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Mechanical behavior of Glulam samples subjected to thermal and moisture gradients
No full textArticle soumis en cours de validation. Résumé sous la responsabilité de H. Daher.International audienceGlued laminated timber (Glulam) thanks to its sustainability and structural performance, is increasingly used in construction. However, during fire exposure, the structural integrity of buildings and the safety of occupants may be significantly compromised. One of the current challenges is to better understand the mechanical properties of non-carbonized wooden structural elements subjected to temperatures up to 200- 250°C.Research conducted at CSTB and the Navier laboratory aims to investigate the effects of temperature and moisture content on the mechanical properties of wood. This work presents tests considering thermal and moisture gradients within the wood samples. Additionally, the thermal recovery behavior after exposure to elevated temperatures is investigated to assess the structural performance of timber elements upon cooling. Moreover, the experiments were conducted on samples with three different dimensions (S1, S2 and S3) to evaluate the scale effects on compressive strength
Declining coral calcification to enhance twenty-first-century ocean carbon uptake by gigatonnes
No full textInternational audienceThe sensitivity of coral reefs to climate change is well established. As the oceans warm and acidify, the calcification of coral reefs declines with net calcium carbonate dissolution projected under even moderate emissions trajectories. The impact of this on the global carbon cycle is however yet to be accounted for. Here, we use a synthesis of the sensitivity of coral reef calcification to climate change, alongside reef distribution products to estimate alkalinity and dissolved inorganic carbon fluxes resulting from reductions in reef calcification. Using a global ocean biogeochemical model, we simulate the impact on ocean carbon uptake under different emissions scenarios, accounting for uncertainty in present-day calcification rates. Reductions in net coral reef carbonate production can enhance the ocean carbon sink by up to 1.25 GtCO 2 y −1 by midcentury (0.48 GtCO 2 y −1 median estimate) with cumulative ocean carbon uptake up to 13% greater by 2300 (7% median estimate). Our findings indicate that accounting for the coral reef feedback in projections will increase estimates of the remaining carbon budget associated with global warming thresholds, as well as the likelihood that net zero emissions can be achieved without negative emissions
Ammonium-based polymers as clay swelling inhibitors to improve water resistance of earthen plasters
No full textInternational audienceRaw earth can be a sustainable and low-impact alternative to conven-tional building materials, but its vulnerability to water remains a critical limita-tion, particularly in regions subject to variable climate conditions. Biopolymers have shown promise in improving the mechanical properties of earthen materials, but their impact on water resistance is often inconsistent and poorly understood. In this study, we explored a new approach combining biopolymers with ammo-nium-based compounds to stabilize earthen plasters by inhibiting clay swelling. Using model clay systems (montmorillonite and kaolinite), we evaluated the ef-fects of several amine-based polymers, including polyethyleneimine, chitosan and ε-polylysine. X-ray diffraction (XRD) and Dynamic Vapor Sorption (DVS) measurements revealed that polymers of low molecular mass significantly reduce both crystalline and macroscopic swelling, with oligoethyleneimine proving more effective than its longer-chain counterparts. Similarly, short chains chitosan and ε-polylysine demonstrated effective swelling inhibition and reduced water affinity. This work highlights the potential of using ammonium-based polymers to enhance the durability and long-term stability of earthen constructions subject to environmental moisture variations
Table ronde : Pratiques, expérimentations et Plan Préservation Espaces Naturel
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Oracle-Orgeval, Long-term Research observatory of the critical zone
No full textInternational audienceThe Orgeval Long-term Research Observatory, part of the French critical zone network (OZCAR RI), is a 104 km² agricultural catchment, located 70 km east of Paris, in France. The Orgeval catchment is representative of intensive agriculture (80 % of its total area), the main land use in the Seine river basin. For more than 50 years, both quantity and quality of water are monitored throughout the catchment, from sub-hourly to yearly time scales. This rich dataset allows improving the understanding of critical zone structure and reactivity, in a holistic and interdisciplinary approach. Specific basic and applied research topics relate to extreme hydrological events, agricultural tile drainage, land use planning, and more generally the evolution of agricultural activities facing climate change and urban growth. The Orgeval research observatory is a unique testbed to investigate the functioning and evolution of the Critical Zone. Multidisciplinary approaches are implemented thanks to collaborations between research institutes and universities, combining knowledge and methods from different disciplines, such as hydrology, ecology, biogeochemistry, geophysics and socioeconomics. Created in 1962, the observatory was initially devoted to study floods and weathering research questions. Since then, is evolved towards other societal and environmental topics. Initiated in 1975, lots of monitoring and research was dedicated to diffuse agricultural pollution, especially nitrates, which contributed to a better understanding of the interactions between agricultural activities and surface and groundwater quality. Since the 2000’s, research questions opened to pesticides and biology and biodiversity. The