Publications

2025

• Reconstruction 3D en tomographie radar : apprentissage profond basé sur un Matching Pursuit déroulé
  
  • Ulondu Mendes Cristiano
  • Denis Loïc
  • Kervazo Christophe
  • Tupin Florence
  , 2025. La tomographie radar en milieu urbain consiste à séparer des réflecteurs situés à des hauteurs différentes mais vus dans un même pixel car situés à une distance similaire du radar. Les méthodes d'apprentissage profond proposées récemment pour résoudre cette tâche sont basées sur le déroulement d'algorithmes de poursuites de base avec contrainte de parcimonie. Ils dépendent d'une discrétisation des hauteurs et ne permettent pas un contrôle simple du nombre de réflecteurs détectés. On présente dans cet article une approche alternative permettant d'estimer la position des cibles sur un intervalle continu. Notre approche s'inspire des itérations des algorithmes gloutons de reconstruction parcimonieuse tels que Matching Pursuit ou RELAX. Nous montrons des résultats de reconstruction satisfaisants sur des données simulées et sur une pile d'images satellitaires.
• Détection non supervisée de changements radiométriques en imagerie radar à synthèse d'ouverture
  
  • Bultingaire Thomas
  • Kervazo Christophe
  • Denis Loïc
  • Tupin Florence
  , 2025, pp.1-4. L'imagerie radar à synthèse d'ouverture est un mode d'imagerie clé pour la détection de changements en télédétection. Cette tâche est difficile à cause du phénomène de chatoiement, un phénomène qui nécessite de réaliser une étape de débruitage pour y être davantage robuste. Cependant, il est nécessaire de prendre en compte les incertitudes de débruitage pour contrôler la probabilité de fausse alarme des changements détectés car les instabilités de débruitage doivent être distinguées des changements. Nous proposons donc un réseau, entraîné de manière auto-supervisée, pour prédire les incertitudes de débruitage menant à une détection de changements radiométriques dont la performance est évaluée sur des images du satellite TerraSAR-X.
• Design, synthesis, biophysical and biological evaluation of original condensed pyrrolopyrimidine and pyrrolopyridine ligands as anti-SARS-CoV-2 agents targeting G4
  
  • Guillon Jean
  • Savrimoutou Solène
  • da Rocha Nicolas
  • Albenque-Rubio Sandra
  • Helynck Olivier
  • Durand Cyrielle
  • Chiaravalli Jeanne
  • Pinaud Noël
  • Ronga Luisa
  • Moreau Stéphane
  • Chirold Simon
  • Zangmo Tshering
  • Arab Melika
  • Lari Lindita
  • Mergny Jean‐louis
  • Munier-Lehmann Hélène
  • Lavigne Marc
  European Journal of Medicinal Chemistry, Elsevier, 2025, 292, pp.117655. The design and synthesis of novel bis[(substituted-aminomethyl)phenyl]phenyl pyrrolopyrimidines, pyrrolopyridines, pyrazolopyrimidines, imidazopyrimidines, and tris[(substituted-aminomethyl)phenyl]phenyl pyrrolopyrimidines are reported here. These original G-quadruplex (G4) ligands have been then subjected to a screening on SARS-CoV-2 using a competition HTRF assay by targeting the SUD-NM/TRF2 RNA G4 interaction. The more promising derivatives have been evaluated in vitro to determine their potential antiviral effect on two different cell lines infected by two SARS-CoV-2 strains. This study revealed a clear correlation between their antiviral property and their efficacy to prevent the SUD/G4 interaction. This correlation supports the choice of SUD/RNA G4 complexes formed during SARS-CoV-2 infection as new antiviral targets (10.1016/j.ejmech.2025.117655)
  DOI : 10.1016/j.ejmech.2025.117655
• Structural interactions in global trade
  
  • Lebert Didier
  • Poindron Alexis
  Theory and Decision, Springer Verlag, 2025. We provide a methodological framework for investigating global trade networks thatdistinguish between categories of goods. We introduce a multi-layer network version of the Lantner diffusion model, in which each layer represents a specific good and each node corresponds to a country. By establishing several mathematical results involving structural alterations of the network, and by leveraging interaction indices, we show how to quantify structural interactions between categories of goods and offer recommendations for decision-makers designing embargoes against target countries. (10.1007/s11238-025-10061-z)
  DOI : 10.1007/s11238-025-10061-z
• Fiber-based high-energy 1550 nm laser for generating high-order harmonics
  
