Publications

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Microsystems Enabled Photovoltaics (MEPV) is a relatively new field that uses microsystems tools and manufacturing techniques familiar to the semiconductor industry to produce microscale photovoltaic cells. The miniaturization of these PV cells creates new possibilities in system designs that may be able to achieve the US Department of Energy (DOE) price target of $1/Wp by 2020 for utility-scale electricity generation. In this article, we introduce analytical tools and techniques to estimate the costs associated with a concentrating photovoltaic system that uses microscale photovoltaic cells and miniaturized optics. The overall model comprises the component costs associated with the PV cells, concentrating optics, balance of systems, installation, and operation. Estimates include profit margin and are discussed in the context of current and projected prices for non-concentrating and concentrating photovoltaics. Our analysis indicates that cells with a width of between 100 and 300 μm will minimize the module costs of the initial design within the range of concentration ratios considered. To achieve the DOE price target of $1/Wp by 2020, module efficiencies over 35% will likely be necessary. © 2013 IEEE.

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The accuracy of digital in-line holography to detect particle position and size within a 3D domain is evaluated with particular focus placed on detection of nonspherical particles. Dimensionless models are proposed for simulation of holograms from single particles, and these models are used to evaluate the uncertainty of existing particle detection methods. From the lessons learned, a new hybrid method is proposed. This method features automatic determination of optimum thresholds, and simulations indicate improved accuracy compared to alternative methods. To validate this, experiments are performed using quasi-stationary, 3D particle fields with imposed translations. For the spherical particles considered in experiments, the proposed hybrid method resolves mean particle concentration and size to within 4% of the actual value, while the standard deviation of particle depth is less than two particle diameters. Initial experimental results for nonspherical particles reveal similar performance.

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We present a method to use mask/anti-mask coded aperture data with maximum likelihood expectation maximization (MLEM) image reconstruction. The mask/anti-mask approach eliminates 'unmodulated' data, improving image quality when backgrounds, room scatter, or noisy detectors are significant. MLEM permits complex detector response models, desirable in gamma-ray or fast neutron imaging with thick masks, near-field imaging, or tomographic reconstruction. Subtracted mask/anti-mask data is not Poisson distributed, and cannot be used with MLEM. Instead, we treat unmodulated data as generated by source terms indexed by detector pixel, so that MLEM converges to simultaneous estimates of the true image and the unmodulated event rates. © 2013 IEEE.

Time-encoded imaging is an approach to directional radiation detection that is being developed at SNL with a focus on fast neutron directional detection. In this technique, a time modulation of a detected neutron signal is induced - typically, a moving mask that attenuates neutrons with a time structure that depends on the source position. An important challenge in time-encoded imaging is to develop high-resolution two-dimensional imaging capabilities; building a mechanically moving high-resolution mask presents challenges both theoretical and technical. We have investigated an alternative to mechanical masks that replaces the solid mask with a liquid such as mineral oil. Instead of fixed blocks of solid material that move in predefined patterns, the oil is contained in tubing structures, and carefully introduced air gaps - bubbles - propagate through the tubing, generating moving patterns of oil mask elements and air apertures. Compared to current moving-mask techniques, the bubble mask is simple, since mechanical motion is replaced by gravity-driven bubble propagation; it is flexible, since arbitrary bubble patterns can be generated by a software-controlled valve actuator; and it is potentially high performance, since the tubing and bubble size can be tuned for high-resolution imaging requirements. We have built and tested various single-tube mask elements, and will present results on bubble introduction and propagation for different tube sizes and cross-sectional shapes; real-time bubble position tracking; neutron source imaging tests; and reconstruction techniques demonstrated on simple test data as well as a simulated full detector system. © 2013 IEEE.

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Use of second generation sequencing (SGS) technologies for transcriptional profiling (RNA-Seq) has revolutionized transcriptomics, enabling measurement of RNA abundances with unprecedented specificity and sensitivity and the discovery of novel RNA species. Preparation of RNA-Seq libraries requires conversion of the RNA starting material into cDNA flanked by platform-specific adaptor sequences. Each of the published methods and commercial kits currently available for RNA-Seq library preparation suffers from at least one major drawback, including long processing times, large starting material requirements, uneven coverage, loss of strand information and high cost. We report the development of a new RNA-Seq library preparation technique that produces representative, strand-specific RNA-Seq libraries from small amounts of starting material in a fast, simple and cost-effective manner. Additionally, we have developed a new quantitative PCR-based assay for precisely determining the number of PCR cycles to perform for optimal enrichment of the final library, a key step in all SGS library preparation workflows. © 2013 Landes Bioscience.

Tests are ongoing to conduct ~20 MA z-pinch implosions on the Z accelerator at Sandia National Laboratory using Ar, Kr, and D2 gas puffs as the imploding loads. The relatively high cost of operations on a machine of this scale imposes stringent requirements on the functionality, reliability, and safety of gas puff hardware. Here we describe the development of a prototype gas puff system including the multiple-shell nozzles, electromagnetic drivers for each nozzle's valve, a UV pre-ionizer, and an inductive isolator to isolate the ~2.4 MV machine voltage pulse present at the gas load from the necessary electrical and fluid connections made to the puff system from outside the Z vacuum chamber. This paper shows how the assembly couples to the overall Z system and presents data taken to validate the functionality of the overall system.

We present an algorithm to maintain the connected components of a graph that arrives as an infinite stream of edges. We formalize the algorithm on X-stream, a new parallel theoretical computational model for infinite streams. Connectivity-related queries, including component spanning trees, are supported with some latency, returning the state of the graph at the time of the query. Because an infinite stream may eventually exceed the storage limits of any number of finite-memory processors, we assume an aging command or daemon where "uninteresting" edges are removed when the system nears capacity. Following an aging command the system will block queries until its data structures are repaired, but edges will continue to be accepted from the stream, never dropped. The algorithm will not fail unless a model-specific constant fraction of the aggregate memory across all processors is full. In normal operation, it will not fail unless aggregate memory is completely full. Unlike previous theoretical streaming models designed for finite graphs that assume a single shared memory machine or require arbitrary-size intemediate files, X-stream distributes a graph over a ring network of finite-memory processors. Though the model is synchronous and reminiscent of systolic algorithms, our implementation uses an asynchronous message-passing system. We argue the correctness of our X-stream connected components algorithm, and give preliminary experimental results on synthetic and real graph streams.

In some situations involving weak grids or high penetration scenarios, the variability of photovoltaic systems can affect the local electrical grid. In order to mitigate destabilizing effects of power fluctuations, an energy storage device or other controllable generation or load can be used. This paper describes the development of a controller for coordinated operation of a small gas engine-generator set (genset) and a battery for smoothing PV plant output. There are a number of benefits derived from using a traditional generation resource in combination with the battery: the variability of the photovoltaic system can be reduced to a specific level with a smaller battery and Power Conditioning System (PCS) and the lifetime of the battery can be extended. The controller was designed specifically for a PV/energy storage project (Prosperity) and a gas engine-generator (Mesa Del Sol) currently operating on the same feeder in Albuquerque, NM. A number of smoothing simulations of the Prosperity PV system were conducted using power data collected from the site. By adjusting the control parameters, tradeoffs between battery use and ramp rates could be tuned. A cost function was created to optimize the control in order to balance - in this example - the need to have low ramp rates with reducing battery size and operation. © 2013 IEEE.

Imagery from GOES satellites is analyzed to determine how solar variability is related to the NOAA classification of cloud type. Without using a model to convert satellite imagery to average insolation on the ground, this paper investigates using cloud categories to directly model the expected statistical variability of ground irradiance. Hourly cloud classified satellite images are compared to multiple years of ground measured irradiance at two locations to determine if measured irradiance, ramp rates, and variability index are correlated with cloud category. Novel results are presented for ramp rates grouped by the cloud category during the time period. This correlation between satellite cloud classification and solar variability could be used to model the solar variability for a given location and time and could be used to determine the variability of a location based on the prevalence of each cloud category.

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Low-temperature combustion (LTC) achieved by using exhaust-gas recirculation (EGR) is an operating strategy of current interest for heavy-duty and other compression-ignition (diesel) engines because it offers low nitrogen oxides (NOx) and soot emissions compared to conventional diesel combustion. While the long ignition-delay of EGR-LTC helps increase pre-combustion mixing to reduce soot formation, other emissions, including unburned hydrocarbons (UHC), can be problematic. Particularly an issue at low-load conditions, a considerable portion of UHC emissions in large-bore diesels is often due to overly-lean fuel/air mixtures formed near the injector during the long ignition delay. In this study, we explore the use of multiple post-injection strategies, which have a large main injection and one or two smaller post injections, to help reduce engine-out UHC emissions. The short post-injections closely timed after the end of the main injection help to enrich the overly-lean region near the injector, allowing for more complete combustion of a greater portion of the fuel/air mixture. Optical results from formaldehyde and OH planar laser-induced fluorescence provide evidence of the in-cylinder spatial and temporal progression toward complete combustion.

