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Hepatitis E virus (HEV) is an enteric virus divided into eight genotypes. Genotype 1 (G1) and G2 are specific to humans; G3, G4 and G7 are zoonotic genotypes infecting humans and animals. Transmission to humans through water has been demonstrated for G1 and G2, mainly in developing countries, but is only suspected for the zoonotic genotypes. Thus, the water-related HEV hazard may be due to human and animal faeces. The high HEV genetic variability allows considering the presence in wastewater of not only different genotypes, but also quasispecies adding even greater diversity. Moreover, recent studies have demonstrated that HEV particles may be either quasi-enveloped or non-enveloped, potentially implying differential viral behaviours in the environment. The presence of HEV has been demonstrated at the different stages of the water cycle all over the world, especially for HEV G3 in Europe and the USA. Concerning HEV survival in water, the virus does not have higher resistance to inactivating factors (heat, UV, chlorine, physical removal), compared to viral indicators (MS2 phage) or other highly resistant enteric viruses (Hepatitis A virus). But the studies did not take into account genetic (genogroups, quasispecies) or structural (quasi- or non-enveloped forms) HEV variability. Viral variability could indeed modify HEV persistence in water by influencing its interaction with the environment, its infectivity and its pathogenicity, and subsequently its transmission by water. The cell culture methods used to study HEV survival still have drawbacks (challenging virus cultivation, time consuming, lack of sensitivity). As explained in the present review, the issue of HEV transmission to humans through water is similar to that of other enteric viruses because of their similar or lower survival. HEV transmission to animals through water and how the virus variability affects its survival and transmission remain to be investigated.

International audience; This paper investigates a problem of passive mitigation of vibratory instabilities caused by two unstable modes by means of a single nonlinear energy sink (NES). For this purpose, a linear four-degree-of-freedom (DOF) primary structure having two unstable modes (reproducing the typical dynamic behavior of a friction system) and undergoing, as it is linear, unbounded motions when it is unstable, is coupled to a NES. In this work, the NES involves an essentially cubic restoring force and a linear damping force. We are interested in characterizing analytically the response regimes resulting from the coupling of the two unstable linear modes of the primary structure and the nonlinear mode of the NES. To this end, from a suitable rescaling of the governing equations of the coupled system in which the dynamics of the primary structure is reduced to its unstable modal coordinates, the complexification-averaging method is applied. The resulting averaged system appears to be a fast-slow system with four fast variables and two slow ones related to the two unstable modes of the primary structure. The critical manifold of the averaged dynamics is obtained through the geometric singular perturbation theory and appears as a two-dimensional parametric surface (with respect to two of the four fast variables) which evolves in the whole six-dimensional variable space. The asymptotic analysis reveals that the NES attachment can produce some bounded responses and suggests that the system may have simultaneous stable attractors. Numerical simulations complement the study, highlighting a possible competition between stable attractors and allowing us to investigate their basins of attraction. In each considered situation, a good agreement has been observed between theoretical results and numerical simulations, which validates the proposed asymptotic analysis.

International audience; Usually, within stochastic framework, a testing dataset is used to evaluate the approximation error between a surrogate model (e.g. a Polynomial Chaos expansion) and the exact model. We propose here another method to estimate the quality of an approximated solution of a stochastic process, within the context of structural dynamics. We demonstrate that the approximation error is governed by an equation based on the residue of the approximate solution. This problem can be solved numerically using an approximated solution, here a coarse Monte Carlo simulation. The developed estimate is compared to a reference solution on a simple case. The study of this comparison makes it possible to validate the efficiency of the proposed method. This validation has been observed using different sets of simulations. To illustrate the applicability of the proposed approach to a more challenging problem, we also present a problem with a large number of random parameters. This illustration shows the interest of the method compared to classical estimates.