  • Mikhneva Anastasiia
  • Boukhaoui Djamila
  • Idlahcen Saïd
  • Houard Jonathan
  • Blum Ivan
  • Godin Thomas
  • Guiramand Leo
  • Amrani Foued
  • Gérôme Frédéric
  • Benabid Fetah
  • Gauthier David
  • Merdji Hamed
  • Boutu Willem
  • Vella Angela
  • Hideur Ammar
  , 2025, pp.CG-4.4. The demand for precise, high-energy Extreme Ultraviolet (EUV) sources is growing across scientific and industrial fields. Studies have demonstrated that bulk crystals driven by mid-infrared laser pulses can generate high-order harmonics with enhanced intensities, extended cut-off energies, and improved damage thresholds [1]. While high-energy OPCPA and OPA systems have been successfully utilized to achieve these results, their complexity highlights the need for simpler, more compact solutions [1, 2, 3]. Ultrafast mid-IR fiber lasers have emerged as a promising alternative for high-harmonic generation (HHG). However, their pulse energies are limited to the nanojoule range [4]. Here, we report the first demonstration of high-order harmonics generated in bulk crystals using a high-energy fiber laser operating near 1550 nm. Our laser system integrates an erbium-doped fiber amplifier with a gas-filled hollow-core photonic crystal fiber (HC-PCF) for post-compression, delivering few-cycle pulses with durations under 50 fs, microjoule-level pulse energies, and a repetition rate of 660 kHz (fig. 1) [5].
• Toughening effects of out-of-crack-path architected zones
  
  • Triclot Julie
  • Corre Thomas
  • Lazarus Véronique
  • Gravouil Anthony
  , 2024. The increasing use of architected materials has broadened the possibilities of mechanical behaviour. In this article, we aim to explore these new possibilities in terms of in-service behaviour, especially in terms of crack propagation by performing an in-depth study in the framework of Linear Elastic Fracture Mechanics (LEFM). The specific configuration studied here is the case where the architected zones are symmetrically positioned adjacently to the crack path and no propagation occurs within the zone. This problem is addressed both numerically and experimentally. Numerically, an path-following algorithm is used to simulate the crack propagation. Different toughening aspects of the addition of architected zones are identified. First, a temporary increase in crack propagation resistance is shown. It comes from a temporary increase of stored elastic energy in the architected zones, thus acting as mechanical springs. Second, a snap-back instability appears, linked to the release of the previously stored energy. It leads to a higher energy dissipated by the crack propagation process. Experimentally, we evidence the possibility to reproduce the theoretical results using 3D printing. A good quantitative comparison is obtained between numerical and experimental approaches. This study shows that it is possible to improve crack propagation resistance while lightening the component by addition of architected zones outside the crack path. This opens up the way to tune finely, through the use of optimization tools, the crack propagation response.
• Observation of a Multimode Displaced Squeezed State in High-Harmonic Generation
  
  • Theidel David
  • Cotte Viviane
  • Heinzel Philip
  • Griguer Houssna
  • Weis Mateusz
  • Sondenheimer René
  • Merdji Hamed
  , 2024. High harmonic generation is a resource of extremely broad frequency combs of ultrashort light pulses. The non-classical nature of this new quantum source has been recently evidenced in semiconductors by showing that high harmonic generation generates multimode squeezed states of light. Applications in quantum information science require the knowledge of the mode structure of the created states, defining how the quantum properties distribute over the spectral modes. To achieve that, an effective Schmidt decomposition of the reduced photonic state is performed on a tripartite harmonic set by simultaneously measuring the second- and third-order intensity correlation function. The Schmidt number is estimated which indicates an almost single-mode structure for each harmonic, a useful resource in quantum technology. By modelling our data with a displaced squeezed state, we retrieve the dependencies of the measured correlation as a function of the high harmonic driving laser intensity. The effective high-harmonic mode distribution is retrieved, and the strength of the contributing squeezing modes is estimated. Additionally, we demonstrate a significant violation of a Cauchy-Schwarz-type inequality for three biseparable partitions by multiple standard deviations. Our results confirm non-classicality of the high-harmonic generation process in semiconductors. The source operates at room temperature with compact lasers, and it could become a useful resource for future applications in quantum technologies. (10.48550/arXiv.2411.02311)
  DOI : 10.48550/arXiv.2411.02311
• Les spécialisations industrielles des PECO membres de l’Union européenne sur la période 1992-2018 : Une lecture structurale
  
