The Pipe Overpack Container (POC) was developed at Rocky Flats to transport plutonium residues with higher levels of plutonium than standard transuranic (TRU) waste to the Waste Isolation Pilot Plant (WIPP) for disposal. In 1996 Sandia National Laboratories (SNL) conducted a series of tests to determine the degree of protection POCs provided during storage accident events. One of these tests exposed four of the POCs to a 30-minute engulfing pool fire, resulting in one of the 7A drum overpacks generating sufficient internal pressure to pop off its lid and expose the top of the pipe container (PC) to the fire environment. The initial contents of the POCs were inert materials, which would not generate large internal pressure within the PC if heated. However, POCs are now being used to store combustible Transuranic (TRU) waste at Department of Energy (DOE) sites. At the request of DOE's Office of Environmental Management (EM) and National Nuclear Security Administration (NNSA), SNL started conducting a new series of fire tests in 2015 to examine whether PCs with combustibles would reach a temperature that would result in (1) decomposition of inner contents and (2) subsequent generation of sufficient gas to cause the PC to overpressurize and release its inner content. In 2016, Phase II tests showed that POCs tested in a pool fire failed within 3 minutes of ignition with the POC lid ejecting. These POC lids were fitted with an all-metal (NUCFIL019DS) filter and revealed that this specific filter did not relieve sufficient pressure to prevent lid ejection. For the test phase discussed in this report, Phase II-A, the POCs are exposed to a 30-minute pool fire, with similar configurations to those tested in Phase II, except that the POC lids are fitted with a hybrid metal-polyethylene (UT9424S) filter instead. This report will: describe the various tests conducted in Phase II-A, present results from these tests, and discuss implications for the POCs based on the test results.
A usability study on the comprehension and readability of transformed Corporate Policy System (CPS) content was conducted April 9-18, 2018. The purpose of the study included the following: 1. Measure participant's ability to comprehend transformed Corporate Policy Content using a multiple-choice quiz; 2. Measure participant's ability to comprehend transformed Corporate Policy Content using the Cloze Test Methodology; 3. Measure text readability of existing Corporate Policy Content; 4. Measure text readability of transformed Corporate Policy Content; 5. Measure text readability of a broad set of reading materials and see where the Corporate Policy System content ranked in comparison.
In this paper, we present the effect of installation parameters (tilt angle, height above ground, and albedo) on the bifacial gain and energy yield of three south-facing photovoltaic (PV) system configurations: a single module, a row of five modules, and five rows of five modules utilizing RADIANCE-based ray tracing model. We show that height and albedo have a direct impact on the performance of bifacial systems. However, the impact of the tilt angle is more complicated. Seasonal optimum tilt angles are dependent on parameters such as height, albedo, size of the system, weather conditions, and time of the year. For a single bifacial module installed in Albuquerque, NM, USA (35 °N) with a reasonable clearance (∼1 m) from the ground, the seasonal optimum tilt angle is lowest (∼5°) for the summer solstice and highest (∼65°) for the winter solstice. For larger systems, seasonal optimum tilt angles are usually higher and can be up to 20° greater than that for a single module system. Annual simulations also indicate that for larger fixed-tilt systems installed on a highly reflective ground (such as snow or a white roofing material with an albedo of ∼81%), the optimum tilt angle is higher than the optimum angle of the smaller size systems. We also show that modules in larger scale systems generate lower energy due to horizon blocking and large shadowing area cast by the modules on the ground. For albedo of 21%, the center module in a large array generates up to 7% less energy than a single bifacial module. To validate our model, we utilize measured data from Sandia National Laboratories' fixed-tilt bifacial PV testbed and compare it with our simulations.
We combined the miniature cylinder expansion test (Mini-Cylex), with the Disk Acceleration Test (DAX) using Type K copper, Picatinny Liquid Explosive, and photonic Doppler velocimetry. We estimated the CJ state using plate reverberation methods at the test cap. We extracted velocities at 2, 7, and 10 volume expansions to fit Jones-Wilkins-Lee Equation of State and estimated Gurney velocity at the tube wall. The test also provides an additional method to estimate reaction products Hugoniot through knowledge of the copper test cap. Our experiments and simulations are within expected uncertainty. The test and the analysis effectively reduce costs while keeping or increasing fidelity.
Heath, Jason; Frash, Luke P.; Hawley, Marilyn E.; Ding, Mei; Xu, Hongwu; Barker, John; Olds, Daniel; Dewers, Thomas D.
In situ measurements of geological materials under compression and with hydrostatic fluid pressure are important in understanding their behavior under field conditions, which in turn provides critical information for application-driven research. In particular, understanding the role of nano- to micro-scale porosity in the subsurface liquid and gas flow is critical for the high-fidelity characterization of the transport and more efficient extraction of the associated energy resources. In other applications, where parts are produced by the consolidation of powders by compression, the resulting porosity and crystallite orientation (texture) may affect its in-use characteristics. Small-angle neutron scattering (SANS) and ultra SANS are ideal probes for characterization of these porous structures over the nano to micro length scales. Here we show the design, realization, and performance of a novel neutron scattering sample environment, a specially designed compression cell, which provides compressive stress and hydrostatic pressures with effective stress up to 60 MPa, using the neutron beam to probe the effects of stress vectors parallel to the neutron beam. We demonstrate that the neutron optics is suitable for the experimental objectives and that the system is highly stable to the stress and pressure conditions of the measurements.
Fatigue crack growth rate (FCGR) data were measured in high pressure hydrogen gas versus stress intensity factor range (ΔK) in specimens removed from a X100 welded steel pipe. Three distinct regions of the pipe weld were examined: base metal, weld fusion zone, and heat affected zone. Tests were performed at a load ratio (R) of 0.5, frequency of 1 Hz, and at a hydrogen gas pressure of 21 MPa. Tests were also performed in air at 10 Hz as a reference. Fatigue crack growth rates were observed to be over an order of magnitude higher for tests performed in hydrogen compared to the rates from tests in air. Residual stress measurements were collected on identical specimens cut from the base metal, weld, and heat affected zone to account for their influence on measured FCGR data. The slitting method provided residual stress and residual stress intensity factor (Kres), the effect of which was removed from the FCGR data using Knorm in order to provide a more direct comparison of crack growth resistance of the base metal, weld and heat affected zone. Prior to accounting for residual stress, FCGR in hydrogen gas appeared to be highest in the weld fusion zone. After accounting for residual stress effects, the weld fusion zone FCGR data converged to the base metal FCGR data, which underscores the importance of accounting for residual stress effects when assessing fatigue performance.
The goals of this feasibility study are to determine the technical, regulatory, and economic feasibility of a coastal research vessel powered solely by hydrogen fuel cells, assess the environmental benefits and determine the prospects for refueling such a vessel at the expected ports of call.
The Air Delivered Weapons Tester Development Group (2256) is currently designing a new type of test system, the Universal Real Time Controller (URTCON). The URTCON will provide the surveillance community with technologies that advance the state of knowledge in stockpile stewardship. Success for its implementation depends on whether the components comprising the URTCON can be reliably and accurately maintained in the field. A system is maintainable when the worker has visual and physical access to the components that need to be serviced. To address this need, a layout was determined that best facilitates the worker's ability to easily see and reach components. A list of user-system requirements was initially prepared to guide decisions affecting the layout. Then, five design options depicting various ways to lay out the components were evaluated. Based on this effort, a best design option was identified for implementation. It is expected that the design recommended herein will provide the workers with a workplace that permits unhindered access to the components requiring their attention.
To determine the in-plane crush properties of a perforated aluminum and Kevlar® layered composite, confined compression tests were performed. Cylindrical samples were used in the test. The samples were cut by waterjet from bulk material. The tests were conducted in the geomechanics laboratory at Sandia National Laboratories. Force and displacement data were recorded to determine the stress versus volumetric strain up to full compaction of the material. Full compaction was determined to be when the displacement was negligible or when the material had compacted about 63 percent in volume, which was the open volume percent of the aluminum layers in the uncompressed specimens. This testing is intended to capture data for use in the structural models used in support of the certification of the AWG-711 hazardous materials air transportation package.
The problem statement from which the Causal Analysis Team focused was, "A Member of the Workforce (MOW) from Department 8862 sustained a fractured ankle while traversing a 7.5- inch-high elevated aluminum cover over conduits located in NM Building 905, laboratory 1201 that houses a gas gun." The analysis revealed the following causes that directly contributed to this event: Root Causes: 1. The landing area from the downslope on the flammable cabinet side of the aluminum conduit cover was not sufficient; and 2. The surface of the aluminum conduit cover was too smooth.
This report provides a summary of the radionuclide releases from the United States (U.S.) Department of Energy (DOE) National Nuclear Security Administration facilities at Sandia National Laboratories/Tonopah Test Range (SNL/TTR) during Calendar Year (CY) 2017, including the data, calculations, and supporting documentation for demonstrating compliance with 40 Code of Federal Regulation (CFR) 61, Subpart H--NATIONAL EMISSION STANDARDS FOR EMISSIONS OF RADIONUCLIDE OTHER THAN RADON FROM DEPARTMENT OF ENERGY FACILITIES (Radionuclide NESHAP).
This document is a reference guide to the Xyce Parallel Electronic Simulator, and is a companion document to the Xyce Users' Guide. The focus of this document is (to the extent possible) exhaustively list device parameters, solver options, parser options, and other usage details of Xyce. This document is not intended to be a tutorial. Users who are new to circuit simulation are better served by the Xyce Users' Guide.
This manual describes the use of the Xyce Parallel Electronic Simulator. Xyce has been designed as a SPICE-compatible, high-performance analog circuit simulator, and has been written to support the simulation needs of the Sandia National Laboratories electrical designers. This development has focused on improving capability over the current state-of-the-art in the following areas: Capability to solve extremely large circuit problems by supporting large-scale parallel com- puting platforms (up to thousands of processors). This includes support for most popular parallel and serial computers. A differential-algebraic-equation (DAE) formulation, which better isolates the device model package from solver algorithms. This allows one to develop new types of analysis without requiring the implementation of analysis-specific device models. Device models that are specifically tailored to meet Sandia's needs, including some radiation-aware devices (for Sandia users only). Object-oriented code design and implementation using modern coding practices. Xyce is a parallel code in the most general sense of the phrase — a message passing parallel implementation — which allows it to run efficiently a wide range of computing platforms. These include serial, shared-memory and distributed-memory parallel platforms. Attention has been paid to the specific nature of circuit-simulation problems to ensure that optimal parallel efficiency is achieved as the number of processors grows.
