Second-harmonic generation in an infinite layered structure with nonlinear spring-type interfaces

The second-harmonic generation characteristics in the elastic wave propagation across an infinite layered structure consisting of identical linear elastic layers and nonlinear spring-type interlayer interfaces are analyzed theoretically. The interlayer interfaces are assumed to have identical linear interfacial stiffness but can have different quadratic nonlinearity parameters. Using a perturbation approach and the transfer-matrix method, an explicit analytical expression is derived for the second-harmonic amplitude when the layered structure is impinged by a monochromatic fundamental wave. The analysis shows that the second-harmonic generation behavior depends significantly on the fundamental frequency reflecting the band structure of the layered structure. Two special cases are discussed in order to demonstrate such dependence, i.e., the second-harmonic generation by a single nonlinear interface as well as by multiple consecutive nonlinear interfaces. In particular, when the second-harmonic generation occurs at multiple consecutive nonlinear interfaces, the cumulative growth of the second-harmonic amplitude with distance is only expected in certain frequency ranges where the fundamental as well as the double frequencies belong to the pass bands of the layered structure. Furthermore, a remarkable increase of the second-harmonic amplitude is found near the terminating edge of pass bands. Approximate expressions for the low-frequency range are also obtained, which show the cumulative growth of the second-harmonic amplitude with quadratic frequency dependence.     

Generation of acoustic solitary waves in a lattice of Helmholtz resonators

This paper addresses the propagation of high amplitude acoustic pulses through a 1D lattice of Helmholtz resonators connected to a waveguide. Based on the model proposed by Sugimoto (1992), a new numerical method is developed to take into account both the nonlinear wave propagation and the different mechanisms of dissipation: the volume attenuation, the linear viscothermal losses at the walls, and the nonlinear absorption due to the acoustic jet formation in the resonator necks. Good agreement between numerical and experimental results is obtained, highlighting the crucial role of the nonlinear losses. Different kinds of solitary waves are observed experimentally with characteristics depending on the dispersion properties of the lattice.     

Quantitative assessment of voice quality following laser surgery for reinke''s edema

Although laser surgery has been widely advocated for use in the treatment of vocal fold papilloma because it does not incur bleeding, it has been questioned for use in treating Reinke's edema due to the possibility of heat dispersion to normal surrounding tissue and of scarring. We present a series of 8 cases in which laser surgery was the method of treatment for bilateral Reinke's edema. In each case, voice therapy was selected as the initial treatment; laser surgery was performed following voice therapy. Prior to and following surgery, videostroboscopic examinations were performed on the subjects. Only 4 subjects were available for assessment at the 1-month postoperative period. From the audio track of the videotape, the speaking fundamental frequency, perturbation measures for the vowel /i/, and noise-to-harmonic ratio of a completely voiced sentence were obtained. From the videostroboscopic recordings, the symmetry of the vocal folds, the presence or absence of the mucosal wave and the glottic closure pattern, prior to and after surgery, were judged independently by 3 examiners. The fundamental frequencies approximated the normal male and female ranges for those subjects seen 1 month after surgery. In addition, the noise-to-harmonic ratio and the relative average perturbation improved. Stroboscopy revealed irregularities in the symmetry of vocal folds, mucosal wave, and glottic closure 1 month after surgery.     

小型矢量阵深海被动定位方法

文中提出一种适用于深海条件下并已知各项有关环境参数时,利用七元小型矢量立体阵,借助测定目标辐射噪声由不同途径自声源到达接收点的天顶角及方位角的结果,依据射线声学方法求得目标方位、距离和所在深度的被动定位方法。给出了矢量阵依多极子原理进行波束形成的计算公式,并就一种简单水文模型,给出解析计算公式。     

Direct regressions for underwater acoustic source localization in fluctuating oceans

In this paper, we show the potential of machine learning regarding the task of underwater source localization through a fluctuating ocean. Underwater source localization is classically addressed under the angle of inversion techniques. However, because an inversion scheme is necessarily based on the knowledge of the environmental parameters, it may be not well adapted to a random and fluctuating underwater channel. Conversely, machine learning only requires using a training database, the environmental characteristics underlying the regression models. This makes machine learning adapted to fluctuating channels. In this paper, we propose to use non linear regressions for source localization in fluctuating oceans. The kernel regression as well as the local linear regression are compared to typical inversion techniques, namely Matched Field Beamforming and the algorithm MUSIC. Our experiments use both real tank-based and simulated data, introduced in the works of Real et al. Based on Monte Carlo iterations, we show that the machine learning approaches may outperform the inversion techniques.     

