Three-dimensional size and orientation of the precipitates in AZ91 magnesium alloys measured by TEM techniques

Knowledge of the microscopic structure, including three-dimensional (3-D) size and orientation of the precipitates, is essential to fully understand the mechanical properties of the magnesium alloys and designing the alloys with better performance. Analytical TEM with high spatial resolution offers the simultaneous measurements of 3-D size, structure, orientation, composition of the precipitates from one typical sample along an established crystallographic axis. Besides popular Burgers orientation relationship (OR), other ORs such as Pitsch--Schrader OR, Crawley OR, Potter OR and a new OR with the form of [0001]_α 1.0° from [311]_γ and (11\bar 20)_α 2.0° from (03\bar 3)_γ between the magnesium matrix and the precipitate γ -Mg₁₇Al₁₂ are identified by TEM imaging and diffraction techniques. As a case study, the thicknesses of the individual precipitates with Burgers OR are further measured to be 100--200~nm through both electron energy-loss spectroscopy and x-ray energy dispersive spectroscopy combining differential x-ray absorption and extrapolation, which are in agreement with the overall 3-D size statistic distribution results obtained through analysing various samples along various directions. Furthermore, the fabricated wedge-shape structure provides a platform on which to study the dependence of the interfacial strain on the variation of the thickness.     

Observation of coexistence of 1D and 2D nanostructures in cobalt dipyrromethene trimer complexes adsorbed on a graphite surface

We report the direct observation of 1D and 2D nanostructures of cobalt dipyrromethene trimer complexes adsorbed on a highly oriented pyrolytic graphite surface using scanning tunneling microscopy (STM). STM images showed two types of ordered structures coexisting on the surface: long 1D molecular chains isolated on the terraces, and 2D hexagonal patterns confined by a 1D chain and/or a graphite step edge. These 1D and 2D structures are attributed to ‘edge-on’ and ‘face-on’ complex alignments on the surface, respectively. In both configurations, substrate-mediated molecule-molecule interactions may play a significant role in stabilizing the nanostructures.     

Navier-Stokes方程带Backtracking技巧的两重网格算法

1 引 言考虑二维不可压 Navier-Stokes方程:     

光纤激光共孔径光谱合成实现5 kW高效优质输出

采用多层介质膜衍射光栅实现多路高功率光纤激光共孔径光谱合成有望成为光纤激光同时实现高功率、高效率和高光束质量的最具发展潜力的技术途径。搭建了一套基于双光栅色散补偿设计的5 kW共孔径光谱合成系统。采用国产多层介质膜衍射光栅实现了5路kW级窄谱子束激光的高效优质共孔径光谱合成,最大输出功率达5.07 kW,光束质量因子(M2)小于3,合成效率达到91.2%。初步研究表明：多层介质膜衍射光栅在较高功率水平、较宽光谱范围内均能保持较高衍射效率,是实现高功率光纤激光高效率光谱合成的重要器件;参与合成的子束自身的光束质量水平和线宽是影响合成输出光束质量的重要因素,光谱合成系统的输出功率主要受限于窄谱子束的输出功率和合成路数,增加窄谱子束的功率或合成路数均可进一步提升系统的输出功率。     

Compare study CaCO3 crystals on the cellulose substrate by microwave-assisted method and ultrasound agitation method

The purposes of this article were to investigate the influences of synthesis strategy on the CaCO₃ crystals on the cellulose substrate. In this study, CaCO₃ crystals were synthesized using cellulose as matrix by the microwave-assisted method and ultrasound agitation method, respectively. The CaCO₃ crystals on the cellulose substrate were characterized by means of X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), and scanning electron microscopy (SEM). Experimental results demonstrated that the synthesis strategy had a dramatically influences on the phase, microstructure, morphology, thermal stability, and biological activity of the CaCO₃ crystals. The pure phase of vaterite spheres with the diameter of about 320–600 nm were obtained by ultrasound agitation method, meanwhile, the mixed phases of calcite and vaterite with the diameter of about 0.82–1.24 μm were observed by microwave-assisted method. In view of experimental results, one can conclude that the ultrasound agitation method do more favors to the synthesis of CaCO₃ crystals with uniform morphology and size, compared with microwave-assisted method. Furthermore, cytotoxicity experiments indicated that the CaCO₃ crystals on the cellulose substrate had good biocompatibility and could be a candidate for the biomedical applications.     

