Publications

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The screening process for DG interconnection procedures needs to be improved in order to increase the PV deployment level on the distribution grid. A significant improvement in the current screening process could be achieved by finding a method to classify the feeders in a utility service territory and determine the sensitivity of particular groups of distribution feeders to the impacts of high PV deployment levels. This report describes the utility distribution feeder characteristics in California for a large dataset of 8,163 feeders and summarizes the California feeder population including the range of characteristics identified and most important to hosting capacity. The report describes the set of feeders that are identified for modeling and analysis as well as feeders identified for the control group. The report presents a method for separating a utility's distribution feeders into unique clusters using the k-means clustering algorithm. An approach for determining the feeder variables of interest for use in a clustering algorithm is also described. The report presents an approach for choosing the feeder variables to be utilized in the clustering process and a method is identified for determining the optimal number of representative clusters.

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A laboratory testing program was developed to examine the short-term mechanical and time-dependent (creep) behavior of salt from the Bayou Choctaw Salt Dome. This report documents the test methodologies, and constitutive properties inferred from tests performed. These are used to extend our understanding of the mechanical behavior of the Bayou Choctaw domal salt and provide a data set for numerical analyses. The resulting information will be used to support numerical analyses of the current state of the Bayou Choctaw Dome as it relates to its crude oil storage function as part of the US Strategic Petroleum Reserve. Core obtained from Drill Hole BC-102B was tested under creep and quasi-static constant mean stress axisymmetric compression, and constant mean stress axisymmetric extension conditions. Creep tests were performed at 100 degrees Fahrenheit, and the axisymmetric tests were performed at ambient temperatures (72-78 degrees Fahrenheit). The testing performed indicates that the dilation criterion is pressure and stress state dependent. It was found that as the mean stress increases, the shear stress required to cause dilation increases. The results for this salt are reasonably consistent with those observed for other domal salts. Also it was observed that tests performed under extensile conditions required consistently lower shear stress to cause dilation for the same mean stress, which is consistent with other domal salts. Young's moduli ranged from 3.95 x 10⁶ to 8.51 x 10⁶ psi with an average of 6.44 x 10⁶ psi, with Poisson's ratios ranging from 0.10 to 0.43 with an average of 0.30. Creep testing indicates that the BC salt is intermediate in creep resistance when compared with other bedded and domal salt steady-state behavior.

This report summarizes the work performed in developing a framework for the prioritization of cavern access wells for remediation and monitoring at the Big Hill Strategic Petroleum Reserve site. This framework was then applied to all 28 wells at the Big Hill site with each well receiving a grade for remediation and monitoring. Numerous factors affecting well integrity were incorporated into the grading framework including casing survey results, cavern pressure history, results from geomechanical simulations, and site geologic factors. The framework was developed in a way as to be applicable to all four of the Strategic Petroleum Reserve sites.

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This white paper focuses on "advanced microgrids," but sections do, out of necessity, reference today's commercially available systems and installations in order to clearly distinguish the differences and advances. Advanced microgrids have been identified as being a necessary part of the modern electrical grid through a two DOE microgrid workshops, the National Institute of Standards and Technology, Smart Grid Interoperability Panel and other related sources. With their grid-interconnectivity advantages, advanced microgrids will improve system energy efficiency and reliability and provide enabling technologies for grid-independence to end-user sites. One popular definition that has been evolved and is used in multiple references is that a microgrid is a group of interconnected loads and distributed-energy resources within clearly defined electrical boundaries that acts as a single controllable entity with respect to the grid. A microgrid can connect and disconnect from the grid to enable it to operate in both grid-connected or island-mode. Further, an advanced microgrid can then be loosely defined as a dynamic microgrid.

The power output variability of photovoltaic systems can affect local electrical grids in locations with high renewable energy penetrations or weak distribution or transmission systems. In those rare cases, quick controllable generators (e.g., energy storage systems) or loads can counteract the destabilizing effects by compensating for the power fluctuations. Previously, control algorithms for coordinated and uncoordinated operation of a small natural gas engine-generator (genset) and a battery for smoothing PV plant output were optimized using MATLAB/Simulink simulations. The simulations demonstrated that a traditional generation resource such as a natural gas genset in combination with a battery would smooth the photovoltaic output while using a smaller battery state of charge (SOC) range and extending the life of the battery. This paper reports on the experimental implementation of the coordinated and uncoordinated controllers to verify the simulations and determine the differences in the controllers. The experiments were performed with the PNM PV and energy storage Prosperity site and a gas engine-generator located at the Aperture Center at Mesa Del Sol in Albuquerque, New Mexico. Two field demonstrations were performed to compare the different PV smoothing control algorithms: (1) implementing the coordinated and uncoordinated controls while switching off a subsection of the PV array at precise times on successive clear days, and (2) comparing the results of the battery and genset outputs for the coordinated control on a high variability day with simulations of the coordinated and uncoordinated controls. It was found that for certain PV power profiles the SOC range of the battery may be larger with the coordinated control, but the total amp-hours through the battery-which approximates battery wear-will always be smaller with the coordinated control.

The objective of this project was to evaluate the use of the Johnson-Cook strength and failure models in an adiabatic finite element model to simulate the puncture of 7075- T651 aluminum plates that were studied as part of an ASC L2 milestone by Corona et al (2012). The Johnson-Cook model parameters were determined from material test data. The results show a marked improvement, in particular in the calculated threshold velocity between no puncture and puncture, over those obtained in 2012. The threshold velocity calculated using a baseline model is just 4% higher than the mean value determined from experiment, in contrast to 60% in the 2012 predictions. Sensitivity studies showed that the threshold velocity predictions were improved by calibrating the relations between the equivalent plastic strain at failure and stress triaxiality, strain rate and temperature, as well as by the inclusion of adiabatic heating.

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The line-imaging ORVIS or VISAR provides velocity as a function of position and time for a line on an experimental setup via a streak camera record of interference fringes. This document describes a Matlab-based program which guides the user through the process of converting these fringe data to a velocity surface. The data reduction is of the "fringe trace" type, wherein the changes in velocity at a given position on the line are calculated based on fringe motion past that point. The analyst must establish the fringe behavior up front, aided by peak-finding routines in the program. However, the later work of using fringe jumps to compensate for phase problems in other analysis techniques is greatly reduced. This program is not a standard GUI construction, and is prescriptive. At various points it saves the progress, allowing later restarts from those points.

The Saturn accelerator, owned by Sandia National Laboratories, has been in operation since the early 1980s and still has many of the original systems. A critical legacy system is the oil transfer system which transfers 250,000 gallons of transformer oil from outside storage tanks to the Saturn facility. The oil transfer system was identified for upgrade to current technology standards. Using the existing valves, pumps, and relay controls, the system was automated using the National Instruments cRIO FGPA platform. Engineered safety practices, including a failure mode effects analysis, were used to develop error handling requirements. The uniqueness of the Saturn Oil Automated Transfer System (SOATS) is in the graphical user interface. The SOATS uses an HTML interface to communicate to the cRIO, creating a platform independent control system. The SOATS was commissioned in April 2013.

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An evaluation of calcium tungsten oxide (CaWO4) nanoparticles' properties was conducted using the powders generated from an all-alkoxide solvothermal (SOLVO) route. The reaction involved a toluene/pyridine mixture of tungsten(V) ethoxide ([W(OEt)5]) with calcium bis(trimethyl silyl) amide ([Ca(N(Si(CH3)3)2]) modified in situ by a series of alcohols (H-OR) including neo-pentanol (H-OCH2C(CH 3)3 or H-ONep) or sterically varied aryl alcohols (H-OC6H3R2-2,6 where R = CH3 (H-DMP), CH(CH3)2 (H-DIP), C(CH3)3 (DBP))]. Attempts to identify the intermediates generated from this series of reactions led to the crystallographic identification of [(OEt) 4W(μ-OEt)2Ca(DBP)2] (1). Each different SOLVO generated "initial" powder was found by transmission electron microscopy (TEM) and powder X-ray diffraction (PXRD) to be nanomaterials roughly assigned as the scheelite phase (PDF 00-041-1431); however, these initial powders displayed no luminescent behavior as determined by photoluminescence (PL) measurements. Thermal processing of these powders at 450, 650, and 750 C yielded progressively larger and more crystalline scheelite nanoparticles. Both PL and cathodoluminescent (CL) emission (422-425 and 429 nm, respectively) were observed for the nanomaterials processed at 750 C. Ion beam induced luminescence (IBIL, 478 nm) appeared to be in agreement with these PL and CL measurements. Further processing of the materials at 1000 C, led to a coalescence of the particles and significant improvement in the observed PL (445 nm) and CL measurements; however, the IBIL spectrum of this material was significantly altered upon exposure. These data suggest that the smaller nanoparticles were more stable to radiation effects possibly due to the lack of energy deposits based on the short track length; whereas the larger particles appear to suffer from radiation induced structural defects. © 2013 American Chemical Society.

Various components of a cell tester are shown and specifications described.

