This report describes an LDRD-supported experimental-theoretical collaboration on the enhanced low-dose-rate sensitivity (ELDRS) problem. The experimental work led to a method for elimination of ELDRS, and the theoretical work led to a suite of bimolecular mechanisms that explain ELDRS and is in good agreement with various ELDRS experiments. The model shows that the radiation effects are linear in the limit of very low dose rates. In this limit, the regime of most concern, the model provides a good estimate of the worst-case effects of low dose rate ionizing radiation.
This document describes the 2003 SNL ASCI Software Quality Engineering (SQE) assessment of twenty ASCI application code teams and the results of that assessment. The purpose of this assessment was to determine code team compliance with the Sandia National Laboratories ASCI Applications Software Quality Engineering Practices, Version 2.0 as part of an overall program assessment.
An increase in photocurrent has been observed at silicon electrodes coated with nanostructured porous silica films as compared to bare, unmodified silicon. Ultimately, to utilize this effect in devices such as sensors or microchip power supplies, the physical phenomena behind this observation need to be well characterized. To this end, Electrochemical Impedance Spectroscopy (EIS) was used to characterize the effect of surfactant-templated mesoporous silica films deposited onto silicon electrodes on the electrical properties of the electrode space-charge region in an aqueous electrolyte solution, as the electrical properties of this space-charge region are responsible for the photobehavior of semiconductor devices. A significant shift in apparent flat-band potential was observed for electrodes modified with the silica film when compared to bare electrodes; the reliability of this data is suspect, however, due to contributions from surface states to the overall capacitance of the system. To assist in the interpretation of this EIS data, a series of measurements at Pt electrodes was performed with the hope of decoupling electrode and film contributions from the EIS spectra. Surprisingly, the frequency-dependent impedance data for Pt electrodes coated with a surfactant-templated film was nearly identical to that observed for bare Pt electrodes, indicating that the mesoporous film had little effect on the transport of small electrolyte ions to the electrode surface. Pore-blocking agents (tetraalkylammonium salts) were not observed to inhibit this transport process. However, untemplated (non-porous) silica films dramatically increased film resistance, indicating that our EIS data for the Pt electrodes is reliable. Overall, our preliminary conclusion is that a shift in electrical properties in the space-charge region induced by the presence of a porous silica film is responsible for the increase in observed photocurrent.
The waters of the Pecos River in New Mexico must be delivered to three primary users: (1) The Pecos River Compact: each year a percentage of water from natural river flow must be delivered to Texas; (2) Agriculture: Carlsbad Irrigation District has a storage and diversion right and Fort Sumner Irrigation District has a direct flow diversion right; and, (3) Endangered Species Act: an as yet unspecified amount of water is to support Pecos Bluntnose Shiner Minnow habitat within and along the Pecos River. Currently, the United States Department of Interior Bureau of Reclamation, the New Mexico Interstate Stream Commission, and the United States Department of the Interior Fish and Wildlife Service are studying the Pecos Bluntnose Shiner Minnow habitat preference. Preliminary work by Fish and Wildlife personnel in the critical habitat suggest that water depth and water velocity are key parameters defining minnow habitat preference. However, river flows that provide adequate preferred habitat to support this species have yet to be determined. Because there is a limited amount of water in the Pecos River and its reservoirs, it is critical to allocate water efficiently such that habitat is maintained, while honoring commitments to agriculture and to the Pecos River Compact. This study identifies the relationship between Pecos River flow rates in cubic feet per second (cfs) and water depth and water velocity.
We have developed infrastructure, utilities and partitioning methods to improve data partitioning in linear solvers and preconditioners. Our efforts included incorporation of data repartitioning capabilities from the Zoltan toolkit into the Trilinos solver framework, (allowing dynamic repartitioning of Trilinos matrices); implementation of efficient distributed data directories and unstructured communication utilities in Zoltan and Trilinos; development of a new multi-constraint geometric partitioning algorithm (which can generate one decomposition that is good with respect to multiple criteria); and research into hypergraph partitioning algorithms (which provide up to 56% reduction of communication volume compared to graph partitioning for a number of emerging applications). This report includes descriptions of the infrastructure and algorithms developed, along with results demonstrating the effectiveness of our approaches.
