • Sarlin Wladimir
  • Grivet Rodolphe
  • Xu Julien
  • Huerre Axel
  • Séon Thomas
  • Josserand Christophe
  Journal of Fluid Mechanics, Cambridge University Press (CUP), 2024, 996, pp.A14. The present study reports experiments of water droplet impacting on ice or on a cold metallic substrate, with the aim of understanding the effect of phase change on the impingement process. Both liquid and substrate temperatures are varied, as well as the height of fall. The dimensionless maximum spreading diameter, $\beta_m$, is found to increase with both temperatures as well as with the impact velocity. Furthermore, $\beta_m$ is reduced when solidification, which enhances dissipation, is present, whereas fusion favours the liquid film spreading. These observations are rationalized by extending an existing model of effective viscosity, in which phase change alters the size and shape of the developing viscous boundary layer, thereby modifying the value of $\beta_m$. The use of this correction allows to adapt a scaling law existing for isothermal drop impacts to propose a universal law giving the maximum diameter of an impacting water droplet in the presence of melting or solidification. (10.1017/jfm.2024.817)
  DOI : 10.1017/jfm.2024.817
• Guaranteed Satisfaction of a Temporal Logic Formula with a Confidence Parameter
  
  • Tillet Joris
  • Vanneaux Elena
  • Alexandre Dit Sandretto Julien
  , 2024.
• Plasma-enhanced detonability: experimental and calculated reduction of the detonation cell size
  
  • Cherif Mhedine Ali
  • Masuda Ryu
  • Claverie Alain
  • Vidal Pierre
  • Starikovskaia Svetlana
  Combustion and Flame, Elsevier, 2024, 268, pp.113639. This work analyzes the interaction between non-equilibrium plasma and detonation. The aim is to enhance the detonability of gaseous mixtures by reducing the detonation cell width through dissociation of a fresh gas mixture by plasma action. The experiments were performed in a square-section detonation tube, and the diagnostic tools used were ICCD chemiluminescence imaging, soot-plate recording, dynamic pressure sensors, and back current shunt technique. The results show that the application of a nanosecond plasma ahead of a self-sustained detonation reduces the cell width by a factor of about 2 in H₂:O₂:Ar, H₂:O₂, CH₄:H₂:O₂:Ar and CH₄:O₂:Ar mixtures for initial pressures between 100 and 200 mbar. A parametric study of plasma properties focused on the effect of the initial pressure on the deposited energy and homogeneity. A kinetic mechanism was proposed to estimate the dissociation effect of plasma chemistry on the fresh combustible mixture. The obtained densities of atoms produced in the plasma were used as input parameters to calculate the thermicity and temperature profiles of the detonation reaction zone according to the Zel’dovich-von Neumann-D¨oring model. The reduction factor of the ZND characteristic chemical length is about the same as the experimental cell widths, i.e. 2. This combination of experiments and calculations substantiates the relationship between plasma parameters, ZND chemical lengths, and detonation cell widths and, thus, demonstrates the possibility of controlling detonability using a nanosecond discharge. (10.1016/j.combustflame.2024.113639)
  DOI : 10.1016/j.combustflame.2024.113639
• Unsupervised radiometric change detection from synthetic aperture radar images
  
  • Bultingaire Thomas
  • Meraoumia Inès
  • Kervazo Christophe
  • Denis Loïc
  • Tupin Florence
  , 2024. Change detection is an important data processing task in remote sensing, with applications such as deforestation monitoring or natural disaster assessment. Synthetic Aperture Radar (SAR) imaging offers key advantages for change detection, in particular due to its robustness to weather condition and cloud coverage. Because of the speckle phenomenon, the intensity of SAR images suffer from strong fluctuations, making the detection of radiometric changes challenging. Our method builds on a recently introduced self-supervised despeckling technique. It estimates despeckling uncertainty to better identify meaningful differences between two despeckled images. Conformal prediction permits to approach the change detection problem from the angle of anomaly detection. Thus, we develop a fully unsupervised change detection approach with a controlled probability of false alarm. Experimental results on TerraSAR-X satellite images with metric resolution show the capability of our method to detect changes without any supervision.
• The genuinely multipartite nonlocality of graph states is model-dependent
  
