DNA体外缩合的研究进展

DNA缩合不仅是自然界常见的生理现象,也是非病毒载体介导基因转染的关键步骤。了解DNA体外缩合的性质与特征,将有助于设计出高效的非病毒转基因载体。本文综述了近十几年来以多价阳离子为缩合剂诱发的DNA体外缩合的研究进展,着重介绍了缩合的机理、过程、影响缩合的因素以及应用于转基因的最新成果。     

吸管法和比重计法测定土壤机械组成的比对研究

土壤机械组成是土壤的基本属性,也是第三次全国土壤普查(“三普”)的重要指标。参照“三普”规定的测定土壤机械组成的吸管法和比重计法的分析规范对来自河南封丘、江西鹰潭和新疆乌鲁木齐等地区的3种土壤试样进行分析,讨论平行测定的精密度和测定过程中的关键点,进而对两种测定方法进行评价。结果表明,吸管法和比重计法的分析过程中存在一些影响分析结果的重点步骤,这些关键细节对提升“三普”土壤机械组成结果准确性和分析效率至关重要。吸管法和比重计法测定获得的土壤质地类型结果基本一致。通过平行试样测定结果允许的绝对相差分析发现吸管法的精密度较比重计法稍差,但两者都能达到土壤普查的要求。通过两种土壤机械组成测定方法的比对研究,为基层实验室顺利开展本项目的测定提供借鉴,为第三次全国土壤普查工作提供技术支撑。     

有红利美式看跌期权定价的Crank-Nicolson有限差分法

本文基于B-S微分方程,采用Crank-Nicolson差分格式(简称C-N差分格式)求解支付固定红利的美式看跌期权价值,给出实证分析,并对C-N差分格式和隐含的差分格式进行了比较.结果表明,用C-N差分格式可以得到更加精确、有效的数值解.     

纳米二氧化钛-高锰酸钾协同光催化氧化体系快速测定化学需氧量

以纳米TiO2-KMnO4协同光催化氧化体系为基础,结合分光光度法建立了一种快速测定水样中化学需氧量(COD)的简便方法。本方法具有线性范围宽、抗氯离子干扰能力强等优点。在选定的最优条件下,线性范围为0.1~320mg/L;当氯离子含量在1500mg/L以内时,相对误差小于5%。此方法适用于污染程度低的自来水、地表水或中等污染程度的工业废水中COD值的快速测定。     

Effect of Stress-Dependent Thermal Conductivity on Thermo-Mechanical Coupling Behavior in GaN-Based Nanofilm Under Pulse Heat Source

The thermal properties of a nanostructured semiconductor are affected by multi-physical fields,such as stress and electromagnetic fields,causing changes in temperature and strain distributions.In this work,the influence of stress-dependent thermal conductivity on the heat transfer behavior of a GaN-based nanofilm is investigated.The finite element method is adopted to simulate the temperature distribution in a prestressed nanofilm under heat pulses.Numerical results demonstrate the effect of stress field on the thermal conductivity of GaN-based nanofilm,namely,the prestress and the thermal stress lead to a change in the heat transfer behavior in the nanofilm.Under the same heat source,the peak temperature of the film with stress-dependent thermal conductivity is significantly lower than that of the film with a constant thermal conductivity and the maximum temperature difference can reach 8.2 K.These results could be useful for designing GaN-based semiconductor devices with higher reliability under multi-physical fields.     

变温场中具损伤粘弹性矩形板的非线性动力响应分析

基于热粘弹性理论、Von Karman板理论和连续损伤力学,导出了二维状态下各向同性材料的变温粘弹性本构方程,建立了含损伤效应的各向同性粘弹性矩形板在变温场中的非线性运动控制方程,且应用有限差分法对问题进行求解.算例中,讨论了损伤演化及温度场等因素对粘弹性矩形板非线性动力学行为的影响,得出一些有意义的结论.     

低压供热涂层材料制备及热性能研究

低压供热技术具有安全系数高和节能降耗等优势,因而成为石化稠油长输管线、风力发电叶片冬季防覆冰和室内供暖等领域的研究热点之一。本文制备了一系列低压供热涂层材料,研究不同碳功能填料对涂层发热速率、发热功率及最高发热温度的影响规律,并揭示石墨烯和碳纤维对提升涂层材料热性能的协同作用。其中石墨烯纳米片的还原程度对材料热性能具有重要影响,降低其表面官能团密度对提升涂层供热特性具有促进作用,但是官能团密度过低会导致石墨烯纳米片的团聚现象,引起涂层发热不均匀。加入适量碳纤维可以提高石墨烯的均匀分散性,提升发热速率。优化石墨烯纳米片和碳纤维的比例后,采用24V电压驱动时,涂层材料的发热速率达到7.1℃·s^-1,功率密度为800W·m^-2,最高发热温度为124℃。     

A Novel 3D Na(I) Coordination Polymer Constructed by 3,5-Bis(4'-Carboxy-Phenyl)-1,2,4-Triazole: Synthesis,Crystal Structure,and Photocatalytic Property

Crystallography Reports - A novel 3D metal coordination polymer, {[Na4(µ2-H2O)(DMF)2(BCT)2]?DMF}n (I) (DMF = N,N-dimethylformamide, H2BCT =...     

Positron lifetime study in BaTiO3 ceramics with different Ba/Ti ratios

The positron lifetime spectra in 0.25 at.% La-doped BaTiO₃ with different Ba/Ti ratios have been measured at room temperature. It was found from the experiments that with deviating from exact stoichiometry the positron lifetime τ₂ decreases and the intensity I₂ increases for Ba/Ti ratio smaller than stoichiometric and they have more significantly similar changes for Ba/Ti ratio larger than stoichiometric. The non-monotonic dependence of positron lifetime parameters on Ba/Ti ratio is regarded as that the τ₂ component is contributed together by positrons annihilating at the grain boundaries and Ba vacancies and/or Ti vacancies, and small deviations from exact stoichiometry would be expected to increase the concentration of defects such as Ba vacancies for Ba/Ti < and Ti vacancies for Ba/Ti > 1.     

稀土发光配合物在水溶液中的组装及生物成像研究

稀土配合物具有较窄的f-f跃迁光谱带、较长的荧光寿命及较大的Stokes位移等独特的发光性质,同时其优异的顺磁性,赋予其在生物检测、疾病诊断及生物学活动研究中的重要应用价值.然而,稀土配合物大多水溶解性差,且荧光容易被环境中水分子O-H键的热振动淬灭等,极大地限制了其在水溶液及生物体系中的应用.近年来有研究表明,将稀土...