Publications

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A finite temperature version of 'exact-exchange' density functional theory (EXX) has been implemented in Sandia's Socorro code. The method uses the optimized effective potential (OEP) formalism and an efficient gradient-based iterative minimization of the energy. The derivation of the gradient is based on the density matrix, simplifying the extension to finite temperatures. A stand-alone all-electron exact-exchange capability has been developed for testing exact exchange and compatible correlation functionals on small systems. Calculations of eigenvalues for the helium atom, beryllium atom, and the hydrogen molecule are reported, showing excellent agreement with highly converged quantumMonte Carlo calculations. Several approaches to the generation of pseudopotentials for use in EXX calculations have been examined and are discussed. The difficult problem of finding a correlation functional compatible with EXX has been studied and some initial findings are reported.

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Microelectromechanical systems (MEMS) will play an important functional role in future DOE weapon and Homeland Security applications. If these emerging technologies are to be applied successfully, it is imperative that the long-term degradation of the materials of construction be understood. Unlike electrical devices, MEMS devices have a mechanical aspect to their function. Some components (e.g., springs) will be subjected to stresses beyond whatever residual stresses exist from fabrication. These stresses, combined with possible abnormal exposure environments (e.g., humidity, contamination), introduce a vulnerability to environmentally assisted cracking (EAC). EAC is manifested as the nucleation and propagation of a stable crack at mechanical loads/stresses far below what would be expected based solely upon the materials mechanical properties. If not addressed, EAC can lead to sudden, catastrophic failure. Considering the materials of construction and the very small feature size, EAC represents a high-risk environmentally induced degradation mode for MEMS devices. Currently, the lack of applicable characterization techniques is preventing the needed vulnerability assessment. The objective of this work is to address this deficiency by developing techniques to detect and quantify EAC in MEMS materials and structures. Such techniques will allow real-time detection of crack initiation and propagation. The information gained will establish the appropriate combinations of environment (defining packaging requirements), local stress levels, and metallurgical factors (composition, grain size and orientation) that must be achieved to prevent EAC.

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Microfluidic devices have been proposed for 'Lab-on-a-Chip' applications for nearly a decade. Despite the unquestionable promise of these devices to allow rapid, sensitive and portable biochemical analysis, few practical devices exist. It is often difficult to adapt current laboratory techniques to the microscale because bench-top methods use discrete liquid volumes, while most current microfluidic devices employ streams of liquid confined in a branching network of micron-scale channels. The goal of this research was to use two phase liquid flows, creating discrete packets of liquid. Once divided into discrete packets, the packets can be moved controllably within the microchannels without loss of material. Each packet is equivalent to a minute test tube, holding a fraction from a separation or an aliquot to be reacted. We report on the fabrication of glass and PDMS (polydimethylsiloxane) devices that create and store packets.

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This project focused on research and algorithmic development in optimization under uncertainty (OUU) problems driven by earth penetrator (EP) designs. While taking into account uncertainty, we addressed three challenges in current simulation-based engineering design and analysis processes. The first challenge required leveraging small local samples, already constructed by optimization algorithms, to build effective surrogate models. We used Gaussian Process (GP) models to construct these surrogates. We developed two OUU algorithms using 'local' GPs (OUU-LGP) and one OUU algorithm using 'global' GPs (OUU-GGP) that appear competitive or better than current methods. The second challenge was to develop a methodical design process based on multi-resolution, multi-fidelity models. We developed a Multi-Fidelity Bayesian Auto-regressive process (MF-BAP). The third challenge involved the development of tools that are computational feasible and accessible. We created MATLAB{reg_sign} and initial DAKOTA implementations of our algorithms.

Representatives from the U.S. Department of Energy, the National Nuclear Security Administration, and Sandia National Laboratories met with mid-level representatives from Iraq's oil and gas companies and with former employees and senior managers of Iraq's Ministry of Oil September 3-5 in Amman, Jordan. The goals of the workshop were to assess the needs of the Iraqi Oil Ministry and industry, to provide information about capabilities at DOE and the national laboratories relevant to Iraq, and to develop ideas for potential projects.

