مجله انجمن مهندسی صوتیات ایران
سال نهم شماره 2 (پاییز و زمستان 1400)

In this paper, the phononic and thermal properties of tungsten disulfide have been studied. The aim of this study was to investigate the phonon and thermal properties such as heat capacity and enthalpy. The calculations are performed within the framework of density functional theory by pseudo-potential methood and by Quantum Espresso computational package and their exchange-correlation function is of LDA and GGA type. From the study of thermal properties, we find that the drop in heat capacity at low temperatures is T3. At high temperatures, the heat capacity approaches (3NKB =71.673J / K.mol Dulong-Petit law). Also, the specific heat value and entropy of this compound at room temperature were 65.221 J / K.mol and 68.757 J / K.mol, respectively. In the phonon scattering diagram, 3 Acoustic branches and 15 optical branches were obtained. Also, the phonon scatter diagram and the density of phonon states were compared in terms of state matching. The results obtained are consistent with other available data.

The study aimed was to measure left ventricular (LV) strain using speckle tracking echocardiography (STE) for assessment of LV function. Eighty-two subjects (mean age 57±9 years) with suspected chest pain underwent two-dimensional (2D)-echocardiography before coronary angiography. Conventional echocardiographic parameters were used for the assessment of LV function. Longitudinal strain and its strain rate (SR) and circumferential strain, and its SR with 2D-STE were calculated for the assessment of myocardial function. According to the angiography results, patients were divided into two groups: CAD patients (n=60) and healthy group (n=22). There was a significant decrease in longitudinal and circumferential strain and strain rate in patients with CAD compared to healthy individuals (longitudinal strain in patients -16.2±2.4 vs -19.5±2.1 for a healthy group) (P-value<0.05). Discriminate analysis of longitudinal and circumferential strain with values of 78% and 83% indicated the highest sensitivity respectively. ST as a non-invasive method for measurement of strain and strain rate parameters is proposed in the early diagnosis of LV dysfunction in patients with CAD.

Mosques are among the buildings that sound has a special role in the explanation of their quality. It seems that different physical forms in mosques also play a role in the field of acoustics, domed, columned and arched buildings offer different qualities of sound. To analyze this feature, the current study has selected 5 samples of large historical mosques in Tabriz as a study sample, which are classified into 5 formal groups. The method is field research based on ISO3382 and visual surveys and Background Noise, Sound Pressure Level and Reverberation Time were measured in the empty position of the samples and at two standing and sitting heights to simulate the prayer positions. Findings of the study consider the arched form to have a balanced behavior, evaluating the maximum RT both at standing and sitting position at a frequency of 100 Hz and related to the domed sample. Another part of the findings, according to the visual surveys, shows that the combination of spatial elements plays a great role in the distribution of sound, and the scattering of the main frequencies of the speech in all the mosques is desirable and intense.

Aerospace engines testing is a source of noise pollution and determining the low frequency acoustic characteristics of the test cell, plays an important role in optimally control of the sound field and reducing the level of sound pressure and pollution. In this study, the drop in average sound pressure level is numerically predicted by constructing a test cell according to ISO 140 standard. To solve the sound propagation equations, modeling the contact between the structure and the fluid, dynamic coupling of the structure and the fluid is performed and to calculate the acoustic energy distribution in the fluid and the structure, Abaqus finite element software is used. Cells with different dimensions and insulation and simply support conditions are modeled and the average sound pressure level drop of each model is calculated and compared. The optimal dimensions of the cell are determined, then the independence of the mesh is checked and the results are verified using experimental data. The measured sound pressure drop values are reported for the quarter band. To ensure that it is not resonated by acoustic force, the frequency analysis of the structure was performed and it was determined that the designed test cell eliminates noise pollution. Cell size optimization shows that the best test cell radius for the 90 to 150 Hz frequency range is 2.25 m.

In this paper, according to the  density functional theory and semiharmonic approximation and solving kohen's equations using plane wave, band structure, phonon scattering; Dielectric tensor, Bourne effective charge, Raman cross-section; We calculated the infrared and specific heat capacity of indium phosphide in two-phase structures on zincblend (ZB) and salt rock (Rs). The results show that this compound is more crystalline and stable in the Zb phase. Examination of phonon modes shows the existence of IR modes in both phases. Also, the effective boron charge values ​​are close to the nominal ion values, which indicates the ion bond in this system. The calculated phonon spectrum shows a frequency gap in the range of 1179 to 288 cm-1, which will be fully reflected in this range. Also, the specific heat capacity at high temperatures is close to an asymptotic value that is highly consistent with experimental results.