International audience; In vehicle transmission systems, frictional forces acting during the sliding phase of the clutch engagement may produce unwanted vibrations. The prediction of the stability of a clutch system remains however a laborious task, as the parameters which have the highest impact on the stability, such as the friction law or the damping, lead to significant dispersions and must be considered as uncertain in such studies. Non-intrusive generalized polynomial chaos (PC) expansions have already been used in this context. However, the number of deterministic model evaluations (i.e. the computational cost) required to compute the PC coefficients becomes prohibitive for large numbers of uncertain parameters. The sparse polynomial chaos, recently developed by Blatman and Sudret, may overcome this issue. In this paper, the method has been applied to the stability analysis of a clutch system owning up to 8 uncertain parameters. Comparisons with the reference Monte Carlo method and classic full PC expansions show that sparse PC expansions allow substantial computational cost reductions while ensuring a high accuracy of the results.

International audience; In this paper, a friction system with uncertain parameters and coupled to two Nonlinear Energy Sinks (NESs) is studied. The dispersion of some physical parameters due to their uncertain nature may generate a dynamic instability which leads to a Limit Cycle Oscillations (LCO) causing a propensity of squeal. The concept of Targeted Energy Transfer (TET) by means of NESs to mitigate this squealing noise is proposed. In this kind of unstable dynamical system coupled to NES, the transition from harmless regimes (i.e. the LCO is mitigated) to harmful regimes (i.e. the LCO is not mitigated) as a function of the uncertain parameters implies a discontinuity in the steady-state amplitude profiles. In this context, a Multi-Element generalized Polynomial Chaos (ME-gPC) based method is proposed to locate this discontinuity (called mitigation limit) and therefore to predict the Propensity of the system to undergo an Harmless Steady-State Regime (PHSSR). The results obtained with this original method lead to a good compromise between computational cost and accuracy in comparison with a reference method.

Background and objectives Hepatitis E virus (HEV) is emerging but its circulation between humans and the environment remains misunderstood. HEV ORF2 gene encodes the capsid playing a key role in viral interactions with surfaces, ORF3 products are involved in the viral cycle. Our aim was to study the molecular characteristics of ORF2 and ORF3 which could favor HEV fitness in patients and the environment. Study design Samples from 69 patients with hepatitis (blood/stools), 20 urban wastewaters, 20 effluents of a pig slaughterhouse, 22 farm pigs (stools), 20 wild boars (liver/stools) were collected in North-Eastern France. HEV strains were analyzed by direct sequencing within the ORF2 M region, of ORF2/ORF3, for phylogeny and physicochemical prediction and for ORF2 by ultra-deep sequencing. Results The results showed frequent HEV-positive samples: 9.1% of the patient bloods, 23.1% of their stools; 25.0% of wastewaters, 75.0% for the slaughterhouse, 10.0% of the boar livers, 5.3% of their stools. The strains were classified as HEV genotype 3. In ORF2, HEV highlighted one homogeneous major viral variant within quasispecies and a decrease in predicted antigenicity for two minor mutations (D442G, V402A). A cysteine signature at position 81 in ORF3 was observed in the boars. Conclusions HEV RNA genotype 3 was detected in patients and in animals, in a slaughterhouse effluent and in wastewater. Moreover, the low variability of amino acids in the ORF2 M region and molecular features in ORF2 and ORF3 suggested that HEV strains could be advantageous for key properties.

International audience; In this paper, we study the problem of passive control of friction-induced vibrations due to mode coupling instability in braking systems. To achieve that, the well-known two degrees of freedom Hultén's model, which reproduces the typical dynamic behavior of friction systems, is coupled to two ungrounded nonlinear energy sinks (NES). The NES involves an essential cubic restoring force and a linear damping force. First, using numerical simulations it is shown that the suppression or the mitigation of the instability is possible and four steady-state responses are highlighted: complete suppression , mitigation through periodic response, mitigation through strongly modulated response, and no suppression of the mode coupling instability. Then the system is analyzed applying a complexification-averaging method and the resulting slow-flow is finally analyzed using geometric singular perturbation theory. This analysis allows us to explain the observed steady-state response regimes and predict some of them. The boundary values of the friction coefficient for some of the transitions between these regimes are predicted. However, the appearance of a three-dimensional super-slow flow subsystem highlights the limitation of the local linear stability analysis of the slow-flow to predict all these boundaries.

