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Markidis S.,University of Illinois at Urbana - Champaign | Markidis S.,Lawrence Berkeley National Laboratory | Lapenta G.,Computational Science Center | Rizwan-uddin,University of Illinois at Urbana - Champaign
Mathematics and Computers in Simulation | Year: 2010

The implicit Particle-in-Cell method for the computer simulation of plasma, and its implementation in a three-dimensional parallel code, called iPIC3D, are presented. The implicit integration in time of the Vlasov-Maxwell system, removes the numerical stability constraints and it enables kinetic plasma simulations at magnetohydrodynamics time scales. Simulations of magnetic reconnection in plasma are presented to show the effectiveness of the algorithm. © 2009 IMACS. Source

Seo J.-H.,Nano Analysis Center | Seo J.-H.,Korea University | Yoo Y.,KAIST | Park N.-Y.,Kookmin University | And 12 more authors.
Nano Letters | Year: 2011

We report that defect-free Au nanowires show superplasticity on tensile deformation. Evidences from high-resolution electron microscopes indicated that the plastic deformation proceeds layer-by-layer in an atomically coherent fashion to a long distance. Furthermore, the stress-strain curve provides full interpretation of the deformation. After initial superelastic deformation, the nanowire shows superplastic deformation induced by coherent twin propagation, completely reorientating the crystal from <110> to <100>. Uniquely well-disciplined and long-propagating atomic movements deduced here are ascribed to the superb crystallinity as well as the radial confinement of the Au nanowires. © 2011 American Chemical Society. Source

Elbau P.,Johann Radon Institute for Computational and Applied Mathematics RICAM | Grasmair M.,Computational Science Center | Lenzen F.,University of Heidelberg | Scherzer O.,Computational Science Center
Numerical Functional Analysis and Optimization | Year: 2010

We establish a semi-group solution concept for flows that are generated by generalized minimizers of non-convex energy functionals. We use relaxation and convexification to define these generalized minimizers. The main part of this work consists in exemplary validation of the solution concept for a non-convex energy functional. For rotationally invariant initial data it is compared with the solution of the mean curvature flow equation. The basic example relates the mean curvature flow equation with a sequence of iterative minimizers of a family of non-convex energy functionals. Together with the numerical evidence this corroborates the claim that the non-convex semi-group solution concept defines, in general, a solution of the mean curvature equation. Copyright © Taylor and Francis Group, LLC. Source

