Unified collision operator demonstrated for both radiation transport and PIC-DSMC. A side-by-side comparison between the DSMC method and the radiation transport method was conducted for photon attenuation in the atmosphere over 2 kilometers in physical distance with a reduction of photon density of six orders of magnitude. Both DSMC and traditional radiation transport agreed with theory to two digits. This indicates that PIC-DSMC operators can be unified with the radiation transport collision operators into a single code base and that physics kernels can remain unique to the actual collision pairs. This simulation example provides an initial validation of the unified collision theory approach that will later be implemented into EMPIRE.
This National Emission Standards for Hazardous Air Pollutants (NESHAP) Annual Report has been prepared in a format to comply with the reporting requirements of 40 CFR 61.94 and the April 5, 1995 Memorandum of Agreement (MOA) between the Department of Energy (DOE) and the Environmental Protection Agency (EPA). According to the EPA approved NESHAP Monitoring Plan for the Tonopah Test Range (TTR), 40 CFR 61, subpart H, and the MOA, no additional monitoring or measurements are required at TTR in order to demonstrate compliance with the NESHAP regulation.
This report provides a summary of the radionuclide releases from the United States (U.S.) Department of Energy (DOE) National Nuclear Security Administration facilities at Sandia National Laboratories, New Mexico (SNL/NM) during Calendar Year (CY) 2015, including the data, calculations, and supporting documentation for demonstrating compliance with 40 Code of Federal Regulation (CFR) 61.
The XVis project brings together the key elements of research to enable scientific discovery at extreme scale. Scientific computing will no longer be purely about how fast computations can be performed. Energy constraints, processor changes, and I/O limitations necessitate significant changes in both the software applications used in scientific computation and the ways in which scientists use them. Components for modeling, simulation, analysis, and visualization must work together in a computational ecosystem, rather than working independently as they have in the past. This project provides the necessary research and infrastructure for scientific discovery in this new computational ecosystem by addressing four interlocking challenges: emerging processor technology, in situ integration, usability, and proxy analysis.
The Contingency Contractor Optimization Tool – Prototype (CCOT-P) database is used to store input and output data for the linear program model described in [1]. The database allows queries to retrieve this data and updating and inserting new input data.
This document describes the final software design of the Contingency Contractor Optimization Tool - Prototype. Its purpose is to provide the overall architecture of the software and the logic behind this architecture. Documentation for the individual classes is provided in the application Javadoc. The Contingency Contractor Optimization project is intended to address Department of Defense mandates by delivering a centralized strategic planning tool that allows senior decision makers to quickly and accurately assess the impacts, risks, and mitigation strategies associated with utilizing contract support. The Contingency Contractor Optimization Tool - Prototype was developed in Phase 3 of the OSD ATL Contingency Contractor Optimization project to support strategic planning for contingency contractors. The planning tool uses a model to optimize the Total Force mix by minimizing the combined total costs for selected mission scenarios. The model optimizes the match of personnel types (military, DoD civilian, and contractors) and capabilities to meet mission requirements as effectively as possible, based on risk, cost, and other requirements.
The goal of the field trial of EDAS was to demonstrate the utility of secure branching of operator instrumentation for nuclear safeguards, identify any unforeseen implementation and application issues with EDAS, and confirm whether the approach is compatible with operator concerns and constraints.
Sandia National Laboratories (SNL) Fuel Cycle Technologies (FCT) program activities are conducted in accordance with FCT Quality Assurance Program Document (FCT-QAPD) requirements. The FCT-QAPD interfaces with SNL approved Quality Assurance Program Description (SNL-QAPD) as explained in the Sandia National Laboratories QA Program Interface Document for FCT Activities (Interface Document). This plan describes SNL's FY16 assessment of SNL's FY15 FCT M2 milestone deliverable's compliance with program QA requirements, including SNL R&A requirements. The assessment is intended to confirm that SNL's FY15 milestone deliverables contain the appropriate authenticated review documentation and that there is a copy marked with SNL R&A numbers.
This is the definitive user manual for the I FPACK 2 package in the Trilinos project. I FPACK 2 pro- vides implementations of iterative algorithms (e.g., Jacobi, SOR, additive Schwarz) and processor- based incomplete factorizations. I FPACK 2 is part of the Trilinos T PETRA solver stack, is templated on index, scalar, and node types, and leverages node-level parallelism indirectly through its use of T PETRA kernels. I FPACK 2 can be used to solve to matrix systems with greater than 2 billion rows (using 64-bit indices). Any options not documented in this manual should be considered strictly experimental .
CdS homoepitaxy growth was performed by molecular dynamics using different substrate orientations and structures in order to analyze the CdS crystallinity. As anticipated from thermodynamics of homoepitaxy, highly crystalline films with only point defects were obtained on substrates with rectangular surface geometries, including [112¯] zinc blende (ZB), [101¯0] wurtzite (WZ), [112¯0] WZ, [110] ZB, [010] ZB, and [1101110] ZB. In contrast, films grown on substrates with hexagonal surface geometries, corresponding to the [0001] WZ and [111] ZB growth directions, showed structures with a large number of defects including; anti-sites, vacancies, stacking faults, twinning, and polytypism. WZ and ZB transitions and grain boundaries are identified using a lattice identification algorithm and represented graphically in a structural map. A dislocation analysis was performed to detect, identify, and quantify linear defects within the atomistic data. Systematic simulations using different temperatures, deposition rates, and substrate polarities were perform to analyze the trends of dislocation densities on [0001] WZ direction and showed persistent polytypism. The polytypism observed in the films grown on the substrates with hexagonal surface geometry is attributed to the similar formation energies of the WZ and ZB phases.
