Pour une science de la Transition Énergétique au Service de la Société: Rapport du groupe interdisciplinaire ARPEGES CNRS pour la Transition énergétique

National audienceResearch on the energy transition raises a series of major challenges: it is a problem-oriented field of research (that of decarbonising the energy mix), which must be resolutely ethical and include principles of social and environmental justice from the very beginning... and this despite the problematic nature of the notion of transition which gives a misleading notion of the process that will lead to desired changes - if there are any. Taking this observation as its starting point, this paper sets out a number of avenues for research into key issues. It begins by examining the way in which the energy transition is transforming the interplay between actors in the energy sector and the scales at which decisions are taken and implemented. While inviting to take account of the wide variety of national contexts and levels of development, the article acknowledges the certainties and uncertainties surrounding the composition of the energy mix. It also stresses the importance of taking account of the externalities of technological choices, particularly in environmental terms. This enables us to draw up a research agenda focusing not only on the spatial aspects of transitions, but also on the ways in which economic models need to incorporate new parameters and new constraints. The article also invites to consider how the relationship between energy production and consumption is changing, and how consumption needs to be reduced. In so doing, the article defends the idea that research, which is necessarily interdisciplinary and reflexive, has a strong role to play in basing transition action on scientifically sound findings.La recherche sur la transition énergétique pose plusieurs défis de taille : c’est une recherche orientée problème (celui de la décarbonation du mix énergétique), qui doit être résolument éthique et intégrer dès sa formulation des principes de justice sociale et environnementale... et ce alors même que la notion de transition est problématique en ceci qu’elle donne une fausse idée du processus qui mènera aux changements attendus – si changements il y a. Partant de ce constat, ce Regard dresse des pistes de recherche sur des thématiques saillantes, notamment sur les acteurs et échelles des transitions, les techniques et leurs externalités, les modèles économiques et sociaux qui permettent de guider l’action, les modèles de consommation production et s’interroge sur les rapports entre consommation et production. Il défend in fine l’idée que la recherche, forcément interdisciplinaire et réflexive, a un rôle fort à jouer pour fonder l’action en matière de transition sur des constats scientifiquement fondés

Seismic Velocities of Subducted Serpentinites Through the Lizardite‐Antigorite Transition

International audienceThe mineralogical transition (lizardite to antigorite) occurring in serpentinites dragged down in subduction zones depends on the metamorphic pressure and temperature conditions. The seismic Vp/Vs ratio is useful for distinguishing serpentinites from other mantle rocks. To understand the effects of the metamorphic conditions and the associated microstructural evolution on the serpentinite velocity, we collected seven natural serpentinite rocks with different metamorphic imprints in the Western Alps, from blueschists to eclogite facies conditions. We measured the ultrasonic velocity of the samples at confining pressures up to 70 MPa. The measured seismic Vp and Vs increase with the increasing metamorphic conditions, while the Vp/Vs ratio decreases. The petrological results are used to explain the velocity anisotropy and the weak pressuredependency of velocity. The new Vp/Vs transition trend provides new constraints for tracking the lizardite/ antigorite transition with increasing metamorphic condition from field seismic data and thus studying geodynamic evolution in the subduction environment

Vers des réappropriations protéiformes des villages abandonnés en montagne : analyse à partir du cas du Val Grana dans le Piémont italien

International audienceLe siècle dernier fut marqué par une vague d’abandon de villages sans précédent à la hauteur de l’exode rural qu’ont connu les sociétés d’Europe occidentale. Alors que dans la seconde partie du xxe siècle, les villages abandonnés semblaient sans avenir, condamnés à disparaître, des trajectoires actuelles illustrent des formes de réappropriation. Cet article propose de s’intéresser au Val Grana localisé dans la région du Piémont en Italie

A parabolic Hardy-Hénon equation with quasilinear degenerate diffusion

Local and global well-posedness, along with finite time blow-up, are investigated for the following Hardy-H\'enon equation involving a quasilinear degenerate diffusion and a space-dependent superlinear source featuring a singular potential $\partial_t u=\Delta u^m+|x|^{\sigma}u^p$, t>0, $x\in\mathbb{R}^N$, when m>1, p>1 and $\sigma\in \big(\max\{-2,-N\},0 \big)$. While the superlinear source induces finite time blow-up when $\sigma=0$, whatever the value of p>1, at least for sufficiently large initial conditions, a striking effect of the singular potential $|x|^\sigma$ is the prevention of finite time blow-up for suitably small values of $p$, namely, 1<p≤p_G := [2-\sigma(m-1)]/2. Such a result, as well as the local existence of solutions for p>p_G, is obtained by employing the Caffarelli-Kohn-Nirenberg inequalities. Another interesting feature is that uniqueness and comparison principle hold true for generic non-negative initial conditions when p>p_G, but their validity is restricted to initial conditions which are positive in a neighborhood of $x=0$ when $p\in (1,p_G)$, a range in which non-uniqueness holds true without this positivity condition. Finite time blow-up of any non-trivial, non-negative solution is established when p_G<p≤p_F := m +(\sigma+2)/N. Optimal temporal growth rates are also derived for global solutions when $p\in (1,p_G]$. All the results are sharp with respect to the exponents $(m,p,\sigma)$ and conditions on $u_0$

