Mass-spring model for acoustic metamaterials consisting of a compact linear periodic array of dead-end resonators.

This paper presents a mass-spring model to predict the normal incidence acoustic response of a metamaterial composed of a compact linear periodic array of dead-end resonators. The dead-end resonators considered are ring-shaped Helmholtz resonators. The model is based on a mass-spring analogy and considers the thermoviscous losses in the metamaterial following an effective fluid approach. A matrix equation of acoustic motion is derived for the finite case of N-periodic arrays. Under external excitation, its direct solution predicts the sound absorption coefficient and transmission loss. Under the homogeneous case, the solution of its associated eigenvalue problem predicts the acoustic eigenfrequencies and mode shapes. The dispersion relation is also solved to predict the beginning of the first stopband, and a low frequency approximation allows development of a formula to estimate the first eigenfrequency. The results show that the system with N degrees of freedom has three stopbands over the frequency range studied, with zero sound absorption and transmission. The model also helps to understand how the acoustic dissipation, at a given resonant frequency, is affected by the position of the acoustic velocity nodes (eigenmodes) in the geometry of the metamaterial. Prototypes are designed, manufactured, and tested in an impedance tube to validate the model.

Thermoviscous-acoustic metamaterials to damp acoustic modes in complex shape geometries at low frequencies.

This article proposes a hybrid numerical-analytical approach to effectively predict the sound absorption coefficient of complex periodic metamaterials with a reasonably low computation time. A variation of an existing metamaterial, consisting of a periodic succession of necks and cavities, is also proposed. The design variation was intended to decrease the frequencies of the absorption coefficient resonant peaks and consists in adding eccentricity in the neck position. The hybrid approach combines a thermoviscous-acoustic (TVA) approach with the transfer matrix (TM) method. The TVA approach estimates the thermoviscous losses of acoustic waves in a periodic unit cell (PUC) of the metamaterial. The TM method is used to simulate the acoustic behaviour of the complete metamaterial from the TM of the PUC calculated numerically. The approach is compared to impedance tube measurements on prototypes of the metamaterial. The comparison shows that the proposed approach is in good agreement with the measured sound absorption coefficient. In addition, numerical simulations and experiments demonstrate that the proposed variation of the existing metamaterial results in a shift of the absorption peaks down in frequency without deteriorating their sound absorption performance.

Comparison between parallel transfer matrix method and admittance sum method.

A transfer matrix method to predict absorption coefficient and transmission loss of parallel assemblies of materials which can be expressed by a 2 × 2 transfer matrix was published recently. However, the usual method based on the sum of admittances is largely used to predict also surface admittance of parallel assemblies. This paper aims to highlight differences between both methods through three examples on a parallel assembly backed by (1) a rigid wall, (2) an air cavity, and (3) an anechoic termination.

Possible alternative strategies to implement basophil activation testing in multicentric studies.

The Basophil Activation Test (BAT) enables flow cytometry characterization of basophil reactivity against specific allergenic molecules. The focus now revolves around democratizing this tool, but, as blood sample stability could be challenging, after having developed a simplified approach, herein, we aimed to characterize two strategies for implementing BAT in multicentric studies: store and ship blood before or after sample processing. Fresh heparin- and EDTA-anticoagulated whole blood samples followed both BAT workflows: "collect, store, process & analyze" or "collect, process, store & analyze". Storage temperatures of 18-25 °C or 2-8 °C and preservation times from 0 to 7 days were considered. Interleukin-3 was also evaluated. With the "collect, store, process & analyze" workflow, heparin-anticoagulated blood and 18-25 °C storage were better than other conditions. While remaining possible, basophil activation exhibited a possible reactivity decay after 24 h. Under the conditions tested, interleukin-3 had no role in enhancing basophil reactivity after storage. Conversely, the "collect, process, store & analyze" workflow demonstrated that either heparin- or EDTA-anticoagulated blood can be processed and kept up to 7 days at 18-25 °C or 2-8 °C before being analyzed. Various strategies can be implemented to integrate BAT in multicentric studies. The "collect, store, process & analyze" workflow remains a simplified logistical approach, but depending on time required to ship from the clinical centers to the reference laboratories, it might not be applicable, or should be used with caution. The "collect, process, store & analyze" workflow may constitute a workflow improvement to provide significant flexibility without impact on basophil reactivity.

