Portail HAL de l'Université du Littoral Côte d'Opale
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Multiscale assessment of the heterogeneity of scutched flax fibers
No full textInternational audienceThe industrial process of extracting flax fibers from a plant ( Linum usitatissimum L.), which involves a combination of retting and scutching, could lead to matter heterogeneity within individual roll bales. Although many studies have investigated the variability of flax fiber compositions and properties as functions of various factors throughout the value chain, no researchers have focused on long-fiber bale heterogeneity and its impact on quality. In this work, five batches were empirically identified based on visual and textural criteria, and were subsequently characterized. The study of their differences and similarities using a combination of physicochemical methods allowed them to be classified into several groups, depending on the criteria measured and the structural scale. Thus, variations in surface composition were related to the presence of external tissue residues and microbial biomass but were not related to the measured polysaccharide composition. Additionally, the technical fibers displayed different mechanical and hygroscopic properties, which could be distributed within 2-4 groups, independent of color and surface composition criteria. This study is a first step in determining fiber heterogeneity, which constitutes a global quality assessment for the further application of flax fibers
: Nighttime Chemistry of Furanic Compounds: Temperature Dependence of Kinetics with NO₃ and Reaction Mechanisms
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Les usages de l'eau à l'ère du dérèglement climatique: principes, conflits, priorités
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Femtosecond Laser Fabrication of Gradient Index Micro-Optics in Chalcogenide Glass
No full textInternational audienceGradient refractive index (GRIN) lenses have been widely used for many applications. However, the traditional manufacturing methods of GRIN lenses are very time-consuming and only suitable for macro-scale operations. In addition, those methods do not have the ability to produce other GRIN optical components with complex refractive index profiles like aspheric or freeform components. We report here an approach to produce GRIN micro-optical components in chalcogenide glass based on a direct laser writing technique. Using this approach, we are able to locally modulate the refractive index of the glass subtrates and create an arbitrary refractive index profile. To prove the flexibility of the method for the production of GRIN micro-optics, we fabricated GRIN micro-lenses and a micro-Fresnel axicon (Fraxicon). The optical properties of micro-lenses can be controlled by varying the writing parameters or the substrate thickness. As a result, the working distance of the micro-lenses can extend from 0 to more than 1000 µm. Also, the micro-Fraxicon exhibits the ability to convert a Gaussian beam to a Bessel-like beam which concentrates the mid-infrared light into an approximately 1200 µm long confinement zone
Supramolecular deep eutectic solvents in extraction processes: a review
No full textInternational audienceAbstract Solvent selection is essential for industrial and analytical extraction processes to ensure environmental safety and neutrality. Nevertheless, toxic and hazardous solvents are often used, due to their cost-effectiveness and ready availability. In green chemistry, alternative solvents such as supramolecular deep eutectic solvents are gaining attention due to their superior performance compared with traditional non-green solvents in certain applications. Here we review the use of supramolecular deep eutectic solvents as a green solvent for analytical and industrial liquid–liquid extraction processes, with focus on physicochemical properties, extraction conditions, the capacity factor, the enrichment factor, fuel desulfurization, extraction of biological active compounds, lignin valorization, and sample preparation
Otolith morphogenesis during the early life stages of fish is temperature‐dependent: Validation by experimental approach applied to European seabass (<i>Dicentrarchus labrax</i>)
No full textInternational audienceOtolith shape is often used as a tool in fish stock identification. The goal of this study was to experimentally assess the influence of changing temperature and ontogenic evolution on the shape component of the European seabass ( Dicentrarchus labrax ) otolith during early‐life stages. A total of 1079 individuals were reared in a water temperature of 16°C up to 232 days post hatch (dph). During this experiment, several specimens were transferred into tanks with a water temperature of 21°C to obtain at the end of this study four different temperature treatments, each with varying ratios between the number of days at 16 and 21°C. To evaluate the otolith morphogenesis, samples were examined at 43, 72, 86 and 100 dph. The evolution of normalized otolith shape from hatching up to 100 dph showed that there were two main successive changes. First, faster growth in the antero‐posterior axis than in the dorso‐ventral axis changed the circular‐shaped otolith from that observed at hatching and, second, increasing the complexity relating to the area between the rostrum and the anti‐rostrum. To test the effect of changing temperature, growing degree‐day was used in three linear mixed‐effect models. Otolith morphogenesis was positively correlated to growing degree‐day, but was also dependent on temperature level. Otolith shape is influenced by environmental factors, particularly temperature, making it an efficient tool for fish stock identification
The Influence of Natural and Anthropogenic Environmental Pressures on European Eel Abundances in French Estuaries
No full textInternational audienceThe aim of this study was to investigate the influence of environmental characteristics and anthropogenic pressures on the abundance of estuarine European eels (Anguilla anguilla L.) during their continental growth phase. European eels were collected with fyke nets from spring to autumn in twenty-nine estuaries along the French English Channel and the Atlantic coast. Eel abundance (catch per unit effort, CPUE) was assessed for all eels and by size class for small (total length < 300 mm), intermediate (≥300 to <450 mm), and large (≥450 mm) eels. The environmental characteristics of the French estuaries were described by twelve descriptor variables, mainly related to hydro-morphological and sedimentary factors. Based on principal component analysis and hierarchical clustering analysis, estuary size was identified as the main explanatory variable and used to compare eel abundance. Eel abundance differed significantly according to estuary size, with higher abundances observed in small estuaries (7.22 to 13.00 ind. fyke nets 24 h−1) compared to large estuaries (0.13 to 0.71 ind. fyke nets 24 h−1). Spatial variation in eel abundance was correlated with differences in estuary size for all eel size classes. The influence of anthropogenic pressures on eel abundance was assessed by nine anthropogenic estuarine pressure indicators. The results indicate that high values of the anthropogenic pressure indicators were correlated with low eel abundance. This study highlights that large French estuaries subject to stronger anthropogenic pressures were less favourable habitats than small estuaries with less anthropogenic pressure
Les contours du délit de pantouflage, forme de prise illégale d’intérêt postérieure à la cessation des fonctions: note sous Cass. Crim., 13 sept. 2023, n° 23-80.347
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Nombres de Carmichael réellement forts
No full textA composite number is called a Carmichael number if for any integer coprime with . D. H. Lehmer considered the class of these numbers such that for any integer coprime with . Here denotes the Jacobi symbol. It turns out and it is shown by Lehmer himself that this class is empty. Here, we replace in Lehmer's congruence by and get a new class which is not empty