In this late-start Tier I Seniors Council sponsored LDRD, we have designed, simulated, microfabricated, packaged, and tested ion traps to extend the current quantum simulation capabilities of macro-ion traps to tens of ions in one and two dimensions in monolithically microfabricated micrometer-scaled MEMS-based ion traps. Such traps are being microfabricated and packaged at Sandia's MESA facility in a unique tungsten MEMS process that has already made arrays of millions of micron-sized cylindrical ion traps for mass spectroscopy applications. We define and discuss the motivation for quantum simulation using the trapping of ions, show the results of efforts in designing, simulating, and microfabricating W based MEMS ion traps at Sandia's MESA facility, and describe is some detail our development of a custom based ion trap chip packaging technology that enables the implementation of these devices in quantum physics experiments.

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Typical shock testing requirements specify shock pulses of several hundred to several thousand g's, with pulse duration usually less than a few milliseconds. A requirement to qualify a shipping container to a head-on tractortrailer crash environment led to the development of a new test technique capable of low-g (< 50 g), long-duration (> 100 ms) shock pulses. This technique utilizes nylon webbing engaged in tension to shape the pulse produced by the interaction of two sleds on an indoor track. A combination of experimental and computational methodology was used to successfully develop the test technique to solve a specific testing requirement. The process used to develop the test technique is emphasized in this paper, where a prudent balance between experiment and analysis resulted in a cost effective solution. The results show that the quasi-static load-elongation behavior of the nylon webbing can be used to adequately model the dynamic behavior of the webbing, allowing design of the experimental setup with a simple computational model. The quasi-static load-elongation measurements are described along with the development of the computational model. Results of a full-scale experiment are presented, showing that the required shock pulse could be achieved with this test technique.

Laser Doppler vibrometers (LDVs) have become the standard for out-of-plane velocity measurement because they are non-contacting, have wide signal bandwidth and high resolution, and are relatively easy to use. A typical drawback of LDVs is their limitation to single point measurements. This limitation is mitigated by scanning technology, but at the cost of the time required to sample all the points on a surface and the inability to measure transient, non-repetitive events. A more proficient alternative is a Widefield LDV (WLDV), which heterodynes the Doppler frequency down from the typical MHz range (depending on velocity) to the kHz range. In WLDV, the modulated signal is detected via a high-speed CMOS camera and the optimum modulation signal is calculated from a measured velocity on the target obtained with a traditional single point LDV. This paper will present preliminary lab results of a full-field velocity animation obtained using a WLDV system to measure the velocity of a block on a turntable. A comparison highlighting the similarities and differences of similar systems, such as Temporal Speckle Pattern Interferometry and traditional LDV is discussed.

Accurate material models are fundamental to predictive structural finite element models. Because potting foams are routinely used to mitigate shock and vibration of encapsulated components in mechanical systems, accurate material models of foams are needed. A linear-viscoelastic foam constitutive model has been developed to represent the foam's stiffness and damping throughout an application space defined by temperature, strain rate or frequency and strain level. Validation of this linear-viscoelastic model, which is integrated into the Saunas structural dynamics code, is achieved by modeling and testing a series of structural geometries of increasing complexity that have been designed to ensure sensitivity to material parameters. Both experimental and analytical uncertainties are being quantified to ensure the fair assessment of model validity. Quantitative model validation metrics are being developed to provide a means of comparison for analytical model predictions to observations made in the experiments. This paper is one of several parallel papers documenting the validation process for simple to complex structures with foam encapsulated components. This paper will describe the development of a linear-viscoelastic constitutive model for EF-AR20 epoxy foam with density, modulus, and damping uncertainties and apply the model to the simplest of the series of foam/component structural geometries for the calibration and validation of the constitutive model.

Based primarily on the results of a month-long experiment and a crisis management exercise, synchronous multimedia collaboration within a taskoriented, time-constrained distributed team appears to exhibit three layers of structure. The first layer is episodic, and results in collections of related multimedia collaboration artifacts that can be called "chapters" or "scenes" in the collaboration. The second layer is the multivalent nature of collaboration, in which collaboration conversations at multiple subgroup levels take place at the same time. The third, top-level, layer is the agenda that drives the collaboration. The implications for the design of synchronous collaboration systems are that multiple views, representations, and metaphors for this conversation structure are needed. Chapter views, subgroup views, and agenda views are presented as alternative packaging mechanisms and entry points into the collaboration data. Other metaphors and presentations include the collaboration tree and infinitely recursive conference room, as well as network graphs of subgroup structure and agenda-based group awareness. © 2006 IEEE.

