International Journal of Modern Physics C

We consider the Penna model for biological aging to investigate correlations between early fertility and late life survival rates in populations at equilibrium. We consider inherited initial reproduction ages together with a reproduction cost translated in a probability that mother and offspring die at birth, depending on the mother age. For convenient sets of parameters, the equilibrated populations present genetic variability in what regards both genetically programmed death age and initial reproduction age. In the asexual Penna model, a negative correlation between early life fertility and late life survival rates naturally emerges in the stationary solutions. In the sexual Penna model, selection experiments are performed where individuals are sorted by initial reproduction age from the equilibrated populations and the separated populations are evolved independently. After a transient, a negative correlation between early fertility and late age survival rates also emerges in the sense that populations that start reproducing earlier present smaller average genetically programmed death age. These effects appear due to the age structure of populations in the steady state solution of the evolution equations. We claim that the same demographic effects may be playing an important role in selection experiments in the laboratory.

A probabilistic model is proposed with dynamics which naturally leads to a bottleneck in the number of mitochondria transmitted from one host-cell generation to the other. We take into account deleterious mutations during the replication of mitochondria within a cell of a germ-line and introduce selection inside the cell reproduction mechanism. The bottleneck size strongly depends on the selection mechanism and on the maximum number of mitochondria per cell. We obtain that the smaller the maximum allowed number of mitochondria per cell during replication, the tighter the bottleneck. Such a result is in agreement with the fact that species producing small litters provide developing oocytes with a smaller number of mitochondria. This amplifies the differences among oocytes leading to competition and removal of inferior cells.

A comparison of sexual with asexual reproduction in the Penna aging model for a single species shows the separation into males and females at a disadvantage due to the halved number of births. Also meiotic and apomictic parthenogenesis and hermaphroditism seem better than sex, even when the individuals follow the suggestion of Jan et al. to engage in sex only when their lifes are endangered by a large number of harmful mutations. In our comparison, we looked only for intrinsic effects, not for external influences like parasites or environmental catastrophes.

In order to see the phase conversion taking place in a weak first-order phase transition, we have simulated the q = 3 state Potts model in three dimensions and studied the time evolutions of oriented clusters forming after a rapid temperature quench. Our results indicate that the phase conversion mechanism following a deep temperature quench is spinodal decomposition while a rather shallow quench to temperatures near the phase transition point proceeds through usual nucleation.

In collision-based computing, quanta of information are represented by autonomous mobile signals. The signals travel in a uniform architectureless medium. They collide to each other. Assuming the presence or abscence of a signal represent truth or falsity values of logical variable, we can consider logical functions are calculated at the sites of signals' collision. Physically, the signals are localized compact disturbances of medium's characteristics. In this paper, we extensively exploit results published in Refs. 1–7. We consider three types of localizations: breathers in one-dimensional arrays of DNA molecules, excitons and groups of antialigned dipoles in two-dimensional arrays of Scheibe aggregates and microtubules respectively. Several forms of logical gates are extracted from published results on numerical simulation of breathers and excitons. In cellular automata models, we study interactions of the localizations with each other. We show what kinds of logical gates can be realized in such interactions. Parallels between physical and discrete automata models are provided.

We consider the Hamilton operator . We assume that has a discrete spectrum. We show that the energy eigenvalues and eigenvectors obey an autonomous system of ordinary differential equations. An implementation of this system of differential equations is given using SymbolicC++.

Diffusion on 2D site percolation clusters at p = 0.7, 0.8, and 0.9 above p_c on the square lattice in the presence of two crossed bias fields, a local bias B and a global bias E, has been investigated. The global bias E is applied in a fixed global direction whereas the local bias B imposes a rotational constraint on the motion of the diffusing particle. The rms displacement R_t ~ t^k in the presence of both biases is studied. Depending on the strength of E and B, the behavior of the random walker changes from diffusion to drift to no-drift or trapping. There is always diffusion for finite B with no global bias. A crossover from drift to no-drift at a critical global bias E_c is observed in the presence of local bias B for all disordered lattices. At the crossover, value of the rms exponent changes from k = 1 to k < 1, the drift velocity v_t changes from constant in time t to decreasing power law nature, and the "relaxation" time τ has a maximum rate of change with respect to the global bias E. The value of critical bias E_c depends on the disorder p as well as on the strength of local bias B. Phase diagrams for diffusion, drift, and no-drift are obtained as a function of bias fields E and B for these systems.

