Cultural propagation on social networks

In this work we present a model for the propagation of culture on networks of different topology and by considering different underlying dynamics. We extend a previous model proposed by Axelrod by letting a majority govern the dynamics of changes. This in turn allows us to define a Lyapunov functional for the system.Comment: 8 pages, 9 figures include

How and why ethnic groups provoke genocidal retaliation

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Political Science, 2002.Includes bibliographical references (p. 395-406).This dissertation explores the causes of, and possible remedies for, extremely violent ethnic conflict. It starts from a robust yet under-explored finding in the literature: Most groups that fall victim to genocidal violence actually trigger their own demise by launching armed secessions or revolutions against state authorities that only then retaliate with genocide or forced migration ("ethnic cleansing"). Accordingly, the dissertation asks why groups that are vulnerable to genocidal retaliation would provoke that very outcome by launching such "tragic challenges." To explain this phenomenon, the dissertation employs three case studies to test three hypotheses drawn from rational deterrence theory. The cases focus on three subordinate groups whose armed challenges provoked genocidal retaliation: Bosnia's Muslims in 1992-95; Rwanda's Tutsi in 1990-94; and Kosovo's Albanians in 1998-99. To gain further insight by adding variation on the theory's dependent variable, the dissertation also examines an earlier period of the third case during which the subordinate group did not launch a violent challenge, despite having substantial grievances, and thereby avoided genocidal violence (Kosovo's Albanians in 1989-97). he three hypotheses are as follows: (1) the group did not expect its armed challenge to provoke genocidal retaliation; (2) the group expected to suffer genocidal violence regardless of whether or not it launched an armed challenge; (3) the group expected its armed challenge to provoke genocidal retaliation but viewed this as an acceptable cost to achieve its goal of secession or revolution. The dissertation confirms the third hypothesis: subordinate groups launch tragic challenges when they expect to prevail and are willing to civilians as the cost of doing so.(cont.) Most surprisingly, the dissertation finds that a key cause of the optimism leading to tragic challenges is the expectation by subordinate groups of receiving humanitarian military intervention if they provoke genocidal retaliation against themselves. This reveals that international policies of humanitarian intervention create moral hazard, encouraging vulnerable groups to launch armed challenges and thereby potentially causing the tragic outcomes that these policies are intended to prevent. The dissertation concludes by exploring prescriptions to mitigate this newly discovered "moral hazard of humanitarian intervention."Alan J. Kuperman.Ph.D

Optimization as a result of the interplay between dynamics and structure

In this work we study the interplay between the dynamics of a model of diffusion governed by a mechanism of imitation and its underlying structure. The dynamics of the model can be quantified by a macroscopic observable which permits the characterization of an optimal regime. We show that dynamics and underlying network cannot be considered as separated ingredients in order to achieve an optimal behavior.Comment: 12 pages, 4 figures, to appear in Physica

Periodically Varying Externally Imposed Environmental Effects on Population Dynamics

Effects of externally imposed periodic changes in the environment on population dynamics are studied with the help of a simple model. The environmental changes are represented by the temporal and spatial dependence of the competition terms in a standard equation of evolution. Possible applications of the analysis are on the one hand to bacteria in Petri dishes and on the other to rodents in the context of the spread of the Hantavirus epidemic. The analysis shows that spatio-temporal structures emerge, with interesting features which depend on the interplay of separately controllable aspects of the externally imposed environmental changes.Comment: 7 pages, 8 figures, include

Applicability of the Fisher Equation to Bacterial Population Dynamics

The applicability of the Fisher equation, which combines diffusion with logistic nonlinearity, to population dynamics of bacterial colonies is studied with the help of explicit analytic solutions for the spatial distribution of a stationary bacterial population under a static mask. The mask protects the bacteria from ultraviolet light. The solution, which is in terms of Jacobian elliptic functions, is used to provide a practical prescription to extract Fisher equation parameters from observations and to decide on the validity of the Fisher equation.Comment: 5 pages, 3 figs. include

Opinion and community formation in coevolving networks

In human societies opinion formation is mediated by social interactions, consequently taking place on a network of relationships and at the same time influencing the structure of the network and its evolution. To investigate this coevolution of opinions and social interaction structure we develop a dynamic agent-based network model, by taking into account short range interactions like discussions between individuals, long range interactions like a sense for overall mood modulated by the attitudes of individuals, and external field corresponding to outside influence. Moreover, individual biases can be naturally taken into account. In addition the model includes the opinion dependent link-rewiring scheme to describe network topology coevolution with a slower time scale than that of the opinion formation. With this model comprehensive numerical simulations and mean field calculations have been carried out and they show the importance of the separation between fast and slow time scales resulting in the network to organize as well-connected small communities of agents with the same opinion.Comment: 10 pages, 5 figures. New inset for Fig. 1 and references added. Submitted to Physical Review

Why, when, and how fast innovations are adopted

When the full stock of a new product is quickly sold in a few days or weeks, one has the impression that new technologies develop and conquer the market in a very easy way. This may be true for some new technologies, for example the cell phone, but not for others, like the blue-ray. Novelty, usefulness, advertising, price, and fashion are the driving forces behind the adoption of a new product. But, what are the key factors that lead to adopt a new technology? In this paper we propose and investigate a simple model for the adoption of an innovation which depends mainly on three elements: the appeal of the novelty, the inertia or resistance to adopt it, and the interaction with other agents. Social interactions are taken into account in two ways: by imitation and by differentiation, i.e., some agents will be inclined to adopt an innovation if many people do the same, but other will act in the opposite direction, trying to differentiate from the "herd". We determine the conditions for a successful implantation of the new technology, by considering the strength of advertising and the effect of social interactions. We find a balance between the advertising and the number of anti-herding agents that may block the adoption of a new product. We also compare the effect of social interactions, when agents take into account the behavior of the whole society or just a part of it. In a nutshell, the present model reproduces qualitatively the available data on adoption of innovation.Comment: 11 pages, 13 figures (with subfigures), full paper (EPJB 2012) on innovation adoption mode