Durable and inexpensive graphitic carbon nitride(g-C_(3)N_(4))demonstrates great potential for achieving efficient photocatalytic hydrogen evolution reduction(HER).To further improve its activity,g-C_(3)N_(4)was subje...Durable and inexpensive graphitic carbon nitride(g-C_(3)N_(4))demonstrates great potential for achieving efficient photocatalytic hydrogen evolution reduction(HER).To further improve its activity,g-C_(3)N_(4)was subjected to atomic-level structural engineering by doping with transition metals(M=Fe,Co,or Ni),which simultaneously induced the formation of metal-N active sites in the g-C_(3)N_(4)framework and modulated the bandgap of g-C_(3)N_(4).Experiments and density functional theory calculations further verified that the as-formed metal-N bonds in M-doped g-C_(3)N_(4)acted as an"electron transfer bridge",where the migration of photo-generated electrons along the bridge enhanced the efficiency of separation of the photogenerated charges,and the optimized bandgap of g-C_(3)N_(4)afforded stronger reduction ability and wider light absorption.As a result,doping with either Fe,Co,or Ni had a positive effect on the HER activity,where Co-doped g-C_(3)N_(4)exhibited the highest performance.The findings illustrate that this atomic-level structural engineering could efficiently improve the HER activity and inspire the design of powerful photocatalysts.展开更多
The Lancaster House negotiations from September 1979 to the close of the year sought to bring to an end the chapter of the Second Chimurenga of Zimbabwe. Outside discussions on the land issue, one of the agreements ma...The Lancaster House negotiations from September 1979 to the close of the year sought to bring to an end the chapter of the Second Chimurenga of Zimbabwe. Outside discussions on the land issue, one of the agreements made at the Lancaster was that 12 Assembly Points be set up throughout the country to house guerrillas and initiate a demobilising exercise. Each was to be manned by a small contingent of the British Army and all the Zimbabwean National Liberation Army （ZANLA） and Zimbabwe People＇s Revolution Army （ZIPRA） guerrillas, in any one area, were to go to the closest assembly point. The Assembly Points, which included Dzapasi/Foxtrot in Buhera, Chitungwiza, Connemara, and Mike in Lupane, at one time housed 17,000 guerrillas. Tension was very high inside and outside these Assembly Points. In 1980, there were sporadic outbursts of violence around these points all over the country. The fights recurred in 1983 killing over 300 people. This research proposes to pore over the nature of the violence in this historical epoch to try and understand its roots as well as to establish whether attempts at accountability, reconciliation, healing, and integration were made after the Assembly Points era and if not, whither Zimbabwe？展开更多
The performance of a reversible pump turbine with S-shaped characteristics is of great importance to the transition processes such as start-up and load rejection. In order to predict the S-shaped curve accurately and ...The performance of a reversible pump turbine with S-shaped characteristics is of great importance to the transition processes such as start-up and load rejection. In order to predict the S-shaped curve accurately and develop a reliable tool for design improvement, a shear stress transport model (SST) with various numerical schemes for pressure term in the governing equation was investigated in a whole pump turbine including spiral casing, stay vanes, guide vanes, runner and draft tube. Through the computation, it was shown that different zones in the curve should employ different schemes to get the solution converged. Comparison of discharge-speed performance showed that good correspondence is got between experimental data and CFD results. Based on this, internal flow analysis was carried out at three typical operating points representing turbine mode, shut-off mode and reversible pump mode, respectively. According to the flow field concerned, the mechanism for the speed-no-load instability was explained, which provides good guidelines to take countermeasures in future design.展开更多
文摘Durable and inexpensive graphitic carbon nitride(g-C_(3)N_(4))demonstrates great potential for achieving efficient photocatalytic hydrogen evolution reduction(HER).To further improve its activity,g-C_(3)N_(4)was subjected to atomic-level structural engineering by doping with transition metals(M=Fe,Co,or Ni),which simultaneously induced the formation of metal-N active sites in the g-C_(3)N_(4)framework and modulated the bandgap of g-C_(3)N_(4).Experiments and density functional theory calculations further verified that the as-formed metal-N bonds in M-doped g-C_(3)N_(4)acted as an"electron transfer bridge",where the migration of photo-generated electrons along the bridge enhanced the efficiency of separation of the photogenerated charges,and the optimized bandgap of g-C_(3)N_(4)afforded stronger reduction ability and wider light absorption.As a result,doping with either Fe,Co,or Ni had a positive effect on the HER activity,where Co-doped g-C_(3)N_(4)exhibited the highest performance.The findings illustrate that this atomic-level structural engineering could efficiently improve the HER activity and inspire the design of powerful photocatalysts.
文摘The Lancaster House negotiations from September 1979 to the close of the year sought to bring to an end the chapter of the Second Chimurenga of Zimbabwe. Outside discussions on the land issue, one of the agreements made at the Lancaster was that 12 Assembly Points be set up throughout the country to house guerrillas and initiate a demobilising exercise. Each was to be manned by a small contingent of the British Army and all the Zimbabwean National Liberation Army （ZANLA） and Zimbabwe People＇s Revolution Army （ZIPRA） guerrillas, in any one area, were to go to the closest assembly point. The Assembly Points, which included Dzapasi/Foxtrot in Buhera, Chitungwiza, Connemara, and Mike in Lupane, at one time housed 17,000 guerrillas. Tension was very high inside and outside these Assembly Points. In 1980, there were sporadic outbursts of violence around these points all over the country. The fights recurred in 1983 killing over 300 people. This research proposes to pore over the nature of the violence in this historical epoch to try and understand its roots as well as to establish whether attempts at accountability, reconciliation, healing, and integration were made after the Assembly Points era and if not, whither Zimbabwe？
基金supported by the National Natural Science Foundation of China (Grant No. 50979095)
文摘The performance of a reversible pump turbine with S-shaped characteristics is of great importance to the transition processes such as start-up and load rejection. In order to predict the S-shaped curve accurately and develop a reliable tool for design improvement, a shear stress transport model (SST) with various numerical schemes for pressure term in the governing equation was investigated in a whole pump turbine including spiral casing, stay vanes, guide vanes, runner and draft tube. Through the computation, it was shown that different zones in the curve should employ different schemes to get the solution converged. Comparison of discharge-speed performance showed that good correspondence is got between experimental data and CFD results. Based on this, internal flow analysis was carried out at three typical operating points representing turbine mode, shut-off mode and reversible pump mode, respectively. According to the flow field concerned, the mechanism for the speed-no-load instability was explained, which provides good guidelines to take countermeasures in future design.
