Publications

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This paper presents constitutive models for the anisotropic, finite-deformation viscoelastic behavior of soft fiber-reinforced composites. An essential assumption of the models is that both the fiber reinforcements and matrix can exhibit distinct time-dependent behavior. As such, the constitutive formulation attributes a different viscous stretch measure and free energy density to the matrix and fiber phases. Separate flow rules are specified for the matrix and the individual fiber families. The flow rules for the fiber families then are combined to give an anisotropic flow rule for the fiber phase. This is in contrast to many current inelastic models for soft fiber-reinforced composites which specify evolution equations directly at the composite level. The approach presented here allows key model parameters of the composite to be related to the properties of the matrix and fiber constituents and to the fiber arrangement. An efficient algorithm is developed for the implementation of the constitutive models in a finite-element framework, and examples are presented examining the effects of the viscoelastic behavior of the matrix and fiber phases on the time-dependent response of the composite.

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Cube-corner indenters, by virtue of their acuity, possess a lowered threshold load for cracking. Shorter crack lengths allow the sampling of residual stresses in small spatial dimensions. We conducted cube-corner indentation on tempered and annealed glasses. Indentation crack geometry was found to be "quarter-penny." A stress-intensity factor for this geometry, and crack length decrements on tempered materials were used in a stress-intensity superposition to provide reasonable estimates of residual stress. Stresses ∼100 MPa over a length scale of 10 μm, and 30 MPa over 20 μm were measured accurately, indicating that cube-corner indentation is a promising tool for materials characterization. © 2006 The American Ceramic Society.

A novel hyperspectral fluorescence microscope for high-resolution 3D optical sectioning of cells and other structures has been designed, constructed, and used to investigate a number of different problems. We have significantly extended new multivariate curve resolution (MCR) data analysis methods to deconvolve the hyperspectral image data and to rapidly extract quantitative 3D concentration distribution maps of all emitting species. The imaging system has many advantages over current confocal imaging systems including simultaneous monitoring of numerous highly overlapped fluorophores, immunity to autofluorescence or impurity fluorescence, enhanced sensitivity, and dramatically improved accuracy, reliability, and dynamic range. Efficient data compression in the spectral dimension has allowed personal computers to perform quantitative analysis of hyperspectral images of large size without loss of image quality. We have also developed and tested software to perform analysis of time resolved hyperspectral images using trilinear multivariate analysis methods. The new imaging system is an enabling technology for numerous applications including (1) 3D composition mapping analysis of multicomponent processes occurring during host-pathogen interactions, (2) monitoring microfluidic processes, (3) imaging of molecular motors and (4) understanding photosynthetic processes in wild type and mutant Synechocystis cyanobacteria.

This report describes a Cooperative Research and Development Agreement (CRADA) between Salt River Project Agricultural Improvement and Power District (SRP) and Sandia National Laboratories to jointly develop advanced methods of controlling distributed energy resources (DERs) that may be located within SRP distribution systems. The controls must provide a standardized interface to allow plug-and-play capability and should allow utilities to take advantage of advanced capabilities of DERs to provide a value beyond offsetting load power. To do this, Sandia and SRP field-tested the IEC 61850-7-420 DER object model (OM) in a grid environment, with the goal of validating whether the model is robust enough to be used in common utility applications. The diesel generator OM tested was successfully used to accomplish basic genset control and monitoring. However, as presently constituted it does not enable plug-and-play functionality. Suggestions are made of aspects of the standard that need further development and testing. These problems are far from insurmountable and do not imply anything fundamentally unsound or unworkable in the standard.

This report describes efforts by the Performance Modeling and Analysis Team to investigate performance characteristics of Sandia's engineering and scientific applications on the ASC capability and advanced architecture supercomputers, and Sandia's capacity Linux clusters. Efforts to model various aspects of these computers are also discussed. The goals of these efforts are to quantify and compare Sandia's supercomputer and cluster performance characteristics; to reveal strengths and weaknesses in such systems; and to predict performance characteristics of, and provide guidelines for, future acquisitions and follow-on systems. Described herein are the results obtained from running benchmarks and applications to extract performance characteristics and comparisons, as well as modeling efforts, obtained during the time period 2004-2006. The format of the report, with hypertext links to numerous additional documents, purposefully minimizes the document size needed to disseminate the extensive results from our research.

