Publications

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Spectrofluorometric imaging microscopy is demonstrated in a confocal microscope using a supercontinuum laser as an excitation source and a custom-built prism spectrometer for detection. This microscope system provides confocal imaging with spectrally resolved fluorescence excitation and detection from 450 to 700 nm. The supercontinuum laser provides a broad spectrum light source and is coupled with an acousto-optic tunable filter to provide continuously tunable fluorescence excitation with a 1-nm bandwidth. Eight different excitation wavelengths can be simultaneously selected. The prism spectrometer provides spectrally resolved detection with sensitivity comparable to a standard confocal system. This new microscope system enables optimal access to a multitude of fluorophores and provides fluorescence excitation and emission spectra for each location in a 3D confocal image. The speed of the spectral scans is suitable for spectrofluorometric imaging of live cells. Effects of chromatic aberration are modest and do not significantly limit the spatial resolution of the confocal measurements.

What constitutes a validated model? What are the criteria that allow one to defensibly make the claim that they are using a validated model in an analysis? These questions get to the heart of what model validation really implies (conceptually, operationally, interpretationally, etc.), and these details are currently the subject of substantial debate in the V&V community. This is perhaps because many contemporary paradigms of model validation have a limited modeling scope in mind, so the validation paradigms do not span different modeling regimes and purposes that are important in engineering. This paper discusses the different modeling regimes and purposes that it is important for a validation theory to span, and then proposes a validation paradigm that appears to span them. The author's criterion for validated models proceeds from a desire to meet an end objective of "best estimate plus uncertainty" (BEPU) in model predictions. Starting from this end, the author works back to the implications on the model validation process (conceptually, operationally, interpretationally, etc.). Ultimately a shift is required in the conceptualization and articulation of model validation, away from contemporary paradigms. Thus, this paper points out weaknesses in contemporary model validation perspectives and proposes a conception of model validation and validated models that seems to reconcile many of the issues. Copyright © 2007 SAE International.

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New low-temperature combustion (LTC) strategies can reduce both NOx and soot emissions from compression-ignition engines, but unburned hydrocarbon (UHC) emissions typically increase. Incylinder UHC evolution can be marked by formaldehyde, an intermediate species in the combustion process. Formaldehyde is formed during the first stage of ignition of diesel-like fuels, and it persists along with UHC in regions that do not achieve complete combustion. During the second stage of ignition, fuel and formaldehyde are largely consumed as OH radicals become prominent. The appearance of OH therefore indicates second-stage ignition and relatively complete combustion of fuel. Simultaneous planar laser-induced fluorescence (PLIF) images of formaldehyde and OH are acquired for two LTC conditions with different ignition delays, using neat n-heptane fuel. For both cases, formaldehyde PLIF is initially observed throughout the jet. Later, OH PLIF first appears downstream in the jet, where formaldehyde and UHC are locally consumed. For the shorter ignition-delay condition, OH PLIF quickly appears upstream locally where formaldehyde PLIF decreases, marking second-stage ignition and consumption of formaldehyde and UHC. For the longer ignition-delay condition, however, OH PLIF does not appear upstream, even late in combustion. Rather, formaldehyde PLIF, and therefore UHCs, persist near the injector late in combustion, indicating that regions near the injector do not achieve complete combustion, and may contribute to UHC emissions for the longer ignition delay condition.

Specially designed Pnp heterojunction bipolar transistors (HBT's) in the AlGaAs/GaAs material system can offer improved radiation response over commercially-available silicon bipolar junction transistors (BJT's). To be a viable alternative to the silicon Pnp BJT, improvements to the manufacturability of the HBT were required. Utilization of a Pd/Ge/Au non-spiking ohmic contact to the base and implementation of a PECVD silicon nitride hard mask for wet etch control were the primary developments that led to a more reliable fabrication process. The implementation of the silicon nitride hard mask and the subsequent process improvements increased the average electrical yield from 43% to 90%. © The Electrochemical Society.

As the amount of real time data collected during drilling continues to rise, sophisticated methods for analyzing and displaying data are needed to make sense out of large volumes of data. This paper describes a novel use of the concepts of computational geometry to analyze and display data from a downhole drilling data tool. The use of a mathematical transformation called a convex hull allows one to create a boundary around a set (cloud) of data points. This is most easily visualized in two dimensions as putting a rubber band around the set of points. Imagine that the rubber band is such that it will be tightly stretched when it is around all the points, so that certain points in the data cloud dictate the resulting outline. A convex hull software routine, the best known of which is the"qhull" program from the University of Minnesota, fits line segments around a cloud of points in up to nine dimensions. Utilizing the convex hull output one can calculate the volume in 3-D or area in 2-D described by data clouds. The result is used as an indicator of bit and drill string behavior. Copyright 2007, Society of Petroleum Engineers.

This report contains the results of a research effort on advanced robot locomotion. The majority of this work focuses on walking robots. Walking robot applications include delivery of special payloads to unique locations that require human locomotion to exo-skeleton human assistance applications. A walking robot could step over obstacles and move through narrow openings that a wheeled or tracked vehicle could not overcome. It could pick up and manipulate objects in ways that a standard robot gripper could not. Most importantly, a walking robot would be able to rapidly perform these tasks through an intuitive user interface that mimics natural human motion. The largest obstacle arises in emulating stability and balance control naturally present in humans but needed for bipedal locomotion in a robot. A tracked robot is bulky and limited, but a wide wheel base assures passive stability. Human bipedal motion is so common that it is taken for granted, but bipedal motion requires active balance and stability control for which the analysis is non-trivial. This report contains an extensive literature study on the state-of-the-art of legged robotics, and it additionally provides the analysis, simulation, and hardware verification of two variants of a proto-type leg design.

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Over the years, researchers have been investigating large-scale pool fores, both experimentally and numerically, because of the risk they pose during transport accidents. In the course of developing and validating computational models, researchers have come to realize that knowledge of the soot concentration, temperature and optical properties within fires is required to quantify the amount of heat transferred. In turn, such knowledge may help in understanding the dynamics of fires, particularly large accidental ones.

A shear test was used to investigate the effect of shielding gas (Argon, Nitrogen and air) on the mechanical properties of laser spot welds in Fe-28Ni-17Co alloy (Kovar). The load vs. displacement curves obtained, while superficially resembling those of a standard tensile test, were quite non-reproducible, and obscured the differences due to process conditions. Fractographic examination of the samples and analysis of the testing conditions led to significant conclusions about how to correctly interpret the shear test results, which in turn enabled a determination of the real effects of the change in shielding gas. Several different types of fracture morphology were noted, depending upon how the fracture surface developed relative to the original weld. This resulted in the disparate nature of the load-displacement curves. The results of the shear testing, fractography and metallography will be used to support interpretation of the differences found with respect to porosity formation, strength and work hardening behavior.

A top level overview of the effect cables have on the dynamic response of precision structures is presented. The focus of this paper is on precision, low-damping, low-first modal frequency space structures where cables are not implicitly designed to be in the load path. The paper presents the top-level, Phase I results which include pathfinder tests, an industry/government/academia survey, modeling and testing of individual cable bundles, and modeling and testing of cables on a simple structure. The end goal is to discover a set of practical approaches for updating well defined dynamical models of cableless structures. Knowledge of the cable type, position and tie-down method is assumed to be known. Simulation sensitivity analysis of the effect cables have on a precision structure has also been completed. Each section of the paper will focus on the details of each area.

This paper presents experimental results and modeling aspects for electrical power and signal cable harnesses used for space applications. Dynamics of large precision structures can be significantly influenced by subsystems such as electrical cables and harnesses as the structural mass of those structures tends to become smaller, and the quantity of attached cables continues to increase largely due to the ever increasing complexity of such structures. Contributions of cables to structural dynamic responses were observed but never studied, except for a low scale research effort conducted at the Air Force Research Laboratory, Space Vehicles Directorate (AFRL/VSSV). General observations were that at low frequencies cables have a mass loading effect while at higher frequencies they have a dissipative effect. The cables studied here adhere to space industry practices, identified through an extensive industry survey. Experimental procedures for extracting structural properties of the cables were developed. The structural properties of the cables extracted from the extensive experimental database that is being created can be used for numerical modeling of cabled structures. Explicit methods for analytical modeling of electrical cables attached to a structure in general are yet to be developed and the goal of this effort is to advance the state of the art in modeling cable harnesses mounted on lightweight spacecraft structures.

