This paper describes the design and implementation of a proof-of-concept Pacific dc Intertie (PDCI) wide area damping controller and includes system test results on the North American Western Interconnection (WI). To damp inter-area oscillations, the controller modulates the power transfer of the PDCI, a ±500 kV dc transmission line in the WI. The control system utilizes real-time phasor measurement unit (PMU) feedback to construct a commanded power signal which is added to the scheduled power flow for the PDCI. After years of design, simulations, and development, this controller has been implemented in hardware and successfully tested in both open and closed-loop operation. The most important design specifications were safe, reliable performance, no degradation of any system modes in any circumstances, and improve damping to the controllable modes in the WI. The main finding is that the controller adds significant damping to the modes of the WI and does not adversely affect the system response in any of the test cases. The primary contribution of this paper, to the state of the art research, is the design methods and test results of the first North American real-time control system that uses wide area PMU feedback.
In recent years the use of security gateways (SG) located within the electrical grid distribution network has become pervasive. SGs in substations and renewable distributed energy resource aggregators (DERAs) protect power distribution control devices from cyber and cyber-physical attacks. When encrypted communications within a DER network is used, TCP/IP packet inspection is restricted to packet header behavioral analysis which in most cases only allows the SG to perform anomaly detection of blocks of time-series data (event windows). Packet header anomaly detection calculates the probability of the presence of a threat within an event window, but fails in such cases where the unreadable encrypted payload contains the attack content. The SG system log (syslog) is a time-series record of behavioral patterns of network users and processes accessing and transferring data through the SG network interfaces. Threatening behavioral pattern in the syslog are measurable using both anomaly detection and graph theory. In this paper it will be shown that it is possible to efficiently detect the presence of and classify a potential threat within an SG syslog using light-weight anomaly detection and graph theory.
A generic constant-efficiency energy flow model is commonly used in techno-economic analyses of grid energy storage systems. In practice, charge and discharge efficiencies of energy storage systems depend on state of charge, temperature, and charge/discharge powers. Furthermore, the operating characteristics of energy storage devices are technology specific. Therefore, generic constant-efficiency energy flow models do not accurately capture the system performance. In this work, we propose to use technology-specific nonlinear energy flow models based on nonlinear operating characteristics of the storage devices. These models are incorporated into an optimization problem to find the optimal market participation of energy storage systems. We develop a dynamic programming method to solve the optimization problem and perform two case studies for maximizing the revenue of a vanadium redox flow battery (VRFB) and a Li-ion battery system in Pennsylvania New Jersey Maryland (PJM) interconnection's energy and frequency regulation markets.
Two perspectives are used to reframe Simonton’s recent three-factor definition of creative outcome. The first perspective is functional: that creative ideas are those that add significantly to knowledge by providing both utility and learning. The second perspective is calculational: that learning can be estimated by the change in probabilistic beliefs about an idea’s utility before and after it has played out in its environment. The results of the reframing are proposed conceptual and mathematical definitions of (a) creative outcome as the product of two overarching factors (utility and learning) and (b) learning as a function of two subsidiary factors (blindness reduction and surprise). Learning will be shown to depend much more strongly on surprise than on blindness reduction, so creative outcome may then also be defined as “implausible utility.”.
Leakage along wellbores is of concern for a variety of applications, including sub-surface fluid storage facilities, geothermal wells, and CO2 storage wells. We have investigated whether corroded casing is permeable to gas and can serve as a leakage pathway along wellbores. Three specimens were prepared from laboratory steel plates corroded using different mechanisms to reflect different possible field conditions and produce a variety of corrosion rates. Single-phase gas flow measurements were made under a range of gas pressures to investigate flow in both the viscous and visco-inertial flow regimes. Tests were conducted at different confining stresses (range from 3.45 to 13.79 MPa) following both loading and unloading paths. The gas flow test results suggest corroded casing can serve as a significant leakage path along the axis of a wellbore. Transmissivity was found to be sensitive to the variation in confining stress suggesting that the corrosion product is deformable. Gas slip factors and the coefficients of inertial resistance of the corrosion product were comparable to those available in the literature for other porous media. Post-test examination of the corrosion product revealed it to be a heterogeneous, mesoporous material with mostly non-uniform slit type porosity. There was no discernable difference in the composition of corrosion product from specimens corroded by different mechanisms.
Stress intensity factors (SIFs) are used in continuum fracture mechanics to quantify the stress fields surrounding a crack in a homogeneous material in the linear elastic regime. Critical values of the SIFs define an intrinsic measure of the resistance of a material to propagate a crack. At atomic scales, however, fracture occurs as a series of atomic bonds breaking, differing from the continuum description. As a consequence, a formal analog of the continuum SIFs calculated from atomistic simulations can have spatially localized, microstructural contributions that originate from varying bond configurations. The ability to characterize fracture at the atomic scale in terms of the SIFs offers both an opportunity to probe the effects of chemistry, as well as how the addition of a microstructural component affects the accuracy. We present a novel numerical method to determine SIFs from molecular dynamics (MD) simulations. The accuracy of this approach is first examined for a simple model, and then applied to atomistic simulations of fracture in amorphous silica. MD simulations provide time and spatially dependent SIFs, with results that are shown to be in good agreement with experimental values for fracture toughness in silica glass.
