Dosimetry results from 1 January 2008 through 31 December 2017 were reviewed to demonstrate that radiation protection methods used at Sandia National Laboratories are compliant with regulatory limits and consistent with the philosophy to keep exposures to radiation As Low As is Reasonably Achievable (ALARA). Personnel dosimetry (external and internal) and environmental thermoluminescent dosimeter results were reviewed for the Sandia National Laboratories in New Mexico, California, and Nevada. ALARA is a philosophical approach to radiation protection by managing and controlling radiation exposures (individual and collective) to the work force and to the public to levels that are As Low As is Reasonably Achievable taking social, technical, economic, practical, and public policy considerations into account. ALARA is not a dose limit but a planning tool with the objective to keep doses below applicable dose limits As Low As is Reasonably Achievable. In the case of Sandia National Laboratories, formal ALARA goals are not needed since Collective and individual doses are well below applicable limits through operational ALARA practices implemented during Work Planning and Control activities.
The limiting frequency resolution of a PDV measurement is: σf = $\sqrt\frac{6 η}{fsτ^3π}$ where fs is the sample rate, τ is the analysis time duration, and 11 is the noise fraction. Although T is a strong lever for reducing uncertainty, this parameter must be kept small to preserve time resolution. Consider a PDV measurement with sampled at 80 GS/s and analyzed in 1 ns durations. A 1% noise fraction corresponds to 0.87 MHz of frequency uncertainty, which at 1550 nm works out to 0.68 m/s. A 10% noise fraction has a limiting velocity resolution of about 7 m/s; for comparison, a VISAR system with similar response time (0.5 ns delay, 532 m/s fringe constant) would have a limiting uncertainty of 5-6 m/s. Noise fractions of 10-20% or less are desirable for measurements at this time scale.
Predicting chemical-mechanical fracture initiation and propagation in materials is a critical problem, with broad relevance to a host of geoscience applications including subsurface storage and waste disposal, geothermal energy development, and oil and gas extraction. In this project, we have developed molecular simulation and coarse- graining techniques to obtain an atomistic-level understanding of the chemical- mechanical mechanisms that control subcritical crack propagation in materials under tension and impact the fracture toughness. We have applied these techniques to the fracture of fused quartz in vacuum, in distilled water, and in two salt solutions - 1M NaC1, 1M NaOH - that form relatively acidic and basic solutions respectively. We have also established the capability to conduct double-compression double-cleavage experiments in an environmental chamber to observe material fracture in aqueous solution. Both simulations and experiments indicate that fractures propagate fastest in NaC1 solutions, slower in distilled water, and even slower in air.
Energy, environmental, and economic challenges are spurring more widespread consideration and use of energy storage systems (ESSs), which in turn are driving increased development of new ways to store energy electrochemically, mechanically, and thermally. These new methods necessitate an increased focus on ensuring that public health, safety, and welfare are not adversely affected—something that has been addressed for many years through codes, standards, and regulations (CSR5)1. CSRs provide requirements that establish a basis for determining if an ESS is safe, whether electrochemical, mechanical, or thermal and regardless of the range of ESS applications, energy capacities, physical sizes, location, or number installed at any given site. The key to achieving desired safety goals, as memorialized through CSRs, is through documenting and validating compliance with applicable CSRs. The process of documenting and validating compliance, which is a key component to the initial approval as well as continuing acceptance of an ESS installation, is generally called conformity assessment.
In October the team merged in updated ATDM/Trilinos configuration to include SPARC requirements. Assisted and worked on issues identified by the EMPIRE switchover to the ATDM/Trilinos configuration. Progress was made on automating dashboard triaging. Discovered and began addressing issues with mixed language calling with gcc-7.2 on Power8. Worked on new Python tool to filter CDASH reports to only show new issues. Completed ECP ST review. In October the team put an algorithm in place to prevent inverted elements in SPARC during refinement and worked on tests to morph mesher and should be ready for SGM integration soon. The team worked on solver rebalance and corrected issues. Complete SIMD work. Worked out next steps for solver improvements for EMPIRE. Adjusted some solver settings and to improve performance; strong scaling curves are flat instead of ascending etc. Worked on optimizing kernels for SPARC. Completed ECP ST reviews. The team worked on cleaning up branch for merge into SPARC master dev branch. Progress was made building scripts for catalyst builds on all HPC platforms of interest. Worked on adding TuckerMPl reader as plugin for catalyst. Completed ECP project review. Work has continued on NimbleSM, which now runs in a container and can be used modularly with an MPI code. The team also made progress on a qthreads version of NibleSM. Worked on build system issues within NimbleSM and Sierra for GPUs. Progressed on getting kookfied material models in NimbleSM. The team incorporated panel feedback form ECP project reviews into FY19 plans.
The Reproducing Kernel Particle Method (RKPM), a meshfree method, has been implemented in Sandia's Sierra/SolidMechanics in a collaboration between Sandia and the University of California San Diego's Center for Extreme Events Research (UCSD/CEER). Meshfree methods, like RKPM, have an advantage over mesh-based methods, like the Finite Element Method (FEM), in applications where achieving or maintaining a quality mesh becomes burdensome or impractical. For example, using FEM for problems with very large deformations will result in poor element Jacobians which causes problems with the parametric mapping. RKPM constructs the approximation functions in the physical domain, circumventing the parametric mapping issue. Also, reconstructing the approximation functions at very large deformations is straight-forward. RKPM has an advantage over traditional meshfree methods such as Smoothed-Particle Hydrodynamics (SPH) due to its ability to reproduce linear or higher-order functions exactly. This removes the tensile instabilities that are present in SPH and allows preservation of angular momentum. The point of this memo is to explore the capabilities and limitations of the current implementation by testing it on three different applications: 1) a quasi-static ductile shearing problem 2) a dynamic concrete panel perforation problem and 3) a set of dynamic metal panel perforation problems. In summary, areas where RKPM appears to be a promising alternative to current methods have been identified. Also, outstanding inefficiencies and issues (bugs) with code are noted, ways to improve the capabilities using material from literature are mentioned and areas deserving of new research are highlighted.
This report represents completion of milestone deliverable M2SF-18SNO10309013 "Inventory and Waste Characterization Status Report and OWL Update that reports on FY2018 activities for the work package (WP) SF-18SNO1030901. This report provides the detailed final information for completed FY2018 work activities for WP SF-18SN01030901, and a summary of priorities for FY2019. This status report on FY2018 activities includes evaluations of waste form characteristics and waste form performance models, updates to the OWL development, and descriptions of the two planned management processes for the OWL. Updates to the OWL include an updated user's guide, additions to the OWL database content for wastes and waste forms, results of the Beta testing and changes implemented from it. There are two processes being planned in FY2018, which will be implemented in FY2019. One process covers methods for interfacing with the DOE SNF DB (DOE 2007) at INL on the numerous entries for DOE managed SNF, and the other process covers the management of updates to, and version control/archiving of, the OWL database. In FY2018, we have pursued three studies to evaluate/redefine waste form characteristics and/or performance models. First characteristic isotopic ratios for various waste forms included in postclosure performance studies are being evaluated to delineate isotope ratio tags that quantitatively identify each particular waste form. This evaluation arose due to questions regarding the relative contributions of radionuclides from disparate waste forms in GDSA results, particularly, radionuclide contributions of DOE-managed SNF vs HLW glass. In our second study we are evaluating the bases of glass waste degradation rate models to the HIP calcine waste form. The HIP calcine may likely be a ceramic matrix material, with multiple ceramic phases with/without a glass phase. The ceramic phases are likely to have different degradation performance from the glass portion. The distribution of radionuclides among those various phases may also be a factor in the radionuclide release rates. Additionally, we have an ongoing investigation of the performance behavior of TRISO particle fuels and are developing a stochastic model for the degradation of those fuels that accounts for simultaneous corrosion of the silicon carbide (SiC) layer and radionuclide diffusion through it. The detailed model of the TRISO particles themselves, will be merged with models of the degradation behavior(s) of the graphite matrix (either prismatic compacts or spherical "pebbles") containing the particles and the hexagonal graphite elements holding the compacts.
This manual describes the use of the Xyce Parallel Electronic Simulator. Xyce has been de- signed 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 document is a reference guide to the Xyce Parallel Electronic Simulator, and is a companion document to the Xyce Users' Guide [1] . 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 [1] . Copyright c 2002 National Technology & Engineering Solutions of Sandia, LLC (NTESS). Acknowledgements We would like to acknowledge all the code and test suite developers who have contributed to the Xyce project over the years: Alan Lundin, Arlon Waters, Ashley Meek, Bart van Bloemen Waanders, Brad Bond, Brian Fett, Christina Warrender, David Baur, David Day, David Shirley, Deborah Fixel, Derek Barnes, Eric Rankin, Erik Zeek, Gary Hennigan, Herman "Buddy" Watts, Jim Emery, Keith Santarelli, Laura Boucheron, Lawrence Musson, Mary Meinelt, Mingyu "Genie" Hsieh, Nicholas Johnson, Philip Campbell, Rebecca Arnold, Regina Schells, Richard Drake, Robert Hoekstra, Roger Pawlowski, Russell Hooper, Samuel Browne, Scott Hutchinson, Smitha Sam, Steven Verzi, Tamara Kolda, Timur Takhtaganov, and Todd Coffey. Also, thanks to Hue Lai for the original typesetting of this document in L A T E X. Trademarks Xyce Electronic Simulator TM and Xyce TM are trademarks of National Technology & Engineering Solutions of Sandia, LLC (NTESS). All other trademarks are property of their respective owners. Contact Information Outside Sandia World Wide Web http://xyce.sandia.gov Email xyce@sandia.gov Inside Sandia World Wide Web http://xyce.sandia.gov Email xyce-sandia@sandia.gov Bug Reports http://joseki-vm.sandia.gov/bugzilla http://morannon.sandia.gov/bugzilla
This study examines methods that can help maximize confidence in maintaining Continuity of Knowledge (CoK) on plutonium-bearing wastes, from a final safeguards-verification measurement through emplacement underground. The study identifies Containment and Surveillance (C/S) measures that can be applied during packaging of plutonium wastes at the Savannah River Site (SRS) in South Carolina, USA, through shipment to, and receipt and disposal at the Waste Isolation Pilot Plant (WIPP) near Carlsbad, New Mexico, USA. Results of this study could apply to countries with a Comprehensive Safeguards Agreement (CSA) that plan to dispose in a geological repository plutonium or other non-fuel nuclear materials that are under international safeguards.
The purpose of this document is to provide an initial overview of (new) information regarding the gaps in DOE's work on HPC, ML & algorithms, and human systems emerging from the Sep. 2018 Summit, and to briefly forecast the attendee community's next steps.
Personnel at Sandia National Laboratories (hereinafter referred to as Sandia) comply with U.S. Department of Energy (DOE) P 450.4A, Chg 1, Integrated Sgfeo Management Polig, and implement an Integrated Safety Management System (ISMS) to ensure safe operations. Sandia personnel integrate safety into management and work practices at all levels so that missions are accomplished while protecting Members of the Workforce, the public, and the environment. As a result, safety is effectively integrated into all facets of work planning and execution. Thus, the management of safety functions becomes an integral part of mission accomplishment and meets the requirements outlined in the DOE Acquisition Regulation (DEAR) 970.5223-1, Integration of Environment, S qleo, and Health into Work Planning and Execution clause incorporated into the Prime Contract. The DEAR 970.5223-1, Integration of Environment, Sqfeo, and Health into Work Planning and Execution clause requires DOE contractors to manage and perform work in accordance with a documented Safety Management System that fulfills conditions of the DEAR clause, at a minimum. For purposes of this clause, safety encompasses environment, safety, and health, including pollution prevention and waste minimization.
Through a series of measurements with a high purity germanium detector, we have established that the past presence of neutron emitting material can be detected by the decay of activation products in aluminum containers, tungsten shielding, and concrete floors even several days after last exposure. The time since last exposure can also be estimated by the gamma-ray detection rate. These findings may lead to interesting new CONOPS in the detection of illicit SNM or the verification of the absence (or presence) of SNM containing objects in facilities and/or transit even after the material has been removed.
