Aerosol particles that deposit on surfaces may be subsequently resuspended by air flowing over the surface. A review of models for this liftoff process is presented and compared to available data. Based on this review, a model that agrees with existing data and is readily computed is presented for incorporation into a system level code such as MELCOR.
The effort to collect and process foam for the purpose of recycling performed by the Material Sustainability and Pollution Prevention (MSP2) team at Sandia National Laboratories is an incredible one, but in order to make it run more efficiently it needed some tweaking. This project started in June of 2015. We used the Value Stream Mapping process to allow us to look at the current state of the foam collection and processing operation. We then thought of all the possible ways the process could be improved. Soon after that we discussed which of the "dreams" were feasible. And finally, we assigned action items to members of the team so as to ensure that the improvements actually occur. These improvements will then, due to varying factors, continue to occur over the next couple years.
Gross, Johann; Armand, Jason; Lacayo, Robert M.; Reuss, Pascal; Salles, Loic; Schwingshackl, Christoph W.; Truster, Timothy; Brake, M.R.W.; Allen, Matthew
Sandia National Laboratories performs third-party witness testing for energy storage systems installed on the electric grid. Witness testing verifies that the energy storage system that is installed can meet its performance specifications through a thorough evaluation which includes testing, document review, and physical inspection. This document contains the results for the Sandia National Laboratories witness test on the UniEnergy Technologies 1 MW / 3.2 MWh vanadium flow battery known as the Uni.SystemTM.
Sandia journal manuscript; Not yet accepted for publication
Song, Xuehang; Chen, Xingyuan; Ye, Ming; Dai, Zhenxue; Hammond, Glenn E.
This study develops a new framework of facies-based data assimilation for characterizing spatial distribution of hydrofacies and estimating their associated hydraulic properties. This framework couples ensemble data assimilation with transition probability-based geostatistical model via a parameterization based on a level set function. The nature of ensemble data assimilation makes the framework efficient and flexible to be integrated with various types of observation data. The transition probability-based geostatistical model keeps the updated hydrofacies distributions under geological constrains. The framework is illustrated by using a two-dimensional synthetic study that estimates hydrofacies spatial distribution and permeability in each hydrofacies from transient head data. Our results show that the proposed framework can characterize hydrofacies distribution and associated permeability with adequate accuracy even with limited direct measurements of hydrofacies. Our study provides a promising starting point for hydrofacies delineation in complex real problems.
This report presents conceptual design information for a system to handle and emplace packages containing radioactive waste, in boreholes 16,400 ft deep or possibly deeper. Its intended use is for a design selection study that compares the costs and risks associated with two emplacement methods: drill-string and wireline emplacement. The deep borehole disposal (DBD) concept calls for siting a borehole (or array of boreholes) that penetrate crystalline basement rock to a depth below surface of about 16,400 ft (5 km). Waste packages would be emplaced in the lower 6,560 ft (2 km) of the borehole, with sealing of appropriate portions of the upper 9,840 ft (3 km). A deep borehole field test (DBFT) is planned to test and refine the DBD concept. The DBFT is a scientific and engineering experiment, conducted at full-scale, in-situ, without radioactive waste. Waste handling operations are conceptualized to begin with the onsite receipt of a purpose-built Type B shipping cask, that contains a waste package. Emplacement operations begin when the cask is upended over the borehole, locked to a receiving flange or collar. The scope of emplacement includes activities to lower waste packages to total depth, and to retrieve them back to the surface when necessary for any reason. This report describes three concepts for the handling and emplacement of the waste packages: 1) a concept proposed by Woodward-Clyde Consultants in 1983; 2) an updated version of the 1983 concept developed for the DBFT; and 3) a new concept in which individual waste packages would be lowered to depth using a wireline. The systems described here could be adapted to different waste forms, but for design of waste packaging, handling, and emplacement systems the reference waste forms are DOE-owned high- level waste including Cs/Sr capsules and bulk granular HLW from fuel processing.
Methane hydrates are extremely important naturally-occurring crystalline materials that impact climate change, energy resources, geological hazards, and other major environmental issues. Whereas significant experimental effort has been completed to understanding the bulk thermodynamics of methane hydrate assemblies, little is understood on heterogeneous nucleation and growth of methane hydrates in clay-rich environments. Controlled synthesis experiments were completed at 265-285 K and 6.89 MPa to examine the impact of montmorillonite surfaces in clay-ice mixtures to nucleate and form methane hydrate. The results suggest that the hydrophilic and methane adsorbing properties of Namontmorillonite reduce the nucleation period of methane hydrate formation in pure ice systems.
The United States Strategic Petroleum Reserve (SPR) maintains an underground storage system consisting of caverns that were leached or solution mined in four salt domes located near the Gulf of Mexico in Texas and Louisiana. The SPR comprises more than 60 active caverns containing approximately 700 million barrels of crude oil. Sandia National Labo- ratories (SNL) is the geotechnical advisor to the SPR. As the most pressing need at the inception of the SPR was to create and fill storage volume with oil, the decision was made to leach the caverns and fill them simultaneously (leach-fill). Therefore, A.J. Russo developed SANSMIC in the early 1980s which allows for a transient oil-brine interface (OBI) making it possible to model leach-fill and withdrawal operations. As the majority of caverns are currently filled to storage capacity, the primary uses of SANSMIC at this time are related to the effects of small and large withdrawals, expansion of existing caverns, and projecting future pillar to diameter ratios. SANSMIC was identified by SNL as a priority candidate for qualification. This report continues the quality assurance (QA) process by documenting the "as built" mathematical and numerical models that comprise this document. The pro- gram flow is outlined and the models are discussed in detail. Code features that were added later or were not documented previously have been expounded. No changes in the code's physics have occurred since the original documentation (Russo, 1981, 1983) although recent experiments may yield improvements to the temperature and plume methods in the future.