Acoustic methods for measuring the porosities of porous materials incorporating dead-end pores.

The acoustic properties of porous materials containing dead-end (DE) pores have been proposed by Dupont et al. [J. Appl. Phys. 110, 094903 (2011)]. In the theoretical description, two physical parameters were defined (the dead-end porosity and the average length of the dead-end pores). With the knowledge of the open porosity (measured with non-acoustic methods), and the measurement of kinematic porosity (also called the Biot porosity in this article), it is possible to deduce the dead-end porosity. Two acoustic methods for measuring the Biot porosity for a wide range of porosities are proposed. These methods are based on acoustic transmission and on the low and high frequency behaviors of acoustic indicators. The low frequency method is valid for high porosities. It involves measurements in a transmission tube and the knowledge of the theoretical asymptotic behavior of the phase velocity at high frequencies. The high frequency method is based on ultrasonic measurements and on the high frequency asymptotic behavior of the transmission coefficient. It is well adapted for material with relatively low values of porosity. Good precision was found for both methods and materials containing dead end porosity were tested.

Transfer matrix method applied to the parallel assembly of sound absorbing materials.

The transfer matrix method (TMM) is used conventionally to predict the acoustic properties of laterally infinite homogeneous layers assembled in series to form a multilayer. In this work, a parallel assembly process of transfer matrices is used to model heterogeneous materials such as patchworks, acoustic mosaics, or a collection of acoustic elements in parallel. In this method, it is assumed that each parallel element can be modeled by a 2 × 2 transfer matrix, and no diffusion exists between elements. The resulting transfer matrix of the parallel assembly is also a 2 × 2 matrix that can be assembled in series with the classical TMM. The method is validated by comparison with finite element (FE) simulations and acoustical tube measurements on different parallel/series configurations at normal and oblique incidence. The comparisons are in terms of sound absorption coefficient and transmission loss on experimental and simulated data and published data, notably published data on a parallel array of resonators. From these comparisons, the limitations of the method are discussed. Finally, applications to three-dimensional geometries are studied, where the geometries are discretized as in a FE concept. Compared to FE simulations, the extended TMM yields similar results with a trivial computation time.

Acoustic properties of plates with unevenly distributed macroperforations backed by woven meshes.

A hybrid model describing the acoustic properties of plates with macroperforations that can be unevenly distributed on the plate surface and backed by woven or precision woven meshes with microscopic perforations is proposed. The plate perforations may be of circular or rectangular shapes. Since the perforated plate may not necessarily be considered as an equivalent fluid, its impedance is calculated by the Maa model [Noise Control Eng. J. 29, 77-84 (1987)], whereas the Johnson-Champoux-Allard model [J. Appl. Phys. 70, 1975-1979 (1991)] is used for the mesh, considered as an equivalent fluid. A simple model for the elementary cell of the mesh structure is proposed in order to calculate parameters that can be considered as the thermal characteristic length Λ' and the viscous characteristic length Λ. An effective airflow resistivity is introduced to account for the increase of particle velocity through the mesh placed behind the carrying macroperforated plate and is used in the transfer matrix approach to obtain the impedance of the whole multilayer system. The hybrid model seems to represent a good approach of this multilayer system. The theoretical predictions are compared with experimental measurements.

Design and pharmacological evaluation of PF-4840154, a non-electrophilic reference agonist of the TrpA1 channel.

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.

Method for controlling boundary condition effects on the measurement of acoustic properties of small samples in tubes.

