Ag负载TiO2纳米管微波辅助水热法制备及其光催化性能

以微波辅助水热法制备了二氧化钛纳米管,然后通过浸渍法在其表面负载了银纳米颗粒.所得样品用X射线衍射(XRD)、扫描电镜(SEM)、透射电镜(TEM)、氮吸附、X射线光电子能谱(XPS)、紫外-可见漫反射等测试方法表征.微波加热处理可以大大缩短反应时间,产物为无定型纳米管,经高温焙烧后转变成锐钛矿型二氧化钛.所得纳米管的外径为7-8 nm,内径为5-6 nm,管长约200 nm,比表面积可达371 m2·g-1.负载的银分散在纳米管的表面,对纳米管的结构与晶型没有影响,但是拓宽了二氧化钛的光吸收范围,使吸收边红移至可见光区,并且有效抑制了光生电子空穴的复合.在可见光降解罗丹明B的实验过程中,与Ag负载的P25及纯二氧化钛纳米管相比,Ag负载二氧化钛纳米管具有更高的可见光催化活性,并且当Ag/Ti 物质的量的比为0.5%时,可见光催化性能最好.     

Loading characteristics and chemical stability of headgroup‐functionalized poly(ethylene glycol)‐lipid ligand tethers on polypropylene capillary‐channeled polymer fibers

Polypropylene capillary‐channeled polymer fibers have been modified by adsorption of headgroup‐functionalized poly(ethylene glycol)‐lipids to generate a species‐specific stationary phase. In order to study ligand binding characteristics, a fluorescein‐labeled poly(ethylene glycol)‐lipid was used as a model system. Breakthrough curves and frontal analysis were employed to characterize the surface loading characteristics across a range of lipid concentrations and mobile phase flow rates. Efficient mass transfer and fluid transport yield a linear adsorption isotherm up to the maximum loading concentration of 3 mg/mL, at a linear velocity of 57.1 mm/s. Under these conditions, the dynamic binding capacity was found to be 1.52 mg/g of fiber support. Variation of the linear velocity from 8.6 to 57.1 mm/s showed only small changes in breakthrough volume. The maximum capacity of 1.8 mg/g is found under conditions of a load velocity of 34.2 mm/s and a concentration of 3 mg/mL lipid. Exposure of the lipid modified fibers to several challenge solvents reveals a chemically robust system, with only 50% acetonitrile and hexanes able to disrupt the lipid adsorption. The straightforward capillary‐channeled polymer fiber surface modification with headgroup‐functionalized lipids provides both a diverse yet practically robust ligand tethering system.     

阻尼对空爆荷载等效静载动力系数的影响

为考查阻尼参数对空爆荷载等效静载动力系数的影响,理论推导了空爆荷载下结构等效单自由体系弹塑性位移解及延性比解,设计并计算了阻尼比0.000 1～0.1、延性比1～4的20种典型工况的动力系数,并与现行抗爆设计规范动力系数公式结果进行了对比。结果表明:阻尼比小于0.000 1时可基本代表无阻尼状态,阻尼比0.01的动力系数比无阻尼的最大降低幅度为2.08%,数值差异很小,因此阻尼比为0.01以内时,可忽略阻尼对动力系数的影响;阻尼比0.05的动力系数比无阻尼的降低幅度约9.92%,数值差异较大,认为阻尼比0.05以上时将具有明显的经济效益;现行设计规范动力系数更适用于柔性结构体系,运用于刚性结构抗爆设计时,计算误差较大,对阻尼比较小的结构设计更不利。     

