Publications

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The presentation outline of this paper is: (1) How identification of chemical hazards fits into a security risk analysis approach; (2) Techniques for target identification; and (3) Identification of chemical hazards by different organizations. The summary is: (1) There are a number of different methodologies used within the chemical industry which identify chemical hazards: (a) Some develop a manual listing of potential targets based on published lists of hazardous chemicals or chemicals of concern, 'expert opinion' or known hazards. (b) Others develop a prioritized list based on chemicals found at a facility and consequence analysis (offsite release affecting population, theft of material, product tampering). (2) Identification of chemical hazards should include not only intrinsic properties of the chemicals but also potential reactive chemical hazards and potential use for activities off-site.

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Technologies that could quickly detect and identify virus particles would play a critical role in fighting bioterrorism and help to contain the rapid spread of disease. Of special interest is the ability to detect the presence and movement of virions without chemically modifying them by attaching molecular probes. This would be useful for rapid detection of pathogens in food or water supplies without the use of expensive chemical reagents. Such detection requires new devices to quickly screen for the presence of tiny pathogens. To develop such a device, we fabricated nanochannels to transport virus particles through ultrashort laser cavities and measured the lasing output as a sensor for virions. To understand this transduction mechanism, we also investigated light scattering from virions, both to determine the magnitude of the scattered signal and to use it to investigate the motion of virions.

This overview is intended to provide the reader with insight into basic reliability issues often confronted when designing long-term geothermal well monitoring equipment. No single system is looked at. General examples of the long-term reliability of other industries are presented. Examples of reliability issues involving electronic components and sensors along with fiber optic sensors and cables are given. This paper will aid in building systems where a long operating life is required. However, as no introductory paper can cover all reliability issues, basic assembly practices and testing concepts are presented.

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IFPACK provides a suite of object-oriented algebraic preconditioners for the solution of preconditioned iterative solvers. IFPACK constructors expect the (distributed) real sparse matrix to be an Epetra RowMatrix object. IFPACK can be used to define point and block relaxation preconditioners, various flavors of incomplete factorizations for symmetric and non-symmetric matrices, and one-level additive Schwarz preconditioners with variable overlap. Exact LU factorizations of the local submatrix can be accessed through the AMESOS packages. IFPACK , as part of the Trilinos Solver Project, interacts well with other Trilinos packages. In particular, IFPACK objects can be used as preconditioners for AZTECOO, and as smoothers for ML. IFPACK is mainly written in C++, but only a limited subset of C++ features is used, in order to enhance portability.

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Porphyrin nanotubes represent a new class of nanostructures for which the molecular building blocks can be altered to control their structural and functional properties. Nanotubes containing tin(IV) porphyrins are photocatalytically active and can reduce metal ions from aqueous solution. The metal is deposited selectively onto tube surfaces, producing novel composite nanostructures that have potential applications as nanodevices. Two examples presented here are nanotubes with a continuous gold wire in the core and a gold ball at the end and nanotubes coated with platinum nanoparticles mainly on their outer surfaces. The latter are capable of photocatalytic reduction of water to hydrogen. Copyright © 2004 American Chemical Society.

Optical reflectance and atomic force microscopy (AFM) are used to develop a detailed description of GaN nucleation layer (NL) evolution upon annealing in ammonia and hydrogen to 1050°C. For the experiments, the GaN NLs were grown to a thickness of 30nm at 540°C, and then heated to 1050°C, following by holding at 1050°C for additional time. As the temperature, T, is increased, the NL decomposes uniformly beginning at 850°C up to 980°C as observed by the decrease in the optical reflectance signal and the absence of change in the NL AFM images. Decomposition of the original NL material drives the formation of GaN nuclei on top of the NL, which begin to appear on the NL near 1000°C, increasing the NL roughness. The GaN nuclei are formed by gas-phase transport of Ga atoms generated during the NL decomposition that recombine with ambient NH3. The gas-phase mechanism responsible for forming the GaN nuclei is demonstrated in two ways. First, the NL decomposition kinetics has an activation energy, EA, of 2.7 eV and this EA is observed in the NL roughening as the GaN nuclei increase in size. Second, the power spectral density functions measured with atomic force microscopy reveal that the GaN nuclei grow via an evaporation and recondensation mechanism. Once the original NL material is fully decomposed, the GaN nuclei stop growing in size and begin to decompose. For 30 nm thick NLs used in this study, approximately 1/3 of the NL Ga atoms are reincorporated into GaN nuclei. A detailed description of the NL evolution as it is heated to high temperature is presented, along with recommendations on how to enhance or reduce the NL decomposition and nuclei formation before high T GaN growth. © 2004 Elsevier B.V. All rights reserved.

