Having a universal, fair, democratic and practical higher education system plays a particularly important role in the future development of the country. However, the higher education system in various countries is une...Having a universal, fair, democratic and practical higher education system plays a particularly important role in the future development of the country. However, the higher education system in various countries is uneven. It is of great significance to establish a general evaluation system for the development of global education. In this paper, 23 indicators are preliminarily selected from the education data of Universitas 21 and Global Statistical Yearbook. After the gray correlation analysis, 12 indicators were selected. On the one hand, principal component analysis is used to reduce the dimension of these 12 indicators in 50 countries, and the first four principal components with cumulative contribution rate of 99% are finally selected as the input parameters of BP neural network. On the other hand, 12 indicators are divided into four aspects as the standard of scheme decision-making. Finally, a higher education quality evaluation and decision-making model based on BP neural network and analytic hierarchy process are established. Then eight countries are selected to use the model to evaluate their current higher education quality. Based on the input and evaluation results of the four aspects of higher education in various countries, the analytic hierarchy process is used to make program decision, and several improvement suggestions are put forward for the current education policies of various countries.展开更多
特高压直流输电工程中,及时发现并排除换流阀冷却系统的主循环泵的故障,对保障换流阀的稳定运行具有重要意义,为此针对主循环泵在故障时产生的振动信号,提出一种基于二维图像和卷积神经网络的阀冷系统主循环泵故障诊断方法。首先,通过...特高压直流输电工程中,及时发现并排除换流阀冷却系统的主循环泵的故障,对保障换流阀的稳定运行具有重要意义,为此针对主循环泵在故障时产生的振动信号,提出一种基于二维图像和卷积神经网络的阀冷系统主循环泵故障诊断方法。首先,通过变分模态分解(variational mode decomposition,VMD)联合奇异值分解(singular value decomposition,SVD)对振动信号进行去噪处理:使用VMD分解轴向、竖直径向和水平径向的振动信号,基于相关系数法获取最优本征模态分量;使用SVD对分量信号滤波后,通过分量空间重构获取去噪后的振动信号。然后,通过格拉姆矩阵将时序振动信号转换为振动图像,提取振动信号的时空特征。最后,将轴向、竖直径向和水平径向振动图像多通道并行输入AlexNet深度卷积神经网络,通过卷积层和池化层实现多层次特征融合,提高故障诊断准确率。分析结果表明,该模型故障诊断精度为91%,优于多层感知机算法、一维卷积神经网络和浅层卷积神经网络,可以为阀冷系统主循环泵的故障诊断提供方法基础,为现场人员安排计划检修提供理论依据。展开更多
文摘Having a universal, fair, democratic and practical higher education system plays a particularly important role in the future development of the country. However, the higher education system in various countries is uneven. It is of great significance to establish a general evaluation system for the development of global education. In this paper, 23 indicators are preliminarily selected from the education data of Universitas 21 and Global Statistical Yearbook. After the gray correlation analysis, 12 indicators were selected. On the one hand, principal component analysis is used to reduce the dimension of these 12 indicators in 50 countries, and the first four principal components with cumulative contribution rate of 99% are finally selected as the input parameters of BP neural network. On the other hand, 12 indicators are divided into four aspects as the standard of scheme decision-making. Finally, a higher education quality evaluation and decision-making model based on BP neural network and analytic hierarchy process are established. Then eight countries are selected to use the model to evaluate their current higher education quality. Based on the input and evaluation results of the four aspects of higher education in various countries, the analytic hierarchy process is used to make program decision, and several improvement suggestions are put forward for the current education policies of various countries.
文摘特高压直流输电工程中,及时发现并排除换流阀冷却系统的主循环泵的故障,对保障换流阀的稳定运行具有重要意义,为此针对主循环泵在故障时产生的振动信号,提出一种基于二维图像和卷积神经网络的阀冷系统主循环泵故障诊断方法。首先,通过变分模态分解(variational mode decomposition,VMD)联合奇异值分解(singular value decomposition,SVD)对振动信号进行去噪处理:使用VMD分解轴向、竖直径向和水平径向的振动信号,基于相关系数法获取最优本征模态分量;使用SVD对分量信号滤波后,通过分量空间重构获取去噪后的振动信号。然后,通过格拉姆矩阵将时序振动信号转换为振动图像,提取振动信号的时空特征。最后,将轴向、竖直径向和水平径向振动图像多通道并行输入AlexNet深度卷积神经网络,通过卷积层和池化层实现多层次特征融合,提高故障诊断准确率。分析结果表明,该模型故障诊断精度为91%,优于多层感知机算法、一维卷积神经网络和浅层卷积神经网络,可以为阀冷系统主循环泵的故障诊断提供方法基础,为现场人员安排计划检修提供理论依据。
