Publications

Sandia National Laboratories is investigating advanced Brayton cycles using supercritical working fluids for application to a variety of heat sources, including geothermal, solar, fossil, and nuclear power. This work is centered on the supercritical CO{sub 2} (S-CO{sub 2}) power conversion cycle, which has the potential for high efficiency in the temperature range of interest for these heat sources and is very compact-a feature likely to reduce capital costs. One promising approach is the use of CO{sub 2}-based supercritical fluid mixtures. The introduction of additives to CO{sub 2} alters the equation of state and the critical point of the resultant mixture. A series of tests was carried out using Sandia's supercritical fluid compression loop that confirmed the ability of different additives to increase or lower the critical point of CO{sub 2}. Testing also demonstrated that, above the modified critical point, these mixtures can be compressed in a turbocompressor as a single-phase homogenous mixture. Comparisons of experimental data to the National Institute of Standards and Technology (NIST) Reference Fluid Thermodynamic and Transport Properties (REFPROP) Standard Reference Database predictions varied depending on the fluid. Although the pressure, density, and temperature (p, {rho}, T) data for all tested fluids matched fairly well to REFPROP in most regions, the critical temperature was often inaccurate. In these cases, outside literature was found to provide further insight and to qualitatively confirm the validity of experimental findings for the present investigation.

Experts agree that the exascale machine will comprise processors that contain many cores, which in turn will necessitate a much higher degree of concurrency. Software will require a minimum of a 1,000 times more concurrency. Most parallel analysis and visualization algorithms today work by partitioning data and running mostly serial algorithms concurrently on each data partition. Although this approach lends itself well to the concurrency of current high-performance computing, it does not exhibit the appropriate pervasive parallelism required for exascale computing. The data partitions are too small and the overhead of the threads is too large to make effective use of all the cores in an extreme-scale machine. This paper introduces a new visualization framework designed to exhibit the pervasive parallelism necessary for extreme scale machines. We demonstrate the use of this system on a GPU processor, which we feel is the best analog to an exascale node that we have available today. © 2011 IEEE.

The structures, energies, and energy levels of a comprehensive set of simple intrinsic point defects in aluminum arsenide are predicted using density functional theory (DFT). The calculations incorporate explicit and rigorous treatment of charged supercell boundary conditions. The predicted defect energy levels, computed as total energy differences, do not suffer from the DFT band gap problem, spanning the experimental gap despite the Kohn-Sham eigenvalue gap being much smaller than experiment. Defects in AlAs exhibit a surprising complexity - with a greater range of charge states, bistabilities, and multiple negative-U systems - that would be impossible to resolve with experiment alone. The simulation results can be used to populate defect physics models in III-V semiconductor device simulations with reliable quantities in those cases where experimental data is lacking, as in AlAs. © 2011 Materials Research Society.

Most statistical software packages implement a broad range of techniques but do so in an ad hoc fashion, leaving users who do not have a broad knowledge of statistics at a disadvantage since they may not understand all the implications of a given analysis or how to test the validity of results. These packages are also largely serial in nature, or target multicore architectures instead of distributed-memory systems, or provide only a small number of statistics in parallel. This paper surveys a collection of parallel implementations of statistics algorithm developed as part of a common framework over the last 3 years. The framework strategically groups modeling techniques with associated verification and validation techniques to make the underlying assumptions of the statistics more clear. Furthermore it employs a design pattern specifically targeted for distributed-memory parallelism, where architectural advances in large-scale high-performance computing have been focused. Moment-based statistics (which include descriptive, correlative, and multicorrelative statistics; principal component analysis (PCA); and k-means statistics) scale nearly linearly with the data set size and number of processes. Entropy-based statistics (which include order and contingency statistics) do not scale well when the data in question is continuous or quasi-diffuse but do scale well when the data is discrete and compact. We confirm and extend our earlier results by now establishing near-optimal scalability with up to 10,000 processes. © 2011 IEEE.

By utilizing an equilibrium processing strategy that enables co-firing of oxides and base metals, a means to integrate the lithium-stable fast lithium-ion conductor lanthanum lithium tantalate directly with a thin copper foil current collector appropriate for a solid-state battery is presented. This resulting thin-film electrolyte possesses a room temperature lithium-ion conductivity of 1.5 × 10 -5 S cm -1, which has the potential to increase the power of a solid-state battery over current state of the art. Copyright © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

The need for generic, standard, non-proprietary models for wind power plants continues to be the subject of much discussion and debate. From a technical point of view, the representation of the often complex dynamic behavior of modern wind power plants is not trivial. However, system planners and compliance organizations continue to struggle with the process deficiencies associated with the black-box and proprietary nature of manufacturer-specific models. For several years, the Western Electricity Coordinating Council (WECC) has championed the development of generic models for wind power plant models, and the progress to date is reported in this document. Recently, other organizations including the International Electromechanical Commission (IEC), manufacturers, software developers, and even utilities have been pursuing similar technical goals. It is anticipated that, through the collective efforts of these stakeholders, generic models will fulfill a much needed gap. This paper reports on the progress made to-date within the Western Electricity Coordinating Council (WECC) regarding the development of generic models suitable for representing wind power plants in typical transmission planning studies. The manuscript address technical issues associated with the representation of wind turbine generators for load flow and transient stability analyses. Current capabilities and envisioned enhancements to existing models are also discussed. © 2011 IEEE.

This paper describes the modeling efforts undertaken during a recently completed feasibility study of a generic shale repository for disposal of high-level radioactive waste within the United States. A coupled thermal-hydrological-mechanical-chemical analysis of the shale repository was performed using the SIERRA Mechanics code developed at Sandia National Laboratories. Because U.S. efforts have focused on the volcanic tuff site at Yucca Mountain, radioactive waste disposal in U.S. shale formations has not been considered for many years. However, advances in multi-physics computational modeling and research into clay mineralogy continue to improve the scientific basis for assessing nuclear waste repository performance in such formations. Disposal of high-level radioactive waste in suitable shale formations is attractive because the material is essentially impermeable and self-sealing, conditions are chemically reducing, and sorption tends to prevent radionuclide transport. Vertically and laterally extensive shale and clay formations exist in multiple locations in the contiguous 48 states. © 2011 ARMA, American Rock Mechanics Association.

We present a filter consisting of cascaded ring resonators with integrated SOAs. The filter demonstrates an extinction ratio >30 dB, a free spectral range of 56 GHz and a FWHM bandwidth of 3 GHz. © 2010 Optical Society of America.

Abstract not provided.

This paper explores various frameworks to quantify and propagate sources of epistemic and aleatoric uncertainty within the context of decision making for assessing system performance relative to design margins of a complex mechanical system. If sufficient data is available for characterizing aleatoric-type uncertainties, probabilistic methods are commonly used for computing response distribution statistics based on input probability distribution specifications. Conversely, for epistemic uncertainties, data is generally too sparse to support objective probabilistic input descriptions, leading to either subjective probabilistic descriptions (e.g., assumed priors in Bayesian analysis) or non-probabilistic methods based on interval specifications. Among the techniques examined in this work are (1) Interval analysis, (2) Dempster-Shafer Theory of Evidence, (3) a second-order probability (SOP) analysis in which the aleatory and epistemic variables are treated separately, and a nested iteration is performed, typically sampling epistemic variables on the outer loop, then sampling over aleatory variables on the inner loop and (4) a Bayesian approach where plausible prior distributions describing the epistemic variable are created and updated using available experimental data. This paper compares the results and the information provided by different methods to enable decision making in the context of performance assessment when epistemic uncertainty is considered.

This paper discusses testing and modeling efforts to experimentally determine, and numerically model the behavior of aluminum at incipient melt conditions. More particularly, the role of the oxide layer which develops on the surface of aluminum which is heating in an oxidizing environment has been found to influence deformation. Several configurations where tested composed of aluminum rods at different orientations with regard to standard gravity, and video images were taken to record movement. Modeling with comparable materials shows similar behavior and encourages additional work where some numerical comparisons could be researched further. © 2011 INTERNATIONAL ASSOCIATION FOR FIRE SAFETY SCIENCE.

We present a novel approach to predicting the sentiment of documents in multiple languages, without translation. The only prerequisite is a multilingual parallel corpus wherein a training sample of the documents, in a single language only, have been tagged with their overall sentiment. Latent Semantic Indexing (LSI) converts that multilingual corpus into a multilingual "concept space". Both training and test documents can be projected into that space, allowing crosslingual semantic comparisons between the documents without the need for translation. Accordingly, the training documents with known sentiment are used to build a machine learning model which can, because of the multilingual nature of the document projections, be used to predict sentiment in the other languages. We explain and evaluate the accuracy of this approach. We also design and conduct experiments to investigate the extent to which topic and sentiment separately contribute to that classification accuracy, and thereby shed some initial light on the question of whether topic and sentiment can be sensibly teased apart. © 2011 IEEE.

COMET is a single-pass MapReduce algorithm for learning on large-scale data. It builds multiple random forest ensembles on distributed blocks of data and merges them into a mega-ensemble. This approach is appropriate when learning from massive-scale data that is too large to fit on a single machine. To get the best accuracy, IVoting should be used instead of bagging to generate the training subset for each decision tree in the random forest. Experiments with two large datasets (5GB and 50GB compressed) show that COMET compares favorably (in both accuracy and training time) to learning on a subsample of data using a serial algorithm. Finally, we propose a new Gaussian approach for lazy ensemble evaluation which dynamically decides how many ensemble members to evaluate per data point; this can reduce evaluation cost by 100X or more. © 2011 IEEE.

