Be掺杂对ZnO电子结构和光学性质的影响

基于密度泛函理论（DFT）第一性原理计算了Zn1-xBexO化合物的电子结构和光学性质. 计算结果表明Zn1-xBexO带隙随掺杂浓度的增加而变大. 这种现象主要是由于价带顶O2p随掺杂量x的增加几乎保持不变,而Zn4s随掺杂量x的增加向高能端移动. 光学介电函数虚部计算结果表明：在2.0, 6.76eV位置随掺杂浓度的增加峰形逐渐消失,是由于Be替代Zn导致Zn3d电子态逐渐减少所致;而9.9eV峰形逐渐增强,是由于逐渐形成的纤锌矿结构BeO的价带O2p到导带Be2s的跃迁增加所致.     

A time-domain method with isotropic dispersion and increased stability on an overlapped lattice

A time-domain method on an overlapped lattice is presented for the accurate and efficient simulation of electromagnetic wave propagation through inhomogeneous media. The method comprises a superposition of complementary approximations to electromagnetic theory on a lattice. The discrete space-time (DST) method, is set on a pair of dual lattices whose field components are collocated on their respective lattice sites. The other, the time-domain element (TDE) method, is set on overlapping dual lattices whose field components are noncollocated. The TDE method is shown to be a generalization and reinterpretation of the Yee algorithm. The benefits of the combined algorithm over comparable methods include: (1) increased accuracy over larger bandwidths; (2) increased stability allowing larger time steps; (3) local stencil-satisfying boundary conditions on interfaces; (4) self-contained mathematical framework; (5) it is physically intuitive.     

利用自适应滤波星载激光测高仪回波噪声抑制方法

具有波形记录功能的星载激光测高仪,通过回波信息解算地表与卫星平台距离和反演地物特性。目前广泛采用的固定宽度高斯滤波方法在抑制回波噪声过程中造成有效信号变形,对提取信号有效参量造成严重干扰。根据分块信号统计特性不同的规律,提出了激光测高仪回波噪声均值和方差的估计方法;根据回波信号的统计特性,设计了一种宽度自适应的高斯滤波器。通过GLAS系统实测回波信号的噪声估计与自适应高斯滤波、高斯拟合,得到的波形处理结果与GLAS官方数据有很好的吻合度,噪声均值估计误差小于0.4个数字化仪单位,有效高斯参数计算误差小于1%。该方法能准确地提取波形参量,为地表高程解算和目标表面信息反演提供有效数据。     

卫星目标光学测量大气折射修正

本文从实测的大气参数廓线出发,讨论了对卫星目标进行光学定位测量时,进行大气折射误差修正时的几个问题,如大气色散、大气湍流和大气水平不均匀性等对折射修正的影响。首先计算了不同仰角下卫星目标光学测量的大气折射修正量的大小,讨论了用不同波长测量时大气色散所造成的修正量的偏差。同时还讨论了大气湍流、大气水平不均匀以及大气条件及昼夜变化等气象因素所引起的折射修正误差。     

Perfect difference codes for synchronous fiber-optic CDMAcommunication systems

In this paper, we introduce the perfect difference sets and propose a synchronous fiber-optic code-division multiple-access system (CDMA) using these sets to generate the signature codes. Two interesting properties of these codes are discussed: (1) any two different codes are cyclic-shifted with each other; and (2) the cross correlation between any two different codes is exactly one. Thus, we may treat these codes as quasi-orthogonal codes. Using the first property of these codes, we can simplify design of the transmitter. In the receiver, we can use the second property to effectively eliminate the multiple-user interference (MUI) without reducing the number of usable codes. Based on the proposed transmitter and receiver, the system performance is derived. The numerical examples reveal that the proposed system can provide reliable communication even under heavy load. We believe that the proposed system using perfect difference codes outperforms any other synchronous fiber-optic CDMA systems     

Analysis of low frequency scattering from penetrable scatterers

A method is presented for solving the surface integral equation using the method of moments (MoM) at very low frequencies, which finds applications in geoscience. The nature of the Helmholtz decomposition leads the authors to choose loop-tree basis functions to represent the surface current. Careful analysis of the frequency scaling property of each operator allows them to introduce a frequency normalization scheme to reduce the condition number of the MoM matrix. After frequency normalization, the MoM matrix can be solved using LU decomposition. The poor spectral properties of the matrix, however, makes it ill-suited for an iterative solver. A basis rearrangement is used to improve this property of the MoM matrix. The basis function rearrangement (BFR), which involves inverting the connection matrix, can be viewed as a pre-conditioner. The complexity of BFR is reduced to O(N), allowing this method to be combined with iterative solvers. Both rectilinear and curvilinear patches have been used in the simulations. The use of curvilinear patches reduces the number of unknowns significantly, thereby making the algorithm more efficient. This method is capable of solving Maxwell's equations from quasistatic to electrodynamic frequency range. This capability is of great importance in geophysical applications because the sizes of the simulated objects can range from a small fraction of a wavelength to several wavelengths     

一种高功率宽带光源的研制

报道一种新型的高功率宽带光源 ,它利用 1480nm激光器对掺铒光纤进行抽运 ,经啁啾光纤光栅反射后二次放大输出 ,其功率高达 1 41mW ,线宽为 10nm。该光源工作的线性区间对应的电流为 375～ 6 45mA。     

60km车载瑞利测风激光雷达研制

目前我国尚缺乏25~60 km大气风场实时探测手段,为此研制了60 km车载瑞利测风激光雷达。介绍了系统总体结构,对分系统的研制做了详细描述。为提高风场反演的精度,设计了标准具通过率函数校准系统。提出了标准具通过率函数校准方法,并开展实验对标准具通过率函数进行了校准。校准结果表明,接收机性能稳定,各参数测量标准差均小于0.06。该系统在德令哈地区对15~60 km大气风场进行了观测,获得了水平风场的测量结果,并与当地探空气球的探测结果进行了比对,30 km以下一致性较好。对风速、风向测量误差进行了计算,40 km以下,风速测量误差4 m/s,风向测量误差6,40 km以上,风速测量误差8 m/s,风向测量误差18。该系统设计合理,性能稳定,能够实时探测10~60 km大气风场。     

Performance analysis of M-PAM signaling with Tomlinson-Harashima precoding over ISI channels

An analytical method is developed to evaluate the symbol error probability of multilevel pulse amplitude modulation system using Tomlinson-Harashima precoding over inter-symbol interference channels. Analytical and simulation results are in an excellent agreement for different values of M.