自回归谱分析中Marple算法的阶数的考虑

在自回归谱分析中,Marple的LS算法是最有效的方法之一,它减少了谱线频率的偏移,避免了谱线的分裂,而且具有更高的分辨率.但是,判阶问题仍未解决.本文从实验的角度详细讨论了Marple提出的病态条件和两个容限因子,并且研究了在不同的噪声电平下,分辨率和阶数的关系.最后还讨论了出现假峰的问题.     

Homology of the universal covering of a co-H-space

The problem 10 posed by Tudor Ganea is known as the Ganea conjecture on a co-H-space, a space with co-H-structure. Many efforts are devoted to show the Ganea conjecture under additional assumptions on the given co-H-structure. In this paper, we show a homological property of co-H-spaces in a slightly general situation. As a corollary, we get the Ganea conjecture for spaces up to dimension 3.

     

Raman tensor analysis of (K0.5Na0.5)NbO3–LiSbO3 lead‐free ceramics and its application to study grain/domain orientation

A quantitative polarized Raman analysis of ferroelectric grain/domain orientation in LiSbO₃ (LS‐modified) (K_0.5Na_0.5)NbO₃ (KNN) ceramics is presented, based on the analysis of the complex orientation dependence in space of their Raman‐active modes. Complete sets of Raman tensor elements of A_g, and E_g phonon modes for orthorhombic/tetragonal structures of KNN have been determined. Through this spectroscopic algorithm, quantitative information could be extracted in terms of three Euler angles in space for KNN samples consisting of mixed phases, thus enabling quantitative visualization of the local distribution of grains/domains in the solid angle. As an application of the method, we quantitatively examined the unknown crystallographic grain orientation patterns on the surfaces of pure KNN and of KNN‐0.05LS ceramics. These two samples were useful to clarify a polymorphic phase transition from the orthorhombic to the tetragonal phase taking place in the LS‐modified KNN system. Thus, we demonstrated that polarized Raman spectroscopy is a valuable and efficient tool for nondestructive three‐dimensional assessments of grain/domain orientation in ferroelectric materials with complex polymorphic structures. We believe that the data shown here represent a typical scenario encountered in grain/domain orientation assessments of piezoelectric perovskites. Copyright © 2012 John Wiley & Sons, Ltd.