K-space algorithmic reconstruction (KAREN): a robust statistical methodology to separate Bragg and diffuse scattering
K-space algorithmic reconstruction (KAREN): a robust statistical methodology to separate Bragg and diffuse scattering
复制标题
DOI：
10.1107/s1600576719017060
复制
发表时间：
2020-02
影响因子：
6.1
通讯作者：
James Weng;Eric D. Dill;James D. Martin;R. Whitfield;C. Hoffmann;F. Ye
中科院分区：
文献类型：
--
作者：
James Weng;Eric D. Dill;James D. Martin;R. Whitfield;C. Hoffmann;F. Ye
在长程有序结构的布拉格衍射图案中发生的漫散射代表了与控制规则晶格的局部偏离。然而，从衍射图案解释真实空间结构提出了一个重大的挑战，因为总散射函数的布拉格和漫反射分量之间的强度的显着差异。与尖锐的布拉格衍射相反，漫射信号通常被认为是弱扩展或连续的背景信号。在这里，使用1D和2D模型，它表明，漫散射实际上由一个复杂的阵列的高频特征，必须不被平均到一个低频背景信号。为了有效地评估实际的漫散射，已经开发了一种算法，该算法使用稳健的统计和传统的信号处理技术来识别布拉格峰作为信号异常值，该信号异常值可以从整体散射数据中去除，然后由统计上有效的填充值代替。这种方法被描述为“K空间算法重建”（KAREN），可以独立于系统单位单元的先验知识来识别布拉格反射。凯伦不改变任何数据以外的直接附近的布拉格反射，并重建周围的布拉格峰的漫射分量，而不引入不均匀的不均匀性，诱导傅立叶波纹或文物从填充不足的“穿孔”空隙。用于重建漫散射的KAREN算法提供了比从先前描述的打孔和填充方法可以获得的更好的分辨率。使用KAREN方法获得的上级结构分辨率证明通过评估从CBr 4的单个塑料晶体的中子衍射使用对分布函数分析观察到的复杂的有序漫散射。
Diffuse scattering occurring in the Bragg diffraction pattern of a long-range-ordered structure represents local deviation from the governing regular lattice. However, interpreting the real-space structure from the diffraction pattern presents a significant challenge because of the dramatic difference in intensity between the Bragg and diffuse components of the total scattering function. In contrast to the sharp Bragg diffraction, the diffuse signal has generally been considered to be a weak expansive or continuous background signal. Herein, using 1D and 2D models, it is demonstrated that diffuse scattering in fact consists of a complex array of high-frequency features that must not be averaged into a low-frequency background signal. To evaluate the actual diffuse scattering effectively, an algorithm has been developed that uses robust statistics and traditional signal processing techniques to identify Bragg peaks as signal outliers which can be removed from the overall scattering data and then replaced by statistically valid fill values. This method, described as a `K-space algorithmic reconstruction' (KAREN), can identify Bragg reflections independent of prior knowledge of a system's unit cell. KAREN does not alter any data other than that in the immediate vicinity of the Bragg reflections, and reconstructs the diffuse component surrounding the Bragg peaks without introducing discontinuities which induce Fourier ripples or artifacts from underfilling `punched' voids. The KAREN algorithm for reconstructing diffuse scattering provides demonstrably better resolution than can be obtained from previously described punch-and-fill methods. The superior structural resolution obtained using the KAREN method is demonstrated by evaluating the complex ordered diffuse scattering observed from the neutron diffraction of a single plastic crystal of CBr4 using pair distribution function analysis.