线束中四直线交比定义的讨论

对梅向明等编《高等几何》关于线束中四直线交比的内容作重新编排，既保证其内容的完整性，又弥补原书理论上的不足．     

Structure and Performance of Fe-N_x-C Catalyst for Oxygen Reduction Reaction Prepared by Vacuum Casting Method and the Second Pyrolysis

Affordable non-precious metal(NPM) catalysts played a vital role in the wide application of polymer electrolyte membrane fuel cells(PEMFC). In current work, a facile vacuum casting reacting method based on vacuum casting was introduced to prepare Fe-N_x-C oxygen reduction reaction(ORR) catalysts with high efficient in acid medium. The catalysts were prepared with ammonium ferrous sulfate hexahydrate(AFS) and 1,10-phenanthroline monohydrate utilizing homemade mesoporous silica template. The heat treatment and its influence on structure and performance were systematically evaluated to achieve superior ORR performance and some clues were found. And 850 ℃ was found to be the best temperature for the first and second pyrolysis. The linear sweep voltammetry(LSV) results showed that there were only 18 mV slightly negative shifts of half-wave potential(E_(1/2)) of the optimal catalyst(749 mV) compared with the commercial Pt/C(20 μg·Pt·cm~(-2)). Besides, I850 R also showed better electrochemical stability and methanol-tolerance than that of Pt/C. All evidences proved that our vacuum casting reacting strategy and heat treatment process were prospective for the future RD of high performance Fe-N_x-C ORR catalysts.     

我国农村小城镇建设探微

通过对我国农村小城镇建设的探究,从缓解大城市社会资源方面的压力、以小城镇建设促进新农村发展两个方面分析了当前强化农村小城镇建设的必要性,指出科学规划、资金短缺是农村小城镇建设面临的重要问题,提出了科学规划发展蓝图、大力发展当地经济等对策与相关建议.