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A reduced-order homogenization framework is proposed, providing a macro-scale-enriched continuum model for locally resonant acoustic metamaterials operating in the subwavelength regime, for both time and frequency domain analyses. The homogenized continuum has a non-standard constitutive model, capturing a metamaterial behaviour such as negative effective bulk modulus, negative effective density and Willis coupling. A suitable reduced space is constructed based on the unit cell response in a steady-state regime and the local resonance regime. A frequency domain numerical example demonstrates the efficiency and suitability of the proposed framework. This article is part of the theme issue 'Current developments in elastic and acoustic metamaterials science (Part 2)'. [ABSTRACT FROM AUTHOR]

Many species of fishes around the world are soniferous. The types of sounds fishes produce vary among species and regions but consist typically of low-frequency (< 1.5 kHz) pulses and grunts. These sounds can potentially be used to monitor fishes non-intrusively and could complement traditional monitoring techniques. However, the significant time required for human analysts to manually label fish sounds in acoustic recordings does not yet allow passive acoustics to be used as a viable tool for monitoring fishes. In this paper, we compare two different approaches to automatically detect fish sounds. One is a more traditional machine learning technique based on the detection of acoustic transients in the spectrogram and the classification using Random Forest (RF). The other is using a deep learning approach and is based on the classification of overlapping segments (0.2 s) of spectrogram using a ResNet18 Convolutional Neural Network (CNN). Both algorithms were trained using 21,950 manually annotated fish and non-fish sounds collected from 2014 to 2019 at five different locations in the Strait of Georgia, British Columbia, Canada. The performance of the detectors was tested on part of the data from the Strait of Georgia that was withheld from the training phase, data from Barkley Sound, British Columbia, and data collected in the Port of Miami, Florida, United States. The CNN performed up to 1.9 times better than the RF (F1 score: 0.82 vs. 0.43). In some cases, the CNN was able to find more faint fish sounds than the analyst and performed well in environments different from the one it was trained in (Miami F1 score: 0.88). Noise analysis in the 20--1,000 Hz frequency band shows that the CNN is still reliable in noise levels greater than 130 dB re 1 μPa in the Port of Miami but becomes less reliable in Barkley Sound past 100 dB re 1 μPa due to mooring noise. The proposed approach can efficiently monitor (unidentified) fish sounds in a variety of environments and can also facilitate the development of species-specific detectors. We provide the software FishSound Finder, an easy-to-use open-source implementation of the CNN detector with detailed documentation. [ABSTRACT FROM AUTHOR]

A paper by the current authors Paul and Nelson [JASA Express Lett. 3(9), 094802 (2023)] showed how the singular value decomposition (SVD) of the matrix of real weights in a neural network could be used to prune the network during training. The paper presented here shows that a similar approach can be used to reduce the training time and increase the implementation efficiency of complex-valued neural networks. Such networks have potential advantages compared to their real-valued counterparts, especially when the complex representation of the data is important, which is the often case in acoustic signal processing. In comparing the performance of networks having both real and complex elements, it is demonstrated that there are some advantages to the use of complex networks in the cases considered. The paper includes a derivation of the backpropagation algorithm, in matrix form, for training a complex-valued multilayer perceptron with an arbitrary number of layers. The matrix-based analysis enables the application of the SVD to the complex weight matrices in the network. The SVD-based pruning technique is applied to the problem of the classification of transient acoustic signals. It is shown how training times can be reduced, and implementation efficiency increased, while ensuring that such signals can be classified with remarkable accuracy. [ABSTRACT FROM AUTHOR]

Multiple power ultrasounds were employed to investigate the phase transition process of ternary Al81.5Cu14.7Bi3.8 immiscible alloy by various exerting modes. As the ultrasonic sources increased, the liquid phase separation pattern transformed from (Bi)-rich layered macrosegregation into the uniform distribution of secondary (Bi) droplets. Meanwhile, the primary (Al) phase evolved from coarse dendrites into plenty of small spherical grains and also tended to be uniformly dispersed. The subsequently formed ternary (Al) + (Al2Cu) + (Bi) monotectic structure, featured by the alternative (Al) and (Al2Cu) lamellar structure with fine (Bi) grains distributed, was coarsened first and then refined. Numerical simulations showed that the transient cavitation and the acoustic streaming strength were significantly enhanced by increasing ultrasonic beams, with the fourfold ultrasounds producing the most prominent effects on the phase separation process. The intensive and enlarged cavitation areas greatly accelerated the nucleation of both the secondary liquid phase and primary solid phase, which refined the growing (Bi) droplets and (Al) dendrites. The strength and morphology of acoustic streaming were the key factors in offsetting Stokes motion and carrying the growing grains to various regions, resulting in a uniform microstructure. Furthermore, increasing ultrasonic sources improved the friction and wear properties of the solidified alloy, which indicated that the Al81.5Cu14.7Bi3.8 immiscible alloy may become an excellent wear-resistant material owing to the uniform monotectic structure fabricated by the fourfold ultrasounds. [ABSTRACT FROM AUTHOR]

The dynamic (acoustic pressure) and kinematic (acoustic acceleration and velocity) properties of time-limited signals are studied in terms of acoustic dose metrics as might be used to assess the impact of underwater noise on marine life. The work is relevant for the study of anthropogenic transient acoustic signals, such as airguns, pile driving, and underwater explosive sources, as well as more generic transient signals from sonar systems. Dose metrics are first derived from numerical simulations of sound propagation from a seismic airgun source as specified in a Joint Industry Programme benchmark problem. Similar analyses are carried out based on at-sea acoustic measurements on the continental shelf, made with a vector sensor positioned 1.45 m off the seabed. These measurements are on transient time-limited signals from multiple underwater explosive sources at differing ranges, and from a towed, sonar source. The study demonstrates, both numerically and experimentally, that under many realistic scenarios, kinematic based acoustic dosage metrics within the water column can be evaluated using acoustic pressure measurements. [ABSTRACT FROM AUTHOR]