We present a dynamic model of a population under selection pressure and in a changing habitat. Two kinds of changes are considered: In the first climate changes in one direction only, like in coming of the glacial era; in the second, the changes are randomly fluctuating. We compare four evolutionary strategies: First: evolution without any external influence; second: evolution where ill-fitted individuals are eliminated; third: where the phenotypes of the progeny are improved to make them better fit to the existing conditions, and finally evolution where the last two procedures are applied together. We show that the systematic phenotype improvement is the most successful strategy in the long run and the elimination of the ill-fitted almost always leads to a disaster.

In economics, comparative analysis plays the same role as experimental research in physics. In this paper, we closely examine several methodological problems related to comparative analysis by investigating the specific example of grain markets in China and France respectively. This enables us to answer a question in economic history which has so far remained pending, namely whether or not market integration progressed in the 18th century. In economics as in physics, before any new result being accepted, it has to be checked and re-checked by different researchers. This is what we call the replication and comparison procedures. We show how these procedures should (and can) be implemented.

We study the ratio of the number of sites in the largest and second largest clusters in random percolation. Using the scaling hypothesis that the ratio <M₁>/<M₂> of the mean cluster sizes M₁ and M₂ scales as f ((p - p_c) L^1/ν), we employ finite-size scaling analysis to find that <M₁>/<M₂> is nonuniversal with respect to the boundary conditions imposed. The mean <M₁/M₂> of the ratios behaves similarly although with a distinct critical value reflecting the relevance of mass fluctuations at the percolation threshold. These zero exponent ratios also allow for reliable estimates of the critical parameters at percolation from relatively small lattices.

The vacancy mechanism is simulated by means of Monte Carlo (MC) method. In this model, the impurity diffusion occurs by migration of substitutional atoms B via the exchange with vacancies whose frequencies near a solute atom differ from a free vacancy. Whenever a defect leaves the lattice, periodic boundary conditions are made to bring it into the lattice. The solute concentration profiles are given using a technique developed by Murch which has been shown to be equivalent to a finite source. The fit of these profiles allows the comparison between our results and analytical solutions. The parameters extracted from a Gaussian function fit which agrees well with numerical profiles are in very good quantitative agreement with theoretical predictions.

A quasi-three-dimensional mathematical model has been developed to study the morphological processes based on equilibrium sediment transport method. The flow velocities are computed by a two-dimensional horizontal depth-averaged flow model (H2D) in combination with logarithmic velocity profiles. The transport of sediment particles by a flow water has been considered in the form of bed load and suspended load. The bed load transport rate is defined as the transport of particles by rolling and saltating along the bed surface and is given by the Van Rijn relationship (1987). The equilibrium suspended load transport is described in terms of an equilibrium sediment concentration profile (ce) and a logarithmic velocity (u). Based on the equilibrium transport, the bed change rate is given by integration of the sediment mass-balance equation. The model results have been compared with a Van Rijn results (equilibrium approach) and good agreement has been found.

In Ref. 1, a new model for the description of the financial markets dynamics has been proposed. Traders move on a two dimensional lattice and interact by means of mechanisms of mutual influence. In the present paper, we present results from large-scale simulations of the same model enhanced by the introduction of rational traders modeled as moving-averages followers. The dynamics now accounts for log-normal distribution of volatility which is consistent with some observation of real financial indexes⁷ at least for the central part of the distribution.

We consider different versions of exploration in reinforcement learning. For the test problem, we use navigation in a shortcut maze. It is shown that chaotic ∊-greedy policy may be as efficient as a random one. The best results were obtained with a model chaotic neuron. Therefore, exploration strategy can be implemented in a deterministic learning system such as a neural network.

We investigate the dynamic relaxation for SU(2) gauge theory at finite temperatures in (3 + 1) dimensions. Using the Hybrid Monte Carlo algorithm, we examine the time dependence of the system in the short-time regime. Starting from the ordered state, the critical exponents β, ν and z are calculated from the power law behavior of the Polyakov loop and the cumulant at or near the critical point. The results for the static exponents are in agreement with those obtained from simulations in equilibrium and those of the three-dimensional Ising model. The value for the dynamic critical exponent was determined with z = 2.0(1).

Brazilian drivers caught in traffic violations accumulate points in their official personal files. Here, we analyze the distribution probability of these data for the state of Rio de Janeiro where 4199 drivers accumulated 20 or more penalty points during one year.

From numerical methods point of view of dynamical systems, we have determined dynamical behaviors of the corresponding systems (i.e., chaotic, stable, bifurcations possibility, etc.). New versions of numerical methods are derived and we have compared the dynamical behaviors of the continuous dynamical systems with their corresponding discrete dynamical systems. An application of partial differential equations is given for reaction-diffusion and telegraph equations.