Publications

Results 82401–82600 of 101,000

Search results

Jump to search filters

Molten salt-based growth of bulk GaN and InN for substrates

Waldrip, Karen E.

An atmospheric pressure approach to growth of bulk group III-nitrides is outlined. Native III-nitride substrates for optoelectronic and high power, high frequency electronics are desirable to enhance performance and reliability of these devices; currently, these materials are available in research quantities only for GaN, and are unavailable in the case of InN. The thermodynamics and kinetics of the reactions associated with traditional crystal growth techniques place these activities on the extreme edges of experimental physics. The novel techniques described herein rely on the production of the nitride precursor (N{sup 3-}) by chemical and/or electrochemical methods in a molten halide salt. This nitride ion is then reacted with group III metals in such a manner as to form the bulk nitride material. The work performed during the period of funding (February 2006-September 2006) focused on establishing that mass transport of GaN occurs in molten LiCl, the construction of a larger diameter electrochemical cell, the design, modification, and installation of a made-to-order glove box (required for handling very hygroscopic LiCl), and the feasibility of using room temperature molten salts to perform nitride chemistry experiments.

More Details
TYPE SAND Report YEAR 2007
DOIOSTI

Update of the Z Refurbishment project (ZR) at Sandia National Laboratories

Bloomquist, Douglas D.; McDaniel, Dillon H.; Mckee, G.R.; Donovan, Guy L.; Weed, John W.; Faturos, Thomas V.; Tabor, Debra; Jordan, Carla M.

Sandia's Z Refurbishment (ZR) Project formally began in February 2002 to increase the Z Accelerator's utilization by providing the capability to perform more shots, improve precision and pulse shape variability, and increase delivered current. A project update was provided at the 15th International Pulsed Power Conference in 2005. The Z facility was shut down in July 2006 for structural/infrastructure modifications and installation of new pulsed power systems. The refurbishment will conclude in 2007. This paper provides a status update of the project covering the past 2 years of activities.

More Details
TYPE Conference YEAR 2007
OSTI

Final report : PATTON Alliance gazetteer evaluation project

Bleakly, Denise

In 2005 the National Ground Intelligence Center (NGIC) proposed that the PATTON Alliance provide assistance in evaluating and obtaining the Integrated Gazetteer Database (IGDB), developed for the Naval Space Warfare Command Research group (SPAWAR) under Advance Research and Development Activity (ARDA) funds by MITRE Inc., fielded to the text-based search tool GeoLocator, currently in use by NGIC. We met with the developers of GeoLocator and identified their requirements for a better gazetteer. We then validated those requirements by reviewing the technical literature, meeting with other members of the intelligence community (IC), and talking with both the United States Geologic Survey (USGS) and the National Geospatial Intelligence Agency (NGA), the authoritative sources for official geographic name information. We thus identified 12 high-level requirements from users and the broader intelligence community. The IGDB satisfies many of these requirements. We identified gaps and proposed ways of closing these gaps. Three important needs have not been addressed but are critical future needs for the broader intelligence community. These needs include standardization of gazetteer data, a web feature service for gazetteer information that is maintained by NGA and USGS but accessible to users, and a common forum that brings together IC stakeholders and federal agency representatives to provide input to these activities over the next several years. Establishing a robust gazetteer web feature service that is available to all IC users may go a long way toward resolving the gazetteer needs within the IC. Without a common forum to provide input and feedback, community adoption may take significantly longer than anticipated with resulting risks to the war fighter.

More Details
TYPE SAND Report YEAR 2007
DOIOSTI

Optimization of screening for radioactivity in urine by liquid scintillation

Reese, Robert; Shanks, Sonoya T.

