Direct numerical simulation of the dynamics of sliding rough surfaces

The noise generated by the friction of two rough surfaces under weak contact pressure is usually called roughness noise. The underlying vibration which produces the noise stems from numerous instantaneous shocks (in the microsecond range) between surface micro-asperities. The numerical simulation of this problem using classical mechanics requires a fine discretization in both space and time. This is why the finite element method takes much CPU time. In this study, we propose an alternative numerical approach which is based on a truncated modal decomposition of the vibration, a central difference integration scheme and two algorithms for contact: The penalty algorithm and the Lagrange multiplier algorithm. Not only does it reproduce the empirical laws of vibration level versus roughness and sliding speed found experimentally but it also provides the statistical properties of local events which are not accessible by experiment. The CPU time reduction is typically a factor of 10.Comment: 16 pages, 16 figures, accepted versio

Etude comparative d'itinéraires techniques mécanisés en culture d'oignon à la Réunion : critères techniques et agronomiques, évaluation des coûts des opérations d'installation

Cette étude a consisté à comparer des itinéraires mécanisés d'installation d'une culture d'oignon Allium cepa, selon des critères techniques, économiques et agronomiques. On analyse les effets de successions d'outils de travail profond (charrue et machine à bêcher) de reprise (cultivateur léger à dent et cultivateur rotatif lourd) sur les performances du tracteur, sur les coûts, et sur les performances du peuplement végétal. On observe le rôle déterminant de l'opération de reprise, notamment réalisée avec l'outil anim

Détermination pratique de quelques espèces de convolvulacées, adventices de l'Afrique du Centre et de l'Ouest

Détermination pratique de quelques espèces de convolvulacées, adventices de l'Afrique du Centre et de l'Ouest. Les auteurs décrivent une clé d'identification utilisant uniquement des critères végétatifs pour 22 espèces de Convolvulaceae, adventices des cultures en Afrique du Contre et de l'Ouest. Elle est accompagnée d'une liste des synonymes usuels pour chaque espèce, d'un tableau des caractères végétatifs des espèces volubiles, d'un texte de description et de planches. Ces éléments permettent la détermination des adventices au stade végétatif à partir de caractères visibles et facilement repérables, ne nécessitant pus une formation de botaniste. (Résumé d'auteur

A mixed analog/digital shaper for the LHCb preshower

This note describes, first, the experimental and theoretical studies of the LHCb's preshower signals performed with a prototype cell. Four designs of the very front end electronic are then discuted and a choice is proposed

Total Break of the l-IC Signature Scheme

The original publication is available at www.springerlink.comInternational audienceIn this paper, we describe efficient forgery and full-key recovery attacks on the l-IC- signature scheme recently proposed at PKC 2007. This cryptosystem is a multivariate scheme based on a new internal quadratic primitive which avoids some drawbacks of previous multivariate schemes: the scheme is extremely fast since it requires one exponentiation in a finite field of medium size and the public key is shorter than in many multivariate signature schemes. Our attacks rely on the recent cryptanalytic tool developed by Dubois et al. against the SFLASH signature scheme. However, the final stage of the attacks require the use of Grobner basis techniques to conclude to actually forge a signature (resp. to recover the secret key). For the forgery attack, this is due to the fact that Patarin's attack is much more difficult to mount against l-IC. The key recovery attack is also very efficient since it is faster to recover equivalent secret keys than to forge

Testing the efficacy of medium chain fatty acids against rabbit colibacillosis

Enteropathogenic Escherichia coli (EPEC) represents a major cause of lethal diarrhea in young mammals. Although the pathogenicity mechanisms of EPEC are now well understood, the intrinsic and environmental factors that control the expression of EPEC virulence remain largely unknown. In the rabbit, suckling reduces pups’ sensitivity to EPEC infection. Hence, we have hypothesized that uncharacterized factors present in doemilkmay mediate this protection. Medium chain fatty acids (MCFA), known to possess antimicrobial properties, are highly abundant in doe milk.We demonstrate that caprylic acid exhibits a clear bacteriostatic effect in vitro against the rabbit EPEC strain E22 (O103:H2:K-), in a dose-dependent manner. In vivo, the dietary inclusion of triglycerides of MCFA did not however reduce the sensitivity of young rabbits challenged with this EPEC strain. The mortality and fecal excretion of EPEC were not reduced, and the bacterial adhesion to ileum was not inhibited. Amount of MCFA reaching the ileal level might have been too low and/or their association to other milk antimicrobials may have been required to observe a positive effect on disease evolution in a context of a highly virulent challenge