3.2.5 Group development Next on the list of priorities in the functioning of groups is the process of group development. One popular conception of the way in which groups ‘gel’ and become effective was first suggested by Tuckman (1965) and then extended by Tuckman and Jensen (1977). Tuckman originally identified four stages in this development process, which he named ‘forming’, ‘storming’, ‘norming’ and ‘performing’. These stages (see Author(s):
3.2.4 Functional and team roles When individuals are being selected for membership of a team, the choice is usually made on the basis of task-related issues, such as their prior skills, knowledge, and experience. However, team effectiveness is equally dependent on the personal qualities and attributes of individual team members. It is just as important to select for these as well. When we work with other people in a group or team we each bring two types of role to that relationship. The first, and more obvious, is our
6.5 Market experience It is some 20 years since the Topper project was conceived by Peter Bean, Technical Director of Rolinx and Ian Proctor, the designer of the original GRP boat. Sales initially were excellent, especially to sailing schools and clubs where there was much demand for a small, light and very safe sailing boat for children. But after that, the market became saturated, sales were heavily dependant on individuals and families, so decreased despite attempts to export the boat to the USA and Israel, for
6.4 Case history: the Topper boat Replacement of one polymeric material by another may be undertaken entirely for manufacturing reasons, and this is what happened in the redesign of the Topper dinghy for thermoplastic polymer. The dinghy was originally designed for hand lay-up GRP in 1969 by Ian Proctor, a well known designer of small boats and yachts (Figure 61
5.5.1 Non-uniform mixtures Moulded rubbers and plastics are compounds of a polymer matrix and a variety of additives. The mixing history of the material before and during the moulding process can have a critical influence upon the final product properties. If mixing is done badly then the microstructure of the moulding can be non-uniform. Lack of uniformity can cause variations of strength and other physical properties within the moulding. The degree of dispersion or distribution of relatively minor quantities of addit
4.6.1 Prices of polymers Prices of bulk and speciality polymers (Table 9) broadly reflect the degree of chemical processing and treatment needed to make them. Thus the polyolefins, which are directly polymerized from cracker streams, are generally the cheapest followed by vinyl derivatives of ethylene like PS and PVC. Derived polymers which require mo
4.4 Step growth polymerization 4.3.1 Initiation Initiation is the mechanism which starts the polymerization process. Vinyl monomers are quite easily polymerized by a variety of activating methods. Styrene, for example, can be converted to solid polymer simply by heating, and ultraviolet light can have exactly the same effect. Usually, however, an activating agent is used. This is an unstable chemical which produces active species that attack the monomer. A good example is benzoyl peroxide which splits up when heated:
Author(s): 4.1 Understanding the polymerization process Converting monomer to long chain polymer is the final step in the polymer manufacturing sequence. Polymerization is usually highly favourable in thermodynamic terms, mainly on energetic grounds because ordering molecules into linked chains is a process where the entropy is decreased. Heat is always given out during polymerization owing to the very favourable energetics of reaction, a point you may have noticed if you have ever made GRP parts for your car, for example! Advances in cataly 3.3 Petrochemical intermediates and monomers About 80 per cent of all petrochemicals end up in polymers, the most important building blocks being ethylene, propylene, butadiene and benzene. The first three can be polymerized directly but an important slice of their production is used to create more complex monomers. Ethylene is the progenitor of most vinyl monomers (Figure 3 2.7 Commercial polymers The increasing control of polymer structure by fine-tuned catalysis of polymerization opened up an enormous area for commercial exploitation, and new polymers are still being produced in this way (such as the metallocene polymers). A revolution of equal magnitude has occurred with polymers containing functional groups, for example, the nylons, polyesters and polyurethanes, resulting in polymers ranging from quite simple structures like aramid fibre to relatively complex repeat units like thos 2.5.1 Homologous series Another approach to the problem is to consider what happens to the properties of a related series of compounds of increasing chain length. The simplest precedent is the sequence of properties for the saturated paraffin hydrocarbons (normal alkanes). Such a series of compounds is known as an homologous series. The lowest members are gases like methane and ethane, but as the length of the chain increases the hydrocarbons become first liquids and then waxy solids. Both the melting points 2.1 Understanding the polymer state It was the pioneering scientific work of Hermann Staudinger in the early part of the twentieth century which led to an understanding of the polymer state at an atomic and molecular level. Until then, plastics and rubbers had been developed from naturally occurring substances or discovered during routine synthesis. His research laid the basis for all subsequent discoveries and their commercial development. In essence, he realised that polymers were large molecules built up by the repetition of Acknowledgements Except for third party materials and otherwise stated (see terms and conditions), this content is made available under a Creative Commons Attribution-NonCommercial-ShareAlike 2.0 Licence Grateful acknowledgement is made to the following sources for permission to reproduce material within this unit 2.5 A model of systems modelling Much, if not most quantitative modelling is carried out in the context of engineering, business and financial studies. These uses of quantitative models are usually not part of a systems approach. Furthermore much of the modelling carried out in systems studies is not quantitative, since issues can often be resolved by using diagrammatic or conceptual models. It is therefore important to clarify the systems context in which modelling in general, and quantitative modelling in particular, will Stage 2: The situation analysed The first step is to develop a picture (called in soft systems terminology a rich picture) that encapsulates all the elements that people think are involved in the problem. Once the rich picture has been drawn, the analyst will attempt to extract ‘issues’ and key tasks. Issues are areas of contention within the problem situation. Key tasks are the essential jobs that must be undertaken within the problem situation. 1.5 Increasing complication, complexity and risk: the underlying relationship Figure 3 showed five commonly encountered problems of effecting different types of change. These are notionally located on a spectrum of change that ranges from no change at all, to complete revolution. The relationship suggested on the figure is that as the degree of change – represented 2.3 Style and rhetoric In the dialogues in Section 2.2, Plato, the author, is trying to point out convincingly the features of a ‘virtuous’ life and, therefore, offers templates for presenting a case with an ethical content. In looking at the style of the dialogues, most of Protagoras is in the form of a narrative similar to something you might find in a novel, as I suggested earlier. Meno is much more like a play script, but it is noticeable that Meno (the character) mostly agrees with what 1.2 Ethical examples But is this a tenable position? In other words, is it only the people who use the technologies who carry the ethical burden? Conversely, is ethics of any interest to engineers, programmers and scientists? What, in the first place, constitutes an ethical issue? To begin examining these questions, let's look at some examples. 6.1 Introduction The overall process of making the case is shown schematically in Figure 13.
Author(s):
Example 1: Th
