Scaling relations in food webs.

In the last three decades, researchers have tried to identify universal patterns in the structure of food webs. It was recently proposed that the exponent _ characterizing the efficiency of the transport of energy in large and small food webs might have a universal value __ =1.13_. In this work we establish lower and upper bounds for this exponent in a general spanning tree with a fixed number of trophic species and levels. When the number of species is large, the lower and upper bounds are equal to 1, implying that the result _ =1.13 is due to finite-size effects and that the value of this exponent depends on the size of the web. We also evaluate analytically and numerically the exponent _ for hierarchical and random networks. In all cases the exponent _ depends on the number of trophic species K, and when K is large we have that _?1. Moreover, this result holds for any fixed number M of trophic levels

A smooth path to plot hydrogen atom via Monte Carlo method.

In this paper, we show how to build a basic computer program using the Monte Carlo method to display the hydrogen atomic orbitals. For this, in a heuristic way, we applied a von Neumann acceptance-rejection method in simple problems of potential wells, and we end with the hydrogen orbitals representation. In this technique, we spread points uniformly on the 1D and 2D charts of probability density distributions, then we filtered points under these ?curves or surfaces?, and we extended this logic to 3D cases. Throughout the work, we also made some comments to help beginner students better understand the term ?wave function? present in the Schr?dinger equation. Also, we made all source code available at a third-party platform, for any purpose under the MIT license. Keywords: hydrogen atom, quantum mechanics, Monte Carlo method, Neumann acceptance-rejection method

Business networks and their effects on tourism.

O presente artigo tem como objetivo propor um modelo de alinhamento competitivo para a rede de atores do turismo, visando aumentar sua coes?o e facilitar a busca de objetivos comuns. Tal proposta foi definida com base na expertise dos autores na analise de redes de turismo, aliada a resultados obtidos na pesquisa em Ouro Preto (MG). Dessa forma, foi poss?vel perceber o peso dos atores envolvidos em fun??o dos crit?rios de escolha utilizados pelos visitantes para configurar seu caminho dentro da regi?o tur?stica analisada e, assim, refor?ar os relacionamentos existentes.The relationships between firms, to be successful, demand high levels of transparency, information and physical flows of goods and services, in order to provide free access for all people involved in doing business together. The same can be said regarding flow of money resources and talents needed by the processes and operations performed by the network. Thus, the main idea involves reaching balance conditions in terms of sharing the results obtained by all participants, considering their objectives and goals, to keep the network form of organization as being an adequate strategy. This proposal was defined from the authors? expertise in analysis of tourism networks, together with results obtained on research in Ouro Preto. Thus it was possible to realize the weight of the players involved depending on the selection criteria used by visitors to configure their way into of the tourist region analyzed and thereby strengthen existing relationships

Estudos sobre complexidade em dinâmica populacional e embriogênese

Exportado OPUSMade available in DSpace on 2019-08-12T06:06:48Z (GMT). No. of bitstreams: 1 alcides.pdf: 2986990 bytes, checksum: 0d5a921bae4b7d61b3922d3c49a1bff5 (MD5) Previous issue date: 27Os sistemas complexos pertencem a uma classe de sistemas capazes de exibirem um rico comportamento apesar de serem formados a partir de elementos simples sujeitos à interações simples. Os conceitos associados aos sistemas complexos têm sido usados para modelar e descrever as propriedades apresentadas por várias classes de sistemas, em diferentes campos de pesquisa, como economia, ciência da computação, arquitetura, física, biologia. Nesse presente trabalho usamos tais conceitos em alguns sistemas biológicos, tentando fazer uma conexão entre física e biologia. Inicialmente fazemos uma introdução das características gerais de sistemas complexos, incluindo um tipo especial: os sistemas auto organizados. Sob tal ponto de vista, analisamos um comportamento complexo exibido por um modelo de dinâmica populacional baseado na teoria evolutiva de envelhecimento. Discutimos os resultados obtidos de acordo com algumas teorias usadas para explicar a evolução de sistemas biológicos. Finalmente introduzimos alguns aspectos básicos de outro processo biológico: o desenvolvimento embrionário. Em seguida propomos um modelo computacional simples que imita os estágios iniciais da formação do embrião. Conclusões e algumas futuras perspectivas do modelo também são mostradas

Gastrulation as a self-organized symmetry breaking process.

Among the stages a fertilized egg undergoes until reaching its final shape, gastrulation represents the first step in breaking its initial symmetry. This process is of enormous importance in development of the embryos sagittal symmetry plane or dorso-ventral axis. Gastrulation also results in the appearance of three regions, the germ layers, from which all of the organs and systems of the organism originate. In this paper, following the hypothesis which affirms that pattern formation at some stages of organism development are due to morphogens gradient, we introduce a model which mimics the early stages of gastrulation of many multicellular organisms. In this model, the cause of symmetry breaking is given by the intrinsic dynamics of the system

Analysis of chaotic behaviour in the population dynamics.

Recently, we have shown that the Penna bitstring model for population senescence can be used to model cyclic or chaotic behaviours in population dynamics. In this paper, we analyse the attractor of the dynamics, through the calculation of the Lyapunov exponents. We obtained that the dynamics is characterized by the existence of some small exponents, which we relate to the existence of homeochaos, needed for the generation of stability and diversity in living systems

Mean-field and non-mean-field behaviors in scale-free networks with random boolean dynamics.

We study two types of simplified Boolean dynamics in scale-free networks, both with synchronous update. Assigning only Boolean functions AND and XOR to the nodes with probability 1 − p and p, respectively, we are able to analyze the density of 1’s and the Hamming distance on the network by numerical simulations and by a mean-field approximation (annealed approximation). We show that the behavior is quite different if the node always enters in the dynamics as its own input (self-regulation) or not. The same conclusion holds for the Kauffman NK model. Moreover, the simulation results and the mean-field ones (i) agree well when there is no self-regulation, and (ii) disagree for small p when self-regulation is present in the model

Roughness exponents to calculate multi-affine fractal exponents

We propose a new method to determine the multi-affine fractal exponents based on a generalization of the roughness concept. For synthetic multi-attine fractal profiles with exactly known exponents, we show that the results obtained in this method are more accurate than the results obtained with the height-height correlation function method. Also in the present method, scaling is observed using profiles with a number of points more than one order of magnitude smaller

Medidas de centralidade como parâmetros para se avaliar os atores da rede de turismo : o caso de Ouro Preto.

No turismo as medidas de centralidade são altamente justificadas pelo fato de gerarem dados precisos do comportamento quantitativo dos atores de uma rede. Desta forma, este artigo tem como objetivo mapear a rede de atores do turismo da cidade de Ouro Preto, identificar e descrever as medidas de centralidade desta rede como parâmetros para se avaliar o desempenho de seus atores. Foi utilizado o Ucinet 2.0 e os resultados apontam para a utilização destas medidas como fortes aliados às ações de marketing, tais como disseminação de informação, divulgação de novas ações, políticas e programas públicos e privados

Arranjos produtivos locais e seus efeitos sobre o turismo.

O presente artigo tem como objetivo apresentar um conjunto de indicadores de desempenho visando orientar os atores no sentido de aumentar sua coesão mútua e facilitar a busca de objetivos comuns. Tais indicadores foram definidos a partir da expertise dos autores na analise de redes de turismo, aliado a resultados obtidos na pesquisa em Ouro Preto. Dessa forma foi possível perceber, o grau de significância dos atores envolvidos em função dos critérios de escolha utilizados pelos visitantes para configurar seu caminho dentro da região turística analisada e assim reforçar os relacionamentos existentes