Huynhmunk7165

The predictions are verified with simulations.Multiple approaches for depth estimation in deep-ocean environments are discussed. First, a multispectral transformation for depth estimation (MSTDE) method based on the low-spatial-frequency interference in a constant sound speed is derived to estimate the source depth directly. To overcome the limitation of real sound-speed profiles and source bandwidths on the accuracy of MSTDE, a method based on a convolution neural network (CNN) and conventional beamforming (CBF) preprocessing is proposed. Further, transfer learning is adapted to tackle the effect of noise on the estimation result. At-sea data are used to test the performance of these methods, and results suggest that (1) the MSTDE can estimate the depth; however, the error increases with distance; (2) MSTDE error can be moderately compensated through a calculated factor; (3) the performance of deep-learning approach using CBF preprocessing is much better than those of MSTDE and traditional CNN.In the field of measuring the complex wave number and characteristic impedance of porous materials, available impedance tube approaches assume that only plane wave is propagating such that the maximum frequency is limited below the cut-off frequency of the first higher order mode. This indicates that if measurements at higher frequencies are required, the tube size has to be reduced, as well as the size of porous material sample, which may cause inaccurate results due to tube attenuation and edge-constraint effects. Through simulations, this paper presents an extended transfer matrix method to remove the plane wave assumption based on the fact that the propagation of plane wave through the porous sample can be characterized by the same transfer matrix whether higher order modes exist or not. This method arranges measuring points upstream and downstream the sample for implementing mode decomposition to extract the transfer matrix for plane wave in a multi-modal field. From the matrix elements, the complex wave number and characteristic impedance are determined in the same way as the original transfer matrix method. Based on numerical simulations and the Monte Carlo approach, the method effectiveness and a suitable measuring points layout are studied in this paper.Listeners differ widely in the ability to follow the speech of a single talker in a noisy crowd-what is called the cocktail-party effect. Differences may arise for any one or a combination of factors associated with auditory sensitivity, selective attention, working memory, and decision making required for effective listening. The present study attempts to narrow the possibilities by grouping explanations into model classes based on model predictions for the types of errors that distinguish better from poorer performing listeners in a vowel segregation and talker identification task. Two model classes are considered those for which the errors are predictably tied to the voice variation of talkers (decision weight models) and those for which the errors occur largely independently of this variation (internal noise models). Regression analyses of trial-by-trial responses, for different tasks and task demands, show overwhelmingly that the latter type of error is responsible for the performance differences among listeners. The results are inconsistent with models that attribute the performance differences to differences in the reliance listeners place on relevant voice features in this decision. The results are consistent instead with models for which largely stimulus-independent, stochastic processes cause information loss at different stages of auditory processing.Frequency-difference beamforming (FDB) provides a robust estimation of wave propagation direction by shifting signal processing to a lower frequency which, however, produces a decline in the spatial resolution. In this letter, the beam pattern of FDB for a distant point source is proved to be shift invariant and therefore can be regarded as the point spread function corresponding to FDB's beam output. Then, deconvolved frequency-difference beamforming (Dv-FDB) is proposed to improve array performance. Dv-FDB yields a narrower beam and lower sidelobe levels while maintaining robustness. The superior performance of Dv-FDB is verified by simulations and experimental data.Aberrations induced by soft tissue inhomogeneities often complicate high-intensity focused ultrasound (HIFU) therapies. In this work, a bilayer phantom made from polyvinyl alcohol hydrogel and ballistic gel was built to mimic alternating layers of water-based and lipid tissues characteristic of an abdominal body wall and to reproducibly distort HIFU fields. The density, sound speed, and attenuation coefficient of each material were measured using a homogeneous gel layer. A surface with random topographical features was designed as an interface between gel layers using a 2D Fourier spectrum approach and replicating different spatial scales of tissue inhomogeneities. Distortion of the field of a 256-element 1.5 MHz HIFU array by the phantom was characterized through hydrophone measurements for linear and nonlinear beam focusing and compared to the corresponding distortion induced by an ex vivo porcine body wall of the same thickness. Both spatial shift and widening of the focal lobe were observed, as well as dramatic reduction in focal pressures caused by aberrations. The results suggest that the phantom produced levels of aberration that are similar to a real body wall and can serve as a research tool for studying HIFU effects as well as for developing algorithms for aberration correction.Arctic glacial bays are among the loudest natural environments in the ocean, owing to heavy submarine melting, calving, freshwater discharge, and ice-wave interactions. Understanding the coherence and vertical directionality of the ambient sound there can provide insights about the mechanisms behind the ice loss in these regions. It can also provide key information for operating technologies such as sonar, communication, and navigation