Angle of incidence response of a photovoltaic module describes its light gathering capability when incident sunlight is at an orientation other than normal to the module's surface. At low incident angles (i.e. close to normal), most modules have similar responses. However, at increasing incident angles, reflective losses dominate response and relative module performance becomes differentiated. Relative performance in this range is important for understanding the potential power output of utility - scale ph otovoltaic systems. In this report, we document the relative angle of incidence response of four utility - grade panels to each other and to four First Solar modules. We found that response was nearly identical between all modules up to an incident angle of ~55°. At higher angles, differences of up to 5% were observed. A module from Yingli was the best performing commercial module while a First Solar test module with a non - production anti - reflective coating was the best overall performer. This page left blank
This proposal is focused on the multidisciplinary, exploratory study of highly selective materials for distinguishing peaceful nuclear facilities from clandestine nuclear weapons development. In particular, we are focused on iodine fission off-gas species. This is a 1-year project; herein is the final FY1 8 report on the project. The project was divided into four Tasks: speciation, flowsheets, fission gas adsorption materials, and detection devices. We successfully addressed all four tasks and reported on them during this year's quarterly reports. This final report will serve as a summary of the accomplishments.
The goal for this effort is a validated method which can be used to implement an updated physical security regime to optimize the physical security at domestic nuclear power plants (existing and future). It is the intent for the evaluation recommendations to provide the technical basis for an optimized plant security posture, which could consider reduce conservatisms in that posture, and potentially reduce security costs for the nuclear industry while meeting all security requirements.
This paper looks at the performance of residential refrigeration units in off-grid photovoltaic and small wind hybrid (PV/wind) systems with battery storage. Off grid hybrid power systems, dispatched by Navajo Tribal Utility Authority (NTUA), allow Navajo Nation residents in rural areas to have the benefits of electricity. On the Navajo Nation, the rural and rugged nature of the land results in a high capital cost to connecting a house to the grid. In this case, a hybrid PV/wind power generation system may be used at a much lower cost to the customer. In providing affordable power systems to customers, the systems are designed to provide adequate power for use. This requires a constant conservative use of electricity. For systems with refrigerators which are large alternating current (AC) loads, there are performance issues that arise. NTUA reports that new energy star rated refrigerators have performance issues in working with these off grid systems. This paper looks at ways to improve the performance of these systems with the use of a refrigeration unit. This involves looking at conventional refrigerators with its operation. This paper also looks at alternative methods of refrigeration. Also, the power system is looked at to increase the performance in maintaining a proper balance of the system. Lastly, solutions will be recommended to solve the refrigeration issues faced by NTUA.
This document provides analysis and proposed modifications to correct current issues at Building 1090. Electrical modifications will add additional emergency Iighting in Labs 170, 174, 178, 182, 184, 186, and 190, and back-up power for the exhaust systems, fume hood lighting and exhaust system controls during a power outage. Mechanical modifications will address building pressurization between the lab and office areas, and replacement of corroded exhaust ductwork and fume hoods related to boil-off operations of corrosive chemicals. Mechanical modifications include the installation of a dedicated, chemical boil-off exhaust fan and ductwork to support corrosive boil-off operations in Lab 184. It should be noted that the proposed solution increases the overall building exhaust demand, also increasing the supply air needed. Electrical modifications include the installation of an uninterruptible power supply (UPS) to provide power to the exhaust fan, controls, and fume hoods to allow safe exit from Laboratory 186 during a power outage. The existing lighting inverter will also be replaced with a larger model to support additional emergency lighting within the labs. Architectural modifications include exterior doors on the east wall of the IDR room. An additional door in the corridor west of Lab 184 will provide direct access to Lab 186 without entering a common building corridor. Lab casework will be modified as-required to accommodate the new layout.
Renewable energy has grown throughout the years. It is not just something for today. With the United States power electrical grid being 100 plus years old, renewable energy is the future. There are many different types of renewable energy. Solar photovoltaic array units and wind turbines seem to be the most common community scale renewable energy systems. There are new solar and wind farms popping up in more and more places each day. It is said that installing the farms is a fast process as compared to dotting the "i's" and crossing the "t's" (paper work), which is really the most time-consuming part of the entire project. During the internship at Sandia, the Indian Energy interns attended many field visits to various tribal reservations. On these field visits, the interns were able to experience first-hand some amazing renewable energy plans and projects which have now become a reality. With each site visit, the success of tribal projects is seen where hard work and persistence pays off. It brings joy to see these tribes making their dreams a reality. It is heartwarming to hear the stories of why the tribe chose to bring renewable projects to their people. It is also very informative because the tribal hosts encourage as many questions as can be asked. The field visits are what make ideas possible and to dream of what could be pursued. Research is a big part making these goals and dreams a reality. Without the field visits and knowledge shared by the tribal staff and leaders, a relevant research topic would have been difficult to focus on. Returning for a second summer as an intern at Sandia National Laboratories' Indian Energy program, several research topics were considered. Ultimately, this research paper's focus is to incorporate renewable energy specifically to take care of Mother Nature as well as the Turtle Mountain Band of Chippewa Indian people. There have been many deaths on North Dakota Highway 281, which it is the main road of the Turtle Mountain Band of Chippewa reservation. The highway has a high volume of traffic every day, in addition to many people who frequently walk this road. There is no walking or bike path along the road; most people tend to walk the shoulders of the road. This research paper is a way to help protect these pedestrians with an idea of lighting the highway from the west end of Belcourt to one of are housing developments that is 5.34 miles to the west of town. This research paper will look at the various types of street lighting methods and provide recommendations for a suitable and economical project.
Navajo (Diné) tribal members experience alarming rates of diabetes and food insecurity on the reservation. Increasing involvement with food production through gardening is a crucial step to rebuilding Diné food systems and improving the health of Navajos. The main challenges are drought, lack of available land, limited food production knowledge, and large up-front costs. However, implementing community-based gardens would help alleviate land space issues, leverage community knowledge, and shift financial responsibility to local community level or chapter level. Greenhouses are advantageous because they reduce water consumption and allow for year-round production, but require energy intensive heating, ventilation, and air conditioning (HVAC) systems. Therefore, the purpose of this paper is to compare a propane heating and evaporative cooling HVAC system to a ground source heat pump (GSHP). Using EnergyPlus to simulate annual energy loads, this paper compares the financial feasibility and environmental impact of each system. The operating cost of GSHPs was found to be 57% — 72% less than traditional HVAC systems based on location and fuel prices. Additionally, GSHPs required 72% — 90% less water and emitted 35% — 69% less carbon dioxide annually. Given the large up-front cost of GSHPs, conservative estimates showed payback periods from 5.2 — 10.8 years when using renewable energy grants. A life cycle cost analysis over 20 years showed greenhouses with GSHPs could cost $1,272 — $1,605 per year or 27% — 44% less than traditional HVAC systems. Tax revenue for chapters showed that funding is available to carry out such projects. Food produced using GSHP systems was found to cost $2.26 — $2.30 per daily serving of fruit and vegetables, which is competitive with grocery store prices. More importantly, greenhouses equipped with GSHPs present a compelling case because they cost less to operate and are more environmentally friendly than traditional HVAC systems. Future work should focus on adding a photovoltaic (PV) and battery storage system, which would completely eliminate HVAC water consumption and carbon dioxide emissions.
Walton, Chris C.; Pardini, Tom; Brejnholt, Nicolai F.; Ayers, Jay J.; Mccarville, 1.; Pickworth, Louisa A.; Bradley, David K.; Decker, Todd A.; Hau-Riege, Stefan P.; Hill, Randal M.; Michael J PivovaroffMichael J.; Regina SouflRegina; Author, No; Vogel, Julia K.; Bell, Perry M.; Ampleford, David A.; Fein, Jeffrey R.; Ball, Christopher R.; Bourdon, Christopher B.; Romaine, Suzanne; Ames, Andrew O.; Bruni, Ricardo J.; Kilaru, Kiranmayee; Roberts, Oliver J.; Ramsey, Brian D.
Previously published calculations predict that the "staged z-pinch" (SZP) can achieve 400 MJ of fusion yield on a Z-class machine. The SZP is touted to need no external preheat mechanism and no external pre-magnetization method. Instead, it is claimed that the imploding liner can adequately "shock preheat" the fuel and magnetic field diffusion through the liner can adequately magnetize the fuel. In this paper, we analyze a number of published SZP calculations and demonstrate that the calculations have major errors - the computer code used to do the calculations does not appear to be accurately solving the physical model it is intended to solve. A variety of independent analyses lead to this conclusion. This conclusion is confirmed by detailed one-dimensional magnetohydrodynamic (MHD) calculations conducted on different computer codes using a variety of proposed SZP operating parameters. Although using parameters similar or identical to the published calculations, our MHD calculations do not reach fusion conditions; there is no conceivable modification of the parameters that would lead to high-gain fusion conditions using these other codes. Our analyses and a review of the magnetized target parameter space leads to further conclusion that the SZP should not be considered to be a potential high-gain fusion source.
Despite the increasing number of small scientific balloon missions with payloads in the gram-to- kilogram mass range, little is known about the injury risk they pose to humans on the ground. We investigated the risk of head injury using the head injury criterion (HIC) from impact with a 1.54 kg (3.40 pound) payload. Study parameters were impact speeds of 670, 1341, and 2012 cm s-1 (15, 30, and 45 mph) and protective padding wall thicknesses between zero and 10 cm (3.9 inch). Padding provided meaningful reductions of injury risk outcomes at all speeds. The maximum risk of AIS 3+ injury was approximately 3.6% (HIC 249) for the 670 cm s-1 (15 mph) case with 0.5 cm (0.2 inch) of padding, 34% (HIC 801) for the 1341 cm s-1 (30 mph) case with 3.0 cm (1.2 inch) of padding, and 67% (HIC 1147) for the 2012 cm s-1 (45 mph) case with 7.0 cm (2.8 inch) of padding. Adding 1.0 cm (0.39 inch) of padding to these two latter cases reduced AIS 3+ injury risk to approximately 13% (HIC 498) and 37% (HIC 835), respectively. Public safety can be increased when balloon operators use padded payload enclosures as adjuncts to parachutes.
We recently developed a one-dimensional imager of neutrons on the Z facility. The instrument is designed for Magnetized Liner Inertial Fusion (MagLIF) experiments, which produce D-D neutrons yields of ∼3 × 1012. X-ray imaging indicates that the MagLIF stagnation region is a 10-mm long, ∼100-μm diameter column. The small radial extents and present yields precluded useful radial resolution, so a one-dimensional imager was developed. The imaging component is a 100-mm thick tungsten slit; a rolled-edge slit limits variations in the acceptance angle along the source. CR39 was chosen as a detector due to its negligible sensitivity to the bright x-ray environment in Z. A layer of high density poly-ethylene is used to enhance the sensitivity of CR39. We present data from fielding the instrument on Z, demonstrating reliable imaging and track densities consistent with diagnosed yields. For yields ∼3 × 1012, we obtain resolutions of ∼500 μm.
LiXFePO4 (0 < X < 1) is one of the most well-studied cathode battery materials and is notable for its large miscibility gap. Although its phase-separating behaviors under equilibrium conditions have been well documented, recent research has shown that phase separation is suppressed at elevated rates of lithium insertion and removal. Specifically, LiXFePO4 exhibits a nonequilibrium solid solution behavior at elevated cycling rates. This article reviews recent research on nonequilibrium solid solution in LiXFePO4; these insights have been largely enabled by operando characterization techniques. Such studies have not only unambiguously confirmed the existence of this solid solution, but also show how surface reaction and diffusion kinetics ultimately affect phase separation and other spatially nonuniform lithiation and delithiation behavior.
