Graph-based complex network features for the auscultation of mitral incompetence

The paper unravels the potential of graph theory in the heart murmur auscultation by constructing a complex network from the single murmur time-series signals. In this study, forty-eight murmur signals of mitral incompetence (MI) and healthy heart (NM) are subjected to complex network and wavelet analyses. For the complex network analysis, the correlation coefficient is fixed as 0.8 and the time series is segmented based on the time delay obtained from the autocorrelation function. The signals are classified based on graph features, reflecting the haemodynamic through the mitral valve, using unsupervised principal component analysis and supervised k-nearest neighbour classifier. The appearance of many frequency components in the murmur due to MI is understood from the wavelet analysis. The graphs of NM and MI are found to show two well-defined clusters. When the graph of NM shows a large number of uncorrelated nodes due to the absence of signal in the systolic region that of MI shows interconnected nodes. The improper closing of the mitral valve and the regurgitation of blood in MI results in sound signals in the systolic region, responsible for the increased number of edges compared to NM. The present economical and sensitive graph-based method opens up the plausibility of remote auscultation in primary health centres in the context of the outbreak of pandemic COVID 19.     

一种双正交心音小波的构造方法

为了提高小波分析在心音信号处理中的性能, 在分析小波构造理论的基础上, 构造了一种专门用于心音信号处理的小波基. 首先提出一种构造滤波器长度为偶数的紧支撑双正交小波的一般方法; 然后根据心音信号的特点, 讨论心音小波的构造原则和一种基于心音 小波族的心音信号合成模型, 并且在此基础上构造出心音小 波. 为了突出使用心音小波处理心音信号的先进性和实用性, 对心音小波进行了比较全面的理论和数值仿真分析. 实验结果表明, 相比常用的db, bior系列小波, 运用心音小波对心音信号进行处理, 能够获得更好的去噪效果、 更精确的心音分类信息以及更小的重构误差率, 为心音特征提取和身份识别的深入研究提供了一种新方法, 在表征心音个体特征的细节方面具有积极的意义. 本文根据应用对象设计专用小波的方法也为工程应用中小波基的选择提供了一种新途径. 关键词： 双正交小波 心音小波 构造方法 心音合成模型     

The discovery of the underwater sound channel,experimental studies,and regional differences

More than half a century has passed since the discovery of the underwater sound channel. In this period of time, the Acoustics Institute has performed a number of experiments on the long-range propagation of explosion-generated sound signals in different ocean regions. These experiments included the studies of such phenomena as the frequency-dependent sound attenuation in the sea medium and the sound field formation in the underwater sound channel. A combined analysis of the data obtained revealed considerable regional differences in the time structure of the sound field. In the experiments, a number of phenomena were observed that required special explanation and additional theoretical treatment. These phenomena include: the unexpectedly high attenuation of low-frequency sound in the sea medium, the “spectrum-analyzing” properties of the underwater sound channel in the Black Sea, the existence of the reverberation forerunner (the so-called prereverberation), the frequency-independent deviation of the phase shift from the usual value of 90° between the signals in classical quartets differing in the number of contacts with the caustic, the splitting of individual signals into quartets, and the transformation of these quartets into groups of nearly irresolvable signals at long distances. The most interesting data of the aforementioned studies are described in the present paper.     

Long-range sound propagation in the northeastern Atlantic

Experimental data on the long-range propagation of explosion-generated signals are analyzed. The experiments were performed in the northeastern Atlantic under the conditions of a two-axis underwater sound channel. The sound field in the upper channel was governed by the vertical redistribution of the ray structure and sound energy under the influence of a smooth increase in the depth of the channel’s axis along the propagation path. The explosions were produced in the upper sound channel at a depth of 200 m, which was constant along the path. The time structure of the sound field is analyzed for the upper channel (a reception depth of 200 m) and for deeper layers lying somewhat below the boundary between the upper and lower sound channels (a reception depth of 1200 m). The deviation of the decay law obtained for the sound field level in the upper channel from the cylindrical law is used to estimate the attenuation coefficient. The low-frequency (several hundreds of hertz) attenuation coefficients experimentally determined with allowance for the sound field redistribution agree well with the calculated sound absorption in seawater. The attenuation coefficients determined by the differential method also agree well with the absorption calculated by the formulas proposed earlier. The analysis of the time structure of the sound field near the boundary between the upper and lower channels reveals a permanent insonification of this horizon by weak water-path signals propagating with the velocity typical of the signals traveling in the upper channel.     

