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The acoustic properties of an air-saturated porous material depend on its microstructure and the thickness of the sample. Thick samples of conventional acoustic materials are required to achieve good absorption at low frequencies. This study suggests a new micro-structure for the design of low-frequency resonant acoustic absorbers. A perforated material is studied, in which the main perforations are connected to a collection of periodically spaced very thin annular dead-end pores with respect to the lateral size, these absorbers are called multi-pancake materials. It is shown, that at low frequencies, the periodic array of annular dead-end pores increases the effective compressibility without modifying the effective dynamic density. Due to this effect, the first sound absorption peak appears at much lower frequency, compared to that of the structure without dead-end pores. A transfer matrix approach is proposed to model and optimize the absorber. Prototypes have been 3D printed and tested for sound absorption and transmission loss. This design allowed to design materials capable of producing absorption peaks at a few hundred Hz and constituted of a stacking of 10–20 annular dead-end pores, each dead-end having a thickness of the order of 1 mm or less so that the overall material thickness was of a few cm. A good agreement between the data and the model predictions is demonstrated. [ABSTRACT FROM AUTHOR]

Abstract: This paper experimentally investigates the holes interaction effect on the sound absorption coefficient of micro-perforated panels under high and medium sound levels. The theoretical formulations are based on a semi-empirical approach and the use of Fok’s function to model the acoustic surface impedance. For the high sound level regime, an empirical power law involving three coefficients is adapted. It is shown theoretically and experimentally that these coefficients can lead to optimized absorption performance and particularly, a formula relating the critical Reynolds number (Reynolds number value after which the absorption coefficient decreases with the increase of sound level) and the center-to-center distance between the perforations is derived. It is demonstrated that the first coefficient of the nonlinear acoustic resistance strongly depends on the separation distance between the apertures and decreases with a decrease of this latter distance. Analysis of the data reveals the fact that even with Holes Interaction Effect (HIE), the nonlinear reactance dependence on velocity is still very low compared to the resistance-velocity dependence. Four perforated panels of 1.5mm thickness with different separation distances between the holes (from widely to closely separation) were built and tested. Experimental results performed with an impedance tube are compared with the described model for HIE. To test the dependence of the coefficients on frequency, the experiments are carried out for two different excitation frequencies (292Hz and 506Hz). The results can be used for designing optimal perforated panels for ducts, silencers and for the automotive industry. [Copyright &y& Elsevier]

In the context of structural dynamics, recent works by the authors showed that microperforations can be used to mitigate vibration. Microperforated plates (MPP) have been shown to exhibit substantial added damping arising from fluid-structure interactions and visco-thermal effects in the boundary layers of the perforations during relative motion between the solid and the fluid contained in the perforations. The added damping reaches a maximum for a characteristic frequency, depending only on the diameter of the perforation. Choosing the diameter of the perforation so that the characteristic frequency coincides with a given natural frequency of the plate reduces the contribution of the associated plate mode. However, the MPP studied had a single set of perforations homogeneously distributed throughout the structure. In this work, it is proposed to extend the added damping to several modes of the plate by using MPP with multi-size perforations and an optimized spatial distribution of these perforations. As an extension of the previous vibratory model of the authors, the dynamics of MPP with perforations of multiple sizes based on a homogenization model is established. In addition, the effect of the spatial distribution of perforations on the additional damping is captured by including a spatially dependent perforation ratio in the model. Experimental measurements on MPP validate the proposed analytical models. The results show that (i) MPP with multiple-size perforations feature a wider effective damping frequency band, and (ii) the added damping is accentuated when the perforations are distributed in the zone of the antinodes of the considered modes. Thus, by combining the two effects, it is possible to achieve MPP that effectively reduce the vibratory responses on several modes. • A homogenization approach is proposed for MPP with multiple perforation sizes. • Perforation ratio is a spatial function for MPP with nonuniform perforation distributions. • Multi-perforation MPP broaden the frequency range of effective additional damping. • MPP with nonuniform perforation distribution maximizes the added damping on a given mode. • The damping effects of the two configurations can be cumulated. [ABSTRACT FROM AUTHOR]

Highlights: [•] The architecture of a self-learning, ontology-based framework is presented. [•] Framework enables context-aware applications to change their behavior at run-time. [•] Knowledge added to the ontology is given a probability to convey its reliability. [•] An implemented use case is presented: mining the reasons for patients’ nurse calls. [•] Datasets of size >1000 with <5% noise yield correct results in negligible time. [Copyright &y& Elsevier]

