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4.3.2 Competing processes

Let's look graphically at the way the rate of a thermally activated process changes with temperature. Figure 16 shows two rates with different activation energies of 1.0 and 0.5 eV – which curve is which?

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1.5 Organising information

How confident are you that you know when it is appropriate to cite references (refer to the work of other people) in your written work?

  • 5 – Very confident

  • 4 – Confident

  • 3 – Fairly confident

  • 2 – Not very confident

  • 1 – Not confident at all

How confident do you feel about producing bibliographies (lists of references) in an appropriate format to accompany you
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3.3.1 Ethylene, propylene and butadiene

Nowadays ethylene is the most important building block for the chemical industry, particularly as a monomer in its own right, as a co-monomer with other vinyls, and as a source of vinyl monomers. It is the prime source for ethylene oxide, which is another major source of polymers, glycols and ethers. They can also be used to build up more complex C4 molecules and aromatics.

Some of the ways in which the ethylene molecule is modified to create other chemicals and polymers are
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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:

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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
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2.1 Light sources and detectors

The basic building blocks of an optical-fibre link are the light source, the fibre and the detector (Figure 1).


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5.7 Being ethical

As outlined in Table 2, ethics within systemic practice are perceived as operating on multiple levels. Like the systems concept of hierarchy, what we perceive to be good at one level might be bad at another. Because an epistemological position must be chosen, rather than taken as a given, the choi
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8.3.6 Deep silicon etching

MEMS structures often require etching to a much greater depth than is needed for microelectronics. A rate of 1–2 μm min−1 may be quite sufficient for making transistors less than 1 mm deep, but to etch through 600 mm of silicon to form an accelerometer would take all day. The advent of MEMS and wafer-level packaging applications, therefore, brought a need for yet faster anisotropic etches, requiring advances both in the process and in the etching equipment.

Capacitive co
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8.3.1 Fluorine-based etching of silicon

Given the noxious chemistry needed to etch silicon with a liquid, it is perhaps surprising that a gas can do the job at all. However, both xenon fluoride (XeF2) and chlorine trifluoride (ClF3) gases have been used successfully for just this purpose. Each acts as a source of fluorine atoms, which are just barely bound together into molecules and are easily rearranged around silicon atoms with which they form strong bonds, turning them into inert SiF4 gas. These
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7.4.5 Atomic layer deposition (ALD)

For very thin conformal films, where rate is unimportant but precise thickness control is critical, a form of CVD allows deposition one monolayer at a time. One precursor gas is introduced into the chamber, which is then pumped away leaving only a monolayer adsorbed onto the wafer and chamber walls. The second precursor gas can then be supplied to complete the reaction at the surface, and then this gas is pumped away along with any gaseous reaction products. This cycle is repeated several tim
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5.2 Material comparisons

I want to depart from the specific example of the bicycle to make some more general points.

In most simple structural analysis the self-weight of the structure is ignored, as it is considered to be small in comparison with the loads carried. However, as an illustration of engineering practice in the search for efficient structures to employ in product design, it is worth examining how the strength and weight of particular materials compare.

These comparisons are illustrated throug
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Learning outcomes

After studying this unit, you should be able to:

  • understand the basic structural issues of the Forth Road Bridge;

  • give examples of how engineers are trying to alleviate the wear and tear on the bridge.


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5.2 Vibrating string: speed of wave propagation

If standing waves are set up when two travelling waves moving in opposite directions interact, then how are standing waves set up on a string and why are they set up only at certain frequencies?

To help answer these questions, I want you first to imagine a length of string that is fixed at one end and held in someone's hand at the other. Suppose the person holding the string flicks their end of the string in such a way that an upward pulse is sent along the string.

As the pulse pa
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Critical systems thinking

Critical systems thinking (CST) is regarded as a systems approach to research and intervention in complex situations. The approach developed from the concerns held initially by C. Wes Churchman and his student Werner Ulrich. Later, Mike Jackson and Bob Flood, who were then professors at the University of Hull in the UK (e.g. Jackson, 1991, 2000; Flood and Jackson, 1991) developed their interpretations of the earlier work. Jackson and Flood were concerned that existing systems methods, includi
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Systems dynamics

In the 1950s, Jay Forrester, a systems engineer at MIT, was commissioned by the US company Sprague Electric to study the extreme oscillations of their sales and establish a means to correct them. From previous experience, Forrester knew the essence of the problem stemmed from the oscillations present in situations that contain inertia effects, or delays and reverse effects, or feedback loops as basic structural characteristics.

Subsequently, in 1961, Forrester published his report on in
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5.6 Developing the Open University hard systems method

When the writers of the course T301 Complexity Management and Change, the predecessor to T306 (the course from which this unit is taken), started in 1982 they had to decide what to include and what to leave out (just as we have). They started with the systems analysis approach of the engineers De Neufville and Stafford (1971), which had been developed in a civil engineering group at the Massachusetts Institute of Technology (MIT). De Neufville and Stafford defined systems analysis as
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2.2 The nature of systems thinking and systems practice

There are no simple definitions for either systems thinking or systems practice. It's difficult to find definitions that capture all the perspectives that the ideas carry for people who think of themselves as systems thinkers and systems practitioners. Most systems practitioners seem to experience the same kind of difficulty in explaining what they do or what it means to be systemic in their thinking. Through experience I've developed some criteria by which I characterise systems thinking, bu
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2 Part 1 Starting the unit

Welcome to T306_2 Managing complexity: a systems approach – introduction. As I write, I experience a sense of excitement. For me, as for you, this is the beginning of the unit. These are the first few sentences I'm writing and so, although I have a good idea of how the unit is going to turn out, the details are by no means clear. Nevertheless, the excitement and anticipation I, and maybe you, are experiencing now is an important ingredient in what will become our experiences of the u
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12.3 Market pull

The alternative market pull model suggests that the stimulus for innovation comes from the needs of society or a particular section of the market (Figure 55). These might be needs perceived by an entrepreneur or manufacturer like Shaw and his cat's-eyes or they m
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12.2 Technology push

The technology push model is a simple linear model that suggests that the innovation process starts with an idea or a discovery – it is sometimes called ‘idea push’ (Figure 51). Sometimes this is by a creative individual who has the knowledge and imaginatio
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