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A Self Referencing Technique for the RC-pLMS Adaptive Beamformer and Its Hardware Implementation
No full textInternational audienceIn this paper, we propose a self referencing scheme for the reduced complexity parallel least mean square (RC-pLMS) adaptive beamforming algorithm as means of robustness against possible interruptions in the reference signal and its hardware implementation. The RC-pLMS is a single stage, non-blind, least mean square (LMS) algorithm with modified input vectors formed as a linear combination of the current and the previous input sample. In this context, its convergence and its stability are critically dependent on the availability of its reference signal and are known to severally degrade when discontinued. Thus, for robustness against the pre-mentioned and with respect to the RC-pLMS accelerated convergence and low residual error profile, we propose the use of it’s filtered output, as an alternative learning sequence, whenever the original reference signal is discontinued, i.e. self-referencing. The proposed self referencing approach is evaluated in infinite and finite precision modes on software and on hardware, i.e. Field Programmable Gate Array (FPGA), respectively. Hardware and software simulation validates the RC-pLMS robustness against different reference signal obstruction scenarios, through the use of the proposed self-referencing approach, while maintaining an accelerated convergence behavior, a low complexity architecture and a high precision beam pointing accuracy
Femtosecond laser filamentation and applications
No full textInternational audienceFemtosecond filamentation is a spectacular phenomenon whereby a short laser pulse propagates nonlinearly through a transparent medium allowing high peak light intensities to be transferred over distances far exceeding the beam Rayleigh length, as if diffraction were suppressed. In this chapter, after a brief description of some key features of filamentation, we put the accent upon some potential applications
A Novel Thick Ellipsoid Approach for Verified Outer and Inner State Enclosures of Discrete-Time Dynamic Systems
No full textInternational audienceSimulating dynamic systems with bounded uncertainty in initial conditions and selected parameters is a common task for the reliability analysis of closed-loop control structures as well as for a simulation-based parameter identification on the basis of uncertain measurements. However, dealing with bounded uncertainty is not a trivial task. On the one hand, the naive application of interval analysis often leads to excessively large bounds which may yield state enclosures that are by far too pessimistic to be useful in practice. On the other hand, the use of grid-based or probabilistic and Monte-Carlo like simulation approaches suffers from the disadvantage that they do not provide a guarantee of the correctness of the obtained solutions. Using insufficiently many or badly chosen samples may lead to the phenomenon that critical system states are not detected so that the computed results underestimate the range of reachable states. Therefore, a novel ellipsoidal state enclosure technique is presented which does not require the online solution of linear matrix inequalities (LMIs). It uses the newly introduced representation of state domains by means of thick ellipsoids. These domains simultaneously represent inner and outer enclosures of the reachable states and directly provide a measure for the tightness of the obtained results, regardless of whether the system is linear or nonlinear or whether it is stable or not
Palladium‐Catalyzed C8‐Oxygenation of Naphthalene Derivatives: Direct Access to Naphtholactone Skeleton
No full textInternational audienceHerein, a direct C8-oxygenation of naphthalene derivatives is described. Different carbonyl groups were used as directing group to deliver corresponding naphthols via a palladium-catalyzed oxidation reaction using PhI(OAc)2 in a TFA/TFAA mixture. Interestingly, when Weinreb amide was employed as the directing group, the naphtholactone skeleton was directly obtained. This methodology was applied to the synthesis of variously substituted naphtholactones
DMS and MultiGLODS: Black-Box Optimization Benchmarking of Two Direct Search Methods on the bbob-biobj Test Suite
No full textInternational audienceDirect Multisearch (DMS) and MultiGLODS are two derivative-free solvers for approximating the entire set of Pareto-optimal solutions of a multiobjective (blackbox) problem. They both follow the search/poll step approach of direct search methods, employ Pareto dominance to avoid aggregating objectives, and have theoretical limit guarantees. Although the original publications already compare the two algorithms empirically with a variety of multiobjective solvers, an analysis on their scaling behavior with dimension was missing. Here, we run the publicly available implementations on the bbob-biobj test suite of the COCO platform and by investigating their performances in more detail, observe (i) a small defect in the default initialization of DMS, (ii) for both algorithms a decrease in relative performance to other algorithms of the original studies (even matching the performance of random search for MultiGLODS in higher dimension), and (iii) consequently, an under-performance to previously untested stochastic solvers from the evolutionary computation field, especially when the dimension is higher
3D Spatial Distribution of Nanoparticles in Mice Brain Metastases by X-ray Phase-Contrast Tomography
