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

A web platform for the analysis of hierarchical models in decision-making problems

The purpose of this thesis is to design and elaborate web application, which will provide tools for design and analysis of decision problems. The platform aims at maximizing independence from operating systems and different types of devices, as well as executing tasks in decision making process. Application is meant to be used on personal computers as much as mobile devices like, tablets and smart mobile phones. Web platorm cosists of input of data, designing hierachical modela and model analysis. This thesis descibes in detail design and functions of hierachical model analysis, methods and technologies used in the development. The thesis also represents user manual for the web platform

Algorithms for Contractibility of Compressed Curves on 3-Manifold Boundaries

In this paper we prove that the problem of deciding contractibility of an arbitrary closed curve on the boundary of a 3-manifold is in NP. We emphasize that the manifold and the curve are both inputs to the problem. Moreover, our algorithm also works if the curve is given as a compressed word. Previously, such an algorithm was known for simple (non-compressed) curves, and, in very limited cases, for curves with self-intersections. Furthermore, our algorithm is fixed-parameter tractable in the complexity of the input 3-manifold. As part of our proof, we obtain new polynomial-time algorithms for compressed curves on surfaces, which we believe are of independent interest. We provide a polynomial-time algorithm which, given an orientable surface and a compressed loop on the surface, computes a canonical form for the loop as a compressed word. In particular, contractibility of compressed curves on surfaces can be decided in polynomial time; prior published work considered only constant genus surfaces. More generally, we solve the following normal subgroup membership problem in polynomial time: given an arbitrary orientable surface, a compressed closed curve ?, and a collection of disjoint normal curves ?, there is a polynomial-time algorithm to decide if ? lies in the normal subgroup generated by components of ? in the fundamental group of the surface after attaching the curves to a basepoint

Role of evaporation rate on the particle organization and crack patterns obtained by drying a colloidal layer

International audience– A scientific hurdle in manufacturing solid films by drying colloidal layers is preventing them from fracturing. This paper examines how the drying rate of colloidal liquids influences the particle packing at the nanoscale in correlation with the crack patterns observed at the macroscale. Increasing the drying rate results in more ordered, denser solid structures, and the dried samples have more cracks.Yet, introducing a holding period (at a prescribed point) during the drying protocol results in a more disordered solid structure with significantly less cracks. To interpret these observations, this paper conjectures that a longer drying protocol favors the formation of aggregates. It is further argued that the number and size of the aggregates increase as the drying rate decreases. This results in the formation of a more disordered, porous film from the viewpoint of the particle packing, and a more resistant film, i.e. less cracks, from the macroscale viewpoint

RETRATO SIN IDENTIFICAR [Material gráfico]

Copia digital. Madrid : Ministerio de Educación, Cultura y Deporte, 201

Inverse design of a suspended Kirchhoff rod: From theory to practice

International audienceEstimating the natural shape of a given hanging deformed rod, made of a known material, is a relevant problem in many industrial, graphic design, or even biological applications. To tackle this problem we examine the static Kirchhoff equations for thin elastic rods in the reverse direction, that is, when the shape at equilibrium is known and the natural shape is unknown. Our study is focussed on the case of an isotropic rod clamped at one end and free at the other, subjected to gravity

Eliminating Hepatitis C Virus From a Prevalent Kidney Transplant Recipient Population: A Single-Center Study in Belgium in the Direct-Acting Antivirals Era

Background: Direct-acting antivirals (DAAs) have revolutionized the treatment of hepatitis C virus (HCV) infection. Although previous studies have reported positive results with DAAs after kidney transplantation (KT), their impact on the prevalence of HCV viremia (HCVv) in prevalent kidney transplant recipients (KTRs) remains ill defined. Methods: We retrospectively reviewed the HCV status of all patients followed at Cliniques Universitaires Saint-Luc, Brussels, Belgium, outpatient KT clinic between January 2014 and December 2018. We collected the clinical features of KTRs treated with DAAs during this period and calculated the annual prevalence of HCVv over this period. Results: Out of 1451 KTRs, 22 (1.52%) had HCVv in 2014 to 2018. From 2014 to 2018, the annual prevalence of HCVv dropped from 1.97% to 0.43%, (P < .001). Fourteen KTRs were treated with DAAs a median of 197 months (range: 5-374) after KT, mostly (79%) in 2017 after reimbursement restrictions of DAAs for KTRs in Belgium were removed. DAA treatment was safe with a sustained virological response rate at 12 weeks after treatment (SVR12) of 93%. Two patients died 14 months (lymphoma, despite SVR12) and 7 months (hepatocarcinoma, no SVR12) after DAAs initiation, respectively. Among HCVv KTRs not treated with DAAs (n = 8), 2 lost their graft, 5 died, and 1 is initiating therapy. The current prevalence of HCVv in the cohort is 0.08%, with a single patient currently on treatment. Conclusion: Treatment with DAAs led to a dramatic decrease of HCVv prevalence in this KTR cohort. DAA use was safe and effective. Elimination of HCV is possible at KT clinics

Estimating friction in cloth, using simulation and machine learning

International audienceWe explore the utility of deep neural networks to estimate parameters in cloth motion, specifically the friction coefficient. Our idea is to use realistic cloth motion sequences as video training data for our model and use both spatial and temporal features for parameter estimation. Following recent works, we aim to avoid complex experimental setup for the generation of training data by leveraging cloth simulation as a ground truth model for cloth dynamics. However, this is only meaningful if the simulation is accurate and predictable enough in the range of scenarios envisioned. To ensure realistic simulations, we validate the physical accuracy of Argus, a recent cloth simulator developed in computer graphics which relies on an implicit contact friction solver for capturing exact Coulomb friction. We successfully verify the physical realism of this simulator by conducting physical experiments analogous with simulations, following a protocol previously suggested in literature for measuring Coulomb's friction coefficient in a Hookean elastic material contacting a rigid surface. We further investigate utilizing a similar protocol for cloth with varying material properties, which is modelled as an orthotropic material in the simulator