The evolution of Coulomb interactions across the metal insulator transition (MIT) in a 3D localized conductor was experimentally investigated. The data were used to construct a phase diagram of the macroscopic Coulomb-correlated states as a function of single-particle energy and density. The phase diagrams show the existence of a phase boundary that separates low-energy distinctive metallic or insulating behavior from a higher energy mixed state. The data indicate a diverging screening radius at the critical density, which may signal an interaction-driven thermodynamic state change.

This document transmits the U.S. Fish and Wildlife Service's (Service) biological and conference opinions based on our review of National Nuclear Security Administration's (NNSA) proposed Maximum Operations Alternative at Sandia National Laboratories (SNL/CA), Alameda County, California.

Sandia has been investigating the use of "intelligent sensors" and their integration into "Smart Networks" for security applications. Intelligent sensors include devices that assess various phenomenologies such as radiation, chem-bio agents, radars, and video/video-motion detection. The main problem experienced with these intelligent sensors is in integrating the output from these various sensors into a system that reports the data to users in a manner that enables an efficient response to potential threats. The overall systems engineering is a critical part of bringing these intelligent sensors on-line and is important to ensuring that these systems are successfully deployed. The systems engineering effort includes designing and deploying computer networks, interfaces to make systems inter-operable, and training users to ensure that these intelligent sensors can be deployed property. This paper focuses on Sandia's efforts to investigate the systems architecture for "smart" networks and the various interfaces required between "smart" sensors to implement these "Smart Networks." ©2004 IEEE.

One effect noted during the March 1975 fire at the Browns Ferry plant is that fire-induced cable damage caused a range of unanticipated circuit faults including spurious reactor status signals and the apparent spurious operation of plant systems and components. Current USNRC regulations require that licensees conduct a post-fire safe shutdown analysis that includes consideration of such circuit effects. Post-fire circuit analysis continues to be an area of both technical challenge and regulatory focus. This paper discusses risk perspectives related to post-fire circuit analysis. An opening background discussion outlines the issues, concerns, and technical challenges. The paper then focuses on current risk insights and perspectives relevant to the circuit analysis problem. This includes a discussion of the available experimental data on cable failure modes and effects, a discussion of fire events that illustrate potential fire-induced circuit faults, and a discussion of risk analysis approaches currently being developed and implemented.

The complexity associated with the dynamics of wire arrays from individual wire ablation to wire-wire interaction and finally stagnation have been observed with relatively recent advances in experimental diagnostics. These experimental snapshots illustrate the existence of three-dimensional effects (e.g. wire precursor ablation and stagnation, array mass left behind, current density redistribution, multiple stagnations) that have a significant impact on the total radiation output. A detailed understanding of the magnitude and impact of these perturbations is lacking, especially those perturbations in three-dimensions. Sandia National Laboratories has developed a new multi-physics simulation framework tailored to high energy density physics (HEDP) environments. ALEGRA-HEDP[1] has begun to simulate this environment and has produced the highest fidelity, two-dimensional simulations of wire-array precursor ablation to date. The three-dimensional code capability now provides the ability to solve for the magnetic field and current density distribution associated with both the wire array and the complex current return structure. With this new capability the impact that experimental view-ports (e.g., slots in the current return can and radial spokes) have on the magnetic field surrounding the array can be investigated. Specifically, the impact that the perturbed magnetic field has on an idealized cylindrical liner implosion has been investigated.

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The turbulent convection that takes place in a Chandrasekhar-mass white dwarf during the final few minutes before it explodes determines where and how frequently it ignites. Numerical simulations have shown that the properties of the subsequent Type la supernova are sensitive to these ignition conditions. A heuristic model of the turbulent convection is explored. The results suggest that supernova ignition is likely to occur at a radius of order 100 km, rather than at the center of the star.