Publications

Results 68201–68300 of 99,299

Search results

Jump to search filters

Enhanced Chemical Incident Response Plan (ECIRP). Appendix F, remediation analysis with Decision Support Tools (DSTs) for wide-area chemical hazards

Miller, Trisha H.; Foltz, Greg W.

The Defense Threat Reduction Agency (DTRA) commissioned an assessment of the Consequence Management (CM) plans in place on military bases for response to a chemical attack. The effectiveness of the CM plans for recovering from chemical incidents was modeled using a multiple Decision Support Tools (DSTs). First, a scenario was developed based on an aerial dispersion of a chemical agent over a wide-area of land. The extent of contamination was modeled with the Hazard Prediction and Assessment Capability (HPAC) tool. Subsequently, the Analyzer for Wide Area Restoration Effectiveness (AWARE) tool was used to estimate the cost and time demands for remediation based on input of contamination maps, sampling and decontamination resources, strategies, rates and costs. The sampling strategies incorporated in the calculation were designed using the Visual Sample Plan (VSP) tool. Based on a gaps assessment and the DST remediation analysis, an Enhanced Chemical Incident Response Plan (ECIRP) was developed.

More Details
TYPE SAND Report YEAR 2011
DOIOSTI

Final report : testing and evaluation for solar hot water reliability

Caudell, Thomas P.; He, Hongbo; Menicucci, David F.; Mammoli, Andrea A.; Burch, Jay

Solar hot water (SHW) systems are being installed by the thousands. Tax credits and utility rebate programs are spurring this burgeoning market. However, the reliability of these systems is virtually unknown. Recent work by Sandia National Laboratories (SNL) has shown that few data exist to quantify the mean time to failure of these systems. However, there is keen interest in developing new techniques to measure SHW reliability, particularly among utilities that use ratepayer money to pay the rebates. This document reports on an effort to develop and test new, simplified techniques to directly measure the state of health of fielded SHW systems. One approach was developed by the National Renewable Energy Laboratory (NREL) and is based on the idea that the performance of the solar storage tank can reliably indicate the operational status of the SHW systems. Another approach, developed by the University of New Mexico (UNM), uses adaptive resonance theory, a type of neural network, to detect and predict failures. This method uses the same sensors that are normally used to control the SHW system. The NREL method uses two additional temperature sensors on the solar tank. The theories, development, application, and testing of both methods are described in the report. Testing was performed on the SHW Reliability Testbed at UNM, a highly instrumented SHW system developed jointly by SNL and UNM. The two methods were tested against a number of simulated failures. The results show that both methods show promise for inclusion in conventional SHW controllers, giving them advanced capability in detecting and predicting component failures.

More Details
TYPE SAND Report YEAR 2011
DOIOSTI

Summary compilation of shell element performance versus formulation

Heinstein, Martin; Breivik, Nicole L.

This document compares the finite element shell formulations in the Sierra Solid Mechanics code. These are finite elements either currently in the Sierra simulation codes Presto and Adagio, or expected to be added to them in time. The list of elements are divided into traditional two-dimensional, plane stress shell finite elements, and three-dimensional solid finite elements that contain either modifications or additional terms designed to represent the bending stiffness expected to be found in shell formulations. These particular finite elements are formulated for finite deformation and inelastic material response, and, as such, are not based on some of the elegant formulations that can be found in an elastic, infinitesimal finite element setting. Each shell element is subjected to a series of 12 verification and validation test problems. The underlying purpose of the tests here is to identify the quality of both the spatially discrete finite element gradient operator and the spatially discrete finite element divergence operator. If the derivation of the finite element is proper, the discrete divergence operator is the transpose of the discrete gradient operator. An overall summary is provided from which one can rank, at least in an average sense, how well the individual formulations can be expected to perform in applications encountered year in and year out. A letter grade has been assigned albeit sometimes subjectively for each shell element and each test problem result. The number of A's, B's, C's, et cetera assigned have been totaled, and a grade point average (GPA) has been computed, based on a 4.0-system. These grades, combined with a comparison between the test problems and the application problem, can be used to guide an analyst to select the element with the best shell formulation.

