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
6.3 Materials selection Good design fulfils the product specification under the required service conditions as well as contributing to the cost effectiveness of its manufacture and maintenance. The product specification itself must be an interpretation of the market needs. Hence good design means giving product appeal at the point of sale. Selecting the polymer is just one stage in this design exercise, both in terms of information on various properties of materials, as well as the detailed evaluation and selection
4.3.4 Ionic polymerization Free radicals are indiscriminate in the compounds they attack, and their non-selective nature in polymerization reactions leads to problems such as chain branching and transfer which affect the structure of the polymer produced. Anionic polymerization overcomes many of these problems. A typical commercial (but also see Box 8
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.
3.2.2 Ethane cracking Although ethane can be cracked thermally, the reaction is slow and does not necessarily yield ethylene at high severity. Careful control of reaction conditions, however, allows the reaction to occur The yield of ethylene is typically nearly 50 wt% with the rest composed o
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: 5.1 Introduction: the general framework The general framework of systems engineering adopted in the course consists of: a hierarchy of elements; aims associated within its outputs and process; a set of principles; a division into technical and managerial components of the process. The lexicon of system engineering used in the course contains the hierarchy of elements:
strategy: meaning the accumulated decisions concerning the areas in which an organisation operates and its lon 6.4 Choosing to distinguish between complex situations and complex systems Within some of the lineages of systems thinking and practice (Figure 7), the idea that system complexity is a property of what is observed about some ‘real-world’ system, is known as classical or type 1 complexity. Exploring type 1 complexity, Russell Ackoff (1981, pp.26–33) claimed for a set 3.4 Negotiation and adaptation I suggested that one way out of our contradictions is to begin to negotiate. This implies that negotiation and what you do during negotiation is a part of the business of ethics. Ethical texts normally focus on contradictions, but, as I also mentioned above, actually people do agree a lot of the time, so life is not all contradictions. Contradictions, however, do pose a problem, and I used the play Antigone to illustrate that conflict can arise. In the case of Antigone, it 8.4 Stopping the etch Just as important as being able to remove material is being able to stop doing so once the intended etch depth has been reached. Success or failure in this aspect of etching determines whether or not any of the benefits of parallel processing of thousands of devices will be obtained. Uniformity of result from device to device, and repeatability from wafer to wafer, are crucial to the economic viability of the whole exercise. There are three broad categories of approach to this problem:< 3.1 Introduction The atomic force microscope is a key visualisation tool for the ‘invisible’ world of micro and nano technology. Within it, right at the heart, is a probe tip that is itself a triumph of nanotechnology. This section is going to begin with a fair amount of detail about how scanning probe microscopes of various types work, starting with a description of the scanning tunnelling microscope (STM). After that I want to concentrate on its close relative, the atomic force microscope. Then we 2.4 Thermal and electrical conductance Thermal conductance, Gt, is analogous to electrical conductance, Ge. The longer a conductor is and the smaller its cross section, the lower its conductance will be. Thermal conductance is given by: and electrical conductance by: 1.4 Sensitivity Since a biased MOS structure builds up a depletion region with an electric field similar to that in a p–n junction, it's worth thinking about what would happen if light were to be absorbed in an MOS capacitor, generating electron–hole pairs. 1.2 MOS structures Carefully designed metal–oxide–semiconductor (MOS) structures are a common building block in digital electronics, primarily intended to form part of a transistor-based switch. However, throughout the active regions of a microelectronic chip there will be secondary MOS structures that arise because metal tracks are insulated from the semiconductor substrate by a layer of oxide; equally careful design is necessary to ensure that these do not form part of a switch. The acronym is a mixture o 7.4 The impact of technology on society Engineering is apparently driven by the needs of society. The technology that results, in turn, drives other changes in our everyday lives. One of the basic needs identified in Section 2 was for shelter. There are many fine examples of long-surviving structures such as pyramids, aqueducts, bridges, walls, functional buildings, and so on. Remarkably these constructions were completed without the depth of analysis and understanding that is available today (though we don't necessarily know much 7.1 The engineer and society Section 2 outlined some of the needs for engineering. Society relies on engineers to create solutions to the problems involved in meeting those needs. This is a good time to pause and point out that inevitably, in return for all this fun and power, engineers have a responsibility to society. The people who employ our services, directly or indirectly, have to have an assurance that we are working within certain social, safety and ethical boundaries. Particularly given the increasing tren 2.3 Berliner experiments with plates Emile Berliner was a young German immigrant to the USA with an interest in science. Whilst working in several menial jobs he educated himself in basic physics and chemistry, eventually building a small laboratory at his boarding house. Experiments with electricity and acoustics led to his invention of a new telephone transmitter, which he sold, enabling him to set up as a full-time inventor. He became interested in recording sound through studying a device called the phonoautograph. This appa 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 unit: 5.1 Phase and phase difference In this section I am considering sine waves that have the same frequency, but are out of step with each other. Suppose we have two detectors at fixed points, A and B. At this moment in time A is in a high pressure region and B in a low pressure region. If we were to look again shortly later B would now in a high pressure region and A in a low pressure region. The pressures at A and B would be out of step with each other. The pressure variation at B is not in phase with that at A. The ex 4.3 Summary The speed of sound in air, symbol v, is approximately constant at 340 metres per second. (You do not need to memorise this value.) As temperature increases, the speed increases slightly. Speed, frequency and wavelength are related by the formula v = f × λ. Other forms of this relationship are f = v/λ and λ = v/f. Because the speed is approximately constant, it follows that frequency and wavelength are inversely pr
Exercise 2
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