The variational theory of complex rays for the calculation of medium-frequency vibrations

A new approach called the ``variational theory of complex rays’’ (VTCR) is developed for calculating the vibrations of weakly damped elastic structures in the medium-frequency range. Here, the emphasis is put on the most fundamental aspects. The effective quantities (elastic energy, vibration intensity, etc.) are evaluated after solving a small system of equations which does not derive from a finite element discretization of the structure. Numerical examples related to plates show the appeal and the possibilities of the VTCR

Vibrational analysis of structures with stochastic interfaces in the medium-frequency range: Experimental validation on a touch screen

This paper proposes a dedicated approach and its experimental validation when dealing with structures (including stochastic parameters, such as interface parameters) in medium-frequency vibrations. The first ingredient is the use of a dedicated approach – the Variational Theory of Complex Rays (VTCR) – to solve the medium-frequency problem. The VTCR, which uses two-scale shape functions verifying the dynamic equation and the constitutive relation, can be viewed as a means of expressing the power balance at the different interfaces between substructures. The second ingredient is the use of the Polynomial Chaos Expansion (PCE) to calculate the random response. Since the only uncertain parameters are those which appear in the interface equations (which, in this application, are the complex connection stiffness parameters), this approach leads to very low computation costs. This method is validated on a new kind of touch screen. The simulated mobilities are compared with experimental ones obtained with a laser vibrometer and a good agreement is founded on a large medium-frequency bandwidth

Niaux – Grotte de Niaux et réseau Clastres

Identifiant de l'opération archéologique : Date de l'opération : 1970 (FP) Inventeur(s) : Andrieux Claude ; Bakalowicz Michel ; D'Hulst Dominique ; Mangin Alain ; Rouch Raymond ; Laboratoire souterrain du CNRS (Moulins) Le réseau Clastres est isolé du reste des galeries de la grotte de Niaux par une série de voûtes mouillantes permanentes. Lors de sa découverte en 1970 (Clottes, 1973), et à l'initiative de Dr L. Pales, une étude climatique fut engagée par Claude Andrieux (CNRS, Moulis). Il ..

La théorie variation des rayons complexes pour le calcul des vibrations moyennes fréquences

A new approach named the "Variational Theory of Complex Rays" is introduced for computing the vibrations of elastic structures weakly damped in the medium frequency range. Emphasis has been placed here on the most fundamental aspects. The effective quantities (elastic energy, vibration intensity ...) are evaluated after computing a small system of equations which does not derive from a finite element dicretization of the structure. Numerical examples related to plates show the interest and the possibilities ofthe VTRC

Hypothalamic AgRP-neurons control peripheral substrate utilization and nutrient partitioning

Obesity-related diseases such as diabetes and dyslipidemia result from metabolic alterations including the defective conversion, storage and utilization of nutrients, but the central mechanisms that regulate this process of nutrient partitioning remain elusive. As positive regulators of feeding behaviour, agouti-related protein (AgRP) producing neurons are indispensible for the hypothalamic integration of energy balance. Here, we demonstrate a role for AgRP-neurons in the control of nutrient partitioning. We report that ablation of AgRP-neurons leads to a change in autonomic output onto liver, muscle and pancreas affecting the relative balance between lipids and carbohydrates metabolism. As a consequence, mice lacking AgRP-neurons become obese and hyperinsulinemic on regular chow but display reduced body weight gain and paradoxical improvement in glucose tolerance on high-fat diet. These results provide a direct demonstration of a role for AgRP-neurons in the coordination of efferent organ activity and nutrient partitioning, providing a mechanistic link between obesity and obesity-related disorders

Mid-frequency vibration analysis of a touch screen with stochastic interfaces

International audienc

A multiscale " Trefftz" computational method for medium-frequency vibrations of assemblies of heterogeneous plates with uncertainties

International audienceA new approach, called the "Variational Theory of Complex Rays", is being developed for the calculation of the vibrations of slightly damped elastic plates in the medium-frequency range. In this approach, the resolution of a small system of equations which does not result from a refined spatial discretization of the structure leads to the evaluation of effective quantities (deformation energy, vibration amplitude, ...). This theory has already been validated for assemblies of homogeneous substructures and extended to the case of heterogeneous substructures. In this paper, we propose some improvements to deal with sensitivity analysis. The objective is to evaluate the influence of discontinuities with uncertain positions, sizes or directions on the structural response. A specific partial inversion of the constrained system of equations enables multiple resolutions for combinations of the parameters defining the possible shapes of the discontinuity to be carried out at low cost

A multiscale computational method for medium-frequency vibrations of assemblies of heterogeneous plates

International audienc

Impact d'une perfusion centrale chronique de leptine ou de son antagoniste sur la signalisation hypothalamique de la leptine

National audienc