特高压变电站1 000 k V系统采用3/2主接线,由于导电主回路电阻不平衡度较大及特高压变电站输送容量大,导致3/2主接线系统存在较大幅值的不平衡环流,极端情况下个别断路器相电流有过零甚至反相现象。结合特高压南阳站,从理论上分析不平...特高压变电站1 000 k V系统采用3/2主接线,由于导电主回路电阻不平衡度较大及特高压变电站输送容量大,导致3/2主接线系统存在较大幅值的不平衡环流,极端情况下个别断路器相电流有过零甚至反相现象。结合特高压南阳站,从理论上分析不平衡环流中零序分量及其产生原因;论述了大负荷运行期间零序环流给站内二次系统带来的显著问题和严重后果;提出保护装置采用两断路器合流、单断路器最小相电流制动零序电流元件和两断路器合流制动单断路器零序电流元件的几种解决方案。以期后续交流特高压工程对此有足够的重视,供设计、施工和运行维护借鉴。展开更多
The Dahurian larch forest in northeast China is important due to its vastness and location within a transitional zone from boreal to temperate and at the southern distribution edge of the vast Siberian larch forest. T...The Dahurian larch forest in northeast China is important due to its vastness and location within a transitional zone from boreal to temperate and at the southern distribution edge of the vast Siberian larch forest. The continuous carbon fluxes were measured from May 2004 to April 2005 in the Dahurian larch forest in Northeast China using an eddy covariance method. The results showed that the ecosystem released carbon in the dormant season from mid-October 2004 to April 2005, while it assimilated CO2 from the atmosphere in the growing season from May to September 2004. The net carbon sequestration reached its peak of 112 g.m^-2.month ^-1 in June 2004 （simplified expression of g （carbon）.m^-2.month^-1） and then gradually decreased. Annually, the larch forest was a carbon sink that sequestered carbon of 146 g-m^-2.a^-1 （simplified expression of g （carbon）.m^-2.a^-1） during the measurements. The photosynthetic process of the larch forest ecosystem was largely affected by the vapor pressure deficit （VPD） and temperature. Under humid conditions （VPD 〈 1.0 kPa）, the gross ecosystem production （GEP） increased with increasing temperature. But the net ecosystem production （NEP） showed almost no change with increasing temperature because the increment of GEP was counterbalanced by that of the ecosystem respiration. Under a dry environment （VPD 〉 1.0 kPa）, the GEP decreased with the increasing VPD at a rate of 3.0 μmol.m^-2.s^-1kPa -1 and the ecosystem respiration was also enhanced simultaneously due to the increase of air temperature, which was linearly correlated with the VPD. As a result, the net ecosystem carbon sequestration rapidly decreased with the increasing VPD at a rate of 5.2 μmol.m^-2.s-1.kPa^-1. Under humid conditions （VPD 〈 1.0 kPa）, both the GEP and NEP were obviously restricted by the low air temperature but were insensitive to the high temperature because the observed high temperature value comes within the category of the optimum range.展开更多
One dimensional periodic hopping model is useful to understand the motion of microscopic particles in thermal noise environment. In this research, by formal calculation and based on detailed balance, the explicit expr...One dimensional periodic hopping model is useful to understand the motion of microscopic particles in thermal noise environment. In this research, by formal calculation and based on detailed balance, the explicit expressions of the limits of mean velocity and diffusion constant of this model as the number of internal mechanochemical sates tend to infinity are obtained.These results will be helpful to understand the limit of the one dimensional hopping model.At the same time, the work can be used to get more useful results in continuous form from the corresponding ones obtained by discrete models.展开更多
The article presents a population balance model by mass developed for studying char gasification by steam occuring in a fluidized bed. The model has been validated by comparison with existing theoretical and experimen...The article presents a population balance model by mass developed for studying char gasification by steam occuring in a fluidized bed. The model has been validated by comparison with existing theoretical and experimental cases. Its main goal is to have a better understanding on particles size distribution behaviour during operation of the fluidized bed, and in particular to be applied on the case of Fast Internally Circulating Fluidized Beds for char gasification. Results have shown that the initial properties of the fluidized bed particles （bed and size distribution） are almost not involved in the steady state obtained in continous operation, which is excusively dependent on the properties of the fed particles flow rate and size distribution, the withdrawal flow rate and the reaction properties. Morevoer, it has been proven that the steady state fluidized bed mass and size distribution may be theroretically controlled by an adequate choice of feeding and withdrawal flow rates.展开更多
The Antarctic Circumpolar Current (ACC) and its associated Meridional Overturning Circulation (MOC) is investigated through a nonlinear inertia theory model, which consists of two layers--an upper Ekman layer driven m...The Antarctic Circumpolar Current (ACC) and its associated Meridional Overturning Circulation (MOC) is investigated through a nonlinear inertia theory model, which consists of two layers--an upper Ekman layer driven mainly by sea surface wind stress and a lower thermocline controlled by ideal fluid nonlinear equations which can be solved by identifying the form of the arbitrary functions. The results show that the thermocline has a two-equilibrium solution though given the same Ekman layer condition. Compared to the first equilibrium, the second one has a heavier intensity and deeper circulation, which seems more consistent with the existing data.展开更多