The study of transient acoustic wave propagation across the Arctic Ocean ice layer provides theoretical guidance for the design of trans-ice acoustic communication systems. In this study, the Arctic Ocean was modeled as an ice–water composite structure, where the ice and water are regarded as an elastic solid and liquid, respectively. An analytical transient solution for acoustic wave propagation in this structure was derived using the eigenfunction expansion method. Further, the numerical procedures were presented and used to analyze the acoustic wave propagation characteristics across the ice layer. The results show that waveforms corresponding to the radial displacements are more severely distorted than the axial displacements. The amplitudes of the radial and axial displacements decreased rapidly with increasing propagation distance. The ice thickness had a greater impact on the radial displacement than axial displacement; the thicker the ice, the greater the distortion for both radial and axial displacements. [ABSTRACT FROM AUTHOR]

The deformation of a fluid interface by the acoustic radiation pressure has been used for surface tension measurements or to design exotic structures such as acoustic diodes. However, few studies focus on the characterization of the spatial characteristics of deformation induced by transient excitation, making research requiring precise spatial control of deformation challenging. This paper investigates experimentally and numerically the effects of transient excitation on deformation generated by an acoustic radiation pressure at the water–air interface. A numerical model using the finite-element method and based on theoretical background for permanent excitation is generalized to transient excitation. An experimental setup is developed to evaluate the maximum height of interface deformation for different durations and amplitudes of ultrasonic excitation using two complementary methods: the first using a camera and an edge detection algorithm and the other using a multichromatic confocal displacement sensor. Numerical and experimental results for a non-steady-state excitation show a quadratic evolution of the height of deformation as a function of incident pressure and also a linear increase as a function of the excitation duration. The evaluation of the deformation height induced by acoustic radiation pressure at a water–air interface for a transient excitation paves the way to applications requiring noncontact space-time interface modulation, such as subwavelength phenomena. [ABSTRACT FROM AUTHOR]

On the path to an optoacoustic hearing implant for stimulation of residual hearing, one possibility for tone generation in liquids is the concatenation of acoustic click events, which can be realized i. a. by the acoustic transients that accompany an optical breakdown. The application of a viscous gel is helpful in this context, as this results in an attenuation of the distortion of tone quality caused by higher harmonic components. To further understand the underlying cavitation bubble dynamics both in the viscous gel and in a confined volume that is dimensioned similarly to the human cochlea, a numerical model built in OpenFOAM was adapted and compared to additional experiments. Experimentally, the acoustic transients were generated by optical breakdown by nanosecond laser pulses with a pulse duration of 0.7 ns and a wavelength of 1064 nm. The pulses were focused on a viscous gel inside a water container. The pressure transients were measured by a needle hydrophone. The comparison of the bubble dynamics in different viscosities between the model and the experiment shows that, except for high viscosities, the experimental observations could be modeled by the simulation. We assume that the maximum size of the cavitation bubble strongly decreases with increasing viscosity, which can be used for high-frequency attenuation as reported in our previous research. In conclusion, this study aims at an application-oriented realization of the numerical cavitation bubble dynamics model to understand the experimental findings on the pathway to an optoacoustic hearing implant. [ABSTRACT FROM AUTHOR]

We describe studies of the interaction of a pulsed Nd:YAG laser with bovine serum albumin (BSA) solution (i.e., S0) and S0 containing gold nanourchin (GNU) (i.e., S1: S0 + 0.1 ml GNU) using combined photoacoustic (PA) and probe beam deflection (PBD) techniques. The changes in absorbance and chemical bonds are studied by UV–Vis and near-FTIR spectroscopy. The results showed a decrease in absorbance of the bio-plasmonic solution, which further decreased by increasing the concentration. The PA pressure increased with fluence in the order of GNU > S0 > S1, and all exhibited a non-linear response at ≈9.5 J cm−2 and reached a maximum at 12.5 J cm−2. No PBD was observed in S0 indicating the role of GNU in producing the heating effect. ∂n/∂T increased in the order of S2 > S1 > S0, respectively, where S2 is (S0 + 0.2 ml GNU). The absorbance of S0 and S1 increased after heating due to protein denaturation. For S1, surface-enhanced FTIR showed an increase in the intensity of most bands between 6320 and 6630 cm−1, and the band at 5264 cm−1, which likely corresponds to β-sheet structure, significantly diminished after heating. The collapse of cavitation and plasma shock waves produced significant acoustic transients, hence some photomechanical effects. The acoustic energy released after the collapse of bubbles at 1.8 and 12.5 J cm−2 was calculated to be ≈140 μJ and 7 mJ, respectively, corresponding to 4% and 28% of the input optical energy being converted to sound energy in the early phase of the expansion. [ABSTRACT FROM AUTHOR]

In field-effect transistors (FETs) with two-dimensional (2D) transition metal dichalcogenide channels, the dependence of field-effect mobility on atomic layer thickness has been studied and interpreted in terms of interface scattering and interlayer coupling resistance (Rint). However, a model for 1/f noise, such as in MoS2 and in MoSe2 FETs, for various contact metals and layer number thicknesses has not been reported. In this work, we have experimentally studied current–voltage and 1/f noise on MoS2 and MoSe2 FETs with source and drain contacts of high and low work function metals to understand both the mobility and the noise behavior. We have developed a noise model incorporating layer number dependent Hooge parameters and Rint. The noise and mobility models utilize screening lengths for charge, mobility, and Hooge parameter to describe the variation of these quantities with a layer number. Using our single model topology with appropriate fitting parameters for each material and each contact metal, the model captures the experimentally observed layer thickness dependence of the Hooge parameter. Our noise analysis is fully comprehensive and, hence, could be applied to any 2D layered systems. [ABSTRACT FROM AUTHOR]

• The behavior of the linear compress with transient acoustic load is analyzed. • The temperature distribution along the regenerator is theoretically calculated. • The variation of the efficiency and displacement of the compressor is analyzed. The working condition of the linear compressor greatly affects the performance of the cryocooler. When the cryocooler operates during a transient working state like the cool down process, the linear compressor is also in a transient working state and could lead to deviation from designed steady state condition. In order to study the transient behavior of a linear compressor during the cool down process, a theoretical model based on the finite difference method is proposed. The temperature distribution of the regenerator during the cool down process is calculated. The variation of the impedance of the cold finger is then calculated. The transient behavior of the linear compressor are studied according to the impedance match between the compressor and the cold finger. The theoretical model shows that the transient behavior of the linear compressor is determined by the variation of the cold finger impedance during the cool down process and the increase of the input power could be larger than 40% with constant input voltage through the whole cool down process. A Sage simulation model of the cryocooler is built and the cool down experiments are carried out. The simulation and the experiment results are consistent with the theoretical model. It's also shown that the theoretical model could provide better prediction of the transient behavior of the linear compressor. The study of the transient behavior of the linear compressor could help improve the design and control of the linear compressor especially for the transient process. [ABSTRACT FROM AUTHOR]