This report presents four concepts for packaging of radioactive waste for disposal in deep boreholes. Two of these are reference-size packages (11 inch outer diameter) and two are smaller (5 inch) for disposal of Cs/Sr capsules. All four have an assumed length of approximately 18.5 feet, which allows the internal length of the waste volume to be 16.4 feet. However, package length and volume can be scaled by changing the length of the middle, tubular section. The materials proposed for use are low-alloy steels, commonly used in the oil-and-gas industry. Threaded connections between packages, and internal threads used to seal the waste cavity, are common oilfield types. Two types of fill ports are proposed: flask-type and internal-flush. All four package design concepts would withstand hydrostatic pressure of 9,600 psi, with factor safety 2.0. The combined loading condition includes axial tension and compression from the weight of a string or stack of packages in the disposal borehole, either during lower and emplacement of a string, or after stacking of multiple packages emplaced singly. Combined loading also includes bending that may occur during emplacement, particularly for a string of packages threaded together. Flask-type packages would be fabricated and heat-treated, if necessary, before loading waste. The fill port would be narrower than the waste cavity inner diameter, so the flask type is suitable for directly loading bulk granular waste, or loading slim waste canisters (e.g., containing Cs/Sr capsules) that fit through the port. The fill port would be sealed with a tapered, threaded plug, with a welded cover plate (welded after loading). Threaded connections between packages and between packages and a drill string, would be standard drill pipe threads. The internal flush packaging concepts would use semi-flush oilfield tubing, which is internally flush but has a slight external upset at the joints. This type of tubing can be obtained with premium, low-profile threaded connections at each end. The internal-flush design would be suitable for loading waste that arrives from the originating site in weld-sealed, cylindrical canisters. Internal, tapered plugs with sealing filet welds would seal the tubing at each end. The taper would be precisely machined onto both the tubing and the plug, producing a metal-metal sealing surface that is compressed as the package is subjected to hydrostatic pressure. The lower plug would be welded in place before loading, while the upper plug would be placed and welded after loading. Conceptual Waste Packaging Options for Deep Borehole Disposal July 30, 2015 iv Threaded connections between packages would allow emplacement singly or in strings screwed together at the disposal site. For emplacement on a drill string the drill pipe would be connected directly into the top package of a string (using an adapter sub to mate with premium semi-flush tubing threads). Alternatively, for wireline emplacement the same package designs could be emplaced singly using a sub with wireline latch, on the upper end. Threaded connections on the bottom of the lowermost package would allow attachment of a crush box, instrumentation, etc.
The purpose of this document is to briefly frame the challenges of detecting low, slow, and small (LSS) unmanned aerial systems (UAS). The conclusion drawn from internal discussions and external reports is the following; detection of LSS UAS is a challenging problem that can- not be achieved with a single detection modality for all potential targets. Classification of LSS UAS, especially classification in the presence of background clutter (e.g., urban environment) or other non-threating targets (e.g., birds), is under-explored. Though information of avail- able technologies is sparse, many of the existing options for UAS detection appear to be in their infancy (when compared to more established ground-based air defense systems for larger and/or faster threats). Companies currently providing or developing technologies to combat the UAS safety and security problem are certainly worth investigating, however, no company has provided the statistical evidence necessary to support robust detection, identification, and/or neutralization of LSS UAS targets. The results of a market survey are included that highlights potential commercial entities that could contribute some technology that assists in the detection, classification, and neutral- ization of a LSS UAS. This survey found no clear and obvious commercial solution, though recommendations are given for further investigation of several potential systems.
The Johnson Criteria metric calculates probability of detection of an object imaged by an optical system, and was created in 1958 by John Johnson. As understanding of target detection has improved, detection models have evolved to better model additional factors such as weather, scene content, and object placement. The initial Johnson Criteria, while sufficient for technology and understanding at the time, does not accurately reflect current research into target acquisition and technology. Even though current research shows a dependence on human factors, there appears to be a lack of testing and modeling of human variability.
We report on experiments where cylindrical beryllium liners filled with liquid deuterium were compressed to extreme pressure and density with current pulse shaping. In one set of experiments the pressure at stagnation is inferred to be & 100 Mbar using penetrating radiography. A peak liner convergence ratio (initial radius over final radius) of 7.6 was measured resulting in an average deuterium density of 10 g=cm3 and areal density of 0.45 g=cm2. The stagnation shock propagating radially outward through the liner wall was directly measured with a strength of ≈ 120 Mbar. In a second set of experiments the liner was imploded to a peak convergence of 19 resulting in a density of 55 g=cm3 and areal density of 0.5 g=cm2. The pressure at stagnation in this experiment is estimated to be 2 Gbar. This platform enables the study of high-pressure, high-density, implosion deceleration and stagnation dynamics at spatial scales that are readily diagnosable (R ~ 0.1 -- 0.4 mm). Thus, these experiments are directly relevant to both Inertial Con nement Fusion and the study of material properties under extreme conditions.
Tin (Sn) whiskers are not a recent development. Studies in the late 1930’s investigated thin filaments that grew spontaneously from Sn coatings used for the corrosion protection of electronic hardware. It was soon recognized that these Sn filaments,or whiskers, could create short circuits in the same electronic equipment. Figure 1a illustrates whisker growth in the hole of a printed circuit board having an immersion Sn surface finish. The engineering solution was to contaminate the Sn with > 3wt.% of lead (Pb). The result was that whisker growth was replaced with hillock formation (Fig. 1b) that posed a minimal reliability concernto electrical circuits. Today, Pb-containing finishes are being replaced with pure Sn coatings to meet environmental restrictions on Pb use. The same short-circuit concerns have been raised, once again, with respect to Sn whiskers. The present authors have taken the approach that, in order to develop more widely applicable, first-principles strategies to mitigate Sn whisker formation, it is necessary to understand the fundamental mechanism(s) and rate kinetics underlying their development. Numerous mechanisms have been proposed by other authors to describe whisker growth, including static recrystallization by Boguslavsky and Bush.
