Validating optimisations for chaotic simulations

It is non-trivial to optimise computations of chaotic systems since slightly perturbed simulations diverge exponentially over time due to the well-known butterfly effect if bit-reproducible results are not achieved. Therefore, two model setups that show the same quality in the representation of a chaotic system will show uncorrelated behaviour if integrated long enough, hence it is challenging to check whether a given optimisation degrades model quality. Most models in computational fluid dynamics show chaotic behaviour. In this paper we focus on models of atmosphere and ocean that are vital for predictions of future weather and climate. Since forecast quality is usually limited by the available computational power, optimisation is highly desirable. We describe a new method for accepting or rejecting an optimised implementation of a reconfigurable design to simulate dynamics of a chaotic system. We apply this method to optimise numerical precision to a minimal level of stencil computations that can be used in an idealised ocean model, and show the performance improvements gained on an FPGA. The proposed method enables precision reduction for the FPGA so that it computes up to 9 times faster with 6 times lower energy consumption than an implementation on the same device with double precision arithmetic, while ensuring the optimised design to have acceptable numerical behaviour

Lower precision for higher accuracy: precision and resolution exploration for shallow water equations

Accurate forecasts of future climate with numerical models of atmosphere and ocean are of vital importance. However, forecast quality is often limited by the available computational power. This paper investigates the acceleration of a C-grid shallow water model through the use of reduced precision targeting FPGA technology. Using a double-gyre scenario, we show that the mantissa length of variables can be reduced to 14 bits without affecting the accuracy beyond the error inherent in the model. Our reduced precision FPGA implementation runs 5.4 times faster than a double precision FPGA implementation, and 12 times faster than a multi-Threaded CPU implementation. Moreover, our reduced precision FPGA implementation uses 39 times less energy than the CPU implementation and can compute a 100×100 grid for the same energy that the CPU implementation would take for a 29×29 grid

The morphologies of massive galaxies at 1 < z < 3 in the CANDELS-UDS field : compact bulges, and the rise and fall of massive discs

We have used high-resolution, Hubble Space Telescope, near-infrared imaging to conduct a detailed analysis of the morphological properties of the most massive galaxies at high redshift, modelling the WFC3/IR H-160-band images of the similar or equal to 200 galaxies in the CANDELS-UDS field with photometric redshifts 1 10(11)M(circle dot). We have explored the results of fitting single-Sersic and bulge+disc models, and have investigated the additional errors and potential biases introduced by uncertainties in the background and the on-image point spread function. This approach has enabled us to obtain formally acceptable model fits to the WFC3/IR images of > 90 per cent of the galaxies. Our results indicate that these massive galaxies at 1 2 the compact bulges display effective radii a factor of similar or equal to 4 smaller than local ellipticals of comparable mass. These trends also appear to extend to the bulge components of disc-dominated galaxies. In addition, we find that, while such massive galaxies at low redshift are generally bulge-dominated, at redshifts 1 2 they are mostly disc-dominated. The majority of the disc-dominated galaxies are actively forming stars, although this is also true for many of the bulge-dominated systems. Interestingly, however, while most of the quiescent galaxies are bulge-dominated, we find that a significant fraction (25-40 per cent) of the most quiescent galaxies, with specific star formation rates sSFR < 10(-10) yr(-1), have disc-dominated morphologies. Thus, while our results show that the massive galaxy population is undergoing dramatic changes at this crucial epoch, they also suggest that the physical mechanisms which quench star formation activity are not simply connected to those responsible for the morphological transformation of massive galaxies into present-day giant ellipticals

Malaria vaccines and their potential role in the elimination of malaria

Research on malaria vaccines is currently directed primarily towards the development of vaccines that prevent clinical malaria. Malaria elimination, now being considered seriously in some epidemiological situations, requires a different vaccine strategy, since success will depend on killing all parasites in the community in order to stop transmission completely

From Tensor Algebra to Hardware Accelerators: Generating Streaming Architectures for Solving Partial Differential Equations

Hardware accelerators are attractive targets for running scientific simulations due to their power efficiency. Since, large software simulations can take person years to develop, it is often impractical to use hardware acceleration, which requires significantly more development effort and expertise than software development. We present the design and implementation of a proof-of-concept compiler toolchain which enables rapid prototyping of hardware finite difference solvers for partial differential equations, generated from a high-level domain specific language. Multiple fields, grid staggering and non-linear terms are supported. We demonstrate that our approach is practical by generating and evaluating hardware designs derived from the heat and simplified shallow water equations

A robust sample of submillimetre galaxies: constraints on the prevalence of dusty, high-redshift starbursts

The modest significance of most sources detected in current ( sub) millimetre [( sub) mm] surveys can potentially compromise some analyses due to the inclusion of spurious sources in catalogues typically selected at >= 3.0 -3.5 sigma. Here, we develop and apply a dual-survey extraction technique to Submillimetre Common-User Bolometer Array ( SCUBA) and Max-Planck Millimetre Bolometer( MAMBO) images of the Lockman Hole. Cut above 5 sigma, our catalogue of submillimetre galaxies ( SMGs) is more robust than previous samples, with a reduced likelihood of real, but faint SMGs (beneath and around the confusion limit) entering via superposition with noise. Our selection technique yields 19 SMGs in an effective area of 165 arcmin(2), of which we expect at most two to be due to chance superposition of SCUBA and MAMBO noise peaks. The effective flux limit of the survey (similar to 4 mJy at similar to 1 mm) is well matched to our deep 1.4-GHz image (sigma = 4.6 mu Jy beam(-1)). The former is sensitive to luminous, dusty galaxies at extreme redshifts whilst the latter probes the z less than or similar to 3 regime. A high fraction of our robust SMGs (similar to 80 per cent) have radio counterparts which, given the similar to 10 per cent contamination by spurious sources, suggests that very distant SMGs (z >> 3) are unlikely to make up more than similar to 10 per cent of the bright SMG population. This implies that almost all of the S-1mm greater than or similar to 4 mJy SMG population is amenable to study via the deepest current radio imaging. We use these radio counterparts to provide an empirical calibration of the positional uncertainty in SMG catalogues. We then go on to outline the acquisition of redshifts for radio-identified SMGs, from sample selection in the submm, to counterpart selection in the radio and optical/infrared, to slit placement on spectrograph masks. We determine a median of z = 2.05 +/- 0.41 from a sample of six secure redshifts for unambiguous radio-identified submm sources and z = 2.14 +/- 0.27 when we include submm sources with multiple radio counterparts and/or less reliable redshifts. These figures are consistent with previous estimates, suggesting that our knowledge of the median redshift of bright SMG population has not been biased by the low significance of the source catalogues employed