This study reports an inventory of marsh dieback events from spatial and temporal perspectives in the North Inlet-Winyah Bay(NIWB)estuary,South Carolina(SC).Past studies in the Gulf/Atlantic coast states have reported...This study reports an inventory of marsh dieback events from spatial and temporal perspectives in the North Inlet-Winyah Bay(NIWB)estuary,South Carolina(SC).Past studies in the Gulf/Atlantic coast states have reported acute marsh dieback events in which marsh rapidly browned and thinned,leaving stubble of dead stems or mudflat with damaged ecosystem services.Reported marsh dieback in SC,however,have been limited.This study identified all marsh dieback events in the estuary since 1998.With 20 annually collected Landsat images,the Normalized Difference Vegetation Index(NDVI)series was extracted.A Stacked Denoising Autoencoder neural network was developed to identify the NDVI anomalies on the trajectories.All marsh dieback patches were extracted,and their inter-annual changes were examined.Results showed a continuous,spatially variable multi-year dieback event in 1998–2005,which aligned with the reported dieback in the early 2000s from other states.The identified patches mostly returned to normal within one year while the phenomenon reoccurred in other areas of the estuary during the prolonged dieback period.This study presents the first attempt to explore long-term dieback dynamics in an estuary using satellite time series.It provides valuable information in documenting marsh healthiness and environmental resilience on SC coasts.展开更多
A fractional frequency transmission system(FFTS)is the most competitive choice for long distance transmission of offshore wind power,while the Hexverter,as a newly proposed direct AC/AC converter,is an attractive choi...A fractional frequency transmission system(FFTS)is the most competitive choice for long distance transmission of offshore wind power,while the Hexverter,as a newly proposed direct AC/AC converter,is an attractive choice for its power conversion.This paper proposes a novel control scheme characterizing the global stability and strong robustness of the Hexverter in FFTS applications,which are based on the interconnection and damping assignment passivity-based control(IDA-PBC)methodology.Firstly,the frequency decoupled model of the Hexverter is studied and then a port-controlled Hamiltonian(PCH)model is built.On this basis,the IDAPBC scheme of the Hexverter is designed.Considering the interference of system parameters and unmodeled dynamics,integrators are added to the IDA-PB controller to eliminate the steady-state error.In addition,the voltagebalancing control is applied in order to balance the capacitor DC voltages to obtain a better performance.Finally,the simulation results and experimental results are presented to verify the effectiveness and superiority of the IDA-PB controller.展开更多
基金supported by NASA EPSCoR Research Grant Program[Award#:NNX15AK53A]in South Carolina,USA.
文摘This study reports an inventory of marsh dieback events from spatial and temporal perspectives in the North Inlet-Winyah Bay(NIWB)estuary,South Carolina(SC).Past studies in the Gulf/Atlantic coast states have reported acute marsh dieback events in which marsh rapidly browned and thinned,leaving stubble of dead stems or mudflat with damaged ecosystem services.Reported marsh dieback in SC,however,have been limited.This study identified all marsh dieback events in the estuary since 1998.With 20 annually collected Landsat images,the Normalized Difference Vegetation Index(NDVI)series was extracted.A Stacked Denoising Autoencoder neural network was developed to identify the NDVI anomalies on the trajectories.All marsh dieback patches were extracted,and their inter-annual changes were examined.Results showed a continuous,spatially variable multi-year dieback event in 1998–2005,which aligned with the reported dieback in the early 2000s from other states.The identified patches mostly returned to normal within one year while the phenomenon reoccurred in other areas of the estuary during the prolonged dieback period.This study presents the first attempt to explore long-term dieback dynamics in an estuary using satellite time series.It provides valuable information in documenting marsh healthiness and environmental resilience on SC coasts.
基金supported by National Natural Science Foundation of China(No.51677142)Science and Technology Foundation of SGCC(Research on efficient integration of large scale long distance offshore wind farm and its key technologies in operation and control).
文摘A fractional frequency transmission system(FFTS)is the most competitive choice for long distance transmission of offshore wind power,while the Hexverter,as a newly proposed direct AC/AC converter,is an attractive choice for its power conversion.This paper proposes a novel control scheme characterizing the global stability and strong robustness of the Hexverter in FFTS applications,which are based on the interconnection and damping assignment passivity-based control(IDA-PBC)methodology.Firstly,the frequency decoupled model of the Hexverter is studied and then a port-controlled Hamiltonian(PCH)model is built.On this basis,the IDAPBC scheme of the Hexverter is designed.Considering the interference of system parameters and unmodeled dynamics,integrators are added to the IDA-PB controller to eliminate the steady-state error.In addition,the voltagebalancing control is applied in order to balance the capacitor DC voltages to obtain a better performance.Finally,the simulation results and experimental results are presented to verify the effectiveness and superiority of the IDA-PB controller.
