固体介质中超声应力场的定量测量*

回顾了基于动态光弹技术的超声应力测量方法,分析了各方法的优缺点。优化了现有光弹系统的前端光路,提出了电控旋转偏振和自动判读技术,研制了高稳定性的动态光弹实验系统。利用Senarmont补偿法实现了高精度的应力测量。多次重复测量结果表明,该系统测量结果的相对标准偏差小于1%。光弹测量数据与电测结果相比,其相似系数为99.95%,显著性水平小于0.001,证明了测量结果的可靠性。     

中国声学学会成功获得2021年国际超声大会(ICU)的会议举办权

中国声学学会成功获得2021年国际超声大会（ICU）的会议举办权     

光纤光栅法布里-珀罗腔的腔、栅边缘特性分析

把组成光纤光栅法布里-珀罗腔的两个光纤光栅的初相位纳入了讨论范围,用耦合波方程推导了任意初相位下光纤光栅法布里-珀罗腔的透射和反射率的表达式.其中的相位因子包含了由光传播常数调制的腔长、光纤光栅的相位突变、光纤光栅仞相位和由光纤光栅空间频率涮制的光栅长度等四部分.分析了光纤光栅初相、由光栅空间频率调制的光栅长度两个因子对反射谱的影响,并提出了一种把光纤光栅法布里-珀罗腔等效为理想法布里-珀罗腔的方法.     

Unstable Manifolds of Euler Equations

We consider a steady state v₀ of the Euler equation in a fixed bounded domain in ?ⁿ. Suppose the linearized Euler equation has an exponential dichotomy of unstable and center‐stable subspaces. By rewriting the Euler equation as an ODE on an infinite‐dimensional manifold of volume‐preserving maps in W^{k, q} the unstable (and stable) manifolds of v₀ are constructed under a certain spectral gap condition that is satisfied for both two‐dimensional and three‐dimensional examples. In particular, when the unstable subspace is finite dimensional, this implies the nonlinear instability of v₀ in the sense that arbitrarily small W^{k, q} perturbations can lead to L² growth of the nonlinear solutions. © 2013 Wiley Periodicals, Inc.     

Small BGK Waves and Nonlinear Landau Damping

Consider a 1D Vlasov-poisson system with a fixed ion background and periodic condition on the space variable. First, we show that for general homogeneous equilibria, within any small neighborhood in the Sobolev space ${W^{s,p}\left( p >1 ,s <1 +\frac{1}{p}\right)}${W^{s,p}\left( p >1 ,s <1 +\frac{1}{p}\right)} of the steady distribution function, there exist nontrivial travelling wave solutions (BGK waves) with arbitrary minimal period and traveling speed. This implies that nonlinear Landau damping is not true in W^s,p( s < 1 +\frac1p){W^{s,p}\left( s <1 +\frac{1}{p}\right)} space for any homogeneous equilibria and any spatial period. Indeed, in a W^s,p(s < 1 +\frac1p){W^{s,p}\left(s <1 +\frac{1}{p}\right)} neighborhood of any homogeneous state, the long time dynamics is very rich, including travelling BGK waves, unstable homogeneous states and their possible invariant manifolds. Second, it is shown that for homogeneous equilibria satisfying Penrose’s linear stability condition, there exist no nontrivial travelling BGK waves and unstable homogeneous states in some ${W^{s,p}\left( p >1 ,s >1 +\frac{1}{p}\right)}${W^{s,p}\left( p >1 ,s >1 +\frac{1}{p}\right)} neighborhood. Furthermore, when p = 2, we prove that there exist no nontrivial invariant structures in the ${H^{s}\left( s > \frac{3}{2}\right) }${H^{s}\left( s > \frac{3}{2}\right) } neighborhood of stable homogeneous states. These results suggest the long time dynamics in the ${W^{s,p}\left( s >1 +\frac{1}{p}\right) }${W^{s,p}\left( s >1 +\frac{1}{p}\right) } and particularly, in the ${H^{s}\left( s > \frac{3}{2}\right) }${H^{s}\left( s > \frac{3}{2}\right) } neighborhoods of a stable homogeneous state might be relatively simple. We also demonstrate that linear damping holds for initial perturbations in very rough spaces, for a linearly stable homogeneous state. This suggests that the contrasting dynamics in W ^{s, p} spaces with the critical power s=1+\frac1p{s=1+\frac{1}{p}} is a truly nonlinear phenomena which can not be traced back to the linear level.     

粘接件拉伸强度的超声检测实验研究

利用RAM-5000 SNAP超声测试系统,在水池中对穿透环氧树脂粘接件的超声信号的基频波和二次谐波进行测量,二者振幅的重复测量误差分别在1%和3%以下,实验具有较好的可重复性.利用反向传播人工神经网络算法,将穿透样品的超声波的基频波振幅、二次谐波振幅、粘接前样品表面的粗糙度作为输入参量,粘接件的拉伸强度作为输出参量进...     

2014年度全国检测声学会议在北京成功召开

2014年度全国检测声学会议在北京成功召开     

Phase diagram of androsterol-dipalmitoylphosphatidylcholine mixtures dispersed in excess water

The effect of androsterol, whose structure resembles that of cholesterol but without the alkyl side chain, on the phase behavior of aqueous dispersions of dipalmitoylphosphatidylcholine has been studied to understand the role of the side chain played in the formation of ordered phases of the type observed in membrane rafts. Thermotropic changes in the structure of mixed dispersions and transition enthalpies have been examined by synchrotron X-ray diffraction, Fourier transform infrared spectroscopy, and differential scanning calorimetry. From these results a partial phase diagram of the binary system has been constructed. The three-phase line is determined to be 34.5 degrees C, which is 3-5 degrees C lower than that observed in binary mixtures of cholesterol, ergosterol, or stigmasterol with dipalmitoylphosphatidylcholine. The proportions of androsterol in mixtures representing the "left end point" and "right end point" of the three-phase line are 11.1 and 30.9 mol %, respectively. These proportions are greater than that seen in phase diagrams of other sterols codispersed with dipalmitoylphosphatidylcholine. We conclude that androsterol is less effective in promoting the formation of an ordered phase, and furthermore, this ordered phase is less compact than the normal lamellar liquid-ordered phase.     

Erosion resistance of bionic functional surfaces inspired from desert scorpions

In this paper, a bionic method is presented to improve the erosion resistance of machine components. Desert scorpion (Androctonus australis) is a typical animal living in sandy deserts, and may face erosive action of blowing sand at a high speed. Based on the idea of bionics and biologic experimental techniques, the mechanisms of the sand erosion resistance of desert scorpion were investigated. Results showed that the desert scorpions used special microtextures such as bumps and grooves to construct the functional surfaces to achieve the erosion resistance. In order to understand the erosion resistance mechanisms of such functional surfaces, the combination of computational and experimental research were carried out in this paper. The Computational Fluid Dynamics (CFD) method was applied to predict the erosion performance of the bionic functional surfaces. The result demonstrated that the microtextured surfaces exhibited better erosion resistance than the smooth surfaces. The further erosion tests indicated that the groove surfaces exhibited better erosion performance at 30° injection angle. In order to determine the effect of the groove dimensions on the erosion resistance, regression analysis of orthogonal multinomials was also performed under a certain erosion condition, and the regression equation between the erosion rate and groove distance, width, and height was established.