Signal and power harnesses on spacecraft buses and payloads can alter structural dynamics, as has been noted in previous flight programs. The community, however, has never undertaken a thorough study to understand the impact of harness dynamics on spacecraft structures. The Air Force Research Laboratory is leading a test and analysis program to develop fundamental knowledge of how spacecraft harnesses impact dynamics and develop tools that structural designers could use to achieve accurate predictions of cable-dressed structures. The work described in this paper involved a beam under simulated free boundary conditions that served as a validation test bed for model development.

In this paper, we evaluate a commercially available high density plasma chemical vapor deposition (HDP-CVD) process to grow low temperature (i.e., Tin-situ & Tepitaxy < ∼460°C) germanium epitaxy for a p+-Ge/p-Si/n+-Si NIR separate absorption and multiplication avalanche photodetectors (SAM-APD). A primary concern for SAM-APDs in this material system is that high fields will not be sustainable across a highly defective Ge/Si interface. We show Ge-Si SAM-APDs that show avalanche multiplication and avalanche breakdown. A dark current of ∼0.1 mA/cm2 and a 3.2×10-4 A/W responsivity at 1310 nm were measured at punch-through. An over 400x photocurrent multiplication was demonstrated at room temperature. These results indicate that high avalanche multiplication gain is achievable in these Ge/Si heterostructures despite the highly defective interface and therefore trap assisted tunneling through the defective Ge/Si interface is not dominant at high fields. © 2007 Materials Research Society.

Current published models for predicting squeeze film damping (SFD), which are based on different assumptions, give widely different results in the free-molecule regime. The work presented here provides experimental data for validating SFD models in that regime. The test device was an almost rectangular micro plate supported by beam springs. The structure was base-excited. The rigid plate oscillated vertically while staying parallel to the substrate. The velocities of the plate and of the substrate were measured with a laser Doppler vibrometer and a microscope. The damping ratio was calculated by performing modal analysis of the frequency response functions. The test structures were contained in a vacuum chamber with air pressures controlled to provide a five-order-of-magnitude range of Knudsen numbers. The damping coefficients from the measurements were compared with predictions from various published models. The results show that the continuum-base Reynolds equation predicts squeeze-film damping accurately if used with correct boundary conditions. The accuracy of molecular-based models depends heavily on the assumptions used in developing the models.

Full-waveform seismic reflection responses of an isolated porous sandstone layer are simulated with three-dimensional (3D) isotropic poroelastic and isotropic elastic finite-difference (FD) numerical algorithms. When the pore-filling fluid is brine water with realistic viscosity, there is about a ∼10% difference in synthetic seismograms observed in an AVO recording geometry. These preliminary results suggest that equivalent elastic medium modeling is adequate for general interpretive purposes, but more refined investigations (such as AVO waveform analysis) should account for poroelastic wave propagation effects.

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Visual simultaneous localization and mapping (VSLAM) is the problem of using video input to reconstruct the 3D world and the path of the camera in an 'on-line' manner. Since the data is processed in real time, one does not have access to all of the data at once. (Contrast this with structure from motion (SFM), which is usually formulated as an 'off-line' process on all the data seen, and is not time dependent.) A VSLAM solution is useful for mobile robot navigation or as an assistant for humans exploring an unknown environment. This report documents the design and implementation of a VSLAM system that consists of a small inertial measurement unit (IMU) and camera. The approach is based on a modified Extended Kalman Filter. This research was performed under a Laboratory Directed Research and Development (LDRD) effort.

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Open MPI was initially designed to support a wide variety of high-performance networks and network programming interfaces. Recently, Open MPI was enhanced to support networks that have full support for MPI matching semantics. Previous Open MPI efforts focused on networks that require the MPI library to manage message matching, which is sub-optimal for some networks that inherently support matching. We describes a new matching transport layer in Open MPI, present results of micro-benchmarks and several applications on the Cray XT platform, and compare performance of the new and the existing transport layers, as well as the vendor-supplied implementation of MPI. © Springer-Verlag Berlin Heidelberg 2007.

The default messaging model for the OpenFabrics "Verbs" API is to consume receive buffers in order - regardless of the actual incoming message size - leading to inefficient registered memory usage. For example, many small messages can consume large amounts of registered memory. This paper introduces a new transport protocol in Open MPI implemented using the existing OpenFabrics Verbs API that exhibits efficient registered memory utilization. Several real-world applications were run at scale with the new protocol; results show that global network resource utilization efficiency increases, allowing increased scalability - and larger problem sizes - on clusters which can increase application performance in some cases. © Springer-Verlag Berlin Heidelberg 2007.

Pre-oxidized and glass-to-metal (GtM) sealed austenitic stainless steels were found to display a ferritic layer near the metal/oxide interface, as determined by electron backscatter diffraction (EBSD). Electron probe microanalysis (EPMA) showed that this layer was depleted in alloying elements due to the oxidation and sealing process. Characterization of the morphology suggested that it formed through the martensite transformation mechanism. Moreover, this observed layer was correlated to the composition gradient through published empirical relationships for martensite-start (Ms) temperatures. Due to Cr, Mn, and Si depletion during pre-oxidation and glass sealing, Ms temperatures near room temperature are possible in this surface region. Further support for a martensitic transformation was provided by thermochemical modeling. Possible detrimental ramifications of bulk composition, surface depletion, and phase transformations on GtM sealing are discussed. Copyright © 2007 MS&T'07®.

The impact of localized polarization of aluminum in aqueous chloride is studied using in situ atomic force microscopy (AFM). The primary goal of this study is to determine whether nanostructural degradation in the form of passivity loss and pit initiation can be induced by applying potential pulses between a conductive AFM probe tip and an aluminum surface. Nanoscopic imaging of the mechanically compliant hydrous oxide on an Al(111) textured film with 0.5 wt.% Cu is demonstrated. A correlation is made between characteristic nanostructural changes observed for localized and macroscopic area polarization. Pit initiation proximity to the AFM tip is also demonstrated arguing for millisecond time periods as being sufficient to drive pit initiation within a targeted area. A significant degree of spatial variance in proximity is observed, which suggests a larger length scale, intrinsic susceptibility to pit initiation not dictated by known structural heterogeneity like grain boundary structure. © The Electrochemical Society.

The ability to study material response during isentropic compression has been a grand challenge of the scientific community for several decades. However, development of precision techniques for producing isentropic compression at high pressures has been limited. The revolutionary advance for using planar magnetic loading on the Z accelerator accelerated this goal by enabling quasi-isentropic studies on macroscopically sized materials to over 5 Mbar. In addition, the accelerator is easily configured to launch flyer plates to velocities more than four times higher than possible with conventional launchers, thus allowing shock compression studies in the laboratory to pressures exceeding 20 Mbar.

Advantages and limitations of fiber-based laser systems for trace-gas detection will be reviewed. I will present example applications and instruments for in situ and remote detection at wavelengths from the mid-IR through the deep-UV. © 2007 Optical Society of America.

An experimental apparatus is described that measures gas-surface thermal accommodation coefficients from the pressure dependence of the conductive heat flux between parallel plates separated by a gas-filled gap. Heat flux between the plates is inferred from measurements of temperature drop between the plate surface and an adjacent temperature-controlled water bath. Thermal accommodation coefficients are determined from the pressure dependence of the heat flux at a fixed plate separation. The apparatus is designed to conduct tests with a variety of gases in contact with interchangeable, well-characterized surfaces of various materials (e.g., metals, ceramics, semiconductors) with various surface finishes (e.g., smooth, rough). Experiments are reported for three gases (argon, nitrogen, and helium) in contact with pairs of 304 stainless steel plates prepared with one of two finishes: lathe-machined or mirror-polished. For argon and nitrogen, the measured accommodation coefficients for machined and polished plates are near unity and independent of finish to within experimental uncertainty. For helium, the accommodation coefficients are much lower and show a slight variation with surface roughness. Two different methods are used to determine the accommodation coefficient from experimental data: the Sherman-Lees formula and the GTR formula. These approaches yield values of 0.87 and 0.94 for argon, 0.80 and 0.86 for nitrogen, 0.36 and 0.38 for helium with the machined finish, and 0.40 and 0.42 for helium with the polished finish, respectively, with an uncertainty of ±0.02. The GTR values for argon and nitrogen are generally in better agreement with the results of other investigators than the Sherman-Lees values are, and both helium results are in reasonable agreement with values in the literature.