By using the global atmospheric general circulation model CAM4.0 including an urban canopy parameterization scheme,the possible impacts of large-scale urbanization in East China on East Asian winter monsoon was invest...By using the global atmospheric general circulation model CAM4.0 including an urban canopy parameterization scheme,the possible impacts of large-scale urbanization in East China on East Asian winter monsoon was investigated via idealized numerical experiments.Results suggest that large-scale urbanization can cause a significant warming effect in both surface temperature and air temperature near the surface over most areas of East China.Meanwhile,large-scale urbanization also alters the surface energy balance,causing evident increases in net surface long-wave radiation and sensible heat flux as well as intensified surface thermal heating to the atmosphere.Forced by the surface thermal heating anomalies induced by the large-scale urban expansion,East Asian winter monsoon circulation exhibits distinct changes.Overall,the extensive urbanization over East China will weaken East Asian winter monsoon,but intensify winter monsoon in northeast China.展开更多
Recently,by combining a swirl flow with non-equilibrium condensation phenomena of condensate gas generated in a supersonic flow,a separating and extracting techniques of condensate gas have been developed.This techniq...Recently,by combining a swirl flow with non-equilibrium condensation phenomena of condensate gas generated in a supersonic flow,a separating and extracting techniques of condensate gas have been developed.This technique can reduce the size of the device and don't use chemicals.In the present study,by using a non-equilibrium condensation phenomenon of moist air occurred in the supersonic flow in the annular nozzle composed of an inher body and an outer nozzle with a swirl,the possibility of separation of the condensable gas and the effect of shape of nozzle inlet on the flow field were examined numerically.展开更多
文摘特高压变电站1 000 k V系统采用3/2主接线,由于导电主回路电阻不平衡度较大及特高压变电站输送容量大,导致3/2主接线系统存在较大幅值的不平衡环流,极端情况下个别断路器相电流有过零甚至反相现象。结合特高压南阳站,从理论上分析不平衡环流中零序分量及其产生原因;论述了大负荷运行期间零序环流给站内二次系统带来的显著问题和严重后果;提出保护装置采用两断路器合流、单断路器最小相电流制动零序电流元件和两断路器合流制动单断路器零序电流元件的几种解决方案。以期后续交流特高压工程对此有足够的重视,供设计、施工和运行维护借鉴。
基金the Global Environment Research Fund,Ministry of the Environment,Japan (S-1: Integrated Study for Terrestrial Carbon Management of Asia in the 21st Century Based on Scientific Advancements)the Chinese Academy of Sciences (07W70000SZ)+1 种基金the National Natural Science Foundation of China (30300271)the State Key Basic Research and Development Plan of China (2004CCA02700)
文摘The Dahurian larch forest in northeast China is important due to its vastness and location within a transitional zone from boreal to temperate and at the southern distribution edge of the vast Siberian larch forest. The continuous carbon fluxes were measured from May 2004 to April 2005 in the Dahurian larch forest in Northeast China using an eddy covariance method. The results showed that the ecosystem released carbon in the dormant season from mid-October 2004 to April 2005, while it assimilated CO2 from the atmosphere in the growing season from May to September 2004. The net carbon sequestration reached its peak of 112 g.m^-2.month ^-1 in June 2004 （simplified expression of g （carbon）.m^-2.month^-1） and then gradually decreased. Annually, the larch forest was a carbon sink that sequestered carbon of 146 g-m^-2.a^-1 （simplified expression of g （carbon）.m^-2.a^-1） during the measurements. The photosynthetic process of the larch forest ecosystem was largely affected by the vapor pressure deficit （VPD） and temperature. Under humid conditions （VPD 〈 1.0 kPa）, the gross ecosystem production （GEP） increased with increasing temperature. But the net ecosystem production （NEP） showed almost no change with increasing temperature because the increment of GEP was counterbalanced by that of the ecosystem respiration. Under a dry environment （VPD 〉 1.0 kPa）, the GEP decreased with the increasing VPD at a rate of 3.0 μmol.m^-2.s^-1kPa -1 and the ecosystem respiration was also enhanced simultaneously due to the increase of air temperature, which was linearly correlated with the VPD. As a result, the net ecosystem carbon sequestration rapidly decreased with the increasing VPD at a rate of 5.2 μmol.m^-2.s-1.kPa^-1. Under humid conditions （VPD 〈 1.0 kPa）, both the GEP and NEP were obviously restricted by the low air temperature but were insensitive to the high temperature because the observed high temperature value comes within the category of the optimum range.
