Publications

The effects of ozone (O 3) on tin oxide growth rates from mixtures of monobutyltintrichloride (MBTC), O 2 and H 2O are reported. The results indicate that O 3 increases the growth rate under kinetically controlled conditions (MBTC + O 2, 25 torr), but under mass-transport-control (200 torr and/or addition of H 2O to the reactant gases), growth rates are either unaffected or decrease. Kinetic modeling of the gas-phase reactions suggests that O, H, and OH radicals react at the surface to increase the growth rate, but higher pressures reduce their concentrations via recombination. In addition, higher pressures result in increased concentrations of less reactive tin halides, which are decomposition products of MBTC. It appears that when H 2O is a reactant, these radicals reduce the concentration of the tin oxide precursor (thought to be an MBTC-H 2O complex), which significantly decreases the growth rate.

The simulated annealing algorithm is used to seek optimal radiant heater configurations that provide a desired distribution of incident radiant energy onto a surface. The problem is motivated by a need to create well-understood boundary conditions that simulate fire environments. A bank of halogen lamps irradiates the back of a thin black plate (called a shroud), which simulates the fire environment. For such fire simulations, shroud temperatures routinely exceed 1000°C and thermal radiation is the dominant mode of heat transfer. The test specimen is then heated by placing it in front of the shroud. The panel, accommodating the radiant heaters (lamps), provides equally spaced slots all of which are powered at the same voltage. Lamp positioning is crucial to obtaining a uniform temperature on the shroud, but determining the best positioning of the lamps experimentally through trial and error has proven difficult. The discrete optimization problem searches possible lamp configurations by simulating adding or removing lamps from the panel. Inverse heat transfer methods have been successfully applied to similar problems. Applying inverse heat transfer methods to this problem, the desired boundary conditions on the shroud are used to solve for the required heater settings. Two boundary conditions are needed: the temperature profile and the heat flux profile on the shroud. The heat flux profile is determined by calculating the radiation heat transfer between the shroud and the test object. However, because the heaters used in the design can only assume discrete positions and are all maintained at the same power level, traditional inverse methods fail. A discrete inverse radiation heat transfer solution method is needed. In this study, a simulated annealing optimization routine is used to determine optimal heater positions given desired boundary conditions on the shroud. Computational characteristics of simulated annealing are presented as well as results of the optimization. Copyright © 2005 by ASME.

We investigate the accuracy of chemical transport in network models for small geometric configurations. Network model have successfully simulated the general operations of large water distribution systems. However, some of the simplifying assumptions associated with the implementation may cause inaccuracies if chemicals need to be carefully characterized at a high level of detail. In particular, we are interested in precise transport behavior so that inversion and control problems can be applied to water distribution networks. As an initial phase, Navier Stokes combined with a convection-diffusion formulation was used to characterize the mixing behavior at a pipe intersection in two dimensions. Our numerical models predict only on the order of 12-14 % of the chemical to be mixed with the other inlet pipe. Laboratory results show similar behavior and suggest that even if our numerical model is able to resolve turbulence, it may not improve the mixing behavior. This conclusion may not be appropriate however for other sets of operating conditions, and therefore we have started to develop a 3D implementation. Preliminary results for duct geometry are presented. © copyright ASCE 2005.

We present the design and implementation of InfoStar, an adaptive visual analytics platform for mobile devices such as PDAs, laptops, Tablet PCs and mobile phones, InfoStar extends the reach of visual analytics technology beyond the traditional desktop paradigm to provide ubiquitous access to interactive visualizations of information spaces. These visualizations are critical in addressing the knowledge needs of human agents operating in the field, in areas as diverse as business, homeland security, law enforcement, protective services, emergency medical services and scientific discovery. We describe an initial real world deployment of this technology, in which the InfoStar platform has been used to offer mobile access to scheduling and venue information to conference attendees at Supercomputing 2004. © 2005 IEEE.

