Artículos con la etiqueta ‘Sistemas de adaptación y auto organización’

Zipf’s Law for All the Natural Cities around the World

Por • 13 feb, 2014 • Category: sociologia

Two fundamental issues surrounding research on Zipf’s law regarding city sizes are whether and why Zipf’s law holds. This paper does not deal with the latter issue with respect to why, and instead investigates whether Zipf’s law holds in a global setting, thus involving all cities around the world. Unlike previous studies, which have mainly relied on conventional census data, and census- bureau-imposed definitions of cities, we adopt naturally and objectively delineated cities, or natural cities, to be more precise, in order to examine Zipf’s law. We find that Zipf’s law holds remarkably well for all natural cities at the global level, and remains almost valid at the continental level except for Africa at certain time instants. We further examine the law at the country level, and note that Zipf’s law is violated from country to country or from time to time.

The Evolution of Natural Cities from the Perspective of Location-Based Social Media

Por • 7 feb, 2014 • Category: sociologia

Nobody agrees on how to define a city. But the emergence of “natural cities” from social media data sets may change that, say computational geographers. A city is a large, permanent human settlement. But try and define it more carefully and you’ll soon run into trouble. A settlement that qualifies as a city in Sweden may not qualify in China, for example. And the reasons why one settlement is classified as a town while another as a city can sometimes seem almost arbitrary. City planners know this problem well. They tend to define cities by administrative, legal or even historical boundaries that have little logic to them. Indeed, the same city can sometimes be defined in various different ways. That causes all kinds of problems from counting the total population to working out who pays for the upkeep of the place. Which definition do you use?

Social Influences in the Voter Model: the Role of Conformity

Por • 7 ene, 2014 • Category: sociologia

We introduce a model to study the effects of social influences in opinion dynamics. In particular, we analyze the voter model, from a socio psychological perspective, by considering the role of conformity. Conformity is a central issue in social psychology as it represents one of people’s behaviors that emerge as result of their interactions. We introduce a voter model where agents, linked in a network, change their opinion according to those of their neighbors and to their degree of conformity. In particular, agents can behave as conformists or non-conformists. In the former case, agents change opinion according to that of the majority of their social circle (i.e., the majority of their neighbors); in the latter case, they do the opposite, i.e., they assume the opposite opinion. We perform a computational study of the proposed model, with the aim to analyze the role of conformity in the voter model. Moreover, we want to investigate whether it is possible to achieve some kind of equilibrium or of order in the system. The two more interesting results are that the amount of non-conformist agents in the population plays a central role in these dynamics, and the topology of the agent network has not a prominent role in the proposed model. Finally, we study the outcomes of the model by considering that agents can change also their degree of conformity over time, i.e., they can turn their behavior from conformist to non-conformist and vice-versa.

Complexity measurement of natural and artificial languages

Por • 2 dic, 2013 • Category: Ambiente

We compared entropy for texts written in natural languages (English, Spanish) and artificial languages (computer software) based on a simple expression for the entropy as a function of message length and specific word diversity. Code text written in artificial languages showed higher entropy than text of similar length expressed in natural languages. Spanish texts exhibit more symbolic diversity than English ones. Results showed that algorithms based on complexity measures differentiate artificial from natural languages, and that text analysis based on complexity measures allows the unveiling of important aspects of their nature. We propose specific expressions to examine entropy related aspects of tests and estimate the values of entropy, emergence, self-organization and complexity based on specific diversity and message length.

Modelling Complexity for Policy: Opportunities and Challenges

Por • 10 oct, 2013 • Category: sociologia

This chapter reviews the purpose and use of models from the field of complex systems and, in particular, the implications of trying to use models to understand or make decisions within complex situations, such as policy makers usually face. A discussion of the different dimensions one can formalise situations, the different purposes for models and the different kinds of relationship they can have with the policy making process, is followed by an examination of the compromises forced by the complexity of the target issues. Several modelling approaches from complexity science are briefly described, with notes as to their abilities and limitations. These approaches include system dynamics, network theory, information theory, cellular automata, and agent-based modelling. Some examples of policy models are presented and discussed in the context of the previous analysis. Finally we conclude by outlining some of the major pitfalls facing those wishing to use such models for policy evaluation.