Hermetic sealing of lids in ceramic microelectronic chip carriers is typically performed with eutectic solder in relatively large belt-style reflow furnaces. This process is characterized by 30 to 45-minute cycle times at temperatures above 350 C. An experimental study was undertaken with the goal of establishing a low-cost lid sealing method marked by a compact belt furnace with lower reflow temperature and lesser cycle time. This is particularly advantageous for GaAs devices which are limited to packaging process temperatures below 300 C. A series of instrumented test samples consisting of a representative die packaged in a HTCC leadless chip carrier (LCC) was prepared. Package lids were installed and sealed in a nitrogen environment with 80-20 Au-Sn lead-free solder under various cycle time and temperature conditions. Gross and fine leak testing confirmed hermeticity. Results indicate that practical sealing can be realized in the compact furnace apparatus with measurable reductions in temperature and cycle time. Seal performance is dependent upon package orientation, which suggests the process must be calibrated for unique package designs. Sandia is a multiprogram laboratory operated by Sandia Corporation, a Lockheed Martin Company, for the United States Department of Energy's National Nuclear Security Administration under Contract DE-AC04-94AL85000. © 2011 by ASME.

The inability to do visual solder joint inspection has been a major road block to using advanced ICs with high I/O count in area array packaging technologies like flip-chip, Quad Flat No Lead (QFN) and Ball grid Arrays (BGAs). In this paper, we report the results of a study to evaluate 3D X-Ray Computed Tomography (3DXRay-CT) as a solder inspection technique for area array package assemblies. We have conducted an experiment with board assemblies having intentionally designed solder defects like cold solder joints, solder-mask defects, unfilled vias in solder pads, and different shape and size solder pads. We have demonstrated that 3D X-Ray-CT technique was able to detect all these defects. This technique is a valid technique to inspect solder joints in area array packaging technologies.

Sandia National Laboratories has developed a modeling approach to simulate time-synchronized, 1-minute power output from large PV plants in locations where only hourly irradiance measurements are available via satellite sources. The approach uses 1-min irradiance measurements from analogue sites in a similar geographic area. PV output datasets generated for 2007 in southern Nevada are being used for a Solar PV Grid Integration Study to estimate the integration costs associated with various utility-scale PV generation levels. Plant designs considered include both fixed-tilt thin-film, and singleaxis- tracked polycrystalline Si systems ranging in size from 5 to 300 MWAC. Simulated power output profiles at 1-min intervals were generated for five scenarios (149.5 MW, 222 WM, 292 MW, 492 MW, and 892 MW) each comprising as many as 10 geographically separated PV plants. Copyright© (2011) by the American Solar Energy Society.

This paper discusses the development of a consistent methodology for mapping one-dimensional distributed beam loads to a three-dimensional shell structure. The resultant force distribution is a linear approximation to the actual aerodynamic pressure distribution but is sufficient to obtain accurate strain and displacement results. The purpose of the mapping technique is to apply more realistic wind loads to the shell model of a wind turbine blade without the need to set up and run expensive computational fluid dynamics or fluid structure interaction problems. Subsequent buckling and stress analysis reveal how this approach compares to other simplified methods of defining the loads. Copyright © 2011 by the American Institute of Aeronautics and Astronautics, Inc.

The paper describes a computational simulation approach for durability, damage tolerance (D&DT) and reliability of composite wind turbine blade structures in presence of uncertainties in material properties. This computer-based prediction methodology combines composite mechanics with finite element analysis, damage and fracture tracking capability, probabilistic analysis and a robust design algorithm to reduce weight of turbine bales without loss in structural durability and reliability. A composite turbine blade was first assessed with finite element based multi-scale progressive failure analysis to determine failure modes and locations as well as the fracture load. Analysis D&DT results were validated with static test performed at Sandia National Laboratories. The work was followed by detailed weight analysis to identify contribution of various materials to the overall weight of the blade. The methodology ensured that certain types of failure modes, such as delamination progression, are contained to reduce risk to the structure. Probabilistic analysis indicated that composite shear strength has a great influence of the blade ultimate load under static loading. Weight was reduced by 12% with robust design without loss in reliability or D&DT. It was achieved by replacing a small volume of key materials with foam. Copyright © 2011 by Alpha STAR Corp.

A micromechanics based computational approach is put to use to assess the durability of composite laminates with ply drop features commonly used in wind turbine applications. Ply drops are used in composite joints and closures of wind turbine blades to reduce skin thicknesses along the blade span. They increase localized stress concentration, which may cause premature delamination failure in composite and reduced fatigue service life. The use of computational simulation in the design of tapered composites structures will reduce risk of failure under service. Durability and damage tolerance (D&DT) is evaluated utilizing a Multi-scale MicroMacro Progressive failure analysis (PFA) technique. The PFA approach is finite element based and is capable of detecting all stages of material damage including initiation and propagation of delamination. Two different approaches have been used within the PFA to investigate these issues. The first approach is Virtual Crack Closure Technique (VCCT) PFA while the second one is strength based approach. The PFA assesses multiple failure criteria and includes the effects of manufacturing anomalies (i.e., void, fiber waviness). In the work presented here, constituent stiffness and strength properties for glass and carbon based material systems are reverse engineered for use in D&DT evaluation of coupons with ply drops under static loading. Lamina and laminate properties calculated using manufacturing and composite architecture details matched closely published test data. Similarly, resin properties are also determined for fatigue life calculation. The simulation not only reproduced static strength and fatigue life as observed in the test, it also showed composite damage and fracture modes that resemble those reported in the test. The results presented in the paper show that computational simulation can be relied on to enhance the design of tapered composite structures such as the ones used in turbine wind blades. Copyright © 2011 by Alpha STAR.

As semantic graph database technology grows to address components ranging from large triple stores to SPARQL endpoints over SQL-structured relational databases, it will become increasingly important to be able to understand their inherent semantic structure, whether codified in explicit ontologies or not. Our group is researching novel methods for what we call descriptive semantic analysis of RDF triplestores, to serve purposes of analysis, interpretation, visualization, and optimization. But data size and computational complexity makes it increasingly necessary to bring high performance computational resources to bear on this task. Our research group built a high performance hybrid system comprising computational capability for semantic graph database processing utilizing the multi-threaded architecture of the Cray XMT platform, conventional servers, and large data stores. In this paper we describe that architecture and our methods, and present the results of our analyses of basic properties, connected components, namespace interaction, and typed paths of the Billion Triple Challenge 2010 dataset.

This paper presents some statistical concepts and techniques for refining the expression of uncertainty arising from: a) random variability (aleatory uncertainty) of a random quantity; and b) contributed epistemic uncertainty due to limited sampling of the random quantity. The treatment is tailored to handling experimental uncertainty in a context of model validation and calibration. Two particular problems are considered. One involves deconvolving random measurement error from measured random response. The other involves exploiting a relationship between two random variates of a system and an independently characterized probability density of one of the variates.

This paper discusses the handling and treatment of uncertainties corresponding to relatively few data samples in experimental characterization of random quantities. The importance of this topic extends beyond experimental uncertainty to situations where the derived experimental information is used for model validation or calibration. With very sparse data it is not practical to have a goal of accurately estimating the underlying variability distribution (probability density function, PDF). Rather, a pragmatic goal is that the uncertainty representation should be conservative so as to bound a desired percentage of the actual PDF, say 95% included probability, with reasonable reliability. A second, opposing objective is that the representation not be overly conservative; that it minimally over-estimate the random-variable range corresponding to the desired percentage of the actual PDF. The performance of a variety of uncertainty representation techniques is tested and characterized in this paper according to these two opposing objectives. An initial set of test problems and results is presented here from a larger study currently underway.

The blades of a modern wind turbine are critical components central to capturing and transmitting most of the loads experienced by the system. Blades are complex structural items composed of many layers of fiber and resin composite material and typically, one or more shear webs. Simplification of the blade structure into equivalent beams is an important step prior to aeroelastic simulation of the turbine structure. There are a variety of approaches that can be used to reduce the three-dimensional continuum blade structure to a simpler beam representation: two-dimensional cross section analysis, extraction of equivalent properties from three-dimensional blade finite element models and variational asymptotical beam sectional analysis. This investigation provides insight into discrepancies observed in outputs from these three approaches for a real blade geometry. Wind turbine blades of the future will be longer and more flexible as weight is optimized. Innovative large blade designs may present challenges with respect to aeroelastic flutter instabilities. Sensitivity of computed flutter speed with respect to variations in computed beam properties is demonstrated at the end of this paper. Copyright © 2011 by the American Institute of Aeronautics and Astronautics, Inc.

With the increasing levels of parallelism in a compute node, it is important to exploit multiple levels of parallelism even within a single compute node. We present ShyLU (pro- nounced\Shy-loo"for Scalable Hybrid LU), a\hybrid-hybrid" solver for general sparse linear systems that is hybrid in two ways: First, it combines direct and iterative methods. The iterative method is based on approximate Schur com- plements. Second, the solver uses two levels of parallelism via hybrid programming (MPI+threads). Our solver is use- ful both in shared-memory environments and on large par- allel computers with distributed memory (as a subdomain solver). We compare the robustness of ShyLU against other algebraic preconditioners. ShyLU scales well up to 192 cores for a given problem size. We compare at MPI performance of ShyLU against a hybrid implementation. We conclude that on present multicore nodes at MPI is better. However, for future manycore machines (48 or more cores) hybrid/ hi- erarchical algorithms and implementations are important for sustained performance. Copyright is held by the author/owner(s).

Approximate counting [18] is useful for data stream and database summarization. It can help in many settings that allow only one pass over the data, want low memory usage, and can accept some relative error. Approximate counters use fewer bits; we focus on 8-bits but our results are general. These small counters represent a sparse sequence of larger numbers. Counters are incremented probabilistically based on the spacing between the numbers they represent. Our contributions are a customized distribution of counter values and efficient strategies for deciding when to increment them. At run-time, users may independently select the spacing (accuracy) of the approximate counter for small, medium, and large values. We allow the user to select the maximum number to count up to, and our algorithm will select the exponential base of the spacing. These provide additional flexibility over both classic and Csurös's [4] floating-point approximate counting. These provide additional structure, a useful schema for users, over Kruskal and Greenberg [13]. We describe two new and efficient strategies for incrementing approximate counters: use a deterministic countdown or sample from a geometric distribution. In Csurös's all increments are powers of two, so random bits rather than full random numbers can be used. We also provide the option to use powers-of-two but retain flexibility. We show when each strategy is fastest in our implementation. © 2011 ACM.

