Joint estimation of DOA, frequency, and polarization based on cumulants and UCA

A joint estimation algorithm of direction of arrival （DOA）, frequency, and polarization, based on fourth-order cumulants and uniform circular array （UCA） of trimmed vector sensors is presented for narrowband non-Gaussian signals. The proposed approach, which is suitable for applications in arbitrary Gaussian noise environments, gives a closed-form representation of the estimated parameters, without spectral peak searching. An efficient method is also provided for elimination of cyclic phase ambiguities. Simulations are presented to show the performance of the algorithm.

CONVERGENCE PROPERTIES OF HIGHER-ORDER MOMENT AND CUMULANT ESTIMATES

The sample estimates of higher-order statistics are studied. Under certain conditions, the almost sure convergence of the third- and fourth-order moment and cumulant estimates of stationary processes is established. The rate of almost sure convergence is obtained for the sample estimates of third- and fourth-order moment and cumulant. Additionally, it is shown that the third- and fourth-order moment and cumulant estimates are asymptotic normal.

Resolution performance analysis of cumulants-based rank reduction estimator in presence of unexpected modeling errors

Compared to the rank reduction estimator （RARE） based on second-order statistics （called SOS-RARE）, the RARE employing fourth-order cumulants （referred to as FOC-RARE） is capable of dealing with more sources and mitigating the negative influences of the Gaussian colored noise. However, in the presence of unexpected modeling errors, the resolution behavior of the FOC-RARE also deteriorate significantly as SOS-RARE, even for a known array covariance matrix. For this reason, the angle resolution capability of the FOC-RARE was theoretically analyzed. Firstly, the explicit formula for the mathematical expectation of the FOC-RARE spatial spectrum was derived through the second-order perturbation analysis method. Then, with the assumption that the unexpected modeling errors were drawn from complex circular Gaussian distribution, the theoretical formulas for the angle resolution probability of the FOC-RARE were presented. Numerical experiments validate our analytical results and demonstrate that the FOC-RARE has higher robustness to the unexpected modeling en＇ors than that of the SOS-RARE from the resolution point of view.

Performance of cumulant-based rank reduction estimator in presence of unexpected modeling errors

Compared with the rank reduction estimator(RARE) based on second-order statistics(called SOS-RARE), the RARE based on fourth-order cumulants(referred to as FOC-RARE) can handle more sources and restrain the negative impacts of the Gaussian colored noise. However, the unexpected modeling errors appearing in practice are known to significantly degrade the performance of the RARE. Therefore, the direction-of-arrival(DOA) estimation performance of the FOC-RARE is quantitatively derived. The explicit expression for direction-finding(DF) error is derived via the first-order perturbation analysis, and then the theoretical formula for the mean square error(MSE) is given. Simulation results demonstrate the validation of the theoretical analysis and reveal that the FOC-RARE is more robust to the unexpected modeling errors than the SOS-RARE.

Normalized solutions for a fourth-order Schrődinger equation with a positive second-order dispersion coefficient

In this paper,we study normalized solutions to a fourth-order Schrődinger equation with a positive second-order dispersion coefficient in the mass supercritical regime.Unlike the well-studied case where the second-order term is zero or negative,the geometrical structure of the corresponding energy functional changes dramatically and this makes the solution set richer.Under suitable control of the second-order dispersion coefficient and mass,we find at least two radial normalized solutions,a ground state and an excited state,together with some asymptotic properties.It is worth pointing out that in the considered repulsive case,the compactness analysis of the related Palais-Smale sequences becomes more challenging.This forces the implementation of refined estimates of the Lagrange multiplier and the energy level to obtain normalized solutions.

