Publications

The use of uniaxial strain ramp loading experiments to measure strength at extremely high strain rates is discussed. The technique is outlined and issues associated with it are examined. Results for 6061-T6 aluminum are presented that differ from the conventional view of strain rate sensitivity in aluminum alloys. ©2010 Society for Experimental Mechanics Inc.

We develop and study the high-order conservative and monotone optimization-based remap (OBR) of a scalar conserved quantity (mass) between two close meshes with the same connectivity. The key idea is to phrase remap as a global inequality-constrained optimization problem for mass fluxes between neighboring cells. The objective is to minimize the discrepancy between these fluxes and the given high-order target mass fluxes, subject to constraints that enforce physically motivated bounds on the associated primitive variable (density). In so doing, we separate accuracy considerations, handled by the objective functional, from the enforcement of physical bounds, handled by the constraints. The resulting OBR formulation is applicable to general, unstructured, heterogeneous grids. Under some weak requirements on grid proximity, but not on the cell types, we prove that the OBR algorithm is linearity preserving in one, two and three dimensions. The paper also examines connections between the OBR and the recently proposed flux-corrected remap (FCR), Liska et al. [1]. We show that the FCR solution coincides with the solution of a modified version of OBR (M-OBR), which has the same objective but a simpler set of box constraints derived by using a "worst-case" scenario. Because M-OBR (FCR) has a smaller feasible set, preservation of linearity may be lost and accuracy may suffer for some grid configurations. Our numerical studies confirm this, and show that OBR delivers significant increases in robustness and accuracy. Preliminary efficiency studies of OBR reveal that it is only a factor of 2.1 slower than FCR, but admits 1.5 times larger time steps. © 2011 Elsevier Inc.

Radioactive iodine, 129I, a component of spent nuclear fuel, is of particular concern due to its extremely long half-life, its potential mobility in the environment and its effects on human health. In the spent fuel reprocessing scheme under consideration, the 129I is released in gaseous form and collected using Ag-loaded zeolites such as Ag-mordenite. The 129I can react with the Ag to form insoluble AgI. We have investigated the use of low temperature-sintering glass powders mixed with either AgI or AgI-zeolite to produce dense waste forms that can be processed at 500°C, where AgI volatility is low. These mixtures can contain up to 20 wt% crushed AgI-mordenite or up to 50 wt% AgI. Both types of waste forms were found to have the high iodine leach resistance in these initial studies.

This work uses a bifurcation approach to develop theoretical predictions for deformation band formation for a suite of true triaxial tests on Castlegate sandstone. In particular, the influence of the intermediate principal stress on strain localization is examined. Using common simplifying assumptions (localization occurs at peak stress, and the failure surface is similar to the yield surface), theoretical predictions captured the overall trends observed experimentally. However, agreement between predicted and observed band orientations for individual specimens was varied. This highlights the importance of detailed data analyses to accurately determine key material parameter values at the inception of localization.

A low-hazard approach is presented to prepare metallographic cross-sections of moisture-sensitive battery components. The approach is tailored for evaluation of thermal (molten salt) batteries composed of thin pressed-powder pellets, but has general applicability to other battery electrochemistries. Solution-cast polystyrene is used to encapsulate cells before embedding in epoxy. Nonaqueous grinding and polishing are performed in an industrial dry room to increase throughput. Lapping oil is used as a lubricant throughout grinding. Hexane is used as the solvent throughout processing; occupational exposure levels are well below the limits. Light optical and scanning electron microscopy on cross-sections are used to analyse a thermal battery cell. Spatially resolved X-ray diffraction on oblique angle cut cells complement the metallographic analysis. Published 2011. This article is a US Government work and is in the public domain in the USA.

A new Kolsky tension bar has been re-designed and developed at Sandia National Laboratories, CA. The new design uses the concept that a solid striker is fired to impact an end cap attached to the open end of the gun barrel to generate dynamic tensile loading. The gun barrel here serves as part of the loading device. The incident bar that is connected to the gun barrel and the transmission bar follow the design similar to the Kolsky compression bar. The bar supporting and aligning systems are the same as those in the Kolsky compression bar design described by Song et al (2009 Meas. Sci. Technol. 20 115701). Due to the connection complication among the gun barrel, bars and specimen, stress-wave propagation in the new Kolsky tension bar system is comprehensively analyzed. Based on the stress-wave analysis, the strain gage location on the incident bar needs to be carefully determined. A highly precise laser-beam measurement system is recommended to directly measure the displacement of the incident bar end. Dynamic tensile characterization of a 4330-V steel using this new Kolsky tension bar is presented as an example. © 2011 IOP Publishing Ltd.

There occasionally occur situations in field measurements where direct optical access to the area of interest is not possible. In these cases the borescope is the standard method of imaging. Furthermore, if shape, displacement, or strain are desired in these hidden locations, it would be advantageous to be able to do digital image correlation (DIC) through the borescope. This paper will present the added complexities and errors associated with imaging through a borescope for DIC. Discussion of non-radial distortions and their effects on the measurements, along with a possible correction scheme will be discussed.

