Geodesic equations and algebro-geometric methods

For an investigation of the physical properties of gravitational fields the observation of massive test particles and light is very useful. The characteristic features of a given space-time may be decoded by studying the complete set of all possible geodesic motions. Such a thorough analysis can be accomplished most effectively by using analytical methods to solve the geodesic equation. In this contribution, the use of elliptic functions and their generalizations for solving the geodesic equation in a wide range of well known space-times, which are part of the general Pleba\'nski-Demia\'nski family of solutions, will be presented. In addition, the definition and calculation of observable effects like the perihelion shift will be presented and further applications of the presented methods will be outlined.Comment: 8 pages, no figures; based on presentation at the conference "Relativity and Gravitation: 100 Years after Einstein in Prague," Prague, 2012. Relativity and Gravitation, volume 157 of Springer Proceedings in Physics, p 91. Springer International Publishing, 201

Prevention of catheter lumen occlusion with rT-PA versus heparin (Pre-CLOT): study protocol of a randomized trial [ISRCTN35253449]

BACKGROUND: Many patients with end-stage renal disease use a central venous catheter for hemodialysis access. A large majority of these catheters malfunction within one year of insertion, with up to two-thirds due to thrombosis. The optimal solution for locking the catheter between hemodialysis sessions, to decrease the risk of thrombosis and catheter malfunction, is unknown. The Prevention of Catheter Lumen Occlusion with rt-PA versus Heparin (PreCLOT) study will determine if use of weekly rt-PA, compared to regular heparin, as a catheter locking solution, will decrease the risk of catheter malfunction. METHODS/DESIGN: The study population will consist of patients requiring chronic hemodialysis thrice weekly who are dialyzed with a newly inserted permanent dual-lumen central venous catheter. Patients randomized to the treatment arm will receive rt-PA 1 mg per lumen once per week, with heparin 5,000 units per ml as a catheter locking solution for the remaining two sessions. Patients randomized to the control arm will receive heparin 5,000 units per ml as a catheter locking solution after each dialysis session. The study treatment period will be six months, with 340 patients to be recruited from 14 sites across Canada. The primary outcome will be catheter malfunction, based on mean blood flow parameters while on hemodialysis, with a secondary outcome of catheter-related bacteremia. A cost-effectiveness analysis will be undertaken to assess the cost of maintaining a catheter using rt-PA as a locking solution, compared to the use of heparin. DISCUSSION: Results from this study will determine if use of weekly rt-PA, compared to heparin, will decrease catheter malfunction, as well as assess the cost-effectiveness of these locking solutions

Cultural measurement on whose terms? Critical friends as an experiment in participant-led evaluation

Critical Friends is an enquiry into the commissioning, planning and delivery of participatory art carried out by the people that such projects claim to empower. Participants become interviewers, researchers and evaluators, acting as ‘productive parasites’ to a process of socially-engaged art. Aims of social cohesion and active citizenship underpinned a series of publicly-funded art commissions in North Greenwich, London (2008-2011). The group of Critical Friends were residents of North Greenwich who came together to investigate what, why and how these socially engaged art projects were happening in their area. Did the projects reflect the ambitious aims to ‘stimulate debate to generate action and change’ and ‘develop connections and relations between people’? Facilitated by myself and Rebecca Maguire over three years, Critical Friends developed their own questions and methods for finding out. While participation and engagement is usually measured for such projects in terms of numbers of people who attend workshops, Critical Friends was a space for enacting a different kind of cultural measurement. The group focused on trying to find out the qualitative experiences of other participants and interrogated the underlying motives, targets and politics behind the commissions. They did this by acting as participant observers in the projects themselves and by interviewing artists, commissioners, board members, their neighbours and friends (http://criticalfriends.sophiehope.org.uk/)