Nonlinear random stability of viscoelastic cable with small curvature

The nonlinear planar mean square response and the random stability of a viscoelastic cable that has a small curvature and subjects to planar narrow band random excitation is studied. The Kelvin viscoelastic constitutive model is chosen to describe the viscoelastic property of the cable material. A mathematical model that describes the nonlinear planar response of a viscoelastic cable with small equilibrium curvature is presented first. And then a method of investigating the mean square response and the almost sure asymptotic stability of the response solution is presented and regions of instability are charted. Finally , the almost sure asymptotic stability condition of a viscoelastic cable with small curvature under narrow band excitation is obtained.     

小曲率粘弹性索非线性随机稳定性分析

基于Kelvin粘弹性材料本构模型,研究小曲率粘弹性索在窄带随机激励作用下的非线性随机稳定性及均方响应。首先建立小曲率粘弹性索数学模型;然后提出一种确定粘弹性索均方响应及概率渐近稳定性方法;给出了系统均方稳定对激励带宽、幅值、中心频率等要求;给出系统的稳定区域;最后讨论了材料粘性、波速比及介质阻尼对系统不稳定区域的影响。     

First-Principles Studies for the Electronic Structures of Diluted Magnetic Semiconductors （Ga, Fe）As

First-principles LMTO-ASA band calculations are performed for Ga1-xFezAs (x = 1, 1/4, 1/8) by assuming supercell structures. It is found that the antiferromagnetic (AFM) state is stable for x = 1/4. For x = 1/8, ferromagnetic (FM) state is more stable than AFM state, and no stable magnetic state exists for x = 1. In both the cases the magnetic moments of As and Ga atoms are parallel to those of the nearest Fe atoms due to the p-d hybridization. Fhrther, the band structure shows rather localized Fe 3d state in the gap, and the parallel polarization is confined rather in the vicinity of Fe site.     

薄壁箱梁的翘曲连续性条件

基于薄壁杆件理论,分析了薄壁箱梁弯曲剪流和约束扭转翘曲剪流计算时的翘曲连续性 条件. 从翘曲连续性条件出发,推导了薄壁箱梁约束扭转翘曲剪流的一般公式,此外,还指 出了有关文献中的错误并进行了更正. 最后对一个悬臂箱梁的约束扭转翘曲剪流进行了计算 比较.     

基于偶应力理论剪切带问题的弹塑性有限元分析

对于软化材料的剪切带问题,传统弹塑性有限元分析遇到了困难,进入弹塑性阶段,计算结果对网格划分敏感,出现所谓的有限元网格依赖性问题,随着网格的细分,计算常常因不收敛导致失效. 用有限元软件ABAQUS计算了3个例题,证实了传统弹塑性有限元分析软化材料剪切带问题的局限性,同时证实对于无剪切带的厚壁筒问题不会出现上述问题. 进一步引入细观非局部化理论,对非局部理论含有的细观参数\ell进行了深入讨论,并采用可通过C0 -1分片检验的18参偶应力三角形单元,重新计算了3个例题,结果避免了上述问题,说明细观偶应力有限元尤其适用于分析剪切带问题.      

Energy Band Structure of Alq3/TCAQ Heterostructure Complex Film Determinedby Surface Photovoltage Spectroscopy (SPS)

IntroductionOrganic light--emitting diodes (OLEDs) have been extensively investigated since Tanget al. [l] reported a low-voltage high-efficient device in 198712'3]. It has been found that multilayer heterostructures have fascinating advantages in the whole selection of emission color, intensive brightness, high efficiency and relatively low operating voltage['--'J. It is important todetermine the energy band structure of the multilayered film, which will be helpful to interpret the electrol…     

有限体积法求解圆柱形散射介质内辐射与导热耦合换热

将谱带模型与有限体积解法相结合;求吸收、发射、散射性非灰介质圆柱体内辐射传递方程。考虑辐射强度场与热扩散温度场的耦合,将控制容积法与有限体积法结合,求解辐射与导热耦合换热。经与光线踪迹法、离散传递法的计算结果比较表明,谱带模型与有限体积解法相结合能处理多场耦合下非灰介质内的辐射换热。     

Diffraction effects in guided photonic band gap structure

The concept of the photonic band gap (PBG) structures stems from ideas of Yablonovitch. The idea is to design components so that they affect the properties of photons, in much the same way that ordinary semiconductor crystals affect the properties of electrons. In fact, the PBG structures forbid propagation of photons for a particular range of energy. They can be used to realise optical filters with large stop band and sharp transmission resonance. In the guided PBG structures, the existence of diffractive effects in the vertical dimension could limit the quality factor of such filters. In this paper, we have investigated the origin of diffraction losses in one-dimensional guided PGB structures using 2D and 3D numerical tools. We propose an analytical approach based on Bragg diffraction relation to explain these losses phenomenon. From this approach, the influence of some design parameters on the electromagnetic behaviour and the spectral response of PBG resonators will be explained.     

Discrete embedded modes in the continuum in 2D lattices

We study the problem of constructing bulk and surface embedded modes (EMs) inside the quasi-continuum band of a square lattice, using a potential engineering approach à la Wigner and von Neumann. Building on previous results for the one-dimensional (1D) lattice, and making use of separability, we produce examples of two-dimensional envelope functions and the two-dimensional (2D) potentials that produce them. The 2D embedded mode decays like a stretched exponential, with a supporting potential that decays as a power law. The separability process can cause that a 1D impurity state (outside the 1D band) can give rise to a 2D embedded mode (inside the band). The embedded mode survives the addition of random perturbations of the potential; however, this process introduces other localized modes inside the band, and causes a general tendency towards localization of the perturbed modes.     

翘曲度对锗烯的电子结构及光学性质的影响

本文采用基于密度泛函理论的第一性原理方法研究不同翘曲度下锗烯的电子结构及光学性质,分析翘曲度对电子结构及光学性质的影响。采用六种不同的近似方法对锗烯的几何结构进行优化,得到最稳定的结构体系,在此基础上选取不同的翘曲度,并对翘曲度的稳定性进行论证得到三种较稳定的翘曲结构。通过翘曲度的调节打开锗烯的带隙,并且通过调节翘曲度实现锗烯带隙在间接带隙和直接带隙之间的转化,通过分析态密度解释了能带结构的调控机制,以及翘曲度对锗烯光学性质的影响。研究表明翘曲度能够有效地调控锗烯的电子结构和光学性质,提高光电子利用效率。