Qualification vibration tests are routinely performed on prototype hardware. Model validation cannot generally be done from the qualification vibration test because of multiple uncertainties, particularly the uncertainty of the boundary condition. These uncertainties can have a dramatic effect on the modal parameters extracted from the data. It would be valuable if one could extract a modal model of the test article with a known boundary condition from the qualification vibration test. This work addresses an attempt to extract fixed base modes on a 1.2 meter tall test article in a random vibration test on a 1.07 meter long slip table. The slip table was supported by an oil film on a granite block and driven by a 111,000 Newton shaker, hereinafter denoted as the big shaker. This approach requires obtaining dominant characteristic shapes of the bare table. A vibration test on the full system is performed. The characteristic table generalized coordinates are constrained to zero to obtain fixed base results. Results determined the first three fixed base bending mode frequencies excited by the shaker within four percent. A stick-slip nonlinearity in the shaker system had a negative effect on the final damping ratios producing large errors. An alternative approach to extracting the modal parameters directly from transmissibilities proved to be more accurate. Even after accounting for distortion due to the Harm window, it appears that dissipation physics in the bare shaker table provide additional damping beyond the true fixed base damping.

One of the most influential results in network analysis is that many natural networks exhibit a power-law or log-normal degree distribution. This has inspired numerous generative models that match this property. However, more recent work has shown that while these generative models do have the right degree distribution, they are not good models for real life networks due to their differences on other important metrics like conductance. We believe this is, in part, because many of these real-world networks have very different joint degree distributions, i.e. the probability that a randomly selected edge will be between nodes of degree k and l. Assortativity is a sufficient statistic of the joint degree distribution, and it has been previously noted that social networks tend to be assortative, while biological and technological networks tend to be disassortative. We suggest that the joint degree distribution of graphs is an interesting avenue of study for further research into network structure. We provide a simple greedy algorithm for constructing simple graphs from a given joint degree distribution, and a Monte Carlo Markov Chain method for sampling them. We also show that the state space of simple graphs with a fixed degree distribution is connected via endpoint switches. We empirically evaluate the mixing time of this Markov Chain by using experiments based on the autocorrelation of each edge. Copyright © 2011 by SIAM.

Recently, a new substructure coupling/uncoupling approach has been introduced, called Modal Constraints for Fixture and Subsystem (MCFS) [Allen, Mayes, & Bergman, Journal of Sound and Vibration, vol. 329, 2010]. 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 fixture. An analytical representation of the fixture is then used to subtract its effects in order to create an experimental model for the subcomponent of interest. However, it has been observed that indefinite mass and stiffness matrices can be obtained for the experimental substructure in some situations. This paper presents two simple metrics that can be used by the analyst to determine the cause of indefinite mass or stiffness matrices after substructure uncoupling. The metrics rank the experimental and fixture modes based upon their contribution to offending negative eigenvalues. Once the troublesome modes have been identified, they can be inspected and often reveal why the mass has become negative. Two examples are presented to demonstrate the metrics and to illustrate the physical phenomena that they reveal.

Packaging high power radio frequency integrated circuits (RFICs) in low temperature cofired ceramic (LTCC) presents many challenges. Within the constraints of LTCC fabrication, the design must provide the usual electrical isolation and interconnections required to package the IC, with additional consideration given to RF isolation and thermal management. While iterative design and prototyping is an option for developing RFIC packaging, it would be expensive and most likely unsuccessful due to the complexity of the problem. To facilitate and optimize package design, thermal and mechanical simulations were used to understand and control the critical parameters in LTCC package design. The models were validated through comparisons to experimental results. This paper summarizes an experimentally-validated modeling approach to RFIC package design, and presents some results and key findings. © (2011) Trans Tech Publications, Switzerland.

We characterize the measured electric field-derivative (dE/dt) waveforms of lightning stepped-leader steps from three negative lightning flashes at distances of tens to hundreds of meters. Electromagnetic signatures of leader steps at such close distances have rarely been documented in previous literature. Individual leader-step three-dimensional locations are determined by a dE/dt TOA system. The leader-step field derivative is typically a bipolar pulse with a sharp initial half-cycle of the same polarity as that of the return stroke, followed by an opposite polarity overshoot that decays relatively slowly to background level. This overshoot increases in amplitude relative to the initial peak and becomes dominant as range decreases. The initial peak is often preceded by a "slow front," similar to the slow front that precedes the fast transition to peak in first return stroke dE/dt and E waveforms. The overall step-field waveform duration is typically less than 1 s. The mean initial peak of dE/dt, range-normalized to 100 km, is 7.4 V m ^-1 s^-1 (standard deviation (S.D.), 3.7 V m^-1 s^-1, N = 103), the mean half-peak width is 33.5 ns (S.D., 11.9 ns, N = 69), and the mean 10-to-90% risetime is 43.6 ns (S.D., 24.2 ns, N = 69). From modeling, we determine the properties of the leader step currents which produced two typical measured field derivatives, and we use one of these currents to calculate predicted leader step E and dE/dt as a function of source range and height, the results being in good agreement with our observations. The two modeled current waveforms had maximum rates of current rise-to-peak near 100 kA s^-1, peak currents in the 5-7 kA range, current half-peak widths of about 300 ns, and charge transfers of ∼3 mC. As part of the modeling, those currents were propagated upward at 1.5 × 10⁸ m s^-1, with their amplitudes decaying exponentially with a decay height constant of 25 m. Copyright 2011 by the American Geophysical Union.

