Publications

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As increasing numbers of photovoltaic (PV) systems are connected to utility systems, distribution engineers are becoming increasingly concerned about the risk of formation of unintentional islands. Utilities desire to keep their systems secure, while not imposing unreasonable burdens on users wishing to connect PV. However, utility experience with these systems is still relatively sparse, so distribution engineers often are uncertain as to when additional protective measures, such as direct transfer trip, are needed to avoid unintentional island formation. In the absence of such certainty, utilities must err on the side of caution, which in some cases may lead to the unnecessary requirement of additional protection. The purpose of this document is to provide distribution engineers and decision makers with guidance on when additional measures or additional study may be prudent, and also on certain cases in which utilities may allow PV installations to proceed without additional study because the risk of an unintentional island is extremely low. The goal is to reduce the number of cases of unnecessary application of additional protection, while giving utilities a basis on which to request additional study in cases where it is warranted.

This report explores the technical feasibility of prospective utility-scale photovoltaic system (PV) deployments in Utah. Sandia National Laboratories worked with Rocky Mountain Power (RMP), a division of PacifiCorp operating in Utah, to evaluate prospective 2-megawatt (MW) PV plants in different locations with respect to energy production and possible impact on the RMP system and customers. The study focused on 2-MW{sub AC} nameplate PV systems of different PV technologies and different tracking configurations. Technical feasibility was evaluated at three different potential locations in the RMP distribution system. An advanced distribution simulation tool was used to conduct detailed time-series analysis on each feeder and provide results on the impacts on voltage, demand, voltage regulation equipment operations, and flicker. Annual energy performance was estimated.

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The annual program report provides detailed information about all aspects of the Sandia National Laboratories, California (SNL/CA) Chemical Management Program. It functions as supporting documentation to the SNL/CA Environmental Management System Program Manual. This program annual report describes the activities undertaken during the calender past year, and activities planned in future years to implement the Chemical Management Program, one of six programs that supports environmental management at SNL/CA. SNL/CA is responsible for tracking chemicals (chemical and biological materials), providing Material Safety Data Sheets (MSDS) and for regulatory compliance reporting according to a variety of chemical regulations. The principal regulations for chemical tracking are the Emergency Planning Community Right-to-Know Act (EPCRA) and the California Right-to-Know regulations. The regulations, the Hazard Communication/Lab Standard of the Occupational Safety and Health Administration (OSHA) are also key to the CM Program. The CM Program is also responsible for supporting chemical safety and information requirements for a variety of Integrated Enabling Services (IMS) programs primarily the Industrial Hygiene, Waste Management, Fire Protection, Air Quality, Emergency Management, Environmental Monitoring and Pollution Prevention programs. The principal program tool is the Chemical Information System (CIS). The system contains two key elements: the MSDS library and the chemical container-tracking database that is readily accessible to all Members of the Sandia Workforce. The primary goal of the CM Program is to ensure safe and effective chemical management at Sandia/CA. This is done by efficiently collecting and managing chemical information for our customers who include Line, regulators, DOE and ES and H programs to ensure compliance with regulations and to streamline customer business processes that require chemical information.

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This document describes the implementation level changes in the source code and input files of Sandia National Laboratories Environmental Fluid Dynamics Code (SNL-EFDC) that are necessary for including pH effects into algae-growth dynamics. The document also gives a brief introduction to how pH effects are modeled into the algae-growth model. The document assumes that the reader is aware of the existing algae-growth model in SNL-EFDC. The existing model is described by James, Jarardhanam and more theoretical considerations behind modeling pH effects are presented therein. This document should be used in conjunction with the original EFDC manual and the original water-quality manual.

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Water quality signals from sensors provide a snapshot of the water quality at the monitoring station at discrete sample times. These data are typically processed by event detection systems to determine the probability of a water quality event occurring at each sample time. Inherent noise in sensor data and rapid changes in water quality due to operational actions can cause false alarms in event detection systems. While the event determination can be made solely on the data from each signal at the current time step, combining data across signals and backwards in time can provide a richer set of data for event detection. Here we examine the ability of algebraic combinations and other transformations of the raw signals to further decrease false alarms. As an example, using operational events such as one or more pumps turning on or off to define a period of decreased detection sensitivity is one approach to limiting false alarms. This method is effective when lag times are known or when the sensors are co-located with the equipment causing the change. The CANARY software was used to test and demonstrate these combinatorial techniques for improving sensitivity and decreasing false alarms on both background data and data with simulated events. Sandia is a multiprogram laboratory operated by Sandia Corporation, a Lockheed Martin Company, for the United States Department of Energy's National Nuclear Security Administration under contract DE-AC04-94AL85000. © 2012 ASCE.

