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D. Stauffer

Publications and source records attributed to D. Stauffer.

At least 55 records · Page 3Linked to original sources
arXiv2005

Bonabeau model on a fully connected graph

Numerical simulations are reported on the Bonabeau model on a fully connected graph, where spatial degrees of freedom are absent. The control parameter is the memory factor f. The phase transition is observed at the dispersion of the agents power h_i. The critical value f_C shows a hysteretic behavior with respect to the initial distribution of h_i. f_C decreases with the system size; this decrease can be compensated by a greater number of fights between a global reduction of the distribution width of h_i. The latter step is equivalent to a partial forgetting.

physics.soc-ph↗
arXiv2005

Interdisciplinary Monte Carlo Simulations

Biological, linguistic, sociological and economical applications of statistical physics are reviewed here. They have been made on a variety of computers over a dozen years, not only at the NIC computers. A longer description can be found in our new book, an emphasis on teaching in Eur.J.Phys. 26, S 79 and AIP Conf. Proc. 779, 49, 56, 69 and 75.

physics.pop-ph↗
arXiv2005

Species Numbers versus Area in Chowdhury Ecosystems

For a fixed number of food levels on a lattice, the Chowdhury model for ecosystem is simulated and found to give a number of different species which approaches exponentially a plateau if the considered area is increased.

q-bio.PE↗
arXiv2005

Ising model simulation in directed lattices and networks

On directed lattices, with half as many neighbours as in the usual undirected lattices, the Ising model does not seem to show a spontaneous magnetisation, at least for lower dimensions. Instead, the decay time for flipping of the magnetisation follows an Arrhenius law on the square and simple cubic lattice. On directed Barabasi-Albert networks with two and seven neighbours selected by each added site, Metropolis and Glauber algorithms give similar results, while for Wolff cluster flipping the magnetisation decays exponentially with time.

cond-mat.stat-mech↗
arXiv2005

Absence of ferromagnetism in Ising model on directed Barabasi-Albert network

With up to 7 million spins, the existence of spontaneous magnetization of Ising spins on directed Barabasi-Albert networks is investigated by Monte Carlo simulations. We confirm our earlier result that the magnetization for different temperatures T decays after a characteristic time tau(T), which we extrapolate to diverge at zero temperature by a modified Arrhenius law,or perhaps a power law.

cond-mat.dis-nn↗
arXiv2004

Scaling effects in the Penna ageing model

We have analysed the possibility of scaling the sexual Penna ageing model. Assuming that the number of genes expressed before the reproduction age grows linearly with the genome size and that the mutation rate per genome and generation is constant, we have found that the fraction of defective genes expressed before the minimum reproduction age drops with the genome size, while the number of defective genes eliminated by the genetic death grows with genome size. Thus, the evolutionary costs decrease with enlarging the genome. After rescaling the time scale according to the mutational clock, age distributions of populations do not depend on the genome size. Nevertheless, enlarging the genome increases the reproduction potential of populations.

q-bio.PE↗
arXiv2004

Simple Bit-String Model for Lineage Branching

We introduce a population dynamics model, where individual genomes are represented by bit-strings. Selection is described by death probabilities which depend on these genomes, and new individuals continuously replace the ones that die, keeping the population constant. An offspring has the same genome as its (randomly chosen) parent, except for a small amount of (also random) mutations. Chance may thus generate a newborn with a genome that is better than that of its parent, and the newborn will have a smaller death probability. When this happens, this individual is a would-be founder of a new lineage. A new lineage is considered created if its alive descendence grows above a certain previously defined threshold. The time evolution of populations evolving under these rules is followed by computer simulations and the probability densities of lineage duration and size, among others, are computed. These densities show a scale-free behaviour, in accordance with some conjectures in paleoevolution, and suggesting a simple mechanism as explanation for the ubiquity of these power-laws.

