Residential segregation and cultural dissemination: An Axelrod-Schelling model

In the Axelrod's model of cultural dissemination, we consider mobility of cultural agents through the introduction of a density of empty sites and the possibility that agents in a dissimilar neighborhood can move to them if their mean cultural similarity with the neighborhood is below some threshold. While for low values of the density of empty sites the mobility enhances the convergence to a global culture, for high enough values of it the dynamics can lead to the coexistence of disconnected domains of different cultures. In this regime, the increase of initial cultural diversity paradoxically increases the convergence to a dominant culture. Further increase of diversity leads to fragmentation of the dominant culture into domains, forever changing in shape and number, as an effect of the never ending eroding activity of cultural minorities

Slightly generalized Generalized Contagion: Unifying simple models of biological and social spreading

We motivate and explore the basic features of generalized contagion, a model mechanism that unifies fundamental models of biological and social contagion. Generalized contagion builds on the elementary observation that spreading and contagion of all kinds involve some form of system memory. We discuss the three main classes of systems that generalized contagion affords, resembling: simple biological contagion; critical mass contagion of social phenomena; and an intermediate, and explosive, vanishing critical mass contagion. We also present a simple explanation of the global spreading condition in the context of a small seed of infected individuals.Comment: 8 pages, 5 figures; chapter to appear in "Spreading Dynamics in Social Systems"; Eds. Sune Lehmann and Yong-Yeol Ahn, Springer Natur

Nonequilibrium phase transition in the coevolution of networks and opinions

Models of the convergence of opinion in social systems have been the subject of a considerable amount of recent attention in the physics literature. These models divide into two classes, those in which individuals form their beliefs based on the opinions of their neighbors in a social network of personal acquaintances, and those in which, conversely, network connections form between individuals of similar beliefs. While both of these processes can give rise to realistic levels of agreement between acquaintances, practical experience suggests that opinion formation in the real world is not a result of one process or the other, but a combination of the two. Here we present a simple model of this combination, with a single parameter controlling the balance of the two processes. We find that the model undergoes a continuous phase transition as this parameter is varied, from a regime in which opinions are arbitrarily diverse to one in which most individuals hold the same opinion. We characterize the static and dynamical properties of this transition

Persistence of brucellosis in pastoral systems

Regarded as a highly contagious, zoonotic disease with worldwide distribution, brucellosis is endemic in many countries and settings and is responsible for a considerable economic and health-related burden. Limited information is available on the persistence and prevalence of brucellosis in pastoral communities, due to the difficulty in gathering information and to their mobility. However, since these communities are economically and culturally dependent on livestock, it is important to further determine the cause of persistent disease and develop possible methods for its management. The two main objectives of this paper are to review the literature, identifying various epidemiological and social factors that affect the persistence of brucellosis in pastoral ecosystems, and determine prevalence estimates within these communities. The general trend of the summarised studies indicates low-level, relatively stable transmission of brucellosis in pastoral areas, when compared to transmission in intensive and semi-intensive peri-urban production systems. A formal mathematical analysis can be undertaken using matrix models or coupled differential equations. This allows an examination of the various conditions under which the number of diseased, infected or exposed animals remains stable. The authors examined an existing mathematical differential equation model for brucellosis in Mongolia for its equilibrium conditions and found it reasonably robust, though clearly more data are needed to estimate threshold densities for brucellosis transmission in other regions of the world. However, the results indicate the importance of livestock demographic determinants for brucellosis persistence. The paper concludes that brucellosis remains largely persistent in pastoral areas of the world, despite (varying) control efforts. Plans to control brucellosis in pastoral settings should include ecological considerations, such as sustaining ecosystem services in pastoral areas. This approach would include placing limitations on livestock stocking density, land reform, improved governance and integrated social and economic development

Statistical physics of the Schelling model of segregation

We investigate the static and dynamic properties of a celebrated model of social segregation, providing a complete explanation of the mechanisms leading to segregation both in one- and two-dimensional systems. Standard statistical physics methods shed light on the rich phenomenology of this simple model, exhibiting static phase transitions typical of kinetic constrained models, nontrivial coarsening like in driven-particle systems and percolation-related phenomena.Comment: 4 pages, 3 figure

