分析了 Ad Hoc 网络的性能与拓扑结构的密切相关性和网络特点,提出了一种适用于 Ad Hoc 网络的基于计算几何方法和功率控制技术的分布式拓扑控制算法。该算法利用天线判断邻居节点方向,构建局部网络拓扑;采用计算几何法减少邻居数,简化...分析了 Ad Hoc 网络的性能与拓扑结构的密切相关性和网络特点,提出了一种适用于 Ad Hoc 网络的基于计算几何方法和功率控制技术的分布式拓扑控制算法。该算法利用天线判断邻居节点方向,构建局部网络拓扑;采用计算几何法减少邻居数,简化拓扑结构;使用对称机制保障节点间的双向连通,兼顾网络连通性;通过调整功率实现具有健壮性的网络拓扑优化控制。仿真结果表明,该算法在满足网络覆盖度和连通性的前提下,形成了优化的拓扑结构,能够节约能量,延长节点寿命,减少相互干扰,提高信道利用率,降低传输时延,增加吞吐量,改善了网络整体性能。展开更多
Hybrid precoding can reduce the number of required radio frequency(RF)chains in millimeter-Wave(mmWave) massive MIMO systems. However, existing hybrid precoding based on singular value decomposition(SVD) requires the ...Hybrid precoding can reduce the number of required radio frequency(RF)chains in millimeter-Wave(mmWave) massive MIMO systems. However, existing hybrid precoding based on singular value decomposition(SVD) requires the complicated bit allocation to match the different signal-to-noise-ratios(SNRs) of different sub-channels. In this paper,we propose a geometric mean decomposition(GMD)-based hybrid precoding to avoid the complicated bit allocation. Specifically,we seek a pair of analog and digital precoders sufficiently close to the unconstrained fully digital GMD precoder. To achieve this, we fix the analog precoder to design the digital precoder, and vice versa. The analog precoder is designed based on the orthogonal matching pursuit(OMP) algorithm, while GMD is used to obtain the digital precoder. Simulations show that the proposed GMD-based hybrid precoding achieves better performance than the conventional SVD-based hybrid precoding with only a slight increase in complexity.展开更多
The first-principles method based on density-functional theory is used to investigate the geometries of the lowest-lying isomers of AunAg2 （n = 1 - 4） clusters. Several low-lying isomers are determined, and many of ...The first-principles method based on density-functional theory is used to investigate the geometries of the lowest-lying isomers of AunAg2 （n = 1 - 4） clusters. Several low-lying isomers are determined, and many of them in electronic configurations with a high spin multiplicity. The stability trend of Ag-doped Aun dusters is compared to that of pure Aun clusters. Our results indicate that the inclusion of two Ag atoms in the clusters lowers the cluster stability, indicating higher stability as the structures grow in size. The bigger energy difference between the Aun and AunAg2 curves as the structures grows in size. This information will be useful to understanding the enhanced catalytic activity and selectivity gained by using silver-doped gold catalyst.展开更多
According to the configuration,mixed-conducting membranes are classified as symmetric membranes and asymmetric membranes consisting of a thin dense layer and a porous support.In this study,these two kinds of SrCo0.4Fe...According to the configuration,mixed-conducting membranes are classified as symmetric membranes and asymmetric membranes consisting of a thin dense layer and a porous support.In this study,these two kinds of SrCo0.4Fe0.5Zr0.1O3-δ oxide-based membranes were systematically compared in terms of oxygen permeability and chemical stability,and their differences were elucidated by means of the theoretical calculation.For the oxygen permeability,the asymmetric membrane was greater than the symmetric membrane due to the significant decrease of bulk diffusion resistance in the thin dense layer of the asymmetric membrane.In regard to the chemical stability,the increase of oxygen partial pressure on the asymmetric membrane surface at CH4 side produced the stable time of over 1032h in partial oxidation of methane at 1123K,while the symmetric membrane was only of 528h.This study demonstrated that the asymmetric membrane was a promising geometrical configuration for the practical application.展开更多
This paper presents a method for tracing a planar implicit curve f（x, y）=0 on a rectangular region based on continuation scheme. First, according to the starting track-point and the starting track-direction of the c...This paper presents a method for tracing a planar implicit curve f（x, y）=0 on a rectangular region based on continuation scheme. First, according to the starting track-point and the starting track-direction of the curve, make a new fimction F（x, y）=0 where the same curve withf（x, y）=0 is defined. Then we trace the curve between the two domains where F（x, y）〉0 and F（x, y）〈0 alternately, according to the two rules presented in this paper. Equal step size or adaptive step size can be used, when we trace the curve. An irregular planar implicit curve （such as the curve with large curvatures at some points on the curve）, can be plotted if an adaptive step size is used. Moreover, this paper presents a scheme to search for the multiple points on the curve. Our method has the following advantages： （1） it can plot Co planar implicit curves; （2） it can plot the planar implicit curves with multiple points; （3） by the help of using the two rules, our method does not need to compute the tangent vector at the points on the curve, and directly searches for the direction of the tracing curve; （4） the tracing procedure costs only one of two evaluations of function f（x, y）=0 per moving step, while most existing similar methods cost more evaluations of the function.展开更多
