螺旋缝焊管静水压爆破试验分析

通过对螺旋缝焊管进行静水压爆破试验,得出钢管的屈服压力、最大压力值和爆破压力值,验证钢管成型和焊接工艺的合理性,为管线的设计单位和用户提供参考依据.介绍了螺旋缝焊管静水压爆破试验所用的装置;分析了爆破试验管的管内承压状况、爆破试验过程以及不同起爆点的由来,并以X65钢级Φ813 mm×9.5mm螺旋缝焊管的爆破试验进行...     

会话初始协议安全认证机制的分析与改进

通过分析会话初始协议相关认证机制,指出认证中可能存在的安全威胁,如离线密钥猜测攻击和Denning-Sacco攻击。针对安全漏洞提出一种结合椭圆曲线密码的改进认证机制。安全性分析表明,改进的认证机制在提供客户端和服务器间双向认证的同时,能够完成会话密钥传递,确保认证的时效性,有效抵御离线密钥猜测攻击和Denning-Sacco攻击。     

基于P2P的无线Mesh网中SIP服务器协作方案

在SIP服务实现中,传统的多服务器独立工作方案存在资源利用率低和信息更新代价大的问题,基于对等计算的思想,将所有的SIP服务器组织到覆盖网中,对Chord路由表的结构进行改进,采用基于等距地址Hash的多副本发布策略,提出一种改进的多服务器协作方案.给出了该方案与多服务器独立工作方案、基于传统Chord的服务器协作方案的性能比较分析.仿真结果表明,该方案能够确保较高的消息查询成功率和转发速度,减小网络流量开销.     

Effects of hydrogen addition on oblique detonations in methane–air mixtures

As a low-carbon fuel, methane has been used in various engines; however, the studies on its application in hypersonic propulsion are few. Here, oblique detonation waves (ODWs) in methane–air mixtures have been simulated to facilitate methane applications in shock-induced combustion ramjets. The shortcoming of using methane in hypersonic air-breathing propulsions has been presented via examining initiation distance of ODWs. Results demonstrate that ODWs are difficult to be initiated in the methane–air mixture, and similar to normal detonations studies before, this leads to a long initiation length; therefore, methane-fueled ODW is only applicable for high flight Mach number (M₀). To broaden the M₀ regime, hydrogen has been added to methane to decrease the initiation length. An increasing in the hydrogen percentage leads to the nonlinear decrease of the initiation length, and the initiation structures also vary simultaneously. To elaborate the physical mechanism of the initiation length variation, a theoretical model of the initiation length for fuel blends has been proposed. Meanwhile, the advantages of methane fuel in ODW-based propulsion have been discussed by analyzing on the effects of hydrogen addition on the total pressure.     

抵御SIP分布式洪泛攻击的入侵防御系统

针对SIP分布式洪泛攻击检测与防御的研究现状,结合基于IP的分布式洪泛攻击和SIP消息的特点,提出了一种面向SIP分布式洪泛攻击的两级防御分布式拒绝服务(DDoS)攻击体系结构(TDASDFA):一级防御子系统(FDS)和二级防御子系统(SDS)。FDS对SIP的信令流进行粗粒度检测与防御,旨在过滤非VoIP消息和丢弃超出指定速率的IP地址的SIP信令,保证服务的可用性;SDS利用一种基于安全级别设定的攻击减弱方法对SIP信令流进行细粒度检测,并过滤具有明显DoS攻击特征的恶意攻击和低流量攻击。FDS和SDS协同工作来实时检测网络状况,减弱SIP分布式洪泛攻击。实验结果表明,TDASDFA能实时地识别和防御SIP分布式洪泛攻击,并且在异常发生时有效地减弱SIP代理服务器/IMS服务器被攻击的可能性。     

船坞围堰爆破拆除过流控制研究及工程应用

船坞围堰爆破拆除采用围堰内不充水爆破方案时,必须控制过流。本文针对围堰爆后易发生过流的特点,从爆破参数设计、钻孔形式、起爆技术及爆破时潮位选择等方面对过流控制措施进行论述。此控制措施在工程实践中应用表明是有效的,可供类似的爆破工程参考。     

Analysis and Design of Instant Message System Based on P2P

By analyzing current development conditions of mainstream Instant Message technologies and services,some detailed discussion about technical solution and formal operation deployment strategies of P2P Instant Message Services based on Internet is made.Several crucial problems of P2P Instant Message System about services management,interconnection with other instant message,security and profit-making mode are analyzed,,and how to develop P2P IM Services is proposed.     

基于SigComp的会话初始化协议压缩算法

独立媒体服务(IMS)是第三代合作伙伴计划(3GPP)在版本5中提出的支持IP多媒体业务的子系统,而基于文本的SIP消息过大成为其在IMS无线环境应用下的瓶颈,因此采用会话初始化协议（SIP）来建立和维护多媒体会话。在SigComp框架下,将改进后的LZSS算法与算术编码相结合对SIP信令进行压缩。实验表明新的算法有较高的压缩率,对改善IMS的SIP会话建立延时有一定的参考价值。     

Characteristics of fatigue crack initiation and fatigue strength of nitrided lCr-lMo-0.25V turbine rotor steels

To investigate the effect of nitriding layer on both fatigue crack initiation and fatigue life, turbine rotor steel (lCr-IMo-0.25V steel) specimens were nitrided by the nitemper method and then put to a rotary bending fatigue test at room and elevated temperatures. In nitriding, temperature and time were controlled to obtain a different nitrided thickness. Microstructure analysis, micro-Vickers hardness test, and scanning electron microscope observation were carried out for evaluating experiments. In results, the fatigue cracks of nitrided specimens were initiated at inclusion near the interface between nitrided layer and substrate, which showed fish-eye type appearance in fractograph. The fatigue life of nitrided specimens at every temperature was prolonged compared to that of the non-nitrided. However, there was not observable improvement in fatigue characteristics with the increase of a nitrided thickness.     

喷丸对中碳钢表面短裂纹萌生与扩展的影响

通过对中碳钢在非喷丸与喷丸二情形下表面疲劳短裂纹的萌生与扩展试验，研究了喷丸对中碳钢表面疲劳短裂纹萌生与扩展的影响。试验表明：喷丸延迟了裂纹萌生时间并增长了等幅扩展寿命；降低了裂纹的扩展速率，尤其在裂纹的早期扩展阶段。运用显微结构断裂力学理论对上述试验结果进行了较为深入的分析。