Branch-shaped NaGdF4:Eu3+ nanocrystals: Selective synthesis,and photoluminescence properties

The branch-shaped NaGdF₄:Eu³⁺ nanocrystals (NCs) were synthesized by using polyvinylpyrrolidone (PVP) as a capping agent in ethylene glycol (EG) solution. The NCs were readily dispersed into water or ethanol to form a relatively stable suspension, which may facilitate their applications in biological fields. Meanwhile, the crystal structures of the NCs were tunable from the mixture of the α-(cubic) and β-(hexagonal) phases to the pure β-phase by varying the F^?/Ln³⁺ molar ratio or the reaction temperature. The pure β-phase NCs were obtained at relatively high F^?/Ln³⁺ molar ratio and reaction temperature. In addition, the Eu³⁺-doping concentration—dependent optical properties of the NaGdF₄:Eu³⁺ NCs were investigated in detail. The result shows that the emissions from high energy level transitions (e.g., ⁵D₁, ⁵D₂, and ⁵D₃) are significantly impaired with increasing the Eu³⁺-doping concentration due to the cross-relaxation process, and the emission at 612 nm is predominant since the doped Eu³⁺ ions locate in the crystal fields without inversion center.     

现代手工青砖回弹测强曲线研究

针对河北省范围内越来越多的古建筑维修保护工程,尤其是长城及各古城墙的修复工程中,大量使用现代新制手工制作青砖的现状,选取河北省地区较有代表性的维修保护古城墙用现代手工青砖试件60组,参照行业标准《回弹仪评定烧结普通砖强度等级的方法》,分析了回弹值与相应抗压强度之间的相关性,经数据回归分析,建立了该地区保护维修古城墙用现代新制手工青砖回弹专用测强曲线。根据项目的验证,该曲线的精度较好。     

A Rapid Colorimetric Detection of Melamine in Raw Milk by Unmodified Gold Nanoparticles

We report a rapid, visual, facile colorimetric detection of melamine in raw milk by unmodified gold nanoparticles (AuNPs). AuNPs can be induced by melamine from dispersion to aggregation rapidly, along with the color change from red to blue (or purple). After the optimization of reaction conditions, the whole analysis only needs about 20 min including the simple pretreatment we designed. The analysis can be observed by the naked eye and simple to operate without sophisticated instruments. In the raw milk, the present limit of detection for melamine is down to ～70 ppb. Furthermore, we explore the interaction principle between melamine and citrate-stabilized AuNPs in this work and establish the foundation for modifying the AuNPs and optimizing the system of AuNPs–melamine in the future.     

大学生选课态度的现状与对策

以某高校学生为研究对象,运用问卷和访谈相结合的方式进行调查,分析了大学生选课态度的现状,发现其存在的问题,并从师资队伍、选修课开设、教学管理水平、考核方式等方面提出相应对策.     

预应力空心方桩在实际工程中的应用

通过工程实例,介绍了预应力空心方桩在盐城地区的运用,指出作为预应力管桩的替代品,预应力空心方桩在9层-12层的小高层建筑中有着较好的经济效益和社会效应,也符合国家节能减排的方针。     

Diagnosis of PTFE‐Nafion MEA degradation modes by an accelerated degradation technique

Cost and durability are central issues in the commercialization of proton‐exchange membrane fuel cells. This study used complex accelerated‐degradation protocols to diagnose the degradation modes of low‐cost polytetrafluoroethylene–Nafion membrane electrode assemblies (MEAs). Acceleration protocols included open‐circuit voltage, relative humidity cycling, and load cycling. Failure modes included measurements of cyclic voltammetry, linear sweep voltammetry, polarization curve, and AC impedance. The four modes (stages) of degradation were determined to be (i) catalyst aging, (ii) creep deformation, (iii) pinhole formation, and (iv) membrane failure. During catalyst aging, the maximum power density decreased by 0.117 mW cm^?2 cycle^?1. After the 280th cycle, creep deformation occurred, and the maximum power density decreased by 0.227 mW cm^?2 cycle^?1. Pinholes led to membrane failure and a final dramatic loss of performance (?0.453 mW cm^?2 cycle^?1). Therefore, membrane failure is the major factor in the failure of MEAs. Copyright © 2010 John Wiley & Sons, Ltd.     

A digital technique for the on-line measurement of dissipationfactor and capacitance

This paper reports a computer-aided system for on-line monitoring of dielectric dissipation factor tan δ, and capacitance of HV apparatus. The method employs the discrete Fourier transform (DFT) which is performed on the scaled down analog voltage and current signals obtained using a digital storage oscilloscope (DSO) board. The results are displayed using the graphic user interface implemented with graphic (G) language, This technique uses optimal values of measurement parameters as indicated by software simulation and laboratory tests. Field tests were conducted at Manitoba Hydro's Dorsey station to evaluate the insulation of a 230 kV current transformer unit using the developed system     

核主分量分析法提取液体火箭发动机故障特征

某型号液体火箭故障仿真过程中涉及大量描述发动机状态的参数,因此在对该设备进行故障诊断前,需要对监测或仿真数据进行特征提取,以减少存储空间,缩短故障诊断时间.采用主分量分析法及其改进算法核主分量分析法对其故障仿真数据进行特征提取,从多个描述该型号一级火箭发动机故障状态的变量中选取了少量特征,采用这些特征进行故障诊断时,诊断结果正确,同时显著提高了故障诊断的实时性能.     

装载机差力差速器的虚拟设计与运动仿真

装载机使用的普通锥齿轮差速器,只有差速功能而无差力功能,为了改进此缺点,研制了一种性能优良的差力差速器,介绍了装载机差力差速器的结构及工作原理,并基于Pro/E软件对差力差速器进行了虚拟设计及其运动仿真分析.     

磁光盘径向偏摆测试的新方法

简述研制磁光盘机械特性测试仪的必要性，介绍径向测试可供选择的几种方案，并进一步提出光栅定标过道信号的测试方法。