This study investigated the characteristics and formation of the online social trust network of Epinions.com, a general consumer review site. An analysis of the static structure of this social trust network revealed a...This study investigated the characteristics and formation of the online social trust network of Epinions.com, a general consumer review site. An analysis of the static structure of this social trust network revealed a high clustering coefficient, short average path length, and power-law degree distribution;it is therefore a small-world and scale-free trust network. The dynamic evolutionary characteristics of the online social network (OSN) were also examined. The results showed that the scale of the network followed a sigmoidal curve;the average degree of the network was nonconstant and changed into a bell-shaped distribution;the density of the network decreased and subsequently stabilized;and user trust diffusion in the network conformed to the Bass model. Finally, the formation of trust within the network was researched at the overall network (macro) and individual user (micro) levels. Compared with their accumulated contribution and reputation, user activeness had a larger effect on trust formation in OSNs, indicating a “diminishing returns” phenomenon. This phenomenon contrasts with the Matthew effect (i.e. , the more reputation a person has, the more likely he or she is to be trusted) in real-world social networks.展开更多
为研究当无线基站通信塔上避雷针遭受雷击时位于闪电通道附近天线的耦合效应,基于CST Studio Suite电磁仿真软件建立闪电通道-通信塔和工作在中国移动通信GSM1800/1900频段下的微带阵列天线的仿真模型。基于闪电回击电磁模型的继后回击...为研究当无线基站通信塔上避雷针遭受雷击时位于闪电通道附近天线的耦合效应,基于CST Studio Suite电磁仿真软件建立闪电通道-通信塔和工作在中国移动通信GSM1800/1900频段下的微带阵列天线的仿真模型。基于闪电回击电磁模型的继后回击过程,研究从天线极化方向讨论天线的雷击耦合特性以及天线单元连接由不同功分器构成的馈电网络进行组阵时阵列天线的雷击耦合特性。发现天线的耦合电压峰值与极化旋转角呈现线性关系,天线在垂直极化下的耦合电压比在水平极化下的耦合电压大得多;同时,对于通信塔上GSM频段的微带阵列天线,阵列天线的耦合电压受到馈电网络的影响,采用由威尔金森功分器构成的馈电网络进行组阵比采用由T型功分器构成的馈电网络进行组阵阵列天线的耦合电压更小。展开更多
文摘This study investigated the characteristics and formation of the online social trust network of Epinions.com, a general consumer review site. An analysis of the static structure of this social trust network revealed a high clustering coefficient, short average path length, and power-law degree distribution;it is therefore a small-world and scale-free trust network. The dynamic evolutionary characteristics of the online social network (OSN) were also examined. The results showed that the scale of the network followed a sigmoidal curve;the average degree of the network was nonconstant and changed into a bell-shaped distribution;the density of the network decreased and subsequently stabilized;and user trust diffusion in the network conformed to the Bass model. Finally, the formation of trust within the network was researched at the overall network (macro) and individual user (micro) levels. Compared with their accumulated contribution and reputation, user activeness had a larger effect on trust formation in OSNs, indicating a “diminishing returns” phenomenon. This phenomenon contrasts with the Matthew effect (i.e. , the more reputation a person has, the more likely he or she is to be trusted) in real-world social networks.
文摘为研究当无线基站通信塔上避雷针遭受雷击时位于闪电通道附近天线的耦合效应,基于CST Studio Suite电磁仿真软件建立闪电通道-通信塔和工作在中国移动通信GSM1800/1900频段下的微带阵列天线的仿真模型。基于闪电回击电磁模型的继后回击过程,研究从天线极化方向讨论天线的雷击耦合特性以及天线单元连接由不同功分器构成的馈电网络进行组阵时阵列天线的雷击耦合特性。发现天线的耦合电压峰值与极化旋转角呈现线性关系,天线在垂直极化下的耦合电压比在水平极化下的耦合电压大得多;同时,对于通信塔上GSM频段的微带阵列天线,阵列天线的耦合电压受到馈电网络的影响,采用由威尔金森功分器构成的馈电网络进行组阵比采用由T型功分器构成的馈电网络进行组阵阵列天线的耦合电压更小。
文摘针对热力站二次回水温度预测模型特征多计算量大、模型准确性难以提升的问题,提出一种极限梯度提升-人工神经网络(xtreme gradient boosting-artifical neural network,XGBoost-ANN)二次回水温度预测模型,模型由特征筛选层和预测层组成。特征筛选层利用XGBoost算法计算原始数据特征的重要性分数,确定影响二次回水温度的主要特征,从而降低模型复杂度,并提高计算效率;采用贝叶斯正则化算法训练三层前馈ANN作为二次回水温度预测层,并通过灰狼优化(grey wolf optimizer,GWO)算法对ANN模型的初始权值和阈值进行优化,用灰狼的位置向量表示ANN模型的权值和阈值,引入适应度函数来评估每组权值和阈值的性能,帮助模型在训练初期避免陷入局部最优,以提升模型的性能与泛化能力。实验结果表明,所构建的XGBoost-GWO-ANN二次回水温度预测模型,相比特征筛选前的模型,均方根误差(root mean squared error,RMSE)性能提升26.8%,R^(2)提升11.3%,模型推理时间降低了46.1%;使用GWO算法对ANN初始权值和阈值进行寻优,相比于未经优化的ANN模型,RMSE性能提升20.0%,R^(2)提升3.4%,预测模型的精度以及泛化能力得到有效提升。