This paper discusses sea clutter models, developed and validated for X-band radar returns, and extrapolated to Ku-band. Statistical distributions for sea clutter both with and without sea spikes are presented. Equations and predictions for sea clutter returns versus grazing angle and sea-state at Ku-band are also detailed.
Bender, Michael A.; Berry, Jonathan W.; Farach-Colton, Martin; Jacobs, Justin; Johnson, Rob; Kroeger, Thomas M.; Mayer, Tyler; Mccauley, Samuel; Pandey, Prashant; Phillips, Cynthia A.; Porter, Alexandra; Singh, Shikha; Raizes, Justin; Xu, Helen; Zage, David
This report summarizes the work performed under the project "Advanced Data Structures for Improved Cyber Resilience and Awareness in Untrusted Environments." The goal of the project was to design, analyze, and test new data structures for cybersecurity applications. We had two major thrusts: 1) using new/improved write-optimized data structures and/or algorithms to better man- age and analyze high-speed massive-volume cyberstreams, and 2) adding security features to data structures at minimum cost. Write optimization allows data structures to better use secondary memory to store and search a larger amount of useful information. Secondary memory is large compared to main memory, but data movement to and from secondary memory must be carefully managed to run quickly enough to keep up with fast streams. The first thrust included managing cyberstreams in parallel, both multi-threaded and distributed, and improving the benchmarking infrastructure for testing new streaming data structures. We considered both (near) real-time discovery of particular patterns, and improved logging for improved forensics. We considered two kinds of security-feature problem. The first was high-performance history- independent external-memory data structures. These provide certain protections to data if a disk is stolen. We also prove some trade-offs between speed and security in this setting. The second data-security problem is more secure data look-up in secret-shared data bases. This report summarizes the project's major accomplishments, with the background to under- stand these accomplishments. It gathers the abstracts and references for the six refereed publications that have appeared as part of this work. We summarize several accomplishments that will be submitted for publication. We then archive one piece of partial work that is not likely to be published in the near future: validation of history-independent data structure implementations.
This report provides a summary of the radionuclide releases from the United States (U.S.) Department of Energy (DOE) National Nuclear Security Administration facilities at Sandia National Laboratories, New Mexico (SNL/NM) during Calendar Year (CY) 2017, including the data, calculations, and supporting documentation for demonstrating compliance with 40 Code of Federal Regulation (CFR) 61, Subpart H--NATIONAL EMISSION STANDARDS FOR EMISSIONS OF RADIONUCLIDE OTHER THAN RADON FROM DEPARTMENT OF ENERGY FACILITIES (Radionuclide NESHAP). A description is given of the sources and their contributions to the overall dose assessment. In addition, the maximally exposed individual (MEI) Radionuclide dose calculation and the population dose to local and regional residents are discussed.
Moore's law is driving an information revolution, worldwide economic growth, and is a tool for national security. This report explains how dire proclamations that "Moore's law is ending" are due to a natural redefinition of the phrase, but computing remains positioned to both drive economic growth and support national security. The computer industry used to be led by the semiconductor companies that made ever faster microprocessors with larger memories. However, control is shifting to new ways of designing computers, notably based on 3D chips and new analog and digital architectures. While artificial intelligence and quantum computing research have become mainstream pursuits, these latter two areas seem destined split off from Moore's law rather than become a part of it. We include a discussion of recent developments and opportunities in optical communications and computing.
The Causal Analysis Team focused on the following problem statement: "A Member of the Workforce (MOW) sustained an electrical shock upon touching a power strip (PS) in a laboratory."
Achieving computational rates beyond the petascale requires an increasing amount of heterogeneity in our highperformance computing (HPC) hardware. This heterogeneity, in turn, means that a node of an HPC system can no longer be considered a monolithic resource. Rather, a node has many individual components such as processors, cores, SMT threads, accelerators, and tierd memories that must be further allocated and managed by... something. Currently, that something is an ad-hoc mix of arguments and environments when launching jobs. We follow the same process used on prior HPC systems with nodes of uniform components; unfortunately, the shims introduced to provide the additional specification of node-level components are inconsistent and unwieldy. As we shall see, even at our current moderate level of heterogeneity our effective utilization of HPC software is hampered by poor resource management. Future systems will continue to grow in heterogeneity both in number and type of resources. Our current approach to resource management cannot scale. We need a more cohesive approach to managing heterogeneous resources in HPC systems.
This document details the computational fluid dynamic and system-level modeling, including a mechanistic representation of a turbine/pump, for Fukushima Daiichi Unit 2. Until this recent effort, mechanistic modeling had been confined to an otherwise coarse model of Fukushima Daiichi Unit 2 laden with manipulations of boundary conditions that substituted for detailed representations of the reactor, drywell, and wetwell. This work has provided insights in modeling uncertainties and provides confirmation for experimental efforts for the Terry turbopump.
This monthly report is intended to communicate the status of North Slope ARM facilities managed by Sandia National Labs. Report includes budget, summary of current management issues, safety, tethered balloon operations, and North Slope facilities.
Understanding rock damage induced by explosions is critical for a number of applications including the monitoring and verification of underground nuclear explosions, mine safety issues, and modeling fluid flow through fractured rock. We use core observations, televiewer logs, and thin section observations to investigate fracture damage associated with two successive underground chemical explosions (SPE2 and SPE3) in granitic rock at both the mesoscale and microscale. We compare the frequency and orientations of core-scale fractures, and the frequency of microfractures, between a pre-experiment core and three post-experiment cores. Natural fault zones and explosion-induced fractures in the vicinity of the explosive source are readily apparent in recovered core and in thin sections. Damage from faults and explosions is not always apparent in fracture frequency plots from televiewer logs, although orientation data from these logs suggests explosion-induced fracturing may not align with the pre-existing fracture sets. Core-scale observations indicate the extent of explosion-induced damage is 10.0 m after SPE2 and 6.8 m after SPE3, despite both a similar size and location for both explosions. At the microscale, damage is observed to a range distance of 10.2 ± 0.9 m after SPE2, and 16.6 ± 0.9 and 11.2 ± 0.6 in two different cores collected after SPE3. Additional explosion-induced damage, interpreted to be the result of spalling, is readily apparent near the surface, but only in the microfracture data. This depth extent and intensity of damage in the near-surface region also increased after an additional explosion. This study highlights the importance of evaluating structural damage at multiple scales for a more complete characterization of the damage, and particularly shows the importance of microscale observations for identifying spallation-induced damage.
Journal of Quantitative Spectroscopy and Radiative Transfer
Arienti, Marco A.; Geier, Manfred; Yang, Xiaoyuan; Orcutt, John; Zenker, Jake; Brooks, Sarah D.
We investigate the optical properties of ice crystals nucleated on atmospheric black carbon (BC). The parameters examined in this study are the shape of the ice crystal, the volume fraction of the BC inclusion, and its location inside the crystal. We report on new spectrometer measurements of forward scattering and backward polarization from ice crystals nucleated on BC particles and grown under laboratory-controlled conditions. Data from the Cloud and Aerosol Spectrometer with Polarization (CASPOL) are used for direct comparison with single-particle calculations of the scattering phase matrix. Geometrical optics and discrete dipole approximation techniques are jointly used to provide the best compromise of flexibility and accuracy over a broad range of size parameters. Together with the interpretation of the trends revealed by the CASPOL measurements, the numerical results confirm previous reports on absorption cross-section magnification in the visible light range. Even taking into account effects of crystal shape and inclusion position, the ratio between absorption cross-section of the compound particle and the absorption cross-section of the BC inclusion alone (the absorption magnification) has a lower bound of 1.5; this value increases to 1.7 if the inclusion is centered with respect to the crystal. The simple model of BC-ice particle presented here also offers new insights on the effect of the relative position of the BC inclusion with respect to the crystal's outer surfaces, the shape of the crystal, and its size.
We present a parallel hierarchical solver for general sparse linear systems on distributed-memory machines. For large-scale problems, this fully algebraic algorithm is faster and more memory-efficient than sparse direct solvers because it exploits the low-rank structure of fill-in blocks. Depending on the accuracy of low-rank approximations, the hierarchical solver can be used either as a direct solver or as a preconditioner. The parallel algorithm is based on data decomposition and requires only local communication for updating boundary data on every processor. Moreover, the computation-to-communication ratio of the parallel algorithm is approximately the volume-to-surface-area ratio of the subdomain owned by every processor. We present various numerical results to demonstrate the versatility and scalability of the parallel algorithm.
Morphology and microstructure of organic explosive films formed using physical vapor deposition (PVD) processes strongly depends on local surface temperature during deposition. Currently, there is no accurate means of quantifying the local surface temperature during PVD processes in the deposition chambers. This work focuses on using a multiphysics computational fluid dynamics tool, STARCCM+, to simulate pentaerythritol tetranitrate (PETN) deposition. The PETN vapor and solid phase were simulated using the volume of fluid method and its deposition in the vacuum chamber on spinning silicon wafers was modeled. The model also included the spinning copper cooling block where the wafers are placed along with the chiller operating with forced convection refrigerant. Implicit time-dependent simulations in two- and three-dimensional were performed to derive insights in the governing physics for PETN thin film formation. PETN is deposited at the rate of 14 nm/s at 142.9 °C on a wafer with an initial temperature of 22 °C. The deposition of PETN on the wafers was calculated at an assumed heat transfer coefficient (HTC) of 400 W/m2 K. This HTC proved to be the most sensitive parameter in determining the local surface temperature during deposition. Previous experimental work found noticeable microstructural changes with 0.5 mm fused silica wafers in place of silicon during the PETN deposition. This work showed that fused silica slows initial wafer cool down and results in ∼10 °C difference for the surface temperature at 500 μm PETN film thickness. It was also found that the deposition surface temperature is insensitive to the cooling power of the copper block due to the copper block's very large heat capacity and thermal conductivity relative to the heat input from the PVD process. Future work should incorporate the addition of local stress during PETN deposition. Based on simulation results, it is also recommended to investigate the impact of wafer surface energy on the PETN microstructure and morphology formation.
