Incremental Magnetoelastic Deformations, with Application to Surface Instability

In this paper the equations governing the deformations of infinitesimal (incremental) disturbances superimposed on finite static deformation fields involving magnetic and elastic interactions are presented. The coupling between the equations of mechanical equilibrium and Maxwell's equations complicates the incremental formulation and particular attention is therefore paid to the derivation of the incremental equations, of the tensors of magnetoelastic moduli and of the incremental boundary conditions at a magnetoelastic/vacuum interface. The problem of surface stability for a solid half-space under plane strain with a magnetic field normal to its surface is used to illustrate the general results. The analysis involved leads to the simultaneous resolution of a bicubic and vanishing of a 7x7 determinant. In order to provide specific demonstration of the effect of the magnetic field, the material model is specialized to that of a "magnetoelastic Mooney-Rivlin solid". Depending on the magnitudes of the magnetic field and the magnetoelastic coupling parameters, this shows that the half-space may become either more stable or less stable than in the absence of a magnetic field.Comment: 24 page

Determining the implied volatility in the Dupire equation for vanilla European call options

The Black-Scholes model gives vanilla Europen call option prices as a function of the volatility. We prove Lipschitz stability in the inverse problem of determining the implied volatility, which is a function of the underlying asset, from a collection of quoted option prices with different strikes

Relancer le rôle économique de la production cotonnière dans un marché défavorable : quel appui de la recherche ?

Les analyses de long terme éclairent sur le développement économique et sur les relations entre production et utilisation industrielle du coton. La tendance est d'évaluer l'intérêt économique du coton à partir du seul prix d'achat : cela reste insuffisant pour une évaluation plus globale et plus juste des impacts socio-économiques, à laquelle la recherche doit s'associer. Pour l'Afrique zone franc, l'importance du rôle économique du coton est constatée. Mais ce fait est hypothéqué par un marché mondial défavorable. Au delà des cours historiquement bas depuis la fin 1998, plusieurs facteurs, dont les fibres artificielles, limitent la demande en coton et conduisent à une perte de marché sur le marché des fibres textiles. Les doutes sur les modes de production, notamment les effets des pesticides, portent atteinte au caractère naturel du coton, qui est un élément essentiel de promotion depuis les années 70. Pour rester présents sur le marché mondial, les pays producteurs doivent être plus compétitifs, tant par les coûts que par la qualité. Cela est d'autant plus vrai pour les pays qui ne peuvent pas soutenir leurs producteurs. La notion de qualité ne renvoie pas qu'aux caractéristiques technologiques de la fibre, mais aussi à la façon dont elle est obtenue - organisation sociale, protection de l'environnement. Pour l'Afrique zone franc, l'objectif est une production compétitive et durable, adaptée aux conditions socio-économiques des producteurs. Cela implique des pratiques culturales tenant compte de leurs contraintes, fruits d'une démarche de recherche adéquate. (Résumé d'auteur

Inhibition of proximal convoluted tubule transport by dopamine

Inhibition of proximal convoluted tubule transport by dopamine.BackgroundDopamine can produce a natriuresis and diuresis independent of changes in renal hemodynamics. However, previous studies have failed to demonstrate an inhibition of transport by dopamine in intact proximal convoluted tubules.MethodsRabbit proximal convoluted tubules were perfused in vitro with an ultrafiltrate-like solution and bathed in a serum-like albumin solution.ResultsIn the present study, the addition of 10-5m dopamine to the lumen or bath of proximal convoluted tubules perfused in vitro had no effect on transport. In proximal convoluted tubules, addition of 10-6m bath norepinephrine increased the rate of volume absorption from 0.65 ± 0.08 to 0.93 ± 0.08nl/mm · min (P < 0.01). Addition of 10-5m luminal dopamine in the presence of bath norepinephrine inhibited the rate of volume absorption to 0.72 ± 0.10nl/mm · min (P = 0.01). The inhibition in the rate of volume absorption by luminal dopamine in the presence of bath norepinephrine was completely blocked by the DA1 antagonist, SCH 23390. The DA1 agonist luminal 10-5m fenoldopam also inhibited volume absorption in the presence of bath norepinephrine, but the DA2 agonist luminal 10-5m quinpirole was without effect. Bath 10-5m dopamine had no effect on volume absorption in the presence of bath norepinephrine.ConclusionDopamine has no direct epithelial action on the proximal convoluted tubule. However, luminal dopamine antagonizes the stimulation in transport produced by norepinephrine. These studies suggest that luminal dopamine may play a role to modulate sodium transport in the presence of renal nerve activity

Financial Elites and Photographic Creation

Most of the essays in this issue were originally presented as papers at a recent conference entitled Les élites économiques européennes et la création photographique (Europe’s Economic Elites and Art Photography). United around a common aim, they seek to open new fields of research by analyzing the relationship between art photography and money, and by examining how, from the middle of the nineteenth century to the present, the former is incorporated into the general economy. In­spired by a v..