Molten salt synthesis and luminescent properties of YVO4:Ln (Ln = Eu3+, Dy3+) nanophosphors

Eu3+ and Dy(3+)-doped YVO4 nanocrystallites were successfully prepared at 400 degrees C in equal moles of NaNO3 and KNO3 molten salts. X-ray diffraction (XRD), Fourier transform infrared (FT-IR) spectroscopy, transmission electronic microscopy (TEM), photoluminescence (PL) spectrum and lifetime were used to characterize the nanocrystallites. XRD results demonstrate that NaOH concentration and annealing temperature play important roles in phase purity and crystallinity of the nanocrystallites, the optimum NaOH concentration and annealing temperature being 6:40 and 400 degrees C respectively. TEM micrographs show the nanocrystallites are well crystallized with a cubic morphology in an average grain size of about 18 nm. Upon excitation of the vanadate group at 314 nm, YVO4:Eu3+ and YVO4:Dy3+ nanocrystallites exhibit the characteristic emission of Eu3+ and Dy3+, which indicates that there is an energy transfer from the vanadate group to the rare earth ions. Moreover, the structure and luminescent properties of the nanocrystallites were compared with their bulk counterparts with same composition in detail.     

社会资本视域下城市失意群体问题研究

自改革开放以来,经济制度的转变带来了三十多年的高速增长,社会发展的同时社会矛盾也逐步显现,譬如近几年来引起社会的普遍关注的、各地接连发生的恶性伤害暴力案件。诸多案件的背后都指向一个共同群体——城市失意群体。社会资本的缺失是城市失意群体的产生原因,也是目前处于转型时期中国社会面临的重要现实问题之一。通过社会资本视角对城市失意群体的探究,具有重大的现实意义。     

碳化硅致密陶瓷材料研究进展

碳化硅材料以其优异的性能得到了越来越广泛的应用,通过简要介绍碳化硅致密陶瓷的制备方法及其性能和总结近年来国内外的研究进展,来展望碳化硅致密陶瓷材料的研究发展趋势。     

高温钛合金和颗粒增强钛基复合材料的研究和发展

简要回顾了高温钛合金的研究和发展历程,指出现代高温钛合金进一步发展需要解决的主要难题.综述了颗粒增强钛基复合材料的研究现状,从基体的选择、增强相的选择和制备工艺等3个方面,较详细地阐述了颗粒增强钛基复合材料设计中的基本任务.最后对今后的发展趋势进行了展望.     

一种基于语义与QoS感知的Web服务匹配机制

Web服务匹配是动态服务组合的一个重要环节,然而目前大多数的研究仅从单个抽象服务的角度进行局部语义匹配,没有考虑到服务组合的全局匹配,此外,即使考虑了全局匹配也仅从QoS角度进行匹配,没有考虑到全局语义匹配.针对服务组合流程,提出了基于抽象服务的局部语义匹配与基于QoS感知的全局语义匹配,设计了语义匹配算法,并扩展对服务输入/输出匹配的可用性分析,建立了全局匹配的QoS模型及其评价方法,基于该模型及评价方法,采用遗传算法实现全局语义匹配度最大化及满足用户的QoS指标需求.仿真实验结果表明：基于语义与QoS感知的服务匹配算法是可行的和有效的.     

Performance of a proton exchange membrane fuel cell stack using conductive amorphous carbon-coated 304 stainless steel bipolar plates

In this study, 304 stainless steel (SS) bipolar plates are fabricated by flexible forming process and an amorphous carbon (a-C) film is coated by closed field unbalanced magnetron sputter ion plating (CFUBMSIP). The interfacial contact resistance (ICR), in-plane conductivity and surface energy of the a-C coated 304SS samples are investigated. The initial performance of the single cell with a-C coated bipolar plates is 923.9 mW cm⁻² at a cell voltage of 0.6 V, and the peak power density is 1150.6 mW cm⁻² at a current density of 2573.2 mA cm⁻². Performance comparison experiments between a-C coated and bare 304SS bipolar plates show that the single cell performance is greatly improved by the a-C coating. Lifetime test of the single cell over 200 h and contamination analysis of the tested membrane electrode assemble (MEA) indicate that the a-C coating has excellent chemical stability. A 100 W-class proton exchange membrane fuel cell (PEMFC) short stack with a-C coated bipolar plates is assembled and shows exciting initial performance. The stack also exhibits uniform voltage distribution, good short-term lifetime performance, and high volumetric power density and specific power. Therefore, a-C coated 304SS bipolar plates may be practically applied for commercialization of PEMFC technology.     

Highly selective removal of 2,4-dinitrophenol by a surface imprinted sol–gel polymer

In this work, 2,4-dinitrophenol (2,4-DNP), a new molecularly imprinted polymer (MIP) with excellent performance was synthesized in ethanol by the sol–gel method using 3-aminopropyltriethoxysilane as functional monomer on the surface of silica particles. The structure and morphology of MIP were characterized via scanning electron microscopy, nitrogen adsorption–desorption analysis, infrared spectra, and thermogravimetry analysis. Results demonstrated that MIP had excellent selectivity toward the template molecule (2,4-DNP) with an imprinting factor of 9.55 and a maximum static adsorption capacity of 114.7 mg g⁻¹. Data obtained from the adsorption isotherm of 2,4-DNP were fitted well with the Freundlich isotherm model, and the adsorption process can be described by the pseudo-second-order model. The investigation of adsorption mechanism revealed that the specific recognition process of MIP toward 2,4-DNP was dominated by the hydrogen bond and molecular structure. By employing as a sorbent, the as-prepared MIP was applied to recognize and remove 2,4-DNP in poster paper, nonwoven fabric and brown curtain with recoveries in the range from 85.74 to 100.00%. However, the MIP can effectively remove 2,4-DNP after five cycles.     

祈年殿式混凝土仿古建筑模态分析

在对天坛祈年殿结构特点分析的基础上,结合有限元模态分析基本理论和ANSYS软件模态分析过程,运用通用数值分析软件Ansys11.0对天坛祈年殿式混凝土结构前五阶模态进行了计算.介于古建筑构件尺寸相对偏大,整体刚度偏大,使得结构固有频率偏大,自振周期偏小;对称结构致使结构特征周期和振型呈对称特征.根据模态分析数据和振型图对天坛祈年殿式钢筋混凝土结构动力特征进行了分析和总结,为对该类建筑的进一步动力分析提供了依据.     

制造业综合自动化现状和今后发展

提出制造业综合自动化的含义、主要目标和要解决的关键问题。综述国内外现状和发展趋势，对国内制造企业实际调查情况作了统计分析和预测。     

球磨速度和过程控制剂对Ti-Cr合金机械合金化的影响研究

研究了球磨速度变化(125r／rain-225r／min)和不同过程控制剂(乙醇、硬脂酸和二者的混合物)及其加入量(0％-4．5％)对Ti-Cr合金机械合金化(MA)的影响。研究结果表明，球磨速度的高低对所获得的MA粉末的粒度有显著性影响。在其它条件相同的情况下，球磨速度越高，MA的效率越高，粉末的粒度越小。在Ti-Cr合金的MA过程中，使用乙醇作为过程控制剂，能够有效地降低球磨带人的杂质量，但是粉末的细化速度将减慢；乙醇的加入量不宜超过1．5％。硬脂酸不适合用做Ti-Cr合金MA过程的过程控制剂。通过调整球磨速度和合理选用过程控制剂，可以实现对球磨杂质来源的调控。