Publications

Sandia National Laboratories (SNL) continued evaluation of total system performance assessment (TSPA) computing systems for the previously considered Yucca Mountain Project (YMP). This was done to maintain the operational readiness of the computing infrastructure (computer hardware and software) and knowledge capability for total system performance assessment (TSPA) type analysis, as directed by the National Nuclear Security Administration (NNSA), DOE 2010. This work is a continuation of the ongoing readiness evaluation reported in Lee and Hadgu (2014) and Hadgu et al. (2015). The TSPA computing hardware (CL2014) and storage system described in Hadgu et al. (2015) were used for the current analysis. One floating license of GoldSim with Versions 9.60.300, 10.5 and 11.1.6 was installed on the cluster head node, and its distributed processing capability was mapped on the cluster processors. Other supporting software were tested and installed to support the TSPA-type analysis on the server cluster. The current tasks included verification of the TSPA-LA uncertainty and sensitivity analyses, and preliminary upgrade of the TSPA-LA from Version 9.60.300 to the latest version 11.1. All the TSPA-LA uncertainty and sensitivity analyses modeling cases were successfully tested and verified for the model reproducibility on the upgraded 2014 server cluster (CL2014). The uncertainty and sensitivity analyses used TSPA-LA modeling cases output generated in FY15 based on GoldSim Version 9.60.300 documented in Hadgu et al. (2015). The model upgrade task successfully converted the Nominal Modeling case to GoldSim Version 11.1. Upgrade of the remaining of the modeling cases and distributed processing tasks will continue. The 2014 server cluster and supporting software systems are fully operational to support TSPA-LA type analysis.

The Reduced Order Modeling Unlimited Localized Interface Simulator (ROMULIS) is a set of toolbox scripts in MATLAB designed to perform nonlinear transient integration on a system of reduced order structural models that interact with each other at localized interfaces. ROMULIS is meant to provide a user-friendly interface for applying the latest developments in numerical techniques and modeling in structural dynamics analysis while also giving the freedom to implement new technologies from forthcoming research. This report documents how to use and interpret the toolbox scripts. The theory behind the code is given, followed by a manual for interacting with the scripts to perform simulations. Lastly, a high-level introduction that explains how the scripts interact with each other is given for aspiring developers.

Multiphase flow in capillary regimes is a fundamental process in a number of geoscience applications. The ability to accurately define wetting characteristics of porous media can have a large impact on numerical models. In this paper, a newly developed automated three-dimensional contact angle algorithm is described and applied to high-resolution X-ray microtomography data from multiphase bead pack experiments with varying wettability characteristics. The algorithm calculates the contact angle by finding the angle between planes fit to each solid/fluid and fluid/fluid interface in the region surrounding each solid/fluid/fluid contact point. Results show that the algorithm is able to reliably compute contact angles using the experimental data. The in situ contact angles are typically larger than flat surface laboratory measurements using the same material. Wetting characteristics in mixed-wet systems also change significantly after displacement cycles.

A modified version of a published slug test model for unconfined aquifers is applied to cross-hole slug test data collected in field tests conducted at the Widen site in Switzerland. The model accounts for water-table effects using the linearized kinematic condition. The model also accounts for inertial effects in source and observation wells. The primary objective of this work is to demonstrate applicability of this semi-analytical model to multi-well and multi-level pneumatic slug tests. The pneumatic perturbation was applied at discrete intervals in a source well and monitored at discrete vertical intervals in observation wells. The source and observation well pairs were separated by distances of up to 4 m. The analysis yielded vertical profiles of hydraulic conductivity, specific storage, and specific yield at observation well locations. The hydraulic parameter estimates are compared to results from prior pumping and single-well slug tests conducted at the site, as well as to estimates from particle size analyses of sediment collected from boreholes during well installation. The results are in general agreement with results from prior tests and are indicative of a sand and gravel aquifer. Sensitivity analysis show that model identification of specific yield is strongest at late-time. However, the usefulness of late-time data is limited due to the low signal-to-noise ratios.

This article details the implementation and application of the glass-specific computational constitutive model by Holmquist and Johnson (J Appl Mech 78:051003, 2011) to simulate the dynamic response of soda-lime glass under high rate and high pressure shock conditions. The predictive capabilities of this model are assessed through comparison of experimental data with numerical results from computations using the CTH shock physics code. The formulation of this glass model is reviewed in the context of its implementation within CTH. Using a variety of experimental data compiled from the open literature, a complete parameterization of the model describing the observed behavior of soda-lime glass is developed. Simulation results using the calibrated soda-lime glass model are compared to flyer plate and Taylor rod impact experimental data covering a range of impact and failure conditions spanning an order of magnitude in velocity and pressure. The complex behavior observed in the experimental testing is captured well in the computations, demonstrating the capability of the glass model within CTH.

Wireless systems and networks have experienced rapid growth over the last decade with the advent of smart devices for everyday use. These systems, which include smartphones, vehicular gadgets, and internet-of-things devices, are becoming ubiquitous and ever-more important. They pose interesting research challenges for design and analysis of new network protocols due to their large scale and complexity. In this work, we focus on the challenging aspect of simulating the inter-connectivity of many of these devices in wireless networks. The quantitative study of large scale wireless networks, with counts of wireless devices in the thousands, is a very difficult problem with no known acceptable solution. By necessity, simulations of this scale have to approximate reality, but the algorithms employed in most modern-day network simulators can be improved for wireless network simulations. In this report, we present advances that we have made and propositions for continuation of progress towards a framework for high fidelity simulations of wireless networks. This work is not complete in that a final simulation framework tool is yet to be produced. However, we highlight the major bottlenecks and address them individually with initial results showing enough promise.

Dissipation spectra of velocity and reactive scalars—temperature and fuel mass fraction—in turbulent premixed flames are studied using direct numerical simulation data of a temporally evolving lean hydrogen-air premixed planar jet (PTJ) flame and a statistically stationary planar lean methane-air (SP) flame. The equivalence ratio in both cases was 0.7, the pressure 1 atm while the unburned temperature was 700 K for the hydrogen-air PTJ case and 300 K for methane-air SP case, resulting in data sets with a density ratio of 3 and 5, respectively. The turbulent Reynolds numbers for the cases ranged from 200 to 428.4, the Damköhler number from 3.1 to 29.1, and the Karlovitz number from 0.1 to 4.5. The dissipation spectra collapse when normalized by the respective Favre-averaged dissipation rates. However, the normalized dissipation spectra in all the cases deviate noticeably from those predicted by classical scaling laws for constant-density turbulent flows and bear a clear influence of the chemical reactions on the dissipative range of the energy cascade.

In June 2013, the Department of Defense published a congressionally mandated, unclassified update on the U.S. Nuclear Employment Strategy. Among the many updates in this document are three key ground rules for guiding the sizing of the non-deployed U.S. nuclear stockpile. Furthermore, these ground rules form an important and objective set of criteria against which potential future stockpile hedging strategies can be evaluated.

Traditional multiple imputation approaches may perform poorly for datasets with high rates of missingness unless many m imputations are used. This paper implements an alternative machine learning-based approach to imputing data that are missing at high rates. Here, we use boosting to create a strong learner from a weak learner fitted to a dataset missing many observations. This approach may be applied to a variety of types of learners (models). The approach is demonstrated by application to a spatiotemporal dataset for predicting dengue outbreaks in India from meteorological covariates. A Bayesian spatiotemporal CAR model is boosted to produce imputations, and the overall RMSE from a k-fold cross-validation is used to assess imputation accuracy.

The correct storage for critical surface samples is a concern for high fidelity testing. This study compares some common storage for clean parts at Sandia. Time of Flight Secondary Ion Mass Spectroscopy (ToFSIMS) and contact angle are employed to measure relative amount of residue on surface of clean metal sample after extended storage.

A number of critical science, engineering and advanced technology applications require predictive analysis of complex shock-hydrodynamics of fluid/solid materials with possible electromagnetic interaction. The physical mechanisms include wave-phenomena, material-transport, diffusion, chemical reactions, and electromagnetics. The highly nonlinear multiple-time and length-scale response of these mechanisms include discontinuities formed from shocks, contact surfaces, and complex tabular equations-of-state (EOS). Current dominant computational solution strategies use ad-hoc combinations of operator- splitting, semi-implicit, and explicit time-integration methods and decoupled nonlinear-solvers. While these approaches have enabled progress in forward simulation, the inherited mathematical structure has not provided stability, accuracy and efficiency to resolve all the dynamical time-scales of interest, nor has it enabled integrated fast sensitivity analysis and uncertainty quantification (UQ). This draft report describes initial progress towards developing a new multiphysics shock-hydro capability that is intended to be more robust, mathematically well-structured and can readily be combined with advanced higher-order implicit/explicit (IMEX) time integration and efficient adjoint-enhanced uncertainty quantification (UQ) techniques.

The purpose of this one-year LDRD was to investigate the use of the helium ion microscope (HeIM) for imaging dopant profiles in silicon relevant to integrated circuit technologies. HeIM is a new technology that offers improved spatial resolution over scanning electron microscopy and different beam-solid interaction physics which leads to unique contrast mechanisms. Two parallel thrusts were pursued: 1) traditional imaging via the secondary electron signal and 2) a novel topographical approach. To obtain the experimental details and results, please refer to the classified report from the project manager, Ed Cole, or the Cyber IA lead, Justin Ford.