A laser safety and hazard analysis was performed for the airborne AURA (Big Sky Laser Technology) lidar system based on the 2000 version of the American National Standard Institute's (ANSI) Standard Z136.1, for the Safe Use of Lasers and the 2000 version of the ANSI Standard Z136.6, for the Safe Use of Lasers Outdoors. The AURA lidar system is installed in the instrument pod of a Proteus airframe and is used to perform laser interaction experiments and tests at various national test sites. The targets are located at various distances or ranges from the airborne platform. In order to protect personnel, who may be in the target area and may be subjected to exposures, it was necessary to determine the Maximum Permissible Exposure (MPE) for each laser wavelength, calculate the Nominal Ocular Hazard Distance (NOHD), and determine the maximum 'eye-safe' dwell times for various operational altitudes and conditions. It was also necessary to calculate the appropriate minimum Optical Density (ODmin) of the laser safety eyewear used by authorized personnel who may receive hazardous exposures during ground base operations of the airborne AURA laser system (system alignment and calibration).
The Advanced Concepts Group (ACG) at Sandia National Laboratories is exploring the use of Red Teaming to help intelligence analysts with two key processes: determining what a piece or pieces of information might imply and deciding what other pieces of information need to be found to support or refute hypotheses about what actions a suspected terrorist organization might be pursuing. In support of this effort, the ACG hosted a terrorism red gaming event in Albuquerque on July 22-24, 2003. The game involved two 'red teams' playing the roles of two terrorist cells - one focused on implementing an RDD attack on the DC subway system and one focused on a bio attack against the same target - and two 'black teams' playing the role of the intelligence collection system and of intelligence analysts trying to decide what plans the red teams might be pursuing. This exercise successfully engaged human experts to seed a proposed compute engine with detailed operational plans for hypothetical terrorist scenarios.
The Accurate Time-Linked data Acquisition System (ATLAS II) is a small, lightweight, time-synchronized, robust data acquisition system that is capable of acquiring simultaneous long-term time-series data from both a wind turbine rotor and ground-based instrumentation. This document is a user's manual for the ATLAS II hardware and software. It describes the hardware and software components of ATLAS II, and explains how to install and execute the software.
This report describes work done in FY2003 under Advanced and Exploratory Studies funding for Advanced Weapons Controllers. The contemporary requirements and envisioned missions for nuclear weapons are changing from the class of missions originally envisioned during development of the current stockpile. Technology available today in electronics, computing, and software provides capabilities not practical or even possible 20 years ago. This exploratory work looks at how Weapon Electrical Systems can be improved to accommodate new missions and new technologies while maintaining or improving existing standards in nuclear safety and reliability.
A concurrent computational and experimental investigation of thermal transport is performed with the goal of improving understanding of, and predictive capability for, thermal transport in microdevices. The computational component involves Monte Carlo simulation of phonon transport. In these simulations, all acoustic modes are included and their properties are drawn from a realistic dispersion relation. Phonon-phonon and phonon-boundary scattering events are treated independently. A new set of phonon-phonon scattering coefficients are proposed that reflect the elimination of assumptions present in earlier analytical work from the simulation. The experimental component involves steady-state measurement of thermal conductivity on silicon films as thin as 340nm at a range of temperatures. Agreement between the experiment and simulation on single-crystal silicon thin films is excellent, Agreement for polycrystalline films is promising, but significant work remains to be done before predictions can be made confidently. Knowledge gained from these efforts was used to construct improved semiclassical models with the goal of representing microscale effects in existing macroscale codes in a computationally efficient manner.
The work discussed in this report was supported by a Campus Fellowship LDRD. The report contains three papers that were published by the fellowship recipient and these papers form the bulk of his dissertation. They are reproduced here to satisfy LDRD reporting requirements.
As MEMS transducers are scaled up in size, the threshold is quickly crossed to where magnetoquasistatic (MQS) transducers are superior for force production compared to electroquasistatic (EQS) transducers. Considerable progress has been made increasing the force output of MEMS EQS transducers, but progress with MEMS MQS transducers has been more modest. A key reason for this has been the difficulty implementing efficient lithographically-fabricated magnetic coil structures. The contribution of this study is a planar multilayer polyphase coil architecture which provides for the lithographic implementation of efficient stator windings suitable for linear magnetic machines. A millimeter-scale linear actuator with complex stator windings was fabricated using this architecture. The stators of the actuator were fabricated using a BCB/Cu process, which does not require replanarization of the wafer between layers. The prototype stator was limited to thin copper layers (3 {micro}m) due to the use of evaporated metal at the time of fabrication. Two layers of metal were implemented in the prototype, but the winding architecture naturally supports additional metal layer pairs. It was found in laboratory tests that the windings can support very high current densities of 4 x 10{sup 9}A/m{sup 2} without damage. Force production normal to the stator was calculated to be 0.54 N/A. For thin stators such as this one, force production increases approximately linearly with the thickness of the windings and a six-layer stator fabricated using a newly implemented electroplated BCB/Cu process (six layers of 15 {micro}m thick metal) is projected to produce approximately 8.8 N/A.
