数字信封在智能卡对称密钥传输中的应用

伴随智能卡EMV迁移,使用智能卡进行交易日趋频繁,应用系统对数据交换提出了高安全要求,特别是对称密钥导入和导出的安全.基于RSA数字信封体系的应用很好的解决了对称密钥的安全性问题,可以有效的防止对称密钥在导入或者导出过程中被窃取.     

温度对2E12铝合金疲劳性能与断裂机制的影响

采用疲劳实验、SEM及TEM等分析测试手段,研究温度对2524-T4合金疲劳寿命及断裂机制的影响.实验结果表明,服役温度对合金疲劳寿命及断裂机制有显著的影响,温度升高导致合金在寿命106次条件下疲劳强度降低,100℃合金的疲劳强度较-55℃下降约30MPa.由于不同温度条件下疲劳过程中位错、二次相及晶界间相互作用机制的不同,-55℃条件下合金断裂表现出较强的晶体学裂纹特征,室温和高温条件下断口主要以穿晶断裂为主,同时伴随局部沿晶断裂特征.     

原理性电控旋翼系统试验研究

电控旋翼是于本世纪初提出的一种新概念旋翼系统。本文首次开展了电控旋翼的试验研究。首先自行研制了一套用于试验的原理性电控旋翼系统。以此为基础,进行了悬停和前飞状态下的电控旋翼襟翼总距和周期变距操纵试验。试验结果表明,电控旋翼的襟翼总距和周期变距操纵效果与常规旋翼类似,电控旋翼完全可以取代传统的自动倾斜器操纵系统实现旋翼操纵。理论与试验结果的对比则相互印证了正确性。     

复杂载荷下疲劳寿命估算

 本文给出了LY12CZ铝合金板材的循环硬化规律;以材料在循环载荷作用下累积的塑性滞后能作为疲劳损伤准则,证明了应力控制等幅循环加载条件下损伤累积随循环次数变化的非线性,导出了材料瞬态塑性应变能的计算公式,算出了破坏发生时材料耗散的总塑性应变能,并给出了它与应力变程的关系。文中把疲劳损伤分为静拉伸损伤与循环损伤两部分,给出了损伤累积模型。以该模型为基础,计算了两级加载、4级加载和程序加载下光滑试件的疲劳寿命。计算结果与试验结果符合很好。     

循环应力一应变特性的统计分析

鉴于试验数据分散性，用随机过程的方法对循环应力－应变特性进行了理论分析，并给出了统计测定的方法，试验结果得到了呈分布状的循环应力－应变曲线族，证实了理论分析的正确性。     

定应力幅值往复拉伸过程中推进剂的损伤扩展

对复合固体推进剂进行不同应力幅值条件下的纯复拉仲试验,找出加载过程中往复拉伸曲线、特征应变以及耗散能的变化规律,以分析定应力幅值往复拉伸过程中推进剂的损伤特性.结果表明:往复拉伸过程中耗散能的变化反映了推进剂在不同拉伸应变下损伤形式不同,往复过程中的耗散能主要由基体的粘性耗散与破坏提供,应力幅值与往复拉伸寿命的对数之间...     

The interaction of symmetry and verbal codability in children's reconstruction of spatial configurations

Although the physical organization of spatialinformation clearly influences how it is recognized,recalled, and mentally transformed, few studies haveexplored how different levels of organizationinteract. This study focused on 4- and 6-year-oldchildren's memory for spatial configurations andexamined the relative influence of two levels oforganization: symmetry (vertical, horizontal, or none)and codability (verbal or nonverbal). We predictedthat the influence of symmetry would be lesspronounced among the older children for whom thepatterns were more codable. The results partiallysupported this prediction: Older children'sreconstructions were accurate regardless of patternsymmetry; younger children's reconstructions ofvertically-symmetric patterns were more accurate thantheir reconstructions of horizontally-symmetric andasymmetric patterns. Taken together, the resultsrevealed an interaction between age and symmetry onthe accuracy of children's reconstructions, suggestingthat younger children were more sensitive than olderchildren to differences in pattern symmetry. Thus,different levels of organization may influencechildren's ability to recall spatial information andthe relative influence of these levels may changeduring development.     

Representing space in a PDP network: Coarse allocentric coding can mediate metric and nonmetric spatial judgements

In one simulation, an artificial neural networkwas trained to rate the distances between pairsof cities on the map of Alberta, given onlyplace names as input. Distance ratings rangedfrom 0 (when the network rated the distancebetween a city and itself) to 10. The questionof interest was the nature of therepresentations developed by the network's sixhidden units after it successfully learned tomake the desired responses. Analyses indicatedthat the network used coarse allocentric codingto solve this problem. Each hidden unit couldbe described as occupying a position on the mapof Alberta, and each connection weight feedinginto a hidden unit was related to the distanceon the map between the hidden unit and one ofthe stimulus cities. On its own, a singlehidden unit's response was a relativelyinaccurate distance measure. However, bycombining all six hidden unit responses in acoarse coding scheme, accurate responses weregenerated by the network. In a secondsimulation, a second network was trained tomake similar judgements, but was trained toviolate the minimality constraint on metricspace when trained to judge the distancebetween a city and itself. An analysis of thisnetwork indicated that it too was using coarseallocentric coding.     

小型二冲程航空发动机燃烧循环变动研究

利用峰值压力、最大压力上升率、燃烧百分率以及它们各自所对应的曲轴转角和相空间重构投影法评价小型二冲程航空发动机的燃烧循环变动.通过比较,认为燃烧百分率所对应的曲轴转角能更好地表征发动机的燃烧循环变动.针对发动机在中速和不同负荷条件下的燃烧循环变动分析,结果表明随负荷的加大,缸内燃烧的循环变动会变小,认为是负荷加大,气体...     

周期对称性在叶盘结构瞬态响应求解中的应用

研究了利用结构周期对称性计算叶盘结构瞬态响应的方法.首先用ANSYS得到扩充扇区的刚度和质量矩阵,通过周期对称边界上节点的对应关系得到扩充扇区到基本扇区的转换矩阵.利用叶盘结构中各扇区所受载荷的特点,得到任意时刻载荷的空间分布,并对其进行Fourier展开,以得到周期对称模型的载荷.采用Newmark法进行时域积分,利...