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Quantitative low-temperature spectral asymptotics for reversible diffusions in temperature-dependent domains
No full textWe derive novel sharp low-temperature asymptotics for the spectrum of the infinitesimal generator of the overdamped Langevin dynamics. The novelty is that this operator is endowed with homogeneous Dirichlet conditions at the boundary of a domain which depends on the temperature. From the point of view of stochastic processes, this gives information on the long-time behavior of the diffusion conditioned on non-absorption at the boundary, in the so-called quasistationary regime. Our results provide sharp estimates of the spectral gap and principal eigenvalue, extending the Eyring--Kramers formula. The phenomenology is richer than in the case of a fixed boundary and gives new insight into the sensitivity of the spectrum with respect to the shape of the domain near critical points of the energy function. Our work is motivated by--and is relevant to--the problem of finding optimal hyperparameters for accelerated molecular dynamics algorithms
The slow and difficult implementation of high speed rail interoperability in Europe: the case of the Atlantic Corridor
No full textInternational audienceThe European Union (EU) has started to create a railway transport network with all the national networks of it member states, in join all them event its differences and building some corridors as priority work. This article presents the current situation of the Atlantic Corridor and the difficulties in integrating the importance of rail interoperability in its development. First, our methodology is presented (section 2). Then, it attempts to define the corridor object and the way in which European governance has set up the TEN-T (section 3) by presenting the concept of interoperability as European standardisation (section 4). It analyses the current problem of implementing all the necessary steps to homogenise the various national networks in order to reach a true European Corridor (section 5). To put all these concepts into perspective, we focus on one of the nine corridors proposed in the TEN-T: the Atlantic Corridor (section 6). Through its history and development, we present the current status, the difficulties and barriers to its effective implementation and the solutions envisaged to enable the construction of the true continental network (section 7)
Les coûts de la restauration des sols urbains
No full textUrbanisation leads to soil compaction, pollution and sealing, degrading soils’ ecological functions and ecosystem services essential for urban resilience, such as flood mitigation and climate regulation. Ecological restoration of urban soils is thus critical for sustainable and climate-adapted cities. However, the economic dimensions of urban soil restoration, particularly its costs, remain unexplored. This study estimates that median urban soil restoration costs range from 50 to 320€/m2for compacted, sealed, or built-up soils, escalating to over 800€/m2 for polluted soils. Urban soil restoration involves a sequence of up to ten steps, combining several techniques, with significant cost variation. Preliminary analysis is the least expensive, while building deconstruction and pollution remediation are the most costly. These new cost estimates will facilitate the prioritization of restoration areas and the development of economic incentives for ecological restoration in cities.These finding also highlight the need for healthy soil preservation, alongside restoration efforts.L'urbanisation entraîne de multiples formes de dégradations des sols -comme la compaction, la pollution et l'imperméabilisation -, ce qui compromet leur capacité à fournir des services écosystémiques essentiels aux milieux urbains, tels que la protection contre les inondations et les vagues de chaleur. La restauration écologique des sols urbains est donc essentielle pour des villes durables et adaptées au changement climatique. Cependant, les dimensions économiques de la restauration des sols urbains, en particulier ses coûts, restent largement inexplorées. A partir d'entretiens avec une cinquantaine d'acteurs du secteurs, cette étude estime que les coûts médians de restauration des sols urbains varient de 50 à 320 €/m2 pour les sols compactés, imperméabilisés ou construits, et atteignent plus de 800 €/m2 pour les sols pollués. La restauration des sols urbains comprend une séquence impliquant jusqu'à dix étapes, combinant plusieurs techniques, avec une variation significative des coûts. Les études préalables sont l'étape la moins coûteuse, tandis que la démolition du bâti et l'assainissement du sol sont les plus onéreuses. Ces nouvelles estimations de coûts aideront notamment à estimer les investissements nécessaires à l'atteinte des objectifs de restauration, à sélectionner des zones de restauration et à développer des incitations économiques pour la restauration écologique dans les villes. Ces résultats soulignent également la nécessité de préserver les sols fonctionnels, parallèlement aux efforts de restauration
L’adaptation des logements au changement climatique : une équation impossible ?
