On ‘ sudden death’ testing

Application of basic statistical theory shows that ‘ sudden death testing ’ is an accelerated teat procedure for specimens having a Weibull ‘ life to failure’ distribution only if the shape parameter is less than 1-6. In no case do the non-failed test specimens contribute to estimating efficiency and sudden death testing is in general a more costly procedure, than full tests of equivalent statistical content.     

The Health Effects of Low-Contact Water Activities in Fresh and Estuarine Waters

Four studies were carried out at separate locations to investigate the relationship between health effects and low-contact water sports, and intensive microbiological sampling was conducted in parallel to the health studies at each site. The two sports examined were marathon canoeing and rowing.
The extremes of water quality were at the estuarine sites on the River Torridge, where pollution levels varied from a geometric mean faecal coliform value of 62/100 ml at the Appledore/Instow site to 4613/100 ml at the Bideford site.
A comparison of 'exposed' and 'unexposed' groups, 5–7 days after exposure, showed that the health effects of low-contact water sports are minimal, within the water quality ranges which were studied.     

Optical Spectra of 3d Transition Metal Ions in MgO 3·52O3 Spinel

Large gem-quality boules of MgO·3.5A1₂, O₃ spinel, both pure and incorporating controlled amounts of Ti³, V₃₊, Cr³⁺, Mn₂, Fe₂₊, Co²⁺, or Ni₂₊ were synthesized by a modified verneuil technique. Each crystal was characterized by measuring the lattice parameter, chemical composition, and density. Using thin polished slices as specimens, the absorption spectrum of each crystal was measured from 400 to 50, 000 cm⁻¹, and band centers and order-of-magnitude oscillator strengths were calculated from the spectrum for each specimen. For these well characterized crystals, the absorption spectra were interpreted satisfactorily in terms of crystal field theory when the complete individual spectrum as well as the spectrum of the host matrix was considered. On this basis, the oxidation state and coordination of the 3d ion could be determined. Covalent bonding effects were of definite significance in these spinels and caused an inexact correspondence between observed band centers and those predicted by the Orgel diagrams. The ratio Dq (tetrahedral)/ Dg (octahedral) was 0.67 in the 1:3.5 spinel and verified the theoretical relation expressing this ratio in terms of a constant, 4/9, times the fifth power of the ratio of the site radii. Coordination preferences of the incorporated transition metal ions are also discussed.     

The effectiveness of preventive maintenance

The usual criterion of choice between preventive and contingency maintenance, availability, is restrictive in the sense that improvement is, even in ideal circumstances, at most of the order of 10%. Economic criteria are shown to obtain optima at values that do not maximize availability but show better percentage increases in net revenue rate or percentage decreases in maintenance cost.

A decision model, valid for all types of life to failure distribution is given and demonstrated by a graph for the Weibull distribution.

Finally, if life to failure has the Weibull distribution an easily calculated approximate optimal maintenance schedule is derived and shown to be within predictable limits of the true optima.     

An Assessment of the Impact of Inland Surface Water Input to the Bacteriological Quality of Coastal Waters

The introduction of ultraviolet disinfection in Jersey has achieved significant improvements in water quality. However, bathing waters in St Aubin's Bay and shellfish flesh have failed to comply with microbial standards. Streams and seepages from coastal structures were investigated as potential indicator organism sources (total and faecal coliforms, faecal streptococci). Seepages were an unimportant bacterial source as concentrations were low. Geometric mean concentrations in streams were up to four orders of magnitude higher than in final sewage-treatment works effluent, and concentrations increased significantly at high stream discharge. Rainfall-induced pulses of poor water quality occurred two to three times per week during the 1993 summer season. Natural discharges from island catchments thus contribute significantly to the bacterial load received at the coast, especially during high flow events. These observations have implications for other UK and European schemes using tertiary disinfection technology to attain water quality targets in coastal waters.