Finite element reduced order models for nonlinear vibrations of piezoelectric layered beams with applications to NEMS

This article presents a finite element reduced order model for the nonlinear vibrations of piezoelectric layered beams with application to NEMS. In this model, the geometrical nonlinearities are taken into account through a von Kármán nonlinear strain–displacement relationship. The originality of the finite element electromechanical formulation is that the system electrical state is fully described by only a couple of variables per piezoelectric patches, namely the electric charge contained in the electrodes and the voltage between the electrodes. Due to the geometrical nonlinearity, the piezoelectric actuation introduces an original parametric excitation term in the equilibrium equation. The reduced-order formulation of the discretized problem is obtained by expanding the mechanical displacement unknown vector onto the short-circuit eigenmode basis. A particular attention is paid to the computation of the unknown nonlinear stiffness coefficients of the reduced-order model. Due to the particular form of the von Kármán nonlinearities, these coefficients are computed exactly, once for a given geometry, by prescribing relevant nodal displacements in nonlinear static solutions settings. Finally, the low-order model is computed with an original purely harmonic-based continuation method. Our numerical tool is then validated by computing the nonlinear vibrations of a mechanically excited homogeneous beam supported at both ends referenced in the literature. The more difficult case of the nonlinear oscillations of a layered nanobridge piezoelectrically actuated is also studied. Interesting vibratory phenomena such as parametric amplification or patch length dependence of the frequency output response are highlighted in order to help in the design of these nanodevices.This research is part of the NEMSPIEZO project, under funds from the French National Research Agency (Project ANR-08-NAN O-015-04), for which the authors are grateful

Life-Cycle Equilibrium Unemployment

This paper develops a life-cycle approach to equilibrium unemployment. Workers only differ respectively to their distance from deterministic retirement. A non age-directed search equilibrium is then typically featured by increasing (decreasing) firing (hiring) rates with age and a hump-shaped age profile for employment. Because of intergenerational inefficiencies, the Hosios condition no longer achieves efficiency. We then explore the optimal age-pattern of some policy tools to restore this efficiency. The optimal profile for employment subsidies should increase with age, whereas firing taxes and hirings subsidies would have to be hump-shaped. Lastly, we examine the robustness of our results. We show that age-directed recruitment policies cannot exist in equilibrium even if it would have been ex-ante possible, and that introducing endogenous search effort of unemployed workers reinforces our main results.job search, matching, life cycle

Age-Dependent Employment Protection

This paper examines the age-related design of firing taxes by extending the theory of job creation and job destruction to account for a finite working life-time. We first argue that the potential employment gains related to employment protection are high for older workers, but higher firing taxes for these workers increase job destruction rates for the younger generations. On the other hand, age-decreasing firing taxes can lead to lower job destruction rates at all ages. Furthermore, from a normative standpoint, because firings of older (younger) workers exert a negative (positive) externality on the matching process, we find that the first best age-dynamic of firing taxes and hiring subsidies is typically hump-shaped. Taking into account distortions related to unemployment benefits and bargaining power shows the robustness of this result, in contradiction with the existing policies in most OECD countries.foo

3D mechanical analysis of aeronautical plain bearings: Validation of a finite element model from measurement of displacement fields by digital volume correlation and optical scanning tomography

On Airbus aircraft, spherical plain bearings are used on many components; in particular to link engine to pylon or pylon to wing. Design of bearings is based on contact pressure distribution on spherical surfaces. To determine this distribution, a 3D analysis of the mechanical behaviour of aeronautical plain bearing is presented in this paper. A numerical model has been built and validated from a comparison with 3D experimental measurements of kinematic components. For that, digital volume correlation (DVC) coupled with optical scanning tomography (OST) is employed to study the mechanical response of a plain bearing model made in epoxy resin. Experimental results have been compared with the ones obtained from the simulated model. This comparison enables us to study the influence of various boundary conditions to build the FE model. Some factors have been highlighted like the fitting behaviour which can radically change contact pressure distribution. This work shows the contribution of a representative mechanical environment to study precisely mechanical response of aeronautical plain bearings

