Four-winged dinosaurs from China

Although the dinosaurian hypothesis of bird origins is widely accepted, debate remains about how the ancestor of birds first learned to fly. Here we provide new evidence suggesting that basal dromaeosaurid dinosaurs were four-winged animals and probably could glide, representing an intermediate stage towards the active, flapping-flight stage. The new discovery conforms to the predictions of early hypotheses that proavians passed through a tetrapteryx stage.     

正偏置式凸轮转子叶片泵的最佳参数

通过对ＴＹＢ-Ｅ６３型正偏置式凸轮转子叶片泵的受力情况和磨损状况的深入分析,优化出最佳的结构参数和动力参数．理论分析和试验结果表明：与普通凸轮转子叶片泵相比,采用最佳结构参数和动力参数的正偏置式凸轮转子叶片泵能进一步减少磨损、提高寿命、降低流量脉动和噪声．     

基于X.509的VPN的安全认证模型

目前VPN广泛应用,但没有一个完善的认证体系,针对于此,提出了基于X.509技术的VPN安全认证模型。论述了确定怎样为VPN通道颁发X.509数字证书,怎样进行证书体系管理的问题,实现了CA系统的证书认证PKI体系在VPN中的安全认证模型。可用于使用公钥认证的VPN中。