Finally, results from Gravity Probe-B

Nearly fifty years after its inception, the Gravity Probe B satellite mission delivers the first measurements of how a spinning gyroscope precesses in the gravitational warping of spacetime.Comment: A Viewpoint article, published in Physics 4, 43 (2011), available at http://physics.aps.org/articles/v4/43 Submitted to the arXiv by permission of the American Physical Societ

Dynamic temperature selection for parallel-tempering in Markov chain Monte Carlo simulations

Modern problems in astronomical Bayesian inference require efficient methods for sampling from complex, high-dimensional, often multi-modal probability distributions. Most popular methods, such as Markov chain Monte Carlo sampling, perform poorly on strongly multi-modal probability distributions, rarely jumping between modes or settling on just one mode without finding others. Parallel tempering addresses this problem by sampling simultaneously with separate Markov chains from tempered versions of the target distribution with reduced contrast levels. Gaps between modes can be traversed at higher temperatures, while individual modes can be efficiently explored at lower temperatures. In this paper, we investigate how one might choose the ladder of temperatures to achieve more efficient sampling, as measured by the autocorrelation time of the sampler. In particular, we present a simple, easily-implemented algorithm for dynamically adapting the temperature configuration of a sampler while sampling. This algorithm dynamically adjusts the temperature spacing to achieve a uniform rate of exchanges between chains at neighbouring temperatures. We compare the algorithm to conventional geometric temperature configurations on a number of test distributions and on an astrophysical inference problem, reporting efficiency gains by a factor of 1.2-2.5 over a well-chosen geometric temperature configuration and by a factor of 1.5-5 over a poorly chosen configuration. On all of these problems a sampler using the dynamical adaptations to achieve uniform acceptance ratios between neighbouring chains outperforms one that does not.Comment: 21 pages, 21 figure

If the government wants to introduce a real revolution in law and order, it should devolve powers and budgets for all criminal justice and emergency services to PCCs

Will Tanner argues that if the Prime Minister is serious about his ‘tough but intelligent’ approach to crime and justice then resources should be directed to what is proven to work. The astonishing success of the Violence Reduction Unit (VRU) in Glasgow is just such a project. Only through such localism could initiatives like the VRU become the norm

Integration and the Achievement Gap: Innovation in Dallas, Texas

Educatio

Police force mergers are unnecessary and miss the point; the best policing is local

Much of the focus during the PCC elections has been on the principle of representation. Will Tanner argues that localism is equally important and that the future of policing in England and Wales must be local and democratic, not regional and bureaucratic