基于虚拟时间反转镜的垂直阵舰船辐射噪声级测量方法

研究了利用垂直阵测量舰船辐射噪声过程中因水声信道的多径效应对测量性能产生的影响,建立了基于声场模型的舰船辐射噪声测量的数学模型,推导了基于虚拟时间反转镜辐射噪声测量的理论公式,提出了一种基于虚拟时间反转镜技术的垂直阵舰船辐射噪声级测量方法。该方法首先采用基于波束积分的SCOOTER模型,根据海洋环境参数计算出辐射声源至测量水听器之间的信道传输函数,然后,用计算出的信道传输函数对接收信号做虚拟时反处理,以消除或减弱信道多径效应对接收信号的影响,从而提高舰船辐射噪声级测量精度。针对典型的浅海声信道,进行了计算机仿真试验。结果表明,该方法能有效地进行舰船宽带辐射噪声测量,当阵元个数满足一定要求时,测量得到的声源级与实际声源级相比,误差小于1 dB。      

一种水下三维被动定位技术

本文给出了一种三维被动定位方法。该方法利用三元水平阵和二元垂直阵实现对目标的三维定位。由三元水平阵首先求得目标斜距和目标方位,在此基础上利用垂直阵估计目标深度坐标,最后综合已有测量结果来求解目标水平坐标。本文还通过仿真分析了该方法的定位性能。     

虚拟时反镜在水声被动测距中的应用

水声信道多途干涉使被动测距产生偏差．接收信号的自相关输出波形含有信道冲激响应结构的信息，本文提出通过简化模型可估计出信道冲激响应，并将其时间反转构造一前置预处理器，可实现虚拟时间反转镜（VTRM）．虚拟时反镜可获得时间、空间上的自适应聚焦效果，克服多途干涉对被动测距的影响，并且实现简单，可实时对目标进行测距．通过计算机仿真研究，验证VTRM技术可匹配声信道，提高被动测距的精度．     

基于时间反转扩频的隐蔽水声通信方法

针对低信噪比条件下水下小尺度平台与通信浮标间进行隐蔽水声通信时,强多径干扰导致通信困难的问题,提出了一种基于时间反转技术的直接序列扩频隐蔽通信方法。该方法利用多通道主/被动时间反转的空时聚焦效应,提高了低信噪比条件下直接序列扩频通信的抗多径干扰能力,并且具有良好的低检测概率通信能力。仿真和水池实验结果表明:该方法满足水下小尺度平台处理结构简单、低功耗的要求,实现了水下单阵元平台与通信浮标之间的双向隐蔽通信。     

一种水平变化波导中匹配场定位的虚拟时反实现方法

在水平变化波导中,匹配场被动定位的计算量非常大,严重阻碍了其工程应用.本文提出了一种水平变化波导中匹配场定位的虚拟时反实现方法,其抛物方程模型计算网格总数远小于匹配场处理,从而大大减小计算代价.与匹配场处理不同,虚拟时反实现方法是一个利用介质互易性和叠加性的后向传输过程.通过在各水听器位置放置虚拟声源,并在搜索区域产生相应的模糊平面,对各个模糊平面进行相应加权求和,获得的定位模糊平面.利用地中海浅海实验数据验证了虚拟时反实现方法的快速性能.     

虚拟时间反转水声信号检测

针对目标辐射声信号特性未知的情况,在不增加额外水声换能器的条件下,研究提高水听器阵列对水声信号检测性能的方法。首先,按照经典二元检测问题处理方法分析了常规能量检测方法的性能,在此基础上,根据虚拟时间反转处理原理,对处理后的信号构建检测统计量,推导得到了虚拟时间反转检测方法的理论门限和检测性能的表达式,并通过与常规能量检测的对比分析了虚拟时间反转检测的处理增益。使用计算机仿真实验从声源频率、接收阵列阵元数、目标距离与深度等方面分析了两种方法的检测性能。结果表明,所提出的算法相对于常规能量检测算法在性能上有显著优势,且接收阵元数是对算法性能影响最为明显的因素。      

结合主动时间反转算法的短基线定位研究

短基线声学定位技术是水下运动目标定位的重要研究内容。为了解决定位系统工作于浅水或近岸时多途扩展严重造成的时延估计误差和系统工作不稳定的问题,本文提出一种结合时间反转算法的短基线宽带应答定位技术,该方法利用短基线阵元发射宽带信号,通过应答器接收该信号时间反转处理后再返回给短基线阵元位置,实现信道多途的自适应聚焦,进而提高时延估计精度及信号检测的鲁棒性。仿真研究和湖上试验表明,该方法能够充分利用信道多途信息实现聚焦,减少信道多途对定位信号时延估计的影响,具有较强的抗噪声和多途干扰的能力。相对传统定位方法,该方法可以抑制短基线定位过程中误差及野点的产生,改善了物体定位导航的精度。      

