T. J. P. Penna

A bit-string model for biological aging

We present a simple model for biological aging. We study it through computer simulations and fint it to reflect some features of real populations.

Crossover in the Cont–Bouchaud percolation model for market fluctuations

Monte Carlo simulations of the Cont–Bouchaud herding model for stock market traders show power-law distributions for short times and exponential truncation for longer time intervals, if they are made at the percolation threshold in two to seven dimensions.

Broad histogram Monte Carlo

Abstract:We propose a new Monte Carlo technique in which the degeneracy of energy states is obtained with a Markovian process analogous to that of Metropolis used currently in canonical simulations. The obtained histograms are much broader than those of the canonical histogram technique studied by Ferrenberg and Swendsen. Thus we can reliably reconstruct thermodynamic functions over a much larger temperature scale also away from the critical point. We show for the two-dimensional Ising model how our new method reproduces exact results more accurately and using less computer time than the conventional histogram method. We also show data in three dimensions for the Ising ferromagnet and the Edwards Anderson spin glass.

Mutation accumulation and the catastrophic senescence of the Pacific salmon.

The bit-string model of biological aging is used to simulate the catastrophic senescence of Pacific Salmon. We have shown that reproduction occuring only once and at a fixed age is the only ingredient needed to explain the catastrophic senescence according the mutation accumulation theory. Several results are presented, some of them with up to

Simulating the vanishing of northern cod fish

10^8

Agent-based model to rural–urban migration analysis

fishes, showing how the survival rates in catastrophic senescence are affected by changes in the parameters of the model.

Long-range anticorrelations and non-Gaussian behavior of a leaky faucet

Introducing fishing in a recently presented model for biological ageing we show, through computer simulations, how a slight increase of fishing may destroy a whole stable population.

Theoretical approach to biological aging

In this paper, we analyze the rural–urban migration phenomenon as it is usually observed in economies which are in the early stages of industrialization. The analysis is conducted by means of a statistical mechanics approach which builds a computational agent-based model. Agents are placed on a lattice and the connections among them are described via an Ising-like model. Simulations on this computational model show some emergent properties that are common in developing economies, such as a transitional dynamics characterized by continuous growth of urban population, followed by the equalization of expected wages between rural and urban sectors (Harris–Todaro equilibrium condition), urban concentration and increasing of per capita income.

Computer simulations for biological aging and sexual reproduction

We find that intervals between successive drops from a leaky faucet display scale-invariant, long-range anticorrelations characterized by the same exponents of heart beat-to-beat intervals of healthy subjects. This behavior is also confirmed by numerical simulations on lattice and it is faucet-width- and flow-rate-independent. The histogram for the drop intervals is also well described by a Levy distribution with the same index for both histograms of healthy and diseased subjects. This additional result corroborates the evidence for similarities between leaky faucets and healthy hearts underlying dynamics.

Detrended fluctuation analysis of a systolic blood pressure control loop

We present a model for biological aging that considers the number of individuals whose (inherited) genotype determines the maximum age for death: each individual may die before that age due to some external factor, but never after that limit. The genotype of the offspring is inherited from the parent with some mutations, described by a transition matrix. The model can describe different strategies of reproduction and it is exactly soluble. We applied our method to the bit-string model for aging and the results are in perfect agreement with numerical simulations.