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Multistage stochastic optimization of a mono-site hydrogen infrastructure by decomposition techniques
No full textInternational audienceThe development of hydrogen infrastructures requires to reduce their costs. In this paper, we develop a multistage stochastic optimization model for the management of a hydrogen infrastructure which consists of an electrolyser, a compressor and a storage to serve a transportation demand. This infrastructure is powered by three different sources: on-site photovoltaic panels (PV), renewable energy through a power purchase agreement (PPA) and the power grid. We consider uncertainties affecting on-site photovoltaic production and hydrogen demand. Renewable energy sources are emphasized in the hydrogen production process to ensure eligibility for a subsidy, which is awarded if the proportion of nonrenewable electricity usage stays under a predetermined threshold. We solve the multistage stochastic optimization problem using a decomposition method based on Lagrange duality. The numerical results indicate that the solution to this problem, formulated as a policy, achieves a small duality gap, thus proving the effectiveness of this approach
Metrology of the acoustic seafloor response: how to accurately estimate backscatter and its intrinsic uncertainty using single-beam echosounder
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Inverse optimal control problem in the non autonomous linear-quadratic case
No full textInverse optimal control problem emerges in different practical applications, where the goal is to design a cost function in order to approximate given optimal strategies of an expert. Typical application is in robotics for generation of human motions. In this paper we analyze a general class of non autonomous inverse linear quadratic problems. This class of problems is of particular interest because it arises as a linearization of a nonlinear problem around an optimal trajectory. The addressed questions are the injectivity of the inverse problem and the reconstruction. We show that the nonlinear problem admits the same characterization of the injectivity as the autonomous one. In the autonomous case we show moreover that the injectivity property is generic in the considered class. We also provide a numerical test of the reconstruction algorithm in the autonomous setting
Real-time braking control based on optic flow divergence onboard an underwater vehicle
No full textInternational audienceObstacle avoidance is a major challenge for underwater robot navigation, especially in cluttered environments where sonars are subject to reverberation and noise. Optic flow cues are widely used for aerial drone navigation, as they can be measured with broadly available sensors such as monocular cameras. Few studies have explored the possibility of using optic flow cues for underwater robot navigation, although this is more difficult due to imaging conditions and natural scene characteristics. In this study, we investigate the use of optic flow divergence for real-time collision avoidance onboard a Remotely Operated underwater Vehicle (ROV) equipped with monocular cameras. The measured optic flow divergence was first used to trigger an autonomous emergency braking response, then to estimate the relative distance of the underwater vehicle from the detected obstacle using an Extended Kalman Filter. This relative distance was used to maintain a predefined safe distance from the obstacle. Tests were first carried out in a pool, then in a harbour, in a lake and in the sea. Our findings show that this minimalistic method is effective under a wide range of visibility and turbidity conditions
The Electrochemical and Structural Changes of Phosphorus-Doped TiO 2 through In Situ Raman and In Situ X-Ray Diffraction Analysis
No full textInternational audienceDoping is a widely employed technique to enhance the functionality of lithium-ion battery materials, tailoring their performance for specific applications. In our study, we employed in situ Raman and in situ X-ray diffraction (XRD) spectroscopic techniques to examine the structural alterations and electrochemical behavior of phosphorus-doped titanium dioxide (TiO2) nanoparticles. This investigation revealed several notable changes: an increase in structural defects, enhanced ionic and electronic conductivity, and a reduction in crystallite size. These alterations facilitated higher lithiation rates and led to the first observed appearance of LiTiO2 in the Raman spectra due to anatase lithiation, resulting in a reversible double-phase transition during the charging and discharging processes. Furthermore, doping with 2, 5, and 10 wt % phosphorus resulted in an initial increase in specific capacity compared to undoped TiO2. However, higher doping levels were associated with diminished capacity retention, pinpointing an optimal doping level for phosphorus. These results underscore the critical role of in situ characterization techniques in understanding doping effects, thereby advancing the performance of anode materials, particularly TiO2, in lithium-ion batteries
