To provide input to numerical models for hazard and vulnerability analyses, thermal decomposition of eight polymers has been examined in both nitrogen and air atmospheres. Experiments have been done with poly(methyl methacrylate), poly(diallyl phthalate), Norwegian spruce, polyvinyl chloride), polycarbonate, poly(phenylene sulphide), and two polyurethanes. Polymers that formed a substantial amount of carbonaceous char during decomposition in a nitrogen atmosphere were completely consumed in an air atmosphere. However, in the case of polyurethanes, complete consumption did not occur until temperatures of 700° C or higher. Furthermore, to varying degrees, the presence of oxygen appeared to alter the decomposition processes in all of the materials studied.
The deployment of optical fibers in adverse radiation environments, such as those encountered in a low-Earth-orbit space setting, makes critical the development of an understanding of the effect of large accumulated ionizing-radiation doses on optical components and systems. In particular, gamma radiation is known to considerably affect the performance of optical components by inducing absorbing centers in the materials. Such radiation is present both as primary background radiation and as secondary radiation induced by proton collisions with space-craft material. This paper examines the effects of gamma radiation on erbium-, ytterbium-, and Yb/Er co-doped optical fibers by exposing a suite of such fibers to radiation from a Co-60 source over long periods of time while monitoring the temporal and spectral decrease in transmittance of a reference signal. For same total doses, results show increased photodarkening in erbium-doped fibers relative to ytterbium-doped fibers, as well as significant radiation resistance of the co-doped fibers over wavelengths of 1.0-1.6 microns. All three types of fibers were seen to exhibit dose-rate dependences.
A firing set capable of charging a 0.05 μF capacitor to 1.7 kV is constructed using a 2.5 mm diameter Series Connected Photovoltaic Array (SCPA) in lieu of a transformer as the method of high voltage generation. The source of illumination is a fiber coupled 3 W 808 nm laser diode. This paper discusses the performance and PSpice modeling of an SCPA used in a firing set application.
Split grating-gate field effect transistors (FETs) detectors made from high mobility quantum well two-dimensional electron gas material have been shown to exhibit greatly improved tunable resonant photoresponse compared to single grating-gate detectors due to the formation of a 'diode-like' element by the split-gate structure. These detectors are relatively large for FETs (1mm × 1mm area or larger) to match typical focused THz beam spot sizes. In the case where the focused THz spot size is smaller than the detector area, we have found evidence, through positional scanning of the detector element, that only a small portion of the detector is active. To further investigate this situation, detectors with the same channel width (1mm), but various channel lengths, were fabricated and tested. The results indicate that indeed, only a small portion of the split grating gated FET is active. This finding opens up the possibility for further enhancement of detector sensitivity by increasing the active area.
Sandia National Laboratories has developed a means of manufacturing high precision aspheric lenslet arrays turned on-center. An innovative chucking and indexing mechanism was designed and implemented which allows the part to be indexed in two orthogonal directions parallel to the spindle face. This system was designed to meet a need for center to center positioning of 2μm and form error of λ/10. The part utilizes scribed orthogonal sets of grooves that locate the part on the chuck. The averaging of the grooves increases the repeatability of the system. The part is moved an integral number of grooves across the chuck by means of a vacuum chuck on a tool post that is mated to the part and holds the part while the chuck repositions to receive the part. The current setup is designed to create as many as 169 lenslets distributed over a 3mm square area while holding a true position tolerance of 1μm for all lenslets.
