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Six‐Month Outdoor Performance Study of Stable Perovskite Solar Cells Under Real Operating Conditions
No full textInternational audiencePerovskite solar cells (PSCs) have sparked great excitement in the photovoltaics community due to their remarkable efficiency, flexibility, and ability to be synthesized at low cost. However, their instability poses a major roadblock to their widespread adoption. Recognizing this challenge, this work describes the performance of stable PSCs operating under real‐life conditions in the Paris area. Two state‐of‐the‐art 2D/3D (HOOC(CH 2 ) 4 NH 3 )2PbI 4 /CH 3 NH 3 PbI 3 encapsulated cells are considered—one with maximum power point tracking and hourly current–voltage curve measurements, and another connected to a fixed resistive load. Their performance is compared over six months, and a detailed analysis is conducted on the cells’ hysteresis and electrical response to varying weather conditions. Although the first cell starts to degrade after a few months of operation, the second one remains remarkably stable, highlighting critical issues with outdoor tracking. Given that the stability of this PSC architecture has already been established under controlled standard conditions for over one year, these exciting findings pave the way for the commercialization of perovskite‐based photovoltaic devices
AROMA: Preserving Spatial Structure for Latent PDE Modeling with Local Neural Fields
No full textInternational audienceWe present AROMA (Attentive Reduced Order Model with Attention), a framework designed to enhance the modeling of partial differential equations (PDEs) using local neural fields. Our flexible encoder-decoder architecture can obtain smooth latent representations of spatial physical fields from a variety of data types, including irregular-grid inputs and point clouds. This versatility eliminates the need for patching and allows efficient processing of diverse geometries. The sequential nature of our latent representation can be interpreted spatially and permits the use of a conditional transformer for modeling the temporal dynamics of PDEs. By employing a diffusion-based formulation, we achieve greater stability and enable longer rollouts compared to conventional MSE training. AROMA's superior performance in simulating 1D and 2D equations underscores the efficacy of our approach in capturing complex dynamical behaviors
Réduction des oxydes de fer, déstockage du carbone des sols noyés, et émission de méthane par un réservoir tropical
No full textInternational audienceThe impoundment of the Petit-Saut reservoir (French Guyana) in 1994 flooded over 300 km2 of tropical forest, causing the anoxia of the hypolimnion and a considerable emission of GHGs. The parallel evolution of dissolved iron and methane suggested that both originated from the reduction of flooded soils. The comparison of flooded with control soils showed a 50% loss in organic matter, as well as a drop in its hydrogen index, and an increase in Δ13C. The strong correlation between organic matter and iron oxide content in control soils became weak in flooded soils, while the weak correlation between Fe-oxide and amorphous-Fe in control soils became strong in flooded soils, suggesting a massive transformation of Fe-oxide into amorphous Fe. Measured in the lab in anoxic conditions, the carbon mineralization rate of flooded and control soils was proportional to their carbon content, suggesting continuous mineralization of organic matter in flooded soils. In contrast, the rate of methane production by flooded soils was very low. In addition, the 14C ages of flooded soils, methane bubbles in flooded soils, and dissolved methane in the hypolimnion were close to the age of the reservoir. This suggests that a fraction of reactive soil OM, bound to iron oxyhydroxides and released by iron reduction and dissolution when soils are flooded, is the source of the methane emitted by tropical reservoirs.Los grandes lagos artificiales creados por las represas hidroeléctricas tropicales contribuyen en gran medida a las emisiones de gases de efecto invernadero (GEI) de los hidrosistemas continentales. Aunque estos depósitos de agua han inundado suelos, la mineralización a largo plazo de la materia orgánica (MO) que contienen es muy poco documentada en la literatura. La inundación del embalse de Petit Saut (Guyana Francesa) en 1994 ahogó más de 300 km 2 de selva tropical y provocó la anoxia del hipolimnión y la emisión de un flujo considerable de GEI. Después de un pico en 1996-1998, las concentraciones de CH 4 disuelto en aguas que salen de embalses disminuyeron considerablemente entre 1998 y 2005, y desde entonces se han estabilizado en un nivel bajo. El paralelismo entre la evolución del hierro y del metano disueltos en las aguas de salida de la presa sugiere que provienen de la reducción de los suelos inundados. La comparación de los suelos de control muestreados bajo los bosques en el borde de la presa y de los suelos ahogados desde hace 25 años muestra:- una disminución de casi el 50 % del contenido de MO de los suelos inundados en comparación con los suelos de control, así como una disminución de su índice de hidrógeno, y un aumento de su δ13 C, lo que sugiere una rápida mineralización de la MO de los suelos en ausencia de oxígeno y sobre todo de su fracción más energética.