United States Department of Energy

About: United States Department of Energy is a government organization based out in Washington D.C., District of Columbia, United States. It is known for research contribution in the topics: Catalysis & Coal. The organization has 13656 authors who have published 14177 publications receiving 556962 citations. The organization is also known as: DOE & Department of Energy.

A Quantum Alloy: The Ligand-Protected Au25–xAgx(SR)18 Cluster

Abstract: Recent synthetic advances have produced very small (sub-2 nm), ligand-protected mixed-metal clusters. Realization of such clusters allows the investigation of fundamental questions: (1) Will heteroatoms occupy specific sites within the cluster? (2) How will the inclusion of heteroatoms affect the electronic structure and chemical properties of the cluster? (3) How will these very small mixed-metal systems differ from larger, more traditional alloy materials? In this report we provide experimental and computational characterization of the ligand-protected mixed-metal Au25–xAgx(SC2H4Ph)18 cluster (abbreviated as Au25–xAgx, where x = 0–5 Ag atoms) compared with the unsubstituted Au25(SC2H4Ph)18 cluster (abbreviated as Au25). Density functional theory analysis has predicted that Ag heteroatoms will preferentially occupy sites on the surface of the cluster core. X-ray photoelectron spectroscopy revealed Au–Ag state mixing and charge redistribution within the Au25–xAgx cluster. Optical spectroscopy and nonaqueo...

Testing and parameterizing a conceptual model for solute transport in a fractured granite using multiple tracers in a forced-gradient test

Abstract: [1] A cross-hole tracer test involving the simultaneous injection of two nonsorbing solute tracers with different diffusion coefficients (bromide and pentafluorobenzoate) and a weakly sorbing solute tracer (lithium ion) was conducted in a fractured granite near an underground nuclear test cavity in central Nevada. The test was conducted to (1) test a conceptual radionuclide transport model for the site and (2) obtain transport parameter estimates for predictive modeling. The differences between the responses of the two nonsorbing tracers (when normalized to injection masses) are consistent with a dual-porosity transport system in which matrix diffusion is occurring. The large concentration attenuation of the sorbing tracer relative to the nonsorbing tracers suggests that diffusion occurs primarily into matrix pores, not simply into stagnant water within the fractures. The relative responses of the tracers at late times suggest that the diffusion-accessible matrix pore volume is possibly limited to only half the total volume of the flow system, implying that the effective retardation factor due to matrix diffusion may be as small as 1.5 for nonsorbing solutes in the system. The lower end of the range of possible sorption Kd values deduced from the lithium response is greater than the upper 95% confidence bound of Kd values measured in laboratory sorption tests using crushed granite from the site. This result suggests that the practice of using laboratory sorption data in field-scale transport predictions of cation-exchanging radionuclides, such as 137Cs+ and 90Sr++, should be conservative for the SHOAL site.

Approximation of turbulent conditional averages by stochastic estimation

Abstract: Conditional averages of turbulent flow quantities can be approximated in terms of unconditional correlation data by means of stochastic estimation. The validity and accuracy of this procedure are investigated by comparing stochastic estimates to conditional averages measured in four turbulent flows: grid turbulence, the axisymmetric shear layer of a round jet, a plane shear layer, and pipe flow. Comparisons are made for quantities that are separated from the conditional data in time or space, and for turbulent pressures, as well as turbulent velocities. In each case, the linear estimate accurately represents large scale structure. Nonlinear quadratic estimation shows little improvement over linear estimation, because the second‐order terms are small for probable values of the turbulent fluctuations.

Optimized predictions for heats of formation of transition-metal alloys II

Abstract: A simple electron band theory model of the heat of formation ΔH, of transition metal alloys is used to predict Δ for 276 transition metal alloys at equiatomic composition. The model employs a rectangular d-band electron density of states. Some of the input parameters, namely bandwidth, Fermi level position, and number of electrons in the band, are allowed to vary within certain constraints, to closely approximate any known value of ΔH. The resulting predictions are considered to have errors of the same order as the experiments.