二维准分形结构声子晶体透射特性的数值研究

本文用时域有限差分方法研究了几种具有相似几何结构的准分形声子晶体的透射特性.计算了由水中钨柱组成的二维准分形结构声子晶体的ΓX和FM方向禁带,计算表明,对于钨柱分布在水背景中的情况,这种具有正方形点阵特点的准分形声子晶体存在多频带隙的特点,能带随级数的增大整体地趋向于低频部分.而且这种准分形声子晶体带隙的宽度及中心频率会随声子晶体单胞内结构单元几何形状的改变而改变.     

静电纺丝技术制备Y_2O_3∶Yb~(3+),Er~(3+)上转换纳米纤维及其表征

采用静电纺丝技术制备了PVA/[Y(NO3)3+Yb(NO3)3+Er(NO3)3]复合纳米纤维,将其在适当的温度下进行热处理,得到Y2O3∶Yb3+,Er3+上转换纳米纤维.XRD分析表明,复合纳米纤维为无定形,Y2O3∶Yb3+,Er3+上转换纳米纤维属于体心立方晶系,空间群为Ia3.SEM分析表明,复合纳米纤维的平均直径约为150nm;随着焙烧温度的升高,纤维直径逐渐减小.经过600℃焙烧后,获得了直径约60nm的Y2O3∶Yb3+,Er3+上转换纳米纤维.TG-DTA分析表明,当焙烧温度高于600℃时,复合纳米纤维中水分、有机物和硝酸盐分解挥发完毕,样品不再失重,总失重率为83%.FTIR分析表明,复合纳米纤维与纯PVA的红外光谱一致,当焙烧温度高于600℃时,生成了Y2O3∶Yb3+,Er3+上转换纳米纤维.该纤维在980nm的半导体激光器激发下发射出中心波长为521,562nm的绿色和656nm的红色上转换荧光,分别对应于Er3+离子的2H11/2/4S3/2→4Il5/2跃迁和4F9/2→4Il5/2跃迁.对Y2O3∶Yb3+,Er3+上转换纳米纤维的形成机理进行了讨论.     

A high-quality-factor ultra-narrowband perfect metamaterial absorber based on monolayer molybdenum disulfide

In order to significantly improve the absorption efficiency of monolayer molybdenum disulfide (M-MoS₂), an ultra-narrowband M-MoS₂ metamaterial absorber was obtained through theoretical analysis and numerical calculation using the finite difference time domain method. The physical mechanism can be better analyzed through critical coupling and guided mode resonance. Its absorption rate at λ = 806.41 nm is as high as 99.8%, which is more than 12 times that of bare M-MoS₂. From the simulation results, adjusting the geometric parameters of the structure can control the resonant wavelength range of the M-MoS₂. In addition, we also found that the maximum quality factor is 1256.8. The numerical result shows that the design provides new possibilities for ultra-narrowband M-MoS₂ perfect absorbers in the near-infrared spectrum. The results of this work indicate that the designed structure has excellent prospects for application in wavelength-selective photoluminescence and photodetection.     

Enhanced optical nonlinear absorption of graded Au--TiO2 composite films

This paper reports that single-layer and graded Au-TiO2 granular composite films with Au atom content 15%- 66% were prepared by using reactive co-sputtering technique. The third-order optical nonlinearity of single-layer and graded composite films was investigated by using s- and p-polarized Z-scans in femtosecond time scale. The nonlinear absorption coefficient βeff of single-layer Au-TiO2 films is measured to be -2.3×10^3-0.76×10^3 cm/GW with Au atom content 15%-66%. The βeff value of the 10-layer Au-TiO2 graded film is enhanced to be -2.1×10^4cm/GW calculated from p-polarized Z-scans, which is about ten times the maximum βeff of single-layer films. Broadened response in the wavelength region 730-860 nm of the enhanced optical nonlinearity of graded Au-TiO2 composite films was also investigated.     

求矩阵方程组的反对称最小二乘解的递推算法

讨论了矩阵方程组A_1XB_1=D_1,A_2XB_2=D_2反对称最小二乘解的递推算法,该算法不仅能够用于计算反对称最小二乘解,而且在选取特殊的初始矩阵时,算法能够求出矩阵方程组的极小范数反对称最小二乘解,以及对给定的矩阵进行最佳逼近的反对称解.     

常利率风险模型中破产时刻、破产前瞬时盈余和破产赤字的矩

本文通过常利率风险模型中罚金折现期望值函数解的形式, 研究了破产时刻、破产前瞬时盈余和破产赤字矩的性质, 得到关于这些矩的递归表达式.     

分数阶时滞微分方程的Hyers-Ulam稳定性（英文）

本文致力于研究非齐次分数阶时滞微分方程的Hyers-Ulam稳定性,其中阶数α∈(0,1).首先我们利用时滞型Mittag-Leffler矩阵函数,通过拉普拉斯变换方法找到了非齐次分数阶时滞微分方程的解的表达式.进一步地,我们证明了非齐次分数阶时滞微分方程在区间[0,T]上是Hyers-Ulam稳定的.最后,我们通过一个例子说明了结果的正确性.     

可调谐环形腔掺铒光纤激光器

使用高掺杂掺铒光纤制成了低噪声的环形腔光纤激光器。通过对文献中报道的环形腔结构光纤激光器输出的分析,指出了其存在的问题,并提出了减小其输出背景噪声的改进方案。通过实验验证了改进后的环形腔结构的低噪声特点,从原理上进行了解释。用不同掺铒光纤长度、泵浦功率、光栅波长及光栅反射率进行了实验,得到它们对输出光的性能影响。这种环形腔结构的光纤激光器可实现1525nm~1565nm连续可调谐输出。     

HL-2A等离子体边界识别的模拟研究

采用电流丝模型对HL-2A等离子体边界重建做了模拟计算。结果表明,对于孔栏位形、双零位形和下单零位形,重建的等离子体边界与平衡计算的边界能很好地吻合,最大径向距离小于8mm。     

HL-2A装置等离子体水平位移控制

介绍了HL-2A装置等离子体水平位移反馈控制系统的硬件组成、控制流程和控制算法,反馈控制的调试过程。在相同参数放电条件下比较了等离子体位移的受控情况。等离子体位移的控制结果较为满意。