Interplay between partial incoherence, partial inelasticity, resonance, and heterogeneity in long-range electron transfer and transport

A generalized scattering matrix formalism is constructed to elucidate the interplay of electron resonance, coherence, dephasing, inelastic scattering, and heterogeneity, which play important roles in the physics of long-range electron transfer/transport. The theory consists of an extension of the standard Buttiker phase-breaking model and an analytical expression of the electron transmission coefficient for donor-bridge-acceptor systems with arbitrary length and sequence. The theory incorporates the following features: Dephasing-assisted off-resonance enhancement, inelasticity-induced turnover, resonance enhancement and its dephasing-induced suppression, dephasing-induced smooth superexchange-hopping transition, and heterogeneity effects. (C) 2002 American Institute of Physics.

Determination of mercury in biological samples using organic compounds as matrix modifiers by inductively coupled plasma mass spectrometry

A method was developed for the determination of total mercury in biological samples. The effects of aqueous ammonia, ethylenediamine and triethanolamine on Hg signal intensity by inductively coupled plasma mass spectrometry has been evaluated and the possible mechanisms discussed. It has been proved that the signal intensity of Hg significantly increases with adding, in the presence of small amounts of aqueous ammonia, ethylenediamine or triethanolamine. The normalized intensity (the signal intensity ratio with amine and without amine) of Hg increases as the concentration of aqueous ammonia, ethylenediamine or triethanolamine increases, but the degree of enhancement of aqueous ammonia was smaller than that of ethylenediamine and triethanolamine. The normalized intensity of Hg with aqueous ammonia, ethylenediamine and triethanolamine decreases as the nebulizer flow rate increases, but decreasing degree of aqueous ammonia was smaller than that of ethylenediamine and triethanolamine. The higher the RF powers the higher the normalized intensity of Hg at the same nebulizer flow rate. The addition of aqueous ammonia, ethylenediamine and triethanolamine into analytical solutions significantly improved the transport efficiency of Hg. The detection limit of Hg is improved about ten times by the addition of ethylenediamine or triethanolamine under the optimum experimental parameters. The method has been used to determine mercury in biological standard reference materials (SRM). The analytical results are very close to the certified values and the determined values for similar samples.

Transfer and transport of phosphorus and silica in the turbidity maximum zone of the Changjiang estuary

The concentration of suspended particulate matter (SPM), sedimentation flux, and various forms of phosphorus and silica in turbidity maximum zone (TMZ) in the Changjiang (Yangtze) estuary was studied. Based on the budget of P and Si, their mass balances in the TMZ were calculated. Results show that the variation in concentration of dissolved inorganic silicon (DISi) was mainly controlled by seawater dilution, while that of dissolved inorganic phosphor-us (DIP) was considerably affected by the buffering of suspended matter and sediment. Our experiments showed that the sedimentation fluxes of SPM and particulate inorganic phosphorus (PIP), total particulate phosphorus (TPP), particulate inorganic silicon (PISi), and biological silicon (BSi) in the TMZ were 238.4 g m(-2) d(-1) and 28.3, 43.1, 79.0, 63.0 mg m(-2) d(-1), respectively. In addition, a simple method to estimate the ratio of resuspension of sediment in the TMZ was established, with which the rate in surface and bottom waters of the TMZ accounted for 55.7 and 66.1% of the total SPM, respectively, indicating that the sediment resuspension in the TMZ influenced significantly the mass balances of P and Si. Particulate adsorbed P (60.8%) and 35.5% of total particulate P discharged from the river were filtered and then deposited in the TMZ. The input flux of PIP from the river mouth was 55.9% of that of DIP, being important as biologically available P, while that of PISi was only 3.5% of DISi, showing that particulate adsorbed Si was much less important than particulate adsorbed P. (c) 2008 Elsevier Ltd. All rights reserved.