Science

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Now showing 1 - 10 of 129
  • (2009) Lim, Wee Han; Huebl, Hans; Willems van Beveren, Laurens; Rubanov, Sergey; Spizzirri, Paul; Angus, Susan; Clark, Robert; Dzurak, Andrew
    Journal Article
    A few-electron double quantum dot was fabricated using metal-oxide-semiconductor-compatible technology and low-temperature transport measurements were performed to study the energy spectrum of the device. The double dot structure is electrically tunable, enabling the inter-dot coupling to be adjusted over a wide range, as observed in the charge stability diagram. Resonant single-electron tunneling through ground and excited states of the double dot was clearly observed in bias spectroscopy measurements.

  • (2009) Highfield, Linda D; Ward, Michael P; Laffan, Shawn; Norby, Bo; Wagner, Gale G
    Journal Article
    Modeling potential disease spread in wildlife populations is important for predicting, responding to and recovering from a foreign animal disease incursion such as foot and mouth disease (FMD). We conducted a series of simulation experiments to determine how seasonal estimates of the spatial distribution of white-tailed deer impact the predicted magnitude and distribution of potential FMD outbreaks. Outbreaks were simulated in a study area comprising 2 distinct ecoregions in south Texas, USA, using a susceptible-latent-infectious-resistant geographic automata model (Sirca). Seasonal deer distributions were estimated by spatial autoregressive lag models and the normalized difference vegetative index. Significant (P < 0.0001) differences in both the median predicted number of deer infected and number of herds infected were found both between seasons and between ecoregions. Larger outbreaks occurred in winter within the higher deer-density ecoregion, whereas larger outbreaks occurred in summer and fall within the lower deer-density ecoregion. Results of this simulation study suggest that the outcome of an FMD incursion in a population of wildlife would depend on the density of the population infected and when during the year the incursion occurs. It is likely that such effects would be seen for FMD incursions in other regions and countries, and for other diseases, in cases in which a potential wildlife reservoir exists. Study findings indicate that the design of a mitigation strategy needs to take into account population and seasonal characteristics.

  • (2009) Wang, Daming; Laffan, Shawn; Yu, Liu; Wu, Lun
    Journal Article
    We describe a method of morphometric characterisation of landform from DEMs. The method is implemented by first classifying every location into morphometric classes based on the mathematical shape of a locally fitted quadratic surface and its positional relationship with the analysis window. Single-scale fuzzy terrain indices of peakness, pitness, passness, ridgeness, and valleyness are then calculated based on the distance of the analysis location from the ideal cases. These can then be combined into multi-scale terrain indices to summarise terrain information across different operational scales. The algorithm has four characteristics: (1) the ideal cases of different geomorphometric features are simply and clearly defined; (2) the output is spatially continuous to reflect the inherent fuzziness of geomorphometric features; (3) the output is easily combined into a multi-scale index across a range of operational scales; and (4) the standard general morphometric parameters are quantified as the first and second order derivatives of the quadratic surface. An additional benefit of the quadratic surface is the derivation of the R2 goodness of fit statistic, which allows an assessment of both the reliability of the results and the complexity of the terrain. An application of the method using a test DEM indicates that the single- and multi-scale terrain indices perform well when characterising the different geomorphometric features.

  • (2009) Huang, Zhi; Laffan, Shawn
    Journal Article
    We analysed the sensitivity of a decision tree derived forest type mapping to simulated data errors in input DEM, geology and remotely sensed (Landsat Thematic Mapper) variables. We used a stochastic Monte Carlo simulation model coupled with a one-at-a-time approach. The DEM error was assumed to be spatially autocorrelated with its magnitude being a percentage of the elevation value. The error of categorical geology data was assumed to be positional and limited to boundary areas. The Landsat data error was assumed to be spatially random and follow a Gaussian distribution. Each layer was perturbed using its error model with increasing levels of error, and the effect on the forest type mapping was assessed. The results of the three sensitivity analyses were markedly different, with the classification being most sensitive to the DEM error, then to the Landsat data errors, but with only a limited sensitivity to the geology data error used. A linear increase in error resulted in non-linear increases in effect for the DEM and Landsat errors, while it was linear for geology. As an example, a DEM error of as small as ±2% reduced the overall test accuracy by more than 2%. More importantly, the same uncertainty level has caused nearly 10% of the study area to change its initial class assignment at each perturbation, on average. A spatial assessment of the sensitivities indicates that most of the pixel changes occurred within those forest classes expected to be more sensitive to data error. In addition to characterising the effect of errors on forest type mapping using decision trees, this study has demonstrated the generality of employing Monte Carlo analysis for the sensitivity and uncertainty analysis of categorical outputs which have distinctive characteristics from that of numerical outputs.