The efficient and controlled assembly of complex structures from macromolecular building blocks is a critical open question in both biological systems and nanoscience. Using molecular dynamics simulations we study the self-assembly of tubular structures from model macromolecular monomers with multiple binding sites on their surfaces [Cheng et al., Soft Matter, 2012, 8, 5666-5678]. In this work we add chirality to the model monomer and a lock-and-key interaction. The self-assembly of free monomers into tubules yields a pitch value that often does not match the chirality of the monomer (including achiral monomers). We show that this mismatch occurs because of a twist deformation that brings the lateral interaction sites into alignment when the tubule pitch differs from the monomer chirality. The energy cost for this deformation is small as the energy distributions substantially overlap for small differences in the pitch and chirality. In order to control the tubule pitch by preventing the twist deformation, the interaction between the vertical surfaces must be increased without resulting in kinetically trapped structures. For this purpose, we employ lock-and-key interactions and obtain good control of the self-assembled tubule pitch. These results explain some fundamental features of microtubules. The vertical interaction strength is larger than the lateral in microtubules because this yields a controlled assembly of tubules with the proper pitch. We also generally find that the control of the assembly into tubules is difficult, which explains the wide range of pitch values and protofilament numbers observed in microtubule assembly. © The Royal Society of Chemistry.

The Piecewise Parabolic Method (PPM) was designed as a means of exploring compressible gas dynam-ics problems of interest in astrophysics, including super-sonic jets, compressible turbulence, stellar convection, and turbulent mixing and burning of gases in stellar interiors. Over time, the capabilities encapsulated in PPM have co-evolved with the availability of a series of high performance computing platforms. Implementation of the algorithm has adapted to and advanced with the architectural capabilities and characteristics of these machines. This adaptability of our PPM codes has enabled targeted astrophysical applica-tions of PPM to exploit these scarce resources to explore complex physical phenomena. Here we describe the means by which this was accomplished, and set a path forward, with a new miniapp, mPPM, for continuing this process in a diverse and dynamic architecture design environment. Adaptations in mPPM for the latest high performance machines are discussed that address the important issue of limited bandwidth from locally attached main memory to the microprocessor chip.

Disruptive changes to computer architecture are paving the way toward extreme scale computing. The co-design strategy of collaborative research and development among computer architects, system software designers, and application teams can help to ensure that applications not only cope but thrive with these changes. In this paper, we present a novel combined co-design approach of emulation and simulation in the context of investigating future Processing in Memory (PIM) architectures. PIM enables co-location of data and computation to decrease data movement, to provide increases in memory speed and capacity compared to existing technologies and, perhaps most importantly for extreme scale, to improve energy efficiency. Our evaluation of PIM focuses on three mini-applications representing important production applications. The emulation and simulation studies examine the effects of locality-aware versus locality-oblivious data distribution and computation, and they compare PIM to conventional architectures. Both studies contribute in their own way to the overall understanding of the application-architecture interactions, and our results suggest that PIM technology shows great potential for efficient computation without negatively impacting productivity.

Controlling the size and shape of nanopores in polymer membranes can significantly impact transport of molecular or ionic species through these membranes. Here we describe a facile method to controllably form conical nanopores in ion-tracked polycarbonate membranes. Commercial polycarbonate ion-tracked membranes were placed between a concentrated alkaline solution and an acidic solution. By varying the height of the acidic solution, the hydrostatic pressure was controlled, regulating the acid flux through the nanopores. The resulting asymmetric etching of the membrane produced conical pores with controllable aspect ratios. Scanning electron microscopy of both the pores and nickel nanostructures electrolessly templated in the pores confirms their conical shape. This safe, straightforward approach obviates the need to use large voltages, currents, and/or plasma etching equipment traditionally employed to create conical nanopores. © 2014 The Royal Society of Chemistry.

Understanding how resources of High Performance Compute platforms are utilized by applications both individually and as a composite is key to application and platform performance. Typical system monitoring tools do not provide sufficient fidelity while application profiling tools do not capture the complex interplay between applications competing for shared resources. To gain new insights, monitoring tools must run continuously, system wide, at frequencies appropriate to the metrics of interest while having minimal impact on application performance. We introduce the Lightweight Distributed Metric Service for scalable, lightweight monitoring of large scale computing systems and applications. We describe issues and constraints guiding deployment in Sandia National Laboratories' capacity computing environment and on the National Center for Supercomputing Applications' Blue Waters platform including motivations, metrics of choice, and requirements relating to the scale and specialized nature of Blue Waters. We address monitoring overhead and impact on application performance and provide illustrative profiling results.

Krylov subspace projection methods are widely used iterative methods for solving large-scale linear systems of equations. Researchers have demonstrated that communication avoiding (CA) techniques can improve Krylov methods' performance on modern computers, where communication is becoming increasingly expensive compared to arithmetic operations. In this paper, we extend these studies by two major contributions. First, we present our implementation of a CA variant of the Generalized Minimum Residual (GMRES) method, called CAGMRES, for solving no symmetric linear systems of equations on a hybrid CPU/GPU cluster. Our performance results on up to 120 GPUs show that CA-GMRES gives a speedup of up to 2.5x in total solution time over standard GMRES on a hybrid cluster with twelve Intel Xeon CPUs and three Nvidia Fermi GPUs on each node. We then outline a domain decomposition framework to introduce a family of preconditioners that are suitable for CA Krylov methods. Our preconditioners do not incur any additional communication and allow the easy reuse of existing algorithms and software for the sub domain solves. Experimental results on the hybrid CPU/GPU cluster demonstrate that CA-GMRES with preconditioning achieve a speedup of up to 7.4x over CAGMRES without preconditioning, and speedup of up to 1.7x over GMRES with preconditioning in total solution time. These results confirm the potential of our framework to develop a practical and effective preconditioned CA Krylov method.

The potential impacts of man-made and natural disasters on chemical plants, complexes, and supply chains are of great importance to homeland security. To be able to estimate these impacts, we developed an agent-based chemical supply chain model that includes: chemical plants with enterprise operations such as purchasing, production scheduling, and inventories; merchant chemical markets, and multi-modal chemical shipments. Large-scale simulations of chemical-plant activities and supply chain interactions, running on desktop computers, are used to estimate the scope and duration of disruptive-event impacts, and overall system resilience, based on the extent to which individual chemical plants can adjust their internal operations (e.g., production mixes and levels) versus their external interactions (market sales and purchases, and transportation routes and modes). To illustrate how the model estimates the impacts of a hurricane disruption, a simple example model centered on 1,4-butanediol is presented. © 2013 Elsevier Ltd.

This study examines the single-event response of the Xilinx 28 nm Kintex-7 FPGA irradiated with heavy ions. Results for single-event effects on configuration SRAM cells, user-accessible Flip-Flop cells, and BlockRAM™ memory are provided. This study also describes an unconventional single event latch-up signature observed during testing.

This study examines the single-event response of the Xilinx 28 nm Kintex-7 FPGA irradiated with heavy ions. Results for single-event effects on configuration SRAM cells, user-accessible Flip-Flop cells, and BlockRAM™ memory are provided. This study also describes an unconventional single event latch-up signature observed during testing.

We present a new optimization-based method for atomistic-to-continuum (AtC) coupling. The main idea is to cast the latter as a constrained optimization problem with virtual Dirichlet controls on the interfaces between the atomistic and continuum subdomains. The optimization objective is to minimize the error between the atomistic and continuum solutions on the overlap between the two subdomains, while the atomistic and continuum force balance equations provide the constraints. Separation, rather then blending of the atomistic and continuum problems, and their subsequent use as constraints in the optimization problem distinguishes our approach from the existing AtC formulations. We present and analyze the method in the context of a one-dimensional chain of atoms modeled using a linearized two-body potential with next-nearest neighbor interactions.

Perovskite oxides (ABO3) are a largely unexplored class of materials in solar fuel applications. In this paper we examine the use of nonstoichiometric perovskite-type oxides in a two-step, solar-thermochemical water or carbon dioxide splitting cycle. We find that O2 begins to evolve during thermal reduction from a Sr- and Mn-doped LaAlO3 fully 300 °C lower than that of CeO2, and that these compounds will split both H2O and CO2. The yield of H2 and CO is significantly greater than CeO2, a benchmark material in solar fuels research, at a thermal reduction temperature 150 °C below that commonly reported for CeO2. In addition, the perovskite redox kinetics compare favorably to CeO2, which is known for its rapid reaction rates. We also find that an Fe-doped CaTiO3 is redox active and will split H2O, though the performance of this material is similar to that of CeO2. Finally, we introduce an experimental protocol that combines an ideal stagnation-flow reactor with detailed numerical modeling to effectively deconvolve intrinsic material behavior from interference induced by physical processes occurring inside the flow reactor. This method utilizes rate information contained within the entire time domain of the oxidation reaction, and assigns rate-governing processes to the material within the context of solid-state kinetic theory. © 2013 The Authors.