Journal of Vacuum Science and Technology B: Nanotechnology and Microelectronics
Douglas, Erica A.; Sheng, Josephine J.; Verley, Jason C.; Carroll, Malcolm S.
Demand for integration of near infrared optoelectronic functionality with silicon complementary metal oxide semiconductor (CMOS) technology has for many years motivated the investigation of low temperature germanium on silicon deposition processes. This work describes the development of a high density plasma chemical vapor deposition process that uses a low temperature (<460 °C) in situ germane/argon plasma surface preparation step for epitaxial growth of germanium on silicon. It is shown that the germane/argon plasma treatment sufficiently removes SiOx and carbon at the surface to enable germanium epitaxy. The use of this surface preparation step demonstrates an alternative way to produce germanium epitaxy at reduced temperatures, a key enabler for increased flexibility of integration with CMOS back-end-of-line fabrication.
Gallium nitride nanowires have garnered much attention in recent years due to their attractive optical and electrical properties. An understanding of carrier transport, relaxation, and recombination in these quasi-one-dimensional nanosystems is therefore important in optimizing them for various applications. Here, we present ultrafast optical microscopic measurements on single GaN nanowires. Our experiments, performed while varying the light polarization, excitation fluence, and position, give insight into the mechanisms governing carrier dynamics in these nanosystems.
Reno, John L.; Kao, Tsung Y.; Cai, Xiaowei; Lee, Alan W.M.; Hu, Qing
Slope efficiency (SE) is an important performance metric for lasers. In conventional semiconductor lasers, SE can be optimized by careful designs of the facet (or the modulation for DFB lasers) dimension and surface. However, photonic wire lasers intrinsically suffer low SE due to their deep sub-wavelength emitting facets. Inspired by microwave engineering techniques, we show a novel method to extract power from wire lasers using monolithically integrated antennas. These integrated antennas significantly increase the effective radiation area, and consequently enhance the power extraction efficiency. When applied to wire lasers at THz frequency, we achieved the highest single-side slope efficiency (∼450 mW/A) in pulsed mode for DFB lasers at 4 THz and a ∼4x increase in output power at 3 THz compared with a similar structure without antennas. This work demonstrates the versatility of incorporating microwave engineering techniques into laser designs, enabling significant performance enhancements.
The design of high-performance computing architectures demands performance analysis of large-scale parallel applications to derive various parameters concerning hardware design and software development. The process of performance analysis and benchmarking an application can be done in several ways with varying degrees of fidelity. One of the most cost-effective ways is to do a coarse-grained study of large-scale parallel applications through the use of program skeletons. The concept of a “program skeleton” that we discuss in this article is an abstracted program that is derived from a larger program where source code that is determined to be irrelevant is removed for the purposes of the skeleton. In this work, we develop a semiautomatic approach for extracting program skeletons based on compiler program analysis. Finally, we demonstrate correctness of our skeleton extraction process by comparing details from communication traces, as well as show the performance speedup of using skeletons by running simulations in the SST/macro simulator.
In this study, the use of maltodextrin supramolecular structures (MD SMS) as a reducing agent and colloidal stabilizing agent for the synthesis of Ag nanoparticles (Ag NPs) identified three key points. First, the maltodextrin (MD) solutions are effective in the formation of well-dispersed Ag NPs utilizing alkaline solution conditions, with the resulting Ag NPs ranging in size from 5 to 50 nm diameter. Second, in situ characterization by Raman spectroscopy and small angle X-ray scattering (SAXS) are consistent with initial nucleation of Ag NPs within the MD SMS up to a critical size of ca. 1 nm, followed by a transition to more rapid growth by aggregation and fusion between MD SMS, similar to micelle aggregation reactions. Third, the stabilization of larger Ag NPs by adsorbed MD SMS is similar to hemi-micelle stabilization, and monomodal size distributions are proposed to relate to integer surface coverage of the Ag NPs. Conditions were identified for preparing Ag NPs with monomodal distributions centered at 30–35 nm Ag NPs.
Single quantum dots (QDs) are frequently used as single-photon sources, taking advantage of the final exciton decay in a cascade that produces energetically detuned photons. We propose and analyze a new concept of single-photon source, namely, a few-QD microcavity system driven close to, but below the lasing threshold under strong excitation. Surprisingly, even for two or three QDs inside a cavity, antibunching is observed. To quantify the results, we find that a classification of single-photon emission in terms of antibunching in the autocorrelation function g(2)(0) is insufficient and more details of the photon statistics are required. Our investigations are based on a quantum-optical theory that we solve to obtain the density operator for the quantum-mechanical active medium and radiation field.
Materials in the LaxSr1–xCoyMn1–yO3–δ (LSCM) and LaxSr1–xCoyFe1–yO3–δ (LSCF) families are candidates for high-temperature thermochemical energy storage due to their facility for cyclic endothermic reduction and exothermic oxidation. A set of 16 LSCM and 21 LSCF compositions were synthesized by a modified Pechini method and characterized by powder X-ray diffraction and thermogravimetric analysis. All materials were found to be various symmetries of the perovskite phase. LSCM was indexed as tetragonal, cubic, rhombohedral, or orthorhombic as a function of increased lanthanum content. For LSCF, compositions containing low lanthanum content were indexed as cubic while materials with high lanthanum content were indexed as rhombohedral. An initial screening of redox activity was completed by thermogravimetric analysis for each composition. The top three compositions with the greatest recoverable redox capacity for each family were further characterized in equilibrium thermogravimetric experiments over a range of temperatures and oxygen partial pressures. As a result, these equilibrium experiments allowed the extraction of thermodynamic parameters for LSCM and LSCF compositions operated in thermochemical energy storage conditions.
