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We propose a novel hybrid acoustic metamaterial that can achieve broadband sound insulation below 452 Hz and almost perfect sound absorption at 864 Hz. The metastructure was fabricated using additive manufacturing. Finite element method simulations were used to study the acoustic properties of the fabricated metamaterials. An equivalent electrical circuit was built using an electro-acoustic analogy to evaluate the sound absorption coefficient. The unique design of this meta-structure possesses two resonant frequencies. Low-frequency sound insulation is found due to the effective negative density at frequencies lower than the cutoff frequency of the elastic membrane. In contrast, a negative effective bulk modulus is the reason behind the broadband sound absorption. The theoretical and simulation results were validated through experiments. Experiments carried out showed an overall average sound transmission loss of 26.31 dB between 50 and 1600 Hz and 24.72 dB in the low-frequency zone (<400 Hz). Furthermore, over 69% of the sound intensity is absorbed in the 500–1000 Hz frequency range. The designed meta-structure exhibits broadband effective negative density below 452 Hz and effective negative bulk modulus from 864 to 1220 Hz. The design specifies a sample thickness of 3.8 cm, corresponding to a subwavelength thickness of approximately λ/10. As a result, the developed meta-structure can potentially be employed for sound insulation and absorption at low frequencies in the aerospace and automotive industries and in-room acoustic applications. [ABSTRACT FROM AUTHOR]

In response to the increasing traffic noise problem, we designed a combined acoustic metamaterial (CAM) based on the multi-channel Fano resonance principle. By utilizing the Fano resonance coupling between the acoustic spiral structure and the hollow structure, efficient sound insulation under effective ventilation conditions is achieved. Simulation results of acoustic transmission loss show that the acoustic transmission loss of CAM is more than 13 dB in the frequency band of 520–989 Hz. The broadband sound insulation characteristic can block the oblique angle incident sound waves from different angles. Simulation results of the elastic strain energy and acoustic pressure field validate the sound insulation mechanism of the Fano resonance of the combined acoustic metamaterial. The experimental results in the impedance tube generally agree with the simulation results. To explore the possibility of wider engineering applications of CAM, we propose a combined CAM and CAM0.7 structure. The results show that a series structure of acoustic metamaterials can be selected to further realize broadband sound insulation within 500–1574 Hz. [ABSTRACT FROM AUTHOR]

In this paper, a new type of fully symmetric single-phase metamaterial structure is proposed. Based on the finite element method, the band gap characteristics of different forms of the structure and the generation principle of the band gap are discussed. The analysis of the formation mechanism of the band gap shows that the proposed structure can achieve the purpose of expanding the band gap in the low frequency range by changing the structure and adding inclusions. Then, the variation trend of the band gap frequency range in the case of small deformation of the proposed structure is discussed. In addition, the propagation characteristics of elastic waves in the proposed structure are analyzed according to the variation characteristics of frequency contours, phase velocities and group velocities. Finally, the frequency response spectrum obtained from the propagation of elastic waves in a finite lattice composed of Model No. 3 elements further confirms the role of the proposed structure in suppressing wave propagation. The results show that the proposed structure has good band gap characteristics in a certain frequency range, which can provide ideological guidance for the design of metamaterials for achieve low-frequency sound insulation and vibration reduction. [ABSTRACT FROM AUTHOR]

This paper proposes a sublaminate layer-wise finite element modeling method to accurately evaluate the damping and sound insulation characteristics of composite constrained layer damping plates. It incorporates the frequency-dependent property of viscoelastic interlayer into fully coupled structure-acoustic interaction equations, and employs the generalized high-order displacement hypothesis with tailored polynomial series expansion. The method is applicable to various boundary conditions and material layer combinations. Validation is conducted using numerical and experimental data. Parametric study identifies optimal thickness and stiffness for maximizing modal loss factor. Additionally, sound insulation performance is examined in narrow frequency bands, highlighting the damping enhancement of viscoelastic interlayer. [ABSTRACT FROM AUTHOR]

Silica aerogels are regarded as potential thermal and acoustic insulation materials with low density and porous structure. However, the hydrophilicity due to surface hydroxyl groups and the low mechanical intensity have limited its further application. Generally, it can be achieved by adjusting the process parameters of the sol-gel to refine the structure of silica aerogels and optimize performance. In this study, we adopted an appropriate modification strategy of incorporating glass fiber felts as the reinforcing phase and trimethylchlorosilane (TMCS) as the hydrophobic modifier. By adjusting the solvent exchange time, the micro-nano structure, i.e. hierarchical networks, was optimized. The TMCS-modified silica aerogel/glass fiber/hot-melt fiber composites (TSGMs) exhibited great sound insulation, and the maximum sound transmission loss (STL) was up to 34 dB at 6300 Hz. Compared to unmodified, STL improved by 8 dB in simulated practical applications. In addition, TSGMs also exhibited high hydrophobicity with a water contact angle of 147° and excellent thermal insulation with a thermal conductivity of 0.0345 W (m k)−1. The results could contribute to the refinement in the preparation process of silica aerogel composites and use in the fields of thermal and acoustic insulation. [ABSTRACT FROM AUTHOR]

With the waste of resources caused by human activities, it has gradually become an increasingly prominent social problem. The development of self-healing polymers in the field of insulation has attracted widespread attention. Develop polymer matrices with efficient healing efficiency and sound insulation properties to achieve green and sustainable resource conservation. In addition, improving the dielectric properties of intrinsic self-healing matrices has been a hot topic. In this work, we developed a new PEI matrix-modified self-healing polymer substrate that provides a breakdown field strength of 240 kV/mm and self-healing properties at room temperature, this has significantly improved the dielectric properties over other previously reported self-healing polymers. In addition to the abovementioned performance, we found significant differences in thermodynamic behavior in the synthesized end-modified polymers. By dielectric characterization (LCR), the breakdown composite can be left at room temperature for 60 min, and the material can recover 80 % of the initial properties without external intervention(This is demonstrated by the fact that its DC conductivity at 60 min of autonomous healing was significantly changed from that of the freshly electrically pierced DC conductivity and remained around 5.38 × 10−11 S/cm for a longer period of time thereafter). The microscopic morphology of the modified PEI matrix was observed by scanning electron microscopy (SEM) and EDS surface elemental analysis, which further supports the existence of metal coordination structures. These findings can further deepen the thinking of self-healing dielectric composites. The work inspired by this may break the limits and take self-healing composite dielectric materials to a new height. [ABSTRACT FROM AUTHOR]

