1.6 Defining global markets Global markets for manufactured goods, as opposed to, say, primary commodities such as oil and timber, arose largely in the second half of the twentieth century as trade between countries intensified. The lowering of transport costs and the relative fall in trade barriers enabled firms in one country to compete wit 1.2 Offshore fragments of industry The rise of global factories in the 1970s owed much to the rapid improvement in transport and communications technologies which took place at that time and which made it possible to keep in touch with, and control, production processes in different parts of the world. Just as significant was the fragmentation of industrial production whereby parts of the manufacturing process could be relocated over vast distances. Sewing in garment and footwear production, for instance, was among the 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 Getty disc All other material contained within this unit originated at t 2.2 Introduction to communication In Reading 2.1 I identified communication with others as being an important way in which humans learn. Unlike many other animals, we don’t have to interact directly with our Author(s): 2.1 Learning and culture As discussed in Reading 1.6, the behaviour of all living organisms that determines their resource use is mostly controlled by a set of models encoded in their genetic material. Most significant changes in the behaviour of a particular species of organism are usually a result of genetic evolution. 1.3 Activities Activity 2A sets the scene by focusing on the ‘big picture’ where you will be asked to choose between four alternative visions of the future. This activity radically shifts the scale of investigation from the personal to the global. However, as with all systems, the emergent behaviour of societ 1.2 Readings In considering the environmental and social challenges that we are currently facing, we are clearly dealing with so-called ‘wicked’ problems: the ‘problems’ manifest themselves only as you try to engage and change society and the Author(s): 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 6.1 Review Let's see if we have made any progress in studying thermal effects. The following SAQ is based on Exercise 3, although this time I have a higher expectation of how much you should be able to do. 4.3.1 Arrhenius's law In 1889 Arrhenius, a Swedish chemist, put forward a model to describe the way in which the rates of many chemical reactions could be accelerated by increasing temperature. His model is based on the idea that the rate at which such chemical reactions happen is proportional to the number of particles with enough thermal energy to overcome some sort of energy barrier. In other words, it relates the rate at which things happen to the fraction of particles having energies beyond some threshold ene 4.3 Thermally activated processes
Thermally activated processes are those that get going not because of average effects, but because the fraction of particles in the tail of the distribution increases with temperature. This is a basic property of the thermal distribution we have been discussing. For instance, what would take 30 000 years at room temperature may happen in under one second at 1000 K if it depends on how many particles have an energy in excess of 1 eV. The next step in the study of energy distribu 4.2 Energy distribution Atoms without much thermal energy will not be doing very much. Consider fifty million million million (50 × 1018) silicon atoms, bonded into a single massive network; I've chosen silicon, but any elemental solid would do. It will be a speck just large enough to be seen without a microscope. You know that if it is heated it will expand, at some stage it will melt and then eventually it will vaporise – that is because thermal energy effectively ‘rattles it to bits’. Having the 3.3 Thermal stresses When the temperature of an object increases (say, by ΔT) it expands. According to the linear model of thermal expansion the length increase is described by What if there is a temperature change, but some constraint prevents the proper thermal size changes? The constraint 3.2 Room to rattle: modelling thermal expansion In general, as the temperature of a piece of solid is raised the volume it occupies increases. I say ‘in general’ because as we shall see it is not always the case, and we ought to investigate whether we can exert any control over the phenomenon – which could be useful. Evidently, if a solid expands, the average spacing between its constituent parts must have increased. Since matter is made up of atoms, the issue is really about the volume occupied by the arrangements of atoms that make 2.2 Thermal effects in outline Temperature is, of course, the measure of ‘thermal’ conditions. Nowadays it is measured by thermometers and expressed as a number on an agreed scale. Some features of thermometers and of their use are discussed in Thermometers and process control
The theoretical construct of temperature relates it to the kinetic energies of atoms. This gives clear insights into the way temperature affects the behaviour of materials. Energy is given to things to make them hot and taken Module team Dr Peter Lewis (Chair) Dr George Weidmann (Lecturer in Materials) Dr Bob Dyson (Senior Lecturer, University of North London) Richard Black (Microphotographer) Dr Keith Cavanagh (Editor) Dr Clive Fetter (Editor) Sarah Hofton (Designer) Caryl Hunter-Brown (Technology Librarian) Gordon Imlach (Technician) Mike Levers (Photographer) Laurence Newman (Course Manager) Jennifer Seabrook (Secretary) Ian Spratley (BBC)< 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 in this block: 6.4.1 Materials selection Among the common thermoplastics available in the mid-1970s, polypropylene appeared as a front runner on grounds of toughness, density and cost Table 9). However, it is subject to creep (being uncrosslinked) and possesses a low tensile modulus of ca. 1500 MN m−2. Its merit index is 12.7 due to the low density of 0. 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 3.5 Wavelength multiplexing and demultiplexing Wavelength multiplexers and demultiplexers are needed in order to be able to use wavelength division multiplexing. With just two wavelengths, the multiplexers and demultiplexers can be based on directional couplers because, as mentioned earlier in Section 3.2, couplers are naturally wavelength-de
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