Helioseismic holography applied to HMI observations of a sunquake associated with the SOL20140207T10:29M1.9 flare hosted by NOAA AR11968 shows the signature of a compact submerged acoustic source. In the 9 – 11-mHz bandpass, this source appears to be at a depth of 2 Mm. This is nearly double the depth of the highly impulsive acoustic transient, referred to as an ultra-impulsive transient source recently found in the SOL20110730T02:09M9.3 flare, emerging from NOAA AR11261 in 2011. The latter source was compound, having multiple surface components overlaying a single submerged component. Many of the sources observed have evidence of being constituted of multiple components, some of which are staggered in depth. The helioseismic source of the flare of 2014-02-07 is distinguished by the apparent absence of a strong shallow compact overlying source component matching the character of those apparent in the flare of 2011-07-30. This suggests that the volume several Mm beneath active-region photospheres could possibly harbor many more ultra-impulsive transient acoustic sources than the rarities that have so far appeared in familiar surface-focal-plane diagnostics. Based on weak surface signatures that appear in place of the strong ones, we find a temporal delay between weak surface and strong submerged sources similar to that found between surface-and-submerged sources in the flare of 2011-07-30. While it remains highly speculative based on the limited statistics we have at this point, this temporal delay supports a model in which the submerged source is perturbed by some presently invisible triggering disturbance that propagates downward from the flaring outer atmosphere at ∼ 5 km s−1. This is slower than the sound speed anywhere in the 0 – 2-Mm depth range. However, this potentially could be an Alfvèn speed if submerged magnetic flux densities along which the trigger propagates are as high as possible. The standard local-helioseismic diagnostics we have used in the past have been heavily reinforced in this study by a powerful new control resource found in the recognition of temporal defocusing of compact transient sources. In particular, its tight relationship to the standard spatial defocusing upon which helioseismic holography has capitalized from its early advent. [ABSTRACT FROM AUTHOR]

A transformer's acoustic signal contains rich information. The acoustic signal can be divided into a transient acoustic signal and a steady-state acoustic signal under different operating conditions. In this paper, the vibration mechanism is analyzed, and the acoustic feature is mined based on the transformer end pad falling defect to realize defect identification. Firstly, a quality–spring–damping model is established to analyze the vibration modes and development patterns of the defect. Secondly, short-time Fourier transform is applied to the voiceprint signals, and the time–frequency spectrum is compressed and perceived using Mel filter banks. Thirdly, the time-series spectrum entropy feature extraction algorithm is introduced into the stability calculation, and the algorithm is verified by comparing it with simulated experimental samples. Finally, stability calculations are performed on the voiceprint signal data collected from 162 transformers operating in the field, and the stability distribution is statistically analyzed. The time-series spectrum entropy stability warning threshold is given, and the application value of the threshold is demonstrated by comparing it with actual fault cases. [ABSTRACT FROM AUTHOR]

We develop a three‐dimensional shape optimization (SO) framework for the wave equation with taking the unsteadiness into account. Resorting to the adjoint variable method, we derive the shape derivative (SD) with respect to a deformation (perturbation) of an arbitrary point on the target surface of acoustic scatterers. Successively, we represent the target surface with non‐uniform rational B‐spline patches and then discretize the SD in term of the associated control points (CPs), which are useful for manipulating a surface. To solve both the primary and adjoint problems, we apply the time‐domain boundary element method (TDBEM) because it is the most appropriate when the analysis domain is the ambient air and thus infinitely large. The issues of the severe computational cost and instability of the TDBEM are resolved by exploiting the fast and stable TDBEM proposed by the present authors. Instead, since the TDBEM is mesh‐based and employs the piecewise‐constant element for space, we introduce some approximations in evaluating the discretized SD from the two solutions of TDBEM. By regarding the evaluation scheme as the computation of the gradient of the objective functional, given as the summation of the absolute value of the sound pressure over the predefined observation points, we can solve SO problems with a gradient‐based non‐linear optimization solver. To assess the developed SO system, we performed several numerical experiments from the perspective of verification and application with satisfactory results. [ABSTRACT FROM AUTHOR]

In cleaning Industries, Vibro Cleaner has unique impact for removal of contaminations like rust, dirt, oil etc. from critical objects. This is completely safe for humans and non-hazardous for nature. The aim of this research is to improve the efficiency of vibro cleaning process by using multiple transducers model matrix (MTMM) with 40 kHz frequency transducers. For the investigation, COMSOL Multiphysics software has been used by clubbing acoustic and CFD approaches in pressure acoustic transient module. By effect of cavitation erosion phenomenon, recommended results in cleaning erosion rates have been achieved and importance of placement of transducer also has been found out using different matrix in various models. Here among all matrix, The Erosion rate 9.62 x 10-3 kg/m2s has been obtained maximum in transducer matrix of 2 transducers at bottom with 1 transducer at each 4 sides of tank. [ABSTRACT FROM AUTHOR]

The porous ice layer formed upon the SAW (surface acoustic wave) propagation path will produce transient acoustic attenuation, and a new icing sensing method can be constructed based on this feature. Obtaining the pore characteristics of an ice layer is a prerequisite and basis for deriving the sensing mechanism of SAW icing. Employing the U-net network, a segmentation model of frozen pores is developed by collecting frozen images and calibrating sample data sets for training in this work. The MIOU and the MPA of the model reach 92.16 % and 95.15 % respectively. Then, the watershed algorithm and post-processing were used to accurately obtain the pore characteristic parameters (porosity, pore number, and average pore area) of the ice layer. On this basis, applying the Biot's theory for two-phase porous media, a theoretical model of the SAW icing sensing mechanism was established, and the acoustic sensing response under different icing types was theoretically simulated. To prove the accuracy of the theoretical simulation, a SAW sensor using a waveguide structure of SU-8/ST-90 °X quartz operating at 80 MHz was constructed and evaluated experimentally. The results demonstrate that the acoustic sensing responses of different ice types are completely consistent with the theoretical results. This fully verifies the accuracy of the ice pore parameters extracted in this work and also confirms the feasibility of using pore microscopic information to achieve ice detection and ice type discrimination. [Display omitted] • We experimentally acquired icing images and created an icing pore dataset. Based on the U-net network, an icing pore segmentation model have been developed. • The images of frozen pores at different temperatures were collected, while the parameters of frozen pores at different temperatures were obtained and analyzed. • Based on the extracted ice pore parameters at different temperatures, we further refined the acoustic surface wave icing sensing mechanism. • A love waveguide-type acoustic surface wave device was designed for experimental verification to demonstrate the reliability of the ice pore parameter extraction method. [ABSTRACT FROM AUTHOR]

