The space charge behavior of a dielectric under HVDC is influenced by the charge trap energy distribution in it. Hence, we in- vestigated the charge trap distributions in several kinds of typical polymer materials usi...The space charge behavior of a dielectric under HVDC is influenced by the charge trap energy distribution in it. Hence, we in- vestigated the charge trap distributions in several kinds of typical polymer materials using thermally stimulated discharge (TSD) and photo-stimulated discharge (PSD) methods, respectively. The experimental results show that,there is a significant difference between the trap energy distributions obtained by the two methods, but the difference decreases with the increase of the melting point of polymers. This is attributed to the change of the trap center environment during TSD caused by the increasing movements of both main chains and branched chains in polymers. PSD method is more accurate for investigating charge trap distribution in dielectrics, especially for polymers with low melting points.展开更多
Rapid urbanization and population growth of the Amman Area were combined with land resource degradation when the city was heading for mounting urbanization from the early 1950s. The deterioration of natural resources ...Rapid urbanization and population growth of the Amman Area were combined with land resource degradation when the city was heading for mounting urbanization from the early 1950s. The deterioration of natural resources and green areas, was coupled with the creation of different urban public open spaces in the city. The transformation from large single-family houses to dense residential apartments was associated with social and behavioral changes among the inhabitants living in the dense apartments. Consequently, a large private sector has been developed to provide public and social spaces. Photo-interpretation and satellite images were used to map and characterize land use/cover changes have been occurred in the Amman area between 1953 and 2017. Maximum Likelihood Classification method was employed to identify land use/cover changes between 1986 and 20017, and GIS was utilized also to map examples of the recently emerged socio-economic open spaces. Excessive urban development in the last two decades, and the adoption of neo-liberal privatization policies by the government, enhanced social stratification and residential segregation. So, instead of encouraging outdoor activity and social interaction among all groups of Amman residents, the freedom of accessibility to major open spaces has been restricted within the same urban fabric, thus, the “two Ammans” paradigm, a “tale of two cities”, has been recently acknowledged.展开更多
从研究APD光电检测接收机被检测光场的量子统计模型出发,构造了一种适用于强度调制/直接检测的自由空间光通信系统中LDPC译码的精确实现方法。该方法在APD接收机输出统计模型（Webb-Gaussian模型）的基础上,推导了M-PPM的LDPC译码算法...从研究APD光电检测接收机被检测光场的量子统计模型出发,构造了一种适用于强度调制/直接检测的自由空间光通信系统中LDPC译码的精确实现方法。该方法在APD接收机输出统计模型（Webb-Gaussian模型）的基础上,推导了M-PPM的LDPC译码算法中初始似然比值的精确计算方法,并给出了详细的译码过程。理论分析和仿真结果表明,与目前普遍采用的APD近似非对称Gaussian统计模型下的译码性能相比较,在相同的信道条件下,该方法可以获得大约1~2 d B的性能增益。这为进一步提高自由空间光通信系统的性能提供了一定的理论依据。展开更多
基金Project supported by National Natural Science Foundation of China （51077101, 51277133）, National Basic Research Program of China （973 Program） （2009CB 724505）.
文摘The space charge behavior of a dielectric under HVDC is influenced by the charge trap energy distribution in it. Hence, we in- vestigated the charge trap distributions in several kinds of typical polymer materials using thermally stimulated discharge (TSD) and photo-stimulated discharge (PSD) methods, respectively. The experimental results show that,there is a significant difference between the trap energy distributions obtained by the two methods, but the difference decreases with the increase of the melting point of polymers. This is attributed to the change of the trap center environment during TSD caused by the increasing movements of both main chains and branched chains in polymers. PSD method is more accurate for investigating charge trap distribution in dielectrics, especially for polymers with low melting points.
文摘Rapid urbanization and population growth of the Amman Area were combined with land resource degradation when the city was heading for mounting urbanization from the early 1950s. The deterioration of natural resources and green areas, was coupled with the creation of different urban public open spaces in the city. The transformation from large single-family houses to dense residential apartments was associated with social and behavioral changes among the inhabitants living in the dense apartments. Consequently, a large private sector has been developed to provide public and social spaces. Photo-interpretation and satellite images were used to map and characterize land use/cover changes have been occurred in the Amman area between 1953 and 2017. Maximum Likelihood Classification method was employed to identify land use/cover changes between 1986 and 20017, and GIS was utilized also to map examples of the recently emerged socio-economic open spaces. Excessive urban development in the last two decades, and the adoption of neo-liberal privatization policies by the government, enhanced social stratification and residential segregation. So, instead of encouraging outdoor activity and social interaction among all groups of Amman residents, the freedom of accessibility to major open spaces has been restricted within the same urban fabric, thus, the “two Ammans” paradigm, a “tale of two cities”, has been recently acknowledged.
文摘从研究APD光电检测接收机被检测光场的量子统计模型出发,构造了一种适用于强度调制/直接检测的自由空间光通信系统中LDPC译码的精确实现方法。该方法在APD接收机输出统计模型（Webb-Gaussian模型）的基础上,推导了M-PPM的LDPC译码算法中初始似然比值的精确计算方法,并给出了详细的译码过程。理论分析和仿真结果表明,与目前普遍采用的APD近似非对称Gaussian统计模型下的译码性能相比较,在相同的信道条件下,该方法可以获得大约1~2 d B的性能增益。这为进一步提高自由空间光通信系统的性能提供了一定的理论依据。