The convergence behavior of the Direct Simulation Monte Carlo (DSMC) method is investigated for transient flows. Two types of flows are considered: a Couette-like flow, in which an initial velocity profile decays in time, and a Fourier-like flow, in which an initial temperature profile decays in time. DSMC results are presented for hard-sphere argon with Knudsen numbers in the range 0.01-0.4. Low-Knudsen-number DSMC results are compared with Navier-Stokes results. The DSMC discretization errors from finite time step and finite cell size (in the limit of infinite number of computational molecules per cell) are compared with the predictions of Green-Kubo theory for conditions in this regime.

By using a radio frequency (RF) audio distortion measurement test setup, communication devices can be evaluated for degradation caused by electromagnetic interference (EMI) from active vehicle components. This measurement technique can be used to determine the performance of a radio receiver under a variety of conditions. The test setup consists of making measurements on a baseband audio signal that is sent to the device under test (receiver) via over-the-air RF transmissions. Once a baseline is established, active components on the vehicle can be powered on to determine their contribution to the receiver's degradation. The degradation measured is a result of distortion caused by conducted, radiated, and/or coupled EMI from active components into the receiver's passband.

The electrical, thermal, and mechanical responses of surface micromachined (SMM) 2-beam actuators have been simulated using the Calagio code, a coupled physics analysis tool. The present analysis, unlike previous analyses, includes the surrounding air in the computational domain so that heat losses from the beams onto the silicon substrate will be accurately modeled. This setup is essential because the existing 'shape factor' correlations have difficulty capturing the threedimensional geometric effect of the heat loss in the shuttle at the center that connects the bent beams. In addition, results from the present analysis reveal that because the local heat flux can be extremely high, a significant temperature jump can occur across the air-structure interfaces.

Boundary layer transition continues to be a critical factor in hypersonic fight vehicle design. Measurements of transition during hypersonic flight testing provide valuable data for the development and verification of transition prediction techniques. A summary of transition measurement techniques used on vehicles flown by Sandia National Laboratories is presented, including sample flight data to illustrate the type of transition indication obtained from each measurement technique. SHARP-B2, a ballistic vehicle flown by Sandia for NASA, is used as a case study to illustrate how transition is determined for a flight vehicle and to illustrate some of the difficulties associated with these types of measurements.

This paper presents heterodyne mixer measurements at 2.9 THz using quantum cascade lasers (QCLs) as sources. The linewidth of the laser was explored by biasing it to run in dual mode operation and observing the linewidth of the beat note. In addition the frequency of the QCL is determined by beating it against a deuterated methanol line from a molecular gas laser.

Prior HCCI optical engine experiments utilizing laser-induced fluorescence (LIF) measurements of stratified fuel-air mixtures have demonstrated the utility of probability density function (PDF) statistics for correlating mixture preparation with combustion. However, PDF statistics neglect all spatial details of in-cylinder fuel distribution. The current computational paper examines the effects of spatial fuel distribution on combustion using a novel combination of a 3-D CFD model with a 1-D linear-eddy model of turbulent mixing. In the simulations, the spatial coarseness of initial fuel distribution prior to the start of heat release is varied while keeping PDF statistics constant. Several cases are run, and as the initial mixture is made coarser, combustion phasing monotonically advances due to high local equivalence ratios that persist longer. The effect of turbulent mixing is more complex. For the case where the length scale of the initial distribution matches the integral length scale of turbulence, turbulent mixing leads to moderation of peak heat-release rate. The randomness of turbulence is captured in the simulation, and for the above case, cycle-to-cycle variation of the combustion is evident. In contrast, when the initial fuel distribution is significantly finer or coarser than the turbulence length scale, turbulent mixing does not affect combustion for two different reasons. For fine distributions, molecular diffusion alone homogenizes the fuel-air mixture prior to ignition, so turbulence adds nothing. For initial distributions that are coarse compared to the turbulence length scale, diffusion and turbulence are both ineffective at mixing, so again turbulence has a minimal effect on combustion.

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Cracking was observed in the side walls of gold (Au) filled vias in low-temperature, co-fired ceramic (LTCC) substrates. Further analysis indicated the likely source as the constituents of the glassy phase component of the gold-platinum-palladium (Au-Pt-Pd) thick film used for the conductor traces and pads. The successful approach toward mitigating the cracking phenomenon was to place a Au thick film layer between the Au-Pt-Pd layer and the LTCC substrate, which significantly curtailed the diffusion of glassy phase components into the latter. However, it was necessary to determine the effects of the additional thick film layer on the microstructure and overall mechanical strength of tin-lead (Sn-Pb) solder joints made to device pads. Acceptable pull strengths were measured in the range of 3.5 - 4.0 lbs. The solder joint pull strength was sensitive to the number of firing steps as defined by the thick film layer construction. Both the solder/thick film and thick film/LTCC interface strengths had roles in this trend, thereby affirming the synergism between material, interfaces, and the firing processes The pull strength was optimized when the pad length ratio, 4596:5742, was 1.0:0.5, which was characterized by a reduced occurrence of the thick film/LTCC failure mode. © 2007 IEEE.

Sandia National Laboratories has world-class facilities for building and testing lithium and lithium-ion batteries. In this article we describe the in-house facilities for fabricating electrodes and cells in detail. Our in-house facility includes equipment for: 1) electrode coating, 2) electrode slitting, 3) electrode winding, 4) cell grooving, 5) electrolyte filling, 6) cell crimping and more. We also have a 48-channel Maccor tester and several impedance units for electrochemical characterization. These facilities provide flexibility for cell fabrication techniques which in turn allows us to continually improve cell performance. Under an internally funded program we are developing in-house capability to fabricate and evaluate 18650 Li/(CFx)n cells using "Li-ion" electrode fabrication methodologies to prepare the thin film (CFx)n electrodes. At a C/400 discharge rate cell delivered ~3.6 Ahrs capacity. We also evaluated cathodes of two different lengths for uniformity of loading. The loading along the electrode length was found to be extremely uniform, as the delivered capacity was proportional to cathode length. For example, a 0.91 meters long x 4.2 mil thick electrode gave 3.6 Ahrs capacity while a 0.72 meters long × 4.2 mil thick electrode (19.4% less length) gave 2.9 Ahr of capacity (19.4% less capacity). We also discharged the cells with 0.71 meters long electrodes at different temperatures. The cells delivered practically the same capacity over temperatures from 25 to 72°C. At -20°C the cells delivered 81% of the room temperature capacity at a C/200 rate; however, at -40°C the cells delivered close to 47% of the room temperature capacity under similar test conditions. The performance behavior of 18650 cells will be discussed in more detail in the paper. © 2007 by ESG.

The influence of the constant C3, which multiplies the mean flow divergence term in the model equation for the turbulent kinetic energy dissipation, is examined in a motored diesel engine for three different swirl ratios and three different spatial locations. Predicted temporal histories of turbulence energy and its dissipation are compared with experimentally-derived estimates. A "best-fit" value of C3 = 1.75, with an approximate uncertainty of ±0.3 is found to minimize the error between the model predictions and the experiments. Using this best-fit value, model length scale behavior corresponds well with that of measured velocity-correlation integral scales during compression. During expansion, the model scale grows too rapidly. Restriction of the model assessment to the expansion stroke suggests that C3 = 0.9 is more appropriate during this period. Copyright © 2007 SAE International.