Operation and performance of the CMS silicon strip tracker with proton-proton collisions at the CERN LHC

International audienceSalient aspects of the commissioning, calibration, and performance of the CMS silicon strip tracker are discussed, drawing on experience during operation with proton-proton collisions delivered by the CERN LHC. The data were obtained with a variety of luminosities. The operating temperature of the strip tracker was changed several times during this period and results are shown as a function of temperature in several cases. Details of the system performance are presented, including occupancy, signal-to-noise ratio, Lorentz angle, and single-hit spatial resolution. Saturation effects in the APV25 readout chip preamplifier observed during early Run 2 are presented, showing the effect on various observables and the subsequent remedy. Studies of radiation effects on the strip tracker are presented both for the optical readout links and the silicon sensors. The observed effects are compared to simulation, where available, and they generally agree well with expectations

A robust neural determination of the source-count distribution of the Fermi-LAT sky at high latitudes

International audienceOver the past 16 years, the Fermi Large Area Telescope (LAT) has significantly advanced our view of the GeV gamma-ray sky, yet several key questions remain - such as the composition of the isotropic gamma-ray background, the origin of the Fermi Bubbles or the potential presence of signatures from exotic physics like dark matter. Addressing these challenges requires sophisticated astrophysical modeling and robust statistical methods capable of handling high-dimensional parameter spaces. In this work, we analyze 14 years of high-latitude ($|b|\geq30^{\circ}$) Fermi-LAT data in the range from 1 to 10 GeV using simulation-based inference (SBI) via neural ratio estimation. This approach allows us to detect individual gamma-ray sources and derive a list of significant gamma-ray emitters containing more than 98% of all sources listed in the Fermi-LAT Fourth Source Catalog (4FGL) with a flux $S>3\times10^{-10}\;\mathrm{cm}^{-2}\,\mathrm{s}^{-1}$ (about a factor of three larger than the flux above which 4FGL is nearly complete), without any non-4FGL source detected in that flux range. Additionally, we reconstruct the source-count distribution in both parametric and non-parametric forms, achieving large agreement with previous literature results as well as those sources detected by our SBI pipeline. We also quantitatively validate our gamma-ray emission simulator via an anomaly detection technique, demonstrating that the synthetic data closely reproduces the complexity of the real observations

Uncertainties in future ecosystem services under land and climate scenarios: The case of erosion in the Alps

International audienceHow ecosystems will provide ecosystem services in the future given uncertain changes in climate and land use is an open question that challenges decision-making on adaptation to climate change. Prospective assessments of ecosystem services should carefully include and communicate the sources of uncertainties that affect the predictions. We used the ecosystem service of soil protection against erosion in the Maurienne Valley (French Alps) as a case study to illustrate how several sources of uncertainties can be integrated into an assessment of future ecosystem service supply. We modeled future erosion rates in the Maurienne Valley for years 2020 and 2085 using the Revised Universal Soil Loss Equation (RUSLE) and six climatic and socioeconomic scenarios. We quantified how the ecosystem service supply will be likely affected by climate and land-use change, separately and jointly. We assessed the effects of different sources of uncertainty on projected erosion rates: scenarios, climate models choice, and methods to parametrize the ecosystem service model. Land-use change increased erosion (+ 3.3 ton.ha-1.yr-1 on average, with significant increases in 81 % of the study site), while climate change contributed to a slight reduction (-0.21 ton.ha-1.yr-1 on average with significant decrease 20 % of the study site). The uncertainty of the ecosystem service model parameterization explained 93 % of the variance in erosion values. Furthermore, uncertainty linked to climate models and future scenarios contributed almost equally to the variability in the direction (positive or negative) of erosion change (41 % and 38 % respectively). The uncertainties surrounding the direction of future changes in ecosystem services come mainly from uncertainties in climate models and future scenarios rather than from uncertainties in the ecosystem service model parameters. Assessing the likelihood of future changes in ecosystem services helps prioritize locations where adaptation solutions are likely to be needed

Induced polarization of clay-rich materials - Part 4 : Water content and temperature effects in bentonites

