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In this paper, we have studied particle collision around a rotating acoustic black hole in 2 + 1 dimensions. This black hole is analog to a fluid flow in a draining bath tub with a sink. Center of mass energy for two-particle collision at the horizon of the rotating acoustic black hole is considered. There is a possibility of the two-mass collision to create infinite center of mass energy for certain fine tuning of the parameters of the theory.

In this paper, a new two-dimensional (2D) phononic crystal structure composed of periodic slit metal tubes, in which the unit cell consists of straight or curved backstraps, is proposed, and the propagation characteristics of acoustic waves in this structure are theoretically investigated. Using the finite-element method, we calculate the dispersion relations and transmission coefficients of this structure. The results show that, in contrast to the only slit metal tubes, the periodic slit metal tubes with straight or curved backstraps are proved to display band gaps (BGs) at much lower frequency range. Meanwhile, the effect of the slit width of the backstraps on the BGs is investigated. The results show that the positions and widths of the BGs can be effectively modulated by the backstraps without changing the mass density or lattice constant of the material. The lowest frequency falls by about 200 Hz. Moreover, we investigated how the BGs are affected by the location parameter of the backstraps, finding that the acoustic BGs are sensitive to the location parameter of the backstraps. Numerical results show that BGs are significantly dependent upon the slit width and location parameters of the backstraps. The BGs are optimized because, the effect of the Helmholtz resonators of the slit tube is strengthened and changed when the location and slit width of the backstraps change. These results provide a good reference for optimizing BGs, generating filters and designing devices.

In order to investigate the gas inertial effect on bearing capacity of acoustic levitation on condition of complex exciting shapes, a new kind of numerical model including inertial effect in cylindrical coordinates was proposed. The inertial terms in Navier–Stokes equations are packaged to derive modified Reynolds equations. The amplitudes of standing waves were tested by distance probe in experiment and film thickness equation were reconstructed by sum of the sinusoidal functions. The theoretical and experimental results implied that the inertial effect is strongly related to the exciting modal shapes. It is concluded that the proposal of modified Reynolds equation can provide more optimized numerical solutions to solve the problems about the deviation between theoretical and experimental data.

Electron-piezoelectric phonon interaction provides a significant extrinsic channel for energy relaxation in a graphene sheet placed on a polar substrate. We report in this paper our analytical and numerical investigations on energy relaxation rate and power loss density in graphene sheet on a polar substrate considering the electron-piezoelectric phonon scattering channel in the Boltzmann transport approach. We overcome the earlier crude approximations made to achieve the reported analytical results and compare the obtained results for their compliance with the numerical findings for the graphene sheet on the GaAs substrate. The obtained analytical expression for energy relaxation rate is valid for all temperatures and electron energies. The analytical result for power loss density limits its validity for low electron densities $(<{10}^{12}{\mathrm{\text{cm}}}^{-2})$. It is observed that the relaxation rate due to surface piezoelectric phonons in graphene on GaAs substrate is directly proportional to temperatures above $\sim 10\mathrm{\text{K}}$, below which temperature independence is seen. Also, it is observed that the relaxation rate is linearly dependent on electron energy, $E_k$ at low temperatures, and $E_k$ independent at high temperatures. Moreover, the relaxation rate is electron density-independent for all (low to high) temperatures. The seemingly odd (from earlier reported behavior) temperature-independent, linearly dependent $E_k$ and n independent relaxation rate behavior for low temperatures is attributed to the approximation used so far in the phononic statistical occupation factor in deriving the relaxation rate in the low-temperature Bloch-Gruneisen (BG) regime. In undoped graphene, we have found that the power loss behavior follows a crossover from $T_e^5$ to $T_e^4$ behavior while moving from low $(\sim 20\mathrm{\text{K}})$ to high $(\sim 1000\mathrm{\text{K}})$ electron temperature. This behavior contradicts the study by Zhang et al. [Phys. Rev. B 87, 075443 (2013)] and M. Ansari [Physica E: Low Dimens. Syst. Nanostruct. 131, 114722 (2021)] which reported low-temperature BG behavior of $T_e^3$. This behavior is again attributed to using BG regime approximation for statistical occupation factors. Our findings are in agreement with the experimental work by Chen et al. [Nature Nanotechnol.  3, 206 (2008)] and You et al. [Appl. Phys. Lett. 115, 043104 (2019)].

In order to satisfy the requirements of precise components with tidiness, low power and high stability in the field of biological engineering, medical equipment and semiconductors etc. a pre-stress acoustic transport prototype without horn was proposed in this paper. The mechanism of levitation and transport which is driven by orthogonal waves was revealed by the analysis of waveform and squeeze film characteristics in high-frequency exciting condition; also, the electric, solid and acoustic coupled finite element method (FEM) was established to investigate the effect of pre-stress and acoustic pressure distribution in the near field. The levitation and driving capacity of near field acoustic levitation (NFAL) transport platform without horns can be proved in this experiment and further to achieve the goal of parameters optimization. The theoretical and experimental results indicate that the pre-stress has a significant effect on resonant frequency and levitating stability, the pre-stress are determined by the DC voltage offset which is related to the system working point so that we cannot increase the offset and exciting voltage unlimitedly to improve the stability. At the same time, the calculated pressure distribution of acoustic radiation can generally reflect the regional bearing capacity in near and far field for levitation. These achievements can partly solve the problem of accuracy design of prototype and thickness of gas film, supporting for accuracy close loop control of levitating height.

