Application d'une méthode de Galerkin multiharmonique au calcul des densités spectrales de puissance évolutives

Les systèmes mécaniques sous entrée aléatoire peuvent posséder, dans le cas de sollicitations sismiques par exemple, des réponses telles que l'amplitude mais aussi le contenu fréquentiel sont modulés dans le temps et conduisent à des DSP évolutives. La réponse instationnaire est approchée, sur un intervalle de temps T, par un développement de Galerkin, en sinus et cosinus, à un ordre fini M dont les coefficients sont lentement variables en fonction du temps et conduisent à une DSP évolutive. Les équations déterminantes, algébriques dans le cas stationnaire, sont remplacées par des équations différentielles dont les coefficients et le terme forçant dépendent uniquement du temps lent. Le calcul de l'accélération pour un modèle d'excitation sismique est donné comme exemple de résulta

Elastic perfectly plastic oscillator under random loads: Linearization and response power spectral density

International audienceThe randomly-excited elastic-perfectly-plastic oscillator-hysteretic bilinear oscillator with zero secondary stiffness-has been extensively researched. The vast majority of the work on that system has investigated the time-domaine statistics of the response. No studies have focused on the power spectral densities. This study specifically examines the system's velocity power spectral density-the system's displacement is nonstationary-under wide-band random excitations by means of a statistical linearization/stochastic averaging technique that is developed in one existing and two new procedures, one with constant, the other with amplitude-dependent parameters. The three procedures are evaluated against Monte Carlo simulation and classical Gaussian linearization in terms of the velocity average power, the peak frequency of the power spectral density, its peak value, its bandwidth, and its overall shape around the main frequency. The best predictions were yielded by the new procedure with amplitude-dependent parameters, which combines an extended amplitude-phase transformation, a linearization with random parameters into a Maxwell system, a correlation-function-based criterion, the conditional power spectral density concept, and a power conservation correction step. The new procedures can be adapted to apply to other hysteretic systems

Nonlinear modes of clarinet-like musical instruments

The concept of nonlinear modes is applied in order to analyze the behavior of a model of woodwind reed instruments. Using a modal expansion of the impedance of the instrument, and by projecting the equation for the acoustic pressure on the normal modes of the air column, a system of second order ordinary differential equations is obtained. The equations are coupled through the nonlinear relation describing the volume flow of air through the reed channel in response to the pressure difference across the reed. The system is treated using an amplitude-phase formulation for nonlinear modes, where the frequency and damping functions, as well as the invariant manifolds in the phase space, are unknowns to be determined. The formulation gives, without explicit integration of the underlying ordinary differential equation, access to the transient, the limit cycle, its period and stability. The process is illustrated for a model reduced to three normal modes of the air column

Current issues in medically assisted reproduction and genetics in Europe: research, clinical practice, ethics, legal issues and policy. European Society of Human Genetics and European Society of Human Reproduction and Embryology.

In March 2005, a group of experts from the European Society of Human Genetics and European Society of Human Reproduction and Embryology met to discuss the interface between genetics and assisted reproductive technology (ART), and published an extended background paper, recommendations and two Editorials. Seven years later, in March 2012, a follow-up interdisciplinary workshop was held, involving representatives of both professional societies, including experts from the European Union Eurogentest2 Coordination Action Project. The main goal of this meeting was to discuss developments at the interface between clinical genetics and ARTs. As more genetic causes of reproductive failure are now recognised and an increasing number of patients undergo testing of their genome before conception, either in regular health care or in the context of direct-to-consumer testing, the need for genetic counselling and preimplantation genetic diagnosis (PGD) may increase. Preimplantation genetic screening (PGS) thus far does not have evidence from randomised clinical trials to substantiate that the technique is both effective and efficient. Whole-genome sequencing may create greater challenges both in the technological and interpretational domains, and requires further reflection about the ethics of genetic testing in ART and PGD/PGS. Diagnostic laboratories should be reporting their results according to internationally accepted accreditation standards (International Standards Organisation - ISO 15189). Further studies are needed in order to address issues related to the impact of ART on epigenetic reprogramming of the early embryo. The legal landscape regarding assisted reproduction is evolving but still remains very heterogeneous and often contradictory. The lack of legal harmonisation and uneven access to infertility treatment and PGD/PGS fosters considerable cross-border reproductive care in Europe and beyond. The aim of this paper is to complement previous publications and provide an update of selected topics that have evolved since 2005

Expert consensus document: Clinical and molecular diagnosis, screening and management of Beckwith-Wiedemann syndrome: an international consensus statement.

Beckwith-Wiedemann syndrome (BWS), a human genomic imprinting disorder, is characterized by phenotypic variability that might include overgrowth, macroglossia, abdominal wall defects, neonatal hypoglycaemia, lateralized overgrowth and predisposition to embryonal tumours. Delineation of the molecular defects within the imprinted 11p15.5 region can predict familial recurrence risks and the risk (and type) of embryonal tumour. Despite recent advances in knowledge, there is marked heterogeneity in clinical diagnostic criteria and care. As detailed in this Consensus Statement, an international consensus group agreed upon 72 recommendations for the clinical and molecular diagnosis and management of BWS, including comprehensive protocols for the molecular investigation, care and treatment of patients from the prenatal period to adulthood. The consensus recommendations apply to patients with Beckwith-Wiedemann spectrum (BWSp), covering classical BWS without a molecular diagnosis and BWS-related phenotypes with an 11p15.5 molecular anomaly. Although the consensus group recommends a tumour surveillance programme targeted by molecular subgroups, surveillance might differ according to the local health-care system (for example, in the United States), and the results of targeted and universal surveillance should be evaluated prospectively. International collaboration, including a prospective audit of the results of implementing these consensus recommendations, is required to expand the evidence base for the design of optimum care pathways

Drifting response of hysteresis oscillators to stochastic excitation

International audienc

Nonlinear modes as tool to analyse nonlinear dynamical systems

CDROMInternational audienc

An amplitude phase formulation for nonlinear modes and limit cycles analysis through invariant manifolds

International audienceThe aim of this paper is to show how the concept of nonlinear modes can be used to characterize periodic orbits and limit cycles in multi-degree-of-freedom nonlinear mechanical systems. In line with previous studies by Shaw and Pierre, the concept of nonlinear modes is introduced here in the framework of invariant manifold theory for dynamical systems. A nonlinear mode is defined in terms of amplitude, phase, frequency, damping coefficient and mode shape, where the last three quantities are amplitude and phase dependent. An amplitude-phase transformation is performed on the nonlinear dynamical system, giving the time evolution of the nonlinear mode motion via the two first-order differential equations governing the amplitude and phase variables, as well as the geometry of the invariant manifold. The system of formulation adopted here is suitable for use with a Galerkin-based computational procedure. The existence and stability of periodic orbits such as limit cycles on the associated invariant manifolds can be studied from the differential equations governing the amplitude and phase variables.The examples given here involve adding gyroscopic and/or “negative” nonlinear damping terms of Van der Pol type, and nonlinear restoring force to the system equations