2.5.2 Polymer families But how do small changes in chain configuration for a given family of polymers affect their properties? A very clear example of slight changes in the repeat unit structure is exhibited by polyamides, polyesters and polyurethanes. They are all polymers linked together by a particular kind of functional group, which gives the name to each family. Their backbone chain may either be aliphatic or aromatic in nature, although here we'll only be examining trends for the aliphatic polymers. One way o
2.3.1 Structural isomerism In the saturated hydrocarbons, whose structural formulae are shown in Figure 16, it is not possible to form distinct isomers with just three or less carbon atoms linked together. There is only one way in which one carbon and four hydrogen atoms can be linked together, the single compound being methane, CH4. A simila
2.4 Models as part of systems work Thinking systemically involves identifying systems relevant to some situation, and models are invariably used as part of this process. An example of this forms part of Checklands' Soft Systems Methodology (SSM) (Checkland, 1981). One aspect of this methodology concerns the formulation of a root definition of some system that is relevant to the situation of interest and the construction of a conceptual model of this system. The root definition is a concise, verbal description of what a
2.3 Some general categories of model The preceding text has probably suggested several examples of different types of model to you, and at a very broad level, we can categorise the sorts of model we are likely to use in systems work as
Mental models: We have already seen how the ways in which we think and act are shaped by these. As well as the internal representations discussed in Section 2.1, mental models also include language and linguistic models, in particular the metaphors that we use in thinking and talking
1 Preamble I have assumed that you have come to this unit because you are interested in the use of models as part of a systems or systemic approach to some situation. This means that I expect certain things of you: You to have an interest in understanding and interacting with some situation which you find puzzling, intriguing, worrying or which you are trying to manage. You believe the situation involves more than ju 4.4 The use of systems engineering in organisations: different organisational arrangements Hall identified three different organisational arrangements that might provide a framework within which systems engineering work could take place within the organisation. The first of these, which he termed the departmental form and regarded as the lowest level of arrangement, was essentially a temporary team of specialists brought together, under the management of a team leader, to undertake a specific project. The team consisted of members of each of the specialist development departments a 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. 1.9 Increasing complication, complexity and risk: summary The three levels of change problem, simplicity, complication and complexity, can be associated with craft, engineering and systems engineering knowledge. The three categories of change problem represent different levels of uncertainty of what needs to be done and how to do it. The greater uncertainty brings increased risk. Although we tend to be risk averse we will take on greater risk if the returns are commensurate with doing so. Human experience can be divided into three worlds. 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 Grateful acknowledgement is made to the following source for permission to reproduce material within this unit: 4.5.2 10 Gigabit Ethernet The standard for 10 Gigabit Ethernet (IEEE 802.3ae, lOGbE) was approved in July 2002. The main use of lOGbE, initially at least, is for backbone networks which interconnect 10, 100 or 1000 Mbit/s Ethernet hubs. These hubs might be widely separated geographically, so the standard includes physical layer specifications specifically for WAN (wide area network) applications as well as LAN applications. The WAN specification is for operation at slightly under 10 Gbit/s, 9.95328 Gbit/s, so as to be 4.5 Fibre in LANs Fibre has been slower to be exploited in LANs than in the core transmission network, for similar reasons to the delay in the use of fibre in the access network, but as the data rate demanded of LANs has increased, the case for using fibre has strengthened. Although Ethernet specifications (IEEE 802.3 series) have contained standards for the use of fibre backbones for some time, it was with the development of Gigabit Ethernet and 10 Gigabit Ethernet (10 GbE) standards that fibre became t 4.3 Optical networking DWDM improves the utilisation of optical fibre for point-to-point links, but a further step in exploiting the potential of optical fibre comes from optical networking in which routeing or switching is done optically. Optical networking is in its infancy, but the concept of the optical layer based upon wavelength channels is emerging. The optical layer effectively sits below the SDH layer in the network, and provides wavelength channels from one location to another. An analogy can 2.4.1 Multimode distortion With multimode fibre, the main cause of pulses spreading is the multiple paths that signals can traverse as they travel along the fibre. This phenomenon of multimode distortion is illustrated in Figure 5. 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: References 6.5 Appreciating some implications for practice I think for most people, the National Health Service would be experienced as a complex situation. If so this would be a good example of perceived complexity. Remember though, if you engaged with it as if it were a difficulty you would not describe the situation as one of perceived complexity. I could not call it a complex system unless I had tried to make sense of it using systems thinking and found, or formulated, a system of interest within it. This means I would have to have a stake in the 4.6 What matters? When the laptop is confirmed to be uncompromised, it is interesting that none of the characters cheers, although they all seem to be relieved. In other words, when the statement comes up, ‘laptop is uncompromised’, people seem to think that is ‘good’, the outcome is fine. They seem to have forgotten that the technician is probably dead at the time. So, in their deliberations, a person's life is forgotten. I am sure that, if they were reminded of it, they would, of course, say that thi References 6.9 Supporting evidence 20. Are all the assertions concerning costs, benefits and risks backed up by relevant supporting evidence? 21. If not, how can this evidence be collected and presented? As was mentioned in Author(s): 6.7 Cost-benefit analysis 17. Does the case clearly and unequivocally demonstrate that benefits outweigh costs? In some contexts ‘cost-benefit analysis’ implies some specific formal method of assessing costs in relation to expected benefits. For example, i
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