More Details
TYPE SAND Report YEAR 2011
DOIOSTI

Conformational study of a single molecule of poly para phenylene ethynylenes in dilute solutions

Journal of Chemical Physics

Maskey, Sabina; Pierce, Flint; Perahia, Dvora; Grest, Gary S.

The conformation of single molecules of dialkyl poly para phenylene ethynylenes (PPEs), electro-active polymers, is studied in solutions using molecular dynamics simulations. The conformation of conjugated polymers affects their electro-optical properties and therefore is critical to their current and potential uses, though only limited theoretical knowledge is available regarding the factors that control their configuration. The present study investigates the affects of molecular parameters including molecular weight of the polymer and chemical structure of the side chains of PPEs in different solvents on the conformation of the polymers. The PPEs are modeled atomistically where the solvents are modeled both implicitly and explicitly. The study finds that PPEs assume extended configuration which is affected by the length of the polymer backbone and the nature and length of substituting side chains. While the polymer remains extended, local dynamics is retained and no long range correlations are observed within the backbone. The results are compared with scattering experiments. © 2011 American Institute of Physics.

More Details
TYPE Journal Article YEAR 2011
ScopusOSTI

Electrospinning of nanofiber Chevrel phase materials

Journal of Materials Chemistry

Woan, Karran V.; Scheffler, Raymond H.; Bell, Nelson S.; Sigmund, Wolfgang M.

A modified sol-gel synthesis for non-oxide sulfide ceramics is presented. Sols are electrospun into continuous nanofiber precursors and then heat treated to obtain Chevrel-phase sulfide materials. In particular, the Mg-Chevrel fibers formed have average diameters of 230 ± 57 nm with grain sizes of 10 ± 3 nm after heat-treatment. © 2011 The Royal Society of Chemistry.

More Details
TYPE Journal Article YEAR 2011
ScopusOSTIDOI

Mutual injection locking of monolithically integrated coupled-cavity DBR lasers

IEEE Photonics Technology Letters

Tauke-Pedretti, Anna; Vawter, Gregory A.; Skogen, Erik J.; Peake, Gregory M.; Overberg, Mark E.; Alford, Charles; Chow, Weng W.; Yang, Zhenshan Y.; Torres, David; Cajas, Florante

We present a photonic integrated circuit (PIC) composed of two strongly coupled distributed Bragg reflector (DBR) lasers. This PIC utilizes the dynamics of mutual injection locking to increase the relaxation resonance frequency from 3 GHz to beyond 30 GHz. Mutual injection-locking and external injection-locking operation are compared. © 2011 IEEE.

More Details
TYPE Journal Article YEAR 2011
ScopusOSTIDOI

Bioinformatic processing to identify single nucleotide polymorphism that potentially affect Ape1 function

Mutation Research - Genetic Toxicology and Environmental Mutagenesis

Yu, Eizadora T.; Hadi, Masood Z.

Inactivation of DNA damage response mechanisms is associated with several disease syndromes, including cancer, aging and neurodegeneration. A major corrective pathway for alkylation or oxidative DNA damage is base excision repair (BER). As part of an effort to identify variation in DNA repair genes, we used the expressed sequence tag (EST) database to identify amino acid variation in Ape1, an essential gene in the BER repair pathway. Nucleotide substitutions were considered valid only if the amino acid changes were observed in at least two independent EST sequencing runs (i.e. two independent EST reports). In total eighty amino acid variants were identified for the Ape1 gene. Using software tools SIFT and PolyPhen, which predict impacts of amino acid substitutions on protein structure and function, twenty-six variants were predicted by both algorithms to be deleterious to protein function. Majority of these intolerant mutations such as V206C and F240S, lie within the core of the protein and may affect the stability and folding of Ape1, or in the case of N212H, N212K, and Y171N, are close to the enzyme's active site and could drastically affect its function. A few of the intolerant mutations, i.e., G178V and E217R, are surface residues and are far from the active site, and as such, the predicted effect on Ape1 stability or function is not evident. These variants are reagents for further protein function studies and molecular epidemiology studies of cancer susceptibility. © 2010 Elsevier B.V.

