Publications

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We have investigated a model athermal system consisting of polystyrene (PS) nanoparticles (NPs) in PS melts. Neutron scattering shows that the chain dimensions expand in the presence of the NPs. We investigate this result theoretically using self-consistent PRISM theory, and also find an expansion in chain dimensions as a function of NP volume fraction. Recently it has been shown that nanoparticles can suppress dewetting in thin polymer films, a counterintuitive result since particles usually induce dewetting. Neutron reflectivity measurements have shown that the NPs phase separate to the surface, so one proposed mechanism for the inhibition of dewetting is that this segregation changes the surface energies. We calculate the density profiles for dilute NPs in polymer melts near a substrate using classical density functional theory, which shows that the NPs do indeed segregate to the surface.

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Computer simulation tools used to predict the energy production of photovoltaic systems are needed in order to make informed economic decisions. These tools require input parameters that characterize module performance under various operational and environmental conditions. Depending upon the complexity of the simulation model, the required input parameters can vary from the limited information found on labels affixed to photovoltaic modules to an extensive set of parameters. The required input parameters are normally obtained indoors using a solar simulator or flash tester, or measured outdoors under natural sunlight. This paper compares measured performance parameters for three photovoltaic modules tested outdoors at the National Institute of Standards and Technology (NIST) and Sandia National Laboratories (SNL). Two of the three modules were custom fabricated using monocrystalline and silicon film cells. The third, a commercially available module, utilized triple-junction amorphous silicon cells. The resulting data allow a comparison to be made between performance parameters measured at two laboratories with differing geographical locations and apparatus. This paper describes the apparatus used to collect the experimental data, test procedures utilized, and resulting performance parameters for each of the three modules. Using a computer simulation model, the impact that differences in measured parameters have on predicted energy production is quantified. Data presented for each module includes power output at standard rating conditions and the influence of incident angle, air mass, and module temperature on each module's electrical performance. Measurements from the two laboratories are in excellent agreement. The power at standard rating conditions is within 1% for all three modules. Although the magnitude of the individual temperature coefficients varied as much as 17% between the two laboratories, the impact on predicted performance at various temperature levels was minimal, less than 2%. The influence of air mass on the performance of the three modules measured at the laboratories was in excellent agreement. The largest difference in measured results between the two laboratories was noted in the response of the modules to incident angles that exceed 75 deg.

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Vapor pressure and heats of vaporization are computed for the industrial fluid properties simulation challenge (IFPSC) data set using the Towhee Monte Carlo molecular simulation program. Results are presented for the CHARMM27 and OPLS-aa force fields. Once again, the average result using multiple force fields is a better predictor of the experimental value than either individual force field.

We present an exchange-correlation functional that enables an accurate treatment of systems with electronic surfaces. The functional is developed within the subsystem functional paradigm [1], combining the local density approximation for interior regions with a new functional designed for surface regions. It is validated for a variety of materials by calculations of: (i) properties where surface effects exist, and (ii) established bulk properties. Good and coherent results are obtained, indicating that this functional may serve well as universal first choice for solid state systems. The good performance of this first subsystem functional also suggests that yet improved functionals can be constructed by this approach.

We develop a specialized treatment of electronic surface regions which, via the subsystem functional approach [1], can be used in functionals for self-consistent density-functional theory (DFT). Approximations for both exchange and correlation energies are derived for an electronic surface. An interpolation index is used to combine this surface-specific functional with a functional for interior regions. When the local density approximation (LDA) is used for the interior region, the end result is a straightforward density-gradient dependent functional that shows promising results. Further improvement of the treatment of the interior region by the use of a local gradient expansion approximation is also discussed.

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Economists, systems analysts, engineers, regulatory specialists, and other experts were assembled from academia, the national laboratories, and the energy industry to discuss present restoration practices (many have already been defined to the level of operational protocols) in the sectors of the energy infrastructure as well as other infrastructures, to identify whether economics, a discipline concerned with the allocation of scarce resources, is explicitly or implicitly a part of restoration strategies, and if there are novel economic techniques and solution methods that could be used help encourage the restoration of energy services more quickly than present practices or to restore service more efficiently from an economic perspective. AcknowledgementsDevelopment of this work into a coherent product with a useful message has occurred thanks to the thoughtful support of several individuals:Kenneth Friedman, Department of Energy, Office of Energy Assurance, provided the impetus for the work, as well as several suggestions and reminders of direction along the way. Funding from DOE/OEA was critical to the completion of this effort.Arnold Baker, Chief Economist, Sandia National Laboratories, and James Peerenboom, Director, Infrastructure Assurance Center, Argonne National Laboratory, provided valuable contacts that helped to populate the authoring team with the proper mix of economists, engineers, and systems and regulatory specialists to meet the objectives of the work.Several individuals provided valuable review of the document at various stages of completion, and provided suggestions that were valuable to the editing process. This list of reviewers includes Jeffrey Roark, Economist, Tennessee Valley Authority; James R. Dalrymple, Manager of Transmission System Services and Transmission/Power Supply, Tennessee Valley Authority; William Mampre, Vice President, EN Engineering; Kevin Degenstein, EN Engineering; and Patrick Wilgang, Department of Energy, Office of Energy Assurance.With many authors, creating a document with a single voice is a difficult task. Louise Maffitt, Senior Research Associate, Institute for Engineering Research and Applications at New Mexico Institute of Mining & Technology (on contract to Sandia National Laboratories) served a vital role in the development of this document by taking the unedited material (in structured format) and refining the basic language so as to make the flow of the document as close to a single voice as one could hope for. Louise's work made the job of reducing the content to a readable length an easier process. Additional editorial suggestions from the authors themselves, particularly from Sam Flaim, Steve Folga, and Doug Gotham, expedited this process.