We present a comprehensive physics investigation of electrothermal effects in III-V heterojunction bipolar transistors (HBTs) via extensive Technology Computer Aided Design (TCAD) simulation and modeling. We show for the first time that the negative differential resistances of the common-emitter output responses in InGaP/GaAs HBTs are caused not only by the well-known carrier mobility reduction, but more importantly also by the increased base-To-emitter hole back injection, as the device temperature increases from self-heating. Both self-heating and impact ionization can cause fly-backs in the output responses under constant base-emitter voltages. We find that the fly-back behavior is due to competing processes of carrier recombination and self-heating or impact ionization induced carrier generation. These findings will allow us to understand and potentially improve the safe operating areas and circuit compact models of InGaP/GaAs HBTs.
We parallelize the LU factorization of a hierarchical low-rank matrix (H-matrix) on a distributed-memory computer. This is much more difficult than the H-matrix-vector multiplication due to the dataflow of the factorization, and it is much harder than the parallelization of a dense matrix factorization due to the irregular hierarchical block structure of the matrix. Block low-rank (BLR) format gets rid of the hierarchy and simplifies the parallelization, often increasing concurrency. However, this comes at a price of losing the near-linear complexity of the H-matrix factorization. In this work, we propose to factorize the matrix using a “lattice H-matrix” format that generalizes the BLR format by storing each of the blocks (both diagonals and off-diagonals) in the H-matrix format. These blocks stored in the linear complexity of the-matrix format are referred to as lattices. Thus, this lattice format aims to combine the parallel scalability of BLR factorization with the near-linear complexity of linear complexity of the-matrix factorization. We first compare factorization performances using the L-matrix, BLR, and lattice H-matrix formats under various conditions on a shared-memory computer. Our performance results show that the lattice format has storage and computational complexities similar to those of the H-matrix format, and hence a much lower cost of factorization than BLR. We then compare the BLR and lattice (H-matrix factorization on distributed-memory computers. Our performance results demonstrate that compared with BLR, the lattice format with the lower cost of factorization may lead to faster factorization on the distributed-memory computer.
The emergence of deep learning as a leading computational workload for machine learning tasks on large-scale cloud infrastructure installations has led to plethora of accelerator hardware releases. However, the reduced precision and range of the floating-point numbers on these new platforms makes it a non-trivial task to leverage these unprecedented advances in computational power for numerical linear algebra operations that come with a guarantee of robust error bounds. In order to address these concerns, we present a number of strategies that can be used to increase the accuracy of limited-precision iterative refinement. By limited precision, we mean 16-bit floating-point formats implemented in modern hardware accelerators and are not necessarily compliant with the IEEE half-precision specification. We include the explanation of a broader context and connections to established IEEE floating-point standards and existing high-performance computing (HPC) benchmarks. We also present a new formulation of LU factorization that we call signed square root LU which produces more numerically balanced L and U factors which directly address the problems of limited range of the low-precision storage formats. The experimental results indicate that it is possible to recover substantial amounts of the accuracy in the system solution that would otherwise be lost. Previously, this could only be achieved by using iterative refinement based on single-precision floating-point arithmetic. The discussion will also explore the numerical stability issues that are important for robust linear solvers on these new hardware platforms.
Triangle counting is a representative graph problem that shows the challenges of improving graph algorithm performance using algorithmic techniques and adopting graph algorithms to new architectures. In this paper, we describe an update to the linear-algebraic formulation of the triangle counting problem. Our new approach relies on fine-grained tasking based on a tile layout. We adopt this task based algorithm to heterogeneous architectures (CPUs and GPUs) for up to 10.8x speed up over past year's graph challenge submission. This implementation also results in the fastest kernel time known at time of publication for real-world graphs like twitter (3.7 second) and friendster (1.8 seconds) on GPU accelerators when the graph is GPU resident. This is a 1.7 and 1.2 time improvement over previous state-of-the-art triangle counting on GPUs. We also improved end-to-end execution time by overlapping computation and communication of the graph to the GPUs. In terms of end-to-end execution time, our implementation also achieves the fastest end-to-end times due to very low overhead costs.
We present a comprehensive physics investigation of electrothermal effects in III-V heterojunction bipolar transistors (HBTs) via extensive Technology Computer Aided Design (TCAD) simulation and modeling. We show for the first time that the negative differential resistances of the common-emitter output responses in InGaP/GaAs HBTs are caused not only by the well-known carrier mobility reduction, but more importantly also by the increased base-To-emitter hole back injection, as the device temperature increases from self-heating. Both self-heating and impact ionization can cause fly-backs in the output responses under constant base-emitter voltages. We find that the fly-back behavior is due to competing processes of carrier recombination and self-heating or impact ionization induced carrier generation. These findings will allow us to understand and potentially improve the safe operating areas and circuit compact models of InGaP/GaAs HBTs.
This report summarizes the 2019 fiscal year (FY19) status of the borehole heater test in salt funded by the US Department of Energy Office of Nuclear Energy (DOE-NE) Spent Fuel and Waste Science & Technology (SFWST) campaign. This report satisfies SFWST level-three milestone report M3SF-19SN010303033. This report is an update of the April 2019 level-two milestone report M2SF-19SNO10303031 to reflect the nearly complete as-built status of the borehole heater test. This report discusses the fiscal year 2019 (FY19) design, implementation, and preliminary data interpretation plan for a set of borehole heater tests call the brine availability tests in salt (BATS), which is funded by the DOE Office of Nuclear Energy (DOE-NE) at the Waste Isolation Pilot Plant (WIPP), a DOE Office of Environmental Management (DOE-EM) site. The organization of BATS is outlined in Project Plan: Salt In-Situ Heater Test (SNL, 2018). An early design of the field test is laid out in Kuhlman et al. (2017), including extensive references to previous field tests, which illustrates aspects of the present test. The previous test plan by Stauffer et al. (2015) places BATS in the context of a multi-year testing strategy, which involves tests of multiple scales and processes, eventually culminating in a drift-scale disposal demonstration. This level-3 milestone report is an update of a level-2 milestone report from April 2019 by the same name. The update adds as-built details of the heater test, which at the time of writing (August 2019) is near complete implementation.