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This study characterizes theoretical and industry approaches to organizational capabilities management and ascertains whether there is a distinct ''best practice'' in this regard. We consider both physical capabilities, such as technical disciplines and infrastructure, and non-physical capabilities such as corporate culture and organizational procedures. We examine Resource-Based Theory (RBT), which is the predominant organizational management theory focused on capabilities. RBT seeks to explain the effect of capabilities on competitiveness, and thus provide a basis for investment/divestment decisions. We then analyze industry approaches described to us in interviews with representatives from Goodyear, 3M, Intel, Ford, NASA, Lockheed Martin, and Boeing. We found diversity amongst the industry capability management approaches. Although all organizations manage capabilities and consider them to some degree in their strategies, no two approaches that we observed were identical. Furthermore, we observed that theory is not a strong driver in this regard. No organization used the term ''Resource-Based Theory'', nor did any organization mention any other guiding theory or practice from the organizational management literature when explaining their capabilities management approaches. As such, we concluded that there is no single best practice for capabilities management. Nevertheless, we believe that RBT and the diverse industry experiences described herein can provide useful insights to support development of capabilities management approaches.

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This paper highlights key topic areas to be discussed the authors in a panel format during the Augmented Cognition thematic area paper session: 'Augmented Cognition Lessons Learned and Future Directions for Enabling 'Anyone, Anytime, Anywhere' Applications'. The term 'killer app' has been part of the vernacular in the commercial computer software and electronic devices industry to refer to breakthrough technologies [2]. A 'killer app' generally emerges with the development of related technologies that extends over some time and involves numerous variations on a basic concept. Hypotheses may be offered with respect to the conditions that will be needed to enable a similar situation with augmented cognition technologies. This paper and resulting panel session will address the numerous concepts that have emerged from the augmented cognition field to date and postulate how and when this field's first 'killer app' may emerge (e.g., 5, 10, 15, or more years from now).

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A velocity interferometer system for any reflector (VISAR) was recently deployed at the light initiated high explosive facility (LIHE) to measure the velocity of an explosively accelerated flyer plate. The velocity data from the flyer plate experiments, using the vendor's fringe constant of 100m/s/fringe, were consistently lower than model predictions. The goal of the VISAR validation test series was to confirm the VISAR system fringe constant. A low velocity gas gun was utilized to impact and accelerate a target at the LIHE facility. VISAR velocity data from the accelerated target was compared against an independent velocity measurement. The data from this test series did in fact reveal the fringe constant was significantly higher than the vendor's specification. The correct fringe constant for the LIHE VISAR system has been determined to be 123 m/s/fringe. The Light Initiated High Explosive (LIHE) facility recently completed a Phase I test series to develop an explosively accelerated flyer plate (X-Flyer). The X-Flyer impulse technique consists of first spraying a thin layer of silver acetylide silver nitrate explosive onto a thin flyer plate. The explosive is then initiated using an intense flash of light. The explosive detonation accelerates the flyer across a small air gap towards the test item. The impact of the flyer with the test item creates a shock pulse and an impulsive load in the test unit. The goal of Phase I of the X-Flyer development series was to validate the technique theory and design process. One of the key parameters that control the shock pulse and impulsive load is the velocity of the flyer at impact. To measure this key parameter, a velocity interferometer system for any reflector (VISAR) was deployed at the LIHE facility. The VISAR system was assembled by Sandia personnel from the Explosive Projects and Diagnostics department. The VISAR was a three leg, push-pull system using a fixed delay cavity. The primary optical components consisted of a delay bar and stand off that holds the air-reference mirror. When this component was ordered 2 years ago, a fringe constant of 100 m/s/fringe for a 532nm laser was specified. The fabrication/assembly vendor went out of business shortly after delivering the component and did not deliver the certification papers with the component. The vendor documentation to verify the fringe constant was not made available to Sandia. VISAR systems were generally not calibrated because the fringe constant could be determined from a known glass index of refraction and length. The VISAR system was deployed at the LIHE facility using the specified 100m/s/fringe. The Phase I X-Flyer development series was completed successfully measuring flyer velocities using the VISAR system. However flyer velocity measurements were on average 18% lower than analytical model predictions. In an effort to resolve the consistently slow velocity data, the VISAR data was under scrutiny. The purpose of the LIHE VISAR validation test series is to verify the velocity data taken with the VISAR system.

