基于椭圆曲线的盲数字签名及其身份识别

椭圆曲线密码体制以其特有的优越性被广泛用于进行数据加密和构建数字签名方案。同样,它也可以用来构建盲数字签名方案。介绍了椭圆曲线密码体制的相关知识,基于求解椭圆曲线离散对数问题的困难性,设计了一种基于椭圆曲线离散对数问题的盲数字签名方案,并在此基础上设计了一种身份识别协议,该方案可以同时满足盲数字签名的正确性、匿名性、不可伪造性和不可追踪性等特性要求。从理论上分析该方案是安全的,并具有一定的实用价值。     

Flux creep and fishtail in melt-textured and single-crystalline YBa2Cu3O7

Time-dependent decay of the magnetic moment and magnetization measurements were used to study pinning and flux creep in two samples with and without aj(B) maximum in nonzero field (fishtail effect). From both measurements theE(j) relation was reconstructed forBc and the characteristic current exponent was obtained. At highj and lowB values are between 1 and 4; with increasingB passes a maximum and approaches negative values. At lowj is below 0.5 and not dependent onB orj. This behavior, which is qualitatively the same in both samples, is compared with proposed phase diagrams of the vortex lattice. Large values are correlated with the plateau of the normalized creep rateS 0.025; both observations indicate low relaxation and are found in that lowB region for whichj(B) has its minimum. This observation rejects a dominating influence of relaxation on the fishtail effect.     

Fitting fatigue data with a bi‐conditional model

The formulation of a probability‐stress‐life (P‐S‐N) curve is a necessary step beyond the basic S‐N relation when dealing with reliability. This paper presents a model, relevant to materials that exhibits a fatigue limit, which considers the number of cycles to failure and the occurrence of the failure itself as statistically independent events, described with different distributions and/or different degree of scatter. Combining these two as a parallel system leads to the proposed model. In the case where the S‐N relation is a Basquin's law, the formulations of the probability density function, cumulative distribution function, quantiles, parameter and quantile confidence interval are presented in a procedure that allows practically any testing strategy. The result is a flexible model combined with the tools that deliver a wide range of information needed in the design phase. Finally, an extension to include static strength and applicability to fatigue crack growth and defects‐based fatigue approach are presented.     

噻二唑型缓蚀剂缓蚀性能的研究

利用电化学测试和表面分析技术,研究了2,5-二巯基-1,3,4噻二唑(DMTD)在硫-乙醇溶液中对金属银、铜的缓蚀性能,结合量子化学计算和分子动力学模拟对DMTD在金属表面的吸附行为和缓蚀作用机理进行了分析讨论。结果表明,DMTD在50mg/L的硫-乙醇溶液中,对金属银、铜均起到较好的缓蚀作用。极化曲线结果表明,当缓蚀剂DMTD浓度达到50mg/L时,缓蚀效率可以达到92.3%。表面分析技术表明,缓蚀剂的加入在金属表面形成吸附膜,明显抑制了腐蚀速率。量化计算和分子动力学模拟得到了缓蚀剂分子的活性位点和缓蚀剂在金属表面的吸附形态。     

盐酸介质中咪唑离子液体对铜的缓蚀作用

以1-甲基咪唑、1,4-丁烷磺内酯和浓硫酸为原料,用乙醚洗涤合成了1-甲基-3-(4-硫酸基丁基)咪唑硫酸盐(4-BMIM)缓蚀剂。采用动电位极化和交流阻抗技术研究了4-BMIM在5%HCl溶液中对铜的缓蚀性能及作用机理。实验结果表明:缓蚀效率随着缓蚀剂浓度的增加先增大后降低,当浓度为0.03mol/L时,缓蚀效率最高;同一浓度下,随着温度的升高缓蚀效率降低。动电位极化表明咪唑离子的加入对铜的阴、阳极腐蚀过程均有抑制作用,是混合型缓蚀剂。热力学计算结果表明咪唑离子液体吸附在铜表面,其吸附机制为自发进行的物理吸附,并且在铜/溶液界面的吸附遵循Langmuir吸附等温式。     

