Various nonconforming approximation of thin shell problems and the question of their convergence

Projet MODULE

On the convergence of a D.K.T. method valid for shells of arbitrary shape

In a recent paper by the same authors, we have thoroughly described how to extend to the case of general shells the well known D.K.T. methods (i.e. Discrete Kirchhoff Triangle) which are now classically used to solve plate problems. In this paper we have also detailed how to realize the implementation and we have reported some numerical results obtained over classical benchmarks. The aim of this paper is to prove the convergence ofa closely related method and to obtain corresponding error estimates

A New nonconforming finite element method for the computation of electromagnetic guided waves (I) mathematical analysis

We are concerned with the problem of computing electromagnetic guided waves in a closed, inomogeneous, cylindrical wave guide. These waves correspond to solutions of an eigenvalue problem and classical methods produce in addition to approximations to the solutions, spurious modes which are particularly troublesome because they correspond to nonzero approximations of the 0 eigenvalue. A nonconforming finite element method for the calculation of guided waves without spurious modes is introduced and analyzed

Reproductive and mate choice strategies in the hermaphroditic flatworm Echinostoma caproni

Due to the important role that mating systems play in the evolution of species, we investigate the selfing rate and mate choice in the simultaneous hermaphroditic parasite Echinostoma caproni (Trematoda). The echinostomes were maintained in two situations in mice: (1) double infections where the two individuals do or do not belong to the same geographic area isolate, and (2) triple infections where two of the three individuals originate from the same isolate and the third one originates from a different isolate. This experimental design permits analysis of intra- and interisolate selfing rates and of mate preference. We predict, in the first experiment, no difference between intra- and interisolate selfing rates. In the second experiment we expect a preferential outcrossing between individuals originating from the same isolate in order to avoid hybrid breakdown. The results obtained corroborate our predictions and emphasize the important and synergistic roles of selfing, inbreeding depression, and hybrid breakdown in the evolution of echinostome reproductive strategies

The response of perennial and temporary headwater stream invertebrate communities to hydrological extremes

The headwaters of karst rivers experience considerable hydrological variability, including spates and streambed drying. Extreme summer flooding on the River Lathkill (Derbyshire, UK) provided the opportunity to examine the invertebrate community response to unseasonal spate flows, flow recession and, at temporary sites, streambed drying. Invertebrates were sampled at sites with differing flow permanence regimes during and after the spates. Following streambed drying at temporary sites, dewatered surface sediments were investigated as a refugium for aquatic invertebrates. Experimental rehydration of these dewatered sediments was conducted to promote development of desiccation-tolerant life stages. At perennial sites, spate flows reduced invertebrate abundance and diversity, whilst at temporary sites, flow reactivation facilitated rapid colonisation of the surface channel by a limited number of invertebrate taxa. Following streambed drying, 38 taxa were recorded from the dewatered and rehydrated sediments, with Oligochaeta being the most abundant taxon and Chironomidae (Diptera) the most diverse. Experimental rehydration of dewatered sediments revealed the presence of additional taxa, including Stenophylax sp. (Trichoptera: Limnephilidae) and Nemoura sp. (Plecoptera: Nemouridae). The influence of flow permanence on invertebrate community composition was apparent despite the aseasonal high-magnitude flood events