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Verification and validation (V&V) are the primary means to assess the accuracy and reliability of computational simulations. V&V methods and procedures have fundamentally improved the credibility of simulations in several high-consequence fields, such as nuclear reactor safety, underground nuclear waste storage, and nuclear weapon safety. Although the terminology is not uniform across engineering disciplines, code verification deals with assessing the reliability of the software coding, and solution verification deals with assessing the numerical accuracy of the solution to a computational model. Validation addresses the physics modeling accuracy of a computational simulation by comparing the computational results with experimental data. Code verification benchmarks and validation benchmarks have been constructed for a number of years in every field of computational simulation. However, no comprehensive guidelines have been proposed for the construction and use of V&V benchmarks. For example, the field of nuclear reactor safety has not focused on code verification benchmarks, but it has placed great emphasis on developing validation benchmarks. Many of these validation benchmarks are closely related to the operations of actual reactors at near-safety-critical conditions, as opposed to being more fundamental-physics benchmarks. This paper presents recommendations for the effective design and use of code verification benchmarks based on manufactured solutions, classical analytical solutions, and highly accurate numerical solutions. In addition, this paper presents recommendations for the design and use of validation benchmarks, highlighting the careful design of building-block experiments, the estimation of experimental measurement uncertainty for both inputs and outputs to the code, validation metrics, and the role of model calibration in validation. It is argued that the understanding of predictive capability of a computational model is built on the level of achievement in V&V activities, how closely related the V&V benchmarks are to the actual application of interest, and the quantification of uncertainties related to the application of interest.

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Nd:YAG laser joining is a high energy density (HED) process that can produce high-speed, low-heat input welds with a high depth-to-width aspect ratio. This is optimized by formation of a ''keyhole'' in the weld pool resulting from high vapor pressures associated with laser interaction with the metallic substrate. It is generally accepted that pores form in HED welds due to the instability and frequent collapse of the keyhole. In order to maintain an open keyhole, weld pool forces must be balanced such that vapor pressure and weld pool inertia forces are in equilibrium. Travel speed and laser beam power largely control the way these forces are balanced, as well as welding mode (Continuous Wave or Square Wave) and shielding gas type. A study into the phenomenon of weld pool porosity in 304L stainless steel was conducted to better understand and predict how welding parameters impact the weld pool dynamics that lead to pore formation. This work is intended to aid in development and verification of a finite element computer model of weld pool fluid flow dynamics being developed in parallel efforts and assist in weld development activities for the W76 and future RRW programs.

This report is a review of progress made by the Center for the Simulation of Accidental Fires and Explosions (C-SAFE) at the University of Utah, during the ninth year (Fiscal 2006) of its existence as an activity funded by the Department of Energy's Advanced Simulation and Computing Program (ASC). The ten-member Review Team composed of the TST and AST spent two days (August 24-25, 2006) at the University, reviewing formal presentations and demonstrations by the C-SAFE researchers and conferring privately. The Review Team found that the C-SAFE project administrators and staff had prepared well for the review. C-SAFE management and staff openly shared extensive answers to unexpected questions and the advance materials were well prepared and very informative. We believe that the time devoted to the review was used effectively and hope that the recommendations included in this 2006 report will provide helpful guidance to C-SAFE personnel and ASC managers.

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I am pleased to present the CFO's FY06 Financial Report for Sandia National Laboratories (SNL). As a contractor to DOE and other government agencies, the bulk of SNL's revenue is from tax dollars. SNL's FY06 total revenue, total expenditures, and total employment levels were slightly below the FY05 record high levels. Throughout FY06, SNL business staff continued to improve SNL's financial stewardship of entrusted taxpayer funds through implementation of best-in-class practices in financial business operations and internal control policies and procedures to ensure compliance with all accounting standards and provide accountability to our customers. Our FY06 efforts focused on process certification and improvement, implementing OMB Circular A-123, achieving assurance activities, implementation of a Financial Management Competency Program throughout SNL, and continuous assessment of trends and emerging issues.

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The annual program report provides detailed information about all aspects of the Sandia National Laboratories, California (SNL/CA) Environmental Planning and Ecology Program for a given calendar year. It functions as supporting documentation to the SNL/CA Environmental Management System Program Manual. The 2006 program report describes the activities undertaken during the past year, and activities planned in future years to implement the Planning and Ecology Program, one of six programs that supports environmental management at SNL/CA.

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Scanning probe recognition microscopy is a new scanning probe microscopy technique which enables selective scanning along individual nanofibers within a tissue scaffold. Statistically significant data for multiple properties can be collected by repetitively fine-scanning an identical region of interest. The results of a scanning probe recognition microscopy investigation of the surface roughness and elasticity of a series of tissue scaffolds are presented. Deconvolution and statistical methods were developed and used for data accuracy along curved nanofiber surfaces. Furthermore, nanofiber features were also independently analyzed using transmission electron microscopy, with results that supported the scanning probe recognition microscopy-based analysis.