No full textInternational audienceCharacterizing nanoparticles (NPs) distribution in multiple and complex metastases is of fundamental relevance for the development of radiological protocols based on NPs administration. In the literature, there have been advances in monitoring NPs in tissues. However, the lack of 3D information is still an issue. X-ray phase-contrast tomography (XPCT) is a 3D label-free, non-invasive and multi-scale approach allowing imaging anatomical details with high spatial and contrast resolutions. Here an XPCT qualitative study on NPs distribution in a mouse brain model of melanoma metastases injected with gadolinium-based NPs for theranostics is presented. For the first time, XPCT images show the NPs uptake at micrometer resolution over the full brain. Our results revealed a heterogeneous distribution of the NPs inside the melanoma metastases, bridging the gap in spatial resolution between magnetic resonance imaging and histology. Our findings demonstrated that XPCT is a reliable technique for NPs detection and can be considered as an emerging method for the study of NPs distribution in organs
Direct computation of nonlinear mapping via normal form for reduced-order models of finite element nonlinear structures
No full textInternational audienceThe direct computation of the third-order normal form for a geometrically nonlinear structure discretised with the finite element (FE) method, is detailed. The procedure allows to define a nonlinear mapping in order to derive accurate reduced-order models (ROM) relying on invariant manifold theory. The proposed reduction strategy is direct and simulation free, in the sense that it allows to pass from physical coordinates (FE nodes) to normal coordinates, describing the dynamics in an invariant-based span of the phase space. The number of master modes for the ROM is not a priori limited since a complete change of coordinate is proposed. The underlying theory ensures the quality of the predictions thanks to the invariance property of the reduced subspace, together with their curvatures in phase space that accounts for the nonresonant nonlinear couplings. The method is applied to a beam discretised with 3D elements and shows its ability in recovering internal resonance at high energy. Then a fan blade model is investigated and the correct prediction given by the ROMs are assessed and discussed. A method is proposed to approximate an aggregate value for the damping, that takes into account the damping coefficients of all the slave modes, and also using the Rayleigh damping model as input. Frequency-response curves for the beam and the blades are then exhibited, showing the accuracy of the proposed method
Determinants of employees' participation in decision-making in developing countries: Does a firm's formal vs. informal status matter?
No full textPrior studies on the determinants of employees' participation in decision-making have ignored the sector dualism (formal sector vs. informal sector) in developing countries, despite the differences in the characteristics of formal and informal firms. This paper tests the idea that a firm's formal vs. informal status matters, using firm-level data from Côte d’Ivoire. It emerges that a firm's formality status influences positively its probability to involve employees in decision-making. This result holds after controlling for manager-, firm- and sector- level factors. Ultimately, the paper contributes to sending the signal that formalization of informal firms in developing countries should be beneficial to their decision-making process, and thereby to their performance
Integrated water vapour observations in the Caribbean arc from a network of ground-based GNSS receivers during EUREC4A
No full textInternational audienceGround-based Global Navigation Satellite System (GNSS) measurements from nearly fifty stations distributed over the Caribbean Arc have been analysed for the period 1 January-29 February 2020 in the framework of the EUREC 4 A (Elucidate the Couplings Between Clouds, Convection and Circulation) field campaign. The aim of this effort is to deliver high-quality Integrated Water Vapour (IWV) estimates to investigate the moisture environment of mesoscale cloud patterns in the Tradewinds and their feedback on the large-scale circulation and energy budget. This paper describes the GNSS data processing procedures and assesses the quality of the GNSS IWV retrievals from four operational streams and one reprocessed research stream which is the main data set used for offline scientific applications
3D printing: rapid manufacturing of a new small-scale tidal turbine blade
No full textInternational audienceThe 3D printing technology used for small tidal and wind turbines has great potential to change and overcome certain weaknesses in traditional manufacturing techniques. In rural areas and isolated communities, small turbine systems could be locally fabricated and assembled by using additive manufacturing machines and also can be employed to decrease residential energy consumption. The objective of the paper is to study the thermomechanical performance of 3D printing of a small-scale tidal turbine blade and their process using Digimat-AM because more research efforts are needed in this area. In this work, the tidal turbine blade is printed by using the selective laser sintering (SLS) method with polyamide 12 (PA12) and polyether ether ketone (PEEK) polymers reinforced by carbon beads (CB) and glass beads (GB). This research examines conceptual considerations of small tidal turbines including material properties and aerodynamic parameters. Once the finite element evaluation has been completed, the deflection, residual stresses, temperature distribution, and the deformed blade or warpage can be obtained. It is concluded that PA12-CB has warpage higher than PA12-GB by 3.78%, and PEEK-CB has warpage lower than PEEK-GB by 8.4%. Also, the warpage of PA12-CB is lower than PEEK-CB by 10.31%, and the warpage of PA12-GB is lower than PEEK-GB by 20.95%. Therefore, the lowest warpage is observed for PA12-GB. Finally, the results showed that 3D printing presents an excellent opportunity in the design and development of tidal energy systems in the future