滑坡冲击铲刮变量的计算方法研究

高速远程滑坡运动过程中,冲击铲刮效应不仅增加滑坡的体积与规模,而且会增大滑坡成灾范围,风险预测与判断出现明显误差,导致灾难性事件的发生。目前对于高速滑坡的铲刮深度、铲刮范围和铲刮体积等变量计算往往是采用基于经验的铲刮率算法,其是通过体积增量来反算铲刮变量的数学方法,而实际情况中高速滑坡的冲击铲刮是滑体冲击力和地表可铲刮材料之间的力学屈服破坏作用的结果。本文基于接触力学、弹塑性力学和岩土力学,提出了地表可铲刮层在附加冲击荷载作用下铲刮变量的理论计算方法,认为竖向冲击和切向剪切是滑体冲击铲刮过程的两种主要作用方式。结合实际岩土体材料参数,发现不考虑切向荷载时,铲刮层塑性区主要以竖向破裂区为主,考虑切向荷载时,铲刮层塑性区沿切向迁移,直至塑性边界贯通至地表,符合实际情况,实现了对铲刮变量的定量化计算。     

Electromechanical cracking in ferroelectrics driven by large scale domain switching

Experimental results indicate three regimes for cracking in a ferroelectric double cantilever beam (DCB) under combined electromechanical loading. In the loading, the maximum amplitude of the applied electric field reaches almost twice the coercive field of ferroelectrics. Thus, the model of small scale domain switching is not applicable any more, which is dictated only by the singular term of the crack tip field. In the DCB test, a large or global scale domain switching takes place instead, which is driven...     

对主成分分析法三个问题的剖析

从主成分分析法的基本原理入手,针对教学过程中学生对主成分分析法感到费解的三个问题进行了逐一剖析:1.为什么主成分系数是经标准差标准化后原始变量的协方差矩阵的特征向量?2.特征向量正负号如何选取?对进一步的研究如计算综合得分和聚类分析有何影响?3.主成分载荷值是如何得来的?同时指出有些教材在计算主成分得分时混淆了主成分载荷和特征向量的概念,以致造成错误的结果.     

光通量法在SHPSB剪切应变测量中的应用

利用光通量方法对分离式霍普金森压剪杆实验技术中的剪切应变测量进行了实验研究。实验装 置主要包括:准直激光器、光电接收器、光学挡板。由装置性能验证实验结果以及不确定度分析结果表明:利 用基于光通量法的剪切应变测量技术能够可靠地测量SHPSB(splitHopkinsonpressurebar)试样的剪切应 变。并对比了基于光通量法测量的剪切应变值与理论近似结果,结果显示前者小于后者,分析并讨论了原因。     

红宝石脉冲激光动态光力学方法研究与进展

本文提出了瞬态图像采集技术和电磁脉冲加载装置。应用红宝石脉冲激光光源,介绍了动态全息光弹性、动态散斑干涉、动态云纹干涉、水下爆炸全息干涉、动态电子散斑干涉和动态数字散斑相关等多种方法的测试原理和测试技术。为动态位移场、应变场和应力场的定量分析提供了广泛的应用前景。     

A tree search method for the container loading problem with shipment priority

This paper addresses a special kind of container loading problem with shipment priority. We present a tree search method, which is based on a greedy heuristic. In the greedy heuristic, blocks made up of identical items with the same orientation are selected for packing into a container. Five evaluation functions are proposed for block selection, and the different blocks selected by each evaluation function constitute the branches of the search tree. A method of space splitting and merging is also embedded in the algorithm to facilitate efficient use of the container space. In addition, the proposed algorithm covers an important constraint called shipment priority to solve practical problems. The validity of the proposed algorithm is examined by comparing the present results with those of published algorithms using the same data.     

Analysis of dynamic stress intensity factors of three-point bend specimen containing crack

A new formula is obtained to calculate dynamic stress intensity factors of the three-point bending specimen containing a single edge crack in this study. Firstly, the weight function for three-point bending specimen containing a single edge crack is derived from a general weight function form and two reference stress intensity factors, the coefficients of the weight function are given. Secondly, the history and distribution of dynamic stresses in uncracked three-point bending specimen are derived based on the vibration theory. Finally, the dynamic stress intensity factors equations for three-pointing specimen with a single edge crack subjected to impact loadings are obtained by the weight function method. The obtained formula is verified by the comparison with the numerical results of the finite element method (FEM). Good agreements have been achieved. The law of dynamic stress intensity factors of the three-point bending specimen under impact loadings varing with crack depths and loading rates is studied.