In the process of metal milling, especially in the machining of low?stiffness workpieces, chatter is a key factor affecting many aspects such as surface quality, machining efficiency and tool life. In order to avoid the chatter, a milling chatter recognition method based on dynamic and Wavelet Packet Decomposition(WPD) is proposed from the signal processing. The modal parameters of the system are obtained by modal experiments. Based on the principle that the chatter frequency will peak near the natural frequency of the system, the original milling force signal is decomposed by WPD, and the sub?signals containing rich chatter information are selected for signal reconstruction. Finally, the time?frequency and Hilbert spectrum characteristics of the reconstructed signal are compared and analysed, and the chatter recognition is performed. At last, the proposed method is verified by the experiments. The results demonstrate the effectiveness and reliability of the proposed method.

In order to study the performance of Indonesian oil sand tailings/polyethylene (HDPE) composites, scanning electron microscopy (SEM) and X⁃ray fluorescence spectrometry (XRF) were used to obtain the morphology, size and main component calcium carbonate (CaCO3), the main component of oil⁃sand tailings before and after modification, which is about 77.170%. And the surface was dried with different mass fractions of stearic acid, the best modifier content is 5%; the mechanical properties of oil sand tailings/HDPE composites were characterized by impact strength, tensile strength, elastic modulus and differential scanning calorimetry (DSC). The results show that with the increase of tailings filling, the oil sand tailings have obvious strengthening and toughening effect on HDPE. When the tailing sand content is 50%, the toughening effect is best. However, a large amount of oil sand tailings is distributed in HDPE to increase the defects in the matrix, and causes stress concentration phenomenon when subjected to external force, which results in the decrease of tensile strength. The crystallization property study shows that the addition of oil sand tailings has heterogeneous nucleation effect on polyethylene and enhances the toughness of composites.

With the rapid development in recent years, ultra low permeability oil and gas resources, the main controlling factors of the elastic recovery stage has attracted wide attention. In order to study the factors affecting oil recovery in ultralow permeability reservoir during elastic exploitation stage, the permeability, viscosity, failure pressure and failure radius are combined into 4 factors and 3 levels orthogonal experiment, through laboratory experiments, the order of influence degree is as follows: failure pressure difference>permeability>failure radius>crude oil viscosity. Combined with the scanning electron microscope images, it is found that the degree of recovery is related to the stress sensitivity and the startup pressure gradient, besides the initial elastic energy. In addition, the starting pressure gradient mathematical models of permeability, fluidity, fluiditypressure difference are compared and analyzed. Through the error analysis of numerical simulation and experimental data, the model which is closer to the real situation is chosen as the pressure difference mobility model.

Pattern matching is an important algorithm in intrusion detection system．The efficiency of this algorithm directly affects the intrusion detection system's performance. As in the process of traditional pattern matching algorithm, matches were done according to the character order in the pattern, a pattern matching algorithm based on statistics was proposed. By using the statistical characteristics of the string itself, the algorithm chooses the least frequency substring's characters in the main string as the key characters. According to this characters' position in the main string, jump matching are done. Thus the speed of pattern matching was accelerated greatly. The experiment results show that this algorithm is more efficient than other similar algorithms.