Experimental Studies on Cyclic Shear Behavior of Steel-Clay Interface Under Constant Normal Load

The degradation of the shear stress between pile-clay interface caused by undrained cyclic jacking affects the jacking force.A series of large displacement monotonic shear,cyclic shear and post-cyclic monotonic steel plate-clay interface shear te sts were performed under the constant normal load(CNL)condition to inve stigate the effects of normal stre ss,cyclic amplitude,and number of cycles on a steel plate-clay interface using the GDS multi-function interface shear tester.Based on the experimental results,in monotonic shear tests,change of shear stress took place in the specimen,the shear stress rapidly reached the peak value at shear displacement of 1 mm,and then abruptly decreased to the residual value.In cyclic shear te sts,accumulated displacement was a better parameter to describe the soil degradation characteristics,and the degradation degree of shear stress became greater with the increasing of normal stress and accumulated displacement.Shear stress in post-cyclic monotonic shear tests did not generate a peak value and was lower than that in monotonic shear tests under the same normal stress.The soil was completely disturbed and reached the residual strength when the cumulative displacement approached 6 m.An empirical equation to evaluate shear stress degradation mechanism was formulated and the procedure of parameter identification was presented.

运输类飞机实测突风谱编制方法研究

目的针对运输类飞机突风载荷谱编制需求,基于实测载荷数据和任务分析法原理,采用5×5谱编制方法,建立一种运输类飞机实测突风谱编制方法。方法首先依据任务分析确定飞机典型任务剖面和任务段,对实测载荷数据进行预处理和统计分析,获得突风增量过载超越数的分布参数。然后通过得到的平均突风增量过载累积超越数曲线,编制各任务段载荷谱,进而编制任务剖面谱,按任务剖面比例,对任务剖面谱进行随机排序,编制得到了突风增量过载飞-续-飞谱。最后给出了一个示例以详细阐明该编谱方法。结果该型运输机爬升任务段突风载荷谱相较其余任务段偏重。结论通过该方法编制的突风载荷谱能够较好地反映实测突风载荷数据特点,方法具备合理性和可行性。

基于正态曲线和有效积温的美国白蛾发生预测和除治效果评估机制研究

经拟合,美国白蛾成虫羽化符合正态分布。求算出成虫-成虫高峰日有效积温常数为877.6±84.3日度、当年成虫高峰日有效积温常数309.3±31.5日度,并给出了通过高峰日有效积温和成虫种群消长趋势指数进行当代和下一代成虫数量预测的方法。在全种群治理理念的指导下,提出了空间覆盖量和种群覆盖量的概念,并在此基础上制定了一套幼虫种群死亡量计算方法,其可靠性在对往年飞防除治实践中得到了验证。

基于多维数据融合的个性化旅游信息推荐模型研究

为了更好地促进旅游信息个性化推荐效果的提升,需对用户行为信息进行深度挖掘。文中基于多维数据融合,构建并研究了个性化旅游信息推荐模型。首先,结合用户的历史浏览、检索、点赞及评论数据,分析用户对不同景区的兴趣度。其次,结合用户的旅行次数、旅行时间以及具体的旅行地点信息,分析用户的偏好选择对旅游大数据的影响力。接着,结合用户对景区兴趣度的分析结果,综合计算用户对景区所在地的偏好选择。最后,以地区偏好为范围,将对旅游大数据影响力较高用户的兴趣度TOP-N景区信息作为最终的推荐结果。测试结果表明,归一化折损累计增益NDCG随着推荐信息数量k的增加呈现出稳定提升的趋势,且相比对比模型,文中提出的模型得到的参数值始终处于较高水平,说明该模型具有可靠的推荐效果。

Joint frequency, 2D AOA and polarization estimation using fourth-order cumulants

Based on fourth-order cumulant and ESPRIT algorithm, a novel joint frequency, two-dimensional angle of arrival (2D AOA) and the polarization estimation method of incoming multiple independent spatial narrow-band non-Gaussian signals in arbitrary Gaussian noise environment are proposed . The array is composed of crossed dipoles parallel to the coordinate axes. The crossed dipole positions are arbitrarily distributed. Computer simulation confirms its feasibility.

