Snort入侵检测系统中数据包捕获模块的分析与设计

随着网络的高速发展,网络带宽得到了极大的提升。高速网络环境下对入侵检测系统提出了更高的要求,其中入侵检测系统的数据包捕获能力成为其发展的瓶颈。目前大多数系统使用传统的Libpcap库来实现数据包捕获功能,文章对一个基于Snort入侵检测系统中数据包捕获模块进行了分析设计,给出了设计架构,详细说明了工作流程,并对系统的性能进行了对比分析。     

结合编码交织的频数质心零水印算法

针对传统数字水印算法的透明性随嵌入强度的增加而下降,且存在鲁棒性和稳定性差的问题,提出了一种基于极化码与二维交织算法相结合的频数质心零水印算法.该算法依次对水印信息进行极化码编码,二维交织构造出交织矩阵,然后对载体图像进行非下采样轮廓波变换获得其低频系数,再通过分块非负矩阵分解得到一维基矩阵;根据频数分布特征计算局部频数质心以构造出特征矩阵,最后将含有水印信息的交织方阵和特征矩阵进行异或操作生成零水印.大量实验表明,该零水印算法可以有效地抵抗常规的信号处理攻击、几何攻击以及组合攻击,水印提取的归一化系数值在0.88以上,具有较强的鲁棒性和稳定性,且具有良好的实用价值.     

Analytical and experimental analysis of deep drawing process for bimetal elements

The paper presents the concepts of solving of deep drawing process for bimetal elements of sheet materials. The inertia forces, plastic hardening behaviour of the deformed material and dynamic stress are utilized in the problems of plasticity. The experimental results and general conclusion are presented at the end of the paper.     

基于断电后残余电压的感应电机定子故障诊断

为了提高感应电机定子绕组故障诊断的准确性,提出了一种基于Hilbert-Huang变换(HHT)的故障诊断新方法.选取断电后零序电压的基波分量作为定子故障特征,可有效避免电源不平衡和负荷波动的影响,直接反映电机定子的不对称度.利用Hilbert-Huang变换中经验模态分解(EMD)方法对断电后的零序电压进行了分解,提取出基波分量,通过计算其均方根值可以诊断出电机定子绕组故障.在一台4 kW的感应电机上进行的实验证明了该方法的可行性和有效性.     

高效高功率密度车载双向电能变换器设计

研究设计了一种用于电动汽车电池充放电的车载双向电能变换器。充电状态下,前级采用PWM整流技术,后级采用移相全桥零电压开关电路,实现电气隔离高效的降压变换。放电状态下,双向DC-DC变换器实现升压变换,双向AC-DC作为单相全桥逆变器采用电压前馈、电压电流双闭环控制策略。本系统采用全控型器件GaN控制电流电压通断,能够使得电流电压在正负四象限工作,实现能量的正向和反向的双向传递。依据此方案设计一款开关频率100 kHz、输出功率2 kW的原理样机,经测试该系统能够有效实现能量的双向流动,并且有效提升了效率和功率密度,验证了方案的可行性。     

Elastic-plastic analytical solution for centric crack loaded by two pairs of point shear forces in finite plate

1 Introduction A great number of cracks exist in metal materials. Their existence and interaction often lead to high stress concentration and become the source of weakening and failure of metal materials[1- 4]. The elastic-plastic analysis for a cracked p…     

水下隧道穿越管道保护效果测试评价

本文通过对四川气田北干线涪江隧道穿越管道阴极保护电参数的现场测试，取得了实际可信的基础数据，验证了处于水下隧道洞内的穿越段管道，能得到陆上强制电流阴极保护系统的有效保护，保护电流所必经的岩石层和锚喷钢筋混凝土层对保护电流没有构成屏蔽的结论，对管道工程设计和运行管理具有指导作用。     

An improved cutting force and surface topography prediction model in end milling

During the milling operation, the cutting forces will induce vibration on the cutting tool, the workpiece, and the fixtures, which will affect the surface integrity of the final part and consequently the product's quality. In this paper, a generic and improved model is introduced to simultaneously predict the conventional cutting forces along with 3D surface topography during side milling operation. The model incorporates the effects of tool runout, tool deflection, system dynamics, flank face wear, and the tool tilting on the surface roughness. An improved technique to calculate the instantaneous chip thickness is also presented. The model predictions on cutting forces and surface roughness and topography agreed well with experimental results.     

铬盐清洁生产中铬渣的综合利用

利用二氧化碳与液相氧化铬盐清洁生产工艺所产生的铬渣反应 ,得到碳酸氢镁溶液和富铁渣。碳酸氢镁溶液经加热分解得到轻质碳酸镁产品 ,富铁渣可以作为水泥行业原料铁精矿的替代品 ,最终实现了铬铁矿资源的充分利用和铬盐生产的零排放。     

Electrodiffusion diagnostics of the flow and mass transfer inside a network of crossing minichannels

The global mass transfer and the local flow structure inside a set of crossing minichannels were characterized using the electrodiffusion method. The individual square-cross channel sections (a = 1.5 mm in sides) intersect at right-angles in order to form the flow cell. An array of 39 circular platinum electrodes (0.25 mm in diameter) was flush-mounted into the wall of the flow cell to investigate the wall shear rate at different locations. This array of small sensors allowed characterization of longitudinal and lateral variations in wall shear rate across the flow cell, flow distribution at the inlet and outlet sections, transition between laminar and turbulent flow regimes, and flow behaviour at the channel crossings. The results of global wall mass transfer measurements demonstrated that, from a mass transfer point of view, the flow cell exhibits similar behaviour to a porous medium.