File fragment classification is an important step in the task of file carving in digital forensics. In file carving, files must be reconstructed based on their content as a result of their fragmented storage on disk or in memory. Existing methods for classification of file fragments typically use hand-engineered features, such as byte histograms or entropy measures. In this paper, we propose an approach using sparse coding that enables automated feature extraction. Sparse coding, or sparse dictionary learning, is an unsupervised learning algorithm, and is capable of extracting features based simply on how well those features can be used to reconstruct the original data. With respect to file fragments, we learn sparse dictionaries for n-grams, continuous sequences of bytes, of different sizes. These dictionaries may then be used to estimate n-gram frequencies for a given file fragment, but for significantly larger n-gram sizes than are typically found in existing methods which suffer from combinatorial explosion. To demonstrate the capability of our sparse coding approach, we used the resulting features to train standard classifiers, such as support vector machines over multiple file types. Experimentally, we achieved significantly better classification results with respect to existing methods, especially when the features were used in supplement to existing hand-engineered features.
The apparent ion temperature and neutron-reaction history are important characteristics of a fusion plasma. Extracting these quantities from a measured neutron-time-of-flight signal requires accurate knowledge of the instrument response function (IRF). This work describes a novel method for obtaining the IRF directly for single DT neutron interactions by utilizing n-alpha coincidence. The t(d,α)n nuclear reaction was produced at Sandia National Laboratories' Ion Beam Laboratory using a 300 keV Cockcroft-Walton generator to accelerate a 2.5 μA beam of 175 keV D+ ions into a stationary ErT2 target. The average neutron IRF was calculated by taking a time-corrected average of individual neutron events within an EJ-228 plastic scintillator. The scintillator was coupled to two independent photo-multiplier tubes operated in the current mode: a Hamamatsu 5946 mod-5 and a Photek PMT240. The experimental setup and results will be discussed.
In engineering practice, models are typically kept as simple as possible for ease of setup and use, computational efficiency, maintenance, and overall reduced complexity to achieve robustness. In solid mechanics, a simple and efficient constitutive model may be favored over one that is more predictive, but is difficult to parameterize, is computationally expensive, or is simply not available within a simulation tool. In order to quantify the modeling error due to the choice of a relatively simple and less predictive constitutive model, we adopt the use of a posteriori model-form error-estimation techniques. Based on local error indicators in the energy norm, an algorithm is developed for reducing the modeling error by spatially adapting the material parameters in the simpler constitutive model. The resulting material parameters are not material properties per se, but depend on the given boundary-value problem. As a first step to the more general nonlinear case, we focus here on linear elasticity in which the “complex” constitutive model is general anisotropic elasticity and the chosen simpler model is isotropic elasticity. The algorithm for adaptive error reduction is demonstrated using two examples: (1) A transversely-isotropic plate with hole subjected to tension, and (2) a transversely-isotropic tube with two side holes subjected to torsion.
Triplet sets of replaceable graphite rod collector probes (CPs), each with collection surfaces on opposing faces and oriented normal to the magnetic field, were inserted at the outboard mid-plane of DIII-D to study divertor tungsten (W) transport in the Scrape-Off Layer (SOL). Each CP collects particles along field lines with different parallel sampling lengths (determined by the rod diameters and SOL transport) giving radial profiles from the main wall inward to R-Rsep ∼ 6 cm. The CPs were deployed in a first-of-a-kind experiment using two toroidal rings of distinguishable isotopically enriched, W-coated divertor tiles installed at 2 poloidal locations in the divertor. Post-mortem Rutherford backscatter spectrometry of the surface of the CPs provided areal density profiles of elemental W coverage. Higher W content was measured on the probe side facing along the field lines toward the inner target indicating higher concentration of W in the plasma upstream of the CP, even though the W-coated rings were in the outer target region of the divertor. Inductively coupled plasma mass spectroscopy validates the isotopic tracer technique through analysis of CPs exposed during L-mode discharges with the outer strike point on the isotopically enriched W coated-tile ring. The contribution from each divertor ring of W to the deposition profiles found on the mid-plane collector probes was able to be de-convoluted using a stable isotope mixing model. The results provided quantitative information on the W source and transport from specific poloidal locations within the lower divertor region.
Uniaxial mechanical testing conducted at room temperature (RT) and 77 K on hydrogen (H)-exposed nickel was coupled with targeted microscopy to evaluate the influence of deformation temperature, and therefore mobile H-deformation interactions, on intergranular cracking in nickel. Results from interrupted tensile tests conducted at cryogenic temperatures (77 K), where mobile H-deformation interactions are effectively precluded, and RT, where mobile H-deformation interactions are active, indicate that mobile H-deformation interactions are not an intrinsic requirement for H-induced intergranular fracture. Moreover, an evaluation of the true strain for intergranular microcrack initiation for testing conducted at RT and 77 K suggests that H which is segregated to grain boundaries prior to the onset of straining dominates the H-induced fracture process for the prescribed H concentration of 4000 appm. Finally, recent experiments suggesting that H-induced fracture is predominately driven by mobile H-deformation interactions, as well as the increased susceptibility of coherent twin boundaries to H-induced crack initiation, are re-examined in light of these new results.
Neural-inspired spike-based computing machines often claim to achieve considerable advantages in terms of energy and time efficiency by using spikes for computation and communication. However, fundamental questions about spike-based computation remain unanswered. For instance, how much advantage do spike-based approaches have over conventionalmethods, and underwhat circumstances does spike-based computing provide a comparative advantage? Simply implementing existing algorithms using spikes as the medium of computation and communication is not guaranteed to yield an advantage. Here, we demonstrate that spike-based communication and computation within algorithms can increase throughput, and they can decrease energy cost in some cases. We present several spiking algorithms, including sorting a set of numbers in ascending/descending order, as well as finding the maximum or minimum ormedian of a set of numbers.We also provide an example application: a spiking median-filtering approach for image processing providing a low-energy, parallel implementation. The algorithms and analyses presented here demonstrate that spiking algorithms can provide performance advantages and offer efficient computation of fundamental operations useful in more complex algorithms.
Nanoporous adsorbents are a diverse category of solid-state materials that hold considerable promise for vehicular hydrogen storage. Although impressive storage capacities have been demonstrated for several materials, particularly at cryogenic temperatures, materials meeting all of the targets established by the U.S. Department of Energy have yet to be identified. In this Perspective, we provide an overview of the major known and proposed strategies for hydrogen adsorbents, with the aim of guiding ongoing research as well as future new storage concepts. The discussion of each strategy includes current relevant literature, strengths and weaknesses, and outstanding challenges that preclude implementation. We consider in particular metal-organic frameworks (MOFs), including surface area/volume tailoring, open metal sites, and the binding of multiple H2 molecules to a single metal site. Two related classes of porous framework materials, covalent organic frameworks (COFs) and porous aromatic frameworks (PAFs), are also discussed, as are graphene and graphene oxide and doped porous carbons. We additionally introduce criteria for evaluating the merits of a particular materials design strategy. Computation has become an important tool in the discovery of new storage materials, and a brief introduction to the benefits and limitations of computational predictions of H2 physisorption is therefore presented. Finally, considerations for the synthesis and characterization of hydrogen storage adsorbents are discussed.
Despite their ubiquity in nanoscale electronic devices, the physics of tunnel barriers has not been developed to the extent necessary for the engineering of devices in the few-electron regime. This problem is of urgent interest, as this is the specific regime into which current extreme-scale electronics fall. Here, we propose theoretically and validate experimentally a compact model for multielectrode tunnel barriers, suitable for design-rules-based engineering of tunnel junctions in quantum devices. We perform transport spectroscopy at approximately T=4 K, extracting effective barrier heights and widths for a wide range of biases, using an efficient Landauer-Büttiker tunneling model to perform the analysis. We find that the barrier height shows several regimes of voltage dependence, either linear or approximately exponential. Effects on threshold, such as metal-insulator transition and lateral confinement, are included because they influence parameters that determine barrier height and width (e.g., the Fermi energy and local electric fields). We compare these results to semiclassical solutions of Poisson's equation and find them to agree qualitatively. Finally, this characterization technique is applied to an efficient lateral tunnel barrier design that does not require an electrode directly above the barrier region in order to estimate barrier heights and widths.
A new Wolter x-ray imager has been developed for the Z machine to study the emission of warm (>15 keV) x-ray sources. A Wolter optic has been adapted from observational astronomy and medical imaging, which uses curved x-ray mirrors to form a 2D image of a source with 5 × 5 × 5 mm3 field-of-view and measured 60-300-μm resolution on-axis. The mirrors consist of a multilayer that create a narrow bandpass around the Mo Kα lines at 17.5 keV. We provide an overview of the instrument design and measured imaging performance. In addition, we present the first data from the instrument of a Mo wire array z-pinch on the Z machine, demonstrating improvements in spatial resolution and a 350-4100× increase in the signal over previous pinhole imaging techniques.
NNSA Order 56XB (Chapter 13.2) requires the Primary Standards Laboratory (PSL) to perform technical surveys on the integrated contractors participating in the NNSA Standards and Calibration Program. In addition to Chapter 13.2, the surveys check for compliance with ISO/IEC 17025 and the PSLM. The PSL Technical Survey is a joint activity of the NNSA and the PSL. The PSL is responsible for the technical portion of the survey and the NNSA is responsible for the quality portion. The Technical Survey report is issued by the NNSA.
The National Nuclear Security Agency (NNSA) created a Minority Serving Institution Partnership Plan (MSIPP) to 1) align investments in a university capacity and workforce development with the NNSA mission to develop the needed skills and talent for NNSA's enduring technical workforce at the laboratories and production plants and 2) to enhance research and education at underrepresented colleges and universities. Out of this effort, MSIPP launched a new program in early FY17 focused on Tribal Colleges and Universities (I'CUs). The following report summarizes the project focus and status update during this reporting period.
This report describes a seedling project in which we developed experimental paradigms for studying patterns of analyst attention to streaming data. The project identified key structure features that can be used to generate appropriate stimuli for nearly any mission domain.
The Grid of the Future was a one-day workshop to discuss a resilient grid for the 21st and 22nd century. The workshop gathered experts from various fields to explore concepts for the electric power grid of the future with an emphasis on improving resilience. The event was co-sponsored by Sandia National Laboratories, the Albuquerque IEEE Section, the University of New Mexico, New Mexico State University, and the Santa Fe Institute. The presenters identified radical changes to the grid that are expected to occur over the next 25-50 years and the role of resilience. The workshop was held at the University of New Mexico on Wednesday, August 22nd, 2018. This report summarizes presentations and discussions from the workshop.
As part of the DOE's multi-laboratory effort to provide analysis and tools to support reconstruction and modernization of the Puerto Rico electric grid, Sandia National Laboratory was tasked with making recommendations for how to use energy storage to support the transmission system. Puerto Rico's electric grid is outdated and still recovering from the 2017 hurricane season, and targeted improvements are needed to restore reliability and to provide resilience for future extreme events. This report examined the most critical near-term issues with the transmission system: frequency regulation and response, and analyzed the impacts of incorporating energy storage systems of varying sizes with the goal of immediately minimizing load shedding while laying the foundation for future renewable energy integration. The analysis concluded that 240 MW/60 MWh of energy storage would stabilize system frequency sufficiently to avoid loss of load for rapid load changes or generation outages up to and including loss of the largest generation unit on the island.
This document serves to guide a researcher through the process of predicting atmospheric conditions in a region of interest utilizing the Weather Research and Forecasting (WRF) model. This documentation is specific to WRF and WRF Preprocessing System (WPS) version 3.8.1. WRF is an atmospheric prediction system designed for meteorological research and numerical atmospheric prediction. In WRF, simulations may be generated utilizing real data or idealized atmospheric conditions. Output from WRF serves as input into the Time-Domain Atmospheric Acoustic Propagation Suite (TDAAPS) which performs staggered-grid finite difference modeling of the acoustic velocity pressure system to produce Green's functions through these atmospheric models.
This report is an assessment of the computational fluid dynamics (CFD) code Fire Dynamics Simulator (FDS), version 6.5.3, using the Model Evaluation Protocol (MEP) for Liquefied Natural Gas (LNG). The MEP consists of model validation and a scientific assessment that encompasses model information and model verification activities. Model validation entails comparison against various field and wind-tunnel trials for LNG and other dense gases with and without obstructions. The results indicate that FDS is generally over-predictive for most of the field scale dense gas releases and cases involving obstructions without requiring a safety factor of 2, however, since there are uncertainties in extrapolating to accident scales a safety factor of 2 (1/2 LFL criteria) may be appropriate. The results of this scientific assessment and prior verification efforts demonstrate the soundness of the numerical techniques and robustness of FDS. The validation results indicate that FDS is suitable for modeling dense gas dispersion with and without obstructions.
