Bacteria have transient influences on marine corrosion of steel

The contribution of bacteria to the corrosion mass loss and to pitting of mild steel was observed over 2.5 years using parallel streams of unpolluted natural (biotic) and nominally sterilized (abiotic) Pacific Ocean coastal seawater. As also observed by others, in artificial laboratory exposures, corrosion mass loss within the first few days of exposure was much greater in the biotic stream. However, after only about 10 days the difference in mass losses were gradually reduced and were very similar up to about one year of exposure. Thereafter, the corrosion loss in the biotic stream again became more severe. Pitting corrosion in the biotic stream was more severe from the very first exposure throughout the 2.5 years. Corrosion in both seawater streams exhibited three distinct but transient time-dependent phases. Of these only the first and third obviously involve bacteria. Similar longer-term observations in real seawaters have not been described previously but are generally consistent with some long-term field data. The results show that longer-term corrosion behavior and possible microbial influences cannot be predicted from short-term laboratory observations, even if natural seawater is used

Field experience and the long-term durability of reinforced concrete structures

For reinforced concrete structures the conventional wisdom is that after some years of exposure to marine conditions reinforcement corrosion is inevitable. Much attention is paid in the literature to the rate of ingress of chlorides through the concrete cover to the reinforcing bars and to ensuring highly impermeable cover and/or deeper cover, to try top prevent chloride-induced or carbonation-induced corrosion initiation. Actual field experience shows that there are many reinforced concrete structures that have survived remarkably well for many decades despite having very high chloride concentrations next to the reinforcing bars. Even with very modest concrete cover by modern standards, exhumation often finds bars free from corrosion. Detailed investigations of a number of such cases showed no corrosion if the concrete pH levels are above about 9. On the other hand, very severe reinforcement corrosion was observed in the few cases where the concrete had cracked right through the cover to the bars. Often there was no external evidence or signs of interior corrosion, including longitudinal cracking. The implications of these findings for practice are discussed

Emericella quadrilineata as Cause of Invasive Aspergillosis

This opportunistic fungus is frequently misidentified because of its morphologic similarity to E. nidulans

Emergence of Azole Resistance in Aspergillus fumigatus and Spread of a Single Resistance Mechanism

Paul Verweij and colleagues show that azole resistance has emerged inAspergillus fumigatus in The Netherlands and that a dominant resistance mechanism is present in clinical isolates

Longitudinal intravital imaging of the femoral bone marrow reveals plasticity within marrow vasculature.

The bone marrow is a central organ of the immune system, which hosts complex interactions of bone and immune compartments critical for hematopoiesis, immunological memory, and bone regeneration. Although these processes take place over months, most existing imaging techniques allow us to follow snapshots of only a few hours, at subcellular resolution. Here, we develop a microendoscopic multi-photon imaging approach called LIMB (longitudinal intravital imaging of the bone marrow) to analyze cellular dynamics within the deep marrow. The approach consists of a biocompatible plate surgically fixated to the mouse femur containing a gradient refractive index lens. This microendoscope allows highly resolved imaging, repeatedly at the same regions within marrow tissue, over months. LIMB reveals extensive vascular plasticity during bone healing and steady-state homeostasis. To our knowledge, this vascular plasticity is unique among mammalian tissues, and we expect this insight will decisively change our understanding of essential phenomena occurring within the bone marrow

Predicting the environmental suitability for onchocerciasis in Africa as an aid to elimination planning

