Publications

A Ka-Band RF MEMS enabled frequency reconfigurable triangular microstrip patch antenna has been designed for monolithic integration with RF MEMS phase shifters to demonstrate a low-cost monolithic passive electronically scanned array (PESA). This paper introduces our first prototype reconfigurable triangular patch antenna currently in fabrication. The aperture coupled patch antenna is fabricated on a dual-layer quartz/alumina substrate using surface micromachining techniques. Full-wave MoM simulation results will be compared to laboratory measurements in the oral presentation. © 2005 IEEE.

Advances in FPGA technology have led to dramatic improvements in double precision floating-point performance. Modern FPGAs boast several GigaFLOPs of raw computing power. Unfortunately, this computing power is distributed across 30 floating-point units with over 10 cycles of latency each. The user must find two orders of magnitude more parallelism than is typically exploited in a single microprocessor; thus, it is not clear that the computational power of FPGAs can be exploited across a wide range of algorithms. This paper explores three implementation alternatives for the Fast Fourier Transform (FFT) on FPGAs. The algorithms are compared in terms of sustained performance and memory requirements for various FFT sizes and FPGA sizes. The results indicate that FPGAs are competitive with microprocessors in terms of performance and that the "correct" FFT implementation varies based on the size of the transform and the size of the FPGA. © 2005 IEEE.

In modal testing, the most popular tools for exciting a structure are hammers and shakers. This paper reviews the applications for which shakers have an advantage. In addition the advantages and disadvantages of different forcing inputs (e.g. sinusoidal, random, burst random and chirp) that can be applied with a shaker are noted. Special considerations are reported for the fixtures required for shaker testing (blocks, force gages, stingers) to obtain satisfactory results. Various problems that the author has encountered during single and multi-shaker modal tests are described with their solutions.

This paper provides an overview of several approaches to formulating and solving optimization under uncertainty (OUU) engineering design problems. In addition, the topic of high-performance computing and OUU is addressed, with a discussion of the coarse- and fine-grained parallel computing opportunities in the various OUU problem formulations. The OUU approaches covered here are: sampling-based OUU, surrogate model-based OUU, analytic reliability-based OUU (also known as reliability-based design optimization), polynomial chaos-based OUU, and stochastic perturbation-based OUU.

Latin Hypercube Sampling (LHS) is widely used as sampling based method for probabilistic calculations. This method has some clear advantages over classical random sampling (RS) that derive from its efficient stratification properties. However, one of its limitations is that it is not possible to extend the size of an initial sample by simply adding new simulations, as this will lead to a loss of the efficient stratification associated with LHS. We describe a new method to extend the size of an LHS to n (>=2) times its original size while preserving both the LHS structure and any induced correlations between the input parameters. This method involves introducing a refined grid for the original sample and then filling in empty rows and columns with new data in a way that conserves both the LHS structure and any induced correlations. An estimate of the bounds of the resulting correlation between two variables is derived for n=2. This result shows that the final correlation is close to the average of the correlations from the original sample and the new sample used in the infilling of the empty rows and columns indicated above.

There have been many papers proposing the use of logarithmic numbers (LNS) as an alternative to floating point because of simpler multiplication, division and exponentiation computations [1,4-9,13]. However, this advantage comes at the cost of complicated, inexact addition and subtraction, as well as the need to convert between the formats. In this work, we created a parameterized LNS library of computational units and compared them to an existing floating point library. Specifically, we considered multiplication, division, addition, subtraction, and format conversion to determine when one format should be used over the other and when it is advantageous to change formats during a calculation. © 2005 IEEE.

Chemiresistor microsensors have been developed to provide continuous in-situ detection of volatile organic compounds (VOCs). The chemiresistor sensor is packaged in a rugged, waterproof housing that allows the device to detect VOCs in air, soil, and water. Preconcentrators are also being developed to enhance the sensitivity of the chemiresistor sensor. The "micro- hotplate" preconcentrator is placed face-to-face against the array of chemiresistors inside the package. At prescribed intervals, the preconcentrator is heated to desorb VOCs that have accumulated on the sorbent material on the one-micron-thick silicon-nitride membrane. The pulse of higher-than-ambient concentration of VOC vapor is then detected by the adjacent chemiresistors. The plume is allowed to diffuse out of the package through slots adjacent to the preconcentrator. The integrated chemiresistor/preconcentrator sensor has been tested in the laboratory to evaluate the impacts of sorbent materials, fabrication methods, and repeated heating cycles on the longevity and performance of the sensor. Calibration methods have also been developed, and field tests have been initiated. Copyright ASCE 2005.

