As two existing networks, the telecom network and the Internet differ greatly in terms of business patterns, service quality, security and regulations, whilst technical development makes services provided by the two n...As two existing networks, the telecom network and the Internet differ greatly in terms of business patterns, service quality, security and regulations, whilst technical development makes services provided by the two networks penetrate each other. This article describes the status quo of the telecom network and the Internet as well as the problems faced by each of them, analyzes the causes of those problems, and makes suggestions on coordinated and balanced development of the telecom network and the Internet.展开更多
One of the greatest challenges in the agroecosystem is to improve cropland intensification while preserving agroecosystem services.While many studies have investigated the effect of cropland intensification on agroeco...One of the greatest challenges in the agroecosystem is to improve cropland intensification while preserving agroecosystem services.While many studies have investigated the effect of cropland intensification on agroecosystem service,the interactive coupling and coordination among these factors remain largely unexplored.In view of this,this study performed a case study of the Loess Plateau in Shaanxi Province,China and constructed comprehensive evaluation models to quantify the cropland intensification and agroecosystem service in this area.Balance analysis and the coupling coordination degree model were used to evaluate the interactive relationship between cropland intensification and agroecosystem service,and statistical analysis and spatial autocorrelation were used to analyze the spatial characteristics and potential mechanism of the coupling coordination.Results show that both the cropland intensification and agroecosystem service in the study area were relatively low yet gradually increased from 2000 to 2020.Agroecosystem service lag was identified as the dominant unbalanced development type.Improving the supply capacity of agroecosystem services plays a key role in the balanced development of cropland in the Loess Plateau.The coupling coordination degree between cropland intensification and agroecosystem service ranges from basic coordination to serious incoordination.Therefore,cropland intensification practices in the area should be optimized to enhance this coordination degree.An upward trend was also observed in the coupling coordination degree from2000 to 2020.The withdrawal of marginal cropland in the Grain for Green program is one of the most important reasons for this trend,especially for the northern region.Around 83.6%of the high-high clusters are concentrated in the southern region of the Loess Plateau,whereas 70.5%of the low-low clusters are distributed in the northern region.These clustering characteristics are mainly attributed to the environmental suitability of these areas for agriculture and their degree of economic development.展开更多
The final balanced state of an initial unbalanced flow is discussed with the same method as Vallis (1992). For the two-dimensional, inviscid, rotating and nonlinear model, the final state of the flow depends on the in...The final balanced state of an initial unbalanced flow is discussed with the same method as Vallis (1992). For the two-dimensional, inviscid, rotating and nonlinear model, the final state of the flow depends on the initial conditions. If the initial potential vortcity of the flow is non-uniform, the final state is not necessarily geostrophic. However, for the zero and uniform potential vorticity flow, the final state will satisfy the thermal wind relation when the length scale of the initial disturbance is large enough. Otherwise, discontinuity will occur in the geostrophic solution. In this case, the final balanced state will not be geostrophic any longer and an extended momentum coordinate is introduced to overcome the mult-value problem. Key words Frontogenesis - Geostrophic adjustment - Thermal wind balance - Extended momentum coordinates The work was supported by the National Natural Science Foundation of China (Grant Nos. 49735180 and 40075011) and the State Key Basic Program: CHERES.展开更多
新一代低压直流供用电系统(low voltage direct current supply and utilization system,LVDCSUS)强调了可再生能源的消纳以及直流用户侧电能产–销–储–用之间的协调统一,为推动直流用户侧灵活参与电力系统运行提供了全新思路。开展LV...新一代低压直流供用电系统(low voltage direct current supply and utilization system,LVDCSUS)强调了可再生能源的消纳以及直流用户侧电能产–销–储–用之间的协调统一,为推动直流用户侧灵活参与电力系统运行提供了全新思路。开展LVDCSUS用户侧电能的使用与生产相结合的研究,可有效挖掘直流用户侧的多元化电能资源灵活供给能力,为此该文首先依据LVDCSUS系统能量平衡关系将系统划分为全直流运行、余电上网运行、交流支撑运行3种运行模式;进而给出各模式下满足直流母线电压稳定、储能荷电状态均衡、灵活性电力资源利用三方面整体要求的协调策略;最后建立了多运行模式切换规则,实现通过切换多种运行模式改变能量协调控制策略,使LVDCSUS在稳定运行状态下主动参与电力系统能量互动。仿真结果验证了LVDCSUS多运行模式控制策略的有效性和可靠性。展开更多
可再生能源和负荷的波动性、不确定性等给综合能源系统(integrated energy system,IES)的安全灵活运行带来了极大挑战。为提高IES灵活调节能力与可再生能源消纳水平,提出一种计及灵活性资源的IES源荷协调优化调度方法。针对系统内运行...可再生能源和负荷的波动性、不确定性等给综合能源系统(integrated energy system,IES)的安全灵活运行带来了极大挑战。为提高IES灵活调节能力与可再生能源消纳水平,提出一种计及灵活性资源的IES源荷协调优化调度方法。针对系统内运行灵活性需求,精细刻画各类资源灵活性能力,源侧根据电氢耦合单元运行特性构建热电联产机组(combined heating and power,CHP)和氢燃料电池(hydrogen fuel cell,HFC)联合运行模型,荷侧考虑综合需求响应的灵活性供给能力,建立系统综合灵活性供给模型。根据不同时刻运行灵活性不足问题分成2种调度模式,构建基于IES灵活性约束的优化调度模型,并进行仿真分析。仿真结果表明,所提出的优化调度方法能够有效提高IES灵活调节能力和可再生能源消纳水平。展开更多
文摘As two existing networks, the telecom network and the Internet differ greatly in terms of business patterns, service quality, security and regulations, whilst technical development makes services provided by the two networks penetrate each other. This article describes the status quo of the telecom network and the Internet as well as the problems faced by each of them, analyzes the causes of those problems, and makes suggestions on coordinated and balanced development of the telecom network and the Internet.
