Is visitors’ attendance a fair indicator of a web site's quality? Internet sub-domains are usually characterized by power-law distributions of visits, thus suggesting a rich-get-richer process. If this is the case, the number of visits is not a relevant measure of quality. If, on the other...

We study various aspects of the self-organized critical phenomena. A continuous-energy model is analyzed using a self-consistent effective medium method. We find that energy is homogeneously and isotropically distributed in space. We have calculated analytically the critical energy, which is...

We study the scaling behavior in currency exchange rates. Our results suggest that they satisfy scaling with an exponent close to 0.5, but that it differs qualitatively from that of a simple random walk. Indeed price variations cannot be considered as independent variables and subtle...

A binary game is introduced and analysed. N players have to choose one of the two sides independently and those on the minority side win. Players use a finite set of ad hoc strategies to make their decision, based on the past record. The analysing power is limited and can adapt when necessary....

Recommender systems help people cope with the problem of information overload. A recently proposed adaptive news recommender model [M. Medo, Y.-C. Zhang, T. Zhou, Europhys. Lett. <Emphasis Type="Bold">88, 38005 (2009)] is based on epidemic-like spreading of news in a social network. By means of agent-based...</emphasis>

We study simultaneous price drops of real stocks and show that for high drop thresholds they follow a power-law distribution. To reproduce these collective downturns, we propose a minimal self-organized model of cascade spreading based on a probabilistic response of the system elements to...

We propose a continuum model for the description of buyer and seller dynamics in an Internet market. The relevant variables are the research effort of buyers and the sellers' reputation building process. We show that, if a commercial website gives consumers the possibility to rate credibly...

The unprecedented access offered by the World Wide Web brings with it the potential to gather huge amounts of data on human activities. Here we exploit this by using a toy model of financial markets, the Minority Game (MG), to investigate human speculative trading behaviour and information...

When assets are correlated, benefits of investment diversification are reduced. To measure the influence of correlations on investment performance, a new quantity--the effective portfolio size--is proposed and investigated in both artificial and real situations. We show that in most cases, the...