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Boltzmann social learning with heterogeneous rationality
No full textThis paper analyzes a novel social learning model in which, at each discrete time step, agents with private preferences repeatedly select actions via a softmax (Boltzmann) rule, and update their preferences based on public observations of others' choices. This work addresses a critical gap by introducing rational heterogeneity through agent-specific rationality parameters gamma-i. Unlike previous models, our approach accounts for the diverse ways individuals process social information by using a discrete-time deterministic mean-field approximation map. We establish fundamental equilibrium properties that were previously unexplored. In particular, we prove the existence of fixed points and show that, on complete graphs, every mean-field equilibrium is a consensus state, where all agents share identical preferences. We further derive sufficient conditions for the uniqueness of this equilibrium and its local asymptotic stability. Numerical simulations validate our theoretical findings and illustrate how rational heterogeneity and network structure interact to shape collective behavior in social learning systems
Leaf litter chemistry contributes to shape the chemical footprint of macrodetritivore communities
No full textInternational audienceAddressing the factors underlying community patterns is a crucial endeavor as it contributes to a better understanding of the relationship between biodiversity and ecosystem functioning, as well as the associated ecosystem services. For example, detritivore communities play a major role in decomposition processes and related matter and energy fluxes in ecosystems. However, compared to living plant resources, leaf litter resources are nutritionally poor, with low macroelement concentrations. Although detritivore communities are known to depend on the local leaf litter resources, it remains unclear whether the chemical composition of detritivores depends on the locally available leaf litter. The macroelement composition of detritivores is rarely studied and is seldom compared directly to leaf litter chemical quality. Furthermore, leaf litter elements other than carbon (C), nitrogen (N), and phosphorus (P) are not systematically investigated even though large differences in elements such as calcium (Ca), potassium (K), or magnesium (Mg) can occur among both detritivore taxa and leaf litter types.To investigate whether the chemical composition of macrodetritivore communities depends on leaf litter chemistry, we sampled 24 paired French forests sites that differed in their leaf litter chemical composition. At each site, we quantitatively sampled leaf litter transformers (Diplopoda and Isopoda) to estimate their abundance. For each morphospecies, we measured mean individual body mass and analyzed body concentrations of C, N, P, K, Ca, and Mg (hereafter called chemical traits). We also analyzed the same macroelements in the dominant leaf litter at each site. We examined the detritivore taxonomic diversity, chemical community diversity, biomass, and abundance in communities, and tested whether these parameters were influenced by leaf litter chemistry.Results at the morphospecies level were consistent with the homeostasis hypothesis, indicating no specific physiological adaptation to the chemical composition of their trophic resources. Chemical community diversity (i.e., the FDis index based on all six chemical elements) of detritivores was higher at sites with high-quality leaf litter than at the corresponding low-quality leaf litter sites. Furthermore, community-level concentrations of P and Mg in detritivores were positively influenced by litter P and Mg concentrations, respectively.Although effect sizes were limited, our results suggest that leaf litter chemical composition can influence detritivore chemical composition through shifts in the relative abundance of taxa. Ultimately, this may lead to a closer match between the chemical composition of detritivore communities and that of their resources
Structuration de la recherche en éducation: L’héritage scientifique de Jacques Ginestié
No full textInternational audienceCet ouvrage rend hommage à Jacques Ginestié, dont les travaux ont profondément structuré la recherche en éducation et la formation des enseignants, grâce à des contributions qui offrent une synthèse précieuse des enjeux éducatifs actuels : didactique de l’enseignement technologique, efficacité des processus d’apprentissage et structuration des politiques de formation. Clair, engagé et nourri d’une expertise de terrain, ce livre s’adresse aux professionnels de l’éducation, aux chercheurs et aux lecteurs voulant comprendre les dynamiques qui traversent l’éducation
Optimization of the representation of results in interval arithmetic
No full textInterval arithmetic enables rigorous bounding of rounding errors, but standard representations require storing two floating-point numbers per interval, which increases memory costs and data transfer in large-scale computations. We propose a compressed interval representation inspired by the FP-ANR format, encoding both the center and the radius within a single floating-point word while preserving the strict inclusion of the original interval. We present an efficient algorithm to convert center-radius intervals into this format with minimal over-approximation. Its applications to the interval matrix product and the interval Newton method demonstrate the practical benefits of this representation. Additionally, the proposed approach enables the integration of mixed-precision computations, paving the way for scalable and memory-efficient interval arithmetic in scientific computing
Splitting methods for stochastic Hodgkin-Huxley type systems and a localized fundamental mean-square convergence theorem