铝合金在盐水环境中腐蚀性能的电化学研究

为了深入研究温度对铝合金材料的腐蚀行为和机理,采用盐水腐蚀方法研究了其在高温条件下的电化学特性及腐蚀机理.选用7A04和5A06铝合金作为研究对象,在质量分数为3.5%的氯化钠溶液中,利用增重法、蔡司显微镜并结合电化学测试方法研究了其在20~80 ℃范围内的腐蚀性能,分析了腐蚀产物的微观形貌,探讨了腐蚀机理.结果表明：两种铝合金试样的腐蚀速率均随温度升高而增大.在Tafel极化曲线图中,对于同一种铝合金,自腐蚀电位随腐蚀温度增加向负方向移动,自腐蚀电流密度和年腐蚀深度随腐蚀温度增加而减小.对同一腐蚀温度下的两种铝合金,5A06铝合金自腐蚀电位低于7A04铝合金,腐蚀电流密度和年腐蚀深度均小于7A04铝合金.电化学阻抗图谱中,两种铝合金在不同条件下的Nyquist图均存在一个容抗弧,极化电阻随腐蚀温度增加而减小.对于同一种铝合金,在3.5%氯化钠溶液中的腐蚀速率会随着温度的升高而增大;在同一腐蚀温度下,5A06铝合金比7A04铝合金更容易发生腐蚀,但腐蚀速率比7A04铝合金慢.     

超声导波频散曲线反演皮质骨参数的研究

皮质骨参数的变化可以反映骨质的健康状况,因此文章提出了一种频散能量匹配算法来反演皮质骨参数。首先,通过频散特性方程计算出预定义参数下的频散曲线数据库;其次,利用时域有限差分算法建立皮质骨声场模型,将仿真的时域信号通过功率谱估计得到频散能量信息,并与数据库进行匹配,通过分析匹配结果的能量从而得到皮质骨的厚度、纵波速度和横波速度。仿真结果显示：与理论值相比,厚度的平均相对误差为3.8%,纵波速度与横波速度的平均相对误差分别为0.6%、0.9%。对三组离体牛胫骨皮质骨进行反演,离体实验结果显示：与真实值相比,厚度相对误差为4.9%,且实验频散曲线与反演得到的理论频散曲线吻合。因此文中所提出的反演算法可以有效获取皮质骨的厚度,横波速度和纵波速度,从而为评价骨质的健康状况提供可靠的依据。     

不同缓冲材料的堆码包装振动特性分析

目的 研究物流运输中采用不同缓冲材料的堆码包装件的振动特性。方法 以缓冲材料聚乙烯泡沫(EPE)和聚苯乙烯泡沫(EPS)为研究对象,采用三维建模软件SoildWorks和有限元仿真软件Workbench建立有限元模型进行模态与谐响应分析,结合扫频振动试验和随机振动试验对各层堆码件的振动响应特性进行分析。结果 2类包装件共振频率处的第一激励能量都大于第二激励能量,振动幅值随层数增加而升高。EPE包装件第一和第二共振频率的激励能量占比分别为35.7%和3%,EPS包装件第一和第二共振频率的激励能量占比分别为26.8%和16.8%。EPE包装件共振区域主要分布于15～40 Hz,而EPS包装件共振频率区域分布于15～40 Hz和60～80 Hz。三层堆码件的中上层包装件受第一共振频率控制,EPS材料的底层包装件受多个共振频率影响,EPE材料的底层包装件受到第二共振频率控制。结论 经过循环载荷作用后的EPE的吸振缓冲性能优于EPS的。通过试验与有限元仿真数据绘制了相应的防振性能曲线,同时验证了有限元仿真的可靠性。这为堆码产品选择不同缓冲材料组合提供了的理论指导。     

Curvature continuous path generation for autonomous vehicle using B-spline curves

In this paper we introduce a roadmap algorithm for generating collision-free paths in terms of cubic B-spline curves for unmanned vehicles used in mining operations. The algorithm automatically generates collision-free paths that are curvature continuous with an upper bounded curvature and a small slope discontinuity of curvature at knots, when we are given the locations of the obstacles, the boundary geometry of the working area, positions and directions of the vehicle at the start, loading, and the goal points. Our algorithm also allows us to find a switch back point where the vehicle reverses its direction to enter the loading area. Examples are provided to demonstrate the effectiveness of the proposed algorithms.