We consider the problem of decomposing a real-valued symmetric tensor as the sum of outer products of real-valued vectors. Algebraic methods exist for computing complex-valued decompositions of symmetric tensors, but here we focus on real-valued decompositions, both unconstrained and nonnegative, for problems with low-rank structure. We discuss when solutions exist and how to formulate the mathematical program. Numerical results show the properties of the proposed formulations (including one that ignores symmetry) on a set of test problems and illustrate that these straightforward formulations can be effective even though the problem is nonconvex.
This paper presents a physics-based compact modeling approach that incorporates the impact of total ionizing dose (TID) and stress-induced defects into simulations of metal-oxide-semiconductor (MOS) devices and integrated circuits (ICs). This approach utilizes calculations of surface potential (ψs) to capture the charge contribution from oxide trapped charge and interface traps and to describe their impact on MOS electrostatics and device operating characteristics as a function of ionizing radiation exposure and aging effects. The modeling approach is demonstrated for bulk and silicon-on-insulator (SOI) MOS device. The formulation is verified using TCAD simulations and through the comparison of model calculations and experimental I-V characteristics from irradiated devices. The presented approach is suitable for modeling TID and aging effects in advanced MOS devices and ICs.
We spectroscopically measure multiple hydrogen Balmer line profiles from laboratory plasmas to investigate the theoretical line profiles used in white dwarf (WD) atmosphere models. X-ray radiation produced at the Z Pulsed Power Facility at Sandia National Laboratories initiates plasma formation in a hydrogen-filled gas cell, replicating WD photospheric conditions. We also present time-resolved measurements of Hβ and fit this line using different theoretical line profiles to diagnose electron density, ne, and n = 2 level population, n2. Aided by synthetic tests, we characterize the validity of our diagnostic method for this experimental platform. During a single experiment, we infer a continuous range of electron densities increasing from ne ~ 4 to ~30 × 1016 cm-3 throughout a 120-ns evolution of our plasma. Also, we observe n2 to be initially elevated with respect to local thermodynamic equilibrium (LTE); it then equilibrates within ~55 ns to become consistent with LTE. This also supports our electron-temperature determination of Te ~ 1.3 eV (~15,000 K) after this time. At ne≲ 1017 cm-3, we find that computer-simulation-based line-profile calculations provide better fits (lower reduced χ2) than the line profiles currently used in the WD astronomy community. The inferred conditions, however, are in good quantitative agreement. Lastly, this work establishes an experimental foundation for the future investigation of relative shapes and strengths between different hydrogen Balmer lines.
Zavadil, Kevin R.; Kundu, Dipan; Black, Robert; Adams, Brian; Harrison, Katharine; Nazar, Linda F.
The development of nonaqueous Li-oxygen batteries, which relies on the reversible reaction of Li + O2 to give lithium peroxide (Li2O2), is challenged by several factors, not the least being the high charging voltage that results when carbon is typically employed as the cathode host. We report here on the remarkably low 3.2 V potential for Li2O2 oxidation on a passivated nanostructured metallic carbide (Mo2C), carbon-free cathode host. Online mass spectrometry coupled with X-ray photoelectron spectroscopy unequivocally demonstrates that lithium peroxide is simultaneously oxidized together with the LixMoO3-passivated conductive interface formed on the carbide, owing to their close redox potentials. The process rejuvenates the surface on each cycle upon electrochemical charge by releasing LixMoO3 into the electrolyte, explaining the low charging potential.
The photosensitization of photorefractive polymeric composites for operation at 633 nm is accomplished through the inclusion of narrow band gap semiconductor nanocrystals composed of PbS. Unlike previous studies involving photosensitization of photorefractive polymer composites with inorganic nanocrystals, we employ an off-resonance approach where the first excitonic transition associated with the PbS nanocrystals lies at ∼1220 nm and not the wavelength of operation. Using this methodology, internal diffraction efficiencies exceeding 82%, two-beam-coupling gain coefficients of 211 cm-1, and response times of 34 ms have been observed, representing some of the best figures of merit reported for this class of materials. These data demonstrate the ability of semiconductor nanocrystals to compete effectively with traditional organic photosensitizers. In addition to superior performance, this approach also offers an inexpensive and easy means by which to photosensitize composite materials. The photoconductive characteristics of the composites used for this study will also be considered.
Here, the Poisson–Boltzmann theory for electrolytes near a charged surface is known to be invalid due to unaccounted physics associated with high ion concentration regimes. In order to investigate this regime, fluids density functional theory (f-DFT) and molecular dynamics (MD) simulations were used to determine electric surface potential as a function of surface charge. Based on these detailed computations, for electrolytes with nonpolar solvent, the surface potential is shown to depend quadratically on the surface charge in the high charge limit. We demonstrate that modified Poisson–Boltzmann theories can model this limit if they are augmented with atomic packing densities provided by MD. However, when the solvent is a highly polar molecule water an intermediate regime is identified in which a constant capacitance is realized. Simulation results demonstrate the mechanism underlying this regime, and for the salt water system studied here, it persists throughout the range of physically realistic surface charge densities so the potential’s quadratic surface charge dependence is not obtained.
The high mechanical stiffness of single-nanoparticle-thick membranes is believed to result from the local structure of ligand coatings that mediate interactions between nanoparticles. These ligand structures are not directly observable experimentally. We use molecular dynamics simulations to observe variations in ligand structure and simultaneously measure variations in membrane mechanical properties. We have shown previously that ligand end group has a large impact on ligand structure and membrane mechanical properties. Here we introduce and apply quantitative molecular structure measures to these membranes and extend analysis to multiple nanoparticle core sizes and ligand lengths. Simulations of nanoparticle membranes with a nanoparticle core diameter of 4 or 6 nm, a ligand length of 11 or 17 methylenes, and either carboxyl (COOH) or methyl (CH3) ligand end groups are presented. In carboxyl-terminated ligand systems, structure and interactions are dominated by an end-to-end orientation of ligands. In methyl-terminated ligand systems large ordered ligand structures form, but nanoparticle interactions are dominated by disordered, partially interdigitated ligands. Core size and ligand length also affect both ligand arrangement within the membrane and the membrane's macroscopic mechanical response, but are secondary to the role of the ligand end group. Moreover, the particular end group (COOH or CH3) alters the nature of how ligand length, in turn, affects the membrane properties. The effect of core size does not depend on the ligand end group, with larger cores always leading to stiffer membranes. Asymmetry in the stress and ligand density is observed in membranes during preparation at a water-vapor interface, with the stress asymmetry persisting in all membranes after drying.
