Characterisation of microstructures in nickel based transition joints

The microstructural changes occurring at the low alloy steel fusion line in nickel based transition welds are believed to be critical to the development of creep cavities and cracks. The progressive changes in Type I carbides observed following laboratory ageing at 625°C and from interrupted creep specimens tested at 590–625°C have been evaluated by optical and electron microscopy. In general, these carbides appear to be M₂₃C₆ type and grow in an approximately elliptical shape with the long dimension in the plane of the interface. The behaviour noted is in good general agreement with a cubic growth law and predictions made from laboratory results are in agreement with previous observations from plant welds. The accuracy of these predictions is such that measurements of carbides in service can be used to estimate an equivalent operating temperature.     

Yeast flocculation: reconciliation of physiological and genetic viewpoints.

Yeast flocculation results from surface expression of specific proteins (lectins). Two flocculation phenotypes were suggested by physiological and biochemical tests, whereas genetic data suggested a larger number of mechanisms of flocculation. After reviewing the biochemistry, physiology and genetics of flocculation, a new hypothesis combining the data available from these different sources, is proposed. Flocculation results when lectins present on flocculent cell walls bind to sugar residues of neighbouring cell walls. These sugar receptors are intrinsic to the mannan comprising cell walls of Saccharomyces cerevisiae. Two lectin phenotypes were revealed by sugar inhibition studies. The gluco- and mannospecific NewFlo phenotype is not, as yet, found in genetically defined strains. Mannospecific flocculation (Flo1 phenotype) is found in strains containing the genes FLO1, FLO5 and FLO8. This phenotype is also found following mutation of the TUP1 or CYC8 loci, in previously non-flocculent strains. It is therefore proposed that the structural gene for mannospecific flocculation is common or possibly ubiquitous in non-flocculent strains and in consequence, FLO1, FLO5 and FLO8 are probably regulatory genes, exerting positive control over the structural gene. Flocculation expression requires lectin secretion to the cell surface. Many of the observed 'suppressions' of flocculation may be due to mutations of the secretory process, involved in transporting structural proteins to the cell wall. The possible involvement of killer L double-stranded RNA with flocculation is suggested, given the lectin properties of viral coat proteins and an association between L double-stranded RNA and the Flo1 phenotype.     

Measurement properties of the RM-18. A modified version of the Roland-Morris Disability Scale

STUDY DESIGN: This investigation had two components: one was an item analysis that examined data obtained at the initial patient assessment, and the second was a validation study that used a pretest-posttest design. OBJECTIVES: The authors' goal, in this study, was to determine whether a shorter version of the Roland-Morris Questionnaire could be developed with measurement properties equal to or better than the original 24-item questionnaire. SUMMARY OF BACKGROUND DATA: The measurement properties of the Roland-Morris Questionnaire have been shown to be better than or equal to competing measures. A number of studies have reported modified versions of the Roland-Morris without providing the measurement properties of the modified tool. METHODS: The item analysis investigated endorsement frequency, interitem correlations, item-corrected item total correlations, and coefficient alpha with various combinations of items deleted. The validation study examined reliability, concurrent validity, and longitudinal validity (sensitivity to change). The analyses included comparisons with the Oswestry and Jan van Breeman Pain Questionnaires. RESULTS: The item analysis suggested than six items could be detected from the Roland-Morris Questionnaire. The validation study demonstrated that the shorter version, named the RM-18, has measurement properties that are equal to those of the longer version. CONCLUSIONS: The RM-18 can be used as an outcome measure in clinical trials or as a tool to aid in decision making concerning individual patients. In either case, its measurement properties are equal to those of the 24-item Roland-Morris Questionnaire.     

Book reviews

COMMUNITY PARTICIPATION: A Practical Guide. Wendy Sarkissian, Andrea Cook & Kelvin Walsh. Institute for Science and Technology. Murdoch University, Murdoch, WA, June 1997. ISBN 0 86905 556 9. 242pp, RRP $35.00, Spiral Bound.

