OPTIMAL MAINTENANCE SCHEDULING FOR WATER DISTRIBUTION SYSTEMS

The scheduling of maintenance for water distribution systems is a complex task encompassing a wide range of alternatives. The methodology presented in this paper can consider the major piping alternatives of replacing and cleaning, and relining. It also considers the potential of pumping improvements while accounting for the costs of maintenance, failure and operations for a multiple-period planning horizon. To solve the problem a nonlinear optimization model is linked with a network simulation model. The application showed that the procedure can determine solutions in reasonable times.     

Lead and cadmium in teeth,bone and kidneys of rats with a standard Pb‐Cd supply

Male Wistar rats received a combination of 25 ppm PbCl₂ and 5 ppm CdCl₂ in drinking water at different developmental stages. Pb and Cd levels of incisors, molars, epiphyses, diaphyses and kidney cortex were recorded by atomic absorption spectrophotometry. The results confirmed that Pb has an affinity for hard tissue and especially to teeth, but it also accumulated in soft tissues under the above conditions. In addition, the results indicated none or only a moderate placental or mammary barrier for Pb, and suggested a high absorption of lead from the intestine of sucklings. The results also confirmed that kidney cortex is a primary target for Cd, and indicated that Cd has crossed the placental and mammary barriers to some degree. The positive significant correlation between Cd levels in molars and kidney cortex suggested that rodent molars indicate a degree of Cd absorption, whereas incisors do not. It is supposed that rodent molars are comparable to human deciduous teeth. It is thus confirmed that human deciduous teeth indicate previous lead exposure. It is further inferred that they also can be used as indicators of previous Cd‐exposures.     

Legislation and the motor car

Vehicle legislation for safety and emission control is led by the USA where half the world's cars and one‐third of the world's road deaths are found. The 1975/6 standards will cause confrontations between industry and government in the U.S.A. and have costly implications for the American people. The rest of the world is affected by what happens in the U.S.A. but for language and other reasons fragmented laws are normal with conflicting requirements for manufacturers who supply the many markets. The greatest force for harmonization of legislation may be the enlarged Common Market including, as it does, the four major European Car manufacturing countries. The Common Market Commission may displace WP 29 of the United Nations as the leading law‐making body. Type approval is the compliance system used in Europe, but the growth in scope of safety and other legislation is bringing into focus a weakness of the system which is reducing production efficiency to an alarming degree. American style self‐certification is not acceptable to European governments.     

Effect of dietary and synthetic chelating agents on the intestinal absorption of lead

The effect of a number of dietary and synthetic chelating agents on the intestinal absorption of lead has been examined using the everted sac preparation and the tracer isotope ²⁰³Pb. All the agents examined increased lead transport into the serosal compartment. An explanation of the way in which these agents modify the model to describe lead transport is proposed.     

A short communication on growing Jatropha in Oman

A stripping technique has been used to cencentrate selected hydrocarbons present in water samples at the parts per billion level for analysis by gas chromatography. The chromatograms of hydrocarbons thus stripped from several different water samples show similarities. Washing out of atmospheric pollutants by rainfall is postulated as an explanation of these results. This hypothesis is supported by a comparison of the data with those for trace atmospheric analysis. The comparison shows that the same compounds are present in similar relative amounts both in water samples and the atmosphere. After a period of rain the atmospheric concentrations decrease whilst the water bound concentrations increase.