Publications

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The stress evolution during electrodeposition of NiMn from a sulfamate-based bath was investigated as a function of Mn concentration and current density. The NiMn stress evolution with film thickness exhibited an initial high transitional stress region followed by a region of steady-state stress with a magnitude that depended on deposition rate, similar to the previously reported stress evolution in electrodeposited Ni [S. J. Hearne and J. A. Floro, J. Appl. Phys. 97, 014901-1 (2005)]. The incorporation of increasing amounts of Mn resulted in a linear increase in the steady-state stress at constant current density. However, no significant changes in the texture or grain size were observed, which indicates that an atomistic process is driving the changes in steady-state stress. Additionally, microstrain measured by ex situ x-ray diffraction increased with increasing Mn content, which was likely the result of localized lattice distortions associated with substitutional incorporation of Mn and/or increased twin density.

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The summary of this report is: (1) The Kernal Density Estimator (KDE) model using log data provides the most conservative estimates; (2) The Empirical Tolerance Limit (ETL) model provides the least conservative estimates; (3) The results for the Karhunen-Loeve (K-L) and Normal Tolerance Limit (NTL) models lie in between the extremes; (4) The NTL results ended up being as credible as any of the other methods. This may be related to the fact that the data appeared to fit a lognormal distribution for higher values of {beta}; (5) The discrepancy between these methods appears to widen for higher values of {beta} and {gamma}; (6) The reasons for the extreme difference in the KDE results depending on whether one uses the raw data or the log of the data is not clear at this time; and (7) Which model will best suit our needs is not clear at this time.

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Blue-emitting, cubic phase CdSe nanorods with an approximate diameter of 2.5 nm and lengths up to 12 nm have been synthesized at low temperature (100 °C) in a single surfactant using a single-source molecular precursor. Transmission electron microscopy and dynamic light scattering measurements indicate that the nanorods are formed from self-assembly of isotropic nanoclusters. Anisotropic growth in a single surfactant appears to be favored when growth occurs below the thermal decomposition temperature of the single-source precursor. © 2005 American Chemical Society.

Sodium aluminum hydrides have gained attention due to their high hydrogen weight percent (5.5% ideal) compared to interstitial hydrides, and as a model for hydrides with even higher hydrogen weight fraction. The purpose of this paper is to investigate the Ti-compounds that are formed under solution-doping techniques, such as wet doping in solvents such as tetrahydrofuran (THF). Compound formation in Ti-doped sodium aluminum hydrides is investigated using X-ray diffraction (XRD) and magic angle spinning (MAS) nuclear magnetic resonance (NMR). We present lattice parameter measurements of crushed single crystals, which were exposed to Ti during growth. Rietveld refinements indicate no lattice parameter change and thus no solubility for Ti in NaAlH4 by this method of exposure. In addition, X-ray diffraction data indicate that no Ti substitutes in NaH, the final decomposition product for the alanate. Reaction products of completely reacted (33.3 at.%-doped) samples that were solvent-mixed or mechanically milled are investigated. Formation of TiAl 3 is observed in mechanically milled materials, but not solution mixed samples, where bonding to THF likely stabilizes Ti-based nano-clusters. The Ti in these clusters is activated by mechanical milling. © 2004 Elsevier B.V. All rights reserved.

Three-dimensional Direct Simulation Monte Carlo simulations of Columbia Shuttle Orbiter flight STS-107 are presented. The aim of this work is to determine the aerodynamic and heating behavior of the Orbiter during aerobraking maneuvers and to provide piecewise integration of key scenario events to assess the plausibility of the candidate failure scenarios. The flight of the Orbiter is examined at two altitudes: 350 kft and 300 kft. The flow field around the Orbiter and the heat transfer to it are calculated for the undamaged configuration. The flow inside the wing for an assumed damage to the leading edge in the form of a 10-inch hole is studied. © 2005 American Institute of Physics.

