Enabling a High Throughput Real Time Data Pipeline for a Large Radio Telescope Array with GPUs

The Murchison Widefield Array (MWA) is a next-generation radio telescope currently under construction in the remote Western Australia Outback. Raw data will be generated continuously at 5GiB/s, grouped into 8s cadences. This high throughput motivates the development of on-site, real time processing and reduction in preference to archiving, transport and off-line processing. Each batch of 8s data must be completely reduced before the next batch arrives. Maintaining real time operation will require a sustained performance of around 2.5TFLOP/s (including convolutions, FFTs, interpolations and matrix multiplications). We describe a scalable heterogeneous computing pipeline implementation, exploiting both the high computing density and FLOP-per-Watt ratio of modern GPUs. The architecture is highly parallel within and across nodes, with all major processing elements performed by GPUs. Necessary scatter-gather operations along the pipeline are loosely synchronized between the nodes hosting the GPUs. The MWA will be a frontier scientific instrument and a pathfinder for planned peta- and exascale facilities.Comment: Version accepted by Comp. Phys. Com

Glider observations of enhanced deep water upwelling at a shelf break canyon: a mechanism for cross-slope carbon and nutrient exchange

Using underwater gliders we have identified canyon driven upwelling across the Celtic Sea shelf-break, in the vicinity of Whittard Canyon. The presence of this upwelling appears to be tied to the direction and strength of the local slope current, which is in itself highly variable. During typical summer time equatorward flow, an unbalanced pressure gradient force and the resulting disruption of geostrophic flow can lead to upwelling along the main axis of two small shelf break canyons. As the slope current reverts to poleward flow, the upwelling stops and the remnants of the upwelled features are mixed into the local shelf water or advected away from the region. The upwelled features are identified by the presence of sub-pycnocline high salinity water on the shelf, and are upwelled from a depth of 300 m on the slope, thus providing a mechanism for the transport of nutrients across the shelf break onto the shelf

Quasi-particle Lifetimes in a d_{x^2-y^2} Superconductor

We consider the lifetime of quasi-particles in a d-wave superconductor due to scattering from antiferromagnetic spin-fluctuations, and explicitly separate the contribution from Umklapp processes which determines the electrical conductivity. Results for the temperature dependence of the total scattering rate and the Umklapp scattering rate are compared with relaxation rates obtained from thermal and microwave conductivity measurements, respectively.Comment: 14 pages, 4 figure

The Initial Mass Function in disc galaxies and in galaxy clusters: the chemo-photometric picture

The observed brightness of the Tully-Fisher relation suggests a low stellar M/L ratio and a "bottom-light" IMF in disc galaxies, but the corresponding efficiency of chemical enrichment tends to exceed the observational estimates. Either suitable tuning of the IMF slope and mass limits or metal outflows from disc galaxies must then be invoked. A standard Solar Neighbourhood IMF cannot explain the high metallicity of the hot intra-cluster medium: a different IMF must be at work in clusters of galaxies. Alternatively, if the IMF is universal and chemical enrichment is everywhere as efficient as observed in clusters, substantial loss of metals must occur from the Solar Neighbourhood and from disc galaxies in general; a "non-standard" scenario challenging our understanding of disc galaxy formation.Comment: 6 pages, 4 figures; in Proceedings of IMF@50: the Initial Mass Function 50 years later; Corbelli, Palla and Zinnecker (eds.

Dust attenuation and star formation in the nearby universe: the ultraviolet and far-infrared points of view

We make use of the on-going All Imaging Survey of the UV GALEX satellite cross-correlated with the IRAS all sky survey to build samples of galaxies trully selected in far-infrared or in ultraviolet. We discuss the amount of dust attenuation and the star formation rates for these galaxies and compare the properties of the galaxies selected in FIR or in UV.Comment: 4 pages, proceedings of the conference: "Starbursts 2004 - From 30 Doradus to Lyman break galaxies" held in Cambridge, 6-10 September 200

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Does wage rank affect employees' well-being?

How do workers make wage comparisons? Both an experimental study and an analysis of 16,000 British employees are reported. Satisfaction and well-being levels are shown to depend on more than simple relative pay. They depend upon the ordinal rank of an individual's wage within a comparison group. “Rank” itself thus seems to matter to human beings. Moreover, consistent with psychological theory, quits in a workplace are correlated with pay distribution skewness

The Spatial Distribution of the Young Stellar Clusters in the Star-forming Galaxy NGC 628

We present a study of the spatial distribution of the stellar cluster populations in the star-forming galaxy NGC 628. Using Hubble Space Telescope broadband WFC3/UVIS UV and optical images from the Treasury Program LEGUS (Legacy ExtraGalactic UV Survey), we have identified 1392 potential young ($\lesssim 100$ Myr) stellar clusters within the galaxy using a combination of visual inspection and automatic selection. We investigate the clustering of these young stellar clusters and quantify the strength and change of clustering strength with scale using the two-point correlation function. We also investigate how image boundary conditions and dust lanes affect the observed clustering. The distribution of the clusters is well fit by a broken power law with negative exponent α. We recover a weighted mean index of $\alpha \sim -0.8$ for all spatial scales below the break at 3farcs3 (158 pc at a distance of 9.9 Mpc) and an index of $\alpha \sim -0.18$ above 158 pc for the accumulation of all cluster types. The strength of the clustering increases with decreasing age and clusters older than 40 Myr lose their clustered structure very rapidly and tend to be randomly distributed in this galaxy, whereas the mass of the star cluster has little effect on the clustering strength. This is consistent with results from other studies that the morphological hierarchy in stellar clustering resembles the same hierarchy as the turbulent interstellar medium

Evolution of the infrared luminosity density and star formation history up to z~1: preliminary results from MIPS

Using deep observations of the Chandra Deep Field South obtained with MIPS at 24mic, we present our preliminary estimates on the evolution of the infrared (IR) luminosity density of the Universe from z=0 to z~1. We find that a pure density evolution of the IR luminosity function is clearly excluded by the data. The characteristic luminosity L_IR* evolves at least by (1+z)^3.5 with lookback time, but our monochromatic approach does not allow us to break the degeneracy between a pure evolution in luminosity or an evolution in both density and luminosity. Our results imply that IR luminous systems (L_IR > 10^11 L_sol) become the dominant population contributing to the comoving IR energy density beyond z~0.5-0.6. The uncertainties affecting our measurements are largely dominated by the poor constraints on the spectral energy distributions that are used to translate the observed 24mic flux into luminosities.Comment: 4 pages, 2 figures. To be published in "Starbursts: From 30 Doradus to Lyman Break Galaxies", held in Cambridge, 6-10 September 2004, Ed. R. de Grijs & R. M. Gonzalez Delgad