By far the most widely used tool in shock data analysis is the shock response spectrum (SRS). The SRS has gained popularity because of several primary considerations. It has physical significance, it is simple to understand and it is believed to indicate shock severity. Despite its popularity, the SRS has limitations. Foremost among them is the underlying assumption that shock severity is proportional to a time derivative of position, which does not agree with accepted material failure models. Also, the SRS cannot distinguish between naturally occurring, complex shocks and the chirps sometimes used to achieve a desired SRS using electrodynamic shakers with inadequate force capabilities. Thirdly, SODF models used in the computation of the SRS do not accurately predict accelerations in MDOF structures. A relatively new concept has been introduced whereby an analysis is made on the work done on structures by the excitation force. Since work is equal to the change in the energy of a system, this quantity is closely related to failure models based on strain energy such as the Von Mesis criterion. This paper is the first in a series exploring the use of energy-based description of shock motion and structural response. The input energy spectrum has attractive properties which include intuitive physical significance, insensitivity to system parameters such as viscous damping or hysteretic loss, the ability to distinguish between realistic shocks and chirps, and a close relation to accepted material failure models. Input energy spectra can be calculated using SDOF models and, in many cases, accurately predict the energy input to MDOF structures. Finally, this paper gives an introduction to these methods, derives the equations for relevant energy measures and presents relationships to several other shock analysis tools.

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The static and dynamic compaction of ceramic powders was investigated experimentally using a high-pressure friction-compensated press to achieve static stresses of 1.6 GPa and with a novel gas gun setup to stresses of 5.9 GPa for a tungsten carbide powder. Experiments were performed in the partial compaction region to nearly full compaction. The effects of variables including initial density, particle size distribution, particle morphology, and loading path were investigated in the static experiments. Only particle morphology was found to significantly affect the compaction response. Post-test examination of the powder reveals fracture of the grains as well as breaking at particle edges. In dynamic experiments, steady structured compaction waves traveling at very low velocities were observed. The strain rate within the compaction waves was found to scale nearly linearly with the shock stress, in contrast with many fully dense materials where strain rate scales with stress to the fourth power. Similar scaling is found for data from the literature on TiO2 powder. The dynamic response of WC powder is found to be significantly stiffer than the static response, probably because deformation in the dynamic case is confined to the relatively narrow compaction wave front. Comparison of new static powder compaction results with shock data from the literature for SiO2 also reveals a stiffer dynamic response. © 2006 Elsevier Ltd. All rights reserved.

Digital Elevation Models (DEMS) are traditionally acquired from a stereo pair of aerial photographs sequentially captured by an airborne metric camera. Standard DEM extraction techniques can be naturally extended to satellite imagery, but the particular characteristics of satellite imaging can cause difficulties. The spacecraft ephemeris with respect to the ground site during image collects is the most important factor in the elevation extraction process. When the angle of separation between the stereo images is small, the extraction process typically produces measurements with low accuracy, while a large angle of separation can cause an excessive number of erroneous points in the DEM from occlusion of ground areas. The use of three or more images registered to the same ground area can potentially reduce these problems and improve the accuracy of the extracted DEM. The pointing capability of some sensors, such as the Multispectral Thermal Imager (MTI), allows for multiple collects of the same area from different perspectives. This functionality of MTI makes it a good candidate for the implementation of a DEM extraction algorithm using multiple images for improved accuracy. Evaluation of this capability and development of algorithms to geometrically model the MTI sensor and extract DEMs from multi-look MTI imagery are described in this paper. An RMS elevation error of 6.3-meters is achieved using 11 ground test points, while the MTI band has a 5-meter ground sample distance. © 2007 American Society for Photogrammetry and Remote Sensing.

An epoxy-based conformal coating with a very low modulus has been developed for the environmental protection of electronic devices and for stress relief of those devices. The coating was designed to be removable by incorporating thermally-reversible Diels-Alder (D-A) adducts into the epoxy resin utilized in the formulation. The removability of the coating allows us to recover expensive components during development, to rebuild during production, to upgrade the components during their lifetime, to perform surveillance after deployment, and it aids in dismantlement of the components after their lifetime. The removability is the unique feature of this coating and was characterized by modulus versus temperature measurements, dissolution experiments, viscosity quench experiments, and FTIR. Both the viscosity quench experiments and the FTIR measurements allowed us to estimate the equilibrium constant of the D-A adducts in a temperature range from room temperature to 90 °C. © 2007 American Chemical Society.

