Portail HAL de l'Université du Littoral Côte d'Opale
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Ni exsolution from (NiO) (ZrO2)1- for catalytic CO2 valorization
No full textInternational audienceNickel (Ni) exsolution from (NiO)x(ZrO2)1-x is presented here as an innovative strategy towards catalytic CO2 hydrogenation, contrasting with conventional catalyst preparation methods such as incipient wetness impregnation and bringing exsolution beyond the field of perovskites. This approach involves a one-pot synthesis of (NiO)x(ZrO2)1-x through co-precipitation, followed by controlled thermal treatment under reducing conditions. During this reduction process, Ni2+ migrates from the bulk towards the surface of the NiO-ZrO2 matrix, where it is reduced to Ni0, forming well-dispersed and strongly anchored Ni species. For a cost-effective 3.2 wt% NiO catalyst, we investigate Ni exsolution among others through in situ X-ray diffraction. The phenomenon appears to occur at moderate temperatures (500–600 °C), leading to a high Ni dispersion while maintaining a significant specific surface area. The Ni-exsolved catalysts demonstrate superior CO selectivity and stability in the reverse water-gas shift (RWGS) reaction as compared to their Ni-impregnated counterparts. This paves the way for designing new sustainable and cost-effective catalysts for CO2 valorization
L'île à hélice, de l'imaginaire vernien à la conquête des océans
No full textInternational audienceLe roman de Jules Verne L'île à hélice décrit un artefact technique gigantesque, une île artificielle propulsée par la force électrique, abritant uniquement des personnes fortunées produites par le capitalisme américain. L'article s'intéresse à l'imaginaire de l'île flottante dans les mythologies du monde, qui a pu inspirer le récit vernien. Par ailleurs, il développe le concept de mythe techno-gestationnel, c'est-à-dire un imaginaire préparant l'avènement d'une nouvelle technologie en inspirant les esprits, parfois sur plusieurs générations, jusqu'à sa matérialisation sous la forme d'une innovation. En effet, s'il n'existe pas encore d'îles à hélice, des architectes comme Callebaut dessinent des prototypes et des design fictions qui pourraient inspirer dans un avenir plus ou moins proche des entrepreneurs, des investisseurs et ingénieurs cherchant à développer une telle île artificielle. Cette solution pourrait permettre de résoudre des problèmes de surpopulation et des réfugiés climatiques, privés de territoires en raison de la montée des eaux
A 64-modular Hadamard matrix of order 668
No full textInternational audienceSince 2005, the smallest open case in Hadamard's conjecture from 1893 is n = 668. A 32-modular Hadamard matrix of that order has been known since 2001, and the modulus m = 32 has remained the record since then. In this note, we improve it and reach m = 64, by constructing a square matrix H of order n = 668, with coefficients ±1 and whose rows are pairwise orthogonal mod 64
“Expanding the Lactococcal Cell Wall Polysaccharide Paradigm: Novel Structures and Metabolic Pathways in the Emerging Dairy Species <i>Pseudolactococcus laudensis</i> and <i>Pseudolactococcus raffinolactis</i> ”
No full textInternational audienceCell surface-associated polysaccharides, including cell wall polysaccharides (CWPSs), capsular polysaccharides (CPSs), and exopolysaccharides (EPSs), play vital roles in bacterial interactions with their environment, influencing critical aspects of dairy fermentations, such as phage-host dynamics. Pseudolactococcus laudensis and Pseudolactococcus raffinolactis (formerly Lactococcus laudensis and Lactococcus raffinolactis) are emerging dairy-associated species whose CWPSs remain uncharacterized. This study analyzed the complete genomes of 21 P. laudensis and seven P. raffinolactis strains to investigate the genetic diversity underlying CWPS and EPS production. Eight novel cwps genotypes (E-L) were identified, significantly expanding the known diversity within the dairy-associated (pseudo)lactococci. Notably, E and G genotypes diverge from the classical rhamnan-PSP organization, suggesting a CWPS biosynthesis pathway distinct from the dual-chain assembly found in previously studied Lactococcus. Additionally, eps loci were identified in 25 of the 28 strains, uncovering 11 distinct genotypes (I-XI) with evidence of horizontal gene transfer. Their integration into chromosomal genomic islands highlights their mobility and potential role in evolutionary adaptation. Chemical analysis revealed unprecedented CWPS structures. P. laudensis DSM 28961 (type E) presented a 6-deoxy-α-L-talan polysaccharide and a β-(1,4)-galactan, marking the first instance of D-talose replacing rhamnose and the first homopolysaccharide in (pseudo)lactococcal CWPS, respectively. These were structurally independent, confirming a novel CWPS organization and biosynthetic pathway. Conversely, P. raffinolactis DSM 20443 (type I) exhibited a typical rhamnan-PSP structure, composed of a variably glycosylated rhamnan and a glucose-lactose hexapolysaccharide, respectively. This study provides the first resolved CWPS structures for the Pseudolactococcus genus, expanding the understanding of polysaccharide biosynthesis in Lactic Acid Bacteria
Defiwaide : Pertinence de la waide dans le phytomanagement des sols pollués par les ETM ?
