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Dynamic mode decomposition as a framework for denoising ultrafast power doppler images
No full textInternational audienc
Spatial Distribution of European Grayling Reflects Longitudinal Temperature Patterns in a Swiss River
No full textInternational audienceMost salmonid populations are declining across their entire habitat range, partly because of large‐scale loss of crucial physical habitats. Alterations in river flow and temperature resulting from climate change are likely to further degrade habitat quality, particularly summer thermal conditions experienced by temperature‐sensitive fish species. Understanding how summer thermal conditions control the spatial distribution of ectotherms is thus central to helping project the consequences of climate change and develop management solutions. This study uses snorkelling fish surveys collected over 10 years and airborne thermal infrared (TIR) mapping of surface temperature acquired in 2022 to assess the relationship between European grayling distribution and thermal habitats along a 9‐km long reach of the Allondon River, Switzerland. Results show that all 3 grayling life stages (adults, sub‐adults and juveniles) respond negatively to elevated summer temperature, with distribution patterns highlighting thermal structuring effects on fish populations. The presence of two cooler reaches appears critical to the survival of the Allondon's declining grayling population, while the warmest reach that separates these habitats potentially acts as a thermal barrier during critical summer conditions. These results were used to guide local stakeholders towards short‐term and longer‐term actions to be taken on the river, which include: concerted trans‐national management to protect key upstream tributaries, tree planting to limit summer peak temperature and strategic protection of cold‐water patches that may act as thermal refuges during critical periods
Topological Properties of Photonic Bands with Synthetic Momentum
No full textInternational audienceWe investigate topological aspects of photonic crystal bands in a hybrid momentum space consisting of a genuine momentum and a synthetic one. The system is realised by a one-dimensional system of bilayer photonic grating, with the translational displacement between the two layers naturally taking the role of the synthetic momentum. Remarkably, the unconventional behaviour of the synthetic momentum allows for the existence of non-trivial topological phases of the system associated with a non-zero total Berry flux without breaking the time-reversal symmetry. Moreover, the resulting band structure in the hybrid momentum space realises the interesting dynamics of merging and splitting of twin Dirac points, as well as gap opening as the system parameters vary. Introducing a simple topological argument, we explain all the changes of the total Berry flux associated with the topological phase transitions. As a signature of different topological phases, edge states at their interface are calculated and analysed in detail. The optomechanical nature of the system also allows for the investigation of the adiabatic evolution of the edge states. Our results pave the way to the paradigm of rich topological phenomena of photonic systems with hybrid momentum space
Hydrodynamic limit for an open facilitated exclusion process with slow and fast boundaries
No full text44 pagesInternational audienceWe study the symmetric facilitated exclusion process (FEP) on the finite one-dimensional lattice {1, . . . , N − 1} when put in contact with boundary reservoirs, whose action is subject to an additional kinetic constraint in order to enforce ergodicity, and whose speed is of order N^{−θ} for some parameter θ. We derive its hydrodynamic limit as N goes to infinity, in the diffusive space-time scaling, when the initial density profile is supercritical. More precisely, the macroscopic density of particles evolves in the bulk according to a fast diffusion equation as in the periodic case, which is now subject to boundary conditions that can be of Dirichlet, Robin or Neumann type depending on the parameter θ. In the Dirichlet case, the FEP exhibits a very peculiar behaviour: unlike for the classical SSEP, and due to the two-phased nature of FEP, the reservoirs impose boundary densities which do not coincide with their equilibrium densities. The proof is based on the classical entropy method, but requires significant adaptations to account for the FEP’s non-product stationary states and to deal with the non-equilibrium settin
Expérimenter la ville autrement : les balades urbaines sensibles d’étudiant·es internationaux·ales à Lyon
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Global Hopf Bifurcation Analysis for a Delayed Nicholson's Blowflies Model with Constant Reproductive Supply
No full textWe investigate the dynamics of a delayed Nicholson's blowflies equation incorporating a constant reproductive supply that influences both density-dependent competition and egg production. The existence and local stability of the positive equilibrium are characterized via the analysis of the associated implicit and characteristic equations. Both local and global Hopf bifurcations are examined to establish conditions for the emergence of periodic solutions. Analytical and numerical results show that increasing the reproductive supply can restore the stability of the positive equilibrium by increasing the critical delay for the onset of Hopf bifurcation, in parameter regimes where sustained oscillations would otherwise occur
Évaluation de la segmentation des cavités nasales à l'aide d'une métrique topologique Betti-1
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Présentation de l'exposition recherche-création “Vivre le végétal en ville à Dakar, Ibadan, Porto-Novo et Yaoundé”
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Deepest voting on rankings
No full textThis article aims to present a unified framework for ranking-based voting rules based on the use of depth functions on permutations, as a counterpart of deepest voting rules on evaluation introduced in Aubin et al. [2022]. It introduces the notion of depth functions, in continuous sets and in permutation sets, the later using the notion of Fréchet means. Deepest voting procedures are then formally defined, and some classical voting rules are expressed as deepest voting procedures, using a large variety of distances on the set of permutations. Links are done between the depth functions mathematical properties and some behaviours of the voting rule, such as Neutrality, Anonymity, Universality, Condorcet winner/loser property and so on
Spatially-Controlled Planar Guided Crystallization of Low-Loss Phase Change Materials for Programmable Photonics
No full textInternational audiencePhotonic integrated devices are progressively evolving beyond passive components into fully programmable systems, notably driven by the progress in chalcogenide phase-change materials (PCMs) for non-volatile reconfigurable nanophotonics. However, the stochastic nature of their crystal grain formation results in strong spatial and temporal crystalline inhomogeneities. Here, we propose the concept of spatially-controlled planar Czochralski growth, a novel method for programming the quasi-monocrystalline growth of low-loss Sb2S3 PCM, leveraging the seeded directional and progressive crystallization within confined channels. This guided crystallization method is experimentally shown to circumvent the current limitations of conventional PCM-based nanophotonic devices, including a multilevel non-volatile optical phase-shifter exploiting a silicon nitride-based Mach-Zehnder interferometer, and a programmable metasurface with spectrally reconfigurable bound state in the continuum. Precisely controlling the growth of PCMs to ensure uniform crystalline properties across large areas is the cornerstone for the industrial development of non-volatile reconfigurable photonic integrated circuits