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Numerical experiments on unstructured PIC stability

Day, David M.

Particle-In-Cell (PIC) is a method for plasmas simulation. Particles are pushed with Verlet time integration. Fields are modeled using finite differences on a tensor product mesh (cells). The Unstructured PIC methods studied here use instead finite element discretizations on unstructured (simplicial) meshes. PIC is constrained by stability limits (upper bounds) on mesh and time step sizes. Numerical evidence (2D) and analysis will be presented showing that similar bounds constrain unstructured PIC.

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TYPE SAND Report YEAR 2011
DOIOSTI

Characterization and assessment of novel bulk storage technologies : a study for the DOE Energy Storage Systems program

Huff, Georgianne

This paper reports the results of a high-level study to assess the technological readiness and technical and economic feasibility of 17 novel bulk energy storage technologies. The novel technologies assessed were variations of either pumped storage hydropower (PSH) or compressed air energy storage (CAES). The report also identifies major technological gaps and barriers to the commercialization of each technology. Recommendations as to where future R&D efforts for the various technologies are also provided based on each technology's technological readiness and the expected time to commercialization (short, medium, or long term). The U.S. Department of Energy (DOE) commissioned this assessment of novel concepts in large-scale energy storage to aid in future program planning of its Energy Storage Program. The intent of the study is to determine if any new but still unproven bulk energy storage concepts merit government support to investigate their technical and economic feasibility or to speed their commercialization. The study focuses on compressed air energy storage (CAES) and pumped storage hydropower (PSH). It identifies relevant applications for bulk storage, defines the associated technical requirements, characterizes and assesses the feasibility of the proposed new concepts to address these requirements, identifies gaps and barriers, and recommends the type of government support and research and development (R&D) needed to accelerate the commercialization of these technologies.

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TYPE SAND Report YEAR 2011
DOIOSTI

Effect of polymer architecture and ionic aggregation on the scattering peak in model ionomers

Physical Review Letters

Hall, Lisa M.; Stevens, Mark J.; Frischknecht, Amalie L.

We perform molecular dynamics simulations of coarse-grained ionomer melts with two different architectures. Regularly spaced charged beads are placed either in the polymer backbone (ionenes) or pendant to it. The ionic aggregate structure is quantified as a function of the dielectric constant. The low wave vector ionomer scattering peak is present in all cases, but is significantly more intense for pendant ions, which form compact, discrete aggregates with liquidlike interaggregate order. This is in qualitative contrast to the ionenes, which form extended aggregates. © 2011 American Physical Society.

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TYPE Journal Article YEAR 2011
ScopusOSTI

Factors impacting performance of multithreaded sparse riangular solvet

Lecture Notes in Computer Science (including subseries Lecture Notes in Artificial Intelligence and Lecture Notes in Bioinformatics)

Heroux, Michael A.; Boman, Erik G.

As computational science applications grow more parallel with multi-core supercomputers having hundreds of thousands of computational cores, it will become increasingly difficult for solvers to scale. Our approach is to use hybrid MPI/threaded numerical algorithms to solve these systems in order to reduce the number of MPI tasks and increase the parallel efficiency of the algorithm. However, we need efficient threaded numerical kernels to run on the multi-core nodes in order to achieve good parallel efficiency. In this paper, we focus on improving the performance of a multithreaded triangular solver, an important kernel for preconditioning. We analyze three factors that affect the parallel performance of this threaded kernel and obtain good scalability on the multi-core nodes for a range of matrix sizes. © 2011 Springer-Verlag Berlin Heidelberg.

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TYPE Conference YEAR 2011
OSTIScopus

The stability of Lomer-Cottrell jogs in nanopillars

Scripta Materialia

Weinberger, C.R.

Single arm spiral sources, or truncated Frank-Read sources, have been used frequently to interpret the size dependent plasticity in micropillars. The basis for these sources is strong pinning points which have been proposed to exist based on immobile Lomer-Cottrell jogs. Here, we show, using molecular dynamics of face-centered cubic nanopillars, that Lomer-Cottrell jogs are not as immobile as initially thought and that they do not provide strong pinning points for single arm sources. © 2010 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

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TYPE Journal Article YEAR 2011
OSTIScopus

High-performance computing for materials design to advance energy science

MRS Bulletin

Lusk, Mark T.; Mattsson, Ann E.

The development of new materials typically requires an iterative sequence of synthesis and characterization, but high-performance computing (HPC) adds another dimension to the process: materials can be synthesized and/or characterized virtually as well, and it is often an overlapping quilt of data from these four aspects of design that is used to develop a new material. This is made possible, in large measure, by the algorithms and hardware collectively referred to as HPC. Prominent within this developing approach to materials design is the increasingly important role that quantum mechanical analysis techniques have come to play. These techniques are reviewed with an emphasis on their application to materials design. This issue of MRS Bulletin highlights specific examples of how such HPC tools are used to advance energy science research in the areas of nuclear fission, electrochemical batteries, photovoltaic energy conversion, hydrocarbon catalysis, hydrogen storage, clathrate hydrates, and nuclear fusion. © 2011 Materials Research Society.

