Non Parametric Instrumental Regression

The focus of the paper is the nonparametric estimation of an instrumental regression function ϕ defined by conditional moment restrictions stemming from a structural econometric model: E [Y − ϕ (Z) | W] = 0, and involving endogenous variables Y and Z and instruments W . The function ϕ is the solution of an ill-posed inverse problem and we propose an estimation procedure based on Tikhonov regularization. The paper analyses identification and overidentification of this model and presents asymptotic properties of the estimated nonparametric instrumental regression function.

Nonparametric Instrumental Regression

The focus of the paper is the nonparametric estimation of an instrumental regression function P defined by conditional moment restrictions stemming from a structural econometric model : E[Y-P(Z)|W]=0 and involving endogenous variables Y and Z and instruments W. The function P is the solution of an ill-posed inverse problem and we propose an estimation procedure based on Tikhonov regularization. The paper analyses identification and overidentification of this model and presents asymptotic properties of the estimated nonparametric instrumental regression function.Nous nous intéressons à l'estimation non paramétrique d'une fonction de régression instrumentale P . Cette fonction est définie à l'aide de conditions de moment provenant d'un modèle économétrique structurel de la forme E[Y-P(Z)|W]=0 où les Y et Z sont des variables endogènes et les W des instruments. La fonction P est alors la solution d'un problème inverse mal posé, et nous proposons une procédure d'estimation utilisant la régularisation de Tikhonov. Le papier analyse l'identification et la suridentification du modèle et donne les propriétés asymptotiques de l'estimateur de la régression instrumentale non paramétrique

Editorial:Omics and Systems Approaches to Study the Biology and Applications of Lactic Acid Bacteria

Editorial on the Research Topic Omics and Systems Approaches to Study the Biology and Applications of Lactic Acid Bacteri

Design of formal specifications by normal logic programs : merging formal text and good comments

Projet CHLOEFormal specifications are a kind of art : they mixture formal text and informal comments in an unstructured manner. We present a method based on logic programming in which formal text and comments can be also formally related through proofs. The paper is focused on the description of the proofs system used in the design of such specifications. The specification language uses normal clauses (definite clauses with possibly negative literals in the body) for its formal part and is aimed at defining relations. The comments are expressed as logic formulas written with some of the specified relations and define some local properties that the relations must satify. They introduce some redundancy which helps to understand the specification. The proofs are partial and partly automatized. They are not aimed at complete validation of the specification, but rather at debuging it and improving the comments such that its understanding is facilitated. This approach is illustrated by the example of the design of draft standard Prolog on which this methodology is currently applied

Genomics of Streptococcus macedonicus: moving from pathogenicity to adaptation to the dairy environment

Background: Lactic acid bacteria (LAB constitute a significant group of microorganisms found in foods, but also contribute to human health. The Streptococcus bovis/ Streptococcus equinus complex within LAB includes members that have been implicated in human diseases, like endocarditis and colon cancer. Objectives: In this study we compared the three available genome sequences of Streptococcus macedonicus strains isolated from dairy products. Only one strain has its genome complete sequenced and previous analysis showed diminished pathogenic potential and adaptation to the milk environment. Here we present the in silico analysis of these strains, in order to better understand the S. macedonicus species. Methods: Chromosomal maps were constructed using DNA Plotter and whole genome sequence alignments were performed by progressiveMAUVE and Webact in order to visualize conserved genomic regions or chromosomal rearrangements. Genomic islands were identified and visualized by IslandViewer, potential bacteriocins were predicted by BAGEL3 and CRISPRs were analyzed by the tools available in the CRISPRcompar web-service. Conclusions: The analysis revealed that the strains have lost genes involved in the catabolism of complex plant carbohydrates, in the adhesion to the host’s cells and in haemolysis. On the other hand, an extra lactose operon and a proteolytic system characteristic of LAB were identified. Even though our whole genome analysis of S. macedonicus shows adaptation traits to the nutrient-rich dairy environment, analysis of additional S. macedonicus genomes, including non-dairy isolates, may be necessary to clarify its pathogenic potential

Adaptation of Streptococcus macedonicus and Streptococcus thermophilus in milk. Common strategies, distinct ways.

