How to Make Virtual Community More Active and Cohesive:From Brand and Perceived Protection Perspectives

With the increasing popularity of the Internet and mobile Internet, the Virtual Community （VC） is becoming an important medium for person-to-person communication. To realise the potential of the VC, it is neces- sary to cultivate within it good group cohesion and vitality. Using empirical and experimental research methods, this study explores the ef- fect of users＇ trust in the VC Platform （VCP） on group cohesion and vitality and how brand and perceived privacy security can affect us- ers＇ trust in the VC. The research results indi- cate that the brand of the VCP can directly af- fect users＇ trust in the VC, and can also influe- nce it indirectly through users＇ perceived pri- vacy protection and perceived security protec- tion. Further, this study also confu＇ms that the performance of the VC （group cohesion and vitality） is significantly affected by users＇ trust in the VC. The results of this study can provide theoretical guidance for internet companies to maintain and enhance the value of VCs.

地基激光雷达的玉兰林冠层叶面积密度反演

叶面积密度LAD(Leaf Area Density)是表征冠层内部叶面积垂直分布的重要参数,其分布廓线的准确反演对研究植被碳氮循环、初级生产力和生物量估算等具有重要意义。本文在电子科技大学校内建立实验样区,利用地基激光雷达Leica Scan Station C10和数码相机获取玉兰林高分辨率3维激光点云数据和真彩色影像。利用监督分类将真彩色影像中枝干等非光合组织与叶片分离,再将像素分类信息映射给点云数据,从而提取叶片点云。通过点云数据体元化,并引入2维凸包算法确定垂直方向分层树冠边界,获取激光接触冠层的频率;随机选择不同高度的多个叶片,利用特征值法进行叶片平面拟合,估算出叶倾角,并结合天顶角估算叶倾角校正因子;最后基于体元的冠层分析VCP(Voxel-based Canopy Profiling)方法实现树林冠层LAD反演。结果表明体元化的叶片点云数据能准确确定树林冠层边界和统计接触频率实现LAD反演;反演的LAD变化走势与区域林木冠层叶片垂直分布相吻合,在冠层中下部随着高度的增加叶面积密度也随之增加,在4 m高度处达到最大值1 m2/m3,之后随着高度的增加叶面积密度逐渐降低。根据LAD计算得到的累积叶面积指数LAI为3.20 m2/m2,与LAI-2200实测的叶面积指数相比,相对误差为1.26%。