HAL Université de Savoie
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Grammatical Path Network: Unveiling Cycles Through Path Computation
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Electrical resistance of a glass-polymer bilayer under medium voltage for photovoltaic modules and related phenomena
No full textInternational audienceThe increase in voltage within photovoltaic networks enables significant reductions in CAPEX (Capital Expenditures) due to the use of smaller cable cross-sections. However, this voltage increase leads to an intensification of PID (Potential Induced Degradation) effects, which are already present at voltages below 1.5 kV. This work focuses on the electrical conduction and field distribution within PV modules through an electrical study of glass-polymer assemblies. Current measurements were carried out in a plane-to-plane configuration (with a guard electrode) on 10 cm² assemblies of a 3 mm thick glass sheet with a 500 µm laminated polymer film (encapsulant). Several assemblies of glasses and polymers were compared at different temperature and relative humidities. Monolayers of glass and polymers were also characterized. Glass-encapsulant assemblies were submitted to HVDC voltages at both polarities. The measured current is different in the two cases. Considering a soda-lime glass and a type of polyolefin, the current is at least four times larger when the glass is connected to the positive polarity than when it is connected to the negative one. Therefore, the two dielectrics do not behave like two resistors in series. In the glass, sodium ions (Na⁺) are known to migrate under the effect of the electric field. They can also enter the polymer and migrate through. If they are numerous enough, these charge migrations may change the field distribution in the dielectric. Tentative explanations of the observed differences in the steady-state current magnitudes are proposed considering these changes in the electric field distribution
Préserver l'invisible. Étude géographique du lynx dans les Alpes françaises : le cas du massif de la Chartreuse
No full textThis dissertation explores the expansion dynamics of the Eurasian lynx in the Chartreuse massif, a key territory in the species’ recolonization within the French Alps. Situated within the field of animal geography, this work examines the ecological, territorial, and social conditions surrounding the lynx’s presence. By analyzing animal mobility, ecological connectivity, and the perceptions and positions of stakeholders, it aims to assess the drivers and barriers to the long-term establishment of the species. This work aims, within a national context, to understand the role of the Chartreuse in the structuring of lynx populations at the Alpine scale and the modalities of its coexistence with the human territory. The results highlight the crucial importance of the massif as both a habitat and a corridor linking to the Jura, despite structural limitations. Although local perceptions are generally positive and the lynx could represent a potential axis for development, its cryptic nature and lack of local conflict mean it remains largely overlooked by political territorial authorities and human territorialities. Characteristic of the Alpine context, the presence of the wolf and the confusion often made between the two large predators, is a factor that could alter the current level of acceptance among local livestock farmers and hunters. This work highlights the importance of adopting a territorial anticipatory approach to the challenges of species conservation.Ce mémoire explore la dynamique d’expansion du lynx boréal dans le massif de la Chartreuse, un territoire clé dans la recolonisation de l’espèce au sein des Alpes françaises. En s’inscrivant dans le champ de la géographie animale, ce travail interroge les conditions écologiques, territoriales et sociales de l’accueil du lynx. À travers une lecture des mobilités animales, de la connectivité écologique, des perceptions et positions des différentes parties prenantes, il s’agit d’évaluer les leviers et obstacles à la présence durable du félin. Ce travail s’attache, dans un contexte national, à comprendre le rôle de la Chartreuse dans la structuration des populations de lynx à l’échelle alpine et les modalités de sa cohabitation avec le territoire. Les résultats démontrent l’importance cruciale que représente le massif en tant que territoire d’accueil et corridor avec le Jura malgré des limites structurelles restreignant l’expansion de l’espèce. Bien que la perception locale soit positive et qu’il puisse représenter un axe de développement économique, le lynx, cryptique et non conflictuel localement reste peu considéré par le territoire politique et les territorialités humaines. Au cœur des Alpes, la présence du loup et l’amalgame avec le félin, tous deux grands prédateurs, est un facteur capable de modifier l’acceptation actuelle par les éleveurs et chasseurs locaux. Ce travail souligne l’importance d’une posture d’anticipation territoriale des enjeux de conservation de l’espèce
Understanding UV-induced degradation mechanisms in SHJ solar cells and their reversibility: The role of hydrogen and doping
