Publications

Abstract not provided.

Abstract not provided.

This paper describes the development of a set of software tools useful for analyzing ultra-wideband (UWB) antennas and structures. These tools are used to perform finite difference time domain (FDTD) simulation of a conical antenna with continuous wave (CW) and UWB pulsed excitations. The antenna is analyzed using spherical coordinate-based FDTD equations that are derived from first principles. The simulation results for CW excitation are compared to simulation and measured results from published sources; the results for UWB excitation are new.

Abstract not provided.

Abstract not provided.

Abstract not provided.

This document contains a description of the verification and validation process used for the RADTRAN 5.5 code. The verification and validation process ensured the proper calculational models and mathematical and numerical methods were used in the RADTRAN 5.5 code for the determination of risk and consequence assessments. The differences between RADTRAN 5 and RADTRAN 5.5 are the addition of tables, an expanded isotope library, and the additional User-Defined meteorological option for accident dispersion. 3

Abstract not provided.

Abstract not provided.

Abstract not provided.

Here the analytical plate penetration relationship derived by De Chant [An explanation for the minimal effect of body curvature on hypervelocity penetration hole formation. Sandia National Laboratories, Albuquerque, NM, no. SAND2003-2696J. To appear in: International Journal of Solids and Structures] using an analogy between hydrodynamics and penetration processes is combined with the Grady-Kipp dynamic fragmentation model [International Journal of Impact Engineering 14 (1993) 427; Fragmentation of solids under dynamic loading. In: Wierzbicki, T., Jones, N. (Eds.), Structural Failure. Wiley, New York, 1989; Mechanisms of dynamic fragmentation: factors governing growth size, SAND84-2304C, Sandia National Laboratories, Albuquerque, NM, 1984] to estimate the size and distribution of fragments generated due to impact and penetration of thin plates by spherical projectiles. Fragment statistics estimated using this analytical model are then compared to fragmentation as predicted by CTH, a shock-physics hydrocode [International Journal of Impact Engineering 10 (1990) 351]. Agreement between analytically based model and CTH simulations shows good agreement. Extending the hydrodynamic based analogy used to develop the analytical plate penetration model to include fragmentation processes, we derive expressions relation fragmentation to plate impact and penetration. The functional form of these equations is also in good agreement with CTH simulation. Finally, a deterministic (as opposed to statistical) cumulative particle size distribution relationship is derived using mass conservation concepts and gives a power law distribution. The power law distribution requires the presence of a non-zero minimum fragment size rather than a continuous distribution that includes particles approaching zero size. The presence of a non-zero fragment size is in agreement with computational models and theoretically based cumulative lognormal fragment distributions. © 2004 Elsevier Ltd. All rights reserved.

The length scale of stress domain patterns formed at solid surfaces is usually calculated using isotropic elasticity theory. Because this length depends exponentially on elastic constants, deviations between isotropic and anisotropic elasticity can lead to large errors. Another inaccuracy of isotropic elasticity theory is that it neglects the dependence of elastic relaxations on stripe orientation. To remove these inaccuracies, we calculate the energy of striped domain patterns using anisotropic elasticity theory for an extensive set of surfaces encountered in experimental studies of self-assembly. We present experimental and theoretical evidence that elastic anisotropy is large enough to determine the stripe orientation when Pb is deposited on Cu(111). Our analytical and numerical results should be useful for analysis of a broad range of experimental systems. ©2005 The American Physical Society.

As interest in 3D face recognition increases the importance of the initial alignment problem does as well. In this paper we present a method utilizing the registered 2D color and range image of a face to automatically identify the eyes, nose, and mouth. These features are important to initially align faces in both standard 2D and 3D face recognition algorithms. For our algorithm to run as fast as possible, we focus on the 2D color information. This allows the algorithm to run in approximately 4 seconds on a 640X480 image with registered range data. On a database of 1,500 images the algorithm achieved a facial feature detection rate of 99.6% with 0.4% of the images skipped due to hair obstruction of the face.