Laboratory and field developments are underway to use solar energy to power a desalination technology - capacitive deionization - for water produced by remote Coal Bed Methane (CBM) natural gas wells. Due to the physical remoteness of many CBM wells throughout the Southwestern U.S., as shown in Figure 1, this approach may offer promise. This promise is not only from its effectiveness in removing salt from CBM water and allowing it to be utilized for various applications, but also for its potentially lower energy consumption compared to other technologies, such as reverse osmosis. This, coupled with the remoteness (Figure 1) of thousands of these wells, makes them more feasible for use with photovoltaic (solar, electric, PV) systems. Concurrent laboratory activities are providing information about the effectiveness and energy requirements of each technology under various produced water qualities and water reuse applications, such as salinity concentrations and water flows. These parameters are being used to driving the design of integrated PV-powered treatment systems. Full-scale field implementations are planned, with data collection and analysis designed to optimize the system design for practical remote applications. Early laboratory studies of capacitive deionization have shown promise that at common CBM salinity levels, the technology may require less energy, is less susceptible to fouling, and is more compact than equivalent reverse osmosis (RO) systems. The technology uses positively and negatively charged electrodes to attract charged ions in a liquid, such as dissolved salts, metals, and some organics, to the electrodes. This concentrates the ions at the electrodes and reduces the ion concentrations in the liquid. This paper discusses the results of these laboratory studies and extends these results to energy consumption and design considerations for field implementation of produced water treatment using photovoltaic systems.

This paper discusses issues that arise in controlling high quality mechanical shock inputs for mock hardware in order to validate a model of a bolted connection. The dynamic response of some mechanical components is strongly dependent upon the behavior of their bolted connections. The bolted connections often provide the only structural load paths into the component and can be highly nonlinear. Accurate analytical modeling of bolted connections is critical to the prediction of component response to dynamic loadings. In particular, it is necessary to understand and correctly model the stiffness of the joint and the energy dissipation (damping) that is a nonlinear function of the forces acting on the joint. Frequency-rich shock inputs composed of several decayed sinusoid components were designed as model validation tests and applied to a test item using an electrodynamic shaker. The test item was designed to isolate the behavior of the joint of interest and responses were dependent on the properties of the joints. The nonlinear stiffness and damping properties of the test item under study presented a challenge in isolating behavior of t4he test hardware from the stiffness, damping and boundary conditions of the shaker. Techniques that yield data to provide a sound basis for model validation comparisons of the bolted joint model are described.

Lifetime prediction of polymeric materials often requires extrapolation of accelerated aging data with the suitability and confidence in such approaches being subject to ongoing discussions. This paper reviews the evidence of non-Arrhenius behaviour (curvature) instead of linear extrapolations in polymer degradation studies. Several studies have emphasized mechanistic variations in the degradation mechanism and demonstrated changes in activation energies but often data have not been fully quantified. To improve predictive capabilities a simple approach for dealing with curvature in Arrhenius plots is examined on a basis of two competing reactions. This allows for excellent fitting of experimental data as shown for some elastomers, does not require complex kinetic modelling, and individual activation energies are easily determined. Reviewing literature data for the thermal degradation of polypropylene a crossover temperature (temperature at which the two processes equally contribute) of ∼83 °C was determined, with the high temperature process having a considerably higher activation energy (107-156 kJ/mol) than the low temperature process (35-50 kJ/mol). Since low activation energy processes can dominate at low temperatures and longer extrapolations result in larger uncertainties in lifetime predictions, experiments focused on estimating Ea values at the lowest possible temperature instead of assuming straight line extrapolations will lead to more confident lifetime estimates. © 2005 Elsevier Ltd. All rights reserved.

We report the results of experiments using a small Q-switched Nd:YAG laser at 532 and 1064 nm to trigger a 170-kV pulse-charged water switch. 1-σ jitters as low as ±1.7 ns were demonstrated; an order of magnitude improvement over the ±25-ns jitter of the switch in its self-breaking mode. At the optimum observed triggering wavelength of 532 nm, a 7-ns laser pulse gave better results than a 0.15-ns laser pulse. Time resolved optical diagnostics suggest a multistage triggering process in which the laser forms a string of point plasmas between the switch electrodes. These point plasmas expand, cool and merge, forming a vapor column between the electrodes that breaks down rapidly with low jitter. © 2005 IEEE.

The research goal presented here is to model the electrical response of gold plated copper electrical contacts exposed to a mixed flowing gas stream consisting of air containing 10ppb H 2S at 30°C and a relative humidity of 70% This environment accelerates the attack normally observed in a light industrial environment (similar to, but less severe than, the Battelle class 2 environment). Corrosion rates were quantified by measuring the corrosion site density, size distribution, and the electrical resistance of a probe contact with the aged surface, as a function of exposure time. A pore corrosion numerical model was used to predict both the growth of copper sulfide corrosion product which blooms through defects in the gold layer and the resulting electrical contact resistance of the aged surface. Assumptions about the distribution of defects in the noble metal plating and the mechanism for how corrosion blooms affect electrical contact resistance were needed to close the numerical model. Comparisons are made to the experimentally observed corrosion-bloom number density, bloom size distribution, and the cumulative probability distribution of the electrical contact resistance. Experimentally, the bloom site density increases as a function of time, whereas the bloom size distribution remains relatively independent of time. These two effects are included in the numerical model by adding a corrosion initiation probability proportional to the surface area and a probability for bloom-growth extinction proportional to the bloom volume, due to Kirkendall voiding. The cumulative probability distribution of electrical resistance becomes skewed as exposure time increases. While the resistance increases as a function of time for a fraction of the bloom population, the median value remains relatively unchanged. In order to model this behavior, the resistance calculated for large blooms is heavily weighted by contributions from the halo region.