Progress towards next-generation internal combustion engine technologies is dramatically hindered by the complexity of both simulating and measuring key processes, such as thermal stratification and soot formation, in an operating prototype. In general, spectroscopic methods for in-operando probing become limitingly complex at the high pressures and temperature encountered in such systems, and numerical methods for simulating device performance become computationally expensive due to the turbulent flow field, detailed chemistry, and range of important length-scales involved. This report presents parallel experimental and theoretical advances to conquer these limitations. We report the development of high pressure and high temperature ultrafast coherent anti-Stokes Raman spectroscopy measurements, up to a pressure and temperature regime relevant to engine conditions. This report also presents theoretical results using a stochastic one-dimensional turbulence (ODT) model providing insight into the local thermochemical state and its consequences by resolving the full range of reaction-diffusion scales in a stochastic model.
A finite element numerical analysis model has been constructed that consists of a realistic mesh capturing the geometries of Big Hill (BH) Strategic Petroleum Reserve (SPR) site using the multi-mechanism deformation (M-D) salt constitutive model and including data taken daily of the wellhead pressure and level of the oil-brine interface. The salt creep rate is not uniform in the salt dome, and creep test data for BH salt is limited. Therefore, a model calibration is necessary to simulate the geomechanical behavior of the salt dome. Cavern volumetric closures of SPR caverns calculated from sonar survey reports are used for the field baseline measurement. The structure factor, A2, and transient strain limit factor, Ko, in the M-D constitutive model are used for model calibration. An A2 value obtained experimentally from the BH salt and Ko value of WIPP salt are used as the baseline values. To adjust the magnitude of A2 and Ko, multiplication factors A2F and KOF are defined, respectively. The A2F and KOF values of the salt dome and salt drawdown layer of elements surrounding each SPR cavern have been determined through a number of back fitting analyses. The trendlines of the predictions and sonar data match up well for BH 101, 103, 104, 106, 110, 111, and 113. The prediction curves are close to the sonar data for BH 102 and 114. However, the prediction curves for BH 105, 107, 108, 109, and 112 are not close to the sonar data. An inconsistency was found in the sonar data, i.e. the sonar measurements of cavern volumes increase with time, during some periods for BH 101, 104, 106, 107, and 112. A follow-up report in 2019 will provide a resolution for these issues.
The goal of the DOE OE Energy Storage System Safety Roadmap is to foster confidence in the safety and reliability of energy storage systems. There are three interrelated objectives to support the realization of that goal: research, codes and standards (C/S) and communication/coordination. The objective focused on C/S is "To apply research and development to support efforts that refocused on ensuring that codes and standards are available to enable the safe implementation of energy storage systems in a comprehensive, non-discriminatory and science-based manner."
Acid phthalate crystals such as KAP crystals are a method of choice to record x-ray spectra in the soft x-ray regime (E ∼ 1 keV) using the large (001) 2d = 26.63 Å spacing. Reflection from many other planes is possible, and knowledge of the 2d spacing, reflectivity, and resolution for these reflections is necessary to evaluate whether they hinder or help the measurements. Burkhalter et al. [J. Appl. Phys., 52, 4379 (1981)] showed that the (013) reflection has efficiency comparable to the 2nd order reflection (002), and it can overlap the main first order reflection when the crystal bending axis (b-axis) is contained in the dispersion plane, thus contaminating the main (001) measurement in a convex crystal geometry. We present a novel spectrograph concept that makes these asymmetric reflections helpful by setting the crystal b-axis perpendicular to the dispersion plane. In such a case, asymmetric reflections do not overlap with the main (001) reflection and each reflection can be used as an independent spectrograph. Here we demonstrate an achieved spectral range of 0.8-13 keV with a prototype setup. The detector measurements were reproduced with a 3D ray-tracing code.
This Part 2 study examined the microstructural characteristics of braze joints made between two KOVarTM base materials using the filler metals, Ag-xAl, having x = 0, 2, 5, and 10 wt.% Al additions. Brazing processes had temperatures of 965°C (1769°F) and 995°C and brazing times of 5 and 20 min. All brazing was performed under high vacuum.
Hansen, Nils H.; Tao, Tao; Kang, Shiqing; Sun, Wenyu; Wang, Jiaxing; Liao, Handong; Moshammer, Kai; Law, Chung K.; Bin YangBin
Acetaldehyde is an important intermediate and a toxic emission in the combustion of fuels, especially for biofuels. To better understand its combustion characteristics, a detailed chemical kinetic model describing the oxidation of acetaldehyde has been developed and comprehensively validated against various types of literature data including laminar flame speeds, oxidation and pyrolysis in shock tubes, chemical structure of premixed flames, and low-temperature oxidation in jet-stirred reactors. To extend the validation range, the chemical structure of a counterflow flame fueled by acetaldehyde at 600 Torr has been measured using vacuum ultra-violet photoionization molecular-beam mass spectrometry. In addition, ignition delay times at 10 atm and 700-1100 K were measured in a rapid compression machine, and a negative temperature coefficient (NTC) behavior was observed. The present kinetic model well reproduces the results of various acetaldehyde combustion experiments covering wide ranges of temperatures (300–2300 K) and pressures (0.02–10 atm), and explains well the observed NTC behavior based on the competition between multiple oxidation pathways for the methyl radicals and their self-recombination forming ethane, a relatively stable species at temperatures below 1000 K.
This report describes research into three health physics parameters used by Launch Safety (LS) for which the appropriate value, distribution, or applicability came into question during preparation of the Mars 2020 LS analysis. These parameters and associated issues include the Dose and Dose Rate Effectiveness Factor (DDREF) and its use in health effects calculations, a methodology for translating projected contamination per unit area into dose to aquatic and terrestrial biota, and plutonium transfer factors for use in ingestion pathway consequence analyses.
Regulatory drivers and market demands for lower pollutant emissions, lower carbon dioxide emissions, and lower fuel consumption motivate the development of cleaner and more fuel-efficient engine operating strategies. Most current production engines use a combination of both in-cylinder and exhaust emissions control strategies to achieve these goals. The emissions and efficiency performance of in-cylinder strategies depend strongly on flow and mixing processes associated with fuel injection and heat losses.
HT-PEMFCs offer advantages over LT-PEMFCs because of their higher operating temperatures. These advantages include higher catalytic activity, higher tolerance to impurities, and easier thermal management. LANL, in collaboration with SNL, has developed phosphate-quaternary ammonium ionpair coordinated proton exchange membranes for use in HT-PEMFCs. Fuel cells made with the ion-pair membranes have the potential to be operated at temperatures above 200 °C, however there is a tendency for the phosphoric acid to evaporate from the electrodes at temperatures above 180 °C. Thus, there is a need to develop an ionomer that can conduct protons at high temperatures and which can be processed into MEAs. Such a polymer also needs to be extremely durable in order to function at low pH, low RH, high temperature conditions.
Adoption of plug-in electric vehicles (PEVs) has expanded over the last few years, yet introduction of PEV smart charging has been stalled due to barriers in communication, controls, and an unclear method for determining the value PEVs will bring to the grid. This project will consider the grid impact of a variety of future scenarios, including adoption of different vehicle types, proliferation of extreme fast charging (xFC), expanded adoption of distributed energy resources (DER), and multiple smart charge management approaches. This project will determine how PEV charging at scale should be managed to avoid negative grid impacts, allow for critical strategies and technologies to be developed, and increase the value for PEV owners, building managers, charge network operators, grid services aggregators, and utilities.
Cybersecurity is essential for interoperable power systems and transportation infrastructure in the US. As the US transitions to transportation electrification, cyber attacks on vehicle charging could impact nearly all US critical infrastructure. This is a growing area of concern as more charging stations communicate to a range of entities (grid operators, vehicles, OEM vendors, etc.), as shown in Figure I.1.1.1. The research challenges are extensive and complicated because there are many end users, stakeholders, and software and equipment vendors. Poorly implemented electric vehicle supply equipment (EVSE) cybersecurity is a major risk to electric vehicle (EV) adoption because the political, social, and financial impact of cyberattacks—or public perception of such—ripples across the industry and has lasting and devastating effects. Unfortunately, there is no comprehensive EVSE cybersecurity approach and limited best practices have been adopted by the EV/EVSE industry. For this reason, there is an incomplete industry understanding of the attack surface, interconnected assets, and unsecured interfaces. Thus, comprehensive cybersecurity recommendations founded on sound research are necessary to secure EV charging infrastructure. This project is providing the automotive industry with a strong technical basis for securing this infrastructure by developing threat models, prioritizing technology gaps, and developing effective countermeasures. Specifically, the team is creating a cybersecurity threat model and performing a technical risk assessment of EVSE assets, so that automotive, charging, and utility stakeholders can better protect customers, vehicles, and power systems in the face of new cyber threats.
This project is part of a multi-lab consortium that leverages U.S. research expertise and facilities at national labs and universities to significantly advance electric drive power density and reliability, while simultaneously reducing cost. The final objective of the consortium is to develop a 100 kW traction drive system that achieves 33 kW/L, has an operational life of 300,000 miles, and a cost of less than $\$6$/kW. One element of the system is a 100 kW inverter with a power density of 100 kW/L and a cost of $\$2.7$/kW. New materials such as widebandgap semiconductors, soft magnetic materials, and ceramic dielectrics, integrated using multi-objective cooptimization design techniques, will be utilized to achieve these program goals. This project focuses on a subset of the power electronics work within the consortium, specifically the design, fabrication, and evaluation of vertical GaN power devices suitable for automotive applications.
Faster combustion improves the efficiency of a diesel engine, and in medium-duty diesel engines, interactions between the fuel sprays and the piston bowl walls play a key role in determining heat-release rates. Stepped-lip pistons can promote the formation of vortices that are correlated with faster, more efficient heat-release, but this behavior is primarily observed for late injection timings at which the engine is not operating at its peak efficiency. The objectives of this part of the project are to explain the physical mechanisms responsible for this phenomenon, to identify measures that may enhance vortex formation, and to quantify the extent to which these measures may improve the engine's thermal efficiency.
A copolymer of maleic anhydride and styrene is functionalized with Diels–Alder (DA) capable pendant groups to enable the study of this material with different crosslink densities. This constituent is synthesized using commercially available starting materials and relatively simple and uncomplicated chemistries which open the possibility for its use in large-scale applications. The 10%, 25%, 50%, and 100% DA nominal crosslinking based on available pendant furan groups on the polymeric component is investigated. The reaction kinetics are monitored using infrared spectroscopy and rheology. Based on the rheological results, carbon nanotube (CNT) incorporation into the DA matrix is explored in order to determine its effects on the complex modulus of the material. This work is meant as a proof of concept for this DA material with the possibility of its incorporation into other commonly used bulk materials and/or adhesives to allow for an easily reversible product formulation.
This work uses market analysis and simulation to explore the potential of public charging infrastructure to spur US battery electric vehicle (BEV) sales, increase national electrified mileage, and lower greenhouse gas (GHG) emissions. By employing both scenario and parametric analysis for policy driven injection of public charging stations we find the following: (1) For large deployments of public chargers, DC fast chargers are more effective than level 2 chargers at increasing BEV sales, increasing electrified mileage, and lowering GHG emissions, even if only one DC fast charging station can be built for every ten level 2 charging stations. (2) A national initiative to build DC fast charging infrastructure will see diminishing returns on investment at approximately 30,000 stations. (3) Some infrastructure deployment costs can be defrayed by passing them back to electric vehicle consumers, but once those costs to the consumer reach the equivalent of approximately 12¢/kWh for all miles driven, almost all gains to BEV sales and GHG emissions reductions from infrastructure construction are lost.