The use of machines and technology in the industrial sector has led to noise pollution, which requires attention. The practice of noise control through soundproofing is closely linked to the use of various acoustic materials, whether they are synthetic or natural fibers. Natural materials are preferred for biocomposite reinforcement due to the design flexibility, eco-friendliness, sustainability, and ease of availability. Therefore, this research aimed to analyze the variation of grinting grass (Cynodon dactylon) composite material as damper with safe working distance from noise exposure. This experimental research was conducted using industrial grinding machine and damper from grinting grass as the object and composite material. The instruments used for measurement included an Impedance tube (sound absorption coefficient), a sound level meter (noise intensity), and a Surfer 13 noise mapping application. The data obtained were analyzed using the Wilcoxon test to determine the differences before and after the intervention. The results showed that the most effective composite had a 60:40 ratio with a sound absorption coefficient of 0.30. Before using damper, the highest noise intensity recorded was 106 dBA, which was reduced to 83 dBA. Safe working distance from exposure before damper was 6.1 meters, which decreased to 1 meter after the intervention. In conclusion, there was a significant difference in noise intensity (p = 0.000) and safe working distance from exposure (p = 0.001) before and after the use of grinting grass as damper [ABSTRACT FROM AUTHOR]

Objective: This study presents a novel membrane-type acoustic metamaterial (MAM) with loaded masses of asymmetric dimensions and arrangements. The transmission losses (TL) of the proposed structures were investigated theoretically. The two types of loaded ornaments investigated were arc masses and platelets. The dependence of TL characteristics on mass positions was also investigated. Method: An analytical model based on the Galerkin method was established to predict the TL behavior. Finite element (FE) simulations were conducted to verify the analytical results. Results and Conclusions: In comparison with traditional MAMs of symmetric loaded mass, asymmetric masses are more effective in increasing the number of TL peaks as well as reducing the overall weight of the structure. The TL peak frequency coincides with the frequency of the unbound mass and steep phase change. A good agreement between theoretical and FE results was observed. [ABSTRACT FROM AUTHOR]

Building acoustics simulation of a wooden frame wall Building physics simulations have already become firmly established in the everyday planning of hygrothermal conditions. In contrast, simulating real physical effects in building acoustics, especially in lightweight construction, to enable precise predictions is still a challenge. With the increasing demand in timber construction, both the requirements and the need for planning security are growing. Reliable frequency‐dependent prediction of the sound insulation of lightweight components could save resource‐consuming measurements. So far, the Finite Element Method (FEM) has proven to be a suitable method for conducting building acoustics parameter studies on lightweight components and evaluating constructive changes in relation to each other. This article presents the simulation of a timber frame wall in window size using the FEM. The simulation results, conducted with the software "COMSOL Multiphysics 6.1", are compared with building acoustic measurements. Using the simulation, the sound insulation is predicted with a maximum deviation of 5 dB per 1/3‐octave band. In FEM, the quality of the input data is crucial, with relevant stiffness values and loss factors of all materials determined through modal analyses. This approach becomes particularly relevant for multi‐layered anisotropic components. In addition to the validation, parameter variations were carried out based on the model. The results of these studies are also discussed in this work. [ABSTRACT FROM AUTHOR]

The unique core structure makes the corrugated sandwich plate with enhanced strength and stiffness while maintaining a relatively lighter mass, with simple structure and low manufacturing cost, which has a significant potential for widespread applications. To better evaluate its acoustic performance, a theoretical model for vibration analysis under simply supported boundary conditions is established using the first-order shear deformation theory (FSDT) and Hamilton's principle, as well as formulates the sound insulation equation for the sandwich panel subjected to simple harmonic pressure excitation. The solution is further solved analytically based on the fluid-structure coupling condition and the Navier method, and the sound transmission loss (STL) is described analytically. The validity of the proposed model is verified by comparing with the results of impedance tube acoustic insulation experiment and commercial software COMSOL finite element simulation. Based on the approach presented in this article, the effects of sandwich layer thickness, corrugation angle, sandwich plate size and corrugation wall thickness on the acoustic and vibration characteristics of the structure are discussed. The findings demonstrate that, the natural frequency of the sandwich panel undergoes a decrease as the corrugated inclination increases. Specifically, when the corrugated inclination angle rises from 30° to 70°, the overall sound insulation effect improves by 8.73 %. An increase in the core thickness results in a decrease in the resonance frequency of the sandwich plate, and the sandwich plate exhibits good sound insulation across a wide frequency band when the core thickness reaches 12 mm. As the thickness of the corrugated wall increases, a trend towards lower frequencies of the sound insulation trough is observed, and when the corrugated wall thickness increases from 1 mm to 3 mm, the average STL of sandwich panel enhanced by 12.57 % in the whole frequency analysis. [ABSTRACT FROM AUTHOR]

The panel cavity structure is one of the key components of the aircraft (vehicle) body and is among the main noise transmission pathways. Based on the modal superposition and Galerkin method, this paper realizes the theoretical model of sound insulation of the clamped, double-panel structure. The non-dominated sorting genetic algorithm-II (NSGA-II) is used to realize the sound insulation of the clamped double-panel structure. Through optimization, the fitting function and law of structural surface density and the optimized normal weighted sound insulation Pareto fronts were obtained. The results show that among the optimization, for the Pareto front cases, their double-panel thickness ratio h 1/ h 2 is relatively far away from 1, and the corresponding cavity thickness H is relatively large. The influence of boundary conditions and size effects of lightweight sound insulation optimization are also discussed. The research on the influence of boundary and size indicates that the difference in the optimal weighted sound insulation Pareto fronts corresponding to the same surface density is mostly within the 1 dB range. Both the boundary and thickness of the panel will affect the frequency STL, while the boundary conditions or structure size changed, even the total thickness of panels needs to be the same, and the structure can also have similar weighted sound transmission loss (R w) when the thickness ratio of the double-panel structure is chosen properly. The difference of material effects is also discussed. This research provides a method for the sound insulation optimization of clamped double-panel structures concerning the boundary and size effect. [ABSTRACT FROM AUTHOR]