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Construction of pre-and post-Lie algebras for stochastic PDEs
No full textWe give and study a construction of pre-Lie algebra structures on rooted trees whose edges and vertices are decorated, with a grafting product acting, through a map , both on the decoration of the created edge and on the vertex that holds the grafting. We show that this construction gives a pre-Lie algebra if, and only if, the map satisfies a commutation relation, called tree-compatibility. We show how to extend this pre-Lie algebra structure to a post-Lie one by a semi-direct extension with another post-Lie algebra. We also define several constructions to obtain tree-compatible maps, and give examples, including a description of all tree-admissible maps when the space of decorations of the vertices is -dimensional and the space of decorations of the edges is finite-dimensional. A particular example of such a construction is used by Bruned, Hairer and Zambotti for the study of stochastic partial differential equations: when no noise is involved, we show that the underlying tree-compatible map is the exponential of a simpler one and deduce an explicit isomorphism with a classical pre-Lie algebra of rooted trees; when a noise is involved, we obtain the underlying tree-compatible map as a direct sum. We also obtain with our formalism the post-Lie algebras described by Bruned and Katsetsiadis
Outrage à magistrat par publications sur une page d'un réseau social
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Is the Gelatinous Matrix of Nassellaria (Radiolaria) a Strategy for Coping With Oligotrophy?
No full textInternational audienceRadiolaria are heterotrophic protists abundant in the world's oceans, playing important roles in biogeochemical cycles. Some host photosynthetic algae, contributing to primary production. Such mixotrophic behaviour is believed to explain their success in oligotrophic waters, notably Collodaria, exclusively mixotrophic radiolarians within a gelatinous matrix. Yet, understanding of Radiolaria ecology is limited to direct observations, as they have so far withstood reproduction in culture and lack genome data. Sampling oligotrophic California Current revealed abundant, rarely observed Nassellaria of the genus Phlebarachnium , characterised to live within a gelatinous matrix. Phylogenetic reconstruction of ribosomal DNA suggests that distantly related Nassellaria lineages independently developed the ability to produce a gelatinous matrix ~150 million years ago. By matching physical samples with genetic data, we identified these rarely observed organisms in global datasets, revealing their affinity for oligotrophic conditions. Co‐occurrence networks showed distinct biogeography patterns for gelatinous matrix‐forming Radiolaria compared to those without. Results suggest the matrix might be an adaptation to oligotrophic waters, increasing the effective volume, favouring prey capture, and creating a larger microenvironment for symbionts, thus promoting ecological success in nutrient‐depleted waters. This study advances our understanding of the adaptation of poorly known eukaryotic groups, specifically when evolution occurs independently across lineages
Multispecies expression of coccolithophore vital effects with changing CO2 concentrations and pH in the laboratory with insights for reconstructing CO2 levels in geological history
No full textInternational audienceThe coccolith sedimentary and micropalaeontological archive has fostered great interest in palaeoclimate applications. Indeed, the geochemistry of coccolith calcite has the potential to reconstruct both palaeo-CO2 concentrations and palaeo-temperature of seawater. Studying coccolith geochemistry aims at better understanding the changes in the vital effect of coccoliths with changes in environmental parameters, especially the carbonate chemistry of seawater. To this aim, we need to deconvolve the biological imprint from the environmental signals recorded in the composition of coccoliths. We have undertaken culture experiments of four coccolithophore strains with various sizes and growth rates, grown under eight CO2/pH conditions typifying the CO2 evolution of the Cenozoic era. We propose an assessment of the expression of the vital effects for Emiliania huxleyi, Gephyrocapsa oceanica, Helicosphaera carteri and Coccolithus braarudii with simultaneous changes in dissolved inorganic carbon (DIC) and pH in the medium resulting in variations in dissolved CO2 (CO2 aq) availability to the cells. We have identified a distinct isotopic response of C. braarudii to pCO2 levels on both sides of the 600 ppmv (pH 7.89) condition. We propose that this discrepancy is the result of a modification of the proton efflux across the plasma membrane through voltage-dependent proton channels. We further show that as the CO2 level rises and