The pulse radiolysis of N2O saturated aqueous solutions of KSCN was studied under neutral pH conditions. The observed optical absorption spectrum of the SCN• radical in solution is more complex than previously reported, but it is in good agreement with that measured in the gas phase. Kinetic traces at 330 nm and 472 nm corresponding to SCN• and (SCN)2•¯, respectively, were fit using a Monte Carlo simulation kinetic model. The rate coefficient for the oxidation of SCN¯ ions by OH radicals, an important reaction used in competition kinetics measurements, was found to be 1.4 ± 0.1 x 1010 M-1 s-1, about 30 % higher than the normally accepted value. A detailed discussion of the reaction mechanism is presented.

The seesaw mechanism that explains the small neutrino masses comes naturally with supersymmetric (SUSY) grand unification and leptogenesis. However, the framework suffers from the SUSY flavor and CP problems, and has a severe cosmological gravitino problem. We propose anomaly mediation as a simple solution to all these problems, which is viable once supplemented by the D-terms for U(1)_Y and U(1)_B-L. Even though the right-handed neutrino mass explicitly breaks U(1)_B-L and hence reintroduces the flavor problem, we show that it lacks the logarithmic enhancement and poses no threat to the framework. The thermal leptogenesis is then made easily consistent with the gravitino constraint.

We construct the New Minimal Standard Model that incorporates the new discoveries of physics beyond the Minimal Standard Model (MSM): Dark Energy, non-baryonic Dark Matter, neutrino masses, as well as baryon asymmetry and cosmic inflation, adopting the principle of minimal particle content and the most general renormalizable Lagrangian. We base the model purely on empirical facts rather than aesthetics. We need only six new degrees of freedom beyond the MSM. It is free from excessive flavor-changing effects, CP violation, too-rapid proton decay, problems with electroweak precision data, and unwanted cosmological relics. Any model of physics beyond the MSM should be measured against the phenomenological success of this model.

An experiment was conducted to investigate the role of weld residual stress on stress corrosion cracking in welded carbon steel plates prototypic to those used for nuclear waste storage tanks. Carbon steel specimen plates were butt-joined with Gas Metal Arc Welding technique. Initial cracks (seed cracks) were machined across the weld and in the heat affected zone. These specimen plates were then submerged in a simulated high level radioactive waste chemistry environment. Stress corrosion cracking occurred in the as-welded plate but not in the stress-relieved duplicate. A detailed finite element analysis to simulate exactly the welding process was carried out, and the resulting temperature history was used to calculate the residual stress distribution in the plate for characterizing the observed stress corrosion cracking. It was shown that the cracking can be predicted for the through-thickness cracks perpendicular to the weld by comparing the experimental KISCC to the calculated stress intensity factors due to the welding residual stress. The predicted crack lengths agree reasonably well with the test data. The final crack lengths appear to be dependent on the details of welding and the sequence of machining the seed cracks, consistent with the prediction.

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We describe a hot-filament chemical vapor deposition process for growing freestanding nanostructured diamond films, {approx}80 {micro}m thick, with residual tensile stress levels {le} 90 MPa. We characterize the film microstructure, mechanical properties, chemical bond distribution, and elemental composition. Results show that our films are nanostructured with columnar grain diameters of {le} 150 nm and a highly variable grain length along the growth direction of {approx}50-1500 nm. These films have a rms surface roughness of {le} 200 nm for a 300 x 400 {micro}m{sup 2} scan, which is about one order of magnitude lower than the roughness of typical microcrystalline diamond films of comparable thickness. Soft x-ray absorption near-edge structure (XANES) spectroscopy indicates a large percentage of sp{sup 3} bonding in the films,consistent with a high hardness of 66 GPa. Nanoindentation and XANES results are also consistent with a high phase and elemental purity of the films, directly measured by x-ray and electron diffraction, Rutherford backscattering spectrometry, and elastic recoil detection analysis. Cross-sectional transmission electron microscopy reveals a large density of planar defects within the grains, suggesting a high rate of secondary nucleation during film growth. These films represent a new class of smooth, ultra-thick nanostructured diamond.

