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Subcritical annulus crossing in spatial random graphs
No full textWe consider general continuum percolation models obeying sparseness, translation invariance, and spatial decorrelation. In particular, this includes models constructed on general point sets other than the standard Poisson point process or the Bernoulli-percolated lattice. Moreover, in our setting the existence of an edge may depend not only on the two end vertices but also on a surrounding vertex set and models are included that are not monotone in some of their parameters. We study the critical annulus-crossing intensity λc, which is smaller or equal to the classical critical percolation intensity λc and derive a condition for λc > 0 by relating the crossing of annuli to the occurrence of long edges. This condition is sharp for models that have a modicum of independence. In a nutshell, our result states that annuli are either not crossed for small intensities or crossed by a single edge. Our proof rests on a multiscale argument that further allows us to directly describe the decay of the annulus-crossing probability with the decay of long edges probabilities. We apply our result to a number of examples from the literature. Most importantly, we extensively discuss the weight-dependent random connection model in a generalised version, for which we derive sufficient conditions for the presence or absence of long edges that are typically easy to check. These conditions are built on a decay coefficient ζ that has recently seen some attention due to its importance for various proofs of global graph properties.</div
Microclimat urbain Arboré dans un contexte de changement Global –Identification des interrelations Climat/biodiversité/humains dans un square
No full textInternational audienc
Guy Avanzini et la Pédagogie Freinet
No full textInternational audienceÀ ma connaissance, Guy Avanzini fut un des rares universitaires des années 60 du XXème siècle et suivantes qui a pris au sérieux les propositions pédagogiques énoncées, dès les années 20, par Célestin Freinet et ses compagnons réunis dans le Mouvement Pédagogique institué par la création de l’I.C.E.M. – Institut Coopératif de l’École Moderne en 1947. Probablement, il était aussi un des rares universitaires à être écouté par Célestin Freinet. Ma contribution vise à travers un témoignage personnel, en tant militant du Mouvement Freinet depuis 1972 et pionnier dans les approches pédagogiques Freinet de l’enseignement des mathématiques au lycée, étayé par des documents d’archive, à identifier et à expliciter les relations de Guy Avanzini avec l’I.C.E.M.. Compte tenu de l’esprit de cet hommage rendu à Guy Avanzini, lors de la Journée scientifique le 17 novembre 2023, fondé en partie sur des témoignages, nous avons pris le parti d’utiliser le « je » au lieu du « nous » habituel
Security of differential phase shift QKD from relativistic principles
No full textPublished version with slightly expanded introductionInternational audienceThe design of quantum protocols for secure key generation poses many challenges: On the one hand, they need to be practical concerning experimental realisations. On the other hand, their theoretical description must be simple enough to allow for a security proof against all possible attacks. Often, these two requirements are in conflict with each other, and the differential phase shift (DPS) QKD protocol exemplifies these difficulties: It is designed to be implementable with current optical telecommunication technology, which, for this protocol, comes at the cost that many standard security proof techniques do not apply to it. After about 20 years since its invention, this work presents the first full security proof of DPS QKD against general attacks, including finite-size effects. The proof combines techniques from quantum information theory, quantum optics, and relativity. We first give a security proof of a QKD protocol whose security stems from relativistic constraints. We then show that security of DPS QKD can be reduced to security of the relativistic protocol. In addition, we show that coherent attacks on the DPS protocol are, in fact, stronger than collective attacks. Our results have broad implications for the development of secure and reliable quantum communication technologies, as they shed light on the range of applicability of state-of-the-art security proof techniques
The underground weathering of Toarcian black shales from SE France and its paleoenvironmental, taphonomical and biogeochemical consequences
