Accuracy of the half-power bandwidth method with a third-order correction for estimating damping in multi-DOF systems

A third-order correction was recently suggested to improve the accuracy of the half-power bandwidth method in estimating the damping of single DOF systems.This paper analyzes the accuracy of the half-power bandwidth method with the third-order correction in damping estimation for multi-DOF linear systems.Damping ratios in a two-DOF linear system are estimated using its displacement and acceleration frequency response curves,respectively.A wide range of important parameters that characterize the shape of these response curves are taken into account.Results show that the third-order correction may greatly improve the accuracy of the half-power bandwidth method in estimating damping in a two-DOF system.In spite of this,the half-power bandwidth method may significantly overestimate the damping ratios of two-DOF systems in some cases.

基于分子模拟的壳寡糖-金属配合物的结合模式分析

目的:探讨壳寡糖分子与金属离子之间的相互作用。方法:在构建壳寡糖分子结构基础上,将相同数量壳寡糖分子与Fe2+/Zn2+/Mg2+离子混合,进而采用分子动力学模拟法,分析壳寡糖与金属离子之间的配位结合模式。结果:每个金属离子与1~2个壳寡糖分子相结合,而每个壳寡糖结合Fe2+、Zn2+和Mg2+数量分别为2.37,2.22和2.21个。金属离子在壳寡糖分子上的结合位点,主要为氨基中氮原子(N,N1和N2)和羟基中氧原子(O1,O2,O3,O6,O7,O10,O11和O12),而基本不与醚氧原子(O,O4,O5,O8)发生配位结合。在壳寡糖与金属离子混合体系中,主要存在壳寡糖与金属离子以1∶1和2∶1的两种配位模式,进而形成“悬挂”和“桥式”两种典型特征结构。壳寡糖与3种金属离子反应产物的稳定性,依次表现为Zn2+>Fe2+>Mg2+。结论:动力学模拟与文献报道(光谱研究)结果相一致,其可作为研究金属配合物结构、糖分子与金属离子的作用机制提供重要参考。