Glaucoma drainage implants in Asian eyes

OBJECTIVE: Previous studies have suggested that there are racial differences in the outcome of conventional filtration surgery. This study aims to evaluate the outcome of glaucoma drainage implants in Asian eyes with complicated glaucoma and to determine whether there are racial differences in the results of such implant surgery compared to previous reports in non-Asian patients. DESIGN: The study design was a retrospective review of all patients with more than 6-months' follow-up after glaucoma implant surgery at the Singapore National Eye Centre between January 1993 and August 1996. PARTICIPANTS: A total of 83 Asian patients with uncontrolled complicated glaucoma participated. INTERVENTION: A total of 29 patients received Molteno implants and 54 received Baerveldt implants. MAIN OUTCOME MEASURES: The surgical outcome was assessed in terms of final intraocular pressure (IOP), visual acuity outcome, and incidence of complications. Success was defined as final IOP less than 22 mmHg with no medications and qualified success as an IOP less than 22 mmHg with medication. RESULTS: With mean follow-up of 13.41 months, success in IOP control was achieved in 73.5% of patients and qualified success in 12%. Visual acuity remained stable or improved in 85.5%. There were no patients who encountered intraoperative complications, and the incidence of serious postoperative complications was low. The most frequently observed short- and long-term postoperative complication was hyphema in 14 eyes (16.9%) and bullous keratopathy in 7 eyes (8.4%), respectively. CONCLUSIONS: Glaucoma drainage implants have good outcome and visual stabilization in Asian eyes with success rates for IOP control comparable to those reported in previous studies in non-Asian eyes.     

Evolution of corrosion in cast Al alloy in antifreeze radiator coolant

Corrosion is an important issue for cast Al alloy in an engine cooling system, but how the microstructural features affect the coolant‐related corrosion behaviour is not well understood. In this research, the evolution of corrosion in an ISO 2379 cast Al alloy was studied in an antifreeze radiator coolant under heat‐rejecting conditions. Extensive analyses of microstructures and corroded surfaces were carried out using an optical microscope, scanning electron microscope equipped with energy dispersive spectroscopy and X‐ray diffractometer. Intergranular cavitation corrosion was observed to occur at interfaces between α‐Al matrix and intermetallics (Al₂Cu and Al₅FeSi) or to a less degree at interfaces between α‐Al matrix and Si phase. The large area fraction of the cathodic phases (Al₂Cu, Al₅FeSi and Si) led to the galvanic coupling between them and the adjacent anodic α‐Al matrix. The heat‐rejecting condition in antifreeze radiator coolant was favourable condition to cavitation process while severe crevice corrosion was predominant at oxygen‐depleted regions in the heat‐transfer corrosion cell.     

Monitoring pitting‐crevice corrosion using the WBE‐noise signatures method

An electrochemically integrated multi‐electrode array namely the wire beam electrode (WBE) and noise signatures analysis have been applied in novel combinations to study crevice corrosion behaviour in the presence of pits. Characteristic electrochemical noise signatures were found to correlate with characteristic changes in WBE current distribution maps, which indicate corrosion rates distributions, corrosion patterns and the degree of pitting and crevice corrosion. Specifically, two characteristic noise patterns were observed: (i) the characteristic noise pattern of quick potential changes towards more negative direction with no recovery (termed noise signature I) was found to correspond with the initiation and stabilization of the anode inside crevice; and (ii) the characteristic noise pattern of the cyclic potential oscillation at a constant frequency (termed noise signature II) was found to correspond with the stable anodic dissolution in the occluded cavity site in WBE current distribution maps. A new parameter namely the localization parameter (LP) has been proposed to describe the degree of localization. The LP for crevice corrosion was found to be low compared to that for pitting corrosion.     

Novel corrosion experiments using the wire beam electrode: (II) Monitoring the effects of ions transportation on electrochemical corrosion processes

An electrochemically integrated multi-electrode system namely the wire beam electrode (WBE) has been applied for the first time to study the effects of the transportation of electrochemically active species on the process, rate and pattern of electrochemical corrosion. The objective of this work is to demonstrate the applicability of the WBE method for investigating ion transportation related corrosion processes. A series of experiments have been carried out using WBEs made from mild steel and stainless steel wires. The WBE working surfaces were exposed to simulated diffusion-controlled corrosion environments where there were diffusion induced ions concentration gradients (termed diffusion-corrosion environment). Corrosion potential and current distribution maps (CPCD maps) were measured from WBE surfaces in continuous bases. Typical patterns have been identified from CPCD maps and the characteristics of these patterns have been found to depend heavily upon the type of electrode material and the type of corrosive ion. For mild steel WBE surface exposed to a diffusion-corrosion environment containing NiSO₄ or FeCl₃, the characteristic pattern in CPCD maps was found to emulate NiSO₄ or FeCl₃ concentration gradients, suggesting an ion-concentration controlled corrosion behaviour. However, when the mild steel WBE surface was exposed to a diffusion-corrosion environment containing NaCl, the characteristic pattern was found to show higher cathodic currents along the WBE edges with the magnitude decreasing in a contour-like manner towards the centre of the WBE surface, suggesting an oxygen concentration-controlled corrosion behaviour. When a stainless steel (SS316L) WBE surface was exposed to a diffusion-corrosion environment containing NiSO₄ or NaCl, the corrosion pattern appeared to be mainly determined by the random distribution of weak sites in passive film. When the SS316L WBE was exposed to a diffusion-corrosion environment containing FeCl₃, the CPCD map revealed a characteristic pattern that shows localised damage to passive film. This work demonstrates that the recognition and analysis of characteristic maps from WBE measurements can be used as a means of studying diffusion, migration and other forms of mass transportation related electrochemical corrosion processes.     

