Oxygen enhanced crack growth in nickel-based superalloys and materials damage prognosis

This paper summarizes the results from a comprehensive multidisciplinary study to better understand the role of niobium and other strengthening elements in enhancing crack growth by oxygen in nickel-based superalloys at high temperatures, and considers its importance for materials damage prognosis and life cycle engineering in high temperature service. Three γ′ strengthened powder metallurgy (P/M) alloys, with 0, 2.5 and 5 wt pct Nb and comparable volume fractions (about 53 vol pct) of γ′′ precipitates, were specially designed for this study. Coordinated crack growth, microstructural and surface chemistry studies were conducted on the alloys. They were complemented by oxidation studies of Nb, Ni₃Nb, NbC, Ni₃Al and Ni₃Ti, and analyses of fracture surfaces of interrupted crack growth specimens by X-ray photoelectron spectroscopy (XPS). The findings taken in toto show that oxygen enhancement of crack growth is the result of the formation of a brittle film of surface oxides along grain boundaries and interfaces ahead of the crack tip by the preferential oxidation of Nb, Ti and Al in the Nb-rich carbides and Ni₃Al, Ni₃Ti and Ni₃Nb (in Inconel 718) precipitates. The results also showed that the oxidation of Nb-rich carbides alone can significantly enhance crack growth in oxygen. The findings are discussed in relation to the previously proposed crack growth mechanisms, and their applications.     

Contamination of potable roof-collected rainwater in Auckland, New Zealand

One-hundred and twenty-five domestic roof-collected rainwater supplies in four rural Auckland districts were investigated in a cross-sectional survey to determine water quality. Samples of cold faucet water were analysed for physico-chemical and microbiological determinands, including metals (zinc, copper and lead), bacterial indicator organisms--heterotrophic plate count (HPC), total coilforms (TC), faecal coliforms (FC), enterococci (ENT), bacterial pathogens including Salmonella spp., Legionella spp., Campylobacter spp., Aeromonas spp. and the protozoa, Cryptosporidium and Giardia. Twenty-two supplies (17.6%) exceeded one or more of the maximum acceptable values (MAV) or maximum guideline values for chemical determinands of the New Zealand Drinking Water Standards (NZDWS) and 70 (56.0%) supplies exceeded the microbiological criteria of < 1 FC/100 mL. Eighteen supplies (14.4%) exceeded the NZDWS MAV for lead of 0.01 mg/L and three (2.4%) exceeded that for copper, of 2 mg/L. Those supplies with lead or galvanised iron comprising part of the roof or collecting system were more likely to show lead contamination (p = 0.019) as were those supplies with a pH less than 7 (p = 0.013). The presence of the indicator organisms HPC, TC, FC and ENT were all significantly correlated with one another. Aeromonas spp. were identified in 20 (16.0%) supplies. There was a positive association between the presence of Aeromonas and the bacterial indicator organisms. Households reporting at least one member with gastrointestinal symptoms in the month prior to sampling, were more likely to have Aeromonas spp. identified in their water supply than those households without symptoms (odds ratio 3.22, 95% CI 1.15-9.01, p = 0.021). Salmonella typhimurium was detected in one of 115 (0.9%) supplies. Legionella spp. and Campylobacter spp. were not detected. There were 50 supplies sampled for protozoa (sampling criteria: > or = 30 FC or > or = 60 ENT). Cryptosporidium oocysts were detected in 2 (4%) of these. Giardia was not detected. This study demonstrates that roof-collected rainwater systems provide potable supplies of relatively poor physiochemical and microbiological quality in the Auckland area. Further research is required on Aeromonas spp. as potential indicators of both microbiological quality and health risk along with design and maintenance strategies to minimise contamination of potable roof-collected rainwater supplies.     

