建筑结构用再生混凝土水平受力构件研究进展

对29个尺寸为300 mm×300 mm×600 mm的自密实再生块体混凝土棱柱体试件开展直剪性能和单轴受压性能试验研究。探讨了废旧混凝土块体取代率及特征尺寸对自密实再生块体混凝土的直剪强度、抗压强度的影响,并进一步分析了自密实再生块体混凝土棱柱体的直剪强度与抗压强度之间的关系。试验表明：自密实再生块体混凝土内新混凝土与废旧混凝土粘结良好;当自密实再生块体混凝土中的自密实混凝土强度高于废旧混凝土块体强度时,试件的直剪性能会由于废旧混凝土块体的取代率的增加而劣化;特征尺寸比介于0.22~0.44时,块体的特征尺寸对自密实再生块体混凝土直剪强度和抗压强度的影响不明显,可以近似忽略;自密实再生块体混凝土的剪压比随废旧混凝土块体取代率和特征尺寸均无显著变化,其值近似为0.1。基于试验结果,提出了棱柱体自密实再生块体混凝土试件的直剪强度计算公式,建立了直剪强度测试值与抗压强度计算值之间的关系,计算结果与试验值吻合良好。     

近海大气环境下锈蚀平面钢框架抗震性能试验研究及有限元分析

焊接空心球节点(WHSJs)自1966年被提出以来,已经广泛地应用于空间网格结构中,至今已有55年的应用历史。由于环境的侵蚀、后期维护不到位等,焊接球节点锈蚀的现象屡见不鲜。该文针对随机锈蚀后焊接空心球节点的抗压承载力的变化规律进行了研究,基于随机有限元分析方法进行了大量的随机数值分析,研究了锈蚀深度概率分布模型对抗压承载力折减系数的影响;利用曲线拟合技术提出了折减系数下限和上限曲线的理论计算公式;通过随机有限元的大量分析结果揭示了抗压折减系数随锈蚀深度概率分布模型的变化规律;提出了用于预测抗压折减系数概率分布模型的拟合公式;通过对具有不同几何参数的焊接空心球节点的分析,得到了该文结论对不同几何尺寸下焊接球节点的适用性。研究结果表明,所提出的方法可以准确确定随机锈蚀焊接空心球节点抗压承载力折减系数的随机概率分布模型,可为随机锈蚀焊接球节点承载力的评估提供理论分析基础。     

基于非线性控制理论的突发需求订货策略研究

基于非线性控制理论,建立生产商、分销商和零售商在内的三阶供应链动态订货模型,使用混沌理论的李雅普诺夫指数度量突发需求扩散产生的订货量、库存量和缺货量不确定性.通过仿真软件Simulink比较了突发需求情景下,采用APIOBPCS订货策略和OUT订货策略时的系统不确定性变化.研究发现:在降低突发需求产生的库存量、订货量和...     

Deformation band and texture of a cast Mg-RE alloy under uniaxial hot compression

Microstructural evolution and texture of a cast Mg-9Gd-4Y-0.6Zr ingot under hot compression were studied in this paper. Post-deforming microstructures were characterized by optical microscopy, scanning electron microscopy and transmission electron microscopy, while crystallographic orientation information was obtained from X-Ray macro-texture measurement and EBSD micro-texture analysis. Dynamic recrystallization (DRX) initiated from the deformation bands (DB) forming on original grain boundaries; the DB became widen with continuously conversion of low-angle-boundary grains into high-angle-boundary grains. The tendency of strain localization increased with Z parameter. The macro-texture analysis indicates that uniaxial compression yielded out the randomized basal texture component. This texture component was found to be strengthened with increasing Z parameter. The micro-texture analysis shows that the deviation from the ideal basal texture arose from orientated growth within DBs. Moreover, the localization deformation promoted dynamic precipitation within DBs, which inhibited the development of DRX.     

