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Chlorométhylation directe de liaisons C(sp<sup>3</sup>)-H par activation du CH₂Cl₂ à l'aide d'un plasma non thermique
No full textInternational audienceNon-thermal plasma has been implemented for chemical activation of CH₂Cl₂ in a continuous flow gas-liquid system operating at ambient temperature and pressure. In this study, we present a direct and catalyst-free approach for the chloromethylation of saturated hydrocarbons. The reaction test resulted in the functionalization of cyclohexane without a catalyst or additives, achieving a total yield of 30% of chlorinated products with a residence time of 60 s. The influence of substrate concentration, gas/liquid flow ratio, energy density and residence time was studied, which resulted in a proposal of reaction pathway where the reaction is initiated by the C-Cl dissociation in CH₂Cl₂ , followed by H-abstraction on C(sp3)-H and radical recombination. These mechanistic insights provide valuable knowledge for the advancement of plasma chemistry. Furthermore, the use of deuterated dichloromethane allows the introduction of deuterium into saturated hydrocarbons.Le plasma non thermique a été utilisé pour l’activation chimique du CH₂Cl₂ dans un système gaz-liquide en flux continu fonctionnant à température et pression ambiantes. Dans cette étude, nous présentons une approche directe et sans catalyseur pour la chlorométhylation des hydrocarbures saturés. Le test de réaction a permis la fonctionnalisation du cyclohexane sans catalyseur ni additifs, atteignant un rendement total de 30 % de produits chlorés avec un temps de séjour de 60 secondes. L’influence de la concentration du substrat, du ratio de flux gaz/liquide, de la densité énergétique et du temps de séjour a été étudiée, ce qui a conduit à une proposition de mécanisme réactionnel où la réaction est initiée par la dissociation C-Cl dans le CH₂Cl₂, suivie d’une abstraction d’hydrogène sur C(sp3)-H-H et d’une recombinaison radicalaire. Ces éléments mécanistiques apportent des connaissances précieuses pour le développement de la chimie plasma. De plus, l’utilisation du dichlorométhane deutéré permet l’introduction de deutérium dans les hydrocarbures saturés
Меховая торговля в Северной Европе в эпоху Великого переселения народов
No full textInternational audienceFur Trade in Northern Europe in the Great Migration Period uring the Great Migration Period, there was a demand for fur in the Mediterranean, probably due to general climate changes in Europe. In the 6th century, according to written sources, there were already two trade routes by which fur was delivered to the Eastern Roman Empire: from Scandinavia through the mouth of the Vistula and from the forest zone of Eastern Europe through the Don and the Black Sea basin. The main fur hunters and suppliers were northern peoples, such as the Saami in Northern Finnoscandia. Still, the fur trade was carried out by intermediaries -the Germanic Suehans / Svionians in Scandinavia and the Huns -Hunnuguri on the Don route. Undoubtedly, other peoples were also involved in the trade chain between the Mediterranean and Northern Europe. Trade with northern hunters certainly had the character of a direct exchange of fur for goods (primarily metal products or iron bars). But there was also often a violent expropriation of furs from the local population, either as tribute or by outright robbery. Therefore, military-political formations of the "barbarian kingdoms" type sometimes arise on the southern border of the fur production zone -their archaeological traces for the 5 th -6 th centuries have been recorded in the Gulf of Bothnia, in Norrland and in Osterbothnia. In general, the fur trade, or rather its income, inevitably had to complicate the military situation, both in the fur production zone and on the routes of its export. The latter circumstance was probably one of the reasons for the degradation of the military situation in Eastern Europe during the Great Migration Period
Tissue stiffness controls neuroblast migratory behavior and reprogramming during myelin repair
No full textInternational audienceAfter brain insults, neuronal progenitors of the adult mouse sub-ventricular zone can change migration mode to emigrate toward lesioned tissues and participate in regenerative processes. During demyelination, these progenitors change fate to generate oligodendrocytes that contribute to myelin replacement. Herein, we examined the possible link between neuroblast behavior and mechanical tissue properties. Using sub-ventricular zone organotypic explant, we found that matrix stiffness influences neuroblast migratory mode and fate. A softer matrix promotes a switch from collective (chain) to isolated cell migration and reprogramming into oligodendrocytes. Nanoindentation on fresh brain slices provided evidence for changes in the mechanical properties of the corpus callosum following lysophosphatidylcholine-induced focal demyelination. In particular, we propose that the decrease in stiffness may be due to myelin loss and extracellular matrix modification. Overall, our work suggests that postlesional changes in mechanical cues regulate neuroblast mobilization and fate conversion in the adult mammalian central nervous system
Representação e presentação política ameríndia: coexistência e hibridização de regimes do político na América do Sul tropical
No full textInternational audienceApresentação do dossiê Representação e presentação política ameríndia: coexistência e hibridização de regimes do político na América do Sul tropical, vol. 1
Ultra‐Fast Crystallization of Nanozeolite via Hydroxyl Radicals Generated by Electron‐Beam‐Induced Radiolysis
No full textInternational audienceThe development of nanozeolites is crucial for advancing applications in catalysis, adsorption, and separation due to their unique structural and functional properties. Herein, we demonstrate the ultra‐fast crystallization of RHO‐type nanozeolite (in just a few tenths of a seconds) in a colloidal aluminosilicate suspension is demonstrated and is observed by transmission electron microscopy. Nucleation occurs almost instantaneously, within 5 s, under electron beam irradiation, followed by rapid, homogeneous crystal growth completed within 14–20 s. The crystallization of RHO nanocrystals is driven by hydroxyl radicals (OH • ) generated through radiolysis, allowing for real‐time tracking of nanozeolite formation. By systematically varying the electron dose rate from 0.66 to 80.7 e − Å −2 s −1 , its critical role in controlling induction time, nucleation density, and particle coalescence is demonstrated. The latter stages involve Ostwald ripening, resulting in the formation of larger RHO nanocrystals. Notably, coalescence occurs earlier at higher electron doses (80.7 e − Å −2 s −1 ) due to accelerated nucleation from a higher generation of OH • radicals. These findings provide direct evidence of the ultra‐fast kinetics of nanozeolite nucleation and growth, highlighting the pivotal role of hydroxyl radicals in driving amorphous nanoparticle formation and stabilizing zeolite crystallites with uniform crystals size
