Publications

In this study, we extend self-similar, far-field, turbulent wake concepts to estimate the 2-d drag coefficient for a range of bluff body problems. The self-similar wake velocity defect that is normally independent of the near field wake (and hence body geometry) is modified using a combined approximate Green's function/Gram-Charlier series approach to retain the body geometry information. Formally a near field velocity defect profile is created using small disturbance theory and the inviscid flow field associated with the body of interest. The defect solution is then used as an initial condition in the approximate Green's function solution. Finally, the Green's function solution is matched to the Gram-Charlier series yielding profiles that are integrated to yield the net form drag on the bluff body. Preliminary results indicate that drag estimates computed using this method are within approximately 15% as compared to published values for flows with large separation. This methodology may be of use as a supplement to CFD and experimental solutions in reducing the heavy computational and experimental burden of estimating drag coefficients for blunt body flows for preliminary design type studies. © 2004 by the American Institute of Aeronautics and Astronautics, Inc.

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Three-dimensional Direct Simulation Monte Carlo simulations of Columbia Shuttle Orbiter flight STS-107 are presented. The aim of this work is to determine the aerodynamic and heating behavior of the Orbiter during aerobraking maneuvers and to provide piecewise integration of key scenario events to assess the plausibility of the candidate failure scenarios. The flight of the Orbiter is examined at two altitudes: 350-kft and 300-kft. The flowfield around the Orbiter and the heat transfer to it are calculated for the undamaged configuration. The flow inside the wing for an assumed damage to the leading edge in the form of a 10- inch hole is studied.

Abstract not provided.

This report covers the basic design of the Sandia downhole geothermal reservoir monitoring system. The monitoring system can operate continuously at temperatures up to 240°C (464°F) while measuring small pressure and temperature changes in reservoirs. Future improvements in the existing system will come from research and development programs by such agencies as NASA, JPL, USAF and NETL. An explanation of the benefits of this research to the Geothermal HT electronics program will be given.

Chemical transport through human skin can play a significant role in human exposure to toxic chemicals in the workplace, as well as to chemical/biological warfare agents in the battlefield. The viability of transdermal drug delivery also relies on chemical transport processes through the skin. Models of percutaneous absorption are needed for risk-based exposure assessments and drug-delivery analyses, but previous mechanistic models have been largely deterministic. A probabilistic, transient, three-phase model of percutaneous absorption of chemicals has been developed to assess the relative importance of uncertain parameters and processes that may be important to risk-based assessments. Penetration routes through the skin that were modeled include the following: (1) intercellular diffusion through the multiphase stratum corneum; (2) aqueous-phase diffusion through sweat ducts; and (3) oil-phase diffusion through hair follicles. Uncertainty distributions were developed for the model parameters, and a Monte Carlo analysis was performed to simulate probability distributions of mass fluxes through each of the routes. Sensitivity analyses using stepwise linear regression were also performed to identify model parameters that were most important to the simulated mass fluxes at different times. This probabilistic analysis of percutaneous absorption (PAPA) method has been developed to improve risk-based exposure assessments and transdermal drug-delivery analyses, where parameters and processes can be highly uncertain. © 2004 Elsevier B.V. All rights reserved.

Abstract not provided.

The system design of the Advanced Exterior Sensor (AES), test data and Sandia National Laboratories' current work on the AES is described. The AES integrates three sensor technologies (thermal infrared waveband, visible waveband, and microwave radar) in a Remote Sensor Module communicating with three motion detection target trackers and a sensor fusion software module in the Data Processor Module to achieve higher performance than single technology devices. Wide areas are covered by continuously scanning the three sensors 360 degrees in about one second. The images from the infrared and visible detector sets and the radar range data are updated as the sensors rotate each second. The radar provides range data with approximately one-meter resolution. Panoramic imagery is generated for immediate visual assessment of alarms using the Display Control Module. There is great potential for site security enhancement using the AES, which was designed for low-cost, easy use and rapid deployment to cover wide areas beyond typical perimeters, possibly in place of typical perimeter sensors, and for tactical applications around fixed or temporary high-value assets. Commercial-off-the-shelf (COTS) systems have neither the three sensor technologies nor the imaging sensor resolution. Cost and performance will be discussed for different scenarios. ©2004 IEEE.

Recent attempts to fabricate free-standing MEMS structures using electrodeposited Ni have run into difficulty due to the curvatures that result from stress gradients intrinsic to electrodeposition. We have investigated the intrinsic stress behavior during electrodeposition of Ni from an additive-free sulfamate bath. It was determined that the stress during the first 1000 Å of growth was dependent only on the substrate materials, whereas the stress after that point was dependent on the deposition rate. Additionally, the stress in this region was found to be independent of the stress-state of the underlying material. Therefore, by varying the plating dynamically during deposition it is possible to reduce or eliminate the curvature in Ni MEMS structures.