In this study, two flames of iso-pentanol were stabilized on a 60-mm flat flame burner at a low pressure of 15 Torr and analyzed by a flame-sampling molecular-beam setup coupled to a mass spectrometer (MBMS). Singlephoton ionization by synchrotron-generated vacuum-UV radiation with high energy resolution (E/ΔE ∼0.04 eV) and/or electron ionization was combined with a custom-built reflectron time-of-flight spectrometer providing high mass resolution (m/Δm = 3000). Mole fraction profiles for more than 40 flame species and the temperature profile were determined experimentally. The flame temperatures were measured using OH laser induced fluorescence and used as input parameters for the model calculations. The experimental dataset was used to guide the development of a combustion chemistry model for the high-temperature oxidation chemistry of iso-pentanol. The chemical kinetic model is herein validated for the first time against detailed speciation profiles of combustion intermediates and product species including C5 branched aldehydes, enols, and alkenes. In a separated study, the model was validated against a number of different datasets including low and high temperature ignition delay in rapid compression machines and shock tubes, jet stirred reactor speciation data, premixed laminar flame speed, and opposed-flow diffusion flame strained extinction.

Microsystems-enabled photovoltaics (MEPVs) are microfabricated arrays of thin and efficient solar cells. The scaling effects enabled by this technique results in great potential to meet increasing demands for light-weight photovoltaic solutions with high power density. This paper covers failure analysis techniques used to support the development of MEPVs with a focus on the laser beam-based methods of LIVA, TIVA, OBIC, and SEI. Each FA technique is useful in different situations, and the examples in this paper show the relative advantages of each method for the failure analysis of MEPVs. Copyright © 2013 ASM International® All rights reserved.

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Mathematical modeling of anatomically-constrained neural networks has provided significant insights regarding the response of networks to neurological disorders or injury. A logical extension of these models is to incorporate treatment regimens to investigate network responses to intervention. The addition of nascent neurons from stem cell precursors into damaged or diseased tissue has been used as a successful therapeutic tool in recent decades. Interestingly, models have been developed to examine the incorporation of new neurons into intact adult structures, particularly the dentate granule neurons of the hippocampus. These studies suggest that the unique properties of maturing neurons, can impact circuit behavior in unanticipated ways. In this perspective, we review the current status of models used to examine damaged CNS structures with particular focus on cortical damage due to stroke. Secondly, we suggest that computational modeling of cell replacement therapies can be made feasible by implementing approaches taken by current models of adult neurogenesis. The development of these models is critical for generating hypotheses regarding transplant therapies and improving outcomes by tailoring transplants to desired effects.

Power and energy concerns are motivating chip manufacturers to consider future hybrid-core processor designs that combine a small number of traditional cores optimized for single-thread performance with a large number of simpler cores optimized for throughput performance. This trend is likely to impact the way compute resources for network protocol processing functions are allocated and managed. In particular, the performance of MPI match processing is critical to achieving high message throughput. In this paper, we analyze the ability of simple and more complex cores to perform MPI matching operations for various scenarios in order to gain insight into how MPI implementations for future hybrid-core processors should be designed.

Imagery from GOES satellites is analyzed to determine how solar variability is related to the NOAA classification of cloud type. Without using a model to convert satellite imagery to average insolation on the ground, this paper investigates using cloud categories to directly model the expected statistical variability of ground irradiance. Hourly cloud classified satellite images are compared to multiple years of ground measured irradiance at two locations to determine if measured irradiance, ramp rates, and variability index are correlated with cloud category. Novel results are presented for ramp rates grouped by the cloud category during the time period. This correlation between satellite cloud classification and solar variability could be used to model the solar variability for a given location and time and could be used to determine the variability of a location based on the prevalence of each cloud category.

This paper describes the MELCOR Accident Consequence Code System, Version 2 (MACCS2) dose-truncation sensitivity of offsite consequences for the uncertainty analysis of the State-of-the-Art Reactor Consequence Analyses unmitigated long-term station blackout severe accident scenario at the Peach Bottom Atomic Power Station. Latent-cancer-fatality (LCF) risk results for this sensitivity study are presented for three dose-response models. LCF risks are reported for circular areas ranging from a 10-to a 50-mile radius centered on the plant. For the linear, no-threshold, sensitivity analysis, all regression methods consistently rank the MACCS2 dry deposition velocity and the MELCOR safety relief valve (SRV) stochastic failure probability, respectively, as the most important input parameters. For the alternative dose-truncation models (i.e., USBGR (0.62 rem/yr) and HPS (5 rem/yr with a lifetime limit of 10 rem)) sensitivity analyses, the regression methods consistently rank the MACCS2 inhalation protection factor for normal activity, the MACCS2 lung lifetime risk factor for cancer death, and the MELCOR SRV stochastic failure probability as the most important input variables. The important MELCOR input parameters are relatively independent of the dose-response model used in MACCS2. However, the MACCS2 input variables depend strongly on the dose-response model. The use of either the USBGR or the HPS dose-response model emphasizes MACCS2 input variables associated with doses received in the first year and deemphasizes MACCS2 input parameters associated with long-term phase doses beyond the first year.

This paper describes the MELCOR Accident Consequence Code System, Version 2(MACCS2), parameters and probabilistic results of offsite consequences for the uncertainty analysis of the State-of-the-Art Reactor Consequence Analyses unmitigated long-term station blackout accident scenario at the Peach Bottom Atomic Power Station. Consequence results are presented as conditional risk (i.e., assuming the accident occurs) to individuals of the public as a result of the accident - latent-cancer-fatality (LCF) risk per event or prompt-fatality risk per event. For the mean, individual, LCF risk, all regression methods at each of the circular areas around the plant that are analyzed (10-mile to 50-mile radii are considered) consistently rank the MACCS2 dry deposition velocity, the MELCOR safety relief valve (SRV) stochastic failure probability, and the MACCS2 residual cancer risk factor, respectively, as the most important input parameters. For the mean, individual, prompt-fatality risk (which is zero in over 85% of the Monte Carlo realizations) within circular areas with less than a 2-mile radius, the non-rank regression methods consistently rank the MACCS2 wet deposition parameter, the MELCOR SRV stochastic failure probability, the MELCOR SRV open area fraction, the MACCS2 early health effects threshold for red bone marrow, and the MACCS2 crosswind dispersion coefficient, respectively, as the most important input parameters. For the mean, individual prompt-fatality risk within the circular areas with radii between 2.5-miles and 3.5-miles, the regression methods consistently rank the MACCS2 crosswind dispersion coefficient, the MACCS2 early health effects threshold for red bone marrow, the MELCOR SRV stochastic failure probability, and the MELCOR SRV open area fraction, respectively, as the most important input parameters.

One of the characteristics of CO2 that influences the oxy-fuel combustion of pulverized coal char is its low diffusivity, in comparison to N2. To further explore how the gas diffusivity influences the apparent rate of pulverized char combustion, experiments were conducted in a laminar, optical flow reactor that has been extensively used to quantify char particle combustion rates. Helium, nitrogen, and CO2 diluent gases were employed as diluent gases. The diffusivity of oxygen through helium is 3.5 times higher than through nitrogen, tending to supply more oxygen to the particle and accelerating the particle combustion rate and heat release. However, the thermal conductivity of helium is 5 times larger than that of nitrogen, tending to keep the burning char particle temperature close to that of the surrounding gas. The combination of these two factors makes char combustion in helium atmospheres significantly more kinetically controlled than combustion of char particles in nitrogen atmospheres. The char particle combustion temperatures were highest for combustion in N2 environments, with combustion in CO2 and He environments producing nearly identical char combustion temperatures, despite much more rapid particle burnout in helium. Preliminary analysis of the apparent char kinetic burning rate in He yields a rate that is approximately three times greater than the rate in N2, likely reflecting the greater internal penetration of oxygen into char particles burning in helium. Analysis with intrinsic kinetic models is being applied to better understand the data and therefore the role of gas diffusivity on apparent kinetic rates of char combustion.

Soot emissions from internal combustion engines and aviation gas turbine engines face increasingly stringent regulation, but available experimental datasets for sooting turbulent combustion model development and validation are largely lacking, in part due to the difficulty of making quantitative space- and time-resolved measurements in this type of flame. To address this deficiency, we have performed a number of different laser and optical diagnostic measurements in sooting, nonpremixed jet flames fueled by ethylene or a prevaporized JP-8 surrogate. Most laser diagnostic techniques inherently lose their quantitative rigor when significant laser beam and signal attenuation occur in sooting flames. However, the '3-line' approach to simultaneous measurement of soot concentration (on the basis of laser extinction) and soot temperature (on the basis of 2-color pyrometry) actually relies on the presence of significant laser attenuation to yield accurate measurements. In addition, the 3-line approach yields complete time-resolved information. In the work reported here, we have implemented the 3-line diagnostic in well-controlled non-premixed ethylene and JP-8 jet flames with a fuel exit Reynolds number of 20,000 using tapered, uncooled alumina refractory probes with a 10 mm probe end separation. Bandpass filters with center wavelengths of 850 nm and 1000 nm were used for the pyrometry measurement, with calibration provided by a hightemperature blackbody source. Extinction of a 635 nm red diode laser beam was used to determine soot volume fraction. Data were collected along the flame centerline at many different heights and radial traverses were performed at selected heights. A data sampling rate of 5 kHz was used to resolve the turbulent motion of the soot. The results for the ethylene flame show a mean soot volume fraction of 0.4 ppm at mid-height of the flame, with a mean temperature of 1450 K. At any given instant, the soot volume fraction typically falls between 0.2 and 0.6 ppm with a temperature between 1300 and 1650 K. At greater heights in the flame, the soot intermittency increases and its mean concentration decreases while its mean temperature increases. In the JP-8 surrogate flame, the soot concentration reaches a mean value of 1.3 ppm at mid-height of the flame, but the mean soot temperature is only 1270 K. Elevated soot concentrations persist for a range of heights in the JP-8 flame, with a rise in mean temperature to 1360 K, before both soot volume fraction and temperature tail off at the top of this smoking flame.

