HAL-Ecole des Ponts ParisTech
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Accuracy of the Ensemble Kalman Filter in the Near-Linear Setting
No full textThe filtering distribution captures the statistics of the state of a dynamical system from partial and noisy observations. Classical particle filters provably approximate this distribution in quite general settings; however they behave poorly for high dimensional problems, suffering weight collapse. This issue is circumvented by the ensemble Kalman filter which is an equal-weight interacting particle system. However, this finite particle system is only proven to approximate the true filter in the linear Gaussian case. In practice, however, it is applied in much broader settings; as a result, establishing its approximation properties more generally is important. There has been recent progress in the theoretical analysis of the algorithm, establishing stability and error estimates in non-Gaussian settings, but the assumptions on the dynamics and observation models rule out the unbounded vector fields that arise in practice and the analysis applies only to the mean field limit of the ensemble Kalman filter. The present work establishes error bounds between the filtering distribution and the finite particle ensemble Kalman filter when the model exhibits linear growth
A CFD Study on Different Configurations of Spacer-Filled Membrane Distillation System Using OpenFOAM
No full textInternational audienceCircular economy initiatives like the EC funded iWAYS project (grant agreement: 958274) promote the reuse of waste heat in industrial sites. This presents opportunities and challenges for technological adaptation. Membrane distillation (MD) is a thermally driven process for water treatment that can use waste heat. However, effectively treating complex industrial wastewater requires adapting MD units to achieve reliable and efficient performance. Filament spacers within the MD units play a key role in structural maintenance and flow mixing. CFD simulations can help to characterize filament spacer configuration impacts on the hydrodynamic of feed and permeate channels, which affects both trans-membrane temperature gradient and membrane fouling control. Here, we performed a CFD study on a direct contact membrane distillation (DCMD) sub-unit with the goal of evaluating impact on robustness and performance of a set of designed filament spacer configurations. The modeled membrane distillation system has an overall length of 200 mm, width of 10 mm and height of 4.1 mm, containing two layers of filaments in each of the feed and permeate channels. The diameter of the filaments was 1 mm, and they had a 45• degree angle to the flow direction in the channels.Variations of this standard filament configuration were also tested and simulated to optimize their mixing performance.The numerical simulations to approximate in a 3D solution of Navier-stokes equations for steady state conditions were performed using OpenFOAM code. The computational domains were meshed using OpenFOAM snappyHexMesh utility, and finite-volume based simulation relying on the chtMultiRegionFoam solver was executed in parallel over 40 CPU cores. Comparing the CFD analysis of different filaments´ configurations lead to an assessment of an improved spacer structure. The selected configuration is to be 3D printed for laboratory-scale experimental confirmation of the validity of the CFD model and the optimal configuration finding.</div
How pollinator dependence may mediate farmer adoption of pollinator supporting practices and perceptions: a case study from western France
No full textInternational audienceThere is limited knowledge on why farmers adopt pollinator-supporting practices, which is crucial to stimulate their adoption. The dependence of farmers on pollination may influence their perception of pollinators and their willingness to adopt these practices. We addressed why farmers adopt pollinator-supporting practices using a 2011 survey conducted within a cereal plain in western France, where farmers were moderately dependent on pollination for crops like oilseed rape and sunflower. We assessed the factors influencing the adoption of practices to promote pollination, including pollination dependence. We found no effect for pollination dependence. Conversely, we found that farm size, pesticide use, advisory services and the perception of costs decreased the willingness to adopt, while older farmers were more incline to adopt. We also evaluated perceptions related to pollinators: more than 85% of farmers considered bees important for crop production and recognized pesticides as a major cause of decline. We found no effect of pollination dependence on farmers’ perceptions. Compared to similar studies over the past decade, we found similarities, particularly regarding pollinator-related perceptions. Finally, we compared the willingness to adopt in 2011 with the actual adoption in 2024, showing that there has been little change. This raises questions on the pathways to promote the adoption of pollinator-supporting practices to ensure for the future of pollinator conservation
THE AMBIGUOUS ECOLOGIZATION OF FRENCH SPATIAL PLANNING
No full textInternational audienceAt the time of the signing of the European Charter, the European horizon was still a source of hope and fitted well with the French government's efforts to continue providing the region with a "modern" object. Institutional security depended on prosperity, and infrastructure was what marked the modernization of French space. At that time, the economic perspective seemed more central than ever to the development of planning policies in France and Europe. The idea of ecological planning emerged in the mid-2010s. On the one hand, it was intended to preserve the bases of economic activity, on the other, it has been expressed, especially since the Paris COP in 2015, that climate change and its effects due to catastrophic events represented new challenges for security and sovereignty. The figures of water, soil and air protection, decarbonization, sobriety and the circular economy are among the pillars of this new spatial planning discourse. The text attempts to demonstrate that this public policy maintains a stable doctrinal framework, despite the emergence of new concepts and approaches and the variability of political tools, located at different institutional levels but always heavily financed by the central stat
Robust DNNs for power allocation problems in cognitive relay networks
