基于熵可拓物元模型的城市竞争力评价研究——以我国西部省会城市为例

"一带一路"战略背景下,西部地区省会城市竞争力的提升对于我国国家综合竞争力的提升意义重大.以西部省会11个城市竞争力的评价指标体系为基础,构建熵权可拓物元模型比较评价了2016年各个省会城市的竞争力.结论如下:①从总体上来看,11个省会城市竞争力水平在空间上具有较大的分异.②从综合指标关联度分析来看重庆城市竞争力较强,其次是西安、成都,竞争力较弱的为银川、呼和浩特和贵阳.③由于重庆、西安等市在对外开放竞争力中水平较高,而兰州、银川、呼和浩特等在此指标中水平较低而导致其城市竞争力水平较低.通过构建物元可拓模型,得出西部省会城市竞争力等级及排名,同时也可为西部省会城市发展提供对策建议.     

双能谷效应对N型掺杂Si基Ge材料载流子晶格散射的影响

性能优越的Si基高效发光材料与器件的制备一直是Si基光电集成电路中最具挑战性的课题之一.Si基Ge材料不仅与成熟的硅工艺相兼容,而且具有准直接带特性,被认为是实现Si基激光器最有希望的材料.对Si基Ge材料N型掺杂的研究有利于提示出其直接带发光增强机理.本文研究了N型掺杂Si基Ge材料导带电子的晶格散射过程.N型掺杂Si基Ge材料具有独特的双能谷(Γ能谷与L能谷)结构,它将通过以下两方面的竞争关系提高直接带导带底电子的占有率:一方面,处于Γ能谷的导带电子通过谷间光学声子的散射方式散射到L能谷;另一方面,处于L能谷的导带电子通过谷内光学声子散射以及二次谷间光学声子散射或者直接通过谷间光学声子散射的方式跃迁到Γ能谷.当掺杂浓度界于10~(17)cm~(-3)到10~(19)cm~(-3)时,适当提高N型掺杂浓度有利于提高直接带Γ能谷导带底电子占有率,进而提高Si基Ge材料直接带发光效率.     

Surface plasmon polariton waveguides with subwavelength confinement

Surface plasmon polaritons(SPPs) are evanescent waves propagating along metal-dielectric interfaces, which provide an effective way to realize optical wave guiding with subwavelength confinement. Metallic nanostructures supporting SPPs,that is, plasmonic waveguides, are considered as required components to construct nanophotonic devices and circuits with a high degree of miniaturization and integration. In this paper, various types of plasmonic waveguides operating in the visible, infrared, and terahertz regions are reviewed, and the status of the research on their fundamentals, fabrications,and applications is provided as well. First, we discuss the mechanisms of SPPs beyond the diffraction limit, and their launching methods. Then, the characteristics of SPPs on various plasmonic waveguides are reviewed, including top-down and bottom-up fabricated types. Considering applications, certain prototypes of plasmonic devices and circuits constructed by plasmonic waveguides for bio/chemo sensing, router, and light modulation are demonstrated. Finally, a summary and future outlook of plasmonic waveguides are given.