Electrical and optical properties of the four-terminaldouble-heterostructure opto-electronic switch

The authors extend the theory of the three-terminal double-heterostructure opto-electronic switch (DOES) device, in which the third terminal (the injector) makes contact to the bulk section of the active region, to the four-terminal DOES, in which the fourth terminal (the source) accesses the inversion channel at the n-n heterojunction. The source is shown to be capable of initiating switching at lower current densities than the injector. The effects of incident light on the device are also examined, yielding results similar to the injection of carriers at the source and injector. Incomplete ionization of the charge sheet and two-dimensional quantum effects in the channel, which have been neglected in previous DOES models, have been included. These effects are shown to affect significantly the characteristics of the device and to reduce the discrepancy between simulated and experimental results     

Effects of bulk trapping on the memory characteristics of thick-oxide MNOS variable-threshold capacitors

Charge-storage measurements have been performed at room temperature on thick-oxide MNOS structures using on automatic measuring system which allows a detailed and quite accurate investigation of the hysteresis loops (flat-band voltage versus stress voltage characteristics) of such devices. The experimental data have revealed several anomalous features, previously unreported in the literature, which are very general properties of double-layer devices. It is found that the initial hysteresis loop of a virgin device is very similar to the ‘conventional’ hysteresis loop, with flat bottoms and tops and steeply-rising sides. However, the second and subsequent hysteresis loops show dramatic changes in the flat-band voltage in the formerly flat regions. The results are interpreted in a selfconsistent manner, in terms of trapping phenomena throughout the bulk of both insulator regions. The trapped charge is found to produce strong internal fields that cause redistribution of the trapped charge in both the nitride and the oxide; it is these trapping effects which lead to the dramatic changes in the hysteresis loops after the initial pulse sequence. The existence of trapping levels in the bulk of the nitride is a necessary extension of the idealized model in which trapping levels are assumed to exist only at the oxide-nitride interface.     

Effects of Microbial Transglutaminase on the Wheat Proteins of Bread and Croissant Dough

ABSTRACT: Transglutaminase is a crosslinking enzyme that is finding increasing use in foods, yet the molecular changes responsible for its effects are not fully understood. Proteins were extracted from bread and croissant doughs that had been treated with transglutaminase and compared to those from control doughs by size exclusion high performance liquid chromatography and sodium dodecyl sulfate polyacrylamide gel electrophoresis analysis. Transglutaminase increased the amount of protein extracted in the gliadin fraction in both bread and croissant doughs. In croissant doughs, a corresponding decrease in the protein extracted in the albumin to globulin fraction was seen. In each case, crosslinking of the high molecular weight glutenins was observed. The possible role of each of these changes on the functional properties of baked products is discussed.     

Perception of mistuned harmonics in complex sounds by the bullfrog (Rana catesbeiana).

The ability of 73 male bullfrogs (Rana catesbeiana) to detect single mistuned harmonics in an otherwise periodic signal was studied. Bullfrogs in their natural environment were presented with playbacks of synthetic signals, resembling their species advertisement calls, that differed in the frequency of 1 harmonic component (out of 22). There were significant differences in the number and latency of the males' evoked vocal responses to these stimuli, suggesting that males were sensitive to the differences between the sounds. Differences in envelope shape (rate and depth of amplitude modulation) produced by the harmonic mistunings may underlie the differences in response. Frogs, like birds and humans, can discriminate sounds on the basis of harmonic structure, indicating that this is a general perceptual trait shared among vertebrates. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Severe tardive dystonia: treatment with continuous intrathecal baclofen administration

A retrospective clinical study to evaluate the effects of paralyzing vermifuges on the course of intestinal obstructions complicating ascariasis was performed. Forty-two patients, 26 patients with partial and 16 patients with complete intestinal obstructions, were treated over 7 years. Although 24 patients have not received any medications two patients with partial obstructions received flaccid paralyzing agent before referral. However, 12 of 16 patients with complete obstruction received spastic paralyzing agent, and the remaining patients received flaccid paralyzing agent before referral. Paralyzing agents, especially those causing spastic paralysis, should be avoided in patients with abdominal symptoms presumed to be related to ascariasis because of the risk of causing complete obstruction and making surgery more complex.