This paper studies autoignition characteristics and HCCI engine combustion of ketone fuels, which are important constituents of recently discovered fungi-derived biofuels. Two ketone compounds, 2,4-dimethyl-3-pentanone (DMPN) and cyclopentanone (CPN), are systematically investigated in the Sandia HCCI engine, and the results are compared with conventional gasoline and neat ethanol. It is found that CPN has the lowest autoignition reactivity of all the biofuels and gasoline blends tested in this HCCI engine. The combustion timing of CPN is also the most sensitive to intake-temperature (Tin) variations, and it is almost insensitive to intake-pressure (Pin) variations. These characteristics and the overall HCCI performance of CPN are similar to those of ethanol. In contrast, DMPN shows multi-faceted autoignition characteristics. On the one hand, DMPN has strong temperature-sensitivity, even at boosted Pin, which is similar to the low-reactivity ethanol and CPN. On the other hand, DMPN shows much stronger pressure-sensitivity than ethanol and CPN. This pressure-sensitivity reduces the Tin requirement for DMPN as Pin increases, in a manner similar to gasoline, and it allows the same Tin = 60ŶC for DMPN as for gasoline at Pin = 2.4 bar. At this Pin, DMPN reaches a maximum HCCI load similar to gasoline, ∼ 14 bar IMEP. Unlike gasoline, which requires significant combustion-timing retard to prevent knock at this maximum load, DMPN allows a more advanced combustion timing because its high temperature-sensitivity causes a lower heat release rate. As a result, DMPN yields a higher thermal efficiency than gasoline at comparable loads. Copyright © 2013 SAE International and Copyright © 2013 KSAE.

A Yellow Brick Road can be thought of as the fabled path to a "promised land" where achievement of hopes and dreams is highly probable. Yellow bricks highlight the appropriate road, and destination mileage and speed limit signs support progress assessment to the chosen objective. Similarly, a common systems engineering (SE) framework, properly implemented at the approproate level of rigor, facilitates monitoring and achievement of a quality product that supports the intended mission. Bricks for a lean SE Yellow Brick Road ae described. The bricks include a) using a common framework that integrates SE, project management and quality management; b) right sizing project implementation of this framework using a graded approach; c) applying the framework as early as possible; d) tailoring and waiving as needed; e) using project archetypes; and f) providing a repository that contains reuseable processes, plans, templates, examples, training and associated subject matter experts. © 2013 by Ann Hodges.

The increasing global appetite for energy within the transportation sector will inevitably result in the combustion of more fossil fuel. A renewable-derived approach to carbon-neutral synthetic fuels is therefore needed to offset the negative impacts of this trend, which include climate change. In this communication we report the use of nonstoichiometric perovskite oxides in two-step, solar-thermochemical water or carbon dioxide splitting cycles. We find that LaAlO₃ doped with Mn and Sr will efficiently split both gases. Moreover the H₂ yields are 9× greater, and the CO yields 6× greater, than those produced by the current state-of-the-art material, ceria, when reduced at 1350 °C and re-oxidized at 1000 °C. The temperature at which O₂ begins to evolve from the perovskite is fully 300 °C below that of ceria. The materials are also very robust, maintaining their redox activity over at least 80 CO₂ splitting cycles. This discovery has profound implications for the development of concentrated solar fuel technologies.

The thermal processing of a proposed durable waste form for 129I was investigated. The waste form is a composite with a matrix of low-temperature sintering glass that encapsulates particles of AgI-mordenite. Ag-mordenite, an ion-exchanged zeolite, is being considered as a capture medium for gaseous 129I2 as part of a spent nuclear fuel reprocessing scheme under development by the US Department of Energy/Nuclear Energy (NE). The thermal processing of the waste form is necessary to densify the glass matrix by viscous sintering so that the final waste form does not have any open porosity. Other processes that can also occur during the thermal treatment include desorption of chemisorbed I2, volatilization of AgI and crystallization of the glass matrix. We have optimized the thermal processing to achieve the desired high density with higher AgI-mordenite loading levels and with minimal loss of iodine. Using these conditions, 625°C for 20 minutes, the matrix crystallizes to form a eulytite phase. Results of durability tests indicate that the matrix crystallization does not significantly decrease the durability in aqueous environments.

There has been much work done in implementing various GPU-based Computed Tomography reconstruction algorithms for medical applications showing tremendous improvement in computational performance. While many of these reconstruction algorithms could also be applied to industrial-scale datasets, the performance gains may be modest to non-existent due to a combination of algorithmic, hardware, or scalability limitations. Previous work presented showed an irregular dynamic approach to GPU-Reconstruction kernel execution for industrial-scale reconstructions that dramatically improved voxel processing throughput. However, the improved kernel execution magnified other system bottlenecks such as host memory bandwidth and storage read/write bandwidth, thus hindering performance gains. This paper presents a multi-GPU-based reconstruction algorithm capable of efficiently reconstructing large volumes (between 64 gigavoxels and 1 teravoxel volumes) not only faster than traditional CPU- and GPU-based reconstruction algorithms but also while consuming significantly less energy. The reconstruction algorithm exploits the irregular kernel approach from previous work as well as a modularized MIMD-like environment, heterogeneous parallelism, as well as macro- and micro-scale dynamic task allocation. The result is a portable and flexible reconstruction algorithm capable of executing on a wide range of architectures including mobile computers, workstations, supercomputers, and modestly-sized hetero or homogeneous clusters with any number of graphics processors. © 2013 IEEE.

In this paper, fusing of a metallic conductor is studied by judiciously using the solution of the one-dimensional heat equation, resulting in an approximate method for determining the threshold fusing current. The action is defined as an integration of the square of the wire current over time. The burst action (the action required to completely vaporize the material) for an exploding wire is then used to estimate the typical wire gapping action (involving wire fusing), from which gapping time can be estimated for a gapping current greater than a factor of two over the fusing current. The test data are used to determine the gapped length as a function of gapping current and to show, for a limited range, that the gapped length is inversely proportional to gapping time. The gapping length can be used as a signature of the fault current level in microelectronic circuits.

Physical security analyses for nuclear reactors have historically sought to ensure that there is an acceptably low probability of success for a "design basis" adversary to accomplish a theft or sabotage objective, even for the adversary's most advantageous path. While some have used probabilistic risk assessment to characterize these risks, the lack of a validated attack frequency, among other things, has made this difficult. Recent work at Sandia National Laboratories (SNL) characterizes a facility's security risk for a scenario in terms of level of difficulty an adversary would encounter in order to be reasonably sure of success (the Risk Informed Management of Enterprise Security (RIMES) methodology). Scenarios with lower levels of difficulty can then be addressed through design changes or improvements to the physical protection system. This work evaluates the level of difficulty of a number of attack scenarios for Small Modular Reactors (SMRs), and provides insight to help designers optimize the protection of their facilities. The methodology and general insights are described here.

The existence of a critical dissipation rate, above which a nonpremixed flame is extinguished, has been known for decades. Recent advances in modeling have allowed the simulation of turbulent nonpremixed flames that include local extinction as a consequence of the stochastic variation in mixing rates. In this paper we present the critical dissipation impulse magnitude that will lead to extinction even if the mean dissipation rate is well below the criteria for a steady flame. This critical impulse magnitude depends on the time-integrated excess dissipation rate, stoichiometric factors and the form of the S-curve describing the steady-state flame. This criteria is evaluated in a diverse set of flames including n-heptane, diluted n-heptane and CO/H2/N2 mixtures.

Carbon fiber composite materials are increasingly being used in the design and fabrication of transportation vehicles. In particular, the aviation industry is increasing transitioning from metals to this class of composites due to the high strength and low weight of the materials. Most aviation structural composites are thermoset, meaning they require thermal processing to harden the epoxy. In the event of a fire, they will behave significantly different than the metals they replace. Because they are not homogeneous, they also differ significantly from homogeneous solid combustibles. Sandia National Laboratories is motivated to study burning composites because we maintain experimental and modeling capabilities for assessing transportation safety. Understanding the thermal environment created by transportation fires is therefore paramount. This type of focus is not typical of the general literature on these materials in the fire environment. A serious issue with the majority of fire performance data found in the open literature is that the length and mass scales are generally orders of magnitude below those used in vehicle design. With a non-traditional perspective on composite fires, Sandia has performed several test series. Together with a review of the work from other institutions as found in the literature, this report presents a phenomenological overview of the relevant work on the behavior of composite materials in a fire environment.