Visualization in scientific computing refers to the process of transforming data produced by a simulation into graphical representations that help scientific users interpret the results. While the back-end rendering phase of this work can be performed efficiently in graphics card hardware, the front-end 'post processing' portion of visualization is currently performed entirely in software. Field-Programmable Gate Arrays (FPGAs) are an attractive option for accelerating post-processing operations because they enable users to offload computations into reconfigurable hardware. A key challenge in utilizing FPGAs for this work is developing an infrastructure that allows FPGAs to be integrated into a distributed visualization system. We propose a networked approach, where each post-processing FPGA is equipped with specialized network interface (NI) hardware that is capable of transporting graphics commands across the network to existing rendering resources. In this paper we discuss a NI for FPGAs that is comprised of a Chromium OpenGL interface, a TCP Offload Engine, and a Gigabit Ethernet module. A prototype system has been tested for a distributed isosurfacing application.

The two primary uses for SOAR are: (1) Predictive--(i) Science based process models enable optimized automated weld procedures, (ii) virtual manufacturing enables the user to ask 'what if' and quickly find the answer, (iii) with SOAR, multiple welds do not need to be made in order to determine weld effects and required parameters; and (2) Investigative--(i) welding problem mysteries can be solved by gathering evidence, identifying problem suspects, and testing with SOAR; (ii) most SOAR models are universal and can be applied to many different weld processes; and (iii) understand your welding process.

The appearance of phosphatidylserine on the membrane surface of apoptotic cells (Jurkat, CHO, HeLa) is monitored by using a family of bis(Zn{sup 2+}-2,2{prime}-dipicolylamine) coordination compounds with appended fluorescein or biotin groups as reporter elements. The phosphatidylserine affinity group is also conjugated directly to a CdSe/CdS quantum dot to produce a probe suitable for prolonged observation without photobleaching. Apoptosis can be detected under a wide variety of conditions, including variations in temperature, incubation time, and binding media. Binding of each probe appears to be restricted to the cell membrane exterior, because no staining of organelles or internal membranes is observed.

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Optimization-ready reduced-order models should target a particular output functional, span an applicable range of dynamic and parametric inputs, and respect the underlying governing equations of the system. To achieve this goal, we present an approach for determining a projection basis that uses a goal-oriented, model-based optimization framework. The mathematical framework permits consideration of general dynamical systems with general parametric variations. The methodology is applicable to both linear and nonlinear systems and to systems with many input parameters. This paper focuses on an initial presentation and demonstration of the methodology on a simple linear model problem of the two-dimensional, time-dependent heat equation with a small number of inputs. For this example, the reduced models determined by the new approach provide considerable improvement over those derived using the proper orthogonal decomposition.

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The Sandia Z accelerator has become a unique platform to study matter at extreme conditions. The large currents (20 MA, 200-300 ns rise time) and magnetic fields (several MG) produced by Z generate magnetic compression in the multi-Mbar regime, enabling quasi-isentropic compression experiments (ICE) to several Mbar stresses. Thus, the Z platform is useful in determining high stress material isentropes, performing phase transition studies (including rapid solidification), obtaining constitutive property information, and estimating material strength at high stress. Furthermore, the magnetic pressure can also accelerate macroscopic flyer plates to velocities in excess of 30 km/s. Thus, impact experiments can be performed to ultra-high pressures. Furthermore, the adiabatic release response of materials can be investigated through shock and release experiments, allowing hot, dense liquid states to be probed. The Z platform allows a large expanse of the equation of state surface to be explored enabling new and exciting material dynamics experiments. Specific examples from each of the areas mentioned above will be discussed.

Ohmic contacts on p-type GaN utilizing Pd/Ir/Au metallization were fabricated and characterized. Metallized samples that were rapid thermally annealed at 400 C for 1 min exhibited linear current-voltage characteristics. Specific ohmic contact resistivities as low as 2 x 10{sup -5} {Omega} cm{sup 2} were achieved. Auger electron spectroscopy and x-ray photoelectron spectroscopy depth profiles of annealed Pd/Ir/Au contact revealed the formation of Pd- and Ir-related alloys at the metal-semiconductor junction with the creation of Ga vacancies below the contact. The excellent contact resistance obtained is attributed to the formation of these Ga vacancies which resulted in the reduction of the depletion region width at the junction.

The performance and reliability of microelectromechanical (MEMS) devices can be highly dependent on the control of the surface energetics in these structures. Examples of this sensitivity include the use of surface modifying chemistries to control stiction, to minimize friction and wear, and to preserve favorable electrical characteristics in surface micromachined structures. Silane modification of surfaces is one classic approach to controlling stiction in Si-based devices. The time-dependent efficacy of this modifying treatment has traditionally been evaluated by studying the impact of accelerated aging on device performance and conducting subsequent failure analysis. Our interest has been in identifying aging related chemical signatures that represent the early stages of processes like silane displacement or chemical modification that eventually lead to device performance changes. We employ a series of classic surface characterization techniques along with multivariate statistical methods to study subtle changes in the silanized silicon surface and relate these to degradation mechanisms. Examples include the use of spatially resolved time-of-flight secondary ion mass spectrometric, photoelectron spectroscopic, photoluminescence imaging, and scanning probe microscopic techniques to explore the penetration of water through a silane monolayer, the incorporation of contaminant species into a silane monolayer, and local displacement of silane molecules from the Si surface. We have applied this analytical methodology at the Si coupon level up to MEMS devices. This approach can be generalized to other chemical systems to address issues of new materials integration into micro- and nano-scale systems.