油膜覆盖的非线性海面电磁散射多普勒谱特性研究

当海面上方漂浮油膜时,海面的毛细波成分将因油膜的阻尼作用而被破坏.本文采用PM谱,基于Marangoni阻尼效应,建立油膜覆盖的一维Creamer非线性海面模型,并简单分析了油膜的阻尼作用对海面轮廓的影响.在此基础上,利用迭代物理光学方法研究了L波段下该模型的后向散射回波的多普勒谱特性,通过与基于线性模型的海面散射回波多普勒谱对比发现,在大中入射角下,非线性海面散射回波与线性海面多普勒谱的差异不可忽略,说明采用Creamer非线性理论建立海面几何模型的必要性.研究发现,油膜覆盖海面的散射回波的多普勒频移及展宽与干净海面雷达回波的多普勒特性具有明显差异,这表明海面上漂浮的油膜对雷达散射回波的多普勒特性具有显著的影响.数值结果重点分析了入射角、油膜参数以及风速对油膜覆盖海面散射回波多普勒谱展宽和频移的影响规律.     

声学Burton-Miller方程边界元法GPU并行计算

基于GPU,对声学Burton-Miller积分方程的边界元解法进行并行计算.提出并行计算格式和程序实现方法,以及Burton-Miller方程中各类奇异(包括强奇异、超奇异)积分的GPU计算和局部修正方法.典型算例结果表明,在特征频率处可获得正确的解,具有较高精度,可在普通个人计算机上快速完成自由度超过2×10⁵的声学边界元分析.为计算声学及相关工程领域的中、大规模声场分析问题提供一种快速、高效、简便的数值计算工具.     

The relation between spatial impression and the law of the first wavefront

In the field of room acoustics, it is popular belief that the early and late reflections contribute to auditory source width (ASW) and listener envelopment (LEV), respectively. However, some papers have demonstrated results not necessarily in agreement with the belief. In this paper, a hypothesis is proposed to clarify the essentials of ASW and LEV from point of view of the auditory phenomenon. The hypothesis is that the components of reflections under and beyond the upper limit of validity for the law of the first wavefront contribute to ASW and LEV, respectively. Two experiments were performed to evaluate the hypothesis. In the first experiment, the results showed directly that the components of reflections under the upper limit of validity for the law contribute to ASW. In the second experiment, four kinds of threshold were measured to evaluate the relation between the effect and LEV: image-splitting which corresponds to the upper limit of validity for the law, LEV, reverberation perception, and reverberation disturbance. The results showed that the threshold of image-splitting coincides with the that of LEV. This suggests that the components of reflections beyond the upper limit of validity for the law contribute to LEV. In conclusion, it seems that the results of experiments shown in this paper favor the hypothesis.     

The mechanism of the attracting acoustic radiation force on a polymer-coated gold sphere in plane progressive waves

Acoustic plane progressive waves incident on a sphere immersed in a nonviscous fluid exert a steady force acting along the direction of wave motion. It is shown here that when an elastic gold sphere is coated with a polymer-type (polyethylene) viscoelastic layer, this force becomes a force of attraction in the long wavelength limit. Kinetic, potential and Reynolds stress energy densities are defined and evaluated with and in the absence of absorption in the layer. Without absorption, the mechanical energy density counteracts the Reynolds stress energy density, which causes a repulsive force. However, in the case of absorption, the attractive force is predicted to be a physical consequence of a mutual contribution of both the mechanical and the Reynolds stress energy densities. This condition provides an impetus for further designing acoustic tweezers operating with plane progressive waves as well as fabricating polymer-coated gold particles for specific biophysical and biomedical applications.     

基于生物光学算法的海洋赤潮监测

机载海洋激光雷达具有高效搜索的能力,已成为海洋环境监测的重要手段。以机载蓝绿激光雷达监测海洋赤潮为研究应用背景,通过检测海洋中叶绿素的质量浓度来实现对海洋赤潮消长信息的获取。在分析海水固有光学性质的基础上,基于生物光学算法,构建了机载蓝绿激光雷达后向散射信号检测的的叶绿素质量浓度监测模型。仿真计算证明该模型能够有效探测出叶绿素质量浓度的大小,为机载海洋赤潮监测增加了一种方法。