Mass timber panels including cross-laminated timber (CLT), dowel-laminated timber (DLT), and nail-laminated timber (NLT) are used increasingly as floor slabs in mass timber buildings and hybrid timber buildings. The sound insulation performance of bare mass timber structural floors is insufficient due to their lightweight and relatively high bending stiffness. Floating concrete toppings are commonly applied for improved sound insulation performance with an elastic interlayer. The effect of different elastic interlayers and thickness of concrete toppings on improving the impact sound insulation performance was investigated experimentally according to ASTM standards in this study. The results showed that with the same elastic layer, thicker concrete toppings resulted in better impact sound insulation performance with a higher apparent impact insulation class (AIIC). However, by increasing the concrete thickness from 38 to 50 mm and to 70 mm, the improvement of AIIC between two thicknesses was only within 3, and a significant improvement up to 9 was observed with a 100-mm-thick concrete topping. In general, elastic interlayers with lower dynamic stiffness values performed better; however, the performance was product dependent though the apparent dynamic stiffness was measured using the same standard method. Moreover, with the same panel thickness and wood species, a bare DLT floor provided higher AIIC (35) than a bare CLT (21), but each mass timber floor with the same interlayer and floating concrete topping had the same impact sound attenuation performance. The ISO empirical prediction equation overestimated the impact sound attenuation of floating concrete toppings on mass timber floors. [ABSTRACT FROM AUTHOR]

Laboratory and field measurements of the impact sound acoustic performance of a CLT wood-based floors have been performed. French national regulation requires the use of the standardized tapping machine for impact sound performance measurements. Since the early 2000s, rubber ball impact source has been standardized in some Asian countries to measure and evaluate the low frequency impact sound performance of floors; this excitation source is now part of international standards concerning building acoustic measurement in laboratories and in-situ. Indeed, the impact sound level associated to this soft impact source is supposed to provide a better correlation with annoyance from jumping and/or running children in buildings. The paper reviews the measurements performed using the standard tapping machine and the rubber ball as impact source, on CLT based floors in a laboratory, as well as those on the CLT based experimental building. Impact sound improvements are presented and discussed. The necessity of measuring with both impact sources, rather than only with the tapping machine is examined. [ABSTRACT FROM AUTHOR]

With the requirement of green construction, the building envelope system urgently needs lightweight material with high sound insulation performance. In this study, a kind of plywood with furfuryl alcohol/multilayer graphene oxide (FA/MLGO) layer was prepared by lamination. The four-microphone impedance tube method measured the sound insulation to evaluate optimal process parameters. At the same time, the acoustic impedance, damping performance, interface microstructure, and chemical components were characterized to discuss the sound insulation mechanism of FA/MLGO as a shielding layer. It showed that the weighted transmission loss of plywood with different FA/MLGO layers was enhanced, and acoustic impedance increased while the acoustic radiation damping coefficient decreased. In addition, considering economic costs, the optimal preparation process was three layers with 0.5 wt.% MLGO concentration and 50 wt.% FA concentration, followed by curing for three h. The surface properties, micromorphology, and chemical composition results indicated that FA/MLGO layer formed more complex sound propagation paths in the plywood, thereby increasing the loss of sound energy inside. Thus, the sound insulation of the plywood was improved. [ABSTRACT FROM AUTHOR]

This study introduces a new method for fabricating biphasic architectured structures using self-developed hybrid material extrusion (MEX) process. This approach involves filling the voids of closed-cell structures with a powder material in a single process. The architectured structures were 3D printed using thermoplastic polyurethane (TPU) and subsequently filled with polyamide 12 (PA12) powder in two distinct configurations: partially filled (50%) and fully filled (100%), named as biphasic architectured structures. Experimental and numerical uniaxial quasistatic compression tests were conducted on partially filled and fully filled local and global closed-cell architectured structures, and their results were compared with those of empty architectured structures. The comparative analysis revealed that the partially filled structures, representing a transitional phase, exhibit enhanced properties which is influenced by the amount of powder filling within the structure. A substantial enhancement in stiffness and specific energy absorption (SEA) was observed in the consolidation phase. The fully filled architectured structures exhibit rapid increase in its loading response, characterized by high stiffness and SEA. Furthermore, this study paves the way for future exploration into strategic filling of multiple powders in different regions, thereby tailoring the mechanical and functional responses. Potential applications include manufacturing components and equipment that absorb energy, provide impact protection, and offer vibration damping and soundproofing capabilities. [ABSTRACT FROM AUTHOR]

This paper proposes a universal vibroacoustic coupling theoretical analysis model for investigating the sound insulation characteristic of corrugated core sandwich panel (CCSP) under different boundary conditions. The vibroacoustic coupling model consists of CCSP (structural field) and two three-dimensional acoustic cavities which simulate the incident sound field and accept the sound field, respectively. Based on first-order shear deformation plate and shell theories and acoustic theory, the dynamic model of CCSP and three-dimensional acoustic cavities are established by employing the differential quadrature finite element method in conjunction with the energy principle. The coupling of CCSP and three-dimensional acoustic cavities is realized by the velocity continuity condition at the acoustic–structure interfaces. The validation of the vibroacoustic coupling model is verified by comparing the results calculated by the established model with the corresponding results calculated by ABAQUS. The influence of model parameters on the vibroacoustic characteristic of vibroacoustic coupling model is investigated systematically for determining the critical structure parameters which have influence on the vibroacoustic behaviors. The effect of critical structure parameters on the sound insulation characteristic of CCSP is analyzed systematically for the optimization of the sound insulation performance of CCSP and provides theoretical basis and technique guidance. [ABSTRACT FROM AUTHOR]