Single-photon detectors have historically consisted of macroscopic-sized materials but recent experimental and theoretical progress suggests new approaches based on nanoscale and molecular electronics. Here, we present a theoretical study of photodetection in a system composed of a quantum electronic transport channel functionalized by a photon absorber. Notably, the photon field, absorption process, transduction mechanism, and measurement process are all treated as part of one fully coupled quantum system, with explicit interactions. Using nonequilibrium, time-dependent quantum transport simulations, we reveal the unique temporal signatures of the single-photon detection process, and show that the system can be described using optical Bloch equations, with a new nonlinearity as a consequence of time-dependent detuning caused by the back-action from the transport channel via the dynamical Stark effect. We compute the photodetector signal-to-noise ratio and demonstrate that single-photon detection at high count rate is possible for realistic parameters by exploiting a unique nonequilibrium control of back-action.
The SNL EBS International activities were focused on two main collaborative efforts for FY19 — 1) Developing analytical tools to study and better understand multi-phase flow and coupled process physics in engineered barrier materials and at the interface between EBS materials and host media, and 2) Benchmarking of reactive transport codes (including PFLOTRAN) used for chemical evolution of cementitious EBS components. Topic 1 is being studied as part of the SKB EBS Task Force, while Topic 2 is being pursued as a collaboration with researchers from Vanderbilt University and NRG in the the Netherlands.
A preliminary study on the microstructural characteristics and stress corrosion cracking susceptibility of a friction stir welded (FSW) 304L stainless steel plate was carried out. The weld examined was characterized by several typical microstructural features of friction stir welds including a gradient of dynamically recrystallized microstructure with distinct material flow patterns reflective of the complex distribution of thermomechanical histories. Evidence of process-induced microstructural sensitization was lacking Immersion testing of the friction stir welded plate in boiling magnesium chloride solution indicated the FSW region was more susceptible to SCC than the base 304L material, especially along the weld toes. The microstructural origins of this SCC susceptibility are not clear, but it is likely driven by residual stress imparted by the welding process. Future work will focus on direct examination of the SCC damaged microstructure and residual stress of the weld zone to further clarify the operative characteristics controlling SCC susceptibility.
This report will describe an improved computer code for two-photon opacity. The new code incorporates many recent advances and is ready to start to face the experiments. It incorporates the difficult mathematical techniques for handling free states and free-free matrix elements.
This report is based on discussions held during an unclassified workshop hosted by Sandia National Laboratories (SNL) and the Council on Strategic Risks (CSR) on August 29, 2019. The first in a planned series, this workshop brought together experts from government, national laboratories, academia, industry, and the policy and entrepreneur communities to examine the potential to use strategy, technology advances, policy, and other tools to make bioweapons obsolete. The workshop provided participants with a rare opportunity to step back from their day-to-day jobs and think strategically about how to achieve this goal more effectively and rapidly. The conversation was held under the Chatham House Rule. The objective was to generate and share ideas and identify questions that will be critical to answer in pursuit of making bioweapons obsolete. Its purpose was not to create consensus. This report does not represent consensus among participants, nor does it assign specific perspectives to any individual participant or represent the official views of any United States (U.S.) government agency or the organizing institutions namely, SNL and CSR.
Luketa, Anay; Blanchat, Thomas K.; Lord, David; Hogge, Joseph; Cruz-Cabrera, Alvaro A.; Allen, Ray
This report describes an experimental study of physical, chemical, and combustion characteristics of selected North American crude oils, and how these associate with thermal hazard distances resulting from pool fires and fireballs. The emergence of large volumes of tight oils within the North American Transportation system over the last decade coupled with several high-profile train accidents involving crude oils, has raised questions about the role of oil properties in general, and tight oils in particular, in affecting the severity of hazard outcomes in related crude oil fires. The objective of the pool fire experiments is to measure parameters necessary for hazard evaluation, namely, burn rate, surface emissive power, flame height, and heat flux to an engulfed object. To carry out this objective, a series of 2-m diameter indoor and 5-m diameter outdoor experiments were performed. The objective of the fireball experiments is to measure parameters required for hazard evaluation which include fireball maximum diameter, height at maximum diameter, duration, and surface emissive power using 400-gallons of crude oil per test. The crude oil samples used for the experiments were obtained from several U.S. locations, including including “tight” oils from the Bakken region of North Dakota and Permian region of Texas, and a conventionally produced oil from the U.S. Strategic Petroleum Reserve stockpile. These samples spanned a measurable range of vapor pressure (VPCRx(T)) and light ends content representative of U.S. domestic conventional and tight crudes. The results indicate that all the oils tested here have comparable thermal hazard distances and the measured properties are consistent with other alkane-based hydrocarbon liquids. The similarity of pool fire and fireball burn characteristics pertinent to thermal hazard outcomes of the three oils studied indicate that vapor pressure is not a statistically significant factor in affecting these outcomes. Thus, the results from this work do not support creating a distinction for crude oils based on vapor pressure with regards to these combustion events.
