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Impaired unsaturated fatty acid elongation alters mitochondrial function and accelerates metabolic dysfunction-associated steatohepatitis progression
No full textInternational audienceAlthough qualitative and quantitative alterations in liver Polyunsaturated Fatty Acids (PUFAs) are observed in MASH in humans, a causal relationship of PUFAs biosynthetic pathways is yet to be clarified. ELOVL5, an essential enzyme in PUFA elongation regulates hepatic triglyceride metabolism. Nonetheless, the long-term consequences of elongase disruption, particularly in murine models of MASH, have not been evaluated
Nontargeted urine metabolomic analysis of acute intermittent porphyria reveals novel interactions between bile acids and heme metabolism: New promising biomarkers for the long‐term management of patients
No full textInternational audienceAbstract Acute intermittent porphyria is an inherited error of heme synthesis. The underlying pathophysiology, involving mainly hepatic heme synthesis, is poorly understood despite its occurrence, and the severity of acute porphyria attack is still difficult to control. A better understanding of the interactions between heme synthesis and global metabolism would improve the management of AIP patients. An untargeted metabolomic analysis was performed on the urine of 114 patients with overt AIP and asymptomatic carriers using liquid chromatography coupled to high‐resolution mass spectrometry. The collected data were analyzed by combining univariate and multivariate analyses. A total of 239 metabolites were annotated in urine samples by matching chromatographic and mass spectral characteristics with those from our chemical library. Twenty‐six metabolites, including porphyrin precursors, intermediates of tryptophan or glycine metabolism and, unexpectedly, bile acids, showed significant concentration differences between the phenotypic groups. Dysregulation of bile acid metabolism was confirmed by targeted quantitative analysis, which revealed an imbalance in favor of hydrophobic bile acids associated with changes in conjugation, which was more pronounced in the severe phenotype. Using a random forest model, the cholic acid/chenodeoxycholic acid ratio enables the differential classification of severe patients from other patients with a diagnostic accuracy of 84%. The analysis of urine samples revealed significant modifications in the metabolome of AIP patients. Alteration in bile acids provides new insights into the pathophysiology of chronic complications, such as primary liver cancer, while also providing new biomarker candidates for predicting the most severe phenotypes
Exploring Forest Vertical Structure With TomoSense: GEDI and SAR Tomography Insights
No full textInternational audienceExploring vertical forest structures worldwide via remote sensing faces challenges. Recent technologies like waveform light detection and ranging (LiDAR) from NASA’s global ecosystem dynamics investigation (GEDI) and SAR tomography (TomoSAR) from future European Space Agency (ESA) BIOMASS offer promising solutions. This article assesses the performance of spaceborne GEDI and TomoSAR airborne data from an ESA’s TomoSense campaign to highlight the important role of GEDI measurements in BIOMASS algorithm training and establishing precise site-specific processing parameters. Our study in Germany’s Eifel National Park delves into the precision of GEDI and P-band TomoSAR in measuring surface [digital terrain model (DTM)] and vegetation [canopy height model (CHM)] heights. Results demonstrate that GEDI and P-band TomoSAR offer high-resolution and precise surface and vegetation heights and vertical profile measurements. While GEDI relative height (RH) at 98% (RH98) was previously recommended for tropical forests, our findings advocate for RH85 as the optimal metric for temperate forests. The research supports improving the accuracy of both DTM and CHM utilizing GEDI beams with full-power lasers coupled with high sensitivity and signal-to-noise ratio (SNR). Ground elevation measurements are more accurate than canopy height estimates for temperate forests, with DTM RMSE about 2 m and CHM RMSE about 3 m for GEDI and TomoSAR measurements. By analyzing the vertical structure of monthly GEDI data, we note a 1-m shift in the volume peak between GEDI’s leaf-on and leaf-off periods. At the same time, TomoSAR consistently exhibits a lower volume peak by about 2 m compared to GEDI during leaf-on seasons. In conclusion, our research underscores the complementary roles of TomoSAR and GEDI in accurately mapping diverse forest types, thereby bolstering the effectiveness of the BIOMASS mission
Comprehensive assessment of empirical potentials for molecular dynamics simulations of chromia
No full textInternational audienceThe importance of Cr2O3 (chromia) lies in its ability to form protective layers on chromium-rich metallic alloys, which is utilized in the industry for constructing corrosion-resistant austenitic steels and nickel-based alloys. A better understanding of large defects in Cr2O3 is critical because these defects play a crucial role in the growth kinetics of the protective chromia scale, influencing self-diffusion mechanisms, dominant defect types, and diffusion behavior, all of which can influence the performance and durability of chromium-based alloys. This study presents a comprehensive evaluation of various empirical potentials for simulating the properties of Cr2O3 in order to determine the best model to use to simulate extended defects. The assessment is focused on structural, thermodynamic, elastic, point defect, and grain boundary characteristics. An extensive literature review was conducted to compile a dataset for validating the available empirical potentials for Cr2O3 from the literature. The evaluation of these empirical potentials provides valuable insights into their strengths and limitations, enabling researchers to make informed decisions when selecting appropriate potentials for simulating various properties of Cr2O3. This study's findings contribute to the ongoing efforts to improve the accuracy and reliability of computational materials science methods for predicting the behavior of complex oxides
