基于SSC-BP神经网络的异常检测算法

针对物联网环境下产生的新型网络攻击的数量持续上升和复杂性不断升高,传统的异常检测算法误报率高、检测率低以及数据量大而造成计算困难等问题,提出了一种基于子空间聚类(Subspace Clustering,SSC)和BP神经网络相结合的异常检测算法.首先在网络数据集上通过子空间聚类算法中最常用的CLIQUE算法得到不同的子空间;其次对不同子空间中的数据进行BP神经网络异常检测,计算预测误差值,通过与预先设定好的精度进行比较,来不断更新阈值进行修正,以达到提高识别网络攻击的能力.仿真实验采用NSL-KDD公开数据集和物联网环境下的网络攻击数据集,将NSL-KDD公开数据集分割为4种单一攻击子集和1种混合攻击子集,通过与K-means,DBSCAN,SSC-EA以及k-KNN异常检测模型进行比较,在混合攻击子集中,SSC-BP神经网络模型的检测率比传统的K-means模型的检测率提高了6％,误检率降低了0.2％;而在4种单一攻击子集中,SSC-BP神经网络模型都能以最低的误检率检测出最多的受到攻击的网络.在物联网环境下的网络攻击数据集上,SSC-BP神经网络模型的性能均优于其他几种对比模型.     

Mixed H2/H∞ State Feedback Attitude Control of Microsatellite Based on Extended LMI Method

For the appearance of the additive perturbation of controller gain when the controller parameter has minute adjustment at the initial running stage of system,to avoid the adverse effects,this paper investigates the mixed H_2/H_∞ state feedback attitude control problem of microsatellite based on extended LMI method.Firstly,the microsatellite attitude control system is established and transformed into corresponding state space form.Then,without the equivalence restriction of the two Lyapunov variables of H_2 and H∞performance,this paper introduces additional variables to design the mixed H_2/H_∞ control method based on LMI which can also reduce the conservatives.Finally,numerical simulations are analyzed to show that the proposed method can make the satellite stable within 20 s whether there is additive perturbation of the controller gain or not.The comparative analysis of the simulation results between extended LMI method and traditional LMI method also demonstrates the effectiveness and feasibility of the proposed method in this paper.     

空间遥感器反射镜组件的设计与有限元分析

针对某空间遥感器反射镜的设计指标要求,分析并优化了反射镜的支撑形式和结构参数,得到了质量为23.7kg,轻量化率达到76.2%的反射镜结构。在反射镜基本构型确定的基础上,设计了镜体的支撑结构,通过合理设计柔性卸载结构满足了反射镜结构系统的动静态刚度和热尺寸稳定性要求。采用有限元软件ABAQUS对反射镜组件进行了精确有限元分析,分析结果表明,在1g重力作用下反射镜的面形精度RMS达到3.66nm,在4℃均匀温升载荷作用下反射镜的面形精度RMS达到4.16nm,在1g重力和4℃均匀温升载荷耦合作用下反射镜的面形精度RMS达到5.51nm,反射镜组件的一阶固有频率为137.51Hz。得到的结果显示该反射镜组件完全满足设计指标要求。     

采用多分辨率广义S变换的电能质量扰动识别

为提高电能质量复合扰动识别能力,提出一种采用多分辨率广义S变换(multiresolution generalized S-transform,GST)的扰动识别方法.首先,将信号频谱分为低频、中频、高频3个频域,分别设定窗宽调整因子,使其在各个频域具有不同的时-频分辨率,满足不同扰动信号识别要求.并针对高频振荡识别问题,设计基于基频傅里叶谱特征的自适应窗宽调整方法.在此基础上,提取6种特征用于构建决策树.最后,提出最小分类损失原则,确定决策树节点分类阈值,设计扰动分类器.仿真与实测信号实验证明,新方法能够准确识别含5种复合扰动在内的13种扰动.相较于S变换、广义S变换和Hyperbolic S变换,新方法具有更好的特征表现能力,分类效果好,抗噪声干扰能力强.     

