Epitaxial growth La0.67Ca0.33MnO3 thin film by radio frequency sputtering method

Perfect epitaxial growth of La_0.67Ca_0.33MnO₃ (LCMO) thin film has been achieved on (1 0 0) LaAlO₃ (LAO) single crystal substrate by radio frequency sputtering method. X-ray diffraction (XRD) and electron diffraction analysis indicates that La_0.67Ca_0.33MnO₃ film grows epitaxially on LaAlO₃ along [1 0 0] direction of the substrate. The resistivity variation with temperature of the film shows a sharp metal to semiconductor transition peak around 253 K, which is close to that of the target. The magnetoresistance (MR) also reveals high quality epitaxy film characteristic at low temperatures and near the metal to semiconductor transition temperature.     

First-principles investigations of Cr doping effects on electronic structure and magnetic properties in Sr2FeReO6

The electronic structures and magnetic properties of double perovskites Sr₂Fe_1−xCr_xReO₆ (x=0.0, 0.25, 0.5, 0.75, 1.0) have been studied within the local spin density approximation (LSDA) and LSDA+U schemes. The calculated results reveal that with increasing Cr content the cell volume shrinks 2.61%; the Fe/Cr site magnetic moment decreases while the Re-site moment increases. The total spin magnetic moment linearly decreases with the Cr doping from 3.00μB for x=0.00 down to 1.00μB for x=1.00 per formula unit. The magnetic coupling constants increase with increasing x. The electronic structure calculations indicate that the electronic concentration in the Re spin-down subband slightly increases resulting from the increase of bonding-antibonding interaction between the localised and the delocalised states in spin-down band; the coupling of O-2p_↑ and transition-metal-3d_↑ is substantially enhanced with the Cr doping. We discuss the origin of the anomalously high TC of Cr-doped Sr₂FeReO₆ compounds in terms of band hybridization effects.     

An approximation of the analytical solution of the Jeffery-Hamel flow by decomposition method

Many researchers have been interested in application of mathematical methods to find analytical solutions of nonlinear equations and for this purpose, new methods have been developed. Since most of fluid mechanics problems due to boundary layer are strongly nonlinear, so analytical solution of them is confronted with some difficulty. In this Letter, the Jeffery-Hamel flow—a nonlinear equation of 3rd order—is studied by Adomian decomposition method. After introducing Adomian decomposition method and the way of obtaining Adomian's polynomial, we solved the problem for divergent and convergent channels. Finally, velocity distribution and shear stress constant is depicted at various Reynolds numbers and comparing our results with some earlier works illustrated their excellent accuracy.     

Widely phase-matched tunable difference-frequency generation in periodically poled LiNbO3 crystal

We report on the development of a laser source in the mid-infrared spectral region based on difference-frequency generation (DFG) in a periodically poled LiNbO₃ (PPLN) crystal. Continuously tunable coherent radiation from 2.75 to 4.78 μm was produced by optical parametric interaction between a diode-pumped monolithic continuous-wave (CW) Nd:YAG laser operating at 1.064 μm and a CW Ti:Sapphire laser tunable from 767 to 871 nm. Temperature-dependent quasi-phase-matched DFG wavelength acceptance bandwidth was studied and characterized. An empiric formula is given to estimate the phase-matched wavelength acceptance bandwidth as a function of the crystal temperature at Λ = 22.5 μm. A large frequency scan of 128 cm⁻¹ (about 78 cm⁻¹ above 1 μW) near 4.2 μm was achieved. The whole absorption spectrum of the P and R branches of the ν₃ band of atmospheric carbon dioxide has been recorded with a single phase-matched frequency scan.     

Surface-enhanced resonant Raman spectroscopy (SERRS) of single-walled carbon nanotubes absorbed on the Ag-coated anodic aluminum oxide (AAO) surface

In this paper, we developed a new kind of substrate, the silver-coated anodic aluminum oxide (AAO), to investigate the characters of surface-enhanced resonant Raman scattering (SERRS) of the dilute single-walled carbon nanotubes. Homogeneous Ag-coated AAO substrate was obtained by decomposing the AgNO₃ on the surface of AAO. single-walled carbon nanotubes (SWNTs) were directly grown onto this substrate through floating catalyst chemical vapor deposition method (CVD). SERRS of SWNTs was carried out using several different wavelength lasers. The bands coming from metallic SWNTs were significantly enhanced. The two SERRS mechanisms, the “electromagnetic” and “chemical” mechanism, were mainly responsible for the experiment results.     

