Engineering

Publication Search Results

Now showing 1 - 10 of 99
  • (2001) Diessel, Oliver; Milne, George
    Journal Article
    Reconfigurable computers based on field programmable gate array technology allow applications to be realised directly in digital logic. The inherent concurrency of hardware distinguishes such computers from microprocessor-based machines in which the concurrency of the underlying hardware is fixed and abstracted from the programmer by the software model. However, reconfigurable logic provides us with the potential to exploit `real` concurrency. It is therefore interesting to know how to exploit this concurrency, how to model concurrent computations, and which languages allow this dynamic hardware to be programmed most effectively. The purpose of this work is to describe an FPGA compiler for the Circal process algebra. In so doing, the authors demonstrate that behavioural descriptions expressed in a process algebraic language can be readily and intuitively compiled to reconfigurable logic and that this contributes to the goal of discovering appropriate high-level languages for run-time reconfiguration.

  • (2008) Song, Dengyuan; Cho, E.-C; Conibeer, Gavin; Huang, Yidan; Flynn, Christopher; Green, Martin
    Journal Article
    Amorphous Si1-xCx /SiC multilayer films were prepared by alternating deposition of Si-rich Si1-xCx and near-stoichiometric SiC layers by using magnetron sputtering. The as-deposited films were annealed at different temperatures Ta from 800 to 1100 oC. The influence of Ta and Si content in the Si-rich layer on the layered structural stability and on the formation of Si and/or SiC nanocrystals NCs is investigated by a variety of analytical techniques, including x-ray reflectivity XRR, x-ray diffraction XRD, transmission electron microscopy TEM, Raman spectroscopy, and Fourier transform infrared spectrometry FTIR. XRR showed that Si1-xCx /SiC multilayers annealed at temperatures of up to 800 oC retain their layered structure. XRD revealed that Si NCs were formed in samples with a high Si content in the Si-rich layer for Ta 800 oC. At annealing temperatures of 900 oC or greater, the formation of Si NCs was accompanied by the formation of -SiC NCs. Additionally, the formation of Si and SiC NCs was confirmed by TEM imaging and Raman spectroscopy. The Si-NC size obtained from the TEM micrographs is within the range of 3-5 nm. The -SiC NCs are smaller 2-3 nm than Si NCs. Raman analysis identified an 9 cm-1 Raman peak shift in the Si-NC peak to a lower energy with respect to that for bulk Si. FTIR Si-C bond absorption spectra exhibited narrowing of the full width at half maximum and a peak shift toward a higher wave number with increasing Ta. This behavior can be explained by an increase in order as well as an increase in the number of Si-C bonds.

  • (2007) Song, Dengyuan; Cho, E.-C; Conibeer, Gavin; Huang, Yidan; Green, Martin
    Journal Article
    Heterojunctions HJs were fabricated from p-type Si nanocrystals Si NCs embedded in a SiC matrix on an n-type crystalline Si substrate. Transmission electron microscopy revealed that Si NCs are clearly established, with sizes in the range of 3-5 nm. The HJ diodes showed a good rectification ratio of 1.0 104 at ±1.0 V at 298 K. The ideality factor, junction built-in potential, and open-circuit voltage are 1.24, 0.72 V, and 0.48 V, respectively. Measurement of temperature-dependent I-V curves in forward conduction suggests that, in the medium voltage range, junction interface recombination can be described as the dominant current transport mechanism.

  • (2007) Heiser, Gernot; Elphinstone, Kevin; Kuz, Ihor; Klein, Gerwin; Petters, Stefan
    Journal Article
    As computer systems become increasingly mission-critical, used in life-critical situations, and relied upon to protect intellectual property, operating-system reliability is becoming an ever growing concern. In the past, mission- and life-critical embedded systems consisted of simple microcontrollers running a small amount of software that could be validated using traditional and informal techniques. However, with the growth of software complexity, traditional techniques for ensuring software reliability have not been able to keep up, leading to an overall degradation of reliability. This paper argues that microkernels are the best approach for delivering truly trustworthy computer systems in the foreseeable future. It presents the NICTA operating-systems research vision, centred around the L4 microkernel and based on four core projects. The seL4 project is designing an improved API for a secure microkernel, L4, verified will produce a full formal verification of the microkernel, Potoroo combines execution-time measurements with static analysis to determine the worst case execution profiles of the kernel, and CAmkES provides a component architecture for building systems that use the microkernel. Through close collaboration with Open Kernel Labs (a NICTA spinoff) the research output of these projects will make its way into products over the next few years.

