Ecole normale supérieure de Lyon
Recent publications
In the so-called 1-2-3 Conjecture, the question is, for any connected graph not isomorphic to K2, whether we can label its edges with 1,2,3 so that no two adjacent vertices are incident to the same sum of labels. Many aspects of this conjecture have been investigated over the last past years, related both to the conjecture itself and to variations of it. Such variations include different generalisations, such as generalisations to more general graph structures (digraphs, hypergraphs, etc.) and generalisations with stronger distinction requirements. In this work, we introduce a new general problem, which holds essentially as a generalisation of the 1-2-3 Conjecture to a larger range. In this variant, a radius r≥2 is fixed, and the main task, given a graph, is, if possible, to label its edges so that any two vertices at distance at most r are distinguished through their sums of labels assigned to their edges at distance at most r. We investigate several general aspects of this problem, in particular the importance of r and its influence on the smallest number of labels needed to label graphs. We also show connections between our general problem and several other notions of graph theory, from both the distinguishing labelling field (e.g. irregularity strength of graphs) and the more general chromatic theory field (e.g. chromatic index of graphs).
Although mesoporous silica nanoparticles (MSNs) have been intensively investigated, their mesostructure and formation mechanism are still a topic of debate. Here, we demonstrate that the formation of MSNs is a result of dynamic two-level template collaborative self-assembly of microemulsion droplets and spherical micelles, whose surfaces are both partly covered by silicate species. The stability of microemulsion droplets spontaneously formed by water-surfactant-tetraalkoxysilanes (TAOS) ternary system determines the final morphology and particle size of MSNs, and we definitively confirms that the dendritic MSNs (DMSNs) with unique hierarchical pore structures is a metastable intermediate product, which could be kinetically transferred to regular MSNs undergoing a fast structural collapse of microemulsion droplets with the continuous consumption of TAOS. Our research further highlights the prominent role of self-emulsification of organic silane reagents in sol-gel chemistry to tune the morphology and structure of final products.
Artisanal and small-scale mines ( asm ) are on the rise. They represent a crucial source of wealth for numerous communities but are rarely monitored or regulated. The main reason being the unavailability of reliable information on the precise location of the asm which are mostly operated informally or illegally. We address this issue by developing a strategy to map the asm locations using a convolutional neural network for image segmentation, aiming to detect surface mining with satellite data. Our novel dataset is the first comprehensive measure of asm activity over a vast area: we cover 1.75 million km ² across 13 countries in Sub-Tropical West Africa. The detected asm activities range from 0.1 ha to around 2, 000 ha and present a great diversity, yet we succeed in hitting acceptable compromises of performance, as achieving 70% precision while maintaining simultaneously 42% recall. Ultimately, the remarkable robustness of our procedure makes us confident that our method can be applied to other parts of Africa or the world, thus facilitating research and policy opportunities in this sector.
In this chapter, we analyse the phenomenon of Visual Marginalia (VM)—that is drawings, doodles and writings at the margin of books, notebooks, etc.—as a “blueprint of thought” in educational contexts. Collateral productions on the margins (drawings, sketches, modifications of structured and recognized elements, ornaments, etc.) are something humans do more often than we think as their self-expression and transformation of the environment. In this chapter, we consider and extend the concept of marginalia as the reader’s graphical and textual productions on the margin of written texts to include all more or less spontaneous, deliberate and accepted forms of drawing and writing, produced by students during a lesson (not when they read solipsistically a book) in different supports, Visual Marginalia. Here we present a brief overview of our previous exploratory study where we collected and analysed data from Visual Marginalia productions and from a first questionnaire, submitted to two school level students. The general purpose is to analyse the collateral cognitive productions and to integrate them into learning processes that help students to construct personal meanings affectively integrating their needs. Visual Marginalia are usually relegated to the periphery of educational studies and generally considered signs of distraction or annotations in the white space of printed and hand-written books or notebooks. We explore the possibility that VM, by mediating the process of internalization and externalization, become arenas of discourses where our inner mental activity finds expression and play a role in learning processes. Thus, the written and printed text is not something fixed and immutable but a place of dialogue with the context and the margin.KeywordsInner speechMind-wanderingVisual marginaliaBlueprints of thoughtExplorative study
Understanding the connection between the molecular structure of ionic liquids and their properties is of paramount importance for practical applications. However, this connection can only be established if a broad range of physicochemical properties on different length and time scales is already available. Even then, the interpretation of the results often remains ambiguous due to the natural limits of experimental approaches. Here we use fast-field cycling (FFC) to access both translational and rotational dynamics of ionic liquids. These combined with a comprehensive physicochemical characterization and MD simulations provide a toolkit to give insight into the mechanisms of molecular mechanics. The FFC results are consistent with the computer simulation and conventional physicochemical approaches. We show that curling of the side chains around the positively charged cationic core is essential for the properties of ether-functionalized ionic liquids, and we demonstrate that neither geometry nor polarity alone are sufficient to explain the macroscopic properties.