Welcome to CUBIT, the Sandia National Laboratory automated mesh generation toolkit. CUBIT is a full-featured software toolkit for robust generation of two- and three-dimensional finite element meshes (grids) and geometry preparation. Its main goal is to reduce the time to generate meshes, particularly large hex meshes of complicated, interlocking assemblies. It is a solidmodeler based preprocessor that meshes volumes and surfaces for finite element analysis.
The efficiency of ultraviolet (UV) light-emitting diodes (LEDs) is critically limited by absorption losses in p-type and metal layers. In this work, surface-roughening-based light extraction structures were combined with tunneling-based top-layer contacts to achieve highly efficient top-side light extraction in UV LEDs. By using self-assembled Ni nanoclusters as an etch mask, the top surface-roughened LEDs were found to enhance the external quantum efficiency by over 40% for UV LEDs with a peak emission wavelength of 326 nm. The method described here can be used for fabricating highly efficient UV LEDs without the need for complex manufacturing techniques such as flip chip bonding.
Gade, Dinakar; Hackebeil, Gabriel; Ryan, Sarah M.; Watson, Jean-Paul; Wets, Roger J.B.; Woodruff, David L.
We present a method for computing lower bounds in the progressive hedging algorithm (PHA) for two-stage and multi-stage stochastic mixed-integer programs. Computing lower bounds in the PHA allows one to assess the quality of the solutions generated by the algorithm contemporaneously. The lower bounds can be computed in any iteration of the algorithm by using dual prices that are calculated during execution of the standard PHA. We report computational results on stochastic unit commitment and stochastic server location problem instances, and explore the relationship between key PHA parameters and the quality of the resulting lower bounds.
In this work, a crystal plasticity-finite element (CP-FE) model is used to investigate the effects of microstructural variability at a notch tip in tantalum single crystals and polycrystals. It is shown that at the macroscopic scale, the mechanical response of single crystals is sensitive to the crystallographic orientation while the response of polycrystals shows relatively small susceptibility to it. However, at the microscopic scale, the local stress and strain fields in the vicinity of the crack tip are completely determined by the local crystallographic orientation at the crack tip for both single and polycrystalline specimens with similar mechanical field distributions. Variability in the local metrics used (maximum von Mises stress and equivalent plastic strain at 3% deformation) for 100 different realizations of polycrystals fluctuates by up to a factor of 2-7 depending on the local crystallographic texture. Comparison with experimental data shows that the CP model captures variability in stress-strain response of polycrystals that can be attributed to the grain-scale microstructural variability. This work provides a convenient approach to investigate fluctuations in the mechanical behavior of polycrystalline materials induced by grain morphology and crystallographic orientations.
High-performance computing (HPC) systems enable scientists to numerically model complex phenomena in many important physical systems. The next major milestone in the development of HPC systems is the construction of the rst supercomputer capable executing more than an exa op, 1018 oating point operations per second. On systems of this scale, failures will occur much more frequently than on current systems. As a result, resilience is a key obstacle to building next-generation extremescale systems. Coordinated checkpointing is currently the most widely-used mechanism for handling failures on HPC systems. Although coordinated checkpointing remains e ective on current systems, increasing the scale of today's systems to build next-generation systems will increase the cost of fault tolerance as more and more time is taken away from the application to protect against or recover from failure. Rollback avoidance techniques seek to mitigate the cost of checkpoint/restart by allowing an application to continue its execution rather than rolling back to an earlier checkpoint when failures occur. These techniqes include failure prediction and preventive migration, replicated computation, fault-tolerant algorithms, and softwarebased memory fault correction. In this thesis, we examine how rollback avoidance techniques can be used to address failures on extreme-scale systems. Using a combination of analytic modeling and simulation, we evaluate the potential impact of rollback avoidance on these systems. We then present a novel rollback avoidance technique that exploits similarities in application memory. Finally, we examine the feasibility of using this technique to protect against memory faults in kernel memory.
We report on the development of a highly miniaturized vacuum package for use in an atomic clock utilizing trapped ytterbium-171 ions. The vacuum package is approximately 1 cm3 in size and contains a linear quadrupole RF Paul ion trap, miniature neutral Yb sources, and a non-evaporable getter pump. We describe the fabrication process for making the Yb sources and assembling the vacuum package. To prepare the vacuum package for ion trapping, it was evacuated, baked at a high temperature, and then back filled with a helium buffer gas. Once appropriate vacuum conditions were achieved in the package, it was sealed with a copper pinch-off and was subsequently pumped only by the non-evaporable getter. We demonstrated ion trapping in this vacuum package and the operation of an atomic clock, stabilizing a local oscillator to the 12.6 GHz hyperfine transition of 171Y b+. The fractional frequency stability of the clock was measured to be 2 × 10-11/τ1/2.
We present a simple algorithm for identifying periods of time with broadband global horizontal irradiance (GHI) similar to that occurring during clear sky conditions from a time series of GHI measurements. Other available methods to identify these periods do so by identifying periods with clear sky conditions using additional measurements, such as direct or diffuse irradiance. Our algorithm compares characteristics of the time series of measured GHI with the output of a clear sky model without requiring additional measurements. We validate our algorithm using data from several locations by comparing our results with those obtained from a clear sky detection algorithm, and with satellite and ground-based sky imagery.
