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A LiNbO<sub>3</sub> Platform with Tailored Thickness Bridging Bulk and Thin Film: Application to Broadband Frequency Conversion
No full textInternational audienceWe introduce a monolithic LiNbO3 membrane platform that bridges bulk and thinfilm approaches, enabling custom-tailored waveguide cross-sections. Using a combination of saw dicing and reactive ion etching (RIE), we fabricate LiNbO3 structures with adaptable thicknesses ranging from 400 nm to several microns, identifying 2 µm as an optimal value for addressing key challenges in frequency conversion. Our platform demonstrates robust second harmonic generation (SHG) with a broad pump wavelength response of up to 150 nm within the C-band at room temperature, achieved by tuning the waveguide thickness, while maintaining low coupling losses of 0.8 dB/facet. These results represent a significant step toward versatile integrated photonic systems, advancing applications in broadband spectroscopy, quantum information processing, and sensing through efficient and spectrally agile nonlinear frequency conversion
Unravelling Holocene climate, human impact and hydrological variations and their impact on Lake Ecosystem Dynamics: A Multi-proxy Case Study from Lake Fazilman, Uzbekistan
No full textInternational audienc
Extended-range and faster photon-counting Brillouin optical time domain reflectometer
No full textInternational audienceDistributed fiber optic sensors are used to monitor civil infrastructures and detect earthquakes and for energy transport surveillance. Over the past 20 years, various technological and numerical advances have pushed back the limits of these sensors and diversified their applications. However, the maximum range of distributed fiber optic sensors such as Brillouin optical time domain reflectometers (BOTDRs) is currently limited by the signal-to-noise level of the detectors. We present a fast, long-range measurement technique with a high signal-to-noise ratio that overcomes these difficulties. We propose to use a gated single-photon detector triggered by multiple gating pulses delayed by sub-dead time duration. The length of the pulse sequence considerably reduces measurement time without compromising spatial resolution, maximum range, or sensitivity. The proposed approach is demonstrated experimentally by measuring the Brillouin signal up to a distance of 150 km in a standard single-mode fiber. The measurements were performed without need for an optical amplification module remotely placed along a standard single-mode fiber, thus surpassing the state of the art and providing excellent agreement with theory. We experimentally demonstrate a hot-spot measurement at 125 km with a spatial resolution of 20 m. By extrapolating our results, we pave the way for the future 200 km BOTDRs
Boundary stabilization of random reaction-diffusion systems
No full textInternational audienceThe boundary stabilization of a class of reaction-diffusion systemsperturbed by second-order processes is investigated in this work.It extends the results from random ordinary differential equationsto random reaction-diffusion systems (RRDSs). First, the stabilityanalysis of RRDSs with boundary input is presented. Using theLyapunov method and stochastic process estimation, two criteria ofasymptotic stability are established in 2nd moment and inprobability, by applying Wirtinger's inequality and the weak law oflarge numbers. Second, based on the obtained stability criteria, aclass of boundary control problems is solved by constructing aLyapunov functional and designing integral boundary controllers.Additionally, the influence of nonlinear terms and the diffusioncoefficient on stability is analyzed. Finally, numericalsimulations demonstrate the effectiveness of the boundarycontroller
A new criterion based on the distribution of cluster onsets for interpreting acoustic emission data signals : three case studies in structural and process monitoring
No full textInternational audienceStructural health monitoring relies on non-destructive techniques such as acoustic emission that generate large amounts of data over the lifespan of systems. Clustering methods are used to interpret these data and gain insights into damage progression and mechanisms. Conventional methods for evaluating clustering results utilise clustering validity indices (CVI) that prioritise compact and separable clusters. This paper introduces a novel approach based on the temporal sequence of cluster onsets, indicating the initial appearance of potential damage and allowing for early detection of defect initiation. The proposed CVI is based on the Kullback–Leibler divergence and can incorporate prior information about damage onsets when available. Three experiments on real-world datasets validate the effectiveness of the proposed method. The first benchmark focuses on detecting the loosening of bolted plates under