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Université de Fribourg

Note on two-phase phenomena in financial markets

Jiang, Shi-Mei ; Cai, Shi-Min ; Zhou, Tao ; Zhou, Pei-Ling

In: Chinese Physics Letters, 2008, vol. 25, no. 6, p. 2319-2322

The two-phase behaviour in financial markets actually means the bifurcation phenomenon, which represents the change of the conditional probability from an unimodal to a bimodal distribution. We investigate the bifurcation phenomenon in Hang–Seng index. It is observed that the bifurcation phenomenon in financial index is not universal, but specific under certain conditions. For Hang–Seng index...

Université de Fribourg

Singularities and symmetry breaking in swarms

Li, Wei ; Zhang, Hai-Tao ; Chen, Michael ZhiQiang ; Zhou, Tao

In: Physical Review E, 2008, vol. 77, no. 5, p. 021920

A large-scale system consisting of self-propelled particles, moving under the directional alignment rule (DAR), can often self-organize to an ordered state that emerges from an initially rotationally symmetric configuration. It is commonly accepted that the DAR, which leads to effective long-range interactions, is the underlying mechanism contributing to the collective motion. However, in this...

Université de Fribourg

Mixing navigation on networks

Zhou, Tao

In this article, we propose a mixing navigation mechanism, which interpolates between random-walk and shortest-path protocol. The navigation efficiency can be remarkably enhanced via a few routers. Some advanced strategies are also designed: For non-geographical scale-free networks, the targeted strategy with a tiny fraction of routers can guarantee an efficient navigation with low and stable...

Université de Fribourg

A limited resource model of fault-tolerant capability against cascading failure of complex network

Li, P. ; Wang, B.-H. ; Sun, H. ; Gao, P. ; Zhou, Tao

In: The European Physical Journal B, 2008, vol. 62, no. 1, p. 101-104

We propose a novel capacity model for complex networks against cascading failure. In this model, vertices with both higher loads and larger degrees should be paid more extra capacities, i.e. the allocation of extra capacity on vertex i will be proportional to ki γ , where ki is the degree of vertex i and γ > 0 is a free parameter. We have applied this model on...

Université de Fribourg

Opinion spreading with mobility on scale-free networks

Guo, Qiang ; Liu, Jian-Guo ; Wang, Bing-Hong ; Zhou, Tao ; Chen, Xing-Wen ; Yao, Yu-Hua

In: Chinese Physics Letters, 2008, vol. 25, no. 2, p. 773-775

A continuum opinion dynamic model is presented based on two rules. The first one considers the mobilities of the individuals, the second one supposes that the individuals update their opinions independently. The results of the model indicate that the bounded confidence ∈c, separating consensus and incoherent states, of a scale-free network is much smaller than the one of a...

Université de Fribourg

Effect of initial configuration on network-based recommendation

Zhou, Tao ; Jiang, L.-L. ; Su, R.-Q. ; Zhang, Yi-Cheng

In: Europhysics Letters, 2008, vol. 81, no. 5, p. 58004

In this paper, based on a weighted object network, we propose a recommendation algorithm, which is sensitive to the configuration of initial resource distribution. Even under the simplest case with binary resource, the current algorithm has remarkably higher accuracy than the widely applied global ranking method and collaborative filtering. Furthermore, we introduce a free parameter β to...

Université de Fribourg

Empirical study on clique-degree distribution of networks

Xiao, Wei-Ke ; Ren, Jie ; Qi, Feng ; Song, Zhi-Wei ; Zhu, Meng-Xiao ; Yang, Hong-Feng ; Jin, Hui-Yu ; Wang, Bing-Hong ; Zhou, Tao

In: Physical Review E, 2007, vol. 76, no. 3, p. 037102

The community structure and motif-modular-network hierarchy are of great importance for understanding the relationship between structures and functions. We investigate the distribution of clique degrees, which are an extension of degree and can be used to measure the density of cliques in networks. Empirical studies indicate the extensive existence of power-law clique-degree distributions in...

Université de Fribourg

Bipartite network projection and personal recommendation

Zhou, Tao ; Ren, Jie ; Medo, Matúš ; Zhang, Yi-Cheng

In: Physical Review E, 2007, vol. 76, no. 4, p. 046115

One-mode projecting is extensively used to compress bipartite networks. Since one-mode projection is always less informative than the bipartite representation, a proper weighting method is required to better retain the original information. In this article, inspired by the network-based resource-allocation dynamics, we raise a weighting method which can be directly applied in extracting the...

Université de Fribourg

Scaling behaviour and memory in heart rate of healthy human

Cai, Shi-Min ; Peng, Hu ; Yang, Hui-Jie ; Zhou, Tao ; Zhou, Pei-Ling ; Wang, Bing-Hong

In: Chinese Physics Letters, 2007, vol. 24, no. 10, p. 3002

We investigate a set of complex heart rate time series from healthy human in different behaviour states with the detrended fluctuation analysis and diffusion entropy (DE) method. It is proposed that the scaling properties are influenced by behaviour states. The memory detected by DE exhibits an approximately same pattern after a detrending procedure. Both of them demonstrate the long-range strong...

Université de Fribourg

Enhancing the network synchronizability

Zhao, Ming ; Chen, Guan-rong ; Zhou, Tao ; Wang, Bing-hong

In: Frontiers of Physics in China, 2007, vol. 2, no. 4, p. 460-468

The structural and dynamical properties, particularly the small-world effect and scale-free feature, of complex networks have attracted tremendous interest and attention in recent years. This article offers a brief review of one focal issue concerning the structural and dynamical behaviors of complex network synchronization. In the presentation, the notions of synchronization of dynamical systems...