Here, this paper focuses on scheduling antennas to track satellites using a novel heuristic method. The objectives pursued in developing a schedule are two-fold: (1) minimize the priority weighted number of time periods that satellites are not tracked; and (2) equalize the percent of time each satellite is uncovered. The heuristic method is a population-based local search tailored to the unique characteristics of this problem. In order to validate the performance of the heuristic, bounds are developed using Lagrangian relaxation. The heuristic method and the bounds are applied to several test problems. In all cases, the heuristic identifies a solution that is better than the upper bound and is generally quite close (but obviously larger) than the lower bound with about an order of magnitude reduction in computation time. Lastly, a comparison with CPLEX 12.7 is provided.
Nanocrystalline materials have been proposed as superior radiation tolerant materials in comparison to coarse grain counterparts. However, there is still a limited understanding whether a particular nanocrystalline grain size is required to obtain significant improvements in key deleterious effects resulting from energetic irradiation. This work employs the use of in-situ heavy ion irradiation transmission electron microscopy experiments coupled with quantitative defect characterization and precession electron diffraction to explore the sensitivity of defect size and density within the nanocrystalline regime in platinum. Under the explored experimental conditions, no significant change in either the defect size or density between grain sizes of 20 and 100 nm was observed. Furthermore, the in-situ transmission electron microscopy irradiations illustrate stable sessile defect clusters of 1-3 nm adjacent to most grain boundaries, which are traditionally treated as strong defect sinks. The stability of these sessile defects observed in-situ in small, 20-40 nm, grains is the proposed primary mechanism for a lack of defect density trends. This scaling breakdown in radiation improvement with decreasing grain size has practical importance on nanoscale grain boundary engineering approaches for proposed radiation tolerant alloys.
In previous studies, we found that the nitroplasticizer in the HMX-based explosive PBX 9501 played a crucial role in cookoff, especially when predicting response in larger systems. We have recently completed experiments with a similar explosive, LX-14, that has a relatively nonreactive binder. We expected the ignition times for LX-14 to be longer than PBX 9501 since PBX 9501 has a more reactive binder. However, our experiments show the opposite trend. This paradox can be explained by retention of reactive gases within the interior of LX-14 by the higher strength binder resulting in faster ignition times. In contrast, the binder in PBX 9501 melts at low temperatures and does not retain decomposition gases as well as the LX- 14 binder. Retention of reactive gases in LX-14 may also explain the more violent response in oblique impact tests when compared to PBX 9501.
This paper examines the variability of predicted responses when multiple stress-strain curves (reflecting variability from replicate material tests) are propagated through a finite element model of a ductile steel can being slowly crushed. Over 140 response quantities of interest (including displacements, stresses, strains, and calculated measures of material damage) are tracked in the simulations. Each response quantity’s behavior varies according to the particular stress-strain curves used for the materials in the model. We desire to estimate response variability when only a few stress-strain curve samples are available from material testing. Propagation of just a few samples will usually result in significantly underestimated response uncertainty relative to propagation of a much larger population that adequately samples the presiding random-function source. A simple classical statistical method, Tolerance Intervals, is tested for effectively treating sparse stress-strain curve data. The method is found to perform well on the highly nonlinear input-to-output response mappings and non-standard response distributions in the can-crush problem. The results and discussion in this paper support a proposition that the method will apply similarly well for other sparsely sampled random variable or function data, whether from experiments or models. Finally, the simple Tolerance Interval method is also demonstrated to be very economical.
We show that Sb substitution for As in a MBE grown InAs/InAsSb strained layer superlattice (SLS) is accompanied by significant strain fluctuations. The SLS was observed using scanning transmission electron microscopy along the [100] zone axis where the cation and anion atomic columns are separately resolved. Strain analysis based on atomic column positions reveals asymmetrical transitions in the strain profile across the SLS interfaces. The averaged strain profile is quantitatively fitted to the segregation model, which yields a distribution of Sb in agreement with the scanning tunneling microscopy result. The subtraction of the calculated strain reveals an increase in strain fluctuations with the Sb concentration, as well as isolated regions with large strain deviations extending spatially over ∼1 nm, which suggest the presence of point defects.
Krishnamoorthy, Siddharth; Komjathy, Attila; Pauken, Michael T.; Cutts, James A.; Garcia, Raphael F.; Mimoun, David; Cadu, Alexandre; Sournac, Anthony; Jackson, Jennifer M.; Lai, Voon H.; Bowman, Daniel B.
We conducted an experiment in Pahrump, Nevada, in June 2017, where artificial seismic signals were created using a seismic hammer, and the possibility of detecting them from their acoustic signature was examined. In this work, we analyze the pressure signals recorded by highly sensitive barometers deployed on the ground and on tethers suspended from balloons. Our signal processing results show that wind noise experienced by a barometer on a free-flying balloon is lower compared to one on a moored balloon. This has never been experimentally demonstrated in the lower troposphere. While seismoacoustic signals were not recorded on the hot air balloon platform owing to operational challenges, we demonstrate the detection of seismoacoustic signals on our moored balloon platform. Our results have important implications for performing seismology in harsh surface environments such as Venus through atmospheric remote sensing.
The evolution and characterization of single-isolated-ion-strikes are investigated by combining atomistic simulations with selected-area electron diffraction (SAED) patterns generated from these simulations. Five molecular dynamics simulations are performed for a single 20 keV primary knock-on atom in bulk crystalline Si. The resulting cascade damage is characterized in two complementary ways. First, the individual cascade events are conventionally quantified through the evolution of the number of defects and the atomic (volumetric) strain associated with these defect structures. These results show that (i) the radiation damage produced is consistent with the Norgett, Robinson, and Torrens model of damage production and (ii) there is a net positive volumetric strain associated with the cascade structures. Second, virtual SAED patterns are generated for the resulting cascade-damaged structures along several zone axes. The analysis of the corresponding diffraction patterns shows the SAED spots approximately doubling in size, on average, due to broadening induced by the defect structures. Furthermore, the SAED spots are observed to exhibit an average radial outward shift between 0.33% and 0.87% depending on the zone axis. This characterization approach, as utilized here, is a preliminary investigation in developing methodologies and opportunities to link experimental observations with atomistic simulations to elucidate microstructural damage states.
A method for creating nanoparticles directly from bulk metal by applying ultrasound to the surface in the presence of a two-part surfactant system is presented. Implosive collapse of cavitation bubbles near the bulk metal surface generates powerful microjets, leading to material ejection. This liberated material is captured and stabilized by a surfactant bilayer in the form of nanoparticles. The method is characterized in detail using gold, but is also demonstrated on other metals and alloys, and is generally applicable. It is shown that nanoparticles can be produced regardless of the bulk metal form factor, and the method is extended to an environmentally important problem, the reclamation of gold from an electronic waste stream.
Thermal degradation of polyethylene is studied under the extremely high rate temperature ramps expected in laser-driven and X-ray ablation experiments - from 1010 to 1014 K/s in isochoric, condensed phases. The molecular evolution and macroscopic state variables are extracted as a function of density from reactive molecular dynamics simulations using the ReaxFF potential. The enthalpy, dissociation onset temperature, bond evolution, and observed cross-linking are shown to be rate dependent. These results are used to parametrize a kinetic rate model for the decomposition and coalescence of hydrocarbons as a function of temperature, temperature ramp rate, and density. The results are contrasted to first-order random-scission macrokinetic models often assumed for pyrolysis of linear polyethylene under ambient conditions.
Here, this study describes the evolving state of electrolyte and corrosion processes associated with sodium chloride on copper at the initial stage of corrosion and the critical implications of this behavior on controlling kinetics and damage distributions. Sodium chloride droplets were placed on copper in humid conditions and the resulting electrolyte properties, corrosion products and damage were characterized over time using time-lapse imaging, micro Raman spectroscopy, TOF-SIMS and optical profilometry. Within minutes of NaCl droplet placement, NaOH-rich films resultant from oxygen reduction advanced stepwise from the droplets, leaving behind concentric trenching attack patterns suggestive of moving anode-cathode pairs at the alkaline film front. Corrosion attack under these spreading alkaline films was up to 10x greater than under the original NaCl drops. Furthermore, solid Cu2Cl(OH)3 shells formed over the surface of the NaCl drops within hours of exposure. Thermodynamic modeling along with immersed electrochemical experiments in simulated droplet and films electrolytes were used to rationalize this behavior and build a description of the rapidly evolving corroding system.
Major advances in thin-film solid-state batteries (TFSSBs) may capitalize on 3D structuring using high-aspect-ratio substrates such as nanoscale pits, pores, trenches, flexible polymers, and textiles. This will require conformal processes such as atomic layer deposition (ALD) for every active functional component of the battery. Here we explore the deposition and electrochemical properties of SnO2, SnNy, and SnOxNy thin films as TFSSB anode materials, grown by ALD using tetrakisdimethylamido(tin), H2O, and N2 plasma as precursors. By controlling the dose ratio between H2O and N2, the N-O fraction can be tuned between 0% N and 95% N. The electrochemical properties of these materials were tested across a composition range varying from pure SnO2, to SnON intermediates, and pure SnNy. In TFSSBs, the SnNy anodes are found to be more stable during cycling than the SnO2 or SnOxNy films, with an initial reversible capacity beyond that of Li-Sn alloying, retaining 75% of their capacity over 200 cycles compared to only 50% for SnO2. Furthermore, the performance of the SnOxNy anodes indicates that SnNy anodes should not be negatively impacted by small levels of O contamination.
