Engineering

Publication Search Results

Now showing 1 - 10 of 70
  • (2006) Altermatt, Pietro; Schenk, Andreas; Heiser, Gernot
    Journal Article
    A parametrization of the density of states (DOS) near the band edge of phosphorus-doped crystalline silicon is derived from photoluminescence and conductance measurements, using a recently developed theory of band gap narrowing. It is shown that the dopant band only `touches` the conduction band at the Mott (metal-insulator) transition and that it merges with the conduction band at considerably higher dopant densities. This resolves well-known contradictions between conclusions drawn from various measurement techniques. With the proposed DOS, incomplete ionization of phosphorus dopants is calculated and compared with measurements in the temperature range from 300 to 30 K. We conclude that (a) up to 25% of dopants are nonionized at room temperature near the Mott transition and (b) there exists no significant amount of incomplete ionization at dopant densities far above the Mott transition. In a forthcoming part II of this paper, equations of incomplete ionization will be derived that are suitable for implementation in device simulators. (c) 2006 American Institute of Physics.

  • (2006) Altermatt, Pietro; Schenk, Andreas; Schmithuesen, B; Heiser, Gernot
    Journal Article
    Building on Part I of this paper [Altermatt , J. Appl. Phys. 100, 113714 (2006)], the parametrization of the density of states and of incomplete ionization (ii) is extended to arsenic- and boron-doped crystalline silicon. The amount of ii is significantly larger in Si:As than in Si:P. Boron and phosphorus cause a similar amount of ii although the boron energy level has a distinctly different behavior as a function of dopant density than the phosphorus level. This is so because the boron ground state is fourfold degenerate, while the phosphorus ground state is twofold degenerate. Finally, equations of ii are derived that are suitable for implementation in device simulators. Simulations demonstrate that ii increases the current gain of bipolar transistors by up to 25% and that it decreases the open-circuit voltage of thin-film solar cells by up to 10 mV. The simulation model therefore improves the predictive capabilities of device modeling of p-n-junction devices.

  • (2006) Ho, Minh; Leamon, Gregory; Ailinson, G; Wiley, Dianne
    Journal Article
    Greenhouse gas emission sources generally produce mixed gases. Previous studies of CCh capture and storage have typically examined only sequestration of pure CO2. This paper analyzes the cost of separating a gas mixture from a power station flue gas stream and injecting it into an offshore subsurface reservoir. The costs of separating and storing various gas mixtures were analyzed at two extremes. One extreme in which the entire flue gas stream containing both CO2 and N2 is stored. The other extreme in which as much CO2 is separated as is technically possible using gas membrane capture coupled with chemical absorption. The results indicate that for the gases investigated, using a gas membrane capture system, the lowest sequestration cost per tonne of CO2 avoided occurs when a mixed gas with a CO2 content of about 60% is sequestered. Lower costs and higher tonnages of CO2 avoided can be achieved using an amine based absorption capture system. At the lowest cost point, and for most of the range of cases studied, the cost of capture is significantly greater than the cost of storage. However, this depends on the source of the CO 2, the distance between the source and the injection site, and the reservoir into which CO2 is injected.

  • (2006) Ho, Minh; Allinson, G; Wiley, Dianne
    Journal Article
    The sequestration of CO2 as a greenhouse mitigation option is becoming an increasingly important priority for industry. Theoretically membrane based CO2 removal systems have the potential to provide a cost effective, low maintenance approach for removing CO2 from gas streams. This study examines the effect of membrane characteristics, operating parameters and system design on sequestration costs for any source-sink combination. The total sequestration cost per tonne of CO2 avoided for separation, transport and storage are compared for the separation of CO2 from a black coalfired power plant in Australia. The results show that the membranes currently available have a total sequestration cost of US$55-61/tonne CO2 avoided. Lower costs for CO2 avoided can be achieved using an MEA amine based absorption separation system. Gas separation membranes would require significant improvements in CO2 permeability and selectivity, together with reductions in the cost of membranes and changes to the process configurations and operating pressures to be competitive against MEA systems for the purposes of geo-sequestration.

  • (2006) Lee, Cathryn; Gaeta, Bruno; Malming, H; Bain, Michael; Sewell, William; Collins, Andrew
    Journal Article
    We have used a bioinformatics approach to evaluate the completeness and functionality of the reported human immunoglobulin heavy-chain IGHD gene repertoire. Using the hidden Markov-model-based iHMMune-align program, 1,080 relatively unmutated heavy-chain sequences were aligned against the reported repertoire. These alignments were compared with alignments to 1,639 more highly mutated sequences. Comparisons of the frequencies of gene utilization in the two databases, and analysis of features of aligned IGHD gene segments, including their length, the frequency with which they appear to mutate, and the frequency with which specific mutations were seen, were used to determine the reliability of alignments to the less commonly seen IGHD genes. Analysis demonstrates that IGHD4-23 and IGHD5-24, which have been reported to be open reading frames of uncertain functionality, are represented in the expressed gene repertoire; however, the functionality of IGHD6-25 must be questioned. Sequence similarities make the unequivocal identification of members of the IGHD1 gene family problematic, although all genes except IGHD1-14*01 appear to be functional. On the other hand, reported allelic variants of IGHD2-2 and of the IGHD3 gene family appear to be nonfunctional, very rare, or nonexistent. Analysis also suggests that the reported repertoire is relatively complete, although one new putative polymorphism (IGHD3-10*p03) was identified. This study therefore confirms a surprising lack of diversity in the available IGHD gene repertoire, and restriction of the germline sequence databases to the functional set described here will substantially improve the accuracy of IGHD gene alignments and therefore the accuracy of analysis of the V-D-J junction.

  • (2006) Lundie, S; Peters, G; Ashbolt, Nicholas; Lai, Elizabeth; Livingston, Daniel
    Journal Article
    In this article we discuss the application of strategic planning tools in the Australian water industry and a framework for assessing the sustainability of new investments in water cycle management. Created in a research project partly funded by the Water Services Association of Australia, the Sustainability Framework is based on taking the best of current strategic planning and sustainability assessment approaches, including appropriate levels of interaction with public and government stakeholders. It embraces recent developments in the application of life cycle assessment and other information tools. The intent is to deliver a guide which provides for both analytical and participatory aspects of sustainability assessment.

  • (2006) Ashbolt, Nicholas; Lai, Elizabeth; Livingston, Daniel
    Journal Article

  • (2006) Janapsatya, Andhi; Ignjatovic, Aleksandar; Parameswaran, Sri
    Journal Article
    A method to both reduce energy and improve performance in a processor-based embedded system is described in this paper. Comprising of a scratchpad memory instead of an instruction cache, the target system dynamically (at runtime) copies into the scratchpad code segments that are determined to be beneficial (in terms of energy efficiency and/or speed) to execute from the scratchpad. We develop a heuristic algorithm to select such code segments based on a metric, called concomitance. Concomitance is derived from the temporal relationships of instructions. A hardware controller is designed and implemented for managing the scratchpad memory. Strategically placed custom instructions in the program inform the hardware controller when to copy instructions from the main memory to the scratchpad. A novel heuristic algorithm is implemented for determining locations within the program where to insert these custom instructions. For a set of realistic benchmarks, experimental results indicate the method uses 41.9% lower energy (on average) and improves performance by 40.0% (on average) when compared to a traditional cache system which is identical in size.

  • (2006) Gouget, B; Coves, Jacques; Avoscan, Laure; Collins, Richard; Carriere, Marie
    Journal Article