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Using a high temperature solid state reaction at 1600 ℃ for 6 h, (Nd1－xCax)(Al1－xFex)O3－x/2(x=0, 0.1, 0.2, 0.3) was synthesized by introducing Ca2+ and Fe3+ into NdAlO3, and spark plasma sintering (SPS) ceramic samples were used to investigate the effects of Ca2+ and Fe3+ addition on the phase composition, emissivity and ferroelasticity of NdAlO3. The results show that a solid solution can be successfully fabricated through the high temperature solid state reaction. The doping of Ca2+ and Fe3+ in NdAlO3 increases oxygen vacancies and slight lattice distortion occurs, emissivity of NdAlO3 within the wavelength range of 2.5-10 μm increases the maximum to 0.9. The introduction of impurity ions makes the phase gradually transform from rhombohedral to cubic, leading to the ferroelastic domains vanish. However, the fracture toughness of ceramic samples remains at a high level.

Based on the self-made Zr0.5Hf0.5C precursor and commercial liquid polycarbosilane, C/Zr0.5Hf0.5C-SiC composite was successfully prepared by the precursor impregnation and pyrolysis(PIP) process. The influence of the thickness of pyrolytic C coating on the structure and bending properties of composite materials was studied. The results show that the self-made Zr0.5Hf0.5C precursor can be converted into Zr0.5Hf0.5C solid solution at a relatively low temperature of 1400 ℃. Because of its good permeability, the transformed Zr0.5Hf0.5C matrix exists in both the inter-bundle and intra-bundle regions of the C/Zr0.5Hf0.5C-SiC composite, which presents as a layered structure on SiC matrix. The phase composition of C/Zr0.5Hf0.5C-SiC composite mainly includes C, SiC and Zr0.5Hf0.5C. The densities of three groups of composites with different thicknesses of pyrolytic C coating (0.67, 0.84, 1.36 μm) are 2.07, 1.99, 1.98 g/cm3, respectively. SiC content in the composite decreases with the increase of the thickness of pyrolytic C coating. The three groups of composites with different thicknesses show pseudoplastic fracture mode during bending loading tests, bending strength, bending modulus and fracture toughness are above 410 MPa, 60 GPa and 15.6 MPa·m1/2, respectively. Good interface bonding and pre-introduced SiC matrix are the keys to obtaining excellent bending properties of C/Zr0.5Hf0.5C-SiC composites.

Using carbon fiber cloth with different areal densities and tow sizes, two kinds of carbon fiber preforms with same carbon cloth laminated structure were produced through different z-direction stitching methods. Then, C/C-SiC composites were prepared by combining chemical vapor infiltration (CVI) with gas silicon infiltration (GSI). The influence of carbon fiber preform structure on the microstructure and mechanical properties of CVI-GSI C/C-SiC composites was studied. The results show that the density, phase composition, structure, and properties of the two composites prepared from preforms with the same fiber volume fraction and C/C preform density are significantly different. The smaller carbon fiber tow (1K) and carbon cloth surface density (92 g/m2), as well as the larger voids left by lock stitching, provide more sufficient channels for the infiltration of Si vapor in the GSI reaction process. Thus T1 composite finally prepared has low porosity, uniform structure, and higher performance, with bending strength, modulus, and fracture toughness of 300.97 MPa, 51.75 GPa, and 11.32 MPa·m1/2, respectively. The comprehensive control of the initial preform structure and the C/C intermediate structure is the key to the preparation of high performance C/C-SiC composites by the CVI-GSI process.

Unmanned aerial vehicle(UAV)with the advantages of high effectiveness and flexible autonomy has gradually replaced manned aircraft to combat,and multi-UAV cooperative combat mission planning becomes the hot research issue.An end-to-end cooperative attack intelligent planning method for multi-UAV based on deep reinforcement learning(DRL)is presented to overcome the shortcomings of traditional mission planning algorithms,such as static dependence,low-dimensional simple scenarios and slow on-board computing speed.The suppression of enemy air defense(SEAD)mission planning is modeled as the Markov decision process.The SEAD intelligent planning model based on proximal policy optimization(PPO)algorithm is established,and two groups of experiments are used to verify the effectiveness and robustness of the intelligent planning model.The results show that the DRL-based intelligent planning method can realize fast and fine planning,adapt to unknown,continuous and high-dimensional environment situation.The SEAD intelligent planning model has the capacity of tactics cooperative planning.

Deoxyribonucleic acid (DNA), an important material in life science, is considered a natural and highly specific functional biopolymer. Various analytical techniques were used to analyze the interaction of chrysene with free DNA in vitro, and based on this interaction, we studied the removal of chrysene from contaminated water by DNA via magnetic beads-based separation. The results of UV-visible spectroscopy, DNA thermal denaturation measurement, circular dichroism (CD) spectroscopy, and fluorescence microscopy showed that chrysene interacted with DNA through an intercalating mode. The results of fluorescence spectroscopy demonstrated that DNA had a static quenching effect on chrysene, indicating the formation of a stable complex between chrysene and DNA. Thermodynamic studies revealed that the interaction of chrysene with free DNA was spontaneous in vitro. In addition, chrysene could be efficiently removed from contaminated water by DNA via DNA-intercalation and magnetic bead-based separation. The chrysene removal efficiency of DNA was better than that of activated carbon even when the amount of activated carbon was 400 times more than that of DNA. The results of this study provide insights into the development of new chrysene elimination processes based on DNA-intercalation in water pollution., Polycyclic aromatic hydrocarbons (PAHs) are the most abundant environmental pollutants, and are composed of two or more benzene rings connected via fused rings (1,2). Many natural and man-made activities, such [...]