Le choix des plantes nourricières et la spécialisation trophique chez les Acridoidea (Orthoptères)

Les études récentes ont montré la diversité des régimes alimentaires et des relations acridiens-plantes. Toutes les étapes de la spécialisation trophique, de la monophagie à la polyphagie sont observées. Les différents facteurs susceptibles de réduire le spectre de plantes consommables par une population acridienne sont envisagés à travers les exemples pris dans la faune ouest-africaine et la littérature. La taxonomie des plantes intervient seulement dans la définition de trois grands types de régime : graminivore, non-graminivore et mixte. La constitution biochimique, la distribution spatiale, le cycle annuel des végétaux doivent être considérés ensemble pour tenter d'expliquer les situations décrites. La structure du tapis végétal est un élément fondamental dans la description de la niche écologique des criquets. Enfin, les Orthoptères sont l'objet d'une importante prédation. Les mécanismes d'échappement au prédateur créent des contraintes essentielles dans la mise en place des relations criquets-plantes. La plante est non seulement la source nutritive, mais aussi l'habitat du criquet. Les deux composantes peuvent être ou non confondues dans la même espèce végétale. (Résumé d'auteur

On the Connectivity of Unions of Random Graphs

Graph-theoretic tools and techniques have seen wide use in the multi-agent systems literature, and the unpredictable nature of some multi-agent communications has been successfully modeled using random communication graphs. Across both network control and network optimization, a common assumption is that the union of agents' communication graphs is connected across any finite interval of some prescribed length, and some convergence results explicitly depend upon this length. Despite the prevalence of this assumption and the prevalence of random graphs in studying multi-agent systems, to the best of our knowledge, there has not been a study dedicated to determining how many random graphs must be in a union before it is connected. To address this point, this paper solves two related problems. The first bounds the number of random graphs required in a union before its expected algebraic connectivity exceeds the minimum needed for connectedness. The second bounds the probability that a union of random graphs is connected. The random graph model used is the Erd\H{o}s-R\'enyi model, and, in solving these problems, we also bound the expectation and variance of the algebraic connectivity of unions of such graphs. Numerical results for several use cases are given to supplement the theoretical developments made.Comment: 16 pages, 3 tables; accepted to 2017 IEEE Conference on Decision and Control (CDC

LiCe9Mo16O35

The structure of lithium nona­cerium hexa­deca­molybdenum penta­trideca­oxide, LiCe9Mo16O35, is isotypic with LiNd9Mo16O35 [Gougeon Gall, Cuny, Gautier, Le Polles, Delevoye & Trebosc (2011 ▶). Chem. Eur. J. 17, 13806–13813]. It is characterized by Mo16O26 iO10 a units (where i = inner and a = apical) containing Mo16 clusters that share some of their O atoms to form infinite molybdenum cluster chains running parallel to the b axis and separated by Li+ and Ce3+ cations. The Mo16 cluster units are centred at Wyckoff positions 2c and have point-group symmetry 2/m. The Li+ atom, in a flattened octa­hedron of O atoms, is in a 2a Wyckoff position with 2/m symmetry. The Ce3+ cations have coordination numbers to the O atoms of 6, 9 or 10. Two Ce, two Mo and five O atoms lie on sites with m symmetry (Wyckoff site 4i), and one Ce and one O atom on sites with 2/m symmetry (Wyckoff sites 2b and 2d, respectively)

Contribution to the knowledge of the Cicindelidae of Benin with collecting notes (Coleoptera Cicindelidae)

A checklist of Coleoptera Cicindelidae presently known from Benin is given. Nine taxa are recorded for the first time from this country. Collecting data, habitat and behaviour observations of adults made by the first author during two expeditions are given along with collecting data provided by the second author

Na4.25Mo15S19: a novel ternary reduced molybdenum sulfide containing Mo6 and Mo9 clusters

International audienceThe structure of tetra-sodium penta-deca-molybdenum nona-deca-sulfide, Na4.25Mo15S19, is isotypic with Na3.9Mo15Se19 [Salloum et al. (2013 ). Acta Cryst. E69, i67-i68]. It is characterized by Mo6S (i) 8S (a) 6 and Mo9S (i) 11S (a) 6 (where i represents inner and a apical atoms) cluster units that are present in a 1:1 ratio. The cluster units are centered at Wyckoff positions 2b and 2c, and have point-group symmetry -3 and -6, respectively. The clusters are inter-connected through additional Mo-S bonds. The Na(+) cations occupy inter-unit voids formed by six or seven S atoms. One Mo, one S and one Na site [occupancy 0.751 (12)] are situated on mirror planes, and two other S atoms and one Na site (full occupancy) are situated on threefold rotation axes