层状粘接结构超声检测信号的同态解卷积脱粘界面定征

本文利用建立的多层粘接结构超声无损检测信号的卷积模型,推导出了检测信号的解析表达式,并用同态滤波解卷积方法有效地提取出粘接结构的系统响应,进而由其中界面多次反射响应的位置、幅度和包络等特征参数,实现了脱粘二界面（指空气脱粘）的定征和识别。仿真和实验数据的处理结果表明本文方法对脱粘检测的应用有积极的意义。     

多层粘接结构中脱粘界面的人工神经网络余弦变换谱特征识别

针对钢－橡胶多层粘接结构中界面脱粘的超声检测难题,利用余弦变换（ＤＣＴ）提取的表征检测信号的模式特征矢量,通过人工神经网络模式识别方法对不同界面脱粘时实验检测信号的正确识别,实现了脱粘一、二、三和四界面的检测。本文脱粘界面信号模式的人工神经网络识别系统对现代工业中ＮＤＴ＆ＮＤＥ的自动化有着积极的意义。     

电磁声实验平台的研制与实验研究

研制了一个多功能的电磁声实验平台,在此实验平台,进行了"减小盲区"、"钢层下多层橡胶层脱粘检测"、"线性调频脉冲压缩"等方面的实验研究。实验结果表明,该平台可精确控制实验参数,提供单一频率脉冲串和线性调频脉冲两种激励波形,具有信噪比高盲区小的优点和线性调频脉冲压缩的功能。将该实验平台应用在钢层与多层橡胶层粘接件的脱粘检测,取得了与压电检测相当的结果。作为一个电磁声方法和技术研究的工具,该实验平台对开展电磁声检测方法和技术研究以及实际检测应用都是有意义的。      

钢-混凝土结构弱粘接界面缺陷的超声导波检测*

钢-混凝土结构是土木工程中的一种常用结构形式,钢与混凝土粘接处可能出现弱粘接甚至完全脱粘的缺陷,严重影响结构的安全性。该文提出利用空气耦合超声导波衰减的方法实现钢-混凝土结构粘接状态的非接触无损检测方法,分析不同厚度粘接界面对超声导波衰减的影响。基于全局矩阵技术对钢-混凝土结构求解理论频散方程和衰减曲线,得到界面层不同粘接条件下的理论参数及衰减特性。建立不同粘接条件的有限元模型,定量分析不同模态对粘接缺陷的检测敏感度。研究界面层厚度分别为1 mm和2 mm两种情况下S0能量的衰减情况。研究结果表明:S0模态可有效判断粘接结构的粘接状态,对于同一界面层厚度,随着界面粘接条件变弱,S0最大幅值与A0最大幅值比不断增大;不同厚度同一粘接条件下,2 mm相较于1 mm该值更大。该方法在钢-混凝土结构粘接界面缺陷的检测方面具有良好的应用价值和发展前景。     

电磁超声界面回波瞬时图谱分析与神经网络识别

针对钢板背后多层橡胶粘接结构,选择较佳实验频率值作为电磁声换能器的激励源频率。提取了检测回波的瞬时振幅、瞬时相位和瞬时频率三种瞬时参数,将瞬时参数构成三维瞬时图谱定性识别不同粘接状态。将敏感时间窗内的平均瞬时参数组成特征向量,利用BP神经网络进行识别,对训练集与测试集的识别结果表明,该方法可以实现电磁超声界面回波的自动识别与分类,识别正确率不低于95%。     

电磁超声多界面检测信号去噪方法研究

为了解决传统压电超声换能器检测方式耦合不稳定的问题,将电磁超声应用于多层粘接结构界面检测。针对电磁超声界面检测信号噪声高和盲区大的问题,在电磁声换能原理和盲区成因分析的基础上,用小波阈值滤波和自适应抵消滤波方法对检测信号进行了处理,达到了降低信号噪声和减小盲区的目的。对钢板和双层橡胶粘接样品的回波信号处理结果表明:小波阈值滤波将信噪比提高了约12 dB,自适应抵消滤波有效地减小了由感生信号产生的盲区。     