We demonstrate a pump-probe approach for the detection of organophosphonate compounds on substrates, in which the pump pulse fragments the parent molecule and the released phosphorous monoxide (PO) fragment is probed using laser-induced fluorescence. © 2011 OSA.

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A common purpose for performing an aerodynamic analysis is to calculate the resulting loads on a solid body immersed in the flow. Pressure or heat loads are often of interest for characterizing the structural integrity or thermal survivability of the structure. This document describes two algorithms for tightly coupling the mass, momentum and energy conservation equations for a compressible fluid and the energy conservation equation for heat transfer through a solid. We categorize both approaches as monolithically coupled, where the conservation equations for the fluid and the solid are assembled into a single residual vector. Newton's method is then used to solve the resulting nonlinear system of equations. These approaches are in contrast to other popular coupling schemes such as staggered coupling methods were each discipline is solved individually and loads are passed between as boundary conditions, and demonstrates the viability of the monolithic approach for aeroheating problems.

We discuss recent experiments for the characterization of our femtosecond purerotational CARS facility for observation of Raman transients in N 2 and atmospheric air. The construction of a simplified femtosecond four-wave mixing system with only a single laser source is presented. Pure-rotational Raman transients reveal well-ordered time-domain recurrence peaks associated with the near-uniform spacing of rotational Raman peaks in the spectral domain. Long-time, 100-ps duration observations of the transient Raman polarization are presented, and the observed transients are compared to simulated results. Fourier transformation of the transients reveals two distinct sets of beat frequencies. Simulation results for temperatures from 300-700 K are used to illustrate the temperature sensitivity of the time-domain transients and their Fourier-transform counterparts. And strategies for diagnostics are briefly discussed. These results are being utilized to develop gas-phase measurement strategies for temperature and species concentration.

In this work, we developed a self-organizing map (SOM) technique for using web-based text analysis to forecast when a group is undergoing a phase change. By 'phase change', we mean that an organization has fundamentally shifted attitudes or behaviors. For instance, when ice melts into water, the characteristics of the substance change. A formerly peaceful group may suddenly adopt violence, or a violent organization may unexpectedly agree to a ceasefire. SOM techniques were used to analyze text obtained from organization postings on the world-wide web. Results suggest it may be possible to forecast phase changes, and determine if an example of writing can be attributed to a group of interest.

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Sandia National Laboratories and General Motors Global Energy Systems team conducted a joint biofuels systems analysis project from March to November 2008. The purpose of this study was to assess the feasibility, implications, limitations, and enablers of large-scale production of biofuels. 90 billion gallons of ethanol (the energy equivalent of approximately 60 billion gallons of gasoline) per year by 2030 was chosen as the book-end target to understand an aggressive deployment. Since previous studies have addressed the potential of biomass but not the supply chain rollout needed to achieve large production targets, the focus of this study was on a comprehensive systems understanding the evolution of the full supply chain and key interdependencies over time. The supply chain components examined in this study included agricultural land use changes, production of biomass feedstocks, storage and transportation of these feedstocks, construction of conversion plants, conversion of feedstocks to ethanol at these plants, transportation of ethanol and blending with gasoline, and distribution to retail outlets. To support this analysis, we developed a 'Seed to Station' system dynamics model (Biofuels Deployment Model - BDM) to explore the feasibility of meeting specified ethanol production targets. The focus of this report is water and its linkage to broad scale biofuel deployment.

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This study explores self-aligning patterns to achieve sub-micron alignment of die/wafers. We have patterned 2-d arrays of gold lines, whose width is half the periodicity, onto substrates. When commensurate patterns are brought into contact, the surface interactions between the Au lines enables high-resolution alignment, manually. Self-assembled monolayers of alkanethiols on the Au, further enhance the surface interactions, enabling alignment in less than half the time as for the uncoated die. A computation of the alignment force and torque between two featured surfaces illustrates how best to partern surfaces to maximize the tendency to align. An array of lines with a sinusoidal modulation in their spacing is more tolerant of initial misalignment, yet retains the high registration force of periodic line arrays. The optimal registration pattern might be a single spiral, as it generates both a radial force and a torque. Such patterns on die/wafers would enable precision device integration. ©The Electrochemical Society.

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When estimating parameters for a material model from experimental data collected during a separate effects physics experiment, the quality of fit is only a part of the required data. Also necessary is the uncertainty in the estimated parameters so that uncertainty quantification and model validation can be performed at the full system level. The uncertainty and quality of fit of the data are many times not available and should be considered when fitting the data to a specified model. There are many techniques available to fit data to a material model and a few of them are presented in this work using a simple acoustical emission dataset. The estimated parameters and the affiliated uncertainty will be estimated using a variety of techniques and compared.