Concerns about acts of terrorism against critical infrastructures have been on the rise for several years. Critical infrastructures are those physical structures and information systems (including cyber) essential to the minimum operations of the economy and government. The President's Commission on Critical Infrastructure Protection (PCCIP) probed the security of the nation's critical infrastructures. The PCCIP determined the water infrastructure is highly vulnerable to a range of potential attacks. In October 1997, the PCCIP proposed a public/private partnership between the federal government and private industry to improve the protection of the nation's critical infrastructures. In early 2000, the EPA partnered with the Awwa Research Foundation (AwwaRF) and Sandia National Laboratories to create the Risk Assessment Methodology for Water Utilities (RAM-W{trademark}). Soon thereafter, they initiated an effort to create a template and minimum requirements for water utility Emergency Response Plans (ERP). All public water utilities in the US serving populations greater than 3,300 are required to undertaken both a vulnerability assessment and the development of an emergency response plan. This paper explains the initial steps of RAM-W{trademark} and then demonstrates how the security risk assessment is fundamental to the ERP. During the development of RAM-W{trademark}, Sandia performed several security risk assessments at large metropolitan water utilities. As part of the scope of that effort, ERPs at each utility were reviewed to determine how well they addressed significant vulnerabilities uncovered during the risk assessment. The ERP will contain responses to other events as well (e.g. natural disasters) but should address all major findings in the security risk assessment.

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Poly(N-isopropyl acrylamide) (PNIPAM) is perhaps the most well known member of the class of responsive polymers. Free PNIPAM chains have a lower critical solution temperature in water at {approx}31 C. This very sharp transition ({approx}5 C) is attributed to alterations in the hydrogen bonding interactions of the amide group. Grafted chains of PNIPAM have shown promise for creating responsive surfaces. Examples include controlling the adsorption of proteins or bacteria, regulating the flow of liquids in narrow filaments or mesoporous materials, control of enzymatic activity, and releasing the contents of liposomes. Conformational changes of the polymer are likely to play a role in some of these applications, in addition to changes in local interactions. In this work we investigated the T-dependent conformational changes of grafted PNIPAM chains in D2O using neutron reflection and AFM. The molecular weight (M) and surface density of the PNIPAM brushes were controlled using atom-transfer radical polymerization. We discovered a strong effect of surface density. At lower surface densities, in the range typically achieved with grafting-to methods, we observed very little conformational change. At higher surface densities, significant changes with T were observed. The results will be compared with numerical SCF calculations employing an effective (conc.-dependent) Flory-Huggins chi parameter extracted from the solution phase diagram. For the case of high M and high surface density, a non-monotonic change in profile shape with T was observed. This will be discussed in the context of vertical phase separation predicted for brushes of water-soluble polymers within two-state models.

Our study (1) reported on the deformation response of nanocrystalline Ni during in situ dark-field transmission electron microscopy (DFTEM) straining experiments and showed what we view as direct and compelling evidence of grain boundary-mediated plasticity. Based on their analysis of the limited experimental data we presented, however, Chen and Yan (2) propose that the reported contrast changes more likely resulted from grain growth caused by electron irradiation and applied stress rather than from plastic deformation. Here, we give specific reasons why their assertions are incorrect and discuss how the measurement approaches they have used are inappropriate. Additionally, we present further evidence that supports our original conclusions. The method Chen and Yan employed to measure displacement merely probes the in-plane (two-dimensional) components of incremental strain occurring during the very short time interval shown [figure 3 in (1)] instead of the accumulated strain. As we noted explicitly in the supporting online material in (1), the loading was applied by pulsing the displacement manually. After each small displacement pulse, the monitored area always moved significantly within or even out of the field of view. Clear images could be obtained only when the sample position stabilized within the field of view, and at that time severe deformation was nearly complete. Thus, little incremental strain occurs during this short image sequence [figure 3 in (1)], as one might expect. We believe that the images shown in figure 3 of (1) are particularly valuable in understanding deformation in nanocrystalline materials. In general, the formation process of grain agglomerates simply occurred too fast to be recorded clearly. Moreover, instead of remaining constant after formation, the sizes of the grain agglomerates changed in a rather irregular manner in responding to the deformation and fracture process (see, for example, Fig. 1, B to D). This indicates that strong grain boundary-related activity occurred inside the grain agglomerates. Figure 3 in (1), a short (0.5 s) extract from more than 6 hours of videotaped experimentation (imaged ahead of cracks), not only reveals the formation process of a grain agglomerate, but also shows conclusive evidence for grain rotation and excludes the effect of overall sample rotation. It should be noted that other small grains still exhibit some minor contrast changes in figure 3 in (1). Hence, using them as reference points yields measurements that may not be accurate to {+-}1 nm [as Chen and Yan (2) claim in their analysis] and limits the accuracy of their conclusions. Chen and Yan also claim that no deformation has occurred, yet simultaneously state that the analysis has a deformation measurement error of 0.5%. This is simply not consistent; even small strains of this order may cause plastic deformation. In contrast with previous in situ TEM experiments (3-5), the special sample design adopted in our investigation (1) ensured that all deformation was primarily concentrated in a bandlike area ahead of the propagating crack. We found that these grain agglomerates were observed only in this bandlike thinning area as a response to the applied loads (Fig. 1B). No similar phenomena were detected under the electron beam alone or in stressed areas apart from the main deformation area, and these phenomena have not been reported during in situ observations of this same material made by other researchers (5). Subsequent cracks were always observed to follow this deformation area upon further displacement pulses (Fig. 1, C and D). This clearly indicates that the enlarged agglomerates do not result simply from electron irradiation plus stress, but rather from stress-induced deformation. In their comment, Chen and Yan claimed a linear relation between 'grain' area and time based on their measurements made from figure 3 in (1) and claimed that these measurements are exactly consistent with the classical grain growth equation. However, as we noted (1), the growth in size of this agglomerate is not isotropic and occurs in an irregular manner. For example, after bright contrast emerged from a grain about 6 nm in diameter, it remained well defined in size as a single, approximately equiaxed grain until t = 0.1 s (fig. S1). We have reproduced the 'grain growth' plot of Chen and Yan (Fig. 2) using our entire video image sequence (fig. S1). Clearly, the growth in area of the agglomerate is not consistent with linear grain growth. (Unfortunately, only a portion of these data could be included in the original paper for reasons of space.) Notably, Chen and Yan did not apply a similar 'grain growth' analysis to nearby grains; this would have yielded no information in support of their argument, as those grains show essentially no growth.