No full textIn this paper, we investigate deep neural network (DNN)-based power allocation policies maximizing the opportunistic rate of a relay-aided cognitive radio network under a quality of service (QoS) constraint protecting the primary transmission. The full-duplex relay performs either Decode-and-Forward (DF) or Compress-and-Forward (CF) and assists the opportunistic communication. The considered primary QoS constraint is expressed in terms of the tolerated primary rate degradation compared to the case of no opportunistic interference. In order to cope with imperfect channel state information (CSI) especially regarding the links to/from the primary network, we propose a self-supervised learning approach that skillfully exploits both perfect and imperfect CSI knowledge within the training phase. Since none of the two relaying schemes is optimal in all system setups (e.g., relative position of the different transmitters, receiver and of the relay), we then propose a novel supervised DNN-based relaying scheme selection. Finally, we extend all these results by proposing a self-supervised DNN-based power allocation policy that is able to generalize over system parameters such as the individual power budget, and the allowed level of primary degradation. Our extensive numerical results on synthetic data demonstrate the effectiveness of our proposed deep learning approaches.</div
Weak anvil cloud area feedback suggested by physical and observational constraints
No full textInternational audienceChanges in anvil clouds with warming remain a leading source of uncertainty in estimating Earth’s climate sensitivity. Here we develop a feedback analysis that decomposes changes in anvil clouds and creates testable hypotheses for refining their proposed uncertainty ranges with observations and theory. To carry out this storyline approach, we derive a simple but quantitative expression for the anvil area feedback, which is shown to depend on the present-day measurable cloud radiative effects and the fractional change in anvil area with warming. Satellite observations suggest an anvil cloud radiative effect of about ±1 W m−2, which requires the fractional change in anvil area to be about 50% K−1 in magnitude to produce a feedback equal to the current best estimate of its lower bound. We use quantitative theory and observations to show that the change in anvil area is closer to about −4% K−1. This constrains the area feedback and leads to our revised estimate of 0.02 ± 0.07 W m−2 K−1, which is many times weaker and more constrained than the overall anvil cloud feedback. In comparison, we show the anvil cloud albedo feedback to be much less constrained, both theoretically and observationally, which poses an obstacle for bounding Earth’s climate sensitivity
Implementing the iCORAL (version 1.0) coral reef CaCO 3 production module in the iLOVECLIM climate model
No full textInternational audienceCoral reef development is intricately linked to both climate and the concentration of atmospheric CO2, specifically through temperature and carbonate chemistry in the upper ocean. In turn, the calcification of corals modifies the concentration of dissolved inorganic carbon (DIC) and total alkalinity in the ocean, impacting air–sea gas exchange, atmospheric CO2 concentration, and ultimately the climate. This feedback between atmospheric conditions and coral biogeochemistry can only be accounted for with a coupled coral–carbon–climate model. Here we present the implementation of a coral reef calcification module into an Earth system model. Simulated coral reef production of the calcium carbonate mineral aragonite depends on photosynthetically active radiation, nutrient concentrations, salinity, temperature, and the aragonite saturation state. An ensemble of 210 parameter perturbation simulations was performed to identify carbonate production parameter values that optimize the simulated distribution of coral reefs and associated carbonate production. The tuned model simulates the presence of coral reefs and regional-to-global carbonate production values in good agreement with data-based estimates, despite some limitations due to the imperfect simulation of climatic and biogeochemical fields driving the simulation of coral reef development. When used in association with methods accounting for bathymetry changes resulting from different sea levels, the model enables assessment of past and future coral–climate coupling on seasonal to millennial timescales, highlighting how climatic trends and variability may affect reef development and the resulting climate–carbon feedback
Modelling the water isotope distribution in the Mediterranean Sea using a high-resolution oceanic model (NEMO-MED12-watiso v1.0): evaluation of model results against in situ observations
No full textInternational audienceStable water isotopes (δ 18 O w and δD w ) have been successfully implemented for the first time in a high-resolution model of the Mediterranean Sea (NEMO-MED12). In this numerical study, model results are compared with available in situ observations to evaluate the model performance of the present-day distribution of stable water isotopes and their relationship with salinity on a subbasin scale. There is good agreement between the modelled and observed distributions of δ 18 O w in the surface water. The model successfully simulates the observed east-west gradient of δ 18 O w characterising surface, intermediate, and deep waters. The results also show good agreement between the simulated δD w and the in situ data. The δD w shows a strong linear relationship with δ 18 O w (r 2 = 0.98) and salinity (r 2 = 0.94) for the whole Mediterranean Sea. Moreover, the modelled relationships between δ 18 O w and salinity agree well with observations, with a weaker slope in the eastern basin than in the western basin. We investigate the relationship of the isotopic signature of the planktonic foraminifera shells (δ 18 O c ) with temperature and the influence of seasonality. Our results suggest a more quantitative use of δ 18 O records, combining reconstruction with modelling approaches
Microplastic assessment in remote and high mountain lakes of Gilgit Baltistan, Pakistan
No full textInternational audienceMicroplastic (MP) pollution is a critical environmental challenge worldwide, however limited research is reported in remote lakes of Pakistan. This study assessed MPs (>5mm) prevalence, distribution and risk perspective in water and sediment of eight remote and high-altitude lakes (> 1,500 meter above sea level) of Gilgit Baltistan, Pakistan. The lakes exhibited an average abundance of 152.6 ± 104.6 to 12.1±7 MPs/kg of dry sediments and 2 ± 0.9 to 17.1 ± 17.2 MPs/L of surface water. MPs <200μm dominated in both matrices. Surface water predominantly contained polyester and polypropylene, while polypropylene and polyethylene dominated in sediments. The gradient of elevation did not show any pronounced impact on the fiber loading or MP count in both matrices. Backward air mass trajectory revealed that air masses vastly travelled from western-Asia, Arabian sea and Bay of Bengal with an average transmission distance of 2,500-3,500 km (500 m a.s.l) that can be a potential deposition MP source in the area. Pollution Load Index of the lakes were >1 exhibiting pollution. All other lakes except Batura and Borith manifested a moderate hazard index. Naltar lake along with aforementioned two lakes also manifested high polymer toxicity. Further research should emphasize understanding the mechanisms and biotic interactions in high-mountain ecosystems
