Search results for "Populations"
showing 10 items of 493 documents
Fragmentation-related patterns of genetic differentiation in pedunculate oak (Quercus robur) at two hierarchical scales
2016
Populations at species' range margins are expected to show lower genetic diversity than populations at the core of the range. Yet, long-lived, widespread tree species are expected to be resistant to genetic impoverishment, thus showing comparatively high genetic diversity within populations and low differentiation among populations. Here, we study the distribution of genetic variation in the pedunculate oak (Quercus robur L.) at its range margin in Finland at two hierarchical scales using 15 microsatellite loci. At a regional scale, we compared variation within versus among three oak populations. At a landscape scale, we examined genetic structuring within one of these populations, growing …
Intérêt des méthodes alternatives dans l’évaluation du médicament dans les populations particulières
2020
Well conducted randomized clinical trial is considered gold standard in drug safety and efficacy evaluation. Drug development can be challenging in rare diseases, or in ethically sensitive populations (pregnant women, children, patient with cognitive defect), because of low number of subjects. The low rate of observed events at a sample scale in this population can lead to a biased evaluation of drugs compared to the general population. The aim of this work was to address alternative methods for drug evaluation in particular populations, especially pharmaco-epidemiology on populational database of the SNDS (Système National des Données de Santé). We first evaluate the safety of anti-TNFα in…
Mitochondrial DNA Gene Diversity and Morphological Variability of the Common Vole (Microtus arvalis) in France
2006
International audience
Blue Moon: Is This a Property of Background Aerosol?
2010
Stellar extinction measurements made at three astronomical observatories showed that on ~50% of the nights the extinction due to aerosol light scattering increased rather than decreased with increasing wavelength (anomalous extinction) for wavelengths close to 500 nm. This extinction behavior is analyzed in this paper and limits are established for the aerosol characteristics necessary for this phenomenon to exist, including geometric standard deviations, imaginary part of refractive index, mean radius, and gaseous NO(2).
Dynamics of Confined Crowd Modelled Using Fermionic Operators
2014
An operatorial method based on fermionic operators is used to describe the dynamics of a crowd made of different kind of populations mutually interacting and moving in a two–dimensional bounded closed region. The densities of the populations are recovered through the Heisenberg equation and the diffusion process is driven by the Hamiltonian operator defined by requiring that the populations move along optimal paths. We apply the model obtained in a concrete situation and we discuss the effect of the interaction between the populations during their motion.
Moment Equations for a Spatially Extended System of Two Competing Species
2005
The dynamics of a spatially extended system of two competing species in the presence of two noise sources is studied. A correlated dichotomous noise acts on the interaction parameter and a multiplicative white noise affects directly the dynamics of the two species. To describe the spatial distribution of the species we use a model based on Lotka-Volterra (LV) equations. By writing them in a mean field form, the corresponding moment equations for the species concentrations are obtained in Gaussian approximation. In this formalism the system dynamics is analyzed for different values of the multiplicative noise intensity. Finally by comparing these results with those obtained by direct simulat…
Constraints on massive sterile neutrino species from current and future cosmological data
2011
Sterile massive neutrinos are a natural extension of the Standard Model of elementary particles. The energy density of the extra sterile massive states affects cosmological measurements in an analogous way to that of active neutrino species. We perform here an analysis of current cosmological data and derive bounds on the masses of the active and the sterile neutrino states as well as on the number of sterile states. The so-called (3+2) models with three sub-eV active massive neutrinos plus two sub-eV massive sterile species is well within the 95% CL allowed regions when considering cosmological data only. If the two extra sterile states have thermal abundances at decoupling, Big Bang Nucle…
Perturbations of the classical Lotka-Volterra system by behavioral sequences
1995
The complexity and the variability of parameters occurring in ecological dynamical systems imply a large number of equations.
Noise-induced effects in population dynamics
2002
We investigate the role of noise in the nonlinear relaxation of two ecosystems described by generalized Lotka-Volterra equations in the presence of multiplicative noise. Specifically we study two cases: (i) an ecosystem with two interacting species in the presence of periodic driving; (ii) an ecosystem with a great number of interacting species with random interaction matrix. We analyse the interplay between noise and periodic modulation for case (i) and the role of the noise in the transient dynamics of the ecosystem in the presence of an absorbing barrier in case (ii). We find that the presence of noise is responsible for the generation of temporal oscillations and for the appearance of s…
Transient behavior of a population dynamical model
2005
The transient behavior of an ecosystem with N random interacting species in the presence of a multiplicative noise is analyzed. The multiplicative noise mimics the interaction with the environment. We investigate different asymptotic dynamical regimes and the role of the external noise on the probability distribution of the local field.