阐述了低压电力线载波通信技术研究的主要方向,概括了国内外学者在阻抗特征、信号衰减特性、噪声特性、信道模型等方面的研究成果和相应解决策略。针对电力线通信的调制解调技术和组网技术等方面进行了分析。其中,调制解调技术主要包括...阐述了低压电力线载波通信技术研究的主要方向,概括了国内外学者在阻抗特征、信号衰减特性、噪声特性、信道模型等方面的研究成果和相应解决策略。针对电力线通信的调制解调技术和组网技术等方面进行了分析。其中,调制解调技术主要包括当前热点研究的正交频分复用(orthogonal frequency division multiplexing,OFDM)相关技术以及跳频调制/解调技术,组网技术则主要分析考虑网络有效性和服务需求的蚁群优化路由算法。对国内外电力线标准的最新研究工作进行了总结。最后,结合低压电力线载波通信技术现状和发展要求,对低压电力线载波通信的技术研究方向和发展潜力进行了展望和探讨。展开更多
Aquatic vegetation can influence the transport of sediment and contaminants by changing the mean velocity and turbulent flow structure in channels. It is important to understand the hydraulics of the flows over vegeta...Aquatic vegetation can influence the transport of sediment and contaminants by changing the mean velocity and turbulent flow structure in channels. It is important to understand the hydraulics of the flows over vegetation in order to manage fluvial processes. Experiments in an open-channel flume with natural vegetation were carried out to study the influence of vegetation on the flows. In a half channel with two different densities of vegetation, the flow velocity, Reynolds stresses, and turbulence intensities were measured using an Acoustic Doppler Velocimeter （ADV）. We obtained velocity profiles in the lateral direction, Reynolds stresses in the vertical direction, and the flow transition between the vegetated and non-vegetated zones in different flow regimes. The results show that the streamwise velocity in the vegetated zone with higher density is almost entirely blocked. Reynolds stress distribution distinguishes with two different regions： inside and above the vegetation canopies. The turbulence intensities increase with increasing Reynolds number. The coherent vortices dominate the vertical transport of momentum and are advected clockwise between the vegetated zone and non-vegetated zone by secondary currents （a relatively minor flow superimposed on the primary flow, with significantly different speed and direction）, generated by the anisotropy of the turbulence.展开更多
文摘阐述了低压电力线载波通信技术研究的主要方向,概括了国内外学者在阻抗特征、信号衰减特性、噪声特性、信道模型等方面的研究成果和相应解决策略。针对电力线通信的调制解调技术和组网技术等方面进行了分析。其中,调制解调技术主要包括当前热点研究的正交频分复用(orthogonal frequency division multiplexing,OFDM)相关技术以及跳频调制/解调技术,组网技术则主要分析考虑网络有效性和服务需求的蚁群优化路由算法。对国内外电力线标准的最新研究工作进行了总结。最后,结合低压电力线载波通信技术现状和发展要求,对低压电力线载波通信的技术研究方向和发展潜力进行了展望和探讨。
基金supported by the National Basic Research Program of China (973 Program, 2008CB418203)the National Natural Science Foundation of China (Grant No. 50709009)the Elitist Support Project of Ministry of Education (Grant No. NCET-07-0254)
文摘Aquatic vegetation can influence the transport of sediment and contaminants by changing the mean velocity and turbulent flow structure in channels. It is important to understand the hydraulics of the flows over vegetation in order to manage fluvial processes. Experiments in an open-channel flume with natural vegetation were carried out to study the influence of vegetation on the flows. In a half channel with two different densities of vegetation, the flow velocity, Reynolds stresses, and turbulence intensities were measured using an Acoustic Doppler Velocimeter （ADV）. We obtained velocity profiles in the lateral direction, Reynolds stresses in the vertical direction, and the flow transition between the vegetated and non-vegetated zones in different flow regimes. The results show that the streamwise velocity in the vegetated zone with higher density is almost entirely blocked. Reynolds stress distribution distinguishes with two different regions： inside and above the vegetation canopies. The turbulence intensities increase with increasing Reynolds number. The coherent vortices dominate the vertical transport of momentum and are advected clockwise between the vegetated zone and non-vegetated zone by secondary currents （a relatively minor flow superimposed on the primary flow, with significantly different speed and direction）, generated by the anisotropy of the turbulence.
