3,350 research outputs found
Advanced Architectures for Astrophysical Supercomputing
Astronomers have come to rely on the increasing performance of computers to
reduce, analyze, simulate and visualize their data. In this environment, faster
computation can mean more science outcomes or the opening up of new parameter
spaces for investigation. If we are to avoid major issues when implementing
codes on advanced architectures, it is important that we have a solid
understanding of our algorithms. A recent addition to the high-performance
computing scene that highlights this point is the graphics processing unit
(GPU). The hardware originally designed for speeding-up graphics rendering in
video games is now achieving speed-ups of in general-purpose
computation -- performance that cannot be ignored. We are using a generalized
approach, based on the analysis of astronomy algorithms, to identify the
optimal problem-types and techniques for taking advantage of both current GPU
hardware and future developments in computing architectures.Comment: 4 pages, 1 figure, to appear in the proceedings of ADASS XIX, Oct 4-8
2009, Sapporo, Japan (ASP Conf. Series
Spotting Radio Transients with the help of GPUs
Exploration of the time-domain radio sky has huge potential for advancing our
knowledge of the dynamic universe. Past surveys have discovered large numbers
of pulsars, rotating radio transients and other transient radio phenomena;
however, they have typically relied upon off-line processing to cope with the
high data and processing rate. This paradigm rules out the possibility of
obtaining high-resolution base-band dumps of significant events or of
performing immediate follow-up observations, limiting analysis power to what
can be gleaned from detection data alone. To overcome this limitation,
real-time processing and detection of transient radio events is required. By
exploiting the significant computing power of modern graphics processing units
(GPUs), we are developing a transient-detection pipeline that runs in real-time
on data from the Parkes radio telescope. In this paper we discuss the
algorithms used in our pipeline, the details of their implementation on the GPU
and the challenges posed by the presence of radio frequency interference.Comment: 4 Pages. To appear in the proceedings of ADASS XXI, ed. P.Ballester
and D.Egret, ASP Conf. Serie
Astrophysical Supercomputing with GPUs: Critical Decisions for Early Adopters
General purpose computing on graphics processing units (GPGPU) is
dramatically changing the landscape of high performance computing in astronomy.
In this paper, we identify and investigate several key decision areas, with a
goal of simplyfing the early adoption of GPGPU in astronomy. We consider the
merits of OpenCL as an open standard in order to reduce risks associated with
coding in a native, vendor-specific programming environment, and present a GPU
programming philosophy based on using brute force solutions. We assert that
effective use of new GPU-based supercomputing facilities will require a change
in approach from astronomers. This will likely include improved programming
training, an increased need for software development best-practice through the
use of profiling and related optimisation tools, and a greater reliance on
third-party code libraries. As with any new technology, those willing to take
the risks, and make the investment of time and effort to become early adopters
of GPGPU in astronomy, stand to reap great benefits.Comment: 13 pages, 5 figures, accepted for publication in PAS
Understanding Earth– Ocean Processes using Real-time Data from NEPTUNE, Canada’s Widely Distributed Sensor Networks, Northeast Pacific
After several years of planning, NEPTUNE Canada [www.neptunecanada.ca], as part of the Ocean Networks Canada Observatory, largely completed the installation of the world’s first regional cabled observatory network in 2009. The 800 km cable loop west of Vancouver Island connects five nodes in coastal, continental slope, abyssal plain and spreading-ridge environments. Abundant power and high-bandwidth communications support a network of hundreds of sensors that deliver data and imagery in real- or near real-time, and will transform our knowledge of the ocean environment and interacting processes. With the world’s oceans and climate in a state of crisis, the development of cabled observatory technologies is most timely and offers a growing data archive of unparalleled importance for new discoveries.
Sommaire
Apres plusieurs années de planification, l’essentiel du premier reseau observatoire régional, NEPTUNE Canada [www.neptunecanada.ca], partie intégrante du Ocean Network Observatory, a été installé en 2009. Ses 800km de cable forment une boucle à l’ Ouest de l’ Isle de Vancouver et sont connectés à cinq noeuds situés au niveau de la zone cotière, du talus continental, de la plaine abyssale et de la dorsale océanique. Grace à cet acces à l’ énergie et la communication à haut débit, un réseau de centaines de capteurs transmettent des données et images en temps réel ou quasi réel, qui transformeront nos connaissances du mileu et processus océaniques. Alors que les océans et le climat sont en état de stress, le dévelopment des technologies liées aux observatoires sous marins représente une opportunité exceptionelle et un recueil de données sans cesse croissant et d’ un potentiel inégalé pour permettre de nouvelles découvertes
Cosmic Texture from a Broken Global SU(3) Symmetry
We investigate the observable consequences of creating cosmic texture by
breaking a global SU(3) symmetry, rather than the SU(2) case which is generally
studied. To this end, we study the nonlinear sigma model for a totally broken
SU(3) symmetry, and develop a technique for numerically solving the classical
field equations. This technique is applied in a cosmological context: the
energy of the collapsing SU(3) texture field is used as a gravitational source
for the production of perturbations in the primordial fluids of the early
universe. From these calculations, we make predictions about the appearance of
the anisotropies in the cosmic microwave background radiation (CMBR) which
would be present if the large scale structure of the universe was
gravitationally seeded by the collapse of SU(3) textures.Comment: 28 pages, latex, 11 figures, submitted to Phys. Rev.
