Publications

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Simulating HPC systems is a difficult task and the emergence of “Beyond CMOS” architectures and execution models will increase that difficulty. This document presents a “tutorial” on some of the simulation challenges faced by conventional and non-conventional architectures (Section 1) and goals and requirements for simulating Beyond CMOS systems (Section 2). These provide background for proposed short- and long-term roadmaps for simulation efforts at Sandia (Sections 3 and 4). Additionally, a brief explanation of a proof-of-concept integration of a Beyond CMOS architectural simulator is presented (Section 2.3).

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The goal of this session is to introduce five security system design concepts that will enable the development of an integrated security system and will increase the likelihood of effective security management. As a regulator, it’s important to be aware of these design concepts so that when you inspect or evaluate a facility’s security system, you can ensure that these concepts have been applied.

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This monthly report is intended to communicate the status of North Slope ARM facilities managed by Sandia National Labs.

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DOE Fellow, Andres Cremisini, completed a 10-week internship with Sandia National Laboratories (SNL) in Albuquerque, New Mexico. Under the management of Kristopher Klingler and the mentorship of Jon Bradley, he was tasked with conceiving and coding a realistic weather model for use in physical security applications. The objective was to make a weather model that could use real data to accurately predict wind and precipitation conditions at any location of interest on the globe at any user-determined time. The intern received guidance on software design, the C++ programming language and clear communication of project goals and ongoing progress. In addition, Mr. Cremisini was given license to structure the program however he best saw fit, an experience that will benefit ongoing research endeavors.

The objective of this report is to determine the feasibility of a combined pulsed - power accelerator machine, similar to HERMES - III, with the Annular Core Research Reactor (ACRR) Fueled - Ring External Cavity (FREC - II) in a new facility. The document is conceptual in nature, and includes some neutronic analysis that i llustrates that that the physics of such a concept would be feasible. There would still be many engineering design considerations and issues that would need to be investigated in order to determine the true viability of such a concept. This report does n ot address engineering design details, the cost of such a facility, or what would be required to develop the safety authorization of the concept. The radiation requirements for the "on - target" gamma - ray dose and dose rate are not addressed in this report . It is assumed that if the same general on - target specifications for a HERMES - III type machine could be met with the proposed concept, that the machine would b e considered highly useful as a radiation effects sciences platform. In general, the combined accelerator/ACRR reactor concept can be shown to be feasible with no major issues that would preclude the usefulness of such a facility. The new facility would provide a capability that currently does not exist in the radiation testing complex.

The International Biological and Chemical Threat Reduction Program at Sandia National Laboratories is developing a 15 - year technology road map in support the United States Government efforts to reduce international chemical and biological dangers . In 2017, the program leadership chartered an analysis team to explore dangers in the future international chemical and biological landscape through engagements with national security experts within and beyond Sandia to gain a multidisciplinary perspective on the future . This report offers a hi gh level landscape of future chemical and biological dangers based upon analysis of those engagements and provides support for further technology road map development.

We study the optimization of an energy function used by the meshing community to measure and improve mesh quality. This energy is non-traditional because it is dependent on both the primal triangulation and its dual Voronoi (power) diagram. The energy is a measure of the mesh's quality for usage in Discrete Exterior Calculus (DEC), a method for numerically solving PDEs. In DEC, the PDE domain is triangulated and this mesh is used to obtain discrete approximations of the continuous operators in the PDE. The energy of a mesh gives an upper bound on the error of the discrete diagonal approximation of the Hodge star operator. In practice, one begins with an initial mesh and then makes adjustments to produce a mesh of lower energy. However, we have discovered several shortcomings in directly optimizing this energy, e.g. its non-convexity, and we show that the search for an optimized mesh may lead to mesh inversion (malformed triangles). We propose a new energy function to address some of these issues.

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The FY18Q1 milestone of the ECP/VTK-m project includes the implementation of a multiblock data set, the completion of a gradients filtering operation, and the release of version 1.1 of the VTK-m software. With the completion of this milestone, the new multiblock data set allows us to iteratively schedule algorithms on composite data structures such as assemblies or hierarchies like AMR. The new gradient algorithms approximate derivatives of fields in 3D structures with finite differences. Finally, the release of VTK-m version 1.1 tags a stable release of the software that can more easily be incorporated into external projects.

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We propose a porous materials analysis pipeline using persistent homology. We rst compute persistent homology of binarized 3D images of sampled material subvolumes. For each image we compute sets of homology intervals, which are represented as summary graphics called persistence diagrams. We convert persistence diagrams into image vectors in order to analyze the similarity of the homology of the material images using the mature tools for image analysis. Each image is treated as a vector and we compute its principal components to extract features. We t a statistical model using the loadings of principal components to estimate material porosity, permeability, anisotropy, and tortuosity. We also propose an adaptive version of the structural similarity index (SSIM), a similarity metric for images, as a measure to determine the statistical representative elementary volumes (sREV) for persistence homology. Thus we provide a capability for making a statistical inference of the uid ow and transport properties of porous materials based on their geometry and connectivity.

