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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
Bilateral parking procedures
No full textWe introduce the class of bilateral parking procedures on the integer line. While cars try to park in the nearest available spot to their right in the classical case, we consider more general parking rules that allow cars to use the nearest available spot to their left. We show that for a natural subclass of local procedures, the number of corresponding parking functions of length r is always equal to . The setting can be extended to probabilistic procedures, in which the decision to park left or right is random. We finally describe how bilateral procedures can naturally be encoded by certain labeled binary forests, whose combinatorics shed light on several results from the literature
Reduced Vegetation Uptake During the Extreme 2023 Drought Turns the Amazon Into a Weak Carbon Source
No full textInternational audienceIn 2023, the biogeographic Amazon experienced temperature anomalies of 1.5°C above the 1991-2020 average from September to November. These conditions were driven by high sea surface temperature in the Atlantic and Pacific oceans, together with reduced moisture advection from the Atlantic, causing large vapor pressure and water deficits in the second semester of 2023. Here, we evaluate the response of the Amazon carbon cycle to this extreme event across different spatial scales. We combined atmospheric CO 2 mole fractions and eddy covariance flux data from the Amazon Tall Tower Observatory (ATTO, -2.1441, -58.99), low-latency simulations by Dynamic Global Vegetation Models (DGVMs), an atmospheric inversion, and remote sensing data. We find that in 2023 the Amazon region was, including fires, a net carbon source of 0.01-0.17 PgC. Fire emissions (0.15 [0.13-0.17] PgC) were within typical variability of the 2003-2023 period, thus we attribute the weak carbon source to reduced vegetation uptake during the dry season (August-October). A stronger-than-normal vegetation uptake early in the year (January-April), consistent across data streams and spatial scales, mitigated the total carbon losses by the end of the year. We find a shift from carbon sink to source in May and a peak source in October. Our findings show a reduced vegetation carbon uptake over the Amazon region, leading to a weak carbon source that contributed up to 30% of the net carbon loss in the tropical land in 2023.</div
Discrétisation de milieux multicouches à forts contrastes : qu'en est-il des interfaces ?
No full textWave propagation in multilayered media with high material contrasts poses significant numerical challenges, as large variations in wavenumbers lead to strong reflections and complex transmission of the incoming wave field. To address these difficulties, we employ a boundary integral formulation thereby avoiding volumetric discretization. In this framework, the accuracy of the numerical solution depends strongly on how the material interfaces are discretized. In this work, we demonstrate that standard meshing strategies based on resolving the maximum wavenumber across the domain become computationally inefficient in multilayered configurations, where high wavenumbers are confined to localized subdomains. Through a systematic study of multilayer transmission problems, we show that no simple discretization rule based on the maximum wavenumber or material contrasts emerges. Instead, the wavenumber of the background (exterior) medium plays a dominant role in determining the optimal boundary resolution. Building on these insights, we propose an adaptive approach that achieves uniform accuracy and efficient computation across multiple layers. Numerical experiments for a range of multilayer configurations demonstrate the scalability and robustness of the proposed approach
DBS-related infections in Parkinson's disease: Incidence, risk factors, management and outcome
No full textInternational audienc
Le capital économique. Remettre sur l'établi un concept classique pour analyser le travail
No full textInternational audienc
The alpha rhythm: from physiology to behaviour
No full textInternational audienceThe alpha rhythm, first identified by Hans Berger 100 years ago, is the dominant non-invasive electrophysiological signature of the healthy human brain in the awake state. For decades, it was believed that the alpha rhythm reflected rest or idling; however, this perspective changed in the 2000s when researchers found that alpha oscillations increase with cognitive demands. This discovery led to a paradigm shift, demonstrating that alpha oscillations reflect the functional inhibition of brain regions that are not needed for a specific task, thereby directing information to task-specific areas. We have reviewed the physiological mechanisms involved in generating alpha oscillations, which has informed computational models explaining how these oscillations emerge within physiologically realistic networks. At the behavioural level, alpha oscillations are strongly modulated across nearly all cognitive paradigms tested in humans, reflecting the allocation of computational resources within the active brain network. Research in individuals with attention-related issues has highlighted their impaired ability to modulate alpha oscillations, which is associated with performance deficits. Therefore, further exploration of alpha oscillations has the potential to uncover causal mechanisms underlying attention problems, such as those related to ADHD and ageing. Lastly, advancements in technology are opening new avenues for characterising alpha oscillations in ecologically valid settings and across the lifespan. This progress sets the stage for exploring the role of alpha oscillations in cognitive development and their functioning in natural environments
Conjecture de Kakeya et algèbres de von Neumann de réseaux de rang supérieur
No full textIf the non-commutative L p space of SLn(Z) has the completely bounded approximation property for some non-trivial value of p, then some form of the Kakeya conjecture holds in dimension d, for all d ≤ n+12 . The proof relies on a spherical analogue of the following question in Euclidean harmonic analysis, that we raise and investigate: does a radially symmetric Fourier multiplier that is bounded on Lp(R d ) for some p ̸ = 2 necessarily have a continuous symbol? We leave the question open, but we prove that the primitive of such function is smooth in the sense of Zygmund, give some necessary conditions for Lp-boundedness in terms of Besov spaces and Littlewood-Paley decomposition for the symbol, and observe that a negative answer implies some form of the Kakeya conjecture in dimension d. We then provide spherical forms of these results, which, when combined with a refinement of Lafforgue's rank 0 reduction, leads to the claimed result.</div