The detection of DDoS attacks is an important topic in the field of network security. The occurrence of software defined network (SDN) (Zhang et al., 2018) brings up some novel methods to this topic in which some deep learning algorithm is adopted to model the attack behavior based on collecting from the SDN controller. However, the existing methods such as neural network algorithm are not practical enough to be applied. In this paper, the SDN environment by mininet and floodlight (Ning et al., 2014) simulation platform is constructed, 6-tuple characteristic values of the switch flow table is extracted, and then DDoS attack model is built by combining the SVM classification algorithms. The experiments show that average accuracy rate of our method is 95.24% with a small amount of flow collecting. Our work is of good value for the detection of DDoS attack in SDN.

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Six cadmium(II) complexes containing the N 2 O 2 donor tetradentate asymmetrical Schiff base ligand 2-{[2-(dimethylamino)ethylimino]methyl}-6-methoxyphenol (HL 5 ), namely, 6), have been synthesized using cadmium(II) chloride and the asymmetrical Schiff base ligand HL 5 under different pH conditions at room temperature. The diverse structures show the marked sensitivity of the structural chemistry of the tetradentate asymmetrical Schiff base ligand HL 5 . Complex 1 formed at pH = 10 exhibits a rare zero-dimensional structure of trinuclear cadmium(II). At pH = 8-9, a dinuclear cadmium(II) complex 2 is formed. The reaction at pH = 5-7 leads to two one-dimensional structures of 3 and 4. A further decrease of the pH to 3-5 results in a zero-dimensional structure 5. Owing to the departure of lattice water molecules in the crystal, complex 5 at room temperature can gradually undergo single-crystal-to-single-crystal transformation to result in complex 6. The results further show that conversions of complex 1-5 can also be achieved by adjusting the pH value of the reaction solution, 1 f 2 pH=8 f 5 pH=3 and 3 f 4 pH=5 . Comparing these experimental results, it is clear that the pH plays a crucial role in the formation of the resulting structures, which simultaneously provides very effective strategies for constructing the Cd II compounds with N 2 O 2 donor tetradentate asymmetrical Schiff base ligand. The strong fluorescent emissions of the six compounds (1-6) make them potentially useful photoactive materials. Furthermore, six Schiff base cadmium complexes (1-6), with 2,2-dipheny1-1-picrylhydrazy1 (DPPH) as a cooxidant exhibited the stronger scavenging activity.