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 4.1 The experimental result One way to establish the speed of sound is to measure it experimentally. That is, one measures how long the sound takes to travel a known distance, and from this works out the speed. The answer turns out to depend somewhat on the prevailing temperature and humidity. At an air temperature of 14 °C the speed is 340 metres per second and at about 22.5 °C it is 345 metres per second. That is a change of speed of less than 1.5 per cent for an appreciable change of temperature. To a reasonable ap 2.7 Summary Pressure in the air is related to how closely packed the molecules are. Other things being equal, more closely packed molecules are at a higher pressure than more dispersed molecules. Sound is associated with fluctuations of the air pressure caused by local disturbance. Fluctuations of pressure travel outwards away from the disturbance, carrying energy imparted by the disturbance. A simple form of local disturbance to air pressure is a vibrating tuning fork. It generates a pressure wave 2.3 Pressure waves and cycles In this section we shall be looking at the behaviour and properties of pressure waves in the atmosphere. Sound originates from the motion or vibration of an object. Let's look at an example of a sound wave generated by a vibrating tuning fork. The prongs of the tuning fork move backwards and forwards cyclically. A cycle is a complete series of movements up to the point where the movement starts to repeat itself. As the prongs of the fork vibrate back and forth they push on neighbouring 1.2 What is sound? In the previous section I posed a question: what is sound? Take a few minutes to think about this. This may seem a straightforward question, but in fact sound is a rather more complicated thing to pin down than you might think on a first analysis. In this section I would like to explore and map out this complexity, and we shall do this together, based on your own experience with sound. To start, I'd like to propose some listening activities. 1.1 Music and technology Music technology in one guise or another is part of everybody's life, because music is a part of almost everybody's life. For instance, if you are an instrumental performer of music, professional or not, then your instrument, be it the harp or the rock'n'roll drums, will be the result of considerable technological expertise on the part of the instrument maker. On the other hand, if you are not a performer but like to listen to music, the chances are that most of your listening is done via a h Learning outcomes After studying this unit, you should be able to: explain correctly the meaning of the emboldened terms in the main text and use them correctly in context; describe simply what a pressure wave is and give a simple explanation of sound in terms of a travelling pressure wave;
explain ‘cycle’ in terms of an oscillating source and the pressure wave it produces;
relate amplitude (including peak-to-peak and r.m.s.), frequency, period a
Exercise 2
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