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Pore-scale shear distributions in unsaturated porous media and their role in transport and mixing
No full textInternational audienceUnderstanding the probability distributions of flow velocities in heterogeneous porous media is crucial for the study of transport phenomena, as velocity variability controls residence times and dispersion phenomena. However, our knowledge of velocity distributions and their relation to medium structure remains incomplete, especially under partially-saturated conditions, where phase heterogeneity plays a key role in determining the flow structure. In addition, the distributions of shear (the spatial rate of change of velocity transverse to the flow) are essential for understanding the impact of flow on mixing processes, because they represent a key control on solute plume deformation and its interplay with diffusion. Yet, these distributions are far less explored, particularly at the pore scale and under unsaturated conditions. This gap limits our ability to predict the impact of microscopic dynamics on macroscopic plume structure.In this work, we focus on pore-scale velocity and shear distributions in unsaturated systems. Velocity fields are obtained through numerical simulations based on experimental data for the structure of the medium and fluid-phase distributions. The media are quasi-two-dimensional, with cylindrical pillars of variable radii and different correlation structures, and the flow conditions are such that the spatial phase distributions are time-independent. We characterize velocity and shear distributions and use this information to parameterize Continuous Time Random Walk (CTRW) models to predict solute transport and mixing
RQC2 is a major player in peptide release from stalled ribosomes
No full textInternational audienceEukaryotic cells prevent the accumulation of potentially toxic aberrant polypeptides and maintain ribosome availability through surveillance and clearance mechanisms, including the evolutionarily conserved ribosome-associated quality control complex (RQC). RQC pathways have been widely investigated, with the identification of several factors ANKZF1/Vms1p, Ptrh1, and Arb1p involved in release/cleavage of the peptide-tRNA from 60S subunits. We aimed here to identify the genes involved in peptide release from stalled ribosomes. Using a genetic screen, we identified a mutant allele of RQC2 as involved in this process. We present the cryoelectron microscopy (cryo-EM) structure of RQC, which reveals how the F340I mutation affects mutant binding. This altered binding, in turn, disrupts the A-site's ability to bind the tRNA in the presence of Ltn1. These data account for the limitation of C-terminal alanine and threonine (CAT) tailing by the F340I mutation and suggest a model explaining the role of the Rqc2 protein in peptide release
Investigating aquifer properties in the Himalayas through stream flow response to the 2015 Gorkha earthquake
No full textInternational audienceHigh-mountain water storage in the form of ice, snow, and groundwater is crucial for predicting water routing to rivers. While snow and ice volumes are diminishing considerably in mountains as a result of global warming, subsurface storage volumes and transfer mechanisms remain largely elusive.Earthquakes can act as natural experiments by changing aquifer properties and causing a hydrological response in streams. These responses can provide indications of aquifer parameters that are impossible to acquire without intrusive measurements. A range of effects including changes in streamflow, spring discharge and water table were reported. These observations can be explained by mechanisms involving water release from new sources by changing hydrological conductivity, e.g. opening new cracks or un-clogging existing conduits. The way that hydrological systems respond to seismic event can provide valuable insights into the underlying aquifers properties.On the 25th of April 2015, which represents the end of the dry season, when rivers levels are low, a 7.8 Mw earthquake occurred in Gorkha, in central Nepal, rupturing a 140 km segment propagating from west to south-east. We observed that rivers draining the rupture area responded by a marked increase in rivers discharge. We analyzed 26 river gauging stations covering the wider rupture area. Stations within the rupture area recorded an instantaneous rise in river water level, lasting for 1-2 days after the earthquake. Stations outside the rupture area also exhibited delayed but noticeable responses, surprisingly only in the east. The 16 stations showing a marked stream flow response are spread over an area of 90,000 km², from middle to eastern Nepal.To identify the factors influencing the patterns of response, we compared disturbed hydrographs with precipitation data, watershed characteristics, and changes in boundary conditions. For watersheds located at the western end of the rupture zone, the co-seismic response is transient while at the eastern end the response is sustained until the onset of monsoon. The time delay recorded at the outlets of large watersheds corresponds to the time required for water to travel from the seismic affected areas to the outlet.To estimate the additional groundwater release induced by the earthquake, we applied a low-pass filter to the hydrographs. Then, we analyzed the recession curve parameters before and after the earthquake to investigate the modification of the aquifer permeability by the event.During the dry season, rivers are predominantly groundwater fed. In the absence of recharge from precipitation, the volume of groundwater stored in aquifers decreases, leading to a decline in water table levels. Since the event occurred at the end of this period, the excess of water likely source from deep groundwater. Our estimates indicate that the event released around 1.3-1.5 km3 of additional groundwater. Furthermore, the sustained rise in water levels following (and induced by) the earthquake, suggests the presence of an important deep groundwater reservoir in the Himalayan mountain range.Earthquakes provide valuable opportunities to investigate the dynamics of fractured bedrock aquifers in high mountains such as the Himalayas
