Pattern selection in a biomechanical model for the growth of walled cells

In this paper, we analyse a model for the growth of three-dimensional walled cells. In this model the biomechanical expansion of the cell is coupled with the geometry of its wall. We consider that the density of building material depends on the curvature of the cell wall, thus yield-ing possible anisotropic growth. The dynamics of the axisymmetric cell wall is described by a system of nonlinear PDE including a nonlin-ear convection-diffusion equation coupled with a Poisson equation. We develop the linear stability analysis of the spherical symmetric config-uration in expansion. We identify three critical parameters that play a role in the possible instability of the radially symmetric shape, namely the degree of nonlinearity of the coupling, the effective diffusion of the building material, and the Poisson's ratio of the cell wall. We also investigate numerically pattern selection in the nonlinear regime. All the results are also obtained for a simpler, but similar, two-dimensional model

Canal des provisions bancaires et cyclicité du marché du crédit

International audienceRésumé : Des travaux empiriques portant sur les comportements de provisionnement des banques montrent que les provisions pour pertes évoluent de façon contracyclique. Ce fait stylisé est intégré dans un modèle théorique déterminant le comportement d'une banque représentative sur le marché du crédit. Le modèle et les simulations réalisées montrent que les modi…cations du coût de provisionnement supportées par la banque à travers un cycle économique ampli…ent les uctuations sur le marché du crédit. Deux mécanismes sont identi…és pour éliminer cette e¤et d'ampli…cation. D'un point de vue réglementaire, l'adoption d'un système de provisionnement dynamique représente une première solution. Au niveau de la banque, la constitution d'un "coussin de sécurité" en capital bancaire représente une seconde solution. Abstract :The literature on provisioning bank behaviour shows that loan loss provisions are counter-cyclical. Based on this stylised fact, this paper develops a partial equilibrium model of a banking …rm that analyzes how provisioning rules inuence credit market uctuations. The model and the simulations show that a backward-looking provisioning system ampli…es the uctuations in the credit market over an economic cycle. Two solutions are proposed to remove this bank provision channel. First, the regulatory authority can implement a forward-looking provisioning system. Second, if a backward-looking provisioning system rules are implemented, banks can build a capital bu¤er to cover the expected losses which are not covered by loan loss reserves

Banks' procyclicality behavior: does provisioning matter?

URL des Cahiers : https://halshs.archives-ouvertes.fr/CAHIERS-MSECahiers de la Maison des Sciences Economiques 2006.35 - ISSN 1624-0340A panel of 186 European banks is used for the period 1992-2004 to determine if banking behaviors induced by the capital adequacy constraint and the provisioning system, amplify credit fluctuations. Our finding is consistent with the bank capital channel hypothesis, which means that poorly capitalized banks are constrained to expand credit. We also find that loan loss provisions (LLP) made in order to cover identified credit losses (non discretionary LLP) amplify credit fluctuations. Indeed, non discretionary LLP evolve cyclically. This leads to a misevaluation of expected credit risk which affect banks' incentives to grant new loans since lending costs are misstated. By contrast, LLP use for management objectives (discretionary LLP) do not affect credit fluctuations. The findings of our research are consistent with the call for the implementation of dynamic provisioning in Europe.Un panel de 186 banques européennes sur la période 1992-2004 est utilisé pour déterminer si les fluctuations de l'offre de crédit des banques sont amplifiées par la contrainte réglementaire sur les fonds propres et par les règles de provisionnement. Nos résultats sont en accord avec l'hypothèse du canal du capital bancaire : les banques faiblement capitalisées se trouvent contraintes pour accroître leur offre de crédit. Nous montrons également que les provisions contractées pour couvrir des pertes identifiées (provisions non discrétionnaires) amplifient les fluctuations de l'offre de crédits. En effet, ces provisions non discrétionnaires évoluent de façon cyclique et conduisent à une mauvaise prise en compte des pertes anticipées. L'incitation de la banque à offrir du crédit est donc affectée dans la mesure où les coûts liés à l'accord d'un crédit sont mal évalués. D'autre part, la proportion des provisions utilisée pour des objectifs de management (provisions discrétionnaires) n'affecte pas les fluctuations de l'offre de crédit. Les résultats de cet article conduisent à recommander la mise en place d'un système de provisionnement dynamique en Europe

