Structure and Dynamics of Surface Adsorbed Clusters

Extensive numerical simulation are reported for the structure and dynamics of large clusters on metal(100) surfaces. Different types of perimeter hopping processes makes center-of-mass of the cluster to follow a a random walk trajectory. Then, a {\it diffusion coefficient} $D$ can be defined as $\lim\limits_{t\to \infty} D(t)$, with $D(t)=/(4t)$ and $d$ the displacement of the center-of-mass. In the simulations, the dependence of the diffusion coefficient on those perimeter hopping processes can be analyzed in detail, since the relations between different rates for the processes are explicitly considered as parameters.Comment: 8 pages, 4 figure

A Model of Coupled-Maps for Economic Dynamics

An array system of coupled maps is proposed as a model for economy evolution. The local dynamics of each map or agent is controlled by two parameters. One of them represents the growth capacity of the agent and the other one is a control term representing the local environmental pressure which avoids an exponential growth. The asymptotic state of the system evolution displays a complex behavior. The distribution of the maps values in this final regime is of power law type. In the model, inequality emerges as a result of the dynamical processes taking place in the microscopic scales.Comment: 4 pages, 2 figure

Symmetry pattern transition in cellular automata with complex behavior

A transition from asymmetric to symmetric patterns in time-dependent extended systems is described. It is found that one dimensional cellular automata, started from fully random initial conditions, can be forced to evolve into complex symmetrical patterns by stochastically coupling a proportion $p$ of pairs of sites located at equal distance from the center of the lattice. A nontrivial critical value of $p$ must be surpassed in order to obtain symmetrical patterns during the evolution. This strategy is able to classify the cellular automata rules -with complex behavior- between those that support time-dependent symmetric patterns and those which do not support such kind of patterns.Comment: 6 pages, 3 figure

On the objective existence of physical processes: a physicist's philosophical view

Inspired by philosophical ideas of Boltzmann, which are briefly recalled, we provide strong support for the possibility and convenience of a realistic world picture, properly nuanced. The arguments have consequences for the interpretation of quantum mechanics, and for relevant concepts of quantum field and string theory, like monopoles and branes. Our view is illustrated with a cybernetic analogy and complemented with a summary of the basic philosophical concepts.Comment: 15 pages, 1 figur

Algorithmic Complexity in Noise Induced Transport Systems

Time correlated fluctuations interacting with a spatial asymmetry potential are sufficient conditions to give rise to transport of Brownian particles. The transfer of information coming from the nonequilibrium bath, viewed as a source of negentropy, give rise to the correlated noise. The algorithmic complexity of an object provides a means of quantitating its information contents. The Kolmogorov information entropy or algorithmic complexity is investigated in order to quantitate the transfer of information that occurs in computational models showing noise induced transport. The complexity is measured in terms of the average number of bits per time unit necessary to specify the sequence generated by the system.Comment: 7 pages, 2 figure

Gaseous wakes and dynamical friction: mass-losing and mass-gaining perturbers

An extended gravitational object embedded in a parent system comprised of gas and collisionless particles may undergo both dynamical friction (DF) and mass loss by tidal forces. If the object is compact enough, it can increase its mass through accretion of material from the surrounding medium. We extend the classical linear analysis of DF on a constant-mass body in a gaseous medium to the case where its mass changes with time. We show that the structure of the wake may differ significantly from the constant-mass case. For instance, the front-back symmetry of density about subsonic constant-mass perturbers is broken down for variable-mass perturbers. The density wake keeps a memory of the past mass history of the perturber. For dissolving perturbers, the density field is more dense than expected using the instantaneous mass of the perturber in the classical formula. As a consequence, the instantaneous-mass approximation underestimates the drag force for mass-losing perturbers and overestimates it for mass-gaining perturbers. We present cases in which the percentage error in the drag force using the instantaneous-mass approximation is greater than 50%.Comment: 16 pages, 15 figures, accepted for publication in MNRA

Charged Higgs production at photon colliders in 2HDM-III

We study charged Higgs production in the process $\gamma\gamma\to A^0\to W^- H^+$. The processes $\gamma\gamma\to A^0$ are loop mediated in a 2HDM. This is due to the fact that photons only couple directly to charged particles and the Higgs only couples to particles with mass acquired via Higgs mechanism. Although in MSSM the contribution from the process $\gamma\gamma\to A^0$ is too small, it has been found that in a more general 2HDM it could be enhanced. On the other hand, the boson $A^0$ can decay in $W^- H^+$ at tree level and the charged Higgs can decay in fermions. So, the whole process under study is $\gamma\gamma\to A^0\to (W^-\to l\nu) (H^+\to f_if_j)$ in 2HDM-III. Evidence about charged Higgs existence could demonstrate that structure of the Higgs sector has several multiplets.Comment: 5 pages, 4 figures, to appear Brazilian Journal of Physic

Motion of grains in a vibrated U-tube

We investigate experimentally the behavior of the rate of growth of a column of grains, in a partially filled vertically shaken U-tube. For the set of frequencies used we identify three qualitatively different behaviors for the growth rate $\gamma$ as a function of the dimensionless acceleration $\Gamma$: 1) an interval of zero growth for low $\Gamma$ with a smooth change to nonzero growth, analogous to a continuous phase transition; 2) a sigmoidal region for $\gamma$ at intermediate values of the dimensionless acceleration $\Gamma$; and 3) an abrupt change from high values of $\gamma$ to zero growth at high values of $\Gamma$, similar to a first order phase transition. We obtain that our data is well described by a simple differential equation for the change of the growth rate with the dimensionless acceleration of the vertical vibrations.Comment: 5 pages, 6 figures, original pape

Scaling properties of discontinuous maps

We study the scaling properties of discontinuous maps by analyzing the average value of the squared action variable $I^2$. We focus our study on two dynamical regimes separated by the critical value $K_c$ of the control parameter $K$: the slow diffusion ($K<K_c$) and the quasilinear diffusion ($K>K_c$) regimes. We found that the scaling of $I^2$ for discontinuous maps when $K\ll K_c$ and $K\gg K_c$ obeys the same scaling laws, in the appropriate limits, than Chirikov's standard map in the regimes of weak and strong nonlinearity, respectively. However, due to absence of KAM tori, we observed in both regimes that $I^2\propto nK^\beta$ for $n\gg 1$ (being $n$ the $n$-th iteration of the map) with $\beta\approx 5/2$ when $K\ll K_c$ and $\beta\approx 2$ for $K\gg K_c$.Comment: 5 pages, 7 figure

A model of coupled maps with Pareto behavior

A deterministic system of coupled maps is proposed as a model for economic activity among interacting agents. The values of the maps represent the wealth of the agents. The dynamics of the system is controlled by two parameters. One parameter expresses the growth capacity of the agents and the other describes the local environmental pressure. For some values of the parameters, the system exhibits nontrivial collective behavior, characterized by macroscopic periodic oscillations of the average wealth of the system, emerging out of local chaos. The probability distribution of wealth in the asymptotic regime shows a power law behavior for some ranges of parameters.Comment: 2 pages, 3 figures, accepted in the European Physical Journal - Special Topics. Presented in the Workshop on Complex Systems: New Trends and Expectation, Santander, Spain (2006