A continuum-scale, evolutionary model of bubble nucleation, growth and He release for aging metal tritides is described which accounts for major features of the tritide database. Bubble nucleation, modeled as self-trapping of interstitially diffusing He atoms, occurs during the first few days following tritium introduction into the metal. Bubble growth by dislocation loop punching yields good agreement between He atomic volumes and bubble pressures determined from bulk swelling and 3He NMR data. The bubble spacing distribution determined from NMR is shown to remain fixed with age, justifying the separation of nucleation and growth phases and providing a sensitive test of the growth formulation. Late in life, bubble interactions are proposed to produce cooperative stress effects, which lower the bubble pressure. Helium generated near surfaces and surface-connected porosity accounts for the low-level early helium release. Use of an average ligament stress criterion predicts an onset of inter-bubble fracture in good agreement with the He/Metal ratio observed for rapid He release. From the model, it is concluded that He retention can be controlled through control of bubble nucleation.

Numerical methods are employed to examine the work, electric power input, and efficiency of electrokinetic pumps at a condition corresponding to maximum pump work. These analyses employ the full Poisson-Boltzmann equations and account for both convective and conductive electric currents, including surface conductance. We find that efficiencies at this condition of maximum work depend on three dimensionless parameters, the normalized zeta potential, normalized Debye layer thickness, and a fluid property termed the Levine number indicating the nominal ratio of convective to conductive electric currents. Efficiencies at maximum work exhibit a maximum for an optimum Debye layer thickness when the zeta potential and Levine number are fixed. This maximum efficiency increases with the square of the zeta potential when the zeta potential is small, but reaches a plateau as the zeta potential becomes large. The maximum efficiency in this latter regime is thus independent of the zeta potential and depends only on the Levine number. Simple analytical expressions describing this maximum efficiency in terms of the Levine number are provided. Geometries of a circular tube and planar channel are examined. © 2005 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

The diminished response of thermoluminescent phosphors over time is a well-documented challenge to thermoluminescent dosimetry. Wide ranges in fading rates for various phosphor types have been reported, making it necessary for many external dosimetry programs to perform individual studies on thermoluminescent fade. Sandia National Laboratories currently uses the Thermo 8802 LiF:Mg,Ti thermoluminescent dosimeter (TLD) in its personnel external dosimetry program. Doses received in the field are calculated by applying a fade algorithm published by the manufacturer to TLD readings. Since the algorithm was established by characterizing the diminished response of a TLD similar to the 8802, Sandia chose to model its fade study after the analysis done by Thermo. As a result, the parameters of each experiment were comparable, and data from the two studies were compared to determine whether or not the current algorithm should be modified specifically for use at Sandia. Cards were irradiated using an internal 90Sr/90Y source, and pre- and post-irradiation fading rates were monitored over a period of 18 wk. While significant fading was demonstrated, results closely matched those found in the original Thermo study.

The molten salt Flibe, a combination of lithium and beryllium fluorides studied for molten salt fission reactors, has been proposed as a breeder and coolant for fusion applications. The melting points of 2LiF-BeF2 and LiF-BeF2 are 460°C and 363°C, but LiF-BeF2 is rather viscous and has less lithium for breeding. In the Advanced Power Extraction (APEX) Program, concepts with a free flowing liquid for the first wall and blanket were investigated. Flinabe (a mixture of LiF, BeF2 and NaF) was selected for a molten salt design because a melting temperature below 350°C appeared possible and this provided an attractive operating temperature window for a reactor. To confirm that a ternary salt with a low melting temperature existed, several combinations of the fluoride salts, LiF, NaF and BeF2, were melted in a stainless steel crucible under vacuum. One had an apparent melting temperature of 305°C. The test system, preparation of the mixtures, melting procedures and temperature curves for the melting and cooling are presented along with the apparent melting points. Thermal modeling of the salt pool and crucible is reported in an accompanying paper.

It is generally accepted that thermal (Zeldo'vich) chemical kinetics dominate NO formation in diesel engines, so control of temperature is critical for reducing exhaust NOx emissions. Recent optical engine data revealed that when the start of injection (SOI) was retarded to very late timings, combustion luminosity decreased while exhaust NOx emissions increased, causing a "NOx bump." This data suggested that changes in radiative heat transfer from soot may affect in-cylinder temperatures and subsequent NOx formation. In this study, soot thermometry measurements of in-cylinder temperature and radiative heat transfer were correlated with exhaust NOx to quantify the role of radiative heat transfer on in-cylinder temperatures and NOx formation. The engine was operated at low-load conditions, for which the premixed burn was a significant fraction of the total heat release. Soot thermometry showed that radiative cooling reduced flame temperatures by 25-50 K for early SOI, reducing exhaust NOx by 12-25%. Near the NOx bump, radiative cooling was essentially absent, and the NOx reduction was thus removed. Radiative cooling alone, however, was found to be insufficient to be solely responsible for the observed changes in NOx emissions. Thermodynamic analysis showed that in the slow-mixing limit, compression-heating of burned gases for the large premixed-burn conditions near the NOx bump can also increase temperatures by about 25 K, for a further 12% increase in NOx. The data also shows that these two factors can contribute to other exhaust NO observations, such as the intake temperature optimum for minimizing NOx emissions. Finally, although it was not directly measured, the rate of post-flame mixing was identified and examined as a third primary factor affecting in-cylinder temperatures and NOx formation in diesel engines.Copyright © 2005 SAE International.

