高斯信号的量化分析

由于器件的约束条件不同,在数字信号处理中通常要对AD采样后的信号进行量化处理,如何提高量化的性能是量化的关键。针对N(μ,σ2)高斯分布的量化信号,使用理论推导的方式,得到量化损耗与限幅门限的关系式,并推导出对应量化损耗最小的最优限幅门限公式,其推导方法同样适用于其他随机信号。仿真试验证明了该公式的正确性,结论可应用于工程实现。     

基于混合高斯概率密度的加权打分方法

针对当前评比打分方法不能有效反映选手真实情况的问题,提出了一种基于混合高斯概率密度的加权打分方法。该方法的重点在于引入混合高斯分布来确定专家评分的权重。首先利用EM算法确定混合高斯分布模型参数,然后通过区间划分得到每个区间上的概率,再将专家打分映射到混合高斯概率密度函数区间上得到对应的权重,最后经加权求和得到选手的最终成绩。通过实例证明了该方法的合理性和公正性。     

Three-dimensional coordinates test method with uncertain projectile proximity explosion position based on dynamic seven photoelectric detection screen

To objectively obtain the three-dimensional coordinates of the projectile fuze proximity explosion when projectile intersects the head of missile target, we propose a dynamic seven photoelectric detection screen test method, which is made up of six plane detection screens and a flash photoelectric dynamic detection screen. The three-dimensional coordinates calculation model of the projectile proximity explosion position based on seven plane detection screens with dynamic characteristics is established. According to the relation of the dynamic seven photoelectric detection screen planes and the time values, the analytical function of the projectile proximity explosion position parameters under non-linear motion is derived. The projectile signal filtering method based on discrete wavelet transform is explored in this work. Additionally, the projectile signal recognition algorithm using an improved particle swarm is proposed. Based on the characteristics of the time duration and the signal peak error for the projectile passing through the detection screen, the signals attribution of the same projectile passing through six detection screens are analyzed for obtaining precise time values of the same projectile passing through the detection screens. On the basis of the projectile fuze proximity explosion test, the linear motion model and the proposed non-linear motion model are used to calculate and compare the same group of projectiles proximity explosion position parameters. The comparison of test results verifies that the proposed test method and calculation model in this work accurately obtain the actual projectile proximity explosion position parameters.     

正弦高斯组合的UWB脉冲波形设计

针对美国FCC关于超宽带传输系统提出的辐射掩蔽特性,提出了一种基于正弦高斯组合的UWB脉冲波形设计新方案。以一组正弦高斯脉冲为基函数,利用最小均方误差准则(LSE)选取加权系数对基函数进行线性组合,通过调整基函数的载波频率和脉冲形成因子,对波形进一步优化。分析了TH-PPM UWB多用户系统的误码率性能。仿真结果表明,与高斯二阶微分脉冲、随机系数组合脉冲相比,基于正弦高斯组合脉冲具有更高的频谱利用率,误码性能更优。     

非高斯码元检测的马尔可夫链蒙特卡洛算法

针对实际超低频接收机不仅受非高斯噪声的影响,还受接收机内部和外部环境中高斯噪声影响的问题,对噪声采用非高斯分布和高斯分布的混合模型建模,根据混合模型的性质,设计了一种利用马尔可夫链蒙特卡洛方法的超低频信号码元盲检测算法。盲检测算法在贝叶斯层次模型下,采用Gibbs抽样和M-H抽样更新参数,同步估计信道衰落系数和噪声模型参数,并实现对信号码元的检测。算法迭代效率快、精度高。通过与最优检测算法性能比较,盲检测算法性能优异,对超低频信号接收具有重要的现实意义。     

Effect of tool rotational speed on the particle distribution in friction stir welding of AA6092/17.5 SiCp-T6 composite plates and its consequences on the mechanical property of the joint

This study investigates the effect of tool rotational speed (TRS) on particle distribution in nugget zone (NZ) through quantitative approach and its consequences on the mechanical property of friction stir welded joints of AA6092/17.5 SiC_p-T6 composite. 6 mm thick plates are welded at a constant tool tilt angle of 2° and tool traverse speed of 1 mm/s by varying the TRS at 1000 rpm, 1500 rpm and 2000 rpm with a taper pin profiled tool. Microstructure analysis shows large quantity of uniformly shaped smaller size SiC particle with lower average particle area which are homogeneously distributed in the NZ. The fragmentation of bigger size particles has been observed because of abrading action of the hard tool and resulting shearing effect and severe stress generation due to the rotation of tool. The particles occupy maximum area in the matrix compared to that of the base material (BM) due to the redistribution of broken particles as an effect of TRS. The migration of particles towards the TMAZ-NZ transition zone has been also encountered at higher TRS (2000 rpm). The microhardness analysis depicts variation in average hardness from top to bottom of the NZ, minimum for 1500 rpm and maximum for 2000 rpm. The impact strength at 1000 rpm and 1500 rpm remains close to that of BM (21.6 J) while 2000 rpm shows the accountable reduction. The maximum joint efficiency has been achieved at 1500 rpm (84%) and minimum at 1000 rpm (68%) under tensile loading. Fractographic analysis shows mixed mode of failure for BM, 1000 rpm and 1500 rpm, whereas 2000 rpm shows the brittle mode of failure.     

一种GMM-SVM混合说话人辨认模型

文中提出了一种GMM和SVM混合说话人识别模型,在特征参数域和概率得分域对两种模型进行了融合。混合模型结合了GMM和SVM各自的优势,使SVM的概率输出兼顾各说话人模型内部和模型之间的信息,并有效解决了SVM训练算法复杂,难以处理大量样本的问题。采用TIMIT数据库进行了说话人辨认实验,结果证明本文提出的GMM-SVM模型比传统的GMM模型和SVM模型具有更好的辨识性能。     

侧壁激波诱导下凹腔燃烧室冷态流场实验观测

在单凹腔燃烧室中引入侧壁激波,为研究燃烧室内部流动特性,采用纳米粒子平面激光散射技术和粒子图像测速技术对全尺寸玻璃燃烧室模型进行流场观测,获得了冷态流场展向和法向的瞬态灰度图及平均速度场。实验结果表明:在远壁面区域,凹腔内部速度与密度都较低;引入侧壁激波后,近壁面区域凹腔与主流的质量与动量交换增强,速度与密度升高;受到侧壁激波影响,燃烧室底壁边界层不再均匀,凹腔中后部产生大规模低速区,具有明显三维特性。     

多机动目标跟踪的BFG-GMPHD算法

针对高斯混合概率假设密度(GMPHD)滤波算法中的机动目标跟踪问题,提出BFG-GMPHD算法,扩展了GMPHD滤波算法的适用范围。算法利用最佳拟合高斯(BFG)分布来近似目标动态模型中的状态转移矩阵和过程噪声的协方差矩阵,实现了滤波器与不同动态模型的匹配;在对BFG分布进行递推时,引入了模型概率更新过程,解决了BFG仅依赖于先验信息的问题;并利用UKF算法对GMPHD的高斯分量进行递推,使得算法能处理量测方程为非线性的情况。仿真实验表明,BFG-GMPHD算法能快速匹配目标模型的变化,实现对多机动目标的有效跟踪,准确估计出目标的数目和状态。