全球气候变暖和大气CO_(2)浓度(Ca)急剧上升已成为不争的事实,并对森林生态系统有着深远的影响,全面理解森林生态系统对全球变化的响应至关重要。中亚干旱区特有树种雪岭云杉(Picea schrenkiana Fisch. et Mey)树轮稳定碳同位素(δ^(13...全球气候变暖和大气CO_(2)浓度(Ca)急剧上升已成为不争的事实,并对森林生态系统有着深远的影响,全面理解森林生态系统对全球变化的响应至关重要。中亚干旱区特有树种雪岭云杉(Picea schrenkiana Fisch. et Mey)树轮稳定碳同位素(δ^(13)C)和水分利用效率(iWUE)对气候变暖和大气CO2浓度急剧上升的响应缺乏研究。本研究利用天山西部伊犁河流域的雪岭云杉树轮样本,使用树木年代学方法和树轮稳定碳同位素技术,建立树轮宽度年表、稳定碳同位素(δ^(13)C)以及内禀水分利用效率(iWUE)序列,分析了树轮δ13C和iWUE的长期变化特征,探讨了树轮δ13C和iWUE对气候的响应规律以及iWUE与树轮宽度的关系。结果表明,主要的气候因子并没有强烈地限制树木径向生长;夏季平均气温对树轮δ^(13)C分馏有重要影响,iWUE的长期变化受到全球Ca增加和升温趋势影响,但直接影响iWUE年际变化的主要因素是饱和水汽压亏缺(VPD)。全球升温和Ca增加导致了iWUE的持续升高,但并没有导致雪岭云杉树木径向生长的明显增加。展开更多
Ultra-dense networks (UDNs) are expected to be applied for the fifth generation wireless system (5G) to meet the requirements of very high throughput density and connections of a massive number of users. Consideri...Ultra-dense networks (UDNs) are expected to be applied for the fifth generation wireless system (5G) to meet the requirements of very high throughput density and connections of a massive number of users. Considering the large amount of small base stations (SBSs), how to choose proper backhaul links is an important problem under investigation. In this paper, we propose a wireless backhaul algorithm to find an effective backhaul method for densely-deployed SBSs and to maximize energy efficiency of the system. We put forward adaptive backhaul methods of indirect and direct modes. The SBS can select the direct baekhaul which con- nects to the macro base station (MBS) directly, or the indirect backhaul which selects an idle SBS as a relay based on the backhaul channel condition. The algorithm also allocates network resources, including the power of SBSs and system bandwidth, to solve the serious interference problem in UDN. Finally, the simulation results show that the proposed wireless backhaul algorithm has desired performance to achieve higher energy efficiency with required data rate.展开更多
文摘全球气候变暖和大气CO_(2)浓度(Ca)急剧上升已成为不争的事实,并对森林生态系统有着深远的影响,全面理解森林生态系统对全球变化的响应至关重要。中亚干旱区特有树种雪岭云杉(Picea schrenkiana Fisch. et Mey)树轮稳定碳同位素(δ^(13)C)和水分利用效率(iWUE)对气候变暖和大气CO2浓度急剧上升的响应缺乏研究。本研究利用天山西部伊犁河流域的雪岭云杉树轮样本,使用树木年代学方法和树轮稳定碳同位素技术,建立树轮宽度年表、稳定碳同位素(δ^(13)C)以及内禀水分利用效率(iWUE)序列,分析了树轮δ13C和iWUE的长期变化特征,探讨了树轮δ13C和iWUE对气候的响应规律以及iWUE与树轮宽度的关系。结果表明,主要的气候因子并没有强烈地限制树木径向生长;夏季平均气温对树轮δ^(13)C分馏有重要影响,iWUE的长期变化受到全球Ca增加和升温趋势影响,但直接影响iWUE年际变化的主要因素是饱和水汽压亏缺(VPD)。全球升温和Ca增加导致了iWUE的持续升高,但并没有导致雪岭云杉树木径向生长的明显增加。
基金jointly supported by the National Natural Science Foundation of China under Grant Nos.61771070 and 61671088the National Science and Technology Major Project under Grant No.2016ZX03001017
文摘Ultra-dense networks (UDNs) are expected to be applied for the fifth generation wireless system (5G) to meet the requirements of very high throughput density and connections of a massive number of users. Considering the large amount of small base stations (SBSs), how to choose proper backhaul links is an important problem under investigation. In this paper, we propose a wireless backhaul algorithm to find an effective backhaul method for densely-deployed SBSs and to maximize energy efficiency of the system. We put forward adaptive backhaul methods of indirect and direct modes. The SBS can select the direct baekhaul which con- nects to the macro base station (MBS) directly, or the indirect backhaul which selects an idle SBS as a relay based on the backhaul channel condition. The algorithm also allocates network resources, including the power of SBSs and system bandwidth, to solve the serious interference problem in UDN. Finally, the simulation results show that the proposed wireless backhaul algorithm has desired performance to achieve higher energy efficiency with required data rate.