2.3.3 The matrix team In a matrix team, staff report to different managers for different aspects of their work. Matrix structures are often, but not exclusively, found in projects. Staff will be responsible to the project manager for their work on the project while their functional line manager will be responsible for other aspects of their work such as appraisal, training and career development, and ‘routine’ tasks. This matrix project structure is represented in Figure 2. 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)< 5.2.2 Viscous behaviour Viscous flow is not recoverable. When the stress is removed from a viscous fluid the strain remains. Hence the work energy is not returned to the forcing agency and has to be otherwise dissipated. Figure 45 illustrates this schematically by showing the strain response in such a viscous material when a simple stress history has 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: 2.3.1 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 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. Stage 6: Developing the options (what would the options be like?) The objective here is to develop the routes to objectives generated in Stage 4 to the position where they could be implemented if the decision to go ahead were given. This involves doing sufficient work on each option for technical and other details to be defined, and for costs and benefits to be assessed, and for a sound decision to be taken, while at the same time minimising the time and resources devoted to the task. Stage 1: Problem definition (what is the problem?) The aim of the first stage is to identify and describe the problem or opportunity. While each stage depends on the success of the previous stage, it is the initial stages of a project that set the direction for the work as a whole. For this reason a clear definition and firm agreement on the problem or opportunity are essential. Problems and opportunities are like two sides of a coin: one of them can always be formulated in terms of the other. The best way to distinguish between them is 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 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 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 3.3 Optical amplifiers
Figure 22 shows in outline one possible structure for an Erbium-doped fibre amplifier (EDFA). 3.2 Directional couplers A simple yet valuable device is the directional coupler (Figure 19). A directional coupler can be constructed from two single-mode fibres by bringing them into close contact and heating so that the glass melts and the two fibres fuse. Light can then pass from one fibre to the ot 3.1 Introduction The basic optical-fibre link consisted of the source (laser or LED), the fibre and the detector, as was shown in Figure 1. Improvements in these components can increase the data rate, but the system is still a point-to-point transmission link and all signal processing, such as routeing 2.7 Cabling A distinction must be made between the optical fibre – a single strand of glass fibre – and the optical-fibre cable consisting of one or more strands of fibre and various protective coverings. Bare optical fibre is fragile and vulnerable, and the cabling must provide the properties given below.
Tensile strength: The cable should prevent the fibre being strained when the cable is under tension. When the cable is being laid, for exampl 2.6.1 Connectors Many techniques have been used to design connectors that align the fibre ends accurately with high reliability and a long lifetime. The development of such components, at a low enough price, has been an important part of the overall development which has made fibre a feasible proposition for commercial transmission systems. With fibre attenuation down to 0.2 dB km−1 (for single-mode fibre), the losses resulting from connectors and splices can be very significant over a whol 2.6 Connecting and splicing fibres There are two different types of fibre joint that need to be considered: permanent splices (the equivalent of soldered or crimped connections on copper cables) and demountable connectors. Splices are used along a route to allow a link to be built up from convenient lengths of cable. The lengths are typically 2 km. Fibre is manufactured in lengths longer than this, but, once put in a cable, lengths longer than 2 km are difficult to transport and lay. Splices are also used t 2.5 Non-Linearity A linear system can be defined in two ways: (1) one which obeys the principle of superposition, and (2) one possessing the frequency-preservation property. If we consider an optical fibre with electromagnetic field as the input and output, then provided that the power level of the input signal is not too great (less than 1 mW, which is 0 dBm), the fibre may be well modelled by a linear system for most purposes. When fibre is used for a single point-to-point link to convey a digita 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:
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