Age-Dependent Employment Protection

International audienceThis paper examines the age-related design of firing taxes by extending the theory of job creation and job destruction to account for a finite working life-time. We first argue that the potential employment gains related to employment protection are high for older workers, as they are magnified by the proximity to retirement. But higher firing taxes for these workers increase job destruction rates for the younger generations. Furthermore, from a normative standpoint, when firms cannot ex-ante age-direct their search, the impact of each generation of unemployed workers on the average return on vacancies makes the internalization of the search costs for the other generations imperfect through the ex-post Nash bargaining process. We show that the first best age-profile of firing taxes is typically hump-shaped, partially in contradiction with existing policies in some European countries. Taking into account the fact that the human capital of older workers is more specific than general tends to exacerbate these results

A Quantitative Evaluation of Payroll Tax Subsidies For Low-Wage Workers: An Equilibrium Search Approach

Phelps (1994) presented the case for a low-wage subsidy policy. Since the mid-1990s, France has experimented with this strategy. This paper evaluates the e®ect of this policy on employment and also on output and welfare. We construct an equilibrium search model incorporating wage posting and specific human capital investment, where unemployment and the distribution of both wages and productivity are endogenous. We estimate this model using French data. Numerical simulations show that the prevailing minimum wage allows a high production level to be reached by increasing training investment, even though the optimal minimum wage is lower. We show that payroll tax subsidies enhance welfare more than a reduction in the minimum wage when they are spread over a large range of wages in order to avoid specialization in low productivity jobs

Finding the Core-Genes of Chloroplasts

Due to the recent evolution of sequencing techniques, the number of available genomes is rising steadily, leading to the possibility to make large scale genomic comparison between sets of close species. An interesting question to answer is: what is the common functionality genes of a collection of species, or conversely, to determine what is specific to a given species when compared to other ones belonging in the same genus, family, etc. Investigating such problem means to find both core and pan genomes of a collection of species, \textit{i.e.}, genes in common to all the species vs. the set of all genes in all species under consideration. However, obtaining trustworthy core and pan genomes is not an easy task, leading to a large amount of computation, and requiring a rigorous methodology. Surprisingly, as far as we know, this methodology in finding core and pan genomes has not really been deeply investigated. This research work tries to fill this gap by focusing only on chloroplastic genomes, whose reasonable sizes allow a deep study. To achieve this goal, a collection of 99 chloroplasts are considered in this article. Two methodologies have been investigated, respectively based on sequence similarities and genes names taken from annotation tools. The obtained results will finally be evaluated in terms of biological relevance

Study of the Non-negative Matrix Factorization behavior to estimate the urban traffic sound levels

ICSV'26 ; 26ème International Congress on Sound and Vibration , MONTREAL, CANADA, 11-/07/2019 - 17/07/2019The advent of low-cost acoustic sensor networks in cities raises new interesting approaches for improving the monitoring of the acoustic quality of cities. Many innovative approaches are developed to improve knowledge on sound environments: sound environment recognition, sound source detection, etc. In order to improve the road traffic noise mapping, the use of a specific version of the Non-negative Matrix Factorization (NMF), named thresholded initialized NMF, as a source separation method to estimate the sound level of road traffic from measurements, has proved to be a successful approach. This paper proposes to further detail the functioning of the thresholded initialized NMF on a corpus composed of urban sound scenes mixing traffic and specific interfering components with calibrated sound levels in order to better understand its behavior according to the different sources encountered. The study reveals the different performances of this approach depending on the noise levels of the interfering sources and their proximity to the urban traffic spectrum

A Quantitative Evaluation of Payroll Tax Subsidies For Low-Wage Workers: An Equilibrium Search Approach

Phelps (1994) presented the case for a low-wage subsidy policy. Since the mid-1990s, France has experimented with this strategy. This paper evaluates the e®ect of this policy on employment and also on output and welfare. We construct an equilibrium search model incorporating wage posting and specific human capital investment, where unemployment and the distribution of both wages and productivity are endogenous. We estimate this model using French data. Numerical simulations show that the prevailing minimum wage allows a high production level to be reached by increasing training investment, even though the optimal minimum wage is lower. We show that payroll tax subsidies enhance welfare more than a reduction in the minimum wage when they are spread over a large range of wages in order to avoid specialization in low productivity jobs.Employment ; productivity ; equilibrium search ; labor costs