VisTrails is a new system that enables interactive multiple-view visualizations by simplifying the creation and maintenance of visualization pipelines, and by optimizing their execution. It provides a general infrastructure that can be combined with existing visualization systems and libraries. A key component of VisTrails is the visualization trail (vistrail), a formal specification of a pipeline. Unlike existing dataflow-based systems, in VisTrails there is a clear separation between the specification of a pipeline and its execution instances. This separation enables powerful scripting capabilities and provides a scalable mechanism for generating a large number of visualizations. VisTrails also leverages the vistrail specification to identify and avoid redundant operations. This optimization is especially useful while exploring multiple visualizations. When variations of the same pipeline need to be executed, substantial speedups can be obtained by caching the results of overlapping subsequences of the pipelines. In this paper, we describe the design and implementation of VisTrails, and show its effectiveness in different application scenarios. © 2005 IEEE.

In light of difficulties in realizing a carbohydrate fuel cell that can run on animal or plant carbohydrates, a study was carried out to fabricate a membrane separated, platinum cathode, enzyme anode fuel cell, and test it under both quiescent and flow through conditions. Mediator loss to the flowing solution was the largest contributor to power loss. Use of the phenazine derivative mediators offered decent open circuit potentials for half cell and full cell performance, but suffered from quick loss to the solution which hampered long term operation. A means to stabilize the phenazine molecules to the electrode would need to be developed to extend the lifetime of the cell beyond its current level of a few hours. This is an abstract of a paper presented ACS Fuel Chemistry Meeting (Washington, DC Fall 2005).

A directional scintillating fiber detector for 14-MeV neutrons was simulated using the GEANT4 Monte Carlo simulation tool. Detail design aspects of a prototype 14 MeV neutron fiber detector under development were used in the simulation to assess performance and design features of the detector. Saint-Gobain produced, BCF-12, plastic fiber material was used in the prototype development. The fiber consists of a core scintillating material of polystyrene with 0.48 mm × 0.48 mm dimension and an acrylic outer cladding of 0.02 mm thickness. A total of 64 square fibers, each with a cross-sectional area of 0.25 mm 2 and length of 100 mm were positioned parallel to each other with a spacing of 2.3 mm (fiber pitch) in the tracking of 14-MeV neutron induced recoil proton (n-p) events. Neutron induced recoil proton events, resulting energy deposition in two collinear fibers, were used in reconstructing a two dimensional (2D) direction of incident neutrons. Blurring of recoil protons signal in measurements was also considered to account uncertainty in direction reconstruction. Reconstructed direction has a limiting angular resolution of 3° due to fiber dimension. Blurring the recoil proton energy resulted in further broadening of the reconstructed direction and the angular resolution was 20°. These values were determined when incident neutron beam makes an angle of 45 degree relative to the front surface of the detector. Comparable values were obtained at other angles of incidence. Results from the present simulation have demonstrated promising directional sensitivity of the scintillating fiber detector under development.

As electronic assemblies become more compact and with increased processing bandwidth, the escalating thermal energy has become more difficult to manage. The major limitation has been nonmetallic joining using poor thermal interface materials (TIM). The interfacial, versus bulk, thermal conductivity of an adhesive is the major loss mechanism and normally accounts for an order magnitude loss in conductivity per equivalent thickness. The next generation TIM requires a sophisticated understanding of material and surface sciences, heat transport at sub-micron scales and the manufacturing processes used in packaging of microelectronics and other target applications. Only when this relationship between bondline manufacturing processes, structure and contact resistance is well understood on a fundamental level, would it be possible to advance the development of miniaturized microsystems. We give the status of the study of thermal transport across these interfaces.

