The number of passenger cars equipped with a smart key system continues to increase due to the convenience of the system. A smart key system allows the driver to enter and start a car without using a mechanical key th...The number of passenger cars equipped with a smart key system continues to increase due to the convenience of the system. A smart key system allows the driver to enter and start a car without using a mechanical key through a wireless authentication process between the car and the key fob. Even though a smart key system has its own security scheme, it is vulnerable to the so-called relay attacks. In a relay attack, attackers with signal relaying devices enter and start a car by relaying signals from the car to the owner’s fob. In this study, a method to detect a relay attack is proposed. The signal strength is used to determine whether the signal received is from the fob or the attacker’s relaying devices. Our results show that relay attacks can be avoided by using the proposed method.展开更多
为探究聚乙烯醇(PVA)纤维对粉煤灰-矿渣基地聚物抗硫酸盐侵蚀性能的影响,对掺入不同纤维长度及体积掺量的PVA纤维增强地聚物进行硫酸盐干湿循环侵蚀试验,分析了硫酸盐侵蚀前后试件的质量及抗压强度变化规律;利用灰色系统理论,建立硫酸...为探究聚乙烯醇(PVA)纤维对粉煤灰-矿渣基地聚物抗硫酸盐侵蚀性能的影响,对掺入不同纤维长度及体积掺量的PVA纤维增强地聚物进行硫酸盐干湿循环侵蚀试验,分析了硫酸盐侵蚀前后试件的质量及抗压强度变化规律;利用灰色系统理论,建立硫酸盐干湿循环作用下PVA纤维增强地聚物抗压强度GM(1,1)预测模型。研究结果表明:掺入适量PVA纤维能有效提升试件抗硫酸盐侵蚀性能,但掺入过量则会起反作用,在本研究9个配比方案中,加入体积掺量为0.10%的18 mm PVA纤维时效果最佳;采用建立的GM(1,1)模型对试件抗压强度进行预测,在纤维体积掺量不超过0.20%时具有较高精度。展开更多
Effects of factors such as water to cement ratio, fly ash and silica fume on the resistance of concrete to sulfate attack were investigated by dry-wet cycles and immersion method. The index of the resistance to sulfat...Effects of factors such as water to cement ratio, fly ash and silica fume on the resistance of concrete to sulfate attack were investigated by dry-wet cycles and immersion method. The index of the resistance to sulfate attack was used to evaluate the deterioration degree of concrete damaged by sulfate. The relationship between the resistance of concrete to sulfate attack and its permeability/porosity were analyzed as well as its responding mechanism. Results show that the depth of sulfate crystal attack from surface to inner of concrete can be reduced by decreasing w/c and addition of combining fly ash with silica fume. The variation of relative elastic modulus ratio and relative flexural strength ratio of various specimens before and after being subjected to sulfate attack was compared.展开更多
By micro- and macro-observations, the deterioration mechanisms of concrete under alternate action between repeated sub-high temperature/cooling by water and sodium sulfate solution attack （TW-SA） were studied; meanw...By micro- and macro-observations, the deterioration mechanisms of concrete under alternate action between repeated sub-high temperature/cooling by water and sodium sulfate solution attack （TW-SA） were studied; meanwhile, the single sodium sulfate solution attack （SA） was also done as comparison. Micro-observations included the analysis of attack products by thermal analysis method and the determination of sulfate-ion content from surface to interior by chemical titrating method （modified barium sulfate gravimetric method）. Macro-observations mainly included the mechanical behaviors such as compressive strength, splitting strength. The experimental results indicate, in both cases, the main attack product is ettringite, only in the first layer of case SA some gypsum is checked; in case SA, the sulfate ions mainly concentrate in the surface layer, so the attack is relatively mild; but in case TW-SA, the repeated sub-high temperature/cooling by water promotes the sulfate ions diffusing inwards, which leads to obvious strength degradation.展开更多
文摘The number of passenger cars equipped with a smart key system continues to increase due to the convenience of the system. A smart key system allows the driver to enter and start a car without using a mechanical key through a wireless authentication process between the car and the key fob. Even though a smart key system has its own security scheme, it is vulnerable to the so-called relay attacks. In a relay attack, attackers with signal relaying devices enter and start a car by relaying signals from the car to the owner’s fob. In this study, a method to detect a relay attack is proposed. The signal strength is used to determine whether the signal received is from the fob or the attacker’s relaying devices. Our results show that relay attacks can be avoided by using the proposed method.
文摘为探究聚乙烯醇(PVA)纤维对粉煤灰-矿渣基地聚物抗硫酸盐侵蚀性能的影响,对掺入不同纤维长度及体积掺量的PVA纤维增强地聚物进行硫酸盐干湿循环侵蚀试验,分析了硫酸盐侵蚀前后试件的质量及抗压强度变化规律;利用灰色系统理论,建立硫酸盐干湿循环作用下PVA纤维增强地聚物抗压强度GM(1,1)预测模型。研究结果表明:掺入适量PVA纤维能有效提升试件抗硫酸盐侵蚀性能,但掺入过量则会起反作用,在本研究9个配比方案中,加入体积掺量为0.10%的18 mm PVA纤维时效果最佳;采用建立的GM(1,1)模型对试件抗压强度进行预测,在纤维体积掺量不超过0.20%时具有较高精度。
基金the Postgraduate Science Foundation of China (No.20060400883)the National "863 Program" of China (No.2002AA335020)
文摘Effects of factors such as water to cement ratio, fly ash and silica fume on the resistance of concrete to sulfate attack were investigated by dry-wet cycles and immersion method. The index of the resistance to sulfate attack was used to evaluate the deterioration degree of concrete damaged by sulfate. The relationship between the resistance of concrete to sulfate attack and its permeability/porosity were analyzed as well as its responding mechanism. Results show that the depth of sulfate crystal attack from surface to inner of concrete can be reduced by decreasing w/c and addition of combining fly ash with silica fume. The variation of relative elastic modulus ratio and relative flexural strength ratio of various specimens before and after being subjected to sulfate attack was compared.
基金Funded by the National Natural Science Foundation of China(No. 90715041)Outstanding Youth Science Fund of Henan Province(No.04120002300)
文摘By micro- and macro-observations, the deterioration mechanisms of concrete under alternate action between repeated sub-high temperature/cooling by water and sodium sulfate solution attack （TW-SA） were studied; meanwhile, the single sodium sulfate solution attack （SA） was also done as comparison. Micro-observations included the analysis of attack products by thermal analysis method and the determination of sulfate-ion content from surface to interior by chemical titrating method （modified barium sulfate gravimetric method）. Macro-observations mainly included the mechanical behaviors such as compressive strength, splitting strength. The experimental results indicate, in both cases, the main attack product is ettringite, only in the first layer of case SA some gypsum is checked; in case SA, the sulfate ions mainly concentrate in the surface layer, so the attack is relatively mild; but in case TW-SA, the repeated sub-high temperature/cooling by water promotes the sulfate ions diffusing inwards, which leads to obvious strength degradation.