Self-reinforcing porous mullite ceramics have attracted considerable attention in the field of insulation and sound absorption materials, due to their precise and controllable porous structure, high temperature and corrosion resistance, and low thermal conductivity. However, the high cost and relatively low performance obstruct their practical applications. In this work, self-reinforcing porous mullite ceramics were fabricated by utilizing construction waste via foam-gel casting and freeze-drying methods, and the impact of blowing agent dosage and sintering temperatures on the microstructures, sound absorption, and thermal insulation properties were systematically investigated. In addition, the related mechanism was also discussed in detail. The results show that, at a sintering temperature of 1000 °C and blowing agent dosage of 0.10 wt%, the self-reinforcing porous mullite ceramics can be successfully obtained, which exhibited a bulk density as low as 0.24 g/cm³ and porosity more than 90 %. Consequently, at a frequency of 2000 Hz, its absorption coefficient reached about 0.81. Furthermore, its thermal conductivity also decreased to about 0.06266 W/(m·K). This development not only unveils innovative avenues for the cost-effective fabrication of porous ceramics but also significantly broadens their potential applications within high-performance thermal insulation and sound absorption domains. [ABSTRACT FROM AUTHOR]

Sandwich structures possess a high stiffness-to-mass ratio, which facilitates flexural wave propagation at lower frequencies and enhances their vibration isolation and sound insulation capabilities, therefore, sandwich-like metamaterial plates with the nonlinear local oscillator is constructed in this paper to obtain adjustable bandgap in low-frequency. The buckling beam oscillator consists of a small mass, linear support spring, and buckling elastic elements for nonlinear stiffness. First, governing equations of flexural vibrations of plates are deduced based on the Hamilton principle. By utilizing the harmonic balance method (HBM), the dispersion relation of a sandwich-like plate can be determined. Theoretical analysis reveals the presence of structural bandgap ranges at lower frequencies, which are subject to the excitation amplitudes. And in order to validate the theoretical findings, the finite element method (FEM) is employed. Moreover, the influence of structural parameters, including oscillator mass, linear spring stiffness, buckling beam angle, and Young's modulus, are conducted to enhance the vibration control in the low-frequency. Interestingly, it is observed that the effectiveness of low-frequency suppression in the nonlinear metamaterial plate varies significantly across different boundary conditions. Therefore, the sandwich structures with nonlinear local oscillators can provide an effective way to suppress low-frequency vibration and maintain dynamic stability. [ABSTRACT FROM AUTHOR]

Highlights Ultrasonic methods are more sensitive to defects such as voids, pores, and discontinuities that can diminish the true elastic and acoustic properties of materials compared to destructive testing. Therefore, the elastic properties and some acoustic properties of the epoxy phenol novolac modified with polystyrene (EPN‐PS) matrix‐based nano‐ and hybrid composites were determined for the first time using ultrasonic method. Montmorillonite‐type nanoclay (NC) and industrial red mud waste (RMW) at a rate of 1–4 and 15–35 wt% respectively, were used as fillers in the composite preparation. According to the results, the highest elastic coefficient values (L = 8.14 GPa, G = 1.76 GPa, K = 5.79 GPa and E = 4.80 GPa) were obtained in the EPN‐PS/NC1 (with 1 wt% NC) nanocomposite sample compared to the elastic properties of pure EPN and EPN‐PS, while the highest elastic coefficient values (L = 8.97 GPa, G = 2.19 GPa, K = 6.06 GPa, and E = 5.86 GPa) among hybrid composites (HC) were obtained for the HC35 containing 2 wt. % NC and 35 wt% RMW. Due to both its high elastic and good acoustic properties, wall panels and floors produced using HC35 hybrid composite can be used for sound insulation in noisy environments. First evaluation of the acoustic characteristics of epoxy phenol novolac modified with polystyrene‐nanoclay/red mud waste (EPN‐PS‐NC/RMW) composites. NC4 with 4 wt% nanoclay showed the lowest elastic and acoustic properties. Nanoclay ratio above 1 wt% reduces elastic and acoustic properties. The increasing RMW ratio in hybrid composites increases elastic properties. High elastic and acoustic properties make HC35 ideal for sound insulation. [ABSTRACT FROM AUTHOR]

This paper investigates the acoustic streaming effects (ASEs) and mechanisms behind the transmittance of sound in a metallic micro-cavity acoustic black hole (ABH) structure with an abrupt cross-section and examines the sound field flow characteristics inside the micro-cavity ABH under the sound excitation, such as the velocity, acceleration and pressure fields. And the sound transmission mechanisms are characterized by the ASEs which can be obtained by solving Navier–Stokes equations. The numerical results show that the sharp increase in the velocity and acceleration at the ABH tip position is the main reason for the focusing of the sound energy. And the dramatic increase in the tip cross-section reduces the acoustic streaming velocity, which is the main reason for the attenuation of the sound energy. Additionally, the thermoviscous effect of the acoustic boundary layer can also dissipate the low-frequency sound energy. The sound insulation experiment shows that the proposed micro-cavity ABH structure has a sound transmission loss (STL) of over 15 dB in the low-frequency regime. This research reveals the mechanisms of the ASE's work on the sound transmission properties of the micro-cavity ABH and provides new insight into low-frequency sound wave suppression. The ABH structure proposed in this paper has excellent strength, bearing capacity and long lifecycle, so it can be applied in the construction industry through its integrated design of structure and performance. [ABSTRACT FROM AUTHOR]

Polyurethane incorporated with nanofillers such as carbon nanotubes, basalt fibers, and clay nanoparticles has presented remarkable potential for improving the performance of the polymeric composites. In this study, the halloysite nanofiller-reinforced polyurethane elastomer composites were prepared via the semi-prepolymer method. The impact of different halloysites (halloysite nanotubes and halloysite nanoplates) in polyurethane composites was investigated. Scanning electron microscopy, X-ray diffraction, infrared spectroscopy, electronic universal tensile testing, and acoustic impedance tube testing were employed to characterize the morphology, composition, phase separation, mechanical properties, and sound insulation of the samples. The composite fabricated with 0.5 wt% of halloysite nanotubes introduced during quasi-prepolymer preparation exhibited the highest tensile strength (22.92 ± 0.84 MPa) and elongation at break (576.67 ± 17.99%) among all the prepared samples. Also, the incorporation of 2 wt% halloysite nanotubes into the polyurethane matrix resulted in the most significant overall improvements, particularly in terms of tensile strength (~44%), elongation at break (~40%), and sound insulation (~25%) within the low-frequency range of 50 to 1600 Hz. The attainment of these impressive mechanical and acoustic characteristics could be attributed to the unique lumen structure of the halloysite nanotubes, good dispersion of the halloysites in the polyurethane, and the interfacial bonding between the matrix and halloysite fillers. [ABSTRACT FROM AUTHOR]

