Inside Dynamics of Delayed Traveling Waves

The notion of inside dynamics of traveling waves has been introduced in the recent paper [14]. Assuming that a traveling wave u(t,x) = U(x − c   t) is made of several components υi ≥ 0 (i ∈ I ⊂ N), the inside dynamics of the wave is then given by the spatio-temporal evolution of the densities of the components υi. For reaction-diffusion equations of the form ∂tu(t,x) = ∂xxu(t,x) + f(u(t,x)), where f is of monostable or bistable type, the results in [14] show that traveling waves can be classified into two main classes: pulled waves and pushed waves. Using the same framework, we study the pulled/pushed nature of the traveling wave solutions of delay equations              ∂tu(t,x) = ∂xxu(t,x) + F(u(t −τ,x),u(t,x)) We begin with a review of the latest results on the existence of traveling wave solutions of such equations, for several classical reaction terms. Then, we give analytical and numerical results which describe the inside dynamics of these waves. From a point of view of population ecology, our study shows that the existence of a non-reproductive and motionless juvenile stage can slightly enhance the genetic diversity of a species colonizing an empty environment

A parsimonious approach for spatial transmission and heterogeneity in the COVID-19 propagation

International audienceRaw data on the number of deaths at a country level generally indicate a spatially variable distribution of COVID-19 incidence. An important issue is whether this pattern is a consequence of environmental heterogeneities, such as the climatic conditions, during the course of the outbreak. Another fundamental issue is to understand the spatial spreading of COVID-19. To address these questions, we consider four candidate epidemiological models with varying complexity in terms of initial conditions, contact rates and non-local transmissions, and we fit them to French mortality data with a mixed probabilistic-ODE approach. Using statistical criteria, we select the model with non-local transmission corresponding to a diffusion on the graph of counties that depends on the geographic proximity, with time-dependent contact rate and spatially constant parameters. This suggests that in a geographically middle size centralized country such as France, once the epidemic is established, the effect of global processes such as restriction policies and sanitary measures overwhelms the effect of local factors. Additionally, this approach reveals the latent epidemiological dynamics including the local level of immunity, and allows us to evaluate the role of non-local interactions on the future spread of the disease

Synthèse de trois années de suivi pluridisciplinaire de l'élevage bovin en pays Lobi Burkinabe. Etude de 1991 à 1993

Le suivi zootechnique et sanitaire réalisé durant trois ans s'est avéré être une méthode précieuse de collecte de l'information et de diagnostic des systèmes d'élevage bovin en Pays Lobi burkinabé. L'animal baoulé, réputé pour sa trypanotolérance, y présente des performances zootechniques inférieures à celles de l'animal zébu ou métissé. Parmi les axes zootechniques qui paraissent prioritaires, l'âge à la première mise-bas et l'intervalle entre deux vêlages ont été identifiés. La mortalité très élevée des veaux jusqu'à l'âge de un an est un problème complexe, qui affecte l'ensemble des troupeau

Machine behaviour

Machines powered by artificial intelligence increasingly mediate our social, cultural, economic and political interactions. Understanding the behaviour of artificial intelligence systems is essential to our ability to control their actions, reap their benefits and minimize their harms. Here we argue that this necessitates a broad scientific research agenda to study machine behaviour that incorporates and expands upon the discipline of computer science and includes insights from across the sciences. We first outline a set of questions that are fundamental to this emerging field and then explore the technical, legal and institutional constraints on the study of machine behaviour.publishe