Raviart Thomas Petrov-Galerkin Finite Elements

The general theory of Babu\v{s}ka ensures necessary and sufficient conditions for a mixed problem in classical or Petrov-Galerkin form to be well posed in the sense of Hadamard. Moreover, the mixed method of Raviart-Thomas with low-level elements can be interpreted as a finite volume method with a non-local gradient. In this contribution, we propose a variant of type Petrov-Galerkin to ensure a local computation of the gradient at the interfaces of the elements. The in-depth study of stability leads to a specific choice of the test functions. With this choice, we show on the one hand that the mixed Petrov-Galerkin obtained is identical to the finite volumes scheme "volumes finis \`a 4 points" ("VF4") of Faille, Gallo\"uet and Herbin and to the condensation of mass approach developed by Baranger, Maitre and Oudin. On the other hand, we show the stability via an inf-sup condition and finally the convergence with the usual methods of mixed finite elements.Comment: arXiv admin note: text overlap with arXiv:1710.0439

Local time steps for a finite volume scheme

We present a strategy for solving time-dependent problems on grids with local refinements in time using different time steps in different regions of space. We discuss and analyze two conservative approximations based on finite volume with piecewise constant projections and domain decomposition techniques. Next we present an iterative method for solving the composite-grid system that reduces to solution of standard problems with standard time stepping on the coarse and fine grids. At every step of the algorithm, conservativity is ensured. Finally, numerical results illustrate the accuracy of the proposed methods

Evaluation de la faille alimentaire en algerie par un modele economico demographique?

La «faille alimentaire» est un concept assez proche de celui de «dépendance alimentaire», cependant, si le second terme renvoie plus à une idéologie, le premier se rapporte à une estimation en valeur de la dépendance alimentaire d’un pays. Aussi, l’appréciation de la faille et plus encore le suivi de son évolution nécessite des calculs astreignants. De plus elle est souvent sujette à des erreurs d’interprétations. Dans cette étude, nous avons procédé à une approche basée en partie sur un modèle de Louis Malassis, qui permettrait entre autres, d’évaluer les effets des politiques agricoles sur la sécurité alimentaire. Enfin les résultats auxquels nous avons abouti nous autorisent à conclure qu’il est inapproprié de quantifier la faille en termes de « valeur » parce que d’une part les variations des taux de change et des prix des denrées alimentaires conduisent à des conclusions erronées. D’autre part, les politiques agricoles, entreprises en Algérie et qui visent essentiellement le côté «offre», n’ont pas réussies à réduire la faille (bien au contraire).Mots clés: Autosuffisance, Dépendance alimentaire, Modèle de Malassis, Faille alimentaire, Politiques agricoles.Codes Jel : C51, Q11, Q18

Comparison of Demosaicking Methods for Color Information Extraction

Most digital color cameras are based on a single CCD or CMOS sensor combined with a color filter array (CFA): each pixel measures only one of the RGB colors. The most popular CFA is the Bayer CFA (Bayer, 1976) shown in fig. 1. Demosaicking algorithms interpolat

L'escarpement de faille de la Têt est-il le résultat de la tectonique active Plio-Pléistocène ou d'une exhumation Pléistocène ?

International audienceL'expression morphologique de la faille de la Têt ressemble à celle d'une faille active. Son fonctionnement, attesté pour le Pliocène, reste cependant débattu pour le Pléistocène. Un schéma d'évolution de l'escarpement de faille est proposé. Il se base sur les relations entre morphologie de l'escarpement et remplissage sédimentaire des bassins. Il souligne l'importance des phénomènes d'exhumation par incision du réseau hydrographique au cours du Pléistocène. Ainsi, les mouvements tectoniques pléistocènes apparaissent faibles et leur impact sur les caractéristiques du drainage limité. Le schéma proposé conduit également à minorer le rejet au cours du Pliocène, celui-ci étant réévalué entre 150 et 300 m. Une grande partie des mouvements tectoniques responsables du relief actuel sont donc antérieur

Deletion of the Zinc Transporter Lipoprotein AdcAII Causes Hyperencapsulation of Streptococcus pneumoniae Associated with Distinct Alleles of the Type I Restriction-Modification System.

The capsule is the dominant Streptococcus pneumoniae virulence factor, yet how variation in capsule thickness is regulated is poorly understood. Here, we describe an unexpected relationship between mutation of adcAII, which encodes a zinc uptake lipoprotein, and capsule thickness. Partial deletion of adcAII in three of five capsular serotypes frequently resulted in a mucoid phenotype that biochemical analysis and electron microscopy of the D39 adcAII mutants confirmed was caused by markedly increased capsule thickness. Compared to D39, the hyperencapsulated ΔadcAII mutant strain was more resistant to complement-mediated neutrophil killing and was hypervirulent in mouse models of invasive infection. Transcriptome analysis of D39 and the ΔadcAII mutant identified major differences in transcription of the Sp_0505-0508 locus, which encodes an SpnD39III (ST5556II) type I restriction-modification system and allelic variation of which correlates with capsule thickness. A PCR assay demonstrated close linkage of the SpnD39IIIC and F alleles with the hyperencapsulated ΔadcAII strains. However, transformation of ΔadcAII with fixed SpnD39III alleles associated with normal capsule thickness did not revert the hyperencapsulated phenotype. Half of hyperencapsulated ΔadcAII strains contained the same single nucleotide polymorphism in the capsule locus gene cps2E, which is required for the initiation of capsule synthesis. These results provide further evidence for the importance of the SpnD39III (ST5556II) type I restriction-modification system for modulating capsule thickness and identified an unexpected linkage between capsule thickness and mutation of ΔadcAII Further investigation will be needed to characterize how mutation of adcAII affects SpnD39III (ST5556II) allele dominance and results in the hyperencapsulated phenotype.IMPORTANCE The Streptococcus pneumoniae capsule affects multiple interactions with the host including contributing to colonization and immune evasion. During infection, the capsule thickness varies, but the mechanisms regulating this are poorly understood. We have identified an unsuspected relationship between mutation of adcAII, a gene that encodes a zinc uptake lipoprotein, and capsule thickness. Mutation of adcAII resulted in a striking hyperencapsulated phenotype, increased resistance to complement-mediated neutrophil killing, and increased S. pneumoniae virulence in mouse models of infection. Transcriptome and PCR analysis linked the hyperencapsulated phenotype of the ΔadcAII strain to specific alleles of the SpnD39III (ST5556II) type I restriction-modification system, a system which has previously been shown to affect capsule thickness. Our data provide further evidence for the importance of the SpnD39III (ST5556II) type I restriction-modification system for modulating capsule thickness and identify an unexpected link between capsule thickness and ΔadcAII, further investigation of which could further characterize mechanisms of capsule regulation