Publications

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Biaxially oriented polyethylene terephthalate (BO-PET/Mylar®) polymer film is commonly used as the dielectric in high-voltage, pulse-discharge capacitors because of its high dielectric strength and insulation resistance over a wide temperature range [1]. This study focuses on the use of a systematic physics of failure (PoF) approach to assess possible design and fabrication problems in BO-PET capacitors. A destructive physical analysis (DPA) procedure, which is an essential technique in understanding the failure modes and mechanisms in capacitors, has been developed through this research. Short-term breakdown (STB) testing was performed on capacitors from two independent development builds and the results are compared. It was identified that the two primary failure mechanisms occurring in these capacitors under high voltage conditions were edge margin arc-over and dielectric punch-through. Evaluation of the electrical parameters after accelerated voltage testing revealed that the combination of lower than expected voltage breakdown values (near the voltage rating of 3.6 kV) and in-spec capacitance and dissipation factor (C/DF) values indicated an arc-over failure, while high voltage breakdown values (greater than 2.5 times the voltage rating) and out-of-spec C/DF values indicated a dielectric punch-through failure. Thick buried edges, creasing, high curvature, insufficient inactive wraps, arc spray, and inadequate edge margin were some of the modes that led to arc-over and punch-through failures. Many of these failure modes were traced back to unsuitably designed capacitors or issues with the process control during manufacturing.

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Epitaxially grown silver (Ag) film on silicon (Si) is an optimal plasmonic device platform, but its technological utility has been limited by its tendency to dewet rapidly under ambient conditions (standard temperature and pressure). The mechanisms driving this dewetting have not heretofore been determined. In this study, scanning probe microscopy and low-energy electron microscopy are used to compare the morphological evolution of epitaxial Ag(111)/Si(111) under ambient conditions with that of similarly prepared films heated under ultra-high vacuum (UHV) conditions. Dewetting in both cases is seen to be initiated with the formation of pinholes, which might function to relieve strain in the film. We find that in the UHV environment, dewetting is determined by thermal processes, while under ambient conditions, thermal processes are not required. We conclude that dewetting in ambient conditions is triggered by some chemical process, most likely oxidation.

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We describe and experimentally demonstrate a method for active control of resonant modulators and filters in an integrated photonics platform. Variations in resonance frequency due to manufacturing processes and thermal fluctuations are corrected by way of balanced homodyne locking. The method is compact, insensitive to intensity fluctuations, minimally disturbs the micro-resonator, and does not require an arbitrary reference to lock. We demonstrate long-term stable locking of an integrated filter to a laser swept over 1.25 THz. In addition, we show locking of a modulator with low bit error rate while the chip temperature is varied from 5 to 60° C. © 2014 Optical Society of America.

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Nanoantennas are an enabling technology for visible to terahertz components and may be used with a variety of detector materials. We have integrated subwavelength patterned metal nanoantennas with various detector materials for infrared detection: midwave infrared indium gallium arsenide antimonide detectors, longwave infrared graphene detectors, and shortwave infrared germanium detectors. Nanoantennas offer a means to make infrared detectors much thinner, thus lowering the dark current and improving performance. The nanoantenna converts incoming plane waves to more tightly bound and concentrated surface waves. The active material only needs to extend as far as these bound fields. In the case of graphene detectors, which are only one or two atomic layers thick, such field concentration is a necessity for usable device performance, as single pass absorption is insufficient. The nanoantenna is thus the enabling component of these thin devices. However nanoantenna integration and fabrication vary considerably across these platforms as do the considerations taken into account during design. Here we discuss the motivation for these devices and show examples for the three material systems. Characterization results are included for the midwave infrared detector. © 2014 SPIE.

The use of computational models to simulate the behavior of complex mechanical systems is ubiquitous in many high consequence applications such as aerospace systems. Results from these simulations are being used, among other things, to inform decisions regarding system reliability and margin assessment. In order to properly support these decisions, uncertainty needs to be accounted for. To this end, it is necessary to identify, quantify and propagate different sources of uncertainty as they relate to these modeling efforts. Some sources of uncertainty arise from the following: (1) modeling assumptions and approximations, (2) solution convergence, (3) differences between model predictions and experiments, (4) physical variability, (5) the coupling of various components and (6) and unknown unknowns. An additional aspect of the problem is the limited information available at the full system level in the application space. This is offset, in some instances, by information on individual components at testable conditions. In this paper, we focus on the quantification of uncertainty due to differences in model prediction and experiments, and present a technique to aggregate and propagate uncertainty from the component level to the full system in the applications space. A numerical example based on a structural dynamics application is used to demonstrate the technique.

Recent experimental investigations show that most models are not able to capture the ductile behavior of metal alloys in the entire triaxiality range, especially at low triaxiality. Modelers are moving beyond stress triaxiality as the dominant indicator of material failure and developing constitutive models that incorporate shear into the evolution of the failure model. Available data that cover low triaxiality range are rare and a series of critical experiments is needed. Here, experiments of smooth thin as well as notched tubular specimens of Al6061-T651 under combined tension-torsion loading were conducted. This provides a very basic set of data for phenomenological models. A full-field deformation technique, digital image correlation (DIC), was applied to these tests to allow measurement of the field deformation, including the notched area. The microstructural features of the tested specimens were characterized to better understand the different failure mechanisms which led to ductility variation in the aluminum alloy.

The rapidly improving compute capability of contemporary processors and accelerators is providing the opportunity for significant increases in the accuracy and fidelity of scientific calculations. In this paper we present performance studies of a new molecular dynamics (MD) potential called SNAP. The SNAP potential has shown great promise in accurately reproducing physics and chemistry not described by simpler potentials. We have developed new algorithms to exploit high single-node concurrency provided by three different classes of machine: the Titan GPU-based system operated by Oak Ridge National Laboratory, the combined Sequoia and Vulcan BlueGene/Q machines located at Lawrence Livermore National Laboratory, and the large-scale Intel Sandy Bridge system, Chama, located at Sandia. Our analysis focuses on strong scaling experiments with approximately 246,000 atoms over the range 1-122,880 nodes on Sequoia/Vulcan and 40-18,630 nodes on Titan. We compare these machine in terms of both simulation rate and power efficiency. We find that node performance correlates with power consumption across the range of machines, except for the case of extreme strong scaling, where more powerful compute nodes show greater efficiency. This study is a unique assessment of a challenging, scientifically relevant calculation running on several of the world's leading contemporary production supercomputing platforms. © 2014 Springer International Publishing.

This paper describes the convergence of MELCOR Accident Consequence Code System, Version 2 (MACCS2) probabilistic results of offsite consequences for the uncertainty analysis of the State-of-the-Art Reactor Consequence Analyses (SOARCA) unmitigated long-term station blackout scenario at the Peach Bottom Atomic Power Station. The consequence metrics evaluated are individual latent-cancer fatality (LCF) risk and individual early fatality risk. Consequence results are presented as conditional risk (i.e., assuming the accident occurs, risk per event) to individuals of the public as a result of the accident. In order to verify convergence for this uncertainty analysis, as recommended by the Nuclear Regulatory Commission's Advisory Committee on Reactor Safeguards, a 'high' source term from the original population of Monte Carlo runs has been selected to be used for: (1) a study of the distribution of consequence results stemming solely from epistemic uncertainty in the MACCS2 parameters (i.e., separating the effect from the source term uncertainty), and (2) a comparison between Simple Random Sampling (SRS) and Latin Hypercube Sampling (LHS) in order to validate the original results obtained with LHS. Three replicates (each using a different random seed) of size 1, 000 each using LHS and another set of three replicates of size 1, 000 using SRS are analyzed. The results show that the LCF risk results are well converged with either LHS or SRS sampling. The early fatality risk results are less well converged at radial distances beyond 2 miles, and this is expected due to the sparse data (predominance of "zero" results).

Imagery analysts are given the difficult task of determining, post-hoc, if particular events of importance had occurred, employing Synthetic Aperture Radar (SAR) images, written reports and PowerPoint presentations to make their decision. We were asked to evaluate the current system analysis process and make recommendations for a future temporal geospatial analysis prototype that is envisioned to allow analysts to quickly search for temporal and spatial relationships between image-derived features. As such, we conducted a Hierarchical task analysis (HTA; [3], [6]) to understand the analysts' tasks and subtasks. We also implemented a timeline analysis and workload assessment [4] to better understand which tasks were the most time-consuming and perceived as the most effortful. Our results gave the team clear recommendations and requirements for a prototype. © 2014 Springer International Publishing.

In this paper, we present new research results on the vulnerability of speaker verification (SV) systems to synthetic speech. Using a state-of-the-art i-vector SV system and evaluating with the Wall-Street Journal (WSJ) corpus, our SV system has a 0.00% false rejection rate (FRR) and 1.74 × 10-5 false acceptance rate (FAR). When the i-vector system is tested with state-of-the-art speaker-adaptive, hidden Markov model (HMM)-based synthetic speech generated from speaker models derived from the WSJ journal corpus, 22.9% of the matched claims are accepted highlighting the vulnerability of SV systems to synthetic speech. We propose a new synthetic speech detector (SSD) which uses previously-proposed features derived from image analysis of pitch patterns but extracted on phoneme-level segments and which leverages the available enrollment speech from the SV system. When the SSD is applied to human and synthetic speech accepted by the SV system, the overall system has a FRR of 7.35% and a FAR of 2.34 × 10-4 which is lower than previously-reported systems and thus significantly reduces the vulnerability. © 2014 IEEE.

Within large organizations, the defense of cyber assets generally involves the use of various mechanisms, such as intrusion detection systems, to alert cyber security personnel to suspicious network activity. Resulting alerts are reviewed by the organization's cyber security personnel to investigate and assess the threat and initiate appropriate actions to defend the organization's network assets. While automated software routines are essential to cope with the massive volumes of data transmitted across data networks, the ultimate success of an organization's efforts to resist adversarial attacks upon their cyber assets relies on the effectiveness of individuals and teams. This paper reports research to understand the factors that impact the effectiveness of Cyber Security Incidence Response Teams (CSIRTs). Specifically, a simulation is described that captures the workflow within a CSIRT. The simulation is then demonstrated in a study comparing the differential response time to threats that vary with respect to key characteristics (attack trajectory, targeted asset and perpetrator). It is shown that the results of the simulation correlate with data from the actual incident response times of a professional CSIRT.

As compact and light weight power sources with reliable, long lives, Radioisotope Power Systems (RPSs) have made space missions to explore the solar system possible. Due to the hazardous material that can be released during a launch accident, the potential health risk of an accident must be quantified, so that appropriate launch approval decisions can be made. One part of the risk estimation involves modeling the response of the RPS to potential accident environments. Due to the complexity of modeling the full RPS response deterministically on dynamic variables, the evaluation is performed in a stochastic manner with a Monte Carlo simulation. The potential consequences can be determined by modeling the transport of the hazardous material in the environment and in human biological pathways. The consequence analysis results are summed and weighted by appropriate likelihood values to give a collection of probabilistic results for the estimation of the potential health risk. This information is used to guide RPS designs, spacecraft designs, mission architecture, or launch procedures to potentially reduce the risk, as well as to inform decision makers of the potential health risks resulting from the use of RPSs for space missions.

This paper presents an extension of the all-quad meshing algorithm called LayTracks to generate high quality hex and hexdominant meshes of 3D assembly models. LayTracks3D uses the mapping between the Medial Axis (MA) and the boundary of the 3D domain to decompose complex 3D domains into simpler domains called Tracks. Tracks in 3D are similar to tunnels with no branches and are symmetric, non-intersecting, orthogonal to the boundary, and the shortest path from the MA to the boundary. These properties of tracks result in desired meshes with near cube shape elements at the boundary, structured mesh along the boundary normal with any irregular nodes restricted to the MA, and sharp boundary feature preservation. The algorithm has been tested on a few industrial CAD models and hex-dominant meshes are shown in the result section. The paper also describes how this algorithm can be extended to produce all-hex meshes in general geometries.

Transient responses of high-Q nano-optomechanical modes are characterized with Interleaved-ASOPS, where pump-induced transients are interrogated with multiple probe pulses. Temporal resolution increases linearly with probe-pulse-number beyond conventional ASOPS, achieving sub-ps resolution over μs durations.

Supercritical Carbon Dioxide (S-CO2) is an efficient and flexible working fluid for power production. Research to interface S-CO2 systems with nuclear, thermal solar, and fossil energy sources are currently underway. To proceed, we must address concerns regarding high temperature compatibility of materials and compatibility between significantly different heat transfer fluids. Dry, pure S-CO2 is thought to be relatively inert [1], while ppm levels of water and oxygen result in formation of a protective chromia layer and iron oxide [2] Thin oxides are favorable as diffusion barriers, and for their minimal impact on heat transfer. Chromia, however, is soluble in molten salt systems (nitrate, chloride, and fluoride based salts) [3-8]. Fluoride anion based systems required the development of the alloy INOR-8 (Hastelloy N, base nickel, 17%Mo) [9] to ensure that chromium diffusion is minimized, thereby maximizing the life of containment vessels. This paper reviews the thermodynamic and kinetic considerations for promising, industrially available materials for both salt and S-CO2 systems.

To achieve high performance operation of micro-grids that contain stochastic sources and loads is a challenge that will impact cost and complexity. Developing alternative methods for controlling and analyzing these systems will provide insight into tradeoffs that can be made during the design phase. This paper presents a design methodology, based on Hamiltonian Surface Shaping and Power Flow Control (HSSPFC) [1] for a hierarchical control scheme that regulates renewable energy sources and energy storage in a DC micro-grid. Recent literature has indicated that there exists a trade-off in information and power flow and that intelligent, coordinated control of power flow in a microgrid system can modify energy storage hardware requirements. Two scenarios are considered; i) simple two stochastic source with variable load renewable DC Microgrid example and ii) a three zone electric ship with DC Microgrid and varying pulse load profiles. © 2014 IEEE.

We propose a new algorithm, FAST-PPR, for computing personalized PageRank: given start node s and target node t in a directed graph, and given a threshold δ, it computes the Personalized PageRank πs(t) from s to t, guaranteeing that the relative error is small as long πs(t) > δ. Existing algorithms for this problem have a running-time of Ω(1/δ in comparison, FAST-PPR has a provable average running-time guarantee of O(√d/δ) (where d is the average in-degree of the graph). This is a significant improvement, since δ is often O(1/n) (where n is the number of nodes) for applications. We also complement the algorithm with an Ω(1/√δ) lower bound for PageRank estimation, showing that the dependence on δ cannot be improved. We perform a detailed empirical study on numerous massive graphs, showing that FAST-PPR dramatically outperforms existing algorithms. For example, on the 2010 Twitter graph with 1.5 billion edges, for target nodes sampled by popularity, FAST-PPR has a 20 factor speedup over the state of the art. Furthermore, an enhanced version of FAST-PPR has a 160 factor speedup on the Twitter graph, and is at least 20 times faster on all our candidate graphs. © 2014 ACM.

A primary concern with dry storage of spent nuclear fuel is chloride-induced stress corrosion cracking, caused by deliquescence of salts deposited on the stainless steel canisters. However, limited access through the ventilated overpacks and high surface radiation fields impede direct examination of cask surfaces for CISCC, or sampling of surface deposits. Predictive models for CISCC must be able to predict the occurrence of a corrosive chemical environment (a chloride-rich brine formed by dust deliquescence) at specific locations (e.g. weld zones) on the canister surface. The presence of a deliquescent brine is controlled by the relative humidity (RH), which is a function of absolute humidity and cask surface temperature. This requires a thermal model that includes the canister and overpack design, canister-specific waste heat load, and passive cooling by ventilation. Brine compositions vary with initially-deposited salt assemblage, reactions with atmospheric gases, temperature, and the relative rates of salt deposition and reaction; predicting brine composition requires site-specific compositional data for atmospheric aerosols and acid gases. Aerosol particle transport through the overpack and deposition onto the canister must also be assessed. Initial field data show complex variability in the amount and composition of deposited salts as a function of canister surface location.

Lithium-ion battery electrodes rely on a percolated network of solid particles and binder that must maintain a high electronic conductivity in order to function. Coupled mechanical and electrochemical simulations may be able to elucidate the mechanisms for capacity fade. We present a framework for coupled simulations of electrode mechanics that includes swelling, deformation, and stress generation driven by lithium intercalation. These simulations are performed at the mesoscale, which requires 3D reconstruction of the electrode microstructure from experimental imaging or particle size distributions. We present a novel approach for utilizing these complex reconstructions within a finite element code. A mechanical model that involves anisotropic swelling in response to lithium intercalation drives the deformation. Stresses arise from small-scale particle features and lithium concentration gradients. However, we demonstrate, for the first time, that the largest stresses arise from particle-to-particle contacts, making it important to accurately represent the electrode microstructure on the multi-particle scale. Including anisotropy in the swelling mechanics adds considerably more complexity to the stresses and can significantly enhance peak particle stresses. Shear forces arise at contacts due to the misorientation of the lattice structure. These simulations will be used to study mechanical degradation of the electrode structure through charge/discharge cycles.