More Details
TYPE Journal Article YEAR 2011
ScopusOSTI

Interactions between planar grafted neurofilament side-arms

Journal of Physical Chemistry B

Stevens, Mark J.; Hoh, Jan H.

The side-arms of neurofilaments (NFs) have been proposed to be highly disordered, leading to an entropically and electrostatically based repulsion that modulates interfilament spacing. To characterize the behavior of two interacting polymer brushes in a system of this type, we performed molecular dynamics simulations of neurofilament brushes using a four bead reduced amino acid set coarse-grained model. In these simulations, we examined components of the neurofilament brush, NF-L, NF-M, and phosphorylated NF-H (NF-HP), individually. Each protein type was grafted to planar surfaces and simulations were performed for a range of separations of two apposed grafted surfaces. The calculated force-separation curves show the force increases as the reciprocal separation as predicted for polyelectrolyte brushes at high salt. All three systems can be overlapped on a single force-separation curve, which is not expected given the variation in amino acid sequence and charges on the polymers. Examination of structural properties shows scaling behavior in the average brush height, end-to-end distance, and the density interpenetration. Some of this scaling can be understood in terms of treating the NF proteins as effective polyelectrolytes, but some cannot suggesting a distinct polyampholyte behavior. Correlations are found between oppositely charged residues in opposite brushes. However, these correlations are weak in comparison to the strong correlations within each brush. In comparison with recent experimental data that observes condensed and expanded gel states, our results suggest that the condensed state structure involves significant interdigitation of the side-arms. © 2011 American Chemical Society.

More Details
TYPE Journal Article YEAR 2011
ScopusOSTIDOI

Evaporation of Lennard-Jones fluids

Journal of Chemical Physics

Cheng, Shengfeng; Lechman, Jeremy B.; Plimpton, Steven J.; Grest, Gary S.

Evaporation and condensation at a liquid/vapor interface are ubiquitous interphase mass and energy transfer phenomena that are still not well understood. We have carried out large scale molecular dynamics simulations of Lennard-Jones (LJ) fluids composed of monomers, dimers, or trimers to investigate these processes with molecular detail. For LJ monomers in contact with a vacuum, the evaporation rate is found to be very high with significant evaporative cooling and an accompanying density gradient in the liquid domain near the liquid/vapor interface. Increasing the chain length to just dimers significantly reduces the evaporation rate. We confirm that mechanical equilibrium plays a key role in determining the evaporation rate and the density and temperature profiles across the liquid/vapor interface. The velocity distributions of evaporated molecules and the evaporation and condensation coefficients are measured and compared to the predictions of an existing model based on kinetic theory of gases. Our results indicate that for both monatomic and polyatomic molecules, the evaporation and condensation coefficients are equal when systems are not far from equilibrium and smaller than one, and decrease with increasing temperature. For the same reduced temperature TT c, where Tc is the critical temperature, these two coefficients are higher for LJ dimers and trimers than for monomers, in contrast to the traditional viewpoint that they are close to unity for monatomic molecules and decrease for polyatomic molecules. Furthermore, data for the two coefficients collapse onto a master curve when plotted against a translational length ratio between the liquid and vapor phase. © 2011 American Institute of Physics.

More Details
TYPE Journal Article YEAR 2011
DOIOSTIScopus

Latent clustering on graphs with multiple edge types

Lecture Notes in Computer Science (including subseries Lecture Notes in Artificial Intelligence and Lecture Notes in Bioinformatics)

Rocklin, Matthew; Pinar, Ali P.