With demand for energy increasing worldwide and an ever-stronger case building for anthropogenic climate change, the need for carbon-neutral fuels is becoming an imperative. Extensive transportation infrastructure based on liquid hydrocarbon fuels motivates development of processes using solar energy to convert CO2 and H2O to fuel precursors such as synthesis gas. Here, perspectives concerning the use of solar-driven thermochemical cycles using metal oxides to produce fuel precursors are given and, in particular, the important relationship between reactor design and material selection is discussed. Considering both a detailed thermodynamic analysis and factors such as reaction kinetics, volatility, and phase stability, an integrated analytical approach that facilitates material design is presented. These concepts are illustrated using three oxide materials currently receiving considerable attention: metal-substituted ferrites, ceria, and doped cerias. Although none of these materials is "ideal," the tradeoffs made in selecting any one of them are clearly indicated, providing a starting point for assessing the feasibility of alternative materials developed in the future. Increasing demand for energy and anthropogenic climate change make carbon-neutral fuels an imperative. Transportation infrastructure based on liquid fuels motivates the development of solar-driven processes to convert CO2 and H 2O to fuel precursors. This perspective concerns the use of solar-driven thermochemical cycles based on metal oxides to produce fuel precursors and the synergistic relationship between reactor design and material selection. © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Computational uid dynamics (CFD) is a powerful analysis tool for engineering anal- ysis of aerodynamic devices. Though great effort has been expended to assist the CFD practitioner in mesh generation efforts, investigation of spatial discretization error is still one of the primary time costs associated with field simulations. As complexity in both physics and geometry continues to increase, uniform grid refinement studies are not always practical from either a time or computational cost perspective. Error transport equations have been investigated by many researchers with the goal of providing greater confidence in simulation results while utilizing only a single mesh. One of the primary diffculties in applying these methods is the computation of a reliable error source model. This work presents a method for approximating these error sources with the intent of creating a gen- eral model which is applicable to all flux types within a general gas dynamics framework. Adaptivity results as well as comparison with a popular error source model are presented.

A substantial reduction of net compared to gross erosion of molybdenum and tungsten was observed in experiments conducted in the lower divertor of DIII-D using the divertor material evaluation system. Post-exposure net erosion of molybdenum and tungsten films was measured by Rutherford backscattering (RBS) yielding net erosion rates of 0.4-0.7 nm s-1 for Mo and ∼0.14 nm s-1 for W. Gross erosion was estimated using RBS on a 1 mm diameter sample, where re-deposition is negligible. Net erosion on a 1 cm diameter sample was reduced compared to gross erosion by factors of ∼2 for Mo and ∼3 for W. The experiment was modeled with the REDEP/WBC erosion/re-deposition code package coupled to the Ion Transport in Materials and Compounds - DYNamics mixed-material code, with plasma conditions supplied by the Onion skin modeling + Eirene + Divimp for edGE modeling code with input from divertor Langmuir probes. The code-calculated net/gross erosion rate ratios of 0.46 for Mo and 0.33 for W are in agreement with the experiment. © 2014 The Royal Swedish Academy of Sciences.

Because both the accuracy and spatial resolution of digital image correlation (DIC) are directly related to the field-of-view and the number of pixels, it is sometimes advantageous to have a tight view for high resolution measurements and a wide view for overall object deformation. This approach will be demonstrated using a high-speed measurement of the deformation and strain of a riveted thin plate with an explosive loading. Overall plate deformation was provided by a wide-view stereo system, while a tight view of a section of the rivets was imaged with a second stereo pair to measure the strain around the rivet holes. The challenge is creating a speckle pattern which will work with both systems without creating holes in the overall measurement data. This was accomplished by creating a black/white course pattern for the wide view and a black/grey/white fine pattern for the tight view. The grey speckles were sized such that they are not resolved by the wide view and therefore do not compromise the full-field measurement. Details of the process and example results will be presented. © The Society for Experimental Mechanics, Inc. 2014.

A unique quasi-static temperature dependent low strain rate finite element constitutive failure model has been developed at Sandia National Laboratories (Dempsey JF, Antoun B, Wellman G, Romero V, Scherzinger W (2010) Coupled thermal pressurization failure simulations with validation experiments. Presentation at ASME 2010 international mechanical engineering congress & exposition, Vancouver, 12-18 Nov 2010) and is being to be used to predict failure initiation of pressurized components at high temperature. In order to assess the accuracy of this constitutive model, validation experiments of a cylindrical stainless steel pipe, heated and pressurized to failure is performed. This "pipe bomb" is instrumented with thermocouples and a pressure sensor whereby temperatures and pressure are recorded with time until failure occurs. The pressure and thermocouple temperatures are then mapped to a finite element model of this pipe bomb. Mesh refinement and temperature mapping impacts on failure pressure prediction in support of the model validation assessment is discussed. © The Society for Experimental Mechanics Inc. 2014.

The objective is to calculate the probability, PF, that a device will fail when its inputs, x, are randomly distributed with probability density, p (x), e.g., the probability that a device will fracture when subject to varying loads. Here failure is defined as some scalar function, y (x), exceeding a threshold, T. If evaluating y (x) via physical or numerical experiments is sufficiently expensive or PF is sufficiently small, then Monte Carlo (MC) methods to estimate PF will be unfeasible due to the large number of function evaluations required for a specified accuracy. Importance sampling (IS), i.e., preferentially sampling from “important” regions in the input space and appropriately down-weighting to obtain an unbiased estimate, is one approach to assess PF more efficiently. The inputs are sampled from an importance density, pʹ (x). We present an adaptive importance sampling (AIS) approach which endeavors to adaptively improve the estimate of the ideal importance density, p* (x), during the sampling process. Our approach uses a mixture of component probability densities that each approximate p* (x). An iterative process is used to construct the sequence of improving component probability densities. At each iteration, a Gaussian process (GP) surrogate is used to help identify areas in the space where failure is likely to occur. The GPs are not used to directly calculate the failure probability; they are only used to approximate the importance density. Thus, our Gaussian process adaptive importance sampling (GPAIS) algorithm overcomes limitations involving using a potentially inaccurate surrogate model directly in IS calculations. This robust GPAIS algorithm performs surprisingly well on a pathological test function.

Microalgae have been identified as a promising renewable feedstock for production of lipids for feeds and fuels. Current methods for identifying algae strains and growth conditions that support high lipid production require a variety of fluorescent chemical indicators, such as Nile Red and more recently, Bodipy. Despite notable successes using these approaches, chemical indicators exhibit several drawbacks, including non-uniform staining, low lipid specificity, cellular toxicity, and variable permeability based on cell-type, limiting their applicability for high-throughput bioprospecting. In this work, we used in vivo hyperspectral confocal fluorescence microscopy of a variety of potential microalgae production strains (Nannochloropsis sp., Dunaliella salina, Neochloris oleoabundans, and Chlamydomonas reinhardtii) to identify a label-free method for localizing lipid bodies and quantifying the lipid yield on a single-cell basis. By analyzing endogenous fluorescence from chlorophyll and resonance Raman emission from lipid-solubilized carotenoids we deconvolved pure component emission spectra and generated diffraction limited projections of the lipid bodies and chloroplast organelles, respectively. Applying this imaging method to nutrient depletion time-courses from lab-scale and outdoor cultivation systems revealed an additional autofluorescence spectral component that became more prominent over time, and varied inversely with the chlorophyll intensity, indicative of physiological compromise of the algal cell. This signal could result in false-positives for conventional measurements of lipid accumulation (via spectral overlap with Nile Red), however, the additional spectral feature was found to be useful for classification of lipid enrichment and culture crash conditions in the outdoor cultivation system. Under nutrient deprivation, increases in the lipid fraction of the cellular volume of ~. 500% were observed, as well as a correlated decrease in the chloroplast fraction of the total cellular volume. The results suggest that a membrane recycling mechanism dominates for nutrient deprivation-based lipid accumulation in the microalgae tested.

This paper presents the application of a theoretically developed method, which when applied to a pulsed irradiance signal can provide information about the underlying chemical kinetics and reaction dynamics. The theoretical development uses a combination of state-space, Laplace transform, least-square, and correlation techniques to determine chemical kinetic and reaction dynamic terms from a pulsed discharge. The waveform irradiance signals come from a space-based optical radiometer. Four pulsed radiometry irradiance waveforms are examined where the reaction order, rate constant, and reaction rates are investigated. The application of the theory and the commensurate results demonstrate that irradiance signals obtained under similar circumstances come from distinct pulsed discharge conditions. © 1973-2012 IEEE.

Silver-graphene nanoribbons (Ag-GNRs) were prepared from the chemical unzipping of multiwalled carbon nanotubes (MWCNTs) by reaction with Na/K alloy, Ag(O2CCH3) and then CH3OH. Ag-GNRs exhibited improved electrocatalytic ability for the oxygen reduction reaction (ORR) in 0.1M KOH as compared to the underlying GNR substrate alone and displayed an earlier onset and higher currents than a commercial Ag/Carbon (Ag/C) catalyst. The Ag-GNR hybrid demonstrates an outstanding tolerance to CH3OH crossover which exceeds that of the commercial benchmark, 20% Pt/C. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Much recent research has explored fault-tolerance mechanisms intended for current and future extreme-scale systems. Evaluations of the suitability of checkpoint-based solutions have typically been carried out using relatively uncomplicated computational kernels designed to measure floating point performance. More recent investigations have added scaled-down "proxy" applications to more closely match the composition and behavior of deployed ones. However, the information obtained from these studies (whether floating point performance or application runtime) is not necessarily of the most value in evaluating resilience strategies. We observe that even when using a more sophisticated metric, the information available from evaluating uncoordinated checkpointing using both microbenchmarks and proxy applications does not agree. This implies that not only might researchers be asking the wrong questions, but that the answers to the right ones might be unexpected and potentially misleading. We seek to open a discussion on whether benchmarks designed to provide predictable performance evaluations of HPC hardware and toolchains are providing the right feedback for the evaluation of fault-tolerance in these applications, and more generally on how benchmarking of resilience mechanisms ought to be approached in the exascale design space. © 2014 Springer-Verlag Berlin Heidelberg.