During the course of processing acceleration data from mechanical systems it is often desirable to integrate the data to obtain velocity or displacement waveforms. However, those who have attempted these operations may be painfully aware that the integrated records often yield unrealistic residual values. This is true whether the data has been obtained experimentally or through numerical simulation such as Runge-Kutta integration or the explicit finite element method. In the case of experimentally obtained data, the integration errors are usually blamed on accelerometer zero shift or amplifier saturation. In the case of simulation data, incorrect integrations are often incorrectly blamed on the integration algorithm itself. This work demonstrates that seemingly small aliased content can cause appreciable errors in the integrated waveforms and explores the unavoidable source of aliasing in both experiment and simulation-the sampling operation. Numerical analysts are often puzzled as to why the integrated acceleration from their simulation does not match the displacement output from the same simulation. This work shows that these strange results can be caused by aliasing induced by interpolation of the model output during sampling regularisation. © 2005 Elsevier Ltd. All rights reserved.

We report on algebraic multilevel preconditioners for the parallel solution of linear systems arising from a Newton procedure applied to the finite-element (FE) discretization of the incompressible Navier-Stokes equations. We focus on the issue of how to coarsen FE operators produced from high aspect ratio elements.

The focus of this paper is a penalty-based strategy for preconditioning elliptic saddle point systems. As the starting point, we consider the regularization approach of Axelsson in which a related linear system, differing only in the (2,2) block of the coefficient matrix, is introduced. By choosing this block to be negative definite, the dual unknowns of the related system can be eliminated resulting in a positive definite primal Schur complement. Rather than solving the Schur complement system exactly, an approximate solution is obtained using a substructuring preconditioner. The approximate primal solution together with the recovered dual solution then define the preconditioned residual for the original system.

A new technique is described for the registration of edge-detected images. While an extensive literature exists on the problem of image registration, few of the current approaches include a well-defined measure of the statistical confidence associated with the solution. Such a measure is essential for many autonomous applications, where registration solutions that are dubious (involving poorly focused images or terrain that is obscured by clouds) must be distinguished from those that are reliable (based on clear images of highly structured scenes). The technique developed herein utilizes straightforward edge pixel matching to determine the "best" among a class of candidate translations. A well-established statistical procedure, the McNemar test, is then applied to identify which other candidate solutions are not significantly worse than the best solution. This allows for the construction of confidence regions in the space of the registration parameters. The approach is validated through a simulation study and examples are provided of its application in numerous challenging scenarios. While the algorithm is limited to solving for two-dimensional translations, its use in validating solutions to higher-order (rigid body, affine) transformation problems is demonstrated. © 2007 IEEE.

Flame-sampling photoionization mass spectrometry is used for measurements of the absolute molar composition of fuel-rich (φ = 1.8) low-pressure laminar flames of allene and propyne. The experiment combines molecular-beam mass spectrometry with photoionization by tunable vacuum-ultraviolet synchrotron radiation. This approach provides selective detection of individual isomers and unambiguous identifications of other flame species of near-equal mass by near threshold photoionization efficiency measurements. Mole fraction profiles for more than 30 flame species with ion masses ranging from 2 to 78 are presented. The isomeric composition is resolved for most intermediates, for example, mole fraction profiles are presented for both benzene and the fulvene isomer. The results are compared with predictions based on current kinetic models. The mole fractions of the major species are predicted quite accurately, however, some discrepancies are observed for minor species. © 2006 The Combustion Institute. Published by Elsevier Inc. All rights reserved.

The role of ethanol as a fuel additive was investigated in a fuel-rich, non-sooting (C/O = 0.77) flat premixed propene-oxygen-argon flame at 50 mbar (5 kPa). Mole fractions of stable and radical species were derived using two different in situ molecular beam mass spectrometry (MBMS) set-ups, one located in Bielefeld using electron impact ionization (EI), and the other at the Advanced Light Source (ALS) at Berkeley using vacuum UV photoionization (VUV-PI) with synchrotron radiation. A rich propene flame, previously studied in detail experimentally and with flame model calculations, was chosen as the base flame. Addition of ethanol is believed to reduce the concentrations of benzene and small aromatic compounds, while augmenting the formation of other regulated air toxics such as aldehydes. To study the chemical pathways responsible for these effects, quantitative concentrations of about 35 species were determined from both experiments. This is also the first time that a detailed comparison of quantitative species concentrations from these independent MBMS set-ups is available. Effects of ethanol addition on the species pool are discussed with special attention on benzene precursor chemistry and aldehyde formation. © 2006 The Combustion Institute. Published by Elsevier Inc. All rights reserved.