We study clustering on graphs with multiple edge types. Our main motivation is that similarities between objects can be measured in many different metrics, and so allowing graphs with multivariate edges significantly increases modeling power. In this context the clustering problem becomes more challenging. Each edge/metric provides only partial information about the data; recovering full information requires aggregation of all the similarity metrics. We generalize the concept of clustering in single-edge graphs to multi-edged graphs and discuss how this generates a space of clusterings. We describe a meta-clustering structure on this space and propose methods to compactly represent the meta-clustering structure. Experimental results on real and synthetic data are presented. © 2011 Springer-Verlag.

More Details
TYPE Conference YEAR 2011
ScopusOSTI

Delaminated titanate and peroxotitanate photocatalysts

Applied Catalysis B: Environmental

Stewart, Tom A.; Nyman, May; deBoer, Maarten P.

Delaminated layered titanates are effective, versatile, robust and practical photocatalytic materials for degradation of organic and microbiological contaminants. In prior studies, these have generally been obtained from Cs-titanate lepidocrocite-analogue parent materials. In this study we show that delaminated sodium nonatitanate (SNT) is equally effective as the delaminated Cs-titanate; yet it is cheaper to synthesize and is obtained in about one-third as many processing steps. Two chemical modifications; ligation with peroxide and treatment with phosphate resulted in improved photodegradation of common dyes; bromophenol-blue and methyl-orange. Together these two dyes provided experimental conditions ranging from pH ∼4.5-9. All layered titanate materials proved to be more effective colloidal suspension photocatalysts than standard TiO2. Although most common characterization techniques could not distinguish significant differences between the different delaminated titanates (from different parent materials, with chemical modifications), band-gap measurement via UV-vis spectroscopy proved informative. Generally the closer the match between the band-gap and the UV-light source, the more effective the catalyst. Finally, these layered titanates were electrostatically adhered to a surface, and photocatalytic activity was retained in this form. Furthermore, in this surface-adsorbed form we could see clear morphological differences between the Cs-titanate and SNT derived materials, as well as measure the height of the adsorbed layers. All observations by Atomic Force Microscopy indicated that the titanates layers that adhere to mica have a thickness of 1-10 layers thick (∼1-4nm). These materials in their surface-fixed forms are very promising for water treatment technologies. © 2011 Elsevier B.V.

More Details
TYPE Journal Article YEAR 2011
ScopusOSTI

Tribological challenges in MEMS and their mitigation via vapor phase lubrication

Proceedings of SPIE - The International Society for Optical Engineering

Dugger, Michael T.

MicroElectroMechanical Systems (MEMS) have become commercially successful in a number of niche applications. However, commercial success has only been possible where design, operating conditions, and materials result in devices that are not very sensitive to tribological effects. The use of MEMS in defense and national security applications will typically involve more challenging environments, with higher reliability and more complex functionality than required of commercial applications. This in turn will necessitate solutions to the challenges that have plagued MEMS since their inception - namely, adhesion, friction and wear. Adhesion during fabrication and immediately post-release has largely been resolved using hydrophobic coatings, but these coatings are not mechanically durable and do not inhibit surface degradation during extended operation. Tribological challenges in MEMS and approaches to mitigate the effects of adhesion, friction and wear are discussed. A new concept for lubrication of silicon MEMS using gas phase species is introduced. This "vapor phase lubrication" process has resulted in remarkable operating life of devices that rely on mechanical contact. VPL is also an effective lubrication approach for materials other than silicon, where traditional lubrication approaches are not feasible. The current status and remaining challenges for maturation of VPL are highlighted. © 2011 Copyright Society of Photo-Optical Instrumentation Engineers (SPIE).

More Details
TYPE Conference YEAR 2011
OSTIScopus
Results 68201–68300 of 99,299
Results 68201–68300 of 99,299