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The European Union is promoting the increased use of thermal insulation to ensure energy conservation in the coming years. This will drive increased demand for materials suitable for such applications. However, the rise in the production of goods combined with the prevalent use of non-renewable resources in thermal insulation pose environmental challenges, leading to increased pollution and solid waste accumulation. In response, this study focuses on developing and characterizing a sustainable, biodegradable mycelium-based composite for thermal insulation. The bio-composite, cultivated from Pleurotus Pulmonarius fungus in agro-industrial and textile waste, offers a promising approach. In this work, two distinct combinations of substrates were utilized: one comprising 70% grass cuttings and dry leaves, along with 30% recycled ground textile, predominantly polyester; the other consisting of 70% sugarcane bagasse and 30% ground textile waste. Additionally, an extra 20% of the substrate weight of Pleurotus Ostreatus grain spawn was added to each combination to facilitate mycelium growth. The mycomaterials were tested for tensile and compression analysis (ASTM D3039 and ASTM D695 standards, respectively) and a thermal conductivity assessment (ISO 8301) was done. The materials showed better performance at compression tests than tensile test. Also, results demonstrate the superior performance of sugarcane bagasse mycelium composites over the dry leaves/grass cutting counterparts in thermal conductivity, tensile and compression tests. The inclusion of synthetic fibres to the mycelium composite may have compromised the mechanical and thermal properties of the samples as polyester fibres have a higher thermal conductivity than the natural components included in the sample. The fibres being synthetic, the mycelium could not feed on it, thus impeding binding and proliferation in some sections of the material.

This article reports on impedance tube measurements of the sound absorption coefficient α (-) of selected recycled foam plastics, i.e., ethylene-vinyl acetate (EVA), polyvinyl chloride (PVC), polystyrene (PS), and polypropylene (PP), in different mixtures with a binding adhesive. The effect of the thickness of the sample on the sound absorption spectrum as well as the variability in absorption across the different samples of the same composition and thickness are discussed. For the EVA/ PP and PS/PP mixtures, the spectrum is characterized by two peaks that shift as the thickness is changing. These mixtures were also found to be the most absorbent across the whole audible frequency range.

This article addresses the impact of the occupancy level, the average acoustic absorption and the so-called acoustic capacity of a space, which is proportional with the volume and inversely proportional with the reverberation time, on the behavior of talking people in an eating establishments. Four different settings were compared: two casual dining restaurants, a self-service student canteen and a small faculty club. The Lombard effect was observed in all cases. In a restaurant with an average amount of absorbing surface of 2.4 m2 or more per person, the sound pressure level increased with more than 3 dB per doubling of the number of people. Results for the student canteen show that people started to communicate less when the number of people present was so high that the absorbing surface dropped under 1.5 m2/person (80 people). The level even stopped to increase with increasing occupancy from 150 people present and beyond, corresponding with 0.8 m2 of absorbing surface per person. This is roughly consistent with an estimated value for the acoustic capacity of that space, which was 189 people (corresponding with a table occupancy of about 72%). In the latter circumstances, the background noise level, as expressed by LA,95 was as high as 69 dB. Overcoming this level for oral communication would require a not sustainable vocal effort. In the tests performed in other restaurants, the observed occupancy was below 60%, which, thanks to the higher number of absorbing surfaces in those restaurants, was well below the acoustic capacity.

The development and validation of single number quantities that are meant to serve for straightforward assessment and comparison of airborne sound insulation properties of partition walls are typically challenged by the necessity to perform large numbers of laboratory listening tests with human subjects. This is because a reliable validation of a single number quantity requires testing for many different wall types with multiple real-life stimuli that are representative for daily life soundscapes. In this article, an alternative approach is presented that allows to test a large number of “partition wall – real-life sound stimuli” combinations. This approach uses the well-established and nowadays generally accepted Zwicker’s Loudness for quantifying the subjective loudness of sound passing through a wall, and derive from that the subjectively perceived sound insulation. Using the proposed assessment method, the adequacy of single number quantities that are currently in use, and a number of newly proposed single number quantities, are compared.

ETFE cushions are used as cladding in predominantly mid to large size architectural projects. Smaller cushions are about 10 m2 in size and the biggest single cushions can be several hundreds of square metres large. They are composed of ETFE membranes a few hundred of micrometres thick. From a point of view of room acoustics, their acoustic transparency, which increases with decreasing frequency, makes them to effectively act like sound absorbers. Their voluminous nature and transparency make it challenging to measure the sound absorption coefficient of ETFE cushions in a laboratory. Using the genetic material optimizer of Odeon® software, the effective sound absorption coefficient of ETFE cushions in four rooms was extracted from room acoustic parameters, which were in turn derived from measured room impulse response data. The results were compared and interpreted by the help of theoretical modelling and measurements on small cushions in a reverberant room. There is a relatively good agreement between the three types of results, possible causes for the differences are explained in the paper. [ABSTRACT FROM AUTHOR]