Optimization of new transportation fuels and engine technologies requires the characterization of the combustion chemistry of a wide range of fuel classes. Theoretical studies of elementary reactions - the building blocks of complex reaction mechanisms - are essential to accurately predict important combustion processes such as autoignition of biofuels. The current bottleneck for these calculations is a user-intensive exploration of the underlying potential energy surface (PES), which relies on the "chemical intuition" of the scientist to propose initial guesses for the relevant chemical configurations. For newly emerging fuels, this approach cripples the rate of progress because of the system size and complexity. The KinBot program package aims to accelerate the detailed chemical kinetic description of combustion, and enables large-scale systematic studies on the sub-mechanism level.

Density Functional Theory points to a key role of K+ solvation in the low-energy two-dimensional arrangement of water molecules on the basal surface of muscovite. At a coverage of 9 water molecules per 2 surface potassium ions, there is room to accommodate the ions into wetting layers wherein half of them are hydrated by 3 and the other half by 4 water molecules, with no broken H-bonds, or wherein all are hydrated by 4. Relative to the “fully connected network of H-bonded water molecules” that Odelius et al. found to form “a cage around the potassium ions,” the hydrating arrangements are several tens of meV/H2O better bound. Thus, low-temperature wetting on muscovite is not driven towards “ice-like” hexagonal coordination. Instead, solvation forces dominate.

The Quantum-Kinetic (Q-K) chemical reaction model is implemented in a Navier-Stokes solver, US3D, and tested on the Bow Shock UltraViolet flight experiments. The chemical reaction rates predicted by the Q-K model are compared to a commonly used Park model for flows in thermal non-equilibrium. The results show that in thermal equilibrium the reaction rates between these two models are comparable. The Q-K model predicts greater rates for some chemical reactions and lesser rates for other reactions in an five species air chemistry model. In thermal non-equilibrium, the Q-K model maintains comparable rates near thermal equilibrium, while avoiding issues of strong thermal non-equilibrium seen in the Park model. The application of the Q-K model to the Bow Shock UltraViolet flight experiments show that the model remains consistent with previous Navier-Stokes and DSMC computations over altitudes ranging from 53:5 km up to 87:5 km despite the enforcement of translational-rotational equilibrium. The commonly used Park model was unable to match this performance.

High-frequency pressure sensors were used in conjunction with a high-speed schlieren system to study the growth and breakdown of boundary-layer disturbances into turbulent spots on a 7° cone in the Sandia Hypersonic Wind Tunnel. At Mach 5, intermittent low-frequency disturbances were observed in the schlieren videos. High-frequency secondmode wave packets would develop within these low-frequency disturbances and break down into isolated turbulent spots surrounded by an otherwise smooth, laminar boundary layer. Spanwise pressure measurements showed that these packets have a narrow spanwise extent before they break down. The resulting turbulent fluctuations still had a streaky structure reminiscent of the wave packets. At Mach 8, the boundary layer was dominated by secondmode instabilities that extended much further in the spanwise direction before breaking down into regions of turbulence. The amplitude of the turbulent pressure fluctuations was much lower than those within the second-mode waves. These turbulent patches were surrounded by waves as opposed to the smooth laminar flow seen at Mach 5. At Mach 14, second-mode instability wave packets were also observed. Theses waves had a much lower frequency and larger spanwise extent compared to lower Mach numbers. Only low freestream Reynolds numbers could be obtained, so these waves did not break down into turbulence.

We present ultra-thin single crystal mini-modules built with specific power of 450 W/kg capable of voltages of >1000 V/cm2. These modules are also ultra-flexible with tight bending radii down to 1 mm. The module is composed of hundreds of back contact microcells with thicknesses of approximately 20 μm and diameters between 500-720 μm. The cells are interconnected to a flexible circuit through solder contacts. We studied the characteristics of several mini-modules through optical inspection, evaluation of quantum efficiency, measurement of current-voltage curves, and temperature dependence. Major efficiency losses are caused by missing cells or non-interconnected cells. Secondarily, damage incurred during separation of 500 μm cells from the substrate caused material detachment. The detachment induced higher recombination and low performance. Modules made with the larger cells (720 μm) performed better due to having no missing cells, no material detachment and optimized AR coatings. The conversion efficiency of the best mini module was 13.75% with a total Voc = 7.9 V. © 2013 IEEE.

Tellurium dielectric resonator metamaterials were fabricated using a newly developed multi-cycle deposition-etch process. Deposition and etching of Tellurium were studied in detail. All the samples showed two transmission minima corresponding to magnetic and electric dipole resonances. © 2013 The Optical Society.

In this paper we propose a stacked multi-junction solar cell design that allows the intimate contact of the individual cells while maintaining low resistive losses. The cell design is presented using an InGaP and GaAs multi-junction cell as an illustrative example. However, the methodologies presented in this paper can be applied to other III-V cell types including InGaAs and InGaAsP cells. The main benefits of the design come from making small cells, on the order of 2×10-3 cm2. Simulations showed that series resistances should be kept to less than 5 ω for devices up to 400 μm in diameter to keep resistance power losses to less than 1%. Low resistance AuBe/Ni/Au ohmic contacts to n-type InGaP are also demonstrated with contact resistivity of 5×10-6 ωcm-2 when annealed at 420°C. © 2013 IEEE.

We calculate voltage-matching considerations for stacked independent cells. The calculations show that designs using independent junctions that are voltage matched can achieve better efficiency across temperature, spectrum, and a yearly metric compared to traditional monolithic cells. Voltage matching is shown to be relatively insensitive to temperature and spectrum, but dependent on open circuit voltage as a measure of cell efficiency. Voltage matching can usually yield yearly efficiencies of 98%-99% of the efficiency of a system with each junction operating at its own maximum power point. © 2013 IEEE.

We present ultra-thin single crystal mini-modules built with specific power of 450 W/kg capable of voltages of >1000 V/cm2. These modules are also ultra-flexible with tight bending radii down to 1 mm. The module is composed of hundreds of back contact microcells with thicknesses of approximately 20 μm and diameters between 500-720 μm. The cells are interconnected to a flexible circuit through solder contacts. We studied the characteristics of several mini-modules through optical inspection, evaluation of quantum efficiency, measurement of current-voltage curves, and temperature dependence. Major efficiency losses are caused by missing cells or non-interconnected cells. Secondarily, damage incurred during separation of 500 μm cells from the substrate caused material detachment. The detachment induced higher recombination and low performance. Modules made with the larger cells (720 μm) performed better due to having no missing cells, no material detachment and optimized AR coatings. The conversion efficiency of the best mini module was 13.75% with a total Voc = 7.9 V. © 2013 IEEE.

Abstract not provided.

We optimize reactive, ion-assisted deposition (O2 levels, deposition rate and ion beam settings) using e-beam evaporated Ti for high refractive index, low absorption TiO2 layers and laser damage resistant, broad bandwidth high reflection coatings. © OSA 2013.

Many popular models for photovoltaic system performance (e.g., [1], [2]) employ a single diode model (e.g., [3]) to compute the IV curve for a module or string of modules for given irradiance and temperature conditions. Most commonly (e.g., [4]), parameters are determined using only current and voltage at short circuit, open circuit and maximum power from a single IV curve at standard test conditions, along with reported temperature coefficients. In contrast, module testing frequently records IV curves at a wide range of irradiance and temperature conditions, such as those specified in IEC 61853-1 [5], which, when available, should also be used to parameterize the performance model. We propose a parameter estimation method that makes use of the full range of available IV curves, and demonstrate the accuracy of the resulting performance model. © 2013 IEEE.

Effective evaluation and prediction of photovoltaic performance loss due to soiling requires consistent test methods. Natural grime accumulation is time-consuming and location-specific, and thus does not provide reproducible results across different geographic regions. Therefore, we have demonstrated a technique to apply artificial soiling with NIST-traceable components using an aerosol spray technique. This approach produces consistent soil coatings which were directly correlated to performance loss of multicrystalline Si cells in a laboratory setting. By tailoring the composition of the test blend, termed 'standard grime', the loss due to soiling can be effectively predicted over a range of mass loadings and soil types. © 2013 IEEE.

This paper 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 process includes solution verification, which examines the errors associated with the code's solution techniques. 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. Similarly, highly automated software to vary model inputs was also developed for the purpose of assessing the solution's sensitivity to numerical parameters. The model was subjected to mesh resolution and numerical parameters sensitivity studies. This process not only tests the robustness of the numerical parameters, but also allows for the optimization of robustness and numerical error with computation time. Agglomeration of these studies provides a bound for the uncertainty due to numerical error for the model. An emphasis is placed on the automation of solution verification to allow a rigorous look at uncertainty to be performed even within a tight design and development schedule. © 2013 WIT Press.