Cyclic ethers, like tetrahydrofuran (THF), are formed during the autoignition of alkanes and subsequently influence their combustion chemistry. To learn more about the oxidation chemistry of these ether intermediates, a fuel-rich THF flame (π = 1.75) has been studied using the versatile technique of flame-sampling Molecular Beam Mass Spectrometry (MBMS) in combination with single-photon ionization. Several cyclic intermediates which are potentially formed by dehydrogenation of the fuel are identified by their ionization energies. Ethylene, propene, ketene and formaldehyde are major stable decomposition products of THF and their mole fraction profiles are presented. Detected oxygenated species include ethenol, acetaldehyde and propanal. Despite the fuel-rich conditions, the concentrations of benzene and other aromatic hydrocarbons are near the detection limit.

Modelling soot formation in turbulent nonpremixed combustion is a difficult problem. Unlike most gaseous combustion species, soot lacks a strong state relationship with the mixture fraction due to unsteady formation rates which overlap transport timescales, and strong differential diffusion between gaseous species and soot. The conditional moment closure model (CMC) has recently been applied to the problem of turbulent soot formation. A challenge in CMC modelling is the treatment of differential diffusion. Three-dimensional direct numerical simulation (DNS) of a nonpremixed ethylene jet flame with soot formation has been performed for the first time, using a nineteen species reduced ethylene mechanism and a four-step, three-moment, semi-empirical soot model. The DNS provides full resolution of the turbulent flow field and is used to perform a-priori analysis of a new CMC model derived from the joint scalar PDF transport equation. Unlike other approaches, this CMC model does not require additional transport equations to treat differentially diffusing species. A budget of the terms of the CMC equation for both gaseous species and soot is presented. In particular, exact expressions for unclosed terms are compared to typical closure models for scalar dissipation, cross dissipation, differential diffusion, and reactive source terms.

Direct numerical simulation of a nonpremixed, turbulent, ethylene jet flame is performed to investigate fundamental mechanisms of extinction and reignition processes. A reduced ethylene mechanism consisting of nineteen transported and ten quasi-steady state species, with 167 reactions was used, along with mixture averaged transport properties. The flow configuration is a temporally-evolving slot jet at a Reynolds number of 5,120. Extreme extinction of the nonpremixed flame occurs, followed by a period of intense turbulent scalar mixing between reactants and quenched products in which less than 2stratified mixture with nonhomogeneous composition and temperature. Various modes of reignition are analyzed-autoignition, edge flame propagation, and premixed flame propagation-by monitoring Takeno's flame index [H. Yamashitia, M. Shimada, and T. Takeno, Proc. Combust. Inst., 26 (1996) 27-34], homogeneous ignition delay times by sampling the mixture prior to reignition, and the turbulent displacement speed of the reaction front. The dominant reignition mechanism is found to be premixed flame propagation commencing from a few high temperature flame kernels which survive near global extinction.

Recent advances in electrode fabrication and tailoring electrolyte properties for numerous applications have generated wide-spread interest in (CFx)x chemistry since it has the highest theoretical capacity and hence longer life of the four well known Li-primary chemistries. We are applying "Li-ion technology" electrode fabrication methodologies and preparing thin film (CFx)n electrodes in-house for evaluation. In this program we have evaluated 4 different (CFx) n materials for performance in coin cells in the temperature regime -55 to 72°C. We continue to evaluate the top performer in 18650 cell configuration and obtained ∼3.6 Ahrs capacity at a C/400 rate. We also evaluated cathodes of different lengths for uniformity of loading. For example, a 36'' long × 4.2 mil thick electrode gave 3.6 Ahrs while a 29'' long × 4.2 mil thick electrode gave 2.9 Ahrs of capacity. We also measured impedance at different voltages and thermal abuse response of the 18650 cells. © The Electrochemical Society.

Accurate simulation of biological networks is difficult not only due to the computational cost associated with large-scale systems simulation, but also due to the inherent limitations of mathematical models. We address two components to improve biological circuit simulation accuracy: 1) feasible initial conditions, and 2) identification of critical yet unknown model parameters. For those parameters that may not be available from experimental data, we incorporate reachability analysis to enhance our optimization/simulation framework and estimate those parameters that are capable of creating behaviors consistent with known experimental data. We apply these techniques to a biological circuit model of tryptophan biosynthesis in E. coli, and quantify the improvement in simulation accuracy when reachability analysis is used. © 2008 IEEE.

Lithium-Ion batteries are being considered as a high-energy density replacement for Nickel Metal Hydride (NiMH) batteries in Hybrid Electric Vehicles (HEVs) and in the new Plug-In Hybrids (PHEVs). Although these cells can result in significant reduction in weight and volume, they have several safety related issues that still need to be addressed. We report here on the thermal response of Li-ion cells specifically assembled in our laboratory to test new materials, electrolytes and additives. Improvements in the thermal abuse tolerance of cells are reported and discussed in terms of the need for overall battery system safety. © The Electrochemical Society.

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Surface chemistry is one of the main factors that contributes to the longevity and compliance of cell patterning. Two to three weeks are required for dissociated, embryonic rat neuronal cultures to mature to the point that they regularly produce spontaneous and evoked responses. Though proper surface chemistry can be achieved through the use of covalent protein attachment, often it is not maintainable for the time periods necessary to study neuronal growth. Here we report a new and effective covalent linking approach using (3-glycidoxypropyl) trimethoxysilane (3-GPS) for creating long term neuronal patterns. Micrometer scale patterns of cell adhesive proteins were formed using microstamping; hippocampal neurons, cultured up to 1 month, followed those patterns. Cells did not grow on unmodified 3-GPS surfaces, producing non-permissive regions for the long-term cell patterning. Patterned neuronal networks were formed on two different types of MEA (polyimide or silicon nitride insulation) and maintained for 3 weeks. Even though the 3-GPS layer increased the impedance of metal electrodes by a factor of 2-3, final impedance levels were low enough that low noise extracellular recordings were achievable. Spontaneous neural activity was recorded as early as 10 days in vitro. Neural recording and stimulation were readily achieved from these networks. Our results showed that 3-GPS could be used on surfaces to immobilize biomolecules for a variety of neural engineering applications. © 2006 Elsevier B.V. All rights reserved.

X-ray powder diffraction data for a rhombohedral AlPt phase formed by self-propagating, high-temperature reactions of AlPt bi-layer films are reported. Multilayer AlPt thin film samples, reacted in air or vacuum, transformed into rhombohedral AlPt with space group R-3(148). Indexing and lattice parameter refinement of AlPt powders (generated from thin-film samples) yielded trigonal/hexagonal unit-cell lattice parameters of a=15.623(6) Å and c=5.305(2) Å, Z=39, and V=1121.5 Å3. © International Centre for Diffraction Data.

We present a new family of stabilized methods for the Stokes problem. The focus of the paper is on the lowest order velocity-pressure pairs. While not LBB compliant, their simplicity and attractive computational properties make these pairs a popular choice in engineering practice. Our stabilization approach is motivated by terms that characterize the LBB "deficiency" of the unstable spaces. The stabilized methods are defined by using these terms to modify the saddle-point Lagrangian associated with the Stokes equations. The new stabilized methods offer a number of attractive computational properties. In contrast to other stabilization procedures, they are parameter free, do not require calculation of higher order derivatives or edge-based data structures, and always lead to symmetric linear systems. Furthermore, the new methods are unconditionally stable, achieve optimal accuracy with respect to solution regularity, and have simple and straightforward implementations. We present numerical results in two and three dimensions that showcase the excellent stability and accuracy of the new methods. © 2006 Society for Industrial and Applied Mathematics.

Periodic processes are ubiquitous in biological systems, yet modeling these processes with high fidelity as periodic orbits of dynamical systems is challenging. Moreover, mathematical models of biological processes frequently contain many poorly-known parameters. This paper describes techniques for computing periodic orbits in systems of hybrid differential-algebraic equations and parameter estimation methods for fitting these orbits to data. These techniques make extensive use of automatic differentiation to evaluate derivatives accurately and efficiently for time integration, parameter sensitivities, root finding and optimization. The resulting algorithms allow periodic orbits to be computed to high accuracy using coarse discretizations. Derivative computations are carried out using a new automatic differentiation package called ADMC++ that provides derivatives and Taylor series coefficients of matrix-valued functions written in the MATLAB programming language. The algorithms are applied to a periodic orbit problem in rigid-body dynamics and a parameter estimation problem in neural oscillations.

