3.2 (2B): Developing a relational model of the Powerdown Show programme In this activity you will be challenged to reinterpret the following programme extracted from the Powerdown Show DVD: Energy Descent Pathways. The reason this programme was selected, from the many audio-visual programmes currently available online that tackle environmental and social issues, was because it presents an "ecotopian" approach to tackling the converging social, economic and environmental crises. Your challen
Introduction This unit will facilitate your own exploration of key environmental, social and economic threats that will converge to challenge communities in the near future. You will be required to develop this exploration according to three modes of modelling and communication: verbal, visual, and numeri
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 of this unit.
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1.5 Organising information How confident are you that you know when it is appropriate to cite references (refer to the work of other people) in your written work? 5 – Very confident 4 – Confident 3 – Fairly confident 2 – Not very confident 1 – Not confident at all How confident do you feel about producing bibliographies (lists of references) in an appropriate format to accompany you
4.2 Project life cycles Earlier I said that a project is: ‘a unique venture with a beginning and an end’ (Boddy and Buchanan, 1992, p. 8). But it must have a middle, too. We say that a project has a ‘life cycle’. This is based on an analogy with living things which are born, live for a period of time, doing things like consuming food and water, breathing, moving, etc., and then finally end (die). There is much discussion about whether there is only one ‘true’ model of a project life cycle or many, and wh
6.3.1 Prototyping The first prototypes may be made of any convenient material, such as clay, plaster-of-Paris or wood. Plastic models can also be made by fabrication or vacuum forming of thin sheet. Their primary function is to ensure that the product has ‘customer appeal’ when considered in aesthetic or ergonomic terms. This is particularly important for products which are to be consumer durables. It may be the first time in the design process that the concept sketches and initial engineering drawings are
5.6.3 Conformation and crystallinity If there are key connections between the chain configuration and crystallisation, you might also expect some more subtle effects from rotation about chain bonds. After all, polymer chains must be able to twist into the regular conformation demanded for crystal structures (Figure 57(a)). And what influence will rotation have on
4.3 Chain growth polymerization Chain growth polymerization is basically a three-stage process, involving initiation of active molecules, their propagation and termination of the active chain ends.
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
3.2.1 Thermal cracking The bulk of the major monomer and intermediate, ethylene (C2H4), is still produced in the UK by steam cracking without the use of catalysts. Paraffinic feedstocks are best for optimising ethylene yields, and the severity of cracking is specified by the rate of disappearance of a marker compound, usually n-pentane. The severity of the reaction can then be defined as follows: 2.5.4 Melting and structure For those polymers which can crystallise, one would expect some relation between chain rotation and melting. Since all crystallisation demands that chains form an ordered conformation (e.g. the PE planar zig-zag) before they can pack together, the chance of this happening should be related to the ease of twisting into the required conformation. That there is a rough correlation between Tg and Tm
can be judged from Author(s): 2.5.3 Structure and the glass transition temperature There is a relation between the ease of chain rotation (controlling conformation) and the locked-in configuration of polymer backbone chains. It is most easily appreciated by examining the effect of different backbone configurations on the glass-transition temperature or Tg. As already noted above, the Tg is the temperature when a rigid amorphous thermoplastic becomes elastomeric, and its stiffness drops steeply. How can this transition temperature be inter 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 1.2.1 Natural and synthetic rubbers Natural rubber was the first major polymer to be imported and used for commercial purposes. Long ago the natives of South America learned to tap the indigenous Hevea Brasiliensis trees to collect, dry and coagulate the latex. Today the main rubber plantations are in Malaysia and Indonesia. Natural rubber is well established as an important and versatile engineering material with an excellent balance of properties. However, almost two-thirds of the rubber now consumed world-wide is synt 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 3.3 Types of quantitative systems model There is a wide range of quantitative models, of varying degrees of sophistication and complication. In this pack, we will only cover those that I think you are likely to encounter in systems studies or could use to good effect. The techniques available subdivide broadly into two major classes, static models and dynamic models. The distinction between these will become clearer as you look at some detailed examples. Essentially, dynamic models are those where the set of calculations comprising 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: Analysis of the existing situation (where are we now?) Having defined and agreed on the problem, it is necessary to decide on the system in which you consider it plays a part. In practice the two stages are closely linked and the analysis of the existing system nearly always means a redefinition or refinement of the problem or opportunity. Identifying and defining the problem and the system or systems that relate to it are critical for the success of subsequent analysis. References 5.6 Learning and effective action I claim that learning is about effective action. It is distinguished when I, or another observer, recognize that I can perform what I was unable to perform before. Following Reyes and Zarama (1998), I am going to claim learning is an assessment made by an observer based on observed capacity for action. From this perspective, learning is not about ideas stored in our mind, but about action. So what makes an action effective? Reyes and Zarama (1998, p. 26) make the following claims:
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