Etude des caractères non linéaires et cyclostationnaires des signaux vibratoires de boite de vitesse d'hélicoptère

Dans cet article, nous proposons de traiter les problèmes de l'analyse vibratoire de machines tournantes telles que la boite de vitesse d'un hélicoptère. Pour cela, nous considérons deux approches, maintenant habituelles, pour de tels systèmes : La cyclostationnarité et la bilinéarité. Toutefois, l'originalité de ce travail repose dans l'étude conjointe de ces deux approches. Ainsi, la nouveauté des résultats réside dans la capacité de la corrélation spectrale à analyser précisément des phénomènes non linéaires. Nous étendons également cette première comparaison théorique des approches bilinéaire et cyclostationnaire au cas de signaux réels de machines tournantes

Advanced model-based risk reasoning on automatic railway level crossings

Safety is a core issue in the railway operation. In particular, as witnessed by accident/incident statistics, railway level crossing (LX) safety is one of the most critical points in railways. In the present paper, a Bayesian network (BN) based framework for causal reasoning related to risk analysis is proposed. It consists of a set of integrated stages, namely risk scenario definition, real field data collection and processing, BN model establishment and model performance validation. In particular, causal structural constraints are introduced to the framework forthe purpose of combining empirical knowledge with automatic learning approaches, thus to identify effective causalities and avoid inappropriate structural connections. Then, the proposed framework is applied to risk analysis of LX accidents in France. In details, the BN risk model is established on the basis of real field data and the model performance is validated. Moreover, forward and reverse inferences based on the BN risk model are performed to predict LX accident occurrence and quantify the contribution degree of various impacting factors respectively, so as to identify the riskiest factors. Besides, influence strength and sensitivity analyses are further carried out to scrutinize the influence strength of various causal factors on the LX accident occurrence likelihood and determine which factors the LX accident occurrence is most sensitive to. The main outputs of our study attest that the proposed framework is sound and effective in terms of risk reasoning analysis and offers significant insights on exploring practical recommendations to prevent LX accidents

Application of the Weibull distribution for the optimization of maintenance policies of an electronic railway signaling system

ESREL 2017, European Safety and Reliability Conference, PORTOROZ, SLOVÉNIE, 18-/06/2017 - 22/06/2017This paper presents the advantages of using Weibull distribution to describe reliability figures of an electronic railway signaling system, respect to the commonly used exponential distribution. After presenting the context of reliability estimations within the railway domain, this work introduces the approach to use field-return data to build up reliability parameters instead of predictive methodologies, and it is applied to an existing electronic signaling system. A comparison between the two methodologies is also provided, as well as the introduction of further reliability indicators. A model to improve preventive maintenance tasks defining the optimum time interval is then presented and an example is provided. Some suggestions to improve the process of collecting field-return data are presented impacting both the after-sales logbook and the design of the circuit boards

Proline-Dependent Regulation of Clostridium difficile Stickland Metabolism

Clostridium difficile, a proteolytic Gram-positive anaerobe, has emerged as a significant nosocomial pathogen. Stickland fermentation reactions are thought to be important for growth of C. difficile and appear to influence toxin production. In Stickland reactions, pairs of amino acids donate and accept electrons, generating ATP and reducing power in the process. Reduction of the electron acceptors proline and glycine requires the D-proline reductase (PR) and the glycine reductase (GR) enzyme complexes, respectively. Addition of proline in the medium increases the level of PR protein but decreases the level of GR. We report the identification of PrdR, a protein that activates transcription of the PR-encoding genes in the presence of proline and negatively regulates the GR-encoding genes. The results suggest that PrdR is a central metabolism regulator that controls preferential utilization of proline and glycine to produce energy via the Stickland reactions

Effects of Surotomycin on Clostridium difficile Viability and Toxin Production In Vitro

The increasing incidence and severity of infection by Clostridium difficile have stimulated attempts to develop new antimicrobial therapies. We report here the relative abilities of two antibiotics (metronidazole and vancomycin) in current use for treating C. difficile infection and of a third antimicrobial, surotomycin, to kill C. difficile cells at various stages of development and to inhibit the production of the toxin proteins that are the major virulence factors. The results indicate that none of the drugs affects the viability of spores at 8× MIC or 80× MIC and that all of the drugs kill exponential-phase cells when provided at 8× MIC. In contrast, none of the drugs killed stationary-phase cells or inhibited toxin production when provided at 8× MIC and neither vancomycin nor metronidazole killed stationary-phase cells when provided at 80× MIC. Surotomycin, on the other hand, did kill stationary-phase cells when provided at 80× MIC but did so without inducing lysis

Analyse des mécanismes de dégradation dans un système pile à combustible

International audienceLes systèmes pile à combustible (SPàC) sont considérés comme une solution viable et une alternative prometteuse autant pour des applications embarquées que stationnaires. Cela dit, ces systèmes doivent répondre à des critères essentiels à leur large développement, à savoir, coût, durabilité et fiabilité. Le présent travail se focalise sur l’aspect fiabilité du système pile à combustible. En effet, une meilleure compréhension des mécanismes de dégradation dans le SPàC permettra de développer les stratégies nécessaires à la réduction des dégradations au sein du SPàC et augmenter sa durée de vie utile. Une analyse des mécanismes de dégradation et leurs effets au niveau du SPàC a été faite dans le but de construire un arbre de défaillances le plus complet possible. Le SPàC étudié comprend le stack (membrane, couche catalytique, plaques bipolaires, couche de diffusion des gaz) le système d’alimentation en air (compresseur, capteurs, régulateurs, électrovannes), le système d’alimentation en hydrogène (capteurs, régulateurs, électrovannes) et le système de refroidissement (pompe de circulation, capteurs, électrovannes, régulateurs). Cette étude permettra de déduire les lois de propagation des défauts dans le SPàC qui permettront une meilleure estimation de sa durée de vie