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To support more rigorous analysis on global security issues at Sandia National Laboratories (SNL), there is a need to develop realistic data sets without using "real" data or identifying "real" vulnerabilities, hazards or geopolitically embarrassing shortcomings. In response, an interdisciplinary team led by subject matter experts in SNL's Center for Global Security and Cooperation (CGSC) developed a hypothetical case description. This hypothetical case description assigns various attributes related to international SNF transportation that are representative, illustrative and indicative of "real" characteristics of "real" countries. There is no intent to identify any particular country and any similarity with specific real-world events is purely coincidental. To support the goal of this report to provide a case description (and set of scenarios of concern) for international SNF transportation inclusive of as much "real-world" complexity as possible -- without crossing over into politically sensitive or classified information -- this SAND report provides a subject matter expert-validated (and detailed) description of both technical and political influences on the international transportation of spent nuclear fuel.

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Sandia National Laboratories is the largest of the Department of Energy national laboratories with more than 13,000 staff spread across its two main campuses in New Mexico and California. For more than 60 years, the Sandia National Laboratories campus in Livermore, California has delivered cutting-edge science and technology solutions to resolve the nation’s most challenging and complex problems. As a multidisciplinary laboratory, Sandia draws from virtually every science and engineering discipline to address challenges in energy, homeland security, cybersecurity, climate, and biosecurity. Today, collaboration is vital to ensuring that the Lab stays at the forefront of science and technology innovation. Partnerships with industry, state, and local governments, and California universities help drive innovation and economic growth in the region. Sandia contributed to California’s regional and statewide economy with more than $145 million in contracts to California companies, $92 million of which goes to California small businesses. In addition, Sandia engages the community directly by running robust STEM education programs for local schools and administering community giving programs. Meanwhile, investments like the Livermore Valley Open Campus (LVOC), an innovation hub supported by LLNL and Sandia, help catalyze the local economy.

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This milestone was focused on deploying and verifying a “sliding-mesh interface,” and establishing baseline timings for blade-resolved simulations of a sub-MW-scale turbine. In the ExaWind project, we are developing both sliding-mesh and overset-mesh approaches for handling the rotating blades in an operating wind turbine. In the sliding-mesh approach, the turbine rotor and its immediate surrounding fluid are captured in a “disk” that is embedded in the larger fluid domain. The embedded fluid is simulated in a coordinate system that rotates with the rotor. It is important that the coupling algorithm (and its implementation) between the rotating and inertial discrete models maintains the accuracy of the numerical methods on either side of the interface, i.e., the interface is “design order.”

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This workplan addresses filler attributes (i.e., possible requirements), assumptions needed for analysis, selection of filler materials, testing needs, and a long-range perspective on R&D activities leading to filler demonstration and a safety basis for implementation.

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Purpose: Water vapor trapped in encapsulation materials or enclosed volumes leads to corrosion issues for critical NW components. Sandia National Laboratories has created a new diagnostic to indicate the presence of water in weapon systems. Impact: Component exposure to water now can be determined instantly, without need for costly, time-consuming analytical methods.

The experimental breeder reactor (EBR-II) used fuel with a layer of sodium surrounding the uranium-zirconium fuel to improve heat transfer. Disposing of EBR-II fuel in a geologic repository without treatment is not prudent because of the potentially energetic reaction of the sodium with water. In 2000, the US Department of Energy (DOE) decided to treat the sodium-bonded fuel with an electrorefiner (ER), which produces metallic uranium product, a metallic waste, mostly from the cladding, and the salt waste in the ER, which contains most of the actinides and fission products. Two waste forms were proposed for disposal in a mined repository; the metallic waste, which was to be cast into ingots, and the ER salt waste, which was to be further treated to produce a ceramic waste form. However, alternative disposal pathways for metallic and salt waste streams may reduce the complexity. For example, performance assessments show that geologic repositories can easily accommodate the ER salt waste without treating it to form a ceramic waste form. Because EBR-II was used for atomic energy defense activities, the treated waste likely meets the definition of transuranic waste. Hence, disposal at the Waste Isolation Pilot Plant (WIPP) in southern New Mexico, may be feasible. This report reviews the direct disposal pathway for ER salt waste and describes eleven tasks necessary for implementing disposal at WIPP, provided space is available, DOE decides to use this alternative disposal pathway in an updated environmental impact statement, and the State of New Mexico grants permission.

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The Sandia Analysis Workbench (SAW) project has developed and deployed a production capability for SIERRA computational mechanics analysis workflows. However, the electrical analysis workflow capability requirements have only been demonstrated in early prototype states, with no real capability deployed for analysts’ use. This milestone aims to improve the electrical analysis workflow capability (via SAW and related tools) and deploy it for ongoing use. We propose to focus on a QASPR electrical analysis calibration workflow use case. We will include a number of new capabilities (versus today’s SAW), such as: 1) support for the XYCE code workflow component, 2) data management coupled to electrical workflow, 3) human-in-theloop workflow capability, and 4) electrical analysis workflow capability deployed on the restricted (and possibly classified) network at Sandia. While far from the complete set of capabilities required for electrical analysis workflow over the long term, this is a substantial first step toward full production support for the electrical analysts.