Metal organic framework (MOF) materials are a class of hybrid organic-inorganic crystalline materials whose pore structures and chemical properties can be tailored by the selection of component chemical moieties. Many MOFs have extraordinary intrinsic surface areas, capable of adsorbing large quantities of other chemicals, such as volatile organic compounds or moisture. Upon absorption of guest molecules, many MOFs undergo reversible changes in the dimensions of their unit cells. These properties suggest several routes to chemical sensing in which the transduction mechanisms are: 1) the stress induced at an interface between a flexible MOF layer and a static microcantilever fabricated with a built-in piezoresistive stress sensor; 2) the change in the resonant frequency of an oscillating microcantilever induced by mass adsorption; and 3) the change in the resonant frequency of a acoustic sensor, such as a surface acoustic wave (SAW) sensor through changes in mass loading and film moduli. This paper focuses on humidity sensing by SAWs coated with Cu 3(BTC) 2 (HKUST-1) over a very broad concentration range. Sandia National Laboratories is a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. Department of Energy's National Nuclear Security Administration under contract DE-AC04-94AL85000. © 2011 Materials Research Society.

A study has been performed to quantify the uncertain performance of an environment sensing safety system which senses the unique payload trajectory environment created during parachute deployment. Models for the underlying sources of uncertainty, specifically the parachute inflation uncertainty and the uncertainty in performance of the mechanical switch sensors, have been identified and validated. DAKOTA, a Sandia-developed software package for uncertainty quantification, has been used to perform a probabalistic study of system performance, accounting for sources of uncertainty in the parachute inflation process and in the environment sensing process. This study has been performed across the payload release envelope with margins and uncertainties quantified for a critical sytem performance requirement. © 2011 by the American Institute of Aeronautics and Astronautics, Inc.

Nuclear reactors have served as the neutrino source for many fundamental physics experiments. The techniques developed by these experiments make it possible to use these very weakly interacting particles for a practical purpose. The large flux of antineutrinos that leaves a reactor carries information about two quantities of interest for safeguards: the reactor power and fissile inventory. Our SNL/LLNL collaboration has demonstrated that such antineutrino based monitoring is feasible using a relatively small cubic meter scale liquid scintillator detector at tens of meters standoff from a commercial Pressurized Water Reactor (PWR). With little or no burden on the plant operator we have been able to remotely and automatically monitor the reactor operational status (on/off), power level, and fuel burnup. The initial detector was deployed in an underground gallery that lies directly under the containment dome of an operating PWR. The gallery is 25 meters from the reactor core center, is rarely accessed by plant personnel, and provides a muon-screening effect of some 20-30 meters of water equivalent earth and concrete overburden. Unfortunately, many reactor facilities do not contain an equivalent underground location. We have therefore attempted to construct a complete detector system which would be capable of operating in an aboveground location and could be transported to a reactor facility with relative ease. A standard 6-meter shipping container was used as our transportable laboratory - containing active and passive shielding components, the antineutrino detector and all electronics, as well as climate control systems. This aboveground system was deployed and tested at the San Onofre Nuclear Generating Station (SONGS) in southern California in 2010 and early 2011. We will first present an overview of the initial demonstrations of our belowground detector. Then we will describe the aboveground system and the technological developments of the two antineutrino detectors that were deployed. Finally, some preliminary results of our aboveground test will be shown. © 2011 IEEE.

Next-generation sequencing (NGS) technology is a promising tool for identifying and characterizing unknown pathogens, but its usefulness in time-critical biodefense and public health applications is currently limited by the lack of fast, efficient, and reliable automated DNA sample preparation methods. To address this limitation, we are developing a digital microfluidic (DMF) platform to function as a fluid distribution hub, enabling the integration of multiple subsystem modules into an automated NGS library sample preparation system. A novel capillary interface enables highly repeatable transfer of liquid between the DMF device and the external fluidic modules, allowing both continuous-flow and droplet-based sample manipulations to be performed in one integrated system. Here, we highlight the utility of the DMF hub platform and capillary interface for automating two key operations in the NGS sample preparation workflow. Using an in-line contactless conductivity detector in conjunction with the capillary interface, we demonstrate closed-loop automated fraction collection of target analytes from a continuous-flow sample stream into droplets on the DMF device. Buffer exchange and sample cleanup, the most repeated steps in NGS library preparation, are also demonstrated on the DMF platform using a magnetic bead assay and achieving an average DNA recovery efficiency of 80% ± 4.8% © 2011 Society for Laboratory Automation and Screening.

A dedicated design qualification standard for PV inverters does not exist. Development of a well-accepted design qualification standard, specifically for PV inverters will significantly improve the reliability and performance of inverters. The existing standards for PV inverters such as ANSI/UL 1741 and IEC 62109-1 primarily focus on safety of PV inverters. The IEC 62093 discusses inverter qualification but it includes all the BOS components. There are other general standards for distributed generators including the IEEE 1547 series of standards which cover major concerns like utility integration but they are not dedicated to PV inverters and are not written from a design qualification point of view. In this paper some of the potential requirements for a design qualification standard for PV inverters are addressed. The missing links in existing PV inverter related standards are identified and with the IEC 62093 as a guideline, the possible inclusions in the framework for a dedicated design qualification standard of PV inverter are discussed. Some of the key missing links are related to electric stress tests. Hence, a method to adapt the existing surge withstand test standards for use in design qualification standard of PV inverter is presented. © 2011 IEEE.

Article 690.11 in the 2011 National Electrical Code® (NEC®) requires new photovoltaic (PV) systems on or penetrating a building to include a listed arc fault protection device. Currently there is little experimental or empirical research into the behavior of the arcing frequencies through PV components despite the potential for modules and other PV components to filter or attenuate arcing signatures that could render the arc detector ineffective. To model AC arcing signal propagation along PV strings, the well-studied DC diode models were found to inadequately capture the behavior of high frequency arcing signals. Instead dynamic equivalent circuit models of PV modules were required to describe the impedance for alternating currents in modules. The nonlinearities present in PV cells resulting from irradiance, temperature, frequency, and bias voltage variations make modeling these systems challenging. Linearized dynamic equivalent circuits were created for multiple PV module manufacturers and module technologies. The equivalent resistances and capacitances for the modules were determined using impedance spectroscopy with no bias voltage and no irradiance. The equivalent circuit model was employed to evaluate modules having irradiance conditions that could not be measured directly with the instrumentation. Although there was a wide range of circuit component values, the complex impedance model does not predict filtering of arc fault frequencies in PV strings for any irradiance level. Experimental results with no irradiance agree with the model and show nearly no attenuation for 1 Hz to 100 kHz input frequencies. © 2011 IEEE.

The success of dynamic materials properties research at Sandia National Laboratories has led to research into ultra-low impedance, compact pulsed power systems capable of multi-MA shaped current pulses with rise times ranging from 220-500 ns. The Genesis design consists of two hundred and forty 200 kV, 80 kA modules connected in parallel to a solid dielectric disk transmission line and is capable of producing 280 kbar of magnetic pressure (>500 kbar pressure in high Z materials) in a 1.75 nH, 20 mm wide stripline load. Stripline loads operating under these conditions expand during the experiment resulting in a time-varying load that can impact the performance and lifetime of the system. This paper provides analysis of time-varying stripline loads and the impact of these loads on system performance. Further, an approach to reduce dielectric stress levels through active damping is presented as a means to increase system reliability and lifetime. © 2011 IEEE.

The Sandia Array Performance Model (SAPM) [1] describes the power performance of photovoltaic (PV) modules under variable irradiance and temperature conditions. Model parameters are estimated by regressions involving measured module voltage and current, module and air temperature, and solar irradiance. Measurements are made under test conditions chosen to isolate subsets of parameters and which improve the quality of the regression estimates. Uncertainty in model parameters results from uncertainty in each measurement as well as from the number of measurements. Uncertainty in model parameters can be propagated through the model to determine its effect on model output. In this paper we summarize the process for estimating uncertainty in model parameters for flat-plate, crystalline silicon (cSi) modules from measurements, present example results, and illustrate the effect of parameter uncertainty on model output. Finally, we comment on how analysis of parameter uncertainty can inform model developers about the presence and impacts of model uncertainty. © 2011 IEEE.

We analyze the artificial dissipation introduced by a streamline-upwind Petrov-Galerkin finite element method and consider its effect on the conservation of total enthalpy for the Euler and laminar Navier-Stokes equations. We also consider the chemically reacting case. We demonstrate that in general, total enthalpy is not conserved for the important special case of the steady-state Euler equations. A modification to the artificial dissipation is proposed and shown to significantly improve the conservation of total enthalpy.

Genesis is a compact pulsed power platform designed by Sandia National Laboratories to generate precision shaped multi-MA current waves with a rise time of 200-500 ns. In this system, two hundred and forty, 200 kV, 80 kA modules are selectively triggered to produce 280 kbar of magnetic pressure (>500 kbar pressure in high Z materials) in a stripline load for dynamic materials properties research. This new capability incorporates the use of solid dielectrics to reduce system inductance and size, programmable current shaping, and gas switches that must perform over a large range of operating conditions. Research has continued on this technology base with a focus on demonstrating the integrated performance of key concepts into a Genesis-like prototype called Protogen. Protogen measures approximately 1.4 m by 1.4 m and is designed to hold twelve Genesis modules. A fixed inductance load will allow rep-rate operation for component reliability and system lifetime experiments at the extreme electric field operating conditions expected in Genesis. © 2011 IEEE.

The Direct Simulation Monte Carlo (DSMC) method of molecular gas dynamics is used to simulate the steady flow of an ideal gas through a long thin isothermal microscale tube connecting two infinite reservoirs at different pressures. The tube wall is at the reservoir temperature, and molecules reflect from the walls according to the Maxwell model (i.e., a linear combination of specular reflections and diffuse reflections at the wall temperature). The computed mass flow rates approach the known expressions in the near-continuum and free-molecular regimes and agree reasonably with recent experimental measurements in microscale tubes and channels. Approximate closed-form expressions for the mass flow rate and the pressure profile along the tube are developed and are in reasonable agreement with the DSMC results in all regimes and for all values of the accommodation coefficient. © 2011 by the American Institute of Aeronautics and Astronautics, Inc.

