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On a mode-matching technique for acoustic scattering by a cascade of cambered vanes
No full textInternational audienceA two-dimensional mode-matching technique is developed to compute the scattering of an acoustic wave by a cascade of staggered and cambered vanes in subsonic regime, such as those encountered in axial-flow fan stages. Apart from the need to reproduce a more realistic geometry in analytical modeling, introducing vane camber is a relevant way of retrieving the global evolution of the mean flow away from the vanes, simply by mass-flow conservation through the expanding inter-vane channels. This prevents mean-flow discontinuity and introduces a realistic variation of the equivalent dipole sources along the vane chord. The expansion of the cross-section along the inter-vane channels, induced by curvature, is taken into account by multiple-scale analysis, assuming slow variations of the geometry. The validity of the model is assessed by extensive comparisons with high-fidelity numerical results, with and without flow. The assumptions used in the analytical model are found to be suited to modern geometries of outlet guide vanes
Symplectic circle actions on manifolds with contact type boundary
No full textInternational audienceMany of the existing results for closed Hamiltonian G-manifolds are based on the analysis of the corresponding Hamiltonian functions using Morse-Bott techniques. In general such methods fail for non-compact manifolds or for manifolds with boundary. In this article, we consider circle actions only on symplectic manifolds that have (convex) contact type boundary. In this situation we show that many of the key ideas of Morse-Bott theory still hold, allowing us to generalize several results from the closed setting. Among these, we show that in our situation any symplectic group action is always Hamiltonian, we show several results about the topology of the symplectic manifold and in particular about the connectedness of its boundary. We also show that after attaching cylindrical ends, a level set of the Hamiltonian of a circle action is either empty or connected. We concentrate mostly on circle actions, but we believe that with our methods many of the classical results can be generalized from closed symplectic manifolds to symplectic manifolds with contact type boundary
Private Frequency Estimation via Residue Number Systems
No full textInternational audienceWe present Modular Subset Selection (MSS), a new algorithm for locally differentially private (LDP) frequency estimation. Given a universe of size k and n users, our ε-LDP mechanism encodes each input via a Residue Number System (RNS) over ℓ pairwise-coprime moduli m0, ..., m_{ℓ−1}, and reports a randomly chosen index j ∊ [ℓ] along with the perturbed residue using the statistically optimal Subset Selection (SS) mechanism. This design reduces the user communication cost from Θ(ω log₂(k/ω)) bits required by standard SS (with ω ≈ k/(e^ε+1)) down to ⌈ log₂ ℓ ⌉ + ⌈ log₂ m_j ⌉ bits, where m_j < k. Server-side decoding runs in Θ(n + r k ℓ) time, where r is the number of LSMR iterations. In practice, with well-conditioned moduli (i.e., constant r and ℓ = Θ(log k)), this becomes Θ(n + k log k). We prove that MSS achieves worst-case MSE within a constant factor of state-of-the-art protocols such as SS and Projective Geometry Response (PGR), while avoiding the algebraic prerequisites and dynamic-programming decoder required by PGR. Empirically, MSS matches the estimation accuracy of SS, PGR, and RAPPOR across realistic (k, ε) settings, while offering faster decoding than PGR and shorter user messages than SS. Lastly, by sampling from multiple moduli and reporting only a single perturbed residue, MSS achieves the lowest reconstruction-attack success rate among all evaluated LDP protocols
CytoSyn: a Foundation Diffusion Model for Histopathology - Tech Report
No full textComputational pathology has made significant progress in recent years, fueling advances in both fundamental disease understanding and clinically ready tools. This evolution is driven by the availability of large amounts of digitized slides and specialized deep learning methods and models. Multiple self-supervised foundation feature extractors have been developed, enabling downstream predictive applications from cell segmentation to tumor sub-typing and survival analysis. In contrast, generative foundation models designed specifically for histopathology remain scarce. Such models could address tasks that are beyond the capabilities of feature extractors, such as virtual staining. In this paper, we introduce CytoSyn, a state-of-the-art foundation latent diffusion model that enables the guided generation of highly realistic and diverse histopathology H&E-stained images, as shown in an extensive benchmark. We explored methodological improvements, training set scaling, sampling strategies and slide-level overfitting, culminating in the improved CytoSyn-v2, and compared our work to PixCell, a state-of-the-art model, in an in-depth manner. This comparison highlighted the strong sensitivity of both diffusion models and performance metrics to preprocessing-specific details such as JPEG compression. Our model has been trained on a dataset obtained from more than 10,000 TCGA diagnostic whole-slide images of 32 different cancer types. Despite being trained only on oncology slides, it maintains state-of-the-art performance generating inflammatory bowel disease images. To support the research community, we publicly release CytoSyn's weights, its training and validation datasets, and a sample of synthetic images in this repository: https://huggingface.co/Owkin-Bioptimus/CytoSyn.</div
