On the linearization of operators related to the full waveform inversion in seismology

In this work, we analyze the parameter‐to‐solution map of the acoustic wave equation with respect to its parameters wave speed and mass density. This map is a mathematical model for the seismic inverse problem where one wants to recover the parameters from measurements of the acoustic potential. We show its complete continuity and Fréchet differentiability. To this end, we provide necessary existence, stability, and regularity results. Moreover, we discuss various implications of our findings on the inverse problem and comment on the Born series. Copyright © 2013 John Wiley & Sons, Ltd.     

Research Progress and Development Trends of Acoustic Metamaterials

Acoustic metamaterials are materials with artificially designed structures, which have characteristics that surpass the behavior of natural materials, such as negative refraction, anomalous Doppler effect, plane focusing, etc. This article mainly introduces and summarizes the related research progress of acoustic metamaterials in the past two decades, focusing on meta-atomic acoustic metamaterials, metamolecular acoustic metamaterials, meta-atomic clusters and metamolecule cluster acoustic metamaterials. Finally, the research overview and development trend of acoustic metasurfaces are briefly introduced.     

声悬浮条件下扇谐振荡液滴的内部流动规律

采用激光片光源照明和高速摄影技术,并使用聚苯乙烯微球作为示踪颗粒,研究了声悬浮条件下二阶和三阶扇谐振荡液滴的内部流场.耦合Level Set方法和标记网格法数值求解了不可压两相流的Navier-Stokes方程,模拟了液滴的扇谐振荡过程中的形态演化及其内部流动状态.数值计算的流场与实验结果吻合很好.对液滴扇谐振荡过程中的内部流速分布进行定量分析,发现流速在液滴中心区域几乎为零并沿液滴自由表面方向逐渐增大.二阶和三阶扇谐振荡的内部流速沿径向分别呈线性和二次函数分布并与理论预测结果相一致.     

WSNs中节点协同声源定位协议研究

声源定位是无线传感器网络重要的应用领域之一.由于实际环境中的声源大部分是运动的,因此设计一种快速准确的声源定位协议是关键.文章研究了一种多传感器节点协同的声源定位协议,完整考虑了节点处理声音和射频信号的响应时间,分析了它们对该声源定位协议定位精度的影响,推导出声源定位边界性条件.实验结果表明该协议相对于现有的精确声源定...     

急斜特厚煤层动力学失稳现场声发射监测

急斜特厚煤层开采扰动区(Mining Disturbed Zone,MDZ)煤岩应力与变形规律复杂,采动影响下局部煤岩层滑移造成应力集中,使煤岩体产生"强烈"的动力学失稳与破坏.以大洪沟煤矿B3+6急斜特厚煤层综放开采为工程背景,通过现场声发射(acoustic emission,AE)监测,分析采动条件下煤岩介质动力学失稳及破坏规律,为制定解危对策提供科学依据.     

Application of SH surface acoustic waves for measuring the viscosity of liquids in function of pressure and temperature

Viscosity measurements were carried out on triolein at pressures from atmospheric up to 650 MPa and in the temperature range from 10 °C to 40 °C using ultrasonic measuring setup. Bleustein–Gulyaev SH surface acoustic waves waveguides were used as viscosity sensors. Additionally, pressure changes occurring during phase transition have been measured over the same temperature range. Application of ultrasonic SH surface acoustic waves in the liquid viscosity measurements at high pressure has many advantages. It enables viscosity measurement during phase transitions and in the high-pressure range where the classical viscosity measurement methods cannot operate. Measurements of phase transition kinetics and viscosity of liquids at high pressures and various temperatures (isotherms) is a novelty. The knowledge of changes in viscosity in function of pressure and temperature can help to obtain a deeper insight into thermodynamic properties of liquids.     