gamma-Secretase is a large enzyme complex comprising presenilin, nicastrin, presenilin enhancer 2, and anterior pharynx-defective 1 that mediates the intramembrane proteolysis of a large number of proteins including amyloid precursor protein and Notch. Recently, a novel gamma-secretase activating protein (GSAP) was identified that interacts with gamma-secretase and the C-terminal fragment of amyloid precursor protein to selectively increase amyloid-beta production. In this study we have further characterized the role of endogenous and exogenous GSAP in the regulation of gamma-secretase activity and amyloid-beta production in vitro. Knockdown of GSAP expression in N2a cells decreased amyloid-beta levels. In contrast, overexpression of GSAP in HEK cells expressing amyloid precursor protein or in N2a cells had no overt effect on amyloid-beta generation. Likewise, purified recombinant GSAP had no effect on amyloid-beta generation in two distinct in vitro gamma-secretase assays. In subsequent cellular studies with imatinib, a kinase inhibitor that reportedly prevents the interaction of GSAP with the C-terminal fragment of amyloid precursor protein, a concentration-dependent decrease in amyloid-beta levels was observed. However, no interaction between GSAP and the C-terminal fragment of amyloid precursor protein was evident in co-immunoprecipitation studies. In addition, subchronic administration of imatinib to rats had no effect on brain amyloid-beta levels. In summary, these findings suggest the roles of GSAP and imatinib in the regulation of gamma-secretase activity and amyloid-beta generation are uncertain.

International audience; In the transmission systems of vehicles, unforced vibrations can be observed during the slidingphase of clutch engagement. These vibrations are due to frictional forces and may generate noise. Severalstudies have shown that the stability of such friction systems is highly sensitive to parameters (friction law,damping) which lead to significant dispersions. Therefore, uncertain parameters must be considered in thestability analysis of a clutch system. This paper investigates the ability of the multi-element generalizedpolynomial chaos to take an increasing number of uncertain parameters into account in the stability analysisof a clutch system: it focuses on accuracy, on the criterion for the choice of the order of truncation, on thecriterion for the choice of the number of elements and on computation time. The objective is to propose alow-cost model of high accuracy, compared with the Monte Carlo method.

Les nanosciences et nanotechnologies constituent un domaine en rapide évolution, toujours en expansionaprès son apparition peu avant les années 2000. Elles contribuent à l’ensemble des défis de l’ANR etimpactent, de manière plus ou moins décisive, un grand nombre de filières industrielles. Dans plusieurspays, des initiatives nationales ont été mises en place pour accompagner, orienter et structurer ledéveloppement du domaine, lequel s’est souvent accompagné d’un débat sociétal actif.Dans ce contexte, l’ARP a été structuré afin d’apporter une vision multifactorielle de la dynamique desnanosciences et nanotechnologies, et d’en appuyer la construction sur une expertise large et diversifiée, àmême de contribuer à la construction de conclusions aussi pertinentes que possible.Les facteurs pris en compte sont :• La prospective sur les axes de développements scientifiques et les opportunités de rupturesassociés aux recherches en nanosciences et nanotechnologies. Ce travail éclaire sur lesdynamiques et perspectives scientifiques et technologiques.• L’analyse des domaines d’impact technologique et de marché, et du transfert vers l’industrie desavancées en nanosciences et nanotechnologies. Cette analyse s’est appuyée sur la méthode desscenarios afin de fournir une vision cohérente des développements probables à venir etd’éclairer les conséquences de futures orientations et décisions.• La comparaison des politiques mises en oeuvre dans d’autres pays (comparaison internationale)• L’analyse des aspects sociétaux et éthiques.L’expertise mobilisée est celle• des 12 membres du comité opérationnel de l’ARP, lequel rassemble des experts principalementissus de la recherche publique et également de l’industrie, et associe la direction de l’OMNT, etdes 18 membres du comité d’orientation stratégique de l’ARP, majoritairement issus del’industrie, et également de la recherche publique, et de syndicats ou de la société civile.• de plus de 30 experts issus largement de l’industrie, également de la recherche publique, destructures de valorisation…, mobilisé par le réseau C’Nano qui ont participé aux séminaires deconstruction des scénarios, conduits en appui sur le cabinet de prospective Futuribles, et desnombreux acteurs interrogés au travers d’un questionnaire.• de plus de 100 experts scientifiques, majoritairement issus de la recherche publique, qui ontvolontairement contribué aux 15 groupes de travail thématiques mis en place par l’OMNT pourréaliser une prospective scientifique à « 5 ans » et « 15-20 ans ».• de 5 experts internationaux, spécialiste notamment en la « nano-éthique », rassemblés pour unséminaire spécifique à Paris.