The rapid autonomous detection of pathogenic microorganisms and bioagents by field deployable platforms is critical to human health and safety. To achieve a high level of sensitivity for fluidic detection applications, we have developed a 330 MHz Love wave acoustic biosensor on 36° YX Lithium Tantalate (LTO). Each die has four delay-line detection channels, permitting simultaneous measurement of multiple analytes or for parallel detection of single analyte containing samples. Crucial to our biosensor was the development of a transducer that excites the shear horizontal (SH) mode, through optimization of the transducer, minimizing propagation losses and reducing undesirable modes. Detection was achieved by comparing the reference phase of an input signal to the phase shift from the biosensor using an integrated electronic multi-readout system connected to a laptop computer or PDA The Love wave acoustic arrays were centered at 330 MHz, shifting to 325-328 MHz after application of the silicon dioxide waveguides. The insertion loss was -6 dB with an out-of-band rejection of 35 dB. The amplitude and phase ripple were 2.5 dB p-p and 2-3° pp, respectively. Time-domain gating confirmed propagation of the SH mode while showing suppression of the triple transit. Antigen capture and mass detection experiments demonstrate a sensitivity of 7.19 ± 0.74° mm2/ ng with a detection limit of 6.7 ± 0.40 pg / mm2 for each channel.
Parallel adaptive mesh refinement methods potentially lead to realistic modeling of complex three-dimensional physical phenomena. However, they also present significant challenges in data partitioning and load balancing. As the mesh adapts to the solution, the partitioning requirements change. By explicitly considering these dynamic conditions, the scalability for large, realistic simulations could possibly be significantly improved. Our hypothesis is that adaptive partitioning, meaning dynamic and automatic switching of partitioning techniques, based on the current run-time state, can be beneficial for these simulations. However, switching partitioners can be expensive due to differences in the algorithms' native mapping of data onto processors. We suggest forcing a uniform starting point for all included partitioners. We present a penalty-based method for determining whether switching is beneficial. We study the effects on data migration, as well as on overall cost, of using the uniform starting point and the switching-penalties to select the best partitioning algorithm, among a set of graph-based and geometric partitioning algorithms, for each adaptive time-step for four different adaptive scientific applications. The results show that data migration can be significantly reduced and that adaptive partitioning indeed can be effective for unstructured adaptive applications.
We have developed a system of differential-output monitors that diagnose current and voltage in the vacuum section of a 20-MA 3-MV pulsed-power accelerator. The system includes 62 gauges: 3 current and 6 voltage monitors that are fielded on each of the accelerator's 4 vacuum-insulator stacks, 6 current monitors on each of the accelerator's 4 outer magnetically insulated transmission lines (MITLs), and 2 current monitors on the accelerator's inner MITL. The inner-MITL monitors are located 6 cm from the axis of the load. Each of the stack and outer-MITL current monitors comprises two separate B-dot sensors, each of which consists of four 3-mm-diameter wire loops wound in series. The two sensors are separately located within adjacent cavities machined out of a single piece of copper. The high electrical conductivity of copper minimizes penetration of magnetic flux into the cavity walls, which minimizes changes in the sensitivity of the sensors on the 100-ns time scale of the accelerator's power pulse. A model of flux penetration has been developed and is used to correct (to first order) the B-dot signals for the penetration that does occur. The two sensors are designed to produce signals with opposite polarities; hence, each current monitor may be regarded as a single detector with differential outputs. Common-mode-noise rejection is achieved by combining these signals in a 50-{Omega} balun. The signal cables that connect the B-dot monitors to the balun are chosen to provide reasonable bandwidth and acceptable levels of Compton drive in the bremsstrahlung field of the accelerator. A single 50-{omega} cable transmits the output signal of each balun to a double-wall screen room, where the signals are attenuated, digitized (0.5-ns/sample), numerically compensated for cable losses, and numerically integrated. By contrast, each inner-MITL current monitor contains only a single B-dot sensor. These monitors are fielded in opposite-polarity pairs. The two signals from a pair are not combined in a balun; they are instead numerically processed for common-mode-noise rejection after digitization. All the current monitors are calibrated on a 76-cm-diameter axisymmetric radial transmission line that is driven by a 10-kA current pulse. The reference current is measured by a current-viewing resistor (CVR). The stack voltage monitors are also differential-output gauges, consisting of one 1.8-cm-diameter D-dot sensor and one null sensor. Hence, each voltage monitor is also a differential detector with two output signals, processed as described above. The voltage monitors are calibrated in situ at 1.5 MV on dedicated accelerator shots with a short-circuit load. Faraday's law of induction is used to generate the reference voltage: currents are obtained from calibrated outer-MITL B-dot monitors, and inductances from the system geometry. In this way, both current and voltage measurements are traceable to a single CVR. Dependable and consistent measurements are thus obtained with this system of calibrated diagnostics. On accelerator shots that deliver 22 MA to a low-impedance z-pinch load, the peak lineal current densities at the stack, outer-MITL, and inner-MITL monitor locations are 0.5, 1, and 58 MA/m, respectively. On such shots the peak currents measured at these three locations agree to within 1%.