The US Human Reliability Analysis (HRA) Empirical Study (referred to as the US Study in the article) was conducted to confirm and expand on the insights developed from the International HRA Empirical Study (referred to as the International Study). Similar to the International Study, the US Study evaluated the performance of different HRA methods by comparing method predictions to actual crew performance in simulated accident scenarios conducted in a US nuclear power plant (NPP) simulator. In addition to identification of some new HRA and method related issues, the study design of the US Study allowed insights to be obtained on some issues that were not addressed in the International Study. In particular, because multiple HRA teams applied each method in the US Study, comparing their analyses and predictions allowed separation of analyst effects from method effects and allowed conclusions to be drawn on aspects of methods that are susceptible to different application or usage by different analysts that may lead to differences in results. The findings serve as a strong basis for improving the consistency and robustness of HRA, which in turn facilitates identification of mechanisms for improving operating crew performance in NPPs.

The purpose of the current study was to analyze the work of imagery analysts associated with Sagebrush, a Synthetic Aperture Radar (SAR) imaging system, using an adapted version of cognitive work analysis (CWA). This was achieved by conducting a work domain analysis (WDA) for the system under consideration. Another purpose of this study was to describe how we adapted the WDA framework to include a sequential component and a means to explicitly represent relationships between components. Lastly, we present a simplified work domain representation that we have found effective in communicating the importance of analysts' adaptive strategies to inform the research strategies of computational science researchers who want to develop useful algorithms, but who have little or no familiarity with sensor data analysis work. © 2014 Springer International Publishing.

Solar optical modeling tools are valuable for modeling and predicting the performance of solar technology systems. Four optical modeling tools were evaluated using the National Solar Thermal Test Facility heliostat field combined with flat plate receiver geometry as a benchmark. The four optical modeling tools evaluated were DELSOL, HELIOS, SolTrace, and Tonatiuh. All are available for free from their respective developers. DELSOL and HELIOS both use a convolution of the sunshape and optical errors for rapid calculation of flux profiles on the receiver surfaces. SolTrace and Tonatiuh use ray-tracing methods to determine reflected solar rays on the receiver surfaces and construct flux profiles. We found the raytracing tools, although slower in computation speed, to be more flexible for modeling complex receiver geometries, whereas DELSOL and HELIOS were limited to standard receiver geometries. We provide an example of using SolTrace for modeling non-conventional receiver geometries. We also list the strengths and deficiencies of the tools to show tool preference depending on the modeling and design needs.

Bottom hole assembly (BHA) designs were assessed in field trials for their ability to achieve critical low inclination requirements, while simultaneously enabling high drill rates. Because angle has historically been controlled by reducing weight on bit (WOB), these are often competing priorities. The use of real time surveillance of mechanical specific energy (MSE) provided unique insights into the bit dysfunction that occurs with many practices used to control angle. These quantitative insights supported the development of BHA and operating practices that maintained low angle while also achieving major gains in drilling performance. The McGinness Hills field in Lander County Nevada is a geothermal operation with wells drilled in hard metamorphic and crystalline formations. Wellbore inclinations must be maintained below 2.0 degrees in the critical 20 inch interval in order to allow use of lineshaft pumps, which is challenging in the required hole sizes and rock hardness. Formation strengths are similar to petroleum operations in the Rockies and West Texas. Pendulum and packed-hole assemblies were tested, and straight motors and slick assemblies were used for corrections. Well build rates were assumed to be controlled by the three-point curvature in the lower assembly and stabilizer placement was modified to control this curvature. The effectiveness of the curvature control as WOB was increased was evaluated from inclination measurements. Real time MSE analysis was used to manage bit operating performance and to determine the root causes of bit dysfunction. The results demonstrated that packed-hole assemblies could be designed that controlled inclination while enabling 2-3 times higher WOB, and that the use of pendulum assemblies should be eliminated. Packed assemblies drilled 87% faster. The increased WOB resulted in higher drill rates, major reduction in whirl and extended bit life, which are equally important performance objectives in hard rock drilling. The use of MSE surveillance allowed the physical processes to be understood deterministically, so that the philosophical design principles can be applied in other petroleum and geothermal operations.

We consider the question of predicting solar adoption using demographic, economic, peer effect and predicted system characteristic features. We use data from San Diego county to evaluate both discrete and continuous models. Additionally, we consider three types of sensitivity analysis to identify which features seem to have the greatest effect on prediction accuracy.

In this paper we review the evidence for the Younger Dryas impact hypothesis (YDIH), which proposes that at ∼12.9k cal a BP North America, South America, Europe and the Middle East were subjected to some sort of extraterrestrial event. This purported event is proposed as a catastrophic process responsible for: terminal Pleistocene environmental changes (onset of YD cooling, continent-scale wildfires); extinction of late Pleistocene mammals; and demise of the Clovis 'culture' in North America, the earliest well-documented, continent-scale settlement of the region. The basic physics in the YDIH is not in accord with the physics of impacts nor the basic laws of physics. No YD boundary (YDB) crater, craters or other direct indicators of an impact are known. Age control is weak to non-existent at 26 of the 29 localities claimed to have evidence for the YDIH. Attempts to reproduce the results of physical and geochemical analyses used to support the YDIH have failed or show that many indicators are not unique to an impact nor to ∼12.9k cal a BP. The depositional environments of purported indicators at most sites tend to concentrate particulate matter and probably created many 'YDB zones'. Geomorphic, stratigraphic and fire records show no evidence of any sort of catastrophic changes in the environment at or immediately following the YDB. Late Pleistocene extinctions varied in time and across space. Archeological data provide no indication of population decline, demographic collapse or major adaptive shifts at or just after ∼12.9 ka. The data and the hypotheses generated by YDIH proponents are contradictory, inconsistent and incoherent. © 2014 John Wiley & Sons, Ltd.

The use of an air curtain blowing across the aperture of a falling-particle receiver has been proposed to mitigate convective heat losses and to protect the flow of particles from external winds. This paper presents experimental and numerical studies that evaluate the impact of an air curtain on the performance of a falling particle receiver. Unheated experimental studies were performed to evaluate the impact of various factors (particle size, particle mass flow rate, particle release location, air-curtain flow rate, and external wind) on particle flow, stability, and loss through the aperture. Numerical simulations were performed to evaluate the impact of an air curtain on the thermal efficiency of a falling particle receiver at different operating temperatures. Results showed that the air curtain reduced particle loss when particles were released near the aperture in the presence of external wind, but the presence of the air curtain did not generally improve the flow characteristics and loss of the particles for other scenarios. Numerical results showed that the presence of an air curtain could reduce the convective heat losses, but only at higher temperatures (>600°C) when buoyant hot air leaving the aperture was significant.

High-temperature receiver designs for solar powered supercritical CO2Brayton cycles that can produce ∼1 MW of electricity are being investigated. Advantages of a supercritical CO2closed-loop Brayton cycle with recuperation include high efficiency (∼50%) and a small footprint relative to equivalent systems employing steam Rankine power cycles. Heating for the supercritical CO2system occurs in a high-temperature solar receiver that can produce temperatures of at least 700 °C. Depending on whether the CO2is heated directly or indirectly, the receiver may need to withstand pressures up to 20 MPa (200 bar). This paper reviews several high-temperature receiver designs that have been investigated as part of the SERIIUS program. Designs for direct heating of CO2include volumetric receivers and tubular receivers, while designs for indirect heating include volumetric air receivers, molten-salt and liquid-metal tubular receivers, and falling particle receivers. Indirect receiver designs also allow storage of thermal energy for dispatchable electricity generation. Advantages and disadvantages of alternative designs are presented. Current results show that the most viable options include tubular receiver designs for direct and indirect heating of CO2and falling particle receiver designs for indirect heating and storage.

Cavity receivers have been an integral part of Concentrated Solar Power (CSP) plants for many years. However, falling solid particle receivers (SPR) which employ a cavity design are only in the beginning stages of on-sun testing and evaluation. A prototype SPR has been developed which will be fully integrated into a complete system to demonstrate the effectiveness of this technology in the CSP sector. The receiver is a rectangular cavity with an aperture on the north side, open bottom (for particle collection), and a slot in the top (particle curtain injection). The solid particles fall from the top of the cavity through the solar flux and are collected after leaving the receiver. There are inherent design challenges with this type of receiver including particle curtain opacity, high wall fluxes, high wall temperatures, and high heat losses. CFD calculations using ANSYS FLUENT were performed to evaluate the effectiveness of the current receiver design. The particle curtain mass flow rate needed to be carefully regulated such that the curtain opacity is high (to intercept as much solar radiation as possible), but also low enough to increase the average particle temperature by 200°C. Wall temperatures were shown to be less than 1200°C when the particle curtain mass flow rate is 2.7 kg/s/m which is critical for the receiver insulation. The size of the cavity was shown to decrease the incident flux on the cavity walls and also reduced the wall temperatures. A thermal efficiency of 92% was achieved, but was obtained with a higher particle mass flow rate resulting in a lower average particle temperature rise. A final prototype receiver design has been completed utilizing the computational evaluation and past CSP project experiences.

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Digital in-line holography (DIH) is an optical technique which allows for numerical refocusing after an experiment. Here we discuss application of DIH for high-fidelity visualization and quantification of aluminum drop combustion in propellant plumes. © 2014 OSA.

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This paper describes an experiment to characterize ions generated by a pulsed vacuum arc by using a microwave resonant cavity (MRC) as a transient diagnostic. Specific information is desired on the various species which can drift into the beam during repetitive operations of arc plasma generation. The arc source reference voltage is elevated above ground (∼200V), which results in a separation of ion species in the beam due to the acceleration experienced by the ions. The cylindrical MRC used in this study has a resonant frequency of ∼2.8 GHz when excited by a continuous RF source in the TM01 mode of operation. When the neutralized ion beam propagates through the MRC located downstream from the arc source, the resonant frequency of the MRC is shifted by the local disturbance in electric field inside the cavity due to the presence of the electron space charge in the beam. Coupled with the time-of-flight separation of various ion masses, the MRC resonance shift provides a temporally resolved measurement of beam species and density downstream from the vacuum ion source without the use of a potentially invasive diagnostic such as charge collector plates within the beam cross-section. This diagnostic technique should prove useful in a variety of pulsed ion beam studies and applications in research and industrial environments.

Estimation of the x-ray attenuation properties of an object with respect to the energy emitted from the source is a challenging task for traditional Bremsstrahlung sources. This exploratory work attempts to estimate the x-ray attenuation profile for the energy range of a given Bremsstrahlung profile. Previous work has shown that calculating a single effective attenuation value for a polychromatic source is not accurate due to the non-linearities associated with the image formation process. Instead, we completely characterize the imaging system virtually and utilize an iterative search method/constrained optimization technique to approximate the attenuation profile of the object of interest. This work presents preliminary results from various approaches that were investigated. The early results illustrate the challenges associated with these techniques and the potential for obtaining an accurate estimate of the attenuation profile for objects composed of homogeneous materials.

Solar thermal receivers absorb concentrated sunlight and can operate at high temperatures exceeding 600°C for production of heat and electricity. New fractal-like designs employing light-trapping structures and geometries at multiple length scales are proposed to increase the effective solar absorptance and efficiency of these receivers. Radial and linear structures at the micro (surface coatings and depositions), meso (tube shape and geometry), and macro (total receiver geometry and configuration) scales redirect reflected solar radiation toward the interior of the receiver for increased absorptance. Hotter regions within the interior of the receiver also reduce thermal emittance due to reduced local view factors in the interior regions, and higher concentration ratios can be employed with similar surface irradiances to reduce the effective optical aperture and thermal losses. Coupled optical/fluid/thermal models have been developed to evaluate the performance of these designs relative to conventional designs. Results show that fractal-like structures and geometries can reduce total radiative losses by up to 50% and increase the thermal efficiency by up to 10%. The impact was more pronounced for materials with lower inherent solar absorptances (< 0.9). Meso-scale tests were conducted and confirmed model results that showed increased light-trapping from corrugated surfaces relative to flat surfaces.

This paper will investigate energy-efficiency for various real-world industrial computed-tomography reconstruction algorithms, both CPU- and GPU-based implementations. This work shows that the energy required for a given reconstruction is based on performance and problem size. There are many ways to describe performance and energy efficiency, thus this work will investigate multiple metrics including performance-per-watt, energy-delay product, and energy consumption. This work found that irregular GPU-based approaches1 realized tremendous savings in energy consumption when compared to CPU implementations while also significantly improving the performanceper- watt and energy-delay product metrics. Additional energy savings and other metric improvement was realized on the GPU-based reconstructions by improving storage I/O by implementing a parallel MIMD-like modularization of the compute and I/O tasks.

Solar optical modeling tools are valuable for modeling and predicting the performance of solar technology systems. Four optical modeling tools were evaluated using the National Solar Thermal Test Facility heliostat field combined with flat plate receiver geometry as a benchmark. The four optical modeling tools evaluated were DELSOL, HELIOS, SolTrace, and Tonatiuh. All are available for free from their respective developers. DELSOL and HELIOS both use a convolution of the sunshape and optical errors for rapid calculation of the incident irradiance profiles on the receiver surfaces. SolTrace and Tonatiuh use ray-tracing methods to intersect the reflected solar rays with the receiver surfaces and construct irradiance profiles. We found the ray-tracing tools, although slower in computation speed, to be more flexible for modeling complex receiver geometries, whereas DELSOL and HELIOS were limited to standard receiver geometries such as flat plate, cylinder, and cavity receivers. We also list the strengths and deficiencies of the tools to show tool preference depending on the modeling and design needs. We provide an example of using SolTrace for modeling nonconventional receiver geometries. The goal is to transfer the irradiance profiles on the receiver surfaces calculated in an optical code to a computational fluid dynamics code such as ANSYS Fluent. This approach eliminates the need for using discrete ordinance or discrete radiation transfer models, which are computationally intensive, within the CFD code. The irradiance profiles on the receiver surfaces then allows for thermal and fluid analysis on the receiver.

Adoption of on-chip optical interconnects with silicon photonics requires addressing wavelength stabilization of resonant modulators and filters. We have developed low-power integrated photonic and electronic control circuits, with progress toward minimizing circuit footprint. © 2014 OSA.

Microbial free fatty acids (FFAs) have been proposed as a potential feedstock for renewable energy. The ability to directly convert carbon dioxide into FFAs makes cyanobacteria ideal hosts for renewable FFA production. Previous metabolic engineering efforts using the cyanobacterial hosts Synechocystis sp. PCC 6803 and Synechococcus elongatus PCC 7942 have demonstrated this direct conversion of carbon dioxide into FFAs; however, FFA yields in these hosts are limited by the negative impact of FFA production on the host cell physiology. This work investigates the use of Synechococcus sp. PCC 7002 as a cyanobacterial host for FFA production. In comparison to S. elongatus PCC 7942, Synechococcus sp. PCC 7002 strains produced and excreted FFAs at similar concentrations but without the detrimental effects on host physiology. The enhanced tolerance to FFA production with Synechococcus sp. PCC 7002 was found to be temperature-dependent, with physiological effects such as reduced photosynthetic yield and decreased photosynthetic pigments observed at higher temperatures. Additional genetic manipulations were targeted for increased FFA production, including thioesterases and ribulose-1,5-bisphosphate carboxylase/oxygenase (RuBisCO). Overexpression of non-native RuBisCO subunits (rbcLS) from a psbAI promoter resulted in more than a threefold increase in FFA production, with excreted FFA concentrations reaching >130 mg/L. This work illustrates the importance of host strain selection for cyanobacterial biofuel production and demonstrates that the FFA tolerance of Synechococcus sp. PCC 7002 can allow for high yields of excreted FFA.

Because of relatively recent decisions by the current administration and its renewed assessment of the nuclear life- cycle, the various deep geologic disposal medium options are once again open for consideration. This paper focuses on addressing the favorable creep properties and behavior of rock salt, from the computational modeling perspective, as it relates to its potential use as a disposal medium for a deep geologic repository. The various components that make up a computational modeling capability to address the thermo-mechanical behavior of rock salt over a wide range of time and space are presented here. Several example rock salt calculations are also presented to demonstrate the applicability and validity of the modeling capability described herein to address repository-scale problems. The evidence shown points to a mature computational capability that can generate results relevant to the design and assessment of a potential rock salt HLW repository. The computational capability described here can be used to help enable fuel cycle sustainability by appropriately vetting the use of geologic rock salt for use as a deep geologic disposal medium.

