Sinuosities in vascular structures

International audienceIn most organs, depending on the scale, the nature of the heart pump, the geometry and topology of the organ, some of the blood vessels tend to exhibit sinuous trajectories. We describe a part of this sinuous behavior, including partial biological and strong physical effects in a global physical framework. We will voluntarily focus on physical and topological effects. This study is performed on the vitelline membrane of the chicken embryo. Crossing angles, sinuosity, and the oscillation amplitude of the vascular system are analyzed. Surprisingly, the equation of river meandering dynamics is found to model the sinuosities in the vascular system, and an extension of this equation to non planar case is able to explain the effect of tissue global curvature on the vascular system. Results of this study could lead to a new understanding of the interplay between biological signaling and physical effects in determining the vascular pattern in different tissues

Pedestrian fatality and impact speed squared: Cloglog modeling from French national data

The present study estimates pedestrians' risk of death according to the impact speed when hit by a passenger car in a frontal collision.L'étude actuelle évalue le risque d'être tué pour un piéton selon l'impact de la vitesse quand il est renversé par une voiture dans une collision frontal

L'infiltration des oiseaux forestiers dans les milieux buissonnants de Corse

The bird faunas of two vegetation gradients ranging from open grassland to high forest were compared in southern France and Corsica. On the whole, species richness is lower (ca. 30 % ) in Corsica than on the mainland. However, a low bird species richness does not characterize all Corsican habitats. Moreover, the bird communities of Corsican shrubby habitats are closer in their diversity and frequency distribution to mainland bird forest communities than to the bird communities of mainland shrubby habitats. The study of species composition and species distribution of the birds common to the two areas studied (i.e. 79 % of the species found in Corsica) demonstrates that the existing differences are attributable to a broader habitat use by forest birds which formerly colonized Corsica (i.e. an increased niche breadth). Not only have these species spread into all the available shrubby habitats, but their present local abundance is greater than on the mainland. Several, but not forcibly exclusive, hypotheses are put forward to explain the present Corsican situatio

An experimental study of how variation in deer density affects vegetation and songbird assemblages of recently harvested boreal forests

Intense browsing by abundant large herbivores can threaten the ecological integrity of ecosystems by inducing modifications in the structure and composition of vegetation that trigger trophic cascades affecting plant and animal communities. We investigated the relationships between density of white-tailed deer (Odocoileus virginianus (Zimmermann, 1780)), forest succession after clear-cut, and songbird communities on Anticosti Island, Quebec, Canada. We hypothesized that lower deer densities would alter the trajectory of forest succession after clear-cutting and lead to a rapid recovery of habitat attributes favorable to songbirds associated with a dense complex shrub layer. Six years after establishing a controlled browsing experiment (0, 7.5, 15, and >27 deer·km–2) in recent clearcuts, reducing deer densities ≤7.5 deer·km–2 initiated the restoration of balsam fir (Abies balsamea (L.) Mill.) forests and increased the regeneration of paper birch (Betula papyrifera Marshall). Increasing birch ground cover from 10% to 20% increased songbird total abundance, species richness, and diversity by 17%, 39%, and 31%, respectively. Alder Flycatcher (Empidonax alnorum Brewster, 1895) was only present at ≤7.5 deer·km–2 and strongly associated with birch regeneration. The regeneration of browse-resistant plants such as white spruce (Picea glauca (Moench) Voss) in some areas at high deer density favored the maintenance of many shrub-dependent songbirds but also species usually associated with forest canopy. Active management of deer populations in Canadian harvested boreal forests will mitigate losses in vegetation and songbirds caused by over-browsing.Le broutement intensif par de nombreux grands herbivores peut menacer l’intégrité écologique d’écosystèmes en induisant des modifications de la structure et de la composition de la végétation qui déclenchent des cascades trophiques ayant des incidences sur les communautés végétales et animales. Nous nous sommes penchés sur les liens entre la densité du cerf de Virginie (Odocoileus virginianus (Zimmermann, 1780)), la succession forestière après la coupe à blanc et les communautés d’oiseaux chanteurs sur l’île d’Anticosti (Québec, Canada). Nous avons émis l’hypothèse que de plus faibles densités de cerfs modifieraient la trajectoire de succession forestière après une coupe à blanc et mèneraient au rétablissement rapide des attributs d’habitat favorables aux oiseaux chanteurs associés à une strate arbustive complexe et dense. Six ans après l’établissement d’une expérience de broutement contrôlé (0, 7,5, 15 et >27 cerfs·km–2) dans des coupes récentes, la réduction des densités de cerfs à ≤7,5 cerfs·km–2 s’est traduite par le début du rétablissement des forêts de sapin baumier (Abies balsamea (L.) Mill.) et une régénération accrue du bouleau à papier (Betula papyrifera Marshall). Un passage de la couverture de bouleau de 10 % à 20 % s’est traduit par des augmentations de l’abondance totale d’oiseaux chanteurs, de la richesse spécifique et de la diversité de 17 %, 39 % et 31 %, respectivement. Le moucherolle des aulnes (Empidonax alnorum Brewster, 1895) n’était présent qu’à des densités ≤7,5 cerfs·km–2 et était fortement associé à la régénération du bouleau. La régénération de plantes résistantes au broutement, telles que l’épinette blanche (Picea glauca (Moench) Voss) dans certaines zones à forte densité de cerfs a favorisé le maintien de nombreux oiseaux chanteurs dépendants des arbustes, mais également d’espèces généralement associées à la canopée. La gestion active des populations de cerfs dans les forêts boréales canadiennes exploitées atténuera les pertes de végétation et d’oiseaux chanteurs causées par le surbroutemen

1-kHz table-top ultrashort hard x-ray source for time-resolved x-ray protein

International audienceWe describe a compact, reliable, and high-average-power femtosecond x-ray source and its first application to diffraction on protein crystal. The setup relies on a homemade Ti: sapphire system delivering 12 mJ at a 1 kHz repetition rate, associated with a small vacuum chamber especially designed for laser-plasma interaction and x-ray applications. This device allows the generation of 5×109 photons/s/sr at 8 keV and optimized x-ray irradiation of the studied sample, which can be placed close to the source. We present the diffraction pattern of a protein crystal in a divergent beam geometry, which is a first step to a subpicosecond x-ray diffraction experiment