Distribuição estatística do faturamento das empresas brasileiras: técnica de Zipf

Pós-graduação em Física - IGCE

Comments about some species abundance patterns: classic, neutral, and niche partitioning models

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Power-law distributions for the citation index of scientific publications and scientists

The number of citations of a scientific publication or of an individual scientist has become an important factor of quality assessment in science. We report a study of the statistical distribution of the citation index of both scientific publications and scientists. We give numerical evidence that Tsallis (power law) statistics explains the entire distribution over eight orders of magnitude (10-4 to 10(4)). Also, we draw Zipf plots in order to analyze the statistical distribution of the citation index of Brazilian and international physicists and chemists. The relatively small group of Brazilian scientists seems more adequate to explain the dynamics of the citation index. In this case, we find that the distribution of the citation index can also be explained by a gradually truncated power law with similar parameters. We finally discuss possible mechanisms behind the citation index of scientists and scientific publications.

Gradually truncated log-normal in USA publicly traded firm size distribution

We study the statistical distribution of firm size for USA and Brazilian publicly traded firms through the Zipf plot technique. Sale size is used to measure firm size. The Brazilian firm size distribution is given by a log-normal distribution without any adjustable parameter. However, we also need to consider different parameters of log-normal distribution for the largest firms in the distribution, which are mostly foreign firms. The log-normal distribution has to be gradually truncated after a certain critical value for USA firms. Therefore, the original hypothesis of proportional effect proposed by Gibrat is valid with some modification for very large firms. We also consider the possible mechanisms behind this distribution. (c) 2006 Published by Elsevier B.V.

O encabecamento das armaduras urbanas nacionais: uma revisão

Starting from Jefferson's 'law of the primate city' and Zipf's 'rank-size rule', examines the question of the heading of national urban systems, seeking to stretch the analysis as far as possible in space and time. Thus, 131 countries were included in the study, most of them also viewed from the evolutive side. It was found that there is a main tendency for urban systems to evolve to the primate leadership, maintained by Jefferson as the normal pattern. Among the various factors that act in this direction, the attraction exercised by political power located in the capital cities is dominant.-English summary

Distribuições estatísticas: citações de publicações científicas e de cientistas

Pós-graduação em Física - IGCE