Voltage and temperature distributions along the crucible were measured during VAR of 0.81 m diameter Ti-6Al-4V electrode into 0.91 m diameter ingot. These data were used to determine the current distribution along the crucible. Measurements were made for two furnace conditions, one with a bare crucible and the other with a painted crucible. The VAR furnace used for these measurements is of the non-coaxial type, i.e. current is fed directly into the bottom of the crucible through a stool (base plate) contact and exits the furnace through the electrode stinger. The data show that approximately 63% of the current is conducted directly between the ingot and electrode with the remaining conducted between the electrode and crucible wall. This partitioning does not appear to be sensitive to crucible coating. The crucible voltage data were successfully simulated using uniform current distributions for the current conduction zones, a value of 0.63 for the partitioning, and widths of 0.30 and 0.15 m for the ingot/crucible wall and plasma conduction zones, respectively. Successful simulation of the voltage data becomes increasingly difficult (or impossible) as one uses current partitioning values increasingly different from 0.63, indicating that the experimental value is consistent with theory. Current conducted between the ingot and crucible wall through the ingot/wall contact zone may vary during the process without affecting overall current partitioning. The same is true for current conducted through the ingot/stool and stool/crucible contact zones. There is some evidence that the ingot/stool current decreases with increasing ingot length for the case of the bare crucible. Equivalent circuit analysis shows that, under normal conditions, current partitioning is only sensitive to the ratio of the plasma resistance across the annulus to the plasma resistance across the electrode gap, thereby demonstrating the relationship between current partitioning and gap.

A comparison is made between numerical simulations and experimental data for soot and water vapor concentration in a JP-8 fire. Soot concentration depends on soot generated/destroyed per unit flame area (subgrid soot model) and the overall flame area per unit volume (turbulence treatment). Two different turbulence treatments, a steady RANS variant and an unsteady LES variant, are used to determine the effect of overall flame area per unit volume. The results indicate that the difference in the two turbulence treatments is greater than the difference between the data and either approach. Copyright © 2005 by ASME.

Studies were conducted to determine what relationships may exist between alloy compositions and inertia friction weld microstructures of austenitic stainless steels. Ternary alloys of iron, nickel and chromium with 60-70% Fe and a range in Cr/Ni ratios from 0.34 to 1.9 were investigated. It was found that although grain size and compositional banding were reduced and varied with radial position and weld parameters, no significant solid-state transformation between ferrite and austenite was detected. Ferrite stringers in base materials with high ferrite content were elongated and fragmented, while in base materials with small amounts of ferrite stringers the ferrite dissolved. These findings may vary for different sample geometries and weld schedules. Copyright © 2006 ASM International®.

Tubular specimens of the nitrogen-strengthened alloy 21Cr-6Ni-9Mn were instrumented with thermocouples and inertia welded using a wide range of axial forces and kinetic energies. It was determined that a linear relationship exists between upset and kinetic energy for a given axial force. Furthermore, the peak temperatures are inversely related to the applied axial force. Microstructural characterization was performed using optical and electron microscopy techniques. Ferrite was observed locally at the weld interface, and it was determined that the width of the ferrite zone could vary widely depending on the process parameters. Electron backscattered diffraction analysis revealed that the ferrite and austenite at the weld interface exhibit the Kurdjumov-Sachs orientation relationship, and suggests that a very large amount of ferrite is present during the welding process that subsequently transforms to austenite during cooling. The fracture toughness of inertia welds thermally charged in gaseous hydrogen was also measured. It was found that the hydrogen-assisted fracture susceptibility of the inertia welds was greater than that of the base metal, but less than that of 21Cr-6Ni-9Mn gas tungsten arc welds. Copyright © 2006 ASM International®.

This work investigated the relationship between the resistance degradation in low-force metal contacts and hot-switched operational conditions representative of MEMS devices. A modified nano-indentation apparatus was used to bring electrically-biased gold and platinum surfaces into contact at a load of 100 μN. The applied normal force and electrical contact resistance of the contact materials was measured simultaneously. The influence of parallel discharge paths for stored electrical energy in the contact circuit is discussed in relation to surface contamination decomposition and the observed resistance degradation.

Gap bridging of thin plate pulsed Nd:YAG lap welds is optimized by focused welding at low peak powers without gas shielding. High speed images reveal effects of varying welding parameters and weld pool and laser beam interactions. Improved bridging with out gas shielding is attributed to changes in Marangoni convective flow. Development and verification of finite element models for weld pool physics is being conducted. Copyright © 2006 ASM International®.