Numerous events have or could have resulted in the inadvertent uptake of radionuclides by fairly large populations. Should a population receive an uptake, valuable information could be obtained by using liquid scintillation counting (LSC) techniques to quickly screen urine from a sample of the affected population. This study investigates such LSC parameters as discrimination, quench, volume, and count time to yield guidelines for analyzing urine in an emergency situation. Through analyzing variations of the volume and their relationships to the minimum detectable activity (MDA), the optimum ratio of sample size to scintillating chemical cocktail was found to be 1:3. Using this optimum volume size, the alpha MDA varied from 2100 pCi/L for a 30-second count time to 35 pCi/L for a 1000-minute count time. The typical count time used by the Sandia National Laboratories Radiation Protection Sample Diagnostics program is 30 minutes, which yields an alpha MDA of 200 pCi/L. Because MDA is inversely proportional to the square root of the count time, count time can be reduced in an emergency situation to achieve the desired MDA or response time. Note that approximately 25% of the response time is used to prepare the samples and complete the associated paperwork. It was also found that if the nuclide of interest is an unknown, pregenerated discriminator settings and efficiency calibrations can be used to produce an activity value within a factor of two, which is acceptable for a screening method.

More Details
TYPE SAND Report YEAR 2007
DOIOSTI

One-dimensional ablation in multiwire arrays

Proposed for publication in Physics of Plasmas.

Yu, Edmund; Oliver, Bryan V.; Mehlhorn, Thomas A.

The main physical processes responsible for plasma ablation in multiwire Z pinches are considered via eigensolutions to one-dimensional steady state magnetohydrodynamics. A double scale-length structure of the plasma accelerating layer is demonstrated. The width of the resistive scale-length that defines the current layer structure is significantly larger than the thermal scale-length, where transport of energy toward the cores and plasma pressure play important roles. The transport of energy is provided mainly by radiation, though electron thermal conduction is also important very close to the plasma-core interface. Another type of solution of the steady state problem is revealed, when local Ohmic heating is important down to the interface. Selection between these two types of solutions is considered from multiple points of view. Although the one-dimensional problem is mainly considered in this paper, it is shown how the one-dimensional results may help to understand results of two-dimensional models.

More Details
TYPE Journal Article YEAR 2007
OSTI

Library of Advanced Materials for Engineering : LAME

Scherzinger, William M.; Hammerand, Daniel C.

Constitutive modeling is an important aspect of computational solid mechanics. Sandia National Laboratories has always had a considerable effort in the development of constitutive models for complex material behavior. However, for this development to be of use the models need to be implemented in our solid mechanics application codes. In support of this important role, the Library of Advanced Materials for Engineering (LAME) has been developed in Engineering Sciences. The library allows for simple implementation of constitutive models by model developers and access to these models by application codes. The library is written in C++ and has a very simple object oriented programming structure. This report summarizes the current status of LAME.

More Details
TYPE SAND Report YEAR 2007
DOIOSTI

X-ray optics on the Z-Accelerator backlit with the Z-Beamlet Laser & Z-Petawatt Laser systems

Gonzales, Rita A.; Gurrieri, Thomas; Herrmann, Mark H.; Mulville, Thomas D.; Neely, Kelly A.; Rambo, Patrick K.; Rovang, Dean C.; Ruggles, Larry; Schwarz, Jens; Adams, Richard G.; Simpson, Walter W.; Sinars, Daniel; Smith, Ian C.; Speas, Christopher S.; Tafoya-Porras, Belinda T.; Wenger, D.F.; Young, Ralph W.; Edens, Aaron; Atherton, B.; Bennett, Guy R.; Campbell, David V.; Carroll, M.S.; Claus, Liam; Geissel, Matthias

Abstract not provided.

More Details
TYPE Conference YEAR 2007
OSTI

Sonar atlas of caverns comprising the U.S. Strategic Petroleum Reserve. Volume 2, Big Hill Site, Texas

Rautman, Christopher A.; Lord, Anna S.