The optimization of sensor placements is a key aspect of the design of contaminant warning systems for automatically detecting contaminants in water distribution systems. Although researchers have generally assumed that all sensors are placed at the same time, in practice sensor networks will likely grow and evolve over time. For example, limitations for a water utility's budget may dictate an staged, incremental deployment of sensors over many years. We describe optimization formulations of multi-stage sensor placement problems. The objective of these formulations includes an explicit trade-off between the value of the initially deployed and final sensor networks. This trade-off motivates the deployment of sensors in initial stages of the deployment schedule, even though these choices typically lead to a solution that is suboptimal when compared to placing all sensors at once. These multi-stage sensor placement problems can be represented as mixed-integer programs, and we illustrate the impact of this trade-off using standard commercial solvers. We also describe a multi-stage formulation that models budget uncertainty, expressed as a tree of potential budget scenarios through time. Budget uncertainty is used to assess and hedge against risks due to a potentially incomplete deployment of a planned sensor network. This formulation is a multi-stage stochastic mixed-integer program, which are notoriously difficult to solve. We apply standard commercial solvers to small-scale test problems, enabling us to effectively analyze multi-stage sensor placement problems subject to budget uncertainties, and assess the impact of accounting for such uncertainty relative to a deterministic multi-stage model. © 2012 ASCE.

We present a mixed-integer linear programming formulation to determine optimal locations for manual grab sampling after the detection of contaminants in a water distribution system. The formulation selects optimal manual grab sample locations that maximize the total pair-wise distinguishability of candidate contamination events. Given an initial contaminant detection location, a source inversion is performed that will eliminate unlikely events resulting in a much smaller set of candidate contamination events. We then propose a cyclical process where optimal grab samples locations are determined and manual grab samples taken. Relying only on YES/NO indicators of the presence of contaminant, source inversion is performed to reduce the set of candidate contamination events. The process is repeated until the number of candidate events is sufficiently small. Case studies testing this process are presented using water network models ranging from 4 to approximately 13000 nodes. The results demonstrate that the contamination event can be identified within a remarkably small number of sampling cycles using very few sampling teams. Furthermore, solution times were reasonable making this formulation suitable for real-time settings. © 2012 ASCE.

We consider qubit coupling resulting from the capacitive coupling between two double quantum dot (DQD) singlet-triplet qubits. Calculations of the coupling when the two DQDs are detuned symmetrically or asymmetrically are performed using a full configuration interaction (CI). The full CI reveals behavior that is not observed by more commonly used approximations such as Heitler London or Hund Mulliken, particularly related to the operation of both DQDs in the (0,2) charge sector. We find that there are multiple points in detuning space where a two-qubit entangling gate can be realized, and that tradeoffs between coupling magnitude and sensitivity to fluctuations in detuning make a case for operating the gate in the (0,2) regime not commonly considered. © 2012 American Physical Society.

Decision makers increasingly rely on large-scale computational models to simulate and analyze complex man-made systems. For example, computational models of national infrastructures are being used to inform government policy, assess economic and national security risks, evaluate infrastructure interdependencies, and plan for the growth and evolution of infrastructure capabilities. A major challenge for decision makers is the analysis of national-scale models that are composed of interacting systems: effective integration of system models is difficult, there are many parameters to analyze in these systems, and fundamental modeling uncertainties complicate analysis. This project is developing optimization methods to effectively represent and analyze large-scale heterogeneous system of systems (HSoS) models, which have emerged as a promising approach for describing such complex man-made systems. These optimization methods enable decision makers to predict future system behavior, manage system risk, assess tradeoffs between system criteria, and identify critical modeling uncertainties.

The safe handling of reprocessed fuel addresses several scientific goals, especially when considering the capture and long-term storage of volatile radionuclides that are necessary during this process. Despite not being a major component of the offgas, radioiodine (I 2) is particularly challenging, because it is a highly mobile gas and 129I is a long-lived radionuclide (1.57 × 10 7 years). Therefore, its capture and sequestration is of great interest on a societal level. Herein, we explore novel routes toward the effective capture and storage of iodine. In particular, we report on the novel use of a new class of porous solid-state functional materials (metal-organic frameworks, MOFs), as high-capacity adsorbents of molecular iodine. We further describe the formation of novel glass-composite material (GCM) waste forms from the mixing and sintering of the I 2-containing MOFs with Bi-Zn-O low-temperature sintering glasses and silver metal flakes. Our findings indicate that, upon sintering, a uniform monolith is formed, with no evidence of iodine loss; iodine is sequestered during the heating process by the in situ formation of AgI. Detailed materials characterization analysis is presented for the GCMs. This includes powder X-ray diffraction, scanning electron microscopy coupled with energy-dispersive spectroscopy (SEM-EDS), thermal analysis (thermogravimetric analysis (TGA)), and chemical durability tests including aqueous leach studies (product consistency test (PCT)), with X-ray fluorescence (XRF) and inductively coupled plasma-mass spectrometry (ICP-MS) of the PCT leachate. © 2011 American Chemical Society.

Optical absorption due to surface plasmon resonances in ensembles of gold nanorods (Au NRs) depends strongly on the nanorod separation and orientation. Here, we study the dispersion of polystyrene-functionalized Au NRs in polystyrene (PS) thin films using UV-visible (UV-vis) spectroscopy and transmission electron microscopy (TEM) and find that Au NRs are dispersed for brush chain lengths that exceed the PS matrix chain length and are aggregated otherwise. Monte Carlo simulations using parameters from classical density functional theory (DFT) calculations indicate that this behavior is due to substantial depletion-attraction forces for brush chain lengths that are much smaller than the PS matrix chain length. Both UV-vis measurements and discrete dipole approximation (DDA) calculations confirm that optical absorption is a facile method to determine nanorod morphology in nanocomposite films (i.e., aggregation or dispersion). Futhermore, a dispersion map is constructed showing the conditions required for nanorod dispersion and, correspondingly, the optical absorption properties of Au NR:PS nanocomposites. Using this information, optically active materials with tunable morphologies can be fabricated and routinely characterized using optical spectroscopic methods. © 2011 American Chemical Society.

