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Impact of Alkaline Perturbations on the Self-Sealing Properties of Callovo-Oxfordian Claystone
No full textInternational audienceThis study investigates the influence of alkaline chemical perturbations on the self-sealing behavior of Callovo-Oxfordian (COx) claystone, a candidate host rock for deep geological disposal of radioactive waste in France. X-ray micro-computed tomography (µCT) was used to monitor the evolution of artificially induced fractures under two saturation conditions: synthetic porewater (pH 7.5) and a hyper-alkaline solution (pH 13.5). The results highlight a strong self-sealing capacity under neutral conditions, with significant crack closure observed within the first few days. In contrast, alkaline conditions substantially slowed the sealing process. These findings underline the importance of accounting for chemical interactions between engineered barriers and host rock in the safety assessment of radioactive waste repositories
Behaviour of carbonate reservoir rocks under hydrostatic cyclic loading for hydrogen storage application
No full textInternational audienceBehaviour of carbonate reservoir rocks under hydrostatic cyclic loading for hydrogen storage applicatio
Brownian continuum random tree conditioned to be large
No full textWe consider a Feller diffusion (Zs, s ≥ 0) (with diffusion coefficient √ 2β and drift θ ∈ R) that we condition on {Zt = at}, where at is a deterministic function, and we study the limit in distribution of the conditioned process and of its genealogical tree as t → +∞. When at does not increase too rapidly, we recover the standard size-biased process (and the associated genealogical tree given by the Kesten's tree). When at behaves as αβ 2 t 2 when θ = 0 or as α e 2β|θ|t when θ = 0, we obtain a new process whose distribution is described by a Girsanov transformation and equivalently by a SDE with a Poissonian immigration. Its associated genealogical tree is described by an infinite discrete skeleton (which does not satisfy the branching property) decorated with Brownian continuum random trees given by a Poisson point measure. As a by-product of this study, we introduce several sets of trees endowed with a Gromovtype distance which are of independent interest and which allow here to define in a formal and measurable way the decoration of a backbone with a family of continuum random trees
The carbon perception gap in actual and ideal carbon footprints across wealth groups
No full textInternational audienceCarbon inequality is gaining attention in public discussions surrounding equitable climate policies. It commonly refers to the unequal distribution of individual greenhouse gas emissions, with wealthier individuals contributing disproportionately higher emissions. Little is known about how people perceive the actual carbon footprint distribution across wealth groups and what they would desire as an ideal distribution. Survey data from Germany show awareness of carbon inequality, with respondents recognizing that wealthier individuals emit disproportionately more. Yet, with surprising consensus, all groups, including the wealthy, desired an inverse ideal distribution, with the wealthy having disproportionately smaller carbon footprints. Nonetheless, most perceived their own carbon footprint as far better compared to others in society and within their wealth group. Here, we show a carbon perception gap, particularly among the wealthiest: Collectively, people acknowledge the presence of carbon inequality and desire a more equitable distribution, yet often perceive themselves as already contributing more than others
Dual structure-aware image filterings for semi-supervised medical image segmentation
No full textInternational audienceSemi-supervised image segmentation has attracted great attention recently. The keyis how to leverage unlabeled images in the training process. Most methods maintain consistent predictions of the unlabeled images under variations (e.g., adding noise/perturbations, or creating alternative versions) in the image and/or model level. In most image-level variation, medical images often have prior structure information,which has not been well explored. In this paper, we propose novel dual structure-aware image filterings (DSAIF) as the image-level variations for semi-supervised medical image segmentation. Motivated by connected filtering that simplifies image via filtering in structure-aware tree-based image representation, we resort to the dual contrast invariant Max-tree and Min-tree representation. Specifically, we propose a novel connected filtering that removes topologically equivalent nodes (i.e., connected components) having no siblings in the Max/Min-tree. This results in two filtered images preserving topologically critical structure. Applying the proposed DSAIF to mutually supervised networks decreases the consensus of their erroneous predictions on unlabeled images. This helps to alleviate the confirmation bias issue of overfitting to noisy pseudo labels of unlabeled images, and thus effectively improves the segmentation performance. Extensive experimental results on three benchmark datasets demonstrate that the proposed method significantly/consistently outperforms some state-of-the-art methods. Source code is publicly available at https://github.com/GuGuLL123/DSAIF-SEMI
Prudent aggregation of quasi-hyperbolic experts