Blast waves from an explosion in air can cause significant structural damage. As an example, cylindrically-shaped charges have been used for over a century as dynamite sticks for mining, excavation, and demolition. Near the charge, the effects of geometry, standoff from the ground, the proximity to other objects, confinement (tamping), and location of the detonator can significantly affect blast wave characteristics. Furthermore, nonuniformity in the surface characteristics and the density of the charge can affect fireball and shockwave structure. Currently, the best method for predicting the shock structure near a charge and the dynamic loading on nearby structures is to use a multidimensional, multimaterial shock physics code. However, no single numerical technique currently exists for predicting secondary combustion, especially when particulates from the charge are propelled through the fireball and ahead of the leading shock lens. Furthermore, the air within the thin shocked layer can dissociate and ionize. Hence, an appropriate equation of state for air is needed in these extreme environments. As a step towards predicting this complex phenomenon, a technique was developed to provide the equilibrium species composition at every computational cell in an air blast simulation as an initial condition for hand-off to other analysis codes for combustion fluid dynamics or radiation transport. Here, a bare cylindrical charge of TNT detonated in air is simulated using CTH, an Eulerian, finite volume, shock propagation code developed and maintained at Sandia National Laboratories. The shock front propagation is computed at early times, including the detonation wave structure in the explosive and the subsequent air shock up to 100 microseconds, where ambient air entrainment is not significant. At each computational cell, which could have TNT detonation products, air, or both TNT and air, the equilibrium species concentration at the density-energy state is computed using the JCZS2i database in the thermochemical code TIGER. This extensive database of 1267 gas (including 189 ionized species) and 490 condensed species can predict thermodynamic states up to 20,000 K. The results of these calculations provide the detailed three-dimensional structure of a thin shock front, and spatial species concentrations including free radicals and ions. Furthermore, air shock predictions are compared with experimental pressure gage data from a right circular cylinder of pressed TNT, detonated at one end. These complimentary predictions show excellent agreement with the data for the primary wave structure.

Direct Digital Manufacturing techniques such as laser ablation are proposed for the fabrication of lower cost, miniaturized, and lightweight integrated assemblies with high performance requirements. This paper investigates the laser ablation of a Ti/Cu/Pt/Au thin film metal stack on fired low temperature cofired ceramic (LTCC) surfaces using a 355 nm Nd.YAG diode pumped laser ablation system. It further investigates laser ablation applications using unfil ed, or 'green', LTCC materials: (1) through one layer of a laminated stack of unfiled LTCC tape to a buried thick film conductor ground plane, and (2) in unfiled Au thick films. The UV laser power profile and part fixturing were optimized to address defects such as LTCC microcracking, thin film adhesion failures, and redeposition of Cu and Pt. An alternate design approach to minimize ablation time was tested for efficiency in manufacture. Multichip Modules (MCM) were tested for solder ability', solder leach resistance, and wire bondabilify. Scanning election microscopy (SEM) as well as cross sections and microanalytical techniques were used in this study.

Abstract not provided.

Experiments on the UNR Zebra generator with Load Current Multiplier (LCM) allow for implosions of larger sized wire array loads than at standard current of 1 MA. Advantages of larger sized planar wire array implosions include enhanced energy coupling to plasmas, better diagnostic access to observable plasma regions, and more complex geometries of the wire loads. The experiments with larger sized wire arrays were performed on 1.5 MA Zebra with LCM (the anode-cathode gap was 1 cm, which is half the gap used in the standard mode). In particular, larger sized multi-planar wire arrays had two outer wire planes from mid-atomic-number wires to create a global magnetic field (gmf) and plasma flow between them. A modified central plane with a few Al wires at the edges was put in the middle between outer planes to influence gmf and to create Al plasma flow in the perpendicular direction (to the outer arrays plasma flow). Such modified plane has different number of empty slots: it was increased from 6 up to 10, hence increasing the gap inside the middle plane from 4.9 to 7.7 mm, respectively. Such load configuration allows for more independent study of the flows of L-shell mid-atomic-number plasma (between the outer planes) and K-shell Al plasma (which first fills the gap between the edge wires along the middle plane) and their radiation in space and time. We demonstrate that such configuration produces higher linear radiation yield and electron temperatures as well as advantages of better diagnostics access to observable plasma regions and how the load geometry (size of the gap in the middle plane) influences K-shell Al radiation. In particular, K-shell Al radiation was delayed compared to L-shell mid-atomic-number radiation when the gap in the middle plane was large enough (when the number of empty slots was increased up to ten).

In this study, the authors developed an approach for accurately quantifying the helium content in a gas mixture also containing hydrogen and methane using commercially available getters. The authors performed a systematic study to examine how both H2 and CH4 can be removed simultaneously from the mixture using two SAES St 172® getters operating at different temperatures. The remaining He within the gas mixture can then be measured directly using a capacitance manometer. The optimum combination involved operating one getter at 650 °C to decompose the methane, and the second at 110 °C to remove the hydrogen. This approach eliminated the need to reactivate the getters between measurements, thereby enabling multiple measurements to be made within a short time interval, with accuracy better than 1%. The authors anticipate that such an approach will be particularly useful for quantifying the He-3 in mixtures that include tritium, tritiated methane, and helium-3. The presence of tritiated methane, generated by tritium activity, often complicates such measurements.

Abstract not provided.

Solid rocket propellant plume temperatures have been measured using spectroscopic methods as part of an ongoing effort to specify the thermal-chemical-physical environment in and around a burning fragment of an exploded solid rocket at atmospheric pressures. Such specification is needed for launch safety studies where hazardous payloads become involved with large fragments of burning propellant. The propellant burns in an off-design condition producing a hot gas flame loaded with burning metal droplets. Each component of the flame (soot, droplets and gas) has a characteristic temperature, and it is only through the use of spectroscopy that their temperature can be independently identified.

Advances in node-level architecture and interconnect technology needed to reach extreme scale necessitate a reevaluation of long-standing models of computation, in particular bulk synchronous processing. The end of Dennard-scaling and subsequent increases in CPU core counts each successive generation of general purpose processor has made the ability to leverage parallelism for communication an increasingly critical aspect for future extreme-scale application performance. But the use of massive multithreading in combination with MPI is an open research area, with many proposed approaches requiring code changes that can be unfeasible for important large legacy applications already written in MPI. This paper covers the design and initial evaluation of an extension of a massive multithreading runtime system supporting dynamic parallelism to interface with MPI to handle fine-grain parallel communication and communication-computation overlap. Our initial evaluation of the approach uses the ubiquitous stencil computation, in three dimensions, with the halo exchange as the driving example that has a demonstrated tie to real code bases. The preliminary results suggest that even for a very well-studied and balanced workload and message exchange pattern, co-scheduling work and communication tasks is effective at significant levels of decomposition using up to 131,072 cores. Furthermore, we demonstrate useful communication-computation overlap when handling blocking send and receive calls, and show evidence suggesting that we can decrease the burstiness of network traffic, with a corresponding decrease in the rate of stalls (congestion) seen on the host link and network.

When an optical coating is damaged, deposited incorrectly, or is otherwise unsuitable, the conventional method to restore the optic often entails repolishing the optic surface, which can incur a large cost and long lead time. We propose three alternative options to repolishing, including (i) burying the unsuitable coating under another optical coating, (ii) using ion milling to etch the unsuitable coating completely from the optic surface, and then recoating the optic, and (iii) using ion milling to etch through a number of unsuitable layers, leaving the rest of the coating intact, and then recoating the layers that were etched. Repairs were made on test optics with dielectric mirror coatings according to the above three options. The mirror coatings to be repaired were quarter wave stacks of HfO2 and SiO2 layers for high reflection at 1054 nm at 45° incidence in P-polarization. One of the coating layers was purposely deposited incorrectly as Hf metal instead of HfO2 to evaluate the ability of each repair method to restore the coating's high laser-induced damage threshold (LIDT) of 64 J/cm2. The repaired coating with the highest resistance to laser-induced damage was achieved using repair method (ii) with an LIDT of 49-61 J/cm2.

In this paper we introduce an approach that augments least-squares finite element formulations with user-specified quantities-of-interest. The method incorporates the quantity-ofinterest into the least-squares functional and inherits the global approximation properties of the standard formulation as well as increased resolution of the quantity-of-interest. We establish theoretical properties such as optimality and enhanced convergence under a set of general assumptions. Central to the approach is that it offers an element-level estimate of the error in the quantity-ofinterest. As a result, we introduce an adaptive approach that yields efficient, adaptively refined approximations. Several numerical experiments for a range of situations are presented to support the theory and highlight the effectiveness of our methodology. Notably, the results show that the new approach is effective at improving the accuracy per total computational cost.

Fiber-reinforced composite materials offer light-weight solutions to many structural challenges. In the development of high-performance composite structures, a thorough understanding is required of the composite materials themselves as well as methods for the analysis and failure prediction of the relevant composite structures. However, the mechanical properties required for the complete constitutive definition of a composite material can be difficult to determine through experimentation. Therefore, efficient methods are necessary that can be used to determine which properties are relevant to the analysis of a specific structure and to establish a structure's response to a material parameter that can only be defined through estimation. The objectives of this study deal with the computational examination of the four-point flexural characterization of a carbon fiber composite material. Utilizing a novel, orthotropic material model that is capable of predicting progressive composite damage and failure, a sensitivity analysis is completed to establish which material parameters are truly relevant to a simulation's outcome. Then, a parameter study is completed to determine the effect of the relevant material properties' expected variations on the simulated four-point flexural behavior. Lastly, the results of the parameter study are combined with the orthotropic material model to estimate any relevant material properties that could not be determined through experimentation (e.g., in-plane compressive strength). Results indicate that a sensitivity analysis and parameter study can be used to optimize the material definition process. Furthermore, the discussed techniques are validated with experimental data provided for the flexural characterization of the described carbon fiber composite material.

Radiation magnetohydrodynamic r-z simulations are performed of recent Ar shots on the refurbished Z generator to examine the effective ion temperature as determined from the observed line width of the He-γ line. While many global radiation properties can be matched to experimental results, the Doppler shifts due to velocity gradients at stagnation cannot reproduce the large experimentally determined width corresponding to an effective ion temperature of 50 keV. Ion viscous heating or magnetic bubbles are considered, but understanding the width remains an unsolved challenge.

A new compact Z-pinch x-ray hohlraum design with parallel-driven x-ray sources was experimentally demonstrated in a full configuration with a central target and tailored shine shields (to provide a symmetric temperature distribution on the target) at the 1.7 MA Zebra generator. This presentation reports on the joint success of two independent lines of research. One of these was the development of new sources - planar wire arrays (PWAs). PWAs turned out to be a prolific radiator. Another success was the drastic improvement in energy efficiency of pulsed-power systems, such as the Load Current Multiplier (LCM). The Zebra/LCM generator almost doubled the plasma load current to 1.7 MA. The two above-mentioned innovative approaches were used in combination to produce a new compact hohlraum design for ICF, as jointly proposed by SNL and UNR. Good agreement between simulated and measured radiation temperature of the central target is shown. Experimental comparison of PWAs with planar foil liners (PFL) - another viable alternative to wire array loads at multi-MA generators show promising data. Results of research at the University of Nevada Reno allowed for the study of hohlraum coupling physics at University-scale generators. The advantages of new hohlraum design applications for multi-MA facilities with W or Au double PWAs or PFL x-ray sources are discussed.

We present a new optimization-based method for atomistic-to-continuum (AtC) coupling. The main idea is to cast the latter as a constrained optimization problem with virtual Dirichlet controls on the interfaces between the atomistic and continuum subdomains. The optimization objective is to minimize the error between the atomistic and continuum solutions on the overlap between the two subdomains, while the atomistic and continuum force balance equations provide the constraints. Separation, rather then blending of the atomistic and continuum problems, and their subsequent use as constraints in the optimization problem distinguishes our approach from the existing AtC formulations. We present and analyze the method in the context of a one-dimensional chain of atoms modeled using a linearized two-body potential with next-nearest neighbor interactions.

Resistive random access memory (ReRAM), or memristors, may be capable of significantly improve the efficiency of neuromorphic computing, when used as a central component of an analog hardware accelerator. However, the significant electrical variation within a device and between devices degrades the maximum efficiency and accuracy which can be achieved by a ReRAMbased neuromorphic accelerator. In this report, the electrical variability is characterized, with a particular focus on that which is due to fundamental, intrinsic factors. Analytical and ab initio models are presented which offer some insight into the factors responsible for this variability.

Oil leaks were found in wellbores of Caverns 105 and 109 at the Big Hill Strategic Petroleum Reserve site. According to the field observations, two instances of casing damage occurred at the depth of the interbed between the caprock bottom and salt top. A three-dimensional finite element model, which allows each cavern to be configured individually, was constructed to investigate horizontal and vertical displacements in each well as it crosses the various interbeds. The model contains interfaces between each lithology and a shear zone (fault) to examine the interbed behavior in a realistic manner. This analysis results indicate that the casings of Caverns 105 and 109 failed, respectively, from shear stress that exceeded the casing shear strength due to the horizontal movement of the salt top relative to the caprock and tensile stress due to the downward movement of the salt top from the caprock. The wellbores of Caverns 114 and 104, located at the far end of the field and near the fault, respectively, are predicted to fail by shear stress in the near future. The wellbores of inmost Caverns 107 and 108 are predicted to fail by tensile stress in the near future. The salt top subsides because the volumes of caverns in the salt dome decrease with time due to salt creep closure, while the caprock does not subside at the same rate as the salt top because the caprock is thick and stiff. This discrepancy yields deformation of the well. © 2014 The Author(s).

Molecular dynamics simulations were used to investigate trends in noble gas (Ar, Kr, Xe) diffusion in the metal-organic frameworks HKUST-1 and ZIF-8. Diffusion occurs primarily through inter-cage jump events, with much greater diffusion of guest atoms in HKUST-1 compared to ZIF-8 due to the larger cage and window sizes in the former. We compare diffusion coefficients calculated for both rigid and flexible frameworks. For rigid framework simulations, in which the framework atoms were held at their crystallographic or geometry optimized coordinates, sometimes dramatic differences in guest diffusion were seen depending on the initial framework structure or the choice of framework force field parameters. When framework flexibility effects were included, argon and krypton diffusion increased significantly compared to rigid-framework simulations using general force field parameters. Additionally, for argon and krypton in ZIF-8, guest diffusion increased with loading, demonstrating that guest-guest interactions between cages enhance inter-cage diffusion. No inter-cage jump events were seen for xenon atoms in ZIF-8 regardless of force field or initial structure, and the loading dependence of xenon diffusion in HKUST-1 is different for rigid and flexible frameworks. Diffusion of krypton and xenon in HKUST-1 depends on two competing effects: the steric effect that decreases diffusion as loading increases, and the "small cage effect" that increases diffusion as loading increases. A detailed analysis of the window size in ZIF-8 reveals that the window increases beyond its normal size to permit passage of a (nominally) larger krypton atom. © 2014 Elsevier Inc. All rights reserved.

We present PuLP, a parallel and memory-efficient graph partitioning method specifically designed to partition low-diameter networks with skewed degree distributions. Graph partitioning is an important Big Data problem because it impacts the execution time and energy efficiency of graph analytics on distributed-memory platforms. Partitioning determines the in-memory layout of a graph, which affects locality, intertask load balance, communication time, and overall memory utilization of graph analytics. A novel feature of our method PuLP (Partitioning using Label Propagation) is that it optimizes for multiple objective metrics simultaneously, while satisfying multiple partitioning constraints. Using our method, we are able to partition a web crawl with billions of edges on a single compute server in under a minute. For a collection of test graphs, we show that PuLP uses 8-39× less memory than state-of-the-art partitioners and is up to 14.5× faster, on average, than alternate approaches (with 16-way parallelism). We also achieve better partitioning quality results for the multi-objective scenario.

Abstract not provided.

Two of the more recent developments in thermal transport simulations are the incorporation of multiscale models and requirements for verification, validation, and uncertainty quantification to provide actionable simulation results. The aleatoric uncertainty is investigated for a two component mixture containing a high thermal conductivity and a low thermal conductivity material. The microstructure is varied from a coarse size of 1/8 the domain length to a fine scale of 1/256 the domain length and for volume fractions of high thermal conductivity material from 0 to 1. The uncertainty in the temperatures is greatest near the percolation threshold of around 0.4 and for the coarsest microstructures. Statistical representations of the aleatoric uncertainty for heterogeneous materials are necessary and need to be passed between scales in multiscale simulations of thermal transport.

One-dimensional (1D) nanostructures, often referred to as nanowires, have attracted considerable attention due to their unique mechanical, chemical, and electrical properties. Although numerous novel technological applications are being proposed for these structures, many of the processes used to synthesize these materials involve a vapor phase and require high temperatures and long growth times. Potentially faster methods requiring templates, such as anodized aluminum oxide, involve multiple fabrication steps, which would add significantly to the cost of the final material and may preclude their widespread use. In the present study, it is shown that template-free electrodeposition from an alkaline solution can produce arrays of Sn nanoneedles directly onto Cu foil substrates. This electrodeposition process occurs at 55 C; it is proposed that the nanoneedles grow via a catalyst-mediated mechanism. In such a process, the growth is controlled at the substrate/nanostructure interface rather than resulting from random plating-induced defects such as dendrites or aging defects such as tin whiskers. There are multiple potential applications for 1D Sn nanostructures - these include anodes in lithium-ion and magnesium-ion batteries and as thermal interface materials. To test this potential, type 2032 lithium-ion battery button cells were fabricated using the electrodeposited Sn. These cells showed initial capacities as high as 850 mAh/g and cycling stability for over 200 cycles. © 2013 Springer Science+Business Media New York.