Hydraulic fracture stimulation of low permeability reservoir rocks is an established and cross-cutting technology for enhancing hydrocarbon production in sedimentary formations and increasing heat exchange in crystalline geothermal systems. Whereas the primary measure of success is the ability to keep the newly generated fractures sufficiently open, long-term reservoir management requires a knowledge of the spatial extent, morphology, and distribution of the fractures-knowledge primarily informed by microseismic and ground deformation monitoring. To minimize the uncertainty associated with interpreting such data, we investigate through numerical simulation the usefulness of direct-current (DC) resistivity data for characterizing subsurface fractures with elevated electrical conductivity by considering a geophysical experiment consisting of a grounded current source deployed in a steel cased borehole. In doing so, the casing efficiently energizes the fractures with steady current. Finite element simulations of this experiment for a horizontal well intersecting a small set of vertical fractures indicate that the fractures manifest electrically in (at least) two ways: (1) a local perturbation in electric potential proximal to the fracture set, with limited farfield expression and (2) an overall reduction in the electric potential along the borehole casing due to enhanced current flow through the fractures into the surrounding formation. The change in casing potential results in a measurable effect that can be observed far from fractures themselves. Under these conditions, our results suggest that farfield, timelapse measurements of DC potentials can be interpreted by simple, linear inversion for a Coulomb charge distribution along the borehole path, including a local charge perturbation due to the fractures. This approach offers an inexpensive method for detecting and monitoring the time-evolution of electrically conducting fractures while ultimately providing an estimate of their effective conductivity - the latter providing an important measure independent of seismic methods on fracture shape, size, and hydraulic connectivity.
BACKGROUND The current outbreak of Ebola virus disease (EVD) in West Africa has attacked 24000 people, killed more than 10000 and disrupted social life. METHODS We studied retrospectively the clinical presentation and risk factors for fatal outcome in EVD among all patients admitted to the Ebola Treatment Center in Moyamba District, Sierra Leone. RESULTS Among a total of 88 admitted patients, eighty-two were tested by PCR and 31 (38%) were positive for Ebola virus. Ninety percent reported previous contact with EVD patients and 35% had participated in burials of EVD suspect deceased. No healthworkers were admitted. The most common symptoms on admission were weakness (97%), diarrhea (68%), fever (62%), loss of appetite (62%), vomiting (58%), pain in muscles (62%) and joints (55%), headache (55%), abdominal pain (45%) and conjunctivitis (42%). On admission, bleeding was present in one-third (11/31), while more than half (17/31) bled during the hospital stay. Fifty-eight percent (18/31) died, most within 4-11 days of onset. Significant predictors for fatal outcome were shorter time from onset to admission (P=0.02), high initial viral load (P<0.001), bleeding (P=0.004), and severe pain (P=0.001). The only two patients with hiccups died. CONCLUSIONS Bleeding was more common in our cohort than reported elsewhere during this epidemic, and predicted poor prognosis. Severe pain was common, particularly in fatal cases, and calls for improved and safe palliation, for instance with transdermal opiates. The lack of fever in one third of EBV cases may have implications for screening procedures and case definitions.
Lu, Wei-Yang; Koohbor, Behrad; Kidane, Addis; Sutton, Michael A.
Dynamic stress-strain response of rigid closed-cell polymeric foams is investigated in this work by subjecting high toughness polyurethane foam specimens to direct impact with different projectile velocities and quantifying their deformation response with high speed stereo-photography together with 3D digital image correlation. The measured transient displacement field developed in the specimens during high stain rate loading is used to calculate the transient axial acceleration field throughout the specimen. A simple mathematical formulation based on conservation of mass is also proposed to determine the local change of density in the specimen during deformation. By obtaining the full-field acceleration and density distributions, the inertia stresses at each point in the specimen are determined through a non-parametric analysis and superimposed on the stress magnitudes measured at specimen ends to obtain the full-field stress distribution. The process outlined above overcomes a major challenge in high strain rate experiments with low impedance polymeric foam specimens, i.e. the delayed equilibrium conditions can be quantified.
This report describes the third set of tests (the “DCLa shaker tests”) of an instrumented surrogate PWR fuel assembly. The purpose of this set of tests was to measure strains and accelerations on Zircaloy-4 fuel rods when the PWR assembly was subjected to rail and truck loadings simulating normal conditions of transport when affixed to a multi-axis shaker. This is the first set of tests of the assembly simulating rail normal conditions of transport.
Shale is characterized by the predominant presence of nanometer-scale (1-100 nm) pores. The behavior of fluids in those pores directly controls shale gas storage and release in shale matrix and ultimately the wellbore production in unconventional reservoirs. Recently, it has been recognized that a fluid confined in nanopores can behave dramatically differently from the corresponding bulk phase due to nanopore confinement (Wang, 2014). CO2 and H2O, either preexisting or introduced, are two major components that coexist with shale gas (predominately CH4) during hydrofracturing and gas extraction. Note that liquid or supercritical CO2 has been suggested as an alternative fluid for subsurface fracturing such that CO2 enhanced gas recovery can also serve as a CO2 sequestration process. Limited data indicate that CO2 may preferentially adsorb in nanopores (particularly those in kerogen) and therefore displace CH4 in shale. Similarly, the presence of water moisture seems able to displace or trap CH4 in shale matrix. Therefore, fundamental understanding of CH4-CO2-H2O behavior and their interactions in shale nanopores is of great importance for gas production and the related CO2 sequestration. This project focuses on the systematic study of CH4-CO2-H2O interactions in shale nanopores under high-pressure and high temperature reservoir conditions. The proposed work will help to develop new stimulation strategies to enable efficient resource recovery from fewer and less environmentally impactful wells.
Leung, Kevin; Malliakas, Christos D.; Pupek, Krzysztof Z.; Shkrob, Ilya A.; Abraham, Daniel P.
Fluorinated carbonates are pursued as liquid electrolyte solvents for high-voltage Li-ion batteries. Here we report aggregation of [Li+(FEC)3]n polymer species in fluoroethylene carbonate containing electrolytes and scrutinize the causes for this behavior.