Magnetized inertial fusion (MIF) could substantially ease the difficulty of reaching plasma conditions required for significant fusion yields, but it has been widely accepted that the gain is not sufficient for fusion energy. Numerical simulations are presented showing that high-gain MIF is possible in cylindrical liner implosions based on the MagLIF concept [S. A. Slutz et al Phys. Plasmas 17, 056303 (2010)PHPAEN1070-664X10.1063/1.3333505] with the addition of a cryogenic layer of deuterium-tritium (DT). These simulations show that a burn wave propagates radially from the magnetized hot spot into the surrounding much denser cold DT given sufficient hot-spot areal density. For a drive current of 60 MA the simulated gain exceeds 100, which is more than adequate for fusion energy applications. The simulated gain exceeds 1000 for a drive current of 70 MA. © 2012 American Physical Society.

Rechargeable, all-solid-state Li ion batteries (LIBs) with high specific capacity and small footprint are highly desirable to power an emerging class of miniature, autonomous microsystems that operate without a hardwire for power or communications. A variety of three-dimensional (3D) LIB architectures that maximize areal energy density has been proposed to address this need. The success of all of these designs depends on an ultrathin, conformal electrolyte layer to electrically isolate the anode and cathode while allowing Li ions to pass through. However, we find that a substantial reduction in the electrolyte thickness, into the nanometer regime, can lead to rapid self-discharge of the battery even when the electrolyte layer is conformal and pinhole free. We demonstrate this by fabricating individual, solid-state nanowire core-multishell LIBs (NWLIBs) and cycling these inside a transmission electron microscope. For nanobatteries with the thinnest electrolyte, ≈110 nm, we observe rapid self-discharge, along with void formation at the electrode/electrolyte interface, indicating electrical and chemical breakdown. With electrolyte thickness increased to 180 nm, the self-discharge rate is reduced substantially, and the NWLIBs maintain a potential above 2 V for over 2 h. Analysis of the nanobatteries' electrical characteristics reveals space-charge limited electronic conduction, which effectively shorts the anode and cathode electrodes directly through the electrolyte. Our study illustrates that, at these nanoscale dimensions, the increased electric field can lead to large electronic current in the electrolyte, effectively shorting the battery. The scaling of this phenomenon provides useful guidelines for the future design of 3D LIBs. © 2011 American Chemical Society.

We present the results of large-scale molecular dynamics simulations of two different nanolithographic processes, step-flash imprint lithography (SFIL), and hot embossing. We insert rigid stamps into an entangled bead-spring polymer melt above the glass transition temperature. After equilibration, the polymer is then hardened in one of two ways, depending on the specific process to be modeled. For SFIL, we cross-link the polymer chains by introducing bonds between neighboring beads. To model hot embossing, we instead cool the melt to below the glass transition temperature. We then study the ability of these methods to retain features by removing the stamps, both with a zero-stress removal process in which stamp atoms are instantaneously deleted from the system as well as a more physical process in which the stamp is pulled from the hardened polymer at fixed velocity. We find that it is necessary to coat the stamp with an antifriction coating to achieve clean removal of the stamp. We further find that a high density of cross-links is necessary for good feature retention in the SFIL process. The hot embossing process results in good feature retention at all length scales studied as long as coated, low surface energy stamps are used. © 2011 American Chemical Society.

Due to the high intrinsic thermal conductivity of carbon allotropes, there have been many attempts to incorporate such structures into existing thermal abatement technologies. In particular, carbon nanotubes (CNTs) and graphitic materials (i.e., graphite and graphene flakes or stacks) have garnered much interest due to the combination of both their thermal and mechanical properties. However, the introduction of these carbon-based nanostructures into thermal abatement technologies greatly increases the number of interfaces per unit length within the resulting composite systems. Consequently, thermal transport in these systems is governed as much by the interfaces between the constituent materials as it is by the materials themselves. This paper reports the behavior of phononic thermal transport across interfaces between isotropic thin films and graphite substrates. Elastic and inelastic diffusive transport models are formulated to aid in the prediction of conductance at a metal-graphite interface. The temperature dependence of the thermal conductance at Au-graphite interfaces is measured via transient thermoreflectance from 78 to 400 K. It is found that different substrate surface preparations prior to thin film deposition have a significant effect on the conductance of the interface between film and substrate. © 2012 American Society of Mechanical Engineers.

Simulation of mobility-driven abnormal grain growth in the presence of particles in a 3D Potts Monte Carlo model has been investigated, and even though the driving force in this case is identical to normal grain growth, Zener pinning does not occur. Instead the particles seem merely to have a small inhibiting effect on the number of abnormal grains, and this effect only has a noticeable influence for volume fractions of particles above 5 vol%. © (2012) Trans Tech Publications, Switzerland.

