The electrical properties and d.c. degradation characteristics of silver doped ZnO varistors

ZnO-Bi₂O₃-based ceramic varistors containing up to 2500 p.p.m. Ag₂O were prepared by the mixed oxide route. The products were characterized in terms of current-voltage (I–V) behaviour, capacitance-voltage (C-V) behaviour and d.c. degradation behaviour. Additions of silver did not significantly affect ZnO grain growth or sintered density, but decreased the non-linearity exponent, a, and increased the breakdown voltage. Silver-doped specimens exhibited an unusual d.c. degradation behaviour, with the leakage current initially decreasing before reaching a stable value. For doping levels 500 p.p.m. Ag₂O, the change in breakdown voltage was positive for both forward and reverse directions. Silver doping appeared to increase the Schottky barrier height under conditions of continuous d.c. stress and improve the degradation behaviour. The optimum levels of Ag₂O addition were in the range 500–1000 p.p.m.     

Web-collaborative filtering: recommending music by crawling the Web

We show that it is possible to collect data that are useful for collaborative filtering (CF) using an autonomous Web spider. In CF, entities are recommended to a new user based on the stated preferences of other, similar users. We describe a CF spider that collects from the Web lists of semantically related entities. These lists can then be used by existing CF algorithms by encoding them as ‘pseudo-users'. Importantly, the spider can collect useful data without pre-programmed knowledge about the format of particular pages or particular sites. Instead, the CF spider uses commercial Web-search engines to find pages likely to contain lists in the domain of interest, and then applies previously proposed heuristics to extract lists from these pages. We show that data collected by this spider are nearly as effective for CF as data collected from real users, and more effective than data collected by two plausible hand-programmed spiders. In some cases, autonomously spidered data can also be combined with actual user data to improve performance.     

混合碳四的来料加工

分析了混合碳四中3种关键组分超标对丁二烯生产的不利影响，提出了外加工混合碳四过程中具体的应对措施和解决方案。     

中国电信移动网络HACCG的建设方案

文章对MIP及内容计费进行了详细的总结,并提出了中国电信移动网络HA/CCG的建设方案和策略,以及HA/CCG与周边系统的接口要求,能较好地指导电信运营商的准备工作和HA/CCG的网络建设.     

ERPN32-200离心泵机械密封失效原因分析

通过对ERPN32-200离心泵机械密封失效原因的分析,发现机械密封的实际密封效果不仅与机械密封自身的性能有关,而且与相关零部件的加工尺寸的精度等级以及维修时的装配质量有着重要的关系,同时针对不同的问题提出了相应的措施,延长了机械密封的使用寿命。     

数字电影3D技术浅析

本文介绍目前数字电影3D技术的最新进展，分析了数字3D放映技术的分类、特点及其适用范围，举例阐明主动立体放映技术，并讨论了数字3D技术的应用前景。