In this study, a theoretical model has been constructed to address the optimization of matching layers for tone burst excitation underwater acoustic transducers and to investigate the functional mechanism change of matching layers. Single, double, and triple matching layers are attached to piezoelectric composite plates, and tone burst signals with a different number of burst-cycles are applied. Acoustic pressure function (Sp) and acoustic pressure transient response (PTR) are compared among these transducers. The results demonstrated that when the cycle number M ≤ 2, more matching layers lead to shorter ringdown with similar PTR amplitude. Since the objective is for better axial resolution, three matching layers have noticeable advantage, whereas for the case of M > 5, far detection distance is the main objective, and more matching layers caused the decrease in PTR amplitude. Besides, matching layers become part of the resonance structure; they do not serve as a transmission medium anymore. Therefore, the transducer with single matching is optimal for the long tone burst excitation. For the case of 2–5 cycle excitation, one may use double matching layers, which has a balance between the transmitting voltage response amplitude and bandwidth. With the increase in M, the role of matching layers changes from a bridging transmission medium to amplifying vibration velocity and introducing additional vibration modes to broaden the bandwidth. [ABSTRACT FROM AUTHOR]

Solid fuel combustion in a chamber does not necessarily occur at a constant rate and may show fluctuations due to variables such as varying burning rates, chamber pressure, and residual combustion. These variables can cause the fuel to burn disproportionately. The acoustic environment of obstacle vortex-driven flow due to transient combustion with pressure oscillations in a solid fuel chamber is numerically investigated in the present study. Solid fuel combustion is considered transient, and flow characteristics of the present problem are governed by large eddies shed from an obstacle. Since unsteady Reynolds-averaged Navier-Stokes (URANS) simulations are not appropriate to compute the present flow phenomenon, therefore, a detached eddy simulation (DES) is performed to precisely predict the flow behavior. Simulation of steady-state combustion is carried out to validate the numerical results with available experimental data from the literature. The simulation of transient combustion shows that if the combustion frequency is close to the chamber's modal frequency of the chamber, its amplitude increases greatly and creates an acute acoustic environment. This will result in fuel savings. The amplitude of pressure oscillation up to 18% and 5% of mean pressure are evident at the first and second mode of forced oscillation frequencies respectively. Interestingly, it is also found that pressure oscillation always occurs at inlet mass flux disturbance frequency and not between the disturbance and natural frequency of the chamber. As a result, it is evident that the combustion process or chamber configuration could be modified to ensure that both frequencies are far away enough to interact and create both a harsh acoustic environment and sufficient fuel to burn disproportionately. [ABSTRACT FROM AUTHOR]

The Rayleigh collapse time is the time it would take to shrink an empty spherical bubble in an infinite liquid domain to zero size, which is a function of ambient pressure and initial bubble radius. If a solid boundary is located in the vicinity of the shrinking or collapsing bubble, then liquid flow is hindered, such that the collapse time is prolonged. This can be quantified with the Rayleigh prolongation factor k. Here, we provide k for intermediate to smallest bubble to wall stand-off distances. It is measured with single laser-induced cavitation bubbles in water close to a solid boundary. Maximum bubble radii are determined from microscopic high-speed imaging at one million frames per second. Collapse times are measured acoustically via the acoustic transients emitted during bubble seeding and collapse. The experimental findings are compared, with good agreement, to numerical simulations based on a volume of fluid method. As a result, a polynomial fit of k versus stand-off distance is given for the near-wall bubble collapse in water. Then the influence of the viscosity on k is studied numerically in the near-wall regime. [ABSTRACT FROM AUTHOR]

Humans are able to detect an instantaneous change in correlation, demonstrating an ability to temporally process extremely rapid changes in interaural configurations. This temporal dynamic is correlated with human listeners' ability to store acoustic features in a transient auditory manner. The present study investigated whether the ability of transient auditory storage of acoustic features was affected by the interaural delay, which was assessed by measuring the sensitivity for detecting the instantaneous change in correlation for both wideband and narrowband correlated noise with various interaural delays. Furthermore, whether an instantaneous change in correlation between correlated interaural narrowband or wideband noise was detectable when introducing the longest interaural delay was investigated. Then, an auditory computational description model was applied to explore the relationship between wideband and narrowband simulation noise with various center frequencies in the auditory processes of lower-level transient memory of acoustic features. The computing results indicate that low-frequency information dominated perception and was more distinguishable in length than the high-frequency components, and the longest interaural delay for narrowband noise signals was highly correlated with that for wideband noise signals in the dynamic process of auditory perception. [ABSTRACT FROM AUTHOR]

We present a class of simple algorithms that allows us to find the reaction path in systems with a complex potential energy landscape. The approach does not need any knowledge on the product state and does not require the calculation of any second derivatives. The underlying idea is to use two nearby points in the configuration space to locate the path of the slowest ascent. By introducing a weak noise term, the algorithm is able to find even low-lying saddle points that are not directly reachable by means of the slowest ascent path. Since the algorithm only makes use of the value of the potential and its gradient, the computational effort to find saddle points is linear in the number of degrees of freedom if the potential is short-ranged. We test the performance of the algorithm for three potential energy landscapes. For the Müller-Brown surface, we find that the algorithm always finds the correct saddle point. For the modified Müller-Brown surface, which has a saddle point that is not reachable by means of the slowest ascent path, the algorithm is still able to find this saddle point with high probability. For the case of a three-dimensional Lennard-Jones cluster, the algorithm is able to find the lowest energy barrier with high probability, showing that the method is also efficient in landscapes with many dimensions. [ABSTRACT FROM AUTHOR]