Many large-scale computations involve a mesh and first (or sometimes higher) partial derivatives of functions of mesh elements. In principle, automatic differentiation (AD) can provide the requisite partials more efficiently and accurately than conventional finite-difference approximations. AD requires source-code modifications, which may be little more than changes to declarations. Such simple changes can easily give improved results, e.g., when Jacobian-vector products are used iteratively to solve nonlinear equations. When gradients are required (say, for optimization) and the problem involves many variables, "backward" AD in theory is very efficient, but when carried out automatically and straightforwardly, may use a prohibitive amount of memory. In this case, applying AD separately to each element function and manually assembling the gradient pieces - semiautomatic differentiation - can deliver gradients efficiently and accurately. This paper concerns on-going work; it compares several implementations of backward AD, describes a simple operator-overloading implementation specialized for gradient computations, and compares the implementations on some mesh-optimization examples. Ideas from the specialized implementation could be used in fully general source-to-source translators for C and C++.

Nanometric aluminum (123nm, spherical) was mixed with two different sieve-cut sizes of HMX (106-150 μm and 212-300 μm), and a series of gas gun tests were conducted to compare reactive wave development in pure HMX to that of aluminized HMX. In the absence of added metal, 4-mm-thick, low-density (68% of theoretical maximum density) pressings of the 106-150 μm HMX respond to modest shock loading by developing distinctive reactive waves that exhibit both temporal and meso-scale spatial fluctuations. Similar pressings of Al/HMX containing 10% aluminum (by mass) show an initial suppression of the usual wave growth seen in HMX samples. The suppression is then followed by an induction period where it is hypothesized that a phase change in the aluminum may occur. Data from VISAR, line-ORVIS, and 2-color pyrometry are given and discussed, and numerical modeling of inert sucrose is used to aid the explanation of the resulting data.

Impact-flash phenomenology has been known for decades, and is now being considered for missile-defense applications, in particular for remote engagement diagnostics. To technically establish this capability, we have conducted a series of experiments at impact velocities of ∼6, ∼11, and ∼25 km/s. Two- and three-stage light-gas guns were used for the lower two velocities, and magnetically-driven flyers on the Sandia Z machine achieved the higher velocity. Spectrally- and temporally-resolved flash output addressed data reproducibility, material identification, and target configuration analysis. Usable data were obtained at visible and infrared wavelengths. Standard atomic spectral databases were used to identify strong lines from all principal materials used in the study. The data were unique to the individual materials over the wide range of velocities and conditions examined. The time-varying nature of the signals offered the potential for correlation of the measurements with various aspects of the target configuration. Integrating the records over wavelength helped to clarify those time variations. © 2006 American Institute of Physics.

In conducting a probabilistic safety assessment of a nuclear power plant, it is important to identify unsafe actions (UAs) and human failure events (HFEs) that can lead to or exacerbate conditions during a range of incidents initiated by internal or external events. Identification and analysis of UAs and HFEs during a human reliability analysis can be a daunting process that often depends completely on subject matter experts attempting to divine a list of plant conditions and performance shaping factors (PSFs) that may influence incident outcomes. Key to this process of including the most important UAs and resulting HFEs is to speculate upon deviations of specific circumstances from a base case definition of a scenario that may present confusion regarding system diagnosis and appropriate actions (i.e., due to procedures, training, informal rules, etc.). Intuiting the location and impact of such system weaknesses is challenging and careful organization of analyst's approach to this process is critical for defending any argument for completeness of the analysis. Two dimensional distinguishability-confusability matrices were introduced as a tool to test symbol distinguishability for information displays. This paper expands on the tool by presenting multidimensional confusability matrices as a very helpful, pragmatic tool for organizing the process of combining expert judgment regarding system weaknesses, human performance and highly targeted experimentation in a manner that strengthens the quantitative justification for why particular UAs and HFEs were incorporated into a PSA. Furthermore, the particular approach presented here helps to strengthen the justification for specific likelihood determinations (i.e., human error probabilities) that end up being inserted into a probabilistic risk assessment (PRA) or other numerical description of system safety. This paper first introduces the multidimensional confusability matrix (MCM) approach and then applies it to a set of hypothetical loss of coolant accidents (LOCAs) for which a detailed human reliability analysis is desired. The basic structure of the MCM approach involves showing how actual plant states can be mapped to information available to the operators, and then mapping the information available to operator diagnoses and responses. Finally, there is a mapping of actual plant states to operator performance-each mapping is shown to vary along temporally grounded levels of dominant PSFs (e.g., stress, time available, procedures, training, etc.). MCM facilitates comprehensive analysis of the critical signals/information guiding operator diagnoses and actions. Particular manipulations of plant states, available information and PSFs and resulting operator performance may be experimentally gathered using targeted simulator studies, table top exercises with operators, or thought experiments among analysts. It is suggested that targeted simulator studies will provide the best quantitative mappings across the surfaces generated using the MCMs and the best aid to uncovering unanticipated pieces of 'critical' information used by operators. Details of quantifying overall operator performance using the MCM technique are provided. It is important to note that the MCM tool should be considered neutral regarding the issue of so-called 'reductionist' HRA methods (e.g., THERP-type) versus 'holistic' HRA methods (e.g., ATHEANA, MERMOS). If the analyst's support 'reductionist' approaches, then the MCM will represent more of a traditional interval-type, quantitative response surface in their analysis (i.e., more quantitative resolution and generalizability). If the analysis team places more emphasis on 'holistic' approaches, then the MCM will represent more of a nominal cataloging or ordinal ranking of factors influencing their specific analysis. In both types of analyses, the MCM tool helps in organizing, documenting and facilitating quantification of expert judgments and, when resources allow, targeted experimental data to support human reliability analyses. © 2006 by ASME.

A soft-landing actuation waveform was designed to reduce the bounce of a single-pole single-throw (SPST) ohmic radio frequency (RF) microelectromechanical systems (MEMS) switch during actuation. The waveform consisted of an actuation voltage pulse, a coast time, and a hold voltage. The actuation voltage pulse had a short duration relative to the transition time of the switch and imparted the kinetic energy necessary to close the switch. After the actuation pulse was stopped, damping and restoring forces slowed the switch to near-zero velocity as it approached the closed position. This is referred to as the coast time. The hold voltage was applied upon reaching closure to keep the switch from opening. An ideal waveform would close the switch with near zero impact velocity. The switch dynamics resulting from an ideal waveform were modeled using finite element methods and measured using laser Doppler vibrometry. The ideal waveform closed the switch with an impact velocity of less than 3 cm/s without rebound. Variations in the soft-landing waveform closed the switch with impact velocities of 12.5 cm/s with rebound amplitudes ranging from 75 to 150 nm compared to impact velocities of 22.5 cm/s and rebound amplitudes of 150 to 200 nm for a step waveform. The ideal waveform closed the switch faster than a simple step voltage actuation because there was no rebound and it reduced the impact force imparted on the contacting surfaces upon closure. © 2006 IEEE.

We demonstrate a robust approach to VCSEL polarization control using deeply-etched surface gratings oriented at several different rotational angles. A RCWA model is used to optimize the design for high polarization selectivity and fabrication tolerance. © 2006 Optical Society of America.