Differential forms offer a convenient way to classify physical quantities and set up computational problems. By observing the dimensionality and type of derivatives (divergence,curl,gradient) applied to a quantity, an appropriate differential form can be chosen for that quantity. To use these differential forms in a simulation, the forms must be discretized using basis functions. The 0-form through 2-form basis functions are formed for surfaces. Twisted 1-form and 2-form bases will be presented in this paper. Twisted 1-form (1-forms) basis functions ({Lambda}) are divergence-conforming edge basis functions with units m{sup -1}. They are appropriate for representing vector quantities with continuous normal components, and they belong to the same function space as the commonly used RWG bases [1]. They are used here to formulate the frequency-domain EFIE with Galerkin testing. The 2-form basis functions (f) are scalar basis functions with units m{sup -2} and with no enforced continuity between elements. At lowest order, the 2-form basis functions are similar to pulse basis functions. They are used here to formulate an electrostatic integral equation. It should be noted that the derivative of an n-form differential form basis function is an (n+1)-form, i.e. the derivative of a 1-form basis function is a 2-form. Because …

A detailed chemical kinetic mechanism for 2,4,6-tri-nitrotoluene (TNT) has been developed to explore problems of explosive performance and soot formation during the destruction of munitions. The TNT mechanism treats only gas-phase reactions. Reactions for the decomposition of TNT and for the consumption of intermediate products formed from TNT are assembled based on information from the literature and on current understanding of aromatic chemistry. Thermodynamic properties of intermediate and radical species are estimated by group additivity. Reaction paths are developed based on similar paths for aromatic hydrocarbons. Reaction-rate constant expressions are estimated from the literature and from analogous reactions where the rate constants are available. The detailed reaction mechanism for TNT is added to existing reaction mechanisms for RDX and for hydrocarbons. Computed results show the effect of oxygen concentration on the amount of soot precursors that are formed in the combustion of RDX and TNT mixtures in N{sub 2}/O{sub 2} mixtures.

The application of ultra-sensitive heavy isotope measurements continues to expand in a variety of fields relevant to the management of nuclear materials, including nuclear isotope forensics and radiobioassay. We have developed a heavy isotope accelerator mass spectrometry (AMS) system at Lawrence Livermore National Laboratory's (LLNL) Center for Accelerator Mass Spectrometry (CAMS). The system was designed particularly for the measurement of actinide concentrations and isotopic ratios, but also allows the measurement of other heavy isotopes such as {sup 129}I. The system includes a fast isotope switching capability that allows flexibility in isotope selection and for the quasi-continuous normalization to a reference isotope spike. Current background levels for {sup 239}Pu and {sup 240}Pu are equivalent to <10{sup 6} atoms and measurements of known materials indicate that our {sup 239}Pu and {sup 240}Pu measurements are accurate and precise for samples containing from {approx}10{sup 12} atoms down to the Bq level ({approx}10{sup 6} atoms). Recent exploitation of the fast isotope switching capability has allowed the quasi-simultaneous measurement of several Pu isotopes in individual samples. Our AMS measurement capability has been extended to U isotopes, with particular emphasis on {sup 236}U. Our current {sup 236}U background level is equivalent to {approx}10{sup 6} atoms and the …

We study the diffusion of self-interstitial atoms (SIAs) and SIA clusters in vanadium via molecular dynamics simulations with an improved Finnis-Sinclair potential (fit to first-principles results for SIA structure and energetics). The present results demonstrate that single SIAs exist in a <111>-dumbbell configuration and migrate easily along <111> directions. Changes of direction through rotations into other <111> directions are infrequent at low temperatures, but become prominent at higher temperatures, thereby changing the migration path from predominantly one-dimensional to almost isotropically three-dimensional. SIA clusters (i.e., clusters of <111>-dumbbells) can be described as perfect prismatic dislocation loops with Burgers vector and habit planes of 1/2<111>{l_brace}220{r_brace} that migrate only along their glide cylinder. SIA clusters also migrate along <111>-directions, but do not rotate. Both single SIAs and their clusters exhibit a highly non-Arrhenius diffusivity, which originates from a combination of a temperature dependent correlation factor and the presence of very low migration barriers. At low temperature, the diffusion is approximately Arrhenius, while above room temperature, the diffusivity is a linear function of temperature. A simple model is proposed to describe these diffusion regimes and the transition between them.