  • Coiteux-Roy Xavier
  • Makuta Owidiusz
  • Curran Fionnuala
  • Augusiak Remigiusz
  • Renou Marc-Olivier
  , 2024. Bell's theorem proves that some quantum state correlations can only be explained by bipartite non-classical resources. The notion of genuinely multipartite nonlocality (GMNL) was later introduced to conceptualize the fact that nonclassical resources involving more than two parties in a nontrivial way may be needed to account for some quantum correlations. In this letter, we first recall the contradictions inherent to the historical definition of GMNL. Second, we turn to one of its redefinitions, called Local-Operations-and-Shared-Randomness GMNL (LOSR-GMNL), proving that all caterpillar graph states (including cluster states) have this second property. Finally, we conceptualize a third, alternative definition, which we call Local-Operations-and-Neighbour-Communication GMNL (LONC-GMNL), that is adapted to situations in which short-range communication between some parties might occur. We show that cluster states do not have this third property, while GHZ states do. Beyond its technical content, our letter illustrates that rigorous conceptual work is needed before applying the concepts of genuinely multipartite nonlocality, genuine multipartite entanglement or entanglement depth to benchmark the nonclassicality of some experimentally-produced quantum system. We note that most experimental works still use witnesses based on the historical definitions of these notions, which fail to reject models based on bipartite resources. (10.48550/arXiv.2404.15861)
  DOI : 10.48550/arXiv.2404.15861
• Mealy verifier : an automated, exhaustive, and explainable methodology for analyzing state machines in protocol implementations
  
  • Tran Van Arthur
  • Levillain Olivier
  • Debar Herve
  , 2024 (16), pp.1-10. Many network protocol specifications are long and lack clarity, which paves the way to implementation errors. Such errors have led to vulnerabilities for secure protocols such as SSH and TLS. Active automata learning, a black-box method, is an efficient method to discover discrepancies between a specification and its implementation. It consists in extracting state machines by interacting with a network stack. It can be (and has been) combined with model checking to analyze the obtained state machines. Model checking is designed for exhibiting a single model violation instead of all model violations and thus leads to a limited understanding of implementation errors. As far as we are aware, there is only one specialized exhaustive method available for analyzing the outcomes of active automata learning applied to network protocols,Fiterau-Brostean’s method. We propose an alternative method, to improve the discovery of new bugs and vulnerabilities and enhance the exhaustiveness of model verification processes. In this article, we apply our method to two use cases: SSH, where we focus on the analysis of existing state machines and OPC UA, for which we present a full workflow from state machine inference to state machine analysis. (10.1145/3664476.3664506)
  DOI : 10.1145/3664476.3664506
• A model-based approach for assessing the security of cyber-physical systems
  
  • Teixeira de Castro Hugo
  • Hussain Ahmed
  • Blanc Gregory
  • El Hachem Jamal
  • Blouin Dominique
  • Leneutre Jean
  • Papadimitratos Panos
  , 2024 (121), pp.1-10. Cyber-Physical Systems (CPSs) complexity has been continuously increasing to support new life-impacting applications, such as Internet of Things (IoT) devices or Industrial Control Systems (ICSs). These characteristics introduce new critical security challenges to both industrial practitioners and academics. This work investigates how Model-Based System Engineering (MBSE) and attack graph approaches could be leveraged to model secure Cyber-Physical System solutions and identify high-impact attacks early in the system development life cycle. To achieve this, we propose a new framework that comprises (1) an easily adoptable modeling paradigm for Cyber-Physical System representation, (2) an attack-graph-based solution for Cyber-Physical System automatic quantitative security analysis, based on the MulVAL security tool, (3) a set of Model-To-Text (MTT) transformation rules to bridge the gap between SysML and MulVAL. We illustrated the validity of our proposed framework through an autonomous ventilation system example. A Denial of Service (DoS) attack targeting an industrial communication protocol was identified and displayed as attack graphs. In future work, we intend to connect the approach to dynamic security databases for automatic countermeasure selection. (10.1145/3664476.3670470)
  DOI : 10.1145/3664476.3670470
• OAM driven nucleation of sub-50 nm compact antiferromagnetic skyrmions
  