Grain growth in nanocrystalline Ni has been simulated by molecular dynamics. The simulations show the creation of a high density of twin boundaries during the growth as well as the formation of vacancies consistent with recent experimental observations. The growth follows parabolic kinetics with the diameter increasing with the square root of time consistent with behavior of conventional scale metals but in disagreement with prior simulation results. © (2012) Trans Tech Publications, Switzerland.

During large-strain plastic deformation, subgrain structures typically develop within the grains. At large enough equivalent strains above, say 0.5, recrystallization occurs via abnormal coarsening of the subgrain structure or abnormal (sub-) grain growth (AsGG). The fraction of subgrains that develop into new, recrystallized grains has been quantified as a function of texture spread (Grain Reference Orientation Deviation) using Monte Carlo simulation. When this fraction is combined with the known monotonic increase in mean misorientation with strain, the recrystallized grain size can be predicted as a function of von Mises strain. The prediction is in good agreement with experimental results drawn from the literature. © (2012) Trans Tech Publications, Switzerland.

The focus of the present paper is the design of multi-player role-playing game instances as crucible experiences for the exploration of one’s emotional intelligence. Subsequent sections describe the design of game-based, intercultural crucible experiences and how this design was employed for training with members of the United States Marine Corps (USMC). This work with the USMC is presented as a case study and example of the use of crucible experiences in game-based learning. Crucible experiences are learning opportunities relevant across a number of different domains and disciplines such as education, healthcare, corporate training, diplomacy, crisis management, international business, and intercultural communication. The present paper demonstrates that crucible experiences are catalysts for personal growth and can be incorporated into game-based learning design whose intent is to create defining moments in which learners can explore emotional intelligence and examine who they are under challenging conditions.

A numerical transport model was developed to study the spontaneous transition from smoldering to flaming combustion in polyurethane foam. The numerical transport model is two-dimensional with an eight-step reduced reaction mechanism. The reaction mechanism includes seven heterogeneous and a global homogeneous gas phase reaction and is capable of simulating both forward and opposed smoldering combustion. The current study exami2nes the transition to flaming in normal gravity for flow assisted forward smoldering combustion as a function of an externally applied heat flux and the velocity and oxygen concentration of a forced gas flow. Reaction rates, species profiles, gas phase temperatures, and condensed phase temperatures are examined. Three reactions were found to play a major role in leading to the prediction of transition to flaming. Favorable agreement of temperature response, time to spontaneously transition from smolder to flaming, and location of the transition event between simulation results and experimental data is demonstrated. © 2011 The Combustion Institute.

Ethanol and ethanol/gasoline blends are being widely considered as alternative fuels for light-duty automotive applications. At the same time, HCCI combustion has the potential to provide high efficiency and ultra-low exhaust emissions. However, the application of HCCI is typically limited to low and moderate loads because of unacceptably high heat-release rates (HRR) at higher fueling rates. This work investigates the potential of lowering the HCCI HRR at high loads by using partial fuel stratification to increase the in-cylinder thermal stratification. This strategy is based on ethanol's high heat of vaporization combined with its true single-stage ignition characteristics. Using partial fuel stratification, the strong fuel-vaporization cooling produces thermal stratification due to variations in the amount of fuel vaporization in different parts of the combustion chamber. The low sensitivity of the autoignition reactions to variations of the local fuel concentration allows the temperature variations to govern the combustion event. This results in a sequential autoignition event from leaner and hotter zones to richer and colder zones, lowering the overall combustion rate compared to operation with a uniform fuel/air mixture. The amount of partial fuel stratification was varied by adjusting the fraction of fuel injected late to produce stratification, and also by changing the timing of the late injection. The experiments show that a combination of 60 -70% premixed charge and injection of 30 -40 % of the fuel at 80°CA before TDC is effective for smoothing the HRR. With CA50 held fixed, this increases the burn duration by 55% and reduces the maximum pressure-rise rate by 40%. Combustion stability remains high but engine-out NO x has to be monitored carefully. For operation with strong reduction of the peak HRR, ISNO x rises to around 0.20 g/kWh for an IMEP g of 440 kPa. The single-cylinder HCCI research engine was operated naturally aspirated without EGR at 1200 rpm, and had low residual level using a CR = 14 piston. © 2011 Society of Automotive Engineers of Japan, Inc. and SAE International.

The electronic industry continues to dramatically reduce the size of electrical components. Many of these components are now small enough to allow shock testing with Hopkinson pressure bar techniques. However, conventional Hopkinson bar techniques must be modified to provide a broad array of shock pulse amplitudes and durations. For this study, we evaluate the shock response of accelerometers that measure large amplitude pulses, such as those experienced in projectile perforation and penetration tests. In particular, we modified the conventional Hopkinson bar apparatus to produce relatively long duration pulses. The modified apparatus consists of a steel striker bar, annealed copper pulse shapers, an aluminum incident bar, and a tungsten disk with mounted accelerometers. With these modifications, we obtained accelerations pulses that reached amplitudes of 10 kG and durations of 0.5 ms. To evaluate the performance of the accelerometers, acceleration-time responses are compared with a model that uses data from a quartz stress gage. Comparisons of data from both measurements are in good agreement. © 2012 Elsevier Ltd. All rights reserved.

