Publications

Results 61601–61800 of 99,299

Search results

Jump to search filters

CPLOAS_2 User Manual

Sallaberry, Cedric J.

Weak link (WL)/strong link (SL) systems are important parts of the overall operational design of high-consequence systems. In such designs, the SL system is very robust and is intended to permit operation of the entire system under, and only under, intended conditions. In contrast, the WL system is intended to fail in a predictable and irreversible manner under accident conditions and render the entire system inoperable before an accidental operation of the SL system. The likelihood that the WL system will fail to deactivate the entire system before the SL system fails (i.e., degrades into a configuration that could allow an accidental operation of the entire system) is referred to as probability of loss of assured safety (PLOAS). This report describes the Fortran 90 program CPLOAS_2 that implements the following representations for PLOAS for situations in which both link physical properties and link failure properties are time-dependent: (i) failure of all SLs before failure of any WL, (ii) failure of any SL before failure of any WL, (iii) failure of all SLs before failure of all WLs, and (iv) failure of any SL before failure of all WLs. The effects of aleatory uncertainty and epistemic uncertainty in the definition and numerical evaluation of PLOAS can be included in the calculations performed by CPLOAS_2.

More Details
TYPE SAND Report YEAR 2012
DOIOSTI

Enhancing Safeguards Analysts’ Geospatial Usage

Bleakly, Denise; Horak, Karl E.; Mcdaniel, Michael

This report is the final summation of Sandia‘s Laboratory Directed Research and Development (LDRD) project #151316, "Open Source Information Verification" (OSIV) which ran from FY11 through FY12. The aim of OSIV was to research, develop, and evaluate relevant geospatial analysis capabilities that address open-source information needs for international safeguards. OSIV generated a number of technical, programmatic, and cultural advances, detailed in this report. There were new methodological insights and research that resulted in ten publications and presentations; this report concludes with an abstract-annotated listing of all materials. OSIV generated a substantial prototype, GeoSafeguards, that not only achieved its intended goal of testing our hypothesis, but which also served as a vehicle for customer education and program development. OSIV, as intended, has catalyzed future work in this domain; by the end of two years, it has already brought considerable attention to this work both domestically and with our international partners. Finally, the OSIV project knit together previously disparate research staff and user expertise in a fashion that not only addressed our immediate research goals, which has created cross- understanding, in service of Sandia‘s national security responsibilities in safeguards and nonproliferation.

More Details
TYPE SAND Report YEAR 2012
DOIOSTI

Reduced equations of motion for quantum systems driven by diffusive Markov processes

Physical Review Letters

Sarovar, Mohan; Grace, Matthew D.

The expansion of a stochastic Liouville equation for the coupled evolution of a quantum system and an Ornstein-Uhlenbeck process into a hierarchy of coupled differential equations is a useful technique that simplifies the simulation of stochastically driven quantum systems. We expand the applicability of this technique by completely characterizing the class of diffusive Markov processes for which a useful hierarchy of equations can be derived. The expansion of this technique enables the examination of quantum systems driven by non-Gaussian stochastic processes with bounded range. We present an application of this extended technique by simulating Stark-tuned Förster resonance transfer in Rydberg atoms with nonperturbative position fluctuations. © 2012 American Physical Society.

More Details
TYPE Journal Article YEAR 2012
DOIOSTIScopus

Optical manipulation with plasmonic beam shaping antenna structures

Advances in OptoElectronics

Jun, Young C.; Brener, Igal

Near-field optical trapping of objects using plasmonic antenna structures has recently attracted great attention. However, metal nanostructures also provide a compact platform for general wavefront engineering of intermediate and far-field beams. Here, we analyze optical forces generated by plasmonic beam shaping antenna structures and show that they can be used for general optical manipulation such as guiding of a dielectric particle along a linear or curved trajectory. This removes the need for bulky diffractive optical components and facilitates the integration of optical force manipulation into a highly functional, compact system. © 2012 Young Chul Jun and Igal Brener.

More Details
TYPE Journal Article YEAR 2012
DOIOSTIScopus

A thermodynamic perspective of the metastability of holey sheets: The role of curvature

Physical Chemistry Chemical Physics

van Swol, Frank; Challa, Sivakumar R.; Shelnutt, John A.

Producing nanostructures with high surface area that are stable is important to accomplish sustained use of catalytic materials in practical settings. Avoiding the processes of ripening and sintering that typically hinder stability has long been recognized as a significant challenge and much research is focused on addressing these issues. In this article, we investigate a Pt nanostructure-a holey nanosheet-that exhibits high surface area and stability. The findings from lattice gas simulations produce a stability diagram that relates a critical hole diameter to sheet thickness. The stability is now addressed from a thermodynamic point of view, and, in particular, the crucial role of curvature is considered. We find that the stability of certain sized holes is due to the near zero mean curvature of the surface of the holes and of the surrounding flat sheet. Molecular dynamics simulations of Pt (using an embedded atom potential) are reported for small nanoclusters and model holes in sheets to illustrate the strong effects of curvature on thermodynamic properties such as the lowering of melting and surface melting temperatures. © the Owner Societies.