This paper presents a modified time discontinuous Galerkin finite element method (MDGFEM) for transient acoustic wave propagation problem of multilayered pavement. The pavement consists of cement concrete pavement, semi-rigid base, and natural soil. The multilayered pavement is modeled as poroelastic mediums and assumed to be water-saturated. The well-known generalized Biot's theory is employed to describe the wave propagation problem. The present MDGFEM, based on the artificial damping scheme, employs the Hermite (P3) functions and the linear (P1) shape functions to interpolate the global nodal vector and its temporal gradient respectively in a time step. Numerical results of 1D and 2D problems show that the MDGFEM can filter out spurious numerical oscillations before and after waves, boundaries of the hole, and the interface between the layers more effectively for the propagation of acoustic waves in multilayered pavement. Compared with widely used time-continuous methods such as the Newmark method, the method proposed in this paper presents better capabilities in the fluid–structure interaction behavior of multilayer pavements and provides a more accurate solution, which contributes to the further development of non-destructive testing of multilayer pavement structures. [ABSTRACT FROM AUTHOR]

We investigate how correlated fluctuations affect oscillatory features in rephasing and non-rephasing two-dimensional (2D) electronic spectra of a model dimer system. Based on a beating map analysis, we show that non-secular environmental couplings induced by uncorrelated fluctuations lead to oscillations centered at both cross- and diagonal-peaks in rephasing spectra as well as in non-rephasing spectra. Using an analytical approach, we provide a quantitative description of the non-secular effects in terms of the Feynman diagrams and show that the environment-induced mixing of different inter-excitonic coherences leads to oscillations in the rephasing diagonal-peaks and non-rephasing cross-peaks. We demonstrate that as correlations in the noise increase, the lifetime of oscillatory 2D signals is enhanced at rephasing cross-peaks and non-rephasing diagonal-peaks, while the other non-secular oscillatory signals are suppressed. We discuss that the asymmetry of 2D lineshapes in the beating map provides information on the degree of correlations in environmental fluctuations. Finally we investigate how the oscillatory features in 2D spectra are affected by inhomogeneous broadening. [ABSTRACT FROM AUTHOR]

We propose a new theoretical method and experimental investigation to characterize the growth process of rime ice through surface acoustic waves (SAWs). The Biot theory of dual-phase porous media was employed to construct a theoretical model to describe the acoustic wave propagation in porous rime ice; the transient changes in acoustic propagation attenuation and velocity were simulated; and the icing sensing mechanism of the acoustic wave propagation attenuation (∼18 dB) and the transient change in velocity (0.8 m/s) during the icing process was obtained. A 177.5 MHz waveguide type SAW micro–nano-device with an SU8/ST-90°X quartz multilayer composite film structure and a microfluidic cavity on the top of the acoustic device were designed and fabricated, and the transient attenuation in the growth of rime ice was evaluated experimentally. The experimental results indicated that the appearance of rime ice can be monitored accurately by utilizing the transient changes in acoustic wave velocity and attenuation. Therefore, the acoustic method can aid in the early warning of the development status of rime ice. [ABSTRACT FROM AUTHOR]

The visualization of index-of-refraction (IoR) distribution is one of the common methods to investigate fluid flow or pressure fields. While schlieren and shadowgraphy imaging techniques are widely accepted, their inherent limitations often lead to difficulties in elucidating the IoR distribution and extracting the true IoR information from the resulting images. While sophisticated solutions exist, the IoR-gradient-to-image was achieved by purposely introducing a commonly avoided "defect" into the optical path of a conventional coincident schlieren/shadowgraphy setup; the defect is a combination of slight defocusing and the use of non-conjugate optical components. As such, the method presented in this work is referred to as defocusing shadowgraphy, or DF-shadowgraphy. While retaining the ease of a conventional schlieren/shadowgraphy geometry, this DF approach allows direct visualization of complicated resonant acoustic fields even without any data processing. For instance, the transient acoustic fields of a common linear acoustic resonator and a two-dimensional one were directly visualized without inversion. Moreover, the optical process involved in DF-shadowgraphy was investigated from a theoretical perspective. A numerical solution of the sophisticated impulse response function was obtained, which converts the phase distortion into intensity distributions. Based on this solution, the IoRs of various gas streams (e.g., CO2 and isopropanol vapor) were determined from single images. [ABSTRACT FROM AUTHOR]

Reduced graphene oxide (RGO)/Si Schottky diode has been reported nowadays to show excellent performances in photodetection and other photoelectrical devices. Different from pure graphene, there are large amounts of function groups and structural defects left on the base plane of RGO, which may influence the interfacial properties of RGO/Si Schottky diode. Herein, the barrier inhomogeneity and junction characteristics were systematically investigated to help to describe the interface of RGO/Si diode. From the perspective of its applications, the influences of gas molecule and noise properties are considered to be important. Thus, the photovoltaic performance of RGO/Si devices in air and vacuum is investigated to analyze their effects. Meanwhile, 1/f noise of RGO/Si diodes is investigated under air/vacuum conditions and varied temperatures. It is found that the devices in vacuum and under higher power incident light show much lower 1/f noise. These results are meaningful to the noise control and performance improvement in the development of Schottky diode based devices. [ABSTRACT FROM AUTHOR]

Magnetically isotropic (CoFe-AlN)n/(AlN)n+1 multilayer films, in which the number of CoFe-AlN magnetic layers n ranged from 1 to 27, were prepared by radio frequency sputtering to achieve noise suppression at gigahertz frequencies. The soft CoFe-AlN magnetic layers consisted of nanometer-sized CoFe ferromagnetic grains embedded in an insulating AlN amorphous matrix, while the insulating AlN layers comprised AlN columnar crystals. All films showed a similar frequency dependence of permeability and ferromagnetic resonance of 1.7 GHz. Noise suppression was evaluated using a microstrip line as a noise source by determining the in-line conductive loss and the near-field intensity picked up by magnetic field detective probes. High noise suppression effects were observed in every direction in the film plane. Maximum noise suppression values amounted to 60% for the in-line conductive loss and -20 dB for the magnetic near-field intensity at around 1.7 GHz in the 27-layer film. These high-frequency noise suppression levels may be attributed to eddy current losses and ferromagnetic resonance. [ABSTRACT FROM AUTHOR]

