Validity of the One-Dimensional Limp Model for Porous Media

A straightforward criterion for determining the validity ofthe limp model validity for porous materials is addressed here. The limp model is an “equivalent fluid” model which gives a better description of porous behavior than the well known “rigid frame” model. It is derived from the poroelastic Biot model, assuming that the frame has no bulk stiffness. A criterion is proposed for identifying the porous materials for which the limp model can be used. It relies on a new parameter, the Frame Stiffness Influence FSI, based on porous material properties. The critical values of FSI under which the limp model can be used are determined using 1D analytical modeling for a specific boundary set: radiation of a vibrating plate covered by a porous layer.

Vivencia de la enfermera oncológica frente al COVID en el Hospital Clínic de Barcelona

Màster en Lideratge i Gestió d'Infermeria, Universitat de Barcelona. Escola Universitària d'Infermeria, curs: 2020-2021, Director: Paz Fernández OrtegaIntroducción: el impacto psicológico por el COVID en las enfermeras es incuestionable. El 79,5 % sufre ansiedad, el 53 % de los profesionales presentan sintomatología compatible con estrés postraumático, y el 40 % se sienten emocionalmente agotados. Objetivo: comprender la experiencia vivida por las enfermeras en la atención al paciente oncológico con COVID durante el periodo de pandemia. Ámbito de estudio: se desarrollará en el Hospital Clínic de Barcelona. Metodología: proyecto de metodología cualitativa y paradigma constructivista. Diseño: fenomenológico hermenéutico de Heidegger. Participantes: enfermeras que han ofrecido y ofrecen cuidados al paciente oncológico con COVID durante el periodo de pandemia. Muestreo intencional teórico. Recogida de información: entrevistas semiestructuradas. Análisis de la información: análisis del discurso, llegando a tejer una explicación más amplia de la importancia teórica o práctica. Se utilizará el programa informático NVivo12Pro. Se seguirán las consideraciones éticas de la investigación clínica y los criterios de rigor pertinentes. Implicaciones para la práctica: este estudio ayudará a conocer mejor el impacto emocional y proponer sistemas de apoyo usados para disminuir la sobrecarga emocional secundaria a la pandemia por COVID

Investigations on the sensitivity of the relationships between sound absorption characteristics and microstructure related parameters for polyurethane foams

International audienceStraightforward semi-phenomenological models have been developed for highly porous polyurethane foams to predict the macroscopic nonacoustic parameters involved in the classical Johnson-Champoux-Allard model (i.e., porosity, airflow resistivity...) from microstructure properties (i.e, strut length, strut thickness and reticulation rate). These microstructure properties are measured using sophisticated optical methods (i.e., optical microscope, SEM) and a large variability can be observed due to great complexity of the 3D microstructure; variability which also depends on the precision of the measurement device. This work investigates how the variability associated with the model inputs affects the model outputs (i.e., non-acoustic parameters, surface impedance and sound absorption coefficient). The sensitivity analysis is based on the Fourier Amplitude Sensitivity Test (FAST). It helps quantify the correlation between the input parameters and identify the parameters contributing the most to output variability, thus requiring precise measurement. This study illustrates the preponderant impact of the reticulation rate (i.e, open pore content) on acoustic performances and guides the user on the required optical measurement device

Evaluation of the acoustic and non-acoustic properties of sound absorbing materials using a three-microphone impedance tube

This paper presents a straightforward application of an indirect method based on a three-microphone impedance tube setup to determine the non-acoustic properties of a sound absorbing porous material. First, a three-microphone impedance tube technique is used to measure some acoustic properties of the material (i.e., sound absorption coefficient, sound transmission loss, effective density and effective bulk modulus) regarded here as an equivalent fluid. Second, an indirect characterization allows one to extract its non-acoustic properties (i.e., static airflow resistivity, tortuosity, viscous and thermal characteristic lengths) from the measured effective properties and the material open porosity. The procedure is applied to four different sound absorbing materials and results of the characterization are compared with existing direct and inverse methods. Predictions of the acoustic behavior using an equivalent fluid model and the found non-acoustic properties are in good agreement with impedance tube measurements

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