How reproducible is the acoustical characterization of porous media?

There is a considerable number of research publications on the characterization of porous media that is carried out in accordance with ISO 10534-2 (International Standards Organization, Geneva, Switzerland, 2001) and/or ISO 9053 (International Standards Organization, Geneva, Switzerland, 1991). According to the Web of Science(TM) (last accessed 22 September 2016) there were 339 publications in the Journal of the Acoustical Society of America alone which deal with the acoustics of porous media. However, the reproducibility of these characterization procedures is not well understood. This paper deals with the reproducibility of some standard characterization procedures for acoustic porous materials. The paper is an extension of the work published by Horoshenkov, Khan, Bécot, Jaouen, Sgard, Renault, Amirouche, Pompoli, Prodi, Bonfiglio, Pispola, Asdrubali, Hübelt, Atalla, Amédin, Lauriks, and Boeckx [J. Acoust. Soc. Am. 122(1), 345-353 (2007)]. In this paper, independent laboratory measurements were performed on the same material specimens so that the naturally occurring inhomogeneity in materials was controlled. It also presented the reproducibility data for the characteristic impedance, complex wavenumber, and for some related pore structure properties. This work can be helpful to better understand the tolerances of these material characterization procedures so improvements can be developed to reduce experimental errors and improve the reproducibility between laboratories

How reproducible are methods to measure the dynamic viscoelastic properties of poroelastic media?

There is a considerable number of research publications on the acoustical properties of porous media with an elastic frame. A simple search through the Web of Science™ (last accessed 21 March 2018) suggests that there are at least 819 publications which deal with the acoustics of poroelastic media. A majority of these researches require accurate knowledge of the elastic properties over a broad frequency range. However, the accuracy of the measurement of the dynamic elastic properties of poroelastic media has been a contentious issue. The novelty of this paper is that it studies the reproducibility of some popular experimental methods which are used routinely to measure the key elastic properties such as the dynamic Young's modulus, loss factor and Poisson ratio of poroelastic media. In this paper, fourteen independent sets of laboratory measurements were performed on specimens of the same porous materials. The results from these measurements suggest that the reproducibility of this type of experimental method is poor. This work can be helpful to suggest improvements which can be developed to harmonize the way the elastic properties of poroelastic media are measured worldwide

Egg production in nests and nesting behaviour: genetic correlations with egg quality and BW for laying hens on the floor

In laying hen production, cage-free housing is growing rapidly to provide living conditions that meet hens’ needs. Unlike cages, this housing requires nests for automatic collection of eggs, as eggs laid outside nests must be collected by hand. Selecting hens for nest-related traits, such as egg production in nests and nesting behaviour, could help meet the requirements of cage-free housing. However, genetic correlations between these traits and major traits of breeding programmes, such as egg quality or BW, are poorly known. In addition, the genetic determinism of major traits has rarely been studied under cage-free conditions. The objective of the present study was to estimate the heritability of egg quality and BW measured on the floor and their genetic correlations with nest-related traits. Egg production in nests was based on the laying rate in nests, laying rhythm (clutch number and mean oviposition time), and nest acceptance. Nesting behaviour was based on nest preference (mean distance between nests used for laying) and mean laying duration (time spent in the nest for laying). Nest-related traits were recorded from 24 to 64 weeks of age. BW and egg quality were measured at 50 and 55 weeks of age, respectively. Nest-related traits and identification of the eggs laid by each hen (for individual measurements of egg quality) were obtained using individual electronic nests used by hens raised in groups and on the floor. The phenotypes of 1 455 Rhode Island Red and 1 538 White Leghorn hens were analysed. Heritability coefficients and genetic correlations were estimated using a multi-trait animal model for each line. Heritability estimates for egg quality and BW were moderate to high for both lines (0.17–0.74). Overall, weak genetic correlations were estimated between nest-related traits and egg quality or BW for both lines. However, strong and antagonistic genetic correlations were estimated between eggshell strength and laying rate in the nests (−0.46 to −0.42) or laying rhythm (+0.46 to +0.68) for both lines. Several moderate-to-strong genetic correlations were found for White Leghorn between nest-related traits and egg weight, eggshell shape, albumen height, and BW. This study shows that nest-related traits can be used to select hens better adapted to cage-free housing without degrading overall egg quality and BW. It also shows that some traits, like the eggshell strength, must be carefully monitored if these new traits are included in breeding goals. These results must now be confirmed for other populations and larger datasets

Does Intraneuronal Accumulation of Carboxyl-terminal Fragments of the Amyloid Precursor Protein Trigger Early Neurotoxicity in Alzheimer’s Disease?

