Spectral assessment of mesh adaptations for the analysis of the dynamical longitudinal behavior of railway bridges

Summary  Extensive studies, [1], concerning the longitudinal behavior of long railway bridges due to braking forces have been done by measurements in situ, [2], and by statical, [3, 4], as well as dynamical simulations. Thereby, the only consistent numerical realization with respect to the measured data was the dynamical one. However, the consecutive discretizations in space and time with time-dependent system matrices are extremely time consuming due to the moving loads and varying stiffness of the ballast under, and in front of, the moving train. Therefore, every effort should be made to optimize the discretization in the space domain. This paper presents a strategy for assessing the quality of finite elements in space and for applying an adaptive mesh-refinement for this special engineering problem. The method is characterized by a spectral assessment, comparing a certain set of eigenvalues of the actual discretization with those of a very fine and rather exact numerical model. The error estimator introduced in this paper controls a whole set of global eigenvalues with corresponding natural vibration modes in order to assess certain types of shape functions. Thus, the procedure estimates local modifications on the one hand and p-properties on the other by means of global indication. Received 30 August 1999; accepted for publication 26 September 2000     

Design and implementation of a wireless internet remote access platform

Recently, mobile networks and internet technologies have been widely developed for the voice communication and information retrieval services all over the world. Compared with the wire‐line internet environment, mobile networks have lower bandwidth, longer transmission latency and unreliable connection, and the capability of mobile terminals is restricted by the limited memory size, lower CPU computation capability and inconvenient I/O interface. These limitations restrict the development of the wireless internet applications. In this paper, we design and implement a ‘wireless internet remote access platform’ (WIRAP). The WIRAP platform interconnects the wireless network and internet to provide mobile users a remote centralized storage and computation environment. A mobile user can store large volume of data and execute complex computations on WIRAP instead of on the mobile terminals. WIRAP supports different network interfaces (e.g. short message service (SMS), wireless markup language (WML) and hyper text markup language (HTML) and users may use terminals (with different network capabilities) to access WIRAP. Copyright © 2006 John Wiley & Sons, Ltd.     

基于消息驱动的光栅扫描雷达显示器软件设计

提出了在以TMS340X0图形系统处理器为核心的光栅扫描雷达显示器中,用TMSC语言实现消息驱动软件的方法与过程.用此方法设计的软件移植性好、可移植性强,已成功应用于几种不同体制的光栅扫描雷达显示器中.同时也可应用于DOS下消息驱动程序的设计.     

具有消息恢复的数字签名方案

本文设计一种新的具备消息自动恢复特性的数字签名方案,这种方案的安全性同时建立在因子分解和离散对数之上,并对这种方案进行了安全性分析.     

Message trust‐based secure multipath routing protocol for opportunistic networks

Opportunistic networks (OppNets) are composed of wireless nodes opportunistically communicating with each other. These networks are designed to operate in a challenging environment characterized by high delay, intermittent connectivity, and no guarantee of fixed path between the sender and the destination nodes. One of the most vital issues in designing and maintaining practical networks over a time period is the security of the messages flowing in OppNets. This paper proposes a new method called message trust‐based secure multipath routing protocol (MT‐SMRP) for opportunistic networks. Various routing protocols such as ProPHet, Epidemic, and HiBOp, to name a few, have been proposed for OppNets, but none of these have applied a secure multipath routing technique. The proposed MT‐SMRP scheme relays the message to the destination through the disjoint paths, each applying a soft‐encryption technique to prevent message fabrication attacks. Simulations are conducted using the Haggle Infocom'06 real mobility data traces, showing that when time‐to‐live is varied, (1) the proposed MT‐SMRP scheme outperforms D‐MUST by 18.10%, 7.55%, 3.275%, respectively, in terms of delivery probability, messages dropped, and average latency; (2) it also outperforms SHBPR by 21.30%, 7.44%, and 4.85%, respectively, in terms of delivery probability, messages dropped, and average latency. Under similar performance metrics, the performance of MT‐SMRP is also shown to be better than that of D‐MUST and SHBPR when the buffer size (respondents. the message generation interval) is varied.     

Mobility aware and dual phase AODV protocol with adaptive hello messages over vehicular ad hoc networks

Establishing stable routes over high mobility networks is a challenging field and consequently brought the attention of a lot of current researchers. In this article, a new reactive routing protocol has been proposed which is considered as a major extension of both Ad-hoc On-demand Distance Vector (AODV) and Mobility and Direction Aware AODV (MDA-AODV) prior routing protocols. It is named as Mobility Aware and Dual Phase Ad-hoc On-demand Distance Vector with Adaptive Hello Messages (MA-DP-AODV-AHM). It primarily concentrates on building routes considering vehicles’ speeds and direction of motion with respect to source vehicles, thereby establishing more stable routes and reducing the route breakages. Not only to this extent, but rather, we proposed an adaptive control packet announcement mechanism, which is directly connected to the periodic hello messages approach, with vehicles’ speeds, yielding a significant reduction in the amount of control overhead and congestion over the network. Moreover, the new protocol is proposed to alternate working among two phases, for the reason of guaranteeing the generation of efficient routes on a timely basis, which include MA-DP-AODV-AHM and AODV protocols. Our protocol has been evaluated in terms of control overhead, end-to-end delay, and energy consumption using QualNet simulator version 7.1 in which enormous simulations have been conducted under the base of vehicle density, packet rate, and constant bit rate connections. Simulation results summarize that MA-DP-AODV-AHM contributes efficiently in mitigating the network instability through generating effective stable routes and reducing link failures. Furthermore, it has proved its superiority over AODV and MDA-AODV.     

基于SIP协议的MWI模型设计

针对终端的多种MWI功能需求,提出了一种基于SIP协议扩展的消息等待通知模型,同时在智能网平台完成消息仿真,并结合实例分析如何构造事件通知系统,仿真结果证明SIP MWI易实现且效率高。     

Efficient Key Management Protocol for Secure RTMP Video Streaming toward Trusted Quantum Network

This paper presents an achievable secure videoconferencing system based on quantum key encryption in which key management can be directly applied and embedded in a server/client videoconferencing model using, for example, OpenMeeting. A secure key management methodology is proposed to ensure both a trusted quantum network and a secure videoconferencing system. The proposed methodology presents architecture on how to share secret keys between key management servers and distant parties in a secure domain without transmitting any secrets over insecure channels. The advantages of the proposed secure key management methodology overcome the limitations of quantum point‐to‐point key sharing by simultaneously distributing keys to multiple users; thus, it makes quantum cryptography a more practical and secure solution. The time required for the encryption and decryption may cause a few seconds delay in video transmission, but this proposed method protects against adversary attacks.     

断层泥显微特征研究在桥基稳定性评价中的应用

基于SEM研究了桥基断裂断层泥的原状显微结构和显微构造、石英碎砾的显微构造、表面刻蚀形貌和结构特征 ,并进一步分析和评价了断裂的抗震和抗断关键问题 ,其对系统论证在断裂带上建设特大型过江桥梁工程的稳定性具有重大实际意义 ,并为镇扬大桥工程的合理设计和安全运行提供了地质依据