International audienceDeep Geological Disposals (DGDs) are widely seen to be the best solution to safely contain high-level radioactive wastes. Compacted bentonite and bentonite-sand mixtures are considered as the most appropriate buffers or sealing materials for access drifts, ramps, and shafts due to their favorable physicochemical and hydro-mechanical properties.Bentonite-sand mixtures are expected to swell and seal all voids when in contact with water, forming an impermeable barrier to radioactive elements. The parameters that will most affect the hydraulic performance of these seals are their water content, dry density, water salinity and temperature. Monitoring and assessing these parameters are therefore crucial to confirm that the seals safety functions are fulfilled during the life of a DGD. Induced polarization is a non-intrusive geophysical method able to perform this task. However, its underlying physics for bentonite sand mixtures has not been checked. The complex conductivity spectra of 42 compacted bentonite-sand mixtures were measured in the frequency range 1 Hz -45 kHz in order to develop relationships between in-phase and quadrature conductivities versus water content and saturation, pore water conductivity, bentonite-sand ratio (10% to 90%), temperature (10-60°C), and dry density (0.97 to 1.64 g cm -3 ). We observe that conductivity is mostly dominated by surface conductivity associated with the Stern layer coating the surface of smectite, the main component of bentonite. At a given salinity and temperature, the inphase and quadrature conductivities obey power law relationships with water content and saturation. The in-phase and quadrature conductivities depend on temperature according to a classical linear relationship with the same temperature coefficient. A Stern layer-based model is used to explain the dependence of the complex conductivity with water content, dry density, water salinity and temperature. It could be used to interpret induced polarization field data to monitor the efficiency of the seal of DGD facilities.</p

A methodology for assessing environmental impact of building integrated PV in low carbon footprint electricity generation context

International audienceWith the growing interest in renewable energy to mitigate climate change, photovoltaics are increasingly relevant due to their limited carbon emissions in the use phase. This study focuses on integrating photovoltaic technologies in countries with low-carbon electricity mixes, specifically the cases of France and Norway. It presents a comprehensive methodology assessing the environmental impact of PV technologies and their application in a French and a Norwegian building. The research includes a case study of a single-family house, modeled in TRNSYS for dynamic thermal systems simulation, operating in both locations. The photovoltaic panels' life cycle assessment is conducted using the SimaPro software and a functional unit of 1 kWh from mono-crystalline panels with an expected service life of 25 years. Such analysis aims to evaluate the environmental impact through key performance indicators during the life span of the photovoltaic panel, from cradle to use with a focus on the raw material use, manufacturing processes, transportation, use phase replacements and electricity production. The indicators analysed are global warming potential, cumulative energy demand (non-renewable, fossil), energy payback time and energy return on energy invested. The study also explores the impact of different manufacturing, transportation and installation scenarios of the photovoltaic panels, including a 100% European low carbon footprint electricity mix. In summary, the findings demonstrate that in countries with low-carbon electricity production, the use of photovoltaic panels presents a favorable outcome in terms of global warming potential for the French case (25-38.6 g e/kWh), regardless of their place of manufacturing. For the Norwegian scenarios (spanning 29.5-45.6 g e/kWh), the life cycle benefit in terms of emission reductions is only evident if the panels are locally produced in Europe. This conclusion is based on electricity from the photovoltaic installation modeled to replace the Norwegian production mix of electricity. Thus, the geographical system boundaries in relation to the replaced electricity is an important parameter. Cumulative energy demand (non-renewable, fossil) was found to vary between 0.34 MJ/kWh and 0.44 MJ/kWh, the Norwegian scenarios consistently showing higher numbers than the French. Energy payback times of the mono crystalline photovoltaic panel ranged between 0.75 to 0.97 years depending on the solar potential of the installation place and the scenarios of manufacturing

Study of the operation of Lead-Acid Battery Electrodes under hybrid battery-electrolyzer cycling profiles

International audienceFlooded bead-acid batteries start producing oxygen and hydrogen during the final stages of the charge and the subsequent overcharge. The collection of the produced hydrogen allows increasing the overall energy efficiency and transforms the system into a hybrid device typically referenced as “Battolyzer” (battery-electrolyzer). The present work explores the feasibility of the above approach throughout a detailed study of the long-term ageing process of flooded tubular lead-acid cells subjected to various rates of discharge and overcharge emulating four different scenarios of Battolyzer use, starting from 70% Depth of Discharge cycling to nearly continuous water electrolysis. The combined results from the electrochemical and corrosion studies showed that the Battolyzer cells degradation is driven by the corrosion of the positive current collectors. The progressing of the corrosion process is strongly correlated with the amount of hydrogen produced. The increase of the depth of discharge results in minor decrease of the corrosion current indicating that the battery functionality of the Battolyzer is more advantageous than the continuous water electrolysis