  • Mallick Sougata
  • Ye Peng
  • Boutu Willem
  • Gauthier David
  • Merdji Hamed
  • Bibes Manuel
  • Viret Michel
  • Bouzehouane Karim
  • Cros Vincent
  Advanced Functional Materials, Wiley, 2024, pp.2409528. Abstract Owing to their high mobility and immunity to topological deflection, skyrmions in antiferromagnetic (AFM) systems are gaining attention as a potential solution for next‐generation magnetic data storage. Synthetic antiferromagnets (SAFs) offer a promising avenue to tune the properties of the individual magnetic layers, facilitating the conditions necessary for skyrmions to be used in practical devices. Despite recent advancements achieving fast skyrmion mobility, the nucleation of small and rigid circular skyrmions without an external field remains challenging in SAFs. Theoretical predictions suggest that optical vortex (OAM) beams can stabilize skyrmionic spin textures by transferring their spin and orbital angular momentum to the magnetic material. Here, this intriguing proposal is delved into and the creation of sub‐50 nm compact skyrmions in SAFs using OAM beams is successfully demonstrated, eliminating the need for external magnetic fields. Additionally, the results underscore the importance of beam energy and the number of pulses, as both factors play critical roles in the stabilization of these AFM skyrmionic textures. This breakthrough is significant as it paves the way for stabilizing true zero‐field skyrmions in AFM systems, where magnetization is minimally affected by external magnetic fields. This work will open a potential avenue for stabilizing small, compact skyrmions in antiferroic systems, facilitating their implementation in logic and memory devices. (10.1002/adfm.202409528)
  DOI : 10.1002/adfm.202409528
• An analysis of the mutual information upper bound for sensor-subset selection
  
  • Leroy Idyano
  • Saucan Augustin
  • Saucan Augustin Alexandru
  • Petetin Yohan
  • Clark Daniel
  , 2024, pp.1-8. The ability to rapidly select an optimal subset of sensors is of critical importance in massive multi-sensor target tracking. Various information metrics exist for selecting the subset of sensors that is most informative with respect to the target being tracked. Moreover, information bounds were proposed as approximate metrics in order to speed up the selection algorithms. In this paper, we provide an analysis on the information loss and its impact on the subset selection problem when employing an information upper bound instead of the exact mutual information metric. We design several greedy sensor-selection algorithms that sequentially evaluate the exact mutual information between a set of sensors and the target. Subsequently, we compare these algorithms with a sensor-selection method that employs an information upper bound and highlight situations where the latter finds sub-optimal solutions. (10.23919/FUSION59988.2024.10706439)
  DOI : 10.23919/FUSION59988.2024.10706439
• No distributed quantum advantage for approximate graph coloring
  