Transmission electron microscopy has been used to image the tracks of high-energy 197Au +26 (374 MeV) and 127I +18 (241 MeV) ions incident in a nonchanneling direction through a prethinned specimen of hexagonal α-quartz (SiO 2). These ions have high electronic stopping powers in quartz, 24 and 19 keV/nm, respectively, which are sufficient to produce a disordered latent track. When the tracks are imaged with diffraction contrast using several different reciprocal lattice vectors, they exhibit a radial strain extending outward from their disordered centerline approximately 16 nm into the crystalline surroundings. The images are consistent with a radial strain field with cylindrical symmetry around the amorphous track, like that found in models developed to account for the lateral expansion of amorphous SiO 2 films produced by irradiation with high-energy ions. These findings provide an experimental basis for increased confidence in such modeling. © 2006 American Institute of Physics.

The growth of the flute-type instability for a field-aligned plasma column immersed in a uniform magnetic field is studied. Particle-in-cell simulations are compared with a semi-analytic dispersion analysis of the drift cyclotron instability in cylindrical geometry with a Gaussian density profile in the radial direction. For the parameters considered here, the dispersion analysis gives a local maximum for the peak growth rates as a function of R/r i, where R is the Gaussian characteristic radius and r i is the ion gyroradius. The electrostatic and electromagnetic particle-in-cell simulation results give azimuthal and radial mode numbers that are in reasonable agreement with the dispersion analysis. The electrostatic simulations give linear growth rates that are in good agreement with the dispersion analysis results, while the electromagnetic simulations yield growth rate trends that are similar to the dispersion analysis but that are not in quantitative agreement. These differences are ascribed to higher initial field fluctuation levels in the electromagnetic field solver. Overall, the simulations allow the examination of both the linear and nonlinear evolution of the instability in this physical system up to and beyond the point of wave energy saturation. © 2006 American Institute of Physics.

Cathodes for thermally activated ("thermal") batteries based on CoS2 and LiCl-LiBr-LiF electrolyte and FeS2 (pyrite) and LiCl-KCl eutectic were prepared by thermal spraying catholyte mixtures onto graphite-paper substrates. Composite separator-cathode deposits were also prepared in the same manner by sequential thermal spraying of LiCl-KCl-based separator material onto a pyrite-cathode substrate. These materials were then tested in single cells over a temperature range of 400-600 °C and in 5-cell and 15-cell batteries. A limited number of battery tests were conducted with the separator-cathode composites and plasma-sprayed Li(Si) anodes-the first report of an all-plasma-sprayed thermal battery. Thermal-spraying offers distinct advantages over conventional pressed-powder parts for fabrication of thin electrodes for short-life thermal batteries. The plasma-sprayed electrodes have lower impedances than the corresponding pressed-powder parts due to improved particle-particle contact. © 2006 Elsevier B.V. All rights reserved.

The last decade has seen significant interest in wide field of view (FOV) telescopes for sky survey and space surveillance applications. Prompted by this interest, a multitude of wide-field designs have emerged. While all designs result from optimization of competing constraints, one of the more controversial design choices is whether such telescopes require flat or curved focal planes. For imaging applications, curved focal planes are not an obvious choice. Thirty years ago with mostly analytic design tools, the solution to wide-field image quality appeared to be curved focal planes. Today however, with computer aided optimization, high image quality can be achieved over flat focal surfaces. For most designs, the small gains in performance offered by curved focal planes are more than offset by the complexities and cost of curved CCDs. Modern design techniques incorporating reflective and refractive correctors appear to make a curved focal surface an unnecessary complication. Examination of seven current, wide FOV projects (SDSS, MMT, DCT, LSST, PanStarrs, HyperSuprime and DARPA SST) suggests there is little to be gained from a curved focal plane. The one exception might be the HyperSuprime instrument where performance goals are severely stressing refractive prime-focus corrector capabilities.