Chemical reduction of U(VI) by Fe(II) at the solid-water interface using natural and synthetic Fe(III) oxides

Abiotic reduction of 0.1 mM U(VI) by Fe(II) in the presence of synthetic iron oxides (biogenic magnetite, goethite, and hematite) and natural Fe(III) oxide-containing solids was investigated in pH 6.8 artificial groundwater containing 10 mM NaHCO3. In most experiments, more than 95% of added U(VI) was sorbed to solids. U(VI) was rapidly and extensively (> or = 80%) reduced in the presence of synthetic Fe(III) oxides and highly Fe(II) oxide-enriched (18-35 wt % Fe) Atlantic coastal plain sediments. In contrast, long-term (20-60 d) U(VI) reduction was less than 30% in suspensions of six other natural solids with relatively low Fe(III) oxide content (1-5 wt % Fe). Fe(II) sorption site density was severalfold lower on these natural solids (0.2-1.1 Fe(II) nm(-2)) compared tothe synthetic Fe(lII) oxides (1.6-3.2 Fe(II) nm(-2)), which may explain the poor U(VI) reduction in the natural solid-containing systems. Addition of the reduced form of the electron shuttling compound anthrahydroquinone-2,6-disulfonate (AH2DS; final concentration 2.5 mM) to the natural solid suspensions enhanced the rate and extent of U(VI) reduction, suggesting that AH2DS reduced U(VI) at surface sites where reaction of U(VI) with sorbed Fe(II) was limited. This study demonstrates that abiotic, Fe(II)-driven U(VI) reduction is likely to be less efficient in natural soils and sediments than would be inferred from studies with synthetic Fe(III) oxides.     

Multi-user Quantum Cryptography on Optical Networks

Abstract

Quantum cryptography has been shown to be an effective technology for the secure distribution of keys on point-to-point optical links. We show how the existing techniques can be extended to allow multi-user secure key distribution on optical networks. We demonstrate that using network configurations typical of those found in passive optical network architectures any of the current quantum key distribution protocols can be adapted to implement secure key distribution from any user to any other user. An important feature of these adapted protocols is that the broadcaster, or service provider on the network, does not have to be trusted by the two users who wish to establish a key.     

Polycrystalline Silicon-Film™ Thin-film Solar Cells: Advanced Products

Thin-film polycrystalline silicon has the potential to achieve the cost reduction and performance improvement necessary for large-scale electricity markets. Reduced cost is achieved by capitalizing on the benefits of thin films grown on low-cost, large-area substrates. Improved efficiency is realized, in spite of reduced material quality, by incorporating enhanced optical absorption and back-surface passivation. The cornerstone of AstroPower's thin-film solar cell technology is the Silicon-Film™ process: a method for the manufacture of solar cell-quality, polycrystalline films of silicon on a variety of low-cost, supporting substrates. Three thin-film solar cell designs, based on this technology, are currently under development. This paper presents the key design features of these three products and briefly reviews the current status of the development of the key technologies that comprise the advanced thin-film solar cell products.     

Defect passivation on cast-mono crystalline screen-printed cells

Cast-mono crystalline silicon wafers contain crystallographic defects, which can severely impact the electrical performance of solar cells. This paper demonstrates that applying hydrogenation processes at moderate temperatures to finished screen print cells can passivate dislocation clusters within the cast-mono crystalline silicon wafers far better than the hydrogenation received during standard commercial firing conditions. Efficiency enhancements of up to 2% absolute are demonstrated on wafers with high dislocation densities. The impact of illumination to manipulate the charge state of hydrogen during annealing is investigated and found to not be significant on the wafers used in this study. This finding is contrary to a previous study on similar wafers that concluded increased H^– or H⁰ from laser illumination was responsible for the further passivation of positively charged dangling bonds within the dislocation clusters.     

Influence of hydrogen content on the tensile properties and fracture of austenitic stainless steel welds

This study evaluates the effects of internal hydrogen on the tensile properties and fracture behaviours of a tungsten inert gas (TIG) weld and an autogenous electron beam (EB) weld of a 304L steel tube. Tensile specimens were thermally charged with hydrogen gas to achieve three different levels of hydrogen in these materials. Metallographic examination revealed that the TIG weld contained skeletal and lathy ferrite, whilst the EB weld displayed a fine dispersion of skeletal and vermicular ferrite. Average volume fractions of ferrite in these welds were 8% and 1%, respectively. The tensile data showed that hydrogen increased the yield and tensile strength, and caused a significant loss in ductility, particularly for the TIG weld. Fractographic analysis revealed that hydrogen induced a change in the fracture mode of the welds and promoted cracking at or near ferrite–austenite interfaces. The TIG weld was found to exhibit a higher susceptibility to hydrogen embrittlement than that of the EB and base metal.     