Spectrum splitting is an optical technique that can increase conversion efficiency or add energy storage capability to a photovoltaic (PV) energy system. In this Sandia National Laboratory Campus Executive project, two distinct types of Diffractive Optical Elements (DOEs) for spectrum splitting were developed, fabricated and measured. The first DOE was an algorithmically-designed freeform surface relief structure. A parametric study of the Broadband Gerchberg-Saxton algorithm was performed to show the effect of design variables on device performance. Two DOE designs were fabricated using a grayscale Maskless Lithography Tool (MLT) and measured. The second DOE was a volume holographic lens. This concept was explored in the context of hybrid PV/biofuel implementation, and was later applied to a multiple-bandgap PV module. A design process was developed to ensure diffraction into a single order across the lens and to enable spectral tuning of diffracted light. A proof-of-concept off-axis holographic lens was fabricated and measured. The report concludes with a summary of spectrum splitting performance and discussion of areas for improvement and future work.

Modern computers are constantly faced with the challenge of processing ever-growing quantities of data that span a wide range of modalities. Of particular relevance to national security interests is the ability to integrate multimodal data for the purpose of fast decision making. The brain is a biological system that is specialized for high performance at this task, suggesting that understanding the mechanisms by which neural circuits integrate multimodal data may lead to improved man-made detection systems. This research focused on understanding these neural algorithms, and specifically tested the hypothesis that hippocampal neurons multiplex information from two different input streams. Specifically, we compare the spiking behavior of a computational model of hippocampal circuitry with neurophysiological data recorded from rodent hippocampus.

Traditional singularity-based fracture mechanics theories rely on their ability to infer the crack tip driving force (local field) by surveying macroscopic physical magnitudes far from the crack tip (far field). This key capability allows engineers to employ nominal forces or displacements to estimate the potential for stable or unstable crack growth. In the case of heterogeneous or anisotropic materials, traditional fracture approaches are not fully theoretically sound and applications rely on extrapolating methodologies with ad-hoc corrections. This Express Laboratory Directed Research and Development (ELDRD) program employed mesoscale-sensitive finite element simulations to assess the impact of grain size and texture on the crack tip behavior. A dislocation-based crystal plasticity model conveys grain size effects by computing the constraint on dislocation cell structures. We assessed the effects of microstructural variability on multiple displacement-based measurements of the fracture driving forces for crack opening (Mode I) and sliding (Mode II). We also consider multiple microstructural realizations of single phase metals undergoing ductile failure. The results show that grain size and texture affect the applied fracture driving force and can induce a significant Mode II deformation under force and displacement control, which is completely neglected in homogeneous models. A large variability in driving forces upon identical far field applied conditions is attributed to a buffering effects of the microstructure. Furthermore, crack mouth opening displacement is almost insensitive to microstructure, which suggests that experimental measurements using such a magnitude (e.g., plastic hinge model) may underestimate local crack tip driving force variability.

Overall objectives of the project were: Verify the potential for solar thermochemical cycles for hydrogen production to be competitive in the long term and by 2020, develop this technology to produce hydrogen with a projected cost of $3.00/gge at the plant gate; and, Develop a high-efficiency particle bed reactor for producing hydrogen via a thermochemical water-splitting (WS) cycle, and demonstrate eight continuous hours of operation on a solar simulator producing greater than 3 L of H₂.

A Directional Unfolded Source Term (DUST) method was developed to compute directionally resolved gamma-ray source terms based on back-projection spectra synthesized by Compton Cameras. Spectral features in the unprocessed spectra are indistinct primarily because the rotational angles for the conical projections cannot be determined, so probability distributions are constructed from overlapping cones. The DUST method uses an angular response function to compute a covariance matrix, which is used to process count rates in back-projection spectra by linear regression to partition the gamma-rays among several spatial regions. This method was applied to analyze data collected by the Polaris detector during an evaluation that was conducted at Oak Ridge National Laboratory (ORNL). The evaluation includes measurements of calibration sources with angular separations ranging from 1° to more than 50°. Measurements were also performed for cylindrical depleted uranium castings and a ¹³⁷Cs source inside a large polyethylene sphere. The DUST algorithm was able to differentiate gamma-rays emitted by ¹³⁷Cs and ⁶⁰Co when the sources were separated by less than 2°, but separation greater than 10° was required to isolate the ¹³³Ba emission from gamma-rays emitted by the other sources. The computed source terms were consistent with emission profiles from the calibration sources and from models of the spatially-extended sources. Methods for viewing radiation profiles were also evaluated because user input is required to select spatial regions of interest.

This report documents completion of a Level 2 Milestone on the development of a multi-physics capability to predict the evolving material state through the manufacturing process of a Gas Transfer Systems (GTS) reservoir. We present details on new developments and capability improvements that address the following completion criteria: (i) validation of a microstructure evolution model, including recrystallization and strain aging, (ii) demonstration of the capability to remesh, map and transfer material state (internal state variables) and residual stress from forging to machining to welding processes, and (iii) formal V&V characterization and quantification of uncertainties of material parameters and manufacturing process parameters on residual stress.

The recent boom in the oil and natural gas industry of hydraulic fracture of source rocks has caused a new era in oil and gas production worldwide. However, there are many parts of this process that are poorly understood and thus hard to control. One of the few things that can be controlled is the process of injection to create the fractures in the subsurface and the subsequent injection of proppants to maintain the permeability of the fractured formation, allowing hydrocarbons to be extracted. The goal of this work was to better understand the injection process and resulting proppant distribution in the fracture through a combination of lab-scale experiments and computational models.

This report summaries the work of a 2-year LDRD project aimed at using graphene in integrated circuits in ways that would both obfuscate their function and enhance their level of trust. We have studied (both experimentally and theoretically) process steps, optical properties, design/layout of circuits, and many kinds of analytical techniques. Our conclusion is that graphene shows promise in this application, but additional work must be done to improve compatibility with existing CMOS manufacturing facilities particularly in the area of contamination.

Two-dimensional materials were explored through collaboration with Steve Howell and Catalyn Spataru, led by James Bartz during FY15 and FY16 at Sandia National Laboratories. Because of their two-dimensional nature, these materials may offer properties exceeding those of bulk materials. This work involved Density Functional Theory simulations and optical methods, instrumentation development, materials growth and materials characterization. Through simulation the wide variety of two dimensional materials was down-selected for fabrication and testing. Out of the two dimensional semiconductors studied, black phosphorus bilayers showed the strongest spectral absorption tuning with applied electric field. Laser scanning confocal microscopy, spectroscopy and atomic force microscopy allowed for identification of micron scale samples. A technique involving conductive tip atomic force microscopy and back-side illumination was developed simple assembly and characterization of material spectral response.

The Rayleigh-Taylor instability (RTI) is investigated using the direct simulation Monte Carlo (DSMC) method of molecular gas dynamics. Here, fully resolved two-dimensional DSMC RTI simulations are performed to quantify the growth of flat and single-mode perturbed interfaces between two atmospheric-pressure monatomic gases as a function of the Atwood number and the gravitational acceleration. The DSMC simulations reproduce many qualitative features of the growth of the mixing layer and are in reasonable quantitative agreement with theoretical and empirical models in the linear, nonlinear, and self-similar regimes. In some of the simulations at late times, the instability enters the self-similar regime, in agreement with experimental observations. For the conditions simulated, diffusion can influence the initial instability growth significantly.

This study reports on selective isotropic dry etching of chemically vapor deposited (CVD) Ge thin film, release layers using a Shibaura chemical downstream etcher (CDE) with NF₃ and Ar based plasma chemistry. Relative etch rates between Ge, Si and SiN_x are described with etch rate reductions achieved by adjusting plasma chemistry with O₂. Formation of oxides reducing etch rates were measured for both Ge and Si, but nitrides or oxy-nitrides created using direct injection of NO into the process chamber were measured to increase Si and SiN_x etch rates while retarding Ge etching.

The United States Department of Energy, Office of Nuclear Energy, Fuel Cycle Technology Program sponsors nuclear fuel cycle research and development. As part of its Fuel Cycle Options campaign, the DOE has established the Nuclear Fuel Cycle Options Catalog. The catalog is intended for use by the Fuel Cycle Technologies Program in planning its research and development activities and disseminating information regarding nuclear energy to interested parties. The purpose of this report is to document the improvements and additions that have been made to the Nuclear Fuel Cycle Options Catalog in the 2016 fiscal year.

The Used Fuel Disposition Campaign (UFDC) within the DOE Fuel Cycle Technologies (FCT) program has been engaging in international collaborations between repository R&D programs for high-level waste (HLW) disposal to leverage on gathered knowledge and laboratory/field data of near- and far-field processes from experiments at underground research laboratories (URL). Heater test experiments at URLs provide a unique opportunity to mimetically study the thermal effects of heat-generating nuclear waste in subsurface repository environments. Various configurations of these experiments have been carried out at various URLs according to the disposal design concepts of the hosting country repository program. The FEBEX (Full-scale Engineered Barrier Experiment in Crystalline Host Rock) project is a large-scale heater test experiment originated by the Spanish radioactive waste management agency (Empresa Nacional de Residuos Radiactivos S.A. – ENRESA) at the Grimsel Test Site (GTS) URL in Switzerland. The project was subsequently managed by CIEMAT. FEBEX-DP is a concerted effort of various international partners working on the evaluation of sensor data and characterization of samples obtained during the course of this field test and subsequent dismantling. The main purpose of these field-scale experiments is to evaluate feasibility for creation of an engineered barrier system (EBS) with a horizontal configuration according to the Spanish concept of deep geological disposal of high-level radioactive waste in crystalline rock. Another key aspect of this project is to improve the knowledge of coupled processes such as thermal-hydro-mechanical (THM) and thermal-hydro-chemical (THC) operating in the near-field environment. The focus of these is on model development and validation of predictions through model implementation in computational tools to simulate coupled THM and THC processes.