American crows are acutely sensitive to West Nile virus (WNV) infection, and crow mortality has been used in WNV surveillance to monitor enzootic transmission. However, non-WNV sources of mortality could reduce the reliability of crow death as a surveillance tool. Here, using a combination of histopathologic, toxicologic, virologic, and molecular techniques we describe causes of mortality in 67 American crows (Corvus brachyrhynchos) that were collected from a population in the Sacramento Valley of California in 2012 and 2013. Evidence of infectious disease was detected in 70% (47/67) of carcasses. The majority of deaths were linked to a suite of non-WNV viral, bacterial, and fungal infections (39%; 23/59 cases), WNV (36%; 24/67 cases), and an acute toxic event (25%; 15/59 cases). Coinfections were detected in 20% (12/59) of birds and frequently were associated with WNV and poxviral dermatitis. Inferences about WNV activity based on crow mortality should be supported by laboratory confirmation because crow mortality frequently can be caused by other infectious diseases or toxic events. © American Association of Avian Pathologists.

The traditional metric for the efficiency of a numerical algorithm has been the number of arithmetic operations it performs. Technological trends have long been reducing the time to perform an arithmetic operation, so it is no longer the bottleneck in many algorithms; rather, communication, or moving data, is the bottleneck. This motivates us to seek algorithms that move as little data as possible, either between levels of a memory hierarchy or between parallel processors over a network. In this paper we summarize recent progress in three aspects of this problem. First we describe lower bounds on communication. Some of these generalize known lower bounds for dense classical (O(n 3)) matrix multiplication to all direct methods of linear algebra, to sequential and parallel algorithms, and to dense and sparse matrices. We also present lower bounds for Strassen-like algorithms, and for iterative methods, in particular Krylov subspace methods applied to sparse matrices. Second, we compare these lower bounds to widely used versions of these algorithms, and note that these widely used algorithms usually communicate asymptotically more than is necessary. Third, we identify or invent new algorithms for most linear algebra problems that do attain these lower bounds, and demonstrate large speed-ups in theory and practice. © Cambridge University Press 2014.

Offshore wind power production is an attractive clean energy option, but the difficulty of access can lead to expensive and rare opportunities for maintenance. As part of the Structural Health and Prognostics Management (SHPM) project at Sandia National Laboratories, smart loads management (controls) are investigated for their potential to increase the fatigue life of offshore wind turbine rotor blades. Derating refers to altering the rotor angular speed and blade pitch to limit power production and loads on the rotor blades. High- fidelity analysis techniques like 3D finite element modeling (FEM) should be used alongside beam models of wind turbine blades to characterize these control strategies in terms of their effect to mitigate fatigue damage and extend life of turbine blades. This study will consider a commonly encountered damage type for wind turbine blades, the trailing edge disbond, and show how FEM can be used to quantify the effect of operations and control strategies designed to extend the fatigue life of damaged blades. The Virtual Crack Closure Technique (VCCT) will be used to post-process the displacement and stress results to provide estimates of damage severity/criticality and provide a means to estimate the fatigue life under a given operations and control strategy. © Published under licence by IOP Publishing Ltd.

The wavelength down conversion approach to solid-state lighting (SSL) uses down conversion materials to produce visible light when excited by near-UV or blue emission from InGaN LEDs. This review discusses two classes of down conversion materials: phosphors and semiconductor quantum dots (QDs). Strong absorption of the excitation wavelength; high luminous efficacy of radiation, which enables white light with a high color rendering index and a low correlated color temperature; high quantum efficiency; and thermal and chemical stability are some of the criteria for down converters used in SSL. This review addresses the challenges in the development of down converters that satisfy all these criteria. We will discuss the advantages and disadvantages of several phosphor compositions for blue and near-UV LEDs. The use of core/shell architectures to improve the photoluminescence and moisture resistance of phosphors is presented. QDs are another class of down conversion materials for near-UV and blue LEDs. Strategies to improve the photostability and reduce the thermal quenching of QDs include strain-graded core/shell interfaces and alloying. We discuss Cd-containing II-VI QDs, and Cd-free III-V and I-III-VI QDs and their potential for SSL applications. Finally, a description of different methods to integrate the phosphors and QDs with the LED is given. © 2014 The American Ceramic Society.

Developing a big picture understanding of a severe accident is extremely challenging. Operating crews and emergency response teams are faced with rapidly evolving circumstances, uncertain information, distributed expertise, and a large number of conflicting goals and priorities. Severe accident management guidance (SAMGs) provides support for collecting information and assessing the state of a nuclear power plant during severe accidents. However, SAMGs developers cannot anticipate every possible accident scenario. Advanced Probabilistic Risk Assessment (PRA) methods can be used to explore an extensive space of possible accident sequences and consequences. Using this advanced PRA to develop a decision support system can provide expanded support for diagnosis and response. In this paper, we present an approach that uses dynamic PRA to develop risk-informed "Smart SAMGs". Bayesian Networks form the basis of the faster-than-real-time decision support system. The approach leverages best-available information from plant physics simulation codes (e.g., MELCOR). Discrete Dynamic Event Trees (DDETs) are used to provide comprehensive coverage of the potential accident scenario space. This paper presents a methodology to develop Smart procedures and provides an example model created for diagnosing the status of the ECCS valves in a generic iPWR design.

The availability of offshore wind resources in coastal regions, along with a high concentration of load centers in these areas, makes offshore wind energy an attractive opportunity for clean renewable electricity production. High infrastructure costs such as the offshore support structure and operation and maintenance costs for offshore wind technology, however, are significant obstacles that need to be overcome to make offshore wind a more cost-effective option. A vertical-axis wind turbine (VAWT) rotor configuration offers a potential transformative technology solution that significantly lowers cost of energy for offshore wind due to its inherent advantages for the offshore market. However, several potential challenges exist for VAWTs and this paper addresses one of them with an initial investigation of dynamic aeroelastic stability for large-scale, multi-megawatt VAWTs. The aeroelastic formulation and solution method from the BLade Aeroelastic STability Tool (BLAST) for HAWT blades was employed to extend the analysis capability of a newly developed structural dynamics design tool for VAWTs. This investigation considers the effect of configuration geometry, material system choice, and number of blades on the aeroelastic stability of a VAWT, and provides an initial scoping for potential aeroelastic instabilities in large-scale VAWT designs. © Published under licence by IOP Publishing Ltd.

Concentrating solar energy and transforming it into electricity is clean, economical and renewable. One design of solar power plants consists of an array of heliostats which redirects sunlight to a fixed receiver tower and the generated heat is converted into electricity. Currently, the angles of elevation of heliostats are controlled by motors and drives that are costly and require diverting power that can otherwise be used for producing electricity. We consider replacing the motor and drive system of the heliostat with a photosensitive polymer design that can tilt the mirror using the ability of the polymer to deform when subjected to light. The light causes the underlying molecular structure to change and subsequently, the polymer deforms. The deformation of the polymer is quantified in terms of photostrictive constitutive relations. A mathematical model is derived governing the behaviour of the angle of elevation as the photostrain varies. Photostrain depends on the composition of the polymer, intensity and temperature of light and angle of light polarization. Preliminary findings show a photomechanical rod structural design can provide 60° elevation for temperatures of about 40°C. A photomechanical beam structural design can generate more tilt at lower temperatures. The mathematical analysis illustrates that photostrains on the order of 1% to 10% are desired for both rod and beam designs to produce sufficient tilt under most heliostat field conditions. © 2014 SPIE.

This paper introduces a technique for improving the sensitivity of RF subsamplers in radar and coherent receiver applications. The technique, referred to herein as "delta modulation" (DM), feeds the time-average output of a monobit analog-to-digital converter (ADC) back to the ADC input, but with opposite polarity. Assuming pseudostationary modulation statistics on the sampled RF waveform, the feedback signal corrects for aggregate dc offsets present in the ADC that otherwise degrade ADC sensitivity. Two RF integrated circuits (RFICs) are designed to demonstrate the approach. One uses analog DM to create the feedback signal; the other uses digital DM to achieve the same result. A series of tests validates the designs. The dynamic time-domain response confirms the feedback loop's basic operation. Measured output quantization imbalance, under noise-only input drive, significantly improves with the use of the DM circuit, even for large, deliberately induced dc offsets and wide temperature variation from -5°C to + 85°C. Examination of the corrected versus uncorrected baseband spectrum under swept input signal-to-noise ratio (SNR) conditions demonstrates the effectiveness of this approach for realistic radar and coherent receiver applications. Two-tone testing shows no impact of the DM technique on ADC linearity. © 2014 IEEE.

Through the Department of Energy (DOE)/Office of Nuclear Energy (NE), Used Fuel Disposition Campaign (UFDC), numerous institutions are working to address issues associated with the extended storage and transportation of used nuclear fuel. In 2012, this group published a technical analysis which identified technical gaps that could be addressed to better support the technical basis for the extended storage and transportation of used nuclear fuel. This paper summarizes some of the current work being performed to close some of those high priority gaps. The areas discussed include: 1. developing thermal profiles of waste storage packages, 2. investigating the stresses experienced by fuel cladding and how that might affect cladding integrity, 3. understanding real environmental conditions that could lead to cask stress corrosion cracking, 4. quantifying the stress and strain fuel assemblies experience during normal truck transport and 5. performing a full-scale ten-year confirmatory demonstration of dry cask storage. Data from these R&D activities will reduce important technical gaps and allow us to better assess the risks associated with extended storage and transportation of used nuclear fuel.

We propose a new laboratory method for characterizing synthetic aperture radar (SAR) systems through the use of a synthetic scene generator. Flight tests are the only definitive way to characterize the system level performance of airborne synthetic aperture radar systems. However, due to the expense of flights tests it is beneficial to complete as much testing as possible in a laboratory environment before flight testing is performed. There are many existing tests that are employed to measure the performance of various subsystems in a SAR system, find defective hardware, and indicate design problems that need to be mitigated. However, certain issues can only be found on an integrated system, and laboratory testing at a system level is typically confined to characterizing the impulse response (IPR) of a single point target through the use of an optical delay line. While useful, delay line testing requires running a modified version of real-time image formation code as the delay line does not completely mimic a real target. Ideally, system level tests are performed on unmodified code. On modern SAR systems many algorithms are data driven (e.g., autofocus) and require a substantially more sophisticated data model for testing. We desire to create a complete system test by combining an arbitrary number of point targets and clutter patterns to mimic radar responses from a real scene. This capability enables complete testing of radar systems in a laboratory environment according to prescribed terrain/scene characteristics. This paper presents an overview of the system requirements for a synthetic scene generator. The analysis is limited to SAR systems utilizing chirp waveforms and stretch processing. Furthermore, we derive relationships between IF bandwidth, target position, and the phase history model. A technique to properly compensate for motion pulse to pulse is presented. Finally, our concept is demonstrated with simulation data. © 2014 SPIE.

We propose a new laboratory method for characterizing synthetic aperture radar (SAR) systems through the use of a synthetic scene generator. Flight tests are the only definitive way to characterize the system level performance of airborne synthetic aperture radar systems. However, due to the expense of flights tests it is beneficial to complete as much testing as possible in a laboratory environment before flight testing is performed. There are many existing tests that are employed to measure the performance of various subsystems in a SAR system, find defective hardware, and indicate design problems that need to be mitigated. However, certain issues can only be found on an integrated system, and laboratory testing at a system level is typically confined to characterizing the impulse response (IPR) of a single point target through the use of an optical delay line. While useful, delay line testing requires running a modified version of real-time image formation code as the delay line does not completely mimic a real target. Ideally, system level tests are performed on unmodified code. On modern SAR systems many algorithms are data driven (e.g., autofocus) and require a substantially more sophisticated data model for testing. We desire to create a complete system test by combining an arbitrary number of point targets and clutter patterns to mimic radar responses from a real scene. This capability enables complete testing of radar systems in a laboratory environment according to prescribed terrain/scene characteristics. This paper presents an overview of the system requirements for a synthetic scene generator. The analysis is limited to SAR systems utilizing chirp waveforms and stretch processing. Furthermore, we derive relationships between IF bandwidth, target position, and the phase history model. A technique to properly compensate for motion pulse to pulse is presented. Finally, our concept is demonstrated with simulation data. © 2014 SPIE.

Sandia National Laboratories produces copious amounts of high-resolution, single-polarization Synthetic Aperture Radar (SAR) imagery, much more than available researchers and analysts can examine. Automating the recognition of terrains and structures in SAR imagery is highly desired. The optical image processing community has shown that superpixel segmentation (SPS) algorithms divide an image into small compact regions of similar intensity. Applying these SPS algorithms to optical images can reduce image complexity, enhance statistical characterization and improve segmentation and categorization of scene objects. SPS algorithms typically require high SNR (signal-to-noise-ratio) images to define segment boundaries accurately. Unfortunately, SAR imagery contains speckle, a product of coherent image formation, which complicates the extraction of superpixel segments and could preclude their use. Some researchers have developed modified SPS algorithms that discount speckle for application to SAR imagery. We apply two widely-used SPS algorithms to speckle-reduced SAR image products, both single SAR products and combinations of multiple SAR products, which include both single polarization and multi-polarization SAR images. To evaluate the quality of resulting superpixels, we compute research-standard segmentation quality measures on the match between superpixels and hand-labeled ground-truth, as well as statistical characterization of the radar-cross-section within each superpixel. Results of this quality analysis determine the best input/algorithm/parameter set for SAR imagery. Simple Linear Iterative Clustering provides faster computation time, superpixels that conform to scene-relevant structures, direct control of average superpixel size and more uniform superpixel sizes for improved statistical estimation which will facilitate subsequent terrain/structure categorization and segmentation into scene-relevant regions. © 2014 SPIE.

This paper reports on trap-related shifts of the transfer curve and threshold voltage of power AlGaN/GaN HEMTs under switched bias operating life and reverse and forward DC bias stress. Opposite polarity threshold voltage shifts at room temperature under operating life and reverse bias stress conditions can be explained by means of drain current transient measurements under reverse bias stress conditions. A proposed model to explain the trapping/de-trapping behavior under different stress conditions is described and highlights the critical role of the electric field. Experimental evidence of the importance of the role of the electric field is seen in reduced parametric shift by improving the field plate design. © 2014 IEEE.

A method for extracting interface trap density (DIT) from subthreshold I-V characteristics is used to analyze data on a SiC MOSFET stressed for thirty minutes at 175°C with a gate bias of-20 V. Without knowing the channel doping, the change in DIT can be calculated when referenced to an energy level correlated with the threshold voltage. © 2014 IEEE.

A hybrid rotational CARS scheme with femtosecond pump/Stokes preparation and a high-energy probe, generated by second-harmonic bandwidth compression (SHBC), is described. The instrument is demonstrated for collision- and background-free, kHz-rate temperature/oxygen probing in the product gases of C2H4/air flat flames for both lean and rich conditions. © 2014 OSA.

Sandia and Semprius have partnered to evaluate the operational performance of a 3.5 kW (nominal) R&D system using 40 Semprius modules. Eight months of operational data has been collected and evaluated. Analysis includes determination of Pmp, Imp and Vmp at CSTC conditions, Pmp as a function of DNI, effect of wind speed on module temperature and seasonal variations in performance. As expected, on-sun Pmp and Imp of the installed system were found to be ~10% lower than the values determined from flash testing at CSTC, while Vmp was found to be nearly identical to the results of flash testing. The differences in the flash test and outdoor data are attributed to string mismatch, soiling, seasonal variation in solar spectrum, discrepancy in the cell temperature model, and uncertainty in the power and current reported by the inverter. An apparent limitation to the degree of module cooling that can be expected from wind speed was observed. The system was observed to display seasonal variation in performance, likely due to seasonal variation in spectrum.

Energy storage materials often involve chemical reactions with bulk solids. Porosity within the solids can enhance reaction rates. The porosity can be either within or between individual particles of the material. Greater control of the size and uniformity of both types of pore should lead to enhancements of charging and discharging rates in energy storage systems. To control both particle and pore size in nanoporous palladium (Pd)-based hydrogen storage materials, we have first created uniformly sized copper particles of about 1. μm diameter by the reduction of copper sulfate with ascorbic acid. In turn, these were used as reducing agents for tetrachloropalladate in the presence of a block copolymer surfactant. The copper reductant particles are geometrically self-limiting, so the resulting Pd particles are of similar size. The surfactant induces formation of 10. nm-scale pores within the particles. Some residual copper is alloyed with the Pd, reducing hydrogen storage capacity; use of a more reactive Pd salt can mitigate this. The reaction is conveniently performed in gram-scale batches. © 2014 Elsevier B.V.

We demonstrate and investigate concurrent switching of twenty 10-Gbps channels using a silicon Mach-Zehnder interferometer switching structure with low on-state loss, low power, and microsecond-scale switching time. © 2014 IEEE.

