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Effect of Compression on Microstructure and Fluid Transport Properties on an Electrospun Gas Diffusion Layer for PEMFC from 3D High-Resolution Imaging
No full textInternational audienceThe impact of uniaxial compression of an electrospun Gas Diffusion Layer (eGDL) in the proton exchange membrane fuel cell (PEMFC) on microstructure and fluid transport properties (diffusion, tortuosity, permeability) is studied. An advanced high-resolution imaging method involving synchrotron X-ray tomography (XCT) and focus ion beam scanning electron microscopy (FIB-SEM) is employed. A comprehensive comparison between an eGDL and an MPL-free commercial GDL from Sigracet reveals that increased compression accentuates the local minimum porosity of the commercial GDL, due to the presence of binder and hydrophobic treatment. The effective diffusion coefficient of the commercial GDL is also more impacted than that of the eGDL. The resulting mass transport resistance of the commercial GDL increases by up to 11% with the compression rate, while it decreases by up to 30% for the eGDL. The limiting current density obtained in the cell for the eGDL rises by up to 65% with compression, reaching a value only 9% lower than that of the commercial GDL. High compression helps evacuate the liquid phase from the eGDL structure and subsequently reduces the mass transport resistance of the cell assembly
Co-benefits of nature-based solutions exceed the costs of implementation
No full textInternational audienceNature-based solutions offer multiple benefits for ecosystems and societies, supporting their inclusion in policy and practice. This study contributes to closing the gap in quantifying the multiple outcomes of nature-based solutions by assessing 83 nature-based solutions in the Alps. We assessed biodiversity co-benefits and the monetary value of four ecosystem services (heatwave mitigation, flood regulation, climate regulation, and landslide protection) provided by these nature-based solutions to their respective beneficiaries. Forest nature-based solutions showed high values for the four ecosystem services, river and wetland nature-based solutions showed high values for biodiversity, and urban nature-based solutions contributed a lower biodiversity value but were highly cost effective, benefiting a larger population. We estimated a 2.8:1 return on investment benefiting a total of 91,324 persons. We highlight the need for integrating biodiversity and multiple ecosystem services for future nature-based solutions funding and implementation, together with their role to mitigate and adapt to climate change
Landscape archaeology of the Chuchuwayha sacred site (British Colombia, Canada)
No full textInternational audienceNew research is being conducted at the Chuchuwayha sacred site (British Columbia, Canada) at the request of the Upper Similkameen Indian Band, who want to pass on the site's history to future generations. The project's aims were to determine when this site in the glacial Similkameen Valley became accessible to human communities, to reconstruct the formation of the surrounding landscape, and to describe the rock shelter's evolution during the period of human frequentation (rock art). To this end, we combined geomorphological, archaeometric, and geochemical (cosmogenic dating) data to construct a robust chronological framework for the site's evolution and human occupations. Results showed that the Similkameen Valley became ice‐free 18,000 years ago, that the site's morphology was shaped by postglacial processes, and that its general topography had formed around 7000 years ago. The site's morphology—a rock shelter behind a mound of rockfall boulders—created a trap for eolian and autochthonous sediments, which have preserved a record of human occupations. Our multidisciplinary approach also enabled us to determine age ranges for the shelter's paintings, to draw up a new time frame for human occupations of the site, which lies on a traditional Syilx trail, and to relate these occupations to changes in the surrounding landscape
Nonarchimedean and motivic stationary phase formulas
No full textIn this article, for a non degenerate singular phase, we reconsider a stationary phase formula of Heifetz in the nonarchimedean local field setting and give a motivic analogue using Cluckers-Loeser's motivic integration.Dans cet article, pour une phase singulière non dégénérée, on reconsidère la formule de la phase stationnaire dʼHeifetz sur un corps local non archimédien et on donne un analogue motivique en utilisant lʼintégration motivique à la Cluckers-Loeser
Tourisme en montagne : vers un avenir plus durable ?