Array gain of fourth-order cumulants beamforming under typical probability density background

The fourth-order cumulant of zero mean Gaussian distribution noise always equals to zero theoretically. In practice the probability density of noise and reverberation is the key problem to performance of the fourth-order cumulant beamforming technique. In this paper, the array gain functions of the fourth-order cumulant beamforming are deducted considering the instantaneous amplitude distribution of the ambient sea noise and bottom reverberation respectively. And the relationships are determined between array gain and the factors including the number of the array elements, the fourth-order and second-order statistical properties of the noise and reverberation, and the input signal-to-noise ratio. It is also verified that there is a critical signal-to-interference ratio and the fourth-order cumulant beamforming can obtain higher gain and resolution than the conventional beamforming method when the ratio is larger than it. The results of experiment data processing demonstrate that the gain and the resolution of the fourth-order cumulant beamforming coincide with the theoretic.

基于互信息的中医症状推荐系统

针对中医诊断过于依赖医生经验的问题,提出一种基于互信息的中医症状推荐系统。首先,对原始病例数据进行中医症状规范化,构建症状术语字典,使系统输入规范的症状;然后,通过互信息计算症状之间的关联性;最后,利用归一化折损累计增益(NDCG)指标验证症状的推荐效果,获得症状的推荐列表。实验结果表明,该系统能根据一个症状或多个症状获得其他相关联的症状,实现中医症状推荐功能。

改进粒子群优化超限学习机的调制信号识别

针对现有算法在信噪比较小条件下对调制信号识别精度较差的问题,提出一种基于改进粒子群优化超限学习机的调制信号识别算法。以调制信号的高阶累积量为基础构建4种特征参数,并根据多进制相移键控(Multiple Phase Shift Keying,MPSK)信号的相位特性引入归一化瞬时相位平均值和递归归一化瞬时相位平均值特征两个特征参数,构建调制信号的6种特征参数的数据集。利用粒子群优化(Particle Swarm Optimization,PSO)算法优化超限学习机(Extreme Learning Machine,ELM)算法的神经网络结构,动态调整PSO算法中的惯性权重,以提升算法的识别性能。采用所提算法对7种调制信号进行识别,实验结果表明,当信噪比大于2 dB时,所提算法对7种调制信号的识别正确率均达到100%。与相关算法相比,所提算法的识别效果较佳且更具有稳定性。

基于载荷分级代表性条件的TWIST载荷谱离散方法

增量突风载荷极值对数正态分布是TWIST载荷谱离散的关键要求,现有离散方法存在求解变量较多,载荷分级代表性不足的问题。基于载荷分级代表性条件,提出了一种满足增量突风载荷极值对数正态分布的单迭代变量TWIST载荷谱离散方法。推导了载荷分级代表性条件,得到各级增量载荷极值及其边界所对应的累积超越飞行概率的递推公式;通过增量突风载荷高载截取值求解出各类飞行的飞行次数;以对数正态分布的标准差为迭代变量,利用高载截取值和低载删除值确定了对数正态分布的参数,进而求解出各级离散载荷。通过欧洲10乘10谱和波音5乘5谱2个算例,验证了所提出方法的有效性。

重庆库区地貌1999—2008雷电流幅值频率分布特征

雷电流的幅值及其特性是雷电科学研究的重要基础数据。通过对1999—2008年重庆地区地闪监测资料中雷电流幅值测量数据的数理统计和对数正态分布拟合,重点分析其频率分布特征。结果表明:雷电流幅值频率分布特征随闪电极性具有显著差异,负闪雷电流幅值出现频次满足对数正态分布,并通过显著性检验,可以用对数正态分布曲线很好地拟合其分布特征;正闪的雷电流幅值不符合对数正态分布,而是符合双对数正态函数叠加分布特征。在此基础上,获得了重庆库区地貌的雷电流幅值的概率密度分布曲线方程,它客观地反映了重庆地区雷电活动规律,相对于IEEE工作组给出的雷电参数,该参数能更为准确地为重庆地区这种典型库区地貌区域的城市规划和防雷减灾活动提供了理论依据。