An analysis of microgrids to increase resilience was conducted for the island of Puerto Rico. Critical infrastructure throughout the island was mapped to the key services provided by those sectors to help inform primary and secondary service sources during a major disruption to the electrical grid. Additionally, a resilience metric of burden was developed to quantify community resilience, and a related baseline resilience figure was calculated for the area. To improve resilience, Sandia performed an analysis of where clusters of critical infrastructure are located and used these suggested resilience node locations to create a portfolio of 159 microgrid options throughout Puerto Rico. The team then calculated the impact of these microgrids on the region's ability to provide critical services during an outage, and compared this impact to high-level estimates of cost for each microgrid to generate a set of efficient microgrid portfolios costing in the range of 218-917M dollars. This analysis is a refinement of the analysis delivered on June 01, 2018.
Started in 2016, the PV Lifetime Project is measuring PV module and system degradation profiles over time with the aim of distinguishing different module types and technology. Outdoor energy monitoring in different climates is supplemented with regular testing under repeatable test conditions indoors. The focus is on the PV module, as well as other hardware components (junction boxes, bypass diodes, and module-level electronics) attached to it. Hardware is installed at Sandia National Laboratories in New Mexico, at the National Renewable Energy Laboratory in Colorado, and at the University of Central Florida. The systems are continuously monitored for DC current and voltage, as well as periodic I-V curves at the string level. In the future, once degradation trends have been identified with more certainty, results will be made available to the public online. This data is expected to enable an increase in the accuracy and precision of degradation profiles used in yield assessments that support investments made in new PV plants. Current practice is to assume that degradation is constant over the life of the system. Forthcoming results in the next few years will help to determine whether this assumption is still appropriate.
There are differences in how cyber-attack, sabotage, or discrete component failure mechanisms manifest within power plants and what these events would look like within the control room from an operator's perspective. This research focuses on understanding how a cyber event would affect the operation of the plant, how an operator would perceive the event, and if the operator's actions based on those perceptions will allow him/her to maintain plant safety. This research is funded as part of Sandia's Laboratory Directed Research and Development (LDRD) program to develop scenarios with cyber induced failure of plant systems coupled with a generic pressurized water reactor plant training simulator. The cyber scenario s w ere developed separately and injected into the simulator operational state to simulate an attack. These scenarios will determine if Nuclear Power Plant (NPP) operators can 1) recognize that the control room indicators were presenting incorrect or erroneous information and 2) take appropriate actions to keep the plant safe. This will also provide the opportunity to assess the operator cognitive workload during such events and identify where improvements might be made. This paper will review results of a pilot study run with NPP operators to investigate performance under various cyber scenarios. The discussion will provide an overview of the approach, scenario selection, metrics captured, resulting insights into operator actions and plant response to multiple scenarios of the NPP system.
Rate coefficients are key quantities in gas phase kinetics and can be determined theoretically via master equation (ME) calculations. Rate coefficients characterize how fast a certain chemical species reacts away due to collisions into a specific product. Some of these collisions are simply transferring energy between the colliding partners, in which case the initial chemical species can undergo a unimolecular reaction: dissociation or isomerization. Other collisions are reactive, and the colliding partners either exchange atoms, these are direct reactions, or form complexes that can themselves react further or get stabilized by deactivating collisions with a bath gas. The input of MEs are molecular parameters: geometries, energies, and frequencies determined from ab initio calculations. While the calculation of these rate coefficients using ab initio data is becoming routine in many cases, the determination of the uncertainties of the rate coefficients are often ignored, sometimes crudely assessed by varying independently just a few of the numerous parameters, and only occasionally studied in detail. In this study, molecular frequencies, barrier heights, well depths, and imaginary frequencies (needed to calculate quantum mechanical tunneling) were automatically perturbed in an uncorrelated fashion. Our Python tool, MEUQ, takes user requests to change all or specified well, barrier, or bimolecular product parameters for a reaction. We propagate the uncertainty in these input parameters and perform global sensitivity analysis in the rate coefficients for the ethyl + O2 system using state-of-the-art uncertainty quantification (UQ) techniques via Python interface to UQ Toolkit (www.sandia.gov/uqtoolkit). A total of 10,000 sets of rate coefficients were collected after perturbing 240 molecular parameters. With our methodology, sensitive mechanistic steps can be revealed to a modeler in a straightforward manner for identification of significant and negligible influences in bimolecular reactions.
Here, we report on reliability testing of vertical GaN (v-GaN) devices under continuous switching conditions of 500, 750, and 1000 V. Using a modified double-pulse test circuit, we evaluate 1200 V-rated v-GaN PiN diodes fabricated by Avogy. Forward current–voltage characteristics do not change over the stress period. Under the reverse bias, the devices exhibit an initial rise in leakage current, followed by a slower rate of increase with further stress. The leakage recovers after a day's relaxation which suggests that trapping of carriers in deep states is responsible. Overall, we found the devices to be robust over the range of conditions tested.
The description and notes describe and scope the activities performed under this PHS. All hazards have been identified. Questions are answered correctly and, as necessary, rationale or clarification is provided. All hazards in the HA have been analyzed, including the identification of controls for each hazard. l have performed the above reviews and concur that those items are complete and accurate.
Concurrency and Computation. Practice and Experience
Bernholdt, David E.; Boehm, Swen; Bosilca, George; Venkata, Manjunath G.; Grant, Ryan E.; Naughton, Thomas; Pritchard, Howard P.; Schulz, Martin; Vallee, Geoffroy R.
The Exascale Computing Project (ECP) is currently the primary effort in the United States focused on developing “exascale” levels of computing capabilities, including hardware, software, and applications. In order to obtain a more thorough understanding of how the software projects under the ECP are using, and planning to use the Message Passing Interface (MPI), and help guide the work of our own project within the ECP, we created a survey. Of the 97 ECP projects active at the time the survey was distributed, we received 77 responses, 56 of which reported that their projects were using MPI. Furthermore, this paper reports the results of that survey for the benefit of the broader community of MPI developers.
The US Department of Energy Nuclear Energy Research Initiative (NERI) funded the Burnup Credit Critical Experiment (BUCCX) at Sandia National Laboratories. The BUCCX was designed to investigate the effect of fission product materials on critical systems. The BUCCX assembly was a water-moderated and -reflected array of Zircaloy-clad triangular-pitched U(4.31%)02 fuel elements. Some of the fuel elements could be opened to allow placement of experiment materials between the fuel pellets in the element. The ten BUCCX critical experiments reported here test the effect of the fission product rhodium on the assembly. The calculated reactivity worth of the rhodium in the experiments ranged from 0% for cases with no rhodium to a maximum of 3.5% of keff.
Control systems for critical infrastructure are becoming increasingly interconnected while cyber threats against critical infrastructure are becoming more sophisticated and difficult to defend against. Historically, cyber security has emphasized building defenses to prevent loss of confidentiality, integrity, and availability in digital information and systems, but in recent years cyber attacks have demonstrated that no system is impenetrable and that control system operation may be detrimentally impacted. Cyber resilience has emerged as a complementary priority that seeks to ensure that digital systems can maintain essential performance levels, even while capabilities are degraded by a cyber attack. This paper examines how cyber security and cyber resilience may be measured and quantified in a control system environment. Load Frequency Control is used as an illustrative example to demonstrate how cyber attacks may be represented within mathematical models of control systems, to demonstrate how these events may be quantitatively measured in terms of cyber security or cyber resilience, and the differences and similarities between the two mindsets. These results demonstrate how various metrics are applied, the extent of their usability, and how it is important to analyze cyber-physical systems in a comprehensive manner that accounts for all the various parts of the system.
The purpose of this project was to devise, implement, and demonstrate a method that can use Sandia's existing analysis codes (e.g., Sierra, Alegra, the CTH hydro code) with minimal modification to generate objective function gradients for optimization-based design in transient, non-linear, coupled-physics applications. The approach uses a Moving Least Squares representation of the geometry to substantially reduce the number of geometric degrees of freedom. A Multiple-Program Multiple-Data computing model is then used to compute objective gradients via finite differencing. Details of the formulation and implementation are provided, and example applications are presented that show effectiveness and scalability of the approach.
The course content consisted of 32 modules that included topics necessary to understand how to conduct PPS design and evaluation. An important aspect of ITC-27's training methodology was to ensure that each topic was presented via lecture (hear), and also included demonstrations (see) and hands-on field activities (do), whenever applicable. A final exercise provided participants with the opportunity to apply the design and evaluation knowledge gained during the course. Guest lecturers—both domestic and international—supplemented information from related agency perspectives. A new topic—Unmanned Aerial Systems (UAS)—offered participants a high-level awareness of the types, uses, and capabilities of these systems and how they might be used in both an adversarial and protective capacity.
Presented in this document are the theoretical aspects of capabilities contained in the Sierra / SM code. This manuscript serves as an ideal starting point for understanding the theoretical foundations of the code. For a comprehensive study of these capabilities, the reader is encouraged to explore the many references to scientific articles and textbooks contained in this manual. It is important to point out that some capabilities are still in development and may not be presented in this document. Further updates to this manuscript will be made as these capabilities come closer to production level.
This report summarizes the 2018 fiscal year (FY18) field, laboratory, and modeling work funded by the US Department of Energy Office of Nuclear Energy (DOE-NE) Spent Fuel and Waste Science & Technology (SFWST) campaign as part of the Sandia National Laboratories Salt Research and Development (R&D) and Salt International work packages. This report satisfies level-two milestone M2SF-18SNO10303031and comprises three related but stand-alone sections. The first section summarizes the programmatic progress made to date in the DOE-NE salt program and its goals going forward. The second section presents brine composition modeling and laboratory activities related to salt evaporation experiments, which will be used to interpret data collected during the heater test. The third section presents theoretical and numerical modeling work done to investigate the effects brine composition have on dihedral angle and the permeability of salt.
We study the problem of estimating a function of many parameters acquired by sensors that are distributed in space, e.g., the spatial gradient of a field. We restrict ourselves to a setting where the distributed sensors are probed with experimentally practical resources, namely, field modes in separable displaced thermal states, and focus on the optimal design of the optical receiver that measures the phase-shifted returning field modes. Within this setting, we demonstrate that a locally optimal measurement strategy, i.e., one that achieves the standard quantum limit for all phase-shift values, is a Gaussian measurement, and moreover, one that is separable. We also demonstrate the utility of adaptive phase measurements for making estimation performance robust in cases where one has little prior information on the unknown parameters. In this setting we identify a regime where it is beneficial to use structured optical receivers that entangle the received modes before measurement.
Magnetic property enhancement of alnico, a rare-earth free permanent magnet, is highly dependent on both the initial microstructure and the evolution of the spinodal decomposition (SD) inside each grain during the heat treatment process. The size, shape and distribution of the magnetic FeCo-rich (α1) phase embedded in continuous non-magnetic AlNi-rich (α2) phase as well as a minor Cu-enriched phase residing in between are shown to be crucial in controlling coercivity. Phase and magnetic domain morphology in a commercial alnico 9 alloy was studied using a combination of structural characterization techniques, including scanning electron microscopy, electron backscatter diffraction, aberration-corrected scanning transmission electron microscopy and Lorentz microscopy. Our results showed that casting created structural nonuniformity and defects, such as porosity, TiS2 precipitates and grain misorientation, are heterogeneously distributed, with the center section having the best crystallographic orientation and minimal defects. The optimal spinodal is a “mosaic structure”, composed of rod-shape α1 phase with {110} or {100} planar faceting and diameter of ~30–45nm. There is also a Cu-enriched phase residing at the corners of two < 110 > facets of the α1 phase. Furthermore, it was observed that grain boundary phase reverse magnetization direction at lower external magnetic field compared to the SD region inside the grain. Improving grain orientation uniformity, reducing detrimental grain boundary phase volume fraction, and the branching of the α1 rods, as well as their diameter, are promising routes to improve energy product of alnico.
Attaining high performance with MPI applications requires efficient message matching to minimize message processing overheads and the latency these overheads introduce into application communication. In this paper, we use a validated simulation-based approach to examine the relationship between MPI message matching performance and application time-to-solution. Specifically, we examine how the performance of several important HPC workloads is affected by the time required for matching. Our analysis yields several important contributions: (i) the performance of current workloads is unlikely to be significantly affected by MPI matching unless match queue operations get much slower or match queues get much longer; (ii) match queue designs that provide sublinear performance as a function of queue length are unlikely to yield much benefit unless match queue lengths increase dramatically; and (iii) we provide guidance on how long the mean time per match attempt may be without significantly affecting application performance. The results and analysis in this paper provide valuable guidance on the design and development of MPI message match queues.
