A state-contingent production approach to principal-agent problems with an application to point-source pollution control

Two basic representations of principal-agent relationships, the 'state-space' and 'parameterized distribution' formulations, have emerged. Although the state-space formulation appears more natural, analytical studies using this formulation have had limited success. This paper develops a state-space formulation of the moral-hazard problem using a general representation of production under uncertainty. A closed-form solution for the agency-cost problem is derived. Comparative-static results are deduced. Next we solve the principal's problem of selecting the optimal output given the agency-cost function. The analysis is applied to the problem of point-source pollution control. (C) 1998 Published by Elsevier Science S.A. All rights reserved.

Sedimentologic, petrographic, and sulfur isotope constraints on fine-grained pyrite formation at Mount Isa Mine and environs, Northwest Queensland, Australia

Fine-grained pyrite is the earliest generation of pyrite and the most abundant sulfide within the Urquhart Shale at Mount Isa, northwest Queensland. The pyrite is intimately interbanded with ore-grade Pb-Zn miner alization at the Mount Isa mine but is also abundant north and south of the mine at several stratigraphic horizons within the Urquhart Shale. Detailed sedimentologic, petrographic, and sulfur isotope studies of the Urquhart Shale, mostly north of the mine, reveal that the fine-grained pyrite (delta(34)S = -3.3 to +26.3 parts per thousand) formed by thermochemical sulfate reduction during diagenesis. The sulfate source was local sulfate evaporites, pseudo morphs of which are present throughout the Urquhart Shale (i.e., gypsum, anhydrite, and barite). Deep-burial diagenetic replacement of these evaporites resulted in sulfate-bearing ground waters which migrated parallel to bedding. Fine-grained pyrite formed where these fluids infiltrated and then interacted with carbon-rich laminated siltstones. Comparison of the sulfur isotope systematics of fine-grained pyrite and spatially associated base metal sulfides from the Mount Isa Pb-Zn and Cu orebodies indicates a common sulfur source of ultimately marine origin for all sulfide types. Different sulfur isotope ratio distributions for the various sulfides are the result of contrasting formation mechanisms and/or depositional conditions rather than differing sulfur sources. The sulfur isotope systematics of the base metal and associated iron sulfide generations are consistent with mineralization by reduced hydrothermal fluids, perhaps generated by bulk reduction of evaporite-sourced sulfate-bearing waters generated deeper in the Mount Isa Group, the sedimentary sequence which contains the Urquhart Shale. The available sulfur isotope data from the Mount Isa orebodies are consistent with either a chemically and thermally zoned, evolving Cu-Pb-Zn system, or discrete Cu and Pb-Zn mineralizing events linked by a common sulfur source.

Description of Gluconacetobacter sacchari sp. nov., a new species of acetic acid bacterium isolated from the leaf sheath of sugar cane and from the pink sugar-cane mealy bug

A new species of the genus Gluconacetobacter, for which the name Gluconacetobacter sacchari sp. nov. is proposed, was isolated from the leaf sheath of sugar cane and from the pink sugar-cane mealy bug, Saccharicoccus sacchari, found on sugar cane growing in Queensland and northern New South Wales, Australia, The nearest phylogenetic relatives in the alpha-subclass of the Proteobacteria are Gluconacetobacter liquefaciens and Gluconacetobacter diazotrophicus, which have 98.8-99.3% and 97.9-98.5% 16S rDNA sequence similarity, respectively, to members of Gluconacetobacter sacchari. On the basis of the phylogenetic positioning of the strains, DNA reassociation studies, phenotypic tests and the presence of the Q10 ubiquinone, this new species was assigned to the genus Gluconacetobacter. No single phenotypic characteristic is unique to the species, but the species can be differentiated phenotypically from closely related members of the acetic acid bacteria by growth in the presence of 0.01% malachite green, growth on 30% glucose, an inability to fix nitrogen and an inability to grow with the L-amino acids asparagine, glycine, glutamine, threonine and tryptophan when D-mannitol was supplied as the sole carbon and energy source. The type strain of this species is strain SRI 1794(T) (= DSM 12717(T)).

High-frequency acousto-electric single-photon source

We propose a single optical photon source for quantum cryptography based on the acoustoelectric effect. Surface acoustic waves (SAWs) propagating through a quasi-one-dimensional channel have been shown to produce packets of electrons that reside in the SAW minima and travel at the velocity of sound. In our scheme, the electron packets are injected into a p-type region, resulting in photon emission. Since the number of electrons in each packet can be controlled down to a single electron, a stream of single- (or N-) photon states, with a creation time strongly correlated with the driving acoustic field, should be generated.