More Details
TYPE Journal Article YEAR 2012
ScopusOSTI

Monodisperse fluorescent organic/inorganic composite nanoparticles: Tuning full color spectrum

Chemistry of Materials

Sun, Zaicheng; Bai, Feng; Wu, Huimeng; Boye, Daniel M.; Fan, Hongyou

Monodisperse fluorescent organic/inorganic composite nanoparticles are synthesized through the spontaneous self-assembly of block copolymer polystyrene-block-poly(vinylpyridine) and rare-earth ions (europium, terbium, thulium, etc.). Depending on the rare-earth ions selected, tunable light-emission colors, including the primary red, green, and blue, are accomplished. Further, by stoichiometric mixing of the nanoparticles that emit different colors, the full color spectrum can be accessed. Both electron microscopy and spectroscopic characterizations confirm specific interactions of rare-earth and block copolymers. The resulting nanoparticles are monodisperse as characterized by dynamic light scattering. They are very stable and can be dispersed in common solvents, and together with homopolymers, they form ordered arrays and thin films (both supported and free-standing) upon solvent evaporation. The resulting nanoparticle thin films exhibit mechanical flexibility for ease of processing or device integration. © 2012 American Chemical Society.

More Details
TYPE Journal Article YEAR 2012
ScopusOSTI

A direct numerical simulation study of turbulence and flame structure in transverse jets analysed in jet-trajectory based coordinates

Journal of Fluid Mechanics

Grout, R.W.; Gruber, A.; Kolla, Hemanth; Bremer, P.T.; Bennett, J.C.; Gyulassy, A.; Chen, J.H.

An H2 N2 jet in cross-flow (JICF) of air is studied using three-dimensional direct numerical simulation with and without chemical reaction in order to investigate the role of the complex JICF turbulent flow field in the mechanism of fast fuel-oxidant mixing and of aerodynamic flame stabilization in the near field of the jet nozzle. Focus is on delineating the flow/mixing/chemistry conditions that are necessary and/or sufficient to achieve flame anchoring that ultimately enables the formulation of more reliable and precise guidelines for design of fuel injection nozzles. A mixture averaged diffusion formulation that includes the effect of thermal diffusion is used along with a detailed chemical kinetics mechanism for hydrogen-air combustion. A new parametrization technique is used to describe the jet trajectory: solution of Laplace's equation upon, and then within, an opportune scalar surface anchored by Dirichlet boundary conditions at the jet nozzle and plume exit from the domain provides a smoothly varying field along the jet path. The surface is selected to describe the scalar mixing and reaction associated with a transverse jet. The derived field, j(x), is used as a condition to mark the position along the natural jet trajectory when analysing the variation of relevant flow, mixing and reaction quantities in the present direct numerical simulation (DNS) datasets. Results indicate the presence of a correlation between the flame base location in parameter space and a region of low velocity magnitude, high enstrophy, high mixing rate and high equivalence ratio (flame root region). Instantaneously, a variety of vortical structures, well known from the literature as important contributors to fuel-oxidant mixing, are observed in both inert and reactive cases with a considerable span in length scales. Moreover, instantaneous plots from reactive cases illustrate that the most upstream flame tongues propagate close to the trailing edge of the fuel jet potential core near the jet shear layer vortex shedding position. Some degree of asymmetry with respect to the domain mid-plane in the spanwise direction is observed in the averaged fields, both for the inert and reactive cases. © 2012 Cambridge University Press.

More Details
TYPE Journal Article YEAR 2012
ScopusOSTI

A stochastic multiscale coupling scheme to account for sampling noise in atomistic-to-continuum simulations

Multiscale Modeling and Simulation

Salloum, Maher; Sargsyan, Khachik; Jones, Reese E.; Debusschere, Bert; Najm, Habib N.; Adalsteinsson, Helgi

We present a methodology to assess the predictive fidelity of multiscale simulations by incorporating uncertainty in the information exchanged between the atomistic and continuum simulation components. Focusing on uncertainty due to finite sampling in molecular dynamics (MD) simulations, we present an iterative stochastic coupling algorithm that relies on Bayesian inference to build polynomial chaos expansions for the variables exchanged across the atomistic-continuum interface. We consider a simple Couette flow model where velocities are exchanged between the atomistic and continuum components. To alleviate the burden of running expensive MD simulations at every iteration, a surrogate model is constructed from which samples can be efficiently drawn as data for the Bayesian inference. Results show convergence of the coupling algorithm at a reasonable number of iterations. The uncertainty associated with the exchanged variables significantly depends on the amount of data sampled from the MD simulations and on the width of the time averaging window used in the MD simulations. Sequential Bayesian updating is also implemented in order to enhance the accuracy of the stochastic algorithm predictions. © 2012 Society for Industrial and Applied Mathematics.