Impact of river incision on lower crustal flow: insights from thermo-mechanical models
No full textInternational audienceCrustal deformation is highly influenced by surface processes, such as erosion and sedimentation, particularly in tectonically active regions. While these processes have been intensively studied in large-scale erosive settings and tectonically active areas, the specific effect of river incision on valley morphology and crustal deformation remains poorly constrained. In this study, we show that valley incision can have a significant impact on the morphological and tectonic evolution of orogenic systems. Using a two-dimensional thermo-mechanical model and inspired by the case study of the Nanga Parbat Haramosh Massif (NPHM), we investigated the effects of varying incision rates and topographic diffusion coefficient on crustal deformation in the absence of imposed tectonic boundary forces. Our results indicate that with the lowest incision rates (between 10 and 70mm.yr-1), surface processes predominantly govern the morphology of the valley, with limited tectonic feedback. Conversely, at higher incision rates (over 90mm.yr-1), the tectonic response becomes increasingly significant, impacting the long-term regional deformation and the morphology of the valley. Over a timescale of 10 million years, this dynamic interplay can lead to substantial crustal deformation involving the exhumation of the lower crust (at rates up to 3mm.yr-1) . Our reference model is in very good agreement with natural observations from the NPHM, suggesting that valley incision alone can drive significant crustal deformation, even in the absence of far field stresses (shortening). These results offer valuable insights into the interplay between surface processes and crustal deformation, highlighting the critical role of river incision in shaping mountainous landscapes and promoting the exhumation of deep crustal materials in actively deforming orogenic areas
Secondary progression activity monitoring in MS despite an early highly active treatment the SPAM study
No full textInternational audienceBackground: Real-world data suggest that the early use of highly active therapies (HAT) may reduce the risk of transition to secondary progressive MS (SPMS). However, current knowledge about predictive factors of outcomes needs to be improved. The primary objective of this study was to determine factors associated with the occurrence of SPMS in patients treated early after MS onset with an HAT.Methods: Retrospective, multicentric study based on the French MS database. Patients who initiated a HAT within 5 years after MS onset, EDSS ⩽4, and had a follow-up >5 years were included. The association of each covariate at baseline with time to the occurrence of SPMS was quantified by hazard ratios (HRs) in unadjusted and adjusted Cox proportional hazards models.Results: Two thousand two hundred and thirty-seven patients were included in the analysis: mean age 31.6 years, female/male sex ratio 2.3, and median EDSS 2.0. The estimated probability of reaching SPMS, progression independent of relapse activity (PIRA) and progression independent of activity (PIA) at 10 years was 8%, 22%, and 11%, respectively. After adjustment, we found that female patients (HR 0.64, p = 0.036) had a lower risk of developing SPMS. Older age, EDSS >0 (HR 7.44, p < 0.001), and oral versus intravenous HAT (HR 1.97, p = 0.003) were significantly associated with an increased SPMS risk. Early PIRA and PIA predicted conversion to SPMS.Conclusions: Early HAT use resulted in a low risk of developing SPMS over 10 years. Introducing the HAT before any residual disability was associated with a lower risk of progression
Heat flux evaluation based on active fiber optic distributed temperature sensing tests in southwestern Yukon, Canada
No full textInternational audienceGeothermal energy could decrease remote regions dependence on diesel by offering an alternative baseload energy. However, the geothermal exploration risk is high in remote regions due to limited temperature and ground thermal conductivity data, and resultant heat flux evaluations. Thermal response tests are commonly used in the heat pump industry to evaluate the effective thermal conductivity, but these tests are typically performed in shallow wells (< 200 m), assume the effective thermal conductivity to be purely due to conduction and neglect the influence of groundwater flow. Herein, fibre-optic distributed temperature sensing was used during active thermal response tests to produce a high-resolution in-situ effective thermal conductivity profile. The high-resolution profiles allow