A tremendous amount of waste black tea bags (BTBs) and date palm surface fibers (DPSFs), at the end of their life cycle, end up in landfills, leading to increased pollution and an increase in the negative impact on the environment. Therefore, this study aims to utilize these normally wasted materials efficiently by developing new composite materials for thermal insulation and sound absorption. Five insulation composite boards were developed, two were bound (BTB or DPSF with polyvinyl Acetate resin (PVA)) and three were hybrids (BTB, DPSF, and resin). In addition, the loose raw waste materials (BTB and DPSF) were tested separately with no binder. Thermal conductivity and sound absorption coefficients were determined for all boards. Thermal stability analysis was reported for the components of the tea bag (string, label, and bag) and one of the composite hybrid boards. Mechanical properties of the boards such as flexural strain, flexural stress, and flexural elastic modulus were determined for the bound and hybrid composites. The results showed that the thermal conductivity coefficients for all the hybrid composite sample boards are less than 0.07 at the ambient temperature of 24 °C and they were enhanced as the BTB ratio was reduced in the hybrid composite boards. The noise reduction coefficient for bound and all hybrid composite samples is greater than 0.37. The composite samples are thermally stable up to 291 °C. Most composite samples have a high flexure modulus between 4.3 MPa and 10.5 MPa. The tea bag raw materials and the composite samples have a low moisture content below 2.25%. These output results seem promising and encouraging using such developed sample boards as eco-friendly thermal insulation and sound absorption and competing with the synthetic ones developed from petrochemicals in building insulation. Moreover, returning these waste materials to circulation and producing new eco-friendly composites can reduce the number of landfills, the level of environmental pollution, and the use of synthetic materials made from fossil resources. [ABSTRACT FROM AUTHOR]

This paper explores the effect of waste rubber grain size on the porosity, modulus of elasticity, thermal properties, and soundproofing performance of polymer composites with different thicknesses (10, 15, and 20 mm). All properties were tested in accordance with European standards, with the exception of porosity, which was measured using Archimedes' principle. The findings indicate that with a consistent amount of polyurethane glue, finer rubber grains result in composites with higher porosity, leading to a lower modulus of elasticity but enhanced thermal and sound insulation. In contrast, coarser rubber grains produced composites with lower porosity and a higher modulus of elasticity, though with slightly reduced thermal insulation and significantly worse soundproofing. A combination of fine and coarse rubber grains provided a balanced performance, offering both good thermal and sound insulation while maintaining a high modulus of elasticity. Among the thicknesses tested, 15 mm was identified as optimal, combining a relatively high modulus of elasticity, low thermal conductivity, and better airborne sound insulation index. Future research will focus on applying this composite in concrete building products that meet noise protection and energy efficiency standards. [ABSTRACT FROM AUTHOR]

The influence mechanism of waste rubber particles (WRPs) on the workability, mechanical properties, and sound insulation performance of recycled aggregate sound insulation mortar (RCM) were investigated. According to the principle of volume fraction replacement of recycled fine aggregate by 0 to 50%, WRPs with a particle size of 1–4 mm were incorporated in various mixtures of RCM. Each RCM mixture was tested for workability, mechanical, and sound insulation performance. Mercury intrusion porosimetry was used to analyze the distribution of pores and their sizes inside the material, and X-ray diffraction and scanning electron microscopy were used to analyze the characteristics of the interfacial transition zones (ITZs) between the rubber particles and the cement paste. The results showed that, owing to the hydrophobicity of WRPs, greater WRPs content led to greater fluidity of the mortar mix and a smaller water retention rate. Notably, the rubber in the mortar did not contribute to the hydration reactivity of the cement paste, but it changed the crystal morphology and pore structure of ITZ hydration products. The RCM incorporating 3–10% WRPs produced the optimal pore structure through the aggregate effect, which increased its overall compactness and mechanical performance. Further increase of WRP content significantly improved the sound insulation performance while significantly reducing the strength. Moreover, there was a clear logarithmic relationship between the strength and impact sound level index. This new knowledge can be used to prepare RCM that meets the actual strength and sound insulation requirements of the floor. Thus, the resource utilization of solid waste can be expanded. [ABSTRACT FROM AUTHOR]

In this study, various polymer matrix composites (melamine and flexible polyurethane) combined with 316 L stainless steel hollow spheres were prepared using the casting method. The acoustic properties of the fabricated materials were evaluated under low‐frequency conditions (100–1700 Hz) using an impedance tube. The results indicate that sound absorption and insulation performance are significantly influenced by the incident surface material within this frequency range. Notably, sound waves entering through the polyurethane stainless steel hollow sphere surface yield optimal absorption performance, achieving a maximum sound absorption coefficient of 0.74 at 400 Hz. Conversely, the melamine foam surface provides the best sound absorption at higher frequencies within this range, reaching a coefficient of 0.43 at 1700 Hz. The findings highlight the effective sound absorption and insulation capabilities of the composite materials. [ABSTRACT FROM AUTHOR]

Floor impact sound insulation is essential for improving living environments and has become a mandatory requirement for green buildings in Southern China. This study introduces an innovative inorganic sound insulation coating technology for enhancing building floor acoustic performance. Through comprehensive laboratory experiments and field tests, we evaluated inorganic coatings of 3 mm and 5 mm thickness, comparing their performance against traditional methods, including organic coatings and soundproof mortar. Standardized impact sound pressure level measurements, conducted in accordance with the China GB/T 50121 standard, demonstrated significant acoustic improvements. Laboratory testing revealed impact sound reductions of 6–7 dB and 9–10 dB for the 3 mm and 5 mm inorganic coatings, respectively, while field applications of the 3 mm coating achieved an average reduction of 14.3 dB. The inorganic coating exhibited superior performance characteristics compared to both organic coatings and soundproof mortar in terms of sound insulation efficiency, fire resistance, and application feasibility, demonstrating particularly effective attenuation in the mid- to high-frequency range. This investigation presents an innovative, cost-effective, and environmentally sustainable solution for improving floor sound insulation in green buildings. [ABSTRACT FROM AUTHOR]

