Multiple stability switches and Hopf bifurcation in a damped harmonic oscillator with delayed feedback

This paper takes into consideration a damped harmonic oscillator model with delayed feedback. After transforming the model into a system of first-order delayed differential equations with a single discrete delay, the single stability switch and multiple stability switches phenomena as well as the existence of Hopf bifurcation of the zero equilibrium of the system are explored by taking the delay as the bifurcation parameter and analyzing in detail the associated characteristic equation. Particularly, in view of the normal form method and the center manifold reduction for retarded functional differential equations, the explicit formula determining the properties of Hopf bifurcation including the direction of the bifurcation and the stability of the bifurcating periodic solutions are given. In order to check the rationality of our theoretical results, numerical simulations for some specific examples are also carried out by means of the MATLAB software package.

     

谷胱甘肽-二茂铁的合成及其与牛血清白蛋白的相互作用

采用液相合成法, 以O-苯并三唑-N,N,N',N'-四甲基脲六氟磷酸酯(HBTU)和1-羟基苯并三氮唑(HOBT)为缩合剂, 将二茂铁胺和还原型谷胱甘肽(GSH)反应, 合成了具有电化学活性的谷胱甘肽-二茂铁(GSH-Fc), 其收率为23.2%, 并对目标产物进行了红外、核磁、质谱表征. 通过电化学方法研究了GSH-Fc与牛血清白蛋白(BSA)之间的相互作用特性. 电化学实验结果表明, BSA和GSH-Fc结合位点位于BSA的亚结构域IIA, 结合常数为1.71×106 L·mol-1, 结合位点数为1.30. 同时通过荧光光谱法研究了GSH-Fc与BSA相互作用是一种静态猝灭的过程, 结合常数和结合位点数分别为2.74×106 L·mol-1和1.57, 与电化学方法得到的结果相吻合.     

NiFe/Pt薄膜中角度相关的逆自旋霍尔效应

NiFe/Pt双层薄膜样品在铁磁共振时, NiFe磁矩进动所产生的自旋流注入到Pt层中, 由于逆自旋霍尔效应产生直流电压V_ISHE, 此电压会叠加到NiFe薄膜由于自旋整流效应而产生的电压V_SRE 上, 实验测量所得电压为V_ISHE和V_SRE的叠加. 为了区分这两种不同机理对电压的贡献, 本文采取旋转外加静磁场的方法, 通过分析所测电压随磁场角度的变化从而分离出V_ISHE 的大小. 研究结果表明, 相比于单层NiFe(20 nm)薄膜样品, NiFe(20 nm)/Pt(10 nm)双层膜样品中由于NiFe自旋注入到Pt 中导致铁磁共振线宽增加. 与逆自旋霍尔效应产生的电压相比, 自旋整流效应的贡献较小, 但不可忽略. 本文工作有助于认清铁磁/非磁性金属材料中的自旋相关效应, 并提供了一种准确的分析逆自旋霍尔效应的方法.