Preparation of the nematode-trapping fungus,Arthrobotrys oligospora,for scanning electron microscopy by freeze substitution

A freeze-substitution technique for preparing fungal specimens for scanning electron microscopy is described. This involves cryofixation in liquid nitrogen, freeze substitution in methanol at — 20°C and critical-point drying. The trapping complexes and conidiophores of the nematophagous fungus Arthrobotrys oligospora are well preserved and retain their normal three-dimensional arrangement.     

The influence of nickel-aluminium bronze microstructure and crevice solution on the initiation of crevice corrosion

A new mechanistic model has been established for the chemical and electrochemical mechanisms controlling nickel-aluminium bronze crevice corrosion. The crevice corrosion was initially confined to eutectoid regions with slight attack of the copper rich α-phase within the α+κ_III eutectoid. In the presence of high chloride concentrations, copper and aluminium complexes form and the hydrolysis of these complexes leads to the acidification of the crevice solution chemistry. As the crevice solution becomes increasingly acidic the initial protection of the κ-phases due to their higher aluminium contents is lost and become anodic to the α-phase. The continuous nature of the κ_III-phase makes it vulnerable with an ∼80 μm depth of attack after only the first month which is accompanied by internal copper redeposited at cathodic sites. Crevice corrosion of copper-based alloys is often reported to be controlled by a copper-ion concentration cell, however, for nickel-aluminium bronze it appears that primarily the crevice corrosion propagation results from a combined action of localised acidification and differential aeration between the bold and occluded zones. This mechanistic understanding provides further insights in to the development of crevice corrosion experienced by nickel-aluminium bronze after long-term exposures to natural seawater for up to 3 years.     

Exposure effects of strong alkaline conditions on the microscale abrasion–corrosion of D-gun sprayed WC–10Co–4Cr coating

The synergistic effects between abrasion and corrosion for detonation gun (D-gun) sprayed WC–10Co–4Cr coatings have been studied for alkaline conditions. Comparisons between exposed and freshly polished coating surfaces in strong NaOH solutions (pH 11) show that significantly lower wear rates were seen for the exposed surface due to a negative wear–corrosion synergy. The negative synergy was seen to increase with increasing sliding distances for both fresh and exposed surfaces. The physical mechanisms of this negative synergy are discussed. The effect of anodic surface treatments on wear–corrosion to elucidate the influence of corrosion on the negative synergy is also reported.     

Two-Wavelength switching of luciferase activity using caged compounds

Firefly luciferase, luciferin, 1-(3,4-dimethoxy-6-nitrophenyl) elthyl ATP and 1-(2-nitrophenyl) ethyl acetic acid were immobilised in an agarose gel matrix. By illuminating the gel with 350 nm light through a mask, a positive bioluminescent pattern was written on to the gel by releasing ATP in the illuminated areas. The gel was then illuminated with a brpadbnand UV light through a second mask to release acetic acid, lowering the local pH and deactivating the enzyme. This produced a negative image of the second mask superimposed on the positive image of the first mask. The system represents a two-wavelength switch in which one wavelength of light activates the enzyme while a second deactivates it. This demonstrates the feasibility of using biological molecules as logic element in future devices.