Switching of transducer coupling in aluminum nitride contour-mode resonators provides an enabling technology for future tunable and reconfigurable filters for multi-function RF systems. By using microelectromechanical capacitive switches to realize the transducer electrode fingers, coupling between the metal electrode finger and the piezoelectric material is modulated to change the response of the device. On/off switched width extensional resonators with an area of <0.2 mm2 demonstrate a Q of 2000, K 2 of 0.72, and >24 dB switching ratio at a resonator center frequency of 635 MHz. Other device examples include a 63 MHz resonator with switchable impedance and a 470 MHz resonator with 127 kHz of fine center frequency tuning accomplished by mass loading of the resonator with the MEMS switches.

Abstract not provided.

Enhancement-mode Si/SiGe electron quantum dots have been pursued extensively by many groups for their potential in quantum computing. Most of the reported dot designs utilize multiple metal-gate layers and use Si/SiGe heterostructures with Ge concentration close to 30%. Here, we report the fabrication and low-temperature characterization of quantum dots in the Si/Si0.8Ge0.2 heterostructures using only one metal-gate layer. We find that the threshold voltage of a channel narrower than 1 μm increases as the width decreases. The higher threshold can be attributed to the combination of quantum confinement and disorder. We also find that the lower Ge ratio used here leads to a narrower operational gate bias range. The higher threshold combined with the limited gate bias range constrains the device design of lithographic quantum dots. We incorporate such considerations in our device design and demonstrate a quantum dot that can be tuned from a single dot to a double dot. The device uses only a single metal-gate layer, greatly simplifying device design and fabrication.

A Bayesian statistical framework is presented for Zimmerman and Weissenburger flutter margin method which considers the uncertainties in aeroelastic modal parameters. The proposed methodology overcomes the limitations of the previously developed least-square based estimation technique which relies on the Gaussian approximation of the flutter margin probability density function (pdf). Using the measured free-decay responses at subcritical (preflutter) airspeeds, the joint non-Gaussain posterior pdf of the modal parameters is sampled using the Metropolis–Hastings (MH) Markov chain Monte Carlo (MCMC) algorithm. The posterior MCMC samples of the modal parameters are then used to obtain the flutter margin pdfs and finally the flutter speed pdf. The usefulness of the Bayesian flutter margin method is demonstrated using synthetic data generated from a two-degree-of-freedom pitch-plunge aeroelastic model. The robustness of the statistical framework is demonstrated using different sets of measurement data. In conclusion, it will be shown that the probabilistic (Bayesian) approach reduces the number of test points required in providing a flutter speed estimate for a given accuracy and precision.

We report a combined experimental and quantum chemistry study of the initial reactions in low-temperature oxidation of tetrahydrofuran (THF). Using synchrotron-based time-resolved VUV photoionization mass spectrometry, we probe numerous transient intermediates and products at P = 10-2000 Torr and T = 400-700 K. A key reaction sequence, revealed by our experiments, is the conversion of THF-yl peroxy to hydroperoxy-THF-yl radicals (QOOH), followed by a second O2 addition and subsequent decomposition to dihydrofuranyl hydroperoxide + HO2 or to γ-butyrolactone hydroperoxide + OH. The competition between these two pathways affects the degree of radical chain-branching and is likely of central importance in modeling the autoignition of THF. We interpret our data with the aid of quantum chemical calculations of the THF-yl + O2 and QOOH + O2 potential energy surfaces. On the basis of our results, we propose a simplified THF oxidation mechanism below 700 K, which involves the competition among unimolecular decomposition and oxidation pathways of QOOH.

We present a comprehensive analysis of the nonlinear optical Kerr effect in graphene. We directly solve the S-matrix element to calculate the absorption rate, utilizing the Volkov-Keldysh-type crystal wave functions. We then convert to the nonlinear refractive index coefficients through the Kramers-Kronig relation. In this formalism, the source of Kerr nonlinearity is the interplay of optical fields that cooperatively drive the transition from valence to conduction band. This formalism makes it possible to identify and compute the rates of distinct nonlinear processes that contribute to the Kerr nonlinear refractive index coefficient. The four identified mechanisms are two-photon absorption, Raman transition, self-coupling, and quadratic ac Stark effect. We also present a comparison of our theory with recent experimental and theoretical results.

We designed an optical coating based on TiO₂/SiO₂ layer pairs for broad bandwidth high reflection (BBHR) at 45-deg angle of incidence (AOI), P polarization of femtosecond (fs) laser pulses of 900-nm center wavelength, and produced the coatings in Sandia’s large optics coater by reactive, ion-assisted e-beam evaporation. This paper reports on laser-induced damage threshold (LIDT) tests of these coatings. The broad HR bands of BBHR coatings pose challenges to LIDT tests. An ideal test would be in a vacuum environment appropriate to a high energy, fs-pulse, petawatt-class laser, with pulses identical to its fs pulses. Short of this would be tests over portions of the HR band using nanosecond or sub-picosecond pulses produced by tunable lasers. Such tests could, e.g., sample 10-nm-wide wavelength intervals with center wavelengths tunable over the broad HR band. Alternatively, the coating’s HR band could be adjusted by means of wavelength shifts due to changing the AOI of the LIDT tests or due to the coating absorbing moisture under ambient conditions. In conclusion, we had LIDT tests performed on the BBHR coatings at selected AOIs to gain insight into their laser damage properties and analyze how the results of the different LIDT tests compare.

We have conducted molecular dynamics (MD) simulations of quasi-isentropic ramp-wave compression to very high pressures over a range of strain rates from 1011 down to 108 1/s. Using scaling methods, we collapse wave profiles from various strain rates to a master profile curve, which shows deviations when material response is strain-rate dependent. Thus, we can show with precision where, and how, strain-rate dependence affects the ramp wave. We find that strain rate affects the stress-strain material response most dramatically at strains below 20%, and that above 30% strain the material response is largely independent of strain rate. We show good overall agreement with experimental stress-strain curves up to approximately 30% strain, above which simulated response is somewhat too stiff. We postulate that this could be due to our interatomic potential or to differences in grain structure and/or size between simulation and experiment. Strength is directly measured from per-atom stress tensor and shows significantly enhanced elastic response at the highest strain rates. This enhanced elastic response is less pronounced at higher pressures and at lower strain rates.

We describe a high-resolution patterning approach that combines the spatial control inherent to laser direct writing with the versatility of benchtop chemical synthesis. By taking advantage of the steep thermal gradient that occurs while laser heating a metal edge in contact with solution, diverse materials comprising transition metals are patterned with feature size resolution nearing 1 μm. We demonstrate fabrication of reduced metallic nickel in one step and examine electrical properties and air stability through direct-write integration onto a device platform. This strategy expands the chemistries and materials that can be used in combination with laser direct writing.

Division-wide email survey conducted in May. Survey questions chosen to provide some connection to the 2014 DuPont Safety Perception Survey and address key components of a safety culture.

This administrative operating procedure (AOP) provides the process for performing the initial and final hazard categorization for a nuclear facility or activity to ensure compliance with 10 CFR 830.202. This AOP provides guidance on the application of the PHS process (refer to MN471017, Safety Basis Manual, Appendix NF-01,"Nuclear Facility Hazard Categorization") and describes the analyses that might be required to finalize a facility's hazard categorization.

Contrary to the notion that the use of fumed silica in consumer products can "generally (be) regarded as safe" (GRAS), the high surface reactivity of pyrogenic silica differs from other forms of synthetic amorphous silica (SAS), including the capacity to induce membrane damage and acute proinflammatory changes in the murine lung. In addition, the chain-like structure and reactive surface silanols also allow fumed silica to activate the NLRP3 inflammasome, leading to IL-1β production. This pathway is known to be associated with subchronic inflammation and profibrogenic effects in the lung by α-quartz and carbon nanotubes. However, different from the latter materials, bolus dose instillation of 21 mg/kg fumed silica did not induce sustained IL-1β production or subchronic pulmonary effects. In contrast, the NLRP3 inflammasome pathway was continuously activated by repetitive-dose administration of 3 × 7 mg/kg fumed silica, 1 week apart. We also found that while single-dose exposure failed to induce profibrotic effects in the lung, repetitive dosing can trigger increased collagen production, even at 3 × 3 mg/kg. The change between bolus and repetitive dosing was due to a change in lung clearance, with recurrent dosing leading to fumed silica biopersistence, sustained macrophage recruitment, and activation of the NLRP3 pathway. These subchronic proinflammatory effects disappeared when less surface-reactive titanium-doped fumed silica was used for recurrent administration. All considered, these data indicate that while fumed silica may be regarded as safe for some applications, we should reconsider the GRAS label during repetitive or chronic inhalation exposure conditions.

Wide band gap semiconductors like AlN typically cannot be efficiently p-doped: acceptor levels are far from the valence band-edge, preventing holes from activating. This means that pn-junctions cannot be created, and the semiconductor is less useful, a particular problem for deep Ultraviolet (UV) optoelectronics.