Hattar, Khalid M.; Sun, C.; Kirk, M.; Li, M.; Wang, Y.; Anderoglu, O.; Valdez, J.; Uberuaga, B.P.; Dickerson, R.; Maloy, S.A.
Nickel superalloys with cubic L12 structured γ′ (Ni3(Al, Ti)) precipitates exhibit high strength at high temperatures and excellent corrosion resistance when exposed to water. Unlike prior studies on irradiation damage of other Ni-based superalloys, our study on Rene N4 involves much larger γ′ precipitates, ∼450 nm in size, a size regime where the irradiation-induced disordering and dissolution kinetics and the corresponding mechanical property evolution are unknown. We report that under heavy ion irradiation at room temperature, the submicron-sized γ′ precipitates were fully disordered at ∼0.3 dpa and only later partially dissolved after 75 dpa irradiation. Nanoindentation experiments indicate that the mechanical properties of the alloy change significantly, with a dramatic decrease in hardness, with irradiation dose. Three contributions to the change in hardness were examined: defect clusters, disordering and dissolution. The generation of defect clusters in the matrix and precipitates slightly increased the indentation hardness, while disordering of the submicron-sized γ′ precipitates resulted in a dramatic decrease in the total hardness, which decreased further during the early stages of the intermixing between γ′ precipitates and matrix (<18 dpa). Controlling the long-range-ordering and chemical intermixing can be used to tailor the mechanical properties of Ni-based superalloys under irradiation.
Yi, Xiaoou; Jenkins, Michael L.; Hattar, Khalid M.; Edmondson, Philip D.; Roberts, Steve G.
The displacement damage induced in W and W-5 wt.% Re and W-5 wt.% Ta alloys by 2 MeV W+ irradiation to doses 3.3 × 1017-2.5 × 1019 W+/m2 at temperatures ranging from 300 to 750 °C has been characterised by transmission electron microscopy. An automated sizing and counting approach based on Image J (a Java-based image processing programme developed at the National Institutes of Health) [1] has been performed for all near-bulk irradiation data. In all cases the damage comprised dislocation loops, mostly of interstitial type, with Burgers vectors b = 1/2〈1 1 1〉 (>60%) and b = 〈1 0 0〉. The diameters of loops did not exceed 20 nm with most being ≤6 nm diameter. The loop number density varied between 1022 and 1023 loops/m3. With increasing irradiation temperature, the loop size distributions shifted towards larger sizes, and there was a substantial decrease in loop number densities. The damage microstructure was less sensitive to dose than to temperature. Under the same irradiation conditions, loop number densities in the W-Re and W-Ta alloys were higher than in pure W but loops were smaller. In grains with normals close to z = 〈0 0 1〉, loop strings developed in pure W at temperatures ≥500 °C and doses ≥1.2 dpa, but such strings were not observed in the W-Re or W-Ta alloys. However, in other grain orientations complex structures appeared in all materials and dense dislocation networks formed at higher doses.
Aluminum has been used prolifically as an impedance matching standard in the multimegabar regime (1 Mbar = 100 GPa), particularly in nuclear driven, early laser driven, and early magnetically driven flyer plate experiments. The accuracy of these impedance matching measurements depends upon the knowledge of both the Hugoniot and release or reshock response of aluminum. Here, we present the results of several adiabatic release measurements of aluminum from ∼400-1200 GPa states along the principal Hugoniot using full density polymethylpentene (commonly known as TPX), and both ∼190 and ∼110 mg/cc silica aerogel standards. These data were analyzed within the framework of a simple, analytical model that was motivated by a first-principles molecular dynamics investigation into the release response of aluminum, as well as by a survey of the release response determined from several tabular equations of state for aluminum. Combined, this theoretical and experimental study provides a method to perform impedance matching calculations without the need to appeal to any tabular equation of state for aluminum. As an analytical model, this method allows for propagation of all uncertainty, including the random measurement uncertainties and the systematic uncertainties of the Hugoniot and release response of aluminum. This work establishes aluminum for use as a high-precision standard for impedance matching in the multimegabar regime.
HPDC 2015 - Proceedings of the 24th International Symposium on High-Performance Parallel and Distributed Computing
Ouyang, Jiannan; Kocoloski, Brian; Lange, John; Foulk, James W.
Performance isolation is emerging as a requirement for High Performance Computing (HPC) applications, particularly as HPC architectures turn to in situ data processing and application composition techniques to increase system throughput. These approaches require the co-location of disparate workloads on the same compute node, each with different resource and runtime requirements. In this paper we claim that these workloads cannot be effectively managed by a single Operating System/Runtime (OS/R). Therefore, we present Pisces, a system software architecture that enables the co-existence of multiple independent and fully isolated OS/Rs, or enclaves, that can be customized to address the disparate requirements of next generation HPC workloads. Each enclave consists of a specialized lightweight OS cokernel and runtime, which is capable of independently managing partitions of dynamically assigned hardware resources. Contrary to other co-kernel approaches, in this work we consider performance isolation to be a primary requirement and present a novel co-kernel architecture to achieve this goal. We further present a set of design requirements necessary to ensure performance isolation, including: (1) elimination of cross OS dependencies, (2) internalized management of I/O, (3) limiting cross enclave communication to explicit shared memory channels, and (4) using virtualization techniques to provide missing OS features. The implementation of the Pisces co-kernel architecture is based on the Kitten Lightweight Kernel and Palacios Virtual Machine Monitor, two system software architectures designed specifically for HPC systems. Finally we will show that lightweight isolated co-kernels can provide better performance for HPC applications, and that isolated virtual machines are even capable of outperforming native environments in the presence of competing workloads.
