No abstract

The Internet is more and more integrated into people’s life; because of the complexity and fragility of the network environment, network attack presents a more and more serious trend. Application Layer DDoS (AL-DDoS) attack is the most complex form of DDoS attack, which is hindering the availability for the legitimate users by taking up a large number of requests of web server. The paper introduced the concept of behavior utility to portray the network. The concept of attack and defense utility was defined by a specific property which was the manifestation of the network risk after the offset of attack and defense. In the utility model, traffic metrics were mapped to the multidimensional parallelotope in the Euclidean space to express as a diagonal matrix. To determine the threshold status, the defense strategies of load balancing and limiting the maximum number of connections were used with different attack scales. Finally, the attack and defense utility value was calculated to evaluate the network risk level. The proposed method can master the capacity of network system against each attack means and the defense capability of network system. Its availability and accuracy are verified by comparing with the relevant works.

Web hot topic prediction is now one of the most significant research focus in web data mining,which can reflect the internet users' psychosocial predilection,may greatly benefit us.Markov and neural network are such two typical traditional prediction model, however, the Markov method can neither capture nor express the statistical property of the real data while the computation of neural network is quite complex. In this paper, a new method based on adaptive AutoRegession (AR) model is proposed, the parameter estimation algorithm of this model is referred to as Recursive Weighted Least Square (RWLS) and therefore defines the topic trend according to the model, and the computation is simple and quick. Also included are the advantages and shortcomings of this method.

No abstract

S)-2-aminobutyric acid being initial raw material, (S)-2-hydroxybutyric acid methyl ester was synthesized by means of a three step reaction of hydroxylation, salification and esterification. The product had a yield rate of 60.4%, purity of 99% and ee value higher than 99% by characterization of GC, HPLC and 1 H NMR. This synthesis technique has advantages of high purity and ee value, low cost, short reaction time and mild reaction conditions so that it is suitable for production on industrial scale.