As a type of locally resonant phononic crystal, alloy steel phononic crystals have achieved notable advancements in vibration and noise reduction, particularly in the realm of low-frequency noise. Their exceptional band gap characteristics enable the efficient reduction of vibration and noise at low frequencies. However, the conventional transmission loss (TL) simulation of finite structures remains the benchmark for plate structure TL experiments. In this context, the TL in the XY-direction of phononic crystal plate structures has been thoroughly investigated and analyzed. Given the complexity of sound wave incident directions in practical applications, the conventional TL simulation of finite structures often diverges from reality. Taking tungsten steel phononic crystals as an example, this paper introduces a novel finite element method (FEM) simulation approach for analyzing the TL of alloy steel phononic crystal plates. By setting the Z-direction as the excitation source, the tungsten steel phononic crystal plate exhibits distinct responses compared to excitation in the XY-direction. By combining energy band diagrams and modes, the impact of various excitation source directions on the TL simulations is analyzed. It is observed that the tungsten steel phononic crystal plate exhibits a more pronounced energy response under longitudinal excitation. The TL map excited in the Z-direction lacks the flat region present in the XY-direction TL map. Notably, the maximum TL in the Z-direction is 131.5 dB, which is significantly lower than the maximum TL of 298 dB in the XY-direction, with a more regular peak distribution. This indicates that the TL of alloy steel phononic crystals in the XY-direction is closely related to the acoustic wave propagation characteristics within the plate, whereas the TL in the Z-direction aligns more closely with practical sound insulation and noise reduction engineering applications. Therefore, future research on alloy steel phononic crystal plates should not be confined to the TL in the XY-direction. Further investigation and analysis of the TL in the Z-direction are necessary. This will provide a novel theoretical foundation and methodological guidance for future research on alloy steel phononic crystals, enhancing the completeness and systematicness of studies on alloy steel phononic crystal plates. Simultaneously, it will advance the engineering application of alloy steel phononic crystal plates. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Engineering (17264073) is the property of Republic of Iraq Ministry of Higher Education & Scientific Research (MOHESR) and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Background: Several cognitive functions are related to sex. However, the relationship between auditory attention and sex remains unclear. The present study aimed to explore sex differences in auditory saliency judgments, with a particular focus on bottom-up type auditory attention. Methods: Forty-five typical adults (mean age: 21.5 ± 0.64 years) with no known hearing deficits, intelligence abnormalities, or attention deficits were enrolled in this study. They were tasked with annotating attention capturing sounds from five audio clips played in a soundproof room. Each stimulus contained ten salient sounds randomly placed within a 1-min natural soundscape. We conducted a generalized linear mixed model (GLMM) analysis using the number of responses to salient sounds as the dependent variable, sex as the between-subjects factor, duration, maximum loudness, and maximum spectrum of each sound as the within-subjects factor, and each sound event and participant as the variable effect. Results: No significant differences were found between male and female groups in age, hearing threshold, intellectual function, and attention function (all p > 0.05). Analysis confirmed 77 distinct sound events, with individual response rates of 4.0–100%. In a GLMM analysis, the main effect of sex was not statistically significant (p = 0.458). Duration and spectrum had a significant effect on response rate (p = 0.006 and p < 0.001). The effect of loudness was not statistically significant (p = 0.13). Conclusions: The results suggest that male and female listeners do not differ significantly in their auditory saliency judgments based on the acoustic characteristics studied. This finding challenges the notion of inherent sex differences in bottom-up auditory attention and highlights the need for further research to explore other potential factors or conditions under which such differences might emerge. [ABSTRACT FROM AUTHOR]

Aiming at the low-frequency line spectrum noise characteristics of power equipment noise, based on the principle of energy degradation, this paper combines the energy degradation sound insulation structure with the dynamic vibration absorption technology for the first time and applies it to the research field of noise control of power equipment in substations. Dynamic vibration absorption technology is used to effectively control low-frequency vibration and noise. Considering that there is an upper limit to the capacity of DVA, the sound-vibration energy degradation design of the transformer is completed by setting a sound insulation structure on the outside of the original transformer housing. It is analyzed that the vibration energy of the sound insulation structure in the specific frequency band is significantly reduced compared to the transformer housing, realizing efficient degradation of the vibration energy of the transformer housing and effective isolation of sound radiation. Through the optimized design of dynamic vibration absorption for the sound insulation structure, the structural sound isolation ability at the target frequency is further strengthened, and the system noise radiation level is greatly reduced under the action of multiple mechanisms at the target frequency, verifying the feasibility and high efficiency of the optimal DVAs energy degradation design of the transformer. [ABSTRACT FROM AUTHOR]

Optimization of impact sound insulation of wooden beam ceilings in Wilhelminian style houses, Part 2: Ceiling construction and flanking transmission The research deals with the influence of various parameters in the ceiling structure, such as cavity damping, screed thickness, impact sound insulation, fill and suspended ceilings, on the standard impact sound level of typical Wilhelminian style wooden beam ceilings. The measurements show that a thicker screed, softer impact sound insulation and a heavier fill significantly improve the impact sound level. Binding the fill with polyurethane instead of cement shows a significant improvement in the frequency range from 100 to 500 Hz. While cavity damping with mineral wool only contributes to a limited reduction in the standard impact sound level, decoupling the fill on an elastic intermediate layer delivers significant improvements. The measurements also show that the thickness of the paneling and the type of hangers in suspended ceilings have a significant impact on impact sound insulation. The investigations into flank impact sound transmission make it clear that flank transmission must be taken into account when planning higher requirement levels. Especially in the frequency range between 250 Hz and 800 Hz, the sound transmission of flanking components can play a significant role in the overall transmission. [ABSTRACT FROM AUTHOR]