  • Coiteux-Roy Xavier
  • d'Amore Francesco
  • Gajjala Rishikesh
  • Kuhn Fabian
  • Le Gall François
  • Lievonen Henrik
  • Modanese Augusto
  • Renou Marc-Olivier
  • Schmid Gustav
  • Suomela Jukka
  , 2024, pp.1901-1910. We give an almost complete characterization of the hardness of $c$-coloring $\chi$-chromatic graphs with distributed algorithms, for a wide range of models of distributed computing. In particular, we show that these problems do not admit any distributed quantum advantage. To do that: 1. We give a new distributed algorithm that finds a $c$-coloring in $\chi$-chromatic graphs in $\tilde{\mathcal{O}}(n^{\frac{1}{\alpha}})$ rounds, with $\alpha = \bigl\lfloor\frac{c-1}{\chi - 1}\bigr\rfloor$. 2. We prove that any distributed algorithm for this problem requires $\Omega(n^{\frac{1}{\alpha}})$ rounds. Our upper bound holds in the classical, deterministic LOCAL model, while the near-matching lower bound holds in the non-signaling model. This model, introduced by Arfaoui and Fraigniaud in 2014, captures all models of distributed graph algorithms that obey physical causality; this includes not only classical deterministic LOCAL and randomized LOCAL but also quantum-LOCAL, even with a pre-shared quantum state. We also show that similar arguments can be used to prove that, e.g., 3-coloring 2-dimensional grids or $c$-coloring trees remain hard problems even for the non-signaling model, and in particular do not admit any quantum advantage. Our lower-bound arguments are purely graph-theoretic at heart; no background on quantum information theory is needed to establish the proofs. (10.1145/3618260.3649679)
  DOI : 10.1145/3618260.3649679
• A Study of Deep Perceptual Metrics for Image Quality Assessment
  
  • Kazmierczak Rémi
  • Franchi Gianni
  • Belkhir Nacim
  • Manzanera Antoine
  • Filliat David
  , 2022. Several metrics exist to quantify the similarity between images, but they are inefficient when it comes to measure the similarity of highly distorted images. In this work, we propose to empirically investigate perceptual metrics based on deep neural networks for tackling the Image Quality Assessment (IQA) task. We study deep perceptual metrics according to different hyperparameters like the network's architecture or training procedure. Finally, we propose our multi-resolution perceptual metric (MR-Perceptual), that allows us to aggregate perceptual information at different resolutions and outperforms standard perceptual metrics on IQA tasks with varying image deformations.
• Interval Methods applied to Signal Temporal Logic - Overview and Extension on Tubes
  
  • Tillet Joris
  • Vanneaux Elena
  • Alexandre Dit Sandretto Julien
  , 2024.
• Numerical methods and relaxation techniques for diffuse interface models in high-velocity two-phase flow simulations
  
  • Haegeman Ward
  • Dupays Joël
  • Le Touze Clement
  • Massot Marc
  , 2024. Compressible multiphase flows are at the heart of a great number of engineering applications in several domains. Some examples include the aerospace industry, since many rocket propulsion systems rely on the injection of a liquid reactant into the combustion chamber and the efficiency of the combustion is directly related to the atomization process. Other applications include the civil nuclear industry safety analysis but also the naval industry for which underwater solid propulsion systems are of great interest. The design and optimization requirements of these systems lead to an increasing need for predictive numerical simulations. Diffuse interface models are widely used for these tasks as they provide a good trade-off between accuracy and robustness. We consider the class of Baer-Nunziato type of models, in which the most general one allows for full disequilibrium between the two-phases. Reduced order models are obtained by assuming some local equilibrium (velocity, pressure, temperature or chemical potential equilibrium). Among this hierarchy of models, the pressure and velocity equilibrium model of Kapila et al is of particular interest. It allows to recover the classical Wood sound velocity for two-phase mixtures while still allowing thermal disequilibrium which is paramount for many applications such as high-temperature jets impinging on liquid surfaces and for proper modelling of phase changes. Several strategies to solve this model rely on a 6-equation model endowed with stiff pressure relaxation terms. For cavitating flows, an accurate computation of the pressure equilibrium is particularly important to compute the mass transfer fluxes. The purpose of the present contribution is to study the assumptions on the thermodynamics of the two phases and its impact on the mathematical structure of the resulting system of PDEs (where potentially several relaxation processes are involved either relying on finite-rate or instantaneous relaxation source terms). We propose an analysis of the pressure relaxation process in terms of thermodynamically admissible paths and propose a robust numerical scheme, which preserves the set of admissible states of the system. The robustness and accuracy of the proposed numerical scheme involving convection and sources is then assessed on several challenging configurations including shock-interface interactions and cavitating flows, such as shock-droplet interaction or Richtmyer–Meshkov instability. (10.23967/eccomas.2024.071)
  DOI : 10.23967/eccomas.2024.071
• Rhétorique émotionnelle et montée du populisme au Parlement européen
  
