Sexual networks and the transmission of HIV in London

Copyright @ 1998 Cambridge University Press.This paper discusses ways in which empirical research investigating sexual networks can further understanding of the transmission of HIV in London, using information from a 24-month period of participant observation and 53 open-ended, in-depth interviews with eighteen men and one woman who have direct and indirect sexual links with each other. These interviews enabled the identification of a wider sexual network between 154 participants and contacts during the year August 1994-July 1995. The linked network data help to identify pathways of transmission between individuals who are HIV + and those who are HIV -, as well as sexual links between 'older' and 'younger' men, and with male prostitutes. There appears to be considerable on-going transmission of HIV in London. The majority of participants reported having had unprotected anal and/or vaginal sex within a variety of relationships. The implications of these findings for policies designed to prevent the transmission of HIV are discussed.The Wellcome Trust and The Health Education Authority

Asymptotic Methods for Metal Oxide Semiconductor Field Effect Transistor Modeling

The behavior of metal oxide semiconductor field effect transistors (MOSFETs) with small aspect ratio and large doping levels is analyzed using formal perturbation techniques. Specifically, the influence of interface layers in the potential on the averaged channel conductivity is closely examined. The interface and internal layers that occur in the potential are resolved in the limit of large doping using the method of matched asymptotic expansions. This approach, together with other asymptotic techniques, provides both a pointwise description of the state variables as well as lumped current-voltage relations that vary uniformly across the various bias regimes. These current-voltage relations are derived for a variable doping model respresenting a particular class of devices

First Observations of the Magnetic Field Geometry in Pre-stellar Cores

We present the first published maps of magnetic fields in pre-stellar cores, to test theoretical ideas about the way in which the magnetic field geometry affects the star formation process. The observations are JCMT-SCUBA maps of 850 micron thermal emission from dust. Linear polarizations at typically ten or more independent positions in each of three objects, L1544, L183 and L43 were measured, and the geometries of the magnetic fields in the plane of the sky were mapped from the polarization directions. The observed polarizations in all three objects appear smooth and fairly uniform. In L1544 and L183 the mean magnetic fields are at an angle of around 30 degrees to the minor axes of the cores. The L43 B-field appears to have been influenced in its southern half, such that it is parallel to the wall of a cavity produced by a CO outflow from a nearby T Tauri star, whilst in the northern half the field appears less disturbed and has an angle of 44 degrees to the core minor axis. We briefly compare our results with published models of magnetized cloud cores and conclude that no current model can explain these observations simultaneously with previous ISOCAM data.Comment: 13 pages, 3 figs, to appear in ApJ Letter

Miniature infrared data acquisition and telemetry system

The Miniature Infrared Data Acquisition and Telemetry (MIRDAT) Phase 1 study was performed to determine the technical and commercial feasibility of producing a miniaturized electro-optical telemetry system. This system acquires and transmits experimental data from aircraft scale models for realtime monitoring in wind tunnels. During the Phase 1 study, miniature prototype MIRDAT telemetry devices were constructed, successfully tested in the laboratory and delivered to the user for wind tunnel testing. A search was conducted for commercially available components and advanced hybrid techniques to further miniaturize the system during Phase 2 development. A design specification was generated from laboratory testing, user requirements and discussions with component manufacturers. Finally, a preliminary design of the proposed MIRDAT system was documented for Phase 2 development

Night-time accidents: a scoping study. Report to The AA Motoring Trust and Rees Jeffreys Road Fund

Context: Only a quarter of all travel by car drivers is undertaken between the hours of 19.00 and 08.00, but it is in this period that 40 percent of fatal and serious injuries are sustained by drivers. This indicates that car travel at night carries a greater risk of being killed or seriously injured than does travel during the day. The literature indicates that disproportionate numbers of young drivers, especially young men, are injured at night. But to be able to introduce measures targeted at this group more needs to be known about the purpose of their journeys, the types of roads they travel on, and how far they drive and at what times in the evening and at night. Older drivers tend to have fewer accidents at night, but little is currently known about how much can be accounted for by exposure related to their driving patterns. People over the age of 60 years form about 20 percent of the population, yet they make up over a quarter of traffic fatalities. These two groups of young and older drivers have been selected for study with the following aims: (a) to assess what information exists which relates to night-time exposure by activity and by group (young and older); (b) to assess what is known about exposure and risk to young and older drivers at night, in conjunction with an analysis of relevant accident data to provide a picture of the size of the potential problem areas, and gaps in current knowledge; (c) to identify people’s concerns, attitudes and beliefs with regard to the problems of night-time driving; and (d) to provide the basis for decision on what measures might be brought to bear on the problem, and what further research would be needed in order to point to focused action. This scoping study is in two parts and provides an assessment of the information available and hence the gaps in our knowledge on the nature and extent of night-time driving, and the risks involved at these times. The first part assesses the available data, and the second uses focus groups to gather the views of drivers themselves, together with their concerns, attitudes and beliefs with regard to the problems of night-time driving. The measurement of exposure, or amount of travel by car, of drivers of different age and gender is central to the assessment of the risk of being killed or injured in a road traffic accident. In this study, the measure of exposure used is distance travelled per person per year. This has been combined with casualty data to make preliminary assessments of risk to people of different ages and gender of driving at during the daytime and at night

∗\ast-SDYM fields and heavenly spaces: II. Reductions of the ∗\ast-SDYM system

Reductions of self-dual Yang-Mills (SDYM) system for $\ast$-bracket Lie algebra to the Husain-Park (HP) heavenly equation and to sl(N,{\boldmath{C}) SDYM equation are given. An example of a sequence of $su(N)$ chiral fields ($N\geq 2$) tending for $N\to\infty$ to a curved heavenly space is found.Comment: 18 page

From 2D Integrable Systems to Self-Dual Gravity

We explain how to construct solutions to the self-dual Einstein vacuum equations from solutions of various two-dimensional integrable systems by exploiting the fact that the Lax formulations of both systems can be embedded in that of the self-dual Yang--Mills equations. We illustrate this by constructing explicit self-dual vacuum metrics on $\R^2\times \Sigma$, where $\Sigma$ is a homogeneous space for a real subgroup of SL(2, \C) associated with the two-dimensional system.Comment: 9 pages, LaTex, no figure

Exact Differential O(alpha**2) Results for Hard Bremsstrahlung in e+e- Annihilation to 2f At and Beyond LEP2 Energies

We present the exact O(alpha) correction to the process e+ e- -> f f-bar + gamma, f neq e, for ISR oplus FSR at and beyond LEP2 energies. We give explicit formulas for the completely differential cross section. As an important application, we compute the size of the respective sub-leading corrections of O(alpha L) to the f f-bar cross section, where L is the respective big logarithm in the renormalization group sense so that it is identifiable as L = ln |s|/m_e^2 when s is the squared e+e- cms energy. Comparisons are made with the available literature. We show explicitly that our results have the correct infrared limit, as a cross-check. Some comments are made about the implementation of our results in the framework of the Monte Carlo event generator KK MC.Comment: 26 pages, 5 figs.;improved discussion, figs. and definitions;corrected misprint