Vibro-acoustic noise control treatments for payload bays of launch vehicles: Discrete to fuzzy solutions

Sound transmitted through an enclosing structure into a cavity has been minimised by optimising the locations, numbers and properties of tuned mass dampers placed on the structure and Helmholtz resonators placed in the cavity. Most of the results presented in the literature show the effect of a few well selected acoustic or vibration absorbers on simple vibro-acoustic systems, whereas the results presented here indicate the trends that occur when a few absorbers are replaced by a large number. The results indicate that for low numbers of absorbers, the result of the optimal configuration is to reduce the response of discrete modes, and for a large number of absorbers the result of the optimal configuration is a tendency for the vibro-acoustic energy to be smeared over a range of frequencies, which is similar to the results seen in fuzzy structures. The enormous computational task was achieved using a distributed computing network and an asynchronous parallel genetic algorithm.     

The structural and optical properties of ZnO nanorod arrays

High quality vertical-aligned ZnO nanorod arrays were synthesized by a simple vapor transport process on Si (111) substrate at a low temperature of 520 °C. Field-emission scanning electron microscopy (FESEM) showed the nanorods have a uniform length of about 1 μm with diameters of 40-120 nm. X-ray diffraction (XRD) analysis confirmed that the nanorods are c-axis orientated. Selected area electron diffraction (SAED) analysis demonstrated the individual nanorod is single crystal. Photoluminescence (PL) measurements were adopted to analyze the optical properties of the nanorods both a strong UV emission and a weak deep-level emission were observed. The optical properties of the samples were also tested after annealing in oxygen atmosphere under different temperatures, deep-level related emission was found disappeared at 600 °C. The dependence of the optical properties on the annealing temperatures was also discussed.     

多光子偏振态与单光子高维空间态之间的相互变换及其应用

基于一种特殊的控制非门,实现多光子偏振态与单光子空间高维态之间的相互变换,使得对多光子偏振态的操作可以通过对单光子的操作来完成,由此可以实现任意多光子正定算符值测量和多光子任意幺正操作.这种实现方式是以一定概率完成的,但其效率要优于此前的方案,在目前的实验条件下是可行的. 关键词： 单光子空间态 特殊控制非门 线性光学多端口干涉仪     

激发态Cs2和H2的电子-振转能级的碰撞转移

利用相干反斯托克斯拉曼光谱(CARS)探测技术, 研究了激发态Cs2与H2间的电子-振转能级的碰撞转移。用波长为532 nm和中心波长为716 nm的两束激光同时聚焦到样品池中, 扫描CARS谱确认了H2分子的S支(△v =1, △J=2)仅在v=1, J=4,5及v=2, J=3,4能级上有布居, 用n1、n2、n3、n4分别表示(2,4)、(2,3)、(1,4)及(1,5)上的粒子数密度。从CARS线的峰值得到n2/n1、n3/n1、n4/n1分别为6.34±1.27、3.66±0.73和1.45±0.29。转移能配置到振动、转动和平动的比例分别为0.44、0.06和0.50, 能量主要分配在振动和平动上。在T=523 K和PH2=2.5×103 Pa条件下, 通过求解速率方程组和对时间分辨CARS线轮廓的分析, 得到碰撞转移速率系数k1=(6.0±1.2)×10-14 cm-3s-1和k2=(4.0±0.8)×10-13cm-3 s-1。     

94 GHz回旋管准光模式变换器设计

基于几何光学理论和矢量绕射理论,研究了将回旋管及其他高功率微波器件的振荡输出模式转换成准光高斯波束的模式变换器,采用伏拉索夫(Vlasov)辐射器和三级准光反射面实现了准高斯模TEM₀₀的横向输出.研究了Vlasov辐射器的工作机理,运用矢量绕射理论计算出波导辐射场,口面电流分布的方法计算反射面辐射场.通过编写程序设计了将94 GHz,模式为TE₆₂的毫米波转化为准光高斯波束的内置式准光模式变换器. 关键词： 94 GHz回旋管 内置式准光模式变换器 Vlasov辐射器 矢量绕射理论