With ultrashort duration and ultrahigh energy, femtosecond laser (fs-laser) pulses are very promising for the precision machining of energetic materials. Compared with the mechanical machining methods of energetic materials, fs-laser machining technology has the advantages of high safety, high precision, and absence of pollution. A deep understanding of the mechanisms between fs-lasers and energetic materials is the basis for the development of fs-laser machining technology. In this paper, the method of reactive molecular dynamics (ReaxFF-MD) was adopted to calculate the fs-laser ablation process of octahydro-1,3,5,7-tetranitro-1,3,5,7-tetraazacyclooctane (HMX, a high explosive compound), and the ablation mechanisms of HMX under different fs-laser energies were studied. The results show that the fs-laser ablation mechanisms of HMX are related to the laser power density. When the laser power density is high enough (3.4 × 10 14 W/cm 2 , 1.0 mJ/pulse), HMX undergoes ionization or decomposition reactions at the picosecond level (∼7.65 ps) and produces a high temperature and pressure plasma. Many N, H, and O single atoms and their ionic products occur along with some small molecular fragments of NO 2 , H 2 O, CO 2 , N 2 , H 2 , NH, NH 2 , CO, OH, CNO 2 and very few toxic products of NO and HNO 2 . In this case, the removal process of HMX occurs via a phase explosion mechanism. As the laser energy decreases, the ionization degree of ablation products decreases, in which the number of monatomic and ionic products decreases, while the number of toxic small molecules (such as NO, HNO 2 , and HNO) increases. When the laser power density is relatively low (0.34 × 10 14 W/cm 2 , 0.1 mJ/pulse), the removal process of HMX occurs via a photomechanical mechanism, and the compound escapes as intact initial HMX molecules. When the laser power density is close to the ablation threshold of the explosive, the HMX molecules only undergo a melting state to some extent without escaping from the surface of the crystal. Therefore, the fs-laser can be used in the precise machining of explosives and preparation of highpurity energetic nanomaterials by a reasonable selection of fs-laser energy.

Quantitative analysis for the flue gas of natural gas-fired generator is significant for energy conservation and emission reduction. The traditional partial least squares method may not deal with the nonlinear problems effectively. In the paper, a nonlinear partial least squares method with extended input based on radial basis function neural network (RBFNN) is used for components prediction of flue gas. For the proposed method, the original independent input matrix is the input of RBFNN and the outputs of hidden layer nodes of RBFNN are the extension term of the original independent input matrix. Then, the partial least squares regression is performed on the extended input matrix and the output matrix to establish the components prediction model of flue gas. A near-infrared spectral dataset of flue gas of natural gas combustion is used for estimating the effectiveness of the proposed method compared with PLS. The experiments results show that the root-mean-square errors of prediction values of the proposed method for methane, carbon monoxide, and carbon dioxide are, respectively, reduced by 4.74%, 21.76%, and 5.32% compared to those of PLS. Hence, the proposed method has higher predictive capabilities and better robustness.

Plasma ignition technology utilizes the plasma generated by an electrical explosion of a metal bridge foil under the action of a pulsed current to ignite an ignition charge. The plasma generated by the electrical explosion of a metal array bridge foil can be superimposed and converged to improve the energy utilization efficiency of the electrical explosion process and enhance the ignition capability. A multiphase-flow numerical calculation model of the electrical explosion plasma-ignition process was established, and numerical simulations were carried out. In the simulations, a plasma state equation that considers changes in the number of particles and the Coulomb interactions between particles was employed, and the Arrhenius law, which describes the exothermic heat of the ignition charge, was used. The ignition mechanism of the ignition charge under the action of plasma was analyzed, and the influences of the bridge foil structural characteristics on the ignition effect of the ignition charge were examined. The results of the calculations show that the plasma region, the plasma jet, and the pressure shock wave do not reach the ignition surface of the ignition charge when it is ignited. The ignition of the ignition charge is due to the thermal radiation process of the plasma. Compared to a single bridge foil, a metal array bridge foil has a larger plasma radiation region after an electrical explosion, and the ignition charge absorbs more energy from the plasma radiation, which is more favorable for ignition.

a] 4-amino-3-aminopyrazole-8-trinitropyrazolo- [5, 1-c] [1,2,4] triazine (PTX, C 5 H 2 N 8 O 6 ) has good detonation performance, thermal stability and low mechanical sensitivity, which endow it with good development prospects in insensitive ammunition applications. To study the effects of polymerization on the decomposition of PTX, the reaction processes of PTX at different conditions were simulated by quantum chemistry and molecular dynamics methods. In this paper, the effects of polymerization on the decomposition of PTX were studied in terms of species information, reaction path of PTX, bond formation and bond cleavage, evolution of small molecules and clusters, and kinetic parameters at different stages. The results show that under the high-temperature and high-pressure conditions, the initial reaction path of unimolecular PTX in the thermal decomposition is mainly the cleavage of CÀ NO 2 bonds. At the same time, there are many polymerization reactions in thermal decomposition process, which may greatly affect the reaction rate and path. The higher the degree of polymerization, the larger equilibrium value of potential energy, the less energy release of thermal decomposition. Compared with the activation energy of other explosives, the activation energy of PTX is higher than that of β-HMX and lower than that of TNT.