文摘分析了 Ad Hoc 网络的性能与拓扑结构的密切相关性和网络特点,提出了一种适用于 Ad Hoc 网络的基于计算几何方法和功率控制技术的分布式拓扑控制算法。该算法利用天线判断邻居节点方向,构建局部网络拓扑;采用计算几何法减少邻居数,简化拓扑结构;使用对称机制保障节点间的双向连通,兼顾网络连通性;通过调整功率实现具有健壮性的网络拓扑优化控制。仿真结果表明,该算法在满足网络覆盖度和连通性的前提下,形成了优化的拓扑结构,能够节约能量,延长节点寿命,减少相互干扰,提高信道利用率,降低传输时延,增加吞吐量,改善了网络整体性能。
基金supported by the National Natural Science Foundation of China for Outstanding Young Scholars (Grant No. 61722109)the National Natural Science Foundation of China (Grant No. 61571270)the Royal Academy of Engineering through the UK–China Industry Academia Partnership Programme Scheme (Grant No. UK-CIAPP\49)
文摘Hybrid precoding can reduce the number of required radio frequency(RF)chains in millimeter-Wave(mmWave) massive MIMO systems. However, existing hybrid precoding based on singular value decomposition(SVD) requires the complicated bit allocation to match the different signal-to-noise-ratios(SNRs) of different sub-channels. In this paper,we propose a geometric mean decomposition(GMD)-based hybrid precoding to avoid the complicated bit allocation. Specifically,we seek a pair of analog and digital precoders sufficiently close to the unconstrained fully digital GMD precoder. To achieve this, we fix the analog precoder to design the digital precoder, and vice versa. The analog precoder is designed based on the orthogonal matching pursuit(OMP) algorithm, while GMD is used to obtain the digital precoder. Simulations show that the proposed GMD-based hybrid precoding achieves better performance than the conventional SVD-based hybrid precoding with only a slight increase in complexity.
基金The project supported by the Foundation from the Education Department of Sichuan Province under Grant No. 2004A117
文摘The first-principles method based on density-functional theory is used to investigate the geometries of the lowest-lying isomers of AunAg2 （n = 1 - 4） clusters. Several low-lying isomers are determined, and many of them in electronic configurations with a high spin multiplicity. The stability trend of Ag-doped Aun dusters is compared to that of pure Aun clusters. Our results indicate that the inclusion of two Ag atoms in the clusters lowers the cluster stability, indicating higher stability as the structures grow in size. The bigger energy difference between the Aun and AunAg2 curves as the structures grows in size. This information will be useful to understanding the enhanced catalytic activity and selectivity gained by using silver-doped gold catalyst.
基金Supported by the National Basic Research Program of China （2009CB623406）, the National Natural Science Foundation of China （20636020）, the National High Technology Research and Development Program of China （2006AA030204） and the Specialized Research Fund for the Doctoral Program of Higher Education of China （20060291003）.
文摘According to the configuration,mixed-conducting membranes are classified as symmetric membranes and asymmetric membranes consisting of a thin dense layer and a porous support.In this study,these two kinds of SrCo0.4Fe0.5Zr0.1O3-δ oxide-based membranes were systematically compared in terms of oxygen permeability and chemical stability,and their differences were elucidated by means of the theoretical calculation.For the oxygen permeability,the asymmetric membrane was greater than the symmetric membrane due to the significant decrease of bulk diffusion resistance in the thin dense layer of the asymmetric membrane.In regard to the chemical stability,the increase of oxygen partial pressure on the asymmetric membrane surface at CH4 side produced the stable time of over 1032h in partial oxidation of methane at 1123K,while the symmetric membrane was only of 528h.This study demonstrated that the asymmetric membrane was a promising geometrical configuration for the practical application.
文摘This paper presents a method for tracing a planar implicit curve f（x, y）=0 on a rectangular region based on continuation scheme. First, according to the starting track-point and the starting track-direction of the curve, make a new fimction F（x, y）=0 where the same curve withf（x, y）=0 is defined. Then we trace the curve between the two domains where F（x, y）〉0 and F（x, y）〈0 alternately, according to the two rules presented in this paper. Equal step size or adaptive step size can be used, when we trace the curve. An irregular planar implicit curve （such as the curve with large curvatures at some points on the curve）, can be plotted if an adaptive step size is used. Moreover, this paper presents a scheme to search for the multiple points on the curve. Our method has the following advantages： （1） it can plot Co planar implicit curves; （2） it can plot the planar implicit curves with multiple points; （3） by the help of using the two rules, our method does not need to compute the tangent vector at the points on the curve, and directly searches for the direction of the tracing curve; （4） the tracing procedure costs only one of two evaluations of function f（x, y）=0 per moving step, while most existing similar methods cost more evaluations of the function.