pH decreases (from 200 to 500 ppmv and from 8.29 to 7.96 pH units, respectively), a significant increase in δ13Ccoccolith of C. braarudii is expressed, along with a coeval decrease in δ13Corg. The constant physiological parameters of C. braarudii (growth rate, particulate inorganic carbon (PIC) and particulate organic carbon (POC)) across the 200 to 500 ppmv interval support the idea that the change in δ13Ccoccolith is the consequence of a lower fractionation between dissolved CO2 and organic matter. Meanwhile, the small cells of E. huxleyi and G. oceanica are less carbon-limited and do not exhibit any change in their carbon vital effects with changes in carbonate chemistry of the environment across the whole CO2 spectrum. Using this biogeochemical framework, we have established a calibration between CO2 aq concentration and the differential vital effect (Δδ13C) between isotopically invariant small G. oceanica and large coccoliths C. braarudii, whose vital effect is CO2-dependent at low CO2. The CO2–Δδ13C transfer equation allows palaeo-pCO2 reconstructions based on isotope changes explained by physiological processes, especially at low and medium CO2 levels
La Bienfaisance Préjudiciable de l'Employeur
No full textInternational audienceIl est tentant de penser que les actes a priori de bienfaisance d'un employeur sont bénéfiques à son personnel et à son entreprise. Cette présomption mérite pourtant d’être examinée avec un certain recul. Car les meilleures intentions n’échappent pas toujours à la pesanteur terrestre d’une dégénérescence en dommages. Des dommages pour lesquels le bénéficiaire réclamera certainement réparation. Au mépris de la règle morale selon laquelle : «Le bienfait a pour salaire la reconnaissance. Malheur à celui qui rend le mal pour le bien qu’il a reçu» (François-Joseph Amon d’Aby, La mare aux crocodiles, NEA, 1973).L’ouvrage de Clotaire MOULOUNGUI intitulé : «La Bienfaisance Problématique de l’employeur» se penche sur cet intrigant paradoxe. Comment une intention louable – offrir un soutien financier, apporter un appui salvateur, ou instaurer un climat bienveillant, ou encore accorder des privilèges – peut-elle finalement être considérée comme suspecte, et peut-être produire des conséquences contreproductives ? Quelles dynamiques sous-jacentes transforment un acte généreux en une source potentielle de conflits et de ressentiments ?Les réponses à ces questions révèlent la complexité des rapports humains en milieu professionnel. Elles soulignent aussi les responsabilités accrues de l’employeur qui, dans sa quête de bienfaisance, peut involontairement altérer l’équilibre précaire entre équité, justice et reconnaissance individuelle.L’ouvrage de monsieur MOULOUNGUI offre une analyse approfondie et multidimensionnelle de cette problématique. Il s'attache à l’idéal de bienfaisance selon Sénèque. Il conjugue réflexions théoriques et analyses fines de la jurisprudence pour aider les employeurs, les gestionnaires et les professionnels des ressources humaines à discerner les limites et les implications de leurs actes de générosité. Il ne s’agit pas de dissuader de tels gestes, mais de proposer une approche plus nuancée et stratégique. Afin que l’intention de faire le bien puisse effectivement réaliser ce bien.À travers cet ouvrage, les lecteurs sont amenés à percevoir que des conséquences inattendues, et parfois problématiques, peuvent résulter des actions altruistes ou généreuses des employeurs envers leurs employés. Leurs actes de bienfaisances sont parfois une source de responsabilité dont les racines s’abreuvent de la méfiance qu’ils suscitent auprès des employés. Ainsi, un logement ou un transport gracieusement mis à disposition des employés sera pour ces bénéficiaires l’expression d’une stratégie d’accroissement de la productivité, voire l’instrument d’un meilleur contrôle des ressources humaines et de l’outil de production.Dès lors, le patron devrait habituellement répondre (avec peu ou prou de chance d’absolution) de tout dommage résultant d’un fait ou d’un vice du logement ou du transport offert. Il n’échappe, par exemple, pas à sa responsabilité pour les préjudices causés par des conditions défaillantes ; notamment pour un logement devenu insalubre, ou pour un accident lié au moyen de transport octroyé. Même si son intention avait été bienveillante.L’auteur nous convie à admettre sans doute qu’un bienfait ne peut être durablement magnifié en milieu de travail que si la méfiance et la perception suspicieuse des actes de l’employeur changent ; pour laisser place à une compréhension mutuelle lucide des dynamiques humaines et organisationnelles. Au-delà de l’intérêt juridique indéniable, tant d’un point de vue théorique et pratique, l’auteur garantit à son ouvrage des dividendes intellectuels dans le champ de la philosophie, de l’éthique et de la morale.Komlan ALEMAWO,Agrégé des facultés de droit et Doye