浅海波导中水平接收阵被动时反混响抑制方法研究

使用基于射线简正波异地混响理论建立的水平接收阵接收海底混响模型,提出了水平阵被动时反混响抑制方法。以水平接收阵接收回波信号的某一时刻作为开始,分别对其前一时刻和后一时刻的回波信号做时反算子分解获得两个混响子空间,将这两个混响子空间的平均作为该时刻的混响子空间的一个估计,然后利用投影处理来抑制该时刻接收信号中的混响成分。该方法可以在一定程度上克服由于海底粗糙引起的局部时间(距离)段内接收回波信号的不平稳性,使得估计得到的混响子空间更加接近真实混响子空间。因此,利用其进行被动时反混响抑制可以增强回波信混比,提高对目标的检测和方位估计能力。针对典型浅海波导环境开展的仿真验证了本文方法的有效性。      

基于频带分解和距离加权的单矢量水听器浅海被动测距方法研究

本文针对浅海环境下中低频宽带脉冲声源被动测距问题, 提出了一种声压和水平振速联合处理的被动测距方法. 在浅海波导中, 声压和质点振速的自相关函数卷绕(warping)谱具有稳定的频率特征. 声压和水平振速的自相关卷绕谱具有相同的准线谱特征, 垂直振速自相关卷绕谱具有宽谱叠加线谱的特征, 与声压自相关卷绕谱相比, 其尖峰个数比更多, 且尖峰宽度更宽. 利用引导源, 本文提出了基于频带分解和距离加权的声压和水平振速联合被动测距方法. 利用该方法对2008年冬季青岛海域综合实验中单矢量水听器接收的气枪信号进行处理, 结果表明, 该方法能够实现气枪声源的有效测距. 与传统单声压水听器被动测距方法相比, 该方法可以有效减小代价函数的主瓣宽度、提高测距精度.     

声音目标被动定位算法的野值分析

阐述了基于四元平面十字阵的声音目标被动定位的原理.利用目标与基阵平台分布在不同平面的特点,采用简单的平面阵实现目标的三维定位,简化了布阵的复杂性.针对基于四元平面十字阵的声音目标被动定位算法,分析了野值产生的原因,并研究了水平方位角、垂直俯仰角、时延估计误差度、目标距离、基阵尺寸等因素对野值产生的影响.     

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.     

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.     

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.     

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].     

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.     

Real-time restoration of rotational blurred image using gradient-loading

The key to the restoration of rotational motion blurred image is how to restore the image under a low cost and to correct the irreversibility of the degradation function matrix.Based on the special qualities of degradation function matrix and precise deduction in space-domain, we present a new approach using gradient-loading for restoration of rotational blurred image.By easily adding a gradient operator, the irreversibility of the original matrix is corrected and can be applied for inverse filtering then.Gradientloading is the optimized approach which combines the advantages of both the approaches using constrained least square filtering and traditional diagonal-loading.Compared with the approach using least square filtering, its peak signal-to-noise ratio (PSNR) is improved from 3.18 to 6.46dB, while the computing time is reduced to 1/2-1/3.Experimental results demonstrate the effectiveness, noise-resistibility, robustness, and low complexity of this approach, which make it more suitable for real-time environment.     

All-Optical Logic Device Using Bent Nonlinear Tapered Y-Junction Waveguide Structure

We propose an all-optical logic device made of a bent tapered Y-junction waveguide with a Kerr-type nonlinear interface. It could provide an AND gate, OR gate, and exclusive-OR (XOR) gate. We could obtain different transmission results by adjusting the bending angle. The numerical simulation results show that the device functions as AND, OR, and XOR gates.     

Real-time, continuous-wave terahertz imaging by a pyroelectric camera

Real-time, continuous-wave terahertz (THz) imaging is demonstrated. A 1.89-THz optically-pumped farinfrared laser is used as the illumination source, and a 124 × 124 element room-temperature pyroelectric camera is adopted as the detector. With this setup, THz images through various wrapping materials are shown. The results show that this imaging system has the potential applications in real-time mail and security inspection.