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Tall and skinny QR factorizations in MapReduce architectures

MapReduce'11 - Proceedings of the 2nd International Workshop on MapReduce and Its Applications

Constantine, Paul G.; Gleich, David F.

The QR factorization is one of the most important and useful matrix factorizations in scientific computing. A recent communication-avoiding version of the QR factorization trades flops for messages and is ideal for MapReduce, where computationally intensive processes operate locally on subsets of the data. We present an implementation of the tall and skinny QR (TSQR) factorization in the MapReduce framework, and we provide computational results for nearly terabyte-sized datasets. These tasks run in just a few minutes under a variety of parameter choices. © 2011 ACM.

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The influence of displacement damage on deuterium retention in tungsten exposed to divertor plasma in DIII-D

Journal of Nuclear Materials

Wampler, W.R.; Rudakov, D.L.; Watkins, J.G.; Lasnier, C.J.

Experiments were conducted to determine the influence of displacement damage on retention of deuterium in tungsten plasma-facing components in a tokamak. Tungsten samples, previously damaged by ion irradiation, were exposed to the outer strike point of attached H-mode plasmas in DIII-D. Nuclear reaction analysis (NRA) was used to measure the depth profile of deuterium retained in the tungsten. Displacement damage increased the concentration of retained deuterium to the maximum depth (about 2.5 μm) of the damage, to concentrations up to 0.003 D/W, compared to D/W < 10-5 in undamaged W. Tungsten coverage on adjacent carbon surfaces of the probe was mapped by Rutherford backscattering, giving the average tungsten erosion rate and spatial variation of redeposition. © 2010 Elsevier B.V. All rights reserved.

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A continuum-scale model of hydrogen precipitate growth in tungsten plasma-facing materials

Journal of Nuclear Materials

Kolasinski, Robert; Cowgill, Donald F.; Causey, Rion A.

The low solubility of hydrogen in tungsten leads to the growth of near-surface hydrogen precipitates during high-flux plasma exposure, strongly affecting migration and trapping in the material. We have developed a continuum-scale model of precipitate growth that leverages existing techniques for simulating the evolution of 3He gas bubbles in metal tritides. The present approach focuses on bubble growth by dislocation loop punching, assuming a diffusing flux to nucleation sites that arises from ion implantation. The bubble size is dictated by internal hydrogen pressure, the mechanical properties of the material, as well as local stresses. In this article, we investigate the conditions required for bubble growth. Recent focused ion beam (FIB) profiling studies that reveal the sub-surface damage structure provide an experimental database for comparison with the modeling results. © 2010 Elsevier B.V. All rights reserved.

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Deuterium retention in tungsten at elevated temperatures

Journal of Nuclear Materials

Causey, Rion A.; Cowgill, Donald F.; Doerner, R.; Kolasinski, Robert; Mills, B.; Morse, D.; Smugeresky, John E.; Wampler, W.R.; Wampler, William R.; Huber, D.

The tungsten ITER divertor will be operated at temperatures above 1000 K. Most of the laboratory experiments on hydrogen isotope retention in tungsten have been performed at lower temperatures where the hydrogen is retained as both atoms and molecules. At higher temperatures, atomic trapping plays a smaller role. The purpose of this paper is to see if hydrogen is trapped at internal voids at elevated temperatures, and to see if gas-filled cavities can be formed at high fluences. Additionally, this paper examines the effect of helium bubbles and radiation damage on trapping. © 2010 Elsevier B.V. All rights reserved.

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Effect of ELMs on deuterium-loaded-tungsten plasma facing components

Journal of Nuclear Materials

Umstadter, K.R.; Rudakov, D.L.; Wampler, W.; Watkins, J.G.; Wong, C.P.C.