The performance and efficiency of power devices depends on both high breakdown voltage and low on-state resistance. For semiconductor devices, the critical electric field (EC) affecting breakdown scales approximately as Eg25 [1], making the wide bandgap semiconductor materials logical candidates for high voltage power electronics devices. In particular, AlGaN alloys approaching AlN with its 6.2 eV bandgap have an estimated EC approaching 5x that of GaN. This factor makes AlN/AlGaN high election mobility transistors (HEMTs) extremely interesting as candidate power electronic devices. Until now, such devices have been hampered, ostensibly due to the difficulty of making Ohmic contacts to AlGaN alloys with high Al composition. With the use of an AlN barrier etch and regrowth procedure for Ohmic contact formation, we are now able to report on an AlN/AlGaN HEMT with 85% Al.

The mechanisms that limit the temperature performance of GaAs/Al0.15GaAs-based terahertz quantum cascade lasers (THz-QCLs) have been identified as thermally activated LO-phonon scattering and leakage of charge carriers into the continuum. Consequently, the combination of highly diagonal optical transition and higher barriers should significantly reduce the adverse effects of both mechanisms and lead to improved temperature performance. Here, we study the temperature performance of highly diagonal THz-QCLs with high barriers. Our analysis uncovers an additional leakage channel which is the thermal excitation of carriers into bounded higher energy levels, rather than the escape into the continuum. Based on this understanding, we have designed a structure with an increased intersubband spacing between the upper lasing level and excited states in a highly diagonal THz-QCL, which exhibits negative differential resistance even at room temperature. This result is a strong evidence for the effective suppression of the aforementioned leakage channel.

We present experimental results for a selective epitaxially grown Ge-on-Si separate absorption and charge multiplication (SACM) integrated waveguide coupled avalanche photodiode (APD) compatible with our silicon photonics platform. Epitaxially grown Ge-on-Si waveguide-coupled linear mode avalanche photodiodes with varying lateral multiplication regions and different charge implant dimensions are fabricated and their illuminated device characteristics and high-speed performance is measured. We report a record gain-bandwidth product of 432 GHz for our highest performing waveguide-coupled avalanche photodiode operating at 1510nm. Bit error rate measurements show operation with BER< 10-12, in the range from -18.3 dBm to -12 dBm received optical power into a 50 Ω load and open eye diagrams with 13 Gbps pseudo-random data at 1550 nm.

Manganese oxide/poly(3,4-ethylene-dioxythiophene) (MnO_x/ PEDOT) nanostructured hybrid thin films were prepared using a simple anodic electrodeposition process from aqueous solution, and then tested for oxygen reduction reaction (ORR) activity in alkaline electrolyte using rotating disk electrode and rotating ring disk electrode methods. MnO_x/PEDOT provided improvements over MnO_x-only and PEDOT-only control films, with > 0.2 V decrease in onset and half-wave overpotentials, and > 1.5 times increase in terminal current density. The MnO_x/PEDOT film exhibited only a slightly lower n value (n = 3.86-3.92) than the 20% Pt/C benchmark electrocatalyst (n = 3.98) across all potentials. MnO_x/PEDOT also displayed a more positive half-wave potential and superior electrocatalytic selectivity for the ORR upon methanol exposure than 20% Pt/C. Here, the high activity and synergism of MnO_x/PEDOT towards the ORR is attributed to effective intermixing/dispersion of the two materials, intimate substrate contact with improved charge transfer processes attained by co-electrodepositing MnO_x with PEDOT and due to the increase in Mn³⁺ content at the surface of the oxide.

Cobalt phosphide based thin films and nanoparticles were prepared by the thermal phosphidation of spinel Co₃O₄ precursor films and nanoparticles, respectively. CoP films were prepared with overall retention of the Co₃O₄ nanoplatelet morphology while the spherical/cubic Co₃O₄ and Ni_0.15Co_2.85O₄ nanoparticles were converted to nanorods or nanoparticles, respectively. The inclusion of nickel in the nanoparticles resulted in a 2.5 fold higher surface area leading to higher gravimetric performance. In each case high surface area structures were obtained with CoP as the primary phase. All materials were found to act as effective bifunctional electrocatalysts for both the HER and the OER and compared well to commercial precious metal benchmark materials in alkaline electrolyte. As a result, a symmetrical water electrolysis cell prepared from the CoP-based film operated at a low overpotential of 0.41-0.51 V.

Virulence genes on mobile DNAs such as genomic islands (GIs) and plasmids promote bacterial pathogen emergence. Excision is an early step in GI mobilization, producing a circular GI and a deletion site in the chromosome; circular forms are also known for some bacterial insertion sequences (ISs). The recombinant sequence at the junctions of such circles and deletions can be detected sensitively in high-throughput sequencing data, using new computational methods that enable empirical discovery of mobile DNAs. For the rich mobilome of a hospital Klebsiella pneumoniae strain, circularization junctions (CJs) were detected for six GIs and seven IS types. Our methods revealed differential biology of multiple mobile DNAs, imprecision of integrases and transposases, and differential activity among identical IS copies for IS26, ISKpn18 and ISKpn21. Using the resistance of circular dsDNA molecules to exonuclease, internally calibrated with the native plasmids, showed that not all molecules bearing GI CJs were circular. Transpositions were also detected, revealing replicon preference (ISKpn18 prefers a conjugative IncA/C2 plasmid), local action (IS26), regional preferences, selection (against capsule synthesis) and IS polarity inversion. Efficient discovery and global characterization of numerous mobile elements per experiment improves accounting for the new gene combinations that arise in emerging pathogens.

Vibrational sum frequency generation spectroscopy has the benefit of being very surface-specific, aiding in the the investigation of a given material’s surface chemical and physical properties. As such, the goal of this project was to construct a sum frequency generation microscope that would enable the investigation of surface phenomena on a microscopic scale. Currently, the microscope hardware has been assembled and programmed, and simple spectral images were taken with elastically scattered 532 nm light. These images indicate an image resolution near 3 µm.

We are investigating the accuracy of Lagrangian analysis of time-resolved, 3D velocity measurements in turbulent flames obtained using high-speed tomographic particle image velocimetry (TPIV). A particle-tracking algorithm was implemented in MATLAB to extract Lagrangian statistics from the velocity fields. The accuracy of Lagrangian statistics depends on the accuracy of the estimated particle trajectories. Errors associated with the spatial and temporal resolutions of high-speed TPIV experiments were evaluated using a direct numerical simulation (DNS) of an isotropic turbulent flow. LPT was then implemented onto TPIV measurements of a laminar counterflow flame. Results calculated with LPT were compared to known results of quantities measured with an Eulerian approach.

Deuterium desorption in an automotive-scale hydrogen storage tube was studied in-situ using neutron diffraction. Gradients in the concentration of the various alanate phases were observed along the length of the tube but no significant radial anisotropy was present. In addition, neutron radiography and computed tomography showed large scale cracks and density fluctuations, confirming the presence of these structures in an undisturbed storage system. These results demonstrate that large scale storage structures are not uniform even after many absorption/desorption cycles and that movement of gaseous hydrogen cannot be properly modeled by a simple porous bed model. Furthermore, the evidence indicates that there is slow transformation of species at one end of the tube indicating loss of catalyst functionality. These observations explain the unusually fast movement of hydrogen in a full scale system and shows that loss of capacity is not occurring uniformly in this type of hydrogen-storage system.

One of the most widely-used procedures for dimensionality reduction of high dimensional data is Principal Component Analysis (PCA). More broadly, low-dimensional stochastic representation of random fields with finite variance is provided via the well known Karhunen-Loève expansion (KLE). The KLE is analogous to a Fourier series expansion for a random process, where the goal is to find an orthogonal transformation for the data such that the projection of the data onto this orthogonal subspace is optimal in the L2 sense, i.e., which minimizes the mean square error. In practice, this orthogonal transformation is determined by performing an SVD (Singular Value Decomposition) on the sample covariance matrix or on the data matrix itself. Sampling error is typically ignored when quantifying the principal components, or, equivalently, basis functions of the KLE. Furthermore, it is exacerbated when the sample size is much smaller than the dimension of the random field. In this paper, we introduce a Bayesian KLE procedure, allowing one to obtain a probabilistic model on the principal components, which can account for inaccuracies due to limited sample size. The probabilistic model is built via Bayesian inference, from which the posterior becomes the matrix Bingham density over the space of orthonormal matrices. We use a modified Gibbs sampling procedure to sample on this space and then build probabilistic Karhunen-Loève expansions over random subspaces to obtain a set of low-dimensional surrogates of the stochastic process. We illustrate this probabilistic procedure with a finite dimensional stochastic process inspired by Brownian motion.

In both continuum hydrodynamics simulations and also multimillion atom reactive molecular dynamics simulations of shockwave propagation in single crystal pentaerythritol tetranitrate (PETN) containing a cylindrical void, we observed the formation of an initial radially symmetric hot spot. By extending the simulation time to the nanosecond scale, however, we observed the transformation of the small symmetric hot spot into a longitudinally asymmetric hot region extending over a much larger volume. Performing reactive molecular dynamics shock simulations using the reactive force field (ReaxFF) as implemented in the LAMMPS molecular dynamics package, we showed that the longitudinally asymmetric hot region was formed by coalescence of the primary radially symmetric hot spot with a secondary triangular hot zone. We showed that the triangular hot zone coincided with a double-shocked region where the primary planar shockwave was overtaken by a secondary cylindrical shockwave. The secondary cylindrical shockwave originated in void collapse after the primary planar shockwave had passed over the void. A similar phenomenon was observed in continuum hydrodynamics shock simulations using the CTH hydrodynamics package. The formation and growth of extended asymmetric hot regions on nanosecond timescales has important implications for shock initiation thresholds in energetic materials.