The study of both linear and nonlinear structural vibrations routinely circles the concise yet complex problem of choosing a set of coordinates which yield simple equations of motion. In both experimental and mathematical methods, that choice is a difficult one because of measurement, computational, and interpretation difficulties. Often times, researchers choose to solve their problems in terms of linear, undamped mode shapes because they are easy to obtain; however, this is known to give rise to complicated phenomena such as mode coupling and internal resonance. This work considers the nature of mode coupling and internal resonance in systems containing non-proportional damping, linear detuning, and cubic nonlinearities through the method of multiple scales as well as instantaneous measures of effective damping. The energy decay observed in the structural modes is well approximated by the slow-flow equations in terms of the modal amplitudes, and it is shown how mode coupling enhances the damping observed in the system. Moreover, in the presence of a 3:1 internal resonance between two modes, the nonlinearities not only enhance the dissipation, but can allow for the exchange and transfer of energy between the resonant modes. However, this exchange depends on the resonant phase between the modes and is proportional to the energy in the lowest mode. The results of the analysis tie together interpretations used by both experimentalists and theoreticians to study such systems and provide a more concrete way to interpret these phenomena.
IEEE Transactions on Geoscience and Remote Sensing
Krishnamoorthy, Siddharth; Lai, Voon H.; Komjathy, Attila; Pauken, Michael T.; Cutts, James A.; Garcia, Raphael F.; Mimoun, David; Jackson, Jennifer M.; Bowman, Daniel; Kassarian, Ervan; Martire, Leo; Sournac, Anthony; Cadu, Alexandre
Seismology on Venus has long eluded planetary scientists due to extreme temperature and pressure conditions on its surface, which most electronics cannot withstand for mission durations required for ground-based seismic studies. Here, we show that infrasonic (low-frequency) pressure fluctuations, generated as a result of ground motion, produced by an artificial seismic source known as a seismic hammer, and recorded using sensitive microbarometers deployed on a tethered balloon, are able to replicate the frequency content of ground motion. We also show that weak, artificial seismic activity thus produced may be geolocated by using multiple airborne barometers. The success of this technique paves the way for balloon-based aero-seismology, leading to a potentially revolutionary method to perform seismic studies from a remote airborne station on the earth and solar system objects with substantial atmospheres such as Venus and Titan.
Magnetically launched flyer plates were used to investigate the shock response of beryllium between 90 and 300 GPa. Solid aluminum flyer plates drove steady shocks into polycrystalline beryllium to constrain the Hugoniot from 90 to 190 GPa. Multilayered copper/aluminum flyer plates generated a shock followed by an overtaking rarefaction which was used to determine the sound velocity in both solid and liquid beryllium between 130 and 300 GPa. Disappearance of the longitudinal wave was used to identify the onset of melt along the Hugoniot and measurements were compared to density functional theory calculations to explore the proposed hcp-bcc transition at high pressure. The onset of melt along the Hugoniot was identified at ∼205GPa, which is in good agreement with theoretical predictions. These results show no clear indication of an hcp-bcc transition prior to melt along the beryllium Hugoniot. Rather, the shear stress, determined from the release wave profiles, was found to gradually decrease with stress and eventually vanish at the onset of melt.
Buchholz, Stuart; Keffeler, Evan; Lipp, Karla; Devries, Kerry; Hansen, Francis
The 10th US/German Workshop on Salt Repository Research, Design, and Operation was hosted by RESPEC and South Dakota School of Mines & Technology, both located in the Black Hills of South Dakota. Over 60 registered participants representing Germany, United States, the Netherlands, and the United Kingdom availed themselves to excellent facilities on the School of Mines campus. As the 10th annual workshop, this occasion is a milestone of the modern era of collaboration between the US and Germany, which has extended to other countries with potential for radioactive waste disposal in salt. Thrust areas covered in the annual workshops are selected by participants and typically include elements of continuity from year to year. This year's themes included siting, modeling challenges, seal systems and materials, operational safety, and special topics. Two major breakout sessions addressed test sample conditioning and natural closure of salt openings. When the new-generation US/German workshops were conceived, one goal was to identify challenging issues related to salt repository sciences and then conduct open discussions in special breakout sessions. These timely sessions achieve the workshop paradigm and provide in-depth dialogue on important salt repository considerations. In many respects, general themes of these salt repository workshops reflect advances in the scientific basis for nuclear-waste disposal in salt formations and develop naturally as a consequence of unremitting attention largely as a result of the workshop commitment. Technical capabilities in the laboratory and field continue to improve in concert with accumulating experience. Because we are working together, mechanical deformation at the micro-scale can be interpreted at a large scale, which is fundamental to predictive modeling of salt repository evolution. This document records the Proceedings of the 2019 gathering of salt repository nations and has been compiled by RESPEC, demonstrating an adopted protocol in which the host organization creates that year's Proceedings. To assist with organization and compilation, individual chapters are summarized by volunteer subject-matter experts from the participatory audience; these contributors are recognized in the Acknowledgements. All formal presentations are included in this document, thus providing a resource for referencing and many excellent photographic images. Appendices include the agenda, list of participants, abstracts, and presentations. A primary purpose for recording workshop activities is to create and sustain an accessible record of salt repository research. These archives also illustrate transparent development of research areas each year.
Jasica, M.J.; Kulcinski, Gerald L.; Santarius, John F.
The ITER divertor will feature tungsten monoblocks as the plasma-facing component (PFC) that will be subject to extreme temperature and radiation environments. This paper reports the development of surface morphologies on tungsten under helium bombardment at high temperatures, which has important implications for safety, retention, and PFC erosion. Polycrystalline tungsten samples were implanted in the Dual Advanced Ion Simultaneous Implantation Experiment dual-beam ion implantation experiment at the University of Wisconsin-Madison with He-only and simultaneous He-D implantation at incidence angles of 55 deg, ion energies of 30 keV, and surface temperatures of 900°C to 1100°C. Morphologies resulting from angled incidence conditions differed from those produced under normal incidence bombardment at similar energy and temperature conditions in previous work. A variety of ordered and disordered morphologies dependent on grain orientation were observed for fluences up to 6 × 1018 He cm−2. These morphologies displayed dependencies on crystal orientation at low fluences and incident beam directions at higher fluences. These structures appeared, with variation, under both single-species He and mixed He-D implantations.
