A simple person's approach to understanding the contagion condition for spreading processes on generalized random networks

We present derivations of the contagion condition for a range of spreading mechanisms on families of generalized random networks and bipartite random networks. We show how the contagion condition can be broken into three elements, two structural in nature, and the third a meshing of the contagion process and the network. The contagion conditions we obtain reflect the spreading dynamics in a clear, interpretable way. For threshold contagion, we discuss results for all-to-all and random network versions of the model, and draw connections between them.Comment: 10 pages, 9 figures; chapter to appear in "Spreading Dynamics in Social Systems"; Eds. Sune Lehmann and Yong-Yeol Ahn, Springer Natur

Testing public health intervention guidance on increasing the uptake of HIV testing among men who have sex with men. Final fieldwork report

This guidance is for NHS and other commissioners, managers and practitioners who have a direct or indirect role in, and responsibility for, increasing the uptake of HIV testing among men who have sex with men. This includes those working in local authorities and the wider public, private, voluntary and community sectors. It will also be of interest to members of the public, in particular men who have sex with men. The focus of the guidance is on increasing the uptake of HIV testing to reduce undiagnosed infection and prevent transmission. The recommendations include advice on: planning services, including assessing local need and developing a strategy promoting HIV testing among men who have sex with men, including outreach schemes and providing rapid point-of-care tests offering and recommending an HIV test in primary care, secondary care and specialist sexual health services repeat testing HIV referral pathways

Pharmaceutical HIV prevention technologies in the UK: six domains for social science research

The development of pharmaceutical HIV prevention technologies (PPTs) over the last five years has generated intense interest from a range of stakeholders. There are concerns that these clinical and pharmaceutical interventions are proceeding with insufficient input of the social sciences. Hence key questions around implementation and evaluation remain unexplored whilst biomedical HIV prevention remains insufficiently critiqued or theorised from sociological as well as other social science perspectives. This paper presents the results of an expert symposium held in the UK to explore and build consensus on the role of the social sciences in researching and evaluating PPTs in this context. The symposium brought together UK social scientists from a variety of backgrounds. A position paper was produced and distributed in advance of the symposium and revised in the light this consultation phase. These exchanges and the emerging structure of this paper formed the basis for symposium panel presentations and break-out sessions. Recordings of all sessions were used to further refine the document which was also redrafted in light of ongoing comments from symposium participants. Six domains of enquiry for the social sciences were identified and discussed: self, identity and personal narrative; intimacy, risk and sex; communities, resistance and activism; systems, structures and institutions; economic considerations and analyses; and evaluation and outcomes. These are discussed in depth alongside overarching consensus points for social science research in this area as it moves forward

Packing-limited growth of irregular objects

We study growth limited by packing for irregular objects in two dimensions. We generate packings by seeding objects randomly in time and space and allowing each object to grow until it collides with another object. The objects we consider allow us to investigate the separate effects of anisotropy and non-unit aspect ratio. By means of a connection to the decay of pore-space volume, we measure power law exponents for the object size distribution. We carry out a scaling analysis, showing that it provides an upper bound for the size distribution exponent. We find that while the details of the growth mechanism are irrelevant, the exponent is strongly shape dependent. Potential applications lie in ecological and biological environments where sessile organisms compete for limited space as they grow.Comment: 6 pages, 4 figures, 1 table, revtex

Relative Safety 2: Risk and unprotected anal intercourse among gay men diagnosed with HIV

In 1999 Sigma Research published Relative safety: an investigation of risk and unprotected anal intercourse among gay men diagnosed with HIV (Keogh et al. 1999). This study explored the social, psychological and cultural meanings associated with unprotected anal intercourse (UAI) among men with diagnosed HIV. It highlighted both the complexity of sexual interaction for men with diagnosed HIV, and the many potential costs and benefits perceived by them. Now, with more than 24,000 homosexually active men diagnosed with HIV in the UK (Health Protection Agency 2008), a figure that is set to increase in years to come, it is vital that agencies involved in HIV prevention interrogate their own beliefs about UAI and ensure that their interventions meet the needs of men with diagnosed HIV. . . . . The following chapter explains how the study was undertaken, outlines the broad topic areas addressed during the interviews, and describes the sample of men who took part. Chapter 3 outlines the range of harms that men with HIV perceive when engaging in UAI. Chapters 4 and 5 explore the ways in which men responded to these perceived harms, firstly those relating to the risk of onward HIV infection, or superinfection, and latterly those concerning the potential for harms to their personal and social identities. Chapter 6 considers the implications of these findings for health promotion interventions targeting men with HIV, and with homosexually active men more broadly

Packing-Limited Growth

We consider growing spheres seeded by random injection in time and space. Growth stops when two spheres meet leading eventually to a jammed state. We study the statistics of growth limited by packing theoretically in d dimensions and via simulation in d=2, 3, and 4. We show how a broad class of such models exhibit distributions of sphere radii with a universal exponent. We construct a scaling theory that relates the fractal structure of these models to the decay of their pore space, a theory that we confirm via numerical simulations. The scaling theory also predicts an upper bound for the universal exponent and is in exact agreement with numerical results for d=4.Comment: 6 pages, 5 figures, 4 tables, revtex4 to appear in Phys. Rev. E, May 200