No full textInternational audienceImagine a cohort of economic experts appraising long-term projects through the quasi-hyperbolic discounting criterion. The parameters (long-run and short-run discount rates) used by each expert may differ, which implies different policy recommendations. Subsequently, a decision maker is faced with the task of selecting an efficient aggregation from these varied opinions. This paper proposes a solution to reconcile these conflicting recommendations, taking into account the decision maker’s adoption of a “prudent” behavior
The Role of Freight Transportation in Smart Cities for Advancing the Clean Energy Transition
No full textInternational audienceThis chapter explores the significant impact of logistics and freight transportation on cities, the environment, and the energy transition. Freight and logistics contribute substantially to greenhouse gas emissions, accounting for 8–10% of worldwide emissions, with freight representing 80% of that share and warehousing 20%. In cities like Paris, urban freight generates a considerable share of CO2, NOx, and particulate matter emissions. The chapter also highlights the specific challenges posed by e-commerce and the discussions over its carbon footprint: While reducing total vehicle-kilometers made for shopping in an urban area, e-commerce deliveries contribute to carbon emissions through packaging, last mile delivery, and the high use of computers. The chapter emphasizes the importance of decarbonizing urban freight vehicles and optimizing the location of urban warehouses to reduce emissions. It discusses the role of urban planning, curb management, and technological innovation, such as electric vehicles and logistics micromobility (e.g., bikes and mopeds), in reducing environmental impact. The issue of data collection and the need for better methods to model freight traffic and emissions is discussed. The chapter presents various strategies for green freight solutions and outlines the potential and challenges for transitioning freight transportation to clean energy in smart cities. Examples from cities like Paris, New York, Rotterdam, and global logistics companies like DHL illustrate the complexities and opportunities in this transition
Numerical analysis of evaporation reduction in floating photovoltaic power plants: influence of design parameters
No full textInternational audienceEvaporation reduction is one of the advantages provided by floating photovoltaic (FPV) power plants. However, few studies have yet been carried out to understand how to optimise the layout of FPV power plants in order to provide better water management. Indeed, the interaction between atmospheric conditions, water bodies, and the FPV plant creates a dynamic system that is challenging to study and accurately model. This paper investigates the impact on evaporation of various characteristics of FPV plants, such as float technology, plant positioning and orientation, distribution, and coverage ratio. This study was performed using Computational Fluid Dynamics (CFD) of the surrounding atmosphere, with the impact of the FPV plant modelled using specific boundary conditions to reduce computational costs. The numerical results show that the coverage ratio is the most important factor in reducing evaporation. Full coverage could reduce evaporation by 52.8% for a plant with a large footprint on the water and by 43.4% for a plant with a smaller footprint. Other parameters have only a moderate impact, allowing the fine-tuning of evaporation reduction. The optimal configuration would involve covering the entire water body with a single large water footprint island positioned downwind of the prevailing transversal winds. This setup significantly reduces evaporation, thereby enhancing water conservation and making an FPV power plant a valuable tool in sustainable water management
The clean development mechanism
No full textInternational audienceThe Clean Development Mechanism is one of three flexible mechanisms included in the Kyoto Protocol. It enables Annex I countries to finance emission reductions in developing (non-Annex I) countries and use the credits thus obtained to meet their quantified emission reduction commitments under the Kyoto Protocol. The CDM had two objectives: to reduce the costs of compliance of the Annex I countries’ emission reduction commitments, and to assist developing countries in achieving sustainable development and in contributing to the ultimate objective of the UNFCCC. The major part of certified emission reductions (CERs) comes from renewable energy investments, reduction of non-CO2 greenhouse gases (HFCs, PFCs and N2O), and energy efficiency projects. The geographical distribution of projects and emission reductions is concentrated in a few countries: China, India, Brazil, and Mexico. A substantial amount of CERs was created under the CDM, but the uneven geographical distribution of projects and the lack of consistent control of projects’ contribution to sustainable development have been arguments to contend that the CDM did not fulfil its initial objectives. The restriction by the EU in 2013 to use CERs in the EU-ETS brought down prices and the market for CERs has not recovered since. The CDM was discontinued as of 30 June 2022 and requests for exemptions were considered on a case-specific basis. Nevertheless, the CDM has continued to function while parties are waiting for the flexible mechanisms created in the Paris Agreement of 2015 to become operational, in particular the Sustainable Development Mechanism of Article 6.4 which is similar to the CDM in its objectives
