斜坡补偿电流模式控制开关变换器的动力学建模与分析

降压型、升压型和升压-降压型DC-DC变换器是应用广泛的基本开关DC-DC变换器.电流模式控制开关DC-DC变换器在较宽的电路参数范围内具有两个边界,基于开关切换前后电感电流的上升和下降斜率,建立了斜坡补偿电流模式控制开关DC-DC变换器的统一模型.该模型进行无量纲归一化处理后只有三个参数,可有效展示开关DC-DC变换器在电感电流连续传导模式(CCM)和电感电流不连续传导模式(DCM)时的动力学特性.利用此模型,导出了轨道状态发生转移时的两个分界线方程,由此确定了开关DC-DC变换器的稳定周期1域、CCM鲁棒混沌域和DCM弱混沌强阵发域三个工作状态区域.开关DC-DC变换器二维参数映射图和电流模式控制降压型DC-DC变换器的电路实验观察验证了由两条分界线划分工作状态域的正确性.     

Perturbation to Lie-Mei Symmetry and Adiabatic Invariants for Birkhoffian Systems

Based on the concept of adiabatic invariant, the perturbation to Lie-Mei symmetry and adiabatic invariants for Birkhoffian systems are studied. The definition of the perturbation to Lie-Mei symmetry for the system is presented, and the criterion of the perturbation to Lie-Mei symmetry is given. Meanwhile, the Hojman adiabatic invariants and the Mei adiabatic invariants for the perturbed system are obtained.     

自制四端低值电阻的标定

用直接或间接测量法,标定自制四端低值电阻。将测量数据用加权平均法给出测量结果。     

Two New Types of Conserved Quantities Deduced from Noether Symmetry for Nonholonomic Mechanical System

For a nonholonomic mechanical system, the generalized Mei conserved quantity and the new generalized Hojman conserved quantity deduced from Noether symmetry of the system are studied. The criterion equation of the Noether symmetry for the system is got. The conditions under which the Noether symmetry can lead to the two new conserved quantities are presented and the forms of the conserved quantities are obtained. Finally, an example is given to illustrate the application of the results.     

Security of continuous-variable measurement-device-independent quantum key distribution with imperfect state preparation

The state preparation operation of continuous-variable measurement-device-independent quantum key distribution (CV-MDI-QKD) protocol may become imperfect in practical applications. We address the security of the CV-MDI-QKD protocol based on imperfect preparation of the coherent state under realistic conditions of lossy and noisy quantum channel. Specifically, we assume that the imperfection of Alice's and Bob's practical state preparations equal to the amplification of ideal modulators and lasers at both Alice's and Bob's sides by untrusted third-parties Fred and Gray employing phase-insensitive amplifiers (PIAs), respectively. The equivalent excess noise introduced by the imperfect state preparation is comprehensively and quantitatively calculated by adopting the gains of PIAs. Security analysis shows that CV-MDI-QKD is quite sensitive to the imperfection of practical state preparation, which inevitably deteriorates the performance and security of CV-MDI-QKD system. Moreover, a lower bound of the secret key rate is derived under arbitrary collective attacks, and the upper threshold of this imperfection tolerated by the system is obtained in the form of the specific gains of PIAs. In addition, the methods presented will improve and perfect the practical security of CV-MDI-QKD protocol.     

A coupled-channel lattice study of the resonance-like structure Zc(3900)

In this exploratory study, near-threshold scattering of D and \begin{document}$\bar{D}^*$\end{document} meson is investigated using lattice QCD with \begin{document}$N_f=2+1+1$\end{document} twisted mass fermion configurations. The calculation is performed in the coupled-channel Lüscher finite-size formalism. The study focuses on the channel with \begin{document}$I^G(J^{PC})=1^+(1^{+-})$\end{document} where the resonance-like structure \begin{document}$Z_c(3900)$\end{document} was discovered. We first identify the two most relevant channels and the lattice study is performed in the two-channel scattering model. Combined with the two-channel Ross-Shaw theory, scattering parameters are extracted from the energy levels by solving the generalized eigenvalue problem. Our results for the scattering length parameters suggest that for the particular lattice parameters that we studied, the best fit parameters do not correspond to the peak in the elastic scattering cross-section near the threshold. Furthermore, in the zero-range Ross-Shaw theory, the scenario of a narrow resonance close to the threshold is disfavored beyond the 3\begin{document}$\sigma$\end{document} level.     

刻槽结构高功率微波输出窗次级电子倍增效应

从理论上分析了周期性矩形刻槽对喇叭天线输出窗真空侧次级电子倍增的影响。采用动力学方法分析得到电子沿介质窗表面运动的渡越时间和碰撞能量,验证得到一定尺寸的矩形刻槽介质窗可以有效抑制次级电子倍增效应。在此情况下,对比了刻槽和不刻槽两种输出窗的辐射特性,发现周期2 mm、宽度1 mm、深度1 mm的矩形刻槽对介质窗辐射特性的影响可以忽略。     

放射性核素铀在针铁矿中的占位研究

用第一性原理研究放射性同位素铀在针铁矿(α-FeOOH)中的占位情况, 分别考虑铀原子替代针铁矿中的铁的替位缺陷和铀的多种八面体和多种四面体间隙缺陷. 计算发现了三个最稳定的缺陷构型, 它们分别对应于一个铀替位缺陷(S) 及其中的一个铀的八面体(O)和四面体(T)间隙缺陷, 其形成能分别为-13.49, -3.86, -1.60 eV. 也研究了两个相邻的铀原子在针铁矿中的占位情况, 发现双铀原子很容易掺入到相邻的SS或OS位, 它们的形成能分别为-27.392和-16.214 eV, 结合能分别为-0.417和1.131 eV. 表明双原子铀在针铁矿中会以SS形式发生偏聚而较难以OS形式偏聚. 关键词： 铀 针铁矿 占位 第一性原理     

神经元电生理学等效电路模型及参数特性研究

从考虑神经元轴突朗飞结的电缆模型入手,根据脑磁图和电磁场理论的“场路一致性”原理,讨论了应该从著名的Hodgkin-Huxley一阶静态等效电路扩展为二阶动态电路的合理性和必要性,并通过具体的计算实例进一步研究电生理学材料参数膜电容C 和电感L的频率特性,实验结果表明,有髓神经元纤维轴向信号传递速度越快,其电容和电感值就越小.