在混合均匀的铜颗粒和玻璃颗粒受到不同加速度Г和频率f的正弦振动怍用下,获得了巴西果(BN)、反巴西果(RBN)、三明治(Sandwich)的不同分层相构型及其相图,首次观测到小颗粒在上大颗粒在下的稳定的反巴西果分层(reverse Brazil Nut segre...在混合均匀的铜颗粒和玻璃颗粒受到不同加速度Г和频率f的正弦振动怍用下,获得了巴西果(BN)、反巴西果(RBN)、三明治(Sandwich)的不同分层相构型及其相图,首次观测到小颗粒在上大颗粒在下的稳定的反巴西果分层(reverse Brazil Nut segregation)现象,还观测到区分不同分层区域的Г值具有滞后效应,表明分层过程与系统的初始条件有关.展开更多
A dragonfly wing consists of membranes and both longitudinal and cross veins.We observed the microstructure cross-section at several locations in the dragonfly wing using environmental scanning electron microscopy(ESE...A dragonfly wing consists of membranes and both longitudinal and cross veins.We observed the microstructure cross-section at several locations in the dragonfly wing using environmental scanning electron microscopy(ESEM).The organic nature of the junction between the vein and the membrane was clearly identifiable.The membrane was divided into two layers,the upper epidermis and the lower epidermis.These layers extend around the sandwich structure vein,and combine with the adjacent membrane at a symmetrical location along the vein.Thus,we defined this as an organic junction between the vein and the membranes. The organic junction is able to form a tight corrugation angle,which dramatically increases both the warping rigidity and the strength of the wing,but not the torsional rigidity.The torsional deformation is primarily controlled by the microstructure of the longitudinal veins,and is based on the relative rotation angle between the epidermal layer and the inner layer of the vein that forms the zigzag section.展开更多
Developing low-cost, high-performance elec- trocatalysts for the oxygen reduction reaction （ORR） is crucial for implementation of fuel cells and metal-air batteries into practical applications. Graphene-based cataly...Developing low-cost, high-performance elec- trocatalysts for the oxygen reduction reaction （ORR） is crucial for implementation of fuel cells and metal-air batteries into practical applications. Graphene-based catalysts have been extensively investigated for ORR in alkaline electrolytes. However, their performance in acidic electrolytes still requires further improvement compared to the Pt/C catalyst. Here we report a self-templating approach to prepare graphene-based sandwich-like porous carbon nanosheets for efficient ORR in both alkaline and acidic electrolytes. Graphene oxides were first used to adsorb m-phenylenediamine molecules which can form a nitrogen-rich polymer network after oxidative poly- merization. Then iron （Fe） salt was introduced into the polymer network and transformed into ORR active Fe-N-C sites along with Fe, FeS, and FEN0.05 nanopartides after pyr- olysis, generating ORR active sandwich-like carbon na- nosheets. Due to the presence of multiple ORR active sites. The as-obtained catalyst exhibited prominent ORR activity with a half-wave potential -30 mV more positive than Pt/C in 0.1 mol L-1 KOH, while the half-wave potential of the catalyst was only -40 mV lower than that of commercial Pt/C in 0.1 mol L-1 HClO4. The unique planar sandwich-like structure could expose abundant active sites for ORR. Meanwhile, the graphene layer and porous structure could simultaneously enhance electrical conductivity and facilitate mass transport. The prominent electrocatalytic activity and durability in both alkaline and acidic electrolytes indicate that these carbon na- nosheets hold great potential as alternatives to precious metal- based catalysts, as demonstrated in zinc-air batteries and proton exchange membrane fuel cells.展开更多
文摘在混合均匀的铜颗粒和玻璃颗粒受到不同加速度Г和频率f的正弦振动怍用下,获得了巴西果(BN)、反巴西果(RBN)、三明治(Sandwich)的不同分层相构型及其相图,首次观测到小颗粒在上大颗粒在下的稳定的反巴西果分层(reverse Brazil Nut segregation)现象,还观测到区分不同分层区域的Г值具有滞后效应,表明分层过程与系统的初始条件有关.
基金supported by the National Natural Science Foundation of China (10772091, 11072124)the National Basic Research Program of China (2007CB936803, 2010CB631006)
文摘A dragonfly wing consists of membranes and both longitudinal and cross veins.We observed the microstructure cross-section at several locations in the dragonfly wing using environmental scanning electron microscopy(ESEM).The organic nature of the junction between the vein and the membrane was clearly identifiable.The membrane was divided into two layers,the upper epidermis and the lower epidermis.These layers extend around the sandwich structure vein,and combine with the adjacent membrane at a symmetrical location along the vein.Thus,we defined this as an organic junction between the vein and the membranes. The organic junction is able to form a tight corrugation angle,which dramatically increases both the warping rigidity and the strength of the wing,but not the torsional rigidity.The torsional deformation is primarily controlled by the microstructure of the longitudinal veins,and is based on the relative rotation angle between the epidermal layer and the inner layer of the vein that forms the zigzag section.
基金supported by the National Basic Research Program of China (973 Program, 2015CB351903)the National Key Research and Development Program (2017YFA0207301)+1 种基金the National Natural Science Foundation of China (51402282, 21474095 and 21476104)CAS Key Research Program of Frontier Sciences (QYZDB-SSW-SLH018)
文摘Developing low-cost, high-performance elec- trocatalysts for the oxygen reduction reaction （ORR） is crucial for implementation of fuel cells and metal-air batteries into practical applications. Graphene-based catalysts have been extensively investigated for ORR in alkaline electrolytes. However, their performance in acidic electrolytes still requires further improvement compared to the Pt/C catalyst. Here we report a self-templating approach to prepare graphene-based sandwich-like porous carbon nanosheets for efficient ORR in both alkaline and acidic electrolytes. Graphene oxides were first used to adsorb m-phenylenediamine molecules which can form a nitrogen-rich polymer network after oxidative poly- merization. Then iron （Fe） salt was introduced into the polymer network and transformed into ORR active Fe-N-C sites along with Fe, FeS, and FEN0.05 nanopartides after pyr- olysis, generating ORR active sandwich-like carbon na- nosheets. Due to the presence of multiple ORR active sites. The as-obtained catalyst exhibited prominent ORR activity with a half-wave potential -30 mV more positive than Pt/C in 0.1 mol L-1 KOH, while the half-wave potential of the catalyst was only -40 mV lower than that of commercial Pt/C in 0.1 mol L-1 HClO4. The unique planar sandwich-like structure could expose abundant active sites for ORR. Meanwhile, the graphene layer and porous structure could simultaneously enhance electrical conductivity and facilitate mass transport. The prominent electrocatalytic activity and durability in both alkaline and acidic electrolytes indicate that these carbon na- nosheets hold great potential as alternatives to precious metal- based catalysts, as demonstrated in zinc-air batteries and proton exchange membrane fuel cells.
