The impact of contact tracing in clustered populations

The tracing of potentially infectious contacts has become an important part of the control strategy for many infectious diseases, from early cases of novel infections to endemic sexually transmitted infections. Here, we make use of mathematical models to consider the case of partner notification for sexually transmitted infection, however these models are sufficiently simple to allow more general conclusions to be drawn. We show that, when contact network structure is considered in addition to contact tracing, standard “mass action” models are generally inadequate. To consider the impact of mutual contacts (specifically clustering) we develop an improvement to existing pairwise network models, which we use to demonstrate that ceteris paribus, clustering improves the efficacy of contact tracing for a large region of parameter space. This result is sometimes reversed, however, for the case of highly effective contact tracing. We also develop stochastic simulations for comparison, using simple re-wiring methods that allow the generation of appropriate comparator networks. In this way we contribute to the general theory of network-based interventions against infectious disease

Epidemic space

The aim of this article is to highlight the importance of 'spatiality' in understanding the materialization of risk society and cultivation of risk sensibilities. More specifically it provides a cultural analysis of pathogen virulence (as a social phenomenon) by means of tracing and mapping the spatial flows that operate in the uncharted zones between the microphysics of infection and the macrophysics of epidemics. It will be argued that epidemic space consists of three types of forces: the vector, the index and the vortex. It will draw on Latour's Actor Network Theory to argue that epidemic space is geared towards instability when the vortex (of expanding associations and concerns) displaces the index (of finding a single cause)

Clusters and the Cosmic Web

We discuss the intimate relationship between the filamentary features and the rare dense compact cluster nodes in this network, via the large scale tidal field going along with them, following the cosmic web theory developed Bond et al. The Megaparsec scale tidal shear pattern is responsible for the contraction of matter into filaments, and its link with the cluster locations can be understood through the implied quadrupolar mass distribution in which the clusters are to be found at the sites of the overdense patches. We present a new technique for tracing the cosmic web, identifying planar walls, elongated filaments and cluster nodes in the galaxy distribution. This will allow the practical exploitation of the concept of the cosmic web towards identifying and tracing the locations of the gaseous WHIM. These methods, the Delaunay Tessellation Field Estimator (DTFE) and the Morphology Multiscale Filter (MMF) find their basis in computational geometry and visualization.Comment: 13 pages, 6 figures, appeared in proceedings workshop "Measuring the Diffuse Intergalactic Medium", eds. J-W. den Herder and N. Yamasaki, Hayama, Japan, October 2005. For version with high-res figures see http://www.astro.rug.nl/~weygaert/weywhim05.pd

From beginnings and endings to boundaries and edges: rethinking circulation and exchange through electronic waste

This paper discusses research on electronic waste in Canada and Bangladesh. We engage with ongoing debates in geography and the broader social sciences on the need to move beyond linearity in the analysis of commodity/value chains and global production networks. Our analysis suggests that the problem of linearity may be an artefact of theoretical and methodological presuppositions, which explains its longevity as an issue in methodological approaches and empirical research. Recent theoretical insights from actor network theory, combined with our own research on electronic waste, provide a potential solution to the problem of linearity. Our research points to the need for a focus on ‘actions’, not just ‘things’, in tracing economic activity. This signals a shift away from beginnings and endings in production network approaches to analyses that are concerned with boundaries and edges

The organization of transactions research with the Trust and Tracing Game

This paper presents empirical results of research on the influence of social aspects on the organization of transactions in the domain of chains and networks. The research method used was a gaming simulation called the Trust and Tracing game in which participants trade commodity goods with a hidden quality attribute. Previous sessions of this gaming simulation identified a list of variables for further investigation (Meijer et al., 2006). The use of gaming simulation as data gathering tool for quantitative research in supply chains and networks is a proof-of-principle. This paper shows results from 27 newly conducted sessions and previously unused data from 3 older sessions. Tests confirmed the use of network and market modes of organization. Pre-existing social relations influenced the course of the action in the sessions. Being socially embedded was not beneficial for the score on the performance indicators money and points. The hypothesized reduction in measurable transaction costs when there was high trust between the participants could not be found. Further analysis revealed that participants are able to suspect cheats in a session based on other factors than tracing. Testing hypotheses with data gathered in a gaming simulation proved feasible. Experiences with the methodology used are discusse

Seismic detection of sonic booms

The pressure signals from a sonic boom will produce a small, but detectable, ground motion. The extensive seismic network in southern California, consisting of over 200 sites covering over 50 000 square kilometers, is used to map primary and secondary sonic boom carpets. Data from the network is used to analyze three supersonic overflights in the western United States. The results are compared to ray-tracing computations using a realistic model of the stratified atmospheric at the time of the measurements. The results show sonic boom ground exposure under the real atmosphere is much larger than previously expected or predicted by ray tracing alone. Finally, seismic observations are used to draw some inferences on the origin of a set of "mystery booms" recorded in 1992–1993 in southern California