Original papers 488 Study of the effect of time availability on the consultation Leone Ridsdale, Maria Carruthers, Richard Morris and Jane Ridsdale 492 Mathematical relationship between waiting times and appointment interval for doctor and patients Ian Hill-Smith 495 Factors affecting the decision to consult with dyspepsia: comparison of consulters and non-consulters Susan Lydeard and Roger Jon...

Optical vortices generically arise when optical beams are combined. Recently, we reported how several laser beams containing optical vortices could be combined to form optical vortex loops, links and knots embedded in a light beam (Leach et al 2004 Nature 432 165). Here, we describe in detail the experiments in which vortex loops form these structures. The experimental construction follows a th...