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Dietrich Stauffer

Publications and source records attributed to Dietrich Stauffer.

At least 37 records · Page 2Linked to original sources
arXiv2007

Superdiffusion in a Model for Diffusion in a Molecularly Crowded Environment

We present a model for diffusion in a molecularly crowded environment. The model consists of random barriers in percolation network. Random walks in the presence of slowly moving barriers show normal diffusion for long times, but anomalous diffusion at intermediate times. The effective exponents for square distance versus time usually are below one at these intermediate times, but can be also larger than one for high barrier concentrations. Thus we observe sub- as well as super-diffusion in a crowded environment.

q-bio.SC↗
arXiv2007

Monte Carlo Simulation of Age-Dependent Host-Parasite Relations

The death of a biological population is an extreme event which we investigate here for a host-parasitoid system. Our simulations using the Penna ageing model show how biological evolution can ``teach'' the parasitoids to avoid extinction by waiting for the right age of the host. We also show the dependence of extinction time on the population size.

q-bio.PE↗
arXiv2007

Monte Carlo Simulation of Medical Resource Allocation

Computer simulations prove that we should spend more money on red wine than on medication. We optimise the problem of how to distribute a fixed amount of money between medication and food spendings, using the Penna ageing model.

q-bio.PE↗
arXiv2007

Competition of languages in the presence of a barrier

Using the Schulze model for Monte Carlo simulations of language competition, we include a barrier between the top half and the bottom half of the lattice. We check under which conditions two different languages evolve as dominating in the two halves.

physics.soc-ph↗
arXiv2006

"Antiferromagnetism" in social relations and Bonabeau model

We here present a fixed agents version of an original model of the emergence of hierarchies among social agents first introduced by Bonabeau \textit{et al}. Having interactions occurring on a social network rather than among 'walkers' doesn't drastically alter the dynamics. But it makes social structures more stable and give a clearer picture of the social organisation in a `mixed' regime.

physics.soc-ph↗
arXiv2006

Phase transition in Nowak-Sznajd opinion dynamics

The Nowak modification of the Sznajd opinion dynamics model on the square lattice assumes that with probabilities beta and gamma the opinions flip due to mass-media advertising from down to up, and vice versa. Besides, with probability alpha the Sznajd rule applies that a neighbour pair agreeing in its two opinions convinces all its six neighbours of that opinion. Our Monte Carlo simulations and mean-field theory find sharp phase transitions in the parameter space.

physics.soc-ph↗
arXiv2006

On the relation between structural diversity and geographical distance among languages: observations and computer simulations

The recent availability of larger typological databases such as Haspelmath et al. (2005) has brought the linguistics community closer to having a solid, empirical foundation for making actual claims about prehistoric migrations, deep genealogical relationship, and patterns of areal linguistic interaction. Nevertheless, still more data are needed, and more than anything a number of methodological problems need to be adressed. These problems, which are the focus of this paper. These questions will be addressed from two perspectives. The first perspective is an empirical one, where observations primarily derive from analyses of the data of Haspelmath et al. (2005). The second perspective is a computational one, where simulations are drawn upon to test the effects of different parameters on the development of structural linguistic diversity. The results suggest that there is indeed some hope that we may derive new empirical insights regarding linguistic prehistory by drawing upon typological data. We do not, however, make any specific empirical claims in this paper, but instead concentrate our efforts on methodology

physics.soc-ph↗
arXiv2006

Why are diploid genomes widespread and dominant mutations rare?

We have used the sexual Penna ageing model to show that the relation between dominance and recessiveness could be a force which optimizes the genome size. While the possibility of complementation of the damaged allele by its functional counterparts (recessiveness) leads to the redundancy of genetic information, the dominant effect of defective genes tends to diminish the number of alleles fulfilling the same function. Playing with the fraction of dominant loci in the genome it is possible to obtain the condition where the diploid state of the genome is optimal. If the status of each bit position as dominant or recessive mutations is changed for each individual randomly and rarely, then after a long time a stationary equilibrium of many recessive and few dominant loci is established in the sexual Penna model. This effect vanishes if the same changing distribution of dominant loci applies to all individuals.

q-bio.PE↗
arXiv2006

Monte Carlo simulation of survival for minority languages

Our earlier language model is modified to allow for the survival of a minority language without higher status, just because of the pride of its speakers in their linguistic identity. An appendix studies the roughness of the interface for linguistic regions when one language conquers the whole territory.

physics.soc-ph↗
arXiv2006

Can a few fanatics influence the opinion of a large segment of a society?