Prior heat pulse testing of plasma facing components (PFCs) has been completed in vacuum environments without the presence of background plasma. Edge localized modes (ELMs) will not be this kind of isolated event and one should know the effect of a plasma background during these transients. Heat-pulse experiments have been conducted in the PISCES-A device utilizing laser heating in a divertor-like plasma background. Initial results indicate that the erosion of PFCs is enhanced as compared to heat pulse or plasma only tests. To determine if the enhanced erosion effect is a phenomena only witnessed in the laboratory PISCES device, tungsten and graphite samples were exposed to plasmas in the lower divertor of the DIII-D tokamak using the Divertor Material Evaluation System (DiMES). Mass loss analysis indicates that materials that contain significant deuterium prior to experiencing a transient heating event will erode faster than those that have no or little retained deuterium. © 2010 Elsevier B.V. All rights reserved.

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NSTX plasma response to lithium coated divertor

Journal of Nuclear Materials

Kugel, H.W.; Bell, M.G.; Allain, J.P.; Bell, R.E.; Ding, S.; Gerhardt, S.P.; Jaworski, M.A.; Kaita, R.; Kallman, J.; Kaye, S.M.; Leblanc, B.P.; Maingi, R.; Majeski, R.; Maqueda, R.; Mansfield, D.K.; Mueller, D.; Nygren, Richard; Paul, S.F.; Raman, R.; Roquemore, A.L.; Sabbagh, S.A.; Schneider, H.; Skinner, C.H.; Soukhanovskii, V.A.; Taylor, C.N.; Timberlake, J.R.; Wampler, W.R.; Zakharov, L.E.; Zweben, S.J.

NSTX experiments have explored lithium evaporated on a graphite divertor and other plasma-facing components in both L- and H- mode confinement regimes heated by high-power neutral beams. Improvements in plasma performance have followed these lithium depositions, including a reduction and eventual elimination of the HeGDC time between discharges, reduced edge neutral density, reduced plasma density, particularly in the edge and the SOL, increased pedestal electron and ion temperature, improved energy confinement and the suppression of ELMs in the H-mode. However, with improvements in confinement and suppression of ELMs, there was a significant secular increase in the effective ion charge Zeff and the radiated power in H-mode plasmas as a result of increases in the carbon and medium-Z metallic impurities. Lithium itself remained at a very low level in the plasma core, <0.1%. Initial results are reported from operation with a Liquid Lithium Divertor (LLD) recently installed. © 2010 Elsevier B.V. All rights reserved.

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Low-temperature sintering Bi-Si-Zn-oxide glasses for use in either glass composite materials or core/shell 129I waste forms

Journal of the American Ceramic Society

Garino, Terry J.; Nenoff, Tina M.; Krumhansl, James L.; Rademacher, David X.

Spent nuclear fuel contains 129I, which is of particular concern due to its very long half-life, its potential mobility in the environment, and its deleterious effect on human health. In spent fuel reprocessing schemes under consideration, a gas stream containing 129I2 would be passed through a bed of Ag-loaded zeolites such as Ag-mordenite (Ag-MOR). We have investigated the use of a low-temperature sintering bismuth-silicon-zinc- oxide glass powder mixed with either AgI or AgI-MOR to produce dense glass composite material waste forms that can be processed at 550°C, where AgI volatility is low. We have demonstrated that when fine silver flake is added to the mixture, any adsorbed I2 released during heating of AgI-MOR reacts with the silver to form AgI in situ. Furthermore, we have shown that mixtures of the glass with the AgI-MOR or AgI are durable in aqueous environments. Finally, we have developed a process to fabricate core/shell waste forms where the core of AgI-MOR or AgI and glass is encased in a shell of glass that protects the core from contact with the environment. To prevent cracking of the shell due to thermal expansion mismatch between the core and shell, amorphous silica was added to the shell to form a composite with a lower coefficient of thermal expansion. © 2011 The American Ceramic Society.

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Calculations of buckle-driven delamination using cohesive elements

International Journal of Fracture

Corona, Edmundo; Reedy, Earl D.

Plane strain, elastic calculations of buckle-driven thin film delamination from compliant substrates using finite element models are considered. The interfacial properties between the film and the substrate are modeled using cohesive elements with a tractionseparation law formulated in terms of a potential. The model yielded the geometry of the buckles given the properties of the film and the substrate, the interfacial toughness and the value of the compressive equi-biaxial stress. Results for the relation between the buckle width and the interfacial toughness were very close to similar results by Yu and Hutchinson (2002), thus giving confidence that the cohesive element approach presented can be used in applications where buckle-driven delamination of thin films is an issue. © 2011 Springer Science+Business Media B.V.