In this study, we investigated the performance of perpendicular magnetic recording with squeezed tracks. Based on spinstand signals, we developed a signal generation module to generate the readback signals for tracks of various squeezed track width and bit length. To mitigate the drop in bit error rate (BER) as squeezed track width decreases, we implemented the bidirectional patterndependent noise prediction (BiPDNP) detector with low-density parity check codes. To improve the BiPDNP detector over earlier work, we modified the log-likelihood ratio computation. Our results show that our proposed BiPDNP detector improves the bit error rate, and allows smaller squeezed track width and smaller bit length for the same BER performance. [ABSTRACT FROM AUTHOR]

This study investigated the effect of magnetostriction-induced core magnetomechanical vibrations and noise on the magnetic properties of power transformers. The magnetostriction of grain-oriented Si steels was found to be extremely sensitive to compressive stress applied along the rolling direction and to tensile stress applied along the transverse direction. The compressive stress increased the variation in the magnitude of magnetostriction, which is correlated with core vibration and noise. A 2D model of the power transformer was used to simulate the noise and vibration variables through a finite element analysis. [ABSTRACT FROM AUTHOR]

In this work, we present a systematic modeling analysis of signal-to-noise ratio (SNR) impact on recording under insufficient head field for heat assisted magnetic recording (HAMR). A typical head design in the absence of a medium soft underlayer is utilized in the modeling. The study shows that sufficient head field amplitude is critical for realization of expected HAMR recording performance. The strong correlation between recording time window and medium signal-to-noise ratio provides insightful understanding to medium and recording optimization when head field is not sufficiently high. The analysis is also performed with the inclusion of grain-to-grain Curie temperature (Tc) variation in the medium. [ABSTRACT FROM AUTHOR]

Jitter noise reduction can be achieved by controlling the position of magnetic grains, but write synchronization is needed to take advantage of the potential reduction. A periodic read-back response can be obtained from DC-erased bits, which is composed of rows of grains. In this paper, the feasibility of creating a clock signal for write synchronization using this periodicity of the readback response is investigated. As a result, it was confirmed that a clock signal can be created by using the precise periodicity of the read-back response. [ABSTRACT FROM AUTHOR]

With the advance of additive manufacturing, many researchers are increasingly interested in planar acoustic lenses that are not only easier to fabricate than typical convex/concave lenses, but also have excellent imaging performance. However, the planar acoustic lenses reported so far cannot work for a short-duration pulse used in conventional imaging systems due to their inherent dispersive characteristics. This study addresses the challenge by devising a transient topology optimization formulation to design a planar acoustic lens that works effectively for a short-duration pulse. A planar lens consists of two materials where optimal combination and distribution are obtained with a crisp interface via the level-set method. Design is based on the transient acoustic responses, which are calculated from a time-dependent acoustic model solved by the Newmark method. The proposed method uses the area-fraction approach to compute the acoustic properties of a cut element by the interface. A localizing time-window function is introduced so that acoustic energy can be focused within the desired time range as much as possible. We obtain optimum design solutions designed with the proposed method and verify its effectiveness through the numerical investigations. [ABSTRACT FROM AUTHOR]

mSOUND is an open-source toolbox written in MATLAB. This toolbox is intended for modeling linear/ nonlinear acoustic wave propagation in media (primarily biological tissues) with arbitrary heterogeneities, in which, the speed of sound, density, attenuation coefficient, power-law exponent, and nonlinear coefficient are all spatially varying functions. The computational model is an iterative one-way model based on a mixed domain method. In this article, a general guideline is given along with three representative examples to illustrate how to set up simulations using mSOUND. The first example uses the transient mixed-domain method (TMDM) forward projection to compute the transient acoustic field for a given source defined on a plane. The second example uses the frequency-specific mixed-domain method (FSMDM) forward projection to rapidly obtain the pressure distribution directly at the frequencies of interest, assuming linear or weakly nonlinear wave propagation. The third example demonstrates how to use TMDM backward projection to reconstruct the initial acoustic pressure field to facilitate photoacoustic tomography (PAT). mSOUND (https://m-sound.github.io/mSOUND/home) is designed to be complementary to existing ultrasound modeling toolboxes and is expected to be useful for a wide range of applications in medical ultrasound including treatment planning, PAT, transducer design, and characterization. [ABSTRACT FROM AUTHOR]

The article presents the results of experimental determination of the structure of surface vibrations of a two-dimensional phased ultrasound probe using transient acoustic holography in the frequency range from 0.1 to 10 MHz. It is shown that this method makes it possible to detect individual elements operating with parameter deviations from the nominal values, including inactive ones. A comparison is made with the results of echo pulse measurements for each element, as well as measurements of the electric capacitance of the elements. [ABSTRACT FROM AUTHOR]

We propose a Lévy noise-driven susceptible-exposed-infected-recovered model incorporating media coverage to analyze the outbreak of COVID-19. We conduct a theoretical analysis of the stochastic model by the suitable Lyapunov function, including the existence and uniqueness of the positive solution, the dynamic properties around the disease-free equilibrium and the endemic equilibrium; we deduce a stochastic basic reproduction number R 0 s for the extinction of disease, that is, if R 0 s ≤ 1 , the disease will go to extinction. Particularly, we fit the data from Brazil to predict the trend of the epidemic. Our main findings include the following: (i) stochastic perturbation may affect the dynamic behavior of the disease, and larger noise will be more beneficial to control its spread; (ii) strengthening social isolation, increasing the cure rate and media coverage can effectively control the spread of disease. Our results support the feasible ways of containing the outbreak of the epidemic. [ABSTRACT FROM AUTHOR]

On airfoils at low to moderate Reynolds numbers, trailing edge sound can have a feedback effect on the development of instability waves resulting in strongly periodic vortex shedding and tonal noise. This complex problem is decoupled in this study to investigate the flow response to deterministic noise emissions. The flow receptivity and response to tonal noise are examined using controlled steady and transient acoustic excitation. Experiments are performed on a NACA 0018 airfoil at a Reynolds number of 1.15 × 10 5 and an angle of attack of 5°, with a separation bubble on the suction side. Controlled acoustic perturbations are introduced via a loudspeaker. A combination of mean and time-resolved surface pressure and simultaneous high-speed particle image velocimetry measurements provides insight into the response of the bubble to simulated acoustic forcing. Amplification of shear layer perturbations in the fore portion of the separation bubble is observed only after some time delay from the onset of acoustic forcing. This places the receptivity region within the boundary layer upstream of the separation bubble, extending from the leading edge to just downstream of the suction peak. The acoustically excited perturbations in the receptivity region attain higher amplitudes than natural disturbances and are amplified significantly in the separation bubble, leading to a transient reduction in the separation bubble size. Results elucidate the ensuing transient response of the separation bubble, illustrating the flow dynamics expected during the initiation of the acoustic feedback loop during natural tonal noise emissions on an airfoil. [ABSTRACT FROM AUTHOR]