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Infrastructure resilience is a priority for homeland security in many nations around the globe. This paper describes a new approach forquantitatively assessing the resilience of critical infrastructure systems. The mathematics of optimal control design provides the theoretical foundation for this methodology. This foundation enables the inclusion of recovery costs within the resilience assessment approach, a unique capability for quantitative esilience assessment techniques. This paper describes the formulation of the optimal control problem for a set of representative infrastructure models. Thisexample demonstrates the importance of recovery costs in quantitative resilience analysis, and the increased capability provided by this approach's ability to discern between varying levels of resilience. © 2011 Inderscience Enterprises Ltd.

This paper1 explores some of the important considerations in devising a practical and consistent framework and methodology for working with experiments and experimental data in connection with modeling and prediction. The paper outlines a pragmatic and versatile "real-space" approach within which experimental and modeling uncertainties (correlated and uncorrelated, systematic and random, aleatory and epistemic) are treated to mitigate risk in modeling and prediction. The elements of data conditioning, model conditioning, model validation, hierarchical modeling, and extrapolative prediction under uncertainty are examined. An appreciation can be gained for the constraints and difficulties at play in devising a viable end-to-end methodology. The considerations and options are many, and a large variety of viewpoints and precedents exist in the literature, as surveyed here. Rationale is given for the various choices taken in assembling the novel real-space end-to-end framework. The framework adopts some elements and constructs from the literature (sometimes adding needed refinement), rejects others (even some currently popular ones), and adds pivotal new elements and constructs. Crucially, the approach reflects a pragmatism and versatility derived from working many industrial-scale problems involving complex physics and constitutive models, steady-state and time-varying nonlinear behavior and boundary conditions, and various categories of uncertainty in experiments and models. The framework benefits from a broad exposure to integrated experimental and modeling activities in the areas of heat transfer, structural mechanics, irradiated electronics, and combustion in fluids and solids.2. © 2011 SAE International.

Power and signal cable harnesses on spacecraft are often at 10% of the total mass and can be as much as 30%. These cable harnesses can impact the structural dynamics of spacecraft significantly, specifically by damping the response. Past efforts have looked at how to calculate cable properties and the validation of these cable models on one-dimensional beam structures with uniform cable lengths. This paper looks at how to extend that process to two-dimensional spacecraftlike panels with nonuniform cable lengths. A shear beam model is used for cable properties. Two methods of calculating the tiedown stiffness are compared. Of particular interestis whetherornot handbooks of cable properties canbe created ahead of time and applied with confidence. There are three frequency bands inwhich cable effects canbe described. Before any cables become resonant, the cable effects are dominated by mass and static stiffness. After all the cables become resonant, the effect is dominated by increased damping in the structure. In between these two frequency cutoff points, there is a transition zone. The dynamic cable modeling methodis validated as a distinct improvement over the lumped-mass characterization of cables commonly used today. Copyright © 2011 by the American Institute of Aeronautics and Astronautics,.

Negative bias temperature instability (NBTI) is an issue of critical importance as tile space electronics industry evolves because it may dominate tile reliability lifetime of space based assets. Understanding its physical origin is therefore essential in determining how best to search for methods of mitigation. It has been suggested that the magnitude of the effect is strongly dependent on circuit operation conditions (static or dynamic modes). In the present work, we examine the time constants related to the charging and recovery of trapped charged induced by NBTI in HfSiON and SiO2 gate dielectric devices at room temperature. ©The Electrochemical Society.

Although interdisciplinary research attracts more and more interest and effort, the benefits of this type of research are not always realized. To understand when expertise diversity will have positive or negative effects on research efforts, we examine how expertise diversity and diversity salience affect task conflict and idea sharing in interdisciplinary research groups. Using data from 148 researchers in 29 academic research labs, we provide evidence on the importance of social categorization states (i.e., expertise diversity salience) in understanding both the information processes (i.e., task conflict) and the creativity processes (i.e., idea sharing) in groups with expertise diversity. We show that expertise diversity can either increase or decrease task conflict depending on the salience of group members' expertise in a curvilinear way: at a medium level of expertise diversity the moderating effect of diversity salience is strongest. Furthermore, enriched group work design can strengthen the benefits of task conflict for creative idea sharing only when expertise diversity salience is low. Finally, we show that idea sharing predicts group performance in interdisciplinary academic research labs over and above task conflict.

The process of rank aggregation is intimately intertwined with the structure of skew-symmetric matrices. We apply recent advances in the theory and algorithms of matrix completion to skew-symmetric matrices. This combination of ideas produces a new method for ranking a set of items. The essence of our idea is that a rank aggregation describes a partially filled skew-symmetric matrix. We extend an algorithm for matrix completion to handle skew-symmetric data and use that to extract ranks for each item. Our algorithm applies to both pairwise comparison and rating data. Because it is based on matrix completion, it is robust to both noise and incomplete data. We show a formal recovery result for the noiseless case and present a detailed study of the algorithm on synthetic data and Netix ratings. Copyright 2011 ACM.

We present a filter consisting of cascaded ring resonators with integrated SOAs. The filter demonstrates an extinction ratio ≥30 dB, a free spectral range of 56 GHz and a FWHM bandwidth of 3 GHz. © 2011 Optical Society of America.