Global burden of human brucellosis : a systematic review of disease frequency

BACKGROUND: This report presents a systematic review of scientific literature published between 1990-2010 relating to the frequency of human brucellosis, commissioned by WHO. The objectives were to identify high quality disease incidence data to complement existing knowledge of the global disease burden and, ultimately, to contribute towards the calculation of a Disability-Adjusted Life Years (DALY) estimate for brucellosis.METHODS/PRINCIPAL FINDINGS: Thirty three databases were searched, identifying 2,385 articles relating to human brucellosis. Based on strict screening criteria, 60 studies were selected for quality assessment, of which only 29 were of sufficient quality for data analysis. Data were only available from 15 countries in the regions of Northern Africa and Middle East, Western Europe, Central and South America, Sub-Saharan Africa, and Central Asia. Half of the studies presented incidence data, six of which were longitudinal prospective studies, and half presented seroprevalence data which were converted to incidence rates. Brucellosis incidence varied widely between, and within, countries. Although study biases cannot be ruled out, demographic, occupational, and socioeconomic factors likely play a role. Aggregated data at national or regional levels do not capture these complexities of disease dynamics and, consequently, at-risk populations or areas may be overlooked. In many brucellosis-endemic countries, health systems are weak and passively-acquired official data underestimate the true disease burden.CONCLUSIONS: High quality research is essential for an accurate assessment of disease burden, particularly in Eastern Europe, the Asia-Pacific, Central and South America and Africa where data are lacking. Providing formal epidemiological and statistical training to researchers is essential for improving study quality. An integrated approach to disease surveillance involving both human health and veterinary services would allow a better understand of disease dynamics at the animal-human interface, as well as a more cost-effective utilisation of resources

Physikalische Parameter extrakorporaler Stoßwellen

Prerequisites for the successful investigation of the mechanism of action of ESWT (extracorporeal shockwave therapy) and the establishment of treatment standards, are the ability to measure, and a knowledge of, the physical parameters involved. The most accurate measurements are obtained with laser hydrophones. Various parameters (amplitude, rise time, pulse width, pressure pulse decay, rarification phase) of a typical shock wave can thus be determined. These can then be used to calculate energy flux density, focal extent, focal volume and as well as focal energy, effective energy in a defined area, and effective biological energy. These parameters can be utilized to work out a theoretical treatment protocol

Ripple Texturing of Suspended Graphene Atomic Membranes

Graphene is the nature's thinnest elastic membrane, with exceptional mechanical and electrical properties. We report the direct observation and creation of one-dimensional (1D) and 2D periodic ripples in suspended graphene sheets, using spontaneously and thermally induced longitudinal strains on patterned substrates, with control over their orientations and wavelengths. We also provide the first measurement of graphene's thermal expansion coefficient, which is anomalously large and negative, ~ -7x10^-6 K^-1 at 300K. Our work enables novel strain-based engineering of graphene devices.Comment: 15 pages, 4 figure

Retinol Assessment Among Women and Children in Sahelian Mobile Pastoralists

Micronutrient deficiencies are widespread in developing countries, particularly in remote communities such as mobile pastoralists. The nutritional and vitamin A status of this population is not well-documented in Chad. This study assessed serum retinol levels among women and children under five-year-old in nomadic and semi-nomadic pastoralist and rural-settled communities, who are similarly exposed to risk factors such as gastrointestinal parasitic infection, anaemia and emaciation. The novel method of portable fluorometry was used for the first time to measure β-carotene and retinol levels in a pastoral nomadic area. Moderate level blood retinol deficiency (<0.7μmol/L) was observed in 5% (CI 1-11) of nomadic, 29% (CI 13-45) of semi-nomadic and 22% (CI 8-35) of sedentary women. In children, 1% (CI 0.1-4), 17% (CI 9-25) and 28% (CI 18-39), respectively, had moderate level blood retinol deficiency. In nomadic communities, women and children had blood retinol levels close to normal. Deficiency of retinol was strongly linked with lifestyle (nomadic, semi-nomadic and settled) among women and lifestyle and age among children. The results support an ecological linkage between human retinol levels and livestock milk retinol. This study shows the feasibility of portable retinol and β-carotene measurement in human blood as well as human and animal milk under remote field conditions, but the approach requires further validatio