Recent evidence suggests that, in some foci, elimination of onchocerciasis from Africa may be feasible with mass drug administration (MDA) of ivermectin. To achieve continental elimination of transmission, mapping surveys will need to be conducted across all implementation units (IUs) for which endemicity status is currently unknown. Using boosted regression tree models with optimised hyperparameter selection, we estimated environmental suitability for onchocerciasis at the 5 × 5-km resolution across Africa. In order to classify IUs that include locations that are environmentally suitable, we used receiver operating characteristic (ROC) analysis to identify an optimal threshold for suitability concordant with locations where onchocerciasis has been previously detected. This threshold value was then used to classify IUs (more suitable or less suitable) based on the location within the IU with the largest mean prediction. Mean estimates of environmental suitability suggest large areas across West and Central Africa, as well as focal areas of East Africa, are suitable for onchocerciasis transmission, consistent with the presence of current control and elimination of transmission efforts. The ROC analysis identified a mean environmental suitability index of 0.71 as a threshold to classify based on the location with the largest mean prediction within the IU. Of the IUs considered for mapping surveys, 50.2% exceed this threshold for suitability in at least one 5×5-km location. The formidable scale of data collection required to map onchocerciasis endemicity across the African continent presents an opportunity to use spatial data to identify areas likely to be suitable for onchocerciasis transmission. National onchocerciasis elimination programmes may wish to consider prioritising these IUs for mapping surveys as human resources, laboratory capacity, and programmatic schedules may constrain survey implementation, and possibly delaying MDA initiation in areas that would ultimately qualify

Meso-scale finite element investigation into the short and long term strengths of glass fibre reinforced composites

A finite element model is proposed for simulating the short and long term strength of Glass Fibre Reinforced Plastics. The essence of the model is a division of the composite system into a binary system comprising 'fibre elements' to represent the fibres, and 'effective medium' elements to represent the matrix material, which account for other mechanical properties such as shear and transverse stiffness and Poisson's effect. Such a representation stems from the fact that the performance of a composite material is intrinsically controlled by the microstructure of the component materials. Besides, it has the advantage of the power and versatility of the finite element technique. Typical results for short and long term strengths are compared to similar predictions obtained from shear lag theory. Good agreement is obtained for a variety of finite element discretisations

Statistical characterization of pitting corrosion. Part 1: data analysis

Maximum pit depth is a matter of considerable practical interest. In applied corrosion mechanics it is conventional to represent it by an extreme value distribution, usually Gumbel. However. a detailed examination of recent field data for maximum pit depth of mild steel under marine conditions shows that it can befitted as well or better to a bi-modal probability distribution. similar to that which is typical for the underlying pit depth distribution. A reexamination of some classical maximum pit depth data extracted from the literature for aluminum and stainless steel shows a similar phenomenon. Theoretical arguments suggest one reason for this is that the coupon size typically used may be insufficient to capture the extremes. Also. on the basis of modem understanding of the pitting phenomenon. it is proposed that the formation of pits of maximum depth is consistent only with pits that initiate immediately upon exposure and then experience stable pitting behavior. Pits that undergo metastable pitting are unlikely to become extreme and constitute a different statistical population. Moreover. the depths of maximal pits are likely to be highly dependent. Both factors cast doubt on the conventional use of extreme value theory in representing the uncertainty associated with maximum pit depth

Validity and quality of deterioration models for structural reliability assessment

There are increasing pressures to extend the service lives of existing infrastructure and to provide optimal management of their maintenance. Structural reliability theory now provides a very comprehensive approach to assessing risks for complex infrastructure systems. It requires probabilistic models for the prediction of the long-term changes to structural capacity and resistance as may result, for example, from changes in the management or operation of the asset or from material deterioration in harsh operational environments. While empirical models may be sufficient in some cases, it is preferable for the models to be based on fundamental science and to deal with remaining uncertainty in a probabilistic manner. Herein models for the prediction of the corrosion of structural steel in marine environments are considered. The issues involved are reviewed and some of the pitfalls in model development are considered. These include (i) models based on inadequate underlying theories, (ii) use of inhomogeneous populations, (iii) use of inappropriate influencing factors, (iv) use of laboratory test results rather than field results, (v) insufficient attention to limitations and conditions, (vi) insufficient understanding of the changes in conditions with time, and (vii) invoking model simplifications too early. Drawing on material that has already been published in the literature, examples are given of each to show how these matters may provide misleading information to potential end-users