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.     

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.     

Electronic structure of Mg–Zn-based compounds

We present a comparison between calculated densities of states of the Laves phase MgZn₂ and hexagonal Mg₂₈Zn₆₅Y₇ and experimental results obtained using both X-ray emission and photoabsorption spectroscopy techniques. We show that there is general agreement between both sets of data for both alloys. We also point out that the two samples retain a metallic character, yet the hexagonal approximant of the Mg–Zn–Y quasicrystal family is less metallic than the Laves phase.     

纳米硫化铜近红外吸收材料

采用新型超声喷雾法技术,把摩尔分数都为0.5%的Cu(NO3)2和Na2S水溶液分别作为初始反应溶液,调节溶液体系的pH值在6～8,把经过超声雾化后的Cu(NO3)2溶液逐步加入到处于强力搅拌的Na2S水溶液中,经陈化过滤后获得纳米半导体硫化铜(CuxS,1≤x≤2)粉体。分析了不同热处理温度与原料配比对获得的硫化铜纳米颗粒化学成分的影响,用X射线粉末衍射仪表征了纳米硫化铜粒子的晶相与化学组成,并采用扫描电镜观察了相应化学组成的粒子晶相形貌,测定了不同化学组分纳米硫化铜粒子从可见到近红外胶体状的吸收和透射光谱。研究表明不同化学组成的纳米硫化铜对近红外光都具有显著的吸收效应,这是由于电子在硫化铜半导体纳米粒子能带中的跃迁所致,同时这些半导体粒子对可见光具有很高透过性,但其可见光透射率随着纳米粒子从Cu2S趋向CuS而略有下降。     

Diketopyrrolopyrrole‐based conjugated polymers and small molecules for organic ambipolar transistors and solar cells

The present highlight discusses major work in the synthesis of low bandgap diketopyrrolopyrrole ( DPP )‐based polymers with donor–acceptor–donor ( D–A–D ) approach and their application in organic electronics. It examines the past and recent significant advances which have led to development of low bandgap DPP ‐based materials with phenyl and thiophene as donors. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013, 51, 4241–4260