We present various approximations to joint chance constraints arising in two-stage stochastic programming models. Our approximations are derived from three classical inequalities: Markov's inequality, Chebysev's inequality, and Chernoff's bound. We provide preliminary computational results illustrating the quality of our approximation using a two-stage joint-chance-constrained stochastic program from the literature. We also briefly introduce other alternatives for constructing approximations for joint-chance-constrained two-stage programs.
We propose a method that exploits sparse representation of potential energy surfaces (PES) on a polynomial basis set selected by compressed sensing. The method is useful for studies involving large numbers of PES evaluations, such as the search for local minima, transition states, or integration. We apply this method for estimating zero point energies and frequencies of molecules using a three step approach. In the first step, we interpret the PES as a sparse tensor on polynomial basis and determine its entries by a compressed sensing based algorithm using only a few PES evaluations. Then, we implement a rank reduction strategy to compress this tensor in a suitable low-rank canonical tensor format using standard tensor compression tools. This allows representing a high dimensional PES as a small sum of products of one dimensional functions. Finally, a low dimensional Gauss–Hermite quadrature rule is used to integrate the product of sparse canonical low-rank representation of PES and Green’s function in the second-order diagrammatic vibrational many-body Green’s function theory (XVH2) for estimation of zero-point energies and frequencies. Numerical tests on molecules considered in this work suggest a more efficient scaling of computational cost with molecular size as compared to other methods.
The fundamental understanding of photoexcitation landscape and dynamics in hybrid organic-inorganic perovskites is essential for improving their performance in solar cells and other applications. The dual emission features from the orthorhombic phase in perovskites have been the focus of numerous recent studies, and yet their underlying molecular origin remains elusive. We use optical two-dimensional coherent spectroscopy to study the carrier dynamics and coupling of the dual emissions in a methylammonium lead iodide film at 115 K. The two-dimensional spectra reveal an ultrafast redistribution of the photoexcited carriers into the two emission resonances within 250 fs. The high-energy resonance is a short-lived transient state, and the low-energy emission state interacts with coherent phonons. The observed carrier dynamics provide important experimental evidence that can be compared with potential theoretical models and contribute to the understanding of the dual emissions as well as the overall energy level structure in hybrid organic-inorganic perovskites.
Tallman, Aaron E.; Stopka, Krzysztof S.; Swiler, Laura P.; Wang, Yan; Kalidindi, Surya R.; Mcdowell, David L.
Data-driven tools for finding structure–property (S–P) relations, such as the Materials Knowledge System (MKS) framework, can accelerate materials design, once the costly and technical calibration process has been completed. A three-model method is proposed to reduce the expense of S–P relation model calibration: (1) direct simulations are performed as per (2) a Gaussian process-based data collection model, to calibrate (3) an MKS homogenization model in an application to α-Ti. The new methods are compared favorably with expert texture selection on the performance of the so-calibrated MKS models. Benefits for the development of new and improved materials are discussed.
Hadland, Erik; Falmbigl, Matthias; Medlin, Douglas L.; Johnson, David C.
A significant experimental challenge in testing proposed relationships between structure and properties is the synthesis of targeted structures with atomistic control over both the structure and the composition. SnSe2(MoSe2)1.32 was synthesized to test the hypothesis that the low-temperature synthesis of two interleaved structures would result in complete turbostratic disorder and that the disorder would result in ultralow thermal conductivity. SnSe2(MoSe2)1.32 was prepared by depositing elements to form a precursor containing Sn|Se and Mo|Se bilayers, each containing the number of atoms required to form single dichalcogenide planes. The nanoarchitecture of alternating Sn and Mo layers is preserved as the dichalcogenide planes self-assemble at low temperatures. The resulting compound contains well-formed dichalcogenide planes that closely resemble that found in the binary compounds and extensive turbostratic disorder. As expected from proposed structure-property relationships, the thermal conductivity of SnSe2(MoSe2)1.32 is ultralow, ∼0.05 W m-1 K-1.
We report a novel approach whereby cross-linked polybutadiene (PB) networks can be depolymerized in situ based on thermally activated alkene metathesis. A commercially available latent Ru catalyst, HeatMet, was compared to the common second-generation Hoveyda-Grubbs catalyst, HG2, in the metathetic depolymerization of PB. HeatMet was found to possess exceptional stability and negligible activity toward PB under ambient conditions, in solution and in bulk. This enabled cross-linked networks to be prepared containing homogeneously distributed Ru catalyst. The dynamic mechanical properties of networks containing HeatMet and cross-linked using alcohol-isocyanate or thiol-ene chemistry were evaluated during cross-linking and post-cross-linking under isothermal and nonisothermal heating. In both cases, above minimum catalyst loadings ranging from 0.004 to 0.024 mol %, the networks exhibited rapid degelation into a soluble oil upon heating to 100 °C. At these temperatures, extensive depolymerization of the PB segments through ring-closing metathesis of 1,4/1,2 diads by the activated HeatMet introduced network defects in significantly greater proportion than the original number of cross-links. The in situ depolymerization of cross-linked PB networks through latent catalysis, as described here, may enable facile disposal and recycling of PB encapsulants and adhesives, among other applications.