It is often assumed that distribution-connected PV can help defer the need for distribution system upgrades, but there is not a general approach for assessing the deferment value of distribution-connected PV and distribution-connected PV combined with a storage system (e.g., battery). A vital component of such an analysis is time-coincident load and solar resource data, since load (especially peak load) is usually correlated with solar resource and temperature conditions, and both factors determine PV system performance as well. This paper demonstrates a methodology to analyze the value of using PV to defer distribution system upgrades. The paper also assesses the additional benefit of combining energy storage with PV to increase this deferment value. The case study involves replacement of a station transformer. © 2011 IEEE.

Estimating the energy that should be generated by a PV system under the prevailing conditions of irradiance and temperature is very important for system or fleet investors, energy customers, and operators. Traditionally this has been achieved by measuring irradiance and temperature in the proximity of the PV array in order to calculate the expected energy output either by using an appropriate model or by making assumptions about the system's Performance Ratio. However, this method requires the accurate installation, maintenance, and continuous monitoring of sensors thereby increasing the system's capital and maintenance costs. In this work we present an alternative methodology which can calculate the expected output of one or more systems in a regional fleet based on the measured power output from a subset of the total fleet. This can be achieved thanks to high accuracy energy measurements and the ability to correlate historical performance records. © 2011 IEEE.

A variety of metrics are commonly used to assess whether or not a photovoltaic ("PV") system is operating as expected, but to date no standard metric has been accepted. Three commonly used metrics for assessing PV system power performance are the Power Performance Index ("PPI"), PVUSA rating as contemplated in ASTM WK22009 ("ASTM"), and Performance Energy Ratio ("PER"). This paper evaluates the suitability of each of the three metrics for use with large Cadmium Telluride (CdTe) arrays. Of particular interest is the uncertainty and stability of each result and relative differences between their magnitudes. Two different approaches for propagating measurement uncertainty to final metric uncertainty are discussed: (1) analytical and, (2) bootstrapping (similar to a Monte Carlo method). Additionally, best practices to achieve low uncertainty and high stability of a metric are addressed including choice of regression method, reference conditions and filtering range. Iteratively reweighted least squares regression methods were found to improve the stability of metrics in cloudy climates relative to ordinary least squares methods. Choosing irradiance filtering ranges that are sufficiently large and asymmetrical about the chosen reference condition was found to bias the metrics on the order of 0.6%. Final PPI uncertainty was found to be most sensitive to irradiance and power measurement errors and ranged from +/- 3% to +/- 8% for typical ranges of sensor accuracies. © 2011 IEEE.

The Direct Simulation Monte Carlo (DSMC) method of molecular gas dynamics is used to simulate the steady flow of an ideal gas through a long thin isothermal microscale tube connecting two infinite reservoirs at different pressures. The tube wall is at the reservoir temperature, and molecules reflect from the walls according to the Maxwell model (i.e., a linear combination of specular reflections and diffuse reflections at the wall temperature). The computed mass flow rates approach the known expressions in the near-continuum and free-molecular regimes and agree reasonably with recent experimental measurements in microscale tubes and channels. Approximate closed-form expressions for the mass flow rate and the pressure profile along the tube are developed and are in reasonable agreement with the DSMC results in all regimes and for all values of the accommodation coefficient. © 2011 by the American Institute of Aeronautics and Astronautics, Inc.

Magnetically-Applied Pressure-Shear (MAPS) is a new experimental technique to measure material shear strength at high pressures and has been developed for use on MHD driven pulsed power platforms [1]. By applying an external static magnetic field to the sample region, the MHD drive directly induces a shear stress wave in addition to the usual longitudinal stress wave. Strength is probed by passing this shear wave through a sample material where the transmissible shear stress is limited to the sample strength. The magnitude of the transmitted shear wave is measured via a transverse velocity interferometry system (VISAR) from which the sample strength is determined [2]. This paper presents and analyzes the 2D MHD simulations used to design the MAPS experiments. © 2011 IEEE.

A reassessment of historical drag coefficient data for spherical particles accelerated in shock-induced flows has motivated new shock tube experiments of particle response to the passage of a normal shock wave. Particle drag coefficients were measured by tracking the trajectories of 1-mm spheres in the wake of incident shocks of Mach numbers 1.68, 1.93, and 2.05. Data clearly show that as the Mach number increases, the drag coefficient increases substantially, consistent with past experiments. This increase significantly exceeds the drag predicted by incompressible standard drag models, but recently developed compressible drag models return values quite close to the current measurements. Low values for the acceleration parameter indicate that unsteadiness should not be expected to contribute to the drag increase. These observations suggest that elevated particle drag coefficients can be attributed to increased compressibility rather than flow unsteadiness.

Abstract not provided.

Abstract not provided.

Article 690.11 in the 2011 National Electrical Code® (NEC®) requires new photovoltaic (PV) systems on or penetrating a building to include a listed arc fault protection device. Currently there is little experimental or empirical research into the behavior of the arcing frequencies through PV components despite the potential for modules and other PV components to filter or attenuate arcing signatures that could render the arc detector ineffective. To model AC arcing signal propagation along PV strings, the well-studied DC diode models were found to inadequately capture the behavior of high frequency arcing signals. Instead dynamic equivalent circuit models of PV modules were required to describe the impedance for alternating currents in modules. The nonlinearities present in PV cells resulting from irradiance, temperature, frequency, and bias voltage variations make modeling these systems challenging. Linearized dynamic equivalent circuits were created for multiple PV module manufacturers and module technologies. The equivalent resistances and capacitances for the modules were determined using impedance spectroscopy with no bias voltage and no irradiance. The equivalent circuit model was employed to evaluate modules having irradiance conditions that could not be measured directly with the instrumentation. Although there was a wide range of circuit component values, the complex impedance model does not predict filtering of arc fault frequencies in PV strings for any irradiance level. Experimental results with no irradiance agree with the model and show nearly no attenuation for 1 Hz to 100 kHz input frequencies. © 2011 IEEE.

Mykonos is a linear transformer driver (LTD) pulsed power accelerator currently undergoing testing at Sandia National Laboratories. Mykonos-2, the initial configuration, includes two 1-MA, 200-kV LTD cavities driving a water-filled transmission line terminated by a resistive load. Transmission line and 3D electromagnetic (EM) simulation models of high-current LTD cavities have been developed [D.V. Rose et al. Phys. Rev. ST Accel. Beams 13, 90401 (2010)]. These models have been used to develop an equivalent two-cavity transmission line model of Mykonos-2 using the BERTHA transmission line code. The model explicitly includes 40 bricks per cavity and detailed representations of the water-filled transmission line and resistive load. (A brick consists of two capacitors and a switch connected in series.) This model is compared to 3D EM simulations of the entire accelerator including detailed representations of the individual capacitors and switches in each cavity. Good agreement is obtained between the two simulation models and both models are in good agreement with preliminary data from Mykonos-2. © 2011 IEEE.

The Sunshine to Petrol effort at Sandia National Laboratories aims to convert CO 2 and water to liquid hydrocarbon fuel precursors using concentrated solar energy with redox-active metal oxide systems, such as ferrites: Fe 3O 4→3FeO+ 0.5O 2 (>1350°C) 3FeO + CO 2→Fe 3O 4 + CO (<1200°C). However, the ferrite materials are not repeatedly reactive on their own and require a support, such as yttria-stabilized zirconia (YSZ). The ferrite-support interaction is not well defined, as there has been little fundamental characterization of these oxides at the high temperatures and conditions present in these cycles. We have investigated the microstructure, structure-property relationships, and the role of the support on redox behavior of the ferrite composites. In-situ capabilities to elucidate chemical reactions under operating conditions have been developed. The synthesis, structural characterization (room and high- temperature x-ray diffraction, secondary ion mass spectroscopy, scanning electron microscopy), and thermogravimetric analysis of YSZ-supported ferrites will be discussed.

Abstract not provided.

Hermetic sealing of lids in ceramic microelectronic chip carriers is typically performed with eutectic solder in relatively large belt-style reflow furnaces. This process is characterized by 30 to 45-minute cycle times at temperatures above 350 C. An experimental study was undertaken with the goal of establishing a low-cost lid sealing method marked by a compact belt furnace with lower reflow temperature and lesser cycle time. This is particularly advantageous for GaAs devices which are limited to packaging process temperatures below 300 C. A series of instrumented test samples consisting of a representative die packaged in a HTCC leadless chip carrier (LCC) was prepared. Package lids were installed and sealed in a nitrogen environment with 80-20 Au-Sn lead-free solder under various cycle time and temperature conditions. Gross and fine leak testing confirmed hermeticity. Results indicate that practical sealing can be realized in the compact furnace apparatus with measurable reductions in temperature and cycle time. Seal performance is dependent upon package orientation, which suggests the process must be calibrated for unique package designs. Sandia is a multiprogram laboratory operated by Sandia Corporation, a Lockheed Martin Company, for the United States Department of Energy's National Nuclear Security Administration under Contract DE-AC04-94AL85000. © 2011 by ASME.

Inference techniques play a central role in many cognitive systems. They transform low-level observations of the environment into high-level, actionable knowledge which then gets used by mechanisms that drive action, problem-solving, and learning. This paper presents an initial effort at combining results from AI and psychology into a pragmatic and scalable computational reasoning system. Our approach combines a numeric notion of plausibility with first-order logic to produce an incremental inference engine that is guided by heuristics derived from the psychological literature. We illustrate core ideas with detailed examples and discuss the advantages of the approach with respect to cognitive systems.

A microfluidic RNA interference screening device was designed to study which genes are involved in Rift Valley Fever Virus (RVFV) infection. Spots of small interfering RNA (siRNA) are manually spotted onto a glass microscope slide, and aligned to a screening device designed to accommodate cell seeding, siRNA transfection, cell culture, virus infection and imaging analysis. This portable and disposable PDMS-based microfluidic device for RNAi screening was designed for a 96-well library of transfection against variety of gene targets. Current results show transfection of GFP-22 siRNA within the device, as compared to controls, which inhibit the expression of GFP produced by recombinant RVFV. This technique can be applied to host-pathogen interactions for highly dangerous systems in BSL-3/4 laboratories, where bulky robotic equipment is not ideal.