The authors have developed a chip-scale atomic clock (CSAC) for applications requiring atomic timing accuracy in portable battery-powered applications. At PTTI/FCS 2005, they reported on the demonstration of a prototype CSAC, with an overall size of 10 cm{sup 3}, power consumption > 150 mW, and short-term stability sy(t) < 1 x 10-9t-1/2. Since that report, they have completed the development of the CSAC, including provision for autonomous lock acquisition and a calibrated output at 10.0 MHz, in addition to modifications to the physics package and system architecture to improve performance and manufacturability.
Solute plumes are believed to disperse in a non-Fickian manner due to small-scale heterogeneity and variable velocities that create preferential pathways. In order to accurately predict dispersion in naturally complex geologic media, the connection between heterogeneity and dispersion must be better understood. Since aquifer properties can not be measured at every location, it is common to simulate small-scale heterogeneity with random field generators based on a two-point covariance (e.g., through use of sequential simulation algorithms). While these random fields can produce preferential flow pathways, it is unknown how well the results simulate solute dispersion through natural heterogeneous media. To evaluate the influence that complex heterogeneity has on dispersion, we utilize high-resolution terrestrial lidar to identify and model lithofacies from outcrop for application in particle tracking solute transport simulations using RWHet. The lidar scan data are used to produce a lab (meter) scale two-dimensional model that captures 2-8 mm scale natural heterogeneity. Numerical simulations utilize various methods to populate the outcrop structure captured by the lidar-based image with reasonable hydraulic conductivity values. The particle tracking simulations result in residence time distributions used to evaluate the nature of dispersion through complex media. Particle tracking simulations through conductivity fields produced from the lidar images are then compared to particle tracking simulations through hydraulic conductivity fields produced from sequential simulation algorithms. Based on this comparison, the study aims to quantify the difference in dispersion when using realistic and simplified representations of aquifer heterogeneity.
This paper presents the conceptual framework that is being used to define quantification of margins and uncertainties (QMU) for application in the nuclear weapons (NW) work conducted at Sandia National Laboratories. The conceptual framework addresses the margins and uncertainties throughout the NW life cycle and includes the definition of terms related to QMU and to figures of merit. Potential applications of QMU consist of analyses based on physical data and on modeling and simulation. Appendix A provides general guidelines for addressing cases in which significant and relevant physical data are available for QMU analysis. Appendix B gives the specific guidance that was used to conduct QMU analyses in cycle 12 of the annual assessment process. Appendix C offers general guidelines for addressing cases in which appropriate models are available for use in QMU analysis. Appendix D contains an example that highlights the consequences of different treatments of uncertainty in model-based QMU analyses.
An innovative helium3 high pressure gas detection system, made possible by utilizing Sandia's expertise in Micro-electrical Mechanical fluidic systems, is proposed which appears to have many beneficial performance characteristics with regards to making these neutron measurements in the high bremsstrahlung and electrical noise environments found in High Energy Density Physics experiments and especially on the very high noise environment generated on the fast pulsed power experiments performed here at Sandia. This same system may dramatically improve active WMD and contraband detection as well when employed with ultrafast (10-50 ns) pulsed neutron sources.
We present the results of a three year LDRD project which has focused on the development of novel, compact, ultraviolet solid-state sources and fluorescence-based sensing platforms that apply such devices to the sensing of biological and nuclear materials. We describe our development of 270-280 nm AlGaN-based semiconductor UV LEDs with performance suitable for evaluation in biosensor platforms as well as our development efforts towards the realization of a 340 nm AlGaN-based laser diode technology. We further review our sensor development efforts, including evaluation of the efficacy of using modulated LED excitation and phase sensitive detection techniques for fluorescence detection of bio molecules and uranyl-containing compounds.
