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Yielding in colloidal gels: From local structure to mesoscale strand breakage and macroscopic failure
No full textInternational audienceWe report numerical simulations of creep flow and yielding of particulate depletion gels under constant shear stress, combining data on different length and time scales. We characterize the statistics of mesoscale strand-breaking events in the gel, which are distributed homogeneously in space, corresponding to macroscopically ductile flow. At the microscale, a spatiotemporal analysis of structural and mechanical metrics connects properties of strands before and after they fail, indicating that strand breakage is statistically predictable. Using results from different scales, we discuss the interplay between creeping and aging dynamics, and we demonstrate a viscosity bifurcation
Imagerie matricielle dynamique appliquée à l'échographie transcrânienne
No full textSession Posters;National audienceL'échographie ultrasonore repose sur deux hypothèses fondamentales : une vitesse du son homogène et l’approximation de diffusion simple. En réalité, ces hypothèses sont souvent inexactes dans les tissus du corps humain, où les variations de la vitesse du son entre les tissus peuvent déformer les fronts d’ondes incident et réfléchi ainsi qu'induire des réverbérations qui altèrent la focalisation ainsi que la résolution et le contraste des images Ces problèmes sont particulièrement rédhibitoires pour l'imagerie du cerveau du fait des hétérogénéités du crâne et de la rupture d'impédance qu’il induit à ses interfaces. Pour résoudre ces problèmes, le concept d'imagerie matricielle a été récemment développé et repose sur la mesure de la matrice de réflexion associée au réseau de transducteurs (W. Lambert et al., PNAS 2020). A la différence de l’échographie standard, cette approche consiste à séparer, en post-traitement, les points de focalisation à l'émission et à la réception pour sonder la qualité de focalisation et corriger les aberrations du milieu. Toutefois, cette approche repose sur une invariance locale des aberrations qui n’est pas toujours vérifiée, notamment pour les aberrateurs complexes tels que le crâne (F. Bureau et al., Nat. Commun. 2023). Ce travail consiste à lever cette limite fondamentale en exploitant la dynamique intrinsèque des milieux biologiques. Ce faisant, on peut établir des lois de focalisation spécifiques pour chaque point du milieu étudié, offrant ainsi une amélioration significative de la qualité des images échographiques (E. Giraudat, PhD thesis, 2024), particulièrement dans le cadre du suivi des accidents vasculaires cérébraux. Appliquée à la microscopie de localisation ultrasonore, elle permet en effet une image contrastée et hautement résolue du réseau vasculaire cérébral en transcrânien (F. Bureau et al., arXiv : 2410.14499, 2024)
Elastic Wave Packets Crossing a Space-Time Interface
No full textEffets d'interfaces; GAPSUS - Acoustique Physique, Sous-Marine et Ultra-SonoreNational audienceThe interaction between waves and evolving media presents a unique challenge to traditional conservation laws, particularly with regard to wave properties like wavelength and frequency. In this talk, we experimentally explore the behavior of elastic wave packets as they traverse a moving interface that separates two media with differing propagation characteristics. This investigation reveals that the wavelength and frequency of the waves are not conserved when crossing the interface. Our experimental setup consists of an elastic strip, whose local stretching can be dynamically controlled by pulling one end at a constant velocity. This setup creates a spatiotemporal interface that moves along the strip, introducing a nonuniform medium through which the wave packets propagate. By carefully analyzing the wave packet behavior as it crosses this dynamic interface, we confirm theoretical predictions about the resulting shifts in wave properties, providing valuable insights into the complex interactions between waves and evolving media
Combining population genomics with ancient DNA to understand island colonization history of the Madagascar turtle dove
No full textAbstract The Mascarene archipelago (Mauritius, Reunion and Rodrigues), characterized by first human arrival being recent, offers a unique setting to study species colonization. Here we use a combination of modern and ancient DNA data as a case study to investigate the recent colonization history of a species of concern in relation to conservation programs – the Madagascar turtle dove ( Nesoenas picturata ) on Mauritius and Reunion. We generated a reference genome and re-sequenced genomes from contemporary N. picturata populations, as well as genome-wide data from relevant subfossils. A combination of model-free inferences, site frequency spectrum (SFS) based demographic modelling, and analyses of population structure including that of subfossils indicate that N. picturata colonized both islands independently and naturally from Madagascar, long before human arrival. Summary statistics and SFS-based modeling reveal large effective population sizes ( Ne ) and high genetic diversity in island populations, conflicting with historical accounts of human-induced demographic collapse. Based on goodness-of-fit, genetic structure and diversity indices do not discriminate between two solutions, one of which posits large recent Ne and negligible translocation rates, while the other supports recent severe bottlenecks followed by high post-human translocation from Madagascar. Nonetheless, linkage disequilibrium provides stronger evidence for the latter scenario, which may also explain high genetic diversity. Both modern and ancient DNA data sources independently support the classification of N. picturata as native to both islands. Our findings highlight the importance of validating demographic models with multiple summary statistics, and potential of using a combination of different data sources to resolve colonization history in recent time