The adsorption equilibrium constants of monovalent and divalent cations to material surfaces in aqueous media are central to many technological, natural, and geochemical processes. Cation adsorption-desorption is often proposed to occur in concert with proton transfer on hydroxyl-covered mineral surfaces, but to date this cooperative effect has been inferred indirectly. This work applies density functional theory-based molecular dynamics simulations of explicit liquid water/mineral interfaces to calculate metal ion desorption free energies. Monodentate adsorption of Na+, Mg2+, and Cu2+ on partially deprotonated silica surfaces are considered. Na+ is predicted to be unbound, while Cu2+ exhibits binding free energies to surface SiO- groups that are larger than those of Mg2+. The predicted trends agree with competitive adsorption measurements on fumed silica surfaces. As desorption proceeds, Cu2+ dissociates one of the H2O molecules in its first solvation shell, turning into Cu2+(OH-)(H2O)3, while Mg remains Mg2+(H2O)6. The protonation state of the SiO- group at the initial binding site does not vary monotonically with cation desorption.
Neuromorphic computing has many promises in the future of computing due to its energy efficient and scalable implementation. Here we extend a neural algorithm that is able to solve the diffusion equation PDE by implementing random walks on neuromorphic hardware. Additionally, we introduce four random walk applications that use this spiking neural algorithm. The four applications currently implemented are: generating a random walk to replicate an image, finding a path between two nodes, finding triangles in a graph, and partitioning a graph into two sections. We then made these four applications available to be implemented on software using a graphical user interface (GUI).
Parameter estimation for mechanical models of plastic deformation utilized in nuclear weapons systems is a laborious process for both experimentalists and constitutive modelers and is critical to producing meaningful numerical predictions. In this work we derive an adjoint-based optimization approach for a stabilized, large-deformation J2 plasticity model that is considerably more computationally efficient but no less accurate than current state of the art methods. Unlike most approaches to model calibration, we drive the inversion procedure with full-field deformation data that can be experimentally measured through established digital image or volume correlation techniques. We present numerical results for two and three dimensional model problems and comment on various directions of future research.
Hydrothermal experiments on engineered barrier system (EBS) materials were conducted to characterize high temperature interactions between bentonite and candidate waste container steels (304SS, 316SS, low-C steel) for deep geological disposition of nuclear spent fuel. In this study, hydrothermal experiments were performed using Dickson reaction cells at temperatures and pressure of up to 300 °C and 15–16 MPa, respectively, for four to six weeks. Wyoming bentonite was saturated with a 1900 ppm K-Ca-Na-Cl solution in combination with stainless and low-C steel coupons. Authigenic Fe-saponite precipitated utilizing steel as a growth substrate with Fe being supplied by steel corrosion. Concurrent with Fe-saponite formation, sulfides precipitated from sulfide-bearing fluids, from pyrite dissolution, near the steel interface. Sulfide mineral formation is dependent on the steel substrate composition: stainless steel produced pentlandite ((Ni, Fe)9S8) and millerite (NiS), whereas low C steel generated pyrrhotite (Fe7S8). The presence of sulfides suggests highly reduced environments at the steel-clay barrier interface potentially influencing overall steel corrosion rates and (re)passivation mechanisms. Finally, results of this research show that nuclear waste steel container material may act as a substrate for mineral growth in response to corrosion during hydrothermal interactions with bentonite barriers.
The purpose of this study was to explore the flow rates and aerosol retention of an engineered microchannel with characteristic dimensions similar to those of stress corrosion cracks (SCCs) that could form in dry cask storage systems (DCSS) for spent nuclear fuel. Additionally, pressure differentials covering the upper limit of commercially available DCSS were studied. Given the scope and resources available, these data sets should be considered preliminary and are intended to demonstrate a new capability to characterize SCC under well-controlled boundary conditions. The gap of the microchannel tested was 28.9 gm (0.00110 in.), the width was 12.7 mm (0.500 in.), and the length was 8.86 mm (0.349 in.). Over a nine-hour period, the average mass concentration upstream of the microchannel was 0.048 mg/m3 while the average concentration downstream was 0.030 mg/m3. By the end of the test, the mass of aerosols that entered the test section upstream of the microchannel was 0.207 mg and the mass of aerosols that exited the microchannel was 0.117 mg. Therefore, 44% of the aerosols available for transmission was retained upstream of microchannel.
The goal of the DOE OE ESS Safety Roadmap1 is to foster confidence in the safety and reliability of energy storage systems (ESSs). Three interrelated objectives support the realization of that goal: research, codes and standards, and communication/coordination.
This report documents the completion of milestone STPRO4-7 Kokkos R&D: Remote Memory Spaces for One-Sided Halo-Exchange. The goal of this milestone was to develop and deploy an initial capability to support PGAS like communication models integrated into Kokkos via Remote Memory Spaces. The team developed semantic requirements for Remote Memory Spaces and implemented a prototype library leveraging four different communication libraries: libQUO, SHMEM, MPI-OneSided and NVSHMEM. In conjunction with ADCD02-COPA the Remote Memory Space capability was used in ExaMiniMD — a Molecular Dynamics Proxy Application — to explore the current state of the technology and its usability. The obtained results demonstrate that usability is very good, allowing a significant simplification communication routines, but performance is still lacking.
This report documents the completion of milestone STPRO4-6 Kokkos Support for ASC applications and libraries. The team provided consultation and support for numerous ASC code projects including Sandias SPARC, EMPIRE, Aria, GEMMA, Alexa, Trilinos, LAMMPS and nimbleSM. Over the year more than 350 Kokkos github issues were resolved, with over 220 requiring fixes and enhancements to the code base. Resolving these requests, with many of them issued by ASC code teams, provided applications with the necessary capabilities in Kokkos to be successful.
This report documents the completion of milestone STPRO4-5 Kokkos interoperability with general SIMD types to force vectorization on ATS-1. The Kokkos team worked with application developers to enable the utilization of SIMD intrinsics, which allowed up to 3.7x improvement of the affected kernels on ATS-1 in a proxy application. SIMD types are now deployed in the production code base.
This report documents the completion of milestone STPRO4-4 Kokkos back-ends research, collaborations, development, optimization, and documentation. The Kokkos team updated its existing backend to support the software stack and hardware of DOE's Sierra, Summit and Astra machines. They also collaborated with ECP PathForward vendors on developing backends for possible exa-scale architectures. Furthermore, the team ramped up its engagement with the ISO/C++ committee to accelerate the adoption of features important for the HPC community into the C++ standard.
This report documents the completion of milestone STPRO4-4 Kokkos back-ends research, collaborations, development, optimization, and documentation. The Kokkos team updated its existing backend to support the software stack and hardware of DOE's Sierra, Summit and Astra machines. They also collaborated with ECP PathForward vendors on developing backends for possible exa-scale architectures. Furthermore, the team ramped up its engagement with the ISO/C++ committee to accelerate the adoption of features important for the HPC community into the C++ standard.
Edstrand, Adam E.; Sun, Yiyang; Schmid, Peter J.; Taira, Kunihiko; Cattafesta, Louis N.
Designing effective control for complex three-dimensional flow fields proves to be non-trivial. Often, intuitive control strategies lead to suboptimal control. To navigate the control space, we use a linear parabolized stability analysis to guide the design of a control scheme for a trailing vortex flow field aft of a NACA0012 half-wing at an angle of attack $\unicode[STIX]{x1D6FC}=5^{\circ }$ and a chord-based Reynolds number $Re=1000$. The stability results show that the unstable mode with the smallest growth rate (fifth wake mode) provides a pathway to excite a vortex instability, whereas the principal unstable mode does not. Inspired by this finding, we perform direct numerical simulations that excite each mode with body forces matching the shape function from the stability analysis. Furthermore, relative to the uncontrolled case, the controlled flows show increased attenuation of circulation and peak streamwise vorticity, with the fifth-mode-based control set-up outperforming the principal-mode-based set-up. From these results, we conclude that a rudimentary linear stability analysis can provide key insights into the underlying physics and help engineers design effective physics-based flow control strategies.
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We introduce MPAS-Albany Land Ice (MALI) v6.0, a new variable-resolution land ice model that uses unstructured Voronoi grids on a plane or sphere. MALI is built using the Model for Prediction Across Scales (MPAS) framework for developing variable-resolution Earth system model components and the Albany multi-physics code base for the solution of coupled systems of partial differential equations, which itself makes use of Trilinos solver libraries. MALI includes a three-dimensional first-order momentum balance solver (Blatter-Pattyn) by linking to the Albany-LI ice sheet velocity solver and an explicit shallow ice velocity solver. The evolution of ice geometry and tracers is handled through an explicit first-order horizontal advection scheme with vertical remapping. The evolution of ice temperature is treated using operator splitting of vertical diffusion and horizontal advection and can be configured to use either a temperature or enthalpy formulation. MALI includes a mass-conserving subglacial hydrology model that supports distributed and/or channelized drainage and can optionally be coupled to ice dynamics. Options for calving include eigencalving, which assumes that the calving rate is proportional to extensional strain rates. MALI is evaluated against commonly used exact solutions and community benchmark experiments and shows the expected accuracy. Results for the MISMIP3d benchmark experiments with MALI's Blatter-Pattyn solver fall between published results from Stokes and L1L2 models as expected. We use the model to simulate a semi-realistic Antarctic ice sheet problem following the initMIP protocol and using 2 km resolution in marine ice sheet regions. MALI is the glacier component of the Energy Exascale Earth System Model (E3SM) version 1, and we describe current and planned coupling to other E3SM components.
We present a novel formulation for startup cost computation in the unit commitment problem (UC). Both the proposed formulation and existing formulations in the literature are placed in a formal, theoretical dominance hierarchy based on their respective linear programming relaxations. The proposed formulation is tested empirically against existing formulations on large-scale unit commitment instances drawn from real-world data. While requiring more variables than the current state-of-the-art formulation, our proposed formulation requires fewer constraints, and is empirically demonstrated to be as tight as a perfect formulation for startup costs. This tightening reduces the computational burden in comparison to existing formulations, especially for UC instances with large variability in net-load due to renewables production.
Scott, Ethan A.; Hattar, Khalid M.; Rost, Christina M.; Gaskins, John T.; Fazli, Mehrdad; Ganski, Claire; Li, Chao; Bai, Tingyu; Wang, Yekan; Esfarjani, Keivan; Goorsky, Mark; Hopkins, Patrick E.
Fundamental theories predict that reductions in thermal conductivity from point and extended defects can arise due to phonon scattering with localized strain fields. To experimentally determine how these strain fields impact phonon scattering mechanisms, we employ ion irradiation as a controlled means of introducing strain and assorted defects into the lattice. In particular, we observe the reduction in thermal conductivity of intrinsic natural silicon after self-irradiation with two different silicon isotopes, Si+28 and Si+29. Irradiating with an isotope with a nearly identical atomic mass as the majority of the host lattice produces a damage profile lacking mass impurities and allows us to assess the role of phonon scattering with local strain fields on the thermal conductivity. Our results demonstrate that point defects will decrease the thermal conductivity more so than spatially extended defect structures assuming the same volumetric defect concentrations due to the larger strain per defect that arises in spatially separated point defects. With thermal conductivity models using density functional theory, we show that for a given defect concentration, the type of defect (i.e., point vs extended) plays a negligible role in reducing the thermal conductivity compared to the strain per defect in a given volume.