The effect of exhaust-gas recirculation (EGR) on the equivalence ratio of premixed-burn mixture in diesel combustion was investigated experimentally. The ambient oxygen concentration was systematically decreased from 21% to 10% in a constant-volume combustion vessel to simulate EGR effects in engines. Pressure measurements and time-resolved imaging of high-temperature chemiluminescence were used to characterize the temporal and spatial ignition and premixed burn characteristics of n-heptane diesel jets. With increasing EGR, ignition delay increases and the location of premixed burn occurs further down-stream from the nozzle. Subsequent to first ignition, high temperature reactions stabilize at a quasi-steady lift-off length, showing that lift-off is a bounding parameter for determining premixed-burn region. The equivalence ratio of the fuel-ambient mixture in the premixed-burn region was measured using planar laser Rayleigh scattering. Fuel-oxygen mass distribution functions show that more mass is mixed into the premixed-burn region with increasing EGR, but the equivalence ratio of this mixture is the same. The study shows that an increasing ignition delay with increasing EGR does not necessarily decrease the equivalence ratio as would be desired for reducing soot formation in low-temperature combustion engines. However, measures to improve fuel-ambient mixing, such as shortened injection durations coupled to long ignition delay, could decrease equivalence ratio.

One-dimensional (1-D) line Rayleigh thermometry is used to investigate the effects of spatial resolution and noise on thermal dissipation in turbulent non-premixed CH4/H2/N2 jet flames. The high signal-tonoise ratio and spatial resolution of the measured temperature field enables determination of the cutoff wavenumber in the 1-D temperature dissipation spectrum obtained at each flame location. The local scale inferred from this cutoff is analogous to the Batchelor scale in nonreacting flows. At downstream locations in the flames studied here, it is consistent with estimates of the Batchelor scale based on the scaling laws using local Reynolds numbers. The spectral cutoff information is used to design data analysis schemes for determining mean thermal dissipation. Laminar flame measurements are used to characterize experimental noise and correct for the noise-induced apparent dissipation in the turbulent flame results. These experimentally determined resolution and noise correction techniques are combined to give measurements of the mean thermal dissipation that are essentially fully resolved and noise-free. The prospects of using spectral results from high-resolution 1-D Rayleigh imaging measurements to design filtering schemes for Raman-based measurements of mixture fraction dissipation are also discussed.

The mixture fraction filtered mass density function (FMDF) used in large eddy simulation (LES) of turbulent combustion is studied experimentally using line images obtained in turbulent partially premixed methane flames (Sandia flames D and E). Cross-stream filtering is employed to obtain the FMDF and other filtered variables. The means of the FMDF conditional on the subgrid-scale (SGS) scalar variance at a given location are found to vary from close to Gaussian to bimodal, indicating well-mixed and non-premixed SGS mixing regimes, respectively. The bimodal SGS scalar has a structure (ramp-cliff) similar to the counter-flow model for laminar flamelets. Therefore, while the burden on mixing models to predict the well-mixed SGS scalar is expected to lessen with decreasing filter scale, the burden to predict the bimodal one is not. These SGS scalar structures can result in fluctuations of the SGS flame structure between distributed reaction zones and laminar flamelets, but for reasons different from the scalar dissipation rate fluctuations associated with the turbulence cascade. Furthermore, the bimodal SGS scalar contributes a significant amount of the scalar dissipation in the reaction zones, highlighting its importance and the need for mixing models to predict the bimodal FMDFs. © 2006 The Combustion Institute. Published by Elsevier Inc. All rights reserved.

Direct numerical simulation of a three-dimensional spatially developing turbulent slot-burner Bunsen flame has been performed with a new reduced methane-air mechanism. The mechanism, derived from sequential application of directed relation graph theory, sensitivity analysis and computational singular perturbation over the GRI-1.2 detailed mechanism is non-stiff and tailored to the lean conditions of the DNS. The simulation is performed for three flow through times, long enough to achieve statistical stationarity. The turbulence parameters have been chosen such that the combustion occurs in the thin reaction zones regime of premixed combustion. The data is analyzed to study possible influences of turbulence on the structure of the preheat and reaction zones. The results show that the mean thickness of the turbulent flame, based on progress variable gradient, is greater than the corresponding laminar flame. The effects of flow straining and flame front curvature on the mean flame thickness are quantified through conditional means of the thickness and by examining the balance equation for the evolution of the flame thickness. Finally, conditional mean reaction rate of key species compared to the laminar reaction rate profiles show that there is no significant perturbation of the heat release layer.

Combinatorial algorithms have long played a crucial, albeit under-recognized role in scientific computing. This impact ranges well beyond the familiar applications of graph algorithms in sparse matrices to include mesh generation, optimization, computational biology and chemistry, data analysis and parallelization. Trends in science and in computing suggest strongly that the importance of discrete algorithms in computational science will continue to grow. This paper reviews some of these many past successes and highlights emerging areas of promise and opportunity. © Springer-Verlag Berlin Heidelberg 2007.

