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Earth's Energy Imbalance More Than Doubled in Recent Decades
No full textInternational audienceAbstract Global warming results from anthropogenic greenhouse gas emissions which upset the delicate balance between the incoming sunlight, and the reflected and emitted radiation from Earth. The imbalance leads to energy accumulation in the atmosphere, oceans and land, and melting of the cryosphere, resulting in increasing temperatures, rising sea levels, and more extreme weather around the globe. Despite the fundamental role of the energy imbalance in regulating the climate system, as known to humanity for more than two centuries, our capacity to observe it is rapidly deteriorating as satellites are being decommissioned
Bubbles and Crashes with Partially Sophisticated Investors
No full textNational audienceWe analyze bubbles and crashes in a model in which some investors are partially sophisticated. While the expectations of such investors are endogenously determined in equilibrium, these are based on a coarse understanding of the market dynamics. We highlight how such investors may endogenously switch from euphoria to panic and how this may lead to equilibrium bubbles and crashes even in a purely speculative market in which information is complete and it is commonly understood that the bubble cannot grow forever. We also show how this setting can match stylized empirical facts, and we investigate whether bubbles may last longer when the share of fully rational traders increases
Influence of microstructure on the mechanical behavior of a porous rock under triaxial loading conditions
No full textInternational audienceInfluence of microstructure on the mechanical behavior of a porous rock under triaxial loading condition
Mechanical stability of salt caverns under intensive gas storage conditions using LOCAS and DISROC
No full textInternational audienceIn gas storage operations, injection and withdrawal rates can reach high levels to meet increasing demand. Salt caverns intensive exploitation methods introduce significant mechanical challenges, particularly wall spalling. Spalling involves the detachment of plates or blocks from the cavern walls or roof, occurring with minimal volume loss, unlike progressive closure through creep. This study focuses on the detachment of overhanging blocks within specific salt caverns. Wall spalling is of particular concern because it can compromise the structural stability of the caverns, damaging well tubing posing risks to both the safety and the efficiency of storage operations. This article explores the mechanical stability of salt caverns using two finite element software. LOCAS software identifies potential failure zones in continuous media. It helps to examine damage initiation due to salt dilation and the onset of effective tensile stresses at the cavern wall. Dilatancy refers to the volume increase accompanying material deformation under stress, leading to microcracks formation. DISROC software simulates crack initiation and propagation for detailed failure analysis. It employs joint element model to visualize failure mechanisms in the selected cavern blocks. Simulating crack formation and propagation at the joints between blocks, offers a detailed perspective on how failure develop and extend within the cavern structure. These two methods are compared to assess the onset of damage and associated mechanisms in salt caverns under intensive gas storage conditions
Increasing Value of Information Implies Separable Utility
No full textWe consider decision-making under incomplete information about an unknown state of nature. Utility acts (that is, utility vectors indexed by states of nature) and beliefs (probability distributions over the states of nature) are naturally paired by bilinear duality, giving the expected utility. With this pairing, an expected utility maximizer (DM) is characterized by a continuous closed convex comprehensive set of utility acts (c-utility act set). We show that DM M values information more than DM L if and only if the c-utility act set of DM M is obtained by Minkowski addition from the cutility act set of DM L. In the classic setting of decision theory, this is interpreted as the equivalence between more valuable information, on the one hand, and multiplying decisions and adding utility, on the other hand (additively separable utility). We also introduce the algebraic structure of dioid to describe two operations between DMs: union (adding options) and fusion (multiplying options and adding utilities). We say that DM M is more exible by union (resp. by fusion) than DM L if DM M is obtained by union (resp. by fusion) from DM L. Our main result is that DM M values information more than DM L if and only if DM M is more exible by fusion than DM L.We also study when exibility by union can lead to more valuable information.</p
DIM PAMIR Patrimoines matériels -innovation, expérimentation et résilience Charte de réutilisation des données du projet DEGEL
No full textHomogeneous nucleation on Mars. An unexpected process that deciphers mysterious elongated clouds
No full textInternational audienceHomogeneous nucleation has not been considered a possibility in cloud formation processes in the atmosphere of Mars (e.g. Clancy et al., 2017), since Määttänen et al. (2005) made a careful analysis that indicated that extreme supersaturations in the order of 10⁵ were required. Such extreme supersaturations were considered unlikely, especially because the abundant dust in the atmosphere of Mars was expected to deplete water in excess of saturation very quickly by heterogeneous nucleation.The Arsia Mons Elongated Cloud (AMEC) is an eye-catching and mysterious cloud occurring recurrently every morning during the perihelion season over the Arsia Mons volcano on Mars (Hernández-Bernal et al., 2021). It shows a peculiar elongated shape that in only 3 hours expands up to 1800 km from its origin point. Hernández-Bernal et al. (2022) investigated this cloud based on the LMD Mars Mesoscale model (Spiga and Forget, 2009). The tail of the cloud was not reproduced in the model, but a cold pocket with temperatures down to 30K below the environment and supersaturation up to 105 appeared next to Arsia Mons, in a position, altitude, and local time and season coincident with the origin point of the AMEC in observations. In this work we show that these are conditions conducive to homogeneous nucleation, and when we introduce this process as a new cloud formation process in the LMD Mars Mesoscale model, we obtain a good representation of the AMEC, and its long tail.This provides an excellent explanation for this mysterious cloud and shows that homogeneous nucleation is possible and can have significant effects in the atmosphere of Mars, contrary to the widespread assumptions during the last twenty years of Mars exploration. The finding of supersaturations up to 108 in the surveys performed by Fedorova et al. (2020; 2023) observationally supports that these extreme supersaturations can indeed happen in the atmosphere of Mars and homogeneous nucleation could be happening in other clouds. As a first example, we find that the Perihelion Cloud Trails (Clancy et al., 2009; 2021) could be the result of homogeneous nucleation, as our mesoscale model also predicts cold pockets spatially coincident with locations where Clancy et al. observed cloud trails. We intend to explore these and other clouds on Mars possibly involving homogeneous nucleation
Impact of unconstrained parameters on the global dynamics in the “transition region” of Venus atmosphere with the Venus PCM
No full textInternational audienceIn this study which is a follow-up of [1], we use the most recent version of the ground-to-thermosphere VPCM [2] that includes an ionosphere model, ambipolar diffusion and nitrogen chemistry [3]. This tool allows us to investigate and identify in 3D potential mechanisms responsible for the observed variability in Venus’s atmosphere, in the region between 80 km and 130 km altitude. NO and O2(Δg) airglows, are commonly used to shed light on the global dynamics and circulation patterns above 90 km. Their characteristics are a combination of horizontal, vertical transport and chemical net reactions [1,4].We performed sensitivity tests of unconstrained parameters (e.g. gravity waves drag and eddy diffusion vertical profile) to evaluate the impact on the dynamical structures, O number density, temperature and O2(Δg) nightglow characteristics. These results depict possible scenarios useful to interpret future EnVision observations of trace compounds in those mesosphere layers currently poorly constrained, and not fully explained by current 3D models
Understanding the Importance of HDO and D/H on Venus
No full textInternational audienceThe study of HDO and the deuterium/hydrogen (D/H) ratio plays a critical role in reconstructing the past and present climate of Venus. These isotopic tracers offer valuable insights into the planet’s hydrological history, atmospheric escape processes, and potential ancient reservoirs of water. In particular, variations in D/H can shed light on the mechanisms that led Venus to become the hot, arid world we observe today.In this work, we present the first fully three-dimensional simulation of the HDO cycle on Venus, by implementing HDO in both gas and liquid phases within the Venus Planetary Climate Model (VPCM). Our model allows us to explore the spatial and temporal behavior of HDO, and how it interacts with the atmospheric dynamics and cloud chemistry of Venus.One of our key findings is that the vertical distribution of D/H is strongly influenced by processes previously neglected in earlier models. Notably, we show that the presence of deuterated sulfuric acid (HDSO₄) in Venusian clouds can significantly alter the D/H profile and must be taken into account in future studies.We also assess the individual effects of isotope fractionation during three key processes: condensation, molecular diffusion, and photolysis. Our analysis reveals that photolysis-induced fractionation dominates the D/H ratio in the upper atmosphere, driving its increase to approximately 480 × VSMOW (Vienna Standard Mean Ocean Water) at altitudes near 130 km.In addition, we observe notable diurnal variations in the abundances of H₂O, HDO, and D/H in the upper atmosphere, consistent with expectations based on solar-driven atmospheric dynamics.Overall, our results highlight the complex interplay of physical and chemical processes controlling the distribution of water isotopologues on Venus. These findings not only refine our understanding of the present Venusian atmosphere but also provide essential constraints for reconstructing its climatic evolution and water loss history
3D-HEVC Fast CCL Intra Partitioning Algorithm For Low Bitrate Applications
No full textInternational audienceThree-Dimensional High-Efficiency Video Coding (3D-HEVC) has transformed the transmission and storage of stereoscopic and multi-view video content by efficiently encoding texture and depth information. Depth map coding is essential for synthesised views which create the 3D effect. However faces challenges in meeting the growing demand for low-bitrate encoding with faster processing times in applications like cloud streaming,low-latency broadcasting and 3D video editing software. The Coding Tree Unit (CTU) partitioning, crucial for coding efficiency, is particularly impactful for depth maps due to their sharp edges and large homogeneous regions. To address this problem, we propose a Connected Component Labeling (CCL) approach to optimise CTU partitioning for depth map coding in intra-prediction for QP pairs QP 35-42 and 40-45. By leveraging the structural properties of depth maps, CCL enables precise partitioning, thus reducing unnecessary computations and improving compression efficiency. Our method targets applications requiring efficient and fast low-bitrate encoding. Experimental results show a great reduction in encoding time with 70.64% while slightly increasing bitrate by 0.08% and managing minimal quality degradation