A sulfuric acid catalytic decomposer section was assembled and tested for the Integrated Laboratory Scale experiments of the Sulfur-Iodine Thermochemical Cycle. This cycle is being studied as part of the U. S. Department of Energy Nuclear Hydrogen Initiative. Tests confirmed that the 54-inch long silicon carbide bayonet could produce in excess of the design objective of 100 liters/hr of SO{sub 2} at 2 bar. Furthermore, at 3 bar the system produced 135 liters/hr of SO{sub 2} with only 31 mol% acid. The gas production rate was close to the theoretical maximum determined by equilibrium, which indicates that the design provides adequate catalyst contact and heat transfer. Several design improvements were also implemented to greatly minimize leakage of SO{sub 2} out of the apparatus. The primary modifications were a separate additional enclosure within the skid enclosure, and replacement of Teflon tubing with glass-lined steel pipes.
The geometry of ray paths through realistic Earth models can be extremely complex due to the vertical and lateral heterogeneity of the velocity distribution within the models. Calculation of high fidelity ray paths and travel times through these models generally involves sophisticated algorithms that require significant assumptions and approximations. To test such algorithms it is desirable to have available analytic solutions for the geometry and travel time of rays through simpler velocity distributions against which the more complex algorithms can be compared. Also, in situations where computational performance requirements prohibit implementation of full 3D algorithms, it may be necessary to accept the accuracy limitations of analytic solutions in order to compute solutions that satisfy those requirements. Analytic solutions are described for the geometry and travel time of infinite frequency rays through radially symmetric 1D Earth models characterized by an inner sphere where the velocity distribution is given by the function V (r) = A-Br{sup 2}, optionally surrounded by some number of spherical shells of constant velocity. The mathematical basis of the calculations is described, sample calculations are presented, and results are compared to the Taup Toolkit of Crotwell et al. (1999). These solutions are useful for evaluating the fidelity of sophisticated 3D travel time calculators and in situations where performance requirements preclude the use of more computationally intensive calculators. It should be noted that most of the solutions presented are only quasi-analytic. Exact, closed form equations are derived but computation of solutions to specific problems generally require application of numerical integration or root finding techniques, which, while approximations, can be calculated to very high accuracy. Tolerances are set in the numerical algorithms such that computed travel time accuracies are better than 1 microsecond.
Mode-stirred chamber and anechoic chamber measurements were made on two sets of canonical test objects (cylindrical and rectangular) with varying numbers of thin slot apertures. The shielding effectiveness was compared to determine the level of correction needed to compensate the mode-stirred data to levels commensurate with anechoic data from the same test object.
Er(D,T){sub 2-x} {sup 3}He{sub x}, erbium di-tritide, films of thicknesses 500 nm, 400 nm, 300 nm, 200 nm, and 100 nm were grown and analyzed by Transmission Electron Microscopy, X-Ray Diffraction, and Ion Beam Analysis to determine variations in film microstructure as a function of film thickness and age, due to the time-dependent build-up of {sup 3}He in the film from the radioactive decay of tritium. Several interesting features were observed: One, the amount of helium released as a function of film thickness is relatively constant. This suggests that the helium is being released only from the near surface region and that the helium is not diffusing to the surface from the bulk of the film. Two, lenticular helium bubbles are observed as a result of the radioactive decay of tritium into {sup 3}He. These bubbles grow along the [111] crystallographic direction. Three, a helium bubble free zone, or 'denuded zone' is observed near the surface. The size of this region is independent of film thickness. Four, an analysis of secondary diffraction spots in the Transmission Electron Microscopy study indicate that small erbium oxide precipitates, 5-10 nm in size, exist throughout the film. Further, all of the films had large erbium oxide inclusions, in many cases these inclusions span the depth of the film.
