碱/酸两步催化法制备耐候性SiO2增透膜的研究

以正硅酸乙酯(TEOS)为先驱体,采用碱/酸两步催化溶胶-凝胶法制备出一种兼具碱催化增透膜的高透过率和酸催化增透膜的良好耐摩擦性能的优点的SiO2增透膜。对酸碱催化SiO2相对比例及酸催化时水含量的系统研究表明,当酸催化SiO2的含量为50%时,增透膜综合性能最好,即具有高透过率和高耐摩擦性;当nH2O/nHCl=1∶0.0010时,增透膜的透过率最高。碱/酸两步催化法制备的增透膜与水的接触角仅为11.3°,本文进一步用六甲基二硅氧烷(HMDS)对增透膜表面进行了修饰,修饰后增透膜的接触角提高至52.5°,增透膜的疏水性及环境稳定性得到较大的提高。     

两步双向查找表预测的高光谱图像无损压缩

提出一种基于两步双向查找表预测的高光谱图像无损压缩算法。将谱段内预测和谱间预测有效地结合,去除了高光谱图像强的谱间相关性。根据高光谱图像特点,首先,在光谱线的第1谱段图像采用JPEG-LS中值预测器进行谱段内预测,其它谱段图像采用谱间预测。谱间预测采用两步双向预测算法,第1步预测,采用一种双向四阶预测器,利用该预测器得到参考预测值;第2步预测,采用一种8级查表(LUT)搜索预测算法,得出8个LUT预测值。然后,将参考预测值与其比较得出最终的预测值。最后,将预测差值进行熵编码。实验结果表明,本文算法的平均压缩比达到3.05bpp(bits per pixel),与传统高光谱图像无损压缩算法比较,平均压缩比提高了0.14～2.91bpp,有效提高了高光谱图像无损压缩比低的问题。     

The influence of interfacial barrier engineering on the resistance switching of In2O3：SnO2/TiO2/In2O3：SnO2 device

The I-V characteristics of In2O3：SnO2/TiO2/In2O3：SnO2 junctions with different interracial barriers are inves- tigated by comparing experiments. A two-step resistance switching process is found for samples with two interfacial barriers produced by specific thermal treatment on the interfaces. The nonsynchronous occurrence of conducting filament formation through the oxide bulk and the reduction in the interracial barrier due to the migration of oxygen vacancies under the electric field is supposed to explain the two-step resistive switching process. The unique switching properties of the device, based on interracial barrier engineering, could be exploited for novel applications in nonvolatile memory devices.     

On discrete maximum principle

A model of optimal control for discrete systems and the historical development of the discrete maximum principle are considered. The paper deals with local optimality conditions of the first order, e.g. with a local maximum-principle and a quasi-maximum principle. Furthermore, optimality conditions of higher order, e. g. an optimality condition for singular controls are given.     

基于最小二乘的时差定位算法

时差测量方程是非线性双曲线方程,可以通过引入中间变量将其转化为线性方程,对近年来国内外学者关于这种方法的时差定位算法进行了总结。当已知测量误差的先验信息时,可以采用两步加权最小二乘法和约束加权最小二乘法,当测量误差的先验信息未知时,还可以采用约束总体最小二乘的方法。在求解约束最小二乘问题时,采用常规的拉格朗日法计算复杂、运算量大,而采用高斯一牛顿法不仅可以大为降低运算量,还能提高解的精度和稳定性。此外,对约束加权最小二乘法和约束总体最小二乘法之间的关系进行了探讨,得到了它们等价性的条件。     

Finite element modelling of local scour below a pipeline under steady currents

Local scour has been identified as the main factor that causes failures of structures in offshore engineering. Numerous research efforts have been devoted to local scour around offshore pipelines in the past. In this paper, a finite element numerical model is established for simulating local scour below offshore pipelines in steady currents. The flow is simulated by solving the unsteady Reynolds-averaged Navier–Stokes equations with a standard k ? ? turbulent model closure. A sand slide scheme is proposed for the scour calculation, and bed load is considered in the proposed scour model. To account for changes in bed level, the moving mesh method is adopted to capture the water–sediment interface (bed), and the change of bed level is calculated by solving Exner–Polya equation. All the equations are discretised within the two-step Taylor–Galerkin algorithm in this paper. It is found that the sand slide model works well for the simulation of the scour, and the numerical results are shown to be in good agreement with the available experimental data.     