Cardiac functional analysis by laser speckle interferometry

The laser speckle interference pattern during movement of a rough surface is employed to measure the respective displacements. The purpose of this work is to apply this technique in the form of laser speckle displacement cardiography to analyse the displacement patterns during the I and II heart sounds. The recording is performed by illuminating the chest over the cardiac region by collimated laser beam controlled by an ECG operated electric shutter. By analysis the 3-D displacement patterns are obtained. A comparison shows that the displacement at the apex, right ventricle, aortic and mitral valvular regions are significantly higher during I sound than that of II sound.     

Interference structure of low-frequency reverberation signals in shallow water

Using numerical simulation, an analysis was conducted of the interference structure of a bottomscattered sound field generated by a wideband point source in shallow water under winter and summer conditions. The scattered signals were received from the place where the source was located and were subjected to Fourier transform with a sliding window. The paper demonstrates the possibility of estimating the waveguide invariant for backscattered signals when processing the sound intensity distributions in wide frequency and distance ranges up to the scattering area. A technique is proposed for reconstructing the twodimensional field of internal waves using variations of the interference pattern of reverberation signals. The influence of wind surface waves on the degree of interference band contrast is illustrated.     

Rainforests as concert halls for birds: are reverberations improving sound transmission of long song elements?

In forests reverberations have probably detrimental and beneficial effects on avian communication. They constrain signal discrimination by masking fast repetitive sounds and they improve signal detection by elongating sounds. This ambivalence of reflections for animal signals in forests is similar to the influence of reverberations on speech or music in indoor sound transmission. Since comparisons of sound fields of forests and concert halls have demonstrated that reflections can contribute in both environments a considerable part to the energy of a received sound, it is here assumed that reverberations enforce also birdsong in forests. Song elements have to be long enough to be superimposed by reflections and therefore longer signals should be louder than shorter ones. An analysis of the influence of signal length on pure tones and on song elements of two sympatric rainforest thrush species demonstrates that longer sounds are less attenuated. The results indicate that higher sound pressure level is caused by superimposing reflections. It is suggested that this beneficial effect of reverberations explains interspecific birdsong differences in element length. Transmission paths with stronger reverberations in relation to direct sound should favor the use of longer signals for better propagation.     

Detection of Coronary Artery Disease Using Multi-Domain Feature Fusion of Multi-Channel Heart Sound Signals

Heart sound signals reflect valuable information about heart condition. Previous studies have suggested that the information contained in single-channel heart sound signals can be used to detect coronary artery disease (CAD). But accuracy based on single-channel heart sound signal is not satisfactory. This paper proposed a method based on multi-domain feature fusion of multi-channel heart sound signals, in which entropy features and cross entropy features are also included. A total of 36 subjects enrolled in the data collection, including 21 CAD patients and 15 non-CAD subjects. For each subject, five-channel heart sound signals were recorded synchronously for 5 min. After data segmentation and quality evaluation, 553 samples were left in the CAD group and 438 samples in the non-CAD group. The time-domain, frequency-domain, entropy, and cross entropy features were extracted. After feature selection, the optimal feature set was fed into the support vector machine for classification. The results showed that from single-channel to multi-channel, the classification accuracy has increased from 78.75% to 86.70%. After adding entropy features and cross entropy features, the classification accuracy continued to increase to 90.92%. The study indicated that the method based on multi-domain feature fusion of multi-channel heart sound signals could provide more information for CAD detection, and entropy features and cross entropy features played an important role in it.     

Intensity analysis methods for transient signals

Conventionally, the Fourier transform is applied for sound intensity analysis of stationary signals, but this method can be applied for analyzing non-stationary transient signals. Instead of the Fourier transform analysis, instantaneous spectrum analysis methods such as the Wigner-Ville distribution and the wavelet transform are proposed. By using the mathematical example as a transient signal, advantages and disadvantages of these methods including the short-time Fourier transform are compared. From calculation results, it is considered that the STFT method is the most suitable for the accurate measurement of sound intensity levels, but the WT method is also recommended from its higher resolution of transient signals.     