This report presents the code verification of EMPIRE-PIC to the analytic solution to a cold diode which was first derived by Jaffe. The cold diode was simulated using EMPIRE-PIC and the error norms were computed based on the Jaffe solution. The diode geometry is one-dimensional and uses the EMPIRE electrostatic field solver. After a transient start-up phase as the electrons first cross the anode-cathode gap, the simulations reach an equilibrium where the electric potential and electric field are approximately steady. The expected spatial order of convergence for potential, electric field and particle velocity are observed.
Iodine detection is crucial for nuclear waste clean-up and first responder activities. For ease of use and durability of response, robust active materials that enable the direct electrical detection of I2 are needed. Herein, a large reversible electrical response is demonstrated as I2 is controllably and repeatedly adsorbed and desorbed from a series of metal-organic frameworks (MOFs) MFM-300(X), each possessing a different metal center (X = Al, Fe, In, or Sc) bridged by biphenyl-3,3′,5,5′-tetracarboxylate linkers. Impedance spectroscopy is used to evaluate how the different metal centers influence the electrical response upon cycling of I2 gas, ranging from 10× to 106× decrease in resistance upon I2 adsorption in air. This large variation in electrical response is attributed not only to the differing structural characteristics of the MOFs but also to the differing MOF morphologies and how this influences the degree of reversibility of I2 adsorption. Interestingly, MFM-300(Al) and MFM-300(In) displayed the largest changes in resistance (up to 106×) yet lost much of their adsorption capacity after five I2 adsorption cycles in air. On the other hand, MFM-300(Fe) and MFM-300(Sc) revealed more moderate changes in resistance (10-100×), maintaining most of their original adsorption capacity after five cycles. This work demonstrates how changes in MOFs can profoundly affect the magnitude and reversibility of the electrical response of sensor materials. Tuning both the intrinsic (resistivity and adsorption capacity) and extrinsic (surface area and particle morphology) properties is necessary to develop highly reversible, large signal-generating MOF materials for direct electrical readout for I2 sensing.
Computational prediction of ductile failure remains a challenging and important problem as demonstrated by the recent Sandia Fracture Challenges. In addition to emphasizing the complexity of such problems, the variety of solution strategies also highlighted the number of possible approaches to this problem. A common engineering approach for such efforts is to use a failure model in conjunction with element deletion. In the second Sandia Fracture Challenge, for instance, nine of the fourteen teams used some form of element deletion. For such schemes, a critical decision pertains to the selection of the appropriate failure model; of which many may be found in the literature (see the review of Corona and Reedlunn). The variety may also be observed in the aforementioned second Sandia Fracture Challenge in which at least eight different failure criteria are listed for the nine element deletion based approaches. The selection of the appropriate failure model is a difficult challenge depending on the material being considered and such criteria can variously depend on stress state (i.e. triaxiality, Lode angle) and loading conditions (i.e. strain rate, temperature). Separate implementations of each criteria with different plasticity models can be a repetitive and cumbersome process which may limit available models for an engineering analyst. To mitigate this issue, an effort was pursued to flexibly implement failure models in which different failure models could be specified and utilized within the same elastic-plastic constitutive routine by simply changing the input syntax. Similarly, the same models are implemented across a suite of elastic-plastic formulations enabling consistent definitions. As will be discussed later, a specific "modular failure" model is also implemented which allows for the selection or specification of different dependencies depending on the current need. At this stage, this effort is limited to defining failure models; progression/damage evolution in the constitutive model is not treated and left to future efforts.
Glass-ceramics are a unique class of materials in which the growth of a ceramic phase(s) may be induced in an inorganic glass resulting in a microstructurally heterogeneous material with both glass and ceramic phases. This specialized processing is often referred to as "ceramming''. A wide variety of such materials have been developed through the use of different initial glass compositions and thermomechanical processing routes and that have enabled applications in dentistry, consumer kitchenware, and telescopes mirrors. These materials may also exhibit large apparent coefficients of thermal expansion making them attractive for consideration in glass-ceramic seals. These large apparent coefficients of thermal expansion often arise from silica polymorphs, such as cristobalite, undergoing a solid-to-solid phase transformations producing additional non-linearity in the effective material response.
In order to determine a material's hydrogen storage potential, capacity measurements must be robust, reproducible, and accurate. Commonly, research reports focus on the gravimetric capacity, and often times the volumetric capacity is not reported. Determining volumetric capacities is not as straight-forward, especially for amorphous materials. This is the first study to compare measurement reproducibility across laboratories for excess and total volumetric hydrogen sorption capacities based on the packing volume. The use of consistent measurement protocols, common analysis, and figure of merits for reporting data in this study, enable the comparison of the results for two different materials. Importantly, the results show good agreement for excess gravimetric capacities amongst the laboratories. Irreproducibility for excess and total volumetric capacities is attributed to real differences in the measured packing volume of the material.
We present a new, distributed-memory parallel algorithm for detection of degenerate mesh features that can cause singularities in ice sheet mesh simulations. Identifying and removing mesh features such as disconnected components (icebergs) or hinge vertices (peninsulas of ice detached from the land) can significantly improve the convergence of iterative solvers. Because the ice sheet evolves during the course of a simulation, it is important that the detection algorithm can run in situ with the simulation - - running in parallel and taking a negligible amount of computation time - - so that degenerate features (e.g., calving icebergs) can be detected as they develop. We present a distributed memory, BFS-based label-propagation approach to degenerate feature detection that is efficient enough to be called at each step of an ice sheet simulation, while correctly identifying all degenerate features of an ice sheet mesh. Our method finds all degenerate features in a mesh with 13 million vertices in 0.0561 seconds on 1536 cores in the MPAS Albany Land Ice (MALI) model. Compared to the previously used serial pre-processing approach, we observe a 46,000x speedup for our algorithm, and provide additional capability to do dynamic detection of degenerate features in the simulation.
