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Avatars of Stein's theorem in the complex setting
No full textIn this paper, we establish some variants of Stein's theorem which states that a non-negative function belongs to the Hardy space H 1 (T) if and only if it belongs to L log L(T). We consider Bergman spaces of holomorphic functions in the upper half plane and develop avatars of Stein's Theorem and relative results in this context. We are led to consider weighted Bergman spaces and Bergman spaces of Musielak-Orlicz type. Eventually, we characterize bounded Hankel operators on A 1 (C +). This paper is dedicated to Eleonor Harboure, Pola, a colleague and friend whose memory will live on
Projective and Carrollian geometry at time/space-like infinity on projectively compact Ricci flat Einstein manifolds
No full textInternational audienceIn this article we discuss how to construct canonical strong Carrollian geometries at time/space like infinity of projectively compact Ricci flat Einstein manifolds and discuss the links between the underlying projective structure of the metric . The obtained Carrollian geometries are determined by the data of the projective compactification. The key idea to achieve this is to consider a new type of Cartan geometry based on a non-effective homogeneous model for projective geometry. We prove that this structure is a general feature of projectively compact Ricci flat Einstein manifolds
Reducing metastable continuous-space Markov chains to Markov chains on a finite set
No full textInternational audienceWe consider continuous-space, discrete-time Markov chains on , that admit a finite number of metastable states. Our main motivation for investigating these processes is to analyse random Poincaré maps, which describe random perturbations of ordinary differential equations admitting several periodic orbits. We show that under a few general assumptions, which hold in many examples of interest, the kernels of these Markov chains admit eigenvalues exponentially close to 1, which are separated from the remainder of the spectrum by a spectral gap that can be quantified. Our main result states that these Markov chains can be approximated, uniformly in time, by a finite Markov chain with states. The transition probabilities of the finite chain are exponentially close to first-passage probabilities at neighbourhoods of metastable states, when starting in suitable quasistationary distributions
Biharmonic Hypersurfaces in Euclidean Spaces
No full textAn isometric immersion is biharmonic if , i.e. if , where and are the metric Laplacian and the mean curvature vector field of respectively. More generally, biconservative hypersurfaces (BCH) are isometric immersions for which only the tangential part of the biharmonic equation vanishes. We study and construct BCH that are holonomic, i.e. for which the principal curvature directions define an integrable net, and we deduce that is a holonomic biharmonic hypersurface iff it is minimal
Financements intermédiés et fragilité en Afrique
No full textNonobstant le grand intérêt sur la question du financement des Etats fragiles, très peu d'études se sont penchées jusqu'ici sur l'impact des ressources externes sur la fragilité dans les pays. Cette étude vient compléter la littérature et se penche sur l'impact spécifique des financements intermédiés sur la fragilité des pays africains. L'étude utilise la méthode de l'appariement des scores de propension appliquée à un panel de 50 pays africains sur la période 2009-2019, pour estimer l'effet des financements intermédiés sur la fragilité suivant quatre algorithmes d'appariement. Les résultats sont significatifs à 5% et montrent que le financement intermédié réduit la fragilité des pays concernés de 8,1% à 13,1% dépendamment de l'algorithme retenu. Le test de robustesse confirme cet impact positif et significatif indépendamment de la source de financement. Ces résultats devraient intéresser les décideurs politiques, les institutions financières internationales et les banques centrales, de même que les chercheurs dans la formulation des politiques et stratégies d'inclusion financière et de renforcement de la résilience dans les Etats fragiles.</div
Can liver volatolome reveal poultry exposure to polychlorobiphenyls, metallic trace elements, pesticides, veterinary drugs or mycotoxins?
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Peroxidase 4-Based Enzymatic Synthesis of Stilbene Oligomers in Methyl Jasmonate-Elicited Grapevine Cell Suspensions
No full textInternational audienceStilbenes are specialized metabolites that are particularly abundant in Vitis species. Although the biosynthetic pathways of stilbenes have been well-characterized, the role of specific peroxidases in stilbene oligomerization remains to be investigated. In this study, we used grapevine cell cultures to characterize the functional role of Vitis vinifera peroxidase 4 (VvPRX4) in the production of resveratrol oligomers after elicitation with methyl jasmonate (MeJA). We showed that MeJA triggers the accumulation of t-resveratrol, resveratrol dimers, and predicted resveratrol trimers in culture medium. This accumulation was correlated with upregulation of the PRX4 gene in grapevine cells. Using bacterial crude extracts containing VvPRX4, we demonstrated that VvPRX4 converts t-resveratrol into dimers, t-ε-viniferin into tetramers, and both combined substrates into resveratrol trimers. Additionally, VvPRX4 mediates the formation of glycosylated dimers using t-piceid and t-resveratrol as substrates. These results highlight the functional role of VvPRX4 in stilbene oligomerization in MeJA-elicited grapevine cell cultures
"Principe du contradictoire et contestation du règlement de copropriété"
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