船用三通调节阀流-固耦合噪声数值模拟

针对船用PN10DN32三通调节阀噪声声压频谱、声指向性等声学特性规律不明确,噪声声压级是否满足使用要求的问题,基于流-固耦合理论,同时考虑流-固耦合面及流体域内的脉动声学激励源,开展阀门噪声数值模拟研究。分别对三通调节阀在80%及60%开度阀外1 m处的噪声进行数值模拟,分析研究噪声声压频谱特性及声指向性规律。结果表明：80%及60%开度下的噪声声压级分别为49.14 dB(A)、50.79 dB(A),均小于60 d B(A)的噪声限制,满足使用要求。该文为船用三通调节阀噪声数值模拟提供了理论及方法参考。     

有限液态介质样品声衰减的实验室测试新方法

本文介绍了一种在实验室条件下利用声脉冲测定有限容量液态介质样品声衰减系数的测试方法。该方法根据声纳方程原理导出了与测试系统参数和声场参数无关的计算式，从而避开了对测试系统参数和声场参数的测量，采用截取未被边界散射干扰的直达声脉冲的部分信号进行频谱分析，消除了在有限样品情况下必然存在的边界散射干扰，同时采用多次统计平均的做法抑制了噪声干扰。     

Leak Detection of Gas Pipelines Based on Characteristics of Acoustic Leakage and Interfering Signals

When acoustic method is used in leak detection for natural gas pipelines, the external interferences including operation of compressor and valve, pipeline knocking, etc., should be distinguished with acoustic leakage signals to improve the accuracy and reduce false alarms. In this paper, the technologies of extracting characteristics of acoustic signals were summarized. The acoustic leakage signals and interfering signals were measured by experiments and the characteristics of time-domain, frequency-domain and time-frequency domain were extracted. The main characteristics of time-domain are mean value, root mean square value, kurtosis, skewness and correlation function, etc. The features in frequency domain were obtained by frequency spectrum analysis and power spectrum density, while time-frequency analysis was accomplished by short time Fourier transform. The results show that the external interferences can be removed effectively by the characteristics of time domain, frequency domain and time-frequency domain. It can be drawn that the acoustic leak detection method can be applied to natural gas pipelines and the characteristics can help reduce false alarms and missing alarms.     

Broadband sound generation by confined pulsating jets in a mechanical model of the human larynx

Experiments were performed to study the production of broadband sound in confined pulsating jets through orifices with a time-varying area. The goal was to better understand broadband sound generation at the human glottis during voicing. The broadband component was extracted from measured sound signals by the elimination of the periodic component through ensemble averaging. Comparisons were made between the probability density functions of the broadband sound in pulsating jets and of comparable stationary jets. The results indicate that the quasi-steady approximation may be valid for the broadband component when the turbulence is well established and the turbulence kinetic energy is comparatively large. A wavelet analysis of the broadband sound showed that random sound production was modulated at the driving frequency. Two distinct sound production peaks were observed during one cycle, presumably associated firstly with jet formation and secondly with flow deceleration during orifice closing. Most high-frequency sound was produced during the closing phase. Deviations from quasi-steady behavior were observed. As the driving frequency increased, sound production during the opening phase was reduced, possibly due to the shorter time available for turbulence to develop. These results may be useful for better quality voice synthesis.     

Review of LDA and PIV applied to the measurement of sound and acoustic streaming

A review of laser Doppler anemometry (LDA) and particle image velocimetry (PIV) with their application to the measurement of sound is presented. The fundamental principles behind LDA and PIV are discussed and extended to the application of sound measurement. Special attention is paid to analysis of LDA signals including the Hilbert transform, which enables amplitude information to be obtained about various frequency components of a signal and wavelet analysis, which allows non-stationary signals to be accurately analysed. The influence of the refractive index variations in a medium due to a sound wave on the laser beams of an LDA signal is discussed. Attention is also paid to acoustic streaming which arises due to high-intensity sound, and PIV results are presented to demonstrate the effect.     