The 63Sn-37Pb (wt.%, designated Sn-Pb) solder interconnections made to copper (Cu) pads were examined on two printed wiring assemblies (PWAs) that had been in the field for 17 years and subsequently exposed to an accelerated aging test environment. A qualitative assessment of the solder joints indicated that there was excellent solderabiliry of the pins and Cu pads. Void formation was minimal or did not occur at all. Manufacturing defects were limited to minor Cu pad lifting with cracks in the underlying epoxy resin and local areas of Cu barrel separation from the laminate hole wall. Both defects would not have influenced the effects of the accelerated aging environment. A quantitative analysis examined the intermetallic compound (IMC) layer thickness of selected components on the PWAs. The IMC thickness data indicated that the PWAs were exposed to considerably lower, cumulative temperatures inside the product assembly than were present outside as a result of the accelerated aging environment. The quantitative analysis also evaluated the Pb-rich phase particle size in both fillets and the hole region of the PWA solder joints. The Pb-rich phase size confirmed that the temperature environment at the PWA level was significantly less severe than that of the accelerated aging environment. The Pb-rich phase size data indicated that the solder joints were exposed to a limited degree of thermal mechanical fatigue (TMF) that likely originated from the nominal temperature fluctuations coupled with the thermal expansion of the encapsulant as well as large expansion of the circuit board laminate in the z-axis (through-thickness) direction. This study demonstrated the methodology by which, IMC thickness and Pb-rich phase size were used to assess the temperature/time conditions experienced at the Sn-Pb/Cu interconnection level versus the external environment. Copyright © 2006 ASM International®.

An oxidation treatment, often termed "pre-oxidation", is performed on austenitic stainless steel prior to glass/metal joining to produce hermetic seals. The resulting thin oxide acts as a transitional layer and a source of Cr and other elements which diffuse into the glass during the subsequent bonding process. Pre-oxidation is performed in a low pO 2 atmosphere to avoid iron oxide formation and the final oxide is composed of Cr 2O 3, MnCr 2O 4 spinel, and SiO 2. Significant heat-to-heat variations in the oxidation behavior of 304L stainless steel have been observed, which result in inconsistent glass/metal seal behavior. The objectives of this work were to characterize the oxidation kinetics, the oxide morphology and composition, and the stainless steel attributes that lead to robust glass/metal seals. The oxidation kinetics were determined by thermogravimetric (TG) analysis and the oxide layers were characterized using metallography, SEM, focused ion beam (FIB) analysis, and image analysis. The results show that poor sealing behavior is associated with slower oxidation kinetics and a more continuous layer of SiO 2 at the metal/oxide interface. In addition, the effects of 304L heat composition on oxidation behavior will be discussed. Copyright © 2006 ASM International®.

The solderability of an immersion Ag finish was evaluated after the exposure of test specimens to a Battelle Class II environment, which accelerates the storage conditions of light industrial surroundings. The solderability metric was the contact angle, (θC), as determined by the meniscometer/wetting balance technique. Auger surface and depth profile analyses were utilized to identify changes in the coating chemistry. The solderability test results indicate that there was no appreciable loss in solderability when the immersion Ag coated coupons were packaged in vapor phase corrosion (VPC) inhibitor bags and/or inhibitor bags with VPC inhibitor paper and aged for 8 hours, 1 week or 2 weeks in the Battelle Class II environment. An increase in surface carbon concentration after aging did not appear to significantly affect solderability. Copyright © 2006 ASM International®.

The properties of energetic thin films considered for alternative braze[1] techniques are investigated. Vapor-deposited Ni/Ti multilayer foils having a net 1:1 stoichiometry exhibit self-propagating, high temperature combustion reactions. The rate of reaction depends on Ni/Ti multilayer design with steady-state propagation speeds of freestanding foils measured from 0.2 to 1.0m/s. Transmission electron microscopy and x-ray diffraction further show that NiTi films reacted in a self-propagating mode have a fine-grain, polycrystalline microstructure. All films are composed of cubic B2 and monoclinic B19' phases with some having NiTi2 or Ni3Ti precipitates. Copyright © 2006 ASM International®.

Simulations of a low-speed square cylinder wake and a supersonic axisymmetric base wake are performed using the detached eddy simulation model. A reduced-dissipation form of a shock-capturing flux scheme is employed to mitigate the effects of dissipative error in regions of smooth flow. The reduced-dissipation scheme is demonstrated on a two-dimensional square cylinder wake problem, showing a marked improvement in accuracy for a given grid resolution. The results for simulations on three grids of increasing resolution for the three-dimensional square cylinder wake are compared with experimental data and to other computational studies. The comparisons of mean flow and global flow quantities to experimental data are favorable, whereas the results for second order statistics hi the wake are mixed and do not always improve with increasing spatial resolution. Comparisons to large eddy simulation are also generally favorable, suggesting detached eddy simulation provides an adequate subgrid scale model. Predictions of base drag and centerline wake velocity for the supersonic wake are also good, given sufficient grid refinement. These cases add to the validation library for detached eddy simulation and support its use as an engineering analysis tool for accurate prediction of global flow quantities and mean flow properties.

As the economic and environmental impact arguments for increasing the use of nuclear energy for electricity generation and hydrogen production strengthen, it becomes important to better understand human biases, critical thinking skills, and individual specific characteristics that influence decisions made during probabilistic safety assessments (PSAs), decisions regarding nuclear energy among the general public (e.g., trust of risk assessments, acceptance of new plants, etc.), and nuclear energy decisions made by high-level decision makers (e.g., energy policy makers & government regulators). To promote increased understanding and hopefully to improve decision making capacities, this paper provides four key elements. The foundation of these elements builds on decades of research and associated experimental data regarding risk perception and decision making. The first element is a unique taxonomy of twenty-six recognized biases. Examples of biases were generated by reviewing the relevant literature in nuclear safety, cognitive psychology, economics, science education, and neural science (to name a few) and customizing superficial elements of those examples to the nuclear energy domain. The second element is a listing of ten critical thinking skills (with precise definitions) applicable to risk perception and decision making. Third, three brief hypothetical decision making examples are presented and decomposed relative to the unique, decision making bias framework and critical thinking set. The fourth element is a briefly outlined strategy which may enable one to make better decisions in domains that demand careful reflection and strong adherence to the best available data (i.e., avoiding 'unhelpful biases' that conflict with proper interpretation of available data). The elements concisely summarized in this paper (and additional elements) are available in detail in an unclassified, unlimited release Sandia National Laboratories report (SAND2005-5730). The proposed taxonomy of biases contains the headings of normative knowledge, availability, and individual specific biases. Normative knowledge involves a person's skills in combinatorics, probability theory, and statistics. Research has shown that training and experience in these quantitative fields can improve one's ability to accurately determine event likelihoods. Those trained in statistics tend to seek appropriate data sources when assessing the frequency and severity of an event. The availability category of biases includes those which result from the structure of human cognitive machinery. Two examples of biases in the availability category include the anchoring bias and the retrievability bias. The anchoring bias causes a decision maker to bias subsequent values or items toward the first value or item presented to them. The retrievability bias refers to the bias that drives people to believe those values or items which are easier to retrieve from memory are more likely to occur. Individual specific biases include a particular person's values, personality, interests, group identity, and substantive knowledge (i.e., specific domain knowledge related to the decision to be made). Critical thinking skills are also offered as foundational for competent risk perception and decision making as they can mute the impact of undesirable biases, regulate the application of one's knowledge to a decision, and guide information gathering activities. The list of critical thinking skills presented here was originally articulated by the late Arnold B. Arons, a distinguished physicist and esteemed researcher of learning processes. Finally, in addition to borrowing insights from the literature domains mentioned above, the formal decision making approach supported in this paper incorporates methods used in multi-attribute utility theory. © 2006 by ASME.

