Engineering

Publication Search Results

Now showing 1 - 10 of 24
  • (1999) Peters, G; Maher, WA; Jolley, D; Carroll, BI; Jenkinson, AV; McOrist, GD
    Journal Article
    This paper examines the history of selenium pollution in Lake Macquarie, NSW, Australia, and three factors that may affect the redistribution and remobilisation of particle bound selenium: changes in redox state, bioturbation, and bioaccumulation by macrobenthos and bacteria. Sediment cores were taken from Nords Wharf, a relatively unpolluted area, and from Mannering Bay near the Vales Point coal-fired power station. The age profile at the unpolluted site seems to indicate that mild selenium pollution has been occurring for over 100 years, however, some mixing of the sediments has occurred. At the polluted site, the age profile indicated that major contamination has occurred in the last 30 years, due to an ash dam associated with nearby electric power generation facilities. The contamination chronology suggests that remobilisation and reduction processes have affected the selenium profile. Changing the redox state of Lake Macquarie sediment results in a release of selenium under oxidising conditions and immobilisation under reducing conditions. The sediment-bound selenium was associated with the operationally defined `organic/sulfide' fraction under reducing conditions, and as the redox potential increases this moves into the `exchangeable' and `iron/manganese oxyhydroxide' phases to a limited extent. Bioturbation by the animals Marphysa sanguinea and Spisula trigonella caused increases in the redox potential and pore water selenium concentrations in surfcial sediments relative to unbioturbated controls. Both animals accumulated significantly more selenium when exposed to contaminated sediment than when exposed to uncontaminated control sediments. Selenium concentrations in molluscs from Mannering Bay were all significantly higher than those collected from Nords Wharf. Most of the selenium in the mollusc tissues was found to be associated with the protein fraction. Selenium isolated from hydrolysed muscle tissue was not present as selenate or selenite but as selenomethionine and an unidentified compound. Seven types of bacteria were isolated from Lake Macquarie sediment. All seven isolates were able to transform selenite quantitatively to elemental selenium as evidenced by a red precipitate and identified by X-ray diffraction. Six isolates grew on media containing selenate but no elemental selenium was formed. Mass balances showed that for three isolates total selenium was conserved, selenate decreased and selenium (0; II-) increased indicating the production of non-volatile organic selenium compounds. For two isolates both total selenium and selenate decreased with no increase in selenium (0; II-), therefore, loss of selenium occurred from the media. Selenium is immobile in anoxic reduced sediments but may become available to benthos and fish as a consequence of sediment oxidation associated with bioturbation leading to bioaccumulation and transformation by macrobenthos and bacteria. These mechanisms can be invoked as possible transport pathways to explain the presence of selenium above background concentrations in preindustrial sediments, but further work dating the sediments in which elevated concentrations of selenium are found is needed to confirm this hypothesis.

  • (1999) Peters, G; Maher, WA; Krikowa, F; Roach, AC; Jeswani, HK; Barford, JP; Gomes, VG; Reible, DD
    Journal Article
    Measurements of selenium in sediments and benthic infauna of Lake Macquarie, an estuary on the east coast of Australia, indicate that sediments are a significant source of selenium in the lake's food web. Analysis of surficial sediment samples indicated higher selenium con- concentrations near what are believed to be the main industrial sources of selenium to the lake: a smelter and a power station. Sediment cores taken from sediments in Mannering Bay, near a power station at Vales Point, contained an average of 12 times more selenium in surficial sections than sediment cores from Nord's Wharf, a part of the lake remote from direct inputs of selenium. The highest selenium concentration found in Mannering Bay sediments (17.2 mg/g) was 69 times the apparent background concentration at Nord's Wharf (0.25 mg/g). Pore water concentrations in Mannering Bay were also high, up to 5 mg/l compared to those at Nord's Wharf which were below detection limits (0.2 mg/l). Selenium concentrations in muscle tissues of three benthic-feeding fish species (Mugil cephalus, Platycephalus fuscus, Acanthopagrus australis) were significantly correlated ( p < 0:05) with surficial sediment selenium concentra- tion. Selenium concentrations in polychaetes and molluscs of Mannering Bay were up to 58 times higher than those from Nord's Wharf. Two benthic organisms, the eunicid polychaete Marphysa sanguinea and the bivalve mollusc Spisula trigonella, were maintained at different densities in selenium-spiked sediments. Both animals accumulated selenium from the spiked sediment, confirming that bioaccumulation from contaminated sediments occurs. Collectively, these data suggest that benthic food webs are important sources of selenium to the fish of Lake Macquarie.