基金ACKNOWLEDGMENTS This work was supported by the National Natural Science Foundation of China （No.10701029） and the Shanghai Key Laboratory for Contemporary Applied Mathematics （No.SGST09DZ2272900）.
文摘One dimensional periodic hopping model is useful to understand the motion of microscopic particles in thermal noise environment. In this research, by formal calculation and based on detailed balance, the explicit expressions of the limits of mean velocity and diffusion constant of this model as the number of internal mechanochemical sates tend to infinity are obtained.These results will be helpful to understand the limit of the one dimensional hopping model.At the same time, the work can be used to get more useful results in continuous form from the corresponding ones obtained by discrete models.
文摘The article presents a population balance model by mass developed for studying char gasification by steam occuring in a fluidized bed. The model has been validated by comparison with existing theoretical and experimental cases. Its main goal is to have a better understanding on particles size distribution behaviour during operation of the fluidized bed, and in particular to be applied on the case of Fast Internally Circulating Fluidized Beds for char gasification. Results have shown that the initial properties of the fluidized bed particles （bed and size distribution） are almost not involved in the steady state obtained in continous operation, which is excusively dependent on the properties of the fed particles flow rate and size distribution, the withdrawal flow rate and the reaction properties. Morevoer, it has been proven that the steady state fluidized bed mass and size distribution may be theroretically controlled by an adequate choice of feeding and withdrawal flow rates.
基金supported by National Basic Research Program of China (Grant No. 2010CB950300)
文摘The Antarctic Circumpolar Current (ACC) and its associated Meridional Overturning Circulation (MOC) is investigated through a nonlinear inertia theory model, which consists of two layers--an upper Ekman layer driven mainly by sea surface wind stress and a lower thermocline controlled by ideal fluid nonlinear equations which can be solved by identifying the form of the arbitrary functions. The results show that the thermocline has a two-equilibrium solution though given the same Ekman layer condition. Compared to the first equilibrium, the second one has a heavier intensity and deeper circulation, which seems more consistent with the existing data.
基金supported by the National Basic Research Program of China(2010CB428505 and 2011CB952004)Project Funded by the Priority Academic Program Development of Jiangsu Higher Education Institu-tions(PAPD)
文摘By using the global atmospheric general circulation model CAM4.0 including an urban canopy parameterization scheme,the possible impacts of large-scale urbanization in East China on East Asian winter monsoon was investigated via idealized numerical experiments.Results suggest that large-scale urbanization can cause a significant warming effect in both surface temperature and air temperature near the surface over most areas of East China.Meanwhile,large-scale urbanization also alters the surface energy balance,causing evident increases in net surface long-wave radiation and sensible heat flux as well as intensified surface thermal heating to the atmosphere.Forced by the surface thermal heating anomalies induced by the large-scale urban expansion,East Asian winter monsoon circulation exhibits distinct changes.Overall,the extensive urbanization over East China will weaken East Asian winter monsoon,but intensify winter monsoon in northeast China.
文摘Recently,by combining a swirl flow with non-equilibrium condensation phenomena of condensate gas generated in a supersonic flow,a separating and extracting techniques of condensate gas have been developed.This technique can reduce the size of the device and don't use chemicals.In the present study,by using a non-equilibrium condensation phenomenon of moist air occurred in the supersonic flow in the annular nozzle composed of an inher body and an outer nozzle with a swirl,the possibility of separation of the condensable gas and the effect of shape of nozzle inlet on the flow field were examined numerically.