This report is a summary of the international collaboration and laboratory work funded by the US Department of Energy Office (DOE) of Nuclear Energy Spent Fuel and Waste Science & Technology (SFWST) as part of the Sandia National Laboratories Salt R&D work package. This report satisfies milestone level-four milestone M4SF-19SNO10303064. Several stand-alone sections make up this summary report, each completed by the participants. The first two sections discuss international collaborations on geomechanical benchmarking exercises (WEIMOS), granular salt reconsolidation (KOMPASS), engineered barriers (RANGERS), and documentation of Features, Events, and Processes (FEPs).
This report represents completion of milestone deliverable M2SF-19SNO10309013 "Online Waste Library (OWL) and Waste Forms Characteristics Annual Report" that reports annual status on fiscal year (FY) 2019 activities for the work package SF-19SN01030901 and is due on August 2, 2019. The online waste library (OWL) has been designed to contain information regarding United States (U.S.) Department of Energy (DOE)-managed (as) high-level waste (DHLW), spent nuclear fuel (SNF), and other wastes that are likely candidates for deep geologic disposal, with links to the current supporting documents for the data (when possible; note that no classified or official-use-only (OUO) data are planned to be included in OWL). There may be up to several hundred different DOE-managed wastes that are likely to require deep geologic disposal. This annual report on FY2019 activities includes evaluations of waste form characteristics and waste form performance models, updates to the OWL development, and descriptions of the 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. Also added are descriptions of the management/control processes for the OWL development, version control, and archiving. These processes have been implemented as part of the full production release of OWL (i.e., OWL Version 1.0), which has been developed on, and will be hosted and managed on, Sandia National Laboratories (SNL) systems. The version control/update processes will be implemented for updates to the OWL in the future. Additionally, another process covering methods for interfacing with the DOE SNF Database (DOE 2007) at Idaho National Laboratory on the numerous entries for DOE-managed SNF (DSNF) has been pushed forward by defining data exchanges and is planned to be implemented sometime in FY2020. The INL database is also sometimes referred to as the Spent Fuel Database or the SFDB, which is the acronym that will be used in this report. Once fully implemented, this integration effort will serve as a template for interfacing with additional databases throughout the DOE complex.
Architected structural metamaterials, also known as lattice, truss, or acoustic materials, provide opportunities to produce tailored effective properties that are not achievable in bulk monolithic materials. These topologies are typically designed under the assumption of uniform, isotropic base material properties taken from reference databases and without consideration for sub-optimal as-printed properties or off-nominal dimensional heterogeneities. However, manufacturing imperfections such as surface roughness are present throughout the lattices and their constituent struts create significant variability in mechanical properties and part performance. This study utilized a customized tensile bar with a gauge section consisting of five parallel struts loaded in a stretch (tensile) orientation to examine the impact of manufacturing heterogeneities on quasi-static deformation of the struts, with a focus on ultimate tensile strength and ductility. The customized tensile specimen was designed to prevent damage during handling, despite the sub-millimeter thickness of each strut, and to enable efficient, high-throughput mechanical testing. The strut tensile specimens and reference monolithic tensile bars were manufactured using a direct metal laser sintering (also known as laser powder bed fusion or selective laser melting) process in a precipitation hardened stainless steel alloy, 17-4PH, with minimum feature sizes ranging from 0.5-0.82 mm, comparable to minimum allowable dimensions for the process. Over 70 tensile stress-strain tests were performed revealing that the effective mechanical properties of the struts were highly stochastic, considerably inferior to the properties of larger as-printed reference tensile bars, and well below the minimum allowable values for the alloy. Pre- and post-test non-destructive analyses revealed that the primary source of the reduced properties and increased variability was attributable to heterogeneous surface topography with stress-concentrating contours and commensurate reduction in effective load-bearing area.
In a previous paper, we described a new abstract circuit model for reversible computation called asynchronous ballistic reversible computing (ABRC), in which localized information-bearing pulses propagate ballistically along signal paths between stateful abstract devices and elastically scatter off those devices serially, while updating the device state in a logically-reversible and deterministic fashion. The ABRC model has been shown to be capable of universal computation. In the research reported here, we begin exploring how the ABRC model might be realized in practice using single flux quantum solitons (fluxons) in superconducting Josephson junction (JJ) circuits. One natural family of realizations could utilize fluxon polarity to represent binary data in individual pulses propagating near-ballistically, along discrete or continuous long Josephson junctions or microstrip passive transmission lines, and utilize the flux charge (-1, 0, +1) of a JJ-containing superconducting loop with Φ0 < IcL < 2Φ0 to encode a ternary state variable internal to a device. A natural question then arises as to which of the definable abstract ABRC device functionalities using this data representation might be implementable using a JJ circuit that dissipates only a small fraction of the input fluxon energy. We discuss conservation rules and symmetries considered as constraints to be obeyed in these circuits, and begin the process of classifying the possible ABRC devices in this family having up to three bidirectional I/O terminals, and up to three internal states.