基于THz-TDS的陶瓷纤维复合材料缺陷检测分析

新型陶瓷纤维复合材料由短切氧化硅纤维及其胶合物经高温烧结得到的一种轻质多孔材料,材料微观结构特性直接影响着宏观结构特性和功能特性。该类材料的孔隙度分布在84%~95%之间,微观孔径主要集中在100 μm范围内,偶尔有少量纳米孔。陶瓷纤维复合材料以其耐高温、低密度、高比强和抗烧蚀等优异性能在超高声速飞行器外层隔热部件得到应用,但该类材料可能因为制作和装配的工艺水平等因素出现夹杂、孔洞甚至大面积脱粘等现象。由于陶瓷纤维复合材料结构与应用场景的特殊性使得常规的无损检测手段效果不佳,而太赫兹(THz)技术作为一种新兴的无损检测技术,在该类材料的无损检测具有很大的潜力,可与常规检测技术形成互补。针对陶瓷纤维复合材料构件粘接层缺陷检测问题,研究了太赫兹时域信号和太赫兹层析成像方式对缺陷定位方法。基于太赫兹时域光谱(THz-TDS)无损检测技术获取和对比试样中有粘接层缺陷和粘接层完好位置的时域波形的波形峰值和相位差异,并经过反卷积滤波技术对时域波形进行处理,定性分析时域波形与粘接层缺陷特性的关系,宏观判断缺陷存在;通过对太赫兹波段陶瓷纤维复合材料光学参数提取测定太赫兹波段的平均折射率为1.028,进而分析粘接层缺陷的深度和厚度分别为18.4和0.28 mm,与预置缺陷真实深度和厚度相比准确度分别为92%和90%。但由于通过时域信号提取的平均折射率会给粘接层缺陷位置分析造成误差,因此以太赫兹层析成像方式进一步估计缺陷的位置,分析了太赫兹层析成像噪声来源以及对成像质量的影响并采用了双边滤波对层析成像降噪滤波,基于太赫兹层析成像技术建立了位置评估模型,获取了粘接层缺陷的厚度为0.26 mm,较预置缺陷厚度的准确度为96%,有效地完善了太赫兹检测技术对缺陷定位的形式,实现了陶瓷纤维复合材料构件的粘接层缺陷的高精度定位表征。     

脱粘界面超声检测信号的小波多分辨率分析与重构

针对钢－橡胶分层粘接结构的超声检测回波信号,利用小波变换的多分辨率时频特性提出了小波特征参数提取算法,据此在对检测信号进行的时间－尺度分布分析基础上,重构出脱粘界面回波信号的时域和频域特征。实验检测结果表明本文方法在现代工业ＮＤＴ＆Ｅ中的应用有着可喜的前景。     

接触缺陷的振动调制超声导波检测技术研究

针对常规线性超声检测方法无法实现板结构接触类缺陷(如微裂纹、脱粘等)检测问题,将超声导波技术与振动声调制技术相结合,利用稀疏分布传感器发展了一种板结构中接触缺陷非线性超声检测方法。通过低频振动改变缺陷的接触状况,使得通过接触面的高频导波信号的相位和幅值受到调制。对受低频振动调制的超声导波二维时间序列进行时频分析,由于接触类缺陷的存在,在振动调制超声导波序列的时频分布上出现明显的低频振动频率分量。利用提取出的低频振动频率下的超声导波信号,进行了结构接触缺陷成像处理。检测试验表明,基于振动声调制的超声导波缺陷成像方法可以实现结构中的接触类缺陷检测。      

玻璃纤维蜂窝复合材料的太赫兹无损检测技术(英文)

采用双高斯脉冲反卷积滤波技术对太赫兹时域波形进行滤波优化,提出一种基于太赫兹时域光谱无损检测的太赫兹反射式层析成像技术,用于分析玻璃纤维蜂窝复合材料的粘接质量.结合玻璃纤维蜂窝复合材料结构的特点,分别在蜂窝上层胶膜和下层胶膜中设计了不同直径的圆形和梯形脱粘缺陷,在此基础上,完成了脱粘缺陷蜂窝结构样品的制作.提出的太赫兹反射式层析成像和B-scan成像方法,适用于玻璃纤维蜂窝复合材料的脱粘缺陷分析.针对反射式层析成像图像对比度差的问题,结合脱粘缺陷处的太赫兹时域波形数据特征,采用缺陷特征时间区域成像优化技术,提高了脱粘缺陷的检测能力和识别准确率,实现了玻璃纤维蜂窝材料的上层脱粘厚度50μm、下层脱粘厚度50μm缺陷的太赫兹无损检测.     

Self-organization of five species in a cyclic competition game

Cyclic competition game models, particularly the “rock–paper–scissors” model, play important roles in exploring the problem of multi-species coexistence in spatially ecological systems. We propose an extended “rock–paper–scissors” game to model cyclic interactions among five species, and find that two of the five can coexistent when biodiversity disappears, which is different from the “rock–paper–scissors” game. As the number of fingers is five, we named the new model the “fingers” game, where the thumb, forefinger, middle finger, ring finger, and little finger cyclically dominate their subsequent species and are dominated by their former species. We investigate the “fingers” model in two ways: direct simulations and nonlinear partial differential equations. An important finding is that the number of species in a cyclic competition game has an influence on the emergence of biodiversity. To be specific, the “rock–paper–scissors” model is in favor of maintaining biodiversity in comparison with the “fingers” model when the variables (population size, reproduction rate, selection rate, and migration rate) are the same. It is also shown that the mobility and reproduction rate can promote or jeopardize biodiversity.     