For gas flows in microfluidic configurations, the Knudsen layer close to the wall can comprise a substantial part of the entire flowfield and has a major effect on quantities such as the mass flow rate through micro devices. The Knudsen layer itself is characterized by a highly nonlinear relationship between the viscous stress and the strain rate of the gas, so even if the Navier-Stokes equations can be used to describe the core gas flow they are certainly inappropriate for the Knudsen layer itself. In this paper we propose a "wall-function" model for the stress/strain rate relations in the Knudsen layer. The constitutive structure of the Knudsen layer has been derived from results from kinetic theory for isothermal shear flow over a planar surface. We investigate the ability of this simplified model to predict Knudsen-layer effects in a variety of configurations. We further propose a semi-empirical Knudsen-number correction to this wall function, based on high-accuracy DSMC results, to extend the predictive capabilities of the model to greater degrees of rarefaction. © 2005 American Institute of Physics.

Gain properties of GaInNAs lasers with different nitrogen concentrations in the quantum wells are investigated experimentally and theoretically. Whereas nitrogen incorporation induces appreciable modifications in the spectral extension and the carrier density dependence of the gain, it is found that the linewidth enhancement factor is reduced by inclusion of nitrogen, but basically unaffected by different nitrogen content due to the balancing between gain and index changes. © 2005 American Institute of Physics.

The implementation of variational transition state theory (VTST) for long-range asymptotic potential forms is considered, with particular emphasis on the energy and total angular momentum resolved (μJ -VTST) implementation. A long-range transition state approximation yields a remarkably simple and universal description of the kinetics of reactions governed by long-range interactions. The resulting (μJ -VTST) implementation is shown to yield capture-rate coefficients that compare favorably with those from trajectory simulations (deviating by less than 10%) for a wide variety of neutral and ionic long-range potential forms. Simple analytic results are derived for many of these cases. A brief comparison with a variety of low-temperature experimental studies illustrates the power of this approach as an analysis tool. The present VTST approach allows for a simple analysis of the applicability conditions for some related theoretical approaches. It also provides an estimate of the temperature or energy at which the "long-range transition state" moves to such short separations that short-range effects, such as chemical bonding, steric repulsion, and electronic state selectivity, must be considered. © 2005 American Institute of Physics.

The chemical and structural changes within thin films of (3-glycidoxypropyl)trimethoxysilane (GPS) after exposure for various periods of time to air saturated with either D 2O or H 2O at 80°C were studied. The X-ray and neutron reflectivity (XR and NR), combined wuth attenuated total reflection infrared (ATR-IR) spectroscopy were used. The chemical degradation mechanism was identified by IR as hydrolysis of siloxane bonds. GPS films were prepared by dip-coating, which resulted in a greater and more variable thickness than for the spin-coated samples, for ATR-IR. The little changes in the reflectivity data was observed for films conditioned with D 2O at 80°C for one month.

Identifying the areas to be protected is an important part of the development of measures for physical protection against sabotage at complex nuclear facilities. In June 1999, the International Atomic Energy Agency published INFCIRC/225/Rev.4, 'The Physical Protection of Nuclear Material and Nuclear Facilities.' This guidance recommends that 'Safety specialists, in close cooperation with physical protection specialists, should evaluate the consequences of malevolent acts, considered in the context of the State's design basis threat, to identify nuclear material, or the minimum complement of equipment, systems or devices to be protected against sabotage.' This report presents a structured, transparent approach for identifying the areas that contain this minimum complement of equipment, systems, and devices to be protected against sabotage that is applicable to complex nuclear facilities. The method builds upon safety analyses to develop sabotage fault trees that reflect sabotage scenarios that could cause unacceptable radiological consequences. The sabotage actions represented in the fault trees are linked to the areas from which they can be accomplished. The fault tree is then transformed (by negation) into its dual, the protection location tree, which reflects the sabotage actions that must be prevented in order to prevent unacceptable radiological consequences. The minimum path sets of this fault tree dual yield, through the area linkage, sets of areas, each of which contains nuclear material, or a minimum complement of equipment, systems or devices that, if protected, will prevent sabotage. This method also provides guidance for the selection of the minimum path set that permits optimization of the trade-offs among physical protection effectiveness, safety impact, cost and operational impact.

