Search results for "ACOUSTIC"

Rational solutions to the mKdV equation associated to particular polynomials

2021

International audience; Rational solutions to the modified Korteweg-de Vries (mKdV) equation are given in terms of a quotient of determinants involving certain particular polynomials. This gives a very efficient method to construct solutions. We construct very easily explicit expressions of these rational solutions for the first orders n = 1 until 10.

Digital and handcrafting processes applied to sound-studies of archaeological bone flutes

2016

International audience; Bone flutes make use of a naturally hollow raw-material. As nature does not produce duplicates, each bone has its own inner cavity, and thus its own sound-potential. This morphological variation implies acoustical specificities, thus making it impossible to handcraft a true and exact sound-replica in another bone. This phenomenon has been observed in a handcrafting context and has led us to conduct two series of experiments (the first-one using handcrafting process, the second-one using 3D process) in order to investigate its exact influence on acoustics as well as on sound-interpretation based on replicas. The comparison of the results has shed light upon epistemolo…

L’Observatoire de l’environnement nocturne de La Réunion, un dispositif partenarial de recherche-action territorialisée

2022

Présentation du dispositif Observatoire de l'environnement nocturne (CNRS) et Observatoire de l'environnement nocturne de La Réunion (CNRS/Parc national de La Réunion) aux services internes du Parc national de La Réunion.

Study of acoustic properties and impact behavior of porous materials homogeneous type metal foams and inhomogeneous

2015

This work is concerned with the theoretical and experimental study of the acoustical properties of macroscopically homogenous and inhomogeneous porous media as well as their mechanical response to impacts. The model of Johnson - Champoux - Allard appeared adapted for the acoustical modeling. This model, associated with a recently developed approach involving the concept of parallel transfer matrices has lead to a new approach of macroscopically inhomogeneous porous materials based on “mixtures of materials”. Furthermore, a parametric study of the absorption coefficient as a function of porosity and frequency has been proposed. The maximums of absorption as well as the envelop of the absorpt…

Oblique angle co-deposition of nanocolumnar tungsten thin films with two W sources: Effect of pressure and target current

2022

Two series of tungsten thin films are sputtered on silicon and glass substrates by oblique angle co-deposition technique with an original configuration. Two opposite distinct tungsten targets are simultaneously used, both tilted with an oblique angle of 80°. The growth is performed at low (0.33 Pa) and high (1.5 Pa) argon sputtering pressure and the current intensity applied to the targets varies between 50 and 250 mA. The effect of these deposition parameters on the films microstructure and electrical properties is investigated by scanning and transmission electron microscopy, X-ray diffraction and pole figures, and van der Pauw method. Due to self-shadowing effect, all tungsten sputtered …

Multicriteria optimization of 3D printed wing using PLA reinforced with carbon fiber

2021

The purpose of this work is the optimal conception of a wing built using fused deposition modeling (FDM),<br&gtwhich is one of the main additive manufacturing (AM) process. PLA reinforced with carbon fiber was selected for the<br&gtfilament as we have defined their mechanical properties in previous work. The optimization approach use hybrid strategy<br&gtbased on surface response method with kriging model and a heuristic method to avoid to be trapped in local<br&gtminimization/maximization. The objective functions for this optimization are the weight, the drag (functions to minimize)<br&gtand the lift (function to maximize) with respect to the failure criteria of the composite material used…

Ballistic and thermalized regimes to tune structure and conducting properties of W-Mo thin films

2022

Detection of Indoor Air Pollutants Using Reactive Sputtering/GLAD of Tin Oxide Thin Films

2021

-

Recent developments in the acoustical properties of perforated and porous materials containing dead-end pores

2017

It was shown recently in Nevers, France, Sherbrooke, Canada and Salford, UK, that porous materials with semi-opened pores or materials with open pores bearing lateral cavities or resonators at the microscopic scale of the pores can result in peculiar sound absorption properties. Various examples of these materials can be found in engineering and in everyday life including bio-based materials. The cavities and resonators can be assimilated to dead-end pores, which are opened at one end and closed at the other. The dead-end pores are known to geophysicists. We studied them more recently in the field of engineering acoustics where the saturating fluid is air. The closed ends prevent the fluid …

Guidance of surface elastic waves along a linear chain of pillars

2016

International audience; The propagation of surface elastic waves, or surface phonons, is considered along a linear and periodic chain of cylindrical pillars sitting on a semi-infinite solid substrate. A variety of guided modes, some of them exhibiting a very low group velocity, are shown to exist at frequencies close to the resonance frequencies of the pillars. Although the pillar diameter is typically smaller than half the relevant wavelength, lateral radiation on the surface is found to be canceled. Surface guidance is explained by the hybridization of the resonating pillars with the continuum of elastic waves of the substrate.