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Viscoelastic material inversion using Sierra-SD and ROL

Walsh, Timothy; Aquino, Wilkins; Ridzal, Denis; Kouri, Drew P.; Van Bloemen Waanders, Bart; Urbina, Angel U.

In this report we derive frequency-domain methods for inverse characterization of the constitutive parameters of viscoelastic materials. The inverse problem is cast in a PDE-constrained optimization framework with efficient computation of gradients and Hessian vector products through matrix free operations. The abstract optimization operators for first and second derivatives are derived from first principles. Various methods from the Rapid Optimization Library (ROL) are tested on the viscoelastic inversion problem. The methods described herein are applied to compute the viscoelastic bulk and shear moduli of a foam block model, which was recently used in experimental testing for viscoelastic property characterization.

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TYPE SAND Report YEAR 2014
DOIOSTI

Active Control of Nitride Plasmonic Dispersion in the Far Infrared

Shaner, Eric A.; Dyer, Gregory C.; Seng, William F.; Bethke, Donald; Grine, Albert; Baca, Albert G.; Allerman, A.A.

We investigate plasmonic structures in nitride-based materials for far-infrared (IR) applications. The two dimensional electron gas (2DEG) in the GaN/AlGaN material system, much like metal- dielectric structures, is a patternable plasmonic medium. However, it also permits for direct tunability via an applied voltage. While there have been proof-of-principle demonstrations of plasma excitations in nitride 2DEGs, exploration of the potential of this material system has thus far been limited. We recently demonstrated coherent phenomena such as the formation of plasmonic crystals, strong coupling of tunable crystal defects to a plasmonic crystal, and electromagnetically induced transparency in GaAs/AlGaAs 2DEGs at sub-THz frequencies. In this project, we explore whether these effects can be realized in nitride 2DEG materials above 1 THz and at temperatures exceeding 77 K.

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TYPE SAND Report YEAR 2014
DOIOSTI

Ultrafast Laser Diagnostics for Energetic-Material Ignition Mechanisms: Tools for Physics-Based Model Development

Kearney, Sean P.; Jilek, Brook A.; Kohl, Ian T.; Farrow, Darcie; Urayama, Junji

We present the results of an LDRD project to develop diagnostics to perform fundamental measurements of material properties during shock compression of condensed phase materials at micron spatial scales and picosecond time scales. The report is structured into three main chapters, which each focus on a different diagnostic devel opment effort. Direct picosecond laser drive is used to introduce shock waves into thin films of energetic and inert materials. The resulting laser - driven shock properties are probed via Ultrafast Time Domain Interferometry (UTDI), which can additionally be used to generate shock Hugoniot data in tabletop experiments. Stimulated Raman scattering (SRS) is developed as a temperature diagnostic. A transient absorption spectroscopy setup has been developed to probe shock - induced changes during shock compressio n. UTDI results are presented under dynamic, direct - laser - drive conditions and shock Hugoniots are estimated for inert polystyrene samples and for the explosive hexanitroazobenzene, with results from both Sandia and Lawrence Livermore presented here. SRS a nd transient absorption diagnostics are demonstrated on static thin - film samples, and paths forward to dynamic experiments are presented.

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TYPE SAND Report YEAR 2014
DOIOSTI

Design Process Overview

Halkjaer-Knudsen, Vibeke N.

For the purposes of this paper, a Biocontainment facility is a laboratory, production facility, or similar building that handles contagious biological materials in a safe and responsible manner. This specialized facility, also called a containment facility or a high containment facility reduces the potential for biological agents to be released into the environment, provides a safe work environment for the employees, and supports good laboratory practices.

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TYPE Other Report YEAR 2014
DOIOSTI

Precision circuit calculations in hostile environments

Sandia journal manuscript; Not yet accepted for publication

Hembree, Charles; Keiter, Eric R.

Sensing and calculating electronic systems with stringent accuracy requirements use internal standard voltages for references. Conceptually, this is related to using some unit measurement for counting any quantity. The high precision electronic components used in systems in the nation’s stockpile also make use of these standard voltages. The need for stable voltage references has been long-standing in the overall electronics industry. For many applications, the most pressing need is for stability of a reference voltage as the circuit temperature varies. Typical circuit components have temperature coefficients for their operational characteristics that are given in some delta per degree centigrade and these coefficients can be either positive or negative. Thus, it is natural to consider building a circuit out of components that have complementary temperature coefficients so that the operating characteristics of the circuit have a net zero temperature coefficient. This is the fundamental basis of precision voltage reference (PVR) circuit operation and it is straightforward to extend this type of stabilization to reduce shifts caused by hostile environment radiation.

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TYPE Journal Article YEAR 2014
OSTI

Comparison of Aleph and BOLSIG+ Results for Electron-Nitrogen Chemistry

Hopkins, Matthew M.; Crozier, Paul; Moore, Christopher H.

The goal of this report is to document the current status of Aleph with regards to electron collisions under an electric field. Aleph and the community-accepted BOLSIG+ code are both used to compute reactions rates for a set of 25 electron-nitrogen interactions. A reasonable comparison is found (see below) providing evidence that Aleph is successfully simulating or implementing: (1) Particle-particle collision cross-sections via DSMC methodology, (2) Energy balance for simple particle interactions, and (3) Electron energy distribution function (EEDF) evolution

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TYPE SAND Report YEAR 2014
DOIOSTI

Adaptive Beam Smoothing with Plasma-Pinholes for Laser-Entrance-Hole Transmission Studies

Geissel, Matthias; Awe, Thomas J.; Campbell, Edward M.; Gomez, Matthew R.; Harding, Eric H.; Harvey-Thompson, Adam J.; Jennings, Christopher A.; Kimmel, Mark; Lewis, Sean M.; Mcbride, Ryan; Peterson, K.J.; Schollmeier, Marius; Sefkow, Adam B.; Shores, Jonathon; Sinars, Daniel; Slutz, Stephen A.; Smith, Ian C.; Speas, Christopher S.; Stahoviak, John W.; Porter, John L.

Abstract not provided.

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TYPE Conference Poster YEAR 2014
OSTI
Results 50601–50700 of 99,299
Results 50601–50700 of 99,299