This work presents a methodology based on the concept of error in constitutive equations for the inverse reconstruction of viscoelastic properties using steady-state dynamics. The ECE algorithm presented herein consists of two main steps. In the first step, kinematically admissible strains and dynamically admissible stresses are generated through two auxiliary forward problems. In the second step, a new update of the complex shear and bulk moduli as functions of frequency are obtained by minimizing an ECE functional that measures the discrepancy between the kinematically admissible strains and the dynamically admissible stresses. The feasibility of the methodology is demonstrated through two numerical experiments. It was found that the magnitude and phase of the complex shear modulus can be accurately reconstructed in the presence of noise, while the magnitude of the bulk modulus is more sensitive to noise and can be reconstructed with less accuracy, in general, than the shear modulus. Furthermore, the phase of the bulk modulus, which is related to energy dissipation, can be accurately reconstructed.

Spatially-resolved ultrafast transient absorption measurements on a single GaN nanowire give insight into carrier relaxation dynamics as a function of the laser polarization and position on the nanowire on a femtosecond timescale. © 2011 Optical Society of America.

We present the first complete simulation of the dynamic range and noise of InGaAsP multi-ring channel-drop filters with internal SOAs. The results show gain saturation, and spontaneous emission noise limit the dynamic range. © 2011 Optical Society of America.

Transportation accidents frequently involve liquids dispersing in the atmosphere. An example is that of aircraft impacts, which often result in spreading fuel and a subsequent fire. Predicting the resulting environment is of interest for design, safety, and forensic applications. This environment is challenging for many reasons, one among them being the disparate time and length scales that must be resolved for an accurate physical representation of the problem. A recent computational method appropriate for this class of problems has been developed for modeling the impact and subsequent liquid spread. This involves coupling a structural dynamics code to a turbulent computational fluid mechanics reacting flow code. Because the environment intended to be simulated with this capability is difficult to instrument and costly to test, the existing validation data are of limited scope, relevance, and quality. A rocket sled test is being performed where a scoop moving through a water channel is being used to brake a pusher sled. We plan to instrument this test to provide appropriate scale data for validating the new modeling capability. The intent is to get high fidelity data on the break-up and evaporation of the water that is ejected from the channel as the sled is braking. These two elements are critical to fireball formation for this type of event involving fuel in the place of water. We demonstrate our capability in this paper by describing the pre-test predictions which are used to locate instrumentation for the actual test. We also present a sensitivity analysis to understand the implications of length scale assumptions on the prediction results. Copyright © 2011 by ASME.

There occasionally occur situations in field measurements where direct optical access to the area of interest is not possible. In these cases the borescope is the standard method of imaging. Furthermore, if shape, displacement, or strain are desired in these hidden locations, it would be advantageous to be able to do digital image correlation (DIC) through the borescope. This paper will present the added complexities and errors associated with imaging through a borescope for DIC. Discussion of non-radial distortions and their effects on the measurements, along with a possible correction scheme will be discussed.

Traditional grid models for large-scale simulations assume linear and quasi-static behavior allowing very simple models of the systems. In this paper, a scalable electric circuit simulation capability is presented that can capture a significantly higher degree of fidelity including transient dynamic behavior of the grid as well as allowing scaling to a regional and national level grid. A test case presented uses simple models, e.g. generators, transformers, transmission lines, and loads, but with the scalability feature it can be extended to include more advanced non-linear detailed models. The use of this scalable electric circuit simulator will provide the ability to conduct large-scale transient stability analysis as well as grid level planning as the grid evolves with greater degrees of penetration of renewables, power electronics, storage, distributed generation, and micro-grids. © 2011 AACC American Automatic Control Council.

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ODTLES is a novel multi-scale model for 3D turbulent flow based on the one-dimensional-turbulence model of Kerstein ["One-dimensional turbulence: Model formulation and application to homogeneous turbulence, shear flows, and buoyant stratified flows," J. Fluid Mech. 392, 277 (1999)]. Its key distinction is that it is formulated to resolve small-scale phenomena and capture some 3D large-scale features of the flow with affordable simulations. The present work demonstrates this capability by considering four types of wall-bounded turbulent flows. This work shows that spatial profiles of various flow quantities predicted with ODTLES agree fairly well with those from direct numerical simulations. It also shows that ODTLES resolves the near-wall region, while capturing the following 3D flow features: the mechanism increasing tangential velocity fluctuations near a free-slip wall, the large-scale recirculation region in lid-driven cavity flow, and the secondary flow in square duct flow. © 2011 American Institute of Physics.

This study explores self-aligning patterns to achieve sub-micron alignment of die/wafers. We have patterned 2-d arrays of gold lines, whose width is half the periodicity, onto substrates. When commensurate patterns are brought into contact, the surface interactions between the Au lines enables high-resolution alignment, manually. Self-assembled monolayers of alkanethiols on the Au, further enhance the surface interactions, enabling alignment in less than half the time as for the uncoated die. A computation of the alignment force and torque between two featured surfaces illustrates how best to partern surfaces to maximize the tendency to align. An array of lines with a sinusoidal modulation in their spacing is more tolerant of initial misalignment, yet retains the high registration force of periodic line arrays. The optimal registration pattern might be a single spiral, as it generates both a radial force and a torque. Such patterns on die/wafers would enable precision device integration. ©The Electrochemical Society.