Impact of CodY protein on metabolism, sporulation and virulence in Clostridioides difficile ribotype 027

Toxin synthesis and endospore formation are two of the most critical factors that determine the outcome of infection by Clostridioides difficile. The two major toxins, TcdA and TcdB, are the principal factors causing damage to the host. Spores are the infectious form of C. difficile, permit survival of the bacterium during antibiotic treatment and are the predominant cell form that leads to recurrent infection. Toxin production and sporulation have their own specific mechanisms of regulation, but they share negative regulation by the global regulatory protein CodY. Determining the extent of such regulation and its detailed mechanism is important for understanding the linkage between two apparently independent biological phenomena and raises the possibility of creating new ways of limiting infection. The work described here shows that a codY null mutant of a hypervirulent (ribotype 027) strain is even more virulent than its parent in a mouse model of infection and that the mutant expresses most sporulation genes prematurely during exponential growth phase. Moreover, examining the expression patterns of mutants producing CodY proteins with different levels of residual activity revealed that expression of the toxin genes is dependent on total CodY inactivation, whereas most sporulation genes are turned on when CodY activity is only partially diminished. These results suggest that, in wild-type cells undergoing nutrient limitation, sporulation genes can be turned on before the toxin genes

Approches cyclostationnaire et non linéaire pour l'analyse vibratoire de machines tournantes (aspects théoriques et applications au diagnostic)

LES SYSTEMES DE DIAGNOSTIC NECESSITENT L'UTILISATION DE METHODES DE TRAITEMENT DES SIGNAUX EN RELATION AVEC LA NATURE PHYSIQUE OU STATISTIQUE DE PHENOMENES. DANS PLUSIEURS APPLICATIONS, L'EXISTENCE ET/OU L'APPARITION DE DEFAUTS SE CARACTERISENT PAR DES PHENOMENES NON STATIONNAIRES ET/OU NON LINEAIRES. LA CARACTERISATION FINE, LA DETECTION ET LE DIAGNOSTIC PRECOCE DE CES DEFAUTS PASSENT PAR L'UTILISATION DE METHODES AD HOC ; NON STATIONNAIRES ET/OU NON LINEAIRES. DE NOMBREUSES ETUDES VISENT A ETUDIER LA CONNEXION EXISTANT ENTRE LES ASPECTS NON STATIONNAIRE ET NON LINEAIRE DES SIGNAUX. D'UN POINT DE VUE DIAGNOSTIC, CETTE CONNEXION DOIT PERMETTRE DE MIEUX COMPRENDRE CERTAINS PHENOMENES PHYSIQUES COMPLEXES. NOUS NOUS SOMMES INTERESSES, DANS CE TRAVAIL, A L'ETUDE DE CES CONNEXIONS, MAIS DANS UN CADRE PLUS RESTREINT QUI EST CELUI DES SIGNAUX CYCLOSTATIONNAIRES ET BILINEAIRES. NOUS AVONS NOTAMMENT MONTRE QUE LE BISPECTRE ET LA CORRELATION SPECTRALE DE METTRE EN EVIDENCE DES PHENOMENES AUSSI BIEN CYCLOSTATIONNAIRES QUE NON LINEAIRES. CES APPROCHES NE PERMETTAIENT DONC PAS DE DETERMINER LA NATURE D'UN PHENOMENE MAIS UNIQUEMENT DE SOULIGNER SON EXISTENCE. CETTE OBSERVATION NOUS A ALORS CONDUIT A L'UTILISATION DES STATISTIQUES CYCLIQUES D'ORDRE SUPERIEUR ET PLUS PARTICULIEREMENT DU BISPECTRE. ENFIN, DES APPLICATIONS DU BISPECTRE ET DE LA CORRELATION SPECTRALE (AINSI QU'UN COMPARAISON DE CES APPROCHES) ONT ETE EFFECTUES POUR DES SYSTEMES INDUSTRIELS TELS QU'UN BANC DE TEST RELATIVEMENT SIMPLE OU ENCORE UNE BOITE DE VITESSE D'HELICOPTERE. CES APPLICATIONS ONT PERMIS DE METTRE EN EVIDENCE LES AVANTAGES DE CHAQUE METHODE AINSI QUE LEURS CONDITIONS D'UTILISATION POUR UN DIAGNOSTIC OPTIMAL.COMPIEGNE-BU (601592101) / SudocSudocFranceF

StatAvaries: An original multinet decision support tool for evaluating rail maintenance strategies

International audienceReliability analysis is an integral part of system design and operating. Moreover, it can be an input to optimize maintenance policies. Recently, Dynamic Bayesian Networks (DBN) have been proved relevant to represent complex systems and perform reliability studies. The major drawback of this approach comes from the constraint on the sojourn times which are necessarily exponentially distributed, as in usual Markovian approaches. To avoid this constraint, a new formalism named Graphical Duration Models (GDM) was introduced¹. This approach, based on semi- Markovian models, allows representing all kind of sojourn time distributions. Then, the degradation process of complex systems (multi-components, multi-states, eventually influenced by contextual variables) can be accurately modeled and thus, the related reliability indicators correctly estimated. With this generic approach (named VirMaLab, for Virtual Maintenance Laboratory) various industrial applications were developed, especially as decision support tools for the optimization of railway infrastructure maintenance strategies

UNE NOUVELLE APPROCHE DE RESEAU BAYESIEN HYBRIDE POUR LA MODELISATION DE LA FIABILITE

International audienc