No full textInternational audienceTourisme en montagne : vers un avenir plus durable ?Le réchauffement climatique en montagne est devenu une réalité. Les sports d’hiver semblent menacés. Mais quelles autres perspectives s’offrent aux territoires de montagne ? Le tourisme culturel peut-il constituer une voie vers un tourisme et durable
Investigating the Impact of Reference Electrodes with Mesh Geometry on Lithium-ion Batteries During Cycling
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Extraction of patterns from images using a model of combined frequency localization spaces
No full textInternational audienceAn algorithm for image decomposition and separation of superposed stationary contributions is proposed. It is based on the concept of sparse-to-sparse domain representation achieved through a relationship between block-based and full-size discrete cosine transform. The L-statistics is adapted to discard nonstationary components from the frequency domain vectors, leaving just a few coefficients associated with stationary pattern. These fewer stationary components are then used under the compressive sensing framework to reconstruct the stationary pattern. The original image is observed as a nonstationary component, acting as a non-desired part at this stage of the procedure, while the stationary pattern is observed as a “desired part” that should be extracted through the reconstruction process. The problem of interest is formulated as underdetermined system of equations resulting from a relationship between the two considered transformation spaces. Once the stationary pattern is reconstructed, it can be removed entirely from the image. Furthermore, it will be shown that the efficiency of pattern extraction cannot be affected, even when image contains additional nonstationary disturbance (here, the noisy image is observed as nonstationary undesired part). The proposed approach is motivated by challenges in removing Moiré-like patterns from images, enabling some interesting applications, including extraction of hidden sinusoidal signatures
Proficiency testing and cross-laboratory method comparison to support standardisation of diatom DNA metabarcoding for freshwater biomonitoring
No full textInternational audienceDNA metabarcoding of benthic diatoms has been successfully applied for biomonitoring at the national scale and can now be considered technically ready for routine application. However, protocols and methods still vary between and within countries, limiting their transferability and the comparability of results. In order to overcome this, routine use of DNA metabarcoding for diatom biomonitoring requires knowledge of the sources of variability introduced by the different steps of the procedure. Here, we examine how elements of routine procedures contribute to variability between European laboratories. A set of four experiments were performed focusing on DNA extraction and PCR amplification steps to evaluate their reproducibility between different laboratories and the variability introduced by different protocols currently applied by the scientific community. Under the guidance of a reference laboratory, 17 participants from 14 countries performed DNA extraction and PCR amplification in parallel, using the same fixed protocol and their own choice of protocol. Experiments were performed by each participant on a set of standardised DNA and biofilm samples (river, lake and mock community) to investigate potential systematic and random errors. Our results revealed the successful transferability of a protocol amongst labs and a highly similar and consistent ecological assessment outcome obtained regardless of the protocols used by each participant. We propose an “all for one but prove them all” strategy, suggesting that distinct protocols can be used within the scientific community, as long as their consistency is be proven by following minimum standard requirements
Study of the Cathode/Electrolyte Interface in an All-Sulfide-Solid-State Battery Using Lithium-Rich Transition Metal Sulfide
No full textInternational audienceAll-solid-state lithium batteries (ASSBs) are among the most promising energy storage technologies, particularly for electric vehicles, due to their enhanced safety. However, performances of these systems are still hindered by interfacial side reactions at electrode/electrolyte interfaces, especially when sulfide electrolytes are used, and additional issues of mechanical nature. In this work, an ASSB system composed of an argyrodite (Li5.7PS4.7Cl1.3) electrolyte, a lithium-rich sulfide cathode (Li1.2Ti0.8S2) operating at moderate voltage, and a lithium metal anode is investigated. The positive electrode/electrolyte interface is scrutinized during several battery cycles using X-ray photoelectron spectroscopy (XPS) via two complementary approaches (ex situ and in situ). We show that both titanium and sulfur species contribute to the electrochemical process without any detectable degradation of the electrolyte after 20 cycles and without the use of any protective coating. These results suggest that the electrochemical performances of such an all-sulfide system are not limited by the cathode/electrolyte reactivity, opening a promising route for the development of specific cathode materials adapted to sulfide electrolytes
Rock Glacier Velocity: An Essential Climate Variable Quantity for Permafrost
No full textInternational audienceAbstract Rock glaciers are distinctive debris landforms found worldwide in cold mountainous regions. They express the long‐term movement of perennially frozen ground. Rock Glacier Velocity (RGV), defined as the time series of the annualized surface velocity of a rock glacier unit or a part of it, has been accepted as an Essential Climate Variable Permafrost Quantity in 2022. This review aims to highlight the relationship between rock glacier velocity and climatic factors, emphasizing the scientific relevance of interannual rock glacier velocity in generating RGV products within the context of observed rock glacier kinematics. Under global warming, rock glacier velocity exhibits widespread (multi‐)decennial acceleration. This acceleration varies regionally in onset timing (from the 1950s to the 2010s) and magnitude (up to a factor of 10), and has been observed in regions such as the European Alps, High Mountain Asia, and the Andes. Despite different local conditions, a synchronous interannual velocity pattern prevails in the European Alps since the 2000s, highlighting the primary influence of climate. A common pattern is the seasonal velocity rhythm, which peaks in late summer to autumn and declines in spring. RGV assesses permafrost evolution via (multi‐)decennial and interannual changes in rock glacier velocity, influenced by air temperature shifts with varying time lags and snow cover effects. Although not integrated into the RGV products, seasonal variations should be examined. This rhythmic behavior is attributed to alterations in pore water pressure influenced by air temperature, snow cover, and ground water conditions