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A detailed study of the formation of toroidal condensation produced from the 2700 base pair fragments of plasmid PUCI3 DNA, induced by metal ions, is introduced. We have extracted several typical intermediate structures based on investigation by electron microscopy, and compared their size distributions. The observations suggest that the formation process of DNA condensation is the process of folding and arranging DNA chains and that of disorderorder transition. The result also indicates that the condensed particles are polymeric, but not randomly aggregative, further proving thetoroidal structures are formed in certain regularities. 相似文献
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PVC/ACR共混物微观结构与性能 总被引:3,自引:1,他引:3
本文研究了聚氯乙烯/丙烯酸酯类共聚物(PVC/ACR)共混物的应力-应变行为和冲击强度对ACR 用量的依赖关系。ACR对 PVC有良好的增韧作用,提高了PVC抗冲击性能。考察了三盐基性硫酸铅和硬脂酸钡-硬脂酸镉稳定剂对共混体系的影响,实验结果说明不同的热稳定体系对ACR改性PVC的效果有差别。动态力学性能测定结果表明PVC/ACR共混物存在两个玻璃化转变温度,证明PVC与ACR不相容性;而两个转变温度随共混物组成改变而变化,说明PVC与ACR之间存在着相互作用,PVC/ACR为部分相容体系。通过透射电子显微镜观察PVC/ACR共混物的微观结构形态表明:PVC与 ACR为两相体系,ACR呈粒状分布在PVC连续相中。但是,采用硬脂酸钡-硬脂酸镉稳定体系时,随着ACR用量增加,ACR的分散形态由粒状分散逐渐形成网络结构形态,与此相对应的共混物具有更好的抗冲击性能。 相似文献
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