vibration, where the onset-based CVI outperforms the conventional approach in both cluster quality and the accuracy of bolt loosening detection. The results demonstrate not only superior cluster quality but also unmatched precision in identifying cluster onsets, whether during uniform or accelerated damage growth. The two additional applications stem from industrial contexts. The first focuses on micro-drilling of hard materials using electrical discharge machining, demonstrating, for the first time, that the proposed criterion can effectively retrieve electrode progression to the reference depth, thus validating the setting of the machine to ensure structural integrity. The final application involves damage understanding in a composite/metal hybrid joint structure, where the cluster timeline is used to establish a scenario leading to critical failure due to slippage
Efficient nonlinear integral backstepping control for doubly fed induction generators-based wind farm under unbalanced electrical grid voltage
No full textInternational audienceThis paper proposes a modified and efficient control strategy forwind farm (WF) based on doubly-fed induction generators (DFIGs)under an unbalanced electrical voltage grid. This strategy consistsof two loops: the main and the auxiliary. The main loop controlsthe positive sequence currents of the rotor and grid-side converter(GSC) of each DFIG in the WF. In contrast, the auxiliary one isdesigned to regulate negative sequence currents. In this work, thepositive and negative sequences of the rotor current loops of eachDFIG in the WF are regulated using a nonlinear integratedbackstepping controller (IBSC). The main contribution of thisstrategy is to ensure that the WF remains connected to the gridunder severe asymmetrical faults, to reduce the oscillations causedby such faults in the electromagnetic torque, in the WF powerprofile, and in the DC bus voltage. Additionally, it aims tominimize the total harmonic distortion (THD) in currents of WF andenhance the power quality. To verify these objectives, thesuggested strategy is compared with a single-loop strategy. Thiscomparative study is validated through simulations performed inMatlab/Simulink software, using the S-function builder whichenables its integration into actual control boards for tests underreal environment
Facteurs prédictifs de mortalité des hypertensions pulmonaires associées aux pneumopathies interstitielles diffuses
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Online Health Monitoring of Silicon PV Panels by Converter-Based Impedance Spectroscopy: Panel-Level Equivalent Circuit Model and Health Feature Extraction
No full textInternational audienceWithin the framework of Dexter’s theory, we calculate the energies of the Stark levels of Yb3+-Yb3+ paired centers in lithium niobate doped with Yb3+ ions (LiNbO3:Yb3+) crystal, considering the interaction of optical electrons of ytterbium ions forming the paired center. The calculated Stark level energies are shown to correspond well with the observed cooperative luminescence wavelengths
Conférence De Hardouin et Marie à Gisti
No full textConférence suivie d'une débatPar ses arrêts Hardouin et Marie du 17 février 1995, l’Assemblée du contentieux du Conseil d’État est venue réduire drastiquement la catégorie des mesures d’ordre intérieur, en ouvrant le recours pour excès de pouvoir contre des actes qui, jusqu’alors, échappaient au contrôle du juge. Cette jurisprudence peut être considérée comme le point de départ d’une véritable politique jurisprudentielle du juge administratif, visant à analyser la justiciabilité (et la juridicité) d’un acte administratif unilatéral non plus seulement au regard de l’objet de l’acte, mais également de ses effets sur la situation des administrés. Le point d’aboutissement de cette jurisprudence est marqué par l’arrêt Gisti du 12 juin 2020, lequel ouvre le recours pour excès de pouvoir à l’encontre des documents de portée générale (circulaires, instructions, recommandations, notes, présentations ou interprétations du droit positif, ce qui inclut par exemple les guides d’information en ligne ou foires aux questions sur internet) « lorsqu’ils sont susceptibles d’avoir des effets notables sur les droits ou la situation d’autres personnes que les agents chargés […] de les mettre en œuvre ». La manifestation proposée est l’occasion de revenir sur cette politique jurisprudentielle, qu’il s’agisse d’évoquer les justifications d’hier (contextualisation des arrêts Marie et Hardouin), les balbutiements de la jurisprudence jusqu’à 2020 (concernant notamment les lignes directrices et les circulaires) et la solution d’aujourd’hui. Elle permettra de montrer comment le droit administratif et son contentieux se sont adaptés à la modernisation de l’action et des pratiques administratives, et soulèvera la question des défis que posera, demain, cette approche conséquentialiste pour le juge administratif et l’administration