基于分组时延预处理的时域波束形成方法*

对于不等强度多目标情况下的弱目标检测问题,依据波束形成归一化指向性函数在目标方向上输出值为1、在非目标方向上输出值为小于1的特性,提出一种基于分组时延预处理的时域波束形成方法。该方法首先对线列阵接收数据进行分组处理;然后,按搜索角度对各组数据进行时延预处理,并对各组预处理结果进行相加,得到一组新数据;最后,对该组新数据按时域波束形成进行处理,得到该搜索角度对应波束值。理论推导、数值仿真和试验数据处理结果均表明：相比常规时域波束形成,该方法所得波束形成指向性函数发生了变化,旁瓣级得到了13dB以上的改善,降低了强目标旁瓣级对弱目标检测的影响。     

Some criteria for supersolubility in products of finite groups

Let H and T be subgroups of a finite group G. H is said to be permutable with T in G if HT = TH. In this paper, we use the concept of permutable subgroups to give two new criterions of supersolubility of the product G = AB of finite supersoluble groups A and B.      

Maximal Subgroups of Subnormal Subgroups of GL n (D) with Finite Conjugacy Classes

Let D be an infinite division ring. A famous result due to Herstein says that every noncentral element of D has infinitely many conjugates in D. So, if D* is an FC-group, then D is a field. Now let N be a subnormal subgroup of GL _n (D), where n ≥ 1, and M a maximal subgroup of N. In this article, we prove that if M is an FC-group, then M is contained in the multiplicative group of some subfield of M _n (D).     

Sous-groupes discrets de <Emphasis Type="Italic">PU</Emphasis>(2,1) engendrés par <Emphasis Type="Italic">n</Emphasis> réflexions complexes et Déformation

Let PU(2,1) be the group of holomorphic isometries in the hyperbolic complex plane and let G _n be a sub-group of PU(2,1) which is generated by n complex reflections with respect to complex lines in . Under certain conditions, we prove that G _n is discrete. We construct representations ρ of the fundamental group Γ _g of the compact surface Σ _g of genus g, into PU(2,1), we prove they are discrete, faithful and we compute the dimension their deformation space.      

The Classification of Symmetric Transversal Designs <Emphasis Type="Italic">STD</Emphasis><Subscript>4</Subscript>[12; 3]’s

In this article we prove that there is only one symmetric transversal design STD₄[12;3] up to isomorphism. We also show that the order of the full automorphism group of STD₄[12; 3] is 2⁵· 3³ and Aut STD₄[12;3] has a regular subgroup as a permutation group on the point set. We used a computer for our research.Communicated by: C.J. Colbourn