Algorithm for Resource Redistribution Required for Recovery of Society after Large Scale Disasters

Por • 4 oct, 2013 • Category: Ambiente

The recovery of society after a large scale disaster generally consists of two phases, short- and long-term recoveries. The problem of short-term recovery is rather close to the problem of resilience in their goal, namely, bouncing the damaged system back to the operating standards. The present paper proposes an algorithm for the vital resource redistribution required for implementation of the short-term recovery. The developed model is based on the cooperative interaction of cities during the resource redistribution, ordering the cities according to their priority in resource delivery, and a generating a semi-optimal plan for the desired redistribution. Nonlinear effects caused by the city limit capacities are taken into account.

The spatial meaning of Pareto’s scaling exponent of city-size distribution

Por • 25 sep, 2013 • Category: sociologia

The scaling exponent of a hierarchy of cities used to be regarded as a fractal parameter. The Pareto exponent was treated as the fractal dimension of size distribution of cities, while the Zipf exponent was treated as the reciprocal of the fractal dimension. However, this viewpoint is not exact. In this paper, I will present a new interpretation of the scaling exponent of rank-size distributions. The ideas from fractal measure relation and the principle of dimension consistency are employed to explore the essence of Pareto’s and Zipf’s scaling exponents. The Pareto exponent proved to be a ratio of the fractal dimension of a network of cities to the average dimension of city population. Accordingly, the Zipf exponent is the reciprocal of this dimension ratio. On a digital map, the Pareto exponent can be defined by the scaling relation between a map scale and the corresponding number of cities based on this scale. The cities of the United States of America in 1900, 1940, 1960, and 1980 and Indian cities in 1981, 1991, and 2001 are utilized to illustrate the geographical spatial meaning of Pareto’s exponent. The results suggest that the Pareto exponent of city-size distribution is not a fractal dimension, but a ratio of the urban network dimension to the city population dimension. This conclusion is revealing for scientists to understand Zipf’s law and fractal structure of hierarchy of cities.

Towards a mathematical theory of meaningful communication

Por • 24 ago, 2013 • Category: Leyes

Despite its obvious relevance, meaning has been outside most theoretical approaches to information in biology. As a consequence, functional responses based on an appropriate interpretation of signals has been replaced by a probabilistic description of correlations between emitted and received symbols. This assumption leads to potential paradoxes, such as the presence of a maximum information associated to a channel that would actually create completely wrong interpretations of the signals. Game-theoretic models of language evolution use this view of Shannon’s theory, but other approaches considering embodied communicating agents show that the correct (meaningful) match resulting from agent-agent exchanges is always achieved and natural systems obviously solve the problem correctly. How can Shannon’s theory be expanded in such a way that meaning -at least, in its minimal referential form- is properly incorporated?

Analysis of communities in a mythological social network

Por • 15 jun, 2013 • Category: sociologia

The intriguing nature of classical Homeric narratives has always fascinated the occidental culture contributing to philosophy, history, mythology and straight forwardly to literature. However what would be so intriguing about Homer’s narratives’ At a first gaze we shall recognize the very literal appeal and aesthetic pleasure presented on every page across Homer’s chants in Odyssey and rhapsodies in Iliad. Secondly we may perceive a biased aspect of its stories contents, varying from real-historical to fictional-mythological. To encompass this glance, there are some new archeological finding that supports historicity of some events described within Iliad, and consequently to Odyssey. Considering these observations and using complex network theory concepts, we managed to built and analyze a social network gathered across the classical epic, Odyssey of Homer. Longing for further understanding, topological quantities were collected in order to classify its social network qualitatively into real or fictional. It turns out that most of the found properties belong to real social networks besides assortativity and giant component’s size.

Introduction: The FuturICT Knowledge Accelerator Towards a More Resilient and Sustainable Future

Por • 8 abr, 2013 • Category: Ciencia y tecnología

The FuturICT project is a response to the European Flagship Call in the Area of Future and Emerging Technologies, which is planning to spend 1 billion EUR on each of two flagship projects over a period of 10 years. FuturICT seeks to create an open, global but decentralized, democratically controlled information platform that will use online data and real-time measurements together with novel theoretical models and experimental methods to achieve a paradigm shift in our understanding of today’s strongly interdependent and complex world and make our techno-socio-economic systems more flexible, adaptive, resilient, sustainable, and livable through a participatory approach.