Time dependent photoluminescence and radioluminescence for sodium (Na) and thallium (Tl) activated cesium iodide (CsI) single crystals exposed to 50% and 75% relative humidity (RH) has been investigated. These results indicate that Tl activated crystals are more robust than the Na activated crystals against humidity induced scintillation degradation. The development of 'etching pits' and 'inactive' domains are the characteristics of deteriorated Na activated CsI crystals. These 'inactive' domains, bearing a resemblance to a polycrystalline appearance beneath the crystal surface, can be readily detected by a 250 nm light emitting diode. These features are commonly observed at the corners and deep scratched areas where moisture condensation is more likely to occur. Mechanisms contributing to the scintillation degradation in Na activated CsI crystals were investigated by Time-of-Flight Secondary Ion Mass Spectrometry (ToF-SIMS). ToF-SIMS depth profiles indicate that Na has been preferentially diffused out of CsI crystal, leaving the Na concentration in these 'inactive' domains below its scintillation threshold. © 1963-2012 IEEE.

Constitutive models in nanoscience and engineering often poorly represent the physics due to significant deviations in model form from their macroscale counterparts. In Part 1 of this study, this problem was explored by considering a continuum scale heat conduction constitutive law inferred directly from molecular dynamics (MD) simulations. In contrast, this work uses Bayesian inference based on the MD data to construct a Gaussian process emulator of the heat flux as a function of temperature and temperature gradient. No assumption of Fourier-like behavior is made, requiring alternative approaches to assess the well-posedness and accuracy of the emulator. Validation is provided by comparing continuum scale predictions using the emulator model against a larger all-MD simulation representing the true solution. The results show that a Gaussian process emulator of the heat conduction constitutive law produces an empirically unbiased prediction of the continuum scale temperature field for a variety of time scales, which was not observed when Fourier’s law is assumed to hold. Finally, uncertainty is propagated in the continuum model and quantified in the temperature field so the impact of errors in the model on continuum quantities can be determined.

Recently there has been renewed interest in the dynamic response of composite materials; specifically low density epoxy matrix binders strengthened with continuous reinforcing fibers. This is in part due to the widespread use of carbon fiber composites in military, commercial, industrial, and aerospace applications. The design community requires better understanding of these materials in order to make full use of their unique properties. Planar impact testing was performed resulting in pressures up to 15 GPa on a unidirectional carbon fiber - epoxy composite, engineered to have high uniformity and low porosity. Results illustrate the anisotropic nature of the response under shock loading. Along the fiber direction, a two-wave structure similar to typical elastic-plastic response is observed, however, when shocked transverse to the fibers, only a single bulk shock wave is detected. At higher pressures, the epoxy matrix dissociates resulting in a loss of anisotropy. Greater understanding of the mechanisms responsible for the observed response has been achieved through numerical modeling of the system at the micromechanical level using the CTH hydrocode. From the simulation results it is evident that the observed two-wave structure in the longitudinal fiber direction is the result of a fast moving elastic precursor wave traveling in the carbon fibers ahead of the bulk response in the epoxy resin. Similarly, in the transverse direction, results show a collapse of the resin component consistent with the experimental observation of a single shock wave traveling at speeds associated with bulk carbon. Experimental and simulation results will be discussed and used to show where additional mechanisms, not fully described by the currently used models, are present. © Published under licence by IOP Publishing Ltd.

At the completion of the fuel drying process, used fuel Zry4 cladding typically exhibits a significant population of δ-hydride inclusions. These inclusions are in the form of small platelets that are generally oriented both circumferentially and radially within the cladding material. There is concern that radially-oriented hydride inclusions may weaken the cladding material and lead to issues during used fuel storage and transportation processes. A high fidelity model of the mechanical behavior of hydrides has utility in both designing fuel cladding to be more resistant to this hydride-induced weakening and also in suggesting modifications to drying, storage, and transport operations to reduce the impact of hydride formation and/or the avoidance of loading scenarios that could overly stress the radial inclusions. We develop a mechanical model for the Zry4-hydride system that, given a particular morphology of hydride inclusions, allows the calculation of the response of the hydrided cladding under various loading scenarios. The model treats the Zry4 matrix material as J2 elastoplastic, and treats the hydrides as platelets oriented in predefined directions (e.g., circumferentially and radially). The model is hosted by the Albany analysis framework, where a finite element approximation of the weak form of the cladding boundary value problem is solved using a preconditioned Newton-Krylov approach. Instead of forming the required system Jacobian operator directly or approximating its action with a differencing operation, Albany leverages the Trilinos Sacado package to form the Jacobian via automatic differentiation. We present results that describe the performance of the model in comparison with as-fabricated Zry4 as well as HB Robinson fuel cladding. Further, we also present performance results that demonstrate the efficacy of the overall solution method employed to host the model. © 2013 Elsevier B.V. All rights reserved.

The use of computational models to simulate the behavior of complex mechanical systems is ubiquitous in many high consequence applications such as aerospace systems. Results from these simulations are being used, among other things, to inform decisions regarding system reliability and margin assessment. In order to properly support these decisions, uncertainty needs to be accounted for. To this end, it is necessary to identify, quantify and propagate different sources of uncertainty as they relate to these modeling efforts. Some sources of uncertainty arise from the following: (1) modeling assumptions and approximations, (2) solution convergence, (3) differences between model predictions and experiments, (4) physical variability, (5) the coupling of various components and (6) and unknown unknowns. An additional aspect of the problem is the limited information available at the full system level in the application space. This is offset, in some instances, by information on individual components at testable conditions. In this paper, we focus on the quantification of uncertainty due to differences in model prediction and experiments, and present a technique to aggregate and propagate uncertainty from the component level to the full system in the applications space. A numerical example based on a structural dynamics application is used to demonstrate the technique.

Digital in-line holography (DIH) is an optical technique which measures particle sizes and their three-dimensional (3D) positions and velocities. Here DIH and a recently proposed hybrid method of particle detection are applied to quantify the secondary droplets generated by the impact of a single drop on a thin film. By leveraging the expected symmetry between in-plane and out-of-plane velocities, experimental depth uncertainty is measured to be approximately 0.7 of the mean droplet diameter. Furthermore, comparison with previous measurements using alternative techniques shows good agreement with the measured temporal evolution of drop number, size, and velocity components. Finally, the power of DIH to extract the complex 3D morphology of the protruding jets is demonstrated. © 2014 Springer-Verlag Berlin Heidelberg.

In the coming decades, vehicle and fuel options and their supporting infrastructure must undergo significant transformations to achieve aggressive national targets for reducing petroleum consumption and lowering greenhouse gas (GHG) emissions. Vehicle electrification, advanced biofuels, natural gas, and hydrogen fuel cells are among the promising technology options that are being explored as future alternatives. A number of recent U.S. studies have examined how a mix of technology and policy options can contribute to the aggressive goals of 50- 80% reduction in petroleum consumption and 80% reduction in GHG emissions by 2050. These include reports issued by the National Petroleum Council, National Academies, and U.S. Department of Energy. While these studies all generally point to the need for a portfolio of technologies for the transportation sector, they do not draw the same set of conclusions for the portfolio mix. Moreover, they were commissioned for a variety of reasons, applied different modelling and analytical approaches in their assessments, and used a variety of assumptions in reaching their findings and recommendations. Using four recent major U. S. scenario analyses, this paper will illustrate several factors that can influence the interpretation of their results. Consideration of the underlying technology and policy assumptions, analytical approaches, and presentation of results can enable a more robust comparison across projections for the vehicle and fuel mix.

Microsystems-enabled photovoltaics (MEPV) has great potential to meet the increasing demands for light-weight, photovoltaic solutions with high power density and efficiency. This paper describes effective failure analysis techniques to localize and characterize nonfunctional or underperforming MEPV cells. The defect localization methods such as electroluminescence under forward and reverse bias, as well as optical beam induced current using wavelengths above and below the device band gap, are presented. The current results also show that the MEPV has good resilience against degradation caused by reverse bias stresses. © 2013 IEEE.

This paper examines the effects of long-term, high-temperature corrosion processes on materials used in concentrated solar power tower systems. More specifically, the heat transfer fluid and the containment metal are examined at operating temperatures of 600 and 680°C. A 60/40% NaNO3/KNO3 mixture of molten salt and nickel-based alloys HA230 and In625 were tested for up to 4000h at the given temperatures. HA230 and In625 alloys showed metal losses of 688 and 594μm/year, respectively, after 1000h at 680°C. The solar salt used in this study showed significant decreases (as much as 60°C) in melting point. Further experiments showed that the primary reason for the decrease in melting point is due to high nitrite concentrations in the molten salt. However, other thermophysical properties of aged solar salt appear to change little during high-temperature corrosion tests. © 2014 Elsevier Ltd.

