Self-Consistent Thermal Accretion Disk Corona Models for Compact Objects: II. Application to Cygnus X-1

We apply our self-consistent accretion disk corona (ADC) model, with two different geometries, to the broad-band X-ray spectrum of the black hole candidate Cygnus X-1. As shown in a companion paper (Dove, Wilms, and Begelman), models where the Comptonizing medium is a slab surrounding the cold accretion disk cannot have a temperature higher than about 120 keV for optical depths greater than 0.2, resulting in spectra that are much softer than the observed 10-30 keV spectrum of Cyg X-1. In addition, the slab geometry models predict a substantial ``soft excess'' at low energies, a feature not observed for Cyg X-1, and Fe K\alpha fluorescence lines that are stronger than observed. Previous Comptonization models in the literature invoke a slab geometry with the optical depth \tau_T \gta 0.3 and the coronal temperature T_c \sim 150 keV, but they are not self-consistent. Therefore, ADC models with a slab geometry are not appropriate for explaining the X-ray spectrum of Cyg X-1. Models with a spherical corona and an exterior disk, however, predict much higher self-consistent coronal temperatures than the slab geometry models. The higher coronal temperatures are due to the lower amount of reprocessing of coronal radiation in the accretion disk, giving rise to a lower Compton cooling rate. Therefore, for the sphere+disk geometry, the predicted spectrum can be hard enough to describe the observed X-ray continuum of Cyg X-1 while predicting Fe fluorescence lines having an equivalent width of \sim 40 eV. Our best-fit parameter values for the sphere+disk geometry are \tau_T \approx 1.5 and T_c \approx 90 keV.Comment: 13 pages, Latex, 10 .eps figures, uses emulateapj.sty. To be published in ApJ, October 1, 1997, Vol. 48

Conduct Problems: Effective Programmes for 3-7 year olds

This is the second in a series of reports prepared by the Advisory Group on Conduct Problems (AGCP) on the prevention, treatment and management of conduct problems in young people. For the purpose of this and all reports prepared by the AGCP conduct problems are defined as: Childhood conduct problems include a spectrum of anti-social, aggressive, dishonest, delinquent, defiant and disruptive behaviours. These behaviours may vary from none to severe, and may have the following consequences for the child/young person and those around him/her - stress, distress and concern to adult caregivers and authority figures, threats to the physical safety of the young people involved and their peers, disruption of home, school or other environments, and involvement of the criminal justice system. The focus of this report is on the identification, implementation and evaluation of programmes and interventions for children aged 3-7

'If Michael Owen drinks it, why can't I?' - 9 and 10 year olds' perceptions of physical activity and healthy eating

Objective - To explore the perceptions of physical activity and healthy eating among children from two north west of England primary schools, with the ultimate aim of improving healthy lifestyle choices. Design - A qualitative study in which each child participated in two focus groups. Setting Two primary schools in a deprived ward of Warrington, chosen to contrast with the focus of earlier research on relatively affluent communities. Method - A sample of 32 9 and 10 year olds was randomly selected from two Year 5 classes. Four focus groups were held in total; two in each school. The first explored perceptions of physical activity and the second examined views on food and eating. Discussions were recorded, transcribed verbatim and findings emerged through a process of thematic analysis. Results - Children reported being involved in a range of physical activities and recognized the health benefits associated with being active. Boys and girls differed in their attitude towards physical activity, with boys appearing competitive about sport while girls enjoyed a wider range of activities. Children were able to distinguish between healthy and unhealthy foods, but there was uncertainty over the healthiness of foods containing multiple ingredients (for example, salad in burgers). Children also identified the impact of the local environment, parents, school, the food industry and their peers on their diet and involvement in physical activity. Conclusions - Children receive contradictory messages about food and diet, which they make sense of through their social interactions. The development of obesity prevention strategies and weight management programmes must take into account children's perspectives. Children should be given the opportunity to contribute to the development of initiatives that are set up to prevent and treat obesity