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Université de Fribourg

Cultural evolution: the case of babies’ first names

Xi, Ning ; Zhang, Zi-Ke ; Zhang, Yi-Cheng ; Ge, Zehui ; She, Li ; Zhang, Kui

In: Physica A: Statistical Mechanics and its Applications, 2014, vol. 406, p. 139–144

In social sciences, there is currently rare consensus on the underlying mechanism for cultural evolution, partially due to lack of suitable data. The evolution of first names of newborn babies offers a remarkable example for such researches. In this paper, we employ the historical data on baby names from the United States to investigate the evolutionary process of culture, in particular focusing...

Université de Fribourg

Website-oriented recommendation based on heat spreading and tag-aware collaborative filtering

Zhang, Zi-Ke ; Yu, Lu ; Fang, Kuan ; You, Zhi-Qiang ; Liu, Chuang ; Liu, Hao ; Yan, Xiao-Yong

In: Physica A: Statistical Mechanics and its Applications, 2014, vol. 399, p. 82–88

Recently, Recommender Systems has been widely applied in helping users find potentially interesting items from the era of big data. However, most of researches on this topic have focused on estimating the direct relationships between users and items, neglecting other available information. In this paper, we discuss about mining webs with information extracted from search and browser logs of...

Université de Fribourg

Positive periodic solutions of an epidemic model with seasonality

Sun, Gui-Quan ; Bai, Zhenguo ; Zhang, Zi-Ke ; Zhou, Tao ; Jin, Zhen

In: The Scientific World Journal, 2013, vol. 2013, p. -

An SEI autonomous model with logistic growth rate and its corresponding nonautonomous model are investigated. For the autonomous case, we give the attractive regions of equilibria and perform some numerical simulations. Basic demographic reproduction Rd number is obtained. Moreover, only the basic reproduction number R0 cannot ensure the existence of the positive equilibrium, which needs...

Université de Fribourg

An evolving model of online bipartite networks

Zhang, Chu-Xu ; Zhang, Zi-Ke ; Liu, Chuang

In: Physica A: Statistical Mechanics and its Applications, 2013, vol. 392, no. 23, p. 6100–6106

Understanding the structure and evolution of online bipartite networks is a significant task since they play a crucial role in various e-commerce services nowadays. Recently, various attempts have been tried to propose different models, resulting in either power-law or exponential degree distributions. However, many empirical results show that the user degree distribution actually follows a...

Université de Fribourg

Spatial dynamics of a vegetation model in an arid flat environment

Sun, Gui-Quan ; Li, Li ; Zhang, Zi-Ke

In: Nonlinear Dynamics, 2013, vol. 73, no. 4, p. 2207–2219

Self-organized vegetation patterns in space were found in arid and semi-arid areas. In this paper, we modelled a vegetation model in an arid flat environment using reaction-diffusion form and investigated the pattern formation. By using Hopf and Turing bifurcation theory, we obtain Turing region in parameters space. It is found that there are different types of stationary patterns including...

Université de Fribourg

Deviation of Zipf’s and Heaps’ laws in human languages with limited dictionary sizes

Lü, Linyuan ; Zhang, Zi-Ke ; Zhou, Tao

In: Scientific Reports, 2013, vol. 3, p. -

Zipf's law on word frequency and Heaps' law on the growth of distinct words are observed in Indo-European language family, but it does not hold for languages like Chinese, Japanese and Korean. These languages consist of characters, and are of very limited dictionary sizes. Extensive experiments show that: (i) The character frequency distribution follows a power law with exponent close to one, at...

Université de Fribourg

Hybrid recommendation algorithm based on two roles of social tags

Zhang, Zi-Ke ; Liu, Chuang

In: International Journal of Bifurcation and Chaos, 2012, vol. 22, no. 07, p. 1250166

The past few years have witnessed the great success of a new family of paradigms, social tagging networks, which allows users to freely associate social tags to items and efficiently manage them. Thus it provides us a promising way to effectively find useful and interesting information. In this paper, we consider two typical roles of social tags: (i) an accessorial tool helping users organize...

Université de Fribourg

Recommender systems

Lü, Linyuan ; Medo, Matúš ; Yeung, Chi Ho ; Zhang, Yi-Cheng ; Zhang, Zi-Ke ; Zhou, Tao

In: Physics Reports, 2012, vol. 519, no. 1, p. 1–49

The ongoing rapid expansion of the Internet greatly increases the necessity of effective recommender systems for filtering the abundant information. Extensive research for recommender systems is conducted by a broad range of communities including social and computer scientists, physicists, and interdisciplinary researchers. Despite substantial theoretical and practical achievements, unification...

Université de Fribourg

How altruism works: An evolutionary model of supply networks

Ge, Zehui ; Zhang, Zi-Ke ; Lü, Linyuan ; Zhou, Tao ; Xi, Ning

In: Physica A: Statistical Mechanics and its Applications, 2012, vol. 391, no. 3, p. 647–655

Recently, supply networks have attracted increasing attention from the scientific community. However, it lacks serious consideration of social preference in Supply Chain Management. In this paper, we develop an evolutionary decision-making model to characterize the effects of suppliers’ altruism in supply networks, and find that the performances of both suppliers and supply chains are improved...

Université de Fribourg

Tag-aware recommender systems: a state-of-the-art survey

Zhang, Zi-Ke ; Zhou, Tao ; Zhang, Yi-Cheng

In: Journal of Computer Science and Technology, 2011, vol. 26, no. 5, p. 767-777

In the past decade, Social Tagging Systems have attracted increasing attention from both physical and computer science communities. Besides the underlying structure and dynamics of tagging systems, many efforts have been addressed to unify tagging information to reveal user behaviors and preferences, extract the latent semantic relations among items, make recommendations, and so on. Specifically,...