  • Subtil Hugo
  • Verger Vincent
  , 2024. Les progrès vraisemblables des partis dits populistes a lors des élections européennes du 9 juin prochain sont susceptibles de transformer en profondeur les dynamiques politiques au sein du Parlement européen b. Cette transformation ne se limitera pas aux seuls équilibres numériques entre groupes politiques : elle affectera aussi la forme des débats et les comportements de communication des parlementaires européens, notamment par une adaptation des partis non populistes à la rhétorique populiste, qui mobilise largement les émotions. Cette note s’appuie sur les transcriptions des débats tenus lors des séances plénières du Parlement européen entre 1999 et 2022. Des méthodes de traitement automatique du langage naturel y sont utilisées pour étudier la tonalité des interventions des députés européens. Il apparaît que la tonalité des débats au Parlement européen évolue. Leur niveau d’émotion a en effet nettement augmenté depuis 1999. Les députés européens s’expriment de façons différentes selon les sujets discutés, leur État membre d’origine et leur positionnement idéologique. Ceux des partis dits populistes se distinguent par davantage d’émotion dans leurs prises de parole. Toutefois, en réponse à la progression de ces partis, les autres élus du Parlement européen adaptent leur rhétorique en intensifiant la tonalité de leurs discours dans le même sens. Si cette étude ne permet pas d’identifier les conséquences d’une telle évolution sur la qualité des travaux parlementaires et la perception du Parlement européen par les citoyens européens, elle invite à y réfléchir davantage.
• A unified two-scale gas-liquid multi-fluid model with capillarity and interface regularization through a mass transfer between scales
  
  • Loison Arthur
  • Kokh Samuel
  • Pichard Teddy
  • Massot Marc
  International Journal of Multiphase Flow, Elsevier, 2024. In this contribution, we derive a gas-liquid two-scale multi-fluid model with capillarity effects to enable a novel interface regularization approach for multi-fluid models. As this unified modelling is capable of switching from the interface representation of a separated to a disperse regime it lays a new way of modelling regime transitions as it occurs in atomization processes. Above a preset length threshold at large scale, a multi-fluid diffuse interface model resolves the dynamics of the interface while, at small-scale, a set of geometric variables is used to characterize the interface geometry. These variables result from a reduced-order modelling of the small-scale kinetic equation that describes a collection of liquid inclusions. The flow model can be viewed as a two-phase two-scale mixture, and the equations of motion are obtained thanks to the Hamilton’s Stationary Action Principle, which requires to specify the kinetic and potential energies at play. We particularly focus on modelling the effects of capillarity on the mixture’s energy by including dependencies on additional variables accounting for the interface’s geometry at both scales. The regularization of the large-scale interface is then introduced as a local and dissipative process. The local curvature is limited via a relaxation toward a modified Laplace equilibrium such that an inter-scale mass transfer is triggered when the mean curvature is too high. We propose an original numerical method and assess the properties and potential of the modelling strategy on the relevant test-case of a two-dimensional liquid column in a compressible gas flow. (10.1016/j.ijmultiphaseflow.2024.104857)
  DOI : 10.1016/j.ijmultiphaseflow.2024.104857
• Nanostructured S@VACNTs Cathode with Lithium Sulfate Barrier Layer for Exceptionally Stable Cycling in Lithium-Sulfur Batteries
  
