An Object-Based Approach to Modelling and Analysis of Failure Properties

In protection systems, when traditional technology is replaced by software, the functionality and complexity of the system is likely to increase. The quantitative evidence normally provided for safety certification of traditional systems cannot be relied upon in software-based systems. Instead there is a need to provide qualitative evidence. As a basis for the required qualitative evidence, we propose an object-based approach that allows modelling of both the application and software domains. From the object class model of a system and a formal specification of the failure properties of its components, we generate a graph of failure propagation over object classes, which is then used to generate a graph in terms of object instances in order to conduct fault tree analysis. The model is validated by comparing the resulting minimal cut sets with those obtained from the fault tree analysis of the original system. The approach is illustrated on a case study based on a protection system from..

The development of the concept of conservation in Australian aboriginal children

This study describes the application of Piaget's tests of conservation of quantity, weight, volume, length, area and number to two groups of Aboriginal children living on mission stations in the Northern Territory of Australia. The first part of the thesis is devoted to a consideration of the theoretical background of the study. In the first chapter Piaget 1 s general theory of intellectual development is outlined, and the problem of the comparative study of intellectual development is considered. It is pointed out that little research in this area has been undertaken, and reasons for this neglect are suggested. Levy-Bruhl's theory of primitive thinking is reviewed, and the parallels between the theories of Piaget and Levy-Bruhl are discussed. It is suggested that the techniques developed by Piaget in his study of the intellectual development of children could be applied to the study of intellectual development in primitive peoples, and that these techniques could be used to test Levy-Bruhl's theory. The implications of Piaget's theory and its relation to other problems in psychology are also discussed. In the second chapter the theoretical basis of the tests used in the present study is outlined, and in Chapter III a number of related studies are reviewed. The second part of the thesis deals with the study itself..

The measurement of coal porosity with different gases

Sorption processes can be used to study different characteristics of coal properties, such as gas content (coalbed methane potential of a deposit), gas diffusion, porosity, internal surface area, etc. Coal microstructure (porosity system) is relevant for gas flow behaviour in coal and, consequently, directly influences gas recovery from the coalbed. This paper addresses the determination of coal porosity (namely micro- and macroporosity) in relation to the molecular size of different gases. Experiments entailed a sorption process, which includes the direct method of determining the ‘‘void volume’’ of samples using different gases (helium, nitrogen, carbon dioxide, and methane). Because gas behaviour depends on pressure and temperature conditions, it is critical, in each case, to know the gas characteristics, especially the compressibility factor. The experimental conditions of the sorption process were as follows: temperature in the bath 35 ºC; sample with moisture equal to or greater than the moisture-holding capacity (MHC), particle size of sample less than 212 mm, and mass ca. 100 g. The present investigation was designed to confirm that when performing measurements of the coal void volume with helium and nitrogen, there are only small and insignificant changes in the volume determinations. Inducing great shrinkage and swelling effects in the coal molecular structure, carbon dioxide leads to ‘‘abnormal’’ negative values in coal void volume calculations, since the rate of sorbed and free gas is very high. In fact, when in contact with the coal structure, carbon dioxide is so strongly retained that the sorbed gas volume is much higher than the free gas volume. However, shrinkage and swelling effects in coal structure induced by carbon dioxide are fully reversible. Methane also induces shrinkage and swelling when in contact with coal molecular structure, but these effects, although smaller than those induced by carbon dioxide, are irreversible and increase the coal volume