This report summarizes progress from the Laboratory Directed Research and Development (LDRD) program during fiscal year 2004. In addition to a programmatic and financial overview, the report includes progress reports from 352 individual R and D projects in 15 categories. The 15 categories are: (1) Advanced Concepts; (2) Advanced Manufacturing; (3) Biotechnology; (4) Chemical and Earth Sciences; (5) Computational and Information Sciences; (6) Differentiating Technologies; (7) Electronics and Photonics; (8) Emerging Threats; (9) Energy and Critical Infrastructures; (10) Engineering Sciences; (11) Grand Challenges; (12) Materials Science and Technology; (13) Nonproliferation and Materials Control; (14) Pulsed Power and High Energy Density Sciences; and (15) Corporate Objectives.

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This paper surveys the needs associated with environmental monitoring and long-term environmental stewardship. Emerging sensor technologies are reviewed to identify compatible technologies for various environmental monitoring applications. The contaminants that are considered in this report are grouped into the following categories: (1) metals, (2) radioisotopes, (3) volatile organic compounds, and (4) biological contaminants. United States regulatory drivers are evaluated for different applications (e.g., drinking water, storm water, pretreatment, and air emissions), and sensor requirements are derived from these regulatory metrics. Sensor capabilities are then summarized according to contaminant type, and the applicability of the different sensors to various environmental monitoring applications is discussed.

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Time domain reflectometry (TDR) operates by propagating a radar frequency electromagnetic pulse down a transmission line while monitoring the reflected signal. As the electromagnetic pulse propagates along the transmission line, it is subject to impedance by the dielectric properties of the media along the transmission line (e.g., air, water, and sediment), reflection at dielectric discontinuities (e.g., air-water or water-sediment interface), and attenuation by electrically conductive materials (e.g., salts and clays). Taken together, these characteristics provide a basis for integrated stream monitoring, specifically, concurrent measurement of stream stage, channel profile, and aqueous conductivity. Requisite for such application is a means of extracting the desired stream parameters from measured TDR traces. Analysis is complicated by the fact that interface location and aqueous conductivity vary concurrently and multiple interfaces may be present at any time. For this reason a physically based multisection model employing the S11 scatter function and Debeye parameters for dielectric dispersion and loss is used to analyze acquired TDR traces. Here we explore the capability of this multisection modeling approach for interpreting TDR data acquired from complex environments, such as encountered in stream monitoring. A series of laboratory tank experiments was performed in which the depth of water, depth of sediment, and conductivity were varied systematically. Comparisons between modeled and independently measured data indicate that TDR measurements can be made with an accuracy of {+-} 3.4 x 10{sup -3} m for sensing the location of an air-water or water-sediment interface and {+-} 7.4% of actual for the aqueous conductivity.

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How might the quality of a city's delivered water be compromised through natural or malevolent causes? What are the consequences of a contamination event? What water utility assets are at greatest risk to compromise? Utility managers have been scrambling to find answers to these questions since the events of 9/11. However, even before this date utility mangers were concerned with the potential for system contamination through natural or accidental causes. Unfortunately, an integrated tool for assessing both the threat of attack/failure and the subsequent consequence is lacking. To help with this problem we combine Markov Latent Effects modeling for performing threat assessment calculations with the widely used pipe hydraulics/transport code, EPANET, for consequences analysis. Together information from these models defines the risk posed to the public due to natural or malevolent contamination of a water utility system. Here, this risk assessment framework is introduced and demonstrated within the context of vulnerability assessment for water distribution systems.

