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

Rejection-free Monte Carlo Algorithms for Models with Continuous Degrees of Freedom

We construct a rejection-free Monte Carlo algorithm for a system with continuous degrees of freedom. We illustrate the algorithm by applying it to the classical three-dimensional Heisenberg model with canonical Metropolis dynamics. We obtain the lifetime of the metastable state following a reversal of the external magnetic field. Our rejection-free algorithm obtains results in agreement with a direct implementation of the Metropolis dynamic and requires orders of magnitude less computational time at low temperatures. The treatment is general and can be extended to other dynamics and other systems with continuous degrees of freedom.Comment: 4 pages, including figures. PRE, in pres

Remote Controlling and Monitoring of Safety Devices Using Web-Interface Embedded Systems

To date, access control systems have been hardware-based platforms, where software and hardware parts were uncoupled into different systems. The Department of Electronic Technology in the University of Seville, together with ISIS Engineering, have developed an innovative embedded system that provides all needed functions for controlling and monitoring remote access control systems through a built-in web interface. The design provides a monolithic structure, independence from outer systems, easiness in management and maintenance, conformation to the highest standards in security, and straightforward adaptability to applications other than the original one. We have accomplished it by using an extremely reduced Linux kernel and developing web and purpose- specific logic under software technologies with an optimal resource use.Ministerio de Ciencia y Tecnología TEC2006-0843

Dispersive properties of quasi-phase-matched optical parametric amplifiers

The dispersive properties of non-degenerate optical parametric amplification in quasi-phase-matched (QPM) nonlinear quadratic crystals with an arbitrary grating profile are theoretically investigated in the no-pump-depletion limit. The spectral group delay curve of the amplifier is shown to be univocally determined by its spectral power gain curve through a Hilbert transform. Such a constraint has important implications on the propagation of spectrally-narrow optical pulses through the amplifier. In particular, it is shown that anomalous transit times, corresponding to superluminal or even negative group velocities, are possible near local minima of the spectral gain curve. A possible experimental observation of such effects using a QPM Lithium-Niobate crystal is suggested.Comment: submitted for publicatio

The Quark-Photon Vertex and the Pion Charge Radius

The rainbow truncation of the quark Dyson-Schwinger equation is combined with the ladder Bethe-Salpeter equation for the dressed quark-photon vertex to study the low-momentum behavior of the pion electromagnetic form factor. With model gluon parameters previously fixed by the pion mass and decay constant, the pion charge radius $r_\pi$ is found to be in excellent agreement with the data. When the often-used Ball-Chiu Ansatz is used to construct the quark-photon vertex directly from the quark propagator, less than half of $r_\pi^2$ is generated. The remainder of $r^2_\pi$ is seen to be attributable to the presence of the $\rho$-pole in the solution of the ladder Bethe-Salpeter equation.Comment: 21 pages, 9 figure

Reduced stomatal density in bread wheat leads to increased water-use efficiency

Wheat is a staple crop, frequently cultivated in water-restricted environments. Improving crop water-use efficiency would be desirable if grain yield can be maintained. We investigated whether a decrease in wheat stomatal density via the manipulation of epidermal patterning factor (EPF) gene expression could improve water-use efficiency. Our results show that severe reductions in stomatal density in EPF-overexpressing wheat plants have a detrimental outcome on yields. However, wheat plants with a more moderate reduction in stomatal density (i.e. <50% reduction in stomatal density on leaves prior to tillering) had yields indistinguishable from controls, coupled with an increase in intrinsic water-use efficiency. Yields of these moderately reduced stomatal density plants were also comparable with those of control plants under conditions of drought and elevated CO2. Our data demonstrate that EPF-mediated control of wheat stomatal development follows that observed in other grasses, and we identify the potential of stomatal density as a tool for breeding wheat plants that are better able to withstand water-restricted environments without yield loss

Could thermal fluctuations seed cosmic structure?

We examine the possibility that thermal, rather than quantum, fluctuations are responsible for seeding the structure of our universe. We find that while the thermalization condition leads to nearly Gaussian statistics, a Harrisson-Zeldovich spectrum for the primordial fluctuations can only be achieved in very special circumstances. These depend on whether the universe gets hotter or colder in time, while the modes are leaving the horizon. In the latter case we find a no-go theorem which can only be avoided if the fundamental degrees of freedom are not particle-like, such as in string gases near the Hagedorn phase transition. The former case is less forbidding, and we suggest two potentially successful ``warming universe'' scenarios. One makes use of the Phoenix universe, the other of ``phantom'' matter.Comment: minor corrections made, references added, matches the version accepted to PR

Wave reflection at the origin of a first-generation branch artery and target organ protection: the AGES-Reykjavik study

Excessive pressure and flow pulsatility in first-generation branch arteries are associated with microvascular damage in high-flow organs like brain and kidneys. However, the contribution of local wave reflection and rereflection to microvascular damage remains controversial. Aortic flow, carotid pressure, flow and hydraulic power, brain magnetic resonance images, and cognitive scores were assessed in AGES-Reykjavik study participants without history of stroke, transient ischemic attack, or dementia (N=668, 378 women, 69-93 years of age). The aorta-carotid interface was generalized as a markedly asymmetrical bifurcation, with a large parent vessel (proximal aorta) branching into small (carotid) and large (distal aorta) daughter vessels. Local reflection coefficients were computed from aortic and carotid characteristic impedances. The bifurcation reflection coefficient, which determines pressure amplification in both daughter vessels, was low (0.06 +/- 0.03). The carotid flow transmission coefficient was low (0.11 +/- 0.04) and associated with markedly lower carotid versus aortic flow pulsatility (waveform SD, 7.2 +/- 2.0 versus 98.7 +/- 21.8 mL/s, P<0.001), pulsatility index (1.8 +/- 0.5 versus 4.5 +/- 0.6, P<0.001), and pulsatile power percentage (10 +/- 4% versus 25 +/- 5%, P<0.001). Transmitted as compared to incident pulsatile power (19.0 +/- 9.8 versus 35.9 +/- 17.8 mW, P<0.001) was further reduced by reflection (-4.3 +/- 2.7 mW) and rereflection (-12.5 +/- 8.1 mW) within the carotid. Higher carotid flow pulsatility correlated with lower white matter volume (R=-0.130, P<0.001) and lower memory scores (R=-0.161, P<0.001). Marked asymmetry of characteristic impedances at aorta-branch artery bifurcations limits amplification of pressure, markedly reduces absolute and relative pulsatility of transmitted flow and hydraulic power into first-generation branch arteries, and thereby protects the downstream local microcirculation from pulsatile damage.Neuro Imaging Researc