The use of nanoparticles as a potential building block for photosensitizers has recently become a focus of interest in the field of photocatalysis and photodynamic therapy. Porphyrins and their derivatives are effective photosensitizers due to extended π-conjugated electronic structure, high molar absorption from visible to near-infrared spectrum, and high singlet oxygen quantum yields as well as chemical versatility. In this paper, we report a synthesis of self-assembled porphyrin nanoparticle photosensitizers using zinc meso-tetra(4-pyridyl)porphyrin (ZnTPyP) through a confined noncovalent self-assembly process. Scanning electron microscopy reveals formation of monodisperse cubic nanoparticles. UV-vis characterizations reveal that optical absorption of the nanoparticles exhibits a red shift due to noncovalent self-assembly of porphyrins, which not only effectively increase intensity of light absorption but also extend light absorption broadly covering visible light for enhanced photodynamic therapy. Electron spin-resonance spectroscopy (ESR) studies show the resultant porphyrin nanoparticles release a high yield of singlet oxygen. Nitric oxide (NO) coordinates to central metal Zn ions to form stabilized ZnTPyP@NO nanoparticles. We show that under light irradiation ZnTPyP@NO nanoparticles release highly reactive peroxynitrite molecules that exhibit enhanced antibacterial photodynamic therapy (APDT) activity. The ease of the synthesis of self-assembled porphyrin nanoparticles and light-triggered release of highly reactive moieties represent a completely different photosensitizer system for APDT application.
Loop-mediated isothermal amplification (LAMP), coupled with reverse transcription (RT), has become a popular technique for detection of viral RNA due to several desirable characteristics for use in point-of-care or low-resource settings. The large number of primers in LAMP (six per target) leads to an increased likelihood of primer dimer interactions, and the inner primers in particular are prone to formation of stable hairpin structures due to their length (typically 40-45 bases). Although primer dimers and hairpin structures are known features to avoid in nucleic acid amplification techniques, there is little quantitative information in literature regarding the impact of these structures on LAMP or RT-LAMP assays. In this study, we examine the impact of primer dimers and hairpins on previously published primer sets for dengue virus and yellow fever virus. We demonstrate that minor changes to the primers to eliminate amplifiable primer dimers and hairpins improves the performance of the assays when monitored in real time with intercalating dyes, and when monitoring a fluorescent endpoint using the QUASR technique. We also discuss the thermodynamic implications of these minor changes on the overall stability of amplifiable secondary structures, and we present a single thermodynamic parameter that can be correlated to the probability of non-specific amplification associated with LAMP primers.
Here, we describe a combined proximity, contact and force (PCF) sensor based on a commodity infrared distance sensor embedded in a transparent elastomer with applications in robotic manipulation. Prior to contact, the sensor works as a distance sensor, whereas after contact the elastomer magnifies the near field of the proximity sensors letting the sensor interpret the indentation on elastomer as force. Contact occurs at the transition of proximity and force. We describe in detail the sensor design, its principle of operation and experimentally characterize the design parameters including polymer thickness, its mixing ratio, and emitter current of the infrared sensor. We also show that the sensor response has an inflection point at contact that is independent of an object’s surface properties, making it a robust detector for contact events. We finally demonstrate a series of use cases for the proposed PCF sensor, including (1) improving pre-grasp alignment, (2) determining contact event with objects, (3) obtaining simple 3D point cloud models of objects using both proximity and contact, and (4) registering self-generated point clouds to those from a RGB-D camera using a Baxter robot and Kinova Jaco arm.
There are currently 2,462 dual-purpose canisters (DPCs) containing spent nuclear fuel (SNF) across the United States. Repackaging DPCs into specialized disposal canisters can be financially and operationally costly with undue risks. Technical feasibility of direct disposal of DPCs has been evaluated by the Department of Energy (DOE) and industry over the past 15 years. A concerted effort most recently conducted by DOE Office of Nuclear Energy (NE) Spent Fuel and Waste Science and Technology (SFWST) research and development (R&D) programs is evaluating the technical feasibility of direct disposal of DPCs in various geologies. This report focuses on reviewing the work completed by SFWST for the criticality considerations of DPC geologic disposal. Disposal of DPCs is not only viable, but assured from a technical and assumed regulatory perspective (similar to 10 CFR 63). The analysis approach should be multi-faceted to ensure effective implementation of a licensing basis. Recommendations are provided in this report that could enhance the bases for direct disposal of DPCs by exploiting all technically attainable and regulatorily defensible options. The review objectives, including addressing several questions regarding the value of accumulating asloaded fuel and DPC design data, suitability of DPC designs for disposal, and reasonable modifications for loading of DPCs that could facilitate eventual disposal, are also addressed in this report.
In this study, solubility measurements regarding boracite [Mg3B7O13Cl(cr)] and aksaite [MgB6O7(OH)6·2H2O(cr)] from the direction of supersaturation were conducted at 22.5 ± 0.5 °C. The equilibrium constant (log10K0) for boracite in terms of the following reaction, Mg3B7O13Clcr+15H2Ol⇌3Mg2++7BOH4 −+Cl−+2H+ is determined as −29.49 ± 0.39 (2σ) in this study. The equilibrium constant for aksaite according to the following reaction, MgB6O7OH6·2H2Ocr+9H2Ol⇌Mg2++6BOH4 −+4H+ is determined as −44.41 ± 0.41 (2σ) in this work. This work recommends a set of thermodynamic properties for aksaite at 25 °C and 1 bar as follows: ΔHf 0 = −6063.70 ± 4.85 kJ·mol−1, ΔGf 0 = −5492.55 ± 2.32 kJ·mol−1, and S0 = 344.62 ± 1.85 J·mol−1·K−1. Among them, ΔGf 0 is derived from the equilibrium constant for aksaite determined by this study; ΔHf 0 is from the literature, determined by calorimetry; and S0 is computed in the present work from ΔGf 0 and ΔHf 0. This investigation also recommends a set of thermodynamic properties for boracite at 25 °C and 1 bar as follows: ΔHf 0 = −6575.02 ± 2.25 kJ·mol−1, ΔGf 0 = −6178.35 ± 2.25 kJ·mol−1, and S0 = 253.6 ± 0.5 J·mol−1·K−1. Among them, ΔGf 0 is derived from the equilibrium constant for boracite determined by this study; S0 is from the literature, determined by calorimetry; and ΔHf 0 is computed in this work from ΔGf 0 and S0. The thermodynamic properties determined in this study can find applications in many fields. For instance, in the field of material science, boracite has many useful properties including ferroelectric and ferroelastic properties. The equilibrium constant of boracite determined in this work will provide guidance for economic synthesis of boracite in an aqueous medium. Similarly, in the field of nuclear waste management, iodide boracite [Mg3B7O13I(cr)] is proposed as a waste form for radioactive 129I. Therefore, the solubility constant for chloride boracite [Mg3B7O13Cl(cr)] will provide the guidance for the performance of iodide boracite in geological repositories. Boracite/aksaite themselves in geological repositories in salt formations may be solubility-controlling phase(s) for borate. Consequently, solubility constants of boracite and aksaite will enable researchers to predict borate concentrations in equilibrium with boracite/aksaite in salt formations.
At present, there are many methods to identify the temperature and phase of a material using invasive techniques. However, most current methods require physical contact or implicit methods utilizing light reflectance of the specimen. This work presents a nondestructive inspection method using ultrasonic wave technology that circumvents these disadvantages to identify phase change regions and infer the temperature state of a material. In the present study an experiment is performed to monitor the time of flight within a wax as it undergoes melting and the subsequent cooling. Results presented in this work show a clear relationship between a material's speed of sound and its temperature. The phase change transition of the material is clear from the time of flight results, and in the case of the investigated material, this change in the material state occurs over a range of temperatures. The range of temperatures over which the wax material melts is readily identified by speed of sound represented as a function of material temperature. The melt temperature, obtained acoustically, is validated using Differential Scanning Calorimetry (DSC), which uses shifts in heat flow rates to identify phase transition temperature ranges. The investigated ultrasonic NDE method has direct applications in many industries, including oil and gas, food and beverage, and polymer composites, in addition to many implications for future capabilities of nondestructive inspection of multi-phase materials.
Ultrasound techniques are capable of monitoring changes in the time-of-flight as a material is exposed to different thermal environments. The focus of the present study is to identify the phase of a material via ultrasound compression wave measurements in a through transmission experimental setup as the material is heated from a solid to a liquid and then allowed to re-solidify. The present work seeks to expand upon the authors' previous research, which proved this through transmission phase monitoring technique was possible, by considering different experimental geometries. The relationship between geometry, the measured speed of sound, and the temperature profile is presented. The use of different volumes helps in establishing a baseline understanding of which aspects of the experiment are geometry dependent and which are independent. The present study also investigates the relationship between the heating rate observed in the experiment and the measured speed of sound. The trends identified between the experimental geometry, heat rate and ultrasound wave speed measurement assist in providing a baseline understanding of the applicability of this technique to various industries, including the polymer industry and the oil industry.
The nature of microhydration in sulfonated Diels-Alder poly(phenylene) (SDAPP) polymer membranes is explored using ab initio and density functional theory (DFT) electronic structure calculations. The impact of the aromatic poly(phenylene) structure, including cooperative effects between multiple spatially adjacent sulfonic groups, on the hydration environment is addressed using a series of DFT B3LYP/6-311∗∗-optimized structures for different SDAPP·nH2O clusters. In addition, larger SDAPP polymer fragments, along with selected hydrophilic domain structures extracted from molecular dynamic (MD) simulations, are also evaluated using ONIOM HF/PM6 semiempirical calculations. The SDAPP clusters reveal that spontaneous proton dissociation occurs at low levels of hydration to form sulfonic-acid-associated H3O+ contact ion pairs (CIPs), which then evolve into solvated CIPs at higher hydration levels. For multiple sulfonic acid groups located on the poly(phenylene) side chains, the hydration energies are a function of the relative acid location and backbone configuration. Variations in the phenylene backbone torsional angles allow remote sulfonic acids to adopt an optimal separation to produce an extended hydrogen bonded network of waters between the SDAPP acids groups. These calculations provide a baseline to help describe the proton transport and hydration behavior of SDAPP membranes.
Here, energy-transport effects can alter the structure that develops as a supernova evolves into a supernova remnant. The Rayleigh–Taylor instability is thought to produce structure at the interface between the stellar ejecta and the circumstellar matter, based on simple models and hydrodynamic simulations. Here we report experimental results from the National Ignition Facility to explore how large energy fluxes, which are present in supernovae, affect this structure. We observed a reduction in Rayleigh–Taylor growth. In analyzing the comparison with supernova SN1993J, a Type II supernova, we found that the energy fluxes produced by heat conduction appear to be larger than the radiative energy fluxes, and large enough to have dramatic consequences. No reported astrophysical simulations have included radiation and heat conduction self-consistently in modeling supernova remnants and these dynamics should be noted in the understanding of young supernova remnants.