  • Ezzedine Mariam
  • Jardali Fatme
  • Florea Ileana
  • Cojocaru Costel-Sorin
  Journal of The Electrochemical Society, Electrochemical Society / IOPscience, 2024, 171 (5), pp.050531. Lithium-sulfur technology garners significant interest due to sulfur’s higher specific capacity, cost-effectiveness, and environmentally friendly aspects. However, sulfur’s insulating nature and poor cycle life hinder practical application. To address this, a simple modification to the traditional sulfur electrode configuration is implemented, aiming to achieve high capacity, long cycle life, and rapid charge rates. Binder-free sulfur cathode materials are developed using vertically aligned carbon nanotubes (CNTs) decorated with sulfur and a lithium sulfate barrier layer. The aligned CNT framework provides high conductivity for electron transportation and short lithium-ion pathways. Simultaneously, the sulfate barrier layer significantly suppresses the shuttle of polysulfides. The S@VACNTs with Li 2 SO 4 coating exhibit an extremely stable reversible areal capacity of 0.9 mAh cm −2 after 1600 cycles at 1 C with a capacity retention of 80% after 1200 cycles, over three times higher than lithium iron phosphate cathodes cycled at the same rate. Considering safety concerns related to the formation of lithium dendrite, a full cell Si-Li-S is assembled, displaying good electrochemical performances for up to 100 cycles. The combination of advanced electrode architecture using 1D conductive scaffold with high-specific-capacity active material and the implementation of a novel strategy to suppress polysulfides drastically improves the stability and the performance of Li-S batteries. (10.1149/1945-7111/ad47d5)
  DOI : 10.1149/1945-7111/ad47d5
• Application of a generic path-following method to phase-field fracture
  
  • Loiseau Flavien
  • Lazarus Veronique
  , 2024. The phase-field approach to fracture has emerged as a powerful tool to simulate the nucleation and growth of cracks in a structure. In the past two decades, it has been extensively applied to fracture problems as it captures crack initiation, propagation, and interaction without explicitly tracking the crack path. One of the most popular algorithms to solve phase-field problems is alternate minimization. However, it can suffer from slow convergence, especially when dealing with unstable crack propagation. Moreover, force-controlled loading often leads to unstable crack propagation and the lack of equilibrium solution after the crack propagation, preventing their use. Path-following methods offer a promising solution to those limitations, enabling the tracking of unstable crack propagation while preserving the equilibrium during the whole loading (Rastiello et al., 2022). Based on various control strategies, these methods also improve the solver stability. Singh et al. (2016) and May et al. (2016) proposed path-following approaches specifically tailored to the resolution scheme of Miehe et al. (2010) based on crack surface and fracture dissipation. Additionally, Wu (2018) adapted the nodal displacement control (Borst, 1987) and the fracture surface control (Singh et al., 2016) to the alternate minimization. Nevertheless, the first approach is problem-dependent, and the second approach may fail under force loading (Rastiello et al., 2022). This work proposes a generic path-following method applicable to various fracture problems, regardless of geometry, boundary conditions, or fracture model complexity, by leveraging the maximum strain increment control (Chen & Schreyer, 1990). This method is model-independent, as it relies solely on the displacement field, and problem-independent, it does not rely on a specific choice of control DOF. After presenting the modified alternate minimization solver, we demonstrate its effectiveness through simulations of crack propagation in the SENT test. The results are compared to a semi-analytical solution based on LEFM and to the alternate minimization solution. Notably, the classic alternate minimization fails to capture the snap-back (instability under displacement control) observed in the semi-analytical method. The proposed approach correctly capturesthis phenomenon, which converges towards the semi-analytical solution. Then, this method is also applied to the simulation of Compact Tension (CT) experiments, in which the selection of numerical boundary conditions at the pinhole significantly influences the fracture behavior (Triclot et al., 2023). The proposed solver renders the application of force boundary conditions possible, better representing the experimental conditions. References Borst, R. de. (1987). Computation of post-bifurcation and post-failure behavior of strain-softening solids. Computers & Structures, 25(2), 211–224. https://doi.org/10.1016/0045-7949(87)90144-1 Chen, Z., & Schreyer, H. L. (1990). A numerical solution scheme for softening problems involving total strain control. Computers & Structures, 37 (6), 1043–1050. https://doi.org/10.1016/0045-7949(90)90016-U May, S., Vignollet, J., & Borst, R. de. (2016). A new arc-length control method based on the rates of the internal and the dissipated energy. Engineering Computations, 33(1), 100–115. https://doi.org/10.1108/EC-02-2015-0044 Miehe, C., Hofacker, M., & Welschinger, F. (2010). A phase field model for rate-independent crack propagation: Robust algorithmic implementation based on operator splits. Computer Methods in Applied Mechanics and Engineering, 199(45), 2765–2778. https://doi.org/10.1016/j.cma.2010.04.011 Rastiello, G., Oliveira, H. L., & Millard, A. (2022). Path-following methods for unstable structural responses induced by strain softening: A critical review. Comptes Rendus. Mécanique, 350, 205–236. https://doi.org/10.5802/crmeca.112 Singh, N., Verhoosel, C. V., Borst, R. de, & Brummelen, E. H. van. (2016). A fracture-controlled path-following technique for phase-field modeling of brittle fracture. Finite Elements in Analysis and Design, 113, 14–29. https://doi.org/10.1016/j.finel.2015.12.005 Triclot, J., Corre, T., Gravouil, A., & Lazarus, V. (2023). Key role of boundary conditions for the 2D modeling of crack propagation in linear elastic compact tension tests. Engineering Fracture Mechanics, 277, 109012. https://doi.org/10.1016/j.engfracmech.2022.109012 Wu, J.-Y. (2018). Robust numerical implementation of non-standard phase-field damage models for failure in solids. Computer Methods in Applied Mechanics and Engineering, 340, 767–797. https://doi.org/10.1016/j.cma.2018.06.007
• A Symmetry-Aware Exploration of Bayesian Neural Network Posteriors
  