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An S-band 20 MeV electron linear accelerator formerly used for medical applications has been recommissioned to provide a wide range of photonuclear activation studies as well as various radiation effects on biological and microelectronic systems. Four radiation effect applications involving the electron/photon beams are described. Photonuclear activation of a stable isotope of oxygen provides an active means of characterizing polymer degradation. Biological irradiations of microorganisms including bacteria were used to study total dose and dose-rate effects on survivability and the adaptation of these organisms to repeated exposures. Microelectronic devices including bipolar junction transistors (BJTs) and diodes were irradiated to study photocurrent from these devices as a function of peak dose rate with comparisons to computer modeling results. In addition, the 20 MeV linac may easily be converted to a medium energy neutron source which has been used to study neutron damage effects on transistors.

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Experimental results [1] for the reflection coefficient of shock compressed xenon are compared with results from quantum molecular dynamics calculations with density functional theory (DFT). The real part of the optical conductivity is calculated within the Kubo-Greenwood formalism and the Kramers-Kroenig relations are used to generate the reflectivity and other optical properties. Improved agreement over non-ideal plasma theory [2] is found with the DFT calculations, but significant differences with the data remain. Since DFT in the various local density approximations tends to underestimate the band gap and overestimate the free electron population, we have used the ionizations from [2] to correct the DFT band gaps. This results in much improved agreement with the xenon reflectivity data and demonstrates a new approach to correcting DFT band gaps.

INVICE (INVerse analysis of Isentropic Compression Experiments) is a FORTRAN computer code that implements the inverse finite-difference method to analyze velocity data from isentropic compression experiments. This report gives a brief description of the methods used and the options available in the first beta version of the code, as well as instructions for using the code.

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We report a fully integrated high-Q factor micro-ring resonator using silicon nitride/dioxide on a silicon wafer. The micro-ring resonator is critically coupled to a low loss straight waveguide. An intrinsic quality factor of 2.4 x 10{sup 5} has been measured.

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A series of amorphous silicate materials with the general formula Na{sub x+2y}M{sub x}{sup 3+}Si{sub 1-x}O{sub 2+y}(M{sup 3+} = Al, Mn, Fe, Y) were studied. Samples were synthesized by a precipitation reaction at room temperature. The results indicate that the ion-exchange capacity (IEC) decreases as follows: Al > Fe > Mn > Y. Additionally, the IEC increases with increasing aluminum concentration. Structural studies show that the relative amount of octahedrally coordinated aluminum increases with increasing Al content, as does the total amount of AlO{sub 4} species increases. The data suggest that the IEC value of these amorphous aluminosilicates is dependent on the tetrahedrally coordinated aluminum. Regeneration of the Al-silicate with acetic acid does not decrease the IEC significantly.

Organic light-emitting diodes (OLEDs), with few exvceptions, are fabricated in the standard way of sequentially depositing active layers and elecrodes onto a substrate. The conventional devices have 'a detrimental layer' at the interface between the organic and the top metal electrode because evaporation results in metal in-diffusion and chemical disruption at the metal-organic interface, Here, a different approach is introduced to construct OLEDs: soft contact lamination (SCL) is based on thysical lamination of thin metal electrodes supported by an elastomeric layer against the electrolumnescent organic layer. Thei method produces spatially homogeneous, intimate contacts via van der Waals interaction between the metal and the organic, resulting in no chemical and physical damages to the organic. Devices fabricated by SCL are shown to have no detrimental layer and fewer luminescence-quenching channels than conventional devices that have evaporated top metal electrodes.

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We present experimental observation and theoretical analysis of looping carbon nanotubes connecting two electrodes. The measured conductance of the nanotubes is not strongly affected by the presence of these conformational defects, a result that is confirmed by quantum transport calculations. Our work indicates that solution-based fabrication methods for carbon nanotube devices can have high conformational defect tolerance, except for defects with 5-10 nanometer bending radius. © 2005 American Institute of Physics.

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Agile ready-when-needed patterning of refractive index structures in photosensitive materials requires an understanding of the impact of local application environment on mechanisms contributing to the desired photoinduced index change. The present work examines the impact of atmosphere on the photosensitive response of poly(methylphenylsilane) (PMPS) thin films whose high photoinduced index'change under low incident optical fluence make them attractive candidates for such applications. Changes in optical absorption and refractive index are investigated after exposure to ultraviolet (UV) light resonant with the lowest energy transition exhibited by the Si-Si backbone structure in the material. A comparison between photoinduced absorption changes for thin films exposed in an air atmosphere versus those observed for samples subjected to a nitrogen environment during photoexposure is made for the first time. The study reveals that the anaerobic conditions of the nitrogen atmosphere significantly reduce the photosensitive response of the material to light. These results are discussed in terms of photooxidation processes within the polysilane structure and in the context of the need for predictable photosensitive refractive index change in varied photoimprinting environments. © 2004 Elsevier B.V. All rights reserved.

Policy-based network management (PBNM) uses policy-driven automation to manage complex enterprise and service provider networks. Such management is strongly supported by industry standards, state of the art technologies and vendor product offerings. We present a case for the use of PBNM and related technologies for end-to-end service delivery. We provide a definition of PBNM terms, a discussion of how such management should function and the current state of the industry. We include recommendations for continued work that would allow for PBNM to be put in place over the next five years in the unclassified environment.

