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Charge localization in diatomic ions investigated with a new dipole moment driven approach. Test for Ne2+ and (ArNe)+
No full textInternational audienceA novel method is proposed to develop charge-localized representations of the electronic structure of singly ionized dimers of rare gases. The method is based on an orthogonal transformation of the adiabatic dimer dipole moment matrix to a new basis in which the matrix is as close as possible to its point charge approximation. Upon general considerations and derivations, the method is applied to two specific cases, a homonuclear dimer ofand a heteronuclear dimer of (NeAr)+. High-level ab initio calculations have also been performed for both systems to get accurate input data and are reported
Analyse du vieillissement hygroscopique à long terme de structures sandwichs composites biosourcés à l'aide de l'émission acoustique
No full textInternational audienceThis work investigates the long-term hygroscopic ageing behavior of bio-based sandwich structures with balsa core and glass fiber laminate skins, through the experimental characterization based on the water immersion test monitored by AE wave velocity measurement, as well as the numerical modeling based on the Dual-Fick diffusion model. Based on the relationships between moisture content, AE wave velocity and the stiffness of the sandwich, a new methodology considering AE was proposed to predict the stiffness degradation as a function of moisture content, as well as the localization of moisture content in the thin skin and the thick core. It is demonstrated that the bending stiffness decreases faster in the initial phase before the point at 80 % moisture content, while the strength reduces more quickly during the later absorption period under long-term aging conditions.Ce travail étudie le comportement du vieillissement hygroscopique à long terme de structures sandwichs biosourcées à âme de balsa avec des peaux stratifiées en fibre de verre, à travers la caractérisation expérimentale basée sur l'essai d'immersion dans l'eau suivi par la mesure de la vitesse de l'onde d'émission acoustique (EA), ainsi que la modélisation numérique basée sur le modèle de diffusion Dual-Fick. Sur la base des relations entre la teneur en eau, la vitesse de l'onde d'EA et la rigidité du sandwich, une nouvelle méthodologie compte tenu de l'EA a été proposée afin de prédire la dégradation de la rigidité en fonction de la teneur en eau, ainsi que la localisation de la teneur en eau dans la peau fine et l’âme épaisse. Il est démontré que la rigidité en flexion diminue plus rapidement dans la phase initiale avant le point à 80 % de teneur en eau, tandis que la résistance diminue plus vite au cours de la période d’absorption ultérieure dans des conditions de vieillissement à long terme
Dispersion analysis in a 3D lattice elastic waveguide for the design of an absolute filter
No full textInternational audienceThis study presents a method for analyzing and designing elastic waveguides using 3D printed periodic truss structures to control the propagation of elastic waves. We propose an algorithm, based on the application of Bloch boundary conditions on a beam spectral model, to perform fast and efficient extraction of the full wave dispersion. Thanks to symmetry arguments, we introduce an identification method allowing for a better understanding of the dispersion. We then apply this method to a case study and demonstrate how it can be used to identify and design a structure exhibiting broadband absolute forbidden gaps
Simulation of extreme functionals in meteoceanic data: Application to surge evolution over tidal cycles
No full textWe investigate the influence of time-varying meteoceanic conditions on coastal flooding under the prism of rare events. Focusing on conditions observed over half tidal cycles, we observe that such data fall within the framework of functional extreme value theory, but violate standard assumptions due to temporal dependence and short-tailed behavior.a To address this, we propose a two-stage methodology. First, we introduce an autoregressive model to eliminate temporal dependence between cycles. Second, considering the model residuals, we adapt existing techniques based on Pareto processes. This allows us to build a simulator of extreme scenarios, by applying inverse transformations. These simulations depend on an initial time series, which can be randomly selected to tune the desired level of extremes. We validate the simulator performance by comparing simulated times series with observations, through several criteria, based on principal component analysis, extreme value analysis, and classification algorithms. The approach is applied to the surge data, on the Gâvres site, located in southern Brittany, France.</div
Systematic Analysis of the Links Between Obsolescence–Shortage and Reliability–Maintainability–Availability