  • Laurent Olivier
  • Aldea Emanuel
  • Franchi Gianni
  , 2024. The distribution of modern deep neural networks (DNNs) weights - crucial for uncertainty quantification and robustness - is an eminently complex object due to its extremely high dimensionality. This paper proposes one of the first large-scale explorations of the posterior distribution of deep Bayesian Neural Networks (BNNs), expanding its study to real-world vision tasks and architectures. Specifically, we investigate the optimal approach for approximating the posterior, analyze the connection between posterior quality and uncertainty quantification, delve into the impact of modes on the posterior, and explore methods for visualizing the posterior. Moreover, we uncover weight-space symmetries as a critical aspect for understanding the posterior. To this extent, we develop an in-depth assessment of the impact of both permutation and scaling symmetries that tend to obfuscate the Bayesian posterior. While the first type of transformation is known for duplicating modes, we explore the relationship between the latter and L2 regularization, challenging previous misconceptions. Finally, to help the community improve our understanding of the Bayesian posterior, we release the \href{https://huggingface.co/datasets/torch-uncertainty/Checkpoints}{first large-scale checkpoint dataset}, including thousands of real-world models, along with our \href{https://github.com/ENSTA-U2IS-AI/torch-uncertainty}{codes}.
• Nitrogen atoms ps-TALIF in atmospheric pressure nanosecond volume DBD plasma
  
  • Kreyder G
  • Stefas D
  • Invernizzi L
  • Lombardi G
  • Gazeli K
  • Prasanna S
  • Starikovskaia S M
  , 2024.
• Transient gradient nanosecond plasmas for the initiation of a detonation wave: plasma characterisation with OES and O-TALIF
  
  • Lafaurie V
  • Shu Z
  • Sadauskaite M
  • Vidal Pierre
  • Starikovkaia S M
  , 2024.
• Path differences between quasistatic and fatigue cracks in anisotropic media
  