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This report presents a detailed process for compact model parameter extraction for DC circuit Zener diodes. Following the traditional approach of Zener diode parameter extraction, circuit model representation is defined and then used to capture the different operational regions of a real diode's electrical behavior. The circuit model contains 9 parameters represented by resistors and characteristic diodes as circuit model elements. The process of initial parameter extraction, the identification of parameter values for the circuit model elements, is presented in a way that isolates the dependencies between certain electrical parameters and highlights both the empirical nature of the extraction and portions of the real diode physical behavior which of the parameters are intended to represent. Optimization of the parameters, a necessary part of a robost parameter extraction process, is demonstrated using a 'Xyce-Dakota' workflow, discussed in more detail in the report. Among other realizations during this systematic approach of electrical model parameter extraction, non-physical solutions are possible and can be difficult to avoid because of the interdependencies between the different parameters. The process steps described are fairly general and can be leveraged for other types of semiconductor device model extractions. Also included in the report are recommendations for experiment setups for generating optimum dataset for model extraction and the Parameter Identification and Ranking Table (PIRT) for Zener diodes.

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Simulant polymer bonded explosives are widely used to simulate the mechanical response of real energetic materials. In this paper, the fracture resistance of a simulant polymer bo nded explosive (PBX) is experimentally investigated. The simulant is composed of 80 wt.% soda lime glass beads (SLGB) and 20 wt.% high impact Polystyrene 825 (HIPS). Brazilian disk tests are performed to characterize the tensile and compressive properties. Fracture toughness and energy tests are performed in the semi - circular bending (SCB) configuration on 80, 81, 82, and 83 wt % SLGB compositions. Digital image correlation is performed to record the surface displacements and calculate surface strains during testing. The m icromechanical behavior of ductile and brittle fracture are evaluated using digital microscopy and scanning electron microscopy of the fracture surface. It is determined that (i) the manufacturing process produces a credible simulant of PBX properties, and (ii) the SCB test measures fracture resistance with a reasonable coefficient of variation.

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This monthly report is intended to communicate the status of North Slope ARM facilities managed by Sandia National Labs.

Units Under Tests (UUTs) will be serviced from a "countertop" that's located on the uppermost side of a new temperature chamber. An ergonomic assessment was performed to determine a working height that ensures the technicians will be able to reach the components inside the UUT in a safe and reliable manner. A review of the anthropometric data relative to elbow height was used to make this determination. Nominal work height was 41.89 inches for the population of interest, ranging from 5th to 95th percentile. After adjusting for the height and centerline dimensions of the UUT, the "countertop" was defined to be ~26.0 inches. Next, a range of working heights was defined to accommodate the tasks involved with servicing the UUTs: from 38.0 to 45.8 inches. These values were compared with design guidelines from the general literature. The results were found to converge relatively well with the external references.

Maintaining Continuity of Knowledge (CoK) of spent fuel throughout its life cycle is a key objective of the International Atomic Energy Agency (IAEA). This report describes a project in which two specific technologies, cameras with infrared (IR) imaging capabilities and imaging sonar, were tested to determine their effectiveness in augmenting optical surveillance cameras currently used for maintaining CoK for spent nuclear fuel (SNF) staged in spent fuel pools. Furthermore, the project identifies any modifications required to the technologies to facilitate deployment for international safeguards purposes. This report presents results for the imaging sonar tested at Sandia National Laboratories (SNL) in a mockup spent nuclear fuel pool and for the IR-capable cameras tested by Pacific Northwest National Laboratory (PNNL) in the Oregon State University Training, Research, Isotopes, General Atomics (TRIGA) research reactor.

This document contains 31 use cases generated from the model contained in Rational Software Architect.

In this paper, the experimental results from long-term solubility experiments on micro crystalline neodymium hydroxide, Nd(OH)₃(micro cr), in high ionic strength solutions at 298.15 K under well-constrained conditions are presented. The starting material was synthesized according to a well-established method in the literature. In contrast with the previous studies in which hydrogen ion concentrations in experiments were adjusted with addition of either an acid or a base, the hydrogen ion concentrations in our experiments are controlled by the dissolution of Nd(OH)₃(micro cr), avoiding the possibility of phase change.

We have developed an ambient temperature, SiO₂/Si wafer - scale process for Josephson junctions based on Nb electrodes and Ta x N barriers with tunable electronic properties. The films are fabricated by magnetron sputtering. The electronic properties of the Ta_xN barriers are controlled by adjusting the nitrogen flow during sputtering. This technology offers a scalable alternative to the more traditional junctions based on AlO_x barriers for low - power, high - performance computing.

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This paper describes Sandia National Laboratories' structure, mission, and other directives.

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This report assesses seismic interference generated by a tethered aerostat. The study was motivated by a planned aerostat deployment within the footprint of the Dry Alluvium Geology seismic network. No evidence was found for seismic interference generated by the aerostat, and thus the e ects on the Dry Alluvium Geology sensors will be negligible.