No full textInternational audienceOrganic-rich strata deposited under poorly oxygenated waters known as ‘black shales’ constitute key targets for paleobiological and paleoenvironmental studies. Little is known, however, about how these oxidation-sensitive lithologies and their key paleoenvironmental information can be affected by recent chemical weathering. In this study, we present new geochemical (organic and inorganic stable isotopes, TOC, CaCO3) and mineralogical (concentration and size distribution of pyrite framboids) data from weathered and unweathered black shales and limestone beds recording the Toarcian Oceanic Anoxic Event (T-OAE) from Beaujolais (SE France). These analyses show that the organic carbon of the weathered samples have decreased by 97% and is generally 13C-enriched relative to coeval pristine samples. The resulting offset in organic carbon isotope (δ13Corg) varies from 0.1 to as much as 4‰ along the studied succession, likely reflecting temporal changes in the carbon isotope composition of the labile and refractory end-members across the T-OAE. Mildly weathered samples contain >50% less pyrite framboids than pristine samples, but preserve their size distribution, making this the latter a reliable proxy of original water column oxygenation. Pyrite dissolution was total in the highly weathered samples, which produced sulfuric acid and a moderate loss of the CaCO3 fraction. The substantial 13C- and 18O-depletion recorded in the most weathered samples indicate that a part of the dissolved carbonate reprecipitated after exchanging with CO2-rich meteoric waters. These results imply that underground continental weathering can dramatically alter the paleoenvironmental and taphonomical signals in organic rich-strata located at >40 m below the surface and should hence be more systematically considered when analyzing outcrop and subsurface data. In addition, our tentative estimates of petrogenic carbon oxidation rates at the study site are 2 to 10 times higher than that of other sedimentary rocks, suggesting that the fault-assisted oxidation of black shales in regions located away from active orogenic areas may contribute disproportionately to the global carbon cycle budget
La démocratie du faire : l’action concrète au service d’un empowerment écologique
No full textInternational audienc
Systematic Approach to Parametrization of Disaccharides for the Martini 3 Coarse-Grained Force Field
No full textInternational audienceSugars are ubiquitous in biology; they occur in all kingdoms of life. Despite their prevalence, they have often been somewhat neglected in studies of structure–dynamics–function relationships of macromolecules to which they are attached, with the exception of nucleic acids. This is largely due to the inherent difficulties of not only studying the conformational dynamics of sugars using experimental methods but indeed also resolving their static structures. Molecular dynamics (MD) simulations offer a route to the prediction of conformational ensembles and the time-dependent behavior of sugars and glycosylated macromolecules. However, at the all-atom level of detail, MD simulations are often too computationally demanding to allow a systematic investigation of molecular interactions in systems of interest. To overcome this, large scale simulations of complex biological systems have profited from advances in coarse-grained (CG) simulations. Perhaps the most widely used CG force field for biomolecular simulations is Martini. Here, we present a parameter set for glucose- and mannose-based disaccharides for Martini 3. The generation of the CG parameters from atomistic trajectories is automated as fully as possible, and where not possible, we provide details of the protocol used for manual intervention
October 7: the visual fate of the hostages
No full textInternational audienceThe images of the crimes committed on October 7 provoked not only understandable shock, but also much debate: was it necessary to show the horror that Hamas terrorists sought to film and broadcast? Emmanuel Taïeb examines the fate of these images and the political uses to which they have been put, highlighting their reversibility and the risk of making them invisible
Quantum Hall Edges Beyond the Plasma Analogy
No full textInternational audienceWe demonstrate that the plasma analogy is generally unreliable at predicting the edge properties of quantum Hall (QH) states, as it fails to account for the local edge velocity. This discrepancy arises from a fundamental difference between QH droplets and Coulomb gases (CGs): the former are incompressible liquids subject to area-preserving deformations, while the latter are governed by electrostatics and thus involve conformal transformations. We illustrate this QH/CG mismatch across various examples and show its impact on physical quantities, measurable in both solid-state samples and quantum simulators. Specifically, we discuss fluctuations of local observables and their connection to state-of-the-art microwave absorption experiments