Ultrabroadband coherent anti-Stokes Ra man spectroscopy (CARS) has been developed for one -dimensional imaging of temperature and major species distributions simultaneously in the near-wall region of a methane/air flame supported on a side-wall-quenching (SWQ) burner. Automatic temporal and spatial overlap of the ~7 femtosecond pump and Stokes pulses is achieved utilizing a two-beam CARS phase-matching scheme, and the crossed ~75 picosecond probe beam provide s excellent spatial sectioning of the probed location. Concurrent detection of N₂, O₂, H₂, CO, CO₂, and CH₄ is demonstrated while high-fidelity flame thermometry is assessed from the N₂ pure rotational S-branch in a one-dimensional -CARS imaging configuration. A methane/air premixed flame at lean, stoichiometric, and rich conditions ( Φ = 0.83, 1.0 , and 1.2) and Reynolds number = 5,000 is probed as it quenches against a cooled steel side- wall parallel to the flow providing a persistent flame-wall interaction. Here, an imaging resolution of better than 40 μm is achieved across the field -of-view, thus allowing thermochemical states (temperature and major species) of the thermal boundary layer to be resolved to within ~30 μm of the interface.

The effects of combustion on the strain rate field are investigated in turbulent premixed CH₄/air Bunsen flames using simultaneous tomographic PIV and OH LIF measurements. Tomographic PIV provides three-dimensional velocity measurements, from which the complete strain rate tensor is determined. The OH LIF measurements are used to determine the position of the flame surface and the flame-normal orientation within the imaging plane. This combination of diagnostic techniques enables quantification of divergence as well as flame-normal and tangential strain rates, which are otherwise biased using only planar measurements. Measurements are compared in three lean-to-stoichiometric flames that have different amounts of heat release and Damköhler numbers greater than unity. The effects of heat release on the principal strain rates and their alignment relative to the local flame normal are analyzed. The extensive strain rate preferentially aligns with the flame normal in the reaction zone, which has been indicated by previous studies. The strength of this alignment increases with increasing heat release and, as a result, the flame-normal strain rate becomes highly extensive. These effects are associated with the gas expansion normal to the flame surface, which is largest for the stoichiometric flame. In the preheat zone, the compressive strain rate has a tendency to align with the flame normal. Away from the flame front, the flame – strain rate alignment is arbitrary in both the reactants and products. The flame-tangential strain rate is on average positive across the flame front, and therefore the turbulent strain rate field contributes to the enhancement of scalar gradients as in passive scalar turbulence. As a result, increases in heat release result in larger positive values of the divergence as well as flame-normal and tangential strain rates, the tangential strain rate has a weaker dependence on heat release than the flame-normal strain rate and the divergence.

Given a network of agents interacting over time, which few interactions best characterize the dynamics of the whole network? We propose an algorithm that finds the optimal sparse approximation of a network. The user controls the level of sparsity by specifying the total number of edges. The networks are represented using directed information graphs, a graphical model that depicts causal influences between agents in a network. Goodness of approximation is measured with Kullback-Leibler divergence. The algorithm finds the best approximation with no assumptions on the topology or the class of the joint distribution.

One of the most common causes of structural failure in metals is fatigue induced by cyclic loading. Historically, microstructure-level analysis of fatigue cracks has primarily been performed post mortem. However, such investigations do not directly reveal the internal structural processes at work near micro- and nanoscale fatigue cracks and thus do not provide direct evidence of active microstructural mechanisms. In this study, the tension-tension fatigue behavior of nanocrystalline Cu was monitored in real time at the nanoscale by utilizing a new capability for quantitative cyclic mechanical loading performed in situ in a transmission electron microscope (TEM). Controllable loads were applied at frequencies from one to several hundred hertz, enabling accumulations of 106 cycles within 1 h. The nanometer-scale spatial resolution of the TEM allows quantitative fatigue crack growth studies at very slow crack growth rates, measured here at ∼10-12 m·cycle-1. This represents an incipient threshold regime that is well below the tensile yield stress and near the minimum conditions for fatigue crack growth. Evidence of localized deformation and grain growth within 150 nm of the crack tip was observed by both standard imaging and precession electron diffraction orientation mapping. These observations begin to reveal with unprecedented detail the local microstructural processes that govern damage accumulation, crack nucleation, and crack propagation during fatigue loading in nanocrystalline Cu.

Digital in-line holography (DIH) and plenoptic photography are two techniques for single-shot, volumetric measurement of 3D particle fields. Here we present a comparison of the two methods by applying plenoptic imaging to experimental configurations that have been previously investigated with DIH. These experiments include the tracking of secondary droplets from the impact of a water drop on a thin film of water and tracking of pellets from a shotgun. Both plenoptic imaging and DIH successfully quantify the 3D nature of these particle fields. This includes measurement of the 3D particle position, individual particle sizes, and three-component velocity vectors. For the initial processing methods presented here, both techniques give out-of-plane positional accuracy of approximately 1-2 particle diameters. For a fixed image sensor, digital holography achieves higher effective in-plane spatial resolutions. However, collimated and coherent illumination makes holography susceptible to image distortion through index of refraction gradients, as demonstrated in the shotgun experiments. In contrast, plenoptic imaging allows for a simpler experimental configuration and, due to the use of diffuse, white-light illumination, plenoptic imaging is less susceptible to image distortion in the shotgun experiments.

Understanding the catalyzed formation and evolution of lithium-oxide products in Li-O2 batteries is central to the development of next-generation energy storage technology. Catalytic sites, while effective in lowering reaction barriers, often become deactivated when placed on the surface of an oxygen electrode due to passivation by solid products. Here we investigate a mechanism for alleviating catalyst deactivation by dispersing Pd catalytic sites away from the oxygen electrode surface in a well-structured anodic aluminum oxide (AAO) porous membrane interlayer. We observe the cross-sectional product growth and evolution in Li-O2 cells by characterizing products that grow from the electrode surface. Morphological and structural details of the products in both catalyzed and uncatalyzed cells are investigated independently from the influence of the oxygen electrode. We find that the geometric decoration of catalysts far from the conductive electrode surface significantly improves the reaction reversibility by chemically facilitating the oxidation reaction through local coordination with PdO surfaces. The influence of the catalyst position on product composition is further verified by ex situ X-ray photoelectron spectroscopy and Raman spectroscopy in addition to morphological studies.

This study deals with the design of low-power, high performance, continuous-time filters. The proposed OTA architecture employs current-reuse differential difference amplifiers in order to produce more power efficient Gm-C filter solutions. To demonstrate this, a 6th order low-pass Butterworth filter was designed in 0.18 m CMOS achieving a 65-MHz -3-dB frequency, an in-band input-referred third-order intercept point of 12.0 dBm, and an input referred noise density of 40 nV/Hz1=2, while only consuming 8.07 mW from a 1.8 V supply and occupying a total chip area of 0.21 mm2 with a power consumption of only 1.19 mW per pole.

We demonstrate low energy single ion detection using a co-planar detector fabricated on a diamond substrate and characterized by ion beam induced charge collection. Histograms are taken with low fluence ion pulses illustrating quantized ion detection down to a single ion with a signal-to-noise ratio of approximately 10. We anticipate that this detection technique can serve as a basis to optimize the yield of single color centers in diamond. In conclusion, the ability to count ions into a diamond substrate is expected to reduce the uncertainty in the yield of color center formation by removing Poisson statistics from the implantation process.

Inductive coupling and matching networks are used to increase the bandwidth of filters realized with aluminum nitride contour-mode resonators. Filter bandwidth has been doubled using a wirebonded combination of a wafer-level-packaged resonator chip and a high-Q integrated inductor chip. The three-pole filters have a center frequency near 500 MHz, an area of 9 mm × 9 mm, insertion loss of < 5 dB for a bandwidth of 0.4%, and a resonator unloaded Q of 1600.

We investigate optical polariton modes supported by subwavelength-thick degenerately doped semiconductor nanolayers (e.g. indium tin oxide) on glass in the epsilon-near-zero (ENZ) regime. The dispersions of the radiative (R, on the left of the light line) and non-radiative (NR, on the right of the light line) ENZ polariton modes are experimentally measured and theoretically analyzed through the transfer matrix method and the complex-frequency/real-wavenumber analysis, which are in remarkable agreement. We observe directional near-perfect absorption using the Kretschmann geometry for incidence conditions close to the NR-ENZ polariton mode dispersion. Along with field enhancement, this provides us with an unexplored pathway to enhance nonlinear optical processes and to open up directions for ultrafast, tunable thermal emission.

SWinzip is a Matlab and C++ library for scientific lossy data compression and reconstruction using compressed sensing and tree-wavelets transforms. These methods are known for their large compression and usefulness in data analytics such as features extraction. Compressed sensing and wavelets methods rely heavily on sparse and dense linear algebra operations implemented through the Boost codes in our library. SWinzip accommodates data represented on both regular grids (e.g. image data) and point-clouds (e.g. unstructured meshes).

We report the demonstration of dilute nitride heterostructure core/shell microwire solar cells utilizing the combination of top-down reactive-ion etching to create the cores (GaP) and molecular beam epitaxy to create the shells (GaNP). Systematic studies of cell performance over a series of microwire lengths, array periods, and microwire sidewall morphologies examined by transmission electron microscopy were conducted to shed light on performance-limiting factors and to optimize the cell efficiency. We show by microscopy and correlated external quantum efficiency characterization that the open circuit voltage is degraded primarily due to the presence of defects at the GaP/GaNP interface and in the GaNP shells, and is not limited by surface recombination. Compared to thin film solar cells in the same growth run, the microwire solar cells exhibit greater short circuit current but poorer open circuit voltage due to greater light absorption and number of defects in the microwire structure, respectively. The comprehensive understanding presented in this work suggests that performance benefits of dilute nitride microwire solar cells can be achieved by further tuning of the epitaxial quality of the underlying materials.