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Supercritical CO₂ (sCO₂) is a fluid of interest for advanced power cycles that can reach thermal to electric energy conversion efficiencies of 50% or higher. Of particular interest for fossil-fired natural gas is the Allam cycle that captures nearly all CO₂ emissions and exports it as a fluid stream where it may be of value. The combustion process conditions are unlike any before realized with 90-95% CO₂ concentration, temperatures around 1000°C, and pressures near 300 bar. This work outlines the experimental feasibility of flow measurements to acquire the first known data in pure sCO₂ at similar but reduced temperature and pressure conditions.

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The Aquifer Pumping Test Report for the Burn Site Groundwater (BSG) Area of Concern is being submitted by National Technology and Engineering Solutions of Sandia, LLC and the U.S. Department of Energy (DOE)/National Nuclear Security Administration to describe the results of the aquifer pumping test program and related field activities that were completed at the BSG Area of Concern. This report summarizes the results of the field work and data analyses, and is being submitted to the New Mexico Environment Department (NMED) Hazardous Waste Bureau, as required by the April 14, 2016 letter, Summary of Agreements and Proposed Milestones Pursuant to the Meeting of July 20, 2015, (NMED April 2016).

The purpose of the work presented in this memo was to calibrate the Sierra material model Multilinear Elastic-Plastic Hardening Model with Failure, (MLEP-Fail), for 1/8 inch thick plate of 13-8 PH steel in the H1150 condition. Material testing was pursued first, followed by the actual calibration.

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Cyber-secure, resilient energy is paramount to the prosperity of the United States. As the experience and sophistication of cyber adversaries grow, so too must the US power system’s defenses, situational awareness, and response and recovery strategies. Traditionally, power systems were operated with dedicated communication channels to large generators and utility-owned assets but now there is greater reliance on photovoltaic (PV) systems to provide power generation. PV systems often communicate to utilities, aggregators, and other grid operators over the public internet so the power system attack surface has significantly expanded. At the same time, solar energy systems are equipped with a range of grid-support functions, that—if controlled or programmed improperly—present a risk of power system disturbances. This document is a five-year roadmap intended to chart a path for improving cyber security for communication-enabled PV systems with clear roles and responsibilities for government, standards development organizations, PV vendors, and grid operators.

Analysis with the ParaChoice model addresses three barriers from the VTO Multi-Year Program Plan: availability of alternative fuels and electric charging station infrastructure, availability of AFVs and electric drive vehicles, and consumer reluctance to purchase new technologies. In this fiscal year, we first examined the relationship between the availability of alternative fuels and station infrastructure. Specifically, we studied how electric vehicle charging infrastructure affects the ability of EVs to compete with vehicles that rely on mature, conventional petroleum-based fuels. Second, we studied how the availability of less costly AFVs promotes their representation in the LDV fleet. Third, we used ParaChoice trade space analyses to help inform which consumers are reluctant to purchase new technologies. Last, we began analysis of impacts of alternative energy technologies on Class 8 trucks to isolate those that may most efficaciously advance HDV efficiency and petroleum use reduction goals.

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This report summarizes collaborative efforts between Secure Scalable Microgrid and Korean Institute of Energy Research team members . The efforts aim to advance microgrid research and development towards the efficient utilization of networked microgrids . The collaboration resulted in the identification of experimental and real time simulation capabilities that may be leveraged for networked microgrids research, development, and demonstration . Additional research was performed to support the demonstration of control techniques within real time simulation and with hardware in the loop for DC microgrids .

This report describes a new single-station analysis method to estimate the dispersion and uncer- tainty of seismic surface waves using the multiwavelet transform. Typically, when estimating the dispersion of a surface wave using only a single seismic station, the seismogram is decomposed into a series of narrow-band realizations using a bank of narrow-band filters. By then enveloping and normalizing the filtered seismograms and identifying the maximum power as a function of frequency, the group velocity can be estimated if the source-receiver distance is known. However, using the filter bank method, there is no robust way to estimate uncertainty. In this report, I in- troduce a new method of estimating the group velocity that includes an estimate of uncertainty. The method is similar to the conventional filter bank method, but uses a class of functions, called Slepian wavelets, to compute a series of wavelet transforms of the data. Each wavelet transform is mathematically similar to a filter bank, however, the time-frequency tradeoff is optimized. By taking multiple wavelet transforms, I form a population of dispersion estimates from which stan- dard statistical methods can be used to estimate uncertainty. I demonstrate the utility of this new method by applying it to synthetic data as well as ambient-noise surface-wave cross-correlelograms recorded by the University of Nevada Seismic Network.

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High-mobility two-dimensional (2D) holes residing in a Ge quantum well are a new electronic system with potentials in quantum computing and spintronics. Since for any electronic material, the effective mass and the g factor are two fundamental material parameters that determine the material response to electric and magnetic fields, measuring these two parameters in this material system is thus an important task that needs to be completed urgently. Because of the quantum confinement in the crystal growth direction (z), the biaxial strain of epitaxial Ge on SiGe, and the valance band nature, both the effective mass and the g factor can show very strong anisotropy. In particular, the in-plane g factor (g_ip) can be vanishingly small while the perpendicular g factor (g_z) can be much larger than 2. Here we report the measurement of g_ip at very low hole densities using in-plane magneto-resistance measurement performed at the NHMFL.