• A sparse real-time near-field acoustic holography method is proposed. • The proposed method performs compressed sensing to improve stability of solving inverse process. • The proposed method precisely and stably reconstructs the transient sound field. • The superiority of proposed method is proved by comparing to RTNAH with Tikhonov regularization and YALL1. A sparse real-time near-field acoustic holography method is proposed to precisely and stably reconstruct a transient sound field. By a time-domain impulse response function, a time domain convolution equation between the pressure time-wavenumber spectra on the hologram and reconstruction planes is first established. Then, a smoothed ℓ 0 -norm optimization algorithm is applied to solve the serious ill-conditioned problem of the inverse process to get the pressure time-wavenumber spectrum of the reconstruction plane. The key part of solving this problem is to approximate replace the discontinuous ℓ 0 -norm by using a suitable continuous Gaussian function family, and a steepest ascent algorithm is introduced to minimize the continuous function for obtaining the optimal solution. Finally, the pressure time-wavenumber spectra of the reconstruction plane for all wavenumbers at all times are solved, and the corresponding time-dependent pressures are gained by the two-dimensional space inverse Fourier transform. A numerical simulation is conducted to observe the reconstruction capacity of the proposed method. The simulation effect prove that the proposed method can accurately reconstruct the transient sound field, and its reconstruction results are compared to those of the real-time near-field acoustic holography (RTNAH) with Tikhonov regularization and YALL1 modal for verifying the superiority of the proposed method. The YALL1 module utilizes an alternating direction algorithm for solving the ℓ 1 minimization problems. Several parameters including the noise, position of the holograph plane and two initialization values are discussed in the simulation. The comparison and discussion results show that the reconstruction effect of the proposed method is much better than those of RTNAH with Tikhonov regularization and YALL1 modal under different parameter configurations. An experiment with a percussive steel plate is implemented for further validating the effectivity of the proposed method. [ABSTRACT FROM AUTHOR]

A magnetic resonance (MR) shear wave elastography technique that uses transient acoustic radiation force impulses from a focused ultrasound (FUS) transducer and a sinusoidal-shaped MR displacement encoding strategy is presented. Using this encoding strategy, an analytic expression for calculating the shear wave speed in a heterogeneous medium was derived. Green's function-based simulations were used to evaluate the feasibility of calculating shear wave speed maps using the analytic expression. Accuracy of simulation technique was confirmed experimentally in a homogeneous gelatin phantom. The elastography measurement was compared to harmonic MR elastography in a homogeneous phantom experiment and the measured shear wave speed values differed by less than 14%. This new transient elastography approach was able to map the position and shape of inclusions sized from 8.5 to 14 mm in an inclusion phantom experiment. These preliminary results demonstrate the feasibility of using a straightforward analytic expression to generate shear wave speed maps from MR images where sinusoidal-shaped motion encoding gradients are used to encode the displacement-time history of a transiently propagating wave-packet. This new measurement technique may be particularly well suited for performing elastography before, during, and after MR-guided FUS therapies since the same device used for therapy is also used as an excitation source for elastography. [ABSTRACT FROM AUTHOR]

The acoustic response of a car door latch has been shown to directly impact the customers' perceived quality and value evaluation of the automobile. This work introduces an experimentally validated computational model of three door latch components. The transient sound pressure level response of the three door latch components during door closure was collected in a semianechoic chamber using a three-element condenser microphone array. Postprocessing methodologies such as sound pressure level versus 1/3 octave band and continuous wavelet transform analysis were performed. This provided an in-depth analysis on the overall acoustic response and identification of dominant frequencies corresponding to four specific impact events during latch operation. Computational finite element analysis of the closure system using a rigid body, and explicit dynamic and transient structural acoustic analyses provided additional insights into the latch component interactions and the acoustic response generated empirically. Recorded average sound pressure level, frequency decomposition, and impact reaction forces are presented in addition to a comparison between the acoustic response for two different door closure speeds. It was found that an increased door closure speed increased the response sound pressure level, decreased damping of the primary impact, and decreased the frequency bandwidth of the response, thereby generating an acoustic response that would be perceived as noisier, less safe, and less secure by customers. These findings provide additional insights into the primary impact acoustic response of an automotive door latch during closure. The methodology introduced in this work allows automotive engineers to perform future work with modified latch components to further improve the psychoacoustic response of the automotive car door latch, further increasing the value evaluation of the automobile. [ABSTRACT FROM AUTHOR]

We analyze systematically the acoustic transients emitted during the collapse of a laser-induced cavitation bubble for 0.4 ≤ γ ≤ 5.2. γ is the standoff parameter, the ratio of the distance between the bubble's nucleation place and its maximum size. At the bubble collapse, the acoustic signals recorded contain several pressure peaks with rising times as fast as 18 ns. The time delay, Δ t , between these peaks is a few hundred nanoseconds apart for bubbles nucleated close to the boundary and decreases with γ. The pressure maxima correspond to shock fronts emitted around the time the bubble reaches its minimum volume and is correlated with the high-speed video recordings of the bubble dynamics. We also show that the amplitude ratio of the first to second acoustic transient is strongly dependent on γ. The experimental results are complemented with numerical simulations based on the Volume-of-Fluid method. The simulated results help clarify the physical mechanisms leading to the generation of acoustic transients and unveil in detail the morphology of the bubble approaching its minimum volume, a feature that cannot be resolved with the high-speed data. Furthermore, the numerical results reveal that the impact of the liquid jet on the rigid wall ensues a local increase in pressure over a significant time period, contrary to the shock wave formed during bubble collapse, which produces a sharp transient pressure peak that propagates radially outwards along the rigid wall. We also discuss the validity and shortcomings of the simulation and how to improve them in the future. [ABSTRACT FROM AUTHOR]

