Control of the morphology of micro/nanostructures of polycarbonate via electrospinning

Many of the applications proposed for bioassays, scaffolds for tissue engineering, filtrations, and supports for catalysts require polymeric membranes with large specific surface areas. Polycarbonate （PC） is a possible candidate for these applications because of its excellent mechanical performance and good biocompatibility. Electrospinning is a simple and effective method for large-scale fabrication of micro-/nanofibrous membranes with large specific surface areas. How to control the morphology of electrospun PC fibers, however, has not been systematically investigated. We describe the controllable fabrication of continuous and uniform PC fibers. We electrospin PC/chloroform solutions doped with different types of surfactants including anionic, zwitterionic, nonionic and cationic surfactants. Only cationic surfactants can lead to the successful fabrication of uniform PC fibers. After the analysis of the correlation between solution properties such as viscosity, surface tension, and conductivity and the morphology of electrospun fibers, we conclude that the addition of cationic surfactants such as cetane trimethyl ammonium bromide （CTAB） that leads to a decrease in viscosity is the main factor responsible for the formation of PC fibers. The demonstration of the fabrication of uniform PC fibers will lend experience to processing other polymers into fibers via electrospinning.     

基于改进的MapReduce模型的Web挖掘

基于单一服务器的Web挖掘系统在处理海量数据集时计算能力不足,针对该问题,提出了一种基于云计算的挖掘方法。将大数据集和挖掘任务分解到多台计算机上并行处理。实现了一个基于Hadoop开源框架的并行Web挖掘平台,同时提出了一种改进的MapReduce模型——MapReduce-LP。并通过对电子商务系统中Web日志的挖掘工作验证了系统的有效性和新模型的高效性。实验表明,在集群中使用云计算技术处理大数据集,可以明显提高挖掘效率。