Search

Since malicious nodes may manipulate voting elections through collusion attacks in consensus mechanism of DPoS, the security of block chain can not be guaranteed in the consensus process of DPoS.To deal with the problem, a method for detecting and preventing collusion attack in DPoS based on power index was proposed.Firstly, a weighted voting game model of DPoS was constructed based on the idea of power index in game theory, and the behavioral motivation of the malicious node could be analyzed.Then, the attacks were detected based on changing range of abnormal power index.During the process of preventing collusion attacks in DPoS, the Softsign activation function was adapted to suppress the power index of malicious nodes.Lastly, the effectiveness of the proposed method to detect and prevent collusion attacks in DPoS was verified through theoretical analysis and experiments.

An active SDN measurement mechanism was proposed,which could measure the end-to-end path performance between any two nodes,then the OpenFlow measurement protocol OFMP was designed,and a prototype OFMd was implemented,which could measure multiple performance metrics of the flow between two nodes without changing the switch forwarding rule.The experiment results show that OFMd can acquire multiple end to end path performance metrics only by sending a single probe packet.

Objective: To investigate the effect of augmentative locking compression plate combined with bone graft in treating aseptic femoral shaft nonunion after intramedullary nailing., Methods: Twenty-one cases with aseptic femoral shaft nonunion after intramedullary nailing from January 2007 to January 2013 were treated,including 18 males and 3 females with a mean age of 37.7 years (ranged from 23 to 64 years). The mean period of nonunion after surgery was 23.9 months (ranged from 9 to 62 months). According to Weber-Cech classification,10 of those 21 cases were hypertrophic nonunion,7 were atrophic, and 4 had oligotrophic fracture nonunion. All patients retained the original intramedullary nail, and applied with augmentation plating of 6 to 8 holes locking compression plate, unicortical fixation with 2 to 3 locking screws in the proximal or distal end, with simultaneous autologous iliac bone grafting. After treatment,all patients were allowed to partial weight-bearing until full weight-bearing according to the radiological results. All patients were followed up and were evaluated with clinical and imaging results., Results: All patients were followed up from 8 to 24 months, averaged (13.5±3.5) months,which showed clinical union at 4 to 8 months, averaged (6.0±1.0) months and radiological solid union at 7 to 12 months, averaged (9.1±1.5) months. No such complications as infection,hardware loosening or breaking were found., Conclusion: Augmentative locking compression plate(LCP) combined with bone graft for aseptic femoral shaft nonunion after intramedullary nail has a satisfied clinical efficacy. It's an useful and simple method.