As standard ASTM E2611 reveals, the normal incidence sound transmission loss measured on a small sample in an acoustic tube is not only a property of the material but also strongly dependent on boundary conditions (generally unknown) and on the way the material is mounted. This article proposes an experimental method to control the effects of the lateral boundary conditions in an acoustic tube. The main objective is to deduce the properties of a "client element" (material sample) from the measured global acoustic properties of a patchwork composed by the "client material" and a known "host support." Three patchwork configurations have to be distinguished: patchworks with and without an impervious and rigid interface between the elements and patchworks composed by elements that cannot be identified as equivalent fluids. For each of these configurations, the use of a specific method based on the Mixing Rule Method (MRM) or on the Parallel Transfer Matrix Methods (P-TMM or dP-TMM) used in reverse way is proposed. Numerical and experimental validations are proposed in acoustic tubes on a convenient configuration: a material sample surrounded by an air ring. This configuration allows reducing the material elastic-frame behavior to leave a limp-frame behavior. The proposed methods allow removing the effect of the lateral air ring host surrounding the material. For homogeneous materials, the two methods based on MRM and dP-TMM give similar good results. For non-homogeneous materials or for materials that cannot be modeled as equivalent fluids, only the method based on dP-TMM gives good results.

Comparison of Road Noise Policies across Australia, Europe, and North America.

Developing innovative noise policies that build on international best practices is difficult when policies around the world differ along many dimensions, ranging from different sources covered to different levels of governance involved. This is particularly critical in the context of road traffic, identified as one of the main culprits leading to noise-associated complaints and health issues. In this article, we document the wide range of specifications observed in road traffic policies and propose a methodology to compare noise limits across noise policies. First, we present the responsibilities of administrative governments according to the scope (e.g., emission vs. exposure). Second, we compare noise limits by scope and geographic areas by separating acoustic indicators (overall and event indicators). Third, we convert overall outdoor noise limits into a common basis using the method described by Brink and his associates (2018) and compare them with the World Health Organization (WHO)'s recommendations (2018). Finally, measurement protocols are also compared across outdoor noise policies. This paper shows that road noise is managed at several administrative levels using approaches that are either centralized or decentralized. We also observed disparities in the associated noise limits across geographic areas. The converted outdoor noise limits generally exceeded the WHO's recommendations (2018). Finally, this paper outlines how outdoor measurement protocols vary across geographic areas. However, similarities were identified between state and provincial noise policies within the same country.

On the variations of acoustic absorption peak with particle velocity in micro-perforated panels at high level of excitation.

The acoustic behavior of micro-perforated panels (MPP) is studied theoretically and experimentally at high level of pressure excitation. A model based on Forchheimer's regime of flow velocity in the perforations is proposed. This model is valid at relatively high Reynolds numbers and low Mach numbers. The experimental method consists in measuring the acoustical pressure at three different positions in an impedance tube, the two measurement positions usually considered in an impedance tube and one measurement in the vicinity of the rear surface of the MPP. The impedance tube is equipped with a pressure driver instead of the usual loudspeaker and capable of delivering a high sound pressure level up to 160 dB. MPP specimens made out of steel, dural and polypropylene were tested. Measurements using random noise or sinusoidal excitation in a frequency range between 200 and 1600 Hz were carried out on MPPs backed by air cavities. It was observed that the maximum of absorption can be a positive or a negative function of the flow velocity in the perforations. This suggests the existence of a maximum of absorption as a function of flow velocity. This behavior was predicted by the model and confirmed experimentally.

A concise and selective synthesis of novel 5-aryloxyimidazole NNRTIs.

[reaction: see text] A concise and efficient route to the construction of a 5-aryloxyimidazole has been developed. The key step was the selective O-arylation of a 2,4-dimethoxybenzyl-protected imidazolone. The final compound is a potent inhibitor of HIV reverse transcriptase.

A self-learning nurse call system.

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 100ms execution time and 20MB memory.

Novel indazole non-nucleoside reverse transcriptase inhibitors using molecular hybridization based on crystallographic overlays.

A major problem associated with non-nucleoside reverse transcriptase inhibitors (NNRTIs) for the treatment of HIV is their lack of resilience to mutations in the reverse transcriptase (RT) enzyme. Using structural overlays of the known inhibitors efavirenz and capravirine complexed in RT as a starting point, and structure-based drug design techniques, we have created a novel series of indazole NNRTIs that possess excellent metabolic stability and mutant resilience.