The aerogel performance for industrial uses can be tailored using several chemical and physical strategies. The effects of a controlled densification on polyurethane aerogels are herein studied by analyzing their textural, mechanical, sound, optical, and thermal insulating properties. The produced aerogels are uniaxially compressed to different strains (30%–80%) analyzing the consequent changes in the structures and, therefore, final properties. As expected, their mechanical stiffness can be significantly increased by compression (until 55‐fold higher elastic modulus for 80%‐strain), while the light transmittance does not noticeably worsen until it is compressed more than 60%. Additionally, the modifications produced in the heat transfer contributions are analyzed, obtaining the optimum balance between density increase and pore size reduction. The minimum thermal conductivity (14.5%‐reduction) is obtained by compressing the aerogel to 50%‐strain, where the increment in the solid conduction is surpassed by the reduction of the radiative and gas contributions. This strategy avoids tedious chemical modifications in the synthesis procedure to control the final structure of the aerogels, leading to the possibility of carefully adapting their structure and properties through a simple method such as densification. Thus, it allows to obtain aerogels for current and on‐demand applications, which is one of the main challenges in the field. [ABSTRACT FROM AUTHOR]

Copyright of Journal of East China Jiaotong University is the property of Journal of East China Jiaotong University Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Polymeric wastes, specifically polyethylene terephthalate (PET) and scrap tyre rubber (STR), pose a significant environmental issue. PET, a thermoplastic polymer, is widely used in manufacturing bottles, PET cups, containers, fibres, films, and packaging materials. On the other hand, colossal rubber tyre waste quantities represent other environmental problems. However, PET and STR wastes are often discarded in the immediate vicinity, contributing to water resource pollution and landfill site strain. One solution is to replace aggregates in concrete mixtures with these wastes, a preferable alternative to landfill disposal because of the large volume and slow decomposition rate in landfills. Recycling PET and STR helps mitigate environmental pollution and promotes resource conservation and sustainability. This study aims to review previous research undertaken in the field and validate the findings of concrete’s fresh, mechanical, and functional characteristics. Based on the review, most studies confirmed a noticeable decline in the mechanical characteristics of mortar and concrete. However, these studies did not effectively focus on using PET and STR as sound and thermal insulation aggregates. Replacing PET and STR as aggregate in concrete can reduce thermal conductivity and acoustics. [ABSTRACT FROM AUTHOR]

Slow rebound polyurethane foam (SPUF) has been widely used due to its advantages such as sound insulation, energy absorption, and good tactile sensation. However, SPUF is prone to harden at low temperature, and its application in medical equipment and households requires significant antibacterial properties. In this paper, self‐made silicone modified polyethylene glycol (Si‐APEG) and graphene oxide supported allicin (Alc@GO) were prepared and used as low‐temperature resistant agent and antibacterial agent, respectively. Low‐temperature resistant polyurethane foam (LSPUF) and antibacterial LSPUF (ALSPUF) were prepared respectively with water as foaming agent. The morphology of ALSPUF was observed by scanning electron microscope. Properties studied include apparent core density and porosity, mechanical properties including tensile strength, 40% compressive hardness, and rebound resilience, as well as low‐temperature resistance. Effects of Si‐APEG content on the structures and properties were analyzed and the LSPUF with an Si‐APEG content of 10 wt.% showed the best comprehensive performance. Therefore, ALSPUFs with Si‐APEG content of 10 wt.% and Alc@GO content of 0–3 wt.% were prepared. The addition of Alc@GO increased the antibacterial ratio significantly without obvious effect on the structure and mechanical properties of LSPUF. The antibacterial ratio of ALSPUF reached 99.07% at a Alc@GO content of 2.5 wt.% and testing time of 60 min. This work provides an effective and feasible method for the preparation of ALSPUF which can be widely used in medical devices and households. Highlights: Silicone modified polyether is a suitable low‐temperature resistant agent for PU foam.Allicin supported on GO provides good antibacterial property for PU foam.ALSPUF has better mechanical properties than SPU. [ABSTRACT FROM AUTHOR]

In this study, we experimentally demonstrate a class of lightweight acoustic metamaterial barriers that block low-frequency sound. The acoustic metamaterial barrier is composed of a thin rubber membrane coated over a stiff honeycomb plate. Our findings, combined with high-fidelity finite element simulations, demonstrate that the sound insulation performance of the acoustic metamaterial surpasses the mass law in three distinct frequency ranges: (a) the stiffness law dominates insulation up to 140 Hz, (b) degeneracy and destructive superposition of high-order natural modes dominate within the frequency range of 300–500 Hz, and (c) destructive interference between high-order resonance and membrane resonance dominates in the frequency range of 800–1200 Hz. Notably, our study highlights the potential of high-order shear vibration of the periodic structure for the resonant bending waves of the honeycomb cell that coincide with the wavelengths of longitudinal sound waves in air, thereby offering new design guidelines for lightweight acoustic metamaterial barriers. This study reports for the first time the coincidence of high-order and membrane resonance modes within the honeycomb cell by employing an accurate finite element model and experimental validation. [ABSTRACT FROM AUTHOR]

Asphalt pavements are under extreme strain from high-volume traffic with ultraheavy axle loads, leading to rutting, fatigue, and moisture damage that reduces the useful life of asphalt mixtures. Studies have suggested that nanomaterials can be used in asphalt modification to delay asphalt pavement deterioration. The main objective of this research study is to investigate the influence of nanosilica aerogel (NSA) on the mechanical properties of hot-mix asphalt. The materials employed in the study include the 85/100 penetration grade asphalt binder, limestone aggregate, filler, and NSA additive in varying proportions of 1%, 2%, and 3% by asphalt binder weight. In order to evaluate the mechanical properties of the modified asphalt mixture, Marshall stability and flow, resilient modulus, moisture sensitivity, rutting, indirect tensile fatigue, and semicircular bending tests are performed. The results indicated that the range of 2 to 3% of NSA is a suitable limit for increasing the fatigue life, creep resistance, and strength of asphalt mixtures. Added NSA to asphalt mixtures can lead to a 40% increase in rutting resistance, an 80% increase in fatigue life, and a 12–15% increase in the stability of asphalt mixtures. In conclusion, the increase in aerogel improves the performance of uncracked asphalt mixtures and causes a slight decrease in the load leading to the fracture of cracked samples. Using NSA not only can lead to the creation of thermal, moisture, and sound insulation on the surface but also can lead to an increase in the stability, rutting resistance, and fatigue life of the asphalt mixture. [ABSTRACT FROM AUTHOR]