A compact silicon photonic channelized optical spectrum monitor is designed and realized, which can replace a large rack-mounted OSA's channel power monitoring functionality, and the signal processing algorithm underlying its operation is described. © 2014 OSA.

The solar spectrum varies with atmospheric conditions and composition, and can have significant impacts on the output power performance of each junction in a concentrating solar photovoltaic (CPV) system, with direct implications on the junction that is current-limiting. The effect of changing solar spectrum on CPV module power production has previously been characterized by various spectral performance parameters such as air mass (AM) for both single and multi-junction module technologies. However, examinations of outdoor test results have shown substantial uncertainty contributions by many of these parameters, including air mass, for the determination of projected power and energy production. Using spectral data obtained from outdoor spectrometers, with a spectral range of 336nm-1715nm, this investigation examines precipitable water (PW), aerosol and dust variability effects on incident spectral irradiance. This work then assesses air mass and other spectral performance parameters, including a new atmospheric component spectral factor (ACSF), to investigate iso-cell, stacked multijunction and single-junction c-Si module performance data directly with measured spectrum. This will then be used with MODTRAN5® to determine if spectral composition can account for daily and seasonal variability of the short-circuit current density Jsc and the maximum output power Pmp values. For precipitable water, current results show good correspondence between the modeled atmospheric component spectral factor and measured data with an average rms error of 0.013, for all three iso-cells tested during clear days over a one week time period. Results also suggest average variations in ACSF factors with respect to increasing precipitable water of 8.2%/cmH2O, 1.3%/cmH2O, 0.2%/cmH2O and 1.8%/cmH2O for GaInP, GaAs, Ge and c-Si cells, respectively at solar noon and an AM value of 1.0. For ozone, the GaInP cell had the greatest sensitivity to increasing ozone levels with an ACSF variation of 0.07%/cmO3. For the desert dust wind study, consistent ACSF behavior between all iso-cells and c-Si was found, with only significant reductions beyond 40mph.

The State-of-the-Art Reactor Consequence Analyses (SOARCA) project for the Peach Bottom Atomic Power Station (the pilot boiling-water reactor) and Surry Power Station (the pilot pressurized-water reactor) represents the most complex deterministic MELCOR analyses performed to date. Uncertainty analyses focusing on input parameter uncertainty are now under way for one scenario at each pilot plant. Analyzing the uncertainty in parameters requires technical justification for the selection of each parameter to include in the analyses and defensible rationale for the associated distributions. This paper describes the methodology employed in the selection of parameters and corresponding distributions for the Surry uncertainty analysis, and insights from applying the methodology to the MELCOR parameters.

A method for extracting interface trap density (DIT) from subthreshold I-V characteristics is used to analyze data on a SiC MOSFET stressed for thirty minutes at 175°C with a gate bias of-20 V. Without knowing the channel doping, the change in DIT can be calculated when referenced to an energy level correlated with the threshold voltage. © 2014 IEEE.

We have examined how different cleaning processes affect the laser induced damage threshold of antireflection coatings for large dimension, Z-Backlighter laser optics at Sandia National Laboratories. Laser damage thresholds were measured after the coatings were created, and again 4 months later to determine which cleaning processes were most effective. There is a nearly twofold increase in laser induced damage threshold between the antireflection coatings that were cleaned and those that were not cleaned. The laser-induced damage threshold results also revealed that every antireflection coating had a high defect density, despite the cleaning process used, which indicates that improvements to either the cleaning or deposition processes should provide even higher laser induced damage thresholds.

Spacecraft state-of-health (SOH) analysis typically consists of limit-checking to compare incoming measurand values against their predetermined limits. While useful, this approach requires significant engineering insight along with the ability to evolve limit values over time as components degrade and their operating environment changes. In addition, it fails to take into account the effects of measurand combinations, as multiple values together could signify an imminent problem. A more powerful approach is to apply data mining techniques to uncover hidden trends and patterns as well as interactions among groups of measurands. In an internal research and development effort, software engineers at Sandia National Laboratories explored ways to mine SOH data from a remote sensing spacecraft. Because our spacecraft uses variable sample rates and packetized telemetry to transmit values for 30,000 measurands across 700 unique packet IDs, our data is characterized by a wide disparity of time and value pairs. We discuss how we summarized and aligned this data to be efficiently applied to data mining algorithms. We apply supervised learning including decision tree and principal component analysis and unsupervised learning including k-means and orthogonal partitioning clustering and one-class support vector machine to four different spacecraft SOH scenarios after the data preprocessing step. Our experiment results show that data mining is a very good low-cost and high-payoff approach to SOH analysis and provides an excellent way to exploit vast quantities of time-series data among groups of measurands in different scenarios. Our scenarios show that the supervised cases were particularly useful in identifying key contributors to anomalous events, and the unsupervised cases were well-suited for automated analysis of the system as a whole. The developed underlying models can be updated over time to accurately represent a changing operating environment and ultimately to extend the mission lifetime of our valuable space assets.

When considering the future of offshore wind energy, developing cost effective methods of harnessing the offshore wind resource represents a significant challenge which must be overcome to make offshore wind a viable option. As the majority of the capital investment in offshore wind is in the form of infrastructure and operation and maintenance costs, reducing these expenditures could greatly reduce the cost of energy (COE) for an offshore wind project. Sandia National Laboratory and its partners (TU Delft, University of Maine, Iowa State, and TPI Composites) believe that vertical axis wind turbines (VAWTs) offer multiple advantages over other rotor configurations considering this new COE breakdown. The unique arrangement of a VAWT allows the heavy generator and related components to be located at the base of the tower as opposed to the top, as is typical of a horizontal axis wind turbine (HAWT). This configuration lowers the topside CG which reduces the platform stability requirements, leading to smaller and cheaper platforms. Additionally this locates high maintenance systems close to the ocean surface thus increasing maintainability. To support this project and the general wind research community, the Offshore Wind ENergy Simulation (OWENS) toolkit is being developed in conjunction with Texas A&M as an open source, modular aero-elastic analysis code with the capability to analyze floating VAWTS. The OWENS toolkit aims to establish a robust and flexible finite element framework and VAWT mesh generation utility, coupled with a modular interface that allows users to integrate easily with existing codes, such as aerodynamic and hydrodynamic codes.

Increasing interest in polarimetric characterization of atmospheric aerosols has led to the development of complete sample-measuring (Mueller) polarimeters that are capable of measuring the entire backscattering phase matrix of a probed volume. These Mueller polarimeters consist of several moving parts, which limit measurement rates and complicate data analysis. In this paper, we present the concept of a less complex polarization lidar setup for detection of preferential orientation of atmospheric particulates. On the basis of theoretical considerations of data inversion stability and propagation of measurement uncertainties, an optimum optical configuration is established for two modes of operation (with either a linear or a circular polarized incident laser beam). The conceptualized setup falls in the category of incomplete sample-measuring polarimeters and uses four detection channels for simultaneous measurement of the backscattered light. The expected performance characteristics are discussed through an example of a typical aerosol with a small fraction of particles oriented in a preferred direction. The theoretical analysis suggests that achievable accuracies in backscatter cross-sections and depolarization ratios are similar to those with conventional two-channel configurations, while in addition preferential orientation can be detected with the proposed four-channel system for a wide range of conditions. © 2014 Elsevier Ltd.

Image registration is a digital image processing technique that takes two or more of images of a scene in different coordinate systems and transforms them into a single coordinate system. Image registration is a necessary step in many advanced image processing techniques, such as multi-frame super-resolution. For that reason, registration accuracy is very crucial. While image registration is usually performed on images, one can perform the registration using metric images as well. This paper will present registration methods and their accuracies for various noise levels for the case of pure translational image motion. Registration techniques will be applied to the images themselves as well as to phase congruency images, gradient images, and edge-detected images. This study will also investigate registration of under-sampled images. Noise-free images are degraded using three types of noise: additive Gaussian noise, fixed-pattern noise along the column direction, and a combination of these two. The registration error is quantified for two registration algorithms with three different images as a function of the signal-to-noise ratio. A test on the usefulness of the image registration and registration accuracy performed on the intensity images of the Stokes imaging polarimeter. The Stokes images calculated before and after registration of the intensity images are compared to each other to show the improvement. © 2014 SPIE.

We present both simulation and experimental results showing that circularly polarized light maintains its degree of polarization better than linearly polarized light in scattering environments. This is specifically true in turbid environments like fog and clouds. In contrast to previous studies that propagate single wavelengths through broad particle-size distributions, this work identifies regions where circular polarization persists further than linear by systematically surveying different wavelengths through monodisperse particle diameters. For monodisperse polystyrene microspheres in water, for particle diameters of 0.99 and 1.925 microns and varying optical depths, we show that circular polarization's ability to persist through multiple scattering events is enhanced by as much as a factor of four, when compared to that of linear polarization. These particle diameters correspond to size parameters found for infrared wavelengths and marine and continental fog particle distributions. The experimental results are compared to Monte Carlo simulations for all scattering environments investigated. © 2014 SPIE.

We have examined how different cleaning processes affect the laser induced damage threshold of antireflection coatings for large dimension, Z-Backlighter laser optics at Sandia National Laboratories. Laser damage thresholds were measured after the coatings were created, and again 4 months later to determine which cleaning processes were most effective. There is a nearly twofold increase in laser induced damage threshold between the antireflection coatings that were cleaned and those that were not cleaned. The laser-induced damage threshold results also revealed that every antireflection coating had a high defect density, despite the cleaning process used, which indicates that improvements to either the cleaning or deposition processes should provide even higher laser induced damage thresholds.

Wafer-level step-stress experiments on high voltage Npn InGaP/GaAs HBTs are presented. A methodology utilizing brief, monotonically increasing stresses and periodic, interrupted parametric characterization is presented. The method and various examples of step-stressed HBTs illustrate the value of the technique for screening the reliability of HBT wafers. Degradation modes observed in these InGaP/GaAs HBTs closely correspond to a subset of those in other, longer types of reliability experiments and can be relevant in a reliability screen. A statistical sampling of HBT wafers reveals a consistently realized critical destructive limit over a very narrow power range, which indicates that thermal stress is the main cause of degradation. When stepped just shy of the destructive limit, electrical characteristics are capable of revealing gradual degradation. The end state of stressing typically involves shorting of both the base-emitter and base-collector junctions. Interrupted characterization revealed cases where baseemitter shorts preceded base-collector shorts and other cases where base-collector shorts occurred first. Examples of degradation include reductions in reverse breakdown voltage, increases in the offset voltage, and drops in current gain. These wafer-level stepstress techniques show promise for reducing the large time lag between wafer fabrication and useful reliability screening in HBTs.

Anthrax poses a significant threat to National Security as demonstrated by the terrorist attacks targeting the US Postal Service and Hart Building. Anthrax outbreaks commonly occur in livestock. Consequently, Bacillus anthracis is routinely isolated, propagated, and maintained to diagnose the disease. This practice increases laboratories' repositories of the agent, escalating the risk that it can be stolen. We have developed BaDX (2014 R&D100 Awardee), a credit-card sized diagnostic device for use in ultra-low resource environments that is low cost, requires no power, instrumentation or equipment to operate, no cold chain, self-decontaminates post-assay, and is operable by individuals with little/no technical training.

Multi-megawatt Vertical Axis Wind Turbines (VAWTs) are experiencing an increased interest for floating offshore applications. However, VAWT development is hindered by the lack of fast, accurate and validated simulation models. This work compares six different numerical models for VAWTS: a multiple streamtube model, a double-multiple streamtube model, the actuator cylinder model, a 2D potential flow panel model, a 3D unsteady lifting line model, and a 2D conformal mapping unsteady vortex model. The comparison covers rotor configurations with two NACA0015 blades, for several tip speed ratios, rotor solidity and fixed pitch angle, included heavily loaded rotors, in inviscid flow. The results show that the streamtube models are inaccurate, and that correct predictions of rotor power and rotor thrust are an effect of error cancellation which only occurs at specific configurations. The other four models, which explicitly model the wake as a system of vorticity, show mostly differences due to the instantaneous or time averaged formulation of the loading and flow, for which further research is needed. © Published under licence by IOP Publishing Ltd.

Insights developed within the U.S. nuclear weapon system safety community may benefit system safety design, assessment, and management activities in other high consequence domains. The approach of assured nuclear weapon safety has been developed that uses the Nuclear Safety Design Principles (NSDPs) of incompatibility, isolation, and inoperability to design safety features, organized into subsystems such that each subsystem contributes to safe system responses in independent and predictable ways given a wide range of environmental contexts. The central aim of the approach is to provide a robust technical basis for asserting that a system can meet quantitative safety requirements in the widest context of possible adverse or accident environments, while using the most concise arrangement of safety design features and the fewest number of specific adverse or accident environment assumptions. Rigor in understanding and applying the concept of independence is crucial for the success of the approach. This paper provides a basic description of the assured nuclear weapon safety approach, in a manner that illustrates potential application to other domains. There is also a strong emphasis on describing the process for developing a defensible technical basis for the independence assertions between integrated safety subsystems.

Advancements have been made in the diagnostic techniques to measure accurately the total radiated x-ray yield and power from z-pinch implosion experiments at the Z machine with high accuracy. The Z machine is capable of outputting 2 MJ and 330 TW of x-ray yield and power, and accurately measuring these quantities is imperative. We will describe work over the past several years which include the development of new diagnostics, improvements to existing diagnostics, and implementation of automated data analysis routines. A set of experiments on the Z machine were conducted in which the load and machine configuration were held constant. During this shot series, it was observed that the total z-pinch x-ray emission power determined from the two common techniques for inferring the x-ray power, a Kimfol filtered x-ray diode diagnostic and the total power and energy diagnostic, gave 449 TW and 323 TW, respectively. Our analysis shows the latter to be the more accurate interpretation. More broadly, the comparison demonstrates the necessity to consider spectral response and field of view when inferring x-ray powers from z-pinch sources. © 2014 AIP Publishing LLC.

Three stereoscopic PIV experiments have been examined to test the effectiveness of self-calibration under varied circumstances. Measurements conducted in a streamwise plane yielded a robust self-calibration that returned common results regardless of the specific calibration procedure, but measurements in the crossplane exhibited substantial velocity bias errors whose nature was sensitive to the particulars of the self-calibration approach. Self-calibration is complicated by thick laser sheets and large stereoscopic camera angles and further exacerbated by small particle image diameters and high particle seeding density. Despite the different answers obtained by varied self-calibrations, each implementation locked onto an apparently valid solution with small residual disparity and converged adjustment of the calibration plane. Therefore, the convergence of self-calibration on a solution with small disparity is not sufficient to indicate negligible velocity error due to the stereo calibration.

Boundary-layer transition and stability data were obtained at Mach 10 in the Arnold Engineering Development Complex (AEDC) Hypervelocity Wind Tunnel 9 on a 1.5-m long, 7-deg cone at unit Reynolds numbers between 1.8 and 31 million per meter. A total of 24 runs were performed at angles-of-attack between 0 and 10-deg on sharp and blunted cones with nose radii between 5.1 and 50.8-mm. The transition location was determined with coaxial thermocouples and temperature sensitive paint while stability measurements were obtained using high-frequency response pressure sensors. Mean flow and boundary layer-stability computations were also conducted and compared with the experiment. The effect of angle-of-attack and bluntness on the transition location displays similar trends compared to historical hypersonic wind tunnel data at similar Mach and Reynolds numbers. The N factor at start of transition on sharp cones increases with unit Reynolds number. Values between 4 and 7 were observed. The N factor at start of transition significantly decreases as bluntness increases and is successfully correlated with the ratio of transition location to entropy layer swallowing length. Good agreement between the computed and measured spatial amplification rates and most amplified 2nd mode frequencies are obtained for sharp and moderately blunted cones. For large bluntness, where the ratio of transition to entropy swallowing length is below 0.1, 2nd mode waves were not observed before the start of transition on the frustum.

The discrete ordinates method is a popular and versatile technique for deterministically solving the radiative transport which governs the exchange of radiant energy within a fluid or gas mixture. It is the most common 'high fidelity' technique used to approximate the radiative contribution in combined-mode heat transfer applications. A major drawback of the discrete ordinates method is that the solution of the discretized equations may involve nonphysical oscillations due to the nature of the discretization in the angular space. These ray effects occur in a wide range of problems including those with steep temperature gradients either at the boundary or within the medium, discontinuities in the boundary emissivity due to the use of multiple materials or coatings, internal edges or corners in non-convex geometries, and many others. Mitigation of these ray effects either by increasing the number of ordinate directions or by filtering or smoothing the solution can yield significantly more accurate results and enhanced numerical stability for combined mode codes. When ray effects are present, the solution is seen to be highly dependent upon the relative orientation of the geometry and the global reference frame. This is an undesirable property. A novel ray effect mitigation technique is proposed. By averaging the computed solution for various orientations, the number of ordinate directions may be artificially increased in a trivially parallelizable way. This increases the frequency and decreases the amplitude of the ray effect oscillations. As the number of considered orientations increases a rotationally invariant solution is approached which is quite accurate. How accurate this solution is and how rapidly it is approached is problem dependent. Uncertainty in the smooth solution achieved after considering a relatively small number of orientations relative to the rotationally invariant solution may be quantified.