Liquid injection in systems such as liquid rockets where the working fluid exceeds the thermodynamic critical condition of the liquid phase is not well understood. Under some conditions when operating pressures exceed the liquid phase critical pressure, surface tension forces become diminished when the classical low-pressure gas-liquid interface is replaced by a diffusion-dominated mixing layer. Modern theory, however, still lacks a physically-based model to explain the conditions under which this transition occurs. In this paper, we derive a coupled model to obtain a theoretical analysis that quantifies these conditions for general multicomponent liquid injection processes. Our model applies a modified 32-term Benedict-Webb-Rubin equation of state along with corresponding combining and mixing rules that accounts for the relevant thermodynamic non-ideal multicomponent mixture states in the system. This framework is combined with Linear Gradient Theory, which facilitates the calculation of the vapor-liquid molecular structure. Dependent on oxygen and hydrogen injection temperatures, our model shows interfaces with substantially increased thicknesses in comparison to interfaces resulting from lower injection temperatures. Contrary to conventional wisdom, our analysis reveals that LOX-H2 molecular interfaces break down not necessarily because of vanishing surface tension forces, but because of the combination of broadened interfaces and a reduction in mean free molecular path at high pressures. Then, these interfaces enter the continuum length scale regime where, instead of inter-molecular forces, transport processes dominate. Based on this theory, a regime diagram for LOX-H2 mixtures is introduced that quantifies the conditions under which classical sprays transition to dense-fluid jets.

Accurate performance and reliability evaluation of utility-scale photovoltaic (PV) systems requires accountability of solar gain contributions. A novel solar gain utility-scale inverter model has been developed to characterize inverter efficiency with respect to solar resource, general ambient conditions and thermal system losses. A sensitivity analysis was performed to evaluate the robustness of the model based on four assumed material properties. This analysis revealed 22.9% modeled internal inverter temperature sensitivity to surface absorptivity, with significantly less sensitivity to other parameters studied, indicating the impact of proper surface coating material selection on solar thermal absorption. This analysis was applied to a large utility-scale PV plant, assessing performance data from twelve 500kW inverters, and environmental data from twelve respective meteorological test stations. An RMSE value of 6.1% was found between the model and measured inner inverter temperatures. The results also suggest a negative 3.6×10-4 [W/m2] -1 normalized inverter efficiency correspondence with solar gain heat adsorption across the twelve inverters for a one-day, clear-sky time period. © 2013 IEEE.

Photovoltaic (PV) modules with attached microinverters are becoming increasingly popular in PV systems, especially in the residential system market, as such systems offer several benefits not found in PV systems utilizing central inverters. PV modules with fully integrated microinverters are emerging to fill a similar market space. These 'AC modules' absorb solar energy and produce AC energy without allowing access to the intermediate DC bus. Existing test procedures and performance models designed for separate DC and AC components are unusable when the inverter is integrated into the module. Sandia National Laboratories is developing a new set of test procedures and performance model designed for AC modules. © 2013 IEEE.

The variability of solar PV power plants has led to some utilities imposing ramp limitations. For example, the Puerto Rico Electric Power Authority (PREPA) includes a 10% of capacity per minute limit on ramp rates produced by PV power plants in its minimum technical requirements for photovoltaic generation projects. However, it is difficult to determine storage requirements to comply with ramp limitations for plants in the planning or construction phase since the variability of the plant output is not known. In this paper, we use the wavelet variability model (WVM) to upscale irradiance measured in Mayaguez, PR to simulate various sizes of PV power plants. The results show that ramps will often exceed 10%, even for the largest plants (60MW) that benefit the most from in-plant spatial smoothing, meaning significant amounts of storage will be needed to meet the PREPA requirement. The results from Puerto Rico are compared to sites in San Diego and Oahu, Hawaii. Significant differences are seen in the ramp rate distributions of the three locations, demonstrating the importance of performing location-specific simulations. © 2013 IEEE.

Abstract not provided.

The Quantum-Kinetic (Q-K) chemical reaction model is implemented in a Navier-Stokes solver, US3D, and tested on the Bow Shock UltraViolet flight experiments. The chemical reaction rates predicted by the Q-K model are compared to a commonly used Park model for flows in thermal non-equilibrium. The results show that in thermal equilibrium the reaction rates between these two models are comparable. The Q-K model predicts greater rates for some chemical reactions and lesser rates for other reactions in an five species air chemistry model. In thermal non-equilibrium, the Q-K model maintains comparable rates near thermal equilibrium, while avoiding issues of strong thermal non-equilibrium seen in the Park model. The application of the Q-K model to the Bow Shock UltraViolet flight experiments show that the model remains consistent with previous Navier-Stokes and DSMC computations over altitudes ranging from 53:5 km up to 87:5 km despite the enforcement of translational-rotational equilibrium. The commonly used Park model was unable to match this performance.

Arcing in PV systems has caused multiple residential and commercial rooftop fires. The National Electrical Code® (NEC) added section 690.11 to mitigate this danger by requiring arc-fault circuit interrupters (AFCI). Currently, the requirement is only for series arc-faults, but to fully protect PV installations from arc-fault-generated fires, parallel arc-faults must also be mitigated effectively. In order to de-energize a parallel arc-fault without module-level disconnects, the type of arc-fault must be identified so that proper action can be taken (e.g., opening the array for a series arc-fault and shorting for a parallel arc-fault). In this work, we investigate the electrical behavior of the PV system during series and parallel arc-faults to (a) understand the arcing power available from different faults, (b) identify electrical characteristics that differentiate the two fault types, and (c) determine the location of the fault based on current or voltage of the faulted array. This information can be used to improve arc-fault detector speed and functionality. © 2013 IEEE.

Microsystems Enabled Photovoltaics (MEPV) is a relatively new field that uses microsystems tools and manufacturing techniques familiar to the semiconductor industry to produce microscale photovoltaic cells. The miniaturization of these PV cells creates new possibilities in system designs that may be able to achieve the US Department of Energy (DOE) price target of $1/Wp by 2020 for utility-scale electricity generation. In this article, we introduce analytical tools and techniques to estimate the costs associated with a concentrating photovoltaic system that uses microscale photovoltaic cells and miniaturized optics. The overall model comprises the component costs associated with the PV cells, concentrating optics, balance of systems, installation, and operation. Estimates include profit margin and are discussed in the context of current and projected prices for non-concentrating and concentrating photovoltaics. Our analysis indicates that cells with a width of between 100 and 300 μm will minimize the module costs of the initial design within the range of concentration ratios considered. To achieve the DOE price target of $1/Wp by 2020, module efficiencies over 35% will likely be necessary. © 2013 IEEE.

Deployed on a commercial airplane, proton exchange membrane (PEM) fuel cells may offer emissions reductions, thermal efficiency gains, and enable locating the power near the point of use. This work seeks to understand whether on-board fuel cell systems are technically feasible, and, if so, if they could offer a performance advantage for the airplane when using today’s off-the-shelf technology. Through hardware analysis and thermodynamic simulation, we found that an additional fuel cell system on a commercial airplane is technically feasible using current technology. Recovery and on-board use of the heat and water that is generated by the fuel cell is an important method to increase the benefit of such a system. Although the PEM fuel cell generates power more efficiently than the gas turbine generators currently used, when considering the effect of the fuel cell system on the airplane’s overall performance we found that an overall performance penalty (i.e., the airplane will burn more jet fuel) would result if using current technology for the fuel cell and hydrogen storage. Although applied to a Boeing 787-type airplane, the method presented is applicable to other airframes as well.

A hands-on critical-experiment training class has been developed by the US DOE Nuclear Criticality Safety Program using the water-moderated pin-fueled critical experiments at Sandia National Laboratories. The class is offered as part of the NCSP training program for Nuclear Criticality Safety Engineers in a facility that allows attendance by both cleared and uncleared personnel. Laboratory exercises have been developed that demonstrate the effects of varying a number of the parameters that are considered important to criticality safety. Accompanying the experiments is a series of classroom presentations that emphasize the concepts that are demonstrated in the experiments.

Abstract not provided.

Abstract not provided.

Abstract not provided.

A multi-technique investigation was performed on three copper-based ionic liquids to elucidate the influence of coordinating ligands and charge-balancing anions on the electrochemical properties of the materials. Galvanostatic cycling of Cu(OHCH2CH2NH2)6(BF 4)2 (Cu1) in 1-butyl-3-methyl-imidazolium hexafluorophosphate gave partially reversible plating of copper that was consistent with cyclic voltammetry data (collected using an ionic liquid-based reference electrode verified with measurements of ferrocene, cobaltocene, and lithium). Scanning electron microscopy also showed pitting in the copper-coated surface of the electrode that was consistent with the stripping wave observed by cyclic voltammetry. Potentiostatic deposition in neat Cu1 showed significant dendrite formation. The substitution of the OHCH2CH 2NH2 ligands of Cu1 with stronger coordinating NH(CH 2CH2OH)2 in Cu(NH(CH2CH 2OH)2)6(BF4)2 (Cu2) resulted in the complete suppression of both copper stripping and dendrite formation. Substitution of the BF4- anions of Cu2 with CF3SO3- in Cu(NH(CH2CH2OH)2)6(CF 3SO3)2 (Cu3) shifted the copper deposition 0.1 V more negative and produced slightly larger spherical particles (1.5 μm versus 5 μm). The results suggested that while the anion composition influenced particle size, and the metal-ligand bond strength helped control particle morphology, both factors affected the electrochemical properties including the plating and stripping of copper. © 2013 Elsevier B.V. All rights reserved.