The electrons flowing in a coaxial magnetically insulated transmission line (MITL), if allowed to flow uncontrolled into a radiographic electron diode load, can have an adverse impact on the performance of the system. Total radiation dose, impedance lifetime, and spot quality (size, shape, position, and stability) can all be affected. Current approaches to deal with this problem require a large volume in the vicinity of the electron diode load. For applications where this volume is not available, an alternate method of controlling the feed electrons is needed. In this paper, we will investigate various ideas for dealing with this issue and present results showing the properties of the various schemes investigated. © 2011 IEEE.

As hydrogen fuel cell technologies achieve market penetration, there is a growing need to characterize a range of structural metals that are used in the hydrogen environments that are encountered in gaseous hydrogen fuel systems. A review of existing data show that hydrogen can significantly accelerate fatigue crack growth of many common structural metals; however, comprehensive characterization of the effects of hydrogen on fatigue properties is generally lacking from the literature, even for structural metals that have been used extensively in high-pressure gaseous hydrogen environments. This report provides new testing data on the effects of hydrogen on fatigue of structural metals that are commonly employed in high-pressure gaseous hydrogen. Copyright © 2011 by ASME.

This paper describes an implementation strategy used to develop a high temperature power controller. The system is based on using high-temperature (HT) silicon-on-insulator (SOI) technology with silicon carbide (SiC) based integrated circuits (ICs) to create an efficient, high-temperature power controller. Two drives were tested with this system, one using normally off JFET switching and the other using MOSFET switching. Normally OFF JFETs made from SiC were used to drive the output loads. Such circuit designs will improve the efficiency of future smart grid power controllers.

This presentation will discuss progress towards developing a large-scale parallel CFD capability using stabilized finite element formulations to simulate turbulent reacting flow and heat transfer in light water nuclear reactors (LWRs). Numerical simultation plays a critical role in the design, certification, and operation of LWRs. The Consortium for Advanced Simulation of Light Water Reactors is a U. S. Department of Energy Innovation Hub that is developing a virtual reactor toolkit that will incorporate science-based models, state-of-the-art numerical methods, modern computational science and engineering practices, and uncertainty quantification (UQ) and validation against operating pressurized water reactors. It will couple state-of-the-art fuel performance, neutronics, thermal-hydraulics (T-H), and structural models with existing tools for systems and safety analysis and will be designed for implementation on both today's leadership-class computers and next-generation advanced architecture platforms. We will first describe the finite element discretization utilizing PSPG, SUPG, and discontinuity capturing stabilization. We will then discuss our initial turbulence modeling formulations (LES and URANS) and the scalable fully implicit, fully coupled solution methods that are used to solve the challenging systems. These include globalized Newton-Krylov methods for solving the nonlinear systems of equaitons and preconditioned Krylov techniques. The preconditioners are based on fully-coupled algebraic multigrid and approximate block factorization preconditioners. We will discuss how these methods provide a powerful integration path for multiscale coupling to the neutronics and structures applications. Initial results on scalabiltiy will be presented. Finally we will comment on our use of embedded technology and how this capbaility impacts the application of implicit methods, sensitivity analysis and UQ.

The potential for using the degraded beam of high-energy proton radiation sources for proton hardness assurance testing for ICs that are sensitive to proton direct ionization effects are explored. SRAMs were irradiated using high energy proton radiation sources (∼67-70 MeV). The proton energy was degraded using plastic or Al degraders. Peaks in the SEU cross section due to direct ionization were observed. To best observe proton direct ionization effects, one needs to maximize the number of protons in the energy spectrum below the proton energy SEU threshold. SRIM simulations show that there is a tradeoff between increasing the fraction of protons in the energy spectrum with low energies by decreasing the peak energy and the reduction in the total number of protons as protons are stopped in the device as the proton energy is decreased. Two possible methods for increasing the number of low energy protons is to decrease the primary proton energy to reduce the amount of energy straggle and to place the degrader close to the DUT to minimize angular dispersion. These results suggest that high-energy proton radiation sources may be useful for identifying devices sensitive to proton direct ionization. © 2011 IEEE.

Low dose rate experiments on field-oxide-field-effect-transistors (FOXFETs) fabricated in a 90 nm CMOS technology indicate that there is a dose rate enhancement factor (EF) associated with radiation-induced degradation. One dimensional (1-D) numerical calculations are used to investigate the key mechanisms responsible for the dose rate dependent buildup of radiation-induced defects in shallow trench isolation (STI) oxides. Calculations of damage EF indicate that oxide thickness, distribution of hole traps and hole capture cross-section affect dose rate sensitivity. The dose rate sensitivity of STI oxides is compared with the sensitivity of bipolar base oxides using model calculations. © 2011 IEEE.

The U.S. Department of Energy Office of Nuclear Energy (DOE-NE), Office of Fuel Cycle Technologies (OFCT) has established the Used Fuel Disposition Campaign (UFDC) to conduct research and development (R&D) activities related to storage, transportation and disposal of used nuclear fuel (UNF) and high level radioactive waste (HLW). The U.S. has, in accordance with the U.S. Nuclear Waste Policy Act (as amended), focused efforts for the past twentyplus years on disposing of UNF and HLW in a geologic repository at Yucca Mountain, Nevada. The recent decision by the U.S. DOE to no longer pursue the development of that repository has necessitated investigating alternative concepts for the disposal of UNF and HLW that exists today and that could be generated under future fuel cycles. The disposal of UNF and HLW in a range of geologic media has been investigated internationally. Considerable progress has been made by in the U.S and other nations, but gaps in knowledge still exist. The U.S. national laboratories have participated in these programs and have conducted R&D related to these issues to a limited extent. However, a comprehensive R&D program investigating a variety of storage, geologic media, and disposal concepts has not been a part of the U.S. waste management program since the mid 1980s because of its focus on the Yucca Mountain site. Such a comprehensive R&D program is being developed and executed in the UFDC using a systematic approach to identify potential R&D opportunities. This paper describes the process used by the UFDC to identify and prioritize R&D opportunities. The U.S. DOE has cooperated and collaborated with other countries in many different "arenas" including the Nuclear Energy Agency (NEA) within the Organisation for Economic Co-operation and Development (OECD), the International Atomic Energy Agency (IAEA), and through bilateral agreements with other countries. These international activities benefited the DOE through the acquisition and exchange of information, database development, and peer reviews by experts from other countries. Recognizing that programs in other countries have made significant advances in understanding a wide range of geologic environments, the UFDC has developed a strategy for continued, and expanded, international collaboration. This paper also describes this strategy. Copyright © 2011 by ASME.

The collector aperture and diameter of the receiver of a parabolic trough were studied to investigate the relative impacts of parasitic pressure drop, heat losses, and heat flux intercepted by the receiver tube. The configuration of an LS-2 parabolic trough was used as the baseline, and the size of the HCE and collector aperture were parametrically varied using values between the baseline and twice their original size. A Matlab computer model was created to determine the flux on the receiver, heat loss from the HCE, and pressure drop within the heat transfer fluid (HTF) at each combination of aperture size and receiver diameter. Flux on the receiver is calculated for each geometry assuming a Gaussian flux distribution. Based on pressure data from SEGS VII, the standard Darcy-Weisbach equation for the pressure drop was modified to include the contribution that connective joints of varying quantities and types have on the pressure drop within the HTF. The model employs the Sandia thermal resistive network and iteratively solves for the temperatures accounting for various heat transfer modes that contribute to the heat lost by the HCE. The Matlab model expresses pressure drop and heat losses in terms of electric power. It does this by calculating both the power required to pump the HTF for varying pressure drops and the power that could have been produced if heat was not lost to the environment. The Matlab model displays the results in the form of surface plots that represent the values of heat loss, efficiency, pumping power, etc. as a function of aperture size and receiver diameter. The combined effects of pressure drop, heat loss, and heat flux intercepted by the receiver tube were evaluated, and results show that configurations with receiver diameters ranging from 85-90 millimeters and large (up to 10 meter) aperture sizes minimize the overall power consumption and maximize the efficiency of a single loop. Structural effects, wind and gravity loads, and factors associated with the balance of plant were not considered. Copyright © 2011 by ASME.

Predicting the structural and optical performance of concentrating solar power (CSP) collectors is critical to the design and performance of CSP systems. This paper presents a performance analysis which utilizes finite-element models and ray-tracing of a parabolic trough collector. The finite-element models were used to determine the impact of gravity loads on displacements and rotations of the facet surfaces, resulting in slope error distributions across the reflective surfaces. The geometry of the LUZ LS-2 parabolic trough collector was modeled in SolidWorks, and the effects of gravity on the reflective surfaces are analyzed using SolidWorks Simulation. The ideal mirror shape, along with the 90° and 0° positions (with gravity deformation) were evaluated for the LS-2. The ray-tracing programs APEX and ASAP are used to assess the impact of gravity deformations on optical performance. In the first part of the analysis, a comprehensive study is performed for the parabolic trough to evaluate a random slope error threshold (i.e., induced by manufacturing errors and assembly processes) above which additional slope errors caused by gravity sag decrease the intercept factor of the system. The optical performance of the deformed shape of the collector (in both positions) is analyzed with additional induced slope errors ranging from zero up to 1° (17.44 mrad). The intercept factor for different solar incident angles found from ray-tracing is then compared to empirical data to demonstrate if the simulations provide consistent answers with experimental data. Copyright © 2011 by ASME.

Heliostat vibrations can degrade optical pointing accuracy while fatiguing the structural components. This paper reports the use of structural dynamic measurements for design evaluation and monitoring of heliostat vibrations. A heliostat located at the National Solar Thermal Testing Facility (NSTTF) at Sandia Labs in Albuquerque, New Mexico, has been instrumented to measure its modes of vibration, strain and displacements under wind loading. The information gained from these tests will be used to evaluate and improve structural models that predict the motions/deformations of the heliostat due to gravitational and dynamic wind loadings. These deformations can cause optical errors and motions that degrade the performance of the heliostat. The main contributions of this work include: (1) demonstration of the role of structural dynamic tests (also known as modal tests) to provide a characterization of the important dynamics of the heliostat structure as they relate to durability and optical accuracy, (2) the use of structural dynamic tests to provide data to evaluate and improve the accuracy of computer-based design models, and (3) the selection of sensors and data-processing techniques that are appropriate for long-term monitoring of heliostat motions. Copyright © 2011 by ASME.