  • (2009) Zhang, Kun; Laffan, Shawn; Zhang, Songlin
    Journal Article
    The highly skewed sex ratio at birth (SRB) in China has stimulated numerous studies. However, the geographic distribution of SRB is seldom investigated, particularly at the county level. The need for an understanding at this level has increased since the Chinese government initiated its “Care for Girls” campaign to improve the survival rate of females. This campaign has been initiated in a set of pilot counties. In this paper, we assess the effectiveness of the set of pilot counties in Shandong province, and propose two alternate configurations. To do this, we first assess the spatial distribution of the SRB values by county in Shandong, expressed as a z-score (zSRB) after correcting for the biologically expected SRB value and population size of zero-aged children. A local Moran’s Ii analysis of the zSRB values indicates a significant high-high cluster in the southwest of the province. The Ii, zSRB and female deficit (the difference of the observed from biologically expected number of zero-aged females) were then used to define two alternate configurations for the pilot counties. A comparison of the current and alternate configurations against a Monte Carlo randomisation analysis shows that the current configuration is significantly different from a random selection (p<0.05) for the two criteria of maximising the aggregate female deficit and maximising the zSRB. While this is a good result, both alternate configurations were more significant (p<0.001), and therefore represent potentially better configurations for the campaign given the criteria used. The spatial analysis approach developed here could be used to improve the effectiveness of the Care for Girls campaign in Shandong province, and elsewhere in China.

  • (2009) Gao, Steven; Lees, Justin; Wong, Jennifer; Croll, Tristan; George, Peter; Cooper-White, Justin; Tuch, Bernard
    Journal Article
    Human embryonic stem cells (hESCs) have previously been cultured on three dimensional (3D) biodegradable polymer scaffolds. Although complex structures were formed from the hESCs, very little is known about the mechanism of adhesion of these cells to the surfaces of the scaffolds. In this study, we achieved the efficient adhesion of pluripotent hESCs to 3D poly(lactic-co-glycolic acid) (PLGA) scaffolds based on our data from a novel two dimensional (2D) model that imitates the surface properties of the scaffolds. In the 2D model, single cell preparations of pluripotent hESCs adhered efficiently and predominantly to PLGA surfaces coated with laminin in comparison to collagen I, collagen IV, or fibronectin-coated surfaces. Flow cytometry analysis revealed that almost all of the pluripotent single cells expressed the integrin 6, with a small percentage also expressing 3ß1, which facilitates adhesion to laminin. This data was then translated into the 3D environment, with the efficient binding of single pluripotent hESCs to PLGA scaffolds coated with laminin. The utility of this system was shown by the directed differentiation of single hESCs seeded within laminin-coated scaffolds toward the endoderm lineage.

  • (2009) Burke, C; Kjelleberg, S; Thomas, Torsten
    Journal Article
    A novel method has been developed for the selective extraction of DNA from surface-associated bacterial communities from the two model marine benthic algae Ulva australis and Delisea pulchra. The extracted DNA had no detectable contamination with host DNA, was recovered in high yield and quality, and was representative of the bacterial community on the algal surfaces. The DNA is suitable for a variety of subsequent applications, including the construction of large-insert clone libraries and metagenomic sequencing.

  • (2009) Dall'Osso, Filippo; Gonella, Marco; Gabbianelli, Giovanni; Withycombe, Geoff; Dominey-Howes, Dale
    Journal Article
    Australia is vulnerable to the impacts of tsunamis and exposure along the SE coast of New South Wales is es- pecially high. Significantly, this is the same area reported to have been affected by repeated large magnitude tsunamis during the Holocene. Efforts are under way to complete probabilistic risk assessments for the region but local gov- ernment planners and emergency risk managers need infor- mation now about building vulnerability in order to develop appropriate risk management strategies. We use the newly revised PTVA-3 Model (Dall’Osso et al., 2009) to assess the relative vulnerability of buildings to damage from a “worst case tsunami” defined by our latest understanding of regional risk – something never before undertaken in Australia. We present selected results from an investigation of building vul- nerability within the local government area of Manly – an iconic coastal area of Sydney. We show that a significant proportion of buildings (in particular, residential structures) are classified as having “High” and “Very High” Relative Vulnerability Index scores. Furthermore, other important buildings (e.g., schools, nursing homes and transport struc- tures) are also vulnerable to damage. Our results have seri- ous implications for immediate emergency risk management, longer-term land-use zoning and development, and building design and construction standards. Based on the work un- dertaken here, we recommend further detailed assessment of the vulnerability of coastal buildings in at risk areas, devel- opment of appropriate risk management strategies and a de- tailed program of community engagement to increase overall resilience.

  • (2009) Dall'Osso, Filippo; Gonella, Marco; Gabbianelli, Giovanni; Withycombe, Geoff; Dominey-Howes, Dale
    Journal Article
    The Papathoma Tsunami Vulnerability Assess- ment (PTVA) Model (Papathoma, 2003) was developed in the absence of robust, well-constructed and validated build- ing fragility models for assessing the vulnerability of build- ings to tsunami. It has proven to be a useful tool for pro- viding assessments of building vulnerability. We present an enhanced version (PTVA-3) of the model that takes account of new understanding of the factors that influence building vulnerability and significantly, introduce the use of the Ana- lytic Hierarchy Process (AHP) for weighting the various at- tributes in order to limit concerns about subjective ranking of attributes in the original model. We successfully test PTVA- 3 using building data from Maroubra, Sydney, Australia.