Use of spatiotemporal couplings and an axiparabola to control the velocity of peak intensity
No full textInternational audienceThis paper presents the first experimental realization of a scheme that allows for the tuning of the velocity of peak intensity of a focal spot with relativistic intensity. By combining a tunable pulse-front curvature with the axial intensity deposition characteristics of an axiparabola, an aspheric optical element, this system provides control over the dynamics of laser-wakefield accelerators. We demonstrate the ability to modify the velocity of peak intensity of ultrashort laser pulses to be superluminal or subluminal. The experimental results are supported by theoretical calculations and simulations, strengthening the case for the axiparabola as a pertinent strategy to achieve more efficient acceleration
Cartographie du niveau de la mer par systèmes GNSS pour la validation des données SWOT
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Automated far-field sound field estimation combining robotized acoustic measurements and the boundary elements method
No full textThe identification and reconstruction of acoustic fields radiated by unknown structures isusually performed using either Sound Field Estimation (SFE) or Near-field Acoustic Holog-raphy (NAH) techniques. The latter turns out to be especially useful when data is onlyavailable close to the source, but information throughout the whole space is needed.Yet, the lack of amendable and efficient implementations of state-of-the-art solutions, aswell as the laborious and often lengthy deployment of acoustic measurements continue to besignificant obstacles to the practical application of such methods.The purpose of this work is to address both problems. First, a completely automated metrol-ogy setup is proposed, in which a robotic arm is used to gather extensive, yet accurate ge-ometric and acoustic data without any human intervention. The impact of the robot onacoustic pressure measurements has been cautiously estimated, and proved to remain negli-gible within a defined validity frequency range.The sound field prediction is then tackled using the Boundary Element Method (BEM), andimplemented using the FreeFEM++ BEM library. Numerically simulated measurements haveallowed us to assess the method accuracy, which matches theoretically expected results, androbustness against positioning inaccuracies, provided that the robot is carefully calibrated.The overall solution has been successfully tested using actual robotized measurements of anunknown loudspeaker, with a reconstruction error of less than 30 % on the previously definedvalidity frequency rang
Modeling swarm mission with COTS characterization: a series of return on experience
No full textInternational audienceSystem design in defense systems is a competitive field, in which economical viability relieson a sequence of architectural decisions, aiming at quality, resource and time (Q,R,T) compromises.We observe that low-cost unmanned ground vehicles (UGV) and drones appear as new threats on cur-rent battlefield. To face these new threats, Direction Générale de l’Armement (DGA) have organizedchallenges around robotization of battlefield, to design future employment doctrines and help technol-ogies to reach maturity in a reasonable time. This article exposes a NATO Architecture Framework(NAF) 3.1-based workflow that includes return of experience form the field over yearly iterations ofsuch challenges. The capabilities depicted are requirements to match, constituent systems are based onComponents-Off-The-Shelf (COTS) answering to both edition of the challenge. This article details howmanually re-injecting feedback from field back to the system model failed to ensure the next iterationsof the challenge. Our works propose conclusions on formulation of the “engineering leakage problem”and how resolution of this problem is NP-Hard and should be addressed using optimization
Total Synthesis of Cyclotripeptidic Natural Products Anacine, Aurantiomide C, Polonimides A and C, and Verrucine F
No full textInternational audienceThe total synthesis of cyclotripeptidic natural products possessing a central piperazino[2,1-b]quinazolin-3,6-dione core is described through an original strategy involving the pivotal cyclocondensation of an electrophilic homoserine lactone intermediate. The alkylidene group was spontaneously installed by autoxidation during the cyclocondensation process, while the propionamide side chain was introduced through the nickel-catalyzed aminocarbonylation of a bromoethyl intermediate. This last reaction is unprecedented on such highly functionalized intermediates. Finally, we explored structural modifications and interconversions of the natural products. Overall, this work led to anacine, aurantiomide C, polonimides A and C, and verrucine F