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Microstructure, transport, and acoustic properties of open-cell foam samples

International audienceThis article explores the applicability of numerical homogenization techniques for analyzing transport properties in real foam samples mostly open-cell, to understand long-wavelength acoustics of rigid-frame air-saturated porous media, on the basis of microstructural parameters. Experimental characterization of porosity and permeability of real foam samples are used to provide the scaling of a polyhedral unit-cell. The Stokes, Laplace, and diffusioncontrolled reaction equations are numerically solved in such media by a finite element method in three-dimensions; an estimation of the materials' transport parameters is derived from these solution fields. The frequency-dependent visco-inertial and thermal response functions governing the long-wavelength acoustic wave propagation in rigid-frame porous materials are then determined from generic approximate but robust models and compared to standing wave tube measurements. With no adjustable constant, the predicted quantities were found to be in acceptable agreement with multi-scale experimental data, and further analyzed in light of scanning electron micrograph observations and critical path considerations

Resolving vibro-acoustics in double porosity materials via a coupled multiscale finite element method

Acoustic materials with non-standard material and geometrical layouts are deployed in buildings to improve sound absorption at targeted frequency bandwidths. Classical numerical models such as the Finite Element Method (FEM) can prove prohibitively expensive as very fine mesh discretizations are required to resolve high frequency waves and complex meso-scale morphologies. Upscaling methodologies like the Coupling Multiscale Finite Element Method (CMsFEM) can be used to achieve accelerated modelling strategies without significantly sacrificing accuracy. Here, complex interfaces and heterogeneous morphologies are resolved at the fine scale. These are mapped onto the coarse scale through a set of numerically evaluated basis functions. The governing equations are finally solved at the coarse-scale at a reduced computational cost. We originally apply the CMsFEM to the Biot equations for wave propagation in poroelastic media and employ it to treat porous materials with mesoscale perforations, i.e., double porosity materials. The efficiency and accuracy of the method are discussed with respect to numerical applications, using an in-house MATLAB code

A reliability study concerning the acoustic simulations of timber elements for buildings

Engineered wood constructions and timber buildings are rapidly developing, while the numerical techniques usable for their sound insulation properties are various and often still under development. This research constitutes a first step towards the reliability determination of building acoustics simulations on timber-based elements. A small scale round robin involving five research laboratories is presented. The results obtained show significant deviations depending on the chosen numerical method and indicate how laboratory measurements could not be approximate with a good accuracy. Finally, a sensitivity analysis is presented and challenges as well as requirements for reliable timber structures acoustic predictions are discussed

Microstructure - acoustic properties relationships: Application to membrane and bimodal pore-size distribution effects

International audienceThis paper presents recent developments in the field of multi-scale acoustics of real porous media. The fundamental idea of the proposed approach is that it is possible to get insight into the microstructure of real porous media and how it collectively dictates their acoustical properties, from the three dimensional implementation of micro-acoustics based scaling relations on idealized unit-cells. The homogenization procedure is applied to the problem of long-wavelength wave propagation in rigid porous media saturated with a Newtonian and thermally conducting fluid. The local problems corresponding to the fluid phase have been solved for the three-dimensional tetrakaidecahedronal model. The geometry of the foam is determined based on two measured macroscopic parameters: 1) the porosity and 2) the hydraulic permeability. The complete set of transport phenomena characterizing the asymptotic behavior of the frequency dependant viscous and thermal dissipation functions are systematically determined. The results of this technique are compared to standing wave tube and micrographs measurements for three real samples of predominately open-celled foams, giving evidences of membrane and bimodal pore-size distribution effects

Three-dimensional idealized unit-cell based method for computing acoustic properties of low-density reticulated foams

International audienceThis paper presents recent developments in the field of micro-acoustics of porous media. The fundamental idea of the proposed approach is that it is possible to assess porous microstructure and acoustical properties from the three-dimensional implementation of micro-acoustics based scaling relations on porous materials. We illustrate this approach through results from the application of this technique to real samples of predominately open-cell polymeric foams