Agriculture is still the biggest contributor of non-point source (NPS) pollution to water bodies andrunoff discharges of nutrients and other chemicals are one of the most important pathways. This studywas conducted du...Agriculture is still the biggest contributor of non-point source (NPS) pollution to water bodies andrunoff discharges of nutrients and other chemicals are one of the most important pathways. This studywas conducted during 1998～1999 in a typical watershed with complex agriculture and forestry systems aswell as dotted farmer villages, in a transitional region between the mid- and northern subtropical zones ofChina. Continuous sampling of stream water was performed regularly at a weekly frequency, with additionalsampling after all major rainfall events. The discharges of N and P nutrients and suspended materials weremeasured and the total and area-averaged annual discharges of all components were calculated. The resultsshowed an uneven seasonal distribution of nutrient discharges with summer storms contributing most tothe total fluxes. This study demonstrated a high dependence of runoff volume on rainfall but the overallrunoff coefficients were dependent on land use type and watershed size. The area-averaged annual dischargesvaried greatly among the sub-watersheds with different sizes and land use structures. This is the first studyestimating the area-averaged annual discharges of N and P in the hilly areas of subtropical China, which were1.5 g m-2 a-1 and 0.1 g m-2 a-1, respectively, providing important reference values for the assessment ofregional agricultural non-point source pollution.展开更多
This study, based on the literature, stresses the effectiveness of internal control systems for the prevention, to a reasonable extent, of fraudulent practices that cause resource loss in business. In this context, th...This study, based on the literature, stresses the effectiveness of internal control systems for the prevention, to a reasonable extent, of fraudulent practices that cause resource loss in business. In this context, the key concepts related to fraud and internal control systems are presented first. After the introduction, the relation between fraud and internal control systems is elaborated, and the method for establishing an effective internal control system which is needed to detect and prevent fraud is explained. As for the conclusion, the study connects the effectiveness of the internal control system with the effectiveness of the elements which compose the system, and provides some suggestions for increasing the efficacy of the elements which compose the system, such as control environment, risk analysis, information-communication, control activities, and monitoring.展开更多
Human resource is already in society today one of the most important resources, the human resources stability has important implications, university should how to its important role and how to keep its stability, in t...Human resource is already in society today one of the most important resources, the human resources stability has important implications, university should how to its important role and how to keep its stability, in this thesis are introduced. In addition, concerning human resources loss and its have also means have relevant instruction, how to understand university human resources of stability,handled the problem, the university can better, faster development.展开更多
The hybrid-HVDC topology,which consists of line-commutated-converter(LCC)and voltage source converter(VSC)and combines their advantages,has extensive application prospects.A hybrid-HVDC system,adopting VSC on rectifie...The hybrid-HVDC topology,which consists of line-commutated-converter(LCC)and voltage source converter(VSC)and combines their advantages,has extensive application prospects.A hybrid-HVDC system,adopting VSC on rectifier side and LCC on inverter side,is investigated,and its mathematic model is deduced.The commutation failure issue of the LCC converter in the hybrid-HVDC system is considered,and a novel coordinated control method is proposed to enhance the system commutation failure immunity.A voltage dependent voltage order limiter(VDVOL)is designed based on the constant DC voltage control on the rectifier side,and constant extinction angle backup control is introduced based on the constant DC current control with voltage dependent current order limiter(VDCOL)on the inverter side.The hybrid-HVDC system performances under normal operation state and fault state are simulated in the PSCAD/EMTDC.Then,system transient state performances with or without the proposed control methods under fault condition are further compared and analyzed.It is concluded that the proposed control method has the ability to effectively reduce the probability of commutation failure and improve the fault recovery performance of the hybrid-HVDC system.展开更多
基金Project supported by the International Foundation of Science(No.C/2661-1)the National Key Basic Research Support Foundation of China(No.G1999011809).
文摘Agriculture is still the biggest contributor of non-point source (NPS) pollution to water bodies andrunoff discharges of nutrients and other chemicals are one of the most important pathways. This studywas conducted during 1998～1999 in a typical watershed with complex agriculture and forestry systems aswell as dotted farmer villages, in a transitional region between the mid- and northern subtropical zones ofChina. Continuous sampling of stream water was performed regularly at a weekly frequency, with additionalsampling after all major rainfall events. The discharges of N and P nutrients and suspended materials weremeasured and the total and area-averaged annual discharges of all components were calculated. The resultsshowed an uneven seasonal distribution of nutrient discharges with summer storms contributing most tothe total fluxes. This study demonstrated a high dependence of runoff volume on rainfall but the overallrunoff coefficients were dependent on land use type and watershed size. The area-averaged annual dischargesvaried greatly among the sub-watersheds with different sizes and land use structures. This is the first studyestimating the area-averaged annual discharges of N and P in the hilly areas of subtropical China, which were1.5 g m-2 a-1 and 0.1 g m-2 a-1, respectively, providing important reference values for the assessment ofregional agricultural non-point source pollution.
文摘This study, based on the literature, stresses the effectiveness of internal control systems for the prevention, to a reasonable extent, of fraudulent practices that cause resource loss in business. In this context, the key concepts related to fraud and internal control systems are presented first. After the introduction, the relation between fraud and internal control systems is elaborated, and the method for establishing an effective internal control system which is needed to detect and prevent fraud is explained. As for the conclusion, the study connects the effectiveness of the internal control system with the effectiveness of the elements which compose the system, and provides some suggestions for increasing the efficacy of the elements which compose the system, such as control environment, risk analysis, information-communication, control activities, and monitoring.
文摘Human resource is already in society today one of the most important resources, the human resources stability has important implications, university should how to its important role and how to keep its stability, in this thesis are introduced. In addition, concerning human resources loss and its have also means have relevant instruction, how to understand university human resources of stability,handled the problem, the university can better, faster development.
基金supported by the National High Technology Research and Development Program of China("863" Program)(Grant No.2013AA050105)the National Natural Science Foundation of China(Grant No.51177042)+1 种基金the Fundamental Research Funds for the Central Universities(Grant No.13QN03)2012 science and technology projects of State Grid Corporation of China(Grant No.XT71-12-015)
文摘The hybrid-HVDC topology,which consists of line-commutated-converter(LCC)and voltage source converter(VSC)and combines their advantages,has extensive application prospects.A hybrid-HVDC system,adopting VSC on rectifier side and LCC on inverter side,is investigated,and its mathematic model is deduced.The commutation failure issue of the LCC converter in the hybrid-HVDC system is considered,and a novel coordinated control method is proposed to enhance the system commutation failure immunity.A voltage dependent voltage order limiter(VDVOL)is designed based on the constant DC voltage control on the rectifier side,and constant extinction angle backup control is introduced based on the constant DC current control with voltage dependent current order limiter(VDCOL)on the inverter side.The hybrid-HVDC system performances under normal operation state and fault state are simulated in the PSCAD/EMTDC.Then,system transient state performances with or without the proposed control methods under fault condition are further compared and analyzed.It is concluded that the proposed control method has the ability to effectively reduce the probability of commutation failure and improve the fault recovery performance of the hybrid-HVDC system.