Most attempts to quantify differential diffusion (DD) are based on the difference between different definitions of the mixture fraction. This paper presents a general method for evaluating differential diffusion in premixed or nonpremixed systems based on conservation equations for the elemental mass fractions. These measures form a basis for analysing differential diffusion. Casting these in terms of a mixture fraction gives particular insight into differential diffusion for nonpremixed systems, and provides a single DD measure. Furthermore, it allows direct evaluation of the validity of the traditional assumptions involved in writing a mixture fraction transport equation. Results are presented for one-dimensional opposed flow simulations of hydrogen and methane flames as well as direct numerical simulations (DNS) of CH4/H2-air and CO/H2-air flames. For a common definition of the mixture fraction, the DD measure can be approximated well by considering only the contribution of H2 and CH4 in methane-air flames. Differential diffusion is largely driven by production of H2 in the flame zone for hydrocarbon flames. Effects of strain rate and filter width on the relative importance of differential diffusion are examined. © 2005 Taylor & Francis Group Ltd.

Rapid microchip reversed-phase HPLC of peptides and proteins at pressure gradients of 12 bar/cm (180 psi/cm) has been performed using a microdevice that integrates subnanoliter on-chip injection and separation with a miniaturized fluorescence detector. Proteins and peptides were separated on a C18 side-chain porous polymer monolith defined by contact lithography, and injection was achieved via a pressure-switchable fluoropolymer valve defined using projection lithography. Preliminary separations of peptide standards and protein mixtures were performed in 40-200 s, and switching between samples with no detectible sample carryover has been performed. The injections and separations were reproducible; the relative standard deviation (RSD) for retention time was 0.03%, and peak area RSD was 3.8%. Sample volumes ranging from 220 to 800 pL could be linearly metered by controlling the pressure injection pulse duration with conventional timing and valving. The current prototype system shows the potential for rapid and autonomous HPLC separations with varying modalities and the potential for direct connection to mass spectrometers at nanospray flow rates. © 2005 American Chemical Society.

We have determined limits on the cross section for both electronically nonadiabatic excitation and quenching in the Cl (Pj2) + D2 system. Our experiment incorporates crossed-molecular-beam scattering with state-selective Cl (P 12,32 2) detection and velocity-mapped ion imaging. By colliding atomic chlorine with D2, we address the propensity for collisions that result in a change of the spin-orbit level of atomic chlorine either through electronically nonadiabatic spin-orbit excitation Cl (P 32 2) + D2 → Cl* (P 12 2) + D2 or through electronically nonadiabatic spin-orbit quenching Cl* (P 12 2) + D2 →Cl (P 32 2) + D2. In the first part of this report, we estimate an upper limit for the electronically nonadiabatic spin-orbit excitation cross section at a collision energy of 5.3 kcalmol, which lies above the energy of the reaction barrier (4.9 kcalmol). Our analysis and simulation of the experimental data determine an upper limit for the excitation cross section as σNA ≤0.012 Å2. In the second part of this paper we investigate the propensity for electronically nonadiabatic spin-orbit quenching of Cl * following a collision with D2 or He. We perform these experiments at collision energies above and below the energy of the reaction barrier. By comparing the amount of scattered Cl* in our images to the amount of Cl* lost from the atomic beam we obtain the maximum cross section for electronically nonadiabatic quenching as σNA ≤ 15 -15 +44 Å2 for a collision energy of 7.6 kcalmol. Our experiments show the probability for electronically nonadiabatic quenching in Cl* + D2 to be indistinguishable to that for the kinematically identical system of Cl* +He. © 2005 American Institute of Physics.