conduction-dominated segments to be isolated based on the temperature and effective thermal conductivity profiles. This method was applied to two boreholes in southwestern Yukon on the traditional territory of Kluane First Nation (KFN-L: 387 m and DRGW: 220 m). The heat flux was evaluated based on conductive segments of the temperature and thermal conductivity profiles. The temperature profile was corrected for topography and paleoclimate effects, and the internal heat generation was also considered. This resulted in heat flux estimation of 89 mW m -2 and 99 mWm -2 at KFN-L and DRGW, respectively. These values decrease exploration uncertainty around Burwash Landing, Yukon, where data scarcity is a challenge to geothermal exploration. This method could be applied in diverse geological settings to confidently estimate local terrestrial heat flux in pre-existing boreholes
Experimental evidence of quantum interferences in CO-H rotational energy transfer at room temperature
No full textInternational audienceUsing time-resolved infrared-vacuum-ultraviolet double-resonance spectroscopy, experimental room temperature measurements of state-to-state rate coefficients for rotational energy transfer within the X vibrational state of CO due to H collisions have been compared to accurate 4-D close-coupling quantum calculations. Theoretically predicted quantum interferences in the CO-H collisional system are experimentally observed for the first time at room temperature, and excellent agreement between theory and experiment is observed. These results provide a valuable benchmark for validating the anisotropic part of the potential energy surface, thereby supporting the theoretical modeling of CO emission in warm astrophysical environments such as photodissociation regions
The Power Index Curse Strikes Again: Over-representation of Major Cities in French Inter-communal Structures
No full textIn 2020, the issue of improving local collaboration between French municipalities reached a milestone. From January of this year, every municipality would, for the first time, belong to one of 1,254 French Inter-municipality structures. This achievement was accompanied by precise rules describing the distribution of seats among the different cities of the inter-municipal councils that govern each structure. However, the fairness of seat allocations proposed by French law, based on principles of proportionality can be questioned. Indeed, since the pioneering contributions of Penrose (1946) and Banzhaf (1965), the theory of power indices has warned us that representing cities in proportion to their population would give too much power to major cities. We assess whether this phenomenon can also be observed in France since 2020, using a new database that accurately reports the number of seats per city. Though we encounter a large variety of situations across the country, our results show that the provisions in the seat allocation rules often lead to the over-representation of major cities. Alternative allocation rules are presented to reduce these inequalities in representation.</div
Géohistoire de la forêt domaniale de Bellême, Orne, Normandie.: Prospection thématique, code opération : 165109 - Rapport annuel 2024
No full textClimate changes at the Jurassic/Cretaceous transition vs. supra-regional oceanographic processes: Insights from the Vocontian Basin (Clue de Taulanne section, SE France)
No full textInternational audienceHerein are presented the results of a detailed stratigraphic calibration and palaeoenvironmental studies performed in the upper Tithonian–lowermost Valanginian deposits of the Vocontian Basin (SE France), with special attention being paid to the Clue de Taulanne section. Integration of calpionellid biostratigraphy, magnetostratigraphy and δ13C stratigraphy, supplemented with regional correlations, enables precise dating of the latest Jurassic–earliest Cretaceous climate and oceanographic perturbations. These are recognized based on sedimentologic (microfacies analyses, clay mineralogy) and geochemical (elemental geochemistry, TOC) investigations. This research confirms that the latest Tithonian–early Berriasian (Tintinnopsella remanei–mid Calpionella elliptica subzones) was marked by a phase of dry climate and elevated burial of micronutrients. Furthermore, the uppermost Tithonian (Remanei/Massutiniana subzonal transition) documents an important palaeoecologic turnover, that is the disappearance of Saccocoma and a switch from radiolarian- to calpionellid-dominated microfacies. The subsequent shift towards humid palaeoclimate conditions at the early/late Berriasian transition was relatively rapid (~ 0.5 Ma), as evidenced by a significant increase in kaolinite proportion within the mid-Elliptica Subzone (mid M17r magnetozone; latest early Berriasian). Importantly, this major climate change was associated with lowered burial of nutrient-type elements, relative to lithogenic fraction. Collected data not only evidence the relation between the latest Jurassic–earliest Cretaceous climate and oceanographic processes, but also document biotic response to these perturbations. The regional significance of the above findings is evidenced by correlations between different sedimentary zones of the Vocontian Basin (Clue de Taulanne, Berrias, Montclus and Tré Maroua sections), while supra-regional context is provided by comparison with other Alpine Atlantic successions: Transdanubian Range and the Slovenian Basin