Anticancer immunotherapies are therapeutics aimed at eliciting immune responses against tumor cells. Immunotherapies based on adoptive transfer of engineered immune cells have raised great hopes of cures because of the success of chimeric antigen receptor T-cell therapy in treating some hematologic malignancies. In parallel, advances in detailed analyses of the microenvironment of many solid tumors using high-dimensional approaches have established the origins and abundant presence of tumor-associated macrophages. These macrophages have an anti-inflammatory phenotype and promote tumor growth through a variety of mechanisms. Attempts have been made to engineer macrophages with chimeric receptors or transgenes to counteract their protumor activities and promote their antitumor functions such as phagocytosis of cancer cells, presentation of tumor antigens, and production of inflammatory cytokines. In this review, we cover current breakthroughs in engineering myeloid cells to combat cancer as well as potential prospects for myeloid-cell treatments.
The hybrid and the dressed metric formalisms for the study of primordial perturbations in Loop Quantum Cosmology lead to dynamical equations for the modes of these perturbations that are of a generalized harmonic-oscillator type, with a mass that depends on the background but is the same for all modes. For quantum background states that are peaked on trajectories of the effective description of Loop Quantum Cosmology, the main difference between the two considered formalisms is found in the expression of this mass. The value of the mass at the bounce is especially important, since it is only in a short interval around this event that the quantum geometry effects on the perturbations are relevant. In a previous article, the properties of this mass were discussed for an inflaton potential of quadratic form, or with similar characteristics. In the present work, we extend this study to other interesting potentials in cosmology, namely the Starobinsky and the exponential potentials. We prove that there exists a finite interval of values of the potential (which includes the zero but typically goes beyond the sector of kinetically dominated inflaton energy density) for which the hybrid mass is positive at the bounce whereas the dressed metric mass is negative.
Extreme conditions inside ice giants such as Uranus and Neptune can result in peculiar chemistry and structural transitions, e.g., the precipitation of diamonds or superionic water, as so far experimentally observed only for pure C─H and H 2 O systems, respectively. Here, we investigate a stoichiometric mixture of C and H 2 O by shock-compressing polyethylene terephthalate (PET) plastics and performing in situ x-ray probing. We observe diamond formation at pressures between 72 ± 7 and 125 ± 13 GPa at temperatures ranging from ~3500 to ~6000 K. Combining x-ray diffraction and small-angle x-ray scattering, we access the kinetics of this exotic reaction. The observed demixing of C and H 2 O suggests that diamond precipitation inside the ice giants is enhanced by oxygen, which can lead to isolated water and thus the formation of superionic structures relevant to the planets’ magnetic fields. Moreover, our measurements indicate a way of producing nanodiamonds by simple laser-driven shock compression of cheap PET plastics.