No full textInternational audienceComponent obsolescence and shortages impact virtually all systems, particularly those with extended lifespans, such as aircrafts or trains. Obsolescence (i.e. state of being outdated) and shortage (i.e. lack of components) are distinct yet interconnected challenges and despite their inevitability, systems must maintain acceptable performance levels over extended periods. In this research, the term 'shortage' encapsulates the broader concepts of Diminishing Manufacturing Sources and Material Shortages (DMSMS). This study investigates the impacts of obsolescence and shortages on maintainability, reliability, and availability. Existing scientific literature frequently overlooks this influence when calculating associated indicators, often relegating it to a marginal factor despite its potential significant impact. The aim is to underscore the criticality of incorporating obsolescence and shortage considerations into operational availability assessments. This argument stems from two key factors: the accelerating pace of obsolescence and shortages driven by rapid technological advancements, evolving needs, logistical disruptions, or global conflicts, and the inherent risks associated with overestimating operational availability. This study encompasses both the system design-development phase and the operational phase. It examines the relevant concepts and their interrelationships through the lens of international standards and established scientific literature. Furthermore, an industrial case study from a major automotive supplier, focusing on one of its production lines, serves to illustrate partially these relationships. The paper concludes by presenting the study's findings and outlining potential avenues for future research in this domain
Openprobe: a frugal multiparameter probe for marine and continental waters monitoring
No full textInternational audienceAquatic ecosystems need accurate observation to understand its trajectory in a context of increasing anthropogenic pressure and climate change. These environments are however undersampled in many areas (Brewin et al. 2017, Kirchner et al. 2004): acquiring essential variables at relevant spatial and temporal resolution is often not compatible with traditional methods of sample collection followed by laboratory analysis, but field-deployable or in-situ systems are either too expensive, too complicated to be used by non-trained users or even non-existent. In an effort to propose an alternative in-situ measurement system for biogeochemical and physicochemical measurement in marine and continental waters, we developed a multiparameter probe that measures 7 parameters for a very modest bill-of-materials cost (around 300 € for a single prototype). The performance of this probe is sufficient for most water bodies, both in terms of range and sensitivity, and its replication is facilitated by the use of rapid-prototyping methods. The Openprobe multiparameter (Fig. 1) is able to measure conductivity, temperature, pressure (depth or water level above), dissolved oxygen, turbidity, chlorophyll a, photosynthetically active radiation (PAR) as well as water color. These parameters were chosen based on a compromise between their relevance and our capability to measure them at a scientifically appropriate standard using low-cost components, an approach which resonates with the definition of the Standard Observations in eLTER (Zacharias et al. 2021). The electronic architecture is based around an Adafruit Feather M0 microcontroller board, an Adafruit Adalogger microSD-card logger with a Real-Time-Clock, and two custom Printed Circuit Boards (PCBs) that hosts the different sensors. Housing of the probe uses a Blue Robotics 2" diameter enclosure tubes. The sensor's PCBs are integrated in end-caps fabricated by stereolithography (SLA), using a desktop Formlabs Form 3 SLA printer with Black V4 resin. Compared to conventional fused-deposition modelling 3D printing (FDM), SLA is an isotropic printing technique which delivers fully dense and watertight parts. The higher resolution of SLA also allows to create o-ring grooves with appropriate tolerance, and has shown to be a valid fabrication technique even for the challenging pressures encountered in deep-sea science (Karp et al. 2023, Phillips et al. 2019). Atop of that, the 3D printed end-cads ensures auto-alignment of the optical elements (LEDs, photodiodes) and optical filters. The assembly/disassembly can be done manually without any tool, for easy access to the electronics, the battery, or the micro SD card on the field. Polydimethylsiloxane (PDMS), a silicone-based material with good transparency in the VIS-IR, is used within the end-caps to create optical ports, and also acts similarly to a potting material to ensure watertightness. The first PCB is integrated at the top of the probe, and contains the CTD (Conductivity, Depth, Temperature) as well as the PAR sensor. The conductivity sensor is based around a two-electrode cell on a ceramic substrate connected to an impedance analyzer integrated circuit (IC). Intercomparison with a Decagon CTD-10 and an Atlas Scientific EZO sensor showed that our sensor offered a better sensitivity, together with a smaller cost and a lower power consumption. Pressure and temperature sensors are based around the same IC used by Blue Robotics pressure and temperature sensors, and as such as been validated in many conditions (Poulsen et al. 2022). We worked on their integration on a custom PCB, with special care taken in minimizing the thermal inertia around the temperature sensor to reduce its response time when performing profiling analysis. The PAR sensor completes this part of the probe. It is based around the AMS AS7341, modified with a diffuser cut precisely with the xurography technique (Bartholomeusz et al. 2005), and intercompares with a+/- 5% confidence interval versus an Apogee SQ-512-SS sensor (Fig. 2), a value commonly exceeded when comparing different commercial sensors (Long et al. 2012). The second PCB, located at the opposite end of the probe, contains a chlorophyll a fluorometer, an oxygen optode, and a turbidity sensor. The chlorophyll a fluorometer uses synchronous detection: this approach allows efficient ambient light rejection, and captures the weak fluorescence signals observed due to the small fluorescence yield of in-vivo chl.a (Morrison 2003). The oxygen otpode uses PreSens Pst3 oxygen sensor spots, paired with a custom optoelectronic readout architecture. A DDS (Direct Digital Synthesizer) generates a sine wave to excite the Pst3 luminophore, and an I/Q demodulator measures the phase shift between excitation and the emitted fluorescence. The fluorescence signal is quenched in the presence of oxygen, which translates to a decrease of the fluorescence decay and in-fine by a phase shift . This is similar to the operating principle of Aanderaa optodes, commonly found in the Biogeochemical Argo floats. Our optode is intercompared with a benchtop PreSens Fibox 4 system and shown good accuracy (Fig. 3). Finally, the turbidity sensor implements 90° nephelometry as well as 180° backscattering measurements to cover a broad range of turbidity. Its architecture is based around an Analog Devices ADPD1080, an IC usually found in smartwatches for the measurement of photoplethysmography (PPG). The Openprobe multiparameter probe could be a very valuable tool in order to increase spatial and temporal resolution in aquatic ecosystem monitoring. Through the use of advanced, yet affordable electronic components initially developed for the Internet Of Things market, we created a frugal tool without compromising on accuracy
Filières à prioriser pour atténuer le changement climatique via le recyclage des biomasses résiduelles en produits biosourcés à l'échelle nationale: Construction d'une méthode de sélection des voies de transformation à fort potentiel de réduction des impacts environnementaux en amont d'une analyse approfondie via des ACV complètes.
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Energy Shifts and Broadening of Excitonic Resonances in Electrostatically Doped Semiconductors
No full textInternational audienceTuning the density of resident electrons or holes in semiconductors through electrostatic doping provides crucial insight into the composition of the many excitonic complexes that are routinely observed as absorption or photoluminescence resonances in optical studies. Moreover, we can change the way these resonances shift and broaden in energy by controlling the quantum numbers (e.g., spin and valley) of the resident carriers with applied magnetic fields and doping levels, as well as by selecting the quantum numbers of the photoexcited or recombining electron-hole ( e − h ) pair through optical polarization. Here, we discuss the roles of distinguishability and optimality of excitonic complexes, showing them to be key ingredients that determine the energy shifts and broadening of optical resonances in charge-tunable semiconductors. A distinguishable e − h pair means that the electron and hole undergoing photoexcitation or recombination have quantum numbers that are not shared by any of the resident carriers. An optimal excitonic complex refers to a complex whose particles come with all available quantum numbers of the resident carriers. Based on the carrier density, magnetic field, and light polarization, all optical resonances may be classified as either distinct or indistinct depending on the distinguishability of the e − h pair, and the underlying excitonic complex can be classified as either optimal or suboptimal. The universality of these classifications, inherited from the fundamental Pauli exclusion principle, allows us to understand how optical resonances shift in energy and whether they should broaden as doping is increased. This understanding is supported by conclusive evidence that the broadening and decay of optical resonances cannot be simply attributed to enhanced screening when resident carriers are added to a semiconductor. Finally, applying the classification scheme in either monolayer or moiré heterobilayer semiconductor systems, we relate the energy shift and amplitude of the neutral-exciton resonance to the compressibility of the resident carrier gas
Brightened emission of dark trions in transition metal dichalcogenide monolayers
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Reduced-order Smith predictor for state feedback control with guaranteed stability
No full textInternational audienceThis article deals with the implementation of the Smith Predictor for state feedback control in state space representation. The desired control law, obtained using partial differential equations and backstepping control, contains an integral term that has to be approximated for implementation. In this article, we propose a new way to implement this control law using a dynamic controller. The control law is composed of a state feedback term and a dynamic term that approaches the integral term that has to be estimated for implementation. Using a Lyapunov functional, we provide sufficient conditions, in terms of a linear matrix inequality, to guarantee that the closed-loop system is stable when the proposed control law is applied. We use three examples, taken from the literature, to show the benefits of the proposed approach