International audience

This paper presents the nonlinear dynamic behavior of a flexible shaft. The shaft is mounted in two journal bearings and the axial load is supported by a hydrodynamic thrust bearing. The coupling between the axial thrust bearing behavior and the bending vibrations of the shaft is studied in particular. The shaft is modeled with typical beam finite elements. The dynamic behaviors of the fluid supports are considered as nonlinear. The dynamic behavior is analyzed using an unsteady time integration procedure. The paper shows the coupling between the axial dynamic behavior and the bending vibrations of the shaft.

One of the short-term priorities for renewable energies in Europe is their integration into communities and energy islands for local power supply (blocks of buildings, new neighborhoods in residential areas, shopping centers, hospitals, recreational areas, eco-parks, small rural areas or isolated ones such as islands or mountain communities). Following this strategy, the integration of small solar tower fields into so-called MIUS (Modular Integrated Utility Systems) is proposed. This application strongly influences field concepts leading to modular multi-tower systems able to more closely track demand, meet reliability requirements with fewer megawatts of installed power and spread construction costs over time after output has begun. In addition, integration into single-cycle high-efficiency gas turbines plus waste-heat applications clearly increments the solar share. The main questions are whether solar towers can be redesigned for such distributed markets and how to make them feasible. This paper includes the design and performance analysis of a 1.36 MW plant and its integration in the MIUS system, as well as the expected cost of electricity and a sensitivity analysis of the small tower plant’s performance with design parameters like heliostat configuration and tower height. A practical application is analyzed for a shopping center with a solar tower producing electricity and waste heat for hot water and heating and cooling of spaces.

International audience; This paper is devoted to the robust modeling and prediction of limit cycle oscillations in nonlinear dynamic friction systems with a random friction coefficient. In recent studies, the Wiener-Askey and Wiener-Haar expansions have been proposed to deal with these problems with great efficiency. In these studies, the random dispersion of the friction coefficient is always considered within intervals near the Hopf bifurcation point. However, it is well known that friction induced vibrations - with respect to the distance of the friction dispersion interval to the Hopf bifurcation point - have different properties in terms of tansient, frequency and amplitudes. So, the main objective of this study is to analyze the capabilities of the Wiener-Askey (general polynomial chaos, multi-element generalized polynomial chaos) and Wiener- Haar expansions to be efficient in the modelling and prediction of limit cycle oscillations independently of the location of the instability zone with respect to the Hopf bifurcation point.