This paper presents a type of acoustic metamaterial that combines a labyrinth channel with a Helmholtz cavity and a thin film. The labyrinth-opening design and thin-film combination contribute to the metamaterial's exceptional sound-insulation performance. After comprehensive research, it is observed that in the frequency range of 20–1200 Hz, this acoustic metamaterial exhibits multiple sound-insulation peaks, showing a high overall sound-insulation quality. Specifically, the first sound-insulation peak is 26.3 Hz, with a bandwidth of 13 Hz and giving a transmission loss of 56.5 dB, showing excellent low-frequency sound-insulation performance. To further understand the low-frequency sound-insulation mechanism, this paper uses the equivalent model method to conduct an acoustic–electrical analogy, construct an equivalent model of the acoustic metamaterial, and delve into the sound-insulation mechanism at the first sound-insulation peak. To confirm the validity of the theoretical calculations, physical experiments are carried out by 3D printing experimental samples. The analysis of the experimental data has yielded results that are consistent with the simulation data, providing empirical evidence for the accuracy of the theoretical model. The material has significant practical application value. Finally, various factors are studied in depth based on the established equivalent model, which can provide valuable insights for the design and practical engineering application of acoustic metamaterials. [ABSTRACT FROM AUTHOR]

Copyright of German International Journal of Modern Science / Deutsche Internationale Zeitschrift für Zeitgenössische Wissenschaft is the property of Artmedia24 and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Honeycomb plates, due to their multi-cavity structure, exhibit excellent mechanical properties and sound insulation. Previous studies have demonstrated that altering the cell size and arrangement of honeycomb structures impacts their acoustic performance. Based on these findings, this study developed a wallboard structure with enhanced sound insulation by filling the cavities with paper fiber/cement facesheets and designing a stacked core structure. Through the reverberation chamber–anechoic chamber sound insulation experiment under 100–6300 Hz excitation and conducting orthogonal experiments from three dimensions, it was found that: (1) Compared to no filling, the filling with straw and glazed hollow bead can increase the sound transmission loss (STL) by more than 50% in the frequency bandwidth above 2000 Hz. This indicates that both types of fillings can significantly enhance the sound insulation performance of the honeycomb structure without a significant increase in economic costs. (2) The increase in paper fiber/cement facesheets improves the STL across the entire experimental bandwidth, with a maximum improvement exceeding 70%. This structural design not only offers superior sound insulation performance but also better suits practical engineering applications. (3) Increasing the number of core stacking units (from one to three), taking straw-filled paper honeycomb-core wallboards as an example, effectively increased the STL bandwidth. (4) This test enriches the application of honeycomb plates in sound insulation. Introducing fiber paper fiber/cement facesheets and eco-friendly, low-cost straw improves sound insulation and enhances the strength of honeycomb, making them more suitable for construction, particularly as non-load-bearing structures. [ABSTRACT FROM AUTHOR]

To reduce land use and avoid further pollution, incineration for power generation has become the main method for municipal solid waste treatment. This research focused on the potential for transforming Municipal Solid Waste Incineration Bottom Ash (MSWIBA) into a finely ground powder. The impact of the powder's fineness and the amount of water used on its effectiveness was analyzed using a method called grey theory. MSWIBA was used as a partial substitute for cement in making MSWIBA foam concrete and lightweight wall panels. By modifying the fineness and water utilization of the recycled micro-powder, its maximum activity index can be increased to 90.1. This study determined the influence of factors including apparent dry density, water–cement ratio, foaming agent dilution ratio, and admixture dosage on the strength of the recycled foam concrete, and established the optimal mix ratio. This study employed a combination of physical experiments and numerical simulations to elucidate the impact of panel material, core layer thickness, and layer sequence on sound insulation performance. The simulation results were in close agreement with the experimental findings. [ABSTRACT FROM AUTHOR]

A sandwich plate with a corrugation and auxetic honeycomb hybrid core is constructed, and its sound insulation and optimization are investigated. First, the motion governing equation of the sandwich plate is established by the third-order shear deformation theory (TSDT), and then combined with the fluid-structure coupling conditions, and the sound insulation is solved. The theoretical results are validated by COMSOL simulation results, and the effects of the structural parameter on the sound insulation are analyzed. Finally, the standard genetic algorithm is adopted to optimize the sound insulation of the sandwich plate. [ABSTRACT FROM AUTHOR]

Residential homes and apartments' cooling and heating needs account for 63% of total building energy consumption. Improvements in the properties of building envelopes are among the best ways to reduce their energy consumption. The project's general objective was to compare the performance of externally insulated and traditional envelopes of light wooden frame buildings at full scale. Two houses were constructed and equipped with relative humidity sensors and temperature probes to assess the physical properties of the building envelope. The first house was built according to the conventional method (insulation between the studs), and the second house was built according to the method with the insulation outside the wall (also known as the perfect wall). The results showed that external insulation effectively mitigates internal condensation risks by relocating dew points to the exterior surface, thereby enhancing structural durability and thermal stability. Thermographic imaging confirmed reduced thermal bridging and improved thermal performance in the externally insulated walls. Overall, this study supports, with a full-scale experiment, the adoption of external insulation as a viable strategy for enhancing energy efficiency, thermal comfort, and durability in residential buildings. [ABSTRACT FROM AUTHOR]

This study deals with 3D printing multilayered micro-perforated panels (M-MPPs) coupled with buildings materials as compressed earth block for noise reduction applications. The sound absorption coefficient α is utilized as a metric to assess the sound insulation capabilities across a frequency range spanning from 10 to 3000 Hz, then evaluated and validated by numerical and experimental methods. The FEM model developed makes it possible to predict the acoustic absorption of M-MPPs by tuning the frequency range and varying optimized acoustics parameters, considering hole-hole interaction and taking into account visco-thermal effects that are present in compressed earth blocks. It is shown that the shape of perforations and material properties including the porosity rate, arrangement in the design of multilayer micro-perforated structures are identified to play a significant role in the sound performance of the entire structure. In addition, the application of MPP coupled with compressed earth blocks improve the sound absorption capacity of the composite structure. The developed FEM leads to accurate prediction of performance, efficient optimization, and cost effectiveness. Finally, the present study reveals the importance of M-MPPs combined with compressed earth blocks (CEBs) as viable noise reduction materials, particularly relevant for engineering applications and development initiatives in emerging economies. [ABSTRACT FROM AUTHOR]

Copyright of Automobile Technology is the property of Automobile Technology Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)