Paraxial diodes have been a stronghold for high-brightness, flash x-ray radiography. In its traditional configuration, an electron beam impinges onto an anode foil, entering a gas-filled transport cell. Within the cell, the beam is focused into a small spot onto a high-Z target to generate x-rays for the radiographic utility. Simulations using Lsp, a particle-in-cell code, have shown that within the gas-filled focusing cell the electron beam spot location sweeps axially during the course of the beam pulse. The result is a larger radiographic spot than is desirable. Lsp has also shown that replacing the gas-filled cell with a fully ionized plasma on the order of 1016 cm-3 will prevent the spot from significant beam sweeping, thus resulting in a smaller, more stable radiographic spot size. Sandia National Laboratories (SNL) is developing a plasma-filled focusing cell for future paraxial diode experiments. A z-discharge in a hydrogen fill is used to generate a uniform, highly ionized plasma. Laser interferometry is the key diagnostic to determine electron density in a light lab setting and during future paraxial diode shots on SNL's RITS-3 accelerator. A time-resolved spot diagnostic will also be implemented during diode shots to measure the change in spot size during the course of the pulse. © 2004 IEEE.

Two-dimensional facial recognition has, traditionally, been an attractive biometric, however, the accuracy of 2D facial recognition (FR) is performance limited and insufficient when confronted with extensive numbers of people to screen and identify, and the numerous appearances that a 2D face can exhibit. In efforts to overcome many of the issues limiting 2D FR technology, researchers are beginning to focus their attention on 3D FR technology. In this paper, an analysis of a 3D FR system being developed at Sandia National Laboratories is performed. The study involves the use of 200 subjects on which verification (one-to-one) matches are performed using a single probe database (one correct match per subject) and 30 subjects on which identification matches are performed. The system is evaluated in terms of probability of detection (Pd) and probability of false accepts (FAR). The results presented will aid in providing an initial understanding of the performance of 3D FR © 2004 IEEE.

The effect of variable demands at short time scales on the transport of a solute through a water distribution network has not previously been studied. We simulate flow and transport in a small water distribution network using EPANET to explore the effect of variable demand on solute transport across a range of hydraulic time step scales from 1 minute to 2 hours. We show that variable demands at short time scales can have the following effects: smoothing of a pulse of tracer injected into a distribution network and increasing the variability of both the transport pathway and transport timing through the network. Variable demands are simulated for these different time step sizes using a previously developed Poisson rectangular pulse (PRP) demand generator that considers demand at a node to be a combination of exponentially distributed arrival times with log-normally distributed intensities and durations. Solute is introduced at a tank and at three different network nodes and concentrations are modeled through the system using the Lagrangian transport scheme within EPANET. The transport equations within EPANET assume perfect mixing of the solute within a parcel of water and therefore physical dispersion cannot occur. However, variation in demands along the solute transport path contribute to both removal and distortion of the injected pulse. The model performance measures examined are the distribution of the Reynolds number, the variation in the center of mass of the solute across time, and the transport path and timing of the solute through the network. Variation in all three performance measures is greatest at the shortest time step sizes. As the scale of the time step increases, the variability in these performance measures decreases. The largest time steps produce results that are inconsistent with the results produced by the smaller time steps.

In multispectral imaging, automated cross-spectral (band-to-band) image registration is difficult to achieve with a reliability approaching 100%. This is particularly true when registering infrared to visible imagery, where contrast reversals are common and similarity is often lacking. Algorithms that use mutual information as a similarity measure have been shown to work well in the presence of contrast reversal. However, weak similarity between the long-wave infrared (LWIR) bands and shorter wavelengths remains a problem. A method is presented in this paper for registering multiple images simultaneously rather than one pair at a time using a multivariate extension of the mutual information measure. This approach improves the success rate of automated registration by making use of the information available in multiple images rather than a single pair. This approach is further enhanced by including a cyclic consistency check, for example registering band A to B, B to C, and C to A. The cyclic consistency check provides an automated measure of success allowing a different combination of bands to be used in the event of a failure. Experiments were conducted using imagery from the Department of Energy's Multispectral Thermal Imager satellite. The results show a significantly improved success rate.