Nanoscale control of matter is critical to the design of integrated nanosystems. Here, we describe a method to dynamically control directionality of microtubule (MT) motion using programmable magnetic fields. MTs are combined with magnetic quantum dots (i.e., MagDots) that are manipulated by external magnetic fields provided by magnetic nanowires. MT shuttles thus undergo both ATP-driven and externally-directed motion with a fluorescence component that permits simultaneous visualization of shuttle motion. This technology is used to alter the trajectory of MTs in motion and to pin MT motion. Such an approach could be used to evaluate the MT-kinesin transport system and could serve as the basis for improved lab-on-a-chip technologies based on MT transport.
In this study, we report a micropillar stress relaxation technique employing a stable displacement-controlled, in-situ scanning electron microscope indenter, and unusually large micropillars to precisely measure stress relaxation in electroplated nanocrystalline Ni thin films. The observed stress relaxation is significant under constant displacement: even well below the 0.2% offset yield strength, the stresses relax by ∼4% within a minute; in the work hardening regime, stress relaxes by ∼9% in 1 min. A logarithmic fit of the relaxation curves is consistent with an Arrhenius thermal activation of plasticity and suggests an activation volume in the vicinity of ∼10 b 3. The apparent and effective activation volumes diverge at lower strains, particularly in the elastic regime. These measurements are compared to similar measurements performed on free-standing thin film tensile coupons. Both methods yield similar results, thereby validating the applicability of pillar compression to capture time-dependent plasticity. To our knowledge, these are the first micropillar stress relaxation experiments on metals ever reported.
Long, Christopher M.; Mickovic, Zlatko; Dwir, Benjamin; Caliman, Andrei; Iakovlev, Vladimir; Mereuta, Alexandru; Sirbu, Alexei; Kapon, Eli
Polarization mode control is enhanced in wafer-fused vertical-cavity surface-emitting lasers emitting at 1310 nm wavelength by etching two symmetrically arranged arcs above the gain structure within the laser cavity. The intracavity patterning introduces birefringence and dichroism, which discriminates between the two polarization states of the fundamental transverse modes. We find that the cavity modifications define the polarization angle at threshold with respect to the crystal axes, and increase the gain anisotropy and birefringence on average, leading to an increase in the polarization switching current. As a result, experimental measurements are explained using the spin-flip model of VCSEL polarization dynamics.
The mechanical properties of materials systems are highly influenced by various features at the microstructural level. The ability to capture these heterogeneities and incorporate them into continuum-scale frameworks of the deformation behavior is considered a key step in the development of complex non-local models of failure. In this study, we present a modeling framework that incorporates physically-based realizations of polycrystalline aggregates from a phase field (PF) model into a crystal plasticity finite element (CP-FE) framework. Simulated annealing via the PF model yields ensembles of materials microstructures with various grain sizes and shapes. With the aid of a novel FE meshing technique, FE discretizations of these microstructures are generated, where several key features, such as conformity to interfaces, and triple junction angles, are preserved. The discretizations are then used in the CP-FE framework to simulate the mechanical response of polycrystalline α-iron. It is shown that the conformal discretization across interfaces reduces artificial stress localization commonly observed in non-conformal FE discretizations. The work presented herein is a first step towards incorporating physically-based microstructures in lieu of the overly simplified representations that are commonly used. In broader terms, the proposed framework provides future avenues to explore bridging models of materials processes, e.g. additive manufacturing and microstructure evolution of multi-phase multi-component systems, into continuum-scale frameworks of the mechanical properties.
Xiao, S.; Yoon, Y.; Lee, Y.H.; Bird, J.P.; Ochiai, Y.; Aoki, N.; Reno, John L.; Fransson, J.
A critical aspect of quantum mechanics is the nonlocal nature of the wave function, a characteristic that may yield unexpected coupling of nominally isolated systems. The capacity to detect this coupling can be vital in many situations, especially those in which its strength is weak. In this work, we address this problem in the context of mesoscopic physics, by implementing an electron-wave realization of a Fano interferometer using pairs of coupled quantum point contacts (QPCs). Within this scheme, the discrete level required for a Fano resonance is provided by pinching off one of the QPCs, thereby inducing the formation of a quasibound state at the center of its self-consistent potential barrier. Using this system, we demonstrate a form of nonequilibrium Fano resonance (NEFR), in which nonlinear electrical biasing of the interferometer gives rise to pronounced distortions of its Fano resonance. Our experimental results are captured well by a quantitative theoretical model, which considers a system in which a standard two-path Fano interferometer is coupled to an additional, intruder, continuum. According to this theory, the observed distortions in the Fano resonance arise only in the presence of coupling to the intruder, indicating that the NEFR provides a sensitive means to infer the presence of weak coupling between mesoscopic systems.
Efficient time integration is a necessity for dislocation dynamics simulations of work hardening to achieve experimentally relevant strains. In this work, an efficient time integration scheme using a high order explicit method with time step subcycling and a newly-developed collision detection algorithm are evaluated. First, time integrator performance is examined for an annihilating Frank-Read source, showing the effects of dislocation line collision. The integrator with subcycling is found to significantly out-perform other integration schemes. The performance of the time integration and collision detection algorithms is then tested in a work hardening simulation. The new algorithms show a 100-fold speed-up relative to traditional schemes. Subcycling is shown to improve efficiency significantly while maintaining an accurate solution, and the new collision algorithm allows an arbitrarily large time step size without missing collisions.