Calix[n]arenes' selective recognition of protein surfaces covers a broad range of timely applications, from controlling protein assembly and crystallization to trapping partially disordered proteins. Here, the interaction of para-sulfonated calix-[4]-arenes with cytochrome c is investigated through all-atom, explicit water molecular dynamics simulations which allow characterization of two binding sites in quantitative agreement with experimental evidence. Free energy calculations based on the MM-PBSA and the attach-pull-release (APR) methods highlight key residues implicated in the recognition process and provide binding free energy results in quantitative agreement with isothermal titration calorimetry. Our study emphasizes the role of MD simulations to capture and describe the "walk" of sulfonated calix-[4]-arenes on the cytochrome c surface, with the arginine R13 as a pivotal interacting residue. Our MD investigation allows, through the quasi-harmonic multibasin (QHMB) method, probing an allosteric reinforcement of several per-residue interactions upon calixarene binding, which suggests a more complex mode of action of these supramolecular auxiliaries.
We show that for every ℓ, there exists dℓ such that every 3-edge-connected graph with minimum degree dℓ can be edge-partitioned into paths of length ℓ (provided that its number of edges is divisible by ℓ). This improves a result asserting that 24-edge-connectivity and high minimum degree provides such a partition. This is best possible as 3-edge-connectivity cannot be replaced by 2-edge connectivity.
Social interactions are a ubiquitous feature of the lives of vertebrate species. These may be cooperative or competitive, and shape the dynamics of social systems, with profound effects on individual behavior, physiology, fitness, and health. On one hand, a wealth of studies on humans, laboratory animal models, and captive species have focused on understanding the relationships between social interactions and individual health within the context of disease and pathology. On the other, ecological studies are attempting an understanding of how social interactions shape individual phenotypes in the wild, and the consequences this entails in terms of adaptation. Whereas numerous studies in wild vertebrates have focused on the relationships between social environments and the stress axis, much remains to be done in understanding how socially-related activation of the stress axis coordinates other key physiological functions related to health. Here, we review the state of our current knowledge on the effects that social interactions may have on other markers of vertebrate fitness and health. Building upon complementary findings from the biomedical and ecological fields, we identify 6 key physiological functions (cellular metabolism, oxidative stress, cellular senescence, immunity, brain function, and the regulation of biological rhythms) which are intimately related to the stress axis, and likely directly affected by social interactions. Our goal is a holistic understanding of how social environments affect vertebrate fitness and health in the wild. Whereas both social interactions and social environments are recognized as important sources of phenotypic variation, their consequences on vertebrate fitness, and the adaptive nature of social-stress-induced phenotypes, remain unclear. Social flexibility, or the ability of an animal to change its social behavior with resulting changes in social systems in response to fluctuating environments, has emerged as a critical underlying factor that may buffer the beneficial and detrimental effects of social environments on vertebrate fitness and health.
Variations of ¹⁰⁹Ag/¹⁰⁷Ag in silver coins and ores are particularly useful in assessing the provenance of silver bullion. Silver isotope variability results from the temperature-dependent thermodynamic fractionation of Ag isotopes among the solutions and minerals participating in ore formation. They differ from lead isotopic variations which result from the decay of uranium and thorium and reflect the geochemical properties and the tectonic age of the possible ore sources. A remarkable property of Ag isotopes is the very narrow range of isotopic variations in silver bullion used for coinage (±1×10⁻⁴) with respect to the range of ores (±1×10⁻³). To test the practical usefulness of the technique, we analyzed the Ag isotopic abundances of 29 ore samples from ancient mining districts in the Aegean with major and minor Ag-bearing mineralizations, and of 34 ancient Greek coins minted from the sixth to late fourth centuries BC. We distinguished two groups among the coins: a dominant population (93% of the samples) with ¹⁰⁹Ag/¹⁰⁷Ag consistent with literature data (ε¹⁰⁹Ag = −1 to +1) and an isotopically lighter population (ε¹⁰⁹Ag = −2 to −1) which we show originated from Ag-bearing mineralizations in Lavrion (Attica). We further found that sulfur (also analyzed in this study) and silver isotope compositions in Aegean ores do not correlate, a finding that we confirmed on a selection of Iberian galena samples. This shows that the genetic ore type (whether hypo, meso, or epithermal) and silver productivity are not related. Finally, we undertook chemical analysis of the Aegean ore samples and confirmed that Ag-rich ores are also Sb-rich in both Greece and Iberia. A remarkable outcome of the present Ag isotope studies of galena ores from Iberia and Greece is that silver isotope compositions can exclude, with a high degree of reliability, the majority of mines identified by lead isotope analysis as sources from which coinage silver could plausibly have been extracted and thus significantly narrow down the actual source(s). Silver isotope data on galena ores are thus a useful tool for deciding which Pb isotope data included in ore databases should be included in provenance assessment studies. Contrary to some earlier assessments, subtle silver isotope variations can occasionally help determine ore provenance within a single mining district such as Lavrion.
