Density measurement of 1-d confined water by small angle neutron scattering method: pore size and hydration level dependences

Small angle neutron scattering (SANS) is used to measure the absolute density of water contained in 1-D cylindrical pores of a silica material MCM-41-S with pore diameters of 19 and 15 A. By being able to suppress the homogeneous nucleation process inside the narrow pore, one can keep water in the liquid state down to at least 160 K. From a combined analysis of SANS data from both H(2)O and D(2)O hydrated samples, we determined the absolute value of the density of 1-D confined water. We found that the average density of water inside the fully hydrated 19 A pore is 8% higher than that of the bulk water at room temperature. The temperature derivative of the density shows a pronounced peak at T(L) = 235 K signaling the crossing of the Widom line at ambient pressure and confirming the existence of a liquid-liquid phase transition at an elevated pressure. Pore size and hydration level dependences of the density are also studied.     

基于RFM的机载余度计算机软件快速测试平台

现代飞机普遍采用电传飞行控制系统,飞行控制计算机是该系统的核心。为了提升飞控计算机的可靠性,普遍采用余度技术构建余度飞控计算机,该计算机由多个通道构成,每个通道有一个CPU,互相构成备份。但是,这给飞控计算机的软件调试和测试带来的巨大的困难,因为各个通道的机载软件之间相互同步、通信和交叉监控,必须并行调试和测试,这就造成了机载软件调试和测试的滞后,必须等待真实的飞控计算机开发出来之后才能开展工作。本文提出了一种基于RFM(反射内存)的余度计算机快速原型测试平台设计方法。该平台使用商用货架产品构成余度计算机的多个冗余通道,使用RFM模拟多通道间的通信、同步过程,通过对底层驱动封装实现硬件故障模拟和余度功能模拟,方便实现软件调试和从性能、功能测试,大大提高了开发效率,减少了研制周期。     

纳米(Y0.95Eu0.05)2O3及其SiO2气凝胶介孔组装体的制备与光致发光

采用尿素溶胶法合成（Ｙ０．９５Ｅｕ０．０５）２Ｏ３纳米粉,用超临界干燥技术制备了ｎ－（Ｙ０．９５Ｅｕ０．０５）２Ｏ３／ＳｉＯ２气凝胶介孔组装体。结果表明,当Ｙ＾３＋：Ｅｕ＾３＋＝２０：１,均相反应时间为４ｈ,且经６８０℃、４ｈ灼烧热处理后得到的ｎ－（Ｙ０．９５Ｅｕ０．０５）２Ｏ３中,光致发光强度最大（发光峰位于６１２ｎｍ）,以Ｓｉ与２Ｙ摩尔比为１：７的ｎ－（Ｙ０．９５Ｅｕ０．０５）２Ｏ３／ＳｉＯ２气凝胶介孔组装体,经同样条件热６１６ｎｍ）。对产生上述发光强度减弱和峰位红移现象进行讨论。     

消偏光纤陀螺的理论和实验研究

本文首次在理论上导出消偏型光纤陀螺的零漂和标度因子表达式,并得出以下两个结论:1)在使用约 40 dB偏振器时,导致陀螺漂移的主要因素是强度误差而并不是振幅误差;2)由光学标度因子与各种器件参量关系表明开环解调时陀螺的线性误差较大.试验样机证明了以上结果,并找出减小漂移的方法.     

基于比例积分控制原理预测钻井全过程原始地层温度的新方法研究

应用比例积分控制原理将瞬态传热模型预测结果与出口 温度实测数据逐步进行反馈可准确预测原始静态地层温度. 为此, 本文基于井下各控制组件质量、动量及能量守恒原理, 建立了实际井身结构与钻具组合条件下循环和停止循环期间井筒-地层温度分布全瞬态传热模型, 应用全隐式有限差分法进行求解, 并引入比例积分控制原理对比分析实测温度与预测温度的误差范围进而精确、 快速获取原始地层温度. 结合一口深井基础数据计算表明, 套管下入深度改变了井筒-地层间热交换效率, 进而影响了近井壁地层温度分布状况; 同时, 钻井过程中循环和停止循环作业过程改变了井下各控制组件的初始条件与边界条件, 致使近井壁原始地层温度分布距离产生变化. 建立的数学模型和研究方法可为石油钻井、地热井开采及地球深部原始地层温度信息准确、 经济、快速获取提供理论基础. 关键词： 原始地层温度 循环与停止循环 瞬态传热模型 比例积分控制原理     

Preparation of Antibacterial Waterborne Polyurethane/silver Nanocomposite

Stable aqueous dispersions of silver (Ag) nanoparticles were prepared by reducing silver nitrate solutions with sodium borohydride (NaBH₄) in the presence of waterborne polyurethane as a stabilizing agent. WPU/Ag nanocomposites were obtained after evaporating water. Transmission electron microscope (TEM) shows nanoscale Ag particles are well dispersed in WPU matrix at a lower concentration, while particles exhibit a little aggregation at a higher concentration. UV‐visible spectra, X‐ray powder diffraction, and energy dispersive X‐ray spectrometer (EDS) confirm the existence of Ag particle in WPU matrix. The WPU/Ag composite films show good antibiotic ability.     

一维铁磁金属纳米材料的制备、结构调控及其磁性能

一维铁磁金属纳米材料不但具有普通纳米粒子的各种特殊效应,而且具有独特的形状各向异性和磁各向异性,是构筑新型电磁功能材料的重要组元,在高密度磁记录、敏感元器件、电磁波吸收、催化剂、医学和生物功能材料等领域具有重要的应用。本文以一维铁磁金属纳米材料的制备技术为评述线索,重点论述了一维铁磁金属纳米材料的形貌参数（包括直径、长度、长径比）,晶面取向等微观结构的调控方法以及结构对磁性能的影响规律,指出发展新型的一维铁磁纳米材料的结构控制方法,研究一维材料的定向排布及组装技术,并从更深层次揭示一维结构与性能的关系以及开发一维铁磁纳米材料在各领域的实际应用是未来研究的主要发展方向。     

Conformational entropy of a pseudoknot polymer

The thermodynamics and kinetics of ABAB pseudoknot formation owing to reversible intrachain reactions are investigated for a flexible polymer based on the off-lattice Monte Carlo simulations. The polymer is made of N hard spheres tethered by inextensible bonds and consists of two reactive pairs AA and BB with binding energies -epsilon1 and -epsilon2, respectively, and three loop lengths (l1, l2, and l3). Although two intermediate states, loops A and B, may be formed, the folding path goes mainly through the intermediate loop whose free energy reduction associated with coil-to-loop crossover is greater. The conformational entropy loss is found to follow DeltaS=alpha ln N+G, where alpha approximately 2.48 for coil-loop crossover and alpha approximately 2.43 for loop-pseudoknot crossover. The constant G depends on the three loop lengths and the two end-to-reactive site lengths (L1 and L2). For a given total loop length, G is maximum when the three loop lengths are equal (l1=l2=l3). When l1=l3, the entropy loss is minimum if l2=0. However, the condition l1 not equal l3 makes G even smaller. This consequence indicates that asymmetry in loop lengths is thermodynamically favorable and this fact is consistent with observations of pseudoknotted RNA structures.