- Deutsch Leverages Dot Hill AssuredSAN Arrays (LATEST) 03-06-2014
Dot Hill AssuredSAN is Ideally Suited for High Performance Digital Asset Management With Disaster Recovery and Replication Dot Hill Systems has announced that leading advertising firm Deutsch Inc. is leveraging Dot Hill AssuredSAN storage arrays as part of a digital asset management system with coast-to-coast data replication, supporting disaster...
- CyrusOne Begins Construction on Third Data Center at Houston West Campus (LATEST) 03-06-2014
CyrusOne is hosting a groundbreaking ceremony today at 11 a.m. Central Time for a third data center at its 45-acre Houston West data center services campus along Beltway 8 in Houston’s energy corridor. Upon completion, the new facility will include 428,000 square feet of raised floor capacity, 86,000 square feet of class A office space, and up to 96...
- Detecting software errors via genetic algorithms (LATEST) 03-05-2014
According to a current study from the University of Cambridge, software developers are spending about the half of their time on detecting errors and resolving them. Projected onto the global software industry, according to the study, this would amount to a bill of about 312 billion US dollars every year. "Of course, automated testing is cheaper", explains...
- OU study suggests non-uniform climate warming global (LATEST) 03-05-2014
Affects terrestrial carbon cycle, ecosystems and future predictions A recent University of Oklahoma study of five decades of satellite data, model simulations and in situ observations suggests the impact of seasonal diurnal or daily warming varies between global regions affecting many ecosystem functions and services, such as food production,...
- MIle2 Names Merit Training Center of the Year (LATEST) 03-05-2014
Merit Network has been selected by Mile2 as the North American Authorized Training Center (ATC) of 2013. Merit was chosen from over 100 Mile2 Authorized Training Center locations around the world. One ATC from each of five global regions was chosen to receive this annual award. Mile2 selected Merit for demonstrating a proven dedication to the...
- CFD simulations benefit surgeons making decisions on how to help their patients breathe easier (LATEST) 03-04-2014
A more accurate and successful, yet complex approach used in designing an airplane is now taking off in the health care industry. The end result is helping patients with pulmonary disorders breathe easier, as well as their surgeons in considering novel treatment approaches. Goutham Mylavarapu, a senior research associate in the University of...
- Cybergenetics TrueAllele Validated in Open-Access Scientific Study (LATEST) 03-04-2014
SuperComputers Interpret Rape Kits that Human Experts CannotMixtures of two or more people are the bane of forensic DNA laboratories. Hundreds of thousands of evidence items go unused because human analysts cannot interpret them. Cybergenetics TrueAllele Casework computer system can reliably preserve identification information in these cases, as...
- Merit Network Completes Network Upgrades for 2014 (LATEST) 03-04-2014
Critical paths upgraded to 100G and 40G Merit Network has completed several upgrades to its statewide, fiber-optic backbone. The upgrades bolster critical paths on Merit's core network to better support bandwidth exchange between Members and improve the flow of traffic to key interconnection points with Internet2, the Tier 1 Internet and content...
- Virginia Tech's Barbara Ryder to receive achievement award (LATEST) 03-03-2014
Barbara Ryder, the J. Byron Maupin Professor of Engineering and head of the Department of Computer Science in the College of Engineering at Virginia Tech, will receive the biennial Woman of Achievement award from the American Association of University Women of Virginia at its state conference at the W.E. Skelton 4-H Educational Conference Center at...
- Twitter big data can be used to monitor HIV and drug-related behavior, UCLA study shows (LATEST) 02-28-2014
Studying link between HIV, drug use could help prevention, detection efforts Real-time social media like Twitter could be used to track HIV incidence and drug-related behaviors with the aim of detecting and potentially preventing outbreaks, a new UCLA-led study shows. The study, published in the peer-reviewed journal Preventive Medicine, suggests it...
- NASA Researchers Help Hunt Ice Crystals Down Under (LATEST) 02-27-2014
NASA researchers are part of an international team working to improve aviation safety by studying high altitude ice crystals during a flight campaign now under way in Darwin, Australia.NASA and its North American partners are supporting the European Airbus-led High Altitude Ice Crystals (HAIC)/High Ice Water Content (HIWC) field campaign in the...
- Google Glass could help stop emerging public health threats around the world (LATEST) 02-27-2014
The much-talked-about Google Glass — the eyewear with computer capabilities — could potentially save lives, especially in isolated or far-flung locations, say scientists. They are reporting development of a Google Glass app that takes a picture of a diagnostic test strip and sends the data to computers, which then rapidly beam back a diagnostic...
- OpenMP ARB Releases New Mission Statement (LATEST) 02-27-2014
In recent years, OpenMP has shifted from being solely focused on shared-memory systems to also include accelerators, embedded systems, multicore and real-time systems. Today the OpenMP Architecture Review Board (ARB) releases a new Mission Statement to formalize this change. A technical report on directives for attached accelerators was first...