Calcium fluoride is a desirable material for optical design of space systems in the ultraviolet, visible, and infrared bands. Modern calcium fluoride materials fabricated for the photolithography industry are highly resistant to space radiation. The wide wavelength band and low dispersion are also desirable properties. Unfortunately, calcium fluoride has a host of significant material property issues which hinder its use in the space environment. Low hardness, susceptibility to thermal and mechanical shock, and large coefficient of thermal expansion present significant challenges during development of opto-mechanical designs. Sandia National Laboratories Monitoring Systems and Technology Center has fielded a calcium fluoride based optical system for use in space. The Sandia design solution is based upon a spring-loaded mount which uses no volatile organic compounds. The theory of the Sandia solution is developed and design rules are presented. The Sandia design solution is illustrated for a specific example. Example design and margin calculations are shown. Finally, lessons learned from our design realization and qualification testing efforts are shared for the benefit of the community.

While hyperspectral imaging systems are increasingly used in remote sensing and offer enhanced scene characterization relative to univariate and multispectral technologies, it has proven difficult in practice to extract all of the useful information from these systems due to overwhelming data volume, confounding atmospheric effects, and the limited a priori knowledge regarding the scene. The need exists for the ability to perform rapid and comprehensive data exploitation of remotely sensed hyperspectral imagery. To address this need, this paper describes the application of a fast and rigorous multivariate curve resolution (MCR) algorithm to remotely sensed thermal infrared hyperspectral images. Employing minimal a priori knowledge, notably non-negativity constraints on the extracted endmember profiles and a constant abundance constraint for the atmospheric upwelling component, it is demonstrated that MCR can successfully compensate thermal infrared hyperspectral images for atmospheric upwelling and, thereby, transmittance effects. We take a semi-synthetic approach to obtaining image data containing gas plumes by adding emission gas signals onto real hyperspectral images. MCR can accurately estimate the relative spectral absorption coefficients and thermal contrast distribution of an ammonia gas plume component added near the minimum detectable quantity.

In this paper, we describe an unstructured mesh volume renderer. Our renderer is interactive and accurately integrates light intensity an order of magnitude faster than previous methods. We employ a projective technique that takes advantage of the expanded programmability of the latest 3D graphics hardware. We also analyze an optical model commonly used for scientific volume rendering and derive a new method to compute it that is very accurate but computationally feasible in real time. We demonstrate a system that can accurately produce a volume rendering of an unstructured mesh with a first-order approximation to any classification method. Furthermore, our system is capable of rendering over 300 thousand tetrahedra per second yet is independent of the classification scheme used. © 2004 IEEE.

We've generated high-quality flat-top spatial profiles from a modified Continuum Powerlite 9010 Nd:YAG laser using the Gaussian-to-flat-top refractive beam shaper available from Newport Corporation. The Powerlite is a flashlamp-pumped, Q-switched, injection-seeded Nd:YAG laser manufactured in 1993 that delivers ∼ 1.6 J at 10 Hz using an oscillator and two 9 mm diameter amplifier rods. While its pulse energy is impressive, its beam-quality is typically poor, an all too common characteristic of research-grade Nd:YAG lasers manufactured in the late 1980's and early 1990's. Structure in its near-field spatial fluence profile is reminiscent of round-aperture diffraction that is superposed with additional "hot spots." These characteristics are largely due to poor beam quality from the oscillator coupled with over-filled amplifier rods, and reflect a design philosophy from the era of organic dye lasers. When these older laser systems are used for tasks like pumping optical parametric oscillators (OPO's), or for other applications demanding good beam quality, their designs are simply inadequate. To improve the 9010's beam quality we spatially filter the oscillator beam and remove the resulting Airy rings with an iris, then collimate and magnify the remaining central disk so its diameter is appropriate for input to the refractive shaper. The output of the beam shaper is then double-pass amplified through two amplifier rods with thermally induced focusing compensated by a negative lens before the first pass and by a convex mirror before the second pass. Using this approach we've obtained single-pass energy exceeding 250 mJ with little degradation of the flat-top profile and ∼ 950 mJ after double pass amplification. After double-passing the two amplifier rods the beam suffers some degradation in symmetry and uniformity, but is still much improved compared to the beam obtained using the 9010's original factory configuration. We find the modified 9010's fiat-top profile improves conversion efficiency when used for our applications in crystal nonlinear optics.

Transmission measurements of niobium and zirconium at both extreme-ultraviolet (EUV) and ultraviolet, visible, and near infrared (UV/Vis/NIR) wavelengths are presented. Thin foils of various thicknesses mounted on nickel mesh substrates were measured, and these data were used to calculate the optical constants δ and β of the complex refractive index n = 1-δ+iβ. β values were calculated directly from the measured transmittance of the foils after normalizing for the nickel mesh. The average β values for each set of foils are presented as a function of wavelength. The real (dispersive) part of the refractive index, δ was then calculated from Kramers-Kronig analysis by combining these β values with those from previous experimental data and the atomic tables.

