We introduced a three-tier architecture of intrusion detection system which consists of a blacklist, a whitelist and a multi-class support vector machine classifier. The first tier is the blacklist that will filter out the known attacks from the traffic and the whitelist identifies the normal traffics. The rest traffics, the anomalies detected by the whitelist, were then be classified by a multi-class SVM classifier into four categories: PROBE, DoS, R2L and U2R. Many data mining and machine learning techniques were applied here. We design this three-tier IDS based on the KDD'99 benchmark dataset. Our system has 94.71% intrusion detection rate and 93.52% diagnosis rate. The average cost for each connection is 0.1781. All of these results are better than those of KDD'99 winner's. Our three-tier architecture design also provides the flexibility for the practical usage. The network system administrator can add the new patterns into the blacklist and allows to do fine tuning of the whitelist according to the environment of their network system and security policy.

A combined experimental and theoretical charge density study is made on the compound bis(diiminosuccinonitrilo)nickel, Ni(s-disn) 2 . It is investigated experimentally by an accurate X-ray diffraction measurement on a single crystal of the compound at 110 K and theoretically by various molecular orbital calculations. The crystal belongs to monoclinic crystal system, space group P2 1 /n; a ) 3.639(1), b ) 8.743(1), c ) 15.948(1) Å, β ) 94.74(1)°, Z ) 2. The molecule is planar with pseudo-D 2h symmetry stacked along the a axis. Single-point MO calculations are performed using EHMO, ab initio, and density functional methods. Deformation densities are produced via conventional X-X high , multipole model, and MO calculations. Bonding densities along N-H, C-C, C-N, CtN bonds, and lone-pair electron densities are clearly demonstrated and are in excellent agreement between experiment and theory. The bonding density between the coordinated nitrogen atom of the ligand and the nickel atom indicates a certain degree of dative bond through the donation of nitrogen lone pair electrons to the metal center. The redistribution in electron density around the nickel atom is substantial with electron density depletion along the σ-direction but electron density surplus along the π-direction, which conforms to the crystal field theory. The agreement in deformation density between experiment and theory around nickel atom is reasonably good. Bonding type in the s-disn ligand was further analyzed with orbital wave functions, the complete π-electron delocalization of the ligand is incorporated with the d xz , d yz orbitals of the Ni atom. Three Lewis structures are deduced from the ab initio MO calculation; they are exactly the same as expected by valence bond theory. The resonance between three Lewis structures represents the π-electron delocalization of the molecule. Comparisons between experiment and theory are made on electron density distribution, net atomic charges of the molecule, and d-orbital occupancies of the Ni atom.

The distribution of deformation density of 2,5‐dimethyl thiathiophthene and 2,4‐diphenyl thiathiophthene are calculated via density functional method. The results are in good agreement with the corresponding experimental and theoretical distributions from an ab initio method. The ionization potentials obtained in this calculation on 2,5‐dimethyl thiathiophthene are in good agreement with those obtained experimentally from photoelectron spectroscopy, it is in better agreement than those VIPs based on ab initio calculations. Net atomic charges are compared with the experimental multipole refinement and with those calculated with ab initio and DFT methods for various atomic partitions.