Downhole sonar surveys from the four active U.S. Strategic Petroleum Reserve sites have been modeled and used to generate a four-volume sonar atlas, showing the three-dimensional geometry of each cavern. This volume 2 focuses on the Big Hill SPR site, located in southeastern Texas. Volumes 1, 3, and 4, respectively, present images for the Bayou Choctaw SPR site, Louisiana, the Bryan Mound SPR site, Texas, and the West Hackberry SPR site, Louisiana. The atlas uses a consistent presentation format throughout. The basic geometric measurements provided by the down-cavern surveys have also been used to generate a number of geometric attributes, the values of which have been mapped onto the geometric form of each cavern using a color-shading scheme. The intent of the various geometrical attributes is to highlight deviations of the cavern shape from the idealized cylindrical form of a carefully leached underground storage cavern in salt. The atlas format does not allow interpretation of such geometric deviations and anomalies. However, significant geometric anomalies, not directly related to the leaching history of the cavern, may provide insight into the internal structure of the relevant salt dome.

More Details
TYPE SAND Report YEAR 2007
DOIOSTI

Structure and dynamics of water near the interface with oligo(ethylene oxide) self-assembled monolayers

Langmuir

Ismail, Ahmed E.; Grest, Gary S.; Stevens, Mark J.

We performed molecular dynamics simulations of the oligo(ethylene oxide) (OEO) self-assembled monolayers in water to determine the nature of the systems' interfacial structure and dynamics. The density profiles, hydrogen bonding, and water dynamics are calculated as a function of the area per molecule A of OEO. At the highest coverages, the interface is hydrophobic, and a density drop is found at the interface. The interfacial region becomes more like bulk water as A increases. The OEO and water become progressively more mixed, and hydrogen bonding increases within the interfacial region. Water mobility is slower within the interfacial region, but not substantially. The implications of our results on the resistance of OEO SAMs to protein adsorption are discussed. Our principal result is that as A increases the increasingly waterlike interfacial region provides a more protein-resistant surface. This finding supports recent experimental measurements that protein resistance is maximal for less than full coverage on Au. © 2007 American Chemical Society.

More Details
TYPE Conference YEAR 2007
OSTIOSTIScopusScopus

Pressure and temperature dependence of the reaction of vinyl radical with ethylene

Journal of Physical Chemistry A

Ismail, Huzeifa; Franklin Goldsmith, C.; Abel, Paul R.; Howe, Pui T.; Fahr, Askar; Halpern, Joshua B.; Jusinski, Leonard E.; Georgievskii, Yuri; Taatjes, Craig A.; Green, William H.

This work reports measurements of absolute rate coefficients and Rice-Ramsperger-Kassel-Marcus (RRKM) master equation simulations of the C 2H 3 + C 2H 4 reaction. Direct kinetic studies were performed over a temperature range of 300-700 K and pressures of 20 and 133 mbar. Vinyl radicals (H 2C=CH) were generated by laser photolysis of vinyl iodide (C 2H 3I) at 266 nm, and time-resolved absorption spectroscopy was used to probe vinyl radicals through absorption at 423.2 nm. Measurements at 20 mbar are in good agreement with previous determinations at higher temperature. A weighted three-parameter Arrhenius fit to the experimental rate constant at 133 mbar, with the temperature exponent fixed, gives k = (7 ±1) × 10 -14 cm 3 molecule -1 s -1 (T/298 K) 2 exp[-(1430 ± 70) K/T]. RRKM master equation simulations, based on G3 calculations of stationary points on the C 4H 7 potential energy surface, were carried out to predict rate coefficients and product branching fractions. The predicted branching to 1-methylallyl product is relatively small under the conditions of the present experiments but increases as the pressure is lowered. Analysis of end products of 248 nm photolysis of vinyl iodide/ethylene mixtures at total pressures between 27 and 933 mbar provides no direct evidence for participation of 1-methylallyl. © 2007 American Chemical Society.

More Details
TYPE Journal Article YEAR 2007
ScopusOSTIDOI

First-principles analysis of the STM image heights of styrene on Si(100)

Physical Review B - Condensed Matter and Materials Physics

Bevan, K.H.; Zahid, F.; Kienle, D.; Guo, H.