We demonstrate a pump-probe approach for the detection of organophosphonate compounds on substrates, in which the pump pulse fragments the parent molecule and the released phosphorous monoxide (PO) fragment is probed using laser-induced fluorescence. © 2011 OSA.

A cantilever beam is released from an initial condition. The velocity at the tip is recorded using a laser Doppler vibrometer. The ring-down time history is analyzed using Hilbert transform, which gives the natural frequency and damping. An important issue with the Hilbert transform is vulnerability to noise. The proposed method uses curve fitting to replace some time-differentiation and suppress noise. Linear curve fitting gives very good results for linear beams with low damping. For nonlinear beams with higher damping, polynomial curve fitting captures the time variations. The method was used for estimating quality factors of a few shim metals and PZT bimorphs.

Automatic feature creation is a powerful tool for identifying and reaching goals in the natural world. This paper describes in detail a biologically-inspired method of feature creation that can be applied to sensory information of any modality. The algorithm is incremental and on-line; it enforces sparseness in the features it creates; and it can form features from other features, making a hierarchical feature set. Here it demonstrates the creation of both visual and auditory features. © 2011 The authors and IOS Press. All rights reserved.

Several commercial computational fluid dynamics (CFD) codes now have the capability to analyze Eulerian two-phase flow using the Rohsenow nucleate boiling model. Analysis of boiling due to one-sided heating in plasma facing components (pfcs) is now receiving attention during the design of water-cooled first wall panels for ITER that may encounter heat fluxes as high as 5 MW/m2. Empirical thermalhydraulic design correlations developed for long fission reactor channels are not reliable when applied to pfcs because fully developed flow conditions seldom exist. Star-CCM+ is one of the commercial CFD codes that can model two-phase flows. Like others, it implements the RPI model for nucleate boiling, but it also seamlessly transitions to a volume-of-fluid model for film boiling. By benchmarking the results of our 3d models against recent experiments on critical heat flux for both smooth rectangular channels and hypervapotrons, we determined the six unique input parameters that accurately characterize the boiling physics for ITER flow conditions under a wide range of absorbed heat flux. We can now exploit this capability to predict the onset of critical heat flux in these components. In addition, the results clearly illustrate the production and transport of vapor and its effect on heat transfer in pfcs from nucleate boiling through transition to film boiling. This article describes the boiling physics implemented in CCM+ and compares the computational results to the benchmark experiments carried out independently in the United States and Russia. Temperature distributions agreed to within 10 °C for a wide range of heat fluxes from 3 MW/m² to 10 MW/m² and flow velocities from 1 m/s to 10 m/s in these devices. Although the analysis is incapable of capturing the stochastic nature of critical heat flux (i.e., time and location may depend on a local materials defect or turbulence phenomenon), it is highly reliable in determining the heat flux where boiling instabilities begin to dominate. Beyond this threshold, higher heat fluxes lead to the boiling crisis and eventual burnout. This predictive capability is essential in determining the critical heat flux margin for the design of complex 3d components.

Let C be a depth-3 circuit with n variables, degree d and top fanin k (called ΣΠΣ(k,d,n) circuits) over base field FF. It is a major open problem to design a deterministic polynomial time blackbox algorithm that tests if C is identically zero. Klivans & Spielman (STOC 2001) observed that the problem is open even when k is a constant. This case has been subjected to a serious study over the past few years, starting from the work of Dvir & Shpilka (STOC 2005). We give the first polynomial time blackbox algorithm for this problem. Our algorithm runs in time poly(n)dk, regardless of the base field. The only field for which polynomial time algorithms were previously known is FF = QQ (Kayal & Saraf, FOCS 2009, and Saxena & Seshadhri, FOCS 2010). This is the first blackbox algorithm for depth-$3$ circuits that does not use the rank based approaches of Karnin & Shpilka (CCC 2008). We prove an important tool for the study of depth-3 identities. We design a blackbox polynomial time transformation that reduces the number of variables in a ΣΠΣ(k,d,n) circuit to k variables, but preserves the identity structure. © 2011 ACM.

Traditional parallel programming techniques will suffer rapid deterioration of performance scaling with growing platform size, as the work of coping with increasingly frequent failures dominates over useful computation. To address this challenge, we introduce and simulate a novel software architecture that combines a task dependency graph with a substitution graph. The role of the dependency graph is to limit communication and checkpointing and enhance fault tolerance by allowing graph neighbors to exchange data, while the substitution graph promotes fault oblivious computing by allowing a failed task to be substituted onthe- fly by another task, incurring a quantifiable error. We present optimization formulations for trading off substitution errors and other factors such as available system capacity and low-overlap task partitioning among processors, and demonstrate that these can be approximately solved in real time after some simplifications. Simulation studies of our proposed approach indicate that a substitution network adds considerable resilience and simple enhancements can limit the aggregate substitution errors. © Springer-Verlag 2011.

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Abstract not provided.