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An In-Situ Bioremediation (ISB) Pilot Test Treatability Study is planned at Sandia National Laboratories, New Mexico (SNL/NM) Technical Area-V (TA-V) Groundwater Area of Concern. The Treatability Study is designed to gravity inject an electron-donor substrate and bioaugmentation bacteria into groundwater using an injection well. The constituents of concern (COCs) are nitrate and trichloroethene (TCE). The Pilot Test Treatability Study will evaluate the effectiveness of bioremediation and COC treatment over a prescribed period of time. Results of the pilot test will provide data that will be used to evaluate the cost and effectiveness of a full-scale system.

To quantify the resolution limits of scanning microwave impedance microscopy (sMIM), we created scanning tunneling microscope (STM)-patterned donor nanostructures in silicon composed of 10 nm lines of highly conductive silicon buried under a protective top cap of silicon, and imaged them with sMIM. This dopant pattern is an ideal test of the resolution and sensitivity of the sMIM technique, as it is made with nm-resolution and offers minimal complications from topography convolution. It has been determined that typical sMIM tips can resolve lines down to ∼80 nm spacing, while resolution is independent of tip geometry as extreme tip wear does not change the resolving power, contrary to traditional scanning capacitance microscopy (SCM). Going forward, sMIM is an ideal technique for qualifying buried patterned devices, potentially allowing for quantitative post-fabrication characterization of donor structures, which may be an important tool for the study of atomic-scale transistors and state of the art quantum computation schemes.

The performance of commercial nuclear spent fuel dry storage casks is evaluated through detailed analytical modeling of the system’s thermal performance. A recent investigation has been completed that produced a data set that can be used to test the validity of the modeling presently used to determine cladding temperatures in modern vertical dry casks. To produce these data sets under well-controlled boundary conditions, the dry cask simulator (DCS) was built to study the thermal-hydraulic response of fuel under a variety of heat loads, internal vessel pressures, and external configurations [Durbin and Lindgren, 2017]. The experiments were conducted in Albuquerque, New Mexico where the local ambient atmospheric pressure is typically 83 kPa. The purpose of this handbook is to document the pertinent geometric and material property information needed to perform model validation efforts.

Conventional wisdom in the spacecraft domain is that on-orbit computation is expensive, and thus, information is traditionally funneled to the ground as directly as possible. The explosion of information due to larger sensors, the advancements of Moore's law, and other considerations lead us to revisit this practice. In this article, we consider the trade-off between computation, storage, and transmission, viewed as an energy minimization problem.

Perform an industrial ergonomic assessment to evaluate the new procedures for filling, lifting, and delivering high purity de-ionized water to building 9925. The goal was to improve on the previous method by minimizing/eliminating as much lifting and bending as possible to reduce the potential for overexertion-related injuries.

Resistive memory (ReRAM) shows promise for use as an analog synapse element in energy-efficient neural network algorithm accelerators. A particularly important application is the training of neural networks, as this is the most computationally-intensive procedure in using a neural algorithm. However, training a network with analog ReRAM synapses can significantly reduce the accuracy at the algorithm level. In order to assess this degradation, analog properties of ReRAM devices were measured and hand-written digit recognition accuracy was modeled for the training using backpropagation. Bipolar filamentary devices utilizing three material systems were measured and compared: one oxygen vacancy system, Ta-TaOx, and two conducting metallization systems, Cu-SiO2, and Ag/chalcogenide. Analog properties and conductance ranges of the devices are optimized by measuring the response to varying voltage pulse characteristics. Key analog device properties which degrade the accuracy are update linearity and write noise. Write noise may improve as a function of device manufacturing maturity, but write nonlinearity appears relatively consistent among the different device material systems and is found to be the most significant factor affecting accuracy. This suggests that new materials and/or fundamentally different resistive switching mechanisms may be required to improve device linearity and achieve higher algorithm training accuracy.

Molecular dynamics construction of the Arrhenius plot accounts for all possible diffusion paths in defective materials.

Unlike general purpose computer architectures that are comprised of complex processor cores and sequential computation, the brain is innately parallel and contains highly complex connections between computational units (neurons). Key to the architecture of the brain is a functionality enabled by the combined effect of spiking communication and sparse connectivity with unique variable efficacies and temporal latencies. Utilizing these neuroscience principles, we have developed the Spiking Temporal Processing Unit (STPU) architecture which is well-suited for areas such as pattern recognition and natural language processing. In this paper, we formally describe the STPU, implement the STPU on a field programmable gate array, and show measured performance data.