The flow over aircraft bays exhibits many characteristics of cavity flows, namely resonant pressures that can create high structural loading. Most studies have represented these bays as rectangular cavities; however, this simplification neglects many features of the actual flight geometry which could affect the unsteady pressure field and resulting loading in the bay. To address this shortcoming, a complex cavity geometry was developed to incorporate more realistic aircraft-bay features including shaped inlets and internal cavity variations. A parametric study of these features at Mach 1.5, 2.0, and 2.5 was conducted to identify key differences from simple rectangular cavity flows. The frequency of the basic rectangular cavity modes could be predicted by theory; however, most complex geometries shifted these frequencies. Geometric changes that constricted the flow tended to enhance cavity modes and create higher pressure fluctuations. Other features, such as a leading edge ramp, lifted the shear layer higher with respect to the aft cavity wall and led to cavity tone suppression. Complex features that introduced spanwise non-uniformity into the shear layer also led to a reduction of cavity tones, especially at the aft end of the cavity.

Spent nuclear fuel reprocessing may involve some hazardous liquids that may explode under accident conditions. Explosive accidents may result in energetic dispersion of the liquid. The atomized liquid represents a major hazard of this class of event. The magnitude of the aerosol source term is difficult to predict, and historically has been estimated from correlations based on marginally relevant data. A technique employing a coupled finite element structural dynamics and control volume computational fluid dynamics has been demonstrated previously for a similar class of problems. The technique was subsequently evaluated for detonation events. Key to the calculations is the use of a Taylor Analogy Break-up (TAB) based model for predicting the aerodynamic break-up of the liquid drops in the air environment, and a dimensionless parameter for defining the chronology of the mass and momentum coupling. This paper presents results of liquid aerosolization from an explosive event.

Predicting the behavior of solid fuels in response to a fire is a complex endeavor. Heterogeneity, charring, and intumescence are a few examples of the many challenges presented by some common materials. If one desires to employ a 3-dimensional computational fluid dynamics (CFD) model for fire, an accurate solid combustion model for materials at the domain boundary is often desirable. Methods for such modeling are not currently mature, and this is a current topic of research. For some practical problems, it may be acceptable to abstract the surface combustible material as a 1-dimensional reacting boundary condition. This approach has the advantage of being a relatively simple model, and may provide acceptably accurate predictions for problems of interest. Such a model has recently been implemented in Sandia's low-Mach number CFD code for reacting flows, the SIERRA/FUEGO code. Theory for the implemented model is presented. The thermal transport component of the model is verified by approximating a 1-D conduction problem with a closed form solution. The code is further demonstrated by predicting the fire behavior of a block of burning plexiglas (PMMA). The predictions are compared to the reported data from a corresponding experimental program. The predictions are also used to evaluate the sensitivity of model parameters through a sensitivity study using the same test configuration.

A method for extracting interface trap density (DIT) from subthreshold I-V characteristics is used to analyze data on a SiC MOSFET stressed for thirty minutes at 175°C with a gate bias of-20 V. Without knowing the channel doping, the change in DIT can be calculated when referenced to an energy level correlated with the threshold voltage. © 2014 IEEE.

Resistive memory technologies, in particular redox random access memory (ReRAM), are poised as one of the most prominent emerging memory categories to replace NAND flash and fill the important need for a Storage Class Memory (SCM). This is due to low switching energy, low current switching, high speed, outstanding endurance, scalability below 10 nm, and excellent back-end-of-line CMOS compatibility. Furthermore, the analog aspects of memristors have opened the door for many novel applications such as analog math accelerators and neuromorphic computers. This paper provides an overview of resistive memory technologies and their current status, with a focus on redox RAM (ReRAM). © 2014 IEEE.

MCP detector performance at hard x-ray energies from 6 to 25 keV was recently investigated using NSLS beamline X15A at BNL. Measurements were made with an NSTec Gen-II (H-CA-65) framing camera, based on a Photonis MCP with ∼10 μm in diameter pores, ∼12 μm center-center spacing, an L/D ratio of 46, and a bias angle of 8°. The MCP characterizations were focused on (1) energy and angle dependent sensitivity, (2) energy and angle dependent spatial resolution, (3) energy dependent gain performance, and (4) energy dependent dynamic range. These measurement corroborated simulation results using a Monte Carlo model that included hard x-ray interactions and the subsequent electron cascade in the MCP. © 2014 AIP Publishing LLC.

Northern Arizona University (NAU) and the Southwestern Indian Polytechnic Institute (SIPI) conducted a pre- feasibility study for utility-scale solar power on the Jemez Pueblo in New Mexico. Student groups at NAU and SIPI analyzed four different 40-MW solar power projects to understand whether or not such plants built on tribal lands are technically and financially feasible. The NREL System Advisor Model (SAM) was employed to analyze the following four alternatives: fixed, horizontal-axis photovoltaic (PV); fixed, tilted-at-latitude PV; horizontal, single-axis tracking PV; and a solar-thermal "power tower" plant. Under supervision from faculty, the student teams predicted the energy production and net present value for the four options. This paper presents details describing the solar power plants analyzed, the results of the SAM analyses, and a sensitivity analysis of the predicted performance to key input variables. Overall, solar power plants on the Jemez Pueblo lands appear to pass the test for financial feasibility.

Predicting the behavior of solid fuels in response to a fire is a complex endeavor. Heterogeneity, charring, and intumescence are a few examples of the many challenges presented by some common materials. If one desires to employ a 3-dimensional computational fluid dynamics (CFD) model for fire, an accurate solid combustion model for materials at the domain boundary is often desirable. Methods for such modeling are not currently mature, and this is a current topic of research. For some practical problems, it may be acceptable to abstract the surface combustible material as a 1-dimensional reacting boundary condition. This approach has the advantage of being a relatively simple model, and may provide acceptably accurate predictions for problems of interest. Such a model has recently been implemented in Sandia's low-Mach number CFD code for reacting flows, the SIERRA/FUEGO code. Theory for the implemented model is presented. The thermal transport component of the model is verified by approximating a 1-D conduction problem with a closed form solution. The code is further demonstrated by predicting the fire behavior of a block of burning plexiglas (PMMA). The predictions are compared to the reported data from a corresponding experimental program. The predictions are also used to evaluate the sensitivity of model parameters through a sensitivity study using the same test configuration.

We present an actively tunable mid-infrared metamaterial operating in the strong lightmatter coupling regime. We can tune the upper polariton branch continuously over 8% of the center frequency by applying 5 V. © 2014 OSA.

We describe and analyze a novel symmetric triangular factorization algorithm. The algorithm is essentially a block version of Aasen's triangular tridiagonalization. It factors a dense symmetric matrix A as the product A = PLTLT PT , where P is a permutation matrix, L is lower triangular, and T is block tridiagonal and banded. The algorithm is the first symmetric-indefinite communication-avoiding factorization: it performs an asymptotically optimal amount of communication in a two-level memory hierarchy for almost any cache-line size. Adaptations of the algorithm to parallel computers are likely to be communication efficient as well; one such adaptation has been recently published. The current paper describes the algorithm, proves that it is numerically stable, and proves that it is communication optimal.

Experiments have been performed to determine the blowout of jet diffusion flames with pure fuels, oxygenated fuels, mixed fuels, and diluted fuels. Stability tests were conducted with pure hydrocarbons at the C2 level to determine the effects of structural differences in the fuels. Diffusion flame blowout models were also used to correlate and interpret the data. Ethylene is more stable than ethane because of the additional heat release from the double-carbon bond and ethane is more stable than dimethyl ether. The blowout pressures of mixtures of ethylene and ethane are not linear contributions of component blowout pressures. Stability tests were conducted with ethylene diluted with air and nitrogen. Since both diluents have similar properties and also have a similar density to ethylene, factors in the blowout process, such as the laminar flame speed and air-fuel mass ratio, were isolated and measured. Stability tests with hydrogen diluted with helium, nitrogen, carbon dioxide, and sulfur hexafluoride were also conducted. The diluted hydrogen diffusion flames become less stable as the complexity of the diluent increases. © 2013 Elsevier Ltd. All rights reserved.

Sandia Optical Fringe Analysis Slope Tool (SOFAST) is a mirror facet characterization system based on fringe reflection technology that has been applied to dish and heliostat mirror facet development at Sandia National Laboratories and development partner sites. The tool provides a detailed map of mirror facet surface normals as compared to design and fitted surfaces. In addition, the surface fitting process provides insights into systematic facet slope characterization, such as focal lengths, tilts, and twist of the facet. In this paper, an analysis of the sensitivities of the facet characterization outputs to variations of SOFAST input parameters is presented. The results of the sensitivity analysis provided the basis for a linear uncertainty analysis, which is also included here. Input parameters included hardware parameters and SOFAST setup variables. Output parameters included the fitted shape parameters (focal lengths and twist) and the residuals (typically called slope error). The study utilized empirical propagation of input parameter errors through facet characterization calculations to the output parameters, based on the measurement of an Advanced Dish Development System (ADDS) structural gore point-focus facet. Thus, this study is limited to the characterization of sensitivities of the SOFAST embodiment intended for dish facet characterization, using an LCD screen as a target panel. With reasonably careful setup, SOFAST is demonstrated to provide facet focal length characterization within 0.5% of actual. Facet twist is accurate within ±0.03 mrad/m. The local slope deviation measurement is accurate within ±0.05 mrad, while the global slope residual is accurate within ±0.005 mrad. All uncertainties are quoted with 95% confidence. Copyright © 2014 by ASME.

Large-scale computational models have become common tools for analyzing complex man-made systems. However, when coupled with optimization or uncertainty quantification methods in order to conduct extensive model exploration and analysis, the computational expense quickly becomes intractable. Furthermore, these models may have both continuous and discrete parameters. One common approach to mitigating the computational expense is the use of response surface approximations. While well developed for models with continuous parameters, they are still new and largely untested for models with both continuous and discrete parameters. In this work, we describe and investigate the performance of three types of response surfaces developed for mixed-variable models: Adaptive Component Selection and Shrinkage Operator, Treed Gaussian Process, and Gaussian Process with Special Correlation Functions. We focus our efforts on test problems with a small number of parameters of interest, a characteristic of many physics-based engineering models. We present the results of our studies and offer some insights regarding the performance of each response surface approximation method. © 2014 Springer International Publishing Switzerland.

It is common practice to utilize lower fidelity payloads to represent a complex aerospace payload during delivery system-with-payload, ground testing. Typically, the high fidelity payload hardware is not only costly but hard to acquire. Admittance testing can theoretically be used to experimentally model responses of a payload due to interface forces. In this paper we will consider the question, "Can the response of high fidelity payload hardware be predicted from an environmental test on a delivery system with low fidelity payloads and admittance data on all the substructures?" In theory, by acquiring the admittance models of the high and low fidelity payloads as well as the delivery system, one can adjust the measured interface responses and predict the response as if the high fidelity unit had been present in the ground test instead of the low fidelity payload. In this paper, work in progress is described to demonstrate the payload substitution capability for a specific complex aerospace structure. © The Society for Experimental Mechanics, Inc. 2014.

Abstract not provided.

In previous work, a modal test of a large beam like structure on a vibration slip table was analytically constrained to fixed base providing estimates of the first three bending modes active in the direction of slip table motion. This work extends the frequency band of the method to extract the first ten fixed base modes of the test article. All ten fixed base modal frequencies are within two percent of the truth test fixed base modes. When compared to the truth test, the estimated damping of the lower modes has large error, but at higher frequencies the estimated damping converges on the truth value. © The Society for Experimental Mechanics, Inc. 2014.

The objective is to calculate the probability, PF, that a device will fail when its inputs, x, are randomly distributed with probability density, p (x), e.g., the probability that a device will fracture when subject to varying loads. Here failure is defined as some scalar function, y (x), exceeding a threshold, T. If evaluating y (x) via physical or numerical experiments is sufficiently expensive or PF is sufficiently small, then Monte Carlo (MC) methods to estimate PF will be unfeasible due to the large number of function evaluations required for a specified accuracy. Importance sampling (IS), i.e., preferentially sampling from “important” regions in the input space and appropriately down-weighting to obtain an unbiased estimate, is one approach to assess PF more efficiently. The inputs are sampled from an importance density, pʹ (x). We present an adaptive importance sampling (AIS) approach which endeavors to adaptively improve the estimate of the ideal importance density, p* (x), during the sampling process. Our approach uses a mixture of component probability densities that each approximate p* (x). An iterative process is used to construct the sequence of improving component probability densities. At each iteration, a Gaussian process (GP) surrogate is used to help identify areas in the space where failure is likely to occur. The GPs are not used to directly calculate the failure probability; they are only used to approximate the importance density. Thus, our Gaussian process adaptive importance sampling (GPAIS) algorithm overcomes limitations involving using a potentially inaccurate surrogate model directly in IS calculations. This robust GPAIS algorithm performs surprisingly well on a pathological test function.

This paper summarizes the historical events from the identification of the Yucca Mountain site in southern Nevada in 1978 to its selection by the US Congress as the sole site to characterize for a repository for spent nuclear fuel and high-level radioactive waste in 1987. Coincident with this selection process and later site characterization, the US spent from 1977 to 2009 establishing long-term, radiation protection standards and a regulatory framework for demonstrating compliance. When first promulgated, the US Environmental Protection Agency's radiation protection standards limited cumulative release of radionuclides at a boundary ≤5 km from the edge of a generic repository over a 104-year regulatory period. But in 2001, site-specific standards for a repository at Yucca Mountain were promulgated to limit the dose to an individual at a point ≤∼18 km from the repository edge in the predominant direction of groundwater flow over a 106-year period. Also during the 33-year effort, the regulatory framework of the US Nuclear Regulatory Commission, which implemented the radiation protection standards, changed from setting performance criteria on barrier subsystem components in 1983 to the identification and technical justification for barrier performance based on a performance assessment. Also, reasonable expectation as the standard of proof for evaluating compliance was clarified. © 2013 Elsevier Ltd.

This paper summarizes the investigations conducted to characterize the geologic barrier of the Yucca Mountain disposal system. Site characterization progressed through (1) non-intrusive evaluation and borehole completions to determine stratigraphy for site identification; (2) exploration from the surface through well testing to evaluate the repository feasibility; (3) underground exploration to study coupled processes to evaluate repository suitability; and (4) reporting of experimental conclusions to support the repository compliance phase. Some of the scientific and technical challenges encountered included the evolution from a small preconstruction characterization program with much knowledge to be acquired during construction of the repository to a large characterization program with knowledge acquired prior to submission of the license application for construction authorization in June 2008 (i.e., the evolution from a preconstruction characterization program costing <$0.04×109 as estimated by the Nuclear Regulatory Commission in 1982 to a thorough characterization, design, and analysis program costing $11×109 - latter in 2010 constant dollars). Scientific understanding of unsaturated flow in fractures and seepage into an open drift in a thermally perturbed environment was initially lacking, so much site characterization expense was required to develop this knowledge. © 2013 Elsevier Ltd.

This paper summarizes the evolution of the engineered barrier design for the proposed Yucca Mountain disposal system. Initially, the underground facility used a fairly standard panel and drift layout excavated mostly by drilling and blasting. By 1993, the layout of the underground facility was changed to accommodate construction by a tunnel boring machine. Placement of the repository in unsaturated zone permitted an extended period without backfilling; placement of the waste package in an open drift permitted use of much larger, and thus hotter packages. Hence in 1994, the underground facility design switched from floor emplacement of waste in small, single walled stainless steel or nickel alloy containers to in-drift emplacement of waste in large, double-walled containers. By 2000, the outer layer was a high nickel alloy for corrosion resistance and the inner layer was stainless steel for structural strength. Use of large packages facilitated receipt and disposal of high volumes of spent nuclear fuel. In addition, in-drift package placement saved excavation costs. Options considered for in-drift emplacement included different heat loads and use of backfill. To avoid dripping on the package during the thermal period and the possibility of localized corrosion, titanium drip shields were added for the disposal drifts by 2000. In addition, a handling canister, sealed at the reactor to eliminate further handling of bare fuel assemblies, was evaluated and eventually adopted in 2006. Finally, staged development of the underground layout was adopted to more readily adjust to changes in waste forms and Congressional funding. © 2013 Elsevier Ltd.

This paper summarizes modeling of waste degradation and mobilization in performance assessments (PAs) conducted between 1984 and 2008 to evaluate feasibility, viability, and assess compliance of a repository for spent nuclear fuel and high-level radioactive waste at Yucca Mountain in southern Nevada. As understanding of the Yucca Mountain disposal system increased, the waste degradation module, or succinctly called the source-term, evolved from initial assumptions in 1984 to results based on process modeling in 2008. In early PAs, waste degradation had significant influence on calculated behavior but as the robustness of the waste container was increased and modeling of the container degradation improved, waste degradation had much less influence in later PAs. The variation of dissolved concentrations of radionuclides progressed from simple probability distributions in early PAs to functions dependent upon water chemistry in later PAs. Also, transport modeling of radionuclides in the waste, container, and invert were added in 1995; and, colloid-facilitated transport of radionuclides was added in 1998. © 2013 Elsevier Ltd.