The objectives of this study are to identify and evaluate alternative protective action recommendations (PARs) that could reduce dose to the public during a radiological emergency and to determine whether improvements or changes to the federal guidance would be beneficial. The emergency response strategies considered in this study are the following: (1) standard radial evacuation; (2) shelter-in-place followed by radial evacuation; (3) shelter-in-place followed by lateral evacuation; (4) preferential sheltering followed by radial evacuation; and (5) preferential sheltering followed by lateral evacuation. Radial evacuation is directly away from the plant; lateral evacuation is azimuthally (around the compass) away from the direction of the wind. Shelter-in-place is a protective action strategy in which individuals remain in their residence, place of work, or other facility at the time that a general warning is given. Preferential sheltering involves moving individuals to nearby, large buildings, e.g., high-school gymnasiums or courthouses, that afford greater protection than personal residences. This study shows that there are benefits to sheltering if followed by lateral evacuation. However, if the lateral evacuation strategy cannot be implemented, then early radial evacuation is often preferable. The most appropriate PAR depends on the evacuation time estimate (ETE) and, therefore, it is desirable to reduce the uncertainty associated with the ETE. Nuclear Regulatory Commission (NRC) guidance to commercial power plants currently allows for sheltering and/or evacuation as an emergency response to a serious nuclear accident. Frequently, however, licensees and states default to evacuation strategies and do not consider sheltering. Here we evaluate several alternative strategies to determine if standard radial evacuation is best or if other options could reduce the overall risk to the public. We consider two source terms based on the NUREG-1150 study. These involve a rapid release of radioactive material into the atmosphere and a more gradual release. Two variations in timing have also been investigated, but are not reported here. The evaluation was performed for a generic site, which uses a uniform population distribution and typical Midwest meteorological data (Moline, IL). Additional parameters that are varied in the study are the ETE (4-, 6-, 8-, and 10-hour ETEs are considered) and the duration of sheltering (2-, 4-, and 8-hr sheltering periods are considered). Additional sensitivity studies were performed to investigate nonuniform evacuation speed caused by traffic congestion, the time needed to reach a preferential shelter, and the effect of adverse weather conditions as opposed to favorable weather conditions. Adverse weather conditions are those for which precipitation occurs before the leading edge of the plume exits the 10-mile emergency planning zone (EPZ). Ultimately, emergency response strategies are ranked by their potential to reduce adverse health effects for residents within the EPZ. © 2006 by ASME.

In order to better understand how the US natural gas network might respond to disruptions, a model was created that represents the network on a regional basis. Natural gas storage for each region is represented as a stock. Transmission between each region is represented as a flow, as is natural gas production, importation, and consumption. Various disruption scenarios were run to test the robustness of the network. The system as modeled proved robust to a variety of disruption scenarios. However, a weakness of the system is that production shortfalls or interruptions cannot be replaced, and demand must therefore be reduced by the amount of the shortfall.

An oxidation treatment, often termed "pre-oxidation", is performed on austenitic stainless steel prior to joining to alkali barium silicate glass to produce hermetic seals. The resulting thin oxide acts as a transitional layer and a source of Cr and other elements which diffuse into the glass during the subsequent bonding process. Pre-oxidation is performed in a low pO2 atmosphere to avoid iron oxide formation and the final oxide is composed of Cr2O3, MnCr2O4 spinel, and SiO2. Significant heat-to-heat variations in the oxidation behavior of 304L stainless steel have been observed, which result in inconsistent glass-to-metal (GTM) seal behavior. The objectives of this work were to characterize the stainless steel pre-oxidized layer and the glass/oxide/304L interface region after glass sealing. The 304L oxidation kinetics were determined by thermogravimetric (TG) analysis and the glass/metal seals characteristics were studied using sessile drop tests, in which wetting angles were measured and glass adhesion was analyzed. The pre-oxidized layers and glass/metal interface regions were characterized using metallography, focused ion beam (FIB) sectioning, scanning and transmission electron microscopy, and electron probe microanalysis (EPMA). The results show that poor glass sealing behavior is associated with a more continuous layer of SiO 2 at the metal/oxide interface.

Radio Frequency Microelectromechanical Systems (RF MEMS) are advantageous for reconfigurable antennas providing the potential for steering, frequency agility, and tunable directivity. Until RF MEMS switches can consistently reach cycles into the billions (if not trillions), limited reliability outweighs the promised benefits, preventing the deployment of RF MEMS into systems. Understanding failure mechanisms is essential to improving reliability. This paper describes preliminary reliability results and tests conducted in a vacuum chamber to investigate and understand the impact of contamination related failure mechanisms. © 2006 IEEE.

Many systems can be approximated as linear with coefficients that vary periodically with time. For example, an anisotropic shaft rotating at constant speed on anisotropic bearings can be modeled as periodically time varying (PTV). Similar models can be obtained for wind turbines, some mechanisms, etc... However, the vast majority of modal analysis algorithms and techniques apply only to linear time invariant (LTI) systems. In this paper, two methods are demonstrated by which the free response of a periodically time varying system can be exactly parameterized by an LTI system. The parameters of the LTI representation can then be identified using standard techniques. The analysis techniques are demonstrated on a simple system, representing a rotor mounted on an anisotropic, flexible shaft, supported by anisotropic bearings. They are then applied to synthetic response data for a system with parameters that vary only weakly with time, as might be encountered when attempting to detect small cracks in a rotating shaft. These examples demonstrate the methods' ability to characterize the anisotropy of the shaft, even when both the shaft and supports are anisotropic.

This paper presents a new method for the analysis of sinusoidal aquifer test data that extends current analytical techniques to include the analysis of pressure responses in multi-layer aquifers. The multi-layer sinusoidal solution is applied to data from a series of sinusoidal aquifer tests conducted in the two-layered Culebra dolomite at the Waste Isolation Pilot Plant near Carlsbad, NM. In addition to the multilayered solution, a summary of available sinusoidal solutions is provided along with tools to pre-process sinusoidal response data.

Gaussian processes are used as emulators for expensive computer simulations. Recently, Gaussian processes have also been used to model the "error field" or "code discrepancy" between a computer simulation code and experimental data, and the delta term between two levels of computer simulation (multi-fidelity codes). This work presents the use of Gaussian process models to approximate error or delta fields, and examines how one calculates the parameters governing the process. In multi-fidelity modeling, the delta term is used to correct a lower fidelity model to match or approximate a higher fidelity model. The terms governing the Gaussian process (e.g., the parameters of the covariance matrix) are updated using a Bayesian approach. We have found that use of Gaussian process models requires a good understanding of the method itself and an understanding of the problem in enough detail to identify reasonable covariance parameters. The methods are not "black-box" methods that can be used without some statistical understanding. However, Gaussian processes offer the ability to account for uncertainties in prediction. This approach can help reduce the number of high-fidelity function evaluations necessary in multi-fidelity optimization.

Forces generated by a static magnetic field interacting with eddy currents can provide a novel method of vibration damping. This paper discusses an experiment performed to validate modeling [3] for a case where a static magnetic field penetrates a thin sheet of conducting, non-magnetic material. When the thin sheet experiences motion, the penetrating magnetic field generates eddy currents within the sheet. These eddy currents then interact with the static field, creating magnetic forces that act on the sheet, providing damping to the sheet motion. In the presented experiment, the sheet was supported by cantilever springs attached to a frame, then excited with a vibratory shaker. The recorded motions of the sheet and the frame were used to characterize the effect of the eddy current damping.

Multiple references are often used to excite a structure in modal testing programs. This is necessary to excite all the modes and to extract accurate mode shapes when closely spaced roots are present. An algorithm known as SMAC (Synthesize Modes And Correlate), based on principles of modal filtering, has been in development for several years. This extraction technique calculates reciprocal modal vectors based on frequency response function (FRF) measurements. SMAC was developed to accurately extract modes from structures with moderately damped modes and/or high modal density. In the past SMAC has only worked with single reference data. This paper presents an extension of SMAC to work with multiple reference data. If roots are truly perfectly repeated, the mode shapes extracted by any method will be a linear combination of the "true" shapes. However, most closely spaced roots are not perfectly repeated but have some small difference in frequency and/or damping. SMAC exploits these very small differences. The multi-reference capability of SMAC begins with an evaluation of the MMIF (Multivariate Mode Indicator Function) or CMIF (Complex Mode Indicator Function) from the starting frequency list to determine which roots are likely repeated. Several seed roots are scattered in the region of the suspected multiple roots and convergence is obtained. Mode shapes are then created from each of the references individually. The final set of mode shapes are selected based on one of three different selection techniques. Each of these is presented in this paper. SMAC has long included synthesis of FRFs and MIFs from the roots and residues to check extraction quality against the original data, but the capability to include residual effects has been minimal. Its capabilities for including residual vectors to account for out-of-band modes have now been greatly enhanced. The ability to resynthesize FRFs and mode indicator functions from the final mode shapes and residual information has also been developed. Examples are provided utilizing the SMAC package on multi-reference experimental data from two different systems.

