数字控制DC-DC Buck变换器中低频振荡现象分析

在考虑采样保持器的作用下,建立了数字控制Buck变换器系统的z域模型,由此揭示了系统发生低频分岔现象的原因.根据系统特征值的变化趋势,预测了该数字控制变换器失稳时分岔点的位置和类型,同时,推导出系统发生低频振荡的频率以及振幅,即系统波动方程.最后,通过PSpice电路仿真实验验证了理论分析结果的合理性与有效性. 关键词： 低频振荡 数字控制 变换器 z域模型')" href="#">z域模型     

半圆形容器等离子体源离子注入过程中离子动力学的两维PIC计算机模拟

利用两维particle-in-cell方法研究了半圆形容器表面等离子体源离子注入过程中鞘层的时空演化规律. 详尽考察了鞘层内随时间变化的电势分布和离子密度分布规律,离子在鞘层中的运动轨迹和运动状态,得到了半圆容器内、外表面和边缘平面上各点离子注入剂量分布规律,获得了工件表面各点注入离子的入射角分布规律. 研究结果揭示了半圆容器边缘附近鞘层中离子聚焦现象,以及离子聚焦现象导致工件表面注入剂量分布和注入角度分布存在很大不均匀的基本物理规律. 关键词： 等离子体源离子注入 鞘层 两维particle-in-cell方法 离子运动轨迹     

激光场中一维和三维氢分子离子模型经典动力学行为的比较

应用经典轨迹方法,采用辛算法数值求解激光场中的一维和三维氢分子离子(H2 )的Hamilton正则方程,得到氢分子离子在激光场作用下的经典轨迹,并比较分析氢分子离子一维模型与三维模型的存活、解离、电离和库仑爆炸等动力学行为,以及电子的运动情况的相似之处.数值结果表明,采用一维模型能近似定性反映氢分子离子的动力学行为,并且简便可行.     

改进的基于主成分分析的三维人脸形状建模

针对基于主成分分析(PCA)的三维(3D)人脸形状重构不精确的缺点,对位移向量、缩放因子、旋转矩阵、重构系数等参数进行了精确的定义和计算,并对重构模型进行了有效的调整。根据CVL Face Database建立了113个3D人脸形状模型,经迭代运算后重构出了由特征点组成的稀疏3D人脸形状模型。利用径向基函数(RBF)得到了密集3D人脸形状模型。试验结果表明,算法可以得到精确的重构模型,对深度旋转的人脸图像和特征点定位误差也有很好的鲁棒性。     

氧化铟锡薄膜的椭偏光谱研究

用溅射法在Si片上制备了厚度为140nm的氧化铟锡(ITO)薄膜。X射线衍射研究表明所制备的薄膜为多晶结构。在1.5~4.5eV范围内对ITO薄膜进行了椭偏测量。分别用德鲁德-洛伦茨谐振子(Drude Lorenz oscillators)模型、层进模型结合有效介质近似模型对椭偏参量ψ、Δ进行了拟合,得到ITO薄膜的折射指数n的变化范围在1.8~2.6之间,可见光范围内消光系数k接近于零,在350nm波长附近开始明显变化,且随着波长的减小k迅速增加。计算得到直接和间接光学带隙分别是3.8eV和4.2eV。并在1.5~4.5eV段给出一套较为可靠的、具有实用价值的ITO介电常量和光学常量。     

基于各向异性扩散的红外图像噪声滤波算法

抑制红外焦平面阵列探测器噪声时,为了有效保持边缘细节,在塔基(Tukey)扩散模型的基础上,提出了一种基于各向异性扩散的滤波算法.算法由微分法提取边界点集,利用信号和噪声的空间分布特性对图像进行预处理,从而改善了Perona-Malik(P-M)方程的病态性.建立了新的扩散系数且该系数在理论上满足Charbonnier等人构造准则.通过给定边界条件实现了有利于保持边缘的目的.该算法已在基于DSP FPGA的硬件平台上实时运行,较好地抑制了噪声,又有效地保持了边缘,处理后的图像具有良好的视觉效果.     

A unified approach to fuzzy modelling and robust synchronization of different hyperchaotic systems

In this paper, a Takagi Sugeno （T-S） fuzzy model-based method is proposed to deal with the problem of synchronization of two identical or different hyperchaotic systems. The T S fuzzy models with a small number of fuzzy IF-THEN rules are employed to represent many typical hyperchaotic systems exactly. The benefit of employing the T-S fuzzy models lies in mathematical simplicity of analysis. Based on the T-S fuzzy hyperchaotic models, two fuzzy controllers arc designed via parallel distributed compensation （PDC） and exact linearization （EL） techniques to synchronize two identical hyperchaotic systems with uncertain parameters and two different hyperchaotic systems, respectively. The sufficient conditions for the robust synchronization of two identical hyperchaotic systems with uncertain parameters and the asymptotic synchronization of two different hyperchaotic systems are derived by applying the Lyapunov stability theory. This method is a universal one of synchronizing two identical or different hyperchaotic systems. Numerical examples are given to demonstrate the validity of the proposed fuzzy model and hyperchaotic synchronization scheme.     

Evidence for an isomeric 3/2- state in 53Co

The fragmentation of a 550MeV/u primary beam of ⁵⁸Ni on a ⁹Be target has been used to measure time- and energy-correlated γ decays following the implantation of event-by-event discriminated secondary fragments into a ⁹Be stopper plate. A new isomeric γ decay with T _1/2 = 14( ) ns and E _γ = 646.2(2) keV is observed and attributed to the decay of the yrast 3/2^- state in ⁵³ ₂₇Co₂₆ . This short-lived isomeric state has been populated by means of nuclear reactions during the stopping process of the secondary fragments. The experimental findings are discussed in the framework of large-scale spherical shell model calculations in conjunction with isospin symmetry-breaking residual interactions for the A = 53 , T _z = ±1/2 mirror nuclei ⁵³Co and ⁵³Fe .     

A U（4） QCD Model Using Generalized Yang-Mills Theory

Generalized Yang-Mills theory has a covariant derivative which contains both vector and pseudoscalar gauge bosons. Based on this theory, we construct a U（4） strong interaction model. By using this U（4） generalized Yang-Mills model, we obtain that mesons can be realized as the colorless pseudoscalar gauge bosons. We also obtain a gauge potential solution which can be used to explain the asymptotic behavior and color confinement.     

Ground State Properties of Superheavy Nuclei in Macroscopic-Microscopic Model

The ground state properties of superheavy nuclei are systematically calculated by the macroscopic- microscopic （MM） model with the Nilsson potential. The calculations well produced the ground state binding energies, α-decay energies, and half lives of superheavy nuclei. The calculated results are systematically compared with available experimental data. The calculated results are also compared with theoretical results from other MM models and from relativistic mean-field model. The calculations and comparisons show that the MM model is reliable in superheavy region and that the MM model results are not very sensitive to the choice of microscopic single-particle potential.