Kim, Jeongnim; Baczewski, Andrew D.; Beaudet, Todd D.; Benali, Anouar; Bennett, Michael B.; Berrill, Mark A.; Blunt, Nick S.; Casula, Michele; Ceperley, David M.; Chiesa, Simone; Clark, Bryan K.; Clay III, Raymond C.; Delaney, Kris T.; Dewing, Mark; Esler, Kenneth P.; Hao, Hongxia; Hein, Olle; Kent, Paul R.C.; Krogel, Jaron T.; Kylanpaa, Ilkka; Li, Ying W.; Lopez, M.G.; Luo, Ye; Martin, Richard M.; Mathuriya, Amrita; Mcminis, Jeremy; Melton, Cody A.; Mitas, Lubos; Neuscamman, Eric; Parker, William D.; Pineda Flores, Sergio D.; Romero, Nichols A.; Rubenstein, Brenda M.; Shea, Jacqueline A.R.; Shin, Hyeondeok; Shulenburger, Luke N.; Tillack, Andreas F.; Townsend, Joshua P.; Tubman, Norm M.; Van Der Goetz, Brett; Vincent, Jordan E.; Yang, Yubo; Zhang, Shuai; Morales, Miguel A.; Zhao, Luning
QMCPACK is an open source quantum Monte Carlo package for ab-initio electronic structure calculations. It supports calculations of metallic and insulating solids, molecules, atoms, and some model Hamiltonians. Implemented real space quantum Monte Carlo algorithms include variational, diffusion, and reptation Monte Carlo. QMCPACK uses Slater-Jastrow type trial wave functions in conjunction with a sophisticated optimizer capable of optimizing tens of thousands of parameters. The orbital space auxiliary field quantum Monte Carlo method is also implemented, enabling cross validation between different highly accurate methods. The code is specifically optimized for calculations with large numbers of electrons on the latest high performance computing architectures, including multicore central processing unit (CPU) and graphical processing unit (GPU) systems. We detail the program’s capabilities, outline its structure, and give examples of its use in current research calculations. The package is available at http://www.qmcpack.org.
We report that a critical component of the magnetically driven implosion experiments at Sandia National Laboratories is the delivery of high-current, 10s of MA, from the Z pulsed power facility to a target. In order to assess the performance of the experiment, it is necessary to measure the current delivered to the target. Recent Magnetized Liner Inertial Fusion (MagLIF) experiments have included velocimetry diagnostics, such as PDV (Photonic Doppler Velocimetry) or Velocity Interferometer System for Any Reflector, in the final power feed section in order to infer the load current as a function of time. However, due to the nonlinear volumetrically distributed magnetic force within a velocimetry flyer, a complete time-dependent load current unfold is typically a time-intensive process and the uncertainties in the unfold can be difficult to assess. In this paper, we discuss how a PDV diagnostic can be simplified to obtain a peak current by sufficiently increasing the thickness of the flyer. This effectively keeps the magnetic force localized to the flyer surface, resulting in fast and highly accurate measurements of the peak load current. Additionally, we show the results of experimental peak load current measurements from the PDV diagnostic in recent MagLIF experiments.
Irradiation induced creep (IIC) rates are measured in compression on Ag nanopillar (square) beams in the sink-limited regime. The IIC rate increases linearly with stress at lower stresses, i.e. below ≈2/3 the high temperature yield stress and parabolically with pillar width, L, for L less than ≈300 nm. The data are obtained by combining in situ transmission electron imaging with simultaneous ion irradiation, laser heating, and nanopillar compression. Results in the larger width regime are consistent with prior literature.
A discrete De Rham complex enables compatible, structure-preserving discretizations for a broad range of partial differential equations problems. Such discretizations can correctly reproduce the physics of interface problems, provided the grid conforms to the interface. However, large deformations, complex geometries, and evolving interfaces makes generation of such grids difficult. We develop and demonstrate two formally equivalent approaches that, for a given background mesh, dynamically construct an interface-conforming discrete De Rham complex. Both approaches start by dividing cut elements into interface-conforming subelements but differ in how they build the finite element basis on these subelements. The first approach discards the existing non-conforming basis of the parent element and replaces it by a dynamic set of degrees of freedom of the same kind. The second approach defines the interface-conforming degrees of freedom on the subelements as superpositions of the basis functions of the parent element. These approaches generalize the Conformal Decomposition Finite Element Method (CDFEM) and the extended finite element method with algebraic constraints (XFEM-AC), respectively, across the De Rham complex.
A hybrid, design-order sliding mesh algorithm, which uses a control volume finite element method (CVFEM), in conjunction with a discontinuous Galerkin (DG) approach at non-conformal interfaces, is outlined in the context of a low-Mach fluid dynamics equation set. This novel hybrid DG approach is also demonstrated to be compatible with a classic edge-based vertex centered (EBVC) scheme. For the CVFEM, element polynomial, P, promotion is used to extend the low-order P=1 CVFEM method to higher-order, i.e., P=2. An equal-order low-Mach pressure-stabilized methodology, with emphasis on the non-conformal interface boundary condition, is presented. A fully implicit matrix solver approach that accounts for the full stencil connectivity across the non-conformal interface is employed. A complete suite of formal verification studies using the method of manufactured solutions (MMS) is performed to verify the order of accuracy of the underlying methodology. The chosen suite of analytical verification cases range from a simple steady diffusion system to a traveling viscous vortex across mixed-order non-conformal interfaces. Results from all verification studies demonstrate either second- or third-order spatial accuracy and, for transient solutions, second-order temporal accuracy. Significant accuracy gains in manufactured solution error norms are noted even with modest promotion of the underlying polynomial order. The paper also demonstrates the CVFEM/DG methodology on two production-like simulation cases that include an inner block subjected to solid rotation, i.e., each of the simulations include a sliding mesh, non-conformal interface. The first production case presented is a turbulent flow past a high-rate-of-rotation cube (Re, 4000; RPM, 3600) on like and mixed-order polynomial interfaces. The final simulation case is a full-scale Vestas V27 225 kW wind turbine (tower and nacelle omitted) in which a hybrid topology, low-order mesh is used. Both production simulations provide confidence in the underlying capability and demonstrate the viability of this hybrid method for deployment towards high-fidelity wind energy validation and analysis.
A diffusion-limited reaction model was calibrated for Al/Pt multilayers ignited on oxidized silicon, sapphire, and tungsten substrates, as well as for some Al/Pt multilayers ignited as free-standing foils. The model was implemented in a finite element analysis code and used to match experimental burn front velocity data collected from several years of testing at Sandia National Laboratories. Moreover, both the simulations and experiments reveal well-defined quench limits in the total Al + Pt layer (i.e., bilayer) thickness. At these limits, the heat generated from atomic diffusion is insufficient to support a self-propagating wave front on top of the substrates. Quench limits for reactive multilayers are seldom reported and are found to depend on the thermal properties of the individual layers. Here, the diffusion-limited reaction model is generalized to allow for temperature- and composition-dependent material properties, phase change, and anisotropic thermal conductivity. Utilizing this increase in model fidelity, excellent overall agreement is shown between the simulations and experimental results with a single calibrated parameter set. However, the burn front velocities of Al/Pt multilayers ignited on tungsten substrates are over-predicted. Possible sources of error are discussed and a higher activation energy (from 41.9 kJ/mol.at. to 47.5 kJ/mol.at.) is shown to bring the simulations into agreement with the velocity data observed on tungsten substrates. This higher activation energy suggests an inhibited diffusion mechanism present at lower heating rates.
Molecular tracers that can be selectively placed underground and uniquely identified at the surface using simple on-site spectroscopic methods would significantly enhance subsurface fluid monitoring capabilities. To ensure their widespread utility, the solubility of these tracers must be easily tuned to oil- or water-wet conditions as well as reducing or eliminating their propensity to adsorb onto subsurface rock and/or mineral phases. In this work, molecular dynamics simulations were used to investigate the relative solubilities and mineral surface adsorption properties of three candidate tracer compounds comprising Mg–salen derivatives of varying degrees of hydrophilic character. Simulations in water–toluene liquid mixtures indicate that the partitioning of each Mg–salen compound relative to the interface is strongly influenced by the degree of hydrophobicity of the compound. Simulations of these complexes in fluid-filled mineral nanopores containing neutral (kaolinite) and negatively charged (montmorillonite) mineral surfaces reveal that adsorption tendencies depend upon a variety of parameters, including tracer chemical properties, mineral surface type, and solvent type (water or toluene). Simulation snapshots and averaged density profiles reveal insight into the solvation and adsorption mechanisms that control the partitioning of these complexes in mixed liquid phases and nanopore environments. As a result, this work demonstrates the utility of molecular simulation in the design and screening of molecular tracers for use in subsurface applications.
JOM. Journal of the Minerals, Metals & Materials Society
Lawrence, Samantha K.; Somerday, Brian P.; Ingraham, Mathew D.; Bahr, David F.
Hydrogen effects on small-volume plasticity and elastic stiffness constants are investigated with nanoindentation of Ni-201 and sonic velocity measurements of bulk Ni single crystals. Elastic modulus of Ni-201, calculated from indentation data, decreases ~22% after hydrogen charging. This substantial decrease is independently confirmed by sonic velocity measurements of Ni single crystals; c44 decreases ~20% after hydrogen exposure. Furthermore, clear hydrogen-deformation interactions are observed. The maximum shear stress required to nucleate dislocations in hydrogen-charged Ni-201 is markedly lower than in as-annealed material, driven by hydrogen-reduced shear modulus. Additionally, a larger number of depth excursions are detected prior to general yielding in hydrogen-charged material, suggesting cross-slip restriction. Together, these data reveal direct correlation between hydrogen-affected elastic properties and plastic deformation in Ni alloys.
The SNL Sierra Mechanics code suite is designed to enable simulation of complex multi-physics scenarios. The code suite is composed of several specialized applications which can operate either in standalone mode or coupled with each other. Arpeggio is a supported utility that enables loose coupling of the various Sierra Mechanics applications by providing access to Framework services that facilitate the coupling. More importantly Arpeggio orchestrates the execution of applications that participate in the coupling. This document describes the various components of Arpeggio and their operability. The intent of the document is to provide a fast path for analysts interested in coupled applications via simple examples of its usage.
