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(1998)Conference PaperThe ecosystem of Lake Macquarie, N.S.W., has been subject to heavy metal and metalloid inputs since 1897 from a lead-zinc smelter, and subsequently coal-fired power stations, coal mines and washeries and sewage treatment plants. Reports in 1994 of contamination of commercial fish species from the Lake with selenium levels up to twelve times those recommended for human consumption has lead to calls for bans on commercial and recreational fishing in the Lake, which could potentially devastate local fishing and tourism industries. Selenium biogeochemical cycling in estuarine environments such as Lake Macquarie is subject to factors including sediment redox potential, sediment characteristics, solubility of Se-containing mineral phases, ligand complexing ability, and microbially-mediated oxidation-reduction, mineralisation and methylation reactions. Understanding this biogeochemistry is important so as to evaluate the potential risk to ecosystems and human health posed by selenium, and to determine the likely impact of potential management strategies. The research described in this paper examines the importance and role of two of these specific factors which impact selenium biogeochemical cycling in Lake Macquarie: sediment redox potential and microbial methylation reactions. The role of sediment redox potential was examined utilising sediment from the Lake, dosed with known quantities of selenium and then studied under different conditions, comprising: addition of various macrofauna to the sediments to examine the impact of bioturbation on sediment redox status and therefore selenium availability; and exposure of sediment plugs to oxygenated and deoxygenated seawater to quantify selenium release. Bioturbation caused deepening of the oxidised conditions in the sediment, impacting upon speciation and mobility of selenium, whilst exposure of contaminated reduced sediment to oxidising porewater arising from bioturbation resulted in selenium mobilisation from the strongly binding “organic fraction” of the sediment. Separately, bacterial cultures were isolated from the Lake with the ability to tolerate high selenium levels. Organisms were cultured in flasks with nutrient broth containing selenate (Se(VI)) at 100mg/l and incubated at 28oC for several weeks. Analysis by hydride generation atomic absorption spectroscopy revealed that the mass balance on the flasks would not close, indicating loss of selenium to the culture headspace. Samples of culture headspace gases were then collected using a cryogenic trapping system and injected into a GC/MS where methylated selenium species including dimethylselenyl sulfide and dimethylselenyl disulfide were identified. These experiments indicated that both sediment redox potential and microbial methylation are important in the biogeochemical cycling of selenium in Lake Macquarie. The impact of bioturbation upon sediment redox potential is important for any consideration of capping sediments, as the depth of the cap must be sufficient to prohibit bioturbative organisms from accessing the sediment below the cap, whilst the demonstrated ability of indigenous microorganisms from the Lake to methylate selenium may represent a potential remediation options for contaminated sediments or selenium-containing waste streams.
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(1998)Conference PaperRipple Down Rules (RDR) is a knowledge acquisition method for knowledge based systems (KBS) which facilitates incremental acquisition of knowledge and ensures that the previous performance of the KBS is not degraded by the incremental addition of the new knowledge. This approach is now well established for single classification tasks and more recently has been extended to multiple classification tasks. This paper describes the further extension of the approach to configuration tasks. The test domain for this study is the configuration of ion chromatography methods in analytical chemistry.
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(1998)Conference PaperThe major focus of recent knowledge acquisition research has been on problem-solving methods (PSM). This paper present results where a PSM developed for classification has been extended to handle a configuration or parametric design task, designing ion chromatography methods in analytical chemistry. Surprisingly good results have been obtained seemingly because any knowledge that has been added to the knowledge base, has been added precisely to overcome any limitations of the PSM. These results suggest a trade-off between domain knowledge and the power of the PSM and that greater use of domain knowledge would facilitate re-use by allowing PSMs to be used for a broader range of tasks.
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(1998)Conference PaperProducing vegetation maps is one of a myriad of uses that remotely sensed data is being used for. Low error rate classifers can be obtained from the training data generated from surveyed sites and expert knowledge. However, when these classifers are applied to an entire remotely sensed image to produce a map they contain at least many generalisations and at worst gross errors. This is, in part, due to the limited nature of spectral information and limited amounts of training data. In this paper we investigate a technique, called reinforcement classifcation, to generate more accurate classifcations of remotely sensed images. We demonstrate reinforcement classifcation using C4.5 although it is general enough to be applied to any domain and classifcation scheme.
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(1998)Conference PaperFinal year students enrolled in mechanical and manufacturing engineering undertake individual projects to meet the requirements of the 'Thesis' subject.These students are also enrolled in a concurrent subject 'Communications for Professional Engineers' which is designed to develop skills in the various media of communication. A major part of the assessment for this subject is based on conference presentations of each student's thesis project. An average of four staff carry out an assessment of the presentation, together with a similar number of peer assessors. This paper reports the mark outcomes of teacher and peer assessments, and outlines work currently being undertaken to improve the reliability and validity of the assessment procedures used in the subject.
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(1998)Conference PaperIn previous studies of the reliability of peer assessment has been inferred by comparing marks from peer raters with those obtained from teachers. These approaches, whether employing correlation analysis or mark differences, are based on an implicit assumption that the teacher marks represent the benchmark or 'gold standard' by which the reliability or accuracy of peer scores can be gauged. This paper reports the outcomes of teacher and peer assessments of 119 final year engineering students' oral presentation skills within a fourth year Communication subject in 1996. A major part of the assessment for this subject is based on seminar presentations of their thesis project. An average of 5 staff carry out an assessment of each seminar presentation, together with a similar number of peer assessors. The data sets consisting of multiple assessments by both peers and teaching staff for every student's presentation meant that separate reliability estimates using ANOVA techniques could be made for both. Analysis of these data revealed that teacher assessments yielded much higher levels of agreement than did peer assessments. However, further analysis using the reverse Spearman-Brown formula indicated that Scores based on average of four or more peer raters are likely to be more reliable than ratings provided by a single teacher assessor. Findings are discussed in relation to concerns raised in the literature on the reliability of peer assessments, and questions the conventional notion of teacher assessment being the benchmark or 'gold standard' by which the reliability of multiple peer assessments is estimated.
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(1998)Conference PaperIn 1997 a system was introduced to moderate variability in teacher marking standards in a 'Communications for Professional Engineers' subject. The paper describes implementation of the moderation procedures and of methods used to determine the reliability of teacher assessments. Results from the study indicate that moderation had improved the reliability of teacher assessments, but resulted in very minor changes in the marks for most students. Outcomes of the study are discussed in relation to the importance of assuring the fairness and consistency of marking in situations where assessments were perceived to be highly subjective.
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(1998)Conference Paper