More Details
TYPE Journal Article YEAR 2012
OSTIScopus

Impact of atmospherically deposited solid contaminants on materials of interest for the interim and long term storage of high level nuclear waste

NACE - International Corrosion Conference Series

Enos, David

For both the interim and long term storage of high level nuclear waste, the storage casks/containers will be exposed to conditions under which considerable dust and/or atmospheric aerosols may be deposited on the surface. These dust layers may contain a sizeable portion of water soluble salts, particularly in marine environments where many interim storage systems are located. These soluble salts will deliquesce if sufficient moisture is present, resulting in the formation of potentially corrosive brine on the material surface. While this is not a concern for highly corrosion resistant materials such as Alloy 22 (UNS N06022) (which was pursued for long term geologic storage), it could be an issue for the less corrosion resistant stainless steels and carbon steels used for interim storage applications. Experimental results have illustrated that some stainless steels can and will undergo localized corrosion in elevated temperature conditions where a chloride rich brine has formed on the surface. In this presentation, the results of this test program, as well as efforts to address the potential for corrosion stifling under conditions where a limited quantity of reactant is present will be discussed. ©2012 by NACE International.

More Details
TYPE Conference YEAR 2012
ScopusOSTI

Efficient expression templates for operator overloading-based automatic differentiation

Lecture Notes in Computational Science and Engineering

Phipps, Eric T.; Pawlowski, Roger

Expression templates are a well-known set of techniques for improving the efficiency of operator overloading-based forward mode automatic differentiation schemes in the C++ programming language by translating the differentiation from individual operators to whole expressions. However standard expression template approaches result in a large amount of duplicate computation, particularly for large expression trees, degrading their performance. In this paper we describe several techniques for improving the efficiency of expression templates and their implementation in the automatic differentiation package Sacado (Phipps et al., Advances in automatic differentiation, Lecture notes in computational science and engineering, Springer, Berlin, 2008; Phipps and Gay, Sacado automatic differentiation package. http://trilinos.sandia.gov/packages/sacado/, 2011). We demonstrate their improved efficiency through test functions as well as their application to differentiation of a large-scale fluid dynamics simulation code. © 2012 Springer-Verlag.

More Details
TYPE Conference YEAR 2012
OSTIScopus

Physiological effects of free fatty acid production in genetically engineered Synechococcus elongatus PCC 7942

Biotechnology and Bioengineering

Ruffing, Anne R.; Jones, Howland D.T.

The direct conversion of carbon dioxide into biofuels by photosynthetic microorganisms is a promising alternative energy solution. In this study, a model cyanobacterium, Synechococcus elongatus PCC 7942, is engineered to produce free fatty acids (FFA), potential biodiesel precursors, via gene knockout of the FFA-recycling acyl-ACP synthetase and expression of a thioesterase for release of the FFA. Similar to previous efforts, the engineered strains produce and excrete FFA, but the yields are too low for large-scale production. While other efforts have applied additional metabolic engineering strategies in an attempt to boost FFA production, we focus on characterizing the engineered strains to identify the physiological effects that limit cell growth and FFA synthesis. The strains engineered for FFA-production show reduced photosynthetic yields, chlorophyll-a degradation, and changes in the cellular localization of the light-harvesting pigments, phycocyanin and allophycocyanin. Possible causes of these physiological effects are also identified. The addition of exogenous linolenic acid, a polyunsaturated FFA, to cultures of S. elongatus 7942 yielded a physiological response similar to that observed in the FFA-producing strains with only one notable difference. In addition, the lipid constituents of the cell and thylakoid membranes in the FFA-producing strains show changes in both the relative amounts of lipid components and the degree of saturation of the fatty acid side chains. These changes in lipid composition may affect membrane integrity and structure, the binding and diffusion of phycobilisomes, and the activity of membrane-bound enzymes including those involved in photosynthesis. Thus, the toxicity of unsaturated FFA and changes in membrane composition may be responsible for the physiological effects observed in FFA-producing S. elongatus 7942. These issues must be addressed to enable the high yields of FFA synthesis necessary for large-scale biofuel production. © 2012 Wiley Periodicals, Inc.

More Details
TYPE Journal Article YEAR 2012
DOIOSTIScopus

From OO to FPGA :

Brooks, Jeffrey A.

