含气泡液体中声传播的解析解及其强非线性声特性

声波在含气泡的液体中传播时,气泡的受迫振动会引起强的声散射,并且由于振动的非线性,使得气泡产生的次级波不仅含有基频成分,而且还会有高次谐波。本文从理论上描述了气泡个数随尺并给出了含气泡液体的等效非线性声参数Ｂ／Ａ的计算公式理论与已有的实验观测符合较好,文中对含气泡水的声速和声衰减等特性也进行了讨论。     

非线性(声)参数及其在超声成像中的应用

本文系统地介绍了声学中的非线性参数研究工作的现状和应用前景,特别着重介绍它在超声医学成像中的应用。     

多参量光声成像及其在生物医学领域的应用

光声成像兼具声学成像和光学成像两者的优点, 因而成为近十年来发展最迅速的生物医学成像技术之一. 本文介绍了光声成像的特点及其相对于广泛应用的光学成像技术和声学成像技术的优点; 其次, 解释了光声成像的成像原理, 在此基础上介绍了光声断层成像和光声显微镜这两种典型的光声成像方案, 并介绍了它们的技术特点; 然后, 介绍了光声成像对生物组织的生化特性、组织力学特性、血液流速分布、温度分布参数、微结构特性等多信息参量的提取能力, 及其在生物系统的结构成像、功能成像、代谢成像、分子成像、基因成像等多领域的应用; 最后, 展望了光声成像在生物医学领域的应用潜力并讨论了其局限性.     

微小缺陷的非线性超声检测及其成像技术

采用通用超声检测设备并结合高通滤波技术获取了非线性超声的高次谐波信号,并将其用于薄板点焊焊核的微小缺陷检测及焊核的超声C扫描成像中。较之传统超声检测方法,采用非线性高次谐波检测薄板点焊焊核缺陷具有更高的时域分辨率及缺陷敏感度,能够更加准确的确定内部缺陷的位置及尺寸。此外,本研究还采用非线性高次谐波对薄板焊核进行超声成像分析,获得了清晰准确的焊核结构图像。非线性超声检测技术具有更高的检测效力,能够显著拓展检测系统的检测能力。     

多元高斯声束衍射修正下液体非线性系数检测方法

有效检测材料的非线性系数β是非线性超声评价材料力学性能及早期疲劳损伤等的前提和关键,针对当前的有限幅值法仅适用于有限孔径探头近场测量的现状,本论文研究了一种不受检测距离影响的测量方法。为抑制实际检测过程中声能的损失和声场扩散对测量结果的影响,对基波和二次谐波检测值进行衍射和衰减修正,其中利用多元高斯声束精确计算二次谐波衍射系数,在此基础上计算非线性系数β以消除其与理想的平面波推导结果间的差异,提高不同距离下测量值的精度。针对水的非线性系数β进行了仿真分析和实验验证,结果均显示本文方法相比于传统有限幅值法具有明显的精度优势,且表明该方法测量材料的β不受检测距离的影响,为放宽非线性超声检测的应用条件提供了理论依据。     

脉冲压缩在双光子荧光显微成像中的应用研究

本刊讯自20世纪90年代末,双光子荧光显微成像技术已经逐步成为利用光学手段研究生物组织和细胞的重要工具。由于双光子激发属于非线性光学过程,     

The influence of molecular structure of protein on the acoustic nonlinearity parameter B/A

I.IntroductionAcousticnonlinearityparameterB/Adescrjbesthenonlilleareffectsofasoundwavetrav-ellingthroughamedium.Withtheapplicationofhighmowerultrasonicwavetomedicine,thenonlineareffectsbecomemoreandmoreimportant.EspeciallybecauseB/Aissensitivetothepathologicalstateofbiologicaltissues[1-2])thisprovidesprospectiveapplicationinmedicaldiagnosis.Atpresent,thestudyinthisareaemphasizesontwoaspects.OneistodevelopnewmedicalimagingtechniquesbyusingthisnonlinearityparameterB/Al1'3-'];theotheristostu…     

Enhancement of Kerr nonlinearity and its application to entangled state discrimination

In this paper, the recent research on the enhanced Kerr nonlinearity and its application in entangled state discrimination is reported. Two kinds of dynamics, including interacting double dark resonances and spontaneously generated coherence, are presented to enhance the Kerr nonlinearity. The application of Kerr nonlinearity in quantum state discrimination is also discussed. An arbitrary Greenberger-Horne-Zeilinger state can be discriminated using two-photon polarization parity detection which resorts to cross-Kerr nonlinearity between a single-photon qubit and probe field. In addition, a scheme for Greenberger-Horne-Zeilinger state discrimination of matter qubits is also proposed using the dipole induced transparency in a cavity-dipole system.      