Application resilience is a key challenge that must be ad-dressed in order to realize the exascale vision. Previous work has shown that online recovery, even when done in a global manner (i.e., involving all processes), can dramatically re-duce the overhead of failures when compared to the more traditional approach of terminating the job and restarting it from the last stored checkpoint. In this paper we suggest going one step further, and explore how local recovery can be used for certain classes of applications to reduce the over-heads due to failures. Specifically we study the feasibility of local recovery for stencil-based parallel applications and we show how multiple independent failures can be masked to effectively reduce the impact on the total time to solution.
Nuclear Instruments and Methods in Physics Research. Section A, Accelerators, Spectrometers, Detectors and Associated Equipment
Marleau, P.; Monterial, Mateusz; Clarke, Shaun; Pozzi, Sara
A Bayesian approach is proposed for pulse shape discrimination of photons and neutrons in liquid organic scinitillators. Instead of drawing a decision boundary, each pulse is assigned a photon or neutron confidence probability. In addition, this allows for photon and neutron classification on an event-by-event basis. The sum of those confidence probabilities is used to estimate the number of photon and neutron instances in the data. An iterative scheme, similar to an expectation-maximization algorithm for Gaussian mixtures, is used to infer the ratio of photons-to-neutrons in each measurement. Therefore, the probability space adapts to data with varying photon-to-neutron ratios. A time-correlated measurement of Am–Be and separate measurements of 137Cs, 60Co and 232Th photon sources were used to construct libraries of neutrons and photons. These libraries were then used to produce synthetic data sets with varying ratios of photons-to-neutrons. Probability weighted method that we implemented was found to maintain neutron acceptance rate of up to 90% up to photon-to-neutron ratio of 2000, and performed 9% better than the decision boundary approach. Furthermore, the iterative approach appropriately changed the probability space with an increasing number of photons which kept the neutron population estimate from unrealistically increasing.
The CMD subprogram develops and deploys multi-application weapon component manufacturing capabilities needed to replace sunset technologies, upgrade existing technologies, and introduce new technologies that support the nuclear weapons stockpile. Sandia National Laboratories (SNL) is currently developing an Electronic Production Control System (EPCS) for ASIC production in the back end of line (BEOL) flow. A pre-production version of EPCS has been released and is operating as intended. We are currently processing all ASIC products, including CVV validation ASICs. The BEOL flow includes wafer probe, packaging, quality inspection, initial electrical test, dynamic burn-in, final electrical test, quality inspection, final visual inspection, radiation testing, SNL acceptance, DOE SSO acceptance, and qualification testing steps. EPCS will execute this production workflow (initiate, control, and electronically track each product); it will implement defect prevention strategies; it will create an electronic inventory control system that is accountable for all ASIC material from inception to delivery; it will electronically collect and store any and all required quality evidence and most of the electronic BEOL data; and it will create a management reporting module with production statistics and timelines. The defect prevention strategies include the use of 2D marks on our ASICs with 2D scanners so that there will be no manual entry of part numbers (scanners), will not allow testing the wrong parts in Test and Burn-in. Other defect prevention strategies will negate the possibility of neither using the wrong test or burn-in program for any part nor the use of BEOL machines or boards that are out of calibration. In summary, EPCS is being implemented and it will greatly improve the product acceptance through full electronic data collection and quality control and defect prevention through bar codes, scanners, tracking training of personnel, and tracking tool availability.
Flexible energy storage devices are critical components for emerging flexible electronics. Electrode design is key in the development of all-solid-state supercapacitors with superior electrochemical performances and mechanical durability. Herein, we propose a bamboo-like graphitic carbon nanofiber with a well-balanced macro-, meso-, and microporosity, enabling excellent mechanical flexibility, foldability, and electrochemical performances. Our design is inspired by the structure of bamboos, where a periodic distribution of interior holes along the length and graded pore structure at the cross section not only enhance their stability under different mechanical deformation conditions but also provide a high surface area accessible to the electrolyte and low ion-transport resistance. The prepared nanofiber network electrode recovers its initial state easily after 3-folded manipulation. The mechanically robust membrane is explored as a free-standing electrode for a flexible all-solid-state supercapacitor. Without the need for extra support, the volumetric energy and power densities based on the whole device are greatly improved compared to the state-of-the-art devices. Even under continuous dynamic operations of forceful bending (90°) and twisting (180°), the as-designed device still exhibits stable electrochemical performances with 100% capacitance retention. Such a unique supercapacitor holds great promise for high-performance flexible electronics. (Figure Presented).
This special issue of Computers & Chemical Engineering contains extended versions of selected contributions from the 8th International Conference on the Foundations of Computer-Aided Process Design (FOCAPD-2014), held at the Suncadia Resort in Cle Elum, Washington, USA, July 13–17, 2014. These papers were recommended by the International Programming Committee and constitute a representative sample of the invited plenary lectures,future perspectives, and contributed papers.
In high performance computing (HPC), applications usually have many parallel tasks running on multiple machine nodes. As these tasks intensively communicate with each other, the communication overhead has a significant impact on an application's execution time. This overhead is determined by the application's communication pattern as well as the network distances between communicating tasks. By mapping the tasks to the available machine nodes in a communication-aware manner, the network distances and the execution times can be significantly reduced. Existing techniques first allocate available nodes to an application, and then map the tasks onto the allocated nodes. In this paper, we discuss the potential benefits of simultaneous allocation and mapping for applications with irregular communication patterns. We also propose a novel graphbased allocation and mapping technique to reduce the execution time in HPC machines that use non-contiguous allocation, such as Cray XK series. Simulations calibrated with real-life experiments show that our technique reduces hop-bytes up to 30% compared to the state-of-the-art.