Hydrogen diffusion impacts the performance of solid-state hydrogen storage materials and contributes to the embrittlement of structural materials under hydrogen-containing environments. In atomistic simulations, the diffusion energy barriers are usually calculated using molecular statics simulations where a nudged elastic band method is used to constrain a path connecting the two end points of an atomic jump. This approach requires prior knowledge of the "end points". For alloy and defective systems, the number of possible atomic jumps with respect to local atomic configurations is tremendous. Even when these jumps can be exhaustively studied, it is still unclear how they can be combined to give an overall diffusion behavior seen in experiments. Here we describe the use of molecular dynamics simulations to determine the overall diffusion energy barrier from the Arrhenius equation. This method does not require information about atomic jumps, and it has additional advantages, such as the ability to incorporate finite temperature effects and to determine the pre-exponential factor. As a test case for a generic method, we focus on hydrogen diffusion in bulk aluminum. We find that the challenge of this method is the statistical variation of the results. However, highly converged energy barriers can be achieved by an appropriate set of temperatures, output time intervals (for tracking hydrogen positions), and a long total simulation time. Our results help elucidate the inconsistencies of the experimental diffusion data published in the literature. The robust approach developed here may also open up future molecular dynamics simulations to rapidly study diffusion properties of complex material systems in multidimensional spaces involving composition and defects.
The search for solid electrolytes with sufficiently high ionic conductivities and stabilities is underway to enable the commercial viability of all-solid-state rechargeable batteries. LiCB9H10 and NaCB9H10 compounds exhibit the most impressive superionic conductivities yet among complex-hydride-based materials, including this class of large-polyhedral-anion-based salts. The pseudoaromatic nature of the CB9H10 anions makes them relatively stable like their B12H122-, B10H102-, and CB11H122- cousins, rendering their salts prime candidates for incorporation into next-generation, all-solid-state devices. Preliminary cyclic voltammetry measurements indicate that only cathodic and anodic currents are observed near 0 v corresponding to Li/Na deposition on the Au electrode and Li/Na stripping, respectively, without signifi cant anodic currents, at least ≤ 5 v for both LiCB9H10 (363 K) and NaCB9H10 (303 K). The similar conductivity behaviors with temperature for LiCB9H10 and NaCB9H10 compared to those for LiCB11H12 and NaCB11H12 , and their order-of-magnitude enhancements over disordered NaCB9H10, irrespective of structural symmetries, further reinforces the notion that anion monovalency better facilitates high cation translational mobility in these large- polyhedral-anion-based systems.
Dieni, Cristina V.; Panichi, Roberto; Aimone, James B.; Kuo, Chay T.; Wadiche, Jacques I.; Overstreet-Wadiche, Linda
Persistent neurogenesis in the dentate gyrus produces immature neurons with high intrinsic excitability and low levels of inhibition that are predicted to be more broadly responsive to afferent activity than mature neurons. Mounting evidence suggests that these immature neurons are necessary for generating distinct neural representations of similar contexts, but it is unclear how broadly responsive neurons help distinguish between similar patterns of afferent activity. Here we show that stimulation of the entorhinal cortex in mouse brain slices paradoxically generates spiking of mature neurons in the absence of immature neuron spiking. Immature neurons with high intrinsic excitability fail to spike due to insufficient excitatory drive that results from low innervation rather than silent synapses or low release probability. Our results suggest that low synaptic connectivity prevents immature neurons from responding broadly to cortical activity, potentially enabling excitable immature neurons to contribute to sparse and orthogonal dentate representations.
This milestone is focused on utilizing NMR and various gas chromatograph set ups (thermal conductivity and/ionizing detection) at SNL, to analyze the relative ratio of water and deuterated water in Ag-MOR samples of natural zeolite sent to SNL in FY15 by ORNL.
Grain boundary engineered materials are of immense interest for their resistance to hydrogen embrittlement. This work builds on the work undertaken in Part I on the thermodynamic stability and structure of misoriented grain boundaries vicinal to the Σ3 (111) <11¯0> (coherent-twin) boundary to examine hydrogen segregation to those boundaries. The segregation of hydrogen reflects the asymmetry of the boundary structure with the sense of rotation of the grains about the coherent-twin boundary, and the temperature-dependent structural transition present in one sense of misorientation. This work also finds that the presence of hydrogen affects a change in structure of the boundaries with increasing concentration. The structural change effects only one sense of misorientation and results in the reduction in length of the emitted stacking faults. Moreover, the structural change results in the generation of occupied sites populated by more strongly bound hydrogen. The improved understanding of misoriented twin grain boundary structure and the effect on hydrogen segregation resulting from this work is relevant to higher length-scale models. To that end, we examine commonly used metrics such as free volume and atomic stress at the boundary. In conclusion, free volume is found not to be useful as a surrogate for predicting the degree of hydrogen segregation, whereas the volumetric virial stress reliably predicts the locations of hydrogen segregation and exclusion at concentrations below saturation or the point where structural changes are induced by increasing hydrogen concentration.
A Fiscal Year (FY) 2016 Environmental Management Systems (EMS) objective for Division 2000 is to reduce solid waste being generated. The stated target for this objective was to conduct a waste assessment on one building occupied by Center 2700, Neutron Generator Enterprise.
The temperature dependence of grain boundary mobility is complex, varied, and rarely fits ideal Arrhenius behavior. This work presents a series of case studies of planar grain boundaries in a model FCC system that were previously demonstrated to exhibit a variety of temperature-dependent mobility behaviors. It is demonstrated that characterization of the mobility versus temperature plots is not sufficient to predict the atomic motion mechanism of the grain boundaries. Herein, the temperature-dependent motion and atomistic motion mechanisms of planar grain boundaries are driven by a synthetic, orientation-dependent, driving force. The systems studied include CSL boundaries with Σ values of 5, 7, and 15, including both symmetric and asymmetric boundaries. These boundaries represent a range of temperature-dependent trends including thermally activated, antithermal, and roughening behaviors. Examining the atomic-level motion mechanisms of the thermally activated boundaries reveals that each involves a complex shuffle, and at least one atom that changes the plane it resides on. The motion mechanism of the antithermal boundary is qualitatively different and involves an in-plane coordinated shuffle that rotates atoms about a fixed atom lying on a point in the coincident site lattice. Furthermore, this provides a mechanistic reason for the observed high mobility, even at low temperatures, which is due to the low activation energy needed for such motion. However, it will be demonstrated that this mechanism is not universal, or even common, to other boundaries exhibiting non-thermally activated motion. This work concludes that no single atomic motion mechanism is sufficient to explain the existence of non-thermally activated boundary motion.