- Mouse brain atlas maps neural networks to reveal how brain regions interact (LATEST) 02-27-2014
Different brain regions must communicate with each other to control complex thoughts and behaviors, but relatively little is known about how these areas organize into broad neuronal networks. In a study published by Cell Press February 27th in the journal Cell, researchers developed a mouse whole-brain atlas that reveals hundreds of neuronal...
- Bull's profit falls 62% on lower supercomputer sales (LATEST) 02-27-2014
Bull said 2013 income fell 62%, as its sales were hurt by reduced supercomputer orders. In fourth quarter of 2012, Bull won several major supercomputer orders. Similar orders did not recur in 2013. Therefore, order intake decreased to €432.0 million in the fourth quarter. As a result, net income was €10.9 million in 2013, as opposed to €28.6...
- Software maps ambiguous names in texts to the right person (LATEST) 02-27-2014
If a name is ambiguous and given without context, even humans struggle. When reading the last name "Merkel", people do not know if it refers to the Chancellor of Germany Angela Merkel or the famous soccer coach Max Merkel. It is a drawback for web search, too. Up to now, the programs can capture character strings like "Angela Merkel", but they do...
- DOD Awards $70 Million for Digital Manufacturing, Design Innovation Institute (LATEST) 02-27-2014
SCRA to Manage the Consortium for the UI LABS-led Multi-Partner Team SCRA Applied R&D will act as the consortia manager for the recently announced Digital Manufacturing and Design Innovation (DMDI) Institute. United States President Barack Obama announced the award at a press conference yesterday. The federal investment for the DMDI Institute will...
- Offshore wind farms could tame hurricanes before they reach land (LATEST) 02-26-2014
Supercomputer simulations by Professor Mark Z. Jacobson have shown that offshore wind farms with thousands of wind turbines could have sapped the power of three real-life hurricanes, significantly decreasing their winds and accompanying storm surge, and possibly preventing billions of dollars in damages. For the past 24 years, Mark Z. Jacobson,...
- Merit Network, Center for Internet Security Collaborate (LATEST) 02-26-2014
Partnership will help public sector entities improve their cybersecurity Merit Network and Center for Internet Security (CIS) have announced today a collaborative partnership to help entities across the nation improve their cyber defenses by offering Michigan Cyber Range cybersecurity training courses and Merit Secure Sandbox service to state,...
- President Obama Announces Two New Public-Private Manufacturing Innovation Institutes (LATEST) 02-25-2014
A Detroit-area based consortium of 60 companies, nonprofits, and universities and a Chicago based consortium of 73 companies, nonprofits, and universities are partnering with the federal government to launch two new manufacturing innovation hubs. The first new manufacturing innovation institute competition this year is launching today, one of...
- Published: 24 May 2012
Simulations of standard candles will help astrophysicists understand dark energy
Understanding a Type Ia supernova—an exploding white dwarf star—requires supercomputers. A team of astrophysicists and computational scientists is using the power of Oak Ridge National Laboratory’s (ORNL’s) Jaguar to virtually blow up these white dwarfs. In the process the researchers are revealing the secrets of the biggest thermonuclear explosions in the universe and finding the answers needed to measure the size of the universe.
“The physics of supernova explosions is something astrophysicists have been trying to figure out for about 50 years now,” said Stan Woosley, principal investigator of an Innovative and Novel Computational Impact on Theory and Experiment (INCITE) project and professor of astrophysics at the University of California–Santa Cruz. “It is an interesting physics problem in turbulent combustion, but it is also important because—as the 2011 Nobel Prize attested—Type Ia supernovae can be used to show that the expansion of the universe is accelerating.” This is because the supernovas function as “standard candles,” brilliant lights of known properties usable as measuring tools because their distance can be inferred by how bright they appear.
Using an empirical correlation between the peak luminosity of Type Ia supernovas and the rate at which their brightness declines, three Nobel Prize winners—Saul Perlmutter, Adam Reiss, and Brian Schmidt—determined that distant galaxies were farther away than expected for a universe expanding at a constant rate. Their work showed that the expansion of the universe is, in fact, accelerating and refuted a long-held belief that the universe was expanding at a constant rate or even slowing down. It is as if a tennis ball, thrown straight up, did not fall back to Earth but continued to move away faster and faster. The driver behind this acceleration, called dark energy, is a force not yet fully understood that counters the pull of gravity on matter.
Woosley said his team seeks to understand the nature of the supernovas, find other ways of predicting the supernova’s peak luminosity, and explain the empirical relation between brightness and decline rate (the ratio of maximum light declining over time). Even with the world’s most powerful telescopes, the data obtained through observations is limited and sometimes corrupted by the effects of interstellar dust or the particular characteristics of the telescopes used. Given a valid physical description, the supercomputer can model the supernova without these observational biases. The simulations not only give the supernova’s light curve (the total intensity of light over time) and spectrum (the intensity of light at certain frequencies) at all angles over time, but also allow researchers to look for other measurable quantities that might correlate with peak luminosity.
Presently cosmologists use Type Ia supernovas to measure distances to about 10 percent accuracy. The immediate goal is to reduce the error below 5 percent. To do that, they need a better yardstick, and numerical experiments on the supercomputer are a way to build one.