基于贝叶斯优化模型的涡轮增压4缸发动机故障诊断

为提高故障诊断方法的精度并减少评估时间,通过对涡轮增压4缸发动机的声信号分析,提出了一种新的发动机故障诊断方法。利用小波包变换（WPT）进行时频分析,并从小波包变换的高、低系数中提取统计特征;然后,利用提取的特征对标准分类模型、贝叶斯优化模型和主成分分析（PCA）结合贝叶斯优化模型进行分析比较。结果表明：与标准模型相比,后2个模型都具有更高的准确度、精密度、灵敏度、特异度和F1值（调和均值）;在相似的准确度水平下,PCA结合贝叶斯优化模型比贝叶斯优化模型减少了20%左右的总评估时间和19%的测试时间。PCA结合贝叶斯优化模型在降低计算复杂度和减少评估时间的同时保证了良好的精密度,可为发动机实时故障诊断提供参考。     

Investigation of cubic non-linearity-driven electrostatic structures in the presence of double spectral index distribution function

In this article, modified Korteweg-de Vries equation (which involves cubic non-linearity) was derived to study non-linear ion acoustic waves in a plasma in which electrons follow the double spectral index distribution function. The double spectral index distribution successfully apes the distribution functions that have been frequently observed in space plasmas. The spectral index r moulds the distribution function at low energy and by increasing its value, flatness of the distribution enhances. The spectral index r can also have negative values due to which distribution becomes spiky at low energies. The index q , on the other hand, controls the shape of the tail of distribution function. It has been shown that propagation of the solitary structures gets significantly altered by the choice of the double spectral indices, namely, r and q . A comparison was also made, using the parameters of the auroral zone, between the quadratic and cubic non-linearities-driven non-linear structures and it was shown that the solitary structures form on a much shorter scale for cubic non-linearity compared to their quadratic counterpart.     

Dynamical behaviour of non-linear quantum ion acoustic wave in weakly magnetized electron–positron–ion plasma

In order to investigate the propagation characteristics of linear and non-linear ion acoustic waves (IAWs) in electron–positron–ion quantum plasma in the presence of external weak magnetic field, we have used a quantum hydrodynamic model, and degenerate statistics for the electrons and positrons are taken into account. It is found that the linear dispersion relation of the IAW was modified by the externally applied magnetic field. By using the reductive perturbation technique, a gyration-modified Korteweg-de Vries equation is derived for finite amplitude non-linear IAWs. Time-dependent numerical simulation shows the formation of an oscillating tail in front of the ion acoustic solitons in the presence of a weak magnetic field. It is also seen that the amplitude and width of solitons and oscillating tails are affected by the relevant plasma parameters such as quantum diffraction, positron concentration, and magnetic field. We have performed our analysis by extending it to account for approximate soliton solution by asymptotic perturbation technique and non-linear analysis via a dynamical system approach. The analytical results show the distortion of the shape of the localized soliton with time, and the non-linear analysis confirms the generation of oscillating tails.     

Nonlinear ion acoustic waves in dissipative and dispersive magneto-rotating relativistic plasmas with two temperature superthermal electrons

A study has been presented for the nonlinear features of ion-acoustic (IA) shock waves in a magnetorotating plasma consisting of warm viscous streaming ions along with kappa-distributed electrons having two different temperatures. In this regard, we have employed the reductive perturbation technique to derive the Zakharov-Kuznetsov-Burgers (ZKB) equation that governs the dynamics of IA shock waves. The solution obtained by the hyperbolic tangent method has been shown to depend on various plasma parameters such as spectral index (κ_c), density fraction (f), effective rotation frequency (Ω_c), ion kinematic viscosity (η_o), and temperature ratio (σ). In the limiting case when dissipative coefficient D → 0 , we have also examined the solitary potential distributions, which are the solutions of Zakharov Kuznetsov (ZK) equation. It is found that both rarefactive and compressive structures exist for the system under consideration. The transition in the nature of such profiles is due to the enhancement in the density of cold electrons. The importance of present theoretical investigations has been carried out with regard to Saturn's magnetosphere, where two temperature superthermal electron populations have been observed by various satellite missions.