To understand the mechanism that controls low-aspect-ratio lithium deposition morphologies for Li-metal anodes in batteries, we conducted direct visualization of Li-metal deposition and stripping behavior through nanoscale in situ electrochemical scanning transmission electron microscopy (EC-STEM) and macroscale-cell electrochemistry experiments in a recently developed and promising solvate electrolyte, 4 M lithium bis(fluorosulfonyl)imide in 1,2-dimethoxyethane. In contrast to published coin cell studies in the same electrolyte, our experiments revealed low Coulombic efficiencies and inhomogeneous Li morphology during in situ observation. We conclude that this discrepancy in Coulombic efficiency and morphology of the Li deposits was dependent on the presence of a compressed lithium separator interface, as we have confirmed through macroscale (not in the transmission electron microscope) electrochemical experiments. Our data suggests that cell compression changed how the solid-electrolyte interphase formed, which is likely responsible for improved morphology and Coulombic efficiency with compression. Furthermore, during the in situ EC-STEM experiments, we observed direct evidence of nanoscale self-discharge in the solvate electrolyte (in the state of electrical isolation). This self-discharge was duplicated in the macroscale, but it was less severe with electrode compression, likely due to a more passivating and corrosion-resistant solid-electrolyte interphase formed in the presence of compression. By combining the solvate electrolyte with a protective LiAl0.3S coating, we show that the Li nucleation density increased during deposition, leading to improved morphological uniformity. Furthermore, self-discharge was suppressed during rest periods in the cycling profile with coatings present, as evidenced through EC-STEM and confirmed with coin cell data.

Most existing concepts for hardware implementation of reversible computing invoke an adiabatic computing paradigm, in which individual degrees of freedom (e.g., node voltages) are synchronously transformed under the influence of externallysupplied driving signals. But distributing these "power/clock" signals to all gates within a design while efficiently recovering their energy is difficult. Can we reduce clocking overhead using a ballistic approach, wherein data signals self-propagating between devices drive most state transitions? Traditional concepts of ballistic computing, such as the classic Billiard-Ball Model, typically rely on a precise synchronization of interacting signals, which can fail due to exponential amplification of timing differences when signals interact. In this paper, we develop a general model of Asynchronous Ballistic Reversible Computing (ABRC) that aims to address these problems by eliminating the requirement for precise synchronization between signals. Asynchronous reversible devices in this model are isomorphic to a restricted set of Mealy finite-state machines. We explore ABRC devices having up to 3 bidirectional I/O terminals and up to 2 internal states, identifying a simple pair of such devices that comprises a computationally universal set of primitives. We also briefly discuss how ABRC might be implemented using single flux quanta in superconducting circuits.

We present an 8-beam local oscillator (LO) for the astronomically significant [OI] line at 4.7 THz. The beams are generated using a quantum cascade laser (QCL) in combination with a Fourier phase grating. The grating is fully characterized using a third order distributed feedback (DFB) QCL with a single mode emission at 4.7 THz as the input. The measured diffraction efficiency of 74.3% is in an excellent agreement with the calculated result of 75.4% using a 3D simulation. We show that the power distribution among the diffracted beams is uniform enough for pumping an array receiver. To validate the grating bandwidth, we apply a far-infrared (FIR) gas laser emission at 5.3 THz as the input and find a very similar performance in terms of efficiency, power distribution, and spatial configuration of the diffracted beams. Both results represent the highest operating frequencies of THz phase gratings reported in the literature. By injecting one of the eight diffracted 4.7 THz beams into a superconducting hot electron bolometer (HEB) mixer, we find that the coupled power, taking the optical loss into account, is in consistency with the QCL power value.

Polymers confined to the liquid/vapor interface are studied using molecular dynamics simulations. We show that for polymers which are weakly immiscible with the solvent, the density profile perpendicular to the liquid/vapor interface is strongly asymmetric. On the vapor side of the interface, the density distribution falls off as a Gaussian with a decay length on the order of the bead diameter, whereas on the liquid side, the density profile decays as a simple exponential. This result differs from that of a polymer absorbed from a good solvent with the density profile decaying as a power law. As the surface coverage increases, the average end-to-end distance and chain mobility systematically decreases toward that of the homopolymer melt.

Remote Direct Memory Access (RDMA) is expected to be an integral communication mechanism for future exascale systems enabling asynchronous data transfers, so that applications may fully utilize CPU resources while simultaneously sharing data amongst remote nodes. We examine Network-induced Memory Contention (NiMC) on Infiniband networks. We expose the interactions between RDMA, main-memory and cache, when applications and out-of-band services compete for memory resources. We then explore NiMCs resulting impact on application-level performance. For a range of hardware technologies and HPC workloads, we quantify NiMC and show that NiMCs impact grows with scale resulting in up to 3X performance degradation at scales as small as 8K processes even in applications that previously have been shown to be performance resilient in the presence of noise. In addition, this work examines the problem of predicting NiMC's impact on applications by leveraging machine learning and easily accessible performance counters. This approach provides additional insights about the root cause of NiMC and facilitates dynamic selection of potential solutions. Finally, we evaluated three potential techniques to reduce NiMCs impact, namely hardware offloading, core reservation and network throttling.