Surface processes and drivers of the snow water stable isotopic composition at Dome C, East Antarctica – a multi-dataset and modelling analysis
No full textInternational audienceWater stable isotope records in polar ice cores have been largely used to reconstruct past local temperatures and other climatic information such as evaporative source region conditions of the precipitation reaching the ice core sites. However, recent studies have identified post-depositional processes taking place at the ice sheet's surface, modifying the original precipitation signal and challenging the traditional interpretation of ice core isotopic records. In this study, we use a combination of existing and new datasets of precipitation, snow surface, and subsurface isotopic compositions (δ18O and deuterium excess (d-excess)); meteorological parameters; ERA5 reanalyses; outputs from the isotope-enabled climate model ECHAM6-wiso; and a simple modelling approach to investigate the transfer function of water stable isotopes from precipitation to the snow surface and subsurface at Dome C in East Antarctica. We first show that water vapour fluxes at the surface of the ice sheet result in a net annual sublimation of snow, from 3.1 to 3.7 mm w.e. yr−1 (water equivalent) between 2018 and 2020, corresponding to 12 % to 15 % of the annual surface mass balance. We find that the precipitation isotopic signal cannot fully explain the mean, nor the variability in the isotopic composition observed in the snow, from annual to intra-monthly timescales. We observe that the mean effect of post-depositional processes over the study period enriches the snow surface in δ18O by 3.0 ‰ to 3.3 ‰ and lowers the snow surface d-excess by 3.4 ‰ to 3.5 ‰ compared to the incoming precipitation isotopic signal. We also show that the mean isotopic composition of the snow subsurface is not statistically different from that of the snow surface, indicating the preservation of the mean isotopic composition of the snow surface in the top centimetres of the snowpack. This study confirms previous findings about the complex interpretation of the water stable isotopic signal in the snow and provides the first quantitative estimation of the impact of post-depositional processes on the snow isotopic composition at Dome C, a crucial step for the accurate interpretation of isotopic records from ice cores
A numerical investigation of heat transfer and pressure drop correlations in Gyroid and Diamond TPMS-based heat exchanger channels
No full textInternational audienceThe recent advances in metal additive manufacturing technologies have made TPMS (triply periodic minimal surface) structures a promising alternative for the design of heat exchangers. This numerical study has characterized the thermohydraulic performance of heat exchange channels based on Schwarz-diamond and Schoen-gyroid TPMS structures. The operating ranges applicable to molten salt reactor intermediate exchangers, which have been little studied in the existing literature, were investigated (2961 < Re < 18254; 3 < Pr < 5; 4 mm < dh < 12 mm). On the basis of these numerical calculations, two correlations were established to characterize the heat transfer coefficient and the friction factor of such flows. In addition to the classical dependencies observed for Reynolds and Prandtl numbers, an additional parameter was identified to characterize heat exchange, thereby accounting effects of wall boundary conditions. This parameter is defined as the ratio between the mean viscosity of the fluid and its viscosity evaluated at wall temperature. Moreover, the expressions obtained to characterize the Nusselt number and the friction factor are independent of the hydraulic diameter of the channels (serving as a characteristic length) and the density (or porosity) of the TPMS structures. Finally, while both structures exhibit comparable thermal performance, the Schwarz-diamond TPMS appears to be the optimal choice for heat exchanger application, as it involves less pressure drop than Schoen-gyroid TPMS
A methodology for assessing environmental impact of building integrated PV in low carbon footprint electricity generation context
No full textInternational 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
Patterns of spin and pseudo-spin symmetries in nuclear relativistic mean-field approaches
No full textInternational audienceThe behavior of spin doublets is known to play a major role in nuclear structure and shell effects. Pseudo-spin doublets are also known to impact the single-particle spectrum. The covariant framework, having these two effects encoded in its approach, is an excellent tool to understand the main mechanism driving theses spin and pseudo-spin symmetries and their breaking. A perturbative expansion of the degeneracy raising related to spin and pseudo-spin effects is proposed, up to second order. It allows to understand the main behavior of spin and pseudo-spin energy doublets, such as their A dependence, as well as their common footing and differences. In the case of the spin symmetry, only the lower component of the Dirac bi-spinor is involved, whereas in the case of the pseudo-spin one, both the upper and lower components are involved. Their interplay with the covariant potentials is also analyzed