Laboratory experiments on the interaction of a plasma flow, produced by laser ablation of a solid target with the inhomogeneous magnetic field from the Zebra pulsed power generator demonstrated the presence of strong wave activity in the region of the flow deceleration. The deceleration of the plasma flow can be interpreted as the appearance of a gravity-like force. The drift due to this force can lead to the excitation of flute modes. In this paper a linear dispersion equation for the excitation of electromagnetic flute-type modes with plasma and magnetic field parameters, corresponding to the ongoing experiments is examined. Results indicate that the wavelength of the excited flute modes strongly depends on the strength of the external magnetic field. For magnetic field strengths ∼ 0.1 MG the excited wavelengths are larger than the width of the laser ablated plasma plume and cannot be observed during the experiment. But for magnetic field strengths ∼ 1 MG the excited wavelengths are much smaller and can then be detected. © Springer Science+Business Media B.V. 2007.

Atomistic models of the Si(1 0 0)/SiO2 interface were generated using a classical reactive force field, and subsequently optimized using density functional theory. The interfaces consist of amorphous oxide bound to crystalline silicon substrate. Each system has a sub-oxide layer of partially oxidized silicon atoms at the interface, and a distribution of oxygen-deficient centers in the oxide. Both periodic and slab configurations are considered. © 2006.

Oxygen/carbon dioxide recycle coal combustion is actively being investigated because of its potential to facilitate CO2 sequestration and to achieve emission reductions. In the work reported here, the effect of enhanced oxygen levels and CO2 bath gas is independently analyzed for their influence on single-particle pulverized coal ignition of a U.S. eastern bituminous coal. The experiments show that the presence of CO2 and a lower O2 concentration increase the ignition delay time but have no measurable effect on the time required to complete volatile combustion, once initiated. For the ignition process observed in the experiments, the CO 2 results are explained by its higher molar specific heat and the O2 results are explained by the effect of O2 concentration on the local mixture reactivity. Particle ignition and devolatilization properties in a mixture of 30% O2 in CO2 are very similar to those in air.

A 70-MA, 7-MV, ∼100-ns driver for a Z-pinch Inertial Fusion Energy (Z-IFE) power plant has been proposed. In this summary we address the transition region between the 70 Linear Transformer Driver (LTD) modules and the center Recyclable Transmission Line (RTL) load section, which convolves from the coaxial vacuum Magnetically Insulated Transmission Lines (MITL) to a parallel tri-plate and then a bi-plate disk feed. An inductive annular chamber terminates one side of the tri-plate in a manner that preserves vacuum and electrical circuit integrity without significant energy losses. The simplicity is offset by the disadvantage of the chamber size, which is proportional to the driver impedance and decreases with the addition of more parallel modules. Inductive isolation chamber sizes are estimated in this paper, based on an optimized LTD equivalent circuit simulation source driving a matched load using transmission line models. We consider the trade-offs between acceptable energy loss and the size of the inductive isolation chamber; accepting a 6% energy loss would only require a 60-nH chamber.

Numerous molecular dynamics simulation studies of radiation cascades in Si have elucidated many of the general features of the initial defect production. However, the resulting defect structures have been analyzed with techniques that are not sensitive to changes in the local bonding topology. Here the results of analyzing the ring content in Si cascades, in addition to more traditional defect characterization such as Wigner-Seitz cell analysis, will be presented for recoil energies ranging from 25 eV up to 25 keV. The ring content of local amorphous regions in the cascades will be compared to the ring content in simulations of bulk amorphous Si. The number of atoms in the amorphous regions and the number of point defects as a function of recoil energy are determined. © 2006 Elsevier B.V. All rights reserved.

This paper focuses on the application of the large eddy simulation (LES) technique to a swirling particle-laden flow in a model combustion chamber. A series of calculations have been performed and compared directly with detailed experimental measurements. The computational domain identically matches the laboratory configuration, which effectively isolates effects related to dilute particle dispersion and momentum coupling. Results highlight the predictive capabilities of LES when implemented with the appropriate numerics, grid resolution (as dictated by the class of models employed) and well-defined boundary conditions. The case study provides a clearer understanding of the effectiveness and feasibility of current state-of-the-art models and a quantitative understanding of relevant modeling issues by analyzing the characteristic parameters and scales of importance. The novel feature of the results presented is that they establish a baseline level of confidence in our ability to simulate complex flows at conditions representative of those typically observed in gas-turbine (and similar) combustors. © 2006 The Combustion Institute. Published by Elsevier Inc. All rights reserved.