The effects of copper on the microbial community of a coral reef sponge

Marine sponges often harbour communities of symbiotic microorganisms that fulfil necessary functions for the well-being of their hosts. Microbial communities associated with the sponge Rhopaloeides odorabile were used as bioindicators far sublethal cupric ion (Cu2+) stress. A combined strategy incorporating molecular, cultivation and electron microscopy techniques was adopted to monitor changes in microbial diversity. The total density of sponge-associated bacteria and counts of the predominant cultivated symbiont (alpha -proteobacterium strain NW001) were significantly reduced in response to Cu2+ concentrations of 1.7 mug l(-1) and above after 14 days of exposure. The number of operational taxonomic units (OTUs) detected by restriction fragment length polymorphism (RFLP) decreased by 64% in sponges exposed to 223 mug l(-1) Cu2+ for 48 h and by 46% in sponges exposed to 19.4 mug l(-1) Cu2+ for 14 days. Electron microscopy was used to identify 17 predominant bacterial morphotypes, composing 47% of the total observed cells in control sponges. A reduction In the proportion of these morphotypes to 25% of observed cells was evident in sponges exposed to a Cu2+ concentration of 19.4 mug l(-1). Although the abundance of most morphotypes decreased under Cu2+ stress, three morphotypes were not reduced in numbers and a single morphotype actually increased in abundance. Bacterial numbers, as detected using fluorescence in situ hybridization (FISH), decreased significantly after 48 h exposure to 19.4 mug l(-1) Cu2+. Archaea, which are normally prolific in R. odorabile, were not detected after exposure to a Cu2+ concentration of 19.4 mug l(-1) for 14 days, indicating that many of the microorganisms associated with R. odorabile are sensitive to free copper. Sponges exposed to a Cu2+ concentration of 223 mug l(-1) became highly necrosed after 48 h and accumulated 142 +/- 18 mg kg(-1) copper, whereas sponges exposed to 19.4 mug l(-1) Cu2+ accumulated 306 +/- 15 mg kg(-1) copper after 14 days without apoptosis or mortality. Not only do sponges have potential for monitoring elevated concentrations of heavy metals but also examining changes in their microbial symbionts is a novel and sensitive bioindicator for the assessment of pollution on important microbial communities.

The geochemistry of late Archaean microbial carbonate: Implications for ocean chemistry and continental erosion history

Trace element concentrations and combined Sr- and Nd-isotope compositions were determined on stromatolitic carbonates (microbialites) from the 2.52 Ga Campbellrand carbonate platform (South Africa). Shale-normalised rare earth element and yttrium patterns of the ancient samples are similar to those of modern seawater in having positive La and Y anomalies and in being depleted in light rare earth elements. In contrast to modem seawater (and microbialite proxies), the 2.52 Ga samples lack a negative Ce anomaly but possess a positive Eu anomaly. These latter trace element characteristics are interpreted to reflect anoxic deep ocean waters where, unlike today, hydrothermal Fe input was not oxidised, and scavenged and rare earth elements were not coprecipitated with Fe-oxyhydroxides. The persistence of a positive Eu anomaly in relatively shallow Campbellrand platform waters indicates a dramatic reversal from hydrothermally dominated (Archaean) to continental erosion-dominated (Phanerozoic) rare earth element flux ratio. The dominant hydrothermal input is also expressed in the initial Sr- and Nd-isotope ratios. There is collinear variation in Sr-Nd systematics, which range from primitive values (Sr-87/Sr-86 of 0.702386 and epsilon (Nd) of +2.1) to more evolved crustal ratios. Mixing calculations show that the range in trace element ratios (e.g., Y/Ho) and initial isotope ratios is not a result of contamination by trapped sediment, but that the chemical band isotopic variation reflects carbonate deposition in an environment where different water masses mixed. Calculated Nd flux ratios yield a hydrothermal input into the 2.52 Ga oceans one order of magnitude larger than continental input. Such a change in flux ratio most likely required substantially reduced continental inputs, which could, in turn, reflect a plate tectonic causation (e.g., reduced topography or expansion of epicontinental seas). Copyright (C) 2001 Elsevier Science Ltd.

Historical PCDD Inputs and Their Source Implications from Dated Sediment Cores in Queensland (Australia)

Recent investigations have demonstrated the presence of an unidentified source of polychlorinated dibenzo-p-dioxins (PCDDs) in the coastal zone of Queensland (Australia). The present study provides new information on the possible PCDD sources and their temporal input to this environment. Two estuarine sediment cores were collected in northern Queensland for which radiochemical chronologies were established. Core sections from different depositional ages, up to three centuries, have been analyzed for 2,3,7,8-substituted PCDDs and polychlorinated dibenzofurans (PCDFs). Variations of PCDD concentrations in the sediment cores over several centuries of depositional history were relatively small, and elevated PCDD levels were still present in sediment slices from the early 17th century. PCDD/F isomer patterns and congener profiles in sediments deposited during the last 350 years were almost identical and correlated well to the characteristic profiles observed in surface sediments and soils from the entire Queensland coastline. Profiles were dominated by higher chlorinated PCDDs, in particular octachlorodibenzodioxin (OCDD), whereas PCDF concentrations were below or near the limit of detection. These results indicate the presence of a PCDD source prior to industrialization and production of commercial organochlorine products. Further, the present study demonstrates that PCDD input patterns have been similar along an extensive but localized area over at least several centuries, contributing relatively high concentrations of PCDDs to the coastal system of Queensland.

Evidence for the presence of a widespread PCDD source in coastal sediments and soils from Queensland, Australia

Recent studies have demonstrated the occurrence of elevated levels of higher chlorinated PCDDs in the coastal environment of Queensland, Australia. This study presents new data for OCDD contamination and full PCDD/F profile analysis in the environment of Queensland. Marine sediments, irrigation drain sediments and topsoil were collected from sites that were expected to be influenced by specific land-use types. High OCDD concentrations were associated mainly with sediments collected near the mouth of rivers which drain into large catchments in the tropical and subtropical regions. Further, analysis of sediments from irrigation drains could be clearly differentiated on the basis of OCDD contamination, with high concentrations in samples from sugarcane drains collected from coastal regions, and low concentrations in drain sediments from drier inland cotton growing areas. PCDD/F congener-specific analysis demonstrated almost identical congener profiles in all samples collected along the coastline. This indicates the source to be widespread. Profiles were dominated by higher chlorinated PCDDs, in particular OCDD whereas 2,3,7,8-substituted PCDFs were below the limit of quantification in the majority of samples. The full PCDD/F profile analysis of samples strongly resemble those reported for lake sediments from Mississippi and kaolinite samples from Germany, Strong similarities to these samples with respect to congener profiles and isomer patterns may indicate the presence of a similar source and/or formation process that is yet unidentified. (C) 2001 Elsevier Science Ltd. All rights reserved.