Stronger oceanic CO₂ sink in eddy-resolving simulations of global warming

International audienceKeypoints 1. We conducted an ensemble of idealized ocean simulations under global warming and rising atmospheric CO 2 at coarse and eddy-resolving resolutions 2. CO2 sink is larger by 34% at eddy resolution, due to larger anthropogenic CO 2 uptake combined with weaker climate feedback 3. This ensues from the model's overturning circulation sensitivity to resolution in both historical and future stat

Coupled heat transfers resolution by Monte Carlo in urban geometry including direct and diffuse solar irradiations

International audienceModelling transient combined heat transfer in complex urban geometry is a key step to predict human exposure or energy consumption and to quantify the effect of climate change mitigation and adaptation measures. A difficulty lies in the possibility for a model to scale up and integrate large and complex urban morphology. We develop a probabilistic approach to solve heat transfers with the Monte Carlo method that is insensitive to the complexity of both the urban geometry and the boundary conditions. The integral formulation that includes random walks for each heat transfer mode is presented and the computation of absorbed solar irradiations at walls with the double randomization technique is detailed. Numerical validations are given through comparisons with deterministic method results for single and two-layer slabs, but also a three-dimensional thermal bridge geometry. The developed probabilistic heat transfer model is then used in a demonstration heat wave scenario where are computed: the outdoor mean radiant temperature showing the influence of trees; and the indoor average wall temperature showing the influence of solar gains through windows

The twin blow-up method for Hamilton-Jacobi equations in higher dimension

In this paper, we show how to extend the twin blow-up method recently developped by the authors (Comptes Rendus. Math., 2024), in order to obtain a new comparison principle for an evolution coercive Hamilton-Jacobi equation posed in a domain of an Euclidian space of any dimension and supplemented with a boundary condition. The method allows dealing with the case where tangential variables and the variable corresponding to the normal gradient of the solution are strongly coupled at the boundary. We elaborate on a method introduced by P.-L. Lions and P. Souganidis (Atti Accad. Naz. Lincei, 2017). Their argument relies on a single blow-up procedure after rescaling the semi-solutions to be compared while two simultaneous blow-ups are performed in this work, one for each variable of the classical doubling variable technique. A one-sided Lipschitz estimate satisfied by a combination of the two blow-up limits plays a key role

Orchestrer la politique de la géothermie profonde. Étude à partir du cas de l’exploitation du Dogger parisien (1950-1990)

International audienceLa géothermie du Dogger parisien (1970-mi 1980’s) est érigée en France, voire à l’international, comme un cas exemplaire de développement d’une ressource en géochaleur grâce à un soutien ambitieux des pouvoirs publics. Ce chapitre propose une analyse historique et critique de ces développements. Il s’agit de suivre les temps et les contretemps qui ont marqué cette expérience et qui ont pu en troubler le déploiement et les apprentissages. L’analyse aborde la géothermie profonde comme un cas de système énergétique polyrythmique à la recherche de ses modalités d’orchestration. Elle étudie la mise en place de cette politique et de ses développements locaux à l’aune de la pulsation des fossiles (les chocs et contre-chocs pétroliers) et des fluctuations du milieu géologique. Si cette politique parvient dans les années 70’s à réunir les conditions de son déploiement, elle découvre progressivement les liens qu’elle entretenait avec des mutations économiques et des processus bio-géologiques dont elle sous-estimait l’importance et qui mettent à l’épreuve ses moyens et ses ambitions au cours des années 1980’s. Alors que la France s’apprête à réengager une politique ambitieuse de développement de la géothermie profonde après plusieurs décennies de désinvestissement de ce secteur (PPE, 2019), cette analyse souhaite contribuer à dégager les leçons de cette expérience pionnière

Influenceurs et influencés

International audienceThe question of the propagation of beliefs, which was historically one of the first fields of application of the calculus of probabilities, is addressed here as a tool for analyzing certain aspects of contemporary society. It allows us to link the climate and ecological transition to the influence of certain trends in scientific development, notably biological. This leads us to anticipate, in the form of a hypothesis, certain changes in the relations between the elites and the popular classes.La question de la propagation des croyances, qui fut historiquement un des premiers champs d'application du calcul des probabilités, est abordée ici comme outil d'analyse de certains aspects de la société contemporaine. Elle permet de relier la transition climatique et écologique à des processus d'influence de certaines tendances du développement scientifique notamment biologique. Ceci conduit à anticiper, sous la forme d'une hypothèse, certaines modifications des relations entre les élites et les classes populaires

A framework for integrating indoor air quality into the life cycle assessment of buildings: application to the sizing of ventilation rates

