A homotopy double groupoid of a Hausdorff space II: a van Kampen theorem

This paper is the second in a series exploring the properties of a functor which assigns a homotopy double groupoid with connections to a Hausdorff space. We show that this functor satisfies a version of the van Kampen theorem, and so is a suitable tool for nonabelian, 2-dimensional, local-to-global problems. The methods are analogous to those developed by Brown and Higgins for similar theorems for other higher homotopy groupoids. An integral part of the proof is a detailed discussion of commutative cubes in a double category with connections, and a proof of the key result that any composition of commutative cubes is commutative. These results have recently been generalised to all dimensions by Philip Higgins.Comment: 19 pages, uses picte

Simulation studies and background measurements for a laser based beam size monitor for the future linear collider

At several locations of the beam delivery system (BDS) of a future linear collider (FLC), beam spot sizes ranging from several hundreds to a few micrometers have to be measured. It is anticipated that laser wires will be used for this task in any FLC design. In order to optimize a laser wire system, simulations and background measurements have been carried out. Results are presented from simulations of the Compton scattering for the PETRA scenario. Furthermore results from measurements of backgrounds like synchrotron radiation and gas scattering have been measured at the positron storage ring PETRA at DESY and will be discussed

Beam Profile Measurements and Simulations of the PETRA Laser-Wire

The Laser-wire will be an essential diagnostic tool at the International Linear Collider. It uses a finely focussed laser beam to measure the transverse profile of electron bunches by detecting the Compton-scattered photons (or degraded electrons) downstream of where the laser beam intersects the electron beam. Such a system has been installed at the PETRA storage ring at DESY, which uses a piezo-driven mirror to scan the laser-light across the electron beam. Lat- est results of experimental data taking are presented and compared to detailed simulations using the Geant4 based program BDSIM.Comment: 3 pagesm 4 figures. Submitted as a conference paper for the Particle Accelerator Conference 2005 (PAC05

Medical students’ perception of general practice:a cross-sectional survey

Background: An increase in the demand for general practitioners is expected in many countries, but only a minority of medical students consider a career in general practice. More detailed and up-to-date knowledge about medical student’s perception of general practice would be helpful for efforts to encourage medical students to consider a career in general practice. Methods: We performed a cross-sectional single center survey among Dutch medical students to evaluate their perception of general practice at three different stages in their study: Ba1: first-year bachelor students; Ba3: third-year bachelor students; Ma3: third-year master students. The impact of different factors on their attitudes and perceptions was quantified. A multivariate logistic regression was performed with ‘interest in general practice’ as the outcome variable. Results: The median age for Ba1 was 18 (IQR: 18–19) and 71.5% were female, for Ba3 the median age was 20 (IQR: 20–21) and 70.6% were female and for Ma3 the median age was 25 years (IQR: 24–26) and 73.3% were female. On average, 31.2% of the respondents had a migration background. The mean response rate for this study was 77.1%. Of the participating Ba1 students (n = 340) only 22.4% considered working as a GP after medical school; for Ba3 students (n = 231) this percentage was 33.8%, and for Ma3 students (n = 210) it was significantly higher at 70.5%; in the final multivariate model this corresponded to an odds ratio (OR) of 4.3 (95%-CI:2.6–6.9) compared to Ba1 students. The strongest predictor in the final model was the opinion that general practice provides a pleasant working environment (OR 9.5; 95%-CI: 6.2–14.5). Conclusion: This study showed that multiple factors are significantly related to medical students’ interest in general practice. Although students believed that general practice does not have a high status within the medical profession, they acknowledged the social importance and the pleasant working environment of general practice. Knowledge obtained in this study can be used when designing a medical curriculum or a general practice course.</p