For critical infrastructure facilities, mitigation techniques for insider threats are primarily non-technical in nature and rely heavily on policies/procedures. Traditional access control measures (access cards, biometrics, PIN numbers, etc.) are built on a philosophy of trust that enables those with appropriate permissions to access facilities without additional monitoring or restrictions. Systems based on these measures have three main limitations: 1) access is typically bound to a single authentication occurrence; 2) the authentication factors have little impact against human (insider) threats to security systems; and 3) many of the authentication systems inconvenience end-users. In order to mitigate the aforementioned deficiencies, we propose utilizing the concept of Ephemeral Biometrics to construct strong, persistent authentication protocols.

A 100X magnification, ±3° field of view micro-concentrating optical array has been developed with better than 90% transmission for a microsystems-enabled photovoltaic (MEPV) prototype module using 250 μm diameter multi-junction "stacked" PV cells. Renewable Energy and the Environment Congress. © 2013.

Abstract not provided.

Development of mathematical models for built-up struc-tures, particularly those with many interfaces, is still primitive. This limitation is particularly evident when complex loads and load histories are considered, an example of which is random vibration. Two steps in simplifying this problem are explored here. First, the system response is approximated as that of the super-position of numerous decoupled modes, the coordinates of which evolve according to a constitutive model designed to capture the nonlinearity of the structure. Second, because among the cat-egories of load for which dynamic analysis on nonlinear struc-tures is particularly difficult is that of random loads and the re-sulting random vibration, and given the previous approximation, it is natural to apply the method of stochastic equivalent lin-earization to the governing equation of each mode. Both of these approximations are explored for the case where the nonlinear behavior of the interfaces is represented by a Masing-Prandtl-Ishlinskii-Iwan model employing a Palmov kernel. Copyright © 2013 by ASME.

The pace of research and development efforts to integrate renewable power sources into modern electric utilities continues to increase. These efforts are motivated by a desire for cleaner, cheaper and more diverse sources of energy. As new analyses and controls approaches are developed to manage renewable sources and tie them into the grid, the need for these controls to be tested in hardware becomes paramount. In particular, hydrokinetic power is appealing due to its high energy density and superior forecastability; however, its development has lagged behind that of wind and solar due in part to the difficulty of acquiring hardware results on an integrated system. Thus, as an alternative to constructing an elaborate wave-tank or locating a power lab riverside, this paper presents a method based on electromechanical emulation of the energy source using a commercially available induction motor drive. Using an electromechanical emulator provides an option for universities and other laboratories to expand their research on hydrokinetics in a typical laboratory setting. © 2013 MTS.

The manycore revolution in computational hardware can be characterized by increasing thread counts, decreasing memory per thread, and architecture specific performance constraints for memory access patterns. High performance computing (HPC) on emerging many core architectures requires codes to exploit every opportunity for thread-level parallelism and satisfy conflicting performance constraints. We developed the Kokkos C++ library to provide scientific and engineering codes with a user accessible many core performance portable programming model. The two foundational abstractions of Kokkos are (1) dispatch work to a many core device for parallel execution and (2) manage multidimensional arrays with polymorphic layouts. The integration of these abstractions enables users' code to satisfy multiple architecture specific memory access pattern performance constraints without having to modify their source code. In this paper we describe the Kokkos abstractions, summarize its application programmer interface (API), and present performance results for a molecular dynamics computational kernel and finite element mini-application. © 2013 IEEE.

In this paper, we present the design, implementation, and preliminary evaluation of AstroTouch, a prototype desktop surface application to support analysis and visualization in the field of astrodynamics. We describe the fundamental characteristics of this complex scientific domain and discuss how these characteristics, combined with an assessment of current research surrounding multi-touch and the digital desktop, informed the design of our system. We detail the prototype implementation and present the results of an initial design critique conducted with domain experts. © 2013 ACM.

In our development team at Sandia National Laboratories we have honed our Scrum processes to where we continually deliver high-performance engineering analysis software to our customers. We deliver despite non-ideal circumstances, including development work that can be categorized as exploratory research, regular use of part-time developers, team size that varies widely among Sprints, highly specialized technical skill sets and a broad range of deliverables. We believe our methodologies can be applied to many research-oriented environments such as those found in government laboratories, academic institutions and corporate research facilities. Our goal is to increase the adoption of Lean/Agile project management in these environments by sharing our experiences with those research-oriented development teams who are considering using Lean/Agile, or have started and are encountering problems. In this paper we discuss how we create and prioritize our product backlog, write our user stories, calculate our capacity, plan our Sprints, report our results and communicate our progress to customers. By providing guidance and evidence of success in these areas we hope to overcome real and perceived obstacles that may limit the adoption of Lean/Agile techniques in research-oriented development environments. © 2013 IEEE.

Abstract not provided.

Metal-Organic Frameworks (MOFs) are nanoporous materials with tunable pore sizes that can accommodate and stabilize small molecules. Because of their long-range order and wellunderstood pore environment, the nano-confinement of donoracceptor materials within MOFs offers a new methodology for creating uniform phase-segregated donor-acceptor interfaces. Phase segregation and the photo-physical effects of confining α,ω-Dihexylsexithiophene (DH-6T) and [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) in several MOFs and the potential role of the MOF in creating a nano-heterojunction for organic photovoltaics are discussed. We demonstrate infiltration of both molecules into MOF pores and use luminescence and absorption spectroscopies to characterize the MOF-guest energy transfer processes. Comparison with density functional theory allows us to determine the energetics and band alignment within the MOF. The results demonstrate the utility of MOFs as scaffolds for sub-nanoscale ordering of donor and acceptor species within a highly uniform environment, allowing both the interaction and separation distance to be much more controlled than in the classical bulk heterojunction. © The Electrochemical Society.

Thermochemical cycles that divide the energetically unfavorable thermolysis of water or carbon dioxide into two or more reactions were used for solar driven fuel production. A large number of diverse metal oxides have been proposed for solar thermochemical fuel production (STFP) including stoichiometric compounds such as ferrites and other transition metal spinels. The design parameter is determined by a set of interacting factors, including reaction thermodynamics, target efficiency, and durability of reactor materials. Operating temperature window is determined by a set of interacting factors, including reaction thermodynamics, target efficiency, and durability of reactor materials. In the absence of kinetic data, however, it can be stated that achieving high average annual solar-to-fuel efficiencies (AASFE) requires that energy consumption of the reactions, and hence the reaction rates, be matched to the solar flux entering the system.

A series of redox flow batteries utilizing mixed addenda (vanadium and tungsten), phosphorus-based polyoxometalates (A-α-PV3W 9O40^6-, B-α-PV3W 9O40^6-, and P2V3W 15O62^9-) were prepared and tested. Cyclic voltammetry and bulk electrolysis experiments on the Keggin compounds (A-α-PV3W9O40^6- and B-α-PV3W9O40^6-) established that the vanadium centers of these compounds could be used as the positive electrode (PV^IV3W^VI9O 40^9-/PV^V3W^VI 9O40^6-), and the tungsten centers could be used as the negative electrode (PV^IV3W^VI 9O40^9-/PV^IV3W ^V3W^VI6O40^12-) since these electrochemical processes are separated by about 1 V. The results showed that A-α-PV3W9O40^6- (where A indicates adjacent, corner-sharing vanadium atoms) had coulombic efficiencies (charge in divided by charge out) above 80%, while the coulombic efficiency of B-α-PV3W9O40^6- (where B indicates adjacent edge-sharing vanadium atoms) fluctuated between 50% and 70% during cycling. The electrochemical yield, a measurement of the actual charge or discharge observed in comparison with the theoretical charge, was between 40% and 50% for A-α-PV3W9O40 ^6-, and ³¹P NMR showed small amounts of PV 2W10O40^5- and PVW11O 40^4- formed with cycling. The electrochemical yield for B-α-PV3W9O40^6- decreased from 90% to around 60% due to precipitation of the compound on the electrode, but there were no decomposition products detected in the solution by ³¹P NMR, and infrared data on the electrode suggested that the cluster remained intact. Testing of P2V3W15O62 ^9- (Wells-Dawson structure) suggested higher charge density clusters were not as suitable as the Keggin structures for a redox flow battery due to the poor stability and inaccessibility of the highly reduced materials. © The Royal Society of Chemistry 2013.

In this paper, we present the design, implementation, and preliminary evaluation of AstroTouch, a prototype desktop surface application to support analysis and visualization in the field of astrodynamics. We describe the fundamental characteristics of this complex scientific domain and discuss how these characteristics, combined with an assessment of current research surrounding multi-touch and the digital desktop, informed the design of our system. We detail the prototype implementation and present the results of an initial design critique conducted with domain experts. © 2013 ACM.