Network measurement is a discipline that provides the techniques to collect data that are fundamental to many branches of computer science. While many capturing tools and comparisons have made available in the literature and elsewhere, the impact of these packet capturing tools on existing processes have not been thoroughly studied. While not a concern for collection methods in which dedicated servers are used, many usage scenarios of packet capturing now requires the packet capturing tool to run concurrently with operational processes. In this paper we perform experimental evaluations of the performance impact that packet capturing process have on webbased services; in particular, we observe the impact on web servers. We find that packet capturing processes indeed impact the performance of web servers, but on a multi- core system the impact varies depending on whether the packet capturing and web hosting processes are co-located or not. In addition, the architecture and behavior of the web server and process scheduling is coupled with the behavior of the packet capturing process, which in turn also affect the web server's performance. © 2011 IEEE.

A newly invented, multi-megampere inverse diode converts the currents in many electron beams to current in a single Magnetically Insulated Transmission Line (MITL) for driving a common load. Electrons are injected through a transparent anode, cross a vacuum gap, and are absorbed in the cathode of the inverse diode. The cathode current returns to the anode through a load and generates electric and magnetic fields in the anode-cathode gap. Counter streaming electron flow is prevented by self-magnetic insulation in most of the inverse diode and by self-electrostatic insulation where the magnetic field is insufficient. Two-dimensional simulations with a 40 MA, 4 MeV, 40 ns electron beam at 3.5 kA/cm 2 current density, 5 degree beam divergence, and up to 60 degree injection angle show 85% of the injected electron beam current is captured and fed into the MITL. Exploratory experiments with a 2.5 MA, 2.8 MeV, 40 ns electron beam at 2 kA/cm 2at injection normal to the anode gave 70+/-10% collection efficiency in an unoptimized inverse diode. The inverse diode appears to have the potential of coupling multiple pulsed power modules into a common load at rates of change of current ∼1.6× 10 15 A/s required for a fusion energy device called the Plasma Power Station with a Quasi Spherical Direct Drive fusion target. © 2011 IEEE.

Implementation of molten salt compounds as the heat transfer fluid and energy storage medium provides specific benefits to energy collection and conversion. Nitrate salts have been identified as a strong candidate for energy transfer and storage and have been demonstrated for use in these applications over time. As nitrate salts have solidification temperatures above ambient, concern for recovery from salt freezing events has instigated efforts to understand and predict this behavior. Accurate information of salt property behavior in the solid-phase is necessary for understanding recovery from a freeze event as well as for phase change thermal energy storage applications. Thermal properties for three representative salts (that span the range of melting temperatures from approximately 90-221 °C), have been obtained. These properties include specific heat, coefficient of thermal expansion, and thermal conductivity. Specific heat and thermal conductivity were measured using differential scanning calorimetry. Copyright © 2011 by ASME.

Abstract not provided.

Although the propene+OH reaction has been in the center of interest of numerous experimental and theoretical studies, rate coefficients have never been determined experimentally between ∼600 and ∼ 750 K, where the reaction is governed by the complex interaction of addition, back-dissociation and abstraction. In this work OH time-profiles are measured in two independent laboratories over a wide temperature region (200-950 K) and are analyzed incorporating recent theoretical results. The datasets are consistent both with each other and with the calculated rate coefficients. We present a simplified set of reactions validated over a broad temperature and pressure range, that can be used in smaller combustion models for propene+OH. In addition, the experimentally observed kinetic isotope effect for the abstraction is rationalized using ab initio calculations and variational transition-state theory. We recommend the following approximate description of the OH+C 3H6 reaction: C3H6+OH⇄C 3H6OH (R1a,R-1a) C3H6+OH→C 3H5+H2O (R1b) k1a(200K ≤ T ≤ 950 K;1 bar ≤ P) = 1.45×10-11 (T/K)-0.18e 460K/Tcm3 molecule-1s-1 k -1a(200 K ≤ T ≤ 950 K; 1 bar ≤ P) = 5.74×10 12e-12690K/Ts-1 k1b(200 K ≤ T ≤ 950 K) = 1.63×10-18 (T/K)2.36e -725K/T cm3 molecule-1s-1. © by Oldenbourg Wissenschaftsverlag, München.

The use of Low Temperature Co-Fired Ceramics (LTCC) is a very attractive material option for advanced packaging. For applications, a variety of features are printed in the base material: thermal and electrical vias, resistors, solder pads to name a few. Most of these features have materials that are thermally and elastically mismatched from the LTCC, producing a localized residual stress. These stresses impact the strength and reliability of the LTCC package. Here we present results and analysis for the strength and reliability assessment of an LTCC (DupontTM 951) with and without Au vias. The reliability of the ceramic material is assessed from the perspective of its susceptibility to sub-critical crack growth (SCG). Metallic vias can significantly lower the strength of the LTCC, however, their presence does not change the measured susceptibility of the material to SCG. Using our experimental data, and empirical descriptions of SCG laws, safe design life for LTCC packages under a particular stress state is estimated.

Automated randomized testing, known as fuzzing, is an effective and widely used technique for detecting faults and vulnerabilities in digital systems, and is a key tool for security assessment of smart-grid devices and protocols. It has been observed that the effectiveness of fuzzing can be improved by sampling test inputs in a targeted way that reflects likely fault conditions. We propose a systematic prescription for such targeting, which favors test inputs that are "simple" in an appropriate sense. The notion of Kolmogorov complexity provides a rigorous foundation for this approach. Under certain assumptions, an optimal fuzzing procedure is derived for statistically evaluating a system's security against a realistic attacker who also uses fuzzing. Copyright © 2011 Association for Computing Machinery.

A mesoscale dimensional artifact based on silicon bulk micromachining fabrication has been developed and manufactured with the intention of evaluating the artifact both on a high precision coordinate measuring machine (CMM) and video-probe based measuring systems. This hybrid artifact has features that can be located by both a touch probe and a video probe system. A key feature is that the physical edge can be located using a touch probe CMM, and this same physical edge can also be located using a video probe. While video-probe based systems are commonly used to inspect mesoscale mechanical components, a video-probe system's certified accuracy is generally much worse than its repeatability. To solve this problem, an artifact has been developed which can be calibrated using a commercially available high-accuracy tactile system and then be used to calibrate typical production vision-based measurement systems. This allows for error mapping to a higher degree of accuracy than is possible with a typical chrome-on-glass reference artifact. Details of the designed features and manufacturing process of the hybrid dimensional artifact are given, and a comparison of the designed features to the measured features of the manufactured artifact is presented and discussed. Measurement results are presented using a meter-scale CMM with submicron measurement uncertainty; an optical CMM with submicron measurement uncertainty; a micro-CMM with submicron measurement uncertainty using three different probes; and a form contour instrument.

Many subsystems encountered in communication systems can be modeled as linear periodic time-varyiing (LPTV) systems. In this paper, we present a novel structure preserving reduced-order modeling algorithm for LPTV systems. A key advance of our approach is that it preserves the periodic time-varying structure during the reduction process, thus resulting in reduced LPTV systems. Unlike prior LPTV model order reduction (MOR) techniques which recast the LPTV systems to artificial linear time-invariant (LTI) systems and apply LTI MOR techniques for reduction, our structure preserving algorithm uses a time-varying projection directly on the original LPTV systems. Our approach always produces a smaller system than the original system, which was not valid for previous LPTV MOR techniques. We validate the proposed technique with several circuit examples, demonstrating significant size reductions and excellent accuracy. © 2011 IEEE.

Low temperature cofired ceramic (LTCC) is a multilayer 3D packaging, interconnection, and integration technology. One of the advantages of LTCC is the ability it affords to integrate passive components via the coining processes. For LTCC modules with embedded resonator functions targeting high frequency applications, the temperature coefficient of resonant frequency (τf) is a critical parameter. The base dielectrics of commercial LTCC systems have a xf in the range -50 ∼80 ppm/°C. This study explores a method to achieve zero or near zero τf embedded resonators by incorporating τf compensating materials locally into a multilayer LTCC structure. Chemical interactions and physical compatibility between the τf modifiers and the host LTCC dielectrics are investigated. A stripline (SL) ring resonator with near zero τf is demonstrated in a non-zero τf commercial LTCC.

This paper will review the ignition fusion research program that is currently being carried out on the National Ignition Facility (NIF) located at Lawrence Livermore National Laboratory. This work is being conducted under the auspices of the National Ignition Campaign (NIC) that is a broad collaboration of national laboratories and universities that together have developed a detailed research plan whose goal is ignition in the laboratory. The paper will begin with a description of the NIF facility and associated experimental facilities. The paper will then focus on the ignition target and hohlraum designs that will be tested in the first ignition attempts on NIF. The next topic to be introduced will be a description of the diagnostic suite that has been developed for the initial ignition experiments on NIF. The paper will then describe the experimental results that were obtained in experiments conducted during the fall of 2009 on NIF. Finally, the paper will end with a description of the detailed experimental plans that have been developed for the first ignition campaign that will begin later this year. © 2011 The Japan Society of Plasma Science and Nuclear Fusion Research.

Solutions for analytical models of systems with nonlinear constraints have focused on exact methods for satisfying the constraint conditions. Exact methods often require that the constraint can be expressed in a piecewise-linear manner, and result in a series of mapping equations from one linear regime of the constraint to the next. Due to the complexity of these methods, exact methods are often limited to analyzing a small number of constraints for practical reasons. This paper proposes a new method for analyzing continuous systems with arbitrary nonlinear constraints by approximately satisfying the constraint conditions. Instead of dividing the constraints into multiple linear regimes, a discontinuous basis function is used to supplement the system's linear basis functions. As a result, precise contact times are not needed, enabling this method to be more computationally efficient than exact methods. While the discontinuous basis functions are continuous in displacement, their derivatives contain discontinuities that allow for the nonlinear forces to be accounted for with the assumption that the nonlinear constraints are able to be modeled in a discrete manner. Since each nonlinear constraint requires only one associated discontinuous basis function, this method is easily expanded to handle large numbers of constraints. In order to illustrate the application of this method, an example with a pinned-pinned beam is presented. © 2011 by ASME.

