冲击作用下金属表面微喷射的分子动力学模拟

利用二维分子动力学程序,结合类紧束缚杂化多体势,研究冲击载荷下金属表面包含沟槽型缺陷的微喷射动力学过程.在产生微喷射以后,结果表明材料内部传播着两种波系:反射稀疏波和二次加载压缩波,其中,反射稀疏波波面与沟槽形状相似,而二次压缩波波面随沟槽夹角的变化而变化;并形成了两个压强区:负压区和正压区,负压区的存在表明材料中可能产生微损伤.同时,统计结果表明微喷射体的速度随沟槽半角增加而增加的趋势,微喷射体的粒子数随沟槽半角增大而减少的趋势,当沟槽半角大于60°,微喷射效应消失.以上计算结果可以定性说明射流是沟槽型 关键词： 冲击波 沟槽型缺陷 微喷射 分子动力学     

压力振荡管引射性能实验研究

气波引射技术利用激波和膨胀波在压力振荡管内的运动来实现压力能传递,从而实现低压气体增压的目的。本文首先介绍了该技术工作原理和装置结构,然后建立了气波引射技术实验平台,测试了几个关键结构参数对其引射性能的影响。实验结果表明:随着高压喷嘴宽度,偏转距离和固壁长度的增加,设备的效率和抽射率均呈先上升后下降的趋势;实验结果验证了理想波图的正确性,其可用于指导设备设计。     

Compressed wormlike chain moving out of confined space: A model of DNA ejection from bacteriophage

The molecular biomechanics of DNA ejection from bacteriophage is of interest to not only fundamental bi- ological understandings but also practical applications such as the design of advanced site-specific and controllable drug delivery systems. In this paper, we analyze the viscous motion of a semiflexible polymer chain coming out of a strongly confined space as a model to investigate the effects of various structure confinements and frictional resistances encountered during the DNA ejection process. The theoretically predicted relations between the ejection speed, ejection time, ejection length, and other physical parameters, such as the phage type, total genome length and ionic state of external buffer solutions, show excellent agreement with in vitro experimental observations in the literature.     

Uptake of hydrogen from some carbon fibres examined by Secondary Ion Mass Spectrometry

The use of carbonaceous materials for hydrogen storage is not as simple as it may seem. Hydrogen atoms have different bonding energies and are incorporated into different types of these materials. Therefore, it is particularly important to distinguish between the surfacial atoms and those that are embedded in the bulk of the sample.SIMS spectrograph with periodical interruptions of the ion beam enables us to appreciate that at room temperature and in high vacuum, some outgassing of the surfacial hydrogen takes place.     

Mechanics of DNA packaging and ejection from elastic phage capsid

This study intends to investigate how the elasticity of a bacterial phage can affect the process of DNA packaging and ejection. For this purpose, we propose a unified continuum and statistical mechanics model by taking into account the effects of DNA bending deformation, electrostatic repulsion between DNA-DNA strands and elastic deformation of the phage capsid. Based on such a model, we derive the quantitative relations between packaging force, elasticity of capsid, DNA length remaining in the capsid, osmotic pressure and ejection time. The theoretically predicted results are found to agree very well with in vitro experimental observations in the literature.     

微喷颗粒与气体混合过程的数值模拟研究

冲击波作用下金属与气体界面将发生微喷混合现象,即金属表面产生的微喷射物质在气体中的输运过程.提出采用散体颗粒分布代替微喷初始状态,基于气体-颗粒两相流模型对微喷混合现象进行了模拟研究.数值模拟给出了微喷混合的动力学演化过程,分析了初始气体压力和颗粒尺寸因素对混合层的影响规律;在数值模拟中发现了微喷颗粒的气动破碎现象,这可导致颗粒尺度明显减小,成为影响微喷混合演化性质的重要物理因素.本文模拟结果与相关实验结果取得一致,初步表明,气粒两相流模型是模拟微喷混合过程的一种有效方法.     

Study of the interplay of vaporisation, melt displacement and melt ejection mechanisms under multiple pulse irradiation of metals

A threefold study combining profilometry, high speed imaging and recoil momentum measurements is used to deconvolve the relative contributions to material removal attributable to vaporisation, melt displacement and explosive melt ejection. The interplay of these three mechanisms is studied as a function of the number of laser pulses incident on an aluminium target and pulse repetition frequency. This study shows cumulative heating affects matter removed as both vapour and liquid melt, and highlights the influence of the vapour plume and ablation crater morphology on the proportions of material removed as melt displacement and melt ejection.     

ASAY膜法测量微物质喷射总质量不确定度的初步实验研究

 采用在不锈钢样品上用油脂粘贴给定质量的铝粉作为模拟喷射体的方法，对ASAY膜法测量微物质喷射总质量的不确定度进行了初步实验检验。实验结果表明，对于mg/cm²量级的微物质喷射总质量，目前ASAY膜法测量的不确定度可以小于50%。     

金属表面几何缺陷微细结构对微喷射特性的影响

基于光滑粒子流体动力学方法, 分别采用实测样品几何缺陷模型和简化V形沟槽模型对铅的微喷射过程进行了模拟. 重点分析了金属表面几何缺陷微细结构对微喷射特性的影响, 并将数值计算结果与相应的实验测量值进行对比. 结果表明, 基于实测样品几何缺陷模型计算的最快喷射速度和累积喷射量与实验测量结果符合得很好. 进一步研究发现, 在实测样品几何缺陷诱导的微喷射过程中存在“二次汇聚喷射”现象, 与单次喷射相比, 该过程会诱导产生更高的喷射速度并显著影响微喷物的空间密度分布. 这说明除了受扰动波长、深度影响外,表面几何缺陷微细结构也是影响金属微喷射过程的重要因素.