We investigate the online processing consequences of encountering compound words with transposed letters (TLs), in order to determine if cross-morpheme TLs are more disruptive to reading than those within a single morpheme, as would be predicted by accounts of obligatory morpho-orthopgrahic decomposition. Two measures of online processing, eye movements and event-related potentials (ERPs), were collected in separate experiments. Participants read sentences containing correctly spelled compound words (cupcake), or compounds with TLs occurring either across morphemes (cucpake) or within one morpheme (cupacke). Results showed that between- and within-morpheme transpositions produced equal processing costs in both measures, in the form of longer reading times (Experiment 1) and a late posterior positivity (Experiment 2) that did not differ between conditions. Our findings converge to suggest that within- and between-morpheme TLs are equally disruptive to recognition, providing evidence against obligatory morpho-orthographic processing and in favour of whole-word access of English compound words during sentence reading.

Resistive switches are non-volatile memory cells based on nano-ionic redox processes that offer energy efficient device architectures and open pathways to neuromorphics and cognitive computing. However, channel formation typically requires an irreversible, not well controlled electroforming process, giving difficulty to independently control ionic and electronic properties. The device performance is also limited by the incomplete understanding of the underlying mechanisms. Here, we report a novel memristive model material system based on self-assembled Sm-doped CeO 2 and SrTiO 3 films that allow the separate tailoring of nanoscale ionic and electronic channels at high density (â 1/410 12 inch â '2). We systematically show that these devices allow precise engineering of the resistance states, thus enabling large on-off ratios and high reproducibility. The tunable structure presents an ideal platform to explore ionic and electronic mechanisms and we expect a wide potential impact also on other nascent technologies, ranging from ionic gating to micro-solid oxide fuel cells and neuromorphics.

Low-mobility twin grain boundaries dominate the microstructure of grain boundary-engineered materials and are critical to understanding their plastic deformation behaviour. The presence of solutes, such as hydrogen, has a profound effect on the thermodynamic stability of the grain boundaries. This work examines the case of a Σ3 grain boundary at inclinations from 0° ≤ Φ ≤ 90°. The angle Φ corresponds to the rotation of the Σ3 (1 1 1) < 1 1 0 > (coherent) into the Σ3 (1 1 2) < 1 1 0 > (lateral) twin boundary. To this end, atomistic models of inclined grain boundaries, utilising empirical potentials, are used to elucidate the finite-temperature boundary structure while grand canonical Monte Carlo models are applied to determine the degree of hydrogen segregation. In order to understand the boundary structure and segregation behaviour of hydrogen, the structural unit description of inclined twin grain boundaries is found to provide insight into explaining the observed variation of excess enthalpy and excess hydrogen concentration on inclination angle, but the explanatory power is limited by how the enthalpy of segregation is affected by hydrogen concentration. At higher concentrations, the grain boundaries undergo a defaceting transition. In order to develop a more complete mesoscale model of the interfacial behaviour, an analytical model of boundary energy and hydrogen segregation that relies on modelling the boundary as arrays of discrete 1/3 < 1 1 1 > disconnections is constructed. Lastly, the complex interaction of boundary reconstruction and concentration-dependent segregation behaviour exhibited by inclined twin grain boundaries limits the range of applicability of such an analytical model and illustrates the fundamental limitations for a structural unit model description of segregation in lower stacking fault energy materials.

The interplay between thermodynamics and mechanical properties in the transformation of studtite, (UO2)(O2)(H2O)2·2H2O, into metastudtite, (UO2)(O2)(H2O)2, two important corrosion phases observed on the surface of uranium dioxide exposed to water, is revealed using density functional perturbation theory. Phonon calculations within the quasi-harmonic approximation predict that the standard entropy change for the (UO2)(O2)(H2O)2·2H2O → (UO2)(O2)(H2O)2 + 2H2O reaction is ΔS0 = +80 J·mol-1·K-1 for the production of water in the liquid state and +389 J·mol-1·K-1 for water vapor. Similar to bulk H2O(l), the bulk modulus of (UO2)(O2)(H2O)2·2H2O increases with temperature, contrasting with (UO2)(O2)(H2O)2 which features the typical Anderson-Gruneisen temperature dependence of oxide solids. Upon removal of interstitial H2O in studtite, the most important changes in the shear modulus, the parameter limiting the mechanical stability, arise in the planes normal to chain propagation directions. The present findings have important implications for the dehydration of other hygroscopic materials.

High-performance memristors based on AlN films have been demonstrated, which exhibit ultrafast ON/OFF switching times (≈85 ps for microdevices with waveguide) and relatively low switching current (≈15 μA for 50 nm devices). Physical characterizations are carried out to understand the device switching mechanism, and rationalize speed and energy performance. The formation of an Al-rich conduction channel through the AlN layer is revealed. The motion of positively charged nitrogen vacancies is likely responsible for the observed switching.

For more than three decades, the US Department of Energy has investigated the potential for permanent disposal of high-level radioactive waste and spent nuclear fuel in a deep-mined repository at Yucca Mountain, Nevada (USA). A detailed license application submitted to the US Nuclear Regulatory Commission in 2008 provides full documentation of the case for permanent disposal of nuclear waste in tuff. The aridity of the site and great depth to the water table provide a disposal environment and a design concept unique among deep-mined repositories currently or previously proposed worldwide.

Phase locking of an array of lasers is a highly effective method in beam shaping because it increases the output power and reduces the lasing threshold. Here, we show a conceptually novel phase-locking mechanism based on 'antenna mutual coupling' in which laser elements interact through far-field radiations with definite phase relations. This allows a long-range global coupling among the array elements to achieve a robust phase locking in two-dimensional laser arrays. The scheme is ideal for lasers with a deep subwavelength confined cavity, such as nanolasers, whose divergent beam patterns could be used to achieve a strong coupling among the elements in the array. We demonstrated experimentally such a scheme based on subwavelength short-cavity surface-emitting lasers at terahertz frequencies. More than 37 laser elements that span over ∼8 λo were phase locked to each other, and delivered up to 6.5 mW (in a pulsed operation) single-mode radiation at ∼3 THz, with a maximum 450 mW A -1 slope efficiency and a near-diffraction-limited beam divergence.

In many scientific fields, empirical models are employed to facilitate computational simulations of engineering systems. For example, in fluid mechanics, empirical Reynolds stress closures enable computationally-efficient Reynolds Averaged Navier Stokes simulations. Likewise, in solid mechanics, constitutive relations between the stress and strain in a material are required in deformation analysis. Traditional methods for developing and tuning empirical models usually combine physical intuition with simple regression techniques on limited data sets. The rise of high performance computing has led to a growing availability of high fidelity simulation data. These data open up the possibility of using machine learning algorithms, such as random forests or neural networks, to develop more accurate and general empirical models. A key question when using data-driven algorithms to develop these empirical models is how domain knowledge should be incorporated into the machine learning process. This paper will specifically address physical systems that possess symmetry or invariance properties. Two different methods for teaching a machine learning model an invariance property are compared. In the first method, a basis of invariant inputs is constructed, and the machine learning model is trained upon this basis, thereby embedding the invariance into the model. In the second method, the algorithm is trained on multiple transformations of the raw input data until the model learns invariance to that transformation. Results are discussed for two case studies: one in turbulence modeling and one in crystal elasticity. It is shown that in both cases embedding the invariance property into the input features yields higher performance at significantly reduced computational training costs.

As the world transitions from fossil fuels to clean energy sources in the coming decades, many technological challenges will require chemists and material scientists to develop new materials for applications related to energy conversion, storage, and efficiency. Because of their unprecedented adaptability, metal-organic frameworks (MOFs) will factor strongly in this portfolio. By utilizing the broad synthetic toolkit provided by the fields of organic and inorganic chemistry, MOF pores can be customized to suit a particular application. Of particular importance is the ability to tune the strength of the interaction between the MOF pores and guest molecules. By cleverly controlling these MOF-guest interactions, the chemist may impart new function into the Guest@MOF materials otherwise lacking in vacant MOF. Herein, we highlight the concept of the Guest@MOF as it relates to our efforts to develop these materials for energy-related applicatons. Our work in the areas of H2 and noble gas storage, hydrogenolysis of biomass, light-harvesting, and conductive materials will be discussed. Of relevance to light-harvesting applications, we report for the first time a postsynthetic modification strategy for increasing the loading of a light-sensitive electron-donor molecule in the pores of a functionalized MIL-101 structure. Through the demonstrated versatility of these approaches, we show that, by treating guest molecules as integral design elements for new MOF constructs, MOF science can have a significant impact on the advancement of clean energy technologies.

