DOA estimation of incoherently distributed sources using importance sampling maximum likelihood

In this paper, an importance sampling maximum likelihood(ISML) estimator for direction-of-arrival(DOA) of incoherently distributed(ID) sources is proposed. Starting from the maximum likelihood estimation description of the uniform linear array(ULA), a decoupled concentrated likelihood function(CLF) is presented. A new objective function based on CLF which can obtain a closed-form solution of global maximum is constructed according to Pincus theorem. To obtain the optimal value of the objective function which is a complex high-dimensional integral,we propose an importance sampling approach based on Monte Carlo random calculation. Next, an importance function is derived, which can simplify the problem of generating random vector from a high-dimensional probability density function(PDF) to generate random variable from a one-dimensional PDF. Compared with the existing maximum likelihood(ML) algorithms for DOA estimation of ID sources, the proposed algorithm does not require initial estimates, and its performance is closer to CramerRao lower bound(CRLB). The proposed algorithm performs better than the existing methods when the interval between sources to be estimated is small and in low signal to noise ratio(SNR)scenarios.

isthmin 1对斑马鱼胚胎汇聚延伸运动的影响

目的在原肠期,斑马鱼胚胎细胞进行着外包(epiboly)、内卷(involution)以及汇聚延伸(convergence and extension)运动,对于胚胎的形态发生起关键作用。本文旨在研究isthmin 1(ism1)在斑马鱼胚胎发育中的表达图谱,并进一步探讨其在原肠期胚胎汇聚延伸运动中的功能。方法通过原位杂交技术,检测ism1在斑马鱼早期胚胎发育中的表达图谱;利用过表达和特异敲降等实验技术,活体拍照及原位杂交检测ism1对胚胎汇聚延伸运动的影响。结果整胚原位杂交实验结果显示ism1是合子表达的基因,在30%外包时期开始表达于胚胎背部,原肠期表达在整个胚胎边缘区,尤其在胚盾部位表达更为明显。活体拍摄及原位杂交结果表明,与野生型斑马鱼胚胎相比,过表达或敲低ism1均会使胚胎的汇聚延伸运动受到影响。结论 ism1是调控斑马鱼胚胎原肠期汇聚延伸运动的重要基因。