Growth Route Toward III-V Multispectral Solar Cells on Silicon

To date, high efficiency multijunction solar cells have been developed on Ge or GaAs substrates for space applications, and terrestrial applications are hampered by high fabrication costs. In order to reduce this cost, we propose a breakthrough technique of III-V compound heteroepitaxy on Si substrates without generation of defects critical to PV applications. With this technique we expect to achieve perfect integration of heterogeneous Ga1-xInxAs micro-crystals on Si substrates. In this paper, we show that this is the case for x=0. GaAs crystals were grown by Epitaxial Lateral Overgrowth on Si (100) wafers covered with a thin SiO2 nanostructured layer. The cristallographic structure of these crystals is analysed by MEB and TEM imaging. Micro-Raman and Micro-Photomuminescence spectra of GaAs crystals grown with different conditions are compared with those of a reference GaAs wafer in order to have more insight on eventual local strains and their cristallinity. This work aims at developping building blocks to further develop a GaAs/Si tandem demonstrator with a potential conversion efficiency of 29.6% under AM1.5G spectrum without concentration, as inferred from our realistic modeling. This paper shows that Epitaxial Lateral Overgrowth has a very interesting potential to develop multijunction solar cells on silicon approaching the today 30.3% world record of a GaInP/GaAs tandem cell under the same illumination conditions, but on a costlier substrate than silicon.Comment: Preprint of the 28th EUPVSEC proceedings, September 2013, Paris, France. (5 pages

Spinocerebellar ataxia type 2 (SCA2): clinical features and genetic analysis.

Spinocerebellar ataxia type 2 (SCA2) is an autosomal dominant neurodegenerative disease that results from the expansion of an unstable trinucleotide CAG repeat encoding for a polyglutamine tract. In normal individuals, alleles contain between 14 and 31 CAG repeats, whereas the pathological alleles have more than 35 CAG repeats. The clinical phenotype of SCA2 includes a progressive cerebellar ataxia with additional features such as ophthalmoplegia, extra-pyramidal or pyramidal signs and peripheral neuropathy. We report a SCA2 large African family with several affected individuals. A major pathological allele carrying 43 CAG repeats was identified in the proband. To our knowledge, this is a first report of a SCA disorder described in Central African patients, thus indicating the need to consider this diagnosis in young African ataxic patients

Photodimerization as an alternative to photocrosslinking of nanoparticles: proof of concept with amphiphilic linear polyoxazoline bearing coumarin unit

International audiencePhotosensitive amphiphilic linear polyoxazolines (CoumC 11-POx n) bearing alkyl chain decorated by a UV-active coumarin end group have been synthesized by cationic ring-opening polymerization (CROP). Using DLS and DOSY NMR experiments, their self-assemblies in water were compared with those of homologous photo-unreactiveamphiphilic polyoxazolines (C m-POx n). In both cases, spherical nanoparticles with D H-values around 10 nm were observed. The CoumC 11-POx n nanoparticles were illuminated upon 300 nm inducing the photo-dimerization of the coumarin units located in theinnercompartment of the nanoparticles. Finally, the pros and the cons of the photo-dimerization of linear copolymersrelated to the photo-crosslinking of graft copolymerswere discussed

Strain superlattices and macroscale suspension of Graphene induced by corrugated substrates

We investigate the organized formation of strain, ripples and suspended features in macroscopic CVD-prepared graphene sheets transferred onto a corrugated substrate made of an ordered arrays of silica pillars of variable geometries. Depending on the aspect ratio and sharpness of the corrugated array, graphene can conformally coat the surface, partially collapse, or lay, fakir-like, fully suspended between pillars over tens of micrometers. Upon increase of pillar density, ripples in collapsed films display a transition from random oriented pleats emerging from pillars to ripples linking nearest neighboring pillars organized in domains of given orientation. Spatially-resolved Raman spectroscopy, atomic force microscopy and electronic microscopy reveal uniaxial strain domains in the transferred graphene, which are induced and controlled by the geometry. We propose a simple theoretical model to explain the transition between suspended and collapsed graphene. For the arrays with high aspect ratio pillars, graphene membranes stays suspended over macroscopic distances with minimal interaction with pillars tip apex. It offers a platform to tailor stress in graphene layers and open perspectives for electron transport and nanomechanical applications