Historically tracking systems have provided limited quantitative data such as approximate range, speed, and trajectory. Today's tracking systems are now being tasked with accurately quantifying a broader range of dynamic state variables (e.g., absolute and relative position, orientation, linear and angular velocity/acceleration, spin rate, trajectory, angle of attack, angle of impact) for high-speed test articles. This information is needed to demonstrate that the required test conditions are achieved, to develop, validate, and apply predictive models, and to document a system's response to a test environment. Few existing and emerging optical tracking methods accurately provide the dynamic state variables. Even fewer quantify the measurement uncertainty. Past measurement error estimates have been either qualitative or lacked the rigor needed to accurately validate and apply predictive models. This presentation will discuss tracking options and approaches for characterizing tracking measurement uncertainty.

Transmission electron microscope (TEM) tomography provides three-dimensional structural information from tilt series with nanoscale resolution. We have collected TEM projection data sets to study the internal structure of photocatalytic nanoparticles. Multiple cross-sectional slices of the nanoparticles are reconstructed using an algebraic reconstruction technique (ART) and then assembled to form a 3D rendering of the object. We recently upgraded our TEM with a new sample holder having a tilt range of ±70° and have collected tomography data over a range of 125°. Simulations were performed to study the effects of field-of-view displacement (shift and rotation), limited tilt angle range, hollow (missing) projections, stage angle accuracy, and number of projections on the reconstructed image quality. This paper discusses our experimental and computational approaches, presents some examples of TEM tomography, and considers future directions.

Abstract not provided.

We present the design and fabrication of voltage tunable two-color superlattice infrared photodetectors (SLIPs), where the detection wavelength switches from the long-wavelength infrared (LWIR) range to the mid-wavelength infrared (MWIR) range upon reversing the polarity of applied bias. The photoactive region of these detectors contains multiple periods of two distinct short-period SLs that are designed for MWIR and LWIR detection. The voltage tunable operation is achieved by using two types of thick blocking barriers between adjacent SLs - undoped barriers on one side for low energy electrons and heavily-doped layers on the other side for high energy electrons. We grew two SLIP structures by molecular beam epitaxy. The first one consists of two AlGaAs/GaAs SLs with the detection range switching from the 7-11 μm band to the 4-7 μm range on reversing the bias polarity. The background-limited temperature is 55 and 80 K for LWIR and MWIR detection, respectively. The second structure comprises of strained InGaAs/GaAs/AlGaAs SLs and AlGaAs/GaAs SLs. The detection range of this SLIP changes from the 8-12 μm band to the 3-5 μm band on switching the bias polarity. The background-limited temperature is 70 and 110 K for LWIR and MWIR detection, respectively. This SLIP is the first ever voltage tunable MWIR/LWIR detector with performance comparable to those of one-color quantum-well infrared detectors designed for the respective wavelength ranges. We also demonstrate that the corrugated light coupling scheme, which enables normal-incidence absorption, is suitable for the two-color SLIPs. Since these SLIPs are two-terminal devices, they can be used with the corrugated geometry for the production of low-cost large-area two-color focal plane arrays.

While there currently are a number of effective technologies and methodologies for explosive screening when close proximity to the person, package, or vehicle being screened is feasible, the problem of detecting explosives at significant stand-off distances remains one of the most difficult - and most important - challenges confronting physical security specialists. Among the major detection techniques, trace detection suffers from the fact that available vapor plumes are normally too dilute for detection at appreciable standoff under all but the most favorable conditions, and probing bulk techniques suffer from an intrinsic 1/r 4 fall-off of the signal intensity with distance. Research into potential means of standoff detection is necessary to try to address this important problem. This paper presents an overview of detection technologies that could prove useful in certain standoff detection applications, along with comments on future research needs. A distinction will be made between remote detection, in which the personnel searching for explosives maintain a safe standoff distance from the object being screened but where a sampling and/or detection unit may approach the object closely, and true standoff detection, where both the personnel and the sampling/detection equipment maintain a large standoff distance © 2004 IEEE.

Under traditional fire PRA methods, operating experience was used primarily to support statistical analysis of fire frequencies for specific plant locations and/or specific classes of fire ignition sources. While this application of the data continues, recent efforts to improve fire PRA methods, tools, and data are drawing more widely on insights from operating experience. This paper will describe some of the ways in which operating experience is being used to support fire PRA development activities.