In the 1980's the dosimetry community embraced the need for a high fidelity quantification of uncertainty in nuclear data used for dosimetry applications. This led to the adoption of energy-dependent covariance matrices as the accepted manner of quantifying the uncertainty data. The trend for the dosimetry community to require high fidelity treatment of uncertainty estimates has continued to the current time where requirements on nuclear data are codified in standards such as ASTM E 1018. This paper surveys the current state of the dosimetry cross sections and investigates the quality of the current dosimetry cross section evaluations by examining calculated-to-experimental ratios in neutron benchmark fields. In recent years more nuclear-related technical areas are placing an emphasis on uncertainty quantification. With the availability of model-based cross sections and covariance matrices produced by nuclear data codes, some nuclear-related communities are considering the role these covariance matrices should play. While funding within the dosimetry community for cross section evaluations has been very meager, other areas, such as the solar-related astrophysics community and the US Nuclear Criticality Safety Program, have been supporting research in the area of neutron cross sections. The Cross Section Evaluation Working Group (CSEWG) is responsible for the creation and maintenance of the ENDF/B library which has been the mainstay for the reactor dosimetry community. Given the new trends in cross section evaluations, this paper explores the path forward for the US nuclear reactor dosimetry community and its use of the ENDF/B cross-sections. The major concern is maintenance of the sufficiency and accuracy of the uncertainty estimate when used for dosimetry applications. The two major areas of deficiency in the proposed ENDF/B approach are: 1) the use of unrelated covariance matrices in ENDF/B evaluations and 2) the lack of "due consideration" of experimental data in the evaluation. Copyright © 2012 by ASTM International.

Carrier generation characteristics in n-type substrate SiC MOS capacitors induced by sub-bandgap energy light are reported. The generation rate is high enough to create an inversion layer in ∼20 minutes with monochromatic light (front side illumination) of energy 2.1 eV (intensity ∼5×10 16 cm-2s-1) in 4H-SiC for electric fields smaller than 1 MV/cm. Generation and recovery results strongly indicate involvement of a metastable defect whose efficiency as a generation center increases under hole-rich and decreases under electron-rich conditions. The generation dependence on bias history and light energy shows the defect to have properties consistent with the metastable silicon vacancy / carbon vacancy-antisite complex (VSi/Vc-CSi). © (2012) Trans Tech Publications.

The authors report on the integration of delocalized surface plasmon resonances (SPRs) and localized surface plasmon resonances (LSPRs) on a single device. The submicron SPR device was fabricated with nanoimprint lithography (NIL). Gold nanoparticles for LSPR generation were created and deposited via three methods and analyzed with rhodamine 6 G and surface-enhanced Raman spectroscopy (SERS). Compared to drop-cast and thin film annealing methods, gold nanoparticles fabricated from a diblock-copolymer NIL template produced the most significant effect on the charge-transfer component of the SERS enhancement mechanism due to near-field interactions at the 10 nm inter-particle separation region. The authors also report a 26 enhancement of optical resonance with an integrated SPR-LSPR plasmonic device consisting of a two-dimensional submicron aluminum grating fully coupled with gold nanoparticles measuring 20.4 nm in diameter in a water medium. If the 2D aluminum grating were coupled to an optimized nanoparticle SERS device fabricated from a DBCP NIL template, the coupled nanoparticle-grating device could exhibit an even higher enhancement and optical resonance performance. © 2012 American Vacuum Society.

The Meier-Moir economic model for Pulsed Power Driven Inertial Fusion Energy shows at least two approaches for fusion energy at 7 to 8 cents/kw-hr: One with large yield at 0.1 Hz and presented by M. E. Cuneo at ICENES 2011 and one with smaller yield at 3 Hz presented in this paper. Both use very efficient and low cost Linear Transformer Drivers (LTDs) for the pulsed power. Here, we report the system configuration and end-to-end simulation for the latter option, which is called the Plasma Power Station (PPS), and report the first results on the two, least mature, enabling technologies: a magnetically driven Quasi Spherical Direct Drive (QSDD) capsule for the fusion yield and an Inverse Diode for coupling the driver to the target. In addition, we describe the issues and propose to address the issues with a prototype of the PPS on the Saturn accelerator and with experiments on a short pulse modification of the Z accelerator test the validity of simulations showing megajoule thermonuclear yield with DT on a modified Z.

