Infrared spectra study of Nd1.85−xRxCe0.15CuO4±δ (R = Gd and Sm) single crystals

The X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectra, and resistivity ρ are measured on Nd_1.85?xR_xCe_0.15CuO_4±δ (R = Gd and Sm) single crystals. From the XRD and FTIR spectra studies, the lattice constant c are found to decrease faster for Gd doping than that for Sm doping with increasing doping concentration x. Upon Gd doping, all the transmission peaks shift to high frequency but nearly unchanged with increasing Sm doping content. The volume of the unit cell observed through XRD and FTIR spectra decreases faster for Gd doping than that for Sm doping. Furthermore, for Gd doping the superconducting T_c decreases rapidly with increasing the doping concentration, while the T_c decreases slowly for Sm doping with increasing Sm content, which is found to be very well consistent with the evolution of the volume of the unit cell for two series.     

Gradient force evolution of Gaussian beam induced by a phase plate

The evolution of gradient force pattern induced by an annular phase distribution plate is numerically investigated in this paper. The phase plate, which may alter the wavefront phase of incident Gaussian beam with tunable topological charge, consists of two concentric portions, one center circle portion and one annular portion. Numerical simulations show that the proposed plate can induce the tunable gradient force on the particles in the focal region. By adjusting the geometrical parameters or changing the topological charge of the phase-shifting plate, some novel trap patterns may occur, such as triangle shape trap, quadrangle shape trap, pentagon shape trap, hexagon shape trap, and the shapes of optical traps change very considerably. Therefore, the phase plate may be very advantageous for constructing tunable optical traps. The method is more versatile in that it allows precise control of the parameters and has the possibility of generating specific patterns of optical vortices. The gradient force pattern focal of intensity distribution depends on both the annular width and the topological charge.     

主成分分析方法在空间干涉仪图像处理中的应用

在干涉仪图像数据处理过程中,目前采用的多行平均图像处理算法会引入较大随机误差,且当CCD相机与狭缝之间存在小转角时,会引入较大系统误差。本文主要探究利用主成分分析（PCA）算法处理空间干涉仪图像的可行性与优势。利用MATLAB模拟空间干涉仪图像,并加入随机噪声和图像旋转,利用PCA方法和多行平均算法处理数据,比较两种算法的得到的结果误差大小。并设计CCD相机小转角实验和干涉图像弱信号实验,评估PCA算法在数据处理过程中纠正CCD相机小转角和重建弱信号图像中的效果。理论和实验均证明,PCA算法较目前多行平均算法,能更有效地降低噪声,分析弱信号图像及纠正CCD相机小转角,消除其带来的系统误差。     

基于粒子滤波的一种改进的资料同化方法

针对在粒子数较少时传统的集合卡尔曼滤波和粒子滤波方法不能有效表征后验概率密度函数(PDF)的问题, 提出了一种改进的粒子滤波方法. 主要思想是在预测步之后引入更新步, 并且将观测时刻与非观测时刻的同化分析进行区别处理. 对典型的低维和高维混沌系统的仿真结果表明:改进粒子滤波方法是一种非常有效的估计非线性非高斯随机系统状态的方法.     

在巴黎势的波函数中氘核的形状因子A(Q~2)(英文)

在非相对论的框架内和应用描述了高动量过程的巴黎势所产生的氘核的波函数,计算了氘核的电磁形状因子A(Q~2)。A(Q~2)因子化为氘核的结构函数Z(t)和偶极形状G_D(t)之积。结构函数Z(t)是用巴黎势的波函数做数值计算而得到的。对A(Q~2)的预言跟实验数据的分析非常一致,这一对实验结果的成功描述说明:氘核形状因子A(Q~2)这一简单的理论描述是非常成功的,并且可以用到氘核的其他静态性质的研究。     

有限时间Lyapunov指数的高精度计算新方法

针对目前有限时间Lyapunov指数(FTLE)计算方法准确度不高和无法获得边界值的问题,基于对偶数理论提出了一种新的高精度计算方法.首先描述了基于有限空间差分方法计算FTLE的缺点和问题:其次介绍了基于对偶数理论的高精度导数计算方法及其显著优点,并将动力系统的柯西一格林形变张量计算问题转化为对偶数空间中非线性微分方程数值求解问题;最后对单摆和非线性Duffing振子两个典型物理动力系统进行了数值实验.结果表明:基于对偶数理论的新方法能有效、方便和高精度地计算出有限时间Lyapunov指数场,并成功识别出所包含的拉格朗日相关结构.     

Terahertz-wave parametric oscillator with a misalignment-resistant tuning cavity

We demonstrate a terahertz-wave parametric oscillator (TPO) with a corner-cube resonator consisting of a corner-cube prism (CCP) and a flat mirror. By using the cavity configuration proposed in this Letter, the generation of tunable monochromatic terahertz (THz) waves can be achieved just by rotating the flat mirror instead of rotating the TPO cavity relative to the pump beam. The THz-wave output intensity and pulse width can be controlled periodically by rotating the CCP around the cavity axis. The TPO stability against cavity misalignment is significantly improved by at least 1 to 2 orders of magnitude compared with the conventional plane-parallel resonator configuration.     

Optical characterization of antimony-based bismuth-doped thin films with different annealing temperatures

Antimony-based bismuth-doped thin film,a new kind of super-resolution mask layer,is prepared by magnetron sputtering.The structures and optical constants of the thin films before and after annealing are examined in detail.The as-deposited film is mainly in an amorphous state.After annealing at 170-370℃,it is converted to the rhombohedral-type of structure.The extent of crystallization increased with the annealing temperature.When the thin film is annealed,its refractive index decreased in the most visible region,whereas the extinction coefficient and reflectivity are markedly increased.The results indicate that the optical parameters of the film strongly depend on its microstructure and the bonding of the atoms.     

Oscillating viscosity in a lyotropic lamellar phase under shear flow

We report some time-dependent behavior of lyotropic lamellar phase under shear flow. At fixed stress, near a layering instability, the system presents an oscillating shear rate. We build up a new stress versus shear rate diagram that includes temporal behavior. This diagram is made of two distinct branches of stationary states which correspond, respectively, to disordered and ordered multilamellar vesicle phases. When increasing the shear stress, prior to the transition to the ordered structural state, sustained oscillations of the viscosity are recorded. They correspond to periodic structural change of the entire sample between a disordered and a ordered state of multilamellar vesicles.     

双轴晶体光学参量放大的研究

介绍了新近提出的光学啁啾脉冲参量放大技术,并以高增益、宽谱带的双轴非线性晶体LBO为例,研究了抽运光和信号光的相位匹配的关系、增益、增益带宽、匹配角的选择,以及增益随晶体长度变化的趋势和双曲正割和高斯脉冲输入非线性晶体前后变化的情况。