毫米波与太赫兹波在等离子体中传输特性

针对黑障区高速飞行器测控通信研究需求,在激波管设备上开展了Ka波段毫米波与太赫兹波在等离子体中传输特性的实验研究,获得了不同电子密度和碰撞频率的等离子体中传输衰减特性实验数据。采用辅助差分方程的时域有限差分（ADE-FDTD）方法对实验进行了数值模拟,数值模拟结果和实验结果有很好的一致性。实验结果和数值模拟结果均表明：太赫兹波信号在相同的实验等离子体中传输衰减比毫米波信号小得多,具有更强的穿透等离子体能力;毫米波与太赫兹波信号在等离子体中传输衰减量随着等离子体电子密度的增加而增加,二者的差值也增加;太赫兹波能够作为解决高密度等离子体中电磁波传输的有效技术手段。     

Electroweak radiative corrections to $$W^+W^-\gamma $$ production at the ILC

We consider holographic superconductors in a rotating black string spacetime. In view of the mandatory introduction of the \(A_\varphi \) component of the vector potential we are left with three equations to be solved. Their solutions show that the rotation parameter \(a\) influences the critical temperature \(T_\mathrm{c}\) and the conductivity \(\sigma \) in a simple but non-trivial way.     

Field-induced ionization and Coulomb explosion of nitrogen

Femtosecond-laser field-induced ionization and Coulomb explosion of diatomic nitrogen were systematically investigated using time-of-flight mass and photoelectron spectrometry. Both linearly and circularly polarized femtosecond laser pulses were used at intensities varying from 5×10¹³ to 2×10¹⁵ W/cm². Strong N₂ ⁺, N₂ ²⁺, N⁺, N²⁺ and N³⁺ ion signals were observed for horizontally polarized pulses. Moreover, signals from the atomic ions exhibited a double-peak structure. Suppression of ionization was observed for circularly polarized pulses, while for vertically polarized pulses, only N₂ ⁺ and N₂ ²⁺ ions were observed. The angular distributions of the ions were measured under zero-field conditions in the ionization zone. The atomic ions N⁺, N²⁺ and N³⁺ exhibited highly anisotropic distributions, with maxima along the laser polarization vector and zeroes normal to the laser polarization vector. In contrast to the atomic ions, N₂ ⁺ exhibited a strong isotropic angular distribution. These observations indicate that dynamic alignment is responsible for the observed anisotropic angular distribution of the atomic ions. The kinetic energy spectrum of the photoelectrons is featureless and broad, extending above the ponderomotive potential of the laser pulse. The angular distribution is markedly anisotropic, with a maximum along the laser polarization vector. These observations further support the notion that the field-ionization mechanism is dominant under our experimental conditions. Received: 29 January 2002 / Revised version: 15 March 2002 / Published online: 12 July 2002     

5D Dirac Equation in Induced-Matter Theory

According to an induced-matter approach, Liu and Wesson obtained the rest mass of a typical particle from the reduction of a 5D Klein–Gordon equation to a 4D one. Introducing an extra-dimension momentum operator identified with the rest mass eigenvalue operator, we consider a way to generalize the 4D Dirac equation to 5D. An analogous normal Dirac equation is gained when the generalization reduces to 4D. We find the rest mass of a particle in curved space varies with spacetime coordinates and check this for the case of exact solitonic and cosmological solution of the 5D vacuum gravitational field equations.     

光子图像统计处理

讨论了一种对有限光子图像累加的统计处理方法。在超微弱发光的研究中（例如细胞的超微弱光），由于发光强度较弱，需要用像增强器对超微弱发光图像进行增强得到可视光子图像，超微弱发光的光子图像不可避免地受到像增强系统暗噪声及背景噪声的影响，使光子图像湮没在噪声中。为从原始图像中检验出信号，常将采集到的有限光子图像进行累加以增加样本数，根据信号光子和噪声光子的不同统计分布，运用似然比检验方法得到有效判断累加图像中某像素是否含有信号光子，由此剔除图像中的噪声光子，得到信噪比改善的光子图像。