Stable multispeed lattice Boltzmann methods

We demonstrate how to produce a stable multispeed lattice Boltzmann method (LBM) for a wide range of velocity sets, many of which were previously thought to be intrinsically unstable. We use non-Gauss--Hermitian cubatures. The method operates stably for almost zero viscosity, has second-order accuracy, suppresses typical spurious oscillation (only a modest Gibbs effect is present) and introduces no artificial viscosity. There is almost no computational cost for this innovation. DISCLAIMER: Additional tests and wide discussion of this preprint show that the claimed property of coupled steps: no artificial dissipation and the second-order accuracy of the method are valid only on sufficiently fine grids. For coarse grids the higher-order terms destroy coupling of steps and additional dissipation appears. The equations are true.Comment: Disclaimer about the area of applicability is added to abstrac

Stabilisation of the lattice-Boltzmann method using the Ehrenfests' coarse-graining

The lattice-Boltzmann method (LBM) and its variants have emerged as promising, computationally efficient and increasingly popular numerical methods for modelling complex fluid flow. However, it is acknowledged that the method can demonstrate numerical instabilities, e.g., in the vicinity of shocks. We propose a simple and novel technique to stabilise the lattice-Boltzmann method by monitoring the difference between microscopic and macroscopic entropy. Populations are returned to their equilibrium states if a threshold value is exceeded. We coin the name Ehrenfests' steps for this procedure in homage to the vehicle that we use to introduce the procedure, namely, the Ehrenfests' idea of coarse-graining. The one-dimensional shock tube for a compressible isothermal fluid is a standard benchmark test for hydrodynamic codes. We observe that, of all the LBMs considered in the numerical experiment with the one-dimensional shock tube, only the method which includes Ehrenfests' steps is capable of suppressing spurious post-shock oscillations.Comment: 4 pages, 9 figure

Knowledge Sharing and Development in a Digital Age

Digital technologies are reaching ever further into remote parts of the world, changing how people access, use, and create information and knowledge. These changes may improve people’s lives by making information more available, increasing avenues for political and economic engagement, and making governments more transparent and responsive. However, they also carry dangers of growing digital divides, threats to privacy, and the potential loss of diversity of knowledge. Governments, development agencies and civil society organisations need to work together to make knowledge more inclusive and open. This calls for investment in Information and Communications Technology (ICT) infrastructure, information professionals, and search and discovery tools.UK Department for International Developmen

The Future of Knowledge Sharing in a Digital Age: Exploring Impacts and Policy Implications for Development

We live in a Digital Age that gives us instant access to information at greater and greater volumes. The rapid growth of digital content and tools is already changing how we create, consume and distribute knowledge. Even though globally participation in the Digital Age remains uneven, more and more people are accessing and contributing digital content every day. Over the next 15 years, developing countries are likely to experience sweeping changes in how states and societies engage with knowledge. These changes hold the potential to improve people’s lives by making information more available, increasing avenues for political and economic engagement, and making government more transparent and responsive. But they also carry dangers of a growing knowledge divide influenced by technology access, threats to privacy, and the potential loss of diversity of knowledge. Our research sets out with a 15-year horizon to look at the possible ways in which digital technologies might contribute to or damage development agendas, and how development practitioners and policymakers might best respond.UK Department for International Developmen

A SEASON-LONG COMPARISON OF SOCCER REFEREE MATCH DEMANDS BETWEEN THE ENGLISH PREMIER LEAGUE AND CHAMPIONSHIP

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