地球化学基线的确定方法研究——以攀枝花地区为例

地球化学基线指的是地球表层物质中化学元素浓度的自然变化 ,是区分自然的和人为的环境影响的重要参照。地球化学基线的确定方法和相关方法技术研究是目前国内外地球化学基线研究的重点和难点。作者采用标准化方法、相对累积频率方法、地层对比方法确定了攀枝花地区土壤的地球化学基线 ,结果表明 ,根据不同方法确定的地球化学基线值略有不同。应根据研究对象、研究目标的不同并结合地质地球化学分析 。

基于粒子群优化的有序盲信号分离算法

为了按照规范四阶累积量的绝对值有序分离出源信号,提出了一种新的基于粒子群优化的有序盲信号分离算法.本算法采用信号的规范四阶累积量作为代价函数,使用粒子群优化算法代替传统的梯度算法对代价函数进行优化,通过消源去相关方法从混合信号中消去已分离出的源信号成分,逐次按序提取出源信号,解决了梯度算法容易陷入局部极值而不能正确提取源信号的缺点.仿真结果表明,本算法能够有效实现对各类源信号的有序盲分离,且分离顺序能够确保按照源信号的规范四阶累积量绝对值的降序进行.

基于水系流域的地球化学异常分析方法——以1∶50000丫他幅水系沉积物分析为例

地球化学异常靶区优选一直是勘查地球化学所面临的核心问题。目前地球化学异常靶区优选所采取的方法,主要是基于不同地质构造单元的地球化学异常评价方法和基于多元统计而发展的多元素定量化评价指标方法,然而这些异常评价方法缺少对水系中沉积物的物质来源区域进行限定。由于在一级水系中沉积的水系沉积物主要由一级水系流域内的岩石经过风化、剥蚀、搬运,最后在水系内沉积而成,因此一级水系中的水系沉积物的物源区域可近似与水系流域等同。本文通过水系流域的提取,以水系流域作为分析单元,对1∶50000丫他幅水系沉积物进行地球化学分析评价,通过与地质矿产资料对比,证明了本方法的有效性,并且缩小了地球化学异常区域,更精确地进行靶区定位。根据本文提出的方法,通过分析区内已知矿点所处流域的地球化学元素特征,将丫他幅内已有金矿划分为两种类型,对后期找矿工作有一定的指导意义。

三维表面的曲面描述与相似性判别

针对三维物体表面的描述和识别问题 ,从描述三维表面变化的基本参数——法向量出发 ,以法向量累积分布曲线 NVCDC为不变量 ,对比较光滑的三维曲面 ,给出了一种描述形状的方法和相似性判别准则 ,并依法向量的方向角将三维空间分割成子空间 ,然后统计落入每个子空间的法向量个数 ,以得到法向量的分布 ,再将其排序后 ,即得到法向量累积分布曲线 NVCDC.由于与不同的法向量累积分布曲线对应的三维曲面也是不同的 ,所以采用 NVCDC之间的差异为相似性判别准则 ,对不同三维曲面进行了一对一的相似性判别 .为检验该方法的效果 ,还对足底表面进行了实验 ,结果表明 。

基于细菌群体趋药性的有序盲信号分离算法

提出了一种基于细菌趋药性的细菌群优化算法。将探测判断策略和优势细菌随机扰动策略引入细菌群体的进化过程,解决了细菌个体在进化后期处于随机摄动状态而难以定位于全局最优位置的问题。通过使用测试函数对算法性能进行测试以及同其他算法的比较表明,所提出的算法在收敛速度和求解质量方面均有很好的性能。进一步将细菌群优化算法应用于解决盲信号分离问题,实现了对源信号的逐一有序盲分离。仿真实验表明,基于细菌群优化算法的盲信号分离算法具有很好的分离效果,可以将源信号按照其规范四阶累积量绝对值的降序进行有效分离。