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We examined two persistent MRSA-carrier nurses in a maternity hospital to elucidate the transmission of methicillin-resistant Staphylococcus aureus(MRSA) from healthcare providers to newborn infants and to the nurses’ own families. Genotyping of the MRSA strains was performed by analyzing genomic DNA restriction length polymorphisms from pulsed-field gel electrophoresis (PFGE-RFLPs). The children of these nurses were carrying genotypically identical MRSA strains as their mother. Both MRSA carrier families remained asymptomatic over a two-year follow-up period. Eradication of nasal MRSA carriage from the two nurses resulted in declining MRSA carriage rates among infants in the nursery. Healthcare providers may become transient or persistent MRSA carriers whilst working in hospitals in which MRSA is endemic. They may then become a source of infection for patients as well as their own families. We recommend that healthcare providers should be examined for MRSA if an MRSA epidemic occurs in a hospital. The families of any such carriers should also be examined for MRSA.

The development of mechanical properties of autoclaved aerated concrete (AAC) block was investigated using ground quartz of different particle sizes. The samples were prepared at 180 ^oC under saturated steam pressure for various times from 0.5 to 64 h. With increasing tobermorite formation, the compressive strength, Young's modulus and fracture energy increased for the samples made using the coarser quartz, and decreased for the samples made using the finer quartz. After the completion of tobermorite formation, the coarser quartz yielded the higher compressive strength, Young's modulus, fracture energy and crack growth resistance. Using the finer quartz, gyrolite was formed by the decomposition of tobermorite after 64 h autoclaving, reducing the compressive strength and Young's modulus with changes in the micropore size distribution.

The chemical reactions in the hardening of autoclaved aerated concrete (AAC) block were investigated using ground quartz of different particle sizes. The samples were prepared at 180 ^oC under saturated steam pressure for various times from 0.5 to 64 h Autoclaving for 0.5 h yielded 1.1-nm tobermorite, suggesting that the utilization of finer quartz has the advantage of reducing the processing time. The tobermorite formed had higher crystallinity with coarser quartz. The degree of reaction of finer quartz was higher than that of coarser quartz after shorter periods of autoclaving, but lower after longer periods of autoclaving. Gyrolite was formed after 64h when finer quartz was used.

SummaryZ-phase was obtained hydrothermally at 120 °C by decomposition of Al-substituted tobermorite and by reaction of lime and colloidal silica. X-ray and electron diffraction show that the structural element is hexagonal, with a9·65, c15·3 Å, and good {0001} cleavage. Reversible water loss and lattice shrinkage occur on heating, the layer thickness (c) decreasing to 12.1 Å at 400 °C. For material in equilibrium with air of normal humidity, the composition is probably between CaO. 2SiO2. 1·7H2O and CaO. 2SiO2. 2H2O; Z= 8 for the structural element. New t.g. and infrared absorption data are presented; the infra-red spectrum closely resembles that of gyrolite, but OH ions attached only to Ca appear to be absent. Conditions of formation are discussed; if Z-phase has any stability field, it is below 120 °C. Crystal structures for Z-phase, gyrolite, and truscottite are suggested, based on the known structure of reyerite.

SummaryTobermorite minerals vary in some proper lies, notably in whether or not unidimensional lattice shrinkage occurs by about 300 °C to give a 9·3 form; specimens that do this are called normal, and ones that do not, anomalous. Data are compared for thirteen natural tobermorites and the extent to which normal or anomalous character is related to other properties is examined. The most definite correlations found are with chemical composition and morphology. The conditions of formation of normal and anomalous tobermorites are discussed in the light of synthetic evidence.