GENDER, WORK AND SPACE. Susan Hanson and Geraldine Pratt. Routledge, New York, 1995. 272 pp, $90 Hardback. ISBN 0-415-09940-4 (hbk); 0-415-09941-2(pbk).

SUSTAINABILITY, THE ENVIRONMENT AND URBANISATION. Cedric Pugh (Ed). Earthscan Publications Ltd, London, 1996. ISBN 1 85383 357 6. 250 pp, cost unknown, paperback.

RATIONALITY & POWER: Democracy in Practice. Bent Flyvbjerg (transl. S. Sampson). The University of Chicago Press, Chicago, 1998. ISBN 0 226 25451 6 (pbk). 290pp, incl. notes, bibli. & index. US$16.95 (app. A$30).

TOWARDS COSMOPOLIS. Leonie Sandercock. Chichester, John Wiley & Sons, 1998, 258pp.     

Analysis and Control of Harmonic Current in Systems with Static Power Converters

In the last 50 or 60 years, the development of rectifier and semiconductor technology has led to new products and applications for drives in all industries. These semiconductor converters produce harmonics in the ac power system. With the widespread application of these economical power supplies, problems are arising that should be approached from a logical standpoint and preventive measures taken. The theory of the problem and the solution to it is discussed.     

Sorbic acid resistance: the inoculum effect

Zygosaccharomyces is a genus associated with the more extreme spoilage yeasts. Zygosaccharomyces spoilage yeasts are osmotolerant, fructophiles (preferring fructose), highly-fermentative and extremely preservative-resistant. Zygosaccharomyces bailii can grow in the presence of commonly-used food preservatives, benzoic, acetic or sorbic acids, at concentrations far higher than are legally permitted or organolepically acceptable in foods. An inoculum effect has been described for many micro-organisms and antimicrobial agents. The minimum inhibitory concentration (MIC) increases with the size of the inoculum; large inocula at high cell density therefore require considerably higher concentrations of inhibitors to prevent growth than do dilute cell suspensions. A substantial inoculum effect was found using sorbic acid against the spoilage yeast Zygosaccharomyces bailii NCYC 1766. The inoculum effect was not caused by yeasts metabolizing or adsorbing sorbic acid, thereby lowering the effective concentration; was not due to absence of cell-cell signals in dilute cell suspensions; and was not an artefact, generated by insufficient time for small inocula to grow. The inoculum effect appeared to be caused by diversity in the populations of yeast cells, with higher probability of sorbic acid-resistant cells being present in large inocula. It was found that individual cells of Zygosaccharomyces bailii populations, grown as single cells in microtitre plate wells, were very diverse, varying enormously in resistance to sorbic acid. 26S ribosomal DNA sequencing did not detect differences between the small fraction of resistant 'super cells' and the average population. Re-inoculation of the 'super cells' after overnight growth on YEPD showed a normal distribution of resistance to sorbic acid, similar to that of the original population. The resistance phenotype was therefore not heritable and not caused by a genetically distinct subpopulation. It was concluded that resistance of the spoilage yeast Zygosaccharomyces bailii to sorbic acid was due to the presence of small numbers of phenotypically resistant cells in the population.     

Yeast flocculation: Flo1 and NewFlo phenotypes and receptor structure.

Flocculation characteristics of 42 flocculent strains of Saccharomyces cerevisiae were examined. Two entirely distinct 'lectin-like' mechanisms of flocculation were distinguished by sugar, salt, and low pH inhibitions, protease sensitivity, and selective expression of flocculation. One group, termed Flo1 phenotype, was inhibited by mannopyranoses and contained all strains bearing known genes affecting flocculation. The other group, termed NewFlo phenotype, contained the majority of brewery ale stains and was inhibited by manno- and glucopyranoses. Detailed sugar-inhibition work revealed the probable receptor identity of both Flo1 and NewFlo flocculation, as being non-reducing termini of alpha-(1-3)-linked mannan side branches, two or three mannopyranose residues in length.