Aria is a Galerkin finite element based program for solving coupled-physics problems described by systems of PDEs and is capable of solving nonlinear, implicit, transient and direct-to-steady state problems in two and three dimensions on parallel architectures. The suite of physics currently supported by Aria includes thermal energy transport, species transport, and electrostatics as well as generalized scalar, vector and tensor transport equations. Additionally, Aria includes support for manufacturing process flows via the incompressible Navier-Stokes equations specialized to a low Reynolds number ($Re$ < 1) regime. Enhanced modeling support of manufacturing processing is made possible through use of either arbitrary Lagrangian- Eulerian (ALE) and level set based free and moving boundary tracking in conjunction with quasi-static nonlinear elastic solid mechanics for mesh control. Coupled physics problems are solved in several ways including fully-coupled Newton's method with analytic or numerical sensitivities, fully-coupled Newton-Krylov methods and a loosely-coupled nonlinear iteration about subsets of the system that are solved using combinations of the aforementioned methods. Error estimation, uniform and dynamic $h$-adaptivity and dynamic load balancing are some of Aria's more advanced capabilities.
The SIERRA Low Mach Module: Fuego along with the SIERRA Participating Media Radiation Module: Syrinx, henceforth referred to as Fuego and Syrinx, respectively, are the key elements of the ASCI fire environment simulation project. The fire environment simulation project is directed at characterizing both open large-scale pool fires and building enclosure fires. Fuego represents the turbulent, buoyantly-driven incompressible flow, heat transfer, mass transfer, combustion, soot, and absorption coefficient model portion of the simulation software. Syrinx represents the participating-media thermal radiation mechanics. This project is an integral part of the SIERRA multi-mechanics software development project. Fuego depends heavily upon the core architecture developments provided by SIERRA for massively parallel computing, solution adaptivity, and mechanics coupling on unstructured grids.
SIERRA/Aero is a two and three dimensional, node-centered, edge-based finite volume code that approximates the compressible Navier-Stokes equations on unstructured meshes. It is applicable to inviscid and high Reynolds number laminar and turbulent flows. Currently, two classes of turbulence models are provided: Reynolds Averaged Navier-Stokes (RANS) and hybrid methods such as Detached Eddy Simulation (DES). Large Eddy Simulation (LES) models are currently under development. The gas may be modeled either as ideal, or as a non-equilibrium, chemically reacting mixture of ideal gases. This document describes the mathematical models contained in the code, as well as certain implementation details. First, the governing equations are presented, followed by a description of the spatial discretization. Next, the time discretization is described, and finally the boundary conditions. Throughout the document, SIERRA/ Aero is referred to simply as Aero for brevity.
SIERRA/Aero is a compressible fluid dynamics program intended to solve a wide variety compressible fluid flows including transonic and hypersonic problems. This document describes the commands for assembling a fluid model for analysis with this module, henceforth referred to simply as Aero for brevity. Aero is an application developed using the SIERRA Toolkit (STK). The intent of STK is to provide a set of tools for handling common tasks that programmers encounter when developing a code for numerical simulation. For example, components of STK provide field allocation and management, and parallel input/output of field and mesh data. These services also allow the development of coupled mechanics analysis software for a massively parallel computing environment. In the definitions of the commands that follow, the term Real_Max denotes the largest floating point value that can be represented on a given computer. Int_Max is the largest such integer value.
This document describes the theoretical foundation of thermal analysis in Sierra Mechanics. The SIERRA Multimechanics Module: Aria, henceforth referred to as Aria for brevity, was developed at Sandia National Laboratories under the ASC program, and approximates linear and nonlinear continuum models of heat transfer. Aria uses the SIERRA Framework, which provides data management services commonly required by computational mechanics software, and facilitates the development of coupled, multi-mechanics applications for massively parallel computers. The mathematical models in Aria are based heavily on those of COYOTE, a well-established thermal analysis program that was also developed at Sandia and its ASC code predecessor, Calore. Aria, Calore and COYOTE share a significant body of numerical methods, which are described in detail by Reddy and Gartling. Throughout this document, the terms software and implementation are syn onymous with the Aria thermal-fluid analysis computer program. Whether one uses Aria to perform heat transfer analysis, or in developing a new capability for the Aria application, this document provides the information needed understand the existing numerical algorithm implementations. Justification for the fundamental assumptions of heat transfer, nor derivation of the energy conservation equations are included in this document. For a more thorough theoretical background, one is referred to one of the many available textbooks, e.g. Another reference, which is freely available in downloadable electronic form, is Lienhard and Lienhard.
The SIERRA Low Mach Module: Fuego along with the SIERRA Participating Media Radiation Module: Syrinx, henceforth referred to as Fuego and Syrinx, respectively, are the key elements of the ASC fire environment simulation project. The fire environment simulation project is directed at characterizing both open large-scale pool fires and building enclosure fires. Fuego represents the turbulent, buoyantly-driven incompressible flow, heat transfer, mass transfer, combustion, soot, and absorption coefficient model portion of the simulation software. Syrinx represents the participating-media thermal radiation mechanics. This project is an integral part of the SIERRA multi-mechanics software development project. Fuego depends heavily upon the core architecture developments provided by SIERRA for massively parallel computing, solution adaptivity, and mechanics coupling on unstructured grids.
Building on recent work by Gammelmark et al. [Phys. Rev. Lett. 111, 160401 (2013)10.1103/PhysRevLett.111.160401] we develop a formalism for prediction and retrodiction of Gaussian quantum systems undergoing continuous measurements. We apply the resulting formalism to study the advantage of incorporating a full measurement record and retrodiction for impulselike force detection and accelerometry. We find that using retrodiction can only increase accuracy in a limited parameter regime, but that the reduction in estimation noise that it yields results in better detection of impulselike forces.
A team of experts from Sandia National Laboratories (SNL) and Pacific Northwest National Laboratory (PNNL) partnered to revise the International Atomic Energy Agency's (IAEA) Training Course on Physical Protection of Nuclear Materials and Facilities. This two-week course is a modified version of the three-week International Training Course (ITC) that is delivered on location at SNL. The last significant update to the IAEA Regional Training Course (RTC) RTC material was about 10 years ago. Prior revision efforts for two of the IAEA Materials and Facilities (MAFA) section courses, which were each one week in length, consisted of five consultancy meetings each with US DOE/NNSA personnel and international experts and held in Vienna, Austria. The level of effort anticipated to revise a two-week course was expected to double these previous efforts, which prompted development of an alternative approach to the revision process. The goal of the revision of the two-week course, labeled the RTC, was focused on the capability for delivery at any appropriate international location, most likely regionally by the IAEA.
Photonic integrated circuits provide a compact and stable platform for quantum photonics. Here we demonstrate a silicon photonics quantum key distribution (QKD) encoder in the first high-speed polarization-based QKD field tests. The systems reach composable secret key rates of 1.039 Mbps in a local test (on a 103.6-m fiber with a total emulated loss of 9.2 dB) and 157 kbps in an intercity metropolitan test (on a 43-km fiber with 16.4 dB loss). Our results represent the highest secret key generation rate for polarization-based QKD experiments at a standard telecom wavelength and demonstrate photonic integrated circuits as a promising, scalable resource for future formation of metropolitan quantum-secure communications networks.
Espinoza, D.N.; Jung, Hojung; Major, Jonathan R.; Sun, Zhuang; Ramos, Matthew J.; Eichhubl, Peter; Balhoff, Matthew T.; Choens, Robert C.; Dewers, Thomas D.
CO2 geological storage in saline aquifers results in acidification of resident brine. Chemical reactions between acidified brine and rock minerals lead to dissolution and precipitation of minerals at various time scales. Mineral dissolution and precipitation are often neglected in assessing the mechanical integrity of target storage formations, yet, changes in rock strength and deformational behavior can impact trapping mechanisms. This paper shows the impact of exposure to CO2-charged brine on shear strength and stiffness of various outcrop rocks evaluated through triaxial testing. The tested rocks were exposed to CO2-charged brine over geological time at a naturally occurring near-surface seepage along the Little Grand Wash Fault and Salt Wash Grabens, which include the Crystal Geyser site near the town of Green River, Utah. Prior work suggests that this site provides a near-surface structural analog for possible fault-controlled CO2 leakage over time scales that exceed expected injection time scales (10–100 years). Results show mechanical alteration in various aspects: (1) CO2-charged brine alteration at near-surface conditions results in mineral dissolution/precipitation and reduction of shear strength and brittleness of Entrada sandstone and Summerville siltstone samples, and (2) carbonate precipitation in fractured Mancos shale leads to matrix stiffening and fracture mineralization resulting in overall stiffer and likely tighter shale. Additional discrete element simulations coupled with a bonded-particle-model confirm the role of cement bond size alteration as one of the main controls for rock chemo-mechanical alteration in sandstones. The chemo-mechanical alteration path that mimics cement dissolution (under stressed subsurface conditions) results in vertical compaction and lateral stress relaxation. Overall, results show that rock exposure to CO2-charged brine can impart distinct petrophysical and geomechanical changes according to rock lithology and location with respect to major CO2 conduits. Finally, while mineral dissolution in the storage rock may result in undesired reservoir strains and changes of stresses, mineral precipitation downstream from a leakage path can help seal potentially induced fractures.