Modeling of Mechanical Characteristics in Hot Deformation of 4130 Steel

In this investigation, hot compression tests were performed at 900 °C ? 1100 °C and strain rate of 0.001 ? 0.1 s^?1 to study hot deformation behavior and flow stress model of 4130 steel. Based on the classical stress–dislocation relations and the kinematics of the dynamic recrystallization, the flow stress constitutive equations of the work hardening‐dynamical recovery period and dynamical recrystallization period were established for 4130 steel, respectively. The validity of the model was demonstrated by comparing the experimental data with the numerical results. The agreement of this comparison is quite reasonable.     

短纤维链板式松弛热定型机流场的研究

分析了链板式松弛热定型机的结构及运行特点;通过对链板式松弛热定型机的冷态测试实验,获得了热定型机内部流场气流的速度分布数据,以探讨热定型机内部流场的特点。结果表明:在纤维层上部存在着明显的气流不均匀现象,匀风板上部具有高速气流区;指出热定型风板开孔不合理,导致纤维层上部气流分布不均匀,气流短路使得散热器下部流场分布不均匀;提出改善热定型机匀风板的开孔率,可实现均匀布风的初步方案。     

Cooperative detection and protection for Interest flooding attacks in named data networking

Named data networking (NDN) is a new emerging architecture for future network, which may be a substitute of the current TCP/IP‐based network, for the content‐oriented data request mode becoming the future trend of development. The security of NDN has attracted much attention, as an implementation of next‐generation Internet architecture. Although NDN is immune to most current attack, it cannot resist the distributed denial of service like attack – Interest flooding attack (IFA) – effectively. IFA takes advantages of the forwarding mechanism of NDN, flooding a large number of malicious Interest packets at quite a high rate, and exploits the network resources, which may cause the paralysis of the network. Taking into account the severity of the destruction, we propose an algorithm to counter such new type of attack. We analyze three properties of IFA, and use them to judge and filter Interest packets. Vector space model and Markov model are used in our method to realize a cooperative detection. Meanwhile, we present the retransmission forwarding mechanism to ensure legitimate user request. The ndnSIM module of ns3 is used for the corresponding simulation, and results of the simulation will be given to show the effectiveness of our algorithm. Copyright © 2014 John Wiley & Sons, Ltd.     

16kbit/s分带自适应预测语音压缩系统中的正交镜象滤波器

本文讨论了16kbit/s分带自适应(SB—APC)预测语音压缩编码系统中的正交镜象滤波器(QMF)的原理和设计过程,并给出了实现QMF的硬件和软件结构。     

Proxy-cryptocurrency payment system

The decentralized cryptocurrency which was based on block chain has been thought the most successful one in history.In the system,public keys were used as the users’ accounts which guaranteed the anonymity in real transactions.However,all the transaction information was recorded in the block chain,it was a potential threat for users’ privacy which might leak the payment information.Moreover,to avoid double-spending,it was agreed that the transaction on the target block was valid only if another k blocks were generated after the target one.The long waiting time reduced the efficiency of the payment system.A model of payment system based on a proxy-cryptocurrency was proposed,and a solution based on blind signature techniques was proposed.The scheme introduced a proxy in the payment phase,by which transaction confirmation time could be reduced and the transaction efficiency could be improved.Meanwhile,the system implements better anonymity,namely as the privacy protection function.     

基于FPGA的多模式频域脉冲压缩系统实现

针对合成孔径雷达系统,提出一种多模式数字接收机频域脉冲压缩模块设计方案。不同模式的脉冲压缩设置了不同的工作周期以及脉冲扫频时宽和带宽,从而实现了不同距离分辨率和探测距离,满足了不同用户的需求。首先在MATLAB平台上完成了对FPGA实现流程的仿真,并对不同模式参数进行了验证。然后在Quartus软件平台下联合Modelsim完成了功能仿真。测试方面,分别利用了放在对FPGA的只读存储器中的MATLAB模拟回波数据和信号发生器产生的模拟回波进行板级测试。仿真与测试结果表明,设计实现了4种模式的中频信号的频域脉冲压缩,并证明了该方案的可行性。