Presentation attack detection based on two-stream vision transformers with self-attention fusion

Aiming at the performance degradation of the existing presentation attack detection methods due to the illumination variation, a two-stream vision transformers framework (TSViT) based on transfer learning in two complementary spaces is proposed in this paper. The face images of RGB color space and multi-scale retinex with color restoration (MSRCR) space are fed to TSViT to learn the distinguishing features of presentation attack detection. To effectively fuse features from two sources (RGB color space images and MSRCR images), a feature fusion method based on self-attention is built, which can effectively capture the complementarity of two features. Experiments and analysis on Oulu-NPU, CASIA-MFSD, and Replay-Attack databases show that it outperforms most existing methods in intra-database testing and achieves good generalization performance in cross-database testing.     

Large eddy simulation of flow over square cylinder arrays in an octagonal configuration at subcritical Reynolds numbers

In this study, fluid flow over an array of eight, 0.029 m × 0.029 m, square cross‐section cylinders in an octagonal configuration is studied numerically. The mean force coefficients (drag and lift) and the vortex formation characteristics of the array are calculated numerically by utilizing a three‐dimensional large eddy simulation mathematical model for turbulence. The numerical simulation is performed with commercial software ANSYS Fluent 19R1. To investigate the parametric influences, three spacings between the cylinders (0.07, 0.14, and 0.2 m), two array attack angles (0° and 15°), and two Reynolds numbers (4060 and 45 800) are considered. The results comprise flow patterns and force coefficients' variations with Reynolds numbers. The lift force of the downstream cylinder reaches its maximum at α = 15°, and the drag force of the upstream cylinders finds its peak at α = 0°. It is observed through velocity and viscosity contour plots that vortex formation length near the cylinder increases at higher Reynolds number. Velocity vector plots are also presented to show fluid flow behavior near the cylinder. Furthermore, the predicted mean forces on the cylinders are slightly different for different Reynolds numbers, spacings, and angles of attack.     

矿井电气自动化控制系统优化探究

随着煤矿产业的持续发展,矿井生产的自动化要求也不断提升,将PLC可编程技术应用到矿井电气自动化控制系统中,对于提升矿井综合效益意义重大。以此为着手点,以矿井提升机为对象,在分析PLC技术在提升机电气自动控制系统中应用的基础上,对电气设备单片机选型开展分析,同时总结了矿井提升机电气自动化控制系统的改造要求,希望能够为其他矿井相似工程的开展提供借鉴与参考。     

复卷机伺服张力控制系统设计及优化

本研究通过对复卷机工艺流程进行分析,分别对纸幅张力、速度和纠偏的控制系统进行了设计及优化,采用罗克韦尔PLC作为主控制器,结合伺服驱动器和伺服电机等,实现对纸幅张力的稳定控制。该控制系统在实际生产中取得了良好的控制效果,张力调整时间由之前的10 s缩短到5 s内,并且无超调量。     

埋弧焊数字焊机现场应用及其配套控制改造

随着信息化技术的发展和应用，数字焊接设备和焊接技术取得了长足的进步，介绍了林肯Power Wave埋弧焊数字焊机在直缝埋弧焊管生产线的应用，在此基础上简述了数字焊机组网技术、弧压反馈检测环境搭建、数字焊机与PLC集成控制改造，重点介绍了林肯Power Wave数字焊机的直流并联、交流串联技术应用，为我国数字焊机的现场应用提供一定的参考。     

煤矿井下主排水系统的设计与实现

针对煤矿井下主排水系统人工就地操作的问题，介绍了一种基于PLC的水泵控制方式，该系统选用PLC为控制核心，通过液位、压力、流量、温度等传感器采集水泵运行参数，对水泵及管路阀门、高压开关等设备进行控制与监测，使设备在无人干涉的情况下实现了多台水泵和关联设备的联动运行和参数采集、状态监测、数据处理、故障报警、报表查询等，使设备达到最佳运行状态，满足了煤矿生产环境及安全生产的需要，提高了煤矿自动化水平，降低了劳动力强度，为实现煤矿数字化矿井打下良好的基础。     

一种标准模型下无证书签名方案的安全性分析与改进

无证书签名具有基于身份密码体制和传统公钥密码体制的优点，可解决复杂的公钥证书管理和密钥托管问题.Wu和Jing提出了一种强不可伪造的无证书签名方案，其安全性不依赖于理想的随机预言机.针对该方案的安全性，提出了两类伪造攻击.分析结果表明，该方案无法实现强不可伪造性，并在"malicious-but-passive"的密钥生成中心攻击下也是不安全的.为了提升该方案的安全性，设计了一个改进的无证书签名方案.在标准模型中证明了改进的方案对于适应性选择消息攻击是强不可伪造的，还能抵抗恶意的密钥生成中心攻击.此外，改进的方案具有较低的计算开销和较短的私钥长度，可应用于区块链、车联网、无线体域网等领域.     

GreyFan:一种Wi-Fi隐蔽信道攻击框架

针对现实网络中诸如侧信道攻击、HID 攻击等传统的物理攻击，物理隔离被认为是一种较为彻底的抵御网络攻击的安全防护手段。2018 年，业界首次提出了一种物理隔离环境下的 Wi-Fi 隐蔽信道方法——Ghost Tunnel，即在Wi-Fi尚未连接的状态下，无线AP可成功将数据传给发起连接请求的计算机。提出了一种基于Ghost Tunnel方法的攻击框架—— GreyFan，利用该攻击框架攻击者可以对未连接Wi-Fi的用户实施无感知攻击，如文件隐蔽传输、任意代码执行等，并分析了相应的防御技术。     

基于人体关节点数据的攻击性行为识别

针对人体攻击性行为识别问题，提出一种基于人体关节点数据的攻击性行为识别方法。首先，利用OpenPose获得单帧图像中的人体关节点数据，并通过最近邻帧特征加权法和分段多项式回归完成由人体自遮挡和环境因素所导致缺失值的补全；然后，对每个人体定义动态"安全距离"阈值，如果两人真实距离小于阈值，则构建行为特征矢量，其中包括帧间人体重心位移、人体关节旋转角角速度和发生交互时的最小攻击距离等；最后，提出改进的LightGBM算法w-LightGBM，并对攻击性行为进行识别。采用公共数据集UT-interaction对所提出的攻击性行为分类识别方法进行测试实验，准确率达到95.45%。实验结果表明，所提方法能够有效识别各种角度的攻击性行为。     

Key-dependent side-channel cube attack on CRAFT

CRAFT is a tweakable block cipher introduced in 2019 that aims to provide strong protection against differential fault analysis. In this paper, we show that CRAFT is vulnerable to side-channel cube attacks. We apply side-channel cube attacks to CRAFT with the Hamming weight leakage assumption. We found that the first half of the secret key can be recovered from the Hamming weight leakage after the first round. Next, using the recovered key bits, we continue our attack to recover the second half of the secret key. We show that the set of equations that are solvable varies depending on the value of the key bits. Our result shows that 99.90% of the key space can be fully recovered within a practical time.