We report on theoretical investigations of scanning tunneling spectroscopy (STM) image heights on Si(100). Calculations are performed using density functional theory (DFT) within the Keldysh nonequilibrium Green's function (NEGF) formalism. The nonequilibrium potential drop between Si(100) and a STM tip is determined self-consistently. This potential drop is found to play an important role in the calculated image height characteristics of adsorbed hydrocarbons by lowering the vacuum barrier and shifting molecular levels. Numerical data collected for image heights of styrene against a hydrogen passivated Si(100) background are found to agree quantitatively with the corresponding experimental results. We also present a comparison between results obtained by the NEGF-DFT formalism and the Tersoff-Hamann approximation, showing that nonequilibrium analysis can be important in the study of STM image heights of molecules. © 2007 The American Physical Society.

More Details
TYPE Journal Article YEAR 2007
ScopusOSTIDOI

Path ANalysis

Snell, Mark K.

The PANL software determines path through an Adversary Sequence Diagram (ASD) with minimum Probability of Interruption, P(I), given the ASD information and data about site detection, delay, and response force times. To accomplish this, the software generates each path through the ASD, then applies the Estimate of Adversary Sequence Interruption (EASI) methodology for calculating P(I) to each path, and keeps track of the path with the lowest P(I). Primary use is for training purposes during courses on physical security design. During such courses PANL will be used to demonstrate to students how more complex software codes are used by the US Department of Energy to determine the most-vulnerable paths and, where security needs improvement, how such codes can help determine physical security upgrades.

More Details
TYPE Presentation YEAR 2007
OSTI

Model selection in applied science and engineering: A decision-theoretic approach

Journal of Engineering Mechanics

Field, Richard V.; Grigoriu, M.

Mathematical models are developed and used to study the properties of complex systems in just about every area of applied science and engineering. Information on the system being modeled is, in general, incomplete, so that there may be two or more models consistent with the available information. The collection of these models is called the class of candidate models. A decision-theoretic method is developed for selecting the optimal member from the collection. The optimal model depends on the available information, the class of candidate models, and the model use. The candidate models may be deterministic or random. Classical methods for model selection, including the method of maximum likelihood and Bayesian methods, are briefly reviewed. These methods ignore model use and require data to be available. In addition, examples are used to show that classical methods for model selection can be unreliable in the sense that they can deliver unsatisfactory models when data is limited. The proposed decision-theoretic method for model selection does not have these limitations. The method accounts for model use via a utility function. This feature is especially important when modeling high-risk systems where the consequences of using an inappropriate model for the system can be disastrous. © 2007 ASCE.

More Details
TYPE Journal Article YEAR 2007
ScopusOSTI

Ion beam induced charge (IBIC) studies of silicon germanium heterojunction bipolar transistors (HBTs)

Nuclear Instruments and Methods in Physics Research, Section B: Beam Interactions with Materials and Atoms

Vizkelethy, G.; Reed, R.A.; Marshall, P.W.; Pellish, J.A.

SiGe HBTs are strong candidates for space communication applications because of their resistance to total dose effects and their overall high performance. However, they seem to be sensitive to single event upsets (SEUs). These devices were designed using deep trench isolation geometry to reduce charge collection due to ion hits outside the active area. Using four electrode (base, emitter, collector, and substrate) IBIC measurements at the Sandia Nuclear Microprobe Facility, we found that the largest fraction of the induced charge occurred on the collector and on the substrate; significantly less induced charge was found on the base electrode, and practically no induced charge was detected on the emitter. These devices showed a very well defined, high charge collection area enclosed by the deep trench. There was a sudden drop of induced charge at the trench but a long tail was present outside of the active area extending several tens of microns. The charge collection mechanisms inside and outside of the deep trench will be discussed and first results of Time Resolved IBIC in SiGe HBTs will be presented. © 2007.

More Details
TYPE Conference YEAR 2007
ScopusOSTI

Model reduction of systems with localized nonlinearities

Journal of Computational and Nonlinear Dynamics

Segalman, Daniel J.