We examine several methods to create a sheet of magnesium oxide (MgO) macroporous ceramic material via tape casting. These methods include the approach pioneered by Akartuna et al. in which an oil/water emulsion is stabilized by surface-modified metal oxide particles at the droplet interfaces. Upon drying, a scaffold of the self-assembled particles is strong enough to be removed from the substrate material and sintered. We find that this method can be used with MgO particles surface modified by short amphiphilic molecules. This approach is compared with two more traditional methods to induce structure into a green ceramic: 1) creation of an MgO ceramic slip with added pore formers, and 2) sponge impregnation of a reticulated foam with the MgO slip. Green and sintered samples made using each method are hardness tested and results compared for several densities of the final ceramics. Optical and SEM images of the materials are shown.

The thermal conductivity of single crystal silicon was engineered using lithographically formed phononic crystals. Specifically, sub-micron periodic through-holes were patterned in 500nm-thick silicon membranes to construct phononic crystals, and through phonon scattering enhancement, heat transfer was significantly reduced. The thermal conductivity of silicon phononic crystals was measured as low as 32.6W/mK, which is a ∼75% reduction compared to bulk silicon thermal conductivity [1]. This corresponds to a 37% reduction even after taking into account the contributions of the thin-film and volume reduction effects, while the electrical conductivity was reduced only by as much as the volume reduction effect. The demonstrated method uses conventional lithography-based technologies that are directly applicable to diverse micro/nano-scale devices, leading toward huge performance improvements where heat management is important. © 2011 IEEE.

This paper compares measurements made by Raman and infrared thermometry on a SOI (silicon on insulator) bent-beam thermal microactuator. Both techniques are noncontact and used to experimentally measure temperatures along the legs and on the shuttle of the thermal microactuators. Raman thermometry offers micron spatial resolution and measurement uncertainties of ±10 K; however, typical data collection times are a minute per location leading to measurement times on the order of hours for a complete temperature profile. Infrared thermometry obtains a full-field measurement so the data collection time is much shorter; however, the spatial resolution is lower and calibrating the system for quantitative measurements is challenging. By obtaining thermal profiles on the same SOI thermal microactuator, the relative strengths and weaknesses of the two techniques are assessed. Copyright © 2011 by ASME.

Massively parallel computations consist of a mixture of computation, communication, and I/O. Of these three components, implementing an effective parallel I/O solution has often been overlooked by application scientists and has typically been added to large scale simulations only when existing serial techniques have failed. As scientists' teams scaled their codes to run on hundreds of processors, it was common to call on an I/O expert to implement a set of more scalable I/O routines. These routines were easily separated from the calculations and communication, and in many cases, an I/O kernel was derived from the application which could be used for testing I/O performance independent of the application. These I/O kernels developed a life of their own used as a broad measure for comparing different I/O techniques. Unfortunately, as years passed and computation and communication changes required changes to the I/O, the separate I/O kernel used for benchmarking remained static, no longer providing an accurate indicator of the I/O performance of the simulation, and making I/O research less relevant for the application scientists. In this paper we describe a new approach to this problem where I/O kernels are replaced with skeletal I/O applications that are automatically generated from an abstract set of simulation I/O parameters. We realize this abstraction by leveraging the ADIOS [1] middleware's XML I/O specification with additional runtime parameters. Skeletal applications offer all of the benefits of I/O kernels including allowing I/O optimizations to focus on useful I/O patterns. Moreover, since they are automatically generated, it is easy to produce an updated I/O skeleton whenever the simulation's I/O changes. In this paper we analyze the performance of automatically generated I/O skeletal applications for the S3D and GTS codes. We show that these skeletal applications achieve performance comparable to that of the production applications. We wrap up the paper with a discussion of future changes to make the skeletal application better approximate the actual I/O performed in the simulation. © 2011 IEEE.

Sandia National Laboratories' Metamaterial Science and Technology Program has developed novel HPC-based design tools, wafer scale 3D fabrication processes, and characterization tools to enable thermal IR optical metamaterial application studies. © 2011 IEEE.

Because of past military operations, lack of upkeep and looting there are now enormous radioactive waste problems in Iraq. These waste problems include destroyed nuclear facilities, uncharacterized radioactive wastes, liquid radioactive waste in underground tanks, wastes related to the production of yellow cake, sealed radioactive sources, activated metals and contaminated metals that must be constantly guarded. Iraq currently lacks the trained personnel, regulatory and physical infrastructure to safely and securely manage these facilities and wastes. In 2005 the International Atomic Energy Agency (IAEA) agreed to organize an international cooperative program to assist Iraq with these issues. Soon after, the Iraq Nuclear Facility Dismantlement and Disposal Program (the NDs Program) was initiated by the U.S. Department of State (DOS) to support the IAEA and assist the Government of Iraq (GOI) in eliminating the threats from poorly controlled radioactive materials. The Iraq NDs Program is providing support for the IAEA plus training, consultation and limited equipment to the GOI. The GOI owns the problems and will be responsible for implementation of the Iraq NDs Program.

In this paper, we demonstrate gate-all-around (GAA) single crystalline nanowires (SiNWs) that are fabricated using top-down standard CMOS front-end processes. The GAA silicon nanowires are fabricated in well-defined locations with high-quality electrical contacts, and controlled geometry and alignment. These SiNW FETs fabricated in this process have demonstrated repeatable electrical performance with threshold voltages of ∼0.2V and subthreshold slopes of ∼80mV/dec. The p-i-n silicon nanowires are highly sensitive to the intensity and polarization of the incident light. The results in this work demonstrate that individual SiNWs are good candidates for high resolution optical sensing and allow for tuning of the optical properties of the nanoscale devices by precise control of the nanowire geometry and orientation of the incident light. These top-down fabricated SiNWs can be easily integrated in high density arrays for enhanced light absorption, resulting in imaging sensors with nanoscale spatial resolution. © 2011 IEEE.

Inference techniques play a central role in many cognitive systems. They transform low-level observations of the environment into high-level, actionable knowledge which then gets used by mechanisms that drive action, problem-solving, and learning. This paper presents an initial effort at combining results from AI and psychology into a pragmatic and scalable computational reasoning system. Our approach combines a numeric notion of plausibility with first-order logic to produce an incremental inference engine that is guided by heuristics derived from the psychological literature. We illustrate core ideas with detailed examples and discuss the advantages of the approach with respect to cognitive systems.

The increasing fidelity of scientific simulations as they scale towards exascale sizes is straining the proven IO techniques championed throughout terascale computing. Chief among the successful IO techniques is the idea of collective IO where processes coordinate and exchange data prior to writing to storage in an effort to reduce the number of small, independent IO operations. As well as collective IO works for efficiently creating a data set in the canonical order, 3-D domain decompositions prove troublesome due to the amount of data exchanged prior to writing to storage. When each process has a tiny piece of a 3-D simulation space rather than a complete 'pencil' or 'plane', 2-D or 1-D domain decompositions respectively, the communication overhead to rearrange the data can dwarf the time spent actually writing to storage [27]. Our approach seeks to transparently increase scalability and performance while maintaining both the IO routines in the application and the final data format in the storage system. Accomplishing this leverages both the Nessie [23] RPC framework and a staging area with staging services. Through these tools, we employ a variety of data processing operations prior to invoking the native API to write data to storage yielding as much as a 3X performance improvement over the native calls. © 2011 ACM.

The effects of surrounding gaseous environment on the reaction behaviors and product formation for sputter-deposited Ti/2B reactive multilayers are reported. With the surrounding environment set to different air pressures, from atmospheric conditions to 10-4 Torr, Ti/2B samples were reacted in a self-propagating mode, and the average reaction wave velocities were determined through high-speed imaging. Propagation speeds for 3.0 μm-thick multilayers were in the range of 10.89 to 0.05 m/s depending on bilayer thickness (i.e., reactant layer periodicity) and ambient pressure. X-ray diffraction analysis showed that single-phase TiB2 forms within multilayers that have small bilayer thickness. Multilayers that have a large bilayer thickness developed a mixture of TiB2, TiB and TiO2. © 2012 Materials Research Society.

We explore the issue of interactions between metamaterial resonators and different types of absorbers placed in proximity to these resonators. Very clear anticrossing behaviour and level splitting is observed when IR phonons interact with planar metamaterials. More complex dipole transitions can be designed using semiconductor bandgap engineering. We show experimentally the coupling between metamaterial resonances and intersubband transitions and discuss this mechanism for electrical tuning of metamaterials throughout the optical infrared spectral region. Finally we will discuss interactions in 3D dielectric resonator metamaterials. © 2011 IEEE.

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An important application for low impedance pulsed power drivers is creating high pressures for shock compression of solids. These experiments are useful for studying material properties under kilobar to megabar pressures. The Z driver at Sandia National Laboratories has been used for such studies on a variety of materials, including heavy water, diamond, and tantalum, to name a few. In such experiments, it is important to prevent shock formation in the material samples. Shocks can form as the sound speed increases with loading; at some depth in the sample a pressure significantly higher than the surface pressure can result. The optimum pressure pulse shape to prevent such shocks depends on the test material and the sample thickness, and is generally not a simple sinusoidal-shaped current as a function of time. A system that can create a variety of pulse shapes would be desirable for testing various materials and sample thicknesses. A large number of relatively fast pulses, combined, could create the widest variety of pulse shapes. Linear transformer driver systems, whose cavities consist of many parallel capacitor-switch circuits, could have considerable agility in pulse shape. © 2011 IEEE.