Sharks occupy all living environments of the marine realm as well as some freshwater systems. They display varied and flexible feeding behaviors, but understanding their diet remains challenging due to their elusive ecology and the invasiveness of stomach content analyses in regard of their threatened status. As a potential alternative, we discuss the variability in δ44/42Ca values recorded in tooth enamel of size‐graded individuals belonging to three species of large sharks with distinct diets (Isurus oxyrinchus, Hexanchus griseus and Carcharodon carcharias). The preliminary results highlight shifts in diet linked to ontogeny (I. oxyrinchus and H. griseus) and spatial distribution (C. carcharias) characterizing feeding behavior in these species at individual and population level. These outcomes agree with the results of traditional stomach analyses supporting that non‐traditional stable isotopes thus represent new perspectives for the study of modern and extinct shark ecology. In addition, for the first time, the Sr/Ca elemental ratios measured in H. griseus reflect sexual differences that could be interpreted in terms of spatial segregation or physiological heterogeneities. This article is protected by copyright. All rights reserved.
A series of tris‐dipicolinate europium complexes featuring different complexes has been prepared, and their photophysical study has been performed in the solid state highlighting the crucial role of second sphere water molecules. The non‐radiative deactivation constant (k nr ) varies significantly with the number of interstitial water molecules and their distance to the europium emitting center. The complex (NBu 4 ) 3 [Eu(DPA) 3 ], featuring the most lipophilic cation, exhibits excellent solubility and remarkable photophysical properties in aprotic solvents.
We present a reconstruction of human demography and shell fishing activity in the Sine-Saloum mangrove Delta (Senegal) in the past 6000 years using the summed probability density (SPD) of radiocarbon dates in archaeological shell middens. We explore how this local history relates to the climatic and political history of West Africa. We find that traces of human presence were scarce from 6000 to 2000 yr BP, partly because the geomorphology of the estuary was less favorable to human settlements at that time. A specialized shell fishing population migrated massively to the Sine-Saloum around 2000 yr BP, at the end of the aridification trend that followed the African humid period. This population, likely coming from the northern coast in search of land and resources, fleeing from aridity and the subsequent warfare, found refuge in the coastal mangroves and reached a maximum activity at about 1700 yr BP. This period corresponds to the beginning of trans-Saharan trade, and to a political complexification that would give rise to the Ghana empire. The incoming migration may have occurred in two waves as suggested by two peaks in the SPD curve at 200–400 CE and 600–800 CE and by cultural differences within the Delta. Most sites in the Sine-Saloum islands were abandoned in the early 15th century, before the arrival of Europeans, possibly because intensive shell fishing was not sustainable anymore, or because of the regional political destabilization associated to the fall of the Ghana empire and the beginning of the Mali empire. Shortly after, in agreement with oral traditions, a new population lead by the Manding Guelwars, moved to the Sine Saloum after a military defeat and founded the modern towns. They had a reduced shellfishing activity compared to previous inhabitants, possibly because activities were more oriented to the new trade with Europeans or to a prosperous agriculture in more humid climatic conditions that prevailed from 1500 to 1800 CE.
