Efficient two-photon sensitized luminescence of europium （Ⅲ） complex based on hypersensitive transitions

Red frequency-upconversion fluorescence emission is observed in europium(Ⅲ) complex with encapsulating polybenzimidazole tripodal ligands, pumped with 930- and 1070-nm picosecond laser pulses. The lumines- cence of transition 5D0 →7F2 (612 nm) is induced by two-photon absorption of hypersensitive transitions 7F0 →5D2 (465 nm) and 7F1 →5D1 (535 nm). Analysis results suggest that the two-photon excitation strength of these hypersensitive transitions is increased dramatically owing to the C3 symmetry of the coordination field.     

Tunneling of Boseben-Einstein condensate and interference effect in a harmonic trap with a Gaussian energy barrier

The tunneling effect of Bose-Einstein condensate (BEC) in a harmonic trap with a Gaussian energy barrier is studied in this paper. The initial condensate evolves into two separate moving condensates after the tunneling time under certain conditions. The interference pattern between the two moving condensates is given as a comparison and as a further demonstration of the existence of the global phase.     

Varistor behavior study in undoped tungsten trioxide ceramic

In this paper, varistor property and mechanism of undoped tungsten trioxide (WO₃) ceramic have been studied. Experimental results revealed that pure WO₃ ceramic could exhibit a nonohmic behavior which was formed in the cooling process of ceramic, and very sensitive to heat treatment in different atmospheres. By comparison with the reported SnO₂ and ZnO varistor systems, it is supposed that the surface of WO₃ grain is more ready to adsorb oxygen and form high enough barriers at grain boundaries responsible for varistor behavior. The influences of heat treatments on the varistor properties of WO₃ ceramic have been investigated.     

First-principles calculations on electronic structures of Fe-vacancy-codoped TiO2 anatase (1 0 1) surface

The electronic structures of Fe-doped TiO₂ anatase (1 0 1) surfaces have been investigated by all spin-polarized density functional theory (DFT) plane-wave pseudopotential method. The general gradient approximation (GGA)+U (Hubbard coefficient) method has been adopted to describe the exchange-correlation effects. Through the density functional calculations for the formation energies of various configurations, the complex of a substitutional Fe plus an O vacancy was found to form easily in the most range of O chemical potential. The calculated density of the states of the system of Fe-doped surface with a surface oxygen vacancy shows a band gap narrowing from 2.8 to 1.9 eV comparing with the pure surface due to the synergistic effects of surface Fe impurities with O vacancies. The system processes high visible light sensitivity and photocatalytic ability by decreasing extrinsic absorption energy. By comparing the partial DOS of some O and Ti atoms lying in the outermost and bottom layers of Fe-doped surfaces, it was found that the influence of Fe impurities on the electronic structure of the system is localized.     

Synthesis of dimension-tunable ZnO nanostructures via the design of zinc hydroxide precursors

A facile synthesis route is presented to achieve dimension-tunable ZnO nanostructures by the design of zinc hydroxide precursors under the surfactant-free condition. From three types of zinc hydroxide precursors, namely, crystalline Zn(OH)(NO₃)(H₂O) nanobelts, amorphous zinc hydroxides microparticles and soluble Zn(OH)^2-₄\mathrm{Zn}(\mathrm{OH})^{2-}_{4} species, the porous ZnO nanosheets, ZnO nanoparticles and ZnO nanowires can be achieved, respectively. The porous ZnO nanosheets exhibit large polar surface area. Thermal analysis indicates that the crystalline Zn(OH)(NO₃)(H₂O) nanobelts were converted to the porous ZnO nanosheets by in situ lattice reconstruction, which was attributed to the unique fibrous structure of Zn(OH)(NO₃)(H₂O) nanobelts. The as-prepared dimension-tunable ZnO nanostructures have potential applications in solar cells, photocatalysis, novel chemical and biological sensors, etc.     

Synthesis,formation mechanism and electric property of hollow InP nanospheres

The present work reports on novel four-layer thermally driven piezoresistive cantilevers implemented in one- and two-dimensional arrays for parallel proximity scanning. There, the heater (metallic meander), the piezoresistive deflection sensor, and the metal actuation film with significantly higher thermal expansion coefficient make up separate layers. Actuation efficiency and cross-talk of the novel cantilever design are studied and compared with two recent designs: thin metallic film and ion-implanted heater. The novel actuator, integrated on a 240 μm long and 3 μm thick silicon cantilever and supplied by V _dc=1 V enables deflections up to 5 μm of the AFM-tip with an actuation efficiency of about 170 nm/mW and suppressed cross-talk between actuator and sensor.     

基于随机矩阵理论的城市人群移动行为分析

移动通信应用为人类移动规律的研究提供了独特的数据来源. 本文通过城市手机用户的分布数据,研究城市移动人群的整体动力学行为. 借助随机矩阵理论的方法,通过比较移动人群数据与随机数据在互相关矩阵谱分布上的差异,发现移动人群数据互相关矩阵的相关系数均值、最大本征值及其对应的本征向量明显偏离于随机互相关矩阵的分布,指出这种差异体现了城市移动人群的整体行为特性,且这种差异在不同时间段也会有所不同. 研究结果体现出相关系数的均值和最大本征值的波动趋势,并指出本征向量成员权重的时空模式与城市移动人群整体行为特征的波动过 关键词： 随机矩阵理论 移动人群 宏观行为     

立方五次方非线性Schrdinger方程的动力学性质研究

采用辛算法数值求解了一维立方五次方非线性Schrdinger方程,研究了不同非线性参数下非线性Schrdinger方程的动力学性质.数值结果表明,随着立方非线性参数的增加,系统经历了拟周期状态、混沌状态和周期状态,且在五次方项的调制下,呼吸子解可以退化为单孤子解.     

关于B~0→π~-~+■_衰变过程分支比的计算

通过构造适当的关联函数,计算B→π跃迁形状因子fB+π(q2),fBπ(q2)和标量形状因子f0(q2),从而就能研究轻子质量对B0→π-+ν(l=e,μ,τ)衰变过程的影响.首次分别计算B0→π-e+νe,B0→π-μ+νμ,B0→π-τ+ντ衰变过程的分支比,并发现轻子质量me,mμ可以忽略,但重轻子质量mτ不能忽略,它对分支比计算有一定的贡献.把计算结果与最近的实验数据进行比较,发现理论结果与实验数据基本符合.     

应用于扫描探针显微镜的石英音叉机械模型研究

石英音叉作为力传感器广泛地应用于各种扫描探针显微镜,主要涉及石英音叉的同相振动和反相振动两种振动模式.通过实验方法和有限元仿真方法对石英音叉的两种振动模式进行研究,发现石英音叉的双臂之间以及双臂与音叉的基部之间都存在耦合作用,双臂之间的耦合使音叉的反相共振频率升高,双臂与基部之间的耦合使音叉的同相共振频率降低.针对两种振动模式的动态特性建立了石英音叉的机械模型并进行合理简化.简化模型是一个四弹簧三质点系统,计算了简化模型的参数.通过一个音叉臂等效质量变化与音叉反相共振频率变化之间的定量关系证明了简化机械模 关键词： 扫描探针显微镜 石英音叉 振动模式 机械模型