The salt compounds NaB₁₁H₁₄, Na-7-CB10H13, Li-7-CB₁₀H₁₃, Na-7,8-C₂B₉H₁₂, and Na-7,9-C₂B₉H₁₂ all contain geometrically similar, monocharged, nido-undeca(carba)borate anions (i.e., truncated icosohedral-shaped clusters constructed of only 11 instead of 12 {B-H} + {C-H} vertices and an additional number of compensating bridging and/or terminal H atoms). We used first-principles calculations, X-ray powder diffraction, differential scanning calorimetry, neutron vibrational spectroscopy, neutron elastic-scattering fixed-window scans, quasielastic neutron scattering, and electrochemical impedance measurements to investigate their structures, bonding potentials, phase-transition behaviors, anion orientational mobilities, and ionic conductivities compared to those of their closo-poly(carba)borate cousins. All exhibited order-disorder phase transitions somewhere between room temperature and 375 K. All disordered phases appear to possess highly reorientationally mobile anions (> ~10¹⁰ jumps s^-1 above 300 K) and cation-vacancy-rich, close-packed or body-center-cubic-packed structures [like previously investigated closo-poly(carba)borates]. Moreover, all disordered phases display superionic conductivities but with generally somewhat lower values compared to those for the related sodium and lithium salts with similar monocharged 1-CB₉H₁₀- and CB₁₁H₁₂- closo-carbaborate anions. This study significantly expands the known toolkit of solid-state, poly(carba)borate-based salts capable of superionic conductivities and provides valuable insights into the effect of crystal lattice, unit cell volume, number of carbon atoms incorporated into the anion, and charge polarization on ionic conductivity.

Here, a solubility model is presented for ferrous iron hydroxide (Fe(OH)₂(s)), hibbingite (Fe₂Cl(OH)₃(s)), siderite (FeCO₃(s)), and chukanovite (Fe₂CO₃(OH)₂(s)). The Pitzer activity coefficient equation was utilized in developing the model to account for the excess free energies of aqueous species in the background solutions of high ionic strength. Solubility limiting minerals were analyzed before and after experiments using X-ray diffraction. Formation of Fe(OH)₂(s) was observed in the experiments that were initiated with Fe₂Cl(OH)₃(s) in Na₂SO₄ solution. Coexistence of siderite and chukanovite was observed in the experiments in Na₂CO₃ + NaCl solutions. Two equilibrium constants that had been reported by us for the dissolution of Fe(OH)₂(s) and Fe₂Cl(OH)₃(s) (Nemer et al.) were rederived in this paper, using newer thermodynamic data selected from the literature to maintain internal consistency of the series of our data analyses in preparation, including this paper. Three additional equilibrium constants for the following reactions were determined in this paper: dissolution of siderite and chukanovite and dissociation of the aqueous species Fe(CO₃)₂^–2. Five Pitzer interaction parameters were derived in this paper: β⁽⁰⁾, β⁽¹⁾, and C^φ parameters for the species pair Fe⁺²/SO₄^–2; β⁽⁰⁾ and β⁽¹⁾ parameters for the species pair Na+/Fe(CO3)2–2. Our model predicts that, among the four inorganic ferrous iron minerals, siderite is the stable mineral in two WIPP-related brines (WIPP: Waste Isolation Pilot Plant), i.e., GWB and ERDA6 (Brush and Domski), and the electrochemical equilibrium between elemental iron and siderite provides a low oxygen fugacity (10^–91.2 atm) that can keep the actinides at their lowest oxidation states. (Nemer et al., Brush and Domski; references numbered 1 and 2 in the main text).

Sintering refers to a manufacturing process through which mechanically pressed bodies of ceramic (and sometimes metal) powders are heated to drive densification thereby removing the inherit porosity of green bodies. As the body densifies through the sintering process, the ensuing material flow leads to macroscopic deformations of the specimen and as such the final configuration differs form the initial. Therefore, as with any manufacturing step, there is substantial interest in understanding and being able to model the sintering process to predict deformation and residual stress. Efforts in this regard have been pursued for face seals, gear wheels, and consumer products like wash-basins. To understand the sintering process, a variety of modeling approaches have been pursued at different scales.

Recently a novel design concept of a reactor—the cascading pressure reactor—for the thermochemical fuel production, using a solar-driven redox cycle, was proposed. In this concept, thermal reduction of metal oxide particles is completed in multiple stages, at successively lower pressures. This leads to an order of magnitude decrease in the pumping power demand as compared to a single stage, which in turn increases the solar to fuel efficiency. An important step in the process is the transfer of heat in the form of concentrated solar radiation to the particles, while providing reducing conditions in the space surrounding the particles. In this context, a novel system for heating and reducing particles, with a focus on operating at the small prototype scale (below 20 kW), is investigated. The key goals of the system are continuous operation, uniform heating of the reactive material, the ability to heat reactive material to 1723 K or higher, and flexibility of control. These criteria have led to the conceptual design of a continuous thin-layer particle conveyor, contained in an apertured, windowed cavity and enclosed in a vacuum chamber. This chamber, in combination with a water-splitting chamber and other system components, allows the possibility of testing multiple redox materials without any significant change in the reactor design. The present work shows a potential design for the proposed component, feasibility tests of the physics of moving particles with relevant materials, and series of interconnected numerical models and calculations that can be used to size such a system for the appropriate scales of power and mass flow rates. The use of a unified design strategy has led to efficient development of the system. Experimental investigations of the horizontal motion plate allowed effective determination of motion profiles and bed uniformity. The most important factors determined through the modeling effort were the aperture diameter, which serves as the coupling point between the solar simulator lamp array and the cavity particle heating, and the particle bed thickness, which has a strong effect on the outlet temperature of the particles.