News Article
Site: http://www.scientificcomputing.com/rss-feeds/all/rss.xml/all

In the research projects it conducts and in the way it conducts research, the National Renewable Energy Laboratory (NREL) in Golden, CO, lives out the true meaning of its energy-efficient creed. In this way, NREL, one of the U.S. Department of Energy’s national laboratories, is that rarest of entities: a preacher of virtue that incorporates virtue into its daily life. NREL’s sincerity of purpose begins with its Intel-based Peregrine supercomputer and the ultra-efficient data center in which it resides. This supercomputer is operated as a computational user facility supporting the mission of U.S. Department of Energy’s Office of Energy Efficiency and Renewable Energy. Peregrine is used by scientists and engineers advancing energy efficiency and renewable energy research, including such areas as bioenergy, wind, solar and energy system integration. The innovative, liquid-cooled system and ultra-efficient data center not only require a fraction of the electricity needed to cool conventional HPC systems, they also serve a central role in the highly efficient heating system at the facility’s office and laboratory space, saving approximately one million dollars in annual energy costs, relative to a typical energy-efficient data center. NREL is pioneering new integrated strategies and techniques for cutting the energy use by a major consumer of electrical power: the data center. As systems grow larger and hotter, the day is approaching when electrical demands from data centers — in the form of air conditioning and fans — will outstrip some municipalities’ ability to deliver power. Unless, that is, there’s a change in the way systems and data centers are cooled. NREL is leading this change. Adopting the mission to build the world’s most energy-efficient data center six years ago, NREL embarked on achieving that goal using a holistic “chips to bricks” approach that would utilize both the bytes of information and the BTUs of heat generated by the computers. The lab wanted not only world-class compute power but also a supercomputing system and data center that consume a fraction of the electrical power of HPC systems on the market. The result is Peregrine, launched in 2013, which utilizes more than 30,000 Intel Xeon processor cores and 576 Intel Xeon Phi co-processors. Peregrine was recently expanded with an additional 1152 nodes (each with 64 GB of memory), delivering overall peak performance of 2.24 petaflops (more than two quadrillion calculations per second). The nodes are connected using 56 Gb/sec InfiniBand. Peregrine runs the Linux operating system and has a dedicated Lustre file system with about 2.25 petabytes of online storage. Beyond compute power, Intel processors contribute to Peregrine’s energy efficiency. Intel’sw latest generation of chip technology is “the most power-efficient parallel processor in the world,” according to the Green 500, an organization that assesses supercomputer energy consumption. Researchers are using Peregrine to Beyond its support of key clean energy research, Peregrine plays a central role in another aspect of NREL’s mission: serve as a leader and a showcase for energy efficiency at its own facility that other organizations, in both the private and public sectors, can use as a model. NREL teamed with Intel and Hewlett-Packard Enterprise in the use of Peregrine as the primary source of heat for NREL’s 182,000-square-foot Energy Systems Integration Facility (ESIF). As supercomputers scale up by orders of magnitude, energy consumption and heat dissipation put enormous stress on HPC systems, the facilities in which they are housed, and organizational operating budgets. According to NREL, Peregrine’s direct component liquid cooling system allows much greater performance density, cutting energy consumption in half, and creating efficiencies with other building energy systems. “Cooling supercomputers with the usual way, with fans and so forth, is like putting a glass of water in a room and turning up the air conditioning in your house to cool it,” said Steve Hammond, Director of NREL’s Computational Science Center. “Conventional data center heat rejection techniques are incredibly wasteful.” The liquid that circulates through the Peregrine system is heated to 95 to 110°F. About 95 percent of the heat generated by Peregrine is captured directly to liquid. Rather than rejecting the waste heat and separately heating the research facility office and laboratory space, the heat is captured and circulated through the heating system of the ESIF. This waste heat use saves about $200,000 a year that would otherwise have to be paid to separately heat the offices and laboratories. The results are impressive. The NREL campus central plant boiler is normally turned on in September as Colorado’s early autumn sets in. This past year, that was postponed a month because of the ability to use Peregrine’s waste heat. In addition, the heat is piped under the sidewalks and plaza areas on the NREL campus around the ESIF, melting snow and ice in the winter. Bottom line: NREL has demonstrated a power usage effectiveness (PUE) rating far better than their design goal of 1.06, typically achieving a PUE between 1.03 and 1.04. Developed by The Green Grid consortium, PUE is the ratio of total amount of energy used by a data center facility to the energy delivered to computing equipment. There were plenty of skeptics about NREL’s plans for Peregrine and for the holistic energy efficiency strategy for the ESIF, and there were concerns about risks associated with using liquid to cool an HPC system. But Hammond said Peregrine has performed better and has delivered a lower failure rate than expected because water is a superior way to eject waste heat, providing a more thermally stable systems environment. The efficiencies are impressive. For example, in conventional air-cooled computer systems that consume 20 megawatts of power, six megawatts are typically necessary for rejection of waste heat. But with Peregrine’s water-cooling system that number is cut to 1.0 megawatt, a factor of six reduction. The ultra-efficient liquid cooled supercomputer earned NREL and Hewlett-Packard Enterprise a 2014 R&D 100 Award, helped the ESIF earn R&D Magazine’s 2014 Laboratory of the Year award and the Energy Department’s 2015 Sustainability Award. NREL’s showcase facility is being used to evangelize data center energy efficiency, hosting an average of two groups per week that tour the data center and study NREL’s green techniques. “The trend in computing is toward higher levels of integration, more kilowatts of power consumed per square foot in the data center, and liquid cooling provides the most effective way to get heat out of higher power density compute racks,” said Hammond. “The data center culture, in general, tends to be risk-averse, everyone ‘knows’ water and electronics don’t mix. However, for two years now, we’ve been demonstrating that this can be done very cost effectively, reliably, efficiently and safely.”

Kim H.-K.,Pohang University of Science and Technology | Ko W.-S.,Pohang University of Science and Technology | Lee H.-J.,Pohang University of Science and Technology | Kim S.G.,Kunsan National University | And 2 more authors.
Scripta Materialia | Year: 2011

We have developed a systematic scheme to identify and distinguish individual grain boundaries from one another according to the misorientation and inclination in polycrystalline materials. This allows us to construct a grain boundary energy database in a suitable form for implementation on mesoscale grain growth simulations. The scheme can be equally applied to identify interfaces between two different phase grains, and enables realistic simulations of phase transformations as well as grain growth, assigning real crystallographic orientations to individual grains. © 2011 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved. Source

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