- Una fuerte correlación entre el contenido de materia orgánica (MO) y de óxido de hierro en los suelos de control, que se vuelve baja en los suelos inundados. En cambio, la baja correlación entre Fe-óxido y Fe-amorfo en los suelos de control, se vuelve fuerte en los suelos ahogados, lo que sugiere una transformación de Fe óxido en Fe amorfo. La tasa de mineralización en relación con su contenido de carbono de los suelos de control e inundados, medida en anoxia en el laboratorio, difiere poco, lo que sugiere una mineralización continua y permanente de la MO de los suelos inundados. En cambio, la tasa de producción de metano por los suelos inundados es muy baja. Las edades 14 C de la MO de los suelos inundados, de las burbujas de metano presentes en estos suelos, y del metano disuelto en el hipolimnión cerca de la presa son próximas a la edad del embalse. El conjunto sugiere que una fracción de MO reactiva de los suelos, vinculada a los oxihidróxidos de hierro, liberada por reducción y disolución del hierro cuando los suelos se ahogan, es la fuente a corto y largo plazo del metano y de una parte importante de los GEI emitidos por los embalses tropicales.Les grands lacs artificiels créés par les barrages hydro-électriques tropicaux contribuent largement aux émissions de gaz à effets de serre (GES) par les hydrosystèmes continentaux. Bien que ces réservoirs d’eau aient noyé des sols, la minéralisation à long terme de la matière organique (MO) qu’ils contiennent est très peu documentée dans la littérature. La mise en eau du réservoir de Petit Saut en 1994 a noyé plus de 300 km2 de forêt tropicale et provoqué l'anoxie de l'hypolimnion et l’émission d’un flux considérable de GES. Après un pic en 1996-1998, les concentrations de CH4 dissous dans les eaux en sortie de barrage ont fortement diminué entre 1998 à 2005, et se sont stabilisées à un niveau faible depuis. Le parallélisme entre évolutions du fer et du méthane dissous dans les eaux en sortie de barrage suggère qu’ils proviennent de la réduction des sols noyés. La comparaison de sols témoins prélevés sous forêt en bordure de la retenue et de sols noyés depuis 25 ans montre : - Une baisse de près de 50 % de la teneur en MO des sols noyés par rapport aux sols témoins, ainsi qu’une baisse de l’indice d’hydrogène de la MO, et une augmentation de son δ13 C, ce qui suggère une minéralisation rapide de la MO des sols en l’absence d’oxygène et surtout de sa fraction la plus énergétique. - Une forte corrélation entre teneurs en MO et en oxyde de fer dans les sols témoins, qui devient faible dans les sols noyés. En revanche, la faible corrélation entre Fe-oxyde et Fe-amorphe dans les sols témoins devient forte dans les sols noyés, ce qui suggère une transformation de Fe oxyde en Fe amorphe. Les taux de minéralisation de la MO des sols témoins et noyés rapportés à leur teneur en carbone, mesuré en anoxie au laboratoire, diffère peu, ce qui suggère une minéralisation continue et permanente de la MO des sols noyés. En revanche, le taux de production de méthane par les sols noyés est très faible. Les âges 14 C de la MO des sols noyés, des bulles de méthane présentes dans ces sols, et du méthane dissous dans l'hypolimnion près du barrage sont proches de l'âge de la retenue. L’ensemble suggère qu’une fraction de MO réactive des sols, liée aux oxy-hydroxydes de fer, libérée par réduction et dissolution du fer lorsque les sols sont noyés, est la source à court et à long terme du méthane et d’une fraction importante des GES émis pas les réservoirs tropicaux
LOCA transient - Beneficial effects of the pressure and temperature evolution on fine fuel fragmentation
No full textInternational audienceAs part of various international projects and programs, it has been experimentally observed that high burnup fuel could over-fragment and lead to fine fragments (fuel fragments smaller than one millimeter) during loss-of-coolant accident (LOCA)-type temperature ramps with cladding rupture. These experimental tests were carried out at the scales of fuel fragments, pellet-cladding sections (heating tests) and fuel rodlets (semi-integral tests). The tests intended to investigate the effects of the following parameters on the fine fuel fragmentation: the maximum temperature reached during the thermal ramp, the heating rate, the holding time at high temperature, and, to a certain degree fuel rod internal pressure, via the test rodlet pressure and the size and gas content of the plenum. These tests do not accurately simulate important characteristics of a real Light Water Reactor (LWR) LOCA transient. Importantly, in a LWR LOCA event, the temperature and pressure evolution during the transient are more complex than those of the experimental tests, i.e., three phases (blowdown, refill, and reflood) with typically two temperature peaks, vs. monotonic temperature increase. To date, there are few investigations on the effects of temperature and pressure histories on fine fuel fragmentation and dispersal. The aim of this paper is to present the results of two successive temperature ramps simulating a more realistic LOCA transient on the fine fuel fragmentation and dispersal. These tests showed that the degree of fine fragmentation was drastically reduced despite the high burnup. One suggested explanation is that during the first temperature peak some of the intergranular fission gases are released into the free volume of the rod, reducing one of the driving forces for fuel over-fragmentation during the second temperature peak and explaining this low degree of fine fragmentation and dispersal. We are attempting to consolidate this explanation with numerical simulations
Suivi de l’efficacité des actions de restauration écologique : les pièges à éviter lors de la mise en œuvre