Abstract Purpose Life cycle assessment (LCA) methods are used in building ecodesign, but do not currently consider indoor air quality (IAQ). Since we spend about 85% of our time indoors, and are exposed to potentially hazardous substances, IAQ is of particular importance to human health. Its consideration in LCA could help make adequate design choices (e.g. materials, window layouts or ventilation rates) and reduce the building’s impacts, while avoiding their transfer to other life cycle stages. Methods To address this gap, we propose a methodology combining building LCA and models that encompass the whole pollutant pathway, from emission to quantified impacts on human health using the disability-adjusted life years (DALYs) indicator. We account for volatile organic compounds (VOCs) and fine particulate matter (PM 2.5 ), emitted from materials and indoor activities. An optimal ventilation rate allowing to reduce overall IAQ and LCA impacts (namely from energy for space heating and ventilation fans) is identified. The framework’s applicability is demonstrated on a case study: different rooms having distinct uses, occupancy and activity patterns, lead to different emission rates, impacts and optimal ventilation rates. The influence of heat sources (gas, electricity, wood) on optimal rates is assessed and different window layouts for natural ventilation are tested. Results and discussion PM 2.5 and heating are the main sources of impacts, respectively ranging from 40–94%, and 1–31% of total impacts of each room, which range from 2500 µDALY/year to 14200 µDALY/year. Rooms with higher indoor emissions have higher optimal ventilation rates: 1.2 ACH (air changes per hour), 2.9 ACH and 13.2 ACH in the meeting room, office and kitchen respectively. These rates also vary for different heat sources due to their different IAQ and LCA impacts: 2.7 ACH, 5 ACH and 15 ACH for coal (still a common fuel in rural Asian countries), gas and electric fan heating respectively in the living room. The combined use of double-flow ventilation to lower heating needs and filters that reduce PM 2.5 concentrations leads to a 56% decrease in total impacts of the meeting room. Conclusions This study shows the applicability of the framework to building ecodesign. For instance, distinct optimal ventilation strategies can be devised, depending on the room or building use. The framework can also have a regulatory application in public health, through representative archetypes, by providing general recommendations in the tertiary and residential sectors

Stationary solutions and large time asymptotics to a cross-diffusion-Cahn-Hilliard system

Code can be consulted at \url{https://doi.org/10.5281/zenodo.8117581}.We study some properties of a multi-species degenerate Ginzburg-Landau energy and its relation to a cross-diffusion Cahn-Hilliard system. The model is motivated by multicomponent mixtures where crossdiffusion effects between the different species are taken into account, and where only one species does separate from the others. Using a comparison argument, we obtain strict bounds on the minimizers from which we can derive first-order optimality conditions, revealing a link with the single-species energy, and providing enough regularity to qualify the minimizers as stationary solutions of the evolution system. We also discuss convexity properties of the energy as well as long time asymptotics of the time-dependent problem. Lastly, we introduce a structure-preserving finite volume scheme for the time-dependent problem and present several numerical experiments in one and two spatial dimensions

Does Tax-Benefit Linkage Matter for the Incidence of Payroll Taxes?

We study the earnings responses to six large payroll tax and income tax reforms in France. We find evidence of full pass-through to workers in cases where there is a strong and clear relationship between contributions and expected benefits. By contrast, we find a limited pass-through of employer payroll taxes to workers for reforms with no tax-benefit linkage, and close to full pass-through to workers for income tax reforms nominally incident on employees. Together with a meta-analysis of the literature, we interpret these results as evidence that tax-benefit linkage matters for incidence of payroll taxes, a claim long made by the literature but not backed by empirical evidence to date. Absent tax-benefit linkage, our results suggest that the individual-level incidence of payroll taxes aligns with their statutory incidence

On-demand Autonomous Vehicles in a periurban territory: a Cost Benefit Analysis

International audienceWith the advent of Autonomous Vehicles (AV) technology, extensive researches around the design of on-demand mobility systems powered by such vehicles are performed. An important part of these studies consists in the evaluation of the socio-economic impact of such systems for involved stakeholders. A Cost-Benefit Analysis (CBA) methodology has been proposed in previous work and applied in the context of Berlin. In this work, the appraisal methodology is applied to the introduction of AV services in Paris-Saclay, an intercommunity, south of Paris, simulated through MATSim, an agent-based model. In the study at hand, AVs would be implemented as a feeder service, working as a last-mile, last-mile service to public transit, allowing intermodal trips for travellers. To our knowledge, this study is one of the first CBA analyses of an intermodal AV system relying on an agent-based simulation. The introduction of AV in a periurban environment would generate more pressure on the road network but would improve traveller utilities. Some private car users suffer from longer travel times, resulting in a loss in terms of consumer surplus that could offset the new AV users’ benefits, depending on the consumer surplus estimation method. In this configuration, a Stop-Based routing service have a greater ability to benefit from economies of scale than a Door-to-Door routing. Finally, in a periurban environment where on-demand AVs would be added to reduce the access and egress cost of public transit, the social impact would be nuanced for travellers, but externality would increase. This would benefit some travellers but would also involve additional congestion. In that case, a Stop-Based routing seems less impacting than a Door-to-Door one and it could allow to equip a downsized network

Recent advances in Accelerated Molecular Dynamics Methods: Theory and Applications

International audienceBy providing fully spatio-temporally-resolved atomistic trajectories, Molecular Dynamics (MD) simulations can reveal fundamental characteristics of the thermodynamics and kinetics of materials. While the exponential increase in computing power and the advance of modern data-science techniques since the method was introduced in the late 1950s has dramatically extended the spatial reach of MD, as well as allowed a significant increase in the fidelity of simulations, the accessible simulation timescales have remained limited by the fundamentally sequential nature of the numerical solution of atomic equations of motion, often confining simulations to sub-microsecond timescales even on modern computers. This stringent restriction strongly limits the ability of MD to directly observe the rare, thermally-activated, reactions that underpin vast swaths of chemistry, biology, and materials science. In this contribution, we present a family of methods based on MD – the so-called Accelerated MD (AMD) methods – that were developed to alleviate this limitation. Each AMD method will be introduced, its mathematical justification presented, its recent generalizations discussed, and illustrative applications presented