Ultrasonic irradiation and its application for improving the corrosion resistance of phosphate coatings on aluminum alloys

In this paper, ultrasonic irradiation was utilized for improving the corrosion resistance of phosphate coatings on aluminum alloys. The chemical composition and morphology of the coatings were analyzed by X-ray diffraction analysis (XRD) and scanning electron microscopy (SEM). The effect of ultrasonic irradiation on the corrosion resistance of phosphate coatings was investigated by polarization curves and electrochemical impedance spectroscopy (EIS). Various effects of the addition of Nd₂O₃ in phosphating bath on the performance of the coatings were also investigated. Results show that the composition of phosphate coating were Zn₃(PO₄)₂ · 4H₂O(hopeite) and Zn crystals. The phosphate coatings became denser with fewer microscopic holes by utilizing ultrasonic irradiation treatment. The addition of Nd₂O₃ reduced the crystallinity of the coatings, with the additional result that the crystallites were increasingly nubby and spherical. The corrosion resistance of the coatings was also significantly improved by ultrasonic irradiation treatment; both the anodic and cathodic processes of corrosion taking place on the aluminum alloy substrate were suppressed consequently. In addition, the electrochemical impedance of the coatings was also increased by utilizing ultrasonic irradiation treatment compared with traditional treatment.     

Density functional theory study on Ni-doped MgnNi (n=1-7) clusters

The possible geometrical and the electronic structures of small MgnNi(n = 1-7) clusters are optimised by the density functional theory with a LANL2DZ basis set.The binding energy,the energy gap,the electron affinity,the dissociation energy and the second difference in energy are calculated and discussed.The properties of Mg n Ni clusters are also discussed when the number of Mg atom increases.     

机械刻划光栅的光线追迹方法

为了评价光栅的光谱质量,完成所设计光栅的光线追迹,针对机械刻划光栅的光线追迹提出了一种改进方法.在费马原理的基础上利用光程函数法得到入射光通过光栅后的光谱分布情况,再使用传输矩阵的计算方法构造出光谱的点列图.该方法适用于刻划在平面、球面和非球面基坯上的等间距和变间距光栅,光栅的光谱面可以为平面或者二次曲面. 通过刻划在非球面基坯上的凹面光栅验证了光线追迹方法的可靠性.     

基于表面等离子体激元共振的飞秒抽运探测技术研究

对基于表面等离子体激元共振（SPR）的飞秒抽运探测技术进行了系统地数字分析.计算结果表明,利用SPR技术可将飞秒抽运探测信号强度ΔR/R提高2—3个数量级,其提高的比例依赖于金属膜的厚度和探测光的入射角,其中R和ΔR分别为探测光反射率的总量和变化量.特别地,对于金属-吸收介质体系,金属膜的介电常数变化对ΔR的影响仅为吸收介质影响的2%,所以ΔR/R主要反应吸收介质中的动力学过程,因此该技术对研究表面和界面的超 关键词： 超快光学 表面等离子体共振 飞秒抽运探测技术 信号强度     

等离子体在任意强度的直流电场中产生电流的过程

通过Fokker-Planck模拟,研究了等离子体在任意强度的直流电场中产生电流的过程以及电子分布函数的演变过程.研究发现,不同强度的电场中等离子体的行为存在着明显的差别.在弱电场中,电流与电场满足Spitzer公式,且电流产生的响应时间约等于撤销电场后电流衰减的弛豫时间;在中等强度的电场中,电子分布函数呈现为静止Maxwell分布和漂移Maxwell分布之和,而且在中等强度或者强直流电场中弛豫时间也将远远大于响应时间.根据电子分布函数的演变规律,推导了一组类似于流体力学方程的公式,这组方程像Spitzer公式一样简便地描述了等离子体中电流与电场的关系,并且对电场强度没有限制.数值模拟显示这组方程比Spitzer公式更适用于等离子体的混合粒子模拟中. 关键词： 等离子体电流 电子分布函数 Fokker-Planck模拟 Spitzer公式     

BaCuO_2的添加对YBa_2Cu_3O_(7-δ)临界电流密度的影响

掺入BaCuO2杂相的YBa2Cu3O7-δ(YBCO)粉末样品采用固相反应方法制备获得。XRD的Rietveld精修显示BaCuO2杂相和YBCO并存。在YBCO+xBaCuO2(x=0,0.05,0.1,0.2,0.3)的一系列样品中,当x=0.05时,样品的临界电流密度最大。在磁场中,微量BaCuO2杂相的添加,使YBCO的临界电流(Jc)提高了,但超导转变温度(Tc)稍微有所下降。临界电流密度的这些特征行为来自于两方面的共同作用,一方面是超导性的变化,另一方面纳米尺寸范围内的空间分布的非均匀性。     

Structural Deformation of CO22+ in Intense Femtosecond Laser Fields

The angular distributions of CO^＋ from the dissociation of CO2^2＋ and CO2^＋ in intense femtosecond laser fields （45 fs, about 5 × 10^15 W/cm^2） are studied at a laser wavelength of 800nm based on the time-of-flight mass spectra of CO^＋ fragment ions. The experimental results show that structural deformation occurs in the charge state of CO2^2＋ and the CO^＋ maintains linear geometrical structure.     

改进的tanh函数方法与广义变系数KdV和MKdV方程新的精确解

利用改进的tanh函数方法将广义变系数KdV方程和MKdV方程化为一阶变系数非线性常微分方 程组-通过求解这个变系数非线性常微分方程组，获得了广义变系数KdV方程和MKdV方程新的 精确类孤子解、有理形式函数解和三角函数解- 关键词： 改进的tanh函数方法 类孤子解 有理形式函数解 三角函数解     

高频脉冲管制冷机流动特性实验分析

系统的测量了不同运行条件下,高频脉冲管制冷机蓄冷器冷端压力波幅值、速度波幅值以及它们之间相位差的变化规律。结合焓流理论,解释了小孔开度、充气压力、压比和运行频率,在高频条件下对制冷性能的影响规律。所得结果定性解释了制冷机中相应的实验现象,对于高频脉冲管制冷机的机理理解和实验研究有重要指导意义。     

用雅可比-傅里叶矩进行图像描述

提出了雅可比—傅里叶矩,它是用雅可比多项式作为径向函数,用傅里叶因子作为角向函数构造而成的,是广义正交傅里叶—梅林矩。经过归一化处理后的雅克比—傅立叶矩具有平移、尺度、旋转、灰度多畸不变性。从归一化图像重建误差、噪声灵敏度等方面对雅可比—傅里叶矩的图像描述能力进行了研究,结果显示雅可比—傅里叶矩在各种参量选择的情况下,具有良好的图像描述和抗噪声能力,是一个优良的图像特征。以前的研究多为单纯构建某一个函数,而现在将其扩展为构建一个函数族,开阔了矩描述量的研究视野。