We explore the relation between the development of a non-negligible probability of negative states and the instability of numerical integration of the intrusive Galerkin ordinary differential equation system describing uncertain chemical ignition. To prevent this instability without resorting to either multi-element local polynomial chaos (PC) methods or increasing the order of the PC representation in time, we propose a procedure aimed at modifying the amplitude of the PC modes to bring the probability of negative state values below a user-defined threshold. This modification can be effectively described as a filtering procedure of the spectral PC coefficients, which is applied on-the-fly during the numerical integration when the current value of the probability of negative states exceeds the prescribed threshold. We demonstrate the filtering procedure using a simple model of an ignition process in a batch reactor. This is carried out by comparing different observables and error measures as obtained by non-intrusive Monte Carlo and Gauss-quadrature integration and the filtered intrusive procedure. The filtering procedure has been shown to effectively stabilize divergent intrusive solutions, and also to improve the accuracy of stable intrusive solutions which are close to the stability limits. © 2014.

The monoclinic-to-tetragonal phase transition (∼70 °C) in vanadium dioxide (VO2) strongly impacts the infrared properties, which enables its use in applications such as smart window devices. Synthesis of VO 2 can be challenging due to the variability of vanadium oxide phases that may be formed. We have employed high-temperature X-ray diffraction (HTXRD) to monitor the reaction process of vanadium oxide precursor powders to form the desired tetragonal VO2 phase. Single-phase tetragonal VO2 was formed within 30 min at 420 °C in flowing N2 gas (∼50 ppm O2). The monoclinic-to-tetragonal phase transformation was observed via HTXRD at ∼70 °C with the typical ∼10 °C hysteresis (i.e. approached from above or below the transition). © International Centre for Diffraction Data 2014.

Lennard-Jones parameters for use in combustion modeling, as transport parameters and in pressure-dependent rate-coefficient calculations as collision rate parameters, are calculated from accurate full-dimensional intermolecular potentials. Several first-principles theoretical methods are considered. In the simplest approach, the intermolecular potential is spherically averaged and used to determine Lennard-Jones parameters. This method works well for small species, but it is not suitable for larger species due to unphysical averaging over the repulsive wall. Another method considered is based on full-dimensional trajectory calculations of binary collisions. This method is found to be very accurate, predicting Lennard-Jones collision rates within ~10% of those obtained via tabulated (experimentally-based) Lennard-Jones parameters. Finally, a computationally efficient method is presented based on one-dimensional minimizations averaged over the colliding partners' relative orientations. This method is shown to be both accurate and efficient. The good accuracy of the latter two approaches is shown to be a result of their explicit treatment of anisotropy. The effects of finite temperature vibrations and multiple conformers are quantified and are shown to be small. The choice of potential energy surface has a somewhat larger effect, and strategies based both on efficient semiempirical methods and on first-principles direct dynamics are considered. Overall, 75 systems are considered, including seven baths, targets as large as heptane, both molecules and radicals, and both hydrocarbons and oxygenates. © 2013 The Combustion Institute.

The chemical equilibrium distribution of point defects modeled as non-overlapping, spherical inclusions with purely positive dilatational eigenstrain in an isotropically elastic solid is derived. The compressive self-stress inside existing inclusions must be excluded from the stress dependence of the equilibrium concentration of the point defects, because it does no work when a new inclusion is introduced. On the other hand, a tensile image stress field must be included to satisfy the boundary conditions in a finite solid. Through the image stress, existing inclusions promote the introduction of additional inclusions. This is contrary to the prevailing approach in the literature in which the equilibrium point defect concentration depends on a homogenized stress field that includes the compressive self-stress. The shear stress field generated by the equilibrium distribution of such inclusions is proved to be proportional to the pre-existing stress field in the solid, provided that the magnitude of the latter is small, so that a solid containing an equilibrium concentration of point defects can be described by a set of effective elastic constants in the small-stress limit. © 2014 Elsevier Ltd.

In response to the accident at the Fukushima Daiichi nuclear power station in Japan, the U.S. Nuclear Regulatory Commission and US. Department of Energy agreed to jointly sponsor an accident reconstruction study as a means of assessing the severe accident modeling capability of the MELCOR code and developing an understanding of the likely accident progression. Objectives of the project included reconstruction of the accident progressions using computer models and accident data, and validation of MELCOR and the Fukushima models against plant data. In this study Sandia National Laboratories developed MELCOR 2.1 models of Fukushima Daiichi Units 1 (IFI), 2, and 3 as well as the Unit 4 spent fuel pool. This paper reports on the analysis of the 1F1 accident. Details are presented on the modeled accident progression, hypothesized mode of failures in the reactor pressure vessel (RPV) and containment pressure boundary, and release of fission products to the environment. The MELCOR-predicted RPV and containment pressure trends compare well with available measured pressures. Conditions leading up to the observed explosion of the reactor building are postulated based on this analysis where drywell head flange leakage is thought to have led to accumulation of flammable gases in the refueling bay. The favorable comparison of the results from the analyses with the data from the plant provides additional confidence in MELCOR to reliably predict real-world accident progression. The modeling effort has also provided insights into future data needs for both model development and validation.

A new algorithm was developed, which reduces the self-force in particle-in-cell codes on unstructured meshes in a predictable and controllable way. This is accomplished by computing a charge density weighting function for a particle, which reproduces the Green's function solution to Poisson's equation at nodes when using a standard finite element method methodology. This provides a superior local potential and allows for particle-particle particle-mesh techniques to be used to subtract off local force contributions, including fictitious self-forces resulting in accurate long-range forces on a particle and improved local Coulomb collisions. Local physical forces are then computed using the Green's function on local particle pairs and added to the long-range forces. Results were shown with up to five orders reduction in self-force and superior intraparticle forces for two test cases. © 2013 IEEE.

The Lagrangian Material Point Method (MPM) [1, 2] has been implemented into the Eulerian shock physics code CTH [3] at Sandia National Laboratories. Eulerian hydrodynamic methods are useful for large deformation problems, where mesh tangling typically leads to difficulties for Lagrangian finite element methods. However, Eulerian techniques suffer from numerical diffusion due to advection, which can be problematic for many material models requiring the transport of a damage parameter or other state variables that need to remain sharp [4]. The inclusion of the MPM in CTH allows for the accurate simulation of structural response to shock loading in a single framework. This paper presents a comparison of the shock response of the MPM and CPDI to the CTH hydrodynamics code. © Published under licence by IOP Publishing Ltd.

Risks of transporting radioactive materials can be estimated using the programme and code RADTRAN. Potential radiation doses to various receptors are calculated by RADTRAN, including doses from routine, incident free transportation and from transportation accidents. If radioactive material is released from a transportation vehicle in an accident, agricultural products in the plume footprint could be contaminated. This paper discusses a method for calculating radiation doses from ingestion of such radioactively contaminated food stuffs. Transportation of radioactive materials occurs throughout the USA, so that agricultural products along many transportation corridors could be affected. However, doses from ingesting agricultural crops contaminated from a traffic accident would be very small compared to natural background radiation. © W. S. Maney & Son Ltd 2014.

Controlling the materials chemistry of the solid-state ion conductor NaSICON is key to realizing its potential utility in emerging sodium-based battery technologies. We describe here the influence of excess sodium on phase evolution of sol-gel synthesized NaSICON. Alkoxide-based sol-gel processing was used to produce powders of Na3Zr2PSi2O12 NaSICON with 0-2 atomic % excess sodium. Phase formation and component volatility were studied as a function of temperature. NaSICON synthesis at temperatures between 900-1100C with up to 2% excess sodium significantly reduced the presence of zirconia, sodium phosphate, and sodium silicate secondary phases in fired NaSICON powders. Insights into the role of sodium on the phase chemistry of sol-gel processed NaSICON may inform key improvements in NaSICON development.

Graphs are used to model interactions in a variety of contexts, and there is a growing need to quickly assess the structure of such graphs. Some of the most useful graph metrics are based on triangles, such as those measuring social cohesion. Algorithms to compute them can be extremely expensive, even for moderately sized graphs with only millions of edges. Previous work has considered node and edge sampling; in contrast, we consider wedge sampling, which provides faster and more accurate approximations than competing techniques. Additionally, wedge sampling enables estimating local clustering coefficients, degree-wise clustering coefficients, uniform triangle sampling, and directed triangle counts. Our methods come with provable and practical probabilistic error estimates for all computations. We provide extensive results that show our methods are both more accurate and faster than state-of-the-art alternatives. © 2014 Wiley Periodicals, Inc.

Deep-level optical spectroscopy (DLOS) and photoluminescence (PL) were used to understand the role of defects in reducing the internal quantum efficiency (IQE) of InxGa1-xN/GaN multiple quantum wells (MQWs) as the emission wavelength increased from approximately 450 to 530 nm, i.e., the "green gap". DLOS studies of light emitting diodes (LEDs) identified QW defects whose concentration increased significantly with increasing x. The effect of increased QW defect density on IQE was assessed by examining the PL of MQW samples. Green-emitting MQWs had lower IQE and required higher pump power to reach peak IQE, corroborating the important impact of enhanced non-radiative recombination at defects. © 2014 The Japan Society of Applied Physics.

