Phase field simulation of the columnar dendritic growth and microsegregation in a binary alloy

This paper applies a phase field model for polycrystalline solidification in binary alloys to simulate the formation and growth of the columnar dendritic array under the isothermal and constant cooling conditions. The solidification process and microsegregation in the mushy zone are analysed in detail. It is shown that under the isothermal condition solidification will stop after the formation of the mushy zone, but dendritic coarsening will progress continuously, which results in the decrease of the total interface area. Under the constant cooling condition the mushy zone will solidify and coarsen simultaneously. For the constant cooling solidification, microsegregation predicted by a modified Brody- Flemings model is compared with the simulation results. It is found that the Fourier number which characterizes microsegregation is different for regions with different microstructures. Dendritic coarsening and the larger area of interface should account for the enhanced Fourier number in the region with well developed second dendritic arms.     

双光子吸收的Franz-Keldysh效应

从实验上证实Hg_0.695Cd_0.305Te 光电二极管空间电荷区中存在双光子吸收的Franz-Keldysh效应.利用一个皮秒Nd:YAG激光器抽运的光学参量产生器和差频产生器作为激发光源，测量了入射波长为λ₀=7.92μm的脉冲激光所激发的光响应随入射光强的变化关系.脉冲光响应峰值强度随入射光强的增大呈现二次幂函数增强趋势.采用等效RC电路模型将脉冲光伏信号峰值与入射光强相关联，得到空间电荷区中强电场下单光束     

Dynamics of cooperative emissions in a cascade three-level molecular system driven by an ultrashort laser pulse

This paper investigates the dynamics of cooperative emissions in a cascade three-level system driven by an ultra, short laser pulse by solving numerically the full-wave Maxwell-Bloch equations. The 4, 4＇-bis（dimethylamino） stilbene molecule is used as the model molecule because of its strong two-photon absorption property. The two-colour cooperative emissions are studied as functions of molecular number density and dephasing rate of the dipole coherence. The propagation effects on the evolution of the cooperative radiations are also taken into account. The cooperative radiations are enhanced for large number density of the molecule, while the fast dephasing of the dipole coherence reduces the intensity of the cooperative radiations and delays the emission times or even inhibits the formation of the emissions. The delay time of the radiation decreases with the increase of the molecular number density and the propagation distance.     

带铁芯托卡马克装置的等离子体平衡数值解法

本文提出一种计算铁芯变压器托卡马克装置中等离子体平衡的数值方法。将铁芯对等离子体平衡的影响等效地看作外部线圈电流的作用,这样问题就转化为求解空芯变压器装置的等离子体平衡问题。这一方法的另一特点是计算区域减至最小。     

SP的钱被谁吃了

广告里面的运营商个个拿捏十足，嘴边总挂着把合作伙伴看得比自己还重要，但事实上，一系列的肮脏交易体现了他们丑陋不堪的一面。     

一种基于不完全信息环境下多议题协商的最优化

文章探讨了Agent之间双边多议题的协商。主要以议程和协商程序这两个因素研究了其结果．并分析了不完全信息环境下不同议程和程序的协商过程，在此基础上，我们确定了逐一问题和一揽子交易两个协商程序的平衡策略，最后，给出了每个Agent所有可能议程和过程组合优化的协商结局。     

IKEv2在基于IP的无线自组网中的应用研究

无线自组网络没有专门的密钥管理协议,其安全性一直备受关注.IKEv2是目前IP网络中使用最广泛的密钥管理协议,但它不是专门为无线网络环境设计的.文章根据IKEv2使用的认证方法的不同提出了两个改进协议.这两个协议都使用无线自组网络认证方法-MANA证书来认证响应者,从而减少密码算法计算量,让IKEv2为无线自组网提供密钥管理服务.     

多功能脉冲恒流源的研究

针对微弧氧化、离子渗氮等离子体表面处理工艺中有时需要电流恒定这一特点,提出一种新型的多功能脉冲恒流源,此电源既可以实现峰值电流恒流也可以实现平均值电流恒流,并且可以进行实时的转换。该电源的设计思想和具体实现方法在文中有详细的阐述,且其2种功能在不同的参数条件下均能稳定工作。另外,将此电源用于部分工艺实验后也产生了较好的效果。     

基于复图像分析的点散射体分辨和位置测量

传统的雷达高分辨率ISAR图像分析都是基于图像幅度或强度信息,丢弃了相位信息,从而使实际雷达分辨能力达不到理论分辨水平.复图像技术综合应用了图像幅度/相位信息,实现了雷达的理论分辨能力,并同时实现了精确的散射体位置测量,而后者对于目标识别有着更重要的意义.文中研究了复图像技术分析目标上理想点散射体的方法.仿真结果表明复图像技术具备了上述优势.     

Q-Coder算术编码器的VHDL实现

现介绍了一种适合于硬件实现的二进制算术编码器Q-Coder，并使用VHDL语言实现了该算法。在Acfive-HDL软件中进行了功能仿真，并在Quartus Ⅱ软件中完成了综合以及后仿真。综合得到的最高时钟频率为36．3MHz。