We study the year-after-year properties of three different portfolios traded in the Athens Stock Exchange (ASE) for the time period 1987–2004. We use the minimum spanning tree (MST) technique and the random matrix theory (RMT), which make it possible to examine at the same time the temporal...

A model of Brownian particles with the ability to take up energy from the environment, to store it in an internal depot, and to convert internal energy into kinetic energy of motion, is discussed. The general dynamics outlined in Section 2, is investigated for the deterministic and stochastic...

A stochastic theory is presented for nucleation and growth of clusters in a finite system. We consider a discrete cluster distribution for which the free energy and the equilibrium probability distribution are derived. The cluster growth and shrinkage occurs by the attachment/evaporation of free...

We study phase transitions in models of opinion formation which are based on the social impact theory. Two different models are discussed: (i) a cellular-automata-based model of a finite group with a strong leader where persons can change their opinions but not their spatial positions, and (ii)...

This paper investigates the agglomeration of active walkers (component A) on a two- dimensional surface, described by a potential U(r,t), that determines the motion of the walkers. The walkers are able to change U(rt) locally by producing a second component B, that decreases U(r,t) and which can...

We present analytical investigations of a multiplicative stochastic process that models a simple investor dynamics in a random environment. The dynamics of the investor’s budget, x(t), depends on the stochasticity of the return on investment, r(t), for which different model assumptions are...

For a binary choice problem, the spatial coordination of decisions in an agent community is investigated both analytically and by means of stochastic computer simulations. The individual decisions are based on different local information generated by the agents with a finite lifetime and...