  • Anedda Raffaele
  • Lebert Didier
  Economie appliquée, Classiques Garnier, 2025 (6), pp.119-147. L’histoire de la transformation des systèmes productifs des pays anciennement socialistes ayant rejoint l’Union européenne durant les années 2000 est aujourd’hui établie. Après une période de transition marquée par de fortes perturbations macro- et méso-économiques débordant pour certains d’entre eux leurs dates d’entrée dans l’Union, ces pays ont stabilisé ces systèmes quelquefois caractérisés désormais par des spécialisations industrielles high tech prononcées. L’objectif de l’article consiste à proposer une architecture empirique fondée sur la théorie de la dominance économique pour représenter cette transformation à l’échelle de chacun des onze pays concernés. Une typologie des trajectoires constatées est ensuite établie. (10.48611/isbn.978-2-406-18063-0.p.0119)
  DOI : 10.48611/isbn.978-2-406-18063-0.p.0119
• Les inégalités d’intégration au sein de l’espace économique méditerranéen au tournant du xxie siècle
  
  • Lebert Didier
  Economie appliquée, Classiques Garnier, 2025 (6), pp.11-35. Nous proposons un nouvel indicateur mesurant les inégalités d’intégration des pays au sein d’un espace d’échanges commerciaux. Cet indicateur associe une approche globale à une autre révélant la contribution spécifique de chaque pays à sa valeur. Nous l’appliquons à l’espace économique méditerranéen (EEM) sur la période 1980-2004, période précédant une intense dynamique institutionnelle visant à intégrer davantage le Nord et le Sud de la Méditerranée. Avant ces transformations institutionnelles, l’EEM reste une zone globalement peu intégrée, et cette faible intégration est entretenue par les principaux pays d’Europe qui en sont membres. (10.48611/isbn.978-2-406-18063-0.p.0011)
  DOI : 10.48611/isbn.978-2-406-18063-0.p.0011
• POLSAR2POLSAR: A SEMI-SUPERVISED DESPECKLING ALGORITHM FOR POLARIMETRIC SAR IMAGES
  
  • Mendes Cristiano Ulondu
  • Dalsasso Emanuele
  • Zhang Yi
  • Denis Loïc
  • Tupin Florence
  ISPRS Journal of Photogrammetry and Remote Sensing, Elsevier, 2025, 220 (0924-2716), pp.783-798. <div><p>Polarimetric Synthetic Aperture Radar (PolSAR) imagery is a valuable tool for Earth observation. This imaging technique finds wide application in various fields, including agriculture, forestry, geology, and disaster monitoring. However, due to the inherent presence of speckle noise, filtering is often necessary to improve the interpretability and reliability of PolSAR data. The effectiveness of a speckle filter is measured by its ability to attenuate fluctuations without introducing artifacts or degrading spatial and polarimetric information. Recent advancements in this domain leverage the power of deep learning. These approaches adopt a supervised learning strategy, which requires a large amount of speckle-free images that are costly to produce. In contrast, this paper presents PolSAR2PolSAR, a semi-supervised learning strategy that only requires, from the sensor under consideration, pairs of noisy images of the same location and acquired in the same configuration (same incidence angle and mode as during the revisit of the satellite on its orbit). Our approach applies to a wide range of sensors. Experiments on Radarsat-2 and RCM data demonstrate the capacity of the proposed method to effectively reduce speckle noise and retrieve fine details. The code of the trained models is made freely available at https://gitlab.telecom-paris.fr/ring/polsar2polsar. The repository additionally contains a model fine-tuned on SLC PolSAR images from NASA's UAVSAR sensor.</p></div>
• Small-scale interface dynamic modelling based on the geometric method of moments for a two-scale two-phase flow model with a disperse small scale
  