In recent years, high pressure gaseous hydrogen has become increasingly popular as a vehicle fuel. The National Fire Protection Association (NFPA) is one of several organizations developing codes and standards to ensure the safety of the vehicular hydrogen infrastructure. As part of code development activities, NFPA is exploring the use of Quantitative Risk Assessment (QRA) to help provide a technical basis for specific requirements in the Hydrogen Technologies Code (NFPA 2). The authors conducted the QRA activity to 1) provide screening-level insights into the fatality risk from code-compliant, indoor hydrogen fueling systems for NFPA 2 Chapter 10 (Gaseous Hydrogen Vehicle Fueling Facilities) and 2) identify gaps in QRA that must be resolved to enable more detailed, robust QRA analyses. This paper documents the results of this early-stage QRA activity and suggests several QRA improvements that would enable more widespread use of QRA for vehicular hydrogen applications. © 2014 Taylor & Francis Group, London.

Scanning electron microscopes (SEMs) are used in neuroscience and materials science to image square centimeters of sample area at nanometer scales. Since imaging rates are in large part SNR-limited. imaging time is proportional to the number of measurements taken of each sample; in a traditional SEM. large collections can lead to weeks of around-the-clock imaging time. We previously reported a single-beam sparse sampling approach that we have demonstrated on an operational SEM for collecting "smooth" images. In this paper, we analyze how measurements from a hypothetical multi-beam system would compare to the single-beam approach in a compressed sensing framework. To that end. multi-beam measurements are synthesized on a single-beam SEM. and fidelity of reconstructed images are compared to the previously demonstrated approach. Since taking fewer measurements comes at the cost of reduced SNR, image fidelity as a function of undersampling ratio is reported.

A new metric has been developed to evaluate and compare selective absorber coatings for concentrating solar power applications. Previous metrics have typically considered the performance of the selective coating (i.e., solar absorptance and thermal emittance), but cost and durability were not considered. This report describes the development of the Levelized Cost of Coating (LCOC), which is similar to the levelized cost of energy (LCOE) commonly used to evaluate alternative energy technologies. The LCOC is defined as the ratio of the annualized cost of the coating (and associated costs such as labor) to the average annual thermal energy produced by the receiver. The baseline LCOC using Pyromark 2500 paint was found to be $0.055/MW ht, and marginal costs were determined in a probabilistic analysis to range from -$0.09/MW ht to $1.01/MW ht, accounting for the cost of additional (or fewer) heliostats required to yield the same baseline average annual thermal energy produced by the receiver. A stepwise multiple rank regression analysis showed that the initial solar absorptance was the most significant parameter impacting the LCOC, followed by thermal emittance, reapplication interval, degradation rate, reapplication cost, and downtime during reapplication. © 2014 Elsevier Ltd. All rights reserved.

In this article we discuss scaling the magnetically accelerated flyer plate technique to currents greater than is available on the Z accelerator. Peak flyer plate speeds in the range 7-46 km/s are achieved in pulsed power driven, hyper-velocity impact experiments on Z for peak currents in the range 8-20 MA. The highest (lowest) speeds are produced using aluminum (aluminum-copper) flyer plates. In either case, the ≈1 mm thick flyer plate is shocklessly accelerated by magnetic pressure to ballistic speed in ≈400 ns; it arrives at the target with a fraction of material at standard density. During acceleration a melt front, due to resistive heating, moves from the drive-side toward the target-side of the flyer plate; the speed of the melt front increases with increasing current. Peak flyer speeds on Z scale quadratically (linearly) with current at the low (high) end of the range. Magnetohydrodynamic simulation shows that the change in scaling is due to geometric deformation, and that linear scaling continues as current increases. However, the combined effects of shockless acceleration and resistive heating lead to an upper bound on the magnetic field feasible for pulsed power driven flyer plate experiments, which limits the maximum possible speed of a useful flyer plate to < 100 km/s. © Published under licence by IOP Publishing Ltd.

This paper considers underwater wireless sensor networks (UWSNs) for submarine surveillance and monitoring. Nodes produce data with an associated value, decaying in time. An autonomous underwater vehicle (AUV) is sent to retrieve information from the nodes, through optical communication, and periodically emerges to deliver the collected data to a sink, located on the surface or onshore. Our objective is to determine a collection path for the AUV so that the Value of Information (VoI) of the data delivered to the sink is maximized. To this purpose, we first define an Integer Linear Programming (ILP) model for path planning that considers realistic data communication rates, distances, and surfacing constraints. We then define the first heuristic for path finding that is adaptive to the occurrence of new events, relying only on acoustic communication for exchanging short control messages. Our Greedy and Adaptive AUV Path-finding (GAAP) heuristic drives the AUV to collect packets from nodes to maximize the VoI of the delivered data. We compare the VoI of data obtained by running the optimum solution derived by the ILP model to that obtained from running GAAP over UWSNs with realistic and desirable size. In our experiments GAAP consistently delivers more than 80% of the theoretical maximum VoI determined by the ILP model. © 2014 IEEE.

Negative valve overlap (NVO) is an operating mode that enables efficient, low-temperature gasoline combustion in automotive engines. In addition to retaining a large fraction of residuals, NVO operation also enables partial fuel injection during the recompression period as a means of enhancing and controlling main combustion. Thermal effects of NVO fueling on main combustion are well understood, but chemical effects of the products of NVO reactions remain uncertain. To address this topic, we have fabricated a dump valve that extracts a large fraction of cylinder charge at intake valve closing (IVC), yielding a representative sample of NVO products mixed with intake air. Sample composition is determined by gas chromatography. Results from a sweep of NVO start-of-injection (SOI) timings show that concentrations of the reactive species acetylene and hydrogen rise to several hundred parts-per-million as NVO SOI is retarded toward top center of NVO. Since experiments have previously demonstrated that low concentrations of acetylene seeded into the intake flow advance combustion phasing, the current results support the conclusion that NVO fueling can chemically enhance main combustion. This conclusion is further strengthened by a one-dimensional chemical kinetics simulation of main combustion that uses measured compositions as initial conditions at IVC. Comparing early and late NVO SOI, the model predicts that the hydrogen and acetylene produced by late NVO injection significantly advance the phasing of main combustion. © 2014 SAE International.

In a companion study [1], experimental observations in a stratified-charge DISI engine operated with late injection of E70 led to the formation of two hypotheses: (1) For highly stratified spray-guided combustion, the heat-release rate of the main combustion phase is primarily controlled by mixing rates and turbulence level associated with fuel-jet penetration. (2) During the main combustion phase, the role of the in-cylinder flow field generated by the intake and compression strokes is primarily its stochastic disturbance of the mixing and flow associated with the fuel jets, thereby causing cycle-to-cycle variations of the spray-guided stratified combustion. Here, these hypotheses are tested. An optical engine was operated skip fired at 1000 and 2000 rpm, and exhibited the same combustion properties observed in the steady-state all-metal engine tests. High-speed particle image velocimetry (PIV) and spray imaging are used to quantify the intake-generated in-cylinder flow momentum, the spray induced momentum, and the resulting liquid spray variability. The PIV measurements reveal that the spatially-averaged gas-flow speed (momentum) without injection at 2000 rpm is twice that of 1000 rpm. In contrast, just after injection the gas flow spatial average speed at 2000 rpm is only 24% higher due to the dominance of spray momentum. This is comparable to the 16% increase of the measured ensemble-averaged heat-release rate (in kW). The cyclic variability of the in-cylinder flow speed prior to injection is measured to be considerably higher at 2000 rpm compared to 1000 rpm. Though the injected liquid spray reduced the flow-speed cyclic-variability after injection, the higher variability did persist. The spray imaging reveals that the increased flow-speed variability at 2000 rpm causes increased variability of the spray jet trajectory, jet coalescence, and spray rotation from cycle to cycle. This work supports both the hypotheses that motivated this study. Copyright © 2014 SAE International.

Density Functional Theory (DFT) based molecular dynamics has been established as a method capable of yielding high fidelity results for many materials at a wide range of pressures and temperatures and has recently been applied to complex polymers such as polyethylene, compounds such as ethane or CO2, and oxides such as MgO. We use this method to obtain a Grïneisen Γ and thereby build a Mie-Grüneisen equation of state (EOS) and a Rice-Walsh EOS for tantalum pentoxide (Ta2O5 or tantala) and compare to experimental data. The experimental data have initial densities (ρ00) of approximately 1.13, 3, and 7.4 g/cm 3 reduced from a crystalline of 8.36 g/cm3. We found that r becomes constant at higher temperatures and pressure, but is a function of both density and temperature at lower densities and temperatures. Finally, the Mie-Gruneisen EOS is adequate for modeling the slightly distended Hugoniot with an initial density of 7.4 g/cm3 however it is inadequate for the more porous Hugoniot, while the Rice-Walsh EOS combined with a P-λ crush model approximates the experimental data quite well. © Published under licence by IOP Publishing Ltd.

Increasing parallelism and transistor density, along with increasingly tighter energy and peak power constraints, may force exposure of occasionally incorrect computation or storage to application codes. Silent data corruption (SDC) will likely be infrequent, yet one SDC suffices to make numerical algorithms like iterative linear solvers cease progress towards the correct answer. Thus, we focus on resilience of the iterative linear solver GMRES to a single transient SDC. We derive inexpensive checks to detect the effects of an SDC in GMRES that work for a more general SDC model than presuming a bit flip. Our experiments show that when GMRES is used as the inner solver of an inner-outer iteration, it can 'run through' SDC of almost any magnitude in the computationally intensive orthogonalization phase. That is, it gets the right answer using faulty data without any required roll back. Those SDCs which it cannot run through, get caught by our detection scheme. © 2014 IEEE.