Consumer electronics today such as cell phones often have one or more low-power FPGAs to assist with energy-intensive operations in order to reduce overall energy consumption and increase battery life. However, current techniques for programming FPGAs require people to be specially trained to do so. Ideally, software engineers can more readily take advantage of the benefits FPGAs offer by being able to program them using their existing skills, a common one being object-oriented programming. However, traditional techniques for compiling object-oriented languages are at odds with todays FPGA tools, which support neither pointers nor complex data structures. Open until now is the problem of compiling an object-oriented language to an FPGA in a way that harnesses this potential for huge energy savings. In this paper, we present a new compilation technique that feeds into an existing FPGA tool chain and produces FPGAs with up to almost an order of magnitude in energy savings compared to a low-power microprocessor while still retaining comparable performance and area usage.

More Details
TYPE SAND Report YEAR 2012
DOIOSTI

Characterization of volatile nylon 6.6 thermal-oxidative degradation products by selective isotopic labeling and cryo-GC/MS

Journal of the American Society for Mass Spectrometry

Von White II, Gregory; White, Michael I.; Bernstein, Robert; Hochrein, James M.

Aged materials, such as polymers, can exhibit modifications to their chemical structure and physical properties, which may render the material ineffective for its intended purpose. Isotopic labeling was used to characterize low-molecular weight volatile thermal-oxidative degradation products of nylon 6.6 in an effort to better understand and predict changes in the aged polymer. Headspace gas from aged (up to 243 d at 138 °C) nylon 6.6 monomers (adipic acid and 1,6- hexanediamine) and polymer were preconcentrated, separated, and detected using cryofocusing gas chromatography mass spectrometry (cryo-GC/MS). Observations regarding the relative concentrations observed in each chromatographic peak with respect to aging time were used in conjunction with mass spectra for samples aged under ambient air to determine the presence and identity of 18 degradation products. A comparison of the National Institute of Standards and Technology (NIST) library, unlabeled, and isotopically labeled mass spectra (C-13 or N-15) and expected fragmentation pathways of each degradation product were used to identify the location of isotopically labeled atoms within the product's chemical structure, which can later be used to determine the exact origin of the species. In addition, observations for unlabeled nylon 6.6 aged in an O-18 enriched atmosphere were used to determine if the source of oxygen in the applicable degradation products was from the gaseous environment or the polymer. Approximations for relative isotopic ratios of unlabeled to labeled products are reported, where appropriate. © American Society for Mass Spectrometry, 2012.

More Details
TYPE Journal Article YEAR 2012
DOIOSTIScopus

Hawaii Electric System Reliability

Silva-Monroy, Cesar A.

This report addresses Hawaii electric system reliability issues; greater emphasis is placed on short-term reliability but resource adequacy is reviewed in reference to electric consumers’ views of reliability “worth” and the reserve capacity required to deliver that value. The report begins with a description of the Hawaii electric system to the extent permitted by publicly available data. Electrical engineering literature in the area of electric reliability is researched and briefly reviewed. North American Electric Reliability Corporation standards and measures for generation and transmission are reviewed and identified as to their appropriateness for various portions of the electric grid and for application in Hawaii. Analysis of frequency data supplied by the State of Hawaii Public Utilities Commission is presented together with comparison and contrast of performance of each of the systems for two years, 2010 and 2011. Literature tracing the development of reliability economics is reviewed and referenced. A method is explained for integrating system cost with outage cost to determine the optimal resource adequacy given customers’ views of the value contributed by reliable electric supply. The report concludes with findings and recommendations for reliability in the State of Hawaii.

More Details
TYPE SAND Report YEAR 2012
DOIOSTI

Electrothermal instability growth in magnetically driven pulsed power liners

Physics of Plasmas

Sinars, Daniel; Yu, Edmund; Herrmann, Mark H.; Cuneo, Michael E.; Slutz, Stephen A.; Smith, Ian C.; Atherton, B.; Knudson, Marcus D.; Nakhleh, Charles

This paper explores the role of electro-thermal instabilities on the dynamics of magnetically accelerated implosion systems. Electro-thermal instabilities result from non-uniform heating due to temperature dependence in the conductivity of a material. Comparatively little is known about these types of instabilities compared to the well known Magneto-Rayleigh-Taylor (MRT) instability. We present simulations that show electrothermal instabilities form immediately after the surface material of a conductor melts and can act as a significant seed to subsequent MRT instability growth. We also present the results of several experiments performed on Sandia National Laboratories Z accelerator to investigate signatures of electrothermal instability growth on well characterized initially solid aluminum and copper rods driven with a 20 MA, 100 ns risetime current pulse. These experiments show excellent agreement with electrothermal instability simulations and exhibit larger instability growth than can be explained by MRT theory alone. © 2012 American Institute of Physics.

More Details
TYPE Journal Article YEAR 2012
OSTIScopus
Results 61601–61800 of 99,299
Results 61601–61800 of 99,299