We consider the Helmholtz transmission problem with one penetrable star-shaped Lipschitz obstacle. Under a natural assumption about the ratio of the wavenumbers, we prove bounds on the solution in terms of the data, with these bounds explicit in all parameters. In particular, the (weighted) $H^1$ norm of the solution is bounded by the $L^2$ norm of the source term, independently of the wavenumber. These bounds then imply the existence of a resonance-free strip beneath the real axis. The main novelty is that the only comparable results currently in the literature are for smooth, convex obstacles with strictly positive curvature, while here we assume only Lipschitz regularity and star-shapedness with respect to a point. Furthermore, our bounds are obtained using identities first introduced by Morawetz (essentially integration by parts), whereas the existing bounds use the much-more sophisticated technology of microlocal analysis and propagation of singularities. We also adapt existing results to show that if the assumption on the wavenumbers is lifted, then no bound with polynomial dependence on the wavenumber is possible.

During the last years, big data has become the new emerging trend that increasingly attracting the attention of the R&D community in several fields (e.g., image processing, database engineering, data mining, artificial intelligence). Marine data is part of these fields which accommodates this growth, hence the appearance of marine big data paradigm that monitoring advocates the assessment of human impact on marine data. Nonetheless, supporting acoustic sounds classification is missing in such environment, with taking into account the diversity of such data (i.e., sounds of living undersea species, sounds of human activities, and sounds of environmental effects). To overcome this issue, we propose in this paper an approach that efficiently allowing acoustic diversity classification using machine learning techniques. The aim is to reach an automated support of marine big data analysis. We have conducted a set of experiments, using a real marine dataset, in order to validate our approach and show its effectiveness and efficiency. To do so, three machine learning techniques are employed: (i) classic machine learning models (i.e., k-nearest neighbor and support vector machine), (ii) deep learning based on convolutional neural networks, and (iii) transfer learning based on the reuse of pretrained models.

This paper is dedicated to the optimal convergence properties of a domain decomposition method involving two-Lagrange multipliers at the interface between the subdomains and additional augmented interface operators. Most methods for optimizing these augmented interface operators are based on the discretization of continuous approximations of the optimal transparent operators.^1–5 Such approach is strongly linked to the continuous equation, and to the discretization scheme. At the discrete level, the optimal transparent operator can be proved to be equal to the Schur complement of the outer subdomain. Our idea consists of approximating directly the Schur complement matrix with purely algebraic techniques involving local condensation of the subdomain degree of freedom on small patch defined on the interface between the subdomains. The main advantage of such approach is that it is much more easy to implement in existing code without any information on the geometry of the interface and of the finite element formulation used. Such technique leads to a so-called "black box" for the users. Convergence results and parallel efficiency of this new and original algebraic optimization technique of the interface operators are presented for acoustics applications.

An approach, called the "Variational Theory of Complex Rays," was proposed recently for calculating the vibrations of slightly damped elastic structures in the medium-frequency range. One key feature of this approach is the use of a new variational formulation of the vibration problem which allows the shape functions to be discontinuous across element boundaries, thus giving this strategy great flexibility and robustness. This method was fully developed for structural vibrations. In this paper, we apply it to acoustics problems. Examples of two-dimensional Helmholtz problems show that this method is very robust and accurate yet requires much less computational effort than the finite element method, which enables one to use it up to much higher frequencies.

The boundary element–Rayleigh integral method (BERIM) is developed for the solution of acoustic problems consisting of a cavity with a single opening. The method is a hybrid of the interior boundary element method (BEM) and the Rayleigh integral method for the solution of the Helmholtz equation. FORTRAN codes for expressing the method for axisymmetric problems and general three-dimensional problems are developed. Both methods are applied to the problem of simulating the acoustic field produced by horn loudspeakers. The results are compared with measured data and the traditional exterior BEM. It is shown that the method can have significant computational advantages over the traditional BEM for problems consisting of an open cavity.

For a vehicular hands-free communication system, the sound quality of communication is usually degraded by noise which is known to be detrimental to system performance. In this paper, a novel adaptive filtering algorithm and an integrated system for acoustic echo and noise cancellation are presented. The proposed system includes adaptive noise cancellation, line enhancer, and echo cancellation which are based on a variable step-size affine-projection algorithm (VSS APA). The proposed VSS APA filtering algorithm is a combination of a variable step-size least-mean-square (VSS LMS) and an affine-projection algorithm (APA). The matrix of the APA allows more accurate, thorough input data and transforms the data into the structure of orthogonality, thus making the estimate of the weight vector faster and more accurate. To understand and verify the effectiveness of the proposed system, performance evaluation and comparison were conducted to compare the proposed algorithm and various traditional adaptive filtering algorithms in this application. The results demonstrated that the VSS APA has an effective performance and convergence in sound quality improvement of hands-free communication systems.

