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INTRODUCTION: Although Staphylococcus aureus is the leading cause of biofilm-related infections, the lipidomic distributions within these biofilms is poorly understood. Here, lipidomic mapping of S. aureus biofilm cross-sections was performed to investigate heterogeneity between horizontal biofilm layers. METHODS: S. aureus biofilms were grown statically, embedded in a mixture of carboxymethylcellulose/gelatin, and prepared for downstream matrix-assisted laser desorption/ionization imaging mass spectrometry (MALDI IMS). Trapped ion mobility spectrometry (TIMS) was also applied prior to mass analysis. RESULTS: Implementation of TIMS led to a ∼ threefold increase in the number of lipid species detected. Washing biofilm samples with ammonium formate (150 mM) increased signal intensity for some bacterial lipids by as much as tenfold, with minimal disruption of the biofilm structure. MALDI TIMS IMS revealed that most lipids localize primarily to a single biofilm layer, and species from the same lipid class such as cardiolipins CL(57:0) - CL(66:0) display starkly different localizations, exhibiting between 1.5 and 6.3-fold intensity differences between layers (n = 3, p < 0.03). No horizontal layers were observed within biofilms grown anaerobically, and lipids were distributed homogenously. CONCLUSIONS: High spatial resolution analysis of S. aureus biofilm cross-sections by MALDI TIMS IMS revealed stark lipidomic heterogeneity between horizontal S. aureus biofilm layers demonstrating that each layer was molecularly distinct. Finally, this workflow uncovered an absence of layers in biofilms grown under anaerobic conditions, possibly indicating that oxygen contributes to the observed heterogeneity under aerobic conditions. Future applications of this workflow to study spatially localized molecular responses to antimicrobials could provide new therapeutic strategies.

Fracture modelling using numerical methods is well-advanced in 2D using techniques such as the extended finite element method (XFEM). The use of meshless methods for these problems lags somewhat behind, but the potential benefits of no meshing (particularly in 3D) prompt continued research into their development. In methods where the crack face is not explicitly modelled (as the edge of an element for instance), two procedures are instead used to associate the displacement jump with the crack surface: the visibility criterion and the diffraction method. The visibility criterion is simple to implement and efficient to compute, especially with the help of level set coordinates. However, spurious discontinuities have been reported around crack tips using the visibility criterion, whereas implementing the diffraction method in 3D is much more complicated than the visibility criterion. In this paper, a tying procedure is proposed to remove the difficulty with the visibility criterion so that crack tip closure can be ensured while the advantages of the visibility criterion can be preserved. The formulation is based on the use of level set coordinates and the element-free Galerkin method, and is generally applicable for single or multiple crack problems in 2D or 3D. The paper explains the formulation and provides verification of the method against a number of 2D crack problems.

Secondary Ion Mass Spectroscopy is applied to cast and ribbon-grown multicrystalline silicon in an attempt to discover the major metallic impurities present in these important photovoltaic materials. By analysing a thin diffused layer, in which the impurities are concentrated, the effective sensitivity of the method is increased significantly. The results indicate that Fe and Cr are present in large quantities in cast multicrystalline silicon, while Cu exists in significant amounts in Edge-defined Film-fed Growth ribbon silicon.

1) This is an ecological review of the 'ACT Government Environmental Flow Guidelines' (1999) (or EFG). The EFG are a statutory document that establishes the water requirements in streams and lakes in the ACT, to ensure aquatic ecosystems are sustained. The CRC for Freshwater Ecology has been asked to provide advice on the efficacy of the EFG, and on improvements that can be made in the general approaches and actual flow rules for sustaining ecological values. 2) The approach taken in the review is to assess the effectiveness of prescribed environmental flows by reference to monitoring data and research on rivers within the ACT, and by consulting with local scientific experts. Advice is provided on the retention of current flow practices, or their modification to better achieve ecological objectives. This information could contribute to adaptive management in the near term, or to a more systematic formulation of environmental flow guidelines, should that be undertaken in the future. Performance of the environmental flow guidelines 3) The performance of environmental flows needs to be considered in reference to objectives that reflect catchment uses as well as river condition. The approach taken in this review is to judge sustainability in reference to established 'performance criteria' where they exist. 4) In regulated parts of the Cotter River system the current EFG low-flow levels (supplemented by unmanaged reservoir spills and inflows), are delivering many desirable ecological benefits. General river condition is at or above levels specified in performance criteria, and appears to have improved since the implementation of the EFG, despite the drought and fires. Both Macquarie Perch and Two-spined Blackfish have successfully spawned during the drought. 5) Adaptive management principles embedded in the EFG, and further developed in practice, worked well in the Cotter River during 2003/04 in relation to setting environmental flows during drought and under a demonstra