Laminar-Turbulent Patterns in Shear Flows: Evasion of Tipping, Saddle-Loop Bifurcation, and Log Scaling of the Turbulent Fraction
No full textInternational audienceWe analyze a one-dimensional two-scalar fields reaction-advection-diffusion model for the globally subcritical transition to turbulence. In this model, the homogeneous turbulent state is disconnected from the laminar one and disappears in a tipping catastrophe scenario. The model however exhibits a linear instability of the turbulent homogeneous state, mimicking the onset of the laminar-turbulent patterns observed in the transitional regime of wall shear flows. Numerically continuing the solutions obtained at large Reynolds numbers, we construct the Busse balloon associated with the multistability of the nonlinear solutions emerging from the instability. In the core of the balloon, the turbulent fluctuations, encoded into a multiplicative noise, select the pattern wavelength. On the lower Reynolds number side of the balloon, the pattern follows a cascade of destabilizations towards larger and larger, eventually infinite wavelengths. In that limit, the periodic limit cycle associated with the spatial pattern hits the laminar fixed point, resulting in a saddle-loop global bifurcation and the emergence of solitary pulse solutions. This saddle-loop scenario predicts a logarithmic divergence of the wavelength, which captures experimental and numerical data in two representative shear flows.</div
Polymères magnétiques à empreinte moléculaire en synthèse organique : du déroulement standard au dédoublement cinétique dynamique
No full textDynamic kinetic resolution (DKR) has emerged as a powerful approach for asymmetric synthesis, allowing the efficient conversion of a racemic mixture of a compound, easier to obtain, into a unique enantiomer. This significant improvement of standard kinetic resolution (KR), limited with a maximum of 50% conversion, proceeds through the selective transformation of one enantiomer by organometallic catalysis or biocatalysis and the racemization of the remaining one which can be converted in turn. The last few years have witnessed great improvements in the field of Molecularly Imprinted Polymers (MIPs), highly cross-linked macromolecular architectures capable of selective molecular recognition. MIPs exhibit excellent binding properties with affinity and selectivity often comparable to those of antibodies. Their combination with magnetic nanoparticles (Fe2O3) has conferred them new separation properties using a magnet. We propose here to design a new DKR system that simply combines enantiomer recognition by the magnetic MIP nanoparticles and racemization methods according to the substrate used. In other words, one enantiomer is trapped by magnetic MIP nanoparticles, the other one is racemized allowing the progressive shift of the equilibrium in the direction of formation of a single enantiomer. The polymer can then release the enantiomerically enriched product. Proofs of concept have already been established for standard KR, and then in the DKR. Extension to other examples of asymmetric resolution will be considered on the basis of our initial studies.La résolution cinétique dynamique est apparue comme une approche puissante pour la synthèse asymétrique, permettant la conversion efficace d'un mélange racémique d'un composé, plus facile à obtenir, en un énantiomère unique. Cette amélioration significative de la résolution cinétique standard, limitée à un maximum de 50% de conversion, passe par la transformation sélective d'un énantiomère par catalyse organométallique ou biocatalyse et la racémisation de l'autre qui peut être converti à son tour. Ces dernières années ont vu de grandes améliorations dans le domaine des polymères à empreinte moléculaire, des architectures macromoléculaires hautement réticulées capables de reconnaissance moléculaire sélective. Les MIP présentent d'excellentes propriétés de liaison avec une affinité et une sélectivité souvent comparables à celles des anticorps. Leur association avec des nanoparticules magnétiques (Fe2O3) leur a conféré de nouvelles propriétés de séparation par aimant. Nous proposons ici de concevoir un nouveau système DKR qui combine simplement la reconnaissance des énantiomères par les nanoparticules magnétiques MIP et les méthodes de racémisation selon le substrat utilisé. En d'autres termes, un énantiomère est piégé par des nanoparticules magnétiques de MIP, l'autre est racémisé permettant le déplacement progressif de l'équilibre dans le sens de la formation d'un seul énantiomère. Le polymère peut alors libérer le produit énantiomériquement enrichi. Des preuves de concept ont déjà été établies pour le KR standard, puis dans le DKR. L'extension à d'autres exemples de résolution asymétrique sera envisagée sur la base de nos premières études
Sociohydrodynamics: data-driven modelling of social behavior
No full textInternational audienceLiving systems display complex behaviors driven by physical forces as well as decision-making. Hydrodynamic theories hold promise for simplified universal descriptions of socially-generated collective behaviors. However, the construction of such theories is often divorced from the data they should describe. Here, we develop and apply a data-driven pipeline that links micromotives to macrobehavior by augmenting hydrodynamics with individual preferences that guide motion. We illustrate this pipeline on a case study of residential dynamics in the United States, for which census and sociological data is available. Guided by Census data, sociological surveys, and neural network analysis, we systematically assess standard hydrodynamic assumptions to construct a sociohydrodynamic model. Solving our simple hydrodynamic model, calibrated using statistical inference, qualitatively captures key features of residential dynamics at the level of individual US counties. We highlight that a social memory, akin to hysteresis in magnets, emerges in the segregation-integration transition even with memory-less agents. This suggests an explanation for the phenomenon of neighborhood tipping, whereby a small change in a neighborhood's population leads to a rapid demographic shift. Beyond residential segregation, our work paves the way for systematic investigations of decision-guided motility in real space, from micro-organisms to humans, as well as fitness-mediated motion in more abstract genomic spaces
