悬链曲面上的点粒子动力学及扩展空间约束系统量子化

扩张型正则量子化方案的核心内容是位置、动量以及哈密顿量同时量子化. 通过分析悬链面上粒子的扩张型正则量子化方案, 并且与薛定谔理论进行比较, 发现内禀几何中二维悬链面给不出与薛定谔理论相一致的结果, 而考虑将二维悬链面嵌入在三维欧氏空间之后, 还需要将正则量子化方案进行扩张, 可以得到体系的几何势能和几何动量, 并与薛定谔理论相一致.     

Computational mechanistic investigation of radiation damage of adenine induced by hydroxyl radicals

The radiation damage of adenine base was studied by B3LYP and MP2 methods in the presence of hydroxyl radicals to probe the reactivities of five possible sites of an isolated adenine molecule. Both methods predict that the C8 site is the more vulnerable than the other sites. For its bonding covalently with the hydroxyl radicals, B3 LYP predicts a barrierless pathway, while MP2 finds a transition state with an energy of 106.1 kJ/mol. For the hydroxylation at the C2 site, the barrier was calculated to be 165.3 k J/mol using MP2 method. For the dehydrogenation reactions at five sites of adenine, B3 LYP method predicts that the free energy barrier decreases in the order of H8 H2 HN62 HN61 HN9.     

Liquid to glass transition of tetrahydrofuran and 2-methyltetrahydrofuran

Both tetrahydrofuran(THF) and 2-methyltetrahydrofuran(MTHF) are studied systematically at desired temperatures using molecular dynamics simulations.The results show that the calculated densities are well consistent with experiment.Their glass transition temperatures are obtained:115K ～ 130K for THF and 131K ～ 142K for MTHF.The calculated results from the dipolar orientational time correlation functions indicate that the "long time" behavior is often associated with a glass transition.From the radial and spatial distributions,we also find that the methyl has a direct impact on the structural symmetry of molecules,which leads to the differences of physical properties between THF and MTHF.     

探测棒在湿颗粒堆中的最大静摩擦力

实验研究了探测棒在湿颗粒堆中的最大静摩擦力。结果表明,探测棒在湿颗粒堆中受到的最大静摩擦力随颗粒填充高度的增加呈指数增长。当湿颗粒堆的填充高度相同时,圆棒受到的最大静摩擦力最大,三角棒次之,方棒最小。研究还发现,在含水量不同的湿颗粒堆中,液桥力和浮力存在着一种     

Molecular dynamics simulations of A-DNA in bivalent metal ions salt solution

A-form DNA is one of the biologically active double helical structure. The study of A-DNA structure has an extensive application for developing the field of DNA packaging in biotechnology. In aqueous solution, the A-DNA structure will have a free transformation, the A-DNA structure will be translated into B-form structure with the evolution of time, and eventually stabilized in the B-DNA structure. To explore the stability function of the bivalent metal ions on the A-DNA structure, a series of molecular dynamics simulations have been performed on the A-DNA of sequence (CCCGGCCGGG). The results show that bivalent metal ions (Mg²⁺, Zn²⁺, Ca²⁺) generate a great effect on the structural stability of A-DNA in the environment of high concentration. As the interaction between metal ions and electronegative DNA chains, the stability of A-DNA in solution is gradually improved with the increasing solution concentration of ions. In metal salt solution with high concentration, metal ions can be easily distributed in the solvation shells around the phosphate groups and further lead to the formation of shorter and more compact DNA structure. Also, under the condition of the same concentration and valency of the metal ions, the stability of A-DNA structure is different. The calculations indicate that the structure of A-DNA in CaCl₂ solution is less stable than in MgCl₂ and ZnCl₂ solution.