Facile hydrothermal synthesis of CeO2 nanosheets with high reactive exposure surface

CeO₂ nanosheets with (1 1 0) dominated surface were synthesized for the first time by a facile one-step hydrothermal method without the assistance of any surfactant or template. The role of NH₃·H₂O on tailoring the morphology of CeO₂ nanocrystals was investigated. It was found the NH₃·H₂O not only serves as the precipitant, but also acts as structural direction agent in the formation of (1 1 0)-dominated CeO₂ nanosheets. Raman and XRD spectra showed that the sample has a cubic fluorite structure. Compared with bulk CeO₂ materials, the prepared CeO₂ nanosheets exhibit an obvious blue-shift in UV absorbance. The increase of the direct band gap energy of the obtained sample exceeds 8%. This method provides an environmentally friendly way for preparing CeO₂ nanostructures and tailoring their morphology. It may also be extended to the synthesis of other nanomaterials.     

EG-2490型称重式给煤机典型跳闸原因分析与防范

文就临汾热电公司给煤机维护过程中出现的跳闸案例进行典型分析,对不同的跳闸原因提出了针对性的防范措施,旨在总结EG-2490型称重式给煤机运行维护的大量经验,为机组安全运行和经济运行提供保障。     

城市客运模型系统的研究

本文在长春市1984年居民出行调查资料的基础上,用运输系统分析的理论和方法,建立了适合我国城市的客运模型系统——四步骤模型,并对重力模型进行了标定。综合费用函数可用作预测公交和自行车出行量比率。     

串补线路故障点位置的模型识别方法

文中提出了一种判断串补线路单相接地故障时故障点相对于串联补偿电容位置的模型识别方法，该方法通过比较不同模型计算出线路电感值的离散度来识别故障位置。将该方法和传统的距离保护相配合，可以解决传统距离保护在串补线路中超越的问题，使得距离Ⅰ段可以按全线阻抗整定，而不必考虑电容的容抗，很大程度地提高了距离Ⅰ段的灵敏度。判别过程仅利用MOV导通前一段时间的暂态量数据，不受MOV非线性特性的影响，避开了MOV导通后串补电容上电压准确值难以获得的问题。该方法仅利用单端电气量，无需通讯通道；数字仿真结果表明：该方法具有很好的适应性，适合于各种电压等级、各种频率的系统，线路各处故障。     

PSL641型微机线路保护误动原因分析及改进措施

针对PSL641保护装置在发生区外故障时保护误动的现象，找出了保护误动的原因，提出了自己的建议。     

混沌序列在3G安全通信中的应用研究

混沌映像生成的混沌序列具有不规则和对初值敏感等优点，特别适合应用于保密通信。本文在3G安全结构的基础上．提出了一种改进的安全通信方法．它利用混沌序列来定时改变3G通信中的初始密钥，以提高资料的安全性。通过计算机模拟分析得出，在合理选择改变密钥的频率时，该方法具有在不明显增加计算时间的基础上“一次一密”的优点。     

基于遗传算法的检测路段选择的优化

在分析交通检测点分布优化问题的现有算法的基础上，本文构造了交通检测点优化问 题的染色体表达式，建立了此问题的遗传算法．这是第一次将遗传算法应用于交通检测点分 布优化问题．实验结果表明，此算法可以有效求得交通检测点分布问题的优化解或近似优化 解，是求解交通检测点分布问题的一个较好的方法．     

步进电机自动升降速闭环控制的单片机实现

本文提出了一种步进电机闭环控制原理。根据这一原理 ,介绍了由单片机实现对步进电机自动升降速闭环控制的方法。     

An evaluation of dimension reduction techniques for one-class classification

Dimension reduction (DR) is important in the processing of data in domains such as multimedia or bioinformatics because such data can be of very high dimension. Dimension reduction in a supervised learning context is a well posed problem in that there is a clear objective of discovering a reduced representation of the data where the classes are well separated. By contrast DR in an unsupervised context is ill posed in that the overall objective is less clear. Nevertheless successful unsupervised DR techniques such as principal component analysis (PCA) exist—PCA has the pragmatic objective of transforming the data into a reduced number of dimensions that still captures most of the variation in the data. While one-class classification falls somewhere between the supervised and unsupervised learning categories, supervised DR techniques appear not to be applicable at all for one-class classification because of the absence of a second class label in the training data. In this paper we evaluate the use of a number of up-to-date unsupervised DR techniques for one-class classification and we show that techniques based on cluster coherence and locality preservation are effective.     

Visual Basic中常用网格控件的区别与应用

该文对使用VB开发数据库时常用到的各种网格控件进行了分析比较,对读者灵活使用网格控件进行数据库应用系统开发具有参考作用。