  • Zhai Xinyuan
  • Corre Thomas
  • Mesgarnejad Ataollah
  • Karma Alain
  • Lazarus Véronique
  Physical Review E, American Physical Society (APS), 2024, 110 (6), pp.L063001. The propagation path of quasistatic cracks under monotonic loading is known to be stronglyinfluenced by the anisotropy of the fracture energy in crystalline solids or engineered materials witha regular microstructure. Such cracks generally follow directions close to minima of the fractureenergy. Here we demonstrate both experimentally and computationally that fatigue cracks undercyclic loading follow dramatically different paths that are predominantly dictated by the symmetryof the loading with the microstructure playing a negligible or subdominant role. (10.1103/PhysRevE.110.L063001)
  DOI : 10.1103/PhysRevE.110.L063001
• Online Locality Meets Distributed Quantum Computing
  
  • Akbari Amirreza
  • Coiteux-Roy Xavier
  • d'Amore Francesco
  • Le Gall François
  • Lievonen Henrik
  • Melnyk Darya
  • Modanese Augusto
  • Pai Shreyas
  • Renou Marc-Olivier
  • Rozhoň Václav
  • Suomela Jukka
  , 2024. We extend the theory of locally checkable labeling problems (LCLs) from the classical LOCAL model to a number of other models that have been studied recently, including the quantum-LOCAL model, finitely-dependent processes, non-signaling model, dynamic-LOCAL model, and online-LOCAL model [e.g. STOC 2024, ICALP 2023]. First, we demonstrate the advantage that finitely-dependent processes have over the classical LOCAL model. We show that all LCL problems solvable with locality $O(\log^\star n)$ in the LOCAL model admit a finitely-dependent distribution (with constant locality). In particular, this gives a finitely-dependent coloring for regular trees, answering an open question by Holroyd [2023]. This also introduces a new formal barrier for understanding the distributed quantum advantage: it is not possible to exclude quantum advantage for any LCL in the $\Theta(\log^\star n)$ complexity class by using non-signaling arguments. Second, we put limits on the capabilities of all of these models. To this end, we introduce a model called randomized online-LOCAL, which is strong enough to simulate e.g. SLOCAL and dynamic-LOCAL, and we show that it is also strong enough to simulate any non-signaling distribution and hence any quantum-LOCAL algorithm. We prove the following result for rooted trees: if we can solve an LCL problem with locality $o(\log \log n)$ in the randomized online-LOCAL model, we can solve it with locality $O(\log^\star n)$ in the classical deterministic LOCAL model. Put together, these results show that in rooted trees the set of LCLs that can be solved with locality $O(\log^\star n)$ is the same across all these models: classical deterministic and randomized LOCAL, quantum-LOCAL, non-signaling model, dynamic-LOCAL, and deterministic and randomized online-LOCAL.
• High harmonic generation in Solids driven by high energy fiber laser source
  
  • Boukhaoui Djamila
  • Idlahcen Saïd
  • Houard Jonathan
  • Blum Ivan
  • Godin Thomas
  • Amrani Foued
  • Gérôme Frédéric
  • Benabid Fetah
  • Gauthier David
  • Boutu Willem
  • Merdji Hamed
  • Hideur Ammar
  • Vella Angela
  , 2024, pp.1299208. We present findings on High Harmonic Generation (HHG) in solids utilizing a high-energy fiber laser system operating at 1550 nm. The driving laser source comprises an Erbium-Doped Fiber chirped pulse Amplifier (EDFA) combined with a post-compression stage employing a hollow-core photonic crystal fiber (HC-PCF) filled with noble gases. Nonlinear self-compression in the HC-PCF enables the generation of ultrashort pulses with a duration of 50 fs and energy of 0.91 μJ at a repetition rate of 660 kHz. In a first step, harmonics up to H7 were observed when focusing the laser into small bandgap materials such as Zinc Oxide (ZnO). Subsequently, the system was enhanced to measure high harmonics in the extreme ultraviolet (XUV) range, with harmonics up to H25 observed using a large bandgap material, magnesium oxide (MgO). To the best of our knowledge, this represents the first solid-state HHG source driven by a high-energy few-cycle fiber laser in the telecom region