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.