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
Acknowledgements The following material is Proprietary and is used under licence: Various pages: Arup, O., material accessed in January 2002 and December 2000, from. Box 1: Inman, P. ‘Chaotic scheme that left families relying on food parcels’, The Guardian, 6 July 2005. © Guardian News and Media Ltd 2005. Box 2: ‘Fly-away drones put robot air force plans off cou
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References 6 Summary This unit has covered the background to systems engineering. It began by addressing the question ‘Why is systems engineering important?’ Two reasons were discussed: projects go wrong, and the increasing incorporation of software means that they go wrong more often now than in the past complication, complexity and risk are all increasing and need to be managed. In the second section I examined the development of en 5.2 The aims and principles of system engineering The aims of systems engineering can be divided into those to do with its outputs and those associated with the process itself. As far as its outputs are concerned, systems engineering aims to ensure that: the requirements of all the stakeholders are taken into account in engineering the system the system, as engineered and realised, meets the requirements of stakeholders the system, while meeting the req 4.6 Systems engineering: the recent development of a discipline The recent development of systems engineering can be dated from two events. First, following the lead of the US Department of Defense and its introduction of standards for contractors, systems engineering was taken up by companies such as Boeing, Lockheed Martin and, in the UK, British Aerospace, Marconi and the Lucas Group. Second, in August 1990, a group of individuals interested in systems engineering met in Seattle (Box 10 – extract from a paper presented at the International Committee 3.11 Summary This topic has introduced the systems approach, which is the foundation of systems engineering. The systems approach consists of three elements. A set of concepts that can be used to understand the structural and dynamic features of operations systems. Methodologies for managing change. Two current methodologies have been presented: the hard systems approach can be applied in situations where there is a measure of agreement about the Stage 6: Debate on feasible and desirable changes The comparison undertaken in the previous stage can have two results. It can cause opinions to change on the problem situation and the issues arising from it. It can provide an agenda for change. In either case (though both may result), the objective of this stage is to debate, with all concerned, the changes proposed to ensure that they are both desirable and feasible. The aim is to arrive at consensus about the prop Stage 4: Conceptual model The conceptual (or activity) model contains all the activities that the relevant system would have to perform. The model is usually drawn as a block diagram. Stage 4: Generation of routes to objectives (how could we get there?) This stage explores the different ways of achieving the defined objectives. It is the most imaginative and free-thinking stage of the approach. The idea is initially to generate as many ideas as possible, then to whittle the list down to two or three ‘definite possibilities’ that can be carried further in the development stage. 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. 3.8 Systems methodologies for managing change: hard systems approach The stages of the hard systems approach are illustrated in Figure 34 and simplified in Figu 3.5 Systems concepts: dynamic behaviour: input-transformation-output Utilitarian systems, as previously discussed, are the means we use to transform resource inputs into useful goods and services. Any system can be divided into a set of input-transformation-output blocks. These are usually represented as in Figure 31. This way of looking at systems can be use 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 Introduction The aim of this unit is to answer five questions: Why is systems engineering important? What is modern engineering? What is systems? What is systems engineering? What approach to systems engineering does the course adopt? This unit is from our archive and is an adapted extract from Systems engineering (T837) which is no longer taught by The Open University. If you wan 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: 5 Summary The building blocks of a basic optical-fibre communications link are the modulated light source, the fibre and the detector. There are choices to be made between different types of light source and fibre, with trade-offs between cost and performance. For example, for high signalling rates over long distances single-mode fibre will be used with a single-mode laser (possibly with external modulation) operating in the 1550 nm window, whereas for short-distance links operating at lower signalling 4.5.1 Gigabit Ethernet Gigabit Ethernet specifies four categories: 1000BASE-SX, for transmission over multimode fibre using an LED in the 800 nm window (the wavelength is specified to be between 770 and 860 nm). The specification is for up to 275 m on 62.5/125 mm multimode fibre, or 550 m on 50/125 mm multimode fibre; 1000BASE-LX, for transmission over multimode or single-mode fibre using a laser in the 1300 nm window (specified to be between 1270 and 1355 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
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