Simulating Turbulence Using the Astrophysical Discontinuous Galerkin Code TENET

In astrophysics, the two main methods traditionally in use for solving the Euler equations of ideal fluid dynamics are smoothed particle hydrodynamics and finite volume discretization on a stationary mesh. However, the goal to efficiently make use of future exascale machines with their ever higher degree of parallel concurrency motivates the search for more efficient and more accurate techniques for computing hydrodynamics. Discontinuous Galerkin (DG) methods represent a promising class of methods in this regard, as they can be straightforwardly extended to arbitrarily high order while requiring only small stencils. Especially for applications involving comparatively smooth problems, higher-order approaches promise significant gains in computational speed for reaching a desired target accuracy. Here, we introduce our new astrophysical DG code TENET designed for applications in cosmology, and discuss our first results for 3D simulations of subsonic turbulence. We show that our new DG implementation provides accurate results for subsonic turbulence, at considerably reduced computational cost compared with traditional finite volume methods. In particular, we find that DG needs about 1.8 times fewer degrees of freedom to achieve the same accuracy and at the same time is more than 1.5 times faster, confirming its substantial promise for astrophysical applications.Comment: 21 pages, 7 figures, to appear in Proceedings of the SPPEXA symposium, Lecture Notes in Computational Science and Engineering (LNCSE), Springe

Word Works Satellite Exhibition/Performance Event 4th Biennale Sydney

‘Word Works’ were performed by Jon Cockburn on Tuesday, 27 April 1982, 7.30-9.30pm, at ‘An Evening of Performance Art’ a satellite program organized by Derek Kreckler, during the 4th Biennale of Sydney, and held at the Shepherd and Newman Warehouse, Darlinghurst, Sydney. The list of word works performed by Jon Cockburn included some, if not all, of the following titles • Suicide • Terence Maloon • A Shove in the Right Direction • The Reason Why • Terry Smith • Loosing Confidence...or Post Modern Sexuality • of Joseph Beuys • Four light pieces for interlude in a Performance (Above word works written between early 1981 and April 1982). Other participants in ‘An Evening of Performance Art’ on Tuesday 27 April 1982 were: • Simone Mangos • John Lyall • Kim Machin • Lionel Doolan • John Gillies • Sally Hollis-McLeod and Derek War

Ab initio methods for finite temperature two-dimensional Bose gases

The stochastic Gross-Pitaevskii equation and modified Popov theory are shown to provide an ab initio description of finite temperature, weakly-interacting two-dimensional Bose gas experiments. Using modified Popov theory, a systematic approach is developed in which the momentum cut-off inherent to classical field methods is removed as a free parameter. This is shown to yield excellent agreement with the recent experiment of Hung et al. [Nature, 470, 236 (2011)], verifying that the stochastic Gross-Pitaevskii equation captures the observed universality and scale-invariance.Comment: 5 pages, 4 figure

Speech at the exhibition opening of Metropolis: Rotwang\u27s Robot, Revolution, and Redemption A Selection of Memorabiia Relating to Fritz Lang\u27s 1927 Sci-Fi Fantasy Film. From the Collection of Michael Organ.

Opening speech by Dr Jon Cockburn for the exhibition “Metropolis: Rotwang’s Robot, Revolution, and Redemption”. The exhibition contains a selection of memorabilia relating to Fritz Lang’s 1927 Sci-Fi fantasy film. The memorabilia is on loan to the Wollongong City Gallery from the collection of Michael Organ. The opening speech reflects on the development and production of the film Metropolis (1927), its reception on first release in Germany and then abroad. The film’s influence on the genre of science fiction to the present day is noted. The film’s ambiguous themes are of particular interest especially when considered in the light of world events in the late 1930s and the different career trajectories of the film’s director, Fritz Lang, and the film’s screenplay writer Thea von Harbou. However, of equal significance is how the film stands as a case study in archiving, preserving and restoring fragile film media with the aim of recouping the film’s importance as a work and as a document to the time of its production

Historical roots of Agile methods: where did “Agile thinking” come from?

The appearance of Agile methods has been the most noticeable change to software process thinking in the last fifteen years [16], but in fact many of the “Agile ideas” have been around since 70’s or even before. Many studies and reviews have been conducted about Agile methods which ascribe their emergence as a reaction against traditional methods. In this paper, we argue that although Agile methods are new as a whole, they have strong roots in the history of software engineering. In addition to the iterative and incremental approaches that have been in use since 1957 [21], people who criticised the traditional methods suggested alternative approaches which were actually Agile ideas such as the response to change, customer involvement, and working software over documentation. The authors of this paper believe that education about the history of Agile thinking will help to develop better understanding as well as promoting the use of Agile methods. We therefore present and discuss the reasons behind the development and introduction of Agile methods, as a reaction to traditional methods, as a result of people's experience, and in particular focusing on reusing ideas from histor

Phase coherence in quasicondensate experiments: an ab initio analysis via the stochastic Gross-Pitaevskii equation

We perform an ab initio analysis of the temperature dependence of the phase coherence length of finite temperature, quasi-one-dimensional Bose gases measured in the experiments of Richard et al. (Phys. Rev. Lett. 91, 010405 (2003)) and Hugbart et al. (Eur. Phys. J. D 35, 155-163 (2005)), finding very good agreement across the entire observed temperature range ($0.8<T/T_{\phi}<28$). Our analysis is based on the one-dimensional stochastic Gross-Pitaevskii equation, modified to self-consistently account for transverse, quasi-one-dimensional effects, thus making it a valid model in the regime $\mu ~ few \hbar \omega_\perp$. We also numerically implement an alternative identification of $T_{\phi}$, based on direct analysis of the distribution of phases in a stochastic treatment.Comment: Amended manuscript with improved agreement to experiment, following some additional clarifications by Mathilde Hugbart and Fabrice Gerbier and useful comments by the reviewer; accepted for publication in Physical Review

Matter-wave dark solitons: stochastic vs. analytical results

The dynamics of dark matter-wave solitons in elongated atomic condensates are discussed at finite temperatures. Simulations with the stochastic Gross-Pitaevskii equation reveal a noticeable, experimentally observable spread in individual soliton trajectories, attributed to inherent fluctuations in both phase and density of the underlying medium. Averaging over a number of such trajectories (as done in experiments) washes out such background fluctuations, revealing a well-defined temperature-dependent temporal growth in the oscillation amplitude. The average soliton dynamics is well captured by the simpler dissipative Gross-Pitaevskii equation, both numerically and via an analytically-derived equation for the soliton center based on perturbation theory for dark solitons.Comment: 4 pages, 3 figures. Added several reference

Discontinuous high-order finite-volume/finite-element method for inviscid compressible flows

The discontinuous, hybrid control-volume/finite-element method merges the desirable conservative properties and intuitive physical formulation of the finite-volume technique, with the capability of local arbitrary high-order accuracy distinctive of the discontinuous finite-element method. This relatively novel scheme has been previously applied to the solution of advection-diffusion problems and the shallow-water equations, and is in the present work extended to the Euler equations. The derivation of the method is presented in the general multi-dimensional case, and selected numerical problems are solved in the one- and two-dimensional case