This paper summarizes modeling of waste container degradation in performance assessments conducted between 1984 and 2008 to evaluate feasibility, viability, and assess compliance of a repository for spent nuclear fuel and high-level radioactive waste at Yucca Mountain, Nevada. As understanding of the Yucca Mountain disposal system increased, modeling of container degradation evolved from a component of the source term in 1984 to a separate module describing both container and drip shield degradation in 2008. A thermal module for evaluating the influence of higher heat loads from more closely packed, large waste packages was also introduced. In addition, a module for evaluating drift chemistry was added in later PAs to evaluate the potential for localized corrosion of the outer barrier of the waste container composed of Alloy 22, a highly corrosion-resistant nickel-chromium-tungsten-molybdenum alloy. The uncertainty of parameters related to container degradation contributed significantly to the estimated uncertainty of performance measures (cumulative release in assessments prior to 1995 and individual dose, thereafter). © 2013 Elsevier Ltd.

This paper summarizes the progression of results through four early performance assessments (PAs) conducted to support selection and to evaluate feasibility and three major PAs conducted to evaluate viability, recommend the site, and assess compliance of a repository for spent nuclear fuel and high-level radioactive waste at Yucca Mountain, Nevada. The early PAs in 1984, 1991, 1993, and 1995 evaluated cumulative release over 104 yr at a 10-km or 5-km boundary as specified in the draft and final 1985 radiation protection standard, respectively. During the early PAs, the fission products 99Tc, 129I, and activation products 14C, and 36Cl were identified as important radionuclides at the beginning of the regulatory period. The actinide, 237Np, often dominated at the end of the regulatory period. Package and repository design options were evaluated during the early PAs but modeling did not identify strong preferences. In 1992 Congress mandated a change to a dose measure. Dose at a 20-km boundary from the repository was evaluated through 106 yr for the undisturbed scenario class via the groundwater pathway for the Congressionally mandated viability assessment in 1998. For the assessment for the site recommendation in 2000, doses from igneous eruption dominated in the first ∼3000 yr, doses from igneous intrusion between ∼3000 yr and ∼40,000 yr, and doses from the undisturbed scenario class through 106 yr. The 2008 compliance assessment for the license application incorporated the influence of the seismic scenario class on waste package performance. The compliance assessment found that doses from the igneous intrusive scenario class and the combined undisturbed and seismic scenario class were important contributors at the ∼18-km boundary. In the compliance PA, 99Tc and 129I fission products and 14C activation product were important in the first 104 yr. Beyond 104 yr, actinides 239Pu, 242Pu, 237Np, and 238U decay product 226Ra were important. In all PAs, parameters of the natural barrier were important, but in the three latter PAs, the slow degradation of the large, in-drift container had an important role in explaining the uncertainty in the peak dose. © 2013 Elsevier Ltd.

The use of nanostructured materials in lithium-ion batteries is reviewed with discussion of commercialization or potential for commercialization. Nanomaterials have the advantages of shorter distances for transport of ions or electrons and accommodation of strains associated with lithium insertion. These advantages enable the use of high-capacity electrode materials and offer the possibility of improved rate capability or cycle life. Nanostructuring has enabled the use of inexpensive, low-conductivity electrode materials, such as lithium iron phosphate and lithium titanate, and has resulted in the commercialization of batteries with these materials. Conversion-type electrode materials and lithium alloys, which offer significantly higher charge-storage capacity compared to conventional intercalation-type materials, have also been enabled by nanotechnology. The use of carbon nanostructures and carbon-based nanocomposites in lithium-ion electrodes is also discussed. © 2014 Elsevier B.V. All rights reserved..

Heliostats are structures that track the sun and reflect sunlight to a centrally located receiver on top of a tower to produce heat for electricity generation. Commercial power towers can consist of thousands of heliostats that are subject to wind-induced loads, vibration, and gravity-induced sag. This paper presents modal tests of a heliostat located at the National Solar Thermal Test Facility (NSTTF) at Sandia National Labs in Albuquerque, New Mexico. The heliostat was instrumented with 22 accelerometers, 4 strain gauges, and 3 wind anemometers to examine manually and wind-induced vibrations of the structure. Data acquisition software was developed to provide real-time monitoring of the wind velocity, heliostat strain, mode shapes, and natural frequencies which will be used to validate finite element models of the heliostat. The ability to test and monitor full-scale heliostats under dynamic wind loads will provide a new level of characterization and understanding compared to previous tests that utilized scaled models in wind-tunnel tests. Also, the development of validated structural dynamics models will enable improved designs to mitigate the impacts of dynamic wind loads on structural fatigue and optical performance. © The Society for Experimental Mechanics 2014.

Recently, a new experimental based substructure formulation was introduced, called Modal Constraint for Fixture and Subsystem (MCFS). This method reduces ill-conditioning by imposing constraints on substructure modal coordinates instead of the physical interface coordinates. The experimental substructure is tested in a free-free configuration, and the interface is exercised by attaching a flexible transmission simulator. An analytical representation of the fixture is then used to subtract its effects from the experimental substructure. The resulting experimental component is entirely modal based, and can be attached in an indirect manner to other substructures using MCFS. In contrast, this work presents a formulation in which the analytical representation of the transmission simulator is in the form of a Craig-Bampton (CB) substructure including fixed-interface modal coordinates and physical interface coordinates. The negative of the analytical representation of the transmission simulator is constrained to the experimental modal model using MCFS by eliminating the fixed-interface modal coordinates. The resulting experimental substructure contains a hybrid set of coordinates, including modal coordinates and the physical interface degrees of freedom, analogous to a CB representation. This new formulation offers the improved conditioning of the MCFS approach, but can be directly connected through the physical interface coordinates to other finite element based substructures. © The Society for Experimental Mechanics, Inc. 2014.

In previous work, a modal test of a large beam like structure on a vibration slip table was analytically constrained to fixed base providing estimates of the first three bending modes active in the direction of slip table motion. This work extends the frequency band of the method to extract the first ten fixed base modes of the test article. All ten fixed base modal frequencies are within two percent of the truth test fixed base modes. When compared to the truth test, the estimated damping of the lower modes has large error, but at higher frequencies the estimated damping converges on the truth value. © The Society for Experimental Mechanics, Inc. 2014.

This paper presents an example of the transmission simulator method of experimental dynamic substructuring combining two substructures of the Substructures Focus Group's test bed, the Ampair 600 Wind Turbine. The two substructures of interest are the hub-and-blade assembly and the tower assembly that remains after the hub is removed. The hub-and-blade substructure was developed from elastic modes of a free-free test of the hub and blades, and rigid body modes were constructed from measured mass properties. Elastic and rigid body modes were extracted from experimental data for the tower substructure. A bladeless hub was attached to the tower to serve as the transmission simulator for this substructure. Modes up to the second bending mode of the blades and tower were extracted. Substructuring calculations were then performed using the transmission simulator method, and a model of the full test bed was derived. The combined model was compared to truth data from a test on the full turbine. © The Society for Experimental Mechanics, Inc. 2014.

The need to process streaming data, which arrives continuously at high-volume in real-time, arises in a variety of contexts including data produced by experiments, collections of environmental or network sensors, and running simulations. Streaming data can also be formulated as queries or transactions which operate on a large dynamic data store, e.g. a distributed database. We describe a lightweight, portable framework named PHISH which provides a communication model enabling a set of independent processes to compute on a stream of data in a distributed-memory parallel manner. Datums are routed between processes in patterns defined by the application. PHISH provides multiple communication backends including MPI and sockets/ZMQ. The former means streaming computations can be run on any parallel machine which supports MPI; the latter allows them to run on a heterogeneous, geographically dispersed network of machines. We illustrate how streaming MapReduce operations can be implemented using the PHISH communication model, and describe streaming versions of three algorithms for large, sparse graph analytics: triangle enumeration, sub-graph isomorphism matching, and connected component finding. We also provide benchmark timings comparing MPI and socket performance for several kernel operations useful in streaming algorithms. © 2014 Elsevier Inc. All rights reserved.

Sandia National Laboratories has developed an experimental procedure for characterizing the input and transfer impedance functions of flight test units. Admittance relations that describe the force-acceleration relations can be derived from this procedure and used for a variety of purposes ranging from environmental response prediction to substructure coupling and numerical model validation. The theoretical developments described herein have been developed using substructure coupling methods. The method allows characterization in six degrees of freedom as well as the removal of fixture effects from the measured frequency response functions. This paper describes the basic theory, presents a numerical validation of the procedure, and illustrates a complete experimental example. © The Society for Experimental Mechanics, Inc. 2014.

Extensive work has been carried out by the U.S. Department of Energy (DOE) in the development of a proposed geologic repository at Yucca Mountain (YM), Nevada, for the disposal of high-level radioactive waste. In support of this development and an associated license application to the U.S. Nuclear Regulatory Commission (NRC), the DOE completed an extensive performance assessment (PA) for the proposed YM repository in 2008. This presentation describes uncertainty and sensitivity analysis results for the early waste package failure scenario class and the early drip shield failure scenario class obtained in the 2008 YM PA. The following topics are addressed: (i) engineered barrier system conditions, (ii) release results for the engineered barrier system, unsaturated zone, and saturated zone, (iii) dose to the reasonably maximally exposed individual (RMEI) specified in the NRC regulations for the YM repository, and (iv) expected dose to the RMEI. The present article is part of a special issue of Reliability Engineering and System Safety devoted to the 2008 YM PA; additional articles in the issue describe other aspects of the 2008 YM PA. © 2013 Elsevier Ltd.

We consider the problem of designing (or augmenting) an electric power system at a minimum cost such that it satisfies the N-k-survivability criterion. This survivability criterion is a generalization of the well-known N-k criterion, and it requires that at least 1-j fraction of the steady-state demand be met after failures of j components, for j=0,1,,k. The network design problem adds another level of complexity to the notoriously hard contingency analysis problem, since the contingency analysis is only one of the requirements for the design optimization problem. We present a mixed-integer programming formulation of this problem that takes into account both transmission and generation expansion. We propose an algorithm that can avoid combinatorial explosion in the number of contingencies, by seeking vulnerabilities in intermediary solutions and constraining the design space accordingly. Our approach is built on our ability to identify such system vulnerabilities quickly. Our empirical studies on modified instances of the IEEE 30-bus and IEEE 57-bus systems show the effectiveness of our methods. We were able to solve the transmission and generation expansion problems for k=4 in approximately 30 min, while other approaches failed to provide a solution at the end of 2 h. © 2014 IEEE.

The transmission simulator method of experimental dynamic substructuring has the capability to couple substructures with continuous connections. A hardware example with continuous connections is presented in which the method is used to couple an experimental substructure with a finite element substructure to predict full system response. The predicted response is compared with frequency response functions measured on the full system hardware. The experimental substructure captures the motion of a component packed in foam. This is coupled to a finite element model of a cylindrical metal case which contains the foam and is attached through a flange to a plate and beam structure. © The Society for Experimental Mechanics, Inc. 2014.

Quantitative measurements of the total radiative heat transfer from high-pressure diesel spray flames under a range of conditions will enable engine modelers to more accurately understand and predict the effects of advanced combustion strategies on thermal loads and efficiencies. Moreover, the coupling of radiation heat transfer to soot formation processes and its impact on the temperature field and gaseous combustion pollutants is also of great interest. For example, it has been shown that reduced soot formation in diesel engines can result in higher flame temperatures (due to less radiative cooling) leading to greater NOx emissions. Whereas much of the previous work in research engines has evaluated radiation based on two- or three-color detection with limited spatial resolution, this work uses an imaging spectrometer in conjunction with a constant volume pre-burn vessel to quantify soot temperatures, optical thickness, and total radiation with spatial and spectral (360-700 nm) resolution along the flame axis. Sprays of n-dodecane were injected from a single hole, 90-m diameter orifice into a range of ambient temperature conditions while holding ambient density and oxygen concentration constant at 22.8 kg/m 3 and 15%, respectively. Soot surface temperatures derived by fitting a model to the spectral data were within 10 K of the stoichiometric computed adiabatic flame temperature for lower ambient temperature, lower sooting cases. As ambient temperature was increased, leading to greater soot formation, the spectrally derived peak soot temperature decreased relative to the calculated adiabatic flame temperature. For the highest ambient temperature case (1200 K), the spectrally derived soot surface temperature was more than 140 K lower than the calculated adiabatic flame temperature. Values of optical thickness, KL, were also derived by fitting the spectral data and these values were compared to extinction based KL measurements. The spectrally derived KL was within a factor of about 1.5 from the extinction based data for the higher sooting cases. Under lower sooting conditions the differences were larger. For the lowest sooting case, the radiant fraction-defined as the fraction of energy emitted by radiation relative to the chemical energy available from the fuel injection-was negligible at less than 0.01%. The highest temperature flame with the greatest optical thickness resulted in a radiant fraction of 0.46%. Copyright © 2014 SAE International.

Abstract not provided.

A simple demonstration of nonlocality in a heterogeneous material is presented. By analysis of the microscale deformation of a two-component layered medium, it is shown that nonlocal interactions necessarily appear in a homogenized model of the system. Explicit expressions for the nonlocal forces are determined. The way these nonlocal forces appear in various nonlocal elasticity theories is derived. The length scales that emerge involve the constituent material properties as well as their geometrical dimensions. A peridynamic material model for the smoothed displacement field is derived. It is demonstrated by comparison with experimental data that the incorporation of nonlocality in modeling improves the prediction of the stress concentration in an open-hole tension test on a composite plate. © 2014 Mathematical Sciences Publishers.

Achieving high spatial resolutions for imaging with terahertz (THz) waves requires near-field probes, such as a sub-wavelength aperture probe. Bethe's theory of transmission through a sub-wavelength aperture of size a predicts that the transmitted electric field scales as Eαa3. This strong dependence limits the size of apertures that can be employed and hence the spatial resolution. This dependence however changes for the evanescent field components in very close proximity (∼1μm for THz waves) to the aperture, as shown by electromagnetic simulations. To exploit this effect in a THz near-field probe, we developed a photoconductive THz near-field detector structure, which incorporates a thinned photo-conductive detector region and a distributed Bragg reflector between the detector and the aperture plane. Near-field probes are manufactured with different aperture sizes to investigate transmission of THz pulses through apertures as small as 3μm. The experimental results confirm that the transmitted field amplitude, and therefore the sensitivity, increases by about one order of magnitude for the new probes. A 3μm aperture probe with a spatial resolution of λ/100 at 1THz is demonstrated.. © 2014 SPIE.

A hybrid fs/ps pure-rotational CARS scheme is demonstrated in the product gases of premixed hydrogren/air and ethylene/air flat flames. Near-transform-limited, broadband femtosecond pump and Stokes pulses impulsively prepare a rotational Raman coherence, which is later probed by a high-energy, frequency-narrow picosecond pulse, generated by sum-frequency mixing of linearly chirped broadband pulses with conjugate temporal phase. Spectral fitting is demonstrated for both shot-averaged and single-laser-shot spectra. Measurement accuracy is quantified by comparison to adiabatic-equilibrium calculations for the hydrogen/air flames, and by comparison to nanosecond CARS measurements for the ethylene/air flames. Temperature-measurement precision is 1-3% and O2/N2 precision is 2-10% based on histograms constructed from 1000 single-shot measurements acquired at a data rate of 1 kHz. These results indicate that hybrid fs/ps rotational CARS is a quantitative tool for kHz-rate combustion temperature/species data.

This study explores the use of two conventional ignition improvers, 2-ethylhexyl nitrate (EHN) and di-tert-butyl peroxide (DTBP), to enhance the autoignition of the regular gasoline in an homogeneous charge compression ignition (HCCI) engine at naturally aspirated and moderately boosted conditions (up to 180 kPa absolute) with a constant engine speed of 1200 rpm. The results showed that both EHN and DTBP are very effective for reducing the intake temperature (Tin) required for autoignition and for enhancing stability to allow a higher charge-mass fuel/air equivalence ratio (φ{symbol}m). On the other hand, the addition of these additives can also make the gasoline too reactive at some conditions, so significant exhaust gas recirculation (EGR) is required at these conditions to maintain the desired combustion phasing. Thus, there is a trade-off between improving stability and reducing the oxygen available for combustion when using ignition improvers to extend the high-load limit. Because previous works have shown that partial fuel stratification (PFS) can be applied with more reactive fuels to reduce the heat release rate to allow higher loads or more advanced combustion timing without knock, the potential of the ignition improvers to allow effective PFS was also explored over the same range of intake pressures. The effect of the additives on NOx emissions was also studied. The results showed that NOx emissions increase with increased EHN concentration but are not affected by DTBP. This work indicates that conventional ignition improvers can effectively enhance the HCCI autoignition reactivity of conventional gasoline at naturally aspirated and modestly boosted operations, offering significant benefits for HCCI engines. © 2014 SAE International.

