双峰分布的超细颗粒动态光散射信号模拟及精度分析

为获取双峰分布超细颗粒的动态光散射模拟信号,通过建立动态光散射随机过程的AR模型,利用修正的Levison Durbin递推算法确定模型参数和阶数的方法模拟光散射信号.分别对10 nm与90 nm,200 nm与1 000 nm双峰分布颗粒的动态光散射信号进行模拟,得到的模拟信号光强自相关函数与理论值吻合,用双指数法对颗粒粒径反演,相对误差小于3.55%.通过分析模型阶数、采样时间、采样频率、模拟数据长度等参数对模拟精度的影响,得出双峰分布颗粒光散射信号的模拟精度与各参数的关系:在低于阈值阶数时,模型阶数选择对精度影响大,模型阶数越高,信号模拟的精度越高,高于阈值阶数时,模型阶数选择对精度影响不大,可选阈值阶数模型模拟信号.选定一定的采样时间,采样频率越高,模拟数据长度越长,模拟精度越高.     

Electronic structure,Dirac points and Fermi arc surface states in three-dimensional Dirac semimetal Na_3Bi from angle-resolved photoemission spectroscopy

The three-dimensional(3D) Dirac semimetals have linearly dispersive 3D Dirac nodes where the conduction band and valence band are connected. They have isolated 3D Dirac nodes in the whole Brillouin zone and can be viewed as a 3D counterpart of graphene. Recent theoretical calculations and experimental results indicate that the 3D Dirac semimetal state can be realized in a simple stoichiometric compound A_3Bi(A = Na, K, Rb). Here we report comprehensive high-resolution angle-resolved photoemission(ARPES) measurements on the two cleaved surfaces,(001) and(100), of Na_3Bi. On the(001) surface, by comparison with theoretical calculations, we provide a proper assignment of the observed bands, and in particular, pinpoint the band that is responsible for the formation of the three-dimensional Dirac cones. We observe clear evidence of 3D Dirac cones in the three-dimensional momentum space by directly measuring on the k_x–k_y plane and by varying the photon energy to get access to different out-of-plane k_zs. In addition, we reveal new features around the Brillouin zone corners that may be related with surface reconstruction. On the(100) surface, our ARPES measurements over a large momentum space raise an issue on the selection of the basic Brillouin zone in the(100) plane. We directly observe two isolated 3D Dirac nodes on the(100) surface. We observe the signature of the Fermi-arc surface states connecting the two 3D Dirac nodes that extend to a binding energy of ~150 me V before merging into the bulk band. Our observations constitute strong evidence on the existence of the Dirac semimetal state in Na_3Bi that are consistent with previous theoretical and experimental work. In addition, our results provide new information to clarify on the nature of the band that forms the3 D Dirac cones, on the possible formation of surface reconstruction of the(001) surface, and on the issue of basic Brillouin zone selection for the(100) surface.     

基于PIC单片机的CAN总线扩展技术

目前现场CAN总线驱动节点数量有限,通信速率随着通信距离的增加快速下降,在通信节点数量大、通信距离远的大空间场所不能应用。针对这个问题,设计了基于PIC16位单片机dsPIC30F6011的CAN网关,给出了CAN网关的硬件设计原理和软件设计框图;详细描述了CAN总线扩展原理及CAN总线扩展后的网络拓扑结构。dsPIC30F6011片上集成了双CAN总线数据链路层,外围电路简单,消息通过中断来处理,实时迅速。通过该CAN网关,两个CAN网络之间的消息实时、快速转发。扩展后的CAN网络驱动能力强、通信速率高、通信距离远,完全可以应用于通信节点数量大、通信距离远的场所。     

基于模板的二维多通道形态小波的构造

基于提升方案和模板,提出一种通用方便的二维多通道形态小波构造新方法。预测步骤时,采用指定的梯度模板提取信号中的细节信息;更新步骤中用最大、最小和中值等各种形态算子来获取低频信息。为了实现非线性精确重建,给出了模板选择的必要性条件。根据该新框架构造的非线性小波在低频和细节信号上都非常符合图像处理的需要和特点。最后通过实例说明了该方法的优点和实用性。     

Laser Induced Damage Threshold at 355 and 1064nm of Ta2O5 Films of Different Phases

Ta2O5 films axe deposited on fused silica substrates by conventional electron beam evaporation method. By annealing at different temperatures, Ta2 O5 films of amorphous, hexagonal and orthorhombic phases are obtained and confirmed by x-ray diffractometer （XRD） results. X-ray photoelectron spectroscopy （XPS） analysis shows that chemical composition of all the films is stoichiometry. It is found that the amorphous Ta2 O5 film achieves the highest laser induced damage threshold （LIDT） either at 355 or 1064nm, followed by hexagonal phase and finally orthorhombic phase. The damage morphologies at 355 and 1064nm are different as the former shows a uniform fused area while the latter is centred on one or more defect points, which is induced by different damage mechanisms. The decrease of the LIDT at 1064nm is attributed to the increasing structural defect, while at 355nm is due to the combination effect of the increasing structural defect and decreasing band gap energy.     

CSM多播路由协议在移动环境中的改进

适用于视频会议与在线聊天室的CSM（Conference Steiner Multicast）协议，在支持移动主机时存在多播树切换频率过高，网络开销过大的问题。运用Range（服务范围）的概念，结合Mobile IP隧道技术，提出了一种改进的CSM协议－－RBCSM（Range Based CSM）协议。RBCSM协议在降低多播切换频率，节省网络带宽方面性能优越。同时由于运用了Mobile IP的隧道技术，还有进一步提高网络安全性的可能，最后，对CSM和RBCSM的多播树切换频率及多播树路径总长度两个性能指标进行了仿真模拟比较。     

Comparison of TiO2 and ZrO2 Films Deposited by Electron-Beam Evaporation and by Sol-Gel Process

TiO2 and ZrO2 films are deposited by electron-beam （EB） evaporation and by sol-gel process. The film properties are characterized by visible and Fourier-transform infrared spectrometry, x-ray diffraction analysis, surface roughness measure, absorption and laser-induced damage threshold （LIDT） test. It is found that the sol-gel films have lower refractive index, packing density and roughness than EB deposited films due to their amorphous structure and high OH group concentration in the film. The high LIDT of sol-gel films is mainly due to their amorphous and porous structure, and low absorption. LIDT of EB deposited film is considerably affected by defects in the film, and LIDT of sol-gel deposited film is mainly effected by residual organic impurities and solvent trapped in the film.     

基于共掺杂调控C32多极矩的二阶非线性光学响应

基于密度泛函(DFT)理论,采用CAM-B3LYP方法,以C₃₂分子为多极矩构建骨架,设计了两类替位式共掺杂的富勒烯衍生物C₂₈B₂N₂和C₂₈B₂P₂,共16种同分异构体,并对它们的电子性质、线性极化率α和一阶超极化率β进行研究。结果表明,掺杂后分子的HOMO-LUMO能隙变小,C₂₈B₂P₂的α和β值均大于C28B2N2系列。其中偶极分子具有大的β值,八极分子则有较小的β值,筛选出具有优异的二阶非线性光学(NLO)响应特性的结构。含时密度泛函理论(TD-DFT)的结果表明,与C₃₂相比,掺杂后所有结构的吸收光谱的响应范围变宽,最大吸收强度减弱,且最大吸收波长的位置发生红移或蓝移。基于完全态求和(SOS)方法,分别用二能级或三能级公式解释了两类共掺杂结构中β值最大的来源,并且证明了与之有关的电子激发类型为π→π*激发。