基于均匀形核的金属液滴凝固过程

研究了均匀形核的金属液滴凝固过程,应用渐近分析法求得金属液滴内晶核生长数学模型的渐近解,分析了表面张力、界面动力学参数、初始晶核尺寸和过冷度对晶核界面生长速度、晶核半径以及液滴凝固时间的影响。在一定的过冷条件下,表面张力和界面动力学参数显著减缓了晶核界面生长速度。在凝固开始的很短时间内晶核界面生长速度迅速上升,当速度上升到最大值后,随着晶核半径的增大,界面生长速度逐渐减慢,表面张力和界面动力学参数对晶核生长速度的作用也逐渐减小。过冷度越大,液滴凝固时间越短。经过在开始的瞬变凝固阶段之后,温度场从设定的初始分布迅速地调整为由过冷度、表面张力、界面动力学参数等所确定的特定温度分布。     

不同冰核核化过程对雷暴云微物理过程和降水的影响

基于已有的二维对流云模式,加入一种新冰晶核化参数化方案;并通过对不同冰晶核化方式进行模拟对比,探讨不同冰晶核化过程对云内微物理过程及降水的影响。结果表明:考虑气溶胶异质核化作用以及均质冻结核化与异质核化的竞争关系后,地面降雨明显延后,地面累积降雨量减弱,降雨整体受到抑制。通过对微物理过程分析发现,主要有两个成因。异质核化过程的加入,导致冰晶特别是在高温区快速增长,加剧了云水以及水蒸气的消耗,致使云水碰并效率降低,抑制了雨滴的碰并增长;云滴和雨滴含量的减小减弱了其与霰粒子的碰并效率,霰粒子增长变缓,下落末速度降低,霰融化过程明显滞后。     

磁场对CaCO3结晶过程的影响

研究了磁化对ＣａＣＯ３结晶过程的影响。发现磁处理掏了晶体的成核过程但加速了晶体的生长，生成晶粒数量少，体积大。磁场对ＣａＣＯ３结晶过程的影响主要是通过成垢阴离子起作用。磁记忆效应至少可持续７２ｈ。     

金刚石薄膜的研究进展

介绍了近几年来发展较快的合成金刚石薄膜的几种方法 ,以及合成过程中的成核机理 ,并重点讨论了影响金刚石薄膜质量的几个因素。同时对目前金刚石薄膜的应用领域和其中存在的问题作了简要讨论。     

The mechanism of nucleation of hydrogen blister in metals

The nucleating, growing and cracking of hydrogen blister have been investigated experimentally and theoretically. The results show that atomic hydrogen induces superabundant vacancies in metals. The superabundant vacancies and hydrogen aggregate into a hydrogen-vacancy cluster (microcavity). The hydrogen atoms in the microcavity become hydrogen molecules which can stabilize the cluster. And the hydrogen blister nucleates. With the entry of vacancies and hydrogen atoms, the blister nucleus grows and the pressure in the cavity increases. When the stress induced by hydrogen pressure on the blister is up to the cohesive strength, cracks will initiate from the wall of the blister.     

关于双曲守恒型方程式黎曼问题解的核心判别位置的确定

关于标量双曲守恒型方程式ut fx=0的黎曼问题u=ul(x＜0),u=ur(x＞0),当f为非凸时解的性质同ur,ul的位置及同曲线f=f(u)的某些核心判别位置Uncl(nucleation criterion)有关.如何决定它,对于求解关系很大.过去文献只对f为非凸三次典型曲线研究过,但尚未明确在一般情形下求解的型式及方法.本文目的是应用更清晰的几何方法寻求当f为4次标量函数时的Uncl,并讨论它与解的性质及型式关系.     

蔗糖溶液成核起晶点临界尺寸的研究

本文论述了现有文献资料中关于蔗糖成核临界尺寸的各种不同报道及产生差异的原因，在研究过程中引入了溶剂夺水成核的概念和方法，比较合理地设定了晶核形成的初始时刻，并根据一系列试验数据建立了临界晶核尺寸推算公式，为蔗糖晶的理论研究和过程设计提供一个新的计算参考依据。     

The polymerization of sickle hemoglobin in solutions and cells

The polymerization of sickle hemoglobin occurs by the same mechanisms in solutions and in cells, and involves the formation of 14 stranded fibers from hemoglobin molecules which have assumed a deoxy quaternary structure. The fibers form via two types of highly concentration-dependent nucleation processes: homogeneous nucleation in solutions with hemoglobin activity above a critical activity, and heterogeneous nucleation in similarly supersaturated solutions which also contain hemoglobin polymers. The latter pathway is dominant, and creates polymer arrays called domains. The individual polymers bend, but also cross-link, and the resulting mass behaves as a solid. The concentration of polymerized hemoglobin increases exponentially unless clamped by rate limiting effects such as oxygen delivery.     

强磁场下Cu-25%Ag合金的凝固行为

研究了强磁场对Cu-25%Ag(质量分数)合金凝固组织的影响,分析了不同磁场条件对合金凝固组织的作用机理.研究发现,均恒磁场和梯度磁场对合金的凝固组织有重要影响,改变了富Cu枝晶形貌和尺寸,无磁场条件下初生富Cu枝晶分布不均匀,一次枝晶比较长且粗大,枝晶主要以柱状枝晶为主;在12 T磁场条件下,富Cu枝晶分布比较均匀,一次枝晶变短、粗化,枝晶主要以胞状枝晶为主;在负梯度磁场条件下,富Cu枝晶分布不均匀,在试样下部,树枝晶减少,以小平面方式生长的粗大胞晶为主.通过实验研究表明,利用均恒强磁场控制Cu-Ag合金凝固组织,细化晶粒、减小偏析是具有可行性的.     

Effect of void nucleation on microstructure and stress state in aluminum alloy tailor-welded blank

The microscopic damage initiation characteristic in welded joint greatly determines the subsequent damage evolution and fracture behavior of aluminum alloy tailor-welded blank(TWB) during plastic forming. In this study, the interactive dependence of void nucleation on microstructure and stress state in the welded joint of a2219 aluminum alloy TWB was quantitatively explored by in-situ SEM testing. Moreover, a micromechanical model based on actual microstructure was adopted to reveal the underlying mechanisms from the perspective of microscopic heterogeneous deformation. The results showed that three void nucleation mechanisms, including particle-cracking, interface-debonding and matrix-cracking, coexisted in the deformation at different microstructure regions and stress states. The nucleation strain of each mechanism mainly depended on the particle volume fraction, grain size and stress triaxiality. Besides, the proportions of particle-cracking and interfacedebonding greatly varied with the grain size and particle volume fraction, and the variation law changed with the stress state. The proportion of matrix-cracking had a weak dependence on the microstructure, while increased with the stress triaxiality decreasing. It made the damage initiation in aluminum alloy welded joint transit from particle-cracking dominance to matrix-cracking dominance with the stress triaxiality decreasing.The micromechanical modeling results suggested that the changes of evolutions and distributions of Mises stress in particle, hydrostatic stress at interface and plastic strain in matrix with microstructure and stress state were responsible for the above effects.