Reverse-transcription-loop-mediated isothermal amplification (RT-LAMP) has frequently been proposed as an enabling technology for simplified diagnostic tests for RNA viruses. However, common detection techniques used for LAMP and RT-LAMP have drawbacks, including poor discrimination capability, inability to multiplex targets, high rates of false positives, and (in some cases) the requirement of opening reaction tubes postamplification. Here, we present a simple technique that allows closed-tube, target-specific detection, based on inclusion of a dye-labeled primer that is incorporated into a target-specific amplicon if the target is present. A short, complementary quencher hybridizes to unincorporated primer upon cooling down at the end of the reaction, thereby quenching fluorescence of any unincorporated primer. Our technique, which we term QUASR (for quenching of unincorporated amplification signal reporters, read "quasar"), does not significantly reduce the amplification efficiency or sensitivity of RT-LAMP. Equipped with a simple LED excitation source and a colored plastic gel filter, the naked eye or a camera can easily discriminate between positive and negative QUASR reactions, which produce a difference in signal of approximately 10:1 without background subtraction. We demonstrate that QUASR detection is compatible with complex sample matrices such as human blood, using a novel LAMP primer set for bacteriophage MS2 (a model RNA virus particle). Furthermore, we demonstrate single-tube duplex detection of West Nile virus (WNV) and chikungunya virus (CHIKV) RNA.
This paper evaluates the performance of multiphysics coupling algorithms applied to a light water nuclear reactor core simulation. The simulation couples the k-eigenvalue form of the neutron transport equation with heat conduction and subchannel flow equations. We compare Picard iteration (block Gauss-Seidel) to Anderson acceleration and multiple variants of preconditioned Jacobian-free Newton-Krylov (JFNK). The performance of the methods are evaluated over a range of energy group structures and core power levels. A novel physics-based approximation to a Jacobian-vector product has been developed to mitigate the impact of expensive on-line cross section processing steps. Numerical simulations demonstrating the efficiency of JFNK and Anderson acceleration relative to standard Picard iteration are performed on a 3D model of a nuclear fuel assembly. Both criticality (k-eigenvalue) and critical boron search problems are considered.
The objective of this work was to advance falling particle receiver designs for concentrating solar power applications that will enable higher temperatures (>700 °C) and greater power-cycle efficiencies (≥50% thermal-to-electric). Modeling, design, and testing of components in Phases 1 and 2 led to the successful on-sun demonstration in Phase 3 of the world’s first continuously recirculating high-temperature 1 MWt falling particle receiver that achieved >700 °C particle outlet temperatures at mass flow rates ranging from 1 – 7 kg/s.
In this study, oxygen selectivity in metal-organic frameworks (MOFs) at exceptionally high temperatures originally predicted by Density Functional Theory (DFT) and Grand Canonical Monte Carlo (GCMC) modeling is now confirmed by synthesis, sorption metal center access, in particular Sc and Fe. Based on DFT M-O2 binding energies, we chose the large pored MIL-100 framework for metal center access, in particular Sc and Fe. Both resulted in preferential O2 and N2 gas uptake at temperatures ranging from 77 K to ambient temperatures (258 K, 298 K and 313 K).
Paul, J.; Stevens, C.E.; Liu, C.; Dey, P.; Mcintyre, C.; Turkowski, V.; Reno, John L.; Hilton, D.J.; Karaiskaj, D.
In modulation doped quantum wells, the excitons are formed as a result of the interactions of the charged holes with the electrons at the Fermi edge in the conduction band, leading to the so-called "Mahan excitons." The binding energy of Mahan excitons is expected to be greatly reduced and any quantum coherence destroyed as a result of the screening and electron-electron interactions. Surprisingly, we observe strong quantum coherence between the heavy hole and light hole excitons. Such correlations are revealed by the dominating cross-diagonal peaks in both one-quantum and two-quantum two-dimensional Fourier transform spectra. Theoretical simulations based on the optical Bloch equations where many-body effects are included phenomenologically reproduce well the experimental spectra. Time-dependent density functional theory calculations provide insight into the underlying physics and attribute the observed strong quantum coherence to a significantly reduced screening length and collective excitations of the many-electron system.
This article discusses the problem of identifying extreme climate events such as intense storms within large climate data sets. The basic storm detection algorithm is reviewed, which splits the problem into two parts: a spatial search followed by a temporal correlation problem. Two specific implementations of the spatial search algorithm are compared: the commonly used grid point search algorithm is reviewed, and a new algorithm called Stride Search is introduced. The Stride Search algorithm is defined independently of the spatial discretization associated with a particular data set. Results from the two algorithms are compared for the application of tropical cyclone detection, and shown to produce similar results for the same set of storm identification criteria. Differences between the two algorithms arise for some storms due to their different definition of search regions in physical space. The physical space associated with each Stride Search region is constant, regardless of data resolution or latitude, and Stride Search is therefore capable of searching all regions of the globe in the same manner. Stride Search's ability to search high latitudes is demonstrated for the case of polar low detection. Wall clock time required for Stride Search is shown to be smaller than a grid point search of the same data, and the relative speed up associated with Stride Search increases as resolution increases.
