Can Local Stress Enhancement Induce Stability in Fracture Processes? Part I: Apparent Stability

By comparing the evolution of the local and equal load sharing fiber bundle models, we point out the paradoxical result that stresses seem to make the local load sharing model stable when the equal load sharing model is not. We explain this behavior by demonstrating that it is only an apparent stability in the local load sharing model, which originates from a statistical effect due to sample averaging. Even though we use the fiber bundle model to demonstrate the apparent stability, we argue that it is a more general feature of fracture processes.Comment: 7 pages, 8 figure

Developing a Virtual Interdisciplinary Research Community in Clinical Education: Enticing People to the “Tea-Room”

Background: Many interdisciplinary collaborative research programs in the health sector are adopting the community of practice concept within virtual environments. This study explores the factors that affect the members of a geographically dispersed group of health professionals in their attempt to create an interprofessional Virtual Community of Practice (VCoP) from which to promote clinical education research.Method & Findings: A survey was used to determine participants’ degree of computer competency. System logs recorded members’ access details and site activity. Member perceptions and beliefs were established using focus groups. While members stated they were enthusiastic about the VCoP, the primary use was viewing. Their online behaviour indicated that on average it took six visits to generate a post. This suggests a stronger focus on viewing (consumption of) information than on contributing (construction of) information.Conclusions: We believe it is crucial for members to contribute during the initial phase of any pre-structured VCoP in order to overcome the consumption-construction dilemma. It is during this initial phase that members will decide on the community’s value. If the community cannot offer added value, members who engage are likely to consume for a time and then leave

Paediatric cardiac surgery for a continent – The experience of the Walter Sisulu Paediatric Cardiac Centre for Africa

Very few African countries have the resources to provide optimum paediatric cardiac services to their largely indigent populations. In the current era, in countries with access to modern paediatric cardiac care, mortality for congenital heart disease occurs more often in adulthood than in childhood. This level of care is largely unavailable in Africa. The Walter Sisulu Paediatric Cardiac Centre for Africa was set up in 2003 as a public-private collaborative initiative to extend modern paediatric cardiac care to the continent. Three core functions form the basis of our operations: service delivery, training, and research. This communication reviews our experience with this effort over an eight-year period. We have performed 2 023 procedures on 1 738 patients including a large proportion of neonates and infants with an overall mortality of 7.1%. Our charity arm sponsored 21.5% of these patients. We have encountered problems peculiar to the African context which we discuss. We also describe innovative techniques in management of specific patient populations. Our training efforts yielded two qualified paediatric cardiac surgeons who now work at the centre and two additional surgeons are in training. We have participated in research leading to publication of papers in peer-reviewed journals. In spite of our achievements, we recognise the enormous challenges faced by the continent in terms of paediatric cardiac care. An attempt has been made to quantify the burden of congenital disease in Africa to guide planning and training. We offer recommendations on how to address some of these pressing health issues for children of the continent

Antikaon Production in Proton-Nucleus Reactions and the K−K^- properties in nuclear matter

We calculate the momentum-dependent potentials for $K^+$ and $K^-$ mesons in a dispersion approach at nuclear density $\rho_0$ using the information from the vacuum $K^+ N$ and $K^- N$ scattering amplitudes, however, leaving out the resonance contributions for the in-medium analysis. Whereas the $K^+$ potential is found to be repulsive ($\approx$ + 30 MeV) and to show only a moderate momentum dependence, the $K^-$ selfenergy at normal nuclear matter density turns out to be $\approx$ - 200 MeV at zero momentum in line with kaon atomic data, however, decreases rapidly in magnitude for higher momenta. The antikaon production in p + A reactions is calculated within a coupled transport approach and compared to the data at KEK including different assumptions for the antikaon potentials. Furthermore, detailed predictions are made for $p + ^{12}C$ and $p + ^{207}Pb$ reactions at 2.5 GeV in order to determine the momentum dependent antikaon potential experimentally.Comment: 27 pages, LaTeX, including 14 ps-figures, UGI-98-1