ALEGRA is an arbitrary Lagrangian-Eulerian finite element code that emphasizes large distortion and shock propagation in inviscid fluids and solids. This document describes user options for modeling resistive magnetohydrodynamics, thermal conduction, and radiation transport effects, and two material temperature physics.

To establish mechanical properties and failure criteria of silicon carbide (SiC-N) ceramics, a series of quasi-static compression tests has been completed using a high-pressure vessel and a unique sample alignment jig. This report summarizes the test methods, set-up, relevant observations, and results from the constitutive experimental efforts. Results from the uniaxial and triaxial compression tests established the failure threshold for the SiC-N ceramics in terms of stress invariants (I{sub 1} and J{sub 2}) over the range 1246 < I{sub 1} < 2405. In this range, results are fitted to the following limit function (Fossum and Brannon, 2004) {radical}J{sub 2}(MPa) = a{sub 1} - a{sub 3}e -a{sub 2}(I{sub 1}/3) + a{sub 4} I{sub 1}/3, where a{sub 1} = 10181 MPa, a{sub 2} = 4.2 x 10{sup -4}, a{sub 3} = 11372 MPa, and a{sub 4} = 1.046. Combining these quasistatic triaxial compression strength measurements with existing data at higher pressures naturally results in different values for the least-squares fit to this function, appropriate over a broader pressure range. These triaxial compression tests are significant because they constitute the first successful measurements of SiC-N compressive strength under quasistatic conditions. Having an unconfined compressive strength of {approx}3800 MPa, SiC-N has been heretofore tested only under dynamic conditions to achieve a sufficiently large load to induce failure. Obtaining reliable quasi-static strength measurements has required design of a special alignment jig and load-spreader assembly, as well as redundant gages to ensure alignment. When considered in combination with existing dynamic strength measurements, these data significantly advance the characterization of pressure-dependence of strength, which is important for penetration simulations where failed regions are often at lower pressures than intact regions.

A laser hazard analysis and safety assessment was performed for the 3rd Tech model DeltaSphere-3000{reg_sign} Laser 3D Scene Digitizer, infrared laser scanner model based on the 2000 version of the American National Standard Institute's Standard Z136.1, for the Safe Use of Lasers. The portable scanner system is used in the Robotic Manufacturing Science and Engineering Laboratory (RMSEL). This scanning system had been proposed to be a demonstrator for a new application. The manufacture lists the Nominal Ocular Hazard Distance (NOHD) as less than 2 meters. It was necessary that SNL validate this NOHD prior to its use as a demonstrator involving the general public. A formal laser hazard analysis is presented for the typical mode of operation for the current configuration as well as a possible modified mode and alternative configuration.

Several SIERRA applications make use of third-party libraries to solve systems of linear and nonlinear equations, and to solve eigenproblems. The classes and interfaces in the SIERRA framework that provide linear system assembly services and access to solver libraries are collectively referred to as solver services. This paper provides an overview of SIERRA's solver services including the design goals that drove the development, and relationships and interactions among the various classes. The process of assembling and manipulating linear systems will be described, as well as access to solution methods and other operations.

The Finite Element Interface to Linear Solvers (FEI) is a linear system assembly library. Sparse systems of linear equations arise in many computational engineering applications, and the solution of linear systems is often the most computationally intensive portion of the application. Depending on the complexity of problems addressed by the application, there may be no single solver package capable of solving all of the linear systems that arise. This motivates the need to switch an application from one solver library to another, depending on the problem being solved. The interfaces provided by various solver libraries for data assembly and problem solution differ greatly, making it difficult to switch an application code from one library to another. The amount of library-specific code in an application can be greatly reduced by having an abstraction layer that puts a 'common face' on various solver libraries. The FEI has seen significant use by finite element applications at Sandia National Laboratories and Lawrence Livermore National Laboratory. The original FEI offered several advantages over using linear algebra libraries directly, but also imposed significant limitations and disadvantages. A new set of interfaces has been added with the goal of removing the limitations of the original FEI while maintaining and extending its strengths.

This report summarizes the research and development performed from October 2002 to September 2004 at Sandia National Laboratories under the Laboratory-Directed Research and Development (LDRD) project ''Massively-Parallel Linear Programming''. We developed a linear programming (LP) solver designed to use a large number of processors. LP is the optimization of a linear objective function subject to linear constraints. Companies and universities have expended huge efforts over decades to produce fast, stable serial LP solvers. Previous parallel codes run on shared-memory systems and have little or no distribution of the constraint matrix. We have seen no reports of general LP solver runs on large numbers of processors. Our parallel LP code is based on an efficient serial implementation of Mehrotra's interior-point predictor-corrector algorithm (PCx). The computational core of this algorithm is the assembly and solution of a sparse linear system. We have substantially rewritten the PCx code and based it on Trilinos, the parallel linear algebra library developed at Sandia. Our interior-point method can use either direct or iterative solvers for the linear system. To achieve a good parallel data distribution of the constraint matrix, we use a (pre-release) version of a hypergraph partitioner from the Zoltan partitioning library. We describe the design and implementation of our new LP solver called parPCx and give preliminary computational results. We summarize a number of issues related to efficient parallel solution of LPs with interior-point methods including data distribution, numerical stability, and solving the core linear system using both direct and iterative methods. We describe a number of applications of LP specific to US Department of Energy mission areas and we summarize our efforts to integrate parPCx (and parallel LP solvers in general) into Sandia's massively-parallel integer programming solver PICO (Parallel Interger and Combinatorial Optimizer). We conclude with directions for long-term future algorithmic research and for near-term development that could improve the performance of parPCx.