Numerical modeling is increasingly becoming an indispensable tool for investigations in many fields of physics. Such modeling is especially useful in today's big science projects as a tool that can provide predictions and design parameters. The reliability of simulation results is thus essential. Code-to-code comparisons can help increase our confidence in simulation results, especially when other verification methods - such as comparison to theoretical models or experimental results - are limited or unavailable. In this paper, we describe a code-to-code comparison exercise wherein we compare one-dimensional vacuum arc discharge simulation results from two independent particle-in-cell (PIC) codes. As part of our case study, we define a vacuum arc discharge test problem that can be used by other research groups for further comparison. Early disagreement between the two sets of our results motivated us to re-examine the underlying methods in our codes. After remedying discrepancies, we observe good agreement in vacuum arc discharge time-to-breakdown, as well as in the time evolution of particle and current densities. This exercise demonstrates the usefulness of code-to-code comparisons and provides an example case study for the benefit of other research groups who may wish to carry out similar code-to-code comparisons. © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Difficulties in adequately characterising food supply chain topologies contribute major uncertainty to risk assessments of the food sector. The capability to trace contaminated foods forward (to consumers) and back (to providers) is needed for rapid recalls during food contamination events. The objective of this work is to develop an approach for risk mitigation that protects us from an attack on the food distribution system. This paper presents a general methodology for the stochastic mapping of fresh produce supply chains and an application to a single, relatively simple case - edible sprouts in one region. The case study demonstrates how mapping the network topology and modeling the potential relationships allows users to determine the likely contaminant pathways and sources of contamination. The stochastic network representation improves the ability to explicitly incorporate uncertainties and identify vulnerabilities. Copyright © 2012 Inderscience Enterprises Ltd.

The Meier-Moir economic model for Pulsed Power Driven Inertial Fusion Energy shows at least two approaches for fusion energy at 7 to 8 cents/kw-hr: One with large yield at 0.1 Hz and presented by M. E. Cuneo at ICENES 2011 and one with smaller yield at 3 Hz presented in this paper. Both use very efficient and low cost Linear Transformer Drivers (LTDs) for the pulsed power. We report the system configuration and end-toend simulation for the latter option, which is called the Plasma Power Station (PPS), and report the first results on the two, least mature, enabling technologies: a magnetically driven Quasi Spherical Direct Drive (QSDD) capsule for the fusion yield and an Inverse Diode for coupling the driver to the target. In addition, we describe the issues and propose to address the issues with a prototype of the PPS on the Saturn accelerator and with experiments on a short pulse modification of the Z accelerator test the validity of simulations showing megajoule thermonuclear yield with DT on a modified Z.

Refractory metallic foams can increase heat transfer efficiency in gas-to-gas and liquid metal-to-gas heat exchangers by providing an extended surface area for better convection, i.e. conduction into the foam ligaments providing a "fin-effect, " and by disruption of the thermal boundary layer near the hot wall and ligaments by turbulence promotion. We present the relative contributions of the heat transfer mechanisms stated above, and show how the design of a gas regenerator or liquid metal-to-gas heat exchanger can be optimized for use in high-temperature Brayton cycle applications for nuclear power generation or hydrogen production. Our results include temperature and thermal stress distributions for several densities of Nb1Zr, Mo and W foams compared to Cu. For instance, the simulations reveal that unconnected W foam can increase the convective heat transfer coefficient by almost a factor of two compared to an open rectangular channel and a factor of three if the foam ligaments are thermally connected to the sidewalls under the same flow conditions. The effect of ligament thermal conductivity is also highlighted by comparing the performance of W foams to identical Cu foams and the use of SiC foams in thermal barrier applications. The studies indicate that thermal stresses increase with foam density, but are not clearly correlated with pore cell size. For thermal management applications, the presence of the connected foam minimizes the thermal stresses in the wall, by concentrating them in the ligaments where the temperature gradients are higher. In addition, the large number of small connected ligaments provides a modest degree of compliance for thermal expansion of the hotter walls in relation to the colder portions of the heat exchanger. These CFD studies have led to design strategies for creating compact, high-temperature, high-pressure heat exchangers that are easily fabricated and perform better than plate-type heat exchangers.

Proposed exascale systems will present a number of considerable resiliency challenges. In particular, DRAM soft-errors, or bit-flips, are expected to greatly increase due to the increased memory density of these systems. Current hardware-based fault-tolerance methods will be unsuitable for addressing the expected soft error frequency rate. As a result, additional software will be needed to address this challenge. In this paper we introduce LIBSDC, a tunable, transparent silent data corruption detection and correction library for HPC applications. LIBSDC provides comprehensive SDC protection for program memory by implementing on-demand page integrity verification. Experimental benchmarks with Mantevo HPCCG show that once tuned, LIBSDC is able to achieve SDC protection with 50% overhead of resources, less than the 100% needed for double modular redundancy. © 2012 Springer-Verlag Berlin Heidelberg.

This study compares several block-oriented preconditioners for the stabilized finite element discretization of the incompressible Navier-Stokes equations. This includes standard additive Schwarz domain decomposition methods, aggressive coarsening multigrid, and three preconditioners based on an approximate block LU factorization, specifically SIMPLEC, LSC, and PCD. Robustness is considered with a particular focus on the impact that different stabilization methods have on preconditioner performance. Additionally, parallel scaling studies are undertaken. The numerical results indicate that aggressive coarsening multigrid, LSC and PCD all have good algorithmic scalability. Coupling this with the fact that block methods can be applied to systems arising from stable mixed discretizations implies that these techniques are a promising direction for developing scalable methods for Navier-Stokes. © 2011.