Atomic-scale phenomena fundamentally influence materials form and function that makes the ability to locally probe and study these processes critical to advancing our understanding and development of materials. Atomic-scale chemical imaging by scanning transmission electron microscopy (STEM) using energy-dispersive X-ray spectroscopy (EDS) is a powerful approach to investigate solid crystal structures. Inefficient X-ray emission and collection, however, require long acquisition times (typically hundreds of seconds), making the technique incompatible with electron-beam sensitive materials and study of dynamic material phenomena. Here we describe an atomic-scale STEM-EDS chemical imaging technique that decreases the acquisition time to as little as one second, a reduction of more than 100 times. We demonstrate this new approach using LaAlO3 single crystal and study dynamic phase transformation in beam-sensitive Li[Li0.2Ni0.2Mn0.6]O2 (LNMO) lithium ion battery cathode material. By capturing a series of time-lapsed chemical maps, we show for the first time clear atomic-scale evidence of preferred Ni-mobility in LNMO transformation, revealing new kinetic mechanisms. These examples highlight the potential of this approach toward temporal, atomic-scale mapping of crystal structure and chemistry for investigating dynamic material phenomena.
The importance of credible, trustworthy numerical simulations is obvious especially when using the results for making high-consequence decisions. Determining the credibility of such numerical predictions is much more difficult and requires a systematic approach to assessing predictive capability, associated uncertainties and overall confidence in the computational simulation process for the intended use of the model. This process begins with an evaluation of the computational modeling of the identified, important physics of the simulation for its intended use. This is commonly done through a Phenomena Identification Ranking Table (PIRT). Then an assessment of the evidence basis supporting the ability to computationally simulate these physics can be performed using various frameworks such as the Predictive Capability Maturity Model (PCMM). There were several critical activities that follow in the areas of code and solution verification, validation and uncertainty quantification, which will be described in detail in the following sections. Here, we introduce the subject matter for general applications but specifics are given for the failure prediction project. In addition, the first task that must be completed in the verification & validation procedure is to perform a credibility assessment to fully understand the requirements and limitations of the current computational simulation capability for the specific application intended use. The PIRT and PCMM are tools used at Sandia National Laboratories (SNL) to provide a consistent manner to perform such an assessment. Ideally, all stakeholders should be represented and contribute to perform an accurate credibility assessment. PIRTs and PCMMs are both described in brief detail below and the resulting assessments for an example project are given.
The Center for Integrated Nanotechnologies (CINT) plays a leadership role in integration of nanostructured materials to enable novel capabilities and applications through its function as a Department of Energy/Office of Science Nanoscale Science Research Center (NSRC) national user facility. By coupling open access to unique and world-class capabilities and scientific expertise to an active user community, CINT supports high-impact research that no other single institution could achieve—the whole of CINT including its user community is greater than the sum of its parts.
An absolute stress-density path for shocklessly compressed copper is obtained to over 450 GPa. A magnetic pressure drive is temporally tailored to generate shockless compression waves through over 2.5-mm-thick copper samples. The free-surface velocity data is analyzed for Lagrangian sound velocity using the iterative Lagrangian analysis (ILA) technique, which relies upon the method of characteristics. We correct for the effects of strength and plastic work heating to determine an isentropic compression path. By assuming a Debye model for the heat capacity, we can further correct the isentrope to an isotherm. Our determination of the isentrope and isotherm of copper represents a highly accurate pressure standard for copper to over 450 GPa.
Reaching exceptionally long times up to 500 ns in equilibrium and nonequilibrium molecular dynamics simulations studies, we have attained a fundamental molecular understanding of the correlation of ionomer clusters structure and multiscale dynamics, providing new insight into one critical, long-standing challenge in ionic polymer physics. The cluster structure in melts of sulfonated polystyrene with Na+ and Mg2+ counterions are resolved and correlated with the dynamics on multiple length and time scales extracted from measurements of the dynamic structure factor and shear rheology. We find that as the morphology of the ionic clusters changes from ladderlike for Na+ to disordered structures for Mg2+, the dynamic structure factor is affected on the length scale corresponding to the ionic clusters. Rheology studies show that the viscosity for Mg2+ melts is higher than for Na+ ones for all shear rates, which is well correlated with the larger ionic clusters' size for the Mg2+ melts.
High-speed (20 kHz) digital in-line holography (DIH) is applied for 3D quantification of the size and velocity of fragments formed from the impact of a single water drop onto a thin film of water and burning aluminum particles from the combustion of a solid rocket propellant. To address the depth-of-focus problem in DIH, a regression-based multiframe tracking algorithm is employed, and out-of-plane experimental displacement accuracy is shown to be improved by an order-of-magnitude. Comparison of the results with previous DIH measurements using low-speed recording shows improved positional accuracy with the added advantage of detailed resolution of transient dynamics from single experimental realizations. The method is shown to be particularly advantageous for quantification of particle mass flow rates. For the investigated particle fields, the mass flows rates, which have been automatically measured from single experimental realizations, are found to be within 8% of the expected values.
By providing active defect sinks that capture and annihilate radiation induced defect clusters immiscible metallic multilayers with incoherent interfaces can effectively reduce defect density in ion irradiated metals. Although it is anticipated that defect density within the layers should vary as a function of distance to the layer interface, there is, to date, little in situ TEM evidence to validate this hypothesis. In our study monolithic Cu films and Cu/Fe multilayers with individual layer thickness, h, of 100 and 5 nm were subjected to in situ Cu ion irradiation at room temperature to nominally 1 displacement-per-atom inside a transmission electron microscope. Rapid formation and propagation of defect clusters were observed in monolithic Cu, whereas fewer defects with smaller dimensions were generated in Cu/Fe multilayers with smaller h. Moreover, in situ video shows that the cumulative defect density in Cu/Fe 100 nm multilayers indeed varies, as a function of distance to the layer interfaces, supporting a long postulated hypothesis.