  • (1998) Gu, Genda; Han, Shaowei; Lin, Zheng; Zhao, Yong; Russell, Graeme
    Journal Article

  • (1999) Han, Shaowei; Zhao, Yong; Choi, C; Andrikidis, C
    Journal Article
    Flux pinning force and irreversibility lines have been investigated for melt-textured YBa2Cu3Oy crystals containing Y2BaCuO5 (211) particles with an average size ranging from 20 to 0.02 microns. We found that the irreversibility lines are increasingly improved and that the pinning force as well as the Jc is greatly enhanced as the average size of the 211 particles decreases. The Fp-H curve exhibits two peaks in the samples containing very fine 211 particles (nanometer size particles), which suggests that an addition pinning mechanism is involved in this type of samples. The experimental results can be well explained with combining the interface-pinning mechanism and the match effect.

  • (1998) Han, Shaowei; Zhao, Yong; Gu, Genda; Russell, Graeme
    Journal Article
    During magnetoresistance measurement of Bi-2212 single crystals, we found the resistance in the c-axis direction exhibited a huge magnetic enhancement (H perpendicular to the a-b-plane) while the onset transition temperature along the c-axis showed a large depression when the magnetic fields were over a certain value (H > 180 Oe). No such phenomena were observed in small applied magnetic fields (H < 180 Oe) and in a-b-plane magnetoresistance measurements. By changing different probes (eight probes being attached to the sample, each side having four probes) for the measurement of the magnetoresistance along the c-axis with H = 2000 Oe, we found that the resistance along the c-axis in the temperature region T/Tc > 0.90 was only related to the measuring dimensions and Tc onset remained unchanged. Our results provided evidence that both Lorentz-force-independent fluctuation-induced dissipation and Lorentz-force-dependent vortex motion dissipation exist in the mixed state.

  • (1999) Gosbell, Iain; Ross, Alfred; Turner, Ian
    Journal Article

  • (1998) Han, Shaowei; Zhao, Yong; Gu, Genda; Russell, Graeme
    Journal Article

  • (1998) Han, Shaowei; Zhao, Yong; Yang, C; Cheng, Chun-Chung; Zhang, Hua; Gu, Genda; Russell, Graeme; Koshizu, N
    Journal Article

  • (1998) Han, Shaowei; Zhao, Yong; Yang, C; Cheng, Chun-Chung; Zhang, Hua; Gu, Genda; Russell, Graeme; Koshizuka, N
    Journal Article
    The vortex-glass-liquid transition in Bi---Sr---Ca---Cu---O (BSCCO) intergrowth single crystals in which some CuO2 trilayers are inserted into the Bi2Sr2CaCu2O8 matrix has been studied. The curvature of the log V-logI curves for CuO2 trilayers is found to change from negative to positive with increasing magnetic field and a scaling behaviour for the vortex-glass state is observed. The magnetic field dependence of the vortex-glass transition temperature, TG, qualitatively obeys the relation H(TG) (Tc − Tg)2v0, with v0 = 1.15 ± 0.2, which is larger than the 2/3 predicted theoretically for an isotropic 3D system. Our results reveal that the vortex-glass transition exists in a system constructed with CuO2 trilayers.