International audience; This paper is devoted to the stability analysis of uncertain nonlinear dynamic dry friction systems. The stability property of dry friction systems is known to be very sensitive to the variations of friction laws. Moreover, the friction coefficient admits dispersions due to the manufacturing processes. Therefore, it becomes necessary to take this uncertainty into account in the stability analysis of dry friction systems to ensure robust predictions of stable and instable behaviours. The generalized polynomial chaos formalism is proposed to deal with this challenging problem treated in most cases with the prohibitive Monte Carlo based techniques. Two equivalent methods presented here combine the non-intrusive generalized polynomial chaos with the indirect Lyapunov method. Both methods are shown to be efficient in the estimation of the stability and instability regions with high accuracy and high confidence levels and at lower cost compared with the classic Monte Carlo based method.

International audience; This paper presents the robust design of a suspension system suitable for tyres whose camber angle can cover a large interval. The originality of this study is to take account of the tyre camber angle within the range (+/- 20 °) in the robust design of a vehicle suspension system. The methodology is based on the hierarchical organization of the design process, on simplified models, on sensitivity analysis and on robust optimization. The paper describes the robust design methods, the modelling of the tyre, the design process and the results. Two models of car tyres valid for high camber angles have been defined. The design strategy based on ''First Design'' and ''Rational Design'' methods, as well as on the ''Electre'' decision support method, shows its strong potential for finding efficient and robust solutions. The feasibility of integrating an axle into the steering system at high camber angles is demonstrated.

International audience; The prediction of self friction-induced vibrations is of major importance in the design of dry friction systems. This is known to be a challenging problem since dry friction systems are very complex nonlinear systems. Moreover, it has been shown that the friction coefficients admit dispersions depending in general on the manufacturing process of dry friction systems. As the dynamic behavior of these systems is very sensitive to the friction parameters, it is necessary to predict the friction- induced vibrations by taking into account the dispersion of friction. So, the main problem is to define efficient methods which help to predict friction- induced vibrations by taking into account both nonlinear and random aspect of dry friction systems. The Multi-element generalized polynomial chaos formalism is proposed to deal with this question in a more general setting. It is shown that, in the case of friction-induced vibrations obtained from long time integration, the proposed method is efficient by opposite to the generalized polynomial chaos based method and constitutes an interesting alternative to the prohibitive Monte Carlo method.

International audience; This paper deals with the modeling and prediction of the dynamic behaviour of uncertain nonlinear systems. An efficient method is proposed to treat these problems. It is based on the Wiener-Haar chaos concept resulting from the polynomial chaos theory and it generalizes the use of the multi-resolution analysis well known in the signal processing theory. The method provides a powerful tool to describe stochastic processes as series of orthonormal piecewise functions whose weighting coefficients are identified using the Mallat pyramidal algorithm. This paper shows that the Wiener-Haar model allows an efficient description and prediction of the dynamic behaviour of nonlinear systems with probabilistic uncertainty in parameters. Its contribution- compared to the representation using the generalized polynomial chaos model, is illustrated by evaluating the two models via their application to the problems of the modeling and prediction of the dynamic behaviour of a self-excited uncertain nonlinear system.

The optical properties of single-wall carbon nanotubes (SWNTs) are dominated by the excitonic character of the transitions even at room temperature. The very peculiar properties of these excitons arise from both the one-dimensional (1D) nature of carbon nanotubes and from the electronic properties of graphene from which nanotubes are made. We first propose a brief qualitative review of the structure of the excitonic manifold and emphasize the role of dark states. We describe recent experimental investigations of this excitonic structure by means of temperature dependent PL measurements. We investigate the case of upper sub-bands and show that high-order optical transitions remain excitonic for large diameter nanotubes. A careful investigation of Rayleigh scattering spectra at the single nanotube level reveals clear exciton–phonon side-bands and Lorentzian line profiles for all semi-conducting nanotubes. In contrast, metallic nanotubes show an ambivalent behavior which is related to the reduced excitonic binding energy. Schematic of the exciton manifold in single-wall carbon nanotubes.