No full textInternational audienceSilicon heterojunction solar cells are among the leading PV technologies for high-efficiency modules, but their sensitivity to UV radiation raises durability concerns for outdoor deployment. In this study, we investigate the UV-induced degradation of silicon heterojunction cell precursors by isolating the impact of subcell layers under controlled UVA and UVB irradiations. Our results identify the front hydrogenated amorphous silicon (i/n)a-Si:H layers as key degradation sites, exhibiting significant losses in minority carrier lifetime and iV (>40 mV). Fourier-transform infrared (FTIR) spectroscopy indicated a selective degradation of high stretching mode Si–Hn bonding configurations, creating defects at the c-Si/a-Si:H interface and releasing free hydrogen. These mobile and reactive hydrogen species intensely degrade both passivation mechanisms (chemical and field-effect) by electrically inhibiting dopants via P–H complex formation. Light soaking treatments combining thermal and light activation enable significant passivation and conductivity recovery through hydrogen redistribution, though reversibility diminishes at high UVA doses, indicating a photon-dose-dependent degradation threshold. These findings provide mechanistic insights into UVID pathways and highlight the importance of hydrogen management and UV attenuation strategies for long-term SHJ module reliability
A numerical approach for estimating the probability of earthquake surface rupture
No full textInternational audienceThis study is part of the Probabilistic Fault Displacement Hazard Analysis (PFDHA) framework, which assesses the hazard posed by coseismic surface faulting to infrastructure systems (e.g., lifelines, nuclear power plants, and dams) located on or near an earthquake fault trace. The primary objective of this study is to estimate the probability of surface rupture on the principal fault—the main fault responsible for seismic moment release—based on faulting style, seismogenic thickness, fault geometry, and rupture size (i.e., earthquake magnitude). Current methods for estimating the probability of surface rupture on the principal fault are primarily based on empirical models. These models rely on observations of surface rupture occurrences versus non-occurrences, analyzed through logistic regressions using global or regional datasets of historical crustal earthquakes. However, empirical models have several limitations, including potential biases, catalog incompleteness (i.e., missing surface rupture data), and inconsistencies in fault geometry information and seismotectonic settings (e.g., seismogenic thickness). To overcome these limitations, we propose a numerical approach to compute the Conditional Probability of Surface Rupture (CPSR). This approach incorporates faulting style (normal, reverse, strike-slip), seismogenic thickness, fault dip, magnitude-dependent scaling relations for rupture shape and size, nucleation position within the rupture, and the statistical distribution of hypocenters within the seismogenic crust. These parameters are derived from statistical analyses of global fault rupture databases and earthquake distributions in various non-subduction seismotectonic settings. Our results indicate that CPSR probabilities are strongly influenced by seismogenic thickness and fault dip angle. Moreover, comparison between numerical results and empirical models suggests that CPSR depends on the specific characteristics of the study area. This model can be integrated into PFDHA as an epistemic alternative to purely empirical approaches. Additionally, the numerical code for CPSR computation has been developed and is openly available on GitHub
Using Long‐Term Ecological Datasets to Unravel the Impacts of Short‐Term Meteorological Disturbances on Phytoplankton Communities
No full textInternational audienceExtreme meteorological events such as storms are increasing in frequency and intensity, but our knowledge of their impacts on aquatic ecosystems and emergent system properties is limited. Understanding the ecological impacts of storms on the dynamics of primary producers remains a challenge that needs to be addressed to assess the vulnerability of freshwater ecosystems to extreme weather conditions and climate change. One promising approach to gain insights into storm impacts on phytoplankton community dynamics is to analyse long‐term monitoring datasets. However, such an approach requires disentangling the impacts of short‐term meteorological disturbances from the effects of the seasonal trajectories of meteorological conditions. To this end, we applied boosted regression tree models to phytoplankton time series from eight relatively large lakes on four continents, coupled with a procedure adapted to detect and quantify rare events. Overall, the patterns and potential drivers we identified provide important insights into the responses of lakes to short‐term meteorological events and highlight differences in the response of phytoplankton communities according to lake morphological characteristics. Our results indicated that deepened thermoclines and lake‐specific combinations of drivers describing altered thermal structures caused deviations from the typical trajectories of seasonal phytoplankton succession. For shallow polymictic lakes, shifts in phytoplankton succession also depended on changes in light availability. Overall, our study highlights the value of long‐term monitoring to improve our understanding of phytoplankton sensitivity to short‐term meteorological disturbances
From anarchy to clarity, data pre‐processing and statistical choices influence quantitative environmental DNA ( eDNA ) analyses
