高压熔渗生长法制备金刚石聚晶中碳的转化机制研究

在6 GPa和1500 ℃的压力和温度范围内, 利用高压熔渗生长法制备了纯金刚石聚晶, 深入研究了高温高压下金刚石聚晶生长过程中碳的转化机制. 利用光学显微镜、X-射线衍射、场发射扫描电子显微镜检测, 发现在熔渗过程中金刚石层出现了石墨化现象, 在烧结过程中金刚石颗粒表面形貌发生了变化. 根据实验现象分析, 在制备过程中存在三种碳的转化机制: 1)金属熔渗阶段金刚石颗粒表面石墨化产生石墨; 2)产生的石墨在烧结阶段很快转变为填充空隙的金刚石碳; 3)金刚石直接溶解在金属溶液中, 以金刚石形式在颗粒间析出, 填充空隙. 本文研究碳的转化机制为在高温高压金属溶剂法合成金刚石的条件下(6 GPa和1500 ℃的压力和温度范围内)工业批量化制备无添加剂、无空隙的纯金刚石聚晶提供了重要的理论指导.     

两类广义Petersen 图的Euler亏格

广义 Petersen 图 P(n, m) 是这样的一个图:它的顶点集是{u_i, v_i | i=0,1, ^… , n-1}, 边集是 {u_iu_i+1, v_iv_i+m, u_iv_i | i=0,1, ^…, n-1}, 这里 m, n 是正整数、加法是在模n 下且 m<|n/2| . 这篇文章证明了P(2m+1, m)(m≥ 2) 的 Euler 亏格是1, 并且 P(2m+2, m)(m≥ 5) 的 Euler 亏格是2.     

MKdV方程的多辛Fourier拟谱方法

基于谱微分矩阵方法,给出MKdV方程的多辛Fourier拟谱格式及其相应多辛离散守恒律,证明了它等价于通常的Fourier拟谱格式．数值结果表明,格式对于长时间计算具有稳定性与高精度．     

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.     

Size and Shape Effect of Gold Nanoparticles in “Far‐Field” Surface Plasmon Resonance

The “far‐field” surface plasmon resonance (FSPR) of metal nanoparticles, which have built a facile way to emission enhancement of red, green, blue, and white with nice reproducibility, has big potential application in solution‐processed organic light‐emitting diodes (OLEDs). According to the theory of the “far‐field” effect, the reflectivity of the metal surface and the phase shift at the reflection play an important role in enhancing ratio, which strongly relate to the size and shape of nanoparticles. In this work, gold nanospheres with different sizes and nanorods are synthesized in order to determine the size and shape effect of FSPR. The results demonstrate that the one with higher reflectivity in a certain range induces a better emission enhancement in the luminous efficiency and the maximum brightness. The nanoparticles with bigger sizes and shape of rods have higher reflectivity, which is consistent with the simulation based on FSPR effect. The phase shifts of different nanoparticles are optimized by the distance between gold nanoparticles and emitters. The metal NPs with a high reflectivity and the applicable phase shift will have big potential for the emission enhancement in OLEDs.     

Hopf bifurcation in doubly fed induction generator under vector control

This paper first presents the Hopf bifurcation phenomena of a vector-controlled doubly fed induction generator (DFIG) which is a competitive choice in wind power industry. Using three-phase back-to-back pulse-width-modulated (PWM) converters, DFIG can keep stator frequency constant under variable rotor speed and provide independent control of active and reactive power output. Main results are illustrated by “exact” cycle-by-cycle simulations. The detailed mathematical model of the closed-loop system is derived and used to analyze the observed bifurcation phenomena. The loci of the Jacobian’s eigenvalues are computed and the analysis shows that the system loses stability via a Hopf bifurcation. Moreover, the boundaries of Hopf bifurcation are also given to facilitate the selection of practical parameters for guaranteeing stable operation.     

"习得性无助"现象的分析与干预

我们经常会遇到这样的现象：学生在学习时缺少动力和进取心，遇到挫折时又大多倾向放弃，甚至对自己力所能及的任务也不能胜任，而且认为自己无论怎样努力都不能取得成功，心理学上称这种现象为“习得性无助”（learned helplessness）．它是一个人经历了失败和挫折后，面对新老问题时产生的无能为力的心理状态和行为．     

夸克胶子混合真空凝聚和Dyson-Schwinger方程

基于夸克传播子的Dyson-Schwinger方程，计算了夸克胶子混合真空凝聚和夸克真空凝聚. 这些凝聚不仅联系着夸克在真空态中的虚度，而且也表征了真空中夸克分布的空间宽度. 真空凝聚的存在直接反映着QCD真空的非微扰结构. 计算表明：上夸克与下夸克的虚度为λ²_u,d=0.7GeV²，奇异夸克的虚度为λ²_s=1.6GeV². 这些结果与许多用完全不同的方法得到的结果一致.     

求解矩阵方程AXB+CXD=F参数迭代法的最优参数分析

本文针对求矩阵方程AXB+CXD=F唯一解的参数迭代法，分析当矩阵A，B，C，D均是Hermite正（负）定矩阵时，迭代矩阵的特征值表达式，给出了最优参数的确定方法，并提出了相应的加速算法.     

A percolation study of RTS noise in deep sub-micron MOSFET by Monte Carlo simulation

Based on percolation theory and random telegraph signal (RTS) noise generation mechanism, a numerical model for RTS in deep submicron metal-oxide-semiconductor field-effect transistor (MOSFET) was presented, with which the dependence of Tc/Te (where Tc=capture time, Te=emission period ) on energy levels and trap depth with respect to the interface of traps can be simulated. Compared with experimental results, the simulated ones showed a good qualitative agreement.