No full textInternational audienceThe erosion of biodiversity is unprecedented, and one way to mitigate it is to initiate ecological restoration actions. The effectiveness of these actions, often carried out as part of voluntary initiatives or as a result of regulatory requirements, must be assessed as accurately as possible on the basis of data from ecological monitoring. However, attempts to gather feedback based on this data have encountered difficulties in France and around the world. To understand some of these difficulties, we analyzed the monitoring of restoration actions initiated by EDF at various French sites between 2008 and 2022. The actions focused on open terrestrial environments and wetlands. Monitoring, defined and carried out with reference partners, was based on referenced protocols developed according to restoration objectives on a case-by-case basis. We analyzed the targets selected for monitoring, the protocols and methods used, and their conditions of application. We show that monitoring is mainly focused on certain taxonomic groups, in line with regulations, rather than on the structure or functionality of the habitats of the target species. We observe changes in protocols, methods, and conditions of application occurring during monitoring due to changes in the environment and/or knowledge, as well as differences in practices among service providers. The use of standardized and consistent protocols and methods, along with the systematic collection of information on their conditions of application, would allow for a more quantitative assessment of the effectiveness of restoration actions.L’érosion de la biodiversité est sans précédent et un des moyens de l’atténuer est d’initier des actions de restauration écologique. L’efficacité de ces actions, souvent menées dans le cadre d’initiatives volontaires ou issues d’exigences réglementaires, doit être évaluée au mieux sur la base de données issues de suivis écologiques. Pourtant les tentatives de retour d’expérience basées sur ces données se heurtent à des difficultés en France et dans le monde. Pour comprendre certaines de ces difficultés, nous avons analysé les suivis d’actions de restauration de 2008 à 2022 initiés par EDF sur différents sites français. Les actions portaient sur des milieux terrestres ouverts et des milieux humides. Les suivis, définis et réalisés avec des partenaires de référence étaient basés sur des protocoles référencés et élaborés en fonction des objectifs de restauration au cas par cas. Nous avons analysé les cibles retenues pour le suivi, les protocoles et méthodes utilisées ainsi que leurs conditions d’application. Nous montrons que les suivis sont essentiellement ciblés sur certains groupes taxonomiques, en lien avec la réglementation, et non sur la structure ou la fonctionnalité des habitats des espèces visées. Nous observons des changements de protocoles, de méthodes et de conditions d’application des protocoles se produisant au cours des suivis inhérents à l’évolution des milieux et/ou des connaissances, aux différences de pratiques des prestataires. Le recours à des protocoles et des méthodes standardisés et homogènes et le renseignement systématique des informations sur leurs conditions d’application permettraient une évaluation plus quantitative de l’efficacité des actions de restauration
Suivis de l’efficacité des actions de restauration écologique : comment améliorer leur exploitabilité et leur pérennité ?
No full textInternational audienceThe erosion of biodiversity is unprecedented due to an accelerated rate of extinction and its anthropogenic origins. One way to mitigate this is to initiate ecological restoration actions as a complement to conservation and protection measures. The effectiveness of these actions, whether carried out as part of voluntary initiatives or as a result of regulatory requirements, needs to be assessed on the basis of ecological monitoring data. However, attempts to provide feedback based on such data generally face difficulties (inappropriate sampling, changes in monitoring methods, et cetera). In order to understand some of these difficulties, we analysed the monitoring of restoration actions initiated by Electricité de France (EDF) between 2008 and 2022 at 10 sites in France. The actions concerned both terrestrial and wetland environments. The monitoring was defined and carried out in collaboration with naturalist partners (consultants, naturalist associations, researchers, et cetera), using either referenced protocols or those developed on a case-by-case basis. We analysed the targets selected for monitoring, the protocols, methods and techniques used, and the conditions under which they were applied. We have shown that monitoring tends to focus on specific taxonomic groups, rather than on the structure or functionality of the targeted habitats. Changes in protocols, methods and techniques during monitoring were minor. On the other hand, the conditions under which the protocols were applied changed from one monitoring session to the next, modifying the sampling plan and possibly complicating or preventing the analysis of the data collected. The publication of new protocols and differences in practice between monitoring organisations may explain some of the observed changes. We conclude with recommendations for the implementation of ecological monitoring of restoration projects.L'érosion de la biodiversité est sans précédent en raison d’un rythme d’extinction accéléré et de son origine anthropique. Un des moyens de l'atténuer est d'initier des actions de restauration écologique en complément des opérations de préservation et conservation. L'efficacité de ces actions, menées dans le cadre d'initiatives