Stable homogeneous suspensions of multi-walled carbon nanotubes （MWCNTs） were prepared using gum arabic （GA） as dispersant and were incorporated to Portland cement paste. The dispersion was examined by ultraviolet...Stable homogeneous suspensions of multi-walled carbon nanotubes （MWCNTs） were prepared using gum arabic （GA） as dispersant and were incorporated to Portland cement paste. The dispersion was examined by ultraviolet visible spectroscopy （UV-vis）, and the concentration measurement shows that the optimum concentration of GA is 0.45 g · L^-1. The dispersibility of the surface-modified MWCNTs in aqueous solution and cement matrix were investigated by transmission electron microscopy （TEM） and energy dispersive spectroscopy （EDS）, and the mechanical properties of the composites were investigated. The results show that the addition of the treated nanotubes can improve both the flexural strength and the compressive strength of the Portland cement composite significantly. The flexural strength of the composite increases up to 43.38% with the MWCNT concentration of 0.08% （by weight of cement）. The porosity and pore size distribution of the composites were measured by mercury intrusion porosimetry （MIP）, and the results indicate that the cement paste doped with MWCNTs obtained lower porosity and concentrated pore size distribution. The morphological structure was analyzed by field emission scanning electron microscopy （FESEM） and EDS. It is shown that MWCNTs act as bridges and networks across cracks and voids, which transfer the load in case of tension, and the interface bond strength between the nanotubes and matrix is very strong.展开更多
The efficiency of the seaport has been variously studied utilizing either data envelopment analysis( DEA) or stochastic Frontier analysis( SFA). Given the strengths and weaknesses associated with these two approaches,...The efficiency of the seaport has been variously studied utilizing either data envelopment analysis( DEA) or stochastic Frontier analysis( SFA). Given the strengths and weaknesses associated with these two approaches, applying both models to compute efficiency estimates for the 11 seaports of the China and Korea from 2012-2016 and comparing the results obtained. Main finding facts of this paper are as follows:( i) there are some differences among relative efficiency levels,but almost no differences among efficiency ranks in DEA and SFA results.( ii) The tendency of VRS is stronger in Chinese coastal seaports during the past several years.( iii) The values among seaports in SFA model are relatively smaller than those in the DEA models. The results show that the efficiency of major seaports in Korea is far lower than that of ports in China.展开更多
基金Funded by the National Natural Science Foundation of China(Nos.51278086,51178085)the Program for New Century Excellent Talentsin University(NCET)+1 种基金the State Key Laboratory of Coastal and Offshore Engineering(No.LP1109)the Fundamental Research Funds for the Central Universities(No.DUT11NY11)
文摘Stable homogeneous suspensions of multi-walled carbon nanotubes （MWCNTs） were prepared using gum arabic （GA） as dispersant and were incorporated to Portland cement paste. The dispersion was examined by ultraviolet visible spectroscopy （UV-vis）, and the concentration measurement shows that the optimum concentration of GA is 0.45 g · L^-1. The dispersibility of the surface-modified MWCNTs in aqueous solution and cement matrix were investigated by transmission electron microscopy （TEM） and energy dispersive spectroscopy （EDS）, and the mechanical properties of the composites were investigated. The results show that the addition of the treated nanotubes can improve both the flexural strength and the compressive strength of the Portland cement composite significantly. The flexural strength of the composite increases up to 43.38% with the MWCNT concentration of 0.08% （by weight of cement）. The porosity and pore size distribution of the composites were measured by mercury intrusion porosimetry （MIP）, and the results indicate that the cement paste doped with MWCNTs obtained lower porosity and concentrated pore size distribution. The morphological structure was analyzed by field emission scanning electron microscopy （FESEM） and EDS. It is shown that MWCNTs act as bridges and networks across cracks and voids, which transfer the load in case of tension, and the interface bond strength between the nanotubes and matrix is very strong.
基金Qianjiang Talent Plan,China(No.QJC1402014)National Natural Science Foundation of China(No.71473235)+1 种基金National Social Science Foundation of China(No.17BGJ018)Natural Science Foundation of Zhejiang Province,China(LY15G030027)
文摘The efficiency of the seaport has been variously studied utilizing either data envelopment analysis( DEA) or stochastic Frontier analysis( SFA). Given the strengths and weaknesses associated with these two approaches, applying both models to compute efficiency estimates for the 11 seaports of the China and Korea from 2012-2016 and comparing the results obtained. Main finding facts of this paper are as follows:( i) there are some differences among relative efficiency levels,but almost no differences among efficiency ranks in DEA and SFA results.( ii) The tendency of VRS is stronger in Chinese coastal seaports during the past several years.( iii) The values among seaports in SFA model are relatively smaller than those in the DEA models. The results show that the efficiency of major seaports in Korea is far lower than that of ports in China.