This paper is devoted to the stability analysis of uncertain nonlinear dynamic systems. The generalized polynomial chaos formalism is proposed to deal with this challenging problem treated in most cases by using the prohibitive Monte Carlo based techniques. Two equivalent methods combining the non-intrusive generalized polynomial chaos with the indirect Lyapunov method are presented. Both methods are shown to be efficient in the estimation of the stability and instability regions of nonlinear dynamic systems with probabilistic uncertainties. Indeed, it is illustrated that the proposed methods give results of high accuracy and high confidence levels at lower cost compared with the classic Monte Carlo based method.

International audience; This paper presents a dynamic behaviour study of non-linear friction systems subject to uncertain friction laws. The main aspects are the analysis of the stability and the associated non-linear amplitude around the steady-state equilibrium. As friction systems are highly sensitive to the dispersion of friction laws, it is necessary to take into account the uncertainty of the friction coefficient to obtain stability intervals and to estimate the extreme magnitudes of oscillations. Intrusive and non-intrusive methods based on the polynomial chaos theory are proposed to tackle these problems. The efficiency of these methods is investigated in a two degree of freedom system representing a drum brake system. The proposed methods prove to be interesting alternatives to the classic methods such as parametric studies and Monte Carlo based techniques.

International audience; The aim of this paper is to present a new strategy based on the interval analysis for the prediction of stable and unstable regions of mechanical systems subjected to friction-induced instability. For the sake of simplicity, a twodegree- of-freedom minimal model is constructed and analysed to examine the numerical procedure and interval algorithm. The efficiency and robustness of the proposed method is demonstrated through numerical simulations versus the variation of the friction coefficient and the damping factor.

International audience; Ce travail présente l'étude du comportement dynamique d'un système soumis à des instabilités de type Sprag-Slip générées par du frottement. La mise en équation de ce système conduit à un système d'équations différentielles non linéaire. Dans un premier temps, une approche déterministe du comportement est réalisée : la résolution classique de ces équations différentielles permet de déterminer le comportement dynamique du système étudié, ainsi que sa sensibilité aux différents paramètres. Dans un second temps, une analyse par intervalle permet de prendre en compte la dispersion du coefficient de frottement pour l'intégration des équations différentielles. L'objectif est d'obtenir une modélisation robuste du comportement dynamique de systèmes frottants.

International audience; We report on environmental effects on the optical properties of single-wall carbon nanotubes in a gelatin-based composite material designed to foster their photoluminescence. We show that the dielectric screening of excitons due to the surrounding medium is responsible for a sizeable shift of the luminescence lines, which hardly depends on the tube geometry. In contrast, the temperature dependence from 4 to 300 K of the luminescence is clearly chirality dependent; the first and second excitonic lines shift in opposite directions with a magnitude that can be related quantitatively to a strain-induced modification of the electronic structure due to an expansivity mismatch between the nanotube and the matrix.

International audience; Friction-induced vibration due to mode coupling is a major concern in a wide variety of mechani cal systems. Stability analysis and the associated non-linear amplitudes around a steady-state equilibrium point actually are two of the most important points in the study of non-linear dynamical systems de­ pending on given control parameters. Determining stable and unstable regions is only one aspect of the problem of friction-induced ftutter instability. The instability magni tude is a more significant design factor than the instability region. In this paper, we propose to apply interval analysis to obtain the ma.ximum and minimum amplitudes of a complete non-linear mechanical system. This approach allows us to avoid numerical procedures that are both time and cast consuming to perform when parametric design studies are needed.

International audience; This paper presents a two dimensional phenomenological non-linear model of a windscreen wiper system. This non-linear model describes the instabilities arising from the frictional contact between the glass and the rubber. The objective of this paper is to illustrate the fact that a very simple non-linear phenomenological system may be used to model and simulate chatter vibrations for wiper systems stability analysis. First, the complete non-linear phenomenological system which represents the non-linear wiper system is described. Then, the stability analysis of the system is performed by considering the eigenvalues of the linearized system around the non-linear equilibrium points. Finally, the non-linear behaviour of the mechanical system which corresponds to the “limit cycles” is investigated using a Runge-Kutta method.