It is often prohibitively expensive to integrate the response of a high order nonlinear system, such as a finite element model of a nonlinear structure, so a set of linear eigenvectors is often used as a basis in order to create a reduced order model (ROM). By augmenting the linear basis with a small set of discontinuous basis functions, ROMs of systems with local nonlinearities have been shown to compare well with the corresponding full order models.When evaluating the quality of a ROM, it is common to compare the time response of the model to that of the full order system, but the time response is a complicated function that depends on a predetermined set of initial conditions or external force. This is difficult to use as a metric to measure convergence of a ROM, particularly for systems with strong, non-smooth nonlinearities, for two reasons: (1) the accuracy of the response depends directly on the amplitude of the load/initial conditions, and (2) small differences between two signals can become large over time. Here, a validation metric is proposed that is based solely on the ROM’s equations of motion. The nonlinear normalmodes (NNMs) of the ROMs are computed and tracked as modes are added to the basis set. The NNMs are expected to converge to the true NNMs of the full order system with a sufficient set of basis vectors. This comparison captures the effect of the nonlinearity through a range of amplitudes of the system, and is akin to comparing natural frequencies and mode shapes for a linear structure. In this research, the convergencemetric is evaluated on a simply supported beam with a contacting nonlinearity modeled as a unilateral piecewise-linear function. Various time responses are compared to show that the NNMs provide a good measure of the accuracy of the ROM. The results suggest the feasibility of using NNMs as a convergencemetric for reduced order modeling of systems with various types of nonlinearities.

Despite economic, political, legal, and technical challenges, carbon dioxide (CO2) capture and storage (CCS) holds promise as a means to substantially reduce anthropogenic atmospheric emissions of carbon dioxide. One of the technical challenges to CCS is an accurate quantification of the potential geologic storage resource. This analysis uses the publically available national-scale, systems-level Water Energy and Carbon Sequestration simulation model (WECSsim), to show that, depending on assumed boundary conditions, the majority of storage associated with large-scale CCS in the U.S. (on the order of 90-100GT of total reduced emissions) would occur at a small number of well-located sites with favorable geologic properties. WECSsim, through the use of marginal abatement cost curves, shows that under such a scenario, added costs associated with resident saline water extraction, transport, and treatment (SWETT) are justified by resulting increases in carbon dioxide storage efficiency in the geologic formation. This argument is strengthened when geologic uncertainty is taken into consideration. Like an insurance policy, the enhanced carbon dioxide storage efficiency that comes from SWETT adds well-defined costs to reduce potential economic risks associated with overestimates of the available geologic storage resource. © 2014 Elsevier Ltd.

Finding the strongly connected components (SCCs) of a directed graph is a fundamental graph-theoretic problem. Tarjan's algorithm is an efficient serial algorithm to find SCCs, but relies on the hard-to-parallelize depth-first search (DFS). We observe that implementations of several parallel SCC detection algorithms show poor parallel performance on modern multicore platforms and large-scale networks. This paper introduces the Multistep method, a new approach that avoids work inefficiencies seen in prior SCC approaches. It does not rely on DFS, but instead uses a combination of breadth-first search (BFS) and a parallel graph coloring routine. We show that the Multistep method scales well on several real-world graphs, with performance fairly independent of topological properties such as the size of the largest SCC and the total number of SCCs. On a 16-core Intel Xeon platform, our algorithm achieves a 20X speedup over the serial approach on a 2 billion edge graph, fully decomposing it in under two seconds. For our collection of test networks, we observe that the Multistep method is 1.92X faster (mean speedup) than the state-of-the-art Hong et al. SCC method. In addition, we modify the Multistep method to find connected and weakly connected components, as well as introduce a novel algorithm for determining articulation vertices of biconnected components. These approaches all utilize the same underlying BFS and coloring routines. © 2014 IEEE.

The reflection of an optical wave from metal, arising from strong interactions between the optical electric field and the free carriers of the metal, is accompanied by a phase reversal of the reflected electric field. A far less common route to achieving high reflectivity exploits strong interactions between the material and the optical magnetic field to produce a “magnetic mirror” that does not reverse the phase of the reflected electric field. At optical frequencies, the magnetic properties required for strong interaction can be achieved only by using artificially tailored materials. Here, we experimentally demonstrate, for the first time to the best of our knowledge, the magnetic mirror behavior of a low-loss all-dielectric metasurface at infrared optical frequencies through direct measurements of the phase and amplitude of the reflected optical wave. The enhanced absorption and emission of transverse-electric dipoles placed close to magnetic mirrors can lead to exciting new advances in sensors, photodetectors, and light sources.

Post injections have been shown to reduce engine-out soot emissions in a variety of engine architectures and at a range of operating points. In this study, measurements of the engine-out soot from a heavy-duty optical diesel engine have conclusively shown that interaction between the post-injection jet and soot from the main injection must be, at least in part, responsible for the reduction in engine-out soot. Extensive measurements of the spatial and temporal evolution of soot using high-speed imaging of soot natural luminosity (soot-NL) and planar-laser induced incandescence of soot (soot-PLII) at four vertical elevations in the piston bowl at a range of crank angle timings provide definitive optical evidence of these interactions. The soot-PLII images provide some of the most conclusive evidence to date that the addition of a post injection dramatically changes the topology and quantity of in-cylinder soot. As the post jet penetrates toward the bowl wall, it carves out regions from the main-injection soot structures, either through displacement of the soot or through rapid and progressive oxidation of the soot. Later in the cycle, the regions of main-injection soot on either side of the jet centerline, clearly present in the main-injection-only case, have all but disappeared when the post-injection is added - only the soot in the post-injection pathway remains. Evidence of this apparent late-cycle oxidation of main-injection soot appears in both the soot-PLII and soot-NL images, providing substantial support for the mixing mechanism of soot reduction with post injections. Implications of these findings and future work are also discussed. © 2014 SAE International.

The Tall-Skinny QR (TSQR) algorithm is more communication efficient than the standard Householder algorithm for QR decomposition of matrices with many more rows than columns. However, TSQR produces a different representation of the orthogonal factor and therefore requires more software development to support the new representation. Further, implicitly applying the orthogonal factor to the trailing matrix in the context of factoring a square matrix is more complicated and costly than with the Householder representation. We show how to perform TSQR and then reconstruct the Householder vector representation with the same asymptotic communication efficiency and little extra computational cost. We demonstrate the high performance and numerical stability of this algorithm both theoretically and empirically. The new Householder reconstruction algorithm allows us to design more efficient parallel QR algorithms, with significantly lower latency cost compared to Householder QR and lower bandwidth and latency costs compared with Communication-Avoiding QR (CAQR) algorithm. As a result, our final parallel QR algorithm outperforms ScaLAPACK and Elemental implementations of Householder QR and our implementation of CAQR on the Hopper Cray XE6 NERSC system. We also provide algorithmic improvements to the ScaLAPACK and CAQR algorithms. © 2014 IEEE.

A thorough molecular dynamics study is performed to investigate the predicted {1 1 2} yield behavior associated with the slip of a single screw dislocation using classical atomistic potentials of body-centered cubic metals. Previous works have drawn an association between the structure of the stable screw dislocation core and the resulting slip nature showing that a polarized core can lead to {1 1 2} slip, while a non-polarized core is expected to slip on {1 1 0} planes. Here, results from five different potentials for tantalum are presented as they all show slip to be primarily active along {1 1 2} planes even though the stable core structure is non-polar. This {1 1 2} slip occurs through dislocation glide on two different {1 1 0} planes due to the presence of a metastable split core structure, and regardless of the relative magnitudes of resolved shear stresses for the two {1 1 0} planes. Further investigations shows that the split core structure, an artifact of the atomic potentials used, also influences slip behavior associated with dynamic motion of kinked dislocations in ambient temperature simulations. © 2014 Elsevier B.V. All rights reserved.

The voltage on a single-turn loop inside an enclosure characterizes the enclosure shielding effectiveness against a lightning insult. In this paper, the maximum induced voltage on a single-turn loop inside an enclosure from lightning coupling to a metal enclosure wall is expressed in terms of two multiplicative factors: (A) the normalized enclosure wall peak penetration ratio (i.e., ratio of the peak interior electric field multiplied by the sheet conductance to the exterior magnetic field) and (B) the DC voltage on an ideal optimum coupling loop assuming the ideal penetration ratio of one. As a result of the decomposition, the variation of the peak penetration ratio (A) for different coupling mechanisms is found to be small; the difference in the maximum voltage hence arises from the DC voltage on the optimum coupling loop (B). Maximum voltages on an optimum coupling loop inside a finite cylinder enclosure for direct attachment and a lightning line source at different distances from the enclosure are given in Table 3.