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TYPE Journal Article YEAR 2011
ScopusOSTI

An experimental assembly for precise measurement of thermal accommodation coefficients

Review of Scientific Instruments

Trott, Wayne M.; Castaeda, Jaime N.; Torczynski, John R.; Gallis, Michael A.; Rader, Daniel J.

An experimental apparatus has been developed to determine thermal accommodation coefficients for a variety of gas-surface combinations. Results are obtained primarily through measurement of the pressure dependence of the conductive heat flux between parallel plates separated by a gas-filled gap. Measured heat-flux data are used in a formula based on Direct Simulation Monte Carlo (DSMC) simulations to determine the coefficients. The assembly also features a complementary capability for measuring the variation in gas density between the plates using electron-beam fluorescence. Surface materials examined include 304 stainless steel, gold, aluminum, platinum, silicon, silicon nitride, and polysilicon. Effects of gas composition, surface roughness, and surface contamination have been investigated with this system; the behavior of gas mixtures has also been explored. Without special cleaning procedures, thermal accommodation coefficients for most materials and surface finishes were determined to be near 0.95, 0.85, and 0.45 for argon, nitrogen, and helium, respectively. Surface cleaning by in situ argon-plasma treatment reduced coefficient values by up to 0.10 for helium and by ∼0.05 for nitrogen and argon. Results for both single-species and gas-mixture experiments compare favorably to DSMC simulations. © 2011 American Institute of Physics.

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TYPE Journal Article YEAR 2011
OSTIScopus

The thermodynamic ladder in geomicrobiology

American Journal of Science

Bethke, Craig M.; Sanford, Robert A.; Kirk, Matthew F.; Jin, Qusheng; Flynn, Theodore M.

A tenet of geomicrobiology is that anaerobic life in the subsurface arranges itself into zones, according to a thermodynamic ladder. Iron reducers, given access to ferric minerals, use their energetic advantage to preclude sulfate reduction. Sulfate reducers exclude methanogens in the same way, by this tenet, wherever the environment provides sulfate. Examining usable energy-the energy in excess of a cell's internal stores-in subsurface environments, we find that in groundwater of near neutral pH the three functional groups see roughly equivalent amounts. Iron reducers hold a clear energetic advantage under acidic conditions, but may be unable to grow in alkaline environments. The calculations fail to identify a fixed thermodynamic hierarchy among the groups. In long-term bioreactor experiments, usable energy did not govern microbial activity. Iron reducers and sulfate reducers, instead of competing for energy, entered into a tightly balanced mutualistic relationship. Results of the study show thermodynamics does not invariably favor iron reducers relative to sulfate reducers, which in turn do not necessarily have an energetic advantage over methanogens. The distribution of microbial life in the subsurface is controlled by ecologic and physiologic factors, and cannot be understood in terms of thermodynamics alone.

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TYPE Journal Article YEAR 2011
ScopusOSTIDOI

Assessing the Near-Term Risk of Climate Uncertainty:Interdependencies among the U.S. States

Backus, George A.; Trucano, Timothy G.; Robinson, David G.; Adams, Brian M.; Richards, Elizabeth H.; Siirola, John D.; Boslough, Mark; Taylor, Mark A.; Conrad, Stephen H.; Kelic, Andjelka; Roach, Jesse D.; Warren, Drake E.; Ballantine, Marissa D.; Stubblefield, William A.; Snyder, Lillian A.; Finley, Ray E.; Horschel, Daniel S.; Ehlen, Mark; Klise, Geoffrey T.; Malczynski, Leonard A.; Stamber, Kevin L.; Tidwell, Vincent C.; Vargas, Vanessa N.; Zagonel, Aldo A.

Abstract not provided.

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TYPE Conference YEAR 2011
OSTI

Raman and infrared thermometry for microsystems

Phinney, Leslie; Lu, Wei-Yang; Serrano, Justin R.

This paper compares measurements made by Raman and infrared thermometry on a SOI (silicon on insulator) bent-beam thermal microactuator. Both techniques are noncontact and used to experimentally measure temperatures along the legs and on the shuttle of the thermal microactuators. Raman thermometry offers micron spatial resolution and measurement uncertainties of {+-}10 K; however, typical data collection times are a minute per location leading to measurement times on the order of hours for a complete temperature profile. Infrared thermometry obtains a full-field measurement so the data collection time is much shorter; however, the spatial resolution is lower and calibrating the system for quantitative measurements is challenging. By obtaining thermal profiles on the same SOI thermal microactuator, the relative strengths and weaknesses of the two techniques are assessed.

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TYPE Conference YEAR 2011
OSTI
Results 69401–69500 of 99,299
Results 69401–69500 of 99,299