The value of total coliforms, faecal coliforms and faecal streptococci in predicting the presence of Salmonella spp. and the numbers of Staphylococcus aureus and Candida albicans in sewage polluted coastal water were assessed. All indicators had strong positive association with Salmonella and moderate positive correlations with Staph. aureus and C. albicans. Total coliforms correlated better with salmonellas and Staph. aureus than did the two faecal groups. Regression analysis revealed that total coliforms have a better value as predictors of the presence of Salmonella and Staph. aureus, while faecal coliforms are better predictors of C. albicans, in moderately polluted areas. The conclusion reached is that enumeration of total coliforms is sufficient to predict the presence of Salmonella spp. or Staph. aureus in sea water moderately affected by sewage pollution, without the additional measurement of faecal coliforms and faecal streptococci.

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In this paper we introduce an analytical approach for predicting the melting radius during powder melting in selective laser melting (SLM) with minimum computation duration. The purpose of this work is to evaluate the suggested analytical expression in determining the melt pool geometry for SLM processes, by considering heat transfer and phase change effects with density variation and cylindrical symmetry. This allows for rendering first findings of the melt pool numerical prediction during SLM using a quasi-real-time calculation, which will contribute significantly in the process design and control, especially when applying novel powders. We consider the heat transfer problem associated with a heat source of power Q' (W/m) per unit length, activated along the span of a semi-infinite fusible material. As soon as the line heat source is activated, melting commences along the line of the heat source and propagates cylindrically outwards. The temperature field is also cylindrically symmetric. At small times (i.e., neglecting gravity and Marangoni effects), when the density of the solid material is less than that of the molten material (i.e., in the case of metallic powders), an annulus is created of which the outer interface separates the molten material from the solid. In this work we include the effect of convection on the melting process, which is shown to be relatively important. We also justify that the assumption of constant but different properties between the two material phases (liquid and solid) does not introduce significant errors in the calculations. A more important result; however, is that, if we assume constant energy input per unit length, there is an optimum power of the heat source that would result to a maximum amount of molten material when the heat source is deactivated. The model described above can be suitably applied in the case of selective laser melting (SLM) when one considers the heat energy transferred to the metallic powder bed during scanning. Using a characteristic time and length for the process, we can model the energy transfer by the laser as a heat source per unit length. The model was applied in a set of five experimental data, and it was demonstrated that it has the potential to quantitatively describe the SLM process.

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