The design and evaluation of an auditory way-finding system in a train station

Previous studies have shown that auditory cues contribute to the identification of several components of a public space such as the volume, but also the type of activity to which the space is dedicated. This paper demonstrates that solutions to improve way-finding in a public place can be based on providing additional auditory information. A methodical approach in three phases is proposed and applied in the case of a train station. First, problems encountered by travellers in a train station are identified by way of an ergonomic study under real conditions with recruited travellers. The results reveal three kinds of problems: orientation errors, lack of confirmation of direction, and lack of information about the remaining distance to be covered. In the second phase, functional and environmental specifications were developed in order to create sound signals for each identified problem. A sound designer proposed several non-speech sound signals based on two schemas: a pair of sounds for the orientation and confirmation functions, and a timeline sequence for the remaining distance. Finally, in the third phase, the sound signals were installed in the train station using an experimental broadcasting system and were evaluated in a second ergonomic study using the same method. The results show that the number of orientation errors decreased and that participants felt more confident during their walk. Sound signals for the orientation and confirmation functions were understood and used by the participants. However, the timeline sequence signalling remaining distance was not understood.     

Experimental evidence of a zonal magnetic field in a toroidal plasma

A zonal magnetic field is found in a toroidal plasma. The magnetic field has a symmetric bandlike structure, which is uniform in the toroidal and poloidal directions and varies radially with a finite wavelength of mesoscale, which is analogous to zonal flows. A time-dependent bicoherence analysis reveals that the magnetic field should be generated by the background plasma turbulence. The discovery is classified as a new kind of phenomenon of structured magnetic field generation, giving insight into phenomena such as dipole field generation in rotational planets.     

Nonlinear behavior of vocal fold vibration: The role of coupling between the vocal folds

Coupling between the vocal folds is one of the nonlinear mechanisms allowing regulation and synchronization of mucosal vibration. The purpose of this study was to establish that modulations such as diplophonia and abnormalities observed in vocal signals that may be observed in some cases of laryngeal pathology can be considered as nonlinear behavior due to the persistence of some physical interaction (coupling). An experimental model using excised porcine larynx was designed to create tension asymmetry between the vocal folds and to obtain vocal signals with modulations. Signals were analyzed by spectral analysis and the phase portrait method. Results were compared with computer-generated synthetic signals corresponding to nonlinear combinations of sinusoid signals. Under these conditions, evidence of nonlinear behavior was detected in 85% of experimental signals. These findings were interpreted as a demonstration of vocal fold interaction. Based on these findings, the authors conclude that (1) coupling must be taken into account in physical models of laryngeal physiology, and that (2) methods of nonlinear dynamics may be used for objective voice analysis.     

Study on the effect of sound duration on the annoyance of helicopter noise by applying a technique of time compression and expansion of sound signals

The number of helicopter operations has rapidly increased during the last 20 years in Japan. Helicopter noise sounds different from other aircraft; the waveform of the sound pressure is impulsive and the signal duration is relatively long. The Environmental Agency of Japan implemented new guidelines for evaluating noise exposure around small airports, including heliports, in 1990. This study was executed in connection with the development of provisional guidelines. Psychoacoustic experiments were carried out to identify an evaluation index for helicopter noise. In order to examine the effect of duration independently, we not only used original sound recordings, but also synthesized sound signals. The durations of these sound signals were time compressed or expanded without degrading the quality of the original sound recording. The test results show that the effect of duration is significant, and that the A-weighted sound exposure level is a better index than the maximum A-weighted sound pressure level for the evaluation of helicopter noise.     

基于声音的跟踪摄像的初步研究

仿照生物的趋声性,可以实现摄像头追踪拍摄一个不在其视场范围内的声源;依据图像处理技术,可以精确定位在摄像头视场内的声源。将这两种技术结合起来,建立了一套实验系统。从利用声源发出的声音信号传输到两个分开一定距离的声音探测器上的时间差初步定位声源,再利用声源的运动规律使用图像处理技术识别并精确定位声源,通过系统与PC机间的实时通信和回转部件带动声音探测器和摄像头一起做精确灵活的转动,摄像头最终对准了声源。实现了基于声音的跟踪摄像过程。