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In this paper, the term tensor refers simply to a multidimensional or N-way array, and we consider how specially structured tensors allow for efficient storage and computation. First, we study sparse tensors, which have the property that the vast majority of the elements are zero. We propose storing sparse tensors using coordinate format and describe the computational efficiency of this scheme for various mathematical operations, including those typical to tensor decomposition algorithms. Second, we study factored tensors, which have the property that they can be assembled from more basic components. We consider two specific types: A Tucker tensor can be expressed as the product of a core tensor (which itself may be dense, sparse, or factored) and a matrix along each mode, and a Kruskal tensor can be expressed as the sum of rank-1 tensors. We are interested in the case where the storage of the components is less than the storage of the full tensor, and we demonstrate that many elementary operations can be computed using only the components. All of the efficiencies described in this paper are implemented in the Tensor Toolbox for MATLAB. © 2007 Society for Industrial and Applied Mathematics.

MFI zeolite membranes have been synthesized on tubular α-alumina substrates to investigate the separation of p-xylene (PX) from m-xylene (MX) and o-xylene (OX) in multicomponent mixtures and ranges of feed pressure and operating temperature. 1,3,5-triisopropylbenzene was added to the feed stream for online membrane modification. Separation of PX from MX and OX through the MFI membranes relies primarily on shape-selectivity when the xylene sorption level in the zeolite is sufficiently low. For an eight-component mixture containing hydrogen, hydrocarbons, PX, MX, and OX, PX/(MX+OX) selectivity of 7.71 with PX flux of 6.8×10-6mol/m2.s was obtained at 250°C and atmospheric feed pressure. © 2007 Elsevier B.V. All rights reserved.

Evaluating the performance of finite-difference algorithms typically uses a technique known as von Neumann analysis. For a given algorithm, application of the technique yields both a dispersion relation valid for the discrete time-space grid and a mathematical condition for stability. In practice, a major shortcoming of conventional von Neumann analysis is that it can be applied only to an idealized numerical model - that of an infinite, homogeneous whole space. Experience has shown that numerical instabilities often arise in finite-difference simulations of wave propagation at interfaces with strong material contrasts. These interface instabilities occur even though the conventional von Neumann stability criterion may be satisfied at each point of the numerical model. To address this issue, I generalize von Neumann analysis for a model of two half-spaces. I perform the analysis for the case of acoustic wave propagation using a standard staggered-grid finite-difference numerical scheme. By deriving expressions for the discrete reflection and transmission coefficients, I study under what conditions the discrete reflection and transmission coefficients become unbounded. I find that instabilities encountered in numerical modeling near interfaces with strong material contrasts are linked to these cases and develop a modified stability criterion that takes into account the resulting instabilities. I test and verify the stability criterion by executing a finite-difference algorithm under conditions predicted to be stable and unstable. © 2007 Society of Exploration Geophysicists.

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We report what is believed to be the first application of coherent anti-Stokes Raman scattering (CARS) to full-scale fire testing. A CARS instrument has been constructed at the newly commissioned FLAME (Fire Laboratory for Accreditation of Models and Experiments) facility at Sandia, where the CARS system has been used for thermometry in 2-m-diameter, turbulent methanol pool fires. Fielding of CARS in such a large-scale facility presents several challenges, including long-distance propagation of laser beams, shielding of optics from intense heat, the impact of beam steering and fiber-optic coupling of the CARS signal to remotely located detection equipment. The details of a CARS instrument that meets these challenges are presented, along with the construction of the unique new FLAME facility itself, which has been designed to accommodate optical and laser-based diagnostics to full-scale fire experimentation. The performance of the CARS instrument is investigated in a premixed methane-air flat flame to estimate the precision in single-shot CARS temperatures. Single-shot CARS spectra and best-fit temperatures from a methanol pool fire are presented, and an estimate of the pdf of the temperature fluctuations from the pool-fire environment is obtained.

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This paper examined the high frequency time harmonic localization of modal fields in two dimensional cavities along unstable periodic orbits. The elliptic formalism, combined with the random phase approach, allowed the treatment of both convex and concave boundary geometries.

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It is shown that for any material or structural model expressible as a Masing model, there exists a unique parallel-series (displacement-based) Iwan system that characterizes that model as a function of displacement history. This poses advantages both in terms of more convenient force evaluation in arbitrary deformation histories as well as in terms of model inversion. Characterization as an Iwan system is demonstrated through the inversion of the Ramberg-Osgood model, a force(stress)-based material model that is not explicitly invertible. An implication of the inversion process is that direct, rigorous comparisons of different Masing models, regardless of the ability to invert their constitutive relationship, can be achieved through the comparison of their associated Iwan distribution densities.

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