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Phoenix: Complex Adaptive System of Systems (CASoS) Engineering (V.1.0)

Glass Jr., Robert J.; Ames, Arlo; Brown, Theresa J.; Linebarger, John; Beyeler, Walter E.

Complex Adaptive Systems of Systems, or CASoS, are vastly complex ecological, sociological, economic and/or technical systems which we must understand to design a secure future for the nation and the world. Perturbations/disruptions in CASoS have the potential for far-reaching effects due to pervasive interdependencies and attendant vulnerabilities to cascades in associated systems. Phoenix was initiated to address this high-impact problem space as engineers. Our overarching goals are maximizing security, maximizing health, and minimizing risk. We design interventions, or problem solutions, that influence CASoS to achieve specific aspirations. Through application to real-world problems, Phoenix is evolving the principles and discipline of CASoS Engineering while growing a community of practice and the CASoS engineers to populate it. Both grounded in reality and working to extend our understanding and control of that reality, Phoenix is at the same time a solution within a CASoS and a CASoS itself.

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Economic analysis of large-scale hydrogen storage for renewable utility applications

Keller, Jay O.

The work reported here supports the efforts of the Market Transformation element of the DOE Fuel Cell Technology Program. The portfolio includes hydrogen technologies, as well as fuel cell technologies. The objective of this work is to model the use of bulk hydrogen storage, integrated with intermittent renewable energy production of hydrogen via electrolysis, used to generate grid-quality electricity. In addition the work determines cost-effective scale and design characteristics and explores potential attractive business models.

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Survey of techniques for reduction of wind turbine blade trailing edge noise

Barone, Matthew F.

Aerodynamic noise from wind turbine rotors leads to constraints in both rotor design and turbine siting. The primary source of aerodynamic noise on wind turbine rotors is the interaction of turbulent boundary layers on the blades with the blade trailing edges. This report surveys concepts that have been proposed for trailing edge noise reduction, with emphasis on concepts that have been tested at either sub-scale or full-scale. These concepts include trailing edge serrations, low-noise airfoil designs, trailing edge brushes, and porous trailing edges. The demonstrated noise reductions of these concepts are cited, along with their impacts on aerodynamic performance. An assessment is made of future research opportunities in trailing edge noise reduction for wind turbine rotors.

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Control Volume Finite Element Method with Multidimensional Edge Element Scharfetter-Gummel upwinding. Part 2. Computational Study

Peterson, Kara J.; Bochev, Pavel B.

In [3] we proposed a new Control Volume Finite Element Method with multi-dimensional, edge- based Scharfetter-Gummel upwinding (CVFEM-MDEU). This report follows up with a detailed computational study of the method. The study compares the CVFEM-MDEU method with other CVFEM and FEM formulations for a set of standard scalar advection-diffusion test problems in two dimensions. The first two CVFEM formulations are derived from the CVFEM-MDEU by simplifying the computation of the flux integrals on the sides of the control volumes, the third is the nodal CVFEM [2] without upwinding, and the fourth is the streamline upwind version of CVFEM [10]. The finite elements in our study are the standard Galerkin, SUPG and artificial diffusion methods. All studies employ logically Cartesian partitions of the unit square into quadrilateral elements. Both uniform and non-uniform grids are considered. Our results demonstrate that CVFEM-MDEU and its simplified versions perform equally well on rectangular or nearly rectangular grids. However, performance of the simplified versions significantly degrades on non-affine grids, whereas the CVFEM-MDEU remains stable and accurate over a wide range of mesh Peclet numbers and non-affine grids. Compared to FEM formulations the CVFEM-MDEU appears to be slightly more dissipative than the SUPG, but has much less local overshoots and undershoots.