Real-time water quality and chemical-specific sensors are becoming more commonplace in water distribution systems. The overall objective of the sensor network is to protect consumers from accidental and malevolent contamination events occurring within the distribution network. This objective can be quantified several different ways including: minimizing the amount of contaminated water consumed, minimizing the extent of the contamination within the network, minimizing the time to detection, etc. We examine the ability of a sensor network to meet these objectives as a function of both the detection limit of the sensors and the number of sensors in the network. A moderately-sized network is used as an example and sensors are placed randomly. The source term is a passive injection into a node and the resulting concentration in the node is a function of the volumetric flow through that node. The concentration of the contaminant at the source node is averaged for all time steps during the injection period. For each combination of a certain number of sensors and a detection limit, the mean values of the different objectives across multiple random sensor placements are evaluated. Results of this analysis allow the tradeoff between the necessary detection limit in a sensor and the number of sensors to be evaluated. Results show that for the example problem examined here, a sensor detection limit of 0.01 of the average source concentration is adequate for maximum protection. Copyright ASCE 2005.

Previously unpublished results from multiscalar point measurements in the series of piloted CH4/air jet flames [R.S. Barlow, J.H. Frank, Proc. Combust. Inst. 27 (1998) 1087-1095] are presented and analyzed. The emphasis is on features of the data that reveal the relative importance of molecular diffusion and turbulent transport in these flames. The complete series A-F is considered. This includes laminar, transitional, and turbulent flames spanning a range in Reynolds number from 1100 to 44,800. Results on conditional means of species mass fractions, the differential diffusion parameter, and the state of the water-gas shift reaction all show that there is an evolution in these flames from a scalar structure dominated by molecular diffusion to one dominated by turbulent transport. Long records of 6000 single-point samples at each of several selected locations in flame D are used to quantify the cross-stream (radial) dependence of conditional statistics of measured scalars. The cross-stream dependence of the conditional scalar dissipation is determined from 6000-shot, line-imaging measurements at selected locations. The cross-stream dependence of reactive scalars, which is most significant in the near field of the jet flame, is attributed to radial differences in both convective and local time scales of the flow. Results illustrate some potential limitations of common modeling assumptions when applied to laboratory-scale flames and, thus, provide a more complete context for interpretation of comparisons between experiments and model calculations. © 2005 The Combustion Institute. Published by Elsevier Inc. All rights reserved.

We have developed and implemented a method which given a three-dimensional object can infer from topology the two-dimensional masks needed to produce that object with surface micromachining. This design tool calculates the two-dimensional mask set required to produce a given three-dimensional model by investigating the vertical topology to the model. The 3D model is first separated into bodies that are non-intersecting, made from different materials or only linked through a ground plane. Next, for each body unique horizontal cross sections are located and arranged into a tree based on their topological relationship. A branch-wise search of the tree uncovers locations where deposition boundaries must lie and identifies candidate masks creating a generic mask set for the 3D model. Finally, in the last step specific process requirements are considered that may constrain the generic mask set.

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.

Thermal conduction codes can be used as solvers for the diffusion approximation for radiation heat transfer. Energy fluxes and temperature distributions that result from thermal radiation in an optically-thick participating medium can be estimated. Allowing dependence on temperatures from either side of the interface, a contact resistance algorithm can be used to implement "jump" (or slip) boundary conditions appropriate for the diffusion approximation in solving the radiation transfer equation. For steady, pure radiation (no conduction) systems analytical expressions exist to specify the temperature in the radiating medium at the wall as a function of the wall temperature, wall emissivity, and extinction coefficient. Radiation and conduction solutions for gray, absorbing/emitting and conducting media bound by diffuse surfaces for the simple case of the steady planar layer are considered. Reference solutions are developed by detailed zone-methods solving the coupled differential forms of both the radiation and conduction heat transfer equations. From the reference solutions, empirical relations are developed for surface resistance as functions of the local wall and adjacent media temperatures, the wall emissivity, the absorptivity, and the thermal conductivity of the medium. Performance of the approximate solution is compared to the reference solutions. 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.

Described below are major electromagnetic test facilities at Sandia National Laboratories; each has undergone recent upgrades. This paper will discuss each facility, their uses, and upgrades pertaining to the facilities performance and diagnostic capabilities. The facilities discussed here are the Sandia Lightning Simulator, the Electromagnetic Environments Simulator, the Mode-Stirred Chamber, and Anechoic Chamber. Sandia's expertise in electromagnetics also extends to theoretical analysis and modeling, which can be done in conjunction with tests or experiments. © 2005 IEEE.

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).

This paper is about making reversible logic a reality for supercomputing. Reversible logic offers a way to exceed certain basic limits on the performance of computers, yet a powerful case will have to be made to justify its substantial development expense. This paper explores the limits of current, irreversible logic for supercomputers, thus forming a threshold above which reversible logic is the only solution. Problems above this threshold are discussed, with the science and mitigation of global warming being discussed in detail. To further develop the idea of using reversible logic in supercomputing, a design for a 1 Zettaflops supercomputer as required for addressing global climate warming is presented. However, to create such a design requires deviations from the mainstream of both the software for climate simulation and research directions of reversible logic. These deviations provide direction on how to make reversible logic practical. Copyright 2005 ACM.

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.