A second life
A white dwarf star begins, as do all stars, when gravity compresses a cloud of helium, hydrogen, and dust. As the density increases, so does the force of gravity. The temperature and density are highest at the center of the cloud. The pressure of the compaction increases the internal temperature. As the pressure and temperature climb, the compaction and heat set off the star’s core fusion reaction. The star begins to glow. After shining 10 billion years or so (for a star of our sun’s mass), its fuel is spent and the star—cooling, fading, and dwindling to the size of Earth—becomes a white dwarf.
With its own energy depleted, the star will continue cooling into a cold, black dwarf unless it can accrete mass from a nearby star.
The white dwarf can accumulate mass in two ways. It can steal mass slowly, from a younger, vibrant companion star still undergoing nuclear fusion until the dwarf reaches its maximum mass while remaining stable—a relationship known as the Chandrasekhar limit. Or, in what is known as the double-degenerate model, two white dwarves can merge their masses into one.
The increasing mass adds to the star’s density and internal pressure, and its core temperature climbs. After centuries the star reaches critical mass. Its carbon and oxygen ignite in a fusion reaction deep inside, and a thermonuclear runaway begins. For roughly a century the dwarf interior bubbles and churns as convection carries away the energy generated by carbon fusion. Hot gases rise, cool, drift back to the reaction zone, and are reheated. Eventually convection cannot carry away the heat fast enough. The burning becomes isolated and rapidly escalates. Temperature rises in a small region from hundreds of millions of degrees to ten billion degrees. A deflagration—a moving flame front of burning gases—is born.
At this point the star has reached full runaway mode and will soon explode. In the second before the final runaway, ashes rapidly rise like a giant mushroom cloud. The floating deflagration approaches the speed of sound as it rips through the surface of the star.
Simulations suggest that this breakout accelerates the subsonic burning into a supersonic detonation. The burning happens in a strong shock wave that rebounds to the unburned areas, completely incinerating the star. It then explodes violently, leaving behind rapidly expanding radioactive gases. An isotope of nickel, which decays first to cobalt and then to iron, keeps the debris hot and as bright as a medium-sized galaxy before fading away over months. The star’s life is over.
Replicating supernovas in the lab
Previous simulations in two dimensions by Woosley and Daniel Kasen from the University of California–Berkeley and Lawrence Berkeley National Laboratory (LBNL) have explained the observed asymmetrical explosions of the Type Ia.
“We found the most popular kind of supernova model—the Chandrasekhar mass model—doesn’t ignite in the dead center of the star,” said Woosley. “The explosion, once ignited off-center, stayed off-center and the supernova blew up asymmetrically, one side before the other.” This knowledge explains the differences in the appearance of supernovas when viewed from various directions and must be considered when calibrating the standard candle.
Jaguar is now running three-dimensional (3D) simulations with varying ignition-point locations, focused on the two-stage, deflagration-to-detonation sequence.
Because of the size of the computational runs, the studies are decoupled and done in three successive stages—ignition, explosion, and supernova. The team is using three codes developed for this project: MAESTRO, CASTRO, and SEDONA. John Bell and Ann Almgren at LBNL wrote MAESTRO to model the ignition and CASTRO to model the explosion. SEDONA, written by Kasen, is a hydrodynamics code that calculates the spectra and light curves of the supernovas.
The multiyear project was allocated 50 million computing hours on Jaguar in 2011 and 47 million in 2012 through the INCITE program, which is jointly managed by the US Department of Energy’s Leadership Computing Facilities at Argonne and Oak Ridge National Laboratories.
Additionally, Woosley has begun investigating another variety of Type Ia supernova—a white dwarf that accretes a thick layer of helium from a companion star. This helium-rich celestial object may detonate in a straightforward blast after an ignition in the star’s outer layer compresses its inner core.
After the simulations at ORNL blow up several 3D models of white dwarf stars and their light curves and spectra have been determined, the findings will be put into an archive available to researchers. Observers will especially analyze the data to find other, more accurate indicators of luminosity to compare with a rapidly growing library of observational data. The data will also be used to help plan future large surveys of supernovas by missions such as the Large Synoptic Survey Telescope and the Palomar Transient Factory. Said Woosley, “It is our eventual ambition to have hundreds of model supernovae sampled at all wavelengths, angles, and times available for comparison by machine intelligence with thousands of observations in order to get the very best distance measurements possible.” —by Sandra Allen McLean
D. Kasen, F. K. Röpke, and S. E. Woosley. 2009. “The Diversity of Type Ia Supernovae from Broken Symmetries.” Nature 460:869.
A. Nonaka, A. J. Aspden, M. Zingale, A. S. Almgren, J. B. Bell, S. E. Woosley. 2012. “High-Resolution Simulations of Convection Preceding Ignition in Type Ia Supernovae Using Adaptive Mesh Refinement.” Astrophysical Journal 745:73.
S. Blondin, D. Kasen, F. K. Röpke, R. P. Kirschner, K. S. Mandel. 2011. “Confronting 2D Delayed-Detonation Models with Light Curves and Spectra of Type Ia Supernovae.” Monthly Notices of the Royal Astronomical Society 417:1280.