Bi1-xTbxFeO3 （x = 0, 0.01, 0.03 and 0.05） nanoparticles are synthesized by the sol-gel method. A single phase perovskite rhombohedral structure of all the samples is established from the Rietveld refined XRD pattern...Bi1-xTbxFeO3 （x = 0, 0.01, 0.03 and 0.05） nanoparticles are synthesized by the sol-gel method. A single phase perovskite rhombohedral structure of all the samples is established from the Rietveld refined XRD patterns. The substitution of Tb^3＋ ions to Bi^3＋ decreases the particle size and enhances the ferromagnetic properties of this system. Interestingly a large maximum magnetization value of 1.73emu/g at 50kOe can be observed in 1% Tb-doped sample at 300 K. The decrease in band gap may result from the reduced particle size, while the leakage current density also decreases, which is mainly explained by the variation of oxygen vacancies.展开更多
现有的电离层总电子含量(Total Electron Content,TEC)时空预测模型主要以堆叠ConvLSTM单元及其变体为主.这种依赖于ConvLSTM的TEC时空预测模型在捕捉局部时空依赖性的时候比较有效.但由于缺乏存储长距离空间记忆的单元,致使长距离的TE...现有的电离层总电子含量(Total Electron Content,TEC)时空预测模型主要以堆叠ConvLSTM单元及其变体为主.这种依赖于ConvLSTM的TEC时空预测模型在捕捉局部时空依赖性的时候比较有效.但由于缺乏存储长距离空间记忆的单元,致使长距离的TEC空间特征依赖难以被ConvLSTM及其变体捕捉.为解决该问题,本文提出了一个基于自注意力记忆卷积长短期记忆网络的电离层TEC时空预测模型SA-ConvLSTM,该模型在具有短期记忆依赖的ConvLSTM基础上,增加了具有长距离记忆依赖的自注意力记忆(self-attention memory,SAM)模块,以便在TEC时空预测中同时兼顾短期记忆和长距离记忆.为了验证SA-ConvLSTM的性能,本文在12.5°S—87.5°N,25°E—180°E区域内选择3年太阳活动高年和3年太阳活动低年的TEC网格数据,在该数据上,将SA-ConvLSTM与目前主流的TEC时空预测模型ConvGRU、ConvLSTM、PredRNN、Residual Attention-BiConvLSTM及CODE提供的电离层预测产品C1PG进行了对比.结果表明,与C1PG、ConvGRU、ConvLSTM、PredRNN和Residual Attention-BiConvLSTM相比,SA-ConvLSTM的RMSE在太阳活动高年分别降低了6.58%、3.89%、5.79%、1.44%、1.21%;在太阳活动低年分别降低了13.42%、10.26%、11.40%、3.20%、4.37%.此外,本文还在不同月份和纬度区域情况下进行了对比,结果表明,在绝大多数月份和绝大多数纬度区域内,SA-ConvLSTM的预测性能更好.最后本文选取了两次磁暴事件来验证SA-ConvLSTM在极端情况下的预测能力.结果表明,SA-ConvLSTM在磁暴的大多数阶段均优于对比模型.展开更多
基金Supported by the National Natural Science Foundation of China under Grant Nos 11004148,51074112,and 11104202the Natural Science Foundation of Guangxi Province under Grant No 2012GXNSFGA060002
文摘Bi1-xTbxFeO3 （x = 0, 0.01, 0.03 and 0.05） nanoparticles are synthesized by the sol-gel method. A single phase perovskite rhombohedral structure of all the samples is established from the Rietveld refined XRD patterns. The substitution of Tb^3＋ ions to Bi^3＋ decreases the particle size and enhances the ferromagnetic properties of this system. Interestingly a large maximum magnetization value of 1.73emu/g at 50kOe can be observed in 1% Tb-doped sample at 300 K. The decrease in band gap may result from the reduced particle size, while the leakage current density also decreases, which is mainly explained by the variation of oxygen vacancies.
