In this paper, under the constraint that the average distance and the average degree （k） remain approximately constant, we studied a random scale-free network model. We found that, if the network maintains the form ...In this paper, under the constraint that the average distance and the average degree （k） remain approximately constant, we studied a random scale-free network model. We found that, if the network maintains the form of its degree distribution and the maximal degree kc is N-dependent cutoff function kc（N）〈 N, the degree distribution would be approximately power-law with an exponent between 2 and 3. The distribution exponent has little relationship with the average degree, denoted by （k）. The diameter constraint can be interpreted as an environmental selection pressure, which could explain the scale-free nature of networks. The numerical results indicate that, under the diameter constraint, the preferential attachment can produce the cutoff function kc（N）〈 N and power-law degree distribution.展开更多
The establishment of effective null models can provide reference networks to accurately describe statistical properties of real-life signed networks.At present,two classical null models of signed networks(i.e.,sign an...The establishment of effective null models can provide reference networks to accurately describe statistical properties of real-life signed networks.At present,two classical null models of signed networks(i.e.,sign and full-edge randomized models)shuffle both positive and negative topologies at the same time,so it is difficult to distinguish the effect on network topology of positive edges,negative edges,and the correlation between them.In this study,we construct three re-fined edge-randomized null models by only randomizing link relationships without changing positive and negative degree distributions.The results of nontrivial statistical indicators of signed networks,such as average degree connectivity and clustering coefficient,show that the position of positive edges has a stronger effect on positive-edge topology,while the signs of negative edges have a greater influence on negative-edge topology.For some specific statistics(e.g.,embeddedness),the results indicate that the proposed null models can more accurately describe real-life networks compared with the two existing ones,which can be selected to facilitate a better understanding of complex structures,functions,and dynamical behaviors on signed networks.展开更多
Analyzing network robustness under various circumstances is generally regarded as a challenging problem.Robustness against failure is one of the essential properties of large-scale dynamic network systems such as powe...Analyzing network robustness under various circumstances is generally regarded as a challenging problem.Robustness against failure is one of the essential properties of large-scale dynamic network systems such as power grids,transportation systems,communication systems,and computer networks.Due to the network diversity and complexity,many topological features have been proposed to capture specific system properties.For power grids,a popular process for improving a network’s structural robustness is via the topology design.However,most of existing methods focus on localized network metrics,such as node connectivity and edge connectivity,which do not encompass a global perspective of cascading propagation in a power grid.In this paper,we use an informative global metric algebraic connectivity because it is sensitive to the connectedness in a broader spectrum of graphs.Our process involves decreasing the average propagation in a power grid by minimizing the increase in its algebraic connectivity.We propose a topology-based greedy strategy to optimize the robustness of the power grid.To evaluate the network robustness,we calculate the average propagation using MATCASC to simulate cascading line outages in power grids.Experimental results illustrate that our proposed method outperforms existing techniques.展开更多
With the help of 1∶20 000 satellite image of Kunming City and its satellite remote sensing image with resolution ratio 10 m, based on statistic data from Greening Department of Wuhua District and data collected throu...With the help of 1∶20 000 satellite image of Kunming City and its satellite remote sensing image with resolution ratio 10 m, based on statistic data from Greening Department of Wuhua District and data collected through field study, by making use of landscape ecological theory and methods, the paper had selected three indexes reflecting landscape spatial characteristic including average patch area, landscape fragmentation and landscape connectivity, to analyze landscape spatial characteristic of urban green land. And then it obtained that urban green land of Wuhua District was dominated by small patches, and patches' average area was small; urban green patches were small and fragmented, and landscape fragmentation was high; landscape connectivity was weak and ecological corridor was narrow, failing to bring ecological effect of landscape corridor into full display. Finally, in view of these problems, it had proposed suggestions for optimization, so as to provide reference and theoretical guidance for optimizing and creating excellent landscape spatial characteristic of urban green land in Wuhua District and constructing landscape pattern of ecological security.展开更多
文摘In this paper, under the constraint that the average distance and the average degree （k） remain approximately constant, we studied a random scale-free network model. We found that, if the network maintains the form of its degree distribution and the maximal degree kc is N-dependent cutoff function kc（N）〈 N, the degree distribution would be approximately power-law with an exponent between 2 and 3. The distribution exponent has little relationship with the average degree, denoted by （k）. The diameter constraint can be interpreted as an environmental selection pressure, which could explain the scale-free nature of networks. The numerical results indicate that, under the diameter constraint, the preferential attachment can produce the cutoff function kc（N）〈 N and power-law degree distribution.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.61773091 and 61603073)the LiaoNing Revitalization Talents Program(Grant No.XLYC1807106)the Natural Science Foundation of Liaoning Province,China(Grant No.2020-MZLH-22).
文摘The establishment of effective null models can provide reference networks to accurately describe statistical properties of real-life signed networks.At present,two classical null models of signed networks(i.e.,sign and full-edge randomized models)shuffle both positive and negative topologies at the same time,so it is difficult to distinguish the effect on network topology of positive edges,negative edges,and the correlation between them.In this study,we construct three re-fined edge-randomized null models by only randomizing link relationships without changing positive and negative degree distributions.The results of nontrivial statistical indicators of signed networks,such as average degree connectivity and clustering coefficient,show that the position of positive edges has a stronger effect on positive-edge topology,while the signs of negative edges have a greater influence on negative-edge topology.For some specific statistics(e.g.,embeddedness),the results indicate that the proposed null models can more accurately describe real-life networks compared with the two existing ones,which can be selected to facilitate a better understanding of complex structures,functions,and dynamical behaviors on signed networks.
基金supported by the National Natural Science Foundation of China(No.U1866602)the National Key R&D Program of China(Nos.2019YFB1600700 and 2018AAA0101505)。
文摘Analyzing network robustness under various circumstances is generally regarded as a challenging problem.Robustness against failure is one of the essential properties of large-scale dynamic network systems such as power grids,transportation systems,communication systems,and computer networks.Due to the network diversity and complexity,many topological features have been proposed to capture specific system properties.For power grids,a popular process for improving a network’s structural robustness is via the topology design.However,most of existing methods focus on localized network metrics,such as node connectivity and edge connectivity,which do not encompass a global perspective of cascading propagation in a power grid.In this paper,we use an informative global metric algebraic connectivity because it is sensitive to the connectedness in a broader spectrum of graphs.Our process involves decreasing the average propagation in a power grid by minimizing the increase in its algebraic connectivity.We propose a topology-based greedy strategy to optimize the robustness of the power grid.To evaluate the network robustness,we calculate the average propagation using MATCASC to simulate cascading line outages in power grids.Experimental results illustrate that our proposed method outperforms existing techniques.
文摘With the help of 1∶20 000 satellite image of Kunming City and its satellite remote sensing image with resolution ratio 10 m, based on statistic data from Greening Department of Wuhua District and data collected through field study, by making use of landscape ecological theory and methods, the paper had selected three indexes reflecting landscape spatial characteristic including average patch area, landscape fragmentation and landscape connectivity, to analyze landscape spatial characteristic of urban green land. And then it obtained that urban green land of Wuhua District was dominated by small patches, and patches' average area was small; urban green patches were small and fragmented, and landscape fragmentation was high; landscape connectivity was weak and ecological corridor was narrow, failing to bring ecological effect of landscape corridor into full display. Finally, in view of these problems, it had proposed suggestions for optimization, so as to provide reference and theoretical guidance for optimizing and creating excellent landscape spatial characteristic of urban green land in Wuhua District and constructing landscape pattern of ecological security.