We develop computable a posteriori error estimates for linear functionals of a solution to a general nonlinear stochastic differential equation with random model/source parameters. These error estimates are based on a variational analysis applied to stochastic Galerkin methods for forward and adjoint problems. The result is a representation for the error estimate as a polynomial in the random model/source parameter. The advantage of this method is that we use polynomial chaos representations for the forward and adjoint systems to cheaply produce error estimates by simple evaluation of a polynomial. By comparison, the typical method of producing such estimates requires repeated forward/adjoint solves for each new choice of random parameter. We present numerical examples showing that there is excellent agreement between these methods. © 2011 Society for Industrial and Applied Mathematics.

Data have been acquired from a spanwise array of fluctuating wall pressure sensors beneath a wind tunnel wall boundary layer at Mach 2, then invoking Taylor's Hypothesis allows the temporal signals to be converted into a spatial map of the wall pressure field. Improvements to the measurement technique were developed to establish the veracity of earlier tentative conclusions. An adaptive filtering scheme using a reference sensor was implemented to cancel effects of wind tunnel acoustic noise and vibration. Coherent structures in the pressure fields were identified using an improved thresholding algorithm that reduced the occurrence of broken contours and spurious signals. Analog filters with sharper frequency cutoffs than digital filters produced signals of greater spectral purity. Coherent structures were confirmed in the fluctuating wall pressure field that resemble similar structures known to exist in the velocity field, in particular by exhibiting a spanwise meander and merging of events. However, the pressure data lacked the common spanwise alternation of positive and negative events found in velocity data, and conversely demonstrated a weak positive correlation in the spanwise direction.

A unified creep plasticity damage (UCPD) model for Sn-Pb and Pb-free solders was developed and implemented into finite element analysis codes. The new model will be described along with the relationship between the model's damage evolution equation and an empirical Coffin-Manson relationship for solder fatigue. Next, two significant developments were needed to model crack initiation and growth in solder joints. First, an ability to accelerate the simulations such that the effects of hundreds or thousands of thermal cycles could be modeled in a reasonable amount of time was needed. This was accomplished by applying a user prescribed acceleration factor to the damage evolution; then, damage generated by an acceleration factor of cycles could be captured by the numerical simulation of a single thermal cycle. Second, an ability to capture the geometric effects of crack initiation and growth was needed. This was accomplished by replacing material in finite elements that had met the cracking failure criterion with very flexible elastic material. This diffuse crack modeling approach with local finite elements is known to generate mesh dependent solutions. However, introduction of an element size dependent term into the damage evolution equation was found to be effective in controlling mesh dependency. Finally, experimentally observed cracks in a typical solder joint subjected to thermal mechanical fatigue are compared with model predictions. Copyright © 2011 by ASME.

Flexible AC Transmission Systems (FACTS) use advanced power electronics to minimize reactive power loss on the grid. Power devices used in FACTS systems must be capable of switching several thousand amps at voltages of 1-10 kV. Traditionally, these systems have relied on silicon thyristors, but recently have also began to incorporate insulated gate bipolar transistors. FACTS systems present an opportunity for emerging SiC and GaN power transistors, which offer major efficiency gains. However, for these advanced materials to be considered for use in high consequence grid level systems like FACTS controllers, excellent reliability must be demonstrated. ©The Electrochemical Society.

Material control and accountability (MC&A) operations that track and account for critical assets at nuclear facilities provide a key protection approach for defeating insider adversaries. MC&A activities, from monitoring to inventory measurements, provide critical information about target materials and define security elements that are useful against insider threats. However, these activities have been difficult to characterize in ways that are compatible with the path analysis methods that are used to systematically evaluate the effectiveness of a site's protection system. The path analysis methodology focuses on a systematic, quantitative evaluation of the physical protection component of the system for potential external threats, and often calculates the probability that the physical protection system (PPS) is effective (PE) in defeating an adversary who uses that attack pathway. In previous work, Dawson and Hester observed that many MC&A activities can be considered a type of sensor system with alarm and assessment capabilities that provide reccurring opportunities for "detecting" the status of critical items. This work has extended that characterization of MC&A activities as probabilistic sensors that are interwoven within each protection layer of the PPS. In addition, MC&A activities have similar characteristics to operator tasks performed in a nuclear power plant (NPP) in that the reliability of these activities depends significantly on human performance. Many of the procedures involve human performance in checking for anomalous conditions. Further characterization of MC&A activities as operational procedures that check the status of critical assets provides a basis for applying human reliability analysis (HRA) models and methods to determine probabilities of detection for MC&A protection elements. This paper will discuss the application of HRA methods used in nuclear power plant probabilistic risk assessments to define detection probabilities and to formulate "timely detection" for MC&A operations. This work has enabled the development of an integrated path analysis methodology in which MC&A operations can be combined with traditional sensor data in the calculation of PPS effectiveness. Explicitly incorporating MC&A operations into the existing evaluation methodology provides the basis for an effectiveness measure for insider threats, and the resulting PE calculations will provide an integrated effectiveness measure that addresses both external and insider threats. The extended path analysis methodology is being further investigated as the basis for including the PPS and MC&A activities in an integrated safeguards and security system for advanced fuel cycle facilities. Copyright © 2011 by ASME.