This note examines the effect of interfacial roughness on the initiation and growth of channel cracks in a brittle film. A conformal film with cusp-like surface flaws that replicate the substrate roughness is investigated. This type of surface flaw is relatively severe in the sense that stress diverges as the cusp-tip is approached (i.e., there is a power-law stress singularity). For the geometry and range of film properties considered, the analysis suggests that smoothing the substrate could substantially increase the film’s resistance to the formation of the through-the-thickness cracks that precede channel cracking. Furthermore, smoothing the substrate’s surface has a relatively modest effect on the film stress needed to propagate a channel crack.
Impact sensitivity testing was performed using a modified Bureau of Mines (MBOM) impactor manufactured by Safety Management Services, Inc. Type-12 tooling was utilized on this machine with a 2.5kg impactor and matching intermediate mass. This particular machine is capable of a maximum drop height of 115cm with 0.1 cm increments, though 1 cm increments are typically used. Sample material was placed (35 ± 2mg) onto 1 inch squares of Norton brand 180A Garnet sandpaper. Positive results were detected visually or audibly by the operator as smoke, flash, report, charring/tearing of the sandpaper, etc. The test was conducted using the Bruceton technique to calculate the height at which there is a 50% chance of initiation (H50).
Harms, Gary A.; Kahler, Albert C.; Miller, Thomas M.; Heinrichs, David P.
This report examines proposed Seven Percent Critical Experiment (7uPCX) experiments with fuel arrays larger than would be critical when fully reflected. In these experiments, the reactivity of the assembly will be controlled by varying the moderator/reflector level in the core tank. The analysis uses two configurations, each completely filling the 45x45 fuel rod array with fuel rods and water holes, as representative examples of the proposed experiments. The proposed configurations are compared to the experiments documented in LEU-COMP-THERM-078 [Reference 1] and to fully-reflected experiments with the same fully-loaded fuel arrays that are poisoned with boron in the moderator. The conclusion is drawn that the proposed experiments can be performed with acceptably low uncertainties given a calibrated moderator/reflector level measurement system.
Harms, Gary A.; Kahler, A.C.; Miller, Thomas M.; Heinrichs, David P.
Under IER-206, the hardware for the Burnup Credit Critical Experiment will be removed from storage and placed in operation. This is the hardware we used in 2002 to perform the experiments that eventually documented in the International Handbook of Evaluated Criticality Safety Benchmark Experiments as LEU-COMP-THERM-079.
The separation of oxygen from nitrogen using metal–organic frameworks (MOFs) is of great interest for potential pressure-swing adsorption processes for the generation of purified O2 on industrial scales. This study uses ab initio molecular dynamics (AIMD) simulations to examine for the first time the pure-gas and competitive gas adsorption of O2 and N2 in the M2(dobdc) (M = Cr, Mn, Fe) MOF series with coordinatively unsaturated metal centers. Effects of metal, temperature, and gas composition are explored. Lastly, this unique application of AIMD allows us to study in detail the adsorption/desorption processes and to visualize the process of multiple guests competitively binding to coordinatively unsaturated metal sites of a MOF.
A method for patterning on vertical silicon surfaces in high aspect ratio silicon topography is presented. A Faraday cage is used to direct energetic reactive ions obliquely through a patterned suspended membrane positioned over the topography. The technique is capable of forming high-fidelity pattern (100 nm) features, adding an additional fabrication capability to standard top-down fabrication approaches.
The conventional value of the result of weighing in air is frequently used in commercial calibrations of balances. The guidance in OIML D-028 for reporting uncertainty of the conventional value is too terse. When calibrating mass standards at low measurement uncertainties, it is necessary to perform a buoyancy correction before reporting the result. When calculating the conventional result after calibrating true mass, the uncertainty due to calculating the conventional result is correlated with the buoyancy correction. We show through Monte Carlo simulations that the measurement uncertainty of the conventional result is less than the measurement uncertainty when reporting true mass. The Monte Carlo simulation tool is available in the online version of this article.
This article examines the localization of high-frequency electromagnetic fields in three-dimensional axisymmetric cavities along periodic paths between opposing sides of the cavity. When these orbits lead to unstable localized modes, they are known as scars. This article treats the case where the opposing sides, or mirrors, are convex. Particular attention is focused on the normalization through the electromagnetic energy theorem. Both projections of the field along the scarred orbit as well as field point statistics are examined. Statistical comparisons are made with a numerical calculation of the scars run with an axisymmetric simulation.
The drag force exerted on a moving dislocation by a field of mobile solutes is studied in the steady state. The drag force is numerically calculated as a function of the dislocation velocity for both perfect and extended dislocations. The sensitivity of the non-dimensionalized force-velocity curve to the various controlling parameters is assessed, and an approximate analytical force-velocity expression is given. A non-dimensional parameter S characterizing the strength of the solute-dislocation interaction, the background solute fraction, and the dislocation character angle θ, are found to have the strongest influence on the force-velocity curve. Within the model considered here, a perfect screw dislocation experiences no solute drag, but an extended screw dislocation experiences a non-zero drag force that is about 10 to 30% of the drag on an extended edge dislocation. The solutes can change the spacing between the Shockley partials in both stationary and moving extended dislocations, even when the stacking fault energy remains unaltered. Under certain conditions, the solutes destabilize an extended dislocation by either collapsing it into a perfect dislocation or causing the partials to separate unboundedly. It is proposed that the latter instability may lead to the formation of large faulted areas and deformation twins in low stacking fault energy materials containing solutes, consistent with experimental observations of copper and stainless steel containing hydrogen.