This paper explores the revenue potential for electric storage resources (ESRs), also referred to as electrical energy storage, in the Southwest Power Pool Integrated Marketplace. In particular, opportunities in the day-ahead market with the energy and frequency regulation products are considered. The revenue maximization problem is formulated as a linear program model, where an ESR seeks to maximize its revenue through the available revenue streams. The ESR has perfect foresight of historical prices and determines the optimal policy accordingly. A case study using FY2018 data shows that frequency regulation services are the most lucrative for revenue potential. This paper also explores different methods of using area control error data to infer the regulation control signal and the consequent effect on the optimization. Finally, the paper conducts a sensitivity analysis of ESR payback period to energy capacity and power rating.
We present experimental studies of atom-ion collisions using buffer-gas cooled, trapped ytterbium (Yb+) ions immersed in potassium (K) vapor. The range of the collisional temperature is on the order of several hundred kelvin (thermal regime). We have determined various collisional rate coefficients of the Yb+ ion per K-atom number density. We find the upper bounds of charge-exchange rate coefficients κce to be (12.7±1.6)×10-14cm3s-1 for K-Yb+171 and (5.3±0.7)×10-14cm3s-1 for K-Yb+172. For both isotopes, the spin-destruction rate coefficient κsd has an upper bound at (1.46±0.77)×10-9cm3s-1. The spin-exchange rate coefficient κse is measured to be (1.64±0.51)×10-9cm3s-1. The relatively low charge-exchange rate reported here demonstrates the advantage of using K atoms to sympathetically cool Yb+ ions and the relatively high spin-exchange rate may benefit research work in quantum metrology and quantum information processing on an atom-ion platform using K atoms and Yb+ ions.
In this study, a multiscale electron microscopy-based approach is applied to understanding how different aspects of the microstructure in a notched AA6061-T6, including grain boundaries, triple junctions, and intermetallic particles, promote localized dislocation accumulation as a function of applied tensile strain and depth from the sample surface. Experimental measurements and crystal plasticity simulations of dislocation distributions as a function of distance from specified microstructural features both showed preferential dislocation accumulation near intermetallic particles relative to grain boundaries and triple junctions. High resolution electron backscatter diffraction and site-specific transmission electron microscopy characterization showed that high levels of dislocation accumulation near intermetallic particles led to the development of an ultrafine sub-grain microstructure, indicative of a much higher level of local plasticity than predicted from the coarser measurements and simulations. In addition, high resolution measurements in front of a crack tip suggested a compounding influence of intermetallic particles and grain boundaries in dictating crack propagation pathways.
Use of insensitive high explosives (IHEs) has significantly improved ammunition safety because of their remarkable insensitivity to violent cook-off, shock and impact. Triamino-trinitrobenzene (TATB) is the IHE used in many modern munitions. Previously, lightning simulations in different test configurations have shown that the required detonation threshold for standard density TATB at ambient and elevated temperatures (250 C) has a sufficient margin over the shock caused by an arc from the most severe lightning. In this paper, the Braginskii model with Lee-More channel conductivity prescription is used to demonstrate how electrical arcs from lightning could cause detonation in TATB. The steep rise and slow decay in typical lightning pulse are used in demonstrating that the shock pressure from an electrical arc, after reaching the peak, falls off faster than the inverse of the arc radius. For detonation to occur, two necessary detonation conditions must be met: the Pop-Plot criterion and minimum spot size requirement. The relevant Pop-Plot for TATB at 250 C was converted into an empirical detonation criterion, which is applicable to explosives subject to shocks of variable pressure. The arc cross-section was required to meet the minimum detonation spot size reported in the literature. One caveat is that when the shock pressure exceeds the detonation pressure the Pop-Plot may not be applicable, and the minimum spot size requirement may be smaller.
The Virtual Fields Method (VFM) is an inverse technique used for parameter estimation and calibration of constitutive models. Many assumptions and approximations—such as plane stress, incompressible plasticity, and spatial and temporal derivative calculations—are required to use VFM with full-field deformation data, for example, from Digital Image Correlation (DIC). This work presents a comprehensive discussion of the effects of these assumptions and approximations on parameters identified by VFM for a viscoplastic material model for 304L stainless steel. We generated synthetic data from a Finite-Element Analysis (FEA) in order to have a reference solution with a known material model and known model parameters, and we investigated four cases in which successively more assumptions and approximations were included in the data. We found that VFM is tolerant to small deviations from the plane stress condition in a small region of the sample, and that the incompressible plasticity assumption can be used to estimate thickness changes with little error. A local polynomial fit to the displacement data was successfully employed to compute the spatial displacement gradients. The choice of temporal derivative approximation (i.e., backwards difference versus central difference) was found to have a significant influence on the computed rate of deformation and on the VFM results for the rate-dependent model used in this work. Finally, the noise introduced into the displacement data from a stereo-DIC simulator was found to have negligible influence on the VFM results. Evaluating the effects of assumptions and approximations using synthetic data is a critical first step for verifying and validating VFM for specific applications. The results of this work provide the foundation for confidently using VFM for experimental data.
Thin tellurium (Te) has been predicted as a potential two dimensional system exhibiting superior thermoelectric and electrical properties. Here, we report the synthesis of high quality ultrathin Te nanostructures and the study of their electrical properties at room temperature. High quality ultrathin Te nanostructures are obtained by high temperature vapor phase deposition on c-plane sapphire substrates. The obtained nanostructures are as thin as 3 nm and exhibit α-Te phase with trigonal crystal structure. Room temperature electrical measurements show significantly higher electrical conductivity compared to prior reports of Te in bulk form or in nanostructure form synthesized by low temperature vapor deposition or wet chemical methods. Additionally, these nanostructures exhibit high field effect hole mobility comparable to black-phosphorous measured previously under similar conditions.