A "best-effort" authentication method, which is easier to attack than generic authentication methods (but requires fewer computations for benign nodes), may be sufficient for certain networking scenarios. We illustrate this point by examining the case of fragment authentication by intermediaries in an opportunistic network. We describe mechanisms for implementing best-effort authentication, with the caveat that an authentication strength sufficient in one scenario may be unfit for another. © 2011 IEEE.

As part of the liquefied natural gas (LNG) Cascading Damage Study, a series of structural tests were conducted to investigate the thermal induced fracture of steel plate structures. The thermal stresses were achieved by applying liquid nitrogen (LN₂) onto sections of each steel plate. In addition to inducing large thermal stresses, the lowering of the steel temperature simultaneously reduced the fracture toughness. Liquid nitrogen was used as a surrogate for LNG due to safety concerns and since the temperature of LN₂ is similar (-190°C) to LNG (-161°C). The use of LN₂ ensured that the tests could achieve cryogenic temperatures in the range an actual vessel would encounter during a LNG spill. There were four phases to this test series. Phase I was the initial exploratory stage, which was used to develop the testing process. In the Phase II series of tests, larger plates were used and tested until fracture. The plate sizes ranged from 4 ft square pieces to 6 ft square sections with thicknesses from ¼ inches to ¾ inches. This phase investigated the cooling rates on larger plates and the effect of different notch geometries (stress concentrations used to initiate brittle fracture). Phase II was divided into two sections, Phase II-A and Phase II-B. Phase II-A used standard A36 steel, while Phase II-B used marine grade steels. In Phase III, the test structures were significantly larger, in the range of 12 ft by 12 ft by 3 ft high. These structures were designed with more complex geometries to include features similar to those on LNG vessels. The final test phase, Phase IV, investigated differences in the heat transfer (cooling rates) between LNG and LN₂. All of the tests conducted in this study are used in subsequent parts of the LNG Cascading Damage Study, specifically the computational analyses.

Conventional full spectrum gamma spectroscopic analysis has the objective of quantitative identification of all the radionuclides present in a measurement. For low-energy resolution detectors such as NaI, when photopeaks alone are not sufficient for complete isotopic identification, such analysis requires template spectra for all the radionuclides present in the measurement. When many radionuclides are present it is difficult to make the correct identification and this process often requires many attempts to obtain a statistically valid solution by highly skilled spectroscopists. A previous report investigated using the targeted principal component analysis method (TPCA) for detection of embedded sources for RPM applications. This method uses spatial/temporal information from multiple spectral measurements to test the hypothesis of the presence of a target spectrum of interest in these measurements without the need to identify all the other radionuclides present. The previous analysis showed that the TPCA method has significant potential for automated detection of target radionuclides of interest, but did not include the effects of shielding. This report complements the previous analysis by including the effects of spectral distortion due to shielding effects for the same problem of detection of embedded sources. Two examples, one with one target radionuclide and the other with two, show that the TPCA method can successfully detect shielded targets in the presence of many other radionuclides. The shielding parameters are determined as part of the optimization process using interpolation of library spectra that are defined on a 2D grid of atomic numbers and areal densities.

In 1965 Gordon Moore wrote an article claiming that integrated circuit density would scale exponentially. His prediction has remained valid for more than four decades. Integrated circuits have changed all aspects of everyday life. They are also the 'heart and soul' of modern systems for defense, national infrastructure, and intelligence applications. The United States government needs an assured and trusted microelectronics supply for military systems. However, migration of microelectronics design and manufacturing from the United States to other countries in recent years has placed the supply of trusted microelectronics in jeopardy. Prevailing wisdom dictates that it is necessary to use microelectronics fabricated in a state-of-the-art technology for highest performance and military system superiority. Close examination of silicon microelectronics technology evolution and Moore's Law reveals that this prevailing wisdom is not necessarily true. This presents the US government the possibility of a totally new approach to acquire trusted microelectronics.

This Pollution Prevention Opportunity Assessment (PPOA) was conducted for the MicroFab and SiFab facilities at Sandia National Laboratories/New Mexico in Fiscal Year 2011. The primary purpose of this PPOA is to provide recommendations to assist organizations in reducing the generation of waste and improving the efficiency of their processes and procedures. This report contains a summary of the information collected, the analyses performed, and recommended options for implementation. The Sandia National Laboratories Environmental Management System (EMS) and Pollution Prevention (P2) staff will continue to work with the organizations to implement the recommendations.

A dynamic reactor model has been developed for pulse-type reactor applications. The model predicts reactor power, axial and radial fuel expansion, prompt and delayed neutron population, and prompt and delayed gamma population. All model predictions are made as a function of time. The model includes the reactivity effect of fuel expansion on a dynamic timescale as a feedback mechanism for reactor power. All inputs to the model are calculated from first principles, either directly by solving systems of equations, or indirectly from Monte Carlo N-Particle Transport Code (MCNP) derived results. The model does not include any empirical parameters that can be adjusted to match experimental data. Comparisons of model predictions to actual Sandia Pulse Reactor SPR-III pulses show very good agreement for a full range of pulse magnitudes. The model is also applied to Z-pinch externally driven neutron assembly (ZEDNA) type reactor designs to model both normal and off-normal ZEDNA operations.

We present the results of a three year LDRD project that has focused on overcoming major materials roadblocks to achieving AlGaN-based deep-UV laser diodes. We describe our growth approach to achieving AlGaN templates with greater than ten times reduction of threading dislocations which resulted in greater than seven times enhancement of AlGaN quantum well photoluminescence and 15 times increase in electroluminescence from LED test structures. We describe the application of deep-level optical spectroscopy to AlGaN epilayers to quantify deep level energies and densities and further correlate defect properties with AlGaN luminescence efficiency. We further review our development of p-type short period superlattice structures as an approach to mitigate the high acceptor activation energies in AlGaN alloys. Finally, we describe our laser diode fabrication process, highlighting the development of highly vertical and smooth etched laser facets, as well as characterization of resulting laser heterostructures.

Structural Considerations for Solar Installers provides a comprehensive outline of structural considerations associated with simplified solar installations and recommends a set of best practices installers can follow when assessing such considerations. Information in the manual comes from engineering and solar experts as well as case studies. The objectives of the manual are to ensure safety and structural durability for rooftop solar installations and to potentially accelerate the permitting process by identifying and remedying structural issues prior to installation. The purpose of this document is to provide tools and guidelines for installers to help ensure that residential photovoltaic (PV) power systems are properly specified and installed with respect to the continuing structural integrity of the building.

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A microkinetic chemical reaction mechanism capable of describing both the storage and regeneration processes in a fully formulated lean NOx trap (LNT) is presented. The mechanism includes steps occurring on the precious metal, barium oxide (NOx storage), and cerium oxide (oxygen storage) sites of the catalyst. The complete reaction set is used in conjunction with a transient plug flow reactor code (including boundary layer mass transfer) to simulate not only a set of long storage/regeneration cycles with a CO/H2 reductant, but also a series of steady flow temperature sweep experiments that were previously analyzed with just a precious metal mechanism and a steady state code neglecting mass transfer. The results show that, while mass transfer effects are generally minor, NOx storage is not negligible during some of the temperature ramps, necessitating a re-evaluation of the precious metal kinetic parameters. The parameters for the entire mechanism are inferred by finding the best overall fit to the complete set of experiments. Rigorous thermodynamic consistency is enforced for parallel reaction pathways and with respect to known data for all of the gas phase species involved. It is found that, with a few minor exceptions, all of the basic experimental observations can be reproduced with the transient simulations. In addition to accounting for normal cycling behavior, the final mechanism should provide a starting point for the description of further LNT phenomena such as desulfation and the role of alternative reductants.

Development of an effective strategy for shelter and evacuation is among the most important planning tasks in preparation for response to a low yield, nuclear detonation in an urban area. Extensive studies have been performed and guidance published that highlight the key principles for saving lives following such an event. However, region-specific data are important in the planning process as well. This study examines some of the unique regional factors that impact planning for a 10 kT detonation in the National Capital Region. The work utilizes a single scenario to examine regional impacts as well as the shelter-evacuate decision alternatives at one exemplary point. For most Washington, DC neighborhoods, the excellent assessed shelter quality available make shelter-in-place or selective transit to a nearby shelter a compelling post-detonation strategy.

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The DAKOTA (Design Analysis Kit for Optimization and Terascale Applications) toolkit provides a flexible and extensible interface between simulation codes and iterative analysis methods. DAKOTA contains algorithms for optimization with gradient and nongradient-based methods; uncertainty quantification with sampling, reliability, and stochastic expansion methods; parameter estimation with nonlinear least squares methods; and sensitivity/variance analysis with design of experiments and parameter study methods. These capabilities may be used on their own or as components within advanced strategies such as surrogate-based optimization, mixed integer nonlinear programming, or optimization under uncertainty. By employing object-oriented design to implement abstractions of the key components required for iterative systems analyses, the DAKOTA toolkit provides a flexible and extensible problem-solving environment for design and performance analysis of computational models on high performance computers. This report serves as a theoretical manual for selected algorithms implemented within the DAKOTA software. It is not intended as a comprehensive theoretical treatment, since a number of existing texts cover general optimization theory, statistical analysis, and other introductory topics. Rather, this manual is intended to summarize a set of DAKOTA-related research publications in the areas of surrogate-based optimization, uncertainty quantification, and optimization under uncertainty that provide the foundation for many of DAKOTA's iterative analysis capabilities.

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For a CASL grid-to-rod fretting problem, Sandia's Percept software was used in conjunction with the Sierra Mechanics suite to analyze the convergence behavior of the data transfer from a fluid simulation to a solid mechanics simulation. An analytic function, with properties relatively close to numerically computed fluid approximations, was chosen to represent the pressure solution in the fluid domain. The analytic pressure was interpolated on a sequence of grids on the fluid domain, and transferred onto a separate sequence of grids in the solid domain. The error in the resulting pressure in the solid domain was measured with respect to the analytic pressure. The error in pressure approached zero as both the fluid and solids meshes were refined. The convergence of the transfer algorithm was limited by whether the source grid resolution was the same or finer than the target grid resolution. In addition, using a feature coverage analysis, we found gaps in the solid mechanics code verification test suite directly relevant to the prototype CASL GTRF simulations.

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