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6.4 Case history: the Topper boat

Replacement of one polymeric material by another may be undertaken entirely for manufacturing reasons, and this is what happened in the redesign of the Topper dinghy for thermoplastic polymer. The dinghy was originally designed for hand lay-up GRP in 1969 by Ian Proctor, a well known designer of small boats and yachts (Figure 61
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6.1 A fresh approach?

Polymeric materials offer substantial benefits over conventional materials in terms of their low density, relative freedom from corrosion, transparency or translucency, and a range of physical properties which cannot be achieved with metals, glasses or ceramics. Such unique properties include low coefficients of friction (e.g. PTFE), resistance to extreme environments (e.g. PTFE, silicones) as well as the ability to absorb and modulate damaging vibrations (e.g. most rubbery polymers). It is t
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5.6.3 Conformation and crystallinity

If there are key connections between the chain configuration and crystallisation, you might also expect some more subtle effects from rotation about chain bonds. After all, polymer chains must be able to twist into the regular conformation demanded for crystal structures (Figure 57(a)). And what influence will rotation have on
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5.5.2 Molecular orientation

As polymers are processed and shaped by flowing into moulds the shear stress fields induce preferred orientations in the molecules. The hydrostatic components of the stress field cause packing. These orientation and packing effects will relax with time if the temperatures are high enough, but the moulding cycle is frequently such that they are ‘frozen-in’ by cooling or perhaps fixed into the structure because the material has been crosslinked. The consequent moulded-in or residual stresse
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5.3 Viscoelasticity and master curves

An immediate consequence of the viscoelasticity of polymers is that their deformations under stress are time dependent. If the imposed mechanical stress is held constant then the resultant strain will increase with time, i.e. the polymer creeps. If a constant deformation is imposed then the induced stress will relax with time (stress relaxation). Author(s): The Open University

4.6.2 Material costs in manufacturing

For high added-value products like boats and cars, material costs form a relatively small proportion of total costs. For directly manufactured products, however, which are sold without much assembly or finishing, material costs do form a relatively large proportion of the total production cost. This applies particularly to polymeric containers for foods and drinks but not, for example, to containers for more sophisticated products like electronic or electrical goods. What is much more importa
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3.3.3 Higher aromatics

Benzene rings can be fused in various ways to create component parts for some of the complex aromatic repeat units shown in Table 5. One of the most important is bisphenol A, made by fusing two phenol rings with acetone:

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2.5.3 Structure and the glass transition temperature

There is a relation between the ease of chain rotation (controlling conformation) and the locked-in configuration of polymer backbone chains. It is most easily appreciated by examining the effect of different backbone configurations on the glass-transition temperature or Tg. As already noted above, the Tg is the temperature when a rigid amorphous thermoplastic becomes elastomeric, and its stiffness drops steeply. How can this transition temperature be inter
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2.5.2 Polymer families

But how do small changes in chain configuration for a given family of polymers affect their properties? A very clear example of slight changes in the repeat unit structure is exhibited by polyamides, polyesters and polyurethanes. They are all polymers linked together by a particular kind of functional group, which gives the name to each family. Their backbone chain may either be aliphatic or aromatic in nature, although here we'll only be examining trends for the aliphatic polymers. One way o
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References

IEC 60793-2-10 (1992) International Standard 60793-2-10 Optical Fibres – Part 2-10: Product Specifications – Sectional specification for category A1 multimode fibres, International Electrotechnical Commission.
IEC 60793-2-50 (1992) International Standard 60793-2-10 Optical Fibres – Part 2-;50: Product Specifications – Sectional specification for category B single mode fibres, International Electr
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Appendix 2 Acronyms

APC angle-polished convex (connector)
ASEamplified spontaneous emission
ASKamplitude shift keying
cwcontinuous wave
DSF dispersion-shifted fibre
DWDMdense wavelength division multiplexing
EDFAerbium-doped fi
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4.6 Conclusion to Section 4

This brief account has introduced a few of the most rapidly developing areas of optical-fibre communications as of January 2004. By the time you are reading it things will certainly have moved on, and if you want to find the current state of the art you should read journals such as IEEE Communications Magazine or trade magazines such as Lightwave. It is also possible to find out more on the world wide web.

I hope you will agree that this is a fascinating field, and that yo
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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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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
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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
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2.6.2 Splicing

The usual technique for splicing in the field is electric arc fusion splicing. This involves aligning the two fibre ends and then fusing them with an electric arc.

Figure 17
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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
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Activity answers

Study Note: As outlined in the text I have not provided answers to all Activities. This is for two reasons:

  1. For some activities only you can devise the answer and any I gave would be distracting or unhelpful.

  2. For others in-text answers are given.


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6.1 Articulating your appreciation of complexity

I have organized the material in this section so that you can follow the activity route shown in Figure 6.

This section is primarily concerned with what can be understood by the term complexity, and how to compare it with the ideas of difficulty and mess. To do this, you are firs
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5.4 Intellectual property rights and value

Another important theme raised in the play is intellectual property rights (IPR). Ned's fortunes seem to rely on control of the IPR issues surrounding his invention. He challenges the rights of others to share in the IP because, as he sees it, they have not contributed anything. The assumption is that those that have the idea have IPR, but the IPR has value and, therefore, any proceeds accrued should be due to the person who has the idea. A problem arises here because of the phrase ‘intelle
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