How Host Mobility Patterns Shape Antigenic Escape During Viral-Immune Coevolution
No full textInternational audienceViruses like influenza have long coevolved with host immune systems, gradually shaping the evolutionary trajectory of these pathogens. Host immune systems develop immunity against circulating strains, which in turn avoid extinction by exploiting antigenic escape mutations that render new strains immune to existing antibodies in the host population. Infected hosts are also mobile, which can spread the virus to regions without developed host immunity, offering additional reservoirs for viral growth. While the effects of migration on viral persistence have been investigated, we know little about how antigenic escape coupled with migration changes the survival and spread of emerging viruses. By considering the two processes on equal footing, we show that on short timescales an intermediate host mobility rate increases the survival probability of the virus through antigenic escape. We show that more strongly connected migratory networks decrease the survival probability of the virus. Using data from high traffic airports, we argue that current human migration rates are beneficial for viral survival
The gut-brain vagal axis governs mesolimbic dopamine dynamics and reward events
No full textAbstract Reward-related processes have traditionally been ascribed to neural circuits centered on the dopamine (DA) system. While exteroceptive stimuli, such as food and drugs of abuse, are well-established activators of DA-neuron activity, growing evidence indicates that interoceptive signals also play a critical role in modulating reward. Among these, the gut-brain vagal axis has emerged as a key pathway, yet its precise contribution to mesolimbic DA-dependent signaling, dynamics and behaviors remains poorly defined. Here, we combine complementary ex vivo and in vivo approaches across multiple scales to investigate how the gut-brain vagal axis regulates DA dynamics and reward-related behaviors. We show that gut-brain vagal tone is essential for gating mesolimbic DA system activity and functions, modulating DA-dependent molecular and cellular processes, and scaling both food- and drugs-induced reinforcement. These findings challenge the traditional brain-centric view of reward processing, supporting a more unified and integrated model in which gut-derived and vagus-mediated interoceptive signals are pivotal in intrinsically shaping motivation and reinforcement. By uncovering the influence of gut-brain vagal communication on mesolimbic DA functions, this work offers new insights into the neurobiological mechanisms underlying both adaptive and maladaptive reward processes, with broad implications for eating disorders and addiction
Phylogeny, systematics and evolution of mimicry patterns in Neotropical limenitidine butterflies
No full textDATA AVAILABILITY STATEMENT: The data that support the findings of this study are openly available in the Dryad repository at https://doi.org/10.5061/dryad.7h44j104b (Pàez et al, 2025). Newly generated sequences were deposited in GenBank at https://www.ncbi.nlm.nih.gov and are registered with the following accession numbers: PX243222–PX243274, PX244453–PX244551 (COI); PX114826–PX114854 (EF1a); PX172283–PX172334 (GAPDH); PX172335, PX254824–PX254850 (IDH); PX254786–PX254823 (RpS5); PX207538–PX207552 (ArgKin); PX172259–PX172282 (CAD); PX207522–PX207537 (CycY); PX172235–PX172258 (DDC); PX270910–PX270945 (Exp1); PX172202–PX172234 (Nex9); PX114965–PX115012 (PolII); PX114932–PX114964 (ProSup); PX114890–PX114931 (PSb); PX114855–PX114889 (RpS2); PX207556–PX207592 (UDPG6DH) (see Table S1 for details).International audienceThe Neotropical butterfly genus Adelpha Hübner exhibits remarkable species diversity and striking convergence in wing colour patterns potentially explained by mimicry, making it an exceptional model for exploring trait evolution and its relationship with speciation. To date, unresolved phylogenetic relationships hinder a comprehensive understanding of the evolutionary biology of the genus. Using a novel multi‐marker dataset combining one mitochondrial and 15 nuclear gene fragments, we generate the most comprehensive phylogeny of the genus Adelpha to revisit its systematics and investigate the evolution of mimicry colour patterns. Our dataset encompasses 83 of the 87 known extant species and six Limenitis species that were recently excluded from Adelpha (134 of c . 160 subspecies in total), collectively displaying 14 distinct mimicry patterns. We provide conclusive evidence that corroborates previous work on the polyphyly of Adelpha as historically conceived and describe the genus Adelphina Páez & Willmott n. gen . to stabilise the nomenclature. The comprehensive phylogeny provided in this study lays a solid foundation for future research into the processes driving diversification within these species interacting through mimicry. Ancestral character state reconstruction reveals the gradual evolution of mimicry patterns. The more common mimicry pattern IPHICLUS (forewing with orange subapical spot and white band) is inferred as ancestral, but repeated convergent evolution is also recovered. Evolutionary convergence is also observed for the second most abundant mimicry pattern, COCALA (orange‐white banded). Increased rates of mimicry pattern evolution are also found towards the equator. These results underscore the complexity of mimicry evolution in the Neotropical limenitidines, i.e., Adelpha and Adelphina n. gen. , emphasising the need to explore its interplay with other biotic and abiotic factors