No full textInternational audienceEnvironmental DNA (eDNA) analyses hold great potential for increasing species detection sensitivities and estimating species abundances. The rapidly growing user base, continuous method development and optimisation have led to diverse approaches for capturing and analysing eDNA. While significant efforts have been made to standardise field and laboratory protocols, a notable gap remains in understanding the consequences of data pre‐processing and statistical choices on the final results obtained, particularly in quantitative eDNA analyses. These insights are crucial for developing best‐practice guidelines that can harmonise analytical workflows. To address this gap, we conducted an extensive literature review focusing on quantitative species‐specific eDNA studies. We assessed the diversity of data pre‐processing and statistical choices made to evaluate the correlation between eDNA concentrations and species' abundance or biomass, and collected the raw datasets when available. We then applied commonly used data analysis strategies to the datasets to formulate general recommendations for improving the reliability and reproducibility of quantitative eDNA analyses. Our results indicate that, within the available literature, statistical methods are not always clearly described and raw data are rarely made publicly available. Furthermore, the choice of data pre‐processing strategies and statistical tests used to assess quantitative correlations can significantly influence the likelihood of detecting positive correlations and the effect sizes. Overall, we recommend the following: (i) increase transparency in method descriptions and data availability; (ii) assess correlations using mixed‐effect models that can account for data characteristics; (iii) avoid pre‐processing quantitative eDNA data, especially when combined with sub‐optimal statistical tests. Implementing these guidelines should enhance the accessibility and transparency of quantitative eDNA data and ultimately their use for managers and policy makers
Effect of modified electrodes with HER catalysts on electromethanogenesis performances at different potentials
No full textInternational audienc
A deep learning approach for wet snow monitoring in mountainous regions from SAR image time series based on Sentinel-1 and Sentinel-2 snow products
No full textInternational audienceSnow is a vital environmental parameter that holds significance across various disciplines, such as hydrology, meteorology, and natural disaster management. With the increasing accessibility of snow products derived from Synthetic Aperture Radar (SAR) and optical data, like Sentinel-1 wet snow and Sentinel-2 total snow, users have benefited from improved snow mapping and monitoring. However, snow mapping in the mountainous areas remains challenging due to the difficulty of obtaining reliable ground truth data on steep mountain terrain. In this study, we introduce a deep semantic segmentation framework, SACUNet, specifically designed for wet snow detection from SAR image time series in mountainous environments. To address the lack of ground truth, we constructed a high-confidence training and validation database through a rigorous decision-fusion process combining multi-temporal Sentinel-1 wet snow detections with Sentinel-2 total snow maps. We also propose two complementary metrics, the Conditional Agreement Rate (CAR) and the Wet Snow Intersection over Union (WSIoU), to quantify the robustness and consistency of the fusion procedure, therefore ensuring the reliability of training labels in the absence of in-situ data. SACUNet integrates advanced techniques like: (i) Depthwise Separable Convolution, which captures cross-channel dependencies and adapts feature representations, and (ii) Atrous Separable Convolution, which further refines and consolidates the learned features, into the U-Net architecture. The proposed framework has been successfully employed to monitor wet snow in the Mont-Blanc massif, using a time series of 69 Sentinel-1 images acquired from 05 July 2020, to 29 August 2021. SACUNet demonstrates remarkable accuracy in wet snow detection, with an Overall Accuracy of 97%, Precision of 94%, Recall of 97%, Intersection over Union at 92%, and an F1-Score reaching 96%. Validation against meteorological records from four alpine stations confirmed that SACUNet effectively tracks seasonal wet snow dynamics, suppresses false detections during cold periods, and captures realistic high-altitude melt events. Moreover, the model trained in Mont-Blanc generalized successfully to the Vanoise massif, demonstrating its transferability to other alpine regions. Beyond quantitative accuracy, SACUNet enables the spatio-temporal analysis of wet snow evolution, offering insights into its extent, frequency, and seasonal progression across elevation bands. These findings highlight the framework’s potential as an operational tool for large-scale wet snow monitoring in mountainous environments
Perceptions étudiantes de la valeur des enseignements dans un contexte universitaire de déclinaison des connaissances en compétences: Éléments perçus d’une transformation pédagogique et organisationnelle
No full textInternational audienceThe value of knowledge for university students is called into question in a context marked by the transformation of educational provision through a competency-based approach. Indeed, the translation of knowledge into lists of competencies challenges students’ relationship to knowledge. Presented as a pedagogical paradigm requiring the adoption of “new” practices, this approach raises questions about the aims of education in a knowledge- and market-oriented society. An analysis of interviews conducted with undergraduate students highlights the value of knowledge for them, as reflected in their perceptions of teacher-researchers, the courses delivered, and the assessment of knowledge and competencies.La valeur de la connaissance pour les étudiants à l’université pose question dans un contexte de transformation de l’offre de formation en approche par compétences. En effet, la déclinaison des savoirs en liste de compétences interroge le rapport au savoir de l’étudiant. Présentée comme un paradigme pédagogique, nécessitant l’adoption de « nouvelles » pratiques, cette approche interpelle sur les visées de l’éducation dans une société de la connaissance et de marché. L’analyse des entretiens auprès d’étudiants de Licence met en évidence la valeur du savoir pour ces derniers, à travers leurs perceptions des enseignants-chercheurs, des enseignements dispensés et de l’évaluation des connaissances et des compétences