Relationship between the molecular constant,isothermal volume derivative of thermodynamic Grüneisen parameter,nonlinearity parameter and intermolecular forces in liquids

The isochoric temperature derivative of sound velocity, Beyer’s nonlinearity parameter, the isothermal volume derivatives of thermodynamic Grüneisen parameter and isochoric heat capacity and the repulsive exponent of intermolecular potential are shown to be related to the molecular constant representing the ratio of internal pressure to cohesive pressure of liquids. The calculated values are reasonably satisfactory and explain the experimental results on sound propagation data of liquids. The results have been used to develop further understanding of the significance of molecular constant, fractional free volume and repulsive exponent of intermolecular potential in describing various thermoacoustic and nonlinear properties and the anharmonic behaviour with regard to molecular order and intermolecular interactions in liquids.     

Synchronization of the time—varying parameter chaotic system and its application to secure communication

In this paper we propose and investigate the synchronization of a new chaotic model with time-varying parameters and apply it to improve the security of chaotic communication. In this model, the chaotic system is modulated by both the message and the varying parameters. The varying parameters distort the phase space so heavily that they prevent the carrier from being broken by nonlinear dynamic forecasting method. Theory and simulation experiments with speech signal communication indicate that the receiver can gain a perfect synchronization with the transmitter, and the intruder cannot break down this communication system. We also discuss the robustness of the new communication system.     

消声管道声学性能计算的二维等几何有限元方法及应用

将等几何有限元方法应用于消声管道的声学性能计算,使用二维等几何有限元方法求解管道截面的声学特征值,考虑了存在穿孔边界和吸声材料边界的情况,进而使用特征值计算消声管道的传递损失。对包覆式消声管道进行传递损失的计算,结果与二维有限元方法吻合较好.对圆形截面的特征值计算结果表明,在计算量相同的情况下,等几何有限元方法取得了比传统有限元方法更好的计算精度.在不同结构参数条件下对消声管道的声学性能进行计算,结果与三维数值方法吻合良好。方法能够在宽频范围内较好地预测消声管道的传递损失。     

虚拟式声显微镜及应用技术研究

本文描述一台虚拟式扫描声显微镜及应用技术研究，它的硬件特别简单，仅由一台带有超高速A/D卡和快脉冲收发卡的PC机和机械扫描系统组成，主要的功能均由软件完成，脉冲收发卡仅包括脉冲产生和高频放大器，A/D卡采用PCI总线，采样率1GSPS，数据传输率100MB/s，系统能采集并实时显示频率达百兆的未检波回波信号，采修订本以的信号经软件处理，可在屏幕上实时显示样品的A、B、C型幅度像或相位像，仪器利用信号处理技术提高信号的信噪比；进行特征提取，识别，该仪器在材料识别，电子、光电子器件和焊接质量检测等方面功能较强，具有广阔的开发应用前景。     

滨海公共空间声环境感知评价及影响因素*

滨海公共空间是滨海城市人居环境的重要组成部分,其声环境质量是影响公共空间环境体验的关键因素。本研究以青岛沿海岸线四类滨海公共空间（步道类、广场类、公园类、沙滩类）的声环境为对象,通过问卷调查和实地测量探索滨海公共空间声环境的特征、感知评价及其影响因素。结果表明：（1）滨海公共空间当前环境噪声水平基本不超过国家标准限值55dB(A) ,各类空间声环境客观特征显著不同：公园噪声水平最低,自然声源丰富;广场噪声水平最高,各种城市噪声较多;步道噪声水平较低,但受到交通噪声的影响;沙滩噪声水平较高,但以中低频的海浪声为主,比较稳定。（2）各类滨海公共空间的声源感知以自然声为主,但是广场的自然声源感知较少。此外,声环境的愉悦感评价普遍较高,但在事件感、吵闹度和总体满意度评价上具有显著差异：沙滩声环境总体评价最好,其次是公园,广场和步道的声环境则亟待改善。（3）交通噪声和最大声级Lmax对声环境的负面影响最为显著,此外受访者年龄也是影响滨海公共空间声环境感知评价的关键因素。研究结论可以为滨海公共空间声环境的优化设计提供理论依据。     

A transmit/receive volume strip array and its mode mixing theory in MRI

MRI is increasingly moving towards higher magnetic field, prompting the need for multi-port transmit/receive RF coil arrays to overcome high-frequency limitations such as penetration depth and dielectric resonance effects. In this work, an arbitrary n-element transmit/receive volume strip array (VSA) and an associated mixing mode theory are described to understand the behavior of a multiple-port cyclic symmetrical VSA in both the physical port space and the complementary mode space; the relations between the two spaces are explicitly formulated. The advantage of mode-space analysis is that an arbitrary n x n impedance matrix which describes any VSA in port space can be diagonalized to a diagonal n x n matrix; thus an analytical solution of Kirchhoff's laws for the VSA becomes manageable when n is large. Based on such an analytical solution, we can (a) generate excitation profile of any desired mixed mode during transmission by manipulating external power sources without the need of physically tuning VSA to the mixed mode; (b) identify the sensitivity profiles of the complementary mode distributions during reception, which were unknown in quadrature and decoupled coils. Many predictions are rigidly verified by extensive test measurements from network analyzer and by MR imaging experiments.