两步化学沉积法制备ZnO薄膜及其场发射特性

在低温常压条件下,以ITO玻璃为衬底,采用电化学法与湿化学法结合的两步化学沉积法制备了团簇状ZnO薄膜。利用XRD,SEM分析了薄膜结构和表面形貌,并采用二极管结构在高真空条件下对薄膜进行了场发射性能测试。稳定发射后,开启电场为3.0 V/μm。当电场为5.8 V/μm时,电流密度为583.3 μA/cm²。研究表明:两步化学沉积法低温制备ZnO薄膜是可行的,且该薄膜具有良好的场发射性能。     

重叠PCR法构建嗜酸乳杆菌分选酶A基因外源打靶片段

为比较单步法、分步法重叠PCR在构建嗜酸乳杆菌Lactobacillus acidophilus ATCC4356分选酶A(SrtA)外源打靶片段的差异性, 设计了5对具有20~25bp互补末端的引物, 分别扩增两对上下游同源臂和卡那霉素基因, 先采用分步法、单步法重叠PCR构建不含筛选基因的外源打靶片段SrtA-up2-SrtA-down2, 比较两者优劣, 随后取较优者构建含抗生素筛选基因的打靶片段SrtA-up1-Kan-SrtA-down1. 结果显示单步法优于分步法, 非特异性扩增少, 拖尾现象少, 且扩增打靶片段SrtA-up1-Kan-SrtA-down1条带单一, 无非特异性扩增. 即在构建两种外源打靶片段时, 单步法重叠PCR优于分步法PCR, 为之后构建嗜酸乳杆菌基因打靶载体、构建融合基因打下了基础.     

钙钛矿太阳能电池的制备工艺与光伏性能研究

设计和制备结构为FTO玻璃/TiO2致密层/TiO2介孔层/CH3NH3PbI3吸收层/C电极的钙钛矿太阳能电池.采用两步法制备CH3NH3PbI3吸收层:首先通过旋涂技术制备PbI2薄膜,然后将PbI2薄膜在浓度为0.044 mol/L的甲基碘化胺/异丙醇(MAI/IPA)溶液中分别浸泡反应0.5 h、2.5 h、3.5 h和4.0 h后获得CH3NH3PbI3吸收层.研究了浸泡反应时间对CH3NH3PbI3吸收层的结构和形貌以及对电池光伏性能的影响.结果表明:PbI2薄膜在MAI/IPA溶液中反应后形成四方结构的CH3NH3PbI3晶粒,当浸泡反应3.5 h时,CH3NH3PbI3晶粒的平均尺寸最大,均匀性较好;XRD图谱中只有CH3NH3PbI3的特征峰,而PbI2的特征峰完全消失.同时,该条件下制备的钙钛矿太阳能电池的光伏性能最佳,其开路电压0.881 V、短路电流密度达到22.17 mA/cm2,光电转化效率6.79;,且在整个可见光区的光子-电子的转换效率接近50;.     

金属氧化物两步热化学循环分解水制氢*

金属氧化物两步热化学循环分解水制氢技术集太阳能储备与氢能制备于一体,是当前新能源研究和开发领域的热点之一。本文介绍了该技术制氢原理,综述了其关键材料金属氧化物体系和太阳能反应器的研究进展,分析了制约该技术规模化应用的“瓶颈”因素。最后,对近年出现的基于金属氧化物两步热化学循环分解水制氢的两步蒸汽重整新工艺的原理和金属氧化物材料研究进行了介绍,并对该领域的发展趋势进行了展望。