Detection Technique of Software-Induced Rowhammer Attacks

Side-channel attacks have recently progressed into software-induced attacks. In particular, a rowhammer attack, which exploits the characteristics of dynamic random access memory (DRAM), can quickly and continuously access the cells as the cell density of DRAM increases, thereby generating a disturbance error affecting the neighboring cells, resulting in bit flips. Although a rowhammer attack is a highly sophisticated attack in which disturbance errors are deliberately generated into data bits, it has been reported that it can be exploited on various platforms such as mobile devices, web browsers, and virtual machines. Furthermore, there have been studies on bypassing the defense measures of DRAM manufacturers and the like to respond to rowhammer attacks. A rowhammer attack can control user access and compromise the integrity of sensitive data with attacks such as a privilege escalation and an alteration of the encryption keys. In an attempt to mitigate a rowhammer attack, various hardware- and software-based mitigation techniques are being studied, but there are limitations in that the research methods do not detect the rowhammer attack in advance, causing overhead or degradation of the system performance. Therefore, in this study, a rowhammer attack detection technique is proposed by extracting common features of rowhammer attack files through a static analysis of rowhammer attack codes.     

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.     

硫酸盐-干湿循环下高延性纤维增强水泥基材料的自愈合

采用1.0%,1.5%和2.0%预加拉伸应变,使养护7,28d龄期的高延性纤维增强水泥基复合材料(ECC)试件产生裂缝,研究其在经历10,20和30次硫酸盐-干湿循环后的裂缝特性、自愈合后的拉伸性能及自愈合产物.结果表明:带裂缝试件在经历不同循环次数后均表现出了良好的自愈合效果,残余裂缝的最大宽度和数量明显减少;养护7d试件经历10次循环后的残余裂缝最大宽度由愈合前的80μm降至25μm,养护28d试件经历30次循环后的残余裂缝最大宽度由愈合前的100μm降至50μm;67%以上带裂缝试件自愈合后的单轴拉伸应变能力接近甚至超过同样经历的对比用无裂缝空白试件;养护7d试件自愈合后的最终应力可分别恢复至75%以上,养护28d试件可恢复至131%以上;层状结构的CaCO_3晶体是ECC试件的主要自愈合产物.     

混凝土硫酸盐侵蚀速度影响因素研究

研究了水灰比、胶砂比、试件尺寸、预养方式、溶液浓度及温度对混凝土硫酸盐侵蚀速度的影响.结果表明:试件的水灰比越大、胶砂比越小、试件尺寸越小(比表面积越大),则硫酸盐侵蚀速度越快;提高养护温度、缩短养护时间可以加快硫酸盐侵蚀速度;硫酸盐侵蚀速度随着硫酸盐溶液浓度增大和温度提高而加快,但当浓度和温度超过某一数值后,硫酸盐侵蚀速度反而减慢.在各种条件下,混凝土硫酸钠侵蚀速度比混凝土硫酸镁侵蚀快;对硫酸钠型侵蚀,采用抗折抗蚀系数作为判定指标较为合理,而对硫酸镁型侵蚀,应该综合考虑抗折、抗压抗蚀系数.     

硫酸盐侵蚀下石膏形成引起的水泥净浆破坏

通过掺加石灰石粉,对长期浸泡在5%(质量分数)Na2SO4溶液中的水泥净浆试件所产生的有害化合物进行了研究.结果表明:在Na2SO4溶液侵蚀下,水泥净浆试件因产生石膏膨胀开裂、表面软化而形成从表到里的破坏,石膏膨胀是其主要劣化方式;水泥净浆破坏机理是石膏膨胀和胶凝物质分解;保持浸泡溶液的pH值,会抑制水泥净浆试件中钙矾石的生成.因此,在水泥混凝土中加入石灰石粉可以检验其抗硫酸盐侵蚀性能.     

低温耐盐蚀混凝土复合外加剂试验研究

从不同养护条件下水泥类胶凝材料需要满足的性能要求出发，在试验中采用不同的胶凝材料，通过试验分析，表明高效复合外加剂能有效提高混凝土耐腐蚀性能。     

外加剂与矿物掺合料对混凝土抗硫酸盐侵蚀的有效性研究

本文通过2年多的砂浆棒浸泡试验，系统研究了高效减水剂、膨胀剂、硅灰、粉煤灰等常用外加剂与矿物掺合料对混凝土抗硫酸盐、硫酸侵蚀作用的有效性。结果表明，高效减水剂提高密实度只能延缓混凝土的侵蚀破坏；膨胀剂、硅灰、粉煤灰能显著提高温凝土的抗蚀性，但抗蚀系数的经时变化规律不同。     

高强和高性能混凝土在青海盐湖卤水中的抗腐蚀性

针对青海盐湖地区特定的自然环境，配制了普通、高强和高性能混凝土，同时进行了不同混凝土的卤水腐蚀单因素试验和卤水腐蚀－－干湿循环双因素试验。结果表明，普通混凝土的耐久性很差，高强混凝土的抗腐蚀性不尽人意，高性能混凝土具有优良的抗腐蚀性能，钢纤维和高强高弹模聚乙烯纤维增强高性能混凝土在双因素作用下抗腐蚀性更好。     

混凝土外部硫酸盐侵蚀破坏的研究

硫酸盐侵蚀是影响混凝土耐久性的重要因素之一。对于混凝土硫酸盐侵蚀问题的研究具有重要的意义。主要研究了外界环境中硫酸盐对混凝土的侵蚀破坏,从物理硫酸盐侵蚀和化学硫酸盐侵蚀两方面论述了混凝土外部硫酸盐侵蚀的类型及破坏特征,并对外部硫酸盐侵蚀过程中石膏的形成作为膨胀源进行了讨论。     

水泥基材料的碳硫硅钙石型硫酸盐侵蚀(TSA)

主要介绍了近年来国外关于TSA的研究情况和一些报道的工程实例,分析了TSA发生与发展的影响因素.