Comparing Symmetrized Determinant Neural Quantum States for the Hubbard Model
No full textAccurate simulations of the Hubbard model are crucial to understanding strongly correlated phenomena, where small energy differences between competing orders demand high numerical precision. In this work, Neural Quantum States are used to probe the strongly coupled and underdoped regime of the square-lattice Hubbard model. We systematically compare the Hidden Fermion Determinant State and the Jastrow-Backflow ansatz, parametrized by a Vision Transformer, finding that in practice, their accuracy is similar. We also test different symmetrization strategies, finding that output averaging yields the lowest energies, though it becomes costly for larger system sizes. On cylindrical systems, we consistently observe filled stripes. On the torus, our calculations display features consistent with a doped Mott insulator, including antiferromagnetic correlations and suppressed density fluctuations. Our results demonstrate both the promise and current challenges of neural quantum states for correlated fermions
Evolution of opsin genes in closely-related species of butterflies specialized in different microhabitats
No full textInternational audienceMultiple selective pressures can shape the evolution of color vision in animals, by acting on the co- evolution of the opsin genes. How do adaptive processes shape the duplications of opsins, the evolution of their amino acids and the modification of their patterns of expression? At large phylogenetic scales, natural selection due to the contrasted light environments has been found to have a profound impact on the evolution of the opsin gene family. However, in closely-related species, species interactions due to sexual selection or competition may also influence opsin evolution. Here, we investigate the diversification of opsin sequences and their expression in closely-related blue Morpho butterfly species, living in different microhabitats, to shed light on the effect of biotic and abiotic selective pressures shaping the evolution of their opsin gene family. First, we combined genomics, transcriptomics and immunochemistry to precisely characterize the expression and the spatial distribution of the opsin proteins found in the eyes of Morpho helenor . We found unique ommatidial types compared to other butterfly species. We then investigated the evolution of opsin genes among 18 Morpho species, found signature of positive selection on two opsin genes, and identified key co-evolving amino-acids shaping the diversification of the Morpho visual system. We showed that such opsin evolution was correlated to both light environment and wing coloration, highlighting the joint effect of several selective pressures in the evolution of those proteins. Overall, our study underlines the peculiar evolution of visual systems in closely-related species specialized in divergent microhabitats
Affirmer son attachement au territoire. Le cas des monuments sacrés de Mongolie-Intérieure
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Perceptual maps reveal rampant convergence in butterfly wing patterns across the Neotropics
No full textIn 1879, Fritz Müller formulated the first mathematical evolutionary model to explain mutualistic mimicry between coexisting defended prey. Yet, whether local mimicry drives the structure of aposematic prey signals across their entire geographic distribution remains untested because the perception of pattern similarity has never been assessed at large spatial scale. Here, we implement a citizen science survey to map, throughout the Neotropics, variation in the wing patterns of heliconiine butterflies (Nymphalidae) as perceived by vertebrate cognitive systems. We show that despite a continuum of perceived similarity in wing patterns at the continental scale, the convergence of sympatric species into discrete mimicry rings is ubiquitous among local communities. These results expand Müller’s historical predictions by quantifying the rampant convergence of prey signals across an entire continent
Genetic parallelism underpins convergent mimicry coloration across Lepidoptera
No full textAbstract Convergent evolution, the repeated evolution of similar phenotypes in response to the same selective pressures across multiple lineages, is widespread in nature. The extent to which the same genetic mechanisms contribute to convergent evolution could reveal whether the pathway towards these optimal endpoints is flexible or constrained to follow a particular route. Although mimicry of aposematic colour patterns is well known in Lepidoptera, our knowledge of the genetic basis of these convergent patterns is mostly restricted to a few closely-related species. Here we study the genetic basis of mimicry across seven species of Ithomiini and Heliconius butterflies and a day-flying Chetone moth, representing lineages that diverged between ∼1-120 Mya, each presenting similar colour pattern switches. In all the butterfly species, the genetic variants most strongly associated with convergent colour pattern switches are similarly located in non-coding regions near the genes ivory and optix . Colour pattern variation in the moth is associated with a ∼1 Mb inversion around ivory paralleling the supergene architecture of the co-mimic Heliconius numata . In contrast to previous studies in Heliconius , there is limited evidence of alleles shared by means of hybridization in convergence among closely-related ithomiine species. Repeated parallel evolution of regulatory switches via reuse of the same two genes suggests that convergent colour pattern evolution is highly constrained, even across large evolutionary timescales