The equation of state based on the mean spherical approximation (MSA) can describe electrolyte solutions as a primitive model, where the ions are charged hard-sphere particles and the solvent is a continuum medium. In recent years, many propositions of the classical density functional theory (cDFT) for electrolyte solutions have been presented. One of these is the functionalized MSA (fMSA) which has proven to be a great functional approach of MSA to calculate the electric double layer structures. This work demonstrates how the fMSA theory can describe real electrolyte solutions (e.g., NaCl, KI, and LiBr) where hydration and solvent concentration effects are present. Experimental data of the mean activity coefficients of different simple salts were successfully reproduced. When the hydrated diameter and the electrolyte solution electric permittivity are used, the fMSA predicts a charge inversion on the electrostatic potential near a charged surface at high salt concentrations.
Bisimilarity as an equivalence notion of systems has been central to process theory. Due to the recent rise of interest in quantitative systems (probabilistic, weighted, hybrid, etc.), bisimilarity has been extended in various ways, such as bisimulation metric between probabilistic systems. An important feature of bisimilarity is its game-theoretic characterization, where Spoiler and Duplicator play against each other; extension of bisimilarity games to quantitative settings has been actively pursued too. In this paper, we present a general framework that uniformly describes game characterizations of bisimilarity-like notions. Our framework is formalized categorically using fibrations and coalgebras. In particular, our characterization of bisimilarity in terms of fibrational predicate transformers allows us to derive what we call codensity bisimilarity games: a general categorical game characterization of bisimilarity. Our framework covers known bisimilarity-like notions (such as bisimulation metric and bisimulation seminorm) as well as new ones (including what we call bisimulation topology).
Due to the COVID-19 pandemic in Shanghai, China, all school classes were delivered through an online environment from February 24 to May 22, 2020. To support this transition, the Shanghai Education Commission led expert teachers and specialists to develop a series of online video lessons based on the Shanghai unified curriculum, and suggested students watch the online video lessons individually from home, followed by an online synchronous lesson supported by class teachers. This study investigated what primary mathematics teachers learned from addressing these challenges through a case study. By following two purposefully selected teachers over 2 weeks during the transition, multiple data sets including online video lessons, online synchronous lessons, daily reflections, and post-online teacher interviews were collected. A fine-grained analysis of the data from the lens of the documentational approach to didactics found that teachers adaptively used online video lessons as important resources for their online synchronous lessons and virtual Teaching Research Groups as a teachers' collaboration mechanism supported them to develop online video lessons and address various technological constraints. Finally, implications of this case study for mathematics education globally are discussed. Supplementary information: The online version contains supplementary material available at 10.1007/s10649-022-10172-2.
Since last decade, firms are facing the challenge of strict compliance in response to the stakeholders’ awareness about climate change and environmental degradation. Considering these trends, we examine the effect of environmental innovation such as product innovation and process innovation on firm value and the moderating effect of organizational capital on environmental innovation-firm value nexus. Using the data of U.S. listed firms from 2002 to 2019, we find a significantly positive impact of environmental innovation on firm value. Our findings also reveal that organizational capital strengthens the positive association between environmental innovation and firm value, suggesting that firms with higher organizational capital are more likely to consider the demands of stakeholders to be environment friendly which in turn enhances their market value. These findings are aligned with the resource-based view (RBV) and highlight that organizational capital can play a significant role to increase the firm value through environmental innovation. Our results remain robust to subsample analyses, alternative proxies of main variables and are not subject to potential endogeneity concerns. Our study provides new insights into the environmental innovation–firm value nexus and presents important policy implications.
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1,964 members
Emiliano Ricci
  • U1111 (INSERM)-UMR5308 (CNRS) - Centre international de recherche en infectiologie (CIRI)
Bihai Shi
  • Laboratoire Reproduction et Developpement des Plantes
Fabrice Besnard
  • UMR 5667 - Laboratoire Reproduction et Développement des Plantes (RDP)
Lyon, France