cond-mat.stat-mech↗
arXiv2004

Simulation and Experiment of Extinction or Adaptation

Can unicellular organisms survive a drastic temperature change, and adapt to it after many generations? In simulations of the Penna model of biological ageing, both extinction and adaptation were found for asexual and sexual reproduction as well as for parasex. These model investigations are the basis for the design of evolution experiments with heterotrophic flagellates.

q-bio.PE↗
arXiv2004

Discretized opinion dynamics of Deffuant on scale-free networks

The consensus model of Deffuant et al is simplified by allowing for many discrete instead of infinitely many continuous opinions, on a directed Barabasi-Albert network. A simple scaling law is observed. We then introduce noise and also use a more realistic network and compare the results. Finally, we look at a multi-layer model representing various age levels, and we include advertising effects.

cond-mat.stat-mech↗
arXiv2003

Tobin tax and market depth

This paper investigates - on the basis of the Cont-Bouchaud model - whether a Tobin tax can stabilize foreign exchange markets. Compared to earlier studies, this paper explicitly recognizes that a transaction tax-induced reduction in market depth may increase the price responsiveness of a given order. We find that the imposition of a transaction tax may still achieve a triple dividend: (1) exchange rate fluctuations decrease, (2) currencies are less mispriced, and (3) central authorities raise substantial tax revenues. However, if the price impact function is too sensitive with respect to market depth, stabilization may turn into destabilization.

cond-mat.stat-mech↗
arXiv2003

Simulation of Consensus Model of Deffuant et al on a Barabasi-Albert Network

In the consensus model with bounded confidence, studied by Deffuant et al. (2000), two randomly selected people who differ not too much in their opinion both shift their opinions towards each other. Now we restrict this exchange of information to people connected by a scale-free network. As a result, the number of different final opinions (when no complete consensus is formed) is proportional to the number of people.

cond-mat.stat-mech↗
arXiv2003

Are the Tails of Percolation Thresholds Gaussians ?

The probability distribution of percolation thresholds in finite lattices were first believed to follow a normal Gaussian behaviour. With increasing computer power and more efficient simulational techniques, this belief turned to a stretched exponential behaviour, instead. Here, based on a further improvement of Monte Carlo data, we show evidences that this question is not yet answered at all.

cond-mat.stat-mech↗
arXiv2003

Corrections to Finite Size Scaling in Percolation

A 1/L-expansion for percolation problems is proposed, where L is the lattice finite length. The square lattice with 27 different sizes L = 18, 22 ... 1594 is considered. Certain spanning probabilities were determined by Monte Carlo simulations, as continuous functions of the site occupation probability p. We estimate the critical threshold pc by applying the quoted expansion to these data. Also, the universal spanning probability at pc for an annulus with aspect ratio r=1/2 is estimated as C = 0.876657(45).

cond-mat.stat-mech↗
arXiv2003

Positive mutations and mutation-dependent Verhulst factor in Penna ageing model

We twice modify the Penna model for biological ageing. First we introduce back (good) mutations and a memory for them into the model. It allows us to observe an improvement of the species fitness over long time scales as well as punctuated equilibrium. Second we adopt a food/space competition factor that depends on the number of accumulated mutations in the individuals genomes, and get rid of the fixed limiting number of allowed mutations. Besides reproducing the main results of the standard model, we also observe a mortality maximum for the oldest old.

cond-mat.stat-mech↗
arXiv2003

Asymmetry in hierarchy model of Bonabeau et al

The 1995 model of Bonabeau et al. explains the emergence of social hierarchies through randomness, but gives as many leaders as followers. A simple modification allows a more realistic asymmetry with much less leaders.

cond-mat.stat-mech↗
arXiv2003

Simulation of Galam's contrarian opinions

Galam's model of people voting always against the majority is shown to give for the quenched case different results than the original annealed model. For people diffusing on a lattice, Galam's phase transitions happen only at higher concentrations of people.

cond-mat.stat-mech↗