Isotope identification algorithms that are contained in the Gamma Detector Response and Analysis Software (GADRAS) can be used for real-time stationary measurement and search applications on platforms operating under Linux or Android operating systems. Since the background radiation can vary considerably due to variations in naturally-occurring radioactive materials (NORM), spectral algorithms can be substantially more sensitive to threat materials than search algorithms based strictly on count rate. Specific isotopes or interest can be designated for the search algorithm, which permits suppression of alarms for non-threatening sources, such as such as medical radionuclides. The same isotope identification algorithms that are used for search applications can also be used to process static measurements. The isotope identification algorithms follow the same protocols as those used by the Windows version of GADRAS, so files that are created under the Windows interface can be copied directly to processors on fielded sensors. The analysis algorithms contain provisions for gain adjustment and energy linearization, which enables direct processing of spectra as they are recorded by multichannel analyzers. Gain compensation is performed by utilizing photo-peaks in background spectra. Incorporation of this energy calibration tasks into the analysis algorithm also eliminates one of the more difficult challenges associated with development of radiation detection equipment.
We report continuous, dynamic, reversible, and widely tunable lasing from 367 to 337 nm from single GaN nanowires (NWs) by applying hydrostatic pressure up to ∼7 GPa. The GaN NW lasers, with heights of 4-5 μm and diameters ∼140 nm, are fabricated using a lithographically defined two-step top-down technique. The wavelength tuning is caused by an increasing Γ direct bandgap of GaN with increasing pressure and is precisely controllable to subnanometer resolution. The observed pressure coefficients of the NWs are ∼40% larger compared with GaN microstructures fabricated from the same material or from reported bulk GaN values, revealing a nanoscale-related effect that significantly enhances the tuning range using this approach. This approach can be generally applied to other semiconductor NW lasers to potentially achieve full spectral coverage from the UV to IR.
In this paper, we provide an overview of the current knowledge of radiation effects in anion-based memristive devices. We will specifically look at the impact of high dose rate ionizing radiation, total ionizing dose (TID), and heavy ions on the electrical characteristics of tantalum oxide (TaOx), titanium dioxide (TiO2), and hafnium oxide (HfOx) memristors. The primary emphasis, however, will be placed on TaOx memristors. While there are several other anion-based memristive devices being fabricated by the semiconductor community for possible use in valence change memories, most of the present radiation work has focused on one of these types of devices. There have also been numerous studies on radiation effects in cation-based chalcogenides such as germanium sulfides and selenides. However, that will not be discussed in this paper.
We present a new analysis of airburst risk based on updated estimates for the population of undiscovered NEOs, taking into account the enhanced damage potential of directed airbursts. We define airbursts as events in which small (meters to tens-of-meters in diameter) asteroids deposit most of their energy in the atmosphere as large bolides and where the total energy is comparable to or greater than small nuclear explosions (>0.1 kilotons of TNT). Our tens-of-meter population estimate from optical surveys is now much closer to bolide frequency estimates, resolving most of an earlier discrepancy. Our Tunguska-class (∼40 meters) population estimate has doubled, and Chelyabinsk-class (∼20 meters) has increased by a factor of 2.6. Uncertainty in this population remains quite large, and can only be unambiguously reduced by expanded surveys focused on objects in the tens-of-meters size range. The assessed risk from this population is also increasing for two reasons. First, airbursts are significantly more damaging than assumed in the original risk assessments, because for typical impact geometries they more efficiently couple energy to the surface than nuclear explosions of the same energy. Second, the greater numbers mean that they are more frequent than previously thought. We review the evidence that asteroid airbursts are more damaging than nuclear explosions, and provide arguments that such events are more frequent.
Deep Borehole Disposal (DBD) of high-level radioactive wastes has been considered an option for geological isolation for many years (Hess et al. 1957). Recent advances in drilling technology have decreased costs and increased reliability for large-diameter (i.e., ≥50 cm [19.7”]) boreholes to depths of several kilometers (Beswick 2008). These advances have therefore also increased the feasibility of the DBD concept (Brady et al. 2009), and the current field test, introduced herein, is a demonstration of the DBD concept and these advances. The US Department of Energy (DOE) Strategy for the Management and Disposal of Used Nuclear Fuel and High-Level Radioactive Waste (DOE 2013) specifically recommended developing a research and development plan for DBD as a key strategy objective. DOE’s Assessment of Disposal Options for DOE-Managed High-Level Radioactive Waste and Spent Nuclear Fuel (DOE 2014a) concludes “effective implementation of a strategy for management and disposal of all High-Level Waste and Spent Nuclear Fuel” would include focused research on deep boreholes, especially to retain flexible options for disposal of physically smaller DOEmanaged solid radioactive waste forms. More information regarding the characteristics, quantities, and sizes of these physically smaller waste forms is in the Evaluation of Options for Permanent Geologic Disposal of Spent Nuclear Fuel and High-Level Radioactive Waste (SNL 2014).
Until 2012, Sandia participated regularly in non-fusion R&D that was supported primarily through our collaborations with companies in the DOE program for Small Business Innovative Research but also in some work-for-others contracts. In this work, funds were recovered from collaborating institutions for the staff time and materials used, but FES had supported the facility itself and in doing so enabled the contributions to the non-fusion R&D below.
In this study, the scientific community relies on the peer review process for assuring the quality of published material, the goal of which is to build a body of work we can trust. Computational journals such as The ACM Transactions on Mathematical Software (TOMS) use this process for rigorously promoting the clarity and completeness of content, and citation of prior work. At the same time, it is unusual to independently confirm computational results.
