No description available.

No description available.

A range of ion-selective electrodes (ISEs) for the determination of nitrate has been produced based upon rubbery membranes having covalently bound betaine salt sensor molecules. The best performing electrode contained N,N,N-triallyl leucine betaine (6.5 % m/m) covalently bound to polystyrene-block-polybutadiene-block-polystyrene (SBS) (43.5% m/m), with 2-nitrophenyIoctyl ether (2-NPOE) as solvent mediator (40 % m/m) and dicumyl peroxide (DCP) as free radical initiator (10% m/m). The Nemstian slope was -59.1 mV per decade over a linear range of 1 x 10'^-5 x 10"^ mol dm'^ nitrate, a limit of detection of 0.34 pmol dm'^ nitrate and a selectivity coefiBcient for nitrate against chloride ( ^ ° N 0 3 . , CI-) of 3.4 X IQ"^. The speed of response was less than 1 minute over the linear Nerastian range. The lifetime in the laboratory exceeded 5 months with no potentiometric drift over the linear Nemstian range. Temperafure dependency (0-25°C), pH range (2-12) and a selection of interfering anions (F', CI", B r , T, SCN, CIO4", HCO3", NO2", S04^ phthalate) were studied. A field evaluation by continuous immersion in both agricultural drainage weirs and a river were undertaken. The nitrate results obtained with the ISEs compared very favourably (R^=0.99) with those obtained with a segmented-flow instmment in a concentration range 0.47-16 ppm nitrate-N. The electrodes perfonned continuously for over 5 months in mnoff water from a field and over 2 months in river water. The ISEs did not require recalibration and no deterioration in performance or fouling of the membrane surface was observed. A preliminary investigation of a phosphate ionophore based upon a heterocyclic macrocycle was also undertaken. This work, based on previous literature, resulted in a dibasic phosphate electrode having a linear Nemstian range from 3 x lO"'' to 1 x 10"^ mol dm'^, a slope of -27 mV per activity decade and a Umit of detection of 1 x 10"^ mol dm"^ HP04^".

No description available.

The credibility of the scientific methodology of mathematical models and their adequacy to form the basis of public policy decisions has frequently been challenged. Skeptical views of the scientific value of modelling argue that there is no true model of an ecological system, but rather several adequate descriptions of different conceptual basis and structure. The purpose of this work was to first advance the Bayesian calibration of process-based models for guiding the water quality criteria setting process in Hamilton Harbour, Ontario, Canada. The analysis suggests that the water quality targets for total phosphorus and chlorophyll a concentrations will likely be met, if the recommendation for phosphorus loading at the level of 142 kg day-1 is achieved. My dissertation also examines how the Bayesian approach can effectively support the decision making process by synthesizing the predictions of different models developed for the same system. The model averaging approach consolidates the finding that the existing total phosphorus goal is most likely unattainable. The discrepancy between the chlorophyll a predictions of the two models pinpoints the need to delve into the dynamics of phosphorus in the sediment-water column interface. This work also aims to examine statistical formulations that explicitly accommodate the covariance among the process error terms for various model endpoints. The analysis suggests that the statistical characterization of the model error can be influential to the inference drawn by a modelling exercise. Finally, my dissertation challenges the capacity of the ecological foundation of eutrophication models to predict the role of nutrient regeneration. It shows that the recycled nutrients can be significant drivers in low as well as in high-productivity ecosystems depending on the period of the year examined. My dissertation also discusses several prescriptive guidelines that should be helpful towards a structural and methodological improvement of eutrophication modelling.

The credibility of the scientific methodology of mathematical models and their adequacy to form the basis of public policy decisions has frequently been challenged. Skeptical views of the scientific value of modelling argue that there is no true model of an ecological system, but rather several adequate descriptions of different conceptual basis and structure. The purpose of this work was to first advance the Bayesian calibration of process-based models for guiding the water quality criteria setting process in Hamilton Harbour, Ontario, Canada. The analysis suggests that the water quality targets for total phosphorus and chlorophyll a concentrations will likely be met, if the recommendation for phosphorus loading at the level of 142 kg day-1 is achieved. My dissertation also examines how the Bayesian approach can effectively support the decision making process by synthesizing the predictions of different models developed for the same system. The model averaging approach consolidates the finding that the existing total phosphorus goal is most likely unattainable. The discrepancy between the chlorophyll a predictions of the two models pinpoints the need to delve into the dynamics of phosphorus in the sediment-water column interface. This work also aims to examine statistical formulations that explicitly accommodate the covariance among the process error terms for various model endpoints. The analysis suggests that the statistical characterization of the model error can be influential to the inference drawn by a modelling exercise. Finally, my dissertation challenges the capacity of the ecological foundation of eutrophication models to predict the role of nutrient regeneration. It shows that the recycled nutrients can be significant drivers in low as well as in high-productivity ecosystems depending on the period of the year examined. My dissertation also discusses several prescriptive guidelines that should be helpful towards a structural and methodological improvement of eutrophication modelling.

Thesis (M. Sc.)--University of New South Wales, 1999. / Also available online.

Thesis (Ph. D.)--Virginia Polytechnic Institute and State University, 1990. / Vita. Abstract. Includes bibliographical references (leaves 128-135). Also available via the Internet.

Thesis (Ph.D.)(Microbiology))--University of Pretoria, 2009. / Includes English summary. Includes bibliographical references.

Thesis (Ph. D.)--Duke University, 1970. / eContent provider-neutral record in process. Description based on print version record.