基于时频分布的盲信号分离方法研究长骨中的多模式导波信号

由于超声导波对长骨皮质骨的材料特性及厚度变化非常敏感,因此用导波评价长骨状况的研究已成为近年来的一个研究热点。在接收到的导波中,往往多种模式混叠在一起,使得进一步求取每种导波模式的群速度等与骨质状况密切相关的参数时遇到困难。本文采用基于时频分布的盲信号分离(TFBSS)方法对长骨中混叠的多模式进行分离,然后对分离后的单一导波模式求取群速度。研究结果表明TFBSS方法能够准确的分离出混叠的多模式导波,且实验测量的群速度与其理论值吻合。利用导波的群速度就可以得到长骨皮质骨的厚度,这对诊断其骨质状况具有重要意义。     

强外电场作用下二甲基硅酮的分子结构和激发态

采用密度泛函(DFT)方法B3P86在6 311++G(d,p)基组水平上优化得到了分子轴方向不同电偶极 场(-0.04～0.04a.u.)作用下,二甲基硅酮的基态电子状态、几何结构、电偶极矩和分子总能量.在优化构型下 用同样的基组采用杂化CIS DFT方法(CIS B3P86)研究了同样外电场条件下对二甲基硅酮的激发能和振子强度 的影响.计算结果表明,分子几何构型与电场大小和方向呈现强烈的依赖,正向电场下基态偶极矩随电场强度线 性增加,分子总能量降低,当反向电场大于0.03a.u.时,偶极距方向改变,总能量增加;激发能随电场增加急剧减 小,且对电场方向的依赖呈现出不对称性,满足Grozema关系.电场对振子强度的影响比较复杂,但仍满足跃迁选 择定则.     

Hybrid optoelectronic bistability in a fiber Bragg grating by use of a tunable fiber laser

We report the observation of hybrid optoelectronic bistability in a fiber Bragg grating (FBG) by use of an electro-optically tuned cw fiber laser in which another wavelength-matched FBG is employed to constitute a tunable resonant cavity. The potential application of such a device as a fiber-optic sensor is also discussed.     

ICP-AES测定向日葵花盘中13种金属元素

向日葵花盘经湿法消解,采用ICP-AES对其中钾、钙、钠、钡、铝、铬、铜、镁、铁、锰、镍、锶、锌13种元素进行测定.对光谱仪的工作条件及分析谱线等测定条件进行了选择,并进行了方法的回收率及精密度试验,其回收率在95％-122％之间.     

基于压电探测判定激光支持燃烧波和爆轰波的点燃阈值

为了获得激光支持燃烧波和爆轰波的点燃阈值,采用压电探测器检测波长为1 064 nm的Nd:YAG激光作用在铝靶表面所产生的应变和冲压。从实验结果观察到压电信号的变化分为3个阶段,分别为光热弹性应变阶段、等离子体增强耦合阶段和激光支持爆轰波对靶表面的压力阶段,并从理论上研究了这3个阶段的激光与靶材料相互作用的机理,从而可以从压电信号是否发生跃变判断出激光支持燃烧波和激光支持爆轰波的点燃阈值,与其它方法所得到结果基本吻合。     

Laser plasma shockwave cleaning of SiO2 particles on gold film

A Nd:YAG laser (1064 nm) induces optical breakdown of the airborne above the gold-coated K9 glass surface and the created shockwave removes the SiO₂ particles contaminated on the gold films. The laser cleaning efficiency has been characterized by optical microscopy, dark field imaging, ultraviolet-visible-near infrared spectroscopy, Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy and the Image-pro software. The relationships between removal ratio and particle position and laser gap distance have been studied in the case of single pulse laser cleaning. The results show that the 1064 nm laser induced plasma shockwave can effectively remove the SiO₂ particles. The removal ratio can reach above 90%. The effects of particle position and laser gap distance on the cleaning efficiency are simulated for the single pulse laser cleaning. The simulated results are consistent with the experimental ones.     