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The manipulation of physical interactions between structural moieties on the molecular scale is a fundamental hurdle in the realization and operation of nanostructured materials and high surface area microsystem architectures. These include such nano-interaction-based phenomena as self-assembly, fluid flow, and interfacial tribology. The proposed research utilizes photosensitive molecular structures to tune such interactions reversibly. This new material strategy provides optical actuation of nano-interactions impacting behavior on both the nano- and macroscales and with potential to impact directed nanostructure formation, microfluidic rheology, and tribological control.

As part of the U.S. Department of Energy (DOE) Office of Industrial Technologies (OIT) Industries of the Future (IOF) Forest Products research program, a collaborative investigation was conducted on the sources, characteristics, and deposition of particles intermediate in size between submicron fume and carryover in recovery boilers. Laboratory experiments on suspended-drop combustion of black liquor and on black liquor char bed combustion demonstrated that both processes generate intermediate size particles (ISP), amounting to 0.5-2% of the black liquor dry solids mass (BLS). Measurements in two U.S. recovery boilers show variable loadings of ISP in the upper furnace, typically between 0.6-3 g/Nm{sup 3}, or 0.3-1.5% of BLS. The measurements show that the ISP mass size distribution increases with size from 5-100 {micro}m, implying that a substantial amount of ISP inertially deposits on steam tubes. ISP particles are depleted in potassium, chlorine, and sulfur relative to the fuel composition. Comprehensive boiler modeling demonstrates that ISP concentrations are substantially overpredicted when using a previously developed algorithm for ISP generation. Equilibrium calculations suggest that alkali carbonate decomposition occurs at intermediate heights in the furnace and may lead to partial destruction of ISP particles formed lower in the furnace. ISP deposition is predicted to occur in the superheater sections, at temperatures greater than 750 C, when the particles are at least partially molten.

The thermal hazard posed by large hydrocarbon fires is dominated by the radiative emission from high temperature soot. Since the optical properties of soot, especially in the infrared region of the electromagnetic spectrum, as well as its morphological properties, are not well known, efforts are underway to characterize these properties. Measurements of these soot properties in large fires are important for heat transfer calculations, for interpretation of laser-based diagnostics, and for developing soot property models for fire field models. This research uses extractive measurement diagnostics to characterize soot optical properties, morphology, and composition in 2 m pool fires. For measurement of the extinction coefficient, soot extracted from the flame zone is transported to a transmission cell where measurements are made using both visible and infrared lasers. Soot morphological properties are obtained by analysis via transmission electron microscopy of soot samples obtained thermophoretically within the flame zone, in the overfire region, and in the transmission cell. Soot composition, including carbon-to-hydrogen ratio and polycyclic aromatic hydrocarbon concentration, is obtained by analysis of soot collected on filters. Average dimensionless extinction coefficients of 8.4 {+-} 1.2 at 635 nm and 8.7 {+-} 1.1 at 1310 nm agree well with recent measurements in the overfire region of JP-8 and other fuels in lab-scale burners and fires. Average soot primary particle diameters, radius of gyration, and fractal dimensions agree with these recent studies. Rayleigh-Debye-Gans theory of scattering applied to the measured fractal parameters shows qualitative agreement with the trends in measured dimensionless extinction coefficients. Results of the density and chemistry are detailed in the report.

The measurement of heat flux in hydrocarbon fuel fires (e.g., diesel or JP-8) is difficult due to high temperatures and the sooty environment. Un-cooled commercially available heat flux gages do not survive in long duration fires, and cooled gages often become covered with soot, thus changing the gage calibration. An alternate method that is rugged and relatively inexpensive is based on inverse heat conduction methods. Inverse heat-conduction methods estimate absorbed heat flux at specific material interfaces using temperature/time histories, boundary conditions, material properties, and usually an assumption of one-dimensional (1-D) heat flow. This method is commonly used at Sandia.s fire test facilities. In this report, an uncertainty analysis was performed for a specific example to quantify the effect of input parameter variations on the estimated heat flux when using the inverse heat conduction method. The approach used was to compare results from a number of cases using modified inputs to a base-case. The response of a 304 stainless-steel cylinder [about 30.5 cm (12-in.) in diameter and 0.32-cm-thick (1/8-in.)] filled with 2.5-cm-thick (1-in.) ceramic fiber insulation was examined. Input parameters of an inverse heat conduction program varied were steel-wall thickness, thermal conductivity, and volumetric heat capacity; insulation thickness, thermal conductivity, and volumetric heat capacity, temperature uncertainty, boundary conditions, temperature sampling period; and numerical inputs. One-dimensional heat transfer was assumed in all cases. Results of the analysis show that, at the maximum heat flux, the most important parameters were temperature uncertainty, steel thickness and steel volumetric heat capacity. The use of a constant thermal properties rather than temperature dependent values also made a significant difference in the resultant heat flux; therefore, temperature-dependent values should be used. As an example, several parameters were varied to estimate the uncertainty in heat flux. The result was 15-19% uncertainty to 95% confidence at the highest flux, neglecting multidimensional effects.