Models that provide insight into how extreme positions regarding any social phenomenon may spread in a society or at the global scale are of great current interest. A realistic model must account for the fact that globalization and internet have given rise to scale-free networks of interactions between people. We propose a novel model which takes into account the nature of the interactions network, and provides some key insights into this phenomenon, including: (1) There is a fundamental difference between a hierarchical network whereby people are influenced by those that are higher on the hierarchy but not by those below them, and a symmetrical network where person-on-person influence works mutually. (2) A few "fanatics" can influence a large fraction of the population either temporarily (in the hierarchical networks) or permanently (in symmetrical networks). Even if the "fanatics" disappear, the population may still remain susceptible to the positions advocated by them. The model is, however, general and applicable to any phenomenon for which there is a degree of enthusiasm or susceptibility to in the population.

physics.soc-ph↗
arXiv2006

Modelling linguistic taxonomic dynamics

This paper presents the results of the application of a bit-string model of languages (Schulze and Stauffer 2005) to problems of taxonomic patterns. The questions addressed include the following: (1) Which parameters are minimally ne eded for the development of a taxonomic dynamics leading to the type of distribution of language family sizes currently attested (as measured in the i number of languages per family), which appears to be a power-law? (2) How may such a model be coupled with one of the dynamics of speaker populations leading to the type of language size seen today, which appears to follow a log-normal distribution?

physics.soc-ph↗
arXiv2006

Computer simulation of language competition by physicists

Computer simulation of languages is an old subject, but since the paper of Abrams and Strogatz (2003) several physics groups independently took up this field. We shortly review their work and bring more details on our own simulations.

physics.soc-ph↗
arXiv2006

Power Laws and Gaussians for Stock Market Fluctuations

The daily volume of transaction on the New York Stock Exchange and its day-to-day fluctuations are analysed with respect to power-law tails as well long-term trends. We also model the transition to a Gaussian distribution for longer time intervals, like months instead of days.

physics.soc-ph↗
arXiv2006

Microscopic Abrams-Strogatz model of language competition

The differential equations of Abrams and Strogatz for the competition between two languages are compared with agent-based Monte Carlo simulations for fully connected networks as well as for lattices in one, two and three dimensions, with up to 10^9 agents.

physics.comp-ph↗
arXiv2005

Simulation of language competition by physicists

Following Abrams and Strogatz 2003 and Patriarca and Leppanen 2004, five other physics groups independently started to simulate the competition of languages, as opposed to the evolution of a human language out of ape sounds, or the learning of a language by a child. This talk concentrates on the models of Christian Schulze et al and of Viviane de Oliveira et al which allow the simulation of a large number of languages, similar to today's 8,000 human languages. The first model deals with a continuous process of random mutations of a language, transfer from and to other languages, and flight away from languages spoken by only a few people. The second model combines these flight and mutation aspects, ignores transfer and describes the colonization of a large geographical region by people starting at one lattice point. The size of a language is defined by the number of people speaking it. The first model gives a realistic log-normal shape for the histogram of language sizes but the numbers are bad. For the second model our Monte Carlo simulations give sizes up to thousand million, but not the nearly log-normal shape. A meeting is planned for mid-September 2006 in Poland.

physics.soc-ph↗
arXiv2005

Simulation of Rapoport's rule for latitudinal species spread

Rapoport's rule claims that latitudinal ranges of plant and animal species are generally smaller at low than at high latitudes. However, doubts as to the generality of the rule have been expressed, because studies providing evidence against the rule are more numerous than those in support of it. In groups for which support has been provided, the trend of increasing latitudinal ranges with latitude is restricted to or at least most distinct at high latitudes, suggesting that the effect may be a local phenomenon, for example the result of glaciations. Here we test the rule using two models, a simple one-dimensional one with a fixed number of animals expanding in a northern or southerly direction only, and the evolutionary/ecological Chowdhury model using birth, ageing, death, mutation, speciation, prey-predator relations and food levels. Simulations with both models gave results contradicting Rapoport's rule. In the first, latitudinal ranges were roughly independent of latitude, in the second, latitudinal ranges were greatest at low latitudes, as also shown empirically for some well studied groups of animals.

q-bio.PE↗
arXiv2005

Does telomere elongation lead to a longer lifespan if cancer is considered?

As cell proliferation is limited due to the loss of telomere repeats in DNA of normal somatic cells during division, telomere attrition can possibly play an important role in determining the maximum life span of organisms as well as contribute to the process of biological ageing. With computer simulations of cell culture development in organisms, which consist of tissues of normal somatic cells with finite growth, we otain an increase of life span and life expectancy for longer telomeric DNA in the zygote. By additionally considering a two-mutation model for carcinogenesis and indefinite proliferation by the activation of telomerase, we demonstrate that the risk of dying due to cancer can outweigh the positive effect of longer telomeres on the longevity.

q-bio.PE↗