Stationary and non-stationary fluid flow of a Bose-Einstein condensate through a penetrable barrier

We experimentally study the fluid flow induced by a broad, penetrable barrier moving through an elongated dilute gaseous Bose-Einstein condensate. The barrier is created by a laser beam swept through the condensate, and the resulting dipole potential can be either attractive or repulsive. We examine both cases and find regimes of stable and unstable fluid flow: At slow speeds of the barrier, the fluid flow is stationary due to the superfluidity of the condensate. At intermediate speeds, we observe a non-stationary regime in which the condensate gets filled with dark solitons. At faster speeds, soliton formation completely ceases and a remarkable absence of excitation in the condensate is seen again.Comment: 4 pages, 4 figure

Deformation and chaining of flexible shells in a nematic solvent

A micrometer-scale elastic shell immersed in a nematic liquid crystal may be deformed by the host if the cost of deformation is comparable to the cost of elastic deformation of the nematic. Moreover, such inclusions interact and form chains due to quadrupolar distortions induced in the host. A continuum theory model using finite elements is developed for this system, using mesh regularization and dynamic refinement to ensure quality of the numerical representation even for large deformations. From this model, we determine the influence of the shell elasticity, nematic elasticity and anchoring condition on the shape of the shell and hence extract parameter values from an experimental realization. Extending the model to multi-body interactions, we predict the alignment angle of the chain with respect to the host nematic as a function of aspect ratio, which is found to be in excellent agreement with experiments and greatly improves upon previous theoretical predictions.Comment: 6 pages, 5 figure

The Australian experience of World Wide Views on global warming: The first global deliberation process

World Wide Views on Global Warming was the first ever global-scale citizen deliberation process, held on 25-26 September 2009 and involving approximately 4,000 citizens in 38 countries. WWViews sought to provide citizens with a voice in the 2009 UN Climate Summit in Copenhagen (COP15) by engaging them in a deliberative process about global political positions on climate change. The process produced clear, comparable results across all participating countries that were given to COP15 negotiators. The Danish Government agencies, the Danish Board of Technology and the Danish Cultural Institute, initiated the global process. Organisers in each participating country ran events using the same standardised process. The University of Technology Sydney, the organisers of the Australian WWViews event, paid special attention to several elements of the process to maximise participation and impact within the local context. This paper outlines the standardised global process used for this deliberative event and describes and reflects upon the tailored approaches developed for Australia. It examines in detail the objectives, processes and outcomes of recruiting and supporting participants and recruiting, training and coordinating facilitators, communications and dissemination of results and specific features of the Australian event. It includes the organisers' reflections on success factors, challenges and surprises, as well as feedback from facilitators and participants. This paper concludes with a number of critical questions arising from the Australian experience of World Wide Views on Global Warming that are pertinent for practitioners designing other deliberative forums and particularly anyone concerned about future prospects for global deliberative democracy. Copyright © 2011 The Berkeley Electronic Press. All rights reserved