1,720,988 research outputs found
Ergun-Wu equation: a novel approach for the determination of physical parameters in low/medium porosity materials.
No full textThe experimental determination of effective porosity and tortuosity in medium/ low porosity materials (typically ≤0.5) is still a challenge debated in
metrology. In this paper is proposed a semi-empirical approach to the problem, based on the implementation of a new resistive model and accurate
experimental input data. The empirical model is based on the recent redefinition of Ergun’s equation (Wu et al., 2008) and on the geometric model for tortuosity (Yu et al., 2000). On the basis of measured quantities, such as the airflow resistivity and the average pore diameter, it is possible to
determine the average effective porosity and the average tortuosity of the
material in a defined range with a proper confidence level. In this work is
also addressed the problem of a suitable determination of the average pore
diameter and a definition of an average equivalent pore diameter in fibrous
materials is also proposed
Effective scale of microstructure of fibrous permeable materials
No full textMicrostructure properties of fibrous permeable materials, such as effective porosity, pore size and tortuosity, and related transport phenomena, is of great importance to many practical and industrial application, as well as in several manufacturing process-es. Several resistance models, based on Darcy’s law and Forchheimer’s equation, were derived through the last decades to predict the behavior of fluid flow and permeability in fibrous materials. In existing resistance models the effective scale of microstructure (also called specific surface area or pore size), is assumed as the hydraulic diameter of the capillary in Hagen-Poiseuille law, from Carman geometrical model. Nevertheless, the disordered nature of fibre arrangement suggests the existence of different relation-ships, linked to the transport phenomena within the fibre network. In this work a new approach is proposed in order to evaluate the effective scale of microstructure (in terms of pore size) of fibrous permeable materials
On the influence of different facade materials on the auditory perception of a urban space
No full textThe study investigates the influence of different façade materials on acoustic characteristics of a small urban square and on listeners’ space wideness perception on the basis of auditory stimuli. It is aimed at enhancing awareness on how different façade design can influence the outdoor environment under multiple aspects.
The investigation has been conducted through virtual acoustics, by means of simulations and auralisations performed with Odeon (v.13) software. A listening test with a 3 factorial design levels has been implemented to investigate subjective assessment of space wideness.
Results showed that the absorption coefficient of the facades and the listener position significantly affect the perceived wideness of spaces, while scattering coefficient is not influential. Moreover, a comparison with objective parameters resulting from simulations has being perfomed, in order to draw a first hypothesis on what parameters could explain the differences in the perception of dimensions of a urban space through auditory stimuli
Enhancement of the hygroscopic and acoustic properties of indoor plasters with a Super Adsorbent Calcium Alginate BioPolymer
Full text linkThe present study introduces a novel-composition lime plaster that contains a Super Adsorbent BioPolymer (SABP) based on Calcium Alginate (CaAlg) for indoor applications, to improve hygrothermal and acoustic comfort. The sorption isotherm of the plaster, the moisture buffering value (MBV), the acoustic absorption, and the thermal conductivity have been assessed. The hygrothermal and acoustic properties of the modified plaster have been compared with those of the original composition to evaluate its performance under different concentrations of CaAlg (between 10 and 30% wt). Adding the CaAlg SABP to a conventional lime plaster consistently enhanced its hygroscopic properties. The results show a substantial increase in the equilibrium moisture uptake (between 10 and 23 fold) and MBV, from 0.9 to 9.3 g/(m2⋅%RH). The sound absorption coefficient improved by 0.1–0.2 at higher frequencies than 500 Hz. This paper provides detailed information on the characterization of the material. It includes details about using a dynamic vapor sorption (DVS) analyzer to evaluate the sorption isotherm and MBV. It also contains information on the impedance tube method used to measure the acoustic absorption of the material
Super adsorbent bio-polymer additive to improve hygroscopic and acoustic properties of a conventional lime plaster
Full text linkThe paper introduces a new lime plaster composition, with a Super Bio-Polymeric Adsorbent (SABP), for interior applications to improve hygrothermal and acoustic comfort. Alginate SABP is added to a conventional lime plaster to improve hygroscopic and acoustic performance. The hygrothermal and acoustic properties of the modified plaster are compared with the ones of the original plaster with a preliminary moisture uptake test, the evaluation of the sorption isotherm, the moisture buffering value (MBV), and the acoustic absorption. The results show a significant increase in the equilibrium moisture contents and the MBV (from 0.7 to 6.2 g/(m2 ...%RH)). At the same time, the sound absorption coefficient is slightly improved, increasing 0.1-0.2 at frequencies higher than 500 Hz compared to the reference conventional lime plaster. The paper describes the material characterization: the sorption isotherm and the MBV are obtained using a dynamic vapor sorption (DVS) analyzer. The acoustic absorption is measured using the impedance tube method
Measurements of acoustical parameters in the ancient open-air theatre of Tyndaris (Sicily, Italy)
Full text linkThe emerging field of archaeoacoustics is attracting increasing research attention from scholars of different disciplines: the investigation of the acoustic features of ancient open-air theatres is possibly one of its main themes. In this paper, the outcomes of a measurement campaign of acoustical parameters in accordance with ISO 3382-1 in the ancient theatre of Tyndaris (Sicily) are presented and compared with datasets from other sites. Two sound sources were used (firecrackers and dodecahedron) and their differences were analysed. A very good reproducibility has been shown between the two measurement chains, with differences on average of 0.01 s for reverberation time T20, and less than 0.3 dB for Clarity C50 and C80 and for sound strength. In general, results show that the reverberation time and strength of sound values are relatively low when compared with other theatres because of the lack of the original architectural element of the scaenae frons. When combining this effect with the obvious condition of an unroofed space, issues emerge in terms of applicability of the protocols recommended in the ISO standard. This raises the question of whether different room acoustics parameters should be used to characterise open-air ancient theatres
Effect of façade shape and acoustic cladding on reduction of leisure noise levels in a street canyon
No full textEnvironmental noise is a rising problem in contemporary cities, and the awareness of its consequences on human health is growing. Although the leisure noise generated by people talking in the streets is not generally the most relevant noise source, it has a significant impact in certain urban scenarios, such as nightlife areas. Buildings façades are the primary surfaces upon which the sound emitted within the street is reflected and their design contributes to the reduction of noise level over their fronts. By means of acoustic performance-based design, this research investigates the sound level reduction provided by the shape and the acoustic cladding of an urban façade in front of a talking noise source in a street canyon. The results highlight the screening effect provided by the balconies and the benefits of the application of sound absorbing material on the noise reduction over the façade. Up to 1 dB decrease in the mean level over the entire façade has been achieved with balconies depth of 1.5 m compared to 0.9 m, with a maximum abatement of 2.8 dB at the highest floor. When the entire façade is cladded with sound absorbing material, the mean noise level decrease is up to 10 dB over the façade and up to 3 dB over the opposite one. These reductions are much higher than those obtained by increasing the sound absorption properties of the street paving, that is limited to 1.5 dB averagely, thus underlining the crucial role of façade design in outdoor noise mitigation
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
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