The Seven Percent Critical Experiment (7uPCX) at Sandia National Laboratories was designed to provide benchmark criticality and reactor physics data for water-moderated pin-fueled nuclear reactor cores in the 5 to 10 percent enrichment range. Approach-to-critical experiments were performed on fifteen roughly cylindrical pure water-moderated and -reflected 7uPCX configurations with a fuel-to-water volume ratio of 0.52. Those configurations are described and the results of the measurements are reported in this paper.

Safety Relief Valves (SRVs) are an important component of the safety case for a Light Water Reactor (LWR). The number and types of SRVs in LWRs vary from plant to plant, but they generally operate to perform the same safety function. During accidents in which the coolant pressurizes beyond a predetermined set-point, the SRV will open, releasing coolant from the primary system and into the containment. Once enough coolant has been released to lower the coolant pressure, the SRV will reset. This cycle will continue until the SRV fails, in either a "Failed to Open (FTO)" or "Failed To Close (FTC)" mode. These failures can be caused either through cyclic loading or as a result of thermalinduced stresses from the coolant passing through the valve. SRV failures can be important, because an SRV that has FTC will cause a small "Loss of Cooling Accident", which depressurizes the primary system. Alternatively, SRVs that have FTO will allow system pressure to rise until it reaches the next SRV set-point. If the pressure is not reduced through the successful operation of other safety systems, either creep rupture elsewhere in the system, such as in the steam line, or high-pressure core damage may occur. While some SRV failure data is recorded in NUREG/CR-6928, the spread of the epistemic uncertainty distributions for FTO and FTC are wide. These large uncertainties may cause an analyst to be overconfident in the results of a severe accident simulation that uses only point-estimates calculations of FTO and FTC.

Time-encoded imaging is an approach to directional radiation detection that is being developed at SNL with a focus on fast neutron directional detection. In this technique, a time modulation of a detected neutron signal is induced - typically, a moving mask that attenuates neutrons with a time structure that depends on the source position. An important challenge in time-encoded imaging is to develop high-resolution two-dimensional imaging capabilities; building a mechanically moving high-resolution mask presents challenges both theoretical and technical. We have investigated an alternative to mechanical masks that replaces the solid mask with a liquid such as mineral oil. Instead of fixed blocks of solid material that move in predefined patterns, the oil is contained in tubing structures, and carefully introduced air gaps - bubbles - propagate through the tubing, generating moving patterns of oil mask elements and air apertures. Compared to current moving-mask techniques, the bubble mask is simple, since mechanical motion is replaced by gravity-driven bubble propagation; it is flexible, since arbitrary bubble patterns can be generated by a software-controlled valve actuator; and it is potentially high performance, since the tubing and bubble size can be tuned for high-resolution imaging requirements. We have built and tested various single-tube mask elements, and will present results on bubble introduction and propagation for different tube sizes and cross-sectional shapes; real-time bubble position tracking; neutron source imaging tests; and reconstruction techniques demonstrated on simple test data as well as a simulated full detector system. © 2013 IEEE.

Abstract not provided.

A second set of experiments in the Seven Percent Critical Experiment (7uPCX) has been completed. Additionally, an evaluation of the experiments as criticality safety benchmark experiments has been performed. The Reviews of the benchmark evaluation have been completed. This evaluation will be published in the 2013 edition of the International Handbook of Evaluated Criticality Benchmark Experiments as LEU-COMP-THERM-078 (LCT078). This presentation is a brief tour of these experiments.

Scalable parallel computing is essential for processing large scale-free (power-law) graphs. The distribution of data across processes becomes important on distributed-memory computers with thousands of cores. It has been shown that two dimensional layouts (edge partitioning) can have significant advantages over traditional one-dimensional layouts. However, simple 2D block distribution does not use the structure of the graph, and more advanced 2D partitioning methods are too expensive for large graphs. We propose a new two-dimensional partitioning algorithm that combines graph partitioning with 2D block distribution. The computational cost of the algorithm is essentially the same as 1D graph partitioning. We study the performance of sparse matrix-vector multiplication (SpMV) for scale-free graphs from the web and social networks using several different partitioners and both 1D and 2D data layouts. We show that SpMV run time is reduced by exploiting the graph's structure. Contrary to popular belief, we observe that current graph and hypergraph partitioners often yield relatively good partitions on scale-free graphs. We demonstrate that our new 2D partitioning method consistently outperforms the other methods considered, for both SpMV and an eigensolver, on matrices with up to 1.6 billion nonzeros using up to 16,384 cores. Copyright 2013 ACM.

Abstract not provided.

The uniform strain hexahedral element mesh has long been a work horse for getting accurate and convergent answers in high deformation solid mechanics analyses. Obtaining an allhexahedral mesh can be a difficult and time consuming process thus limiting the element's use in design phase computations. Unconstrained paving and plastering offers a technique to get an all-hexahedral mesh automatically but still can leave un-meshable voids [1] . While degenerated forms of the uniform strain hexahedral element such as the wedge have been used sparingly, they have garnered limited general acceptance. We present a more exhaustive numerical exploration of the degenerated hexes with the hope of encouraging their use to resolve the un-meshable voids. The results of patch tests are used to numerically demonstrate linear completeness of the degenerate elements. A manufactured solution analysis is then used to show optimal convergence rates for meshes containing degenerate elements. Additionally, applications to a torsion rod and high velocity impact are used to highlight the accuracy and applicability of degenerates for solving more complex problems. Copyright © 2013 by ASME.

A systematic approach to defining margin in a manner that incorporates statistical information and accommodates data uncertainty, but does not require assumptions about specific forms of the tails of distributions is developed. This approach extends to calculations underlying validation assessment and quantitatively conservative predictions.

Arc faults in photovoltaic (PV) modules have caused multiple rooftop fires. The arc generates a high-temperature plasma that ignites surrounding materials and subsequently spreads the fire to the building structure. While there are many possible locations in PV systems and PV modules where arcs could initiate, bypass diodes have been suspected of triggering arc faults in some modules. In order to understand the electrical and thermal phenomena associated with these events, a finite element model of a busbar and diode was created. Thermoelectrical simulations found Joule and internal diode heating from normal operation would not normally cause bypass diode or solder failures. However, if corrosion increased the contact resistance in the solder connection between the busbar and the diode leads, enough voltage potential would be established to arc across micron-scale electrode gaps. Lastly, an analytical arc radiation model based on observed data was employed to predicted polymer ignition times. The model predicted polymer materials in the adjacent area of the diode and junction box ignite in less than 0.1 seconds.

The earth isn't flat, and radar beams don't travel straight. This becomes more noticeable as range increases, particularly at shallow depression/grazing angles. This report explores models for characterizing this behavior.

The Signal-to-Noise Ratio (SNR) of a radar echo signal will vary across a range swath, due to spherical wavefront spreading, atmospheric attenuation, and antenna beam illumination. The antenna beam illumination will depend on antenna pointing. Calculations of geometry are complicated by the curved earth, and atmospheric refraction. This report investigates optimizing antenna pointing to maximize the minimum SNR across the range swath.

This paper presents a case study of a 3 kW photovoltaic system with Enphase microinverters. A brief introduction to microinverters and central inverters is first presented, followed by an overview of the installation, features, operation, monitoring, and costs of the system. The monthly and annual energy production during the first three years is presented and compared against modeled results using the System Advisor Model. Various factors that have impacted the performance (e.g., shading, weather, temperature, wind, tilt, orientation) are discussed, and the performance of the system is compared against a simulated optimized system. The optimal sizing of microinverters is also discussed to explain why the power rating of the microinverter may be less than the power rating of the module to achieve maximum energy production.

Variability of photovoltaic (PV) power output is a potential concern to utilities because it can lead to voltage changes on the distribution system and have other adverse impacts on power quality unless additional equipment is added or operational practices are changed to mitigate these effects. This paper develops and evaluates a simple yet novel approach for quantifying irradiance variability over various timescales. The approach involves comparison between measured irradiance and a reference, clear sky irradiance, determined from a model. Conceptually, the "Variability Index" is the ratio of the "length" of the measured irradiance plotted against time divided by the "length" of the reference clear sky irradiance signal. Adjustments are proposed that correct for different measurement intervals. By evaluating the variability index at several sites, we show how annual and monthly distributions of this metric can help to classify sites and periods of time when variability is significant. Copyright © (2012) by American Solar Energy Society.

Module temperature is modeled using a transient heat-flow model. Module temperature predicted in this fashion is important in the calculation of cell temperature, a vital input in performance modeling. Parameters important to the model are tested for sensitivity, and optimized to a single day of measured module temperature using simultaneous non-linear least squares regression. These optimized parameters are then tested for accuracy using a year's worth of data for one location. The results obtained from this analysis are compared with modeled data from a different site, as well as to results obtained using a steadystate model. We find that the transient model best captures the variability in module temperature, and that the transient model works best when calibrated for a specific location.

