不同压缩算法性能的研究

移动通信网络中，建立一次多媒体会话通常需要数十秒钟的时间。通过对信令消息的压缩可以有效地减少所需时延，改善服务质量。文章先后使用了LZ77、LZW和Deflate压缩算法对因特网协议多媒体子系统中的会话发起协议信令消息的压缩进行了研究。仿真结果显示：Deflate算法的压缩性能最好，不使用辞典时压缩率可以达到30％，使用辞典时压缩率可以达到50％以上；接着是LZW算法，而LZ77算法的压缩性能最差。     

爆炸逻辑网络起爆控制系统研究

介绍了采用微处理器控制爆炸逻辑网络起爆的方法．初步探讨了该技术的发展和应用。     

A Component-Based Conference Control Model and Implementation for Loosely Coupled Sessions

1　ＩｎｔｒｏｄｕｃｔｉｏｎＲｅｃｅｎｔｒｅｓｅａｒｃｈｈａｓｉｄｅｎｔｉｆｉｅｄｃｏｍｐｏｓａｂｉｌｉｔｙ ,ｅｘｔｅｎｓｉｂｉｌｉｔｙ ,ａｎｄｔａｉｌｏｒａｂｉｌｉｔｙａｓｋｅｙａｓｐｅｃｔｓｏｆｓｙｓ ｔｅｍｓｔｈａｔｓｕｐｐｏｒｔ ｇｒｏｕｐｓｏｆｉｎｔｅｒａｃｔｉｎｇ ｐｅｏｐｌｅ.Ｃｏｍｐｏｎｅｎｔ ｂａｓｅｄｄｅｓｉｇｎｉｓａｍｅａｎｓｔｏａｃｈｉｅｖｅｔｈｅｓｅｒｅｑｕｉｒｅｍｅｎｔｓｉｎ ｇｒｏｕｐｗａｒｅｓｙｓｔｅｍｓ.Ｍｅａｎｗｈｉｌｅ,ｃｏｍｐｏｎｅｎｔ ｂａｓｅｄｄｅｓｉｇｎｏｆｓ…     

电子雷管起爆法的安全技术探讨

针对我国电子雷管起爆安全技术及措施目前尚未有一个完整的标准和规程,介绍了电子雷管的结构原理,并针对隆芯1号数码电子雷管及其起爆系统进行了安全技术方面的探讨,对电子雷管起爆法在爆破工程中安全技术的制定提出了一些见解。可为使用电子雷管的爆破作业人员提供参考。     

基于身份的SIP认证与密钥协商机制研究

对SIP中的安全威胁和已有安全机制进行了分析,提出一种基于身份的SIP认证与密钥协商方案,通过3次交互实现双向认证,并在该过程中完成密钥协商.方案不需要公钥证书,以用户身份标识作为公钥,降低了计算复杂度和通信开销,保证了SIP消息传递过程中的完整性和真实性.     

Fretting fatigue life prediction using the extended finite element method

In this work, an efficient procedure to predict fatigue lives in fretting fatigue problems is presented. This is accomplished by means of a combined initiation-propagation approach in which the extended finite element method (X-FEM) is used. The procedure is verified by modelling several fretting fatigue tests available in the literature. The application of the X-FEM enables to numerically evaluate the stress intensity factors (SIFs) for cracks of different lengths emanating at the end of the contact zone and to estimate the propagation life corresponding to each of the tests. This propagation life is combined with the initiation life calculated using a multiaxial fatigue criterion (Fatemi-Socie). The predicted lives are then compared with the reported experimental lives, showing that the consideration of the crack-contact interaction through the numerical models tends to improve the life estimation when compared with a fully analytical approach. The procedure can be applied to more general fretting problems for which analytical solutions are not available.     

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.