基金Under the auspices of the National Natural Science Foundation of China(No.41901262)Natural Science Basic Research Program of Shaanxi(No.2024JC-YBQN-0300)Fundamental Research Funds for the Central Universities(No.GK202103125,GK202207005)。
文摘One of the greatest challenges in the agroecosystem is to improve cropland intensification while preserving agroecosystem services.While many studies have investigated the effect of cropland intensification on agroecosystem service,the interactive coupling and coordination among these factors remain largely unexplored.In view of this,this study performed a case study of the Loess Plateau in Shaanxi Province,China and constructed comprehensive evaluation models to quantify the cropland intensification and agroecosystem service in this area.Balance analysis and the coupling coordination degree model were used to evaluate the interactive relationship between cropland intensification and agroecosystem service,and statistical analysis and spatial autocorrelation were used to analyze the spatial characteristics and potential mechanism of the coupling coordination.Results show that both the cropland intensification and agroecosystem service in the study area were relatively low yet gradually increased from 2000 to 2020.Agroecosystem service lag was identified as the dominant unbalanced development type.Improving the supply capacity of agroecosystem services plays a key role in the balanced development of cropland in the Loess Plateau.The coupling coordination degree between cropland intensification and agroecosystem service ranges from basic coordination to serious incoordination.Therefore,cropland intensification practices in the area should be optimized to enhance this coordination degree.An upward trend was also observed in the coupling coordination degree from2000 to 2020.The withdrawal of marginal cropland in the Grain for Green program is one of the most important reasons for this trend,especially for the northern region.Around 83.6%of the high-high clusters are concentrated in the southern region of the Loess Plateau,whereas 70.5%of the low-low clusters are distributed in the northern region.These clustering characteristics are mainly attributed to the environmental suitability of these areas for agriculture and their degree of economic development.
基金the National Natural Science Foundation of China (Grant Nos.49735180and 40075011) and the State Key Basic Program: CHERES.
文摘The final balanced state of an initial unbalanced flow is discussed with the same method as Vallis (1992). For the two-dimensional, inviscid, rotating and nonlinear model, the final state of the flow depends on the initial conditions. If the initial potential vortcity of the flow is non-uniform, the final state is not necessarily geostrophic. However, for the zero and uniform potential vorticity flow, the final state will satisfy the thermal wind relation when the length scale of the initial disturbance is large enough. Otherwise, discontinuity will occur in the geostrophic solution. In this case, the final balanced state will not be geostrophic any longer and an extended momentum coordinate is introduced to overcome the mult-value problem. Key words Frontogenesis - Geostrophic adjustment - Thermal wind balance - Extended momentum coordinates The work was supported by the National Natural Science Foundation of China (Grant Nos. 49735180 and 40075011) and the State Key Basic Program: CHERES.
文摘新一代低压直流供用电系统(low voltage direct current supply and utilization system,LVDCSUS)强调了可再生能源的消纳以及直流用户侧电能产–销–储–用之间的协调统一,为推动直流用户侧灵活参与电力系统运行提供了全新思路。开展LVDCSUS用户侧电能的使用与生产相结合的研究,可有效挖掘直流用户侧的多元化电能资源灵活供给能力,为此该文首先依据LVDCSUS系统能量平衡关系将系统划分为全直流运行、余电上网运行、交流支撑运行3种运行模式;进而给出各模式下满足直流母线电压稳定、储能荷电状态均衡、灵活性电力资源利用三方面整体要求的协调策略;最后建立了多运行模式切换规则,实现通过切换多种运行模式改变能量协调控制策略,使LVDCSUS在稳定运行状态下主动参与电力系统能量互动。仿真结果验证了LVDCSUS多运行模式控制策略的有效性和可靠性。
文摘可再生能源和负荷的波动性、不确定性等给综合能源系统(integrated energy system,IES)的安全灵活运行带来了极大挑战。为提高IES灵活调节能力与可再生能源消纳水平,提出一种计及灵活性资源的IES源荷协调优化调度方法。针对系统内运行灵活性需求,精细刻画各类资源灵活性能力,源侧根据电氢耦合单元运行特性构建热电联产机组(combined heating and power,CHP)和氢燃料电池(hydrogen fuel cell,HFC)联合运行模型,荷侧考虑综合需求响应的灵活性供给能力,建立系统综合灵活性供给模型。根据不同时刻运行灵活性不足问题分成2种调度模式,构建基于IES灵活性约束的优化调度模型,并进行仿真分析。仿真结果表明,所提出的优化调度方法能够有效提高IES灵活调节能力和可再生能源消纳水平。