三维裂隙网络管单元模型确定岩体渗透张量

根据现场测量所获得的裂隙产状统计参数,利用Monte-Carlo法模拟生成相应的裂隙网络。采用管单元模型,将三维裂隙渗流网络简化为空间一维渗流网络,以工程实际校正的渗透张量作为目标,采用改进的遗传算法进行拟合,得到等效管单元直径与隙宽比值为12.337 1。据此,可得到给定产状岩体的等效渗透张量。同时,利用裂隙几何参数张量法计算渗透张量,通过比较可见裂隙网络模型更加符合实际。     

An effective thermal conductivity model for unsaturated compacted bentonites with consideration of bimodal shape of pore size distribution

An effective thermal conductivity model was proposed for unsaturated compacted bentonites with consideration of the bimodal shape of pore size distribution curves.The pores of soils were grouped into two dominant pore size modes corresponding to the intra-and inter-particle pores,and were simulated with randomly distributed spheroidal inclusions of different aspect ratios.With the assumption of preferential invasion of the wetting fluid(water)into pores of smaller sizes and by virtue of the analytical solution to the inhomogeneous inclusion problem in heat conduction,the model was developed using the Mori-Tanaka(MT),Ponte Casta?eda-Willis(PCW)and self-consistent(SC)homogenization approaches for different considerations of the interactions between pores and the solid phase.The proposed model is functions of the thermal conductivities of the solid,liquid and gas phases,porosity,the degree of saturation,the aspect ratios of pores and/or soil particles,and the fraction of the smaller group of pores.The proposed model was validated against five sets of laboratory measurement data on the MX-80,FEBEX,Kunigel-V1 and GMZ01 bentonites,showing a good agreement between the model predictions and the laboratory measurements.The responses of the model with respect to the geometries of pores and solid particles were examined.Compared to series-parallel structural models,the proposed model may overall exhibit better performance if proper homogenization schemes are adopted,but as an advantage,the model has clearer physical mechanisms and a smaller number of parameters.     

公路减隔震桥梁的地震反应简化分析

采用单自由度反应谱方法对满足一定条件的减隔震桥梁进行地震反应分析可以简化计算过程,但需要解决精度问题。针对规范反应谱阻尼修正方法对计算精度的影响进行了分析并提出了改进方法。为了验证改进方法的合理性,对一座常规减隔震桥梁分别采用不同计算方法进行了比较分析,结果表明采用改进的阻尼修正公式后,简化反应谱方法的计算精度得到很大提高,且结果偏于安全。     

超声波辅助电镀沉积Ni镀膜工艺研究

采用超声波辅助电镀沉积工艺方法研究工艺参数对电镀沉积金属镍镀膜的表面形貌及力学性能的影响规律.实验结果表明:超声波辅助电镀沉积镍镀层时,超声波能够细化镀层的晶粒,降低镀层的孔隙率,同时显著地改善异性工件电镀层的均匀性.当超声波作用时间20 min时,电镀镍镀层的孔隙率为2个/cm2.随着超声波作用时间的延长,电镀镍镀层的显微硬度呈现出先增加后降低的变化趋势.     

基于思维进化算法的工业过程粗糙建模及应用

在工业过程建模中,传统的建模方法依赖数学模型.当实际系统模型难于用解析式精确表达时,智能建模成为研究热点之一.对具有非线性、时变性、不精确性等复杂系统,智能建模弥补了机理建模、辨识建模等方法的不足,能够避开数学表达式模型.模糊建模的隶属函数不容易得到,而粗糙集能直接从数据库中提取规则,不需要任何先验知识.但粗糙集不能处理连续属性,需要将属性离散化.对水泥回转窑控制系统进行建模,首先应用思维进化算法对决策表中的连续属性进行离散化,然后利用粗糙集理论化简决策表,提取最优的决策规则,最后分析决策规则,得出结论,说明该建模方法的可行性,且由此建模方法得到的决策规则覆盖度较高.     

A novel spherical-ordered macroporous CuO nanocatalyst for the electrochemical reduction of carbon dioxide

Journal of Applied Electrochemistry - The electrocatalytic reduction of CO2 is a promising research direction in resource utilization and sustainable energy development. However, there is still a...