Publications

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Most test methodologies referenced in this Test Definition and Test Procedures were designed by Sandia specifically for geophysical instrumentation evaluation. When appropriate, test instrumentation calibration is traceable to the National Institute for Standards Technology (NIST).

This Test Definition for the Evaluation of Digitizing Waveform Recorders (DWR) defines the process that can be performed as part of the evaluation and testing of geophysical sensors, digitizers, sensor subsystems and geophysical station/array systems. The objectives are to (1) evaluate the overall technical performance of the DWR, measure the distortions introduced by the high resolution digitizers and provide a performance check of the internal calibrator if provided and (2) evaluate the technical performance of the DWR for a specific sensor application. The results of these evaluations can be compared to the manufacturer's specifications and any relevant application requirements or specifications.

Most test methodologies referenced in this Test Definition and Test Procedures were designed by Sandia specifically for geophysical instrumentation evaluation. When appropriate, test instrumentation calibration is traceable to the National Institute for Standards Technology (NIST). The objectives are to evaluate the overall technical performance of the infrasound sensor. The results of these evaluations can be compared to the manufacturer's specifications and any relevant application requirements or specifications.

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We report a semiconductor based mechanism for electrically controlling the frequency of light transmitted through extraordinary optical transmission gratings. In doing so, we demonstrate active control over the surface plasmon (SP) resonance at the metal/dielectric interface. The gratings, designed to operate in the midinfrared spectral range, are fabricated upon a doped GaAs epilayer. Tuning of over 25 cm{sup -1} is achieved, and the devices are modeled to investigate the physical origin of the tuning mechanism. Though our structures are designed for the midinfrared, the tuning mechanism demonstrated could be applied to other wavelength ranges, especially the visible and near infrared.

The Divertor Materials Evaluation System (DiMES) at General Atomics has successfully advanced the understanding of plasma surface interaction phenomena involving ITER-relevant materials and has been utilized for advanced diagnostic designs in the lower divertor of DIII-D. This paper describes a series of recent successful experiments. These include the study of carbon deposition in gaps and metallic mirrors as a function of temperature, study of dust migration from the divertor, study of methane injection in order to benchmark chemical sputtering diagnostics, and the measurement of charge exchange neutrals with a hydrogen sensor. In concert with the modification of the lower divertor of DIII-D, the DiMES sample vertical location was modified to match the raised divertor floor. The new Mid-plane Material Exposure Sample (MiMES) design will also be presented. MiMES will allow the study and measurement of erosion and redeposition of material at the outboard mid-plane of DIII-D, including effects from convective transport. We will continue to expose relevant materials and advanced diagnostics to different plasma configurations under various operational regimes, including material erosion and redeposition experiments, and gaps and mirror exposures at elevated temperature. © 2007 Elsevier B.V. All rights reserved.

XRD analysis of plasma-vapor-deposited ErT2 films during aging (T decay to He3) reveals an hkl-dependent unit-cell expansion in which (200) grains expand out-of-plane as much as 0.01 Å more than (111) out-of-plane grains. Texture analysis of an aged ErT2 film reveals a bimodal (111)/(200) out-of-plane preferred orientation. Sin2 ψ analysis reveals significant in-plane macro-strain due to He3 bubble formation/growth. The mechanistic origins regarding these observations are also discussed. © 2007 International Centre for Diffraction Data.

We present a reformulation of the Bayesian approach to inverse problems, that seeks to accelerate Bayesian inference by using polynomial chaos (PC) expansions to represent random variables. Evaluation of integrals over the unknown parameter space is recast, more efficiently, as Monte Carlo sampling of the random variables underlying the PC expansion. We evaluate the utility of this technique on a transient diffusion problem arising in contaminant source inversion. The accuracy of posterior estimates is examined with respect to the order of the PC representation, the choice of PC basis, and the decomposition of the support of the prior. The computational cost of the new scheme shows significant gains over direct sampling. © 2006 Elsevier Inc. All rights reserved.

We present a theory for size-dependent shapes of Pb nanoprecipitates in Al, introducing the concept of "magic shapes," i.e., shapes having near-zero homogeneous elastic strains. Our quantitative atomistic calculations of edge energies show their effect on precipitate shape to be negligible, thus it appears that shapes must be due to the combined effect of strain and interface energies. By employing an algorithm for generating magic shapes, we replicate the experimental observations by selecting magic-shape precipitates with interfacial energies less than a cutoff value. © 2007 The American Physical Society.

In this paper, relative integrated cross sections are measured for spin-orbit-conserving, rotationally inelastic scattering of NO (²Π_1/2), hexapole-selected in the upper Λ-doublet level of the ground rotational state (j = 0.5), in collisions with D₂ at a nominal energy of 551 cm^-1. The final state of the NO molecule is detected by laser-induced fluorescence (LIF). The state-selected NO molecule is oriented with either the N end or the O end toward the incoming D₂ molecule by application of a static electric field E in the scattering region. This field is directed parallel or antiparallel to the relative velocity vector v. Comparison of signals taken for the different applied field directions gives the experimental steric asymmetry SA, defined by SA = (σ_v↑↓E - σ_v↑↑E)/(σ_v↑↓E + σ_v↑↑E), which is equal to within a factor of -1 to the molecular steric effect, S_i→f ≡ (σ_D2→NO - σ_D2→ON)/(σ_D2→NO + σ_D2→ON). The dependence of the integral inelastic cross section on the incoming Λ-doublet component is also measured as a function of the final rotational (j_final) and Λ-doublet (ε_final) state. The measured steric asymmetries are similar to those previously observed for NO-He scattering. Spin-orbit manifold-conserving collisions exhibit a larger propensity for parity conservation than their NO-He counterparts. The results are interpreted in the context of the recently developed quasi-quantum treatment (QQT) of rotationally inelastic scattering. The QQT predictions can be inverted to obtain a fitted hard-shell potential that reproduces the experimental steric asymmetry; this fitted potential gives an empirical estimate of the anisotropy of the repulsive interaction between NO and D₂. Finally, QQT computation of the differential cross section using this simple model potential shows reasonable agreement with the measured differential cross sections.

RADTRAN is a program and code for calculating the risks of transporting radioactive materials. The first versions of the program, RADTRAN I and II, were developed for NUREG-0170 (USNRC, 1977), the first environmental impact statement on transportation of radioactive materials. RADTRAN and its associated software have undergone a number of improvements and advances consistent with improvements in computer technology.