An approach to development of reduced order models for systems with local nonlinearities is presented. The key of this approach is the augmentation of conventional basis functions with others having appropriate discontinuities at the locations of nonlinearity. A Galerkin solution using the above combination of basis functions appears to capture the dynamics of the system very efficiently - employing small basis sets. This method is particularly useful for problems of structural dynamics, but may have application in other fields as well. For problems involving small amplitude dynamics, when one employs as a basis the eigenmodes of a reference linear system plus the discontinuous (joint) modes, the resulting predictions, though still nonlinear, are approximated well as linear combinations of the eigenmodes. This is in good agreement with the experimental observation that jointed structures, though demonstrably nonlinear, manifest kinematics that are well described using eigenmodes of a corresponding system where the joints are replaced by linear springs. Copyright © 2007 by ASME.

More Details
TYPE Journal Article YEAR 2007
OSTIScopusOSTIScopus

Development and validation of bonded composite doubler repairs for commercial aircraft

Rackow, Kirk A.

A typical aircraft can experience over 2,000 fatigue cycles (cabin pressurizations) and even greater flight hours in a single year. An unavoidable by-product of aircraft use is that crack, impact, and corrosion flaws develop throughout the aircraft's skin and substructure elements. Economic barriers to the purchase of new aircraft have placed even greater demands on efficient and safe repair methods. The use of bonded composite doublers offers the airframe manufacturers and aircraft maintenance facilities a cost effective method to safely extend the lives of their aircraft. Instead of riveting multiple steel or aluminum plates to facilitate an aircraft repair, it is now possible to bond a single Boron-Epoxy composite doubler to the damaged structure. The FAA's Airworthiness Assurance Center at Sandia National Labs (AANC), Boeing, and Federal Express completed a pilot program to validate and introduce composite doubler repair technology to the U.S. commercial aircraft industry. This project focused on repair of DC-10 fuselage structure and its primary goal was to demonstrate routine use of this repair technology using niche applications that streamline the design-to-installation process. As composite doubler repairs gradually appear in the commercial aircraft arena, successful flight operation data is being accumulated. These commercial aircraft repairs are not only demonstrating the engineering and economic advantages of composite doubler technology but they are also establishing the ability of commercial maintenance depots to safely adopt this repair technique. This report presents the array of engineering activities that were completed in order to make this technology available for widespread commercial aircraft use. Focused laboratory testing was conducted to compliment the field data and to address specific issues regarding damage tolerance and flaw growth in composite doubler repairs. Fatigue and strength tests were performed on a simulated wing repair using a substandard design and a flawed installation. In addition, the new Sol-Gel surface preparation technique was evaluated. Fatigue coupon tests produced Sol-Gel results that could be compared with a large performance database from conventional, riveted repairs. It was demonstrated that not only can composite doublers perform well in severe off-design conditions (low doubler stiffness and presence of defects in doubler installation) but that the Sol-Gel surface preparation technique is easier and quicker to carry out while still producing optimum bonding properties. Nondestructive inspection (NDI) methods were developed so that the potential for disbond and delamination growth could be monitored and crack growth mitigation could be quantified. The NDI methods were validated using full-scale test articles and the FedEx aircraft installations. It was demonstrated that specialized NDI techniques can detect flaws in composite doubler installations before they reach critical size. Probability of Detection studies were integrated into the FedEx training in order to quantify the ability of aircraft maintenance depots to properly monitor these repairs. In addition, Boeing Structural Repair and Nondestructive Testing Manuals were modified to include composite doubler repair and inspection procedures. This report presents the results from the FedEx Pilot Program that involved installation and surveillance of numerous repairs on operating aircraft. Results from critical NDI evaluations are reported in light of damage tolerance assessments for bonded composite doublers. This work has produced significant interest from airlines and aircraft manufacturers. The successful Pilot Program produced flight performance history to establish the durability of bonded composite patches as a permanent repair on commercial aircraft structures. This report discusses both the laboratory data and Pilot Program results from repair installations on operating aircraft to introduce composite doubler repairs into mainstream commercial aircraft use.