In light-duty direct-injection (DI) diesel engines, combustion chamber geometry influences the complex interactions between swirl and squish flows, spray-wall interactions, as well as late-cycle mixing. Because of these interactions, piston bowl geometry significantly affects fuel efficiency and emissions behavior. However, due to lack of reliable in-cylinder measurements, the mechanisms responsible for piston-induced changes in engine behavior are not well understood. Non-intrusive, in situ optical measurement techniques are necessary to provide a deeper understanding of the piston geometry effect on in-cylinder processes and to assist in the development of predictive engine simulation models. This study compares two substantially different piston bowls with geometries representative of existing technology: a conventional re-entrant bowl and a stepped-lip bowl. Both pistons are tested in a single-cylinder optical diesel engine under identical boundary conditions. Utilizing high-speed soot natural luminosity (NL) imaging, 20 kHz time-resolved combustion image velocimetry (CIV) technique is developed to quantify the macro-scale motions of soot clouds during the mixing-controlled portion of combustion. Under a part-load conventional combustion regime, CIV-resolved swirl ratio and the tumble-plane projection of velocity fields confirm that the injection-induced redistribution of angular momentum, rather than squish/reverse squish flow, is a dominant source for swirl amplification between two piston geometries. A strong connection has been found between the CIV-resolved combusting flow structure and its succeeding enhanced late-stage burn rate. With SOI main shortly after TDC, combustion in stepped-lip piston exhibits shorter late-burn duration (CA50-CA90) and faster burn rate compared to re-entrant piston. In the same boundary condition, a unique combusting flow structure is observed with CIV in the stepped-lip piston: a long-lasting flow structure with opposing radial velocity directions between the squish region and stepped-lip region. Interestingly, this flow structure is never optically observed with the re-entrant piston. The best hypothesis is that there exists a long-lasting vertical toroidal vortex on the shoulder of stepped-lip piston crown near CA50. A phenomenological model is proposed to provide a partial, but valuable picture of late-stage combusting flow structure which is a key to understand how piston bowl geometry can influence thermal efficiency for swirl-supported diesel engines.
Two radar towers at the Tonopah Test Range (TTR), Contraves Towers 22-00 and 12-00, were torn down prior to completion of the required National Environmental Policy Act (NEPA) process. National Technology and Engineering Solutions of Sandia, LLC, (NTESS) submission of the NEPA checklist triggered a Sandia Field Office (SFO) review of the proposed work scope and was to include a required consultation between SFO and the Nevada State Historic Preservation Office (SHPO) to assess any adverse effect(s) on historic properties or contributing element(s) to a historic district and, if so, determine a resolution. Following the consultation, SFO provides approval/denial of the proposed work detailed on the submitted NEPA checklist. Contraves Tower 22-00 is a historic structure, as formally determined by the SFO in consultation with the SHPO. The historical eligibility of Contraves Tower 12-00 is yet to be determined. On February 13, 2018, NTESS notified SFO that Contraves Tower 22-00 at TTR was torn down in May 2017 prior to completion of the required the NEPA process, including consultation with the SHPO. NTESS submitted two NEPA checklists to SFO in 2016 for the removal of several structures no longer required by NTESS. The first NEPA checklist listed three historic structures (one of which was Contraves Tower 22-00) and SFO determination on whether consultation with the SHPO is necessary as well as approval/denial of the NEPA checklist is pending. The second NEPA checklist listed five non-historic structures, one of which was Contraves Tower 12-00. SFO approved the NEPA checklist covering non historic structures except for the Contraves Tower 12-00, as the Contraves Tower 12-00 requires further consultation with the SHPO by SFO. Only after completion of the consultation would SFO determine approval/denial on the remaining property cited within the NEPA checklist. In late January 2018, NTESS personnel discovered that Contraves Tower 22-00 was no longer listed in the Facility Information Management System (FIMS). Upon further investigation, NTESS personnel verified that the Contraves Tower 22-00 had been removed in May 2017. During the initial extent of condition, it was discovered that Contraves Tower 12-00 had also been torn down in May 2017 as part of this same destruction and demolition (D&D) activity. Both Contraves Towers 22-00 and 12-00) had been torn down prior to completion of the NEPA process, including consultation with the SHPO.
Architectures with multiple classes of memory media are becoming a common part of mainstream supercomputer deployments. So called multi-level memories offer differing characteristics for each memory component including variation in bandwidth, latency and capacity. This paper investigates the performance of sparse matrix multiplication kernels on two leading highperformance computing architectures — Intel's Knights Landing processor and NVIDIA's Pascal GPU. We describe a data placement method and a chunking-based algorithm for our kernels that exploits the existence of the multiple memory spaces in each hardware platform. We evaluate the performance of these methods w.r.t. standard algorithms using the auto-caching mechanisms Our results show that standard algorithms that exploit cache reuse performed as well as multi-memory-aware algorithms for architectures such as Ki\iLs where the memory subsystems have similar latencies. However, for architectures such as GPUS where memory subsystems differ significantly in both bandwidth and latency, multi-memory-aware methods are crucial for good performance. In addition, our new approaches permit the user to run problems that require larger capacities than the fastest memory of each compute node without depending on the software-managed cache mechanisms.
We experimentally demonstrated an actively tunable optical filter that controls the amplitude of reflected long-wave-infrared light in two separate spectral regions concurrently. Our device exploits the dependence of the excitation energy of plasmons in a continuous and unpatterned sheet of graphene on the Fermi-level, which can be controlled via conventional electrostatic gating. The filter enables simultaneous modification of two distinct spectral bands whose positions are dictated by the device geometry and graphene plasmon dispersion. Within these bands, the reflected amplitude can be varied by over 15% and resonance positions can be shifted by over 90 cm-1. Electromagnetic simulations verify that tuning arises through coupling of incident light to graphene plasmons by a grating structure. Importantly, the tunable range is determined by a combination of graphene properties, device structure, and the surrounding dielectrics, which dictate the plasmon dispersion. Thus, the underlying design shown here isapplicable across a broad range of infrared frequencies.
In this work, a solubility study on brucite [Mg(OH)2(cr)] in Na2SO4 solutions ranging from 0.01 to 1.8 mol·kg−1, with 0.001 mol·kg−1 borate, has been conducted at 22.5 °C. Based on the solubility data, the Pitzer interaction parameters for MgB(OH)4 + − SO4 2− and MgB(OH)4 + − Na+ along with the formation constant for MgSO4(aq) are evaluated using the Pitzer model. The formation constant (log10β10 = 2.38 ± 0.08) for MgSO4(aq) at 25 °C and infinite dilution obtained in this study is in excellent agreement with the literature values. The experimental data on the solubility of gypsum (CaSO4·2H2O), at 25 °C, in aqueous solutions of MgSO4 with ionic strengths up to ~ 11 mol·kg−1 were analyzed using models with and without considering the MgSO4(aq) species. The model incorporating MgSO4(aq) fits better to the experimental data than the model without MgSO4(aq), especially in the ionic strength range beyond ~ 4 mol·kg−1, demonstrating the need for incorporation of MgSO4(aq) into the model to improve the accuracy.
In the presence of accelerated fault rates, which are projected to be the norm on future exascale systems, it will become increasingly difficult for high-performance computing (HPC) applications to accomplish useful computation. Due to the fault-oblivious nature of current HPC programming paradigms and execution environments, HPC applications are insufficiently equipped to deal with errors. We believe that HPC applications should be enabled with capabilities to actively search for and correct errors in their computations. The redundant multithreading (RMT) approach offers lightweight replicated execution streams of program instructions within the context of a single application process. However, the use of complete redundancy incurs significant overhead to the application performance. In this paper we present RedThreads, an interface that provides application-level fault detection and correction based on RMT, but applies the thread-level redundancy adaptively. We describe the RedThreads syntax and semantics, and the supporting compiler infrastructure and runtime system. Our approach enables application programmers to scope the extent of redundant computation. Additionally, the runtime system permits the use of RMT to be dynamically enabled, or disabled, based on the resiliency needs of the application and the state of the system. Our experimental results demonstrate how adaptive RMT exploits programmer insight and runtime inference to dynamically navigate the trade-off space between an application’s resilience coverage and the associated performance overhead of redundant computation.
The two-dimensional elastic Green’s function is calculated for a general anisotropic elastic bimaterial containing a line dislocation and a concentrated force while accounting for the interfacial structure by means of a generalized interfacial elasticity paradigm. The introduction of the interface elasticity model gives rise to boundary conditions that are effectively equivalent to those of a weakly bounded interface. The equations of elastic equilibrium are solved by complex variable techniques and the method of analytical continuation. The solution is decomposed into the sum of the Green’s function corresponding to the perfectly bonded interface and a perturbation term corresponding to the complex coupling nature between the interface structure and a line dislocation/concentrated force. Such construct can be implemented into the boundary integral equations and the boundary element method for analysis of nano-layered structures and epitaxial systems where the interface structure plays an important role.
The results presented here were obtained with a self-magnetic pinch (SMP) diode mounted at the front high voltage end of the RITS accelerator. RITS is a Self-Magnetically Insulated Transmission Line (MITL) voltage adder that adds the voltage pulse of six 1.3 MV inductively insulated cavities. The RITS driver together with the SMP diode has produced x-ray spots of the order of 1 mm in diameter and doses adequate for the radiographic imaging of high area density objects. Although, through the years, a number of different types of radiographic electron diodes have been utilized with SABER, HERMES III and RITS accelerators, the SMP diode appears to be the most successful and simplest diode for the radiographic investigation of various objects. Our experiments had two objectives: first to measure the contribution of the back-streaming ion currents emitted from the anode target and second to try to evaluate the energy of those ions and hence the Anode-Cathode (A-K) gap actual voltage. In any very high voltage inductive voltage adder utilizing MITLs to transmit the power to the diode load, the precise knowledge of the accelerating voltage applied on the A-K gap is problematic. This is even more difficult in an SMP diode where the A-K gap is very small (∼1 cm) and the diode region very hostile. The accelerating voltage quoted in the literature is from estimates based on the measurements of the anode and cathode currents of the MITL far upstream from the diode and utilizing the para-potential flow theories and inductive corrections. Thus, it would be interesting to have another independent measurement to evaluate the A-K voltage. The diode's anode is made of a number of high-Z metals in order to produce copious and energetic flash x-rays. It was established experimentally that the back-streaming ion currents are a strong function of the anode materials and their stage of cleanness. We have measured the back-streaming ion currents emitted from the anode and propagating through a hollow cathode tip for various diode configurations and different techniques of target cleaning treatment: namely, heating at very high temperatures with DC and pulsed current, with RF plasma cleaning, and with both plasma cleaning and heating. We have also evaluated the A-K gap voltage by energy filtering technique. Experimental results in comparison with LSP simulations are presented.