  • (2007) Kuz, Ihor; Liu, Yan; Gorton, Ian; Heiser, Gernot
    Journal Article
    Component-based software engineering promises to provide structure and reusability to embedded-systems software. At the same time, microkernel-based operating systems are being used to increase the reliability and trustworthiness of embedded systems. Since the microkernel approach to designing systems is partially based on the componentisation of system services, component-based software engineering is a particularly attractive approach to developing microkernel-based systems. While a number of widely used component architectures already exist, they are generally targeted at enterprise computing rather than embedded systems. Due to the unique characteristics of embedded systems, a component architecture for embedded systems must have low overhead, be able to address relevant non-functional issues, and be flexible to accommodate application specific requirements. In this paper we introduce a component architecture aimed at the development of microkernel-based embedded systems. The key characteristics of the architecture are that it has a minimal, low-overhead, core but is highly modular and therefore flexible and extensible. We have implemented a prototype of this architecture and confirm that it has very low overhead and is suitable for implementing both system-level and application level services.

  • (1997) Peters, G; Maher, WA; Barford, JP; Gomes, VG
    Journal Article
    Selenium (Se) is a contaminant of concern in environments affected by discharges from smelting and coal-burning industries. Experiments have been performed to investigate the phase associations of selenium in contaminated sediments under a range of controlled redox conditions. In this study, Se sediment associations were examined using the BCR sequential extraction technique after stabilisation at different redox states. It was shown that although most of the sediment-bound Se is associated with the operationally-defined "organic/sulfide" fraction, as the measured redox potential of the system is increased, more Se moves into the "exchangeable" and "iron/manganese oxyhydroxide" fractions. In these fractions, contaminants can be expected to be more bioavailable. As the mass of Se absorbed to sediments is typically at least an order of magnitude higher than the mass dissolved in porewaters, significant Se exposure may result from oxidative shifts in Se sediment associations.

  • (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.

  • (1997) Nobbs, Denis M.; Barford, John P.; Carroll, Brett I.; Peters, Gregory M.
    Journal Article
    Lake Macquarie, an estuarine lake on Australia's eastern seaboard, has been subject for almost a century to anthropogenic contamination by heavy metals and metalloids, including selenium, arising from industrial sources including a lead-zinc smelter, coal-fired power stations and sewage works. , Selenium tissue concentrations in fish from the Lake have recently been reported at up to twelve times those recommended for human consumption. This paper describes an integrated investigation into selenium contamination in the Lake over a four-year period. One key component of these investigations is the ability of indigenous micro-organisms to reduce selenium in estuarine sediments from higher to lower oxidation states, therefore immobilising or volatilising it, and the use of this in the treatment of industrial wastewaters or potentially the in-situ bioremediation of contaminated sediments. A second key component is a study of the mechanisms controlling sediment-stored selenium concentrations and the extent to which they can be influenced by bioturbative organisms. Integrated into these two broad areas and described here are a number of related investigations into: bioavailability of sediment-bound selenium; computer modelling of selenium biogeochemistry; representation of heavy metal data in a GIS format; and determination of the specific historical contributions of a power station to selenium loads in the Lake. Through this integrated approach we have built on synergies between the separate components of our research program to add to our understanding of the nature of selenium biogeochemistry in the Lake and to propose potential bioremediation strategies for both the Lake and contaminated industrial wastewaters or surface water.

  • (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.

  • (2001) Peters, G; Lundie, S
    Journal Article
    Biosolids are the reusable organic materials removed from sewage during treatment. Different options for biosolids handling in Sydney, Australia, are compared using life-cycle assessment. Two key comparisons are made: of system scenarios (scenario one - local dewatering and lime-amendment; scenario two - a centralized drying system) and of technologies (thermal drying versus lime-amendment). The environmental issues addressed are energy consumption, global warming potential (GWP) and human toxicity potential (HTP). Scenario two would consume 24% more energy than scenario one. This is due to the additional electricity for pumping and particularly the petrochemical methane that supplements biogas in the dryer. A centralized system using the same technologies as scenario one has approximately the same impacts. The GWP and HTP of the different scenarios do not differ significantly. The assessment of technology choices showed significant differences. The ample supply of endogenous biogas at North Head Sewage Treatment Plant (STP) for the drying option for allows reductions, relative to the lime amendment option, of 68% in energy consumption, 45% in GWP and 23% in HTP. Technology choices have more significant influence on the environmental profile of biosolids processing than the choice of system configurations. Controlling variables for environmental improvement are the selection of biogas fuel, avoidance of coal-sourced electrical energy, minimization of trucking distances and raising the solids content of biosolids products.