Publications

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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.

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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.

This paper investigates the performance of tensor methods for solving small-to large-scale systems of nonlinear equations where the Jacobian matrix at the root is ill-conditioned or singular. This condition occurs on many classes of problems, such as identifying or approaching turning points in path-following problems. The singular case has been studied more than the highly ill-conditioned case, for both Newton and tensor methods. It is known that Newton-based methods do not work well with singular problems because they converge linearly to the solution and, in some cases, with poor accuracy. On the other hand, direct tensor methods have performed well on singular problems and have superlinear convergence on such problems under certain conditions. This behavior originates from the use of a special, restricted form of the second-order term included in the local tensor model that provides information lacking in a (nearly) singular: Jacobian. With several implementations available for large-scale problems, tensor: methods now are capable oi solving larger problems. We compare the performance of tensor methods and Newton-based methods for small-to large-scale problems over a range of conditionings, from well-conditioned to ill-conditioned to singular. Previous studies with tensor methods concerned only the ends of this spectrum. Our results show that tensor methods are increasingly superior to Newton-based methods as the problem grows more ill-conditioned. © 2007 Society for Industrial and Applied Mathematics.

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.