The pyridazine–tetrathiafulvalene conjugates: synthesis,photophysical, and electrochemical properties

To study the electronic interactions in donor–acceptor (D–A) conjugates as a precursor of optoelectronic materials, a series monopyridazine-annulated tetrathiafulvalenes and a bispyridazine-annulated tetrathiafluvalene were synthesized by a condensation reaction of 2,3-dimethoxycarbonyl-6,7-dibutylthiotetrathiafulvalene or/and 2,3,6,7-tetramethoxycarbonyltetrathiafulvalene with hydrazine hydrate and structurally characterized by conventional chemical and physical methods. Their electronic properties have been studied experimentally by the combination of electrochemistry and UV–vis spectroscopy. All of monopyridazine-tetrathiafulvalene conjugates 7–13 show intramolecular charge transfer interaction in ground states, which is rationalized on the basis of density functional theory. Their HOMO energy levels and E_g^opt values were estimated to be ?4.88 to ?5.07 eV from cyclic voltammetry and 2.43–2.79 eV from the absorption spectra, respectively. The X-ray crystallographic analyses of the pyridazine–tetrathiafulvalene conjugates 7, 11–13 are also reported.     

Spatial pattern formations in diffusive predator-prey systems with non-homogeneous Dirichlet boundary conditions

A reaction-diffusion predator-prey system with non-homogeneous Dirichlet boundary conditions describes the persistence of predator and prey species on the boundary. Compared with homogeneous Neumann boundary conditions, the former conditions may prompt or prevent the spatial patterns produced through diffusion-induced instability. The spatial pattern formation induced by non-homogeneous Dirichlet boundary conditions is characterized by the Turing type linear instability of homogeneous state and bifurcation theory. Furthermore, transient spatiotemporal behaviors are observed through numerical simulations.     

An Optimal Strategy for Pairs Trading Under Geometric Brownian Motions

This paper is concerned with an optimal strategy for simultaneously trading of a pair of stocks. The idea of pairs trading is to monitor their price movements and compare their relative strength over time. A pairs trade is triggered by their prices divergence and consists of a pair of positions to short the strong stock and to long the weak one. Such a strategy bets on the reversal of their price strengths. From the viewpoint of technical tractability, typical pairs-trading models usually assume a difference of the stock prices satisfies a mean-reversion equation. In this paper, we consider the optimal pairs-trading problem by allowing the stock prices to follow general geometric Brownian motions. The objective is to trade the pairs over time to maximize an overall return with a fixed commission cost for each transaction. The optimal policy is characterized by threshold curves obtained by solving the associated HJB equations. Numerical examples are included to demonstrate the dependence of our trading rules on various parameters and to illustrate how to implement the results in practice.     

A nonmonotone smoothing Newton algorithm for solving general box constrained variational inequalities

In this paper, based on a new smoothing function, the general box constrained variational inequalities are solved by a smoothing Newton algorithm with a nonmonotone line search. The proposed algorithm is proved to be globally and locally superlinearly convergent under suitable assumptions. The preliminary numerical results are reported.     

轴棱锥对无衍射光束的线聚焦特性

基于汉克尔波理论和衍射积分理论详细分析了轴棱锥对无衍射光束的线聚焦特性, 提出了一种产生周期性局域空心光束的新方法, 即无衍射贝塞尔光束经过轴棱锥聚焦后产生具有塔尔博特效应的局域空心光束. 数值模拟了无衍射贝塞尔光束照射轴棱锥后, 沿传输距离变化的光强分布及一个周期内光强的演变和局域空心光束的形成过程. 设计实验系统, 由He-Ne激光经过一套光学系统后透过轴棱锥, 产生近似无衍射贝塞尔光束, 再由第二个轴棱锥对产生的无衍射贝塞尔光束进行线聚焦, 在第二个轴棱锥后面由显微镜观测到周期性局域空心光束, 并用CCD照相机拍摄了两个周期内的光斑图, 实验结果和理论分析相符合. 研究结果可用于多层面微粒的操控, 对周期性局域空心光束在光学微操控领域的应用具有重要的指导意义. 关键词： 贝塞尔光束 轴棱锥 线聚焦 局域空心光束     

Magnetic behaviour investigation on symmetric spin valves of Co／Cu／NiFe and NiFe／Cu／Co

In this paper,we have obtained and investigated the magnetic behaviours of the ferromagnetic layer in the symmetric spin valves of Co/Cu/NiFe and NiFe/Cu/Co by measuring with a vibrating sample magnetometer and analysing in terms of the multi-domain Ising models.It has been found that some magnetic layer can have quite different magnetic behaviours in different structures of spin valves,depending on the properties of the under-layer.In our investigation,we have found that the magnetic behaviour of a Co layer depends mainly on the magnetization of the under-layer,whereas this is not the case for the NiFe layer.     

金属有机分解法制备的SrTiO3薄膜的光学特性

采用金属有机分解法（MOD）在石英衬底上沉积了SrTiO3薄膜。所制备的薄膜是晶格常数为a=b=c=3.90?的多晶结构。通过测量190—1100nm波段内的透射光谱，采用包络方法计算了薄膜的光学常数（折射率n和消光系数k）。结果表明，采用MOD方法制备的薄膜的折射率大于采用射频磁控溅射、溶胶—凝胶和化学气相沉积方法制备的薄膜的折射率；薄膜的折射率色散关系满足单振子模型，其中振子强度S0为0.88′1014m-2，振子能量E0为6.40eV；薄膜的禁带宽度为3.68eV。     

掺铕钼酸钆荧光粉的制备与发光性能分析

通过共沉淀法制备了红色荧光粉Gd_2-xEu_x(MoO₄)₃,并采用X射线衍射(XRD)、扫描电子显微镜(SEM)和荧光光谱对所制备的样品进行结构表征分析,讨论了不同掺杂量下合成的荧光材料的发光性质。研究结果表明:所制备的Gd_2-xEu_x(MoO₄)₃红色荧光粉的三处激发峰分别位于394,465,534 nm。发射光谱中在589 nm和613 nm处有很强的发射峰,其中最强发射峰位于613 nm左右,与Eu³⁺的⁵D₀→⁷F₂跃迁对应。随着Eu³⁺掺杂量的增加,所合成的荧光粉的发光强度逐渐增强。在三组实验结果中,Gd_1.4Eu_0.6(MoO₄)₃(x=0.6)的发光强度最强。     

金属杆内疲劳裂纹与振动/超声相互作用及其定量表征

根据同步解调的原理,考察振动声调制检测输出信号中的调制成分,对金属杆内振动/超声在裂纹面上的相互作用进行了分析.制作了含有不同尺寸裂纹的铝杆试样,以扫频激励的方式得到合适的高频激励参数,分析输出信号中的调制信息,发现工件中的高频超声可分为两部分:一部分声波通过裂纹面,受到低频振动信号的调制,另一部分则保持不变。在此基础上对非线性调制模型进行了修正,并提出了一种用于裂纹检测的定量方法。与超声C扫描检测结果对比表明,此定量方法可用于估计金属杆中疲劳裂纹尺寸。     

双曲型积分-微分方程的有限体积元方法

本文研究了双曲型积分—微分方程的有限体积元方法，利用基于有限体积元的Ritz—Volterra投影的逼近性质，得到了半离散有限体积元解的最优阶L2，H^1，L∞和W^1,∞模误差估计．