Sandia National Laboratories has completed thermal performance testing on the Schott parabolic trough receiver using the LS-2 collector on the Sandia rotating platform at the National Solar Thermal Test Facility in Albuquerque, NM. This testing was funded as part of the US DOE Sun-Lab USA-Trough program. The receiver tested was a new Schott receiver, known as Heat Collector Elements (HCEs). Schott is a new manufacturer of trough HCEs. The Schott HCEs are 4m long; therefore, two were joined and mounted on the LS-2 collector module for the test. The Schott HCE design consists of a 70mm diameter high solar absorptance coated stainless steel (SS) tube encapsulated within a 125mm diameter Pyrex® glass tube with vacuum in the annulus formed between the SS and glass tube to minimize convection heat losses. The Schott HCE design is unique in two regards. First, the bellows used to compensate for the difference in thermal expansion between the metal and glass tube are inside the glass envelope rather than outside. Second, the composition of materials at the glass-to-metal seal has very similar thermal expansion coefficients making the joint less prone to breakage from thermal shock. Sandia National Laboratories provided both the azimuth and elevation collector module tracking systems used during the tests. The test results showed the efficiency of the Schott HCE to be very similar to current HCEs being manufactured by Solel. This testing provided performance verification for the use of Schott tubes with Solargenix trough collector assemblies at currently planned trough power plant projects in Arizona and Nevada. Copyright © 2005 by ASME.

Sandia National Laboratories (Sandia) has an active relationship with the Navajo Nation. Sandia has grown this relationship with through joint formation of strategic multiyear plans oriented toward the development of sustainable Native American renewable energy projects and associated business development. For the last decade, the Navajo Tribal Utility Authority (NTUA) has installed stand-alone photovoltaic (PV) systems on the Navajo Reservation to provide some of its most remote customers with electricity. Sandia and New Mexico State University - Southwest Technology Development Institute's technical assistance supports NTUA as a leader in rural solar electrification, assists NTUA's solar program coordinator to create a sustainable program and conveys NTUA's success in solar to others, including the Department of Energy (DOE). In partnership with DOE's Tribal Energy Program, summer interns' Jennifer Coots (MBA student) and Benjamin Mar (Electrical and Computer Engineering student) prepared case studies that summarize the rural utility's experience with solar electric power.

Noncontinuum gas-phase heat transfer in two microscale geometries is investigated using two computational methods. The motivation is microscale thermal actuation produced by heating-induced expansion of a near-substrate microbeam in air. The first geometry involves a 1-μm microgap filled with gas and bounded by parallel solid slabs. The second geometry involves a heated I-shaped microbeam 2 μm from the adjacent substrate, with gas in between. Two computational methods are applied. The Navier-Stokes slip-jump (NSSJ) method uses continuum heat transfer in the gas, with temperature jumps at boundaries to treat noncontinuum effects. The Direct Simulation Monte Carlo (DSMC) method uses computational molecules to simulate noncontinuum gas behavior accurately. For the microgap, the heat-flux values from both methods are in good agreement for all pressures and accommodation coefficients. For the microbeam, there is comparably good agreement except for cases with low pressures and near-unity accommodation coefficients. The causes of this discrepancy are discussed. Copyright © 2005 by ASME.

A numerical model of the ESR process was used to study the effect of the various process parameters on the resulting temperature profiles, flow field, and pool shapes. The computational domain included the slag and ingot, while the electrode, crucible, and cooling water were considered as external boundary conditions. The model considered heat transfer, fluid flow, solidification, and electromagnetic effects. The predicted pool profiles were compared with experimental results obtained over a range of processing parameters from an industrial-scale 718 alloy ingot. The shape of the melt pool was marked by dropping nickel balls down the annulus of the crucible during melting. Thermocouples placed in the electrode monitored the electrode and slag temperature as melting progressed. The cooling water temperature and flow rate were also monitored. The resulting ingots were sectioned and etched to reveal the ingot macrostructure and the shape of the melt pool. Comparisons of the predicted and experimentally measured pool profiles show excellent agreement. The effect of processing parameters, including the slag cap thickness, on the temperature distribution and flow field are discussed. The results of a sensitivity study of thermophysical properties of the slag are also discussed.

Experimentally measured temperature profiles along the micron-scale beam of a working thermal actuator are reported for the first time. Using a surface Raman scattering technique, temperature measurements are obtained in a noncontact fashion with submicron spatial resolution and to within an uncertainty of better than ± 10 K. The experimental data are used to validate computational predictions of the actuator thermal performance with reasonable agreement between the data and predicted temperatures. Copyright © 2005 by ASME.

The structural characteristics of buttress thread mechanical joints are not well understood and are difficult to accurately model. As an initial step towards understanding the mechanics of the buttress thread, a 2D plane stress model was created. An experimental investigation was conducted to study the compliance, damping characteristics, and stress field in an axial test condition. The compliance and damping were determined experimentally from a steel cross section of a buttress thread. The stress field was visualized using photoelastic techniques. The mechanics study combined with the photoelastic study provided a set of validation data.