No full textInternational audienceExisting fundamental theorems for mean-square convergence of numerical methods for stochastic differential equations (SDEs) require globally or one-sided Lipschitz continuous coefficients, while strong convergence results under merely local Lipschitz conditions are largely restricted to Euler-Maruyama type methods. To address these limitations, we introduce a novel localized version of the fundamental mean-square convergence theorem for SDEs with locally Lipschitz coefficients, which naturally arise in a wide range of applications. Specifically, we show that if a numerical scheme is locally consistent in the mean-square sense of order q > 1, then it is locally mean-square convergent with rate q-1. Building on this result, we further prove that global mean-square convergence follows, provided that both the exact solution and its numerical approximation admit bounded th moments for some p > 1. This new convergence result is illustrated on a class of locally Lipschitz SDEs of Hodgkin-Huxley type, characterized by a conditionally linear drift structure. For these systems, we construct different Lie-Trotter and Strang splitting methods exploiting their conditional linearity. The proposed convergence framework is then applied to these schemes, requiring innovative proofs of local consistency and boundedness of moments. In addition, we establish key structure-preserving properties of the splitting methods, in particular state-space preservation and geometric ergodicity. Numerical experiments support the theoretical results and demonstrate that the proposed splitting schemes significantly outperform Euler-Maruyama type methods in preserving the qualitative features of the model
La nuit de Didon dans le Roman d’Énéas (v. 1302-1346). De la lettre ovidienne à la scène romanesque
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Biodiversity of Aspergillus section Flavi species isolated along the peanut paste production chain in Côte d'Ivoire
No full textSource Agritrop Cirad (https://agritrop.cirad.fr/616500/) * Autres projets (id;sigle;titre): DCI-NSAPVD-2010-64;3CI;(EU) 3C Ivoire project//International audienceThe contamination of staple foods by mycotoxins is a significant issue in sub-Saharan Africa, particularly the presence of aflatoxins in raw peanuts and peanut-based products. This contamination has severe health and economic consequences. The main aflatoxin-producing fungi belong to Aspergillus section Flavi and are grouped in three main clades: A. flavus, A. tamarii and A. nomius, newly qualified as Flavi, Kitamyces and Nomiarum series respectively. The present study assessed the biodiversity of Aspergillus section Flavi species along the peanut paste production chain in the Korhogo region in northern Côte d'Ivoire. A polyphasic approach was used to identify 256 potentially aflatoxigenic strains isolated on AFPA medium. Experiments included (i) morphological characterization, (ii) aflatoxin production on PDA medium, (iii) molecular identification using a PCR-DGGE method and DNA sequencing, and (iv) phylogenetic analyses. Three species of A. flavus clade were isolated. The most prevalent was A. flavus, which comprised mainly aflatoxin-producing strains but also atoxigenic strains, followed by A. aflatoxiformans and A. korhogoensis. The latter two produced B and G aflatoxins at higher levels than A. flavus, which only produced B aflatoxins. A. aflatoxiformans, A. korhogoensis and aflatoxigenic A. flavus strains were mainly isolated after the stages of peanut pod drying and storage in villages, as well as after seed storage by wholesalers and retailers. However, AF production requires confirmation on most appropriate inducing media. The study also indicates that the PCR-DGGE method when combined with a multi-locus phylogenetic analysis is an effective strategy for discriminating and identifying Aspergillus section Flavi species, particularly those in the A. flavus clade
Simultaneous joint inversion of synthetic seismic and ground penetrating radar data with petrophysical variable change
No full textInternational audienceIn this work, we address the characterization of porosity and water saturation in a synthetic model of a shallow alluvial subsurface using frequency electromagnetic and seismic data. The inversion method employs a Gauss–Newton scheme, where the Jacobian of the merged seismic and electromagnetic data is formulated with respect to the spatially heterogeneous petrophysical parameters. This is made possible by introducing realistic petrophysical relationships, which significantly reduce the number of unknowns in the inverse problem and incorporate a strong prior correlation between the information contained in both data types regarding the subsurface composition. The results obtained show that this simultaneous joint petrophysical inversion produces reconstructions with clear improvements compared to independent petrophysical inversion. Indeed, it greatly enhances the spatial resolution of subsurface mapping, as well as the quantitative estimation of porosity and saturation
Seeing yew for the forest: a call to action for improving conservation and restoration of the European yew (Taxus baccata L.)
No full textInternational audienceThe European yew (Taxus baccata L.) is a long-lived conifer of ecological, cultural, and historical importance across Eurasia. Despite its remarkable resilience, wide distribution, and symbolic importance, the species has experienced a long-term decline due to a complex interplay of climatic fluctuations, megafaunal extinctions, human exploitation, and insufficient regeneration. Recent studies in palaeoecology, archaeology, dendroecology, and conservation have revealed a species with greater ecological plasticity and a broader historical distribution than previously assumed. However, many fundamental questions remain unresolved, particularly regarding its biogeographical history, population dynamics, recruitment processes, and the drivers of its decline.This review stems from prior investigations of yew in the French Pyrenees and, more broadly, across Europe. These efforts led to a transdisciplinary seminar and opened a collaboration uniting >30 researchers across Eurasia. By synthesizing a wide array of data and perspectives, the article highlights key knowledge gaps and outlines emerging research priorities. These are organized thematically—past, present, and future—and include 25 questions on the species' ecological niche, life-history strategies, human interactions, genetic resilience, and conservation under global change. The article advocates for a shift towards integrative and long-term conservation strategies that embrace the historical legacies of yew populations, the general ecology of the species along with local ecological context dependence, and the urgency of future threats. By identifying pressing research needs, this review seeks to lay the foundation for new collaborative initiatives and to support evidence-based conservation of this emblematic yet understudied species
