arXiv subjects

M. Ravasz

Publications and source records attributed to M. Ravasz.

5 recordsLinked to original sources

arXiv2005

Species Abundances Distribution in Neutral Community Models

An analytical approximation is derived for the Zero Sum Multinomial distribution which gives the Species Abundance Distribution in Neutral Community Models. The obtained distribution function describes well computer simulation results on the model, and leads to an interesting relation between the total number of individuals, total number of species and the size of the most abundant species of the considered metacommunity. Computer simulations on neutral community models, proves also the validity of this scaling relation.

q-bio.PE↗

arXiv2005

The Species Abundances Distribution in a new perspective

Studies on distribution, abundance and diversity of species revealed fascinating universalities in macroecology. Many of these patterns, like the species-area and range-abundance relationship or the year-to-year fluctuations in population sizes are expressed as power-law distributions, and indicate thus scale-invariance. The species abundance distribution (SAD) apparently shows this scale-free nature only for rare species, and its mathematical form is much debated. In the present work we propose a new mathematical expression for SAD which describes reasonable well most of the presently available large-scale experimental data and the results of the neutral models. This distribution function leads to an interesting relation between the total number of individuals, total number of species and the size of the most abundant species of the meta-community. This novel scaling relation is confirmed by computer simulations on neutral models.

q-bio.PE↗

arXiv2002

Percolation-like behavior of some optimal coalition formation models

The ground-state of an infinite-range Potts glass-type model with +/- J bonds and unrestricted number of states is used to investigate coalition formation. As a function of the q probability of +J bonds in the system it is found that the r relative size of the largest cluster (a cluster being the group of elements in the same state) shows a percolation like behavior. By a simple renormalization approach and several optimization methods we investigate the r(q) curves for finite systems sizes. Non-trivial consequences for social percolation problems are discussed.

cond-mat.stat-mech↗

arXiv2002

Spiral cracks in drying precipitates

We investigate the formation of spiral crack patterns during the desiccation of thin layers of precipitates in contact with a substrate. This symmetry-breaking fracturing mode is found to arise naturally not from torsion forces, but from a propagating stress front induced by the fold-up of the fragments. We model their formation mechanism using a coarse-grain model for fragmentation and successfully reproduce the spiral cracks. Fittings of experimental and simulation data show that the spirals are logarithmic, corresponding to constant deviation from a circular crack path. Theoretical aspects of the logarithmic spirals are discussed. In particular we show that this occurs generally when the crack speed is proportional to the propagating speed of stress front.

cond-mat.soft↗

arXiv2001

Spiral cracks without twisting

A fascinating class of patterns, often encountered in nature as meandering cracks on rocks, dried-out fields and tectonic plates is produced by the fracture of solids. Here we report the observation and modeling of an unusual type of patterns consisting of spiral cracks within fragments of a thin layer of drying precipitate. We find that this symmetry-breaking cracking mode arises naturally not from twisting forces, but from a propagating stress front induced by the fold-up of the fragments.

cond-mat.mtrl-sci↗