Ducted fuel injection is a strategy that can be used to enhance the fuel/charge-gas mixing within the combustion chamber of a direct-injection compression-ignition engine. The concept involves injecting the fuel through a small tube within the combustion chamber to make the most fuel-rich regions of the micture in the autoignition zone leaner relative to a conventional free-spray configuration (i.e., a fuel spray that is not surrounded by a duct). This study is a follow-on to initial proof-of-concept experiments that also were conducted in a constant-volume combustion vessel. While the initial natural luminosity imaging experiments demonstrated that ducted fuel injection lowers soot incandescence dramatically, this study adds a more quantitative diffuse back-illumination diagnostic to measure soot mass, as well as investigates the effects on performance of varying duct geometry (axial gap, length, diameter, and inlet and outlet shapes), ambient density, and charge-gas dilution level. The result is that ducted fuel injection is further proven to be effective at lowering soot by 35–100% across a wide range of operating conditions and geometries, and guidance is offered on geometric parameters that are most important for improving performance and facilitating packaging for engine applications.
The reduced elastic modulus of a material is measured with a nanoindenter probe that is operated in the tapping mode. The resonant frequency of a freely oscillating cantilever is reduced when contact is made between the indenter tip and surface under investigation. It's shown using elasticity theory that the elastic deformation is a function of the indenter tip radius. A deeper penetration within the elastic range can change the tip radius, and introduce an error of 10% in calculating the reduced elastic modulus.
A comprehensive V&V study of hypersonic flow in SPARC validated against several experiments was produced. This work was successfully completed as an official ASC L2 milestone with an external review of the team's work. Our work has provided a basis for utilizing SPARC as credible analysis tool for hypersonic re-entry flows. The V&V process has been exercised in full breadth including applicable frameworks, professional standards, code and solution verification, calibration, sensitivity analysis and parametric uncertainty.
Kokkos and DARMA teams worked together on several significant proposals for the C++ standards body, including the MDSpan and Exectutors proposals. This work has potential for long-term impact into the language standard reflecting core abstractions needed for our HPC programming and development efforts. Kokkos team collaborating with AMD via the Path Forward effort. This is advancing Kokkos support for [AMD] backends, necessary for future exascale/HPC architectures.
Very recently, we have introduced correlation consistent effective core potentials (ccECPs) derived from many-body approaches with the main target being its use in explicitly correlated methods but also in mainstream approaches. The ccECPs are based on reproducing excitation energies for a subset of valence states, i.e., achieving a near-isospectrality between the original and pseudo Hamiltonians. Additionally, binding curves of dimer molecules have been used for refinement and overall improvement of transferability over a range of bond lengths. Here we apply similar ideas to the second row elements and study several aspects of the constructions in order to find the optimal (or nearly-optimal) solutions within the chosen ECP forms with 3s, 3p valence space (Ne-core). New constructions exhibit accurate low-lying atomic excitations and equilibrium molecular bonds (on average within ≈ 0.03 eV and 3 mA), however, the errors for A1 and Si oxide molecules at short bond lengths are notably larger for both ours and existing ECPs. Assuming this limitation, our ccECPs show a systematic balance between the criteria of atomic spectra accuracy and transferability for molecular bonds. Finally, in order to provide another option with much higher uniform accuracy, we also construct He-core ECPs for the whole row with typical discrepancies of ≈ 0.01 eV or smaller.
Some of the most remarkable recent developments in metal–organic framework (MOF) performance properties can only be rationalized by the mechanical properties endowed by their hybrid inorganic–organic nanoporous structures. While these characteristics create intriguing application prospects, the same attributes also present challenges that will need to be overcome to enable the integration of MOFs with technologies where these promising traits can be exploited. In this review, emerging opportunities and challenges are identified for MOF-enabled device functionality and technological applications that arise from their fascinating mechanical properties. This is discussed not only in the context of their more well-studied gas storage and separation applications, but also for instances where MOFs serve as components of functional nanodevices. Recent advances in understanding MOF mechanical structure–property relationships due to attributes such as defects and interpenetration are highlighted, and open questions related to state-of-the-art computational approaches for quantifying their mechanical properties are critically discussed.
A stochastic sparse particle approach is coupled with an artificial thickening flame (ATF) model for large eddy simulations (LES) to predict a series of turbulent premixed-stratified flames with and without shear and stratification. The thickened reaction progress variable serves as reference variable for the multiple mapping conditioning (MMC) mixing model which emulates turbulent mixing of the stochastic particles. The key feature of MMC is to enforce localness in this reference space when particle pairs are mixed and prevents unphysical mixing of burnt and unburnt fluid across the flame front. We apply MMC-ATF to three flames of a series of turbulent stratified flames and validate the method by comparison with experimental data. The new measurements feature increased accuracy in comparison to previously published data of the same flames due to a better signal-to-noise ratio and a setup which is less prone to beam steering. All flame locations are well predicted by the LES-ATF approach and an analysis of the MMC particle statistics demonstrates that MMC preserves the flamelet-like behaviour in regions where the experiments show low scatter around the flamelet solution. Predicted (local) deviations from the flamelet-solution are comparable to deviations observed in the measurements and variations in the flame structure due to differences in stratification and shear are reasonably well captured by the method.
Schneider, Silvan; Geyer, Dirk; Magnotti, Gaetano; Dunn, Matthew J.; Barlow, R.S.; Dreizler, Andreas
To explore the effect of H2 addition (20 percent by volume) on stratified-premixed methane combustion in a turbulent flow, an experimental investigation on a new flame configuration of the Darmstadt stratified burner is conducted here. Major species concentrations and temperature are measured with high spatial resolution by 1D Raman-Rayleigh scattering. A conditioning on local equivalence ratio (range from φ = 0.45 to φ = 1.25) and local stratification is applied to the large dataset and allows to analyze the impact of H2 addition on the flame structure. The local stratification level is determined as Δφ/ΔT at the location of maximum CO mass fraction for each instantaneous flame realization. Due to the H2 addition, preferential diffusion of H2 is different than in pure methane flames. In addition to diffusing out of the reaction zone where it is formed, particularly in rich conditions, H2 also diffuses from the cold reactant mixture into the flame front. For rich conditions (φ = 1.05 to φ = 1.15) H2 mass fractions are significantly elevated within the intermediate temperature range compared to fully-premixed laminar flame simulations. This elevation is attributed to preferential transport of H2 into the rich flame front from adjacent even richer regions of the flow. Additionally, when the local stratification across the flame front is taken into account, it is revealed that the state-space relation of H2 is not only a function of the local stoichiometry but also the local stratification level. In these flames H2 is the only major species showing sensitivity of the state-space relation to an equivalence ratio gradient across the flame front.
The multiple scattering of light presents major challenges in realizing useful in vivo imaging at tissue depths of more than about one millimeter, where many answers to health questions lie. Visible through near-infrared photons can be readily and safely detected through centimeters of tissue; however, limited information is available for image formation. One strategy for obtaining images is to model the photon transport and a simple incoherent model is the diffusion equation approximation to the Boltzmann transport equation. Such an approach provides a prediction of the mean intensity of heavily scattered light and hence provides a forward model for optimization-based computational imaging. While diffuse optical imaging methods have received substantial attention, they remain restricted in terms of resolution because of the loss of high-spatial-frequency information that is associated with the multiple scattering of photons. Consequently, only relatively large inhomogeneities, such as tumors or organs in small animals, can be effectively resolved. Here, we introduce a superresolution imaging approach based on point localization in a diffusion framework that enables over two orders of magnitude improvement in the spatial resolution of diffuse optical imaging. The method is demonstrated experimentally by localizing a fluorescent inhomogeneity in a highly scattering slab and characterizing the localization uncertainty. The approach allows imaging through centimeters of tissue with a resolution of tens of microns, thereby enabling cells or cell clusters to be resolved. More generally, this high-resolution imaging approach could be applied with any physical transport or wave model and hence to a broad class of physical problems. Paired with a suitable optical contrast mechanism, as can be realized with targeted fluorescent molecules or genetically modified animals, superresolution diffuse imaging should open alternative dimensions for in vivo applications.
Sandia performs work safely, in a manner that ensures adequate protection for the Members of the Workforce, the public, and the environment; is accountable for the safe performance of work; exercises a degree of care commensurate with the work and associated hazards; and integrates environment, safety, and health management into work planning and execution.
We show that olefin metathesis can be used in an extremely simple process to rapidly alter the morphology of self-assembled poly(butadiene-b-ethylene oxide) (PB-PEO) dispersions in situ. The addition of a water-insoluble Hoveyda-Grubbs catalyst to aqueous assemblies of PB-PEO leads to degradation of the hydrophobic PB block by well-established metathesis pathways and a concomitant change in the composition of the block copolymer. This phenomenon drives morphological transitions characterized by rapidly decreasing sizes of the self-assembled aggregates, the ultimate extent of which is readily controlled by catalyst concentration. Exemplary cases are presented in which transitions from worm-like micelles to spherical micelles or from vesicles to worm-like micelles can be accomplished within minutes.
This report documents the outcome from the ASC ATDM Level 2 Milestone 6358: Assess Status of Next Generation Components and Physics Models in EMPIRE. This Milestone is an assessment of the EMPIRE (ElectroMagnetic Plasma In Realistic Environments) application and three software components. The assessment focuses on the electromagnetic and electrostatic particle-in-cell solutions for EMPIRE and its associated solver, time integration, and checkpoint-restart components. This information provides a clear understanding of the current status of the EMPIRE application and will help to guide future work in FY19 in order to ready the application for the ASC ATDM L1 Milestone in FY20. It is clear from this assessment that performance of the linear solver will have to be a focus in FY19.
In this paper we describe a method for controlling both the residual stress and the through-thickness stress gradient of aluminum nitride (AlN) thin films using a multi-step deposition process that varies the applied radio frequency (RF) substrate bias. The relationship between the applied RF substrate bias and the AlN residual stress is characterized using AlN films grown on oxidized silicon substrates is determined using 100 nm-1.5 μm thick blanket AlN films that are deposited with 60-100 W applied RF biases; the stress-bias relationship is found to be well described using a power law relationship. Using this relationship, we develop a model for varying the RF bias in a series of discrete deposition steps such that each deposition step has zero average stress. The applied RF bias power in these steps is tailored to produce AlN films that have minimized both the residual stress and the film stress gradient. AlN cantilevers were patterned from films deposited using this technique, which show reduced curvature compared to those deposited using a single RF bias setting, indicating a reduction of the stress gradient in the films.
Mystery surrounds the transition from gas-phase hydrocarbon precursors to terrestrial soot and interstellar dust, which are carbonaceous particles formed under similar conditions. Although polycyclic aromatic hydrocarbons (PAHs) are known precursors to high-temperature carbonaceous-particle formation, the molecular pathways that initiate particle formation are unknown. We present experimental and theoretical evidence for rapid molecular clustering–reaction pathways involving radicals with extended conjugation. These radicals react with other hydrocarbon species to form covalently bound complexes that promote further growth and clustering by regenerating resonance-stabilized radicals through low-barrier hydrogen-abstraction and hydrogen-ejection reactions. Such radical–chain reaction pathways may lead to covalently bound clusters of PAHs and other hydrocarbons that would otherwise be too small to condense at high temperatures, thus providing the key mechanistic steps for rapid particle formation and surface growth by hydrocarbon chemisorption.
A new apparatus-"Dropkinson Bar"-has been successfully developed for material property characterization at intermediate strain rates. This Dropkinson bar combines a drop table and a Hopkinson bar. The drop table is used to generate a relatively long and stable low-speed impact to the tensile specimen, whereas the Hopkinson bar principle is applied to measure the load history with accounting for inertia effects in the system. In addition, pulse shaping techniques were applied to the Dropkinson bar to facilitate uniform stress and strain as well as constant strain rate in the specimen. The Dropkinson bar was used to characterize 304L stainless steel and 6061-T6 aluminum at a strain rate of ~600 s-1. The experimental data obtained from the Dropkinson bar tests were compared with the data obtained from conventional Kolsky tensile bar tests of the same material at similar strain rates. Both sets of experimental results were consistent, showing the newly developed Dropkinson bar apparatus is reliable and repeatable.