SMART Cables for Observing the Global Ocean: Science and Implementation
The ocean is key to understanding societal threats including climate change, sea level rise, ocean warming, tsunamis, and earthquakes. Because the ocean is difficult and costly to monitor, we lack fundamental data needed to adequately model, understand, and address these threats. One solution is to integrate sensors into future undersea telecommunications cables. This is the mission of the SMART subsea cables initiative (Science Monitoring And Reliable Telecommunications). SMART sensors would “piggyback” on the power and communications infrastructure of a million kilometers of undersea fiber optic cable and thousands of repeaters, creating the potential for seafloor-based global ocean observing at a modest incremental cost. Initial sensors would measure temperature, pressure, and seismic acceleration. The resulting data would address two critical scientific and societal issues: the long-term need for sustained climate-quality data from the under-sampled ocean (e.g., deep ocean temperature, sea level, and circulation), and the near-term need for improvements to global tsunami warning networks. A Joint Task Force (JTF) led by three UN agencies (ITU/WMO/UNESCO-IOC) is working to bring this initiative to fruition. This paper explores the ocean science and early warning improvements available from SMART cable data, and the societal, technological, and financial elements of realizing such a global network. Simulations show that deep ocean temperature and pressure measurements can improve estimates of ocean circulation and heat content, and cable-based pressure and seismic-acceleration sensors can improve tsunami warning times and earthquake parameters. The technology of integrating these sensors into fiber optic cables is discussed, addressing sea and land-based elements plus delivery of real-time open data products to end users. The science and business case for SMART cables is evaluated. SMART cables have been endorsed by major ocean science organizations, and JTF is working with cable suppliers and sponsors, multilateral development banks and end users to incorporate SMART capabilities into future cable projects. By investing now, we can build up a global ocean network of long-lived SMART cable sensors, creating a transformative addition to the Global Ocean Observing System
Teraflop per second gravitational lensing ray-shooting using graphics processing units
Gravitational lensing calculation using a direct inverse ray-shooting
approach is a computationally expensive way to determine magnification maps,
caustic patterns, and light-curves (e.g. as a function of source profile and
size). However, as an easily parallelisable calculation, gravitational
ray-shooting can be accelerated using programmable graphics processing units
(GPUs). We present our implementation of inverse ray-shooting for the NVIDIA
G80 generation of graphics processors using the NVIDIA Compute Unified Device
Architecture (CUDA) software development kit. We also extend our code to
multiple-GPU systems, including a 4-GPU NVIDIA S1070 Tesla unit. We achieve
sustained processing performance of 182 Gflop/s on a single GPU, and 1.28
Tflop/s using the Tesla unit. We demonstrate that billion-lens microlensing
simulations can be run on a single computer with a Tesla unit in timescales of
order a day without the use of a hierarchical tree code.Comment: 21 pages, 4 figures, submitted to New Astronom
Hubble Space Telescope Observations of NGC 6240: a Case Study of an Ultra-Luminous Infrared Galaxy with Obscured Activity
We present results from an HST study of the morphology and kinematics of NGC
6240. This merging galaxy with a double nucleus is one of the nearest and
best-studied ultraluminous infrared galaxies. HST resolves both nuclei into
seperate components. The distance between the northern and southern
optical/near-infrared components is greater than that observed in radio and
X-ray studies, arguing that even in K-band we may not be seeing all the way
through the dust to the true nuclei. The ionized gas does not display rotation
around either of the nuclei, or equilibrium motion in general. There is a
strong velocity gradient between the nuclei, similar to what is seen in CO
data. There is no such gradient in our stellar kinematics. The velocity
dispersion of the gas is larger than expected for a cold disk. We also map and
model the emission-line velocity field at an off-nuclear position where a steep
velocity gradient was previously detected in ground-based data. Overall, the
data indicate that line-of-sight projection effects, dust absorption,
non-equilibrium merger dynamics, and the possible influence of a wind may be
playing an important role in the observed kinematics. Chandra observations of
hard X-rays have shown that both of the nuclei contain an Active Galactic
Nucleus (AGN). The HST data show no clear sign of the two AGNs: neither
continuum nor narrow-band imaging shows evidence for unresolved components in
the nuclei, and there are no increased emission line widths or rapid rotation
near the nuclei. This underscores the importance of X-ray data for identifying
AGNs in highly dust-enshrouded environments.Comment: LaTeX, 32 pages, 9 figures, 2 tables, accepted for publication in The
Astronomical Journal (Jan 2004). Paper with high-resolution (non-compressed)
color figures in gzipped postscript format available at
http://www.stsci.edu/~marel/psgzdir/ngc6240v11.ps.g
Estimating Soil Moisture Under Low Frequency Surface Irrigation Using Crop Water Stress Index
The present study investigated the relationship between the crop water stress index (CWSI) and soil moisture for surface irrigated cotton (Gossypium hirsutum, Delta Pine 90b) at Maricopa, Arizona during the 1998 season. The CWSI was linked to soil moisture through the water stress coefficient Ks that accounts for reduced crop evapotranspiration when there is a shortage of soil water. A stress recovery coefficient Krec was introduced to account for reduced crop evapotranspiration as the crop recovered from water stress after irrigation events. A soil water stress index (SWSI) was derived in terms of Ks and Krec . The SWSI compared reasonably well to the CWSI, but atmospheric stability correction for the CWSI did not improve comparisons. When the CWSI was substituted into the SWSI formulation, it gave good prediction of soil moisture depletion (fDEP; when to irrigate) and depth of root zone depletion (Dr ; how much to irrigate). Disagreement was greatest for fDEP\u3c0.6 because cotton is less sensitive to water stress in this range
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