Stabilization methods of turbulent flames often involve mixing of reactants with hot products of combustion. The stabilizing effect of combustion product enthalpy has been long recognized, but the role played by the chemical composition of the product gases is typically overlooked. We employ a counterflow system to pinpoint the effects of the combustion product stoichiometry on the structure of turbulent premixed flames under conditions of both stable burning and local extinction. To that end, a turbulent jet of lean-to-rich, CH4/O2/N2-premixed reactants at a turbulent Reynolds number of 1050 was opposed to a stream of hot products of combustion that were generated in a preburner. While the combustion product stream temperature was kept constant, its stoichiometry was varied independently from that of the reactant stream, leading to reactant-to-product stratification of relevance to practical combustion systems. The detailed structure of the turbulent flame front was analyzed in two series of experiments using laser-induced fluorescence (LIF): joint CH2O LIF and OH LIF measurements and joint CO LIF and OH LIF measurements. Results revealed that a decrease in local CH2O+OH and CO+OH reaction rates coincide with the depletion of OH radicals in the vicinity of the combustion product stream. These critical combustion reaction rates were more readily quenched in the presence of products of combustion from a stoichiometric flame, whereas they were favored by lean combustion products. As a result, stoichiometric combustion products contributed to a greater occurrence of local extinction. Furthermore, they limited the capacity of premixed reactants to ignite and of the turbulent premixed flames to stabilize. In contrast, lean and rich combustion products facilitated flame ignition and stability and reduced the rate of local extinction. The influence of the combustion product stream on the turbulent flame front was limited to a zone of approximately two millimeters from the gas mixing layer interface (GMLI) of the product stream. Flame fronts that were separated from the GMLI by larger distances were unaffected by the product stream stoichiometry.

Using template waveforms from aftershocks of the Wenchuan earthquake (12 May 2008, Ms 7.9) listed in a global bulletin and continuous data from eight regional stations, we detected more than 6000 additional events in the mainshock source region from 1 May to 12 August 2008. These new detections obey Omori’s law, extend the magnitude of completeness downward by 1.1 magnitude units, and lead to a more than fivefold increase in number of known aftershocks compared with the global bulletins published by the International Data Centre and the International Seismological Centre. Moreover, we detected more M >2 events than were listed by the Sichuan Seismograph Network. Several clusters of these detections were then relocated using the double-difference method, yielding locations that reduced travel-time residuals by a factor of 32 compared with the initial bulletin locations. Our results suggest that using waveform correlation on a few regional stations can find aftershock events very effectively and locate them with precision.

This study offers experimental observation of the effect of low strain conditions (ε < 10%) on abnormal grain growth (AGG) in Nickel-200. At such conditions, stored mechanical energy is low within the microstructure enabling one to observe the impact of increasing mechanical deformation on the early onset of AGG compared to a control, or nondeformed, equivalent sample. The onset of AGG was observed to occur at specific pairings of compressive strain and annealing temperature and an empirical relation describing the influence of thermal exposure and strain content was developed. The evolution of low-Σ coincident site lattice (CSL) boundaries and overall grain size distributions are quantified using electron backscatter diffraction preceding, at onset and during ensuing AGG, whereby possible mechanisms for AGG in the low strain regime are offered and discussed.

High resolution magic angle spinning (HRMAS) 1H NMR spectroscopy has been used to resolve different surface and in-pore solvent environments of ethylene carbonate (EC) and dimethyl carbonate (DMC) mixtures absorbed within nanoporous carbon (NPC). Two dimensional (2D) 1H HRMAS NMR exchange measurements revealed that the inhomogeneous broadened in-pore resonances have pore-to-pore exchange rates on the millisecond timescale. Pulsed-field gradient (PFG) NMR diffusometry revealed the in-pore self-diffusion constants for both EC and DMC were reduced by up to a factor of five with respect to the diffusion in the non-absorbed solvent mixtures.

The form of a sheath near a small electrode, with bias changing from below to above the plasma potential, is studied using 2D particle-in-cell simulations. When the electrode is biased within Te/2e below the plasma potential, the electron velocity distribution functions (EVDFs) exhibit a loss-cone type truncation due to fast electrons overcoming the small potential difference between the electrode and plasma. No sheath is present in this regime, and the plasma remains quasineutral up to the electrode. The EVDF truncation leads to a presheath-like density and flow velocity gradients. Once the bias exceeds the plasma potential, an electron sheath is present. In this case, the truncation driven behavior persists, but is accompanied by a shift in the maximum value of the EVDF that is not present in the negative bias cases. The flow moment has significant contributions from both the flow shift of the EVDF maximum, and the loss-cone truncation.

The US DOE Protocol for uniformly measuring and expressing the performance of energy storage systems, first developed in 2012 through inclusive working group activities, provides standardized methodologies for evaluating an energy storage system's ability to supply specific services to electrical grids. This article elaborates on the data and decisions behind the duty-cycle used for frequency regulation in this protocol. Analysis of a year of publicly available frequency regulation control signal data from a utility was considered in developing the representative signal for this use case. This showed that signal standard deviation can be used as a metric for aggressiveness or rigor. From these data, we select representative 2 h long signals that exhibit nearly all of dynamics of actual usage under two distinct regimens, one for average use and the other for highly aggressive use. These results were combined into a 24-h duty-cycle comprised of average and aggressive segments. The benefits and drawbacks of the selected duty-cycle are discussed along with its potential implications to the energy storage industry.

Battery performance, while observed at the macroscale, is primarily governed by the bicontinuous mesoscale network of the active particles and a polymeric conductive binder in its electrodes. Manufacturing processes affect this mesostructure, and therefore battery performance, in ways that are not always clear outside of empirical relationships. Directly studying the role of the mesostructure is difficult due to the small particle sizes (a few microns) and large mesoscale structures. Mesoscale simulation, however, is an emerging technique that allows the investigation into how particle-scale phenomena affect electrode behavior. In this manuscript, we discuss our computational approach for modeling electrochemical, mechanical, and thermal phenomena of lithium-ion batteries at the mesoscale. We review our recent and ongoing simulation investigations and discuss a path forward for additional simulation insights.

Ferroelectric materials are well-suited for a variety of applications because they can offer a combination of high performance and scaled integration. Examples of note include piezoelectrics to transform between electrical and mechanical energies, capacitors used to store charge, electro-optic devices, and nonvolatile memory storage. Accordingly, they are widely used as sensors, actuators, energy storage, and memory components, ultrasonic devices, and in consumer electronics products. Because these functional properties arise from a noncentrosymmetric crystal structure with spontaneous strain and a permanent electric dipole, the properties depend upon physical and electrical boundary conditions, and consequently, physical dimension. The change in properties with decreasing physical dimension is commonly referred to as a size effect. In thin films, size effects are widely observed, whereas in bulk ceramics, changes in properties from the values of large-grained specimens is most notable in samples with grain sizes below several micrometers. It is important to note that ferroelectricity typically persists to length scales of about 10 nm, but below this point is often absent. Despite the stability of ferroelectricity for dimensions greater than ~10 nm, the dielectric and piezoelectric coefficients of scaled ferroelectrics are suppressed relative to their bulk counterparts, in some cases by changes up to 80%. The loss of extrinsic contributions (domain and phase boundary motion) to the electromechanical response accounts for much of this suppression. In this article, the current understanding of the underlying mechanisms for this behavior in perovskite ferroelectrics is reviewed. We focus on the intrinsic limits of ferroelectric response, the roles of electrical and mechanical boundary conditions, grain size and thickness effects, and extraneous effects related to processing. In many cases, multiple mechanisms combine to produce the observed scaling effects.

The SMASH (Sandia Matlab AnalysiS Hierarchy) toolbox is a collection of MATLAB code for data analysis. The toolbox contains general purpose functions, custom class definitions, and self-contained programs aimed at the needs of experimental physicists working in pulsed power research. The initial release (version 1.0) supports file access, signal/image analysis, and user interface creation; custom graphics and generic system tools are also provided. Much of the package is object oriented, encouraging users to build new capabilities from established classes. Future releases will continue this goal, expanding capabilities and streamlining application development.

An investigation of the temperature-dependent friction behavior of PTFE, MoS2, and PTFE-on-MoS2 is presented. Friction behavior was measured while continuously varying contact temperature in the range −150 to 175 °C while sliding in dry nitrogen, as well as for self-mated PTFE immersed in liquid nitrogen. These results contrast with previous reports of high-friction transitions and plateaus for pure and composite MoS2 at temperatures below about −20 °C; instead, we have found persistently weak thermal behavior between 0 and −196 °C, providing new insight about the molecular mechanisms of macroscale friction. The temperature-dependent friction behavior characteristic of self-mated PTFE was found also for PTFE-on-MoS2 sliding contacts, suggesting that PTFE friction was defined by subsurface deformation mechanisms and internal friction even when sliding against a lamellar lubricant with extremely low friction coefficient (µ ~ 0.02). The various relaxation temperatures of PTFE were found in the temperature-dependent friction behavior, showing excellent agreement with reported values acquired using rheological techniques measuring energy dissipation through internal friction. Additionally, hysteresis in friction behavior suggests an increase in near-surface crystallinity upon exceeding the high-temperature relaxation, Tα ~ 116 °C.

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The Sandia National Laboratories’ (SNL) Corporate Behavioral Health Program is a workplace based program that 1) assists in the early identification and resolution of personal concerns which may impact job performance, 2) assists managers and the organization in addressing productivity issues, and 3) supports the SNL commitment to provide a safe and healthful work environment. The program is offered to approximately 10,711 employees in New Mexico. The Behavioral Health Program is a corporate program combining services in NM and CA. It is integrated with other occupational health and clinical services including disability, disease management and preventive health programs. In addition, Sandia’s Behavioral Health Program interfaces with external organizations in Human Resources, the Department of Energy and Security through the Clinical Evaluation (CE) Human Reliability Program (HRP) and Workplace Violence programs. The program supports Sandia National Laboratories’ mission to safeguard national security, the environment, the public and is a proactive approach to early identification, intervention and assessment. Last, it reduces barriers to accessing mental health services and assists with reducing health care costs attributed to illness or injuries related to unhealthy lifestyles and behaviors. The EAP team is comprised of a professional staff including a licensed Clinical Psychologist who has a NM state license for psychotropic medication prescriptive authority, is board certified in Clinical Neuropsychology, and a Certified Employee Assistance Professional (CEAP), a licensed professional clinical counselor NM State Licensed (LPCC) and a licensed Marriage and Family counselor (MFT) who is also a Certified Employee Assistance Professional and who holds a doctorate in counseling psychology.

