Assessment of a geochemical extraction procedure to determine the solid phase fractionation and bioaccessibility of potentially harmful elements in soils: A case study using the NIST 2710 reference soil

Three mineral acid sequential extraction regimes (HNO₃ only, HNO₃ followed by HCl and aqua regia) were applied to the NIST 2710 contaminated reference soil. The major and trace element chemical analysis data from the extractions were subjected to a chemometric self-modelling mixture resolution procedure which identified that 12 distinct physico-chemical components were extracted. The fractionation of As, Cd, Ni and Pb between these components were determined. Tentative assignments of the mineralogical sources of the components were made. The human ingestion bioaccessible fraction of As, Cd and Pb were determined using the in vitro BARGE UBM bioaccessibility test and were found to be 51.6%, 68.0% and 68.4% respectively. The relationship between the lability of the physico-chemical components and the bioaccessible fraction of the soils was investigated and the bioaccessible fractions were assigned to specific components. The extraction scheme using aqua regia was found to be the most suitable as it was the only one which extracted the iron sulphide phase in the soil.     

Manifestations of damage to a silver–gold alloy sheathed Bi-2223 tape through the AC losses and V–I characteristics

AC losses are measured using the null calorimetric method on a silver–gold sheathed Bi-2223 tape. The dependencies on current and on frequency give the usual results, showing the predominance of hysteretic losses. After damaging the tape, the same measurements are repeated. Loss variations with current still follow a power law but with an increased coefficient. Furthermore, the loss now depends on the square root of the frequency. This result is attributed to the presence of cracks in the superconducting core. Some of them reduce locally the cross-section at a point where the transport current is shared nearly equally between the few remaining superconducting grains, and the silver–gold alloy. This explanation is supported by a micrograph of the peeled tape, which shows a thin layer of superconducting material adhering to the silver–gold alloy, even where large cracks are present. The comparison of critical current distributions, extracted from V–I characteristics of the tape before and after the damage, shows a broadening of the good condition peaks. Also a sharp peak at very low current appears and is attributed to a huge fracture in the core.     

Equilibrium and perfection in discounted supergames

In this paper, we discuss equilibrium and perfect equilibrium in a simplified model of the supergame. We assume that players can observe the mixed moves employed by all players at each previous stage. For this model, we obtain a complete characterization of the set of equilibrium outcomes, and a fairly weak sufficient condition for this set to coincide with the set of perfect equilibrium outcomes.Inter alia, simple proofs of the Folk Theorem and the result that the requirement of perfection does not eliminate any equilibrium outcomes for the undiscounted supergame are presented.     

Ab initio study of the ground and excited states of HCP and its isomer HPC

The potential energy surface of HCP converting to HPC in its ground electronic state has been investigated with ab initio methods at levels up to MP2/6-311G**//MP4/6-311G** as well as TZV + + ** CASSCF. All geometries are fully optimized and compare favorably to previous theoretical and experimental values. The HCP molecule is predicted to be 85.4 kcal/mol lower in energy than its linear isomer at the-MP2/6-31G*//MP2/6-31G* level. The energy barrier for hydrogen rearrangement is found to be merely 2.3 kcal from the HPC end. CASSCF studies were initiated to clarify the low barrier and lent support to a flat surface as HPC converts to stable, linear HCP at the TZV + + ** level. CASSCF also predicts that HPC is unstable with respect to bending. Harmonic vibrational frequencies for HCP results in 5% accuracy or better. A bent triplet is found to be the lowest excited state using the CASSCF method. © 1993 John Wiley & Sons, Inc.     

Calculation of electric dipole transition moments using quasi-degenerate variational perturbation theory and averaged coupled-pair functional theory

Results are reported from calculations of electric dipole transition moments for various electronic transitions in Be, CH₂, and A1H using multireference singles and doubles configuration interaction, quasi-degenerate variational perturbation theory, and multireference averaged coupled pair functional theory. A simple normalization scheme is used for the quasi-degenerate variational perturbation theory and multireference averaged coupled pair functional theory wave functions. In all cases, comparison is made with full configuration interaction results in the valence space. For Be and CH₂, all methods are of comparable quality in calculating the transition moments and excitation energies, with averaged coupled-pair functional theory yielding slightly quicker convergence of the excitation energies and transition moments in most cases. For AlH, multireference singles and doubles configuration interaction is somewhat more accurate for the calculation of the transition moment. Factors that affect the accuracy of the methods are discussed. © 1994 John Wiley & Sons, Inc.