基于特征分析的自适应干扰抑制

针对水声环境中真实目标常常被强干扰掩盖而无法识别的问题,提出了一种基于特征分析的自适应干扰抑制方法(EAAIS)。根据目标信号可能的方向范围,通过构造合适的判决因子来自适应地估计并抑制互谱密度矩阵特征空间中的非目标信号子空间,得到具有更高信干比和信噪比的目标信号,为更好地实现目标识别与跟踪提供技术基础。数值仿真和海试数据验证结果表明,EAAIS方法能够自适应地抑制目标信号可能方向范围之外的强干扰,显著提高接收目标信号的信噪比和信干比,并获得更可靠的目标方位参数。相对于其它干扰抑制方法,本文提出的方法表现出了更为稳健的干扰抑制能力,具有更宽的适用条件。      

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．     

基于改进卡尔曼滤波的水声通信盲自适应多用户检测算法

针对水声通信网络中遇到的多用户检测中目标用户的多址干扰等检测问题,提出了基于改进Kalman算法的盲自适应多用户检测算法,解决了多用户检测中的多址干扰对水声通信信道用户变动时的干扰抑制问题。仿真分析分别针对同步多用户、异步多用户通信过程,对比了传统Kalman算法及改进的Kalman算法的性能差异,通过仿真对比表明,改进后的Kalman检算法不需要训练序列即可以实现同步和异步通信状态下的多水声目标用户的盲自适应检测,改进后的算法目标检测的信干比比传统算法最大可提高6dB。新算法对于水下多用户检测、区分,准确、稳定的实现基于CDMA协议的快速水声通信具有重要意义。     

空时多普勒频移域运动小目标的抗干扰探测方法

有源声呐使用多普勒敏感信号可在多普勒频移域分离杂波、混响等干扰和运动目标,但低信干比时强干扰的时间旁瓣泄露和多普勒旁瓣泄露会淹没弱目标.针对该问题,提出了一种基于自适应最小均方(LMS)算法和宽带模糊函数(WAF)的运动小目标抗干扰探测方法.首先在空间多普勒频移域上利用基于LMS的自适应陷波器抑制干扰,然后在快时间多普...     

不确定环境下的稳健自适应匹配场处理研究

针对浅海中由于水声环境参数不确定、水面强干扰的存在、以及目标运动等因素会导致水下弱目标检测与定位性能严重下降的问题,将协方差矩阵降阶、环境宽容性约束和运动补偿进行有机结合,在对运动补偿算法加以改进的基础上,提出了一种在不确定环境和强干扰背景下检测水下微弱目标的稳健自适应匹配场处理方案。典型浅海环境下的数值仿真和实测数据分析表明,该方案在一定的环境失配条件下不仅能有效地抑制水面强干扰,还能为水下微弱运动目标的检测提供较大范围的空时相干累积,有利于提高目标的定位精度和输出信干比。     

子空间判决分析的强干扰抑制

针对海洋中存在的强干扰和环境噪声导致水下目标方位估计算法性能剧烈下降的问题,提出了一种子空间判决分析的强干扰抑制方法 (SSJ),可实现多个强干扰下的目标方位估计。根据常规波束形成粗估的目标角度区间,利用目标-干扰-噪声子空间与导向矢量的相关性,设置判决项和估计合适的判决阈值来分离和抑制样本协方差矩阵中的非目标信息,降低干扰和噪声的输出功率,同时提高输出信干噪比,为增强阵列的目标方位分辨能力提供方法支撑。仿真和海试数据处理结果显示,SSJ方法可抑制目标角度区间外的强干扰和噪声,明显降低了干扰的输出功率和目标主瓣附近的旁瓣级,提高了目标方位角度的分辨力。相比于现有的子空间干扰抑制方法,所提方法具有更加稳健的干扰抑制能力。     

利用辐射噪声多线谱的多普勒进行距离估计

提出了一种利用辐射噪声多线谱的多普勒频移去估计直线匀速运动目标正横距离的方法,这种方法用单水听器进行无源测距,且不需要知道海深和其它环境参数。先用Wigner-Ville分布作为瞬时频率估计器估计出多线谱瞬时频率随时间变化作为一个信号,再定义多普勒频移的基函数,依据一种匹配投影原理,在五维空间中用一种可变步长的搜索策略去寻找该信号与多普勒频移基函数之间的最小空间距离。所找到最小距离的基函数对应于目标距离和速度的估计值。计算机模拟给出不同强度干扰噪声下的测距测速的统计误差。当干扰噪声的标准差为最大多普勒频移的10％及时间窗宽度为1．47倍的参考时宽时,测距相对误差小于5．4％,测速相对误差小于1．4％。对某海上实际目标的距离估计为42 m,速度为52 kn,与实际航行的值相符。此单点无源测距方法可应用于声呐浮标、水雷、水声实验中水声目标的运动分析和水下目标声源级测量。     