PDC drill bit performance has been greatly improved over the past three decades by innovations in bit design and how these designs are applied. The next leap forward is most likely to come from using high-speed, real-time downhole data to optimize the performance of these sophisticated bits on an application-by-application basis. By effectively managing conditions of lateral, axial and torsional acceleration, damage to cutting structures can be minimized for improved penetration rates. Avoiding these damaging vibrations is essential to increasing bit durability and improving overall drilling economics. This paper describes one set of independent drilling optimization results obtained as part of a series of controlled demonstrations of PDC bits. Sandia National Laboratories on behalf of the U. S. Department of Energy (DOE) managed this work. The effort was organized as a Cooperative Research and Development Agreement (CRADA) established between Sandia and four bit manufacturers with DOE funding and in-kind contributions by the industry partners. The goal of this CRADA was to demonstrate drag bit performance in formations with degrees of hardness typical of those encountered while drilling geothermal wells. The test results indicate that the surface weight-on-bit (WOB), revolutions per minute (RPM) and torque readings traditionally used to guide adjustments in the drilling parameters do not always provide the true picture of what is really taking place at the bit. Instead, a holistic approach combining traditional methods of optimization together with high-speed, real-time data enables far better decisions for improving bit performance and avoiding damaging situations that may have otherwise gone unnoticed.

The Z-Pinch Power Plant uses the results from Sandia National Laboratories' Z accelerator in a power plant application to generate energy pulses using inertial confinement fusion. A collaborative project has been initiated by Sandia to investigate the scientific principles of a power generation system using this technology. Research is under way to develop an integrated concept that describes the operational issues of a 1000 MW electrical power plant. Issues under consideration include: 1-20 gigajoule fusion pulse containment, repetitive mechanical connection of heavy hardware, generation of terawatt pulses every 10 seconds, recycling often thousand tons of steel, and manufacturing of millions of hohlraums and capsules per year. Additionally, waste generation and disposal issues are being examined. This paper describes the current concept for the plant and also the objectives for future research.

Optical parametric chirped-pulse amplifiers utilizing a 300-ps Nd:YAG pump system, a tunable 1.6-μm fiber signal, and KNbO3, KTA, RTP, or BBO nonlinear crystals were designed and built. Gain >109, and peak powers >30GW were obtained. © 2005 Optical Society of America.

An experimental investigation is made into the fluid mechanics and heat transfer of a circular cylinder immersed in a wall-bounded turbulent mixed-convection flow of water. The cylinder is oriented spanwise to the forced channel flow and within the thermal boundary layer of the heated lower wall. The flow channel is capped with a cold, near-adiabatic upper wall producing a fully turbulent gap Rayleigh number of 108. A low-speed crossflow is applied to advect the turbulent thermal plumes over the cylinder surface. We present spatially resolved cylinder-surface heat-flux data alongside 2-D PIV imaging of the streamwise and wall-normal velocity components for two flow conditions in the mixed-convection heat-transfer regime. The measured cylinder-wake flowfield reflects the complex coupling between the separated wake flow, the highly turbulent freestream and the buoyant wall and cylinder boundary layers. A method for measurement of spatially resolved surface heat fluxes based on the measured cylinder-surface temperature distribution and a well-posed two-dimensional solution to the conduction problem in the cylinder wall is presented. The resulting spatially resolved flux measurements show enhanced surface heat transfer, which results from the intense buoyancy generated free-stream turbulence and mixing in the cylinder wake. This work extends the literature on thermal convection with crossflow well into the turbulent regime and is, to our knowledge, the first investigation of surface heat-transfer to an object of engineering importance placed in this type of turbulent mixed-convection flowfield. The data are currently being utilized for validation of mixed-convection turbulence models at Sandia and comparisons between the computational and experimental results are presented.

Abstract not provided.

Abstract not provided.

Abstract not provided.