An important issue concerning the safe use of hydrogen-powered fuel-cell vehicles is the possibility of accidents inside tunnels resulting in the release of hydrogen. To investigate the potential consequences, a combined experimental and modeling study has been performed to characterize releases from a hydrogen fuel-cell vehicle inside a tunnel. In the scenario studied, all three of the fuel-cell vehicle's onboard hydrogen tanks were simultaneously released through three thermal pressure relief devices (TPRDs) toward the road surface. Computation fluid dynamics (CFD) simulations were used to model the release of hydrogen from the fuel-cell vehicle and to study the behavior of the ignitable hydrogen cloud inside the tunnel. Deflagration overpressure simulations of the hydrogen cloud within the tunnel were also performed for different ignition delay times and ignition locations. To provide model validation data for these simulations, experiments were performed in a scaled tunnel test facility at the SRI Corral Hollow Experiment Site (CHES). The scaled tunnel tests were designed to resemble the full-scale tunnel simulations using Froude scaling. The scale factor, based on the square route of the ratio of the SRI tunnel area to the full-scale tunnel area was 1/2.53. The same computational models used in the full-scale tunnel simulations were applied to these scaled tunnel tests to validate the modeling approach. © 2011, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.

Microbial biomass can clog porous media and ultimately affect both structural and mineral trapping of CO2 in geological carbon storage reservoirs. Whether biomass can remain intact following a sudden decrease in groundwater pH, a geochemical change associated with CO2 injection, is unclear. We examined this question using twelve biologically-active and three control column-reactor experiments. Cell abundance and distribution was monitored using confocal microscopy, plating, and direct counting. Hydraulic conductivity (K) was monitored using pressure sensors. Growth occurred for four days at neutral pH. During that time, K within the clogged portion of the reactors decreased from 0.013 to 0.0006cm s-1 on average, a 1.47log reduction. Next, the pH of the inflowing aqueous medium was lowered to pH 4 in six experiments and pH 5.7 in six experiments. As a result, K increased in five of the pH 4 experiments and two of the pH 5.7 experiments. Despite this increase, however, the columns remained largely clogged. Compared to pre-inoculation K values, log reductions averaged 1.13 and 1.44 in pH 4 and pH 5.7 experiments, respectively. Our findings show that biomass can largely remain intact following acidification and continue to reduce K, even when considerable cell stress and death occurs. © 2012 Elsevier Ltd.

This study systematically investigates the effects of various engine operating parameters on the thermal efficiency of a boosted HCCI engine, and the potential of E10 to extend the high-load limit beyond that obtained with conventional gasoline. Understanding how these parameters can be adjusted and the trade-offs involved is critical for optimizing engine operation and for determining the highest efficiencies for a given engine geometry. Data were acquired in a 0.98 liter, single-cylinder HCCI research engine with a compression-ratio of 14:1, and the engine facility was configured to allow precise control over the relevant operating parameters. The study focuses on boosted operation with intake pressures (Pin) ≥ 2 bar, but some data for Pin < 2 bar are also presented. Two fuels are considered: 1) an 87-octane gasoline, and 2) E10 (10% ethanol in this same gasoline) which has a lower autoignition reactivity for boosted operation. This study considers several engine operating parameters, including: intake temperature, fueling rate, engine speed, fuel type, and the effect of various amounts of mixture stratification using three fueling methods: fully premixed, early-DI, and premixed + late-DI (termed partial fuel stratification, PFS). The effects of these operating parameters on the factors affecting thermal efficiency, such as combustion phasing (CA50), amount of EGR required, ringing intensity, combustion efficiency, γ = cp/cv, and heat transfer are also explored and discussed. The study showed that in general, thermal efficiency improves when parameters are adjusted for lower intake temperatures, less CA50 retard, and less EGR, as long as the ringing intensity is ≤ 5 MW/m 2 to prevent knock, and combustion efficiency is good (i.e. ≥ about 96%). Additionally, applying a small amount of mixture stratification (using PFS or early-DI fueling) improves efficiency by allowing more CA50 advance when boost levels are sufficient for these fuels to be φ-sensitive. E10 gives a small increase in thermal efficiency because EGR requirements are reduced. E10 is also effective for increasing the maximum load for P in ≥ 2.4 bar, and increasing the high-load limit to IMEPg = 18.1 bar, with no engine knock and ultra-low NOx and soot emissions, compared to IMEPg = 16.3 bar for gasoline. Overall, this study showed that the efficiencies for boosted HCCI can be increased above their already good baseline values. For our engine configuration, improvements of 3-5 thermal-efficiency percentage units were achieved corresponding to a reduction in fuel consumption of 7-11%. Copyright © 2012 SAE International.

A short-standoff bistatic lidar system coupled with an aerosol chamber has been built to measure aerosol optical backscatter and laser induced fluorescence cross-sections. Preliminary results show good sensitivity across all channels with high signal-to-noise ratio. © OSA 2012.

Despite the technological importance of body-centered cubic (BCC) metals, models of their plastic deformation are less common than those of face-centered cubic (FCC) metals, due in part to the complexity of slip in BCC crystals caused by the thermal activation of screw dislocation motion. This paper presents a physically based crystal plasticity model that incorporates atomistic models and experimental measurements of the thermally activated nature of screw dislocation motion. This model, therefore, reproduces the temperature, stress, and strain rate dependence of flow in BCC metals in a simple formulation that will allow for large, grain-scale simulations. Furthermore, the results illustrate the importance of correctly representing mechanistic transitions in materials with high lattice friction. © 2012 Elsevier Ltd. All rights reserved.