A laser safety hazard evaluation and pertinent output measurements were performed (June 2003 through August 2003) on several VITAL-2 Variable Intensity Tactical Aiming Light--infrared laser, associated with the Proforce M-4 system used in force-on-force exercises. The VITAL-2 contains two diode lasers presenting 'Extended Source' viewing out to a range on the order of 1.3 meters before reverting to a 'Small Source' viewing hazard. Laser hazard evaluation was performed in concert with the ANSI Std. Z136.1-2000 for the safe use of lasers and the ANSI Std. Z136.6-2000 for the safe use of lasers outdoors. The results of the laser hazard analysis for the VITAL-2, indicates that this Tactical Aiming IR laser presents a Class 1 laser hazard to personnel in the area of use. Field measurements performed on 71 units confirmed that the radiant outputs were at all times below the Allowable Emission Limit and that the irradiance of the laser spot was at all locations below the Maximum Exposure Limit. This system is eye-safe and it may be used under current SNL policy in force-on-force exercises. The VITAL-2 Variable Intensity Tactical Aiming Light does not present a laser hazard greater than Class 1, to aided viewing with binoculars.
Alloying element loss from the weld pool during laser spot welding of stainless steel was investigated experimentally and theoretically. The experimental work involved determination of work-piece weight loss and metal vapor composition for various welding conditions. The transient temperature and velocity fields in the weld pool were numerically simulated. The vaporization rates of the alloying elements were modeled using the computed temperature profiles. The fusion zone geometry could be predicted from the transient heat transfer and fluid flow model for various welding conditions. The laser power and the pulse duration were the most important variables in determining the transient temperature profiles. The velocity of the liquid metal in the weld pool increased with time during heating and convection played an increasingly important role in the heat transfer. The peak temperature and velocity increased significantly with laser power density and pulse duration. At very high power densities, the computed temperatures were higher than the boiling point of 304 stainless steel. As a result, evaporation of alloying elements was caused by both the total pressure and the concentration gradients. The calculations showed that the vaporization occurred mainly from a small region under the laser beam where the temperatures were very high. The computed vapor loss was found to be lower than the measured mass loss because of the ejection of tiny metal droplets owing to the recoil force exerted by the metal vapours. The ejection of metal droplets has been predicted by computations and verified by experiments.
Detailed experiments involving extensive high resolution transmission electron microscopy (TEM) revealed significant microstructural differences between Cu sulfides formed at low and high relative humidity (RH). It was known from prior experiments that the sulfide grows linearly with time at low RH up to a sulfide thickness approaching or exceeding one micron, while the sulfide initially grows linearly with time at high RH then becomes sub-linear at a sulfide thickness less than about 0.2 microns, with the sulfidation rate eventually approaching zero. TEM measurements of the Cu2S morphology revealed that the Cu2S formed at low RH has large sized grains (75 to greater than 150 nm) that are columnar in structure with sharp, abrupt grain boundaries. In contrast, the Cu2S formed at high RH has small equiaxed grains of 20 to 50 nm in size. Importantly, the small grains formed at high RH have highly disordered grain boundaries with a high concentration of nano-voids. Two-dimensional diffusion modeling was performed to determine whether the existence of localized source terms at the Cu/Cu2S interface could be responsible for the suppression of Cu sulfidation at long times at high RH. The models indicated that the existence of static localized source terms would not predict the complete suppression of growth that was observed. Instead, the models suggest that the diffusion of Cu through Cu2S becomes restricted during Cu2S formation at high RH. The leading speculation is that the extensive voiding that exists at grain boundaries in this material greatly reduces the flux of Cu between grains, leading to a reduction in the rate of sulfide film formation. These experiments provide an approach for adding microstructural information to Cu sulfidation rate computer models. In addition to the microstructural studies, new micro-patterned test structures were developed in this LDRD to offer insight into the point defect structure of Cu2S and to permit measurement of surface reaction rates during Cu sulfidation. The surface reaction rate was measured by creating micropatterned Cu lines of widths ranging from 5 microns to 100 microns. When sulfidized, the edges of the Cu lines show greater sulfidation than the center, an effect known as microloading. Measurement of the sulfidation profile enables an estimate of the ratio of the diffusivity of H2S in the gas phase to the surface reaction rate constant, k. Our measurements indicated that the gas phase diffusivity exceeds k by more than 10, but less than 100. This is consistent with computer simulations of the sulfidation process. Other electrical test structures were developed to measure the electrical conductivity of Cu2S that forms on Cu. This information can be used to determine relative vacancy concentrations in the Cu2S layer as a function of RH. The test structures involved micropatterned Cu disks and thin films, and the initial measurements showed that the electrical approach is feasible for point defect studies in Cu2S.