When multiple blasts occur at different times, the situation arises in which a blast wave is propagating into a medium that has already been shocked. Determining the evolution in shape of the second shock is not trivial, as it is propagating into air that is not only non-uniform, but also non-stationary. To accomplish this task, we employ the method of Kompaneets to determine the shape of a shock in a non-uniform media. We also draw from the work of Korycansky [1] on an off-center explosion in a medium with radially varying density. Extending this to treat non-stationary flow, and making use of approximations to the Sedov solution for the point blast problem, we are able to determine an analytic expression for the evolving shape of the second shock. Specifically, we consider the case of a shock in air at standard ambient temperature and pressure, with the second shock occurring shortly after the original blast wave reaches it, as in a sympathetic detonation.

The CABle ANAlysis (CABANA) portion of the EMPHASIS™ suite is designed specifically for the simulation of cable SGEMP. The code can be used to evaluate the response of a specific cable design to threat or to compare and minimize the relative response of difference designs. This document provides user-specific information to facilitate the application of the code to cables of interest.

The Unstructured Time-Domain ElectroMagnetics (UTDEM) portion of the EMPHASIS suite solves Maxwell’s equations using finite-element techniques on unstructured meshes. This document provides user-specific information to facilitate the use of the code for applications of interest.

Using scanning tunneling microscopy (STM), we investigate oxide-induced growth pits in Si thin films deposited by molecular beam epitaxy. In the transition temperature range from 2D adatom islanding to step-flow growth, systematic controlled air leaks into the growth chamber induce pits in the growth surface. We show that pits are also correlated with oxygen-contaminated flux from Si sublimation sources. From a thermodynamic standpoint, multilayer growth pits are unexpected in relaxed homoepitaxial growth, whereas oxidation is a known cause for step-pinning, roughening, and faceting on elemental surfaces, both with and without growth flux. Not surprisingly, pits are thermodynamically metastable and heal by annealing to recover a smooth periodic step arrangement. STM reveals new details about the pits' atomistic origins and growth dynamics. Here, we give a model for heterogeneous nucleation of pits by preferential adsorption of Å-sized oxide nuclei at intrinsic growth antiphase boundaries, and subsequent step pinning and bunching around the nuclei.

Li2B12H12, Na2B12H12, and their closo-borate relatives exhibit unusually high ionic conductivity, making them attractive as a new class of candidate electrolytes in solid-state Li- and Na-ion batteries. However, further optimization of these materials requires a deeper understanding of the fundamental mechanisms underlying ultrafast ion conduction. To this end, we use ab initio molecular dynamics simulations and density-functional calculations to explore the motivations for cation diffusion. We find that superionic behavior in Li2B12H12 and Na2B12H12 results from a combination of key structural, chemical, and dynamical factors that introduce intrinsic frustration and disorder. A statistical metric is used to show that the structures exhibit a high density of accessible interstitial sites and site types, which correlates with the flatness of the energy landscape and the observed cation mobility. Furthermore, cations are found to dock to specific anion sites, leading to a competition between the geometric symmetry of the anion and the symmetry of the lattice itself, which can facilitate cation hopping. Finally, facile anion reorientations and other low-frequency thermal vibrations lead to fluctuations in the local potential that enhance cation mobility by creating a local driving force for hopping. We discuss the relevance of each factor for developing new ionic conductivity descriptors that can be used for discovery and optimization of closo-borate solid electrolytes, as well as superionic conductors more generally.

The discovery of emergent phenomena in 2D materials has sparked substantial research efforts in the materials community. A significant experimental challenge for this field is exerting atomistic control over the structure and composition of the constituent 2D layers and understanding how the interactions between layers drive both structure and properties. While no segregation for single bilayers was observed, segregation of Pb to the surface of three bilayer thick PbSe–SnSe alloy layers was discovered within [(PbxSn1−xSe)1+δ]n(TiSe2)1 heterostructures using electron microscopy. This segregation is thermodynamically favored to occur when PbxSn1−xSe layers are interdigitated with TiSe2 monolayers. DFT calculations indicate that the observed segregation depends on what is adjacent to the PbxSn1−xSe layers. The interplay between interface- and volume-free energies controls both the structure and composition of the constituent layers, which can be tuned using layer thickness.

Measurement of the Hugoniot and sound velocity provides information on the bulk modulus and Grüneisen parameter of a material at extreme conditions. The capability to launch multilayered (copper/aluminum) flyer plates at velocities in excess of 20 km/s with the Sandia Z accelerator has enabled high-precision sound-velocity measurements at previously inaccessible pressures. For these experiments, the sound velocity of the copper flyer must be accurately known in the multi-Mbar regime. Here we describe the development of copper as an absolutely calibrated sound-velocity standard for high-precision measurements at pressures in excess of 400 GPa. Using multilayered flyer plates, we performed absolute measurements of the Hugoniot and sound velocity of copper for pressures from 500 to 1200 GPa. These measurements enabled the determination of the Grüneisen parameter for dense liquid copper, clearly showing a density dependence above the melt transition. Combined with earlier data at lower pressures, these results constrain the sound velocity as a function of pressure, enabling the use of copper as a Hugoniot and sound-velocity standard for pressures up to 1200 GPa.