This report is the latest in a continuing series that highlights the recent technical accomplishments associated with the work being performed within the Materials and Process Sciences Center. Our research and development activities primarily address the materials-engineering needs of Sandia's Nuclear-Weapons (NW) program. In addition, we have significant efforts that support programs managed by the other laboratory business units. Our wide range of activities occurs within six thematic areas: Materials Aging and Reliability, Scientifically Engineered Materials, Materials Processing, Materials Characterization, Materials for Microsystems, and Materials Modeling and Simulation. We believe these highlights collectively demonstrate the importance that a strong materials-science base has on the ultimate success of the NW program and the overall DOE technology portfolio.

Iron, the most ubiquitous of the transition metals and the fourth most plentiful element in the Earth's crust, is the structural backbone of our modern infrastructure. It is therefore ironic that as a nanoparticle, iron has been somewhat neglected in favor of its own oxides, as well as other metals such as cobalt, nickel, gold, and platinum. This is unfortunate, but understandable. Iron 's reactivity is important in macroscopic applications (particularly rusting), but is a dominant concern at the nanoscale. Finely divided iron has long been known to be pyrophoric, which is a major reason that iron nanoparticles have not been more fully studied to date. This extreme reactivity has traditionally made iron nanoparticles difficult to study and inconvenient for practical applications. Iron however has a great deal to offer at the nanoscale, including very potent magnetic and catalytic properties. Recent work has begun to take advantage of iron's potential, and work in this field appears to be blossoming. © 2005 Wiley-VCH Verlag GmbH & Co. KGaA.

This Final Report on the Monitoring Phase of the former Weeks Island Strategic Petroleum Reserve crude oil storage facility details the results of five years of monitoring of various surface accessible quantities at the decommissioned facility. The Weeks Island mine was authorized by the State of Louisiana as a Strategic Petroleum Reserve oil storage facility from 1979 until decommissioning of the facility in 1999. Discovery of a sinkhole over the facility in 1992 with freshwater inflow to the facility threatened the integrity of the oil storage and led to the decision to remove the oil, fill the chambers with brine, and decommission the facility. Thereafter, a monitoring phase, by agreement between the Department of Energy and the State, addressed facility stability and environmental concerns. Monitoring of the surface ground water and the brine of the underground chambers from the East Fill Hole produced no evidence of hydrocarbon contamination, which suggests that any unrecovered oil remaining in the underground chambers has been contained. Ever diminishing progression of the initial major sinkhole, and a subsequent minor sinkhole, with time was verification of the response of sinkholes to filling of the facility with brine. Brine filling of the facility ostensively eliminates any further growth or new formation from freshwater inflow. Continued monitoring of sinkhole response, together with continued surface surveillance for environmental problems, confirmed the intended results of brine pressurization. Surface subsidence measurements over the mine continued throughout the monitoring phase. And finally, the outward flow of brine was monitored as a measure of the creep closure of the mine chambers. Results of each of these monitoring activities are presented, with their correlation toward assuring the stability and environmental security of the decommissioned facility. The results suggest that the decommissioning was successful and no contamination of the surface environment by crude oil has been found.

Goal of this study was to develop and characterize novel polymeric materials as pseudostationary phases in electrokinetic chromatography. Fundamental studies have characterized the chromatographic selectivity of the materials as a function of chemical structure and molecular conformation. The selectivities of the polymers has been studied extensively, resulting in a large body of fundamental knowledge regarding the performance and selectivity of polymeric pseudostationary phases. Two polymers have also been used for amino acid and peptide separations, and with laser induced fluorescence detection. The polymers performed well for the separation of derivatized amino acids, and provided some significant differences in selectivity relative to a commonly used micellar pseudostationary phase. The polymers did not perform well for peptide separations. The polymers were compatible with laser induced fluorescence detection, indicating that they should also be compatible with chip-based separations.