systems. To study the unexplored sound coherence and vertical directionality in glacial bays, a vertical hydrophone array was deployed, and acoustic measurements were made at four glacier termini in Hornsund Fjord, Spitsbergen, in June and July 2019. The measurements show that the sound generated by melting glacier ice is more dominant in the upper portion of the water column near the glacier terminus. The melt water from the submarine melting and the freshwater discharge from the glacier create a glacially modified water duct near the sea surface. This disrupts the inter-sensor vertical coherence in the channel. However, some coherence across the duct is preserved for sound arising from spatially localized events at low frequencies. Overall, the observations in this study can help improve the understanding of the submarine melting phenomenon in glacial bays.Based on the notion of similarity or "distance" between cross-spectral density matrices (CSDMs), a recent analysis of matched-field source localization in a stochastic ocean waveguide provided evidence that geodesic distances between CSDMs could be employed to estimate the source location in range and depth. For M acoustic sensors configured as a vertical array, these M×M matrices were estimated from source and replica fields propagated to the array and interpreted as points in a Riemannian manifold whose dimension is M2. Because they serve as fundamental constructs for many source localization algorithms, visualizations of CSDM manifolds are illustrated here in an attempt to gain insight into this geometric approach by using simulated acoustic fields propagated through an ocean waveguide with internal wave-induced variability. The manifold is treated as an undirected, weighted graph whose nodes are CSDMs with edges (weights) describing a measure of similarity between nodes. A non-linear dimensionality reduction technique, diffusion maps, is applied to project these high-dimensional matrices onto a three-dimensional subspace using a spectral decomposition of the graph in an attempt to grasp relationships among such matrices. The mapping is designed to preserve the notion of distance between matrices, allowing for a meaningful visualization of the high-dimensional manifold.Many studies have reported a musical advantage in perceiving lexical tones among non-native listeners, but it is unclear whether this advantage also applies to native listeners, who are likely to show ceiling-like performance and thus mask any potential musical advantage. The ongoing tone merging phenomenon in Hong Kong Cantonese provides a unique opportunity to investigate this as merging tone pairs are reported to be difficult to differentiate even among native listeners. In the present study, native Cantonese musicians and non-musicians were compared based on discrimination and identification of merging Cantonese tone pairs to determine whether a musical advantage in perception will be observed, and if so, whether this is seen on the phonetic and/or phonological level. check details The tonal space of the subjects' lexical tone production was also compared. Results indicated that the musicians outperformed the non-musicians on the two perceptual tasks, as indexed by a higher accuracy and faster reaction time, particularly on the most difficult tone pair. In the production task, however, there was no group difference in various indices of tonal space. Taken together, musical experience appears to facilitate native listeners' perception, but not production, of lexical tones, which partially supports a music-to-language transfer effect.This article presents a finite element based solution of the exact governing wave equation for a stratified inhomogeneous moving media. The model is applied to a two dimensional range independent problem in outdoor sound propagation in which the ground is treated as perfectly reflecting. The sound pressure field is expanded as a sum over eigenmodes propagating in the range direction, and the semi analytic finite element method is used to solve the governing eigenequation. This delivers faster solution times when compared to traditional finite element based methods while simultaneously accommodating continuous variations in fluid properties in the vertical direction. In principle, the method converges toward the exact solution and so delivers a benchmark method for range independent problems. The method is shown to provide excellent agreement with analytic solutions, and good convergence is demonstrated for more complex problems, including temperature inversions and logarithmic profiles for wind velocity. Finally, qualitative comparisons are made against infrasound predictions, including those obtained using wide angle parabolic equations. The method is shown to provide a focussed image of the sound pressure field over large distances, as well as to reproduce multiple turning points and ground interactions.The phase velocity dispersion of longitudinal waves in polycrystals with elongated grains of arbitrary crystallographic symmetry is studied in all frequency ranges by the theoretical second-order approximation (SOA) and numerical three-dimensional finite element (FE) models. The SOA and FE models are found to be in excellent agreement for three studied polycrystals cubic Al, Inconel, and a triclinic material system. A simple Born approximation for the velocity, not containing the Cauchy integrals, and the explicit analytical quasi-static velocity limit (Rayleigh asymptote) are derived. As confirmed by the FE simulations, the velocity limit provides an accurate velocity estimate in the low-frequency regime where the phase velocity is nearly constant on frequency; however, it exhibits dependence on the propagation angle. As frequency increases, the phase velocity increases towards the stochastic regime and then, with further frequency increase, behaves differently depending on the propagation direction. It remains nearly constant for the wave propagation in the direction of the smaller ellipsoidal grain radius and decreases in the grain elongation direction.