Metallurgical Analysis on a Cracked Super Duplex Stainless Steel Flange

A flange-to-pipe weldment in a seawater-intake-return-line suffered from cracking on its flange portion after in service for 4 months. The flange was fabricated from S32750 super duplex stainless steel. The cracked flange was investigated by visual inspection and fractographic examination on the crack surface, metallographic examination, hardness measurement, and chemical composition analysis of the flange-to-pipe weldment. The results of laboratory analysis showed that the flange had cracked in a brittle manner resulting from the presence of large amount of sigma phase in the flange material. Formation of such brittle second phase precipitates in the flange material was due to improper heat treatment.     

Heat-transfer corrosion behaviour of cast Al alloy

Heat-transfer corrosion behaviour of an ISO 2379 cast Al alloy was studied in antifreeze radiator coolant under heat-rejecting condition. Extensive analyses of microstructures and corroded surfaces were carried out under the optical microscope, scanning electron microscope equipped with energy dispersive spectroscopy and X-ray diffractometer. Heat-rejecting condition led to a cavitation process and cavities were observed within the α-Al matrix. Crevice corrosion was predominant at oxygen depleted regions in heat-transfer corrosion cell. Al₂Cu, Al₁₅(Fe,Mn)₃Si₂ dendrites, Al₄Cu₂Mg₈Si₇ and Si phases served as the effective cathodes resulting microgalvanic corrosion at the anodic site of α-Al matrix.     

Surface alignment of liquid crystal multilayers evaporated on photoaligned polyimide film observed by surface profiler

The investigation of the surface alignment of liquid crystal (LC) multilayers evaporated on photoaligned polyimide vertical alignment (PI-VA) film was carried out by means of the novel three-dimensional (3D) surface profiler. We report the first use of the surface profiler to visualize a microscopic image of the monolayer arrangement of LC molecules in contact with the surface of photo-treated PI-VA film. The photoinduced anisotropy of partially UV-exposed PI-VA film can be visualized as a topological image of LC multilayers. It seems that the topology of LC multilayers is indicating the orientational distribution of LC molecules on the treated film. It was found that the periodically photoaligned PI-VA film surface can align an adsorbed LC monolayer and the LC molecular alignment can be extended to the bulk via the epitaxylike LC–LC interaction, i.e. a short-range molecular interaction. With regard to the unexposed PI-VA film surface, noticeable anisotropy in the monolayer alignment was not observed, indicating that the long-range elastic interaction may be responsible for the bulk alignment. The appearance of small droplets in the masked region may be presumably related to the dewetting phenomena.     

Antioxidant Activities of Compounds Isolated from Fermented Broth of Zygosaccharomyces Rouxii

Previously, a sugar-tolerant strain of Zygosaccharomyces rouxii that had moderate antioxidant activity was isolated. In this investigation four active substances were isolated and their antioxidant activity was determined with different methods. The yeast strain (MAFF 237555) was cultured in yeast extract-malt extract (YM) medium, and the fermented broth was extracted with ethyl acetate. Dried solid extract was separated into neutral and acidic fractions. The neutral fraction was fractionated on a silica-gel column and purified on a Sephadex LH-20 column. The acidic fraction was recrystallized from acetone. The mother liquor was fractionated on two successive silica gel columns, followed by purification on a Sephadex column. The combined active aliquots were further purified on ODS and Phenyl high performance liquid chromatography (HPLC) columns, successively. The chemical structures of isolated substances were analyzed by electron ionization mass spectrometry (EIMS) and nuclear magnetic resonance (NMR) spectroscopy and were identified as tyrosol, succinic acid, vanillic acid and para-hydroxy benzoic acid. Using available commercial compounds, we determined the antioxidant activity of isolated substances with seven assay methods was determined and compared to natural and synthetic standard compounds. It was observed that the activity of each substance varied with the assay mode. No single substance could be identified as an all-round highly active antioxidant, which was also true with the standard compounds. The diverse activities suggested that Z. rouxii could be used as a source of wide-spectrum natural antioxidant.