This paper evaluates the effects of ionizing radiation on tantalum oxide (TaOx) memristors. The data obtained from 60Co gamma ray and 10 keV X-ray ionizing radiation experiments indicate that it is possible for the devices to switch from a high resistance off-state to a low resistance on-state after a total ionizing dose (TID) step stress threshold has been surpassed. During irradiation, the devices were floating, grounded, or biased with a 1 Hz square wave with an amplitude of ±100 mV. While floating the terminals is not a typical bias condition within a circuit, it is speculated that this condition might be worst-case because of the lack of a discharge path. If a read measurement is performed prior to reaching the charge threshold, the devices 'reset' back to a pre-irradiation state. This suggests that the devices do not have a cumulative TID effect. However, it was observed that having a continuous bias on the device during the TID exposure did not always have the same effect. The TID threshold level at which the devices switch resistance states varies from device to device; the enhanced susceptibility observed in some devices is still under investigation. After a radiation-induced resistance change, all of the devices could be reset and still functioned properly. When the devices were set into a low resistance on-state prior to irradiation, there was not a significant variation in the resistance post-irradiation (i.e., the devices were still in the on-state). Overall, the memristor TID performance is promising and could potentially enable the discovery of a radiation-hardened nonvolatile memory technology to be used in space and aerospace applications. © 2014 IEEE.

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This study details a methodology for quantification of errors and uncertainties of a finite element heat transfer model applied to a Ruggedized Instrumentation Package (RIP). The proposed verification and validation (V&V) process includes solution verification to examine errors associated with the code's solution techniques, and model validation to assess the model's predictive capability for quantities of interest. The model was subjected to mesh resolution and numerical parameters sensitivity studies to determine reasonable parameter values and to understand how they change the overall model response and performance criteria. To facilitate quantification of the uncertainty associated with the mesh, automatic meshing and mesh refining/coarsening algorithms were created and implemented on the complex geometry of the RIP. Automated software to vary model inputs was also developed to determine the solution’s sensitivity to numerical and physical parameters. The model was compared with an experiment to demonstrate its accuracy and determine the importance of both modelled and unmodelled physics in quantifying the results' uncertainty. An emphasis is placed on automating the V&V process to enable uncertainty quantification within tight development schedules.

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Several tensor eigenpair definitions have been put forth in the past decade, but these can all be unified under generalized tensor eigenpair framework, introduced by Chang, Pearson, and Zhang [J. Math. Anal. Appl., 350 (2009), pp. 416-422]. Given mth-order, n-dimensional realvalued symmetric tensors A and B, the goal is to find λ ε ℝ and x ε ℝn, x ≠= 0 such that Axm-1 = λBxm-1. Different choices for B yield different versions of the tensor eigenvalue problem. We present our generalized eigenproblem adaptive power (GEAP) method for solving the problem, which is an extension of the shifted symmetric higher-order power method (SS-HOPM) for finding Z-eigenpairs. A major drawback of SS-HOPM is that its performance depended on choosing an appropriate shift, but our GEAP method also includes an adaptive method for choosing the shift automatically.

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We present results from laser annealing experiments in Si using a passively Q-switched Nd:YAG microlaser. Exposure with laser at fluence values above the damage threshold of commercially available photodiodes results in electrical damage (as measured by an increase in photodiode dark current). We show that increasing the laser fluence to values in excess of the damage threshold can result in annealing of a damage site and a reduction in detector dark current by as much as 100x in some cases. A still further increase in fluence results in irreparable damage. Thus we demonstrate the presence of a laser annealing window over which performance of damaged detectors can be at least partially reconstituted. Moreover dark current reduction is observed over the entire operating range of the diode indicating that device performance has been improved for all values of reverse bias voltage. Additionally, we will present results of laser annealing in Si waveguides. By exposing a small (<10 um) length of a Si waveguide to an annealing laser pulse, the longitudinal phase of light acquired in propagating through the waveguide can be modified with high precision, <15 milliradian per laser pulse. Phase tuning by 180 degrees is exhibited with multiple exposures to one arm of a Mach-Zehnder interferometer at fluence values below the morphological damage threshold of an etched Si waveguide. No reduction in optical transmission at 1550 nm was found after 220 annealing laser shots. © 2014 SPIE.

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The integration of optics for efficient light delivery and the collection of fluorescence from trapped ions in surface electrode ion traps is a key component to achieving scalability for quantum information processing. Diffractive optical elements (DOEs) present a promising approach as compared to bulk optics because of their small physical profile and their flexibility in tailoring the optical wavefront. The precise alignment of the optics for coupling fluorescence to and from the ions, however, poses a particular challenge. Excitation and manipulation of the ions requires a high degree of optical access, significantly restricting the area available for mounting components. The ion traps, DOEs, and other components are compact, constraining the manipulation of various elements. For efficient fluorescence collection from the ions the DOE must be have a large numerical aperture (NA), which results in greater sensitivity to misalignment. The ion traps are sensitive devices, a mechanical approach to alignment such as contacting the trap and using precision motors to back-off a set distance not only cannot achieve the desired alignment precision, but risks damage to the ion trap. We have developed a non-contact precision optical alignment technique. We use line foci produced by off-axis linear Fresnel zone plates (FZPs) projected on alignment targets etched in the top metal layer of the ion trap and demonstrate micron-level alignment accuracy. © 2014 SPIE.

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Nanoantennas are an enabling technology for visible to terahertz components and may be used with a variety of detector materials. We have integrated subwavelength patterned metal nanoantennas with various detector materials for infrared detection: midwave infrared indium gallium arsenide antimonide detectors, longwave infrared graphene detectors, and shortwave infrared germanium detectors. Nanoantennas offer a means to make infrared detectors much thinner, thus lowering the dark current and improving performance. The nanoantenna converts incoming plane waves to more tightly bound and concentrated surface waves. The active material only needs to extend as far as these bound fields. In the case of graphene detectors, which are only one or two atomic layers thick, such field concentration is a necessity for usable device performance, as single pass absorption is insufficient. The nanoantenna is thus the enabling component of these thin devices. However nanoantenna integration and fabrication vary considerably across these platforms as do the considerations taken into account during design. Here we discuss the motivation for these devices and show examples for the three material systems. Characterization results are included for the midwave infrared detector. © 2014 SPIE.

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During an environment, it is desirable to know the forces or inputs on the system of interest. With the inputs, one can directly use a finite element or experimental model to predict responses not measured in a field test. One can attempt to measure point forces using force gauges, however, these gauges are insufficient due to the inability to place a gauge at a forcing interface or to measure a force applied over an area. SWAT (Sum of weighted acceleration technique) is a method that uses mode shapes as a modal filter with measured accelerations and to solve the inverse problem and calculate the forces and moments on the system. This paper will examine an application where the use of a force gauge is impossible due to the external forces being applied over an area. The paper will calculate the sum of the forces and moments imparted on the system and will use a finite element model to check the plausibility of the calculated forces.

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Scanning electron microscopes (SEMs) are used in neuroscience and materials science to image square centimeters of sample area at nanometer scales. Since imaging rates are in large part SNR-limited. imaging time is proportional to the number of measurements taken of each sample; in a traditional SEM. large collections can lead to weeks of around-the-clock imaging time. We previously reported a single-beam sparse sampling approach that we have demonstrated on an operational SEM for collecting "smooth" images. In this paper, we analyze how measurements from a hypothetical multi-beam system would compare to the single-beam approach in a compressed sensing framework. To that end. multi-beam measurements are synthesized on a single-beam SEM. and fidelity of reconstructed images are compared to the previously demonstrated approach. Since taking fewer measurements comes at the cost of reduced SNR, image fidelity as a function of undersampling ratio is reported.

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We demonstrate that THz pulses transmitted through small apertures (~λ/100) exhibit strong evanescent components within 1μm of the aperture. Using this effect, we developed subwavelength aperture THz near-field probes that provide 3μm resolution. © 2014 OSA.

Microalgal biotechnology is a nascent yet burgeoning field for developing the next generation of sustainable feeds, fuels, and specialty chemicals. Among the issues facing the algae bioproducts industry, the lack of efficient means of cultivar screening and phenotype selection represents a critical hurdle for rapid development and diversification. To address this challenge, we have developed a multi-modal and label-free optical tool which simultaneously assesses the photosynthetic productivity and biochemical composition of single microalgal cells, and provides a means for actively sorting attractive specimen (bioprospecting) based on the spectral readout. The device integrates laser-trapping micro-Raman spectroscopy and pulse amplitude modulated (PAM) fluorometry of microalgal cells in a flow cell. Specifically, the instrument employs a dual-purpose epi-configured IR laser for single-cell trapping and Raman spectroscopy, and a high-intensity VISNIR trans-illumination LED bank for detection of variable photosystem II (PSII) fluorescence. Micro-Raman scatter of single algae cells revealed vibrational modes corresponding to the speciation and total lipid content, as well as other major biochemical pools, including total protein, carbohydrates, and carotenoids. PSII fluorescence dynamics provide a quantitative estimate of maximum photosynthetic efficiency and regulated and non-regulated non-photochemical quenching processes. The combined spectroscopic readouts provide a set of metrics for subsequent optical sorting of the cells by the laser trap for desirable biomass properties, e.g. the combination of high lipid productivity and high photosynthetic yield. Thus the device provides means for rapid evaluation and sorting of algae cultures and environmental samples for biofuels development. © 2014 SPIE.

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We have demonstrated single-mode lasing in a single gallium nitride nanowire using distributed feedback by external coupling to a dielectric grating. By adjusting the nanowire grating alignment we achieved a mode suppression ratio of 17dB.

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Transient responses of high-Q nano-optomechanical modes are characterized with Interleaved-ASOPS, where pump-induced transients are interrogated with multiple probe pulses. Temporal resolution increases linearly with probe-pulse-number beyond conventional ASOPS, achieving sub-ps resolution over μs durations.