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The need for metrics for planning and response measures was identified as key gap to be addressed in the National Hurricane Program's (NHP) Technology Modernization effort. This document proposes a framework for defining a set of metrics for planning and response that will be implemented in the NHP products of hurricane evacuation studies (HES) and post-storm assessments (PSA). To determine the feasibility of this framework, a survey of current HES and PSAs was carried out followed by and then used to determine if the proposed metrics are currently captured. While there is a wide variety in data availability and detail, the implementation of these metrics is not only feasible but presents an opportunity to improve on current practices. The final implementation of this framework shall require the ongoing feedback from local, state, tribal, and federal stakeholders.

The Hurricane Evacuation Study (HES) Tool prototype is a key component of the Federal Emergency Management Agency (FEMA) National Hurricane Program (NHP) Technology Modernization (TM) effort. To ensure the HES Tool captured the necessary capabilities and functionality, engagement with potential end-users and key stakeholders was considered a priority throughout development. Pilot studies with representatives from North Carolina and New York City were done to validate the HES Tool process with their current HES undertaking. These pilot studies let the development of additional capabilities and feedback on the needs of diverse regions. A usability study was carried out with key stakeholders identified by NHP leadership through individualized sessions with identified personnel. The results showed the value of the HES Tool compared to the current process as well as key issues that must be addressed to ensure a final transition.

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This report documents key elements of the conceptual design for deep borehole disposal of radioactive waste to support the development of a universal canister concept of operations. A universal canister is a canister that is designed to be able to store, transport, and dispose of radioactive waste without the canister having to be reopened to treat or repackage the waste. This report focuses on the conceptual design for disposal of radioactive waste contained in a universal canister in a deep borehole. The general deep borehole disposal concept consists of drilling a borehole into crystalline basement rock to a depth of about 5 km, emplacing WPs in the lower 2 km of the borehole, and sealing and plugging the upper 3 km. Research and development programs for deep borehole disposal have been ongoing for several years in the United States and the United Kingdom; these studies have shown that deep borehole disposal of radioactive waste could be safe, cost effective, and technically feasible. The design concepts described in this report are workable solutions based on expert judgment, and are intended to guide follow-on design activities. Both preclosure and postclosure safety were considered in the development of the reference design concept. The requirements and assumptions that form the basis for the deep borehole disposal concept include WP performance requirements, radiological protection requirements, surface handling and transport requirements, and emplacement requirements. The key features of the reference disposal concept include borehole drilling and construction concepts, WP designs, and waste handling and emplacement concepts. These features are supported by engineering analyses.

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The Federal Emergency Management Agency's (FEMA) National Hurricane Program (NHP), helps protect communities and residents from hurricane hazards by providing evacuation preparedness technical assistance to State, local, and tribal governments. The Department of Homeland Security (DHS) Science and Technology Directorate (S&T) and FEMA are co- sponsoring an effort to modernize technology components of the NHP, including the Hurricane Evacuation Study (HES), which addresses planning and impact assessments for coastal regions. The current HES process is manual, financially costly, and can take up to several years to complete. To streamline this process, the NHP Technology Modernization Program is developing an automated HES Tool that will reduce the cost and time requirements of the HES process by up to 70%. This document outlines the requirements of the current HES process and explains how the HES Tool can be used to fulfill those requirements. It also contains a detailed list of the modeling and simulation capabilities available within the HES tool.

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Netflow data is a specific format for looking at network traffic. With this format, many security tests are easy to run. Cloud Service Providers produce logs that do not contain all of the content that Netflow data contains. There is a possibility that the fields that are in Netflow data but absent in Cloud Service Provider logs can be inferred from the fields that are present in the Cloud Service Provider logs. By inferring the missing data fields, the same test that can be run with Netflow data would be possible to run on the logs produced by Cloud Service Providers. Cloud Service Providers include Amazon Web Services and Box.com. There are multiple different types of Cloud Services, and each provider handles them differently and produces different logs. There are IaaS (meaning infrastructure as a service), Saas (meaning software as a service), and Paas (meaning platform as a service). Each provides a different use for the user.

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The subject report from High Bridge Associates (HBA) was issued on March 2, 2016, in reaction to a U.S. Department of Energy (DOE) program decision to pursue down-blending of surplus Pu and geologic disposal at the Waste Isolation Pilot Plant (WIPP). Sandia National Laboratories was requested by the DOE to review the technical arguments presented in the HBA report. Specifically, this review is organized around three technical topics: criticality safety, radiological release limits, and thermal impacts. Questions raised by the report pertaining to legal and regulatory requirements, safeguards and security, international agreements, and costing of alternatives, are beyond the scope of this review.

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The Sandia National Laboratories Annular Core Research Reactor (ACRR) has been experiencing intermittent failures of its pneumatically operated transient rod system. The most frequent failures have been to the dashpot rod where it connects to the upper aluminum connecting rod. Within the three systems, Transient Rod (TR) A has the most frequent failures. In order to conduct the pulse operations, the Transient Rods are pneumatically driven to quickly remove "poison" from the reactor core. During these pulse operations increased forces and vibrations are placed on the TR system. In an effort to fix these problems, Sandia's TA-V Nuclear Reactor and Systems Engineering Department (Engineering Department) has started an extensive Transient Rod Pneumatic System Design Study. The goal of this study is to determine the causes of the elevated failure rates in TR A. This necessitates an increased understanding of the dynamics in the TR systems. This report will cover the approach taken and reasoning behind the choices of instrumentation, calibration, data collection and data analysis used to diagnose these failures. In order to determine the types and specifications for the sensors that will be installed, estimates of the TR system performance needed to be determined. Using known and assumed parameters, mechanical and thermodynamic models were developed, and calculations performed to estimate ranges of displacement, speed, and acceleration experienced by the transient rod system. After some preliminary data collection, the thermodynamic models were refined for better accuracy. After installation of the full suite of sensors, data can be collected and analyzed in order to determine the cause of the increased failures.

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This memo documents the mechanical loading analysis performed on the second set of DTOcean program WP4 foundation and anchor systems submodule design iterations [4]. Finite Element Analysis (FEA) simulations were performed to validate design requirements defined by Python based analytic simulations of the WP4 program Naval Facilities Engineering Command (NAVFAC) tool. This FEA procedure focuses on worst case loading scenarios on shallow gravity foundation and pile anchor designs produced by WP4. These models include a steel casing and steel anchor with soft clay surrounding the steel components respectively.

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This guide is a compilation of best practices and resources from three of Sandia's leading strategic intern programs which make up the Technical Internships to Advance National Security (TITANS) program. TITANS consist of the Center for Analysis Systems and Applications (CASA), the Center for Cyber Defenders (CCD), and the Monitoring Systems & Technology Intern Center (MSTIC).

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A study of aerosol filtration was conducted to improve U.S. Radionuclide Monitoring Station (RMS) performance for Nuclear Treaty Verification. The primary objectives of this study were to improve system operability and maintainability, reduce power consumption and operational cost, and reduce baseline radionuclide sensitivity. To meet these goals, Sandia National Laboratories (SNL) studied the performance of alternate filter materials and aerosol collection technologies that could be engineered into U.S. Radionuclide Monitoring Stations. Laboratory-scale filtration experiments were conducted with Filter Material 1, FM1 (current filter), Filter Material 2, FM2, and Filter Material 3, FM3. All three materials employ electrostatically charged filter fibers to enhance nanoparticle collection. FM2 and FM3 both had higher air permeability with respect to FM1 which is advantageous for high volume collection and power savings. Particle pre-charging, a well-established industrial technique used in electrostatic precipitators, was tested to see if electrostatically charging particles prior to filtration could enhance filter performance. We found that particle-pre-charging did enhance aerosol collection efficiencies for materials which would not have otherwise satisfied RMS performance requirements. Laboratory-scale testing indicated it may be possible to reduce the baseline radionuclide sensitivity to approximately 60% of its current value by increasing the volume of air sampled in 24 hours to 2.5 times the current air volume. Improvements to geolocation may also be possible with shorter air samples (e.g., 12 hours). A new methodology was developed at SNL to assess filter performance using established RMS certification procedures. We coined these tests “mid-scale” since they bridged the gap between laboratory-scale and full-scale RMS testing. Four filter specimens were drawn from the exact same atmospheric aerosol. Gamma spectroscopy was used to assess radiological backgrounds due to radon progeny and other naturally occurring radionuclides. Direct comparisons between the four filters allowed SNL to quantify the relative change in baseline sensitivity by altering air flow rate, filter material, and particle-pre charging. Mid-scale results agreed with laboratory-scale results: alterations to RMS configuration (filter, flow, and particle charge) may result in baseline sensitivities approximately 55-60% of their current values. Finally, an assessment of scalability was performed to determine if technical approaches used in laboratory-scale and mid-scale testing could be engineered into full-scale Radionuclide Monitoring Stations. Results suggested that particle-pre-charging is a viable technical approach if reductions in baseline sensitivity or power consumption are desired.

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