A finite element (FE) model of a shell-payload structure is to be used to predict structural dynamic acceleration response to untestable blast environments. To understand the confidence level of these predictions, the model will be validated using test data from a blast tube experiment. The first step in validating the structural response is to validate the loading. A computational fluid dynamics (CFD) code, Saccara, was used to provide the blast tube pressure loading to the FE model. This paper describes the validation of the CFD pressure loading and its uncertainty quantification with respect to experimental pressure data obtained from geometrical mock-up structures instrumented with pressure gages in multiple nominal blast tube tests. A systematic validation approach was used from the uncertainty quantification group at Sandia National Labs. Significant effort was applied to distill the pressure loading to a small number of validation metrics important to obtaining valid final response which is in terms of acceleration shock response spectrum. Uncertainty in the pressure loading amplitude is quantified so that it can be applied to the validation blast tube test on the shell payload structure which has significant acceleration instrumentation but only a few pressure gages.

This paper presents a fictional scenario describing the effects of a category four hurricane on a metropolitan area, accompanied by a challenge: Describe, and eventually realize, a system able to carry out the necessary power system operations without human participation. We outline the capabilities of an automated system for managing electric power. The overarching task of the automated system is islanding: To separate the metro area's power system from the primary power grid and manage its operation during several hurricane-induced contingencies, with the power system operational throughout. The essential technology needed to support this automation is agents. We address the roles agents play in the transition to the islanded state and in power system operation within the island; features of an appropriate agent substrate; the way the agents are organized; and information exchange among agents, the power system, and human operators. ©2006 IEEE.

This work reports on the densification of iron nanoparticles by slow drying followed by pressureless sintering. In contrast, most previous work has used high heating rates to both dry and density the nanoparticle suspension in a single step. Laser heating has been required to achieve high densities by this approach. The slow drying/pressureless sintering approach is shown to be sensitive to reactions between the particles, the stabilizing ligands, the atmosphere, and the substrate. The sintering rate of iron nanoparticles and the final composition of the deposits are significantly impacted by these interactions. However, in both the cases studied, the nanoparticles densify under pressureless sintering. When the iron nanoparticle colloid is dried in a porous steel skeleton, it is shown to increase high-temperature strength and reduce the sintering shrinkage.

Oxygen-fuel fired glass melting furnaces have successfully reduced NO x and particulate emissions and improved the furnace energy efficiency relative to the more conventional air-fuel fired technology. However, full optimisation of the oxygen/fuel approach (particularly with respect to crown refractory corrosion) is unlikely to be achieved until there is improved understanding of the effects of furnace operating conditions on alkali vaporization, batch carryover, and the formation of gaseous air pollutants in operating furnaces. In this investigation, continuous online measurements of alkali concentration (by laser induced breakdown spectroscopy) were coupled with measurements of the flue gas composition in the exhaust of an oxygen/natural gas fired container glass furnace. The burner stoichiometry was purposefully varied while maintaining normal glass production. The data demonstrate that alkali vaporization and SO2 release increase as the oxygen concentration in the exhaust decreases. NOx emissions showed a direct correlation with the flow rate of infiltrated air into the combustion space. The extent of batch carryover was primarily affected by variations in the furnace differential pressure. The furnace temperature did not vary significantly during the measurement campaign, so no clear correlation could be obtained between the available measurements of furnace temperature and alkali vaporization.

Techniques to ensure shock data quality and to recognize bad data are discussed in this paper. For certain shock environments, acceleration response up to ten kHz is desired for structural model validation purposes. The validity and uncertainty associated with the experimental data need to be known in order to use it effectively in model validation. In some cases the frequency content of impulsive or pyrotechnic loading or metal to metal contact of joints in the structure may excite accelerometer resonances at hundreds of kHz. The piezoresistive accelerometers often used to measure such events can provide unreliable data depending on the level and frequency content of the shock. The filtered acceleration time history may not reveal that the data are unreliable. Some data validity considerations include accelerometer mounting systems, sampling rates, band-edge settings, peak acceleration specifications, signal conditioning bandwidth, accelerometer mounted resonance and signal processing checks. One approach for uncertainty quantification of the sensors, signal conditioning and data acquisition system is also explained.

A flexible, robust method for linking grids of locally refined ground-water flow models constructed with different numerical methods is needed to address a variety of hydrologic problems. This work outlines and tests a new ghost-node model-linking method for a refined "child" model that is contained within a larger and coarser "parent" model that is based on the iterative method of Steffen W. Mehl and Mary C. Hill (2002, Advances in Water Res., 25, p. 497-511; 2004, Advances in Water Res., 27, p. 899-912). The method is applicable to steady-state solutions for ground-water flow. Tests are presented for a homogeneous two-dimensional system that has matching grids (parent cells border an integer number of child cells) or nonmatching grids. The coupled grids are simulated by using the finite-difference and finite-element models MODFLOW and FEHM, respectively. The simulations require no alteration of the MODFLOW or FEHM models and are executed using a batch file on Windows operating systems. Results indicate that when the grids are matched spatially so that nodes and child-cell boundaries are aligned, the new coupling technique has error nearly equal to that when coupling two MODFLOW models. When the grids are nonmatching, model accuracy is slightly increased compared to that for matching-grid cases. Overall, results indicate that the ghost-node technique is a viable means to couple distinct models because the overall head and flow errors relative to the analytical solution are less than if only the regional coarse-grid model was used to simulate flow in the child model's domain.

A discussion on an active gas imager that can potentially improve system performance and reliability in Smart Leak Detection and Repair covers conventional single-wavelength imaging; differential imaging; methane detection; modification for detecting fugitive emissions relevant to refineries and chemical plants; and system description. This is an abstract of a paper presented at the AWMA's 99th Annual Conference and Exhibition (New Orleans, LA 6/20-23/2006).

The RADTRAN Loss of Shielding (LOS) Model was benchmarked using MicroShield 6.20®. This analysis considers an intact spent fuel truck cask as well as a set of damaged truck casks. Ratios of dose rates are calculated for casks with a loss of lead shielding to those of intact casks, and are then compared to ratios generated by the LOS model. LOS Model results were considered verified if two main constraints were satisfied. First, the dose rate profiles for both the LOS and MicroShield 6.20® calculations must have the same general shape and behavior. Additionally, the largest factor difference between any two points of the dose rate profiles may not exceed an order of magnitude. Reasonable agreement is shown for large-fraction LOS scenarios; however the differences in results are not satisfactory for cases with small fractions of slump.

A wide variety of MicroElectroMechanical Systems (MEMS) are fabricated using existing novel technologies. State-of-the art integrated circuit (IC) fabrication methods are used for the fabrication of these MEMS. The fabrication of these structures requires many process steps that include deposition, patterning, etching, and CMP. The use of CMP enables the fabrication of complex, multi-level MEMS. Similar to IC fabrication, there are concerns about non-uniformity, erosion and dishing after CMP, but because of the thickness of the materials, CMP processing issues are amplified. Unlike ICs, there is no transistor basic building block so processing must be technology specific and process development is driven by the device/system performance requirements, which are very specific to the application.

Abstract not provided.

We apply ab initio molecular dynamics (AIMD) to study the hydration structures and electronic properties of the formohydroxamate anion in liquid water. We consider the cis- nitrogen-deprotonated, cis- oxygen-deprotonated, and trans- oxygen-deprotonated formohydroxamate tautomers. They form an average of 6.3, 6.9, and 6.0 hydrogen bonds with water molecules, respectively. The predicted pair correlation functions and time dependence of the hydration numbers suggest that water is highly structured around the nominally negatively charged oxime oxygen in O-deprotonated tautomers but significantly less so around the nitrogen atom in the N-deprotonated species. Wannier function analysis suggests that, in the O-deprotonated anions, the negative charge is concentrated on the oxime oxygen, while in the N-deprotonated case, it is partially delocalized between the nitrogen and the adjoining oxime oxygen atom. © 2006 Elsevier B.V. All rights reserved.