An edge-based smoothed tetrahedron radial point interpolation method (ES-T-RPIM) is formulated for the 3D acoustic problems, using the simplest tetrahedron mesh which is adaptive for any complicated geometry. In present ES-T-RPIM, the gradient smoothing operation is performed with respect to each edge-based smoothing domain, which is also serving as building blocks in the assembly of the stiffness matrix. The smoothed Galerkin weak form is then used to create the discretized system equations. The acoustic pressure is constructed using radial point interpolation method, and two typical schemes of selecting nodes for interpolation using RPIM have been introduced in detail. It turns out that the ES-T-RPIM provides an ideal amount of softening effect, and significantly reduces the numerical dispersion error in low- to mid-frequency range. Numerical examples demonstrate the superiority of the ES-T-RPIM for 3D acoustic analysis, especially at mid-frequency.

Natural fibers are extracted from natural resources such as stems of plants. In contrast to synthetic fibers (e.g., carbon fibers), natural fibers are from renewable resources and are eco-friendlier. Plant fibers are important members of natural fibers. Review papers discussing the microstructures, performances and applications of natural plant fiber composites are available in the literature. However, there are relatively fewer review reports focusing on the modeling of the mechanical properties of plant fiber composites. The microstructures and mechanical behavior of plant fiber composites are briefly introduced by highlighting their characteristics that need to be considered prior to modeling. Numerical works that have already been carried out are discussed and summarized. Unlike synthetic fibers, natural plant fiber composites have not received sufficient attention in terms of numerical simulations. Existing technical challenges in this subject are summarized to provide potential opportunities for future research.

The acoustic monitoring, omni-directional system (AMOS) in the Galileo Project is a passive, multi-band, field microphone suite designed to aid in the detection and characterization of aerial phenomena. Acoustic monitoring augments the Project’s electromagnetic sensors suite by providing a relatively independent physical signal modality with which to validate the identification of known phenomena and to more fully characterize detected objects. The AMOS system spans infrasonic frequencies down to 0.05Hz, all of audible, and ultrasonic frequencies up to 190kHz. It uses three distinct systems with overlapping bandwidths: infrasonic (0.05Hz – 20Hz), audible (10Hz – 20kHz), and ultrasonic (16kHz – 190kHz). The sensors and their capture devices allow AMOS to monitor and characterize the tremendous range of sounds produced by natural and human-made aerial phenomena, and to encompass possible acoustic characteristics of novel sources.

Sound signals from aerial objects can be captured and classified with a single microphone under the following conditions: the sound reaches the sensor; the sound level is above ambient noise; and the signal has not been excessively distorted by the transmission path. A preliminary examination of the signal and noise environment required for the detection and characterization of aerial objects, based on theoretical and empirical equations for sound attenuation in air, finds that moderately loud audible sources (100dB) at 1km are detectable, especially for frequencies below 1kHz and in quiet, rural environments. Infrasonic sources are detectable at much longer distances and ultrasonic at much shorter distances.

Preliminary aircraft recordings collected using the single, omni-directional audible microphone are presented, along with basic spectral analysis. Such data will be used in conjunction with flight transponder data to develop algorithms and corresponding software for quickly identifying known aircraft and characterizing the sound transmission path.

Future work will include multi-sensor audible and infrasonic arrays for sound localization; analysis of larger and more diverse data sets; and exploration of machine learning and artificial intelligence integration for the detection and identification of many more types of known phenomena in all three frequency bands.

Research on the acoustic micro-nano manipulation starts from the discovery of Chladni effect. Acoustic manipulation is expected to be applied to the culture of biological tissue and cell, micro nano element assembling, allocation of chemical raw materials and other micro nano scale fields. Meanwhile, acoustic manipulation shows the characteristic of contactless, biocompatibility, environmental compatibility and functional diversity. Whereas, the accuracy and intelligence of acoustic manipulation still have a big gap to be crossed. Very recently, the method of the deep reinforcement learning is hotly discussed, which provides a new idea for micro nano manipulation. In this paper, the Deep Q Network(DQN) algorithm is considered to improve the efficiency and intelligence in the process of acoustic manipulation. As a demonstration, linear motion tasks based on acoustic wave are trained and displayed. Consequently, the accurate acoustic frequency sequence can be obtained to direct the actual process of acoustic manipulation.

For deepen the understanding of the mechanism of effervescent atomization: it is necessary to have a better observation on the gas-liquid flow near the exit orifice. Both image and acoustic ways were introduced to observe the gas-fluid flow by a transparent effervescent atomizer. The results show that: It can be clearly seen from images that internal flow regimes make great influence on the spray behavior. Spray acoustic observation is an effective way to grasp the gas-liquid two phases flow behavior when they ejecting from the exit orifice. The acoustic analyzing in time and frequency domain has the ability to obtain the discrete phenomenon existing in effervescent sprays, in thus way, acoustic features could give a new perspective on effervescent spray over time. What's more, the discrete phenomenon in dilute bubbly flow and slug flow can be easily captured from after acoustic analyzing. Uniform two-phase distribution of internal flow shows continues acoustic performance after observing the homogeneous bubbly flow and chum flow.