Determination of multifractal dimensions of complex networks by means of the sandbox algorithm

Complex networks have attracted much attention in diverse areas of science and technology. Multifractal analysis (MFA) is a useful way to systematically describe the spatial heterogeneity of both theoretical and experimental fractal patterns. In this paper, we employ the sandbox (SB) algorithm proposed by T\'{e}l et al. (Physica A, 159 (1989) 155-166), for MFA of complex networks. First we compare the SB algorithm with two existing algorithms of MFA for complex networks: the compact-box-burning (CBB) algorithm proposed by Furuya and Yakubo (Phys. Rev. E, 84 (2011) 036118), and the improved box-counting (BC) algorithm proposed by Li et al. (J. Stat. Mech.: Theor. Exp., 2014 (2014) P02020) by calculating the mass exponents tau(q) of some deterministic model networks. We make a detailed comparison between the numerical and theoretical results of these model networks. The comparison results show that the SB algorithm is the most effective and feasible algorithm to calculate the mass exponents tau(q) and to explore the multifractal behavior of complex networks. Then we apply the SB algorithm to study the multifractal property of some classic model networks, such as scale-free networks, small-world networks, and random networks. Our results show that multifractality exists in scale-free networks, that of small-world networks is not obvious, and it almost does not exist in random networks.Comment: 17 pages, 2 table, 10 figure

Triggered massive and clustered stars formation by together H II regions G38.91-0.44 and G39.30-1.04

We present the radio continuum, infrared, and CO molecular observations of infrared dark cloud (IRDC) G38.95-0.47 and its adjacent H II regions G38.91-0.44 (N74), G38.93-0.39 (N75), and G39.30-1.04. The Purple Mountain Observation (PMO) 13.7 m radio telescope was used to detect12CO J=1-0,13CO J=1-0 and C18O J=1-0 lines. The carbon monoxide (CO) molecular observations can ensure the real association between the ionized gas and the neutral material observed nearby. To select young stellar objects (YSOs) associated this region, we used the GLIMPSE I catalog. The13CO J=1-0 emission presents two large cloud clumps. The clump consistent with IRDC G38.95-0.47 shows a triangle- like shape, and has a steep integrated-intensity gradient toward H II regions G38.91-0.44 and G39.30-1.04, suggesting that the two H II regions have expanded into the IRDC. Four submillmeter continuum sources have been detected in the IRDC G38.95-0.47. Only the G038.95-00.47-M1 source with a mass of 117 Msun has outflow and infall motions, indicating a newly forming massive star. We detected a new collimated outflow in the clump compressed by G38.93-0.39. The derived ages of the three H II regions are 6.1*10^5yr, 2.5*10^5yr, and 9.0*10^5yr, respectively. In the IRDC G38.95-0.47, the significant enhancement of several Class I YSOs indicates the presence of some recently formed stars. Comparing the ages of these H II regions with YSOs (Class I sources and massive G038.95-00.47-M1 source), we suggest that YSOs may be triggered by G38.91-0.44 and G39.30-1.04 together, which supports the radiatively driven implosion model. It may be the first time that the triggered star formation has occurred in the IRDC compressed by two H II regions. The new detected outflow may be driven by a star cluster.Comment: 6 pages, 4 figures, Accepted for publication in A&

Multifractal analysis of weighted networks by a modified sandbox algorithm

Complex networks have attracted growing attention in many fields. As a generalization of fractal analysis, multifractal analysis (MFA) is a useful way to systematically describe the spatial heterogeneity of both theoretical and experimental fractal patterns. Some algorithms for MFA of unweighted complex networks have been proposed in the past a few years, including the sandbox (SB) algorithm recently employed by our group. In this paper, a modified SB algorithm (we call it SBw algorithm) is proposed for MFA of weighted networks.First, we use the SBw algorithm to study the multifractal property of two families of weighted fractal networks (WFNs): "Sierpinski" WFNs and "Cantor dust" WFNs. We also discuss how the fractal dimension and generalized fractal dimensions change with the edge-weights of the WFN. From the comparison between the theoretical and numerical fractal dimensions of these networks, we can find that the proposed SBw algorithm is efficient and feasible for MFA of weighted networks. Then, we apply the SBw algorithm to study multifractal properties of some real weighted networks ---collaboration networks. It is found that the multifractality exists in these weighted networks, and is affected by their edge-weights.Comment: 15 pages, 6 figures. Accepted for publication by Scientific Report