The DSMC method is used to model the interaction of the jovian plasma torus with Io's SO2 sublimation and sputtered atmosphere just prior to eclipse. The SO2 frost sublimes on the warm dayside and photo and neutral chemistry, the dominant source of the daughter species (SO, O 2, O, and S) are included. To model the plasma interaction with the sublimation atmosphere, a two-timestep method is utilized in which the neutrals are assumed to be stationary while electrons and ions are moved and collided over a much smaller timestep. The dominant ion-neutral interactions (non-reactive and resonant charge exchange) are included. Sputtering of SO 2 molecules from the frost-covered surface is dependent on the incident ion energy and the surface frost temperature. Io's surface is assumed to be uniformly covered by SO2 surface frosts with the temperature computed based on radiative equilibrium with insolation. We investigate the effect that the plasma interaction with Io's atmosphere has on atmospheric composition and structure, circumplanetary winds, and the escape rate of material from Io to the plasma torus. The dense sublimation atmosphere reduces sputtering from SO2 surface frosts over much of the dayside; however, sputtering was found to be a significant contributor to the nightside atmosphere. The plasma pressure on the sublimation atmosphere has a substantial effect on the day-to-night winds. Not only does the plasma pressure induce an overall retrograde wind in Io's atmosphere just prior to entry into eclipse, but the atmospheric scale height is reduced by the plasma pressure on the trailing hemisphere. Molecular oxygen is a minor species on the dayside but is found to be the dominant nightside species because it is non-condensable and the loss rates due to atmospheric escape or dissociation are slow. © 2012 by Chris Moore.

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New aircraft are being designed with increasing quantities of composite materials used in their construction. Different from the more traditional metals, composites have a higher propensity to burn. This presents a challenge to transportation safety analyses, as the aircraft structure now represents an additional fuel source involved in the fire scenario. Performance testing data for composites burning in a fire at the integral scales of an accident event are nearly non-existent. This report describes fire tests for relevant carbon fiber epoxy materials that were designed to explore the bulk decomposition behavior of said material in a severe fire. Together with TGA decomposition data, the material is found to decompose in three mostly distinctive and sequential phases, epoxy pyrolysis, char oxidation, and carbon fiber oxidation. Fires were not severe in their thermal intensity compared to liquid fuel fires. Peak thermal intensities of around 220 kW/m2 or 1100 °C are achieved at very low air flow rates. The burn tests were remarkable in their duration, lasting 4-8 hours for 25-40 kg of combustible material.

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Sandia National Laboratories (Sandia) and SunPower Corporation (SunPower) have completed design and deployment of an autonomous irradiance monitoring system based on wireless mesh communications and a battery operated data acquisition system. The Lanai High-Density Irradiance Sensor Network is comprised of 24 LI-COR{reg_sign} irradiance sensors (silicon pyranometers) polled by 19 RF Radios. The system was implemented with commercially available hardware and custom developed LabVIEW applications. The network of solar irradiance sensors was installed in January 2010 around the periphery and within the 1.2 MW ac La Ola PV plant on the island of Lanai, Hawaii. Data acquired at 1 second intervals is transmitted over wireless links to be time-stamped and recorded on SunPower data servers at the site for later analysis. The intent is to study power and solar resource data sets to correlate the movement of cloud shadows across the PV array and its effect on power output of the PV plant. The irradiance data sets recorded will be used to study the shape, size and velocity of cloud shadows. This data, along with time-correlated PV array output data, will support the development and validation of a PV performance model that can predict the short-term output characteristics (ramp rates) of PV systems of different sizes and designs. This analysis could also be used by the La Ola system operator to predict power ramp events and support the function of the future battery system. This experience could be used to validate short-term output forecasting methodologies.

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Cyanobacteria are oxygenic photosynthetic prokaryotes that are the progenitors of the chloroplasts of algae and plants. These organisms harvest light using large membrane-extrinsic phycobilisome antenna in addition to membrane-bound chlorophyllcontaining proteins. Similar to eukaryotic photosynthetic organisms, cyanobacteria possess thylakoid membranes that house photosystem (PS) I and PSII, which drive the oxidation of water and the reduction of NADP+, respectively. While thylakoid morphology has been studied in some strains of cyanobacteria, the global distribution of PSI and PSII within the thylakoid membrane and the corresponding location of the light-harvesting phycobilisomes are not known in detail, and such information is required to understand the functioning of cyanobacterial photosynthesis on a larger scale. Here, we have addressed this question using a combination of electron microscopy and hyperspectral confocal fluorescence microscopy in wild-type Synechocystis species PCC 6803 and a series of mutants in which phycobilisomes are progressively truncated. We show that as the phycobilisome antenna is diminished, large-scale changes in thylakoid morphology are observed, accompanied by increased physical segregation of the two photosystems. Finally, we quantified the emission intensities originating from the two photosystems in vivo on a per cell basis to show that the PSI:PSII ratio is progressively decreased in the mutants. This results from both an increase in the amount of photosystem II and a decrease in the photosystem I concentration. We propose that these changes are an adaptive strategy that allows cells to balance the light absorption capabilities of photosystems I and II under light-limiting conditions. © 2012 American Society of Plant Biologists. All Rights Reserved.

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