No full textNational audienceThis chapter focuses on the links between characteristics of housing production in France and climate change. Several factors show that the search for an ecodesign of buildings can be counterproductive. Three areas, among others, can illustrate it : (i) The enhancement of an aesthetic image of a city-nature offering a living environment with low energy consumption, at the risk of an architectural and urban universalism. (ii) The difficult adaptation of the action of developers and property owners to many changing regulations. (iii) The energy behaviour of residents that transfers the effects of building improvements to other consumption posts (rebound effect).Ce chapitre porte sur les liens entre les caractéristiques de la production de logements en France et le changement climatique. Plusieurs éléments montrent que la recherche d’une écoconception des bâtiments peut être contre-productive. Trois domaines, entre-autres, peuvent l’illustrer : (i) L’affichage d’une image esthétique d’une ville-nature en offrant un cadre de vie faiblement énergivore, au risque d’un universalisme architectural et urbain. (ii) La difficile adaptation de l’action des promoteurs immobiliers et des maîtres d’ouvrage à des réglementations nombreuses et évolutives. (iii) Le comportement énergétique des habitants qui reporte les effets de l’amélioration des bâtiments vers d’autres postes de consommation (effet rebond)
Analysis of the impact of vertical variation and temporal frequency of the chlorophyll forcing field on modelled temperature in the Mediterranean Sea and potential implications for regional climate projections
No full textInternational audienceThe urgency of climate change calls for the exploration of a variety of multi-forcing scenarios based on Shared Socio-economic Pathways. Ensuring the reliability of the climate projections is therefore an imperative prerequisite. In this paper, we examined the impact of the vertical variability and temporal frequency of the chlorophyll field used to force the NEMOMED12 ocean circulation model in the absence of a biogeochemical model on some key physical characteristics, mainly seawater temperature. Our analysis reveals that forcing by a chlorophyll field that is homogeneous in the vertical direction favours heat accumulation below the Deep Chlorophyll Maximum, leading to a positive temperature bias increasing with time. The extrapolation of the trend determined over the 11-year simulations leads to a bias in temperature as high as +1 • C after 100 years in the intermediate layer. Comparison with in situ data clearly shows that forcing the model with a realistically varying Chl field over the vertical allows the model to better represent temperature and avoid the presence of this bias. Additionally, we find that using the same chlorophyll field saved at different time frequencies, namely daily, monthly and monthly climatology, to force the NEMOMED12 model also creates temperature differences between simulations that increase with time, especially in the intermediate layer. The simulation forced by the daily chlorophyll is warmer in the surface layers than the two others, and we suggest that this is due to the asymmetric role of chlorophyll extremes on heat distribution. Finally, using a monthly chlorophyll climatology to force the NEMOMED12 ocean circulation model seems to be sufficient for physical modelling of the Mediterranean basin if the vertical variability of the Chl field is realistic.</div
Comparative analysis of beam models for vertical rail vibrations under dynamic forces
No full textInternational audienceAn analytical model of the rails of ballasted railway track subjected to the dynamic loads are developed to study forced vertical vibration. In this work, the two rails are modelled as infinite uniform beams posed on a system of periodical supports with the help of Timoshenko beam theory. Besides, each support is considered as a beam posed on a visco-elastic foundation. A linear relation between the sleeper displacement at the crossing-points with two rails and the two reaction forces is established via the Green's function in the frequency domain. In other words, the mechanical behaviour of the support can be written as a spring with an equivalent stiffness. By replacing this relation into the periodically supported rail models, the forced vertical vibrations of two rails are obtained analytically. This analytical model allows calculate rapidly the rail responses in different load, especially in the non-symmetric configuration. In addition, the comparison of rail responses calculated by two beam models are investigated. This work concerns the study of peak
Informing the uninformed, sensitizing the informed: The two sides of consumer environmental awareness
No full textHow do environmental information and awareness interact to improve environmental quality by changing consumer behavior and firm strategies? This article provides theoretical insights using an original differentiation model within a general framework whose specific cases have been studied previously. On the demand side, only informed consumers differentiate brown from green product quality, while uninformed consumers consider these perfect substitutes. Moreover, all informed consumers value the green product and devalue the brown product as a result of an aversion effect but are heterogeneous in their environmental awareness. On the supply side, two firms offer different environmental qualities and compete on price. We consider two types of environmental campaigns: one that increases the number of informed consumers and one that increases the environmental awareness of informed consumers. We show that these campaigns crucially determine three market configurations: segmented; fragmented, with a brown product that appeals to both uninformed consumers and a fraction of informed consumers; and covered. Assuming that the greenest consumer behavior is abstention, we find that both campaigns do not always lead to better environmental quality; that is, a situation in which all consumers are informed and some highly environmentally aware is not necessarily the greenest situation. Depending on the aversion effect, the budget of the campaign organizer, and their relative cost-effectiveness, information and awareness-raising campaigns must be carefully combined to achieve the best possible environmental quality
Limited factors and why optimal growth has led to destruction
No full textWe revisit the classical Ramsey (1928) model with time discounting and a linear production function, explicitly accounting for the inevitable limitations of tangible production factors, which must remain both finite and positive. By employing Pontryagin's (1962) maximum principle, we transform state constraints into control constraints and provide a complete solution for all impatience rates under the linear production framework. While we classify the levels of impatience as established in the existing literature, we show that the behaviors associated with this threshold fundamentally differ when input limitations are considered -a factor previously overlooked. Our analysis extends beyond the literature's traditional focus on agents with mild impatience, encompassing the entire spectrum of impatience. For highly patient agents, the policymaker prioritizes investment over consumption, ensuring the economy reaches its maximum capital level in finite time. Once this level is attained, consumption stabilizes indefinitely, achieving the golden rule trajectory -an outcome previously deemed unattainable under time discounting. Conversely, beyond the classical impatience threshold, capital and consumption decline over time. For agents with extreme impatience, we identify a second threshold where investment ceases entirely, leading to rapid depletion of capital and output
Meteorological Conditions Influence the Migration of a Marine Dune Field in the Southern North Sea
No full textInternational audienceA field of marine dunes has been studied in the Southern Bight of the North Sea. These large dunes, 1–5 m in height and several hundred meters in length, are highly mobile: migration rates of up to 30 m/year have been observed in places. The area is dominated by tides and is characterized by strong currents. Winds are predominantly from the southwest and, to a lesser extent, from the north. A large‐scale 3D numerical model was used to simulate the migration of this dune field over time. It is based on the process‐based openTELEMAC system. The model has been calibrated and validated against in situ bathymetric data and is therefore suited to our objective: to explore the contribution of weather (wind and atmospheric pressure) to the propagation of large marine dunes, in relation to that of tidal currents. To do this, a 4‐month period was simulated, with and without meteorological effects being taken into account in the numerical model. The results highlight the fundamental role of wind conditions in an accurate representation of seabed changes over time. They also show how meteorological events that are different from the prevailing conditions influence the short‐term evolution of the dune field