Understanding the dynamics of microbubble oscillation in an elastic microvessel is important for the safe and effective applications of ultrasound contrast agents in imaging and therapy. Numerical simulations based on 2D finite element model are performed to investigate the effect of acoustic parameters such as pressure and frequency on the dynamic interaction of the fluid-blood-vessel system. The results show that acoustic waves cause bubble oscillation, pressure on the vessel wall as well as vascular deformation. For a bubble (with a radius of 1.5 μm) in a microvessel with a radius of 5 μm exposed to ultrasonic waves with a frequency of 1 MHz and out put pressures of 0.25 MPa, 0.22 MPa, 0.18 MPa and 0.13 MPa the modeling has been done. It can be seen that with increasing ultrasound pressure, the radius of the bubble changes, the displacement of the vessel wall and the pressure and also shear stress on the vessel wall increase. Also, by increasing the initial radius of the microbubble (1.5, 2.5 and 2.5 micrometers) at constant radiant wave pressure, the pressure on the capillary wall and the amount of capillary wall displacement increase. With increasing capillary wall diameter (1, 1.5, 2 and 2.5 μm) at constant radiant wave pressure, no significant change in pressure applied to the capillary wall and capillary wall displacement is observed. This work was evaluated with the simulation results of other researchers.

This paper investigates the effect of the wind-generated bubble layer on the underwater sound source localization in the Persian Gulf shallow-water environment through computer simulation and the matched field processing technique. An underwater sound source of 2-10 kHz located at depths of 10, 45, and 75 m was considered at a distance of 4 km from a linear vertical receiver array. The estimation of the source range and depth was performed in the match condition using the maximum-likelihood matched field processor. Next, the errors due to the effect of the sound-speed mismatch of the bubble layer (affected by different wind speeds) were extracted. The results showed that, although errors increased by increasing the degree of the mismatch and by increasing the source frequency, the error values are significant (above 1%) only at frequencies greater than or equal to 8 kHz for wind speeds greater than 8 m/s. Also, the maximum error in estimating the range and depth of the source is 2.5% and 4.5%, respectively. Besides, the values of these errors were dependent on the source depth, so the errors for the sound source located at depth 10 m (closer to the bubble layer) were more than the errors in the other two source depths.

In this paper, we design, simulate, and build an ultrasonic heat generator. In thermoacoustics, heat generated by the passage of alternating current through a thin conductor produces a sound wave. In this method, unlike other methods of sound production, moving parts are not used to vibrate air molecules, and as a result, the frequency response of these generators is flatter than other sound generators and they are used in a wider range. In this study, samples of sound generators were made using different conductive materials and different structures and measured in the laboratory. The study aimed to construct an ultrasonic generator with a wide and flat frequency response in the frequency range of 50 to 90 kHz. The results obtained from the measurements show the ability to produce sound with a sound pressure level of 90 decibels at frequencies of 40 to 90 kHz and suitable stability for long operation.

Referring to the rear wall in a hall is the furthest element rather than the voice source, therefor the reflections of this structural member play important role in music and speech intelligibly, especially for one-third behind audiences. Hence the form of these structures can be very effective in the acoustical quality of speech halls and auditoria. In this study, four formic structures are examined in EASE acoustical software. Duo to results, the columned shape structure was more optimum in speech range and concave shape was most reverberant. Along with this research, halls with plane and concave shape were proposed for music performances and convex as well as columned shapes for speech approaches. The achieved results can be used for other effective walls in similar studies.

Iron aluminide intermetallic compound, including compounds that have great features is that it's so great properties, due to its increasing use in industry is different. In thiswork, structural and dynamic properties of FeAl compounds including the structure of energybands, density of states, phonon and thermal properties in two-phase structures regularly evaluated and calculated. Calculations using a Pseudoptential, within the framework of density functional theory have been studied PWscf code. The study found that the combination of these features in your base has a metal in ferromagnetic order, the results of the electronicstructure of this compound are indicative of metal and the structure of the electron cloud indicates the ionic bond -covalent for two phases results in good agreement with the experimental results are available.

In large aquatic environments including oceans and seas, acoustic waves are widely used due to their ease of propagation, which in addition to helping to build accurate systems and equipment, can also be very useful in analyzing and processing data. The mode of propagation depends on the mass density and speed of acoustic waves in this completely heterogeneous environment, both of which depend on parameters such as temperature, salinity and pressure. In each region of ​​this environment, the conditions of the mentioned parameters are completely unique. Therefore, as an example, two regions in the Atlantic ocean and the Indian ocean were studied and after extracting the variation of the above parameters in depth, using the applied method of transfer matrix, the amount of transmission of acoustic waves in these regions were investigated. The results show that significant changes in salinity and temperature in the layers near the surface, cause significant changes in mass density and speed of sound propagation and, consequently, sound impedance. Also, in various sedimentary layers near the ocean floor, the sound impedance experiences sudden and sharp changes, reducing the transmission by about 55%.

In general, recording audio in different environments deals with different challenges. Wind noise in outdoors recording often leads to critical degradation to the speech signal. Because of wide band and nonstationary nature of wind noise, it is very difficult to remove it. Singular Spectrum Analysis (SSA) is a powerful method for time series analysis that is used in applications such as noise reduction, time series prediction and so on. The SSA selects and groups the principal components of the Eigen-space decomposed signals, based on their contributions; then the reconstructed main components are transferred to time domain. In our research, the SSA method combined with K-MEANS algorithm are used to reduce wind noise in speech signals. SNR and PESQ, are used to evaluate the proposed method’s results. Speech signals from TIMIT dataset and wind noise from Rheinisch-Westfälische Technische Hochschule Aachen have been utilized in this research. The results show great increase in the quality of speech signal, in terms of perceptual quality and signal to noise ratio. The proposed algorithm shows the good performance compared with other reference algorithms.