Contrastive analysis on tone between Putonghua and Taiwan Mandarin

The differences of the pitch and duration of Chinese syllables between Putonghua （PTH） and Taiwan Mandarin （TM） were studied. The speech materials to be used are not only isolated syllables, but also sentences. The results reveal that： For the isolated syllables, T1 and T2 in TM are influenced by Minnan dialect, therefore their pitch are lower than those in PTH. T3 is fall-rise in PTH, while it is fall in TM. Moreover, the syllable duration sequence for different tone is T3〉T2〉T1〉T4 in PTH, while it is T1〉T2〉T3〉T4 in TM. For the syllables in sentences, T2 is mid-rise in PTH, while it is mid-level in TM. And the T3 is longer than T4 but shorter than T1 or T2 in PTH, while it is the shortest in TM. Furthermore the effects of prosodic phrase boundary on duration for different tones are almost the same in PTH, but the lengthening part of T1 or T2 is longer than that of T3 or T4 in TM.     

Experimental study on downstep in Chinese intonation

Downstep in pitch contour of Chinese Putonghua is examined using subtly designed sentences by controlling tone combinations. The results show both automatic and nonautomatic downstep phenomena exist in Chinese. In non-automatic downstep, low tones compress downwards the pitch range of the following syllables. and the main influence of downstep is on topline. Low tone not only lower the topline behind it, but also raise the high tones before it, the effects are compatible with each other. In automatic downstep, the topline of pitch contour in intonational phrase is presented as a linear downtrend, but it differs among speakers due to the effect of personal stress practice. In comparison with downstep phenomenon in other tone or non-tone languages, the downstep ratio in Chinese is not constant, and the domain of downstep is not limited within the adjacent tones.     

Abelian-Higgs phase of SU(2) QCD and glueball energy

It is shown that SU(2) QCD admits an dual Abelian-Higgs phase, with a Higgs vacuum of a type-Ⅱ superconductor. This is done by using a connection decomposition for the gluon field and the random-direction approximation. Using a bag picture with soft wall, we presented a calculational procedure for the glueball energy based on the recent proof for wall-vortices [Nucl. Phys. B 741(2006)1].     

Theoretical analysis and simulation of conjugate heights for dual-conjugate AO system in lidar

A multi-conjugate adaptive optics （MCAO） can offer a possibility of widening field of view （FOV） characterized by the isoplanatic angle, and the choose of conjugate height becomes a basic problem for MCAO, which influences the size of iosplanatic angle. Considering the application of lidar, the isoplanatic angle＇s expressions of two deformable mirrors （DMs） MCAO for uplink and downlink are deduced. The effects of conjugate heights for dual-conjugate AO are thoughtfully discussed, and the isoplanatic angles are further analyzed. The results show that the isopanatic angle varies with the conjugate height and reaches the maximum as the conjugate height is at the optimal altitude. Moreover, the optimal conjugate height changes with the propagation distance.     

Quick single-photon detector with many avalanche photo diodes working on the time division

Due to the limit of response speed of the present single-photon detector, the code rate is still too low to come into practical use for the present quantum key distribution (QKD) system.A new idea is put up to design a quick single-photon detector.This quick single-photon detector is composed of a multi-port optic-fiber splitter and many avalanche photo diodes (APDs).Au of the ports with APDs work on the time division and cooperate with a logic discriminating and deciding unit driven by the clock signal.The operation frequency lies on the number N of ports, and can reach N times of the conventional single-photon detector.The single-photon prompt detection can come true for high repetition-rate pulses.The applying of this detector will largely raise the code rate of the QKD, and boost the commercial use.     

Signal generation in an isotropic medium in scanning electron acoustic microscope

Based on the research in Ref. [5][Materials Science and Engineering, 1989; A122： 57 63], an improved model of heat source is set up, the different modes of Lamb wave in an isotropic sample generated by a chopped electron beam at frequency f are obtained with integral transform and normal function expansion method, and the output signal of PZT coupled at the back surface of the sample is found out. The generation mechanism of SEAM （Scanning Electron Acoustic Microscopy） signal is discussed. It shows that the SEAM is a near field imaging technique with high spatial resolution and its best lateral spatial resolution is about 2√2α （α is the radius of the focused electron beam）. Some of experimental results of SEAM images are presented in the paper and it shows that the spatial resolution of SEAM is better than 0.5 μm and smaller than the thermal diffusion length of the sample. Therefore the character of near field imaging in SEAM is also proved experimentally.     

High efficiency filtering using two-dimensional photonic crystal coupled cavity structures

Transmission spectra of coupled cavity structures (CCSs) in two-dimensional (2D) photonic crystals (PCs) are investigated using a coupled mode theory, and an optical filter based on CCS is proposed. The performance of the filter is investigated using finite-difference time-domain (FDTD) method, and the results show that within a very short coupling distance of about 3λ, where λ is the wavelength of signal in vacuum, the incident signals with different frequencies are separated into different channels with a contrast ratio of 20 dB. The advantages of this kind of filter are small size and easily tunable operation frequencies.