Laser beam‐induced graphene oxides (GOs) with excellent tunable properties have to find attention in various applications. But, the understanding of the complex mechanics involved in this reduction process is incomplete, most primarily the reduction using ultrashort laser beam pulses. Herein, the influence of laser beam‐induced acoustic waves on the photoreduction as well as the generation of a reversible phase in the GOs using photoacoustic studies is presented. However, these waves influence the phase transition in GOs. These observations find aspiring applications for next‐generation optical technologies, such as data storage and neural chips. [ABSTRACT FROM AUTHOR]

Detecting acoustic transients by signal-to-noise ratio (SNR) becomes problematic in nonstationary ambient noise environments characteristic of coral reefs. An alternate approach presented here uses signal directionality to automatically detect and localize transient impulsive sounds collected on underwater vector sensors spaced tens of meters apart. The procedure, which does not require precise time synchronization, first constructs time-frequency representations of both the squared acoustic pressure (spectrogram) and dominant directionality of the active intensity (azigram) on each sensor. Within each azigram, sets of time-frequency cells associated with transient energy arriving from a consistent azimuthal sector are identified. Binary image processing techniques then link sets that share similar duration and bandwidth between different sensors, after which the algorithm triangulates the source location. Unlike most passive acoustic detectors, the threshold criterion for this algorithm is bandwidth instead of pressure magnitude. Data collected from shallow coral reef environments demonstrate the algorithm's ability to detect SCUBA bubble plumes and consistent spatial distributions of somniferous fish activity. Analytical estimates and direct evaluations both yield false transient localization rates from 3% to 6% in a coral reef environment. The SNR distribution of localized pulses off Hawaii has a median of 7.7 dB and interquartile range of 7.1 dB. [ABSTRACT FROM AUTHOR]

This paper presents a numerical scheme of arbitrary order of accuracy in both space and time, based on the arbitrary high-order derivatives methodology, for transient acoustic simulations. The scheme combines the nodal discontinuous Galerkin method for the spatial discretization and the Taylor series integrator (TSI) for the time integration. The main idea of the TSI is a temporal Taylor series expansion of all unknown acoustic variables in which the time derivatives are replaced by spatial derivatives via the Cauchy-Kovalewski procedure. The computational cost for the time integration is linearly proportional to the order of accuracy. To increase the computational efficiency for simulations involving strongly varying mesh sizes or material properties, a local time-stepping (LTS) algorithm accompanying the arbitrary high-order derivatives discontinuous Galerkin (ADER-DG) scheme, which ensures correct communications between domains with different time step sizes, is proposed. A numerical stability analysis in terms of the maximum allowable time step sizes is performed. Based on numerical convergence analysis, we demonstrate that for nonuniform meshes, a consistent high-order accuracy in space and time is achieved using ADER-DG with LTS. An application to the sound propagation across a transmissive noise barrier validates the potential of the proposed method for practical problems demanding high accuracy. [ABSTRACT FROM AUTHOR]

Road traffic noise pollution has been recognized as a serious issue which affects human health as well as affects urban regions. Noise maps are very beneficial to identify the impact of noise pollution. A noise mapping study performed to study the propagation of noise in tier-II city along with field measurements. The noise maps are developed using a computer simulation model (SoundPLAN essential 4.0 software). The noise prediction models like U.K's CoRTN, Germany's RLS-90, and their modified versions, which can be used for homogenous road traffic conditions, cannot be successfully applied in heterogeneous road traffic conditions of India. In developing country like India, road traffic noise pollution depends on the composition of heterogeneous traffic volume, variance in road geometrical, honking conditions, un-authorized parking, and varying density of the building on either side of the road. These traffic compositions contain vehicles, which have different sizes, speeds variations, a different dimension of vehicles. Because of fluctuating speeds, lack of lane disciplines, and un-authorized parking on main road lanes, honking events becomes inevitable, which changes and affects the urban soundscape of nations like India. Analysis of noise maps showed that horn honking due to un-authorized parked vehicles contributed an additional increase up to 11 dB (A) noise, which is quite significant. [ABSTRACT FROM AUTHOR]

Summary: Three‐dimensional (3D) rapid transient acoustic problems are difficult to solve numerically when dealing with large geometries, because numerical methods based on geometry discretization (mesh), such as the boundary element method (BEM) or the finite element method (FEM), often require to solve a linear system (from the spacial discretization) for each time step. We propose a numerical method to efficiently deal with 3D rapid transient acoustic problems set in large exterior domains. Using the 𝒵‐transform and the convolution quadrature method, we first present a straightforward way to reframe the problem to the solving of a large amount (the number of time steps, M) of frequency‐domain BEMs. Then, taking advantage of a well‐designed high‐frequency approximation, we drastically reduce the number of frequency‐domain BEMs to be solved, with little loss of accuracy. The complexity of the resulting numerical procedure turns out to be O(1) in regard to the time discretization and O(NlogN) for the spacial discretization, the latter being prescribed by the complexity of the used fast BEM solver. Examples of applications are proposed to illustrate the efficiency of the procedure in the case of fluid‐structure interaction: the radiation of an acoustic wave into a fluid by a deformable structure with prescribed velocity and the scattering of an abrupt wave by simple and realistic geometries. [ABSTRACT FROM AUTHOR]

Spoken language, both perception and production, is thought to be facilitated by an ensemble of predictive mechanisms. We obtain intracranial recordings in 37 patients using depth probes implanted along the anteroposterior extent of the supratemporal plane during rhythm listening, speech perception, and speech production. These reveal two predictive mechanisms in early auditory cortex with distinct anatomical and functional characteristics. The first, localized to bilateral Heschl's gyri and indexed by low-frequency phase, predicts the timing of acoustic events. The second, localized to planum temporale only in language-dominant cortex and indexed by high-gamma power, shows a transient response to acoustic stimuli that is uniquely suppressed during speech production. Chronometric stimulation of Heschl's gyrus selectively disrupts speech perception, while stimulation of planum temporale selectively disrupts speech production. This work illuminates the fundamental acoustic infrastructure—both architecture and function—for spoken language, grounding cognitive models of speech perception and production in human neurobiology. The human brain fluently parses continuous speech during perception and production. Using direct brain recordings coupled with stimulation, the authors identify separable substrates underlying two distinct predictive mechanisms of "when" in Heschl's gyrus and "what" in planum temporale. [ABSTRACT FROM AUTHOR]