  • Loison Arthur
  • Pichard Teddy
  • Kokh Samuel
  • Massot Marc
  Journal of Fluid Mechanics, Cambridge University Press (CUP), 2025, 1003 (A27), pp.1--42. In this contribution, we develop a versatile formalism to derive unified two-phase models describing both the separated and disperse regimes as introduced by Loison et al. (2024). It relies on the stationary action principle and interface geometric variables. This contribution provides a novel method to derive small-scale models for the dynamics of the interface geometry. They are introduced here on a simplified case where all the scales and phases have the same velocity and that does not take into account large-scale capillary forces. The derivation tools yield a proper mathematical framework through hyperbolicity and signed entropy evolution. The formalism encompasses a hierarchy of small-scale reduced-order models based on a statistical description at a mesoscopic kinetic level and is naturally able to include the description of a disperse phase with polydispersity in size. This hierarchy includes both a cloud of spherical droplets and non-spherical droplets experiencing a dynamical behaviour through incompressible oscillations. The associated small-scale variables are moments of a number density function resulting from the geometric method of moments (GeoMOM). This method selects moments as small-scale geometric variables compatible with the structure and dynamics of the interface; they are defined independently of the flow topology and, therefore, this model allows the coupling of the two-scale flow with an inter-scale transfer. It is shown in particular that the resulting dynamics provides partial closures for the interface area density equation obtained from the averaging approach. (10.1017/jfm.2024.1200)
  DOI : 10.1017/jfm.2024.1200
• High-harmonic generation in solids from a high-energy fiber laser system
  
  • Boukhaoui D.
  • Mikhneva A.
  • Idlahcen S.
  • Houard Jonathan
  • Godin T.
  • Guiramand L.
  • Blum Ivan
  • Amrani F.
  • Gérôme F.
  • Benabid F.
  • Gauthier D.
  • Boutu W.
  • Merdji H.
  • Vella Angela
  • Hideur A.
  APL Photonics, AIP Publishing LLC, 2025, 10 (2), pp.026106. We demonstrate high-harmonic generation (HHG) in solids using a high-energy fiber laser system operating at 1550 nm. The driving few-cycle source consists of an erbium-doped fiber chirped pulse amplifier combined with a postcompression stage featuring a gas-filled hollow-core photonic crystal fiber (HC-PCF). The nonlinear self-compression process in the HC-PCF enables the generation of ultrashort pulses with sub-50 fs durations and µJ-levels energies at a 660 kHz repetition rate. Perturbative and non-perturbative harmonics were subsequently generated when focusing the few-cycle pulses into zinc oxide (ZnO) and magnesium oxide (MgO) bulk samples. In the latter, in particular, we observed the generation of EUV harmonics up to H29 (below 55 nm), highlighting the remarkable potential of such a platform for the development of compact HHG sources. (10.1063/5.0244415)
  DOI : 10.1063/5.0244415
• Derivation of a 4-moment model for electron transport in Hall thrusters from a gyrokinetic model
  
  • Tazakkati Zoubaïr
  • Laguna Alejandro Alvarez
  • Massot Marc
  • Pichard Teddy
  , 2025. <div><p>We model the motion of a population of electrons in a strong electromagnetic field undergoing elastic electron/electron collisions. This regime is derived from a dimensional analysis of the electron confinement in Hall-effect thrusters. The electrons exhibit a very high cyclotron frequency and a E × B-drift, modelled by stiff PDEs at the mesoscopic scale. We obtain a gyrokinetic model in which the fastest oscillations of the system are filtered out by averaging the rotation of the electrons around the magnetic field lines. The model is derived in the strong electromagnetic field limit. Based on this gyrokinetic model, we then develop a 10-moment model. The averaging operation performed at the kinetic scale leads to symmetry properties that allow to reduce the 10-moment model to a 4-moment model.</p></div>
• High-Harmonic Generation in an Optical Fiber Functionalized with Zinc Oxide Thin Films
  