Effectiveness of protected areas in limiting agricultural encroachment and conserving herbivores in West‐Central African savannahs
No full textInternational audienceThis study examines the long‐term effectiveness of protected areas (PAs) in the savannahs of West and Central Africa in resisting agricultural encroachment and conserving large herbivore populations. Using Landsat imagery (1973–2018) and wildlife census data, we evaluated land‐use and land‐cover change within ten core PAs and their surrounding 60‐km buffer zones, focusing on four focal species: african buffalo, roan antelope, hartebeest and savannah elephant. Results show that core PAs largely retained their natural vegetation, while surrounding landscapes experienced significant agricultural expansion—particularly in unprotected buffer zones. National parks, especially those embedded within connected networks such as the W–Arly–Pendjari complex, demonstrated stronger resistance to land conversion and higher herbivore biomass. However, wildlife population trends did not consistently align with landscape integrity, indicating that factors such as PA size, governance and ecological connectivity critically shape conservation outcomes. We identify three typologies of PAs—underperforming large reserves, integrated transboundary networks and small but well‐managed sites—each requiring distinct strategic approaches. These findings underscore the need for outcome‐focused conservation strategies that go beyond legal designation to address spatial planning, connectivity and local management capacity
L'univers des courges: Les cultiver, les cuisiner, les savourer
No full textNational audienceLes dérèglements climatiques, l’effondrement de la biodiversité sauvage et cultivée, font peser des risques sur la sécurité alimentaire des populations, et ceci même dans les pays où cette question ne se posait plus. En région stéphanoise, Christophe Gaudry, paysan bio, a entrepris, à son échelle, de renverser cette tendance en diversifiant les variétés cultivées, fruits ou légumes. Il travaille selon des techniques de permaculture et de maraîchage sur sols vivants. Sa ferme ambitionne de devenir une Arche de Noé végétale, où légumes, arbustes à petits fruits et arbres fruitiers se côtoient et participent à une vaste synergie qui bénéficie à l’ensemble des cultures.Parmi les nombreuses espèces cultivées, les courges intéressent particulièrement Christophe Gaudry qui en a cultivé jusqu’à 54 variétés différentes ! Cette étonnante diversité a attiré l’attention de Marie-Thérèse Charreyre, chercheuse au CNRS, rejointe par Éric Tannier, chercheur à l’Inria, qui souhaitent contribuer à la redirection écologique par de la recherche participative. Ainsi est né un projet original associant chercheurs et acteurs de terrain autour de cucurbitacées variées, depuis leur culture jusqu’à leur mise en valeur au travers de créations culinaires réalisées par le pôle Innovation du Centre de Recherche de l’Institut Lyfe, dirigé par Estelle Petit.Ce livre retrace leur aventure commune, en explorant des volets complémentaires de ce projet de recherche : agronomique (de la graine à la récolte des courges), sensoriel (avec la découverte du mode de consommation crue de certaines courges), nutritionnel (avec des analyses sur les sucres, les fibres, les micro-nutriments) et, bien sûr, culinaire (avec des recettes « de tous les jours » et des recettes « gastronomiques »). A l’évidence, la courge est un légume d’avenir
Sound Scattering by Shear Layers of High-Speed Isothermal and Hot Turbulent Jets
No full textInternational audienceThe scattering of sound waves by turbulent shear layers is investigated for jets with acoustic Mach numbers between 0.3 and 1.3 and temperatures equal to 1, 1.5, or 2.25 times the ambient temperature, computed by large-eddy simulations (LESs) in previous work. Sound scattering is studied by solving the two-dimensional linearized Euler equations using the LES unsteady axisymmetric flowfields as the base flow. An acoustic source radiating at Strouhal numbers between 3 and 27 is placed on the jet axis two diameters downstream of the nozzle exit. For all jets, sound scattering is mainly related to the large-scale shear-layer turbulent structures, and spectral broadening occurs, yielding components on both sides of the source frequency. These components have amplitudes increasing strongly with Mach number and slightly with jet temperature and usually form two lobes in the sound spectra. However, for a jet Mach number of 0.9, no lobes clearly emerge upstream of the source because of the leakage of upstream-propagating guided jet waves. An additional lobe associated with the initial shear-layer instability waves is also seen at low Mach numbers. Finally, for hot jets, sound scattering is caused by both the jet velocity fluctuations and the temperature fluctuations