Degradation of LaSr2Fe2CrO9−δ solid oxide fuel cell anodes in phosphine-containing fuels

The performance and stability of La_0.9Sr_0.1Ga_0.8Mg_0.2O_3-δ-electrolyte supported solid oxide fuel cells with composite LaSr₂Fe₂CrO_9-δ-Gd_0.1Ce_0.9O₂ anodes were studied in wet H₂ and coal syngas containing phosphine impurity. Introduction of 5-20 ppm PH₃ into the fuels caused an initial slow cell performance degradation followed by a very rapid complete cell degradation that initiated within 11-24 h - earlier at higher PH₃ concentration. There was no recovery after removing PH₃ impurity from the fuels. Electrochemical impedance analysis suggested that the initial gradual performance degradation was due to conductivity loss of the oxide anode due to chemisorption and reaction of phosphine. X-ray diffraction analysis showed the formation of FeP_x and LaPO₄ compounds. The rapid degradation presumably occurred when most or all of the Fe initially present in the LaSr₂Fe₂CrO_9−δ was consumed. Thermodynamic calculations confirmed that Fe is highly reactive with PH₃ at 800 °C, even at concentrations below 1 ppm.     

On‐line learning: A quality experience

The paper outlines the strategy being developed for the growth of electronic books within the UK academic community and provides a broad analysis of the e‐book industry and critical factors. The role of the JISC E‐Books Working Group is described and an overview given of its programme of activities.     

New low-cost storage in air conditioning

This paper describes the development of a new low-cost phase-change material packaging concept for air conditioning systems.

The realization of the promise of storage assisted air conditioning for saving oil and money is dependent upon the successful development of a low-cost storage subsystem and the adoption of time-of-day electricity rates. Time-of-day rates are currently under consideration or have been adopted in 27 different states and consideration of these rates has been required by federal legislation.

The adoption of this low-cost thermal energy storage technology for storage assisted air conditioning and other storage assisted heat pump applications has the potential of saving 100 million barrels of oil over the next ten years and 12 million barrels of oil per year by 1985. These savings would accrue from a change in the summer air conditioning peak electricity load from oil and gas-fired peak electrical generators to the base load electrical generators fired by coal, nuclear and hydroelectric.

This low-cost air conditioning storage concept is based on hydrated salt phase change material, specifically a mixture based on sodium sulphate decahydrate and a new low-cost packaging technology which uses a film laminate as the phase change material mixture's package and heat exchanger.

In this paper. the relative economics of various technological options for air conditioning storage are compared. It is demonstrated that this economic analysis leads to the necessity to develop a low-cost film package and heat exchanger. An analysis of savings to homeowners based on current and planned off-peak rates is included. Since this is the first product developed utilizing this new low-cost material as a packaging film, it is anticipated that major improvements in both cost and performance specifically related to individual systems will be developed and implemented over the next ten years, with significant improvements coming in the next several years.     

Orthophosphate concentrations in the River Thames: reductions in the past decade

Ten years ago plans were made to reduce the phosphorus load from sewage-treatment works' effluents into the River Thames. This was driven by the EC Urban Wastewater Treatment Directive in relation to sensitive areas (eutrophic). Modelling work identified the most significant loads to tackle first. Phosphorus removal had been commissioned at 36 works by 2003. The orthophosphate load to the River Thames from these works has reduced from 5755 to 688 kg P/day. The impact of the improvement programme on the quality of the river was assessed by comparing pre- and post-investment data. Orthophosphate concentrations in the river have reduced from between about 0.5 and 2 mg P/L to 0.2 and 0.4 mg P/L. These observations match the model predictions. Chlorophyll a concentrations in the river have also reduced. This was unexpected given that the orthophosphate concentrations still exceed the values thought to be limiting for algal growth.     

Bayes' theorem and quantum retrodiction

Abstract

We derive on the basis of Bayes' theorem a simple but general expression for the retrodicted premeasurement state associated with the result of any measurement. The retrodictive density operator is the normalized probability operator measure element associated with the result. We examine applications to quantum optical cryptography and to the optical beam splitter.