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This study demonstrates that containment of municipal and hazardous waste in arid and semiarid environments can be accomplished effectively without traditional, synthetic materials and complex, multi-layer systems. This research demonstrates that closure covers combining layers of natural soil, native plant species, and climatic conditions to form a sustainable, functioning ecosystem will meet the technical equivalency criteria prescribed by the U. S. Environmental Protection Agency. In this study, percolation through a natural analogue and an engineered cover is simulated using the one-dimensional, numerical code UNSAT-H. UNSAT-H is a Richards. equation-based model that simulates soil water infiltration, unsaturated flow, redistribution, evaporation, plant transpiration, and deep percolation. This study incorporates conservative, site-specific soil hydraulic and vegetation parameters. Historical meteorological data are used to simulate percolation through the natural analogue and an engineered cover, with and without vegetation. This study indicates that a 3-foot (ft) cover in arid and semiarid environments is the minimum design thickness necessary to meet the U. S. Environmental Protection Agency-prescribed technical equivalency criteria of 31.5 millimeters/year and 1 x 10{sup -7} centimeters/second for net annual percolation and average flux, respectively. Increasing cover thickness to 4 or 5 ft results in limited additional improvement in cover performance.

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Metallic Phases in extraterrestrial materials are composed of Fe-Ni with minor amounts of Co, P, Si, Cr, etc. Electron microscopy techniques (SEM, TEM, EPMA, AEM) have been used for almost 50 years to study micron and submicron microscopic features in the metal phases (Fig. 1) such as clear taenite, cloudy zone, plessite, etc [1,2]. However lack of instrumentation to prepare TEM thin foils in specific sample locations and to obtain micro-scale crystallographic data have limited these investigations. New techniques such as the focused ion beam (FIB) and the electron backscatter electron diffraction (EBSD) techniques have overcome these limitations. The application of the FIB instrument has allowed us to prepare {approx}10 um long by {approx} 5um deep TEM thin sections of metal phases from specific regions of metal particles, in chondrites, irons and stony iron meteorites, identified by optical and SEM observation. Using a FEI dual beam FIB we were able to study very small metal particles in samples of CH chondrites [3] and zoneless plessite (ZP) in ordinary chondrites. Fig. 2 shows a SEM photomicrograph of a {approx}40 um ZP particle in Kernouve, a H6 chondrite. Fig. 3a,b shows a TEM photograph of a section of the FIB prepared TEM foil of the ZP particle and a Ni trace through a tetrataenite/kamacite region of the particle. It has been proposed that the Widmanstatten pattern in low P iron meteorites forms by martensite decomposition, via the reaction {gamma} {yields} {alpha}{sub 2} + {gamma} {yields} {alpha} + {gamma} in which {alpha}{sub 2}, martensite, decomposes to the equilibrium {alpha} and {gamma} phases during the cooling process [4]. In order to show if this mechanism for Widmanstatten pattern formation is correct, crystallographic information is needed from the {gamma} or taenite phases throughout a given meteorite. The EBSD technique was employed in this study to obtain the orientation of the taenite surrounding the initial martensite phase and the kamacite which forms as {alpha}{sub 2} or as Widmanstatten plates in a series of IVB irons. Fig. 4a,b shows EBSD orientation maps of taenite and kamacite from the Tawallah Valley IVB iron. We observe that the orientation of the taenite in the IVB meteorites is the same throughout the sample consistent with the orientation of the high temperature single phase taenite before formation of the Widmanstatten pattern.

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Effective, high-performance, networked file systems and storage is needed to solve I/O bottlenecks between large compute platforms. Frequently, parallel techniques such as PFTP, are employed to overcome the adverse effect of TCP's congestion avoidance algorithm in order to achieve reasonable aggregate throughput. These techniques can suffer from end-system bottlenecks due to the protocol processing overhead and memory copies involved in moving large amounts of data during I/O. Moreover, transferring data using PFTP requires manual operation, lacking the transparency to allow for interactive visualization and computational steering of large-scale simulations from distributed locations. This paper evaluates the emerging Internet SCSI (iSCSI) protocol [2] as the file/data transport in order that remote clients can transparently access data through a distributed global file system available to local clients. We started our work characterizing the performance behavior of iSCSI in Local Area Networks (LANs). We then proceeded to study the effect of propagation delay on throughput using remote iSCSI storage and explored optimization techniques to mitigate the adverse effects of long delay in high-bandwidth Wide Area Networks (WANs). Lastly, we evaluated iSCSI in a Storage Area Network (SAN) for a Global Parallel Filesystem. We conducted our benchmark based on typical usage model of large-scale scientific applications at Sandia. We demonstrated the benefit of high-performance parallel VO to scientific applications at the IEEE 2004 Supercomputing Conference, using experiences and knowledge gained from this study.

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The potential energy surface for the reaction between OH and acetylene has been calculated using the RQCISD(T) method and extrapolated to the complete basis-set limit. Rate coefficients were determined for a wide range of temperatures and pressures, based on this surface and the solution of the one-dimensional and two-dimensional master equations. With a small adjustment to the association energy barrier (1.1 kcal/mol), agreement with experiments is good, considering the discrepancies in such data. The rate coefficient for direct hydrogen abstraction is significantly smaller than that commonly used in combustion models. Also in contrast to previous models, ketene + H is found to be the main product at normal combustion conditions. At low temperatures and high pressures, stabilization of the C{sub 2}H{sub 2}OH adduct is the dominant process. Rate coefficient expressions for use in modeling are provided.