Orgeval observatory is also highly adapted to develop technological innovations, such as in situ biochemical monitoring. A multi-scale observation strategy is implemented in both space and time, ranging from local (with more than 80 monitoring sites) to regional scale, and from time-lapse campaigns to high-frequency measurements (from 1 Hz for geophysics to 1 h or 1 week for chemistry), most often with a long-term approach. The main measurements include: Water level and water discharge : at the outlet of each sub-catchment. groundwater level : in piezometers in the riverbanks and in the aquifers. Precipitation : in addition to Météo-France stations. Main weather variables : air temperature, humidity, and radiation. Soil moisture : from the soil surface to a depth of 1.5 meters. Water quality : dissolved organic and inorganic carbon, dissolved gases (O 2 , CO 2 , Rn), major and trace ions, nutrients, but also water, carbon or strontium stable isotopes. This includes the RiverLab prototype, installed in June 2015 at the outlet of Avenelles sub-catchment for high-frequency measurement (every 30 minutes) of the river's chemical composition. Organic and inorganic contaminants : pesticides but also metals and microplastics in surface and groundwater. Ecotoxicological and ecological indices : ecological assessment. Surface and groundwater temperature : using heat as a tracer of surface-groundwater exchanges. Hydrogeophysics : ERT, GPR, seismic, especially in the riparian areas. Borehole core samples and logging : lithofacies description and characterization. Water level and water discharge : at the outlet of each sub-catchment. groundwater level : in piezometers in the riverbanks and in the aquifers. Precipitation : in addition to Météo-France stations. Main weather variables : air temperature, humidity, and radiation. Soil moisture : from the soil surface to a depth of 1.5 meters. Water quality : dissolved organic and inorganic carbon, dissolved gases (O 2 , CO 2 , Rn), major and trace ions, nutrients, but also water, carbon or strontium stable isotopes. This includes the RiverLab prototype, installed in June 2015 at the outlet of Avenelles sub-catchment for high-frequency measurement (every 30 minutes) of the river's chemical composition. Organic and inorganic contaminants : pesticides but also metals and microplastics in surface and groundwater. Ecotoxicological and ecological indices : ecological assessment. Surface and groundwater temperature : using heat as a tracer of surface-groundwater exchanges. Hydrogeophysics : ERT, GPR, seismic, especially in the riparian areas. Borehole core samples and logging : lithofacies description and characterization. All these data support the development and use of numerical models, for scientific questions but also for environmental impact assessment and territorial management. This catchment is used to develop and/or validate numerical methodologies at the headwater catchment scale, in parallel to larger scale modeling (typically for the Seine river basin
Profit Versus Win Maximization in a League: A Paradox
No full textInternational audienceThe paper studies a very simple game‐theoretical model of sports competition such as the European football leagues. In this oligopoly‐type context, the Cournot‐Nash equilibrium reveals a paradoxical differentiation between clubs: those that include not only profit but also sporting performance in their objectives end up generating more profit than others who purely maximize profit
Convergence of explicit Runge-Kutta discontinuous Galerkin approximations of the first-order form of Maxwell's equations with low regularity solutions
No full textWe establish a convergence result for the approximation of low-regularity solutions to time-dependent PDE systems that have an involution structure similar to Maxwell's equations and the linear wave equations. The approximation is based on an explicit Runge-Kutta (ERK) time-stepping and the discontinuous Galerkin (dG) method with stabilization (so-called upwind fluxes) in space. The regularity setting only assumes that the exact solution and its first time-derivative are in with a Sobolev regularity index ) (here, is the time interval and the space domain), and that its second time-derivative is in . The two main tools for the convergence analysis are a Ritz projection in space that leverages recent convergence results in operator norm for the dG approximation of the steady form of the PDE, and the -stability under a standard CFL condition of three-stage, third-order and four-stage, fourth-order ERK schemes. These latter results are known in the literature, but we provide here a somewhat simpler argumentation to prove the -stability
Ukrainian Voices: Surveying the Spatial and Socio-Economic Trajectories of Ukrainian Refugees across Europe
No full textInternational audienceThe displacement of approximately eight million Ukrainians throughout Europe since February 2022 has had a significant impact on migration governance, and sparked important discussions within migration research. Leveraging novel data from the “Voice of Ukraine” (VOU) survey — a multifaceted longitudinal study of Ukrainian refugees deployed since June 2022 — we examine the migratory and socio-economic trajectories of this community in exile. We posit that the demographic characteristics of Ukrainian refugees, and the asylum and integration policies enacted by European countries of settlement, shape variation in migratory decisions as well as integration outcomes. Our initial analyses of the VOU data show a surprising migratory sedentariness following an initial sorting across Europe. They also reveal a potential association between policies and socio-economic integration tied to housing, education, employment, and personal finances. Our work sets the stage for further exploration of the interplay between refugee attributes and the legislative frameworks of host nations, shedding light on broader dynamics of forced displacement