volontaires ou issues d'exigences réglementaires, doit être évaluée sur la base de données issues de suivis écologiques. Or, les tentatives de retour d'expérience basées sur ces données se heurtent généralement à des difficultés (échantillonnage inadapté, changements de méthodes au cours du suivi, et cetera) . Pour comprendre certaines d’entre-elles, nous avons analysé les suivis d'actions de restauration initiées par l’entreprise française Électricité de France (EDF) entre 2008 et 2022 sur dix sites en France. Les actions portaient sur des milieux terrestres ou humides. Les suivis, définis et réalisés avec des partenaires naturalistes (bureaux d’étude, associations naturalistes, chercheurs, et cetera) étaient basés sur des protocoles référencés ou élaborés au cas par cas. Nous avons analysé les cibles retenues pour les suivis, les protocoles, les méthodes et techniques utilisées ainsi que leurs conditions d'application. Nous montrons que les suivis sont essentiellement ciblés sur certains groupes taxonomiques, et non sur la structure ou la fonctionnalité des habitats visés. Les changements de protocoles, de méthodes et techniques au cours des suivis étaient mineurs. Les conditions d'application des protocoles en revanche, changeaient d’une session de suivi sur l’autre modifiant ainsi le plan d’échantillonnage et pouvant gêner ou empêcher l’analyse des données collectées. La publication de protocoles nouveaux et les différences de pratiques entre organismes réalisant les suivis peuvent expliquer une partie des changements observés. Nous terminons par des recommandations pour la mise en œuvre de suivis écologiques d’actions de restauration
Model order reduction of an electro-quasistatic problem using CLN method
No full textInternational audienceThe Cauer ladder network (CLN) method, as proposed by Kameari et al. (2018), has been extensively studied to construct a reduced model of magneto-quasistatic (MQS) Finite Element (FE) models. In this case, this method enables the construction of an equivalent electrical circuit based on resistances and inductances as well as a reduced basis where the solution of a reduced problem is sought. In this article, we propose to extend the applicability of the CLN method to the development of reduced models for FE electro-quasistatic (EQS) models. It appears that the derivation of the reduction of an EQS model is not similar to the one of an MQS model. After development, the process of reduction using CLN leads to consider two electrical circuits based on the cascade association of resistances and capacitances. Each circuit is associated with a reduced basis constructed by applying the self-adjoint Lanczos method. The reduced solution to the EQS problem is got by first solving the circuit equations to determine the voltages and the currents at the terminals of the resistances and capacitances. Then, the approximated solution of the FE EQS model is got by a linear combination of the vectors of the two reduced bases weighted by the currents (or the voltages) previously calculated. An error estimator is also derived, enabling to calculate the distance between the reduced solution and the FE solution without solving the FE model. The proposed approach has been applied on an industrial application, a resin-impregnated paper bushing, in order to evaluate the accuracy in function of the size of the reduced bases as well as the efficiency in terms of computation time
Generative Diffusion for Regional Surrogate Models From Sea‐Ice Simulations
No full textInternational audienceWe introduce deep generative diffusion for multivariate and regional surrogate modeling learned from sea-ice simulations. Given initial conditions and atmospheric forcings, the model is trained to generate forecasts for a 12-hr lead time from simulations by the state-of-the-art sea-ice model neXtSIM. For our regional model setup, the diffusion model outperforms as ensemble forecast all other tested models, including a free-drift model and a stochastic extension of a deterministic data-driven surrogate model. The diffusion model additionally retains information at all scales, resolving smoothing issues of deterministic models. Furthermore, by generating physically consistent forecasts, previously unseen for such kind of completely data-driven surrogates, the model can almost match the scaling properties of neXtSIM, as similarly deduced from sea-ice observations. With these results, we provide a strong indication that diffusion models can achieve similar results as traditional geophysical models with the significant advantage of being orders of magnitude faster and solely learned from data
Establishing a test-calculation dialogue for shear tests on masonry triplets.
No full textInternational audienceThe development of digital image correlation techniques, particularly in the field of masonry, has allowed for the detection of crack evolution in joints and blocks over time. Recent studies further demonstrate the potential of these techniques for updating model parameters for masonry. Drawing inspiration from practices established in various mechanical domains, this article proposes an experimental-computational dialogue based on digital image correlation. In the initial phase, it serves to design and verify the experimental setup, and subsequently, it helps update and validate the parameters of the proposed model. By implementing this dialogue between experimental tests and numerical simulations, a more profound understanding of the mechanical behavior of masonry triplets should be achieved, thereby enabling improved prediction and interpretation of results