单晶ZnO、TiO_2纳米线拉伸力学特性的分子动力学研究

采用分子动力学方法,模拟了不同加载速度、不同温度下单晶ZnO、TiO_2纳米线的拉伸破坏过程.通过模拟结果,对比、分析了两种单晶金属氧化物纳米线拉伸力学特性的差异.研究表明,1)ZnO纳米线的断裂机制为:表面微裂纹-微孔-微裂纹与微孔贯穿-断裂,而TiO_2纳米线的断裂机制为:局部屈服-颈缩-断裂;2)TiO_2纳米线的承载能力优于ZnO纳米线,而承受变形的能力劣于ZnO纳米线;3)温度较低的情况下,纳米线的抗拉性能较好;加载速度越高,纳米线的抗载性能越好,而抗变形能力越差.     

Effects of Fe doping on ac susceptibility of Pr0.75Na0.25MnO3

Ac susceptibility at low temperatures of Pr_0.75Na_0.25Mn_1-xFe_xO₃ (0 ≤ x ≤ 0.30) is investigated. The peak value of the real component of ac susceptibility χ' at the freezing temperature T_f is suppressed with the increasing frequency. The peak value of χ' shows a linear relation between T_f and the logarithm of the frequency ω. The normalized slope P = ΔT_f/T_fΔlgω, which is much lower than canonical insulating spin glass systems in which 0.06 ≤ P ≤ 0.08. The peak value of the imaginary component of the ac susceptibility χ' at T_f for the x = 0, 0.02, 0.30 samples increases with increasing frequency, suggesting a cluster glass ground state with a coexistence of charge-ordered phase and correlated ferromagnetic clusters in spin glass matrix. The peak value of χ' at T_f for the x = 0.10 sample decreases with increasing frequency, suggesting a phase separation ground state. The peak value of χ' at T_f for the x = 0.05 sample decreases with increasing frequency for ω ≤ 52 Hz and increases subsequently till 701 Hz, and then decreases with further increasing frequency for ω ≥ 1501 Hz. This complex behaviour is ascribed to the competition between the effects of large and little ferromagnetic clusters in the sample. The ground state of x = 0.05 sample is a transition state from cluster glass to phase separation.     

"分子行走理论"模型——分子熵的笼敝效应及其在有机酸碱性比较中的应用

基团的电子、共轭、超共轭、空间位阻、溶剂化等效应在有机酸碱理论及酸碱性分析中一直占据主导地位.但在气相状态下,分析某些物质的酸碱性时单用上述理论远不能满足要求,得不到与实验事实相符的结果.从热力学及分子统计力学角度出发,以量子化学为辅助,研究了分子熵值及其构象改变对物质酸碱性、反应活性、反应速率的影响.提出理想状态下"分子自由行走"、"自由均方行走距"等假设,并以此演绎出理想状态下有机分子构象改变所遵循的统计规律——"类自由结合链高斯模型".建立了"分子熵效应笼敝扩散"分子构象模型,用该理论成功解释了气相状态下甲、乙、丙、丁、戊、己酸酸性大小差异及气相氨、伯胺、仲胺、叔胺、苯胺、二苯胺的碱性差异.结果表明:自由均方行走距及分子笼敝大小是影响物质活性的关键因素.     

再生障碍性贫血患者中药治疗前后微量元素变化初步观察

对20例再生障碍性贫血患者（以下简称再障）头发中12种微量元素的含量进行测定，与正常人做对照，结果发现，阴虚型患者锂、钙、锶、铬显著减少，阴虚型患者锌、镁、钡、钙、锂明显下降，阴阳俱虚型患者则12种元素均减少，并对本院治疗再障贫血的24味中药的微量元素的含量也进行测定。结合微量元素变化对指导再障的辩证组方和辩证施治提供新的思路，同时系统观察再障贫血10例治疗前后微量元素的变化情况，从微量元素角度探求再障的发症因素，认为与部分微量元素缺乏有关，补充相关的微量元素，再障患者可恢复健康。     

急性再障与中药微量元素及某些免疫指标关系的研究

急性再生障碍性贫血(简称急再)，是由多种病因导致骨髓广泛造血功能障碍的一组综合证，此病发病急，进展快，常伴有严重感染及内脏出血，严重威胁着广大患者的生命，本文从微量元素及免疫角度对急再进行了研究。同时对有关中草药进行了微量元素的测定，并与临床治疗密切结合，开阔了诊治急再的新思路。