Improving secret key generation for wireless communications in FDD mode

Most recent research on channel‐based key generation oriented to time division duplex system because the channel reciprocity feature is applied directly for secret key generation. Most of commercial cellular systems depend on frequency division duplex (FDD) systems. In this paper, we investigate the impact of uplink and downlink of FDD systems for the generation of shared secret keys between two parties in the presents of passive eavesdropper. In addition, we are considering improving the rate of the secret key for wireless communication in FDD mode. The main idea is to use the fading coefficient of the channels between the relay and other parties as an additional random common source for the secret key generation. Also, explore the using of channel estimation techniques to reduce the channel training sequence and study its effect on the generation of shared key for wireless communications in FDD mode. We derive the upper bound of the generated shared key rate for four scenarios and give numerical examples to reveal the performance of our suggested improvement approaches.     

Magneto-thermo-visco-elastic waves in an initially stressed conducting layer

The aim of this paper is to investigate magneto-thermo-viscoelastic surface waves in electrically and thermally conducting layers involving time rates of strain and stress of ordern, the media being under an initial stress in the nature of hydrostatic tension or compression. The theory of magneto-thermo-visco-elastic surface waves in the conducting medium involving strain rate and stress rate ofnth order is derived under initial stress. This theory is then employed to obtain wave velocity equations in specific cases. Results obtained in the above cases reduce to well-known classical results when additional fields are absent.     

Finite element approximation of piezoelectric plates

A Reissner–Mindlin‐type modellization of piezoelectric plates is here considered in a suitable variational framework. Both the membranal and the bending behaviour are studied as the thickness of the structure tends to zero. A finite element scheme able to approximate the solution is then proposed and theoretically analysed. Some numerical results showing the performances of the scheme under consideration are discussed. Copyright © 2001 John Wiley & Sons, Ltd.     

Metallurgical characterization and determination of residual stresses of coatings formed by thermal spraying

This work presents an experimental determination of residual stresses in 35CrMo4 (Euronorm) low alloyed steel substrates with thermally sprayed coatings. Two different materials were separately deposited. The first one consisted of a blend of two superalloys: Cr-Ni steel and Cr-Mn steel, designated 55E and 65E, respectively. The second material was molybdenum. In a first part, basic characteristics of the deposited layers (metallographic analysis, hardness, and adhesion) are presented. In a second part, the determination of the residual stresses, in both substrate and thermal sprayed layers is performed using an extensometric method in combination with a simultaneous progressive electrolytic polishing. The influence of a nickel-aluminum (80:20%) bond-coat and/or a post-annealing at 850 °C in air for 1 h is studied.     

基于卷积神经网络的刀具磨损在线监测

为了提高刀具磨损在线监测的精度和泛化性能,提出一种基于卷积神经网络的刀具磨损量在线监测模型。利用时域传感器信号对刀具磨损量进行定量分析,避免数据预处理带来的信息丢失;采用深度网络自适应地提取特征,取代传统的人工特征提取过程,并通过加深网络进一步挖掘信号中隐藏的微小特征。实验结果表明,该模型对刀具后刀面磨损量监测效果较好,可以有效避免人为特征提取的局限,精度和泛化性都有一定程度的提高。与相关研究的对比也证实了其可行性和有效性。     

基于CFD技术优化50 L发酵罐内气体分布器

通过CFD模拟技术对50L通气搅拌发酵罐内不同气体分布器的传质混合效果进行气液双相流模拟。首先对发酵罐自带气体分布器进行流场模拟,针对模拟结果提出两种改进气体分布器。结果表明:双层环形气体分布器表现出一种较理想的混合传质效果,为此类发酵罐的优化和放大提供一种有效的技术手段。     

中压蒸汽管道设计的探讨

结合工程实例,讨论了中压蒸汽管道材质的选取、蠕变监测的设置、球型补偿器和隔热管托的应用及管道绝热设计。     

高层建筑结构转换大梁施工监控

结合工程实例，选择了转换层的施工方案，制订了施工技术方案，分析了转换层梁板的有关强度验算方法，提出了保证转换层混凝土及施工质量的措施，验证了该施工方案的应用是成功的。     

某增层改造工程中的植筋锚固技术

对某实验楼室内增层改造工程中的植筋锚固节点进行了研究，从方案确定、植筋锚固节点构造与设计及植筋锚固施工技术等方面进行了深入分析，可为类似工程提供参考。     

黄河二桥系杆拱桥桥面铺装结构力学性能研究

运用有限元法对黄河二桥下承式系杆拱桥双层沥青混凝土铺装体系进行受力分析,确定了全桥的最不利荷位,提出了系杆拱桥面铺装设计控制指标,并在各个指标的最不利双轮加载方式下,进一步分析了车轮附近区域沥青混凝土铺装层各控制指标的变化规律,同时给出其相应的三维图。为确定水平荷载对铺装层各控制指标的影响,本文还分析了不同水平荷载下各控制指标的变化规律。为更准确地模拟实际边界条件,分析的整个过程是在包括梁、拱肋、吊杆和桥面铺装等部分的整体桥梁结构上实现的。结合力学分析所得结论进行了相应试验研究,建立了不同温度下水泥混凝土桥面板与沥青铺装层间的剪切强度与黏结强度关系式,并确定了15℃时该桥铺装层层间稳定性控制指标——容许黏结强度。最后,进行现场拉拔试验,检验实桥上的层间稳定性。