40Gbps NRZ在基于宽带CFBG色散补偿的G.652光纤中无电中继传输500km

在基于宽带CFBG色散补偿的G.652光纤中,40Gbps NRZ码无电中继传输500km,在误码率BER=10(-10)下的功率代价约为2.2dB,积累1h的误码率为7.3×10(-12).传输系统中采用的CFBG的3dB带宽约为1.2nm,中心波长处时延纹波小于25ps,反射谱纹波小于2dB,差分群时延小于1ps....     

Influence of NH<Subscript>3</Subscript> flow rate on pyridine-like N content and NO electrocatalytic oxidation of N-doped multiwalled carbon nanotubes

Nitrogen-doped multiwalled carbon nanotubes (N-MWCNTs) have been prepared by pyrolysis of pyridine and iron phthalocyanine over an iron catalyst at 850 °C at various ammonia gas (NH₃) flow rates. X-ray photoelectron spectroscopy results reveal that the pyridine-like nitrogen (N) content can be controlled by changing the flow rate of NH₃, and that pyridine-like N plays an important role: it can increase the electrocatalytic activity and the rate of nitric oxide (NO) electrooxidation and decrease the activation energy of NO electrooxidation. Cyclic voltammetry results demonstrate that the N-MWCNTs sample grown with 200 mL/min NH₃ flow has the maximum N content of 3.22 atomic %, and its content of pyridine-like N that is chemically active is also the highest among all the N-MWCNTs samples. Electrochemical impedance spectroscopy results indicate that two-step electron transfer process occurs at the N-MWCNT-modified electrode, and the control step is different in various potential regions. The stability of NO electrooxidation at the N-MWCNT-modified electrode is examined, and the reaction mechanism is discussed.     

Preparation of microporous activated carbon and its electrochemical performance for electric double layer capacitor

Microporous activated carbons were prepared by microwave heating petroleum coke with potassium hydroxide as activation agent. Microporous activated carbons were characterized by infrared spectroscopy, X-ray diffraction and nitrogen adsorption/desorption isotherms. Electrochemical properties of an electric double layer capacitor using microporous activated carbon as electrode materials were investigated by constant current charge-discharge and electrochemical impedance spectroscopic techniques. The results show that the specific surface area and the pore volume of microporous activated carbon increase with increasing activation time before the activation time reaches 37 min. The microporous volume totals 94.0% in the microporous activated carbons and the average pore diameter of microporous activated carbon is 2.00 nm. Microporous activated carbons prepared in the activation time of 31, 35 and 37 min are named as AC-31, AC-35 and AC-37, respectively. Compared with AC-27 electrode, the internal resistance for ions transferring in AC-31, AC-35 or AC-37 electrode is relatively small. The specific capacitance of AC-31 is the biggest among the microporous activated carbons, and it retains 279.6 F g^?1 maintaining 93.5% capacity after 200 recycling number.     

Optical properties of PMN–PT thin films prepared using pulsed laser deposition

(1 ? x)Pb(Mg_1/3Nb_2/3)O₃–xPbTiO₃ (PMN–PT) thin films have been deposited on quartz substrates using pulsed laser deposition (PLD). Crystalline microstructure of the deposited PMN–PT thin films has been investigated with X-ray diffraction (XRD). Optical transmission spectroscopy and Raman spectroscopy are used to characterize optical properties of the deposited PMN–PT thin films. The results show that the PMN–PT thin films of perovskite structure have been formed, and the crystalline and optical properties of the PMN–PT thin films can be improved as increasing the annealing temperature to 750 °C, but further increasing the annealing temperature to 950 °C may lead to a degradation of the crystallinity and the optical properties of the PMN–PT thin films. In addition, a weak second harmonic intensity (SHG) has been observed for the PMN–PT thin film formed at the optimum annealing temperature of 750 °C according to Maker fringe method. All these suggest that the annealing temperature has significant effect on the structural and optical properties of the PMN–PT thin films.