More Details
TYPE SAND Report YEAR 2007
DOIOSTIDOIOSTI

Stressed glass technology for actuators and removable barrier applications

Glass, Sarah J.; Warren, Mial E.; Schwing, Kamilla J.; Tappan, Alexander S.

There are commercial and military applications in which a material needs to serve as a barrier that must subsequently be removed. In many cases it is desirable that once the barrier has served its function that it then be reduced to small pieces. For example, in pipelines and in downhole drilling applications, valves are needed to function as barriers that can sustain high pressures. Later the valves must be removed and essentially disappear or be rendered to such a small size that they do not interfere with the functioning of other equipment. Military applications include covers on missile silos or launch vehicles. Other applications might require that a component be used once as an actuator or for passive energy storage, and then be irreversibly removed, again so as not to interfere with the function or motion of other parts of the device. Brittle materials, especially those that are very strong, or are pre-stressed, are ideal candidates for these applications. Stressed glass can be produced in different sizes and shapes and the level of strength and pre-stress, both of which control the fragmentation, can be manipulated by varying the processing. Stressed glass can be engineered to fracture predictably at a specific stress level. Controlling the central tension allows the fragment size to be specified. The energy that is stored in the residual stress profile that results from ion exchange or thermal tempering processes can be harnessed to drive fragmentation of the component once it has been deliberately fractured. Energy can also be stored in the glass by mechanical loading. Energy from both of these sources can be released either to perform useful work or to initiate another reaction. Once the stressed glass has been used as a barrier or actuator it can never be ''used'' again because it fragments into many small unrecognizable pieces during the actuation. Under some circumstances it will interfere with the motion or functioning of other parts of a device. Our approach was to use stressed glass to develop capabilities for making components that can be used as barriers, as actuating devices that passively store energy, or as a mechanical weaklink that is destroyed by some critical shock or crush load. The objective of this project was to develop one or more prototype devices using stressed glass technology and demonstrate their potential for applications of interest. This work is intended to provide critical information and technologies for Sandia's NP&A and MT&A customers, and is relevant to commercial applications for these same materials. Most of the studies in this project were conducted using the Corning 0317 sodium aluminosilicate glass composition.

More Details
TYPE SAND Report YEAR 2007
DOIOSTI

Pollution prevention opportunity assessment for Sandia National Laboratories/California recycling programs

Wrons, Ralph J.

This Pollution Prevention Opportunity Assessment (PPOA) was conducted for the Sandia National Laboratories/California (SNL/CA) Environmental Management Department between May 2006 and March 2007, to evaluate the current site-wide recycling program for potential opportunities to improve the efficiency of the program. This report contains a summary of the information collected and analyses performed with recommended options for implementation. The SNL/NM Pollution Prevention (P2) staff worked with the SNL/CA P2 Staff to arrive at these options.

More Details
TYPE SAND Report YEAR 2007
DOIOSTIDOIOSTI

CADS:Cantera Aerosol Dynamics Simulator

Moffat, Harry K.

This manual describes a library for aerosol kinetics and transport, called CADS (Cantera Aerosol Dynamics Simulator), which employs a section-based approach for describing the particle size distributions. CADS is based upon Cantera, a set of C++ libraries and applications that handles gas phase species transport and reactions. The method uses a discontinuous Galerkin formulation to represent the particle distributions within each section and to solve for changes to the aerosol particle distributions due to condensation, coagulation, and nucleation processes. CADS conserves particles, elements, and total enthalpy up to numerical round-off error, in all of its formulations. Both 0-D time dependent and 1-D steady state applications (an opposing-flow flame application) have been developed with CADS, with the initial emphasis on developing fundamental mechanisms for soot formation within fires. This report also describes the 0-D application, TDcads, which models a time-dependent perfectly stirred reactor.

More Details
TYPE SAND Report YEAR 2007
DOIOSTIDOIOSTI
Results 82401–82600 of 101,000
Results 82401–82600 of 101,000
Top