The accumulation of soil on photovoltaic (PV) modules may introduce a spectral loss due to the color profile of the accumulated material. In order to compare the spectral and total losses experienced by a cell, soil analogs were formulated to contain common mineral pigments (Fe-2O 3 and göthite) with previously developed 'standard grime' mixtures. These mixtures simulated a wide range of desert soil colors and were applied to glass test coupons. The light transmission through the deposited film was evaluated by UV/vis/NIR spectroscopy and by placing the coupon over a test cell in a 1-sun simulator and quantum efficiency test stand. Distinct peaks in the 300-600-nm range were observed by UV/vis/NIR spectroscopy corresponding to the Fe 2 O3 and göthite. Approximately analogous features were noted in the QE measurement. Overall comparisons were made by integrating the response of a soiled coupon relative to a clean reference. Soils rich in red pigments (Fe2 O3) caused a greater integrated response than soils rich in yellow pigment (göthite). The yellow soils caused a greater attenuation in a specific region of the spectrum (300-450 nm), which may have significant implications to specific devices, such as multijunction and CdTe technologies. © 2011-2012 IEEE.

In the design of high-hydrogen content gas turbines for power generation, ashback of the turbulent ame by propagation through the low velocity boundary layers in the premix- ing region is an operationally dangerous event. Predictive models that could capture the onset of ashback would be indispensable in gas turbine design. For this purpose, modeling of the ashback process using the large eddy simulation (LES) approach is considered here. In particular, the goal is to understand the modeling requirements for predicting ashback in confined goemetries. The ow configuration considered is a turbulent channel ow, for which high-fidelity direct numerical simulation (DNS) data already exists. A suite of LES calculations with different model formulations and filterwidths is considered. It is shown that LES predicts certain statistical properties of the ame front reasonably well, but fails to capture the propagation velocity accurately. It is found that the ashback process is invariant to changes in the initial conditions and additional near-wall grid refinement but the LES filterwidth as well as the subfilter models are found to be important even when the turbulence is almost fully resolved. From the computations, it is shown that for an LES model to predict ashback, suffcient resolution of the near-wall region, proper represen- tation of the centerline acceleration caused by ame blockage, and appropriate modeling of the propagation of a wrinkled ame front near the center of the channel are considered the critical requirements.

In this paper we show that a wide variety of composite structures can be obtained from structuring with multiaxial fields. The properties of these composites are highly responsive to field structuring and so significant increases in a variety of properties can be obtained. These composites have application as high-strain actuators, strain and temperature sensors, chemical sensors, and as thermal interface materials. We discuss these issues and provide a general summary of the research we have done in this area. Copyright © Materials Research Society 2014.

Two model-based algorithms for edge detection in spectral imagery are developed that specifically target capturing intrinsic features such as isoluminant edges that are characterized by a jump in color but not in intensity. Given prior knowledge of the classes of reflectance or emittance spectra associated with candidate objects in a scene, a small set of spectral-band ratios, which most profoundly identify the edge between each pair of materials, are selected to define a edge signature. The bands that form the edge signature are fed into a spatial mask, producing a sparse joint spatiospectral nonlinear operator. The first algorithm achieves edge detection for every material pair by matching the response of the operator at every pixel with the edge signature for the pair of materials. The second algorithm is a classifier-enhanced extension of the first algorithm that adaptively accentuates distinctive features before applying the spatiospectral operator. Both algorithms are extensively verified using spectral imagery from the airborne hyperspectral imager and from a dots-in-a-well midinfrared imager. In both cases, the multicolor gradient (MCG) and the hyperspectral/spatial detection of edges (HySPADE) edge detectors are used as a benchmark for comparison. The results demonstrate that the proposed algorithms outperform the MCG and HySPADE edge detectors in accuracy, especially when isoluminant edges are present. By requiring only a few bands as input to the spatiospectral operator, the algorithms enable significant levels of data compression in band selection. In the presented examples, the required operations per pixel are reduced by a factor of 71 with respect to those required by the MCG edge detector. © 1992-2012 IEEE.

Simulations are used to explore the possibility of achieving breakdown voltage scaling using deep acceptors in the buffer for AlGaN/GaN HEMTs. The existence of an optimal range of deep level acceptor density (1017 cm-3), for which the electric field shows the most uniform distribution over the entire Lgd is demonstrated. The peak electric field can be capped off at a certain value, which can be engineered using deep level defects to be less than the critical electric field for GaN or the critical field for punch-through, whichever is lower. Following the saturation in peak electric field, the additional applied voltage spreads across the device access region. Thus, precise control of defect incorporation in the GaN buffer is shown to be a key factor in achieving high breakdown voltage HEMTs with improved unipolar figure of merit. A novel scheme for the source and drain contacts, using shallow mesa etch and partial mesa sidewall oxidation to increase the allowed range of variation in optimal acceptor density to achieve uniform electric field distribution is presented. © 2013 Elsevier Ltd. All rights reserved.

The chemical potential of water may play an important role in adsorption and capillary condensation of water under multiphase conditions at geologic CO2 storage sites. Injection of large volumes of anhydrous CO 2 will result in changing values of the chemical potential of water in the supercritical CO2 phase. We hypothesize that the chemical potential will at first reflect the low concentration of dissolved water in the dry CO2. As formation water dissolves into and is transported by the CO2 phase, the chemical potential of water will increase. We present a pore-scale model of the CO2-water interface or menisci configuration based on the augmented Young-Laplace equation, which combines adsorption on flat surfaces and capillary condensation in wedge-shaped pores as a function of chemical potential of water. The results suggest that, at a given chemical potential for triangular and square pores, liquid water saturation will be less in the CO2-water system under potential CO2 sequestration conditions relative to the air-water vadose zone system. The difference derives from lower surface tension of the CO2-water system and thinner liquid water films, important at pore sizes <1 × 10 -6 m, relative to the air-water system. Water movement due to capillary effects will likely be minimal in reservoir rocks, but still may be important in finer grained, clayey caprocks, where very small pores may retain water and draw water back into the system via adsorption and capillary condensation, if dry-out and then rewetting were to occur. © 2014. American Geophysical Union. All Rights Reserved.

Abstract not provided.

Because both the accuracy and spatial resolution of digital image correlation (DIC) are directly related to the field-of-view and the number of pixels, it is sometimes advantageous to have a tight view for high resolution measurements and a wide view for overall object deformation. This approach will be demonstrated using a high-speed measurement of the deformation and strain of a riveted thin plate with an explosive loading. Overall plate deformation was provided by a wide-view stereo system, while a tight view of a section of the rivets was imaged with a second stereo pair to measure the strain around the rivet holes. The challenge is creating a speckle pattern which will work with both systems without creating holes in the overall measurement data. This was accomplished by creating a black/white course pattern for the wide view and a black/grey/white fine pattern for the tight view. The grey speckles were sized such that they are not resolved by the wide view and therefore do not compromise the full-field measurement. Details of the process and example results will be presented. © The Society for Experimental Mechanics, Inc. 2014.

Advances in multiple view computer vision techniques have made it possible to make highly accurate three-dimensional (3D) measurements using calibrated stereo image systems. Recent experiments conducted at Sandia National Laboratories have demonstrated the feasibility of applying these techniques on an X-Ray system. Acquiring measurements from stereo image systems, be it visible or x-ray, require the estimation of the system's intrinsic and extrinsic parameters via a calibration process. There are several calibration methods depending on the system's configuration and its intended use. In most cases, one or more image pairs of a calibration artifact such as a 3D object of known dimension or a 2D target board are processed to estimate the system's calibration parameters. For this paper, methods based on both types of calibration artifacts will be discussed along with experimental results. © The Society for Experimental Mechanics, Inc. 2014.

Weak link (WL)/strong link (SL) systems are important parts of the overall operational design of high-consequence systems. In such designs, the SL system is very robust and is intended to permit operation of the entire system under, and only under, intended conditions. In contrast, the WL system is intended to fail in a predictable and irreversible manner under accident conditions and render the entire system inoperable before an accidental operation of the SL system. The likelihood that the WL system will fail to deactivate the entire system before the SL system fails (i.e., degrades into a configuration that could allow an accidental operation of the entire system) is referred to as probability of loss of assured safety (PLOAS). Representations for PLOAS for situations in which both link physical properties and link failure properties are time-dependent are derived and numerically evaluated for a variety of WL/SL configurations, including PLOAS defined by (i) failure of all SLs before failure of any WL, (ii) failure of any SL before failure of any WL, (iii) failure of all SLs before failure of all WLs, and (iv) failure of any SL before failure of all WLs. The indicated formal representations and associated numerical procedures for the evaluation of PLOAS are illustrated with example analyses involving (i) only aleatory uncertainty, (ii) aleatory uncertainty and epistemic uncertainty, and (iii) mixtures of aleatory uncertainty and epistemic uncertainty. © 2013 Elsevier Ltd.

The time-correlated pulse-height technique can distinguish multiplying (special nuclear material) from non-multiplying sources. The technique relies upon the measurement of correlated photon-neutron pairs using organic liquid scintillation detectors. For such interactions, the distribution of measured neutron recoil energy versus the time-of-flight difference between correlated photons and neutrons are imprinted with the fission chain dynamics of the source. The theoretical time-of-arrival assuming the photons and neutrons are created in the same fission is calculated. Correlated pairs with longer time-of-arrival indicate delays caused by self-induced fission chains in a multiplying source. For the specific circumstances of simulated measurements of 25.4 kg of highly enriched uranium at 50 cm source to detector distance, correlated pairs from fission chains can arrive upwards of 40 ns later than correlated pairs with the same neutron energies from non-multiplying sources like 252Cf at the same source detector distance. The use of detectors with ns scale time resolution and the use of pulse digitization allows for the distinction of these events. This method has been used successfully in the past to measure a variety of plutonium-bearing samples. The particle transport code MCNPX-PoliMi has been used to simulate and validate these measurements as well. Due to the much lower signature emission rate of 235U, this technique has not yet been used to measure the presence of highly enriched uranium. In this work we therefore explore the use of the time-correlated pulse-height technique with the introduction of an interrogating neutron source to stimulate fission. The applicability of 252Cf, AmLi and a DD generator neutron sources is explored in a series of simulations. All three sources are viable options with their own pros and cons with the choice of appropriate source depending upon the intended application. The TCPH technique is envisioned as a viable measurement solution of special nuclear material in situations in which the presence of shielding material disqualifies the use of passive gamma spectroscopy or gamma spectroscopy reveals classified information on the special nuclear material's isotopic composition. © 2014 Elsevier Ltd. All rights reserved.

The development and application of optically accessible engines to further our understanding of in-cylinder combustion processes is reviewed, spanning early efforts in simplified engines to the more recent development of high-pressure, highspeed engines that retain the geometric complexities of modern production engines. Limitations of these engines with respect to the reproduction of realistic metal test engine characteristics and performance are identified, as well as methods that have been used to overcome these limitations. Lastly, the role of the work performed in these engines on clarifying the fundamental physical processes governing the combustion process and on laying the foundation for predictive engine simulation is summarized.

A major theme in thermoelectric research is based on controlling the formation of nanostructures that occur naturally in bulk intermetallic alloys through various types of thermodynamic phase transformation processes (He et al., 2013). The question of how such nanostructures form and why they lead to a high thermoelectric figure of merit (zT) are scientifically interesting and worthy of attention. However, as we discuss in this opinion, any processing route based on thermodynamic phase transformations alone will be difficult to implement in thermoelectric applications where thermal stability and reliability are important. Attention should also be focused on overcoming these limitations through advanced post-processing techniques.

Model form error of the type considered here is error due to an approximate or incorrect representation of physics by a computational model. Typical approaches to adjust a model based on observed differences between experiment and prediction are to calibrate the model parameters utilizing the observed discrepancies and to develop parameterized additive corrections to the model output. These approaches are generally not suitable if significant physics is missing from the model and the desired quantities of interest for an application are different than those used for calibration. The approach developed here is to build a corrected surrogate solver through a multi- step process: 1) Sampled simulation results are used to develop a surrogate computational solver that maintains the overall conservative principles of the unmodified governing equations, 2) the surrogate solver is applied to candidate linear and non-linear corrector terms to develop corrections that are consistent with the original conservative principles, 3) constant multipliers on the these terms are calibrated using the experimental observations, and 4) the resulting surrogate solver is used to predict application response for the quantity of interest. This approach and several other calibration-based approaches were applied to an example problem based on the diffusive Burgers' equation. While all the approaches provided some model correction when the measure/calibration quantity was the same as that for an application, only the present approach was able to adequately correct the CompSim results when the prediction quantity was different from the calibration quantity.

Abstract not provided.

A method is investigated to reduce the number of numerical parameters in a material model for a solid. The basis of the method is to detect interdependencies between parameters within a class of materials of interest. The method is demonstrated for a set of material property data for iron and steel using the Johnson-Cook plasticity model.

In the summer of 2020, the National Aeronautics and Space Administration (NASA) plans to launch a spacecraft as part of the Mars 2020 mission. One option for the rover on the proposed spacecraft uses a Multi-Mission Radioisotope Thermoelectric Generator (MMRTG) to provide continuous electrical and thermal power for the mission. An alternative option being considered is a set of solar panels for electrical power with up to 80 Light-Weight Radioisotope Heater Units (LWRHUs) for local component heating. Both the MMRTG and the LWRHUs use radioactive plutonium dioxide. NASA is preparing an Environmental Impact Statement (EIS) in accordance with the National Environmental Policy Act. The EIS will include information on the risks of mission accidents to the general public and on-site workers at the launch complex. This Nuclear Risk Assessment (NRA) addresses the responses of the MMRTG or LWRHU options to potential accident and abort conditions during the launch opportunity for the Mars 2020 mission and the associated consequences. This information provides the technical basis for the radiological risks of both options for the EIS.

In this report, measurements of the prompt radiation-induced conductivity (RIC) in 3 mil samples of Pyralux® are presented as a function of dose rate, pulse width, and applied bias. The experiments were conducted with the Medusa linear accelerator (LINAC) located at the Little Mountain Test Facility (LMTF) near Ogden, UT. The nominal electron energy for the LINAC is 20 MeV. Prompt conduction current data were obtained for dose rates ranging from ~2 x 10⁹ rad(Si)/s to ~1.1 x 10¹¹ rad(Si)/s and for nominal pulse widths of 50 ns and 500 ns. At a given dose rate, the applied bias across the samples was stepped between -1500 V and 1500 V. Calculated values of the prompt RIC varied between 1.39x10^-8 Ω^-1 · m^-1 and 2.67x10^-7 Ω^-1 · m^-1 and the prompt RIC coefficient varied between 1.25x10^-18 Ω^-1 · m^-1/(rad/s) and 1.93x10^-17 Ω^-1 · m^-1/(rad/s).

A simple method for experimentally determining thermodynamic quantities for flow battery cell reactions is presented. Equilibrium cell potentials, temperature derivatives of cell potential (dE/dT), Gibbs free energies, and entropies are reported here for all-vanadium, iron–vanadium, and iron–chromium flow cells with state-of-the-art solution compositions. Proof is given that formal potentials and formal temperature coefficients can be used with modified forms of the Nernst Equation to quantify the thermodynamics of flow cell reactions as a function of state-of-charge. Such empirical quantities can be used in thermo-electrochemical models of flow batteries at the cell or system level. In most cases, the thermodynamic quantities measured here are significantly different from standard values reported and used previously in the literature. The data reported here are also useful in the selection of operating temperatures for flow battery systems. Because higher temperatures correspond to lower equilibrium cell potentials for the battery chemistries studied here, it can be beneficial to charge a cell at higher temperature and discharge at lower temperature. As a result, proof-of-concept of improved voltage efficiency with the use of such non-isothermal cycling is given for the all-vanadium redox flow battery, and the effect is shown to be more pronounced at lower current densities.

A simple demonstration of nonlocality in a heterogeneous material is presented. By analysis of the microscale deformation of a two-component layered medium, it is shown that nonlocal interactions necessarily appear in a homogenized model of the system. Explicit expressions for the nonlocal forces are determined. The way these nonlocal forces appear in various nonlocal elasticity theories is derived. The length scales that emerge involve the constituent material properties as well as their geometrical dimen- sions. A peridynamic material model for the smoothed displacement eld is derived. It is demonstrated by comparison with experimental data that the incorporation of non- locality in modeling dramatically improves the prediction of the stress concentration in an open hole tension test on a composite plate.

For over two decades the dominant means for enabling portable performance of computational science and engineering applications on parallel processing architectures has been the bulk-synchronous parallel programming (BSP) model. Code developers, motivated by performance considerations to minimize the number of messages transmitted, have typically pursued a strategy of aggregating message data into fewer, larger messages. Emerging and future high-performance architectures, especially those seen as targeting Exascale capabilities, provide motivation and capabilities for revisiting this approach. In this paper we explore alternative configurations within the context of a large-scale complex multi-physics application and a proxy that represents its behavior, presenting results that demonstrate some important advantages as the number of processors increases in scale.

Abstract not provided.