In the present paper the act of learner reflection during training with an adaptive or predictive computer-based tutor is considered a learner-system interaction. Incorporating reflection and real-time evaluation of peer performance into adaptive and predictive computerbased tutoring can support the development of automated adaptation. Allowing learners to refine and inform student models from reflective practice with independent open learner models may improve overall accuracy and relevancy. Given the emphasis on selfdirected peer learning with adaptive technology, learner and instructor modeling research continue to be critical research areas for education and training technology.

The chemical industry is one of the largest industries in the United States and a vital contributor to global chemical supply chains. The U.S. Department of Homeland Security (DHS) Science and Technology Directorate has tasked Sandia National Laboratories (Sandia) with developing an analytical capability to assess interdependencies and complexities of the nation's critical infrastructures on and with the chemical sector. This work is being performed to expand the infrastructure analytical capabilities of the National Infrastructure Simulation and Analysis Center (NISAC). To address this need, Sandia has focused on development of an agent-based methodology towards simulating the domestic chemical supply chain and determining economic impacts resulting from large-scale disruptions to the chemical sector. Modeling the chemical supply chain is unique because the flow of goods and services are guided by process thermodynamics and reaction kinetics. Sandia has integrated an agent-based microeconomic simulation tool N-ABLETM with various chemical industry datasets to abstract the chemical supply chain behavior. An enterprise design within N-ABLETM consists of a collection of firms within a supply chain network; each firm interacts with others through chemical reactions, markets, and physical infrastructure. The supply and demand within each simulated network must be consistent with respect to mass balances of every chemical within the network. Production decisions at every time step are a set of constrained linear program (LP) solutions that minimize the difference between desired and actual outputs. We illustrate the methodology with examples of modeled petrochemical supply chains under an earthquake event. The supply chain impacts of upstream and downstream chemicals associated with organic intermediates after a short-term shutdown in the affected area are discussed.

Projection of molten salt performance in thermal storage systems, whether based on sensible heat or latent heat, is highly dependent on the predictions of thermophysical properties. In the absence of experimental data, heat transfer properties rely on theoretical estimations. This work focuses on thermodynamic predictions of mixture properties for molten salts supportive of ongoing advanced heat transfer fluid research at the Sandia National Laboratories. Thus far, the candidate mixtures studied experimentally and theoretically at Sandia are made up of either ternary or quaternary nitrate and mixed nitrate/nitrite salts of various compositions. Experimentally, mixture properties such as melting points and heat of fusion are obtained by thermal gravimetric analysis (TGA) and differential scanning calorimetry (DSC). Classical thermodynamics are applied to resolve phase transitions of molten salt mixtures as well as mixture properties. The Wilson equation, developed originally for organic mixtures, is used to study phase boundaries of molten salts in this work. Molecular thermodynamics (MD), where atomistic simulation forms the basis for constructing the equation of state, are conducted where our fundamental understanding and experimental knowledge are lacking.

An analytical expression for the pressure wavefield radiated from an explosion seismic source with an amplitude distribution in the form of a 3D Gaussian function is developed. This expression provides a useful reference solution for validating various numerical seismic wave propagation algorithms. © 2011 Society of Exploration Geophysicists.

Deep reactive ion etching (DRIE) of silicon enables high aspect ratio, deep silicon features that can be incorporated into the fabrication of microelectromechanical systems (MEMS) sensors and actuators. The DRIE process creates silicon structures and consists of three steps: conformal polymer deposition, ion sputtering, and chemical etching. The sequential three step process results in sidewalls with roughness that varies with processing conditions. This paper reports the sidewall roughness for DRIE etched MEMS as a function of trench width from 5 μm to 500 μm for a 125 μm thick device layer corresponding to aspect ratios from 25 to 0.25. Using a scanning electron microscope (SEM), the surfaces were imaged detecting an upper region exhibiting a scalloping morphology and a rougher lower region exhibiting a curtaining morphology. The height of rougher curtaining region increases linearly with aspect ratio when the etch cleared the entire device layer. The surface roughness for two trench widths: 15 μm and 100 μm were further characterized using an atomic force microscope (AFM), and RMS roughness values are reported as a function of height along the surface. The sidewall roughness varies with height and depends on the trench width. Copyright © 2011 by ASME.

For oxy-fuel combustion with substantial flue gas recirculation, as is commonly employed, pulverized coal combustion occurs in the presence of elevated CO2 levels. Our previous investigations of pulverized coal char combustion in such atmospheres have suggested, through computational modeling of the experimental results, that CO2 gasification rates are sufficiently high under oxy-fuel combustion conditions to significantly influence the char combustion process. Experimental measurements of such rates under the relevant conditions (1 atm, T > 1700 K) are lacking. To address this, we have measured both the char particle temperature statistics and the char mass loss when a high volatile bituminous coal char and a subbituminous coal char are introduced into a high-temperature optical flow reactor with nearly 100% CO2. The experimental measurements show a temperature decrease from the gasifying particles (consistent with the strong endothermicity of the char gasification reaction) and show increasing mass loss with increasing residence time and temperature, as expected.