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3.6 Summary

This section has described how fossil fuels provide the majority of the world's energy requirements, with bioenergy, nuclear energy and hydropower also making major contributions. The other 'renewable' energy sources currently supply only a small fraction of world demand, although the contribution of these 'renewables' seems likely to grow rapidly in coming decades, as we shall see in the following section.


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4.1 When climate changes

We have seen that human-induced climate change poses a challenge for people who live on islands. Such changing patterns and extremes of climate also put pressure on the other living things that are part of the make-up of island territories. However, long before human beings became aware that they could transform the flows that constitute climate, they and other species were already taking advantage of these same flows to help create the very territories that are now under threat. But have the
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2.1 Learning from video footage

You might think that learning from audio-visual sources is very different from learning from written sources yet, somewhat surprisingly, it is much the same. This section of the course will help you to think about how you can turn the very familiar, but usually passive, process of watching a video into the active process of learning. Watching the video will involve the skills of engaging with the material and making sense of it for yourself, just as if it were written materials. The advantage
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1.1Aim

The aim of this section is to practise the use of diagramming techniques as part of a fundamental shift in interpreting issues – from an assembly of static objects to a network of dynamic relationships.


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3.2 (2B): Developing a relational model of the Powerdown Show programme

In this activity you will be challenged to reinterpret the following programme extracted from the Powerdown Show DVD: Energy Descent Pathways. The reason this programme was selected, from the many audio-visual programmes currently available online that tackle environmental and social issues, was because it presents an "ecotopian" approach to tackling the converging social, econ
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3.1 (2A): Exploring the global implications of different mindsets

In this activity the aim is to investigate the implications of different mindsets with regards to the future unfolding of events on a global scale.

Activity

So far, you have focused your attention on exploring your p
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4.3.3 Getting at the activation energy

The final trick I want to show you with Arrhenius's law is how to extract the constants r0 and Ea from experimental data. If the Arrhenius equation (Section 4.3.1) is 'turned inside out' by taking natural logarithms of both sides it becomes:

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4.3.1 Arrhenius's law

In 1889 Arrhenius, a Swedish chemist, put forward a model to describe the way in which the rates of many chemical reactions could be accelerated by increasing temperature. His model is based on the idea that the rate at which such chemical reactions happen is proportional to the number of particles with enough thermal energy to overcome some sort of energy barrier. In other words, it relates the rate at which things happen to the fraction of particles having energies beyond some threshold ene
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2.1 Boiling water

Whether it's to wash clothes, make a cup of tea, or just make it safe to drink, water often has to be heated – sometimes to boiling point. There are many ways to do this, but a very common means is some form of electric water-boiler, such as a kettle or an urn. In all but the crudest ones, a device is fitted to ensure that heating does not continue once the boiling point of water is reached.

In deciding on the type and design of such a device, we can suppose that a company manufacturi
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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 4.0 Licence

Grateful acknowledgement is made to the following sources for permission to reproduce
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7.4.6 Molecular beam epitaxy (MBE)

Where a suitable ALD chemistry cannot be found, or where cleanliness and high crystallinity are required, molecular beam epitaxy may be necessary. This is more akin to evaporation than to CVD, with multiple molecular beams of the separate chemical constituents each focused onto the hot wafer surface. Deposition is performed under extreme vacuum conditions (10−11 mbar) to prevent any contaminants from being incorporated, and the substrate must present a perfect cleaved crystal fac
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7.3.6 Laser ablation deposition

Another close cousin to sputter deposition is laser ablation deposition. Ion bombardment of the target is replaced by a focused pulse of light from an ultraviolet laser. Although each pulse may carry only 1 J of energy, this is delivered within 1 ns to a 1 mm spot on the target surface. This represents an astonishing power density and the target surface explodes into vapour that can be caught on the waiting wafer surface. It is vital to scan the focus point across the target surface or you wi
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7.3.1 Electroplating

Electroplating is a relatively fast process, inexpensive and simple, although fairly messy and limited in applicability. The wafer is dipped into a solution with dissolved salts of the metal (e.g. CuSO4 + H2SO4) and is connected to a negative voltage. A positive metal electrode (anode), also in the solution, completes the circuit. Anywhere that current can flow into the wafer surface, metal will be deposited. Plating has several advantages: it will deposit met
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6.2 Natural frequency of free oscillations

Most of us have a fairly accurate understanding of what is meant by resonance – it's what causes a bell to continue to make a sound long after it has been struck. Yet this is just one example of resonance, a phenomenon that occurs in nature in a surprisingly large number of places.

It is all to do with the reversible transfer of energy from one form to another in a system. The common feature associated with mechanical systems that are able to store energy by oscillating is that they h
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3.7.2 The hybrid probe

Where the benefit to be gained from combining the narrow-angled silicon tip with the super-light, any-shape silicon nitride cantilever outweighs the expense and difficulty of the more complex process sequence, AFM probes can be made with silicon tips on silicon nitride cantilevers. Figure 14 shows one such pr
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3.7.1 The machined-at-once tip and cantilever

Just as in conventional manufacturing, micro engineering is cheapest to do if as few different materials as possible are used and if the number of separate processes involved is minimised. Therefore, the idea of making the cantilever and the probe out of the same material and in the same process step is a very attractive one.

When silicon nitride is deposited onto a silicon surface, it produces a thin film that coats the whole of the material to an equal thickness. We have already seen
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3.6.4 Materials selection for cantilevers

Table 1 shows some of the physical and mechanical properties of materials that can be deposited and etched in thin-film form. One of the consequences of manufacturing these materials in thin-film form is that properties that in the bulk material can be determined to within a few per cent are much less easy to
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Conclusion

We have seen how a solution falls into one of three categories (innovation by context, innovation by development, and routine solution) according to the need that drives it. Furthermore, the need is shown to be the point of reference that should be kept in sight throughout the process of finding solutions. Unless the need is accurately stated, the ideal solution cannot be obtained – a case of 'garbage in, garbage out'.

We have examined the process of finding a solution step by step, u
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5.3 Back to the bicycle

Let's assume that our bicycle frame could still be constructed from ties and struts. If we want to select the material to minimise the weight of a frame for a particular frame strength, we need to devise a merit index as follows.

The mass of the tie-rods and struts needed for the frame is given by:

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4.4 Evaluate solutions

If the obvious solution has been identified and everyone is in agreement, then a formal evaluation of solutions is unnecessary, and we would move on to modelling the design. However, if there is dissent then some stricter method of elimination is required, and this is usually achieved through a process of rank-ordering. There is little to be lost and potentially much to be gained by returning to the customer at this point for opinion, clarification or guidance.


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