By replacing a semiconductor saturable absorber mirror (SESAM) made up of iron doped InGaAs/InP multiple quantum wells (MQW) (Gicquie-Guezo, 2004) by a saturable absorber incorporating nanotubes (SAINT) (Set, 2004) we have drastically decreased the noise level as well as improved the output pulse characteristics delivered by a passively mode-locked Er3+-doped fiber oscillator. Our laser consists of 235 cm-long, highly erbium-doped fiber core-pumped by a single-mode laser diode (120 mw max. power) and pieces of standard telecom fibers . A free space segment settles the cavity in order to manage beam focusing on the SA either constituted of SESAM or SAINT. The latter is made up of SW-CNT obtained by laser ablation of a doped graphitic target.

We study the excitonic recombination dynamics in an ensemble of (9,4) semiconducting single-wall carbon nanotubes by high sensitivity time-resolved photo-luminescence experiments. Measurements from cryogenic to room temperature allow us to identify two main contributions to the recombination dynamics. The initial fast decay is temperature independent and is attributed to the presence of small residual bundles that create external non-radiative relaxation channels. The slow component shows a strong temperature dependence and is dominated by non-radiative processes down to 40 K. We propose a quantitative phenomenological modeling of the variations of the integrated photoluminescence intensity over the whole temperature range. We show that the luminescence properties of carbon nanotubes at room temperature are not affected by the dark/bright excitonic state coupling.

Carrier dynamics is investigated in both luminescent and nonluminescent samples of single wall carbon nanotubes-obtained by laser ablation-by means of two-color pump-probe experiments. The recombination dynamics is monitored by probing the transient photobleaching observed on the interband transitions of semiconducting nanotubes. Interband and intersubband relaxation times are about one order of magnitude slower in isolated nanotubes than in ropes of nanotubes bringing evidence of the environmental influence on the carrier dynamics. The relaxation dynamics is nonexponential and is interpreted as a consequence of the inhomogeneity of the sample. Slow components up to 250 ps are measured which is significantly greater than values previously reported in HiPCO nanotubes. These observations show the great dependence of the electronic properties of carbon nanotubes on the synthesis method and on their environment.

International audience; Cet article fait la synthèse de différents travaux mettant en évidence l'influence que peut avoir un défaut géométrique (de forme ou de position) d'un élément support de ligne d'arbre sur le comportement dynamique du rotor. Sous certaines conditions aussi bien dans le cas des paliers que dans les cas des butées axiales, un défaut géométrique de la partie tournante du support peut faire apparaitre des perturbations non négligeables de l'ensemble de la ligne d'arbre. Après une présentation des différents modèles adoptés, quelques études de cas sont exposées. Il s'agit d'un calcul non linéaire (pas à pas dans le temps) de la ligne d'arbre flexible. Le modèle prend en compte simultanément le comportement non linéaire hydrodynamique du support fluide et le comportement flexible de l'arbre. Les comportements mis en évidence font apparaitre dans les réponses de l'arbre des fréquences supersynchrones dues aux défauts des supports. Ces réponses peuvent avoir des amplitudes du même ordre de grandeur que celles obtenues sous l'effet d'un balourd.

International audience; A new methodology for a robust analysis of uncertain nonlinear dynamic systems is presented in this paper. The originality of the method proposed lies in the combination of the centre manifold theory with the polynomial chaos approach. The first one is known to be a powerful tool for model reduction of nonlinear dynamic systems in the neighbourhood of the Hopf bifurcation point while the polynomial chaos approach is an efficient tool for uncertainty propagation. Therefore, to couple the two methods can help to overcome computational difficulties due to both the complexity of nonlinear dynamic systems and the cost of the uncertainty propagation with the prohibitive Monte Carlo method. The feasibility and efficiency of the proposed methodology is investigated. So, a two degree of freedom model describing a drum brake system subject to uncertain initial conditions is considered.