The modeling work described herein represents Sandia National Laboratories (SNL) portion of a collaborative three-year project with Northrop Grumman Electronic Systems (NGES) and the University of Missouri to develop an advanced, thermal ground-plane (TGP), which is a device, of planar configuration, that delivers heat from a source to an ambient environment with high efficiency. Work at all three institutions was funded by DARPA/MTO; Sandia was funded under DARPA/MTO project number 015070924. This is the final report on this project for SNL. This report presents a numerical model of a pulsating heat pipe, a device employing a two phase (liquid and its vapor) working fluid confined in a closed loop channel etched/milled into a serpentine configuration in a solid metal plate. The device delivers heat from an evaporator (hot zone) to a condenser (cold zone). This new model includes key physical processes important to the operation of flat plate pulsating heat pipes (e.g. dynamic bubble nucleation, evaporation and condensation), together with conjugate heat transfer with the solid portion of the device. The model qualitatively and quantitatively predicts performance characteristics and metrics, which was demonstrated by favorable comparisons with experimental results on similar configurations. Application of the model also corroborated many previous performance observations with respect to key parameters such as heat load, fill ratio and orientation.

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This document is a draft Security-by-Design (SeBD) handbook produced to support the Work Plan of the Nuclear Security Summit to share best practices for nuclear security in new facility design. The Work Plan calls on States to “encourage nuclear operators and architect/engineering firms to take into account and incorporate, where appropriate, effective measures of physical protection and security culture into the planning, construction, and operation of civilian nuclear facilities and provide technical assistance, upon request, to other States in doing so.” The materials for this document were generated primarily as part of a bilateral project to produce a SeBD handbook as a collaboration between the Japan Atomic Energy Agency (JAEA) Nuclear Nonproliferation Science and Technology Center and Sandia National Laboratories (SNL), which represented the US Department Energy (DOE) National Nuclear Security Administration (NNSA) under a Project Action Sheet PAS-PP04. Input was also derived based on tours of the Savannah River Site (SRS) and Japan Nuclear Fuel Limited (JNFL) Rokkasho Mixed Oxide Fuel fabrication facilities and associated project lessons-learned. For the purposes of the handbook, SeBD will be described as the system-level incorporation of the physical protection system (PPS) into a new nuclear power plant or nuclear facility resulting in a PPS design that minimizes the risk of malicious acts leading to nuclear material theft; nuclear material sabotage; and facility sabotage as much as possible through features inherent in (or intrinsic to) the design of the facility. A four-element strategy is presented to achieve a robust, durable, and responsive security system.

This report documents the results of Task 3 of Project Action Sheet PP05 between the United States Department of Energy (DOE) and the Republic of Korea (ROK) Ministry of Education, Science, and Technology (MEST) for Support with Review of an ROK Risk Evaluation Process. This task was to have Sandia National Laboratories collaborate with the Korea Institute of Nuclear Nonproliferation and Control (KINAC) on several activities concerning how to determine the Probability of Neutralization, P_N, and the Probability of System Effectiveness, P_E, to include: providing descriptions on how combat simulations are used to determine P_N and P_E; comparisons of the strengths and weaknesses of two neutralization models (the Neutralization.xls spreadsheet model versus the Brief Adversary Threat-Loss Estimator (BATLE) software); and demonstrating how computer simulations can be used to determine P_N. Note that the computer simulation used for the demonstration was the Scenario Toolkit And Generation Environment (STAGE) simulation, which is a stand-alone synthetic tactical simulation sold by Presagis Canada Incorporated. The demonstration is provided in a separate Audio Video Interleave (.AVI) file.

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In this report we explore claims that phase conjugation of high energy lasers by stimulated Brillouin scattering (SBS) can compensate optical aberrations associated with severely distorted laser amplifier media and aberrations induced by the atmosphere. The SBS media tested was a gas cell pressurized up to 300 psi with SF₆ or Xe or both. The laser was a 10 Hz, 3J, Q-switched Nd:YAG with 25 ns wide pulses. Atmospheric aberrations were created with space heaters, helium jets and phase plates designed with a Kolmogorov turbulence spectrum characterized by a Fried parameter, r_o, ranging from 0.6 – 6.0 mm. Phase conjugate tests in the laboratory were conducted without amplification. For the strongest aberrations, D/r_o ~ 20, created by combining the space heaters with the phase plate, the Strehl ratio was degraded by a factor of ~50. Phase conjugation in SF₆ restored the peak focusable intensity to about 30% of the original laser. Phase conjugate tests at the outdoor laser range were conducted with laser amplifiers providing gain in combination with the SBS cell. A large 600,000 BTU kerosene space heater was used to create turbulence along the beam path. An atmospheric structure factor of C_n² = 5x10^-13 m^2/3 caused the illumination beam to expand to a diameter 250mm and overfill the receiver. The phase conjugate amplified return could successfully be targeted back onto glints 5mm in diameter. Use of a lenslet arrays to lower the peak focusable intensity in the SBS cell failed to produce a useful phase conjugate beam; The Strehl ratio was degraded with multiple random lobes instead of a single focus. I will review literature results which show how multiple beams can be coherently combined by SBS when a confocal reflecting geometry is used to focus the laser in the SBS cell.

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Over the decades, India and the United States have had very little formal collaboration on nuclear issues. Partly this was because neither country needed collaboration to make progress in the nuclear field. But it was also due, in part, to the concerns both countries had about the other's intentions. Now that the U.S.-India Deal on nuclear collaboration has been signed and the Hyde Act passed in the United States, it is possible to recognize that both countries can benefit from such nuclear collaboration, especially if it starts with issues important to both countries that do not touch on strategic systems. Fortunately, there are many noncontroversial areas for collaboration. This study, funded by the U.S. State Department, has identified a number of areas in the prevention of and response to radiological incidents where such collaboration could take place.

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Regulations in the United States that govern the permanent disposal of spent nuclear fuel and high-level radioactive waste in deep geologic repositories require the explicit consideration of hypothetical future human intrusions that disrupt the waste. Specific regulatory requirements regarding the consideration of human intrusion differ in the two sets of regulations currently in effect in the United States; one defined by the Environmental Protection Agency's 40 Code of Federal Regulations part 197, applied only to the formerly proposed geologic repository at Yucca Mountain, Nevada, and the other defined by the Environmental Protection Agencys 40 Code of Federal Regulations part 191, applied to the Waste Isolation Pilot Plant in New Mexico and potentially applicable to any repository for spent nuclear fuel and high-level radioactive waste in the United States other than the proposed repository at Yucca Mountain. This report reviews the regulatory requirements relevant to human intrusion and the approaches taken by the Department of Energy to demonstrating compliance with those requirements.

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In the current study, processes to produce either ethanol or a representative fatty acid ethyl ester (FAEE) via the fermentation of sugars liberated from lignocellulosic materials pretreated in acid or alkaline environments are analyzed in terms of economic and environmental metrics. Simplified process models are introduced and employed to estimate process performance, and Monte Carlo analyses were carried out to identify key sources of uncertainty and variability. We find that the near-term performance of processes to produce FAEE is significantly worse than that of ethanol production processes for all metrics considered, primarily due to poor fermentation yields and higher electricity demands for aerobic fermentation. In the longer term, the reduced cost and energy requirements of FAEE separation processes will be at least partially offset by inherent limitations in the relevant metabolic pathways that constrain the maximum yield potential of FAEE from biomass-derived sugars.

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This SAND report summarizes research conducted as a part of a two year Laboratory Directed Research and Development (LDRD) project to improve our abilities to model algal cultivation. Algae-based biofuels have generated much excitement due to their potentially large oil yield from relatively small land use and without interfering with the food or water supply. Algae mitigate atmospheric CO₂ through metabolism. Efficient production of algal biofuels could reduce dependence on foreign oil by providing a domestic renewable energy source. Important factors controlling algal productivity include temperature, nutrient concentrations, salinity, pH, and the light-to-biomass conversion rate. Computational models allow for inexpensive predictions of algae growth kinetics in these non-ideal conditions for various bioreactor sizes and geometries without the need for multiple expensive measurement setups. However, these models need to be calibrated for each algal strain. In this work, we conduct a parametric study of key marine algae strains and apply the findings to a computational model.

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The purpose of this work was to discover a method to investigate the properties of interfaces as described by a numerical physical model. The model used was adopted from literature and applied to a commercially available multiphysics software package. By doing this the internal properties of simple structures could be elucidated and then readily applied to more complex structures such as valves and pumps in laminate microfluidic structures. A numerical finite element multi-scale model of a cohesive interface comprised of heterogeneous material properties was used to elucidate irreversible damage from applied strain energy. An unknown internal state variable was applied to characterize the damage process. Using a constrained blister test, this unknown internal state variable could be determined for an adherend/adhesive/adherend body. This is particularly interesting for laminate systems with microfluidic and microstructures contained within the body. A laminate structure was designed and fabricated that could accommodate a variety of binary systems joined using nearly any technique such as adhesive, welding (solvent, laser, ultrasonic, RF, etc.), or thermal. The adhesive method was the most successful and easy to implement but also one of the more difficult to understand, especially over long periods of time. Welding methods are meant to achieve a bond that is similar to bulk properties and so are easier to predict. However, methods of welding often produce defects in the bonds.. Examples of the test structures used to elucidate the internal properties of the model were shown and demonstrated. The real life examples used this research to improve upon current designs and aided in creating complex structures for sensor and other applications.

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