一种鲁棒性的最小方差无失真响应波束形成算法及其应用

理论上,自适应波束形成方法要比不依赖于输入数据的常规波束形成方法有更好的目标参数估计能力和干扰抑制能力.但在实际水声环境中,声传播模型、接收阵阵列流形以及信号统计特征等因素往往与实际情况存在一定的差异,导致传统的自适应波束形成方法性能下降.因此,提高自适应波束形成方法对上述因素的鲁棒性变得越来越重要.本文基于最差条件最优化的思想,改进MVDR(最小方差无失真响应)方法的约束条件提出了一种鲁棒性最小方差无失真响应自适应波束形成算法(R-MVDR),并对输入数据协方差矩阵和方向向量存在不确定性的情况进行了性能分析,推导给出了波束形成的加权向量和空间谱估计表达式,最后通过海上实验数据进行了验证.结果证明本文提出的算法在实际环境中有更好的方位分辨能力和干扰抑制能力.     

快速收敛最小方差无畸变响应算法研究及应用

常规最小方差无畸变响应(MVDR)自适应波束形成是一种高分辨窄带波束形成器,它是利用实际声场的窄带互谱密度矩阵(CSDM)估计出自适应波束形成权向量。在实际应用中,MVDR算法需要较长的观测时间估计协方差矩阵,不利于对高速运动目标进行定位;对于宽带目标信号,MVDR算法需要对每一个CSDM进行求逆运算,计算量较大;在相干源条件下,目标信号之间会发生"对消"现象,MVDR算法性能急剧恶化。本文提出了基于子带子阵处理的快速收敛MVDR自适应波束形成方法。首先将全频带划分成一组子带,将接收线阵划分成一组子阵,然后对每一子带计算降维的驾驶协方差矩阵(STCM),从而得到快速收敛MVDR自适应波束形成的权值和空间谱估计结果。同时采用双向空间平滑方法对相干源进行MVDR空间谱估计。仿真和海试数据处理结果表明该算法在保证高分辨力的同时,具有瞬时收敛的性能,双向空间平滑技术具有良好的解相干性能。      

目标自辐射与干扰目标反射光谱的氧气吸收特性分析

为分析不同目标反射太阳光谱的特性,研究被动测距中抑制干扰目标的方法,利用高光谱成像光谱仪作为测量设备,200 W卤钨灯作为模拟探测目标,玻璃板、光滑铝板、塑料板作为干扰目标,对模拟目标发射光谱和干扰目标反射太阳光谱进行了实验采集与分析。实验采集了晴朗天气条件下干扰目标反射光谱及卤钨灯目标辐射光谱的信息,并对其氧气吸收率进行了计算,综合分析了镜面反射干扰目标、漫反射目标及背景反射光与卤钨灯发射光光谱的氧气吸收率差异,结果表明:在455m处,镜面反射目标和漫反射目标反射光的氧气吸收率是卤钨灯的2~3倍。因此,在一定距离下可以利用氧气吸收率的差异设置阈值来对目标进行判别,提高探测概率。     

Femtosecond Transform-Limited Pulse Generation by Compensating for the Linear Chirp of SPM Spectra in Dispersion Shifted Fibers

A simple technique of pulse compression, based on the linear chirp compensation of self-phase modulation (SPM) spectra in dispersion shifted fibers, is demonstrated. The optimization procedure is carried out, for a short span of a single-mode fiber, using a parabolic law, which describes the behavior of the squared output pulse width versus the pump peak power in the case of Gaussian pulses. The experimental results give a minimum pulse duration of 233 fs, which is in good agreement with the model. Shorter and coherent pulses, down to 90 fs, have been obtained by inserting an interference filter at the optical output.     

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.     

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.     

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].     

Sorting of bending magnets for the SSRF booster

The Shanghai Synchrotron Radiation Facility(SSRF)booster ring,a full energy injector for the storage ring,is deigned to accelerate the electron beam energy from 150MeV to 3.5GeV that demands high extraction efficiency at the extraction energy with low beam loss rate when electrons are ramping.Closed orbit distortion(COD)caused by bending magnet field uniformity errors which affects the machine performance harmfully could be effectively reduced by bending magnet location sorting.Considering the affections of random errors in measurement,both ideal sorting and realistic sorting are studied based on measured bending magnet field uniformity errors and one reasonable combination of bending magnets which can reduce the horizontal COD by a factor of 5is given as the final installation sequence of the booster bending magnets in this paper.     

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.