Mechanistic insight into the process of crack growth can be obtained through molecular dynamics (MD) simulations. In this investigation of fracture propagation, a slit crack was introduced into an atomistic amorphous silica model and mode I stress was applied through far-field loading until the crack propagates. Atomic displacements and forces and an Irving–Kirkwood method with a Lagrangian kernel estimator were used to calculate the J-integral of classical fracture mechanics around the crack tip. The resulting fracture toughness (KIC), 0.76 ± 0.16 MPa√m, agrees with experimental values. In addition, the stress fields and dissipation energies around the slit crack indicate the development of an inelastic region ~30Å in diameter. This is one of the first reports of KIC values obtained from up-scaled atomic-level energies and stresses through the J-integral. The application of the ReaxFF classical MD force field in this study provides the basis for future research into crack growth in multicomponent oxides in a variety of environmental conditions.
Progress in understanding liquid ethylene carbonate (EC) and propylene carbonate (PC) on the basis of molecular simulation, emphasizing simple models of interatomic forces, is reviewed. Results on the bulk liquids are examined from the perspective of anticipated applications to materials for electrical energy storage devices. Preliminary results on electrochemical double-layer capacitors based on carbon nanotube forests and on model solid-electrolyte interphase (SEI) layers of lithium ion batteries are considered as examples. The basic results discussed suggest that an empirically parameterized, non-polarizable force field can reproduce experimental structural, thermodynamic, and dielectric properties of EC and PC liquids with acceptable accuracy. More sophisticated force fields might include molecular polarizability and Buckingham-model description of inter-atomic overlap repulsions as extensions to Lennard-Jones models of van der Waals interactions. Simple approaches should be similarly successful also for applications to organic molecular ions in EC/PC solutions, but the important case of Li+ deserves special attention because of the particularly strong interactions of that small ion with neighboring solvent molecules. To treat the Li+ ions in liquid EC/PC solutions, we identify interaction models defined by empirically scaled partial charges for ion-solvent interactions. The empirical adjustments use more basic inputs, electronic structure calculations and ab initio molecular dynamics simulations, and also experimental results on Li+ thermodynamics and transport in EC/PC solutions. Application of such models to the mechanism of Li+ transport in glassy SEI models emphasizes the advantage of long time-scale molecular dynamics studies of these non-equilibrium materials.
In 2004, at the request of the Department of Energy, Sandia National Laboratories (Sandia) prepared a report, "Guidance on the Risk and Safety Analysis of Large Liquefied Natural Gas (LNG) Spills Over Water". That report provided a framework for assessing hazards and identifying approaches to minimize the consequences to people and property from an LNG spill over water. Because of increasing domestic U.S. supplies of natural gas and associated by products, such as liquefied propane gas (LPG), the United states Coast Guard requested that Sandia assess the general scale of possible hazards for a breach and spill of an LPG carrier. Because of the broad range of LPG carriers types -- refrigerated and pressurized, ships and barges, Sandia chose to focus this analysis on the larger LPG refrigerated systems. With cargo capacities ranging up to 100,000 m3, these types of ships can be expected to support potential increased LPG exports. Sandia assessed potential accidental and intentional threats, and based on LPG carrier configurations and designs, estimated potential breach sizes, spill rates and volumes, and conducted fire, vapor dispersion, and detonation hazard analyses. This report summarizes the analyses conducted, the expected range of potential hazards from an associated refrigerated LPG carrier spill over water, and risk management approaches to minimize consequences to people and property from such a spill.
X-ray absorption spectroscopy is proposed as a method for studying the heating of solid-density matter excited by secondary X-ray radiation from a relativistic laser-produced plasma. The method was developed and applied to experiments involving thin silicon foils irradiated by 0.5–1.5 ps duration ultrahigh contrast laser pulses at intensities between 0.5 × 1020 and 2.5 × 1020 W∕cm2. The electron temperature of the material at the rear side of the target is estimated to be in the range of 140–300 eV. The diagnostic approach enables the study of warm dense matter states with low self-emissivity.
This document describes the data strategy for the Nuclear Weapons Program Management Unit (NW PMU), with emphasis on functions related to the product realization lifecycle. It describes a vision to more effectively value and utilize data as an asset: data often is our product, and when it isn't, our products are made possible only through the data produced and consumed throughout each product's lifecycle. True confidence in the nuclear deterrent requires a clear understanding of how our products perform against requirements; both in the near term as well as over long periods of time. Data is the foundation for this understanding, and as such is a key enabler of the success of the NW mission. This document defines principles that enable a "culture of care" around NW data and drive the specific approaches to create a data-centric environment that is sustainable, agile, and responsive to the needs of the NW mission. The strategy outlined within this document must guide the definition of a high-level roadmap to achieve this vision, which in turn will be supported by separate detailed implementation plans.
In high-elevation, boreal and arctic regions, hydrological processes and associated water bodies can be strongly influenced by the distribution of permafrost. Recent field and modeling studies indicate that a fully-coupled multidimensional thermo-hydraulic approach is required to accurately model the evolution of these permafrost-impacted landscapes and groundwater systems. However, the relatively new and complex numerical codes being developed for coupled non-linear freeze-thaw systems require verification. This issue is addressed by means of an intercomparison of thirteen numerical codes for two-dimensional test cases with several performance metrics (PMs). These codes comprise a wide range of numerical approaches, spatial and temporal discretization strategies, and computational efficiencies. Results suggest that the codes provide robust results for the test cases considered and that minor discrepancies are explained by computational precision. However, larger discrepancies are observed for some PMs resulting from differences in the governing equations, discretization issues, or in the freezing curve used by some codes.
Laser-based measurements of the characteristic features of fireball onset and stabilization in response to a stepped voltage applied to an anode immersed in a low pressure (100 mTorr) helium afterglow are reported. These include spatial and temporal evolution of metastable species, electron density, and electric field magnitude as measured by planar laser induced fluorescence, laser-collision induced fluorescence, and laser-induced fluorescence-dip spectroscopy, respectively. These measurements are found to be in qualitative agreement with recent particle-in-cell simulations and theoretical models [Scheiner et al., Phys. Plasmas 24, 113520 (2017)]. The measurements validate the simulations and models in which fireball onset was predicted to follow from the trapping of electrons born from electron impact ionization within a potential well created by a buildup of ions in the sheath. The experimental measurements also demonstrate transient features following the onset that were not present in previous simulations. New simulation results are presented which demonstrate that these features are associated with the abruptness of the voltage step used to initiate fireball onset. An abrupt step in the anode bias causes rapid displacement of ions and an associated plasma potential response following the sheath and fireball expansion.
Beskardes, G.D.; Wu, Qimin; Hole, John A.; Chapman, Martin C.; Davenport, Kathy K.; Brown, Larry D.; Quiros, Diego A.
After the 23 August 2011 Mineral, Virginia, earthquake, a temporary dense array (Aftershock Imaging with Dense Arrays (AIDA)) consisting of ~200 stations was deployed at 200-400 m spacing near the epicenter for 12 days. Backprojection of the data was used to automatically detect and locate aftershocks. The co-deployment of a traditional aftershock network of 36 stations at ~2-10 km spacing enables a quantitative comparison. The AIDA backprojection aftershock catalog is complete to magnitude -1.0 and includes events as small as M-1.8. For comparison, the traditional network was complete to M-0.3 for the same time period. The AIDA backprojection catalog observes the same major patterns of seismicity in the epicentral region, but additional details are illuminated. The primary zone of seismicity is not a single fault but is a tabular zone of multiple small faults, this zone has a subtle concave shape along strike and with depth, and a broader zone of new events is observed at shallow depth. In addition, a new separate, shallow cluster was detected and located to the east of the main aftershock zone. The addition of smaller events to the catalog did not change the b-value or the temporal decay constant, but illuminated spatial and temporal patterns. Both the b-value and temporal decay constant are different for 12 days than for 4 months and are different at < 3km depth than at greater depth. Very low b-value, especially at greater depth, is consistent with observed very high stress drops. Conclusively, the results indicate the benefits of dense arrays and auto-detection by backprojection for aftershock studies. And finally, the reduced detection threshold and higher spatial resolution enabled the study of earthquake mechanisms and strain transfer at an unprecedented small scale.
The National Infrastructure Simulations and Analysis Center (NISAC) conducted a literature review on modeling cyber networks and evaluating cyber risks. The literature review explores where modeling is used in the cyber regime and ways that consequence and risk are evaluated. The relevant literature clusters in three different spaces: network security, cyber-physical, and mission assurance. In all approaches, some form of modeling is utilized at varying levels of detail, while the ability to understand consequence varies, as do interpretations of risk. This document summarizes the different literature viewpoints and explores their applicability to securing enterprise networks.
This project will explicitly investigate and demonstrate on a laboratory scale a two-stage Metal Hydride Compressor (MHC) system with a feed pressure of approximately 100 bar delivering highpurity H2 gas at outlet pressures ≥ 875 bar capable of an energy efficiency of ≤ 4.0 kWh/kg relying on an innovative heat pump configuration at a refueling station.
In many material systems, man-made or natural, we have an incomplete knowledge of geometric or material properties, which leads to uncertainty in predicting their performance under dynamic loading. Given the uncertainty and a high degree of spatial variability in properties of materials subjected to impact, a stochastic theory of continuum mechanics would be useful for modeling dynamic response of such systems. Peridynamic theory is such a theory. It is formulated as an integro- differential equation that does not employ spatial derivatives, and provides for a consistent formulation of both deformation and failure of materials. We discuss an approach to stochastic peridynamic theory and illustrate the formulation with examples of impact loading of geological materials with uncorrelated or correlated material properties. We examine wave propagation and damage to the material. The most salient feature is the absence of spallation, referred to as disorder toughness, which generalizes similar results from earlier quasi-static damage mechanics. Acknowledgements This research was made possible by the support from DTRA grant HDTRA1-08-10-BRCWM. I thank Dr. Martin Ostoja-Starzewski for introducing me to the mechanics of random materials and collaborating with me throughout and after this DTRA project.
The Arctic Methane, Carbon Aerosols, and Tracers Study was a measurement campaign at the NOAA Barrow Observatory and DOE ARM North Slope of Alaska sites in Barrow that involved the deployment of instruments to measure CH4, black carbon (BC), and source tracers. The campaign ran from September 1, 2014 to September 1, 2016 and was extended until July 30, 2017.