• Thin Metamaterial Design for Sound Absorption. • Using Acoustic Black Hole Profiles for Broadband Absorption. • Parametric Analysis with an Adapted Transfer Matrix Model. • Balancing Losses with Complex Frequency Plane Representation. The multi-pancake absorber is a thin acoustic metamaterial composed of periodically arranged thin annular cavities separated by the plates and connected by a main pore, enabling low frequency sound absorption. However, with a constant main pore radius, this structure exhibits tonal absorption behavior characterized by narrow peaks with varying amplitudes due to an imbalance in losses between the modes. This work investigates a geometric variation of the main pore, focusing on the designs with a gradually decreasing radius known as acoustic black hole profiles, to achieve broadband absorption. An analytical model based on the transfer matrix approach and lumped elements is proposed to predict the acoustic properties. Validation is conducted through thermo-visco-acoustic finite element simulations and impedance tube measurements. Multiple main pore profiles are investigated and the complex frequency plane representation is used to improve the balance of losses. An understanding of the influence of the main pore radius at the entrance and backing of the sample, allows design of a decreasing main pore radius profile that results in a high absorption coefficient value across a broad frequency range. Non-linear decreasing main pore profiles can be used, if necessary, to accentuate losses and achieve absorption peaks of similar amplitude. [ABSTRACT FROM AUTHOR]

A recent study investigated the mechanical, thermal and acoustical properties of a bio-based composite made from crushed particles of sunflower stalks binded together by chitosan, a bio-based binder. The acoustical performance in absorption was found to be poor as the material was highly compacted and with low porosity. The present study focuses on the acoustical properties of a higher porosity composite, with lower density while the mechanical rigidity remains fairly high. A higher absorption coefficient is obtained. The experimental results on the absorption coefficient are compared to the prediction of a model involving 5 physical parameters (porosity, tortuosity, airflow resistivity, thermal and viscous characteristic lengths). The characterization methods to determine these parameters are described. The comparison between experimental and theoretical results shows that this material exhibits peculiar microstructural features. It is found that the sound absorption properties can involve dead-end pores or clusters and multiple porosity scales in the material. [ABSTRACT FROM AUTHOR]

The complexity of continuous care settings has increased due to an ageing population, a dwindling number of caregivers and increasing costs. Electronic healthcare (eHealth) solutions are often introduced to deal with these issues. This technological equipment further increases the complexity of healthcare as the caregivers are responsible for integrating and configuring these solutions to their needs. Small differences in user requirements often occur between various environments where the services are deployed. It is difficult to capture these nuances at development time. Consequently, the services are not tuned towards the users' needs. This paper describes our experiences with extending an eHealth application with self-learning components such that it can automatically adjust its parameters at run-time to the users' needs and preferences. These components gather information about the usage of the application. This collected information is processed by data mining techniques to learn the parameter values for the application. Each discovered parameter is associated with a probability, which expresses its reliability. Unreliable values are filtered. The remaining parameters and their reliability are integrated into the application. The eHealth application is the ontology-based Nurse Call System (oNCS), which assesses the priority of a call based on the current context and assigns the most appropriate caregiver to a call. Decision trees and Bayesian networks are used to learn and adjust the parameters of the oNCS. For a realistic dataset of 1050 instances, correct parameter values are discovered very efficiently as the components require at most 100 ms execution time and 20 MB memory. [ABSTRACT FROM AUTHOR]

Abstract: TrpA1 is an ion channel involved in nociceptive and inflammatory pain. It is implicated in the detection of chemical irritants through covalent binding to a cysteine-rich intracellular region of the protein. While performing an HTS of the Pfizer chemical collection, a class of pyrimidines emerged as a non-reactive, non-covalently binding family of agonists of the rat and human TrpA1 channel. Given the issues identified with the reference agonist Mustard Oil (MO) in screening, a new, non-covalently binding agonist was optimized and proved to be a superior agent to MO for screening purposes. Compound 16a (PF-4840154) is a potent, selective agonist of the rat and human TrpA1 channel and elicited TrpA1-mediated nocifensive behaviour in mouse. [Copyright &y& Elsevier]