The objectives of this project were to develop a new scientific tool for studies of chemical processes at the single molecule level, and to provide enhanced capabilities for multiplexed, ultrasensitive separations and immunoassays. We have combined microfluidic separation techniques with our newly developed technology for spectrally and temporally resolved detection of single molecules. The detection of individual molecules can reveal fluctuations in molecular conformations, which are obscured in ensemble measurements, and allows detailed studies of reaction kinetics such as ligand or antibody binding. Detection near the single molecule level also enables the use of correlation techniques to extract information, such as diffusion rates, from the fluorescence signal. The micro-fluidic technology offers unprecedented control of the chemical environment and flow conditions, and affords the unique opportunity to study biomolecules without immobilization. For analytical separations, the fluorescence lifetime and spectral resolution of the detection makes it possible to use multiple parameters for identification of separation products to improve the certainty of identification. We have successfully developed a system that can measure fluorescence spectra, lifetimes and diffusion constants of the components of mixtures separated in a microfluidic electrophoresis chip.
Veloce is a medium-voltage, high-current, compact pulsed power generator developed for isentropic and shock compression experiments. Because of its increased availability and ease of operation, Veloce is well suited for studying isentropic compression experiments (ICE) in much greater detail than previously allowed with larger pulsed power machines such as the Z accelerator. Since the compact pulsed power technology used for dynamic material experiments has not been previously used, it is necessary to examine several key issues to ensure that accurate results are obtained. In the present experiments, issues such as panel and sample preparation, uniformity of loading, and edge effects were extensively examined. In addition, magnetohydrodynamic (MHD) simulations using the ALEGRA code were performed to interpret the experimental results and to design improved sample/panel configurations. Examples of recent ICE studies on aluminum are presented.
This document is considered a mechanical design best-practice guide to new and experienced designers alike. The contents consist of topics related to using Computer Aided Design (CAD) software, performing basic analyses, and using configuration management. The details specific to a particular topic have been leveraged against existing Product Realization Standard (PRS) and Technical Business Practice (TBP) requirements while maintaining alignment with sound engineering and design practices. This document is to be considered dynamic in that subsequent updates will be reflected in the main title, and each update will be published on an annual basis.
Results from recent experimental studies suggest that the N vacancy (V{sub N}) may compensate Mg acceptors in GaN in addition to the compensation arising from H introduced during growth. To investigate this possibility further, density-functional-theory calculations were performed to determine the interactions of V{sub N} with H, Mg, and the MgH center in GaN, and modeling was performed to determine the state populations at elevated temperatures. The results indicate that V{sub N}H and MgV{sub N}H complexes with H inside the vacancy are highly stable in p-type GaN and act to compensate or passivate Mg acceptors. Furthermore, barriers for formation of these complexes were investigated and the results indicate that they can readily form at temperatures > 400 C, which is well below temperatures typically used for GaN growth. Overall, the results indicate that the V{sub N} compensation behavior suggested by experiments arises not from isolated V{sub N}, but rather from V{sub N}H and MgV{sub N}H complexes with H located inside the vacancy.
This work describes the convergence analysis of a Smolyak-type sparse grid stochastic collocation method for the approximation of statistical quantities related to the solution of partial differential equations with random coefficients and forcing terms (input data of the model). To compute solution statistics, the sparse grid stochastic collocation method uses approximate solutions, produced here by finite elements, corresponding to a deterministic set of points in the random input space. This naturally requires solving uncoupled deterministic problems and, as such, the derived strong error estimates for the fully discrete solution are used to compare the computational efficiency of the proposed method with the Monte Carlo method. Numerical examples illustrate the theoretical results and are used to compare this approach with several others, including the standard Monte Carlo.
Alegra is an ALE (Arbitrary Lagrangian-Eulerian) multi-material finite element code that emphasizes large deformations and strong shock physics. The Lagrangian continuum dynamics package in Alegra uses a Galerkin finite element spatial discretization and an explicit central-difference stepping method in time. The goal of this report is to describe in detail the characteristics of this algorithm, including the conservation and stability properties. The details provided should help both researchers and analysts understand the underlying theory and numerical implementation of the Alegra continuum hydrodynamics algorithm.