This paper studies the propagation of symmetric and antisymmetric Lamb waves along a 1 mm thick iodic acid plate (HI[O.sub.3]) in the 1-50 MHz frequency range. The Lamb mode propagation along three crystallographic planes was theoretically investigated, for two mutually orthogonal propagation directions. Several frequencies were found that correspond to Lamb modes with zero group velocity (ZGV) and non-null phase velocity values. The first symmetric Lamb mode, [S.sub.1], was found to possess only one ZGV point, regardless of the propagation direction; higher order symmetric and antisymmetric modes with up to four ZGV points were found, depending on the propagation plane. The dependence of the ZGV frequencies on each elastic constant ([c.sub.11], [c.sub.13], [c.sub.33], [c.sub.55]) of the HI[O.sub.3] plate material was also investigated by changing the constant values by 5% and 10%. It was found that [c.sub.33] and [c.sub.55] affect the number of the ZGV points, while [c.sub.11] and [c.sub.13] affect the frequency of the ZGV points. The existence and frequencies of the ZGV points are strongly dependent on the proximity of standing longitudinal and transverse waves at nearby cutoff frequencies. Key words: Lamb waves, anisotropic plate, HI[O.sub.3], multiple zero group velocity points, elastic properties. Nous etudions ici la propagation des ondes de Lamb symetriques et antisymetriques le long de plaques de 1 mm d'epaisseur d'acide iodique (HI[O.sub.3]) dans le domaine de frequence de 1 a 50 MHz. La propagation des modes de Lamb selon trois plans cristallographiques est etudiee theoriquement pour deux directions mutuellement orthogonales. Nous trouvons plusieurs frequences correspondant a des modes de Lamb a vitesse de groupe nulle (VGN) et vitesse de phase non nulle. Nous trouvons que le premier mode symetrique de Lamb, [S.sub.1], possede un seul point VGN, sans regard a la direction de propagation et nous trouvons les modes symetriques d'ordre plus eleve et les modes antisymetriques qui possedent jusqu'a quatre points VGN, dependant de la direction de propagation. Nous examinons la dependance de chacune des frequences VGN sur les constantes elastiques ([c.sub.11], [c.sub.13], [c.sub.33] et [c.sub.55]) de la plaque de HI[O.sub.3] en changeant la valeur de ces constantes par 5 % et 10 %. Nous trouvons que [c.sub.33] et [c.sub.55] affectent le nombre de points VGN, alors que [c.sub.11] et [c.sub.13] affectent la frequence des points VGN. L'existence et les frequences des points VGN dependent fortement de la proximite des ondes stationnaires longitudinales et transverses aux frequences de coupure voisines. [Traduit par la Redaction] Mots-cles: proprietes elastiques, plaque anisotrope, HI[O.sub.3], points multiples a vitesse de groupe nulle., 1. Introduction An important ultrasonic approach for nondestructive evaluation in industry makes use of the dependence of the experimentally accessible dispersive behavior of the velocity of Lamb waves on the [...]

This contribution intends to convince readers that by virtue of the rich physics involved, optical excitation, thermal diffusion, thermal expansion, and acoustic wave propagation, and of the optical nature of the involved excitation and detection, photoacoustic and photothermal methods offer a unique combination of features that makes them very attractive for exploitation in a wide area of scientific and technological fields that involve material property evaluation. A perspective is also given on the high potential of these methods for substantial advances beyond the state of the art in a diverse selection of scientific disciplines: biomedical diagnostics, cell and tissue mechanobiology, thin film and interface characterization, characterization of the microstructure of solids, and the physics of relaxation in glass-forming liquids. [ABSTRACT FROM AUTHOR]

A numerical demonstration is given of the feasibility of a newly designed tunable asymmetric acoustic transmission device, for which the acoustic transmission coefficients for perpendicularly incident left- and right-running waves are different at a particular single frequency within a forbidden zone. The proposed device consists of a hybrid, sonic-crystal-based resonant structure with horizontal periodicity and a one-dimensional periodic rectangular acoustic grating with vertical periodicity. The former structure exhibits a wide bandgap through which only waves with particular combinations of their frequency and propagation direction can tunnel. The direction dependence of the acoustic transmission is based on the geometrical asymmetry of the placement of the grating, and on the narrowband correspondence between the diffraction angle of the grating and the allowed transmission direction through the sonic-crystal-based structure. Angular and spectral tuning are possible by changing the grating and/or the sonic crystal periodicity. The device has potential applications in underwater acoustics for asymmetric transmission systems and secure communication systems. [ABSTRACT FROM AUTHOR]

Impulsive stimulated thermal scattering (ISTS) allows one to access the structural relaxation dynamics in supercooled molecular liquids on a time scale ranging from nanoseconds to milliseconds. Till now, a heuristic semi-empirical model has been commonly adopted to account for the ISTS signals. This model implicitly assumes that the relaxation of specific heat, C, and thermal expansion coefficient, γ, occur on the same time scale and accounts for them via a single stretched exponential. This work proposes two models that assume disentangled relaxations, respectively, based on the Debye and Havriliak–Negami assumptions for the relaxation spectrum and explicitly accounting for the relaxation of C and γ separately in the ISTS response. A theoretical analysis was conducted to test and compare the disentangled relaxation models against the stretched exponential. The former models were applied to rationalize the experimental ISTS signals acquired on supercooled glycerol. This allows us to simultaneously retrieve the frequency-dependent specific heat and thermal expansion up to the sub-100 MHz frequency range and further to compare the fragility and time scale probed by thermal, mechanical, and dielectric susceptibilities. [ABSTRACT FROM AUTHOR]

This work reports results on the simultaneous spectroscopy of the specific heat and thermal expansivity of glycerol by making use of a wideband time-resolved thermal lens (TL) technique. An analytical model is presented which describes TL transients in a relaxing system subjected to impulsive laser heating. Experimentally, a set of TL waveforms, from 1 ns to 20 ms, has been recorded for a glycerol sample upon supercooling, from 300 to 200 K. The satisfactory fitting of the TL signals to the model allows the assessment of relaxation strength and relaxation frequency of the two quantities up to sub-100 MHz, extending the specific heat and thermal expansion spectroscopy by nearly three and eight decades, respectively. Fragility values, extracted from the relaxation behavior of the specific heat and the thermal expansion coefficient, are found to be similar, despite a substantial difference in relaxation strength. [ABSTRACT FROM AUTHOR]