Hyperelastic foams have excellent impact energy absorption capability and can experience full recovery following impact loading. Consequently, hyperelastic foams are selected for different applications as shock isolators. Obtaining accurate intrinsic dynamic compressive properties of the hyperelastic foams has become a crucial step in shock isolation design and evaluation. Radial inertia is a key issue in dynamic characterization of soft materials. Radial inertia induced stress in the sample is generally caused by axial acceleration and large deformation applied to a soft specimen. In this study, Poisson's ratio of a typical hyperelastic foam-silicone foam-was experimentally characterized under high strain rate loading and was observed to drastically change across the densification process. A transition in the Poisson's ratio of the silicone foam specimen during dynamic compression generated radial inertia which consequently resulted in additional axial stress in the silicone foam sample. A new analytical method was developed to address the Poisson's ratio-induced radial inertia effects for hyperelastic foams during high rate compression.
GaN is an attractive material for high-power electronics due to its wide bandgap and large breakdown field. Verticalgeometry devices are of interest due to their high blocking voltage and small form factor. One challenge for realizing complex vertical devices is the regrowth of low-leakage-current p-n junctions within selectively defined regions of the wafer. Presently, regrown p-n junctions exhibit higher leakage current than continuously grown p-n junctions, possibly due to impurity incorporation at the regrowth interfaces, which consist of c-plane and non-basal planes. Here, we study the interfacial impurity incorporation induced by various growth interruptions and regrowth conditions on m-plane p-n junctions on free-standing GaN substrates. The following interruption types were investigated: (1) sample in the main MOCVD chamber for 10 min, (2) sample in the MOCVD load lock for 10 min, (3) sample outside the MOCVD for 10 min, and (4) sample outside the MOCVD for one week. Regrowth after the interruptions was performed on two different samples under n-GaN and p-GaN growth conditions, respectively. Secondary ion mass spectrometry (SIMS) analysis indicated interfacial silicon spikes with concentrations ranging from 5e16 cm-3 to 2e18 cm-3 for the n-GaN growth conditions and 2e16 cm-3 to 5e18 cm-3 for the p-GaN growth conditions. Oxygen spikes with concentrations ~1e17 cm-3 were observed at the regrowth interfaces. Carbon impurity levels did not spike at the regrowth interfaces under either set of growth conditions. We have correlated the effects of these interfacial impurities with the reverse leakage current and breakdown voltage of regrown m-plane p-n junctions.
The different rate-limiting processes underlying ignition and self-propagating reactions in Al/Pt multilayers are examined through experiments and analytical modeling. Freestanding, ∼1.6 μm-thick Al/Pt multilayers of varied stoichiometries and nanometer-scale layer thicknesses ignite at temperatures below the melting point of both reactants (and eutectics) demonstrating that initiation occurs via solid-state mixing. Equimolar multilayers exhibit the lowest ignition temperatures when comparing structures having a specific bilayer thickness. An activation energy of 76.6 kJ/mol at. associated with solid state mass transport is determined from the model analysis of ignition. High speed videography shows that equimolar Al/Pt multilayers undergo the most rapid self-sustained reactions with wavefront speeds as large as 73 m/s. Al- and Pt-rich multilayers react at reduced rates (as low as 0.3 m/s), consistent with reduced heat of reaction and lower adiabatic temperatures. An analytical model that accounts for key thermodynamic properties, preliminary mixing along interfaces, thermal transport, and mass diffusion is used to predict the wavefront speed dependencies on bilayer thickness. Good fits to experimental data provide estimates for activation energy (51 kJ/mol at.) associated with mass transport subject to high heating rates and thermal diffusion coefficient of premixed interfacial volumes (2.8 × 10-6 m2/s). Pt dissolution into molten Al is identified as a rate-limiting step underlying high temperature propagating reactions in Al/Pt multilayers.
Electric field-based frequency tuning of acoustic resonators at the material level provides an enabling technology for building complex tunable filters. Tunable acoustic resonators were fabricated in thin plates (h/λ ∼ 0.05) of X-cut lithium niobate (90°, 90°, ψ = 170°). Lithium niobate is known for its large electromechanical coupling (SH: K2 40%) and thus applicability for low-insertion loss and wideband filter applications. We demonstrate the effect of a DC bias to shift the resonant frequency by 0.4% by directly tuning the resonator material. The mechanism is based on the nonlinearities that exist in the piezoelectric properties of lithium niobate. Devices centered at 332 MHz achieved frequency tuning of 12 kHz/V through application of a DC bias.
The overall goal of this work was to improve the modeling of laboratory shock and vibration testing. Laboratory shock and vibration testing is used to qualify Nuclear Weapon components for the environment they will experience in the field. Standard practice is to use rigid test fixtures so that no spurious modes are introduced during laboratory testing. Rigid test fixtures may however in some cases change the dynamics of the component being tested, resulting in laboratory testing being more severe than what would occur in the field. This milestone investigated the use of topology optimization to create laboratory test fixtures that would better replicate the dynamics that components experience in field environments.
This memo describes the engineering technical and costing analysis support needed for identifying and evaluating technical and programmatic solutions for spent nuclear fuel (SNF) in dual-purpose canisters (DPCs), and the resources planned to provide that support. The Technical and Programmatic Solutions (T&PS) work scope is intended to identify and evaluate the range of feasible options available for DPC direct disposal, considering the range of DPC designs in the existing fleet and a range of generic geologic disposal concepts. It will also identify changes to the way DPCs are loaded, and/or additional hardware that could be installed in DPCs as they are loaded, to improve disposability (chiefly, post closure criticality control). These two thrusts are the focus of engineering support to the work package.
The overall goal of this work was to improve the modeling of laboratory shock and vibration testing. Laboratory shock and vibration testing is used to qualify Nuclear Weapon components for the environment they will experience in the field. Standard practice is to use rigid test fixtures so that no spurious modes are introduced during laboratory testing. Rigid test fixtures may however in some cases change the dynamics of the component being tested, resulting in laboratory testing being more severe than what would occur in the field.
Maximum power handling, spike leakage, and failure mechanisms have been characterized for limiters based on the thermally triggered metal-insulator transition of vanadium dioxide. These attributes are determined by properties of the metal-insulator material such as on/off resistance ratio, geometric properties that determine the film resistance and the currentcarrying capability of the device, and thermal properties such as heatsinking and thermal coupling. A limiter with greater than 10 GHz of bandwidth demonstrated 0.5 dB loss, 27 dBm threshold power, 8 Watts blocking power, and 0.4 mJ spike leakage at frequencies near 2 GHz. A separate limiter optimized for high power blocked over 60 Watts of incident power with leakage less than 25 dBm after triggering. The power handling demonstrates promise for these limiter devices, and device optimization presents opportunities for additional improvement in spike leakage, response speed, and reliability.
Proceedings - 17th IEEE International Conference on Trust, Security and Privacy in Computing and Communications and 12th IEEE International Conference on Big Data Science and Engineering, Trustcom/BigDataSE 2018
To ensure reliable and predictable service in the electrical grid it is important to gauge the level of trust present within critical components and substations. Although trust throughout a smart grid is temporal and dynamically varies according to measured states, it is possible to accurately formulate communications and service level strategies based on such trust measurements. Utilizing an effective set of machine learning and statistical methods, it is shown that establishment of trust levels between substations using behavioral pattern analysis is possible. It is also shown that the establishment of such trust can facilitate simple secure communications routing between substations.
Failure mode analysis/identification of potential process improvements leading to the development of new engineered controls and facility improvements.
The DARMA many-task framework provides asynchronous communication and load balancing functionality. This functionality is embedded in standard, modern C++ through the use of the template wrapper classes similar to futures. DARMA previously functioned as a single, large repository. This simplified building and installation, but hindered agile development as individual components could not be easily updated or reused in other projects. DARMA components can now be developed independently and reused in other ECP projects. Through Spack and modern CMake, a complete DARMA package can be easily configured and installed with automatic dependency management for each of the configuration options.
Electronic synaptic devices are important building blocks for neuromorphic computational systems that can go beyond the constraints of von Neumann architecture. Although two-terminal memristive devices are demonstrated to be possible candidates, they suffer from several shortcomings related to the filament formation mechanism including nonlinear switching, write noise, and high device conductance, all of which limit the accuracy and energy efficiency. Electrochemical three-terminal transistors, in which the channel conductance can be tuned without filament formation provide an alternative platform for synaptic electronics. In this work, an all-solid-state electrochemical transistor made with Li ion–based solid dielectric and 2D α-phase molybdenum oxide (α-MoO3) nanosheets as the channel is demonstrated. These devices achieve nonvolatile conductance modulation in an ultralow conductance regime (<75 nS) by reversible intercalation of Li ions into the α-MoO3 lattice. Based on this operating mechanism, the essential functionalities of synapses, such as short- and long-term synaptic plasticity and bidirectional near-linear analog weight update are demonstrated. Simulations using the handwritten digit data sets demonstrate high recognition accuracy (94.1%) of the synaptic transistor arrays. These results provide an insight into the application of 2D oxides for large-scale, energy-efficient neuromorphic computing networks.
Sandia National Laboratories is a multimission laboratory managed and operated by National Technology & Engineering Solutions of Sandia, LLC, a wholly owned subsidiary of Honeywell International Inc., for the U.S. Department of Energy's (DOE's), National Nuclear Security Administration. The National Nuclear Security Administration's Sandia Field Office administers the contract and oversees contractor operations at Sandia National Laboratories, New Mexico.
Sandia National Laboratories is a multimission laboratory managed and operated by National Technology & Engineering Solutions of Sandia, LLC, a wholly owned subsidiary of Honeywell International Inc., for the U.S. Department of Energy (DOE), National Nuclear Security Administration. The National Nuclear Security Administration's Sandia Field Office administers the contract and oversees contractor operations at the Sandia National Laboratories Tonopah Test Range (SNL/TTR) in Nevada and the Sandia National Laboratories Kaua`i Test Facility (SNL/KTF) in Hawaii Activities at SNL/TTR are conducted in support of DOE weapons programs and have operated at the site since 1957. SNL/KTF has operated as a rocket preparation launching and tracking facility since 1961.
Future energy applications rely on our ability to tune liquid intermolecular interactions and achieve designer electrolytes with highly optimized properties. In this work, we demonstrate rational, combined experimental-computational design of a new carba-closo-dodecaborate-based salt with enhanced anodic stability for Mg energy storage applications. We first establish, through a careful examination using a range of solvents, the anodic oxidation of a parent anion, the carba-closo-dodecaborate anion at 4.6 V vs Mg0/2+ (2.0 vs Fc0/+), a value lower than that projected for this anion in organic solvent-based electrolytes and lower than weakly associating bis(trifluoromethylsulfonyl)imide and tetrafluoroborate anions. Solvents such as acetonitrile, 3-methylsulfolane, and 1,1,1,3,3,3-hexafluoroisopropanol are shown to enable the direct measurement of carba-closo-dodecaborate oxidation, where the resultant neutral radical drives passive film formation on the electrode. Second, we employ computational screening to evaluate the impact of functionalization of the parent anion on its stability and find that replacement of the carbon-vertex proton with a more electronegative fluorine or trifluoromethyl ligand increases the oxidative stability and decreases the contact-ion pair formation energy while maintaining reductive stability. This predicted expansion of the electrochemical window for fluorocarba-closo-dodecaborate is experimentally validated. Future work includes evaluation of the viability of these derivative anions as efficient and stable carriers for energy storage as a function of the ionic transport through the resulting surface films formed on candidate cathodes.
Understanding of aqueous dissolution of silicate glasses and minerals is of great importance to both Earth science and materials science. Silicate dissolution exhibits complex temporal evolution and spatial pattern formations. Recently, we showed how observed complexity could emerge from a simple self-organizational mechanism: dissolution of the silica framework in a material could be catalyzed by the cations released from the reaction itself. This mechanism enables us to systematically predict many key features of a silicate dissolution process including the occurrence of a sharp corrosion front (vs. a leached surface layer), oscillatory dissolution and multiple stages of the alteration process (e.g., an alteration rate resumption at a late stage of glass dissolution). Here, through a linear stability analysis, we show that this same mechanism can also lead to morphological instability of an alteration front, which, in combination with oscillatory dissolution, can potentially lead to a whole suite of patterning phenomena, as observed on archaeological glass samples, including wavy dissolution fronts, growth rings, incoherent bandings of alteration products, and corrosion pitting. Here, the result thus further demonstrates the importance of the proposed self-accelerating mechanism in silicate material degradation.