In the epitaxial lateral overgrowth of GaN, mass transport and the effects of crystal-growth kinetics lead to a wide range of observed feature growth rates depending on the dimensions of the masked and exposed regions. Based on a simple model, scaling relationships are derived that reveal the dynamic similarity of growth behavior across pattern designs. A time-like quantity is introduced that takes into account the varying transport effects, and provides a dimensionless time basis for analyzing crystal growth kinetics in this system. Illustrations of these scaling relationships are given through comparison with experiment. Published by Elsiver B.V.
The views of state of art in verification and validation (V & V) in computational physics are discussed. These views are described in the framework in which predictive capability relies on V & V, as well as other factors that affect predictive capability. Some of the research topics addressed are development of improved procedures for the use of the phenomena identification and ranking table (PIRT) for prioritizing V & V activities, and the method of manufactured solutions for code verification. It also addressed development and use of hierarchical validation diagrams, and the construction and use of validation metrics incorporating statistical measures.
Estimates of mass transfer timescales from 316 solute transport experiments reported in 35 publications are compared to the pore-water velocities and residence times, as well as the experimental durations. New tracer experiments were also conducted in columns of different lengths so that the velocity and the advective residence time could be varied independently. In both the experiments reported in the literature and the new experiments, the estimated mass transfer timescale (inverse of the mass-transfer rate coefficient) is better correlated to residence time and the experimental duration than to velocity. Of the measures considered, the experimental duration multiplied by 1 + β (where β is the capacity coefficient, defined as the ratio of masses in the immobile and mobile domains at equilibrium) best predicted the estimated mass transfer timescale. This relation is consistent with other work showing that aquifer and soil material commonly produce multiple timescales of mass transfer.
Given a finite set of points in Euclidean space, we can ask what is the minimum number of times a piecewise-linear path must change direction in order to pass through all of them. We prove some new upper and lower bounds for the rectilinear version of this problem in which all motion is orthogonal to the coordinate axes. We also consider the more general case of arbitrary directions.
Deep X-ray lithography based techniques such as LIGA (German acronym representing Lithographie, Galvanoformung, and Abformung) are being currently used to fabricate net-shape components for microelectromechanical systems (MEMS). Unlike other microfabrication techniques, LIGA lends itself to a broad range of materials, including metals, alloys, polymers, as well as ceramics and composites. Currently, Ni and Ni alloys are the materials of choice for LIGA microsystems. While Ni alloys may meet the structural requirements for MEMS, their tribological (friction and wear) behavior poses great challenges for the reliable operation of LIGA-fabricated MEMS. Typical sidewall morphologies of LIGA-fabricated parts are described, and their role in the tribological behavior of MEMS is discussed. The adaptation of commercial plasma-enhanced chemical vapor deposition to coat the sidewalls of LIGA-fabricated parts with diamond-like nanocomposite is described.
The propagation of a 30 kA, 3.5 Mev electron beam which was focused into gas and plasma-filled cells was discussed. Gas cells which were used for X-ray radiography were produced using pulsed-power accelerators, onto a high atomic number target to generate bremsstrahlung radiation. The effectiveness of beam focusing using neutral gas, partially ionized gas, and fully ionized (plasma-filled) cells was investigated using numerical simulation. It was observed in an optimized gas cell that an initial plasma density approaching 1016 cm-3 was sufficient to prevent significant net currents and the subsequent beam sweep.
Our national security, economic prosperity, and national well-being are dependent upon a set of highly interdependent critical infrastructures. Examples of these infrastructures include the national electrical grid, oil and natural gas systems, telecommunication and information networks, transportation networks, water systems, and banking and financial systems. Given the importance of their reliable and secure operations, understanding the behavior of these infrastructures - particularly when stressed or under attack - is crucial. Models and simulations can provide considerable insight into the complex nature of their behaviors and operational characteristics. These models and simulations must include interdependencies among infrastructures if they are to provide accurate representations of infrastructure characteristics and operations. A number of modeling and simulation approaches under development today directly address interdependencies and offer considerable insight into the operational and behavioral characteristics of critical infrastructures.