To investigate the influence of loading rate and high temperature on the dynamic fracture toughness of rock,dynamic fracture tests were carried out on notched semi-circular bend specimens under four temperature condit...To investigate the influence of loading rate and high temperature on the dynamic fracture toughness of rock,dynamic fracture tests were carried out on notched semi-circular bend specimens under four temperature conditions based on the split Hopkinson pressure bar system.Experimental and analytical methods were applied to investigating the effect of temperature gradient on the stress waves.A high-speed camera was used to check the fracture characteristics of the specimens.The results demonstrate that the temperature gradient on the bars will not significantly distort the shape of the stress wave.The dynamic force balance is achieved even when the specimens are at a temperature of 400°C.The dynamic fracture toughness linearly develops with the increase of loading rate within the temperature range of 25-400°C,and high temperature has a strengthening effect on the dynamic fracture toughness.展开更多
Zinc-air battery is one of the most promising next-generation energy conversion and storage systems.Green and low-cost catalysts with high oxygen reduction reaction(ORR)catalytic activity are desired to meet the requi...Zinc-air battery is one of the most promising next-generation energy conversion and storage systems.Green and low-cost catalysts with high oxygen reduction reaction(ORR)catalytic activity are desired to meet the requirements of Zinc-air batteries.Herein,poly-active centric Co3O4-CeO2/Co-N-C(ketjenblack carbon)catalysts were prepared by a facile method.The Co3O4 and CeO2 nanoparticles are uniformly anchored on the surface of Co and N doped carbon support.The half-wave potential of Co3O4-CeO2/Co-N-C in the rotating disk electrode testing is close to that of Pt/C.The Zn-air battery using Co3O4-CeO2/Co-N-C as the cathode catalyst can provide a high specific capacity of 728 mA h g^-1 at 20 mA cm^-2 and maintain a stable discharge voltage.The remarkable catalytic performance is mainly attributed to the synergistic effect among Co3O4,CeO2 and Co-N-C,the outstanding electrical conductivity and the large surface area.Benefitting from the high catalytic activity,environmental friendliness and the facile synthesis process,Co3O4-CeO2/Co-N-C catalyst lends itself well to a great prospect in the application of metalair batteries.展开更多
The classical Schwarz-Pick lemma and Julia lemma for holomorphic mappings on the unit disk D are generalized to real harmonic mappings of the unit disk, and the results are precise. It is proved that for a harmonic ma...The classical Schwarz-Pick lemma and Julia lemma for holomorphic mappings on the unit disk D are generalized to real harmonic mappings of the unit disk, and the results are precise. It is proved that for a harmonic mapping U of D into the open interval I = （-1, 1）, AU（z）/cosU（z）π/2≤4/π 1/1-｜z｜^2 holds for z E D, where Au（z） is the maximum dilation of U at z. The inequality is sharp for any z E D and any value of U（z）, and the equality occurs for some point in D if and only if U（z） = 4Re {arctan ~a（z）}, z E D, with a M＆bius transformation φa of D onto itself.展开更多
基金support from the National Natural Science Foundation of China(No.41972283)。
文摘To investigate the influence of loading rate and high temperature on the dynamic fracture toughness of rock,dynamic fracture tests were carried out on notched semi-circular bend specimens under four temperature conditions based on the split Hopkinson pressure bar system.Experimental and analytical methods were applied to investigating the effect of temperature gradient on the stress waves.A high-speed camera was used to check the fracture characteristics of the specimens.The results demonstrate that the temperature gradient on the bars will not significantly distort the shape of the stress wave.The dynamic force balance is achieved even when the specimens are at a temperature of 400°C.The dynamic fracture toughness linearly develops with the increase of loading rate within the temperature range of 25-400°C,and high temperature has a strengthening effect on the dynamic fracture toughness.
基金financial support from the Department of Science and Technology of Guangdong Province,China(2019A050510043)Shenzhen Science and Technology Innovation Commission(JCYJ20180507183818040)。
文摘Zinc-air battery is one of the most promising next-generation energy conversion and storage systems.Green and low-cost catalysts with high oxygen reduction reaction(ORR)catalytic activity are desired to meet the requirements of Zinc-air batteries.Herein,poly-active centric Co3O4-CeO2/Co-N-C(ketjenblack carbon)catalysts were prepared by a facile method.The Co3O4 and CeO2 nanoparticles are uniformly anchored on the surface of Co and N doped carbon support.The half-wave potential of Co3O4-CeO2/Co-N-C in the rotating disk electrode testing is close to that of Pt/C.The Zn-air battery using Co3O4-CeO2/Co-N-C as the cathode catalyst can provide a high specific capacity of 728 mA h g^-1 at 20 mA cm^-2 and maintain a stable discharge voltage.The remarkable catalytic performance is mainly attributed to the synergistic effect among Co3O4,CeO2 and Co-N-C,the outstanding electrical conductivity and the large surface area.Benefitting from the high catalytic activity,environmental friendliness and the facile synthesis process,Co3O4-CeO2/Co-N-C catalyst lends itself well to a great prospect in the application of metalair batteries.
基金supported by National Natural Science Foundation of China(Grant No.11071083)
文摘The classical Schwarz-Pick lemma and Julia lemma for holomorphic mappings on the unit disk D are generalized to real harmonic mappings of the unit disk, and the results are precise. It is proved that for a harmonic mapping U of D into the open interval I = （-1, 1）, AU（z）/cosU（z）π/2≤4/π 1/1-｜z｜^2 holds for z E D, where Au（z） is the maximum dilation of U at z. The inequality is sharp for any z E D and any value of U（z）, and the equality occurs for some point in D if and only if U（z） = 4Re {arctan ~a（z）}, z E D, with a M＆bius transformation φa of D onto itself.