The rooftop solar PV permitting process involves a number of steps and varies greatly, even between neighboring cities. Jurisdictions follow state or national codes, but each may interpret the codes in their own way and insert additional requirements. In some locations, a rooftop structural analysis conducted by a professional engineer is required before a rooftop solar permit is issued. The extra step is not universally applied across states or municipalities, and can alter scheduling logistics and add hundreds of dollars to the cost of the system.
Current programming languages and programming models make it easy to create software and hardware systems that fulfill an intended function but also leave such systems open to unintended function and vulnerabilities. Software engineering and code hygiene may make systems incrementally safer, but do not produce the wholesale change necessary for secure systems from the outset. Yet there exists an approach with impressive results: We cite recent examples showing that formal methods, coupled with formally informed digital design, have produced objectively more robust code even beyond the properties directly proven. Though discovery of zero-day vulnerabilities is almost always a surprise and powerful tools like semantic fuzzers can cover a larger search space of vulnerabilities than a developer can conceive of, formal models seem to produce robustness of a higher qualitative order than traditionally developed digital systems. Because the claim is necessarily a qualitative one, we illustrate similar results with an idealized programming language in the form of Boolean networks where we have control of parameters related to stability and adaptability. We argue that verifiability with formal methods is an instance of broader design constraints that promote robustness. We draw analogies to real-world programming models and languages that can be mathematically reasoned about in contrast to ones that are essentially undecidable.
Traditionally, safety and impact of failure concerns of lithium ion batteries have dealt with the field failure of single cells. However, large and complex battery systems require the consideration of how a single cell failure will impact the system as a whole. Initial failure that leads to the thermal runaway of other cells within the system creates a much more serious condition than the failure of a single cell. This work examines the behavior of small modules of cylindrical and stacked pouch cells after thermal runaway is induced in a single cell. Cylindrical cells are observed to be less prone to propagate owing to the limited contact between neighboring cells. The electrical connectivity is found to be impactful as the 10S1P cylindrical cell module did not show failure propagation through the module, while the 1S10P module had an energetic thermal runaway consuming the module minutes after the initiation failure trigger. Modules built using pouch cells conversely showed the impact of strong heat transfer between cells. In this case, a large surface area of the cells was in direct contact with its neighbors, allowing failure to propagate through the entire battery within 60-80 s for all configurations (parallel or series) tested.
We present a parametric analysis of factors that can influence advanced fuel and technology deployments in U.S. Class 7-8 trucks through 2050. The analysis focuses on the competition between traditional diesel trucks, natural gas vehicles (NGVs), and ultra-efficient powertrains. Underlying the study is a vehicle choice and stock model of the U.S. heavy-duty vehicle market. The model is segmented by vehicle class, body type, powertrain, fleet size, and operational type. We find that conventional diesel trucks will dominate the market through 2050, but NGVs could have significant market penetration depending on key technological and economic uncertainties. Compressed natural gas trucks conducting urban trips in fleets that can support private infrastructure are economically viable now and will continue to gain market share. Ultra-efficient diesel trucks, exemplified by the U.S. Department of Energy's SuperTruck program, are the preferred alternative in the long haul segment, but could compete with liquefied natural gas (LNG) trucks if the fuel price differential between LNG and diesel increases. However, the greatest impact in reducing petroleum consumption and pollutant emissions is had by investing in efficiency technologies that benefit all powertrains, especially the conventional diesels that comprise the majority of the stock, instead of incentivizing specific alternatives.
Organic dyes such as methylene blue (MB) are often used in the characterization of clays and related minerals, but details of the adsorption mechanisms of such dyes are only partially understood from spectroscopic data, which indicate the presence of monomers, dimers, and higher aggregates for varying mineral surfaces. A combination of quantum (density functional theory) and classical molecular simulation methods was used to provide molecular detail of such adsorption processes, specifically the adsorption of MB onto kaolinite basal surfaces. Slab models with vacuum-terminated surfaces were used to obtain detailed structural properties and binding energies at both levels of theory, while classical molecular dynamics simulations of aqueous pores were used to characterize MB adsorption at infinite dilution and at higher concentration in which MB dimers and one-dimensional chains formed. Results for the neutral MB molecules are compared with those for the corresponding cation. Simulations of the aqueous pore indicate preferred adsorption on the hydrophobic siloxane surface, while charge-balancing chloride ions adsorb at the aluminol surface. At infinite dilution and in the gas-phase models, MB adsorbs with its primary molecular plane parallel to the siloxane surface to enhance hydrophobic interactions. Sandwiched dimers and chains are oriented perpendicular to the surface to facilitate the strong hydrophobic intermolecular interactions. Compared with quantum results, the hybrid force field predicts a weaker MB adsorption energy but a stronger dimerization energy. The structure and energetics of adsorbed MB at infinite dilution are consistent with the gas-phase binding results, which indicate that monomer adsorption is driven by strong interfacial forces rather than by the hydration properties of the dye. These results inform spectroscopic studies of MB adsorption on mineral surfaces while also revealing critical areas for development of improved hybrid force fields.
Implicit numerical integration of nonlinear ODEs requires solving a system of nonlinear algebraic equations at each time step. Each of these systems is often solved by a Newton-like method, which incurs a sequence of linear-system solves. Most model-reduction techniques for nonlinear ODEs exploit knowledge of a system's spatial behavior to reduce the computational complexity of each linear-system solve. However, the number of linear-system solves for the reduced-order simulation often remains roughly the same as that for the full-order simulation.We propose exploiting knowledge of the model's temporal behavior to (1) forecast the unknown variable of the reduced-order system of nonlinear equations at future time steps, and (2) use this forecast as an initial guess for the Newton-like solver during the reduced-order-model simulation. To compute the forecast, we propose using the Gappy POD technique. The goal is to generate an accurate initial guess so that the Newton solver requires many fewer iterations to converge, thereby decreasing the number of linear-system solves in the reduced-order-model simulation.