  • Tiliouine Idris
  • Leventoux Yann
  • Orlianges Jean-Christophe
  • Crunteanu Aurelian
  • Froidevaux Marie
  • Merdji Hamed
  • Février Sébastien
  Photonics, MDPI, 2025, 12 (1), pp.82. High-order harmonic generation (HHG) in semiconductor thin films from ultrashort mid-infrared laser drivers holds the potential for the realization of integrated sources of extreme ultraviolet light. Here, we demonstrate solid-state HHG in zinc oxide thin films synthesized by the radiofrequency reactive magnetron sputtering process directly on the cleaved facets of optical fibers. Harmonics 3 to 13 of the radiation from a fiber-based laser system delivering 500 kW, 96 fs pulses at 3130 nm are produced in the thin film and guided along the fiber. A proper choice of the laser wavelength and fiber material allows for filtering out the mid-IR pump laser and achieving the HHG mode selection. The possibility to nanostructure the fiber exit by, e.g., focused ion beam milling paves the way to an increased control over the HHG spatial mode. (10.3390/photonics12010082)
  DOI : 10.3390/photonics12010082
• Step-by-step verification of particle-in-cell Monte Carlo collision codes
  
  • Parodi Pietro
  • Petronio Federico
  Physics of Plasmas, American Institute of Physics, 2025, 32 (1). The particle-in-cell (PIC) method with Monte Carlo collisions (MCC) is widely used in the simulation of non-equilibrium plasmas for electric propulsion and laboratory applications. Due to the simplicity of the basic PIC algorithm and the specific modeling needs of the different research groups, many codes have been independently developed. Verification of these codes, i.e., ensuring that the computational code correctly implements the intended mathematical models and algorithms, is of fundamental importance. Different benchmark cases, such as one from Turner et al. [Phys. Plasmas 20, 013507 (2013)], Charoy et al. [Plasma Sources Sci. Technol. 28, 105010 (2019)], and Villafana et al. [Plasma Sources Sci. Technol. 30, 075002 (2021)], have been published in recent years. These have consisted of a complex physical setup, in which many computation modules interact to yield the final result. Although this approach has the advantage of testing the code in a realistic case, it may hide some implementation errors. Moreover, in the case of disagreement, the previous works do not provide an easy way to identify the faulty code modules. In this work, we propose a step-by-step approach for the verification of PIC-MCC codes in a 2D-3V electrostatic setup. The criteria for the test cases are (i) they should highlight possible implementation errors by testing the modules separately, whenever possible (ii) they should be free from physical instabilities to avoid chaotic behavior, and (iii) the numerical result should be accompanied by analytical calculations, for confirmation purposes. The seven test cases identified all show excellent agreement between the authors' codes. (10.1063/5.0241527)
  DOI : 10.1063/5.0241527
• Steady-state plasma model of an iodine-fueled Hall thruster
  
  • Chabert Pascal
  • Bourdon Anne
  • Esteves Benjamin
  • Lafleur Trevor
  Journal of Applied Physics, American Institute of Physics, 2025, 138 (4), pp.043303. A time-independent, one-dimensional plasma model is proposed and used to investigate the characteristics and performance of iodine-fueled Hall thrusters. The model accounts for radial plasma-wall losses and includes major iodine collisional reaction processes such as molecular dissociation. Thruster performance is found to be comparable to that obtained with xenon, although iodine allows extension of the operating range to lower mass flow rates and discharge voltages. The model predicts an appreciable fraction of molecular ions (I2+) within the thruster plume that depends on the discharge voltage and propellant mass flow rate and that contributes significantly to the thrust. In contrast to xenon, electron impact dissociation of iodine leads to the unique formation of two distinct ionization zones within the thruster: a region closer to the anode associated with the ionization of molecular iodine and a downstream region associated with the ionization of atomic iodine. (10.1063/5.0263183)
  DOI : 10.1063/5.0263183
• Bridging multifluid and drift-diffusion models for bounded plasmas
  