Lactic acid bacteria (LAB) are the most important bacteria in food fermentations. Among the genera included in LAB is the Streptococcus genus, containing a number of species that are commensals and opportunistic pathogens. Up to now only one species in the Streptococcus genus, Streptococcus thermophilus, has been traditionally used as a starter in milk and is considered a domesticated organism. However, Streptococcus macedonicus, belonging to the S. bovis/S. equinus complex (SBSEC), can be also found in milk. In this study, S. macedonicus was fully sequenced and a comparative analysis was performed against all other SBSEC members. According to our analysis, S. macedonicus missed several genes encoding enzymes for the degradation of complex plant carbohydrates typically met in the genome of Streptococcus gallolyticus, indicating a reduced ability to survive in the gastrointestinal tract of herbivores. In addition, two pilus operons necessary for the adhesion of S. gallolyticus to the host and the initiation of infection were absent from the S. macedonicus genome. Adaptation of S. macedonicus to the milk environment was supported by the presence of an extra lactose operon. Finally, the plasmid pSMA198 found in S. macedonicus also provided evidence about the habituation of the species to milk. Our findings support adaptation of S. macedonicus to the rich in nutrients milk environment characterized by diminished biosynthetic capabilities and loss of pathogenicity-related genes in parallel to gene gain events through horizontal gene transfer, similarly to S. thermophilus. Comparative analysis between S. macedonicus and S. thermophilus though revealed numerous species-specific differences at the genomic and proteomic level, suggesting that common strategies can be used by truly divergent organisms during their evolutionary histor

Modeling of Young's modulus variations with temperature of Ni and oxidized Ni using a magneto-mechanical approach

International audienceThin films and coatings are usually used to give functional properties to the surface of the underlying substrate but are never seen as load bearing due to a very low film to substrate thickness ratio. However, this ratio can increase in some specific domains (such as transportation), where the weight reduction is a high stake. This study deals with the influence of the thermally grown oxide (TGO) NiO on the evolution of the elastic modulus of nickel with temperature. For pure nickel, the Young's modulus evolves non-linearly with temperature, from room temperature up to 360°C, corresponding to the Curie temperature of nickel. The amplitude of these variations can be drastically reduced with the presence of the NiO TGO. The purpose of this study is to propose a modeling of these phenomenon using magneto-mechanical approach. A first analytical modeling takes the change of the saturation magnetization, of the initial anhysteretic susceptibility and of the maximal magnetostriction with a relaxation of magneto-crystalline anisotropy concomitant to increasing temperature, into account. The second modeling is a numerical modeling giving the average behavior of a representative volume element. It allows a continuous description of the change with temperature of the Young's modulus and a clear interpretation of the effect of a coating. This gives an insight for future promising applications

Comparative genomic analysis among three dairy Streptococcus macedonicusstrains

Streptococcus macedonicus and Streptococcus infantarius, two species within the Streptococcus bovis/ Streptococcus equinus complex (SBSEC) are frequently found in spontaneously fermented foods especially of dairy origin. These two species have been suggested to be non-pathogenic and to have been adapted to the dairy environment similarly to Streptococcus thermophilus. Analysis of the first complete genomes of S. macedonicus and S. infantarius indicated that they may be indeed adapted to milk but they also have retained a restricted repertoire of virulence traits when compared to well characterized pathogenic streptococci. In this study we performed comparative genomic analysis among S. macedonicus strains, isolated from Italian, French and Greek dairy products. The contigs of the Italian and French partial genomes were aligned using as a reference the Greek S. macedonicus ACA-DC 198 genome, the only S. macedonicus genome that is completely sequenced to date. Based on these assemblies, we constructed two distinct pseudochromosomes for the French and the Italian strains. Despite the artifactual nature of the two chromosomes, pairwise alignments among the three genomes revealed a high degree of synteny. The genetic information was overall conserved, but strain specific regions also existed. Furthermore, the analysis revealed that the French S. macedonicus strain has lost genes involved in the catabolism of complex plant carbohydrates, in the adhesion to the host’s cells and in haemolysis. On the other hand, an extra lactose operon and a proteolytic system characteristic of lactic acid bacteria were identified, indicating their evolutionary adaptation to the milk environment. Analogous observations could also be made for the Italian strain. Even though our findings further support the adaptation of the S. macedonicus species to milk fermentation, the analysis of the additional S. macedonicus genomes, including non-dairy isolates, may be necessary to clarify its pathogenic potentia