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The COXINEL Seeded Free Electron Laser Driven by the Laser Plasma Accelerator at HZDR
No full textInternational audienceLaser Plasma Accelerators know a tremendous development these recent years. Being able to reach up to ~100 GV/m, they open new perspectives for compact accelerators. Their performance can be qualified by a Free Electron Laser Application. We report here on the COXINEL seeded Free Electron Laser in the UV using the using high-quality electron beam generated by the 150 TW DRACO laser. The COXINEL line developed at Synchrotron SOLEIL (France) is first introduced. First electron beam transport and undulator radiation observation using electrons from the Laser Plasma Accelerator developed at Laboratoire d’Optique Appliquée (France) are described. Then, we present the first COXINEL results driven by the DRACO laser high performance plasma accelerator after its move to Helmholtz-Zentrum Dresden-Rossendorf (HZDR) (Germany): proper electron beam transport, undulator seed and undulator radiation temporal, spectral and spatial overlaps, allowing the seeded Free Electron Laser to be observed in the UV. Good agreement is found between measurements and simulations
Dynamic properties and plastic dissipative mechanisms of polymeric adhesive under dynamic compression at various strain rates
No full textInternational audienceThis work investigated the dynamic compression behavior of structural vinylester adhesive under dynamic compression tests using the Split Hopkinson Pressure Bars technique. The obtained results showed that the dynamic parameters were strain rate sensitive. No macroscopic damage was observed in the specimen at the different applied strain rates. However, the presence of a characteristic second peak mainly at high strain rates on the strain rate profiles was attributed to the plasticity occurrence in the polymer under impact. The non-linear response that appeared on the stress-strain curves of the adhesive had been attributed to the combined material softening and thermal softening. These results demonstrated that the studied adhesive could be considered a potential material for high-rate applications due to the combination of significant toughness with high strength and extensive plasticity. An energetic study determined the energy balance and quantified energy absorption. It was observed that used vinylester adhesive was suitable for dynamic applications because it could absorb a large amount of energy and undergo large compressive deformations without damage. This work provided a complete range of experimental data for structural adhesive, which could help the designer of an energy-absorbing adhesively bonded composite joint structure for high-strain rate applications
Underwater Data Muling: Scenarios, Implementation, and Performances
No full textInternational audienceThe exploration of the seabed is of strategic importance for various applications, including military, scientific, and commercial purposes. However, underwater communication is limited by the poor propagation of radio waves and the low data rates of acoustic communication. This leads to the topic of retrieving large amounts of data over a long range. To address this challenge, the concept of data muling-which involves the use of mobile agents to physically carry data from underwater nodes or Autonomous Underwater Vehicles (AUVs)-seems to be an interesting solution. In this paper, we focus on the scenario of a fixed data source and sink point separated by a large distance. We propose a relay system that uses mobile agents assigned to specific areas. Each agent can communicate with neighbouring agents and travel within its assigned area to transport data and act as a moving relay. We evaluate the performance of this data muling solution using three metrics: equivalent throughput, latency, and energy. We compare our solution with a scenario inspired by previous work and show that our relay system can extend the range and data rate of underwater communication. The paper provides a detailed system model and presents experimental results to implement muling along testing scenarios
Convergence analysis of time-domain PMLs for 2D electromagnetic wave propagation in dispersive waveguides
No full textInternational audienceThis work is dedicated to the analysis of generalized perfectly matched layers (PMLs) for 2D electromagnetic wave propagation in dispersive waveguides. Under quite general assumptions on frequency-dependent dielectric permittivity and magnetic permeability we prove convergence estimates in homogeneous waveguides and show that the PML error decreases exponentially with respect to the absorption parameter and the length of the absorbing layer. The optimality of this error estimate is studied both numerically and analytically. Finally, we demonstrate that in the case when the waveguide contains a heterogeneity supported away from the absorbing layer, instabilities may occur, even in the case of the non-dispersive media. Our findings are illustrated by numerical experiments
Joint Trajectory and Communication Optimization for UAV in Complex Electromagnetic Environment
No full textInternational audienceUnmanned Aerial Vehicle (UAV) is a booming trend in major civil and military applications such, but not limited to, transportation, delivery, and surveillance missions. In order to accomplish the mission's objective, trajectory planning must be optimally achieved. The communication link established between the UAV and the ground/aerial stations is the main factor to account for designing the trajectory. However, this link is highly affected by the shape of the topography, especially when the UAV must fly at a low altitude between mountains of variable elevations. Therefore, this paper addresses the challenge of three-dimensional trajectory optimization for low/mid-altitude flying UAVs in complex propagation environments. To tackle this challenge, we propose a system model for the trajectory using the diffraction phenomenon with Multiple Knife Edge (MKE) to model the channel between the UAV and the station when the Line of Sight (LoS) is absent. Then, we propose a joint optimization to minimize the trajectory and maximize the communication quality via the Mixed Integer Linear Programming (MILP) problem design and solution. We validate the proposed approach by using real terrain profiles in the simulations with a rough topography; where the LoS propagation aspect is barely present. Our approach is able to jointly find, when physically achievable, the UAV trajectory with the shortest path and the "best feasible" communication quality
Palladium-Catalyzed ortho-C-H Alkoxycarbonylation of Aromatic Aldehydes via a Transient Directing Group Strategy
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A Mn(OAc)3-Triggered Formation of Cyclopropanes from Ugi Adducts
No full textInternational audienceAbstract Ugi adducts involving malonic acid monoesters and dialkoxy-substituted aromatic aldehydes can undergo an oxidative dearomatization when treated with Mn(OAc)3 leading to the formation of fused cyclopropanes as observed in the Buchner reaction of diazo compounds
Simulation de problèmes d'entrée-sortie d'eau mettant en évidence des phénomènes de succion par une approche couplée eulérienne-lagrangienne
No full textInternational audienceThe present study aims to assess the possibility of describing suction using coupled Eulerian–Lagrangian approach. The water entry and subsequent exit of conical and hemispherical bodies is investigated numerically using the Finite Element simulation software Radioss. The numerical method relies on an explicit numerical scheme. An Eulerian and a Lagrangian formulation are considered for the fluid and the structure, respectively. The fluid–structure interaction is based on an immersed contact interface. Particular attention is given to the evolution of the hydrodynamic (positive and negative) force and wetted surface. The numerical results are compared to experimental results from the literature for different impact conditions (maximum velocity and penetration depth). The influence of several parameters of the numerical model is analysed to assess its robustness and improve the numerical results. The numerical model especially shows a satisfying ability to predict suction forces.Cette étude vise à évaluer la possibilité de décrire la succion en utilisant une approche couplée eulérienne-lagrangienne. L'entrée-sortie de l'eau de corps coniques et hémisphériques est étudiée numériquement en utilisant le logiciel de simulation par éléments finis Radioss. La méthode numérique repose sur un schéma numérique explicite. Une formulation eulérienne et une formulation lagrangienne sont respectivement considérées pour le fluide et la structure. L'interaction fluide-structure est basée sur une interface de contact immergée. Une attention particulière est accordée à l'évolution de la force hydrodynamique (force de succion) et de la surface mouillée. Les résultats numériques sont comparés aux résultats expérimentaux de la littérature pour différentes conditions d'impact (vitesse maximale et profondeur de pénétration). L'influence de plusieurs paramètres du modèle numérique est analysée pour évaluer sa robustesse et améliorer les résultats numériques. Le modèle numérique montre notamment une capacité satisfaisante à prédire les forces de succion