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A brief history of Sandia National Laboratories and the Department of Energy%3CU%2B2019%3Es Office of Science : interplay between science, technology, and mission

Tsao, Jeffrey Y.; Simmons, Jerry A.; Collis, Samuel S.; Mcilroy, Andrew

In 1957, Sandia National Laboratories (Sandia) initiated its first programs in fundamental science, in support of its primary nuclear weapons mission. In 1974, Sandia initiated programs in fundamental science supported by the Department of Energy's Office of Science (DOE-SC). These latter programs have grown to the point where, today in 2011, support of Sandia's programs in fundamental science is dominated by that Office. In comparison with Sandia's programs in technology and mission applications, however, Sandia's programs in fundamental science are small. Hence, Sandia's fundamental science has been strongly influenced by close interactions with technology and mission applications. In many instances, these interactions have been of great mutual benefit, with synergies akin to a positive 'Casimir's spiral' of progress. In this report, we review the history of Sandia's fundamental science programs supported by the Office of Science. We present: (a) a technical and budgetary snapshot of Sandia's current programs supported by the various suboffices within DOE-SC; (b) statistics of highly-cited articles supported by DOE-SC; (c) four case studies (ion-solid interactions, combustion science, compound semiconductors, advanced computing) with an emphasis on mutually beneficial interactions between science, technology, and mission; and (d) appendices with key memos and reminiscences related to fundamental science at Sandia.

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Simulation of one-minute power output from utility-scale photovoltaic generation systems

Stein, Joshua; Ellis, Abraham

We present an approach to simulate time-synchronized, one-minute power output from large photovoltaic (PV) generation plants in locations where only hourly irradiance estimates are available from satellite sources. The approach uses one-minute irradiance measurements from ground sensors in a climatically and geographically similar area. Irradiance is translated to power using the Sandia Array Performance Model. Power output is generated for 2007 in southern Nevada are being used for a Solar PV Grid Integration Study to estimate the integration costs associated with various utility-scale PV generation levels. Plant designs considered include both fixed-tilt thin-film, and single-axis-tracked polycrystalline Si systems ranging in size from 5 to 300 MW{sub AC}. Simulated power output profiles at one-minute intervals were generated for five scenarios defined by total PV capacity (149.5 MW, 222 WM, 292 MW, 492 MW, and 892 MW) each comprising as many as 10 geographically separated PV plants.

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Simulation of lean NOx trap performance with microkinetic chemistry and without mass transfer

Larson, Richard S.

A microkinetic chemical reaction mechanism capable of describing both the storage and regeneration processes in a fully formulated lean NO{sub x} trap (LNT) is presented. The mechanism includes steps occurring on the precious metal, barium oxide (NO{sub x} storage), and cerium oxide (oxygen storage) sites of the catalyst. The complete reaction set is used in conjunction with a transient plug flow reactor code to simulate not only conventional storage/regeneration cycles with a CO/H{sub 2} reductant, but also steady flow temperature sweep experiments that were previously analyzed with just a precious metal mechanism and a steady state code. The results show that NO{sub x} storage is not negligible during some of the temperature ramps, necessitating a re-evaluation of the precious metal kinetic parameters. The parameters for the entire mechanism are inferred by finding the best overall fit to the complete set of experiments. Rigorous thermodynamic consistency is enforced for parallel reaction pathways and with respect to known data for all of the gas phase species involved. It is found that, with a few minor exceptions, all of the basic experimental observations can be reproduced with these purely kinetic simulations, i.e., without including mass-transfer limitations. In addition to accounting for normal cycling behavior, the final mechanism should provide a starting point for the description of further LNT phenomena such as desulfation and the role of alternative reductants.

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Peirce, pragmatism, and the right way of thinking

Campbell, Philip L.

This report is a summary of and commentary on (a) the seven lectures that C. S. Peirce presented in 1903 on pragmatism and (b) a commentary by P. A. Turrisi, both of which are included in Pragmatism as a Principle and Method of Right Thinking: The 1903 Harvard Lectures on Pragmatism, edited by Turrisi [13]. Peirce is known as the founder of the philosophy of pragmatism and these lectures, given near the end of his life, represent his mature thoughts on the philosophy. Peirce's decomposition of thinking into abduction, deduction, and induction is among the important points in the lectures.

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Results 67501–67600 of 99,299
Results 67501–67600 of 99,299