不同开关频率下电压控制升压变换器中的Hopf分岔分析

由于电压控制升压变换器的传统平均模型中没有包含开关频率,从而无法分析开关频率的大小对电压控制升压变换器中Hopf分岔的影响. 通过建立电压控制升压变换器的含有开关频率的改进平均模型,分析了开关频率对电压控制升压变换器中Hopf分岔的影响,并设计硬件电路,给出电路试验结果. 研究表明:采用电压控制升压变换器的改进平均模型,可以有效地分析不同开关频率对电压控制升压变换器中Hopf分岔的影响; 随着开关频率的减小,电压控制升压变换器更易于发生Hopf分岔. 关键词： 改进平均模型 电压控制升压变换器 开关频率     

自然的改进型节点电压方程

通过对节点导纳矩阵的进一步分析,得出节点电压方程一种新的形式,用节点电压方程能够直观地从电路图直接绘制出信号流图而不需列写KCL,KVL和器件方程.类似的,通过圈阻抗矩阵的分析,也得到了新形式的圈电流方程.     

Analysis of superconducting cavity quench events at SSRF

Quench is important and dangerous to superconducting RF cavities. This paper illustrates the mechanism of quench and how a quench detector works, and analyzes the quench events happening during beam operations and cavity conditioning. We find that the quench protection is mostly triggered by some reasons such as fluctuation of cavity voltage, multipacting or arc, rather than a real cavity thermal breakdown. The results will be beneficial to optimize the operation parameters of superconducting cavities, to discover the real reasons for beam trip by quench interlock, and to improve the operation stability of superconducting RF systems.     

红外光激发作用下分子导电纳米结的非弹性电流研究

将"金属-单分子-金属"模型化为分子导电纳米结,应用扩展主方程方法研究了红外光激发作用下弱耦合分子导电纳米结的非弹性电流的传导过程.分别采用偶极跃迁的指数耦合、平方耦合以及线性耦合模型描述红外光场与分子的相互作用,研究了不同光场作用下非弹性电流与所加电压的关系,并讨论了分子内振动能重新分布效应对电流-电压特性的影响. 关键词： Franck-Condon阻滞 非弹性电流 电流-电压特性 红外光激发     

Surface States in the AlxGa1-xN Barrier in AlxGa1-xN／GaN Heterostructures

Frequency-dependent capacitance-voltage (C-V) measurements have been performed on modulation-doped Al0.22 Ga0.78N/GaN heterostructures to investigate the characteristics of the surface states in the AlxGa1-xN barrier. Numerical fittings based on the experimental data indicate that there are surface states with high density locating on the AlxGa1-xN barrier. The density of the surface states is about 10^12cm^-2eV^-1, and the time constant is about 1μs. It is found that an insulating layer (Si3N4) between the metal contact and the surface of AlxGa1-xN can passlvate the surface states effectively.     

Threshold of Non－Destructive Pulse for Pt Tip of STM on Graphite Surface

The experimental relationship between width and amplitude of the non-destructive threshold pulse for Pt tip of a scanning tunneling microscope (STM) on graphite surface have been studied strictly and systematically in a wide range of pulse width for the first time. The threshold curve of amplitude versus width indicates that the amplitude of threshold pulse will increase with the decrease of the pulse width. A more rigorous explanation is suggested to interpret the dependence of threshold pulse amplitude on width. Fitted with the experimental data,a new empirical formula is given, extrapolated from which the threshold pulse amplitude will rise to 50 V when the pulse width decreases to 10ns.     

Single Cell Element of Chalcogenide Randoul Access Memory Fabricated with the Focused Ion Beam Method

A singie cell element of chalcogenide random access memory was fabricated by using the focused ion beam method.The contact size between the Ge2Sb2Te5 Phase change film and the top electrode film is about 600nm (diameter) and the contact area is caiculated to be 0.28μm^2.The thickness of the phase change film is 83nm.The current-voltage characteristics of the cell element are studied using the home-made current-voltage tester in our laboratory.The minimum threshold current of about 0.6mA is obtained.     

衰减全反射型电压传感器的理论和实验研究

提出了一种新型反射型聚合物波导电压传感器理论,并且进行了实验研究。这种电压传感器采用棱镜波导耦合结构,在棱镜下底面依次镀有金属膜一聚合物一金属膜三层结构。通过两层金属膜对极化聚合物加电压,利用聚合物材料电光效应和导模共振吸收峰对聚合物折射率的敏感特性,通过反射光强的测量来确定作用电压的变化值。实验中的测试电压范围是从-140V至 140V,得到的线性度值为0．991,电压测量的分辨力为0．1V,电压测量灵敏度系数为0．0011V^-1。实验表明这种电压传感器具有良好的线性和较高的灵敏度。