  • Gangemi G M
  • Alvarez Laguna Alejandro
  • Massot M.
  • Hillewaert K.
  • Magin T.
  Physics of Plasmas, American Institute of Physics, 2025, 32 (2), pp.023502. Fluid models represent a valid alternative to kinetic approaches in simulating low-temperature discharges: a well-designed strategy must be able to combine the ability to predict a smooth transition from the quasineutral bulk to the sheath, where a space charge is built at a reasonable computational cost. These approaches belong to two families: multifluid models, where momenta of each species are modeled separately, and drift-diffusion models, where the dynamics of particles is dependent only on the gradient of particle concentration and on the electric force. It is shown that an equivalence between the two models exists and that it corresponds to a threshold Knudsen number, in the order of the square root of the electron-to-ion mass ratio; for an argon isothermal discharge, this value is given by a neutral background pressure Pn≳1000 Pa. This equivalence allows us to derive two analytical formulas for a priori estimation of the sheath width: the first one does not need any additional hypothesis but relies only on the natural transition from the quasineutral bulk to the sheath; the second approach improves the prediction by imposing a threshold value for the charge separation. The new analytical expressions provide better estimations of the floating sheath dimension in collisions-dominated regimes when tested against two models from the literature. (10.1063/5.0240640)
  DOI : 10.1063/5.0240640
• Incoherent Diffraction Imaging with a Pseudo-Thermal Light Source
  
  • Claveria Pablo San Miguel
  • Antunes Sesbastião
  • Biesterfeld Peer
  • Fernandes Matilde
  • Garcia Matilde
  • Nunes Matilde
  • Fernandez Lucas Ansia
  • Williams Gareth
  • Froehlich Sven
  • Theidel David
  • Mosel Philip
  • Fsaifes Ihsan
  • Trabattoni Andrea
  • Piccardo Marco
  • Chanteloup Jean-Christophe
  • Kovacev Milutin
  • Merdji Hamed
  • Fajardo Marta
  Optica Open, 2025. Incoherent Diffraction Imaging - IDI - is a diffraction-based imaging technique that has been recently proposed to exploit the partial coherence of incoherently scattered light to retrieve structural information from the scattering centers. Similar to the stellar intensity interferometry of Hanbury Brown and Twiss, the signal builds up on the second-order spatial correlations of the emitted light. The complex spatial distribution of the target is thereby encoded in the spatial intensity fluctuations of the scattered light. The first experimental realisations of this imaging technique have been realised using the fluorescence excited by an ultra-short X-ray pulse at Free Electron Laser (FEL) facilities. Here, we propose an alternative set-up based on a table-top Pseudo-Thermal Light Source. This set-up allows us to explore IDI under a wide range of physically relevant conditions as well as to benchmark numerical and analytical models currently used to determine the imaging capabilities of this technique. (10.48550/arXiv.2501.05417)
  DOI : 10.48550/arXiv.2501.05417
• Refining the modeling strategy for anomalous electron transport in fluid simulations of Hall thrusters via insights from PIC simulations
  
  • Petronio Federico
  • Alvarez Laguna Alejandro
  • Guillon Martin Jacques
  • Bourdon Anne
  • Chabert Pascal
  Physics of Plasmas, American Institute of Physics, 2025, 32 (7), pp.073513. Modeling anomalous transport in fluid simulations is a fundamental challenge for developing efficient and robust fluid simulation tools for Hall thrusters. This paper investigates optimal strategies for modeling anomalous transport in such simulations. Using the particle-in-cell (PIC) benchmark (BM) setup of Charoy et al., we demonstrate that various terms in the electron momentum equation can be readily identified. In particular, we show that the assumption of expressing the rate of change of the electron momentum due to instability as proportional to the momentum itself does not hold under these simulation conditions. Subsequently, we present two fluid simulations that replicate the conditions of the PIC BM setup. The first employs the conventional empirical anomalous collision frequency approach. While this model provides generally satisfactory results, it fails to capture specific plasma characteristics. The second fluid model adopts a data-driven approach to represent the anomalous force terms in the momentum equation. This approach furnishes significantly improved results, suggesting that although the anomalous collisionality framework provides meaningful outcomes, it can be effectively replaced by more advanced techniques. (10.1063/5.0274535)
  DOI : 10.1063/5.0274535